Question

What is the mechanism of corrosion?

Answer 1

Hint :Corrosion is not a good thing, it is actually harmful for metals and other surfaces. It is not limited to any particular metal or substance, but mostly corrosion is seen on metal surfaces and it grows gradually.

Complete Step By Step Answer:
Corrosion mostly takes place in a moist environment, that conditions help corrosion reaction to take place on the metal surface. Corrosion is not an overnight process, it occurs due to the interaction of the environment with the metal surface and it is gradual.
So corrosion is basically loss of material from the surface of any metal or non-metal. Corrosion occurs due to certain reactions happening on the surface with the environmental conditions.
Let us consider a metal plate for example.
Now, due to the presence of moisture in the air, an oxidation reaction occurs on the metal surface. The high energized area of the metal surface acts as an anode and the low energized area on the metal surface acts as a cathode.
Thus an electrochemical reaction starts on the surface between anode and cathode. The metal on the surface gets ionized due to removal of electrons at anode and hydroxide ion is formed due to the reaction of oxygen and water molecules.
The metal and hydroxide ions combine to form metal hydroxide and ultimately metal oxide from the reaction. Thus, the metal from the surface gets removed in the form of its own oxide.
Let us take an example of iron being corroded. The reactions of corrosion are given below.
  $Fe\stackrel{}{\to }F{e}^{2+}+2e-$
At first iron loses its electrons at anode and forms its ion.
  $O_2+2H_{2}O+4e-\stackrel{}{\to }4O{H}^{-}$
Hydroxide ions are formed by the reaction of oxygen and water present in air.
  $F{e}^{2+}+2O{H}^{-}\stackrel{}{\to }Fe{(OH)}_2$
Thus, iron hydroxide is formed.
Further reaction of iron hydroxide with another hydroxide ion will give us iron oxide. The chemical formula of iron oxide is $F{e}_2{O}_3\times H_{2}O$ . Thus, this is how corrosion takes place on the surface.

Note :
It is not necessary that corrosion takes place only on metal surfaces, it can also take place on non-metal surfaces. The corrosion method shown here mostly occurs on metal surfaces, corrosion taking place on other metal or non-metal surfaces might have a different method.