Silane

From Academic Kids

</table> Silane is a chemical compound with chemical formulaSiH4. It is the silicon analogue of methane. At room temperature, silane is presumed to be a pyrophoric gas — it spontaneously undergoes combustion in air without the need for external ignition. However, there is a school of thought which says that silane is stable and that it is the natural formation of larger silanes during production which 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 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 called silyl, Si2H5- is disilanyl etc. If we have trisilane with a silyl group attached to the middle silicon, we have silyltrisilane. It parallels alkanes. Silanes can also take the same functional groups as alkanes, 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 hydrochloric acid at about 300°C to produce trichlorosilane, HSiCl3, along with hydrogen gas, according to the chemical equation:

Si + 3 HCl → 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:

4 HSiCl3 → SiH4 + 3 SiCl4

The most commonly used catalysts for this process are metal halides, particularly aluminium chloride.

Applications

Several industrial and medical applications exist for silanes. For instance, silanes are used as a coupling agent to adhere glass fibers to a polymer matrix, forming a composite material. They can also be used to couple a bio-inert layer on a titanium implant. Other applications include water repellants, masonry protection, control of graffiti and sealants. Degussa AG is a major producer of commercial silanes.de:Silane ja:シラン (化合物)

zh:硅烷

Properties

General

Name Silane
Chemical formula SiH4
Appearance Colourless gas

Physical

Formula weight 32.1 amu
Melting point 88 K (-185 °C)
Boiling point 161 K (-112 °C)
Density 0.7 ×103 kg/m3 (liquid)
Solubility insoluble

Thermochemistry

ΔfH0gas ? kJ/mol
ΔfH0liquid ? kJ/mol
ΔfH0solid -1615 kJ/mol
S0gas, 1 bar ? J/mol·K
S0liquid, 1 bar ? J/mol·K
S0solid 283 J/mol·K

Safety

Ingestion Relatively low toxicity, but avoid exposure where possible.
Inhalation Relatively low toxicity: may cause coughing, hyperventilation.
Skin Irritant, may cause redness and swelling.
Eyes Similar to skin, may cause irritation. Avoid contact.
More info Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals/8/7034.html)

SI units were used where possible. Unless otherwise stated, standard conditions were used.

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