Corrosion, Steel and Tin plating

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.

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

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

5. Methods to Prevent Corrosion

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

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

8. Alloying of metals

9. Coating with non metallic materials

10. Stainless SteelStainless Steel

11. 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.

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

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

14. 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.

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

16. Tin plating

17. 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.

18. 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.

19. Mechanical tin plating Copper and brass utensils are heated and rubbed with NH 4 Cl to remove oxide layer Tin metal is rubbed over hot surface after sprinkling NH 4 Cl. Utensils are polished with rag until a uniform layer of tin is obtained.

20. 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.

21. End of lesson