It is a white metal produced by electrical processes from the oxide (alumina), which is prepared from a clay mineral called bauxite. Bauxite is hydrated aluminium oxide. The chief impurities are oxide, silica, clay and titanium oxide. It is found in India in the states of Bihar and Madhya Pradesh.
The bauxite is purified and then dissolved in fused cryolite (double fluoride of aluminium and sodium). The aluminium is then separated from this solution by electrolysis at about 910°C.
Pure aluminium has silvery color and lusture. It is ductile, malleable and very good conductor of heat and electricity. It has a very high resistance to corrosion than the ordinary steel. Its specific gravity is 2.7 and melting point is 658°C. Its tensile strength varies from 95 to 157 MN/m2. In proportion to its weight it is quite strong. In its pure state the metal would be weak and soft for most purposes, but when mixed with small amounts of other alloys, it becomes hard and rigid. It may be blanked, formed, drawn, turned, cast, forged and die cast. Its good electrical conductivity is an important property and is broadly used for overhead cables. It forms useful alloys with iron, copper, zinc and other metals.
Applications It is mainly used in aircraft and automobile parts where saving of weight is an advantage.
The high resistance to corrosion and its non-toxicity make it a useful metal for cooking utensils under ordinary conditions. Aluminium metal of high purity has got high reflecting power in the form of sheets and is, therefore, widely used for reflectors, mirrors and telescopes. It is used in making furniture, doors and window components, rail road, trolley cars, automobile bodies and pistons, electrical cables, rivets, kitchen utensils and collapsible tubes for pastes. Aluminium foil is used as silver paper for food packing etc. In a finely divided flake form, aluminium is employed as a pigment in paint. It is a cheap and very important non ferrous metal used for making cooking utensils.
Reference Introduction to basic Manufacturing Processes and Workshop Technology by Rajender Singh.
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