Aluminum

Aluminum, chemical element, symbol Al; for physical constants see Periodic Table. Aluminum in the form of its compounds has been used for hundreds of years. Potassium aluminum sulfate, the most common alum, continues to be used in medicine as an astringent, and as a mordant in dyeing. Aluminum was first isolated by Oersted in 1825 although in an impure form. It occurs primarily in the form of complex silicates, and is the third most abundant element on earth. The principal ore of aluminum is bauxite, a hydrated oxide. Aluminum is a soft, tin-white, reactive, metal, the most abundant metal in the earth's crust. Aluminum is prepared by electrolysis of alumina (aluminum oxide) in fused cryolite, a procedure known as the Hall-Héroult process. Aluminum oxide occurs naturally in other important and useful forms as ruby, sapphire, corundum, and emery. Aluminum has many valuable properties which account for its wide use. It is second in malleability and sixth in ductility of all metals. It is light and a good electrical conductor. Since aluminum is soft, it is almost always alloyed with small amounts of other elements. It is the second most important metal after iron.