Chemistry – Metals - Corrosion of metals | e-Consult
Metals - Corrosion of metals (1 questions)
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Galvanisation is an effective method of preventing rusting because it utilizes a principle of electrochemical protection. It involves coating iron with a layer of zinc. Zinc is more reactive than iron, meaning it has a greater tendency to lose electrons.
When the iron is exposed to the environment, a potential difference is established between the zinc coating and the iron. The zinc acts as the anode and corrodes preferentially, protecting the iron as the cathode. Here's the electrochemical process:
- Anodic Reaction (Zinc): At the zinc coating, zinc atoms lose electrons and become zinc ions (Zn2+). This is oxidation.
Zn(s) → Zn2+(aq) + 2e- - Cathodic Reaction (Iron): At the iron surface, oxygen from the air gains electrons and reacts with water to form hydroxide ions. This is reduction.
O2(g) + 2H2O(l) + 4e- → 4OH-(aq) - Electron Flow: The electrons released from the zinc atoms flow through the zinc coating to the iron surface.
- Protection: The zinc ions (Zn2+) formed at the anode dissolve into the electrolyte (e.g., rainwater) and prevent the iron from being oxidized. The zinc coating essentially sacrifices itself to protect the iron.
Therefore, galvanisation provides a barrier and also offers sacrificial protection, making it a highly effective method for preventing rusting.