Editing Silicon dioxide (section)

==Uses==
===Structural use===
About 95% of the commercial use of silicon dioxide (sand) is in the construction industry, e.g. in the production of concrete ([[Portland cement concrete]]).<ref name=Ull/>

Certain deposits of silica sand, with desirable particle size and shape and desirable [[clay]] and other mineral content, were important for [[sand casting]] of metallic products.<ref>{{cite book|title=Albany moulding sands of the Hudson Valley |first= 	Charles Merrick |last=Nevin|publisher= University of the State of New York at Albany|date= 1925}}</ref> The high melting point of silica enables it to be used in such applications such as iron casting; modern sand casting sometimes uses other minerals for other reasons.

Crystalline silica is used in [[hydraulic fracturing]] of formations which contain [[tight oil]] and [[shale gas]].<ref name="NYT82313">{{cite news|url=https://www.nytimes.com/2013/08/24/business/new-rules-would-cut-silica-dust-exposure.html|title=New Rules Would Cut Silica Dust Exposure|last=Greenhouse S|date=23 Aug 2013|newspaper=[[The New York Times]]|access-date=24 Aug 2013}}</ref>

===Precursor to glass and silicon===
Silica is the primary ingredient in the production of most [[glass]]. As other minerals are melted with silica, the principle of [[freezing point depression]] lowers the melting point of the mixture and increases fluidity. The [[glass transition]] temperature of pure SiO<sub>2</sub> is about 1475 K.<ref>{{cite journal|vauthors=Ojovan MI|year=2004|title=Glass formation in amorphous SiO<sub>2</sub> as a percolation phase transition in a system of network defects|journal=[[Journal of Experimental and Theoretical Physics Letters|JETP Lett.]]|volume=79|issue=12|pages=632–634|bibcode=2004JETPL..79..632O|doi=10.1134/1.1790021|s2cid=124299526}}</ref> When molten silicon dioxide SiO<sub>2</sub> is rapidly cooled, it does not crystallize, but solidifies as a glass.<ref>{{Cite book |last=Stachurski |first=Zbigniew H. |url=https://books.google.com/books?id=DBF1BgAAQBAJ&dq=silicon+dioxide+SiO2+is+rapidly+cooled+but+solidifies+as+a+glass&pg=PA176 |title=Fundamentals of Amorphous Solids: Structure and Properties |date=2015 |publisher=John Wiley & Sons |isbn=978-3-527-68219-5 |pages=176 |language=en}}</ref> Because of this, most [[ceramic glaze]]s have silica as the main ingredient.<ref>{{Cite book |url=https://books.google.com/books?id=qxRhA3MZg6AC&dq=ceramic+glazes+have+silica+as+the+main+ingredient&pg=PA563 |title=Advanced Inorganic Chemistry: Vollume II |publisher=Krishna Prakashan Media |pages=563 |language=en}}</ref>

The structural geometry of silicon and oxygen in glass is similar to that in quartz and most other crystalline forms of silicon and oxygen, with silicon surrounded by regular tetrahedra of oxygen centres. The difference between the glass and crystalline forms arises from the connectivity of the tetrahedral units: Although there is no long-range periodicity in the glassy network, ordering remains at length scales well beyond the SiO bond length. One example of this ordering is the preference to form rings of 6-tetrahedra.<ref>{{cite journal|vauthors=Elliott SR|year=1991|title=Medium-range structural order in covalent amorphous solids|journal=[[Nature (journal)|Nature]]|volume=354|issue=6353|pages=445–452|bibcode=1991Natur.354..445E|doi=10.1038/354445a0|s2cid=4344891}}</ref>

The majority of [[optical fiber]]s for [[telecommunications]] are also made from silica. It is a primary raw material for many ceramics such as [[earthenware]], [[stoneware]], and [[porcelain]].

Silicon dioxide is used to produce elemental [[silicon]]. The process involves [[carbothermic reduction]] in an [[electric arc furnace]]:<ref>{{Cite book|title=Shriver & Atkins' inorganic chemistry|publisher=Oxford University Press|year=2010|isbn=9780199236176|veditors=Atkins PW, Overton T, Rourke J, Weller M, Armstrong F|edition=5th|location=Oxford|pages=354|oclc=430678988|display-editors=3}}</ref>
:<chem>SiO2 + 2 C -> Si + 2 CO</chem>

===Fumed silica===
[[Fumed silica]], also known as pyrogenic silica, is prepared by burning [[silicon tetrachloride|SiCl<sub>4</sub>]] in an oxygen-rich hydrogen flame to produce a "smoke" of SiO<sub>2</sub>.<ref name="Greenwood">{{Greenwood&Earnshaw1st|pages=393–99}}</ref> 
:<chem>SiCl4 + 2 H2 + O2 -> SiO2 + 4 HCl</chem>
It can also be produced by vaporizing quartz sand in a 3000&nbsp;°C electric arc. Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles, a white powder with extremely low bulk density (0.03-0.15 g/cm<sup>3</sup>) and thus high surface area.<ref name=cabot>{{cite web |url=http://www.cabotcorp.com |title= Cab-O-Sil Fumed Metal Oxides}}</ref> The particles act as a [[Thixotropy|thixotropic]] thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications.
[[File:Kieselsaeure380m2prog.jpg|thumb|Manufactured fumed silica with maximum surface area of 380 m<sup>2</sup>/g]]

[[Silica fume]] is an ultrafine powder collected as a by-product of the silicon and [[ferrosilicon]] alloy production. It consists of [[amorphous]] (non-crystalline) spherical particles with an average particle diameter of 150&nbsp;nm, without the branching of the pyrogenic product. The main use is as [[pozzolanic]] material for high performance concrete. Fumed silica nanoparticles can be successfully used as an anti-aging agent in asphalt binders.<ref>{{cite journal |last1=Cheraghian |first1=Goshtasp |last2=Wistuba |first2=Michael P. |last3=Kiani |first3=Sajad |last4=Barron |first4=Andrew R. |last5=Behnood |first5=Ali |title=Rheological, physicochemical, and microstructural properties of asphalt binder modified by fumed silica nanoparticles |journal=Scientific Reports |date=December 2021 |volume=11 |issue=1 |pages=11455 |doi=10.1038/s41598-021-90620-w|pmid=34075083 |pmc=8169902 |bibcode=2021NatSR..1111455C }}</ref>

===Food, cosmetic, and pharmaceutical applications===
Silica, either colloidal, precipitated, or pyrogenic fumed, is a common additive in food production. It is used primarily as a flow or anti-[[caking]] agent in powdered foods such as spices and non-dairy coffee creamer, or powders to be formed into pharmaceutical tablets.<ref name=cabot/> It can [[adsorption|adsorb]] water in [[hygroscopy|hygroscopic]] applications. [[Colloidal silica]] is used as a [[fining agent]] for wine, beer, and juice, with the [[E number]] reference '''E551'''.<ref name=Ull/>

In cosmetics, silica is useful for its light-diffusing properties<ref>{{cite book|url=https://books.google.com/books?id=RIvOBQAAQBAJ&q=silica%20cosmetics%20light%20diffusing&pg=PA444|title=Handbook of Cosmetic Science and Technology|vauthors=Barel AO, Paye M, Maibach HI|publisher=CRC Press|year=2014|isbn=9781842145654|edition=4th|pages=444|quote=These soft-focus pigments, mainly composed of polymers, micas and talcs covered with rough or spherical particles of small diameters, such as silica or titanium dioxide, are used to optically reduce the appearance of wrinkles. These effects are obtained by optimizing outlines of wrinkles and reducing the difference of brightness due to diffuse reflection.}}</ref> and natural absorbency.<ref>{{cite book|url=https://books.google.com/books?id=RIvOBQAAQBAJ&q=silica%20cosmetics%20light%20diffusing&pg=PA444|title=Handbook of Cosmetic Science and Technology|vauthors=Barel AO, Paye M, Maibach HI|publisher=CRC Press|year=2014|isbn=9781842145654|edition=4th|pages=442|quote=The silica is a multiporous ingredient, which absorbs the oil and sebum.}}</ref>

[[Diatomaceous earth]], a mined product, has been used in food and cosmetics for centuries.  It consists of the silica shells of microscopic [[diatoms]]; in a less processed form it was sold as [[Dentifrice#Tooth powder|tooth powder]].<ref>{{Cite journal |last=Gardner |first=J. Starkie |date=1882 |title=On the Causes of Elevation and Subsidence |url=https://www.cambridge.org/core/product/identifier/S0016756800172474/type/journal_article |journal=Geological Magazine |language=en |volume=9 |issue=10 |pages=479–480 |doi=10.1017/S0016756800172474 |bibcode=1882GeoM....9..479G |issn=0016-7568}}</ref><ref>{{Cite book |last=Mann |first=Albert |title=The Economic Importance of the Diatoms |publisher=Smithsonian |year=1917 |location=Washington DC, United States of America}}</ref> Manufactured or mined [[hydrated silica]] is used as the hard abrasive in [[toothpaste]].

===Semiconductors===
{{See also|Surface passivation|Thermal oxidation|Planar process|MOSFET}}

Silicon dioxide is widely used in the semiconductor technology:

* for the primary passivation (directly on the semiconductor surface),
* as an original [[gate dielectric]] in [[MOS technology]]. Today when scaling (dimension of the gate length of the MOS transistor) has progressed below 10&nbsp;nm, silicon dioxide has been replaced by other [[dielectric materials]] like [[hafnium oxide]] or similar with higher dielectric constant compared to silicon dioxide,
* as a dielectric layer between metal (wiring) layers (sometimes up to 8–10) connecting elements and
* as a second passivation layer (for protecting semiconductor elements and the metallization layers) typically today layered with some other dielectrics like [[silicon nitride]].

Because silicon dioxide is a native oxide of silicon it is more widely used compared to other semiconductors like [[gallium arsenide]] or [[indium phosphide]].

Silicon dioxide could be grown on a silicon [[semiconductor]] surface.<ref name="Bassett22">{{cite book |last1=Bassett |first1=Ross Knox |title=To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology |date=2007 |publisher=[[Johns Hopkins University Press]] |isbn=9780801886393 |pages=22–23 |url=https://books.google.com/books?id=UUbB3d2UnaAC&pg=PA22}}</ref> Silicon oxide layers could protect silicon surfaces during [[diffusion processes]], and could be used for diffusion masking.<ref name="Lecuyer">{{cite book |last1=Lécuyer |first1=Christophe |last2=Brock |first2=David C. |title=Makers of the Microchip: A Documentary History of Fairchild Semiconductor |date=2010 |publisher=[[MIT Press]] |isbn=9780262294324 |page=111 |url=https://books.google.com/books?id=LaZpUpkG70QC&pg=PA111}}</ref><ref name="Saxena">{{cite book |last= Saxena|first= A |title = Invention of integrated circuits: untold important facts |url = https://books.google.com/books?id=z7738Wq-j-8C |publisher = [[World Scientific]] |series = International series on advances in solid state electronics and technology |year = 2009 |isbn = 9789812814456 |pages = 96–97}}</ref>

[[Surface passivation]] is the process by which a semiconductor surface is rendered inert, and does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal.<ref name="atalla">{{cite web|title=Martin Atalla in Inventors Hall of Fame, 2009|url=https://www.invent.org/inductees/martin-john-m-atalla|access-date=21 June 2013}}</ref><ref name="Black">{{cite book |last1=Black |first1=Lachlan E. |title=New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface |date=2016 |publisher=[[Springer Science+Business Media|Springer]] |isbn=9783319325217 |page=17 |url=https://books.google.com/books?id=laYFDAAAQBAJ&pg=PA17}}</ref> The formation of a [[Thermal oxidation|thermally]] grown silicon dioxide layer greatly reduces the concentration of [[surface states|electronic states at the silicon surface]].<ref name="Black"/> SiO<sub>2</sub> [[Thin film|films]] preserve the electrical characteristics of [[p–n junction]]s and prevent these electrical characteristics from deteriorating by the gaseous ambient environment.<ref name="Saxena"/> Silicon oxide layers could be used to electrically stabilize silicon surfaces.<ref name="Lecuyer"/> The surface passivation process is an important method of [[semiconductor device fabrication]] that involves coating a [[silicon wafer]] with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. Growing a layer of silicon dioxide on top of a silicon wafer enables it to overcome the [[surface states]] that otherwise prevent electricity from reaching the semiconducting layer.<ref name="atalla"/><ref name="kahng">{{cite web |title=Dawon Kahng |url=https://www.invent.org/inductees/dawon-kahng |website=[[National Inventors Hall of Fame]] |access-date=27 June 2019}}</ref>

The process of silicon surface passivation by [[thermal oxidation]] (silicon dioxide) is critical to the [[semiconductor industry]]. It is commonly used to manufacture [[metal–oxide–semiconductor field-effect transistor]]s (MOSFETs) and silicon [[integrated circuit]] chips (with the [[planar process]]).<ref name="atalla"/><ref name="kahng"/>

===Other===
[[Hydrophobic silica]] is used as a [[anti-foaming agent|defoamer component]].

In its capacity as a [[refractory]], it is useful in fiber form as a high-temperature [[thermal protection]] fabric.<ref>{{Cite journal |last1=Liu |first1=Guoyi |last2=Liu |first2=Yuanjun |last3=Zhao |first3=Xiaoming |date=2017 |title=The Influence of Spherical Nano-SiO 2 Content on the Thermal Protection Performance of Thermal Insulation Ablation Resistant Coated Fabrics |journal=Journal of Nanomaterials |language=en |volume=2017 |pages=1–11 |doi=10.1155/2017/2176795 |doi-access=free |issn=1687-4110}}</ref>

Silica is used in the [[DNA separation by silica adsorption|extraction of DNA]] and [[RNA]] due to its ability to bind to the nucleic acids under the presence of [[chaotropic agent|chaotropes]].<ref>{{cite book|title=An Introduction to Forensic Genetics|vauthors=Goodwin W, Linacre A, Hadi S|publisher=Wiley & Sons|year=2007|isbn=9780470010259|pages=29}}</ref>

[[Silica aerogel]] was used in the [[Stardust (spacecraft)|Stardust spacecraft]] to collect extraterrestrial particles.<ref>{{Cite news|url=https://www.businessinsider.com/aerogel-science-history-kistler-new-applications-2015-8?IR=T|title=This cloud-like, futuristic material has been sneaking its way into your life since 1931|last=Calderone J|date=20 Aug 2015|work=[[Business Insider]]|access-date=11 Feb 2019}}</ref>

Pure silica (silicon dioxide), when cooled as fused quartz into a glass with no true melting point, can be used as a glass fibre for fibreglass.