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SILICA

Silicon dioxide
{{{2}}}
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 1710 °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 R42 R43 R49
S-phrases S22 S36 S37 S45 S53
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. Siliceous is an adjective meaning "referring to silica"

Contents

In nature

Silica is found in nature in several forms, including quartz and opal. In fact, it has 17 crystalline forms (see Nomenclature of Silica).

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.

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

Many forms of life contain silica structures (Biogenic Silica), including microorganisms such as diatoms, plants such as horsetail, and animals such as hexactinellid sponges. It is present in the cell walls of various plants (including edible ones) to strengthen their structural integrity.

Applications

Silica is manufactured in several forms including:

It is used in the production of various products.

  • Inexpensive soda-lime glass is the most common and typically found in drinking glasses, bottles, and windows.
  • Silica, along with alumina (silica-alumina), forms a major part of the crystal lattice of clay minerals. These decompose on firing and form part of the microstructure of clay based ceramics such as earthenware, stoneware and porcelain
  • 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 (see HRSI), as are the firebricks used in steel processing.
  • It is the substance upon which silica aerogels are based.
  • Silica is also used as a food additive, primarily as a flow agent in powdered foods, or to absorb water (see the ingredients list for Burger King).
  • The natural skin, or oxide coating, that grows on silicon is hugely beneficial in microelectronics. It is a superior insulator, possessing high chemical stability, and in electrical applications it can protect the silicon, store charge, block current, and even act as a controlled pathway to allow small currents to flow through a device. At room temperature, however, it grows extremely slowly, and so to manufacture such oxide layers on silicon, the traditional method has been the deliberate heating of silicon in high temperature furnaces within an oxygen ambient.
  • Silica is the central component in most glass optical fibers.
  • Silica in the form of Silicon Dioxide Ph. Eur. 6x. is also used as a homeopathic remedy to treat impure blood, brittle nails and lack lustre hair.
  • Silica is also used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes.
  • Silica is added to medicinal anti-foaming agent, like Simethicone, with a small portion to enhance defoaming activity.

Health Effects

Inhaling crystalline silica dust can lead to silicosis or cancer.

Homeopathic Usage

Silicon Dioxide (Silica) is widely used as a homeopathic remedy to treat impure blood, boils, brittle nails and lack-lustre hair. The homeopathic usage of Silicon Dioxide was introduced in the 19th century by Dr. Wilhelm Heinrich Schüßler (1821-1898) through his Biochemic method of healing.

Dr. Schüßler, a doctor of medicine, physiological chemist and a physicist concluded that the normal functioning of cells are dependant on a normal dosage of 12 inorganic mineral salts, one of which included Silicon Dioxide.

Chemistry

Silicon dioxide can be formed when silicon is exposed to oxygen (or air) at extremely high temperatures.

Silicon dioxide is attacked by hydrofluoric acid (HF). HF is used to remove or pattern silicon dioxide in the semiconductor industry.

Reference

See also

External links