Hydrogen Absorption Behavior Research Articles

Evaluation of hydrogen absorption behaviour during acid etching for surface modification of commercial pure Ti, Ti–6Al–4V and Ni–Ti superelastic alloys

The hydrogen absorption behaviour during acid etching for the surface modification of commercial pure Ti, Ti–6Al–4V and Ni–Ti superelastic alloys has been investigated on the basis of the surface morphology, electrochemical behaviour and hydrogen thermal desorption analysis. To simulate the conventional acid etching for the improvement of the biocompatibility of Ti alloys, the specimens are immersed in 1 M HCl, 1 M H 2SO 4 or 0.5 M HCl + 0.5 M H 2SO 4 aqueous solution at 60 °C. Upon immersion, commercial pure Ti absorbs substantial amounts of hydrogen irrespective of the type of solution. In H 2SO 4 or HCl + H 2SO 4 solutions, the hydrogen absorption occurs for a short time (10 min). For Ti–6Al–4V alloy, no hydrogen absorption is observed in HCl solution, whereas hydrogen absorption occurs in other solutions. For Ni–Ti superelastic alloy, the amount of absorbed hydrogen is large, resulting in the pronounced degradation of the mechanical properties of the alloy even for an immersion time of 10 min, irrespective of the type of solution. The hydrogen absorption behaviour is not necessarily consistent with the morphologies of the surface subjected to corrosion and the shift of the corrosion potential. The hydrogen thermal desorption behaviour of commercial pure Ti and Ni–Ti superelastic alloy are sensitively changed by acid etching conditions. The present results suggest that the evaluation of hydrogen absorption is needed for each condition of acid etching, and that the conventional acid etching often leads to hydrogen embrittlement.

Nanostructured surface coatings for the improvement of AB5-type hydrogen storage intermetallics

Hydrogen absorption behaviour of intermetallic absorbers strongly depends upon the contribution of the surface layers into the overall rate of the hydrogenation process. Activation process, which is normally required to initiate and facilitate the initial hydrogen uptake, may be waved by modifying the surface behaviour, thus offering obvious practical benefits. In the present work a surface nanoengineering approach was developed to enhance the hydrogenation ability of rare earth-containing AB5-type hydride-forming intermetallics. The modification involves three successive steps; (a) fluorination to form a surface-covering REF3 layer with a high specific surface area; (b) surface functionalization by γ-APTES; (c) deposition of Pd nanoparticles into the surface nanocavities of the fluoride. The surface functionalization step was applied to immobilize Pd nuclei inside the nanocavities of the REF3 layer. The deposited Pd nanoparticles exhibited a high degree of coalescence, and were further transformed into a continuous surface layer. Pd/fluoride modified materials exhibited exceptional Pd coating densities and imposed a large facilitation in the kinetics of hydrogenation compared with the conventional nonmodified intermetallics. The approach has a potential in the directed design of new classes of highly efficient and robust composite hydrogen sorption materials for hydrogen storage, separation and purification. Large improvements in the kinetics of hydrogenation of the Pd/fluoride modified intermetallics also manifested by extraordinary surface poisoning tolerance towards oxygen and water vapour, as compared with that of the nonmodified, or just fluorinated/Pd modified intermetallic alloys. The developed classes of highly efficient and robust composite hydrogen sorption materials have the potential for application as sorption media for the high efficiency hydrogen storage, separation and purification systems and may facilitate progress towards the implementation of the key elements of future hydrogen economy. Copyright © 2009 John Wiley & Sons, Ltd.

Determination of the rate-limiting mechanism for permeation of hydrogen through microfabricated palladium–silver alloy membranes

For many years enhancement of the hydrogen permeation rate through Pd and Pd-alloy membranes has been accomplished by decreasing the membrane thickness. This approach is based on the idea that the permeation rate is limited by the diffusion process through the membrane bulk material. Theoretical modeling suggests that as membrane thickness is reduced into the micrometer range the rate-limiting permeation mechanism may shift to desorption from the permeate surface. In order to test the model predictions, free-standing Pd–Ag alloy membranes (23 wt% Ag) with a thickness on the order of 1 μm have been microfabricated and their hydrogen permeation behavior has been experimentally determined. At temperatures between 523 and 723 K, hydrogen permeation is limited by the diffusion process and is characterized by a membrane permeability pre-exponential factor of 5.51E−8 ± 1.34E−8 mol/m/s/Pa 0.5 and an activation energy of 10.8 ± 1.25 kJ/mol. At temperatures below 500 K, the activation energy increases appreciably. This transition is consistent with diffusion-limited permeation in the presence of non-ideal absorption behavior of hydrogen in the Pd–Ag alloy. A transition into a desorption-limited permeation regime is not observed under the operating conditions in this study. Additionally, two distinct failure modes have been observed for these microfabricated devices. The operating conditions leading to failure and cause of each failure mode are discussed.

Non-ideal absorption effects on hydrogen permeation through palladium–silver alloy membranes

Current theoretical models for the permeation behavior of hydrogen through palladium and palladium alloys predict that low temperature operation of thin membranes will result in permeation which is no longer controlled by the diffusion of hydrogen through the metal lattice. Specifically, the process of desorption from the downstream surface is predicted to become the dominant resistance to mass transfer. However, these models neglect the non-ideal absorption behavior of hydrogen in palladium which typically occurs at temperatures below 300 °C. In this work a model is developed which accounts for the non-ideal behavior of hydrogen in palladium–silver alloys (25% silver by weight) which are typically used for hydrogen purification. This model predicts that the diffusion-limited regime should be characterized by an increase in the activation energy to ∼32 kJ/mol at temperatures below 200 °C. This prediction is supported by data available in the literature for thick (>125 μm) palladium–silver alloy membranes.

Hydrogen Absorption in Ion Beam Sputtered Titanium Thin Films

Titanium films were prepared on sapphire substrates in an UHV chamber, by means of ion beam sputter deposition under Ar-atmosphere at the pressure of 1.5ּ10-4 mbar, with a deposition rate of 2,1 nm/min. The crystal structure was investigated by means of X-Ray diffraction using a Phillips X-Pert diffractometer with a Co-Kα radiation. For electrochemical hydrogen loading, the films were covered by a 30 nm thick layer of Pd in order to prevent oxidation and facilitate hydrogen absorption. The samples were step-by-step loaded with hydrogen by electrochemical charging, which was carried out in a mixed electrolyte of phosphoric acid and glycerine (1:2 in volume). An Ag/AgCl (sat.) and Pt wires were used as the reference and the counter electrode, respectively. XRD measurements were performed before and after hydrogenation in order to investigate the effect of hydrogen loading on the microstructure. The main characteristics of hydrogen's absorption behaviour, as well as the thermodynamics and phase boundaries of titanium-hydrogen thin films are discussed in detail with specific emphasis on the comparison to titanium-hydrogen bulk system.

Hydrogen absorption–desorption, optical transmission properties and annealing effect of Mg thin films prepared by magnetron sputtering

We prepared Pd-capped Mg thin films by direct current (DC) magnetron sputtering. We investigated their structural, optical and electrical properties, as well as the effect of annealing on these films during hydrogenation and dehydrogenation. The hydrogen absorption behaviors at both room temperature and 353 K, and dehydrogenation at 353 K, were studied. The Mg film annealed at 473 K for 2 h exhibited the best absorption kinetics and superior switchable mirror properties among all the samples annealed at different temperatures. We concluded that annealing temperature is a crucial parameter in forming high-quality Mg films. The improved hydriding kinetics can be attributed to the favorable morphology and structure induced by the annealing process.

Hydrogen Absorption and Thermal Desorption Behavior of Ni-Ti Superelastic Alloy Immersed in Neutral NaCl and NaF Solutions under Applied Potential

The hydrogen absorption and thermal desorption behavior of Ni-Ti superelastic alloy immersed in neutral NaCl and NaF aqueous solutions at 25 � C under an applied cathodic potential for 2 h have been systematically investigated by hydrogen thermal desorption analysis. The critical potential for hydrogen absorption is independent of the type and concentration of solution. The amount of absorbed hydrogen increases with decreasing applied potential, although it is only slightly changed by the type of solution. The amount of hydrogen desorbed at low temperatures, for the alloy immersed in NaF solutions, is larger than those in NaCl solutions, suggesting that the type of solution affects the hydrogen states in the alloy. The present results indicate that for Ni-Ti superelastic alloy, compared with titanium and its alloys, the critical potential for hydrogen absorption is located in a more noble direction, and the amount of absorbed hydrogen is large in NaCl and NaF solutions. Thus, the hydrogen embrittlement of Ni-Ti superelastic alloy probably occurs more readily than those of titanium and its alloys in NaCl and NaF solutions.

Relationship between Hydrogen Absorption and Corrosion Behavior of Ti-6Al-4V Alloy Immersed in Acidic Fluoride Solutions

The relationship between hydrogen absorption and the corrosion behavior of Ti-6Al-4V alloy has been examined by immersing the alloy in acidulated phosphate fluoride (APF) solution with various concentrations. Upon immersion in 0.1 mass% APF solution, no hydrogen absorption is observed despite the occurrence of general corrosion. In 0.2% APF solution, slight hydrogen absorption occurs soon after immersion, and then the surface of the specimen becomes uniformly covered with a crystalline corrosion product (Na3AlF6), thereby inhibiting further hydrogen absorption. In APF solutions with concentrations higher than 0.4%, the amount of absorbed hydrogen increases with increasing concentration of APF solution and immersion time. The type and morphology of corrosion products sensitively depend on the concentration of APF solution. Upon immersion in 0.4% APF solution, crystalline and massive Na3AlF6 are observed on the surface of the specimen. In 1.0% and 1.5% APF solutions, Na3AlF6 with a foldlike shape and granular Na3AlF6 and Na3TiF6 are observed. In 2.0% APF solution, only granular Na3TiF6 is observed. The corrosion potentials and anodic polarization curves are analogous in all APF solutions except the 0.2% and 0.4% APF solutions. In contrast, the current density of cathodic polarization curves increases with the concentration of APF solution. The results of the present study suggest that the corrosion products play an important role in the hydrogen absorption behavior of Ti-6Al-4V alloy.

ジルコニウム基合金の酸化膜特性評価－水素吸収挙動との関連（2）－

ジルコニウム基合金の酸化膜特性評価－水素吸収挙動との関連（2）－

Infrared emission imaging as a tool for characterization of hydrogen storage materials

Combinatorial thin films provide an opportunity for studying a variety of properties over a wide range of compositions and microstructures on a single substrate, allowing substantial acceleration of both the fabrication and study of materials and their properties. This paper details the use of infrared (IR) emissivity imaging for studying the in situ hydrogenation of Mg x Ni 1− x films with hydrogen gas; the method is shown to be a powerful combinatorial screening tool for metal hydride storage materials. The 100 nm thick Mg x Ni 1− x composition gradient films (0.4 < x < 0.9) capped with a Pd layer of varying thickness were deposited in a combinatorial electron-beam deposition chamber using a shutter-controlled multilayer technique. The microstructure of as-deposited and 250 °C-annealed films was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM studies of the “X-ray amorphous” films show that the microstructure consists of nano-scale grains of a metastable fcc phase as well as Mg 2Ni and MgNi 2 phases over a broad range of higher Ni compositions. The metastable phase appears to be a Ni-stabilized fcc form of Mg. Hydrogenation differences between the studied films and bulk alloys are suggested to be associated primarily with crystallographic differences of the metallic and hydride phases. Hydrogen absorption and desorption of the films were monitored with an infrared camera capable of simultaneously imaging the entire composition spread. The observed changes in infrared intensity during hydrogen loading/unloading demonstrate the sensitivity of the method to hydrogen absorption behavior of different compositions and microstructures.

Superior hydrogen absorption and desorption behavior of Mg thin films

Pd-capped Mg films prepared by magnetron sputtering achieved complete dehydrogenation in air at room temperature and behaved as favorable gasochromic switchable mirrors. Their cyclic hydrogen absorption and desorption kinetics in air were investigated by using the Bruggeman effective medium approximation. The overall activation energy was 80 kJ mol −1, while the reaction orders controlling desorption were deduced to be n = 2 at 328 K and n = 1 at lower temperatures by analyzing the transmittance data. The hydrogen diffusion coefficient and the corresponding activation energy were calculated by electrochemical measurements. Mg thin films exhibited the smaller activation energy and remarkable diffusion kinetics at room temperature which implied potential applications in smart windows.

Thermodynamic assessment of the H–La–Ni system

The H–La–Ni system has been assessed according to the CALPHAD method. To this purpose, an assessment of the La–Ni binary system has been taken from the literature, while the H–Ni system has been partially reassessed with respect to the liquid phase, in order to be consistent with generally used lattice stability of liquid hydrogen. A first assessment of binary H–La system has been carried out in this work. The binary LaH x phase has been described with the sublattice model, in order to take into account a composition variations for 2 ≤ x ≤ 3 . Calculated p – c – T curves and Van’t Hoff plots agree well with experimental data. In the ternary system, hydrogen absorption data have been considered for the LaNi 5 intermetallic compounds, leading to the LaNi 5H 7 hydride. Because the compound and the hydride have the same structure, the equilibrium between the two phases has been described as miscibility gap. Also in this case, calculated p – c – T curves and Van’t Hoff plots agree rather well with experimental data. The equilibrium phases have been calculated in the ternary system. The present thermodynamic description can be a useful tool for predicting the hydrogen absorption and desorption behaviour in commercial vessels based on the AB 5 compounds.

Hydrogen in thin Pd-based layers deposited on reticulated vitreous carbon—A new system for electrochemical capacitors

Reticulated vitreous carbon (RVC) has been used as a matrix for electrodeposition of thin layers of Pd and Pd-rich Pd–Rh alloys. It was found that RVC substrate does not affect qualitatively hydrogen absorption behavior of Pd-based deposits. Similarly to thin Pd or Pd alloy layers deposited on Au wires, the α–β phase transition controls the overall rate of hydrogen absorption and desorption into/from Pd-based/RVC electrodes. The possibility of the application of these materials as phase charging–discharging systems was investigated. The values of specific pseudocapacitance, specific power and specific energy were comparable with those for supercapacitors utilizing various redox reactions.

Effects of potential, temperature and pH on hydrogen absorption and thermal desorption behaviors of Ni–Ti superelastic alloy in 0.9% NaCl solution

The effects of electrochemical potential, solution temperature and pH on the hydrogen absorption and desorption behaviors of Ni–Ti superelastic alloy immersed in 0.9% NaCl solution for 2 h have been investigated systematically by hydrogen thermal desorption analysis. For hydrogen cathodic charging under constant applied potential, upon increasing solution temperature, the critical potential for the hydrogen absorption very slightly shifts to a noble direction. As solution pH decreases, the critical potential for the hydrogen absorption shifts markedly to a noble direction and approaches to the corrosion potential; the critical current density for the hydrogen absorption slightly decreases. At a less noble potential than the critical potential for the hydrogen absorption, the amount of absorbed hydrogen increases markedly with decreasing applied potential. For hydrogen cathodic charging under constant current density, the amount of absorbed hydrogen increases with increasing solution temperature and decreasing solution pH. The basic hydrogen desorption behavior only slightly depends on solution temperature or pH. Nevertheless, hydrogen desorption at low temperatures for specimens subjected to cathodic charging under constant current density is observed distinctly as compared with that under constant applied potential.

Hydrogen absorption in 3.1 nanometre sized palladium samples: does structure matter?

Abstract In this work the hydrogen absorption behaviour of two types of Pd-clusters, different in structure but similar in size (3.1 nm), will be presented. First, icosahedral Pd clusters stabilised in surfactants; second, cubic Pd clusters stabilised in a Teflon-AF matrix. The phase transition in these samples was monitored by in-situ X-ray diffraction. It will be shown that the hydrogen uptake ability depends strongly on the lattice structure, which is affected by the type of stabiliser. Teflon AF stabilised clusters (cubic clusters) show the phase transition which is common for bulk Pd, whereas the surfactant stabilised clusters (icosahedral clusters) show only weak lattice dilatation upon hydrogen absorption. Pressure – lattice parameter isotherms show that the cubic clusters absorb large amounts of hydrogen in comparison to the icosahedral clusters. The measured lattice expansion is 0.130 Å at 105 Pa and 300 K, which is about 320 % the amount measured for icosahedral clusters (0.04 Å). This suggests that surface sites are available for hydrogen in the Pd – Teflon-AF samples which are not accessible for Pd – surfactant-clusters, and that the icosahedral lattice absorbs less hydrogen for similar external pressures.

Nanosize Effects on Hydrogen Storage in Palladium

The size dependencies of the hydrogen-storage properties in polymer-coated Pd nanoparticles with diameters of 2.6 ± 0.4 and 7.0 ± 0.9 nm were investigated by a measurement of hydrogen pressure-composition isotherms. Their storage capacities per constituent Pd atom in the particles decreased with decreasing particle size, whereas the hydrogen concentrations in the two kinds of nanoparticles were almost the same and 1.2 times as much, respectively, as that in bulk palladium after counting zero hydrogen occupancy on the atoms in the first surface layer of the particles. Furthermore, apparent changes in hydrogen absorption behavior with decreasing particle size were observed, that is, a narrowing of the two-phase regions of solid-solution and hydride phases, the lowering of the equilibrium hydrogen pressure, and a decrease in the critical temperature of the two-phase state. By analyzing the isotherms, we quantitatively determined the heat of formation (ΔHα→β) and the entropy change (ΔSα→β) in the hydride form...

Hydrogen Absorption in the Core/Shell Interface of Pd/Pt Nanoparticles

We have investigated the hydrogen absorption behavior of Pd/Pt nanoparticles with a core/shell-type structure. From the results of the hydrogen pressure−composition (PC) isotherm and solid-state 2H NMR measurements, it was revealed that the Pd/Pt nanoparticles can absorb hydrogen, and most of the absorbed hydrogen atoms are situated around the interfacial region between the Pd core and the Pt shell of the Pd/Pt nanoparticles, indicating that the core/shell boundary plays an important role in the formation of the hydride phase of the Pd/Pt nanoparticles.

Effects of Aluminum on Delayed Fracture Properties of Ultra High Strength Low Alloy TRIP-aided Steels

To improve the delayed fracture strength of ultra high-strength low alloy TRIP-aided steels with bainitic ferrite matrix (TBF steels), the effects of aluminum content on hydrogen absorption behavior and delayed fracture properties of 0.2%C–0.2–1.5%Si–1.5%Mn TBF steel were investigated. When aluminum was added to the TBF steel, the diffusible hydrogen increased. It was expected that the hydrogen was charged not only in retained austenite films but also on lath boundary. Delayed fracture strength of TBF steels containing aluminum were significantly increased, compared with conventional TBF steel. This was mainly caused by (1) suppression of the stress-assisted martensite transformation resulting from the stabilized or carbon-enriched retained austenite, (2) hydrogen trapping to refined interlath retained austenite films and lath boundary, and (3) relaxation of localized stress concentration by TRIP effect of the retained austenite.

Susceptibility to Hydrogen Absorption and Hydrogen Thermal Desorption of Titanium Alloys Immersed in Neutral Fluoride Solution under Applied Potential

The susceptibility to hydrogen absorption and hydrogen thermal desorption of titanium alloys has been investigated in a neutral 2.0% NaF solution at 37°C under various applied cathodic potentials. Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys absorb hydrogen under less noble potentials than −1.5 V, −1.9 V and −1.4 V versus a saturated calomel electrode, respectively. The amounts of absorbed hydrogen of Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys under an applied potential of −2.0 V for 24 h are approximately 1200, 100 and 1100 mass ppm, respectively. Upon immersion in the 2.0% NaF solution under an applied potential, the hydrogen thermal desorption behavior of Ti-0.2Pd alloy differs from those immersed in acid fluoride solutions, whereas the hydrogen thermal desorption behaviors of Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys are similar to those immersed in acid fluoride solutions. The present results indicate that in a neutral fluoride solution, the effects of an applied potential on the hydrogen absorption and desorption behaviors of Ti-6Al-4V alloy are considerably smaller than those of commercial pure titanium reported previously, Ti-0.2Pd and Ti-11.3Mo-6.6Zr-4.3Sn alloys.

Thermodynamic and kinetic properties of Ho 1−xTi xCo 2-hydrogen system

The hydrogen absorption behavior of Laves phase Ho 1− x Ti x Co 2 ( x=0.1–0.6) alloys has been investigated by pressure-concentration (PC) isotherms and cyclic-, temperature- and pressure-dependent absorption kinetics. The PC isotherms and kinetics of hydrogen absorption have been studied in the pressure range 0.01–1 bar and temperature range 50–200 °C using Sievert's-type apparatus. The drastic changes in the induction period and particle size during the activation process have been discussed based on the kinetics of repeated hydrogenation cycles and scanning electron microscopy (SEM) images of the hydrides at different hydriding cycles, respectively. The experimental results of kinetic curves are interpreted using the Johnson–Mehl–Avrami (JMA) model, and the reaction order and reaction rate have been determined. The α-, ( α+ β)- and β-phase regions in Ho 1− x Ti x Co 2-H have been identified from the different slope regions of the first-order-type kinetic plots. The dependence of the reaction rate parameter on hydriding pressure and temperature in the ( α+ β)-phase region has been discussed.