Explain zone refining process with an example.

Explanation

(i) Zone refining is based on the principles of fractional crystallisation.
(ii) When an impure metal is melted and allowed solidify, the impurities will prefer to be in the molten region.
(iii) In this process the impure metal is taken in the form of a rod.
(iv) One end of the rod is heated using a mobile induction heater which results in melting of the metal on that portion of the rod.
(v) When the heater is slowly moved to the other end the pure metal crystallises while the impurities will move on to the adjacent molten zone formed due to the movement of the heater.
(vi) As the heater moves further away, the molten zone containing impurities also moves along with it.
(vii) The process is repeated several times by moving the heater in the same direction again and again to achieve the desired purity level.
(viii) THis process is carried out in an inert gas atmosphere of prevent the oxidation of metals.
Ex. Element such as germanium (Ge), silicon (Si) and galium (Ga) are refined using this process.