Abstract

The cathodic reduction of Dy(III) ions at an inert molybdenum electrode in the molten 3LiCl–2KCl eutectic at the temperature range of 723–843 K under an inert atmosphere was studied by electrochemical methods. One cathodic current peak at a potential of –3.19 ± 0.11 V and the corresponding anodic current peak at a potential of –2.95 ± 0.11 V versus chlorine reference electrode were detected on the cyclic voltammetric curve in the “electrochemical window” under study. Therefore, the reduction proceeds via the reaction Dy³⁺ + 3\({{\bar {e}}}\) → Dy. An analysis of the cyclic voltammograms show that the current peak potential shifts to the negative range with an increase of the scan rate and the cathodic peak current is directly proportional to the square root of the polarization rate. An increase of the scan rate leads to a regular increase of the irreversibility of the cathodic process. The number of the exchange electrons (n) of the reduction of Dy(III) ions is determined by the square-wave voltammetry method. The calculated value is n = 2.93 ± 0.05. According to the theory of cyclic voltammetry, the cathodic reduction is irreversible, proceeds in one step, and is controlled by the charge transfer rate. The temperature dependence of the apparent standard potential of the Dy(III)/Dy couple is determined by zero-current chronopotentiometry. The experimental values are described by the linear equation \(E_{{{{{\text{Dy}}\left( {{\text{III}}} \right)} \mathord{\left/ {\vphantom {{{\text{Dy}}\left( {{\text{III}}} \right)} {{\text{Dy}}}}} \right. \kern-0em} {{\text{Dy}}}}}}^{{\text{*}}}\) = –(3.401 ± 0.009) + (6.2 ± 0.1) × 10^–4 T ± 0.007 V. The changes in the apparent standard Gibbs energy, the enthalpy, and the entropy of dysprosium trichloride formation from elements in the molten 3LiCl–2KCl eutectic and the activity coefficient of DyCl₃ are calculated.

中文翻译：

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3LiCl–2KCl共熔物中阴极还原Dy（III）离子的机理研究

摘要

通过电化学方法研究了在惰性气氛下在723-843 K温度范围内，熔融的3LiCl-2KCl共晶中的惰性钼电极上的Dy（III）离子的阴极还原。与氯参比电极相比，在研究的“电化学窗口”中的循环伏安曲线上检测到一个电位为–3.19±0.11 V的阴极电流峰和相应电位为–2.95±0.11 V的相应阳极电流峰。因此，还原通过反应Dy ³⁺ + 3 \（{{\ bar {e}}} \\）进行→Dy。对循环伏安图的分析表明，随着扫描速率的增加，电流峰值电势移至负范围，并且阴极峰值电流与极化率的平方根成正比。扫描速率的增加导致阴极过程不可逆性的规律性增加。通过方波伏安法确定Dy（III）离子还原的交换电子数（n）。计算值是n＝ 2.93±0.05。根据循环伏安法的理论，阴极还原是不可逆的，一步进行，并受电荷转移速率控制。Dy（III）/ Dy对的视在标准电位的温度依赖性由零电流计时电位法确定。实验值由线性方程\（E _ {{{{{\ text {Dy}} \ left（{{\ text {III}}} \ right）} \ mathord {\ left / {\ vphantom {{ {\ text {Dy}} \ left（{{\ text {III}}} \ right）} {{\ text {Dy}}}}} \ right \ kern-0em} {{\ text {Dy}} }}}} ^ {{\ text {*}}} \） =-（3.401±0.009）+（6.2±0.1）×10 ^–4 T±0.007V 。计算了由熔融3LiCl–2KCl共晶中的元素形成的表观标准Gibbs能量，焓和三氯化的熵和DyCl ₃的活度系数的变化。