Sulfur hexafluoride
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{{Chembox new
| Name = Sulfur hexafluoride
| ImageFile = Sulfur-hexafluoride-2D-dimensions.png
| ImageSize = 100px
| ImageName = Structure and dimensions of the sulfur hexafluoride molecule
| ImageFile1 = Sulfur-hexafluoride-3D-balls.png
| ImageSize1 = 100px
| ImageName1 = Ball-and-stick model of sulfur hexafluoride
| ImageFile2 = Sulfur-hexafluoride-3D-vdW.png
| ImageSize2 = 100px
| ImageName2 = Space-filling model of sulfur hexafluoride
| IUPACName = sulfur(VI) fluoride
| OtherNames = sulphur hexafluoride
| Section1 = {{Chembox Identifiers
| SMILES = FS(F)(F)(F)(F)F
| CASNo = 2551-62-4
| RTECS = WS4900000
}}
| Section2 = {{Chembox Properties
| Formula = SF<sub>6</sub>
| MolarMass = 146.06 g/mol
| Appearance = colorless, odorless gas
| Density = 6.164 g/L, gas phase at 1 bar<br />(~5.1 times denser than air)<br />1.329 kg/L, liquid phase at 25 °C<br />2,510 kg/m<sup>3</sup> or 2.510 kg/L, solid phase at −50.8 °C
| Solubility = low
| MeltingPt = −64 °C (209 K) (Sublimes),<br />Decomposes at 500 °C (773 K)
| BoilingPt = Sublimes at Standard Pressure
}}
| Section3 = {{Chembox Structure
| Coordination = octahedral
| Dipole = 0 [[Debye|D]]
| Coordination = O<sub>h</sub>
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://ptcl.chem.ox.ac.uk/MSDS/SU/sulfur_hexafluoride.html External MSDS]
| MainHazards = Inert gas, simple asphyxiant in high concentrations
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Sulfur tetrafluoride|{{chem|SF|4}}]], [[Carbon tetrafluoride|{{chem|CF|4}}]]}}
}}
'''Sulfur hexafluoride''' is an [[inorganic compound]] with the formula {{chem|SF|6}}. It is a colorless, odorless, non-[[toxicity|toxic]] and non-[[flammable]] [[gas]] (under standard conditions). {{chem|SF|6}} has an [[octahedral geometry]], consisting of six [[fluorine]] atoms attached to a central [[sulfur]] atom. It is a [[hypervalent molecule]]. Typical for a nonpolar gas, it is poorly [[soluble]] in water but soluble in nonpolar organic solvents. It is generally transported as a liquified compressed gas. It has a density of 6.13 g/L at sea level conditions.
==Synthesis and chemistry==
{{chem|SF|6}} can be prepared from the elements through exposure of [[Sulfur|{{chem|S|8}}]] to [[fluorine|{{chem|F|2}}]]. This is also the method used by the discoverers [[Henri Moissan]] and [[Paul Lebeau]] in 1901. Some other sulfur fluorides are cogenerated, but these are removed by heating the mixture to [[disproportionation|disproportionate]] any {{chem|S|2|F|10}} and then scrubbing the product with NaOH to destroy remaining [[Sulfur tetrafluoride|{{chem|SF|4}}]].
There is virtually no reaction chemistry for {{chem|SF|6}}. It does not react with molten [[sodium]], but reacts [[exothermic|exothermically]] with [[lithium]].
Starting from {{chem|SF|4}}, one can prepare {{chem|SF|5|Cl}}, which is structurally related to {{chem|SF|6}}. The monochloride is, however, a strong oxidant and readily hydrolyzed to [[sulfate]].
==Applications==
Of the 8000 tonnes produced per year, most of the {{chem|SF|6}} goes into three applications: firstly as a [[gaseous]] [[dielectric]] medium or other use in the [[electric company|electrical industry]], which accounts for 6000 tonnes; secondly as an inert gas for the casting of magnesium; and thirdly as an inert filling for windows.
===Dielectric medium ===
{{chem|SF|6}} is used in the [[electric company|electrical industry]] as a [[gaseous]] [[dielectric]] medium for high-voltage (1 kV and above) [[circuit breaker]]s, [[switchgear]], and other [[electricity|electrical]] equipment, often replacing oil filled circuit breakers (OCBs) that can contain harmful [[PCBs]]. {{chem|SF|6}} gas under [[pressure]] is used as an insulator in [[gas insulated switchgear]] (GIS) because it has a much higher [[dielectric strength]] than air or dry nitrogen. This property makes it possible to significantly reduce the size of electrical gear. This makes GIS more suitable for certain purposes such as indoor placement, as opposed to air-insulated electrical gear, which takes up considerably more room. Gas-insulated electrical gear is also more resistant to the effects of pollution and climate, as well as being more reliable in long-term operation because of its controlled operating environment. Vacuum circuit breakers (VCBs) are displacing {{chem|SF|6}} breakers in industry as they are safer and require less maintenance. Although most of the decomposition products tend to quickly re-form {{chem|SF|6}} , [[Electrical arc|arcing]] or [[Corona discharge|corona]] can produce [[disulfur decafluoride]] ([[Disulfur decafluoride|{{chem|S|2|F|10}}]]), a highly [[toxic]] gas, with toxicity similar to [[phosgene]]. {{chem|S|2|F|10}} was considered a potential [[chemical warfare]] agent in [[World War II]] because it does not produce [[lacrimation]] or skin irritation, thus providing little warning of exposure.
{{chem|SF|6}} is also commonly encountered as a high voltage dielectric in the high voltage supplies of [[particle accelerator]]s, such as [[Van de Graaff generator]]s and [[Pelletron]]s and high voltage transmission [[electron microscope]]s.
===Medical use===
Because {{chem|SF|6}} is relatively slowly absorbed by the bloodstream, it is used to provide a long-term [[tamponade]] or plug of a retinal hole in [[retinal detachment]] repair operations.
In a further medical application, {{chem|SF|6}} is employed as a contrast agent for [[ultrasound]] imaging. Sulfur hexafluoride microbubbles are administered in solution through injection into a peripheral vein. These microbubbles enhance the visibility of blood vessels to ultrasound. This application has been utilized to examine the vascularity of tumours amongst other things.
===Tracer compound===
Gaseous {{chem|SF|6}} is still a commonly used tracer gas for use in short-term experiments of [[Ventilation (architecture)|ventilation]] efficiency in buildings and indoor enclosures, and for determining [[Infiltration (HVAC)|infiltration]] rates. Two major factors recommend its use: Its concentration can be measured with satisfactory accuracy at very low concentrations, and the [[Earth's atmosphere]] has a negligible concentration of {{chem|SF|6}}.
Sulfur hexafluoride was used as a harmless test gas in an experiment at [[St John's Wood tube station]] in [[London]], England on [[25 March]] [[2007]].<ref>{{cite web |title='Poison gas' test on Underground |url=http://news.bbc.co.uk/1/hi/england/london/6492501.stm |accessdate=2007-03-31 |date=25 March 2007 |publisher=BBC News }}</ref> The gas was released throughout the station, and monitored as it drifted around. The purpose of the experiment, which had been announced earlier in March by the [[Secretary of State for Transport]] [[Douglas Alexander]], was to investigate how toxic gas might spread throughout [[London Underground]] stations and buildings during a terrorist attack.
It has been used successfully as a tracer in [[oceanography]] to study diapycnal mixing and air-sea gas exchange.
=== Other uses===
Sulfur hexafluoride is also used as a [[reagent]] for creating thrust in a closed [[Rankine cycle]] propulsion system, reacting with [[solid]] [[lithium]] as used in the [[United States Navy]]'s [[Mark 50 torpedo]].
{{chem|SF|6}} [[plasma (physics)|plasma]] is also used in the [[semiconductor]] industry as an [[etching (microfabrication)|etchant]].
The [[magnesium]] industry uses large amounts of SF<sub>6</sub> as inert gas to fill casting forms.
Due to its high density, sulfur hexafluoride is often used in public "magic" tricks where it is renowned for being "invisible water". One video shows a small 'boat' made from [[aluminium foil]] being carefully placed in a container of {{chem|SF|6}}, where it floats almost exactly as if the container was filled with water. A [[beaker]] is then used to scoop up the gas from the container and into the foil boat, making it heavier and heavier, until finally, it sinks to the bottom of the tank.[http://www.youtube.com/watch?v=tAsOfqCy4A0]
==Greenhouse gas==
According to the [[Intergovernmental Panel on Climate Change]], {{chem|SF|6}} is the most potent [[greenhouse gas]] that it has evaluated, with a [[global warming potential]] of 22,200 times that of [[carbon dioxide|{{chem|CO|2}}]] when compared over a 100 year period--{{chem|SF|6}} is very stable (for countries reporting their emissions to the UNFCCC, a GWP of 23,900 for {{chem|SF|6}} was suggested at the third Conference of the Parties: [[Global warming potential#GWP used in Kyoto protocol|GWP used in Kyoto protocol]]).<ref>{{cite web |url=http://www.grida.no/climate/ipcc_tar/wg1/248.htm |title=Climate Change 2001: Working Group I: The Scientific Basis |accessdate=2007-03-31 |date=2001 |publisher=Intergovernmental Panel on Climate Change }}</ref> Its mixing ratio in the [[atmosphere]] is lower than that of {{chem|CO|2}} about 6.5 parts per trillion ([[Parts per notation|ppt]]) in [[2008]] versus 380 ppm of carbon dioxide, but has steadily increased (from a figure of 4.0 parts per trillion in the late 1990s)<ref>{{cite web |url=http://www.esrl.noaa.gov/gmd/ccgg/iadv/ |title=NOAA ESRL GMD Carbon Cycle - Interactive Atmospheric Data Visualisation |accessdate=2008-4-21 |date=21 April 2008 |publisher=US National Oceanic and Atmospheric Administration }}</ref>. Its atmospheric lifetime is 3200 years.
==Notable characteristics==
Because the gas has a high density (over five times denser than air), {{chem|SF|6}} can be poured into open containers, like beakers and fishtanks. Moreover, light objects, e.g. ship-like vessels made out of light wood or aluminium foil containing air inside, can float on the gas.<ref>{{cite web |url=http://www.youtube.com/watch?v=1PJTq2xQiQ0 |title=Ship floating on nothing! :: Physikshow Uni Bonn |accessdate=2007-03-31 |date=6 January 2007 |author=TheTvelvethMonkey |publisher=YouTube }}</ref>
==Physiological effects and precautions==
Another effect is the gas's ability to alter vocal sound waves. The gas can be inhaled in a small, safe amount and cause the breather's voice to sound very deep. This, too, is due to the gas density. Unlike [[helium]], which is much less dense than air, {{chem|SF|6}} is approximately 5 times more dense than air, and the velocity of sound through the gas is 0.44 times the speed of sound in air. Unlike a gas such as helium, the speed of sound in which is greater than the speed of sound in air, the result of inhaling {{chem|SF|6}} is the opposite of inhaling helium, a reduction in the [[Pitch (music)|pitch]] of the voice.<ref>{{cite web |url=http://www.stevespanglerscience.com/experiment/from-donald-duck-to-barry-white-how-gases-change-your-voice |title=Anti-Helium - Sulfur Hexafluoride |accessdate=2007-06-29 |date= |author=Steve Spangler |publisher= Steve Spangler Science}}</ref>
Although inhaling {{chem|SF|6}} can be a novel amusement, the practice can be dangerous because, like all gases other than oxygen, it displaces the oxygen needed for breathing. In general, dense, odourless gases in confined areas present the hazard of suffocation. A myth exists that {{chem|SF|6}} is too heavy for the lungs to expel unassisted, and that after inhaling {{chem|SF|6}}, it is necessary to bend over completely at the waist to allow the excess gas to "spill" out of the body. In fact, the lungs mix gases very effectively and rapidly, such that {{chem|SF|6}} would be purged from the lungs within a breath or two.<ref>{{cite web |url=http://yarchive.net/med/helium_breathe.html |title=helium inhalation |accessdate=2007-03-31 |date=6 June 1995 |author=Steven B. Harris |publisher=Usenet Archives }}</ref>
== References ==
{{reflist}}
==Further reading==
* {{cite book | Editors = Christophorou, Loucas G., [[Isidor Sauers]] | year = 1991 | title = Gaseous Dielectrics VI | publisher = Plenum Press | id = ISBN 0-306-43894-1 }}
*Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
*Khalifa, from Maller and Naidu (1981)
*[http://www.epa.gov/electricpower-sf6/ SF<sub>6</sub> Reduction Partnership for Electric Power Systems]
==See also==
* [[Selenium hexafluoride]]
* [[Tellurium hexafluoride]]
* [[hypervalent molecule]]
* [[Paschen's Law]]
* [[Electric power]]
* [[Isidor Sauers|Process for Measuring the Degradation of Sulfur Hexafluoride in High-voltage Systems]] {{US patent|4633082}}
==External links==
A video about a boat floating on sulfur hexafluoride is mentioned in the text via a reference.
*[http://www.npi.gov.au/database/substance-info/profiles/44.html National Pollutant Inventory - Fluoride and compounds fact sheet]
* [http://www.epa.gov/highgwp/scientific.html High GWP Gases and Climate Change] from the U.S. [[United States Environmental Protection Agency|EPA]] website.
* [http://www.epa.gov/highgwp/magnesium-sf6/workshops.html International Conference on SF<sub>6</sub> and the Environment] [[United States Environmental Protection Agency]] website
[[Category:Sulfur fluorides]]
[[Category:Greenhouse gases]]
[[Category:Dielectrics]]
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[[de:Schwefelhexafluorid]]
[[es:Hexafluoruro de azufre]]
[[fr:Hexafluorure de soufre]]
[[ko:육플루오린화 황]]
[[hr:Sumporov heksafluorid]]
[[it:Esafluoruro di zolfo]]
[[hu:Kén-hexafluorid]]
[[nl:Zwavelhexafluoride]]
[[ja:六フッ化硫黄]]
[[pl:Sześciofluorek siarki]]
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