Phase equilibria and thermodynamic properties of components in the Cs2O-B2O3-SiO2 system at high temperatures

Abstract

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.

Calculations of the thermodynamic properties of glasses and melts in the Cs2O-B2O3-SiO2 system in the framework of the generalized lattice theory of associated solutions

“…The compositions of the Cs 2 O-B 2 O 3 -SiO 2 glasses and melts investigated by high-temperature mass spectrometry at 1020 K [5] and the emf method at 1200 K [4] are designated in Fig. 1 by points 1-12 and 13-16, respectively.…”

“…For this purpose, we used the constraints on the order of magnitude of the chemical potentials ∆ , ∆ , and ∆ . These constraints were determined by the corresponding calculations for the concentration regions studied by high-temperature mass spectrometry [5].…”

“…x SiO 2 [5] were calculated at the same fitting parameters used in the above case. In order to compare the results of calculations with the experimental data, the activities of Cs 2 O were determined from the activities of cesium metaborate [5] with the use of the equation (14) where ∆ = -181.3 kJ/mol is the energy of formation ∆G 0 of the CsBO 2 compound from Cs 2 O and B 2 O 3 oxides, which was calculated from the reference data [18].…”

“…In this respect, the aim of the present work was to calculate the thermodynamic properties of glasses and melts in the Cs 2 O-B 2 O 3 -SiO 2 system at high temperatures within the generalized lattice theory of associated solutions [1][2][3] with the use of the experimental data on the thermodynamic properties determined by the electromotive force (emf) method [4] and high-temperature differential mass spectrometry [5].…”

Specific features of the glass formation in the R 2O-B2O3, R 2O-SiO2, and R 2O-B2O3-SiO2 (R = Rb, Cs) systems

“…Investigation of the glass formation regions in the aforementioned systems is also important because of the necessity of solving the problems associated with the disposal of radioactive wastes in alkali borosilicate matrices. Some of the physicochemical properties of glasses of particular compositions in these systems were investigated in our previous works [2][3][4][5]. The glass formation in the binary systems can be judged from the relevant data included in the electronic information system [6], specifically from the sections concerned with the determination of the glass transition temperatures and densities of the R 2 O-B 2 O 3 and R 2 O − SiO 2 glasses existing in sufficient amounts.…”