The Online Encyclopedia and Dictionary







Name, Symbol, Number aluminium, Al, 13
Chemical series poor metals
Group, Period, Block 13 (IIIA), 3, p
Density, Hardness 2700 kg/m3, 2.75
Appearance silvery
Atomic properties
Atomic weight 26.981538 amu
Atomic radius (calc.) 125 pm (118 pm)
Covalent radius 118 pm
van der Waals radius no data
Electron configuration [Ne]3s2 3p1
e- 's per energy level 2, 8, 3
Oxidation states (Oxide) 3 (amphoteric)
Crystal structure cubic face centered
Physical properties
State of matter solid (paramagnetic)
Melting point 933.47 K (660.3 ºC / 1220.58 °F)
Boiling point 2792 K (2518 ºC / 4566 °F)
Molar volume 10.00 ×10-6 m3/mol
Heat of vaporization 293.4 kJ/mol
Heat of fusion 10.79 kJ/mol
Vapor pressure 2.42 E-06 Pa at __ K
Speed of sound 5100 m/s at 933 K
Electronegativity 1.61 (Pauling scale)
Specific heat capacity 900 J/(kg*K)
Electrical conductivity 37.7 106/(m·ohm)
Thermal conductivity 237 W/(m*K)
1st ionization potential 577.5 kJ/mol
2nd ionization potential 1816.7 kJ/mol
3rd ionization potential 2744.8 kJ/mol
4th ionization potential 11577 kJ/mol
5th ionization potential 14842 kJ/mol
6th ionization potential 18379 kJ/mol
7th ionization potential 23326 kJ/mol
8th ionization potential 27465 kJ/mol
9th ionization potential 31853 kJ/mol
10th ionization potential 38473 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP
26Al {syn.} 717 E3 y ε 4.004 26Mg
27Al 100% Al is stable with 14 neutrons
SI units & STP are used except where noted.

Aluminium (or aluminum in North American English; see spelling below) is the chemical element in the periodic table with the symbol Al and atomic number 13. A silvery and ductile member of the poor metal group of elements, aluminium is found primarily as the ore bauxite and is remarkable for its resistance to oxidation (due to the phenomenon of passivation), its strength, and its light weight. Aluminium is used in many industries to make millions of different products and is very important to the world economy. Structural components made from aluminium are vital to the aerospace industry and very important in other areas of transportation and building in which light weight, durability, and strength are needed.


Notable characteristics

Aluminium is a soft and lightweight metal with a dull silver-gray appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. Aluminium is about one-third as dense as steel or copper; is malleable, ductile, and easily machined and cast; and has excellent corrosion resistance and durability due to the protective oxide layer. It is also nonmagnetic and nonsparking and is the second most malleable metal (behind gold) and the sixth most ductile.


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. When combined with thermo-mechanical processing these aluminium alloys display a marked increase in mechanical properties.

Aluminium alloys form vital components of aircraft and rockets as a result of their high strength to weight ratio. When aluminium is evaporated in a vacuum it forms a coating that reflects both visible light and radiant heat. These coatings form a thin layer of protective aluminium oxide that does not deteriorate as silver coatings do. In particular, nearly all modern mirrors are made using a thin reflective coating of aluminium on the back surface of a sheet of float glass. Telescope mirrors are also coated with a thin layer of aluminium, but are front coated to avoid internal reflections even though this makes the surface more susceptible to damage.

Some of the many uses for aluminium are in:

  • Transportation (automobiles, airplanes, trucks, railroad cars, marine vessels, etc.)
  • Packaging (cans, foil, etc.)
  • Water treatment
  • Construction (windows, doors, siding, etc.; however it has fallen out of favor for end-user wiring[1])
  • Consumer durable goods (appliances, cooking utensils, etc.)
  • Electrical transmission lines (although its electrical conductivity is only 60% that of copper, it's lighter in weight and lower in price[2])
  • Machinery.
  • Although non-magnetic itself, aluminium is used in MKM steel and Alnico magnets.
  • Super Purity Aluminium (SPA, 99.980%-99.999% Al) is used in electronics and CDs.
  • Powdered aluminium is commonly used for silvering 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.
  • Anodized aluminium is more stable to further oxidation, and is used in various fields of construction.
  • Most modern computer CPU Heat sinks are made of aluminium due to its ease of manufacture and good heat conductivity. Copper is superior although more expensive and harder to manufacture.

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

Aluminium oxidizes very energetically and as a result has found use in solid rocket fuels and thermite.


The oldest suspected (although unprovable) reference to aluminium is in Pliny the Elder's Naturalis Historia:

One day a goldsmith in Rome was allowed to show the Emperor Tiberius a dinner plate of a new metal. The plate was very light, and almost as bright as silver. The goldsmith told the Emperor that he had made the metal from plain clay. He also assured the Emperor that only he, himself, and the Gods knew how to produce this metal from clay. The Emperor became very interested, and as a financial expert he was also a little concerned. The Emperor felt immediately, however, that all his treasures of gold and silver would fall in value if people started to produce this bright metal of clay. Therefore, instead of giving the goldsmith the regard expected, he ordered him to be beheaded. Notes - Source

Ancient Greeks and Romans used salts of this metal as dyeing mordants and as astringents to bind wounds, and alum is still used as a styptic . In 1761 Guyton de Morveau proposed calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he named (see Spelling below for more information on the name).

Friedrich Wöhler is generally credited with isolating aluminium (Latin alumen, alum) in 1827. However, this metal was produced for the first time in impure form two years earlier by Danish physicist and chemist Hans Christian Ørsted.

Aluminium was chosen for the apex point of the Washington Monument at a time when one ounce cost twice the wages of a laborer's full day work. Source

Charles Martin Hall received the patent (400655) in 1886, on electrolytic process to extract aluminium. Henri Saint-Claire Deville (France) improved Wöhler's method (1846) and presented these in a book in 1859 with two improvements to the process as to substitute potassium to sodium and double instead of simple chlorure. The invention of the Hall-Héroult process in 1886 made extracting aluminium from minerals inexpensive and is now in common use throughout the world.

The statue known as Eros in London, was made in and is one of the first statues to be cast in aluminium.
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.

Germany became world leader in aluminium production soon after Adolf Hitler seized power. By 1942, however, new hydrolectric power projects such as the Grand Coulee Dam gave the United States something Nazi Germany could not hope to compete with: the ability to make enough aluminium to produce sixty thousand war planes in four years. [3]

Occurrence and resources

Although Al is an abundant element in Earth's crust (8.1%), it is very rare in its free form and was once considered a precious metal more valuable than gold (It is said that Napoleon III of France had a set of aluminium plates reserved for his finest guests. Others had to make do with gold ones). It is therefore comparatively new as an industrial metal and has been produced in commercial quantities for just over 100 years.

Aluminium was, when it was first discovered, extremely difficult to separate from the rocks it was part of. Since the whole of Earth's aluminium was bound up in the form of compounds, it was the most difficult metal on earth to get, despite the fact that it is one of the planet's most common. The reason is that aluminium is oxidized very rapidly and that its oxide is an extremely stable compound. The very reason for which aluminium is used in many applications is why it is so hard to produce.

Recovery of this metal from scrap (via recycling) has become an important component of the aluminium industry. Recycling involves simply melting the metal, which is far less expensive than creating it from ore. Refining aluminium requires enormous amounts of electricity; recycling it requires only 5% of the energy to produce it. A common practice since the early 1900s, aluminium recycling is not new. It was, however, a low-profile activity until the late 1960s when the exploding popularity of aluminium beverage cans finally placed recycling into the public consciousness. Sources for recycled aluminium include automobiles, windows and doors, appliances, containers and other products.

Aluminium is a reactive metal and it is hard to extract it from its ore, aluminium oxide (Al2O3). Direct reduction, with e.g. carbon, is not economically viable since aluminium oxide has a melting point of about 2000°C. Therefore, it is extracted by electrolysis – the aluminium oxide is dissolved in molten cryolite and then reduced to the pure metal. By this process, the actual operational temperature of the reduction cells is around 950-980°C. Cryolite was originally found as a mineral on Greenland, but by has been replaced by a synthetic cryolite. Cryolite is a mixture of aluminium, sodium, and calcium fluorides: (Na3AlF6. The aluminium oxide (a white powder) is obtained by refining bauxite, which is red since it contains 30-40% iron oxide. This is done using the so-called Bayer process. Previous to this, the process used was the Deville process.

The electolytic process replaced the Wöhler process , which involved the reduction of anhydrous alumium chloride with potassium.

The electrodes used in the electrolysis of aluminium oxide are both carbon. Once the ore is in the molten state, its ions are free to move around. The reaction at the negative cathode is

Al3+ + 3e- → Al

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

At th positive electrode (anode) oxygen gas is formed:

2O2- → O2 + 4e-

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

O2 + C → CO2

Contrary to the anodes, the cathodes are not consumed during the operation, since there is no oxygen present at the cathode. The carbon cathode is protected by the liquid aluminium inside the cells. Cathodes do erode, mainly due to electrochemical processes. After 5-10 years, depending on the amperage used in the electrolysis, a cell has to be reconstructed completely, because the cathodes are completely worn.

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 14.5-15.5 kWh/kg Aluminium produced. The most modern smelters reach approximately 12.8 kWh/kg. Reduction line amperages for older technologies are typically 100,000-200,000 A. State-of-the-art smelters operate with about 350,000 A. Trials have been reported with 500,000 A cells.

Electric power represents about 20-40% of the cost of producing aluminium, depending on the location of the aluminium smelter. Smelters tend to be located where electric power is plentiful and inexpensive, such as South Africa, the South Island of New Zealand, Australia, China, Middle-East, Russia and Quebec in Canada.

China is currently (2004) the top world producer of aluminium.


Aluminium has nine isotopes, whose mass numbers range from 23 to 30. Only Al-27 (stable isotope) and Al-26 (radioactive isotope, t1/2 = 7.2 × 105 y) occur naturally, however Al-27 has a natural abundance of 100%. Al-26 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 Al-26 to beryllium-10 has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales.

Cosmogenic Al-26 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 Al-26 production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further Al-26 production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that Al-26 was relatively abundant at the time of formation of our planetary system. Possibly, the energy released by the decay of Al-26 was responsible for the remelting and differentiation of some asteroids after their formation 4.6 billion years ago.


In the journal Science of 14 January 2005 it was reported that clusters of 13 aluminium atoms (Al13) had been made to behave like an Iodine atom; and, 14 aluminium atoms (Al14) behaved like an alkaline earth atom. The researchers also bound 12 iodine atoms to an Al13 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: "cluster elements". The research teams were led by Shiv N. Khanna (Virginia Commonwealth University) and A. Welford Castleman Jr (Penn State University). [4]


Aluminium is one of the few abundant elements that appears to have no beneficial function in living cells, but a few 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 Kaopectate® (anti-diarrhea product), Amphojel®, and Maalox® (antacids). In other persons, aluminium is not considered as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts, although 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. It has been suggested that aluminium may be linked to Alzheimer's disease, although that research has recently been refuted.

Care must be taken to prevent aluminium from coming into contact with certain chemicals that can cause it to corrode quickly. For example, just a small amount of mercury applied to the surface of a piece of aluminium can break up the normal aluminium oxide barrier usually present. Within a few hours, even a heavy structural beam can be significantly weakened. For this reason, mercury thermometers are not allowed on many airliners, as aluminium is a common structural component in aircraft.


The official IUPAC spelling of the element is aluminium; however, Americans and Canadians generally spell and pronounce it aluminum.

In 1808, Humphry Davy originally proposed the name alumium whilst trying to electrolytically isolate the new metal from the mineral alumina. A couple of years later he changed the name to aluminum to match its Latin root, but was finally persuaded to restore the -ium ending in 1812 giving aluminium. This had the advantage of conforming to the -ium suffix precedent set by other newly discovered elements of the period potassium, sodium, magnesium, calcium, and strontium (all of which Davy had isolated himself). However, for the next thirty years, both the -um and -ium endings were used in the scientific literature.

Curiously America adopted the -ium for most of the 19th century with aluminium appearing in Webster's Dictionary of 1828. However Charles Martin Hall selected the -um spelling in an advertising handbill for his new efficient electrolytic method for the production of aluminium, four years after he had patented the process in 1888. Although this spelling may have been an accident, Hall's domination of aluminium production ensured that the -um ending became the standard in North America, even though the Webster Unabridged Dictionary of 1913 continued to use the -ium version. In 1926 the American Chemical Society decided officially to use aluminum in its publications.

Meanwhile most of Europe had standardized on the -ium spelling. In 1990 the IUPAC adopted aluminium as the standard international name for the element. Aluminium is also the name used in French, Dutch, German, Danish, Norwegian, Swedish and Japanese; Italian uses alluminio, Portuguese alumínio and Spanish aluminio. (The use of these words in these other languages is one of the reasons IUPAC chose aluminium over aluminum.) In 1993, IUPAC recognized aluminum as an acceptable variant, but still prefers the use of aluminium.


Oxidation state 1

  • AlH is produced when aluminium is heated at 1500 °C in an atmosphere of hydrogen.
  • Al2O is made by heating the normal oxide, Al2O3, with silicon at 1800 °C in a vacuum.
  • Al2S can be made by heating Al2S3 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 vapour phase when the tri-halide is heated with aluminium.

Oxidation state 2

  • Aluminium suboxide, AlO can be shown to be present when aluminium powder burns in oxygen.

Oxidation state 3

  • Fajans rules show that the simple trivalent cation Al3+ is not expected to be found in anhydrous salts or binary compounds such as Al2O3. The hydroxide is a weak base and aluminium salts of weak bases, 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, (AlH3)n, can be produced from aluminium trimethyl 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, Al4C3 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, Al2(C2)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, Al2O3, 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, Al2S3, may be prepared by passing hydrogen sulfide over aluminium powder. It is polymorphic.
  • Aluminium fluoride, AlF3, 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.
  • Organo-metallic compounds of empirical formula AlR3 exist and, if not also giant molecules, are at least dimers or trimers. They have some uses in organic chemistry for instance trimethyl aluminium.
  • Alumino-hydrides of the most electropositive elements are known, the most useful being lithium aluminium hydride, Li[AlH4]. It decomposes into lithium hydride, aluminium and hydrogen when heated, and is hydrolysed by water. It has many uses in organic chemistry. The aluminohalides have a similar structure.

Aluminium in fiction

In the film Star Trek IV: The Voyage Home, Mr. Scott devises the fictional material transparent aluminum.


External links

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