Aluminium encyclopaedia

Aluminium

History

In antiquity one was already aware of the aluminium compound alum, which was the inspiration for the naming of the silvery white metal by its discoverer Davy in 1807. Oersted (1825) and Wöhler (1827) were the fist to produce it in its pure form. In 1854, Sainte-Claire Deville developed the first technically feasible process for aluminium extraction, but it was too expensive for widespread use. It was only after Hall and Héroult patented fused-salt electrolysis in 1886 that there was strong growth in aluminium production, thus making low aluminium prices possible. Subsequently, research workers were able to improve the properties of aluminium, for example by alloying. Today, aluminium is the most used metal after ferrous materials; the aluminium industry has developed into a key branch of the economy.

Abundance and extraction

Aluminium does not occur freely in nature, only in aluminium compounds, which are a part of most rocks, especially their products of weathering - such as clay and bauxite. With 8.1 per cent by weight, aluminium is the third most abundant element in the Earths crust after oxygen (47.3 per cent) and silicon (25.8 per cent), and the most abundant metal (iron 5.1 per cent, copper 0.01 per cent). Today, aluminium extraction is almost exclusively carried out in two stages: aluminium oxide is first extracted from bauxite in the Bayer process and the metal is then extracted from the oxide in aluminium smelters using fused-salt electrolysis. The recycling of aluminium products is becoming increasingly more important as it enables considerable energy savings to be made compared with primary extraction, conserves raw materials and makes an important contribution to environmental protection.

Designations

Unlike some other common metals, such as copper, the term aluminium is used rather loosely to describe both the pure metal and aluminium alloys (cf. copper with its alloys brass, bronze etc.). To differentiate between aluminium-base materials one uses a code comprising numbers and letters. In Europe, the EN standards classification system uses Al, as the symbol for the base material aluminium followed by its content in per cent by weight. There then follow, in decreasing order of content, the chemical symbols for the most important alloying elements with their percentage compositions. In some cases, a letter is used to indicate the source of the metal:

  • Primary aluminium: unalloyed e.g. Al99H; as an alloy e.g. AlMg4,5 (i.e. 4.5 per cent magnesium);
  • Refined aluminium: minimum aluminium content > 99.9 per cent; e.g. EN AW-1199 or EN AW-Al99,99
  • Unalloyed aluminium: minimum aluminium content 99.0 - 99.9 per cent; e.g. EN AW-1050A or EN AW-Al99,5