Corrosion is an unwanted reaction of metal atoms with atmospheric oxygen in presence of moisture.

1. Corrosion, Stainless Steel &
Tin Plating
XII CHEMISTRY CHAPTER 5
SIDRA JAVED

2. Corrosion
A harmful and unwanted reaction
of a metal as a result of
exposure to atmosphere or any
chemical agent.
Almost all metals except noble
metals (Ag, Au, Pt) show great
tendency to corrode at
different rates.

4. Types of corrosion
1.Atmospheric Corrosion:
By the action of air
2.Corrosion in Liquids:
Due to reaction of a
liquid on metal surface

5. Disadvantage of
Corrosion
About 1/5th of Iron in use
is lost annually
Reduction in strength of
iron structures
Loss of Billions of dollars

6. Methods to Prevent
Corrosion

7. Protective Metallic Coating
Tin Plating or Galvanization
(Zinc Coated iron)

8. Electroplating
Plating of noble metals
Ag, Au, Pt etc

9. Alloying of metals

10. Coating with non
metallic materials

11. Stainless SteelStainless
Steel

12. Stainless steel
Alloys of iron that are corrosion resistant.
Formed by addition of chromium or chromium and nickel into
steel.
They are oxidizable to such slight degree thata thin layer of
oxide is formed on the surface which prevents further
corrosion.

13. Stainless
Steel
Iron based alloys which show
resistance to corrosion
Formed by the addition of Chromium
or Chromium and Nickel in steel

14. Types
1. Stainless steel containing 13% Cr and 0.1 to 0.4
% C
2. Stainless steel containing 17% Cr and 2% Ni
3. Stainless steel containing 18% Cr and 6% Ni

15. Corrosion resistance
All types of steel are corrosion resistant alloys
Only oxidizable to such slight degree that a thin layer of oxide is
formed on surface of metal which resist further corrosion.
The oxide layer is so thin that the apperance and color of basic
material looks like unchanged.

16. Uses of stainless steel
House hold utensils
Cutlery
Decorative objects
Industrail uses

17. Tin plating

18. Tin plating
An art of making coat of
metallic tin on baser
metals such as iron and
copper for their
protection from corrosion
and poisoning.

19. Mechanical tin plating
Iron sheets are cleaned and dipped in warm dilute
sulphuric acid to remove oxide films
Sheets are washed with water and dried.
Dried sheets are dipped in molten tin.
The sheets are then rolled to remove excess tin.

20. Mechanical tin plating
Copper and brass utensils are heated and rubbed with
NH4Cl to remove oxide layer
Tin metal is rubbed over hot surface after sprinkling
NH4Cl.
Utensils are polished with rag until a uniform layer of
tin is obtained.

21. Electrolytic tin
plating
Iron sheets are cleaned, washed,
dried and then suspended into a
bath containing Stannous chloride
and HCl.
Anode is made up of pure tin and
iron sheets are made the cathode.
On passing current throught the
bath, tin starts depositing on iron
sheets.

22. End of lesson