Dependence of flame characteristics on the bubble generation and hydroxyl content in silica glass

High quality silica glass was prepared by flame fusion Verneuil technique u sing two types of silica powders: purified natural quartz and synthetic sol -gel silica. Two different types of flames, GC2/O-2 and LPG/O-2, with vario us conditions of mixture ratios were used. Bubble generation and hydroxyl i ncorporation were analyzed in these as-fused materials. Silica glass prepar ed with purified natural quartz powder showed large concentration of bubble s in the most recently fused region. The bubbles were generated from the fl uid inclusions present in the grain. Most of the bubbles collapsed during t he fusion process, and depending on the fusion condition it was possible to obtain bubble-free silica glass. A strong dependence of hydroxyl concentra tion on the flame mixture ratio was also observed.