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Tungsten(VI) fluoride



Tungsten(VI) fluoride
IUPAC name Tungsten(VI) fluoride
Other names Tungsten hexafluoride
Identifiers
CAS number 7783-82-6
Properties
Molecular formula WF6
Molar mass 297.83 g/mol
Appearance Colorless gas.
Density 13.1 g/L, gas.
Melting point

2.3°C (275.45 K)

Boiling point

17.1°C (290.25 K)

Solubility in water Hydrolyzes.
Structure
Molecular shape Octahedral
Dipole moment 0 D
Hazards
Main hazards Corrosive, highly toxic.
Related Compounds
Other anions Tungsten(VI) chloride,
Tungsten(VI) bromide
Other cations Chromium(V) fluoride,
Molybdenum(VI) fluoride
Related compounds Tungsten(IV) fluoride,
Tungsten(V) fluoride,
Uranium hexafluoride
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Tungsten(VI) fluoride, also known as tungsten hexafluoride, is a colorless gas. It is nonflammable, but highly corrosive and very toxic. The molecule itself is octahedral with the symmetry point group of Oh. The gas is most commonly used in the production of semiconductor circuits and circuit boards, through the process of chemical vapor deposition.[1]

Additional recommended knowledge

Contents

Industrial Synthesis

Tungsten hexafluoride of a purity high enough for semiconductor CVD is produced by the reaction of fluorine gas with tungsten metal. The metal is placed in a heated reactor, slightly pressurized to 1.2 to 2.0 psi, with a constant flow of WF6 infused with a small amount of fluorine gas.[2]

Reactions

WF6(g) + H2(g) + Al(s) → W(s) + HF(g) + AlF3(s)

This reaction occurs when tungsten is deposited on an aluminum. One application of this would be in the production of studs for semiconductor circuits.[3]

Tungsten can also be deposited on a silicon wafer or other semiconducting material via chemical vapor deposition, or CVD, as follows:[4]

WF6(g) + W* → WF6*

2 SiH4(g) + WF6* → W(s) + 2 SiHF3 (g) + 3 H2(g)

The silane SiH4 reduces the tungsten from an oxidation state of 6+ (VI) to its elemental state of zero.

Safety

On contact with water tungsten(VI) fluoride forms hydrofluoric acid (HF), which can penetrate the skin and cause damage to the subdermal tissues and bone. Inhalation burns the respiratory tract and can be toxic. WF6 is a lachrymator which causes tearing and irritation of the eyes. Contact causes burns to the eyes, skin and mucous membranes.[5]

In Uncle Tungsten, Oliver Sacks comments on how he wanted WF6-filled balloons for his 65th birthday, but the gas was too reactive. Had one of the balloons popped, the tungsten(VI) fluoride would have reacted with moisture in the air to form hydrogen fluoride.

References

  1. ^ Kirss, Rein U., Lamartine Meda. "Chemical Vapor Deposition of Tungsten Oxide." Applied Organometallic Chemistry 12 (1998): 155–160.
  2. ^ Patent Storm
  3. ^ Ip.com
  4. ^ James Clark School of Engineering
  5. ^ Matheson Gas
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tungsten(VI)_fluoride". A list of authors is available in Wikipedia.
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