Editing Silicon dioxide (section)

===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>