Sulfur hexafluoride
Introduction
Sulfur hexafluoride (SF6) is an inorganic, colorless, odorless, non-flammable, 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.
Physical Properties
Sulfur hexafluoride is a dense gas with a density of 6.12 g/L at sea level conditions, considerably higher than the density of air (1.225 g/L). It is colorless and odorless, with a molecular weight of 146.06 g/mol. It is generally transported as a liquefied compressed gas.
Chemical Properties
SF6 is inert, unlike many hexafluorides, due to its symmetrical structure. It exhibits a very high density and stability because of its large electron cloud. Its breakdown voltage is approximately 2.5 times higher than air, and at a pressure of three atmospheres, SF6 has a breakdown voltage 2.5 times the breakdown voltage at one atmosphere of pressure. SF6 molecules are extremely stable, with little chance of reactive encounters.
Production and Synthesis
Sulfur hexafluoride can be prepared by exposing or combining sulfur with fluorine. The sulfur is reacted with fluorine, creating a gas of sulfur hexafluoride. This reaction is exothermic. The most common method of sulfur hexafluoride production is through the reaction of sulfur hexachloride (S2Cl2) with fluorine gas, and then scrubbing the product to get rid of any byproducts.
Applications
Sulfur hexafluoride has numerous applications due to its electrical insulation properties. One of the primary uses is in electrical transformers where it is used as an insulating gas. It is also used in the semiconductor industry, as a dielectric medium for high-voltage circuit breakers, switchgear, and other electrical equipment. Additionally, it is used to fill tennis balls and soccer balls due to its ability to resist leaks and maintain pressure.
Environmental Impact
Sulfur hexafluoride is a potent greenhouse gas, with a global warming potential of 23,900 times that of CO2. Its lifespan in the atmosphere is approximately 3,200 years. Therefore, the release of SF6 into the atmosphere is regulated by international treaties and by industry and government regulations. It is important to detect leaks and to refill the gas compartments regularly.
Safety
While SF6 is nontoxic and nonflammable, it can asphyxiate humans by displacing air. It is also a potent greenhouse gas, so it is important to avoid releasing it into the atmosphere. The Occupational Safety and Health Administration (OSHA) and the Consumer Product Safety Commission (CPSC) regulate SF6. The CPSC has set an exposure limit of 1,000 ppm over an 8-hour workday.