Saturday, October 26, 2013

Silicon, a tetravalent metalloid, Silicon, a tetravalent metalloid is a chemical element with the symbol Si and atomic number 14. It is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive thangermanium, the metalloid directly below it in the table. Controversy about silicon's character dates to its discovery; it was first prepared and characterized in pure form in 1823. HP Pavilion dv7-1157cl CPU Fan In 1808, it was given the name silicium (from Latin:silex, hard stone or flint), with an -ium word-ending to suggest a metal, a name which the element retains in several non-English languages. However, its final English name, first suggested in 1817, reflects the more physically similar elements carbon and boron. Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. HP Pavilion dv6-3163eo CPU Fan It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide(silica) or silicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen.[7] Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. HP Pavilion dv9740us CPU Fan These include direct industrial building-use of clays, silica sand and stone. Silica is used in ceramic brick. Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to makeconcrete. Silicates are also in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass. More modern silicon compounds such as silicon carbide form abrasives and high-strength ceramics. HP COMPAQ NX9420 CPU Fan Silicon is the basis of the ubiquitous synthetic silicon-based polymers called silicones. Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steelrefining, aluminum-casting, and fine chemical industries (often to make fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. HP Pavilion dv7-4150ec CPU Fan Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on it. Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals.[8]However, various sea sponges as well as microorganisms like diatoms need silicon in order to have structure. It is much more important to the metabolism of plants, particularly many grasses. HP Pavilion dv5-1102tu CPU Fan Silicon is a solid at room temperature, with relatively high melting and boiling points of 1414 and 3265 degrees Celsius respectively. It has a greater density in a liquid state than a solid state. It does not contract when it freezes like most substances, but expands, similar to how ice is less dense than water. With a relatively high thermal conductivity of 149 W·m−1·K−1, SONY VGN-SZ220 CPU Fan silicon conducts heat well and as a result is not often used to insulate hot objects. In its crystalline form, pure silicon has a gray color and a metallic luster. Likegermanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a diamond cubic crystal structure, with a lattice spacing of 0.5430710 nm (5.430710 Å).[9] HP Pavilion dv7-6011tx CPU Fan The outer electron orbital of silicon, like that of carbon, has four valence electrons. The 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six. Silicon is a semiconductor. It has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature. HP Pavilion dv5-1040eb CPU Fan The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect. Silicon is a metalloid, readily either donating or sharing its four outer electrons, allowing for many forms of chemical bonding. Like carbon, it typically forms four bonds. Unlike carbon, it can accept additional electrons and form five or six bonds in a sometimes more labile silicate form. ASUS F3Jv CPU Fan Tetra-valent silicon is relatively inert, but still reacts withhalogens and dilute alkalis, but most acids (except for some hyper-reactive combinations ofnitric acid and hydrofluoric acid) have no known effect on it. However, having four bonding electrons gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances. IBM ThinkPad R50p 2887 CPU Fan Naturally occurring silicon is composed of three stable isotopes, silicon-28, silicon-29, and silicon-30, with silicon-28 being the most abundant (92% natural abundance).[11] Out of these, only silicon-29 is of use in NMR and EPR spectroscopy.[12] Twenty radioisotopes have been characterized, with the most stable being silicon-32 with a half-lifeof 170 years, and silicon-31 with a half-life of 157.3 minutes.[11] SONY VGN-CS36GJ/R CPU Fan All of the remaining radioactive isotopes have half-lives that are less than seven seconds, and the majority of these have half-lives that are less than one tenth of a second.[11] Silicon does not have any known nuclear isomers.[11] The isotopes of silicon range in mass number from 22 to 44.[11] The most common decay mode of six isotopes with mass numbers lower than the most abundant stable isotope, silicon-28, is β+, primarily forming aluminium isotopes (13 protons) as decay products.[11] Toshiba Satellite A215-S4807 CPU Fan The most common decay mode(s) for 16 isotopes with mass numbers higher than silicon-28 is β−, primarily forming phosphorus isotopes (15 protons) as decay products. Measured by mass, silicon makes up 27.7% of the Earth's crust and is the second most abundant element in the crust, with only oxygen having a greater abundance.[13] Toshiba Satellite Pro M10-SP405 CPU Fan Silicon is usually found in the form of complex silicate minerals, and less often as silicon dioxide(silica, a major component of common sand). Pure silicon crystals are very rarely found in nature. The silicate minerals—various minerals containing silicon, oxygen and reactive metals—account for 90% of the mass of the Earth's crust. HP Pavilion dv4-1120us CPU Fan Compaq Presario C550EM CPU Fan This is due to the fact that at the high temperatures characteristic of the formation of the inner solar system, silicon and oxygen have a great affinity for each other, forming networks of silicon and oxygen in chemical compounds of very low volatility. Since oxygen and silicon were the most common non-gaseous and non-metallic elements in the debris from supernova dust which formed the protoplanetary disk in the formation and evolution of the Solar System, Toshiba Qosmio E15-AV101 CPU Fan they formed many complex silicates which accreted into larger rocky planetesimals that formed the terrestrial planets. Here, the reduced silicate mineral matrix entrapped the metals reactive enough to be oxidized (aluminum, calcium, sodium, potassium and magnesium). After loss of volatile gases, as well as carbon and sulfur via reaction with hydrogen, this silicate mixture of elements formed most of the Earth's crust. Toshiba Satellite L645D-S4056 CPU Fan These silicates were of relatively low density with respect to iron, nickel, and other metals non-reactive to oxygen and thus a residuum of uncombined iron and nickel sank to the planet's core, leaving a thick mantle consisting mostly of magnesium and iron silicates. These are thought to be mostly silicate perovskites, followed in abundance by the magnesium/iron oxide ferropericlase.[14] Toshiba Satellite A305-S6837 CPU Fan Examples of silicate minerals in the crust include those in the pyroxene, amphibole, mica, and feldspar groups. These minerals occur in clay and various types of rock such as granite and sandstone. Silica occurs in minerals consisting of very pure silicon dioxide in different crystalline forms, quartz, agateamethyst, rock crystal, chalcedony, flint, jasper, and opal. HP Pavilion dv7-4087cl CPU Fan The crystals have the empirical formula of silicon dioxide, but do not consist of separate silicon dioxide molecules in the manner of solid carbon dioxide. Rather, silica is structurally a network-solid consisting of silicon and oxygen in three-dimensional crystals, like diamond. Less pure silica forms the natural glass obsidian. Biogenic silica occurs in the structure of diatoms, radiolaria and siliceous sponges. HP Pavilion dv5-1118es CPU Fan Silicon is also a principal component of many meteorites, and is a component of tektites, a silicate mineral of possibly lunar origin, or (if Earth-derived) which has been subjected to unusual temperatures and pressures, possibly from meteorite strike. Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, Toshiba Satellite A665-S6050 CPU Fan accounts for about 80% of the world's production of elemental silicon, with China, the leading supplier of elemental silicon, providing 4.6 million tonnes (or 2/3 of the world output) of silicon, most of which is in the form of ferrosilicon. It is followed by Russia (610,000 t), Norway (330,000 t), Brazil (240,000 t) and the United States (170,000 t).[15] Ferrosilicon is primarily used by the steel industry (see below). HP Pavilion G72-259WM CPU Fan Aluminum-silicon alloys are heavily used in the aluminum alloy casting industry, where silicon is the single most important additive to aluminum to improve its casting properties. Since cast aluminum is widely used in the automobile industry, this use of silicon is thus the single largest industrial use of "metallurgical grade" pure silicon (as this purified silicon is added to pure aluminum, whereas ferrosilicon is never purified before being added to steel). HP Pavilion dv6-3109ca  CPU  Fan Elemental silicon not alloyed with significant quantities of other elements, and usually > 95%, is often referred to loosely as silicon metal. It makes up about 20% of the world total elemental silicon production, with less than 1 to 2% of total elemental silicon (5–10% of metallurgical grade silicon) ever purified to higher grades for use in electronics. HP Pavilion dv6782eg CPU Fan SONY UDQF2PH52CF0 CPU Fan Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in an electric arc furnace using carbon electrodes. At temperatures over 1,900 °C (3,450 °F), the carbon in the aforementioned materials and the silicon undergo the chemical reaction SiO2 + 2 C → Si + 2 CO. Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. Toshiba UDQFRPH33CCM CPU Fan The silicon produced in this manner is called metallurgical grade silicon and is at least 98% pure. Using this method, silicon carbide (SiC) may also form from an excess of carbon in one or both of the following ways: SiO2 + C → SiO + CO or SiO + 2 C → SiC + CO. However, provided the concentration of SiO2 is kept high, the silicon carbide can be eliminated by the chemical reaction 2 SiC + SiO2 → 3 Si + 2 CO. Toshiba Satellite A505-S6980 CPU Fan As noted above, metallurgical grade silicon "metal" has its primary use in the aluminum casting industry to make aluminum-silicon alloy parts. The remainder (about 45%) is used by the chemical industry, where it is primarily employed to make fumed silica.[17] As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg),[18] up from $0.77 per pound ($1.70/kg) in 2005. HP Pavilion dv7-2025es CPU Fan The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Very pure silicon (>99.9%) can be extracted directly from solid silica or other silicon compounds by molten salt electrolysis.[20][21] This method, known as early as 1854[22] (see also FFC Cambridge process), has the potential to directly produce solar-grade silicon without any carbon dioxide emission at much lower energy consumption. TOSHIBA Satellite L300 CPU Fan Solar grade silicon cannot be used for semiconductors, where purity must be extreme to properly control the process. Bulk silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%), a process which requires repeated applications of refining technology. The majority of silicon crystals grown for device production are produced by the Czochralski process, HP G62-a10EJ CPU Fan (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals. However, single crystals grown by the Czochralski process contain impurities because the crucible containing the melt often dissolves. Historically, a number of methods have been used to produce ultra-high-purity silicon.

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