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.