Abstract
An electron bombardment floating zone melting apparatus for the refractory metals, which was first built-up on trial in Japan (1960), is described. The operation and the performance are further described for the floating zone melting of W, Mo, Ta, Nb, Pt, Pd and Fe rods. The results obtained are as follows:(1) By using emission control, by which the bombardment current is kept constant by automatically adjusting the filament temperature and bombardment voltage in “Temperature Limited characteristics”, the floating zone melting of sintered specimens incurring a great deal of outgassing during melting was performed successfully.(2) The purifying effect of floating zone melting was confirmed by residual resistance ratio measurements and, from the ratio values, it was made clear that the zone melted rods have been purified by vacuum distillation and zone refining. Namely, in the cases of 5 mmφ W and Mo rods three zone passed at zoning rate 3 mm/min in 1×10−5 torr, the ratio values have been decreased to 1/400 for W rod and to 1/150 for Mo rod respectively against the values of starting materials.(3) By only one zoning, 5 mmφ W, Mo, Ta, Nb, Pt and Pd rods were found to be single crystals at 1∼4 mm/min without seed crystals.Moreover, 4 mmφ Nb single crystal was produced by using 〈100〉 seed crystal. Therefore, this apparatus could be used as a single crystal growing apparatus for refractory metals.
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