View source for Silicon tetrafluoride

{{chembox
| Watchedfields = changed
| verifiedrevid = 441025594
| Name = Silicon tetrafluoride
| ImageFile = Silicon-tetrafluoride-2D-dimensions.png

| ImageName = Silicon tetrafluoride
| ImageFile1 = Silicon-tetrafluoride-3D-vdW.png

| ImageName1 = Silicon tetrafluoride
| IUPACName = Tetrafluorosilane<br/>Silicon tetrafluoride
| OtherNames = Silicon fluoride<br/>Fluoro acid air
|Section1={{Chembox Identifiers
| SMILES = F[Si](F)(F)F
| CASNo = 7783-61-1
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = K60VCI56YO
| PubChem = 24556
| RTECS = VW2327000
| UNNumber = 1859
  }}
|Section2={{Chembox Properties
| Formula = SiF<sub>4</sub>
| MolarMass = 104.0791 g/mol
| Appearance = colourless gas, fumes in moist air
| Density = 1.66 g/cm<sup>3</sup>, solid (−95 °C)<br> 4.69 g/L (gas)
| Solubility = decomposes
| MeltingPtC = -95.0
| MeltingPt_ref = <ref name=collins>''Silicon Compounds, Silicon Halides.'' Collins, W.: Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley & Sons, Inc, 2001.</ref><ref name=":1" />
| BoilingPtC = −90.3
| BoilingPt_ref = <ref name=collins/>
| CriticalTP = {{convert|&minus;14.15|C|F K|1}}, {{convert|36.71|atm|kPa psi|1}}<ref>{{cite book|url=https://api.pageplace.de/preview/DT0400.9781000102574_A40413991/preview-9781000102574_A40413991.pdf|last1=Lide|first1=David R.|last2=Kehiaian|first2=Henry V.|title=CRC Handbook of Thermophysical and Themochemical Data|year=1994|page=28|publisher=CRC Press}}</ref>
  }}
|Section3={{Chembox Structure
| MolShape = tetrahedral
| Dipole = 0 [[Debye|D]]
  }}
|Section7={{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0576.htm ICSC 0576]
| MainHazards = toxic, corrosive
| HPhrases = 
| PPhrases = 
| GHS_ref  = 
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 2
| NFPA-S = W
| LCLo = 69.220 mg/m<sup>3</sup> (rat, 4 hr)<ref>{{IDLH|fluoride|Fluorides (as F)}}</ref>
  }}
|Section8={{Chembox Related
| OtherAnions = [[Silicon tetrachloride]]<br/>[[Silicon tetrabromide]]<br/>[[Silicon tetraiodide]]
| OtherCations = [[Carbon tetrafluoride]]<br/>[[Germanium tetrafluoride]]<br/>[[Tin tetrafluoride]]<br/>[[Lead tetrafluoride]]
| OtherCompounds = [[Hexafluorosilicic acid]]
  }}
}}

'''Silicon tetrafluoride''' or '''tetrafluorosilane''' is a [[chemical compound]] with the formula [[silicon|Si]][[Fluorine|F]]<sub>4</sub>.  This colorless gas is notable for having a narrow liquid range: its boiling point is only 4&nbsp;°C above its melting point. It was first prepared in 1771 by [[Carl Wilhelm Scheele]] by dissolving silica in [[hydrofluoric acid]],{{sfn|Greenwood|Earnshaw|1997|p=328}} and later synthesized by [[John Davy (chemist)|John Davy]] in 1812.<ref>{{cite journal
| title = An Account of Some Experiments on Different Combinations of Fluoric Acid
| author = John Davy
| journal = [[Philosophical Transactions of the Royal Society of London]]
| year = 1812
| volume = 102
| issue =
| pages = 352–369
| doi = 10.1098/rstl.1812.0020
| issn = 0261-0523
| jstor =107324
| doi-access = free
}}</ref>  It is a tetrahedral molecule and is corrosive.<ref name=":0">{{Cite web |date=November 2001 |title=Hazardous Substance Fact Sheet |url=https://nj.gov/health/eoh/rtkweb/documents/fs/1667.pdf |publisher=New Jersey Department of Health and Senior services}}</ref>

==Occurrence==
Volcanic plumes contain significant amounts of silicon tetrafluoride. Production can reach several tonnes per day.<ref>{{cite journal
| title = High SiF4/HF ratio detected in Satsuma-Iwojima volcano's plume by remote FT-IR observation
|author1=T. Mori |author2=M. Sato |author3=Y. Shimoike |author4=K. Notsu | journal = Earth Planets Space
| year = 2002  
| volume = 54
| issue =3
| pages = 249–256
|doi=10.1186/BF03353024 |bibcode=2002EP&S...54..249M |s2cid=55173591 | url = http://www.terrapub.co.jp/journals/EPS/pdf/2002/5403/54030249.pdf
| doi-access =free}}</ref> Some amounts are also emitted from spontaneous coal fires.<ref name="Kuszewski et al. 2018">Kruszewski, Ł., Fabiańska, M.J., Ciesielczuk, J., Segit, T.,  Orłowski, R., Motyliński, R., Moszumańska, I., Kusy, D. 2018 – First multi-tool exploration of a gas-condensate-pyrolysate system from the environment of burning coal mine heaps: An in situ FTIR and laboratory GC and PXRD study based on Upper Silesian materials. Science of the Total Environment, 640-641, 1044-1071; DOI: 10.1016/j.scitotenv.2018.05.319</ref> The silicon tetrafluoride is partly hydrolysed and forms [[hexafluorosilicic acid]].

==Preparation==
{{chem|SiF|4}} is a by-product of the production of [[phosphate]] [[fertilizer]]s [[Phosphoric acid#Production|wet process production]], resulting from the attack of [[Hydrofluoric acid|HF]] (derived from [[fluorapatite]] protonolysis) on [[silicate]]s, which are present as impurities in the [[Phosphate mineral|phosphate rocks]].<ref name=":2">{{cite book |title=Inorganic Syntheses |year=1953 |volume=4 |pages=147–8 |doi=10.1002/9780470132357.ch48 |author1=Hoffman, C. J. |author2=Gutowsky, H. S. |chapter=Germanium(IV) Fluoride |isbn=978-0-470-13163-3 }}</ref> The [[hydrofluoric acid]] and silicon dioxide (SiO<sub>2</sub>) react to produce [[hexafluorosilicic acid]]:<ref name=":2" />
: 6 HF + SiO<sub>2</sub>  →   H<sub>2</sub>SiF<sub>6</sub> + 2 H<sub>2</sub>O

In the laboratory, the compound is prepared by heating [[barium hexafluorosilicate]] (Ba[SiF<sub>6</sub>]) above {{Convert|300|C|F}} whereupon the solid releases volatile {{chem|SiF|4}}, leaving a residue of {{chem|link=barium fluoride|BaF|2}}.

: {{chem2|Ba[SiF6] + 400°C -> [[Barium fluoride|BaF2]] + SiF4}}

Alternatively, [[sodium hexafluorosilicate]] ({{chem2|Na2[SiF6]}}) may also be thermally decomposed at {{Convert|400|C|F}}—{{Convert|600|C|F}} (optionally in inert nitrogen gas atmosphere) <ref name=":3">{{Cite patent|country=Us|number=A345458|title=Patent Silicon tetrafluoride generation|status=Granted|pubdate=January 3, 1982|gdate=1982|invent1=Keith|invent2=L. Yaws|inventor1-first=C. Hansen|inventor2-first=Carl}}</ref>{{rp|p=8}}

: {{chem2|Na2[SiF6] + 400°C -> 2[[Sodium fluoride|NaF]] + SiF4}}

==Uses==
This [[Volatility (chemistry)|volatile]] compound finds limited use in microelectronics and [[organic synthesis]].<ref>Shimizu, M. "Silicon(IV) Fluoride" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons. {{doi|10.1002/047084289X.rs011}}</ref>

It is also used in production of [[fluorosilicic acid]] (see above).<ref name=":0" />

Staying in the 1980s, as part of the Low-Cost Solar Array Project by [[Jet Propulsion Laboratory]],<ref>{{Cite book |last=Callaghan |first=William T. |title=Photovoltaic Solar Energy Conference |chapter=Low-Cost Solar Array Project Progress and Plans |date=1981 |editor-last=Palz |editor-first=W. |chapter-url=https://link.springer.com/chapter/10.1007/978-94-009-8423-3_40 |language=en |location=Dordrecht |publisher=Springer Netherlands |pages=279–286 |doi=10.1007/978-94-009-8423-3_40 |isbn=978-94-009-8423-3}}</ref> it was investigated as a potentially cheap feedstock for [[polycrystalline silicon]] production in [[fluidized bed reactor]]s.<ref>{{Cite journal |last1=Acharya |first1=H. N. |last2=Datta |first2=S. K. |last3=Banerjee |first3=H. D. |last4=Basu |first4=S. |date=1982-09-01 |title=Low-temperature preparation of polycrystalline silicon from silicon tetrachloride |url=https://dx.doi.org/10.1016/0167-577X%2882%2990008-8 |journal=Materials Letters |language=en |volume=1 |issue=2 |pages=64–66 |doi=10.1016/0167-577X(82)90008-8 |bibcode=1982MatL....1...64A |issn=0167-577X|url-access=subscription }}</ref> Few methods using it for the said production process were patented.<ref name=":3" /><ref>{{Cite patent|country=CA|number=2741023A1|title=Method for the production of polycrystalline silicon|gdate=2008|invent1=Anatoli|invent2=Tozzoli|inventor1-first=V. Pushko|inventor2-first=Silvio}}</ref>

=== The Ethyl Corporation process ===
In 80s the [[Ethyl Corporation]] came up with a process that uses hexafluorosilicic acid and sodium [[aluminium hydride]] (NaAlH<sub>4</sub>) (or other [[alkali metal]] hydride) to produce [[silane]] (SiH<sub>4</sub>).<ref>{{Cite web |date=August 11, 2015 |title=The Ethyl Corporation Process: Silane and Fluidised Bed Reactor |url=http://energyprofessionalsymposium.com/?p=13250}}</ref>

== Safety ==
In 2001 it was listed by [[New Jersey]] authorities as a hazardous substance that is corrosive and may severely irritate or even burn skin and eyes.<ref name=":0" /> It is fatal if inhaled.<ref name=":1">{{Cite web |date=April 9, 2018 |title=SAFETY DATA SHEET: Silicon Tetrafluoride |url=https://www.airgas.com/msds/001076.pdf |publisher=[[Airgas]]}}</ref>

== See also ==

* [[Silane|SiH<sub>4</sub> (silane)]]
* [[Hexafluorosilicic acid]]

==References==
{{reflist}}
* {{Greenwood&Earnshaw2nd}}

{{silicon compounds}}
{{fluorine compounds}}
{{Authority control}}

[[Category:Fluorides]]
[[Category:Nonmetal halides]]
[[Category:Inorganic silicon compounds]]
[[Category:Silanes]]