Abstract
The rare-earth element dysprosium (Dy) is an important additive that increases the magnetocrystalline anisotropy of neodymium magnets and additionally prevents from demagnetizing at high temperatures. Therefore, it is one of the most important elements for high-tech industries and is mainly used in permanent magnetic applications, for example in electric vehicles, industrial motors and direct-drive wind turbines. In an effort to develop a more efficient electrochemical technique for depositing Dy on Nd-magnets in contrast to commonly used costly physical vapor deposition, we investigated the electrochemical behavior of dysprosium(iii) trifluoromethanesulfonate in a custom-made guanidinium-based room-temperature ionic liquid (RTIL). We first examined the electrodeposition of Dy on an Au(111) model electrode. The investigation was carried out by means of cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The initial stages of metal deposition were followed by in situ scanning tunneling microscopy (STM). CV measurements revealed a large cathodic reduction peak, which corresponds to the growth of monoatomic high islands, based on STM images taken during the initial stages of deposition. XPS identified these deposited islands as dysprosium. A similar reduction peak was also observed on an Nd-Fe-B substrate, and positively identified as deposited Dy using XPS. Finally, we varied the concentration of the Dy precursor, electrolyte flow and temperature during Dy deposition and demonstrated that each of these parameters could be used to increase the thickness of the Dy deposit, suggesting that these parameters could be tuned simultaneously in a temperature-controlled flow cell to enhance the thickness of the Dy layer.
Highlights
The rare-earth element dysprosium (Dy) is rather unique amongst the magnetic materials, exhibiting both the highest magnetic moment per atom (10μB) and the highest saturation magnetization of any element.[1]
In an effort to develop a more efficient electrochemical technique for depositing Dy on Ndmagnets in contrast to commonly used costly physical vapor deposition, we investigated the electrochemical behavior of dysprosium(III) trifluoromethanesulfonate in a custom-made guanidinium-based room-temperature ionic liquid (RTIL)
cyclic voltammetry (CV) measurements revealed a large cathodic reduction peak, which corresponds to the growth of monoatomic high islands, based on scanning tunneling microscopy (STM) images taken during the initial stages of deposition
Summary
Nanoscale two of their most important features along with their low vapor pressures and high thermal stabilities.[17,18,19,20,21,22] the fact that RTILs enable access to the electrodeposition of nonnoble metals, which cannot be deposited from aqueous solutions, more than compensates for their high viscosities and costs, when considering their usefulness in a wide range of applications One of these non-noble metals is dysprosium, the electrodeposition of which several groups have demonstrated from commercially available ionic liquids, e.g. phosphonium[23] or pyrrolidinium-based[8] RTILs. the deposition rates achieved in these studies were not yet sufficient, especially with a view to industrial applications. Based on these results we discuss strategies for increasing the amount of deposited dysprosium on Nd–Fe–B magnets to achieve better permanent magnetic properties by variation of the concentration, flow of the electrolyte and temperature
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