SILICA

Chemical Properties

Silicon dioxide/crystalline silica is a component of many mineral dusts and materials which melts to a glass at very high temperature.

Uses

Because of its unique physical and chemical properties, crystalline silica has many uses. Commercially produced silica products include quartzite, tripoli, ganister, chert, and novaculite. Crystalline silica also occurs in nature as agate, amethyst, chalcedony, cristobalite, flint, quartz, tridymite, and, in its most common form, sand (IARC 1997). Naturally occurring silica materials are classified by end use or industry. Sand and gravel are produced almost exclusively for road building and concrete construction, depending on particle size and shape, surface texture, and porosity (IARC 1987).

Definition

A hygroscopic substance such as activated alumina, calcium chloride, silica gel, or zinc chloride. Such substances adsorb water vapor from the air and are used to maintain a dry atmosphere in containers for food packaging, chemical reagents, etc.

Definition

Cristobalite: a mineral form of silicon(IV) oxide, SiO₂.

General Description

Rounded silica sand is the naturally occurring sand usually mined from glacial deposits, sometimes called Ottawa sands. Silica sand is essentially made of quartz (SiO2 ) grains.
Pressure range: 28 < σc < 35 MPa (4 < σc < 5 ksi)
Advantages: Low cost, low density, wide availability, and excellent chemical resistance in acidic media except those containing free HF
Drawbacks: Low permeability, low crushing strength, and poor resistance to flow back

Safety Profile

Confirmed carcinogen with experimental carcinogenic and tumorigenic data. Poison by intratracheal route. An inhalation hazard. Human systemic effects by inhalation: cough, dyspnea, fibrosis. About twice as toxic as silica in causing sihcosis. See also other sdica entries

Synthesis

Squartz is silica, the chemical molecular formula for SiO2nH2O, because of its use is similar to carbon black and white, so it is named silica. Silica can be divided into precipitated silica (precipitated hydrated silica) and fumed silica (fumed silica) according to the different production methods, the two products have different production methods, properties and uses are also very different.

The fumed production method mainly uses silicon tetrachloride and air combustion of silica, fine particles, median particle size up to 5 microns or less.

Precipitation method uses sodium silicate with sulfuric acid to precipitate the silica. The median particle size is about 7-12 microns. Fumed silica is expensive, does not easily absorb moisture, and is more commonly used in coatings as a matting agent.