Reduction of chlorine content in sol-gel derived silica glass

Abstract

The undesirable influence of chlorine gas in the production of hydroxyl-free and bubble-free silica glass by the sol-gel method was minimized by introducing a dechlorination treatment of the gel during a sintering process. The dechlorination treatment can be effectively carried out in an oxygen atmosphere at 1000 to 1100°C after the gel is chlorinated at 800°C to remove the hydroxyl. The dechlorination reaction seems to be rate-determined by a diffusion process which is probably governed by the adsorption and desorption of chlorine atoms. The reduction of the specific surface area by a pre-sintering process is useful for the reduction of both the hydroxyl and chlorine content in the densified silica glass. The behaviors of adsorbed chlorine and hydroxyl groups are discussed in relation to the densification mechanism.