Kinetics Of Hydrogen Diffusion Research Articles

Mitigating hydrogen embrittlement of advanced high-strength steel by controlling carbides (cementite and alloy carbides) and microstructural modification

This work aims to demonstrate that the resistance to hydrogen embrittlement of conventional advanced high-strength steel (AHSS) with a bainitic ferrite structure can be significantly enhanced through two metallurgical strategies. Firstly, a smaller fraction of cementite in a mixture of bainitic ferrite and lath-martensite structures is realized by an intercritical annealing process with rapid cooling. Secondly, a higher fraction of alloy carbides (MC) with a mean size of less than 30 nm is formed through the combined addition of Ti, Mo, and V as micro-alloying elements. The reduction of cementite precipitation in the matrix leads to an increased resistance to hydrogen evolution/adsorption on the surface under cathodic polarization. Moreover, a large number of V-bearing nanoprecipitates ((Ti,Mo,V)-carbides and V-carbides) provides intermediate trapping for hydrogen atoms, effectively delaying the diffusion kinetics of hydrogen towards potential crack-forming areas in the matrix. Consequently, the lower strain reduction during slow strain rate test and the higher resistance to cracking during the four-point bending test in acidic aqueous solutions are manifested in the newly designed AHSS.

Hydrogen uptake and diffusion kinetics in a quenched and tempered low carbon steel: experimental and numerical study

To better understand hydrogen uptake kinetics, electrochemical permeation tests have been performed in a quenched and tempered low-alloy steel. Hydrogen uptake and transport has been studied with three different surface roughness, in four different solutions (1 M H2SO4, 1 M H2SO4+As2O3, 0.1 M NaOH and 3.5% NaCl) and two different hydrogen charging current densities (1 and 5 mA/cm2). A strong effect of the charging solution, current density and surface roughness has been demonstrated. In 1 M H2SO4 + As2O3 solution and 5 mA/cm2, hydrogen recombination on the surface of the samples is strongly reduced and interstitial diffusion prevails due to the trap saturation (DL≈Dapp). However, in 1 M H2SO4, 0.1 M NaOH and 3.5% NaCl, hydrogen transport is dominated by trapping and detrapping processes (DL>Dapp). Permeation transients are numerically reproduced through Finite Element simulations and compared to the experimental results. The relationship between hydrogen diffusion kinetics at the microstructural level and surface effects is clearly established by a mapping strategy obtained from the wide range of experimental results, combined with a numerical approach.

Assessing the influence of microstructure on uranium hydride size distributions via small angle neutron scattering

The effect of microstructure on the internal hydriding behavior of both cast (1 mm grain size) and rolled (25 μm grain size) uranium containing hydrogen concentrations between 0 and 1.8 wppm were evaluated via small angle neutron scattering (SANS). Increasing hydrogen content up to 1.8 wppm in the cast uranium only weakly affected the average uranium hydride (UH3) precipitate size, calculated from the SANS data. Conversely, the UH3 phase fraction was found to strongly depend on the hydrogen content in the same cast samples. A substantially reduced UH3 particle size distribution was observed in the rolled uranium relative to cast uranium containing the same nominal hydrogen content. It is hypothesized that the suppression of UH3 formation in the rolled uranium is driven by increased hydrogen trapping at grain boundaries, and theoretical calculations that account for trap density, potency, and hydrogen diffusion kinetics support this hypothesis.

Kinetics and mechanism effects of 2D carbon supports in hydrogen spillover composites.

Extensive research has been performed using two-dimensional (2D) carbon materials as catalyst supports to achieve high-performance hydrogen storage composites through the hydrogen spillover phenomenon. However, the kinetics and mechanism effects of different support materials still need to be investigated. This study employed high-energy ball milling to fabricate Co1-xS/C60 and C1-xS/rGO composites with stable structures and abundant hydrogen storage sites. We explored the mechanism of hydrogen adsorption behavior through electrode kinetic studies and density functional theory calculations, revealing the intrinsic relationship between material composition, structure, and hydrogen diffusion kinetics. The 2D flakes of C60 and rGO support and connect C1-xS nanoparticles, providing electron transport pathways for the composites. Theoretically, the spherical C60 support with less steric hindrance showed a more vital ability to increase the hydrogen adsorption capacity, while kinetically, thin film rGO offers fast channels for hydrogen diffusion. These findings contribute to our understanding of hydrogen spillover and present opportunities to investigate the synergistic effects in 2D carbon-based composites.

Hydrogen diffusion kinetics in dual-phase (DP 980) steel: The role of pre-strain and tensile stress

The current study investigates the influence of pre-strain (un-strained, 3 %, and 6 % engineering strain) and in-situ tensile stress (50 %, 110 %, and 125 % of the yield stress (YS)) on the hydrogen diffusion and trapping behaviour in DP 980 steel. Electrochemical hydrogen permeation tests were conducted using a custom-built Devanathan-Stachurski (DS) cell integrated with a horizontal tensometer. The results showed that the value of apparent diffusion coefficient (Dapp) decreased from 5.4 ± 0.1 to 3.8 ± 0.029 × 10−7 cm2 s−1, while trap density (NT) and sub-surface hydrogen concentration (Capp) increased from 1.08 ± 0.01 to 1.58 ± 0.012 × 1021 cm−3, 2.70 ± 0.13 to 3.27 ± 0.10 × 10−4 mol H cm−3, respectively for unstrained and 6 % pre-strain conditions. This is due to increased dislocation density in ferrite and martensite. Hydrogen permeation tests under tensile stress (in-situ) revealed that the applied elastic stress of 50 % of YS showed a slight increase in Dapp and a decrease in NT values. This is due to an increase in the interstitial space between the atoms at applied elastic load favouring hydrogen diffusion. The plastic tensile stress of 110 % of YS showed the highest value of steady-state permeation current density iss (169 ± 10.6 µA cm−2). It could be due to an expanded lattice of martensite accommodating more hydrogen because of its elastic deformation. The tensile stress of 125 % of YS results in a significant reduction in Dapp (2.86 × 10−7 cm2 s−1) and an increase in Capp (5.52 × 10−4 mol H cm−3) and NT (2.11 × 1021 cm−3) as a result of plastic deformation in ferrite and martensite. The decay transient studies revealed that the applied elastic tensile stress enhances the rate of desorption of diffusible hydrogen, increasing lattice diffusion coefficient DL. The plastic pre-strain and plastic tensile stress resulted in slower desorption, lower DL, and an increase in reversible trap density.

Effects of two-step austenitizing processes on hydrogen evolution, permeation, and cracking behaviors of ultra-high-strength martensitic steel

This study examined the effects of microstructural modifications by two-step austenitizing, involving successive martensite-austenite reversion processes, on the hydrogen embrittlement (HE) of ultra-high-strength steel with a tensile strength of more than 1500 MPa. To achieve a deeper understanding of the hydrogen evolution, permeation, and cracking behaviors of steel samples consisting of martensitic structures with different prior austenite grain (PAG) sizes and/or cementite (Fe3C) particles, a series of experimental methods were employed: electrochemical impedance and permeation test, slow-strain rate test (SSRT), and hydrogen microprinting test (HMT). The test results revealed that the undissolved Fe3C remained in the martensite, even after austenitizing at above the A3 temperature, promoted hydrogen evolution on the surface. On the other hand, a reduction in the PAG size with a higher kernel average misorientation (KAM) value, realized by two-step austenitizing processes, led to a decrease in the hydrogen diffusion kinetics and an increase in hydrogen solubility (i.e., total concentration of diffusible hydrogen (Ctot)). Nevertheless, the steel sample developed by two-step austenitizing showed the lowest HE-index (i.e., degree of hydrogen-induced mechanical degradation) from SSRT. Based on HMT using Ag decoration locating hydrogen trapping, the contradictory results between the electrochemical permeation and SSRT indicated that the local concentration of hydrogen trapped preferentially at the PAG boundaries could be more critical to failure by HE rather than the Ctot in steel.

Lightweight alkali-induced lattice-dynamical stability and energy storage mechanism of quaternary Mg-based hydrides under pressure effect

New-discovery compositions of the lightweight quaternary Mg-based hydrides at ambient pressure are found as NaLiMgH4, NaLiMg2H6, and Na3LiMg4H12, which their stabilities were determined by all positive modes of the phonon dispersion relation. The varying compositions of Na-Li-Mg-H were analyzed using the ab initio random structure searching technique and affirmed by mechanical stability and Born stability criteria. Besides, the effects of pressure on stable structures are considered also. High-gravimetric hydrogen capacity introduces us to study H-vacancy occurrence and H-diffusion kinetics in these lightweight quaternary hydrides. Our calculation results indicated that the NaLiMg2H6 in the P21/m system gave more suitable for hydrogen storage material due to lower energy barriers as well as the hydrogen diffusion kinetics in this lightweight hydride for its practical use in energy storage applications.

Pd-modified LaNi5 nanoparticles for efficient hydrogen storage in a carbazole type liquid organic hydrogen carrier

In this work, we report the synthesis and catalytical property of a palladium catalyst loaded on a hydrogen storage support-Pd/LaNi5 in reversible hydrogen storage of N-ethylcarbazole (NEC). We prepare LaNi5 nanoparticles by the molten salt reduction method and use galvanic replacement to deposit a thin Pd layer on the surface. Catalyzed by 1 wt%Pd/LaNi5, NEC absorbs 5.5 wt% H2 in 0.7 h at 453 K and 7 MPa H2, and perhydro-NEC desorbs 5.5 wt% in 2.1 h at 473 K and 0.1 MPa H2, which significantly outperforms Pd/Al2O3 catalyst with the same Pd loading. The significantly promoted catalytic performance is attributed to the ample lattice hydrogen bonding sites and fast bulk hydrogen diffusion kinetics of LaNi5, which breaks the limitation of active hydrogen bonding sites due to the competitive adsorption of hydrogen and the organic molecule in surface catalysis. The active role of the lattice hydrogen bonding sites makes hydrogen storage materials highly attractive for hydrogen-related catalysis

Optimisation of the hydrogen bake-out treatment in steels via Gaussian processes

The presence of hydrogen in structural alloys reduces their ductility, a phenomenon called hydrogen embrittlement. Bake-out heat treatments are employed during processing to allow hydrogen trapped in microstructural features to effuse from the samples, but the optimal times and temperatures depend on the kinetics of hydrogen diffusion in the material. In this work, Gaussian process surrogate models are employed to emulate the outputs of microstructure-sensitive diffusion differential equations in steel. Training the models by sequentially increasing the number of dimensions results in better performances and shorter training times. Two main approaches are developed: single output models with experimental design for the prediction of optimal bake-out times, and multi-output principal component analysis models for the prediction of hydrogen concentration evolution. A novel approach is implemented to shorten the training times of multi-trap models by exploiting the symmetry of the equations with respect to different kinds of traps. The resulting models pave the way for the implementation of Gaussian processes on more computationally expensive diffusion simulations for the optimisation of heat treatments and other applications.

Hydrogen storage and electrochemical properties of annealed low-Co AB5 type intermetallic compounds

The structure, hydrogen storage and electrochemical properties of annealed low-Co AB5-type intermetallic compounds have been investigated. La-alloy, Nd-alloy and Cr-alloy are used to represent La0.8Ce0.2Ni4Co0.4Mn0.3Al0.3, La0.6Ce0.2Nd0.2Ni4Co0.4Mn0.3Al0.3 and La0.6Ce0.2Nd0.2Ni3.8Co0.4Mn0.3Al0.3Cr0.2, respectively. The XRD results indicated that annealed samples are all single-phase alloys with CaCu5 type structure. The maximum of both hydrogen content and discharge capacity is obtained for La-alloy 1.23 wt%H2 and 321.1 mA h/g, respectively. All the investigated alloys are quiet stable with ΔH of hydrogen desorption about 36–38 kJ/mol H2. Cycle life of alloy electrode has been improved by partial substitution of La for Nd and Ni for Cr. The highest capacity retention of 92.2% after 100 charge/discharge cycles at 1C has been observed for Nd-alloy. The hydrogen diffusion coefficient measured by PITT is higher at the start of charging process and dramatically reduces by 2–3 order of magnitude with saturation of β-hydride. The highest value 6.9 × 10−13 cm2/s is observed for La alloy at 100% SOC. Partial substitution La for Nd and Cr for Ni in low-Co AB5 metal hydride alloys slightly reduces maximum discharge capacity, HRD performance and hydrogen diffusion kinetics. Low-Co alloys show good overall electrochemical properties compared to high-Co alloys and might be perspective materials for various electrochemical applications.

Design of a milling reactor coupled to a high-temperature mass spectrometer for thermodynamic/kinetic data of hydrogen-based materials

Identification of species in the gaseous phase of hydride materials and their mixtures (e.g. LiBH4–MgH2) is crucial for understanding the reactional mechanisms and diffusion kinetics of hydrogen across the different interfaces of phase segregation. This phase separation makes the characterization by conventional gas analysis techniques complicated and some analytical information could not be accessible. To overcome this surface/interface related issue, the study of the evolution of the gas phase emitted by the complex hydrides during ball-milling is considered. In this respect, an experimental set-up is designed by coupling a milling reactor with a mass spectrometer through a capillary tubing and an effusion Knudsen cell. A gas flow study (from molecular to viscous regimes) is performed in order to propose a suitable architecture of the entire device (ball-mill, capillary tubing, pipes, effusion cell compartment and pumping system) compatible with the mass spectrometric detection in terms of effused flow and molecular beam. Simulation of the flows and definition of their regimes nature at each stage of the pipes and vessels system is addressed as function of geometric parameters, upstream pressures, and pumping capacity on the downstream side (effusion cell). The study highlights the advantage of using a capillary tubing for the connection and ensure an optimal detection. Different working pressure conditions are demonstrated and associated to its length, meanwhile the diameter of the capillary has been demonstrated to be too sensitive to be varied.

Effects of Alloying Elements (C, Mo) on Hydrogen Assisted Cracking Behaviors of A516-65 Steels in Sour Environments.

This study examined the effects of alloying elements (C, Mo) on hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) behaviors of A516-65 grade pressure vessel steel in sour environments. A range of experimental and analytical methods of HIC, SSC, electrochemical permeation, and immersion experiments were used. The steel with a higher C content had a larger fraction of banded pearlite, which acted as a reversible trap for hydrogen, and slower diffusion kinetics of hydrogen was obtained. In addition, a higher hardness in the mid-thickness regions of the steel, due to center segregation, resulted in easier HIC propagation. On the other hand, the steel with a higher Mo content showed more dispersed banded pearlite and a larger amount of irreversibly trapped hydrogen. Nevertheless, the addition of Mo to the steel can deteriorate the surface properties through localized pitting and the local detachment of corrosion products with uneven interfaces, increasing the vulnerability to SSC. The mechanistic reasons for the results are discussed, and a desirable alloy design for ensuring an enhanced resistance to hydrogen assisted cracking (HAC) is proposed.

Evaluation of hydrogen trapping and diffusion in two cold worked CrMo(V) steel grades by means of the electrochemical hydrogen permeation technique

Hydrogen diffusion kinetics, which is influenced by the hydrogen trapping and de-trapping phenomena within the steel microstructure, plays an important role on the behaviour of steel components under hydrogen environments. Hence, the complex interaction between hydrogen atoms and steel microstructure must be analyzed in order to discuss the impact of hydrogen on the structural damage.Quenched and tempered low-alloy ferritic steels from the Cr-Mo family, with and without vanadium, have been subjected to different plastic deformation ratios by cold rolling. Dislocation densities have been determined by the analysis of the peak broadening on X-Ray diffractograms. Hydrogen diffusion kinetics was characterized by means of hydrogen permeation transients. In addition, binding energies between hydrogen atoms and microstructure were also determined using thermal desorption analysis (TDA). The analysis of the results highlights the influence of dislocations density and vanadium carbides on the hydrogen diffusion kinetics. In the 2.25Cr1Mo steel grade, hydrogen apparent diffusion coefficient decreased after the cold-work due to the increase in the density of traps (mainly related to dislocation core, ΔETL = 55–60 kJ/mol). Nevertheless, after 10% of plastic deformation, apparent diffusion coefficient ‘saturates’ according to the ‘plateau’ determined in the dislocation density evolution at higher deformation levels. Due to the vanadium addition (+0.31%), hydrogen apparent diffusion coefficient was notably reduced (compared to that obtained in the V-free steel grade). Hydrogen trapping and diffusion are the result of the interplay between vanadium carbides (ΔETL = 35 kJ/mol) and dislocation core.

Hydrogen diffusion kinetics under different conditions applied to VT6 alloy

Research of hydrogen diffusion in VT6 alloy is carried out considering different types of heat treating and hydrogen charging. The influence of microalloying on the susceptibility to hydride formation and embrittlement of titanium alloys is analyzed, and also effects of an oxide film on hydrogen charging during heat treatment without protective atmosphere, are studied.

First-principles insights of hydrogen diffusion dynamics at the α-Al2O3 (0001) surface

Hydrogen diffusion dynamics in the α-Al2O3 is very important because it associates directly with the performance of α-Al2O3 as the tritium permeation barrier (TPB) material in the tritium handling systems. In this work, the kinetics of hydrogen diffusion at the α-Al2O3 (0001) surface and hydrogen permeation into the α-Al2O3 bulk have been systematically studied by using the first-principles calculations. Results show that the vacancy defect can reduce the hydrogen migration barrier, while the Fe-doping defect can enhance the hydrogen migration barriers. This result is due to the dopant Fe showing bivalent instead of trivalent, which leads to the formation of a negatively charged center due to the substitution of divalent Fe for trivalent Al. In addition, results show quantitatively that the outer three oxygen layers (9 atomic layers) play a key role in hydrogen resistance. Hydrogen permeation from the outmost surface to the subsurface is the rate-determining step, and the corresponding energy barrier is about 3.327 eV.

Finite Element Modeling of the Behavior of a Hollow Cylinder in a Hydrogen-Containing Environment

The two main research orientations on the problem of hydrogen embrittlement are examined: the study of fundamental principles and the disclosure of micromechanisms and the relation between hydrogen embrittlement and metal aging; the development of models and methods for predicting the kinetics of change in stress-strain state and for evaluating the longevity of structures subjected to hydrogen embrittlement. The state of the problem of hydrogen embrittlement of metals in the first direction is briefly analyzed. More attention is paid to the importance of predicting the behavior of charged metal structures under the influence of hydrogen embrittlement. We then examine the use of finite element modeling using the ANSYS software to compute the calculation analysis of a hollow cylinder subjected to internal and external pressures and hydrogen embrittlement. The cylinder material is nonlinear elastic and its properties depend on the hydrogen concentration at each point of the cylinder. Consideration is given to the influence of the rigidity of the stress state and the hydrogen concentration on the diffusion kinetics of hydrogen in the cylinder body. The problem is solved in time steps. The distributions of the hydrogen concentration and the stresses for a quarter of the volume of the cylinder are given, as well as the graphs of these values ​​according to the thickness of the wall of the cylinder at different times. It is shown that the ANSYS software package adapted to the resolution of such problems can model the behavior of different structures in a hydrogen-containing environment, taking into account the effects caused by both the influence of hydrogen on mechanical properties of the material and by the stress state of the structures, as well as by the influence of the stress state on the interaction kinetics of hydrogen with the structures.

DFT study of boron doped MgH2: Bonding mechanism, hydrogen diffusion and desorption

The impact of boron doping on MgH2 bonding mechanism, hydrogen diffusion and desorption was calculated using density functional theory (DFT). Atomic interactions in doped and non-doped system and its influence on hydrogen and vacancy diffusion were studied in bulk hydride. Slab calculations were performed to study hydrogen desorption energies from (110) boron doped surface and its dependence on the surface configuration and depth position. To study kinetics of hydrogen diffusion in boron vicinity and hydrogen molecule desorption activation energies from boron doped and non-doped (110) MgH2 surface Nudged Elastic Band (NEB) method was used. Results showed that boron forms stronger, covalent bonds with hydrogen causing the destabilization in its first and second coordination. This leads to lower hydrogen desorption energies and improved hydrogen diffusion, while the impact on the energy barriers for H2 desorption from hydride (110) surface is less pronounced.

Hydrogen diffusion in low alloy steels under cyclic loading

Abstract The aim of this work is to analyze hydrogen transport in a low alloy steel by applying the electrochemical permeation technique to matrices subject to cyclic loading conditions, up to the yield strength and beyond this limit. The results indicate that, with an increase in the applied maximum stress, a decrease in the apparent diffusivity takes place, along with a marked and instantaneous reduction of diffusing hydrogen in the lattice and an increase in hydrogen solubility. An effect on the permeation current was observed, together with a variation of hydrogen diffusion kinetics ascribable to the activation on new trapping sites, with an appreciable effect under cyclic loading already at 55% of the yield limit, which becomes more relevant in the plastic domain.

Nanoporous polymer-based composites for enhanced hydrogen storage

The exploration and evaluation of new composites possessing both processability and enhanced hydrogen storage capacity are of significant interest for onboard hydrogen storage systems and fuel cell based electric vehicle development. Here we demonstrate the fabrication of composite membranes with sufficient mechanical properties for enhanced hydrogen storage that are based on a polymer of intrinsic microporosity (PIM-1) matrix containing nano-sized fillers: activated carbon (AX21) or metal–organic framework (MIL-101). This is one of the first comparative studies of different composite systems for hydrogen storage and, in addition, the first detailed evaluation of the diffusion kinetics of hydrogen in polymer-based nanoporous composites. The composite films were characterised by surface area and porosity analysis, hydrogen adsorption measurements, mechanical testing and gas adsorption modelling. The PIM-1/AX21 composite with 60 wt% AX21 provides enhanced hydrogen adsorption kinetics and a total hydrogen storage capacity of up to 9.35 wt% at 77 K; this is superior to the US Department of Energy hydrogen storage target. Tensile testing indicates that the ultimate stress and strain of PIM-1/AX21 are higher than those of the MIL-101 or PAF-1 containing composites, and are sufficient for use in hydrogen storage tanks. The data presented provides new insights into both the design and characterisation methods of polymer-based composite membranes. Our nanoporous polymer-based composites offer advantages over powders in terms of safety, handling and practical manufacturing, with potential for hydrogen storage applications either as means of increasing storage or decreasing operating pressures in high-pressure hydrogen storage tanks.

First-principles localized cluster expansion study of the kinetics of hydrogen diffusion in homogeneous and heterogeneous Fe-Cr alloys

Metal alloys have a wide range of technological applications, from structural materials to catalysts. In many situations, the transport of hydrogen, whether intentionally for hydrogen storage and fuel cell applications or unintentionally in the case of tritium uptake in nuclear materials, is an important concern. Fe-Cr binary alloys, in particular, may be viewed as a simple model system to represent ferritic steels used in nuclear energy systems and, more generally, as a model binary alloy for examining the role of alloying elements on transport. In this work, we used density functional theory, cluster expansion, and kinetic Monte Carlo to study hydrogen kinetics in Fe-Cr alloys. In random homogeneous alloys, we observed that hydrogen diffusivity first decreased with increasing Cr content and then increased to its levels in pure Cr. Furthermore, the effects of heterogeneity, as might be induced by irradiation, were explored and it was concluded that local structural heterogeneities for the same overall Cr concentration may significantly affect the hydrogen diffusivity. The effect was attributed to the relative binding energy of hydrogen in different metals and this understanding was then utilized to predict hydrogen transport behavior in different element-segregated grain/grain boundary combinations and thus identify solute/solvent alloys where hydrogen transport might be either hindered or enhanced. Finally, we comment on the potential impact of radiation-induced segregation on hydrogen behavior in nuclear energy systems.