Sulfur hexafluoride or sulphur hexafluoride (
British spelling
Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the two most notable variations being British and American ...
) is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
with the formula SF
6. It is a colorless, odorless, non-
flammable
A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
, and non-toxic gas. has an
octahedral geometry, consisting of six
fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
atoms attached to a central
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
atom. It is a
hypervalent molecule.
Typical for a
nonpolar gas, 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.
is 23,500 times more potent than as a
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
but exists in relatively minor concentrations in the atmosphere. Its concentration in Earth's
troposphere reached 10.63
parts per trillion (ppt) in 2021, rising at 0.39 ppt/year.
The increase over the prior 40 years was driven in large part by the expanding electric power sector, including
fugitive emissions from banks of gas contained in its medium- and high-voltage
switchgear. Uses in magnesium, aluminium, and electronics manufacturing also hastened atmospheric growth.
Synthesis and reactions
Sulfur hexafluoride on Earth exists primarily as a man-made industrial gas, but has also been found to occur naturally.
can be prepared from the elements through exposure of
to
. This was 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
disproportionate
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...
any
(which is highly toxic) and then scrubbing the product with
NaOH to destroy remaining
.
Alternatively, utilizing
bromine, sulfur hexafluoride can be synthesized from SF
4 and CoF
3 at lower temperatures (e.g. 100 °C), as follows:
There is virtually no reaction chemistry for . A main contribution to the inertness of SF
6 is the
steric hindrance of the sulfur atom, whereas its heavier group 16 counterparts, such as
SeF6 are more reactive than SF
6 as a result of less steric hindrance (See hydrolysis example). It does not react with molten
sodium below its boiling point, but reacts
exothermic
In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...
ally with
lithium.
Applications
The
electrical power industry used about 80% of the sulfur hexafluoride produced in 2000, mostly as a
gaseous dielectric medium. Other main uses as of 2015 included a
silicon etchant for
semiconductor manufacturing, and an
inert gas for the casting of
magnesium.
Dielectric medium
is used in the
electrical industry as a
gaseous dielectric medium for high-voltage
sulfur hexafluoride circuit breaker
Sulfur hexafluoride circuit breakers protect electrical power stations and distribution systems by interrupting electric currents, when tripped by a protective relay. Instead of oil, air, or a vacuum, a sulfur hexafluoride circuit breaker uses ...
s,
switchgear, and other
electrical equipment, often replacing oil-filled circuit breakers (OCBs) that can contain harmful
polychlorinated biphenyls (PCBs). 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. The high dielectric strength is a result of the gas's high
electronegativity and
density. 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. Exposure to an arc chemically breaks down though most of the decomposition products tend to quickly re-form , a process termed "self-healing".
Arcing or
corona can produce
disulfur decafluoride
Disulfur decafluoride is a chemical compound with the formula . It was discovered in 1934 by Denbigh and Whytlaw-Gray. Each sulfur atom of the molecule is octahedral, and surrounded by five fluorine atoms and one sulfur atom. The two sulfur ato ...
(
), a highly
toxic gas, with toxicity similar to
phosgene
Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, espe ...
. was considered a potential
chemical warfare
Chemical warfare (CW) involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from nuclear warfare, biological warfare and radiological warfare, which together make up CBRN, the military acronym ...
agent in
World War II because it does not produce
lacrimation or skin irritation, thus providing little warning of exposure.
is also commonly encountered as a high voltage dielectric in the high voltage supplies of
particle accelerators, such as
Van de Graaff generators and
Pelletrons and high voltage transmission
electron microscopes.
Alternatives to as a dielectric gas include several fluoroketones. Compact GIS technology that combines vacuum switching with clean air insulation has been introduced for a subset of applications up to 420
kV.
Medical use
is used to provide a
tamponade or plug of a retinal hole in
retinal detachment
Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blin ...
repair operations in the form of a gas bubble. It is inert in the
vitreous chamber
The vitreous chamber is the space in the eye occupied by vitreous humor.
Structure
Within the vertebrate eye, there are considered to be three chambers: anterior, posterior, and vitreous. It is important to note that the eye can also be classifie ...
. 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.
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.
It remains visible in the blood for 3 to 8 minutes, and is exhaled by the lungs.
Tracer compound
Sulfur hexafluoride was the
tracer gas used in the first
roadway air dispersion model
Roadway air dispersion modeling is the study of air pollutant transport from a roadway or other linear emitter. Computer models are required to conduct this analysis, because of the complex variables involved, including vehicle emissions, vehicle ...
calibration; this research program was sponsored by the
U.S. Environmental Protection Agency and conducted in
Sunnyvale, California
Sunnyvale () is a city located in the Santa Clara Valley in northwest Santa Clara County in the U.S. state of California.
Sunnyvale lies along the historic El Camino Real and Highway 101 and is bordered by portions of San Jose to the nort ...
on
U.S. Highway 101
U.S. Route 101, or U.S. Highway 101 (US 101), is a north–south United States Numbered Highway that runs through the states of California, Oregon, and Washington, on the West Coast of the United States. It is also known as (The Royal Roa ...
. Gaseous is used as a tracer gas in short-term experiments of
ventilation efficiency in buildings and indoor enclosures, and for determining
infiltration
Infiltration may refer to:
Science, medicine, and engineering
*Infiltration (hydrology), downward movement of water into soil
*Infiltration (HVAC), a heating, ventilation, and air conditioning term for air leakage into buildings
*Infiltration (me ...
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 .
Sulfur hexafluoride was used as a non-toxic test gas in an experiment at
St John's Wood tube station in
London, United Kingdom on 25 March 2007. 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
The Secretary of State for Transport, also referred to as the transport secretary, is a secretary of state in the Government of the United Kingdom, with overall responsibility for the policies of the Department for Transport. The incumbent i ...
Douglas 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 SF
6 to verify the containment properties of the fume hood.
It has been used successfully as a tracer in
oceanography
Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...
to study
diapycnal mixing and air-sea gas exchange.
Other uses
* The
magnesium industry uses as an inert "cover gas" to prevent oxidation during
casting. Once the largest user, consumption has declined greatly with capture and recycling.
*
Insulated glazing windows have used it as a filler to improve their thermal and acoustic insulation performance.
*
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
is used in the
semiconductor industry as an
etchant
Etching is a printmaking technique in art.
Etching may also refer to:
* Etching (microfabrication), a process in producing microelectronics
* Glass etching, a glass decoration technique
* Chemical milling, or industrial etching
* Photochemical ma ...
in processes such as
deep reactive-ion etching
Deep reactive-ion etching (DRIE) is a highly anisotropic etch process used to create deep penetration, steep-sided holes and trenches in wafers/substrates, typically with high aspect ratios. It was developed for microelectromechanical systems ( ...
. A small fraction of the breaks down in the plasma into sulfur and fluorine, with the fluorine ions performing a chemical reaction with silicon.
* Tires filled with it take longer to deflate from
diffusion through rubber due to the larger molecule size.
*
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. 277 tons was used during the peak in 1997.
* The
United States Navy's
Mark 50 torpedo closed
Rankine-cycle propulsion system is powered by sulfur hexafluoride in an
exothermic reaction with solid
lithium.
*
Waveguides in high-power
microwave systems are pressurized with it. The gas electrically insulates the waveguide, preventing internal arcing.
*
Electrostatic loudspeakers have used it because of its high dielectric strength and high molecular weight.
* The
chemical weapon disulfur decafluoride
Disulfur decafluoride is a chemical compound with the formula . It was discovered in 1934 by Denbigh and Whytlaw-Gray. Each sulfur atom of the molecule is octahedral, and surrounded by five fluorine atoms and one sulfur atom. The two sulfur ato ...
is produced with it as a
feedstock
A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials that are feedstock for future finished products. As feedst ...
.
* For entertainment purposes, when breathed, causes the voice to become significantly deeper, due to its density being so much higher than air, as seen i
this video This 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.
* 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
Greenhouse gas
File:SF6 mm.png, 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
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they ...
.
File:AGAGE sulfur hexafluroride growth.png, Abundance and growth rate of in Earth's troposphere (1978-2018).[Simmonds, 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. . ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
File:Halogenated gas concentrations 1978-present.png, Atmospheric concentration of SF6 vs. similar man-made gases (right graph). Note the log scale.
According to the
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) a ...
, is the most potent
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
. Its
global warming potential of 23,900 times that of
when compared over a 100-year period. Sulfur hexafluoride is inert in the
troposphere and
stratosphere
The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air ...
and is extremely long-lived, with an estimated
atmospheric lifetime of 800–3,200 years.
Measurements of SF
6 show that its global average
mixing ratio
In chemistry and physics, the dimensionless mixing ratio is the abundance of one component of a mixture relative to that of all other components. The term can refer either to mole ratio (see concentration) or mass ratio (see stoichiometry).
In at ...
has increased from a steady base of about 54
parts per quadrillion
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they ...
prior to industrialization, to over 11 parts per trillion (ppt) as of June 2022, and is increasing by about 0.4 ppt (3.5 percent) per year.
Average global SF
6 concentrations increased by about seven percent 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 SF
6 released compared to
carbon dioxide, its overall individual contribution to global warming is estimated to be less than 0.2 percent, however the collective contribution of it and similar man-made halogenated gases has reached about 10 percent as of 2020. Alternatives are being tested.
In Europe, falls under the
F-Gas
Fluorinated gases (F-gases) are chemical compounds containing fluorine that are gases near room temperature.
Types of F-gases
The most common F-gases are hydrofluorocarbons (HFCs), which contain hydrogen, fluorine, and carbon. They are used in ...
directive which ban or control its use for several applications.
Since 1 January 2006, is banned as a tracer gas and in all applications except
high-voltage switchgear. 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 . This was done by comparing purchases with inventory, assuming the difference was leaked, then locating and fixing the leaks.
Physiological effects and precautions
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. 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 .
As with all gases, the density of 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, 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.
Sulfur hexafluoride has an
anesthetic potency slightly lower than
nitrous oxide; it is classified as a mild anesthetic.
See also
*
Selenium hexafluoride
Selenium hexafluoride is the inorganic compound with the formula SeF6. It is a very toxic colourless gas described as having a "repulsive" odor. It is not widely encountered and has no commercial applications.
Structure, preparation, and reacti ...
*
Tellurium hexafluoride
Tellurium hexafluoride is the inorganic compound of tellurium and fluorine with the chemical formula TeF6. It is a colorless, highly toxic gas with an unpleasant odor.
Preparation
Tellurium hexafluoride can be prepared by treating tellurium w ...
*
Uranium hexafluoride
Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
*
Hypervalent molecule
*
Halocarbon
Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, organochlori ...
—another group of major greenhouse gases
*
Trifluoromethylsulfur pentafluoride
Trifluoromethylsulfur pentafluoride, CF3SF5, is a rarely used industrial greenhouse gas. It was first identified in the atmosphere in 2000. Trifluoromethylsulfur pentafluoride is considered to be one of the several "super-greenhouse gases".
Prop ...
, a similar gas
References
Further reading
*
*
*
*
*
SF6 Reduction Partnership for Electric Power Systems*
External links
��
National Pollutant Inventory
High GWP Gases and Climate Changefrom the U.S.
EPA
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
website
International Conference on SF6 and the Environment
{{DEFAULTSORT:Sulfur Hexafluoride
Sulfur fluorides
Dielectric gases
Greenhouse gases
Octahedral compounds
Hexafluorides
Industrial gases
Refrigerants
Hypervalent molecules
General anesthetics
Ultrasound contrast agents