Hexafluoroethane

Hexafluoroethane is a perfluorocarbon (a completely fluorinated haloalkane) derived from ethane. It is a non-flammable gas negligibly soluble in water and slightly soluble in alcohol.

Physical properties

Solid phase has two allotropes. Also there has been conflicts in literature of the phase transition temperature, according to last works it is assigned to 103 K (-170 °C). Below 103 K it has slightly disordered structure and over transition point, it has body centered cubic structure.

Table of densities:

State, temperature	Density (kg.m^-3)
liquid, -78.2 °C	1608
gas, -78.2 °C	8.86
gas, 15 °C	5.84
gas, 20.1 °C	5.716
gas, 24 °C	5.734

Vapor density is 4.823 (air = 1), specific gravity at 21 °C is 4.773 (air = 1) 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.

Together with trifluoromethane it is used in refrigerants R508A (61%) and R508B (54%).

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 10000 years and a global warming potential (GWP) of 9200. Atmospheric concentration of tetrafluoroethane is 3 pptv (increase by 3 pptv since 1750). 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 (ODP) 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 on the low places and in high concentrations it can cause asphyxiation. Other effects are similar as at tetrafluoromethane.