Changes in the state of water during phase transformations in silica exposed to water vaporстатья

Статья опубликована в высокорейтинговом журнале

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Дата последнего поиска статьи во внешних источниках: 10 ноября 2014 г.

Работа с статьей


[1] Changes in the state of water during phase transformations in silica exposed to water vapor / M. N. Danchevskaya, V. A. Kreisberg, V. P. Rakcheev et al. // Inorganic Materials. — 1999. — Vol. 35, no. 10. — P. 1060–1063. In the presence of supercritical water vapor (400 degrees C, 20-30 MPa), amorphous silica transforms to SiO2-X in a few hours, then to cristobalite in 5-20 h, and finally to quartz in 10-60 h. Changes in the state of constitutional water were found to closely correlate with the structural transformations of silica. Silica structurization and water desorption were followed by mass spectrometric measurements and H-1 NMR and Si-29 NMR. The water content of silica passes through a maximum (2-2.5 wt %) early in the formation of SiO2-X and then decreases to 0.5 wt % in cristobalite and 0.01-0.03 wt % in quartz. The structural transformations include silica hydroxylation accompanied by the breaking of siloxane bonds and followed by dehydroxylation and structure rearrangement. The rate of water exchange between the silica matrix and supercritical water decreases with time, while the activation energy of water outdiffusion rises. The diffusion coefficient of water in quartz is determined. The states of constitutional water in quartz and corundum prepared in the presence of supercritical water are compared.

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