Thermite

a mixture of powdered aluminum or, less frequently, magnesium and any of a number of metal oxides (iron, nickel, and so on). When thermite is ignited by a firing mixture, simultaneous, strongly exothermic oxidation and reduction reactions occur: the aluminum or magnesium is oxidized by oxygen from the oxide, and the oxide metal is reduced. The large quantity of heat evolved raises the temperature of the reaction products above 2000°C. The quantitative relationship between the components of the mixture is stoichiometric.

Iron-aluminum thermite, which is the most common, contains calcined scale or rich iron ore and is used for welding rails and in casting large machine parts. This type of thermite ignites at about 1300°C (the firing mixture ignites at 800°C), and the iron and slag that are produced may reach a temperature of 2400°C. Iron filings, alloying additives, and fluxes are sometimes added as constituents of iron thermite. The process is performed in a magnesite crucible. Special thermite mixtures are available for welding telephone and telegraph lines.

In military technology, thermites are used as incendiary compositions. In the production of ferroalloys, a thermite mixed with a flux is called a charge.