Structure and electrochemical hydrogen storage behaviors of Mg-Ce-Ni-Al-based alloys prepared by mechanical milling

The influences of milling time and Ce content on the electrochemical property and micro structure of asmilled Mg_(1-x)Ce_xNi_(0.9)Al_(0.1)(x=0,0.02,0.04,0.06,0.08)+50 wt%Ni alloys were investigated systematically.The as-milled alloys have an outstanding activation property.The cycle stability conspicuously grows up with milling time and Ce proportion increasing.The capacity retention rate at 100 th cycle of x=0.02 alloy augments from 47% to 63% when prolonging milling time from 5 to 30 h and it grows from55% to 82% for the 30 h milled alloy with Ce content growing from 0 to 0.08.The discharge capacity of x=0.02 alloy grows up invariably with milling time prolonging,while that of the 30 h milled alloys has the maximal value of 578.4 mAh/g with Ce content increasing.Moreover,the electrochemical kinetic properties of alloys significantly improve with milling duration extending,while they have the maximal values with Ce proportion varying.     

An investigation on electrochemical hydrogen storage performances of Mg-Y-Ni alloys prepared by mechanical milling

The nanocrystalline and amorphous Mg2Ni-type electrode alloys with a composition of Mg20?xYxNi10 (x=0, 1, 2, 3 and 4) were fabricated by mechanical milling. Effects of Y content on the structures and e...     

Hydrogen storage thermodynamic and kinetic characteristics of PrMg12-type alloys synthesized by mechanical milling

To improve the hydrogen storage performance of PrMg_(12)-type alloys,Ni was adopted to replace partially Mg in the alloys. The PrMg_(11)Ni+x wt.% Ni( x = 100,200) alloys were prepared via mechanical m illing. The phase structures and m orphology of the experim ental alloys were investigated by X-ray diffraction and transm ission electron microscopy. The results show that increasing milling time and Ni content accelerate the form ation of nanocrystalline and am orphous structure. The gaseous hydrogen storage properties of the experim ental alloys were determ ined by differential scanning calorim etry( DSC) and Sievert apparatus. In addition,increasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subsequently and the dehydrogenation rate always increases. The maximum capacity is 5. 572 wt. % for the x = 100 alloy and 5. 829 wt. % for the x = 200 alloy,respectively. The enthalpy change( ΔH),entropy change( ΔS) and the dehydrogenation activation energy( E_k~(de)) markedly lower with increasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.     

Highly ameliorated gaseous and electrochemical hydrogen storage dynamics of nanocrystalline and amorphous LaMg12-type alloys prepared by mechanical milling

Nanocrystalline and amorphous LaMg12-type alloy-Ni composites with a nominal composition of LaMg11 Ni+x wt.% Ni (x=100, 200) were synthesized via ball milling.The influences of ball mill-ing duration and Ni adding amount x on the gaseous and electrochemical hydrogen storage dynamics of the alloys were systematically studied.Gaseous hydrogen storage performances were studied by a differential scanning calorimeter and a Sievert apparatus.The dehydrogenation activation energy of the alloy hydrides was evaluated by Kissinger method.The electrochemical hydrogen storage dynam-ics of the alloys was investigated by an automatic galvanostatic system.The H atom diffusion and ap-parent activation enthalpy of the alloys were calculated.The results demonstrate that a variation in Ni content remarkably enhances the gaseous and electrochemical hydrogen storage dynamics perform-ance of the alloys.The gaseous hydriding rate and high-rate discharge (HRD) ability of the alloys ex-hibit maximum values with varying milling duration.However, the dehydriding kinetics of the alloys is always accelerated by prolonging milling duration.Specifically, rising milling time from 5 to 60 h makes the hydrogen desorption ratio (a ratio of the dehydrogenation amount in 20 min to the saturat-ed hydrogenation amount) increase from 57% to 66% for x=100 alloy and from 57% to 70% for x=200.Moreover, the improvement of gaseous hydrogen storage kinetics is attributed to the descending of dehydrogenation activation energy caused by the prolonging of milling duration and growing of Ni content.     

TiFe储氢合金的电化学性能研究

研究了机械合金化（MA）、真空电弧熔炼、熔炼后短时间球磨、退火和辐射照对TiFe合金电化学性能的影响。短时间球磨可提高TiFe合金放电容量和倍率放电性能,高能辐照可以激活电极表面活性,促进活化;机械合金化可以降低电极极化,增加循环寿命;退火对TiFe合金的电化学性能不利,同时,对真空电弧熔炼TiFe合金在高温时的电化学性能作了初步研究。     

Microstructures and electrochemical properties of LaNi3.8-xAlx hydrogen storage alloys

The microstructures and electrochemical properties of LaNi3.8-xAlx (x=0.0,0.1,0.2,0.3 and 0.4) alloys were studied systematically. The microstructures were identified by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The main phases were not changed with the substitution of Ni by Al, but minor phases appeared when x=0.4. With Al content increasing, the cell volume increased and the hydrogen storage capacity increased first and then decreased, and the maximum discharge capacity increased from 209.4 mAh/g (x=0.0) to 285.3 mAh/g (x=0.3) and then decreased to 241.3 mAh/g (x=0.4). Meanwhile, the exchange current density (I0) increased and the diffusion coefficient (D) decreased with the addition of Al.     

Improved electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys with lanthanum partially substituted by yttrium

Yttrium(Y) has been used as the partial substitution element for lanthanum(La) to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. La0.80–xYxMg0.20Ni2.85Mn0.10Co0.55Al0.10(x=0.00, 0.05 and 0.10) alloys were prepared by the inductive melting technique. The alloys were composed of La Ni5 and(La,Mg)2Ni7 phases, the introduction of Y promoted the formation of(La,Mg)2Ni7 phase, and thus the Y-substituted alloy electrodes exhibited higher discharge capacities. Y substitution was also found to be effective to improve the discharge kinetics of the alloy electrodes. When the Y content x increased from 0.00 to 0.10, the high-rate dischargeability of the alloy electrodes at a discharge current density of 1800 m A/g(HRD1800) increased from 23.6% to 39.7% at room temperature. In addition, the measured HRD1800 showed a linear dependence on both the exchange current density and the hydrogen diffusion coefficient at different temperatures, respectively.     

Structure and high-temperature electrochemical properties of La_（0.60）Nd_（0.15）Mg_（0.25）Ni_（3.3）Si_（0.10） hydrogen storage alloys

The structure and high-temperature electrochemical properties of the as-cast and annealed (940 °C, 8 h) La0.60Nd0.15Mg0.25Ni3.3Si0.10 hydrogen storage alloys were investigated. The X-ray diffraction revealed that the multiphase structure of the as-cast alloy with LaNi5 phase as the main phase was converted into a double-phase structure with La2Ni7 phase as the main phase after annealing. The surface morphology studied by scanning electronic microscope (SEM) showed that the annealed alloy had a much higher anti-corrosion ability than the as-cast alloy. Both alloys presented excellent activation characteristics at all test temperatures. The maximum discharge capacity of the as-cast alloy decreased when the test temperature increased, while the temperature almost had no effect on the annealed alloy. As the test temperature increased, the cyclic stability and charge retention of both alloys decreased, and these properties were improved significantly by annealing.     

Composition optimization and electrochemical characteristics of Co-free Fe-containing AB5-type hydrogen storage alloys through uniform design

In order to reduce the cost of AB5-type hydrogen storage alloys, effects of substitution of Ce for La (A side) and Fe, Mn, Al for Ni (B side) on structural and electrochemical properties of (LaCe)1(NiFeMnAl)5 alloys were studied systematically. To make component uniform and operation easy, uniform design (UD) method was introduced into the study of composition optimization of Co-free Fe-containing AB5-type alloys for the first time. X-ray diffraction (XRD) results showed that the designed alloys were of single CaCu5-type structure phase. The replacement of Fe had a severe effect on electrochemical capacity, and the substitution of Fe and Al had a synergetic action among the unit cell volume, cycling stability and high rate discharge property. Interestingly, it was found that the hydrogen storage alloys with exces-sively high plateau pressure showed a tilted line in Nyquist plot instead of the semicircle, and the current decayed rapidly to near zero at the beginning of the step in constant potential step (CPS), indicating that electrochemical impedance spectra (EIS) and CPS cannot accurately measure the electrochemical kinetics process of the hydrogen storage alloys with excessively high plateau pressure.     

A comparison study of hydrogen storage performances of SmMg11Ni alloys prepared by melt spinning and ball milling

The melt spinning(MS) and ball milling(BM) technologies are thought to be efficient to prepare nanostructured Mg and Mg-based alloys for improving their hydrogen storage performances. In this paper, two technologies, viz. melt spinning and ball milling, were employed to fabricate the SmMg_(11)Ni alloy. The structure and hydrogen storage performance of these two kinds of alloys were researched in detail. The results reveal that the as-spun and milled alloys both contain nanocrystalline and amorphous structures. By means of the measurement of PCT curves, the thermodynamic parameters of the alloys prepared by MS and BM are ΔN_(Ms)(des) = 82.51 kJ/mol and ΔH_(BM)(des) = 81.68 kJ/mol, respectively, viz.ΔH_(MS)(des) ΔH_(BM)(des). The as-milled alloy shows a larger hydrogen absorption capacity as compared with the as-spun one. The as-milled alloy exhibits lower onset hydrogen desorption temperature than the as-spun one. As to the as-milled and spun alloys, the onset hydrogen desorption temperatures are557.6 and 565.3 K, respectively. Additionally, the as-milled alloy shows a superior hydrogen desorption property than the as-spun one. On the basis of time that required by desorbing hydrogen of 3 wt% H_2, the as-milled alloy needs 1488.574,390 and 192 s corresponding to hydrogen desorption temperatures 593,613,633 and 653 K, while the as-spun alloy needs 3600,1020,778 and 306 s corresponding to the same temperatures. The dehydrogenation activation energies of the as-milled and spun alloys are 100.31 and105.56 kJ/mol, respectively, the difference of which is responsible for the much faster dehydriding rate of the as-milled alloy.     

Production of chromium base alloys by ball milling in hydrogen iodide

The effects of processing variables on the tensile properties and ductile-to-brittle transition temperature (DBTT) of Cr+4 vol pct ThO₂ alloys and of pure Cr produced by ball milling in hydrogen iodide were investigated. Hot rolled Cr+ThO₂ was stronger than either hot pressed Cr+ThO₂ or pure Cr at temperatures up to 1540°C. Hot pressed Cr+ThO₂ had a DBTT of 500°C as compared with ?8°, to 24°C for the hot rolled Cr+ThO₂ and with 140°C for pure Cr. It is postulated that the dispersoid in the hot rolled alloys lowers the DBTT by inhibiting recovery and recrystallization of the strained structure.     

机械球磨制备纳米晶Ni-30％Fe固溶体的研究

在Ar气氛下用机械球磨方法制备了Ni-30％Fe(质量分数)纳米晶固溶体粉末，用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、电子探针(EPMA)、差热分析(DSC)等方法观察和分析了Ni-30％Fe(质量分数)粉末机械球磨过程中微观组织演变及相变过程。结果表明，在球磨初始阶段粉末颗粒呈现出粗大片层组织，随球磨进行演变为细小片层结构。球磨至25h，形成了晶粒尺寸为10nm的Ni基固溶体。DSC的结果表明在1444．2℃出现固相-液相转变。     

Phase structure and electrochemical properties of laser sintered La2MgNi9 hydrogen storage electrode alloys

Phase structure and electrochemical properties of laser sintered La2MgNi9 alloys were studied. The sintered alloys contained a main phase, LaNi5, and a ternary La-Mg-Ni phase, with a PuNi3 structure and a small amount of LaMgNi4. The ternary La-Mg-Ni phase with a PuNi3 structure had the composition of La1.8Mg1.2Ni9 and La2MgNi9, for alloys laser sintered at 1000 and 1400 W, respectively. Owing to further reactions between LaNi5 and LaMgNi4, the amount of the PuNi3 phase increased for alloys sintered at 1400 W. Both alloys had good activation property (three charge/discharge cycles). The discharge capacities of the sintered alloys were 321.8 and 344.8 mAh/g, respectively. Compared with the alloy laser sintered at 1000 W, the poor cyclic stability of the alloy sintered at 1400 W was mainly attributed to the lower corrosion resistance of the La2MgNi9 phase.     

机械合金化制备Ag-Cu_(28)合金过程的研究

采用机械合金化法制备Ag-Cu28二元共晶合金,通过正交试验研究球磨机转速、球料比及过程控制剂对合金化过程的影响,利用XRD、SEM、TG-DSC等方法对球磨粉料的物相组成、微观形貌、熔化特性等进行表征.结果表明:Ag、Cu经过30h球磨,生成了Ag(Cu)过饱和固溶体,其熔化温度为783.8℃,该合金属于亚稳态结构,退火处理后以富银、富铜相形式存在.合金化过程中,硬脂酸作为过程控制剂的加入可以有效地减小颗粒尺寸,但对合金化不利.     

Gaseous hydrogen storage properties of Mg-Y-Ni-Cu alloys prepared by melt spinning

For purpose of promoting the hydrogen absorption and desorption thermodynamics and kinetics properties of Mg-Ni-based alloys, partially substituting Y and Cu for Mg and Ni respectively and melt spinning technique were applied for getting Mg_(25-x)Y_xNi_9 Cu(χ = 0-7) alloys. Their microstructures and phases were characterized with the help of X-ray diffraction and transmission electron microscopy. Their hydrogen absorbing and desorbing properties were tested by a Sievert apparatus, DSC, and TGA, which were connected with a H_2 detector. In order to estimate the dehydrogenation activation energy of alloy hydride, both Arrhenius and Kissinger methods were applied for calculation. It is found that their hydriding kinetics notably declines, however, their hydrogen desorption kinetics conspicuously improves, with spinning rate and Y content increasing. Their hydrogen desorption activation energy markedly decreases under the same constraint, and it is found that melt spinning and Y substituting Mg improve the real driving force for dehydrogenation. As for the tendency of hydrogen absorption capacity,it presents an elevation firstly and soon after a decline with the rising of spinning rate, however, it always lowers with Y content growing. With Y content and spinning rate increasing, their thermodynamic parameters(△H and △S absolute values) visibly decrease, and the starting hydrogen desorption temperatures of alloy hydrides obviously lower.     

氢化燃烧合成镁基贮氢合金的研究进展

系统综述了氢化燃烧法制备镁基贮氢合金Mg2Ni的研究进展，包括制备原理、与其它制备方法的些较／影响氢化燃烧的因素以及材料的贮氢性能。同时简要介绍了氢化燃烧合成Mg-Fe、Mg-Co和Mg-Ni-Cu等贮氢合金的一些研究成果     

粉末冶金法制备La_(0.75)Mg_(0.25)Ni_(3.5-x)Mn_x(x=0-0.4)合金及其电化学贮氢性能研究

为了改善稀土系A_2B_7型贮氢合金的电化学贮氢性能,采用粉末冶金方法制备的La_(0.75)Mg_(0.25)Ni_(3.5-x)Mn_x(x=0,0.1,0.2,0.3,0.4)贮氢合金,研究少量Mn替代Ni对合金相结构和电化学性能的影响。结果表明:合金由La Ni5、La2Ni7两相组成,随着Mn含量的增加,两相晶胞逐渐膨胀。Mn的加入能显著改善合金的电化学性能,然而过高的Mn含量会对合金的放电性能带来不利影响。其中La_(0.75)Mg_(0.25)Ni_(3.2)Mn_(0.3)合金电极的最大放电容量为362.3m Ah/g,经过100次循环后容量保持率为69.5%。此外,合金电极的高倍率放电性能、线性极化曲线以及电化学交流阻抗谱的测试均表明合金的电化学动力学性能随着Mn含量的增加先增大而后减小。     

粉末粒度对储氢合金电化学性能与气态储氢性能的影响

采用真空中频感应熔炼炉熔炼La_(0.67)Mg_(0.33)Ni_(2.5)Co_(0.5)合金,机械研磨成粉,分级过筛得到一系列不同粒度的合金粉末(平均粒度为10μm、53μm、77μm、119μm、196μm),通过XRD、SEM、激光衍射法等方法系统地研究分析了粉末粒度对储氢合金La_(0.67)Mg_(0.33)Ni_(2.5)Co_(0.5)气态储氢性能和电化学性能的影响。不同粒度合金气态吸放氢循环后都发生了不同程度的粉化,大颗粒以表面剥落的方式产生细粉,小颗粒以体断裂的方式粉化,小颗粒的抗粉化能力更强,电化学循环后,合金粉末粉化造成粉末掉渣形成孔洞。粒度越小,气态储氢孕育期越短,活化时间越短,电化学活化性能越好。随着合金粒度的减小,理论最大放电容量和实际测试的最大放电容量也随之减小,而理论容量发挥值却在增加。随循环次数增加,气态饱和储氢量和电化学放电容量急剧下降,小粒度合金循环寿命略好于大粒度合金粉。