Thermodynamic model and viscosity of Na2O–MgO–CaO–SiO2 glasses

The structure–viscosity relationship of 15Na ₂O· xMgO·(10 − x)CaO·75SiO ₂ ( x = 0, 2, 4, 6, 8, 10) glasses was studied. The structure of studied glasses was described by the thermodynamic model of Shakhmatkin and Vedishcheva. Thermodynamic modeling resulted in eight components with significant abundance in the studied glasses, i.e. SiO ₂, 2MgO·SiO ₂, MgO·SiO ₂, Na ₂O·3CaO·6SiO ₂, Na ₂O·CaO·5SiO ₂, Na ₂O·MgO·4SiO ₂, Na ₂O·SiO ₂ and Na ₂O·2SiO ₂. Due to significant positive correlations between equilibrium molar amounts of (2MgO·SiO ₂–MgO·SiO ₂), (Na ₂O·3CaO·6SiO ₂–Na ₂O·CaO·5SiO ₂), (Na ₂O·MgO·4SiO ₂–Na ₂O·SiO ₂), and (Na ₂O·SiO ₂–Na ₂O·2SiO ₂) only four significant components were considered in the regression treatment, namely SiO ₂, MgO·SiO ₂, Na ₂O·3CaO·6SiO ₂, and Na ₂O·2SiO ₂ . The experimental viscosity data obtained in the viscosity range from 10 ² dPa·s to 10 ¹² dPa·s were alternatively described by various commonly used viscosity equations — Adam and Gibbs, Avramov and Milchev, and MYEGA. The compositional dependence of parameters of the above viscosity equations was described by multi-linear formulas taking as independent variables the equilibrium molar amounts of significant components of the thermodynamic model. The statistical analysis of the non-linear regression results was performed and only the statistically significant members were retained in the multi-linear forms. The assumption of composition independent high temperature viscosity limit was checked for all used viscosity equations. It was found that statistically equivalent description of experimental data is obtained by supposing the compositional dependence of this quantity. It was statistically confirmed that when the system composition is described by molar amounts of true components obtained from proper thermodynamic model the compositional dependence of parameters of considered viscosity equations acquires the simple multilinear linear form.