Abstract
Mutual separation characteristics for binary oxide mixtures Y 2O 3–Dy 2O 3, Y 2O 3–Er 2O 3 and Ho 2O 3–Er 2O 3, in which these four kinds of rare earth ion(III) have very similar ion radius values, using a stepwise chlorination–chemical vapor transport (SC–CVT) reaction mediated by vapor complexes KLnCl 4 have been investigated in different temperature gradients. The unexpected results, together with that for Y 2O 3–Ho 2O 3 reported previously, are used to make a comparative analysis for the effect of ion radius values on the SC–CVT reaction for mutual separation of rare earths. Both the main deposition temperature region tendency and total transport amounts of chlorides for YCl 3 with respect to the ion radius of Y(III) were exceptional compared with those of LnCl 3 (Ln = Dy, Ho and Er), which were observed both in the degressive temperature gradient and the wave-type temperature gradient. The main deposition temperature of the chlorides produced from the oxide mixtures was in the order of DyCl 3 > YCl 3, HoCl 3 < YCl 3, ErCl 3 < YCl 3 and HoCl 3 > ErCl 3, total transported yields of the chlorides was in the order of DyCl 3 > YCl 3, HoCl 3 > YCl 3, ErCl 3 > YCl 3 and HoCl 3 > ErCl 3, and the largest separation factors 11.49 for Dy:Y, 15.28 for Ho:Y, 6.37 for Er:Y and 2.04 for Ho:Er in the lower temperature region were observed in the degressive temperature gradient, respectively. The results were discussed on the difference of ionic structure of Y on the one side and 4f lanthanoid elements of Dy, Ho and Er on the other hand, and verified that the ionic radius of the rare earth is one of the decisive factors of CVT reaction only for lanthanoid elements, not for Y. Furthermore, the improved separation factor values of 4.22 for Ho:Er and 3.20 for Er:Ho were obtained in the wave type temperature gradient due to variation of the dynamic conditions of CVT.
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