Anomalous hydroxyl diffusion profile in silica glass

Hydroxyl and hydride in silica glass can be removed by diffusion process of hydrogen molecules. In the course of our 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 are removed from a plate sample of a silica glass at 1500 degreesC, 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 can be explained by postulating the existence of two hydrogen removal reactions with different kinetics. Namely dropSiOH + dropSiH --> dropSi-O-Sidrop +H-2 and dropSiH + dropSiH --> dropSi-[]-Sidrop + H-2 with the latter reaction taking place more rapidly than the former. (C) 2003 Elsevier Science B.V. All rights reserved.