Properties of Aluminium and Uses of Aluminium
Aluminium is known for its lightness though it possesses considerable strength. It is a soft and silvery-white metal, which conducts heat and electricity. It has a brilliant lustre which becomes dull owing to atmospheric oxidation. The metal reacts with nitrogen, oxygen, sulphur and halogens at elevated temperatures to form nitride, oxide, sulphide and halides, respectively. With hydrochloric acid, it forms aluminium chloride (Al2Cl6) which is a dimer of AlCl3
2Al + 6HCl Al2Cl6 + 3H2
Hot concentrated sulphuric acid reacts with the metal and sulphur dioxide is liberated.
2Al + 12H+ + 3SO4 2- 2Al3+ + 3SO2 +6H2O
With concentrated nitric acid, the metal gets coated with an oxide layer and becomes passive. It dissolves in hot concentrated alkalis forming soluble aluminate.
2Al + 2NaOH + 6H2O 2Na[Al(OH)4] + 3H2
Uses of Aluminium
Aluminium and its alloys are used extensively as building material, in the construction of aircraft and railway coaches, and in shipbuilding. Being inexpensive, light and a good conductor of heat and electricity, the metal is used in transmission cables, household utensils and laboratory apparatus. Finely divided aluminium powder mixed with linseed oil is used in silvery paints and lacquers. Aluminium foil finds immense use as wrapping material in the food industry. Thermite welding and the extraction of chromium, manganese and iron are based on the following reactions:
Cr2O3 + 2Al Al2O3 + 2Cr
3Mn3O4 + 8Al 4Al2O3+9Mn
Fe2O3 + 2Al Al2O3 + 2Fe