The diffusion of water into silica glass, at temperatures below 1000C, exhibited a time-dependence in which the diffusion coefficient first decreased and then increased with time; at a constant temperature under a constant water-vapour pressure. The H2O solubility exhibited the reverse trend, in that it initially increased with time and subsequently decreased. The initial decrease in diffusion coefficient, and increase in solubility, with time was attributed to a decrease in the self-stress around the diffusing water molecules; via stress relaxation in the surrounding glass. The subsequent increase in diffusion coefficient, and decrease in solubility, with time was attributed to structural relaxation of the glass and to a corresponding change in the glass-water reaction equilibrium constant.

Time Dependent Diffusion Coefficient of Water into Silica Glass at Low Temperatures. M.Tomozawa, K.M.Davis: Materials Science and Engineering A, 1999, 272[1], 114-9