Hexafluoroethane

Hexafluoroethane is the perfluorocarbon counterpart to the hydrocarbon ethane. It is a non-flammable gas negligibly soluble in water and slightly soluble in alcohol. It is an extremely potent and long-lived greenhouse gas.

Hexafluoroethane
Structural formula of hexafluoroethane
Ball-and-stick model of the hexafluoroethane molecule
Names
IUPAC name
Hexafluoroethane
Other names
Carbon hexafluoride, 1,1,1,2,2,2-Hexafluoroethane, Perfluoroethane, Ethforane, Halocarbon 116, PFC-116, CFC-116, R-116, Arcton 116, Halon 2600, UN 2193
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.855
EC Number
  • 200-939-8
RTECS number
  • KI4110000
UNII
Properties
C2F6
Molar mass 138.01 g.mol−1
Appearance Colorless odorless gas
Density 5.734 kg.m−3 at 24 °C
Melting point −100.6 °C (−149.1 °F; 172.6 K)
Boiling point −78.2 °C (−108.8 °F; 195.0 K)
0.0015%
log P 2
0.000058 mol.kg−1.bar−1
Hazards
Safety data sheet See: data page
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
1
0
Flash point Non-flammable
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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 (−170 °C). Below 103 K it has a slightly disordered structure, and over the transition point, it has a body centered cubic structure.[1] The critical point is at 19.89 °C (293.04 K) and 30.39 bar.[2]

Table of densities:

State, temperature Density (kg.m−3)
liquid, −78.2 °C 16.08
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. The primary aluminium and the semiconductor manufacturing industries are the major emitters of hexafluoroethane using the Hall-Héroult process.

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

Environmental effects
Hexafluorethane timeseries at various latitudes.

Due to the high energy of C-F bonds, hexafluorethane is nearly inert and thus acts as an extremely stable greenhouse gas, with an atmospheric lifetime of 10,000 years (other sources: 500 years).[3] It has a global warming potential (GWP) of 9200 and an ozone depletion potential (ODP) of 0. Hexafluoroethane is included in the IPCC list of greenhouse gases.

Hexafluorethane did not exist in significant amounts in the environment prior to industrial-scale manufacturing. Atmospheric concentration of hexafluoroethane reached 3 pptv at the start of the 21st century.[4] Its absorption bands in the infrared part of the spectrum cause a radiative forcing of about 0.001 W/m2.

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.

See also

References
  1. Zeng, S.X.; Simmons, R.O.; Timms, D.N.; Evans, A.C. (1999). "Dynamics and structure of solid hexafluoroethane". Journal of Chemical Physics. 110 (3): 1650–61. Bibcode:1999JChPh.110.1650Z. doi:10.1063/1.477806.
  2. Helmut Schan: Handbuch der reinsten Gase. Springer, 2005, ISBN 978-3-540-23215-5, S. 307.
  3. "Perfluoroethane CASRN: 76-16-4". TOXNET Toxicology Data Network. National Library of Medicine. 2016-10-25.
  4. "Climate Change 2001: The Scientific Basis". Archived from the original on 2007-06-15. Retrieved 2007-06-02.
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