Introduction
Corrosion is the gradual deterioration of metals due to chemical or electrochemical reactions with their environment. The most common form is rusting of iron, which causes major economic and structural damage.

🔹 1. Definition of Corrosion

Corrosion is the electrochemical oxidation of metals in the presence of moisture, oxygen, or other reactive substances, leading to surface degradation.

🔹 2. Conditions Required for Corrosion

Especially for iron (rusting), these conditions are required:

• Presence of oxygen (O₂)

• Presence of water (H₂O)

• Electrolytes such as acids, salts, or bases (enhance corrosion)

🔹 3. Electrochemical Mechanism of Rusting (Iron)

Rusting is a redox process that occurs through tiny galvanic cells formed on the iron surface.

At Anode (oxidation):

At Cathode (reduction):

Overall Reaction (in neutral water):

Fe(OH)₃ dehydrates to form Fe₂O₃·xH₂O (brown rust)

🔹 4. Factors Accelerating Corrosion

• High humidity

• Saltwater or acidic rain

• Presence of other metals (galvanic cells)

• Polluted air (SO₂, CO₂)

• High temperatures

🔹 5. Prevention of Corrosion

🧪 Example – Galvanic Series (Tendency to Corrode)

From most active (corrodes faster) to least:

✅ Magnesium protects iron if connected in contact (sacrificial anode)

🧠 NECTA Tips

• Always write half-equations at anode and cathode

• Label oxidation/reduction zones in diagrams

• Mention physical and chemical methods of prevention

• Distinguish between rust and other forms of corrosion

✅ Summary

• Corrosion is the slow oxidation of metals, especially in moist air

• Rusting of iron involves Fe²⁺ formation and oxygen reduction

• Prevent corrosion using coatings, sacrificial metals, or alloys

• Common in NECTA theory, practical, and project-based questions