How can induction heating be used in zone refining?

In zone refining, induction heating is used to create a localized molten zone within a solid material, which then travels along the length of the ingot to redistribute and remove impurities.1

The process works by surrounding the material with a water-cooled induction coil that acts as the primary winding of a transformer. When powered by an alternating current, the coil generates an electromagnetic field that induces eddy currents within the conductive workpiece, heating it to its melting point.21

A notable application of this method is float zoning, which was developed to produce ultrapure silicon for transistor manufacturing. In this technique, a vertical rod is held by end clamps, and induction heating creates a molten zone that is held in place by its own surface tension. This approach is particularly advantageous because it eliminates the need for a container, thereby preventing contamination of the material being refined. Induction heating is also used to purify other high-melting-point substances, such as tungsten, molybdenum, tantalum, and beryllium.1