The aluminum content synthetic quartz glass powder, being the aluminum content quartz glass compact and the silica gel powder which contains

摘要

PROBLEM TO BE SOLVED: To suppress crystallization of a formed body when used at a high temp. by controlling the number of devitrified spots of a specified size to a specified value or smaller produced in an ingot which is obtd. by fusing in vacuum at a specified temp. when the ingot is kept under specified conditions.;SOLUTION: The synthetic quartz glass powder after produced is fused in vacuum at 1,780 to 1,800°C to obtain an ingot. When the ingot is kept at 1,630°C for 5 hours, the number of devitrified spots having ≥20 μm diameter produced in the ingot is specified to ≤10 per 50 g, preferably ≤5 per 50 g. The synthetic quartz glass powder contains Al so as to improve the high temp. viscosity of the final glass product, and the Al content is preferably controlled to 0.5 to 500 ppm. The synthetic quartz glass powder is preferably produced by a sol-gel method by reacting a silicon alkoxide with water to hydrolyze, gelatinizing and drying the product to obtain a silica gel, and vitrifying the gel.;COPYRIGHT: (C)2000,JPO