What is Fused Quartz?
Vitreous silica is the generic term used to describe all types of silica glass with producers referring to the material as either fused quartz or as fused silica. Originally, these terms were used to distinguish between transparent and opaque grades of the material. Fused quartz products were those produced from quartz crystal to make transparent ware, and fused silica described products manufactured from sand into opaque ware.
Today, however, advances in raw material beneficiation permit transparent fusions from sand as well as from crystal. Consequently if naturally occurring crystalline silica (sand or rock) is melted, the material is simply called fused quartz. When silicon dioxide is synthetically derived, however, the material is referred to as synthetic fused silica.
Why is Quartz used in the manufacturing process?
Reactivity
Quartz doesn’t react with most substances, making it an ideal material for demanding and precision process environments. Most acids, metals, chlorine and bromine are unreactive with fused quartz at ordinary temperatures. It is slightly attacked by alkaline solutions, the reaction rate increasing with temperature and concentration of solution. Phosphoric acid will attack fused quartz at temperatures above about 150 C. Hydrofluoric acid alone will attack it at all temperatures. Carbon and some metals will reduce fused quartz; basic oxides, carbonates, sulfates, etc., will react with it at elevated temperatures. For general use, however, it can be concluded that fused quartz is quite unreactive.
Impermeability
Fused quartz is essentially impermeable to most gases, but helium, hydrogen, deuterium and neon may diffuse through the glass. The rate of diffusion increases at higher temperatures and differential pressures.
Flexibility for Manufacturability
Fused quartz can be shaped and fabricated into complex, precision shapes. It’s mechanical properties are much the same as traditional glass. Fused quartz can be used in many demanding environments, from high-pressure to high-vacuum, from high-temperature to very cold temperatures.