Viscosity is an important physico-chemical property of slags and plays a major role in the manufacturing operations of glasses. Experimental measurements of viscosities are often very difficult to make and time consuming. Thus it is important to develop mathematical models that will predict viscosities in a self-consistent manner over the entire composition and temperature range. Also, the viscosity of high temperature glass melts is a structure related property. In the present research, theoretical models are developed to predict viscosities of a series of glass melts like Li₂O-B₂O₃, Na₂O-B₂O₃, K₂O-B₂O₃, Al₂O₃-SiO₂, PbO-SiO₂, and Na₂O-SiO₂ based on thermodynamic principles and experiments are carried out to measure the viscosities. Excellent agreement is observed between the experimental and predicted values. A structure based model is also developed to predict the viscosity of Na₂O-B₂O₃-SiO₂ ternary system. The calculated results showed an excellent agreement with experimental results for the composition with X_SiO2/X_Na2O = 2, 1.5 and 1. At X_SiO2/X_Na2O = 0.5, a large deviation was observed between the experimental and calculated results. This deviation was due to the formation of solid particles in the melt. The type and amount of solid particles formed has been studied by optical microscopy and X-ray diffraction analysis. Based on these results, a structural model has been proposed.

For more than three decades, a number of empirical correlations have been proposed between sulfide capacity and the basicity of slags. Because of deviations of data from predictions based on the basicity concepts, ad hoc correlations to these methods are needed. Recently, we (Reddy-Blander Model) showed that sulfide capacities can be calculated a priori, based on a knowledge of the chemical and solution properties of oxides and sulfides. Sulfide capacities have been calculated in a self-consistent manner for slag compositions ranging from the pure basic oxide to acidic oxide melts for the systems CaO-SiO₂, FeO-SiO₂, MgO-SiO₂, MnO-SiO₂ and Na₂O-SiO₂ as a function of temperature. Fundamental equations for the calculation of sulfide capacities, both in basic melts and in the composition range, 0.33 < X_SiO2 < 1.00 in MO - SiO₂ (where M represents Ca, Fe, Mg, Mn and Na₂) systems have been derived. The results showed that our predictions are in excellent agreement with the experimental data. At a given temperature, the sulfide capacity increases with an increase in the concentration of MO in the melt. For a given composition, the sulfide capacity also increases with an increase in temperature. This is largely related to the large increase in the activity of MO in the melt.