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
Silicon tetrafluoride
| OtherNames = Silicon fluoride
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 = SiF4
| MolarMass = 104.0791 g/mol
| Appearance = colourless gas, fumes in moist air
| Density = 1.66 g/cm3, solid (−95 °C)
4.69 g/L (gas)
| Solubility = decomposes
| MeltingPtC = -95.0
| MeltingPt_ref = Silicon Compounds, Silicon Halides. Collins, W.: Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley & Sons, Inc, 2001.
| BoilingPtC = −90.3
| CriticalTP = {{convert|−14.15|C|F K|1}}, {{convert|36.71|atm|kPa psi|1}}{{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}}
}}
|Section3={{Chembox Structure
| MolShape = tetrahedral
| Dipole = 0 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/m3 (rat, 4 hr){{IDLH|fluoride|Fluorides (as F)}}
}}
|Section8={{Chembox Related
| OtherAnions = Silicon tetrachloride
Silicon tetrabromide
Silicon tetraiodide
| OtherCations = Carbon tetrafluoride
Germanium tetrafluoride
Tin tetrafluoride
Lead tetrafluoride
| OtherCompounds = Hexafluorosilicic acid
}}
}}
Silicon tetrafluoride or tetrafluorosilane is a chemical compound with the formula SiF4. This colorless gas is notable for having a narrow liquid range: its boiling point is only 4 °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 in 1812.{{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
}} It is a tetrahedral molecule and is corrosive.{{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}}
Occurrence
Volcanic plumes contain significant amounts of silicon tetrafluoride. Production can reach several tonnes per day.{{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}} Some amounts are also emitted from spontaneous coal fires.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 The silicon tetrafluoride is partly hydrolysed and forms hexafluorosilicic acid.
Preparation
{{chem|SiF|4}} is a by-product of the production of phosphate fertilizers wet process production, resulting from the attack of HF (derived from fluorapatite protonolysis) on silicates, which are present as impurities in the phosphate rocks.{{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 }} The hydrofluoric acid and silicon dioxide (SiO2) react to produce hexafluorosilicic acid:
: 6 HF + SiO2 → H2SiF6 + 2 H2O
In the laboratory, the compound is prepared by heating barium hexafluorosilicate (Ba[SiF6]) 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 -> 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) {{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}}{{rp|p=8}}
: {{chem2|Na2[SiF6] + 400°C -> 2NaF + SiF4}}
Uses
This volatile compound finds limited use in microelectronics and organic synthesis.Shimizu, M. "Silicon(IV) Fluoride" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons. {{doi|10.1002/047084289X.rs011}}
It is also used in production of fluorosilicic acid (see above).
Staying in the 1980s, as part of the Low-Cost Solar Array Project by Jet Propulsion Laboratory,{{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}} it was investigated as a potentially cheap feedstock for polycrystalline silicon production in fluidized bed reactors.{{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}} Few methods using it for the said production process were patented.{{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}}
= The Ethyl Corporation process =
In 80s the Ethyl Corporation came up with a process that uses hexafluorosilicic acid and sodium aluminium hydride (NaAlH4) (or other alkali metal hydride) to produce silane (SiH4).{{Cite web |date=August 11, 2015 |title=The Ethyl Corporation Process: Silane and Fluidised Bed Reactor |url=http://energyprofessionalsymposium.com/?p=13250}}
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. It is fatal if inhaled.{{Cite web |date=April 9, 2018 |title=SAFETY DATA SHEET: Silicon Tetrafluoride |url=https://www.airgas.com/msds/001076.pdf |publisher=Airgas}}
See also
References
{{reflist}}
- {{Greenwood&Earnshaw2nd}}
{{silicon compounds}}
{{fluorine compounds}}
{{Authority control}}