Question

1. Tin and zinc can be used to protect mild steel from corrosion. Explain the function of

these coatings. Explain how these coatings will behave when scratched to expose the

underlying steel.

Answer 1

The main aim of zinc and tin coating on mild steel is to prevent the corrosion i. e. It prevents corrosive substances like oxygen and water from iron.

Also it gives the good appearance on mild steel and zinc and tin are easily available in nature.

As zinc is more reactive metal than iron, zinc act as a sacrificial material to prevent rusting of iron. If small scratch is present on zinc coated iron, zinc act as anode due to more reactive metal and iron act a cathode and electrons from zinc can give easily to oxygen so it protect the iron.

Due to more reactive nature of zinc metal than iron, even if electrons from iron are loss, zinc will replace it, so it protects the iron. So scratched steel will protect from remaining zinc present over it.

In case of tin, it's less reactive metal than iron so it is not sacrificial material like zinc, so it act only like physical barrier between corrosive medium and iron. If coating scratched in tinning, iron will oxidize so tinning used like painting to avoid corrosion.