Anodic protection: this involves the protection of a metal part by making it more anode by applying a direct current.

The schematic representation of anodic protection is shown in figure

It consist of an auxiliary electrode made of corrosion resistant metal like platinum as cathode .the tank which is the metal part to be protected from corroding medium acts as the anode .the current and potential is maintained such that the metal gets oxidised and retain its passivation for further oxidation . This method is applicable to metals that have a good passivation

Passively or passivation is the phenomenon in which a metal or an alloy exhibits a much higher corrosion resistant than expected from its position in electrochemical series

Protective coating

Protecting the surface of an object by the application of coating for preventing corrosion. A coated surface isolates the underlying metal from the corroding environment to the coating applied must be chemically inert to the penetration of the environment to the material.

Types of protective coatings

There are two types of metallic coatings:

a) Anodic coating These are produces by coating metals which are anodic to the base metal which is to be protected Zn , Al, and Cd are used as anodic coating whose electrode potential are higher than the base metal. Base metal acts as the cathode .when subjected to corroding environment ,the coating undergoes corrosion and protected the base metal

b) Cathodic coatingThese are obtained by coating a more stable metal (which have lower electrode potential)On the base metal .the cathodic coating protect the base metal and have high corrosion resistance Cathodic coating is effective only when it is continues and free from pores and discontinued damaged coatings have severe corrosion problems.Consider the case where iron is to be protected , for example consider a tin coating on iron is very effective when completely coated .if there is a small puncture ,tin becomes the cathode ,while the exposed iron acts as anode and causes on localised corrosion attack and result in severe pitting .