Silicon dioxide

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Silicon dioxide
Image:Silicon dioxide.jpg
General
Other names Silica
see text
Molecular formula SiO2
Molar mass 60.1 g/mol
Appearance white or colourless
solid (when pure)
CAS number [14808-60-7]
Properties
Density and phase 2.6 g/cm3, solid
Solubility in water insoluble
Melting point 1610 °C
Boiling point 2230 °C
Structure
Coordination
geometry 		tetrahedral
Crystal structure various
Hazards
MSDS External MSDS
EU classification  
NFPA 704
Image:Nfpa h0.png Image:Nfpa f0.png Image:Nfpa r0.png
R-phrases  
S-phrases  
Flash point non-flammable
Supplementary data page
Structure and
properties 		n, εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions Silicon disulfide
Other cations Carbon dioxide
Germanium dioxide
Tin(IV) oxide
Lead(IV) oxide
Related compounds Silicic acid
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2.

It is found in nature in several forms, including quartz and opal. In fact, silica has 17 crystalline forms (see Nomenclature of Silica). Also, many forms of life include silica structures, including microorganisms such as diatoms, plants such as horsetail, and animals such as hexactinellid sponges.

It is manufactured in several forms including glass (in colorless high purity form called fused silica), synthetic amorphous silica and silica gel (used e.g. as desiccants in brand new clothes and leather goods). Silica is a major ingredient of Portland cement. The ceramic re-entry heat protection tiles mounted on the bottom side of the Space Shuttles are made mostly of silica, as are the firebricks used in steel processing.

The most common constituent of sand in inland continental settings and non-tropical coastal settings is silica, usually in the form of quartz because the considerable hardness of this mineral resists erosion. However, the composition of sand varies according to local rock sources and conditions.

Inhaling crystalline silica dust can lead to silicosis.

Variants found in high-pressure impacts are coesite and stishovite.

Silica is also used as a food additive, primarily as a flow agent in powdered foods, or to absorb water.

Reference

External links

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