4. CORROSION:
Conversion of metals into various compounds by
natural means or agencies is described as
corrosion. Corrosion of ferrous metals appears in
the form of rusting.
Corrosion of metals is explained in two ways.
One is by the formation of oxides. As in case of
iron, reaction with oxygen, carbon dioxide and
water results in the formation of bicarbonate,
which in turn alters into carbonate and finally
changes into hydrated oxide. Continued---
5. According to other explanation, the
metal surface processes areas which
act as cathode and anodes. The
presence of electrolytes like water or
moisture etc provides a contact
between such areas which results in
corrosion.
6. Protection against Corrosion:
Ferrous metals have tendency for
corrosion. It is maximum for steel and least
for cast iron. Wrought iron has a moderate
tendency to rust. Therefore, all the products
require a protective cover to prevent the
possibility of corrosion and thereby adding
to its durability. Various methods which are
in commonly used include Electroplating,
Galvanizing, Tin plating, Metal spraying,
Painting, etc.
7. (1) Electroplating:
This method involves the use of electric current to
give a coating of chromium or nickel which is
highly resistant to corrosion.
(2) Galvanizing:
In this method zinc is used to give a coating on the
ferrous metal products.
(3)Tin Plating:
This method is similar to the galvanizing process.
The iron products are thoroughly cleaned and
washed. Then these are dipped into the hot molten
tin and it will give protection against corrosion.
8. (4) Metal Spraying:
This method involves the use of a special sprayer
in which fuel gas, oxygen and air are used to
make flame. The wire of metal to be sprayed like
zinc, tin, or aluminium is used in these sprayers.
The wire metals and a thin layer is sprayed over
the ferrous metal items.
(5) Painting:
The iron made goods are often coated with paint.
Care should be taken to first clean the iron surface
thoroughly and then give a good coating of good
quality paint.
