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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.
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.
WF6(g) + H2(g) + Al(s) → W(s) + HF(g) + AlF3(s)
WF6(g) + W* → WF6*
2 SiH4(g) + WF6* → W(s) + 2 SiHF3 (g) + 3 H2(g)
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.
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.
|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.|