Bubble-free (tubular) silica glass prodn. - e.g. for lamps, by heating waste silica powder to convert it to cristobalite

摘要

Silica glass (I) having a low bubble content is produced from waste (I) by crushing (I) to a particle size of 100-400mu and heating the powder in an H2-contg. protective atmos. at 1400-1600 degrees C for 30-300 mins. to form a cristobalite layer whose thickness is >=10 mu (or the whole particle, depending on its size). The powder is then melted by conventional methods and formed into tubes, esp. for lamps. Cristobalite has a higher m.pt. than quartz, and consequently a lower melt viscosity which facilitates degassing and produces tubes of higher quality.