• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.64-70
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• 2012

Samples of pure Mg, 76.5 wt%Mg-23.5 wt%Ni, and 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ were prepared by reactive mechanical grinding and their hydriding and dehydriding properties were then investigated. The reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation and to shorten diffusion distances of hydrogen atoms. After hydriding-dehydriding cycling, the 76.5 wt%Mg-23.5 wt%Ni and 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ samples contained $Mg_2Ni$ phase. In addition to the effects of the creation of defects and the decrease in particle size, the addition of Ni increases the hydriding and dehydriding rates by the formation of $Mg_2Ni$. Expansion and contraction of the hydride-forming materials (Mg and $Mg_2Ni$) with the hydriding and dehydriding reactions are also considered to increase the hydriding and dehydriding rates of the mixture by forming defects and cracks leading to the fragmentation of particles. The reactive mechanical grinding of Mg-Ni alloy with $Fe_2O_3$ is considered to decrease the particle size.

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.2
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• pp.174-180
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• 2006

The eutectic Mg-23.5%Ni alloy was casted by melting and solidification. The powders of Mg-23.5%Ni and (Mg-23.5%Ni)-10% iron oxide were prepared by mechanical grinding of casted Mg-Ni alloy and casted Mg-Ni alloy+oxide, respectively. As milling time increases, hydriding and dehydriding rates of Mg-Ni and Mg-Ni-oxide alloy powders increase. The additions of iron oxide to Mg-Ni alloy and Mg-Ni-oxide increase hydriding rates and slightly decrease dehydriding rates.

• Korean Journal of Metals and Materials
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• v.50 no.2
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• pp.171-175
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• 2012

By measuring the absorbed hydrogen quantity as a function of the number of cycles, the cycling properties of the Mg-15 wt%Ni-5 wt%$Fe_2O_3$ alloy were investigated. The absorbed hydrogen quantity decreased as the number of cycles increased. The $H_a$ value varied almost linearly with the number of cycles. The maintainability of absorbed hydrogen quantity at n=100 was 89.0% for the hydriding reaction time of 10 min. After the $150^{th}$ hydriding-dehydriding cycle, Mg, $Mg_2Ni$, $Mg(OH)_2$, MgO, and Fe were observed. The phases were analyzed by Rietveld analysis from the XRD patterns of the Mg-15 wt%Ni-5 wt%$Fe_2O_3$ alloy after 150 hydriding-dehydriding cycles. The crystallite size and strain of Mg were then estimated with the Williamson-Hall technique.

• Korean Journal of Metals and Materials
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• v.50 no.5
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• pp.383-387
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• 2012

The activation of Mg-10 wt%$Fe_2O_3$ was completed after one hydriding-dehydriding cycle. Activated Mg-10 wt%$Fe_2O_3$ absorbed 5.54 wt% H for 60 min at 593 K under 12 bar $H_2$, and desorbed 1.04 wt% H for 60 min at 593 K under 1.0 bar $H_2$. The effect of the reactive grinding on the hydriding and dehydriding rates of Mg was weak. The reactive grinding of Mg with $Fe_2O_3$ is believed to increase the $H_2$-sorption rates by facilitating nucleation (by creating defects on the surface of the Mg particles and by the additive), by making cracks on the surface of Mg particles and reducing the particle size of Mg and thus by shortening the diffusion distances of hydrogen atoms. The added $Fe_2O_3$ and the $Fe_2O_3$ pulverized during mechanical grinding are considered to help the particles of magnesium become finer. Hydriding-dehydriding cycling is also considered to increase the $H_2$-sorption rates of Mg by creating defects and cracks and by reducing the particle size of Mg.

• Transactions of the Korean hydrogen and new energy society
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• v.9 no.4
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• pp.151-160
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• 1998

The variation of the hydrogen-storage properties of Mg contained in the mechanically-allyed mixture with the weight percentage of nickel in the sample is investigated. The weight percentage of nickel transformed into the Mg2Ni phase, on the basis of the nickel weight, is highest in the Mg-10 wt.%Ni sample. For the first hydriding cycle, the effect of mechanical alloying on the hydriding rate of Mg is highest in the Mg-25 wt.%Ni sample. After activation, the effects of mechanical alloying and hydriding-dehydriding cycling on the hydriding rate of Mg are highest in the Mg-10 wt.%Ni sample. After sufficient hydriding-dehydriding cycling, the effects on the hydrogen-storage capacity of Mg are highest in the Mg-10 wt.%Ni sample. The effects on the hydriding and dehydriding rates of Mg are highest in the Mg-25wt.%Ni sample. Mg-25wt.%Ni, followed by Mg-10 wt.%Ni, is the optimum composition which has the best effects on the hydrogen-storage properties of Mg contained in the sample. The mechanical alloying and the hydriding-dehydriding cycling produce many defects, which can act as active nucleation sites, and increase the specific surface area, shortening the diffusion distance of hydrogen.

• Transactions of the Korean hydrogen and new energy society
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• v.5 no.1
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• pp.51-57
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• 1994

Compaction techniques of hydrogen storage alloy 'powders, to solve the problems due to disintegration during the cyclic hydriding and dehydriding, by using polytetrafluoroethylene (PTFE) and silicon sealant as a polymer binder were studied. Optimum conditions of compaction were as follows. Binder content, 10 % for PTFE and 5 % for silicon sealant ; particle size of alloy powders, $-25{\mu}m$ ; compacting pressure, $4ton/cm^2$. Compacts obtained were easily activated and had a good strength even after 30 cycles of hydriding and dehydriding. PTFE added compacts showed very good rate capability, however, in the silicon added compacts hydrogen absorption rate was somewhat slow because of higher elasticity and adhesiveness of the binder.

• Transactions of the Korean hydrogen and new energy society
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• v.9 no.2
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• pp.47-52
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• 1998

A mixture with a composition $Mg_2Ni$ is mechanically alloyed. Its hydriding and dehydriding properties are compared with those of the intermetallic compound $Mg_2Ni$ prepared by partial melting and sintering. The principal effects of mechanical alloying in a planetary mill and hydriding-dehydriding cycling are considered the enlargement in the specific surface area and the augmentation in the density of defects.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.2
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• pp.137-143
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• 2017

In the present study, Ni and $TaF_5$ were chosen as additives to enhance the hydriding and dehydriding rates of Mg. A sample with a composition of 80 wt% Mg + 14 wt% Ni + 6 wt% $TaF_5$ (named $80Mg+14Ni+6TaF_5$) was prepared by high-energy ball milling in hydrogen. Its hydriding and dehydriding properties were then examined. At the fourth cycle, the activated sample absorbed 3.88 wt% H for 2.5 min, 4.74 wt% H for 5 min, and 5.75 wt% H for 60 min at 593 K under 12 bar $H_2$. $80Mg+14Ni+6TaF_5$ had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed for 60 min) of about 5.8 wt%. The sample desorbed 1.42 wt% H for 5 min, 3.42 wt% H for 15 min, and 5.09 wt% H for 60 min at 593 K under 1.0 bar $H_2$. Line scanning results by EDS for $80Mg+14Ni+6TaF_5$ before and after cycling showed that the peaks of Ta and F appeared at different positions, indicating that the $TaF_5$ in $80Mg+14Ni+6TaF_5$ was decomposed.

• Transactions of the Korean hydrogen and new energy society
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• v.7 no.2
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• pp.181-191
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• 1996

Samples with the compositions of Mg-10wt.%Ni and Mg-25wt.%Ni were prepared by mechanical alloying in a planetary mill. $Mg_2Ni$ phase was formed in the mixture with hydriding dehydriding cycling. The activation of Mg-10wt.%Ni and Mg-25wt.%Ni was completed after n=7 and n=6 around, respectively, at 583K, $0{\sim}8barH_2$. Mg-10wt.% Ni and Mg-25wt. %Ni are considered as excellent hydrogen-storage materials with very high hydriding rates, high dehydriding rates and relatively large hydrogen-storage capacity. The effets of mechanical alloying and hydriding dehydriding cycling are considered the augmentation in the density of active nucleation sites and the diminution in the particle size.

• Korean Journal of Materials Research
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• v.23 no.5
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• pp.266-270
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• 2013

The hydrogen storage properties of pure $MgH_2$ were studied and compared with those of pure Mg. At the first cycle, pure $MgH_2$ absorbed hydrogen very slowly at 573 K under 12 bar $H_2$. The activation of pure $MgH_2$ was completed after three hydriding-dehydriding cycles. At the $4^{th}$ cycle, the pure $MgH_2$ absorbed 1.55 wt% H for 5 min, 2.04 wt% H for 10 min, and 3.59 wt% H for 60 min, showing that the activated $MgH_2$ had a much higher initial hydriding rate and much larger $H_a$ (60 min), quantity of hydrogen absorbed for 60 min, than did activated pure Mg. The activated pure Mg, whose activation was completed after four hydriding-dehydriding cycles, absorbed 0.80 wt% H for 5 min, 1.25 wt% H for 10 min, and 2.34 wt% H for 60 min. The particle sizes of the $MgH_2$ were much smaller than those of the pure Mg before and after hydriding-dehydriding cycling. The pure Mg had larger hydrogen quantities absorbed at 573K under 12 bar $H_2$ for 60 min, $H_a$ (60 min), than did the pure $MgH_2$ from the number of cycles n = 1 to n = 3; however, the pure $MgH_2$ had larger $H_a$ (60 min) than did the pure Mg from n = 4 to n = 6.