Outline the principles involved in the following methods of refining of metals.
Vapour phase refining.

Explanation

Vapour phase refining: This method is based on the principle that certain metals like Ti, Zr, Ní etc., form volatile compounds by heating with a chemical reagent at lower temperature and these volatile compounds can easily be deomposed by heating to give pure metal. Under the reaction conditions, the impurities pressent in the impure compound either do not react with the reagent added or the compound so formed is non-volatile.