G o d i n a LVI B e o g r a d, 2015. B r o j 1idk.org.rs/wp-content/uploads/2015/03... · Dr Vesna Mišković-Stanković, Serbia Dr Milan Jaić, Serbia Dr Zvonko Gulišija, Serbia

ZAŠTITA MATERIJALAG o d i n a LVI B e o g r a d, 2015. B r o j 1

V.d. Glavnog urednika – Editor in ChiefProf. dr Časlav Lačnjevac University ofBelgrade, Faculty of Agriculture, SerbiaPomoćnici urednikaDr Nebojša Nikolić, IHTM, BelgradeDr Vladimir Panić, IHTM, BelgradeDr Mirjana Stojanović, ITNMS, BelgradeUređivački odbor - Editorial BoardDr Benedetto Bozzini, ItalyDr J. G. Gonzalez-Rodriguez, MéxicoDr Heiner Jakob Gores, GermanyDr Tor Henning Hemmingsen, NorwayDr Dragica Jevtić, SerbiaDr S. Hadži Jordanov, R. MacedoniaDr K. F. Khaled, EgyptDr Miomir G. Pavlović, SerbiaDr Andrzej Kowal, PolandDr Ivan Krastev, BulgariaDr Dragica Chamovska, R. MacedoniaDr Refik Zejnilović, MontenegroDr Ronald Latanision, USADr Miodrag Maksimović, SerbiaDr Vesna Mišković-Stanković, SerbiaDr Milan Jaić, SerbiaDr Zvonko Gulišija, SerbiaDr S. Rajendran, IndiaDr A. S. Sarac, TurkeyDr Velu Saraswathu, IndiaDr Miodrag Stojanović, SerbiaDr Aleksandra Daković, SerbiaDr Darko Vuksanović, MontenegroDr Deana Wahyuningrum, IndonesiaDr Jozefita Marku, AlbaniaIzdavački savet – Publisher boardDr Dragoljub Dabić, predsednik, SerbiaMr Ivan Burić, MontenegroZoran Ivljanin, SerbiaGordana Miljević, SerbiaBogdan Vujović, SerbiaDr Zoran Avramović, SerbiaMomir Ilić, SerbiaStevan Buinac, Slovenia

Dosadašnji glavni i odgovorni uredniciProf. dr Sreten Mladenović (1967–2001)

Prof. dr Miodrag Maksimović (2002 – 2005)Prof. dr Milan Antonijević (2006-2012)

Tehnički urednik – Technical editorSlavka VukašinovićZa izdavača – For publisherProf. dr Časlav Lačnjevac, predsednik

Izdavač- PublisherINŽENJERSKO DRUŠTVO ZAKOROZIJU, Beograd, Kneza Miloša 9/I,Tel/fax (011) 3860 - 867, i (011) 3230 - 028,e-mail:[email protected]; www.idk.org.rse-mail:[email protected]; www.sitzam.org.rs

SADRŽAJ – CONTENT

Jozefita MarkuAlkali-silica expansion potentiality of Erzeni riverbedaggregates (Albania) and the risk of corrosion in concretesproduced with them...................................................................... 5

Žaklina Tasić, Milan AntonijevićElektrohemijske osobine bakra i legura bakra kaobiomaterijala................................................................................ 25

Vuk Rajović, Jelena Marković, Aleksandar Jokić, Jelena IlićMembrane technology application in the frameworkof zero emission concept ........................................................... 37

Sanja Krstic, Branka Kaluđerovic, Vladimir Dodevski,Radoslav Aleksic, A. Bjelajac, D. Brkovic

Structural properties of carbon microspheres obtainedby hydrothermal treatment of fructose ..................................... 43

Jadranka Malina, Jagoda RadoševićInfluence of NaCl concentration on pitting corrosionof extruded Al –Mg-Si alloy AA6060.......................................... 47

Snežana Šerbula, Ana Ristić, Srećko Manasijević, Natalija DolićTeški metali u otpadnim vodama Rudnikabakra Majdanpek......................................................................... 52

Vladislav Matković, Branislav Marković, Miroslav Sokić, Vaso ManojlovićValorizacija olova iz međuprodukata rafinacije bizmutapostupkom metalotermijske redukcije...................................... 59

Branko Pejović, Vladan Mićić, Milorad TomićIstraživanje dejstva korozije na dinamičku čvrstoćukod nekih konstrukcionih čelika................................................ 64

Jelena Pješčić, Veselinka Grudić, Darko Vuksanović,Dragan Radonjić, Refik Zejnilović

Uticaj neorganskih inhibitora na koroziono ponašanjeAl-Si legura u vodenim rastvorima hlorida ............................... 70

Milorad V. Tomić, Marija G. Riđošić, Miomir G. Pavlović,Miroslav Jokić, Jelena Bajat

Uticaj hrapavosti Zn-Mn prevlaka na korozionu postojanost . 75Add El-Aziy S. Fouda, Ayman Y. El-Khateeb, Mohamed Fakih,Aly M. El-Azaly

Satirn as pesticide inhibitor for the corrosion of thegalvanized iron in wastewater and its biological effecton Escherichia coli ..................................................................... 81

Željko Stojanović, Spasoje Erić, Sanja Stanisavljev, Mića ĐurđevPovećanje efikasnosti alata za kovanje Toyota difuzionimpostupkom................................................................................... 92

Larisa Jovanović, Dijana Fedjunina, Milan RadosavljevićThe optimization of development process of petrol-gasstations network with the purpose to increase energyefficiency ................................................................................... 100

Miloš PetrovićTemperatura vazduha kao bitan klimatski – meteorološkiparameter za određivanje evapotranspiracije ........................ 105Engineering card – Inženjerska kartica................................... 111An Interview with Mr Lars Funk ............................................... 113

Reklame........................................................................................ 115

EVROPSKA FEDERACIJA ZA KOROZIJU (EFC) SMATRA OVAJ ČASOPIS ZVANIČNOM PUBLIKACIJOMZA OBJAVLJIVANJE IZVEŠTAJA I INFORMACIJA

EUROPEAN FEDERATION OF CORROSION (EFC) CONSIDERES THIS JOURNAL TO BE THE OFFICIALPUBLICATION FOR PUBLISHING THE REPORTS AND INFORMATION

SSuuiizzddaavvaaččiiUUDDRRUUŽŽEENNJJEE IINNŽŽEENNJJEERRAA SSRRBBIIJJEE ZZAA KKOORROOZZIIJJUU II ZZAAŠŠTTIITTUU MMAATTEERRIIJJAALLAA

CCRRNNOOGGOORRSSKKOO DDRRUUŠŠTTVVOO ZZAA ZZAAŠŠTTIITTUU MMAATTEERRIIJJAALLAA

DDoonnaattoorriiSSAAOOBBRRAAĆĆAAJJNNII IINNSSTTIITTUUTT „„CCIIPP““,, BBEEOOGGRRAADDJJPP EELLEEKKTTRROOMMRREEŽŽAA SSRRBBIIJJEE,, BBEEOOGGRRAADDPPDD TTEERRMMOOEELLEEKKTTRRAANNEE II KKOOPPOOVVII,, KKOOSSTTOOLLAACC""NNIISS -- FFAAMM"",, KKRRUUŠŠEEVVAACCJJKKPP BBEEOOGGRRAADDSSKKII VVOODDOOVVOODD II KKAANNAALLIIZZAACCIIJJAA""SSIIKKAA"",, ZZEEMMUUNNPPDD DDRRIINNSSKKOO LLIIMMSSKKEE EELLEEKKTTRRAANNEE,, BBAAJJIINNAA BBAAŠŠTTAAPPDD RRUUDDAARRSSKKII BBAASSEENN KKOOLLUUBBAARRAA,, LLAAZZAARREEVVAACC""EEPPOOKKSSAANN"",, ČČAAČČAAKKCCHHEEMMIIEE NNPPKK,, ddoooo,, KKRRAANNJJ„„HHEELLIIOOSS““,, DDOOMMŽŽAALLEE""PPIITTUURRAA"",, NNOOVVII BBEEOOGGRRAADDPPDD TTEERRMMOOEELLEEKKTTRRAANNAA ““NNIIKKOOLLAA TTEESSLLAA””,, OOBBRREENNOOVVAACCBBIIEESSTTEERRFFEELLDD,, ZZAAGGRREEBBEECCOOLLOOGGIIJJAA,, KKRRAANNJJIINNSSTTIITTUUTT ZZAA VVOODDOOPPRRIIVVRREEDDUU „„JJAARROOSSLLAAVV ČČEERRNNII““,, BBEEOOGGRRAADD„„GGAALLVVAA““,, KKRRAAGGUUJJEEVVAACCPPEERRIIĆĆ && PPEERRIIĆĆ,, PPOOŽŽAARREEVVAACC

U finansiranju izdavanja časopisa "ZAŠTITA MATERIJALA" učestvuju:MMIINNIISSTTAARRSSTTVVOO PPRROOSSVVEETTEE,, NNAAUUKKEE II TTEEHHNNOOLLOOŠŠKKOOGG RRAAZZVVOOJJAA RREEPPUUBBLLIIKKEE SSRRBBIIJJEE

IINNŽŽEENNJJEERRSSKKAA KKOOMMOORRAA SSRRBBIIJJEE

CIP - Katalogizacija u publikacijiNarodna biblioteka Srbije, Beograd

620.1ZAŠTITA MATERIJALA = Materials Protection / v.d. glavni urednik .Časlav Lačnjevac),God. 1, broj 1 (1953) – God. 22 br. 3/4 (1974); God. 23, br. 1 (1982) = Beograd, (Kneza Miloša 9) : Inženjersko društvo za koroziju, 1953 – 1974 ; 1982 – (Zemun : Akademska izdanja ) - 29 cmDostupno i na: htpp:// www.idk.org.rs/zmTromesečno. Akronim na koricama ZMISSN 0351 – 9465 = Zaštita materijalaCOBISS. SR – ID 4506626

Posebnu zahvalnost Upravni odbor Inženjerskog društva za koroziju izražava Savezu inženjera itehničara Srbije, organima, rukovodstvu i Stručnoj službi SITS za pomoć u realizaciji Programa rada.

Redakcija: Beograd, Kneza Miloša 9/I, Tel/fax (011) 3860 - 867, i (011) 3230 - 028,e-mail:[email protected], www.idk.org.rs; e-mail:[email protected] , www.sitzam.org.rs;

Tekući račun: 205 - 24967 – 71, Komercijalna banka, Beograd; Časopis izlazi četiri puta godišnje;Rukopisi se ne vraćaju; Štampa: Akademska izdanja, Zemun

J. MARKU ALKALI-SILICA EXPANSION POTENTIALITY OF ERZENI RIVERBED ...

ZAŠTITA MATERIJALA 56 (2015) broj 1 5

JOZEFITA MARKU Review paperUDC:620.193.4:669.97

Alkali-silica expansion potentiality of Erzeni riverbed aggregates(Albania) and the risk of corrosion in concretes produced with them

The environmental and fuel efficiency reasons led the industry of building raw materials to developnew technologies for production of cements. The cements being produced have high alkali contentwhich in combination with some sorts of aggregates may influence the chemistry of the concretemixture that may cause long term harmful effects to concrete structures.In this paper it is succinctly reviewed a part of scientific research work done on the possibility ofthe manifestation of the harmful effects caused by Alkali-Silica Reaction (ASR) on concretes madeof high alkali cements and riverbed aggregates of Albania, in particular of those of Erzeni River,which is the most exploited one in Albania. The treatment of this topic has been a necessity and isconsidered very important for building industry in Albania, where traditionally low alkali cementshave been produced and used. Especially in the period of transition, when high alkali cementsstarted to be used both from import and domestic production, it is considered very important thestudy of the suitability of the riverbed aggregates in concrete produced with high alkali contentcement since there are no ways of preventing ASR after the concrete has been placed.The results and recommendations of this study serve to increase the builder’s awareness of theneed of proper investigation, from this point of view, of the raw materials prior to construction.They also contribute to environment protection both by recommending alternative aggregates toriverbed ones and by helping to avoid the degradation, in timeframe, of concrete structures.Keywords: Alkali-Silica Reaction (ASR), riverbed aggregates, chert, siliceous aggregate,limestone aggregate.

INTRODUCTION

Deterioration of concrete structures because ofalkaline attack of aggregates and ASR is causing agreat concern in many countries all over the worldand in almost all European countries, both becauseof the potential threat to the service life of concretestructures and the extra costs of repairing thestructures affected by this reaction.

ASR is a so-called heterogeneous chemical re-action between sodium and potassium hydroxidesin cement paste and certain alkaline reactive amor-phous minerals in aggregate producing a hygro-scopic gel which, when moisture is present, ab-sorbs water and expands causing degradation ofappearance (pattern cracking and excessive expa-nsion), deterioration in concrete strength and effec-ting structural behavior of concrete structures. Du-rability of concrete structures may not be directlyaffected by ASR, but expansive cracking of coverconcrete may increase the risk of reaching steelreinforcements by providing a route for water, airand chlorides. It will also increase possibility offreeze-thaw attack.

Author's address: Department of IndustrialChemistry, Faculty of Natural Sciences, Albania

Received for Publication: 17. 07. 2014.

Accepted for Publication: 21. 09. 2014.

There are three essential factors that cause theAlkali-Silica Reaction: alkalis, certain alkaline re-active amorphous silica minerals, and moisture ha-ving the role of the reagent and a transport media.The alkalis are mainly supplied by the cement pas-te of concrete or can under certain circumstancesbe derived from the aggregate material, mix water,ground water, chemical admixtures, pigments, etc.Moisture is mostly provided by “exposure condi-tions”, e.g. atmospheric water or service conditions.The mechanism of silica dissolution is not verymuch controlled by alkalis, as by dissolved OH-ionsbreaking silica bonds which then recombine withpresent alkali-ions.

The main contributor to the alkalinity of poresolution is the soluble alkali in cement.

Wet cement is a very active alkaline chemicalenvironment and chemical reaction occurs betweenthe aggregate particles and the cement filler. Ce-ments with an alkali content (Na2O+K2O) below0.6% (low-alkali cements) has been found to causea little expansion with reactive aggregates. On thecontrary, the high alkali cement is a very activealkaline chemical environment for some alkali reac-tive varieties of silica in aggregate, i.e. non-crysta-lline or imperfectly crystalline silica (such as opal,chalcedony, chert, tridimite, christobalite), strainedquartz or microcrystalline quartz (such as quar-tzite), glassy to cryptocrystalline matrix of igneousrocks (such as pumice), etc. Silica is an amphoteric


ZAŠTITA MATERIJALA 56 (2015) broj 16

material which means it dissolves at extreme pHvalues, in strongly acidic or strongly alkaline con-ditions and less around neutral pH. The dissolutionof silica is affected by pH as well as by foreignspecies in pore solution, foreign species and hyd-rous species in the solid silica, polymorphism ofquartz, the quality of crystal lattice, silica particlesize, coexisting minerals, etc.

The reasons for the recent apparently pre-valence of damage of concrete from ASR are con-sidered to be the changes in concrete technology(concrete mixes richer in cements are being used,producing higher total alkali contents in concrete)as well as in cement technology.

Changes in cement production methods (espe-cially in developed countries, but even in deve-loping ones) in order to comply with environmentalregulations have placed controls on the emission ofstack gases into the atmosphere. Therefore, thetendency is that the alkali content of cement to beincreased, because the dusts from kiln (rich ofalkali) are recycled and returned back to processadding the alkali load of cement. On the otherhand, in order to use fuel more efficiently, the wetprocess of cement production (where alkalis werepartly leached) is being abandoned and is beingsubstituted by dry process. So, the low-alkali ce-ments are unlikely to be produced and found in themarket.

In Albania, until the start of political transitoryperiod (year 1990), the construction sector needswere satisfied with in country produced cements.

After 1990, in the conditions of the upset of thedomestic cement production caused by closure ofseveral of cement factories, the cement needs ha-ve been compensated with cement imported fromother countries, like Italy, Croatia, Greece, etc.

Later on, even in Albania, the previous wetprocess (Fushe Kruja Cement Factory) has beenchanged towards dry clinker production processand the other new cement factories are based ondry cement production process, too.

So, nowadays in Albania, high alkali contentcements are being used in concrete and this islikely to happen even in the future.

In order to evaluate the potential risk of thealready built structures of the time period and forcomparison reasons, we have examined the che-mical content of cements produced in Albania du-ring the period of time 1980-1995, in the factoriesof F. Kruja, Vlora and Elbasan, as well as their rawmaterials.

Also, we have analyzed several of imported ce-ments, used in Albania in the last decades.

Therefore, in the conditions of using of thesehigh-alkali cements and guided by the world expe-rience and recommendations of many scientificauthorities of this field, we proceeded this research

to determine if any potential risk exists for mani-festation of ASR in concretes prepared with theriverbed aggregates of Albania, to evaluate theirpotential reactivity in concrete mixtures made withhigh alkali cement and, based on the classificationof their reactivity, to recommend builders the river-bed aggregates that they must avoid to use inconcrete production; especially in hydraulic struc-tures.

It is significant to point out that, this is the firstwork where the topic of the alkali-silica expansionpotentially of riverbed aggregates in Albania andthe risk of corrosion in concretes produced withthem is considered and evaluated.

In this regard, initially we studied the behaviourof aggregates taken from the main riverbeds ofAlbania.

The experiments are carried out according tothe method of continuity of tests (UNI 8520-22) thatincludes the petrographic examinations of aggre-gates, the accelerated expansion tests and long-term expansion tests. The data taken from theexperimental behavior of samples in these testsare graphically shown and statistically analyzedand commented.

The high values of expansions and the visiblecracks of the samples of Erzen (Tirana capital) andOsum (Berat city) riverbed aggregates classifiedthem as potentially alkali-reactive aggregates [1].

Out of these two potentially alkali-reactiveaggregates we choose the Erzeni riverbed aggre-gates for further more complex study because,being in the vicinity of two big cities Tirana andDurres, they are target of high exploitation due tobig demand for aggregates from the ever-growingbuilding industry in this region.

For this study the aggregate samples are takenat random along Erzen riverbed from Elbasan toDurres.

Based on the expansion values, a classificationof these aggregates from innocuous to moderatereactive aggregates was made [2-11].

But this classification was not definitive takinginto account that the aggregates containing morethan 2% of reactive constituents in the form of po-rous chert, flint or chalcedony (that is the case ofErzeni riverbed aggregates with above 2% mineralchert) may exhibit the so-called “pessimum effect”in accelerated mortar bar tests and can yieldmisleading results and inappropriate approval ofcertain active aggregates to be used in concreteproduction.

According to Hobbs and Shayan, the reason for“the pessimum content” of aggregate in the stan-dard accelerated tests, is that for a certain contentof alkalis, the expansion of mortar bars is increasedas the content of active aggregate is increased upto a point (“negative content”), beyond which there



are no more available alkalis to form expansive gel.At higher contents of active aggregate the amountof alkalis become so low or dilute in mortar thatoccur just a slight or not at all expansion.

So, the latent active character of some Erzeniriverbed aggregates is pointed out during theexperimental determination of the so-colled “pessi-mum content”. The results of continuity of tests areconfirmed by strength tests and durability onfreeze-thaw tests.

The evidence of “pessimum effect” clearlyshows that the mixture of aggregates of differenttypes (the so-called “sweetening of aggregates”)used as one of possible ways of minimizing thenegative effects of Alkali-Silica Reaction in concre-te, not always brings up to positive results [12-14].

Since the aggregate with its specific mineralo-gical composition has a direct influence in concretequality, in addition to the expansion tests of con-crete samples produced with Erzeni riverbed ag-gregates, some mineralogical investigations ofthese aggregates and the concretes produced withthem are carried out to evaluate the alkali-silicapotential reactivity of these aggregates and thequality of concrete produced with them [15,16].

Thin sections of concrete samples, that weretreated in expansion tests, are examined on pola-rized-light microscope and the main raw materialsof concrete (aggregate and cement paste) arestudied.

Also, the interior of concrete samples are exa-mined by SEM to identify the presence of internalcracking and the mapping of elements within theactive aggregate particles.

An attempt is made to study the influence ofconcrete mix design on the ASR, using Erzeniriverbed aggregates.

Through 31 sets of experiments, carried outwith different concrete mixtures, is investigated theinfluence on the expansion caused by Alkali SilicaReaction of water to cement ratio, aggregate to ce-menting material ratio and the percentage ofcopper slag as well as the concentration of alkalinein the experimenting environment.

The findings identified the content of slag andthe aggregate to cementing material ratio as signi-ficantly contributing to ASR expansion with a lessstrong influence of two other factors. Responsesurface modeling has identified a negative trend ofthe two principal factors and a direct trend of theother factors [14, 17 - 19].

SUMMARISED RESULTS AND DISCUSSION

1. As object of experimentations are selectedriverbed aggregates. Why?

The aggregates traditionally used in concreteproduction in Albania are riverbed aggregateswhich are plenty, easy accessible and near the

main towns that makes them attractive to builders.In Albanian language they are called “inerte” thatmeans non-reactive ingredient in concrete pro-duction process but their “non-reactivity” is to bequestioned in certain conditions.

In the other hand, scientific researchers havefound that the aggregates containing more than 4%total silica, when used in concrete production, maymanifest the Alkali-Silica Reaction (ASR).

In Albania there are two options of aggregatesfor use as fillers in concrete production; the river-bed aggregates and the artificial aggregates pre-pared by comminuting the limestone rocks takenfrom limestone quarries.

Since the riverbed aggregates of Albania aremainly siliceous aggregates (total silica content is25-65%) and the total silica content of limestoneaggregates is low (up to 0.5%); we chose to studythe ASR potentiality expansion of the riverbedaggregates without considering the limestone ones;which in our experimental work are used only forcomparison reasons and as additive aggregates[2].

2. The actual possibility of the Alkali-Silica Reaction(ASR) or so-called “cancer of concrete” inconcrete structures in Albania.

In Albania, before the transition period (1990 -1995), in country produced cements are used.

These cements, produced in Fushe-Kruja, Vlo-ra, Elbasan, Shkodra, etc. factories, had low alkalicontent that was as the result of the wet techno-logical process (where the kiln dust, abundant withalkalies, was partially returned back to process, butmost of it was discharged into atmosphere) andbecause of the low content of alkali in cement rawmaterials (limestones and clays).

Most of the concrete structures are made withriverbed aggregates and in country producedcements. In these concrete structures there wasnever noticed any problem that could be related toASR. Probably this is dedicated to low alkalicontent of cements used in that time.

After 1990, with the restoration of the marketeconomy and the policy of open doors, theimported cements from Italy, Greece, Croatia, etc.started to replace domestic cement production.

Due to environmental restrictions and cost ofproduction, the imported cements had higher alkalicontent. The trend of producing high alkali contentcements is followed by the reactivated Albaniancement industry and nowadays almost all cementused in Albania is with high alkali content.

For the evaluation of the possibility of the mani-festation of ASR (or as it is called “the cancer ofconcrete”) in Albania we started with the exami-nation of the cements used and likely to be useddividing them into 2 periods; before and after 1995.



The second period is not much different from todayand the foreseen future trend.

The equivalent alkali content of these cementsis represented in the Graphic 1. In the first row arerepresented some in country produced cements(the mean alkali content of these cements resultedto be up to 1%) and raw materials used for theirproduction before 1995. Whereas, in the secondrow is represented the Na2Oeq content of someimported cements used after 1995 (the mean alkalicontent resulted to be 1.8 %) in Albania [1, 2].

Figure 1 - Na2Oeq content of some in countryproduced cements before 1995 and their raw

materials, as well as the Na2Oeq content of someimported cements after 1995

From the results of cement analyses, shown inFigure 1, and the general knowledge on the mani-festation of ASR, we would preliminarily evaluatethat the risk of manifestation of deterioration effectsof ASR in concrete structures that have been builtbefore 1995 is very low to inexistent, while the riskcould increase to medium or high for structuresbuilt after 1995 or in process of building without theproper check of the reactivity of aggregates.

Since there is a considerable potential risk ofASR manifestation in concretes to be producedwith nowadays available cements and riverbedaggregates of Albania, the right solution is the priorcheck of aggregates and the use of non-reactiveaggregates only; especially in hydraulic concretestructures.

3. Potential risk manifestation of Alkali-SilicaReactions (ASR) in concretes prepared byaggregates from different riverbeds in Albania

In Albania there are many rivers, aggregates ofwhich are used as fillers for mortar and concreteproduction as: Erzen, Tërkuza, River of Tirana,Shkumbin, Fan, Mat, Kir, Drin, Devoll, Vjosa,Osum, Shushica, Bistrica, Drino and Valbona.

In our study, for the determination of potentialalkali-silica reactivity of aggregates in presence of

alkali, the samples are collected from the riverbedsof eight main rivers of Albania (Erzen, Shkumbin,Fan, Mat, Kir, Drin, Vjosa and Osum). The samplesare taken at random in the units of aggregateprocessing. The aggregate samples are collectedin three different levels of each aggregate heap ofthe processing unit. They are mixed together,homogenized and representative samples till 5kilograms are prepared.

Tests are carried out according to the ItalianStandard UNI 8520-22 ''Determination of potentialreactivity of aggregates in presence of alkali'',1999. According to this method, this determinationmust be performed by means of three tests, donein continuity: Expert petrographic examination of aggregates Accelerated expansion testing of mortar bars

made from these aggregates Long term expansion testing of such mortar

barsIf petrographic examination does not indicate

the presence of alkali-active minerals, the exami-ned aggregate may be considered non alkali-reactive and it is considered innocuous to be usedin concrete. Alkali-reactive minerals are siliconminerals where silica is in a reactive form, such asopal, etc. They are characterized by a randomnetwork of tetraedra with irregular spaces betweenthe groups of molecules. The reactive forms have ahigh internal surface area, making them muchmore susceptible to surface hydration and tobreakage by alkali cations of silicon-oxygen bondthat bind together the silicon-oxygen tetraedra.

If petrographic examination proves the presen-ce of alkali-reactive minerals, then the acceleratedexpansion testing of mortar bars must be carriedout. If the expansion does not exceed the limit of0.1%, after 14 days of exposure to the sodiumhydroxide 1N solution at 800 C, the aggregate isconsidered to be non-reactive.

The long-term expansion test must be carriedout if expansion after accelerated expansion testlies at the uncertainty zone (0.1-0.2%). Aggregateis considered appropriate to be used in concrete, ifthe expansion does not exceed the limit of 0.08%,after 3 months of exposure to water, at 380 C or of0.1% after 6 months at the same conditions [3].

From petrographic examination of aggregatestested, resulted that aggregates of some of rivershad reactive mineral, chert (a reactive mineral inwhich predominate microcrystalline chalcedonyand porous opaline silica, with variable percent ofcryptocrystalline quartz) in these quantities:

Samples of Ezen aggregate, Ko: 4%Samples of Shkumbin aggregate: 3%Samples of Fan aggregate: 2%Samples of Drin aggregate: 4%Samples of Osum aggregate: 2%



Accelerated test has been carried out for thesamples of aggregates of all rivers, regardless ofthe presence of chert in them.

The aggregates were crushed and their gra-nulometric content was regulated to fulfill the follo-wing requirements: 10% (by mass) - grains of 2÷4mm; 25% (by mass) - grains of 1÷2 mm; 25% (bymass) - grains of 0.5÷1 mm; 25% (by mass) – gra-ins of 0.25÷0.5 mm; 15% (by mass) - grains of0.125÷0.25 mm.

Portland cement, with alkalis content of 0.78%,CaOfree content of 0.48%, SO3 content of 3.38%and specific surface 4041 cm2/g is used for thetests.

The cement to aggregate ratio was 1 to 2.25and the water to cement ratio was 0.47. For eachaggregate, bars of 4 x 4 x 16 cm were cast. After24 hours we demoulded the bars and submergedthem in a plastic container with water. Afterwards,the container was closed and held at 800 C for 24hours. Immediately after the bars were taken out ofthe water, we measured their length (zero measu-rement).

After the first length measurement, a part ofbars were left for hardening in natural conditionsand the others were submerged in 1N NaOHsolution, at 800 C. During the hardening time of 14days in these conditions, we measured the expan-sions of bars on every working day at the sametime. The average daily length change of treatedbars is measured with a precision of a 0.002 mm

and it is presented graphically as the function of thetime.

Figure 2 - The apparatus used for longitudinalexpansion measurements of mortar bars

Experimental results of average daily expan-sions for treated bars prepared by aggregates ofeight different riverbeds are presented in Figure 3.

From Figure 3, it is evident that the aggregatesbehavior in the treated bars is different. The expan-sions of bars prepared with the aggregates ofErzen and Osum riverbeds are respectively0.287% and 0.291%, while the expansions of thebars prepared with aggregates of the other river-beds are less than 1%.

Figure 3 - The average length change of treated bars as the function of time

These experimental results led us to classifythe aggregates into two types:

The first type include the aggregates of Erzenand Osum rivers with average expansion over0.2% that according to the Standard used for thetests are considered as potentially alkali-reactive.

The second type include the aggregates ofDrin, Fan, Vjosa, Shkumbini, Kiri and Mati river-beds with average expansion of less than 0.1%that are considered as non-reactive.

These experimental results confirmed the needof the use of the method of the continuity of testsforeseen in the Standard because regardless of the



presence of chert in samples of aggregates ofShkumbin, Fan and Drin, the final expansions ofmortar bars prepared by them were under 0.1%.

In fact, there is a complex relation between thequantity and fineness of reactive material in aggre-gate with the degree of expansion caused by itspresence. The evaluation of graphics is doneaccording to Chi^2 test. For a probability α=0.95and k = 1, the calculated Chi^2 values were lowerthan tabular ones. This shows a good accordanceof graphics with experimental values.

The visual examination showed that only thetreated bars of Erzen and Osum were full of mappattern crackings, which are typical for ASR. Theflexure strengths of these mortar bars were decrea-sed at the values 33.15% and 26.76%; the comp-ressive strengths were decreased 32.4% and29.6% [1, 3, 13].

Figure 4 - One of the bars made with aggregates ofErzen riverbed after 14 days treatment in 1N NaOH

solution, at 800 C

4. The alcaline attack of Erzeni riverbedaggregates used in concrete mixtures and therisk of potential manifestation of Alkali-SilicaReactions (ASR) in concretes prepared by them

From the above experimental study we foundthat, out of the riverbed aggregates studied, two ofthem Erzeni and Osum riverbed aggregates, clas-sified by us as first type aggregates, are potentiallydangerous to be used in concrete production.

The aggregates of these two riverbeds are tra-ditionally used for concrete production and actuallythey are very attractive to builders due to their lo-cation.

In particular the aggregates of Erzeni riverbedare highly exploited during the last decades andare a target for more exploitation nowadays and infuture due to vicinity with two biggest cities of Alba-nia which are in a process of fast growing. Thetrend of high multi-floors buildings, massive struc-tures and new complex constructive elements thatare in these cities’ planning requires an urgent veri-fication of the suitability of aggregates to be used inthese concrete structures.

For these reasons out of the two potentiallyalkali-reactive aggregates we choose the Erzeniriverbed aggregates for further more complexstudy.

So, our further study aimed at evaluating andclassifying of Erzeni riverbed aggregates, regardingtheir Alkali-Silica Reactivity. The samples are takenalong Erzen riverbed from Iba village (near Elba-san) to Shijak village (near Durres). The samplesare taken at random in 12 centers of aggregateprocessing facilities along Erzeni riverbed.

Figure 5 - The map of Erzeni river basin and the places where samples are taken along its riverbed



For preparing of the representative aggregatesamples, the same procedure described above isused; as well as the same standard, mentionedabove, is used for the determination of the alkalisilica potentiality of the aggregates.

The aggregate samples are named with num-bers and the zones along Erzeni riverbed wherethey are taken from are indicated on the map,Figure 5.

The main results of the experimental findings ofthe petrographic examinations, the accelerated andlong-term (three months) tests for the 12 aggregatesamples are submitted below in the form ofsummarized tables and graphics.

The mineralogical examination of the aggre-gates is carried out with binocular-stereoscopicmicroscope and the mineral content as well asrelative quantities of constituent minerals of eachsample of aggregate are determined.

Table 1 - The mineralogical content of aggregate samples

Mineral content in %

Samples A1 A2 A3 A4 A5 A6 A7 A8 A9A10

A11A12

Calcite 18 19 25 20 25 20 22 30 30 36 28 30Quartz 28 23 22 18 26 25 18 25 27 28 23 27Chert 1– 2 2– 3 1– 2 2 1– 2 2 2-3 2 3 2 2 2Calcareous Clay 38 42 40 45 35 40 35 30 30 28 40 34

Others (coal, slag, waste, etc) 14 13 11 15 13 13 22 11 10 7 7 7

Figure 6 - The average expansion of bars (produced with each sample of aggregate)during the accelerated tests

Figure 7 - The average expansion of bars (produced with each sample of aggregate) during theaccelerated tests and the further treatment in 1N alkaline solution, in environmental temperature



Figure 8 - The average expansion of bars (produced with each sample of aggregate)during the long-term (there months) tests

As it is shown in the Table 1, all the samplescontain some chert which is an alkali-reactive mi-neral. Referring to the recommendations of scien-tific literature, if the content of chert is over 0.5%,the aggregate may be reactive and therefore mustbe tested further for its alkali-silica reactivity accor-ding to the method of continuity of tests.

From the Figure 6 it is evident that, after 14days of exposure to the sodium hydroxide 1Nsolution at 800 C, the expansions of the mortar barsprepared with aggregate samples A1, A2, A7 and A8(respectively 0.246, 0.267, 0.250 and 0.199%)exceed the limit of 0.2%. Thus, these aggregatesare considered to be reactive (according to UNI8520-22) [2, 3].

The map pattern cracking, which is typical forASR, is easily seen on the surfaces of thesetreated bars.

The expansions of the bars prepared withaggregate samples A3, A4, A5, A6, A11 and A12, afterthe accelerated tests, were from 0.1 to 0.2% (theuncertainty zone). The expansions correspondingto the bars prepared with aggregate samples A9and A10, after the accelerated tests, were below0.1% (respectively 0.053 and 0.089%).

Here we noticed that, in the first two days, theexpansions of bars prepared by all samples werenearly the same; after that the bars prepared withaggregate samples which have resulted as reactiveexpanded more than the others. The daily experi-mental values of expansions of bars prepared withall samples were regressed to sigmoidal graphics.The statistical evaluation of graphics indicated agood accordance of graphics to experimentalvalues.

In addition, we observed that, the degree ofexpansions in the accelerated tests is not in direct

proportion to the quantity of alkali-active material inaggregates.

After the accelerated tests, we left the bars inthe same 1 N alkaline solution but in room tempe-rature and we measured their linear changes. As itis seen from the Figure 7, they continued toexpand. This behavior of the mortar prepared byalkali-active aggregate has been noticed even bysome authors in their experimental studiesdescribed in literature. The ASR gels, formed underthe hard aggressive conditions in accelerated tests(800 C and high alkaline environment), continue toabsorb water and to swell, even in roomtemperature.

The results taken from the long-term tests andespecially the final expansions after three months(higher than the limit of 0.08%), brought out that allthe tested samples of Erzeni riverbed aggregatesare potentially alkali-active.

The expansions of mortar bars prepared withthe aggregate samples and cured in acceleratedand long-term tests conditions are compared withthe expansions of the respective mortar bars har-dened in natural conditions (in distillated water atroom temperature). The compression and flexurestrengths, as well as the water absorption and thechange of mechanical strengths after 16 freeze-thaw cycles for all mortar bars are measured, too.This is done in order to evaluate the influence ofthe test conditions in physico-mechanical perfor-mance of hardened mortars prepared with the ag-gregate samples. The respective results are shownin the Table 2.

From the Table 2 we notice that the flexurestrengths, compared with compressive ones, aremore sensible towards the tests conditions.



Table 2 - Some physico-mecanical characteristics of mortar bars treated in natural conditions, in alkalineenvironment of accelerated tests and in long-term (three months tests)

Expansion (%) After 16 freeze-thaw cyclesMortarbars

preparedwith

aggregatesample

Flexurestrength, Sf

(Mpa)

Compressionstrength, Sc

(MPa)

Waterabsorption

(%)After

expansiontests

After 42days in

1Nalkalinesolution

Thedecrease(%) of Sccomparedwith Sc ofnatural

hardenedmortars

Thedecrease (%)

of Sfcomparedwith Sf ofnatural

hardenedmortars

Compressionstrength,Sc(MPa)

The changeof

compressionstrength (%)

After hardened in natural conditionsA1 9.49 59.64 3.86 - - - - 68.0 4 +14.08A2 9.35 60.05 3.92 - - - - 65.94 +9.81A3 8.79 58.56 3.65 - - - - 61.54 +5.09A4 9.78 56.70 3.20 - - - - 65.56 +15.63A5 9.05 60.64 4.02 - - - - 69.10 +13.96A6 9.54 61.34 3.65 - - - - 69.96 +14.06A7 9.75 54.32 3.64 - - - - 59.68 +9.85A8 8.01 56.37 3.79 - - - - 63.87 +13.32A9 9.45 57.42 3.52 - - - - 61.20 +6.6A10 9.78 55.98 3.04 - - - - 64.42 +15.08A11 10.00 53.94 3.46 - - - - 61.38 +13.80A12 8.45 61.23 3.75 - - - - 66.28 +8.25

After accelerated expansion tests and 42 days of treatment in 1N alkaline solution, in room temperatureA1 9.26 54.76 1.70 0.246 0.290 -8.18 -2.42 53.68 -1.96A2 6.87 50.38 1.20 0.267 0.340 -16.10 -26.55 48.87 -2.99A3 8.52 54.45 1.91 0.110 0.226 -7.04 -3.07 54.19 -0.47A4 9.146 52.67 1.95 0.148 0.225 -7.11 -6.58 52.53 -0.25A5 7.81 53.20 1.40 0.132 0.361 -12.26 -13.69 51.61 -2.98A6 7.45 52.83 1.41 0.100 0.365 -13.88 -21.87 51.06 -3.35A7 9.52 51.72 1.97 0.250 0.268 -4.78 -2.30 50.87 -1.64A8 7,57 54.51 2.47 0.199 0.212 -3.30 -5.44 53.27 -2.27A9 8.65 54.92 2.00 0.053 0.237 -4.36 -8.43 54.45 -0.84A10 9.39 51.38 1.21 0.089 0.282 -8.21 -3.94 50.05 -2.58A11 8.35 44.68 2.00 0.108 0.338 -17.17 -16.53 43.05 -2.64A12 6.55 52.29 1.44 0.116 0.354 -14.60 -22.53 51.05 -2.37

After long-term (there months) testsA1 9.33 57.32 1.63 0.219 - -3.88 -1.63 56.90 -0.73A2 9.03 59.95 2.11 0.227 - -0.16 -3.44 59.62 -0.55A3 8.77 58.40 1.90 0.164 - -0.26 -0.20 58.41 +0.02A4 7,96 49.20 2.65 0.451 - -13.22 -18.56 48.80 -0.68A5 8.55 57.97 2.33 0.213 - -4.40 -5.51 57.94 -0.04A6 9.29 61.08 2.31 0.199 - -0.41 -2.56 61.05 -0.05A7 9.52 53.99 2.16 0.173 - -0.6 -2.39 53.90 -0.15A8 7.10 52.34 2.16 0.284 - -7.14 -11.34 52.05 -0.54A9 8.74 57.33 2.90 0.146 - -0.14 -7.55 57.27 -0.10A10 9.31 55.86 2.40 0.139 - -0.20 -4.78 55.70 -0.28A11 8.10 48.99 2.93 0.283 - -9.16 -19.00 48.63 -0.72A12 7.53 59.35 1.86 0.186 - -3.07 -10.78 58.35 0

According to literature in both types of tests(accelerated and long term) the reaction productsformed are the alkali-silica gels; which have the

same composition because their formation mecha-nisms are the same but the difference exists at therate of alkali-silica reaction and the amount of gelproduced.



The results taken from our experiments alsoshow that the decreases of the mechanicalstrengths of the mortar bars after the acceleratedtests (compared with those of bars hardened innatural conditions) are higher than the decreasesof the mechanical strengths after the long termtests (compared with those of bars hardened innatural conditions). This leads to the conclusionthat with the increase of severity of test conditionsincreases the scale of deterioration of the physico-mechanical characteristics of the mortar samples.

This tendency is verified even by the results ofthe freeze-thaw tests.

Meanwhile the results water absorption shownin table above indicate a different tendency: thewater absorption of mortar samples decreases withthe increase of the test severity. Thus, the waterabsorption of mortar samples, which passedthrough the long term tests (mild condition test), ishigher than of those hardened in natural conditionsand lower than the water absorption of those whichpassed through the accelerated tests condition(severe test).

Since the water absorption of a porous materialis not the same as the porosity, in our case the re-sults of water absorption tests are explained withthe filling of the pores and channels inside the trea-ted mortar bars with gelatinous reaction product,already saturated with water, resulting in lower wa-ter absorption values. The results of water absorp-tion experiment led us to think that ASR productsare present in treated concrete samples and thatthey are proportionally developed with the increaseof severity of the test conditions, that means withthe increase of simulated aging.

The results of the physico-mechanical tests,being in line with the water absorption indicatorsand with verified expansions of treated mortar sam-ples give reason to conclude that the tested aggre-gates are potentially alkali silica active.

5. Complexities of alkali-silica reaction (ASR)manifestation on concretes produced with Erzeniriverbed aggregates

The evaluation of the possibility of manifesta-tion of ASR phenomenon is somewhat complicatedby the fact that sometimes the use of acceleratedtest to determinate the potential alkali-silica react-ivity of concrete aggregates, can yield misleadingresults and inappropriate approval of certain reacti-ve aggregates to be used in concrete production,even though in practice (in concrete structures) andin long-term tests, they perform as alkali reactiveaggregate. This is the case of aggregates contai-ning more than 2% of reactive constituents in theform of porous chert, flint or chalcedony. Theseaggregates exhibit the so-called “pessimum effect”in accelerated mortar bar tests.

According to researches and world experience,in this case there is a specific content of reactivematerial in aggregate, which in accelerated testsgives a maximum expansion or a peak. This quan-tity is called “negative content” (pessimum content)and indicates the worst possible condition. Thereason for “the pessimum content” of aggregate inthe standard accelerated tests is found to be in themechanism of reaction development where for acertain content of alkalis, the expansion of mortarbars is increased as the content of reactive aggre-gate is increased up to a point “negative content”,beyond which there are no more available alkalis toform expansive gel. At higher contents of activeaggregate, the amount of alkalis become so low ordilute in mortar that occur just a slight or not at allexpansion.

It is said, that in this case the concrete has rea-ctive “buffer” silica. If at a further time, some avail-able alkalis from outside sources (e.g. antifreezesalts, ground, etc.) are introduced in the concretepore solution, then the excessive active silica canundergone ASR and can produce enough gelwhich with the water absorption may swell and incontinuity cause the damage of concrete.

The other grave problem is that the dilution oraugmentation of such aggregates with other non-reactive aggregates to avoid their pessimumproportion must not be used to control ASRexpansion without thorough testing to identify non-expansion aggregate combinations.

From the results of tests on Alkali-Silicareactivity of Erzeni riverbed aggregates carried outaccording to the Italian Standard UNI 8520-22 andshown in the paragraph above, one of theaggregate samples (A9, taken near Ndroq village)contained 3% of active mineral chert (this quantityis higher than in other tested aggregate samples).Nevertheless, the average expansion after theaccelerated test was 0.053% (under the limit valueof 0.1%). So, according to the Standard UNI 8520-22, this aggregate might be considered inactiveand appropriate to be used in concrete and mortarproduction.

But, the results of the long–term tests (theexpansion above 0.08% after three months of tre-atment of mortars bars in distillated water, in 380 C)confirmed that all the aggregate samples, includedeven A9, were alkali-reactive.

Based on the respective literature, the resultstaken with the mortars prepared with the Erzeniriverbed aggregate sample with 3% chert, prom-pted us to carry out some further tests to prove ifthis sample displayed “negative content”.

For this purpose, in the mixture of mortar barsbesides Erzeni riverbed aggregate sample (A9) weused as additive aggregate a limestone aggregatesample taken from a quarry near Iba village on theroad Tirana - Elbasan.



From chemical analyses, the total silica contentof this limestone sample resulted 0.28% (on mass).From petrographic examination and acceleratedtest of mortar bars, the limestone aggregate sam-ple resulted non-reactive.

Both aggregate samples (reactive aggregate A9and non-reactive limestone one), were ground andtheir granulometric content was corrected accor-ding to the requirements of Standard UNI 8520 –22.

After homogenization the reactive aggregate A9was used for mortar bars production on the ratios:

0 (G), 25 (A), 50 (B), 70 (C), 80 (D), 90 (E), and100% (A9) of the total weight of the filler.

These ratios corresponded to the respectiveamounts of: 0, 0.75, 1.5, 2.1, 2.4, 2.7, and 3% ofreactive constituent chert in the mixed aggregate.

The mortar bars were tested according toaccelerated test.

Below are shown the results of accelerated testfor mortar bars prepared with various amount ofreactive aggregate.

Figure 9 - The average expansion of mortar bars (produced with mixed aggregate) duringthe accelerated tests

Figure 10 - The final expansion of the mortar bars as function of reactive aggregate content in mixed filler

It is evident that after the accelerated test, theexpansions of all mortar bars prepared with mixedaggregates (reactive aggregate A9 and limestoneaggregate) were higher than expansions of mortarbars prepared by reactive aggregate or limestoneaggregate used individually.

The final expansion of mortar bars, where thereactive aggregate A9 is used in the amounts 25%and 90%, lied at the uncertainty zone (0.1-0.2%).

The final expansion of mortar bars, where thereactive aggregate A9 is used in the amounts 50,70 and 80%, was above (0.2%).



From the Figure 10, where is shown the finalexpansion of the mortar bars as function of reactiveaggregate content in mixed filler, it is seen that forreactive aggregate A9 and its studied ratios withlimestone aggregate, exists a “negative content” inrelation to alkali-silica reactivity. This contentbelongs to the ratio 50:50 (reactive aggregate: non-reactive limestone aggregate), which correspondsto the content of 1.5% of reactive mineral chert.The lower critical limit belongs to the amount round30% reactive aggregate (0.9% chert) and the uppercritical limit belongs to the amount round 85%reactive aggregate (2.55% chert).

From the results of these experiments we cameto the conclusion that the “pessimum effect” happe-ned while treating the aggregate sample A9 withaccelerated test procedure.

In this case, due to velocity of reaction causedby severity conditions of the accelerated test, inmortar bars prepared by 100% reactive aggregate

A9 (3% chert), “an outside zone of reaction” couldhave been formed. The outside zone reactionforms a barrier which confined the further entranceof alkalis from NaOH solution and it seems to bethe determinant (critical) factor in accelerated test.So, the ASR activity at the outside zone ofaggregate, results in formation of a gel type lessropy than in mild testing conditions. This gel blocksthe voids of cement paste and inhibits the furtherentrance of NaOH into the interior part of mortarbars, thus the reaction occurrence there. The“negative content” indicates the latent alkali-silicareactivity of aggregate.

In order to have a full picture of the pheno-menon, we made the physico-mechanical tests ofthe mortar bar samples produced with mixedaggregates before and after the accelerated tests.

The respective results are shown in Figures 11and 12.

Figure 11 - Some physico-mechanical characteristics of mortar bars with mixed aggregatesafter the accelerated tests

Figure 12 - The changes of compressive strengths of mortar bars with mixed aggregates after freeze-thawcycles (The expansions, in %, after accelerated tests are shown for each specific mixed aggregate)



It must be noted that when mixed aggregatesare used as mortar fillers, in addition to the Alkali-Silica Reaction occurrence and its consequences,the different physico-mechanical characteristicsbetween the two types of aggregates (siliceous andlimestone ones) have an importance influence tothe characteristics of hardened mortars. Here aresome indicators: compression strength (comp. strength limestone <

comp. strength siliceous aggregate); water absoption (water absoptionlimestone > water

absoptionsiliceous aggregate); the decrease of compression strength after fre-

eze-thaw cycles (decrease of comp.strengthlimestone >> decrease of comp.strengthsiliceous agregate); etc.So, checking from mortar bars with sample G to

those with A9 it is seen that; there is not any regu-larity for flexure strengths, the compressivestrengths are increased from G to A9, the waterabsorption is decreased from G to A9, the expa-nsion curve shows a peak for B (“pessimum con-tent” of A9 aggregate sample), the compressivestrengths after freeze-thaw tests are at minimumvalues for mortar bars B.

Finally, after analyzing the results taken fromthe continuity tests and other tests described abo-ve, we conclude that: The examined aggregate samples of Erzeni

Riverbed are potentially alkali-reactive. Based on the fact that from 92% of the exami-

ned cases are taken results in line with theStandard UNI 8520-22 recommendations andthe world experience, we consider that theused method for the potentially alkali-silica rea-ctivity determination of aggregate samples isthe right one and permits us to draw correctconclusions and to give useful recommenda-tions.

The fact that for one of aggregate samples,(8% of the examined cases), the result of theaccelerated test conflicts the result of the long-term test, does not show that the acceleratedtests are ineffective, but the fact that the ace-lerated tests have to follow the petrographicexamination and must be used carefully.

The results taken from our experiments confir-med the recommendations given in the respe-ctive literature, for using the method of conti-nuity of tests under a thorough cycle (petro-graphic examination, accelerated tests andlong-term tests 3 or 6 months long) in caseswhen the aggregate to be tested contains morethan 2% of reactive constituents in the form ofporous chert, flint or chalcedony.

The expansion of the mortar bars preparedfrom alkali-silica aggregates is influenced bythe chert presence. But, there isn’t a directrelation between the amount of chert in aggre-gate and the expansion value. Thus, expansionisn’t influenced only by the chert presence inaggregate, but rather by the chert amount abo-ve 2%, the chert composition and its specificcharacteristics in each aggregate, other silice-ous constituents in aggregate, as well as otherfactors that may have effect on the solubility ofactive silica forms.

6. Microscopic observations in relation to thepossibility of the of Alkali-Silica Reactionmanifestation in concrete prepared by ErzeniRiverbed aggregates

In addition to aggregate analyses, the micros-copic examination of the concrete helps to confirmthat a concrete produced with aggregates contai-ning silica could be vulnerable towards ASRphenomenon.

A small magnification of a smoothed concretesurface shows the rings of reaction around parti-cles of reactive aggregate. In a thin section of theconcrete sample, signs of ASR include cracks origi-nating from the particles of the reactive aggregate,discolored zones around the aggregate granulesand the filling of the cracking gaps with gel.

To check if the ASR related signs were obvio-us, besides the recommendations of the StandardUNI 8520-22, 1999, several parts cut from the mor-tar bars treated in the accelerated tests were exa-mined using stereomicroscope (10X). These partswere taken in inner central zones as well as 4 mmfrom the outside surface of these bars. From thestereoscopic microscope observations (10X) of thetreated mortar bars it isn’t seen any visible cracks.

Polished thin sections (0.1 to 0.2 mm) of allmortar samples, that were treated in expansiontests, are examined on polarized-light microscopeand the main raw materials of mortars (aggregateand cement paste as binding material) are analy-zed. The photographs are taken with digital cameraon the microscope’s screen.



Figure 13 - View on stereoscopic microscope (10X) of a mortar bar prepared by aggregate sample A2,after alkaline treatment (on the left – the surface part, on the right – the interior one)

Also, the interior of treated mortar bars are exa-mined by SEM to identify the presence of internalcracking and the mapping of elements within thereactive aggregate particles. For comparison rea-sons, photos of the microstructure of mortarshardened in natural environment are taken, too.The photos of microstructure are taken from theinner zones and the near outside surface of bars’

zones of the irregularly broken parts of bars as wellas of the respective prepared polished surfaces ofbars. Also some useful information is taken by X-Ray Elemental Map (EDX-microanalysis).

The main observed findings are shown here inthe form of a group of photos only for the hardenedmortars prepared by the Erzeni riverbed aggregatesample A2.

Figure 14 - Views of sandy granules from a thin section of mortar bar produced with aggregate of sample A2hardened in natural environment, taken with polarized-light microscope (100X), with and without analyzer (left-

right). The background is dark because it is photographed with digital camera from the screen of the microscope

a) b) c) d)

Figure 15 - Views of sandy granules from thin sections of mortar bar produced with aggregate ofsample A2 hardened in alkaline solution, taken with polarized-light microscope (100X) with analyzer

except for the last one



a) b) c) d)

Figure 16 - SEM photo of the surface of breaking (a, b) and polished surface (c,d) of the mortar barproduced with aggregate of sample A2 hardened in natural environment (a,c) and in alkaline solution (b,d)

Figure 17 - EDX photo where we can trace, at a magnification of 3116 X, the content of elements Si,Na and K within and around of a silica sandy granule in the mortar bar produced with sample A2

aggregate, hardened in alkaline solution

From the observation, using optic microscope,of the thin sections prepared from one of mortars(sample A2), hardened in NaOH 1N solution at thetemperature 800 C, was noticed the presence ofsilica particles that had reacted with bindingmaterial.

In the photos (Figure 14 and 15) of this sample,an interposition of the binding material (cement)with the silica particles of the aggregate wasnoticed, as well as discolored rings around aggre-gates and here and there cracks of silica granules.All these are characteristic signs of Reaction Alkali-Silica.

Results obtained from accelerated tests areconfirmed by the observation using SEM.

Comparing the SEM microstructure photos(Figure16 a, b) of the mortar bar’s surface ofbreaking, it is obvious the distinction between themicrostructure of the cement paste of concretehardened in natural environment and of thathardened in alkali environment where ASR causedan expansion.

In the case of bars hardened in natural environ-ment there is a more homogenous microstructureof cement paste compared with prisms hardened inalkali environment.

Comparing the SEM microstructure photos ofthe polished surfaces of mortar bars produced withthe same aggregate sample A2, but hardened indifferent environments, it is noticed that cracks arepresent only in the sample hardened in alkalineenvironment.

The accelerated tests in presence of alkalishave simulated the aging of the mortar bars andcaused their expansion and consequently thecracks that deteriorate the appearance andfunctional characteristics of the concrete.

From Elemental Distribution Map (distribution ofelements, EDX), Figure 17, it is noticed that wherethe concentration of silica is bigger (in the silicagranule), there is a bigger accumulation of thesodium ions compared with the cement pastearound it. This confirms the conclusion of thepresence of the alkali-silica gel formed as productof ASR.

Based on the above experiments and observa-tions, we confirm that the aggregates of river Erzenare sensitive towards alkali environment of themortars and concretes and may influence negati-vely in the characteristics and life expectancy of themortars and concretes produced with them if noproper intervention is made in mix design [2, 16].



7. Influence of the concrete mix design on Alkali-Silica Reactivity of Erzeni Riverbed aggregates

The purpose of this research has been thedetermination of the influence in the concreteexpansion caused by ASR of these factors: Water to cementing material ratio in the mortar

mix design (z1). Concentration of NaOH solution in accelerated

expansion tests (z2). Quantity of copper slag used for partial

substitution of Portland cement in the mortarmixture design (z3).

Aggregate to cementing material ratio in themortar mix design (z4).The other factors that are considered to have

minor influence in the concrete expansion causedby ASR phenomenon are kept, to a practicalextend, constant in all experiments performed.

An attempt is made to express mathematicallythe relationship of the concrete expansion causedby ASR (y) and the over mentioned four mainfactors (z1, z2, z3 and z4).

Based on the theoretical and practicalconsiderations, the level zero zj

0 and the step ofvariation ∆zj were set up as well as the codifiedvariables for every factor:

1 11

1

;oz z

xz

2 2

22

;oz z

xz

3 33

3

;oz z

xz

4 4

44

oz zx

z

The zone of variation of the participant factors

in the experiment, the level zero zj0 and the step

variation ∆zj set up for each factor are shown in theTable 3.

Table 3 - Level zero and the step variation values for each factor

Water to cementratio, (z1)

Concentration of NaOHsolution, M (z2)

Content of copper slag,in %, (z3)

Aggregate to cementingmaterial ratio, (z4)

zjo 0.47 1 20 2.25

∆zj 0.03 0.2 10 0.4+1 0.50 1.2 30 2.65-1 0.44 0.8 10 1.85+2 0.53 1.4 40 3.05-2 0.41 0.6 0 1.45

Therefore the expansion y will be function ofcodified variables y = f (x1, x2, x3, x4).

The regress equation has been quested in theform of second degree polynomial.

where: j = 1, 2, 3 or 4.Based on the method of experiment planning

for uniform rotational plane of second order with 4factors, a set of 31 experiments are arranged.

The raw materials used in this study includefine reactive aggregate, Portland cement, copperslag and distilled water. The fine aggregate is prepared from riverbed

Erzen which, with round 2% chert in itsmineralogical content is a potential reactiveaggregate as evaluated according to UNI 8520-22 tests [2].

As cementing material is used clinker with 5%gypsum produced in Fushë- Kruja CementFactory, Albania. The content of Na2Oeq in

cement was 1.22%. The cement was ground tospecific surface 3887cm2/gr.

The Copper slag, a waste of the Copper Pro-duction Plant in Laç, Albania, was ground atthe same specific surface as Portland cementand used in various quantities for replacing ofPortland cement.Experiments planning guidelines are based on

the experience and the literature of concrete pro-duction, aiming that the values given to each factorin each experiment were within the limits of thenormal concrete production as well as around thevalues recommended by the Italian standard for theevaluation of the alkali-silica activity of the aggre-gates. The slag quantity range is based on the cur-rent use of the copper slag in cement production inAlbania.

The values of all factors as well as their respe-ctive codified variables involved in each experimentare shown in Table 4.

The evaluation of the Alkali Silica Reactivity ineach of 31 experiments is performed according toUNI 8520-22 testing method.



Table 4 - Mix design of mortar bars and their expansions (measured and calculated) after the acceleratingtests in NaOH solution for all 31 experiments performed

Water tocement ratio

Concentration ofNaOH solution

(M)

Content ofcopper slag (%)

Aggregate tocementing

material ratioTest

Numberz1 x1 z2 x2 z3 x3 z4 x4

Measuredexpansion

%

Calculatedexpansion

%

1 0.44 -1 0.8 -1 10 -1 1.85 -1 0,126 0,1222 0.50 +1 0.8 -1 10 -1 1.85 -1 0,152 0,1553 0.44 -1 1.2 +1 10 -1 1.85 -1 0,141 0,1474 0.50 +1 1.2 +1 10 -1 1.85 -1 0,177 0,1795 0.44 -1 0.8 -1 30 +1 1.85 -1 0,043 0,0476 0.50 +1 0.8 -1 30 +1 1.85 -1 0,080 0,0807 0.44 -1 1.2 +1 30 +1 1.85 -1 0,058 0,0568 0.50 +1 1.2 +1 30 +1 1.85 -1 0,090 0,0899 0.44 -1 0.8 -1 10 -1 2.65 +1 0,055 0,061

10 0.50 +1 0.8 -1 10 -1 2.65 +1 0,066 0,07111 0.44 -1 1.2 +1 10 -1 2.65 +1 0,095 0,09912 0.50 +1 1.2 +1 10 -1 2.65 +1 0,109 0,10913 0.44 -1 0.8 -1 30 +1 2.65 +1 0,031 0,02714 0.50 +1 0.8 -1 30 +1 2.65 +1 0,033 0,03715 0.44 -1 1.2 +1 30 +1 2.65 +1 0,043 0,04916 0.50 +1 1.2 +1 30 +1 2.65 +1 0,057 0,0617 0.41 -2 1 0 20 0 2.25 0 0,074 0,06918 0.53 +2 1 0 20 0 2.25 0 0,117 0,11219 0.47 0 0.6 -2 20 0 2.25 0 0,049 0,04620 0.47 0 1.4 +2 20 0 2.25 0 0,099 0,09321 0.47 0 1 0 0 -2 2.25 0 0,162 0,15422 0.47 0 1 0 40 +2 2.25 0 0,031 0,02923 0.47 0 1 0 20 0 1.45 -2 0,142 0,14124 0.47 0 1 0 20 0 3.05 +2 0,060 0,05125 0.47 0 1 0 20 0 2.25 0 0,086 0,08126 0.47 0 1 0 20 0 2.25 0 0,076 0,08127 0.47 0 1 0 20 0 2.25 0 0,080 0,08128 0.47 0 1 0 20 0 2.25 0 0,087 0,08129 0.47 0 1 0 20 0 2.25 0 0,081 0,08130 0.47 0 1 0 20 0 2.25 0 0,081 0,08131 0.47 0 1 0 20 0 2.25 0 0,080 0,081

With the measured expansion of mortar barsaccording to the experiment procedures, using theappropriate methods for uniform rotational plane ofsecond order with 4 factors (Table 4, penultimatecolumn), as well as the regression and correlationanalyses offered by software program MatLab, arecomputed correlation coefficients.

The regression function found in this way is:

y = 0.08157 + 0.01075x1 + 0.01183x2 –0.03117x3 –– 0.02258x4 – 0.00562x1∙x4 – 0.00387x2∙x3 +

+ 0.00337x2∙x4 + 0.01025x3∙x4 + 0.00231 -

- 0.00306 + 0.00256 + 0.00369

The calculated experiment error is 1.428 E-5and the standard deviation is 0.00378.

According to the regression equation, for everyexperiment the values of y are calculated. Thesevalues are shown too, in the Table Nr. 4, in theultimate column.

From the regress equation it is apparent thatwithin the boundaries of this experiment, theexpansion of mortar bars increases with: The increase of the water to cementing

material ratio The increase of the concentration of NaOH

solution in accelerated expansion tests (that iswhen the alkaline load in mortar is increased).



The decrease of the quantity of copper slagused for partial substitution of Portland cement.

The decrease of the aggregate to cementingmaterial ratio in the mortar.The comparison of the absolute values of the

coefficients in the regress equation clearly showsthat the quantity of slag and the aggregate tocementing material ratio have the biggest influencein the amount of expansion, which means in thedevelopment of ASR.

The fact that some terms of the correlationbetween factors have a considerable value in theregress function signifies that the ASR phenomenaand its manifestation is a complex process. Thevalues of the coefficients show that the correlation

between the quantities of slag with aggregate –cementing material ratios have the biggestinfluence in the amount of expansion caused by theASR.

To create a clearer idea on the influence andthe correlation of the four studied factors, therelationship expressed by the above equation, canbe represented graphically using the MatLabsoftware program.

Since the function represents the dependenceof ASR expansion on four factors, the three-dimensional graphical representation of thefunction is possible by keeping constant the valuesof two factors and varying the values of the othertwo ones.

Figure 18 - ASR expansion y as function of x2 and x3 (x1 = +1; x4 = +2)

As an example, in the Figure 18 is shown thedependence of the expansion y from slag quantityx3 and NaOH concentration x2, keeping constantthe water to cement ratio x1 and aggregate tocement ratio x4. Such graphical displays can begenerated in 6 combinations.

Reasoning from the three dimensional graphics,for a certain expansion that may be allowed in theconcrete to be produced (depending by its useconditions), it is possible to generate two dimen-sional graphics which facilitate the choice of thedue values of those variable factors.

Graphics generated in this way could serve pro-ducers to prepare the due mix receipts in order toavoid the risk of the ASR expansion and dete-rioration of the concretes and mortars [2,15,17 -19].

In order to prevent or mitigate the derogative anddestructive phenomenon caused by the develop-ment of Alkali Silica Reaction in concretes andmortars produced with aggregates taken from theErzeni riverbed, it is recommended to have aspecial attention to the mix design of concretes andmortars, especially for hydraulic concrete struc-

tures and those to be used in moisture and waterenvironment.

REFERENCES[1] Marku J. - "The study on Alkali-Silica Potential

Expansion of Active Aggregates in Concretes",Master of Science micro theses, University ofTirana, Albania, June 2003

[2] Marku J. - "Alkali-Silica Expansion Potentially ofErzeni Riverbed Aggregates and the Risk ofCorrosion in Concretes produced with them", PhDtheses, University of Tirana, Albania, November2006

[3] UNI 8520-22 1999 – “Aggregati per confenzione dicalcestruzzi. - Determinazione della potenzialereattività degli aggregati in prezenza di alkali”, UNIVia Battistotti Sassi, 11B 20133 Milano, Italia

[4] Marku J., Jana N. - “Study on Alkali-Silica PotentialExpansion of Active Aggregates in Concretes”, 3rd

International Symposium “Materials and their use”,Network of Materials Science and Engineering –University of Prishtina, TU Bergakademie Freiberg,Polytechnic Universityof Tirana, Prishtina, Kosovo,November 2003



[5] Marku J. (2010) The incorporation of fly ash assuplementary cementing material in concrete,Zastita materijala 51 (3), 159-164

[6] Marku J., Jana N., Caja Sh. - “Potential Riskmanifestation of Alkali-Silica Reactions in Concretesprepared by aggregates from different riverbeds inAlbania”, 4th International Conference of theChemical Societies of the South-East EuropeanCountries, Chemical Sciences in Changing Times:Visions, Challenges and Solutions, Belgrade,Serbia, July 2004

[7] Korpa A., Kota T., Spahiu E., Trettin R. (2013 ) Aninnovative approach for producing high volume flyash blended cements that meet European standardrequirements by employing a silicious coal fly ashexhibiting unusually high water demand and otherpeculiar properties, Zastita materijala 54 (4), 334-340

[8] Marku J., Jana N. 2004. - “Study on alkali-silicapotentially of some riverbed aggregates used forconcrete production in Albania”, Scientific Bulletin ofUniversity of Shkodra, No. 54, Albania

[9] Marku J., Jana N. – “The risk that menaces ourconcretes”, Journal Monitor, Tirana, Albania, Feb-ruary 2005

[10] Prifti D., Prifti M., (2013) Tuffs and kaolins areasevaluation for use as pozzolanic materials, Zastitamaterijala 54 (1), 17-22

[11] Marku J., Jana N., Caja Sh. - “The alcaline attack ofErzeni riverbed aggregates used in concretemixtures”, XI Balkan Mineral Processing Congress,Durrës, Albania, May 2005

[12] Marku J. - “Concretes with mixed aggregates andthe risk of ASR phenomenon manifestation”, 6th

International Symposium “Materials and their use”,Network of Materials Science and Engineering –University of Prishtina, TU Bergakademie Freiberg,Polytechnic University of Tirana, Tirana, Albania,November 2006

[13] Marku J., Jana N. (2006) “Potential risk manife-station of alkali- silica reactions in concretes prepa-

red by aggregates from different riverbeds inAlbania”, Albanian Journal of Natural and TechnicalSciences AJNTS, No 19-20 (1-2), 45-57.

[14] Marku J., Jana N. (2006) “Complexities of alkali-silica reaction (ASR) manifestation on concretesproduced with Erzeni riverbed aggregates”, Bulletinof mathematics and natyral sciences, No.2, Facultyof Natural Sciences, Tirana, Albania,

[15] Marku J., Caja Sh. - “The influence of water – tocementitious material ratio on corrosion caused byAlkali-Silica Reaction (ASR) of mortars and con-cretes prepared by Erzeni riverbed aggregates”, XYUCORR International Conference on cooperationof researches of different branches in the fields ofcorrosion and protection ofmaterials and theenvironment, Tara Mountain, Belgrade, Serbia, May2008

[16] MarkuJ., Koçi M., DiloT.,CajaSh. - “The mineralo-gical content and the manifestation of Alkali-SilicaReaction in concretes prepared by Erzeni riverbedaggregates”, XI YUCORR International Conferenceon cooperation of researches of different branchesin the fields of corrosion, materials protection andenvironment protection, Tara Mountain, Belgrade,Serbia, May, 2009

[17] Marku J. -“Influence of the concrete mix design onAlkali-Silica Reactivity”, The International Confe-rence of BENA (Ballkan Environmental Association)- Pollution management and environmentalprotection, Tirana, September 2009

[18] Marku J., Vaso K. -“The influence of aggregate tocement ratio on corrosion caused by alkali - silicareaction (ASR) of mortars and concretes preparedby Erzeni riverbed aggregates”, Second Internatio-nal Congress “Engineering, Ecology and Materialsin Processing Industry”, JahorinaMountain, Bosnia&Herzegovina, March 2011

[19] Marku J. (2011) “Influence of the concrete mixdesign on Alkali-Silica Reactivity (ASR)”, Journal ofEnvironment Protection and Ecology, JEPE, Vol 12,No.2, 342-351.

IZVODALKALNO-SILIKATNI AGREGATI IZ KORITA REKE ERZENI (ALBANIJA) I MOGUĆNOSTNASTANKA KOROZIJE U BETONU PROIZVEDENOG OD NJIHRazlozi ekološke efikasnosti i cena goriva vodio je industriju građevinskih sirovina da razvijaju novetehnologije za proizvodnju cementa. Ovi cementi, koji se proizvode, imaju visok sadržaj alkalija, koji ukombinaciji sa nekim vrstama agregata mogu uticati na hemijski sastav vode za betonsku mešavinu, kojamože uzrokovati dugoročne štetne efekte na betonskim konstrukcijama.U ovom radu je sažeto pregledan deo naučno-istraživačkih ispitivanja obavljen na mogućnosti ispoljavanjaštetnih efekata izazvanih alkalno - silikatnih reakcija ( ASR) u betonu napravljenog od visoko alkalnihcementa i agregata iz korita reka u Albaniji, posebno onih agregata iz reke Erzeni, koji su najvišeeksploatisani u Albaniji. Tretman ove teme je bio nužnost i veoma važan za građevinarstvo u Albaniji, gdese proizvedi do polovne količina tradicionalno niskih alkalnih cementa. Posebno u periodu tranzicije, kadasu visoko alkalni cementi počeli da se koristi i iz uvoza i iz domaće proizvodnje, smatra se veoma važnimproučavanje podobnosti korišćenja agregata iz reka u betonu proizvedenih sa visokim sadržajem alkalnogcementa, jer ne postoje načini sprečavanje ASR ako konkretno nije postavljen.Rezultati i preporuke ovih ispitivanja služe da se poveća svest graditelja da je potrebno pravilno istražiti, saove tačke gledišta, sve sirovine pre izgradnje objekta. Oni, takođe, doprinose zaštiti životne sredine ipredlažući alternativne agregate iz korita reke pomažu i da se izbegne propadanje, u roku, betonskihkonstrukcija.Ključne reči: alkalno - silicijumska reakcija (ASR), rečni agregati, silikatni agregat, krečnjački agregati.Pregledni radPrimljeno za publikovanje: 17. 07. 2014.Prihvaćeno za publikovanje: 21. 09. 2014.

JOVAN JOVANOVIĆ, Name of institution, city, state; Faculty of Electrical Engineering,Belgrade,SerbiaJOHN SMITH, University of …. font Arial, font size 11,italic

Instructions for Authors - the title of the work (up to two lines)Style: font Arial, font size 14, bold

Abstract - no longer than 150 words (lines 10-12), should contain subject matter and objective ofthe work, a brief overview of the methods and the main results so that its original text can be usedin reference periodicals, font Arial, font size 10.Keywords: (up to six terms), which provide turn an article in Information systems.

INTRODUCTION

The paper should be written in Serbian or English language. The paper should include: statement,introduction, experimental part, results and discussion, conclusion, references and taught in Englishlanguage if the paper is written in the Serbian language and vice versa. The paper should be writtensingle-spaced (A4 format). In the pages margins should be: top 3 cm, the left and right 2.20 cm, using fontArial, font size 10. All papers will be reviewed .

TITLE ( eg , EXPERIMENTAL WORK)

Subtitles are typed in capital letters, font size 10.Tables and figures are inserted at the place where we talk about them. In the text refer to the serial

number of tables / images.Above the table there should be naziv. Below the image states her name, for example:Table 1 -. Results of experimental measurements., italicFigure 1 - Results of the simulation, italic

SUBTITLE (e.g., RESULTS)Numbering of the equations do the right margin in small (round) brackets, eg.:

e o

d tJ F t T t T t

dt

. (1)

Units: Use the International System of Units (SI) and the Law on the units of measurement andmeasures, as well as the recommended IUPAC symbols of chemical and physical size.

TITLE (e.g CONCLUSION)The manuscript, prepared as a MS Word doc files, e-mailed as an attachment to the address of the

editor, Prof.. Časlav Lačnjevca: e-mail: [email protected] (Acknowlegements): Specifies the name and number of the project from which flowedthe results and the name of the institution which funded the research presented in the paper.

REFERENCES

References within the text says [square] brackets by numerals, so that the same source cites only one, forexample,[1], [2,3], [4-8]. The abbreviated name of the journal should be cited according to the International Code forthe shortening of periodicals ((http://www.efm.leeds.ac.uk/~mark/ISIabbr/).[1] JOURNAL: Sheng J.W. He M. Shi, H.C.(2007) A highly specific immunoassay for microcystin-LR detection based

on a monoclonal antibody, Anal Chim Acta, 603,1, 111–118.[2] BOOKS: Gulišija Z., Lačnjevac Č.:Corrosion and Protection Material, ITNMS, (2012) Belgrade.[3] CHAPTER in the BOOK: M. Stojanovic, Lačnjevac C., Lopičić Z. (2012) Corrosion and Corrosion Behavior ofdepleted uranium, In: Gulišija Z.. Lačnjevac C. (Ed), Corrosion and Protection of Materials, ITNMS, Belgrade, pp 223-261[4] Text from the Web site: Maja Arslanagić M., Kandic - Maglajlić S. (2011) Manual for the source of scientific papers(http://www.efsa.unsa.ba/ef/docs/handbooks/manual_economic_web.pdf, 01.12.2013.)

ABSTRACTAt the end of the paper should be given the name of work and extract the key words in the Englishlanguage, in the form of a Serbian language.

Ž. TASIĆ, M. ANTONIJEVIĆ ELEKTROHEMIJSKE OSOBINE BAKRA I LEGURA BAKRA ...


ŽAKLINA TASIĆ, Pregledni radMILAN ANTONIJEVIĆ UDC:615.465:669.35

Elektrohemijske osobine bakra i legura bakra kao biomaterijala

Različite metalne vrste imaju široku primenu u stomatologiji, kako u cilju lečenja tako i iz estetskihrazloga. Njihovim unošenjem u usnoj duplji dolazi do niza hemijskih i elektrohemijskih reakcija, štodovodi do rastvaranja metala i formiranja hemijskih jedinjenja. Oralna sredina predstavlja agresivnimedijum za metale, dovodeći do njihove korozije. U ovom radu sumirani su dosadašnji rezultati oelektrohemijskom ponašanju bakra i legura bakra u sintetisanim rastvorima pljuvačke.Ključne reči: bakar, dentalni materijali, korozija.

UVODMetali, kao i legure metala, pored značajne in-

dustrijske primene, dugi niz godina koriste se i umedicini. Duže od jednog veka koriste se u stoma-tologiji za različite ispune, proteze, zubne implan-tante, kao i za izradu ortodontskih aparata. Den-talni materijali koji se primenjuju, treba da posedujuodređene mehaničke karakteristike, da su otpornina koroziju, da imaju pristupačnu cenu koštanja ida su dostupni na tržištu [1]. Ono što je još važnijejeste da ne smeju štetno delovati na okolno oralnotkivo, kao i na ceo organizam.

Unošenjem čistog metala ili legure u usnu šup-ljinu, savki od njih težiće da pređe u jonski oblik [2].Pored toga, različiti uticaji kao što su hemijske re-akcije, biološki, mehanički, električni procesi delujuna primenjeni materijal u ustima [3, 4]. Kao posledi-ca delovanja navedenih štetnih uticaja dolazi dopromene oblika i kvaliteta površine same ispune,zatim do promene sastava, građe i svojstava ispu-ne [4].

Bakar i legure na bazi bakra se, osim primeneu industriji [5] vrlo često koriste kao biomaterijalizbog njihove visoke korozione rezistencije [6]. Ba-kar predstavlja važan bioelement u živom organiz-mu jer učestvuje u važnim biološkim procesima kaošto su transport kiseonika, transport elektrona, za-tim redoks procesi, a sastavni je deo i više enzima.Takođe, koristi se i kao kontraceptivno sredstvo [7-9], zatim ima primenu i u forenzici [10-13]. U orga-nizmu čoveka prisutan je u različitim tkivima i će-lijama. Usled velike zastupljenosti metalokeramič-kih krunica u stomatologiji, sadržaj bakra u zubimase kreće od 1-16 mg/g u zavisnosti od karakte-ristika samih zuba i osobina pacijenata [14]. Ne-kada su u stomatologiji više bile zastupljene legurebakra (CuAl, CuAg, CuZn), ali su vremenom odba-čene zbog neodgovarajučih korozionih osobina[15].

Adresa autora: Univerzitet u Beogradu, Tehničkifakultet u Boru, P.O.B 50, 19210 Bor, Srbija

Primljeno za publikovanje: 12.10.2014.Prihvaćeno za publikovanje: 23.12.2014.

Koroziono ponašanje bakra i legura bakra usintetskom rastvoru pljuvačke analizirano je prime-nom elektrohemijskih metoda. Ono što je karakte-ristično za elektrohemijske metode jeste velika ose-tljivost, zatim efikasnost i brzina kojom pružajuinformacije o elektrohemijskim reakcijama izmeđuelektrode i elektrolita. Nisu štetne po životnu sre-dinu pa se primenjuju u procesima obrade otpadnihvoda, kao i prilikom remedijacije zemljišta i muljeva[16, 17]. Pored pomenutih oblasti, brojni istraživačisu [18-21] primenom elektrohemijskih metodaispitivali ponašanje bakra i legura bakra u različitimagresivnim sredinama.

PRIMENA METALA U STOMATOLOGIJII NJIHOVE KARAKTERISTIKE

Najbiokompatibilniji materijal za potrebe sto-matologije jeste zlato, koje se zbog viske cene koš-tanja zamenjuje drugim metalima. U cilju dobijanjamaterijala optimalnih karakteristika, primenjuje setehnološki postupak legiranja, kako bi se potrebnasvojstva metala poboljšala, a štetna smanjila. Da-nas je na tržištu prisutan veliki broj legura u čijojizradi učestvuje više od 35 metala [22], a od kojihse najčešće u stomatologiji koriste amalgami, ple-menite i neplemenite legure [23, 24].

Dentalni amalgam se u stomatologiji primenjujeviše od 200 godina, jer se sa njim lako rukuje, jeftinje, ali ne zadovoljava estetske kriterijume. U sastavove legure osim žive, ulaze i srebro, bakar, kalaj icink [25, 26]. Poznato je da je živa najtoksičnijiteški metal, pa je upotreba amalgama sve manja.Živa je vrlo pokretan metal u okolini, i poseduje ve-liki afinitet prema sumporu pri čemu se vezuje zasulfhidrilne grupe ćelijskih enzima inaktivirajući nataj način ćelijski metabolizam [27-31]. Zbog svihnavedenih osobina, sve veća je upotreba drugihmetalnih legura poput Ni-Ti [32], Ni-Cr, Co-Cr [33-34], legure na bazi titana [35-37].

Podela dentalnih amalgama vrši se na osnovusadržaja bakra u njima, i to na: konvencionalne amalgame (do 3% Cu) i amalgame sa visokim sadržajem bakra (do

28% Cu).



Amalgami sa većim sadržajem bakra koriste sekako bi se smanjila ili eliminisala gama 2 faza(Sn8Hg) koja je zapravo glavni učesnik u procesukorozije. Disocijacijom ove faze oslobađa se živa,koja dalje reaguje sa neproreagovalim česticamagama 2 faze (Ag3Sn) [38]. U ovoj reakciji nastajenova gama 2 faza, dok kalaj reaguje sa hloridnimjonima i kiseonikom, pri čemu nastaju korozioniproizvodi. Analizom proizvoda nastalih korozijomdentalnih amalgama, utvrđeno je da su to uglav-nom oksidi bakra i kalaja i hidroksihloridi:Sn4(OH)6Cl2, SnO, Cu2O, CuCl2∙3Cu(OH)2 [39]. Upoređenju sa konvencionalnim amalgamima, legu-re sa većim sadržajem bakra imaju veću korozionurezistenciju.

Dentalne legure moraju biti netoksične i otpor-ne na koroziju, zatim treba da poseduju dobre me-haničke osobine kao što su čvrstoća, tvrdoća, mo-gućnost obrade, i da je cena koštanja pristupačna[40, 41]. Iako većina legura zadovoljava mehaničkasvojstva, često nisu otporne na koroziju. Na taj na-čin dolazi do otpuštanja jona metala iz legura, kojimogu dovesti do toksičnih i alergijskih reakcija [41,42]. Utvrđeno je da su legure složenijeg sastavatoksičnije po organizam domaćina, jer dolazi dootpuštanja više različiih jona metala [3].

Biokompatibilnost dentalnih legura je povezanasa njihovim korozionim ponašanjem [23, 43, 44].Sposobnost materijala da obavi svoju funkciju uorganizmu domaćina (da leči, da zameni organ ilitkivo u telu) bez ispoljavanja neželjenih efekatapredstavlja biokompatibilnost [45]. U zavisnosti odosobina tela domaćina (pol, starosno doba, zdrav-stveno stanje) i karakteristika biomaterijala, zavisikako će se primenjena legura ponašati u orga-nizmu [42, 46]. Takođe, postoji mogućnost osloba-đanja jona metala iz legure, koji mogu ispoljiti svojutoksičnost na okolno tkivo, zatim mogu dovesti doalergijskih reakcija, mutageneze, kancerogeneze.Metali nisu biorazgradivi i njihovo neprekidno oslo-bađanje može izazvati ireverzibilni toksični efekatusled akumulacije jona metala u tkivu [47].

UTICAJ ORALNE SREDINE NA KOROZIONOPONAŠANJE METALA I LEGURA METALA

Sastav pljuvačke u ustima zavisi od različitehrane koja se konzumira, tečnosti i lekova, ali i oddoba dana. Plak i hrana se vezuju za površinuzuba, što ustvari znači da su različiti oblici bakterijai njihovih proizvoda uvek prisutni u ustima. Kada senakon konzumiranja sladoleda odmah popije šolji-ca kafe, dolazi do promene temperature u ustimakoja je veća od 65oC, a dolazi i do promene pHvrednosti [24, 48]. Sredina u ustima se stalno me-nja na šta utiču različite koncentracije hloridnih jonakoji nastaju razlaganjem hrane, zatim pasta za zu-be i druga sredstva za oralnu higijenu [49-53]. Podovakvim uslovima, očekivan je proces korozije me-

tala i njihovih legura u oralnoj sredini [54]. Takođe,uočeno je i da pušenje doprinosi koroziji dentalnihlegura, povećavajući oksidaciju metala pri čemu sestvaraju jedinjenja između jona metala i sastojakaduvanskog dima [55].

U literaturi se može naći mnoštvo in vivo [56,57] i in vitro [58, 59] studija u kojima je potvrđenoda dolazi do korozije dentalnih materijala i osloba-đanje metalnih jona. Wataha i dr., [23] u svom radupotvrdio je da je korozija legura od izuzetnog zna-čaja zbog biokompatibilnosti same legure sa okol-nim tkivom.

Osim pljuvačke, čiji se pH vrednost menja, ve-lika upotreba proizvoda koji sadrže fluor direktnoutiče na koroziju metala u ustima [60]. Korišćenjetečnosti za ispiranje usta, gelova i paste za zube safluorom doprinosi nastanku, fisurne, frikcione, kao ikorozije prilikom naprezanja. Studije su pokazalepojačano oslobađanje nikla iz NiTi žica kod osobakoji koriste fluorisane paste za zube [61, 62].

Osobine dentalnih materijala mogu se ispitatikorišćenjem rastvora veštačke pljuvačke poznatogsastava [63]. Takođe, treba pomenuti da rastvorveštačke pljuvačke ne može imati identične kara-kteristike kao prirodna, ljudska pljuvačka, koja nijekonzistentna i nije stabilna [64]. U literaturi se mo-gu naći in vitro istraživanja dentalnih materijala urastvoru veštačke pljuvačke [63, 64]. Sa elektro-hemijske tačke gledišta, nijedan rastvor veštačkepljuvačke nije imao isti efekat na dentalni materijalkao prirodna pljuvačka. Nakon toga, formulisan jenovi rastvor bez prisustva proteina i organskih jedi-njenja, izuzev uree i organskih kiselina za podeša-vanje pH vrednosti i u njemu je ispitivano korozionoponašanje 4 različita materijala: Cu-Al legura, 304SS nerđajući čelik, Co-Cr legura i amalgam sa ma-njim sadržajem bakra. Utvrđeno je da se ovaj rast-vor ponaša kao i prirodna pljuvačka [64].

Prirodna pljuvačka predstavlja smešu fluida na-stalih lučenjem žlezda parotidne, submaksilarne isublingvalne. U pitanju je složeni sistem sa brojnimkonstituentima, čiji sastav varira u toku dana. Or-ganske komponente koje se nalaze u pljuvački suuglavnom glukoproteini, koji su odgovorni za vis-koznost pljuvačke. U rastvorima sintetske pljuvačkeza hemijska i elektrohemijska ispitivanja, ne dodajuse agensi za postizanje viskoziteta, zbog praktičnepoteškoće dobijanja stabilnog medijuma. Uglavnomse koriste samo mineralna jedinjenja, koja suprisutna i u prirodnoj pljuvački, kako bi se pokazaonjihov uticaj na ispitivani proces [65].

Jonska jačina i provodljivost sintetisanih rastvo-ra pljuvačke značajne su karakteristike prilikom is-pitivanja korozije u njima. Utvrđeno je da je u ras-tvorima sa velikom provodljivošću brzina procesakorozije izuzetno velika. U tabeli 1 prikazan je sa-stav različitih sintetisanih rastvora pljuvačke koji se



primenjuju za hemijska i elektrohemijska ispiti-vanja. Kao što se može videti iz prikazane tabele,joni tiocianata (SCN-) ne nalaze se u svim sinteti-sanim rastvorima pljuvačke. Pretpostavlja se da ovijoni imaju antibakterijsku ulogu u ustima, ali to još

nije dovoljno ispitano. Prilikom korozionih ispitiva-nja utvrđeno je da u prisustvu SCN-, dolazi do sma-njenja korozionog potencijala amalgama, kao i doobrazovanja brojnih rastvorljivih i nerastvorljivihkompleksa sa metalima [65].

Tabela 1 - Hemijski sastav različitih vrsta rastvora veštačke pljuvačke [64, 65]

Koncentracija, mg/mlPrisutna jedinjenja

Mondelli UFRJ USP-PR SAGFNaCl 500 674 865 125,6KCl 500 960 625 963,9CaCl2∙H2O 795 116,8 72 227,8Citratna kis 5 / / /Na2S∙9H2O 5 / / /NaH2PO4∙H2O 780 / / /KH2PO4 / / 362 654,5KH2PO4∙H2O / 274 / /K2HPO4 / / 802 /Urea 1000 / / 200(NH4)2SO4 300 / / /NH4Cl / / / 178NaHCO3 100 / / 630,8KSCN / / / 189,2Na2SO4∙10H2O / / / 763,2MgCl2∙6H2O / 40,8 125 /NaF / 42 4,25 /Metil paraben / 1000 / /Sorbitol 70% / 24000 42,7 /Karboksimetil celuloza / 8000 / /Nipagin / / 10 ml /Na-benzoat / / 10 ml /Hidroksimetil celuloza / / 5000 /

KOROZIJA DENTALNIH MATERIJALA URATVORU SINTETSKE PLJUVAČKE

Proces korozije odvija se direktnim rastvara-njem metalnih jona u rastvoru u ustima ili progre-sivnim rastvaranjem površinskog filma, koji se obič-no sastoji od odgovarajućih oksida ili sulfida meta-la. Nivo korozije bilo kog metala zavisi od hemijskihosobina medijuma u kome se metal nalazi. Nerđa-jući čelik, zatim legure titanijuma i Co-Cr, kada sekoriste u stomatologiji, formiraju na svojim površi-nama pasivni (oksidni) film kako bi se sprečilakorozija. Ovakav zaštitni sloj podložan je i meha-ničkom i hemijskom razlaganju. Čak iako ne dođedo razlaganja, dolazi do postepenog rastvaranjaoksidnog filma. Kisela sredina i prisustvo Cl- jonaubrzavaju proces pasivacije. Prema tome, hranakoja je bogata natrijum-hloridom i gazirana pićakoja sadrže CO2, konstantno formiraju agense kojisu odgovorni za proces korozije. Još jedan proiz-vod koji je odgovoran za postizanje kisele sredine uustima jeste proizvod koji u sebi sadrži fluoridne

jone, odnosno pasta za zube i tečnost za ispiranjeusta [52, 60]. Kao posledica korozije dolazi do oslo-bađanja jona metala iz dentalnh legura [22].

Koroziona otpornost metala i njihovih legura urazličitim biološkim fluidima privukla je pažnju broj-nih istraživača [66-69]. Za ispitivanja su najčešćekoričćeni sintetisani rastvori krvne plazme, zatimurina [70, 71], pljuvačke [72], Ringerov rastvor [69,73], zatim sintetski intrauterini medijum [74-76].

Legure zlata, paladijuma, srebra, zatim NiCr le-gure su ispitivane u 0,85% rastvoru NaCl sa i bezdodatka goveđeg seruma albumina, pri čemu je ut-vrđeno da dolazi do otpuštanja elemenata iz legura[77]. Kobaltne legure uglavnom podležu piting ko-roziji, što takođe dovodi do oslobađanja kanceroge-nih jona u telo domaćina [78]. Sa druge strane, tita-nijum i legure na bazi titanijuma su otporne na pi-ting koroziju, ali podležu procesu korozije u mediju-mima sa visokom koncentracijom fluoridnih jona,što je potvrđeno u radu Huang i dr., [79]. Što se ti-če binarnih legura paladijuma i srebra, potvrđeno je



da u rastvoru veštačke pljuvačke dolazi do formi-ranja sloja teško rastvornih soli, koji usporava pro-ces korozije [80]. El Medawar i dr., [81] u svom

istraživačkom radu potvrdili su da dolazi do osloba-đanja jona nikla iz legure NiTiNO2 u rastvoru veš-tačke pljuvačke.

Tabela 2 - Sastav legura i medijumi u kojima su vršena koroziona ispitivanja datih leguraLegura Sastav (wt %) Medijum Lit.

Amalgam A 43 Ag 25 Cu 29,4 Sn 0,2 Zn / PdAmalgam B 59 Ag 28 Cu 13 Sn / Zn / PdAmalgam C 49,5 Ag 20 Cu 30 Sn / Zn 0,5 Pd

Rastvor veštačke pljuvačke,pH = 6,7 [25]

Disper / / / / /

Tytin / / / / /

1% rastvor NaClRastvor veštačke pljuvačkeRastvor veštačke pljuvačke + citratnakiselina

[86]

Gaudent 82,42 Cu 9,95 Al 4,15 Ni 2,13 Fe 1,35 Mn

Veštačka pljuvačka, pH = 8,0Veštačka pljuvačka, pH = 2,5Veštačka pljuvačka + F- joni (1000ppm), pH = 2,5

[88]

NPG 80,7 Cu 7,8 Al 4,13 Ni 3 Fe 1,7Mn

2,7 Zn

NPG + 2 77,3 Cu 7,8 Al 4,3 Ni 3 Fe 1,7Mn

2,7Zn 2 Au

Ekstrakap-D 70 Ag 25,7 Sn 3,3 Cu / Zn / / /AmalcapPlus 70 Ag 18 Sn 12 Cu / Zn / / /

NG-2 70 70 Ag 18 Sn 12 Cu / Zn / / /Contour 41 Ag 31 Sn 28 Cu / Zn / / /NG 70 nongamma 2 70 Ag 18,5 Sn 11 Cu 0,5 Zn / / /

0,9% NaCl, pH=6,90,9% NaCl, pH=4,5Veštačka pljuvačka, pH=6,8Veštačka pljuvačka + 0,5%serum albumin, pH=6,8

[4]

Cu-Ni-Ti 42,50 Ni 50 Ti 7,50 Cu / / / /

Rastvor veštačke plazmeRastvor veštačke plazme +50ppm amoksicilinRastvor veštačke plazme +100ppm

[6]

Cu-Ni-Ti / / / / / / /Veštačka krvna plazmaVeštačka krvna plazma +0,05 g glukoze

[89]

Legura bakra 81,5 Cu 7,0 Al 4,5 Ni 3,0 Fe 2,0Mg 2,0 Zn Sintetisani rastvor pljuvačke,

pH= 4,77 [47]

Ni-Ti-Cu 49,1 Ni 5,0 Cu 0,2 Cr 0,06 C TiKiseli rastvor pljuvačke uprisustvu fluoridnih jona (0%,0,2% 0,5% NaF), pH=5,0

[92]

Ti-Cu / / / / / / /Rastvor veštačke pljuvačke, uprisustvu F- jona (0%, 0,25%,0,5%, 0,75% i 1,0%);pH= 2,5; 3,6; 5,0; 7,4

[91]

NiTi legurasa Cu kaomeđuslojem

/ / / / / / /0,9% NaClVeštačka pljuvačka, pH=4,0Veštačka pljuvačka, pH=6,75

[94]

75 Pd 15Ag 10 Cu / / / /60 Pd 30Ag 10 Cu / / / /40 Pd 50Ag 10 Cu / / / /

Pd-Ag-Cu

25 Pd 65Ag 10 Cu / / / /

Rastvor veštačke pljuvačke uprisustvu SCN- jona [95]

Cu-Ni-Al / / / / / / / Rastvor veštačke pljuvačke [96]

TiNiCuCr 49,6 Ti 45,1 Ni 5 Cu 0,3 Cr / / / Rastvor veštačke pluvačke,pH=2,4; pH=5,3; pH=6,2 [42]

Tytin 59 Ag 28 Sn 13 Cu / / / /

Veštačka pljuvačka + mlečnakiselina, pH=6,5Veštačka pljuvačka, pH=7,5Ringerov rastvor, pH=7,4Komercijalni rastvorGlandosan, pH=6,8

[90]



Tabela 3 - Rezultati elektrohemijskog ispitivanja dentalnih legura sa različitim sadržajem bakra u različitimmedijumima

Legura Medijum pH Ekor, V(SCE)

jkor,μA/cm2 Literatura

Rastvor veštačke krvne plazme -0,421 6,037Cu-Ni-Ti

Rastvor veštačke krvne plazme + 0,05g glukoze -0,510 2,661[89]

Rastvor veštačke pljuvačke

6,55,04,54,03,0

-0,273-0,261-0,259-0,271-0,280

3,623,782,203,313,22

Tytin

Rastvor veštačke pljuvačke sa mlečnom kiselinom

7,56,55,04,03,0

-0,274-0,246-0,275-0,292-0,346

3,732,813,273,373,69

[90]

DisperRastvor veštačke pljuvačkeRastvor veštačke pljuvačke + citratna kiselina1% rastvor NaCl

/-0,126-0,219-0,229

0,721,780,6

TytinRastvor veštačke pljuvačkeRastvor veštačke pljuvačke + citratna kiselina1% rastvor NaCl

/-0,125-0,379-0,247

0,250,760,43

[86]

Rastvor veštačke krvne plazme -0,421 6,037

Rastvor veštačke krvne plazme + 50ppmamoksicilina -0,596 3,557Cu-Ni-Ti

Rastvor veštačke krvne plazme + 100ppmamoksicilina -0,596 3,554

[6]

Rastvor veštačke pljuvačke 8,02,5

-0,260-0,104

2,118Gaudent

Rastvor veštačke pljuvačke + F- (1000ppm) 2,5 -0,155 28


-0,265-0,154

315

NPGRastvor veštačke pljuvačke + F- (1000ppm) 2,5 -0,159 45

[88]


-0,208-0,101

225

NPG+2Rastvor veštačkepljuvačke + F- (1000ppm) 2,5 -0,166 110

[88]

U tabeli 2 prikazan je sastav različitih legurakoje sadrže bakar, kao i medijumi u kojima je ispi-tivano njihovo elektrohemijsko ponašanje, dok su utabeli 3 prikazani rezultati analize datih legura.

Ispitivanjem korozionog ponašanja tri različitadentalna amalgama u kojima se sadržaj bakra kre-tao od 20-28 wt%, uočeno je da dolazi do oksida-cije sve tri legure pri potencijalu -1,0 V (SCE) [25].

Najveća gustina struje dobijena je za amalgam B učijem sastavu se nalazi najveći sadržaj bakra, dokje najmanja vrednost bila za amalgma C. Takođe,uočeno je da se na površini ispitivanih materijalaformiraju odgovarajući oksidni filmovi na potencijalu-0,8 V (SCE). U radu Zheng i dr., [42], sprovedenasu elektrohemijska ispiivanja TiNiCuCr legure prirazličitim pH vrednostima medijuma (pH=2,4; 5,3 i



6,2). Merenjem korozionog potencijala u toku 12h,u različitim sredinama, utvrđeno je da se vrednostkorozionog potencijala smanjuje sa povećanjem pHvrednosti što je potvrđeno i u radovima Huang i dr.,[61], Kuhta i dr., [82], Huang i dr., [83]. U istraživa-nju Zhang i saradnika, [84], ispitivana je elektro-hemijska korozija kompozitnih ortodontskih žica uagresivnim rastvorima koristeći potenciodinamičku icikličnu polarizacionu metodu. Koroziona otpornostje procenjena merenjem vrednosti gustine struje ipiting potencijala (Epit). Vrednosti Epit kompozitnihortodontskih žica u četiri ispitivana rastvora sepovećavaju u sledećem redosledu: rastvor hlorida˂ rastvor veštačke pljuvačke sa proteinima ˂ rast-vor veštačke pljuvačke ˂ rastvor veštačke pljuva-čke sa fluoridima. Najmanja vrednost Epit bila je urastvoru NaCl što ukazuje na manju otpornostprema piting koroziji u ovom rastvoru. Pretpostavljase da se slojevi Ca3(PO4)2 prirodno formiraju u rast-voru veštačke pljuvačke, kao i u rastvorima veštač-ke pljuvačke u prisustvu proteina i F- jona. Najvećavrednost Epit uočena je u rastvoru veštačke plju-vačke sa fluoridima, ali ova vrednost ne odgovaranajvećoj korozionoj otpornosti.

Oslobađanje Cu jona iz kompozitnih ortodon-tskih žica, koje je utvrđeno u ovom radu, i dalje jemanje od toksičnih standarda i može se smatrati daje ovakav kompozit pogodan materijal za ortodont-ske žice.

Komozitne ortodontske žice sastavljene od NiTilegure i nerđajućeg čelika sa bakrom kao među-slojem ispitivane su rastvoru veštačke pljuvačke uprisustvu različite koncentracije F- jona (0,1% NaF i0,3% NaF) [85]. U ranijim istraživanjima potvrđenoje da ovi joni imaju negativan uticaj na korozionuotpornost dentalnih legura [50, 51]. Zhang i dr.,[85], potvrdio je u svom radu da u slučaju pove-ćane koncentracije fluorida u rastvoru veštačkepljuvačke (rastvor veštačke pljuvačke u prisustvu0,3% NaF), dolazi do oslobađanja jona bakra izlegure. Samim tim, dentalna legura ima smanjenuotpornost prema koroziji. U rastvoru veštačke plju-vačke, u prisustvu 0,1% rastvora NaF, uočeno jeda dolazi do formiranja zaštitnog oksidnog filma napovršini bakra koji sprečava dalji proces korozije.

U radu Yap i dr., [86], ispitivane su korozioneosobine komercijalnih Disper i Tytin legura u 1%rastvoru NaCl i rastvoru veštačke pljuvačke. Na os-novu dobijenih rezultata, utvrđeno je da korozionipotencijal ispitivanih legura bio negativniji u ras-tvoru veštačke pljuvačke. U sva tri rastvora elektro-lita (NaCl, rastvor veštačke pljuvačke i rastvor veš-tačke pljuvačke sa citratnom kiselinom) negativnavrednost korozionog potencijala legura bila je u op-segu 126 do 379 mV (SCE). Ispitivane legure bilesu reaktivnije u rastvoru NaCl u odnosu na rastvorveštačke pljuvačke. Reaktivnost materijala u rast-

voru veštačke pljuvačke je povećana dodavanjemcitratne kiseline, što se može pripisati smanjenjupH vrednosti od 5,5 do 4,0 [87].

Veći uticaj na reaktivnost Tytin legure imala jepromena pH vrednosti nego na Disper leguru, štose može videti na osnovu negativnije vrednosti po-tencijala korozije. Negativno pomeranje potencijalakorozije može ukazivati na povećanje brzine oksi-dacije metala ili smanjenje brzine redukcije neme-tala. Elektrohemijskim ispitivanjem legura u rastvo-ru NaCl, utvrđena je veća brzina korozije Tytin-a, amanja Disper legure. Najveća brzina korozije zaDisper leguru bila je u rastvoru veštačke pljuvačkeuz dodatak citratne kiseline. Merenjem korozionogpotencijala legura sa visokim sadržajem bakra ut-vrđeno je da poseduju određenu otpornost premakoroziji, ali i dalje treba biti obazriv u intraoralnojsredini [86].

Mareci i dr., [88], u svom radu ispitivali su elek-trohemijsko ponašanje tri bakarne dentalne legureu rastvoru veštačke pljuvačke pri pH=8,0, kiselomrastvoru veštačke pljuvačke (pH 2,5) i u rastvoruveštačke pljuvačke u prisustvu fluorida (1000 ppmF-, pH 2,5). Na osnovu rezultata utvrđeno je da ba-karne dentalne legure imaju relativno dobru koro-zionu stabilnost u rastvoru veštačke pljuvačke pripH= 8,0, dok u kiselom i fluorisanom rastvoru veš-tačke pljuvačke koroziona struja raste. Ovo ukazujeda dentalna legura zadržava njen zaštitni oksidnifilm u alkalnim uslovima. Koroziona struja dostiževisoku vrednost u fluoridnom rastvoru veštačkepljuvačke zbog prisustva samih F- jona. Rezultatidobijeni elektronskom impedansnom spektrosko-pijom (EIS) ukazuju da legure podležu pasivaciji urastvoru veštačke pljuvačke pri pH=8,0, dok u kise-lom i fluoridnom rastvoru zaštitni oksidni film nijeviše prisutan.

U sva tri slučaja dolazi do formiranja filma koro-zionih proizvoda pri čemu najveći sadržaj u filmuima oksid bakra. U neutralnom aerisanom mediju-mu formira se Cu2O. Nakon toga, vrednost poten-cijala otvorenog kola u neutralnom rastvoru neznat-no raste, ukazujući na rast filma na površini metala.Analizom vrednosti Tafelovih nagiba za sve trilegure u rastvoru veštačke pljuvačke pri pH= 8,0,uočeno je da je korozioni proces anodno kontro-lisan, odnosno da se obrazuje na površini zaštitnifilm. U kiselom rastvoru vrednosti korozione gus-tine struje su bile veće u odnosu na vrednosti uneutralnom rastvoru. Dodavanjem 1000 ppm F- jo-na kiselom rastvoru, takođe dolazi do povećanja in-tenziteta struje. Najveća vrednost gustine strujezabeležena je za NPG + 2 leguru u kiselom rast-voru veštačke pljuvačke u kojoj su se nalazili fluo-ridni joni (tabela 3).

John Mary i sar. [6, 89] u svom radu ispitivali suponašanje Cu-Ni-Ti legure u rastvoru veštačke krv-



ne plazme, u prisustvu i u odsustvu amoksicilina[6], kao i prisustvu glukoze [89]. Na osnovu polari-zacione i AC impedansne spektroskopske metode,utvrđeno je da u prisustvu 100 ppm amoksicilinapostiže se najmanja brzina korozije, odnosno naj-veća efikasnost. Do smanjenja brzine korozije legu-re dolazi zbog formiranja zaštitnog filma na površinimetala usled adsorpcije molekula amoksicilina [6].Na osnovu potenciodinamičke polarizacione meto-de, utvrđeno je da se potencijal legure u rastvorukrvne plazme u prisustvu glukoze, pomera ka ne-gativnijim vrednostima. Zaključeno je da ispitivanalegura otporna prema koroziji kada je u rastvoruveštačke krvne plazme prisutno 0,01 g glukoze,dok pri većem sadržaju dolazi do korozije [89].

Bajsman i dr., [4] istraživali su ponašanje razli-čitih dentalnih legura u četiri rastvora, čiji je sastavprikazan u tabeli 2, primenom metode ciklične vol-tametrije. Na osnovu dobijenih rezultata, utvrđenoje da se potiže veća vrednost gustine struje pri ni-žoj pH vrednosti ispitivanog rastvora, u odnosu narastvore veštačke pljuvačke sa i bez prisustva go-veđeg seruma albumina. Pretpostavlja se da na ko-roziono ponašanje dentalnih amalgama ima uticajpH vrednost ispitivanog rastvora i zaključeno je dasu pri većim pH vrednostima korozione osobine le-gura bolje.

Brett i dr., [90] u svom radu ispitivali su elektro-hemijsko ponašanje komercijalne Tytin legure urastvoru veštačke pljuvačke sa i bez dodatka mle-čne kiseline, u Ringer-ovom rastvoru i u komercijal-nom rastvoru „Glandosane“ koji se koristi u stoma-tologiji za površinsku zaštitu amalgamskih ispuna.Na osnovu dobijenih rezultata primenom elektrohe-mijskih metda utvrđeno je da pH vrednost ispitiva-nih rastvora utiče na ponašanje legure i da prisus-tvo organskih jedinjenja ima značajan uticaj nabrzinu korozije i adsorpcije na površini amalgama.Vrednost korozione gustine struje u rastvoru veš-tačke pljuvačke sa mlečnom kiselinom se poveća-va na nižim pH vrednostima u odnosu na rastvorbez mlečne kiseline. Molekuli mlečne kiseline spre-čavaju formiranje oksida na površini metala, koji biimao zaštitnu ulogu, i samim tim veća je brzina ko-rozije. Brzina korozije opada po sledećem redo-sledu: „Glandosane“ < Ringerov rastvor < rastvorveštačke pljuvačke bez mlečne kiseline ~ rastvorveštačke pljuvačke sa mlečnom kiselinom.

Mutlu [91] u svom radu ispitivala je Ti-Cu legu-ra čiji izgled podseća na penu ili sunđer, u rastvoruveštačke pljuvačke u prisustvu F- jona. Elektrohe-mijske metode su korišćene u cilju ispitivanja koro-zione otpornosti legure.

Uočeno je da se na površini legure stvara zaš-titni oksidni film koji koji predstavlja barijeru za daljiproces korozije. Povećanjem koncentracije F- jonau rastvoru veštačke pljuvačke povećava se poroz-

nost oksidnog sloja, i na taj način smanjuje se nje-gova zaštitna uloga. Zapravo, F- joni rastvaraju ok-sidni film. Povećanjem sadržaja bakra u sastavu le-gure, dolazi do povećanja korozione struje i brzinekorozije, dok se potencijal korozije smanjuje. Obla-ganjem ove legure TiN slojem, poboljšavaju senjene korozione osobine.

Grillo i dr., [47] ispitivali su elektrohemijsko po-našanje bakarne legure u kiselom sintetisanomrastvoru pljuvačke (pH= 4,77). Ispitivan je i uticajvremena imerzije u ispitivanom elektrolitu na elek-trohemijsko ponašanje legure. Utvrđeno je da sekorozioni potencijal pomera ka pozitivnijim vred-nostima i smanjuje se koroziona gustina struje sadužim periodom imerzije elektrode. Pretpostavljase da dolazi do formiranja zaštitnog filma na površi-ni elektrode sa povećanjem vremena imerzije.

Lee i dr., [92] u svom radu ispitivali su legure ti-tanijuma, Ni-Ti-Cu, Ni-Ti, Ti-Mo-Zr-Sn i Ti-Nb u ki-selom rastvoru veštačke pljuvačke u prisustvu razli-čite koncentracije fluorida (0%, 0,2% i 0,5% NaF).Na osnovu ciklične potenciodinamičke polarizacio-ne krive, utvrđeno je da dolazi do povećanja gutinestruje i brzine korozije legure Ni-Ti-Cu sa poveća-njem koncentracije fluorida u analiziranom mediju-mu. U prisustvu najveće koncentracije NaF (0,5%)u rastvoru pljuvačke, dolazi do značajnog anodnograstvaranja legura Ni-Ti i Ni-Ti-Cu, dok je kod osta-lih legura titana uočena pojava pasivacionog filma.

Alves i dr., [93] ispitivali su koroziono ponaša-nje bakarnih legura, koje se mogu naći na tržištupod nazivom Duxalloy i Tytin Plus legure. U ovomistraživanju korišćeni su sledeći rastvori: fosfatni puferski rastvor, pH= 6,80 Henkov rastvor (eng. Hanks solution) koji se

karakteriše visokim sadržajem bikarbonatnihjona, pH= 7,40

sintetski rastvor pljuvačke, pH= 6,80 0,9% rastvor NaCl.

Na osnovu dobijenih rezultata, najmanja korozi-ona otpornost ispitivanih amalgama uočena je u fo-sfatnom i 0,9% rastvoru NaCl, zbog visoke koncen-tracije Cl- jona. Uprkos pH vrednosti rastvora veš-tačke pljuvačke, koja po teoriji predstavlja agresivnielektrolit, uočeno je formiranje zaštitnog filma napovršini elektrode. Film se sastojao od nerastvornihjedinjenja, odnosno Ag2SO4, AgCl i Hg2Cl2.

Smanjenje korozione otpornosti legure Duxa-lloy u ispitivanim rastvorima, u zavisnosti od vreme-na imerzije, pratilo je sledeći niz: Vreme imerzije 5 minuta: rastvor veštačke plju-

vačke ˃ 0,9% NaCl ˃ Henkov rastvor ˃ fosfatnipuferski rastvor.

Vreme imerzije 168 sati: rastvor veštačke plju-vačke ˃ Henkov rastvor ˃ 0,9% NaCl ˃ fosfatnipuferski rastvor.



Smanjenje korozione otpornosti Tytin Plus le-gure pratilo je drugačiji redosled: Vreme imerzije 5 minuta: rastvor veštačke plju-

vačke ˃ fosfatni puferski rastvor ~ 0,9% NaCl ~Henkov rastvor.

Vreme imerzije 168 sati: Henkov rastvor ˃ fos-fatni puferski rastvor ˃ 0,9% NaCl ˃ rastvorveštačke pljuvačke.

ZAKLJUČAKBakar i legure bakra pored industrijske prime-

ne, koriste se i kao biomaterijali. Ipak, može se vi-deti da je oralna sredina veoma nepovoljna u pog-ledu primene različitih materijala, zbog stalne pro-mene pH vrednosti, zatim prisustva mikroorganiza-ma, produkata njihovog metabolizma kao i produ-kata razlaganja hrane. Dosadašnji rezultati poka-zali su da se proces korozije javlja kod svih den-talnih legura.

Na osnovu prikazanih podataka o elektrohemij-skom ponašanju bakra i legura bakra, može se za-ključiti sledeće: Kisela sredina i prisustvo Cl- jona ubrzavaju

proces korozije dentalnih legura. Sa povećanjem koncentracije F- jona u ispitiva-

nom medijumu takođe dolazi do povećanja-brzine procesa korozije.

Prisustvo organskih kiselina u medijumu nepo-voljno utiče na korozioni proces. Naime, mole-kuli organskih kiselina sprečavaju formiranjeoksidnog filma na površini metala koji bi mogaoimati zaštitnu ulogu.

Metod predtretmana, koji se vrši uranjanjemelektrode u ispitivani elektrolit, pokazao se efi-kasnim. Dolazi do formiranja zaštitnog filma napovršini elektrode sa dužim vremenom trajanjapredtretmana.

Pri većim pH vrednostima medijuma (neutralni ialkalni) korozione osobine dentalnih legura subolje.

ZahvalnostAutori se zahvaljuju Ministarstvu prosvete, nau-

ke i tehnološkog razvoja Republike Srbije za fina-nsiranje ovog rada u okviru projekta 172031.

REFERENCE[1] J. Živko-Babić, D. Lisjak, L. Ćurković, M. Jakovac

(2008),Estimation of chemical resistance of dentalceramics by neural network,Dental Materials 24,18-27

[2] V. Arancibia, C. Pena, H. E. Allen, G. Lagos (2003),Characterization of copper in uterine fluids of patie-nts who use the copper T-380A intrauterine device,Clinica Chimica Acta 332, 69–78

[3] R. Poljak-Guberina, D. Knezović-Zlatarić, M. Katu-narić (2002), Otpornost zubnih slitina na koroziju,Acta Stomatologica Croatica 36 (4), 441-445

[4] A. Bajsman, A. Vuković, S. Zukić, (2012), Analizaelektrohemijskog ponašanja dentalnih amalgama učetiri otopine primjenom ciklične voltametrije,Stomatološki vjesnik 1, 9-16

[5] S. M. Milić, M. M. Antonijević (2009), Some aspectsof copper corrosion in presence of benzotriazoleand chloride ions, Corrosion Science 51, 28-34

[6] S. John-Mary, S. Rajendran (2013), Corrosionbehavior of Cu-Ni-Ti alloy in artificial blood plasmain presence of Amoxicillin, Zaštita Materijala 54 (4),353-360

[7] F. Alvarez, C. A. Grillo, P. L. Schilardi, A. Rubert, G.Benítez, C. Lorente, M. F. Lorenzo de Mele (2013),Decrease in Cytotoxicity of Copper-Based Intraute-rine Devices (IUD) Pretreated with 6‑Mercapto-purine and Pterin as Biocompatible Corrosion Inhi-bitors, Applied Materials and Interfaces 5, 249−255

[8] B. Cao, T. Xi, Y. Zheng (2008), Release behavior ofcupric ions for TCu380A and TCu220C IUDs,Biomedical Materials 3, 1-7

[9] H. Xue, N. Xu, C. Zhang (1998), Corrosion Behaviorof Copper in a Copper Bearing Intrauterine Devicein the Presence of Indomethacin, Contraception 57,49-53

[10] J. W. Bond (2008), Visualization of Latent Finger-print Corrosion ofMetallic Surfaces, Journal of Fo-rensic Science 53 (4), 812-822

[11] J. W. Bond (2009), Visualization of Latent Fin-gerprint Corrosion of Brass, Journal of ForensicScience 54 (5),1034-1041

[12] J. W. Bond, T. F. Brady (2013), Physical Chara-cterization and Recovery of Corroded FingerprintImpressions from Postblast Copper Pipe BombFragments, Journal of Forensic Science 58 (3),776-781

[13] J. W. Bond (2011), Effect that the Relative Abun-dance of Copper Oxide and Zinc Oxide Corrosionhas on the Visualization of Fingerprints Formedfrom Fingerprint Sweat Corrosion of Brass, Journalof Forensic Science 56 (4), 999-1002

[14] B. M. Kaličanin, R. S. Nikolć (2008), Potentiometricstripping analysis of zinc and copper in human teethand dental materials, Journal of Trace Elements inMedicine and Biology 22, 93-99

[15] S. B. Rao i R. Chowdhary (2011), Evaluation on theCorrosion of the Three Ni-Cr Alloys with DifferentComposition, International Journal of Dentistry2011, 1-5

[16] H. I. Gomes, C. Dias-Ferreira, A. B. Ribeiro (2012),Electrokinetic remediation of organochlorines in soil:Enhancement techniques and integration with otherremediation technologies, Chemosphere 87, 1077-1090

[17] M. T. Alcantara, J. Gomez, M. Pazos, M. A.Sanroman (2012), Electrokinetic remediation of leadand phenanthrene polluted soils, Geoderma 173-174, 128-133

[18] M. M. Antonijević, S. M. Milić, S. M. Šerbula, G. D.Bogdanović (2005), The influence of chloride ionsand benzotriazole on the corrosion behavior ofCu37Zn brass in alkaline medium, ElectrochimicaActa 50, 3693- 3701



[19] M. M Antonijević, S. Č. Alagić, M. B. Petrović, M. B.Radovanović (2009a), The Influence of pH onElectrochemical Behavior of Copper in Presence ofChloride Ions, International Journal of Electroche-mical Science 4, 516-524

[20] M. M Antonijević, S. M. Milić, M. D. Dimitrijević, M.B. Petrović, M. B. Radovanović, A. T. Stamenković(2009b), The Influence of pH and Chlorides onElectrochemical Behavior of Copper in the Pre-sence of Benzotriazole, International Journal ofElectrochemical Science 4, 962-979

[21] M. M Antonijević, S. M. Milić, M. B. Radovanović, M.B. Petrović, A. T. Stamenković (2009c), Influence ofpH and Chlorides on Electrochemical Behavior ofBrass in Presence of Benzotriazole, InternationalJournal of Electrochemical Science 4, 1719-1734

[22] Lj. Ristić (2006), Dentalne legure i korozija, Vojno-sanitetski pregled 63 (12), 1033-1037

[23] J. Wataha (2000), Biocompatibility of dental castingalloys: A review,Journal of Prosthetic Dentistry 83,223-234

[24] D. Upadhyay, M. A. Panchal, R. S. Dubey, V. K.Srivastava (2006),Corrosion of alloys used in denti-stry: A review,Materials Science and Engineering A432, 1–11

[25] E. Angelini, F. Zucchi (1985), High copper dentalamalgams: comparative study of the structure andthe in vitro corrosion resistance,Surface Technology25, 385 - 396

[26] C. M. A. Brett, H. A. Acciari, A. C. Guastaldi (2002),Corrosion of Dental Amalgams - Studies of Indi-vidual Phases, Key Engineering Materials 230-232,463-466

[27] H. Y. Zhou, M. H. Wong (2000), Mercury accu-mulation in freshwater fish with emphasis on thedietary influence,Water Research 34, 4234-4242

[28] J. J. B. Nevado, L. F. G. Bermejoa, R.C. R. M.Doimeadios (2003), Distribution of mercury in theaquatic environment at Almaden, Spain, Environ-mental Pollution 122, 261-271

[29] P.Horsted-Bindslev (2004), Amalgam toxicity—environmental and occupational hazards,Journal ofDentistry 32, 359-365

[30] L. D. Hylander i M. E. Goodsite (2006), Environ-mental costs of mercury pollution, Science of theTotal Environment 368, 352-370

[31] A. Shraim,A. Alsuhaimi, J. T. Al-Thakafy (2011),Dental clinics: A point pollution source, not only ofmercury but also of other amalgam constituents,Chemosphere 84, 1133–1139

[32] M. Dalstra i B. Melsen (2004), Does the transitiontemperature of Cu–NiTiarchwires affect the amountof tooth movement during alignment?, Orthodonticsand Craniofacial Research 7, 21–25

[33] A. Begić, J. Malina, T. Matković (2004), Usporedbakorozijskih svojstava nekih zubnih slitina, Me-talurgija 43 (1), 63-67

[34] T. Puskar, D. Jevremovic, D. Eggbeer, A. Lapcevic,B. Trifkovic, D. Vukelic, R. J. Williams (2012), Deter-mination of corrosion characteristics of dental alloyby inductively coupled plasma mass spectrometry,Journal of Production Engineering 16 (1), 77-80

[35] H. Chai, L. Guo, X. Wang, Y. Fu, J. Guan, L. Tan, L.Ren, K. Yang (2011), Antibacterial effect of 317Lstainless steel contained copper in prevention ofimplant-related infection in vitro and in vivo, Journalof Materials Science: Materials in Medicine 22,2525-2535

[36] D. Mareci, G. Bolat, A. Cailean, J. J. Santana, J.Izquierdo, R. M. Souto (2014), Effect of acidic fluo-ride solution on the corrosion resistance of ZrTialloys for dental implant application, CorrosionScience 87, 334-343

[37] V. A. Alves, R. Q. Reis, I. C. B. Santos, D. G.Souza, T. de F. Goncalves, M. A. P. da Silva, A.Rossi, L. A. da Silva (2009), In situ impedancespectroscopy study of the electrochemical corrosionof Ti and Ti–6Al–4V in simulated body fluid at 25 oCand 37 oC, Corrosion Science 51, 2473-2482

[38] K.-H. Chung, L.-Y. Hsiao, Y.-S. Lin, J.-G. Duh(2008), Morphology and electrochemical behavior ofAg–Cu nanoparticle-doped amalgams, Acta Bio-materialia 4, 717-724

[39] N. Galić, K. Prskalo, G. Prpić-Mehičić, J. Šutalo, I.Anić, Lj. Prester (1997), Toksičnost dentalnih amal-gama I, Acta Stomatologica Croatica 31 (3), 243-251

[40] G. Bayramoglu, T. Alemdaroglu, S. Kedici, A. A.Aksut (2000), The effect of pH on the corrosion ofdental metal alloys, Journal of Oral Rehabilitation27, 563– 575

[41] J. Stipetić, A. Čelebić, I. Baučić, N. Rinčić, A. Ćatić,M. Baučić (2002),Otpuštanje jona nikla iz trijurazličitih zubnih slitina, Acta Stomatologica Croatica36 (4), 375-379

[42] Y.-F. Zheng , Q. Y. Wang, L. Li (2007), TheElectrochemical Behavior and Surface Analysis ofTi49.6Ni45.1Cu5Cr0.3 Alloy for Orthodontic Usage,Journal of Biomedical Materials Research Part B:Applied Biomaterials 86 (2), 335-340

[43] J. L. Pariente, L. Bordenave, R. Bareille, C.Ohayon-Courtes, Ch. Baquey, M. Le Guillou (1999),In vitro cytocompatibility of radio-opaciÞers used inureteral endoprosthesis, Biomaterials 20, 523-527

[44] M. Mikulewicz, K. Chojnacka, B. Wozniak, P.Downarowicz (2012), Release of Metal Ions fromOrthodontic Appliances:An In Vitro Study, BiologicalTrace Elem Research 146, 272–280

[45] D. Williams (2008), Leading Opinion On the mec-hanisms of biocompatibility, Biomaterials 29 (20),2941-2953

[46] A. Klinger, D. Steinberg, D. Kohavi, M. N. Sela(1997), Mechanism of adsorption of human albuminto titanium in vitro, Journal of Biomedical MaterialsResearch Part A 36, 387-392

[47] C. A. Grillo, M. L. Morales, M. V. Mirificio, M. A. F.L. de Mele, Synergistic cytotoxic effects of ionsreleased by zinc–aluminum bronze and the metallicsalts on osteoblastic cells, Journal of BiomedicalMaterials Research A 101 (7) (2013) 2129-2140

[48] H.-S. Ahn, M.-J. Kim, H.-J- Seol, J.-H. Lee, H.-L.Kim, Y. H. Kwon (2006), Effect of pH and Tem-perature on Orthodontic NiTi Wires Immersed inAcidic Fluoride Solution, Journal of Biomedical



Materials Research Part B: Applied Biomaterials 79(1), 7-15

[49] H. S. Hafez, E. M. N. Selim, F. H. K. Eid, W. A.Tawfik, E. A. Al-Ashkar, Y. A. Mostafa (2011), Cyto-toxicity, genotoxicity, and metal release in patientswith fixed orthodontic appliances: A longitudinal in-vivo study, American Journal of Orthodontics andDentofacial Orthopedics 140 (3), 299-308

[50] Y. H. Kwon, H.-S. Cho, D.-J. Noh, H.-L- Kim, K.-H.Kim (2005), Evaluation of the Effect of Fluoride-Containing Acetic Acid on NiTi Wires, Journal ofBiomedical Materials Research Part B: AppliedBiomaterials 72B (1), 102-108

[51] N. Schiff, B. Grosgogeat, M. Lissac, F. Dalard(2002), Influence of fluoride content and pH on thecorrosion resistance of titanium and its alloys,Biomaterials 23 (9), 1995-2002

[52] N. Schiff, B. Grosgogeat, M. Lissac, F. Dalard(2004), Influence of fluoridated mouthwashes oncorrosion resistance of orthodontics wires, Bio-materials 25 (19), 4535-4542

[53] J. Geis-Gerstorfer (1994), In vitro corrosionmeasurements of dental alloys, Journal ofDentistry 22, 247-251

[54] T. Eliades, C. Bourauel (2005), Intraoral aging oforthodontic materials: the picture we miss and itsclinical relevance, American Journal of Orthodonticsand Dentofacial Orthopedics 127, 403-412

[55] H. Ataiwi, R. A . Majed, A. A. Muhsin (2012), Effectof Tobacco Smoking on the Corrosion Behavior ofThree Dental Alloys in Artificial Saliva, Tikrit Journalfor Dental Sciences 2, 145-153

[56] R. Fors, M. Persson (2006), Nickel in dental plaqueand saliva in patients with and without orthodonticappliances, European Journal of Orthodontics 28,292-297

[57] E. Petoumenou, M. Arndt, L. Keilig, S. Reimann, H.Hoederath, T. Eliades, A. Jager, C. Bouraue (2009),Nickel concentration in the saliva of patients withnickel-titanium orthodontic appliances, AmericanJournal of Orthodontics and DentofacialOrthopedics 135, 59-65

[58] M. Es-Souni, M. Es-Souni, H. Fischer-Brandies(2005), Assessing the biocompatibility of NiTi shapememory alloys used for medical applications,Analytical and Bioanalytical Chemistry 381, 557-567

[59] T. H. Huang, S.-Y. Ding, Y. Min, C.-T. Kao (2004),Metal ion release from new and recycled stainlesssteel brackets, European Journal of Orthodontics26, 171-177

[60] J. W. J. Silva, N. A. S. Sampaio, H. A. Acciari, R. Z.Nakazato, E. N.Codaro, Passivity Study of DentalNi-Cr-Mo Alloys in Fluorides Media, InternationalJournal of Business, Humanities and Technology 3(8) (2013) 60-65

[61] H. H. Huang, Y.-H. Chiua, T.-H. Lee, S.-C. Wu, H.-W. Yang, K.-H. Su, C.-C. Hsu (2003), Ion releasefrom NiTi orthodontic wires in artificial saliva withvarious acidities, Journal of Biomedical MaterialsResearch Part A 66, 829-839

[62] N. Schiff, F. Dalard, M. Lissac, L. Morgon, B.Grosgogeat (2005), Corrosion resistance of threeorthodontic brackets: a comparative study of three

fluoride mouthwashes, Europen Journal ofOrthodontics 27, 541-549

[63] V. W.-H. Leung, D. W. Darvell (1997), Artificial Sali-vas for in vi&o studies of dental materials, Journal ofDentistry 25 (6), 475-484

[64] G. M. O. de Queiroz, L. F. Silva, J. T. L. Ferreira, J.A. C. P. Gomes, L. Sathler (2007), Electrochemicalbehavior and pH stability of artificial salivas forcorrosion tests, Brazilian Oral Research 21(3), 209-215

[65] J.-Y. Gal, Y. Fovet, M. Adib-Yadzi (2001), ReviewAbout a synthetic saliva for in vitro studies, Talanta53, 1103-1115

[66] I. E. Castaneda, J. G. Gonzalez-Rodriguez, J. Colin,M. A. Neri-Flores (2010), Electrochemical behaviorof Ni-Al-Fe alloys in simulated human body solution,Journal of Solid State Electrochemistry 14, 1145–1152

[67] J. A. Ruiz, I. Rosales, J. G. Gonzalez-Rodriguez, J.Uruchurtu (2010), Effect of B on the CorrosionResistance of a Ni-Ti Alloy in Simulated HumanBody Solution, International Journal of Electro-chemical Science 5, 593–604

[68] R. Nagalakshmi, S. Rajendran, J. Sathiyabama, M.Pandiarajan, J. L. Christy (2013), Corrosionbehaviour of biomaterials in synthetic biologicalsolutions – an overview, Europen Chemical Bulletin2 (4), 171-179

[69] I. Cvijović-Alagić, Z. Cvijović, S. Mitrović, V. Panić,M. Rakin (2011), Wear and corrosion behaviour ofTi–13Nb–13Zr and Ti–6Al–4V alloys in simulatedphysiological solution, Corrosion Science 53, 796–808

[70] R. W. W. Hsu, C.-C. Yang , C.-A. Huang, Y.-S.Chen (2004), Investigation on the corrosion beha-vior of Ti–6Al–4V implant alloy by electrochemicaltechniques, Materials Chemistry and Physics 86,269–278

[71] R. W. W. Hsu, C.-C. Yang , C.-A. Huang, Y.-S.Chen (2009), Electrochemical corrosion studies onCo–Cr–Mo implant alloy in biological solutions,Materials Chemistry and Physics 93, 531–538

[72] F. C. Giacomelli, C. Giacomelli, A. Spinelli (2004),Behavior of a Co-Cr-Mo Biomaterial in SimulatedBody Fluid Solutions Studied by Electrochemicaland Surface Analysis Techniques, Journal of theBrazilian Chemical Society 15 (4), 541-547

[73] R. Singh, A. Kurella, N. B. Dahotre (2006), LaserSurface Modification of Ti–6Al–4V: Wear andCorrosion Characterization in Simulated Biofluid,Journal of Biomaterials Applications 21, 49-73

[74] J. Gao, Y. Li, J.-p. Liu, X. Gu (2007), Releasing ofCupric Ion of Three types of Copper-bearingIntrauterine Contraceptive Device in SimulatedUterine Fluid, Journal of Reproduction andContraception 18 (1), 33-39

[75] F. Alvarez, P. L. Schilardi, M. F. L. de Mele (2012),Reduction of the “burst release” of copper ions fromcopper-based intrauterine devices by organicinhibitors, Contraception 85, 91-98

[76] B. Cao, T. Xi, Y. Zheng, D. Hui (2011), Corrosionbehavior of copper in the presence of Proteins,Metalurgija-MJoM 17 (3), 111-117



[77] J. C. Wataha, Steven K. Nelson, Petra E. Lockwood(2001), Elemental release from dental casting alloysinto biological media with and without protein,Dental Materials 17, 409-414

[78] G. Manivasagam, D. Dhinasekaran, A. Rajama-nickam (2010), Biomedical Implants: Corrosion andits Prevention - A Review, Recent Patents onCorrosion Science 2, 40-54

[79] H. H. Huang, Tzu-Hsin Lee (2005), Electrochemicalimpedance spectroscopy study of Ti–6Al–4V alloy inartificial saliva with fluoride and/or bovine albumin,Dental Materials 21, 749–755

[80] L. Joska, M. Marek, J. Leitner (2005), Themechanism of corrosion of palladium–silver binaryalloys in artificial saliva, Biomaterials 26, 1605–1611

[81] L. El Medawar, P. Rocher , J.-C. Hornez, M.Traisnel, J. Breme, H. F. Hildebrand (2002),Electrochemical and cytocompatibility assessmentof NiTiNOL memory shape alloy for orthodontic use,Biomolecular Engineering 19, 153-160

[82] M. Kuhta, D. Pavlin, M. Slaj, S.Varga, M. Lapter-Varga, M. Slaj (2009), Type of Archwire and Levelof Acidity: Effects on the Release of Metal Ions fromOrthodontic Appliances, Angle Orthodontist 79 (1),102-110

[83] T. H. Huang, C.-C. Yen, C.-T. Kao (2001),Comparison of ion release from new and recycledorthodontic brackets, American Journal of Ortho-dontics and Dentofacial Orthopedics 120 (1), 68-75

[84] C. Zhang, X. Sun, S. Zhao, W. Yu, D. Sun (2014),Susceptibility to Corrosion and In Vitro Bio-compatibility of a Laser-Welded Composite Ortho-dontic Arch Wire, Annals of Biomedical Engineering42 (1), 222–230

[85] C. Zhang, S. Zhao, X. Sun, D. Sun, X. Sun (2014a),Corrosion of laser-welded NiTi shape memory alloyand stainless steel composite wires with a copperinterlayer upon exposure to fluoride and mechanicalstress, Corrosion Science 82, 404–409

[86] A. U. J. Yap, B. L. Ng, D. J. Blackwood (2004), Cor-rosion behaviour of high copper dental amalgams,Journal of Oral Rehabilitation 31, 595–599

[87] S. P. Kedici, A . A. Aksut, M. A. Kil icarslan, G.Bayramoglu, K. Gokdemir (1998), Corrosion beha-viour of dental metals and alloys in different media,Journal of Oral Rehabilitation 25, 800–808

[88] D. Mareci, D. Sutiman, I. Cretescu, A. Cailean, J. C.Mirza Rosca (2009), Electrochemical Chara-cterization of Some Copper Based Dental Materialsin Accelerated Test Solutions, Revista de Chimie 59(8), 871-877

[89] S. John-Mary, S. Rajendran (2012), Corrosionbehaviour of metals in artificial blood plasma inpresence of glucose, Zaštita Materijala 53 (3), 181-189

[90] C. M. A. Brett, I. Ioanitescu, F. Trandafir (2004),Influence of the biological fluid on the corrosion ofdental amalgam, Corrosion Science 46, 2803–2816

[91] I. Mutlu (2014), Electrochemical Corrosion Behaviorof TiN-Coated Biomedical Ti-Cu Alloy Foam inFluoride Containing Artificial Saliva, Metallurgicaland Materials Transactions 45A, 3640-3649

[92] T.-H. Lee, C.-C. Wang, T.-K. Huang, L.-K. Chen,M.-Y. Chou, H.-H. Huang, Corrosion resistance oftitanium-containing dental orthodontic wires influoride containing artificial saliva, Journal of Alloysand Compounds 488 (2009) 482–489

[93] V. A. Alves i dr., (2009a), D. G. Souza, R. Q. Reis,L. A. da Silva, A. Rossi, Electrochemical impedanceapplied to the corrosion behavior of dentalamalgams in synthetic physiological fluids, Cienciaand Technologia dos Materiais 21 (3/4), 36-43

[94] C. Zhang, X. Sun (2013), Susceptibility to StressCorrosion of Laser-Welded Composite Arch Wire inAcid Artificial Saliva, Advances in Materials Scienceand Engineering 2013, 1-8

[95] L. Joska, M. Poddana, J. Leitner (2008), Corrosionbehavior of palladium–silver–copper alloys in modelsaliva, Dental Materials 24, 1009-1016

[96] M. Sharma, A.V. R. Kumar, N. Singh, N. Adya, B.Saluja (2008), Electrochemical Corrosion Behaviorof Dental/Implant Alloys in Artificial Saliva, Journalof Materials and Performance 17, 695–701

ABSTRACT

THE ELECTROCHEMICAL BEHAVIOR OF COPPER AND COPPER ALLOYSAS BIOMATERIALS

Different types of metals are used in the stomatology for dental applications. The oral environmentis aggressive medium for metals and leads to corrosion. The metals undergo to chemical orelectrochemical reactions in the oral environment which resulting in dissolution and formation ofdifferent chemical compounds.The present article reviews and discussed the electrochemical behavior of copper and copperalloys in synthetic saliva.Keywords: copper, dental alloys, corrosion.

Review paperReceived for Publication: 12.10.2014.Accepted for Publication: 23.12.2014.

JOVAN JOVANOVIĆ, Elektrotehnički fakultet, Beograd, Kategorija radaJOHN SMITH, University of …. font Arial, font size 11,italic

Uputstvo za pripremu rada – naslov rada (najviše dva reda)Stil: font Arial, font size 14, bold

Izvod – ne duži od 150 reči (10-12 redova), treba da sadrži predmet i cilj rada, kratak pregledmetoda i najvažnije rezultate, tako da njegov originalni tekst može da se koristi u referentnojperiodici, font Arial, font size 10.

Ključne reči: (do šest pojmova), koje obezbeđuju uključivanje članka u informacione sisteme.

UVODRad treba da je pisan na srpskom ili engleskom jeziku. Treba da sadrži: izvod, uvod,

eksperimentalni deo, rezultate i diskusiju, zaključak, literaturu i izvod na engleskom jeziku ako je radpisan na srpskom jeziku i obrnuto.

Rukopis treba da je pisan jednostrukim proredom (A4 format). Na stranicama rukopisa marginetreba da budu:gornja, donja 3 cm, leva i desna 2.20 cm, koristeći font Arial, font size 10. Svi radovi serecenziraju.

PODNASLOV (npr., EKSPERIMENTALNI RAD)Podnaslove u rukopisu pisati VELIKIM SLOVIMA, font size 10.Tabele i slike se ubacuju na mesto gde se govori o njima. U tekstu se pozivati na redni broj

tabele/slike.Iznad tabele treba da stoji naziv. Ispod slika se navodi njen naziv, npr:Tabela 1 -. Rezultati eksperimentalnih merenja, italicSlika 1 - Rezultati simulacije, italic

PODNASLOV (npr., REZULTATI)

Numeraciju jednačina uraditi uz desnu marginu u malim (okruglim) zagradama, npr.: .e o

d tJ F t T t T t

dt

(1)

Jedinice: Pridržavati se Međunarodnog sistema jedinica (SI) i Zakona o mernim jedinicama imerama,kao i preporučenih IUPAC simbola hemijskih i fizičkih veličina.

PODNASLOV (na primer ZAKLJUČAK)

Rukopis, pripremljen kao MS Word doc datoteka, poslati e-poštom kao prilog na adresu glavnogurednika, Prof. Dr Časlava Lačnjevca: E mail: [email protected] (Acknowlegements): Navodi se naziv i broj projekta iz kojeg su proistekli rezultati i nazivinstitucije koja je finansirala istraživanja prikazana u radu.

LITERATURALiteratura se u tekstu navodi [uglastim] zagradama po redosledu citiranja, tako što se isti izvor

citira samo jednom, npr.; [1], [2,3], [4-8], Skraćene naziva časopisa treba navoditi prema Međunarodnomkodeksu za skraćivanje naslova periodičnih publikacija (http://www.efm.leeds.ac.uk/~mark/ISIabbr/).

[1] ČASOPIS: Sheng J.W. He M. Shi, H.C. (2007) A highly specific immunoassay for microcystin-LR detection basedon a monoclonal antibody, Anal Chim Acta, 603,1, 111–118.

[2] KNJIGA: Gulišija Z., Lačnjevac Č.: Korozija i Zaštita Materijala, ITNMS, (2012) Beograd.[3] POGLAVLJE U KNJIZI: Stojanović M., Lačnjevac Č., Lopičić Z.(2012) Corrosion and corrosion behavior of

depleted uranium, In: Gulišija Z., .Lačnjevac Č. (Ed), Korozija i zaštita materijala, ITNMS, Beograd, pp223-261.[4] TEKST SA WEB ADRESE: Maja Arslanagić M.,Kadić - Maglajlić S. (2011) Priručnik za navođenje izvora u

naučnim i stručnim radovima (http://www.efsa.unsa.ba/ef/docs/Prirucnici/prirucnik_ekonomski_web.pdf ,01.12.2013.)

ABSTRACTNa kraju rada treba dati naziv rada i izvod sa ključnim rečima na engleskom jeziku, u formi kaona srpskom jeziku.

V. RAJOVIĆ et al.. MEMBRANE TECHNOLOGY APPLICATION IN THE FRAMEWORK OF …


VUK RAJOVIĆ, JELENA MARKOVIĆ, Scientific paperALEKSANDAR JOKIĆ, JELENA ILIĆ UDC:504.3.054

Membrane technology application in the framework of zeroemission concept

The Zero emissions concept envisages all industrial inputs being used in final products orconverted into value-added inputs for other industries or processes. In this way, industries arereorganized into clusters such that each industry's wastes / by-products are fully matched with theinput requirements of another industry, and the integrated whole produces no waste of any kind.This technique is based on the well-established economic analysis tool known as the input/outputapproach. In the framework of the zero emission concept capture of CO2 plays an important role.CO2 can be captured and permanently stored, or it can be re-used.Carbon sequestration is a two-step process where the capture of CO2 from a gas stream isfollowed by its permanent storage. The capture step contributes 75% to the overall carbonsequestration process cost. For this reason, the scientific community has paid a great attention tothe development of new processes for CO2 capture. Currently, there is a wide range oftechnologies to separate CO2 from gas streams. They are based on different physical andchemical processes including absorption, adsorption, cryogenics and membrane technology. Thechoice of a suitable technology depends on the characteristics of the flue gas stream and, as aconsequence, on the power plant technology. As an alternative to conventional processes for CO2separation and capture, membrane technology shows great potentiality for CO2 capture owing toits easy applicability, efficiency, flexibility, ability to maintain high CO2 pressure and to performseparations at low energy penalties. CO2-selective membranes allow separation of CO2 fromdifferent gas streams, such as: flue gas (post-combustion system), natural gas (natural gasprocessing) and hydrogen (pre-combustion systems) or oxygen from nitrogen (in an oxyfuelcombustion system).In the framework of zero emission concept, this paper gives an overview and analysis of the typesof membranes used and membrane technology application in CO2 capture from the point of costand energy consumption.Keywords: zero emission, membrane technology, CO2 capture

INTRODUCTIONZero Emissions represents a shift from the tra-

ditional industrial model in which wastes are consi-dered the norm, to integrated systems in whicheverything has its use. It advocates an industrialtransformation whereby businesses emulate thesustainable cycles found in nature and where so-ciety minimizes the load it imposes on the naturalresource base and learns to do more with what theearth produces.

The Zero Emissions concept envisages allindustrial inputs being used in final products or con-verted into value-added inputs for other industriesor processes. In this way, industries are reorga-nized into clusters such that each industry's was-tes/by-products are fully matched with the inputrequirements of another industry, and the integra-ted whole produces no waste of any kind. Thistechnique is based on the well-established econo-mic analysis tool known as the input/outputapproach.

Author's address: Faculty of Technology, Bulevarcara, Lazara 1, Novi Sad, Serbia

Received for Publication: 11. 02. 2014.Accepted for Publication: 13. 04. 2014.

From an environmental perspective, the elimi-nation of waste represents the ultimate solution topollution problems that threaten ecosystems atglobal, national and local levels. In addition, full useof raw materials, accompanied by a shift towardsrenewable sources, means that utilization of theearth's resources can be brought back to sustai-nable levels.

One of the most important cornerstones of asustainable society consists in an industry thatuses zero waste, zero emissions processes. Theseprocesses require complete recycling or re-use ofall raw and auxiliary materials that are not conta-ined in the final product as well as of all operatingmaterials and energy flows. The goal of this kind ofproduction is to extract only those materials fromthe natural environment that form part of the finalproduct or of by-products. In addition, a sustainableeconomy also requires that the whole product lifefrom the extraction of raw materials to the disposalof the product be taken into account. Finally, it willbe essential to develop a multitude of innovativeservices, which would make it unnecessary to owncertain products.

Today’s ideals in the industry are modern andinnovative processes that aim to reduce emissionsand waste by an efficient and careful input of rawmaterials. The necessity of using zero emission



processes becomes evident if one considers thetrue costs caused by waste and emissionsgenerated in manufacturing processes. The wasteproduced has to be purchased in the form of rawmaterials and has to be accounted for in overallproduction costs (personnel, equipment, disposal).This demonstrates the great potential for savings,which could be realized through the prevention andrecycling of emissions.

The strong anthropogenic increase in the emis-sion of CO2 and the related environmental conse-quences force the developments in the direction ofsustainability and Carbon Capture and Storage(CCS). Fossil fuels are with 86% the dominantenergy source utilized in the world [1]. More thanone third of the CO2 emissions come from the com-bustion of fossil fuels in power plants worldwide [2-3] and also the emission of CO2 associated with theuse of CH4 is more than significant. The combus-tion of gaseous fuels (e.g. natural gas) accountedfor 1521 million metric tons of carbon in 2006,which equals 18.5% of the total emissions fromfossil fuels [3]. In addition, also the emission of CO2associated with the exploration and production ofnatural gas is more than significant [1]. The numberof easy accessible, low CO2 containing natural gassources is only limited, urging the exploration ofnatural gas sources with high(er) concentrations ofCO2.

Next to its environmental impact, CO2 reducesthe heating value of the CH4 gas streams in powerplants [4]. Due to its acidic character, the presenceof CO2 can lead to corrosion in equipment andpipelines. Pipeline specifications for natural gasesgive a maximum value of 2-5% for the CO2 contentwhile the CO2 content for liquefied natural gas

(LNG) even needs to be reduced to 50-100 ppm.This makes the removal of CO2 from natural gas ofcrucial importance. After capturing, the removedCO2 can be reused for different applications in theoil, food and chemical industry. Enhanced oilrecovery [1] as well as algae biofixation, where CO2is used for microalgaes as carbon source, areimportant applications. Smaller fields of application,like CO2 enrichment in greenhouses, where theincrease in CO2 concentration from 350 ppm to500 ppm results in a production increase of 25%for certain bulk crops are of additional interest.Although several possibilities for reuse of CO2exist, the total capacity of the different options forthe reuse of CO2 do not match with the currentproduction and, to reduce the emission of CO2 intothe atmosphere, additional storage of CO2 iscurrently inevitable. Possibilities to store CO2 inclu-de ocean sequestrations, geological sequestrationsand the sequestrations of CO2 in saline aquifers. Inlife cycle investigations, Khoo et al.[5] determinedthe effectiveness of the different CO2 sequestrationways and the potential environmental impact. Theresults showed geological sequestration methodsto be the safest methods with the least environ-mental burdens.

In coal-based power production usually thereare three ways for CO2 capture considered:

1. post-combustion CO2 capture from powerplant flue gas,

2. pre-combustion CO2 capture from gasifiedcoal synthesis gas,and

3. oxy-combustion, which separates oxygenfrom air prior to combustion and produces a nearlysequestration-ready CO2 effluent

Figure 1 - Approaches to power generation with fossil fuels (coal, oil and natural gas) that includecarbon dioxide capture and sequestration (CCS).



SEPARATION METHODSTraditional methods used to separate CO2 from

gas mixtures are pressure swing adsorption, cryo-genic distillation and the most frequently usedmethod amine absorption. Also membrane proces-ses are frequently used for gas separation. Exam-ples are e.g. the separation of oxygen and nitrogenfrom air to produce nitrogen enriched air, but alsofor the separation of CO2 from CH4 [4]. The mainlimitation of currently existing membranes is theoccurrence of severe plasticization of the mem-brane in the presence of (high) pressure CO2. Dueto excessive swelling of the polymer membraneupon exposure to CO2, the performance (selecti-vity) decreases significantly, thus reducing thepurity of the CO2 and consequently reducing thepossibilities for reuse of the gas. Energy require-ments on the other hand significantly benefit theuse of membrane technology over other technolo-gies: membrane technology uses 70-75 kWh perton of recovered CO2 compared to significantlyhigher values for pressure swing adsorption (160-180 kWh), cryogenic distillation (600-800 kWh) oramine absorption (330-340 kWh) [5], making mem-brane technology an attractive alternative.

MEMBRANE TECHNOLOGYMembrane technology is an attractive and com-

petitive alternative to conventional absorptiontechnology. It has a high energy efficiency, is easyto scale-up because of its modular design and ithas a high area-to-volume ratio. A limitation can befound in the permeability-selectivity tradeoff rela-tion: more permeable membrane materials are ge-nerally less selective and vice versa. Since 1980sgas separation with membranes has emerged intoa commercially viable method. Nowadays, severalhundreds of plants use membrane technology forthe separation of gases.

Most plants use cellulose-acetate membranes,which have CO2/CH4 selectivities of only 15 Accor-ding to Baker [6, 7], the competiveness of mem-branes for the separation of CO2/CH4 wouldstrongly increase if stable membranes with a sele-ctivity of 40 during operation would become avai-lable. Due to plasticization in the presence of CO2,membranes often lose their performance at ele-vated pressure. Swelling stresses on the polymernetwork and an increase in free volume andsegmental mobility upon exposure to CO2 cause arise in permeability for all components, and es-pecially the permeability of the low permeatingcomponent, consequently resulting in a decrease inselectivity [7]. The development of polymeric mem-branes and membrane processes with improvedplasticization resistance that maintain selectivityand permeability, even at higher CO2 partial feedpressures is crucial and an important field ofresearch.

MEMBRANE MODULES FOR CO2SEQUESTRATION

Conventionally, the membrane must be packedin a proper device called a ‘membrane module’,which should offer: low production costs high packing density low energy consumption good control of concentration polarization.

For the application of the membranes in gasseparation processes, several confi gurations areconventionally used for the membrane housingsuch as hollow and capillary fi bre systems andspiral wounds.

It should be stated that the commercial mem-brane modules available today are specifi cally de-signed for a specifi c membrane process applica-tion. However, the choice of a module configurationdepends on: type of separation problem ease of cleaning ease of maintenance ease of operation compactness of the system scale possibility of membrane replacement.

MODULES BASED ON HOLLOW FIBREMEMBRANES

Hollow fi bre membranes are made from extre-mely thin polymeric tubes, with a diameter of 50–200 µm [8]. The selective layer is on the outsidesurface of the fi bres, facing the high-pressure gas.A hollow fibre membrane module normally containstens of thousands of parallel fi bres deposited atboth ends in epoxy tube sheets [8]. These kinds ofmembrane play an important role in gas separationowing to their high separation area and selectivity.Hollow fi bres are stable and show high fl ux withmoderate selectivity in a full scale system. The highfl ux of hollow fi bres is due to the combination ofhigh transfer or separation areas and a thinmembrane wall.Moreover, they also possess a lowsurface energy.

MODULES BASED ON CAPILLARY FIBREMEMBRANES

Capillary fi bres are produced using similarequipment to hollow fi bres, but they have a largerdiameter, typically, 200–400 µm [8, 9]. The selec-tive layer is formed on the inside surface of the fibres. The free ends of the capillaries are pottedagents such as epoxy resins, polyurethanes. In acapillary fi bre module, the feed gas fl ows throughthe bore of the fibres.

The pressure difference feed-to-permeate,which capillary fi bres can support, is limited andtypically it does not exceed 10–15 bar. Higher



pressures may rupture fi bres and even a singledefective fi bre can seriously degrade the sepa-ration capability of the module. Capillary embranemodules are not as expensive or compact as hol-low fi bre modules, but they are still very eco-nomical. Their principal drawback is the pressurethat the fibres can support. This limitation meanscapillary modules cannot be used at the highpressures that are necessary for hydrogen ornatural-gas processing applications [9].

SPIRAL WOUND MODULESGenerally, sheets of membrane 1–2 m long are

cut and folded and then packaged as spiral woundmodules [10]. A single module may contain as ma-ny as 30 membranes. Spiral wound elements aregenerally the most economical to operate .

Spiral systems are: Compact – high membrane packing density

results in more effi cient utilization of fl oorspace;

Energy efficient – lower power consumptioncompared to other membrane confi gurations;

Lower capital cost, when extensive feedpretreatment is not required;

Robust – high pressure spiral elements canwithstand pressures in excess of 1000 psi(6.89 MPa).

COMPARISON BETWEEN DIFFERENTMEMBRANE MODULES

It is diffi cult to quantify correctly the cost of amodule because the same module design varieswidely depending on the application considered.Generally, hollow fi bre modules are cheaper thanthe others even if they are produced for very high-volume applications in order to justify the expenseof developing and building the spinning and modulefabrication equipment.

Hollow-fi bre and spiral-wound modules arevery common mainly owing to their higher area tovolume ratio. Spiral-wound modules have distinctadvantages over the hollow-fi bre elements inimportant applications, although the latter can offerhigher packing density.

DESIGN FOR POWER PLANT INTEGRATIONThe design of power stations requires simulta-

neous consideration of heat integration and powergeneration. Simulation models for gas separationmembranes have to consider, generally, an equa-tion describing the gas transport across the mem-brane, a mass balance equation for each compo-nent of the gas mixture, the pressure drops occur-ring on both sides of the membrane and theboundary conditions [11] The major impediment tothe engineering analysis of membrane processesin CO2 separation is the large number and range ofprocess variables. The mixture is often treated as abinary system (generally CO2 and H2) and, there-

fore, the role of impurities (water, SO2, NOx, parti-cles, etc.) has not yet been investigated in detail.Another common assumption is that the constantfeed mixture temperature is either close to or slig-htly above ambient temperature (e.g. 40°C). More-over, the most important parameter, that must beconsidered, is the effi ciency of a membrane sepa-ration process. The effi ciency depends on threemajor variables: the membrane selectivity the pressure ratio between feed and permeate

streams; the stage cut, the ratio of permeate flow rate to

feed flow rate.Particular attention is paid to the calculation of

the CO2 recovery ratio, the fraction of CO2 in thefeed captured in the permeate side:

in

p

yy

R (1)

where yp is the mole fraction of CO2 in thepermeate and xin is the mole fraction of CO2 in thefeed. In general, an increase in θ (and so an incre-ase of the membrane area) is not linear with therecovery of CO2. For this reason, in a problem likeCO2 capture, one major objective of scientificstudies is to determine the relationship between theCO2 recovery ratio (R) and the correspondingpermeate composition (yp).

The International Energy Agency (IEA) guide-lines require R to be above 80% or 90% (Davisonand Thambimuthu, 2004), because values belowthis do not offer a suffi cient decrease in CO2 relea-sed to the atmosphere. The permeate CO2 molefraction yp must also be in the range 0.8–0.95, bothto minimize the compression and transportationcosts [12] and to prevent problems related to deepocean or geological disposal. Unfortunately, therecovery ratio R and permeate composition ypseem to be inversely related, such that an increasein R implies a decrease in yp and vice versa.

COST CONSIDERATIONS AND MEMBRANETECHNOLOGY AT THE INDUSTRIAL SCALE

Economic analysis includes not only the costsfor capture, but also the costs of injection and sto-rage into a geological site, allowing a full compa-rison processes depend on the fi xed charges andthe repayment of the plant investment cost and ofoperating costs (energy, membrane replacement,maintenance).

In particular, quantitative analysis of the costsstrongly depends on the specifi c application, plantand location as well as on the characteristics ofmembranes and modules. In fact, the costs ofcapture using gas separation membrane systemscan be reduced by increasing the membranepermeability and selectivity.

Improvements in the permeability reduce thecapture cost because less membrane area is requi-red for the same CO2 recovery rate. By increasing



the CO2/N2 selectivity, the mole fraction of CO2 inthe permeate increases. As the capture costincludes the compression of CO2 after separation,a higher CO2 fraction in the permeate streamrequires less compression and, thus, less energy;therefore, both the capital expenditure and ope-rating costs are lower.

In contrast, the cost of membranes affects onlymarginally the capture costs [13]. Therefore, reduc-tions in membrane costs will improve the overallcompetitiveness of gas separation membrane sys-tems slightly.

Another important aspect of CO2 separationcosts is the driving force, which, by using embranetechnology, depends on the partial pressure diffe-rence between both sides of the membrane. Byincreasing the pressure across the membrane orreducing the feed gas pressure, the capture costdecreases.

This is because a lower feed pressure requiresa smaller compressor, thereby reducing both thecapital costs and the total energy consumption [13].Nevertheless, decreasing the feed pressure, thedriving force across the membrane decreases.Therefore, to obtain the same CO2 recovery fromthe feed gas, the membrane area required mustincrease. Globally, it is better to increase the costsof the membrane than to use a bigger compressor.

Moreover, just to give a very brief overview ofthe work in CO2 capture direction, some Europeanprojects (in the UE FP6 and FP7 only) are reportedin the following: Innovative CO2 capture (iCap: 2010–2013).

This project is coordinated by the NorwegianUniversity of Science and Technology. The aimof the project is to develop breakthroughtechnologies that can be applied to post-com-bustion CO2 capture. These technologies inclu-de the use of phase change solvents, thecombination of SO2 and CO2 absorption, theuse of CO2-selective low-temperature membra-nes and the development of new energy pro-duction cycles with CO2 capture.

CO2 enhanced separation and recovery(CESAR: 2008–2011. For: CESAR: http://www.co2cesar.eu/index.php). This aims for a break-through in the development of low-cost post-combustion CO2 capture technology in order toprovide an economically feasible solution forboth new large scale power plants and retrofi tof existing power plants. For this project, theresearch is charged with the development ofnew membrane contactors, development car-ried out by SME Polymem and ENSIC-Nancy.

Nanoglowa is a project based on CO2 capturetrough nanostructured membranes (http://www.nanoglowa.com). In this project, the applicationof nanostructured membranes for CO2 captureand separation brings down the energy penaltyrelated to conventional absorption with amines.

CONCLUSIONSMembrane-based technology has several ad-

vantages over conventional separation approachesfor CO2 capture, such as: lower capital cost ease of skid-mounted installation lower energy consumption ability to be applied in remote areas, especially

offshore flexibility.Nevertheless, there are many relevant factors

determining the appropriateness of each membra-ne type for each specifi c application. When selec-ting a suitable membrane for CO2 separation, theoperating temperature and pressure are of para-mount importance since they directly affect the se-paration performance of the membrane. In addition,the composition of the gas mixture to be separated,the material and fabrication costs of the memb-ranes as well as the overall process design need tobe taken into account. Moreover, the energy re-duction required and the corresponding costs mustbe addressed. Currently, chemical modification ofpolymeric membranes is one of the most promisingapproaches for greatly enhancing separation per-formance. Therefore, further development of exis-ting modification methods (e.g. identifying bettercross-linking agents) or the invention of new modifi-cation techniques for existing gas-separation mate-rials may accelerate the commercialization of poly-meric membranes for CO2 separation. However,long term stability and performance of polymericmembranes at elevated temperatures are neces-sary to maintain the robustness of the membrane-based systems. In addition to membrane materialsselection, membrane configuration and moduledesign are important considerations for industrialapplications.

Membrane separation is an attractive and pro-mising technology, which can be applied in com-bination in all types of power plants. Nevertheless,although membrane technology is widely appliedfor gas separation, it is not yet used on the scale ofpower plants. For this reason, a potential objectivecould be the development of innovative membrane-based technologies capable of reducing the cost ofCO2 capture, producing, for example, hydrogenfrom natural gas fuel. This could be, for example,obtained by producing higher selective membra-nes, such as hybrid membrane–absorbent (or sol-vent) systems, which use very high surface area tovolume ratios for mass exchange between a gasstream and a solvent, resulting in a very compactsystem. Overall, even though the separation of CO2using polymer-based membranes is a complexundertaking, it is necessary to address the challen-ges and continue approaches that will produce thenext generation of high performance membranes.



REFERENCES[1] Ipcc, (2005). Special report on carbon dioxide

capture and storage: (England), C.U.P.C.[2] Zhang, H.-Y., Wang, R., Liang, D.T. & Tay, J.H.,

(2006). Modeling and experimental study of CO2absorption in a hollow fiber membrane contactor.Journal of Membrane Science, 279 (1–2), 301-310 ;Iea, (2009). CO2 emissions from fuel combustion1971-2007.

[3] Boden, T.A., Marland, G. & Andres, R.J., (2010).Global, regional and national fossil-fuel CO2emissions. Oak Ridge, Tenn., U.S.A.

[4] Simons, K., (2010). Membrane technologies for co2capture. PhD Thesis. University of Twente, TheNetherlands.

[5] Khoo, H.H. & Tan, R.B.H., (2006). Life cycle in-vestigation of CO2 recovery and sequestration.Environmental Science and Technology, 40

[6] Baker, R.W., (2002). Future directions of membranegas separation technology. Industrial & EngineeringChemistry Research, 41, 1393-1411

[7] Simons, K., Nijmeijer, K., Bara, J.E., Noble, R.D. &Wessling, M., (2010). How do polymerized room-temperature ionic liquid membranes plasticize duringhigh pressure CO2 permeation; Journal ofMembrane Science, 360 (1–2), 202-209

[8] Baker, R.W. ed. (2004). Membrane technology andapplications, Chichester, UK: John Wiley and Sons.

[9] Buysse, C., Kovalevsky, A., Snijkers, F., Bueken-houdt, A., Mullens, S., Luyten, J., Kretzschmar, J. &

Lenaerts, S., (2010). Fabrication and oxygen per-meability of gastight, macrovoid-free ba0.5sr0.5co0.8fe0.2o3−δ capillaries for high temperaturegas separation. Journal of Membrane Science, 359(1–2), 86-92

[10] Lababidi, H., Al-Enezi, G.A. & M, H.M.E.H., (1996).Optimization of module configuration in membranegas separation. Journal of Membrane Science, 112(185–97)

[11] Safari, M., Ghanizadeh, A. & Montazer-Rahmati, M.,(2009). Optimization of membrane based CO2 -removal from natural gas using simple modelsconsidering both pressure and temperature effectsInt J Greenhouse Gas Control,, 3, 3–10 ; Ahmad, F.,Lau, K.K. & Shariff, A.M., (2010). Removal of CO2from natural gas using membrane separationsystem: Modeling and process design. Journal ofApplied Science, 10, 1134–9. ; Hwang, S.T. &Kammermeyer, K., Membranes in SeparationTechniques of chemistry. 1975 New York: WileyInterscience.

[12] Davison, J. & Thambimuthu, K., Year. Technologiesfor capture of carbon dioxideed.^eds. 7thGreenhouse Gas Technology Conference,Vancouver, Canada.

[13] Ho, M.T., Allinson, G. & Wiley, D.E., (2006).Comparison of CO2 separation options for geo-sequestration: Are membranes competitive?Desalination, 192, 288–95

IZVOD

PRIMENA MEMBRANSKE TEHNOLOGIJE U OKVIRU POJMA NULTE EMISIJE

Koncept nulte emisije predviđa sve industrijske inpute koji se koriste u finalnoj proizvodnji ili pretvoreneu inpute koji ulaze u dodatnu vrednost za druge industrije ili procese. Na ovaj način, industrije sereorganizuju u klastere tako da se otpad svake industrije, sporedni proizvod, u potpunosti poklapa saulaznim zahtevima drugih industrije, a integrisana celina ne proizvodi otpad bilo koje vrste. Ova tehnikase zasniva na dobro utvrđenim ekonomskim analizama alata poznatim kao ulazno / izlazni pristupi . Uokviru koncepta nulte emisije hvatanje CO2 igra važnu ulogu. CO2 se može uhvatiti i trajno čuvati, ili semože ponovo koristiti.Sekvestracija ugljenika je proces u dva koraka, gde je hvatanje CO2 iz gasne struje praćeno njegovimstalnim skladištenjem. Proces prikupljanja doprinosi 75% na ukupne troškove proces zaplena ugljena.Iz tog razloga, naučna zajednica je posvetila veliku pažnju razvoju novih procesa za prikupljanje CO2.Trenutno, postoji širok spektar tehnologija za separaciju CO2 iz gasnih struja. Oni su zasnovani narazličitim fizičkim i hemijskim procesima, uključujući apsorpcije, adsorpciji i membranske tehnologije.Izbor odgovarajuće tehnologije zavisi od karakteristika protoka dimnih gasova i, kao posledica toga, natehnologiji elektrane. Kao alternativa konvencionalnim procesima za separaciju i hvatanje CO2,membranska tehnologija pokazuje veliki potencijal za CO2 zbog njegove lakoća postavljanja, efikasnost,fleksibilnost, mogućnost održavanja visokog pritiska CO2 i obavljanja razdvajanja na niskim vrednostimaenergije. CO2- selektivna membrana dozvoljava odvajanje CO2 iz različitih gasnih struja, kao što su:dimnih gasova ( sistem posle sagorevanja ), prirodni gas ( prerada prirodnog gasa ) i vodonika ( sistemipre sagorevanja ) ili kiseonika od azota ( u sistemu ’’oksifuel’’ sagorevanje).U okviru koncepta nulte emisije, ovaj rad daje pregled i analizu vrsta membrana koje se koriste iprimenjenih membranskih tehnologija za prihvatanje CO2 sa stanovišta troškova i energetske potrošnje.Ključne reči: nulta emisija, membranska tehnologija, prihvatanje CO2

Originalni naučni radPrimljeno za publikovanje: 11. 02. 2014.Prihvaćeno za publikovanje: 13. 04. 2014.

S. KRSTIC et al. STRUCTURAL PROPERTIES OF CARBON MICROSPHERES OBTAINED ...


SANJA KRSTIC1, BRANKA KALUĐEROVIC1, VLADIMIR Scientific paperDODEVSKI1, RADOSLAV ALEKSIC2, A. BJELAJAC2, D. BRKOVIC2 UDC:664.165

Structural properties of carbon microspheres obtained byhydrothermal treatment of fructose

A carbon-rich solid product has been synthesized by hydrothermal treatment from fructose withHNO3 at temperature of 140°C. The concentration of the precursor was changed in order toinvestigate how its change influences formation of carbon microspheres. pH value for everysample was the same, i.e. 1. The formation of the carbon rich solid through the hydrothermalcarbonization of fructose is the consequence of dehydration reactions. Obtained carbon material ismade of spherical micrometer-sized particles with the diameter in the 1-6 µm range, which can bemodulated by modifying the concentration of fructose in solution. The best results are obtainedwith smaller concentrations of fructose. Spherical particles have more regular shape and they areless agglomerated. The structure and surface chemical properties of obtained material werecharacterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectraand elemental analysis.Keywords: carbon microspheres; hydrothermal synthesis; fructose.

AIMS AND BACKGROUNDSynthesis of functional and novel carbona-

ceous materials is a very interesting topic due to itsvariety of applications such as adsorbents, storageand production of electrodes, energy, nanocompo-sites, hydrogen storage, catalyst supports [1-4]drug delivery [5,6], filter materials [7] etc. Blacksolid residue contains mostly carbon microspheres(CMSs). Their properties like low weight, thermalisolation and high compressive strength have dri-ven a considerable attention in the world of nano-technology materials. When an aqueous solution//dispersion of a saccharide (e.g. fructose, glucose,sucrose, starch etc.) is heat-treated at a moderatetemperature in the 170–250 °C range (under auto-genous pressure), a carbon-rich black solid is obta-ined as insoluble product. The first research workon the hydrothermal carbonization of saccharideswas carried out during the first decades of the 20thcentury with the aim of understanding the mecha-nism of coal formation. Renewed interest in thehydrothermal carbonization of carbohydrates hasrecently been established, and the objectives ofthese new investigations were completely differentto those previously mentioned [8-13]. At this time,the main purpose is to use the process of thehydrothermal carbonization as a way to producenanostructural carbonaceous materials with spe-cific properties (such as shape, size, chemical fun-ctionalities etc.), depending on their application.

Author's address: 1Institute of Nuclear Sciences,Laboratory for Material Science, University of Bel-grade, Belgrade, Serbia, 2Faculty of Technology andMetallurgy, University of Belgrade, Belgrade, Serbia

Received for Publication: 22. 02. 2014.Accepted for Publication: 18..05..2014.

There are many methods which have beendeveloped to prepare microspheres of this nature.From the two main points of view, economy andconservation of environment, hydrothermal carbo-nization of carbohydrates has advantages on othercomplex and highly cost methods. Precursors suchas xylose[8], glucose [14,15], fructose [9], sucrose[9], cellulose [10] and starch [11] were used ascarbon sources to prepare this kind of microsphe-res by hydrothermal carbonization method. Theobtained microspheres have characteristic chemi-cal structure, and they can be widely applied in thefields of environmental protection and medicine. Ithas been reported that treatment by hydrothermalmethod of different carbohydrates in aqueous solu-tion results in the formation of solid carbonaceousmicro particles. In these works, obtained particlesare regular spheres in the size range of 0.3-10 µm[8,9,12,13,15-18]. Some of these works widely ex-plain dehydration process and formation of carbonmicrospheres using saccharides such as glucose,starch, sucrose and cellulose. Process is followedby aromatization under hydrothermal conditionsand obtained carbonaceous spheres have highlyaromatic nucleus and a hydrophilic shell [8, 12, 13,15,16].

In the process of hydrothermal carbonization ofcarbohydrates, many factors affect the morphology,yield and surface functional groups of carbon. Ithas been found that the diameter of the obtainedCMSs can be changed by modifying the synthesisconditions. In previous works it has been given thatthe diameter of CMSs widens with an increase inreaction temperature, saccharide concentration, orreaction time [13]. Also, researchers induced theself-assembly of colloidal carbon microspheres intospheroids by employing alcohol as a structure



directing agent [19]. The effect of the concentrationchange on the morphology, yield and surfaceproperty of the resultant CMSs were investigated.Most of the works recently published in this areahave been mainly focused on the synthesis ofcarbonaceous products and hybrid carbon/inor-ganic materials.

The main aim of the present work was toinvestigate the effect of certain process parameterson the morphology of carbonaceous microspheresobtained by hydrothermal carbonization. Startingmaterial in this case was a commercial fructosebecause it is cheap precursor and we assumedthat hydrothermal carbonization could happen atlower temperature in comparison with other sac-charide. The concentration of precursor was chan-ged and the dimensions of obtained microsphereswere compared.

EXPERIMENTALHydrothermal synthesis of carbon microsphe-

res was carried out in a glass reactor at 140 °C for3 h. Hydrolysis was performed using HNO3 watersolution with pH value of 1 for all of the samples.Concentration of fructose used in the experimentswas: 0.5 M, 1 M, and 3 M (CMS1, CMS2 andCMS3, respectively). Experiments were conductedin the following sequence: the required concentra-tion of fructose solution was added in 40 ml ofHNO3 and the compound processed in this waywas mixed with the magnetic stirrer for a period of15 min. Then, the solution was placed in a glassreactor, put into the oven and heated under auto-genously pressure at 140 °C for 3 h. The preparedsamples were washed with distilled water severaltimes. The next step was the filtration and washingwith distilled water to pH=7. Finally, the sampleswere dried in an oven at 100 °C to obtain a finalproduct.

The structure of dried samples was investiga-ted by a scanning electron microscope (SEM)JEOL JSM-5800. Fourier-transform infrared (FTIR)spectra of samples were analyzed using BOMEM(Hartmann & Braun) spectrometer in transmissionmode between 400 cm-1 and 4000 cm-1 with reso-lution 4 cm-1. Elemental analysis (C, H and O) ofsamples was performed using a Vario EL III C, H,N, S/O Analyzer (Elementar). The sphere diame-ters were determined applying Image Pro Designprogram and histograms were given.

RESULTS AND DISCUSSIONIn our investigation factors like pH value and

concentration of precursor were changed to get thebest results at 140 °C. In the case of changed pHvalue, only pH=1 gave solid black residue. Obta-ined carbon material was made of particles with aspherical morphology having the diameter in the

1.0 µm to 6.0 µm range, as shown by the SEMmicrographs (Figure 1). The SEM image in Figure1b revealed that the sample CMS2 consisted of alarge amount of more uniform microspheres withaverage diameter of ~3.5 µm. CMS3 sampleshowed microspheres which were piled togetherwith many incompletely developed microspheres.

a)

b)

c)

Figure 1 - SEM micrographs of the carbon micro-spheres obtained by hydrothermal treatment offructose at 140°C for 3h: a) CMS1; bar length

20µm, b) CMS2; bar length 50µm and c) CMS3;bar length 20µm

Figure 2 includes the histogram of the diameterdistribution of the microspheres. It may be seenfrom the histogram that distribution has a highdegree of uniformity. It is clear that for the appliedconditions (140 °C and short reaction time 3 h),with change of concentration of fructose, themicrospheres fuse, and thereby giving rise toparticles which have a peanut shape (Figure 1 b,c). The diameter of the carbon microspheres canbe modulated by modifying the preparationconditions. In comparison with previous workswhere authors have been used water and highertemperatures, carbon microspheres obtained in thisstudy are in the similar size range and they havethe same morphology[12].



a)

b)

c)

Figure 2 - Histograms of the carbon microspheres:a) CMS1, b) CMS2 and c) CMS3

Actually, we observed that increase the con-centration of the reaction mixture, leads to an incre-ase of the mean diameter of the micro particlesdecreasing the regularity of spherical shape of theparticles (see Figure 1b). When the concentrationof precursor is too high, particles lose their sphe-rical structure, smoothness of the external surfaceand become more agglomerated (see Figure 1c).Adequate evidence to enable the identity and purityof all newly synthesized compounds should beprovided.

The surface chemical functional groups of obta-ined carbon microspheres were characterized byFTIR spectroscopy and the resulting diagram isshown in Figure 3. The foremost bands were fo-und, assigning to the broad O-H adsorption in theplan range from 3600 cm-1 to 3000 cm-1 and C=Ostretching adsorption at 1700 cm-1. Aliphatichydrocarbon (-C-H) was at approximately 2900 cm-

1 and the band at 1620 cm-1 could be attributed tothe C=C stretching of aromatic and furanic rings.

The characteristic bands due to C-O (hydroxyl,ester, or ether) stretching vibrations were observedin the range 1300 cm-1 to 1000 cm-1, while the bandat 790 cm-1 assigned to aromatic C-H out-of-planebending vibrations[20]. These data reveal that the-se carbon spheres contained an aromatic core andresident functionalities in their shell.

Figure 3 - FTIR spectra of the carbon microspheresobtained by hydrothermal treatment of fructose

The elemental chemical composition (C, O andH) of the carbon microspheres obtained by differentconcentration of fructose are listed in Table 1. It isshown that the carbon content increases from 40 %in raw fructose to approximately 60 % in obtainedcarbon material samples. Also, there is a reductionin the oxygen and hydrogen contents. It can beseen that there is no significant change of carboncontent when the concentration of the precursorincreases.

Table 1 - Chemical elemental analysis of carbonmicrospheres from the hydrothermaltreatment of fructose

Sample C (wt%) H (wt%) O (wt%)

raw fructose 40.00 6.72 53.28CMS1 60.61 4.48 34.91CMS2 60.64 4.50 34.86CMS3 59.87 4.58 35.55

CONCLUSIONSThe treatment of fructose under hydrothermal

conditions in HNO3 solution at 140 °C and pH=1,leads to the formation of black solid carbonaceousresidue consisting of micrometer sized spheres,with dimensions ranging from 1 µm to 6 µm. Thediameter of obtained spheres can be modulated bychange of precursor concentration. With increaseof the concentration, spherical structure of particlesand their smoothness diminish, agglomeration of



particles is more expressed and the size of parti-cles loses their uniformity. The change of carboncontent is not significant when the concentration ofthe precursor increases.

AcknowledgementThe financial support of this research work was

provided by the Ministry of Education and Scienceof the Republic of Serbia through the project III-45005.

REFERENCES[1] M. Sevilla, C. Sanchis, E. Morallon, A. B. Fuertes

(2009). Highly Dispersed Nanoparticles on CarbonNanocoils and their Catalytic Performance for FuelCell Reaction. Electrochem. Acta, 54, 2234.

[2] E.T.Thostenson, Z. Ren,T. W. Chou (2001)Advances in the Science and Technology of CarbonNanotubes and their Composites: a review. ComposSci and Technol, 61, 1899

[3] P. Serp, P. M. Corrais, P. Kalck (2003) CarbonNanotubes and Nanofibers in Catalysts. Appl Catal.A 253, 337

[4] Y. Liu, Z. Shen (2005) Preparation of CarbonMicrocoils and Nanocoils using Activated CarbonNanotubes as Catalyst Support. Carbon, 43, 1574

[5] N. Venkatesan, J.Yoshimitsu, Y. Ito, N. Shibata, K.Takada (2005) Liquid Field Nanoparticles as DrugDelivery Tool for Protein Therapeutics. Biomaterials,26, 7154

[6] H. Zhu, M. M. J. MC. ShanE (2005) Loading ofHydrophobic Materials into Polymer Particles:Implications for Fluorescent Nanosensors and DrugDelivery, J Am Chem Soc, 127, 13448

[7] A. Matilainen, M. Vieno, T. Tuhkanen (2006)Efficiency of the Activated Carbon Filtration in theNatural Organic Matter Removal. Environ Int, 32,324

[8] M. M. Titirici, M. Antonietti, N. Baccile (2008)Hydrothermal Carbon from Biomass: a Comparisonof the Local Structure from Poly- to Monosac-charides and Pentoses/Hexoses. Green Chem, 10,1204

[9] C. H. Yao, Y.S. SHIN, L. Q. Wang, C. F. Windish,W. D. Samuels, B. W. Arey, C.M. Wang (2007)Hydrothermal Dehydration of Aqueous FructoseSolutions in a Closed System J. Phys Chem C, 111,15141

[10] M. Sevilla, A. B. Fuertes (2009) The Production ofCarbon Materials by Hydrothermal Carbonization ofCellulose Carbon, 47, 2281

[11] M. T. ZHENG, Y. L. LIU, Y. XIAO, Y. ZHU, Q.GUAN, D. S. YUAN, J. X. ZHANG (2009) An EasyCatalyst-Free Hydrothermal Method to PrepareMonodisperse Carbon Microspheres on a LargeScale. J Phys Chem C, 113, 8455

[12] J. Ryu, Y. W. Suh, D. J. Suh, D. J. Ahn (2010)Hydrothermal Preparation of Carbon Microspheresfrom Mono-Saccharides and Phenolic Compounds.Carbon, 48, 1990.

[13] M. Sevilla, A. B. Fuertes (2009) Chemical andStructural Properties of Carbonaceous ProductsObtained by Hydrothermal Carbonization ofSaccharides. Chem Eur J, 15, 4195.

[14] Y. Z. Mi, W.B. Hu, Y. M. Dan, Y. L. Liu (2008)Synthesis of Carbon Micro-Spheres by a GlucoseHydrothermal Method. Mater Lett, 62, 1194

[15] X. M. Sun, Y. D. Li (2004) Colloidal Carbon Spheresand Their Core/Shell Structures with Noble-MetalNanoparticles. Angew. Chem.,43, 597

[16] Q. Wang, H. LI, L. Chen, X. Huang (2002) NovelSpherical Microporous Carbon as Anode Materialfor Li-ion Batteries. Solid State Ion 152–153, 43

[17] D. Z. Ni, L. Wang, Y. H. Sun, Z. R. Guan, S.Yang,K. B. Zhou (2010) Amphiphilic Hollow Carbona-ceous Microspheres with Permeable Shells. AngewChem Int Ed, 49, 4223

[18] B. Hu, K. Wang, L. Wu, S. H. Yu, M. Antonietti, M.M. TitiricI (2010) Engineering Carbon Materials fromthe Hydrothermal Carbonization Process ofBiomass. Adv Mater, 22, 813

[19] M. Zheng, Y. Liu, K. Jiang,Y. Xiao,D. Yuan (2010)Alcohol-assisted Hydrothermal Carbonization toFabricate Spheroidal Carbons with a TunableShape and Aspect Ratio. Carbon, 48, 1224

[20] W.Shen, Z. LI, Y. Liu (2008) Surface ChemicalFunctional Groups Modification of Porous Carbon.Rec Pat Chem Eng, 1, 27

IZVOD

STRUKTURNE OSOBINE MIKROSFERA UGLJENIKA DOBIJENIH HIDROTERMIČKIMTRETMANOM FRUKTOZEČvrsti proizvod bogat ugljenikom je sintetizovan hidrotermičkim tretmanom fruktoze sa HNO3 natemperaturi od 140 °C. Koncentracija prekursora bila je menjana da bi se istražilo kako njegovapromena utiče na formiranje mikrosfere atoma. pH vrednost za svaki uzorak bila je isti 1. Formiranječvrstog proizvoda bogatog ugljenikom preko hidrotermičke karbonizacije fruktoze posledica jedehidracionih reakcija. Dobijeni ugljeni materijal izrađen je od sfernih čestica veličine prečnika od 1do 6 µm, koji se može modulisati promenom koncentracije fruktoze u rastvoru. Najbolji rezultati sedobijaju sa manjim koncentracijama fruktoze. Sferne čestice imaju više pravilan oblik i oni su manjeaglomerisane. Strukture i površinske hemijske osobine dobijenog materijala su sagledavaneskeniranjem elektronskim mikroskopom (SEM) , FTIR-om i spektralnim i elementarnim analizama.Ključne reči: ugljene mikrosfere, hidrotermalna sinteza, fruktoza.

Scientific paperReceived for Publication: 22. 02. 2014Accepted for Publication: 18. 05. 2014.

J. MALINA, J. RADOŠEVIĆ’ INFLUENCE OF NaCl CONCENTRATION ON PITTING CORROSION ...


JADRANKA MALINA1, Scientific paperJAGODA RADOŠEVIĆ’2 UDC:620.190.4:669.75.721

Influence of NaCl concentration on pitting corrosionof extruded Al –Mg-Si alloy AA6060

Extruded Al–Mg–Si alloys (AA6xxx series alloys) are the most common aluminum alloys forstructural application due to reliable mechanical characteristics and corrosion properties.Spontaneously formed adherent aluminum oxide film on the surface protects Al and Al-alloys fromcorrosive attack in neutral media, but in chloride containing solutions, such thin and compactpassive film is prone to breakdown.In this study the corrosion behavior of commercial extruded Al-Mg-Si alloy AA6060 wasinvestigated in NaCl solutions of different concentrations using anodic potentiodynamicpolarization measurements under deaerated conditions at room temperature. It was shown thatsensitivity to chloride attack increase with increasing Cl- concentration and depends on cathodicmicroconstituents in extruded Al–Mg–Si alloy.Keywords: pitting corrosion, commercial Al-Mg-Si alloy, deaerated NaCl

1. INTRODUCTIONExtruded Al-Mg-Si alloys (AA6xxx series alloys)

are widely used for different kinds of aluminiumproducts including profiles for structural applica-tions in the automotive industry, sections for archi-tectural applications and tubes for the heat transfersegments [1,2]. The major alloying elements in theheat-treatable 6xxx series are magnesium and sili-con. Both elements are required for precipitationstrengthening, which is commonly acquired by so-lutionizing and artificial aging [3-6]. Their recycla-bility, high strength-to–weight ratio and resistanceto corrosion make them more and more used asreplacement material for expensive AA2xxx andAA7xxx in aerospace industry and military appli-cations [7].

Oxide passive layers composed of Al2O3,Al(OH)3 and AlO(OH) grow spontaneously on Aland Al-alloys and provide good corrosion resistan-ce in highly aggressive environments. However,different thermomechanical treatments applied toachieve required mechanical properties lead todestruction of the protective film so that Al-alloysare liable to suffer from various forms of corrosion,mainly pitting and intergranular attack, dependingon the nature of anion in the neutral solution [8]. Itis known that halide ions are aggressive for Alalloys. Physicochemical characteristics of the pas-sive layers govern the adsorption of aggressiveions such as Cl-, their penetration and accumula-tion in imperfections of the protective film. There-fore, such processes are considered as one of thetriggering factors in the nucleation of pitting [9 -13].

Author's address: 1University of Zagreb Faculty ofMetallurgy, Sisak, Croatia, 2University of Split Facultyof Electrical Engineering, Mechanical Engineering andNaval Architecture, Split, Croatia


In order to demonstrate the effect of NaClconcentration on pitting corrosion, the object of thisstudy was to obtain the breakdown potential ofpassive layer by following the anodic polarizationbehavior of commercial extruded profiles producedfrom heat treatable Al-Mg-Si alloy.

2. EXPERIMENT

2.1. Sample composition and preparationExtruded products of Al-Mg-Si alloy are com-

mercially available as EN AW6060 and AA6060[14]. From the hollow quadratic profile shown inFigure 1, the alloy samples for electrochemicalmeasurements were cut into square shaped testplates of 80 x 50 mm and thickness of 2 mm.Investigated 6xxx alloy is characterized by thechemical composition (Al-98.72, Mg-0.45, Si-0.49,Fe-0.21, Mn-0.02); which correlate closely with tho-se generally accepted as suitable one for extrudingprocesses [15-18].

To remove surface contamination before eachmeasurement, specimens were mechanically andchemically treated. The surface of sample wasmechanically abraded using emery papers (grade400, 500, 600 and 1000) on test face and rinsedwith distilled water.

Figure 1 - Commercial hollow profile made ofAA6060 alloy

The test plates were subsequently treated byimmersion for 1 minute in a solution containing 0.1



mol dm-3 NaOH at 40 ºC, in order to remove thesurface oxide layer and eventually incorporatedimpurities. Immediately after the rinsing in distilledwater, the clean specimen was as quickly aspossible placed in the electrochemical cell and thensubjected to the experimental procedure.

2.2. Electrochemical measurementsThe corrosive medium was deaerated NaCl

solution (with concentration varying between 0.35wt.% and 5 wt. %. Bubbling of high purity nitrogen(5N) through the electrolyte was performed 30 minbefore measurements started and subsequentlycontinued (over the solution) during the experi-ments. All the tests were conducted at ambienttemperature (293 ± 1) K and at natural acidity. ThepH 5.5 was measured in 3.5 wt.% NaCl solution,and no significant change was noticed by changingthe NaCl concentration.

Figure 2 - Scheme of 3-electrode cell used forelectrochemical measurements

Three-electrode electrochemical cell shownschematically in Figure 2 was used for the electro-chemical testing. A circular section of alloy AA6060(3.14 cm2) was used as the working electrode WE,while commercial Pt-electrode and SCE (saturatedcalomel electrode) were used as counter and refe-rence electrode, respectively. Electrochemical me-asurements were carried out using a computercontrolled potentiostat (PARSTAT 2273), managedwith appropriate software. After the stabilization ofopen circuit potential, Eocp and subsequent Tafelpolarization measurements (not shown here), theanodic potentiodynamic polarizations curves wererecorded (scan rate: 5 mV/sec) in order to detectthe pitting potential, where breakdown of passivelayer results in pitting corrosion.

The reproducibility of the presented data wasgenerally checked by duplicate or triplicate measu-rements and typical results are reported.

2.3. Metallographic observationsObservations by optical microscope and

SEM/EDS analyses were used to characterize thesurface morphology and microstructural consti-tuents in extruded alloy AA6060, respectively.

3. RESULTS AND DISCUSSIONThe representative anodic polarization curves

registered for AA6060 alloy in deaerated NaClsolutions of various concentrations at 293K arepresented in Figure 3. Their typical shape with noactive oxidation peak during the anodic scan ischaracteristics of passive behavior and reflects thestability of air- formed oxide on the surface ofAA6060. However, at certain anodic potentialdenoted as Epit on the plots presented, thedestruction of passivating layer is marked bysudden increase of the current flowing along thepassive region. Determination of Epit values iscritical issue for structural Al-alloys experiencing avariety of corrosive environments in service: Thelower the Epit, the higher pitting susceptibility[19].

-0,03

-0,02

-0,01

0,00

0,01

0,02

-2,0 -1,8 -1,6 -1,4 -1,2 -1,0 -0,8 -0,6 -0,4

Cur

rent

(A)

Potential (V)

I vs E Al6060zav, 0,9%NaCl, CP(Ovl) Al6060zav, 1,2%NaCl, CP1(Ovl) Al6060zav, 2,3%NaCl, CP1(Ovl) Al6060zav, 3,5 % NaCl, CP

0,00

0,01

0,02

0,03

0,04

-1,0 -0,9 -0,8 -0,7 -0,6 -0,5 -0,4

Curre

nt (A

)

Potential (V)

Figure 3 - Anodic polarization curves of alloyAA6060 in deaerated NaCl solutions at 293K

The shift of breakdown potential Epit to morenegative values in Figure 3, clearly suggests thehigher pitting susceptibility of alloy AA606 in solu-tions with higher Cl- concentration.

In order to reveal this correlation more exactly,dependence between logarithm of Cl− concentra-tion and Epit is modeled by linear regressionanalysis. As a measure of goodness of fit, the highvalue of regression coefficient (R2= 0.9335) is

Epit

5 %

3.5 %

2.3 %

1.2 %

0.35 %



used. The straight line obtained is shown in Figure4 and can be presented by equation:

Epit = a + b log (cCl-)

-750

-700

-650

-600

-550

-500

-0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8

log (cCl-, wt. %)

Epi

t, m

VSC

E

Figure 4 - Breakdown potential of alloy AA6060in dependence on NaCl concentration in deaerated

solutions at 293KComparing results here obtained to the recent

literature, it was found that linear relationship Epit =

f log (cCl-) is also established for high purity Al [20],and for aluminum alloys in non-deaerated chloridesolution [21, 22].

Besides the chloride concentration, anotherimportant factor associated with pitting is thepresence of intermetallic particles in the bulk ofaluminium matrix [23-26]. During extrusion of heattreatable Al-Mg-Si alloys, these microconstituentschange the shape, quantity and distribution in orderto achieve a desired level of mechanical properties.However, their influence on corrosion behavior canbe detrimental [27-29].

Metallographic observations and SEM/EDSanalyses of extruded alloy AA6060 under studyhave shown that the two main intermetallic phasesexist. Dark particles in Figure 5 and Figure 6 arephases composed from Mg and Si (Mg2Si), whileelongated white phases are iron-containing parti-cles characterized by Fe-content higher than that ofsurrounding Al-matrix [30].

(a) (b)

Figure 5 - Microscopic images of commercial Al-Mg-Si alloy AA6060: (a) OM- transversal section, etchedin Barker reagent, polarized light, tint filter; (b) SEM/EDS micrography of intermetallic phases on the

surface of extruded profile

Figure 6 presents the outer layer of extruded Al-alloy AA6060 and surface distribution of secondaryphases identified.



Figure 6 - SEM image of intermetallic particles onthe surface of extruded AA6060; detail 1: bright Fe-

rich phases; detail 2: dark Mg-rich phases

Both Fe-rich and Mg-rich intermetallic particlescontribute to the heterogeneity of the surface, sothat local micro-galvanic couples are formed whenalloy AA6060 is in contact with the NaCl electrolyte.Chemical composition and electrochemical natureof intermetallics can be correlated with difference inpotential between the matrix and these particles:they can be either nobler or more active withrespect to Al. The potential of Mg2Si particles islower than the one of aluminium, while Fe-richphase is nobler than Al-matrix [31,32]. Therefore,the exposure of AA6060-alloy to the aggressivechloride medium results in specific electrochemicalactivity: Fe-rich particles behave as cathodes andinduce local anodic dissolution of surroundingaluminium matrix, i.e. pitting corrosion process.The extent of this process is under the strong influ-ence of chloride concentration, as it is shown inFigure 4.

4. CONCLUSIONIn this study the corrosion behavior of com-

mercial extruded Al-Mg-Si alloy AA6060 was inves-tigated in deaerated NaCl solutions at room tempe-rature. The results obtained indicate significant roleof the chloride concentration on the pitting corro-sion of alloy AA6060. The following conclusion canbe drawn:

During the anodic potentiodynamic polarization,specimens show passive behaviour in solutionscontainig chloride ions in the concentration range0.35 wt.%-5 wt.%.

Detrimental influence of Cl- on pitting resistanceof AA606 is characterized by passive film break-down at Epit –potential.

Increasing the NaCl concentration shifted Epit –potential to more negative values, suggesting thelower resistance to pitting.

Epit -dependence on Cl- - ion concetrationfollows the linear relationship in the interval 0.35wt. %-5 wt. %.

Fe-rich intermetallic particles heterogeneouslydistributed in the surface of the samples wereidentified as cathodic phases which promote pittingcorrosion by local anodic dissolution of Al-matrix.

AcknowledgmentsThis work was supported by the Ministry of

Science, Education and Sports of the Republic ofCroatia, within the projects 1241241565-1524 and023-1252973-2243.

5. REFERENCES

[1] Sheppard, T., (1999) Extrusion of Aluminum Alloys,Kluwer Academic Publishers, Dordrecht, TheNetherlands

[2] Van Geertruyden, W. H., Browne, H. M., Misiolek,W. Z., Wang, P. T., (2005) Evolution of surfacerecrystallization during indirect extrusion of 6xxxaluminum alloys, Metallurg. Materials Trans. A, 36,1049-1056.

[3] Gupta, A. K., Lloyd, D. J., Court, S. A., (2001)Precipitation hardening in Al–Mg–Si alloys with andwithout excess Si, Mat. Sci. Eng. A, 316, 11-17.

[4] Schikorra, M., Donati, L., Tomesani, L., Tekkaya, A.E., (2007) Microstructure analysis of aluminumextrusion: grain size distribution in AA6060, AA6082and AA7075 alloys, J. Mech. Sci. Technol. 21,1445-1451.

[5] Chang, C.S.T., Wieler, I., Wanderka, N., Banhart,J., (2009) Positive effect of natural pre-ageing onprecipitation hardening in Al–0.44 at% Mg-0.38% Sialloy, Ultramicroscopy, 109, 585-592.

[6] Al-Fadhalah, K. J., Almazrouee, A. I., Aloraie, A. S.,(2014) Microstructure and mechanical properties ofmulti-pass friction stir processed aluminum alloy6063 Mater. Design 53, 550-560.

[7] Jegdić, B. V., Živković, Lj. S., Popić, J. P., Bajat, J.B., Mišković-Stanković, V. B., (2013) Electrochemi-cal methods for corrosion testing of Ce-basedcoatings prepared on AA6060 alloy by the dipimmersion method, J. Serb. Chem. Soc. 78, 997-1011

[8] Allachi, H., Chaouket, F., Draoui, K., (2010)Protection against corrosion in marine environmentsof AA6060 aluminium alloy by cerium chlorides, J.Alloys Comp. 491, 223-229.

[9] Radošević J., Malina J., Dolić N., Ljumović P.,Slavica – Matešić S. (2013) Susceptibility tocorrosion of welded AlMgSi alloy EN AW 6060,Zastita materijala 54 (1) 3-7

[10] Vargel, C., (2004) Corrosion of Aluminum, ElsevierLtd., Amsterdam

[11] Davis, J. R., (1999), Corrosion of Aluminum andAluminum Alloys, ASM International, Ohio

[12] Marcus, P., Maurice, V., Strehblow, H. H., (2008)Localized corrosion (pitting): A model of passivitybreakdown including the role of the oxide layernanostructure, Corr. Sci. 50, 2698-2704.

[13] Malina J., Dolić N., Unkic F., (2013) Mikrostrukturniaspekti lokalne korozije Al-slitina u lijevanom stanju,Zastita materijala 54 (3) 240-249

1

2



[14] EN 755 - 2 : 2008 Aluminium and aluminium alloys.Extruded rod/bar, tube and profiles.

[15] Hirsch, J., Skrotzki, B., Gottstein, G., (2008),Aluminium Alloys, Their Physical and MechanicalProperties, Wiley-VCH, Weinheim, Germany

[16] Panchal V., Patel A., Shah N., (2012) Inhibition ofAl-Mg alloy in hydrochloric acid using schiff basesas corrosion inhibitors, Zastita materijala 53 (1) 15-29

[17] Kaufman, J. G., Rooy, E. L., (2004), Aluminum AlloyCastings: Properties,Processes, and Applications,American Society for Materials International,Materials Park, Ohio, USA

[18] Altenpohl, D.G., (1998), Aluminum: Technology,Applications, and Environment, TMS

[19] Trueba, M., Trasatti, S. P., (2010) Study of Al alloycorrosion in neutral NaCl by the pitting scantechnique, Mat. Chem. Physics 121, 523-533

[20] Soltis, J., Laycock, N. J., Krouse, D., (2011)Temperature dependence of the pitting potential ofhigh purity aluminum in chloride containingsolutions,” Corr. Sci. 53, 7–10.

[21] Abdallah, M., Zaafarany, I., Al-Karanee, S. O., AbdEl-Fattah, A. A., (2012) Antihypertensive drugs asan inhibitors for corrosion of aluminum andaluminum silicon alloys in aqueous solutions,Arabian J. Chem. 5, 225– 234.

[22] Zaid, B. Saidi, D., Benzaid A., Hadji, S., (2008)Effects of pH and chloride concentration on pittingcorrosion of AA6061 aluminum alloy, Corr. Sci. 50,1841-1847.

[23] Yasakau, K. A., Zheludkevich, M. L., Lamaka, S.V.,Ferreira, M.G. S., (2007 Role of intermetallic phasesin localized corrosion of AA5083, Electrochim.Acta527,651–7659.

[24] Cavanaugh, M. K., Buchheit, R. G., Birbilis N.,(2010) Modeling the environmental dependence of

pit growth using neural network approaches Corr.Sci. 52, 3070-3077.

[25] Birbilis, N., Buchheit, R. G., (2005) Electrochemicalcharacteristics of intermetallic phases in aluminumalloys: an experimental survey and discussion, J.Electrochem. Soc.152, B140–B151.

[26] Zhu, H., Zhang, X., Couper, M. J., Dahle, A. K.,(2009) Effect of primary intermetallic particles onsurface microstructure and appearance ofaluminium extrusions, Mat. Chem. Physics, 113,401-406.

[27] Birol, Y., (2004) The effect of homogenizationpractice on the microstructure of AA6063 billets, J.Mater. Process. Technol. 148, 250-258.

[28] Schikorra, M., Donati, L., Tomesani, L.,Tekkaya,A.E., (2008) Microstructure analysis of aluminumextrusion: Prediction of microstructure on AA6060alloy, J. Mater. Process. Technol. 201, 156-162.

[29] Kayser, T., Klusemann, B., Lambers, H.G., Maier,H. J., Svendsen, B., (2010) Characterization ofgrain microstructure development in the aluminumalloy EN AW-6060 during extrusion, Mater. Sci.Eng. A 527, 6568-6573.

[30] Z. Brodarac, Z., Dolić, N., Malina, J., (2013),Microstructural characterization of intermetallicphases in HAZ of MIG-welded EN AW-6060 alloy,45th Int. Oct. Conf. Mining Metallurgy, Bor

[31] Wloka, J., Bürklin, G., Virtane, S., (2007) Influenceof second phase particles on initial electrochemicalproperties of AA7010-T76, Electrochim. Acta 53,2055–2059.

[32] El-Menshawy, K., El-Sayed, A. W., Mohammed E.El-Bedawy,M. E., Hafez A. Ahmed,H. A., El-Raghy,S. M., (2012) Effect of aging time at low agingtemperatures on the corrosion of aluminum alloy6061, Corr. Sci. 54, 167-173.

IZVOD

UTJECAJ KONCENTRACIJE NaCl NA PITING KOROZIJU EKSTRUDIRANEAl –Mg-Si LEGURE AA6060

Ekstrudirane Al–Mg–Si legure (serija AA6xxx) najčešće se koriste u konstrukcijske svrhezahvaljujući prihvatljivim mehaničkim i korozijskim svojstvima. Spontano formirani sloj aluminijevaoksida na površini Al i Al-legura štiti od korozijskih oštećenja u neutralnim medijima, ali uotopinama koje sadrže kloride dolazi do proboja takvog tankog i kompaktnog pasivnog filma. Kaoposljedica tog procesa, nastaju na površini lokalna oštećenja i dolazi do pojave jamičaste korozije-pitinga.U ovom je radu proučavano korozijsko ponašanje komercijalne ekstrudirane Al-Mg-Si legureAA6060 u otopinama NaCl različite koncentracije, metodom anodne potenciodinamičke polari-zacije u deaeriranim uvjetima pri sobnoj temperaturi. Pokazalo se da sklonost lokalnoj korozijiraste s koncentracijom kloridnih iona i ovisi o katodnim mikrokonstituentima u ekstrudiranoj Al-Mg-Si leguri.Ključne riječi: piting korozija, komercijalna Al-Mg-Si legura, deaerirana NaCl.

Originalni naučni radPrimljeno za publikovanje: 15. 04. 2014.Prihvaćeno za publikovanje: 10.06.2014.

S. ŠERBULA i dr. TEŠKI METALI U OTPADNIM VODAMA RUDNIKA BAKRA MAJDANPEKA


SNEŽANA ŠERBULA1, ANA RISTIĆ1, Originalni naučni radSREĆKO MANASIJEVIĆ2, NATALIJA DOLIĆ3 UDC:628.312.5(497.11)

Teški metali u otpadnim vodama Rudnika bakra Majdanpek

U radu su prikazane prosečne godišnje koncetracije jona teških metala u otpadnim vodamapogona Filtracije, Rudnika bakra Majdanpek. Na osnovu hemijskih analiza uzoraka otpadne vodeutvrđen povišen sadržaj jona teških metala (Cu, Fe, Mn, Zn, Pb, Cd, i dr.) koji premašuju vrednostimaksimalne dozvoljone koncentracije definisane pravilnikom Republike Srbije. Dobijeni rezultatisu upoređivani sa dozvoljenim graničnim vrednostima koncentracija koje propisuju PravilnikSvetske zdravstevene organizacije i Direktiva 98/83/EC Evropske unije kao i sa nekim literaturnimpodacima. Na kraju rada dat je predlog za smanjenje koncentracije jona teških metala u otpadnimvodama pogona filtracije primenom jonoizmenjivačke smole.Ključne reči: otpadne vode, Rudnik bakra Majdanpek, Veliki Pek, joni teških metala

1. UVODOtpadne vode su složenog sastava i sadrže

različite primese. Njihova koncentracija i vrstazavise od vrste tehnološkog procesa, vrste sirovinei proizvoda. Mnogi procesi su diskontinualni, te je irežim nastajanja i ispuštanja otpadnih voda različitu svakoj proizvodnji [1]. Količina i sastavindustrijskih otpadnih voda zavisi od niza faktora ispecifična je za svaku granu industrije. Otpadnevode industrije obuhvataju procesne, rashladne,sanitarne i otpadne vode od čišćenja sudova iprostorija. Do podataka o programu analizeneophodnih parametra voda dolazi se na osnovurežima rada u proizvodnji. Na osnovu tehnologijeproizvodnje određuje se i dinamika uzorkovanja, tipuzorka, karakteristični period ispitivanja u tokumeseca ili godine, a na osnovu situacionog planazagađivača upoznaje se sa brojem ispusta, loka-cijom ispusta, mestom uzorkovanja i količinaispuštene vode [1−6]. Klasifikacija otpadnih vodavrši se na osnovu porekla i dele se na: komunalneotpadne vode, industrijske otpadne vode i otpadnevode agro-kompleksa [7,8].

Sve vode koje su iskorišćene za neku namenu,bilo da je reč o kućnim, industrijskim ili poljoprivred-nim vodama, potrebno je prikupiti, kao otpadnu vo-du, te je na prikladan način obraditi i odvesti u reci-piente bez štetnih posledica za životnu sredinu ibez narušavanja prirodnog kružnog toka vode[1−4]. Recipienti otpadnih voda mogu biti prirodnevode: reke, jezera, mora, ali u nekim slučajevimaveliki deo otpadne vode moguće je ponovo koristiti

Adresa autora: 1Univerzitet u Beogradu, Tehničkifakultet, Bor, Vojske Jugoslavije 12, Bor, 2Lola Institut,Kneza Viseslava 70a, Beograd, Srbija, 3Univerzitet uZagrebu, Metalurški fakultet, Sisak, Aleja narodnihheroja 3, Sisak, Hrvatska

Primljeno za publikovanje: 10. 04. 2014.Prihvaćeno za publikovanje: 23. 06.2014.

uz određenu obradu. Zbog različitog sastava ot-padnih voda razlikuju se i materijali koji će biti pri-menjeni u izgradnji sistema za odvođenje različitihtipova otpadnih voda [1].

U zavisnosti od tipa industrije, u industrijskimotpadnim vodama mogu se naći različite štetne,opasne i toksične supstance. Zagađujuće materijese mogu naći u vodi u rastvornom obliku, i u oblikujona ili molekula, koloida, suspenzija, mada mogubiti adsorbovane i na čvrstim telima [1]. Uredbom oklasifikaciji voda ("Sl. glasnik SRS", br. 5/68)utvđena je opšta podela voda u četiri klase premastepenu zagađenosti i nameni [7]. Prvoj i drugojklasi voda pripadaju vode koje se koriste za piće,kupanje i rekreaciju, dok III i IV klasa vodaobuhvata vodu koja se koristi u industriji i voda kojase može upotrebljavati nakon posebne obrade.Podela vode u klase i podklase vrši se na osnovupokazatelja i njihovih graničnih vrednosti.

U ovom radu akcenat je dat na analizi jonateških metala u industrijskim odpadnim vodama[1,2,5,6,9,10]. Varol je tokom ispitivanja koncen-tracije jona olova u jezerima Kralkızı, Dicle i Bat-man u Turskoj došao do rezultata da se kon-centracija jona olova kretala u jezeru Kralkizi od0.256−2.648 mg/dm3, u jezeru Dicle 0.184−1.473mg/dm3 i u jezeru Batman 0.409−2.457 mg/dm3

[11]. U periodu od 2005. do 2009. godine napodručiju reke Songhua, Kina vršena su ispitivanjauzoraka sa 6 mernih mesta. Vrednosti koncentra-cije jona olova u uzorcima su se kretala od0.503−2.81 mg/dm3 što pokazuje veliki uticaj teškihmetala, u ovom slučaju olova, koji potiču iz indus-trijskih postojenja koja se nalaze u oblasti oko rekeSonghua [12]. U reci Gomni, Indija vrednosti kon-centracije jona bakra su se kretale od 0.102 0.503mg/dm3 [10]. Kazi i saradnici su vršili ispitivanja napodruèiju jezera Manchar, Pakistan u periodu od2005. do 2006. godine kako bi utvrdili koliki je uticajindustrijskih otpadnih voda, koje se ulivaju u samojezero, na kvalitet vode. Koncentracija jona bakra



se kretala od 0.91−3.84 mg/dm3 u uzorcima uzetihsa pet mernih mesta [13].

Cilj ovog rada je analiza ukupne gubitke bakrau Rudniku Bakra Majdanpek u okviru otpadnihvoda pogona filtracije u periodu od 2008−2012.

2. UZORKOVANJE I ANALIZA VODARuda bakra u Majdanpeku je otkrivena krajem

1953. godine, kada su utvrđene rezerve na Južnomreviru od oko 85 miliona tona sa prosečnim sadrža-jem od 0.83% Cu. Na ovim rezervama rude bakra,uz predpostavku daljeg nastavljanja sa istraživa-njem, u julu 1957. godine odobrena su sredstva zaizgradnju rudnika, a prvi radovi su započeli krajem1957. godine. Početkom 1958. godine, počeli suradovi na pripremanju prve etaže za površinski kop"Južni revir" kada je iz Bora dobijen prvi bager.Pred kraj 1958. godine započeli su prvi radovi najalovini na brdu "Švajs". Za početak proizvodnjerude se može uzeti početak probnog rada flotacije,juna 1961. godine. Prve tone koncentrata bakra izMajdanpeka su isporučene juna 1961. godine. Do1977.godine u okviru RBM-a radio je samo po-vršinski kop "Južni revir", kada započinje sa radompovršinski kop "Severni revir". Do 1993. godineotkopavana je samo ruda bakra i proizvođen kon-centrat bakra. Nakon te godine je započelo otko-pavanje rude cinka i olova i proizvodnja ovog kon-centrata. Radovi na Površinskom kopu "Severnirevir" su se odvijali u okviru tri radilišta: Centralnideo, Tenka i Dolovi.

Celokupni proces proizvodnje u Rudniku bakraMajdanpek može se uglavnom posmatrati kroznekoliko faza: otkopavanje, usitnjavanje i flotiranjerude. Otkopavanje rude vrši se miniranjem eksplo-zivima. Ruda usitnjena miniranjem (do 1 m veli-čine) se transportuje do drobilica na primarnomdrobljenju, gde se usitnjava do 250 mm i kao takvaide trakama na sekundarno drobljenje. Sa sekun-darnog drobljenja izlazi usitnjena do 75 mm i idetrakama u flotaciju na prosejavanje i tercijalnodrobljenje (do 20 mm). Tehnološka operacija mle-venja se odvija u flotaciji, gde se usitnjava u mlino-vima sa šipkama i kuglama do mikronskih veličina.Tokom procesa mlevenja u mlinove se dozira voda,kreč i reagensi potrebni za flotiranje. Tako priprem-ljena pulpa transportuje se u hidrociklone, gde sevrši razdvajanje na preliv koji ide na proces floti-ranja i gruba faza koji se ponovo vraća u mlin sakuglama. Proizvod mlevenja uvodi se u kondicio-nere, zatim u razdeljivač pulpe, odakle se ravno-merno distribuira u flotacione mašine. Flotiranje sesastoji iz osnovnog flotiranja i tri prečišćavanja. Uosnovnom flotiranju dobija se grubi koncentrat kojise melje u dopunskom mlinu i definitivnu jalovinu.Trostepeno prečišćavanje daje definitivni koncen-trat bakra koji u sebi sadrži oko 23% bakra. Kon-centrat, u obliku pulpe sa oko 20% čvrstog mate-

rijala, odvodi se tunelom kroz plastične cevi upogon filtriranja. Iz prihvatnih rezervoara pulpa sepumpama prebacuje na zgušnjavanje, a nakon to-ga na filtriranje. Filtriranje se vrši na kontinualnimdiskfilterima. U toku ovog procesa se odvaja vodaod čvrste frakcije tako da proizvod sadrži oko 10%vlage i naziva se "koncentrat bakra". Iz pogonafiltriranja koncentrat bakra se sistemom transport-nih traka prebacuje do vagona, a zatim železnicomdo Bora [14]. Koncentrat bakra je polazna sirovinaza borsku topionicu

Flotacijski ostatak se pumpama transportuje dojalovišta "Valja Fundata", gde se vrši klasiranje cik-lonima. Pesak ciklona služi za pravljenje zaštitnihbrana. Za tehnološki proces mlevenja i flotiranjakoristi se velika količina vode koja se obezbeđujerecirkulacijom iz flotacijskog jezera. Desno od oba-le reke Veliki Pek izgrađeno je postrojenje filtracijeu neposrednoj blizini sela Debeli Lug. U procesuflotacijske koncentracije dobijaju se dva proizvodakoncentrat koji sadrži oko 20% čvrste faze iflotacijska jalovina koja sadrži od 12−18% čvrstefaze. Tehnološka šema postrojenja filtracije bakar-nog koncentrata prikazana je na slici 1. Koncentratbakra se transportuje u zgušnjivače (1) gde sesadržaj čvrste faze povećava na 50%. Zgusnutiproizvod se gravitacijskim tokom se transportujetunelom dužine 3270 m do Debelog Luga u pogonfiltracije. Iz prihvatnog rezervoara se pumpamaprebacuje do vakuum filtera (2). Kolač sa vakuumfiltera pada na sabirne transportere (4), a zatim uželezničke vagone (5). Tečna faza sa vakuumfiltera (2) odlazi u zgušnjivač (3) i zatim u taložnik(6) gde se vrši gravitaciono prečišćavanje filtratakoji predstavlja otpadnu vodu procesa filtracije. Iztaložnika (6) se gravitaciono prečišćena otpadnavoda ispušta u recipijent, reku Veliki Pek.

Slika 1 - Tehnološka šema postrojenja filtracijebakarnog koncentrata

Uređaj za prečišćavanje otpadnih voda pogonafiltracije izgrađen je 1970. godine, i sastoji se odzgušnjivača i taložnika. Zgušnjivač je betonski ba-zen kružnog oblika prečnika 28 m. Površina zguš-



njivača od 630 m2 obezbeđuje mehaničku spo-sobnost zgušnjivača i za znatno veće mase od onihkoje nastaju u redovnoj proizvodnji. Preliv iz zguš-njivača ispušta se u taložnik gde se dalje vršimehaničko prečišćavanje otpadnih voda [14]. Talo-žnik za gravitaciono prečišćavanje otpadnih voda(slika 2a), je izgrađen od armiranog betona i sastojise od dve komore dimenzija 8x38m, dubine 2.5m.Svaka komora se može naizmenično, nezavisnopuniti i prazniti. Trenutno su u rad uključena obagravitaciona taložnika što obezbeđuje bolju efikas-nost prečišćavanja otpadnih voda zbog dužegvremena zadržavanja u samom taložniku. Na slici2b. je fotografija mesta uzorkovanja otpadnih vodanakon gravitacionog prečišćavanja u taložniku, inakon toga se prečišćena otpadna voda odvodizemljanim kanalom do reke Veliki Pek. Zemljanikanal je širine od 1.5−3 m, dubine 1.4−1.6 m idužina kanala je oko 600 m [14].

a)

b)

Slika 2 - Gravitaciono prečišćavanje otpadnih voda,a). taložnik i b) mesto uzorkovanja

Na slici 3. dat je šematski prikaz pogona filtra-cije. Radi što boljeg odvijanja procesa zgušnja-vanja i filtriranja koncentrata bakra postoje zgušnji-vači prečnika 28 m i 10 m u kojima se vrši pred-prečišćavanje otpadnih voda. Nakon toga otpadnevode odlazi u taložnike odakle se ispušta u reci-pijent, reku Veliki Pek. Voda koja se ispušta u rekuVeliki Pek kontroliše se tri do četiri puta godišnje

kao i kvalitet reke Veliki Pek pre i posle uliva otpad-nih voda pogona filtracija.

Slika 3. Situacioni plan objekata u pogonu filtracije imesta uzorkovanja: I. Veliki Pek pre uliva otpadnevode, II. Otpadna voda pogona filtracije, III. Veliki

Pek posle uliva otpadne vode

Kvalitet voda ispituje akreditovana institucijaZavod za javno zdravlje “Timok” Zaječar [15,16].Primenjena je metoda atomske apsorpcione spek-trofotometrije (AAS) za određivanje koncentracijejona teških metala u otpadnoj vodi. Na slici 4. jeprikazan satelitski snimak pogona filtracije RudnikaBakra Majdanpek sa mestima uzorkovanja i tokomreke Veliki Pek.

Slika 4 - Satelitski snimak pogona filtracije RudnikaBakra Majdanpek sa mestima uzorkovanja i tokom

reke Veliki Pek

Prema Uredbi o klasifikaciji voda RepublikeSrbije, reka Veliki Pek spada u III klasu voda. Ana-lizirano je prisustvo jona teških metala poput gvož-đa, olova, bakra, cinka i dr. koji se nalaze uotpadnoj vodi pogona filtracije.

3. DISKUSIJA I REZULTATIU ovom radu su analizirani rezultati u periodu

od 2008. godine do 2012. godine koji su uzorko-



vani na tri merna mesta. Tabela 1. prikazuje vred-nosti pokazatelja kao što su koncentracije jonabakra, gvožđa, olova, hroma, arsena, mangana,kadmijuma i cinka, pri čemu su pokazane mini-malne, maksimalne i srednje vrednosti koncen-tracije, kao i maksimalna dozvoljena koncentracijapokazatelja (MDK) propisana za III klasu klasuvoda u koju spada reka Veliki Pek.

3.1. Prosečne godišnje koncentracije jona bakraBakar se najviše pojavljuje u sulfidnim rudama

koje se prerađuju u Rudniku bakra Majdanpek saudelom od 0.27 % Cu (halkopirit, kovelit, halkozin ibornit), zatim u oksidnim (kuprit) i u karbonatnimrudama. Pravilnik Svetske zdravstvene organiza-cije i Direktiva 98/83/EC Evropske unije propisujugraničnu vrednost koncentracije jona bakra u voda-ma od 0.2 mg/dm3, dok je u našoj zemlji Uredbomo klasifikaciji voda ta granica do 0.1 mg/dm3

[1,7,16].

Tabela 1 - Vrednosti analiza u periodu od 2008. do2012. godine uzete sa tri merna mesta

Pokazatelji, mg/ dm3Joniteškihmetala

Mestouzorkov.,

slika 2 Min Max Srednjavrednost MDK

I 0.008 4.412 0.313II 0.672 7.552 3.24CuIII 0.035 0.884 0.278

0.1

I 0.092 5.090 1.071II 0.736 6.576 2.989FeIII 0.137 4.810 0.966

1.0

I 0.01 0.333 0.036II 0.01 2.255 0.562PbIII 0,01 0.126 0.027

0.1

I 0.015 0.088 0.054II 0.01 0.132 0.047MnIII 0.019 2.442 0.195

/

I 0.001 0.005 0.0021II 0.001 0,004 0.0020CdIII 0.001 0.004 0.0021

0.01

I 0.025 0.651 0.082II 0.082 1.162 0.316ZnIII 0.049 0.727 0.126

1.0

Na slici 5 prikazane su prosečne koncentracijejona bakra u otpadnim vodama pogona filtracije ireci Veliki Pek pre i posle uliva otpadne vode po-gona filtracije.

Na slici 5 se vidi da je i pre odlivanja sameotpadne vode filtracije u reci Veliki Pek postojalaodređena konentracija jona bakra, što je posledicaprirodnog luženja bakra iz zemljišta koje je bogatosulfidnim mineralima bakra. Pri uzorkovanju vodesa II mernog mesta, te granice su još više preko-račene tokom svih 5 godina. Uzorci sa III mernogmesta pokazuje da i posle prečišćavanja otpadnihvoda pre njihovog izlivanja u recipijent kon-

centracija bakra prevazilazi granične vrednosti.Vrednosti koncentracije jona bakra u reci Veliki Pekposle ispuštanja otpadne vode pogona filtracijekretala se do 0.4 mg/dm3, dok su vrednosti kon-centracije jona bakra izmerene u reci Gomni i je-zeru Manchar [10,13] bile veće što je posledicavelike koncentracije jona bakra u samim otpadnimindustrijskim vodama koje se u njih ulivaju.

Slika 5. Prosečne godišnje koncentracije jonabakra (crvenom linijom označena je MDK)

3.2. Prosečne godišnje koncentracije jona gvožđaGvožđe spada u teške metale i u okolini je pri-

sutan kao posledica korozije cevi, ispiranja kiselihruda, otpadnih industrijskih voda u kojima se nala-zi. Ruda koja se prerađuje u RBM-u sadrži oko0.65% Fe. Postoji u obliku fero (Fe2+) i feri (Fe3+)jona. Dvovalentni jon je nepostojan u aerobnimuslovima i lako podleže oksidaciji do gvožđe(III)oksihidrata koji su u vodi nerastvorni. U našoj ze-mlji MDK jona gvožđa u vodama III klase iznosi 1mg/dm3. Pravilnik Svetske zdravstevene organiza-cije dozvoljava graničnu vrednost za gvožđe od 2mg/dm3, kolika je i prema Direktivi 98/83/EC Evrop-ske unije [1,7,17]. Na slici 6 su prikazane prosečnegodišnje koncentracije jona gvožđa u periodu od2008−2012. godine.

Slika 6 - Prosečne godišnje koncentracije jonagvožđa (crvenom linijom označavamo MDK) [16]



Gvožđe je jedan od elemenata koji se nalaziiznad dozvoljene granice u uzorcima uzetim sa svatri merna mesta tokom godina. Svoju najveću kon-centraciju pokazuje u otpadnim vodama pogonafiltracije kod kojih tokom svih 5 godina uzorkovanjadolazi do prekoračenja MDK. Sa slike 6 se vidi dasu tokom 2010. i 2011. godine dozvoljene koncen-tracije gvožđa u vodama III klase prekoračene ureci Veliki Pek pre ulivanja same otpadne vode.Takođe, vidi se da je u 2008. i 2009. godini MDKprekoračena i u uzorcima uzetih sa III mernogmesta, dok je u kasnijim godina došlo do uvođenjanovih tehničkih i tehnoloških rešenja u samomprocesu prečišćavanja u taložniku.

3.3. Prosečne godišnje koncentracije jona olovaU prirodi se olovo najčešće javlja u vidu sulfida,

PbS, kao ruda galenit. Maksimalna dozvoljena kon-centracija jona olova u III klasi voda je 0.1 mg/dm3

prema Uredbi o klasifikaciji voda Republike Srbije,Pravilniku Svetske zdravstevene organizacije iDirektivi 98/83/EC Evropske unije [1,7,17]. Na slici7. su prikazane prosečne godišnje koncentracijejona olova u uzorcima uzetih sa tri merna mesta.

Olovo se u otpadnim vodama pogona filtracijenašao u velikim koncentracijama u toku 2009.,2010., 2011., i 2012. godine pri čemu njegovekoncentracije dostižu vrednost od 1,4mg/dm3 i akoje MDK za olovo samo 0.1 mg/dm3. U toku 2011.godine vrednosti koncentracija jona olova uzetih saI mernog mesta već prelaze graničnu vrednost štoje posledica prirodnog izluženja jer duž toka rekeVeliki Pek nema nikakve industrije. U samim otpad-nim vodama pogona filtracije još više je prekora-čena, ali je tehnološki proces obrade otpadnih vodapogona filtracije doveo do smanjena koncentracijejona olova, što se vidi u uzorcima uzetih sa III mer-nog mesta gde koncentracija jona olova ne prelaziMDK.

Slika 7 - Prosečne godišnje koncentracije jonaolova (crvenom linijom označavamo MDK) [16]

Vrednosti koncentracije jona olova u reci VelikiPek posle ulivanja otpadne vode pogona filtracije

su manje u odnosu na koncentraciju jona olova ko-ja se pojavljuje u reci Songhua i jezerima u Turskoj[11,12]. Kao glavni izvori velike koncentracije jonateških metala navode se otpadne vode kojeindustrijska postrojenja ispuštaju.

Koncentracije olova u toku 2010. godine prika-zane su na slici 8. Iz uzorka uzetog 06.10.2010.godine zaključujemo da je usled povećanog dotokaatmosferskih voda (kiša) došlo do povećane kon-centracije jona olova u reci Veliki Pek pre ulivaotpadnih voda pogona filtracije. Ulivanjem prečiš-ćene otpadne vode pogona filtracije smanjila sekoncentracija jona Pb, mada je ipak uzorak sa IIImernog mesta imao u sebi olova koji prevazilaziMDK.

Slika 8 - Koncentracije jona olova u 2010. godini(crvenom linijom označavamo MDK) [16]

Površinske i podzemne vode koje formirajureku Veliki Pek svojim tokom prolaze kroz oblastikoje u svom sastavu imaju bakar, gvožđe, cink i dr.elemente i pri tome povećavaju koncentraciju ovihelemenata u vodi što možemo i zaključiti iz rezul-tata dobijenih analizama sa I mernog mesta. Mak-simalna dozvoljena koncentracija jona bakra je većprekoračena u uzorcima sa minimalnom koncentra-cijom, dok su se maksimalne koncentracije jonabakra kretale čak do 7.552 mg/dm3 koliko je izme-reno u uzorku otpadne vode pogona filtracije. Ta-kođe, se iz tabele 1 vidi da su koncentracije jonagvožđa i olova u povećanim količinama u uzorcimauzetim sa II mernog mesta i da posle obradeotpadne vode pogona filtracije njihova koncentra-cija prelazi MDK u uzorcima uzetih sa III mernogmesta. Svi ostali pokazatelji ispitivanih voda suispod zakonski dozvoljenih granica.

3.4. Predlog poboljšanja kvaliteta otpadne vodepogona filtracije

Industrijske otpadne vode ne mogu se prečistitikonvencionalnim postupcima za prečišćavanje vo-de jer sadrže jone metala, kao i druga hemijska je-dinjenja koja su biološki nerazgradiva, što destruk-



tivno deluje na mikroorganizme koji su aktivni uprocesu prirodnog prečišćavanja.

Poboljšanje kvaliteta otpadne vode pogona fil-tracije može se sprovesti korišćenjem raznih adsor-benasa. Za adsorpciju u tečnosti koriste se joniti,akrivni ugalj, silika gel i zeoliti. Joniti kao prirodni ilisintetički adsorbensi, organskog ili neorganskogporekla, mogu biti: zeoliti, glinasti minerali, jonoiz-menjivačke smole, aktivirani minerali i dr. [1,18].Praktično su nerastvorni u vodi ili drugim rastva-račima. Dele se na anjonite i katjonite, zavisno odstructure molekula i reakcija sa jonima koji se nala-ze u rastvoru i koje adsorbuju [1,18]. Za uklanjanjeteških metala iz otpadnih vodu mogu se koristitirazličiti tipovi katjonskih jonoizmenjivača kao što suAmberlite IR-120, Dowex 50, Duolite C-20, LewatitS-100 i dr.

Kako ne bi došlo do velikih gubitka bakra krozotpadne vode, predlaže se dopuna procesa prečiš-ćavanja otpadnih voda. Poželjno je uraditi mrežnikavez adekvatne zapremine, u zavisnosti od pro-sečne koncentracije prekoračenja jona teških meta-la i kvaliteta jonoizmenjivačke smole, u kome bi senalazila jonoizmenjivačka smola. Mrežni kavez bise nalazio na nivou otpadne vode u taložniku u kojibi se slivala prelivna voda iz zgušnjivača. Na taj na-čin smanjila bi se koncentraciju jona bakra, gvožđai olova u otpadnim vodama pogona filtracije. Nakonodređenog vremena upotrebe dolazi do preza-sićenja jonoizmenjivačke smole vezanim jonima te-ških metala. Proces desorpcije jona teških metalaiz jonoizmenjivačke smole određuje proizvođač. Je-dan od načina prečišćavanja mreže sa smolom odjona je regenerisanje smole rastvorom sumpornekiseline. Na taj način bi se bakar preveo u bakar-sulfat i mogao bi da se koristi u pogonu elektrolizeu Boru, čime bi iskorišćenje barka bilo potpuno.Nakon toga, mrežni kavez sa jonoizmenjivačkomsmolom ponovo bi mogao da se koristi. U cilju pra-ćenja procesa jonske izmene odigravaju se sle-deće reakcije [1]:

Cu²+ (aq) + 2R-H+ (s) ↔ R2Cu (s) +2H+ (1)

Fe³+ (aq) + 2R-H+ (s) ↔ R3Fe (s) +3H+ (2)

6. ZAKLJUČAKU ovom radu prikazani su rezultati kvaliteta ot-

padne vode pogona filtracije Rudnika bakra Maj-danpek i reke Veliki Pek pre i posle uliva otpadnevode pogona filtracije. Rezultati pokazuju da kon-centracija jona bakra u uzorcima uzetih iz reke Ve-liki Pek posle ulivanja otpadne vode pogona filtra-cije je prekoračila zakonski dozvoljenu vrednosttokom svih pet godina uzorkovanja. Takođe, kon-centracija jona gvožđa je bila iznad MDK tokom

2008. i 2009. godine u uzorcima uzetih sa III mer-nog mesta, dok je koncentracija jona olova bilaispod zakonski dozvoljenih granica tokom svih petgodina.

Iz prikazanih rezultata može se zaključiti da suse vrednosti parametara u periodu od 2008. godinedo 2012. godine kretale u širokom rasponu. U ra-nijim godinama vidi se da je uticaj bio veći te da seiz godine u godinu smanjivao. Poštujući zakonskuregulativu, kao i smanjenje uticaja na životnu ser-dinu (u ovom slučaju vodotokove) Rudnik bakraMajdanpek je puno radio na poboljšanju kvalitetaotpadnih voda,a samim tim i na smanjenje zaga-đenja reke Veliki Pek.

LITERATURA

[1] Ristić A., Uticaj otpadnih voda Rudnika bakra Maj-danpek na reku Veliki Pek, Završni rad, Univerzitet uBeogradu, Tehnički fakultet u Boru, Bor, oktobar2013.

[2] Bugarin M., Jonović R., Avramović Lj., (2012) Tret-man industrijskih otpadnih voda iz procesa proiz-vodnje bakra u RTB Bor, Rudarski radovi, 4 ,73-78

[3] Kittinger C., Marth E., Reinthaler F.F., Zarfel G.,Pichler-Semmelrock F., Mascher W., Mascher G.,Mascher F., (2013) Water quality assessment of aCentral European River-Does the Directive 2000/60/EC cover all the needs for a comprehensiveclassification, Science of Total Environment 447,424–429.

[4] Hegazi H.A., (2013) Removal of heavy metals fromwastewater using agricultural and industrial wastesas adsorbents, HBRC Journal 9, 3, 276-282.

[5] Kurniawan T.A., Chan Y.S., Lo W.H., Babel S.,(2006) Physico–chemical treatment techniques forwastewater laden with heavy metals, ChemicalEngineering Journal (118) 1–2, 83–98.

[6] Cheremisinoff N.P., Handbook of water andwastewater tretment technologies, Butterworth-Heinemann USA, (2002) 306−312.

[7] Službeni glasnik, Uredba o klasifikaciji voda, SRSbr. 5/68, 16.01.1968.

[8] RBM, Elaborat o otadnim vodama pogona filtraže,Služba za ekologiju RBM-a, (2008)

[9] Šerbula S.,Ristić A.,Manasijević S.,Dolić N., Davit-kov (2014), pH vrednost i koncentracija ukupnogsuvog ostatka i suspendovanih materija u otpadnimvodama Rudnika bakra Majdanpek, Zaštita mate-rijala, Vol. 55, No 3, str. 327-334

[10] Singh K.P., Malik A., Sinha S., (2006) Water qualityassessment and apportionment of pollution sourcesof Gomti river (India) using multivariate statisticaltechniques-a case study, Analytica Chimica Acta538, 355–374.

[11] Varol M., (2013) Dissolved heavy metal concen-trations of the Kralkızı, Dicle and Batman dam reser-voirs in the Tigris River basin, Turkey, Chemosphere22, 56−72.



[12] Wang Y., Wang P., Bai Y., Tian Z., Li J., Shao X.,Mustavich L.F., Li B.L, (2013) Assessment ofsurface water quality via multivariate statistical tech-niques: A case study of the Songhua River Harbinregion, China, Journal of Hydro-environment Re-search 7(6), 30−40.

[13] Kazi T.G., Arain M.B., Jamali M.K., Jalbani N., AfridiH.I., Sarfraz R.A., Baig J.A., Shah A.Q., (2009)Assessment of water quality of polluted lake usingmultivariate statistical techniques: A case study,Ecotoxicology and Environmental Safety 72, 301–309.

[14] http://djovanovic.wordpress.com/projekti/

[15] RBM, Elaborat o otadnim vodama pogona filtraže,Služba za ekologiju RBM-a, (2008).

[16] Zavod za javno zdravlje Timok, Izveštaj o analizamaotpadnih i površinskih voda RBM-a, Zaječar,2008−2012.

[17] EUR-Lex, Council Directive 98/83/EC of 3November 1998 on the quality of water intended forhuman consumption, Official Journal L330, pp. 32,1998, http://eur-lex.europa.eu.

[18] Trivunac K.V., Stevanović S.M., (2012) Uticaj radnihparametara na efikasnost uklanjanja jona olovapomoću kompleksirajuće-mikrofiltracionog proces,Hemijska industrija, ( 66)4, 461−467.

ABSTRACT

HEAVY METAL IONS IN THE WASTEWATER OF THE MAJDANPEK COPPER MINE

The paper presents the average annual concentrations of heavy metal ions in the wastewater ofthe Majdanpek Copper Mine filtration plant. Chemical analyses of wastewater samples found anincreased content of heavy metal ions (Cu, Fe, Mn, Zn, Pb, Cd etc.) that exceed the values of themaximum permissible concentration defined by the relevant Regulation of the Republic of Serbia.The obtained results were compared with the permissible concentration limits prescribed by theRegulation of the World Health Organization and Directive 98/83/EC of the European Union aswell as with some data from the literature. The final section of the paper provides a suggestion forreducing the concentrations of heavy metal ions in the wastewater of the filtration plant by usingion exchange resin.Keywords: wastewater, Majdanpek Copper Mine, Veliki Pek, heavy metal ions.

Scientific paperReceived for Publication: 10. 04. 2014.Accepted for Publication: 23. 06. 2014.

V. MATKOVIĆ i dr. VALORIZACIJA OLOVA IZ MEĐUPRODUKATA RAFINACIJE BIZMUTA ...


VLADISLAV MATKOVIĆ, BRANISLAV MARKOVIĆ, Originalni naučni radMIROSLAV SOKIĆ, VASO MANOJLOVIĆ UDC:669.76.054.1

Valorizacija olova iz međuprodukata rafinacije bizmutapostupkom metalotermijske redukcije

U procesu rafinacije bizmuta, hlorovanjem legure Bi-Pb (bizmut pena) Kroll-Bettertonovimprocesom kao međuprodukt pojavljuje se olovo-hlorid. Predmet ovog rada je valorizacija olova izpomenutog međuprodukta postupcima aluminotermije i cinkotermije. Pored olova pomenutimpostupcima dobijaju se glinica tehničkog kvaliteta (aluminotermija) i cinkhlorid (cinkotermija). Zaispitivanja su korišćeni sekundarni aluminijum i cink različite krupnoće. Ispitan je uticajtemperature, vremena, krupnoće reducenta i brzine mešanja (cinkotermija) na stepen iskorišćenjaolova i definisani optimalni parametri procesa. Stepen iskorišćenja sirovog olova (98%Pb) iznosi95-98% u slučaju aluminotermije i 85-90% u slučaju cinkotermije. Dobijeno sirovo olovo prerađujese u rafinerijama olova. Glinica tehničkog kvaliteta ima primenu u keramičkoj industriji dok se cink-hlorid hidrometalurški tretira u cilju dobijanja 50%-nog rastvora cink-hlorida.Ključne reči: olovo-hlorid, aluminotermija, cinkotermija, glinica, cink-hlorid, olovo

1. UVODU proizvodnji bizmuta hlornim postupkom na-

staje olovo-hlorid (PbCl2) kao međuprodukt, pri če-mu znatne količine olova bivaju zarobljene. Ova či-njenica poskupljuje proces dobijanja olova kao itehnologiju dobijanja bizmuta 1,2. U RMHK “Trep-ča” godišnje se rafinacijom bizmuta dobijalo oko2500 t olovo-hlorida. Pošto je prosečan sadržaj olo-va u olovo-hloridu 72,5%, to se hloridom zarobi oko1800 t olova.

Bilo je mnogo pokušaja da se iznađe tehničko-tehnološko rešenje kojim bi se iskoristilo olovo izhlorida olova 3,4. Između ostalog vršena su istra-živanja redukcije olovo-hlorida pomoću kalcijum-karbonata i sode, kao i redukcije saturacionim mu-ljem iz fabrika za proizvodnju šećera. Ova istra-živanja vršena su u laboratorijskom i poluindustrijs-kom obimu. Obzirom da nijedna od ovih isprobanihmetoda nije dala odgovarajuće tehno-ekonomskeefekte, kao i zadovoljavajuće efekte zaštite ekosistema od degradacije, pokušalo se sa primenommetalotermijskih postupaka.

Metalotermijski postupci dobijanja metala pred-stavljaju redukciju metalnog jedinjenja sa drugimneplemenitijim metalom 5, 6 i baziraju na reakcijiopšteg tipa

AX + B = BX + A. (1)

Metalna jedinjenja koja se redukuju su najčeš-će oksidi, hloridi i fluoridi 7-10. Kao redukcionasredstva najčešće se koriste: natrijum, kalijum,magnezijum, kalcijum, aluminijum i silicijum 11.

Adresa autora: Institut za tehnologiju nuklearnih idrugih mineralnih sirovina, Franše d'Eperea 86,Beograd, Srbija

Primljeno za publikovanje: 06. 04. 2014.Prihvaćenp za publikovanje: 20. 06. 2014,

Izbor reducenta za redukciju metalnih hloridazavisi u prvom redu od termodinamičkih karakteri-stika sistema. Kao što je već poznato, reakcija

PbCl2+Me=MeCl2+Pb (2)

se odvija u željenom pravcu samo onda kada jevrednost standardne Gibsove energije manja odnule.

Nasuprot neplemenitim metalima natrijumu,magnezijumu, kalcijumu i aluminijumu, za redukcijuse može koristiti i relativno plemenit cink. Takonpr., prve količine visoko čistog silicijuma i germa-nijuma dobijene su redukcijom njihovih hlorida saveoma čistim cinkom. Hloridi niobijuma i tantalamogu se, takođe, redukovati cinkom. Dobijenelegure sa cinkom mogu se lako rafinisati ispara-vanjem cinka.

2. EKSPERIMENTALNI POSTUPAKNa osnovu termodinamičkih podataka koji ka-

rakterišu hemijsku aktivnost hlora prema pojedinimmetalima, može se pretpostaviti da se proces me-talotermijske redukcije olovo-hlorida aluminijumomodvija prema jednačini

3PbCl2 + 2Al = 3Pb + 2AlCl3 (3)

a cinkom prema jednačini

PbCl2 + Zn =Pb + ZnCl2 (4)

što je potvrđeno preliminarnim, a u drugoj fazi isistematskim laboratorijskim istraživanjima.

Za eksperimentalna istraživanja korišćen je olo-vo-hlorid sledećeg hemijskog sastava u (%): Pb-72.5, Fe-2.45, Bi-0.650, Ag-0.025, As-0.010, Sb-0.025, Cd-0.001 i Zn-0.001. Kao reducent korišćenje sekundarni aluminijum, odnosno sekundarnicink. Ispitan je uticaj temperature i vremena na



stepen redukcije i iskorišćenje olova. Primećeno jeda oblik korišćenog sekundarnog aluminijuma(prah i komadići), odnosno cinka (trake, komadi iprah) takođe utiču na stepen redukcije.

Ispitivanje procesa redukcije olovo-hlorida alu-minijumom vršeno je na poluindustrijskom postro-jenju prikazanom na slici 1.

Slika 1 - Poluindustrijsko postrojenje za preradu olovo-hlorida postupkom aluminotermije

Postrojenje se sastoji iz: metalnog livenog lon-ca (1) smeštenog u ložište (2) koje je snabdevenogorionikom (3). Na lonac je postavljena komora zasakupljanje gasova (4), povezana sa gosovodom(5) i skruberom snabdevenim injekcionim i rasprši-vajućim diznama (6). Gasovi iz skrubera su puštaniu atmosferu kroz dimnjak (7). Na donjoj straniskrubera postavljen je vodeni zaptivač koji je služioi kao taložnik (8). Preliv taložnika je povezan safilterom (9). Čvrsta faza je odvođena u peć za kalci-naciju (10), dok je tečna faza odlazila u neutraliza-cionu jamu (11).

U toku prerade doziranje olovo-hlorida i alumi-nijuma vrši se kroz otvor na komori za sakupljanjegasova. Reakcija između olovo-hlorida i aluminiju-ma je intenzivna, naročito ako je aluminijum u obli-ku praha ili strugotine, pa se dodaje u porcijama.Olovo nastalo u procesu redukcije zbog razlike uspecifičnoj težini pada na dno lonca odakle sepomoću sifona ispušta iz peći.

Ispitivanje procesa redukcije olovo-hlorida cin-kom vršeno je na postrojenju prikazanom na slici 2.

Poluindustrijsko postrojenje se sastoji iz livnoglonca (1) smeštenog u ložište peći (2), koje jesnabdeveno gorionikom (3). Ložište peći jepovezano sa dimnjakom (4) za odvod gasova odsagorevanja. Na dnu livnog lonca se nalazi otvor(5) za sifonsko izlivanje tečnog olova. Peć zatopljenje je snabdevena mešalicom sa reduktorom(6), radi omogućavanja boljeg kontakta izmeđuolovo-hlorida i cinka

Slika 2 - Poluindustrijsko postrojenje za preraduolovo-hlorida postupkom cinkotermije

Prilikom izvođenja eksperimenta najpre se upeć unese olovo-hlorid i zagreva iznad temperaturetopljenja (774K). Potom se u rastopljeni olovo-hlorid dodaje cink u porcijama uz kontinuiranomešanje. Olovo nastalo u procesu redukcije usledrazlike u specifičnoj težini pada na dno lonca.Nastali cink-hlorid, koji u sebi sadrži znatnu količinuolovo-hlorida, izdvaja se na površini rastopa ipovremeno uklanja iz lonca. Potom se smeša cink-hlorida i olovo-hlorida rastvara u vodi. Nerastvoranolovo-hlorid se vraća u proces na topljenje, arastvor cink-hlorida dalje tretira hidrometalurški radi



dobijanja komercijalnog proizvoda (50%-ni rastvorZnCl2).

Na prikazanim poluindustrijskim postrojenjimabilo je moguće utvrditi sve relevantne tehničko-teh-nološke parametre za projektovanje industrijskogpostrojenja.

3. REZULTATI I DISKUSIJARezultati izvedenih istraživanja uticaja tempe-

rature i vremena i oblika korišćenog aluminijuma nastepen radukcije olovo-hlorida postupkom alumino-termije prikazani su na slikama 3 i 4.

0 10 20 30 40 50 60 70 800

10

20

30

40

50

60

70

80

90

100

500oC 550oC 600oC 650oC 700oCre

cove

ry d

egre

e, %

time, minVreme, min

Step

enis

kori

šćen

ja,%

Slika 3 - Zavisnost stepena iskorišćenja olova odtemperature i vremena postupkom aluminotermije

Laboratorijska istraživanja su pokazala da jeproces redukcije iznad tačke topljenja olovo-hlorida774K (5010C) potpun, a da je na temperaturamaiznad 933K (6600C) jako intenzivan (čak eksplo-zivan) i veoma ga je teško kontrolisati. Na tempera-turama iznad tačke topljenja aluminijuma, iskoriš-ćenje olova opada. Ovo se tumači činjenicom da jepri ovim temperaturama napon para olovo-hloridaprilično visok pa su gubici izazvani isparavanjemznatni i veći su ukoliko je temperatura viša. Među-tim, najveći deo gubitaka nastaje mehaničkim od-nošenjem reaktanata sublimatom aliminijum-hlorida(AlCl3). Laboratorijskim istraživanjima je utvrđenoda stvoreni aluminijum-hlorid sublimiše u momentunastajanja što je i razumljivo, jer je tačka sublima-cije aluminijum-hlorida 456K (1830C), a proces seodvija na temperaturama 823-873K (550-6000C).

Nastali aluminijum-hlorid posle hlađenja reagu-je sa vlagom iz vazduha, dajući aluminijum-hidrok-sid i hlorovodoničnu kiselinu. Proces je definisanjednačinom (5)

AlCl3+3H2O=Al(OH)3+3HCl (5)

Posle toga, aluminijum-hidroksid se prenosi upeć za kalcinaciju, gde se dobija glinica premasledećoj jednačini:

2Al(OH)3Al2O3 + 3H2O (6)

Ova činjenica ukazuje da je za preradu većihkoličina olovo-hlorida na ekološki prihvatljiv načinpotrebno primeniti odgovarajuća tehničko-tehno-loška rešenja.

0 10 20 30 40 50 60 70 800

10

20

30

40

50

60

70

80

90

100

Al pieces Al powder

t = 550oC

reco

very

deg

ree,

%time, minVreme, min

Step

enisk

orišć

enja

,%

Al kom.Al prah

t = 550oC

Slika 4 - Zavisnost stepena iskorišćenja olova odvremena i oblika korišćenog aluminijuma

Analizom odnosa datih jednačinom (3) uočljivoje da se sa utrošenim 1 kilogramom aluminijumamoguće dobiti 11,5 kilograma olova. Kada se ovo-me doda da se za redukciju upotrebljava odpadni(sekundarni) aluminijum, onda je ekonomičnostovog procesa lako uočljiva. Ovome treba dodati dase energija troši veoma malo, jer je proces defi-nisan jednačinom (3) egzoterman.

Nastalo olovo usled razlike u specifičnoj težinipada na dno kazana odakle se pomoću sifonaispušta iz peći. Tokom ispitivanja parametara radapostrojenja prerađeno je oko 5t olovohlorida, pričemu je dobijeno olovo sledećeg sastava (%): Fe-0,040, Bi-0,950, Ag-0,0282, As-0,023, Sb-0,032,Cd-<0,001, Zn-<0,001. Kao sporedni produkt u pro-cesu se dobija i glinica komercijalnog kvaliteta.

Rezultati ispitivanja uticaja temperature i vre-mena na stepen radukcije olovo-hlorida cinkomprikazani su na slici 5.

0 20 40 60 80 100 1200

20

40

60

80

100

Step

en is

koriš

ćenj

a, %

Vreme, min

500oC 550oC 600oC 700oC

Slika 5 - Zavisnost stepena iskorišćenja olova odtemperature i vremena postupkom cinkotermije



Ispitivanja su pokazala visok stepen redukcijena temperaturama iznad tačke topljenja olovo-hlorida. Najviša iskorišćenja na olovu se postižu natemperaturama neposredno iznad temperature top-ljenja olovo-hlorida pri vremenu redukcije od 120min i optimalnoj brzini mešanja od 60 o/min. Pove-ćanjem temperature brzina reakcije se povećava,ali se smanjuje iskorišćenje olova. Ovo se tumačičinjenicom da su pri ovim temperaturama naponipare olovo-hlorida i cinka prilično visoki, pa sugubici izazvani isparavanjem znatni i rastu sa po-rastom temperature.

Proces redukcije je kontinuiran i njegova brzinasa reguliše brzinom dodavanja cinka i odvođenjemprodukata reakcije (ZnCl2 i Pb) iz reakcionogprostora.

Na slici 6 je prikazan uticaj granulacije cinka nabrzinu i stepen redukcije.

0 20 40 60 80 100 1200

20

40

60

80

100

Step

en is

koriš

ćenj

a, %

Vreme, min

Zn kom. Zn prah

t = 550oC

Slika 6 - Zavisnost stepena iskorišćenja olova odoblika korišćenog cinka

Stepen iskorišćenja olova se neznatno poveća-va ako se kao reducent koristi cink prah, dok brzinareakcije značajno raste. Ovo se objašnjava boljimkontaktom između cinka i rastopljenog olovo-hlorida.

Da bi se hemijska reakcija u sistemu PbCl2-Znodvijala zadovoljavajućom brzinom, naophodno jeobezbediti što bolji kontakt komponenata reakcije.Na slici 7 je prikazan uticaj brzine mešanja nastepen iskorišćenja olova.

Povećanjem brzine mešanja dolazi do pove-ćanja brzine reakcije zbog boljeg kontakta cinka iolovo-hlorida. Istovremeno dolazi do smanjenja is-korišćenje olova, jer sa povećanjem brzine meša-nja intenzivnije isparavaju obe komponente.

Nastalo olovo, usled razlike u specifičnoj težinipada na dno lonca, odakle se pomoću sifona is-pušta iz peći. Tokom ispitivanja parametara radapostrojenja prerađeno je oko 10 t olovo-hlorida, pričemu je dobijeno sirovo olovo sa sadržajem

nečistoća (%): Fe-0.035, Bi-0.90, Ag-0.030, As-0.015, Sb-0.030, Zn-0.2 i Cd0.001. Kao sporedniprodukt u procesu se dobija i 50%-ni rastvor cink-hlorida komercijalnog kvaliteta.

0 20 40 60 80 100 1200

20

40

60

80

100

Step

en is

koriš

ćenj

a, %

Vreme, min

60 o/min 120 o/min 180 o/min

t = 550oC

Slika 7 - Zavisnost stepena iskorišćenja olova odbrzine mešanja

Preradom olovo-hlorida postupkom aluminoter-mije dobijeno je olovo i glinica tehničkog kvaliteta,uz visok stepen iskorišćenja olova. Rezultati istra-živanja prerade olovo-hlorida postupkom cinkoter-mije pokazuju bolje ekonomske efekte, bolju i lakšukontrolu procesa i smanjeno zagađenje životnesredine 12.

4. ZAKLJUČAKDetaljnim ispitivanjima određeni su optimalni

parametri redukcije olovo-hlorida aluminotermijskimi cinkotermijskim postupkom.

U slučaju aluminotermije optimalna tempera-tura redukcije nalazi se u opsegu 550-600oC, a ste-pen iskorišćenja iznosi 95-98%. Sa porastom tem-perature preko 600oC brzina reakcije raste, dokstepen iskorišćenja olova opada. Ukoliko tempe-ratura poraste preko 660oC (iznad tačke topljenjaaluminijuma) reakcija postaje vrlo intenzivna takoda ju je vrlo teško kontrolisati, a gubici premašuju20%. Brzina reakcije takođe raste u temperaturnomintervalu 550-600oC ukoliko se koristi praškasti alu-minijum, zbog razvijene površine. U ovom slučajupostaje neophodno dodavanje aluminijuma da bi sereakcija držala pod kontrolom. Pored sirovog olovasledećeg sastava(%):Fe-0,040, Bi-0,950, Ag-0,0282, As-0,023, Sb-0,032, Cd-<0,001, Zn-<0,001, kao sporedni produktdobija se i glinica zadovoljavajućeg kvaliteta.

Kod cinkotermijskog postupka optimalna tem-perature redukcije kreće se u opsegu 550-600oC, astepen iskorišćenja iznosi 85-90%. Sa porastomtemperature redukcije iznad 600oC brzina redukcijeraste, dok stepen iskorišćenja olova opada zbogpovećanog isparavanja olovo-hlorida i cinka.



Uticaj granulacije cinka koji se koristi za re-dukciju pokazuje da sa smanjenjem krupnoće cinkabrzina redukcije raste usled povećanja reakcionapovršine. Na povećanje brzine radukcije utiče ipovećanje brzine mešanja. Istovremeno sa pove-ćanjem brzine mešanja povećava se isparavanjeolovo-hlorida i cinka i smanjuje iskorišćenje olova.Imajući to u vidu, optimalna brzina mešanja je oko60 o/min.

U procesu redukcije dobijeno je sirovo olovosledećeg sastava u (%): Fe-0.035, Bi-0.90, Ag-0.030, As-0.015, Sb-0.030, Zn-0.2 i Cd0.001. Kaosporedni produkt dobijen je i 50%-ni rastvor cink-hlorida komercijalnog kvaliteta.

ZahvalnicaRezultati prikazani u radu predstavljaju deo

istraživanja na projektu TR34023 čiju realizacijufinansira Ministarstvo prosvete, nauke i tehnološ-kog razvoja Republike Srbije.

LITERATURA

[1] R. Vračar, B. Nikolić, (1995), Ekstraktivnametalurgija olova, Naučna knjiga, Beograd, 206.

[2] R. Vračar, Lj. Jakšić, (2001), Sekundarna meta-lurgija olova, Fakultat tehničkih nauka, KosovskaMitrovica.

[3] I. F. Hudjakov, A. P. Doroshkevich, S. V. Karelov,(1987), Metallurgy of secondary nonferrous metals,Metallurgy, Moskow.

[4] P. M. Smirnov, (1977), Lead refining andSemiproducts Processing, Metallurgy, Moscow.

[5] C.B. Alcock, (2001), Chapter 13 - Extractionmetallurgy, Thermochemical Processes, 323-350.

[6] Stanislav S. Naboychenko, (2009), Chapter 8 -Reduction methods of powder production, Handbookof Non-Ferrous Metal Powders, 163-180.

[7] M.R. Parsa, M. Soltanieh, (2011), On the formationof Al3Ni2 intermetallic compound by aluminothermicreduction of nickel oxide, Materials Characterization,Volume 62, Issue 7, 691-696.

[8] K.U. Nair, T.K. Mukherjee, C.K. Gupta, (1975),Production of tantalum metal by the aluminothermicreduction of tantalum pentoxide Journal of the LessCommon Metals, Volume 41, Issue 1, 87-95.

[9] J. Haidar, S. Gnanarajan, J.B. Dunlop, (2009), Directproduction of alloys based on titanium aluminidesIntermetallics, Volume 17, Issue 8, 651-656.

[10] Stefan Luidold, Helmut Antrekowitsch, RobertRessel, (2007), Production of niobium powder bymagnesiothermic reduction of niobium oxides in acyclone reactor, International Journal of RefractoryMetals and Hard Materials, Volume 25, Issues 5–6,423-432.

[11] B. Đurković, D. Đurković, (1991), Metalurgija retkihmetala, TMF, Beograd, 43-54.

[12] B. Nikolić, (2002), Aerozagađenost u metalurgijiolova, IHTM, Beograd, 115.

ABSTRACT

RECOVERY OF LEAD FROM BY-PRODUCTS OF THE BISMUTH REFINING BYMETALLOTHERMIC REDUCTION TREATMENTS

In the refinement process of bismuth by chlorinating of Bi-Pb alloy (Kroll-Betterton process) as aby-product lead chloride is formed. This study was focused on the lead valorization from PbCl2 byaluminothermic and zincothermic reduction. Besides lead, as a main product, duringaforementioned process technical grade alumina (aluminothermic reduction) and ZnCl2(zincothermic reduction) were also obtained. The secondary aluminium and zinc of differentgranulometry were used as a reducent. The effect of temperature, time, granulometry of reducentsand stirring speed (zincothermic reduction) on the lead recovery was investigated. Based on theexperimental results, the optimal process parameters were defined. Recovery of crude lead(containing 98%Pb) was in the range 95-98% for aluminothermic reduction and 85-90% forzincothermic reduction. The crude lead can be further processed in lead smelters. Technical gradealumina was used in ceramic industry, wile zinc-chloride is suitable for hydrometallurgicaltreatment giving 50 % solution of zinc-chloride as the final product.Key words: lead chloride, aluminothermic reduction, zincothermic reduction, alumina, zinc-chloride, lead

Scientific paperReceived for Publication: 06. 04. 2014.Accepted for Publication: 20. 06. 2014.

B. PEJOVIĆ i dr. ISTRAŽIVANJE DEJSTVA KOROZIJE NA DINAMIČKU ČVRSTOĆU ...


BRANKO PEJOVIĆ, VLADAN MIĆIĆ, Originalni naučni radMILORAD TOMIĆ UDC:620.193.4:669.18.018.29

Istraživanje dejstva korozije na dinamičku čvrstoćukod nekih konstrukcionih čelika

Dejstvom korozije spoljna površina metala postaje hrapava tako da dolazi do smanjenja čvrstoćekao posledica dejstva zareza. Ovome treba dodati da nastavljeno dejstvo korozije izgriza duboke ioštre zareze u metalu od čega nastaju sitne pukotine koje omogućuju još dalje prodiranje korozije.Zbog ovoga dinamička čvrstoća uz istovremeno dejstvo korozije jako opada tako da može dovestido zamornog loma, što je pokazano u radu . Isto tako nije moguće uspostavljanje bilo kakvekvalitativne ili kvantitativne zakonitosti između dinamičke čvrstoće, dejstva korozije uostalom štovaži i za dejstvo korozije i kod neopterećenog metalnog elementa. Ovo se mora u svakompojedinom slučaju ispitati.Ključne reči: zamaranje materijala, dinamička čvrstoća, dejstvo korozije, promenljivo opterećenje,konstrukcioni čelici

1. UVODNA RAZMATRANJA

Dinamička ispitivanja uopšte mogu da se izvo-de zatezanjem, pritiskivanjem, savijanjem i uvija-njem i to na epruvetama konstantnog ili promen-ljivog preseka. Isto tako ispitivanja se mogu proširitii na odgovarajuća ispitivanja konstrukcionih eleme-nata i sklopova, [1, 2].

Svrha ovakvih ispitivanja je dobijanje podatakao ponašanju i svojstvima metala izloženih zamara-nju. Pri ovome, pod zamaranjem se podrazumevapojava postepenog razaranja materijala usleddugotrajnog dejstva promenljivih opterećenja.

2. OPTEREĆENJE CIKLUSI I NAPONIOpterećenje koje se menja periodično, približno

je po sinusoidnom zakonu. Ovako opterećenje mo-že se u opštem slučaju shvatiti kao superpozicijanekog stalnog srednjeg opterećenja i nekog koleb-ljivog opterećenja (slika 1). Pod ciklusom se podra-zumeva najmanji deo funkcije opterećenje – vreme,koji se periodično ponavlja dok je frekvencija brojciklusa u jedinici vremena, [3, 4]. Karakterističnevrednosti opterećenja u ciklusu su: gornje optere-ćenje, donje opterećenje, srednje opterećenje, dokje amplituda apsolutna vrednost polovine algebar-ske razlike gornjeg i donjeg opterećenja, slika 1.

Slika 1 - Karakteristične veličine opterećenja u ciklusu

Adresa autora: 1Tehnološki fakultet Zvornik,Univerzitet u Istočnom Sarajevu, Republika Srpska

Primljeno za publikovanje: 13. 07. 2014.

Prihvaćeno za publikovanje: 21. 09. 2014.

Kod promenljivog opterećenja javljaju se dvaslučaja i to: jednosmerno i naizmenično optereće-nje. Kod prvog se veličina menja u toku vremenabez promene predznaka a kod drugog se veličina ipredznak menjaju u toku vremena (slika 2). Pose-ban slučaj naizmeničnog promenljivog opterećenja



nastaje kada je srednje opterećenje jednako nuli tj.kada su apsolutne vrednosti gornjeg i donjegopterećenja jednake – simetrično naizmeničnoopterećenje.

Slika 2 - Karakteristični slučajevi jednosmernopromenljivog i naizmenično promenljivog

opterećenja u dijagramu opterećenje – vremeNapon predstavlja specifično opterećenje u ne-

koj tački poprečnog preseka epruvete ili konstruk-cionog dela. Pri ovome normalni napon σ je naponu pravcu normale na površinu preseka. Normalninapon pri zatezanju je pozitivan a pri pritiskivanjunegativan. Postoji i tangencijalni napon koji se jav-lja u ravni preseka.

Karakteristične vrednosti napona u ciklusu su(slika 3), [2-10]:

Gornji napon: σg

Donji napon: σd

Srednji napon:2

dgsr

(1)

Amplituda napona:2

g da

(2)

Raspon napona: R = σg - σd =2∙ σa (3)

Slika 3 - Karakteristične veličine u dijagramunapon – vreme

3. KARAKTERISTIČNE VELIČINE PRIISPITIVANJU ZAMARANJEM

Kao najvažnije veličine smatraju se [5,6,11-14]:a ) Broj ciklusa n je broj ciklusa do određenog

momenta posmatranjab) Broj ciklusa do loma N je broj ciklusa koje

ispitivana epruveta izdrži do pojave pukotinec) Dinamička izdržljivost (dinamička čvrstoća)

za N ciklusa σN u opštem slučaju predstavlja naponsastavljen od zbira srednjeg napona σSR i najvećeamplitude napona σAN pri kome epruveta izdržavaN ciklusa do loma (slika 4). Određuje se izdijagrama zamaranja i izražava se na dva načina:

1. σN = σSR ±σAN (4)gde σSR + σAN predstavlja gornji granični napon, aσSR -σAN donji granični napon

2. Kao vrednost gornjeg graničnog napona, uznaznačenje srednjeg napona

d) Granični broj ciklusa ND predstavlja najmanjibroj ciklusa posle koga ne nastaje lom ni prineograničenom broju ciklusa. Određuje se izdijagrama zamaranja (slika 4).

Slika 4 - Dijagram zamaranja



4. USLOVI ISPITIVANJAOblik i dimenzije epruvete za normalna ispitiva-

nja propisuju se odgovarajućim standardima u zavi-snosti od svrhe i načina ispitivanja zamaranjem.Umesto epruvete mogu se upotrebiti i sami kon-strukcioni delovi. Postupak obrade epruvete nesme da promeni strukturu ni osobine materijala, [7,8, 15].

Naročitu pažnju treba obratiti kvalitetu hrapavo-sti površina epruvete, pošto pri zamaranju većinalomova počinje na slobodnoj površini epruvete.Broj epruveta potreban za jedno ispitivanje možebiti vrlo različit u zavisnosti od podataka koji setraže, [9, 10, 16].

Sve epruvete upotrebljene za jedno ispitivanjemoraju biti potpuno identične u pogledu materijala,oblika, dimenzija i obrade, [2, 6, 17]. Učvršćenjeepruvete u čeljusti za ispitivanje zamaranjem trebada bude izvedeno pažljivo da epruveta u toku ispiti-vanja ne bi bila izložena dopunskim opterećenjimaili vibracijama. Jedan od oblika epruvete koji se če-sto koristi za dinamička ispitivanja prikazan je naslici 5.

Slika 5 - Epruveta za ispitivanje

Način opterećenja zavisi od vrste naprezanja ipropisuje se odgovarajućim standardima za pojedi-ne postupke. Način opterećenja mora biti podjed-nak za sve epruvete u toku jednog ispitivanja.

Kod normalnog jednostepenog ispitivanja, sred-nje opterećenje je konstantno za sve epruvete aamplitude se stepenasto smanjuju od jedne epru-vete do druge. Frekvencija se tako odabira da seizbegne preterano zagrevanje epruvete u tokuispitivanja.

5. TOK ISPITIVANJAEpruvete se izlažu promenljivim opterećenjima

do pojave vidljive pukotine ili do potpunog loma,[10, 11, 18, 19].

Za jedno ispitivanje zadržava se srednji naponkonstantan a amplituda napona se smanjuje ste-penasto od jedne do druge epruvete i registrujebroj ciklusa N pri kome je došlo do prskanja epru-vete. Ovo smanjenje amplitude napona vrši se doone vrednosti pri kojoj se epruveta ne lomi ni poštoje izdržala granični broj ciklusa ND.

Pošto se vrednost graničnog broja ciklusa NDne zna unapred to se pri ispitivanju zamaranjemprimenjuje uvek neki veći broj ciklusa koji sa do-voljnom sigurnošću premašuje vrednost graničnogbroja ciklusa.

Ovaj broj ciklusa iznosi:10∙10-6 za obične konstrukcione čelike100∙10-6 za čelike koji se ispituju pod dejstvomkorozije

U nekim slučajevima ne postoji dinamička izdr-žljivost σD pa stoga ne postoji ni granični brojciklusa.

Ako u nekoj epruveti dođe do promene pojaveprskotina usled grešaka materijala ili obrade, odgo-varajuće rezultate ispitivanja treba odbaciti.

6. ISPITIVANJE POD DEJSTVOM KOROZIJEZa razliku od normalnih ispitivanja zamaranjem

koja se vrše u vazduhu i na temperaturi oko 20°C,čest slučaj ispitivanja je kada okolina igra bitnuulogu. Takav slučaj je i ispitivanje zamaranjem uzdejstvo korozije.

Ispitivanja pod dejstvom korozije su vremenskiduga. Da bi se vreme ispitivanja smanjilo, pojačaćese dejstvo korozije tako što će stvoriti jako nečistaatmosfera povećanjem koncentracije korodirajućegsredstva iznad stvarne u pogonu. U konkretnomslučaju korišćen je aparat za ispitivanje korozijeprskanjem rastvora soli veće koncentracije (slika6). Ispitivanje se izvodi na taj način što se metalneepruvete izlažu prskanju vrelim rastvorom kuhinj-ske soli u trajanju od nekoliko časova. Nakon togaepruvete se ispituju zamaranjem prema ranije datojproceduri.

Slika 6 - Šematski prikaz aparata za ispitivanjekorozije prskanjem rastvorom soli

7. DIJAGRAM ZAMARANJAPodaci dobijeni ispitivanjem zamaranjem, dati u

zapisniku o ispitivanju, prikazuju se dijagramimazamaranja, [11-20].



U dijagramu zamaranja kao ordinata nanose sedinamičke izdržljivosti ili amplitude napona uz naz-načenje srednjeg napona a kao apscisa odgo-varajući brojevi ciklusa do loma. Iz praktičnih razlo-ga usvojićemo da su podele i na ordinati i na aps-cisi logaritamske. Tačke unesene na osnovu rezul-tata iz zapisnika i dijagram zamaranja spajaju se ukontinualnu krivu. Svakom ispitivanju sa određenimkonstantnim srednjim naponom odgovara po jednakriva linija – dijagram zamaranja (slika 7). Graničnibroj ciklusa ND određuje se grafički prema istoj sliciu preseku kose i horizontalne linije u dijagramu.Očigledno na apscisi je nanesena logaritamskapodela. Karakteristične eksperimentalne tačke su1, 2, 3, 4 i 5.

Slika 7 - Dijagram zamaranja sa karakterističnimeksperimentalnim tačkama

8. MAŠINA ZA ISPITIVANJEIspitivanja u radu, izvedena su na hidrauličnoj

mašini sa pulzatorom. Za razliku od kidalice samehaničkim pogonom ova mašina ima posebanpogonski komandni uređaj. U njemu je smeštenapumpa visokog pritiska za ostvarenje potrebnogstatičkog opterećenja, dinamometar za merenjeopterećenja, kao i uređaj za crtanje dijagrama sila– deformacija. Za dinamička ispitivanja pogon seostvaruje preko pulzatora smeštenog u zasebnokućište iza mašine. Pulzator se pokreće elektro-motorom a glavni njegov element je cilindar sa kli-pom. Frekvenca klipa se reguliše promenom brojaobrtaja motora. Klipni prostor pulzatora povezan ješirokom cevi sa pogonskim cilindrom mašine. Takose ostvaruje promena opterećenja u istom ritmu ukome i klip pulzatora oscilira. Kada mašina radi sapulzatorom na drugom komandnom uređaju moguse očitati maksimalna i minimalna sila pri dinamič-kom opterećenju, ukupan broj promena optereće-nja i željeni broj promena opterećenja u jedinici vre-mena. Pre nego što se pređe na ispitivanje silompromenljive vrednosti potrebno je izvršiti izboropterećenja.

9. REZULTATI EKSPERIMENTAPrema proceduri prikazanoj u prethodnim pro-

menljivima, za konstrukcioni čelik Č.0545, za slučajkada nema dejstva korozije, za dve vrednosti sred-njeg napona, na slici 8 prikazan je dijagramzamaranja.

Slika 8 - Dijagram zamaranja za konstrukcioni čelikČ.0545 pri različitim vrednostima srednjeg napona

Na slici 9 prikazani su rezultati ispitivanja istogmaterijala kao na slici 8., pri srednjem naponu rav-nom nuli za slučaj dejstva korozije. Radi poređenjarezultata na istom dijagramu je prikazana zavisnostsa slici 8 (za slučaj kada nema dejstva korozije).

Slika 9 - Dijagram zamaranja za čelik Č.0545 pridejstvu korozije (σSR = 0)

Na slici 10 dat je dijagram zamaranja, za istimaterijal i to bez korozije i pri dejstvu korozije, alipri srednjem naponu σsr = 400 N/mm2.

Slika 10 - Dijagram zamaranja za čelik Č.0545 pridejstvu korozije (σSR = 400N/mm2)



Amplituda napona u zavisnosti od broja ciklusau logaritamskim koordinatama biće:

logσAN = a + b∙logN (5)

smenom Y= logσAN X=logN, zavisnost (5) prelaziu:

Y = a + b∙X (6)

Za četiri eksperimentalne tačke prema slici 9 priσSR = 0 biće:

log100 = a + b∙log30∙106

log200 = a + b∙log106 (7)log300 = a + b∙log12∙104

log400 = a + b∙log25∙103

Koristeći odgovarajući računarski program, re-šenje sistema jednačina (7) biće:

a=3,4693, b=-0,1959

odnosno, zamenom u (6):

Y = 3,4693 – 0,1959∙X (8)

Prelaskom u logaritamske koordinate prema (5)biće konačno:

logσAN = 3,4693 -0,1959logN (9)

Na isti način, za tri eksperimentalne tačke zaisti konstrukcioni čelik pri σSR = 400 N/mm2 biće:

log100 = a + b∙log 1,1∙106

log200 = a + b∙log 0,8∙105 (10)log250 = a + b∙log 3∙104

Rešenje sistema (10) biće:

a = 3,5511, b= -0,2564

odnosno u logaritamskim koordinatama:

logσAN = 3,5511-0,2564, logN (11)

10. ZAKLJUČAK

Ispitivanja dinamičke čvrstoće, kako bez koro-zije tako i pod dejstvom korozije, su dugotrajna izahtevaju posebnu pripremu i određenu tehnikusamog ispitivanja: izbor naprezanja, izbor epruvetei broj epruveta, izbor srednjeg i amplitudnog napo-na, izbor frekvence. Mašina koja će se koristiti zaispitivanje mora se prethodno proveriti i osposobitiza dugotrajan rad. U radu je primenjen postupak sarelativno malim brojem epruveta kako bi se smanjilitroškovi eksperimenta.

Dijagram zamaranja za konstrukcione čelikekako za slučaj bez dejstva tako i sa dejstvom ko-rozije pogodno je prikazati u logaritamskim koordi-

natama. Kada ne postoji dejstvo korozije, dina-mička čvrstoća (dinamička izdržljivost) kojapredstavlja graničnu vrednost napona pri kojoj nedolazi do loma pri ispitivanju na zamor, bez obzirana broj ponovljenih opterećenja, kao što je poka-zano određuje se iz dijagrama pomoću horizon-talne prave. Ovo važi za proizvoljni srednji naponkoji se unapred definiše. Logaritamske koordinateomogućuju da se precizno odredi najmanji odnos-no granični broj ciklusa ND nakon koga ne možedoći do loma.

Za slučaj dejstva korozije granični broj ciklusaND ne postoji, tako da se u logaritamskim koor-dinatama za celo područje ispitivanja dobija samojedna prava linija kao funkcionalna zavisnost. Pre-ma tome, za ovaj slučaj ne postoji ni dinamičkačvrstoća, već amplituda napona naglo opada. Oda-vde sledi da je slučaj sa dejstvom korozije znatnonepovoljniji sa aspekta dinamičke izdržljivosti.

LITERATURA

[1] Hormuth K. (1986): Härtetabeilen, VEB, Leipzig

[2] Eisenkobb F. (2001): Einfürung in dieWerkstoffkunde, VEB, Berlin

[3] Avdeev B. A. (1995): Tehnika opredeleniyamehanisheskih svojstv materialov, Mashinostroenie,Moskva

[4] Dondik I.T (1992): Mehanisheskie ispitaniyametallov, ANUSSR, Kiev

[5] Nitchsche K. (1997): Ispitaniya metallov,Metalurgiya, Moskva

[6] Rubashkin A.G. (1996): Laboratornue raboti posoprotivleniyu, materialov, VSH, Moskva

[7] Vejbull V. (1994): Ustalosnie ispitaniya i analiz ihrezultatov, Mashinostroenie, Moskva

[8] Vasić P., Arsenijević M., (1995), Ispitivanje mate-rijala, Naučna knjiga, Beograd

[9] Pantelić I. (2002): Osobine i ispitivanje metalnihmaterijala, Naučna knjiga, Beograd

[10] Bahvalov G. (1994), Zashchita metallov ot korozii,Mashinostraenie, Moskva

[11] Evans U. (1982): Precis de corrosion, KN, Paris

[12] Kimov A. (1997): Teoriya i metodi isledovaniyakorosii metalov, Mashinostrenie, Moskva

[13] Esih I. (2003): Osnove površinske zaštite, Fakultetstrojarsta i brodogradnje, Zagreb

[14] Pavlović M., Stanojević D., Mladenović S. (2012):Korozija i zaštita materijala, Tehnološki fakultet,Zvornik



[15] Bjegović D., Serdar M., Beričević A. (2009):Mehanizam korozije metala, Građevinski fakultet,Zagreb

[16] Pierre R. R. (2000): Handbook of CorrosionEngineering, McGraw-Hill, New York

[17] G.Kobrin, (1998), Materials Selection, in ASMHandbook, Vol.13, Corrosion Ohio

[18] Wranglen G., (2012), An Introduction to Corrosionand Protection of Metals, Inst. Metals, 9-14

[19] Cramer S. D., Covino B.S. (2003): ASM HandbookVol.13A, Corrosion, Fundamentals, Testing andProtection, ASM International, Materials Park, Ohio

[20] B. Pejović, V. Mićić, M. Tomić (2012) Istraživanjeuticaja karakterističnih parametara na kvalitetobrađene površine kod nekih nerđajućih čelika prielektrohemijskoj strugarskoj obradi, Zaštitamaterijala 53 (4), 305-312.

ABSTRACT

INVESTIGATION OF CORROSION EFFECT ON THE DYNAMIC STRENGTHOF SOME STRUCTURAL STEELS

By corrosion effect, the surface of the metal becomes so rough that there are reduction in metalstrength as a consequence of nicking. It should be added that the continuing effects of corrosionproduces deep and sharp notches in the metal. It causes tiny cracks that allow further penetrationof corrosion. As results of this activities, the dynamic hardness by simultaneously highly corrosioneffect substantially decreases so that it may lead to fatigue failure, as shown in this paper. It isalso not possible to establish any qualitative or quantitative legality between dynamic strength andcorrosion effects. This hold for the effect of corrosion on unloaded metal element. This must betested in all chance.Keywords: Fatigue of materials, dynamic strength, corrosion effects, variable load, structuralsteels.

Scientific paperReceived for Publication: 13. 07. 2014Accepted for Publication: 21. 09. 2014.

J. PJEŠČIĆ i dr. UTICAJ NEORGANSKIH INHIBITORA NA KOROZIONO PONAŠANJE ...


JELENA PJEŠČIĆ1, VESELINKA GRUDIĆ1, DARKO Originalni naučni radVUKSANOVIĆ1, DRAGAN RADONJIĆ1, REFIK ZEJNILOVIĆ2 UDC:620.193.4:669.75.782

Uticaj neorganskih inhibitora na koroziono ponašanjeAl-Si legura u vodenim rastvorima hlorida

Aluminijum, kao metal koji se može legirati sa velikim brojem elemenata, je veoma interesantan saaspekta njegove primjene, odnosno on u određenim uslovima treba, osim mehaničkih, dazadovolji i korozione karakteristike. Sa ovog aspekta interesantne su legure aluminijuma na bazisistema Al-Si, na čije ponašanje utiče hemijski sastav koji omogućava, pod određenim uslovimadobijanja, da se dobiju legure određene strukture koja zavisi od prisustva i koncentracije ostalihlegirajućih elemenata. Na osnovu ovoga, pretpostavljeno je da se dobijene legure sistema Al-Simogu koroziono „popraviti“ dodatkom inhibitora, koji će dati određenu efikasnost zaštite u 0,5Mrastvoru HCl, odnosno da će se koroziona stabilnost ovih legura korišćenjem inhibitora Na2CO3,NaNO2 i Na2HPO4 dovesti na viši nivo.Ključne riječi: inhibitori korozije, korozija metala, gustina struje, vodeni rastvori.

UVODLegure sistema Al-Si legirane kobaltom, nik-

lom, molibdenom i željezom, predstavljaju specifič-ne visokovatrootporne materijale koji se koriste zarad na povišenim tempraturama. Osim toga, ove le-gure mogu biti interesantne i sa aspekta korozionestabilnosti, odnosno kako legirajući elementi poje-dinačno utiču na korozionu stabilnost i da li je nji-hov međusobni uticaj povoljan da se u konačnomsmislu može govoriti o stepenu korozione stabil-nosti ovih legura i mogućnosti njihove primjene kaokoroziono stabilnih materijala [1-3]. Ovaj rad pred-stavlja nastavak dosadašnjih istraživanja na ovomsistemu legura [4-6], sa razlikom što su ispitivanjavršena u 0,5M rastvorima NaCl, Na2SO4 sa istiminhibitorima. Cilj ovog rada je da se kroz korišćenjeinhibitora korozije Na2CO3, NaNO2 i Na2HPO4 izvršikvantifikacija brzine korozije i izračuna efikasnostzaštite, pri ispitivanjima u 0,5M rastvoru HCl.

EKSPERIMENTALNI DIO

Priprema šarže i dobijanje legura sistema Al-Sivršeno je u laboratoriji za Livarstvo Metalurško-teh-nološkog fakulteta. Legure su dobijene topljenjem uelektrootpornoj peći snage 5,5 kW, čija radna tem-peratura je 1100 oC. Nakon topljenja u elektrootpor-noj peći vršeno je livenje u metalnu kokilu i hla-đenje na vazduhu.

Adrese autora: 1 Univerzitet Crne Gore, Metalur-ško-tehnološki fakultet, Podgorica, 2Farmaceutskifakultet Podgorica, Crna Gora

Primljeno za publikovanje: 16.7.2014.

Prihvaćeno za publikovanje: 12.9.2014.

Kao osnova za njihovo dobijanje korišćena jelegura AlSi10Mg sa ciljem obezbjeđenja što ma-njeg stepena nehomogenosti u toku izrade ovih le-gura. Legurama su nakon topljenja dodavani ostalilegirajući elementi u proračunatom iznosu.

Ispitivanja hemijskog sastava dobijenih leguravršena su u Kombinatu aluminijuma Podgorica naX-RAY kvantometru metodom bez razaranja.

Koroziona i elektrohemijska ispitivanja vršenasu na opremi za ubrzana ispitivanja-sistem PARkoji čine: potenciostat-galvanostat model 273, dife-rencijalni elektrometar, koroziona ćelija K0047, sta-ndardna zasićena kalomel elektroda, pomoćne ele-ktrode-valjkasti elektrografit, računar sa korozionimsoftverom SOFTCORR 352 II i štampač.

Za koroziona ispitivanja korišćene su metode:- metoda polarizacionog otpora, Rp;- potenciodinamička metoda.

REZULTATI I DISKUSIJAZa ispitivanja efikasnosti inhibitora Na2CO3,

NaNO2 i Na2HPO4 korišćene su 4 legure sistemaAl-Si kod kojih se sadržaj silicijuma kretao od11,76% - 12,50%, željeza od 1,64% - 1,77%, bakraod 1,21% - 2,20%, magnezijuma od 0,91% -2,96%, nikla od 0,78% - 1,41%, kobalta od 0,70% -1,00%, mangana 0,09% - 0,44%, molibdena od0,25% - 0,55%, dok je sadržaj berilijuma u svim le-gurama bio 0,25%.

U tabelama 1-6 prikazane su eksperimentalnevrijednosti polarizacionog otpora (Rp), gustine stru-je korozije (jcorr), potencijala e(j=0) u 0,5M rastvoruHCl, bez i uz dodatak neorganskih inhibitoraNaNO2, Na2CO3 i Na2HPO4, koncentracije 10-4M.



Tabela 1 - Vrijednosti Rp, jcorr i e(j=0) dobijene metodom polarizacionog otpora u prisustvu inhibitora Na2CO3

Bez inhibitora 10-4 M Na2CO3Legura

e(j=0) [mV] Rp [Ω] jcorr [μA/cm2] e(j=0) [mV] Rp [Ω] jcorr [μA/cm2]1 -703,6 97,54 222,6 -676,1 168,3 129,02 -694,8 70,23 309,2 -679,0 203,9 106,53 -694,5 68,27 318,1 -683,8 140,4 154,74 -704,9 72,82 298,2 -701,1 94,23 230,4

Tabela 2 - Vrijednosti Rp, jcorr i e(j=0) dobijene metodom polarizacionog otpora u prisustvu inhibitora NaNO2

Bez inhibitora 10-4 M NaNO2Legura


Tabela 3 - Vrijednosti Rp, jcorr i e(j=0) dobijene metodom polarizacionog otpora u prisustvu inhibitora Na2HPO4

Bez inhibitora 10-4 M Na2HPO4Legura


Tabela 4 - Vrijednosti e(j=0) dobijeni potenciodina-mičkom metodom u prisustvu inhibitoraNa2CO3

Bez inhibitora 10-4 M Na2CO3Legurae(j=0) [mV] e(j=0) [mV]

1 -647,4 -641,82 -649,6 -629,33 -649,8 -625,64 -661,8 -650,7

Tabela 5 - Vrijednosti e(j=0) dobijeni potenciodina-mičkom metodom u prisustvu inhibitoraNaNO2

Bez inhibitora 10-4 M NaNO2Legurae(j=0) [mV] e(j=0) [mV]

1 -647,4 -622,42 -649,6 -632,83 -649,8 -632,94 -661,8 -647,7

Tabela 6 - Vrijednosti e(j=0) dobijeni potenciodina-mičkom metodom u prisustvu inhibitoraNa2HPO4

Bez inhibitora 10-4 M Na2HPO4Legurae(j=0) [mV] e(j=0) [mV]

1 -647,4 -618,82 -649,6 -625,23 -649,8 -622,74 -661,8 -644,7

Dodatak inhibitora uticao je na smanjenje vri-jednosti gustine struje korozije, odnosno na pove-ćanje vrijednosti polarizacionog otpora. Efikasnostzaštite na osnovu podataka iz prethodnih tabelaizračunava se po jednačini [7]:

( )corr corr inh

corr

j j

j

gdje je jcorr gustina struje korozije u neinhibiranom,a (jcorr)inh u inhibiranom rastvoru. Izračunatevrijednosti efikasnosti zaštite prikazane su u tabeli7 (u 0,5M rastvoru HCl).

Tabela 7 - Efikasnost zaštite ispitivanih Al legura uprisustvu neorganskih inhibitora, osnovnirastvor 0,5M HCl

Legura 10-4MNa2CO3

10-4MNaNO2

10-4MNa2HPO4

1 42,0% 2,4% 14,4%2 65,6% 44,3% 33,5%3 51,4% 29,4% 37,5%4 24,0% 31,9% 7,3%

Tabela 7 pokazuje da se ispitivane legure po-našaju različito, kada je efikasnost primijenjenih in-hibitora u pitanju. Prilikom korišćenja inhibitoraNa2CO3 i NaNO2, najveću efikasnost pokazuje le-gura 2, kod koje je odnos Cu i Mg oko 1,5. Ova le-gura ima najveći sadržaj cobalta, a najmanji sad-ržaj nikla. Kod korišćenja inhibitora Na2HPO4,



najveću efikasnost pokazuje legura 3 koja ima naj-manji sadržaj cobalta i mangana. Međutim, ako sepogleda ukupan sadržaj legirajućih elemenata, on-da se može vidjeti da je ukupan sadržaj legirajućihelemenata najmanji, upravo kod legure 2, što semože tumačiti činjenicom da je strukturni sastav is-pitivane legure najpovoljniji sa aspekta kvantitativ-nog udjela pojedinih faza u leguri, a koje u 0,5Mrastvoru HCl i u prisustvu korišćenih inhibitora po-kazuje pozitivne efekte, kada je koroziona stabil-nost u pitanju. Takođe, može se konstatovati da sesve ispitivane legure u 0,5M rastvoru NaCl pona-šaju stabilno, bez obzira na različitu efikasnost

korišćenih inhibitora. Najveću prosječnu efikasnostkod svih ispitivanih legura ima inhibitor Na2CO3,koja iznosti 45,75%, a najamnju prosječnu efikas-nost pokazao je inhibitor Na2HPO4, koja iznosi23,175%.

Na slikama 1 i 2 dati su dijagrami dobijeni me-todama polarizacionog otpora i potenciodinamič-kom metodom za leguru 2 u osnovnom rastvorubez inhibitora (0,5M HCl) i sa dodatkom neorgan-skih inhibitora (NaNO2, Na2CO3 i Na2HPO4, kon-centracije 10-4M) u osnovni rastvor.

a) b)

c) d)Slika 1 - Dijagrami polarizacionog otpora za leguru 2: a) bez dodatka inhibitora, b) u prisustvu 10-4M

Na2CO3, c) u prisustvu 10-4M NaNO2, d) u prisustvu 10-4M Na2HPO4

Sl. 2a) Sl. 2b)



c) d)

Slika 2 - Potenciodinamičke katodne i anodne polarizacione krive legure 2: a) bez dodatka inhibitora, b) uprisustvu 10-4M Na2CO3, c) u prisustvu 10-4M NaNO2, d) u prisustvu 10-4M Na2HPO4

Dijagrami linerane polarizacije (slika 1) pokazu-ju da dodatkom neorganskih inhibitora u osnovnirastvor dolazi do pomjeranja potencijala premapozitivnijim vrijednostima u rastvorima, odnosno dosmanjenja brzine korozije [8].

Katodne i anodne polarizacione krive date naslici 2 pokazuju pozitivan uticaj dodatka korišćenainhibitora korozije kroz smanjenje brzine korozijeispitivane legure 2, jer dolazi do pomjeranja poten-cijala e(j=0) prema pozitivnijim vrijednostima, u od-nosu potencijal e(j=0) dobijen u osnovnom rastvorubez dodatka inhibitora.

ZAKLJUČAK

Rezultati izvršenih ispitivanja efikasnosti inhi-bitora Na2CO3, NaNO2 i Na2HPO4 u 0,5M rastvoruHCl pokazuju:1. Na koroziono ponašanje ispitivanih legura u

0,5M rastvoru HCl direktan uticaj ima hemijskisastav dobijenih legura.

2. Što se rezultata korozionog ponašanja tiče,može se zaključiti da je kod legure 2, gene-ralno, efikasnost korišćenih inhibitora bila naj-veća, što se može direktno pripisati hemijskomsastavu legure, odnosno njenim strukturnimkarakteristikama.

3. Od svih ispitivanih inhibitora, ukupno gledano,najveću efikasnost je pokazao inhibitorNa2CO3, čija prosječna efikasnost zaštite kodsvih ispitivanih legura iznosi 45,75 %.

ZahvalnostAutori se zahvaljuju Ministarstvu nauke Crne

Gore na sredstvima dodijeljenim za naučno-istra-živački projekat „Ispitivanje uticaja inhibitora nabrzinu korozije materijala na bazi željeza i alumi-nijuma u vodenim rastvorima“.

LITERATURA

[1] Davis J.R., Corrosion of Aluminum and AluminumAlloys, ASM Intl., Materials Park, Ohio, 1999.

[2] P.Živković „Corrosion Investigation on Al and Al-alloys in Montenegro“, XVIII Yugoslav SymposiumCorrosion and Material protection 2000, p 45.

[3] Radosevic J., Malina J., Dolic N., Ljumovic P.,Slavica-Matesic S., (2013) Susceptibility tocorrosion of welded AlMgSi alloy EN AW 6060,Zastita materijala 54(1) 3-7

[4] Dragan Radonjić, Darko Vuksanović, JelenaPješčić, Refik Zejnilović, Veselinka Grudić, (2012),Ispitivanje ponašanja livačkih legura sistema Al-Si urastvorima hlorida bez i sa prisustvom inhibitora,Zaštita materijala i životne sredine 1 (2) s. 94-100.

[5] Malina J., Dolic N., Unkic F., (2013) Mikrostrukturniaspekti lokalne korozije Al-slitina u lijevanom stanju,Zastita materijala 54 (3) 240-249

[6] D. Radonjić, D. Vuksanović, J. Pješčić, R.Zejnilović, V. Grudić: „Examining the efficiency ofinorganic inhibitors on the corrosion behavior Al-Sisystem alloys in aqueous solutions of Na2SO4“, XVYucorr, Tara, 17-20 September 2013, p.71-76.

[7] A.R.Despić, J. Radošević, M. Kliskić, Inhibition ofcathodic corrosion of aluminium, 7th EuropeanSymposium on Corrosion Inhibitors, N. 9, 1990, p1119-1124.

[8] M.Pourbaix „Atlas of Electrochemical Equilibrium inaqueous solutions“, Oxford, 1966.



ABSTRACT

THE INFLUENCE OF INORGANIC INHIBITORS ON THE CORROSION BEHAVIOROF Al-Si ALLOYS IN AQUEOUS CHLORIDE SOLUTIONS

Aluminum, as a metal which can alloy with the large number of elements, is very interesting fromthe point of its application, i.e. it should, in certain circumstances, in addition to mechanical, satisfythe corrosion characteristics. From this point of interest, the alloys based on Al-Si systems, whosebehavior affects the chemical composition, allow, under certain conditions, the obtain ing of certainalloy structure that depends on the presence and concentration of other alloying elements. On thisbasis, it was assumed that the resulting alloy system Al-Si corrosion can "fix" the addition ofinhibitors, which will give some protection efficiency in 0.5M HCl solution, i.e. the corrosion stabilityof these alloys using inhibitors of Na2CO3 and Na2HPO4 NaNO2, bring to a higher level.Keywords: corrosion inhibitors, corrosion of metals, current density, aqueous solutions.

Scientific paperReceived for Publication: 16. 07.2014.Accepted for Publication: 12. 09. 2014.

M. V. TOMIĆ i dr. UTICAJ HRAPAVOSTI Zn-Mn PREVLAKA NA KOROZIONU POSTOJANOST


MILORAD V. TOMIĆ1, MARIJA G. RIĐOŠIĆ1, Originalni naučni radMIOMIR G. PAVLOVIĆ1, MIROSLAV JOKIĆ1, JELENA BAJAT2 UDC:669.58:620.193

Uticaj hrapavosti Zn-Mn prevlaka na korozionu postojanostU ovom radu je vršeno elektrohemijsko taloženje Zn-Mn prevlaka iz četiri rastvora, merena jenjihova hrapavost i koroziona postojanost. Korišćene su katode od čelika nepoznatog sastava kojesu podvgnute hemijskoj pripremi pre taložena dvojnih prevlaka Zn-Mn elektrohemijskim putem, akorišćene su anode od cinka čistoće 99,99%.Dvojne Zn-Mn prevlake su elektrohemijski taložene15 minuta iz svih rastvora pri gustinama struje 1А/dm2, 2А/dm2 i 4 А/dm2. Svi eksperimenti suizvođeni galvanostatski (pri konstantnoj struji) u elektrohemijskoj ćeliji zapremine 500 cm3 i nasobnoj temperaturi.Hrapavost elektrohemijski taloženih prevlaka Zn-Mn merena je uređajem TR200, a korozionapostojanost taloženih prevlaka određivanjem spektroskopije elektrohemijske impedance (SEI).Rezultati pokazuju da najmanju hrapavost imaju prevlake taložene pri gustini struje2 A/dm2 iz svihrastvovora. Izuzetak je rastvor 3sa odnosom [Mn2+]:[Zn2+]=1:2 kod koga je hrapavost najmanja uodnosu na sve rastvore i kreće se od 0,71 – 0,875 μm , anajmanja je pri gustini struje 4 А/dm2 iiznosi 0,71 μm. Na osnovu elektrohemijskih merenja utvrđeno je da je koroziono najpostojanijaprevlaka Zn-Mn taložena pri gustini struje od 2 A/dm2 iz svih rastvora i pri gustini struje 4 А/dm2izrastvora 3 sa odnosom [Mn2+]:[Zn2+]=1:2. To govori da je koroziona postojanost u direktnoj vezi sahrapavošću i kompaktnosti Zn-Mn prevlake. Koroziono su najpostojanije prevlake sa najmanjomhrapavošću.Ključne reči: brzina korozije, elektrohemijsko taloženje, gustina struje, hrapavost, spektroskopijaelektrohemijske impedanse

UVODElektrohemijsko taloženje prevlaka legura Zn

na čeliku u poslednjoj deceniji je privuklo velikupažnju posebno u automobilskoj industriji, kao os-nova pre nanošenja organskih prevlaka [1-10].Zbog povećanih zahteva da prevlake legura Zn bu-du dobra osnova za organske prevlake i zaštita zaduži radni vek, kao i dobra zamena za toksičnuprevlaku kadmijuma [11-14]. Ako legura cinka imadovoljno veliku količinu cinka ona još uvek može daima dovoljno negativan potencijal u odnosu na če-lik, a ipak, pružaju bolju zaštitu od korozije odsamog cinka [12].

Neki autori su pokazali da u agresivnim sredi-nama gde su prisutni natrijumhlorid i sumpor-dio-ksid, prevlaka legure Zn-Mn pokazuju bolju otpor-nost na koroziju [14-17]. Danas se organski pre-maz nanosi na površine metalnih prevlaka u ciljustvaranja otpornijeg sistema zaštite od korozije [17,18]. Cilj ovog rada je bio elektrohemijsko dobijanjekvalitetne i jeftine prevlake (legure), dobrih zaštitnihosobina i korozione postojanosti, kao i dobijanjenetoksične prevlake sa izuzetnim hemijskim imehaničkim osobinama. Takođe, jedan od ciljevaistraživanja je bilo iznalaženje optimalnih uslova zaelektrohemijsko taloženje prevlake Zn-Mn legure,koja je ekološki prihvatljiva i sa dobrom korozionompostojanošću, kao i određivanje optimalnog odnosa

Adrese autora: 1Tehnološki fakultet Zvornik,Univerzitet u Istočnom Sarajevu, Republika Srpska,2Univerzitet u Beogradu, Tehnološko-metalurškifakultet, Karnegijeva 4, Beograd, Srbija

Primljeno za publikovanje: 23. 06. 2014.Prihvaćeno za publikovanje: 19. 09. 2014.

Zn i Mn u rastvoru za dobijanje koroziono najposto-janije prevlake i da se ispita uticaj hrapavosti istalo-ženih prevlaka na njihovu korozionu postojanost.

EKSPERIMENTALNI DEOKao radna elektroda za taloženje legure Zn-Mn

korišćena je pločica od čelika nepoznatog sastavadimenzija 3 x 3 cm. Kao anoda korišćen je cink či-stoće 99,99%. Pre taloženja prevlake vršena je pri-prema uzoraka na sledeći način: odmašćivanje de-terdžentom, ispiranje protočnom i destilovanom vo-dom, hemijsko odmašćivanje u rastvoru (NaOH35g/dm3, Na2CO345g/dm3, Na3PO4 x 10H2O4g/dm3) na temperaturi od 850C u trajanju od 15minuta, ispiranje protočnom i destilovanom vodom,nagrizanje u 20%H2SO4 na temperaturi od 650C utrajanju od 60 sekundi, ispiranje protočnom i des-tilovanom vodom, ispiranje alkoholom, sušenje imerenje uzorka(početna masa).

Na ovako pripremljene uzorke čelika (katode)taložene su prevlake legure galvanostatski pri gus-tinama struje od 1; 2 i 4 А/dm2 na sobnoj tempe-raturi. Korišćena je elektrohemijska ćelija zapre-mine 0,5 dm3. Nakon taloženja prevlake uzorci suispirani u protočnoj i destilovanoj vodi, a potomsušeni ventilatorskom grejalicom u trajanju od 15minuta. Korišćeni su hloridni rastvori za taloženjeprevlaka, pH=5,0; prikazani u tabeli 1.

Pri korozionim merenjima kao pomoćna elek-troda je korišćena DSA TiO2-RuO2, a kao referent-na elektroda korišćena je zasićena kalomelovaelektroda (ZKE) i svi potencijali su prikazani u od-nosu na nju. Sve korišćene hemikalije su p.a čis-toće, i rastvori su pravljeni sa dva puta destilo-vanom vodom. Svi eksperimenti su vršeni nasobnoj temperaturi.



Tabela 1 - Rastvori za taloženje

Sastav rastvora R1(mol/dm3)

R2, (mol/dm3)[Mn2+]:[Zn2+]=1:1

R3, (mol/dm3)[Mn2+]:[Zn2+]=1:2

R4, (mol/dm3)[Mn2+]:[Zn2+]=2:1

KCl 3 3 3 3H3BO3 0,42 0,42 0,42 0,42ZnCl2 0,45 0,45 0,45 0,45MnCl2x4H2O 0,45 0,25 0,9

Radni uslovi

gustina struje 1 А/dm2; 2 А/dm2 i 4 А/dm2

temperatura sobna bez mešanja elektrolita

REZULTATI I DISKUSIJAU tabeli 2 dat je prikaz izmerenih parametara

hrapavosti na dužini puta od 0.8mm, za prevlaketaložene iz četiri rastvora pri gustinama struje 1; 2 i4 A/dm2 gde su: Ra-aritmetička sredina devijacijeprofila; Rq-kvadratni korijen aritmetičke sredine

kvadrata devijacije profila; Rz-maksimalna visinaprofila; Ry (DIN) maksimalna visina profila; Rt-ukupna visina vrh, dno; Rp-maksimalna visina vrhaprofila; Rm-maksimalna dubina dna profila; Sm-srednji razmak elemenata profila; S-središnjirazmak lokalnih vrhova profila; Sk-kosina profila.

Tabela 2 - Izmereni parametri hrapavosti taloženih prevlaka

Rastvor j(A/dm2) Ra(μm) Rq(μm) Rz(μm) Ry(μm) Rt(μm) Rp(μm) Rm(μm) S(mm) Sm(mm) Sk1 1,901 2,341 7,675 10,84 14,3 6,104 4,743 0,0563 0,08 0,3032 0,612 0,819 3,446 4,983 8,699 1,708 3,276 0,0547 0,0851 -1,9374 1,575 2,057 7,824 11,49 15,89 6,067 5,227 0,0434 0,0634 -0,1151 1,487 1,835 5,762 7,892 10,26 3,612 4,28 0,0588 0,0833 -0,2362 0,935 1,31 4,421 7,868 10,81 2,736 5,131 0,0677 0,1111 -1,4784 1,831 2,394 8,47 12,64 17,02 7,472 5,175 0,0563 0,074 0,8641 0,875 1,145 4,289 5,812 6,92 2,335 3,476 0,0454 0,0714 -0,5652 0,831 1,145 3,772 6,852 10,31 2,9 3,952 0,0701 0,0975 -1,2714 0,71 0,903 3,293 4,907 6,34 2,579 2,328 0,0392 0,0615 -0,0091 2,651 3,74 10,15 17,78 26,95 10,05 7,727 0,1176 0,1481 0,6862 1,775 2,246 7,864 11,34 14,8 5,012 6,335 0,0454 0,0689 -0,2534 3,242 4,366 12,97 22,17 31,79 13,77 8,395 0,0909 0,1052 1,216

III

IV

I

II

Na slici 1 dat je grafički prikaz hrapavostielektrohemijski taloženih Zn-Mn prevlaka.

Iz tabele 2 i sa slike 1 može se videti da je hra-pavost najmanja (0,71-0,875 μm) kod prevlakataloženih iz rastvora 3 gde je odnos [Mn2+]:[Zn2+] =1:2. Najveću hrapavost imaju prevlake taložene izrastvora 4. sa odnosom [Mn2+]:[Zn2+]=2:1. To značida povećanje koncentracije mangana u rastvoru ileguri daje veću hrapavost prevlake.

Takođe se vidi da se pri gustini struje taloženjaod 2 A/dm2 dobijaju prevlake sa najmanjom hrapa-vošću koja se kreće od 0,612-1,775 μm. Na slici2.a-c. dat je prikaz snimljenih dijagrama hrapavosti

i mikrofotografski prikaz prevlaka taloženih iz ras-tvora 1. Snimljeni dijagrami hrapavbosti i mikrofoto-grafski prikaz za prevlake taložene iz rastvora 2,3 i4 je veoma sličan prikazanom na slici 2, a iz teh-ničkih razloga neće biti prikazani u ovom radu.

Opšti vizuelni utisak sa mikrofotografija na sli-kama 2 a-c. pri uvećanju 35 puta je da se dobijajukompaktne i homogene prevlake iz rastvora 1. prisvim korišćenim gustinama struje. Sa povećanjemgustine struje menja se struktura, izgled i bojaprevlake, kao i hrapavost. Boja prevlake se menjasa povećanjem gustine struje od tamnije sive dosvetlo sive koja poprima nijanse svetlo plaveboje.Na prevlakama taloženim pri manjim gustinama



struje uočljivi su defekti na samoj prevlaci, a sapovećanjem gustine struje dobijaju se kompaktnijeprevlake i defekti su manje uočljivi. Prevlaketaložene pri gustinama struje 2A/dm2 i 4A/dm2sukompaktne i sitnozrne. Takođe, primetno je da su

prevlake taložene iz rastvora 2 i 3 kompaktne imanje hrapave. Veoma slična struktura i izgled sedobijaju iz sva četiri korišćena rastvora, štopotvrđuju i parametri izmerene hrapavosti prikazaniu tabeli 2.

I II

III

IV

I

III

IIIIIIII

IV

IV

Slika 1 - Grafički prikaz hrapavosti elektrohemijski taloženih Zn-Mn prevlaka

Koroziona stabilnost istaloženih prevlaka ispiti-vana je merenjem spektroskopske elektrohemijskeimpedance (SEI) pomoću potenciostata/galvano-stata/ZRA Gamry Series GTM 750 u 3 % rastvoruNaCl.

Na slici 3 prikazani su grafici zavisnosti – Zimagod Zreal(Nyquist-ove krive) snimljene spektrosko-pijom elektrohemijske impedancije za Zn-Mn pre-vlake taložene iz rastvora 1-4 u zavisnosti od gusti-ne struje sa kojom je taložena Zn-Mn prevlaka.

Sa slike 3 (a-d) može se videti da je korozionapostojanost prevlaka dobijenih taloženjem iz rast-vora 1. u kome nema mangana, manja nego koro-ziona postojanost prevlaka dobijenih taloženjem izrastvora 2, 3 i 4 koji sadrže mangan. To se možezaključiti na osnovu –Zimag, koje se kreće do 130 Ωza prevlake dobijene taloženjem iz rastvora 1, dok–Zimag za prevlake iz ostalih rastvora koji sadržemangan ide i preko 200Ω. Ovo znači da mangan uleguri sa cinkom povećava korozionu postojanostprevlake.

Koroziono najpostojanija prevlaka cinka izrastvora 1. se dobija pri gustini struje taloženja od2A/dm2 (slika 3a). Sa dodatkom mangana u odnosu[Mn2+]:[Zn2+]=1:1 (rastvor 2) dobijaju se koroziono

postojanije prevlake pri manjim gustinama strujetaloženja od 1 i 2A/dm2 (slika 3b). Menjanjem od-nosa mangana i cinkana [Mn2+] : [Zn2+] = 1:2 (rast-vor 3) dobijaju se koroziono postojanije prevlake prisvim gustinama struje (slika 3c), što je u skladu saparametrima izmerene hrapavosti. Izmerena jenajmanja hrapavost prevlaka taloženih iz rastvora 3Ra = 0,71 – 0,875 μm. Kod četvrtog rastvora (slika3d) gde je odnos [Mn2+]:[Zn2+] = 2:1 iz kog je ta-ložena dvojna legura Zn - Mn vidi se da se koro-ziono najpostojanije prevlake dobijaju pri većimgustinama struje (2 i 4A/dm2). Takođe, da se pri-metiti da pri odnosu [Mn2+]:[Zn2+]=1:2(rastvor 3) sedobijaju koroziono najpostojanije prevlake taloženepri gustinama struje od 2 i 4A/dm2. Za ove prevlake–Zimag se kreće oko 200Ω, što govori da je ova pre-vlaka legure cinka koroziono znatno postojanija odsame prevlake cinka. Generalno gledano rezultateSEI vidi se da su prevlake legura cinka postojanijeod čiste prevlake cinka i da su koroziono posto-janije prevlake kod kojih je izmerena manja hrapa-vost. Prevlake taložene iz rastvora 3. imaju naj-manju hrapavost i najveću korozionu postojanost.S toga se može zaključiti da je u rastvoru za talo-ženje prevlake legure Zn-Mn optimalan odnos[Mn2+]:[Zn2+]=1:2, kao i gustina struje taloženja pre-vlaka od 2 i 4



A/dm2.

80

60

40

0

20

-20

-40

-60

-80

0

20

40

60

80

-20

-40

-60

-80

0

20

40

60

80

-20

-40

-60

-80

a)

b)

c)

Slika 2 – Dijagrami hrapavosti i mikrofotografski prikaz (uvećanje 35x) Zn-Mn prevlaka taloženih izrastvora 1, a) 1A/dm2;b) 2A/dm2; c) 4A/dm2



0 100 200 300 400 500 600 7000

50

100

150

200

j=1A/dm2

j=2A/dm2

j=4A/dm2

-Zim

ag(o

hm)

Zreal(ohm)

0 100 200 300 400 5000

50

100

150 j=1A/dm2

j=2A/dm2

j=4A/dm2

-Zim

ag(o

hm)

Zreal(ohm)

0 100 200 300 400 500 6000

50

100

150

200 j=1A/dm2

j=2A/dm2

j=4A/dm2

-Zim

ag(o

hm)

Zreal(ohm)

0 100 200 300 400 500 6000

50

100

150

200 j=1A/dm2

j=2A/dm2

j=4A/dm2

-Zim

ag(o

hm)

Zreal(ohm)

a) b)

c) d)

Slika 3 - Nyquist-ovdijagramza Zn –Mn prevlake u zavisnosti od gustine struje taložene iz a) rastvora 1,b) rastvora 2, c) rastvora 3, d) rastvora 4.

ZAKLJUČCIIz sva četiri korišćena rastvora pri svim koriš-

ćenim gustinama struje dobijaju kompaktne i homo-gene prevlake. Sa povećanjem gustine struje me-nja se struktura, izgled i boja prevlake. Na prevla-kama taloženim pri manjim gustinama struje1A/dm2

uočljivi su defekti na samoj prevlaci, a sa poveća-njem gustine struje taloženja dobijaju se kompak-tnije prevlake i defekti su manje uočljivi. Hrapavostprevlaka je najmanja kod prevlaka taloženih izrastvora 3. gde je odnos [Mn2+]:[Zn2+]=1:2, a dalekonajveća kod prevlaka taloženih iz rastvora 4. sa od-nosom [Mn2+]:[Zn2+]=2:1. To znači da povećanjemsadržaja mangana u leguri daje hrapavije prevlake.Takođe se vidi da se pri gustini struje taloženja od2 A/dm2 dobijaju prevlake sa najmanjom hrapa-vošću koja se kreće od 0,612 do 1,775 μm. Koro-ziona postojanost prevlaka dobijenih taloženjem izrastvora 1. u kom nema mangana, manja je negokoroziona postojanost prevlaka dobijenih talo-ženjem iz rastvora 2, 3 i 4 koji sadrže mangan. Tose može zaključiti na osnovu –Zimag, koje se krećedo 130Ω za prevlake dobijene iz rastvora 1, dok –Zimag za prevlake taložene iz ostalih rastvora je i

preko 200 Ω. To znači da mangan u leguri sacinkom daje koroziono postojanije prevlake, tj. daje prevlaka legure koroziono postojanija od čisteprevlake cinka. Najpostojanija prevlaka pri gustinistruje 1A/dm2 dobija se iz rastvora 2 ([Mn2+]:[Zn2+]=1:1), dok se postojanije prevlake dobijaju iz rastvo-ra 2, 3 i 4 taložene pri većim gustinama struje 2 i4A/dm2. To govori da povećanjem sadržaja Mn urastvoru i gustine struje taloženja prevlake dobijajuse koroziono postojanije prevlake legure Zn –Mn.Generalno najmanju hrapavost i najveću korozionupostojanost imaju prevlake taložene iz rastvora 3.pri svim gustinama struje ([Mn2+]:[Zn2+] = 1:2).

LITERATURA

[1] M. M. Petrović, (2011) Master rad, Univerzitet uBeogradu.

[2] M.M. Bučko, M.V. Tomić, S.I. Stevanović, M.G.Pavlović, J.B. Bajat, (2011) The Peculiarities ofElectrochemical Deposition and Morphology of Zn-Mn Alloy Coatings Obtained From PyrophosphateElectrolyte, Hemijska Industrija, vol. 65 br. 3, str.295-303



[3] J. B. Bajat, M. D. Maksimović, M.V. Tomić, M.G.Pavlović, (2012) The Study of Zn-Co Alloy CoatingsElectrochemically Deposited by Pulse Current,Hemijska Industrija, vol. 66 br. 5., 749-757.

[4] M. Pavlović, D. Stanojević, S. Mladenović, (2012)Korozija i zaštita materijala, TF Zvornik.

[5] S. Mladenović, (1990) Korozija materijala, TMF,Beograd.

[6] S. Đorđević, M. Maksimović, M. Pavlović, K.Popov,(1997) Galvanotehnika, Tehnička knjiga,Beograd.

[7] M. V. Tomić, M. M. Bučko, V. B. Mišković-Stanković, M. G. Pavlović, J. B. Bajat, (2013) Epoxycataphoretic coatings on steel modified by Zn-Mnalloys, Contemporary materials, Banja Luka, Ed.ANURS.Book of Abstracts., 93.

[8] M. Pushpavanam, S. R.Natarajan. K. Balakrishnan,L. R.Sharma, (1991) Corrosion behaviour ofelectrodeposited zinc-nickel alloys, J. Appl.Electrochem. 21., 642-645.

[9] D. W. Baudrand, (2001) Aircraft Applications forElectroless Nickel Plate, Metal Fin. 33.

[10] Ramesh S. Bhat, Udaya Bhat K,, A. ChitharanjanHegde, (2011) Corrosion Behavior ofElectrodeposited Zn-Ni, Zn-Co and Zn-Ni-Co Alloys,Anal. Bioanal. Electrochem., Vol. 3, No. 3, 302-315.

[11] J. B. Bajat, A. B. Petrović, M. D. Maksimović, (2005)Electrochemical deposition and characterization ofzinc-nickel alloys deposited by direct and reverse

current, Journal of the Serbian Chemical Society,70(12)., 1427-1439.

[12] M. A. Pech-Canul, R. Ramanauskas, L. Maldonado,(1997) An electrochemical investigation of passivelayers formed on electrodeposited Zn and Zn-alloycoatings in alkaline solutions, Volume 42, Issue 2.,255–260.

[13] Kautek, W., Sahre, M., Paatsch, W., (1994)Transition metal effects in the corrosion protectionof electroplated zinc alloy coatings ElectrochimicaActa, 39, 1151

[14] G. D. Wilcox, D. R. Gabe, (1993) ElectrodepositedZinc Alloy Coatings, Corrosion Science, vol. 35.,Nos 5-8., 1251 -1258.

[15] M. Eyraud, A. Garnier, F. Mazeron, J. Crousier,(1995) Morphology and composition ofelectrodeposited zinc-manganese alloys, Plat. Surf.Finish. 82., 63–70.

[16] B. Bozzini, E. Griskonis, A. Fanigliulo, A. Sulcius,(2002) Surf. Coat. Technol. 154., 294-303.

[17] Z.I. Ortiz, P. Díaz-Arista, Y. Meas, R. Ortega-Borges, G. Trejo, (2009) Characterization of thecorrosion products of electrodeposited Zn, Zn–Coand Zn–Mn alloys coatings, Corrosion Science 11 .,2703-2715.

[18] G.Grundmeier, W.Schmidt, M.Stratmann, (2000)Recent developments in models for the interfacebetween a metal and an aqueous solution,Electrochimica Acta , Volume 45, Issues 15-16.,2317-2674.

ABSTRACT

IMPACT OF ROUGHNESS OF Zn-Mn COATINGS ON CORROSIVE STABILITY

This paper involves electrochemical deposition of Zn-Mn coatings from four solutions. Wemeasured their roughness and corrosion stability. We used cathodes made of steel of unknowncomposition that were licensed under the chemical preparation before the electrochemicaldeposition of dual-Zn-Mn coatings, and we also used the anode of zinc, purity of 99.99%. Dual Zn-Mn coatings were electrodeposited for 15 minutes from all of the solutions at a current densities of1 A/dm2, 2 A/dm2 and 4 A/dm2. All experiments were carried out galvanostatialy (at constantcurrent) in an electrochemical cell, volume of 500 cm3 and at room temperature.The roughness of electrochemically deposited Zn-Mn coatings was measured by a TR200 deviceand corrosion stability of deposited coatings by determining the Electrochemical ImpedanceSpectroscopy (EIS). The results show that the coatings with the smallest roughness are coatingsdeposited at a current density of 2 A/dm2 from all of the solutions. The exception is solution 3 withthe relation [Mn2+]:[Zn2+]=1:2 where the roughness is at the lowest level in comparison to allsolutions, ranging from 0.71 to 0.875 μm, and the roughness is lowest at the current density of 4A/dm2 and is 0.71 μm. Based on electrochemical measurements, the corrosive most stable Zn-Mncoating is deposited at a current density of 2 A/dm2 from all the solutions and at the current densityof 4 A/dm2 from solution 3 with a ratio of [Mn2+]:[Zn2+]=1:2. This suggests that the corrosionstability is related directly to the roughness and compactness of Zn-Mn coatings. When it comes tocorrosion, the most stable coatings are those with the lowest roughness.Keywords: corrosion rate, electrodeposition, current density, roughness, electrochemicalimpedance spectroscopy.

Scientific paperReceived for Publication: 23. 06. 2014.Accepted for Publication:.19..09..2014.

A. S. FOUDA et al. SATIRN AS PESTICIDE INHIBITOR FOR THE CORROSION OF THE ...


Add El-Aziy S. FOUDA1, AYMAN Y. El-KHATEEB2, Scientific paperMOHAMED FAKIH3, ALY M. El-AZALY4 UDC:620.193.4

Satirn as pesticide inhibitor for the corrosion of the galvanizediron in wastewater and its biological effect on Escherichia coli

Satirn is a type of the pesticides has been evaluated as green inhibitor for the corrosion of thegalvanized iron in saline solution which was investigated by chemical and electrochemicalmeasurements. The results of polarization showed that satirn acts as mixed type inhibitor.Inhibition was found to increase with the increase of satirn concentration reaching toapproximately 90% at 250 ppm. The inhibitive action was discussed by the adsorption of a stablecomplex on the metal surface. The adsorption of satirn on the metal surface obeys Temkinadsorption isotherm. Satirn has a slightly effect on Escherichia Coli and can be applied safely insanitation plants.Keywords: corrosion inhibition, satirn, galvanized iron, saline solution.

1. INTRODUCTIONGalvanized iron is widely used in industries due

to its good mechanical property. The investigationof corrosion of galvanized iron is always a subjectof high theoretical as well as practical interest.Chloride and sulfide in aqueous media are parti-cularly aggressive and accelerate corrosion. Theuse of inhibitors is one of the most practical met-hods for protection against corrosion [1]. Amongnumerous inhibitors that have been tested andapplied industrially as corrosion inhibitors, thosethat are non-toxic or low-toxic are now far morestrategic than in the recent past. In the 21st century,the research in the field of green or eco-friendlycorrosion inhibitors has been addressed toward thegoal of using cheep, effective compounds at low orzero environmental impact. Plant extract is low-costand environmental safe, that which is the mainadvantage of it. Many synthetic compounds givegood anticorrosive activity, most of them are highlytoxic to both human beings and the environment[2], and they are often expensive and non-bio-degradable. Low-grade gram flour, natural honey,onion, potato, gelatin, plant roots, and flowersgums have been reported as good inhibitors.However, most of them have been tested on steeland nickel sheets. So the use of green inhibitorplay an important role in the corrosion of the me-tals, that it acts as an incredibly rich source ofnaturally synthesized chemical compounds that arebiodegradable in nature and can be extracted bysimple procedures with low cost [3].

Author's address: 1Department of Chemistry, Fa-culty of Science, El-Mansoura University, El-Man-soura-35516, Egypt, 2Department of Agric. Chemistry,Faculty of Agriculture, Mansoura University, Man-soura, Egypt, 3Lab manager in Talkha sanitationplant, water and waste water company, Dakahlia,Egypt, 4Nile Higher Institute for Engineering andTechnology, El-Mansoura, Egypt


Due to the chemical structure and chemical be-havior, an inorganic compound must be able to oxi-dize the metal, forming a passive layer on its surfa-ce. On the other hand, a molecule of an organiccompound must have the ability to act as a corro-sion inhibitor. Among these, the molecule may ha-ve a large structure, double bonds, an active centeror group, etc. These features give the moleculeability to cover a large area of a metal surface witha firmly attached film [4].

The aim of this work is to study: The effect ofusing satirn pesticide as a green corrosion inhibitorfor the galvanized iron in sulfide polluted salt waterusing different techniques and ii) The biologicaleffect of satirn pesticide on the activity ofEscherichia Coli.

2. EXPERIMENTAL2.1. Material composition of the sample

The material used is galvanized iron which pro-vided from Talkha sanitation plant, Egypt. The che-mical composition (weight %): 0.008% Si, 0.257%Mn, 1.942% Zn and the remainder is iron.

2.2. Preparation of the inhibitorStock solution of 1000 ppm satirn was prepa-

red by dissolving 2 ml of a liquid satirn from itsbottle of a concentration 50 % in 1 litter of bidistilledwater.

2.2.1Chemical structures of SatirnChemical structures of Satirn is given in the

following scheme:



2.3. Preparation of bacterial agriculture mediaSuspend 50 g of the medium in 1 litter of bidi-

stilled water and dissolve it by heating. Sterilize inautoclave at 121oC for 15 min. Cool to 45-50oC,mix well and dispense into plates. Allow the platesto solidify. The prepared medium should be at 8-15oC. The color is violet-red.

2.4. SolutionsThe aggressive solutions of 3.5 % NaCl and 16

ppm Na2S was prepared by dissolving the requiredamount of salts in bidistilled water. All chemicalswere analytical grade reagents. The experimentswere carried out under non-stirred and naturallyaerated conditions. The addition of the extract didnot change the pH of the aggressive media.

2.5. Electrochemical procedureFor electrochemical measurements, the sheets

were welded with Cu-wire for electrical connectionand mounted into glass tubes of appropriate dia-meter using Araldite to offer an active surface of (1cm2) geometric area to contact the test solution.Prior to each experiment, these sheets were firstabraded with different grades of emery papers (800to 1200 grades), washed with bidistilled water, deg-reased with absolute ethanol and then dried. Aconventional electrochemical cell of capacity 100ml was used containing three compartments forworking, platinum foil counter (1 cm2) and saturatedcalomel electrode (SCE) as reference electrode.The measurements were carried out in aeratednon-stirred 3.5% NaCl with 16 ppm sulfide in thepresence of various concentrations of the satirn, asenvironmentally-friendly corrosion inhibitor. Foreach run, a freshly prepared solution as well as acleaned set of electrodes was used. Each run wascarried out in aerated stagnant solutions at the re-quired temperature, using a water thermostat. Thepotentiodynamic polarization curves were carriedout at a scan rate of 1 mV s-1 starting from -1.7 Vup to -0.1 V (SCE). Before polarization, the opencircuit potential of the working electrode was mea-sured as a function of time during 30 min, the timenecessary to reach a quasi-stationary value for theopen-circuit potential. Impedance measurementswere carried out using AC signals of amplitude 5mV peak to peak at the open-circuit potential in the

frequency range 100 kHz and 0.2 Hz. All impedan-ce measurements were recorded at open circuitpotential (OCP) after immersion the electrode for30 minutes in the test solution. Electrochemicalfrequency modulation was carried out using twofrequencies 2 and 5 Hz. The base frequency was0.1 Hz, so the waveform repeats after 1s. TheIntermodulation spectra contain current responsesassigned for harmonical and intermodulation cur-rent peaks. The larger peaks were used to calcula-te the corrosion current density (icorr),the Tafel slo-pes (βc and βa) and the causality factors CF2&CF3[5,6].

All electrochemical experiments were carriedout using Potentiostat/Galvanostat/Zra analyzer(Gamry PCI300/4). A personal computer with DC105 software for polarization, EIS300 software forimpedance, EFM140 software for electrochemicalfrequency modulation and Echem Analyst 5.21 wasused for data fitting and calculating.

3. RESULTS AND DISCUSSION

3.1. Weight loss measurementsThe used inhibitor was tested by six different

concentrations and their corresponding corrosionrate with % protection efficiency (% IE) data at dif-ferent temperature (25- 40oC) are presented inTable 1. In figure1 give the weight loss-time curvesfor the corrosion of galvanized iron in 3.5% NaCland 16 ppm Na2S solutions in the absence andpresence of satirn at 25-40oC. From the experimen-tal data of the weight loss measurements, the % IEwas calculated from Eq. (1):

% IE = 100[1-W2/W1] (1)

where W1 and W2 are the weight losses in theabsence and presence of satirn, respectively. FromTable 1 we found by increasing the concentrationof the satirn the % IE increases, and by raising thetemperature the value of % IE decreases [7]. Thisbehavior can be attributed to the increase of thesurface coverage due to the physical adsorption ofsatirn on the metal surface. The results show thegreat effect of satirn on the corrosion of the gal-vanized iron in 3.5% NaCl and 16 ppm Na2S (250ppm yield 90.7 % IE).

Table 1- Effect of satirn concentrations on weight loss (mg cm-2) and inhibition efficiency (% IE) ofgalvanized iron in sulfide polluted salt water at different temperatures

25oC 30oC 35oC 40oCConc.ppm Weight loss

mg cm-2 % IE Weight lossmg cm-2 % IE Weight loss

mg cm-2 % IE Weight lossmg cm-2 % IE

Blank 0.70710 ------ 0.73230 ------- 0.77020 -------- 0.833330 --------50 0.34520 51.2 0.44050 39.9 0.50000 35.1 0.64630 22.4

100 0.20980 70.3 0.34920 52.3 0.39680 48.5 0.51190 38.6150 0.16990 76.0 0.27710 62.2 0.32900 57.3 0.40040 52.0200 0.12910 81.7 0.19630 73.2 0.25000 67.5 0.31920 61.7250 0.06920 90.2 0.13950 81.0 0.16940 78.0 0.20970 74.8



Figure 1 - Weight loss-time curves for the corrosion of the galvanized iron in sulfide pollutedsalt water in absence and presence of satirn at temperatures 30oC

3.1.1- Effect of TemperatureThe temperature effect on the corrosion para-

meters of the galvanized iron with the addition ofsatirn was studied using weight loss technique.According to the data of the Table 1, the corrosionrate of the galvanized iron increases with the incre-ase of the temperature, the inhibition efficiency ofsatirn decreased Fig. 2. This suggested to thepossibility of the desorption of the desorbed inhi-bitor molecules on the metal surface with the incre-ase of the temperature. This behavior shows thatthe addition of the inhibitor is physically on the me-tal surface. Arrhenius-type dependence is a rela-

tion between corrosion rate and temperature like inEq. (2):

k = A e (- E* a/RT) (2)

where k is the corrosion rate, E*a is the apparent

activation energy, R is the universal gas constant,T is the absolute temperature, and A is the frequ-ency factor. Fig.3 is Arrhenius plot (log k againstthe reciprocal of temperature (1/T)) for the galva-nized iron in 3.5% NaCl and 16ppm Na2S in abse-nce and presence of different concentrations ofSatirn. Straight lines of high correlation coefficientswere obtained.

Figure 2 - The effect of inhibitor concentration and temperature on the inhibition efficiency of satirn

The values of activation energy, Ea* were 8.50,

55.49 k J mol-1 for the blank and in the presence ofSatirn, respectively. The increase in the activationenergy is directly proportional to satirn concentra-tion, indicating that the energy barrier for the corro-sion process is also increased [8]. An alternativeformulation of Arrhenius equation is [9]:

k = RT/Nh exp (ΔS*/R) exp (−ΔH*/RT) (3)

where h is the Planck’s constant and N is the Avo-gadro’s number. Fig. 4 shows a plot of log k/T as a

function of 1/T for galvanized iron. Straight lineswere obtained with a slope of −ΔH*/R and an inter-cept of ln R/Nh + ΔS*/R from which the values ofΔH* and ΔS* were calculated for the blank andSatirn. The values of the activation enthalpy, ΔH*

were 7.1 and 33.5 kJ mol−1 and the values of theactivation entropy, ΔS* were −135.1 −, 272.5 Jmol−1K−1 for the blank and satirn, respectively. Itknown that values of ΔH* lower than 41.9 kJ mol−1

indicative of physical adsorption [10]. The increasein the activation enthalpy (ΔH*) in presence of theinhibitors means that the addition of the satirn to



3.5% NaCl and 16 ppm Na2S solution increasesthe height of the energy barrier of the corrosion re-action to the inhibitor depends on the concentrationof satirn. The adsorption of satirn molecules on themetal surface leads to a lower number of hydrogen

atoms adsorbed on it; this will cause a decrease inhydrogen evolution rate rather than the rate ofmetal dissolution, because of the blocking of thesurface of the metal by the inhibitor molecules.

Figure 3 - Arrhenius plots for the corrosion rate of the galvanized iron in sulfide pollutedsalt water in absence and presence of satirn at different temperatures

Figure 4 - Log (k/T) versus 1/T for the galvanized iron in sulfide polluted salt water in absenceand presence of satirn at different temperature

3.1.2- Adsorption isothermBasic information on the interaction between

the inhibitor and the galvanized iron can be provi-ded by the adsorption isotherm. The adsorption ofthe inhibitors can be described by two main typesof interaction: physical adsorption and chemisorp-tions [11-15]. These are influenced by the chemicalstructure of the inhibitor, the type of the electrolyte,and the charge and nature of the metal. The surfa-ce coverage Ɵ of the metal surface by the adsor-bed inhibitor was calculated assuming no changein mechanism of the cathodic reaction using theequation:

Ɵ = [1-(W2/W1)] (4)where ib corr and ii corr are the current densities in thepresence and absence of the inhibitor. The Ɵ va-

lues for different inhibitor concentrations at differenttemperatures were tested by fitting to various iso-therms. By far the best fit was obtained with theTemkin isotherm. Temkin isotherm:

a Ɵ = ln Kads C (5)where a is heterogeneity factor, C is the concentra-tion of the inhibitor, and Kads is the adsorption equi-librium constant, which is related to the standardfree energy of adsorption (ΔGo

ads ) by the equation:Kads = (1/ 55.5) exp (-ΔGoads / RT) (6)

where 55.5 is the concentration of water in mol/L atmetal solution interface. The plot of surface covera-ge (Ɵ) as a function of logarithm of satirn concen-tration at the studied temperatures is shown inFig.5.



Figure 5 - Temkin adsorption isotherm for satirn at different temperatures for the galvanizediron in sulfide polluted salt water

From the plot, straight lines were obtained forsatirn indicating that the experimental data fit wellinto Temkin adsorption isotherm at all studied tem-peratures. The Temkin isotherm characterizes thechemisorptions of uncharged molecules on hetero-geneous surface [16]. The values of Kads decreasewith increasing temperature, suggesting that theinhibitor is physically adsorbed on the galvanizediron surface. Generally, Kads denotes the strengthbetween adsorbate and adsorbent. The ΔGºads va-lues were calculated from this plot were negativethis mean spontaneous adsorption of the inhibitormolecules on the surface of the galvanized iron.The heat of adsorption (ΔHºads) can be calculatedaccording to the Vant Hoff’s:

log Kads = (−ΔHoads/2.303 RT) + constant (7)

In order to calculate heat of adsorption (ΔHºads),log Kads was plotted against 1000/T Fig.6. Astraight line was obtained. The absolute values of

ΔHºads obtained in this study was lower than 100 kJmol−1, this indicative of physisorption, and thissupport the above mechanism of adsorption. Thenegative value of ΔHo

ads (−46.1 kJ mol−1) in thepresence of the inhibitor reflects the exothermicnature of galvanized iron dissolution process. It isclear that the activation enthalpy vary in the samemanner as the activation energies, supporting theproposed inhibition mechanism. According to thebasic equation:

ΔGoads = ΔHo

ads – TΔSoads (8)

The entropy of adsorption, ΔSoads was calcula-

ted. Large and negative values of entropies implythat the activated complex in the rate determiningstep represents an association rather than disso-ciation step, meaning that a decrease in disorde-ring takes place on going from reactant to theactivated complex.

Figure 6 - Log Kads vs 1000/T for the corrosion of the galvanized iron in presence of satirn



3.2. Polarization measurementsPotentiodynamic anodic and cathodic polariza-

tion were carried out at 25oC in 3.5% NaCl and 16ppm Na2S in the absence and presence of differentconcentrations of the inhibitor are shown in Fig.7.

From the figure, both anodic and cathodic currentswere inhibited by the increase of the inhibitor con-centration. From this result the addition of the inhi-bitor decreases the metal dissolution at the anodeand the hydrogen evolution reaction at the cathode.

Figure 7 - Potentiodynamic polarization curves for the corrosion of the galvanized iron in sulfide pollutedsalt water in the absence and presence of different concentrations of satirn at 25oC

Table 2 shows the values the corrosion poten-tial Ecorr, corrosion current density icorr, Tafel slopes(βa and βc), and the inhibition efficiency for thecorrosion of galvanized iron with different concen-

tration of the inhibitor. The values of icorr were esti-mated by Tafel extrapolation of cathodic and ano-dic curves to open circuit corrosion potential.

Table 2 - The effect of concentration of satirn on the electrochemical parameters calculated by usingpotentiodynamic technique for corrosion of galvanized iron in sulfide polluted salt water at 25oC

Conc.,ppm

Ecorr, V vsSCE

icorr, µAcm-2

-βc,mV dec-1

βa,mV dec-1

C.Rmm y-1 Ɵ % IE

blank 1.056 11470 265 209 133.19 ------ -----

50 1.084 3622 254 188 42.06 0.684 68.4100 1.146 2109 247 176 24.48 0.816 81.6150 1.152 1718 240 154 19.94 0.850 85.0200 1.124 1516 233 131 17.60 0.868 86.8250 1.104 1069 229 128 12.41 0.907 90.7

From this table, it can be concluded that: The icorr values decrease with the increase of

the inhibitor concentration. The change in βa from 278 – 248 mV dec-1 with

the increase in inhibitor concentration indi-cating that the dissolution of the galvanizediron is kinetics in nature.

The change in βc from 241 – 210 mV dec-1 withthe increase in inhibitor concentration indica-ting to the hydrogen evolution reaction [17].

The values of inhibitor efficiency increase withthe increase of the inhibitor concentration reac-hing to a maximum value 90.7 % at 250 ppm

Satirn is a mixed type inhibitor.The values of inhibition efficiency percentage

%IE and the degree of surface coverage Ɵ at eachconcentration was calculated using the equation[18, 19]:

% IE = Ɵ × 100 = [1 – (icorr(inh) /icorr)] × 100 (9)



where icorr and icorr(inh) are the corrosion current den-sities of uninhibited and inhibited solution, respec-tively.

An inspection of the results obtained fromTable 2 reveals that, by increasing the inhibitorconcentration, the cathodic and anodic current den-sities decrease by decreasing the metal dissolutionat the cathode and the hydrogen evolution at theanode which appears from the table that βc > βa,this is due to presence of donor atoms of theoxygen, electron clouds of the benzene rings, andalso the bulky group of the inhibitor making strikehindrance at the metal surface for the reach of thecorrosive media to the metal surface.

3.3. Electrochemical impedance spectroscopy(EIS) measurements

Figure 7 shows the Nyquist plot of galvanizediron in 3.5% NaCl and 16 ppm Na2S in the absenceand presence of different concentrations of investi-gated compound was investigated by EIS methodat 25oC after 30 min immersion. All the impedancespectra were measured at the corresponding open-circuit potentials. The charge-transfer resistance(Rct) values were calculated from the difference in

impedance at lower and higher frequencies, assuggested [20]. The double-layer capacitance (Cdl)and the frequency at which the imaginary compo-nent of the impedance is maximal (-Zmax) are foundas represented in the following equation:

tmaxdl Rf2

1C

(10)

where fmax is maximum frequency at which theimaginary component of the impedance (Zim) ismaximum at Rct is diameter of the loop. Nyquistplots for the galvanized iron in 3.5% NaCl and 16ppm Na2S at various concentration of satirn is pre-sented in Fig.8. Table 3 gives values of chargetransfer resistance, Rct double-layer capacitance,Cdl, and fmax derived from Nyquist plots and inhi-bition efficiency, the inhibition efficiency got fromthe charge-transfer resistance is calculated by thefollowing relation:

% IEct = [ 1- (R'ct/Rct )] x 100 (11)

Rct and R`ct are the charge-transfer resistancevalues without and with inhibitor, respectively.

Figure 8 - Nyquist plots recorded for the galvanized iron in sulfide polluted salt water in the absence andpresence of different concentrations of satirn at 25oC

From Fig. 8 the impedance spectra exhibit onesingle depressed semicircle, and the diameters ofsemicircle increase with the inhibitor concentration.The single semicircle explains that the inhibitiontakes place by the diffusion of the charge transferon the metal surface. Table 3 shows that Rct valuesincrease with inhibitor concentration and conse-quently the inhibition efficiency increase to 89.3%

at 250 ppm. The decrease in Cdl is due to adsor-ption of inhibitor molecules by diffusion on themetal surface through the pure geometric blockingof the electrode surface. The linear decrease of Cdlwith the surface coverage means that the capa-citance contribution from the inhibitor-covered sur-face is solely due to the flat-adsorbed molecules atlow surface coverage [21].



Table 3 - Electrochemical kinetic parameters obtained by EIS technique for the corrosion of galvanizediron using satirn as inhibitor in sulfide polluted salt water at 25oC

Conc.,ppm

Rs

Ω cm2Cdl

µΩ-1 cm-2 n Rt

Ω cm2 θ % IE

blank 1.294 605.5 0.886 268 ---- ----50 1.210 581.4 0.873 800 0.665 66.5

100 1.174 452.3 0.858 1300 0.794 79.4150 1.124 423.6 0.874 1600 0.833 83.3200 1.155 374.5 0.841 1830 0.854 85.4250 1.143 352.3 0.839 2290 0.883 88.3

3.3. Electrochemical frequency modulation (EFM)measurements

Intermodulation spectra obtained from EFMmeasurements are presented in Fig. (9a-b) asexamples of galvanized iron in absence andpresence of 250 ppm satrin as a pesticide inhibitor

at 25˚C. Each spectrum is a current response as afunction of frequency. The two large peaks are theresponse to the 2 Hz and 5Hz excitationfrequencies. These peaks are used by the EFM140 software package to calculate the corrosioncurrent and Tafel constants.

a)

b)

Figure 9 a, b - Intermodulation spectrum for the galvanized iron in in sulfide polluted salt water in theabsence and presence of 250 ppm of satirn at 25oC

The calculated corrosion kinetic parameters atdifferent concentrations of the inhibitor in 3.5%NaCl and 16 ppm Na2S containing different con-

centrations of inhibitor at 25°C (icorr, βa, βc, CF-2,CF-3 and % IE) are given in Table 4.



Table 4 - Electrochemical Kinetic parameters obtained by EFM technique for galvanized iron in 3.5%NaCl+16 ppm Na2S alone and with different concentrations of satirn at 25 oC

% IE Ө C.R,mmY-1 CF-3 CF-2 βc,

mV dec-1βa,

mV dec-1icorr.,

µA cm-2 Conc., ppm

------ ------ 140.31 2.85 1.85 241 278 13540 blank

67.38 0.6738 43.77 2.70 1.77 238 273 4417 50

80.76 0.8076 27.00 2.64 1.82 232 267 2605 100

84.66 0.8466 21.52 2.76 1.88 228 262 2077 150

86.12 0.8612 19.47 2.88 1.83 218 253 1879 200

89.81 0.8981 14.30 2.91 1.76 210 248 1380 250

The corrosion current densities obtained fromTable 4 are decreasing by increasing the concen-tration of the inhibitor and hence the inhibitionefficiencies increase. The causality factors inTables 4 are very close to theoretical values whichaccording to EFM theory should guarantee thevalidity of Tafel slope and corrosion current den-sities. Values of causality factors in Table 4 indi-cate that the measured data are of good quality[22]. The standard values for CF-2 and CF-3 are2.0 and 3.0, respectively. The obtained results sho-wed good agreement of inhibition efficiency obtai-ned from the potentiodynamic polarization, EIS andEFM methods.

3.4. Biological effect of satirn on escherichia coliFrom the bacterial agriculture of escherichia

coli in absence and presence of satirn pesticideinhibitor, we found a small effect on the bacterial

activity of escherichia coli according to Table 5 andFig. 10, which can be controlled by increasing therecycle life of the bacteria in the station. Satirn hasoxygen donor atom attached with the proteins andlipids on the bacterial tissues having a little activityfor it. So this inhibitor has no toxicity on the bacte-rial activity, and can be applied safety on the sani-tation plants without any problems in the treatingoperations.

Table 5 - Results obtained from the plate counterfor bacterial agriculture

CFU (mean) CFU (R2) CFU (R1) Samples

92 x 104 95 x 104 89 x 104 Control

83 x 104 85 x 104 83 x 104 satirn

Blank The bacterial agriculture in presence of 250 ppm of satirn

Figure 10 - The bacterial agriculture in absence and presence of satirn

3.5. Mechanism of corrosion inhibitionThe isotherm of Fig.5 characterizes the sponta-

neous physisorption of phytochemical composition(2.2.1) of satirn on heterogeneous surface [23]. Sothe mechanism of inhibition of the galvanized ironin 3.5% NaCl and 16 ppm Na2S by the phytoche-mical compounds of satirn explained basically onthe adsorption on the metal surface[24] due to thepresence of the phytochemical constituents. Theadsorption of the inhibitor molecules on the metal

surface is due to the donor – acceptor interactionbetween π electrons of donor atoms O and aroma-tic rings of inhibitor and the acceptor, i.e., vacant dorbital of iron surface atoms [25]. The inhibitormolecules also can be adsorbed in the form of ne-gatively charged species on the metal surfacewhich can interact electrostatically with positivelycharged metal surface, leading to increase thesurface coverage and consequently protect effici-ency even in case of low Satirn concentration.



4. CONCLUSIONSAccording to the obtained results, the following

conclusions can be drawn:The satirn pesticide acts as an inhibitor for the

corrosion of the galvanized iron in sulfide pollutedsalt water. The inhibition efficiency increases withincrease in the concentration of satirn. The inhibi-tion is due to the adsorption of the inhibitor mole-cule on the metal surface by charge transfer or bythe diffusion of the inhibitor molecules. The adsor-ption of satirn on the metal surface follows Temkinadsorption isotherm. Values of Tafel constant (βaand βc) confirm that the inhibitor is a mixed type.Increase in Rp and Rct values and decrease in icorrand Cdl values confirm that satirn is adsorbed onthe carbon steel surface and inhibition process isfollowed by monolayer adsorption. The inhibitionefficiencies determined by different electrochemicalmethods are in reasonable good agreement. Thusthe satirn was proved to be an effective and lowcost inhibitor. This inhibitor has no effect on thebiological activity of Escherichia Coli, and can beapplying safety on sanitation plants.

REFERENCE[1] G. Trabanelli (1991) Inhibitors an old remedy for a

new challenge, Corrosion, 47,pp. 410-419.

[2] Ostovari A., Hoseinieh S.M., Peikari M., ShadizadehS.R., Hashemi S.J., (2009), Corrosion inhibition ofmild steel in 1 M HCl solution by henna extract: Acomparative study of the inhibition by henna and itsconstituents (Lawsone, Gallic acid, α-d-Glucose andTannic acid), Corros.Sci., 51, pp. 1935-1949

[3] Abiola O.K., Otaigbe J.O.E., Kio O.J., (2009)Gossipium hirsutum L. extracts as green corrosioninhibitor for aluminum in NaOH solution, Corros.Sci., 51, pp. 1879-1881

[4] Muller B., (2002), Corrosion inhibition of aluminumand zinc pigments by saccharides, Corros. Sci., 44,pp. 1583-1591

[5] Abdel-Rehim S.S., Khaled K.F., Abd-Elshafi N.S.,(2006), Electrochemical frequency modulation as anew technique for monitoring corrosion inhibition ofiron in acid media by new thiourea derivative,Electrochim. Acta, 51, pp. 3269-3277

[6] Bosch R. W., Hubrecht J., Bogaerts W. F., SyrettB.C., (2001), Electrochemical Frequency Modula-tion: A New Electrochemical Technique for OnlineCorrosion Monitoring Corrosion, 57, pp. 60-70

[7] Bentiss F, Traisnel M, Chaibi N, Mernari B, Vezin H,Lagrenee M., (2002), 2,5- Bis(n-methoxyphenyl)-1,3,4-oxadiazoles used as corrosion inhibitors in

acidic media: correlation between inhibition effi-ciency and chemical structure, Corros. Sci., 44, pp.2271-2289

[8] Popova, A.; Sokolova, E.; Raicheva, S.; Christov,M., (2003), AC and DC study of the temperatureeffect on mild steel corrosion in acid media in thepresence of benzimidazole derivatives, Corros. Sci.,45, pp. 33-58

[9] Fouda, A. S.; Al-Sarawy, A. A.; Ahmed, F.S.; El-Addasy H. M., (2009), Corrosion inhibition of alu-minum 6063 using some pharmaceutical com-pounds, Corros. Sci., 51, pp. 485-492

[10] Umoren, S. A.; Eduok, U. M.; Solomon, M. M.;Udoh, A. P. (2013) Corrosion inhibition by leavesand stem extracts of Sida acuta for mild steel in 1 MH2SO4 Solutions investigated by chemical andspectroscopic technique, Arabian Journal ofChemistry , in press

[11] Larabi L., Benali O., Harek Y., (2006), CorrosionInhibition of Copper in 1 M HNO3 solution by N-Phenyl Oxalic Dihydrazide and Oxalic N-Phe-nylhydrazide N’-Phenylthiosemicarbazide, Port.Electrochim. Acta, 24, pp. 337-346

[12] Larabbi L., Harek Y., Traisnel M., Mansri A., (2004),Synergistic Influence of Poly(4-Vinylpyridine) andPotassium Iodide on Inhibition of Corrosion of MildSteel in 1M HCl, J. Appl. Electrochem., 34, pp. 833-839

[13] Benali O., Ouazene M., (2011), Inhibition of coldrolled steel corrosion in sulphuric acid solution by 2-mercapto-1-methylimidazole: Time and temperatureeffects treatments, Arab. J. Chem. 4, pp. 443-448

[14] Larabi L., Benali O., Harek Y., (2007), Corrosioninhibition of cold rolled steel in 1 M HClO4 solutionsby N-naphtyl N′-phenylthiourea, Mater. Lett. 61, pp.3287-3291

[15] Larabi L., Harek Y., Benali O., Ghalem S., (2005),Hydrazide derivatives as corrosion inhibitors for mildsteel in 1 M HCl, Prog. Org. Coat. 54, pp. 256 - 262

[16] Fouda A.S., Megahed H.E., Younis T., Abd El-Salam Sh., (2014), Corrosion control of steel in HClsolutions by cyanoacetamide derivatives, Protectionof Metals and Physical Chemistry of Surfaces,50(2), pp.254-265

[17] Benali O., Larabi L., mekelleche S.M., Harek y.,(2006), Influence of substitution of phenyl group bynaphthyl in a diphenylthiourea molecule oncorrosion inhibition of cold-rolled steel in 0.5 MH2SO4, J. Mater. Sci. 41, pp. 7064-7073

[18] Ammar, I. A.; Darwish, S. (1967), Effect of someions on inhibition of the acid corrosion of fe bythiourea, Corros. Sci., 7, pp. 579-596



[19] Fisher, H. Ann. Univ. Ferrera. Sez. 3 (suppl. 3)(1960)1.

[20] Tsuru, T., Haruyama, S., Gijutsu, B. J., (1978),Inhibition effect of 3- pyridinecarboxaldehydethiosemicarbazone (META) on the mild steel corro-sion in one Jpn. Soc. Corros. Eng., 27, pp.573-579

[21] Martiez, S., Metikos-Hukovic, M., (2003), Anonlinear kinetic model introduced for the corrosioninhibitive properties of some organic inhibitors,J.Appl. Electrochem. 33, pp. 1137-1142

[22] Ramachandran S., Blanco M., Chen H., Tang W. A.,(1996), Self-Assembled Monolayer Mechanism forCorrosion Inhibition of Iron by Imidazolines,Langmuir, 12, pp. 6419-6428

[23] Oguzi E.E., (2007), Corrosion inhibition of aluminumin acidic and alkaline media by Sansevieriatrifasciata extract, Corros. Sci., 49, pp. 1527-1539

[24] Larabi L., Benali O., M.Mekelleche S.,Harek Y.,(2006), 2-Mercapto-1- methylimidazole as corrosioninhibitor for copper in hydrochloric acid J. Appl.Surf.Sci., 253, pp.1371-1378

[25] Lagrenee M., Mernari B., Bouanis B., Traisnel M.,Bentiss F., (2002), Study of the mechanism andinhibiting efficiency of 3,5-bis(4-methylthiophenyl)-4H - 1,2,4- triazole on mild steel corrosion in acidicmedia, Corros. Sci., 44, pp. 573-588

IZVOD

SATIRN KAO PESTICID INHIBITOR ZA KOROZIJU POCINKOVANOG GVOŽĐA UOTPADNIM VODAMA I NJEGOV BIOLOŠKI EFEKAT NA ESCHERICHIA COLI

Satirn je vrsta pesticida koji je ocenjen kao zeleni inhibitora za koroziju na pocinkovanom gvožđuu slanim rastvorima, što je istraživano hemijskim i elektrohemijskim merenjima. Rezultatipolarizacije pokazali su da satirn deluje kao tip mešovitog inhibitora. Ispitivanjima je pronađeno daraste inhibitorno dejstvo sa povećanjem koncentracije satirna do približno 90% na 250 ppm.Navedenim ispitivanjima je razmatrana adsorpcija stabilnih kompleksa na površini metala.Adsorpcija satirn na površini metala povinuje se Temkinovoj adsorpcijonoj izotermi. Satirn imablagi uticati na Escherichia coli i može se bezbedno primeniti kod sanitarnih biljka.Ključne reči: inhibitori korozije, Satirn, pocinkovano gvožđe , slani rastvor


Ž. STOJANOVIĆ i dr. POVEĆANJE EFIKASNOSTI ALATA ZA KOVANJE TOYOTA ...


ŽELJKO STOJANOVIĆ1, SPASOJE ERIĆ2 Originalni naučni radSANJA STANISAVLJEV3, MIĆA ĐURĐEV4 UDC:621.733.075

Povećanje efikasnosti alata za kovanje Toyota difuzionim postupkom

U radu je dat pregled literaturnih podataka o istraživanjima uticaja sloja vanadijum karbidadeponovanog Toyota difuzionim postupkom na povećanje radnog veka i kvaliteta alata za obradukovanjem. Kalupi za kovanje podvrgnuti su teškom adhezivnom i abrazivnom habanju, visokimnaponima i temperaturama. Površina kalupa i region u blizini površine podvrgnuti su najtežimuslovima tokom obrade kovanjem i s toga većina defekata i uzroka destrukcije potiču iz ovogregiona. Zbog toga, rad uzima u razmatranje i različite komplikovane mehanizme habanja idestrukcije površine alata za obradu kovanjem, odnosno onu mrežu različitih aspekata koji utičuna vek trajanja alata a koji svojim delovanjem prouzrokuju prevremeno uklanjanje alata izupotrebe.Ključne reči: vanadijum karbid, kalup za kovanje, vek trajanja, habanje, destrukcija.

1. UVODRazvoj industrije kovanja značajno je uslovljen

razvojem auto industrije, koja ugrađuje velike količi-ne delova dobijenih ovom tehnologijom. Proizvod-nja otkivaka najveća je u Evropi, Japanu i SevernojAmerici, a uposlednje vreme velike količine otkiva-ka se proizvode u Kini, Koreji i Indiji. Kovanjem setakođe, dobijaju delovikoji nalaze primenu u mno-gim drugim granama industrije. Prema podacimaJapan Forging Association industrija otkivaka u Ja-panu i dalje će biti jedna od vodećih industrijskihgrana koja će biti orijentisana na proizvodnju kom-pleksnih, preciznih i visokokvalitetnih delova [1].

Sa razvojem nauke i tehnologije i povećanjemžestoke konkurencije na tržištu, performanse kalu-pa postaju sve zahtevnije a pitanje veka trajanjapostaje sve izraženije [2]. Kalup je jedan od značaj-nijih delova opreme u masovnoj proizvodnji čiji jekvalitet ključni faktor koji utiče na kvalitet proizvodai na ekonomske koristi za kompanije. Jedan od gla-vnih problema su loša svojstva površine kalupa kaoposledica destrukcije habanjem. Pitanje veka traja-nja kalupa je složeno usled velikog broja faktorakoji mogu uticati na vek trajanja kalupa. Habanjekalupa je kompleksna, vremenski zavisna pojavakoja pre svega zavisi od četiri komponente siste-ma: kalupa, međusklopa, predmeta obrade i uslovaobrade. Učinak ove četiri komponente može se ka-tegorizovati u više procesa – vezanih razmatranja,uključujući dizajn kalupa, materijal kalupa, termičkuobradu, podmazivanje, po-vršinsku obradu i usloveobrade.

Adrese autora:1Partizanska 34/e, 23208 Elemir,2Visoka tehnička škola strukovnih studija, Zrenjanin,3Tehnički fakultet „M. Pupin“, Zrenjanin, 4Fakultettehničkih nauka, Novi Sad

Primljeno za publikovanje: 11. 08. 2014.Dorađeno za publikovanje: 02. 10. 2014.Prihvaćeno za publikovanje: 19. 11. 2014.

Kalup nameće geometriju deformisanom mate-rijalu. Dizajn kalupnih šupljina (gravura) upravljakliznim brzinama, temperaturom i pritiscima međusklopa. Posebno važna razmatranja sa stanovištahabanja i destrukcije su radijusi uglova (ćoškova) izaobljenja u šupljinama kalupa. Još jedno važnorazmatranje za habanje su mikro i makrostrukturneosobine materijala kalupa, njegov sastav, mikro-struktura (jednakost, unutrašnji nedostaci i seku-ndarni karbidi) i mehaničke i fizičke osobine. Me-hanička i hemijska interakcija materijala kalupa saradnim predmetom i kontaminirajućim materijama(podmazivanje, krhotine i ljuske) zavisi od sastava imikrostrukture [3].

Mehanička svojstva i vek trajanja kalupa možese u velikoj meri poboljšati odgovarajućom tehni-kom površinskog ojačavanja. S toga tehnika po-vršinskog ojačavanja igra veoma važnu ulogu u in-dustriji kalupa i privlači široku pažnju. Neophodnoje pronaći naprednu tehnologiju površinske modi-fikacije kako bi se poboljšao vek kalupa i smanjiotrošak ili povećala produktivnost [4]. Nedavno uvo-đenje slojeva vanadijum karbida koji su metalurškivezani za površinu alata za kovanje obezbedilo jeproizvođačima sredstvo za sticanje značajnih ušte-da usled poboljšanja performansi alata [5].

Poštujući napred navedeno, autori su postaviliciljeve ovog rada.Teoretski cilj ovog rada je suš-tinski doprinos boljem razumevanju različitih aspe-kata koji utiču na vek trajanja alata kroz objektivno,detaljno, svestrano i potpuno klasifikova-nje,opisivanje i analiziranje rezultata dosadašnjih istra-živanja, kao i sumiranje i analiza prethodnih isku-stava koja su afirmisala ovaj metod kao recept zapovećanje radnog veka i kvaliteta alata. Praktičnicilj ovog rada bio bi popularizacija metode, saciljem proširenja njene primene u domaćoj industrijikovanja radi proizvodnje fabrikata visokog kvaliteta.



2. MEHANIZMI I MODELI HABANJA IDESTRUKCIJE KALUPA

2.1. Razlozi za uklanjanje alata iz upotrebeHabanje materijala javlja se pomoću mnogih

različitih mehanizama. Terminologija korišćena zaopisivanje ovih mehanizama zavisi od polja prime-ne. Neki od mehanizama habanja identifikovanih uhabanju i destrukciji kalupa su: adhezivno habanje,abrazivno habanje, toplotni zamor, mehanički za-mor, plastična deformacija i velike naprsline (kata-strofalna destrukcija) [3]. U zavisnosti od vrste

obrade plastičnom deformacijom, različite su i uče-stalosti oštećenja alata i nastali troškovi. Zbog vi-sokih opterećenja, prelom je glavni razlog destruk-cije alata u hladnom kovanju. Toplotno opterećenjei kontakt sa vrućim metalom tokom obradedeformisanjem čini habanje najčešćim razlogom zadestrukciju u toplom kovanju. Abrazivno habanje,mehanički zamor, plastična deformacija i toplotnizamor zajednički su većini procesa oblikovanja,slika 1 [3]. Tipični vidovi destrukcije i lokacije nakalupima za kovanje, prikazani su na slici 2 [6].

Slika 1 - Učestanost i lokacija tipičnih destrukcija kalupa tokom kovanja

Slika 2 - Uobičajeni mehanizmi destrukcije zakovačke kalupe. 1, abrazivno habanje; 2, toplotni

zamor; 3, mehanički zamor; 4, plastična deformacija

2.2. Habanje delova kalupaShodno ranijim navodima u ovom radu, u po-

glavlju o razlozima za uklanjanje alata iz upotrebe,kao jedna od glavnih vrsta oštećenja površine kalu-pa uočava se habanje. To je glavni razlog za povla-

čenje alata korišćenih u toplim obradama plasti-čnom deformacijom jer ima veliki uticaj na tolera-ncije i kvalitet površine obrađenog dela a time i naradni vek alata. [7] Generalno je prihvaćeno da jeova pojava veoma komplikovana i da su uključenibrojni mehanizmi i faktori. Stvarni mehanizam kojiizaziva trenje u kontaktnom međusklopu izmeđualata i predmeta obrade razumljiv je samo na osno-vu klasične fizike. Fizički pristup pruža efikasnuosnovu za industrijsko istraživanje. Ovo je poka-zalo da se habanje odvija uprkos visokom stepenutvrdoće. Iako priroda habanja i dalje krije mnogonejasnih aspekata, industrijsko istraživanje jeutvrdilo kako se usled habanja dimenzije i kvalitetpovršine menjaju tokom operacije oblikovanja. Utoplom kovanju, mehanizam adhezivnog habanjamože biti dominantan usled lokalne veze izmeđukalupa i predmeta obrade. Adhezivno habanje jeprouzrokovano adhezivnim silama na spoju izme-đu kontakta površine kalupa i materijala koji seobrađuje. [8]Abrazivno habanje šupljina kalupa senajviše vidi u onim delovima kalupa, gde postojinajveće kretanje materijala tokom kovanja.



2.3. Toplotni i mehanički zamorNaprsline usled toplotnog zamora su glavni na-

čin destrukcije i propadanja alatnog čelika za rad utoplom stanju koji se koristi za izradu kalupa a onese obično javljaju u različitim stepenima zajedno saabrazivnim habanjem u kalupima za kovanje utoplom stanju. Toplotni zamor nastaje usled kova-nja u toplom stanju zbog razlike temperatura izme-đu kalupa i zagrejanog metala. Periodični pritisni izatezni naponi tokom proizvodnje rezultuju toplo-tnim zamorom. Najvažniji faktor u toplotnom za-moru je opseg (amplituda) izduženja tokom ciklusaoblikovanja.

Mehanički zamor kalupa za oblikovanje je poduticajem primenjenih opterećenja, prosečne tempe-rature kalupa i stanja površine kalupa. Zamornenaprsline otpočinju na lokacijama koncentracijenapona (šupljine, ćoškovi, zaobljenja) ili pojavamakao što su rupe, prostori za žleb i oznake u vidudubokog otiska na kalupima. Dominantna vrstazamora koja se nalazi u kalupima za oblikovanjemetala je nisko ciklični zamor, koji je povezan savisokim naponom i temperaturom. Nisko cikličnizamor je definisan kao mehaničko zamorno propa-danje koje se javlja posle manje od 1000 ciklusanapona [3].

2.4. Plastična deformacijaPlastična deformacija u kalupima proizilazi od

prekomernog pritiska i niskog vrućeg napona teče-nja materijala kalupa. Može biti smanjena rediza-jnom šupljina i pravilnim izborom materijala kalu-pa. Hlađenje kalupa takođe smanjuje ove uticaje,ali se mora voditi računa da se izbegnu temperatu-rni ciklusi što može izazvati fazne transformacije.

2.5. Velike naprsline i lom kalupaVelike naprsline ili katastrofalna destrukcija

kalupa je ograničavajući uslov sa aspekta radnogveka kalupa. Propadanje se javlja brzo (u nekolikociklusa) zbog primenjenog visokog napona ili niskežilavosti materijala kalupa. Kao i u slučaju meha-ničkog zamora, visoki naponi mogu biti rezultat lo-šeg dizajna kalupa, nepravilnog naleganja, iskaka-nja dela opreme ili umetka kalupa ili nedostatakkontrole opterećenja i energije pri kovanju. Nepra-vilni izbor materijala kalupa može takođe da dove-de do katastrofičnih destrukcija. Kalupi za teškoobradive materijale ili u kojima postoje tačke savisokom koncentracijom napona zahtevaju čeli-kesa dobrom lomnom žilavošću. Ovi čelici uključujuniskolegirane čelike (kao što su 6F3 i 6F7) i nekehromne čelike za rad u toplom stanju (kao što jeH11). Kada se koriste visokolegirani čelici (kao štosu H19 i H21, npr. zbog njihove otpornosti premahabanju) oni bi trebalo da budu otpuštani natvrdoćunižu od normalne sa ciljem povećanja žilavosti akosu kalupi osetljivi na katastrofalne destrukcije.

Lom alata je glavna opasnost u proizvodnjihladnim oblikovanjem zbog visokih troškova kojinastaju ne samo zamenom alata, već takođe i odoštećenja koje može biti uzrokovano slomljenimalatom u automatskom okruženju. Lom usled pre-opterećenja može se izbeći upotrebom modernihtehnika procene napona i deformacija, kao što jeFEM, ali se lom usled zamora uvek javlja u visoko-opterećenim alatima. Lom se odvija kada zbir me-haničkih i toplotnih opterećenja pređe kritičnu vred-nost. Ova vrednost nije čisto svojstvo materijala,već zavisi od stanja multiaksijalnog napona.

3. UTICAJ RAZLIČITIH FAKTORA NA VEKTRAJANJA ALATA

Neizvesnosti u proceni očekivanog radnog ve-ka alata i time troškova alata po komadu uzrokova-na je:1. ogromnom raznovrsnošću i interakciji štetnih

faktora,2. fabričkim specifičnim karakterom radnog veka

alata,3. stohastičkim fenomenom destrukcije alata,4. specifičnim alatom i5. specifičnom primenom.

Klasična podela faktora koji utiču na radni vekalata pravi razliku između razloga destrukcije. Onipokrivaju mnogo komplikovaniju mrežu faktora,međutim, praktično opisuju čitav sistem oblikova-nja i sve zahteve za kvalitet proizvoda stavljajućisada alat u centar razmatranja. Očigledno, prose-čan vek trajanja alata za proizvodnju blizu konač-nog oblika je znatno niži nego za proizvodnju pred-meta obrade sa većim poljima tolerancije. Razloziza ranu destrukciju alata mogu biti:1. veći naponi zbog visokog stepena punjenja

šupljinašto dovodi do ranijeg zamornog loma,2. manje habanje alata je dozvoljeno zbog uskog

polja tolerancije potrebnog za predmet obrade.Glavna prepreka u objašnjenju uticaja različitih

parametara sistema oblikovanja je složenost među-veze između njih. Izmena podmazivanja, na primer,ne samo da menja kontaktni međusklop izmeđualata i radnog predmeta na mikrogeometrijskom ni-vou, već takođe izaziva promenu u uslovima trenja,kao što su:1. polje brzina (raspodela brzina u datom

regionu),2. normalni i tangencijalni naponi,3. kontaktna brzina,4. temperaturni uslovi na površini i5. pritisak oblikovanja.

Tako se postavlja pitanje: šta je suštinski razlogza promenu radnog veka alata? Povećanje ener-gije oblikovanja, na primer, rezultira višom tempe-



raturom alata. Dodatna visina temperature usledtrenja između predmeta obrade i alata, može podićilokalnu temperaturu površine kritično iznad tempe-rature otpuštanja nekih čelika za rad u hladnomstanju. U toplom kovanju, sve ove pojave kombi-novane su sa dominantnim adhezivnim habanjem isa toplotnim naprslinama.

Druga dimenzija u radnom veku alata je pove-zana sa tradicijom i kulturom proizvodnje - sa ljud-skim faktorima. Zbog toga je nezavisna fabričkaprocena radnog veka alata uvek veoma neizvesna.U nastavku ovog rada daju se dva primera: 1. Neo-prezno podmazivanje, predgrevanje ili hlađenjemogu izazvati povišenu temperaturu kalupa za ko-vanje što može dovesti do trajne deformacije ilitoplotnog zamora, 2. Odstupanje (devijacija) tem-perature radnog predmeta rezultira oksidacijom sapovišenim trenjem i habanjem ili povećanjem kon-taktnog pritiska, višim naponima u elementima ala-ta a time i habanjem ili lomom.Vrste destru-kcija zaidentično dizajnirane alate u identičnim eksploata-cionim okruženjima, takođe variraju. Visokooptere-ćeni alati za hladnu ekstruziju se uvek lome, dok jehabanje glavni uzrok za destrukciju u masovnojproizvodnji jednostavnijih radnih delova. Karakte-rističan odnos destrukcije za alate za hladnu eks-truziju su, na primer, 80 % destrukcija prelomom alisamo 20 % zamene usled habanja. U skladu saovim modelom, sve vrste oštećenja su aktivne u is-to vreme tokom eksploatacije alata. Habanje, hra-pavljenje, plastična deformacija i pro-pagacija (rast)prsline su deterministički (mogu se odrediti i ogra-ničiti), ali je započinjanje mikropu-kotina karakterverovatnoće.

Prema tome, put koji vodi od početnog stanjaalata do dominantnog propadanja, ne zavisi samood dizajna i specifičnih faktora eksploatacije, većod cele preistorije alata. Poklapanje ovih determi-nističkih i stohastičkih procesa rezultuje različito-šću tipova destrukcije koja može biti veoma velika,kao što je već napomenuto.

4. PRIMENA DIFUZIONOG VANADIRANJANA KOMPONENTAMA KALUPA

4.1. Neki teoretski aspektiIz aspekata prikazanih u prethodnom poglavlju

ovog rada, jasno je da ne postoji opšti recept zapovećanje radnog veka i kvaliteta alata. Svaki oduticajnih aspekata sadrži neke mogućnosti za po-većanje veka trajanja alata. Zbog fabrički specifič-nog karaktera radnog veka alata, različita rešenjamogu dovesti do različitih efekata u različitim fabri-kama, tako da možemo formulisati iskaz: ne postojijedinstven način povećanja radnog veka alata, po-stoji samo nekoliko koraka ka tom cilju. Jedan odtih koraka je površinsko ojačavanje reaktivnim slo-jevima karbida prelaznih metala, gde legirajući ele-ment ulazi difuzijom u osnovni materijal. Tehnolo-gija površinskog ojačavanja, kao značajno sredstvo

za poboljšanje performansi i veka trajanja kalupa,zauzima veoma važno mesto u industriji kalupa,dobijajući veliku pažnju u inostranstvu. Karbidi pre-laznih metala proučavani su zbog njihovih odličnihosobina, kao što su visoka tvrdoća, povišena tem-peratura topljenja, dobra hemijska i mehanička po-stojanost i visoka toplotna provodljivost [9]. Zadruge, uobičajene, metode površinskog otvrdnjava-nja čelika (npr. plameno i indukciono kaljenje) nepostoji informacija u literaturi da se koriste za kalu-pe za oblikovanje. To je možda usled velikog gubit-ka žilavosti i distorzije gravura kalupa koje ove me-tode mogu da izazovu.

Tvrdi površinski sloj smanjuje silu trenja i brzinuhabanja kada klizi nasuprot relativno mekanog ma-terijala radnog predmeta ukoliko je spoj materijalasloja/radnog predmeta hemijski postojan a zaštitnisloj dobro vezan i mehanički kompatibilan sa mate-rijalom kalupa. Uloga tvrdog sloja je da spreči pro-diranje, dok hemijska nerastvorljivost treba da osi-gura minimalno rastvaranje.Tvrdi zaštitini slojevi suposebno korisni kada je abrazija dominantan me-hanizam habanja. Jedno od glavnih razmatranjaprilikom izbora materijala zaštitnog sloja je kvalitetveze između zaštitnog sloja i materijala kalupa. Ve-zivanje može biti hemijsko ili mehaničko. Hemijskovezivanje je uzrokovano reakcijom ili difuzijom ato-ma između zaštitnog sloja i osnovnog materijalakako bi formiralo čvrsti rastvor na međusklopu.

4.2. Tribološka evaluacija osobina slojevadeponovanih na kalupe i čelične uzorke

Neke od najranijih metoda za povećanje rad-nog veka kalupa za oblikovanje i alata za maši-nsku obradu su tanke tvrde obloge i termodifuzionipostupci. Tanki tvrdi slojevi su nitridni, karbidni ikarbonitridni slojevi sa debljinom od 3 do 10 μm.Oni se konvencionalno nanose hemijskom i fizič-kom depozicijom iz parne faze. Hemijska depozi-cija može dovesti do teških distorzija obrađivanihdelova a fizička depozicija zahteva skupu i kompli-kovanu opremu. Pored toga, usled ograničene koli-čine difuzije koja se javlja tokom PVD postupka,postupak pokazuje slabiju adheziju obloge. Alte-rnativna tehnika tvrdog oblaganja je termoreaktivnidepoziciono/difuzioni (TRD) postupak koji funkcio-niše na 1073 do 1473 °K. [10]

U industriji hladnog kovanja, kvalitet proizvodaicena kalupa za kovanje značajno utiču na perfor-manse kalupa. Iz tog razloga, činjeno je mnogonapora za poboljšanje performansi kalupa [11].Nažalost, ispitivanja sa različitim površinskim tret-manima nisu uspela da dobiju plodonosne rezu-ltateu mnogim zemljama. U Japanskoj industrijihladnog kovanja, primetan uspeh ostvaren je zah-valjujući upotrebi dve vrste postupka oblaganjakarbidom. Jedan od njih je sloj titanijum karbida(TiC) proizveden postupkom hemijske depozicije iz



parne faze, koji je razvijen u zapadnoj Nemačkoj, azatim predstavljen u Japanu. Drugi je sloj vana-dijum-karbida proizveden upotrebom rastopljenogsonog kupatila, slika 3 [5]. Ovaj proces, nazvan TDprocesom, razvijenje od strane Toyota CentralResearch and DevelopmentLabs of Japan, i pred-stavljen različitim japanskim industrijama počevšiod 1971. godine.

Slika 3 - Rastopljeno sono kupatilo

Trošak kovanja povezan uglavnom sa proizvo-dnjom alata, održavanjem alata i zastojom opremeuspešno je smanjen uvođenjem novorazvijenihmetoda površinskog oblaganja, tj. tankih tvrdihslojeva i novih materijala za alate čiji su hemijskisastav i mikrostruktura dobro dizajnirani za kova-čke alate. U [12] se navodi da je Japanska indu-strija kovanja imala mnogo koristi od oba, i tankihtvrdih slojeva i novih alatnih materijala za ovihdeset do dvadeset godina. Iz [12] se saznaje da supovršinska svojstva alata poboljšana putem tankihtvrdih slojeva na toliko visokom nivou, da se svakedalje modifikacije samih materijala alata u hemij-skom sastavu i metodi proizvodnje ne mogu pore-diti. U [13] termalna difuzija (TD), termoreaktivnadepozicija/difuzija (TRD) ili TD-Toyota difuzioni po-stupak definiše se kao visokotemeraturna obradakoja generiše površinski sloj karbida na čeliku kao ina ostalim materijalima koji sadrže ugljenik kao štosu legure nikla ili kobalta.Jaki karbidoobrazujućielement (Cr, V, Nb, W ili Ti) iz reakcionog mediju-ma (sono kupatilo ili granulat) pri visokim tempera-tura reaguje sa ugljenikom rastvorenim u austenitustvarajući posebne karbide Cr7C3, V8C7, NbC,WC iliTiC, koji imaju visoku tvrdoću i visoku otpornostprema trošenju kod mehanizama trošenja abra-zijom, adhezijom i tribohemijom ali niske otpornostiprema zamoru površine [14]. Najčešće proizvođenkarbidni sloj je vanadijum karbid, mada se, u zavis-nosti od sastava slanog kupatila mogu deponovati idrugi karbidi. Postoji ograničenje u veličini delovakalupa, zbog ograničenja u veličini slanog kupatila,što je ograničavajući faktor u primeni ovogpostupka [15].

Temperatura kupatila se bira kako bi odgova-rala temperaturi kaljenja čelika za kalupe. Na pri-

mer, temperatura kupatila će biti između 1000 i1050 °C za čelik H13. Debljina karbidnog sloja semenja kontrolisanjem temperature i vremena pota-panja. Za čelik H13 potrebno vreme potapanja jeod 4 do 8 časova kako bi se proizveli karbidni slo-jevi sa zadovoljavajućom debljinom (od 5 do 10μm). Kalupi se zatim uklanjaju iz kupatila i hlade uulju, rastopini soli ili na vazduhu zbog otvrdnja-vanja jezgra, a zatim se otpuštaju.

Slika 4 - Mikrografija poprečnog presekavanadiranog uzorka čelika AISI H13

Slika 4 pokazuje poprečni presek nanešenogsloja vanadijum karbida dobijenog nakon potapanjau kupatilu sa rastopljenim boraksom sa dodatkomkarbidoobrazujućih elemenata. Primetno je da os-novni materijal AISI H13 poseduje martenzitnu mik-rostrukturu dok sloj pokazuje dobru jednolikost [16].

Objašnjavajući prednosti postupka, Lister [5] usvom radu navodi da sloj vanadijum karbida pove-ćava vek trajanja alata od 5 do 30 puta više odneobloženih alata, povećanjem površinske tvrdoćeuz istovremeno smanjenje koeficijenta trenja. Sli-čno navodima u literaturi [10] on u daljoj analiziističe da prednosti procesa nad konkurentskimslojevima hemijskog depozicionog isparenja (CVD)uključuju niže troškove investicione opreme, izo-stanak štetnih otrova od produkata a takođe i eli-minaciju višestrukih koraka toplotne obrade. Osta-jući u istom kontekstu, on dalje tvrdi da difuzioniproces takođe proizvodi delove sa poboljšanomdimenzionalnom postojanošću u odnosu na istedelove obrađene tradicionalnim tvrdim oblogama.Objašnjavajući efekte primene vanadiranja na kom-ponentama kalupa za kovanje, u literaturi [17] seističe kako je Venkatesan sa saradnicima utvrdioda vanadirani kalupi pokazuju manje habanje ispiti-vanog uzorka u odnosu na karbonitrirane i borira-ne. Oni su takođe primetili da vanadirani kalupi nepokazuju tra-gove habanja nezavisno od vrstesupstrata koja se koristila.Grafikon 1 pokazuje krive



habanja slojeva dobijenih potapanjem u sono kupa-tilo i postupcima u čvrstom sredstvu za ispitivanematerijale.

Grafikon 1a - Krive habanja sloja karbidavanadijuma i drugih difuzionih slojeva izvedene iz

ispitivanja mikro habajućom mašinom sa fiksiranomkuglom bez korišćenja abraziva

Grafikon 1b - Krive habanja samo obloženihuzoraka

Grafikon 1a pokazuje krive habanja dobijene zaobložene uzorke i za osnovne materijale (sup-strate) da bi se demonstrirala uspešnost svih difu-zionih postupaka u povećanju otpornosti prema ha-banju, koji verifikuju veliko povećanje otpornostiprema habanju za sve difuziono obložene uzorke[16]. Sloj dobijen posle obrade hromiranjem (Cr)ima habajuće performanse bliske slojevima karbidavanadijuma. Habajuće performanse slojeva karbidaniobijuma su snižene nego one od hromiranog slo-ja iako oni imaju višu tvrdoću. Ovo je verovatnozbog veće krtosti. Za bolje poređenje, na grafikonu1b priložene su krive habanja samo obloženih uzo-raka [16]. Slojevi vanadijum karbida na AISI H13(čeliku za izradu kalupa za kovanje u toplom sta-nju) i D2 rezultuju najboljim habajućim performan-sama. Sloj jedinjenja hrom nitrida i karbida pred-stavlja volumen habanja blizak onom od slojevavanadijum karbida, iako je tvrdoća sloja hromaznatno niža (1780 HV) nego onog od vanadijumkarbida (2461 HV). Boridni slojevi, dobijeni pota-panjem ili postupcima u čvrstom sredstvu pokazujunajnižu otpornost prema habanju među obloženimuzorcima.

Prema Matijeviću [14] radi se o postupcima kojise ne mogu jednoznačno svrstati u dve osnovne

grupe (modifikovanje i prevlačenje) jer sadržeelemente procesa koji pripadaju obema grupama.To je zato što se ispod nastalog karbi-dnog slojadelimično menja hemijski sastav usled difuzijekarbidoobrazujućeg elementa od površine premaunutrašnjosti i ugljenika iz unutrašnjosti premapovršini. Taj deo površine je modifikovan a nadnjim se nalazi karbidna prevlaka.

Objašnjavajući mehanizam rasta sloja vana-dijum karbida i u vezi sa tim mikrostrukturu, morfo-logiju, kristalnu strukturu i tvrdoću, Haopeng je sasaradnicima [18] izveo termodifuziono vanadiranjenove vrste čelika SDC99 za kalupe za rad u hla-dnom stanju u kupatilu rastopljenog boraksa koje jesadržalo prahove Na2B4O7 (75,6 %), BaCl2 (8,4 %),V2O5 (10 %) i aluminjuma (6 %). Eksperimente suizveli na 850, 900, 950 i 1000 °C za različito vreme.Mikrostrukturu i morfologiju sloja posmatrali su ko-rišćenjem skenirajuće elektronske mikroskopije imetalografskim merenjima, analizu elemenata napovršini su sproveli sa energetskom disperzivnomspektroskopijom, a kristalnu strukturu uzoraka ka-rakterisali su sa rendgenskom strukturnom ana-lizom. Rezultati su pokazali da sloj prevlake vana-dijum karbida poseduje mnogo veću tvrdoću (oko22 GPa) nego ona od osnovnog materijala (oko 7GPa). Tvrdoća između sloja vanadijum karbida iosnovnog materijala polako opada ukazujući damikrostruktura osnovnog materijala koja se graničisa međusklopom može da obezbedi korisnu i efi-kasnu potporu odnosno oslonac za sloj vanadijumkarbida.

U svom radu oni dalje izveštavaju da je meha-nizam rasta bio nukleacija, rast početnih zrna istvaranje zrna submikronske veličine na njima. Pri-metili su da kristalno zrno sloja raste u zrnima aksi-jalno simetričnog oblika usled uticaja aktivnosti ug-ljenika u osnovnom materijalu, a veličina zrna opa-da sa smanjenjem njegove udaljenosti od osnov-nog materijala. Pored toga, u početnoj fazi rastakristalnog zrna sloja preferencijalna orijentacijarasta kristalnih zrna transformisana je iz (200) pre-ma (111) kristalnoj ravni. Međutim, sa uvećanjemvremena preferencijalna orijentacija rasta kristalnihzrna je bila beznačajna i ona su prerasla u zrnaaksijalno simetričnog oblika.

Sa druge strane, određeni autori [19] izvršili sutermoreaktivno difuziono oblaganje vanadijumkarbidom komercijalnog DIN 1.2367 čelika za kalu-pe za rad u toplom stanju, u mešavini prahakoja sesastojala od fero-vanadijuma, amonijumhlorida, gli-nice i naftalena. Koristili su mešavine praha sa raz-ličitim odnosima NH4Cl/fero-vanadijuma, i konačnosmešu koja se sastojala od 40 % fero-vanadijuma,10 % amonijum hlorida, 45 % glinice i 5 težinskih %naftalena. TRD postupak su sproveli u čeličnoj kuti-ji zapečaćenoj sa aluminijumskim cementom na



temperaturama od 950, 1050 i 1150 °C u trajanjuod 1 do 5 h u elektrootpornoj peći, praćen normal-nim hlađenjem na vazduhu. Karbidne slojeve sukarakterisali mikrostrukturnom analizom, rendgen-skom difrakcijom (XRD), analizom mikrotvrdoće ihemijskom analizom. Skeniranje vanadijum karbid-nog sloja elektronskom mikroskopijom otkrilo je dasloj vanadijum karbida formiranog na površini sup-strata ima ravnomernu debljinu preko cele površinekao i to da je sloj gust, gladak i kompaktan (zbijen).SEM mikrografija tipičnog sloja vanadijum karbidana 1150 °C i 0,5 h je prikazana na slici 5 [19].

Slika 5 - SEM mikrografija vanadijum karbida na1150 °C i 0,5 h [19]

U svom radu oni prijavljuju da se, u zavisnostiod vremena i temperature procesa, debljina slojavanadijumkarbida formiranog na osnovnom mate-rijalukretala u rasponu od 2,3 do 23,2 μm. Rezul-tati su pokazali da je tvrdoćaslojeva vanadijumkarbida bila oko 2487 HV, što je mnogo više negoona od osnovnog materijala (576 HV). Veruje se daje to zbog prisustva tvrde faze vanadijum karbida uobloženom sloju, koji obezbeđuje ekstremno tvrdupovršinu u poređenju sa onima od hromiranja, nitri-ranja, cementacije i karbonitriranja. Glavno ograni-čenje TRD obrade je to da čelični supstrat moraimati sadržaj ugljenika od najmanje 0,3 % inačedebljine sloja postaju ozbiljno ograničene. Ispitiva-nje suvog habanja netretiranog i tretiranog DIN1.2367 čelika za kalupe vršili su na aparaturi pinon-disc (valjčić po disku) pri kliznoj brzini od0,13 m/s.Rezultati su pokazali superiorne karakteristike prihabanju obloženih uzoraka. Takođe je proučavanakinetika vanadijum karbidne obloge ostvarenepack-metodom i aktivaciona energija za termoreak-tivni difuzioni proces je procenjena na173,2 kj/mol.

5. ZAKLJUČCIRazličiti postupci reaktivnog oblaganja imaju

sve veću primenu i u našim proizvodnim pogonimakao uobičajeni postupci obrade. Međutim, takavslučaj nije sa Toyota difuzionim postupkom. Do-

maći naučnici i istraživači se do sada nisu ozbiljnijefokusirali na istraživanja koja bi za svoj cilj imalaproučavanje mehanizama rasta sloja vanadijumkarbida, organizacionu strukturu, otpornost premahabanju i koroziji, koeficijenta trenja i mehanizmahabanja. Za razliku od nas, japanska industrija ko-vanja uspešno je integrisala slojeve vanadijumkarbida proizvedene teromodifuzionim postupkompostižući na taj način poboljšanje radnog vekakalupa i alata, s obzirom da se vanadiranje poka-zalo kao jednostavan i efikasan postupak za dobi-janje tvrdih slojeva na alatnim čelicima.

Govoreći o teoriji procesa, zaključuje se da for-miranje sloja vanadijum karbida predstavlja rezul-tat reakcije atoma vanadijuma i atoma ugljenika napovišenim temperaturama dok je njihov način vezi-vanja metalurško vezivanje. Alatni čelik za rad utoplom i hladnom stanju pripada grupi čelika koji sekoriste u proizvodnji alata za kovanje. Posebno suinteresantni zbog svoje niske cene i veoma dobrihfunkcionalnih osobina, ali je njihova površina jošuvek jednostavna i podložna za destrukciju haba-njem pa je zato neophodno korišćenje tehnologijepovršinskog ojačavanja kako bi se poboljšala njiho-va tvrdoća i otpornost. U prilog tome poređenjeperformansi habanja između osnovnog materijala isloja, izvedeno u ovom radu, pokazalo je da proiz-vedeni sloj vanadijum karbida u svim slučajevimapokazuje veliko povećanje otpornosti prema haba-nju u poređenju prema supstratima.

Saglasno sa ranijim navodima, rezultati istraži-vanja ovog rada potvrđuju veliki potencijal Toyotadifuzionog postupka za proizvodnju slojeva visokihperformansi na onim mestima gde drugi materijaliotkazuju.

LITERATURA

[1] Vilotić D, Movrin D, Milutinović M, Luža-nin O.(2010) Primena savremenih metoda u projektovanjutehnologije kovanja. IMK-14 Istraž. i razv. 35, 1-6.

[2] Jun Z.TD salt-bath vanadizing for application of diesurface strengthening in the cold. Master Disser-tation. China: Wuhan Univerzity of technology.

[3] Shivpuri R, Babu S. (2005)Die wear.Ohio: The OhioState University S.L. Semiatin, Air Force ResearchLaboratory. 62.

[4] Yang KX. (2011)Study on process of vanadizing insalt-bath on cold-work die steels. Master thesis.China: Donghua Unive-rsity.

[5] Lister M.(2005) Vanadium carbide diffusion coatingsfor tool and die components. In:Heat Treating:Proceedings of the 23rd Heat Treating SocietyConference. Pennsylvania USA: Pittsburgh. 162-166.

[6] ASM Handbook. (2002) Forming and Forgi-ng.Volume 14. ASM International, Hand-book Com-mittee. Unated States of America. 994-995.



[7] Lange K, Cser L, Geiger M, Kalas GAJ. (1992) ToolLife and Tool Quality in Bulk Metal Forming.CIRPAnnals - Manufac. Technol. 41, 667-675.

[8] Bílik J, Pompurová A, Ridzoň M.(2012) IncreasingThe Lifetime of Forming Tools. In: 8th InternationalDAAAM Baltic Confere-nce "Industrial Engineering".Estonia: Tallinn University of Technology. 193-197.

[9] Fernandes FAP, ChristiansenTL, DahlKV, SomersMAJ. (2013) Growth of Vanadium Carbide by Halide- Activated Pack Diffu-sion. In: Conference: HeatTreat & Surface Engineering Conference & Expo2013. India: Chennai.

[10] Khafri MA, Fazlalipour F. (2008) Kinetics of V (N,C)coating produced by a duplex surface treatment.Surf.and Coat. Techno.202, 4107-4113.

[11] Stojanović Ž, Stanisavljev S, Radosavljević S.(2013) Primena postupka vanadiranja u funkcijiproduženja radnog veka delova. Zašti. materij. 54,183-188.

[12] Arai T. (1992) Tool materials and surface treat-ments.Journ. of Mater. Processi. Te-chnol. 35, 515-528.

[13] Czerwinski F. (2012) Heat treatment – conve-ntionaland novel application. Ontario: CanmetMATE-RIALS. Natural Resources Canada Hamilton.275.

[14] Matijević B. Stupnišek M. (2000)Pregled postupakamodificiranja i prevlačenja metala. Znanstvenostručni skup s međunarodnim učešćem Toplinskaobradba metala i inženjerstvo površina. RepublikaHrvatska: Zagreb. 53-62.

[15] Smith DA.(2001) Die maintenance hand-book.Society of Manufacturing Engineers, Dearborn.United States of America: Michi-gan. 18.

[16] Casteletti LC, Fernandes FAP, Heck SC, de OliveiraCKN, Neto-Lombardi A, Totten GE. (2009) Packand Salth Bath Diffusion Treat-ments on Steels.Heat. Treat. Progr. 9, 49-52.

[17] Babu S, Ribeiro D, Shivpuri R. (1999) Mate-rial andsurface engineering for precision for-ging dies.Ohio:The Ohio State University. 70.

[18] Haopeng Y, Xiaochun W, Fang Q, LongjiaoY.(2013) Study on Growth Mechanism of Salt BathVanadizing Coating by TD Process on SDC99Steel.Acta Metall. Sin. 49, 146-152.

[19] Khafri MA, Fazlalipour F. (2008)Vanadium CarbideCoatings on Die Steel Deposited by the Thermo-reactive Diffusion Technique.Journ. of Phys. andChem. of Soli. 69, 2465-2470.

ABSTRACT

INCREASING THE EFFICIENCY OF FORGING TOOLS BY TOYOTA DIFFUSIONPROCESS

In this paper is given a review of literature data about research of influence layer of vanadium ca-rbide deposited by Toyota diffusion process on increasing of working life and quality of forgingdies. Forging dies are subjected to severe adhesive and abrasive wear, high stresses andtemperatures. The die surface and near surface region is subjected to the most severe conditionsduring forging and hence most defects and causes of failure of the dies originate from this region.Because of this, paper takes into consideration the different complicated mechanisms of wear andthe destruction of the surface of tools for forging, apropos that network of various aspects whichaffect on the service life of the tool and by their actions causing premature removal tool from theuse.Keywords: vanadium carbide, mould forging, lifetime, wear, destruction.

Scientific paperReceived for Publication: 11. 08. 2014.Paper corrected: 02.10.2014.Accepted for Publication: 19. 11. 2014.

L. JOVANOVIĆ et al. THE OPTIMIZATION OF DEVELOPMENT PROCESS OF PETROL-GAS …


LARISA JOVANOVIĆ, DIJANA FEDJUNINA, Scientific paperMILAN RADOSAVLJEVIĆ UDC:725.384.026

The optimization of development process of petrol-gas stationsnetwork with the purpose to increase energy efficiency

Development of petrol/gas stations network requires a complex approach to the assessment ofenvironmental impact. The use of appropriate indicators according DPSIR methodology enablesoptimization of processes at oil/gas stations and increase energy efficiency.Use of renewable energy and new insulating materials has great importance to reduce energyconsumption for heating of petrol/gas stations buildings. As a replacement styropor and styrodur(for added insulation of walls and floors) is much more efficient to use blocks of innovativeinsulating materials in the construction of new facilities.Widespread application of renewable energy and thermal insulation materials in buildings ofoil/gas stations, reducing electricity consumption by using energy-saving LED technology, as wellas savings in transportation fuels reducing the weight of tankers using Al alloys and compositematerials are the basic methods of increasing energy efficiency. The use of Al alloys in tankersand reservoirs design conductive to increase corrosion resistance.Keywords: petrol/gas station, optimization, DPSIR methodology, indicators, energy efficiency,sustainable energy sources, LED technology, corrosion resistance, Al alloys.

INTRODUCTION

The strategy of building and development ofany retail trade chain is a multivariate permanentmanagement process. Retail network of multi-ser-vice stations imposes on this process a significantnumber of additional conditions and functions, themost important of which are the factors of influenceon the environment. The number of laws and regu-lations governing the procedures and control mec-hanisms is colossal, and the number of technicalparameters describing the environmental impactand governing of technical processes is enormous.

A network of petrol and gas stations in additionto providing consumers with oil products, whichthemselves are a threat to the environment, isobliged to protect staff, customers, neighboringhouseholds and industrial facilities, and to ensure aminimum level of impact on the environment(water, air and soil).

The development strategy cannot be limited tothe description of technical methods, because suchformulaic solutions describe the common cases,and they are not tailored to the specific location ofthe object and the features of its environment.Business effects of the strategy can be offset byproblems caused during the exploitation of petrol/gas stations network, while the errors in the design

Author's address: 1ALFA University, Belgrade,Serbia, 2Lukoil, Moscow, Russia, 3UNION - NikolaTesla University, Belgrade, Serbia


of standard solutions can be multiplied on theentire network and the region.

The aim of this work is to analyze the possibilityfor application of DPSIR methodology in the designand exploitation of petrol/gas stations network onpurpose to increase energy efficiency andcorrosion protection of tankers.

1. OBJECTS AND METHODS

Because of the complexity of the issue,strategy development and a planning network ofretail trade in petrol/gas stations, it is necessaryand advisable to use a systematic approach. Oneof the most successful mechanisms of systematicapproach is the system of the environmentalindicators, based on the methodology developedby the European Environmental Agency (EEA), andthe analysis of the interaction of environmental andtechnological impacts using indicators based onthe model DPSIR [4]. The EEA assesses the state(S) of the environment using DPSIR methodology.The state (S) is the result of specific drivers (D), pressures (P), positive or negative, impact (I) on the environment.

The responses (R) represent the solutions(policies, investments) that should then be done toimprove or maintain that state.

The report also looks at outlooks (O) for thestate of the environment – namely, what willhappen with that state over time (e.g. 2020, 2050)based on various scenarios [EEA, DPSIR, 2010].



Figure 1 - DPSIR framework [4]

Use of the model simplifies and formalizes thedescription of the problems, creating a pattern ofadministrative, organizational and technologicalfactors (events) in the design of the system, and inresponse to the corresponding indicator, includingpreventive measures and emergency response inthe event of emergency.

Below we discuss some specific examples ofpossible applications and uses of a system ofindicators in different situations, and how toimprove such indicators in the design, post-projectand exploitation of petrol/gas stations.

2. CONSTRUCTION OF THE TANKS AND THESUPPLYING INFRASTRUCTURE OF THEPETROL/GAS STATION

When designing the disposition of tanks with oiland liquefied natural gas, as well as the infrastruc-ture of pipes and valves, providing the circulation ofproducts, it is necessary to take into considerationthe following features of operation that have a com-plex effect on the environment [9].

Systems of airway valves of oil tanks con-tinually lead to evaporation of light fractions ofpetroleum products, which affect the air, earth, soil,water, etc. If the constructive solution combinestwo kinds of oil (gasoline and diesel) in the sameapparatus, the amount of emitted fumes increases.When draining of oil products from the cistern, thetotal volume of the air mixture containing asignificant amount of light fractions in the amount of10 to 40 m3 falls into the atmosphere. The problemcan be solved using a number of additional techni-cal elements of reinforcement and implementationof separate valves.

Gas tanks do not use breathing valves, but thesystem of the safety valves in the tank is triggeredwhen the nominal pressure in the tank exceed of25 atm and 12-20 atm in the installation system.The system releases a small amount of gas alwayswhen refueling a vehicle or a container. The sche-duled amount of the gas ejection is affected by theincrease of temperature in the reservoir more than28-30 degrees centigrade, the amount and freque-ncy of the circulation in the system, container fillingprocedure, and other processes. The problem canbe solved by the correct setting and monitoring of abooster pump.

The groundwater can be a significant problemin the exploitation of gas stations. In the case ofimproperly designed base and mountings of thetank, as well as untimely preventive measures, thereservoir may float, damaging elements, installa-tions and fittings, which will inevitably lead to therisk of oil spills with the most negative impact onthe environment (soil, water, air) and the popu-lation.

Leaking fuel and the warning systems andprevention: horizontal and vertical metal tanks ha-ve relatively short lifetime, usually 20 years. De-pending on soil acidity a lifetime can be signify-cantly reduced. In view of the fact that in Serbia isonly allowed exploitation of underground storagetanks, the unique indicator of the correctness of itsuse is the system alerts of leaks and the oil levelcontrol.

On the site, during overload of petroleum pro-ducts, as a rule, there is an uncontrollable shed-ding of fuel as a result of misuse of the equipmentdispenser. During exploitation of these installations



(pipelines), in the case of deviations and violationsin the installation of such equipment, after sometime (months or years) occurs leakage of oil to theground. To resolve this issue, a system for thecollection and treatment of wastewater from thesite with a separator is provided, with the return ofthe primary treated water into the sewage system.System for collection and treatment of waste waterfrom the site must be periodically cleaned byspecialized enterprises, with removing sedimentsoutside gas stations by licensed carriers. Controll-ing body has the right to verify the quality andquantity of work done, including by requestingprimary dispatch notes.

Fire protection systems and activities areprovided in the form of two main procedures: pre-ventive and periodic control measures and actionsof plant personnel and specialized units in theevent of an accident. Between all the cases of theimpacts on the environment - fire on gas station isthe most disastrous in its consequences becauseof the lack of opportunities to eliminate them.

Restoration and reclamation: soil remediationis necessary not only in the case of an accidentalrelease of oil, but also after the long-term use ofgas stations, because there is currently no techno-logy that completely eliminates the ingress of oilinto the soil.

3. FEATURES OF STORAGE, SALE OFPACKAGED MOTOR OILS AND OIL CHANGEPOINTS

In Serbia, the implementation of engine oil inleaky packaging is currently banned. This require-ment is associated with a significant negativeimpact on the environment. There are also regula-tions prescribing enterprises implementing suchproducts, the obligation to ensure the reception ofwaste oil and transport it to a specialized process-sing firm. At present, a company is accountable forthe amount of imported packaging material bypaying the appropriate taxes. In the case when theregulatory acts will come into full force for the gasstations becomes actual formation of oil changepoints and oil collection points.

Oil change points allow quickly and accuratelyextract waste oil from the engine, and replace itwith a new one. The amount of lost product in thiscase, and hence the impact on the environment, isgreatly reduced.

At many gas stations there exist integrated,automated and semi-automated carwashes. Legi-slation provides the phased introduction of fees forthe amount of water discharged into the sewersystem, thus installing treatment systems andwater recycling becomes a pressing issue.

Oil change points equipped with systems forwater collection and its primary treatment usingseparators highly reduce the risk of uncontrolledleaks and accidents.

4. OPTIMIZATION OF OPERATING PROCEDURESFOR PETROL/GAS STATIONS AND THE USE OFRESOURCE-SAVING TECHNOLOGIES ANDRENEWABLE ENERGY SOURCES

Installation of electric heating systems basedon oil convection radiators allows ensuring thenormal circulation of heat, reducing the overheadfor heating, with minimal impact on the compositionof the air in the room. Using the heat-curtain infront entrance combined with automatic slidingdoors provides the optimal composition of fresh airin the room with minimal heat loss.

For complex oil/gas stations, in terms ofeconomy and environmental impact, the source ofused water often is critical point. Purified freshdrinking water from the system of urban or regionalwater supply is expensive, hence the wells may beused to obtain technical water, which together witha system of primary treatment, recycling and re-treatment follow-up, combined with a system ofseparators provides cost-effectiveness andreduces environmental impact. The delivery ofservice water at the gas station is obligatory.

The combination of the cooling systems of abuilt-in refrigerators and open cabinets for drinksand food with the main air-conditioning systemoptimizes the load in summer. Indeed, an addition-nal cooling takes place through the commercialequipment while refrigerator radiates heat over therear wall into the same space, hence such com-bination significantly reduces the use of electricityfor each unit separately.

Saving technologies allow combining severalbusiness decisions. For example, if the gas stationis located near a source of geothermal energy, thisresource can be used to generate electricity. Sincethe station has already qualified service personnel,and system security, and the government providespreferential rates for the production of energy fromrenewable sources, this project could be beneficial,provided to solve some technical problems [5].

Installation of solar-powered heating systemswith accumulation of hot water in the heatinsulating tanks allows for customers and staff ofoil/gas station required amount of hot water aroundthe clock and, when using a small recirculationsystems, to produce additional heating for supportfacilities during the winter in Serbia [7,8].

Light-emitting diode (LED) is a semiconductorlight source. LEDs are used for lighting ofpetrol/gas stations and ancillary buildings. Byinstalling LEDs for indoor and outdoor lighting and



motion sensors in offices and support facilities theenergy consumption can be reduced up to 20%without loss of brightness level of the illuminatedarea. Compared with other electric light sourcesLEDs have the following advantages: highefficiency and long life (30,000 to 100,000 hours).These characteristics make LEDs suitable fortankers illumination [6].

An increase of energy efficiency on installationsof reactive power compensators can not onlyreduce the total cost of electricity, but also greatlyimprove the quality characteristics of the localenergy supply, with all its consequences [1]. Thereare actual savings of up to 10% depending on thepower consumption and the composition of theelectrical equipment.

5. PROTECTION OF RESERVOIRS AND TANKSFROM CORROSION

The main methods of anticorrosion protectioninclude metal alloying, heat treating, inhibiting theenvironment surrounding the metal and protectivecoatings. In the case of electrochemical corrosionby doping, the metal proceeds from the active tothe inactive state, thereby forming a passive filmwith high barrier properties. For example, alloyingiron with chromium allowed to transferring iron intostable passive state and creating a whole class ofalloys, called stainless steels [9]. Additional alloyingof stainless steels with molybdenum and nickeleliminates the tendency to pitting [10]. Stainlesssteel is corrosion-resistant due to alloying Cr, Ni,Nb and Ti components (12-18%).

To fight corrosion, the metal corrosion inhibitorsare widely used. They in small quantities are ente-red in aggressive environment and create adsor-ption film on the metal surface, retarding electrodeprocesses and change the electrochemical para-meters of metals. Close to this method of protect-ion is thermal diffusion surface alloying steels withchromium, aluminum, silicon or zinc to improveheat - and corrosion resistance in aggressiveenvironments. Intensively developed are two typesof steel. Some of them are low alloys intended tobe used at ambient temperature, which must beresistant to corrosion in the presence of H2S [2,3].

The objective of aluminum alloys developmentis the use of materials with low specific weight andincreased corrosion resistance for the tankersconstruction. Therefore aluminum alloy with lithiumis intensively developed, in which it would bepossible to achieve the same strength with about10% less specific weight. Taking into account thatmost of the construction of tankers uses aluminumalloy, the reduction in weight is significant. Thesecond object is achieved by a combination of thealuminum matrix metal carbide, oxide fibers or the

alloying of aluminum oxides in a variety of powder.Alloys of aluminum can replace some of the tita-nium alloys in the manufacturing of tanks and re-servoirs with a significant reduction in weight.

The Al-Mg alloys have significant corrosionresistance and hardness. The most commonlyused Al-Mg alloys contain 1-5% Mg. The Al-Mnalloys are used to significantly increase the corro-sion resistance [11].

Metalized coatings are very convenient forlarge products and structures. The refractory metalcan be applied by plasma spraying and vapordeposition. Vacuum metallization of products bycondensation of metal vapor is used to protectmetal surfaces. This method can deposit layers ofdifferent thickness of aluminum, nickel, chromium,cadmium, and other metals.

To prevent corrosion of underground andhydraulic structures, as well as the chemicalequipment operating with aggressive conductivemedium, electrochemical methods of protection areused. Underground structures, such as gasolinestorage tanks and pipelines, have corrosionprotection of bitumen and asphalt, as well aspolymeric tapes and enamels. Protection from straycurrents is provided by drainage.

CONCLUSION

Strategic management of development of retailtrade network is a complex model, coveringdifferent areas. One of the important parameters ofthis model is the foresight and planning the level ofexposure and the effects on the environment,aggravated by a considerable number of normativeand regulatory acts, as well as technologicalparameters. However, for the purpose of makingplans and strategic management is possible toapply a system of indicators of the environmentalimpact, based on the DPSIR methodology that willallow for both risk assessment procedures andmethods of management influence on suchindicators, as well as continuous monitoring andnecessary adjustments in the project life cycle.

The application of control indicators of DPSIRmodel EEA in the development strategy of retailtrade obtaining the impact on the environment andeconomic effect of the applied technologies ispossible by optimization of some technological andorganizational processes at the petrol/gas stations.

The use of LED technology in petrol/gasstations reduces energy consumption by 20%.Reduce energy consumption by applying energysaving technologies enables the realization ofmeasures to improve energy efficiency and otheressential indicators for sustainable energy.



REFERENCES

[1] Bajin D., Jovanović L., (2010) Energy efficiency infunction of environment protection. Ecologica 59,287-292.

[2] Black J. T., Kohser R.A., (2011) DeGarmo'smaterials and processes in manufacturing, JohnWiley and Sons

[3] DeGarmo E.P., Black J.T., Kohser R.A., KlameckiB.E., (2003) Materials and Processes in Manu-facturing, John Wiley and Sons

[4] EEA, DPSIR indicators, 2010.[5] Jovanović L., Bajin D., (2011) Primena obnovljivih

izvora energije u saobraćaju, Tematski zbornikradova, Međunarodna naučna konferencija"Energetska efikasnost železnice u funkciji održivograzvoja", Beograd, 21-32.

[6] Jovanovic L., Bajin D., (2012) Nove resursoštedljivetehnologije i savremeni ekološki problemi, Ecologica67, 331-336.

[7] Jovanović L., Ermakov V., Čajka Z., (2014)Renewable energy resources in Serbia and Russia,Zaštita materijala 55, No 2, 133-141.

[8] Jovanović L.: Renewable energy resources inSerbia. In: Ermakov V.V. (ed.), (2013) Biogeo-chemistry and Biochemistry of trace elements underconditions of technogeneses of the biosphere,Proceedings of the VIII International Biogeoche-mical School, devoted to the 150th anniversary ofthe birth of V.I. Vernadsky, Grodno State University,Moscow: GEOKHI RAS, 2013, pp. 38-42.

[9] Hinckley James, Hinckley Jim, Robinson J.G.,(2005) The Big Book of Car Culture: The ArmchairGuide to Automotive Americana, MotorbooksInternational

[10] Oettel H., Schumann H. (Eds.), (2011) Metallo-grafie: mit einer Einführung in die Keramografie.John Wiley and Sons, p. 284.

[11] Sanders Jr, R.E., (2001) Technology innovation inaluminum products, JOM 53,No 2, 21-25.

IZVOD

OPTIMIZACIJA RAZVOJNIH PROCESA NA MREŽAMA BENZINSKIH PUMPI U CILJUPOVEĆANJA ENERGETSKE EFIKASNOSTI

Razvoj mreže benzinskih pumpi zahteva kompleksan pristup proceni uticaja na životnu sredinu.Upotreba odgovarajućih indikatora prema DPSIR metodologiji omogućava optimizaciju procesa nabenzinskim pumpama i povećanje energetske efikasnosti.Korišćenje obnovljivih izvora energije i novih izolacionih materijala ima veliki značaj za smanjenjepotrošnje energije za grejanje zgrada benzinskih stanica. Kao zamenu za stiropor i stirodur (zadodatnu izolaciju zidova i podova) i za izgradnju novih objekata mnogo je efikasnije koristitiblokove od inovativnih izolacionih materijala.Široka primena obnovljivih izvora energije i termoizolacionih materijala u zgradama benzinskihstanica, smanjenje potrošnje električne energije korišćenjem LED tehnologija, kao i uštede gorivau transportu usled smanjene težine cisterni načinjenih od Al legura i kompozitnih materijalapredstavljaju osnovne metode povećanja energetske efikasnosti. Upotreba Al legura u konstrukcijicisterni i rezervoara, takođe, povećava otpornost na koroziju.Ključne reči: benzinska pumpa, optimizacija, DPSIR metodologija, indikatori, energetskaefikasnost, obnovljivi izvori energije, LED tehnologija, otpornost na koroziju, Al legure.


M. PETROVIĆ TEMPERATURA VAZDUHA KAO BITAN KLIMATSKI – METEOROLOŠKI ...


MILOŠ PETROVIĆ Originalni naučni radUDC:551.524.7

Temperatura vazduha kao bitan klimatski – meteorološkiparametar za određivanje evapotranspiracije

Temperatura vazduha spada u osnovne klimatske parametre. Kao klimatski parametarobezbeđuje energiju za isparavanje i premeštanje vodene pare sa površine koja isparava iodređuje vrednost evapotranspiracije. Vazduh se zagreva posredstvom zemljine površinetoplotom koja stiže sa Sunca. Veličina isparavanja u velikoj meri zavisi od temperature vazduha.Skoro sve metode zasnivaju svoje proračune na ovom klimatskom parametru, a neke metodesamo na osnovu temperature vrše proračun evapotranspiracije.Ključne reči: temperatura vazduha, klimatski parametar, evapotranspiracija

UVOD

Jedan od osnovnih prirodnih resursa koji odre-đuje ukupan razvoj privrede i društva na nekompodručju je klima [1]. Evapotranspiracija je jedanod najznačajnijih procesa unutar hidrološkog ciklu-sa, čija pouzdana procena je od suštinske važnostipri planiranju i upravljanju zemljišnim i vodnim re-sursima [2]. Na evapotranspiraciju svakako najvećiuticaj ima temperatura vazduha kao klimatski fak-tor. Temperatura vazduha je jedan od osnovnihklimatoloških elemenata. Njena direktna funkcio-nalna zavisnost je vezana za geografsku širinu(bilans zračenja, odnosno, dužina osunčavanja),geografsku dužinu i nadmorsku visinu. Podaci naosnovu kojih se radi analiza toplotnog stanja vaz-duha beleže se u redovnim klimatološkim termi-nima (7, 14 i 21 čas po lokalnom vremenu, na visiniod 2 m od tla). Za većinu lokacija je dovoljno imativrednost minimalne i maksimalne dnevne tempera-ture vazduha. U našim klimatskim uslovima vlaž-nost vazduha se može dobiti na osnovu minimalnetemperature vazduha. Merenja temperature vaz-duha su jednostavna i ne podležu velikim greš-kama za razliku od ostalih klimatskih parametara.Temperatura se meri gotovo na svim mestima ipodaci su lako dostupni.

TEMPERATURA VAZDUHA

Temperaturni podaci, na raznim mestima uSrbiji, su godišnji pokazatelji promene temperaturau tim sredinama. Ovi podaci pokazuju periodičnostu promeni temperature ali i njihove eksreme.

Adresa autora: Tehnička škola “12. februar” Niš,Građevinsko – Arhitektonski fakultet Univerziteta uNišu

Primljeno za publikovanje: 23.12.2013.Dorađeno za publikovanje: 15.03.2014.Prihvaćeno za publikovanje: 20.04.2014.

Temperaturni ekstremi, od kad postoje merenjau Srbiji do sada, su pokazali sledeće vrednosti: Najviša temperatura, + 44.9oC, izmerena je 24.

jula 2007. godine u Smederevskoj Palanci, i Najniža temperatura, - 39.5oC, izmerena je 13.

januara 1985. godine u Karajukića Bunarimana Pešterskoj visoravni.Temperaturni režim, kao mera toplotnih uslova,

na području Srbije je prvenstveno uslovljena Sun-čevom radijacijom, geografskim položajem i relje-fom. Takođe, u zavisnosti od reljefa i ekspozicijapadina, svuda na području naše zemlje susrećemoodlike lokalne klime. Najveći deo teritorije Srbijepripada klimi umerenog pojasa. Jugozapadni deoRepublike Srbije nalazi se na granici sredozemnesuptropske i kontinentalne klime. Prosečna godiš-nja temperatura vazduha za područja sa nadmor-skom visinom do 300 m iznosi 10.9 oC a za pod-ručja sa nadmorskom visinom od 300 m do 500 moko 10.0oC. U planinskim predelima od preko 1000m nadmorske visine srednje godišnje temperaturesu oko 6.0 oC, a na visinama preko 1500 m oko3.0oC. Jesen je toplija od proleća. Najhladniji me-sec je januar sa srednjom mesečnom temperatu-rom u intervalu od -6.0 oC u planinskim predelimado oko 0.0 oC u ravničarskim delovima zemlje.Najvišu srednju januarsku temperaturu od 0.4 oCima Beograd zbog izraženog urbanog uticaja, dokpodručja sa nadmorskom visinom do 300 m imajusrednju januarsku temperaturu od -1.0 do 0.0 oC,gde se izdvaja područje Timočke krajine i izraženihkotlina sa srednjim temperaturama u januaru i do -3.0 oC. Za mesta sa nadmorskom visinom u inter-valu od 300 do 500 m, srednje januarske tempera-ture se kreću od -3.0 do -1.0 oC, a u mestima sanadmorskom visinom preko 1000 m od -6.0 do -3.0oC. Najtopliji mesec je jul sa srednjom mesečnomtemperaturom u intervalu od 11.0 do 22.0 oC. Pod-ručja sa nadmorskom visinom do 300 m imajusrednju julsku temperaturu u intervalu od 20.0 do



22.0 oC, kao i neka mesta u južnoj Srbiji, čija jenadmorska visina od 400 do 500 m. Iznad 1000 mnadmorske visine, srednja julska temperatura je uintervalu od 11.0 do 16.0oC. Najniže temperature uperiodu 1961 – 1990.godine su registrovane u ja-nuaru i kreću se u intervalu od -35.6 oC (Sjenica)do -21.0 oC (Beograd). Apsolutni maksimumi tem-perature u posmatranom periodu izmereni su u jului kreću se u intervalu od 37.1 do 42.3 oC [3].Srednja dnevna temperatura, Tsr, koja se koristi umnogim metodama dobija se kao polovina zbiramaksimalne i minimalne dnevne temperature:

2minmax TT

Tsr

(1)

SOLARNA RADIJACIJA

Proces evapotranspiracije je određen količinomraspoložive energije za isparavanje vode. Solarnaradijacija je najveći izvor energije i sposobna je davelike količine vode pretvori u vodenu paru [4]. Zaisparavanje vode koristi se samo deo solarne ener-gije. Količina energije zračenja Sunca koja dospevado granice atmosfere se naziva ekstraterestrijalnaradijacija (Ra) i zavisi samo od geografske širine iod doba godine. U atmosferu dolazi do apsorbo-vanja i difuznog rasipanja dela ekstraterestrijalnogzračenja. Do Zemlje dospeva deo difuznog zrače-nja i direktno sunčevo zračenje naziva se solarnaradijacija (Rs) i njena vrednost zavisi od ekstratere-strijalne radijacije i provodljivosti atmosfere. Zemlji-na površina ne apsorbuje celokupno zračenje ijedan deo radijacije se reflektuje nazad u atmo-sferu. Količina reflektovanog zračenja zavisi od ref-lektovane površine. Zeleni biljni pokrivač reflektuje20-25% prispelog zračenja, a vodena površina oko5%. Postoji veliki broj metoda za proračun referen-tne evapotranspiracije (ETo), koja nalazi široku pri-menu u mnogim oblastima privrede i nauke. U okvi-ru Organizacije Ujedinjenih nacija za hranu i poljo-privredu, FAO, posle brojnih testiranja poznatihmetoda, model Penman-Monteith-a [5] je prihvaćenkao standard za određivanje ETo i označen je kaoFAO56-PM. Međutim, za korišćenje ovog modelapotreban je veći broj ulaznih parametara. Jednosta-vnija je metoda za proračun referentne evapotran-spiracije. To je jednačina Hargreaves-a [6] kod kojese izračunavanje bazira na maksimalnim, minimal-nim i srednjim dnevnim temperaturama vazduha,kao i na ekstraterestričkom Sunčevom zračenju idužini obdanice tokom godine za dati lokalitet. Ana-liza dnevnih vrednosti evapotranspiracije po metodiHargreaves-a pokazala je njihovo dobro slaganje srezultatima dobijenim standardnom metodomFAO56-PM za podatke sa teritorije RepublikeSrbije, tj. tačnost dovoljnu za praktičnu primenuovih rezultata. U Odeljenju za agrometeorologiju

RHMZS, uz određivanje aktuelnih dnevnih vred-nosti referentne evapotranspiracije na osnovu ope-rativnih podataka sa Glavnih meteoroloških sta-nica, pripremaju se i prognoze ETo za deseto-dnevni period za iste lokacije. Prognozirane vred-nosti se zasnivaju na determinističkim prognozamamaksimalnih i minimalnih dnevnih temperatura vaz-duha (Evropski centar za srednjoročnu prognozu -ECMWF i RHMZS). Operativno izračunavanje iažuriranje rezultata proračuna na Internet prezen-taciji Zavoda obavljaju se svakodnevno, u jutarnjimčasovima. Za odabrane GMS se u obliku tabeledaju vrednosti ETo po danima i to: za prethodnihpet dana (aktuelne vrednosti), za tekući dan i na-rednih devet dana (prognozirane vrednosti). Izme-đu ostalog, ove vrednosti referentne evapotran-spiracije mogu se, pod uslovom da se primene iodgovarajući koeficijenti kulture, koristiti za ocenustanja i procenu potreba za navodnavanjem usevau poljoprivrendoj praksi [7]. Hargreaves u svojojmetodi računa soranu radijaciju, koristeći tempe-rature, prema formuli:

as RTTKR 5,0minmax )( (2)

gde je: Rs - solarna radijacija, Tmax - prosečna dnevna maksimalna tempera-

tura vazduha, Tmin - prosečna dnevna minimalna temperatu-

ra vazduha u nekom periodu (generalno jedanmesec), i

K - empirijski koeficijent koji za područje uunutrašnjosti iznosi 0,16, a za lokacije na obalimora 0,19.Ovaj izraz se preporučuje za desetodnevne i

mesečne proračune. Formula je nastala 1985. Go-dine. Sa promenljivim uspehom koristi se i za dnev-ne proračune [4]. Bristow i Campbell su dali svojizraz za proračun dnevnih vrednosti solarne radi-jacije 1984. godine. U formuli figuriše razlika izme-đu maksimalne i minimalne temperature:

Cas TTBRAR minmaxexp1 (3)

gde je: Rs - dnevna solarna radijacija, Tmax - prosečna dnevna maksimalna tempe-

ratura vazduha, Tmin - prosečna dnevna minimalna tempe-

ratura vazduha, Ra - dnevna ekstraterestrijalna radijacija, i A,B i C - empirijski koeficijenti, imaju fizičko

značenje.Koeficijent A predstavlja maksimalnu solarnu

radijaciju koja se može očekivati u danu bez obla-



ka, dok koeficijenti B i C kontrolišu uticaj promenetemperaturne razlike na vrednost radijacije [4].Predložene vrednosti koeficijenata su: A= 0,7, B= 0,004 - 0,010, i C= 2,4.

Brojni radovi pokazuju da Hargreaves metodaprecenjuje vrednosti referentne evapotranspiracijena humidnim lokacijama [8 - 10].

VLAŽNOST VAZDUHA

Voda koja isparava iz zemljišta, vodenihpovršina i biljaka dospeva u atmosferu u oblikuvodene pare koja ima svoj određeni napon. Sapovećanjem vlažnosti povećava se i napon vodenepare u vazduhu koji na nekoj temperaturi može daprimi samo određenu količinu vodene pare. Kadaprimi najveću moguću količinu vodene pare, kaže

se da je vazduh zasićen vodenom parom. Naponzasićene vodene pare naziva se maksimalni naponvodene pare i označava se sa ea. Maksimalninapon vodene pare zavisi od vrednosti temperaturevazduha i raste sa porastom temperature[4].Temperatura vazduha na kojoj stavrna količinavodene pare predstavlja maksimalni napon vodenepare naziva se temperatura tačke rose. Na ovojtemperaturi vodena para ponovo prelazi u tečnostanje [11]. FAO-56 Penman-Monteith metodazahteva brojne ulazne podatke i to: maksimalna iminimalna temperatura vazduha; maksimalna iminimalna relativna vlažnost vazduha (ili stvarninapon vodene pare), brzina vetra na 2 m visine,stvarno trajanje sunčevog sjaja (ili solarnaradijacija) [12]. U slučaju da nema podataka orelativnoj vlažnosti i sunčevom sjaju, predlaže seproračun relativne vlažnosti i solarne radijacije izizraza u kojima figuriše minimalna temperatura:

3,237

27,17exp611,0

3,237

27,17exp611,0

min

min

T

T

T

Te

dew

dewd (4)

U humidnoj klimi se temperatura tačke rosemože zameniti minimalnim dnevnim temperatura-ma. Temperatura vazduha opada tokom noći usledneto gubitaka dugotalasne radijacije u atmosferi.Za stanice u humidnoj klimi, neto gubici radijacijeomogućavaju kontinuirano hladjenje dok donjigranični sloj ne postane zasićen vodenom parom ine dostigne temperaturu tačke rose. Kada tempe-ratura vazduha padne ispod tačke rose, vodenapara počinje da se kondezuje usled supersaturacijevazduha čime oslobađa latentnu toplotu. Latentnatoplota sprečava dalji pad temperature vazduha.Naučnici Temesgen i Rayvili su 1999. godine po-krenuli proceduru za izmenu temperaturnih para-metara aridnih stanica [13]. Izmenama se pristupakada je ispunjen uslov prema jednačini:

2min dewTTMDD (5)

gde je: MDD - srednje odstupanje tačke rose, Tmin - minimalna temperatura, i Tdew - temperatura tačke rose.

Smatra se da “prozor” od 2 oC reprezentujereferentne uslove i da nema potrebe za izmenamavrednosti temperaturnih parametara [4].

REZULTATI I DISKUSIJA

Da bi se pokazala tačnost prikazanih jednačinauzeto je u razmatranje promena vremenskih para-metara na području grada Niša. Analiza obuhvata

uticaj temperature vazduha na evapotranspiracijuza područje grada Niša. Za tri vremenska periodaanalizirana je mogućnost primene gore navedenihtemperaturnih metoda za proračun referentne eva-potranspiracije. Ovi podaci su u tabelama 1,2 i 3.

Tabela 1 - Upoređivanje dnevnih vrednosti solarneradijacije (MJ 1/㎡ 1/dan) na osnovu izrazaHargreaves et al.

Upoređivanje dnevnih vrednosti solarne radijacije(MJ m-2 dan-1)

NIŠ (1998)

Meseci Rs Rs0.16 PE0.16

I 6.35 6.60 0.039

II 8.97 9.88 0.101

III 13.96 13.9 -0.004

IV 16.24 19.00 0.170

V 17.14 21.45 0.252VI 24.67 25.18 0.021VII 23.45 24.86 0.060

VIII 20.49 21.93 0.071

IX 13.13 14.26 0.086

X 9.81 10.87 0.108

XI 4.97 5.89 0.185

XII 4.46 4.74 0.064

Prosek 13.64 14.88 0.091

PEk=(Rsk-Rs)/Rs



Tabela 2 - Upoređivanje mesečne vrednosti so-larne radijacije (MJ 1/㎡ 1/dan) premaHargreaves et al.

Upoređivanje mesečne vrednosti solarne radijacije(MJ m-2 dan-1)NIŠ (1977/84)

Meseci Rs(A) Rs(H) PEI 4.724 5.801 0.228II 7.303 8.285 0.134III 11.859 13.297 0.121IV 15.577 18.399 0.181V 19.249 21.978 0.142VI 21.527 23.770 0.104VII 22.411 23.436 0.046VIII 19.471 20.827 0.070IX 14.936 16.655 0.115X 9.860 11.390 0.155XI 5.581 6.810 0.220XII 3.931 4.959 0.261

Prosek 13.036 14.634 0.123PE=(Rs(H)-Rs(A))/Rs(A)

U tabeli 1 upoređivane su dnevne vrednostisolarne radijacije (MJ 1/㎡ 1/dan) za godinu 1998.a na osnovu jednačine 2.

Za područje Niša korišćenjem koeficijentaK=0.16 dobija se odstupanje od oko 9%, a umesecu julu ono iznosi 6%.

U tabeli 2 upoređivane su mesečne vrednostisolarne radijacije (MJ 1/㎡ 1/dan) za period 1977-1984 godina a prema jednačini 2.

Mesečne vrednosti solarne radijacije odstupajuza oko 8%.

U tabeli 3 je data vrednost ETo (mm) uzavisnosti od načina proračuna solarne radijacije(MJ m-2 dan-1) i ta vrednost je upoređena sarezultatima Penman-Monteith metode sa solarnomradijacijom dobijenom preko trajanja suncevogsjaja (PM). podaci su dati za period posmatranja uNišu od 1993 do 1996 godine.

Odstupanje pri proračunu evapotranspiracije zaoko 40% manje nego kod solarne radijacije i iznosi6.3% na godišnjem nivou a 7.4% za jul mesec.

Tabela 3 - Penman-Monteith metoda solarne radijacije korišćenjem izraza Hargreaves et al. označene kaoPM(Rs(T) i upoređeno sa rezultatima Penman-Monteith metode sa solarnom radijacijomdobijenom preko trajanja sunčevog sjaja (PM)

ETo (mm) u zavisnosti od načina proračuna solarne radijacije (MJ m-2 dan-1)

NIŠ 1993/96

Meseci Rs(A) Rs(H) PE1 PM PM(Rs(T) PE2

I 5.035 5.882 0.168 0.557 0.545 -0.022

II 7.885 9.109 0.155 0.971 0.995 0.025

III 11.488 13.360 0.163 1.642 1.742 0.061

IV 15.801 18.491 0.170 2.671 2.904 0.088

V 19.294 22.539 0.168 3.642 4.022 0.104

VI 22.605 24.894 0.101 4.487 4.786 0.067

VII 22.625 25.349 0.120 4.823 5.178 0.074

VIII 19.954 21.841 0.095 4.299 4.535 0.055

IX 14.842 16.381 0.104 2.747 2.894 0.053

X 10.042 11.364 0.132 1.496 1.563 0.045

XI 5.806 6.901 0.189 0.691 0.687 -0.006

XII 3.982 5.016 0.260 0.468 0.432 -0.076

Prosek 13.280 15.094 0.137 2.375 2.524 0.063

Formula PE1=(Rs(H)-Rs(A))/Rs(A) PE2=(PM-PM(Rs(T))/PM

U tabelama 4 i 5 upoređivane su vrednostinapona vodene pare za posmatrane period nateritoriji grada Niša.

U tabela 4 date su vrednosti napona vodenepare dobijene preko minimalne temperature ozna-čene ed(T), za period posmatranja od 1977. do1984. godine u Nišu.



Tabela 4 - Vrednosti napona vodene pare dobijenepreko minimalne temperature označene ed(T)

Upoređivanje vrednosti napona vodene pare

NIŠ (1977/84)

Meseci ed (kPa) ed(T) (kPa) (ed(T)-ed)/ed

I 0.525 0.496 -0.054

II 0.569 0.583 0.025

III 0.682 0.741 0.087

IV 0.783 0.884 0.129

V 1.158 1.261 0.089

VI 1.501 1.525 0.016

VII 1.567 1.621 0.034

VIII 1.547 1.612 0.042

IX 1.347 1.303 -0.033

X 1.056 1.002 -0.051

XI 0.723 0.685 -0.053

XII 0.594 0.567 -0.044

Prosek 1.004 1.023 0.019

Prosečno godišnje odstupanje u odnosu namerenu vrednost napona vodene pare je zane-marljivo i iznosi oko 4%.

U tabeli 5 date su vrednosti proračuna evapo-transpiracije FAO-56 Penman-Monteith metodomkorišćenjem temperature vazduha na području Ni-ša u periodu od 1993. do 1996. godine.

Prosečno godišnje odstupanje je 1.9%, a od-stupanje u mesecima maksimalne potrošnje je od1.4% do 3.4%

Tabela 5 - Proračun evapotranspiracije FAO-56 Penman-Monteith metodom korišćenjem temperaturevazduha

Evapotranspiracija u zavisnoti od načina proračuna vodene pare

NIŠ 1993/96

Meseci ed (kPa) ed(T) (kPa) (ed(T)-ed)/ed PM (mm) PM(ed(T) (mm) PM(ed(T))-PM)/PM

I 0.520 0.514 -0.012 0.557 0.548 -0.016

II 0.525 0.527 0.005 0.971 0.958 -0.013

III 0.625 0.644 0.062 1.642 1.582 -0.037

IV 0.853 0.955 0.120 2.671 2.561 -0.041

V 1.268 1.333 0.052 3.642 3.595 -0.013

VI 1.465 1.587 0.083 4.487 4.424 -0.014

VII 1.508 1.762 0.169 4.823 4.715 -0.022

VIII 1.510 1.806 0.196 4.299 4.151 -0.034

IX 1.308 1.398 0.069 2.747 2.703 -0.016

X 1.053 1.029 -0.022 1.496 1.495 -0.001

XI 0.728 0.690 -0.051 0.691 0.732 0.059

XII 0.623 0.600 -0.037 0.468 0.490 0.049

Prosek 0.999 1.072 0.074 2.375 2.330 -0.019

ZAKLJUČAK

Upoređivanjem dnevnih vrednosti solarne radi-jacije dobijene na osnovu stavrnog sunčevog sjaja ina osnovu temperature vidi se da su odstupanjaveća, što važi i za posmatranja na mesečnim ni-voima. Analizom se dolazi do zaključka da i meto-de kod kojih se koristi razlika između maksimalne iminimalne temperature vazduha obezbeđuju zado-voljavajuće rezultate posmatranja. Ovim se dolazido toga da nije potrebno poznavati trajanje sun-čevog sjaja i da se solarna radijacija može dobiti

samo na osnovu maksimalne i minimalne tempe-rature vazduha. Dobijenim rezultatima se može za-ključiti i da se temperatura tačke rose može zame-niti minimalnom temperaturom. Takođe, izvršenomanalizom se može zaključiti da je dovoljno imatiminimalne i maksimalne dnevne temperature vaz-duha kako bi se došlo do potrebnih podataka.Pokazano je da se u našim klimatskim uslovimavlažnost vazduha može dobiti na osnovu tempe-raturne razlike, 7.4%, što je na gornjoj graniciprihvatljivosti.



LITERATURA

[1] Rajić, M. & Štula, S., (2007) Klimatske promene ipojava suša na području Južne Bačke, Letopisnaučnih radova Poljoprivrednog fakulteta, 31(1), 80-89.

[2] Đukić, V. & Mihailović, V., (2012) Kritička analizasavremenih metoda za proračun referentneevapotranspiracije, Glasnik Šumarskog fakulteta,57-70.

[3] www.hidmet.gov.rs/ciril/meteorologija/klimatologija_temp_rezim.php

[4] Trajković, S., (2009) Metode proračuna potrebe zavodom u navodnjavanju, Univerzitet u Nišu,Građevinsko-arhitektonski fakultet.

[5] Allen, R. G., Pereira, L. S., Reas, D., and Smith, M.,(1998) Crop Evapotranspiration. Guidelines forComputing Crop Water Requirements. FAOIrrigation and Drainage Paper 56, FAO, Roma,

[6] Hargreaves, G, H., and Allen, R. G., (2003) Historyand Evaluation of Hargreaves EvapotranspirationEquation, Jurnal of Irrigation and DrainageEngineering, 129(1), 53-63.

[7] www.hidmet.gov.rs/ciril/meteorologija/agro_evapotranspiracija.php

[8] Amatya, D. M., Skaggs, R. W. & Gregory, J. D.,(1995) Comparison of Methods for Estimating REF-ET, Journal of Irrigation and Drainage Engineering,121(6), 427-435.

[9] Jensen, M. E., Burman, R. D. & Allen, R. G., (1990)Evapotranspiration and irrigation waterrequirements, ASCE manuals and reports onengineering practice, ASCE, 70.

[10] Trajkovic, S. & Kolakovic, S., (2009) Evaluation ofReference Evapotranspiration Equations underHumid Conditions, Water Resources Management,23 (14), 3057-3067.

[11] www.sr.wikipedia.org/sr/vlaznost_vazduha[12] Trajković, S., Gocić, M. & Milićević. D., (2011)

Upoređivanje tri temperaturne metode proračunareferentne evapotranspiracije, Zbornik radovaGrađevinsko-arhitektonskog fakulteta Niš, 139-146.

[13] Temesgen, B., Allen, R. G., and Jensen, D. T.,(1999) Adusting Temperature Parameters to ReflectWell-Waterd Conditions, Jurnal of Irrigation andDrainage Engineering, 125(1), 26-33.

ABSTRACT

AIR TEMPERATURE AS AN IMPORTANT CLIMATE - METEOROLOGICAL PARAMETERFOR EVAPOTRANSPIRATION DETERMINATION

The air temperature is one of the major climatic parameter. As climatic parameter, it providesenergy for evaporation, transpiration and water vapor cycling that determine the value ofevapotranspiration. The air is heated by the earth's surface and by the solar radiation. Evaporationamount depend largely on the air temperature. Almost all methods for evapotranspirationestimation are based on climatic parameters, and only few methods use only temperature data.Keywords: air temperature, climatic parameters, evapotranspiration.

Scientific paperReceived for Publication: 23. 12. 2013.Corrected for Publication: 15.03.2014.Accepted for Publication: 20. 04. 2014.

ENGINEERING CARD – INŽENJERSKA KARTICA



FEANI, Evropska federacija nacionalnih inženjerskih udruženja, okuplja nacionalne članice iz 32zemlje i zastupa interese preko 3,5 miliona profesionalnih inženjera u Evropi. Kao asocijacija koja jezvanično priznata od strane Evropske unije i njenih organa, kao predstavnik inženjerske profesije uEvropi, FEANI sarađuje sa Direktoratom za unutrašnje tržište i usluge i drugim organima EU.

U skladu sa Statutom FEANI inženjeri jedne zemlje su u članstvu FEANI zastupljeni preko nacionalnečlanice FEANI iz te zemlje. Savez inženjera i tehničara Srbije je postao nacionalna članica FEANI iz Srbijeprijemom u članstvo na zasedanju Generalne skupštine FEANI održanom u Pragu 2006. godine.

Osnovni ciljevi FEANI, kao profesionalne asocijacije inženjera, su afirmacija inženjerske profesije,podsticanje kreativnosti i inovacija u inženjerstvu i istraživačkom radu, promovisanje dobrih praksi ikontinuiranog profesionalnog usavršavanja i obezbeđivanje priznavanja kvalifikacija inženjera nameđunarodnom nivou. U okviru svojih brojnih aktivnosti, pre svega usmerenih na međusobno povezivanjeinženjera Evrope i afirmisanje statusa i njihove uloge u društvu, a težeći ka jedinstvenom glasuinženjerske profesije u Evropi, FEANI posebnu pažnju posvećuje usavršavanju inženjera i priznavanjunjihovih kvalifikacija, stečenih u okviru nacionalnih obrazovnih sistema, na evropskom nivou.

U tom smislu, osnovni zadatak Evropske komisije za monitoring, koja deluje u okviru FEANI-a, jebriga o FEANI INDEX – listi institucija visokog obrazovanja za inženjere, u zemljama članicama, koje supriznate na evropskom nivou i dodela EUR ING titule.

Titula EUR ING je međunarodna profesionalna titula koja se koristi u mnogim evropskim zemljamai od 1987. godine 31.000 inženjera je postalo nosilac te titule. Pored EUR ING titule FEANI, koji je uprethodnom periodu intenzivno sarađivao u radu na predlozima za izmene Evropske Direktive oprofesionalnim kvalifikacijama, je pre tri godine počeo i sa realizacijom projekta EngineerING Card –inženjerska kartica.

Projekat, originalno osmišljen i pokrenut od strane VDI – nemačke inženjerske asocijacije, imao jeza cilj kreiranje sredstva kojim će da se pomogne mobilnost inženjera u Evropi i omogući prevazilaženjenedostatka postojećeg visokokvalifikovanog kadra, posebno u zemljama Zapadne Evrope. Ceo projekat jepodržan od strane nemačkog Ministarstva ekonomije i rukovodstva velikih kompanija u Nemačkoj, kao štoje npr. AUDI.

Projekat je pokrenut u skladu sa najnovijim izmenama Direktive o profesionalnim kvalfikacijamaEU, kojima se predviđa mogućnost uvođenja profesionalnih kartica kao načina pospešivanja i olakšavanjamobilnosti radne snage. U ceo projekat su do sada uključene nacionalne članice FEANI iz 11 zemaljameđu kojima su Nemačka, Holandija, Češka, Portugalija, Poljska, Irska i dr.

Na osnovu odluke Upravnog odbora SITS o uključivanju u projekat Inženjerska kartica, a u skladusa odredbama FEANI, 2014. godine potpisan je Ugovor između FEANI i SITS o implementaciji projektaInženjerska kartica tj. izdavanju kartice na teritoriji Republike Srbije.

Gore navedenim Ugovorom Savez se obavezao da se prilikom izdavanja kartice strogo pridržavapravila preciziranih od strane FEANI, da se celokupno poslovanje odvija u skladu sa odgovarajućimPriručnikom izdatim od strane FEANI, da se kartica izdaje u tipiziranom formatu i da se vodi Nacionalniregistar inženjera. U cilju realizacije odredbi Ugovora SITS je bio u obavezi da obezbedi podrškunadležnih institucija na nacionalnom nivou, te je u tom smislu potpisan Ugovor o saradnji na izdavanjuinženjerske kartice u Republici Srbiji sa Nacionalnim savetom za visoko obrazovanje, kao regulatornimorganom Narodne skupštine Republike Srbije.



U skladu sa propisanom procedurom formirana je Komisija za Nacionalni registar, u čiji sastav suušli: mr Branislav Vujinović, generalni sekretar Saveza, prof. dr Časlav Lačnjevac, predsednik Saveza,prof. dr Srđan Stanković, predsednik Nacionalnog saveta za visoko obrazovanje, mr Zoran Pendić,rukovodilac Razvojnog centra SITS, dr Milovan Živković, predsednik SMEITS.

Urađeni su proceduralni principi za dodelu inženjerske kartice i usvojeni Pravilnik o radu Komisijeza Nacionalni registar i Pravilnik o radu Odbora za žalbe. U sledećoj fazi realizacije projekta od nemačkeinženjerske asocijacije VDI je preuzet odgovarajući softver, koji je prilagođen našim uslovima i koji trebada omogući pojedincima zainteresovanim za dobijanje inženjerske kartice da apliciraju za istu.

Pošto je jedan od preduslova koji mora da bude zadovoljen, da bi pojedinac mogao da dobijekarticu, taj da se program koji je završio nalazi u FEANI INDEX, listi visokoobrazovnih institucija koju vodeFEANI i u koju su uvrštene preko 960 visokoobrazovnih institucija iz 30 evropskih zemalja među kojima sui prestižne institucije kao što je npr. Cambridge University, ili da je program u skladu sa EUR ACEstandardima, pristupilo se obimnom poslu prijave naših visokoobrazovnih programa.

Prijavljeni su programi sledećih fakulteta: Univerzitet u Beogradu: Mašinski fakultet, Elektrotehnički fakultet, Arhitektonski fakultet, Građevinski

fakultet, Tehnološko metalurški fakultet, Saobraćajni fakultet, Šumarski fakultet, Rudarsko geološkifakultet, Tehnički fakultet u Boru

Univerzitet u Novom Sadu: Fakultet tehničkih nauka, Tehnološki fakultet Univerzitet u Kragujevcu: Fakultet tehničkih nauka Čačak, Agronomski fakultet Čačak, Fakultet za

mašinstvo i građevinarstvo Kraljevo Univerzitet u Nišu: Elektronski fakultet, Fakultet zaštite na radu

Radi provere programa formirana je posebna radna grupa za Srbiju od strane EMC – Evropskekomisije za monitoring, koja je u FEANI nadležna za uvrštavanje programa u INDEX i dodelu EUR INGtitule. Složena procedura provere je još uvek u toku. Prijavljeno je 130 programa osnovnih i masterstudija sa gore navedenih fakulteta.

Do sada je stigao potvrdan odgovor za programe osnovnih i master akademskih studijaMašinskog fakulteta Univerziteta u Beogradu, osnovnih i master akademskih studija Elektrotehničkogfakulteta Univerziteta u Beogradu, osnovnih i master akademskih studija Građevinskog fakultetaUniverziteta u Beogradu, osnovnih i master akademskih studija Saobraćajnog fakulteta Univerziteta uBeogradu, osnovnih i master akademskih studija Rudarsko geološkog fakulteta Univerziteta uBeogradu, neke programe osnovnih i master akademskih studija Tehničkog fakulteta u BoruUniverziteta u Beogradu, neke programe osnovnih i master akademskih studija Fakulteta tehničkihnauka Univerziteta u Novom Sadu, neke programe osnovnih i master akademskih studija Tehničkogfakulteta u Čačku Univerziteta u Kragujevcu, neke programe osnovnih i master akademskih studijaFakulteta za mašinstvo i građevinarstvo u Kraljevu, Univerziteta u Kragujevcu i neke programeosnovnih akademskih studija Agronomskog fakulteta u Čačku, Univerziteta u Kragujevcu. Ostaliprijavljeni programi se nalaze u procesu provere.

Savez je u međuvremenu, na svom WEB sajtu, postavio informaciju o načinu apliciranja zainženjersku karticu i kreiran je poseban sajt sa domenom www.ik.sits.rs koji služi za apliciranje.

Realizacijom celog projekta kod nas rukovodio je generalni sekretar SITS, mr Branislav Vujinović.Pokretanjem ovog projekta u Srbiji, stvorene su mogućnosti za dodatnu afirmaciju naših univerziteta

i fakulteta na međunarodnom planu, njihovu veću prepoznatljivost kada je u pitanju učestvovanje uprojektima, i povećanje interesovanja inostranih studenata za studiranje na našim fakultetima.

Istovremeno omogućeno je brojnim stručnjacima iz Srbije i onim na privremenom radu uinostranstvu da njihove kvalifikacije na jednostavniji način budu prepoznate u međunarodnim okvirima i daiza njih stane najjača inženjerska asocijacija u Evropi, dok je Savez u međunarodnim okvirima prepoznatkao relevantni predstavnik tehničke inteligencije Srbije.

Prof. dr Časlav Lačnjevac, Komisija za Nacionalni registarMr Zoran Pendić, Komisija za Nacionalni registar

Olivera Ćosović, koordinator za međunarodnu saradnju SITS


ENGINEERING CARD - A REAL MOBILITY TOOL

An Interview with Mr Lars Funk Head of the Profession and Society Division in the Association ofGerman Engineers - VDI and Chair of EMC - European Monitoring Committee of FEANI

Mr Funk could you please give us some more detailed information about the project EngineerINGCard? When was the project launched and who was the initiator of the project?VDI as German FEANI member launched the project in 2010. FEANI agreed about the concept at

its General Assembly in October 2010 in Sofia. At the beginning only two countries participated in theproject and started with issuing EngineerING card: The Netherlands and Germany. Until today 11countries joined the project, and some more are looking forward to participate.

Was the main motif for launching this project to increase the mobility of engineers and simplify theprocedure for recognition of their qualifications?Yes, increasing mobility is the main goal of the card. For this purpose, the recognition procedures

have to be simplified. But this is not enough: What we need is also more transparency for employers. Atthe moment it is often not possible for them to get an appreciation of the qualification of an applicant,especially if this qualification has been awarded in a foreign country. The EngineerING card helps toasses this qualification.

Last not least the EngineerING card helps to get a European wide accepted definition of theengineering status. This can be achieved because the engineering card is based on existing Europeanstandards like the EUR-ACE-Framework for learning outcomes of engineering courses.

What does EngineerING Card actually represent? Does this card provide complete insight intoeducation and professional experience of the card holder and what kind of a record is keptregarding the card holders?The card gives a complete overview about the qualification of an applicant. This includes academic

degree(s), professional experience and continuous professional development. The minimum requirementfor awarding the card is an academic degree in engineering with at least 180 ECTS.

The engineering card provides not only a complete information about the qualification of anapplicant, this information is also validated by experts and it is classified referring to internationalstandards. This is the big advantage of the card.How is the issuance of the EngineerING Card regulated and what kind of monitoring is

implemented for the entire process?The card is issued by the FEANI Partners in the participating countries. Applicants are asked to

apply in the country where they got the qualification. If this was done in more than one country they canchoose where to apply.

The FEANI partner has to establish a so called register committee with experts from companies,universities and engineering associations. This register committee is responsible for the issuing of theengineering card at national level. The committee acts according to the FEANI rules as described in amanaging handbook.

At European Level the so called European Monitoring Committee of FEANI is responsible for themonitoring of the whole system. This is done by constant reporting as well as audits in all countries.


In how many countries, the engineering organizations of which are the members of the FEANI, isthe project implementation initiated?At the moment 11 countries are involved in the project: Next to Serbia these are the Czech

Republic, Croatia, Germany, Ireland, Luxemburg, Macedonia, The Netherlands, Poland, Portugal andSlovenia.What does the EngineerING Card possession signify for the members of engineering associations

in such countries? Has the card holder been provided with an easier access to labor marketand employment in major companies in Europe and worldwide? More specifically, can thefact that an engineer from Serbia is the card holder be considered as an advantage whenseeking employment in EU countries?This will definitely be the case. The EngineerING card does not replace a normal application, but it

complement it in a very important point due to the fact the information on the card is validated andclassified. This helps for recognition procedures as well as for applications in industry. In fact theEngineerING card is a real mobility tool.The latest modifications to the EU Directive 2005/36/EC have envisaged the option of introducing

professional cards for the representatives of various professions, at the explicit request ofthe profession members. The representatives of the FEANI participated in work of SteeringCommittee on the Professional Card. Can you tell us to what extent the project is in line withthe Directive modifications?The principles of the European Professional Card as described in the new EU-Directive are fully in

line with the EngineerING card concept. This is a big success for FEANI. Nevertheless, at the momentthere are some differences in the procedures of issuing and handling the card. Unfortunately, theEuropean Commission is only focusing on recognition procedures, completely ignoring the necessarytransparency for employers. In consequence the engineers will not request for the European Professionalcard at this moment. Instead we will move on with the EngineerING card and we think that we have goodarguments to convince the European Commission that our concept is the better one in the long term.How do you expect the project to be developed and implemented in the forthcoming period?

Some more countries will join the project in 2014 and 2015. The Engineering Schools of France arevery much interested and they would like to start soon. Also Spain and Slovakia is preparing theimplementation of the card.

The Countries who still have implemented the card will invest in the marketing. This is veryimportant because due to the fact that the EngineerING card is a new product it is not well known at themoment. But this will change in a little while. For this purpose the engineering associations are workingtogether with universities as well as companies. All in all: The project will grow significantly in the next twoyears.

Olivera ĆosovićUnion of Engineers and Technicians of Serbia

Documents

G o d i n a LVI B e o g r a d, 2015. B r o j 1idk.org.rs/wp-content/uploads/2015/03... · Dr Vesna Mišković-Stanković, Serbia Dr Milan Jaić, Serbia Dr Zvonko Gulišija, Serbia