【作者】 陈丽军；

【导师】 张密林；

【作者基本信息】 哈尔滨工程大学 ， 材料学， 2012， 博士

【摘要】 镁锂基合金作为最轻的结构材料，在工业领域有着广泛的应用前景。Pb、Mn和Yb都是镁锂基合金的合金化元素，在一定程度上可以细化合金晶粒，改善合金性能。目前都是采用对掺法来制备合金，但该方法存在工艺复杂，成本高等缺点。而由于熔盐电解具有工艺简单，制备温度低，能耗少等优点，在制备镁锂合金方面是目前备受关注的取代传统对掺法的途径之一。因此本文采用循环伏安法和计时电位法等电化学方法研究了Pb（Ⅱ）、Mn（Ⅱ）和Yb（Ⅲ）离子在熔盐中的电化学行为及其金属合金的共电沉积机理，并用XRD、SEM、ICP等技术对恒电流电解制备的Mg–Li–M（Pb、Mn、Yb）合金样品进行了表征，这对熔盐电解制备合金有一定的指导意义。本文主要研究了在873K时，以钼电极做研究电极，Pb（Ⅱ）离子在LiCl–KCl和LiCl–KCl–MgCl₂–PbCl₂两个熔盐体系中的电化学行为。Pb（Ⅱ）离子在熔盐中一步得到2个电子被还原为金属Pb，且Pb（Ⅱ）离子在低扫速时的还原和氧化过程是可逆过程，Pb（Ⅱ）离子在熔盐中的扩散系数为1.92×10^-5cm²·s^-1。另外，在LiCl–KCl–MgCl₂–PbCl₂熔盐体系中考察了镁锂铅合金的共电沉积机理。当阴极电流密度达到或负于–0.776A·cm^-2，阴极电位为–1.93V（vs.Ag/AgCl）或更负时，可以实现金属Pb、Mg和Li共电沉积。最后用恒电流电解制备了Mg–Li–Pb合金。合金中含有Mg2Pb、Li7Pb2等多个合金相，且合金中Pb和Li含量与熔盐中MgCl₂和PbCl₂的浓度有关，Pb元素弥散均匀分布在合金中。另外，还研究了LiCl–KCl–MgCl₂–MnCl₂和LiCl–KCl–MgCl₂–MnO₂（纳米）两个熔盐体系中金属Mg、Mn、Li的共电沉积机理。933K时，在LiCl–KCl–MgCl₂–MnCl₂熔盐体系中，Mn（Ⅱ）离子在熔盐中一步得到2个电子被还原为金属Mn，Mn（Ⅱ）离子在该熔盐体系中的扩散系数为1.23×10^-5cm²·s^-1。考察了金属Mn、Mg和Li的共电沉积条件。当阴极电流密度达到或负于-0.781A·cm^-2或阴极电位比–2.28V（vs. Ag/AgCl）更负时，Mn（Ⅱ）、Mg（Ⅱ）和Li（I）离子一起被还原，在该条件下可共电沉积制备Mg–Li–Mn合金。在钼电极上，采用循环伏安法、方波伏安法、计时电流法等电化学研究方法研究了锰离子在LiCl–KCl–MgCl₂–MnO₂（纳米）熔盐体系中的电化学行为。在研究中用于提供Mn元素的纳米MnO₂是通过液相氧化还原法用KMnO₄和MnSO₄制得的。研究结果表明LiCl–KCl–MgCl₂–MnO₂（纳米）熔盐熔融后，MnO₂（纳米）被氯化，Mn以K₄MnCl₆的形式存在。793K时，Mn（Ⅱ）离子在该熔盐体系中是一步得到2个电子被还原为金属Mn。当阴极电流密度负于-0.087A·cm^-2或阴极电位比–2.20V（vs. Ag/AgCl）更负时，可以实现金属Mn、Mg和Li共电沉积。采用恒电流电解法分别在两个熔盐体系中制备了Mg–Li–Mn合金。合金中含有Mg–Mn固溶体、βLi和αMn三个相，且合金中Li和Mn的含量与熔盐中MgCl₂和MnCl₂、MnO₂的浓度有关，Mn元素呈弥散相均匀分布在合金中。本文最后以LiCl–KCl–MgCl₂–Yb₂O₃熔盐体系为电解质共电沉积制备Mg–Li–Yb合金。933K时，通过实验与理论相结合的方法研究了MgCl₂对Yb₂O₃的氯化作用。在氯化过程中，有少量的YbCl₃生成，使在LiCl–KCl–MgCl₂–Yb₂O₃熔盐体系中共电沉积制备镁锂镱合金具备了可行性。而循环伏安法和计时电位研究结果证明，当阴极电流密度负于–0.466A·cm^-2或阴极电位控制在负于–2.15V时，可以实现镁锂镱合金的共沉积。另外，研究了Mg、Li、Yb三元共沉积的电解工艺。对合金的微观测试结果显示，合金中主要存在αMg、βLi和Mg2Yb相；Yb元素在Mg–Li–Yb合金中呈网状分布，主要分布在晶界处。随着Yb在合金中含量的增多，合金晶粒变小，Yb起到细化合金晶粒的作用。更多还原

【Abstract】 Mg-Li based alloys, as the lightest structural materials, have widely applied prospect inthe fields of industry. The main alloying elements of Mg-Li based alloys are Pb, Mn and Yb,which can refine the grain and improve the properties. The frequently-used way, which iscomplicated and costly, to prepare Mg-Li based alloys are directly mixing and fusing themetallic elements. This is why the co-electrodeposition of molten salts is getting more andmore attention in recent years. The electrochemical behavior of Pb（Ⅱ）, Mn（Ⅱ） and Yb（Ⅲ）ions were researched by the transient electrochemical techniques, which were cyclicvoltammetry, chronopotentiometry and chronoamperometry, in LiCl-KCl-MgCl₂molten saltsin this thesis. Moreover, the co-electrodeposition mechanism of Mg-Li-M（Pb, Mn, Yb） alloyswere also investigated. The alloys obtained by galvanostatic electrolysis were characterizedby X-ray diffraction （XRD）, inductively coupled plasma atomic emission spectrometer （ICP）,scan electron micrograph （SEM） and energy dispersive spectrometry （EDS）.The electrochemical behavior of Pb（Ⅱ） ions was investigated in the LiCl-KCl-PbCl₂andLiCl-KCl-MgCl₂-PbCl₂melts on Mo electrode at873K in the first part of this thesis. Theresults show that Pb （Ⅱ） is reduced in a one-step process exchanging two electrons. Then aseries of typical cyclic voltammograms with different scan rates in LiCl-KCl-PbCl₂meltsshow that the cathodic/anodic reaction of Pb（Ⅱ） ions is diffusion controlled and reversible atlower scan rate. Then the diffusion coefficient of Pb（Ⅱ） ions is calculated as1.23×10^-5cm²·s^-1.The co-electrodeposition mechanism of Mg, Li and Pb was investigated on a Mo electrode inLiCl-KCl-MgCl₂-PbCl₂melts by cyclic voltammetry and chronopotentiometry at873K,which indicate that the Mg-Li-Pb alloys will co-electrodeposited when the current densitieslower than–0.776A·cm^-2or the applied potential is more negative than–1.93V（vs. Ag/AgCl）.The XRD results confirme that Mg2Pb and Li7Pb2phases are exist in the Mg-Li-Pb alloysobtained by galvanostatic electrolysis. The variation of Mg-Li-Pb alloys phases can becontrolled by changing the concentrations of MgCl₂and PbCl₂in the melts. The SEM andEDS results suggested that the distribution of Pb elements in Mg-Li-Pb alloys are evenlydispersed.The second part of this thesis mainly researched the co-electrodeposition mechanism ofMg-Li-Mn alloys in the LiCl-KCl-MgCl₂melts which contained MnCl₂or nano-MnO₂. Theelectrochemical behavior of Mn（Ⅱ） ions was investigated in the LiCl-KCl-MgCl₂-MnCl₂melts on Mo electrode at933K. The results show that Mn（Ⅱ） is reduced in a one-step processexchanging two electrons. Then a series of typical cyclic voltammograms with different scanrates show that the cathodic/anodic reaction of Mn（Ⅱ） ions is diffusion controlled andreversible at lower scan rate. The diffusion coefficient of Mn（Ⅱ） ions at different temperatures in the molten salts are also calculated. The co-electrodeposition mechanism of Mg-Li-Mnalloys was investigated on a Mo electrode by cyclic voltammetry and chronopotentiometry,which indicate that the Mg-Li-Mn alloys will co-electrodeposit when the current densitieslower than–0.781A·cm^-2or the applied potential is more negative than–2.28V（vs.Ag/AgCl）.The chemical dissolution occurred in the nano-MnO₂-LiCl-KCl-MgCl₂melts. The XRDresults suggest that nano-MnO₂prepared by liquid oxidation-reduction method with KMnO₄and MnSO₄became K₄MnCl₆in the molten salts. The electrochemical behavior of Mn （Ⅱ）ions provided by K₄MnCl₆was investigated on Mo electrode at793K. The typical cyclicvoltammogram and square wave voltammogram show that the Mn（Ⅱ） is reduced in a one-stepprocess exchanging two electrons and controlled by diffusion. The reaction is reversible atlower scan rate. The co-electrodeposition mechanism of Mg, Li and Mn alloys wasinvestigated on a Mo electrode by cyclic voltammetry, chronopotentiometry andchronoamperometry, which indicate that the electrochemical codeposition of Mg, Li and Mnmetal occur when the current densities lower than–0.087A·cm^-2or the applied potential ismore negative than–2.20V（vs. Ag/AgCl）.Mg-Li-Mn alloys obtained by galvanostatic electrolysis were characterized by XRD,SEM and ICP. The XRD results confirm that Mg-Mn sosoloid, βLi and αMn phases all existin the Mg-Li-Mn alloys. The variation of Mg-Li-Mn alloys phases can be controlled bychanging the concentrations of MgCl₂and MnCl₂in the melts. The SEM and EDS resultssuggest that the distribution of Mn elements is uniform and dispersed in Mg-Li-Mn alloys.The preparation of Mg-Li-Yb alloys by electrochemical codeposition on Mo electrode inLiCl-KCl-MgCl₂-Yb₂O₃melts at the last part of this thesis. The MgCl₂has a certain effect ofchlorination on Yb₂O₃. YbCl₃which was generated in the chlorination process made themethod of preparing Mg-Li-Yb alloys by electrocodeposition in LiCl-KCl-MgCl₂-Yb₂O₃melts feasible. The results of cyclic voltammetry and chronopotentiometry show that thecodeposition of Mg, Li and Yb occurred when the current densities lower than–0.466A·cm^-2or the applied potential is more negative than–2.15V（vs. Ag/AgCl）. Then the relationship ofelectrolytic parameters such as time, temperature and current densities with current efficiencywere also researched. The microscopic test results of Mg-Li-Yb alloys show that Mg2Ybphase are exist in the alloys, the elements of Yb are mainly distribute at grain boundaries andthe grain size decline with the content of Yb increased.更多还原