Aluminium

Aluminium (IPA: ) or aluminum (IPA:, see the "spelling" section below) is a silvery and ductile member of the poor metal group of chemical elements. It has the symbol Al; its atomic number is 13.

Aluminium is found primarily in bauxite ore and is remarkable for its ability to resist corrosion (due to the phenomenon of passivation) and its light weight. Structural components made from aluminium and its alloys are vital to the aerospace industry and very important in other areas of transportation and building.

Properties
Aluminium is a soft, lightweight metal with appearance ranging from silvery to dull gray, depending on the surface roughness. Aluminium is nontoxic, nonmagnetic, and nonsparking. The yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel. It is ductile, and easily machined, cast, and extruded.

Corrosion resistance is excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper.

Aluminium atoms are arranged in an FCC structure. Aluminium has a high stacking-fault energy of approximately 200 mJ/m².

Aluminium is one of the few metals which retain full silvery reflectance in finely powdered form, making it an important component of silver paints. Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3000–10000 nm (far IR) regions, while in the 400–700 nm visible range it is slightly outdone by silver and in the 700–3000 (near IR) by silver, gold, and copper.

Aluminium is a good thermal and electrical conductor, by weight better than copper. Aluminium is capable of being a superconductor, with a superconducting critical temperature of 1.2 Kelvin.

General use
Whether measured in terms of quantity or value, the global use of aluminium exceeds that of any other metal except iron, and it is important in virtually all segments of the world economy.

Relatively pure aluminium is encountered only when corrosion resistance and/or workability is more important than strength or hardness. Pure aluminium serves as an excellent reflector (approximately 99%) of visible light and a good reflector (approximately 95%) of infrared. A thin layer of aluminium can be deposited onto a flat surface by chemical vapour deposition or chemical means to form optical coatings and mirrors.

Pure aluminium has a low tensile strength, but when combined with thermo-mechanical processing, aluminium alloys display a marked improvement in mechanical properties, especially when tempered. Aluminium alloys form vital components of aircraft and rockets as a result of their high strength-to-weight ratio. Aluminium readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon (e.g., duralumin). Today, almost all bulk metal materials that are referred to loosely as "aluminium," are actually alloys. For example, the common aluminium foils are alloys of 92% to 99% aluminium.

Some of the many uses for aluminium metal are in:
 * Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles etc.)
 * Packaging (cans, foil, etc.)
 * Water treatment
 * Treatment against fish parasites such as Gyrodactylus salaris.
 * Construction (windows, doors, siding, building wire, etc.)
 * Cooking utensils
 * Electrical transmission lines for power distribution
 * 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.
 * Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.
 * In the blades of prop swords and knives used in stage combat.

Aluminium compounds

 * Aluminium ammonium sulfate ([Al(NH4)](SO4)2), ammonium alum is used as a mordant, in water purification and sewage treatment, in paper production, as a food additive, and in leather tanning.


 * Aluminium acetate is a salt used in solution as an astringent.


 * Aluminium borate (Al2O3 B2O3) is used in the production of glass and ceramic.


 * Aluminium borohydride (Al(BH4)3) is used as an additive to jet fuel.


 * Aluminium chloride (AlCl3) is used: in paint manufacturing, in antiperspirants, in petroleum refining and in the production of synthetic rubber.


 * Aluminium chlorohydride is used as an antiperspirant and in the treatment of hyperhidrosis.


 * Aluminium fluorosilicate (Al2(SiF6)3) is used in the production of synthetic gemstones, glass and ceramic.


 * Aluminium hydroxide (Al(OH)3) is used: as an antacid, as a mordant, in water purification, in the manufacture of glass and ceramic and in the waterproofing of fabrics.


 * Aluminium oxide (Al2O3), alumina, is found naturally as corundum (rubies and sapphires), emery, and is used in glass making. Synthetic ruby and sapphire are used in lasers for the production of coherent light.


 * 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 sulfate (Al2(SO4)3) is used: in the manufacture of paper, as a mordant, in a fire extinguisher, in water purification and sewage treatment, as a food additive, in fireproofing, and in leather tanning.


 * In many vaccines, certain aluminium salts serve as an immune adjuvant (immune response booster) to allow the protein in the vaccine to achieve sufficient potency as an immune stimulant.

History
Ancient Greeks and Romans used aluminium salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a styptic. 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 named alumium and later aluminum (see Spelling section, below).

Friedrich Wöhler is generally credited with isolating aluminium (Latin alumen, alum) in 1827 by mixing anhydrous aluminium chloride with potassium. The metal, however, had indeed been produced for the first time two years earlier — but in an impure form — by the Danish physicist and chemist Hans Christian Ørsted. Therefore, Ørsted can also be listed as the discoverer of the metal. Further, Pierre Berthier discovered aluminium in bauxite ore and successfully extracted it. The Frenchman Henri Etienne Sainte-Claire Deville improved Wöhler's method in 1846 and described his improvements in a book in 1859, chief among these being the substitution of sodium for the considerably more expensive potassium.

(Note: The title of Deville's book is "De l'aluminium, ses propriétés, sa fabrication" (Paris, 1859). It was quite likely that Deville also thought of the idea of the electrolysis of aluminium oxide dissolved in cryolite. However, Charles Martin Hall and Paul Heroult might have developed the more practical process after Deville.)

Aluminium was selected as the material to be used for the apex of the Washington Monument in 1884, a time when one ounce (30 grams) cost the daily wage of a common worker on the project; aluminium was about the same value as silver.

The American Charles Martin Hall of Oberlin, Ohio applied for a patent in 1886 for an electrolytic process to extract aluminium using the same technique that was independently being developed by the Frenchman Paul Héroult in Europe. The invention of the Hall-Héroult process in 1886 made extracting aluminium from minerals cheaper, and is now the principal method in common use throughout the world. The Hall-Heroult process cannot produce Super Purity Aluminium directly. Upon approval of his patent in 1889, Hall, with the financial backing of Alfred E. Hunt of Pittsburgh, PA, started the Pittsburgh Reduction Company, renamed to Aluminum Company of America in 1907, later shortened to Alcoa. Germany became the world leader in aluminium production soon after Adolf Hitler's rise to power. By 1942, however, new hydroelectric power projects such as the Grand Coulee Dam gave the United States something Nazi Germany could not compete with, provided them with sufficient generating capacity to produce enough aluminium to manufacture sixty thousand warplanes in four years.

Precautions
Aluminium is a neurotoxin that alters the function of the blood-brain barrier. It is one of the few abundant elements that appears to have no beneficial function to living cells. A small percent of people are allergic to it &mdash; they experience contact dermatitis from any form of it: an itchy rash from using styptic or antiperspirant products, digestive disorders and inability to absorb nutrients from eating food cooked in aluminium pans, and vomiting and other symptoms of poisoning from ingesting such products as Amphojel, and Maalox (antacids). In other people, aluminium is not considered as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts. The use of aluminium cookware, popular because of its corrosion resistance and good heat conduction, has not been shown to lead to aluminium toxicity in general. Excessive consumption of antacids containing aluminium compounds and excessive use of aluminium-containing antiperspirants are more likely causes of toxicity. In research published in the Journal of Applied Toxicology, Dr. Philippa D. Darby of the University of Reading has shown that aluminium salts increase estrogen-related gene expression in human breast cancer cells grown in the laboratory. These salts' estrogen-like effects have lead to their classification as a metalloestrogen.

It has been suggested that aluminium is a cause of Alzheimer's disease, as some brain plaques have been found to contain the metal. Research in this area has been inconclusive; aluminium accumulation may be a consequence of the Alzheimer's damage, not the cause. 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.

Mercury applied to the surface of an aluminium alloy can damage the protective oxide surface film by forming amalgam. This may cause further corrosion and weakening of the structure. For this reason, mercury thermometers are not allowed on many airliners, as aluminium is used in many aircraft structures.

Powdered aluminium can react with Fe2O3 to form Fe and Al2O3. This mixture is known as thermite, which burns with a high energy output. Thermite can be produced inadvertently during grinding operations, but the high ignition temperature makes incidents unlikely in most workshop environments.

Etymology and nomenclature history
The earliest citation given in the Oxford English Dictionary for any word used as a name for this element is alumium, which Humphry Davy employed in 1808 for the metal he was trying to isolate electrolytically from the mineral alumina. The citation is from his journal Philosophical Transactions: "Had I been so fortunate as..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."

By 1812, Davy had settled on aluminum, which, as other sources note,  matches its Latin root. He wrote in the journal Chemical Philosophy: "As yet Aluminum has not been obtained in a perfectly free state." But the same year, an anonymous contributor to the Quarterly Review, a British political-literary journal, objected to aluminum 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."

The -ium suffix had the advantage of conforming to the precedent set in other newly discovered elements of the time: potassium, sodium, magnesium, calcium, and strontium (all of which Davy had isolated himself). Nevertheless, -um spellings for elements were not unknown at the time, as for example platinum, known to Europeans since the sixteenth century, molybdenum, discovered in 1778, and tantalum, discovered in 1802.

Americans adopted -ium for most of the nineteenth century, with aluminium appearing in Webster's Dictionary of 1828. In 1892, however, Charles Martin Hall used the -um spelling in an advertising handbill for his new electrolytic method of producing the metal, 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 spelling mistake. Hall's domination of production of the metal ensured that the spelling aluminum became the standard in North America; the Webster Unabridged Dictionary of 1913, though, continued to use the -ium version.

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.

Present-day spelling
In the UK and other countries using British spelling, only aluminium is used. In the United States, the spelling aluminium is largely unknown, and the spelling aluminum predominates. The Canadian Oxford Dictionary prefers aluminum, whereas the Australian Macquarie Dictionary prefers aluminium.

In other English-speaking countries, the spellings (and associated pronunciations) aluminium and aluminum are both in common use in scientific and non-scientific contexts. The spelling in virtually all other languages is analogous to the -ium ending.

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, but places aluminium first. IUPAC officially prefers the use of aluminium in its internal publications, although several IUPAC publications use the spelling aluminum.