Silicon Dioxide

The chemical compound silicon dioxide, also known as silica (from the Latin silex), is an oxide of silicon with the chemical formula SiO2. It has been known for its hardness since ancient times. Silica is most commonly found in nature as sand or quartz, as well as in the cell walls of diatoms.

Silica is manufactured in several forms including fused quartz, crystal, fumed silica (or pyrogenic silica), colloidal silica, silica gel, and aerogel.

Silica is used primarily in the production of glass for windows, drinking glasses, beverage bottles, and many other uses. The majority of optical fibers for telecommunications are also made from silica. It is a primary raw material for many whiteware ceramics such as earthenware, stoneware, porcelain, as well as industrial Portland cement.

Silica is a common additive in the production of foods, where it is used primarily as a flow agent in powdered foods, or to absorb water in hygroscopic applications. It is the primary component of diatomaceous earth which has many uses ranging from filtration to insect control. It is also the primary component of rice husk ash which is used, for example, in filtration and cement manufacturing.

Thin films of silica grown on silicon wafers via thermal oxidation methods can be quite beneficial in microelectronics, where they act as electric insulators with high chemical stability. In electrical applications, it can protect the silicon, store charge, block current, and even act as a controlled pathway to limit current flow.

A silica-based aerogel was used in the Stardust spacecraft to collect extraterrestrial particles. 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. As hydrophobic silica it is used as a defoamer component. In hydrated form, it is used in toothpaste as a hard abrasive to remove tooth plaque.

In its capacity as a refractory, it is useful in fiber form as a high-temperature thermal protection fabric. In cosmetics, it is useful for its light-diffusing properties and natural absorbency. Colloidal silica is used as a wine and juice fining agent. In pharmaceutical products, silica aids powder flow when tablets are formed. It is also used as a thermal enhancement compound in ground source heat pump industry.

Read more about Silicon Dioxide:  Crystal Structure, Quartz Glass, Chemistry, Uses, Biomaterials, Health Effects

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... See also Silicate minerals Measured by mass, silicon makes up 27.7% of the Earth's crust and is the second most abundant element in the crust, with only oxygen having a greater abundance ... Silicon is usually found in the form of complex silicate minerals, and less often as silicon dioxide (silica, a major component of common sand) ... Pure silicon crystals are very rarely found in nature ...
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... with current gate oxides with a thickness of around 1.2 nm (which in silicon is ~5 atoms thick) the quantum mechanical phenomenon of electron tunneling ... Silicon dioxide has traditionally been used as the gate insulator ... Silicon dioxide however has a modest dielectric constant ...
Silicon Dioxide - Health Effects
... Plant materials with high silica phytolith content, appear to be of importance to grazing animals, from chewing insects to ungulates ... Studies have shown that it accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation ...
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... to increase the number of bits in a given area of silicon ... In this drawing the red portions represent conductive polysilicon, the blue is silicon dioxide insulating layers, and the yellow is the nitride charge trapping layer ... such a device layers of conducting polysilicon and silicon dioxide dielectric are deposited first on top of a silicon substrate that contains standard CMOS logic elements ...
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