High-temperature mass spectrometric study of the vaporization processes and thermodynamic properties of samples in the Bi 2 O 3 -P 2 O 5 -SiO 2 system.

RATIONALE: The Bi2 O3 -P2 O5 -SiO2 system possesses a number of valuable properties that may be of use for various practical applications, both for obtaining new materials, e.g. optical fibers, and for replacing systems based on toxic lead silicate. Information on vaporization processes and thermodynamic properties obtained in the present study will be useful for the development of synthetic methods and approaches for modeling the thermodynamic properties of materials based on this system.

METHODS: High-temperature Knudsen effusion mass spectrometry was used to study the vaporization processes and to determine the thermodynamic properties of the components in the Bi2 O3 -P2 O5 -SiO2 system. Measurements were performed with a MS-1301 magnetic sector mass spectrometer. Vaporization was carried out using an iridium-plated molybdenum twin effusion cell containing the sample under study and pure bismuth(III) oxide as a reference substance. Electron ionization at an energy of 30 eV was employed in the study.

RESULTS: At a temperature of 950 K, Bi and O2 were found to be the main vapor species over the samples studied. The Bi2 O3 activity as a function of composition in the Bi2 O3 -P2 O5 -SiO2 system was derived from the obtained Bi partial pressures. The excess Gibbs energy of the system studied was calculated at 950 K and 1273 K. The possibility of using the Kohler method for the calculation of thermodynamic properties in the Bi2 O3 -P2 O5 -SiO2 system was illustrated.

CONCLUSIONS: The excess Gibbs energy of the Bi2 O3 -P2 O5 -SiO2 system obtained in the present study using the Knudsen mass spectrometric method at 950 K and 1273 K demonstrated significant negative deviations from ideal behavior. The excess Gibbs energy values calculated by the Kohler method were shown to be in good agreement with those obtained from experimental data. Copyright © 2016 John Wiley & Sons, Ltd.