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Silicon

Background

Berzelius was credited for the discovery of (amorphous) silicon in 1824 by heating potassium with silicon tetrafluoride and repeatedly washing the product to remove the impurity of fluorosilicates. In 1854, Deville first prepared crystalline silicon (which is the second allotropic form of the element).

Silicon (Si) is present in the stars and our sun, and is a principal component of a class of meteorites known as “aerolites”.

Silicon is the second most abundant element, and makes up 25.7% of the earth’s crust by weight (oxygen being the most). It is not found free in nature, it occurs mainly as its oxide and as silicates. Examples of the oxide form are sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal. Examples of its silicate minerals are granite, hornblende, asbestos, feldspar, clay and mica.

Silicon is produced commercially by heating silica and carbon in an electric furnace, using carbon electrodes. The Czochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon may be produced by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process.

Silicon is a relatively inert metallic element, however it is attacked by halogens and dilute alkali. Most acids except for hydrofluoric do not affect silicon.

Silicon is a semiconductor and is superior to germanium for transistors, due to it being able to withstand a temperature of 149°C (300°F) and carry more power.

Elemental silicon transmits more than 95% of all wavelengths of infrared, from 1.3 to 6.7μm.

Silicon does not posses a metallic-type lattice structure. It lacks plasticity and is more akin to the diamond structure. Due to its weak electronegative nature, silicon has a greater tendency to form compounds with non-metals than with metals.

Silicon forms silicon hybrids of general formula SixH2x+2, which are similar to the paraffin hydrocarbons. These are very unstable however and ignite in air.

Applications

Hyperpure silicon metal and doped hyperpure silicon (doping with boron, gallium, phosphorous, or arsenic) are used in:

        Semiconductors

        Transistors

        Solar cells

        Rectifiers and other solid-state devices that are used extensively in the electronics and space age industry.

Float-zoned single-crystal silicon (100 times purer than hyperpure silicon) is used in wafer form for laser and infrared detectors in guided bomb missiles and for high-power switching devices, such as thyristors.

Hydrogenated amorphous silicon may be used in producing photovoltaic cells for converting solar energy into electricity.

Silicon is also found in:

        Silicones, ranging from liquids to hard glass like solids

        In glass used to make containers, windows, insulators and the like, which have generally used silica as a raw material

        In the form of sand and clay it is used to make concrete and bricks, it is a useful refractory material for high temperature work such as moulding sands for castings in foundry applications

        In the form of silicates it is implemented in making enamels, pottery and the like.

        Silicon is an important ingredient in steel, iron and aluminium alloys. It is used as a fluxing agent for copper alloys

        Silicon carbide is one of the most important abrasives, and has been implemented in lasers to produce coherent light of 4560Å.

Primary author: AZoM.com

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