High purity opaque silica glass

摘要

Opaque silica glass having a density of 2.0 to 2.18 g/cm3, sodium and potassium elements concentrations in the silica glass of each 0.5 ppm or less and an OH group concentration of 30 ppm or less, and containing bubbles which are independent bubbles having the following physical values: a bubble diameter of 300 mu m or less, and a bubble density of 100,000 to 1,000,000 bubbles/cm3, and a production process for opaque silica glass, including: filling quartz raw material grain having a particle size of 10 to 350 mu m in a heat resistant mold, heating it in a non-oxidizing atmosphere from a room temperature up to a temperature lower by 50 to 150 DEG C. than a temperature at which the above raw material grain is melted at a temperature-raising speed not exceeding 50 DEG C./minute, then, slowly heating it up to a temperature higher by 10 to 80 DEG C. than the temperature at which the quartz raw material grain is melted at the speed of 10 DEG C./minute or less, and cooling after maintaining at the above temperature.