Yongde Yan

Electrochemical behaviour of erbium and preparation of Mg-Li-Er alloys by codeposition

Abstract The electrodeposition of erbium on molybdenum electrodes and the formation of Mg-Li-Er alloys were investigated in LiCl-KCl molten salts. At a molybdenum electrode, the electroreduction of Er (III) proceeded in a one-step process involving three electrons. The diffusion coefficient of erbium ions in the melts was determined by cyclic voltammetry, chronopotentiometry and chronoamperometry respectively. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of lithium on pre-deposited Mg-Er alloy led to the formation of a Mg-Li-Er alloy. X-ray diffraction (XRD) indicated that Er 5 Mg 24 phase was formed via potentiostatic electrolysis. Scanning electron microscopy (SEM) showed that Er atoms mainly concentrated at the grain boundaries while Mg element evenly located in the alloy.

Extraction of thorium from LiCl–KCl molten salts by forming Al–Th alloys: a new pyrochemical method for the reprocessing of thorium-based spent fuels

The co-reduction process of Th(IV) and Al(III) ions in the LiCl-KCl-AlCl3-ThO2 molten salts with different concentrations of AlCl3 was investigated at 800 K on the tungsten electrode. Cyclic voltammetry, square wave voltammetry and open-circuit chronopotentiometry techniques were used to study electrochemical behaviors of Al(III), Th(IV) and Al-Th alloy formation processes. The results showed that five kinds of Al-Th intermetallic compounds could be formed in the AlCl3 poor system, whereas only one kind of Al-Th compound formed in the AlCl3 rich system. Al-Th alloys were obtained by potentiostatic electrolysis on aluminum electrodes and by galvanostatic electrolysis on a tungsten electrode. All the Al-Th alloys were characterized by scanning electron microscopy ( SEM) with energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The XRD results showed that the Al-Th compound prepared in the AlCl3 rich system was

Electrochemical behavior of La(III) on liquid Bi electrode in LiCl–KCl melts. Determination of thermodynamic properties of La–Bi and Li–Bi intermetallic compounds

Electrochemical behavior of La(III) was studied on liquid Bi electrodes (i.e. Bi pool and Bi coated W electrodes) in LiCl–KCl melts using cyclic voltammetry, square wave voltammetry, chronopotentiometry and open circuit chronopotentiometry. In both the electrodes, the electrochemical reduction of La(III) was observed at more positive potential values than that on an inert W electrode, due to the lowering of the activity of La in liquid Bi phase. Cyclic voltammogram, using a Bi pool electrode, suggests that the reduction of La(III) to Lain liquid Bi was a quasi-reversible and diffusion controlled process. The diffusion coefficient of La in liquid Bi metal was measured by chronopotentiometry at 773 K and was evaluated by using the Sutherland–Einstein equation, respectively. Both the values of the diffusion coefficient were of the same order of magnitude. From the cyclic voltammogram and square wave voltammogram obtained on the Bi coated W electrode, five couples of cathodic/anodic peaks were observed at more positive potential than that for La metal on an inert electrode due to the formation of five La–Bi intermetallic compounds. Thermodynamic properties such as activities and relative partial molar Gibbs energies of M (M = La, Li) in the M–Bi alloys as well as Gibbs energies of formation for M–Bi (M = La, Li) intermetallic compounds, LaBi2, LaBi, La4Bi3, La5Bi3, La2Bi and Li3Bi were calculated from the open circuit potential measurement. La–Bi and La–Li–Bi alloys were produced on liquid Bi pool electrodes by galvanostatic and potentiostatic electrolysis, and characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The results indicated that La–Bi alloys were comprised of LaBi2, LaBi and La2Bi phases, and LaBi2, LaBi and Li3Bi phases existed in La–Li–Bi alloys.

Preparation of Mg-Li-Sm alloys by electrocodeposition in molten salt

Abstract Electrocodeposition of Mg-Li-Sm alloys was investigated in molten KCl-LiCl-MgCl 2 -SmCl 3 -KF system. The effects of electrolytic temperature and cathodic current density on current efficiency were studied and optimal electrolysis parameters were obtained. The optimum electrolysis condition was a molten salt mixture of LiCl: KCl =50:50 (wt.%), electrolytic temperature: 660 °C, cathode current density: 9.5 A/cm 2 and electrolysis time of 40 min. The current efficiency reached 77.3%. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses of the deposits indicated that Mg-Li-Sm alloys, having Mg, βLi and Mg 41 Sm 5 phases, were obtained by electrocodeposition in molten system. The content and distribution of elements in Mg-Li-Sm alloys were analyzed by ICP-MS and EPMA, respectively. The results showed that the distribution of Mg and Sm was homogeneous in the alloys. ICP analyses of samples obtained by electrolysis showed that lithium contents in Mg-Li-Sm alloys could be controlled by MgCl 2 concentration and electrochemical parameters. It was proved that preparation of Mg-Li-Sm alloys by electrocodeposition in molten salt was feasible.

Electrochemical Codeposition of Mg-Li-Gd Alloys from LiCl-KCl-MgCl2-Gd2O3 Melts

Mg-Li-Gd alloys were prepared by electrochemical codeposition from LiCl-KCl-MgCl2-Gd2O3 melts on molybdenum electrode with constant current density at 823 and 973 K. The microstructure of the Mg-Li-Gd alloys was analyzed by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show that magnesium and gadolinium deposit mainly in the first 30 min, and the alloy obtained contains 96.53% Mg, 0.27% Li and 3.20% Gd (mass fraction). Then, the reduction of lithium ions occurs quickly. The composition of alloy can be adjusted by controlling electrolysis time or Gd2O3 concentration in LiCl-KCl melts. With the addition of Gd into Mg-Li alloys, the corrosion resistance of the alloys is enhanced. XRD results suggest that Mg3Gd and Mg2Gd can be formed in Mg-Li-Gd alloys. The distribution of Gd element in Mg-Li-Gd alloys indicates that Gd element mainly distributes at the grain boundaries of Mg-Li-Gd alloys.

Electrochemical behaviour and codeposition of Al-Li-Er alloys in LiCl-KCl-AlCl3-Er2O3 melts

The electrochemical behaviour of Al, Li, and Er were investigated by electrochemical techniques, such as cyclic voltammograms, chronopotentiometric, chronoamperograms, and open circuit chronopotentiogram on molybdenum electrodes. The results showed that the underpotential deposition of erbium on pre-deposited Al electrodes formed two Al-Er intermetallic compounds. The codeposition of Al, Li, Er occurred and formed Al-Li-Er alloys in LiCl-KCl-AlCl3-Er2O3 melts at 773 K. Different phases such as Al2Er, Al2Er3 and βLi phase of Al-Li-Er alloys were prepared by galvanostatic electrolysis and characterized by X-ray diffraction (XRD). Scanning electron microscopy (SEM) indicated that Er element mainly distributed at the grain boundary. ICP analyses showed that lithium and erbium contents of Al-Li-Er alloys could be controlled by AlCl3 and Er2O3 concentration and electrochemical parameters.

Preparation of Mg–Li—La alloys by electrolysis in molten salt

Abstract An electrochemical method was used to prepare Mg—Li—La alloys in a molten LiCl—KCl—KF—MgCl2 containing La2O3 at 943 K. The results showed preparation of Mg—Li—La alloys by electrolysis is feasible. The Mg—Li—La alloys were analyzed by means of X-ray diffraction (XRD), optical micrograph (OM) and scanning electron microscopy (SEM). XRD analysis indicates that α+Mg17La2, α+β+Mg17La2 and β+LaMg3 Mg—Li—La alloys with different lithium and lanthanum contents were obtained via galvanostatic electrolysis. The microstructures of typical α+β+Mg17La2 and β+LaMg3 phases of Mg—Li—La alloys were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) shows that the element of Mg distributes homogeneously in the Mg—Li—La alloy and the element of La mostly exists at grain boundaries to restrain the grain growth rate due to the larger ionic radius and lower electronegativity compared with Mg.

Electrochemical formation of Mg-Li-Y alloys by co-deposition of magnesium, lithium and yttrium ions in molten chlorides

Abstract An electrochemical approach for the preparation of Mg-Li-Y alloys via co-reduction of Mg, Li, and Y on a molybdenum electrode in LiCl-KCl-MgCl 2 -YCl 3 melts at 943 K was investigated. Cyclic voltammograms (CVs) illuminated that the underpotential deposition (UPD) of yttrium on pre-deposited magnesium led to the formation of a liquid Mg-Y alloy, and the succeeding underpotential deposition of lithium on pre-deposited Mg-Y led to the formation of a liquid Mg-Li-Y alloy. Chronopotentiometry measurements indicated that the order of electrode reactions was as follows: discharge of Mg(II) to Mg-metal, electroreduction of Y on the surface of Mg with formation of e-Mg 24+ x Y 5 and after that the discharge of Li + with the deposition of Mg-Li-Y alloys. X-ray diffraction (XRD) indicated that Mg-Li-Y alloys with different phases were formed via galvanostatic electrolysis. The microstructure of different phases of Mg-Li-Y alloys was characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis results of inductively coupled plasma atomic emission spectrometer (ICP-AES) showed that the chemical compositions of Mg-Li-Y alloys corresponded with the phase structures of the XRD patterns, and the lithium and yttrium contents of Mg-Li-Y alloys depended on the concentrations of MgCl 2 and YCl 3 .

Progress in preparation of rare earth metals and alloys by electrodeposition in molten salts

Rare earth (RE) metals and their alloys have attracted considerable practical interests due to their functional properties. Because of their negative deposition potentials, RE metals cannot be electrochemically deposited from aqueous media. Using molten salt as medium provides a unique opportunity for the electrowinning and electrorefining of high-purity RE metals, as well as for the electrochemical formation of their alloys and intermetallic compounds. Certainly, the electrochemical behaviors of RE metals and their alloys have been investigated in a number of different molten salts comprising all-fluorides, all-chlorides and mixed chloride-fluoride media. Based on the results, RE and their alloys were produced by molten salt electrolysis. In this paper, the developments of preparation of RE metals and their alloys by electrolysis in molten salts in recent years were systematically summarized on both the local and international levels. Attention was paid mainly to the electrodeposition of RE metals and their alloys, including RE–Mg, RE–Al, RE–Ni, RE–Co, RE–Cu, RE–Fe and RE–Zn alloys.

Electrochemical behavior of praseodymium and Pr-Al intermetallics in LiCl-KCl-AlCl3-PrCl3 melts

Abstract The electrochemical behavior of Pr(III) and formation process of Pr-Al intermetallics were investigated by different electrochemical methods. The reduction of Pr(III) ion to metallic Pr is an one-step three-electrons reaction. The reversibility of Pr(III)/Pr(0) system was evaluated by cyclic voltammograms with different scan rates. The co-reduction of Pr(III) and Al(III) ions formed three different Pr-Al intermetallics at electrode potentials around −1.40, −1.80, and −1.95 V vs. Ag/AgCl at 723 K, respectively. Open-circuit chronopotentiometry and electromotive force (emf) measurements were carried out to estimate the relative molar Gibbs energies of Pr for the formation of different Pr-Al intermetallics in the temperature range of 723–843 K. The activities of Pr in the Pr-Al intermetallic compounds were calculated.