Sulfur hexafluoride

EsaflonSulfur(VI) fluorideSulfur tetrafluorideSulfuryl fluorideTellurium hexafluorideSulfur hexafluoride (SF6) is an inorganic, colorless, odorless, non-flammable, non-toxic extremely potent greenhouse gas, and an excellent electrical insulator. SF6 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 is poorly soluble in water but quite soluble in nonpolar organic solvents. It is generally transported as a liquefied compressed gas. It has a density of 6.12 g/L at sea level conditions, considerably higher than the density of air (1.225 g/L). Sulfur hexafluoride (SF6) is an inorganic, colorless, odorless, non-flammable, non-toxic extremely potent greenhouse gas, and an excellent electrical insulator. SF6 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 is poorly soluble in water but quite soluble in nonpolar organic solvents. It is generally transported as a liquefied compressed gas. It has a density of 6.12 g/L at sea level conditions, considerably higher than the density of air (1.225 g/L). SF6 can be prepared from the elements through exposure of S8 to F2. 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 any S2F10 (which is highly toxic) and then scrubbing the product with NaOH to destroy remaining SF4. Alternatively, utilizing bromine, 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 SF6. 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 (See hydrolysis example). It does not react with molten sodium below its boiling point, but reacts exothermically with lithium. More than 10,000 tons of SF6 are produced per year, most of which (over 8,000 tons) is used as a gaseous dielectric medium in the electrical industry. Other main uses include an inert gas for the casting of magnesium, and as an inert filling for insulated glazing windows. SF6 is used in the electrical industry as a gaseous dielectric medium for high-voltage circuit breakers, switchgear, and other electrical equipment, often replacing oil filled circuit breakers (OCBs) that can contain harmful PCBs. SF6 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 SF6 though most of the decomposition products tend to quickly re-form SF6, a process termed 'self-healing'. Arcing or corona can produce disulfur decafluoride (S2F10), a highly toxic gas, with toxicity similar to phosgene. S2F10 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. SF6 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 include fluoroketone. SF6 is used to provide a tamponade 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 and initially doubles its volume in 36 hours before being absorbed in the blood in 10–14 days.