Aluminium: Manufacture, Properties, Applications

Aluminium

Aluminium is a white metal produced by electrical processes from oxide (alumina) which is prepared from a clay mineral called Bauxite. Bauxite is a 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.

Manufacture

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.

Properties

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/m
2. 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.

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