Study On Preparation And Mechanism Of Mg-Li-Sm,Al-Li-Sm,Al-Li-Y Alloys By Electrolysis In Molten Salts

Mg-Li base alloys and Al-Li base alloys are the lightest structural materials which have been widely used in the fields of electricity, weapon industry and spaceflight, etc. These alloys are conventionally prepared by directly mixing and fusing the metallic elements. In this paper, Mg-Li base alloys and Al-Li base alloys are prepared by electrolysis in molten salts. Moreover, the electrochemical process of rare earth ions and electrochemical formation mechanism of alloy were also investigated. Mg-Li-Sm alloys, Al-Li-Sm alloys and Al-Li-Y alloys with different phases have been prepared by electrochemical deposition.There are three sections in this paper.1 Mg-Li-Sm alloys were prepared by codeposition method on an inert electrode in a molten LiCl-KCl-MgCl2-SmCl3 system. Transient electrochemical techniques, such as cyclic voltammetry, square wave voltammetry were used to study the reduction mechanism, transport parameters and reversibility properties of samarium. The reduction of Sm (Ⅲ) into Sm (0) proceeded according to a two-step mechanism. Only the first step, which was diffusion controlled and reversible, could be observed in molten chloride on the molybdenum electrode. The diffusion coefficient of samarium ions in the melts was also determined. The condition of co-electrodeposition of Mg, Li and Sm was investigated. The codepositon of Mg, Li and Sm happened when the current indensity exceed about -0.31 A·cm-2. Different phases (α,α+βandβ) of Mg-Li-Sm alloys were prepared via galvanostatic electrolysis. The content of Mg-Li-Sm alloys can be controlled by MgCl2 and SmCl3 concentrations and the electrolytic parameters. This method of preparing Mg-Li-Sm alloys by co-deposition was provede fessible. The microstructure and the corrosion resistance of Mg-Li alloys with Sm addition have been investigated. In the end, the preparation of Mg-Li-Sm alloys in LiCl-KCl-MgCl2 melts by adding Sm2O3 was also studied.2,Al-Li-Sm alloys were prepared by codeposition method on an inert electrode in a molten LiCl-KCl-AlCl3-Sm2O3 system. First, the formation mechanism of Al-Sm alloy was investigated at a solid Al electrode by cyclic voltammetry and open circuit chronopotentiometry in LiCl-KCl-SmCl3 melts. A new signal was observed at about -1.70 V. Since this potential value was more positive than the potential of samarium metal deposition, the cathodic peak was thought to be caused by the formation of Al-Sm alloy. Sample obtained at-1.65 V～-1.90 V was identified as Al3Sm and Al substrate. However, sample obtained at more cathodic potential,-2.05 V, is found to be Al3Sm, Al2Sm. Potentiostatic electrolysis results showed that the composition of the formed Al-Sm alloys could be controlled by electrochemical potential. In LiCl-KCl-AlCl3-Sm203 molten system, the solid Sm2O3 could be chlorinated by AICl3, and formed SmCl3. ICP analysis and SWV test also proved that. Transient electrochemical techniques such as cyclic voltammetry, chronopotentiometry have been used in order to investigate the deposition behavior of Al, Li, and Sm ions. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of samarium on pre-deposited aluminum led to the formation of Al-Sm alloy. Al-Li-Sm alloys with different phases were prepared via galvanostatic electrolysis. The lithium and samarium contents in Al-Li-Sm alloys could be adjusted by changing the addition of AICl3 into the melts. The microstructure of alloy sample was characterized by scanning electron microscopy (SEM).3,Al-Li-Y alloys were prepared by codeposition method on an inert electrode in a molten LiCl-KCl-AlCl3-Y2O3 system. Transient electrochemical techniques, such as cyclic voltammetry, square wave voltammetry were used to study the reduction mechanism, transport parameters and reversibility properties of Y (III) in LiCl-KCl-YCl3 melts. The reduction of Y (Ⅲ) into Y (0) proceeded according to one step with three electron transfer. The reaction Y (Ⅲ)/Y (0) was diffusion controlled and reversible. The diffusion coefficient of Y (Ⅲ) ions at different temperature in the melts was also determined. These results obey the Arrehnius' law.The formation mechanism of Al-Y alloy was investigated at a solid Al electrode by cyclic voltammetry and open circuit chronopotentiometry. A new signal was observed at about-1.45 V. Since this potential value was more positive than the potential of Y metal deposition, the cathodic peak was thought to be caused by the formation of Al-Y alloy. Potentiostatic electrolysis results showed that Al3Y,Al2Y alloys formed at different potentials. In LiCl-KCI-AICl3-Y2O3 molten system, the solid Y2O3 could be chlorinated by AICl3, and formed YCl3. Transient electrochemical techniques such as cyclic voltammetry, chronopotentiometry have been used in order to investigate the deposition behavior of Al, Li, and Y ions. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of Y on pre-deposited aluminum led to the formation of Al-Y alloy. Al-Li-Y alloys with different phases were prepared via galvanostatic electrolysis. The Li and Y contents in Al-Li-Y alloys could be adjusted by changing the addition of AICl3 into the melts. The microstructure of alloy sample was characterized by SEM.In this thesis, co-electrodepositing mechanism of ternary Mg-Li-Sm alloys, Al-Li-Sm alloys and Al-Li-Y alloys from RE oxides in the molten salts was investigated. During the electrolysis process, the formation of liquid cathode, the depolarization effect and the effect of alloying led to the formation of multicomponent alloy, which make electrolysis condition moderate and is easy to bring about industrialization. All of this supplies a reliable technical routine for new alloy materials.