Silicon And Phosphorus

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Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table. Controversy about silicon's character dates to its discoveryHP Pavilion DV9000 Battery: silicon was first prepared and characterized in pure form in 1824, and given the name silicium (from Latin: silicis, flints), 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, suggested in 1831, reflects the more physically similar elements carbon and boronHP Pavilion DV9500 Battery.

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. 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 oxygenHP Pavilion DV9700t Battery.[5]

Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. 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 make concreteHP Pavilion dv9000T Battery. 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. Silicon is the basis of the ubiquitous synthetic silicon-based polymers called siliconesHP Pavilion dv9000Z Battery.

Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refining, 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. Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on itHP Pavilion dv9001EA Battery.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals,[6] however various sea sponges need silicon in order to have structure. It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatomsHP Pavilion dv9001TX Battery.

Characteristics

[edit]Physical

Silicon crystallizes in a diamond cubic crystal structure

Further information: Monocrystalline silicon

Silicon is a solid at room temperature, with relatively high melting and boiling points of approximately 1,400 and 2,800 degrees Celsius respectively.[7] Interestingly, silicon has a greater density in a liquid state than a solid state. Therefore, it does not contract when it freezes like most substances, but expandsHP Pavilion dv9001XX Battery, similar to how ice is less dense than water and has less mass per unit of volume than liquid water. With a relatively high thermal conductivity of 149 W·m−1·K−1, 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. Like germanium, 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 approximately 0.5430710 nm (5.430710 Å). HP Pavilion dv9002EA Battery

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. The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effectHP Pavilion dv9002TX Battery.[9]

[edit]Chemical

Silicon powder

Silicon is a metalloid, readily either donating or sharing its four outer electrons, allowing for many forms of chemical bonding. Even though it is relatively inert like carbon, silicon still reacts with halogens and dilute alkalis, but most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) have no known effect on itHP Pavilion dv9002XX Battery. However, having four bonding electrons gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances.

[edit]Isotopes

Main article: isotopes of silicon

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).[10] Out of these, only silicon-29 is of use in NMR and EPR spectroscopyHP Pavilion dv9003EA Battery.[11] Twenty radioisotopes have been characterized, with the most stable being silicon-32 with a half-life of 170 years, and silicon-31 with a half-life of 157.3 minutes.[10] 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.[10] Silicon does not have any known nuclear isomersHP Pavilion dv9003TX Battery.[10]

The isotopes of silicon range in mass number from 22 to 44.[10] 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.[10] The most common decay mode(s) for 16 isotopes with mass numbers higher than silicon-28 is β−HP Pavilion dv9003XX Battery

, primarily forming phosphorus isotopes (15 protons) as decay products.[10]

[edit]Occurrence

Quartz crystal cluster from Tibet. The naturally-occurring mineral is a network solid with the formula SiO2.

See also: Silicate minerals

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.[12] 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 natureHP Pavilion dv9004TX Battery.

The silicate minerals—various minerals containing silicon, oxygen and reactive metals—account for 90% of the mass of the Earth's crust. This is due to the fact that at the high temperatures characteristic of 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 volatilityHP Pavilion dv9005CA Battery. 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, 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) HP Pavilion dv9005EA Battery. 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. 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 aboveHP Pavilion dv9005TX Battery.

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, agate amethyst, rock crystal, chalcedony, flint, jasper, and opal. The crystals have the empirical formula of silicon dioxideHP Pavilion dv9005US Battery, 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 spongesHP Pavilion dv9006TX Battery.

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.

[edit]Production

[edit]Alloys

Ferrosilicon alloy

Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, accounts for about 80% of the world's production of elemental silicon, with ChinaHP Pavilion dv9007TX Battery, 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).[13] Ferrosilicon is primarily used by the steel industry (see below).

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 propertiesHP Pavilion dv9008TX Battery. 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).[14]

[edit]Metallurgical grade

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 productionHP Pavilion dv9010CA Battery, 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. 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 COHP Pavilion dv9010TX Battery. Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. The silicon produced via this process 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 COHP Pavilion dv9010US Battery.

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.[15]

As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg),[16] up from $0.77 per pound ($1.70/kg) in 2005HP Pavilion dv9011TX Battery.[17]

[edit]Electronic grade

Monocrystalline silicon ingot grown by the Czochralski process

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.[18][19] This method, known as early as 1854[20] (see also FFC Cambridge process), has the potential to directly produce solar-grade silicon without any carbon dioxide emission at much lower energy consumptionHP Pavilion dv9012TX Battery.

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 technologyHP Pavilion dv9013CA Battery.

The majority of silicon crystals grown for device production are produced by the Czochralski process, (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 siliconHP Pavilion dv9013CL Battery.

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 acidHP Pavilion dv9013TX Battery. 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 rodHP Pavilion dv9014EA Battery, keeping a small length of the rod molten as the silicon cools and re-solidifies behind it. Since most impurities tend to remain in the molten region rather than re-solidify, 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 is desiredHP Pavilion dv9014TX Battery.[21]

A polycrystalline silicon rod made by the Siemens process

At one time, DuPont produced ultra-pure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon by 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 processHP Pavilion dv9015EA Battery. 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 because 2 HSiCl3 → Si + 2 HCl + SiCl4. Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than one part per billion. HP Pavilion dv9015TX Battery

In 2006 REC announced construction of a plant based on fluidized bed (FB) technology using silane: 3 SiCl4 + Si + 2 H2 → 4 HSiCl3, 4 HSiCl3 → 3 SiCl4 + SiH4, SiH4 → Si + 2 H2.[25] The advantage of fluid bed technology is that processes can be run continuously, yielding higher yields than Siemens Process, which is a batch processHP Pavilion dv9016EA Battery.

Today, silicon is purified by converting it to a silicon compound that can be more easily purified by distillation than in its original state, and then converting that silicon compound 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 siliconHP Pavilion dv9016TX Battery.

In addition, there exists the Schumacher process, which utilizes tribromosilane in place of trichlorosilane and fluid bed technology. It requires lower deposition temperatures, lower capital costs to build facilities and operate, no hazardous polymers nor explosive material, and no amorphous silicon dust waste, all of which are drawbacks of the Siemens Process.[26] However, there are yet to be any major factories built on this processHP Pavilion dv9017TX Battery.

[edit]Compounds

PDMS – a silicone compound

Silicon forms binary compounds called silicides with many metallic elements whose properties range from reactive compounds, e.g. magnesium silicide, Mg2Si through high melting refractory compounds such as molybdenum disilicide, MoSi2.[27]

Silicon carbide, SiC (carborundum) is a hard, high melting solid and a well known abrasive. It may also be sintered into a type of high-strength ceramic used in armorHP Pavilion dv9018EA Battery.

Silane, SiH4, is a pyrophoric gas with a similar tetrahedral structure to methane, CH4. When pure, it does not react with pure water or dilute acids; however, even small amounts of alkali impurities from the laboratory glass can result in a rapid hydrolysis.[28] There is a range of catenated silicon hydrides that form a homologous series of compounds, SinH2n+2 where n = 2–8 (analogous to the alkanes) HP Pavilion dv9018TX Battery. These are all readily hydrolyzed and are thermally unstable, particularly the heavier members.[29][30]

Disilenes contain a silicon-silicon double bond (analogous to the alkenes) and are generally highly reactive requiring large substituent groups to stabilize them.[31] A disilyne with a silicon-silicon triple bond was first isolated in 2004; although as the compound is non-linear, the bonding is dissimilar to that in alkynesHP Pavilion dv9019EA Battery.[32]

Tetrahalides, SiX4, are formed with all the halogens.[33] Silicon tetrachloride, for example, reacts with water, unlike its carbon analogue, carbon tetrachloride.[34] Silicon dihalides are formed by the high temperature reaction of tetrahalides and silicon; with a structure analogous to a carbene they are reactive compounds. Silicon difluoride condenses to form a polymeric compound, (SiF2)n. HP Pavilion dv9019TX Battery

Silicon dioxide is a high melting solid with a number of crystal forms; the most familiar of which is the mineral quartz. In quartz each silicon atom is surrounded by four oxygen atoms that bridge to other silicon atoms to form a three dimensional lattice.[34] Silica is soluble in water at high temperatures forming a range of compounds called monosilicic acid, Si(OH)4HP Pavilion dv9020TX Battery.[35]

Under the right conditions monosilicic acid readily polymerizes to form more complex silicic acids, ranging from the simplest condensate, disilicic acid (H6Si2O7) to linear, ribbon, layer and lattice structures which form the basis of the many silicate minerals and are called polysilicic acids {Six(OH)4–2x}nHP Pavilion dv9021TX Battery.[35]

With oxides of other elements the high temperature reaction of silicon dioxide can give a wide range of glasses with various properties.[36] Examples include soda lime glass, borosilicate glass and lead crystal glass.

Silicon sulfide, SiS2 is a polymeric solid (unlike its carbon analogue the liquid CS2).[37]

Silicon forms a nitride, Si3N4 which is a ceramic.[38] Silatranes, a group of tricyclic compounds containing five-coordinate silicon, may have physiological propertiesHP Pavilion dv9022EA Battery.[39]

Many transition metal complexes containing a metal-silicon bond are now known, which include complexes containing SiHnX3−n ligands, SiX3 ligands, and Si(OR)3 ligands.[39]

Silicones are large group of polymeric compounds with an (Si-O-Si) backbone. An example is the silicone oil PDMS (polydimethylsiloxane). These polymers can be crosslinked to produce resins and elastomersHP Pavilion dv9022TX Battery.[40]

Many organosilicon compounds are known which contain a silicon-carbon single bond. Many of these are based on a central tetrahedral silicon atom, and some are optically active when central chirality exists. Long chain polymers containing a silicon backbone are known, such as polydimethysilylene (SiMe2)n.[41] Polycarbosilane, [(SiMe2)2CH2]n with a backbone containing a repeating -Si-Si-C unit, is a precursor in the production of silicon carbide fibersHP Pavilion dv9024EA Battery.[41]

[edit]History

Attention was first drawn to quartz as the possible oxide of a fundamental chemical element by Antoine Lavoisier, in 1787. In 1811, Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon, through the heating of recently isolated potassium metal with silicon tetrafluoride, but they did not purify and characterize the product, nor identify it as a new elementHP Pavilion dv9030EA Battery. In 1824, Berzelius prepared amorphous silicon using approximately the same method as Gay-Lussac (potassium metal and potassium fluorosilicate), but purifying the product to a brown powder by repeatedly washing it. He named the product silicium from the Latin silex, silicis for flint, flints, and adding the "-ium" ending because he believed it was a metal. As a result he is usually given credit for element's discovery. HP Pavilion dv9030US Battery Silicon was given its present name in 1831 by Scottish chemist Thomas Thomson. He retained part of Berzelius's name but added "-on" because he believed silicon a nonmetal more similar to boron and carbon.

Silicon in its more common crystalline form was not prepared until 31 years later, by Deville.[44] By electrolyzing impure sodium-aluminum chloride containing approximately 10% silicon, he was able to obtain a slightly impure allotrope of silicon in 1854.[45] Later, more cost-effective methods have been developed to isolate silicon in several allotrope forms, the most recent being siliceneHP Pavilion dv9033CL Battery.

Because silicon is an important element in semiconductors and high-technology devices, many places in the world bear its name. For example, Silicon Valley in California, since it is the base for a number of technology-related industries, bears the name silicon. Other geographic locations with connections to the industry have since been named after silicon as wellHP Pavilion dv9035EA Battery. Examples include Silicon Forest in Oregon, Silicon Hills in Austin, Texas, Silicon Saxony in Germany, Silicon Valley in India, Silicon Border in Mexicali, Mexico, Silicon Fen in Cambridge, England, and Silicon Gorge in Bristol, England.

Applications

Compounds

Most silicon is used industrially without being separated into the element, and indeed often with comparatively little processing from natural occurrence. Over 90% of the Earth's crust is composed of silicate minerals. Many of these have direct commercial uses, such as claysHP Pavilion dv9035NR Battery, silica sand and most kinds of building stone. Thus, the vast majority of uses for silicon are as structural compounds, either as the silicate minerals or silica (crude silicon dioxide). For example, silica is an important part of ceramic brick. Silicates are used in making Portland cement which is used in building mortar and stucco, but more importantly combined with silica sand, and gravel (usually containing silicate minerals like granite) HP Pavilion dv9036EA Battery, to make the concrete that is the basis of most of the very largest industrial building projects of the modern world. [46]

Silicate minerals are also in whiteware ceramics, an important class of products usually containing various types of fired clay (natural aluminum silicate). An example is porcelain which is based on silicate mineral kaolinite. Ceramics include art objects, and domestic, industrial and building products. Traditional quartz-based soda-lime glass also functions in many of the same rolesHP Pavilion dv9700t Battery.

More modern silicon compounds also function as high-technology abrasives and new high-strength ceramics based upon (silicon carbide), and in superalloys.

Alternating silicon-oxygen chains with hydrogen attached to the remaining silicon bonds form the ubiquitous silicon-based polymeric materials known as silicones. These compounds containing silicon-oxygen and occasionally silicon-carbon bonds have the capability to act as bonding intermediates between glass and organic compoundsHP Pavilion dv9700/CT Battery, and to form polymers with useful properties such as impermeability to water, flexibility and resistance to chemical attack. Silicones are often used in waterproofing treatments, molding compounds, mold-release agents, mechanical seals, high temperature greases and waxes, and caulking compounds. Silicone is also sometimes used in breast implants, contact lensesHP Pavilion dv9605TX Battery, explosives and pyrotechnics.[47] Silly Putty was originally made by adding boric acid to silicone oil.[48]

[edit]Alloys

Elemental silicon is added to molten cast iron as ferrosilicon or silicocalcium alloys to improve performance in casting thin sections, and to prevent the formation of cementite where exposed to outside air. The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steelHP Pavilion dv9604TX Battery, can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is impure, it accounts for 80% of the world's use of free silicon.

The properties of silicon itself can be used to modify alloys. Silicon's importance in aluminum casting is that a significantly high amount (12%) of silicon in aluminum forms a eutectic mixture which solidifies with very little thermal contraction. This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidityHP Pavilion dv9600 Battery. Silicon also significantly improves the hardness and thus wear-resistance of aluminum.[14] Silicon is an important constituent of electrical steel, modifying its resistivity and ferromagnetic properties.

Metallurgical grade silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminum-silicon alloys for aluminum part casts, mainly for use in the automotive industryHP Pavilion dv9535us Battery. The reason for the high silicon use in these alloys is noted above.[15] Much of the rest of metallurgical-grade silicon is used by the chemical industry for production of the important industrial product fumed silica. The remainder is used in production of other fine chemicals such as silanes and some types of siliconesHP Pavilion dv9525us Battery.

[edit]Electronics

Main article: Semiconductor device fabrication

Silicon wafer with mirror finish

Since most elemental silicon produced remains as ferrosilicon alloy, only a relatively small amount (20%) of the elemental silicon produced is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year). The fraction of silicon metal which is further refined to semiconductor purity is estimated at only 15% of the world production of metallurgical grade silicon. HP Pavilion dv9500z Battery However, the economic importance of this small very high-purity fraction (especially the ~ 5% which is processed to monocrystalline silicon for use in integrated circuits) is disproportionately large.

Pure monocrystalline silicon is used to produce silicon wafers used in the semiconductor industry, in electronics and in some high-cost and high-efficiency photovoltaic applications. In terms of charge conduction, pure silicon is an intrinsic semiconductor which means that unlike metals it conducts electron holes and electrons which may be released from atoms within the crystal by heatHP Pavilion dv9500t Battery, and thus increase silicon's electrical conductance with higher temperatures. Pure silicon has too low a conductance to be used as a circuit element in electronics without being doped with small concentrations of certain other elements. This process greatly increases its conductivity and adjusts its electrical response by controlling the number and charge (positive or negative) of activated carriersHP Pavilion dv9500/CT Battery. Such control is necessary for transistors, solar cells, semiconductor detectors and other semiconductor devices, which are used in the computer industry and other technical applications. For example, in silicon photonics, silicon can be used as a continuous wave Raman laser medium to produce coherent light, though it is ineffective as an everyday light sourceHP Pavilion dv9500 Battery.

In common integrated circuits, a wafer of monocrystalline silicon serves as a mechanical support for the circuits, which are created by doping, and insulated from each other by thin layers of silicon oxide, an insulator which is easily produced by exposing the element to oxygen under the proper conditions. Silicon has become the most popular material to build both high power semiconductors and integrated circuits, because of all the elementsHP Pavilion dv9299XX Battery, silicon is the semiconductor which can withstand the highest powers and temperatures without becoming dysfunctional due to avalanche breakdown, a process in which an electron avalanche is created by a chain reaction process where heat produces free electrons and holes, which in turn produce more current which produces more heat. In addition, the insulating oxide of silicon is not soluble in waterHP Pavilion dv9299EA Battery, which gives it an advantage over germanium (an element with similar properties which can also be used in semiconductor devices) in certain type of fabrication techniques.[49]

Monocrystalline silicon is expensive to produce, and is usually only justified in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. For other uses, other types of pure silicon which do not exist as single crystals may be employedHP Pavilion dv9297EA Battery. These include hydrogenated amorphous silicon and upgraded metallurgical-grade silicon (UMG-Si) which are used in the production of low-cost, large-area electronics in applications such as Liquid crystal displays, and of large-area, low-cost, thin-film solar cells. Such semiconductor grades of silicon which are either slightly less pure than those used in integrated circuitsHP Pavilion dv9296EU Battery, or which are produced in polycrystalline rather than monocrystalline form, make up roughly similar amount of silicon as are produced for the monocrystalline silicon semiconductor industry, or 75,000 to 150,000 metric tons per year. However, production of such materials is growing more quickly than silicon for the integrated circuit market. By 2013 polycrystalline silicon production, used mostly in solar cells, is projected to reach 200,000 metric tons per year, while monocrystalline semiconductor silicon production (used in computer microchips) remains below 50,000 tons/year. HP Pavilion dv9296EA Battery

[edit]Biological role

Silica skeletons of radiolaria in false color.

Although silicon is readily available in the form of silicates, very few organisms have a use for it. Diatoms, radiolaria and siliceous sponges use biogenic silica as a structural material to construct skeletons. In more advanced plants, the silica phytoliths (opal phytoliths) are rigid microscopic bodies occurring in the cell; some plants, for example riceHP Pavilion dv9295EA Battery, need silicon for their growth.[50][51][52] Although silicon was proposed to be an ultra trace nutrition its exact function in the biology of animals is still under discussion. Higher organisms are only known to use it in very limited occasions in the form of silicic acid and soluble silicates.

Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO)." HP Pavilion dv9295EA BatterySilicon has been shown in university and field studies to improve plant cell wall strength and structural integrity,[55] improve drought and frost resistance, decrease lodging potential and boost the plant's natural pest and disease fighting systems.[56] Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yieldsHP Pavilion dv9294EU Battery.[55]

Hypothetical silicon-based lifeforms are the subject of silicon biochemistry, in analogy with carbon-based lifeforms. Silicon, being below carbon in the periodic table, is thought to have similar enough properties that would make silicon-based life possible, but much different from life as we know itHP Pavilion dv9294EA Battery.

Phosphorus ( /ˈfɒsfərəs/ fos-fər-əs) is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks. Elemental phosphorus exists in two major forms—white phosphorus and red phosphorus—but due to its high reactivity, phosphorus is never found as a free element on EarthHP Pavilion dv9292EU Battery.

The first form of elemental phosphorus to be produced (white phosphorus, in 1669) emits a faint glow upon exposure to oxygen – hence its name given from Greek mythology, Φωσφόρος meaning "light-bearer" (Latin Lucifer), referring to the "Morning Star", the planet Venus. The term "phosphorescence", meaning glow after illumination, originally derives from this property of phosphorusHP Pavilion dv9291EA Battery, although this word has since been used for a different physical process that produces a glow. The glow of phosphorus itself originates from oxidation of the white (but not red) phosphorus— a process now termed chemiluminescence.

The vast majority of phosphorus compounds are consumed as fertilizers. Other applications include the role of organophosphorus compounds in detergents, pesticides and nerve agents, and matchesHP Pavilion dv9289EA Battery.[4]

Phosphorus is essential for life. As phosphate, it is a component of DNA, RNA, ATP, and also the phospholipids that form all cell membranes. Demonstrating the link between phosphorus and life, elemental phosphorus was historically first isolated from human urine, and bone ash was an important early phosphate source. Phosphate minerals are fossilsHP Pavilion dv9288EA Battery. Low phosphate levels are an important limit to growth in some aquatic systems. The chief commercial use of phosphorus compounds for production of fertilizers is due to the need to replace the phosphorus that plants remove from the soil.

Characteristics

Main article: Allotropes of phosphorus

Physical

P4 molecule

Phosphorus exists as several forms (allotropes) that exhibit strikingly different properties.[5] The two most common allotropes are white phosphorus and red phosphorus. Another form, scarlet phosphorusHP Pavilion dv9287CL Battery, is obtained by allowing a solution of white phosphorus in carbon disulfide to evaporate in sunlight. Black phosphorus is obtained by heating white phosphorus under high pressures (about 12,000 standard atmospheres or 1.2 gigapascals). In appearance, properties, and structure, it resembles graphite, being black and flaky, a conductor of electricity, and has puckered sheets of linked atoms. Another allotrope is diphosphorusHP Pavilion dv9286EA Battery; it contains a phosphorus dimer as a structural unit and is highly reactive.[6]

White phosphorus

White phosphorus exposed to air glows in the darkness

White phosphorus and related molecular forms

The most important form of elemental phosphorus from the perspective of applications and chemical literature is white phosphorus. It consists of tetrahedral P4 molecules, in which each atom is bound to the other three atoms by a single bond. This P4 tetrahedron is also present in liquid and gaseous phosphorus up to the temperature of 800 °C when it starts decomposing to P2 moleculesHP Pavilion dv9285EA Battery.[7] Solid white exists in two forms. At low-temperatures, the β form is stable. At high-temperatures α form is predominant. These forms differ in terms of the relative orientations of the constituent P4 tetrahedra.

White phosphorus is the least stable, the most reactive, more volatile, less dense, and more toxic than the other allotropes. White phosphorus gradually changes to red phosphorus. This transformation, which is accelerated by light and heatHP Pavilion dv9283EA Battery, and samples of white phosphorus almost always contain some red phosphorus and therefore appear yellow. For this reason, it is also called yellow phosphorus. It glows in the dark (when exposed to oxygen) with a very faint tint of green and blue, is highly flammable and pyrophoric (self-igniting) upon contact with air as well as toxic (causing severe liver damage on ingestion) HP Pavilion dv9276EA Battery. Because of pyrophoricity, white phosphorus is used as an additive in napalm. The odour of combustion of this form has a characteristic garlic smell, and samples are commonly coated with white "(di)phosphorus pentoxide", which consists of P4O10 tetrahedra with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is insoluble in water but soluble in carbon disulfideHP Pavilion dv9275LA Battery.[8]

Thermolysis (cracking) of P4 at 1100 kelvin) gives diphosphorus, P2. This species is not stable as a solid or liquid. The dimeric unit contains a triple bond and is analogous to N2. It can also be generated as a transient intermediate in solution by thermolysis of organophosphorus precursor reagents.[9] At still higher temperatures, P2 dissociates into atomic PHP Pavilion dv9275EA Battery.

Although the term phosphorescence is derived from phosphorus, the reaction that gives phosphorus its glow is properly called chemiluminescence (glowing due to a cold chemical reaction), not phosphorescence (re-emitting light that previously fell onto a substance and excited it) HP Pavilion dv9274EU Battery.

Crystal structure of red phosphorus

red phosphorus

Red phosphorus

Red phosphorus is polymeric in structure. It can be viewed as a derivative of P4 wherein one P-P bond is broken, and one additional bond is formed between the neighbouring tetrahedron resulting in a chain-like structure. Red phosphorus may be formed by heating white phosphorus to 250 °C (482 °F) or by exposing white phosphorus to sunlightHP Pavilion dv9273EA Battery.[10] Phosphorus after this treatment is amorphous. Upon further heating, this material crystallises. In this sense, red phosphorus is not an allotrope, but rather an intermediate phase between the white and violet phosphorus, and most of its properties have a range of values. For example, freshly prepared, bright red phosphorus is highly reactive and ignites at about 300 °C,[11] though it is still more stable than white phosphorusHP Pavilion dv9272EA Battery, which ignites at about 30 °C.[12] After prolonged heating or storage, the color darkens (see infobox images); the resulting product is more stable and does not spontaneously ignite in air.[13]

Violet phosphorus

Violet phosphorus is a form of phosphorus that can be produced by day-long annealing of red phosphorus above 550 °C. In 1865, Hittorf discovered that when phosphorus was recrystallized from molten lead, a red/purple form is obtained. Therefore this form is sometimes known as "Hittorf's phosphorus" (or violet or α-metallic phosphorus) HP Pavilion dv9271EA Battery.[6]

Crystal structure of black phosphorus

Black phosphorus

Black phosphorus is the least reactive allotrope and the thermodynamically stable form below 550 °C. It is also known as β-metallic phosphorus and has a structure somewhat resembling that of graphite.[14][15] High pressures are usually required to produce black phosphorus, but it can also be produced at ambient conditions using metal salts as catalystsHP Pavilion dv9269EA Battery.[16]

Isotopes

Main article: Isotopes of phosphorus

Twenty-three isotopes of phosphorus are known,[17] including all possibilities from 24P up to 46P). Only 31P is stable and is therefore present at 100% abundance. The half-integer nuclear spin and high abundance of 31P make phosphorus-31 NMR spectroscopy a very useful analytical tool in studies of phosphorus-containing samplesHP Pavilion dv9268EA Battery.

Two radioactive isotopes of phosphorus have half-lives that make them useful for scientific experiments. 32P has a half-life of 14.262 days and 33P has a half-life of 25.34 days. Biomolecules can be "tagged" with a radioisotope to allow for the study of very dilute samples.

Radioactive isotopes of phosphorus include

32P, a beta-emitter (1.71 MeV) with a half-life of 14.3 days, which is used routinely in life-science laboratories, primarily to produce radiolabeled DNA and RNA probesHP Pavilion dv9267EA Battery, e.g. for use in Northern blots or Southern blots. Because the high energy beta particles produced penetrate skin and corneas, and because any 32P ingested, inhaled, or absorbed is readily incorporated into bone and nucleic acids, Occupational Safety and Health Administration in the United States, and similar institutions in other developed countries require that a lab coatHP Pavilion dv9266EU Battery, disposable gloves and safety glasses or goggles be worn when working with 32P, and that working directly over an open container be avoided in order to protect the eyes. Monitoring personal, clothing, and surface contamination is also required. In addition, due to the high energy of the beta particles, shielding this radiation with the normally used dense materials (e.g. lead) HP Pavilion dv9266EA Battery, gives rise to secondary emission of X-rays via Bremsstrahlung (braking radiation). Therefore shielding must be accomplished with low density materials, e.g. Plexiglas (Lucite), other plastics, water, or (when transparency is not required), even wood.[18]

33P, a beta-emitter (0.25 MeV) with a half-life of 25.4 days. It is used in life-science laboratories in applications in which lower energy beta emissions are advantageous such as DNA sequencingHP Pavilion dv9265LA Battery.

Occurrence

See also Category: Phosphate minerals

In terms of stellar nucleosynthesis, stable forms of phosphorus are produced in large (greater than 3 solar masses) stars by fusing two oxygen atoms together.[citation needed] This requires temperatures above 1,000 megakelvins.

Phosphorus is not found free in nature, but it is widely distributed in many minerals, mainly phosphates. Phosphate rock, which is partially made of apatite (an impure tri-calcium phosphate mineral), is an important commercial source of this elementHP Pavilion dv9260US Battery. About 50 percent of the global phosphorus reserves are in the Arab nations.[19] Large deposits of apatite are located in China, Russia, Morocco, Florida, Idaho, Tennessee, Utah, and elsewhere. Albright and Wilson in the United Kingdom and their Niagara Falls plant, for instance, were using phosphate rock in the 1890s and 1900s from the Îles du Connétable, Tennessee and Florida; by 1950 they were using phosphate rock mainly from Tennessee and North AfricaHP Pavilion dv9260NR Battery.[20] In the early 1990s Albright and Wilson's purified wet phosphoric acid business was being adversely affected by phosphate rock sales by China and the entry of their long-standing Moroccan phosphate suppliers into the purified wet phosphoric acid business.[21]

Scarcity

Recent reports suggest that production of phosphorus may have peaked, leading to the possibility of global shortages by 2040.[22] In 2007, at the rate of consumption, the supply of phosphorus was estimated to run out in 345 yearsHP Pavilion dv9255EA Battery.[23] However, some scientists now believe that a "Peak phosphorus" will occur in 30 years and that "At current rates, reserves will be depleted in the next 50 to 100 years."[24]

Production

Main article: phosphoric acid

The majority of phosphorus-containing compounds are produced for use as fertilisers. For this purpose, phosphate-containing minerals are converted to phosphoric acid. Two distinct routes are employed, the main one being treatment of phosphate minerals with sulfuric acidHP Pavilion dv9254EU Battery. The other process utilises white phosphorus, which may be produced by reaction and distillation from very low grade phosphate sources. The white phosphorus is then oxidised to phosphoric acid and subsequently neutralised with base to give phosphate salts. Phosphoric acid obtained via white phosphorus is relatively pure and is the main source of phosphates used in detergents and other non-fertiliser applicationsHP Pavilion dv9253EA Battery.

Elemental phosphorus

About 1,000,000 short tons (910,000 t) of elemental phosphorus is produced annually. Calcium phosphate (phosphate rock), mostly mined in Florida and North Africa, can be heated to 1,200–1,500 °C with sand, which is mostly SiO2, and coke (impure carbon) to produce vaporized P4. The product is subsequently condensed into a white powder under water to prevent oxidation by airHP Pavilion dv9252EU Battery. Even under water, white phosphorus is slowly converted to the more stable red phosphorus allotrope. The chemical equation for this process when starting with fluoroapatite, a common phosphate mineral, is:

4 Ca5(PO4)3F + 18 SiO2 + 30 C → 3 P4 + 30 CO + 18 CaSiO3 + 2 CaF2

Side products from this production include ferrophosphorus, a crude form of Fe2P, resulting from iron impurities in the mineral precursors. The silicate slag is a useful construction material. The fluoride is sometimes recovered for use in water fluoridationHP Pavilion dv9248EA Battery. More problematic is a "mud" containing significant amounts of white phosphorus. Production of white phosphorus is conducted in large facilities in part because it is energy intensive. The white phosphorus is transported in molten form. Some major accidents have occurred during transportation, train derailments at Brownston, Nebraska and Miamisburg, Ohio led to large firesHP Pavilion dv9244EU Battery. The worst incident in recent times was an environmental one in 1968 when the sea became contaminated due to spillages and/or inadequately treated sewage from a white phosphorus plant at Placentia Bay, Newfoundland.[25]

Another process by which elemental phosphorus is extracted includes applying at high temperatures (1500 °C):[26]

2 Ca3(PO4)2 + 6 SiO2 + 10 C → 6CaSiO3 + 10 CO + P4

Thermphos International is Europe's only producer of elemental phosphorus with the annual capacity of 80,000 t provided by a plant at Vlissingen, the NetherlandsHP Pavilion dv9244EA Battery.[27]

Compounds

See also Category: Phosphorus compounds

Oxyacids of phosphorus

Phosphorous oxyacids are extensive, often commercially important, and sometimes structurally complicated. They all have acidic protons bound to oxygen atoms and some have nonacidic protons that are bonded directly to phosphorus. Although many oxyacids of phosphorus are formed, only six are important, and three of them, hypophosphorous acid, phosphorous acid and phosphoric acid are particularly important onesHP Pavilion dv9243EA Battery.

Phosphorus(V) compounds

Oxides

The most prevalent compounds of phosphorus are derivatives of phosphate (PO43-), a tetrahedral anion.[28] Phosphate is the conjugate base of phosphoric acid, which is produced on a massive scale for use in fertilizers. Being triprotic, phosphoric acid converts stepwise to three conjugate basesHP Pavilion dv9237EU Battery:

H3PO4 + H2O  H3O+ + H2PO4−       Ka1= 7.25×10−3

H2PO4− + H2O  H3O+ + HPO42−       Ka2= 6.31×10−8

HPO42− + H2O  H3O+ +  PO43−        Ka3= 3.98×10−13

Phosphate exhibits the tendency to form chains and rings with P-O-P bonds. Many polyphosphates are known, including ATP. Polyphosphates arise by dehydration of hydrogen phosphates such as HPO42- and H2PO4-. For example, the industrially important trisodium triphosphate (also known as sodium tripolyphosphate, STPP) is produced industrially on a megatonne scale via this condensation reactionHP Pavilion dv9235NR Battery:

2 Na2[(HO)PO3] + Na[(HO)2PO2] → Na5[O3P-O-P(O)2-O-PO3] + 2 H2O

Phosphorus pentoxide (P4O10) is the acid anhydride of phosphoric acid, but several intermediates are known between the two. This waxy white solid reacts vigorously with water.

The tetrahedral structure of P4O10 and P4S10.

With metal cations, phosphate forms a variety of salts. These solids are polymeric, featuring P-O-M linkages. When the metal cation has a charge of 2+ or 3+, the salts are generally insoluble, hence they exist as common minerals. Many phosphate salts are derived from hydrogen phosphate (HPO42-)HP Pavilion dv9233EU Battery.

PCl5 and PF5 are common compounds. Both are volatile and pale or colourless. The other two halides, PBr5 and PI5PI5 are unstable. The pentachloride and pentafluoride adopt trigonal bipyramid molecular geometry and are Lewis acids. With fluoride, PF5 forms PF6–, an anion that is isoelectronic with SF6. The most important oxyhalide is phosphorus oxychloride (POCl3), which is tetrahedralHP Pavilion dv9233CL Battery.

Before extensive computer calculations were feasible, it was proposed that bonding in phosphorus(V) compounds involved d orbitals. It is now accepted that the bonding can be better explained by molecular orbital theory and involves only s- and p-orbitals on phosphorus.[29]

Nitrides

Compounds of the formula (PNCl2)n exist mainly as rings such as the trimer hexachlorophosphazeneHP Pavilion dv9233CA Battery. The phosphazenes arise by treatment of phosphorus pentachloride with ammonium chloride: PCl5 + NH4Cl → 1/n (NPCl2)n + 4 HCl The chloride groups can be replaced by alkoxide (RO-) to give rise to a family of polymers with potentially useful properties.[30]

Sulfides

Main article: phosphorus sulfide

Phosphorus forms a wide range of sulfides, where phosphorus can be P(V), P(III) or other oxidation states. Most famous is the three-fold symmetric P4S3 used in strike-anywhere matches. P4S10 and P4O10 have analogous structuresHP Pavilion dv9232EU Battery.

Phosphorus(III) compounds

Phosphine (PH3) and its organic derivatives (PR3) are structural analogues with ammonia (NH3) b

ut the angles at phosphorus are closer to 90° for phosphine and its organic derivatives. It is an ill-smelling, toxic compound. Phosphine is produced by hydrolysis of calcium phosphide, Ca3P2. Unlike ammonia, phosphine is oxidised by air. Phosphine is also far less basic than ammoniaHP Pavilion dv9231CA Battery.

All four symmetrical trihalides are well known: gaseous PF3, the yellowish liquids PCl3 and PBr3, and the solid PI3. These materials are moisture sensitive, hydrolysing to give phosphorus acid. The trichloride, a common reagent, is produced by chlorination of white phosphorus:

P4 + 6 Cl2 → 4 PCl3

The trifluoride is produced by from the trichloride by halide exchange. PF3 is toxic because it binds to haemoglobinHP Pavilion dv9225US Battery.

Phosphorus(III) oxide, P4O6 (also called tetraphosphorus hexoxide) is the anhydride of P(OH)3, the minor tautomer of phosphorous acid. The structure of P4O6 is like that of P4O10 less the terminal oxide groups.

Mixed oxyhalides and oxyhydrides of phosphorus(III) are almost unknown.

Organophosphorus compounds

Main article: organophosphorus compounds

Compounds with P-C and P-O-C bonds are often classified as organophosphorus compounds. They are widely used commerciallyHP Pavilion dv9221TX Battery. The PCl3 serves as a source of P3+ in routes to organophosphorus(III) compounds. For example it is the precursor to triphenylphosphine:

PCl3 + 6 Na + 3 C6H5Cl → P(C6H5)3 + 6 NaCl

Treatment of phosphorus trihalides with alcohols and phenols gives phosphites, e.g. triphenylphosphite:

PCl3 + 3 C6H5OH → P(OC6H5)3 + 3 HCl

Similar reactions occur for phosphorus oxychloride, affording triphenylphosphate:

OPCl3 + 3 C6H5OH → OP(OC6H5)3 + 3 HCl

Phosphorus(I) and phosphorus(II) compounds

These compounds generally feature P-P bonds.[8] Examples include catenated derivatives of phosphine and organophosphinesHP Pavilion dv9221TX Battery. The highly flammable gas diphosphine (P2H4) is the first of a series of derivatives of this type. Diphosphine is an analogue of hydrazine. Compounds containing P=P double bonds have also been observed, although they are rare.

A stable diphosphene, a derivative of phosphorus(I).

Phosphides

The phosphide ion is P3-. Phosphides arise by reaction of metals with red phosphorus. Salts of P3- do not exist in solution and these derivatives are refractory, reflecting their high lattice energy. Illustrated by the behaviour calcium phosphide, many metal phosphides hydrolyse in water with release of phosphineHP Pavilion dv9220US Battery:

Ca3P2 + 6 H2O → 2 PH3 + 3 Ca(OH)2

Schreibersite is a naturally occurring phosphide found in meteorites. Many polyphosphides are known such as derivatives of OsP2. These can be structurally complex ranging from Na3P7 and derivatives of P264-. Often these species adopt cage-like structures that resemble fragments of violet phosphorusHP Pavilion dv9220TX Battery.

Spelling and etymology

The name Phosphorus in Ancient Greece was the name for the planet Venus and is derived from the Greek words (φως = light, φέρω = carry), which roughly translates as light-bringer or light carrier.[10] (In Greek mythology and tradition, Augerinus (Αυγερινός = morning star, in use until today), Hesperus or Hesperinus (΄Εσπερος or Εσπερινός or Αποσπερίτης = evening star, in use until today) and EosphorusHP Pavilion dv9220TX Battery (Εωσφόρος = dawnbearer, not in use for the planet after Christianity) are close homologues, and also associated with Phosphorus-the-planet).

According to the Oxford English Dictionary, the correct spelling of the element is phosphorus. The word phosphorous is the adjectival form of the P3+ valence: so, just as sulfur forms sulfurous and sulfuric compounds, phosphorus forms phosphorous compounds (e.g., phosphorous acid) and P5+ valence phosphoric compounds (e.g., phosphoric acids and phosphates) HP Pavilion dv9220EU Battery.

History and discovery

Phosphorus was the 13th element to be discovered. For this reason, and also due to its use in explosives, poisons and nerve agents, it is sometimes referred to as "the Devil's element".[32] The discovery of phosphorus is credited to the German alchemist Hennig Brand in 1669, although other chemists might have discovered phosphorus around the same timeHP Pavilion dv9220CA Battery.[33] Brand experimented with urine, which contains considerable quantities of dissolved phosphates from normal metabolism.[10] Working in Hamburg, Brand attempted to create the fabled philosopher's stone through the distillation of some salts by evaporating urine, and in the process produced a white material that glowed in the dark and burned brilliantly. It was named phosphorus mirabilis HP Pavilion dv9219TX Battery ("miraculous bearer of light").[34] His process originally involved letting urine stand for days until it gave off a terrible smell. Then he boiled it down to a paste, heated this paste to a high temperature, and led the vapours through water, where he hoped they would condense to gold. Instead, he obtained a white, waxy substance that glowed in the dark. Brand had discovered phosphorusHP Pavilion dv9219EA Battery, the first element discovered since antiquity. We now know that Brand produced ammonium sodium hydrogen phosphate, (NH4)NaHPO4. While the quantities were essentially correct (it took about 1,100 L of urine to make about 60 g of phosphorus), it was unnecessary to allow the urine to rot. Later scientists would discover that fresh urine yielded the same amount of phosphorusHP Pavilion dv9218TX Battery.

Robert Boyle

Brand at first tried to keep the method secret,[35] but later sold the recipe for 200 thalers to D Krafft from Dresden,[10] who could now make it as well, and toured much of Europe with it, including England, where he met with Robert Boyle. The secret that it was made from urine leaked out and first Johann Kunckel (1630–1703) in Sweden (1678) and later Boyle in London (1680) also managed to make phosphorusHP Pavilion dv9218EA Battery. Boyle states that Krafft gave him no information as to the preparation of phosphorus other than that it was derived from "somewhat that belonged to the body of man". This gave Boyle a valuable clue, however, so that he, too, managed to make phosphorus, and published the method of its manufacture.[10] Later he improved Brand's process by using sand in the reaction (still using urine as base material) HP Pavilion dv9217TX Battery,

4 NaPO3 + 2 SiO2 + 10 C → 2 Na2SiO3 + 10 CO + P4

Robert Boyle was the first to use phosphorus to ignite sulfur-tipped wooden splints, forerunners of our modern matches, in 1680.

In 1769 Johan Gottlieb Gahn and Carl Wilhelm Scheele showed that calcium phosphate (Ca3(PO4)2) is found in bones, and they obtained phosphorus from bone ash. Antoine Lavoisier recognized phosphorus as an element in 1777. HP Pavilion dv9217EA Battery Bone ash was the major source of phosphorus until the 1840s. Phosphate rock, a mineral containing calcium phosphate, was first used in 1850 and following the introduction of the electric arc furnace in 1890, this became the only source of phosphorus. Phosphorus, phosphates and phosphoric acid are still obtained from phosphate rock. Phosphate rock is a major feedstock in the fertilizer industryHP Pavilion dv9217EA Battery.

White phosphorus was first made commercially, for the match industry in the 19th century, by distilling off phosphorus vapour from precipitated phosphates, mixed with ground coal or charcoal, which was heated in an iron pot, in retort.[37] The precipitated phosphates were made from ground-up bones that had been de-greased and treated with strong acidsHP Pavilion dv9216TX Battery. Carbon monoxide and other flammable gases produced during the reduction process were burnt off in a flare stack. This process became obsolete when the submerged-arc furnace for phosphorus production was introduced to reduce phosphate rock.[38][39] The electric furnace method allowed production to increase to the point where phosphorus could be used in weapons of warHP Pavilion dv9216TX Battery.[40][41] In World War I it was used in incendiaries, smoke screens and tracer bullets.[41] A special incendiary bullet was developed to shoot at hydrogen-filled Zeppelins over Britain (hydrogen being highly flammable if it can be ignited).[41] During World War II, Molotov cocktails of benzene and phosphorus were distributed in Britain to specially selected civilians within the British resistance operation, for defenceHP Pavilion dv9216EA Battery; and phosphorus incendiary bombs were used in war on a large scale. Burning phosphorus is difficult to extinguish and if it splashes onto human skin it has horrific effects.[8]

Early matches used white phosphorus in their composition, which was dangerous due to its toxicity. Murders, suicides and accidental poisonings resulted from its use. (An apocryphal tale tells of a woman attempting to murder her husband with white phosphorus in his food, which was detected by the stew's giving off luminous steam) HP Pavilion dv9215TX Battery.[40] In addition, exposure to the vapours gave match workers a severe necrosis of the bones of the jaw, the infamous "phossy jaw". When a safe process for manufacturing red phosphorus was discovered, with its far lower flammability and toxicity, laws were enacted, under the Berne Convention (1906), requiring its adoption as a safer alternative for match manufactureHP Pavilion dv9214TX Battery.[42] The toxicity of white phosphorus led to discontinuation of it use in matches.[43] In a historical coincidence, the Allies used phosphorus incendiary bombs in World War II to destroy Hamburg, the place where the "miraculous bearer of light" was first discovered.[34]

The glow, the explanation, and the term derived from it

It was known from early times that the green glow emanating from white phosphorus would persist for a time in a stoppered jar, but then cease. Robert Boyle in the 1680s ascribed it to "debilitation" of the air; in fact, it is oxygen being consumedHP Pavilion dv9214EA Battery. By the 18th century, it was known that in pure oxygen, phosphorus does not glow at all;[44] there is only a range of partial pressure at which it does. Heat can be applied to drive the reaction at higher pressures.[45]

In 1974, the glow was explained by R. J. van Zee and A. U. Khan.[40] A reaction with oxygen takes place at the surface of the solid (or liquid) phosphorus, forming the short-lived molecules HPO and P2O2 that both emit visible lightHP Pavilion dv9213TX Battery. The reaction is slow and only very little of the intermediates are required to produce the luminescence, hence the extended time the glow continues in a stoppered jar.

Since that time, phosphors and phosphorescence were used loosely to describe substances that shine in the dark without burning. However, as mentioned above, even though the term phosphorescence was originally coined as a term by analogy with the glow from oxidation of elemental phosphorus, is now reserved for another fundamentally different process—re-emission of light after illuminationHP Pavilion dv9213EA Battery.

Applications

Fertiliser

The dominant application of phosphorus is in fertilisers, which provides phosphate as required for all life and is often a limiting nutrient for crops. Phosphorus, being an essential plant nutrient, finds its major use as a constituent of fertilizers for agriculture and farm production in the form of concentrated phosphoric acids, which can consist of 70% to 75% P2O5HP Pavilion dv9212TX Battery. Global demand for fertilisers led to large increase in phosphate (PO43–) production in the second half of the 20th century. Due to the essential nature of phosphorus to living organisms, the low solubility of natural phosphorus-containing compounds, and the slow natural cycle of phosphorus, the agricultural industry is heavily reliant on fertilisers that contain phosphateHP Pavilion dv9212EA Battery, mostly in the form of superphosphate of lime. Superphosphate of lime is a mixture of two phosphate salts, calcium dihydrogen phosphate Ca(H2PO4)2 and calcium sulfate dihydrate CaSO4·2H2O produced by the reaction of sulfuric acid and water with calcium phosphate.

Organophosphorus compounds

White phosphorus is widely used to make organophosphorus compounds, through the intermediates phosphorus chlorides and two phosphorus sulfides, phosphorus pentasulfide, and phosphorus sesquisulfideHP Pavilion dv9211TX Battery.[46] Organophosphorus compounds have many applications, including in plasticizers, flame retardants, pesticides, extraction agents, and water treatment.[8] in particular the herbicide glyphosate sold under the brand name Roundup.

Metallurgical aspects

Phosphorus is also an important component in steel production, in the making of phosphor bronze, and in many other related products. Phosphorus is added to metallic copper during its smelting process to react with oxygen present as an impurity in copper and to produce oxygen-free copper or phosphorus-containing copper HP Pavilion dv9211EA Battery (CuOFP) alloys with a higher thermal and electrical conductivity than normal copper.

Matches

Match striking surface made of a mixture of red phosphorus, glue and ground glass. The glass powder is used to increase the friction.

Main article: Match

Phosphorus-contained matches were first produced in 1830s and contained a mixture of white phosphorus, an oxygen-releasing compound (potassium chlorate, lead dioxide or some nitrate) and a binder in their heads. They were rather sensitive to storage conditions, toxic and unsafe, as they could be lit by striking on any rough surfaceHP Pavilion dv9210US Battery. Therefore, their production was gradually banned between 1872 and 1925 in different countries.[47] The international Berne Convention, adopted in 1906, prohibited the use of white phosphorus in matches. As a consequence, the 'strike-anywhere' matches were gradually replaced by 'safety matches' where white phosphorus was substituted by phosphorus sesquisulfide (P4S3) HP Pavilion dv9210TX Battery, sulfur or antimony sulfide. Such matches are hard to ignite on an arbitrary surface and require a special strip. The strip contains red phosphorus which heats up upon striking, reacts with the oxygen-releasing compound in the head and ignites the flammable material of the head.[11][46]

Water softening

Sodium tripolyphosphate made from phosphoric acid is used in laundry detergents in some countries, but banned for this use in others.[13] It is useful for softening water to enhance the performance of the detergents and to prevent pipe/boiler tube corrosionHP Pavilion dv9210CA Battery.

Niche applications

Phosphates are utilized in the making of special glasses that are used for sodium lamps.[13]

Bone-ash, calcium phosphate, is used in the production of fine china.[13]

Phosphoric acid made from elemental phosphorus is used in food applications such as some soda beverages. The acid is also a starting point to make food grade phosphates.[46] These include mono-calcium phosphate that is employed in baking powder and sodium tripolyphosphate and other sodium phosphatesHP Pavilion dv9209TX Battery.[46] Among other uses these are used to improve the characteristics of processed meat and cheese. Others are used in toothpaste.[46]

White phosphorus, called "WP" (slang term "Willie Peter") is used in military applications as incendiary bombs, for smoke-screening as smoke pots and smoke bombs, and in tracer ammunition. It is also a part of an obsolete M34 White Phosphorus US hand grenade. This multipurpose grenade was mostly used for signalling, smoke screens and inflammationHP Pavilion dv9208TX Battery; it could also cause severe burns and had a psychological impact on the enemy.[48][49] Military uses of white phosphorus are constrained by international law [50]

In trace amounts, phosphorus is used as a dopant for n-type semiconductors.

32P and 33P are used as radioactive tracers in biochemical laboratories.

Phosphate is a strong complexing agent for the hexavalent uranyl (UO22+) species and this is the reason why apatite and other natural phosphates can often be very rich in uranium.

Tributylphosphate is an organophosphate soluble in kerosene and used to extract uranium in the Purex process applied in the reprocessing of spent nuclear fuelHP Pavilion dv9208NR Battery.

Biological role

Inorganic phosphorus in the form of the phosphate PO3−

4 is required for all known forms of life,[51] playing a major role in biological molecules such as DNA and RNA where it forms part of the structural framework of these molecules. Living cells also use phosphate to transport cellular energy in the form of adenosine triphosphate (ATP). Nearly every cellular process that uses energy obtains it in the form of ATPHP Pavilion dv9207TX Battery. ATP is also important for phosphorylation, a key regulatory event in cells. Phospholipids are the main structural components of all cellular membranes. Calcium phosphate salts assist in stiffening bones.[8]

Living cells are defined by a membrane that separates it from its surroundings. Biological membranes are made from a phospholipid matrix and proteins, typically in the form of a bilayer. Phospholipids are derived from glycerol, such that two of the glycerol hydroxyl (OH) protons have been replaced with fatty acids as an esterHP Pavilion dv9206TX Battery, and the third hydroxyl proton has been replaced with phosphate bonded to another alcohol.[52]

An average adult human contains about 0.7 kg of phosphorus, about 85–90% of which is present in bones and teeth in the form of apatite, and the remainder in soft tissues and extracellular fluids (~1%). The phosphorus content increases from about 0.5 weight% in infancy to 0.65–1.1 weight% in adultsHP Pavilion dv9206EU Battery. Average phosphorus concentration in the blood is about 0.4 g/L, about 70% of that is organic and 30% inorganic phosphates.[53] A well-fed adult in the industrialized world consumes and excretes about 1–3 grams of phosphorus per day, with consumption in the form of inorganic phosphate and phosphorus-containing biomolecules such as nucleic acids and phospholipids; and excretion almost exclusively in the form of phosphate ions such as H2PO−HP Pavilion dv9205US Battery

4 and HPO2−

4. Only about 0.1% of body phosphate circulates in the blood, and this amount reflects the amount of phosphate available to soft tissue cells.

Bone and teeth enamel

The main component of bone is hydroxyapatite as well as amorphous forms of calcium phosphate, possibly including carbonate. Hydroxyapatite is the main component of tooth enamel. Water fluoridation enhances the resistance of teeth to decay by the partial conversion of this mineral to the still harder material called fluoroapatite: HP Pavilion dv9205TX Battery

Ca5(PO4)3OH + F− → Ca5(PO4)3F + OH−

Phosphorus deficiency

In medicine, low-phosphate syndromes are caused by malnutrition, by failure to absorb phosphate, and by metabolic syndromes that draw phosphate from the blood (such as re-feeding after malnutrition) or pass too much of it into the urine. All are characterized by hypophosphatemia, which is a condition of low levels of soluble phosphate levels in the blood serum, and therefore inside cellsHP Pavilion dv9205EU Battery. Symptoms of hypophosphatemia include muscle and neurological dysfunction, and disruption of muscle and blood cells due to lack of ATP. Too much phosphate can lead to diarrhoea and calcification (hardening) of organs and soft tissue, and can interfere with the body's ability to use iron, calcium, magnesium, and zincHP Pavilion dv9205CA Battery.[54]

Phosphorus is an essential macromineral for plants, which is studied extensively in edaphology in order to understand plant uptake from soil systems. In ecological terms, phosphorus is often a limiting factor in many environments; i.e. the availability of phosphorus governs the rate of growth of many organisms. In ecosystems an excess of phosphorus can be problematicHP Pavilion dv9204TX Battery, especially in aquatic systems, resulting in eutrophication which sometimes lead to algal blooms.

Food sources

The main food sources of phosphorus are kinds of food containing protein, for example, milk and meat. As a rule, if one holds a meal plan providing sufficient amount of protein and calcium then amount of phosphorus is also sufficient.[55]

Precautions

Organic compounds of phosphorus form a wide class of materials, many are required for life, but some are extremely toxicHP Pavilion dv9203TX Battery. Fluorophosphate esters are among the most potent neurotoxins known. A wide range of organophosphorus compounds are used for their toxicity to certain organisms as pesticides (herbicides, insecticides, fungicides, etc.) and weaponised as nerve agents. Most inorganic phosphates are relatively nontoxic and essential nutrientsHP Pavilion dv9202TX Battery.[8]

The white phosphorus allotrope presents a significant hazard because it ignites in air and produces phosphoric acid residue. Chronic white phosphorus poisoning leads to necrosis of the jaw called "phossy jaw". Ingestion of white phosphorus may cause a medical condition known as "Smoking Stool Syndrome".HP Pavilion dv9202EA Battery

Phosphorus explosion

Upon exposure to elemental phosphorus, in the past it was suggested to wash the affected area with 2% copper sulfate solution to form harmless compounds that can be washed away. According to the recent US Navy's Treatment of Chemical Agent Casualties and Conventional Military Chemical Injuries: FM8-285: Part 2 Conventional Military Chemical InjuriesHP Pavilion dv9201TX Battery, "Cupric (copper(II)) sulfate has been used by U.S. personnel in the past and is still being used by some nations. However, copper sulfate is toxic and its use will be discontinued. Copper sulfate may produce kidney and cerebral toxicity as well as intravascular hemolysis."[57]

The manual suggests instead "a bicarbonate solution to neutralize phosphoric acid, which will then allow removal of visible white phosphorus. Particles often can be located by their emission of smoke when air strikes themHP Pavilion dv9201CA Battery, or by their phosphorescence in the dark. In dark surroundings, fragments are seen as luminescent spots. Promptly debride the burn if the patient's condition will permit removal of bits of WP (white phosphorus) that might be absorbed later and possibly produce systemic poisoning. DO NOT apply oily-based ointments until it is certain that all WP has been removedHP Pavilion dv9200XX Battery. Following complete removal of the particles, treat the lesions as thermal burns."[note 1] As white phosphorus readily mixes with oils, any oily substances or ointments are not recommended until the area is thoroughly cleaned and all white phosphorus removed.

US DEA List I status

Phosphorus can reduce elemental iodine to hydroiodic acid, which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamineHP Pavilion dv9105EU Battery.[58] For this reason, red and white phosphorus were designated by the United States Drug Enforcement Administration as List I precursor chemicals under 21 CFR 1310.02 effective on November 17, 2001.[59] As a result, in the United States, handlers of red or white phosphorus are subject to stringent regulatory controlsHP Pavilion dv9100 Battery.

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