Opakes Quarzglas und Verfahren zu dessen Herstellung

摘要

An 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 an apparent density ranging from 1.7 to 2.1 g/cm<3>, containing bubbles having an average bubble diameter ranging from 10 to 100 mu m in an amount ranging from 3x10<5> to 5x10<6> bubbles/cm<3>, having a total bubble sectional area ranging from 10 to 40 cm<2>/cm<3>, exhibiting a linear transmittance of not higher than 3% at a thickness of 1 mm or larger to projected light of wavelength ranging from 300 to 900 nm, and containing nitrogen at a concentration ranging from 1 to 50 ppm. The opaque quartz glass is produced by a process comprising packing into a heat-resistant mold a powdery source material composed of powdery silica having an average particle diameter ranging from 10 to 500 mu m and powdery silicon nitride dispersed therein in an amount ranging from 0.001 to 0.05 part by weight based on 100 parts by weight of the powdery silica; heating the powdery source material up to a first temperature of not lower than the melting temperature thereof and not higher than 1900 DEG C or heating the powdery source material up to a temperature of not lower than 1400 DEG C and lower than the melting temperature therof in vacuum atmosphere; further heating the source material up to a temperature higher than the melting point and not higher than 1900 DEG C in an inert gas atmosphere for vitrification and bubble formation.