Hydroxyl and hydride in silica glass could be removed by diffusion process of H molecules. In the course of an hydroxyl and hydride removal kinetic study of silica glasses at high temperatures, an unusual concentration profile of hydroxyl was observed. Namely, as hydroxyl and hydride were removed from a plate sample of a silica glass at 1500C, the initially uniform distribution of hydroxyl changed to a distribution with a minimum at the sample center and two maxima on both sides of the center. This distribution could be explained by postulating the existence of two H removal reactions with different kinetics. Namely

SiOH + SiH → Si–O–Si+H2 and SiH+SiH → Si–[ ]–Si+H2

with the latter reaction taking place more rapidly than the former.

Anomalous Hydroxyl Diffusion Profile in Silica Glass. R.Sato, M.Tomozawa: Journal of Non-Crystalline Solids, 2003, 321[1-2], 66-72