Question

The method of zone refining of metals is based on the principle of:

• A. Greater mobility of the pure metal than that of the impurity
• B. Higher melting point of the impurity than that of the pure metal
• C. Greater noble character of the solid metal than that of the impurity
• D. Greater solubility of the impurity in the molten state than in the solid

Answer 1

Answer: (D)

Greater solubility of the impurity in the molten state than in the solid

Answer 2

Zone refining involves the use of a circular mobile heater at one end of a rod of impure metal. The heater creates a molten zone that moves along the rod as it is slowly moved forward. As the molten zone advances through the rod, the pure metal crystallizes out of the melt while the impurities are more soluble in the molten state and are carried along with the advancing molten zone. This repeated process of melting and solidifying results in the gradual purification of the metal.

So, the correct answer is (D): Greater solubility of the impurity in the molten state than in the solid