What is corrosion, its different causes and basic chemistry and how to protect corrosion.
Text of Protection of metals from corrosion
M . A W A I S Y A Q O O B Protection from Corrosion
Contents What is corrosion? Cause of corrosion Chemistry of
What is corrosion? Corrosion is the deterioration of materials
by chemical interaction with their environment.
Cause of corrosion Oxygen Humidity Chemical Salts
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
Protection. There are many methods of protecting metals against
corrosion. They are 1) Design 2) Barrier protection 3) Sacrificial
protection 4) Cathodic protection.
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.
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.
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.
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.
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
2) Sacrificial protection In this method, the surface of metal
is covered with a more electropositive metal. Sacrificial metal can
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).