Investigation of wall stress development and packing ratio distribution in the metal hydride reactor

The strains generated in a reaction vessel of hydrogen storage alloys and the packing ratio distribution inside the vessel were measured in order to analyze the effects of packing on stress. More specifically strains generated on the vessel’s surface were measured when hydrogen is repeatedly absorbed and desorbed by the packed bed in the reaction vessel. The amount of deformation, local packing ratios and relative particle volumes in the vessel were also measured after repeated hydrogen absorption–desorption. As absorption–desorption was performed repeatedly, agglomeration regions where the value of the local packing ratio was around 0.6 were formed, and particularly strong stress was generated in these regions, causing deformation. More hydrogen packing causes agglomeration regions to form over a wider area. Since alloys are pulverized by repeated absorption–desorption, and concentrate in the lower parts of the vessel, agglomeration regions are also formed in the lower parts. Our experiments also revealed that the resulting agglomeration regions have a packing ratio of about 0.6.     

Improving the hydrogen absorption properties of commercial Mg–Zn–Zr alloy

Commercial alloy ZK60 (Mg-6 wt%Zn-0.8 wt% Zr) was used as a hydrogen-storage material to study the effect of cold rolling, ball milling, and plus graphite additives on hydrogen-storage characteristics, hydrogen absorption–desorption behavior, and the related microstructural change of the alloy. Experimental results showed that cold-rolled alloy could not be activated easily. Even after ball milling for 20 h and hydrogen absorption–desorption cycling for 10 times, no saturated hydrogen absorption was observed for cold-rolled alloy. In contrast, alloys with 5 wt% graphite additives could be easily activated after the first hydrogen absorption–desorption cycle, and a saturated hydrogen absorption of 6.9 wt% was obtained after absorption–desorption cycling for five times. A hydrogen absorption of 5.52 wt%, equivalent to 80% of the saturated absorption amount, was measured in 5 min, showing a hydrogen absorption rate of 1.104 wt%/min. The sample reached saturation in 30 min.     

Influence of Fe addition on hydrogen storage characteristics of Ti–V-based alloy

In order to improve the hydrogen storage properties and reduce the cost of Ti–V-based BCC alloys, the effect of Fe substitution for part V on hydrogen absorption–desorption characteristics of Ti–10Cr–18Mn–32V alloy was investigated. It was found that proper amount of Fe addition was effective in improving the activation performance, enhancing the hydrogen absorption–desorption plateau pressure, reducing the hysteresis of hydrogen absorption–desorption plateau, increasing the hydrogen desorption capacity and decreasing the alloy's cost, while it depressed the hydrogen absorption capacity. X-ray diffraction (XRD) patterns and back scattering electron (BSE) images display that the single BCC phase of Fe-free alloy transformed into two phases of, BCC and C14 Laves, of Fe-containing alloy. Three phase transformations happened in the two alloys during the hydrogen release process, which resulted from the formation of three different hydride phases in the two hydrided alloys.     

Crystal structure and cyclic properties of hydrogen absorption–desorption in Pr2MgNi9

We investigated the crystal structure and cyclic hydrogen absorption–desorption properties of Pr₂MgNi₉. The structural model is based on the PuNi₃-type structure; the Mg atom is assumed to substitute for the Pr site in an MgZn₂-type cell. The refined lattice parameters were determined from X-ray diffraction. A wide plateau region was observed in the P–C (pressure composition) isotherm at 298 K. The maximum hydrogen capacity reached 1.12 H/M (1.62 mass%) under a hydrogen pressure of 2.0 MPa. After 1000 hydrogen absorption–desorption cycles, the hydrogen capacity was superior to that of LaNi₅ (82%). Anisotropic lattice strain occurred in the hydriding process. The anisotropic peak-broadening vector was determined to be <001>. The calculated anisotropic lattice strains of the initial cycle and after 1000 cycles were far smaller than those of LaNi₅.     

Development of hydrogen absorption–desorption experimental test bench for hydrogen storage material

A volumetric experimental set-up used for measuring hydrogen absorption–desorption characteristics of hydrogen storage material will be presented. Although the experimental set-up is mainly employed to do hydrogen absorption–desorption cycling (including pressure cycling and thermal cycling) measurement automatically, it also can incidentally provide general measurements such as pressure-composition-temperature (P–C–T) curves and kinetics measurements in manual way in the ranges of 0.004–12 MPa and 213–773 K. The experimental set-up can be used to investigate the influence of hydrogen absorption–desorption cycles to hydrogen storage properties of material. The leakage rate of the whole experimental set-up was evaluated systemically. The usability and reliability of the experimental set-up were checked with LaNi₅ and Pd/K (kieselguhr).     

Local and crystal structure of Mg1.9Al0.1Ni hydrogen storage alloys during hydrogen absorption–desorption cycling

The evolution of crystal structure and chemical state of Mg_1.9Al_0.1Ni alloy during hydrogen absorption–desorption cycling was examined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We research the hydrogen storage capacity of the Mg_1.9Al_0.1Ni by the H/D kinetic curves. The H/D kinetic curves indicate that the hydrogen storage capacity increased with the increased cycles and the samples were activated after 10 cycles have the maximum hydrogen storage capacity. The local structure of Ni atoms was studied by extended X-ray absorption fine structure (EXAFS). The EXAFS results indicate the Ni–Ni bonds distance has no obviously change with the cycles increasing, whereas the Ni–Mg bond lengths increase, and the Ni–Mg bond lengths are longer obviously than before 10 cycles whereas it has no obviously change after 10 cycles.     

Enhanced hydrogen uptake/release in 2LiH–MgB2 composite with titanium additives

The influence of different titanium additives on hydrogen sorption in LiH–MgB₂ system has been investigated. For all the composites LiH–MgB₂–X (X = TiF₄, TiO₂, TiN, and TiC), prepared by ball-milling in molar ratios 2:1:0.1, five hydrogen uptake/release cycles were performed. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and attenuated total reflection infrared spectroscopy (ATR-IR) have been used to characterize crystal phases developed during the hydrogen absorption–desorption cycles.     

Hydrogen storage and cyclic properties of V60Ti(21.4+x)Cr(6.6−x)Fe12 (0 ≤ x ≤ 3) alloys

Hydrogen storage and cyclic properties of V₆₀Ti_(21.4+x)Cr_(6.6−x)Fe₁₂ (0 ≤ x ≤ 3) alloys were investigated systematically. All alloys were composed of single BCC phase and exhibited good activation performance. V₆₀Ti_22.4Cr_5.6Fe₁₂ showed the highest desorption capacity of 2.12 wt% with the plateau pressure of 0.061 MPa. In the absorption–desorption cycle tests, both the hydrogen desorption capacity and the micro-strain of V₆₀Ti_22.4Cr_5.6Fe₁₂ alloy showed exponential relationship with the increase of cycle numbers, which indicated that the micro-strain induced and thereafter accumulated during the absorption–desorption cycles might lead to the decrease of the desorption capacity.     

Crystal structure of GdNi3 with superlattice alloy and its hydrogen absorption–desorption property

We synthesized the intermetallic compound GdNi₃, which has a PuNi₃-type structure (space group R-3m), and investigated its P–C isotherm. The refined lattice parameters were a = 0.4993(1) nm and c = 2.4536(4) nm. In the first absorption process, two plateaus were observed, and the maximum hydrogen capacity reached 1.07 H/M. In the first desorption process, a narrow and sloping plateau was observed at approximately 0.02 MPa. After the first full desorption, 0.6 H/M of hydrogen remained in the sample. This sample showed severe peak broadening in the XRD pattern, indicating that the metal sublattice deformed from the original alloy. No plateau region was observed in the second absorption–desorption cycle.     

Hydriding behavior in Zr-based AB2 alloy by gas atomization process

The hydriding characteristics of Zr-based AB₂ alloy produced by gas atomization have been investigated during its absorption–desorption reaction with hydrogen gas. Its gas-phase hydrogenation properties are different from those of specimens prepared by conventional methods. For the particle morphology of the as-cast and gas-atomized powders, it can be seen that the mechanically crushed powders are irregular, while the atomized powder particles are spherical. In PCT (Pressure–Composition–Temperature) measurements, for the gas-atomized particles smaller than 50 μm, the hydrogen storage capacity is dramatically decreased and the hysteresis loop becomes larger than that of the gas-atomized particles larger than 50 μm. In addition, the increase of jet pressure of gas atomization results in the decrease of hydrogen storage capacity and the slope of plateau pressure significantly increases. TEM and EDS studies showed the increase of jet pressure in the atomization process accelerated the phase separation within grain of the gas-atomized alloy, which brought about a poor hydrogenation property. In the measurements of hydrogen absorption–desorption kinetics, the improvement of desorption kinetics of gas-atomized AB₂ alloys was mainly caused by the higher plateau pressure, which is attributed to the smaller grain size and higher site energy for hydrogen in the gas-atomized alloys.     

Nanostructured rapidly solidified LaMg11Ni alloy: Microstructure,crystal structure and hydrogenation properties

In our earlier publication (Poletaev et al., J Alloys Compd., 509S (2011) S633) we reported a drastic variation of the structural and hydrogenation properties of LaMg_∼12 intermetallic alloy caused by Rapid Solidification (RS). In present work we have probed the effect of nickel during the chemical modification of LaMg₁₂, in combination with RS, on the structure, microstructure and hydrogen absorption–desorption properties of the alloys.     

Crystal structure and hydrogen storage property of Nd2Ni7 superlattice alloy

This study investigates the crystal structure and Pressure–composition (P–C) isotherm of Nd₂Ni₇ prepared by annealing an arc-melted ingot at 1448 K for 10 h followed by ice-water quenching. The crystal structure was further refined by X-ray Rietveld analysis based on the Ce₂Ni₇-type structure. The lattice parameters were determined as a = 0.5001(1) nm and c = 2.4437(4) nm. A single plateau was observed during the first absorption–desorption cycle. In the first absorption cycle, the maximum hydrogen capacity reached 1.22 H/M (1.58 mass%) at 233 K. The absorption and desorption plateau pressures were approximately 1.0 and 0.002 MPa, respectively. In the first desorption process, 0.63 H/M of hydrogen remained in the sample. Further, a single sloping plateau was observed in the second absorption–desorption process. Heavy peak broadening was observed in the X-ray diffraction (XRD) profile after hydrogenation, with no detection of an amorphous phase.     

Hydrogen storage nanocrystalline TiFe intermetallic compound: Synthesis by mechanical alloying and compacting

Equiatomic nanocrystalline TiFe intermetallic compound was synthesized from elementary metals by mechanical alloying in a planetary ball mill. Then the powder produced was compacted by cold pressing into bulk samples keeping the nanocrystalline structure. The hydrogen capacity of TiFe bulk samples was found to be of 1.4 wt.%. The absorption isotherm had a long plateau corresponding to pressures of 0.3–0.4 MPa at room temperature. The bulk samples demonstrated high durability after 20 absorption–desorption cycles.     

Effect of cycling on hydrogen storage properties of Ti2CrV alloy

In the present work, we have studied the hydrogen absorption–desorption properties of the Ti₂CrV alloy, and effect of cycling on the hydrogen storage capacity. The material has been characterized for the structure, morphology, pressure composition isotherms, hydrogen storage capacity, hydrogen absorption kinetics and the desorption profile at different temperatures in detail. The Ti₂CrV crystallizes in body centered cubic (bcc) structure like TiCrV. The pressure composition isotherm of the alloy has been measured at room temperature and at 373K. The Ti₂CrV alloy shows maximum hydrogen storage capacity of 4.37 wt.% at room temperature. The cyclic hydrogen absorption capacity of Ti₂CrV alloy has been investigated at room temperature upto 10th cycle. The hydrogen storage capacity decreased progressively with cycling initially, but the alloy can maintain steady cyclic hydrogen absorption capacity 3.5 wt.% after 5th cycle. To get insight about the desorption behavior of the hydride in-situ desorption has been done at different temperatures and the amount of hydrogen desorbed has been calculated. The TG (Thermo gravimetric) and DTA analysis has been done on uncycled hydride shows that the surface poisoned sample gives a desorption onset temperature of 675K. The DSC measurement of uncycle and multi-cycled saturated hydrides shows that the hydrogen desorption temperature decreasing with cycling.     

Nanostructured rapidly solidified LaMg11Ni alloy. II. In situ synchrotron X-ray diffraction studies of hydrogen absorption–desorption behaviours

Recently, the present authors [17] have reported dramatic improvements in the hydrogenation behaviours of nanostructured LaMg₁₁Ni prepared by Rapid Solidification, caused by modifications of the microstructure and crystal structure. The aim of the present work was to study the mechanism and kinetics of the hydrogen interaction with rapidly solidified LaMg₁₁Ni by employing in situ synchrotron X-Ray diffraction studies of hydrogen absorption–desorption processes in hydrogen gas or in vacuum.     

Ternary compounds in the magnesium–titanium hydrogen storage system

Mg–Ti–H samples were mechano-chemically synthesized by ball milling in argon atmosphere or under elevated hydrogen pressure. The detailed reaction mechanism during hydrogen release and uptake during continuous cycling was investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) experiments. The thermal behaviour of the samples and hydrogen desorption properties were examined by simultaneous thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass spectrometry (MS) measurements. A ternary Ti–Mg–H compound with a fcc lattice form during mechano-chemical sample preparation in hydrogen atmosphere using metal powders, but not using metal hydrides as reactants. The amount of β-MgH₂ increases during the first hydrogen absorption cycle at 300 °C at the expense of the high-pressure polymorph, γ-MgH₂ and the amount of β-MgH₂ remain constant during the following hydrogenations. This study reveals that the ternary compound tends to absorb increasing amounts of magnesium in the dehydrogenated state during cycling. A strong coupling between the amounts of magnesium in the ternary Ti–Mg–H phase and the formation of magnesium and magnesium hydride during hydrogen release and uptake at 300 °C is observed. The composition and the amount of the Ti–Mg–H phase appear to be similar in the hydrogenated state. Fast absorption–desorption kinetics at 300 °C and lower onset temperatures for hydrogen release is observed for all investigated samples (lowest onset temperature of desorption T_on = 217 °C).     

Effect of hydrogen absorption/desorption cycling on hydrogen storage properties of a LaNi3.8Al1.0Mn0.2 alloy

The effect of long-term hydrogen absorption/desorption cycling up to 3500 cycles on the hydrogen storage properties of LaNi_3.8Al_1.0Mn_0.2 alloy was investigated. The pressure-composition (PC) isotherms for absorption/desorption and the absorption kinetics were measured at 433 K, 453 K and 473 K. X-ray diffraction analysis revealed that the alloy had a homogeneous hexagonal CaCu₅ type structure and kept this structure even after 3500 cycles, but the diffraction peaks were broadened. The degree of peak broadening was increased with increase of the cycle number, but exhibiting a maximum after initial activation. The shapes of PCT curves after 300, 2000 and 3500 cycles were similar to that after initial activation. It was found that the alloy subjected to 300 cycles did not exhibit significant changes in hydrogen storage capacity, but the long-term cycling up to 2000 and 3500 cycles resulted in obvious decrease in hydrogen storage capacity. The degradation of the hydrogen capacity might be resulted from the formation of the irreversible sites and more stable hydride phase, though no new phase was found after absorption/desorption cycling from XRD pattern as shown in Fig. 6 because of the limitation of XRD analysis sensibility. The hydrogen absorption kinetics after 300 cycles was deteriorated but improved again after 2000 and 3500 cycles compared with that of after initial activation. The changes in hydrogenation properties of the alloy induced by cycling were discussed by considering the crystal structure, lattice strain and pulverization of the sample.     

Effect of Ni content on the hydrogen storage behavior of ZrCo1−xNix alloys

ZrCo_1−xNi_x (x = 0, 0.1, 0.2 and 0.3) alloys were prepared and their hydrogen storage behavior were studied. ZrCo_1−xNi_x alloys of compositions with x = 0, 0.1, 0.2 and 0.3 prepared by arc-melting method and characterized by X-ray diffraction analysis. XRD analysis showed that the alloys of composition with x = 0, 0.1, 0.2 and 0.3 forms cubic phase similar to ZrCo with traces of ZrCo₂ phase. A trace amount of an additional phase similar to ZrNi was found for the alloy with composition x = 0.3. Hydrogen desorption pressure–composition–temperature (PCT) measurements were carried out using Sievert's type volumetric apparatus and the hydrogen desorption pressure–composition isotherms (PCIs) were generated for all the alloys in the temperature range of 523–603 K. A single sloping plateau was observed for each isotherm and the plateau pressure was found to increase with increasing Ni content in ZrCo_1−xNi_x alloys at the same experimental temperature. A van't Hoff plot was constructed using plateau pressure data of each pressure–composition isotherm and the thermodynamic parameters were calculated for desorption of hydrogen in the ZrCo_1−xNi_x–H₂ systems. The enthalpy and entropy change for desorption of hydrogen were calculated. In addition, the hydrogen absorption–desorption cyclic life studies were performed on ZrCo_1−xNi_x alloys at 583 K up to 50 cycles. It was observed that with increasing Ni content the durability against disproportionation of alloys increases.     

Improvement of hydrogen storage properties of TiCrV alloy by Zr substitution for Ti

The effects of Zr substitution for Ti on the hydrogen absorption–desorption characteristics of Ti_1−xZr_xCrV alloys (x = 0, 0.05, 0.1 and 1.0) have been investigated. The crystal structure, maximum hydrogen absorption capacity, kinetics and hydrogen desorption properties have been studied in detail. While TiCrV crystallizes in body centered cubic (BCC) structure, ZrCrV is a C15 cubic Laves phase compound and the intermediate compositions with 5 and 10 at% Zr substitutions for Ti (x = 0.05 and 0.1) show the presence of a small amount of ZrCr₂ Laves phase along with the main BCC phase. The pressure–composition isotherms have been studied at room temperature. TiCrV shows separation of TiH₂ phase on cycling. A small amount of Zr substitution for Ti is found to have advantageous effects on the hydrogen absorption properties of TiCrV as it suppresses TiH₂ phase separation and decreases hysteresis. It is found that the hydrogen absorption capacity of Ti_1−xZr_xCrV decreases as the Zr content increases due to the increased fraction of Laves phase. Temperature-programmed desorption studies have been carried out on the saturated hydrides in order to find the relative desorption temperatures.     

Hydrogen storage and heat transfer properties for large-capacity double thin-layered annulus ZrCo bed with secondary containment cavity

Fast heat and mass delivery with high cycling stability of the core component, hydrogen storage bed, in SDS are essential for the operation of the future tritium factory in ITER project. However, the aforementioned properties are still perplexing in large-capacity ZrCo bed, especially for that with secondary containment structure required by the actual tritium operation in the future. Herein, the performance including heating, cycling and cooling with two different size ZrCo beds (loading of ZrCo are 200 g and 2000 g respectively) were systematically studied. The experimental data shows that the maximum heating ability of the middle-size/full-scale storage bed are both about 10 °C/min, and the maximum hydrogen absorption capacity of these ZrCo beds are 44.6 L/405.5 L, respectively. Besides, hydrogen pressure and hydrogen retention during the following desorption can affect the cycling performance of the ZrCo bed. The use of transfer pump can reduce the pressure of the bed during the hydrogen desorption process (operated at 500 °C), which inhibits the disproportionation reaction of the ZrCo alloy. However, the degree of hydrogen pressure reduction in two the types of ZrCo bed are different. As a result, the cycling capacity of the middle-size bed (93.4%, lower hydrogen pressure) is higher than the full-scale bed (68.7%, higher hydrogen pressure) after 10 cycles. When the transfer pump was not used and operated at lower temperature (350 °C), the beds cannot release hydrogen completely, and partial hydrogen atoms are retained in the ZrCo alloy. The middle-size bed still maintains a hydrogen storage capacity of 94.5% after 10 cycles, while 75.9% of the hydrogen storage capacity remained for the full-scale bed. Therefore, the increase of hydrogen surplus in ZrCo alloy is helpful to improve its cycling stability. At last, the cooling performances of the beds under 10 different cooling methods were studied. Among the cooling methods, the best cooling rate was achieved by filling nitrogen in the secondary containment cavity and flowing water passing through the cooling circuit of the bed. This work will provide a crucial reference for the design and optimization of the subsequent operation technology of SDS in ITER.