High‐temperature Mass Spectrometric Study and Modeling of the Thermodynamic Properties of the TiO₂‐SiO₂‐ZrO₂ System

Development of the advanced materials based on the TiO ₂ ‐SiO ₂ ‐ZrO ₂ system is hindered by lack of the information on its thermodynamic properties and phase equilibria. In the present study, the samples in the TiO ₂ ‐SiO ₂ ‐ZrO ₂ system were prepared by solid‐state synthesis and analyzed by X‐ray microanalysis, fluorescence, and diffraction techniques. The thermodynamic properties in this system were evaluated by Knudsen effusion mass spectrometric (KEMS) method and optimized within the generalized lattice theory of associated solutions (GLTAS). The main vapor species over the silica‐containing samples vaporized from the tungsten cell at the temperature 1973 K were SiO, O, WO ₂ , and WO ₃ . The vapor over the samples in the TiO ₂ ‐ZrO ₂ system at 2356 K was composed mainly of TiO, TiO ₂ , O, WO ₂ , and WO ₃ . The activity of components in the samples and the partial pressures of the identified vapor species were determined. At 1973 K, the TiO ₂ ‐SiO ₂ ‐ZrO ₂ system is characterized by positive deviations from the ideality. The observed weak dependence of the SiO ₂ activity on the SiO ₂ content suggests the presence of a broad field of immiscibility on the phase diagram in the concentration range 40–100 mol . % SiO ₂ . The thermodynamic data on the TiO ₂ ‐SiO ₂ ‐ZrO ₂ system obtained by KEMS can be of great value for calculation of the phase equilibria.