Question

Explain how, a reduction reaction of aluminium can be used for welding cracked machine parts of iron. Write a chemical equation for the reaction involved.

Answer 1

When iron (III) oxide and aluminium powder are heated together, aluminium acts as a reducing agent, reducing iron (III) oxide to iron metal. It also oxidises to aluminium oxide, releasing excess heat.  As excess heat is liberated during the reaction, the product, i.e., iron metal, forms in a molten state.  This reaction is an oxidation-reduction reaction, and its chemical equation is:

\[\ce{\underset{Iron (III) oxide}{Fe2O3_{(s)}} + \underset{(Reducing agent)}{\underset{Aluminium powder}{2Al_{(s)}}} -> \underset{(Molten state)}{\underset{Iron metal}{2Fe_{(l)}}} + \underset{Aluminium oxide}{Al2O3_{(s)}} + Heat}\]

This reaction is called as thermite reaction. This reaction is widely used to weld cracked iron machine parts. This is called thermite welding.