The aluminothermic process is still used today to prepare metals from their difficult-to-reduce oxides according to the following equation:
2 Al + 3 EO > Al2O3 + 3 E
EO = element oxide
E = element
In this reaction, the high oxygen affinity of aluminium is used to reduce the metal oxide. The energy released suffices to melt the resultant metal, so that it can flow off. The crystallised slag left behind consists of very hard and to some extent sharp-edged corundum (Al2O3).
Goldschmidt made use of the fact that a lot of heat is released during the combustion of aluminium powder, also during thermite or aluminothermic welding, which is widely used today for joining or cutting steel. Aluminium powder is mixed with iron oxide powder and ignited at about 1100 °C. The mixture burns further and produces such high temperatures that the steel parts to be welded or cut, for instance rails, melt and can be joined together or separated. In order to cut steel, concrete or stone, one injects aluminium powder into an oxy-fuel gas flame through a "powder lance", which increases its temperature considerably.