Aluminium: ID

Aluminium is an abundant metal and constitutes 8% of the earth's crust. But it is only found in nature in combination with other elements, especially in the form of oxides because it often pair-bonds with oxygen. 

It was in the 19th century that the metal was identified and isolated. The German scientist German Wöhler first described and record its properties in 1827. The French scientist Sainte-Claire Deville built on his work and in 1854 he was the first person to develop a (complex and costly) refining process to obtain pure aluminium. 

In its various applications, aluminium is almost always combined with other elements to modify, complete, improve its basic characteristics. These additional elements represent up to 15% of the weight of the alloys.

The density of aluminium at 20°C is 2.7 g/cm³. It is approximately three times lower than that of steel (7-8 g/cm ³). Aluminium’s low density makes it particularly prized for its industrial applications, in particular in the aeronautics and aerospace sectors.

The crystal lattice of aluminium has a face-cantered cubic structure. This structure allows many sliding planes: it gives aluminium its great malleability, which is maintained at low temperatures.

Aluminium alloys have a resistance between 25 and 65 nΩm. They are used in electrical equipment and in the transmission of electricity. For aerial cables, alloys are used whose elements reduce conductivity, but which offer an excellent compromise between conductivity and mechanical strength.  Despite having a conductivity that is one third lower than that of copper, aluminium is able to conduct electricity thanks to its low density (2.7 against 8.9 for copper). Thus, for conductors of the same length and the same mass, the conductivity of aluminium is approximately twice that of copper.

The thermal conductivity of aluminium at 20°C is 240 W /m°C. Located between that of copper (400) and that of 18-10 stainless steel (15 to 20), it is showcased in kitchen utensils, heat exchangers, etc.

Polished aluminium reflects 85 to 90% of visible light, 90 to 98% in the infrared. Silver is more reflective than aluminium, but the latter is preferred for coating the surface of telescope mirrors, because it does not tarnish. 

Aluminium’s modulus of elasticity is 67,000 MPa, compared with that of steel, around 200,000 MPa. When exposed to the same stresses, aluminium’s elasticity causes it warp 3 times more than a similar steel structure. The design of aluminium structures must take this particularity into account, which can prove to be an advantage in certain cases, as for example in the superstructures of ships.