Small amounts of very pure metals (Ti, Zr, or Bi) can be produced by this method. This process is based on the fact that iodides are the least stable of the halides. The impure element is heated with iodine, producing a volatile iodide, TiI4, ZrI4, or BiI3. These are decomposed by passing the gas over an electrically heated filament of tungsten or tantalum that is white hot. The element is deposited on the filament and the iodine is recycled. As more metal is deposited on the filament, it conducts electricity better. Thus, more electric current must be passed to keep it white hot. Thus the filament grows fatter and eventually the metal is recovered. The tungsten core is distilled out of the center and a small amount
of high purity metal is obtained.
Impure Ti + 2I2 (50–250ºC)-->TiI4 Tungsten filament(1400ºC)-->Ti+ 2I2
The method is very expensive and is employed for the preparation of very pure metal for specific use.
