A vertical rod-like member is zone refined while supported from below and at its sides, the side support being by means of a plurality of vertical rods spaced around the rod and in contact therewith. As shown a rod 28 is supported in a cage comprising a molybdenum base plate 31, eight molybdenum tie rods 32 slidably fitted in ceramic sleeves 33 allowing longitudinal expansion, and a molybdenum top plate 30. Downward movement of the cage at a rate of 1 1/2 in./hr. is effected in a vacuum PICT:0863493/III/1 PICT:0863493/III/2 chamber 1 by means of a stainless steel wire cable 39. Heating is effected by a molybdenum susceptor ring 52 which is itself heated by an internally water-cooled copper induction coil 24. Further cooling is effected by means of an internally water-cooled tapered flange 16. A tantalum radiation shield 51 is situated above the induction coil 24. An aluminium barrier sleeve 50 is situated between the induction heating equipment and the walls of chamber 1.
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