EMIMBF_4-EG离子液体体系电沉积制备金属镧镀层

Electrodeposition of Lanthanum Coating in EMIMBF_4-EG Ionic Liquid System

以1-乙基-3-甲基咪唑四氟硼酸盐(EMIMBF_4)为溶剂,乙二醇(EG)为添加剂,考察不同体积比例EMIMBF_4-EG体系对LaCl_3的溶解度影响,用循环伏安法考察La(III)在EMIMBF_4-EG-LaCl_3体系中的电化学行为,最后用扫描电镜(SEM)和能谱仪(EDS)分析了所得金属镧的形貌和成分。研究表明:随着EMIMBF_4-EG体系中EG体积比例从1∶2增大到3∶1,EMIMBF_4-EG体系对LaCl_3溶解度递增,至体积比EG∶EMIMBF_4=3∶1时,体系中LaCl_3浓度高达105 g·L^(-1)。然而,随着EG比例的增加,EMIMBF_4-EG体系稳定性逐渐变差;EMIMBF_4-EG离子液体体系中镧的电沉积行为是一步完成的不可逆过程,经计算,其平均传质系数为0.1079,扩散系数D为1.71×10^(-6)cm2·s^(-1);随着沉积电位的增大,基体Pt层表面电流密度增大,镧沉积物逐渐细化,形貌从颗粒物转变为镀层;在优化的实验条件即温度50℃、转速600 r·min^(-1)、沉积电位-1.7 V,在EMIMBF_4-EG-LaCl_3体系中恒电位电沉积1 h后得到表面平滑、颗粒细密的镀层,镧的成分比例大于98%(质量分数)。

The solubility of LaCl3 in the electrolyte consisted of solvent of 1-ethyl-3-methyl imidazole tetrafluoroborate （ EMIMBF4 ） and addition of ethylene glycol （EG） was investigated. Then the electrochemical behavior of tfivalent lanthanum ion in EMIMBF4-EG- LaCl3 system was typically researched with cyclic voltammetry. Eventually, the morphology and La content of the deposits were discussed by means of scanning electron microscope （SEM） and energy dispersive spectrometer （EDS）. The results showed that the solubility of LaCl3 moved up as the proportion of EG in the system increased from 1：2 to 3： 1, the concentration of LaCl3 in EMIMBF4-EG system went up by 105 g·L^-1 when the volume ratio of EG to EMIMBF4 was 3： 1. However, the stability of system got worse accordingly as the proportion of EG went up. The electrodeposition process of trivalent lanthanum ion on the cathode was a one-step reaction which was completely irreversible. The transfer coefficient and diffusion coefficient （D） of trivalent lanthanum ion in the ionic liquid system were 0. 1079 and 1.71×10^-6cm^2·s^-1 respectively. When the potential enlarged, the current density on surface of platinum plate electrode rose up. As a result, the morphology of deposits got smaller in size, transforming a granular layer to a lanthanum plating. The surface of deposits became smooth and fine under the optimized conditions with temperature of 50 ℃, rotating rate of 600 r· min^-1 , depositing potential of - 1.7 V, of which the lanthanum component content was above 98 % （ mass fraction）.