Corrosion is a process that is based on concept of oxidation. In previous sessions, we have discussed about the oxidation & reduction, including the reactions based on this known as Redox reactions.

Previous learning sessions:



Corrosion is a kind of oxidation reaction in which Iron (Fe) metal gets oxidized in the presence of Oxygen. Whenever, metal comes in contact with Oxygen, metal gets oxidized and it leads to deterioration of its metallic properties.

Corrosion - Oxidation of Metal
Corrosion - Oxidation of Metal
Corrosion of Iron
Corrosion - Rusting of Iron

Steps for Corrosion of Iron:

1. Oxidation of Iron

2Fe → 2Fe2+ + 4e-

Corrosion - Oxidation of Metal
Corrosion - Oxidation of Metal

2. Reduction of Oxygen

O2 + 2H2O + 4e → 4OH

3. Iron ion + Hydroxide ion → Iron Hydroxide

2Fe2+ + 4OH → 2Fe(OH)2

4. Iron Hydroxide + Oxygen → Fe2O3.XH2O [Rust]

Effects of Corrosion


Corrosion is a harmful process for metals, because of corrosion metal lost its metallic properties.

Following are the effects of corrosion:

  • Financial Cost
    • Approx. annual worldwide cost of metallic corrosion > $2 trillion
    • 25 – 30% can be prevented with proper corrosion protection
  • Waste of Natural Resources
    • Corroded structures needs to be replaced
  • Safety Concerns
    • Due to corrosion, structures made of metals losses its strength leading to safety concerns
  • Loss of Life
  • Environmental Cost

Prevention of Corrosion


Corrosion is a harmful process for metals, but it can be prevented by using safety measures & protection techniques.

Following are effective ways to prevent corrosion:

  • Alloying
    • Iron can be alloyed with Nickel, Chromium or Carbon to form Stainless Steel
    • It helps to prevent Oxidation of Iron
  • Use Drying Agents
    • To keep metal surface clean and dry
  • Coating of Iron
    • Coating Iron with Grease, Oil, Paint or Carbon fiber
  • Passivation
    • Layer of backfill – Coat the initial site of corrosion to prevent corrosion at that site. Ex. Limestone, with underground piping
  • Galvanization
    • Coating of Zinc on Iron with Electrochemical reaction

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