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Kinetic and energetic aspects of diffusion transport of water in glassy and crystalline SiO2 and Al2O3 at high and middle temperaturesтезисы доклада
- Авторы: Kreisberg V.A., Rakcheev V.P., Spivakova N.Ya
- Сборник: Meeting Guide of the XVIII International Congress on Glass, 5-10 July, 1998, San Francisco, USA
- Тезисы
- Год издания: 1998
- Место издания: American Ceramic Society, San Francisco, CA, USA American Ceramic Society, San Francisco, CA, USA
- Первая страница: AB122
- Последняя страница: AB122
- Аннотация: The problems of gas content and gas dynamics in glass are two sides of the one general topic: the influence of gas incorporation on glass properties. Unfortunately, dynamics of gas transport in glasses is not studied yet. The comparative study of diffusion characteristics of glassy and crystalline materials allowed one to establish the role of structural factors in the mechanism of diffusion of water in SiO2 and Al2O3. Diffusion coefficients of water in silica glass KU-1 (type III) produced by hydrolyzation of SiCl4 in an oxygen-hydrogen flame, quartz of natural and artificial origin, corundum were determined for a wider temperature range (up to 1600 C) and for greater numbers of temperatures than it was made before. Diffusion coefficients were calculated from isothermal mass spectral kinetics of gas release into vacuum. Four fractions of the silica glass KU-1 were investigated. It was found that the values of water diffusion coefficients did not depend on fraction composition of the glass and were close to ones for silica glass Suprasil of type III. According to the Arrhenius temperature dependence of water diffusion coefficients for glasses of type III, two linear plots were identified: at high temperature (higher than 850 C) activation energy of diffusion was equal to 66 kJ/mol, at middle temperatures 550-750 C - 126 kJ/mol that is near to activation energy of water diffusion from quartz in over all temperature range (133 kJ/mol). Activation energy of water diffusion from corundum was equal to 164 kJ/mol. To account for the peculiarities of water diffusion transport in glassy and crystalline materials, the model including some factors was supported: 1) kinetic factor - consideration of quasi-equilibrium between concentration of molecular water and hydroxyls in solids; 2) relaxation factor - relaxation of glass structure at high temperature from the state determined by Tg to the state connected with temperature of measurement; 3) structural factor - forming strained rings with smaller number of silicon-oxygen tetrahedra and decreasing the mean effective diameter of the diffusion channels during dehydroxylation.
- Добавил в систему: Крейсберг Валерий Абрамович