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INTRODUCTIONThe glass corrosion process was described using many
model approachesin the last decades [1]. The kinetic model based on
mass balance of dis-solving glass components in glass-corrosion
solution system was sug-gested in our previous works [2-4]. In this
model, the time dependenceof normalized leach amount of glass
components i can be describedusing simple equation :
(1)
The Eq. 1 is based on the mass balance of component i in
solution :
As it was shown in [4], for the simpler cases, the values of B,
K and W
Complex study of e-glass corrosion Des tests de corrosion
dyna-miques et statiques du verreE ont été réalisés sous
diffé-rentes conditions, tempéra-ture, rapport surface volume(S/V),
débit (F) et facteur F/S.Les résultats obtenus sur desfibres de
verre sont compa-rés à ceux mesurés sur duverre plan et du verre
broyéen grains. L’évaluation desrésultats expérimentaux aumoyen de
modèle cinétiquemontre que les changementsà la surface du verre de
-vraient être pris en comptedans le cas de la corrosiondes fibres.
Le procédé pour-rait être expliqué comme unedissolution du verre
accom-pagné de précipitations deSiO2 ou de silicates. Dans
laplupart des cas, plus de 90 %de SiO2 précipite. La
secondeexplication possible, c’est-à-dire le fait que la
dissolutiondu réseau de SiO2 est accom-pagnée d’une
lixiviationsélective du Ca, du B et del’Al, est peu probable.
Laforme de l’échantillon deverre influence les estima-tions du taux
de dissolution.Avec les modèles cinétiquesexistants, les taux de
dissolu-tion évalués expérimentale-ment sur des échantillons
dedifférentes formes (fibre,grains, plan) ne peuvent plusêtre
utilisés automatique-ment comme une propriétédes matériaux.
Verre VOL.15 N°6 • DÉCEMBRE 200948
Both the static and dynamic corrosion tests of E-glass wereused
for different conditions — temperature, glass surface tosolution
volume ratio (S/V), solution flow rate (F) and F/Sratio. Results
obtained for glass fibres were compared with theones for glass
grains and planar samples. Evaluation of exper-imental results by
kinetic model shows that the change of glasssurface should be taken
into account in the case of fibres cor-rosion. The total
incongruent process of dissolution could beexplained as congruent
dissolution of glass accompanied byback precipitation of SiO2 or
silicates. In most cases, morethen 90 % of SiO2 precipitates back.
The second possibleexplanation, i.e. SiO2 network dissolution
accompanied byselective leaching of Ca, B and Al, is not very
probable. Theglass sample shape can influence the estimation of
dissolutionrate. Up to now, with existing kinetic models, the
dissolutionrates evaluated from experiments with different shapes
of glass(fibres, grains, planar) cannot be used as materials
properties.
SCIENCEFIBRES DE VERRE
Pavel SleminInstitute of Chemical TechnologyPrague
Gerhard Heide, Ales HelebrantTU Bergakademie Freiberg, Dept. of
Mineralogy
With the authorization of the author Ales HelebrantWith the
authorization of the publisher: Trans Tech Publications Ltd,
SwitzerlandOriginal papers are located on: www.scientific.net
(2)
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can be estimated as functions oftest conditions as F, V, S and
ofparameters characterising the par-tial corrosion processes (rate
con-stant of surface reaction k +, thick-ness of precipitated layer
h,diffusion coefficient of surfacereaction products in
precipitatedlayer D, saturated concentration ofcomponent i in
solution cs and k-,characterising back precipitation,i.e. the ratio
between back precip-itated and dissolved component i.The Eq. 1 is
often used as empiricalequation, describing the timedependencies of
NLi satisfactorily– e.g. in [5] it was used for success-ful
description of corrosion of E-glass used as insulation innuclear
power plants reactors.The aim of our study is to comparethe initial
and final dissolutionrates obtained under different testconditions
(S/V, F, F/S, static ordynamic conditions) and for dif-ferent glass
samples (fibres, grains,planar samples) using the existingkinetic
dissolution model. Wewould also like to demonstrate,that the
dissolution rates obtainedby empirical use of the model,although
useful for description ofparticular g lass dissolutionprocess,
cannot be automaticallyused as real material properties. AsE-glass
was available in all differentshapes, i.e. as fibres, grains and
asplanar samples, it was chosen asmaterials tested.
EXPERIMENTAL PARTGLASS SAMPLESCorrosion tests were made onthree
different shapes preparedfrom of E-glass (Eutal type) sam-
ples. The chemical compositionwas obtained using X-ray
fluores-cence analysis (XFA) and it isgiven in table 1.The fibres
for corrosion testingwere drawn using industrial Pt fur-nace but
without lubrication.Every strand of fibres consisted ofapprox. 800
elementary fibres. Thematerial for grains was obtainedalso from
industrial process duringthe exchange of Pt furnaces. Theglass
remained in furnace wasannealed for 8 hours at 550 °C andthen the
grains were prepared incentrifugal mill (Retsch). Forexperiments,
the fraction 0.315-0.5 mm was used, obtainedaccording to DIN 4188.
The sam-ples were cleared from Fe particles,washed in acetone and
in ultra-sonic bath. The planar sampleswere prepared by melting of
E-glass cullet in Pt/Rh crucible at1450 °C for 1.5 hours. For
betterhomogeneity, the melt was 3xstirred during the melting.
Theglass was annealed at 550 °C for 4hours. Polished planar
samples(approx. 1x1x0.1 [cm]) were usedfor testing. The exact
dimensionsof each sample were obtainedusing optical microscopy
andimage analysis LUCIA. The den-sity of grains and fibres
wereobtained by pycnometric methodusing liquid He, the specific
sur-face was measured using BETmethod with Kr gas. The resultsare
summarised in table 2.The initial mean value of fibresthickness
12.7±0.2 Gm was eval-uated by optical microscopy andimage analysis
sample of 300fibres. Particle size distribution in
crushed sample was determinedwith laser diffractometry. The
ini-tial mean value of particle’s sizewas 509.4 Gm and the shape
fac-tor 3.6 was calculated according toDIN 66144.
CORROSION SOLUTIONSTwo corrosion solutions wereused : 2M HCl and
0.2M NaOHprepared using deionised water.
CORROSION TESTSStatic and single-pass flow-through (SPFT) tests
were usedfor obtaining glass dissolutionrates. For static tests,
the sampleswere given into polyethylene bot-tles with corrosion
solution. In thecase of planar samples, the contactwith bottle was
avoided. The bot-tles were placed into the stirredwater bath
(JULABO SW 21C),stirring frequency was 0.75 s-1.Time of exposition
was between 1 and 32 days. The tests were donefor three different
S/V ratios : 12,117 and 1174 m-1. The details ofSPFT tests were
described e.g. in[6]. During this test, the flow ofcorrosion
solution was maintainedusing peristaltic pump (PCD 83.4K Kou.il
s.r.o.). The samples werein polyethylene cells with polyeth-ylene
frits (3 Gm pores). The cellswere placed in water bath( JULABO SW
21C). Time ofexposition for SPFT tests wasbetween 1 and 4 days. The
differ-ent solution flow rates (58-250ml.d-1) and F/S (0.027-0.308
Gm.s-1) ratios were used in the study.After corrosion test, the
solutionwas filtered when necessary (FIL-TRAK 389) and ana lysed
for Al,
VOL.15 N°6 • DÉCEMBRE 2009 Verre 49
SCIENCE ‡ FIBRES DE VERRE
Glass composition [wt. %]sample SiO2 CaO Al2O3 B2O3 K2O MgO TiO2
NaO2 F Fe2O3 Cr2O3
grains 53.8 22.8 14.2 6.9 0.48 0.52 0.37 0.39 0.24 0.13 0.008
99.84planar 54.3 22.7 13.9 6.6 0.51 0.50 0.35 0.32 0.51 0.15 0.007
99.99
Density and specific surface sample density ρ [g/cm3] 2/g]
VL 2.5417 ± 0.0034 0.1174 ± 0.0008
DR 2.6215 ± 0.0030 0.0163 ± 0.0015 Table 2. Density and specific
surface of fibrous samples and grains
Table 1. Chemicalcomposition of fibers,
grains and planarsamples in wt. %
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Si, B and Ca using AAS or ICP/OES or spectropho-tometry.
RESULTS AND DISCUSSIONIn case of fibrous and powder glass
samples that aresubject to significant mass loss (typically more
than10 %) during the test, the S/V ratio used to calculatethe
normalized mass loss must be corrected over time.This correction is
implemented by means of a shrink-ing core model [7] in which the
fibres and the powdergrains are considered as cylinders and spheres
respec-tively. In the case of planar samples, the changes of Swere
very small and could be neglected. The alteredglass mass percentage
(AG %) is defined by :
where cB is boron (alteration tracer element) concen-tration, V
is volume of the corrosion solution, m0 isinitial sample mass, and
xB is boron mass fraction inthe glass.The geometric surface area Si
of the fibrous sample atthe time interval i is
The geometric surface area Si of the powder glass atthe time
interval i is
where d0 is mean initial radius of the fibre or particle,n is
the number of elementary fibres in sample (800),l is a length of
fibrous strand and ρ is the density ofglass sample.The time
dependencies of normalised leach amountof glass components i (i =
Al, Si, B, Ca) were obtainedfrom concentrations of dissolved
compound i (ci)according to Eq. 7 (for static tests) or Eq. 8 (for
SPFTtests)
where NLi is the normalised leach amount of com-pound i, t is
time of interaction, Δt is the intervalbetween sampling, xi the
weight ratio of i in glass, Sthe glass surface in contact with
volume V of corro-sion solution and F is the solution flow
rate.After the corrosion, an outer layer on fibres and par-
ticles was formed, previously made ofSiO2 (figure 1, figure 2).
Assuming thatthe outer layer was formed by back pre-cipitation (see
lower), the surface of innercore was used for calculations.
50
SCIENCE ‡ FIBRES DE VERRE
Verre VOL.15 N°6 • DÉCEMBRE 2009
(4)
(5)
(6)
(7)
(8)
Fig. 1. Formation of outer layer on glass fibres. Static test in
2M HCl, 20°C, S/V = 1174 m-1, after 6 hours (left)
and 16 days of corrosion
Fig. 2. Formation of outer layer on the particles of glassgrain.
Static test in 2M HCl, 20°C, S/V = 1174 m-1, after
16 (left) and 32 days of corrosion
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The typical time dependencies obtainedfrom tests are shown in
figures 3 and 4.
If the dissolution of glass is congruent, thetime dependencies
of NLi should be thesame. Similarly as in examples in figure 3and
figure 4, these time dependencies dif-fer significantly, showing
the incongruentdissolution. Typically, the NLsi was muchsmaller
then the NLi for other compo-nents. This behaviour could be
explainedby back precipitation of Si in the form ofsilica and/or
silicates. Another explana-tion could be by selective leaching of
Ca,B and Al. As it was shown in our previousstudy [8], this
possibility is not very plau-sible because the time dependencies
ofCa, B and Al were often very similar andthe probability of the
same or similar dif-fusion coefficients of networking compo-nents
Al, B and of Ca as typical networkmodifier is very low.
Moreover, the precipitated secondary layer was foundon planar
samples (figure 5) and as well as in form ofpractically pure SiO2
outer layer on fibres (figures 1and 2).The dissolution rates were
obtained by fitting the timedependencies of NLi by Eq. 1 using the
least squaresmethod. The value B + W and W from Eq. 1 thenrepresent
the initial and final dissolution rate [g.m-2s-1]. The movement of
the solution — glass boundaryin [m.s-1] is given by Eqs. 9 and 10
for initial and finaldissolution rate, respectively :
The dissolution rates obtained for different test con-ditions
are summarised in Table 3 for static tests andin Table 4 for SPFT
tests. As the marker (A) for dis-solution of E-glass, boron was
used in most cases.Under several conditions, the total boron
concentra-tions in the solutions were to low for analysis. In sucha
case, the Ca or Al was used.The values of back precipitation ratio
k- for Si werecalculated using Eqs. 11 and 12 both for initial
andfinal stage of dissolution.
It is obvious that these values are very high in mostcases ;
especially in acid solution practically 90 % ofSi precipitates
back. This result could have interestingtheoretical and practical
consequences. If the backprecipitation of Si occurs in the form of
silica gel layer,the fibres or grains could be connected together.
Then
51
SCIENCE ‡ FIBRES DE VERRE
VOL.15 N°6 • DÉCEMBRE 2009 Verre
Fig. 3. The time dependence of NLi. Static test in 2M HCl, S/V=
1174 m-1, 20°C, fibres
Fig. 5. Formation of secondary precipitated layer. Comparison of
corroded (left) and uncorroded sample, SPFT test, samplesdimensions
1x1x0.1 cm, 2M HCl, 51°C, F = 130 ml.d-1,F/S = 2.16 μm.s-1
Fig. 4. The time dependence of NLi. SPFT test in 0.2M NaOH, F=
133 ml.d-1, F/S = 0.027μm.s-1, 52°C, grains
(9)
(11)
(12)
(10)
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52
SCIENCE ‡ FIBRES DE VERRE
Verre VOL.15 N°6 • DÉCEMBRE 2009
sample type
T [°C]S/V
[m-1]F
[ml.d-1]F/S
[μm.s-1]marker
At [d]
Si a0 [μm.d-1]
Si an [μm.d-1]
A a0 [μm.d-1]
A an [μm.d-1]
k-
(t→0) k-(t→∞)
12Ca 1 0.45 0.45 5.29 2.23 0.92 0.80
12Ca 8 0.62 0.62 5.12 1.11 0.88 0.44
117Ca 1 0.35 0.29 4.49 2.21 0.92 0.87
117Ca 8 0.41 0.04 4.36 1.01 0.91 0.96
1174B 1 0.35 0.03 6.60 1.35 0.95 0.98
1174B 8 0.32 0.02 7.96 1.40 0.96 0.99
78.046.063.087.050.082.01Bsniarggrains 20 12 0 0 B 8 0.23 0.08
0.76 0.38 0.70 0.78
67.066.063.087.080.072.023Bsniarg29.089.051.074.310.080.01Bsniarg
grains 1174 B 8 0.08 0.005 3.39 0.13 0.98
0.9689.079.011.082.3200.090.023Bsniarg98.069.065.074.160.060.01Branalp
planar 12 B 8 0.17 0.17 1.51 0.54 0.89
0.6837.029.034.093.121.021.023Branalp
sample type
T [°C]S/V
[m-1]F
[ml.d-1]F/S
[μm.s-1]marker
At [d]
Si a0 [μm.d-1]
Si an [μm.d-1]
A a0 [μm.d-1]
A an [μm.d-1]
k-
(t→0) k- (t→∞)2M HHCl
3173 64 0.026 Al 1 0.11 0.11 1.45 1.45 0.93 0.937196 64 0.026 Al
1 0.11 0.11 1.39 1.39 0.92 0.926421 131 0.027 Ca 1 0.13 0.08 1.83
0.85 0.93 0.9114844 129 0.026 Ca 1 0.11 0.07 1.59 0.90 0.93
0.93
20 12572 227 0.024 Ca 1 0.13 0.08 3.48 0.85 0.96 0.9129831 250
0.027 Ca 1 0.11 0.05 2.53 0.68 0.96 0.92544 58 0.308 Al 1 0.38 0.37
1.49 1.38 0.74 0.731106 117 0.308 Ca 1 0.27 0.27 1.97 1.25 0.86
0.792200 229 0.304 Ca 1 0.10 0.09 2.06 1.52 0.95 0.94
51 14928 134 0 027 B 1 0.24 0.24 10.5 2.62 0.98 0.9151 14928 134
0.027B 2 0.30 0.30 10.4 2.98 0.97 0.90
85 14977 133 0 027 B 1 0.24 0.24 15.2 1.54 0.98 0.8085 14977 133
0.027B 2 0.30 0.30 15.2 0.62 0.98 0.46
grains21510 133 0 027 B 1 0.23 0.23 5.82 5.82 0.96 0.96
grains21510 133 0.027
B 2 0.22 0.22 5.43 5.43 0.96 0.96planar 51 B 1 2.46 2.46 19.6
13.8 0.87 0.82planar 207 130 2.3 B 2 3.20 3.20 19.8 9.92 0.84
0.68planar B 4 3.72 3.72 19.8 8.42 0.81 0.56
00.2M NNaOH
52 15053 133 0.027 B 4 0.12 0.07 0.28 0.15 0.57 0.57grains
5221505 132 0.027 B 4 0.10 0.10 0.07 0.07 0.28 0.28
Table 3. Dissolution rates and back precipitationcoefficients k-
evaluated from static tests under different conditions in 2M
HCl.
Table 4. Dissolution rates and back precipitation coefficientsk-
evaluated from SPFT tests under different conditions in 2M HCl and
0.2M NaOH.
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the total surface of the glass in con-tact with water and
consequentlycorrosion rate decreases, which isnot yet considered in
the theoreti-cal models. On the other hand, inpractice, such
interconnectioncould caused serious problems e.g.during loss of
coolant accident innuclear power plants [5]. In mostcases, the
values of back precipita-tion constant are very near bothfor
initial and for final stages ofdissolution. However, in
general,they can be different for differentstages of corrosion. The
descrip-tion of precipitation kineticsremains the great challenge
for fur-ther modelling of corrosionprocess. It should be also
noticed,that the duration of experiment (tin tables 3 and 4) can
significantlyinfluence the final rates of corro-sion evaluated from
experimentsand the mechanical use of Eq. 1 forshort experimental
times givesbiased results. The fact that thetimes used in the
experiments arenot long enough for obtaining realfinal rates was
confirmed by thevalues obtained from static testresults. Under
static conditions,the final rate should be theoreti-cally zero, due
to solution satura-tion by products of dissolution.Also comparison
of "final" dissolu-tion rates from SPFT tests madeunder same
conditions but withdifferent duration shows that thisrate is
changing and depends ontotal experimental time, i.e. nosteady state
was achieved. More-over, estimating the activationenerg y from SPFT
test in 2MHCl, the plausible value with sat-isfactorily good
correlation coeffi-cient was obtained for initial dis-solution
rates assuming Arrheniusdependence (30.7 kJ. mol-1, R2= 0.89). This
value is in goodagreement with activation energiesobtained by
other, e.g by Mi. ikovaet al. [5]. For the final rate, verypoor
correlation between Arrhe-nius equation and experimentaldata was
obtained.On the other hand, the parametersB, K and W evaluated from
exper-iments could be used for good
interpolation and estimation ofcorrosion rate under similar
orsame corrosion conditions. Initialdissolution rates are
practicallyindependent of time of experi-ments and could serve as
charac-teristic values of glass corrosion.
SUMMARYE-glass dissolves incongruent bothin HCl and NaOH. This
incon-gruence could be explained byback precipitation of
dissolvedcompounds on the glass surface. Inthe case of fibrous and
powdersamples, the time dependence ofglass surface has to be
consideredfor evaluation of glass dissolutionrate. As the marker of
dissolution,the boron should be used insteadof usually used Si
because of its sig-nificant back precipitation. Thisback
precipitation could be up to98 percent in the case of acid
cor-rosion. For the evaluation of dis-solution rates from
experimentalresults, the semiempirical modelcan be used. The final
rate evalu-ated from this model could bestrongly influenced by test
dura-tion. For short-term tests, thisvalue is not exact
sufficiently, espe-cially if the model is used mechan-ically. The
rates obtained fromtesting planar samples, grains orfibres should
be compared verycritically and cannot be mechani-cally used for
prediction of corro-sion behaviour of samples with dif-ferent
shapes. It seems that theexact surface of the samples in con-tact
with corrosion solution andits changes during corrosion couldplay
the crucial role. On the otherhand, the initial dissolution rate
isvery similar for broad range ofexperimental conditions as
e.g.F/S, S/V values and could charac-terise the glass durability.
n
This study was supported by the Minis-try of Education of the
Czech Republicas part of the research project MSM6046137302 Authors
thanks to Centreof Glass Excellence "Vitrum Laugari-tio" in Tren.in
and especially to Dr.Peter Lichvar for preparation of
planarsamples.
53
SCIENCE ‡ FIBRES DE VERRE
VOL.15 N°6 • DÉCEMBRE 2009 Verre
RÉFÉRENCES[1] A. Helebrant, A. Ji.i.ka, J. Ji.i.kova,Glass Sci.
Tech., 77C (2004), p. 85
[2] A. Helebrant, B. To. nerova, GlassTechnology, 30 (1989), p.
220
[3] A. Helebrant, M. Mary.ka,J.Matou.ek, B. To. nerova, Bol. de
laSoc. Espanola de Ceramica y Vidrio, 31-C (1992), p. 87
[4] A. Helebrant, Ceramics-Silikaty, 41(1997), p. 147
[5] L. Mi. ikova, M. Li.ka, D. Galuskova, Ceramics-Silikaty, 51
(2007), p. 131
[6] A. Ji.i.ka, A. Helebrant, CeramicTransactions, 107 (2001),
p. 309
[7] C. Jegou, S. Gin, F. Larche : Journalof Nuclear Materials,
Vol. 280, (2000),p. 216-229
[8] P. .lemin, A. Helebrant, Skla. a kera-mik, 55C (2005), p.
115
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