稀土Yb(II)离子在LiF-CaF2体系下活性阴极界面电还原及合金化机理

In order to preparing for new type ytterbium-alloy and changing the shortcomings of the existing preparation methods, electrochemical reduction method is proposed to completing the process of Yb(III)→Yb(II)→Yb on the surface of active cathode in LiF-CaF2 eutectic system. Fluorination process of Yb2O3 is investigated by isothermal saturation and potentiometric titration, aiding by emission spectroscopy (ICP-OES) as auxiliary means. The configuration of LiF-CaF2-Yb2O3 eutectic was measured by high-temperature X-ray diffraction (XRD) and Raman spectroscopy technique, and so on. Scanning electrochemical microscopy(SECM) and electrochemical transient analytical techniques, such as cyclic voltammetry, were used to studying the electrochemical reduction mechanism and controlling methods of Yb(II) ions. Distribution of electric-field and temperature-field on the interface of a flat Ni electrode were simulated by modern computing software (Comsol Multiphysics) through established physical-mathematical model. The purpose of the project is to master the electro-reduction laws of rare earth Yb(II) ions on the surface of the active Ni cathode in LiF-CaF2 eutectic system and establish the theoretical basis for preparing ytterbium-alloy by electrochemical reduction method.

含Yb稀土合金的性能及应用前景被广泛看好，为改变现有制备方法的局限性，提出在熔融LiF-CaF2-Yb2O3体系下活性阴极表面通过电化学还原完成Yb(III)→Yb(II)→Yb过程。采用等温饱和、电位滴定等方法，辅以发射光谱法(ICP-OES)等现代表征手段研究Yb2O3在LiF-CaF2介质中的氟化机理，并使用高温XRD、拉曼光谱等技术研究熔体的结构特征。运用扫描电化学显微镜(SECM)、循环伏安等现代电化学分析技术研究Yb(II)离子的还原机理及控制方法。同时，建立[熔体|电极]界面电场、温场的物理及数学模型，运用Comsol Multiphysics有限元系统模拟平板Ni阴极界面电场、温场分布规律。项目旨在掌握变价稀土Yb(II)离子在LiF-CaF2介质活性Ni阴极界面还原规律，建立电化学方法制备Yb合金理论基础。

稀土Yb在功能合金材料领域的应用前景非常广阔，项目探索氟化物-氧化物体系熔盐电解制备Ni-Yb合金，克服现有镧热还原和混熔法的不足，开辟更为高效且环境友好的变价稀土Yb合金制备方法。本项目围绕LiF-[CaF2/YbF3]-Yb2O3体系中活性Ni阴极制备Ni-Yb合金展开，内容涵盖LiF-[CaF2/YbF3]体系中Yb2O3的溶解及物理化学属性；Yb(III)离子在阴极的电还原过程及机理；电解体系与活性Ni阴极界面的温场及电场模拟。研究结果表明：Yb2O3在LiF-[CaF2/YbF3]体系中溶解受扩散控制，体系密度、粘度及电导率性质可控，能够与合金产物有效分离；Yb(III)离子经过Yb(III)→Yb(II)→Yb两步还原，在Ni活性阴极表面Yb经过三维连续和三维瞬时成核两个阶段；通过控制活性Ni电极表面活度，能够使Yb(II)离子还原电位正移，有效控制电极表面原位归中反应2Yb(III)+Yb→3Yb(II)的进行并合金化。本项目研究结果能为氟盐-氧化物体系电解制备变价稀土合金提供基础数据及理论依据。