Solubility and Diffusion of Chlorine in Silica Glass

Abstract

Abstract Chlorine diffusion profiles in silica glass have been studied by SEM techniques. From the results the diffusion coefficient D (log 10 ( D ·cm −2 s) = −11080 K/T −3.498), the equilibrium solubility of Cl in silica glass (0.25 or 0.32 weight per cent at 1 bar Cl 2 pressure and 1438 K or 1970 K), and the pressure dependence of the solubility were derived. The latter is proportional to the fourth root of the CI 2 pressure. There are no detectable differences in the behaviour of chlorine in silica made by the PCVD method (plasma activated chemical vapour deposition) or in commercially produced silica (HERALUX, wave guide quality), but the chlorine concentration is much higher in PCVD silica than expected from the small chlorine pressures present during deposition.