Mass spectrometric study of thermodynamic properties in the Yb2O3-ZrO2 system at high temperatures

Rationale: Materials based on the Yb2O3-ZrO2 system have many industrial applications such as high-temperature solid electrolytes, ceramics with special properties and most importantly for thermal barrier coatings. As their synthesis and use take place at high temperatures, information on the vaporization processes, thermodynamic properties and phase equilibria of this system at high temperatures is of great importance.

Methods: Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using two tungsten effusion cells containing the sample under study and pure Yb2O3. The values of component activities in the Yb2O3-ZrO2 system were also calculated using the CALPHAD approach.

Results: The Yb and O vapor species were identified over the samples studied at 2400 K. Using these data the ZrO2 activities, chemical potentials of components and the Gibbs energies of the solid solution formation were calculated in this system. The thermodynamic values were also obtained as the result of modeling of the Yb2O3-ZrO2 system based on the CALPHAD approach using the data available on the phase diagram of this system and calorimetric measurements only.

Conclusions: The thermodynamic functions found in the Yb2O3-ZrO2 system at 2400 K, such as the activities of components and the Gibbs energy of formation, displayed negative deviation from ideality. Mutual agreement was observed between the experimental thermodynamic values and the results of calculations based on the CALPHAD approach.