Aluminium develops a thin oxide layer when exposed to air. This alurninium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker. This process is called anodising.
During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish.
