FULL PAPER

Measurements and model application on the viscositiesof liquid phase in clay based ceramics

Tengfei DENG1,³, Baijun YAN2 and Fangjun YANG1

1State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, 430070, PR China2Department of Physical Chemistry of Metallurgy, School of Metallurgical and Ecological Engineering,University of Science and Technology Beijing, Beijing 100083, PR China

The model used to predict the liquid viscosity value of clay based ceramics was determined in this study. Theviscosity values of liquid phases in clay based ceramic were measured precisely in a closed tube furnace byrotating the spindle in the melts at high temperature. The chemical compositions of the glassy phases in theceramics were analyzed. The glassy phases were prepared by the pure chemicals after the analysis. The viscosityvalues of the melts followed Arrhenius assumption. Four different models were applied to calculate the viscosityvalues of melts in the present study. The predicted results of Urbain model and Riboud model were far awayfrom the experimental results. However, the calculated results of Shaw model (SW model), used to predict theviscosity value of lava), and Modification of Shaw model (M-SW model) were found to be much closer to theexperimental results but were still with some deviations. The calculated viscosity values of M-SW model weresmaller than the experimental results. On the other hand, M-SW was a reliable predictor of viscosity values ofliquid phases in clay based ceramics after modification. The modification of M-SW considered “FeO” asnetwork-modifier and got rid of a part of excess Al2O3. The assumptions of SW model and M-SW model limitedthe accuracy of the prediction results of liquid viscosity values in the clay based ceramics. More experimentswere needed to revise the slope intercept data of K2O and “FeO”.©2019 The Ceramic Society of Japan. All rights reserved.

Key-words : Viscosity, Clay based ceramics, Model

[Received October 29, 2018; Accepted March 5, 2019]

1. Introduction

Industrial ceramics, domestic ceramics and sanitaryware ceramics are strongly connected with people’s dailylife and most of them are clay based ceramics. On the otherhand, mineral resources are always exploited to preparethose ceramics. As the economy develops, the livingconditions of the people have been improved accordinglybut also magnify the consumptions of natural resources.Husbanding precious mineral resources is the keystone ofmost countries in the world consequently. To make theproduct with light weight is the way to save the mineralresource.

Many of the ceramics mentioned above are porcelainsand they contain 50­70wt% glassy phase after produc-tion.1) Most glassy phase is liquid phase at high temper-ature. Due to the presence of liquid phase during theprocessing, the products become soft and deform under thegravity, especially for the heavy sanitary ware ceramics.To thicken the wall is a way to reduce the quantity ofpyroplastic deformation in the heat treatment.2) However,this method strongly increases the weight of the sanitary

ware ceramics and brings on the waste of natural resource.Many researches3)­5) were conducted to reveal the mech-anism of pyroplastic deformation in porcelain ceramics.Particle size of quartz, distribution of pores and chemicalcomposition of green body were found to be the factorswhich affected the pyroplastic deformation of ceramics.On the other hand, those three factors also relate to theproperties of generated liquid phase at firing temperature.Therefore, it is necessary to understand the effect of liquidphase on the pyroplastic deformation of clay basedceramics during heating.According to the previous studies,6),7) the viscosity of

generated liquid phase at firing temperature is related tothe quantity of pyroplastic deformation. Therefore, theviscosity value of liquid phase in the ceramics is a kernel tothe pyroplastic deformation of the ceramics. However, theaccurate measurements of the generated liquid phase in theceramics at high temperature are very hard to be made.Thus, the value of liquid viscosity in the ceramics duringheating was calculated by some empirical formulas.7)

Although many models are used to predict the viscosityvalue of oxide melts, they are applicable for different sys-tems. Urbain model8) and Riboud model9) were both estab-lished according to the Weymann equation.10) However, the³ Corresponding author: T. Deng; E-mail: tengfei@kth.se

Journal of the Ceramic Society of Japan 127 [5] 310-317 2019

DOI http://doi.org/10.2109/jcersj2.18189 JCS-Japan

©2019 The Ceramic Society of Japan310This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by-nd/4.0/),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Urbain model can widely be applied in different systemsbut it is an unreliable predictor of the system with alkalineoxides; on the contrary, Riboud model is too rough topredict many systems but the prediction results of systemcontaining alkaline oxides are more accurate than Urbainmodel. Based on the Arrhenius equation, Shaw model (SWmodel)11) was used to predict the viscosity value of magmaand some other researchers12) did modifications on thismodel according to the experiments, namely Modificationof Shaw model (M-SW model). However, no study hasexamined whether those models can be applied in thecalculation of viscosity value of liquid phase in the claybased ceramics at high temperature.

This work is a continuation of our last study.7) Riboudmodel was applied to predict the viscosity value of the claybased ceramics in the previous study. But whether themodel suits for the prediction of viscosity value in theceramics is unknown. The viscosity of those liquid phasesmust be measured by experiment and the data obtainedfrom the experiment should be used to prove the reliabilityof different models. The aim of present study contains twofolds. The first task is to develop a reliable method tomeasure the viscosity value of liquid phase in the ceramicsprecisely. An analysis of possible uncertainties involved inthis type of measurement is also to be made. The secondtask is to examine the applicability of the existing modelsusing the data obtained at firing temperature.

2. Experiment

The experimental procedure of the present work wasdivided into three steps: (1) obtaining the chemical com-positions of generated liquid phase in the ceramics atdifferent temperature; (2) mixing pure chemicals andstandard materials to simulate the glassy phase obtainedfrom previous step; (3) carrying out the measurements.The first two steps would be described in detail in the“preparation of glasses” part and the third step would begiven in the “experimental procedure” part.

2.1 Preparation of glassesThe chemical compositions of different glasses gained

from the ceramics after quenching have been presented inthe previous study.7) The experimental procedure wasgiven in detail in the article also. Thus, only the main fea-ture of experimental procedure is presented in this articleto orientate the fresh readers.

The samples with different chemical compositions wereprepared by mixing different raw materials and then thesame mixture was divided into two parts. There were con-sistent one-to-one match between those two parts. One partwas applied to measure the quantity of pyroplastic defor-mation of the samples; the other part was used to obtainthe chemical composition of liquid phase in the sampleby quenching method. The sample after quenching wassubjected into scanning electron microscope (SEM) foranalysis. The region of glassy phase was confirmed byback scatter image and the chemical composition of theglassy phase was measured by energy dispersive x-ray

spectroscopy (EDX) analysis. Whether the analysis regionwas liquid phase or not at firing temperature was furtherproved according to the calculation by Factsage 7.0. Theresults were listed in the previous study. Some of themwere selected in the present work and listed in Table 1.Each sample in Table 1 was prepared by mixing the

chemicals of SiO2, Al2O3, KHCO3, NaHCO3 and standardmineral feldspar in an agate mortar. SiO2 and Al2O3 werecalcined at 1273K for 24 h to remove the moisture andCO2. KHCO3, NaHCO3 and standard mineral feldsparwere dried at 373K for 24 h to remove the moisture. Eachsample was weighted about 120 grams. The purities andsuppliers of the chemicals are listed in Table 2. KHCO3

and NaHCO3 were the source of K2O and Na2O. It must bementioned here that the vapor pressure of K2O was highbut Na2O is only slightly volatile from mixtures containingin excess of 60wt% SiO2.13) The chemical composition inTable 1 revealed that K2O is the major alkaline oxide ofeach sample, so the utilization of standard mineral feldsparwas introduced to reduce the loss of K2O. The chemicalcomposition and its stand deviations were given inTable S1 of the supplementary material.The mixture was pressed into disks (º40mm © 14mm).

Each disk was 24 g. As shown in Fig. 1(a), the sample wasconsisted of five disks and placed on the refractory platewhich was strewn with small alumina powders. The sam-ple along with the plate was placed just under the B-typethermocouple in a box-type resistance furnace. The fur-nace has SiC heating elements, which enabled a maxi-mum temperature of 1573K. The sample was heated up to1473K for 2 h for pre-melting. The temperature of sampletreatment was based on the following considerations: (1)every sample in Table 1 contained both liquid phase andsolid phase at 1473K according to the calculation byFactsage 7.0. The presence of liquid phase made the diskstuck together and the solid phase kept the sample with itsoriginal shape; (2) the pre-melting method strongly low-ered the activity of K2O. Thus, the vaporization of K2O in

Table 1. Chemical composition of the liquid phase in part ofsamples in previous study (wt%)

sample Al2O3 SiO2 K2O Na2O CaO Fe2O3

VM1 21.50 68.60 6.50 2.01 ® 1.39VM2 18.56 71.65 6.10 1.83 ® 1.86VM3 18.35 72.25 5.89 1.88 ® 1.63VM4 18.16 72.64 5.76 1.90 ® 1.54VM5 16.60 72.00 5.65 1.76 2.20 1.79VM6 20.05 68.68 4.14 4.27 1.76 1.10VM7 20.68 67.84 5.41 2.08 2.43 1.56

Table 2. Details of the materials used in the present work

Materials Purity (wt%) supplier

KHCO3 99.7 Alfa AesarNaHCO3 99.7 Alfa Aesar¡-Al2O3 99.95 Alfa AesarSiO2 99.7 SinopharmCaO 99.7 Sinopharm

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the viscosity measurements would be reduced. As shownin Fig. 1(b), the disks in the sample were stuck togethertightly and formed as a cylinder. The surface of the samplewas smooth. An important step must be emphasized herethat during the heat treatment, the sample was equilibriumat 973K for 24 h. The consideration is as flows: althoughstandard mineral feldspar was used to replace a portion ofalkaline oxides in the sample, the chemical of KHCO3 wasstill introduced to meet the requirement of the chemicalcomposition in Table 1. As mentioned above, a part ofK2O would vaporize during heating and the vaporizationof K2O would make the chemical composition of thesample inaccurate. Consequently, the vaporization of K2Oshould be avoided in the procedure of glass preparation.The research13) revealed that solid reaction of KHCO3 andSiO2 is effected at 973K and the water and CO2 werereleased. At the same time, no loss was found by volatil-ization, spattering and frothing. Thus, soaking the samplefor 24 h is an approach to the problem solving.

2.2 Experimental procedureThe experimental apparatus was schematically shown in

Fig. 2. A Brookfield digital viscometer (model: DV2T)was used. The viscometer was placed on the steel plat-form, which was on the top of the furnace and was sealedin a Polymethyl methacrylate (PMMA) box. The viscosityvalue was then record by the computer using the softwaresupplied by Brookfield.

A high temperature vertical furnace with alumina tubeas the reaction chamber was employed for this investiga-tion. The furnace had molybdenum-silicide bar as itsheating elements, which enabled a maximum temperatureof 1973K. The variation of the temperature in the eventemperature zone of the furnace was less than «5K. The

furnace could move up and down in the vertical directionby a lifting system. It was closed on both ends by stainlesssteel flange arrangements. The flange arrangement in theupper part was connected to the steel platform. A quench-ing chamber cooled by water was connected to the steelflange arrangement in the lower part. A molybdenum tubewent through the center of the quenching chamber. Amolybdenum holder was screwed on the molybdenumtube. The molybdenum tube along with molybdenumholder could move both downward and upward forintroducing the sample and quenching it after experiment.The experimental procedure is as follows:The viscosity value of liquid phase in the firing temper-

ature is very high according to the calculation of previousstudy.7) However, molybdenum was very hard at high tem-perature, so it was applied as the material of crucible andspindle. After the heat treatment, the disk in the sampleshrank and the diameter of the sample was around 32mm.The sample consisted of 5 disks was put in the cruci-ble (inner diameter: 37mm and inner height: 98mm). Thespindle was consisted of a thin molybdenum rod (diame-ter: 1.5mm and length: 30mm) and a heavy molybdenumcylindrical block to make the spindle easier insert into thesample. The molybdenum rod was screwed on the molyb-denum cylindrical block anticlockwise to avoid molybde-num rod working loose from the block.The spindle multiplier constant (SMC) was calculated

by the Eq. (1). Where, © is viscosity in dPa·s. TK is torqueconstant, and the value of present study is 0.09373. RPMis the rotating speed of spindle in round per minute.Torque means the percentage of the measured torquerelative to the full scale of the spiral spring.

Fig. 1. Photo of sample before and after pre-melting (a) beforepre-melting (b) after pre-melting.

Fig. 2. Experimental setup.

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©ðcPÞ ¼ TK� SMC� 1000

RPM� Torque ð1Þ

Room temperature was carried out to determine thevalue of SMC. The spindle introduced in this study wasinserted into standard oil, which was with known viscosityof 104320 cp at 298K. The value of torque and SMC withdifferent immersion depths in standard oils was listed inTable S2 in supplementary material. Figure 3 presentedthe relationship between SMC value and depth of immer-sion. The fitting line was described as Eq. (2). In here,x is the immersion length of the spindle. x was recordedby the measurement of length of glass attachment on themolybdenum spindle after experiment.

SMC ¼ 4122:9þ 36571:6 � expð�x=0:497Þ ð2ÞIn a general run, the whole system was evacuated after

placing the molybdenum crucible on the holder in the reac-tion tube and the spindle hanging just above the sample.Purified argon gas mixed with 5 vol% H2 was introducedfrom the gas inlet from the top of the PMMA box and ledout situated at the bottom of the reaction chamber. The gasflow of low flow rate (about 0.05 L/min) was maintainedthroughout the whole experiment. The sample was soakedat 1873K for 12 h for equilibrium. After that, the furnacewas moved up to immerse the spindle into the liquid. Alow rotational rate was employed to ensure homogeniza-tion of the sample. Thereafter, the viscosity value of each

sample at different temperature was record and the temper-ature of each sample was from 1873K to 1673K with aninterval of 25K. The sample was kept at every temper-ature stage for another 2 h to ensure the temperature inthe sample homogeneously. The viscosity-time curve wasregistered and was shown in Figure S1 in supplementarymaterial. After measurement, the sample along with thecrucible was quenched by moving the sample to thequenching chamber. At the same time, argon gas with veryhigh flow rate was impinged on the sample to increase thecooling. A number of pieces of the quenched sample werecollected for SEM analysis to confirm the phase. For thispurpose, a Scanning Microscope (QUANTA-FEG450,USA) equipped with EDX analyzer (EDAX/TEAM TM,EDAX Inc., USA) was employed. Another part of thesample was subjected to X-ray fluorescence (Axios-Advanced, PANalytical B.V., Netherlands) for chemicalcomposition analysis of each sample after experiment. Thechemical composition of the sample after experiment wasmeasured precisely by the standard curve of minerals andlisted in Table 3.

3. Results and discussion

3.1 Conformation of the phasesThe viscosity values of 7 samples are measured at differ-

ent temperatures and the results are presented in Table 4.Figure 4 presents the natural logarithm of measuredviscosity value as the function of reciprocal temperature.Linear relation is presented in Fig. 4 which means theviscosity value follows Arrhenius assumption.

ln© ¼ ln©0 þE0

RTð3Þ

where © is viscosity value (all the viscosity values in thisstudy use Pa·s), ©0 is the pre-exponential constant, E0

is activation energy, R is ideal gas constant and T is

Fig. 3. Relationships between SMC value and depth ofimmersion.

Table 3. The chemical compositions of the samples afterexperiement

sample Al2O3 SiO2 K2O Na2O CaO Fe2O3

VM1 21.68 68.63 6.05 2.23 0.56 0.85VM2 19.05 71.50 5.74 2.03 0.55 1.13VM3 18.83 72.11 5.55 1.98 0.55 0.98VM4 18.48 72.86 5.36 1.93 0.42 0.94VM5 16.82 72.02 5.41 1.72 2.36 1.68VM6 20.35 68.46 3.97 4.20 1.97 1.05VM7 21.05 67.65 5.28 1.99 2.59 1.44

Table 4. The measured viscosity (Pa·s) at different temperatures

sampleViscosity values at different temperatures (K)

1648 1673 1698 1723 1748 1773 1798 1823 1848 1873

VM1 ® ® ® ® ® 37371.16 7999.02 2340.5 1456.84 1267.91VM2 ® 19364.68 11994.43 7828.20 5247.81 3613.46 2518.31 1740.18 1270.64 970.09VM3 ® ® ® ® 13262.7 6212.47 3319.43 2146.77 1538.97 1163.7VM4 ® 17533.75 7495.47 4716.16 2776.31 1469.13 952.45 825.24 679.55 370.82VM5 9643.87 6446.88 4232.21 2806.97 2008.93 1299.95 956.66 702.01 575.83 459.01VM6 ® ® 5094.22 3496 2426.78 1713 1202.17 896.49 782.54 489.68VM7 ® 2713.72 1257.22 785.01 520.82 361.66 261.43 194.76 161.32 136.19

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temperature. The viscosity values of sample VM1 arefound to be increasing acutely with the temperaturedecreasing. The study14) shows that the solid particlessuspended in the liquid phase will strongly increase theviscosity value, so all samples after experiments aresubjected to SEM analysis and solid particles are found insample VM1. SEM image of sample VM1 is shown inFig. 5. Two phases are identified by EDAX analysis. Thedark pieces in the glass are the 3Al2O3·2SiO2 compoundand the rest part is glassy phase. The EDAX results arelisted in Table 5. Therefore, the viscosity values of sampleVM1 at 1773 and 1793K are not considered in the com-parison with calculated results by different models.

Many models predicted the viscosity values are basedon the different assumptions. However, not all the modelsmeet the requirement of prediction of the liquid phase in

ceramics during the heating. Based on the previous study,7)

Urbain model, Riboud model, SW model and M-SWmodel are compared with the experimental results of thisstudy. The Urbain model and Riboud model are based onWeymann-Frenkel equation.10) Weymann-Frenkel equa-tion can successfully predict viscosity of liquid phase witha quasi-crystalline structure, but the equation cannot guar-antee the accuracy of silicate melts. As shown in Figs. 6(a)and 6(b), the predictions of Urbain model and Riboudmodel are far away from the experimental results.On the other hand, SW model and M-SW model are

established on the Arrhenius equation which can beapplied in prediction of viscosity of lava. The chemicalcomposition of lava is quite similar as the composition ofthe glassy phase in the ceramics. The calculation resultssatisfy some experimental results but the prediction ofviscosity values of liquid phases in clay based ceramicsstill do not meet the requirements of a part of experimentalresults. The modification of the model is needed to fit theviscosity of liquid phase in ceramics.

3.2 Modification of the modelBased on the model established by Bottinga and

Weill,15) SW model had been established based on theArrhenius Eq. (3) and lots of experimental results. TheE0/R was regarded as a constant slope for different com-position. At the same time, ln©0 was also considered

Fig. 4. Natural logarithm of measured viscosity value as thefunction of reciprocal temperature.

Fig. 5. SEM image of sample VM1.

Table 5. Chemical compositions of detected phases (wt%)

sample PhasesChemical compositions

Al2O3 SiO2 K2O Na2O CaO Fe2O3

VM1 Phase 1 21.94 68.47 6.93 1.34 0.44 0.88Phase 2 69.24 29.53 0.65 0.15 0.04 0.39

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dependable on the chemical composition of the specimen.E0 and ©0 were described as following equations:

E0

R¼ 104s ð4Þ

ln©0 ¼ c© � cTs ð5Þwhere s is the slope for a liquid phase with multi-component, and c© and cT are constants. The Eq. (3) wasgiven as the combination of formula (4) and (5).

ln© ¼ sð104=T Þ � 6:4� 1:5s ð6Þs is regarded as mean slope and is given by the Eq. (7)

s ¼P

Xiðs0iXSiO2Þ

1�XSiO2

ð7Þ

where si0 is slope intercept for different component whichwas listed in Table 6 and XSiO2

is the mole fraction ofSiO2. The calculated results by model SW and M-SW as afunction of experimental results are plotted (the viscosityunit after calculated by SW and M-SW is poise and isconverted to Pa·s in all figures). The comparison resultsare presented in Fig. 7. The results calculated by both (a)SW model and (b) M-SW model deviate from the exper-imental results obtained from this study. The data from

M-SW model are apparently smaller than the experimentalresults.The sAlO2

was modified by Akio Goto et al.12) and thevalue of sAlO2

was divided into two parts if the mole frac-tion of “AlO2” was more than doubled the sum of MO andM2O on a molar basis. However, SW model only con-sidered that the sum of the MO and M2O (MO or M2Orefers to alkali oxide or alkali earth oxide; FeO and MnOare also included) oxides exceeded Al2O3 on a molar basisand the value of slope intercept “AlO2” is 6.7. It was foundthat the viscosity value increased with the addition ofAl2O3 if the mole fraction of Al2O3 is smaller than thesum of the MO and M2O oxides, so the Al2O3 was only

Table 6. Approximation (XSiO2= 1) of Arrhenius slopes for

multicomponent*

Mineral oxide-silica pairs Slope intercept Si0

H2O­ 2.0K2O­, Na2O­, Li2O­ 2.8MgO­, FeO­ 3.4CaO­, TiO2­ 4.5‘AlO2’­ 6.7

*Original data from Ref. 11.

Fig. 7. Comparisons between the measured viscosities andthose estimated by (a) SW model and (b) M-SW model.

Fig. 6. Comparisons between the measured viscosities andthose estimated by (a) Urbain model and (b) Riboud model.

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considered as network-former in that case. On the otherhand, the Al2O3 was regarded as network-former andnetwork-modifier in the M-SW model if excess Al2O3

existed. The assumption is fairly sound. The MAl2O4 orMAlO2 is formed due to the combination of AlO2 and MOor M2O. Meanwhile, the role of excess Al2O3 is network-modifier which also lowers the viscosity in somehow, thusthe value of slope intercept excess “AlO2” is regarded as5.6. However, in the M-SW model, only alkaline oxidesand alkaline earth oxides are considered to combine with“AlO2”. In silicate melts, three types of oxygen have beenintroduced, which are bridging oxygen O0 bonded to twosilicon atoms, non-bridging oxygen O¹ bonded only toone silicon atom and the free oxygen O2¹. For instance,MO can provide non-bridging oxygen to break the net-work and act as the modifier of the network. On the otherhand, component FeO and MnO always have the similarfunction and many researches16),17) showed that FeO canbreak the silicate network and lowers the viscosity of silicamelts. Therefore, they could also be regarded as network-modifier. Furthermore, FeAl2O4 can also be formed.18) Theresearch had already taken MnO into consideration. Thus,the component FeO should also be taken into account asnetwork-modifier and get rid of a part of excess Al2O3.Figure 8 shows that the comparison between calculatedresults of different chemical compositions in Table 3 andthe experimental results of this study. The calculatedresults are somehow closer to the experimental results.

Although the calculated results have approached exper-imental results, still some deviations exist. The SW modelis also an empirical model. The model assumes SiO2 assolvent and figures out the other components effects on theviscosity value of silicate melts. The scope of model appli-cation is limited in the range of silica in between 0.4 and0.8 (mole fraction). The mean slope (s) is calculated frommelt compositions using a total of 5 model parameters. Inthe assumptions, due to the lack of data on the influence ofFe2O3 on the viscosity value, the roughly approximationwas evaluated as the cation of Fe3+ has the same effect on

the viscosity value of silicate melts as Fe2+. The effect onthe viscosity value of silicate melts of Fe3+ differs fromFe2+ 17) but some Fe2O3 would convert to FeO at hightemperature, so this assumption can be accepted but still itwill cause some error. Another approximation was that theNa2O and K2O are with the same slope intercept value butaccording to the Bottinga’s research, the parameter ofKAlO2 was found to be larger than NaAlO2. To facilitatethe calculation, the KAlO2 and NaAlO2 were forced toapply the same value in the study. In this study, we alsouse those assumptions which can’t make the error avoid.However, it must mention here that feldspar is an impor-tant mineral for producing clay based ceramics, so theslope intercept data of K2O need to be revised by furtherexperimental results in order to satisfy the calculationresults of liquid phase in clay based ceramics.

4. Conclusions

M-SW model could accurately predict liquid viscosityvalue in clay based ceramics after modification. The pre-cise measurements of viscosity values of liquid phases inclay based ceramic were carried out experimentally byrotating the spindle in the melts at different high temper-atures. The samples were designed first according to theanalyzed chemical composition and were prepared by thepure chemicals and standard feldspar. Natural logarithm ofmeasured viscosity values and reciprocal temperature werefound to be with linear relation. The linear relationshiprevealed that the viscosity of the melts followed Arrheniusassumption. Four different models, Urbain model, Riboudmodel, SW model and M-SW model were introduced tocalculate the viscosity values of melts and compared withexperimental results in the present study. The calculatedresults of Urbain model and Riboud model differ greatlyfrom the experimental results. The calculated results ofSW model and M-SW model approached the experimentalresults but there are still some deviations in between themodels and experimental results. Although the experi-mental results were larger than the calculated viscosityvalues by M-SW model, M-SW model was more reliableto predict the viscosity values of liquid phases with highsilica content of melts. In clay based ceramics, “FeO”should be regarded as network-modifier in the M-SWmodel to get rid of a part of excess Al2O3. However,M-SW model still needs to be revised to improve theaccuracy of the prediction results of liquid viscosity valuesin the clay based ceramics. The slope intercept data ofK2O and “FeO” were needed to be revised by furtherexperiments.

Acknowledgement The financial supports on the Project51502230 from National Natural Science Foundation ofChina are gratefully acknowledged.

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