Coupled Experimental Study and Thermodynamic Modeling of the Al₂O₃–Ti₂O₃–TiO₂ System

Abstract

A complete critical evaluation and re-optimization of phase diagrams and thermodynamic properties of the Al₂O₃–Ti₂O₃–TiO₂ system at 1 atm pressure has been performed. Equilibration and quenching experiment in the Al₂O₃–TiO₂ system in air was also performed to constrain the solubility limit of Al₂O₃ in TiO₂ rutile solution at high temperatures. The molten oxide phase was described by the Modified Quasichemical Model considering the short-range ordering in molten oxide. While Al₂TiO₅ and Ti₃O₅ were treated as separate stoichiometric phases in the previous optimization, they were described in this study, using the Compound Energy Formalism, as part of pseudobrookite solid solution with a miscibility gap based on new experimental data. Corundum and rutile solutions were also described based on their crystal structures. New high temperature phase, Al₆Ti₂O₁₃, was also considered for the first time. A set of optimized model parameters of all phases was obtained, which reproduces all available and reliable literature data within experimental error limits from 25°C to above the liquidus temperatures under oxygen partial pressures from metallic saturation to 1 atm. The newly optimized database was applied to calculate the inclusion diagram and reoxidation of Al-killed and Ti bearing steels.