Abstract: A fused quartz article, such as a muffle tube or crucible, with enhanced creep resistance. The enhanced creep resistance is the result of controlled devitrification of the fused quartz article. Controlled devitrification is achieved by coating the article with a colloidal silica slurry doped with metal cations, such as barium, strontium, and calcium. The metal cations in the slurry promote nucleation and growth of cristobalite crystals into the fused quartz at temperatures in the range from about 1000° C. to about 1600° C. The cristobalite has significantly higher viscosity, and therefore greater creep resistance at elevated temperatures, than fused quartz. Methods for applying a doped coating to a fused quartz article and improving the creep resistance of a fused quartz article are also disclosed.

Abstract: A fused quartz article, such as a muffle tube or crucible, with enhanced creep resistance. The enhanced creep resistance is the result of controlled devitrification of the fused quartz article. Controlled devitrification is achieved by coating the article with a colloidal silica slurry doped with metal cations, such as barium, strontium, and calcium. The metal cations in the slurry promote nucleation and growth of cristobalite crystals into the fused quartz at temperatures in the range from about 1000° C. to about 1600° C. The cristobalite has significantly higher viscosity, and therefore greater creep resistance at elevated temperatures, than fused quartz. Methods for applying a doped coating to a fused quartz article and improving the creep resistance of a fused quartz article are also disclosed.

Abstract: An opaque silica comprises silica and at least one second phase solid material. The at least one second phase solid material is essentially uniformly dispersed in the silica. A cut surface formed through the silica is free from surface defects since the at least one second phase solid material forms an opaque silica that is free from porosity.

Abstract: A method and apparatus for detecting impurities in quartz sand. The apparatus comprises at least one light source; at least one light detector assembly; a transport device; and a signal processor that receives the at least one signal from the at least one light detector assembly. The method comprises moving the quartz sand; illuminating the quartz sand to excite luminescence emission from impurities; receiving luminescence emission from the impurity; generating at least one signal indicative of the excited luminescence emission from the impurity; and determining if the signal represents an impurity in quartz sand.