Silicon dioxide#Health effects

File:SiO2repeat.png

File:Si-OCage.svg

File:Quartzrn.PNG

In the majority of silicon dioxides, the silicon atom shows tetrahedral coordination, with four oxygen atoms surrounding a central Si atom ([http://www.mindat.org/min-3337.html see 3-D Unit Cell]). Thus, SiO₂ forms 3-dimensional network solids in which each silicon atom is covalently bonded in a tetrahedral manner to 4 oxygen atoms.{{Citation |title=Crystal Structures of Silica and Metal Silicates |date=2006 |url=https://doi.org/10.1007/0-387-36687-3_10 |work=Structure and Chemistry of Crystalline Solids |pages=233–278 |editor-last=Douglas |editor-first=Bodie E. |access-date=2023-10-08 |place=New York, NY |publisher=Springer |language=en |doi=10.1007/0-387-36687-3_10 |isbn=978-0-387-36687-6 |editor2-last=Ho |editor2-first=Shih-Ming}}{{Cite journal |last1=Nekrashevich |first1=S. S. |last2=Gritsenko |first2=V. A. |date=2014-02-01 |title=Electronic structure of silicon dioxide (a review) |url=https://www.researchgate.net/publication/262894199 |journal=Physics of the Solid State |language=en |volume=56 |issue=2 |pages=207–222 |doi=10.1134/S106378341402022X |bibcode=2014PhSS...56..207N |s2cid=255234311 |issn=1090-6460}} In contrast, CO₂ is a linear molecule. The starkly different structures of the dioxides of carbon and silicon are a manifestation of the double bond rule.{{ cite book | title = Periodicity and the s- and p-Block Elements | author = N. C. Norman | publisher = Oxford University Press | year = 1997 | isbn = 978-0-19-855961-0 | pages = 50–52, 65–67 }}

Based on the crystal structural differences, silicon dioxide can be divided into two categories: crystalline and non-crystalline (amorphous). In crystalline form, this substance can be found naturally occurring as quartz, tridymite (high-temperature form), cristobalite (high-temperature form), stishovite (high-pressure form), and coesite (high-pressure form). On the other hand, amorphous silica can be found in nature as opal and diatomaceous earth. Quartz glass is a form of intermediate state between these structures.{{Citation |title=Chapter 1 General chemistry of silica |date=1979 |url=https://www.sciencedirect.com/science/article/pii/S0301477008608052 |series=Journal of Chromatography Library |volume=16 |pages=1–14 |editor-last=Unger |editor-first=K. K. |access-date=2023-09-12 |publisher=Elsevier |doi=10.1016/s0301-4770(08)60805-2|isbn=978-0-444-41683-4 }}

All of these distinct crystalline forms always have the same local structure around Si and O. In α-quartz the Si–O bond length is 161 pm, whereas in α-tridymite it is in the range 154–171 pm. The Si–O–Si angle also varies between a low value of 140° in α-tridymite, up to 180° in β-tridymite. In α-quartz, the Si–O–Si angle is 144°.

Alpha quartz is the most stable form of solid SiO₂ at room temperature. The high-temperature minerals, cristobalite and tridymite, have both lower densities and indices of refraction than quartz. The transformation from α-quartz to beta-quartz takes place abruptly at 573 °C. Since the transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit.{{cite book|url=https://books.google.com/books?id=cUwwoR-RuJ0C&pg=PA93|title=Ceramic Technology for Potters and Sculptors|vauthors=Cuff YH|publisher=University of Pennsylvania|year=1996|isbn=9780812213775|location=Philadelphia|pages=93–95}} The high-pressure minerals, seifertite, stishovite, and coesite, though, have higher densities and indices of refraction than quartz.{{cite book|title=Silica Stories|vauthors=De La Rocha C, Conley DJ|publisher=Springer|year=2017|isbn=9783319540542|location=Cham|pages=50–55|chapter=Mystical Crystals of Silica|doi=10.1007/978-3-319-54054-2_4}} Stishovite has a rutile-like structure where silicon is 6-coordinate. The density of stishovite is 4.287 g/cm³, which compares to α-quartz, the densest of the low-pressure forms, which has a density of 2.648 g/cm³. The difference in density can be ascribed to the increase in coordination as the six shortest Si–O bond lengths in stishovite (four Si–O bond lengths of 176 pm and two others of 181 pm) are greater than the Si–O bond length (161 pm) in α-quartz.{{cite book|title=Structural Inorganic Chemistry|vauthors=Wells AF|publisher=Oxford Science Publications|year=1984|isbn=9780198553700}}

The change in the coordination increases the ionicity of the Si–O bond.{{cite journal|display-authors=3|vauthors=Kirfel A, Krane HG, Blaha P, Schwarz K, Lippmann T|year=2001|title=Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study|journal=Acta Crystallographica Section A|volume=57|issue=6|pages=663–77|doi=10.1107/S0108767301010698|pmid=11679696|doi-access=free|bibcode=2001AcCrA..57..663K }}

Faujasite silica, another polymorph, is obtained by the dealumination of a low-sodium, ultra-stable Y zeolite with combined acid and thermal treatment. The resulting product contains over 99% silica, and has high crystallinity and specific surface area (over 800 m²/g). Faujasite-silica has very high thermal and acid stability. For example, it maintains a high degree of long-range molecular order or crystallinity even after boiling in concentrated hydrochloric acid.{{cite journal|vauthors=Scherzer J|year=1978|title=Dealuminated faujasite-type structures with SiO₂/Al₂O₃ ratios over 100|journal=J. Catal.|volume=54|issue=2|page=285|doi=10.1016/0021-9517(78)90051-9}}

Molten silica exhibits several peculiar physical characteristics that are similar to those observed in liquid water: negative temperature expansion, density maximum at temperatures ~5000 °C, and a heat capacity minimum.{{cite journal|vauthors=Shell SM, Debenedetti PG, Panagiotopoulos AZ|year=2002|title=Molecular structural order and anomalies in liquid silica|url=http://www.engr.ucsb.edu/~shell/papers/2002_PRE_silica.pdf|journal=Phys. Rev. E|volume=66|issue=1|pages=011202|arxiv=cond-mat/0203383|bibcode=2002PhRvE..66a1202S|doi=10.1103/PhysRevE.66.011202|pmid=12241346|s2cid=6109212|access-date=2009-07-07|archive-date=2016-06-04|archive-url=https://web.archive.org/web/20160604062440/http://www.engr.ucsb.edu/~shell/papers/2002_PRE_silica.pdf|url-status=dead}} Its density decreases from 2.08 g/cm³ at 1950 °C to 2.03 g/cm³ at 2200 °C.{{cite journal|vauthors=Aksay IA, Pask JA, Davis RF|year=1979|title=Densities of SiO₂-Al₂O₃ Melts|url=http://www.princeton.edu/~cml/assets/pdf/7962aksay.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.princeton.edu/~cml/assets/pdf/7962aksay.pdf |archive-date=2022-10-10 |url-status=live|journal=J. Am. Ceram. Soc.|volume=62|issue=7–8|pages=332–336|doi=10.1111/j.1151-2916.1979.tb19071.x}}

The molecular SiO₂ has a linear structure like {{CO2}}. It has been produced by combining silicon monoxide (SiO) with oxygen in an argon matrix.

The dimeric silicon dioxide, (SiO₂)₂ has been obtained by reacting O₂ with matrix isolated dimeric silicon monoxide, (Si₂O₂). In dimeric silicon dioxide there are two oxygen atoms bridging between the silicon atoms with an Si–O–Si angle of 94° and bond length of 164.6 pm and the terminal Si–O bond length is 150.2 pm. The Si–O bond length is 148.3 pm, which compares with the length of 161 pm in α-quartz. The bond energy is estimated at 621.7 kJ/mol.{{cite book|title=Silicon chemistry: from the atom to extended systems|vauthors=Jutzi P, Schubert U|publisher=Wiley-VCH|year=2003|isbn=9783527306473}}

File:P-T Diagram for SiO2.svg

{{chem2|SiO2}} is most commonly encountered in nature as quartz, which comprises more than 10% by mass of the Earth's crust.{{Ullmann|title=Silica|vauthors=Flörke OW, Graetsch HA, Brunk F, Benda L, Paschen S, Bergna HE, Roberts WO, Welsh WA, Libanati C, Ettlinger M, Kerner D, Maier M, Meon W, Schmoll R, Gies H, Schiffmann D|year=2018|doi=10.1002/14356007.a23_583.pub3|display-authors=3}} Quartz is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms coesite and stishovite have been found around impact structures and associated with eclogites formed during ultra-high-pressure metamorphism. The high-temperature forms of tridymite and cristobalite are known from silica-rich volcanic rocks. In many parts of the world, silica is the major constituent of sand.{{cite book|title=An Introduction to Forensic Geoscience|vauthors=Berslien E|publisher=Wiley & Sons|year=2012|isbn=9781405160544|pages=138}}

Even though it is poorly soluble, silica occurs in many plants such as rice. Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates. Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by insects may have developed as a defense mechanism against predation.{{cite journal|vauthors=Massey FP, Ennos AR, Hartley SE|year=2006|title=Silica in grasses as a defence against insect herbivores: Contrasting effects on folivores and a phloem feeder|journal=J. Anim. Ecol.|volume=75|issue=2|pages=595–603|doi=10.1111/j.1365-2656.2006.01082.x|pmid=16638012|doi-access=free|bibcode=2006JAnEc..75..595M }}{{cite journal|vauthors=Keeping MG, Kvedaras OL|year=2008|title=Silicon as a plant defence against insect herbivory: Response to Massey, Ennos and Hartley|journal=J. Anim. Ecol.|volume=77|issue=3|pages=631–3|doi=10.1111/j.1365-2656.2008.01380.x|pmid=18341561|doi-access=free|bibcode=2008JAnEc..77..631K }}

Silica is also the primary component of rice husk ash, which is used, for example, in filtration and as supplementary cementitious material (SCM) in cement and concrete manufacturing.{{Cite journal |last1=Zain |first1=M. F. M. |last2=Islam |first2=M. N. |last3=Mahmud |first3=F. |last4=Jamil |first4=M. |date=2011 |title=Production of rice husk ash for use in concrete as a supplementary cementitious material |url=https://www.sciencedirect.com/science/article/pii/S0950061810003703 |journal=Construction and Building Materials |series=Composite Materials and Adhesive Bonding Technology |volume=25 |issue=2 |pages=798–805 |doi=10.1016/j.conbuildmat.2010.07.003 |issn=0950-0618}}

Silicification in and by cells has been common in the biological world and it occurs in bacteria, protists, plants, and animals (invertebrates and vertebrates).{{Cite journal |last=Perry |first=Carole C. |date=2003 |title=Silicification: The Processes by Which Organisms Capture and Mineralize Silica |url=https://pubs.geoscienceworld.org/msa/rimg/article-abstract/54/1/291/87497/Silicification-The-Processes-by-Which-Organisms?redirectedFrom=fulltext |journal=Reviews in Mineralogy and Geochemistry |volume=1 |issue=54 |pages=291–327|doi=10.2113/0540291 |bibcode=2003RvMG...54..291P }}

Prominent examples include:

• Tests or frustules (i.e. shells) of diatoms, Radiolaria, and testate amoebae.
• Silica phytoliths in the cells of many plants{{cite encyclopedia|last=Radini |first=Anita |title=Archaeobotany: Plant Microfossils |date=2024 |encyclopedia=Encyclopedia of Archaeology |edition=Second |pages=698–707 |editor-last=Nikita |editor-first=Efthymia |url=https://www.sciencedirect.com/science/article/pii/B9780323907996001142 |access-date=2024-06-20 |place=Oxford |publisher=Academic Press |doi=10.1016/b978-0-323-90799-6.00114-2 |isbn=978-0-323-91856-5 |editor2-last=Rehren |editor2-first=Thilo}} including Equisetaceae,{{Cite journal |last1=Neumann |first1=Mike |last2=Wagner |first2=Sandra |last3=Noske |first3=Robert |last4=Tiersch |first4=Brigitte |last5=Strauch |first5=Peter |date=2010 |title=Morphology and Structure of Biomorphous Silica Isolated from Equisetum hyemale and Equisetum telmateia |journal=Zeitschrift für Naturforschung B |language=en |volume=65 |issue=9 |pages=1113–1120 |doi=10.1515/znb-2010-0910 |issn=1865-7117|doi-access=free }} many grasses, and a wide range of dicotyledons.{{Citation |last1=Tubaña |first1=Brenda Servaz |title=Silicon in Soils and Plants |date=2015 |work=Silicon and Plant Diseases |pages=7–51 |editor-last=Rodrigues |editor-first=Fabrício A. |url=https://link.springer.com/10.1007/978-3-319-22930-0_2 |access-date=2024-07-19 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-22930-0_2 |isbn=978-3-319-22929-4 |last2=Heckman |first2=Joseph Raymond |editor2-last=Datnoff |editor2-first=Lawrence E.}}{{Cite journal |last1=Irzaman |first1=Irzaman |last2=Yustaeni |first2=Diah |last3=Aminullah |first3=Aminullah |last4=Irmansyah |first4=Irmansyah |last5=Yuliarto |first5=Brian |date=2021-04-19 |title=Purity, Morphological, and Electrical Characterization of Silicon Dioxide from Cogon Grass (Imperata cylindrica) Using Different Ashing Temperatures |url=https://ejchem.journals.ekb.eg/article_165191.html |journal=Egyptian Journal of Chemistry |volume=64 |issue=8 |language=en |pages=4143–4149 |doi=10.21608/ejchem.2019.15430.1962 |issn=2357-0245}}
• The spicules forming the skeleton of many sponges.{{Cite journal |last1=Uriz |first1=MJ |last2=Turon |first2=Xavier |last3=Becerro |first3=Mikel A. |last4=Agell |first4=Gemma |date=2003 |title=Siliceous spicules and skeleton frameworks in sponges: Origin, diversity, ultrastructural patterns, and biological functions |url=https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/jemt.10395 |journal=Microscopy Research and Technique |language=en |volume=62 |issue=4 |pages=279–299 |doi=10.1002/jemt.10395 |pmid=14534903 |issn=1059-910X}}

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).

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.{{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}} 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.{{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}}

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 SiO₂ is about 1475 K.{{cite journal|vauthors=Ojovan MI|year=2004|title=Glass formation in amorphous SiO₂ as a percolation phase transition in a system of network defects|journal=JETP Lett.|volume=79|issue=12|pages=632–634|bibcode=2004JETPL..79..632O|doi=10.1134/1.1790021|s2cid=124299526}} When molten silicon dioxide SiO₂ is rapidly cooled, it does not crystallize, but solidifies as a glass.{{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}} Because of this, most ceramic glazes have silica as the main ingredient.{{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}}

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.{{cite journal|vauthors=Elliott SR|year=1991|title=Medium-range structural order in covalent amorphous solids|journal=Nature|volume=354|issue=6353|pages=445–452|bibcode=1991Natur.354..445E|doi=10.1038/354445a0|s2cid=4344891}}

The majority of optical fibers 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:{{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}}

:SiO2 + 2 C -> Si + 2 CO

Fumed silica, also known as pyrogenic silica, is prepared by burning SiCl₄ in an oxygen-rich hydrogen flame to produce a "smoke" of SiO₂.{{Greenwood&Earnshaw1st|pages=393–99}}

:SiCl4 + 2 H2 + O2 -> SiO2 + 4 HCl

It can also be produced by vaporizing quartz sand in a 3000 °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/cm³) and thus high surface area.{{cite web |url=http://www.cabotcorp.com |title= Cab-O-Sil Fumed Metal Oxides}} The particles act as a 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

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 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.{{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 }}

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. It can adsorb water in hygroscopic applications. Colloidal silica is used as a fining agent for wine, beer, and juice, with the E number reference E551.

In cosmetics, silica is useful for its light-diffusing properties{{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.}} and natural absorbency.{{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.}}

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 tooth powder.{{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}}{{Cite book |last=Mann |first=Albert |title=The Economic Importance of the Diatoms |publisher=Smithsonian |year=1917 |location=Washington DC, United States of America}} Manufactured or mined hydrated silica is used as the hard abrasive in toothpaste.

{{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 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.{{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}} Silicon oxide layers could protect silicon surfaces during diffusion processes, and could be used for diffusion masking.{{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}}{{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}}

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.{{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}}{{cite book |last1=Black |first1=Lachlan E. |title=New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface |date=2016 |publisher=Springer |isbn=9783319325217 |page=17 |url=https://books.google.com/books?id=laYFDAAAQBAJ&pg=PA17}} The formation of a thermally grown silicon dioxide layer greatly reduces the concentration of electronic states at the silicon surface. SiO₂ films preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by the gaseous ambient environment. Silicon oxide layers could be used to electrically stabilize silicon surfaces. 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.{{cite web |title=Dawon Kahng |url=https://www.invent.org/inductees/dawon-kahng |website=National Inventors Hall of Fame |access-date=27 June 2019}}

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 transistors (MOSFETs) and silicon integrated circuit chips (with the planar process).

Hydrophobic silica is used as a defoamer component.

In its capacity as a refractory, it is useful in fiber form as a high-temperature thermal protection fabric.{{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}}

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

Silica aerogel was used in the Stardust spacecraft to collect extraterrestrial particles.{{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}}

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.

Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz.

Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product.{{Cite book |url=http://link.springer.com/10.1007/978-3-642-22161-3 |title=Quartz: Deposits, Mineralogy and Analytics |date=2012 |publisher=Springer Berlin Heidelberg |isbn=978-3-642-22160-6 |editor-last=Götze |editor-first=Jens |series=Springer Geology |location=Berlin, Heidelberg |language=en |doi=10.1007/978-3-642-22161-3 |bibcode=2012qdma.book.....G |editor-last2=Möckel |editor-first2=Robert}}{{Cite journal |last1=Pan |first1=Xiaodong |last2=Li |first2=Suqin |last3=Li |first3=Yongkui |last4=Guo |first4=Penghui |last5=Zhao |first5=Xin |last6=Cai |first6=Yinshi |date=2022 |title=Resource, characteristic, purification and application of quartz: a review |url=https://linkinghub.elsevier.com/retrieve/pii/S0892687522002102 |journal=Minerals Engineering |language=en |volume=183 |pages=107600 |doi=10.1016/j.mineng.2022.107600|bibcode=2022MiEng.18307600P }}

Precipitated silica or amorphous silica is produced by the acidification of solutions of sodium silicate. The gelatinous precipitate or silica gel, is first washed and then dehydrated to produce colorless microporous silica. The idealized equation involving a trisilicate and sulfuric acid is:

:Na2Si3O7 + H2SO4 -> 3 SiO2 + Na2SO4 + H2O

Approximately one billion kilograms/year (1999) of silica were produced in this manner, mainly for use for polymer composites – tires and shoe soles.

Thin films of silica grow spontaneously on silicon wafers via thermal oxidation, producing a very shallow layer of about 1 nm or 10 Å of so-called native oxide.{{cite book|url=https://books.google.com/books?id=Qi98H-iTgLEC|title=Handbook of Semiconductor Manufacturing Technology|publisher=CRC Press|year=2007|isbn=9781574446753|veditors=Doering R, Nishi Y}}

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 oxidation with O₂

:Si + O2 -> SiO2

or wet oxidation with H₂O.{{cite book|title=Encyclopedia of chemical processing|author=Lee S|publisher=CRC Press|year=2006|isbn=9780824755638}}{{cite book|title=An Introduction To Semiconductor Microtechnology|vauthors=Morgan DV, Board K|publisher=John Wiley & Sons|year=1991|isbn=9780471924784|edition=2nd|location=Chichester, West Sussex, England|pages=72}}

:Si + 2 H2O -> SiO2 + 2 H2

The native oxide layer is beneficial in microelectronics, where it acts as electric insulator with high chemical stability. It can protect the silicon, store charge, block current, and even act as a controlled pathway to limit current flow.{{Cite news|url=https://spectrum.ieee.org/the-silicon-dioxide-solution|title=The Silicon Dioxide Solution: How physicist Jean Hoerni built the bridge from the transistor to the integrated circuit|last=Riordan M|date=2007|work=IEEE Spectrum|access-date=11 Feb 2019}}

Many routes to silicon dioxide start with an organosilicon compound, e.g., HMDSO,{{Cite journal|last1=Chrystie|first1=Robin S. M.|last2=Ebertz|first2=Felix L.|last3=Dreier|first3=Thomas|last4=Schulz|first4=Christof|date=2019-01-28|title=Absolute SiO concentration imaging in low-pressure nanoparticle-synthesis flames via laser-induced fluorescence|journal=Applied Physics B|language=en|volume=125|issue=2|pages=29|doi=10.1007/s00340-019-7137-8|issn=1432-0649|bibcode=2019ApPhB.125...29C|s2cid=127735545}} TEOS. Synthesis of silica is illustrated below using tetraethyl orthosilicate (TEOS).{{Cite journal|last1=Romero-Jaime|first1=A. K.|last2=Acosta-Enríquez|first2=M. C.|last3=Vargas-Hernández|first3=D.|last4=Tánori-Córdova|first4=J. C.|last5=Pineda León|first5=H. A.|last6=Castillo|first6=S. J.|date=August 2021|title=Synthesis and characterization of silica–lead sulfide core–shell nanospheres for applications in optoelectronic devices|url=https://link.springer.com/10.1007/s10854-021-06648-1|journal=Journal of Materials Science: Materials in Electronics|language=en|volume=32|issue=16|pages=21425–21431|doi=10.1007/s10854-021-06648-1|s2cid=236182027|issn=0957-4522}} Simply heating TEOS at 680–730 °C results in the oxide:

:Si(OC2H5)4 -> SiO2 + 2 O(C2H5)2

Similarly TEOS combusts around 400 °C:

:Si(OC2H5)4 + 12 O2 -> SiO2 + 10 H2O + 8 CO2

TEOS undergoes hydrolysis via the so-called sol-gel process. The course of the reaction and nature of the product are affected by catalysts, but the idealized equation is:{{Cite journal|display-authors=3|vauthors=Nandiyanto AB, Kim SG, Iskandar F, Okuyama K|year=2009|title=Synthesis of spherical mesoporous silica nanoparticles with nanometer-size controllable pores and outer diameters|journal=Microporous and Mesoporous Materials|volume=120|issue=3|pages=447–453|doi=10.1016/j.micromeso.2008.12.019|bibcode=2009MicMM.120..447N }}

:Si(OC2H5)4 + 2 H2O -> SiO2 + 4 HOCH2CH3

Being highly stable, silicon dioxide arises from many methods. Conceptually simple, but of little practical value, combustion of silane gives silicon dioxide. This reaction is analogous to the combustion of methane:

:SiH4 + 2 O2 -> SiO2 + 2 H2O

However the chemical vapor deposition of silicon dioxide onto crystal surface from silane had been used using nitrogen as a carrier gas at 200–500 °C.{{cite book|title=An Introduction To Semiconductor Microtechnology|vauthors=Morgan DV, Board K|publisher=John Wiley & Sons|year=1991|isbn=9780471924784|edition=2nd|location=Chichester, West Sussex, England|pages=27}}

Silicon dioxide is a relatively inert material (hence its widespread occurrence as a mineral). Silica is often used as inert containers for chemical reactions. At high temperatures, it is converted to silicon by reduction with carbon.

Fluorine reacts with silicon dioxide to form SiF₄ and O₂ whereas the other halogen gases (Cl₂, Br₂, I₂) are unreactive.

Most forms of silicon dioxide are attacked ("etched") by hydrofluoric acid (HF) to produce hexafluorosilicic acid:

:{{chem2|SiO2 + 6 HF -> H2SiF6 + 2 H2O}}

Stishovite does not react to HF to any significant degree.{{cite journal|last1=Fleischer|first1=Michael|year=1962|title=New mineral names|journal=American Mineralogist|volume=47|issue=2|pages=172–174|publisher=Mineralogical Society of America|url=http://rruff.info/uploads/AM47_805.pdf |archive-url=https://web.archive.org/web/20110722000427/http://rruff.info/uploads/AM47_805.pdf |archive-date=2011-07-22 |url-status=live}}

HF is used to remove or pattern silicon dioxide in the semiconductor industry.

Silicon dioxide acts as a Lux–Flood acid, being able to react with bases under certain conditions. As it does not contain any hydrogen, non-hydrated silica cannot directly act as a Brønsted–Lowry acid. While silicon dioxide is only poorly soluble in water at low or neutral pH (typically, 2 × 10⁻⁴ M for quartz up to 10⁻³ M for cryptocrystalline chalcedony), strong bases react with glass and easily dissolve it. Therefore, strong bases have to be stored in plastic bottles to avoid jamming the bottle cap, to preserve the integrity of the recipient, and to avoid undesirable contamination by silicate anions.{{cite book|url=https://books.google.com/books?id=BY8IAAAAQBAJ&pg=PA421|title=Descriptive Inorganic, Coordination, and Solid State Chemistry|vauthors=Rodgers GE|publisher=Cengage Learning|year=2011|isbn=9781133172482|pages=421–2}}

Silicon dioxide dissolves in hot concentrated alkali or fused hydroxide, as described in this idealized equation:

:SiO2 + 2 NaOH -> Na2SiO3 + H2O

Silicon dioxide will neutralise basic metal oxides (e.g. sodium oxide, potassium oxide, lead(II) oxide, zinc oxide, or mixtures of oxides, forming silicates and glasses as the Si-O-Si bonds in silica are broken successively). As an example the reaction of sodium oxide and SiO₂ can produce sodium orthosilicate, sodium silicate, and glasses, dependent on the proportions of reactants:

:2 Na2O + SiO2 -> Na4SiO4;

:Na2O + SiO2 -> Na2SiO3;

:$(0.25-0.8)$ Na2O + SiO2 -> glass.

Examples of such glasses have commercial significance, e.g. soda–lime glass, borosilicate glass, lead glass. In these glasses, silica is termed the network former or lattice former. The reaction is also used in blast furnaces to remove sand impurities in the ore by neutralisation with calcium oxide, forming calcium silicate slag.

File:Fibreoptic.jpgs composed of high purity silica]]

Silicon dioxide reacts in heated reflux under dinitrogen with ethylene glycol and an alkali metal base to produce highly reactive, pentacoordinate silicates which provide access to a wide variety of new silicon compounds.{{cite journal|last1=Laine|first1=Richard M.|last2=Blohowiak|first2=Kay Youngdahl|last3=Robinson|first3=Timothy R.|last4=Hoppe|first4=Martin L.|last5=Nardi|first5=Paola|last6=Kampf|first6=Jeffrey|last7=Uhm|first7=Jackie|title=Synthesis of pentacoordinate silicon complexes from SiO₂|journal=Nature|volume=353|date=17 October 1991|issue=6345|pages=642–644|doi=10.1038/353642a0|bibcode=1991Natur.353..642L|url=https://deepblue.lib.umich.edu/bitstream/2027.42/62810/1/353642a0.pdf |archive-url=https://web.archive.org/web/20170819150753/http://deepblue.lib.umich.edu/bitstream/2027.42/62810/1/353642a0.pdf |archive-date=2017-08-19 |url-status=live|hdl=2027.42/62810|s2cid=4310228|hdl-access=free}} The silicates are essentially insoluble in all polar solvent except methanol.

Silicon dioxide reacts with elemental silicon at high temperatures to produce SiO:

:SiO2 + Si -> 2 SiO

The solubility of silicon dioxide in water strongly depends on its crystalline form and is three to four times higher for amorphous silica than quartz; as a function of temperature, it peaks around {{convert|340|°C}}.{{cite journal|vauthors=Fournier RO, Rowe JJ|year=1977|title=The solubility of amorphous silica in water at high temperatures and high pressures|url=http://www.minsocam.org/ammin/AM62/AM62_1052.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.minsocam.org/ammin/AM62/AM62_1052.pdf |archive-date=2022-10-10 |url-status=live|journal=Am. Mineral.|volume=62|pages=1052–1056}} This property is used to grow single crystals of quartz in a hydrothermal process where natural quartz is dissolved in superheated water in a pressure vessel that is cooler at the top. Crystals of 0.5–1  kg can be grown for 1–2 months.{{Holleman&Wiberg}} These crystals are a source of very pure quartz for use in electronic applications. Above the critical temperature of water {{convert|647.096|K}} and a pressure of {{convert|22.064|MPa}} or higher, water is a supercritical fluid and solubility is once again higher than at lower temperatures.{{cite journal | url=https://ui.adsabs.harvard.edu/abs/2019EGUGA..21.4614O/abstract | bibcode=2019EGUGA..21.4614O | title=Formation of silica particles from supercritical fluids and its impacts on the hydrological properties in the crust | last1=Okamoto | first1=Atsushi | journal=EGU General Assembly Conference Abstracts | year=2019 | page=4614 }}

File:Piasek kwarcowy.jpg

Silica ingested orally is essentially nontoxic, with an {{LD50}} of 5000 mg/kg (5 g/kg). A 2008 study following subjects for 15 years found that higher levels of silica in water appeared to decrease the risk of dementia. An increase of 10 mg/day of silica in drinking water was associated with a reduced risk of dementia of 11%.{{cite journal|display-authors=3|vauthors=Rondeau V, Jacqmin-Gadda H, Commenges D, Helmer C, Dartigues JF|year=2008|title=Aluminum and Silica in Drinking Water and the Risk of Alzheimer's Disease or Cognitive Decline: Findings from 15-Year Follow-up of the PAQUID Cohort|journal=American Journal of Epidemiology|volume=169|issue=4|pages=489–96|doi=10.1093/aje/kwn348|pmc=2809081|pmid=19064650}}

Inhaling finely divided crystalline silica dust can lead to silicosis, bronchitis, or lung cancer, as the dust becomes lodged in the lungs and continuously irritates the tissue, reducing lung capacities.{{Cite web|url=https://www.silica-safe.org/|title=Work Safely with Silica|publisher=CPWR - The Center for Construction Research and Training|access-date=11 Feb 2019}} When fine silica particles are inhaled in large enough quantities (such as through occupational exposure), it increases the risk of systemic autoimmune diseases such as lupus{{Cite web|url=https://www.niams.nih.gov/about/working-groups/lupus-federal/action-plan|title=Action Plan for Lupus Research|date=2017|website=National Institute of Arthritis and Musculoskeletal and Skin Diseases|publisher=National Institutes of Health|access-date=11 Feb 2019}} and rheumatoid arthritis compared to expected rates in the general population.{{Cite journal|display-authors=3|vauthors=Meyer A, Sandler DP, Beane Freeman LE, Hofmann JN, Parks CG|date=2017|title=Pesticide Exposure and Risk of Rheumatoid Arthritis among Licensed Male Pesticide Applicators in the Agricultural Health Study|journal=Environmental Health Perspectives|volume=125|issue=7|pages=077010-1-077010-7|doi=10.1289/EHP1013|pmid=28718769|pmc=5744649|doi-access=free}}

Silica is an occupational hazard for people who do sandblasting or work with powdered crystalline silica products. Amorphous silica, such as fumed silica, may cause irreversible lung damage in some cases but is not associated with the development of silicosis. Children, asthmatics of any age, those with allergies, and the elderly (all of whom have reduced lung capacity) can be affected in less time.{{cite journal|display-authors=3|vauthors=Reuzel PG, Bruijntjes JP, Feron VJ, Woutersen RA|year=1991|title=Subchronic inhalation toxicity of amorphous silica and quartz dust in rats|journal=Food Chem. Toxicol.|volume=29|issue=5|pages=341–54|doi=10.1016/0278-6915(91)90205-L|pmid=1648030}}

Crystalline silica is an occupational hazard for those working with stone countertops because the process of cutting and installing the countertops creates large amounts of airborne silica.{{cite web|url=https://www.cdc.gov/niosh/docs/2015-106/pdfs/2015-106.pdf |archive-url=https://ghostarchive.org/archive/20221010/https://www.cdc.gov/niosh/docs/2015-106/pdfs/2015-106.pdf |archive-date=2022-10-10 |url-status=live|title=Worker Exposure to Silica during Countertop Manufacturing, Finishing and Installation|date=2015|publisher=National Institute for Occupational Safety and Health and Occupational Safety and Health Administration|access-date=26 Feb 2015}} Crystalline silica used in hydraulic fracturing presents a health hazard to workers.

In the body, crystalline silica particles do not dissolve over clinically relevant periods. Silica crystals inside the lungs can activate the NLRP3 inflammasome inside macrophages and dendritic cells and thereby result in production of interleukin, a highly pro-inflammatory cytokine in the immune system.{{cite journal|display-authors=3|vauthors=Hornung V, Bauernfeind F, Halle A, Samstad EO, Kono H, Rock KL, Fitzgerald KA, Latz E|year=2008|title=Silica crystals and aluminum salts activate the NALP3 inflammasome through phagosomal destabilization|journal=Nat. Immunol.|volume=9|issue=8|pages=847–856|doi=10.1038/ni.1631|pmc=2834784|pmid=18604214}}{{Cite book|url=https://www.cdc.gov/niosh/docs/86-102/86-102.pdf?id=10.26616/NIOSHPUB86102|title=Occupational Respiratory Diseases|publisher=US Department of Health and Human Services, NIOSH|year=1986|veditors=Merchant JA|location=Cincinnati, OH|id=DHHS (NIOSH) Publication Number 86-102|doi=10.26616/NIOSHPUB86102|hdl=2027/uc1.31210023588922}}NIOSH (2002) Hazard Review, Health Effects of Occupational Exposure to Respirable Crystalline Silica. Cincinnati, OH: U.S. Department of Health and Human Services, U.S. Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, [https://www.cdc.gov/niosh/docs/2002-129/ DHHS (NIOSH) Publication No. 2002-129].

Regulations restricting silica exposure 'with respect to the silicosis hazard' specify that they are concerned only with silica, which is both crystalline and dust-forming.{{cite web|url=https://www.osha.gov/OshDoc/data_General_Facts/crystalline-factsheet.pdf|title=Crystalline Factsheet|access-date=3 August 2017|archive-date=22 December 2017|archive-url=https://web.archive.org/web/20171222125021/https://www.osha.gov/OshDoc/data_General_Facts/crystalline-factsheet.pdf|url-status=dead}}{{cite web|url=https://www.osha.gov/dsg/topics/silicacrystalline/|access-date=3 August 2017|title=Silica, Crystalline}}{{cite web|url=http://www.silica-safe.org/ask-a-question/faq|access-date=3 August 2017|title=Frequently Asked Questions}}{{cite web|url=http://www.ehs.uconn.edu/Word%20Docs/Silica%20fact%20sheet.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.ehs.uconn.edu/Word%20Docs/Silica%20fact%20sheet.pdf |archive-date=2022-10-10 |url-status=live|access-date=3 August 2017|title=If It's Silica, It's Not Just Dust!}}{{cite web|url=http://osha.oregon.gov/OSHAPubs/3301.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://osha.oregon.gov/OSHAPubs/3301.pdf |archive-date=2022-10-10 |url-status=live|access-date=3 August 2017|title=What you should know about crystalline silica, silicosis, and Oregon OSHA silica rules}}{{cite book|last1=Szymendera|first1=Scott D.|title=Respirable Crystalline Silica in the Workplace: New Occupational Safety and Health Administration (OSHA) Standards|date=January 16, 2018|publisher=Congressional Research Service|location=Washington, DC|url=https://fas.org/sgp/crs/misc/R44476.pdf |archive-url=https://ghostarchive.org/archive/20221010/https://fas.org/sgp/crs/misc/R44476.pdf |archive-date=2022-10-10 |url-status=live|access-date=27 January 2018}}

In 2013, the U.S. Occupational Safety and Health Administration reduced the exposure limit to 50 μg/m³ of air. Prior to 2013, it had allowed 100 μg/m³ and in construction workers even 250 μg/m³.

In 2013, OSHA also required the "green completion" of fracked wells to reduce exposure to crystalline silica and restrict the exposure limit.

SiO₂, more so than almost any material, exists in many crystalline forms. These forms are called polymorphs.

Inhaling finely divided crystalline silica can lead to severe inflammation of the lung tissue, silicosis, bronchitis, lung cancer, and systemic autoimmune diseases, such as lupus and rheumatoid arthritis. Inhalation of amorphous silicon dioxide, in high doses, leads to non-permanent short-term inflammation, where all effects heal.{{Cite journal|display-authors=3|vauthors=Johnston CJ, Driscoll KE, Finkelstein JN, Baggs R, O'Reilly MA, Carter J, Gelein R, Oberdörster G|date=2000|title=Pulmonary Chemokine and Mutagenic Responses in Rats after Subchronic Inhalation of Amorphous and Crystalline Silica|journal=Toxicological Sciences|volume=56|issue=2|pages=405–413|doi=10.1093/toxsci/56.2.405|pmid=10911000|doi-access=free}}

This extended list enumerates synonyms for silicon dioxide; all of these values are from a single source; values in the source were presented capitalized.{{Cite book|last=Lewis|first=Grace Ross|url=https://archive.org/details/1001ChemicalsInEverydayProducts/page/n261/mode/2up|title=1001 chemicals in everyday products|publisher=John Wiley & Sons (Wiley-Interscience)|year=1999|isbn=0-471-29212-5|edition=2nd|pages=250–1|via=Internet Archive}}

{{Columns-list |colwidth=20em |

• CAS 112945-52-5
• Acitcel
• Aerosil
• Amorphous silica dust
• Aquafil
• CAB-O-GRIP II
• CAB-O-SIL
• CAB-O-SPERSE
• Catalogue
• Colloidal silica{{Cite book |url=https://pubs.acs.org/doi/book/10.1021/ba-1994-0234 |title=The Colloid Chemistry of Silica |date=1994-05-05 |publisher=American Chemical Society |isbn=978-0-8412-2103-1 |editor-last=Bergna |editor-first=Horacio E. |series=Advances in Chemistry |volume=234 |pages=1–47 |location=Washington DC |language=en |doi=10.1021/ba-1994-0234.ch001}}
• Colloidal silicon dioxide
• Dicalite
• DRI-DIE Insecticide 67
• FLO-GARD
• Fossil flour
• Fumed silica
• Fumed silicon dioxide
• HI-SEL
• LO-VEL
• Ludox
• Nalcoag
• Nyacol
• Santocel
• Silica
• Silica aerogel
• Silica, amorphous
• Silicic anhydride
• Silikill
• Synthetic amorphous silica
• Vulkasil

}}

• Mesoporous silica
• Orthosilicic acid
• Silicon carbide

{{Reflist|30em}}

{{Commons category}}

• {{Cite EB1911|wstitle=Silica}}
• Tridymite, {{ICSC|0807|08}}
• Quartz, {{ICSC|0808|08}}
• Cristobalite, {{ICSC|0809|08}}
• Amorphous, [https://www.cdc.gov/niosh/npg/npgd0552.html NIOSH Pocket Guide to Chemical Hazards]
• Crystalline, as respirable dust, [https://www.cdc.gov/niosh/npg/npgd0684.html NIOSH Pocket Guide to Chemical Hazards]
• [http://crystec.com/klloxide.htm Formation of silicon oxide layers in the semiconductor industry]. LPCVD and PECVD method in comparison. Stress prevention.
• {{usurped|1=[https://web.archive.org/web/20110715083534/http://piezomaterials.com/Quartz-SiO2.htm Quartz (SiO₂) piezoelectric properties]}}
• [http://water-chemistry.blogspot.com/2008/08/silica-sio2.html Silica (SiO₂) and water]
• [https://web.archive.org/web/20120618153827/http://www.iom-world.org/pubs/IOM_TM9709.pdf Epidemiological evidence on the carcinogenicity of silica: factors in scientific judgement] by C. Soutar and others. Institute of Occupational Medicine Research Report TM/97/09
• [https://web.archive.org/web/20120618132318/http://www.iom-world.org/pubs/IOM_TM9508.pdf Scientific opinion on the health effects of airborne silica] by A Pilkington and others. Institute of Occupational Medicine Research Report TM/95/08
• [http://www.iom-world.org/pubs/IOM_TM8713.pdf The toxic effects of silica] {{Webarchive|url=https://web.archive.org/web/20160415111007/http://www.iom-world.org/pubs/IOM_TM8713.pdf |date=2016-04-15}} by A. Seaton and others. Institute of Occupational Medicine Research Report TM/87/13
• [http://www.antenchem.com/en/News/Silicas-Technology/Structureofprecipitatedsilica.html Structure of precipitated silica]

{{Silica minerals}}

{{Oxides}}

{{Silicon compounds}}

{{Authority control}}

Category:Ceramic materials

Category:Refractory materials

Category:IARC Group 1 carcinogens

Category:Excipients

Category:E-number additives

Category:Oxides

Category:Occupational safety and health