Publication Date:
2017-05-10
Description:
Anomalous water diffusion into SiO 2 glass was observed in a low temperature range, below ~ 850°C, under a constant water vapor pressure of 355 Torr (47.3 kPa). Both the effective water diffusion coefficient and water solubility exhibited an anomalous time-dependence. For example, water solubility in the low temperature range increased initially, achieving much higher values than expected based on extrapolation from higher temperature data, and then decreased with time toward an equilibrium value. This phenomenon was reported earlier, but a complete explanation was not possible; a new model is presented based upon glass surface compressive stress generation and subsequent surface stress relaxation. Water diffusion can promote stress generation and stress relaxation, both of which affect the reaction between diffused molecular water and the glass structure. By considering these stress effects, the anomalous water diffusion behavior in silica glass is explained. Furthermore, the same model can account for the reversal of external tensile and compressive stress effects on water solubility and diffusivity in silica glass observed after a few hours of heat-treatment at 650°C in 355 Torr water vapor pressure. This article is protected by copyright. All rights reserved.
Print ISSN:
0002-7820
Electronic ISSN:
1551-2916
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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