Question

What do you mean by metal corrosion? Explain three methods for prevention of corrosion.

Answer 1

Metal corrosion:
It is deterioration of metals by a redox process in which metals are oxidized by oxygen in presence of moisture. For example, rust on iron, loss of luster of Ag, a green film formed on copper and brass.
Methods for prevention of corrosion:
(1) Galvanisation: Steel and iron is protected from rusting by coating with a thin layer of zinc.The galvanised article is protected against rusting even if the zinc coating is broken.
(2) Cathodic protection: More easily oxidized metal (such as Mg or Zn) is attached to the metal (Fe) to be protected from corrosion. Fe acts as cathode and Mg or Zn acts as sacrificial anode.
(3) Passivation: The metal surface is made inactive. The metal is treated with strong oxidizing agent such as conc $HN{O}_3$. A thin oxide layer is formed on metal surface.
(4) Painting, greasing and oiling.
(5) Chrome plating and making alloys.