Tungsten(VI) fluoride

Chembox new
ImageFileL1 = Tungsten(VI) fluoride.jpg
ImageSizeL1 = 100px
ImageNameL1 = Tungsten(VI) fluoride
ImageFileR1 = Tungsten-hexafluoride-3D-balls.png ImageSizeR1 = 100px
ImageNameR1 = Ball-and-stick model of tungsten hexafluoride
IUPACName = Tungsten(VI) fluoride
OtherNames = Tungsten hexafluoride
Section1 = Chembox Identifiers
CASNo = 7783-82-6
Section2 = Chembox Properties
Formula = WF₆
MolarMass = 297.83 g/mol
Appearance = Colorless gas.
Density = 13.1 g/L, gas.
Solubility = Hydrolyzes.
MeltingPt = 2.3°C (275.45 K)
BoilingPt = 17.1°C (290.25 K)
Section3 = Chembox Structure
MolShape = Octahedral
Dipole = 0 D
Section7 = Chembox Hazards
MainHazards = Corrosive, highly toxic.
Section8 = Chembox Related
OtherAnions = Tungsten(VI) chloride,
Tungsten(VI) bromide
OtherCations = Chromium(V) fluoride,
Molybdenum(VI) fluoride
OtherCpds = Tungsten(IV) fluoride,
Tungsten(V) fluoride,
Uranium hexafluoride

Tungsten(VI) fluoride, also known as tungsten hexafluoride, is a colorless gas. It is nonflammable, but highly corrosive and very toxic. It is the densest known gas at a pressure of 1 atm and room temperature (25 °C). The molecule is octahedral with the symmetry point group of O_h.The gas is most commonly used in the production of semiconductor circuits and circuit boards, through the process of chemical vapor deposition.Kirss, Rein U., Lamartine Meda. "Chemical Vapor Deposition of Tungsten Oxide." "Applied Organometallic Chemistry" 12 (1998): 155–160.]

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. [http://www.patentstorm.us/patents/6544889.html Patent Storm] ]

Reactions

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

This reaction occurs when tungsten is deposited on aluminium.One application of this would be in the production of studs for semiconductor circuits. [http://www.priorartdatabase.com/IPCOM/000038388/ Ip.com] ]

Tungsten can also be deposited on a silicon wafer or other semiconducting material via chemical vapor deposition, or CVD, as follows: [http://www.mne.umd.edu/grad/courses/old_courses_stuff_saved/659s_mats_&_proc_for_microelectronics/659s_spring_1998/enma659S_spr98_final_project_results/wcvd/sih4.html James Clark School of Engineering] ]

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.

afety

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. [https://www.mathesongas.com/msds/index.aspx Matheson Gas] ]

In "", Oliver Sacks comments on how he wanted WF₆-filled balloons for his 65^th 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

External links

* [http://www.npi.gov.au/database/substance-info/profiles/44.html National Pollutant Inventory - Flouride and compounds fact sheet]