High-temperature mass spectrometry is used to investigate vaporization processes and determine SiO 2 activity in the Al 2 O 3 -SiO 2 system between 1850 and 1970 K. The results are consistent with the known phase equilibria in this system.

The phase equilibria in the Cs 2 O-B 2 O 3 -SiO 2 system are investigated in the temperature range 873-1073 K by the annealing-quenching technique, high-temperature microscopy, and X-ray powder diffraction analysis. The vapor composition, the activities of the components, and the Gibbs energies of glasses and melts in the Cs 2 O-B 2 O 3 -SiO 2 system are determined at a temperature of 1020 K. It is demonstrated that glasses and melts in the Cs 2 O · B 2 O 3 -Cs 2 O · SiO 2 system are characterized by positive deviations of the CsBO 2 activities and negative deviations of the Cs 2 O · SiO 2 activities from ideal behavior. As a consequence, the deviations of the Gibbs energies from ideal behavior change their sign.

The possibility of calculating the thermodynamic properties of binary glass-forming systems containing both modifier (Na 2 O) and glass-former (B 2 O 3 ) oxides with the use of the vacancy variant of the generalized lattice theory of associated solutions is demonstrated for glasses and melts in the Na 2 O-SiO 2 and B 2 O 3 -SiO 2 systems.

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The thermodynamic activities of SiO(2) in Al(2)O(3)-SiO(2) liquid slags were measured by the high-temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863-2169 K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF(2) standard. The mass spectra obtained for pure SiO(2) were in agreement with earlier data. The activities of silica, measured in the present work at 2150 K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al.

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The vapor composition, activities of the components, and Gibbs energies of melts in the Cs 2 O-B 2 O 3 system at a temperature of 1020 K are determined by the Knudsen effusion mass spectrometric method. The activities of the components and the Gibbs energies of melts in the Cs 2 O-B 2 O 3 system at a temperature of 1020 are calculated in the framework of the approach based on the generalized lattice theory of associated solutions with the use of the melt model including vacancies. It is demonstrated that the calculated and experimental thermodynamic properties are in reasonable agreement.

The high-temperature Knudsen effusion method was used to study partial pressures of vapour species, activities of components and the Gibbs free energies in the DyF 3 -Dy 2 O 3 system at the temperature (1357 AE 5) K. Partial pressures of the vapour species were obtained by the ion current comparison method, with the DyF 3 partial vapour pressure over pure DyF 3 as a standard. The equilibrium constant of the gaseous reaction DyF 3 DyOF = Dy 2 OF 4 was evaluated. Thermodynamic data obtained are in a agreement with the available phase diagram of the DyF 3 -Dy 2 O 3 system. Results of the present study illustrate the negative deviations from the ideal behaviour in the system. #