Opaque quartz glass and process for production thereof

摘要

Opaque quartz glass is provided which contains gas bubbles uniformly dispersed therein and is excellent in high-temperature viscosity and heat-insulating property. The opaque quartz glass has a defined apparent density, contains bubbles having a defined average bubble diameter in a defined amount, has a defined total bubble sectional area, generally exhibits a defined linear transmittance at a thickness of 1 mm or larger to projected light of a defined wavelength and contains nitrogen in a defined concentration. The opaque quartz glass is produced by a process comprising packing into a mold a powdery source material of powdery silica having a defined average particle diameter and powdery silicon nitride dispersed therein in a defined amount, heating the powdery source material to one of two first defined temperature ranges (both under vacuum) and further heating the source material up to a second temperature higher than the melting point and not higher than 1900 DEG C. in a vacuum or an inert gas atmosphere for vitrification and bubble formation.