Thermite is a pyrotechnic composition of a metal powder and a metal oxide, which produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminum is the reducing agent it is called an aluminothermic reaction. Most varieties are not explosive, but can create short bursts of extremely high temperatures focused on a very small area for a short period of time.
Thermites can be a diverse class of compositions. The fuels are often aluminium, magnesium, calcium, titanium, zinc, silicon, and boron. The oxidizers can be boron(III) oxide, silicon(IV) oxide, chromium(III) oxide, manganese(IV) oxide, iron(III) oxide, iron(II,III) oxide, copper(II) oxide, and lead(II,III,IV) oxide.
The most common thermite is aluminium-iron(III) oxide.
The aluminium reduces the oxide of another metal, most commonly iron oxide, because aluminium is highly reactive:
The products are aluminium oxide, free elemental iron, and a large amount of heat. The reactants are commonly powdered and mixed with a binder to keep the material solid and prevent separation.
The reaction is used for thermite welding, often used to join rail tracks. Other metal oxides can be used, such as chromium oxide, to generate elemental metal. Copper thermite, using copper oxide, is used for creating electric joints in a process called cadwelding:
Some thermite-like mixtures are used as pyrotechnic initiators such as fireworks.
Full article ▸