ALTONJ. BANKS
w h d s the use? Aluminum Symbol: A1 .Atomic number: 13 .Atomic weight: 26.981 'Meltingpoint: 933.570 K 'Boilingpoint:2740'000 .Density: 2.6990 g/cm3
KCttttfflttttl At least one aluminum compound has been used for centuries. Alum, KAI(SO4)2.12H20,was used by the Greeks and Romans as an astringent and as a mordant in dyeing cloth. The element is the most abundant metal in the earth's crust but is not found free in nature. Aluminum is found in such minerals as kaolinite, montmorillonite, and vermiculite. One of the most important commercial sources of aluminum is bauxite, discovered in 1821 by P. Berthier near Les Baux. Credit for this element's name is given to Humphry Davy (L. alumen, bitter salt) although he was unable to isolate the pure metal. The impure metal was first obtained by H. C. Oersted in 1825by the reaction of a potassium amalgam with AM3. In 1827 H. Wohler obtained pure aluminum using metallic potassium. As late as the Paris Exposition af 1855, the metal was relatively rare and cost in excess of $500 per pound. H. St. Clair Deville and R. Bnnsen independently developed a method for isolating the metal by electrolyzing fused NaAIC1,. The breakthrough in commercial production of the metal came in the late 1800's (1886) when Charles M. Hall in the United States and P. L. T. HBroult in k a n c e developed the process in which alumina (Alz03) was electrolyzed in mol-
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Journal of Chemical Education
Nonh Carolina State University Raleigh. NC 27695
ten cryolite, Na3AlF6.The price of aluminum plummeted to less than 50 cents per pound. Present commercial production of aluminum involves the purification of bauxite, via the Bayer process, followed by the reduction ofthe alumina via the Hall-Heroult process. The oxide coating that rapidly forms on the pure metal passivates the surface, making the metal ideal for many decorative applications. The electrical conductivity, ductility, and light weight make the metal useful in electrical transmission lines. The metal has.been used to coat telescope mirrors and to provide inert wrapping material for foods. While the pure metal has limited mechanical strength, aluminum has been alloyed with copper, manganese, silicon, magnesium, and zinc to provide alloys with a wide range of mechanical properties. Such alloys are used in aircraR structural panels, highway signs, gun mounts, heat exchangers, storage tanks, bridges, and kitchen utensils. Aluminum salts are also found in gemstones such as Nbies, sapphires (Alz03containing Cr and Co, respectively), garnet (Ca3A12(Si04)3),and beryl (Be3AlzSi601s).Corundum ( A l z 0 3 ) is a very hard substance and is used as an abrasive. Some of these applications are shown on "The Periodic Table Videodisc" in frames 36447-36464. General References "KC? Dismverer: Exploring the Properties of the Chemical Elements': JCE: &Amore 1988,1B(1). Handbmk of Chemistry & Physics, 71st ed.; Lide, Dadd, R., Ed.; Chemical Rubber: Cleveland, OH, 1990-1991: pp b30. Greenluaod, N N.; Earn6haw.A. C h p m & f ~ 0 f t h s E ~ m t 8 : P e g a m o New n : York, 1984; pp 243-248. Banks. A. J. "The PerbdieTableYldeadise": JCE: Soflwor~1989, Special Issue 1.
