Thermite
A thermite reaction is one in which aluminium metal is oxidized by an oxide of another metal, most commonly that of iron. (The name thermite is also used to refer to a mixture of two such chemicals.) 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 (with iron (III) oxide, commonly 3000°C or more). Thermite contains its own supply of oxygen, and does not require any external source (such as air). Consequently, it cannot be smothered and may ignite in any environment, given sufficient initial heat.
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 such as rail tracks, without requiring complex or heavy equipment. The reaction has also been used to purify the ores of some metals, e.g. uranium.
When thermite is made using iron (III) oxide, for maximum efficiency it should contain, by mass, 25.3% and 74.7% iron oxide. (This mixture is sold under the brand name Thermit as a heat source for welding.) The complete formula for the reaction using iron (III) oxide is as follows:
- Fe2O3 + 2Al ---> Al2O3 + 2Fe; ΔH = 851.5kJ/mol
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
