The adventures of Mr Héroult and Mr Hall

The discovery of both Mr Héroult and of Mr Hall consisted in the use an electro-chemical process to reduce the alumina into aluminium, instead of a purely chemical process as was the case before. This process was named "Héroult-Hall" or "Hall-Héroult"(depending on which side of the Atlantic you are...)

imagesEverybody has heard about this process. Let us explain it in a few words. An electrode (the anode, electrically positive) in coke is plunged into a 'bath' consisting of a mixture of molten cryolite (double fluoride of sodium and of aluminium) and alumina (Al2O3). The other electrode (the cathode, negative), at the bottom of the 'bath', is in graphite.

A very strong DC electrical current passes from the anode (at the top) to the cathode (at the bottom), and the Alumina Al2O3 is "reduced" (i.e. stripped of its 3 O).The mixture is thus gradually transformed into liquid aluminium, which can be collected at the bottom of the 'bath'.

The strength of this electrical current is typically in the range of hundreds of thousands Amps, which is needed to keep all ingredients in the 'bath' in a molten state. Aluminium producing units thus consume huge quantities of electricity. But the resulting product is nevertheless much cheaper than was the case before Messrs Hall and Héroult.

One the process operational at the laboratory stage, both Mr Hall and Mr Héroult went go looking for industrial partners. In the US, Mr Hall soon found partners, to start with what later on become the Alcoa group. In France, Mr Héroult naturally visited the Pechiney company, that was already producing (chimically) aluminium, but was rebuffed. He eventually found partners in Switzerland , including the AEG company. That group of partners later became the Alusuisse company.

Thereafter, thanks to this new production process , the price of aluminium began to drop, very sharply.
Now, gold is worth around 35.000 €/Kg, whilst aluminium costs some 2 €/Kg