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A Thoroughly Modern Metal : A Power-Hungry Metal.

Converting the raw bauxite ore to a pure metal is a complex and energy- intensive process. Aluminum is a master at bonding with other elements to form molecules that in turn form a loose alliance with other molecules, especially water. Thus bauxite consists of 75 percent hydrated aluminum oxides (Al2O3_3H2O and Al2O3_H2O) plus other compounds such as oxides of iron, silicon, and titanium.

After it is mined, bauxite is finely ground, mixed with lime (calcium oxide) and caustic soda (sodium hydroxide) solution, pumped into pressurized vats, and heated. The contained hydrated aluminum oxides are dissolved by the caustic soda, precipitated out of solution, further purified, then dehydrated to produce white, sugarlike alumina, Al2O3.

Alumina is smelted by the Hall-Heroult process, essentially the same one that was developed in 1886. In this process, alumina is dissolved in baths of molten synthetic cryolite (aluminum fluorite, Na3AlF6) inside large, carbon-lined cells called pots, then electrolytically reduced to aluminum metal. Electrolytic reduction is the particularly energy-hungry step through which the aluminum and oxygen in aluminum oxide are separated.

The crude aluminum goes to furnaces, where it is mixed with other metals to form an array of alloys, each with precise properties for specific uses. Molten alloys are purified in fluxing processes, then poured into molds or cast into ingots. The aluminum is rolled, forged, drawn, or extruded into forms suitable for the manufacture of everything from kitchen cookware and foil to electrical cable, aircraft components, and beverage cans.

----S.V.

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Title Annotation:aluminum
Author:Voynick, Steve
Publication:World and I
Article Type:Brief Article
Geographic Code:1CANA
Date:Dec 1, 2001
Words:248
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