Friday, December 17, 2010

Is Aluminum the Cheapest Noble Metal?

Given that once purified it essentially becomes inactive towards oxygen, does aluminum pass muster as the cheapest noble metal around?

By: Ringo Bones

The textbook definition of a noble metal states that any metal that is chemically inert or inactive especially towards oxygen qualifies as a true-blue noble metal which aluminum seems to qualify as such. By comparison, copper – the last time I checked in the commodities index – is much more expensive than aluminum and corrodes much faster in air. And if you include most recent environmentally pro-active recycling adverts stating that it takes probably over 100 years for a discarded aluminum can to recycle itself back to bauxite, you might be forgiven for wondering whether aluminum is indeed a true-blue noble metal, but is there any truth to this?

Indeed, there was a time when aluminum was considered to be a noble metal. When aluminum was newly discovered by Sir Humphry Davy back in 1827, there was a 20-year period when obtaining aluminum by “conventional” smelting methods from bauxite made the metal about a little over twice as expensive as gold. Charles Louis Napoleon Bonaparte – more famously known as Napoleon III – favors aluminum over gold during his time since then existing methods of refining aluminum made it a little over twice as expensive as gold.

Fortunately we have Charles Martin Hall to be thankful for making aluminum cheap enough to wrap our sandwiches in. Hall was the first to develop the modern method – an in currently the most economically viable method – of extracting aluminum from bauxite clay in an electric arc furnace. Because of this, 30% of the cost of aluminum comes from the cost of electricity needed to free the metal from oxygen. Strangely enough, Mother Nature can also create Her own samples of pure aluminum metal during those exceedingly rare circumstances when lightning hits a bauxite-rich lava.

In truth, aluminum does react to atmospheric oxygen at room temperature, although unlike iron, aluminum does not corrode when it reacts to oxygen. Instead it forms a silvery gray oxide that sticks tightly on its surface. The main mirror of the Hubble Space Telescope has its surface coated with a very thin layer of aluminum fluoride to protect it from oxidation. Aluminum is chemically reactive enough to form useful compounds – like aluminum hydroxide which is often mixed with gasoline to create napalm. And despite the advances of high strength non-metal composites, aluminum is still used in the aircraft construction industry because of the metal’s high strength-to-weight ratio. In fact, it was Nikola Tesla who first prophesized that airplane making will only become profitable industry when we find a cheap way to produce aluminum.


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