Describe the underlying principle of each of the following metal refining methods :
Vapour phase refining of metals.

Explanation

This method is used for preparing ultrapure metals. In this method, the impure metal is first converted into a volatile stable compound (generally iodide) leaving behind the impurities. It is then decomposed at a higher temperature to give pure metal. Metals like titanium, thorium, uranium and zirconium are purified.
`{:(Ti+2I_(2)overset(500K)(to)TiI_(4)overset(1700K)(to)Ti+2I_(2)),(" Impure metal Volatile compound Pure metal "):}`.