The silica is a chemical Composé (di Oxyde of Silicium) and a Minéral of formula SiO.

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History

Properties

Silica is a Oxyde Acide which reacts with basic oxides to give silicates (SiO₃^2- ions, similar to the ion Carbonate and SiO₄^4- inter alia). The majority presence of silicates makes silicon the 2nd element masses some in the earth's crust behind oxygen. Silica pure is appeared as a hard mineral and exists in forms varied in nature:

• principal constituting sedimentary rocks detrital (Sand S, sandstone), it accounts for 27% of the Earth's crust;
• attends in the metamorphic rocks;
• attends in the magmatic rocks: quartz in the magmatic rocks acid, Amorphous Crystal smooth or in the volcanic rocks .

Silica is a transparent material in all the visible field what gives him interesting applications in optics. However its properties of transparency are lost in fields UV in infra-red, which imposes the use of other materials to work in these wavelengths for example in infra-red spectrometry. This effect is made profitable in the greenhouse effect where the light can penetrate but whose infra-reds cannot leave, from where a heating or, at least, the maintenance of a more high temperature than outside without heating.

Silica is a formed molecular crystal of tetrahedral reasons SiO₄ dependant between them by the oxygen atoms systematically in the crystals like quartz and irregular in glass.

Silica is used as raw material with obtaining silicon. It is reduced in light-arc furnaces with more 2000°C by carbon according to the reaction:

SiO₂ + 2C - > 2 CO + If

Silica is also used as support insulating in electronic.

Applications

The glass of silica is silica not crystallized used in the manufacture of the instruments of Optique, of laboratoryes apparatus and Glass fiber.

Silica is chemically stable and is hardly attacked but by the hydrofluoric Acid , reaction used in the Gravure on Verre. This reaction prevents from using silica glass to handle the Fluor.

It dissolves in the Eau in the form of If (OH) the silicic acid (weak acid), the limit of Solubilité being of 0,140 g/l with 25°C. This solubility very strongly increases with the temperature and the pressure; thus this solubility reaches 20% in water Supercritique with 500°C and 1000 bars.

In water, the silicic acid forms colloids which are responsible for a coloring opal of water when they are in suspension. It is the case in the water of the geysers like that of Geysir in Iceland. For a concentration given out of silica colloidal, the blue color is all the more intense as water is cold (the solubility of If (OH) is then weaker).

Silica is also one of best the electrical insulator which exists. For cettre reason, it is often used on silicon electrical circuits, simply by oxidizing the desired layers.

In Organic chemistry

The Silicium is in certain organic molecules, like the Silane S - Méthylsilanetriol S, Diméthylsilanediol -, the Silatrane S, the Thujaplicine, the Siloxane S.

By abuse, some speak about “organic silica”. It seems that this denomination is rather a commercial process in the field of the parallel medicines.

See too

• Silica gel

silica|silica

Related articles

• Silicate

• Silicosis
• Citrine Chalcedony
• Cornaline
• Glossary of the minerals
• Petrography

External bonds

• File on silica: In the middle of the silica… of flint to the wafer

Simple: Silicon dioxide

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