Aluminum is a metal in the 3rd period of Group IIIA. Other elements in this group are boron (B), gallium (Ga), indium (In), and thallium (Tl).
Wöhler is generally credited with isolating aluminum in 1827, although an impure form was prepared by Oersted two years earlier.
The method of obtaining the metal by electrolysis of alumina dissolved in cryolite (Na3AlF6) was discovered in 1886 by Hall in the U.S. and independently about the same time by Héroult in France.
The name is derived from the Latin alumen or alum (potassium aluminum sulfate). The symbol Al is derived from the name. In the British Commonwealth the name is spelled aluminium and pronounced accordingly.
Aluminum is a silver-white metal that is ductile, malleable, and an excellent conductor of heat and electricity. The pure metal is soft, but can be made strong and hard when alloyed with small amounts of copper, magnesium, silicon, manganese, and other elements. It is light, nontoxic, has a pleasing appearance, can easily be formed, machined, or cast. In the solid state the metal has a face-centered cubic structure.
The metal is also nonmagnetic and non-sparking, stands second among metals in the scale of malleability, and sixth in ductility.
In 1856, the price of aluminum was about 90 dollars a pound, and just before Hall's discovery in 1886, about 5 dollars. Because of its great value and resistance to corrosion aluminum was used to cap the Washington Monument in the U.S. capital in 1884. Hall's discovery reduced the price by more than a factor of ten.
Although aluminum occurs in larger quantities in the earth's crust than any other metal, it does not appear as the free metal. It is found as many aluminosilicates such as clays, feldspars, and zeolites. The commercial ore is bauxite, an impure hydrated oxide. Its production from clay is possible but not economically feasible at present.
Al also has excellent corrosion resistance due to a coating of oxide on the surface that passivates the metal, preventing further oxidation. (For this reason Al does not react with the oxidizing acid HNO3, while it reacts readily with HCl.)
2 Al(s) + 6 HCl(aq) 2 AlCl3(aq) + 3 H2(g)
Aluminum is extensively used for packaging materials such as soda pop cans, kitchen utensils, outside building decoration, as a foil wrapping material, as powder in paints, and in thousands of industrial applications where a strong, light, easily worked material is needed. It is alloyed with nickel and cobalt to form alnico magnets. A mixture of powdered aluminum and iron(III) oxide, called thermite, is used in welding because enough heat is generated by reaction of Al with the Fe2O3 to melt the iron that is produced.
2 Al(s) + Fe2O3(s) Al2O3(s) + 2 Fe(s)
Although aluminum's electrical conductivity is only about 6% that of copper per area of cross section, it is used in high-voltage electrical transmission lines because of its strength and low density. Aluminum alloys such as duralumin, aluminum bronze, and aluminum-magnesium are of vital importance in the construction of modern aircraft and rockets. Evaporated in a vacuum and condensed onto a plane surface, aluminum forms a highly reflective coating for both visible light and radiant heat; these coatings soon form a thin layer of the protective oxide and do not deteriorate as do silver coatings. They are used in telescope mirrors, decorative paper, packages, toys, and many other applications.
The compounds of greatest importance are aluminum oxide, the sulfate, the soluble sulfate with potassium (alum), and aluminum chlorohydroxide (used in deodorants).
The oxide, alumina, occurs naturally as ruby, sapphire, corundum, and emery and is used in glassmaking. Synthetic ruby and sapphire have found application in the construction of lasers for producing coherent light.