Everything about Sulfur Hexafluoride totally explained
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Sulfur hexafluoride is an
inorganic compound with the formula . It is a colorless, odorless, non-
toxic and non-
flammable gas (under standard conditions). 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's 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
can be prepared from the elements through exposure of [[Sulfur|]] to [[fluorine|]]. 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
disproportionate any and then scrubbing the product with NaOH to destroy remaining [[Sulfurtetrafluoride|]].
There is virtually no reaction chemistry for . It doesn't react with molten
sodium, but reacts
exothermically with
lithium.
Starting from, one can prepare, which is structurally related to . The monochloride is, however, a strong oxidant and readily hydrolyzed to
sulfate.
Applications
Of the 8000 tonnes produced per year, most of the goes into three applications: firstly as a
gaseous dielectric medium or other use in the
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
is used in the
electrical industry as a
gaseous dielectric medium for high-voltage (1 kV and above)
circuit breakers,
switchgear, and other
electrical equipment, often replacing oil filled circuit breakers (OCBs) that can contain harmful
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. 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 breakers in industry as they're safer and require less maintenance. Although most of the decomposition products tend to quickly re-form ,
arcing or
corona can produce
disulfur decafluoride ([[Disulfurdecafluoride|]]), a highly
toxic gas, with toxicity similar to
phosgene. was considered a potential
chemical warfare agent in
World War II because it doesn't 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.
Medical use
Because is relatively slowly absorbed by the bloodstream, it's used to provide a long-term
tamponade or plug of a retinal hole in
retinal detachment repair operations.
In a further medical application, 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 utilized to examine the vascularity of tumours amongst other things.
Tracer compound
Gaseous is still a commonly used tracer gas for use in short-term experiments of
ventilation efficiency in buildings and indoor enclosures, and for determining
infiltration rates. Several 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 harmless test gas in an experiment at
St John's Wood tube station in
London, England 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 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.
plasma is also used in the
semiconductor industry as an
etchant.
The
magnesium industry uses large amounts of SF
6 as inert gas to fill casting forms.
Due to its high density, sulfur hexafluoride is often used in public "magic" tricks where it's renowned for being "invisible water". One video shows a small 'boat' made from
aluminium foil being carefully placed in a container of, 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.
Greenhouse gas
According to the
Intergovernmental Panel on Climate Change, is the most potent
greenhouse gas that it has evaluated, with a
global warming potential of 22,200 times that of [[carbondioxide|]] when compared over a 100 year period-- is very stable (for countries reporting their emissions to the UNFCCC, a GWP of 23,900 for was suggested at the third Conference of the Parties:
GWP used in Kyoto protocol). Its mixing ratio in the
atmosphere is lower than that of about 6.5 parts per trillion (
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).
Notable characteristics
Because the gas has a high density (over five times denser than air), can be poured into open containers, like beakers and fishtanks. Moreover, light objects, for example ship-like vessels made out of light wood or aluminium foil containing air inside, can float on the gas.
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, 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 is the opposite of inhaling helium, a reduction in the
pitch of the voice.
Although inhaling 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 is too heavy for the lungs to expel unassisted, and that after inhaling, it's 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 would be purged from the lungs within a breath or two.
Further Information
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