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Aluminium (Al): properties, occurrence, production and uses

Aluminium (Al, atomic number 13) is a lightweight, corrosion-resistant metal and the most abundant metallic element in Earth’s crust. This article covers its properties, production, history, and common applications.

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Overview

Aluminium (also spelled aluminum in North America) is a chemical element with the symbol Al and atomic number 13. It is the most abundant metal in the Earth’s crust and occurs primarily in combined forms rather than as a free element. Aluminium is notable for a combination of low density, good corrosion resistance and useful mechanical and electrical properties.

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13 (Al I) NIST ASD emission spectrum
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Characteristics

Aluminium is a silvery-white, ductile metal that forms a thin oxide layer which protects it from further corrosion. It is considered a mononuclidic element because it has a single stable isotope. Common characteristics include:

  • Lightweight relative to steel and copper
  • Good electrical and thermal conductivity
  • High reflectivity for visible and infrared light
  • Ease of fabrication: can be cast, rolled, extruded and welded

Occurrence and production

Aluminium is not found in nature as a pure metal; it is extracted from alumina-bearing ores, chiefly bauxite. The industrial pathway typically has two main steps: the Bayer process to refine bauxite into alumina (aluminium oxide), and the Hall–Héroult electrolytic process to reduce alumina to metallic aluminium. Modern production is energy intensive and benefits significantly from recycling, which uses much less energy than producing primary metal.

Uses and importance

Aluminium’s combination of lightness and strength makes it important across many sectors. Typical uses include:

  • Transport: aircraft, automobiles, trains and marine vessels where weight savings improve efficiency
  • Packaging: cans and foil because it is non-toxic and forms an effective barrier
  • Construction: windows, cladding, structural components for its corrosion resistance
  • Electrical: overhead power lines and components where conductivity-to-weight ratio matters
  • Consumer goods and cookware

History and notable facts

Early isolated samples of aluminium date to the early 19th century; chemists such as Ørsted and Wöhler produced impure metal, while the name ‘‘aluminium’’ and the alternative ‘‘aluminum’’ reflect historical variations in nomenclature. The commercial electrolytic production method was developed independently by Hall and Héroult in the 1880s, enabling widespread use. Because aluminium is so common in the crust but rarely found free, its availability and recyclability have shaped its industrial role.

Further reading

For technical summaries and data about the element, see general references on the chemical element and summaries of its abundance in the crust at geochemical resources. For alloying, processing, and industry practices consult metallurgical sources such as process descriptions and standards (atomic information) and technology reviews (symbol and notation).

History

In 1782, Lavoisier was the first to suspect that the alumina (alumina, derived from the Latin alumen 'alum') obtained by Marggraf in 1754 from an alum solution was the oxide of a previously unknown element. In 1825, the Dane Hans Christian Ørsted finally succeeded in producing it by reacting aluminium chloride (AlCl3) with potassium amalgam, with potassium serving as the reducing agent:

{\mathrm {4\ AlCl_{3}+3\ K\rightarrow Al+3\ KAlCl_{4}}}

Davy, who for a long time had also tried his hand at representing the new element, introduced from 1807 the name variants alumium, aluminum, and aluminium, of which the last two persist side by side in English.

In 1827, Friedrich Wöhler succeeded in obtaining purer aluminium using the same method as Ørsted, but using metallic potassium as a reducing agent. Henri Étienne Sainte-Claire Deville refined the Wöhler process in 1846 and published it in a book in 1859. This improved process increased the yield of aluminium extraction, and as a result the price of aluminium, which had previously been higher than that of gold, fell to a tenth within ten years.

In 1886, Charles Martin Hall and Paul Héroult independently developed the electrolysis process named after them for the production of aluminium: the Hall-Héroult process. In 1889, Carl Josef Bayer developed the Bayer process, named after him, for isolating pure aluminium oxide from bauxites. Aluminium is still produced on a large scale using this principle today.

At the end of the 19th century, the metal was held in such high esteem that metal ships made of it were christened Aluminia.

Humphry Davy

Hans Christian Ørsted

Occurrence

With a share of 7.57 percent by weight, aluminium is the third most common element in the earth's crust after oxygen and silicon and thus the most common metal. However, due to its base metal character, it occurs practically exclusively in bound form. The largest quantity is found chemically bound in the form of aluminosilicates, in which it occupies the position of silicon in oxygen tetrahedra in the crystal structure. These silicates are, for example, a component of clay, gneiss and granite.

More rarely, alumina is found in the form of the mineral corundum and its varieties ruby (red) and sapphire (colorless, various colors). The colours of these crystals are based on admixtures of other metal oxides. Corundum has the highest aluminium content of any compound, at almost 53 percent. The even rarer minerals akdalaite (about 51 percent) and diaoyudaoite (about 50 percent) have a similarly high aluminum content. A total of 1156 aluminium-bearing minerals are known to date (as of 2017).

The only economically important raw material for aluminium production is bauxite. Deposits are located in southern France (Les Baux), Guinea, Bosnia and Herzegovina, Hungary, Russia, India, Jamaica, Australia, Brazil and the United States. Bauxite contains about 60 percent aluminum hydroxide (Al(OH)3 and AlO(OH)), about 30 percent iron oxide (Fe2O3), and silicon dioxide (SiO2).

In the production process, a distinction is made between primary aluminium, also known as primary aluminium, which is extracted from bauxite, and secondary aluminium, which is extracted from aluminium scrap. Recycling requires only about 5 percent of the energy of primary extraction.

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