Science Fair Project Encyclopedia
|Formula weight||32.1 amu|
|Melting point||88 K (-185 °C)|
|Boiling point||161 K (-112 °C)|
|Density||0.7 ×103 kg/m3 (liquid)|
|S0gas, 1 bar||? J/mol·K|
|S0liquid, 1 bar||? J/mol·K|
|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|
Silane is a chemical compound with chemical formula SiH4. 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.
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.
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
- 4 HSiCl3 → SiH4 + 3 SiCl4
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.
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