Sulfur hexafluoride



Sulfur hexafluoride
IUPAC name sulfur(VI) fluoride
Other names sulphur hexafluoride
Identifiers
CAS number 2551-62-4
RTECS number WS4900000
SMILES FS(F)(F)(F)(F)F
Properties
Molecular formula SF6
Molar mass 146.06 g/mol
Appearance colorless, odorless gas
Density 6.164 g/L, gas phase at 1 bar
(~5.1 times denser than air)
1.329 kg/L, liquid phase at 25 °C
2,510 kg/m3 or 2.510 kg/L, solid phase at −50.8 °C
Melting point

−64 °C (209 K) (Sublimes),
Decomposes at 500 °C (773 K)

Boiling point

Sublimes at Standard Pressure

Solubility in water low
Structure
Coordination
geometry 		octahedral
Dipole moment 0 D
Hazards
MSDS External MSDS
Main hazards Inert gas, simple asphyxiant in high concentrations
Related Compounds
Related compounds CF4
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Sulfur hexafluoride is an 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.

Contents

Synthesis and chemistry

SF6 can be prepared from the elements, that is exposure of SF4.

There is virtually no reaction chemistry for SF6. It does not react with molten sodium.

Starting from SF4, one can prepare SF5Cl, which is structurally related to SF6. The monochloride is, however, a strong oxidant and readily hydrolyzed to sulfate.

Applications

Of the produced 8000 t per year most of the SF6 goes into three applications. First as gaseous dielectric medium or other use in the electrical industry with 6000 t , second as inert gas for the casting of magnesium and third it is used as inert filling of windows.

Dielectric medium

SF6 is used by the electrical industry as a gaseous dielectric medium for high-voltage (1 kV and above) circuit breakers, switchgear, and other electrical equipment, often replacing harmful chemical warfare agent in World War II because it does not produce lacrimation or skin irritation, thus providing little warning of exposure.

SF6 is also commonly encountered as a high voltage dielectric in the high voltage supplies of particle accelerators, such as Van de Graff generators and Pelletrons.

Medical use

Because SF6 is relatively slowly absorbed by the bloodstream, it is used to provide a long-term tamponade (plug) of a retinal hole in retinal detachment repair operations.

In a further medical application, SF6 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 their visibility of blood vessels, to ultrasound. This application has been utilised to examine the vascularity of tumours amongst other things.

Tracer compound

Gaseous SF6 is still a commonly used tracer gas for use in short-term experiments of Earth's atmosphere has a negligible concentration of SF6.

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.[1] 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 use

Sulfur hexafluoride is also used as a reagent for creating thrust in a closed lithium as used in the United States Navy's Mark 50 torpedo.

SF6 semiconductor industry as an etchant.

The magnesium industry uses large amounts of SF6 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 famous video shows a small 'boat' made from helium. Meaning, after inhalation, one's voice becomes significantly lower-pitched.Youtube video of sulfur hexafluoride inhalation+sulfur hexaflouride in a tank

It is also emitted during the aluminium smelting process.

Greenhouse gas

According to the Intergovernmental Panel on Climate Change, SF6 is the most potent greenhouse gas that it has evaluated, with a global warming potential of 22,200 times that of ppt) in 2007 versus 380 ppm of carbon dioxide),[3] and its contribution to global warming is accordingly low.

Notable characteristics

Because the gas has a high density (over five times denser than air), it 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.[4]

Physiological effects and precautions

Another effect is the gas' ability to alter vocal sound waves. The gas can be breathed 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, SF6 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 SF6 is the opposite of inhaling helium, a reduction in the pitch of the voice.[5]

Although inhaling SF6 can be a novel amusement, the practice can be dangerous because, like all gases other than oxygen, the SF6 displaces the oxygen needed for breathing (a phenomenon known as asphyxiation). A myth exists that SF6 is too heavy for the lungs to expel unassisted, and that after inhaling SF6, 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 SF6 would be purged from the lungs within a breath or two.[6] In general, dense, odourless gases in confined areas present the hazard of suffocation.

References

  1. ^ 'Poison gas' test on Underground. BBC News (25 March 2007). Retrieved on 2007-03-31.
  2. ^ Climate Change 2001: Working Group I: The Scientific Basis. Intergovernmental Panel on Climate Change (2001). Retrieved on 2007-03-31.
  3. ^ High GWP Gases and Climate Change. US Environmental Protection Agency (19 October 2006). Retrieved on 2007-03-31.
  4. ^ TheTvelvethMonkey (6 January 2007). Ship floating on nothing! :: Physikshow Uni Bonn. YouTube. Retrieved on 2007-03-31.
  5. ^ Steve Stangler. Anti-Helium - Sulfur Hexafluoride. Steve Stangler Science. Retrieved on 2007-06-29.
  6. ^ Steven B. Harris (6 June 1995). helium inhalation. Usenet Archives. Retrieved on 2007-03-31.

Further reading

  • (1991) Gaseous Dielectrics VI. Plenum Press. 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)
  • SF6 Reduction Partnership for Electric Power Systems

See also
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sulfur_hexafluoride". A list of authors is available in Wikipedia.