Vaporization and thermodynamic properties of the SrO-Al2 O3 system studied by Knudsen effusion mass spectrometry.

Abstract

Strontium aluminates can be used as refractory construction materials at temperatures up to 2000°С or as the materials for immobilization of long-lived radioactive waste. The SrО-Al2 O3 system is one of the more complicated oxide systems used for the creation of new radio-transparent materials. The exploitation of such materials at high temperatures demands the knowledge of the thermal stability of the compounds and solid solutions formed in the SrО-Al2 O3 system. The synthesis of the samples in the SrO-Al2 O3 system was carried out by a ceramic method at 1250°C. The characterization of the samples was accomplished with the use of X-ray diffraction (XRD). The vaporization of the samples under study was performed from a twin tungsten effusion cell using the Knudsen effusion mass spectrometry method. The temperature dependences of partial pressures of vapor species over 4SrO·Al2 O3 , 3SrO·Al2 O3 , SrO·Al2 O3 , SrO·2Al2 O3 and SrO·6Al2 O3 in a wide range of temperatures were determined. The component activities, the Gibbs energies of mixing and the standard enthalpies of individual strontium aluminates were obtained. The thermodynamic properties of the SrO-Al2 O3 system at high temperatures are characterized by negative deviation from ideality. The vaporization processes and thermodynamic properties of the SrO-Al2 O3 system were obtained for the first time.