Development of hydrogen-storage alloys by mechanical alloying of Mg with Fe and Co

The hydriding and dehydriding kinetics of Mg are reviewed. In order to improve the reaction kinetics of Mg with hydrogen, mechanically-alloyed Mg-10 wt.%Fe and Mg-10 wt.%Co mixtures are prepared and their hydrogen-storage properties are investigated. The activation of Mg-10 wt.%Fe is easier than that of Mg-10 wt.%Co. However, The hydriding rates (at 569–589 K, 7–11 bar H₂) and dehydriding rates (at 589 K, 1.0 bar H₂) of the mechanically-alloyed Mg-10wt.%Co are higher than those of the mechanically-alloyed Mg-10 wt.%Fe after activation. The H_a value of Mg-10 wt.%Co after 60 min is 3.08 wt.% at 589 K under 11 bar H₂ and its H_d value after 60 min is 1.48 wt.% at 589 K under 1.0 bar H₂. Mg-10 wt.%Co has a smaller particle size than has Mg-10 wt.%Fe after hydriding and dehydriding cycling. The mechanical alloying of Mg with Fe and Co and the hydriding-dehydriding cycling increased the hydriding and dehydriding rates by facilitating nucleation (by creating defects on the surface of the Mg particle and by the additive) and by shortening the diffusion distances (by reducing the Mg particle sizes).     

Influences on the H<Subscript>2</Subscript>-sorption properties of Mg of Co (with various sizes) and CoO addition by reactive grinding and their thermodynamic stabilities

We attempted to improve the H₂-sorption properties of Mg by mechanical grinding under H₂ (reactive grinding) with Co (with various particle sizes) and with CoO. The thermodynamic stabilities of the added Co and CoO were also investigated. CoO addition has the best influence and addition of smaller particles of Co (0.5–1.5 μm) has a better effect than the addition of larger particles of Co on the H₂-sorption properties of Mg. The activated Mg+10 wt.% CoO sample has about 5.54 wt% hydrogen-storage capacity at 598 K and the highest hydriding rate, showing an H_a value of 2.39 wt.% after 60 min at 598 K, 11.2 bar H₂. The order of the hydriding rates after activation is the same as that of the specific surface areas of the samples. The reactive grinding of Mg with Co or CoO and hydriding-dehydriding cycling increase the H₂-sorption rates by facilitating nucleation of magnesium hydride or α solid solution of Mg and H (by creating defects on the surface of the Mg particles and by the additive), and by making cracks on the surface of Mg particles and reducing the particle size of Mg, thus shortening the diffusion distances of hydrogen atoms. The cobalt oxide is stable even after 14 hydriding cycles at 598 K under 11.2 bar H₂. Discharge capacities are measured for the sampple Mg+10 wt.%CoO and Mg+10wt.%Co (0.5−1.5 μm) with good hydrogen-storage properties.     

Hydrogen storage properties of a Ni,Fe and Ti-added Mg-based alloy

Mg-5wt%Ni-2.5wt%Fe-2.5wt%Ti (referred to as Mg-5Ni-2.5Fe-2.5Ti) hydrogen storage material was prepared by reactive mechanical grinding, after which the hydrogen absorption and desorption kinetics were investigated using a Sievert-type volumetric apparatus. A nanocrystalline Mg-5Ni-2.5Fe-2.5Ti sample was prepared by reactive mechanical grinding and hydriding-dehydriding cycling. Analysis by the Williamson-Hall method from an XRD pattern of this sample after 10 hydriding-dehydriding cycles showed that the crystallite size of Mg was 37.0 nm and that its strain was 0.0407%. The activation of Mg-5Ni-2.5Fe-2.5Ti was completed after three hydriding-dehydriding cycles. The prepared Mg-5Ni-2.5Fe-2.5Ti sample had an effective hydrogen-storage capacity near 5 wt% H. The activated Mg-5Ni-2.5Fe-2.5Ti sample absorbed 4.37 and 4.90 wt% H for 5 and 60 min, respectively, at 593K under 12 bar H₂, and desorbed 1.69, 3.81, and 4.85 wt% H for 5, 10 and 60 min, respectively, at 593K under 1.0 bar H₂.     

Hydrogenation reaction of Mg-Based alloys fabricated by rapid solidification

Mg-23.5wt%Ni-xwt%Cu (x=2.5, 5 and 7.5) alloys for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The alloys were ground by a planetary ball mill for 2 h in order to obtain a fine powder. The Mg-23.5Ni-5Cu alloy had crystalline Mg and Mg₂Ni phases. Mg-23.5Ni-5Cu had an effective hydrogen capacity of near 5 wt%. The activated Mg-23.5Ni-5Cu alloy absorbed 4.50 and 4.84 wt%H at 573K under 12 bar H₂ for 10 and 60 min, respectively, and desorbed 3. 21 and 4.81 wt%H at 573K under 1.0 bar H₂ for 10 and 30 min, respectively. The activated Mg-23.5Ni-5Cu alloy showed a quite high hydriding rate like Mg-10Fe₂O₃, and higher dehydriding rates than the activated Mg-xFe₂O_3?yNi. This likely resulted because the melting before melt spinning process has led to the homogeneous distribution of Ni and Cu in the melted Mg, and the Mg-23.5Ni-5Cu alloy has a larger amount of the Mg₂Ni phase than the Mg-xFe₂O_3?yNi alloy.     

Comparison of hydrogen-storage properties of Mg-14Ni-3Fe2O3-3Ti and Mg-14Ni-2Fe2O3-2Ti-2Fe

Magnesium with oxides or transition elements prepared by mechanical grinding under H2 (reactive mechanical grinding) showed relatively high hydriding and dehydriding rates when the content of additives was about 20 wt%. Ni, Fe₂O₃, and Fe were chosen as the oxides or transition elements to be added. Ti was also selected since it was considered to increase the hydriding and dehydriding rates by forming Ti hydride. Samples Mg-14Ni-3Fe₂O₃-3Ti (Sample A) and Mg-14Ni-2Fe₂O₃-2Ti-2Fe (Sample B) were prepared by reactive mechanical grinding, and their hydrogen storage properties were compared. The activated Sample A had a little smaller hydriding rate than the activated Sample B, but a higher dehydriding rate than the activated Sample B. Sample A exhibits quite a larger dehydriding rate and quantity of hydrogen desorbed for 60 min than any other Mg-xNi-yFe₂O₃-zM (M=transition metals) samples. An addition of a relatively larger amount of Ti is considered to lead to quite a high hydriding rate and a high dehydriding rate of Sample A.     

Phase transformations and hydrogen-storage characteristics of Mg-transition metal-oxide alloys

Samples with the compositions of 76.5 wt%Mg-23.5 wt%Ni (Mg-Ni), 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe₂O₃ (Mg-Ni-Fe₂O₃) and 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe₂O₃ (spray conversion) (Mg-Ni-scFe₂O₃), 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe (Mg-Ni-Fe) and 80 wt%Mg-13.33 wt%Ni-6.67 wt%Fe (Mg-13Ni-7Fe) were prepared by reactive mechanical grinding. Mg-13Ni-7Fe has the highest hydriding and dehydriding rates. After hydriding-dehydriding cycling, all the samples contain the Mg₂Ni phase. The samples with Fe₂O₃ and Fe₂O₃(spray conversion) as starting materials contain the Mg(OH)₂ phase after hydriding-dehydriding cycling as well as after reactive mechanical grinding. Mg-Ni-Fe and Mg-13Ni-7Fe contain the MgH₂ phase after reactive mechanical grinding. Phases, space groups, cell parameters, contents and crystallite sizes were analyzed by Full Pattern Matching Refinement program, one of the Rietveld analysis programs, from the XRD powder patterns of Mg-Ni-scFe₂O₃ after reactive mechanical grinding and after hydriding-dehydriding cycling. The MgH₂ phase formed in the Mg-Ni-Fe and Mg-13Ni-7Fe mixtures after reactive mechanical grinding is considered to help the pulverization of the materials during reactive mechanical grinding, leading to the high hydriding and dehydriding rates of these mixtures.     

Characterization of a magnesium-based alloy after hydriding-dehydriding cycling (n=1–150)

The cycling performance of Mg-15 wt% Ni-5 wt% Fe₂O₃ alloy (named Mg-15Ni-5Fe₂O₃) was investigated by measuring the absorbed hydrogen quantity as a function of the number of cycles and by examining the variations in the phases and microstructures with cycling. The sample was hydriding-dehydriding cycled 150 times. The absorbed hydrogen quantity decreased as the number of cycles increased from the second to the 150th cycle. The H_a value varied almost linearly with the number of cycles. The maintainability of the absorbed hydrogen quantity was 73.8%, and the degradation rate was 0.007 wt%/cycle for the hydriding reaction time of 60 min. After the 9th hydriding-dehydriding cycle, Mg, Mg₂Ni, MgO, and Fe were observed. After 150 cycles, the quantity of the MgO increased. The phases were analyzed using MDI JADE 6.5, a software system designed for XRD powder pattern processing, from the XRD pattern of the Mg-15Ni-5Fe₂O₃ alloy after the 9th hydriding-dehydriding cycle. The crystallite size and strain of the Mg were then estimated using the Williamson-Hall technique.     

Catalytic effect of Ni nanoparticles on the desorption kinetics of MgH2 nanoparticles

Mg and Ni nanoparticles were prepared by hydrogen plasma-metal reaction (HPMR). MgH₂ nanoparticles were obtained by hydriding the Mg nanoparticles. Hydrogen storage kinetics of the MgH₂ nanoparticles doped with different amount of Ni nanoparticles was investigated by differential scanning calorimetry (DSC) and hydrogen desorption rate measurements. The obtained samples show superior hydrogen storage kinetics. 6.1 wt% hydrogen is desorbed in 10 min at 523 K under an initial pressure of 0.01 bar of H₂ when the proportion of Ni nanoparticles is 10 wt%. The desorption rate increases when enhancing the amount of catalyst. However, the activation energy of desorption does not decrease any more when the amount of Ni exceeds a value. The enhanced desorption kinetics are mainly attributed to the accelerated combination process of hydrogen atoms by the Ni nanoparticles on the surface of MgH₂.     

Phase-structure and Hydrogen Storage Behaviors of Mg+10% Ni2P Composite Prepared by Reactive Ball-Milling

采用反应球磨法制备了Mg+10%Ni2P(质量分数,下同)新型复合物,对比研究了球磨复合物和球磨纯镁的相结构与储氢性能。研究表明:在纯Mg中添加10%的Ni2P进行复合球磨,可以明显提高其吸/放氢性能。此外,添加Ni2P球磨明显地改善了镁的循环放氢性能。复合物的晶粒尺寸随着球磨时间的增加而减小;添加Ni2P能有效地抑制Mg/MgH2在吸/放氢过程中产生团聚;在Mg中添加Ni2P球磨能降低体系的放氢反应温度。     

Effects of Y2O3 additions on mechanically alloyed and sintered W—4 wt.% SiC composites

In this study, the effect of Y₂O₃ additions on the microstructural and the physical properties of W-SiC composites was investigated. Powder blends of W—4 wt.% SiC, W—4 wt.% SiC—1 wt.% Y₂O₃ and W—4 wt.% SiC—5 wt.% Y₂O₃ were mechanically alloyed (MA'd) using a Spex mill for 24 h. MA'd composite powders were sintered under inert Ar and reducing H₂ gas conditions at 1680 °C for 1 h. Microstructural and morphological characterizations of composite powders and sintered samples were carried out via SEM and XRD analyses. Furthermore, density measurements and hardness measurements of sintered samples were carried out. A highest Vickers microhardness value of 11.4 GPa was measured for the sintered W—4 wt.% SiC—5 wt.% Y₂O₃ while W—4 wt.% SiC sample possessed the highest relative density value of 97.7%.     

Preparation by gravity casting and hydrogen-storage properties of Mg–23.5 wt.%Ni–(5, 10 and 15 wt.%)La

Mg–23.5 wt.%Ni–(5, 10 and 15 wt.%)La alloys were prepared by gravity casting and their hydrogen-storage properties were examined after pulverizing. The gravity cast Mg–23.5Ni–(5, 10 and 15)La alloys consist of α-Mg, Mg₂Ni and Mg₁₇La₂ phases. The activated Mg–23.5Ni–10La alloy has the highest hydrogen-storage capacity of 4.96 wt.%H (from P–C–T curve) and the highest initial hydriding rate (hydrogen content 3.83 wt.%H at 10 min) with an initial hydrogen pressure in the channel of 11 bar H₂ at 573 K. This is attributed to its containing the largest amount of the Mg₁₇La₂ phase, which is easily dissociable during the hydriding reaction.     

氢化燃烧法合成Mg2Ni的贮氢性能

用氢化燃烧法合成了Mg2 Ni,PCT实验结果说明了合成的镁基贮氢合金具有很高的活性和高贮氢量 ,5 5 3K时达到 3.40 %。对Mg Ni系的PCT结果作了处理 ,得出温度和氢平衡压的关系式 :吸氢时lg(p/ 0 .1MPa)=- 34 6 9/T 6 .6 39;放氢时lg(p/ 0 .1MPa) =- 35 5 8/T 6 .6 12。用XRD方法进行了物相分析 ,表明存在在Mg2 Ni的氢化物     

Improvement in hydrogen sorption properties of Mg by reactive mechanical grinding with Cr2O3, Al2O3 and CeO2

We tried to improve the hydrogen sorption properties of Mg by mechanical grinding under H₂ (reactive mechanical grinding) with oxides Cr₂O₃, Al₂O₃ and CeO₂. The hydriding rates of Mg are reportedly controlled by the diffusion of hydrogen through a growing Mg hydride layer. The added oxides can help pulverization of Mg during mechanical grinding. A part of Mg is transformed into MgH₂ during reactive mechanical grinding. The Mg+10wt.%Cr₂O₃ powder has the largest transformed fraction 0.215, followed in order by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. The Mg+10wt.%Cr₂O₃ powder has the largest hydriding rates at the first and fifth hydriding cycle, followed in order by Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. Mg+10wt.%Cr₂O₃ absorbs 5.87wt.% H at 573 K, 11 bar H₂ during 60 min at the first cycle. The Mg+10wt.%Cr₂O₃ powder has the largest dehydriding rates at the first and fifth dehydriding cycle, followed by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. It desorbs 4.44 wt.% H at 573 K, 0.5 bar H₂ during 60 min at the first cycle. All the samples absorb and desorb less hydrogen at the fifth cycle than at the first cycle. It is considered that this results from the agglomeration of the particles during hydriding–dehydriding cycling. The average particle sizes of the as-milled and cycled powders increase in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of hydrogen absorbed or desorbed for 1 h for the first and fifth cycles decrease in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of absorbed or desorbed hydrogen increase as the average particle sizes decrease. As the particle size decreases, the diffusion distance shortens. This leads to the larger hydriding and dehydriding rates. The Cr₂O₃ in the Mg+10wt.%Cr₂O₃ powder is reduced after hydriding–dehydriding cycling. The much larger chemical affinity of Mg than Cr for oxygen leads to a reduction of Cr₂O₃ after cycling.     

Plasma spray coating of spray-dried Cr2O3/wt.% TiO2 powder

An agglomerated Cr₂O₃/wt.%TiO₂ powder has been fabricated by the spray drying process under different parameters. The spray-dried powder has well-agglomerated particles of spherical shape. In the conditions of the high slurry feed rate and low binder concentration in the slurry, the powder has large cavities inside some particles and ruggedness over their surface. The optimum plasma spray feed rate has been found by examining the spraying behavior of the powder and melted state of particles. The plasma spray coating has been performed under different process variables such as spraying distance and plasma power. These parameters strongly affect the characteristics of the coated layer: microstructure, hardness, and bond strength.     

Microstructure and hydrogen storage properties of Mg-Sn nanocomposite by mechanical milling

To improve the hydrogen storage properties, the composition and microstructure of Mg-Sn alloys were modified through fabricating Mg/Mg₂Sn nanocomposite by mechanical alloying. The microstructures were characterized by X-ray diffraction and scanning electron microscopy. It is found that Mg₂Sn instead of Mg(Sn) solid solution is preferably formed during milling process. Although Mg₂Sn is not a hydriding phase, the in situ formed nanosized Mg₂Sn facilitates hydrogen absorption/desorption of Mg by forming Mg/Mg₂Sn nanocomposite. The mechanically milled Mg-5 at.% Sn nanocomposite exhibits slightly elevated plateau pressure and destabilized thermodynamics due to the introduction of large amount of interface energy in Mg/Mg₂Sn nanocomposite.     

Enhanced Hydriding and Dehydriding Kinetics of as-Spun Nanocrystalline Mg2Ni-Type Alloy Substituting Ni with Cu

为了改善Mg2Ni型合金的吸放氢动力学性能,用Cu部分替代合金中的Ni。用快淬工艺制备了纳米晶Mg2Ni1-xCux(x=0,0.1,0.2,0.3,0.4)贮氢合金,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设备测试了合金的吸放氢动力学性能。结果表明,快淬态合金具有纳米晶结构,Cu替代Ni不改变合金的主相Mg2Ni,但导致形成第二相Mg2Cu。随Cu含量的增加,合金的吸氢量先增加而后减小,但合金的放氢量随Cu含量的增加而单调增加。快淬显著提高合金的吸放氢量并改善合金的吸放氢动力学。     

Phase structure and hydrogen storage properties of LaMg_（3.70）Ni_（1.18） alloy

The phase structure and hydrogen storage properties of LaMg_3.70Ni_1.18 alloy were investigated. The LaMg_3.70Ni_1.18 alloy consists of main LaMg₂Ni phase, minor La₂Mg₁₇ and LaMg₃ phases. The alloy can be activated in the first hydriding/dehydriding process, and initial LaMg₂Ni, La₂Mg₁₇, and LaMg₃ phases transfer to LaH_2.34, Mg, and Mg₂Ni phases after activation. The reversible hydrogen storage capacity of the LaMg_3.70Ni_1.18 alloy is 2.47 wt.% at 558 K, which is higher than that of the LaMg₂Ni alloy. The pressure-composition-temperature (PCT) curves display two hydriding plateaus, corresponding to the formation of MgH₂ and Mg₂NiH₄. However, only one dehydriding plateau is observed, owing to the synergetic effect of hydrogen desorption between MgH₂ and Mg₂NiH₄. The uptake time for hydrogen content to reach 99% of saturated state is less than 250 s, and 90% hydrogen can be released in 1200 s in the experimental conditions, showing fast kinetics in hydriding and dehydriding. The activation energies of the LaMg_3.70Ni_1.18 alloy are −51.5 ± 1.1 kJ/mol and −57.0 ± 0.6 kJ/mol for hydriding and dehydriding, respectively. The hydriding/dehydriding kinetics of the LaMg_3.70Ni_1.18 alloy is better than that of the Mg₂Ni alloy, owing to the lower activation energy values.     

Hydrogen storage properties of nanocomposite Mg-Ni-MnO2 made by mechanical milling

The hydrogen storage properties of the nanocomposite MggsNi3(MnO2)2(maas fraction, % ) were studied.The temperature changes in hydriding/dehydriding process were investigated. The nanocomposite was fabricated by ball milling process of mixed demental Mg, Ni and oxide maganese MnCh under hydrogen pressure (approximately 0.6 MPa).The hydrogen absorption and desorption properties of the samples milled for various times were investigated. A remarkable enhancement of hydrogen absorption kinetics and low operational desorption temperature have been.found after the sample milled for over 57h. For example, this nanocomposite can absorb hydrogen more than 6.0% (mass fraction) in 60s at 200℃ under 2.0 MPa, and desorption capacity also exceeds 6.0 % (mass fraction) in 400 s at 310℃ under 0.1 MPa.The storage properties of samp1es milled for various times were studied and the kinetics of the samples were analyzed.     

Improvement of hydrogen-storage properties of MgH2 by addition of Ni and Ti via reactive mechanical grinding and a rate-controlling step in its dehydriding reaction

In a shift from prior work, MgH₂, instead of Mg, was used as a starting material in this work. A sample with a composition of 86 wt% MgH₂-10 wt% Ni-4 wt% Ti was prepared by reactive mechanical grinding. Activation of the sample was completed after the first hydriding cycle. The effects of reactive mechanical grinding of Mg with Ni and Ti were discussed. The formation of Mg₂Ni increased the hydriding and dehydriding rates of the sample. The addition of Ti increased the hydriding rate and greatly increased the dehydriding rate of the sample. The titanium hydride, TiH_1.924, was formed during reactive mechanical grinding. This titanium hydride, which is brittle, is thought to help the mixture pulverized by being pulverized during reactive mechanical grinding and further to prevent agglomeration of the magnesium by staying as a hydride among Mg particles. A rate-controlling step for the dehydriding reaction of the hydrided MgH₂-10Ni-4Ti was analyzed by using a spherical moving boundary model on an assumption that particles have a spherical shape with a uniform diameter.     

Mg_2Ni系贮氢合金制备方法的研究进展

本文综述了熔炼法、机械合金化法、烧结法、扩散法、氢化燃烧合成法、表面处理法等制备Mg2Ni合金的基本原理和主要工艺。介绍了扩散法和球磨法等制备技术的联用,总结并讨论了这些合金制备技术制取的合金的充放氢性能和电化学性能及其对合金性能的影响。较先进的机械合金化法制备Mg2Ni系贮氢合金复合材料是比较理想的途径。