Corrosion

• Corrosion occurs when the surface of a solid, usually a metal, is eaten away by the presence of oxygen, moisture and pollutants present in the atomosphere
• When metals corrode, they are initially converted into their oxides
• The higher a metal in the reactivity series, the more rapidly it corrodes
• Corrosion of Aluminium

  A piece of aluminium forms a layer or aluminium oxide which adheres to the metal below and protects it against further corrosion
• Corrosion of Iron and Steel (Rusting)

  Iron and Steel corrode to form rust (hydrated iron oxide). Rust does not adhere to the metal below, instead it flakes off exposing fresh metal for further corrosion.
• Methods of Preventing Rusting:

  1. Coat object with paint, grease, plastic or rubber (prevents air or moisture)
  2. Coat object with zinc (galvanizing). Zinc forms adherent oxide layer to protect against further corrosion
  3. Coat object with tin
  4. Attach sacrificial anode (a piece of metal higher in the reactivity series)