Hexafluoroethane


Hexafluoroethane is a fluorocarbon counterpart to the hydrocarbon ethane. It is a non-flammable gas negligibly soluble in water and slightly soluble in alcohol.

Physical properties

Hexafluoroethane's solid phase has two polymorphs. In the scientific literature, different phase transition temperatures have been stated. The latest works assign it at 103 K. Below 103 K it has a slightly disordered structure, and over the transition point, it has a body centered cubic structure. The critical point is at 19.89 °C and 30.39 bar.
Table of densities:
State, temperatureDensity
liquid, −78.2 °C16.08
gas, −78.2 °C8.86
gas, 15 °C5.84
gas, 20.1 °C5.716
gas, 24 °C5.734

Vapor density is 4.823, specific gravity at 21 °C is 4.773 and specific volume at 21 °C is 0.1748 m3/kg.

Uses

Hexafluoroethane is used as a versatile etchant in semiconductor manufacturing. It can be used for selective etching of metal silicides and oxides versus their metal substrates and also for etching of silicon dioxide over silicon. The primary aluminium and the semiconductor manufacturing industries are the major emitters of hexafluoroethane.
Together with trifluoromethane it is used in refrigerants R508A and R508B.

Environmental effects

Due to the high energy of C-F bonds, it is very inert and thus acts as an extremely stable greenhouse gas, with an atmospheric lifetime of 10,000 years and a global warming potential of 9200. A calculated atmospheric lifetime range of 500 to 10,000 years has been reported.
Atmospheric concentration of tetrafluoroethane is 3 pptv. However, it has a strong absorption potential in the infrared part of the spectrum. Radiative forcing is 0.001 W/m2. Its ozone depletion potential is 0.
Hexafluoroethane is listed in IPCC list of greenhouse gases.
Main industrial emissions of hexafluoroethane besides tetrafluoromethane are produced during production of aluminium using Hall-Héroult process.

Health risks

Due to its high relative density, it gathers in low-lying areas, and at high concentrations it can cause asphyxiation. Other health effects are similar to tetrafluoromethane.