Maximum Hydrogen Content Research Articles

Alkaline hydrogen storage alloy prepared by mechanical alloying.

In hydrogen energy system, hydrogen storage alloy e.g. LaNi5 is expected as one of important materials for energy storage and transportation. However, they weigh so much for sufficient amount of hydrogen, therefore, alloys with much higher storage capacity are required. From this point of view, we have prepared the alkaline metal hydrogen storage alloys using mechanical alloying (MA) and investigated their reaction characteristics. In this study the maximum hydrogen concentration of 1.88wt% at 60 min of MA was obtained, which corresponded to the mass of 70% of LaNi5 for the same amount of hydrogen.

Phase stability and neutron diffraction studies of the laves phase compounds Zr(Cr 1− xMo x) 2 with 0.0≤ x≤0.5 and their hydrides

Laves phase compounds Zr(Cr 1− x Mo x ) 2 with 0.0≤ x≤0.5 were synthesized with the hexagonal C14 and/or cubic C15 type structures. By using X-ray and neutron powder diffraction the structure of the alloys were determined, and in particular the sites for the 3 d metal substitution. The pressure composition ( P– C) isotherms were determined over the temperature range 293–453 K. The effect of the M/Cr substitution was studied with regards to the alloys and hydrides stability and the maximum hydrogen content.

Hydrogen absorption characteristics in Zr 0.2Ho 0.8Fe 0.5Co 1.5

Hydrogen absorption studies have been carried out on the C15 cubic Laves phase alloy of Zr 0.2Ho 0.8Fe 0.5Co 1.5. The p– c data were collected in the pressure and temperature ranges of 0.05 ≤ P (bar) ≤ 45 and 27 ≤ T (°C) ≤ 100, respectively. A maximum hydrogen uptake of 3.6 hydrogen atoms per formula unit at 33 bar and 27°C is observed. The p– c isotherms show one plateau (α + β) region. This is confirmed from the dependence of the thermodynamics of dissolved hydrogen as a function of hydrogen concentration. Δ H H and Δ S H are found to be in the ranges −(5–15) kJ (mol H) −1 and −(23–48) J K −1 (mol H) −1, respectively. Volume expansion of about 20% is found at the maximum hydrogen concentration at RT, without a change in its crystal structure.

Study of hydrogenation of Sm 2Fe 17− yGa y by means of X-ray diffraction

The hydrogenation process of Sm 2Fe 17− y Ga y ( y=0–2) was studied. X-ray investigations show a decreasing hydrogen solubility in the intermetallic alloy with increasing Ga-content from 4.0±0.3 atoms per formula unit for Sm 2Fe 17 to 2.85±0.05 for Sm 2Fe 15Ga 2. The larger Ga atoms reduce the size of the interstitial sites and thereby the maximum hydrogen concentration is decreased. The behaviour of the lattice parameters a and c with increasing Ga content points to a changed hydrogen distribution on the interstitial sites, becoming more statistical. In situ observations by means of high temperature X-ray diffraction show that the hydrogen absorption process is diffusion controlled. The hydrogen absorption starts at an annealing temperature of 120–140°C in all cases. The solubility of hydrogen decreases with increasing temperature. The hydrogen is completely desorbed above 350°C in all cases. The absorption/desorption process is reversible between room temperature and 400°C. Annealing at temperatures above 400°C leads to the decomposition of the Sm 2Fe 17 phase, indicated by emerging of α-Fe. The formation of SmH x is established at 600°C. The decomposition temperature increases with increasing Ga-content. Up to 750°C, only Sm 2Fe 17 is completely decomposed.

Optical and electrical changes of hydrogenated Dy films

Electrical and optical measurements on hydrogenated Pd coated (20 nm) Dy films (250–300 nm) are presented. The films are prepared in a high vacuum chamber and hydrogenated, at room temperature, by exposing them to a hydrogen atmosphere. Maximum hydrogen concentration of the order of 3 is achieved as measured by QCM. Changes in electrical resistance and optical transmission (at λ=632.8 nm) in the films indicate the dielectric nature of the DyH 3. The Hall coefficient measured also as a function of concentration, gives an insight into the evolution of the density of charge carriers as hydrogen is absorbed.

高強度鋼における水素割れ感受性の評価パラメータ

The influences of the applied stress and the stress concentration factor (Kt) on hydrogen embrittlement were investigated in the commercial JIS SCM440 steel with the tensile strength of 1403 MPa. The applied stress was changed from 0.33 times to 0.72 times the tensile strength of the notched specimen, while the Kt was altered from 2.1 to 6.9. The hydrogen embrittlement property was evaluated with the resistance to the diffusible hydrogen in the steel. The diffusible hydrogen concentrations were analyzed by thermal desorption analysis. The results are as follows.(1) The hydrogen embrittlement occurs under the lower diffusible hydrogen concentrations with increasing Kt. However, the HD-t (diffusible hydrogen concentration-time to failure) curves become almost the same when the Kt and the applied stress are high.(2) The criterion of the hydrogen embrittlement cannot be determined by the combination of the maximum local axial stress in the specimen and the maximum diffusible hydrogen concentration locally accumulated in the specimen.In the discussion part, it was proposed that it is very important to consider the stress distribution in the specimen for the evaluation of hydrogen embrittlement.

Structural studies of Laves phases ZrCo(V1−xCrx) with 0⩽x≤1 and their hydrides

Laves phases of the series ZrCo(V1−xCrx) with 0≤x≤1 have been synthesised with the hexagonal C14-type structure. We have analyzed the structure of the alloys by X-ray and neutron diffraction, and determined the sites occupied by transition metals with the V/Cr substitution. The positions of hydrogen atoms in the structure and the occupation of the different interstitial sites of the hydrides have been determined. The effects of the V/Cr substitution have been studied with regard to the phase stability, the maximum hydrogen content and the hydrogen site stability. P–c–T measurements show a good reversibility of the hydrogen uptake.

Hydriding properties of the heat-treated MgNi alloys with nanostructural designed multiphase

Abstract The structural and hydriding properties have been investigated for the heat-treated MgNi alloys with nanoscale structure which consists of the Mg 2 Ni and MgNi 2 phases. The alloys were fabricated by mechanical alloying (MA) and heat treatment (HT), the so called MA/HT method. For the as-alloyed amorphous MgNi (a-MgNi) alloy, the maximum hydrogen content reaches 1.72 mass% at 473 K. The hydride, however, gradually decomposes into Mg 2 NiH 4 and MgNi 2 phases during measurement of pressure–composition isotherm. In the case of nanoscaled crystalline Mg 2 Ni (c-Mg 2 Ni)+amorphous MgNi 2 (a-MgNi 2 ) multiphase alloy, the maximum hydrogen content reaches only 0.35 mass% at 473 K. No plateau-like behavior is observed in the desorption process. In the case of nanoscaled c-Mg 2 Ni+crystalline MgNi 2 (c-MgNi 2 ) multiphase alloy, the maximum hydrogen content reaches 1.45 mass% at 473 K. A well-defined plateau region is observed of nearly 0.012 MPa at 473 K in the desorption process. Therefore, it is concluded that the hydriding properties of the nanoscaled MgNi multiphase alloy will be strongly affected by not only the structural properties of the matrix surrounding the c-Mg 2 Ni grains precipitated but also by the accumulation/release of internal stress on the precipitation process.

Electronic structure and stability of hydrides of intermetallic compounds

We have investigated the electronic structure of several intermetallic compounds of AB and AB 5 type and their hydrides using the ab initio self-consistent linear muffin-tin orbitals method. The energy bands, total densities of states as well as their site and partial wave contributions are used to discuss the metal–hydrogen bonding features, the modifications of the electronic states at the Fermi energy on hydrogen absorption and the factors which control the stability. The specific systems investigated are zirconium-based AB compounds (AZr, BCo, Ni) and their hydrides ABH and ABH 3 . We also discuss the effect of substitution at the Ni site in LaNi 5 by several elements of the 3d series (Mn, Fe, Co). In Zr-based AB hydrides, the Zr–H bonding contribution is crucial to the stability of the system due to the lowering of the energy states below the Fermi energy. The total energies of ZrNiH calculated for different site occupancies by the H atoms are in agreement with experimental trends. For the intermetallic compounds LaNi 4 M (MMn, Fe, Co) the Fermi level is found to lie in a narrow M-3d sub-band above the Ni-d states, and the densities of states are high. The lattice expansion accounts for less than 50% of the decrease in the stability, indicating the importance of the chemical substitution effects, besides the lattice expansion contribution. For the Co-substituted compound, the (3g) sites are found to be more stable than the (2c) sites, in agreement with experimental observations, and the maximum hydrogen content of the hydride LaNi 4 CoH 4 appears to be associated with the filling of the Co-d peak.

Effect of nickel alloying by using ball milling on the hydrogen absorption properties of TiFe

After ball-milling, TiFe under a pure argon atmosphere, with a small amount of pure nickel, can readily absorb large amounts of hydrogen without any activation process. The H⧸M system reaches equilibrium after 8 h under 10 bars of hydrogen pressure (H⧸M = 0.62). Even after 10 days exposure to the air, the same sample reacts with hydrogen, but with slower kinetics. The impact of the ball-milling time on the hydrogen absorption kinetics and the maximum hydrogen content is discussed.

Hydrogen absorption characteristics in the Tb1−xZrxFe3 (x=0.1, 0.2, 0.3) system

The hydrogen absorption pressure-composition-isotherms of the PuNi3 type rhombohedral Tb1−xZrxFe3 (x=0.1, 0.2, 0.3) alloys are investigated by Sievert’s apparatus, in the temperature and pressure ranges 75≤T(°C)≤150 and 0.1≤P(bar)≤25, respectively, with a view to study the dependence of hydrogen solubility and the plateau pressure on Zr content. The P-C isotherms show the presence of a single plateau region in the temperature and pressure ranges studied and it is found that the plateau pressure at any given temperature increases with increase of Zr content along with a reduction in the hydrogen capacity. The absorption of hydrogen is accompanied by a maximum of 17.4% expansion in the unit cell volume of the host material without any change in PuNi3 type structure as evidenced by the X-ray diffraction studies on the alloy– hydrides. The presence of single and two phase regions as seen in the P-C isotherms are confirmed from the powder X-ray diffractogram of the alloy–hydrides with appropriate hydrogen concentration. The powder X-ray diffractograms on the alloy–hydrides with maximum hydrogen concentration further show the absence of hydrogen induced amorphization (H1A) upon hydrogenation.

Hydrogenation of Zr6MeX2 intermetallic compounds (Me=Fe, Co, Ni; X=Al, Ga, Sn): Crystallographic and theoretical analysis

Experimental studies on the series of ternary intermetallic compounds, Zr6MeX2, where Me=Fe, Co, and Ni, and X=Al, Ga, and Sn, show that they have large hydrogen storage capacities ranging from 9.3 to 10.8 H-atoms per formula unit. The crystal structure of the parent intermetallic compounds changes upon hydrogenation with a two-fold increase of the crystallographic c-axis length and a corresponding change in space group from P6m2 to P62c. Full profile (Rietveld) refinement using X-ray powder diffraction data indicates that the crystal structures of the new hydrides, Zr6CoAl2H10, Zr6NiAl2H9.7 and Zr6NiSn2H10.8 are analogous to Zr6FeAl2D10, which was examined by neutron powder diffraction. Thermal desorption of hydrogen in all hydrides occurs in the temperature range between 400 and 900 K and is characterized by two similar events. The compounds Zr6FeAl2Hx (x=0, 10 and 0.1–0.2) order magnetically at 45, 155 and 10 K, respectively. Electronic structure calculations are carried out on Zr6FeAl2Hx (0≤x≤10) to interpret their structural and thermal behavior. Site energies for hydrogen incorporation, energetics of hydrogen desorption, as well as quantitative details of the densities of states are evaluated. Site energies and metal–metal bonding largely affect the maximum hydrogen content, while H–H repulsions constitute the greatest driving force for the change in space group upon hydrogenation.

Hydrogen concentration and its relation to interplanar spacing and layer thickness of 1000-Å Nb(110) films duringin situhydrogen charging experiments

The Nb layers of a $[1000\ensuremath{-}\mathrm{\AA{}}\mathrm{}\mathrm{N}\mathrm{b}/26\ensuremath{-}\mathrm{\AA{}}\mathrm{}\mathrm{Fe}]\ifmmode\times\else\texttimes\fi{}5$ multilayer were repeatedly charged with hydrogen from the gas phase. The equilibrium hydrogen concentration in the Nb layers and the hydrogen-induced layer thickness expansion perpendicular to the film plane were determined as a function of pressure by means of in situ neutron reflectivity measurements. In situ x-ray-diffraction experiments performed on the same sample yielded the corresponding expansion of the out-of-plane Nb(110) interplanar spacing and the time-dependence of the charging and decharging process. It was found that the relative expansion of the Nb layers is considerably larger than the relative increase of the Nb(110) interplanar spacing. This shows that during hydrogen incorporation a large amount of additional volume, presumably in the form of voids in the vicinity of grain boundaries, is created. These lattice imperfections may effectively trap hydrogen atoms. The maximum hydrogen concentration at ${p}_{\mathrm{H}2}=900\mathrm{mbar}$ and $T=185\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ is found to be 95 [H]/[Nb] at. %.

Production rate of acetate during colonic fermentation of lactulose: a stable-isotope study in humans

BackgroundBreath tests are currently used to qualitatively assess colonic fermentation; no quantitative estimations are available for healthy subjects. ObjectiveThis study describes a stable-isotope-dilution method to measure acetate production quantitatively from colonic bacterial fermentation. DesignSix volunteers received a primed, constant, intravenous infusion of [1-13C]acetate at a rate of 1.01 ± 0.04 μmol·kg-1· min-1 for 7 h. They ingested 20 g pure lactulose after 1 h of the tracer infusion. Expired air and arterialized venous blood were sampled every 15 min. ResultsBefore lactulose intake, the breath-hydrogen concentration was 7 ± 2 ppm and the plasma acetate concentration and isotopic enrichment were 141 ± 14 1mol/L and 14.8 ± 1.4 moles percent excess, respectively. Whole-body acetate turnover was 6.0 ± 0.7 μmol·kg-1 · min-1. After lactulose ingestion, maximum breath hydrogen and acetate concentrations reached 63 ± 15 ppm (P = 0.004) and 313 ± 25 μmol/L ( P = 0.002), respectively, whereas [13C]acetate enrichment decreased to 9.9 ± 1.3 moles percent excess (P = 0.03). Whole-body acetate turnover increased to 9.8 ± 1.5 μmol·kg-1· min-1 and later decreased almost to baseline values. Colonic lactulose fermentation yielded 140 ± 12 mmol acetate over 6 h, representing 86% of the production based on stoichiometric equations. ConclusionThis new method provides a quantitative estimate of colonic carbohydrate fermentation via evaluation of acetate production.

Influence of target chemical activity on Balmer lines emission from backscattered hydrogen

We have investigated the influence of implanted hydrogen on Balmer lines emission from backscattered particles under D + irradiation to Si target for an incident energy ranging from 5 to 25 keV at a target temperature from room temperature (RT) to 600 K and the experimental results are compared with Monte Carlo simulation by the TRIM92 code. For clean Si surface, D α photon intensity was proportional to the backscattering coefficients calculated by the TRIM92 code for all incident energies. The intensity stayed constant with increasing the fluence for incident energies of 15 and 25 keV in accordance with the simulation that the backscattering coefficient is not so much influenced by implanted deuterium because the mass of D is much less than that of Si. At 5 keV incidence, the D α photon intensity gradually increased with the fluence until saturated after prolonged irradiation. The difference between the initial intensity and that after saturated was reduced with increasing the target temperature and disappeared above 600 K. The decay of the D α photon intensity accompanied by the thermal release of implanted deuterium was also observed above 370 K. According to the TRIM92 calculation, the D/Si atomic ratio at the top surface for 5 keV incidence with the fluence of 4 × 10 17 D +/cm 2 exceeds 0.4 which is the maximum hydrogen concentration of amorphous hydrogenated Si (a:Si–H), whereas that for 15 keV incidence remains below 0.1 even over the 7 × 10 17 D +/cm 2 irradiation. All these results made us to conclude that the D α intensity at 5 keV incidence is enhanced by retained deuterium near the top surface through modifying the electron capture process of backscattered deuteron.

Effects of prior hydrogenation on the structure and properties of thermally nanocrystallized silicon layers

Nanocrystalline silicon layers have been obtained by thermal annealing of films sputtered in various hydrogen partial pressures. The as-deposited and crystallized films were investigated by infrared, Raman, x-ray diffraction, electron microscopy, and optical absorption techniques. The obtained data show evidence of a close correlation between the microstructure and properties of the processed material, and the hydrogen content in the as-grown deposit. The minimum stress deduced from Raman was found to correspond to the widest band gap and to a maximum hydrogen content in the basic unannealed sample. Such a structure relaxation seems to originate from the so-called “chemical annealing” thought to be due to Si–H2 species, as identified by infrared spectroscopy. The variation of the band gap has been interpreted in terms of the changes in the band tails associated with the disorder which would be induced by stress. Finally, the layers originally deposited with the highest hydrogen pressure show a lowest stress—which does not correlate with the hydrogen content and the optical band gap—and some texturing. These features are likely related to the presence in these layers of a significant crystalline fraction already before annealing.

Hydrogen absorption characteristics in Zr 0.2Ho 0.8CoFe

Hydrogen absorption studies have been carried out on the Zr 0.2Ho 0.8CoFe alloy which has the C15 cubic Laves phase structure. The data were collected in the temperature and pressure ranges 27≤ T(°C)≤150 and 0.05≤ P(bar)≤45 respectively. A maximum hydrogen concentration of 9 hydrogen atoms per formula unit at 43 bar at RT is observed. The P– C isotherms show two plateau regions which are identified as the (α+β) and (β+γ) phases. These are confirmed from the variation of thermodynamic parameters as the function of hydrogen concentration and from the powder X-ray diffractograms of the samples taken at different hydrogen concentrations. The relative partial molar enthalpy (ΔH̄ H) and entropy (ΔS̄ H) of hydrogen are found to be in the ranges - (1–8) kJ (mol H) −1 and - (13–22) J K −1 (mol H) −1, respectively. The unit cell volume expansion (Δ V/ V) up to 22% is found at the maximum hydrogen concentration at RT without a change in its crystal structure. The powder X-ray diffractogram of Zr 0.2Ho 0.8CoFeH 9 does not indicate the occurrence of hydrogen induced amorphization (HIA) unlike the case of Zr 0.2Ho 0.8Co 2H 3 even though the atomic size ratio ( R A/ R B) of Zr 0.2Ho 0.8CoFe is more than the critical value estimated for the formation of an amorphous state upon hydrogenation.

Structural and hydrogen sorption studies of NdNi 5− xAl x and GdNi 5− xAl x

Crystallographic and hydrogen sorption studies of the NdNi 5− x Al x and GdNi 5− x Al x systems have been carried out. It is found that up to x<2 the prototype hexagonal crystal structure of the CaCu 5-type is preserved. However, at x≥2, a larger unit cell of the HoNi 2.6Ga 2.4-type is observed. In both structures, a site preference occupancy between Al and Ni atoms occurs. The structural transition with x is explained by considering steric effects: Al being bigger than Ni. All alloys were subjected to hydrogen sorption. The decrease of maximum hydrogen content and plateau pressure with increasing aluminium content (from 4.1 H/f.u. and 0.87 MPa for GdNi 4.5Al 0.5 to 2.6 H/f.u. and 0.01 MPa for GdNi 3.26Al 1.74) is explained from both the thermodynamic and crystallographic point of view. These results are consistent with: (i) previous observations on the LaNi 5− x Al x system and (ii) the `Westlake criterium' except when the HoNi 2.6Ga 2.4-type structure appears. The huge decrease of the hydrogen content observed when the superstructure appears is explained by the change of possible hydrogen tetrahedral sites from RE 2Ni 2 to RE 2Al 2 (RE=Nd, Gd).

A model of the Temkin isotherm behavior for hydrogen adsorption at Pd–SiO2 interfaces

A simple electrostatic model of the adsorbate–adsorbate interaction of hydrogen atoms at a Pd–SiO2 interface is presented. The model predicts a hydrogen adsorption isotherm of the Temkin type. It is found that, in practice, an upper limit for the hydrogen response of a Pd-metal-oxide-semiconductor device exists. The value (in V) is equal to the difference of the initial heats of adsorption (in eV) of the interface and the Pd bulk, respectively. Furthermore, a corresponding maximum hydrogen concentration, at the interface, of 1×1018 m−2 is predicted. The predictions are in good agreement with previously observed experimental data.

Structural studies of Laves phases Zr(Cr 1− xNi x) 2 with 0≤ x≤0.4 and their hydrides

Hexagonal C14-type Laves phases of the series Zr(Cr 1− x Ni x ) 2 with 0≤ x≤0.4 have been synthesised. Purity and quality of polycrystalline alloys have been checked using SEM and EDX techniques. By X-ray and neutron diffraction we have analyzed the structure of the alloys, and determined the sites for the Ni substitution. The positions of hydrogen atoms in the structure and the occupation of the different interstitial sites of the hydrides have been determined. The effects of the Ni/Cr substitution have been studied with regard to the phase stability, the maximum hydrogen content and the hydrogen site stability.