The Background History About Aluminium.
In 1825, a Danish scientist H.C. Oersted used metallic potassium to chemically reduce aluminium from one of its compounds. The cost of aluminium in the very early days was around 250.00 English pounds per kilo to produce, much more than gold.
Even Napoleon was reported to have been privileged to use Aluminium knives and forks when eating. French nobility had to be content with silver or gold tableware?
Metallurgists, Hall (America) & Heroult, (France) discovered the process for extracting aluminium from the ore of bauxite in the year of 1886, but the metal remained an expensive commodity until the beginning of the 1900s.
The first & second world wars, saw a huge demand for this strong, light & versatile metal, particularly in the manufacture of aircraft.
Modern technology has pushed the annual production of Aluminium second only to iron in world production terms.
The ore of aluminium is called bauxite, it contains aluminium oxide (Al203). Bauxite ore itself cannot be reduced to metal by heating it with coke as with iron, for the simple reason that Aluminium atoms are too firmly combined with oxygen atoms to be detached by carbon.
An electrolytic smelting process is used to decompose the bauxite and release the aluminium, which consumes about 91 mega joules of electricity to produce I.kg of Al metal, so large amounts of cheap electrical power must be available to the smelters.
Most of the world’s aluminium was produced in the USA, Canada, & Norway. However, Australia also has vast deposits of bauxite, and has large smelters located near the major power producers in the country.
Crude pig iron is purified or converted to steel by blowing oxygen through it, which burns out the impurities, this is not possible with aluminium as the metal would simply burn away, and leave you with useless impurities.
A chemical process is first used to purify the bauxite, then the pure aluminium oxide is decomposed by electrolysis.
Aluminium oxide has a very high melting point, (Used in ceramics and foundry crucibles) it is mixed with another aluminium mineral called cryolite, to form an electrolyte, which will melt at a low temperature. (Aluminium oxide is used in abrasive grinding wheels and in the manufacture of crucibles)
The advantage of aluminium is that the metal can be remelted or recycled many times with out too much degradation, aluminium is available in many different grades depending on it’s end use.
Next time you are breaking down a piece of scrap aluminium to place into your crucible to melt, spare a thought for the journey it has travelled before you acquired it for your hobby foundry casting projects!