Explain the effect of following factors on the rate of corrosion.

1. Nature of corrosion product
2. Ratio of anodic to cathodic area 

Nature of corrosion product

Corrosion product is always formation of oxide layer on the surface of the metal. This oxide layer act as protective film. If this product is porous, then rate of corrosion continues If the product is non-porous, rate of corrosion stops. 

 

Ratio of anodic to cathodic area

When anode is small and cathode is large, all the electrons liberated at anode and are consumed at the cathode. This further intensifies the anodic reaction leading to increase in overall rate of corrosion. When anode is large and cathode is small, all the electrons liberated at anode and are not consumed at the cathode. So rate of corrosion is less.