Which metal is resistant to corrosion but weak by itself, so it is used for galvanising to make other materials corrosion resistant?

• A. Zinc
• B. Tin
• C. Lead
• D. Copper

Answer: (A)

Galvanising works by using a coating that is more reactive than the metal it protects, so the coating corrodes first and shields the underlying material. Zinc is ideal for this because it is relatively soft and inexpensive, and it has a more negative electrochemical potential than iron. When zinc coats steel, it will oxidize in preference to the steel, providing sacrificial protection. Even as the coating slowly wears away, the zinc continues to protect the steel underneath, and the patina that forms on zinc helps slow further corrosion. The result is a corrosion-resistant steel product, with the zinc coating doing the protecting while itself taking the hit. Other metals like tin, lead, or copper don’t provide the same effective sacrificial protection for steel, so they aren’t used for galvanising in the same way.