Hydrogen Diffusion Process Research Articles

Hydrogen permeation in 2205 duplex stainless steel under hydrostatic pressure and simulation by COMSOL

This article explores the effect of hydrostatic pressure on hydrogen diffusion process in 2205 duplex stainless steel. The experiments were performed in a homemade high pressure autoclave. The Fick's second law was modified and taken reversible traps into account. The apparent diffusion coefficient decreased by 74.85% when pressure increased from 0.1 to 7 MPa, both of forward and reverse trapping rate constants, apparent hydrogen concentration, and activation energy increased with higher hydrostatic pressure. Additionally, finite element method based on diffusion model was performed using COMSOL Multiphysics software and the trapping constants effects were analyzed, which can be used in ocean industry.

Investigations on kinetics properties of hydrogen adsorbing/desorbing reactions for metal hydride electrodes

As we know, the kinetics properties of hydrogen adsorbing/desorbing reactions for metal hydride electrodes are determined by the rates of the charge transfer, hydrogen transfer and hydrogen diffusion reactions. In previous studies, not only the hydrogen transfer process was always ignored, but also the values of the kinetics parameters for the charge transfer and hydrogen diffusion processes were quite different. Therefore, the purpose of this work is to investigate the key issues of the kinetics properties for hydrogen adsorbing/desorbing reactions. Firstly, the hydrogen transfer process was thoroughly studied by electrochemical impedance spectrum (EIS) method, in which it emphasized the corresponding relationship between the electrode process of hydrogen adsorbing/desorbing reactions and the time constants presented in different frequency regions of impedance spectrum. The values of the hydrogen transfer resistance were calculated as a function of depth of discharge (DOD). Meanwhile, almost all the electrochemical techniques including linear polarization curves (LP), constant potential step method (CPSM), galvanostatic intermittent titration technique (GITT), cyclic voltammetry method (CV) and EIS were used to measure the kinetics parameters for the charge transfer and hydrogen diffusion processes. Moreover, the factors causing the discrepancy of the kinetics parameters were analyzed in detail.

Three-dimensional numerical simulation of hydrogen-induced multi-field coupling behavior in cracked zircaloy cladding tubes

In the high-temperature and high-pressure irradiation environments, the multi-field coupling processes of hydrogen diffusion, hydride precipitation and mechanical deformation in Zircaloy cladding tubes occur. To simulate this hydrogen-induced complex behavior, a multi-field coupling method is developed, with the irradiation hardening effects and hydride-precipitation-induced expansion and hardening effects involved in the mechanical constitutive relation. The out-pile tests for a cracked cladding tube after irradiation are simulated, and the numerical results of the multi-fields at different temperatures are obtained and analyzed. The results indicate that: (1) the hydrostatic stress gradient is the fundamental factor to activate the hydrogen-induced multi-field coupling behavior excluding the temperature gradient; (2) in the local crack-tip region, hydrides will precipitate faster at the considered higher temperatures, which can be fundamentally attributed to the sensitivity of TSSP and hydrogen diffusion coefficient to temperature. The mechanism is partly explained for the enlarged velocity values of delayed hydride cracking (DHC) at high temperatures before crack arrest. This work lays a foundation for the future research on DHC.

A modelling approach on the impact of an oxide layer on the hydrogen permeation through iron membranes in the Devanathan-Stachurski cell

The diffusion and trapping of hydrogen in iron alloys is commonly studied using the Devanathan-Stachurski cell. In this cell, the hydrogen flux through a metal membrane is studied. At the exit side of the membrane, an oxide layer is commonly developed and stabilized as a consequence of the anodic polarization imposed. The process of hydrogen diffusion through the oxide layer and its consecutive oxidation is not fully understood yet. In this paper, we propose a modelling approach that provides additional insights in this process. In particular, we highlight the impact that the presence of the oxide layer can have on the overall hydrogen transport throughout the metal membrane. Moreover, we highlight the complexity of this mechanism and discuss the possible reactions taking place in and at this interface. As a conclusion a possible alternative process to explain the findings is proposed.

First-principles GGA + U calculation investigating the hydriding and diffusion properties of hydrogen in PuH2+x, 0 [formula omitted]x[formula omitted] 1

The hydrogen (H) diffusion process is a crucial issue related to storage of plutonium safely. In this work, first-principles GGA + U calculation is performed to elucidate the hydriding and diffusion behaviors of an additional H atom (Hi) in “perfect” PuH2+x (0 ≤x≤ 1) matrixes. It finds the value of incorporation energy increases with increasing x. The interaction energies show that an extra Hi atom interacts much further with surrounding host atoms in PuH3 than in other Pu hydride matrixes. The minimum migration paths of a Hi atom in PuH2+x are characterized by the image nudged elastic band (CINEB) method. The Hi atom diffuses in PuH2, PuH2.25, and PuH5 matrixes through directly migrating from an octahedral interstice to its nearest octahedral site with energy barriers of 1.36 eV, 1.15 eV, and 1.59 eV, respectively. Oppositely, the metastable IH-site plays a dominant role for the Hi migration into the O-site in PuH2.75. The diffusion path of the Hi atom in PuH3 is IPu → IH0160 → IPU path with the lowest migration energy of 0.72 eV, which concludes the Hi has relatively higher mobility in PuH3. These findings provide detailed insight into how the H atom corrodes the Pu metal by connecting H atom diffusion in PuH2, PuH3, and intermediate compositions, which can be great interest for assisting the development of the new nuclear fuel for next generation reactors.

Interaction of Hydrogen Atoms with Grain Boundaries in Palladium Bicrystals

Hydrogen diffusion in palladium bicrystals containing a small-angle twist or tilt boundary or a large-angle boundary similar to a special boundary is investigated using molecular dynamics simulation. We assess the effect of grain boundaries on the hydrogen diffusion process. The types of grain boundaries considered here are shown to differ in their absorption activity for hydrogen. The temporal grain-boundary segregation of hydrogen atoms can be accounted for in terms of their coordination, which differs significantly from that in the grain bulk.

P‐18: Improvement of Reliability in Coplanar a‐IGZO TFTs by Multilayer SiO2 Gate Insulator

We investigated the PBTS instability of top‐gate self‐aligned coplanar a‐IGZO TFTs with multilayer SiO2 GI. It is confirmed that the PBTS instability due to the deep charge trapping in GI bulk can be improved by increasing activation energy through the interfacial formation with hydrogen‐low SiO2 deposition, and it is demonstrated experimentally that the PBTS instability due to the excess oxygen in the active region can be improved by hydrogen diffusion process through sequential hydrogen‐rich SiO2 deposition after ACT/GI interface formation.

Effect of temperature on behavior of perovskite-type oxide LaGaO3 used as a novel anode material for Ni-MH secondary batteries

To obtain a novel negative electrode for nickel-metal hydride rechargeable batteries, perovskite-type oxide LaGaO3 was synthesized by the sol-gel method. The electrochemical properties of the oxide were systematically investigated at different temperatures by using galvanostatic, chronoamperometric, and potentiodynamic polarization methods. We have selected 298, 313, and 328 K as room, intermediate, and high temperatures, respectively. The galvanostatic results showed that the discharge capacity of the oxide LaGaO3 increased with the temperature elevating during the first 3 cycles. This oxide has the highest discharge capacity of about 220 mAh g−1at high temperature. For room and intermediate temperatures, we observed that the discharge capacity maintains a constant about of 5 and 13 mAh g−1 for 298 and 313 K, respectively, when the number of cycles is increased. The electrochemical kinetic analysis indicates that the exchange current density and the hydrogen diffusion coefficient of the oxide LaGaO3 increase with the rise in temperature. The apparent activation energy (Ea) for hydrogen diffusion process and the activation energy (ΔrH*) for charge-transfer reaction of the investigated oxide electrode LaGaO3 are estimated. The calculated values of the Ea and ΔrH* are 117.46 and 105 kJ mol−1, respectively. The above experimental results indicated that the kinetic properties of the working electrode have been significantly improved by the elevating of the temperature. The best electrochemical performance (faster activation and highest maximum capacity) of the oxide electrode is obtained at high temperature (328 K).

Study on hydrogen enrichment in X80 steel spiral welded pipe

Local hydrogen enrichment would increase the risk of hydrogen embrittlement in welded structures, so the dynamic hydrogen diffusion process and final concentration distribution were investigated numerically by finite element simulation for a hydrogen gas transport X80 steel spiral welded pipe. The results show that the change of microstructure induced by weld thermal cycle would decrease the hydrogen concentration in welded joint, but welding residual stress could cause local hydrogen enrichment. Equivalent hydrogen pressures for base metal, weld metal and three subregions in heat-affected zone were put forward in order to scientifically evaluate the influence of hydrogen enrichment on hydrogen embrittlement.

In Situ Monitoring of Lateral Hydrogen Diffusion in Amorphous and Polycrystalline WO3 Thin Films

AbstractThin films of electrochromic materials such as tungsten trioxide (WO3) are essential components of electrochromic devices such as “Smart Windows.” The transport of charge carriers in WO3 thin films has been investigated intensively over the past decades, yielding a wide spread of diffusion coefficients of hydrogen in WO3. Most of those analyses are based on measurements by electrochemical methods. However, such analyses are only applicable and the results reliable in cases where diffusive transport is the rate‐determining process. Here, WO3 thin films of different morphology are prepared by electron‐beam evaporation of WO3 powder. The combined lateral diffusion of protons and electrons is investigated inside amorphous and polycrystalline WO3 thin films by in situ transmission spectroscopy during electrochemical hydrogen insertion into the film. The insertion of the protons is carried out locally and lateral diffusion of H takes place in the film plane. The induced change of the film absorbance at a wavelength of (637 ± 15) nm is monitored and spatially and temporally resolved. The results reveal a concentration‐dependent diffusion process of hydrogen in both, amorphous and polycrystalline WO3, which are critically discussed in the context of existing sata from literature.

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.

Diffusion coefficient of hydrogen interstitial atom in α-Fe, γ-Fe and ε-Fe crystals by first-principle calculations

The hydrogen diffusion process is a crucial issue related to hydrogen embrittlement. In this work, first-principle calculations were performed to investigate the diffusion behavior of hydrogen atoms in different Fe crystalline lattices. The hydrogen atom diffused in bcc Fe crystal through migrating from tetrahedral interstice to its nearest tetrahedral site; hydrogen atom diffused in fcc Fe along octahedral site-tetrahedral site-octahedral site; the diffusion path of the hydrogen atom in hcp Fe was from an octahedral site to its nearest octahedral site. The order of the diffusion coefficients of the hydrogen in the three crystal structures was Dbcc = 1.379 × 10−4 cm2/s exp (−1120/T) > Dfcc = 3.22 × 10−4 cm2/s exp (−8425/T) > Dhcp = 6.161 × 10−4 cm2/s exp (−8830/T). In addition, the diffusion behavior of a hydrogen atom near a vacancy was also investigated to determine the ability to trap a hydrogen atom in a vacancy defect in bcc-Fe and fcc-Fe, and the results indicated that hydrogen had higher mobility in the presence of a vacancy in the bcc Fe crystal.

Influence of electrolyte concentration on the electrochemical characteristics of LaGaO3 perovskite oxide as novel anode material for Ni/MH batteries

Abstract Recently, the ABO 3 -type perovskite oxides have been proposed as a promising novel anode for (Ni/MH) rechargeable battery due to the best electrochemical performances. In this work, LaGaO 3 perovskite was synthesized by a sol-gel technique and their physico-chemical properties for Ni/MH batteries application are tested in details under various KOH electrolyte concentrations (1 M, 3 M and 7 M). The electrochemical measurements showed that all the electrochemical parameters, such as the activation cycle number, the maximum capacity ( C max ), the hydrogen diffusion ( D H ) and the exchange current density ( I 0 ), have been greatly influenced by the variation of KOH concentration. It was found that with increasing electrolyte concentration, the activation process of this oxide was improved leading to an increase of the highest electrochemical capacity from 10 mAh g −1 (1 M) to 220 mAh g −1 (7 M). Also, the hydrogen diffusion and the current density increase with increasing KOH, which implies that increasing KOH concentration is beneficial to hydrogen diffusion process and charge transfer reaction. All the measurements revealed that the best electrochemical performances of the negative electrode are obtained at KOH 7 M.

Automatic kinetic Monte-Carlo modeling for impurity atom diffusion in grain boundary structure of tungsten material

The diffusion process of hydrogen and helium in plasma-facing material depends on the grain boundary structures. Whether a grain boundary accelerates or limits the diffusion speed of these impurity atoms is not well understood. In the present work, we proposed the automatic modeling of a kinetic Monte-Carlo (KMC) simulation to treat an asymmetric grain boundary structure that corresponds to target samples used in fusion material experiments for retention and permeation. In this method, local minimum energy sites and migration paths for impurity atoms in the grain boundary structure are automatically found using localized molecular dynamics. The grain boundary structure was generated with the Voronoi diagram. Consequently, we demonstrate that the KMC simulation for the diffusion process of impurity atoms in the generated grain boundary structure of tungsten material can be performed.

A fractal process of hydrogen diffusion in a-Si:H with exponential energy distribution

Hydrogen diffusion in a-Si:H with exponential distribution of the states in energy exhibits the fractal structure. It is shown that a probability [Formula: see text] of the pausing time [Formula: see text] has a form of [Formula: see text] ([Formula: see text]: fractal dimension). It is shown that the fractal dimension [Formula: see text]/[Formula: see text] ([Formula: see text]: hydrogen temperature, [Formula: see text]: a temperature corresponding to the width of exponential distribution of the states in energy) is in agreement with the Hausdorff dimension. A fractal graph for the case of [Formula: see text] is like the Cantor set. A fractal graph for the case of [Formula: see text] is like the Koch curves. At [Formula: see text], hydrogen migration exhibits Brownian motion. Hydrogen diffusion in a-Si:H should be the fractal process.

Hydrogen diffusion process in the oxides formed on zirconium alloys during corrosion in pressurized water reactor conditions

During the corrosion in primary water of zirconium alloys, a fraction of hydrogen from the water diffuses through the oxide into the alloy. To better understand the hydriding process, isotopic tracers and SIMS experiments were performed on oxides grown on Zircaloy-4 alloy under simulated primary water conditions. Results showed the oxide film in pre-transition is divided into two sub-layers, an external one, highly permeable to hydrogen and an inner protective one. Thermal Desorption Spectroscopy analyses revealed two interaction sites of hydrogen, located in each oxide sublayer.Apparent diffusion coefficients of hydrogen in both oxide sublayers were estimated with different methods.

Hydrogen-plasma-induced Rapid, Low-Temperature Crystallization of μm-thick a-Si:H Films.

Being a low-cost, mass-production-compatible route to attain crystalline silicon, post-deposition crystallization of amorphous silicon has received intensive research interest. Here we report a low-temperature (300 °C), rapid (crystallization rate of ~17 nm/min) means of a-Si:H crystallization based on high-density hydrogen plasma. A model integrating the three processes of hydrogen insertion, etching, and diffusion, which jointly determined the hydrogenation depth of the excess hydrogen into the treated micrometer thick a-Si:H, is proposed to elucidate the hydrogenation depth evolution and the crystallization mechanism. The effective temperature deduced from the hydrogen diffusion coefficient is far beyond the substrate temperature of 300 °C, which implies additional driving forces for crystallization, i.e., the chemical annealing/plasma heating and the high plasma sheath electric field. The features of LFICP (low-frequency inductively coupled plasma) and LFICP-grown a-Si:H are also briefly discussed to reveal the underlying mechanism of rapid crystallization at low temperatures.

Variation of cavity hydrogen pressure in the forming process of heavy forging

Flake is an irreparable crack type defect in many huge steel products, especially in heavy forging. Lots of previous studies have revealed that flake is usually originated at cavities within heavy forging. In addition, whether it is generated and what size after it is formed both largely depend on the hydrogen pressure within the cavity. However, the most part of previous studies only related cavity hydrogen pressure to steel hydrogen concentration, and few studies considered the metal forming effect. In this paper, the relationship between cavity hydrogen pressure and metal forming process of heavy forging is addressed from a simulation perspective. Different from previous research, this paper wants to emphasize the importance of metal forming process in the flake formation. There are four parts in this paper. We start with a brief introduction to the flake and the importance of cavity hydrogen pressure in its formation. Then, we propose a cavity hydrogen pressure calculation model. After that, the simulation results and discussions are provided. We end the study with the conclusion. We find in our research that metal forming has a great influence on cavity hydrogen pressure, especially with large deformation. Based on these findings, we may conclude that flake formation not only depends on the steel hydrogen content, but also very depends on the way of forming. Admittedly, what we have discussed in this study is far from complete. And some improvements we want to make in our further research include (1) studying the influence of metal forming on flake formation in micro-scale, such as in grain scale; (2) verifying the simulation results with experiment; and (3) considering the hydrogen diffusion process in metal forming process.

Hydrogen sensing via anomalous optical absorption of palladium-based metamaterials

A palladium (Pd)-based optical metamaterial has been designed, fabricated and characterized for its application in hydrogen sensing. The metamaterial can replace Pd thin films in optical transmission schemes for sensing with performances far superior to those of conventional sensors. This artificial material consists of a palladium–alumina metamaterial fabricated using inexpensive and industrial-friendly bottom-up techniques. During the exposure to hydrogen, the system exhibits anomalous optical absorption when compared to the well-known response of Pd thin films, this phenomenon being the key factor for the sensor sensitivity. The exposure to hydrogen produces a large variation in the light transmission through the metamembrane (more than 30% with 4% in volume hydrogen–nitrogen gas mixture at room temperature and atmospheric pressure), thus avoiding the need for sophisticated optical detection systems. An optical homogenization model is proposed to explain the metamaterial response. These results contribute to the development of reliable and low-cost hydrogen sensors with potential applications in the hydrogen economy and industrial processes to name a few, and also open the door to optically study the hydrogen diffusion processes in Pd nanostructures.

Hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy

The hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy were investigated by kinetic model analysis, optical microscopy (OM) and X-ray diffraction (XRD). The results show that the hydrogen absorption reaction occurred during the hydrogen absorption process of TC21 titanium alloy can be divided into two different stages according to the hydrogen absorption kinetics. After hydrogenation, the microstructure of TC21 titanium alloy changes obviously. Just a little hydrogen will change the contrast of transformed β phase. The contrast of α phase darkens when the hydrogen content in TC21 titanium alloy exceeds 0.5% (mass fraction). The phase/grain boundaries become ambiguous or even vanished, and β phase becomes the main phase instead of α phase when the hydrogen content reaches 0.625%. Moreover, α phase disappears when the hydrogen content reaches 1.065%. Additionally, the XRD analysis shows that α′ martensite and FCC δ hydride appear in the hydrogenated alloy. According to the microstructures and XRD analysis, the schematic diagrams of hydrogen diffusion process in TC21 titanium alloy were established.