Thermite mixture is a mixture of aluminum powder and iron(III) oxide. Aluminum does not react with iron(III) oxide at room temperature. However, the reaction is extremely violent if previously initiated by the heat of burning magnesium ribbon. This highly exothermic reaction can be described with the following equation:
The very negative enthalpy of this reaction is the consequence of very strong aluminum – oxygen bond in formed aluminum oxide. Temperature generated during this process is as high as 2500°C (4500°F) which is enough for the iron to be in the molten state (melting point of iron 1530°C). On the video shown you can observe that molten iron leaks out through the hole on the bottom of the pot in which the reaction was performed.
Besides iron(III) oxide, other oxides can be used (e.g. oxides of copper, manganese, cobalt and chromium), but their use is not recommended because cases of explosive reactions of aluminum and these oxides were observed.
Thermite mixture was used earlier for welding and joining metal tramway and rail tracks, but this process was substituted with much more efficient welding.
The thermite process, although generally exceeded nowadays, was used in metal industry to obtain metals from their oxide ores
Thermite mixture can be ignited while wet or under water, but this reaction is highly explosive. Namely, the molten iron extracts oxygen from water molecules, and hydrogen gas is liberated:
The liberated hydrogen gas explodes because of high temperature and oxygen present in the air. This demonstration is extremely dangerous and it is not recommended even for professionals.