Hydrogen Transport Process Research Articles

Investigation of Low-Temperature Hydrogen Permeability of Surface Modified Pd–Cu Membranes

The Pd60%Cu40% membranes were modified with nanostructured coatings to intensify low-temperature (25–100°C) hydrogen transport. Classical palladium black and filamentous particles were applied as surface modifiers by electrodeposition. The experiment results confirmed significant reducing of surface limitations by modifying layer application on both surfaces of the developed membranes of the Pd60%Cu40% alloy. The study of the developed membranes in the low-temperature hydrogen transport processes demonstrated high and stable flux up to 0.36 mmol s–1 m–2, as well as high hydrogen permeability up to 1.33 × 10–9 mol s–1 m–2 Pa–0.5. In numerical terms, the values of the membranes of the Pd60%Cu40% alloy modified with nanofilaments were up to 1.3 and 3.9 times higher compared to membranes modified with classical black and uncoated ones, respectively. The developed Pd60%Cu40% membranes also demonstrated a high level of H2/N2 selectivity – up to 3552. The strategy of surface modification of palladium-based membranes can shed new light on the development and manufacturing of high-performance and selective membranes for ultrapure hydrogen evolution devices.

Hydrogen Permeability of Composite Pd-Au/Pd-Cu Membranes and Methods for Their Preparation.

Thin Pd-40%Cu films were obtained via the classical melting and rolling method, magnetron sputtering, and modified with nanostructured functional coatings to intensify the process of hydrogen transportation. The films were modified by electrodeposition, according to the classical method of obtaining palladium black and "Pd-Au nanoflowers" with spherical and pentagonal particles, respectively. The experiment results demonstrated the highest catalytic activity (89.47 mA cm-2), good resistance to CO poisoning and long-term stability of Pd-40%Cu films with a pentagonal structured coating. The investigation of the developed membranes in the hydrogen transport processes in the temperature range of 25-300 °C also demonstrated high and stable fluxes of up to 475.28 mmol s-1 m-2 (deposited membranes) and 59.41 mmol s-1 m-2 (dense metal membranes), which were up to 1.5 higher, compared with membrane materials with classic niello. For all-metal modified membranes, the increase in flux was up to sevenfold, compared with a smooth membrane made of pure palladium, and for deposited films, this difference was manyfold. The membrane materials' selectivity was also high, up to 4419. The developed strategy for modifying membrane materials with functional coatings of a fundamentally new complex geometry can shed new light on the development and fabrication of durable and highly selective palladium-based membranes for gas steam reformers.

Effect of aprotic solvent on characteristics of Al2O3 ceramic hollow fiber substrates prepared by phase inversion for hydrogen permeation applications

ABSTRACT The phase inversion procedure was used to prepare Al2O3 ceramic hollow fiber substrates (AlCHFS) utilizing the dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), and 1-methyl-2-pyrrolidone (NMP) aprotic solvents. Different aprotic solvent and non-solvent (water) interactions were used to calibrate different ceramic oxide substrates. AlCHFS with an asymmetrical structure consisting of a finger-like structure on the lumen side and a pore structure on the shell side was obtained using an aprotic solvent/non-solvent pair with a high total Hildebrand solubility (δt). As the aprotic strength was reduced, the finger-like structure on the shell sides became more prominent. Hydrogen permeation studies conducted between 350°C and 450°C reveal that the Pd-coated AlCHFS produced from DMAC aprotic solvent has the maximum hydrogen flux (~0.24 mol m−2 s−1). The activation energy for the thermally activated hydrogen transport process through the Pd-coated AlCHFSs is determined to be around 11.06–14.61 kJ mol−1 in the temperature range of 350°C to 450°C, and it increases linearly with increasing surface porosity of ceramic oxide substrate.

The Features of Heat and Mass Transfer in the Operation of Nuclear-Powered Icebreaker Steam Generators

The problem of hydrogen induced embrittlement of and crack formation in the piping systems of nuclear-powered icebreaker steam generators is considered. Information about the relevance of this problem for ensuring reliable operation of the nuclear power installations of transport facilities and similar systems such as floating nuclear power units is given. Hydrogen accumulation in the steam generator feedwater header pipes welding zone and their subsequent hydrogen-induces embrittlement lead to crack formation. For modeling the hydrogen transport processes from the reactor to the steam generator, two types of computer codes are jointly used: 1D approximation and 3D ones. The performed analysis has identified the main characteristic processes. For solving the problem, it was decomposed into subproblems. The transport of vapor-gas bubbles in the steam generator was analyzed with paying special attention to studying their behavior in the steam generator internal cylinder. It is shown that, despite the presence of structural obstacles in the inner cylinder, coolant convective motion and bubble floatation occur. An alternative hypothesis is put forward, according to which cracks may be caused by cavitation on the secondary system coolant side. To check the hypothesis, 3D modeling was carried out, the results of which did not confirm its validity. The obtained study results can be used to substantiate measures on preventing the hydrogen-induced embrittlement of and crack formation in the steam generator piping systems of nuclear-powered icebreakers, floating nuclear power units, and small capacity NPPs.

Comprehensive modeling of hydrogen transport and accumulation in titanium and zirconium

Abstract We developed kinetic models of hydrogen absorption in Ti and Zr. The models comprise series connections of the hydrogen-transport processes of surface dissociative adsorption and recombinative desorption; subsurface transport; and bulk diffusion. Numerical calculations using the models quantitatively reproduce the results of experimental series of time-transient absorption curves at various temperatures, demonstrating the validity of our models. Experimental desorption curves at various temperatures are also reproduced by the same model equations and kinetic parameters, particularly for Zr, demonstrating the dual functionality of our single model for hydrogen-transport directions. We use an effectiveness factor defined as the ratio between the real absorption rate and the virtual rate neglecting bulk diffusion. The transitions of the rate-determining steps of hydrogen transport in Ti and Zr under various conditions – such as temperature, pressure, and metal object size and shape – are systematically analyzed. As a case study to test the applicability of our model, hydrogen accumulation in the fuel claddings of light-water nuclear reactors was simulated to determine the cladding thickness required to prevent hydrogen embrittlement during the practical operation period. Our versatile kinetic models could be a useful tool that can aid the structural design and optimization of nuclear materials and facilities.

Quasielastic neutron scattering of brucite to analyse hydrogen transport on the atomic scale.

It is demonstrated that quasielastic neutron scattering is a novel and effective method to analyse atomic scale hydrogen transport processes occurring within a mineral crystal lattice. The method was previously characterized as sensitive for analysing the transport frequency and distance of highly diffusive hydrogen atoms or water molecules in condensed matter. Here are shown the results of its application to analyse the transport of much slower hydrogen atoms which are bonded into a crystal lattice as hydroxyls. Two types of hydrogen transport process were observed in brucite, Mg(OH)2: a jump within a single two-dimensional layer of the hydrogen lattice and a jump into the next nearest layer of it. These transport processes observed within the prototypical structure of brucite have direct implications for hydrogen transport phenomena occurring within various types of oxides and minerals having layered structures.

Modelling of hydrogen permeation experiments in iron alloys: Characterization of the accessible parameters – Part I – The entry side

The Devanathan-Stachurski cell is an electrochemical technique used to investigate the hydrogen diffusion and trapping in the bulk of a metal. The process of absorption and diffusion of atomic hydrogen through a metal is not fully understood yet. To investigate this problem further, we investigate the effects of hydrogen adsorption, absorption and trapping in iron alloys through the development of a numerical model representing the Devanathan-Stachurski cell. In this paper, we review how each single input parameter can be evaluated and present an investigation of the accessible parameters reporting their influence on the experimental results. In particular, we highlight the impact of the hydrogen adsorption-absorption process on the hydrogen flux passing through the metal sample. Hence, the surface state and the electrolyte influence are proven to be significant parameters influencing the overall hydrogen transport process. This effect is often overlooked in the experimental result evaluation. To come to an even more complete understanding of the situation an evaluation of the influence of the anodic side of the cell will be proposed in our follow-up paper.

Modelling of hydrogen permeation experiments in iron alloys: Characterization of the accessible parameters – Part II – The exit side

Electrochemical permeation tests are used to investigate the diffusion and trapping effects of hydrogen in a metal. For a quantitative and reliable evaluation of these features, the development of a numerical model is required. In the first paper of this series, we developed a model describing the hydrogen transport process in the Devanathan-Stachurski cell and evaluated the influence of the entry interface on the experimental results. Although many models have already been proposed for the description of the hydrogen diffusion in the Devanathan-Stachurski cell, none of them is including the simulations of the anodic side of the cell. In this paper, we present a new model representing the Devanathan-Stachurski cell. With this model, we are able to make a sensitivity analysis of all the parameters that play a role during the hydrogen diffusion process in iron alloys, comprising the adsorption, absorption, diffusion and desorption processes that the hydrogen undertakes in the sample mounted in the Devanathan-Stachurski cell. In particular, we found that the common assumption of constant zero concentration at exit side broadly accepted by researchers may not always reflect the real situation and the evaluation of the desorption process as often used today might be oversimplified. Certainly, the complexity of the desorption/oxidation is of high degree when Pd coating is not applied at the exit side. Consequently, the effect of the anodic electrolyte and the surface state at exit side should be considered as a significant element affecting the experimental results.

Mechanistic Insights into the Cu(I)- and Cu(II)-Catalyzed Cyclization of o-Alkynylbenzaldehydes: The Solvent DMF and Oxidation State of Copper Affect the Reaction Mechanism.

A computational study with the BhandHLYP density functional is conducted to elucidate the mechanisms of Cu(I)- and Cu(II)-catalyzed reactions of o-alkynylbenzaldehydes with a nucleophile (MeOH). Our calculations suggest the following. (a) The use of CuCl as a catalyst deceases significantly the energy barrier and promotes intramolecular cyclization. (b) Solvent DMF is critical in the stepwise hydrogen-transport process involved in an intermolecular nucleophilic addition because it can greatly reduce the free energy barrier of the hydrogen-transfer process as a proton shuttle. In addition, we find that substrate MeOH also plays a role similar to that of DMF in the hydrogen-transport reaction. (c) The 6-endo product P1 is formed exclusively using a catalytic system consisting of CuCl and DMF, whereas a mixture of 6-endo product P1 and 5-exo product P2 in a ratio of ∼1:1 is produced using CuCl2 and DMF as a catalytic system. Our theoretical calculations reproduce the experimental results very well. This study is expected to improve our understanding of Cu(I)- and Cu(II)-catalyzed reactions involving Lewis base solvents and to provide guidance for the future design of new catalysts and new reactions.

A high stability Ni–La0.5Ce0.5O2−δ asymmetrical metal-ceramic membrane for hydrogen separation and generation

In this work, hydrogen permeation properties of Ni–La0.5Ce0.5O2−δ (LDC) asymmetrical cermet membrane are investigated, including hydrogen fluxes (JH2) under different hydrogen partial pressures, the influence of water vapor on JH2 and the long-term stability of the membrane operating under the containing-CO2 atmosphere. Ni-LDC asymmetrical membrane shows the best hydrogen permeability among LDC-based hydrogen separation membranes, inferior to Ni–BaZr0.1Ce0.7Y0.2O3−δ asymmetrical membrane. The water vapor in feed gas is beneficial to hydrogen transport process, which promote an increase of JH2 from 5.64 × 10−8 to 6.83 × 10−8 mol cm−2 s−1 at 900 °C. Stability testing of hydrogen permeation suggests that Ni-LDC membrane remains stable against CO2. A dual function of combining hydrogen separation and generation can be realized by humidifying the sweep gas and enhance the hydrogen output by 1.0–1.5 times. Ni-LDC membrane exhibits desirable performance and durability in dual-function mode. Morphologies and phase structures of the membrane after tests are also characterized by SEM and XRD.

An intermolecular hydrogen transfer process inducing triplet biradical photochromism of 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine in the solid state

An intermolecular hydrogen transport process, as a source of photochromism in a crystal, was identified in 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine (DHP). The photochromic form of that compound, dark violet in color, according to EPR measurements is triplet biradical in nature. According to photoluminescence measurements, the lowest excited triplet state (T 1) as well as the excited singlet state (S 1) of the DHP molecule is of π,π* type. Two active non-symmetrical biradical forms, absorbing at 400 nm and 550 nm, are proposed connected with a hydrogen transfer process created by transformation of the forms on mutual terms (‘hydrogen cascade’). Optical generation of the photochromic form was followed by steady-state UV–vis spectroscopy. The rate constants are equal to k 400 = 4.36 ± 0.17 × 10 −3 s −1 and k 550 = 5.87 ± 0.56 × 10 −4 s −1, respectively. The values of energy of activation of these two parallel processes obtained by analysis of non-isothermal kinetics of the bleaching process are equal to 10.96 kJ/mol and 31.2 kJ/mol, respectively. The IR spectra together with EPR measurements as well as X-ray structural analysis and calculations on the semi-empirical AM1 level method seem to support the intermolecular hydrogen transfer chain process.

Investigation of the Hydrogen Transport Processes in Crystalline Silicon of n-Type Conductivity

The silicon substrates were hydrogenated at approximately room temperature and hydrogen concentration profiles vs. depth have been measured by SIMS. Czochralski grown (CZ) wafers, both n- and p-type conductivity, were used in the experiments under consideration. For analysis of hydrogen transport processes and quasichemical reactions the model of hydrogen atoms diffusion and quasichemical reactions is proposed and the set of equations is obtained. The developed model takes into account the formation of bound hydrogen in the near surface region, hydrogen transport as a result of diffusion of hydrogen molecules 2 H , diffusion of metastable complexes * 2 H and diffusion of nonequilibrium hydrogen atoms. Interaction of 2 H with oxygen atoms and formation of immobile complexes “oxygen atom - hydrogen molecule” (O - H2 ) is also taken into account to explain the hydrogen concentration profiles in the substrates of n-type conductivity. The computer simulation based on the proposed equations has shown a good agreement of the calculated hydrogen profiles with the experimental data and has allowed receiving a value of the hydrogen molecules diffusivity at room temperature.

A micromechanics approach to the study of hydrogen transport and embrittlement

The mechanisms of hydrogen related fracture are briefly outlined. Previous investigations on the physics and treatment of the hydrogen transport processes are reviewed. A hydrogen diffusion model based on the interaction of hydrogen induced strain in the lattice with local material elastoplasticity is presented. Finite element studies were carried out to analyze the hydrogen distribution in the neighborhood of a blunting crack tip under small scale yielding conditions and in the neighborhood of a rounded notch in a four-point bend specimen. The calculated hydrogen concentration profiles and experimental observations of embrittlement in high strength steels are used to make evaluative statements on the occurrence of the first microcracking event.

Dependence of the hydrogen permeation in stainless steel on carbon content, heat treatment and cold work

The hydrogen permeation behaviour in austenitic stainless steel (1.4301, AISI 304) was studied between 25 to 85 °C using the electrochemical double cell permeation technique. Influences of parameters like carbon content, grain size and cold work were investigated. Using the current transient plots from the permeation experiments, apparent diffusion coefficient, Dapp values were calculated. Values ranging from 5.8•10−12 to 2.7•10−10 cm2/s were obtained for various conditions of the material. The increase in carbon mass content from 0.045 to 0.085 % resulted in a decrease in Dapp by a factor of 8. This was attributed to the increased blocking of interstitial sites by higher carbon in the latter steel. The annealing treatment, resulting in a slight grain growth caused a decrease in Dapp to about its half, in contrast to the reduced trapping effect of the grain boundaries. This was explained to be due to a longer hydrogen transport path required through the grain and less contribution of fast diffusion paths in the larger grain size material. A slight cold work (5% reduction in thickness) decreased the Dapp whereas higher cold working (30 %) increased the Dapp. The cold working results in an increase in dislocation density and the dislocations act as traps for hydrogen transport. This results in a decrease in Dapp values for 5 % cold work material. Strain induced martensite (α', bcc phase) formation in the matrix occurred in the higher cold worked material (10 and 30%). The presence of this bcc phase overcame the trapping effect of increased dislocation density resulting in an enhancement of hydrogen transport. From the activation energy calculated, it was concluded that the a' phase present did not provide a continuous medium for hydrogen transport, but added to the overall increase in the hydrogen transport process.

Interaction of graphite with an energetic hydrogen isotope beam

An energetic hydrogen isotope beam was used for implantation into isotropic graphite at room temperature and the thermal desorption behaviour of methane (CH 4) and hydrogen (H 2) was investigated for the purpose of investigating the chemical reaction between hydrogen and graphite. The desorption spectra were obtained under two different hydrogen ion fluences, i.e. 4.5 × 10 17 and 1.2 × 10 16 ions cm −2. An apparent activation energy of methane desorption was evaluated for each fluence. The value obtained was lower for the high fluence case, indicating that a different hydrogen transport process is taking place in the formation of methane in these fluence regimes.

Subject index of vol. 136

Both the 18Ni (200) and 18Ni (250) maraging steels exhibited K-independent (Stage II) sustained-load crack growth in gaseous hydrogen over the stress-intensity range investigated. 18Ni (200) maraging steel was found to be less susceptible to gaseous hydrogen embrittlement than the higher strength 250 grade. Stage II crack growth at low temperatures in both steels appears to be rate limited by the same thermally activated hydrogen transport process characterized by an activation energy of about 18 kJ/mole. A dramatic decrease in susceptibility to gaseous hydrogen was observed at higher temperatures. The change in susceptibility occurred abruptly over a temperature range of about 5°C, at temperatures that depended on alloy composition and/or strength level. This transition may be associated with either hydrogen transport, or the mechanism by which hydrogen weakens the interatomic bonds. Additional work designed to elucidate the phenomenology and mechanism of gaseous hydrogen embrittlement is currently in progress.

Hydrogen in iron

The applicability of advanced permeation techniques to the study of hydrogen and deuterium in iron and iron alloys is described. Time lag measurements lead to detailed information about hydrogen transport processes, including lattice diffusivities and trap binding energies and densities. The experimental technique couples gas phase charging of palladium coated specimens with the sensitive electrochemical detection method. In both annealed and deformed iron the trap binding energy for hydrogen and deuterium is 50 to 58 kJ/mol, while the trap density varies from about 1020 m-3 for annealed iron to over 1023 m-3 for heavily deformed iron. For the metallic glass Fe40Ni40P14B6 hydrogen transport occurs between energetically equivalent sites, with no evidence of trapping. The site density was estimated as about 6 x 1029 m-3 . The hydrogen concentrations studied were several orders of magnitude less. Hydrogen and deuterium in iron differs only in their lattice diffusivities. The diffusivity ratio conforms nearly to the classical inverse square root of mass ratio, but shows a slight temperature dependence. The solubilities, trap binding energies, and partial atomic volumes of the two isotopes in iron are identical.

Hydrogen in iron

The applicability of advanced permeation techniques to the study of hydrogen and deuterium in iron and iron alloys is described. Time lag measurements lead to detailed information about hydrogen transport processes, including lattice diffusivities and trap binding energies and densities. The experimental technique couples gas phase charging of palladium coated specimens with the sensitive electrochemical detection method. In both annealed and deformed iron the trap binding energy for hydrogen and deuterium is 50 to 58 kJ/mol, while the trap density varies from about 1020 m−3 for annealed iron to over 1023 m−3 for heavily deformed iron. For the metallic glass Fe40Ni40P14B6 hydrogen transport occurs between energetically equivalent sites, with no evidence of trapping. The site density was estimated as about 6 × 1029 m−3 . The hydrogen concentrations studied were several orders of magnitude less. Hydrogen and deuterium in iron differs only in their lattice diffusivities. The diffusivity ratio conforms nearly to the classical inverse square root of mass ratio, but shows a slight temperature dependence. The solubilities, trap binding energies, and partial atomic volumes of the two isotopes in iron are identical.

Hydrogen transport process in OH − doped KCl and KBr

It was investigated the kinectics of formation and destruction of hydrogen related defects originated from the randon aggregation of hydrogen atoms in their ground state that were allowed to diffuse through the crystal after the photodissociation of OH − defects. Formation and activation energies for the several processes involved in three main steps were obtained utilizing 1st. order kinectics. A model for a new U 2x center is proposed.

Gaseous hydrogen assisted crack growth in 18 nickel maraging steels

Both the 18Ni (200) and 18Ni (250) maraging steels exhibited K-independent (Stage II) sustained-load crack growth in gaseous hydrogen over the stress-intensity range investigated. 18Ni (200) maraging steel was found to be less susceptible to gaseous hydrogen embrittlement than the higher strength 250 grade. Stage II crack growth at low temperatures in both steels appears to be rate limited by the same thermally activated hydrogen transport process characterized by an activation energy of about 18 kJ/mole. A dramatic decrease in susceptibility to gaseous hydrogen was observed at higher temperatures. The change in susceptibility occurred abruptly over a temperature range of about 5°C, at temperatures that depended on alloy composition and/or strength level. This transition may be associated with either hydrogen transport, or the mechanism by which hydrogen weakens the interatomic bonds. Additional work designed to elucidate the phenomenology and mechanism of gaseous hydrogen embrittlement is currently in progress.