We all know that iron is extremely reactive in that iron oxide (rust) forms after prolonged exposure to the environment. Aluminium oxidises just as quickly, if not more so, but a quirky virtue of aluminium is that its own layer of aluminium oxide eventually prevents the metal from further oxidation. It does not mean aluminium will altogether be immune to corrosion; in time a white powdery coat will form, further degrading the metal. Technologically, however, aluminium, like iron, gets a prolific and indefinite second life. A chemical process known as anodising, gives aluminium invaluable use in the industries and the decorative arts. The process requires aluminium to be immerse in an electrolyte bath, and then passing an electric current through it. Oxygen ions are released from the electrolyte to combine with aluminium atoms forming a more attractive anodic-oxide finished metal that is much more durable and corrosion-resistant.
http://www.badgeranodising.co.uk/chemical-anodising-aluminium-for-the-industries-and-decorative-arts/
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