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Phase equilibria in the TiO2–SiO2 system have been studied experimentally using DTA and SEM/EDX. The thermodynamic parameters for the TiO2–SiO2 system have been assessed considering new experimental data of the present work and from the literature. Moreover, the miscibility of the liquid in the Al2O3–TiO2–SiO2 system has been studied at 2013 K in air and shrinkage of the miscibility gap at 3.8 mol% Al2O3 has been demonstrated. The experimental data obtained in the present work and literature as well as the thermodynamic databases for the binary Al2O3–TiO2, TiO2–SiO2, and Al2O3–SiO2 systems have been used to derive the thermodynamic description of the Al2O3–TiO2–SiO2 system using the CALPHAD approach. Solid phases have been modeled using the compound energy formalism. The liquid phase has been described by the two-sublattice partially ionic liquid model. A set of self-consistent parameters have been proposed, which resulted in a reasonably good agreement between the calculated and experimental data on the phase equilibria, liquid immiscibility, and thermodynamic properties in the Al2O3–TiO2–SiO2 system.

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