The H diffusion in a silica glass was investigated at 750 to 1500C. The starting material was a silica glass that was melted in H atmosphere and contained a high concentration of hydroxyl and hydride. After heat treatment at various temperatures in air, the effective H diffusion coefficients were evaluated from the removal rates of hydroxyl and hydride. The obtained diffusion coefficients exhibited an unusual temperature dependence, with the lower diffusion coefficient being observed at 1000 to 1500C. This was attributed to the higher reactivity of H with the glass network at higher temperatures, effectively slowing down the H mobility. Below 1000C, the effective H diffusion coefficient exhibited a normal temperature dependence. This reversal of the temperature dependence of the effective H diffusion coefficient appeared to be related to the reversal of the temperature dependence of the hydroxyl (or hydride) solubility in silica glass.

Hydrogen Diffusion in Fused Silica at High Temperatures. V.Lou, R.Sato, M.Tomozawa: Journal of Non-Crystalline Solids, 2003, 315[1-2], 13-9