Key learning points

1. Corrosion is a general process of degradation of metals through various causes.
2. Rusting is a specific type of corrosion, affecting iron in the presence of air and moisture.
3. A metal oxide layer can protect the underlying metal if the oxide forms a physical barrier.
4. Some coatings are reactive and contain a more reactive metal to provide sacrificial protection, e.g. zinc to galvanise.
5. Electroplating can be used to improve the appearance and/or the resistance to corrosion of metal objects.

Keywords

• Rusting - The corrosion of iron or steel, in the presence of water and oxygen.

• Corrosion - The gradual deterioration of a substance when it reacts with substances in the environment, for example when a metal oxidises in air.

• Sacrificial protection - Using a more reactive metal to corrode preferentially, to protect another metal from corrosion.

• Tarnishing - The process by which a thin, discoloured layer forms on the surface of a metal due to reactions with the environment, e.g. oxidation.

• Electroplating - A process that uses electricity to deposit a thin layer of metal onto the surface of another conductive object.

Common misconception