What is corrosion, its different causes and basic chemistry and how to protect corrosion.

1. M . A W A I S Y A Q O O B
Protection from Corrosion

2. Contents
 What is corrosion?
 Cause of corrosion
 Chemistry of Corrosion……
 Protection


3. What is corrosion?
 Corrosion is the deterioration of materials by chemical
interaction with their environment.

4. Cause of corrosion
 Oxygen
 Humidity
 Chemical Salts

5. Chemistry of Corrosion……
 When a metal is exposed to atmospheric oxygen in
the presence of water, the well known rusting
process takes place.
 e.g. “Iron”, when exposed to atmosphere, the
metal is degraded to form ferric rust, a red-brown
compound is formed.
4Fe + 3O2 + 2H2O → 4FeO.OH

6. Cont……

7. Protection……….
 There are many methods of protecting metals against corrosion.
 They are
1) Design
2) Barrier protection
3) Sacrificial protection
4) Cathodic protection.

8. 1) Design
 Generally speaking we want a design that:
• Avoids entrapment of water.
• Shape should be round.
• Allows access for surface preparation and coating
operations.

10. 1) Barrier protection
 Here, a thin barrier is developed between the surface of iron and atmosphere
by one of the following methods:
 a) Painting of the surface
 b) Coating the surface with a thin film of oil or grease
 c) Developing a thin layer of some non –corrosive metal like nickel,
chromium copper etc., by electroplating.

11. a) Painting of the surface
To do paint on a metal surface is the most common
and useful method of prevention from corrosion.
Paint, an organic compound , actually prevents the
metal surface from direct interact with the moisture
or any other chemical.

12. b) Coating the surface with a thin film of oil or grease
 This type of method is just as to paint on the surface
of metal but the main difference is that here in oily
method we just cover the surface with an oil or
grease.
 The basic purpose of oiling the surface is is to creat
hindrence for moisture to get interact with metal
surface.
 Grease better than oil as it is more thick than oil and
covers the surface.

13. c) Developing a thin layer of some non –corrosive metal by electroplating.
 This mehtod is known as some how electrochemivcal
metod to avoid from corrosion.
 In this method we use the technique of electroplating
to cover up the surface of objective material

14. 2) Sacrificial protection
 In this method, the surface of metal is covered with a
more electropositive metal.
 Sacrificial metal can be

15. 3) Cathodic protection.
 This method is especially used for underground iron
pipes
 . Here, the iron pipe or tank is connected to a more
electropositive metal like magnesium or aluminum.
 . The more electropositive metal acts like anode
(supplies electrons) and iron acts like cathode (receives
electrons).