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Aluminum (IPA: /əˈluːmɪnəm/ or aluminium (IPA: /ˌaljʊˈmɪniəm, -əˈmɪniəm/), see the "Spelling" section below) is a silvery and ductile member of the poor metal group of chemical elements. In the periodic table it has the symbol Al and atomic number 13.

Aluminum is found primarily in bauxite ore and is remarkable for its resistance to corrosion (due to the phenomenon of passivation) and its light weight. The metal is used in many industries to manufacture a large variety of products and is very important to the world economy. Structural components made from aluminum and its alloys are vital to the aerospace industry and very important in other areas of transportation and building.

Properties Edit

Aluminum is a soft, lightweight metal with normally a dull silvery appearance caused by a thin layer of oxidation that forms quickly when the metal is exposed to air. Aluminum oxide has a higher melting point than pure aluminum. Aluminum is nontoxic (as the metal), nonmagnetic, and nonsparking. It has a tensile strength of about 49 megapascals (MPa) in a pure state and 400 MPa as an alloy. Aluminum is about one-third as dense as steel or copper; it is malleable, ductile, and easily machined and cast. It has excellent corrosion resistance and durability because of the protective oxide layer. Aluminum 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. It is the second-most malleable metal (after gold) and the sixth-most ductile. Aluminum is a good heat conductor.

Applications Edit

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

Pure aluminum has a low tensile strength, but readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon (e.g., duralumin). Today almost all materials that claim to be aluminum are actually an alloy thereof. Pure aluminum is encountered only when corrosion resistance is more important than strength or hardness.

When combined with thermo-mechanical processing aluminum alloys display a marked improvement in mechanical properties. Aluminum alloys form vital components of aircraft and rockets as a result of their high strength to weight ratio.

Aluminum is an excellent reflector (approximately 99%) of visible light and a good reflector (approximately 95%) of infrared. A thin layer of aluminum can be deposited onto a flat surface by chemical vapor deposition or chemical means to form optical coatings and mirrors. These coatings form an even thinner layer of protective aluminum oxide that does not deteriorate as silver coatings do. Nearly all modern mirrors are made using a thin coating of aluminum on the back surface of a sheet of float glass. Telescope mirrors are also made with aluminum, but are front coated to avoid internal reflections, refraction, and transparency losses. These first surface mirrors are more susceptible to damage than household back surface mirrors.

History Edit

The Chinese were using aluminum to make things as early as 300 AD. The ancient Greeks and Romans used aluminum 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 of 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 aluminum (Latin alumen, alum) in 1827 by mixing anhydrous aluminum 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, Luke Sperduto can also be listed as the discoverer of the metal.[1] Further, Pierre Berthier discovered aluminum in bauxite ore and successfully extracted it. [1] The Frenchman Henri Saint-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.

Aluminum was selected as the material to be used for the apex of the Washington Monument, at a time when one ounce cost twice the daily wages of a common worker in the project; aluminum was a semiprecious metal at that time.[2]

The American Charles Martin Hall of Oberlin, Ohio applied for a patent (400655) in 1886 for an electrolytic process to extract aluminum using the same technique that was independently being developed by the Frenchman Paul Héroult in Europe. The invention of the Hall-Heroult process|Hall-Héroult process in 1886 made extracting aluminum from minerals cheaper, and is now the principal method in common use throughout the world. The Hall-Heroult process cannot produce Super Purity Aluminum 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 aluminum 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 hope to compete with, namely the capability of producing enough aluminum to manufacture sixty thousand warplanes in four years.[3]

Aluminum separation Edit

Although aluminum is the most abundant metallic element in Earth's crust (believed to be 7.5% to 8.1%), it is very rare in its free form, occurring in oxygen-deficient environments such as volcanic mud, and it was once considered a precious metal more valuable than gold. Napoleon III of France had a set of aluminum plates reserved for his finest guests. Others had to make do with gold ones. Aluminum has been produced in commercial quantities for just over 100 years. Template:Facts

Recovery of the metal via recycling has become an important facet of the aluminum industry. Recycling involves melting the scrap, a process that uses only five percent of the energy needed to produce aluminum from ore.[4] Recycling was a low-profile activity until the late 1960s, when the growing use of aluminum beverage cans brought it to the public consciousness.

Aluminum is a reactive metal that is difficult to extract from ore, aluminum oxide (Al2O3). Direct reduction — with carbon, for example — is not economically viable since aluminum oxide has a melting point of about 2,000 °C. Therefore, it is extracted by electrolysis; that is, the aluminum oxide is dissolved in molten cryolite and then reduced to the pure metal. By this process, the operational temperature of the reduction cells is around 950 to 980 °C. Cryolite is found as a mineral in Greenland, but in industrial use it has been replaced by a synthetic substance. Cryolite is a mixture of aluminum, sodium, and calcium fluorides: (Na3AlF6). The aluminum oxide (a white powder) is obtained by refining bauxite in the Bayer process. (Previously, the Deville process was the predominant refining technology.)

The electrolytic process replaced the Wöhler process, which involved the reduction of anhydrous aluminum chloride with potassium. Both of the electrodes used in the electrolysis of aluminum oxide are carbon. Once the ore is in the molten state, its ions are free to move around. The reaction at the cathode — the negative terminal — is

Al3+ + 3 e- → Al

Here the aluminum ion is being reduced (electrons are added). The aluminum metal then sinks to the bottom and is tapped off.

At the positive electrode (anode), oxygen is formed:

2 O2- → O2 + 4 e-

This carbon anode is then oxidized by the oxygen, releasing carbon dioxide. The anodes in a reduction must therefore be replaced regularly, since they are consumed in the process:

O2 + C → CO2

Unlike the anodes, the cathodes are not oxidized because there is no oxygen present at the cathode. The carbon cathode is protected by the liquid aluminum inside the cells. Nevertheless, cathodes do erode, mainly due to electrochemical processes. After five to ten years, depending on the current used in the electrolysis, a cell has to be rebuilt because of cathode wear.

Aluminum 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. The world-wide average specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram of aluminum produced from alumina. (52 to 56 MJ/kg). The most modern smelters reach approximately 12.8 kW·h/kg (46.1 MJ/kg). Reduction line current for older technologies are typically 100 to 200 kA. State-of-the-art smelters operate with about 350 kA. Trials have been reported with 500 kA cells.

Electric power represents about 20% to 40% of the cost of producing aluminum, depending on the location of the smelter. Smelters tend to be situated where electric power is both plentiful and inexpensive, such as South Africa, the South Island of New Zealand, Australia, the People's Republic of China, the Middle East, Russia, Quebec and British Columbia in Canada, and Iceland. (Nearly all the power for aluminum smelting in Iceland comes from the heat vents upon which the island sits. Template:Fact)

In 2004, the People's Republic of China was the top world producer of aluminum. Suriname depends on aluminum exports for 70% of its export earnings.[5]

See also aluminum minerals.

Isotopes Edit

Aluminum has nine isotopes, whose mass numbers range from 23 to 30. Only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2 × 105 y) occur naturally, however 27Al has a natural abundance of 100%. 26Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminum isotopes have found practical application in dating marine 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.

Spelling Edit

Etymology/nomenclature historyEdit

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 have procured the metallic substances I was in search of, I should have proposed for them the names of silicium, alumium, zirconium, and glucium." [6]

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."[7] 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." [8]

The -ium suffix had the advantage of conforming to the precedent set in other newly discovered elements of the period: 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 16th century, molybdenum, discovered in 1778, and tantalum, discovered in 1802.

Americans adopted -ium for most of the 19th 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 on the flier was a simple 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 spellingEdit

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.[9][10] The Canadian Oxford Dictionary prefers aluminum.

In other English-speaking countries, the spellings (and associated pronunciations) aluminum and aluminium are both in common use in scientific and nonscientific 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[11]. IUPAC officially prefers the use of aluminium in its internal publications, although several IUPAC publications use the spelling aluminum.[12]

References Edit

  4. Benefits of Recycling, Ohio Department of Natural Resources link
  6. "alumium", Oxford English Dictionary. Ed. J.A. Simpson and E.S.C. Weiner. 2nd ed. Oxford: Clarendon Press, 1989. OED Online Oxford University Press. Accessed October 29, 2006. Citation is listed as "1808 SIR H. DAVY in Phil. Trans. XCVIII. 353". The ellipsis in the quotation is as it appears in the OED citation.
  7. "aluminum", ibid. Citation is listed as "1812 SIR H. DAVY Chem. Philos. I. 355"
  8. "aluminium", ibid. Citation is listed as "1812 Q. Rev. VIII. 72"
  9. Template:Greenwood&Earnshaw
  10. John Bremner, Words on Words: A Dictionary for Writers and Others Who Care about Words, page 22-23. ISBN 0-2310449-3-3
  11. IUPAC Periodic Table of the Elements
  12. IUPAC Web site publication search for 'aluminum'

External links Edit


  • US 400664Process of reducing aluminum from its fluoride salts by electrolysis – C. M. Hall ; (Tiff Viewer required)

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