Attempts to the electrodeposition of Nd from ionic liquids at elevated temperatures

The suitability of triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl)amide [P-2225][TFSA]), room temperature ionic liquid for the electrodeposition of neodymium has been investigated in this study. From the standpoint of the scientific aspects, the temperature dependence of the reduction behavior for Nd(III) in [P-2225][TFSA] was investigated from the cyclic voltammetry and the diffusion coefficient of Nd(III) was investigated by chronopotentiomerry with cylindrically symmetrical diffusion. It was revealed that the over-potential of reduction reaction for Nd(III) was decreasing with elevating the bath temperatures and the diffusion coefficient of Nd(III) was estimated to the order of 10(-11) m(2) s(-1) at 100 degrees C. The activation energy of diffusion for Nd(III) obtained from the temperature dependence was 61 kJ mol(-1). On the other hand, the spectroscopic and thermal analyses were also researched and it was revealed that the complex formation of Nd(III) in [P-2225][TESA] would not be rigid structure. The fusion temperature and the enthalpy of NdTFSA(3) were estimated to be 195 degrees C and 24 kJ mol(-1), respectively. According to the electrochemical, spectroscopic and thermal evaluations, the electrodeposition of neodymium in [P-2225][TFSA] was performed by potentiostatic electrolysis at -3.1 V at 150 degrees C in order to stimulate the mass transfer and to lower solution viscosity. The current efficiency evaluated from the mass change of the anode was more than 90%. A black electrodeposit on a copper substrate was fine and formed uniformly neodymium particle was observed by SEM. It was also identified that the contents of metallic neodymium in electrodeposits were 48% from the evaluation of EDX. The electrodeposit was composed of most of metallic neodymium and a part of neodymium oxide as identified from XPS. (C) 2012 Elsevier Ltd. All rights reserved.