Question

In what respect is galvanisation better than tin coating used for the protection of iron from corrosion?

Answer 1

1. Galvanisation is considered better than tin coating for the protection of iron from corrosion because of the fundamental difference in their protective mechanisms.
2. In galvanisation, a thin layer of zinc is deposited on iron. Zinc, being more electropositive (i.e., more reactive) than iron, undergoes oxidation in preference to iron.
3. Even if the zinc coating is scratched or cracked, the underlying iron does not rust because zinc continues to act as a sacrificial anode.
4. The electrons released from zinc oxidation migrate to the exposed iron and prevent its oxidation.
5. On the other hand, in tin coating (tinning), tin is less electropositive than iron. If the tin layer gets damaged, the exposed iron undergoes oxidation (rusts) because iron has a higher tendency to lose electrons compared to tin.
6. This results in rapid corrosion at the exposed parts, often more aggressive than if the iron were uncoated.

Thus, galvanisation offers continued protection even when damaged, making it superior to tin coating for protecting iron from corrosion.