Thermodynamic analysis of binary and ternary silicate systems by a structural model

Abstract

A critical evaluation of the thermodynamic properties as well as the phase diagrams for the systems MgO-SiO2 and FeO-SiO2 is performed with a structural model and for the systems MnO-MgO, FeO-MnO and FeO-MgO through the regular solution model. The structural model for binary silicate melts is now extended to ternary systems. It is shown that, for systems SiO2-AO-BO, random mixing of cations A2+ and B2+ occurs when the oxides AO and BO behave in a similar way with silicate. If the AO-SiO2 and BO-SiO2 binary systems exhibit similar thermodynamic behavior, that is comparable free energies of mixing, the properties of the ternary SiO2-AO-BO can be extrapolated from those binary systems in a straightforward fashion. This condition is found in simple silicates such as SiO2-MnO-MgO, SiO2-FeO-MnO and SiO2-FeO-MgO systems where the activities and liquidus temperatures calculated solely from data on the binary sub-systems are in good agreement with measured ternary data.