Question

What is the meaning of corrosion of metals? What are the measures to prevent them?

Answer 1

Corrosion is an electrochemical phenomenon. It is a redox process leading to the deteroration of metals. Oxygen and moisture oxidises metals. Examples of corrosion include rust on iron, loss of lustur of silver, a green film formed on copper and brass.
Metals can be protected from corrosion by the following methods.
(1) Metal surface is coated by paints.
(2) The metal to be protected (such as iron) is coated with metal which is stronger reducing agent (such as zinc). The method is known as galvanizing.
(3) In cathodic protection, the metal to be protected from corrosion is connected to more easily oxidisable metal.
(4) In passivation, metal surface is made inactive by treating with strong oxidising agent such as conc. nitric acid. A thin oxide layer is formed on metal surface.
(5) Iron metal is protected from corrosion by forming alloy with other metals. Thus stainless steel is an alloy of iron and chromium.