Join sections of train track by preheating rail ends in preparation for the thermite charge. Thermite [from Thermit, a trade name], is a mixture of powdered or granular aluminum metal and powdered iron oxide. When ignited, it gives off large amounts of heat. It is used in welding large parts, e.g., castings, shafts, pipes, and steel rails.
In the process the thermite, contained in a crucible, is ignited. The aluminum reduces the iron oxide to molten iron and forms a slag of aluminum oxide on its surface. The reaction is very exothermic; temperatures above 2,500°C (4,500°F) are often reached. Typically, the molten iron is poured into the joint to be welded, providing both heat for fusion and filler metal. Excess metal may be removed when the weld cools.
