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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 SF6. It is a colorless, odorless, non- flammable, and non-toxic gas. has an
octahedral geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc ...
, 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 In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus p ...
. Typical for a
nonpolar In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain one or more polar ...
gas, is poorly
soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...
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 The density of air or atmospheric density, denoted '' ρ'', is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variation in atmospheric pressure, temperature a ...
(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 The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
reached 10.63
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 ...
(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 Fugitive emissions are leaks and other irregular releases of gases or vapors from a pressurized containment – such as appliances, storage tanks, pipelines, wells, or other pieces of equipment – mostly from industrial activities. In addition ...
from banks of gas contained in its medium- and high-voltage
switchgear In an electric power system, a switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be ...
. 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 Ferdinand Frédéric Henri Moissan (28 September 1852 – 20 February 1907) was a French chemist and pharmacist who won the 1906 Nobel Prize in Chemistry for his work in isolating fluorine from its compounds. Moissan was one of the original mem ...
and
Paul Lebeau Paul Marie Alfred Lebeau (19 December 1868 – 18 November 1959) was a French chemist. He studied at the elite École supérieure de physique et de chimie industrielles de la ville de Paris (ESPCI). Together with his doctoral advisor Henri Mo ...
in 1901. Some other sulfur fluorides are cogenerated, but these are removed by heating the mixture to disproportionate any (which is highly toxic) and then scrubbing the product with
NaOH Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...
to destroy remaining . Alternatively, utilizing
bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simila ...
, sulfur hexafluoride can be synthesized from SF4 and CoF3 at lower temperatures (e.g. 100 °C), as follows: There is virtually no reaction chemistry for . A main contribution to the inertness of SF6 is the
steric hindrance Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
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 (See hydrolysis example). It does not react with molten
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
below its boiling point, but reacts exothermically with
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
.


Applications

The
electrical power industry Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
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 Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuit (IC) chips such as modern computer processors, microcontrollers, and memory chips such as NAND flash and DRAM that are pres ...
, and an
inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...
for the casting of
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
.


Dielectric medium

is used in the
electrical industry The electric power industry covers the generation, transmission, distribution and sale of electric power to the general public and industry. The commodity sold is actually energy, not power, e.g. consumers pay for kilowatt-hours, power multip ...
as a gaseous dielectric medium for high-voltage sulfur hexafluoride circuit breakers,
switchgear In an electric power system, a switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be ...
, and other
electrical Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
equipment, often replacing oil-filled circuit breakers (OCBs) that can contain harmful
polychlorinated biphenyl Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1979 and internationally by t ...
s (PCBs). gas under
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
is used as an insulator in gas insulated switchgear (GIS) because it has a much higher
dielectric strength In physics, the term dielectric strength has the following meanings: *for a pure electrically insulating material, the maximum electric field that the material can withstand under ideal conditions without undergoing electrical breakdown and beco ...
than
air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
or dry
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
. The high dielectric strength is a result of the gas's high
electronegativity Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...
and
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
. 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 An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. An ...
or
corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
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 Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
gas, with toxicity similar to phosgene. 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 World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
because it does not produce
lacrimation Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. The different types of ...
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 accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...
s, such as
Van de Graaff generator A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate electric charge on a hollow metal globe on the top of an insulated column, creating very high electric potentials. It produces very high voltage ...
s and
Pelletron A Pelletron is a type of electrostatic generator, structurally similar to a Van de Graaff generator. Pelletrons have been built in many sizes, from small units producing voltages up to 500 kilovolts (kV) and beam energies up to 1 megaelectronvolt ...
s and high voltage transmission
electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
s. 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 Tamponade () is the closure or blockage (as of a wound or body cavity) by or as if by a tampon, especially to stop bleeding. Tamponade is a useful method of stopping a hemorrhage. This can be achieved by applying an absorbent dressing directl ...
or plug of a retinal hole in retinal detachment 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 Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...
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 A tracer-gas leak testing method is a nondestructive testing method that detects gas leaks. A variety of methods with different sensitivities exist. Tracer-gas leak testing is used in the petrochemical industry, the automotive industry, and in the ...
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, vehicl ...
calibration; this research program was sponsored by the
U.S. Environmental Protection Agency The Environmental Protection Agency (EPA) is an Independent agencies of the United States government, independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon pro ...
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 Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Ventilator, a m ...
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 The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
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 ST, St, or St. may refer to: Arts and entertainment * Stanza, in poetry * Suicidal Tendencies, an American heavy metal/hardcore punk band * Star Trek, a science-fiction media franchise * Summa Theologica, a compendium of Catholic philosoph ...
in
London London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...
, 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 Douglas Garven Alexander (born 26 October 1967) is a Labour politician who served as Member of Parliament (MP) for Paisley and Renfrewshire South, previously Paisley South, from 1997 until his defeat in 2015. During this time, he served as ...
, was to investigate how toxic gas might spread throughout
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
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 The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE ) is an American professional association seeking to advance heating, ventilation, air conditioning and refrigeration The term refrigeration refers to the ...
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 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 Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
industry uses as an inert "cover gas" to prevent oxidation during
casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
. Once the largest user, consumption has declined greatly with capture and recycling. *
Insulated glazing Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned window, ...
windows have used it as a filler to improve their thermal and acoustic insulation performance. * plasma is used in the
semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
industry as an etchant in processes such as deep reactive-ion etching. 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 Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
through rubber due to the larger molecule size. *
Nike Nike often refers to: * Nike (mythology), a Greek goddess who personifies victory * Nike, Inc., a major American producer of athletic shoes, apparel, and sports equipment Nike may also refer to: People * Nike (name), a surname and feminine give ...
likewise used it to obtain a
patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...
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 The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
's
Mark 50 torpedo The Mark 50 torpedo is a U.S. Navy advanced lightweight torpedo for use against fast, deep-diving submarines. The Mk 50 can be launched from all anti-submarine aircraft and from torpedo tubes aboard surface combatant ships. The Mk 50 was intended ...
closed Rankine-cycle propulsion system is powered by sulfur hexafluoride in an
exothermic reaction In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC defines ...
with solid
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
. *
Waveguide A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...
s in high-power
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
systems are pressurized with it. The gas electrically insulates the waveguide, preventing internal arcing. *
Electrostatic loudspeakers An electrostatic loudspeaker (ESL) is a loudspeaker design in which sound is generated by the force exerted on a membrane suspended in an electrostatic field. Design and functionality The speakers use a thin flat diaphragm usually consisting o ...
have used it because of its high dielectric strength and high molecular weight. * The
chemical weapon A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a ...
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 Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
, which causes someone's voice to become much higher. Both of these effects should only be attempted with caution as these gases displace
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
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 The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
) 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 Global warming potential (GWP) is the heat absorbed by any greenhouse gas in the atmosphere, as a multiple of the heat that would be absorbed by the same mass of carbon dioxide (). GWP is 1 for . For other gases it depends on the gas and the time ...
of 23,900 times that of when compared over a 100-year period. Sulfur hexafluoride is inert in the
troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
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 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 ...
of 800–3,200 years. Measurements of SF6 show that its global average mixing ratio has increased from a steady base of about 54 parts per quadrillion 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 SF6 concentrations increased by about seven percent per year during the 1980s and 1990s, mostly as the result of its use in
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
production, and by electrical utilities and electronics manufacturers. Given the small amounts of SF6 released compared to
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, 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 High voltage switchgear is any switchgear used to connect or disconnect a part of a high-voltage power system. This equipment is essential for the protection and safe operation, without interruption, of a high voltage power system, and is importa ...
. It was reported in 2013 that a three-year effort by the
United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United Stat ...
to identify and fix leaks at its laboratories in the United States such as the
Princeton Plasma Physics Laboratory Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science. Its primary mission is research into and development of fusion as an energy source. It is known ...
, 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 Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that ca ...
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 In music, timbre ( ), also known as tone color or tone quality (from psychoacoustics), is the perceived sound quality of a musical note, sound or musical tone, tone. Timbre distinguishes different types of sound production, such as choir voice ...
, 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 In chemistry, the molar mass of a chemical compound is defined as the mass of a sample of that compound divided by the amount of substance which is the number of moles in that sample, measured in moles. The molar mass is a bulk, not molecular, p ...
. Unlike
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
, 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 An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into two ...
potency slightly lower than
nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...
; 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 In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus p ...
* Halocarbon—another group of major greenhouse gases * Trifluoromethylsulfur pentafluoride, a similar gas


References


Further reading

* * * * *
SF6 Reduction Partnership for Electric Power Systems
*


External links



National Pollutant Inventory The National Pollutant Inventory (NPI) is a database of Australian pollution emissions managed by the Australian Commonwealth, State and Territory Governments. A condensed version of the information collected is available to the public via the NPI ...

High GWP Gases and Climate Change
from 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