Thermal Reduction

a group of processes based on the reduction of metal compounds (oxides, halides, and other compounds) to the corresponding metals by more active metals (aluminum, magnesium, and silicon, which for this purpose is considered to be a metal) and accompanied by the evolution of heat. Such processes have been used since the turn of the 20th century. Thermal reduction processes are classified according to the reducing metal: aluminothermy, magnesiothermy, and silicothermy. Such processes are more costly than reduction processes using carbon; they are used in the production of high-quality carbon-free alloying components (hardeners with rare metals, carbon-free ferrochromium, and other alloys), titanium sponge, and other pure (mainly carbon-free) metals and alloys.

There are several varieties of thermal reduction. The out-of-furnace process is used in cases in which the quantity of heat evolved during the reduction reactions is sufficiently large to yield the reaction products in liquid form and to allow their satisfactory separation (1750°-2300°C)—for example, in aluminothermy. The electric-furnace method is used in cases where the heat evolution is inadequate for the melting and necessary superheating of the fusion products. The additional heat is supplied by means of electric heating. This process is very widespread. Vacuum thermal reduction makes possible separation of highly volatile metals, such as magnesium, during reduction under vacuum (at 800°-1400°C) or the production of metals with a low gas content.