Write short note on van Arkel method of refining of metals.

Explanation

It is a vapour phase refining process used for the purification of metals like titanium and zirconium. In this method impure zirconium (or titanium) is heated in iodine vapour at about 870 K to form volatile `ZrI_(4)`. The latter when heated over a tungsten filament at 2075 K decomposes to give pure zirconium.
`underset(("Impure"))(Zr)+underset((I_(2)"Vapour"))(2I_(2)) overset(870K)to ZrI_(4) overset(2075K) underset("Tungsten Filament")to underset(("Pure"))(Zr)+2I_(2)`