Hydriding-dehydriding Cycles Research Articles

Thermodynamic analysis for hydriding-dehydriding cycle of metal hydride system

Thermodynamic analyses for a hydriding-dehydriding cycle process of a hydrogen storage system are carried out. Assuming the mass flow rate and the mass source term are both constant, the analytical solutions for lumped temperature in the metal hydride hydrogen storage tank are obtained in the absorption, dormancy and desorption processes. The analytical solution is important to understand the hydriding-dehydriding process, which can be used as a benchmark to validate lumped/distributed parameter models for further study. A lumped parameter numerical model is developed on the Matlab/Simulink software platform. The numerical solutions of this model with constant source term coincide with the analytical solutions. Different analytical solutions are solved with various combinations of the hydrogen inflow/outflow temperature. The analytical solution in present work is compared with the reduced model in the reference, and shows more accurate than the reduced model. The variable source term is applied to the validated lumped parameter model. The results of parametric study show that the source term of metal hydride is roughly constant when the hydrogen storage capacity is not beyond about 90% of its limited capacity.

Development of an Mg-Based Alloy with High Hydriding and Dehydriding Rates and Large Hydrogen Storage Capacity by Adding TaF5.

A sample with a composition of 95 wt% Mg + 5 wt% TaF5 (named Mg-5TaF5) was prepared by reactive mechanical grinding. The activation of Mg-5TaF5 was not necessary, and Mg-5TaF5 had an effective hydrogen storage capacity (the quantity of hydrogen absorbed for 60 min) larger than 5 wt%. At the first cycle (n = 1), the sample absorbed 4.50 wt% H for 10 min and 5.06 wt% H for 60 min at 593 K under 12 bar H2. At n = 1, the sample desorbed 1.58 wt% H for 10 min and 4.93 wt% H for 60 min at 593 K under 1.0 bar H2. The Mg-5TaF5 sample dehydrided at n = 3 contained MgF2 and Ta2H. The hydriding-dehydriding cycling of the sample, which forms MgF2 and Ta2H by reaction with hydrogen, is considered to produce defects on the surface of and inside the Mg particles, to create clean surfaces, and to reduce the particle size of Mg, due to the repetition of expansion with hydrogen absorption and contraction with hydrogen release. Mg-5TaF5 had a higher hydriding rate and a higher dehydriding rate after an incubation period and greater quantities of hydrogen absorbed and desorbed for 60 min than Mg-10TaF5, Mg-10MnO, or Mg-10Fe2O3.

Development of a Mg-Based Alloy with a Hydrogen-Storage Capacity of 7 wt% by Adding a Polymer CMC via Transformation-Involving Milling

The addition of CMC (Carboxymethylcellulose, Sodium Salt) may improve the hydriding and dehydriding properties of Mg since it has a relatively low melting point and the melting of CMC during transformation-involving milling may put the milled samples in good states to absorb and release hydrogen rapidly. Samples with compositions of 95 wt% Mg + 5 wt% CMC (named Mg-5CMC) and 90 wt% Mg + 10 wt% CMC (named Mg-10CMC) were made using transformation-involving milling. Mg-5CMC was activated in about 3 hydriding-dehydriding cycles. After activation, Mg-5CMC had a larger amount of hydrogen absorbed in 60 min, Ha (60 min), than Mg-10CMC and milled Mg. At the fourth cycle (CN=4), Mg-5CMC had a very high beginning hydriding rate (1.45 wt% H/min) and Ha (60 min) (7.38 wt% H), showing that the activated Mg-5CMC has an effective hydrogen-storage capacity of about 7.4 wt% at 593 K in hydrogen of 12 bar at CN=4. Mg-5CMC after transformation-involving milling contained Mg and very small amounts of β- MgH2 and MgO, and Mg-5CMC dehydrogenated at 593 K in hydrogen of 1.0 bar at the 4th cycle contained Mg and tiny amounts of β-MgH2 and MgO, with no evidence of the phases related to CMC. The milling of Mg with CMC in hydrogen is believed to introduce defects and cracks and lessen the particle size. To the best of our knowledge, this study is the first in which a polymer CMC is added to Mg by transformation-involving milling to improve the hydriding and dehydriding properties of Mg.

Effects of Milling Time on the Hydrogen Storage Properties of Mg-based Transition Metals-added Alloys

In this work, Mg was employed as a starting material. Ni, Fe and Ti were selected as additives to improve hydriding and dehydriding rates of Mg. A 90 wt.% Mg + 5 wt.% Ni + 2.5 wt.% Fe + 2.5 wt.% Ti sample [named 90Mg-Ni-Fe-Ti (8 h)] was prepared by mechanical grinding under H2 atmosphere (reactive mechanical grinding) for 8 h, using a planetary ball mill. The hydrogen-storage properties of the prepared sample were then investigated and were compared with those of a 90 wt % Mg + 5 wt.% Ni + 2.5 wt.% Fe + 2.5 wt.% Ti sample previously studied by preparing via reactive mechanical grinding for 4 h [named 90Mg-Ni-Fe-Ti (4 h)]. Reactive mechanical grinding for a longer time (for 8 h), compared with that for 4 h, intensified its effects of reactive mechanical grinding. After activation, 90Mg-Ni-Fe-Ti (4 h) had higher initial hydriding and dehydriding rates and larger quantities of hydrogen absorbed and released for 60 min than 90Mg-Ni-Fe-Ti (8 h). Prolonged milling (for example, for 8 h) is considered to bring about coalescence of particles which is caused by severe plastic deformation of ductile Mg particles. The stronger effect of hydriding-dehydriding cycling and the less compact agglomeration are believed to lead to the higher initial hydriding and dehydriding rates and the larger quantities of hydrogen absorbed and released for 60 min of 90Mg-Ni-Fe-Ti (4 h) than those of 90Mg-Ni-Fe-Ti (8 h) after n = 2. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.18395

Characterization of Hydrogen-Storage Properties and Physical Properties of Zinc Borohydride and Transition Metals-Added Magnesium Hydride

In this work, 90 wt.% MgH2 + 5 wt.% Ni + 1.7 wt.% Zn(BH4)2 + 1.7 wt.% Ti + 1.7 wt.% Fe samples (named 90MgH2 + 5Ni + 1.7Zn(BH4)2 + 1.7Ti + 1.7Fe) were prepared by milling in a planetary ball mill in a hydrogen atmosphere. The fraction of additives was small (10 wt.%) in order to increase hydriding and dehydriding rates without decreasing the hydrogen storage capacity much. The hydrogen absorption and release properties of the prepared samples were investigated. 90MgH2 + 5Ni + 1.7Zn(BH4)2 + 1.7Ti + 1.7Fe had an effective hydrogen storage capacity of 5 wt.%. The activation of 90MgH2 + 5Ni + 1.7Zn(BH4)2 + 1.7Ti + 1.7Fe was completed after 2 hydriding-dehydriding cycles. At n = 3, the sample absorbed 4.14 wt.% H for 5 min and 5.00 wt.% H for 60 min at 593 K under 12 bar H2. The sample dehydrided at the 3rd hydriding-dehydriding cycle contained Mg and small amounts of β-MgH2, MgO, Mg2Ni, TiH1.924, and Fe. The BET specific surface areas of the sample after milling in a hydrogen atmosphere and after 3 hydriding-dehydriding cycles were 57.9 and 53.2 m2/g, respectively.DOI: http://dx.doi.org/10.5755/j01.ms.23.1.14878

Hydrogen Storage Characteristics of Metal Hydro-Borate and Transition Element-Added Magnesium Hydride

A metal hydro-borate Zn(BH4)2 was prepared by milling ZnCl2 and NaBH4 in a planetary ball mill in an Ar atmosphere. This sample contained NaCl. 95 wt% MgH2-2.5 wt% Zn(BH4)2-2.5 wt% Ni samples [named MgH2-2.5Zn(BH4)2-2.5Ni] were then prepared by milling in a planetary ball mill in a hydrogen atmosphere. The hydrogen absorption and release properties of the prepared samples were investigated. In particular, variations in the initial hydriding and dehydriding rates with temperature were examined. MgH2-2.5Zn(BH4)2-2.5Ni dehydrided at the fourth cycle contained Mg, MgO, and small amounts of -MgH2 and Mg2Ni. The sample after hydriding-dehydriding cycling had a slightly smaller average particle size and a larger BET specific surface area than the sample after milling. Increasing the temperature from 573 K to 623 K led to a decrease in the initial hydriding rate. The initial dehydriding rate increased as the temperature increased from 573 K to 643 K. At 573 K under 12 bar H2, the sample absorbed 3.85 wt% H for 2.5 min, 4.60 wt% H for 5 min, 4.64 wt% H for 10 min, and 4.80 wt% H for 60 min. The MgH2-2.5Zn(BH4)2-2.5Ni had an effective hydrogen storage capacity (the quantity of hydrogen absorbed for 60 min) of near 5 wt% (4.96 wt% at 593 K). †(Received October 7, 2015; Accepted March 7, 2016)

Preparation of Mg-MgH2 flakes by planetary ball milling with stearic acid and their hydrogen storage properties

Many studies preparing magnesium hydride using catalyst addition were performed, resulting in the preparation of additive-containing magnesium hydride. Preparation of a sample with a MgH2 phase without additives requires high pressure and high temperature and is time-demanding. In order to prepare an additive-free sample with a MgH2 phase, 90 wt% Mg+10 wt% MgH2 (named 90Mg+10MgH2) was milled under a hydrogen atmosphere with 6 wt% stearic acid as a process-controlling agent, which led to a formation of Mg-MgH2 flakes. The hydrogen storing and releasing properties of the prepared flakes were investigated and compared with those of purchased MgH2. A sample with a majority fraction of MgH2 phase was prepared by planetary ball milling of 90 Mg+10 MgH2 with 6 wt% stearic acid. The resultant particles of 90 Mg+10 MgH2 obtained after hydridingdehydriding cycling were much smaller and had significantly more cracks and defects than those of MgH2 after hydriding-dehydriding cycling. 90 Mg+10 MgH2 released 0.12 wt% hydrogen for 4 min, 3.70 wt% for 20 min, and 5.30 wt% for 60 min at 648 K at the first cycle.

Effects of Milling and Hydriding-Dehydriding Cycling on the Hydrogen-Storage Behaviors of a Magnesium-Nickel-Tantalum Fluoride Alloy

In this study, Ni and TaF5 were picked 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% TaF5 (named Mg-14Ni-6TaF5) was prepared by reactive mechanical grinding. Its hydriding and dehydriding properties were then examined and the effects of milling and hydriding-dehydriding cycling were investigated. To activate the prepared sample, two hydriding-dehydriding cycles were required at 573 K and 593 K. At the second cycle, the sample absorbed 5.74 wt% H for 60 min under 12 bar H2 at 573 K. At 623 K, the activated Mg-14Ni-6TaF5 absorbed 2.53 wt% H for 2.5 min, 4.20 wt% H for 10 min, and 5.31wt% H for 60 min under 12 bar H2, and desorbed 2.01 wt% H for 2.5 min, 4.76 wt% H for 15 min, and 4.83 wt% H for 60 min under 1.0 bar H2. The initial hydriding rate increased as the temperature increased from 423 K to 573 K (due to the predominance of the acceleration of the thermally activated process) and then decreased from 573 K to 623 K due to the predominance of the decrease in the driving force for the hydriding reactionunder 12 bar H2.

Hydriding and Dehydriding Properties of Zinc Borohydride, Nickel, and Titanium-Added Magnesium Hydride

A Zn(BH4)2 sample was prepared by milling ZnCl2 and NaBH4 in a planetary ball mill under Ar gas. This sample contained NaCl. Then, 90 wt% MgH2-5 wt% Zn(BH4)2-2.5 wt% Ni-2.5 wt% Ti samples [named 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti] were prepared by milling in a planetary ball mill under H2 gas. The hydrogen absorption and release properties of the prepared samples were investigated. In particular, the variations of the initial hydriding and dehydriding rates with temperature were examined. SEM micrographs and XRD patterns of 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti after reactive mechanical grinding and after hydriding-dehydriding were also studied. Particle size distributions and BET specific surface areas of 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti after reactive mechanical grinding and after 11 hydriding-dehydriding cycles were analyzed. The 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti had an effective hydrogen storage capacity (the quantity of hydrogen absorbed for 60 min) of near 5 wt% (4.91 wt% at 593 K).

Enhancement of the Hydriding and Dehydriding Rates of Mg by Adding TiCl3 and Reactive Mechanical Grinding

A sample with a composition of 95 wt% Mg-5 wt% TiCl3 (named Mg-5TiCl3) was prepared by reactive mechanical grinding, and its hydriding and dehydriding properties were examined. The activation of Mg-5TiCl3 was not required. Mg-5TiCl3 had an effective hydrogen-storage capacity of about 6.2 wt%. At the first cycle (n=1), the sample absorbed 5.77 wt% H for 5 min, 6.07 wt% H for 10 min, 6.17 wt% H for 30 min, and 6.19 wt% H for 60 min at 573 K under 12 bar H2. At n=1, the sample desorbed 0.03 wt% H for 2.5 min, 0.13 wt% H for 30 min, and 0.35 wt% H for 60 min at 573 K under 1.0 bar H2. Mg-5TiCl3 after reactive mechanical grinding contained Mg, β-MgH2, γ-MgH2, and TiH1.924. The XRD pattern of Mg-5TiCl3 dehydrided at the 4th hydriding-dehydriding cycle at 423-573 K contained β-MgH2, Mg, MgO, and TiH1.924. Mg-5TiCl3 had a higher initial hydriding rate and a larger quantity of hydrogen absorbed for 60 min than Mg-5TaF5, Mg-10Fe2O3, Mg-10MnO, and Mg, the hydrogen-storage properties of which were previously reported.(Received February 12, 2014)

Preparation of a sample with a single MgH2 phase by horizontal ball milling and the first hydriding reaction of 90 wt% Mg-10 wt% MgH2

In order to prepare an additive-free sample with a single MgH2 phase, 90 wt% Mg-10 wt% MgH2 (named 90Mg-10MgH2) was milled under a hydrogen atmosphere in a horizontal ball mill, and then hydrided. The hydrogen absorption and desorption properties of the prepared samples were investigated, and compared with those of milled pure Mg and purchased MgH2. X-ray diffraction analysis, measurement of specific BET surface areas, and observation of the prepared samples by scanning electron microscope were performed. The 90Mg-10MgH2 sample after hydriding-dehydriding cycling had small and large particles with fine particles on their surfaces, and had much finer particles and more defects than the milled pure Mg sample after hydridingdehydriding cycling. The specific BET surface areas of the milled Mg and 90Mg-10MgH2 were measured as 7.81 and 99.81 m2/g, respectively. A sample that had almost a single MgH2 phase could be prepared by horizontal ball milling and the first hydriding reaction of 90Mg-10MgH2. 90Mg-10MgH2 released 5.82 wt% H for about 70 min, while unmilled MgH2 (Aldrich) released 6.04 wt% H for about 100 min, at 648 K.

Change in Hydrogen-Storage Performance of Transition Metals and NaAlH4-Added MgH2 with Thermal and Hydriding-Dehydriding Cycling

A sample with a composition of 86 wt% MgH2-10 wt% Ni-2 wt% NaAlH4-2 wt% Ti (designated MgH2-10Ni-2NaAlH4-2Ti) was prepared by reactive mechanical grinding. The sample was subjected to thermal cycling (between room temperature and 623 K) as well as cycling between hydriding (at 593 K under 12 bar H2) and dehydriding (at 623 K in vacuum). At n=1, MgH2-10Ni-2NaAlH4-2Ti absorbed 3.10 wt% H for 5 min, 4.14 wt% H for 10 min, 4.35 wt% H for 15 min, and 4.45 wt% H for 60 min at 593 K under 12 bar H2. From the beginning to about 10 min, the hydriding rate of the sample increased roughly as the number of cycles, n, increased. The quantity of hydrogen absorbed for 60 min, Ha (60 min), decreased on the whole as the number of cycles increased from 1 to 15. At n=15, MgH2-10Ni-2NaAlH4-2Ti absorbed 3.31 wt% H for 5 min, 3.60 wt% H for 10 min, 3.66 wt% H for 15 min, and 3.82 wt% H for 60 min. The quantity of hydrogen desorbed for 30 min, Hd (30 min), increased slowly as the number of cycles increased from n=2 to n=15. After hydriding-dehydriding cycling, β-MgH2, Mg, Mg2Ni, TiH1.924, NiAl, and MgO were observed in the samples. NiAl was formed from the reaction of Ni with Al which was formed by the decomposition of NaAlH4.

PCT Curve and Cycling Performance of MgH2-Ni-NaAlH4-Ti Alloy Milled under H2

In this study, MgH2 was used as a starting material instead of Mg. A sample with a composition of 86 wt% MgH2-10 wt% Ni-2 wt% NaAlH4-2 wt% Ti (designated MgH2-10Ni-2NaAlH4-2Ti) was prepared by reactive mechanical grinding. Its Pressure-Composition-Temperature (PCT) curve measurement, hydriding-dehydriding cycling performance measurement, and microstructure observation were then performed. The desorption PCT curve at 593 K for MgH2-10Ni-2NaAlH4-2Ti at the first cycle exhibited a long plateau at around 2.6 bar, and a short plateau at about 3.6 bar, which correspond to equilibrium plateau pressures of Mg-H and Mg2Ni-H systems, respectively. The hydriding rate at 593 K under 12 bar H2 increased as the number of cycles, n, increased from 1 to 4, and it decreased from n=4 to n=15. At n=14, MgH2-10Ni-2NaAlH4-2Ti absorbed 3.02 wt% H for 2.5 min, 3.36 wt% H for 5 min, 3.51 wt% H for 10 min, and 3.58 wt% H for 30 min, which is 93.0% of the hydrogen absorbed for 30 min at n=4.

Variations of the Hydriding and Dehydriding Rates of As-Milled MgH2-Ni Alloys with Ni Content

In this work, MgH2 was used as a starting material. Samples with compositions of 94 wt% MgH2- 6 wt% Ni, 88 wt% MgH2-12 wt% Ni, 85 wt% MgH2-15 wt% Ni, and 82 wt% MgH2-18 wt% Ni were prepared by reactive mechanical grinding. The variations of the hydriding and dehydriding properties at the first hydriding-dehydriding cycle with Ni content were then investigated. MgH2-12Ni had the highest hydriding rate and the largest quantity of hydrogen absorbed for 60 min, followed in order by MgH2-6Ni, MgH2-15Ni, and MgH2-18Ni. The effects of reactive mechanical grinding were the strongest in the MgH2-12Ni sample. As the Ni content increased from 6 wt% to 18 wt%, the percentage of the hydrogen quantity desorbed for 30 min to the theoretical capacity increased. (Received October 5, 2012)

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 Ha 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.

Effects of Temperature and Initial Hydrogen Pressure on the Hydriding Properties of Zr9Ni11 Alloy

Abstract The hydriding properties of Zr 9 Ni 11 alloy at different temperatures (25∼150 °C) and various initial hydrogen pressures (10∼160 kPa) were investigated. The results show that with the increase of temperature, the equilibrium pressure of the Zr 9 Ni 11 alloy increases significantly, but its hydrogen absorption quantity decreases dramatically. When the temperature is less than 75 °C, the hydriding reaction rate of Zr 9 Ni 11 alloy increases with increasing of temperature; while the temperature is higher than 75 °C, the hydriding reaction rate of the alloy decreases with increasing of temperature. The initial hydrogen pressure has a great influence on the kinetic properties of the alloy. When the initial pressure is lower than 50 kPa, the hydriding reaction rate of the alloy increases obviously with the increase of the initial hydrogen pressure, and even in the case of relatively low pressure, the alloy can still absorb hydrogen dramatically. The hydrogen absorption quantity and the equilibrium pressure of the alloy increase with the increase of the initial hydrogen pressure. The samples of the alloy before and after hydrogenation were analyzed by XRD, SEM(EDS) and TEM(SAED). After several hydriding-dehydriding cycles, the surface of the alloy which is homogeneous and smooth before hydrogenation becomes rough and crannied, and the ratio of Zr and Ni on the surface is varied. It is also found the amorphous states might be increased and mischcrystal formed through hydriding-dehydriding cycles. Zr 9 Ni 11 alloy might be a promising candidate for extracting tritium according to our investigation.

Preparation of Mg-33Al alloy by rapid solidification process and evaluation of its hydrogen-storage properties

A Mg-33Al sample with a eutectic composition, which can be prepared at a relatively low temperature, was prepared by the rapid solidification process. After the Mg-33Al mixture was completely melted by high frequency induction heating at 983 K, the melt was injected through a nozzle with a diameter of 2.5 mm onto the surface of a copper wheel rotating at a linear velocity of 35 m/s. The heat-treatment, and then planetary ball milling under Ar were performed for the sample preparation, and its hydrogen-storage properties were evaluated. The Mg-33Al samples after rapid solidification process, or after RSP and heat treatment contained Mg and Mg17Al12 phases. XRD pattern of Mg-33Al dehydrided after 4 hydriding-dehydriding cycles revealed Mg17Al12 and Mg phases. The activation of the sample was completed after three hydriding-dehydriding cycles. The activated sample desorbed 1.25 wt% H for 25 min, 2.83 wt% H for 50 min, 2.95 wt% H for 75 min, 3.01 wt% H for 100 min, and 3.17 wt% H for 300 min at 623 K.

Hydrogen Storage Properties of Pure MgH2

The hydrogen storage properties of pure <TEX>$MgH_2$</TEX> were studied and compared with those of pure Mg. At the first cycle, pure <TEX>$MgH_2$</TEX> absorbed hydrogen very slowly at 573 K under 12 bar <TEX>$H_2$</TEX>. The activation of pure <TEX>$MgH_2$</TEX> was completed after three hydriding-dehydriding cycles. At the <TEX>$4^{th}$</TEX> cycle, the pure <TEX>$MgH_2$</TEX> 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 <TEX>$MgH_2$</TEX> had a much higher initial hydriding rate and much larger <TEX>$H_a$</TEX> (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 <TEX>$MgH_2$</TEX> 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 <TEX>$H_2$</TEX> for 60 min, <TEX>$H_a$</TEX> (60 min), than did the pure <TEX>$MgH_2$</TEX> from the number of cycles n = 1 to n = 3; however, the pure <TEX>$MgH_2$</TEX> had larger <TEX>$H_a$</TEX> (60 min) than did the pure Mg from n = 4 to n = 6.

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.

Strain variation on the reaction tank of high hydrogen content during hydrogen absorption-desorption cycles

The strain generated in a reaction tank of hydrogen storage alloys were measured in order to analyze strain variation in different locations during hydrogen absorption-desorption cycles. Strain gauges were set on the various locations of the tank. The change of strain was continuously monitored using the strain analyzer. The results indicate that plastic deformation had occurred during activation period, and it did not become larger in the later hydriding-dehydriding cycles though the tank still had the ability for elastic deformation. The stress induced by alloy swell on the tank was over 8 MPa. Tangential strain was greater than longitudinal strain in each place. There wasn't much more difference in Longitudinal at respective points while tangential strain in the middle part was much larger than that in two sides' parts of the tank. The nonuniform packing density lead the deformation tended to occur more serious in tail part than in head part.