Carbon tetrafluoride 

Tetrafluoromethane
IUPAC name Tetrafluoromethane
Carbon tetrafluoride
Other names Perfluoromethane, Tetrafluorocarbon, Freon 14, Halon 14, Arcton 0, CFC 14, PFC 14, R 14, UN 1982
Identifiers
CAS number [75-73-0]
PubChem 6393
EINECS number 200-896-5
RTECS number FG4920000
SMILES
 
InChI
 
Properties
Molecular formula CF4
Molar mass 88.00 g/mol
Appearance Colorless odorless gas
Density 3.72 g/l, gas (15 °C)
Melting point

-183.6 °C (89.6 K)
Boiling point

-127.8 °C (145.4 K)
Solubility in water 0.005 %V at 20 °C

0.0038 %V at 25 °C
Vapor pressure 3.65 MPa at 15 °C

106.5 kPa at -127 °C
Hazards
NFPA 704
0
1
0
 
R-phrases None
S-phrases None
Flash point Non flammable
Autoignition
temperature		 > 1100 °C
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox references

Tetrafluoromethane, also known as carbon tetrafluoride, Freon-14 and R 14, is a carbon fluoride (CF4). It can be considered either a haloalkane, halomethane, perfluorocarbon or an inorganic compound.

At a temperature of −198 °C, it has monoclinic structure with lattice constants a = 8.597, b = 4.433, c = 8.381 (.10-1 nm), β = 118.73°[1].

Contents

Additional physical properties

Property Value
Density (ρ) at −196 °C (solid) 1.943 g.cm−3
Density (ρ) at -183 °C 1.89 g.cm−3
Density (ρ) at −127.8 °C (liquid) 1.603 g.cm−3
Density (ρ) at −80 °C (gas) 1.317 kg.m-3
Density (ρ) at 15 °C (gas) 3.72 kg.m−3
Density (ρ) at 21 °C (gas) 3.858 kg.m−3
Triple point temperature (Tt) −183.7 °C (89.4 K)
Critical temperature (Tc) −45.5 °C (227.6 K)
Critical pressure (pc) 3.793 MPa (37.43 bar)
Critical volume (Vc) 0.142 dm3.mol−1
Critical compressibility (Zc) 2.77
Latent heat of fusion (lf) at triple point 8.09 kJ.kg−1
Latent heat of vaporization (lv) at −127.8 °C 135.7 kJ.kg−1
Specific heat capacity at constant pressure (cp) at 30 °C 58 J.mol−1.K−1
Specific heat capacity at constant pressure (cp) at -145 °C 80.08 J.mol−1.K−1
Specific heat capacity at constant volume (cv) at 30 °C 49 J.mol−1.K−1
Heat capacity ratio (κ) at 30 °C 1.178571
Compressibility Factor (Z) at 15 °C 0.9981
Acentric factor (ω) 0.177
Dipole moment 0 D
Viscosity (η) at 0 °C 16.1 μPa.s (0.0161 cP)
Viscosity (η) at −60.3 °C 17.0 μPa.s (0.0170 cP)
Surface tension (σ) at −80 °C 6.4 mN.m−1
Thermal conductivity (λ) at 0 °C 15.03 mW.m−1.K−1

Chemistry

Pure tetrafluoromethane was first synthesised in 1926[2].

Tetrafluoromethane can be prepared in the laboratory by the reaction of silicon carbide with fluorine:

SiC + 2 F2 → CF4 + Si

or by the fluorination of carbon dioxide, carbon monoxide or phosgene with sulfur tetrafluoride. Commercially it is manufactured by the aggressive reaction of fluorine with dichlorodifluoromethane or chlorotrifluoromethane; it is also produced during the electrolysis of metal fluorides MF, MF2 using a carbon electrode.

Tetrafluoromethane, as other fluorinated hydrocarbons, is very stable due to the strength of C-F bonds with bonding energy of 515 kJ.mol-1 (see Environmental effects). As a result, it is inert to acids and hydroxides. However, it reacts explosively with alkali metals. Thermal decomposition of CF4produces toxic gases (carbonyl fluoride and carbon monoxide) and in the presence of water will also yield hydrogen fluoride.

It is very slightly soluble in water (about 20 mg.l-1), but miscible with ethanol, ether, benzene.

Uses

Tetrafluoromethane is sometimes used as a low temperature refrigerant. It is used in electronics microfabrication alone or in combination with oxygen as a plasma etchant for silicon, silicon dioxide, and silicon nitride.[3]

Environmental effects

Tetrafluoromethane is a potent greenhouse gas that contributes to the greenhouse effect. It is very stable, has an atmospheric lifespan of 50,000 years, and a high greenhouse warming potential of 6500 (CO2 has a factor of 1); however, the low amount in the atmosphere restricts the overall radiative forcing effect.citation needed

Although structurally similar to chlorofluorocarbons (CFCs), tetrafluoromethane does not deplete the ozone layer. This is because the depletion is caused by the chlorine atoms in CFCs, which dissociate when struck by UV radiation. Carbon-fluorine bonds are stronger and less likely to dissociate.citation needed

Health risks

Inhalation of tetrafluoromethane can cause, depending on concentration, headache, nausea, dizziness and damage to the cardiovascular system (mainly the heart). Long-term exposure can cause severe heart damage.

Due to its density, tetrafluoromethane can displace air, creating an asphyxiation hazard in inadequately ventilated areas.

References

  1. ^ F. Brezina, J. Mollin, R. Pastorek, Z. Sindelar. Chemicke tabulky anorganickych sloucenin (Chemical tables of inorganic compounds). SNTL, 1986.
  2. ^ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 
  3. ^ K. Williams, K. Gupta, M. Wasilik. Etch Rates for Micromachining Processing - Part II J. Microelectromech. Syst., vol. 12, pp. 761-777, Dec. 2003.

See also

External links