Xiaoguang Yang

Electrochemical behavior of Y(III) and preparation of Y-Ni intermetallic compounds in molten LiCl-KCl salts

The work concerned the electrochemical behaviors of Y(III) on W and Ni electrodes in molten LiCl-KCl salts by a series of electrochemical techniques. The electrochemical reaction of Y(III) to Y(0) proceeded in a one-step reduction process with the exchange of three electrons, Y(III)+3e−→Y(0). Compared with the cyclic voltammogram and square wave voltammogram obtained on W electrode, the reduction potential of Y(III) on Ni electrode was observed at less negative potential than the one of Y(III) to give pure Y metal on W electrode, which revealed the occurrence of underpotential deposition of Y(III) on Ni electrode. Electromotive force (emf) measurements were performed to calculate the relative partial molar Gibbs energies and activities of Y in Y-Ni alloys. The standard Gibbs energies of formation for different Y-Ni intermetallic compounds were also estimated. The different Y-Ni alloys were formed by potentiostatic electrolysis at different potentials and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). It was found that four intermetallic compounds, YNi5, Y2Ni7, YNi3 and YNi2, were selectively produced by controlling applied potential.

Electrochemical formation and thermodynamic properties of Tb–Bi intermetallic compounds in eutectic LiCl–KCl

The electrochemical reactions of Tb(III) were investigated on a W electrode, Bi pool electrode and Bi film electrode in eutectic LiCl–KCl by transient electrochemical techniques. The exchange current densities of the Tb(III)/Tb(0) redox couple were determined on W and Bi film electrodes at different temperatures by the linear polarization method. On both Bi electrodes, the redox potential of Tb(III)/Tb couple was observed at less negative potential values than that on the W electrode, which indicated underpotential deposition of Tb occurring on the both Bi electrodes. The result of cyclic voltammetry performed on the Bi pool electrode suggested that the electrochemical reaction of Tb(III) to Tbin liquid Bi was a quasi-reversible and diffusion-controlled process. From the cyclic voltammogram and square wave voltammogram of Tb(III) obtained on the Bi film electrode, three reduction signals corresponded to the formation of Tb–Bi intermetallic compounds. The thermodynamic data, such as the activities of Tb in Tb–Bi alloys and the standard Gibbs free energies of formation for different Tb–Bi intermetallic compounds, were estimated using open circuit chronopotentiometry in the temperature range from 673 to 873 K. Moreover, the electrochemical preparation of Tb–Bi alloys was conducted in LiCl–KCl–TbCl3 melts on a liquid Bi electrode by galvanostatic and potentiostatic electrolysis, respectively. The Tb–Bi alloys were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). XRD results showed that the Tb–Bi alloys were composed of the TbBi phase and TbBi, TbBi3/4 and TbBi3/5 phases, respectively.

Electrolytic extraction of dysprosium and thermodynamic evaluation of Cu–Dy intermetallic compound in eutectic LiCl–KCl

The electrochemical reduction of dysprosium(III) was studied on W and Cu electrodes in eutectic LiCl–KCl by transient electrochemical methods. Cyclic voltammogram and current reversal chronopotentiogram results demonstrated that dysprosium(III) was directly reduced to dysprosium (0) on the W electrode through a single-step process with the transfer of three electrons. Electrochemical measurements on the Cu electrode showed that different Cu–Dy intermetallics are formed. Moreover, the thermodynamic properties of Cu–Dy intermetallic compounds were estimated by open circuit chronopotentiometry in a temperature range of 773–863 K. Using the linear polarization method, the exchange current density (j0) of dysprosium in eutectic LiCl–KCl on the Cu electrode was estimated, and the temperature dependence of j0 was studied to estimate the activation energies associated with Dy(III)/Cu5Dy and Dy(III)/Cu9/2Dy couples. In addition, potentiostatic electrolysis was conducted to extract dysprosium on the Cu electrode, and five Cu–Dy intermetallic compounds, CuDy, Cu2Dy, Cu9/2Dy, Cu5Dy and Cu0.99Dy0.01 were identified by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. Meanwhile, the change of dysprosium(III) concentration was monitored using inductively coupled plasma-atomic emission spectrometry, and the maximum extraction efficiency of dysprosium was found to reach 99.2%.

The kinetics process of a Pb(II)/Pb(0) couple and selective fabrication of Li–Pb alloys in LiCl–KCl melts

The electrode reaction of Pb(II) and co-reduction of Li(I) and Pb(II) were investigated on a tungsten electrode in LiCl–KCl eutectic melts by a range of electrochemical techniques. From cyclic voltammetry and square wave voltammetry measurements, the reduction of Pb(II) was found to be a one-step diffusion-controlled reversible process with the exchange of 2 electrons. The diffusion coefficients of Pb(II) were computed, and they obey the Arrhenius law. Using the linear polarization technique, the kinetic parameters, such as exchange current intensity (j0), standard rate constant (k0) and charge transfer resistance (Rct) for the Pb(II)/Pb(0) couple on a tungsten electrode were studied at different temperatures, and the activation energy is 27.32 kJ mol−1, smaller than the one for diffusion of Pb(II), which further confirmed that the reduction of Pb(II) was controlled by diffusion. A depolarisation effect for Li(I) reduction was observed from the results of cyclic voltammetry, square wave voltammetry and chronopotentiometry due to the formation of Li–Pb alloys by co-reduction of Li(I) and Pb(II). Furthermore, five Li–Pb intermetallic compounds, LiPb, Li8Pb3, Li3Pb, Li10Pb3 and Li17Pb4 characterized by scanning electronic microscopy and X-ray diffraction, were selectively prepared by potentiostatic electrolysis on a tungsten electrode and galvanostatic electrolysis on a liquid Pb electrode, respectively.

Electrochemical co-reduction of Y(III) and Zn(II) and extraction of yttrium on Zn electrode in LiCl-KCl eutectic melts

This work presents an electrochemical study of Y(III) ions on W electrode and liquid Zn electrode and co-reduction mechanism of Y(III) and Zn(II) on W electrode in LiCl-KCl eutectic melts. Cyclic voltammogram and current reversal chronopotentiogram revealed that the electrochemical reaction of Y(III) on W electrode proceeds a single step mechanism of Y(III) to Y(0). On liquid Zn electrode, the deposition potential of Y(III) is more positive than that on W electrode due to the formation of Y-Zn solution and the reduction process was found to be a diffusion controlled and quasi-reversible at lower scan rate of 0.1xa0V/s. Based on the results of cyclic voltammometry, square wave voltammetry, and chronopoteniometry, the Y-Zn intermetallics could be formed by co-reduction process of Y(III) and Zn(II) on W electrode in LiCl-KCl-ZnCl2-YCl3 molten salts. Moreover, the electrochemical extracting metallic Y was conducted by galvanostatic and potentiostatic electrolysis on liquid Zn electrode. Electrolysis products consisted of Zn and YZn12 phases characterized by scanning electron microscopy with energy dispersive spectrometry and X-ray diffraction. Meanwhile, the change of Y(III) concentration in LiCl-KCl eutectic melts was detected by inductive coupled plasma atomic emission spectrometer and the extraction efficiency could be estimated.

Electrochemical behaviour of magnesium(II) on Ni electrode in LiCl-KCl eutectic

The electrochemical behaviour of magnesium(II) and the formation mechanism of Mg-Ni alloys on Ni electrode were studied in LiCl-KCl eutectic using various electrochemical techniques. Cyclic voltammogram and square-wave voltammogram revealed that under-potential deposition of magnesium occurred on Ni electrode because Mg-Ni alloy compounds were formed. The thermodynamic properties of the Mg-Ni intermetallics, Mg2Ni and MgNi2, were determined using open circuit chronopotentiometry in the temperature range of 818―893 K. Moreover, the Mg-Ni alloys were produced by potentiostatic and galvanostatic electrolysis under different conditions and charac-terized by means of scanning electron microscopy(SEM) equipped with energy dispersive spectrometry(EDS) and X-ray diffraction(XRD). The experimental results indicate that Mg-Ni intermetallic compounds can be selectively produced by potentiostatic electrolysis.