zone-refininghttp://www.oed.com/dictionary/zone-refining_n%3Ftab%3Dmeaning_and_usezone refining, n.
First published 1986; not fully revised

zone refiningnoun

  1. 1952–
    A method of refining used to produce semiconductors and metals of very high purity by causing narrow zones of molten material to travel slowly along an otherwise solid rod or bar, so that impurities become concentrated at one end or the other if their solubilities in the liquid and the solid phases differ.
    1. 1952
      The particular merit of zone-refining becomes evident when repeated crystallizations are desired.
      W. G. Pfann in Journal Metals vol. IV. 750/2
    2. 1973
      Probably the most effective and generally used method of refining to this kind of standard is zone refining.
      J. G. Tweeddale, Materials Technology vol. I. vi. 152

Originally published as part of the entry for zone, n.

zone, n. was first published in 1921; not fully revised.