Assessment of thermodynamic functions in the ZrO2–Sm2O3–Al2O3 system

A thermodynamic database for the ZrO2–Sm2O3–Al2O3 system is derived using CALPHAD approach taking into account experimental data on isothermal sections and liquidus surface. The compound energy formalism and two-sublattice partially ionic liquid model are applied for phase descriptions in the system. Thermodynamic parameters for the binary systems of ZrO2–Sm2O3 and Sm2O3–Al2O3 are assessed in this study based on phase equilibrium and calorimetric data for binary systems taking into account sub-solidus phase relations in the ternary system of ZrO2–Sm2O3–Al2O3. It is demonstrated that the phase equilibria between solid phases in the ternary ZrO2–Sm2O3–Al2O3 system constrain thermodynamic parameters in the binary systems ZrO2–Sm2O3 and Sm2O3–Al2O3. The ternary interaction parameter is assessed for the liquid phase using experimental data on the liquidus surface. Isothermal sections at 1523 and 1923 K, the liquidus surface and vertical sections are calculated and compared with available experimental data. The experimental data are generally well reproduced by calculations with exception that in contrast to experimental data a primary crystallisation field for pyrochlore was indicated in calculations. Additionally, differences between experimental and calculated liquidus surface phase diagram were found in the Sm2O3-rich corner. Because of these differences several inconsistencies were also found for vertical sections.