The reduction of a metal oxide to form metal by using aluminium powder as a reducing agent is called a thermite reaction.

This property of reduction by aluminium is made use of in thermite welding for joining the broken pieces of heavy iron objects like girders etc.

A mixture of Iron (III) oxide and aluminium powder is ignited with a burning magnesium ribbon. Aluminium reduces iron oxide to produce iron metal with the evolution of a lot of heat. Due to this heat, iron metal is produced in the molten state. This molten iron is then poured between the broken iron pieces to weld them (to join them).

Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat