THERMITE MIXTURES
Thermites are mixtures that produce a high heat concentration, usually in the form of molten products. Thermite compositions contain a metal oxide as the oxidizer and a metal -- usually aluminum - as the fuel, although other active metals may be used.
A minimum amount of gas is produced, enabling the heat of reaction to concentrate in the solid and liquid products. High reaction temperatures can be achieved in the absence of volatile materials; typically, values of 2000-2800°C are reached. A metal product such as iron, with a wide liquid range (melting point 1535°C, boiling point 2800°C) produces the best thermite behavior. Upon ignition, a thermite mixture will form aluminum oxide and the metal corresponding to the starting metal oxide:
Thermite mixtures have found application as incendiary compositions and spot-welding mixtures. They are also used for the intentional demolition of machinery and for the destruction of documents. Thermites are usually produced without a binder or with a minimum of binder), because the gaseous products resulting from the combustion of the organic binder will carry away heat and cool the reaction.
Iron oxide (Fe 2O 3 or Fe3O 4 ) with aluminum metal is the classic thermite mixture. The particle size of the aluminum should be somewhat coarse to prevent the reaction from being too rapid. Thermites tend to be quite safe to manufacture, and they are rather insensitive to most ignition stimuli. In fact, the major problem with most thermites is getting them to ignite, and a strong first fire is usually needed.
Calorific data for a variety of aluminum thermite mixtures are given in the table.
Calorific Data for Thermite Mixturesa