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22 novembre 2011 2 22 /11 /novembre /2011 02:16

Aluminium or aluminum (US English) is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the Earth's crust. Sony VAIO VPCEB190X Battery

It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is too reactive chemically to occur natively. Instead, it is found combined in over 270 different minerals.[4] The chief ore of aluminium is bauxite.

Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon ofpassivation.Sony VAIO VPCEB19FX Battery

Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.Sony VAIO VPCEB19GX Battery

Despite its prevalence in the environment, aluminium salts are not known to be used by any form of life. In keeping with its pervasiveness, it is well tolerated by plants and animals.Because of their prevalence, potential biological roles, beneficial and otherwise, aluminium compounds are of continuing interest.Sony VAIO VPCEB1AFX Battery

Physical

Aluminium is a soft, durable, lightweight, ductile and malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. Aluminium is nonmagnetic and does not easily ignite. Sony VAIO VPCEB1AFX/B Battery

A fresh film of aluminium film serves as a good reflector (approximately 92%) of visible light and an excellent reflector (as much as 98%) of medium and far infrared radiation. The yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa.Sony VAIO VPCEB1AGX Battery

Aluminium has about one-third the density and stiffness of steel. It is easily machined, cast, drawnand extruded.

Corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. Sony VAIO VPCEB1AGX/BI Battery

The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is also often greatly reduced when many aqueous salts are present, particularly in the presence of dissimilar metals.

Aluminium atoms are arranged in a face-centered cubic (fcc) structure. Aluminium has a stacking-fault energy of approximately 200 mJ/m2.Sony VAIO VPCEB1BGX Battery

Aluminium is one of the few metals that retain full silvery reflectance in finely powdered form, making it an important component of silver-colored paints. Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3,000–10,000 nm (far IR) regions;Sony VAIO VPCEB1BGX/BI Battery

in the 400–700 nm visible range it is slightly outperformed by tin and silver and in the 700–3000 (near IR) by silver, gold, and copper.

Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical.Sony VAIO VPCEB1CGX Battery

Aluminium is capable of being a superconductor, with a superconducting critical temperature of 1.2 Kelvin and a critical magnetic field of about 100 gauss (10 milliteslas).

Creation

Stable aluminium is created when hydrogen fuses with magnesium either in large stars or in supernovae. Sony VAIO VPCEB1CGX/BI Battery

Isotopes

Aluminium has many known isotopes, whose mass numbers range from 21 to 42; however, only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2×105 y) occur naturally. 27Al has a natural abundance above 99.9%. 26Al is produced from argonin the atmosphere by spallation caused by cosmic-ray protons. Sony VAIO VPCEB1DGX Battery

Aluminium isotopes have found practical application in datingmarine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of 26Al to 10Be has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales.Sony VAIO VPCEB1DGX/BI Battery

Cosmogenic 26Al was first applied in studies of the Moon and meteorites. Meteoroid fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial 26Al production.Sony VAIO VPCEB1EGX Battery

After falling to Earth, atmospheric shielding drastically reduces 26Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that 26Al was relatively abundant at the time of formation of our planetary system. Sony VAIO VPCEB1EGX/BI Battery

Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.

Natural occurrence

In the Earth's crust, aluminium is the most abundant (8.3% by weight) metallic element and the third most abundant of all elements (after oxygen and silicon).Sony VAIO VPCEB1FGX Battery

Because of its strong affinity to oxygen, it is almost never found in the elemental state; instead it is found in oxides or silicates. Feldspars, the most common group of minerals in the Earth's crust, are aluminosilicates. Native aluminium metal can be found as a minor phase in low oxygen fugacity environments, such as the interiors of certain volcanoes.Sony VAIO VPCEB1FGX/BI Battery

Native aluminium has been reported in cold seeps in the northeastern continental slope of the South China Sea and Chen et al. (2011)have proposed a theory of its origin as resulting by reduction from tetrahydroxoaluminate Al(OH)4- to metallic aluminium by bacteria.Sony VAIO VPCEB1GGX Battery

It also occurs in the minerals beryl, cryolite, garnet, spinel and turquoise. Impurities in Al2O3, such as chromium or ironyield the gemstones ruby and sapphire, respectively.

Although aluminium is an extremely common and widespread element, the common aluminium minerals are not economic sources of the metal. Sony VAIO VPCEB1GGX/BI Battery

Almost all metallic aluminium is produced from the ore bauxite (AlOx(OH)3-2x). Bauxite occurs as a weatheringproduct of low iron and silica bedrock in tropical climatic conditions. Large deposits of bauxite occur in Australia,Brazil, Guinea and Jamaica and the primary mining areas for the ore are in Australia, Brazil, China, India, Guinea,Indonesia, Jamaica, Russia and Surinam.Sony VAIO VPCEB1HGX Battery

Production and refinement

Although aluminium is the most abundant metallic element in the Earth's crust, it is never found in free, metallic form (with above mentioned exceptions).

Aluminium forms strong chemical bonds with oxygen. Compared to most other metals, it is difficult to extract from ore, such asbauxite, due to the energy required to reduce aluminium oxide (Al2O3). Sony VAIO VPCEB1HGX/BI Battery

For example, direct reduction with carbon, as is used to produce iron, is not chemically possible, since aluminium is a stronger reducing agent than carbon. There is an indirect carbothermic reduction possible by using carbon and Al2O3, which forms an intermediate Al4C3 and this can further yield aluminium metal at a temperature of 1900–2000°C.Sony VAIO VPCEB1JFX Battery

This process is still under development. This process costs less energy and yields less CO2 than the Hall-Héroult process, the major industrial process for aluminium extraction. Aluminium oxide has a melting point of about 2,000 °C (3,600 °F). Therefore, it must be extracted by electrolysis. Sony VAIO VPCEB1JFX/B Battery

In this process, the aluminium oxide is dissolved in molten cryolite with calcium fluoride and then reduced to the pure metal. The operational temperature of the reduction cells is around 950 to 980 °C (1,740 to 1,800 °F). Cryolite is found as a mineral in Greenland, but in industrial use it has been replaced by a synthetic substance. Sony VAIO VPCEB1JFX/G Battery

Cryolite is a chemical compound of aluminium and sodium fluorides: (Na3AlF6). The aluminium oxide (a white powder) is obtained by refining bauxite in the Bayer process of Karl Bayer. (Previously, the Deville process was the predominant refining technology.)

The electrolytic process replaced the Wöhler process, which involved the reduction of anhydrous aluminium chloride with potassium.Sony VAIO VPCEB1JFX/L Battery

Both of the electrodes used in the electrolysis of aluminium oxide are carbon. Once the refined alumina is dissolved in the electrolyte, its ions are free to move around. The reaction at the cathode is:

Al3+ + 3 e? ? Al

Here the aluminium ion is being reduced. The aluminium metal then sinks to the bottom and is tapped off, usually cast into large blocks called aluminium billets for further processing.Sony VAIO VPCEB1JFX/P Battery

At the anode, oxygen is formed:

2 O2? ? O2 + 4 e?

To some extent, the carbon anode is degraded by the oxygen. The anodes in a reduction cell must therefore be replaced regularly, since they are consumed in the process. The cathodes do erode, mainly due to electrochemical processes and metal movement.Sony VAIO VPCEB1JFX/W Battery

After five to ten years, depending on the current used in the electrolysis, a cell has to be rebuilt because of cathode wear.

Aluminium electrolysis with the Hall-Héroult process consumes a lot of energy, but alternative processes were always found to be less viable economically and/or ecologically. Sony VAIO VPCEB1KGX Battery

The worldwide average specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram of aluminium produced (52 to 56 MJ/kg). The most modern smelters achieve approximately 12.8 kW·h/kg (46.1 MJ/kg). (Compare this to the heat of reaction, 31 MJ/kg, and the Gibbs free energy of reaction, 29 MJ/kg.)Sony VAIO VPCEB1KGX/B Battery

Reduction line currents for older technologies are typically 100 to 200 kiloamperes; state-of-the-art smelters operate at about 350 kA. Trials have been reported with 500 kA cells.

The Hall-Heroult process produces aluminium with a purity of above 99%. Further purification can be done by the Hoope process.Sony VAIO VPCEB1KGX/W Battery

The process involves the electrolysis of molten aluminium with a sodium, barium and aluminium fluoride electrolyte. The resulting aluminium has a purity of 99.99%.

Electric power represents about 20% to 40% of the cost of producing aluminium, depending on the location of the smelter. Aluminium production consumes roughly 5% of electricity generated in the U.S.Sony VAIO VPCEB1LFX Battery

Smelters tend to be situated where electric power is both plentiful and inexpensive, such as the United Arab Emirates with excess natural gas supplies and Iceland and Norway with energy generated from renewable sources. The world's largest smelters of alumina are People's Republic of China, Russia, and Quebec and British Columbia in Canada.Sony VAIO VPCEB1LFX/BI Battery

In 2005, the People's Republic of China was the top producer of aluminium with almost a one-fifth world share, followed by Russia, Canada, and the USA, reports the British Geological Survey.

Over the last 50 years, Australia has become a major producer of bauxite ore and a major producer and exporter of alumina (before being overtaken by China in 2007).Sony VAIO VPCEB1LFX/WI Battery

Australia produced 62 million tonnes of bauxite in 2005. The Australian deposits have some refining problems, some being high in silica, but have the advantage of being shallow and relatively easy to mine.

Recycling

Production and refinement

Aluminium is theoretically 100% recyclable without any loss of its natural qualities. Sony VAIO VPCEB1MFX Battery

According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of aluminium in use in society (i.e. in cars, buildings, electronics etc.) is 80 kg. Much of this is in more-developed countries (350–500 kg per capita) rather than less-developed countries (35 kg per capita). Sony VAIO VPCEB1MFX/BI Battery

Knowing the per capita stocks and their approximate lifespans is important for planning recycling.

Recovery of the metal via recycling has become an important facet of the aluminium industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverage cans brought it to the public awareness.Sony VAIO VPCEB1NFX Battery

Recycling involves melting the scrap, a process that requires only 5% of the energy used to produce aluminium from ore, though a significant part (up to 15% of the input material) is lost as dross (ash-like oxide).The dross can undergo a further process to extract aluminium.Sony VAIO VPCEB1NFX/B Battery

In Europe aluminium experiences high rates of recycling, ranging from 42% of beverage cans, 85% of construction materials and 95% of transport vehicles.

Recycled aluminium is known as secondary aluminium, but maintains the same physical properties as primary aluminium.Sony VAIO VPCEB1NFX/L Battery

Secondary aluminium is produced in a wide range of formats and is employed in 80% of alloy injections. Another important use is for extrusion.

White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium that can be extracted industrially.Sony VAIO VPCEB1NFX/P Battery

The process produces aluminium billets, together with a highly complex waste material. This waste is difficult to manage. It reacts with water, releasing a mixture of gases (including, among others, hydrogen, acetylene, and ammonia), which spontaneously ignites on contact with air;Sony VAIO VPCEB1NFX/W Battery

contact with damp air results in the release of copious quantities of ammonia gas. Despite these difficulties, the waste has found use as a filler in asphalt and concrete.

Oxidation state +3

The vast majority of compounds, including all Al-containing minerals and all commercially significant aluminium compounds, feature aluminium in the oxidation state 3+. Sony VAIO VPCEB1PFX Battery

The coordination number of such compounds varies, but generally Al3+ is six-coordinate or tetracoordinate. Almost all compounds of aluminium(III) are colorless.[13]

Halides

All four trihalides are well known. Unlike the structures of the three heavier trihalides, aluminium fluoride (AlF3) features six-coordinate Al. Sony VAIO VPCEB1PFX/B Battery

The octahedral coordination environment for AlF3 is related to the compactness of fluoride ion, six of which can fit around the small Al3+ centre. AlF3 sublimes (with cracking) at1,291 °C (2,356 °F). With heavier halides, the coordination numbers are lower. The other trihalides are dimeric or polymeric with tetrahedral Al centers.Sony VAIO VPCEB1QGX Battery

These materials are prepared by treating aluminium metal with the halogen, although other methods exist. Acidification of the oxides or hydroxides affords hydrates. In aqueous solution, the halides often form mixtures, generally containing six-coordinate Al centres, which are feature both halide and aquo ligands.Sony VAIO VPCEB1QGX/BI Battery

When aluminium and fluoride are together in aqueous solution, they readily form complex ions such as [AlF(H2O)5]2+, AlF3(H2O)3, and [AlF6]3?. In the case of chloride, polyaluminium clusters are formed such as [Al13O4(OH)24(H2O)12]7+.

Oxide and hydroxides

Aluminium forms one stable oxide, known by its mineral name corundum.Sony VAIO VPCEB1RGX Battery

Sapphire and ruby are impure corundum contaminated with trace amounts of other metals. The two oxide-hydroxides (AlO(OH) are boehmite and diaspore. There are three trihydroxides: bayerite, gibbsite, and nordstrandite, which differ in their crystalline structure (polymorphs). Most are produced from ores by a variety of wet processes using acid and base. Sony VAIO VPCEB1RGX/BI Battery

Heating the hydroxides leads to formation of corundrum. These materials are of central importance to the production of aluminium and are themselves extremely useful.

Carbide, nitride, and related materials

Aluminium carbide (Al4C3) is made by heating a mixture of the elements above 1,000 °C (1,832 °F). Sony VAIO VPCEB20 Battery

The pale yellow crystals consist of tetrahedral aluminium centres. It reacts with water or dilute acids to give methane. The acetylide, Al2(C2)3, is made by passing acetylene over heated aluminium.

Aluminium nitride (AlN) is the only nitride known for aluminium. Unlike the oxides it features tetrahedral Al centres.Sony VAIO VPCEC20 Battery

It can be made from the elements at 800 °C(1,472 °F). It is air-stable material with a usefully high thermal conductivity. Aluminium phosphide (AlP) is made similarly, and hydrolyses to give phosphine:

AlP + 3 H2O ? Al(OH)3 + PH3

Organoaluminium compounds and related hydrides

A variety of compounds of empirical formula AlR3 and AlR1.5Cl1.5 exist.Sony VAIO VPCEE20 Battery

These species usually feature tetrahedral Al centres, e.g. "trimethylaluminium" has the formula Al2(CH3)6 (see figure). With large organic groups, triorganoaluminium exist as three-coordinate monomers, such as triisobutylaluminium. Such compounds are widely used in industrial chemistry, despite the fact that they are often highly pyrophoric. Sony VAIO VPCEF20 Battery

Few analogues exist between organoaluminium and organoboron compounds except for large organic groups.

The important aluminium hydride is lithium aluminium hydride (LiAlH4), which is used in as a reducing agent in organic chemistry. It can be produced from lithium hydride and aluminium trichloride: Sony VAIO VPCF112FX/B Battery

4 LiH + AlCl3 ? LiAlH4 + 3 LiCl

Several useful derivatives of LiAlH4 are known, e.g. Sodium bis(2-methoxyethoxy)dihydridoaluminate. The simplest hydride,aluminium hydride or alane, remains a laboratory curiosity. It is a polymer with the formula (AlH3)n, in contrast to the corresponding boron hydride with the formula (BH3)2. Sony VAIO VPCF115FG/B Battery

Oxidation states +1 and +2

Although the great majority of aluminium compounds feature Al3+ centres, compounds with lower oxidation states are known and sometime of significance as precursors to the Al3+ species.Sony VAIO VPCF116FGBI Battery

Aluminium(I)

AlF, AlCl and AlBr exist in the gaseous phase when the tri-halide is heated with aluminium. The composition AlI is unstable at room temperature with respect to the triiodide:

3 AlI ? AlI3 + 2 Al

A stable derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, Al4I4(NEt3)4.Sony VAIO VPCF117FJ/W Battery

Also of theoretical interest but only of fleeting existence are Al2O and Al2S is made by heating the normal oxide, Al2O3, with silicon at 1,800 °C (3,272 °F) in a vacuum.[31] Such materials quickly disproportionates to the starting materials.

Aluminium(II)

Very simple Al(II) compounds are invoked or observed in the reactions of Al metal with oxidants. Sony VAIO VPCF117HG/BI Battery

For example, aluminium monoxide, AlO, has been detected in the gas phase after explosion[32] and in stellar absorption spectra.[33]More thoroughly investigated are compounds of the formula R4Al2 where R is a large organic ligand.[34]

Analysis

The presence of aluminium can be detected in qualitative analysis using aluminon.Sony VAIO VPCF118FJ/W Battery

Applications

Aluminium is the most widely used non-ferrous metal.Global production of aluminium in 2005 was 31.9 million tonnes. It exceeded that of any other metal exceptiron (837.5 million tonnes).Forecast for 2012 is 42–45 million tons, driven by rising Chinese output.Sony VAIO VPCF119FC Battery

Aluminium is almost always alloyed, which markedly improves its mechanical properties, especially when tempered. For example, the common aluminium foils and beverage cans are alloys of 92% to 99% aluminium. The main alloying agents are copper, zinc, magnesium, manganese, and silicon (e.g., duralumin) and the levels of these other metals are in the range of a few percent by weight.Sony VAIO VPCF119FC/BI Battery

Some of the many uses for aluminium metal are in:

  • Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, etc.) as sheet, tube, castings, etc.
  • Packaging (cans, foil, etc.)
  • Construction (windows, doors, siding, building wire, etc.)Sony VAIO VPCF119FJ/BI Battery
  • A wide range of household items, from cooking utensils to baseball bats, watches.
  • Street lighting poles, sailing ship masts, walking poles, etc.
  • Outer shells of consumer electronics, also cases for equipment e.g. photographic equipment.
  • Electrical transmission lines for power distribution  Sony VAIO VPCF11AFJ Battery
  • MKM steel and Alnico magnets
  • Super purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs.
  • Heat sinks for electronic appliances such as transistors and CPUs.
  • Substrate material of metal-core copper clad laminates used in high brightness LED lighting.
  • Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.Sony VAIO VPCF11AGJ Battery
  • Aluminium can be reacted with hydrochloric acid or with sodium hydroxide to produce hydrogen gas.
  • A variety of countries, including France, Italy, Poland, Finland, Romania, Israel, and the former Yugoslavia, have issued coinsstruck in aluminium or aluminium-copper alloys.Sony VAIO VPCF11AHJ Battery
  • Some guitar models sports aluminium diamond plates on the surface of the instruments, usually either chrome or black. Kramer Guitars and Travis Bean are both known for having produced guitars with necks made of aluminium, which gives the instrument a very distinct sound.
  • Sustainability of Aluminium in Buildings  Sony VAIO VPCF11JFX/B Battery

Relatively pure aluminium is rarely encountered – only when corrosion resistance and/or workability is more important than strength or hardness. A thin layer of aluminium can be deposited onto a flat surface by physical vapour deposition or (very infrequently) chemical vapour deposition or other chemical means to form optical coatings and mirrors.Sony VAIO VPCF11M1E Battery

Aluminium compounds

Because aluminium is abundant and most of its derivative exhibit low toxicity, the compounds of aluminium enjoy wide and sometimes large-scale applications.

Alumina

Aluminium oxide (Al2O3) and the associated oxy-hydroxides and trihydroxides are produced or extracted from minerals on a large scale. Sony VAIO VPCF11M1E/H Battery

The great majority of this material is converted to metallic aluminium. About 10% of the production capacity is used for other applications. A major use is as an absorbent, for example alumina will remove water from hydrocarbons, to enable subsequent processes that are poisoned by moisture. Sony VAIO VPCF11MFX/B Battery

Aluminium oxides are common catalysts for industrial processes, e.g. the Claus processfor converting hydrogen sulfide to sulfur in refineries and for the alkylation of amines. Many industrial catalysts are"supported", meaning generally that an expensive catalyst (e.g., platinum) is dispersed over a high surface area material such as alumina. Sony VAIO VPCF11S1E Battery

Being a very hard material (Mohs hardness 9), alumina is widely used as an abrasive and the production of applications that exploit its inertness, e.g., in high pressure sodium lamps.

Sulfates

Several sulfates of aluminium find applications. Aluminium sulfate (Al2(SO4)3(H2O)18) is produced on the annual scale of several billions of kilograms. Sony VAIO VPCF11S1E/B Battery

About half of the production is consumed in water treatment. The next major application is in the manufacture of paper. It is also used as a mordant, in fire extinguisher, as a food additive, in fireproofing, and in leather tanning. Aluminium ammonium sulfate ([Al(NH4)](SO4)2)(H2O)12, also called ammonium alum, is used as a mordant and inleather tanning.Sony VAIO VPCF11Z1E Battery

Aluminium potassium sulfate ([Al(K)](SO4)2)(H2O)12 is used similarly. The consumption of both alums is declining.

Chlorides

Aluminium chloride (AlCl3) is used in petroleum refining and in the production of synthetic rubber and polymers.Sony VAIO VPCF11Z1E/BI Battery

Although it has a similar name, aluminium chlorohydrate has fewer and very different applications, e.g. as an hardening agent and an antiperspirant. It is an intermediate in the production of aluminium metal.

Niche compounds

Given the scale of aluminium compounds, a small scale application could still involve thousands of tons. Sony VAIO VPCF11ZHJ Battery

One of the many compounds used at this intermediate level include aluminium acetate, a salt used in solution as an astringent. Aluminium borate (Al2O3 B2O3) is used in the production of glass and ceramics. Aluminium fluorosilicate (Al2(SiF6)3) is used in the production of synthetic gemstones, glass and ceramic.Sony VAIO VPCF127HGBI Battery

Aluminium phosphate (AlPO4) is used in the manufacture: of glass and ceramic, pulp and paper products, cosmetics, paints and varnishes and in making dental cement. Aluminium hydroxide (Al(OH)3) is used as an antacid, as a mordant, inwater purification, in the manufacture of glass and ceramic and in the waterproofing of fabrics. Sony VAIO VPCF137HG/BI Battery

Lithium aluminium hydride is a powerful reducing agent used inorganic chemistry. Organoaluminiums are used as Lewis acids and cocatalysts. For example, methylaluminoxane is a cocatalyst for Ziegler-Natta olefin polymerizationto produce vinyl polymers such as polyethene.Sony VAIO VPC-P111KX/B Battery

Aluminium alloys in structural applications

Aluminium alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system (ANSI) or by names indicating their main alloying constituents (DIN and ISO).Sony VAIO VPC-P111KX/D Battery

The strength and durability of aluminium alloys vary widely, not only as a result of the components of the specific alloy, but also as a result of heat treatments and manufacturing processes. A lack of knowledge of these aspects has from time to time led to improperly designed structures and gained aluminium a bad reputation.Sony VAIO VPC-P111KX/G Battery

One important structural limitation of aluminium alloys is their fatigue strength. Unlike steels, aluminium alloys have no well-defined fatigue limit, meaning that fatigue failure eventually occurs, under even very small cyclic loadings. This implies that engineers must assess these loads and design for a fixed life rather than an infinite life.Sony VAIO VPC-P111KX/P Battery

Another important property of aluminium alloys is their sensitivity to heat. Workshop procedures involving heating are complicated by the fact that aluminium, unlike steel, melts without first glowing red. Forming operations where a blow torch is used therefore require some expertise, since no visual signs reveal how close the material is to melting.Sony VAIO VPC-P111KX/W Battery

Aluminium alloys, like all structural alloys, also are subject to internal stresses following heating operations such as welding and casting. The problem with aluminium alloys in this regard is their low melting point, which make them more susceptible to distortions from thermally induced stress relief. Sony VAIO VPC-P112KX/B Battery

Controlled stress relief can be done during manufacturing by heat-treating the parts in an oven, followed by gradual cooling—in effect annealing the stresses.

The low melting point of aluminium alloys has not precluded their use in rocketry; even for use in constructing combustion chambers where gases can reach 3500 K. Sony VAIO VPC-P112KX/D Battery

The Agena upper stage engine used a regeneratively cooled aluminium design for some parts of the nozzle, including the thermally critical throat region.

Another alloy of some value is aluminium bronze (CuAl5).Sony VAIO VPC-P112KX/G Battery

History

Ancient Greeks and Romans used aluminium salts as dyeing mordants and as astringents for dressing wounds; alum is still used as astyptic. In 1761, Guyton de Morveau suggested calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he at first termed alumium and later aluminum (see etymology section, below).Sony VAIO VPC-P112KX/P Battery

The metal was first produced in 1825 (in an impure form) by Danish physicist and chemist Hans Christian Ørsted. He reactedanhydrous aluminium chloride with potassium amalgam and yielded a lump of metal looking similar to tin. Sony VAIO VPC-P112KX/W Battery

Friedrich Wöhler was aware of these experiments and cited them, but after redoing the experiments of Ørsted he concluded that this metal was pure potassium. He conducted a similar experiment in 1827 by mixing anhydrous aluminium chloride with potassium and yielded aluminium.Sony VAIO VPCP113KX/B Battery

Wöhler is generally credited with isolating aluminium (Latin alumen, alum), but also Ørsted can be listed as its discoverer.Further, Pierre Berthier discovered aluminium in bauxite ore and successfully extracted it. Frenchman Henri Etienne Sainte-Claire Deville improved Wöhler's method in 1846, Sony VAIO VPC-P113KX/B Battery

and described his improvements in a book in 1859, chief among these being the substitution of sodium for the considerably more expensive potassium.[45] Deville likely also conceived the idea of the electrolysis of aluminium oxide dissolved in cryolite; Charles Martin Hall and Paul Héroult might have developed the more practical process after Deville.Sony VAIO VPCP113KX/D Battery

Before the Hall-Héroult process was developed in the late 1880s, aluminium was exceedingly difficult to extract from its variousores. This made pure aluminium more valuable than gold. Bars of aluminium were exhibited at the Exposition Universelle of 1855.Napoleon III, Emperor of France, is reputed to have given a banquet where the most honoured guests were given aluminium utensils, while the others made do with gold.Sony VAIO VPC-P113KX/D Battery

Aluminium was selected as the material to be used for the 100 ounce (2.8 kg) capstone of the Washington Monument in 1884, a time when one ounce (30 grams) cost the daily wage of a common worker on the project; The capstone, which was set in place on December 6, 1884, in an elaborate dedication ceremony, was the largest single piece of aluminium cast at the time, when aluminium was as expensive as silver.Sony VAIO VPCP113KX/G Battery

The Cowles companies supplied aluminium alloy in quantity in the United States and England using smelters like the furnace of Carl Wilhelm Siemens by 1886. Charles Martin Hall of Ohio in the U.S. and Paul Héroult of France independently developed the Hall-Héroult electrolytic process that made extracting aluminium from minerals cheaper and is now the principal method used worldwide. Sony VAIO VPC-P113KX/G Battery

Hall's process, in 1888 with the financial backing of Alfred E. Hunt, started the Pittsburgh Reduction Company today known as Alcoa. Héroult's process was in production by 1889 in Switzerland at Aluminium Industrie, now Alcan, and at British Aluminium, now Luxfer Group and Alcoa, by 1896 in Scotland.Sony VAIO VPCP113KX/P Battery

By 1895, the metal was being used as a building material as far away as Sydney, Australia in the dome of the Chief Secretary's Building.

Many navies have used an aluminium superstructure for their vessels; the 1975 fire aboard USS Belknap that gutted her aluminium superstructure, as well as observation of battle damage to British ships during the Falklands War, Sony VAIO VPC-P113KX/P Battery

led to many navies switching to all steel superstructures. The Arleigh Burke class was the first such U.S. ship, being constructed entirely of steel.

Aluminium wire was once widely used for domestic electrical wiring. Owing to corrosion-induced failures, a number of fires resulted. This discontinuation thus illustrates one failed application of the otherwise highly useful metal.Sony VAIO VPCP113KX/W Battery

In 2008, the price of aluminium peaked at $1.45/lb in July but dropped to $0.70/lb by December.

Etymology

Two variants of the metal's name are in current use, aluminium and aluminum (besides the obsolete alumium).Sony VAIO VPC-P113KX/W Battery

The International Union of Pure and Applied Chemistry(IUPAC) adopted aluminium as the standard international name for the element in 1990 but, three years later, recognized aluminum as an acceptable variant. Hence their periodic table includes both. Sony VAIO VPC-P114KX/B Battery

IUPAC prefers the use of aluminium in its internal publications, although nearly as many IUPAC publications use the spellingaluminum.

Most countries use the spelling aluminium. In the United States, the spelling aluminum predominates.The Canadian Oxford Dictionary prefers aluminum, whereas the Australian Macquarie Dictionary prefers aluminium. Sony VAIO VPC-P114KX/D Battery

In 1926, the American Chemical Society officially decided to use aluminum in its publications; American dictionaries typically label the spelling aluminium as a British variant.

The name aluminium derives from its status as a base of alum. It is borrowed from Old French; its ultimate source, alumen, in turn is a Latin word that literally means "bitter salt".Sony VAIO VPC-P114KX/G Battery

The earliest citation given in the Oxford English Dictionary for any word used as a name for this element is alumium, which British chemist and inventor Humphry Davyemployed in 1808 for the metal he was trying to isolate electrolytically from the mineral alumina. Sony VAIO VPC-P114KX/P Battery

The citation is from the journal Philosophical Transactions of the Royal Society of London: "Had I been so fortunate as to have obtained more certain evidences on this subject, and to have procured the metallic substances I was in search of, I should have proposed for them the names of silicium, alumium, zirconium, and glucium."Sony VAIO VPC-P114KX/W Battery

Davy settled on aluminum by the time he published his 1812 book Chemical Philosophy: "This substance appears to contain a peculiar metal, but as yet Aluminum has not been obtained in a perfectly free state, though alloys of it with other metalline substances have been procured sufficiently distinct to indicate the probable nature of alumina."Sony VAIO VPCP115JC Battery

But the same year, an anonymous contributor to the Quarterly Review, a British political-literary journal, in a review of Davy's book, objected toaluminum and proposed the

name aluminium, "for so we shall take the liberty of writing the word, in preference to aluminum, which has a less classical sound."Sony VAIO VPCP115JC/B Battery

The -ium suffix conformed to the precedent set in other newly discovered elements of the time: potassium, sodium, magnesium, calcium, and strontium (all of which Davy isolated himself). Nevertheless, -um spellings for elements were not unknown at the time, as for example platinum, known to Europeans since the 16th century,Sony VAIO VPCP115JC/D Battery

molybdenum, discovered in 1778, and tantalum, discovered in 1802. The -um suffix is consistent with the universal spelling alumina for the oxide, as lanthana is the oxide of lanthanum, and magnesia, ceria, and thoria are the oxides of magnesium, cerium, and thorium respectively.Sony VAIO VPCP115JC/G Battery

The spelling used throughout the 19th century by most U.S. chemists was aluminium, but common usage is less clear. The aluminumspelling is used in the Webster's Dictionary of 1828. In his advertising handbill for his new electrolytic method of producing the metal 1892, Charles Martin Hall used the -um spelling, Sony VAIO VPCP115JC/P Battery

despite his constant use of the -ium spelling in all the patents he filed between 1886 and 1903. It has consequently been suggested that the spelling reflects an easier to pronounce word with one fewer syllable, or that the spelling on the flier was a mistake. Hall's domination of production of the metal ensured that the spellingaluminum became the standard in North America; the Webster Unabridged Dictionary of 1913, though, continued to use the -ium version.Sony VAIO VPCP115JC/W Battery

Health concerns

Despite its natural abundance, aluminium has no known function in biology. It is remarkably nontoxic, aluminium sulfate having an LD50 of 6207 mg/kg (oral, mouse), which corresponds to 500 grams for a 80 kg person.Sony VAIO VPCP115KG Battery

Despite the extremely low acute toxicity, the health effects of aluminium are of interest in view of the widespread occurrence of the element in the environment and in commerce.

Some toxicity can be traced to deposition in bone and the central nervous system, which is particularly increased in patients with reduced renal function. Sony VAIO VPCP116KG Battery

Because aluminium competes with calcium for absorption, increased amounts of dietary aluminium may contribute to the reduced skeletal mineralization (osteopenia) observed in preterm infants and infants with growth retardation. In very high doses, aluminium can cause neurotoxicity, and is associated with altered function of the blood-brain barrier.Sony VAIO VPC-P116KX/B Battery

A small percentage of people are allergic to aluminium and experience contact dermatitis, digestive disorders, vomiting or other symptoms upon contact or ingestion of products containing aluminium, such as deodorants or antacids. In those without allergies, aluminium is not as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts.Sony VAIO VPC-P116KX/D Battery

Although the use of aluminium cookware has not been shown to lead to aluminium toxicity in general, excessive consumption of antacidscontaining aluminium compounds and excessive use of aluminium-containing antiperspirants provide more significant exposure levels. Sony VAIO VPC-P116KX/G Battery

Studies have shown that consumption of acidic foods or liquids with aluminium significantly increases aluminium absorption,and maltol has been shown to increase the accumulation of aluminium in nervous and osseus tissue. Furthermore, aluminium increases estrogen-related gene expression in human breast cancer cells cultured in the laboratory.Sony VAIO VPC-P116KX/P Battery

The estrogen-like effects of these salts have led to their classification as a metalloestrogen.

The effects of aluminium in antiperspirants has been examined over the course of decades with little evidence of skin irritation.Nonetheless, its occurrence inantiperspirants, dyes (such as aluminium lake), and food additives is controversial in some quarters.Sony VAIO VPC-P116KX/W Battery

Although there is little evidence that normal exposure to aluminium presents a risk to healthy adults, some studies point to risks associated with increased exposure to the metal. Aluminium in food may be absorbed more than aluminium from water. Sony VAIO VPCP118JC Battery

Some researchers have expressed concerns that the aluminium in antiperspirants may increase the risk of breast cancer, and aluminium has controversially been implicated as a factor in Alzheimer's disease. The Camelford water pollution incident involved a number of people consumingaluminium sulfate. Sony VAIO VPCP118JC/B Battery

Investigations of the long-term health effects are still ongoing, but elevated brain aluminium concentrations have been found in post-mortem examinations of victims, and further research to determine if there is a link with cerebral amyloid angiopathy has been commissioned.Sony VAIO VPCP118JC/P Battery

According to The Alzheimer's Society, the overwhelming medical and scientific opinion is that studies have not convincingly demonstrated a causal relationship between aluminium and Alzheimer's disease. Nevertheless, some studies, such as those on the PAQUID cohort, cite aluminium exposure as a risk factor forAlzheimer's disease. Sony VAIO VPCP118JC/W Battery

Some brain plaques have been found to contain increased levels of the metal. Research in this area has been inconclusive; aluminium accumulation may be a consequence of the disease rather than a causal agent. In any event, if there is any toxicity of aluminium, it must be via a very specific mechanism, since total human exposure to the element in the form of naturally occurring clay in soil and dust is enormously large over a lifetime.Sony VAIO VPC-P118KX/B Battery

Scientific consensus does not yet exist about whether aluminium exposure could directly increase the risk of Alzheimer's disease.

Effect on plants

Aluminium is primary among the factors that reduce plant growth on acid soils. Although it is generally harmless to plant growth in pH-neutral soils, the concentration in acid soils of toxic Al3+ cations increases and disturbs root growth and function.Sony VAIO VPC-P118KX/D Battery

Most acid soils are saturated with aluminium rather than hydrogen ions. The acidity of the soil is therefore a result of hydrolysis of aluminium compounds. This concept of "corrected lime potential" to define the degree of base saturation in soils became the basis for procedures now used in soil testing laboratories to determine the "lime requirement" of soils.Sony VAIO VPC-P118KX/G Battery

Wheat's adaptation to allow aluminium tolerance is such that the aluminium induces a release of organic compounds that bind to the harmful aluminium cations. Sorghumis believed to have the same tolerance mechanism. The first gene for aluminium tolerance has been identified in wheat. Sony VAIO VPC-P118KX/P Battery

It was shown that sorghum's aluminium tolerance is controlled by a single gene, as for wheat. This is not the case in all plants.


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