zone melting or zone refiningn. A purification technique for crystalline substances in which a heating system passes slowly over a bar of the material to be refined, creating a molten region that carries impurities with it across the bar.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.zone refining n (Chemical Engineering) a technique for producing solids of extreme purity, esp for use in semiconductors. The material, in the form of a bar, is melted in one small region that is passed along the solid. Impurities concentrate in the melt and are moved to the end of the bar Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014