Assessment of thermodynamic functions in the ZrO2-La2O3-Al2O3 system

The thermodynamic database for the ZrO2-La2O3-Al2O3 system is derived using the Calphad approach. The compound energy formalism and two-sublattice ionic liquid model are applied for phase description in this system. Thermodynamic parameters for the ZrO2-La2O3 system are assessed in this study with special attention to triangulation in the ternary system of ZrO2-La2O3-Al2O3. It is demonstrated that the phase equilibria between solid phases in the ternary ZrO2-La2O3-Al2O3 system constrain thermodynamic parameters in the binary ZrO2-La2O3 system. The ternary interaction parameter is assessed for the liquid phase using experimental data on liquidus surface. Isothermal sections at 1523, 1923 K, liquidus surface and several vertical sections are calculated and compared with available experimental data. The revealed several inconsistencies between calculations and experimental data are due to calculations indicated wider filed of primary crystallisation of pyrochlore. The SEM investigation of melted samples performed in this work confirmed the calculated primary crystallisation field of pyrochlore.