Aluminium is an important metal. It is the third most abundant element in the earth's crust and occurs in various chemical forms in rocks and soils, in vegetation, in water and in the air, but it doesn't occur anywhere in its pure form. It has to be extracted from its ore, a clay-like substance called bauxite.
Deposits of bauxite ore are mined and refined into alumina. Alumina and electricity are combined in a cell with a molten electrolyte called cryolite. Direct current electricity is passed from a consumable carbon anode into the cryolite, splitting the aluminium oxide into molten aluminium metal and carbon dioxide. The molten aluminium collects at the bottom of the cell and is periodically ‘tapped’ into a crucible and cast into ingots.
Aluminium is very versatile. Some of its key characteristics are:
- Lightness: its density is only one-third that of steel.
- Resistance to weather, common atmospheric gases, and a wide range of liquids. It does not rust or corrode.
- Suitability for contact with a wide range of foodstuffs.
- High reflectivity: it is attractive for decorative uses like foil wrappings and drink cans.
- Strength: aluminium alloys can equal or even exceed the strength of normal construction steel.
- High elasticity, which is an advantage in structures under shock loads.
- Retention of toughness down to very low temperatures, without becoming brittle like carbon steels.
- Malleability: it is easily worked and formed, and can be rolled to very thin foil.
- Thermal and electrical conductivity: aluminium’s ability to transfer heat and electricity nearly equals copper’s.
- Recyclability: it can be recycled in a closed loop, without any loss of quality, whilst saving up to 95% of the energy needed to produce the metal from its raw materials.
What is aluminium used for?
- Building and construction - greenhouses and skyscrapers, protective cladding and interior décor; window frames and furniture; wiring and lighting.
- Mobility - trains, planes and cars; bicycles and scooters; wheelchairs and walking frames.
- Healthy living - an ingredient in medicines and toiletries; protective packaging; fire-retardant clothing and thermal recovery blankets.
- Healthy eating - food and drink packaging, including 'aseptic' containers for long-life products.
How are aluminium cans made?
The body of an aluminium drink can is formed from a single piece of aluminium, which is cut from a sheet of thin aluminium and extruded. Can tops are made of a different alloy and fixed at the end of the filling process.