Galvanization is the process of thin coating of zinc to the surface of iron to prevent rusting. It prevents iron from rusting either by opposing the direct contact of iron to the atmosphere or by forming a electrochemical couple.
Since , zinc has higher oxidation potential than iron, the former gets preferentially oxidized by atmospheric oxygen. In other words, zinc functions as sacrificial anode.
Galvanization can be done by any of the following ways:
1. Hot-dip method: Iron which is to be galvanised is cleaned by sand blasting and then it is washed with concentrated HCl and then with water to remove the oxide film. This process is called pickling. Then it is dipped into the molten zinc and immediately taken away. A thin layer of zinc will be coated on the iron sheet which is then passed through a roller to make it's surface smooth.
2. By electrolytic process: For this purpose, a cell is constructed which contains zinc sulphate solution as an electrolyte. Zinc is made anode and iron is made cathode. When electricity is passed, zinc gets oxidized and forms Zn++ ions. These ions again get reduced at cathode and iron gets coated with a thin layer of zinc. This is the commonly known as electrogalvanization.