The pure metal is soft, but it becomes strong and hard when alloyed. Although less conductive than copper wire of the same diameter, aluminum wire is often used for high-tension power transmission because it is lighter and cheaper. Although it is chemically very reactive, aluminum resists corrosion by the formation of a self-protecting oxide coating. Molten aluminum collects at the bottom of the tank, and oxygen is liberated at the anode. The anode is consumed as it combines with the oxygen to form carbon dioxide.
Aluminum foil is used as a wrapping material.
Aluminum powder is used in paints. A mixture of powdered aluminum and iron oxide, called thermite , is used in welding because of the large amount of heat liberated when it is ignited. The development of methods for coloring aluminum led to its use in jewelry, on wall surfaces, and in colored kitchenware. Although the metal was not isolated until the 19th cent., use of aluminum compounds originated in antiquity. Sir Humphry Davy and other chemists in the early 19th cent.