Exothermic welding, also known as exothermic bonding,
thermite welding and thermit welding is a welding
process that employs molten metal to permanently join
process employs an exothermic reaction of a thermite
composition to heat the metal, and requires no external
source of heat or current. The chemical reaction that
produces the heat is an aluminothermic reaction between
aluminium powder and a metal oxide.
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 reacting composition is five parts iron oxide
red (rust) powder and three parts aluminium powder
by weight, ignited at high temperatures.
A strongly exothermic (heat-generating) reaction occurs
that via reduction and oxidation produces a white
hot mass of molten iron and a slag of refractory aluminium
molten iron is the actual welding material; the aluminium
oxide is much less dense than the liquid iron and
so floats to the top of the reaction, so the set-up
for welding must take into account that the actual
molten metal is at the bottom of the crucible and
covered by floating slag.