silicon+dioxide



The [|chemical compound] **silicon dioxide**, also known as **silica** (from the [|Latin] // [|silex] //), is an [|oxide] of [|silicon] with the [|chemical formula] ** SiO 2 **. It has been known for its hardness since antiquity. 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, trademarked Aerosil or Cab-O-Sil), [|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.



Silicon dioxide is formed when silicon is exposed to oxygen (or air). A very shallow layer of so-called native oxide is formed on the surface when silicon is exposed to air under ambient conditions. Higher temperatures and alternative environments are used to grow well-controlled layers of silicon dioxide on silicon, for example at temperatures between 600 and 1200 °C, using so-called dry or wet oxidation with O2 or H2O, respectively. The depth of the layer of silicon replaced by the dioxide is 44% of the depth of the silicon dioxide layer produced.