Corrosion
(Short Note)
Definition
Corrosion is the deterioration of a
metal, as a result of its reactions with the environment or any chemical agent.
It is an oxidation process that
occurs at the surface of the metal.
Causes of
Corrosion
Corrosion may be regarded as the
natural tendency of metals to return to their oxidized state. The main causes
of corrosion are as follows.
1. The atmosphere
2. Submersion in water
3. Underground Soil Attack
4. Emersion in chemicals
5. Corrosive gases
The most important of these is the
atmosphere.
Examples of Corrosion
Some familiar examples of corrosion
are as follows.
1. Rusting of Iron
2. Detarnishing of silver
3. Development of green coating on
copper, brass and bronze.
Types of Corrosion
There are two types of corrosion.
1.
Atmospheric Corrosion
When corrosion in metal is due to the
action of atmosphere, it is known as atmospheric corrosion.
2. Corrosion
in Liquid
When corrosion in metal is due to the
reaction of a liquid on a metal, it is known as corrosion in liquid.
Rate of Corrosion
Corrosion is a chemical process.
Different metals corrode at different rates. Gold does not corrode at all. Iron
corrodes slowly. Tin, lead, copper and silver corrode very slowly.
Prevention From Corrosion
Corrosion causes great damages to
metallic articles such as bridges, ships and vehicles. It has been found out
that due to corrosion, one fifth of iron is lost annually. Therefore, any one
of the following methods are adopted to prevent corrosion.
1. Protective
Metallic Coating
In this method, the metal is coated
with a thin layer of less oxidizing metal, which reduces the rate of corrosion.
For example, corrosion of iron is prevented by coating it with zinc, tin or chromium.
2.
Non-Metallic Material Coating
In this method, the metal is coated
with a thin layer of non metallic material such as paints, oils, grease,
plastic emulsion, enamels etc. For example, red lead (Pb3O4) and zinc chromate
(ZnCrO4) are often used for this purpose.
3. Alloying
of Metals
Metals can be made more reistant
against corrosion by making their alloys. For example, stainless steal is an
alloy of Fe, Cr and Ni.
4.
Electro-Plating
Noble and bare metals are used for
Electro-Plating on any desired metal.
0 comments :
Post a Comment