Silane

SilicaneSilicon hydrider(Si-H) = 1.4798 angstromsVinylsilanedisilanetrisilaneSilane is an inorganic compound with chemical formula, SiH4, making it a group 14 hydride. It is a colourless, pyrophoric gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Silane is an inorganic compound with chemical formula, SiH4, making it a group 14 hydride. It is a colourless, pyrophoric gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. 'Silanes' refers to many compounds with four substituents on silicon, including an organosilicon compound. Examples include trichlorosilane (SiHCl3), tetramethylsilane (Si(CH3)4), and tetraethoxysilane (Si(OC2H5)4). Silane can be produced by several routes. Typically, it arises from the reaction of hydrogen chloride with magnesium silicide: It is also prepared from metallurgical grade silicon in a two-step process. First, silicon is treated with hydrogen chloride at about 300 °C to produce trichlorosilane, HSiCl3, along with hydrogen gas, according to the chemical equation: The trichlorosilane is then converted to a mixture of silane and silicon tetrachloride. This redistribution reaction requires a catalyst: The most commonly used catalysts for this process are metal halides, particularly aluminium chloride. This is referred to as a redistribution reaction, which is a double displacement involving the same central element. It may also be thought of as a disproportionation reaction even though there is no change in the oxidation number for silicon (Si has a nominal oxidation number IV in all three species). However, the utility of the oxidation number concept for a covalent molecule, even a polar covalent molecule, is ambiguous. The silicon atom could be rationalized as having the highest formal oxidation state and partial positive charge in SiCl4 and the lowest formal oxidation state in SiH4 since Cl is far more electronegative than is H. An alternative industrial process for the preparation of very high purity silane, suitable for use in the production of semiconductor grade silicon, starts with metallurgical grade silicon, hydrogen, and silicon tetrachloride and involves a complex series of redistribution reactions (producing byproducts that are recycled in the process) and distillations. The reactions are summarized below: