4: Anodising

Aluminium is often anodised, which means it has an oxide layer artificially induced to protect it from further corrosion.

Apart from giving increased corrosion resistance, the strong protective film or passivating layer also increases the hardness of the component and allows it to be dyed different colours.

To anodise a piece of aluminium, the surface must be very clean and smooth.

If the surface is not clean then the presence of contaminants such as oils and grease will result in the formation of an incomplete oxide layer.

If the surface is not smooth rough patches may cause cracks in the oxide layer.

To anodise aluminium, you will need:

  1. A container or beaker.
  2. Moderate strength sulphuric acid or chromic acid.
  3. A clean piece of aluminium that you wish to use as the anode.
  4. A lead or stainless steel cathode.
  5. A piece of wire as a connection between the aluminium and the cathode.
  6. A power supply.