Thermodynamic modeling of the Mn-Si-O system

Abstract In this study, the thermodynamic parameters of the Mn-Si-O system were re-evaluated using the CALPHAD approach. Available experimental data on phase equilibria were taken into account and thermodynamic properties such as heat capacity, standard entropy and standard enthalpy were reproduced within uncertainties. Three ternary compounds are found to be stable in the Mn-Si-O system: rhodonite (MnSiO₃), braunite (Mn₇SiO₁₂) and tephroite (Mn₂SiO₄). Braunite was modeled by CEF, while tephroite and rhodonite were modeled as stoichiometric compounds. Two-sublattice partially ionic liquid model was used to describe the liquid phase. The braunite phase exhibits a homogeneity range and can dissolve Mn₂O₃ in some extension. Phase diagrams for the MnO-SiO₂ system in the presence of metallic Mn and the MnOx-SiO₂ system in air were calculated and showed good agreement with existing literature data. The thermodynamic parameters were evaluated to describe the experimental data over the entire compositional range of the system.