Silica

Name:
Silica
Detailed information:

Chemistry name:	silicon dioxide
M Formula:	SiO2
Properties:
Colorless crystals or white powder; odorless and tasteless. D 2.2–2.6; thermal conductivity about half that of glass, mp 1710C, bp 2230C, high dielectric constant, high heat and shock resistance. Insoluble in water and acids except hydrogen fluoride; soluble in molten alkai when finely divided and amorphous. Combines chemically with most metallic oxides; melts to a glass with lowest known coefficient of expansion (fused silica). Noncombustible.
Derivation:
Can be made from a soluble silicate (water glass) by acidification, washing and ignition. Arc silica is made from sand, vaporized in a 3000C electric arc.
Grade:
By purity and mesh size, silica aerogel, hydrated, precipitated.
Hazard:
Toxic by inhalation, chronic exposure to dust may cause silicosis.
Use:
(Powder) Manufacture of glass, water glass, ceramics, abrasives, water filtration, microspheres, component of concrete, source of ferrosilicon and elemental silicon, filler in cosmetics, pharmaceuticals, paper, insecticides, hydrated and precipitated grades as rubber reinforcing agent, including silicone rubber, anticaking agent in foods, flattening agents in paints, thermal insulator. (Fused) Ablative material in rocket engines, spacecraft, etc.; fibers in reinforced plastics; special camera lenses. (Amorphous) Silica gel.

See Quartz; Silicic Acid; Silica Gel.