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Purification of Rare-earth Metals.
U S Pat 3 729 306 1973 Apr; :
Metals such as ce, la, or y are concentrated by a combination of electrotransport and zone refining. The bars are melted in an elongated horizontal refractory boat with direct current flowing between the electrodes, one at each end. The anode end is hotter than the cathode end. The current is decreased to start solidification with a liquid portion near the cathode slightly above the melting point. The thermal gradient between the electrodes is approximately 1-5 deg.C/cm. Alloys are thus electrolyzed while in a partly solidified state, and purified by electrotransporting impurities to one end. A suitable apparatus is used under a bell jar at 10-6 torr. Thus, a 90-g ce bar containing 12.5 Atomic percent fe was melted in a horizontal boat of ta tubing 12.7 Cm long by 1.25 Cm maximum width, at 240 a/cm2, with w electrodes 0.1 In diam in experiments lasting 8.5-85 H. The highest concentration of fe within 1 cm of the anode end was approximately 25 atomic percent at 0.15 Cm/h freezing rate, with only 0.1 Atomic percent fe contaminant remaining at the cathode end.
U.S. Pat. 3,729,306; Apr. 24, 1973; Chem. Abstr. 79:95,233W