corrosion and its reason and prevention

1. Submitted to:
Dr. Nida Iqbal
Presented by:
Meezan Hamid 2017-BME-12
Nimra Razzaq 2017-BME-34
Rameen Fatima 2017-BME-45
Iraj Fatima 2017-BME-46

2. Assignment no.2
Lab assignment

3. Corrosion
 The process of corroding or being corroded
 Damage caused to metal, stone, or other materials by corrosion

4. Chemistry of
corrosion in basic
medium:
 Weight of specimen increased in
basic media
 reducing the rate of corrosion as
the pH increases.
 basic medium rate of corrosion is
decreases.
Chemistry of
corrosion in acidic
medium:
 The corrosion of metals is
accelerated in acidic
environment when compare to
basic or neutral environment.
 When ph is less than 3 hydrogen
ion can directly oxidize the metal.
Due to these reactions corrosion
rate of metals increases as ph is
decreases.

5. Effect of mild steel and stainless steel in basic
medium:
 The weight-loss of mild steel in 1M NaOH
 Variation of weight-loss and corrosion rate with exposure time
 The specimen corroded in the solution (control) by an electrochemical
mechanism involving its oxidation as ions according to:
 Fe → Fe2++ 2e–

6. Effect of mild steel and stainless steel in acidic
medium:
 The corrosion behavior of stainless steel and mild steel in HCl acidic solution was
studied by chemicals and electrochemical methods.
 The chemical results revealed that mild steel and stainless steel corrodes in HCl
solution.
 In acidic medium oxide layer is formed on surface of mild steel and stainless
steel which accelerate the rate of corrosion in acidic medium.
 Corrosion crate increase with the increase in acidic concentration. The corrosion
rate of mild steel is high in first 3 days after than it decreases gradually.

7. Reaction at anode:
Oxidized
Metal Reaction Potential
(wrt H2)
Copper: Cu Cu2+ + 2 e- 0.3419
Nickel: Ni Ni2+ + 2 e- -0.257
Magnesium: Mg Mg+ + e- -2.7

8. Reaction at anode

9. How to prevent it
 Maintaining the purity of the metals
 Alloying with other elements
 It is to found that alloying with suitable elements increase corrosion
resistances of most metals
 Modification of environment
 Protective coatings