Zone refining :
→ Zone refining is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal.
→ A circular mobile heater is fixed at one end of a rod of impure metal.
→ The molten zone moves along with the heater moves forward the pure metal crystallises out of the melt and the impurities pass into the adjacent molten zone.
→ The above process is repeated several times and the heater is moved in the same direction form one end to the other end. At one end impurities get concentrated. This end is cut off.
→ This method is very useful for producing semiconductor grade metals of very high purity.
Eg : Ge, Si, B, Ga etc...
