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The chemical compound silicon dioxide, also known as silica or silox (from the Latin "silex"), is the oxide of silicon, chemical formula SiO2, and has been known for its hardness since the 9th century. Silica is most commonly found in nature as sand or quartz. It is a principal component of most types of glass and substances such as concrete.
Silica is manufactured in several forms including:
It is used in the production of various products.
Inhaling finely divided crystalline silica dust in very small quantities (OSHA allows 0.1mg/m3) over time can lead to silicosis, bronchitis or (much more rarely) cancer, as the dust becomes lodged in the lungs and continuously irritates them, reducing lung capacities (silica does not dissolve over time). This effect can be an occupational hazard for people working with sandblasting equipment, products that contain powdered silica, and so on. But children, asthmatics of any age, allergy sufferers and the elderly, all of whom have reduced lung capacity, can be affected in much shorter periods of time.
In all other respects, silicon dioxide is inert and harmless. When silica is ingested orally, it passes unchanged through the gastrointestinal tract, exiting in the feces, leaving no trace behind. Small pieces of silicon dioxide are equally harmless, as long as they are not large enough to mechanically obstruct the GI tract, or jagged enough to lacerate its lining. Silicon dioxide produces no fumes and is insoluble in vivo. It is indigestible, with zero nutritional value and zero toxicity.
Silicon dioxide is formed when silicon is exposed to oxygen (or air). A very thin layer (approximately 1 nm or 10 Å) of so-called 'native oxide' is formed on the surface when silicon is exposed to air under ambient conditions. Higher temperatures and alternate environments are used to grow well-controlled layers of silicon dioxide on silicon.
Silicon dioxide is attacked by hydrofluoric acid (HF). HF is used to remove or pattern silicon dioxide in the semiconductor industry.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Silicon_dioxide". A list of authors is available in Wikipedia.|