CaCl_2熔盐中直接电化学还原制备铽-镝-铁合金机制

Mechanism of Direct Electrochemical Reduction of Tb-Dy-Fe Alloys in Molten Calcium Chloride

CaCl2熔盐为电解质,石墨棒作辅助电极、铂片作参比电极,以定组成Tb2O3、Dy2O3、Fe2O3(1:1:2)均匀混合氧化物粉体制成工作电极,利用循环伏安法和计时电流法对电化学还原制备铽-镝-铁合金的过程进行研究,并以石墨棒为阳极,混合氧化物烧结片为阴极,采用恒电位电解法对电化学测试结果进行检验并利用XRD分析电解产物的组成。结果表明,CaCl2熔盐中电化学还原可以制备出铽-镝-铁合金;混合氧化物电化学还原制备铽镝铁合金是不可逆过程,合金生成按照Fe、DyFe5、TbFe3、DyFe2和TbFe2的先后顺序5步完成;电化学还原过程是在Fe|Fe2O3|CaCl2、Tb-Dy-Fe|Tb2O3-Dy2O3|CaCl2两个三相界线上先后进行。

The mechanism of the direct electrochemical reduction of solid oxides Tb2O3 -Dy2O3 -Fe2O3 was studied by cyclic voltammetry and chronoamperometry measurements. The reduction process was then proved by the constant potential electrolysis for different time. Five cathodic current peaks in the cyclic voltammogram were observed, supporting a mechanism of five-step processes for the electrochemical reduction of Tb2O3 -Dy2O3 -Fe2O3 . The first peak represented the electrochemical reduction reaction of Fe2O3 →Fe, while other peaks could be confirmed as the electrochemical reduction reactions between Fe and Tb2O3 as well as Dy2O3 . The following electrochemical reduction sequence was confirmed by XRD analysis. Firstly Fe2O3 was electrolyzed to form Fe, then intermetallic Tb-Fe and Dy-Fe were electrolyzed from Fe and Tb2O3 as well as Dy2O3 , and finally they were alloyed to form TbDyFe2 . The above electrochemical reduction results could be explained by a theory of ＂diffusion at triplephase boundary lines＂, and hereby the triplephase boundary lines were Fe｜Fe2O3 ｜CaCl2 and Tb-Dy-Fe｜Tb2O3 -Dy2O3 ｜CaCl2 in the electro-reduction process.