CORROSION l RUSTING OF IRON l GALVANIZATION

1. CORROSION
STD 12 SCI ( E )
CHAPTER-3 –
ELECTROCHEMISTRY
BY :- MS. MAYRI R SOMPURA
HJD INSTITUTE KERA-KUTCH

2. CORROSION
Deterioration of the metal ( physical
properties )
Copper – green covering
Aluminum and silver – greyish black spots
Iron – reddish brown spots

3. • it is because of the exposure of iron surface to the atmospheric gases and
moisture.
• It is a reddish brown powder- RUST Fe2O3.X H2O
RUSTING OF IRON

4. ELECTROCHEMICAL THEORY OF RUSTING:-
• Atmospheric gases:-
• CO2 + H2O → H2CO3
• Ionization of H2CO3:-
• H2CO3 → 2H+ + CO-2
3
• Anode (oxidation)
• 2 Fe → 2 Fe+2 + 4 e-
• Cathode (reduction)
• 4 H+ + O2 + 4 e- → 2H2O
• RUSTING :-
• 2 Fe+2 + 4 H2O + O2 → Fe2O3
• Fe2O3 + X H2O → Fe2O3.X H2O

5. FACTORS AFFECTING RUSTING :-
• Moisture content in atmosphere.
• Nature of metal.
Impure iron rusts fast
Pure iron do not rust fast
• Amount of impurities
• Amount of electrolytes present.
• More reactive the metal more readily it corrodes ( forming metal oxides on
the surface)

6. PREVENTION OF CORROSION :-
• Grease oil lubrication
• Anti rust solution
• Barrier method – GALVANIZATION
• Galvanization is covering iron metal surface with a layer of zinc.
• Can also be coated by less electropositive metal like tin (Sn).
Zinc readily reacts
with atmospheric
oxygen.
Hence zinc gets
oxidized and it
depleates eventually
and iron remains safe.