Silicon dioxide

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"

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:

glass (a colorless, high-purity form is called fused silica)
synthetic amorphous silica
silica gel (used e.g. as desiccants in new clothes and leather goods)

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, with alumina (silica-alumina), is a crucial ingredient in clay and allows for the development of an interlocking crystal matrix after firing in earthenware, stoneware and porcelain ceramic processes.
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 marvellous 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. ^*

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. Willhelm Heinrich Shuessler (1821-1898) through his Biochemic method of healing.

Dr. Schuessler, 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

R. K. Iler, The Chemistry of Silica (ISBN 047102404X)

External links

(Tridymite)
(Quartz)
(Cristobalite)
NIOSH Pocket Guide to Chemical Hazards (amorphous)
NIOSH Pocket Guide to Chemical Hazards (crystalline, as respirable dust)

Silicon compounds | Oxides | Ceramic materials | Refractory materials

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