Typical for a nonpolar gas, SF 6 is poorly soluble in water but quite soluble in nonpolar organic solvents. It has a density of 6.12 g/L at sea level conditions, considerably higher than the density of air (1.225 g/L). It is generally transported as a liquefied compressed gas.[citation needed]
SF 6 has 23,500 times greater global warming potential (GWP) than CO2 as a greenhouse gas (over a 100-year time-frame) but exists in relatively minor concentrations in the atmosphere. Its concentration in Earth's troposphere reached 11.50 parts per trillion (ppt) in October 2023, rising at 0.37 ppt/year.[8] The increase since 1980 is driven in large part by the expanding electric power sector, including fugitive emissions from banks of SF 6 gas contained in its medium- and high-voltage switchgear. Uses in magnesium, aluminium, and electronics manufacturing also hastened atmospheric growth.[9] The 1997 Kyoto Protocol, which came into force in 2005, is supposed to limit emissions of this gas. In a somewhat nebulous way it has been included as part of the carbon emission trading scheme. In some countries this has led to the defunction of entire industries.[10]
Sulfur hexafluoride on Earth exists primarily as a synthetic industrial gas, but has also been found to occur naturally.[11]
SF 6 can be prepared from the elements through exposure of S 8toF 2. This was 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 disproportionate any S 2F 10 (which is highly toxic) and then scrubbing the product with NaOH to destroy remaining SF 4[clarification needed]
Alternatively, using bromine, sulfur hexafluoride can be synthesized from SF4 and CoF3 at lower temperatures (e.g. 100 °C), as follows:[12]
2 CoF3 + SF4 + [Br2] → SF6 + 2 CoF2 + [Br2]
There is virtually no reaction chemistry for SF 6. A main contribution to the inertness of SF6 is the steric hindrance of the sulfur atom, whereas its heavier group 16 counterparts, such as SeF6 are more reactive than SF6 as a result of less steric hindrance.[13] It does not react with molten sodium below its boiling point,[14] but reacts exothermically with lithium. As a result of its inertness, SF 6 has an atmospheric lifetime of around 3200 years, and no significant environmental sinks other than the ocean.[15]
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. Exposure to an arc chemically breaks down SF 6 though most of the decomposition products tend to quickly re-form SF 6, a process termed "self-healing".[18]Arcingorcorona can produce disulfur decafluoride (S 2F 10), a highly toxic gas, with toxicity similar to phosgene. S 2F 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.
Alternatives to SF 6 as a dielectric gas include several fluoroketones.[19][20] Compact GIS technology that combines vacuum switching with clean air insulation has been introduced for a subset of applications up to 420 kV.[21]
SF 6 is used to provide a tamponade or plug of a retinal hole in retinal detachment repair operations[22] in the form of a gas bubble. It is inert in the vitreous chamber.[23] The bubble initially doubles its volume in 36 hours due to oxygen and nitrogen entering it, before being absorbed in the blood in 10–14 days.[24]
SF 6 is used 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 used to examine the vascularity of tumours.[25] It remains visible in the blood for 3 to 8 minutes, and is exhaled by the lungs.[26]
Sulfur hexafluoride was used as a non-toxic test gas in an experiment at St John's Wood tube stationinLondon, United Kingdom on 25 March 2007.[28] 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 TransportDouglas Alexander, was to investigate how toxic gas might spread throughout London Underground stations and buildings during a terrorist attack.
Sulfur hexafluoride is also routinely used as a tracer gas in laboratory fume hood containment testing. The gas is used in the final stage of ASHRAE 110 fume hood qualification. A plume of gas is generated inside of the fume hood and a battery of tests are performed while a gas analyzer arranged outside of the hood samples for SF6 to verify the containment properties of the fume hood.
It has been used successfully as a tracer in oceanography to study diapycnal mixing and air-sea gas exchange.[29]
The magnesium industry uses SF 6 as an inert "cover gas" to prevent oxidation during casting,[30] and other processes including smelting.[31] Once the largest user, consumption has declined greatly with capture and recycling.[9]
Insulated glazing windows have used it as a filler to improve their thermal and acoustic insulation performance.[32][33]
SF 6plasma is used in the semiconductor industry as an etchant in processes such as deep reactive-ion etching. A small fraction of the SF 6 breaks down in the plasma into sulfur and fluorine, with the fluorine ions performing a chemical reaction with silicon.[34]
Tires filled with it take longer to deflate from diffusion through rubber due to the larger molecule size.[32]
Nike likewise used it to obtain a patent and to fill the cushion bags in all of their "Air"-branded shoes from 1992 to 2006.[35] 277 tons was used during the peak in 1997.[32]
For entertainment purposes, when breathed, SF 6 causes the voice to become significantly deeper, due to its density being so much higher than air. This phenomenon is related to the more well-known effect of breathing low-density helium, which causes someone's voice to become much higher. Both of these effects should only be attempted with caution as these gases displace oxygen that the lungs are attempting to extract from the air. Sulfur hexafluoride is also mildly anesthetic.[38][39]
For science demonstrations / magic as "invisible water" since a light foil boat can be floated in a tank, as will an air-filled balloon.
It is used for benchmark and calibration measurements in Associative and Dissociative Electron Attachment (DEA) experiments[40][41]
Sulfur hexafluoride (SF6) measured by the Advanced Global Atmospheric Gases Experiment (AGAGE) in the lower atmosphere (troposphere) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in parts-per-trillion.
Abundance and growth rate of SF 6 in Earth's troposphere (1978-2018).[9]
Atmospheric concentration of SF6 vs. similar man-made gases (right graph). Note the log scale.
Measurements of SF6 show that its global average mixing ratio has increased from a steady base of about 54 parts per quadrillion[11] prior to industrialization, to over 11.5 parts per trillion (ppt) as of October 2023, and is increasing by about 0.4 ppt (3.5%) per year.[8][44] Average global SF6 concentrations increased by about 7% per year during the 1980s and 1990s, mostly as the result of its use in magnesium production, and by electrical utilities and electronics manufacturers. Given the small amounts of SF6 released compared to carbon dioxide, its overall individual contribution to global warming is estimated to be less than 0.2%,[45] however the collective contribution of it and similar man-made halogenated gases has reached about 10% as of 2020.[46] Alternatives are being tested.[47][48]
In Europe, SF 6 falls under the F-Gas directive which ban or control its use for several applications.[49] Since 1 January 2006, SF 6 is banned as a tracer gas and in all applications except high-voltage switchgear.[50] It was reported in 2013 that a three-year effort by the United States Department of Energy to identify and fix leaks at its laboratories in the United States such as the Princeton Plasma Physics Laboratory, where the gas is used as a high voltage insulator, had been productive, cutting annual leaks by 1,030 kilograms (2,280 pounds). This was done by comparing purchases with inventory, assuming the difference was leaked, then locating and fixing the leaks.[51]
Sulfur hexafluoride is a nontoxic gas, but by displacing oxygen in the lungs, it also carries the risk of asphyxia if too much is inhaled.[52] Since it is more dense than air, a substantial quantity of gas, when released, will settle in low-lying areas and present a significant risk of asphyxiation if the area is entered. That is particularly relevant to its use as an insulator in electrical equipment since workers may be in trenches or pits below equipment containing SF 6.[53]
A man's voice is deepened in pitch through inhaling sulfur hexafluoride
As with all gases, the density of SF 6 affects the resonance frequencies of the vocal tract, thus changing drastically the vocal sound qualities, or timbre, of those who inhale it. It does not affect the vibrations of the vocal folds. The density of sulfur hexafluoride is relatively high at room temperature and pressure due to the gas's large molar mass. Unlike helium, which has a molar mass of about 4 g/mol and pitches the voice up, SF 6 has a molar mass of about 146 g/mol, and the speed of sound through the gas is about 134 m/s at room temperature, pitching the voice down. For comparison, the molar mass of air, which is about 80% nitrogen and 20% oxygen, is approximately 30 g/mol which leads to a speed of sound of 343 m/s.[54]
Sulfur hexafluoride has an anesthetic potency slightly lower than nitrous oxide;[55] it is classified as a mild anesthetic.[56]
^Assael MJ, Koini IA, Antoniadis KD, Huber ML, Abdulagatov IM, Perkins RA (2012). "Reference Correlation of the Thermal Conductivity of Sulfur Hexafluoride from the Triple Point to 1000 K and up to 150 MPa". Journal of Physical and Chemical Reference Data. 41 (2): 023104–023104–9. Bibcode:2012JPCRD..41b3104A. doi:10.1063/1.4708620. ISSN0047-2689. S2CID18916699.
^ abcSimmonds, P. G., Rigby, M., Manning, A. J., Park, S., Stanley, K. M., McCulloch, A., Henne, S., Graziosi, F., Maione, M., and 19 others (2020) "The increasing atmospheric burden of the greenhouse gas sulfur hexafluoride (SF6)". Atmos. Chem. Phys., 20: 7271–7290. doi:10.5194/acp-20-7271-2020. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
^Winter RW, Pugh JR, Cook PW (January 9–14, 2011). SF5Cl, SF4 and SF6: Their Bromine−facilitated Production & a New Preparation Method for SF5Br. 20th Winter Fluorine Conference.
^Duward Shriver, Peter Atkins (2010). Inorganic Chemistry. W. H. Freeman. p. 409. ISBN978-1429252553.
^Daniel A. Brinton, C. P. Wilkinson (2009). Retinal detachment: principles and practice. Oxford University Press. p. 183. ISBN978-0199716210.
^Gholam A. Peyman, M.D., Stephen A. Meffert, M.D., Mandi D. Conway (2007). Vitreoretinal Surgical Techniques. Informa Healthcare. p. 157. ISBN978-1841846262.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Hilton GF, Das T, Majji AB, Jalali S (1996). "Pneumatic retinopexy: Principles and practice". Indian Journal of Ophthalmology. 44 (3): 131–143. PMID9018990.
^Lassau N, Chami L, Benatsou B, Peronneau P, Roche A (December 2007). "Dynamic contrast-enhanced ultrasonography (DCE-US) with quantification of tumor perfusion: a new diagnostic tool to evaluate the early effects of antiangiogenic treatment". Eur Radiol. 17 (Suppl. 6): F89–F98. doi:10.1007/s10406-007-0233-6. PMID18376462. S2CID42111848.
^C Michael Hogan (September 10, 2011). "Air pollution line source". Encyclopedia of Earth. Archived from the original on 29 May 2013. Retrieved 22 February 2013.
^Stanley Holmes (September 24, 2006). "Nike Goes For The Green". Bloomberg Business Week Magazine. Archived from the original on June 3, 2013. Retrieved December 14, 2013.
^Hughes, T.G., Smith, R.B., Kiely, D.H. (1983). "Stored Chemical Energy Propulsion System for Underwater Applications". Journal of Energy. 7 (2): 128–133. Bibcode:1983JEner...7..128H. doi:10.2514/3.62644.
^"Sulfur Hexafluoride". Hazardous Substances Data Bank. U.S. National Library of Medicine. Archived from the original on 9 May 2018. Retrieved 26 March 2013.
Maller VN, Naidu MS (1981). Advantages in High Voltage Insulation and Arc Interruption in SF6 and Vacuum. Oxford; New York: Pergamon Press. ISBN978-0-08-024726-7. OCLC7866855.
![Abundance and growth rate of SF 6 in Earth's troposphere (1978-2018).[9]](http://en.m.wikipedia.org/wiki/File:AGAGE_sulfur_hexafluroride_growth.png)
Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
