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A thermite reaction is one in which aluminium metal is oxidized by an oxide of another metal, most commonly iron. The products are aluminium oxide, free elemental metal and a great deal of heat. The reactants are commonly powdered and mixed with a binder to keep the material solid and prevent separation.

Although the reactants are stable at room temperature, when they are exposed to sufficient heat to ignite, they burn with an extremely intense exothermic reaction. The products emerge as liquids due to the high temperatures reached. Since thermite reactions require no external source of oxygen to burn, they cannot be smothered and will ignite in any environment.

Thermite reactions have many uses. Thermite grenades and bombs are used in combat as incendiary devices, able to burn through heavy armor or other fireproof barriers. Thermite can also be used for quickly cutting or welding metal without requiring complex or heavy equipment. The reaction has also been used to purify the ores of some metals, e.g. uranium.

The most common thermite reaction is that of iron oxide, which exceeds 3000°C:

Fe2O3 + 2Al -> Al2O3 + 2Fe + 851.5kJ

Thermit is also a trade name for a mixture of powdered iron oxide and aluminium, sold for use in welding applications.

Thermite should not be confused with a thermal lance.

See also