Migration regularities of impurities C, O, Fe, Co and Ni and effect of crystal transition on C, O and Fe in purification
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ORIGINAL ARTICLE
Migration regularities of impurities C, O, Fe, Co and Ni and effect of crystal transition on C, O and Fe in purification of metal La by solid-state electrotransport Jia-Min Zhong
, De-Hong Chen*, Si-Ming Pang, Zong-An Li, Lin Zhou, Zhi-Qiang Wang
Received: 15 November 2019 / Revised: 22 March 2020 / Accepted: 13 August 2020 Ó The Nonferrous Metals Society of China and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Migration regularities of impurities C, O, Fe, Co and Ni and the effect of crystal transition on C, O and Fe in purification of metal La by solid-state electrotransport (SSE) were studied. The impurity migration direction, removal extent and difficulty were intuitively judged by impurity residual rate distribution curve. It is indicated that major impurities Fe, Co, Ni, C and O in metal La are found to significantly migrate to anode and migration effects are much better with the increase in temperature and prolongation of time in purification of La by SSE. Impurities Fe, Co and Ni in La may be fast diffusion elements, which are very extreme to be removed, and removal difficulty is in the order of Fe \ Co \ Ni \ O \ C. When La was migrated for 100 h at 800 °C by SSE, the residual rates of impurity Fe, Co, Ni, O and C are 0.25%, 10.10%, 40.04%, 64.00% and 70.04%, respectively. The crystal transition of La, transformed from fcc crystal to bcc crystal, has significant effect on migration of interstitial impurities, and removal effect of interstitial impurities C and O can be significantly improved when purification was performed above crystal transition temperature of 865 °C of La. However, there is little effect on Fe. When La was migrated at 880 °C for 100 h, residual rates of impurities C and O are, respectively, 19.90% and 32.67% lower than those at 820 °C for 100 h, while that of Fe is lower than 0.25% in both situations. Therefore, more pure metal La can be obtained through further increasing temperature, especially above crystal transition temperature of 865 °C of La.
J.-M. Zhong, D.-H. Chen*, S.-M. Pang, Z.-A. Li, L. Zhou, Z.-Q. Wang National Engineering Research Center for Rare Earth Materials, Grirem Advanced Materials Co., Ltd., Beijing 100088, China e-mail: [email protected]
Keywords Solid-state electrotransport; Purification; Lanthanum; Impurity distribution; Residual rate; Crystal transition
1 Introduction Impurity in rare earth metals, especially high-concentration interstitial impurities, may mask its intrinsic properties, such as cold storage capability and magnetization [1, 2]. Besides, purity of rare earth metals may also directly affect the performance of related materials, such as superconducting properties of Yb–Al–B alloy [3–5], cooling effect of Gd–Si–Ge alloy [6, 7] and brightness of La–Si–N phosphor for high power light-emitting diode (LED). Therefore, it is necessary to use high-purity rare earth metals to research and develop high and new technology materials of rare earth. Solid-state electrotransport (SSE) is an important me
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