Question

Write the principle involved in zone refining of metals.

Answer 1

Hint: They are a group of similar methods of purifying crystals, during which a narrow area of a crystal is melted, and this molten zone travels along with the crystal. It is the procedure of purifying a crystal wherein a thin section of the crystal experience melting.

Complete answer:
The principle involved in zone refining is that the impurities in a slab or ore of the metal are highly soluble inside the liquify medium in comparison to the counterpart solid-state of the impurities. In the zone refining procedure, the impurities are gathered at one terminal of the block of metal in order that the remainder of the block is purified. It is often noted that the segregation coefficient (which is defined because the ratio of impurity within the solid-state to the impurity within the liquid or melt state) is generally less than 1. This suggests that when the conditions are set at the solid-liquid boundary, the atoms of the impurity serve to diffuse within the liquid region.

Additional information:
In the zone refining procedure, a circular mobile heater is secured at one terminal of the metal rod which is produced from the impure metal. Now the circular mobile heater is progressing randomly beyond the metal rod. The metallic impurities liquify at the temporary area of this heater. The liquefy containing the impurities progress forward alongside the heater by everything on the metal rod. The pure metal is left to solidify as the heater travels across the rod. As the heater travels forward, the concentration of the impurities within the liquify increases. This is because the impurities are highly soluble in their conterminous liquefy state. Ultimately, the impurities are gathered at one end of the metal rod. The terminal of the rod in which the impurities have now gathered is cut off, leaving behind the pure metal.

Note:
Zone refining is a very important and useful procedure to obtain metals with very high purity like silicon and germanium. It is also mentioned as zone melting, floating zone process, and traveling melting zone. For zone melting, numbers of heaters are commonly utilized, with their most important characteristic being the power to make short molten zones that move slowly and uniformly through the ingot. While production of a transistor, an ingot of germanium is firstly purified through zone refining.