Zone refining is a purification technique that is based on the principle that impurities tend to concentrate in the molten zone of a solid. The process involves repeatedly passing a molten zone through the solid material, allowing the impurities to segregate into the molten zone, which is then removed. The molten zone can be created by using a variety of techniques, including resistance heating, induction heating, or electron beam heating.

The process begins with the solid material being placed in a crucible. The crucible is then heated until the material melts, creating a molten zone. The molten zone is then slowly moved through the solid material, allowing the impurities to concentrate in the molten zone. The molten zone is then removed, and the process is repeated until the desired level of purity is achieved.

Zone refining is a very effective purification technique, and it can be used to remove a variety of impurities from metals, semiconductors, and other materials. It is often used in the production of high-purity materials for electronic and medical applications.