Property Modification of Silica Glass by Ultrahigh Pressure Heating

Abstract

A high purity silica glass containing a large amount of OH-group was synthesized from high purity silicon tetrachloride by the oxy-hydrogen flame direct hydrolysis method, and the effects of heat-treatment at 900°C under ultrahigh pressure of 10kbar or 20kbar were examined. The glass so treated was optically isotropic and macroscopically amorphous because no birefringence was observed, but a substantial increase in the refractive index was noted. Structural analysis of the 10kbar-treated glass by the laser Raman scattering spectrometry revealed the occurrence of the Raman spectral shifts, indicating a decrease in the Si-O-Si bond angle even though it is basically of the amorphous silica structure. For the 20kbar-treated glass, on the other hand, the analysis revealed the presence of the Raman spectra that are characteristic of α-quartz in addition to those that are characteristic of silica glass.