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| You are in: Kaye Aluminium Technical Manual > Contents > Introduction to Aluminium | ||||||||||
Aluminium is the second most widely used metal after iron. This is due to its favourable properties, in particular, low weight, high strength, recyclability, malleability, simplicity of fabrication, corrosion resistance, and its thermal and electrical conductivity.Aluminium is also the world's most abundant metal, and the third most plentiful element behind oxygen and silicon. It is not however found in its pure form, but as an orange-brown ore called "bauxite" named after the French village of Les Baux, where it was first discovered in 1821. |
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| Sources | ||||||||||
The main sources of bauxite are Australia, Jamaica, Ghana, France, Africa and India. At the current rate of extraction, bauxite deposits will last 200 – 400 years, although the increase in re-cycling may extend this. |
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| Production | ||||||||||
| To produce aluminium the bauxite must first be refined to give alumina (aluminium oxide Al 2 O 3 ). This is generally done close to the bauxite mine to reduce transport costs as 4 tonnes of bauxite is required to produce 1 tonne of alumina. Bauxite is mechanically crushed, mixed with caustic soda, and heated under pressure to dissolve out the alumina. The resultant mixture is the allowed to settle and dry to give the whitish powder that is alumina.The alumina is then smelted, usually in an area of cheap power (e.g. hydroelectric), as it requires approx. 17000 kWh to produce 1 tonne of aluminium. This investment in energy accounts for the high cost of aluminium, but can be justified, as when converted to its final form (in a train for example), the reduction in fossil fuel consumption is considerable. An aluminium railway carriage for example when compared to a steel railway carriage will provide an energy gain after only two years.Smelting is an electrolytic process. Cryolite and felspar are added to the alumina as catalysts in huge carbon lined steel pots. The mixture is heated to 900 degrees centigrade and an electric current passed between the lining of the pot and carbon rods suspended in the mixture. Aluminium forms at the bottom of the pot, whilst oxygen is given off at the rod. The aluminium is run off in its molten form and cast into ingots. |
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| Recycling | ||||||||||
Aluminium is almost unique amongst other materials, as it can be recycled over and over again without any change to its characteristics. Recycling aluminium uses 5% of the energy used in producing primary aluminium.An increased recycling percentage can be achieved by better sorting of scrap aluminium . |
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| Malleability | ||||||||||
The good malleability of aluminium and its alloys is essential for the extrusion process, and for post-production fabrication processes such as forming and bending. These can be carried out in both hot and cold conditions. Different tempers are available at Kaye for sections that will be fabricated at a later date. |
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| Fabrication | ||||||||||
| Aluminium has several advanced bonding and welding methods available for use, and is simple to fabricate with most punching and machining methods. | ||||||||||
| Corrosion Resistance | ||||||||||
The high reactivity of aluminium and its alloys leads to very high corrosion protection, due to the formation of a thin stable oxide layer on the surface. Aluminium reacts with the oxygen in air to form this layer, which spontaneously rebuilds when damaged.The oxide layer can be electrolytically advanced by using a process called anodising (see section on ANODISING ). The anodic film also possesses the property of absorbing different colour dyes, which can combine decoration with corrosion protection.Aluminium has a good hardness/endurance in slightly acidic or neutral surroundings, but in conditions of extreme acid or alkali pH, corrosion can develop very quickly. |
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| Physical Properties | ||||||||||
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Copyright 2004