Synthetic quartz powder and silica gel powder

摘要

A synthetic quartz powder obtained by calcining a powder of silica gel, characterized in that white devitrification spots having sizes of larger than 20 mu m in diameter formed in an ingot obtained by vacuum melting the synthetic quartz powder at a temperature of from 1780 to 1800 DEG C to form an ingot, followed by maintaining the ingot at a temperature of 1630 DEG C for 5 hours, are at most 10 spots/50 g.