A structural molar volume model was developed to accurately reproduce the molar volume of molten oxides. As the non-linearity of molar volume is related to the change in structure of molten oxides, the silicate tetrahedral Q-species, calculated from the modified quasichemical model with an optimized thermodynamic database, were used as basic structural units in the present model. Experimental molar volume data for unary and binary melts in the Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-Al2O3-SiO2 system were critically evaluated. The molar volumes of unary oxide components and binary Q-species, which are model parameters of the present structural model, were determined to accurately reproduce the experimental data across the entire binary composition in a wide range of temperatures. The non-linear behavior of molar volume and thermal expansivity of binary melt depending on SiO2 content are well reproduced by the present model.

A structural electrical conductivity model for oxide melts was developed based on the Nernst–Einstein relationship of ionic conductivity. In the description of ionic conductivity, the effective diffusivities of cations in oxide slags were described as a function of the polymerization of the melt. The polymerization of oxide melts was calculated from the Modified Quasichemical Model, taking into account the short-range ordering in slags. The parameters of this conductivity model were fixed to reproduce the electrical conductivity data in unary and binary melts, and the model can well predict the conductivity data in ternary and higher order system without any additional model parameters. The model is successfully applied to the CaO-MgO-MnO-PbO-Al 2 O 3 -SiO 2 system.

As part III of this series, the model is extended to iron oxide-containing melts. All available experimental data in the FeO-Fe 2 O 3 -Na 2 O-K 2 O-MgO-CaO-MnO-Al 2 O 3 -SiO 2 system were critically evaluated based on the experimental condition. The variations of FeO and Fe 2 O 3 in the melts were taken into account by using FactSage to calculate the Fe 2+ /Fe 3+ distribution. The molar volume model with unary and binary model parameters can be used to predict the molar volume of the molten oxide of the Li 2 O-Na 2 O-K 2 O-MgO-CaO-MnO-PbO-FeO-Fe 2 O 3 -Al 2 O 3 -SiO 2 system in the entire range of compositions, temperatures, and oxygen partial pressures from Fe saturation to 1 atm pressure.