CHUYN NGNH SILICAT

Ngi son: TS. Nguyn Vn Dng

KHOA HO K THUT TRNG I HC BCH KHOA 2005

N TP HO HC SILIC V HO L SILICAT S b v ho hc silic Nguyn t silic, k hiu ho hc Si, khi lng nguyn t 28.09, s th t trong

bng Phn Hng Tun Hon l 14, thuc Phn Nhm Chnh nhm 4. Silic chim 27% khl v qu t m chng ta c th nghin cu c. L nguyn t

ch yu trong cc khong vt v t (ging nh cacbon trong thnh phn ca tt c cc cht hu c, l nguyn t quan trng nht ca gii thc vt v ng vt)

Trong thin nhin silic tn ti di dng cc hp cht: - SiO2, chng hn nh ct, thch anh, iatmit (l mt dng SiO2 v nh hnh) - Mui ca axit silicic (silicat). Ph bin nht trong thin nhin l cc

aluminsilicat, ngha l silicat m trong thnh phn ca n c nhm. Chng hn nh trng thch, mica, cao lanh...

Cc t phc tp ph bin nht nh granit, gnai cu to t cc tinh th thch anh, fenspat v mica.

Cc axit silicic v cc silicat SiO2 l mt xit axit, n ng vi cc axit silicic t tan trong nc, cng thc chung

nSiO2.mH2O. Ngi ta ch tch ra c trng thi t do axit ctsilicic v axit mtasilicic.

- Axit octsilicic H4SiO4. Vd silicat t axit ny l khong livin (Mg,Fe)2SiO4 hay 2FeO.SiO2 (ctsilicat manh v st);

- Axit metasilicic H2SiO3. Vd silicat t axit ny l khong vlastnit CaSiO3 hay CaO.SiO2 (mtasilicat canxi)

- Axit plisilicic: khng c bng chng v s tn ti ca chng. Tuy nhin cc mui ca chng (silicat) rt phong ph. Vd mui t axit gi s ny:

+ khong ctklaz KAlSi3O8 (hay K2O.Al2O3.6SiO2) (trisilicat aluminkali) + khong caolinit H4Al2Si2O9 (hay Al2O3.2SiO2.2H2O) + mica trng H4K2Al6Si6O24 (hay K2O.3Al2O3.6SiO2.2H2O) + amian CaMg3Si4O12 (hay CaO.3MgO.4SiO2) Cc silicat c bit ph bin trong thin nhin. Fenspat (trng thch), mica, t st,

amian, hot thch (talc) (3MgO.4SiO2.H2O) v nhiu khong vt khc u l cc silicat thin nhin.

Cng thc ho hc ca cc hp cht silicat Kh phc tp. Khng c s tn ti ng ngha ca cc axit silisic tng ng. Ngi

ta c th vit khc i i cht theo nguyn tc mt mui bt k ca axit cha xy c th coi nh hp cht ca xit axit vi xit baz (hoc 2 xit baz trong mui kp).

Vd: CaCO3 l hp cht ca CaO v CO2, Al2(SO4)3 l hp cht Al2O3 v SO3 v.v...

C th vit cng thc ho hc silicat = xit to thnh silicat theo th t cation t thp n cao, gia chng l du chm, v cui cng l xit silic (SiO2). Cc xyt c vit trong cng mt hng.

Cng thc ho hc cc hp cht silicat dng biu din thnh phn ho hc nht nh ca cc khong cht silicat c cu trc tinh th.

Ngoc n cong nu c trong cng thc ho hc th hin s thay th ng hnh cc cation cho nhau.

Cng thc Seger y l mt bin th ca cng thc ho hc trn dng biu din thnh phn ho

hc c thay i ca men gm s c cu trc v nh hnh (bn cht ca men gm s l thu tinh).

Cng thc Seger c vit theo th t tng nhm xit, mi nhm c th c nhiu hng khc nhau nh sau: xit baz (ch yu cc xit ca kim loi kim v kim th) + xit trung tnh + xit axit, trong tng cc xit baz ca kim loi kim v kim th c quy v bng 1.

Vd: 0.1-0.25 K2O 0.1-0.35 Al2O3 0.6-3.0 SiO2 0.9-0.75 CaO 0.9-0.75 B2O3 Cu trc cc hp cht (khong) silicat C s cu trc mng li silicat l t din silic-xy [SiO4]4-, c gi l n v cu

trc. Trong mi hp cht silicat silic lun c s phi tr l 4, lin kt Si-O l lin kt ion-cng ho tr vi 50% l lin kt ion. Cc t din ch c th lin kt vi nhau theo mt nh chung qua mt xy chung. Ion Al+3 c th

- thay th 1 phn Si4+ trong cu silic-xy to nn cu alumin-silic-xy - hay to nn nhng cu trc ring nh [AlO6]9- c s phi tr l 6 v [AlO5]7- c s

phi tr 5. Cng thc cu trc Ngi ta chia ra lm 5 loi, tu theo s trng hp ca t din [SiO4] hay cu

alumin-silic-xy thnh cc nhm cu trc khc nhau - Cu trc tinh th nhn: silicat c nhng t din u ng hng. Vd: khong livin (Mg,Fe)2[SiO4] - Silicat c nhm kch thc gii hn. - Silicat c nhm to nn mng li hnh xch n v xch kp (cu trc bng di

di v tn). Vd: volastonit Ca3[Si3O9] cu trc xch n - Silicat c cu trc tm lp: Vd: caolinit Al4[Si4O10](OH)8 - Silicat c nhm to nn cu trc khung: Vd: cc dng th hnh ca quc, trng thch kali K[AlSi3O8]3

Hnh dng lin hp gia cc t din hnh thnh mng li c nhiu loi: n, nhm cu trc gii hn, trng hp mch thng nh xch n v xch kp, tm lp, khung nh ni trn to nn s phong ph v cu trc cho cc hp cht silicat.

Hp cht silicat nhn to - Thu tinh tan Na2SiO3, K2SiO3 (ngi ta iu ch bng cch nu nng chy SiO2

v NaOH hay K2CO3 hay Na2CO3): ging nh thu tinh, tuy nhin tan c trong nc. Khi tan trong nc gi l thu tinh lng.

- Cc vt liu gm s, thu tinh, xi mng, vt liu chu la: l cc vt liu silicat nhn to, c sn xut t cc hp cht silicat thin nhin.

Nguyn liu chnh ca cc slict nhn to ni trn l cc silicat thin nhin, trong qu trnh nung, nu bin i cc hp cht silicat ban u thnh cc hp cht silicat mi, c cu trc hon ton mi. Trong cc hc phn cng ngh sn xut ring bit chng ta s nghin cu qu trnh trn xy ra nhit cao nh th no, s thay i cu trc cc khong theo nhit , s bin i th hnh, hnh thnh cc khong mi, s hnh thnh pha lng, bin i thnh phn pha, s hnh thnh vi cu trc mi ca vt liu nh th no.

Vt liu silicat Dng ni chung cc vt liu v c khng kim loi thu c bng qu trnh x l

nhit cc nguyn liu thin nhin hay nhn to c cha cc hp cht silic (ch yu l cc hp cht silic thin nhin nh ixit silic SiO2 v cc khong silicat). Ci tn silicat cng c chn ch cho mt ngnh sn xut cng nghip ly nguyn liu c bn l ixyt silic v cc khong silicat, l ngnh cng nghip silicat.

Trong cc ti liu nc ngoi, t ceramics dng ch chung cho tt c cc sn phm silicat hay c dng ch ring cho gm s.

1. CHNG 1: M U 1.1. NH NGHA

Gm: l vt liu v c khng kim loi, c cu trc a tinh th, ngoi ra c th gm c pha thy tinh. Nguyn liu sn xut gm gm mt phn hay tt c l t st hay cao lanh. Phi liu sn xut gm c to hnh v thiu kt nhit cao lm cho vt liu c c nhng tnh cht l ha c trng. T gm cn c dng ch nhng sn phm lm t vt liu gm.

Gm s: s l vt liu gm mn khng thm nc v kh (< 0,5%) thng c mu trng. S c bn c hc cao, tnh n nh nhit v ha hc tt. S c dng sn xut gia dng, m ngh hay trong xy dng. Nh vy s l mt loi gm c trng m ai cng bit. y dng nhn mnh.

gm: Sn phm bng vt liu gm. Ceramics: Gm, gm, ngh sn xut gm. Pottery: gm, ngh sn xut gm, l gm. Ceramic : Ceramic tile, ngha l tm p lt (cn dng t gch) bng gm, dng

phn bit vi tm p lt bng xi mng hay bng granit. Thiu kt: Nung v gi nhit cao vt liu dng bt kt khi. Nung l giai on quan trng nht, di tc dng ca nhit vt liu s kt khi

v c th xy ra phn ng lm thay i mt phn hay thay i hon ton thnh phn pha to nn vt liu mi. Nh vy y xy ra s bin i v cht, t nguyn liu ban u di nh hng ca nhng phn ng nhit cao hnh thnh nn mt vt liu a tinh th c thnh phn pha (khong) hon ton khc vi thnh phn khong ca nguyn liu ban u. Nhng pha tinh th mi hnh thnh (chng hn mullit) c vai tr quyt nh lm cho sn phm c cng, bn ha, bn nhit.

So snh : KIM MC THY HA TH Luyn kim: Qu trnh iu ch kim loi t qung v qu trnh ch bin cc hp

kim. Sn xut gm y c coi nh l luyn th, t l m, la l cha. 5850C caolinit mt nc ha hc thnh metacaolinit : Al2O3.2 SiO2. 2H2O Al2O3.2SiO2 + 2H2O

5850C

Vt liu lc ny rt gin. 9000C bt u hnh thnh spinen Al2O3.SiO2, vt liu ht dn. Thng gm phi

nung qua nhit ny, khong 800 - 9000C. 10000C v ln hn: hnh thnh mullit, y l khong chnh c nh hng quyt

nh hnh thnh nn nhng tnh cht ca s.

Cc giai on cng ngh Gia cng v chun b phi liu th + thy To hnh Sy sn phm th - thy Nung th + ha Ngoi ra cn 1 giai on cng ngh cn thit na l trng men v trang tr sn

phm. Trng men thng sau khi sy hay sau khi nung ln 1. Trong nh ngha gm, cu "nguyn liu sn xut gm gm mt phn hay tt

c l t st hay cao lanh" ch ng vi gm truyn thng. Nhng yu cu cao v rt khc nhau ca cc ngnh luyn kim, k thut in, in t ra cho ngnh gm l nguyn nhn pht trin ca cc loi gm k thut m nguyn liu sn xut khng thuc silicat chng hn nh cc oxit tinh khit, cacbua v cc hp cht khc. Tnh cht ca mt s gm k thut khc hn vi tnh cht ca cc sn phm gm truyn thng ch to t t st v cao lanh, v v th, nhng im ging nhau gia chng l ch cng c sn xut bng cch s dng cc cng ngh ging nhau c bit l qu trnh thiu kt nhit cao. 1.2. LCH S PHT TRIN

Rt kh xc nh chnh xc khi no ngh gm ra i, ngha l bao gm cc qu trnh to hnh, sy v nung, bin nguyn liu t st thnh gm. Ngi ta cho rng ngh gm bt u ti vng Trung ng v Ai Cp khong 4500 - 4000 nm TCN. Khong 4000 - 3000 nm TCN hnh thnh mt s trung tm gm vng ny. Trong thi gian ny pht minh ra bn xoay.

Mt bc tin ln v pha trc l vic pht minh ra thy tinh khong 2000 - 1000 nm TCN, to iu kin pht minh ra men gm m ni ting nht l hn hp Ai Cp, l hn hp ca t st, ct v tro g lm vai tr cht tr dung v cc oxit ng hay mangan to mu. Sau khi nung n lm cho b mt gm c mt lp nhn bng v c mu.

Thi Trung C Chu u c nhng trung tm rt ln sn xut gm nh Faenza (t d danh t faience hay cn gi l snh), hay Mallorca l mt hn o a Trung Hi (t c tn mt hng majolica, cng c ngha l snh. Loi snh ny xng c mu, xp, c trng men c v trang tr nhiu mu sc).

Vo nhng nm 600 TCN nc Trung Hoa c sn xut c s. n th k 9 SCN (i ng) ngh s Trung Quc rt pht trin. n th k 16 i nh Thanh th bc vo thi k cc thnh.

Chu u mi n nm 1709, mt ngi c l Johann Friedrich Bottger sn xut c s ging s Trung Quc. Nm 1759 ngi Anh Josial Wedgwood sn xut c snh dng (mt loi snh c xng mn, trng, kt khi tng i tt, cht lng hn hn snh thng thng tuy cha bng s). Trong 1/4 cui cng ca th k 18 snh dng y li mt hng majolica. Trong th k 19 chu u mt hng ny thay th cho s t tin. Ch sau khi gi c hng s r i, vi nhng tnh cht tuyt vi ca n mi y li c mt hng snh dng .

Vit Nam, ng cha ta sn xut c gm t thi thng c, cch y 4500 nm. Vo thi u cc vua Hng chng ta c gm Phng Nguyn, g Mun (Vnh Ph) nung nhit 800 - 9000C, xng gm bt u c tinh luyn.

T th k 11 chng ta sn xut c gm men i Vit ni ting vi cc trung tm H Bc, Thanh Ha, Thng Long, Nng.

T thi Trn c gm Thin Trng (H Nam Ninh) vi sn phm bt a, bnh l ph men ngc, men nu.

T cui i Trn vo th k 14 bt u hnh thnh lng gm Bt Trng ni ting n ngy nay. 1.3. PHN LOI GM

Theo cu trc v tnh cht sn phm: gm th, gm mn, gm c bit. Theo mt hng: thc cht l phn loi theo nguyn liu ch yu sn xut ra sn

phm nh gch ngi, snh trng thch, snh vi, s frit, s corundon ... Theo lnh vc s dng: theo 1 nhm sn phm c c tnh k thut ging nhau. N

cho ta mt khi nim chung v vai tr ca ngnh k thut gm trong nn kinh t quc dn. PHN LOI GM THEO LNH VC S DNG

Gm dn dng Gm ha hc Gm lm vt liu mi, mi Gm m ngh Gm lm dao tin Gm xy dng gm Gm ph kim loi (Ceramics ) Gm lm rng gi Gm chu la S cch in Gm dng trong k Gm t tnh thut in, v tuyn S t in S p in Gm bn dn

2. CHNG 2: NGUYN LIU Theo truyn thng ngi ta chia nguyn liu sn xut gm s lm 3 loi chnh : Nguyn liu do: cc loi cao lanh v t st, chng to iu kin to hnh phi

liu do. Tnh do y l do cc khong st m ra. Nguyn liu khng do, loi c gi l nguyn liu y: lm gim s co ngt

khi sy v nung, to iu kin chng nt khi sy v nung, nhng ng thi cng lm gim kh nng to hnh. So vi nguyn liu do th nguyn liu y c cc ht th hn, ht thng khng xp, tng i n nh v khng bin tnh khi nung, khi nung khng co ngt. Nguyn liu y in hnh nh thch anh, corundon, t st nung (samt) v.v...

Nguyn liu khng do, loi c gi l cht tr dung : theo quan im to hnh v sy th loi nguyn liu ny tng t nh loi 2, nhng chc nng chnh ca n l to pha lng khi nung. iu ny s to iu kin v thc y nhanh qu trnh kt khi. in hnh cho loi ny l trng thch alkali hay cc nguyn liu cha cc oxyt kim th chng hn.

ng v mt bn cht to thnh vt liu gm th nhm 1 (nguyn liu do) l quan trng nht v khong caolinit trong t st sau qu trnh nung hnh thnh pha tinh th mullit, l khong ng vai tr quyt nh hnh thnh nn nhng tnh cht ca gm.

nh ngha nguyn liu do: nguyn liu khi trn cng vi nc to nn vt th do c th to hnh c.

Tip theo l nhm 3: chc nng chnh ca n l to pha lng khi nung. Sau khi nung tn ti di dng pha thy tinh.

Nhm 2 l nguyn liu y, nhng thc ra cng ng mt vai tr quan trng trong vic hnh thnh nn nhng tnh cht ca s. Chng hn corundon -Al2O3 lm cho sn phm s c bn c v bn in cao.

Nguyn liu c gia cng c c ht thch hp, sau phi theo mt thnh phn nht nh, sau qu trnh nung n cng v st c li v vt liu c thnh phn pha nh yu cu sn phm c nhng tnh cht k thut nht nh.

Ngoi cc loi nguyn liu nu trn, trong cng nghip sn xut gm k thut ngi ta dng cc nguyn liu tng hp nh cc oxit TiO2, Al2O3, ThO2, BeO... v cc loi nguyn liu khc

sn xut khun ngi ta dng thch cao, nha pxy. sn xut bao nung v cc vt liu chu la h tr khi nung ngi ta dng

samt, SiC, -Al2O3... sn xut cht mu v men ngi ta dng cc oxit mang mu nh Cr2O3, CoO,

CrO2, MnO2, hay cc oxit t him v mt s kim loi qu nh Au, Ag, Pt...

2.1. NGUYN LIU DO: CAO LANH V T ST 2.1.1. Ngun gc, s thnh to cao lanh v t st

Cao lanh v t st l sn phm phong ho tn d ca cc loi gc cha trng thch nh pegmatit, granit, gabro, bazan, rhyolit. Ngoi ra n cn c th c hnh thnh do qu trnh bin cht trao i cc gc nh qucphophia.

Cao lanh nguyn sinh (tc cao lanh th) l cao lanh hnh thnh ngay ti m gc. Nu sn phm phong ho tn d, nhng b nc, bng h, gi cun i ri lng ng ti cc ch trng hnh thnh nn cc m cao lanh hay t st trm tch - cn gi l cao lanh th sinh.

Nh vy s hnh thnh cc m cao lanh v t st l do chu s tc dng tng h ca cc qu trnh ho hc, c hc, sinh vt hc bao gm cc hin tng phong ho, ra tri v lng ng trong thi gian di.

C ch phn ng qu trnh phong ho xy ra nh sau, nu chng ta coi gc trc tip phong ho thnh cao lanh l trng thch kali. Khi pH ca mi trng l 3-4 th khong chnh hnh thnh l caolinit Al2(OH)4Si2O5

2KAlSi3O8 + 8H2O 2KOH + 2Al(OH)3 + 2H4Si3O8 Al2(OH)4Si2O5 + K2O + 4SiO2 + 6H2O Khi pH ca mi trng l 8-9 th khong chnh hnh thnh l mntmrilnit

Al1,67Mg0,33[(OH)2/Si4O10]0,33Na0,33(H2O)4. Nh vy l H2CO3 v mt s acid hu c khc ng vai tr rt quan trng trong qu

trnh phong ho gc thnh cao lanh. Qu trnh thnh to cao lanh c th cn qua cc khong trung gian chng hn

muscvit K2O.3Al2O3.6SiO2.2H2O ( mt dng mica ngm nc) ri mi chuyn thnh caolinit.

Trong nhiu trng hp xy ra s thay th ng hnh ca Fe+3 thay Al+3 th c ch cn phc tp hn. 2.1.2. Thnh phn ho v khong vt :

Cao lanh v t st xt theo thnh phn ho, thnh phn khong cng nh cu trc bao gm 28 loi n khong khc nhau, chia thnh cc nhm khong.

Mi nhm khong bao gm cc n khong c cu trc hoc tnh cht gn ging nhau. Ba nhm khong quan trng nht i vi ngnh cng nghip gm s l: 2.1.2.1. Nhm caolinit

c trng ca nhm caolinit l khong caolinit (tn khong ny c ly lm tn cho c nhm), l khong ch yu trong cc m cao lanh v t st, c cng thc ho hc l Al2O3.2SiO2.2H2O. Thnh phn ha ca khong ny l SiO2: 46.54%; Al2O3 : 39.5%; H2O: 13.96%.

Nu m cao lanh no cha ch yu l khong caolinit th c cht lng rt cao v cha rt t tp cht gy mu (hm lng oxit st Fe2O3 < 1%).

Thng thng thnh phn khong ca t st ngoi cc khong st (v d caolinit) cn cha mt lng trng thch (do gc cha phong ha hon ton) v SiO2 t do (hnh thnh trong qu trnh phn ha). thun tin cho vic tnh ton phi liu gm s, ngi ta quy thnh phn khong vt ca mt m cao lanh theo thnh phn khong hp l bao gm:

- Khong vt st (tnh theo caolinit) c k hiu l T, quy ra %. - Thch anh k hiu l Q, quy ra %. - Trng thch kali k hiu l F, quy ra %. T + Q + F = 100% Nu trong thnh phn ha ca mt loi cao lanh no c cha CaO hay MgO

1% th lng CaO hay MgO c coi l ca cacbonat, tc l tn ti dng CaCO3 hay l MgCO3. Nu hm lng cc oxit y < 1% th coi s c mt ca chng l s thay th ng hnh ca cc ion Ca2+ v Mg2+ vo trong mng li tinh th khong st. Tng t nu hm lng FeO, Fe2O3 1% th ta coi chng l hp cht cha st (v d Fe(OH)3).

V mt cu trc mng tinh th caolinit bao gm 2 lp: lp t din cha cation Si4+ tm, lp bt din cha cation Al3+ tm ng vi [SiO4]4- v [AlO6]9- . Hai lp ny to thnh gi h c chiu dy 7.21 7.25 A0 trong cc nhm OH phn b v mt pha. Tinh th caolinit c dng ming hay dng vy 6 cnh, ng knh ht caolinit t 0.1 0.3 m.

Hnh 1. Mng li caolinit (theo Gruner) Caolinit hu nh khng trng n trong nc, do km, kh nng hp ph trao

i ion yu (thng t 5 10 mili ng lng gam i vi 100 g cao lanh kh), khi lng ring ca khong caolinit khong 2.41 2.60 g/cm3.

Trong nhm ny cn c khong haloysit Al2O3.2SiO2.4H2O thng i km vi caolinit. N c coi l sn phm hydrat ha ca caolinit.

2.1.2.2. Nhm mntmrilnit (Al2O3.4SiO2.H2O + nH2O) Mng li tinh th khong ny gm 3 lp (2 t din [SiO4] v 1 bt din [AlO6]).

So vi caolinit th khong ny c lc lin kt yu hn, y cc nhm OH- nm bn trong 3 lp trn to thnh gi kiu kn.

Do c s thay th ng hnh, nn mntmrilnit thng cha cc cation Fe2+, Fe3+, Ca2+, Mg2+ vi hm lng kh ln. phn tn cao, ht mn, kch thc c 0.06 m c th chim n 40% (trong t st thng c ht trn ch chim 5-20%, trong cao lanh t 0.5 1.5%) nn khong ny c do rt ln.

Mntmrilnit l loi silicat 3 lp nn khi c nc cc phn t H2O c th i su vo v phn b gia cc lp lm cho mng li ca n trng n rt ln, cng chnh do cu trc ca bn thn n nn khong ny c kh nng hp ph trao i ion ln. Khi lng ring mntmrilnit t 1.7 2.7 g/cm3. Trong sn xut gm khong ny c tn l bentnit. i vi gm mn khi phi liu c do km ngi ta thng thm mt lng 2 5% bentnit tng do.

Hnh 2. Mng li mnmrilnit Trong nhm ny cn c khong bylit Al2O3.3SiO2.H2O, c cu trc v tnh cht

tng t nh mntmrilnit nhng cha rt nhiu oxit st (c th n 32%) nn t cng dng.

2.1.2.3. Nhm khong cha alkali (cn gi l illit hay mica): Illit hay mica ngm nc l nhng khong chnh trong nhiu loi t st. Cc dng

mica ngm nc thng gp l: Muscvit : K2O.3Al2O3.6SiO2. 2H2O Bitit : K2O.4MgO.2Al2O3.6SiO2. H2O V mt cu trc cc khong ny c mng li tinh th tng t nh cc silicat 3 lp

nn tnh cht ca chng rt ging nhau. Trong nhm ny cn c mt s khong khc c cu trc v tnh cht tng t nh

illit nh l khong hyrophylit, vermiculit v cc dng thy mica khc. 2.1.3. Cc tnh cht k thut 2.1.3.1. Thnh phn ht

Nhn chung kch thc cc ht t st v cao lanh nm trong gii hn phn tn keo (

cc i khi lng nc va thc hin qu trnh hydrat ho hon ton, cho php to hnh do.

Lng nc thc hin qu trnh hydrat ho hon ton ph thuc vo cu trc n khong ca t st. Chng hn t bentnit ( cha khong mnmrilnit) c do cao nht, mn nht. Thng trong bi phi liu ngi ta ch dng khong 5-10% do n c kh nng trao i ion ln v kh nng thay th ng hnh lm hm lng st trong n cao. Bentnit rt kh sy v c co khi sy ln, thi gian sy lu. Trong sn xut nu gp t ny chng ta phi cho lng nc theo ng cng thc ca n (nc cu trc nm gia cc lp khong).

Khi lng nc ln (khong 28%) th h cao lanh, t st li chy thnh dng lin tc, cho php ta to hnh bng phng php h rt.

Ch s do: l hiu s m ca gii hn chy v gii hn ln. Gii hn chy c xc nh theo vica chun. Gii hn ln xc nh theo phng

php c in ( to t thnh si = 2-3 mm). Phng php xc nh ch s do trn dng c ca Perfferkorn cho kt qu chnh

xc hn. Dy Hofman cho bit cc tnh cht ca phi liu gm s bin thin theo cc ion

c trao i nh th no. Dy ny c ngha rt ln khi chun b phi liu gm s, c bit l lc pha long h rt.

H>Al>Ba>Sr>Ca>Mg>NH4>K>Na>Li Chiu dy lp in tch kp tng in th zeta tng Ch s do tng nht tng Mt biu kin tng Dy Hofman

2.1.3.4. S bin i ca t st v cao lanh khi nung : Khong chnh v ph bin nht trong t st v cao lanh l caolinit. Khi nung nng xy ra cc hin tng chnh sau y: - Bin i th tch km theo mt nc l hc. - Bin i thnh phn khong bao gm mt nc ho hc, bin i

cu trc tinh th khong c (k c bin i th hnh). - Cc cu t phn ng vi nhau to ra pha mi. - Hin tng kt khi. kho st din bin lc nung ca cc khong st, chng ta c th s dng nhiu

phng php ring bit hay kt hp cc phng php thu c kt qu vi tin cy cao hn. Cc phng php thng dng l:

- Phng php nhit vi sai.

- Phng php nhiu x Rnghen - Phng php xc nh ng cong co v dn n lin tc qua lnh hin vi nhit

cao hoc bng ilatmet. - Phng php thch hc dng cc loi knh hin vi quan st s thay i cu trc

ca mu nung. V d chng ta s dng phng php xc nh ng cong co dn n lin tc

ca khong caolinit nguyn cht v vi loi t st cao lanh nh hnh 3. T 20 - 5000C: dn n lin tc (ging cc vt th rn khc) Trn 5000C: bt u co (do mt nc ho hc) T 5000C tr i: ng cong co khng t l thun vi nhit (do tc co trong

cc khong nhit khc nhau c th c s t bin bt thng, nht l lc c mt mt vi loi khong khc, v d c nhiu SiO2 t do). Ty tp cht cha trong n (nht l cc oxyt d chy) m nhit kt thc hin tng s khc nhau (thng trn 10000C).

Hnh 3. ng cong co, dn n lin tc

1-t st cha nhiu SiO2 2-t st cha nhiu CaO 3-t st ch yu l caolinit 4-t st ch yu l illit 5-t st ch yu l monmrilnit V d phng php th hai l biu phn tch nhit (DTA) ca cc khong

chnh trong t st v cao lanh nh trn hnh 4. Cc hiu ng nhit chng ta nhn thy trn biu : - Hiu ng thu nhit 5850C ng vi qu trnh mt nc ha hc hnh thnh

mtacaolinit. - Hiu ng ta nhit th nht nm trong khong 900 - 10000C ng vi qu trnh

hnh thnh spinen. - Hiu ng ta nhit th hai khong trn 10000C ng vi s hnh thnh v tng

cng khong mullit. Nu nung n nhit cao hn th mullit u (dng vy nh, nm xen k nhau ging n, d) s ti kt tinh thnh mullit th cp c dnh hnh kim.

Hnh 4. Biu DTA ca cc khong chnh trong t st v cao lanh

Phn ng ho hc tng qut khi nung caolinit c th vit theo s trong hnh 5. Al2O3.2SiO2.2H2O (caolinit) t = 500 - 6000C Al2O3.2SiO2 (mtacaolinit) + 2H2O t 900 - 10000C Al2O3.SiO2 (spinen) + SiO2 t >10000C 3Al2O3. SiO2 (mullit) + SiO2 (cristobalit) Hnh 5. S cc phn ng ho hc xy ra khi nung caolinit Mt im c bit ca cao lanh v t st khi nung nhit cao l hin tng kt

khi. l qu trnh st c v rn chc li ca cc phn t khong vt (sn phm) dng bt ti di tc dng ca nhit hay p sut, hoc tc dng ng thi ca c hai yu t .

Vt th kt khi c cng c hc cao, xp v kh nng ht nc nh, mt hay khi lng th tch s ln nht.

Hin tng kt khi c mt pha lng bao gi cng xy ra mnh lit hn. Sn phm mun kt khi tt trong iu kin thng thng phi nung n nhit

0,8 T (T l chu la hay nhit nng chy).

Khong kt khi l hiu s nhit gia nhit kt thc qu trnh v nhit bt u kt khi (xc nh c bng cch theo di din bin cc tnh cht ca mu nung theo nhit ).

Nhit bt u kt khi l nhit ng vi n cc tnh cht bt u thay i t ngt.

Nhit kt thc qu trnh kt khi l nhit m cc tnh cht ca sn phm nung t c gi tr cc i hay cc tiu.

Mun sn phm nung d dng trong cc l cng nghip thng khong kt khi phi 500C.

biu th qu trnh kt khi ngi ta hay dng cc tnh cht sau y ca sn phm nung: xp, mt , kh nng ht nc. Trong kh nng ht nc c coi nh l tiu chun u tin so snh mc kt khi ca sn phm nung.

i vi gm mn, sn phm c coi l t kt khi tt khi ht nc ca chng xp x 0%. i vi nhm gm xy dng ht nc 1% c gi l im kt khi v nhit tng ng c coi l nhit kt khi.

i vi nhm gm c xng xp v vt liu chu la, ht nc nm trong gii hn 6 - 1% c coi l kt khi kh tt. Chng ta xt biu nhit - ht nc ca sn phm gch clinker vi ht nc l 6% nh trn hnh 6. im nhit nung ng vi ht nc 6% gi l im clinker.

Hnh 6. Biu ht nc - nhit nung ca gch clinker

Xt cht lng v phm vi s dng ca t st v cao lanh bao gm cc im c bn sau: ngun gc, phng php khai thc tuyn chn; thnh phn ha hc trung bnh; thnh phn khong hp l (T-Q-F); cc tnh cht c l nh bn ca mc theo phng php rt, kh nng rt, mu sc sau khi nung 1350 0C, ht nc 13500C, co sy, co nung 13500C, co tng, m t nhin, lng cn li trn sng 0.063 mm, chu la. 2.2. NGUYN LIU GY 2.2.1. Trng thch v cc hp cht cha n

V mt ha hc trng thch l nhng aluminsilicat K, Na, Ca tc K[AlSi3O8] hay Na[AlSi3O8], K+ c th c thay th bi Ba2+, Sr2+ nhng rt him.

Trong thc t t khi chng tn ti dng n khong ring bit m ph bin l cc hn hp ng hnh. Chng c chia ra cc nhm ph sau :

- Nhm ph plagioclaz: l hn hp ng hnh ca trng thch natri (albit Na2O.Al2O3.6SiO2) v trng thch canxi (anortit CaO.Al2O3.2SiO2).

- Nhm ph ortoklaz: l hn hp ng hnh ca trng thch kali (K2O.Al2O3.6SiO2) v natri. Nhm ny c cc dng ng hnh ch yu sau :

+ Ortoklaz n t nhit thp K[AlSi3O8]. + Natriortoklaz NaK[AlSi3O8] n t nhit thp. + Mikrolin K[AlSi3O8], c th cha Na2O, loi tam t. + Anorthoklaz (Na, K)[AlSi3O8], loi tam t. Khong sng pecmatit ca trng thch alkali cha ch yu l microlin. Cc hn hp ng hnh ca trng thch l rt phc tp, cho n nay vn cha tm

thy dung dch rn ca trng thch kali v canxi. Biu 3 cu t ca cc dng ng hnh ca trng thch nh trn hnh 7.

Hnh 7. Hn hp ng hnh ca trng thch

Tc dng ca trng thch: c tc dng to pha lng trong qu trnh nung, h nhit nung v thc y qu trnh kt khi sn phm gm. Chng ta thy r iu qua nghin cu biu pha ca h ortoklaz-albit (theo Bowen v Turtule 1950) trn hnh 8.

Hnh 8. Biu pha ca h ortoklaz-albit (theo Bowen v Turtule 1950) Trng thch kali c tc dng tt trong xng s v cho php h thp nhit nung

song khong nung rng, s t b bin hnh (nn cn gi l trng thch phi liu). Trng thch natri li thch hp cho men s: nht ca men b, d chy, men bng lng hn.

Trong thc t trng thch tn ti dng dung dch rn. i vi xng s khi hn hp chim 60% trng thch kali v 40% trng thch natri vn dng rt tt. i vi men s t l K2O/Na2O 1/1 tnh cht men vn tng t nh trng thch natri nguyn cht.

Tc dng ca trng thch i vi xng s cn ch khi n nng chy c kh nng ha tan thch anh (SiO2) hay sn phm phn hy ca cao lanh khi dung dch t n bo ha s ti kt tinh mullit dng hnh kim.

Vai tr ca trng thch trong cng nghip gm s l rt quan trng v chng nhng n quyt nh iu kin cng ngh (nhit nung) m cn nh hng ln n cc tnh cht k thut ca s. S mun c trong cao (kh nng cho ng sng xuyn qua ln) ngoi vic hn ch cc oxyt gy mu (Fe2O3 + TiO2) phi a vo mt lng trng thch ln (29 - 30 %). i vi s cch in cao th, mun c bn in cao hm lng trng thch 30 %. 2.2.2. Thch anh (quartz)

Cng thc ho hc ca thch anh (quartz) l SiO2, n rt ph bin trong v qu t.

Trong thin nhin thch anh tn ti di 2 dng chnh: - Dng tinh th bao gm ct thch anh, quaczit v sa thch. Ct sch cha ch yu

l SiO2 l nguyn liu chnh cho cng nghip thy tinh v men s. - Dng v nh hnh bao gm cui (flint) v diatomit. cui nu loi c

cng cao, bo mn nh v b mt ngoi nhn th dng lm bi nghin nghin nguyn liu, phi liu gm s rt tt.

Khi s dng thch anh iu c bn l phi quan tm y n c tnh bin i th hnh ca n. c im ny lm chng ta phi quan tm y n cc giai on nung c s bin i th hnh ca quc (c km theo s bin i th tch) khng lm nh hng n cht lng sn phm. Hnh 9 nu ln s tm tt s bin i th hnh v tnh cht ca cc dng .

Hnh Yu cu chun

cng cao v lng2.2.3. Cc loi ng

Cng nghip g3MgO.4SiO2.2H254.27% TL, MgCv.v... Ngoi ra cxyt thuc nhm mu. 9. S tm tt s bin i cc dng th hnh ca thch anh g ca thch anh dng trong cng nghip gm s l hm lng SiO2 cc xyt gy mu cng t cng tt. uyn liu khc m s cn dng nhiu loi nguyn liu khc nh hot thch (talc)

O, vi CaCO3, lmit CaCO3.MgCO3 (trong CaCO3 chim O3 chim 45.73% TL), cc hp cht cha BaO, TiO2, Zr2O3, Al2O3 n dng cc xyt thuc h t him nh La2O3, BeO, ThO2, hay cc chuyn tip nh CoO, Cr2O3 v.v... thng c dng sn xut cht

Khi s dng cc hp cht thin nhin nh hot thch, vi v.v... cn lu n lng tp cht trc ht l Fe2O3, TiO2, MnO2 v.v... c trong hp cht v y l cc xyt lm gim cht lng sn phm (v d gy mu). Trong nhiu trng hp chng c dng nh nguyn liu chnh, mt s trng hp khc c dng nh ph gia. 2.2.4. Nguyn liu lm khun

Ph bin nht ngi ta hay dng l khun thch cao. Ngy xa ngi ta dng khun g.

Trong thin nhin thch cao tn ti di dng ihydrat sulfat canxi CaSO4.2H2O (vi 21 % nc kt tinh). Lc sn xut khun ngi ta dng thch cao cha 0.5 phn t nc (CaSO4.0.5H2O), dng thnh cao ny nhn c bng cch sy bt thch cao sng CaSO4.2H2O nhit 1700C. Khi trn thch cao cha 0.5 phn t nc vi mt lng nc thch hp (thng t 50 -55 % khi lng) n s thc hin phn ng hydrat ha (gi l qu trnh ng rn) cho cng c hc kh cao nhng xp ln. Ch nu sy trn 1800C, c bit n gn 3000C th s lm gim thm ch mt hn kh nng hydrat ha.

Hin nay ngoi thch cao ngi ta cn dng nha nhn to polyester hay epoxy

3. CHNG 3: GIA CNG V CHUN B PHI LIU Gi vai tr rt quan trng v to iu kin ci thin nhiu tnh cht ca nguyn phi

liu cng nh cht lng ca sn phm nung. Bao gm : -Lm giu v tuyn chn nguyn liu. -Gia cng th v gia cng trung bnh cc loi nguyn

liu. -Gia cng tinh (nghin mn) nguyn phi liu. -Chun b phi liu theo yu cu tng loi sn phm ph hp vi cc

phng php to hnh khc nhau. 3.1. NGHIN

To mn cho nguyn phi liu, to iu kin cho phn ng nhit cao khi nung v din tch tip xc gia cc ht ln, mt khc qu trnh nghin mn to ra s khuyt tt trn b mt cc tinh th vt cht nhiu hn.

Chia lm ba loi: nghin th, nghin trung bnh v nghin mn. 3.1.1. Nghin th v nghin trung bnh

Nhm p v nghin nguyn liu dng cc ln n yu cu cho php np vo my nghin mn.

Thng dng my p ba, p hm, nghin bnh xe... cho thch anh, trng thch. Thng dng my thi t, my nghin trc trn hay my nghin trc loi c rng

cho cc nguyn liu mm hn nh phn, t st, cao lanh... 3.1.2. Nghin mn

Yu cu nghin mn l kch thc ht vt liu sau khi nghin phi 63 m (tc qua ht sng 10000 l/cm2) trong c ht t 1- 20 m phi chim a s.

Nguyn liu np vo my nghin bi thng yu cu 1 mm. 3.2. CHUN B PHI LIU :

Yu cu c bn ca vic chun b phi liu l : - t c chnh xc cao nht v thnh phn ho v t l cc loi c ht, thnh

phn phi liu v cc tnh cht k thut ca n cc khu khc nhau trong dy chuyn cng ngh m bo ng tnh cht cn mong mun ca cc loi sn phm sau khi nung.

- t c ng nht cao v thnh phn ho, thnh phn ht, lng nc to hnh, cht in gii hay cc loi ph gia v.v... trong phi liu theo thi gian v v tr khc nhau. 3.2.1. Kim tra nguyn liu v tnh bi phi liu

Ngi ta thng tin hnh nghim ngt vic kim tra cht lng u vo ca tt c cc loi nguyn liu dng cho qu trnh sn xut, nht l i vi cc sn phm gm c yu cu cht lng cao (nh gm mn, gm k thut ...). Vic kim tra bao gm: phn tch thnh phn ho, thnh phn khong, cc tnh cht cng ngh ca nguyn liu

(chng hn nh do v lng nc to hnh thch hp ca t st, kh nng rt, mn, co khi sy v nung v.v...) t tnh ton bi phi liu sn xut xng (hay men) bao gm cp phi ca tng nguyn liu mt, c tnh theo % trng lng hay phn trng lng.

sch cng nh cht lng t yu cu ca nguyn liu, s phn tch chnh xc v tnh ton ng bi phi liu l nhng tin c bn cho sn phm cui cng t cht lng cao.

Vic tnh ton cc bi phi liu sn xut cc loi xng gm s c nu trong phn sau, cc bi phi liu sn xut men gm s c nu trong chng Men ph v cht mu trang tr sn phm gm.

Khi tnh ton v thit lp bi phi liu ngui ta thng dng nhiu nguyn liu ca cng mt loi (chng hn t st c th dng t hai n ba loi). Mc ch l n nh thnh phn phi liu khi mt nguyn liu no c thnh phn dao ng khng mong mun. 3.2.2. Chun b phi liu:

Mc ch ca vic chun b phi liu l: - To ra phi liu ng theo bi cp phi. - Tip tc nghin mn cc loi nguyn liu n c ht yu cu. - To c s ho trn ng nht ca tt c cc loi nguyn liu trong phi liu, c

m ng nht, c nhng thng s cng ngh ti u ph hp vi cng on to hnh tip theo.

Phng php chun b phi liu truyn thng l nghin trn chung cc loi nguyn liu thnh huyn ph nc trong my nghin bi (phung php nghin bi t). Khi my nghin bi quay, s ch xt, va p ca bi n vo nhau v vo thn ca thng nghin lm cho liu c nghin mn v trn u. Cho n nay y vn l phng php hiu qu nht do c nhng u im sau:

- Nc l mi trng tt gip tng cng qu trnh nghin v trn u, phi liu s t ng nht cao.

- t st, cao lanh thng c m dao ng, ta ch cn cc nh chnh xc m ca n tnh ng lng nc cho vo nghin (m khng cn sy kh nguyn liu nu nh chn phng php nghin kh)

- Tiu tn nng lng nghin b hn nhiu so vi nghin kh. - H sau nghin c th em dng ngay to hnh rt hay to hnh do sau khi

qua p lc khung bn. Nhc im l lng hao mn bi n, lp lt thng ln gp 5 ln so vi nghin

kh. Cho nn yu cu ca bi n v lp lt cn c tnh cht ging vt liu em nghin (coi lng hao ht bi n, lp lt nh mt cu t ca phi liu) v sau mi ln nghin cn b sung bi n. i vi snh mn v s vt liu lt nn dng hoa cng (granit) hay lm bng silex (mt dng thch anh v nh hnh), bi l cui (flint, l SiO2 v nh hnh) hay s cng (s crunn chng hn); i vi my nghin phi liu h

titanat (TiO2, BaO v.v...) th vt liu lt v bi n l s rutin TiO2. Lp lt c th lm bng cao su cng khng lm bn liu bi tp cht st t thn thng nghin.

T l np liu thng nh sau: Liu nghin : bi n : nc = 1 : 1: 1 n 1 : 1: 0,5 tu theo yu cu m h ra, lng v loi cht in gii cho vo. T l 1:1:0,5 dng cho h ra my sy phun trong sn xut tm p lt ceramic.

Trnh t nghin nh sau: trc ht ngi ta nghin nguyn liu gy vi khong 10% t st hay cao lanh lc ( iu chnh nht ca huyn ph v ngn cn s lng). Lng t st v cao lanh lc cn li c khuy thnh huyn ph trong b khuy, sau qua kim tra thnh phn ht v c hai huyn ph s trn chung vi nhau trong b khuy trn. H ra phi c nht biu kin thch hp (0,2-1 Pa.s) v trng lng th tch ln.

Thi gian nghin ph thuc vo ln ca thng nghin v mn ca nguyn liu v dao ng trong khong 10-60 h.

Ngi ta theo trnh t nghin trn khi nguyn liu u vo t yu cu, ngha l t st, caolin lc trng thi ht mn t yu cu ( t st s lng ht 2 m ln hn 50%). Ch cn thch anh v trng thch l cn phi nghin mn. Nu ta dng cao lanh khng lc (c lng ht th-ch yu l ct trong cao lanh-ln) th phi iu chnh qu trnh nghin nghin c cao lanh. Ngi ta cng c th nghin trn tt c nguyn liu trong my nghin bi m khng cn dng my khuy trn. 3.2.3. Tnh phi liu : 3.2.3.1. Phi liu nhm gm xy dng :

C s chn phi liu nh hng ca nhm ny l thnh phn ho hc l thuyt trn biu Apgutchinit v biu thnh phn t l cc c ht theo Winkler. 3.2.3.2. Phi liu snh vi :

t st v cao lanh khong 62 % Quc hay ct khong 26 % vi hay phn khong 12 %

3.2.3.3. Snh trng thch (hay snh cng) : t st trng n 40 % Cao lanh n 20 % Trng thch n 6 % Phi liu ny nung nhit 13000C.

3.2.3.4. Phi liu cc loi s : Theo h ba cu t T-Q-F ca Gilchrist v Klinefenter nm 1928. Trong : T- vt cht st tnh theo khong caolinit Q- thch anh (SiO2) F- trng thch kali nguyn cht

Vic tnh phi liu theo T-Q-F khi bit thnh phn ho hc c chun ho bng cc h s sau :

Hm lng K2O x 5.9081 = orthoklaz (K2O.Al2O3.6SiO2) Hm lng K2O x 1.0823 = Al2O3 c trong orthoklaz Hm lng K2O x 3.8230 = SiO2 c trong orthoklaz Hm lng Na2O x 8.4573 = albit (Na2O.Al2O3.6SiO2) Hm lng Na2O x 1.6440 = Al2O3 trong albit Hm lng Na2O x 5.8128 = SiO2 trong albit Hm lng CaO x 1.7840 = CaCO3 Hm lng MgO x 2.0915 = MgCO3 Hm lng Al2O3 x 2.5318 = T (Al2O3..2SiO2.2H2O) Hm lng Al2O3* x 1.1783 = SiO2 trong T Hm lng Al2O3 x 0,3530 = H2O trong T Hm lng mt khi nung x 7.18 = T (dng tnh kim tra) Lc tnh Q : Q = 100 - ( T + F ) F = orthoklaz + albit Lc tnh cn ch l cn c vo lng K2O v Na2O tnh lng orthoklaz hay

albit. Tnh Al2O3* bng cch ly lng Al2O3 tng tr i lng Al2O3 c trong orthoklaz

v albit. Nu kt qu tnh kim tra T bng cch ly lng mt khi nung nhn vi 7.18 sai

khc nhiu so vi vic tnhT = Al2O3* x 2.5318 iu c ngha l trong nguyn liu c thm vt cht hu c hay cacbonat.

Khi quy v T-Q-F thng phi k n lng tng cc oxyt Fe2O3, TiO2, CaO v.v... tc 100 - ( T + Q + F ) bng tng cc oxyt.

Nu gi tr CaO, MgO 1 % c ngha l chng c mt trong nguyn liu dng CaCO3 hay MgCO3.

u im ca cch tnh ton ny l n gin, thun tin, cho php tra cu nhit nung theo biu v s liu thu c l ng tin cy, st vi iu kin thc t sn xut.

Tham kho Bng tnh phi liu xng gm s son trn Excel. Trong trng hp tnh bi phi liu khng theo T-Q-F (trong phi liu c cc nguyn liu khc nh vi, d phn, lmt, talc...) th c th dng Bng tnh phi liu thu tinh. Phi liu xng gm trong trng hp ny c th c tnh nh phi liu thu tinh, tc l tnh trc tip t thnh phn ho ca nguyn liu theo thnh phn ho phn tch c ca sn phm gm. Bi phi liu tnh c trong c hai trng hp u c tnh nh hng, sau chng ta phi iu chnh bi phi liu theo th nghim thc t.

3.2.4. Chun b v gia cng phi liu gm th : Mt hng gm th ch yu l s dng trong lnh vc xy dng v dn dng bao

gm gch ngi, ng snh thot nc v dn nc, gch klinker, chum, vi, vt liu chu axit v cc loi vt liu xy dng dng dm, si nhn to nh keramzit, aglprit v.v... 3.2.4.1. Gia cng t nhin s b.

Khai thc nguyn liu dn thnh ng ti m hay kho. Nu nguyn liu c cng kh cao, dng cc (t i) th tin hnh ngm tm trong cc l ring c phun nc tha ng. Khu ny xc tin qu trnh hydrat ha, trng n th tch, kt qu lm cho cng gim, do tng. 3.2.4.2. Gia cng c kh

Ni chung gm th thng gia cng v chun b theo cc phng php sau : - Chun b phi liu bng phng php t. - Chun b phi liu bng phng php kh. - Chun b phi liu bng phng php bn kh hay na kh, na t. - Chun b phi liu bng phng php nhit. Mi phng php u c u nhc im ring. Phng php kh thch hp vi t

st c cng cao, km do (phin thch st), tp cht nhiu. u dim l: d trn u, iu chnh c cp phi ht theo c ht mong mun. Nhc im l: ch ph hp vi phng php to hnh bn kh.

Phng php t l phng php c in, rt ph bin trong cng nghip gm s. u im: d nng cao cng mc, do phi liu, to hnh d dng, ph phm t, cht lng bn thnh phm v thnh phm cao.

Nguyn liu khai thc m (c gii) vn chuyn bng ti kho, bi cha nc

vn chuyn vo cc l (xe) bng ti my cung cp bng ti nc

nghin qu ln t (xa lun) a gp (hay my trn kiu a) bng ti my nghin trc mn (2 trc) my trn 2 trc luyn lent (n p)

Hnh 10. Dy chuyn in hnh sn xut gch theo phng php t

3.2.5. Chun b phi liu gm mn (gm tinh) : Yu cu chun b phi liu rt k cng k c khu tuyn chn nguyn liu ban u

nht l i vi mt hng s cao cp. Nguyn liu ch yu sn xut gm mn l t st trng, cao lanh v trng thch.

Cc loi nguyn liu ny phn ln c phn loi, tuyn chn, gia cng th, trung bnh ti m hoc cc c s gia cng ring, c trng hp mn t yu cu 63 m.

trng thch (mn) cao lanh, t st quc mn

( lm giu)

nc b khuy nc b khuy nc b khuy

b khuy chung

bm mng

b cha c cao lc khung bn

kho sy

ng ng luyn lent thng nghin thnh bt

luyn lent chn khng kt cha

rt sn phm

trong khun em i to hnh do p sn phm

thch cao bn kh

Hnh 11. Dy chuyn chun b phi liu gm mn

Thng thng cc loi vt liu gy mi ch t mn trung bnh, trng hp ny phi chun b phi liu trong my nghin bi t gin on.

nng cao hiu qu nghin, thng cc loi vt liu gy c cng cao c np vo my trc vi mt lng bi kh ln (km theo mt lng t st hay cao lanh nht nh). Sau mt thi gian nghin kim tra mn nu gn t yu cu th cho ton b nguyn liu ( t mn) cn li v thm bi, nc theo t l nguyn liu/bi/nc = 1/1/1 ri tip tc nghin thm 4 - 5 gi. Trc khi tho h nht thit phi kim tra mn. H t tiu chun tho vo b khuy qua sng rung (4900 l/cm2) v b phi c khuy lin tc.

t mc sau khi qua p lc khung bn c m 25 - 26%. t mc c trong kho vi thi gian t nht 7 ngy. Phi liu c em luyn trong my n p chn khng nhm tng do,

gim lng khng kh c trong t mc ( gim p 750 760 mmHg). Chiu dy mng t i vo bung chn khng cng mng cng tt. Chng ta c th

tnh ton c n v thay i chiu dy mng t theo mun bng cch thay i kch thc mt li phn phi di t u vo bung chn khng.

Thc t kch thc v v tr bt kh trong di t rt phc tp, n gin, chng ta coi nh bn knh bt kh bng chiu dy mng t, nh vy bt kh ch c loi b khi lc ph v mng t P cng ph v ca phi liu. Vi gi thit ta c th tnh c chiu dy di t i vo bung chn khng nh sau :

Khi ph v mng t mng th P = S r12 Q = 2 1 KP 1 = Q r1 / 2 KP = (Q1 - Q2) r1 / 2 KP trong S : tr lc ph v mng t hnh cu. P : lc ph v. Q1 : p sut trong bung chn khng (mmHg) Q2 : p sut trong lng bt kh (mmHg) r1 : bn knh bt kh (cm) 1 : chiu dy mng t i vo bung chn khng (cm) KP : gii hn bn khng v ca mc (KG/cm2) Chiu dy mng t t l nghch vi gii hn bn khng v ca mc v t l thun

vi bn knh bt kh. S bt kh trong mng t c cho trong hnh 12.

r1

1 2 r2

d1 d2

Hnh 12. S tnh ton chiu dy mng t trong my n p chn khng m thch hp trong mt s phng php to hnh nh sau Phng php to hnh m thch hp H rt 28 - 40 % To hnh do 22 - 25 % Tin do 18 % Ep do 12 - 15 % Ep bn kh v kh 3 - 9 % h rt c m thch hp, cng b cng tt cn phi pha long h bng cht

in gii vi hm lng v cht in gii thch hp. 3.3. KIM TRA K THUT PHI LIU

Ni dung kim tra bao gm : - Kim tra chnh xc v ng nht v thnh phn ha, thnh phn ht v m. - Kim tra mu sc ca t mc sau khi nung. - Kim tra mt s tnh cht k thut ca phi liu nhit thng: do, cng

mc, co sy v.v... - Kim tra cc tnh cht ca phi liu nhit cao (ch yu l nhit nung).

4. CHNG 4: TO HNH Mc ch ca khu to hnh cng nh yu cu c bn ca n l tho mn cc ch

tiu v kch thc, hnh dng hnh hc, ng nht ca bn thnh phm v ca sn phm.

Theo mc ng nht (thnh phn, m, mt v cu trc) do cc phng php to hnh t c th tng qut c th sp xp theo th t sau:

- rt sn phm rng (h tha) - rt sn phm c (rt h y) - Xy trn my (loi u nn) - Xy trn my (loi dao bn) v k c vut, gn rp bng tay - p bn kh - p do - Nn p th cng

4.1. CHN PHNG PHP TO HNH C s la chn phng php to hnh bao gm nhiu yu t song tng qut l

cc iu ch yu sau: - Hnh dng v cc tnh cht c trng ca cc loi sn phm. - Tnh cht k thut ca phi liu. - Nng sut v gi thnh (ph). Cn c vo hnh dng sn phm chn phng php to hnh l cha , m iu

quan trng l phi cn c c vo c tnh k thut ca phi liu mi chn ng phng php ti u.

Phi liu c do cao: c th xy trn my, p do hay tin do. Phi liu do va: p do, rt. Phi liu km do nhng ng nht cao: p bn kh, nn p th cngcc sn

phm hnh dng n gin. Khi phi liu c th tha mn nhiu phng php to hnh th chn phng php

no c nng sut cao nht nu hnh dng sn phm cho php. Khi yu cu v chnh xc ca sn phm khng cao lm, chng ta chp nhn kch

thc ca khun (chnh l kch thc sn phm lc to hnh) nh sau: S : co tng (%) L1: chiu di ca sn phm sau khi nung, L0: chiu di ca sn phm t (bng kch

thc khun)

1LLS =

SL

L = 100100 1

0

4.2. CC PHNG PHP TO HNH 4.2.1. To hnh do :

Phng php to hnh do bao gm vut trn b quay, gn rp trong khun thch cao (chum, vi), xy trn my bn tua dao bn hay u nn, p do bng cc loi my (p ngi v gch bng my p ngi hay my n p chn khng).

C s ca phng php ny l da vo tnh do ca nguyn liu, phi liu (tc l ca t st v cao lanh).

n gin, chng ta tha nhn hn hp ca t st v cao lanh hay phi liu gm s (dng phn tn do) thuc loi vt th kiu Bingham nh trong hnh 13 (l loi vt th c tnh cht kiu HUK kt hp vi vt th kiu Newton hay Stverman), ngha l khi c tc dng ca lc bn ngoi vt th s n hi, phng trnh lu bin s chu s chi phi ca nh lut Huk v nh lut Newton.

Ngi ta chia bin dng ra lm ba loi : - Bin dng n hi tc thi (10-10 - 10-3 s) - Bin dng n hi chm (sau 3 - 10 s) - Bin dng do: hon ton khng thun nghch.

Hnh 13. Quan h gia tc bin dng ph thuc vo ng sut tip tuyn ca cc

loi vt th in hnh. A-cht lng Newton (ph thuc tuyn tnh), B-cht lng gi do khng Newton c snh dng, C-vt iu dn n, D-gradient vn tc, -ng sut tip tuyn, o-gii hn dng.

Vai tr ca nc trong hn hp cha t st, ty hm lng nc m c tnh ca hn hp t st rt khc nhau. i vi phi liu do lng nc va cc ht st hydrat ha hon ton th hn hp s c do cc i. Mng nc hp ph mng bao quanh cc ht st ng vai tr bi trn, quyt nh linh ng v nh hng n lc

Van-der-Walls, hin tng ng snh, kh nng keo t ca hn hp t st -nc... Kh nng keo t ca hn hp y c vai tr rt ln v c im ca loi cu trc keo t l c bin dng n hi chm rt ln, nh hng tt n tnh do. m to hnh thch hp trn cc my n p chn khng ca hu ht cc loi phi liu dao ng trong khong 22 - 26 %. Vi h rt cc hin tng trn li l khng mong mun.

Kt qu khi nghin cu nhiu loi phi liu du ch ra rng: trng thi lm vic bn do ca cc loi nguyn liu, phi liu dao ng trong mt gii hn hp t (6-11).10-5 dyn/cm2. iu ny c ngha l: tng lc lin kt phn t gia cc ht vt liu ca cc phi liu khc nhau gn nh mt hng s.

Lng nc ng vi trng thi phi liu c bn do cc i chnh l lng nc to hnh thch hp. 4.2.2. To hnh bng phng php rt 4.2.2.1. S hnh thnh lp mc

Khi rt h vo khun thch cao, do thch cao c kh nng ht nc nn h chuyn ng theo hng thnh khun bm vo khun thnh lp mng u n v st c, theo thi gian chiu dy lp mc tng dn.

Nu gi chiu dy ca lp mc bm vo khun l x, trong mt n v thi gian dt, lp mc tng c dx, dx s gim dn khi chiu dy lp mc tng v kh nng ht nc ca thch cao gim dn. M hnh s ht nc ca thch cao c th hin trn hnh 14. Nu gi thit kh nng ht nc ca thch cao l a v coi a l hng s th quan h gia chiu dy lp mc v thi gian s l:

0

dxa

xdt =

== x xaxdxat 2211 tAatx == 2dt

xadx =

a) Lc bt u

b) Sau mt thi gian rt

Hnh 14. M hnh ht nc ca thch cao t h rt Vi h gm 42.5% vt cht st, 18.5 % trng thch, 33% quc, quan h gia chiu

dy lp mc v thi gian nh cho trong hnh 15.

Hnh 15. S ph thuc ca chiu dy lp mc vo thi gian bm khun

4.2.2.2. Cc phng php rt C hai phng php rt chnh: rt h tha v phng php y. Chn

phng php no l do hnh dng sn phm quyt nh. Phng php rt y i hi 2 khun v do kh nng ht nc trong h theo 2 pha nn nng sut cao. 4.2.2.3. Yu cu c bn ca h rt

- Lng nc t nht gim thi gian rt v thi gian sy. - linh ng ca h tt c ngha l nht b m bo vn chuyn trong

ng ng v rt d. - H phi bn: khng c hin tng lng, khng keo t, khng ng snh, nht

h n nh. - Tc bm khun ln. - Lng cht in gii b nht (chn ng cht in gii ti u, hm lng hp l) - Kh nng thot khun d, t khuyt tt nh r mt v.v...

4.2.2.4. C s ha l ca h Cc ht st phn tn trong nc chng s c bc bi mt v nc v tr thnh

mt ion phc rt phc tp. Khi hp ph trao i cc ht st tr thnh nhng lp in tch kp.

Cc mizel t st khi hp ph trao i to ra mt lp n phn t cc cation. Qu trnh hp ph hnh thnh ion hydrt ha (l mizel t st-n phn t cc cation-

lp nc lng cc). Cc cation nm v tr xa cc ion hydrat mt khong cch nht nh nn chng c kh nng chuyn ng t do.

Chiu dy lp in tch kp c th tng ng mt phn ca v nc lin kt v do bn cht ca ion trung tm v cc cation hay anion hp ph trao i quyt nh (tc l do cu trc ca khong st v loi cation dng lm cht in gii).

Lp in tch kp (t hp keo = mizel t st) c in th ca n, chnh in th l ng lc gy nn s chuyn ng ca h keo. in th ca cc h keo khc nhau s rt khc nhau nhng c th o c. Gi tr nm trong gii hn 16-100 mV.

M hnh ca mizel t st c cho trn hnh 16.

Hnh 16. M hnh m t mizel t st Qu trnh pha long h l da trn c s lm thay i in th zeta ca cc mizel.

Theo Helmholtz v mt s tc gi khc th lp in tch kp ca cc mizel t st ging nh mt t cu, gia cc lp ca t cu tn ti in th bng:

)(...

+= rren

e- in tch cc nguyn t n- s ha tr n t do ca lp bn trong hay ca ion trao i vi lp bn ngoi. - hng s in mi. r- bn knh ca vng bn trong. - khong cch gia vng bn trong v bn ngoi. Khi thm vo h cht in gii th n s tng, mt tng i ca v nc tng v

khong cch gia cc lp s tng, ngc li gim, kt qu l s tng, h s bn. nh hng ca cht in gii cha Na+ ca cc hp cht khc nhau n nht ca

h nh trn biu trn hnh 17. Cc hp cht cha Li+ c tc dng tng t Na+, cn K+ c tc dng km v d to

thnh s phi tr bn KO12. Khi s dng mui Na+ lm cht in gii th Na+ s b cc anion (m) trn b mt

cc ht st hp ph nn d xy ra s x y b mt cc ht st (h bn). Ngc li ht st cha Ca2+ s cn n 2 in tch m dn n cc ht st d dnh kt vi nhau (b keo t).

Hnh 17. nh hng ca cc cht in gii cha natri ca cc hp cht khc nhau

n nht ca h 1. NaP2O7 2. Na2SiO3 3. NaOH 4. Na2CO3 5. Na2C2O4 Hin tng ng snh (thixotropic): y l mt hin tng chng ta hay gp h

rt. H di tc dng c hc th linh ng, nhng yn sau mt thi gian nht nh th tr li trng thi ban u, h c linh ng km, thi gian chy y 100 cm3

s tng. Nguyn nhn l do lp nc trong v solvat lin kt li vi nhau (khng phi do cc mizel b keo t).

nh gi snh ca h, ngi ta so snh t s thi gian h chy y 100 cm3 qua dng c th nghim khi thi gian yn l 30 pht vi thi gian h chy y 100 cm3 nhng ch yn 1 pht.

snh ca h sn xut s t 1.8 2.2, ca h sn xut snh mn t 1.5 2.6. 4.3. CC DNG KHUYT TT DO TO HNH

Yu cu ca sn phm lc mi to hnh l t hnh dng mong mun. Kch thc chnh xc, mt ng u, khng b rn nt, b vt xc hay r mt.

Mi phng php to hnh s c th c cc dng khuyt tt khc nhau nguyn nhn cng rt khc nhau: do thit b, do phi liu, do thao tc ca cng nhn.

Cc dng khuyt tt phng php to hnh do: nt, bin hnh, vt xc mt trong hay mt ngoi, thnh dy hay mng khng u, mt mc cc v tr khc nhau trn cng mt sn phm chnh lch nhau v.v...

Nguyn nhn c th do phi liu c ng nht km, m khng u (qu ln do cng nhn dng nc bi trn em vo), lng khng kh trong phi liu cn ln v khng u. Nguyn nhn c th do thit b: c cu ca my to hnh cha tht hp l, dng lu b mn d b r o (trc).

Cc my n p chn khng t khi trnh khi cc khuyt tt nh nt, rn chn chim hay ch S. Nguyn nhn l do phi liu chu tc dng ca lc p (ma st vi thnh) cc v tr khng u nhau do mt cng khng ng u. st thnh ma st ln, gia tm ma st gim dn tin ti khng.

Sn phm gm mn to hnh trn my bn tua dao bn th dng khuyt tt hay gp l nt, xc mt, r, bin hnh kch thc dy mng khng u v.v... Dng khuyt tt ny thng to iu kin thun li cho khuyt tt nt, bin hnh lc sa, sy.

gim khuyt tt dng to hnh do cn c quy trnh cng ngh chnh xc, thc hin nghim tc, cng tc kim tra k thut phi tin hnh thng xuyn.

Cc dng khuyt tt phng php rt : tnh cht ca h rt trong qu trnh to hnh thay i nhiu hn so vi phi liu do nht l lc rt phn h tha (s dng lng h tha chung vi h mi nghin) d lm thay i t trng ca h.

Tnh cht ca khun thch cao trong cng mt ca sn xut cng thay i rt mmh: m ca khun ko theo l kh nng ht nc ca khun thay i rt ng k, nht l cc khun dng lu.

Khi rt cc loi sn phm kch thc ln, hnh dng li phc tp thng phi rt h vo khun nhiu ln (rt h b sung), thi gian rt di do s thay i tnh cht ca h c th xy ra ngay trong cng mt sn phm (h d lng, ng snh).

Tt c cc iu nu thm ny lm tng thm kh nng gy ra khuyt tt khu thot khun, sa, sy v c khu nung.

5. CHNG 5: SY SN PHM Sn phm gm s sau khi to hnh lng nc c th ti 25%. Tc trong 1 kg phi

liu (hay sn phm mc) c 0.25 kg nc. vic sa mc, vn chuyn, trng men v nung d dng bt buc phi sy sn phm. Nhit ho hi ca 1 kg nc l 585 kcal, vy lng nhit cn thit sy 1kg phi liu c th n 146 kcal.

Khi sy hi m s thot ra, nu chng thot ra t ngt, phn nc trn b mt hay st b mt thot ra d dng nhng hi m bn trong lng sn phm thot ra rt kh khn do p sut ring phn ca n nhng v tr nc tp trung s tng t ngt, nu p sut y vt qu lc lin kt ca cc ht st (tc cng ph v ca mc) s gy nn hin tng n sn phm ngay lc sy (hay lc nung).

Nh vy vn ch yu ca k thut sy l sy ng u bn thnh phm khng b nt, sau l tm cc bin php k thut rt ngn thi gian sy, gim vn u t thit b, gim din tch sy v tng nng sut. 5.1. QU TRNH SY SN PHM GM S

Mc ch ca qu trnh sy l loi b nc lin kt l hc (cn gi l nc t do, nm cc l trng gia cc ht vt liu) hay nc lin kt ho l (bao gm nc hp ph, nc hydrat ho v cc loi khong st ba lp silicat l nc trng n).

Sn phm gm s ni chung l kh dy, lc sy nc b mt d bc hi gy nn chnh lch hm m trn b mt v trong lng sn phm, do nc trong lng s khuych tn ra ngoi b mt v tip tc bc hi. Nh vy tc sy chng nhng ph thuc vo kh nng bc hi trn mt sn phm m cn ph thuc vo tc khuych tn nc t bn trong ra bn ngoi. 5.1.1. Ch sy

l tng hp cc bin php nhm m bo thi gian nh nht cn thit sy sn phm c tnh n nhng tnh cht, hnh dng, kch thc ca chng v nhng c im ca cc thit b sy, cng nh cch a nhit n sn phm mt cch hp l vi tn tht nhit nh nht v h hng sn phm t nht.

Qu trnh sy c c trng bng 3 giai on: giai on t nng, giai on hng tc sy v giai on gim tc sy nh cho trong hnh 18.

Giai on u ca qu trnh sy c c trng bng s t nng nhanh bn thnh phm t nhit ban u n nhit ca cht ti nhit bo ho ( mt hm m cho trc ca cht ti nhit). Nhit ca n tng ng vi cc ch s trn nhit k t, cn nhit mi trng , tng ng cc ch s trn nhit k kh.

Giai on th hai ca qu trnh sy c c trng bng on nm ngang trn ng cong tc sy, iu ch ra rng tc sy v tr s bng tc bc hi m trn b mt ca bn thnh phm. Hm m ca bn thnh phm thay i hu nh theo ng thng.

Giai on ba ca qu trnh sy c c trng bi s gim tc sy v s tng nhit ca bn thnh phm. Cng tch m ca giai on ny t l vi m trung bnh ca vt liu trong khong t m ti hn n m cui cng.

Hnh 18. Cc ng cong sy

5.1.2. co khng kh Biu trn hnh 19 cho chng ta thy: - Nc thot ra hu nh c ton b thi gian sy. - co th tch t n gi tr cao nht sau 70 h. - co bt u ngay giai on 1 cng vi vic bc hi bao ph quanh ht st v

co t l thun vi tc thot m. - Giai on 2 sn phm tip tc co v bt u xut hin l xp. - Giai on 3 tip tc bay hi lng nc t do v nc hp ph, th tch ngay sau

khi bc sang giai on 3 l khng i, sn phm ch co 2 giai on u, lng nc bay ra 2 giai on ny t gn 1/2

Cui giai on 2 sn phm bt u mt tnh do chuyn sang trng thi dn. Nh vy s co khng u giai on ny gy nn bin dng (bin dng do). Cui giai on 2 vt th chuyn sang trng thi dn khi co khng u s dn n hin tng nt nu ng sut vt qu cng ph v ca mc. trnh bin dng v nt phi tm bin php lm cho sn phm co u n trong ton b qu trnh sy.

Bng thc nghim ngi ta xc nh s chnh lch m b mt v tm sn phm. Nhng tht ra m tm cng rt kh xc nh mt cch chnh xc, do ngi ta s dng m trung bnh ca sn phm. Ch s gy n nt Wmax c tnh nh sau:

Wmax = (Wtb - Wm)max (%) Wtb l m trung bnh ca vt th, Wm l m trn b mt ca sn phm. Ch s Wmax ph thuc vo loi khong st nhiu hn l chiu dy sn phm.

5.2. K THUT SY Yu cu chung i vi thit b sy l

- Tc sy ln nht cho php song vn m bo c cht lng sn phm. - Tiu tn nhit nng ring t. - Sy m bo ng u. - Cung bc hi m trn mt n v (m3 ) thit b ln - D iu chnh cc thng s ca ng lc sy - C gii ho vic bc d, vn chuyn sn phm v t iu kin v sinh. Trong cc yu cu trn, yu cu v t ng u l quan trng hn c. Phi liu cha vt cht st v cao lanh ni chung l kh sy. Nghin cu qu trnh sy sn phm gm s bng phng php i lu vi ng lc

sy l hn hp khng kh c gia nhit bng hi nc qu bo ho, Salmang xy dng nn biu nh trn hnh 20.

t c mc ch sy nhanh, an ton, r, mi loi sn phm vi cc c tnh k thut ca phi liu ring cn nghin cu k xy dng cho chng ch sy ti u.

Hnh 19. Biu nghin cu s tng quan gia lng nc thot ra, co,

xp v th tch ban u ca sn phm (phi liu 75% vt th rn, 25% nc) trong qu trnh sy

Vic la chn ng lc sy hp l s gp phn h gi thnh. Vic ny cn da vo tiu chun v cht lng ca cc loi sn phm chn cho ng.

Sy sn phm gm xy dng do i hi v cht lng sn phm v mt mu sc khng nghim ngt, cho php chn l sy tunel, ng lc sy l khi l hay khng kh nng c gia nhit bng khi l.

Sn phm gm tinh vi nh s dn dng (bt, a, m chn), s v sinh, s cch in v.v... i hi mu sc trng, trong, sch, cn chn ng lc sy l khng kh nng c

gia nhit bng hi nc qu nhit. Sy cc loi sn phm ny khi chn thit b sy phi cn c vo hnh dng, kch thc v khi lng tng loi sn phm. Gm tinh vi thit b sy thch hp l l sy xch chuyn, sn phm s v sinh hay s in thch hp l l sy phng loi hin i, sn phm to hnh bng rt nu l gm tinh vi th thit b sy hp l li l bng sy hay a quay.

Vi s cch in cao th, phng thc sy nhanh, an ton, hin i nht l sy cao tn. y gradient nhit v gradient m l cng chiu.

Hnh 20. Biu Salmang

6. CHNG 6: NUNG Nung l khu quan trng nht trong k thut sn xut gm s. N nh hng quyt

nh n cht lng v gi thnh. Khi nung, c th trong vt liu s xy ra phn ng nhit cao ca cc cu t trong

nguyn liu, qu trnh kt khi, qu trnh xut hin pha lng, qu trnh ho tan v ti kt tinh cc tinh th. Tm li, ni tng qut khi nung xy ra ng thi cc qu trnh trao i nhit v trao i cht, cc qa trnh ny li do nhng bin i ho hc v bin i pha din ra rt phc tp.

Tuy nhin, iu quan trng nht l kt qu ca qu trnh nung: to ra vt liu mi c vi cu trc mi.

Cu trc xng sn phm gm l mt h thng nhiu pha phc tp bao gm cc pha thu tinh, pha tinh th v pha kh. T l s lng ca cc pha ny l thnh phn pha ca xng sn phm, n xc nh tnh cht vt l ca xng sn phm.

Vi cu trc ca vt liu c nh ngha nh l nhng c im vi cu to ca vt liu, th hin qua hnh dng v kch thc cc ht, cch phn b, hng v s tip xc gia cc ht, s lng v cht lng pha thu tinh v s hin din ca l xp.

Chng ta bit rng pha rn tinh th tn ti di hai dng: cc tinh th n (trong cc n v cu trc nh nguyn t, ion, phn t c sp xp lp i lp li theo chu k mt cch hon chnh v trong sut ton b mu vt), hay di dng pha rn a tinh th. Pha tinh th trong cu trc vt liu gm s l mt pha rn a tinh th, n c to nn t tp hp ca rt nhiu cc ht tinh th, hay c gi ngn gn l ht. Cc ht ny sp xp st cnh nhau, cch nhau bi vng c cu trc khng trt t gi l bin gii ht nh trong hnh 21. Trong vt liu gm s in hnh cc ht c kch thc nm trong khong 1-50 m v ch c nhn thy di knh hin vi.

Hnh 21. V d cu trc ca mt mu vt liu a tinh th (c to nn t rt nhiu

ht phn cch nhau bi vng khng trt t gi l bin gii ht) Qu trinh nung khng nhng l iu kin hnh thnh nn vt liu mi, m ngay

trong chnh bn thn qu trnh cng cha ng nguy c: c th lm cho sn phm b bin dng hay thm ch ph hoi s nguyn vn ca n, tc l lm cho sn phm c th b cong vnh hay thm ch nt, v. iu ny c bit d xy ra khi dng nhng nguyn liu t st rt nhy khi nung.

6.1. C S L THUYT CA QU TRNH NUNG Sn phm gm s ch c nung n kt khi, qu trnh nung l khng thun

nghch v hu nh khng t c cn bng pha (khng thc hin n cng). 6.1.1. Hin tng kt khi v cc qu trnh xy ra ng thi vi n (phn ng pha

rn, xut hin pha lng v ti kt tinh) Kt khi l qu trnh gim b mt (bn trong v bn ngoi hay ch tip xc vi

nhau) ca cc phn t vt cht do xut hin hay pht trin mi lin kt gia cc ht, do s bin mt ca l xp trong vt liu hnh thnh mt khi th vi th tch b nht. Qu trnh gim b mt xy ra ng thi vi s xut hin hay tng cng cc cu ni gia cc ht vt th di tc dng ca p sut hay nhit , xem hnh 22 minh ho qu trnh kt khi.

i vi hin tng kt khi ch c mt pha rn c cc gi thuyt sau: - Thuyt bin dng do (Frenkel) - Thuyt ngng t v bc hi ca Kysunsky - Thuyt khuych tn ca Kingery Hin nay thuyt khuych tn c nhiu ngi tha nhn hn c. Chng ta i su

nghin cu gi thuyt ny. Coi hai ht vt th l c dng trn, khi nung chng s c qu trnh khuych tn vt cht vo nhau nh trong hnh 23.

Tu thuc vo nhit m hin tng khuych tn xy ra ranh gii b mt hay trong th tch vt th m c s khc nhau v tr s ca h s khuych tn (ch yu l s khuych tn ca cc khuyt tt, cn gi l vacance).

Thc cht ca vn l xt mi lin h gia s thay i th tch hay chiu di vi nhit v thi gian kt khi. Trng hp xy ra khuych tn th tch theo Frenkel mi tng quan gia chng c th biu din bng phng trnh sau

5/43

5/4

0

.80.83 t

KTaDn

VV =

y: V- l s thay i th tch; V0- th tch ban u; n- s im tip xc; - sc cng b mt; - khong cch gia cc nguyn t; D- h s khuych tn; K- hng s Bolzmann; T- nhit tuyt i (K); a- bn knh l xp; t- thi gian.

Trong trng hp khuych tn th tch tr s D c tnh nh sau

taKTXD 3

4

.161

=X- l bn knh tip xc gia hai ht Nu tnh vi trng hp co theo chiu di th cng thc trn c tnh nh sau:

5/25/2

3

3

0 220 t

KTaD

LL

=

Hnh 22. Qu trnh kt khi cc ht trn Al2O3 khi nung nhit 1750-

18400C (phng i 1500 ln)

Hnh 23. M t qu trnh khuych tn vt cht khi nung theo Frenkel

R-bn knh ca ht; cn r tnh bng

rR

xy ==2

2

Trong qu trnh kt khi th tch ca h gim dn cc l xp s c lp y v

bin thnh l xp kn ri tch ra. xp cn li chng 10% th qu trnh kt khi chm li song khng dng hn. Nu xp t khong 8-10% th cc ht khng b ngn cch bi cc bt kh na m tip xc vi nhau bt u qu trnh ti kt tinh. Nu duy tr lu hay tng nhit th th tch cc ht c th t v vt kch thc cc ht vt liu ban u khong 2-3 ln.

Qu trnh ti kt tinh thng tin hnh theo 3 giai on: to mm, cc mm ln ln thnh tinh th thc s, cc tinh th trng thnh. Qu trnh ny xy ra song song vi qu trnh kt khi. ng lc ca qu trnh ti kt tinh l nng lng t do ca h.

Nng lng ca mt li nh hn mt lm, di tc dng ca chuyn ng nhit, cc nguyn t vt qua ranh gii mng tinh th mt li lm cho tinh th mt li ngy mt tng. Qu trnh ti kt tinh s ngng khi nng lng t do trit tiu.

Qu trnh ti kt tinh s tng mnh c bit khi c mt cht khong ho, ngc li cc tp cht ngn cn s ln ln ca tinh th. Khi hin tng ti kt tinh xy ra rt nhanh cc tinh th ln c th xut hin ng sut ni lm gim cng c hc ca mu. Nu c mt tp cht (k c l xp) th mt mt cng ca mu gim, mt khc qu trnh hn l cng gim hay ngng li.

Qu trnh xut hin pha lng tn ti trong i b phn gm khi nung. Cc yu t sau y ca pha lng xut hin ng vai tr quan trng:

- Gc thm t ca pha lng. Tt nht nm trong khong 900-00 l c gc thm t tt, c kh nng xm nhp vo bin gii gia cc ht pha rn.

- Lng pha lng hnh thnh cng nhiu cng tt (tuy nhiin khng c qu nhiu d lm bin dng sn phm), s to iu kin cho qu trnh kt khi mnh lit hn.

Qu trnh xut hin pha lng thng km theo cc tc ng sau - Phn b li cc ht, to nn trt t mi ca vt liu. - Pha mi xut hin thnh l xp c tc dng hn cc l xp v lm cc ht a

tinh th ln ln. Khi kt thc qu trnh kt khi th pha rn ti kt tinh, qu trnh st c tng mnh,

lc ny nht, thm t, sc cng b mt ca pha lng v s ph thuc ca chng vo s bin thin nhit , thi gian lu rt quan trng trong vic hnh thnh nn nhng l xp kn trong vt liu.

6.1.2. Cc h 1, 2, 3 v 4 cu t trong cng nghip gm s (xem gio trnh ho l silicat)

6.1.3. S bin i vt cht ca cc loi nguyn liu khi nung (xem chng nguyn liu)

6.2. CC YU T NH HNG N QU TRNH NUNG V CHT LNG SN PHM

6.2.1. Thnh phn ho hc L thuyt v thc nghim u ch ra rng thnh phn ho hc ca phi liu l yu

t ch yu quyt nh chu la ca n tc l quyt nh nhit v khong kt khi. 6.2.2. Kch thc v thnh phn ht

nh hng n qu trnh to hnh v qu trnh kt khi.Ni chung kch thc ht cng b, phi liu cng kt khi tt. Nu kch thc ht t mn mong mun c th h thp nhit nung cc i n khong 20-350C.

Khi kt khi c mt pha lng kch thc ht vt liu ban u nh hng ng k n ho tan ca ht rn trong pha lng dn n lm thay i mnh cc tnh cht ca pha (chng hn nh ,,...). Kt qu l lm thay i mi tnh cht ca sn phm. V d s giu SiO2 ch t bn c cao nht khi cc ht SiO2 t mn 5-15 m. 6.2.3. Mt ca bn thnh phm

st c ca cc ht ni ring v sn phm ni chung c nh hng n qu trnh kt khi. Mt cng cao, kt khi cng thun li. iu ny cng c ngha ng k khi nung gm c bit (t nguyn liu xit tinh khit) qu trnh kt khi n thun xy ra trng thi rn.

p sn phm bn kh vi p lc cao mc s rt st c. 6.2.4. Nhit nung cc i v thi gian lu

Nhit nung hp l tmax v thi gian lu l yu t rt c bn, c nh hng quyt nh n cht lng sn phm nung v chnh li do thnh phn ho hc ca phi liu quyt nh. Tu theo thnh phn ho hc m hin tng kt khi ni chung hay cc phn ng ho hc gia cc cu t ni ring xy ra trng thi rn hay giai on u l kt khi pha rn v cui cng li xut hin thm pha lng. Trng hp kt khi c mt pha lng th lng pha lng xut hin v tnh cht ca n (v d nh ,, v.v...) quyt nh iu kin nung.

Vi phi liu c khong kt khi hp nn nung nhit nung thc thp hn nhit nung l thuyt t 20-300C v ko di thi gian lu nhit lu hn. Phi liu c khong kt khi rng cho php nung nhit cao hn nhit l thuyt 20-300C song rt ngn thi gian lu nhit mt t vn thu c sn phm tt ng thi gim c nng lng tiu tn cho mt n v sn phm. 6.2.5. Tc nng v tc gim nhit

Tc nng nhit lc nung sn phm gm s ph thuc ch yu l qu trnh bin i cc cu t trong phi liu theo nhit v c tnh ca tng loi sn phm (dy, mng, to, nh v.v...), tu thnh phn khong vt ca phi liu m ng vi cc

khong nhit nht nh s xy ra qu trnh bin i th hnh, hiu ng thu, to nhit, phn ng ho hc, kt khi, xut hin pha lng v.v...

Tm li trong qu trnh nng nhit chng ta phi quan tm n: - Cc nguyn liu ph (nht l cc hp cht thin nhin) nh vi, lmit hay

tp cht c hi khc nhau (Na2SO4, MgSO4 d tan...) - Chiu dy thnh, hnh dng sn phm. - Lu n cc khong nhit c cc hiu ng t bin (bao gm c bin i th

hnh, phn hu ...) - Cu to v loi l nung. - c tnh ca sn phm ( chn nung mt ln hay 2 ln, c trng men hay khng,

nung trong bao hay nung trn) Tc gim nhit khng hp l lc lm ngui (trong trng hp sn phm gm

s loi n gin, thnh mng, khi lng b) cn nguy him hn tc nng nhit khng hp l.

Tc lm ngui chng nhng c nh hng n vic pht trin cc tinh th pha rn m cn lin quan n s xut hin ng sut ni trong sn phm cha pha thu tinh. Pha lng khi h nhit s chuyn t trng thi do nht sang dn km theo co th tch ln. Nu co khng u (ngoi ngui nhanh co trc) gy ng sut lm nt v sn phm nht l loi ln, dy v hnh dng phc tp. Trng hp pha rn c mt cc khong c c tnh bin i th hnh mnh lit s lm thay i cu trc v th tch giai on chuyn pha li cng nguy him nu ch lm ngui khng hp l.

Thng thng pha thu tinh trong sn phm gm s chuyn t trng thi do nht sang dn trong phm vi 900-8000C, do t nhit nung cc i n khong 9500C c php lm ngui nhanh, sau tc lm ngui gim dn.

Loi sn phm cha nhiu SiO2 dng t do th 5730C l giai on nguy him. 6.2.6. Mi trng kh

Trong qu trnh nung sn phm gm s, mi trng kh gi vai tr quan trng v n c th lm thay i thnh phn ho hc v ko theo l lm thay i tnh cht ca sn phm.

Cc loi mi trng: xy ho, kh, trung tnh, chn khng hay c cc kh bo v khc (vi cc loi gm c bit c th dng mi trng kh O2, N2 v.v...).

Khi nung s dn dng ta cn ch cc giai on sau y: 6.2.6.1. i vi s mm chu nung nhit 1280-13000C

+ 900-10500C: duy tr mi trng xy ho mnh to thun li cho qu trnh phn hu cc hp cht CaCO3, MgCO3 hoc thc hin phn ng chy hon ton cc hp cht hu c c trong nguyn liu.

+ 1050-12500C: mi trng xy ho hay trung tnh (thng trng men c) v nu l mi trng kh (d CO) s xy ra phn ng

2CO CO2 + C

v cc ht cacbon s bm ln b mt sn phm gy nn khuyt tt chm en. + 1250-13000C: duy tr mi trng kh (d CO) kh mu nu ca Fe3+ sang

dng Fe+2 s trng hn. Fe2O3 + CO 2FeO + CO2 FeO to nn d dng phn ng vi SiO2 to thnh silicat st d nng chy FeO + SiO2 FeO.SiO2 (wustit, t0nc = 11700C) 2FeO + SiO2 2FeO.SiO2 (fayalit, t0nc = 12050C) Nu nh FeO to nn cha kp phn ng vi SiO2 m mi trng li l xy ho (d

O2) th Fe2+ lai d chuyn thnh Fe+3: 4FeO + O2 2Fe2O3 V ngay c cc silicat st cng c th xy ra phn ng Fe2+ chuyn thnh Fe+3

trong mi trng xy ho (d xy) 2(2FeO.SiO2) + O2 2Fe2O3 + 2SiO2 Hm lng CO d trong khi l giai on kh cn t 2-5%.

6.2.6.2. i vi s mm chu u nung nhit trn 13500C Nung mi trung xy ha. Gii hn nhit ca mi trng xy ho l 13500C.

Trn nhit ny s phi c nung trong mi trng kh. 6.2.6.3. i vi s cng chu u nung nhit 14500C

Trong khong nhit 1000-10500C tuyt i phi c nung trong mi trng xy ho cacbon (b hng) khng ng li trn xng hay khng gi li b hng tn ti trong xng t nhng giai on trc. Trong khong nhit 1050-12500C th nung trong mi trng kh mnh vi h s t chy n = 0.7.

n = lng xy (khng kh) thc t cn khi t chy / lng xy (khng kh) cn trn l thuyt khi t chy.

Trn nhit 12500C n nhit nung cui cng (14500C) th nung trong mi trng trung tnh vi h s t chy n = 0.95-0.98, nh vy hu nh bng lng khng kh cn trn l thuyt khi t chy. 6.2.7. Vai tr v tc dng ca cht khong ho

C vai tr nh cht xc tc, c tc dng thc y qu trnh kt khi, ci thin tnh cht ca sn phm nung (tng bn c, bn nhit, bn in), cho php h thp nhit nung khi chn ng cht khong ho vi hm lng s dng ti u.

Cht khong ho c bit pht huy tc dng tt i vi gm c bit. Tuy nhin vi gm thng dng khi hm lng cc ph gia 3% m ci thin c cht lng sn phm mt cch ng k th cng gi l cht khong ho.

7. CHNG 7: MEN PH V CHT MU TRANG TR SN PHM GM

Khi nim men ph: l lp ph silicat hay l lp ph xit dng ph ln b mt vt liu (gm hay kim loi) gip n bn hn di nh hng ca mi trng v nhit , gip nng cao cng c hc v thm m, lm cho b mt xng gm bng lng v khng thm nc. Thng c s dng nht l lp ph silicat trng ln gm gi l men gm, trng ln kim loi gi l men ph kim loi. y chng ta ch nghin cu v men silicat trng ln sn phm gm s (t nay v sau gi l men).

Mt sn phm gm thng thng cn c trang tr, v bng nhng cht mu hay men mu khc nhau (nht l gm dn dng, xy dng va m ngh). 7.1. MEN S 7.1.1. nh ngha

Men v bn cht l mt lp thu tinh mng (chiu dy 0.1-0.4 mm) ph ln b mt xng gm s. Nhit chy ca n c chn ph thuc vo nhit kt khi ca xng gm s, thng thng dao ng trong khong 900-14000C.

Tuy nhin, so vi thu tinh thng thng th n cng c nhng tnh cht khc: n khng ng nht, lp trn khi nung phn ng vi mi trng ca l nung, lp di th phn ng vi xng, trong lp men c nhng cht khng tan hay kt tinh. 7.1.2. Phn loi men

Men c th c phn loi theo nhiu cch khc nhau. - Theo sn phm: men snh, men s. - Theo lng b mt: men lng, men sn. - Theo mi trng nung trong l: men xi ho hay men kh. - Theo nhit nung: men d chy (nhit nung 710-11200C), men chy trung

bnh (nhit nung 1060-12000C), men kh chy (nhit nung 1200-12800C) v men rt kh chy.(nhit nung trn 12800C, thng dng trng ln s).

- Theo thnh phn cht chy s dng: men ch, men alkali, men trng thch. Cch phn loi ny c lin quan cht ch n cch phn loi theo nhit nung. Chng hn men d chy c hai nhm chnh c nhit chy kh gn nhau l men ch (nhit nung 710-11200C) v men alkali (nhit nung (750-10600C)). Trong men alkali thng dng thm bor (thng dng Na2CO3, borax, clemanit). Men ch v men alkali lm cho b mt men lng bng. Men chy trung bnh thng dng cht chy l xit ch (d chy) v trng thch (kh chy). Men kh chy thng dng trng thch v cc nguyn liu khc nh vi, ZnO, BaO... Men rt kh chy c ch to t quc, trng thch v cao lanh. Cht chy y l trng thch.

- Theo cch sn xut men c th chia ra thnh: + Men sng (hay l men nguyn liu): chun b bng cch nghin chung nguyn

liu, ch yu l trng thch. Ngoi ra cn cc nguyn liu khc l vi, lmit,

magnezit, xit mu v cao lanh. Men sng thuc nhm men c hm lng kim thp dng trang tr ln sn phm s.

+ Men frit: cc nguyn liu c hay l tan trong nc dng trong men d chy cn thit phi nu chy t trc thnh thu tinh t tan trong nc (hp cht ca ch, borax, sa, ptat v.v...). Ngi ta cng frit ho nhng men trong cn s khuych tn cc cht khng ho tan trong men. Cc loi men frit ni chung c nhit nng chy thp hn men sng 60-800C, nhng li c nhc im l rt d lng, v vy thng phi a thm vo men 10-20% caolin, t st cha nung chng lng v trit tiu kim t do, hay c th a thm vo mt lng nh keo hu c carboxymethylcelulozy CMC, dextrin v.v.... Cc v d v men frit:

Men d chy dnh cho snh: 1,0 RO 0,1-0,4 Al2O3 1,5 SiO2 0-0,5 B2O3 Trong RO c th l PbO hoc c thm cc xit baz. Nhit nung men ny 900-

11000C. Men dnh cho s xp nm trong gii hn sau 1.0 RO 0.0-0,25 Al2O3 0.6-3.0 SiO2 0.1-0.752 B2O3 Nhit nung men ny l 1000-10800C, RO ch yu l PbO v c thm mt lng

nh kim v vi. + Men mui: men c to thnh do bay hi mui bm ln b mt sn phm to

nn lp men. Men mui thng c dng trong cng nghip snh dng to cc l qu, trang tr sn phm, tng bn ho cho dng c bn ho, bnh ng axit, s v sinh, ng dn... do men mui l loi men bn axit, kh chy v bn khng kh cao. Vi s hin din ca hi nc, NaCl phn ng vi SiO2 v nhit trn 11500C to nn lp thu tinh c thnh phn nh sau: 1.0 NaO 0.5-1.0 Al2O3 2.8-5.5 SiO2.

- Tu theo v ngoi ca men chng ta c th chia ra: men trong, men c, men mu, men tinh th, men bng hay m (bn m)...

+ Men trong: l lp men mng, khng c bt kh v cc tinh th khng ho tan hay l cc hp cht kt tinh ra, d bo m cho trong ca n. c th l men sng hay men frit c cha 10-20% cao lanh lc.

+ Men c: trong men ny c cc phn t lm c men. H s lm c ti a nu nh c s khuych tn cc ht kch thc 2-200 nm. c th l nhng tinh th nh, bt kh hay cc git lng. S lm c men c th bng:

Pigment (cht gy mu): nhng pigment khng tan trong men khuych tn u n. i vi men c mu trng th dng SnO2, CeO2, Sb2O3, ZrO2, ZrSiO4, cc fluorid l thch hp nht. Thng dng nht ngi ta dng ZrSiO4 c ch s khc x 2.0. ZrSiO4 c a vo khi frit ho v kt tinh li khi lm lnh. Phng php dng SnO2 (ch s khc x 2.0) c khc, n c a vo khi nghin men nh l nhng phn t d th c ch s khc x cao hn mi trng (ch l 1.5).

Cc tinh th kt tinh li: t trong men kt tinh li cc mm tinh th vi h s khc x cao (chng hn TiO2, ZrSiO4). Vic lm c ny tu thuc rt ln vo tc thch hp cu vic lm ngui men.

Cc phn t tch ra: mt cht chy tch ra di dng cc git phn tn m khi lm ngui n vn dng thu tinh (thu tinh bor) hay kt tinh li (thu tinh phtpho). Hiu qu lm c trong trng hp ny khng ln, bi v s khc nhau ca ch s khc x ca hai pha khng ln.

Cc bt kh phn tn: xy ra cc men trng thch c nht cao. Cc phng php lm c hiu qu nht l lm c bng pigment hay cc mm tinh

th tch ra. + Men mu: ch to bng cch nhum mu men trong. Cc phng php nhum

mu nh sau: Nhum mu ion: chng hn mu xanh dng cban, xanh l ng, mu vng st,

mu xanh l hay mu tm ca mangan. Pigment (cht gy mu): a vo cc cht mu khng tan (xanh l crm, mu nu

st) Nhum mu keo: bng s khuych tn cc ht kim loi Cu, Au c kch thc10-

100 nm to nn mu . + Men tinh th: cha cc tinh th vi ln n trn 1mm. Nhng tinh th ny

to nn bi anortit, vlastnit, forsterit, livin (MgO.FeO.SiO2), fayalit, diopsit (CaO.MgO.SiO2), cordierit, celsian, vilemit (2ZnO.SiO2), mullit, corund, hematit, rutil.

+ Men m: c c nh s pht trin cc tinh th nh trn b mt men. Bng cch nung nhit thp hn nhit chy hay tng cao hm lng Al2O3, CaO, ZnO, MgO, hay TiO2 so vi hm lng SiO2 c trong men. Cc tinh th anortit, vlastnit tu theo hm lng thch hp m c th pht trin thnh cc tinh th ln hay ch lm m b mt ca men. Ph gia ZnO hay TiO2 cng lm m b mt tt 7.1.3. Cc tnh cht ca men

y chng ta xt cc tnh cht ca men c vai tr to ln trong qu trnh thnh to n nh nht, sc cng b mt. Tnh cht c vai tr to ln trong qu trnh thnh to cng nh s dng l s dn n nhit ca men. Cc tnh cht sau khi men hnh thnh nh cng, tnh cht in, bn ho hc... 7.1.3.1. S thnh to lp men. S thnh to lp trung gian gia xng v men.

nht ca men Chiu dy lp men to thnh ph thuc vo xp ca xng gm, c bit khi l

xp nh va (d = 50-2 nm) v vi xp (d < 2 nm) t hn s lng l xp ln (d > 50 nm), ph thuc vo thi gian nung men v tnh cht ca huyn ph, dy ca lp men trng.

Khi nung trong men din ra cc qu trnh phn hu cc cht u, chng hn nh CaCO3 v cc phn ng khc v chng nng chy.

MnO2 MnO + 1/2 O2 Sb2O5 Sb203 + O2 Fe2O3 2Fe304 + 1/2 O2

11000C

3Fe3O4 6FeO + O2 Ti nhit ti u men c nht 2.102 - 2.103 Pa.s. nhn b mt ca men ph

thuc vo nht ng ca n khi nung. Nu nht thp men s c nhiu bt kh (do s phn hy, phn ng ca xng v men hay kh ca mi trng trong l b gi li khi men ng rn trong qu trnh nung) ngoi ln trn lp b mt v b mt men cn thi gian n nh sau khi kh thot ra.

Khi nht ca men cao v sc cng b mt ln th kh thot ra to nn trn b mt nhng knh hnh ng hay phu (to khuyt tt l chn kim).

Khi nht ca men ng th th cc bt kh tp trung ni bin gii xng-men v khng lm nh hng n b mt men.

Cc cation kim loi kim lm gim mnh nht nht ca men theo chiu sau Li+>Na+>K+.

S hnh thnh lp trung gian: trong thi gian nung thng ny sinh gia men v xng mt lp trung gian c dy 10-50 m. Lp trung gian ny c thnh phn ho, hm lng v thnh phn pha tinh th, pha kh v.v... khc vi xng v men. S xut hin lp trung gian ph thuc vo thnh phn ho, thnh phn ht ca xng v men, vo thi gian v nhit nung, vo xp ca xng...

Trong cc nguyn liu hnh thnh lp trung gian th CaO l ph gia tt nht, n cng chng nt men tt. Do vy trong hu ht cc loi men u c CaCO3 a vo. Trong qu trnh nung CaO trong men tan ra th trong xng cng nh vy, ko theo s tan ca nhng phn t khc, qua lp trung gian c hnh thnh v pht trin t c hai pha. Ngoi CaCO3 ngi ta cn dng vlastnit (CaO.SiO2) v lmit (c tc dng km hai loi kia).

Ph gia CaCO3 cho vo men c tc dng chng nt men tt do: - Tng h s dn n cho xng. - Tng qu trnh to lp trung gian. - Cn tr s trng n ca xng.

7.1.3.2. Sc cng b mt (nng lng b mt) Sc cng b mt ca mt pha lng tc dng ln ranh gii ca pha lng theo chiu

hng thu nh b mt ca n. i vi cc silicat nng chy nm trong khong 300 dyn/cm2.

Sc cng b mt ca mt pha lng silicat nng chy ph thuc vo nhit nung hay thnh phn ho ca n. Tnh sc cng b mt theo phng php cng tu theo thnh phn ho ca men.

Sc cng b mt ca men tng theo dy sau: B2O3, ZnO, CaO, NiO, V2O5, Al2O3, MgO, SnO2, Cr2O3 v gim theo dy sau: SrO, BaO, SiO2, TiO2, NaO, PbO, K2O, Li2O. 7.1.3.3. S dn n nhit ca men

Khi lm lnh nhit chuyn ho men c nht 1013 Pa.s. nhit phng men c nht 1020 Pa.s. Cng nh mt lp thu tinh di

nhit chuyn ho men c tnh dn v tnh cht quyt nh by gi, nh hng n quan h gia xng v men l h s dn n nhit .

S khc nhau ca ca xng (x) v ca men (m) th hin ra khi lm ngui sn phm, tc l khi c xng v men cng co li.

Nu x < m men chu ng sut ko. Nu x > m men chu ng sut nn. Men chu ng sut nn tt hn nn nu khng to c xng v men c bng

nhau th tt nht x > m, tuy nhin gii hn cho php l x - m 0.5.10-6 K-1. Trn hnh 24 th hin tng quan gia h s dn n nhit x v m.

Hnh 24. So snh gia h s dn n nhit ca xng v men Men mng i th gim c ng sut gia xng v men. Nhng men mng

qu (< 150 m) th s b sn. Nh vy men phi t c dy t nht 150-250 m (0.15-0.25 mm). 7.1.3.4. cng ca men

y l mt thng s quan trng trong qu trnh s dng men. - bn chng li vt xc: dng cho gm dn dng, gch men, gm k thut.

Xc nh bng kim cng hay nhng vt liu c cng cao xong i chiu vi mu xc nh trc.

Vd: Tm p 3 Mohs, tm lt 5 Mohs - bn ln: ca mt mu nn bng kim cng. Cng xc nh cho cc loi gm

s trn.

- bn chng mi mn: biu th bng s hao mn ca vt liu sau khi mi. Tm lt c bit cn tnh cht ny. 7.1.3.5. Tnh cht in ca men

Kh nng dn in l do nh hng chnh ca kim. Hm lng kim cng cao th kh nng dn din cng ln, ng vi s dao ng ca cc ion kim trong mng li thu tinh. V vy men cho s cch in khng dng kim.

0,8 PbO 0,2 Al2O3 1,7 SiO2 /0,2 ZrO2 0,2 ZnO 0,75 B2O3 Men ny nung 8000C. PbO cao lm gim s dao ng ca cc ion kim. in tr ca men tng theo cc xit sau: CaO, BaO, B2O3, PbO, Fe2O3, MgO, ZnO,

SiO2. 7.1.3.6. bn ho

Men trong qu trnh s dng phi bn vi mi trng, chng hn nc, khng kh (CO2), bn trong mi trng axit v kim long. y cn c vn men bn khi gm c dng trong thc phm. Men s trn thc t khng thi ra cc cht c hi. Vn chnh l ch men nh la, rt khng bn vi cc cht axit t trong thc phm.

Men s bn ho nu t kim. PbO v B2O3 cng lm gim bn ho. Cc xit nng cao bn ho: SiO2, Al2O3. Khi Al2O3 tng th bn ho tng nhng phi < 18% nu khng s lm xu i cc tnh cht ca men. 7.1.4. Cng thc men

tnh ton thnh phn men ngi ta dng cng thc Seger di dng: (RO + R2O) nR2O3 mRO2 y (RO + R2O) l cc xit baz, tng ca n c quy v bng 1 mol. R2O3 l cc xit trung tnh, tnh bng mol RO2 l cc xit axit, tnh bng mol. i vi men s th nR2O3/mRO2 thng dao ng trong khong t 1/9 n 1/11,

ngha l lng mol ca xit axit gp 9-11 ln xit trung tnh. Mt yu t na chng ta quan tm l h s axit ca men. y = RO2 / (R2O + RO + 3R2O3) Nh vy h s axit cng ln th SiO2 cng nhiu v men c nhit chy cao hn. Cng thc Seger cho mt ci nhn tng quan v cc thnh phn ca men, chng ta

c th d dng so snh cc loi men vi nhau, cng c th bit kh nng chy ca n. Tuy nhin khng c nh gi n qu cao, v n khng xt dn kh nng phn ng ca nhng nguyn liu khc nhau a vo cng mt xit (NaO trong trng thch, trong cacbnat hay trong sulfat). N ch l nh hng v khng c kh nng xc nh ton din.

7.1.5. Mt s nguyn liu chnh dng sn xut - PbO: nhit nng chy thp (8800C). Silicat ch cng d nng chy. Men ch c

nhit chy thp, chy tt v bng. Men ch thng c dng di dng frit ho. Nguyn liu chnh l PbO, minium Pb3O4 hay ch ccbnat 2PbCO3.Pb(OH)2 (cn gi l ch trng). Men ch c nn khng dng trong dng c ng thc n.

- K2O v Na2O: men kim l men d chy quan trng th hai c dng sau ch. Tnh cht ca n cng tng t men kim. Trong men kim ngi ta hay dng thm B2O3. c a vo di dng trng thch hay cacbnat (chy 8520C), borax (chy 7410C).

- Li2O: mc d c nhit nng chy rt cao (trn 17000C) nhng Li2O li l cht gip chy mnh. Thng a vo bng Li2CO3, t ho tan trong nc nn c th dng trong men sng. c bit hot ng nhit cao. T men chy va tr i dng thay cho ch.

- CaO (bn n 25720C): c dng nhiu trong sn xut men. Thng a vo di dng CaCO3 tinh khit, vi, phn, lmit, vlastnit. T 10000C tr i c tc dng to pha lng. CaO tng chiu dy ca lp trung gian chng nt, bong men.

Tuy nhin CaO li hay kt tinh trn b mt men lm men m trn b mt hay c nn khng c dng nhiu qu. lmit cng c tc dng lm c. Nhng cht lm c tt nht l vlastnit, thng c dng to men m.

- MgO (c nhit nng chy cao): ch c dng vi hm lng nh tng bng ca men hay chng nt men do gim dc h s dn n. Thng c dng to men co trong gm m ngh. a vo di dng lmit hay cc khong khc nh statit 3MgO.4SiO2.H2O, talc (t 3MgO.4SiO2.H2O n 4MgO.5SiO2.H2O), chng cng l ngun cung cp SiO2 cho men.

- ZnO (thng gi l kim trng, c nhit nng chy thp): ch dng trong men vi mt lng nh lm tng chy lng, nu dng nhiu li gy c do kt tinh trong qu trnh lm ngui.

- Al2O3: c tc dng tng nhit chy ca men nhng li ko di khong chy ca men. Tng nht, tng bn ho ca men. Tng bn mu dng trong men (ch Al2O3 d c nh hng ti mu cn to). Nh ni phn trn, t l SiO2/Al2O3 ca men nm trong khong 9 - 11, nu tng qua nhiu Al2O3 (n 2 chng hn th men s c). Al2O3 c a vo trong t st, cao lanh v trng thch.

- SiO2: c vai tr quan trng nht to men. c a vo trong t st, cao lanh, trng thch hay ct quc. SiO2 l mt xit to thu tinh nhng kh chy, c nh hng quyt nh n chy ca men. a vo nhiu qu cng s gy nn kh nng kt tinh. Tng bn ho ca men. L thnh phn ch yu trong cc loi frit.

- B2O3: l thnh phn quan trng trong men. C th thay th SiO2 trong men, to lp trung gian tt nh CaO. C tc dng h nhit nng chy ca men. Thng dng chung trong men kim v chng phi c frit. Dng qu nhiu s to mng bor. Thng c da vo di dng B2O3 tinh th hay ngm nc, borax Na2B2O4.10H2O, clmanit 2CaO.3B2O3.5H2O.

- SnO2: khng ho tan trong men m phn tn u lm cho men c mu trng c. S to c ph thuc vo mn ca n. y l cht gy c in hnh, gy c ngay c khi c mt cc xit gy c khc nh ZrO2, TiO2 ...Thng ngi ta dng cht to c l 5% SnO2 + 5% TiO2. SnO2 khng c.

- TiO2: l cht to c nhng hn ch v kh nng tan rt ln v ph thuc vo tc lm ngui. Thng dng chung vi ZnO cho hiu qu tt.

- ZrO2: l cht gy c thng dng thay cho SnO2. Thng c a vo frit. Thng dng di dng ZrO2 hay ZrO2.SiO2. Thng ngi ta frit ho cng vi cc xit khc nh K2O, Na2O, ZnO, CaO, B2O3, PbO. 7.1.6. Phng php sn xut v trng men

Men c sn xut theo 2 phng php l men sng (men nguyn liu) hay men frit.

Men sng c nghin t n mn qua ht sng 10000 l/cm2 (0.063 mm). Men nghin th hn s gy hin tng nhm trn b mt nht l i vi men c. Nghin qu mn gy cun men v bong men. Men qu long b mt men cng b nhm. Men qu dy d gy nt men. Lng nc khi nghin cng cn tu thuc vo ht nc ca mc khi trng nhng ni chung men c m 67 % v t trng 1.85 l hp l. Xng khi trng men cng c nhng yu cu v xp nht nh. Snh phi c ht nc 10-15%, tm lt tng 6-10%, xng em trng men khng xp th phi cho thm keo vo men.

Men frit thng rt d b lng. Chng lng bng cch thm vo t st hoc cao lanh vi hm lng < 20% (hay c th thay bng bentnit) v cc cht khc nh tinh bt dextrin (loi ny cho qu nhiu d gy cun men, lu ngy gy thi men), keo glutin hay cc keo khc (CMC) vi lng ti a 2-3%.

Sn xut frit cho men: Cn ch t l lng SiO2 /(R2O + RO) khi frit t 1 - 3. Tt nht l 2.5 nu khng lng kim s tan mnh vo nc. C th a thm mt lng rt nh Al2O3 (hay nguyn liu cha Al2O3) rt tt cho frit.

Cc phng php trng men nh sau: di men (hay c th qut men), nhng men, phun men. 7.1.7. Khuyt tt ca men v mt s bin php khc phc

Cc khuyt tt thng xut hin l: nt men, bong men, cun men, phng men, to nn cc bt nh nh l chn kim, trn b mt men c hin tng mu sc khng ng nht hoc c nhng mu khng mong mun, men m nhm.

c bit i vi hin tng l chn kim, nguyn nhn l do kh thot ra trong qu trnh men chy lng. Kh hnh thnh trong xng hay t trong men (nu t trong men th cc bt kh thng rt nh) v bt ngun t

- Khng kh cn li trong phi liu c rt. - Trong phi liu c cha nhng thnh phn chy.

- Trong phi liu c cha nhng cht to kh trong qu trnh nung (SiC, C, SO42-, FeS2).

- Bn thn men thot kh do cc xit trong men hay cht mu sinh ra. Thng l cobalt, crm, mangan, zircon...

T nguyn nhn trn ta c th a ra cc bin php khc phc: - Ht chn khng phi liu. - Lm sch phi liu hoc t st. - Nung cao la ln. - Lm cho men chy dn u tt hn (chy lng hn) - i vi men zircon cn nghin mn hay dng ZrO2.SiO2.

7.2. VIC

T

Mutrn

t b

7.2.

C--

hpbn

-nhimendn TRANG TR SN PHM GM V CHT MU DNG TRONGTRANG TR a c s trang tr sn phm s nh sau: TRANG TR

Cht mu Luster Email Men mu Engob

Mu Mu men trong men di men

Cht mu kim loi

n Bn va Rt bn Bng M Dng bt

1. Bn cht ca cht mu gm

Cht mu gm = (Cht to mu + Cht mang mu) + cht to thu tinh + cht tr mu

hng ta c nhng nh ngha sau:

Cht to mu: sc t (pigment). Cht mang mu: l bn thnh phm sn xut cht mu. Chng thng l cc cht to khong c mng tinh th nht nh. N quyt nh l mu em dng c trong qu trnh sn xut v s dng khng. Cht to thu tinh: l cht tr dung thch hp. Vic la chn n ph thuc vo t nung cht mu. N phi xc nh s lin kt cht ch ca cht mu gm v (phi c h s dn n nhit tng t nh thu tinh) ng thi khng c tc g ln cht tr mu. Thng l cc frit hay bn thn men em dng.

- Cht tr mu: c tc dng lm tng cng tc dng ca cht mu gm. Yu cu ca cht mu gm l mu phi n nh trong qu trnh sn xut cng nh

trong qu trnh s dng. iu ny ph thuc vo vic s dng cht mang mu. S n nh ca cht mang mu li ph thuc vo cu trc tinh th ca n. Mt s cc kiu mng li tinh th ca cht mang mu c cho trong bng 25.

Kiu mng tinh th Cng thc i din Spinel loi I. MgO.Al2O3 Spinel loi II. 2ZnO.TiO2 Zircon ZrO2.SiO2 Baddeleyit ZrO2 Corund -Al2O3 Rutil TiO2 Imenit FeO.TiO2 Perovskit CaO.TiO2 Granat 3CaO.Al2O3.3SiO2 Willemit 2ZnO.SiO2 Titanit CaO.TiO2.SiO2 Mullit 3Al2O3.2SiO2

Bng 25. Phn loi cht mang mu theo kiu mng tinh th Cht mang mu spinel loi 1: Cng thc phn t X2+Y3+2O4 hay XO.Y2O3 trong : X 2+ = Mg2+, Zn2+, Co2+, Ni2+, Fe2+, Mn2+, Ca2+, Cu2+ Y3+ = Al3+, Fe3+, Cr3+, V3+, Mo3+, W3+ S thay th ng hnh gia cc ion X2+ v Y3+ trong cu trc spinel to nn mt lot

cc cht mang mu n nh m mt s v d c cho trong bng 26.

Mu ca spinel Thnh phn ho Xanh dng CoO.Al2O3

NiO.Al2O3 Nu CuO.Al2O3

FeO.Cr2O3 MgO.Fe2O3 NiO.Fe2O3 ZnO.Fe2O3 MnO.V2O3

en FeO.V2O3 MgO.V2O3 ZnO.V2O3

Xanh l FeO.Al2O3 CdO.Cr2O3 CoO.Cr2O3 MgO.Cr2O3 NiO.Cr2O3 ZnO.Cr2O3

Trng ZnO.Al2O3 MgO.Al2O3

Ghi ch: Spinel c V2O3 c tng hp trong mi trng kh tr Bng 26. Cc v d cht mang mu spinel loi I.

Cht mang mu spinel loai 2: Cng thc phn t X2+2Y4+O4.