Corrosion in Electrochemistry

Corrosion is a natural electrochemical process that leads to the deterioration of metals, especially in the presence of moisture and oxygen.

What is Corrosion?

Definition: Corrosion is the gradual destruction of metals due to chemical reactions with their environment, typically involving oxidation.

Common Example: Rusting of Iron

Rusting: When iron reacts with water and oxygen, it forms iron oxide (Fe₂O₃.xH₂O), which weakens the metal.

• Occurs faster in salty or humid conditions
• Electrochemical cells form on the iron surface

Types of Corrosion

• Uniform Corrosion: Even surface degradation
• Pitting Corrosion: Localized holes or pits form
• Galvanic Corrosion: Between two dissimilar metals

Methods of Corrosion Prevention

• Galvanization: Coating with zinc to protect steel
• Painting/Oiling: Prevents moisture contact
• Cathodic Protection: Uses sacrificial anodes like zinc or magnesium
• Alloying: Adding chromium (e.g., stainless steel) increases resistance

Electrochemical Basis of Corrosion

Corrosion involves the formation of electrochemical cells:

• Anode (Oxidation site): Metal loses electrons (Fe → Fe²⁺ + 2e⁻)
• Cathode (Reduction site): Oxygen is reduced (O₂ + 4H⁺ + 4e⁻ → 2H₂O)

This redox reaction is what causes the metal to corrode over time.

Practice MCQs on Corrosion

1. Which of the following metals is most prone to corrosion?
   A. Copper
   B. Gold
   C. Iron ✅
   D. Platinum
2. Rust is chemically:
   A. Fe₂O₃·xH₂O ✅
   B. FeSO₄
   C. FeCl₃
   D. FeCO₃
3. Galvanization involves coating iron with:
   A. Silver
   B. Tin
   C. Zinc ✅
   D. Chromium
4. Which method uses a sacrificial anode?
   A. Painting
   B. Electroplating
   C. Cathodic Protection ✅
   D. Plastic coating
5. Galvanic corrosion occurs between:
   A. Similar metals
   B. Coated surfaces
   C. Two dissimilar metals in contact ✅
   D. Insulated metals

Related Topics:

• Electrochemical Cells
• Electrolysis – Principle and Applications
• Corrosion – Wikipedia
• Corrosion – Britannica

Understanding corrosion is key to protecting infrastructure, saving costs, and ensuring safety.