Galvanised rubbish bin and zinc crystals (inset, lower right). Galvanised metal, steel or iron, has had a protective coating of zinc (Zn) applied to prevent rusting. Steel is an alloy of iron (Fe) and small amounts of carbon (C). Galvanised iron and steel are used in locations where exposure to the air and water vapour would cause rusting (the formation of iron oxide) and corrosion, eventually causing the iron or steel object to weaken and collapse. The zinc coating does react with the oxygen and water in the air, forming an impermeable and protective layer of zinc carbonate that slows further corrosion. Rusting will eventually occur as the zinc coating is lost.