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Aluminium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                13             magnesium ← aluminium → silicon
                 B
                ↑
                Al
                ↓
                Ga

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                    Name, Symbol, Number aluminium, Al, 13
                                               Chemical series poor metals
                                             Group, Period, Block 13, 3, p
                                                        Appearance silvery
                                          Atomic mass 26.9815386 (8) g/mol
                                     Electron configuration [Ne] 3s^2 3p^1
                                               Electrons per shell 2, 8, 3
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 2.70 g·cm^−3
                                   Liquid density at m.p. 2.375 g·cm^−3
                                                   Melting point 933.47  K
                                               (660.32 ° C, 1220.58 ° F)
                                                      Boiling point 2792 K
                                                    (2519 ° C, 4566 ° F)
                                         Heat of fusion 10.71 kJ·mol^−1
                                   Heat of vaporization 294.0 kJ·mol^−1
                         Heat capacity (25 °C) 24.200 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 1482 1632 1817 2054 2364 2790

                                                         Atomic properties
                                    Crystal structure face centered cubic,
                                                                 0.4032 nm
                                                        Oxidation states 3
                                                       ( amphoteric oxide)
                                    Electronegativity 1.61 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 577.5 kJ·mol^−1
                                                  2nd: 1816.7 kJ·mol^−1
                                                  3rd: 2744.8 kJ·mol^−1
                                                      Atomic radius 125 pm
                                              Atomic radius (calc.) 118 pm
                                                    Covalent radius 118 pm
                                                             Miscellaneous
                                            Magnetic ordering paramagnetic
                              Electrical resistivity (20 °C) 26.50 nΩ·m
                        Thermal conductivity (300 K) 237 W·m^−1·K^−1
                       Thermal expansion (25 °C) 23.1 µm·m^−1·K^−1
               Speed of sound (thin rod) ( r.t.) (rolled) 5000   m·s^−1
                                                    Young's modulus 70 GPa
                                                      Shear modulus 26 GPa
                                                       Bulk modulus 76 GPa
                                                        Poisson ratio 0.35
                                                        Mohs hardness 2.75
                                                  Vickers hardness 167 MPa
                                                  Brinell hardness 245 MPa
                                             CAS registry number 7429-90-5
                                                         Selected isotopes

                CAPTION: Main article: Isotopes of aluminium

                                 iso   NA   half-life  DM  DE ( MeV)  DP
                                ^26Al syn  7.17×10^5 y β^+ 1.17      ^26Mg
                                                       ε   -         ^26Mg
                                                       γ   1.8086    -
                                ^27Al 100% Al is stable with 14 neutrons

                                                                References

   Aluminium ( IPA: /ˌaljʊˈmɪniəm, -əˈmɪniəm/) or aluminium ( IPA:
   /əˈluːmɪnəm/, 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.

   Aluminium 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 aluminium and its alloys are vital to
   the aerospace industry and very important in other areas of
   transportation and building.

Properties

   A piece of aluminium metal about 15 centimetres long, with a U.S. cent
   included for scale.
   Enlarge
   A piece of aluminium metal about 15 centimetres long, with a U.S. cent
   included for scale.

   Aluminium 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. Aluminium oxide has a higher melting point
   than pure aluminium. Aluminium 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. Aluminium 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. 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. It is the second-most malleable metal (after
   gold) and the sixth-most ductile. Aluminium is a good heat conductor.
   Bohr Diagram.
   Enlarge
   Bohr Diagram.

Applications

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

   Pure aluminium 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
   aluminium are actually an alloy thereof. Pure aluminium is encountered
   only when corrosion resistance is more important than strength or
   hardness.

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

   Aluminium is 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
   vapor deposition or chemical means to form optical coatings and
   mirrors. These coatings form an even thinner layer of protective
   aluminium oxide that does not deteriorate as silver coatings do. Nearly
   all modern mirrors are made using a thin coating of aluminium on the
   back surface of a sheet of float glass. Telescope mirrors are also made
   with aluminium, 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.

   Some of the many uses for aluminium are in:
     * Transportation (automobiles, aircraft, trucks, railroad 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.)
     * Consumer durable goods (appliances, cooking utensils, etc.)
     * Electrical transmission lines (aluminium components and wires are
       less dense than those made of copper and are lower in price, but
       also present higher electrical resistance. Many localities prohibit
       the use of aluminium in residential wiring practices because of its
       higher resistance and thermal expansion value.)
     * Machinery
     * MKM steel and Alnico magnets, although non-magnetic itself
     * Super purity aluminium (SPA, 99.980% to 99.999% Al), used in
       electronics and CDs.
     * Powdered aluminium, a commonly used silvering agent in paint.
       Aluminium flakes may also be included in undercoat paints,
       particularly wood primer — on drying, the flakes overlap to produce
       a water resistant barrier.
     * Anodised aluminium is more stable to further oxidation, and is used
       in various fields of construction, as well as heat sinking.
     * Most electronic appliances that require cooling of their internal
       devices (like transistors, CPUs - semiconductors in general) have
       heat sinks that are made of aluminium due to its ease of
       manufacture and good heat conductivity. Copper heat sinks are
       smaller although more expensive and harder to manufacture.
     * It is used in the blades of weapons (such as swords) designed for
       stage combat

     * Aluminium oxide, 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 oxidises very energetically and as a result has found use
       in solid rocket fuels, thermite, and other pyrotechnic
       compositions.

   Aluminium is also a superconductor at low temperatures, with a
   superconducting critical temperature of 1.2 kelvins.

Engineering use

   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). Selecting the right alloy for a given application entails
   considerations of strength, ductility, formability, weldability and
   corrosion resistance to name a few. A brief historical overview of
   alloys and manufacturing technologies is given in Ref. Aluminium is
   used extensively in modern aircraft due to its light weight.

   Improper use of aluminium can result in problems, particularly in
   contrast to iron or steel, which appear "better behaved" to the
   intuitive designer, mechanic, or technician. The reduction by two
   thirds of the weight of an aluminium part compared to a similarly sized
   iron or steel part seems enormously attractive, but it should be noted
   that it is accompanied by a reduction by two thirds in the stiffness of
   the part. Therefore, although direct replacement of an iron or steel
   part with a duplicate made from aluminium may still give acceptable
   strength to withstand peak loads, the increased flexibility will cause
   three times more deflection in the part.

   Where failure is not an issue but excessive flex is undesirable due to
   requirements for precision of location or efficiency of transmission of
   power, simple replacement of steel tubing with similarly sized
   aluminium tubing will result in a degree of flex which is undesirable;
   for instance, the increased flex under operating loads caused by
   replacing steel bicycle frame tubing with aluminium tubing of identical
   dimensions will cause misalignment of the power-train as well as
   absorbing the operating force. To increase the rigidity by increasing
   the thickness of the walls of the tubing increases the weight
   proportionately, so that the advantages of lighter weight are lost as
   the rigidity is restored.

   Aluminium can best be used by redesigning the part to suit its
   characteristics; for instance making a bicycle of aluminium tubing
   which has an oversize diameter rather than thicker walls. In this way,
   rigidity can be restored or even enhanced without increasing weight.
   The limit to this process is the increase in susceptibility to what is
   termed " buckling" failure, where the deviation of the force from any
   direction other than directly along the axis of the tubing causes
   folding of the walls of the tubing.

   The latest models of the Corvette automobile, among others, are a good
   example of redesigning parts to make best use of aluminium's
   advantages. The aluminium chassis members and suspension parts of these
   cars have large overall dimensions for stiffness but are lightened by
   reducing cross-sectional area and removing unneeded metal; as a result,
   they are not only equally or more durable and stiff as the usual steel
   parts, but they possess an airy gracefulness which most people find
   attractive. Similarly, aluminium bicycle frames can be optimally
   designed so as to provide rigidity where required, yet have flexibility
   in terms of absorbing the shock of bumps from the road and not
   transmitting them to the rider.

   The strength and durability of aluminium varies widely, not only as a
   result of the components of the specific alloy, but also as a result of
   the particular manufacturing process; for this reason, it has from time
   to time gained a bad reputation. For instance, a high frequency of
   failure in many early aluminium bicycle frames in the 1970s resulted in
   just such a poor reputation; with a moment's reflection, however, the
   widespread use of aluminium components in the aerospace and automotive
   high performance industries, where huge stresses are undergone with
   vanishingly small failure rates, proves that properly built aluminium
   bicycle components should not be unusually unreliable, and this has
   subsequently proved to be the case.

   Similarly, use of aluminium in automotive applications, particularly in
   engine parts which must survive in difficult conditions, has benefited
   from development over time. An Audi engineer commented about the V12
   engine, producing over 500 horsepower (370 kW), of an Auto Union race
   car of the 1930s which was recently restored by the Audi factory, that
   the aluminium alloy of which the engine was constructed would today be
   used only for lawn furniture and the like. Even the aluminium cylinder
   heads and crankcase of the Corvair, built as recently as the 1960s,
   earned a reputation for failure and stripping of threads in holes, even
   as large as spark plug holes, which is not seen in current aluminium
   cylinder heads.

Heat sensitivity

   Often, the metal's sensitivity to heat must also be considered. Even a
   relatively routine workshop procedure involving heating is complicated
   by the fact that aluminium, unlike steel, will melt without first
   turning red. Forming operations where a blow torch is used therefore
   requires some expertise since no visual signs reveal how close the
   material is to melting.

   Aluminium also is subject to internal stresses and strains when it is
   overheated; the tendency of the metal to creep under these stresses
   tends to result in delayed distortions. For instance, the warping or
   cracking of overheated aluminium automobile cylinder heads is commonly
   observed, sometimes years later, as is the tendency of welded aluminium
   bicycle frames to gradually twist out of alignment from the stresses of
   the welding process. Thus, aerospace uses of aluminium avoid heat
   altogether by joining parts with adhesives or mechanical fasteners.
   These adhesive junctures were used for some bicycle frames in the 1970s
   — with unfortunate results when the aluminium tubing corroded slightly,
   loosening the adhesive and collapsing the frame.

   Stresses in overheated aluminium can be relieved by heat-treating the
   parts in an oven and gradually cooling it — in effect annealing the
   stresses. Yet these parts can still become distorted, so that
   heat-treating of welded bicycle frames, for instance, can result in a
   significant fraction becoming misaligned. If the misalignment is not
   too severe, the cooled parts can be bent into alignment; of course, if
   the frame is properly designed for rigidity (see above), that bending
   will require enormous force.

   Aluminium's intolerance to high temperatures has not precluded its use
   in rocketry; even for use for constructing combustion chambers where
   gases can reach 3500K. The Agena upper stage engine used a
   regeneratively cooled aluminium design for some parts of the nozzle,
   including the thermally critical throat region; in fact the extremely
   high thermal conductivity of aluminium prevented the throat from
   reaching the melting point even under massive heat flux, and good
   reliability and light weight resulted.

Household wiring

   Because of its high conductivity and relatively low price compared to
   copper in the 1960s, aluminium was introduced at that time for
   household electrical wiring in the United States even though many
   fixtures had not been designed to accept aluminium wire. But the new
   use brought some problems:
     * The greater coefficient of thermal expansion of aluminium causes
       the wire to expand and contract relative to the dissimilar metal
       screw connection, eventually loosening the connection.

     * Pure aluminium has a tendency to "creep" under steady sustained
       pressure (to a greater degree as the temperature rises), again
       loosening the connection.

     * Galvanic corrosion from the dissimilar metals increases the
       electrical resistance of the connection.

   All of this resulted in overheated connections, and fires broke out.
   Builders then became wary of using the wire, and many jurisdictions
   outlawed its use in very small sizes in new construction. Yet newer
   fixtures eventually were introduced with connections designed to avoid
   loosening and overheating. At first they were marked "Al/Cu", but they
   now bear a "CO/ALR" coding. Another way to forestall the heating
   problem is to crimp the aluminium wire to a short " pigtail" of copper
   wire. A properly done high-pressure crimp by the proper tool is tight
   enough to eliminate any thermal expansion of the aluminium and to
   exclude any atmospheric oxygen, thus preventing corrosion between the
   dissimilar metals. Today, new alloys are used for aluminium wiring in
   combination with aluminium terminations. Connections made with these
   products are as safe as those made with copper.

          See also: Aluminium wire

History

   The Chinese were using aluminium to make things as early as 300 AD. The
   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 aluminium (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 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.
   The statue known as Eros in Piccadilly Circus London, was made in 1893
   and is one of the first statues to be cast in aluminium.
   Enlarge
   The statue known as Eros in Piccadilly Circus London, was made in 1893
   and is one of the first statues to be cast in aluminium.

   Aluminium 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; aluminium was a semiprecious
   metal at that time.

   The American Charles Martin Hall of Oberlin, Ohio applied for a patent
   (400655) 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 Aluminium 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 hope to compete with, namely the capability of
   producing enough aluminium to manufacture sixty thousand warplanes in
   four years.

Aluminium separation

   Although aluminium 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 aluminium plates reserved for his finest
   guests. Others had to make do with gold ones. Aluminium has been
   produced in commercial quantities for just over 100 years. ^[ citations
   needed]

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

   Aluminium is a reactive metal that is difficult to extract from ore,
   aluminium oxide (Al[2]O[3]). Direct reduction — with carbon, for
   example — is not economically viable since aluminium oxide has a
   melting point of about 2,000 °C. Therefore, it is extracted by
   electrolysis; that is, the aluminium 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
   aluminium, sodium, and calcium fluorides: (Na[3]AlF[6]). The aluminium
   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 aluminium chloride with potassium. Both of
   the electrodes used in the electrolysis of aluminium 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

          Al^3+ + 3 e^- → Al

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

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

          2 O^2- → O[2] + 4 e^-

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

          O[2] + C → CO[2]

   Unlike the anodes, the cathodes are not oxidised because there is no
   oxygen present at the cathode. The carbon cathode is protected by the
   liquid aluminium 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.

   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. The world-wide average specific
   energy consumption is approximately 15±0.5 kilowatt-hours per kilogram
   of aluminium 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
   aluminium, 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 aluminium
   smelting in Iceland comes from the heat vents upon which the island
   sits. )

   In 2004, the People's Republic of China was the top world producer of
   aluminium.

Isotopes

   Aluminium has nine isotopes, whose mass numbers range from 23 to 30.
   Only ^27Al ( stable isotope) and ^26Al ( radioactive isotope, t[1/2] =
   7.2 × 10^5 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. Aluminium 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 10^5 to 10^6 year time scales.

   Cosmogenic ^26Al was first applied in studies of the Moon and
   meteorites. Meteorite fragments, after departure from their parent
   bodies, are exposed to intense cosmic-ray bombardment during their
   travel through space, causing substantial ^26Al production. After
   falling to Earth, atmospheric shielding protects the meteorite
   fragments from further ^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. Possibly, the energy released by the decay of
   ^26Al was responsible for the remelting and differentiation of some
   asteroids after their formation 4.6 billion years ago.

Clusters

   In the journal Science of 14 January 2005 it was reported that clusters
   of 13 aluminium atoms (Al[13]) had been made to behave like an iodine
   atom; and, 14 aluminium atoms (Al[14]) behaved like an alkaline earth
   atom. The researchers also bound 12 iodine atoms to an Al[13] cluster
   to form a new class of polyiodide. This discovery is reported to give
   rise to the possibility of a new characterisation of the periodic
   table: superatoms. The research teams were led by Shiv N. Khanna (
   Virginia Commonwealth University) and A. Welford Castleman Jr ( Penn
   State University).

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 — 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 Rolaids, 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. 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 Fe[2]O[3] to form Fe and Al[2]O[3].
   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.

Spelling

Etymology/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 aluminium, which, as other sources note,
   matches its Latin root. He wrote in the journal Chemical Philosophy:
   "As yet Aluminium 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 aluminium and proposed
   the name aluminium, "for so we shall take the liberty of writing the
   word, in preference to aluminium, 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 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 aluminium 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
   aluminium 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 aluminium predominates. The Canadian Oxford Dictionary
   prefers aluminium.

   In other English-speaking countries, the spellings (and associated
   pronunciations) aluminium 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 aluminium 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
   aluminium.

Chemistry

Oxidation state one

     * AlH is produced when aluminium is heated at 1500°C in an atmosphere
       of hydrogen.
     * Al[2]O is made by heating the normal oxide, Al[2]O[3], with silicon
       at 1800°C in a vacuum.
     * Al[2]S can be made by heating Al[2]S[3] with aluminium shavings at
       1300°C in a vacuum. It quickly disproportionates to the starting
       materials. The selenide is made in a parallel manner.
     * AlF, AlCl and AlBr exist in the gaseous phase when the tri-halide
       is heated with aluminium.

Oxidation state two

     * Aluminium monoxide, AlO, is present when aluminium powder burns in
       oxygen.

Oxidation state three

     * Fajans rules show that the simple trivalent cation Al^3+ is not
       expected to be found in anhydrous salts or binary compounds such as
       Al[2]O[3]. The hydroxide is a weak base and aluminium salts of weak
       acids, such as carbonate, can't be prepared. The salts of strong
       acids, such as nitrate, are stable and soluble in water, forming
       hydrates with at least six molecules of water of crystallization.
     * Aluminium hydride, (AlH[3])[n], can be produced from
       trimethylaluminium and an excess of hydrogen. It burns explosively
       in air. It can also be prepared by the action of aluminium chloride
       on lithium hydride in ether solution, but cannot be isolated free
       from the solvent.
     * Aluminium carbide, Al[4]C[3] is made by heating a mixture of the
       elements above 1000°C. The pale yellow crystals have a complex
       lattice structure, and react with water or dilute acids to give
       methane. The acetylide, Al[2](C[2])[3], is made by passing
       acetylene over heated aluminium.
     * Aluminium nitride, AlN, can be made from the elements at 800°C. It
       is hydrolysed by water to form ammonia and aluminium hydroxide.
     * Aluminium phosphide, AlP, is made similarly, and hydrolyses to give
       phosphine.
     * Aluminium oxide, Al[2]O[3], occurs naturally as corundum, and can
       be made by burning aluminium in oxygen or by heating the hydroxide,
       nitrate or sulfate. As a gemstone, its hardness is only exceeded by
       diamond, boron nitride, and carborundum. It is almost insoluble in
       water.
     * Aluminium hydroxide may be prepared as a gelatinous precipitate by
       adding ammonia to an aqueous solution of an aluminium salt. It is
       amphoteric, being both a very weak acid, and forming aluminates
       with alkalis. It exists in various crystalline forms.
     * Aluminium sulfide, Al[2]S[3], may be prepared by passing hydrogen
       sulfide over aluminium powder. It is polymorphic.
     * Aluminium iodide, (AlI[3])[2], is a dimer with applications in
       organic synthesis.
     * Aluminium fluoride, AlF[3], is made by treating the hydroxide with
       HF, or can be made from the elements. It consists of a giant
       molecule which sublimes without melting at 1291°C. It is very
       inert. The other trihalides are dimeric, having a bridge-like
       structure.
     * Aluminium fluoride/water complexes: When aluminium and fluoride are
       together in aqueous solution, they readily form complex ions such
       as AlF(H[2]O)[5]^+2, AlF[3](H[2]O)[3]^0, AlF[6]^-3. Of these,
       AlF[6]^-3 is the most stable. This is explained by the fact that
       aluminium and fluoride, which are both very compact ions, fit
       together just right to form the octahedral aluminium hexafluoride
       complex. When aluminium and fluoride are together in water in a 1:6
       molar ratio, AlF[6]^-3 is the most common form, even in rather low
       concentrations.
     * Organo-metallic compounds of empirical formula AlR[3] exist and, if
       not also giant molecules, are at least dimers or trimers. They have
       some uses in organic synthesis, for instance trimethylaluminium.
     * Alumino-hydrides of the most electropositive elements are known,
       the most useful being lithium aluminium hydride, Li[AlH[4]]. It
       decomposes into lithium hydride, aluminium and hydrogen when
       heated, and is hydrolysed by water. It has many uses in organic
       chemistry, particularly as a reducing agent. The aluminohalides
       have a similar structure.

   This Heatsink is made from anodized aluminium.
   Enlarge
   This Heatsink is made from anodized aluminium.

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