High-temperature mass spectrometric study and modeling of ceramics based on the Al₂ O₃ -SiO₂ -ZrO₂ system

Materials based on the Al₂ O₃ -SiO₂ -ZrO₂ system are promising for a wide range of high-temperature technological applications, such as thermal barrier coatings in the aviation and space industry or advanced materials in nuclear power reactors. Experimental studies of the ceramics based on this system by the Knudsen effusion mass spectrometric (KEMS) method are of significant interest in designing technological processes for the synthesis and exploitation of the Al₂ O₃ -SiO₂ -ZrO₂ materials.

Samples of ceramics in the Al₂ O₃ -SiO₂ -ZrO₂ system, including the Al₂ O₃ -ZrO₂ and SiO₂ -ZrO₂ binaries, were prepared by solid-state synthesis. Analysis of the samples was performed by X-ray fluorescence and diffraction techniques. The vapor composition and thermodynamic properties of the components in this system were determined by KEMS. The derived thermodynamic functions were optimized within the generalized lattice theory of associated solutions (GLTAS).

In the temperature range 1900-2600 K, the SiO, Al, AlO, Al₂ O, ZrO, ZrO₂ , and O vapor species were identified over the samples in the systems under study. For the thermodynamic properties to be determined correctly, the samples of the Al₂ O₃ -SiO₂ -ZrO₂ system had to be vaporized at temperatures less than 2000 K, where data could be obtained only for the SiO species. The SiO₂ activities obtained were taken as the experimental basis for the modeling within the GLTAS approach. This allowed evaluation of the component activities and excess Gibbs energy, and assessment of the relative number of bonds of different types.

At 1920 K, the Al₂ O₃ -SiO₂ -ZrO₂ system is characterized by negative deviations of its thermodynamic properties from the ideal behavior. The consistency of the obtained modeling results was illustrated by comparison of the values derived from the data for the ternary and the boundary binary systems and thereby indicates the reasonable uniformity of the energy parameters of the lattice model derived in the calculations, which may be used in further modeling of multicomponent systems.