Zhi-Jian Zhang

Direct Electrodeposition of Quarternary Mg–Li–Al–Zn Alloys from Their Chloride Melts

Direct electrodeposition of quarternary Mg―Li―Al―Zn alloys on a molybdenum electrode from LiCl―KCl―MgCl 2 ―AlCl 3 ―ZnCl 2 melts at 943 K was investigated. Cyclic voltammograms (CVs) showed that the deposition potential of Mg shifts in a positive direction after adding AlCl 3 and ZnCl 2 . Chronopotentiometry measurements indicated that the codepositon of Mg, Li, Al, and Zn occurs at current densities lower than ―0.47 A cm ―2 . X-ray diffraction (XRD) indicated that Mg―Li―Al―Zn alloys with different phases were prepared via galvanostatic electrolysis. The microstructures of typical α+β and β phases of Mg―Li―Al―Zn alloys were characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the elements of Mg and Al distribute homogeneously in the Mg—Li—AI—Zn alloy, but the element Zn mainly locates at grain boundaries. The results of inductively coupled plasma analysis showed that the chemical compositions of Mg―Li―Al―Zn alloys are consistent with the phase structures of the XRD patterns, and that the lithium, aluminum, and zincum contents of Mg―Li―Al―Zn alloys depend on the concentrations of MgCl 2 , AlCl 3 and ZnCl 2 .

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 .

Electrochemical formation process and phase control of Mg-Li-Ce alloys in molten chlorides

Abstract An electrochemical approach for the preparation of Mg-Li-Ce alloys by co-reduction of Mg, Li and Ce on a molybdenum electrode in KCl-LiCl-MgCl 2 -CeCl 3 melts at 873 K was investigated. Cyclic voltammograms (CVs) and square wave voltammograms indicated that the underpotential deposition (UPD) of cerium on pre-deposited magnesium led to the formation of Mg-Ce alloys at electrode potentials around −1.87 V. The order of electrode reactions was as follows: discharge of Mg(II) to Mg-metal, UPD of Ce on the surface of pre-deposited Mg with formation of Mg-Ce alloys, discharge of Ce(III) to Ce-metal and after that the discharge of Li + with the deposition of Mg-Li-Ce alloys, which was investigated by CVs, chronoamperometry, chronopotentiometry and open circuit chronopotentiometry. X-ray diffraction (XRD) illuminated that Mg-Li-Ce alloys with different phases were obtained via galvanostatic electrolysis by different current densities. The microstructures of Mg-Li-Ce alloys were characterized by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The analysis of energy dispersive spectrometry (EDS) showed that Ce existed at grain boundaries to restrain the grain growth. The compositions and the average grain sizes of Mg-Li-Ce alloys could be obtained controllably corresponding with the phase structures of the XRD patterns.

A new approach for the preparation of variable valence rare earth alloys from nano rare earth oxides at a low temperature in molten salt

The solubility of RE2O3 (RE = Eu, Sm, and Yb) with variable valence in molten salts is extremely low. It is impossible to directly obtain variable valence metals or alloys from RE2O3 using electrolysis in molten salts. We describe a new approach for the preparation of variable valence rare earth alloys from nano rare earth oxide. The excellent dispersion of nano–Eu2O3 in LiCl–KCl melts was clearly observed using a luminescent feature of Eu3+ as a probe. The ratio of solubility of nano-Sm2O3/common Sm2O3 is 16.98. Electrochemical behavior of RE2O3 on a molybdenum and Al electrode in LiCl–KCl melts containing AlCl3 at 480 °C was investigated by different electrochemical techniques, such as cyclic voltammetry (CV), square wave voltammetry, and chronopotentiometry. Prior to the reduction peak of Al, the reduction peaks of Sm(III)/Sm(II), Yb(III)/Yb(II), and Eu(III)/Eu(II) were observed at about −0.85, −0.45, and 0.39 V in square wave voltammetry, respectively. The underpotential deposition of RE on pre-deposited aluminum leads to the formation of Al–RE alloy. The structure, morphology, and energy dispersion analysis of the deposit obtained by potentiostatic electrolysis are analyzed. Al2Sm and Al3Sm alloys were successfully obtained from nano–Sm2O3.

AlCl3 and liquid Al assisted extraction of Nd from NaCl–KCl melts via intermittent galvanostatic electrolysis

The electrochemical reduction of Nd(III) was investigated on an inert W and a liquid Al electrode in molten NaCl–KCl eutectic salt. On both W and liquid Al electrodes, the reduction of Nd(III) ions to Nd(0) metal occurred in a single reaction step, which avoids the corrosion reaction: 2Nd(III) + Nd → 3Nd(II). Therefore, corrosion of Nd metal in this molten chloride media is not expected. The co-reduction behavior of Nd(III) and Al(III) ions was studied on a W electrode in NaCl–KCl–AlCl3–NdCl3 melts. Five kinds of Al–Nd intermetallic compound were detected via cyclic voltammetry and open circuit chronopotentiometry. Intermittent galvanostatic electrolysis was employed on liquid Al electrodes to extract Nd in the form of Al–Nd alloys in NaCl–KCl–NdCl3 melts. Nd, AlNd3, Al2Nd, and AlNd phases were identified by X-ray diffraction (XRD). With the increase of electrolytic time, the content of Nd-rich Al–Nd intermetallic compounds in the Al–Nd alloy increased. The morphology and micro-zone chemical analysis of the deposits were characterized by a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), and the Al11Nd3 phase was confirmed by EDS analysis.

Study on formation and properties of Al–Li–Sm alloy containing whiskers in molten salts

The electrochemical behaviors of samarium ions on a liquid aluminum electrode in LiCl–KCl melts at 973 K were investigated by cyclic voltammetry, square wave voltammetry and a cathodic polarization test. The results show that only one kind of Al–Sm intermetallic compound can be formed under our experimental conditions. The Al–Li–Sm alloy containing whiskers was obtained by galvanostatic electrolysis in LiCl–KCl melts after the addition of 10 wt% SmCl3 on a liquid aluminum electrode at 973 K. The alloy containing whiskers was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to examine the percentage composition of each element. Transmission electron microscopy (TEM) with electron diffraction was employed to characterize the crystal structure of the needle-like precipitates. The mechanical properties of the micro hardness and Young’s modulus were characterized by the Leitz micro hardness tester and the tool for Young’s modulus, respectively.

Electrochemistry of Zn and co-reduction of Zn and Sm from LiCl–KCl melt

The electrochemical behavior of Zn(II) ions in LiCl–KCl and Sm(III) ions in LiCl–KCl–ZnCl2 melts on a Mo electrode at 773 K was studied by various electrochemical techniques. The results showed that the reduction of Zn(II) to Zn(0) consisted of a one-step process. The electrode reaction of LiCl–KCl–ZnCl2 solutions indicated that the under potential deposition of Sm on pre-deposited Zn electrode formed three kinds of Zn–Sm intermetallic compounds at electrode potentials around −1.57, −2.17 and −2.29 V. The electrochemical extraction of samarium was carried out in LiCl–KCl–ZnCl2 melts on a Mo electrode at 773 K by potentiostatic electrolysis (−2.3 V) for 40 h with an extraction efficiency of 99.87%. Zn–Sm bulk alloy was obtained by galvanostatic electrolysis. The microstructure and micro-zone chemical analysis of the Zn–Sm alloy were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS).