High-Temperature Description of Ceramics based on the SrO–La2O3–TiO2–ZrO2(HfO2)–Fe2O3 Multicomponent Systems

This study establishes a high-temperature thermodynamic description of the SrO–La2O3–TiO2–ZrO2–Fe2O3 and SrO–La2O3–TiO2–HfO2–Fe2O3 systems by combining Knudsen effusion mass spectro-metry with optimization of the thermodynamic data obtained using the generalized lattice theory of associated solutions (GLTAS). It was shown that, during heating, iron oxide in these systems is reduced to FeO, which vaporizes at temperatures exceeding 1550 K with dissociation into Fe and oxygen. The Fe partial vapor pressures and the FeO activities as a function of temperature in the range of 1560–1822 K allowed one to obtain for the first time the partial molar enthalpy of FeO vaporization as well as the partial molar enthalpy of FeO mixing in the SrO–La2O3–TiO2–HfO2–FeO system. Based on GLTAS approach and the data on equilibria in the corresponding binary systems, the thermodynamic description of the SrO–La2O3–TiO2–ZrO2–FeO and SrO–La2O3–TiO2–HfO2–FeO systems was obtained. For the first time, the data on excess entropy of the systems under consideration were found as a result of modeling, illustrating higher entropy stabilization in the zirconia-containing system in comparison with the hafnia-containing system.