Describe the principle controlling each of the following processes :
Vapour phase refining of titanium metal.

Explanation

In this method, the metal is converted into its volatile compound and collected elsewhere. It is then decomposed to give pure metal. The requirements are :
(i) The metal should form a volatile compound with an easily available reagent.
(ii) The volatile compound should be easily decomposable, so that the recovery of the metal is easy.
Titanium is purified using this principle.
Titanium is reacted with iodine to form volatile titanium iodine which is then decomposed on tungsten filament at 1800K.
`Ti +2I_(2) to TiI_(4)`
`TiI_(4) overset(1800K) (to) Ti +2I_(2)`.