High-Temperature Thermodynamic Properties of Hafnium and Rare Earth Oxide Ceramics

Previous experimental data on the vaporization and high-temperature thermodynamic properties of hafnium and rare earth oxide ceramics are considered here. The La 2 O 3 –Sm 2 O 3 system is for the first time studied at 2323 K using Knudsen effusion mass spectrometry. As a result of this study, the vapor composition over ceramic samples under investigation is identified, and concentration dependences of the partial pressures of vapor species over the system under study and condensed-phase thermodynamic properties are determined, namely, the component activities and the excess Gibbs energy. The enthalpy of formation from oxides and excess entropy of the La 2 O 3 –Sm 2 O 3 system at 2323 K are determined using the Wilson polynomial. The Kohler, Redlich–Kister, and Wilson semiempirical methods were used to calculate the thermodynamic properties in the La 2 O 3 –Sm 2 O 3 –Y 2 O 3 –HfO 2 and La 2 O 3 –Sm 2 O 3 –ZrO 2 –HfO 2 quaternary systems at 2330 K using the equilibrium data gained in the relevant binary systems. The results of the calculations were compared to previous semiempirical estimates of the respective quantities for the La 2 O 3 –Y 2 O 3 –ZrO 2 –HfO 2 and Sm 2 O 3 –Y 2 O 3 –ZrO 2 –HfO 2 systems taken as examples. Calculations by the Wilson method are shown to provide the best match with the experimentally obtained lanthanoid oxide activities in the La 2 O 3 –Sm 2 O 3 –Y 2 O 3 –HfO 2 and La 2 O 3 –Sm 2 O 3 –ZrO 2 –HfO 2 systems.