A thermite reaction is iron oxide (rust) reacting with aluminum to produce molten iron. The reaction is initiated by the heat from burning magnesium ribbon which is placed in the iron oxide/aluminum mixture.
Thermite reaction is useful because it is often used to join rail tracks, and some thermite mixtures are even used to generate fireworks. Copper thermite is used for welding together thick copper wires. Thermite hand grenades and charges are typically used by armed forces in both an anti-materiel role and in the partial destruction of equipment, the latter being common when time is not available for safer or more thorough methods.
Iron (II) Oxide plus 2 aluminum react to produce 2 iron and aluminum oxide
Fe2O3 + 2Al → 2Fe + Al2O3
