What is Aluminium?

  Making Aluminium

Aluminium is the third most abundant element in the Earth's crust and constitutes 7.3 per cent by mass. In its natural state, it only exists in very stable combinations with other materials (particularly as silicates and oxides). Despite its abundance, it was only in 1808 that aluminium's existence was first established and named by Sir Humphry Davy - even though Sir Humphry failed to actually produce any aluminium at that time.

Aluminium is regarded as a very young metal compared to copper, lead and tin, which have been in use for thousands of years. Despite this, more aluminium is currently produced than any other non-ferrous metals combined. So, what were the historic events that have driven aluminium to such a meteoric height since the naming of the metal in 1808?

The first discovery

In 1821, P. Berthier discovered a hard, reddish, clay-like material, containing 52 per cent aluminium oxide, near the village of Les Baux in southern France. He called it bauxite, the most common ore of aluminium.

Four years later, in 1825, Hans Christian Oersted produced minute quantities of aluminium metal by using dilute potassium amalgam to react with anhydrous aluminium chloride, and distilling the resulting mercury away to leave a residue of slightly impure aluminium.

In 1827, Friedrich Wöhler described a process for producing aluminium as a powder by reacting potassium with anhydrous aluminium chloride. It was 18 years later, in 1845, that Wöhler established the density of aluminium and one of its unique properties - lightness.

The new ‘precious metal’

In 1854, Henri Sainte-Claire Deville improved Wöhler's method to create the first commercial process for making aluminium and the price of aluminium, initially higher than that of gold and platinum, dropped by 90 per cent over the next 10 years. However the price was still high enough to inhibit its widespread adoption by industry and, in 1855, a bar of aluminium, the new 'precious metal', was exhibited at the Paris Exhibition.

In 1885, Hamilton Y. Cassner improved on Deville's process and his annual aluminium output was a record 15 tonnes pa. However, one year later the real breakthrough emerged - two unknown young scientists, Paul Louis Toussaint Héroult and Charles Martin Hall, working separately and unaware of each other's work, simultaneously invented a new electrolytic process known as the Hall-Héroult process, which is the basis for all aluminium production today.

The two enterprising scientists discovered that if they dissolved aluminium oxide (alumina) in a bath of molten cryolite and passed a powerful electric current through it, then molten aluminium would be deposited at the bottom of the bath. This development led to the first aluminium companies being founded in France, Switzerland and the USA in 1888.

Commercial aluminium production was further enhanced in 1889 when Karl Josef Bayer invented the Bayer Process for the large scale production of alumina from bauxite.

Output growth

As you can see below the growth of aluminium has been tremendous:

Changing technology

Since the discovery of the Hall-Heroult method of producing aluminium, and developments in the generation of electric power which have made commercial processing technically viable, the major technical change in the smelting process has been in pot amperage, capacity and design.

The first commercial electrolytic cells carried about 600 amperes per cell. Some cells in more modern smelters now carry more than 300,000 amperes.

The two best known types of technology are called ‘Soderberg’ and ‘Pre-baked’ technologies. The major differences between the two are the outward appearance of the pot itself, and the way electrolysis takes place. The Soderberg pot is open and uses a different type of unbaked material to conduct electricity inside the pot, while the Pre-baked process, like that used at Sohar Aluminium, is fully enclosed and uses a number of smaller, compacted and baked anodes inside the pot.

These changes have been made to incorporate technological, design and environmental advances and have not involved any change in the fundamental aluminium production process.