ALUMINIUM

Aluminium was first generated in year of 1825. Presently it is generated in quantity second only to steel. This is the most abundant metallic element on the crust of the earth simply comprising about 8 percent of the crust. Bauxite, Aluminium's hydrous oxide and some other oxides, is the principal ore of aluminium. Through electrolytic process, Aluminium is extracted from its ore mainly. The ore is first washed off to eliminate clay and dirt; the ore is crushed into powder and treated along with hot sodium hydroxide as caustic soda to eliminate impurities. Alumina or the oxide of aluminium extracted from this solution is dissolved in molten aluminium fluroride and sodium fluoride bath at 940-980^oC. This mixture after that subjected to direct current electrolysis via passing direct current between carbon cathode and anode. The metallic aluminium forms in liquid state and goes under to bottom of the cell. From time to time, this liquid aluminium is tapped off. The aluminium so obtained is 99.5 to 99.9 percent pure along with iron and silicon as the main impurities.

Aluminium then is obtained to large refractory lined furnaces for refining before casting. The chlorine gas is employed as purging agent to eliminate the dissolved hydrogen gas, and the liquid metal surface is skimmed off to eliminate oxidized metal. The molten metal is next that cast into ingots for rolling or remelting.