Everything about Silane totally explained
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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 Si
nH
2n+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 Si
2H
6 is
disilane, Si
3H
8 is trisilane, and so forth. There is no need for a prefix for one; SiH
4 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 ·SiH
3 is termed silyl, ·Si
2H
5 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, for example
–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, HSiCl
3, along with
hydrogen gas, according to the
chemical equation:
» Si + 3HCl → HSiCl
3 + H
2
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:
» 4HSiCl
3 → SiH
4 + 3SiCl
4
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.
Further Information
Get more info on 'Silane'.
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