AskDefine | Define silane

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Noun

  1. Any of a group of silicon hydrides that are analogous to the paraffin hydrocarbons; especially the parent compound SiH4
  2. monosilane (SiH₄)

See also

Extensive Definition

Silane is a chemical compound with chemical formula SiH4. It is the silicon analogue of methane. At room temperature, silane is a gas, and is pyrophoric — it undergoes spontaneous combustion in air, without the need for external ignition. However, one school of thought holds that silane itself is stable and that the natural formation of larger silanes during production causes its pyrophoricity. Above 420°C, silane decomposes into silicon and hydrogen; it can therefore be used in the chemical vapor deposition of silicon.
More generally, a silane is any silicon analogue of an alkane hydrocarbon. Silanes consist of a chain of silicon atoms covalently bound to hydrogen atoms. The general formula of a silane is SinH2n+2. Silanes tend to be less stable than their carbon analogues because the Si–Si bond has a strength slightly lower than the C–C bond. Oxygen decomposes silanes easily, because the silicon-oxygen bond is quite stable.
There exists a regular nomenclature for silanes. Each silane's name is the word silane preceded by a numerical prefix (di, tri, tetra, etc.) for the number of silicon atoms in the molecule. Thus Si2H6 is disilane, Si3H8 is trisilane, and so forth. There is no need for a prefix for one; SiH4 is simply silane. Silanes can also be named like any other inorganic compound; in this naming system, silane is named silicon tetrahydride. However, with longer silanes, this becomes cumbersome.
A cyclosilane is a silane in a ring, just as a cycloalkane is an alkane in a ring.
Branched silanes are possible. The radical ·SiH3 is termed silyl, ·Si2H5 is disilanyl, and so on. Trisilane with a silyl group attached to the middle silicon is named silyltrisilane. The nomenclature parallels that of alkyl radicals.
Silanes can also incorporate the same functional groups as alkanes, e.g. –OH to make a silanol. There is (at least in principle) a silicon analogue for all carbon alkanes.

Production

Industrially, silane is produced from metallurgical grade silicon in a two-step process. In the first step, powdered silicon is reacted with hydrogen chloride at about 300°C to produce trichlorosilane, HSiCl3, along with hydrogen gas, according to the chemical equation:
Si + 3HCl → HSiCl3 + H2
The trichlorosilane is then boiled on a resinous bed containing a catalyst which promotes its disproportionation to silane and silicon tetrachloride according to the chemical equation:
4HSiCl3 → SiH4 + 3SiCl4
The most commonly used catalysts for this process are metal halides, particularly aluminium chloride.

Properties

Silane has a repulsive smell.
Silane has recently been shown to act as superconductor under extremely high pressures, with a transition temperature of 17 K. applying polycrystalline silicon layers on silicon wafers when manufacturing semiconductors, and sealants.
Silane is also used in supersonic combustion ramjets to initiate combustion in the compressed air stream.
Silane and similar compounds containing Si-H-bonds are used as reducing agents in organic and organometallic chemistry.
"Mars sand" exposes regular sand to trimethylhydroxysilane vapors to make the sand waterproof.
Silane may be used to fabricate a super-compressed, superconducting compound.

References

See also

silane in Czech: Silan
silane in German: Monosilan
silane in Spanish: Silano
silane in French: Silane
silane in Galician: Silano
silane in Italian: Silano
silane in Japanese: シラン (化合物)
silane in Polish: Silany
silane in Portuguese: Silano
silane in Russian: Кремневодороды
silane in Finnish: Silaani
silane in Swedish: Silan
silane in Chinese: 硅烷
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