Mass spectrometric study and modeling of the thermodynamic properties in the Gd O -ZrO -HfO system at high temperatures.

RATIONALE

Materials based on the Gd O -ZrO -HfO system are promising for a wide range of high-temperature technological applications, such as for obtaining thermal barrier coatings in the aviation and space industry, as well as advanced materials in nuclear power applications. Experimental studies of the ceramics based on this system by the Knudsen effusion mass spectrometric method provides such valuable information as the vapor composition over the samples and enables derivation of the thermodynamic functions.

METHODS

Samples of ceramics in the Gd O -ZrO -HfO system were synthesized and analyzed by X-ray fluorescence and diffraction techniques. The vaporization processes and partial pressures of the vapor species over the samples were obtained by the high-temperature mass spectrometric method using the ion current comparison method. The derived thermodynamic functions were optimized within the Generalized Lattice Theory of Associated Solutions (GLTAS) approach.

RESULTS

At the temperature of 2600 K, the GdO, ZrO, ZrO , HfO, and O vapor species were found over the samples, but only for the GdO and ZrO species were accurate experimental data on the partial pressures obtained. In all the ceramic samples, the Gd O activity was determined. On this experimental basis, modeling within the GLTAS approach was performed. It allowed the evaluation of the Gd O , ZrO , and HfO activities in the system under study and a rough approximation of the excess Gibbs energy as a function of composition to be obtained.

CONCLUSIONS

At 2600 K the Gd O -ZrO -HfO system is characterized by negative deviations of its thermodynamic properties from the ideal behavior. Consistency of the obtained modeling results indicate reasonable uniformity of the energy parameters of the lattice model derived in calculations of the hafnia-containing oxide systems, which may be used in further modeling of multicomponent systems.