Silane
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.
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 coupling agents to adhere glass fibers to a polymer matrix, stabilizing the composite material. They can also be used to couple a bio-inert layer on a titanium implant. Other applications include water repellants, masonry protection, applying polycrystalline silicon layers on silicon wafers when manufacturing semiconductors, sealants and silane is considered a potential propellant for engines on Mars
