Coupled Experimental Study and Thermodynamic Modeling of the MgO-MnO-Mn2O3-Ti2O3-TiO2 System

Abstract

A coupled phase diagram experiment and thermodynamic modeling of the MgO-MnO-Mn2O3-Ti2O3-TiO2 system at 1 bar total pressure is presented. High temperature equilibration and quenching experiments followed by the phase analysis using electron probe microanalysis and X-ray diffraction were performed to obtain complex phase equilibria between solid solutions and liquid phase in air. Low temperature phases during quenching was inevitable in some samples which lead to inaccuracy in the experimental data. The molten oxide phase was described by using the Modified Quasichemical Model, which considers short-range ordering in liquid state, and the Gibbs energies of the extensive solid solutions (pseudobrookite, ilmenite and spinel) were described using the Compound Energy Formalism based on their crystal structures. A set of optimized model parameters of all phases was obtained, which reproduces all the reliable experimental data within experimental error limits from 25 °C to above the liquidus temperatures over the entire range of composition at air atmosphere. The model can also predict the phase equilibria in the range of oxygen partial pressures from metallic saturation to air. The complex phase relationships in the system have been elucidated for the first time and the database of the model parameters can be used with FactSage software to calculate any phase diagrams and thermodynamic properties of the MgO-MnO-Mn2O3-Ti2O3-TiO2 system.