Fused quartz or silica glass is made of pure quartz, differing from traditional glass in containing no other ingredients. Fused silica has high working and melting temperatures, and has superior optical and thermal properties to other types of glass. Fused quartz glass also has better UV transmission than other types of glasses, and an extremely low coefficient of thermal expansion, around 5.5×10^(-7) (20-320 degrees C), which allows it to undergo rapid temperature changes without being damaged. These properties make quartz suitable for use in semiconductor fabrication, solar PV fabrication, laboratory glassware, lenses and optical applications, and precision mirror substrates. For more details on the qualities of quartz glass, please see our page relating to such.
Fused quartz is produced by melting high purity quartz sand at around 2000 degrees centigrade. This is done either in an electrically heated furnace—electrically fused quartz glass—or gas/oxygen fueled furnace—flame fused quartz glass. The resulting glass is usually transparent, but can be made opaque with the inclusion of small air bubbles trapped within the material. Depending on the water content of the quartz, the infrared transmission can be adjusted for (an IR grade material usually has [OH] content of <10ppm). Flame fusion material always has higher water content due to the hydrocarbons and oxygen forming OH groups within the material.