The electrochemical behavior of Yb3+ and electrodeposition of Mg-Yb alloy film at solid magnesium cathode in the molten LiCl-KCl-YbCl3(2 wt.%) system at 773 K was investigated.Transient electrochemical techniques,such as cyclic voltammetry,chronopotentiometry and chronoamperometry were used in order to explore the deposition mechanism of Yb.The reduction process of Yb3+ is stepwise reactions which are single-electron and double-electron reversible charge transfer reactions.The speed control step was a diffusion-controlled step which is caused by concentration polarization.The microstructures of Mg-Yb alloy film were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and EPMA area analysis.A very thin Mg2Yb alloy film(～200 nm) was formed by potentiostatic electrolysis at ?1.85 V(vs.Ag/AgCl) for 12 h.A much thicker Mg2Yb alloy film(～450 μm) was obtained at ?2.50 V(vs.Ag/AgCl) for 2.5 h.The corrosion resistance of magnesium can be enhanced by electrochemical formation of Mg-Yb alloy film on its surface.
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 diffu-sion 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 Er5Mg24 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.
Electrocodeposition of Mg-Li-Sm alloys was investigated in molten KCl-LiCl-MgCl2-SmCl3-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 oC,cathode current density:9.5 A/cm2 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 Mg41Sm5 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 MgCl2 concentration and electrochemical parameters.It was proved that preparation of Mg-Li-Sm alloys by electrocodeposition in molten salt was feasible.
Different phases of Mg-Li-Sm alloys were prepared by galvanostatic electrolysis in LiCl-KCl-MgCl2-SmCl3 melts at 670 °C.The electrolysis process and phase control of Mg-Li-Sm alloys were studied.The microstructures of α,α+β,β phases of Mg-Li-Sm alloys were characterized by X-ray diffraction(XRD) and optical microscope(OM).Analysis of scanning electron microscopy(SEM) and EDS mapping analysis showed that Mg distributed homogeneously in Mg-Li-Sm alloys.EDS result showed that the distribution of Sm was more at grain boundaries than within the grains.Inductively coupled plasma(ICP) analyses of the samples obtained by electrolysis showed that the chemical compositions of Mg-Li-Sm alloys were consistent with the phase structures of XRD patterns,and the lithium and samarium contents in Mg-Li-Sm alloys could be controlled by the electrolysis time and concentrations of SmCl3.Effect of Sm on corrosion property of Mg-12Li alloy was studied.The corrosion resistance of the alloy improved firstly and then worsened with the increase of Sm content.The optimum Sm content was about 0.7 wt.%.
The electrochemical preparaton of Al-Li-Y alloys from LiCl-KCl-AlCl3-Y2O3 system was studied. The chlorination of Y2O3 by AlCl3 led to the formation of Y (III) ions in the molten salts. Cyclic voltammogram (CV) showed that the underpotential deposition (UPD) of yttrium on pre-deposited aluminum caused the formation of Al-Y alloy. Al-Li-Y alloys with different yttrium contents were obtained by galvanostatic electrolysis and analysed by SEM-EDS and ICP. The ICP results showed that the lithium and yttrium contents in Al-Li-Y alloys depended on the addition of AlCl3 into the melts.
This work presents a study on electrochemical formation of Mg-Li-Al alloys on an inert electrode(Mo electrode) in a molten KCl-LiCl-AlCl3-MgCl2-KF system.It aims at preparation Mg-Li-Al metal alloy directly under an optimal electrolytic parameters.Main factors which affect current efficiency are investigated.We have discussed the co-electrodeposition conditions and the effect of technical parameters on these experiments,and gained a good electrolytic process.The result of calculation shows that co-electrodeposition Mg,Li and Al occurs at the cathode current density higher than 9 A/cm2 and electrolytic voltage between 6 to 9 V.And at the optimal parameters,12-13 A/cm2,620-640 ℃,the highest current effciency reaches as high as 86%.Lithium combined with magnesium forms Li0.92Mg4.08 and Li3Mg7,and aluminum mainly exists in a form of Mg0.58Al0.42,distributing in the alpha phases and beta phases.
