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 using 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 various conditions of mixture ratios were used. Bubble generation and hydroxyl incorporation were analyzed in these as-fused materials. Silica glass prepared with purified natural quartz powder showed large concentration of bubbles in the most recently fused region. The bubbles were generated from the fluid inclusions present in the grain. Most of the bubbles collapsed during the fusion process, and depending on the fusion condition it was possible to obtain bubble-free silica glass. A strong dependence of hydroxyl concentration on the flame mixture ratio was also observed.