Study on electrochemical preparation of Al-Li-Y alloys from Y_2O_3 in LiCl-KCl-AlCl_3 molten salts

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.     

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

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-MgCl2-CeCl3 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.     

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

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.     

Electrochemical Codeposition of Al-Li-Mg Alloys at Solid Aluminum Electrode from LiCl-KCl-MgCl2 Molten Salt System

The electrochemical codeposition of Mg and Li at an aluminium electrode in LiCl-KCl (50:50 wt pct) melts containing different concentrations of MgCl₂ at 893 K (620 °C) to form Al-Li-Mg alloys was investigated. Cyclic voltammograms showed that the potential of Li metal deposition at an Al electrode, before the addition of MgCl₂, is more positive than that of Li metal deposition at an Mo electrode, which indicated the formation of an Al-Li alloy. The underpotential deposition of magnesium at an aluminium electrode leads to the formation of Al-Mg alloys, and the succeeding underpotential deposition of lithium on predeposited Al-Mg alloys leads to the formation of Al-Li-Mg alloys. Chronopotentiometric measurements indicated that the codeposition of Mg and Li occurs at current densities lower than −0.668 A cm⁻² in LiCl-KCl-MgCl₂ (8 wt pct) melts at an aluminium electrode. The chronoamperometric studies indicated that the onset potential for the codeposition of Mg and Li is −2.000 V, and the codeposition of Mg and Li at an aluminium electrode is formed into Al-Li-Mg alloys when the applied potentials are more negative than −2.000 V. X-ray diffraction and inductively coupled plasma analysis indicated that Al-Li-Mg alloys with different lithium and magnesium contents were prepared via potentiostatic and galvanostatic electrolysis. The microstructure of typical dual phases of the Al-Li-Mg alloy was characterized by an optical microscope and by scanning electron microscopy. The analysis of energy dispersive spectrometry showed that the elements of Al and Mg distribute homogeneously in the Al-Li-Mg alloy. The lithium and magnesium contents of Al-Li-Mg alloys can be controlled by MgCl₂ concentrations and by electrolytic parameters.     

Electron Theory Research in Mg-Y Alloy

Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory of solids and molecules (EET). Calculation shows that yttrium is on the fifth hybrid level and magnesium is on the third one in pure metal crystals. By comparing with aluminum in Mg-Al alloy, it is shown that the reason why the solution strengthening effect of yttrium is better than that of aluminum in Mg-Al alloy is the enhanced bond energy according to EET. And it is concluded from EET analysis that intermetallies Mg24Y5 can significantly improve the properties of magnesium alloys because yttrium atoms oceupy the centers of the oetahedron and Mg-Y bonds efficiently strengthen the alloy matrix.     

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 773K. 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.     

Electrochemical formation of Mg–La–Mn alloys by coreduction of Mg(II), La(III) and Mn(II) in LiCl+KCl molten salts

In the present work, cyclic voltammetry (CV), square wave voltammetry (SWV) and chronopotentiometry (CP) were used to investigate the electrochemical coreduction behaviors of La(III) and Mg(II) as well as La(III), Mg(II) and Mn(II) on Mo electrode in LiCl + KCl molten salts. CV and SWV results exhibit that the coreduction mechanism of La (III) and Mg(II) on Mo electrode is that La(III) is reduced and Mg–La intermetallic compound is formed, leading to the deposition potential of La(III) shifting to more positive one. The electrochemical signals pertaining to the formation of metallic La, Mg and Mn as well as Mg–La intermetallic compound are also observed by coreduction of La(III), Mg(II), and Mn(II) in LiCl + KCl molten salt on the inert Mo electrode. However, the electrochemical signals associated with the formation of La–Mn and Mg–Mn alloys are not observed, which means that the depolarization effect of La(III) and Mg(II) does not occur on pre-deposited Mn electrode. The Mg–La–Mn alloys were formed by co-deposition of La(III), Mg(II), and Mn(II) on Mo electrode at various concentration ratios of La(III) and Mg(II). The results of scanning electron microscopy equipped with energy dispersive spectroscopy and X-ray diffraction displays that the Mg–La–Mn alloys are comprised of La–Mg compound Mg₁₇La₂, Mg and Mn phases. The concentration ratio of La(III) and Mn(II) has few effects on the alloy composition.     

Effect of cobalt content on electrochemical performance of La-Mg-Ni system （Ce2Ni7-type） electrode alloys

In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure of the alloys were investigated in detail. XRD results showed that the alloys had multiphase structure composed of （La, Mg）2Ni7, LaNi5 and small amount of LaNi2 phases. The discharge capacity of the alloys first increased and then decreased with increasing Co content. At a discharge current density of 900 mA/g, the HRD of the alloy electrodes increased from 81.3% （x=0） to 89.2 % （x=0.2）, and then reduced to 87.8 % （x=0.6）. After 60 charge/discharge cycles, the capacity retention rate of the alloys enhanced from 52.67% to 61.32%, and the capacity decay rate of the alloys decreased from 2.60 to 2.05 mAh/g per cycle with increasing Co content. The obtained results by XPS and XRD showed that the fundamental reasons for the capacity decay of the La-Mg-Ni system （Ce2Ni7-type） alloy electrodes were corrosion and oxidation as well as passivation of Mg and Lain alkaline solution.     

添加钕对Mg2Ni储氢合金的结构和电极性能的影响

利用两步法制备了一系列添加Nd的三元Mg2-xNdxNi合金。XRD分析证实，当x=0．05，0．1时，制得的三元Mg2-xNdxNi合金均为Mg2Ni单相合金；三元Mg18Nd0．2Ni(x=0．2，0．3)合金为三相合金，三相分别为Mg2Ni，NdNi，NdMgNi4。模拟电池测试结果表明，同Mg2Ni合金相比，球磨10h的三元Mg1．8Nd0．2Ni合金和Mg17Nd03Ni合金电极的放电容量提高明显，且Mg17Nd03Ni合金电极的循环性能有明显改善。这极有可能与合金中NdMgNi4相的存在以及球磨形成的微结构有关。     

钇对纯镁的组织和性能的影响

采用金相显微镜(OM)、扫描电镜(SEM)对Mg-Y合金与纯镁的铸态凝固组织进行了观察,并采用X射线衍射仪(XRD),能谱分析仪(EDS)对合金在凝固过程中形成的相进行了分析,利用析氢法及电化学方法研究了Mg-Y合金与纯镁在3.5%的NaCl溶液中的腐蚀行为。结果表明,纯镁的晶粒比较粗大,合金的晶粒比纯镁小,合金由灰白色的初生α相和深色的共晶组织构成,以及少量呈颗粒状弥散分布在基体中Mg24Y5相。析氢法中,试样在浸泡了8 h左右时,合金腐蚀速率是纯镁的2.85倍,纯镁在浸泡7 h后pH值稳到10.4左右,而合金的pH值变化较快,在1.5 h后就已经达到了10.4,最后稳定在11.2左右。从腐蚀形貌看,纯镁的腐蚀较浅,沿表面扩展,呈纹理状,合金则呈现明显的局部腐蚀特征,表面形成了严重的腐蚀坑。3.5%的NaCl溶液中测得的极化曲线可以得出,合金的腐蚀电流Icorr(4.05×10-4A.cm-2)比纯镁Icorr(6.81×10-5 A.cm-2)要高的多。     

Structure and electrochemical hydrogen storage characteristics of the as-cast and annealed La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 （x=0-0.4） alloys

In order to ameliorate the electrochemical cycle stability of the RE-Mg-Ni based A2B7-type electrode alloys, the Mg content in the alloy was reduced and La in the alloy was partially substituted by Sm. The La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) elec-trode alloys were fabricated by casting and annealing. The microstructures of the as-cast and annealed alloys were characterized by XRD and SEM. The electrochemical hydrogen storage characteristics of the as-cast and annealed alloys were measured. The results revealed that all of the experimental alloys mainly consisted of two phases: (La,Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. As Sm content grew from 0 to 0.4, the discharge capacity and the high rate discharge ability (HRD) first in-creased and then decreased for the as-cast and annealed alloys, whereas the capacity retaining rate (S100) after 100 cycles increased continuously.     

制备工艺对La_(0.80)Mg_(0.20)Ni_(3.75)合金电极性能的影响

采用中频感应真空熔炼(IM)和放电等离子烧结(SPS)工艺制备La0.80Mg0.20Ni3.75合金。XRD分析表明,这两种工艺制备的合金均含有LaNi5和(La,Mg)2Ni7主相,而中频感应真空熔炼法制备的合金(IMLa合金)还含有(La,Mg)Ni3相,放电等离子烧结法制备的合金(SPSLa合金)还含有Ni及La2Mg17相。电化学性能测试结果表明,作为镍氢电池负极材料,IMLa合金的放电容量、损耗角及极限电流密度均较大;而SPSLa合金的循环性能较好,这归因于SPSLa合金晶粒细小,组织均匀,Ni和La2Mg17相弥散分布,可减弱其电极脱落程度。     

Effect of Ni/（La＋Mg） Ratio on Structure and Electrochemical Performance of La-Mg-Ni Alloy System

As the alloy with the most suitable Ni/(La+ Mg) ratio has higher capacity and good cycle stability,theeffects of Ni/(La+Mg) ratios on the electrochemical performances of the La0.80 Mg0.20 Nix (x= 3.5 to 5.0) alloys have been investigated to find the most suitable Ni/(La+ Mg) ratio.The results of XRD and SEM observations show that the phase composition of the alloys varies with different Ni/(La+Mg) ratios.When Ni/(La+Mg) is notmore than 4.25,all the alloys contain LaNi5 and (La,Mg)2Ni7 phases,in addition,the LaMg and (La,Mg)Ni3 phases exist in the x=3.5 and 3.75 alloys,respectively.The LaMg2Ni9 phase exists in the x=4.25 alloy.There are the LaNi5 and LaMg2 Ni9 phases in the x= 4.5,4.75,and 5.0 alloys.The phase abundance and cell volume change with different Ni content.When the Ni/(La+Mg) ratio is not more than 4.25,the alloys possess excellent activation capability,however,the activation capabilities of the alloys decrease with a further increase in the Ni/(La+Mg)ratio.With increasing the Ni/(La+ Mg) ratio,the maximum discharge capacities,the medium voltages,and the cycle stabilities of the alloys first increase and then decrease.When the Ni/(La+Mg) ratio is 3.75,the corresponding alloyhas the maximum discharge capacity among all the alloys.However,the cycle stability of the Ni/(La+ Mg)= 4.0 alloy is better than that of the others.     

快淬纳米晶/非晶Mg2-xLaxNi (x=0～0.6)合金的贮氢动力学

为了改善Mg2Ni型合金气态及电化学贮氢动力学性能,用La部分替代合金中的Mg,用快淬技术制备了Mg2-xLaxNi(x=0,0.2,0.4,0.6)合金,用XRD,SEM,HRTEM分析了铸态及快淬态合金的微观结构;用自动控制的Sieverts设备测试了合金的气态贮氢动力学性能,用程控电池测试仪测试了合金的电化学贮氢动力学.结果发现,快淬无La合金具有典型的纳米晶结构,而快淬含La合金显示了以非晶相为主的结构,表明La替代Mg提高Mg2Ni型合金的非晶形成能力.La替代Mg明显地改变Mg2Ni型合金的相组成.当La替代量x=0.4时,合金的主相改变为(La,Mg) Ni3+ LaMg3.合金的气态及电化学吸放氢动力学对La含量及快淬工艺敏感,La替代使合金的吸氢动力学降低,但适量的La替代可以明显改善合金的放氢动力学及高倍率放电能力.适当的快淬处理可以提高合金的气态及电化学贮氢动力学,但获得最佳贮氢动力学的快淬工艺与合金的成分密切相关.     

Mg_(10)Al_((7-x))Li_2Ti_x(x=0,1,2,3)合金的制备及储氢性能研究

在氩气保护下,采用机械合金化法制备Mg_(10)Al_((7-x))Li_2Ti_x(x=0,1,2,3)合金,并通过XRD、SEM以及DSC等手段对合金进行表征。结果表明,适量的Ti替代Al可以提高合金的吸氢量、降低合金的初始氢化/脱氢温度和提高合金氢化/脱氢动力学性能。Mg_(10)Al_((7-x))Li_2Ti_x(x=1,2,3)合金样品比Mg10Al7Li2合金的初始氢化温度都降低了62K,而初始脱氢温度则分别降低了77、98和59K。当Ti的替代量为x=2时,合金的综合储氢性能最好。     

A Novel Developed Grain Refiner (Al–Y–B Master Alloys) Using Yttrium and KBF<Subscript>4</Subscript> Powders

The present work aims to report and discuss the development of a novel grain refiner (Al–Y–B master alloys) focusing on the characterization of the phenomena that exist during their production. Al–Y–B master alloy is produced by the combined employment of yttrium and boron, instead of yttrium or boron individually. It is discovered as a highly effective grain refiner for inoculating the grain size of Al–Si alloys. The crystallized microstructure can be refined though the effect of Y-based intermetallic on heterogeneity nucleus. The Y-based intermetallic is formed in the melts (Al–Y–B master alloy) by the addition of yttrium and KBF₄ powers. A approach to produce Al–Y–B master alloys as well as its characterization by means of optical micrographs and SEM is presented. The study is assessed by testing the grain refining potency of the produced Al–Y–B master alloys in binary Al–20Si alloy. It is revealed that the approach employed to produce the Al–Y–B master alloys is suitable because the size of the primary phases is significantly reduced in each of the case investigated.     

Influence of rapid quenching on cyclic stability of La-Mg-Ni system （AB3-type） electrode alloys

Aiming at the improvement of the cyclic stability of La-Mg-Ni system （PuNi3-type） hydrogen storage alloy, Ni in the alloy was partly substituted by Fe. The electrode alloys of La0.7Mg0.3Co0.45Ni255-xFex （x=0, 0.1, 0.2, 0.3, 0.4） were prepared by casting and rapid quenching. The influence of the quenching on cyclic stability as well as structure of the alloys was investigated in detail. The results of electrochemical measurement indicated that rapid quenching significantly improved cyclic stability. When the quenching rate rose from 0 （As-cast was defined as a quenching rate of 0 m/s） to 30 m/s, the cyclic life of Fe-free alloy （x=-0） increased from 81 to 105 cycles, and for alloy containing Fe（x=0.4）, it grew from 106 to 166 cycles at a current density of 600 mA/g. The results obtained by XRD, TEM and SEM revealed that the as-cast and quenched alloys had multiphase structures, including two major phases （La, Mg）Ni3 and LaNi5 as well as an imptLrity phase LaNi2. Rapid quenching helped the formation of an amorphous-like structure in Fe containing alloys.     

Influences of Yttrium on Microstructure and Mechanical Properties of NiAl-28Cr-5.5Mo-0.5Hf Alloy

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Effect of annealing temperature on microstructure and electrochemical performance of La0.75Mg0.25Ni3.5Co0.2 hydrogen storage electrode alloy

To improve the cyclic stability of La-Mg-Ni system alloy, as-cast La0.75Mg0.25Ni3.5Co0.2 alloy was annealed at 1123, 1223, and 1323 K for 10 h in 0.3 MPa argon. The microstructure and electrochemical performance of different annealed alloys were investigated systematically by X-Ray Diffraction （XRD）, Scanning Electron Microscopy （SEM）, X-Ray Photoelectron Spectroscopy （XPS）, and electrochemical experiments. The results obtained by XRD and SEM showed that the as-cast and annealed （1123 K） alloys had multiphase structure containing LaNis, （La, Mg）2（Ni, Co）7 and few LaNi2 phases. When annealing temperatures approached 1223 and 1323 K, LaNi2 phase disappeared. The annealed alloys at 1223 and 1323 K were composed of LaNi5, （La, Mg）2（Ni, Co）7 and （La, Mg）（Ni, Co）3 phases. With increasing annealing temperature, the maximum discharge capacity of the alloy decreased monotonously, but the cyclic stability was improved owing to structure homogeneity and grain growth after annealing, as well as the enhancement of anti-oxidation/corrosion ability and the suppression of pulverization during cycling in KOH electrolyte.