Silicon dioxide
The
chemical compound silicon dioxide, also known as
silica, is the
oxide of
silicon,
chemical formula Si
O2.
Siliceous is an adjective meaning "referring to silica"
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.
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.
* 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 ethanol.
Inhaling crystalline silica dust can lead to
silicosis or cancer.
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.
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.
*R. K. Iler,
The Chemistry of Silica (ISBN 047102404X)
*
Amorphous carbonia* (Tridymite)
* (Quartz)
* (Cristobalite)
*
NIOSH Pocket Guide to Chemical Hazards (amorphous)
*
NIOSH Pocket Guide to Chemical Hazards (crystalline, as respirable dust)
