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LIKE HYDROGEN, aluminum is lightweight. Like hydrogen, it is one of the most common of elements. Alas, also like hydrogen, it’s among the most promiscuous.
That is, aluminum loves to mate willy-nilly with other things in nature, a fact that complicates its exploitation. It’s the third most common element in the earth’s crust, after oxygen and silicon, but it almost never appears in pure form.
Its principal source is bauxite, this ore commercially mined in Australia, Brazil, India, China, Indonesia—and the island of Jamaica. The ore is first refined into alumina, Al2O3, through the Bayer Process, a treatment with sodium hydroxide. Then the Hall-Héroult process is applied. This is a high-temperature (1740-1800 degrees F) smelting technique using electrolysis to strip the oxygen from the alumina, finally yielding pure aluminum.
Electrolysis, though, is extremely energy-intensive, its cost accounting for some 20-40% of aluminum production’s total. It’s figured that around 15 kWh of electrical energy is required to make 1 kg (2.2 lb) of aluminum. Let’s put this energy requirement in perspective: A fully charged Chevrolet Volt battery pack, capable of propelling the car perhaps 35 miles, has an energy capacity of 16 kWh.
Costly though it may be to produce, aluminum definitely has its virtues. Its many alloys are generally about 1/3 the weight of steel. They’re highly malleable; that is, readily rolled, stamped, forged, cast or extruded. Aluminum is nonmagnetic and conductive, displaying latter properties about 59% those of copper. (For this reason, the lightning rod atop Washington Monument is made of these two materials.) Aluminum products resist corrosion, especially after a surface coating of aluminum oxide is formed. One of aluminum’s few design tradeoffs is its fatigue strength, its response to repeated stress.
Adroitly employed, aluminum is clearly a means of weight savings, particularly in many automotive applications. For example, at two extremes of manufacture, Audi and Morgan both produce aluminum-intensive automobiles: The Audi A8 is built in large numbers essentially on an automated assembly line; the Morgan Aero 8, in miniscule numbers and largely hand-fabricated.
Nearby is an item on Icelandic aluminum production. And, just for fun, check out my tale of the Dellow, a post-WWII English sports car that profited from this lightweight element—but for different reasons entirely. ds
© Dennis Simanaitis, SimanaitisSays.com, 2012