Aluminum

Aluminium is the most common metal on Earth. It occurs naturally in many different kinds of rocks. But most of the aluminium we use is extracted from an ore called bauxite, which is formed over long periods by the weathering of rocks containing aluminium silicates (aluminium, silicon and oxygen).

Aluminium is extracted from bauxite by the Bayer process and electrolysis. In the Bayer process, bauxite is mixed with caustic soda and heated. This produces sugar-like crystals of pure aluminium oxide. These are dissolved in molten sodium aluminium fluoride, called cryolite. Electrolysis is then used to split up the aluminium and oxygen.

In 1886 two chemists independently discovered how to extract aluminium using electricity. Their discovery reduced the price of aluminium to a fraction of the price of silver in four years. The two chemists were Charles Martin Hall (1863 - 1914), a student at Oberlin College in the USA, and P.L.T. Heroult (1863 - 1914), a young chemist working in France. By coincidence, they were not only the same age when they made their discovery, but also died within eight months of each other.

Before this, the metal was much more expensive than silver and gold. The Emperor of France, Napoleon III, for example, used aluminium plates to impress the most important guests. Today we use aluminium foil to wrap food because it is so cheap.

Aluminium is also durable, light and a good conductor of electricity. It is used to protect metals against corroding because when the surface of aluminium reacts with oxygen in the air, a thick coating of aluminium oxide forms that seals a metal from the air. It is also used to make parts for planes, cars, and lorries, to make electric cables.