Information AboutSilicon |
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Silicon (Latin: ''silicium'') is the Chemical Element in the Periodic Table that has the symbol '''Si''' and Atomic Number 14. A Tetravalent Metalloid , silicon is less reactive than its chemical analog Carbon . It is the second most abundant element in the Earth 's crust, making up 25.7% of it by weight. It occurs in Clay , Feldspar , Granite , Quartz and Sand , mainly in the form of Silicon Dioxide (also known as silica) and as Silicate s, (various compounds containing silicon, oxygen and one or another metal). Silicon is the principal component of most Semiconductor devices and, in the form of silica and silicates, in Glass , Cement , Ceramic s. It is also a component of Silicone s, a name for various plastic substances often confused with silicon itself. Silicon is widely used in semiconductors because it has a lower Reverse Leakage Current than the semiconductor Germanium , and because its Native Oxide is easily grown in a furnace and forms a better semiconductor/dielectric interface than almost all other material combinations. NOTABLE CHARACTERISTICS In its Crystal line form, silicon has a dark gray color and a metallic luster. Even though it is a relatively inert element, silicon still reacts with Halogen s and dilute Alkali s, but most Acid s (except for a combination of Nitric Acid and Hydrofluoric Acid ) do not affect it. Elemental silicon transmits more than 95% of all Wavelength s of infrared light. Pure silicon has a negative Temperature co-efficient of Resistance , since the number of free charge carriers increases with temperature. The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the Piezoresistive Effect . APPLICATIONS Silicon is a very useful element that is vital to many human industries. Silicon and Alloys
Silicon compounds
''See also '' HISTORY Silicon ( Latin ''silex'', ''silicis'', meaning Flint ) was first identified by Antoine Lavoisier in 1787 , and was later mistaken by Humphry Davy , in 1800 , for a compound. In 1811 Gay-Lussac and Thénard probably prepared impure Amorphous Silicon through the heating of Potassium with Silicon Tetrafluoride . In 1824 Berzelius prepared amorphous silicon using approximately the same method of Lussac. Berzelius also purified the product by repeatedly washing it. Because silicon is an important element in semiconductor and high-tech devices, the high-tech region of Silicon Valley , California , is named after this element. OCCURRENCE Measured by Weight , silicon makes up 25.7% of the Earth 's crust and is the second most abundant element on Earth, after Oxygen . Pure silicon crystals are rarely found in nature; natural silicon is usually found in the form of Silicon Dioxide (also known as silica) and Silicate . Sand , Amethyst , agate, Quartz , rock crystal, flint, Jasper , and Opal are some of the forms in which silicon dioxide appears (they are known as " Lithogenic ", as opposed to " Biogenic ", silicas). Granite , Asbestos , Feldspar , clay, Hornblende , and Mica are a few of the many silicate Mineral s. Pure silicon crystals can be found as inclusions with Gold and in volcanic exhalations. Silicon is a principal component of Aerolite s, which are a class of Meteoroid s, and also of Tektite s, which are a natural form of glass. ''See also '' PRODUCTION Silicon is commercially prepared by the reaction of high-purity Silica with wood, charcoal, and coal, in an electric arc furnace using Carbon Electrode s. At temperatures over 1900 °C, the carbon reduces the silica to silicon according to the Chemical Equation :SiO2 + C → Si + CO2 Liquid silicon collects in the bottom of the furnace, and is then drained and cooled. The silicon produced via this process is called ''metallurgical grade silicon'' and is at least 99% pure. Using this method, silicon carbide, SiC, can form. However, provided the amount of SiO2 is kept high, silicon carbide may be eliminated, as explained by this equation: :2 SiC + SiO2 → 3 Si + 2 CO In 2000, metallurgical grade silicon cost about $ 0.56 per pound ($1.23/kg). {Link without Title} . PURIFICATION The use of silicon in Semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Historically, a number of methods have been used to produce high-purity silicon. Physical methods Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make Radar components during World War II , involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an Acid . When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product. In Zone Melting , also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end. Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and resolidifies behind it. Since most impurities tend to remain in the molten region rather than resolidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted. This end is then cut off and discarded, and the process repeated if a still higher purity was desired. Chemical methods Today, silicon is instead purified by converting it to a silicon Compound that can be more easily purified than silicon itself, and then converting that silicon element back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, although Silicon Tetrachloride and Silane are also used. When these gases are blown over silicon at high temperature, they decompose to high-purity silicon. In the Siemens Process , high-purity silicon rods are exposed to trichlorosilane at 1150 °C. The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them according to Chemical Reaction s like :2 HSiCl3 → Si + 2 HCl + SiCl4 Silicon produced from this and similar processes is called ''polycrystalline silicon''. Polycrystalline silicon typically has impurity levels of 1 part per billion or less. At one time, DuPont produced ultrapure silicon by reacting silicon tetrachloride with high-purity Zinc vapors at 950 °C, producing silicon according to the chemical equation :SiCl4 + 2 Zn → Si + 2 ZnCl2 However, this technique was plagued with practical problems (such as the Zinc Chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens Process . CRYSTALLIZATION The majority of silicon crystals grown for device production are produced by the Czochralski Process , since it is the cheapest method available. However, silicon single-crystals grown by the Czochralski method contain impurities since the Crucible which contains the melt dissolves. For certain electronic devices, particularly those required for high power applications, silicon grown by the Czochralski method is not pure enough. For these applications, Float-zone Silicon (FZ-Si) can be used instead. DIFFERENT FORMS OF SILICON |
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