Vaporization and thermodynamics of ceramics in the Sm2 O3 -Y2 O3 -HfO2 system.

Abstract

RATIONALE\nThe Sm2 O3 -Y2 O3 -HfO2 system holds promise for applications in the sphere of high temperature technologies, particularly the development of ultra-high temperature ceramics. However, the reliability of refractory materials is dependent on the possible selective vaporization of their components leading to changes in physicochemical properties of the materials. Thus, information about vaporization processes and thermodynamic properties of ceramics based on the Sm2 O3 -Y2 O3 -HfO2 system may be of importance for the production of high temperature materials as well as for the prediction of the physicochemical properties of ultra-high temperature ceramics.\n\n\nMETHODS\nThe Knudsen effusion mass spectrometric method was employed, with a MS-1301 magnetic mass spectrometer equipped with a tungsten twin effusion cell used to examine the samples in the Sm2 O3 -Y2 O3 -HfO2 system. Electron ionization of vapor species effusing from the cell was carried out at an ionization energy of 25 eV.\n\n\nRESULTS\nIt was shown that, at a temperature of 2373 K, selective vaporization of Sm2 O3 and Y2 O3 took place from the samples of the Sm2 O3 -Y2 O3 -HfO2 system, with the main vapor species being SmO, Sm, YO, and O. The partial pressures of these vapor species were obtained by the ion current comparison method. The Sm2 O3 activities in the Sm2 O3 -Y2 O3 -HfO2 system were determined and allowed evaluation of the excess Gibbs energies at 2373 K. The direction of change of the condensed phase of the samples because of selective vaporization of the components was examined.\n\n\nCONCLUSIONS\nThe Sm2 O3 -Y2 O3 -HfO2 system was characterized by negative deviations from the ideal behavior at 2373 K. The excess Gibbs energies evaluated in the present study were approximated using the Redlich-Kister representation and visualized in the form of curves of constant values in the concentration triangle. The data obtained in the Sm2 O3 -Y2 O3 -HfO2 system were optimized using the Barker-Guggenheim theory of associated solutions.