Distribution Of Hydrogen Atoms Research Articles

Molecular dynamics study on the effect of hydrogen on the plastic behavior of α-Fe crack tip

In this paper, the unilateral tension of α-Fe in the local region of the crack tip are simulated by molecular dynamics method, the plastic deformation behaviors and hydrogen embrittlement mechanism of the crack tip under different hydrogen concentration and hydrogen positions are analyzed. The results show that for the hydrogen-containing models, there exists a critical hydrogen concentration c0 that can make the plasticity of the α-Fe material reduce greatly. For the crack-free model, the main hydrogen embrittlement mechanism is adsorption-induced dislocation emission (AIDE), and the critical hydrogen concentration c0 is 0.3%. When the hydrogen concentration cH<c0, the plastic deformation mechanism is mainly dominated by phase transformation; when cH≥c0, the plastic deformation mechanism is phase transformation at low strains and dislocation motion at high strains. For the cracked model, the main mechanism of hydrogen embrittlement is hydrogen-enhanced local plasticity at the crack tip, with a critical c0 of 1.7%. When cH<c0, the plastic deformation mechanism of the model is a combination of phase transformation and dislocation; when cH≥c0, the plastic deformation mechanism is controlled by phase transformation. When the hydrogen is far away from the crack tip, the local mechanical behavior of the crack tip does not change significantly, while when hydrogen gathered at the crack tip, the addition of a small amount of hydrogen atoms will make the fracture strain decrease rapidly, which shows a mechanism of hydrogen-enhanced strain-induced vacancies (HESIV). A saturation value of hydrogen concentration at the crack tip is confirmed in this paper, when the local hydrogen concentration exceeds this saturation value, the plastic behaviour tends to be stable. The influence of hydrogen atoms distribution on the crack initiation behavior was determined by atomic configuration analysis.

Atomic hydrogen shows its true colours: correlations between H i and galaxy colour in simulations

ABSTRACT Intensity mapping experiments are beginning to measure the spatial distribution of neutral atomic hydrogen H i to constrain cosmological parameters and the large-scale distribution of matter. However, models of the behaviour of H i as a tracer of matter are complicated by galaxy evolution. In this work, we examine the clustering of H i in relation to galaxy colour, stellar mass, and H i mass in IllustrisTNG at z = 0, 0.5, and 1. We compare the H i-red and H i-blue galaxy cross-power spectra, finding that H i-red has an amplitude 1.5 times greater than H i-blue at large scales. The cross-power spectra intersect at ≈3 Mpc in real space and ≈10 Mpc in redshift space, consistent with z ≈ 0 observations. We show that H i clustering increases with galaxy H i mass and depends weakly on detection limits in the range MH i ≤ 108 M⊙. In terms of M⋆, we find massive blue galaxies cluster more than less massive ones. Massive red galaxies, however, cluster the weakest amongst red galaxies. These opposing trends arise from central-satellite compositions. Despite these M⋆ trends, we find that the cross-power spectra are largely insensitive to detection limits in galaxy surveys. Counter-intuitively, all auto and cross-power spectra for red and blue galaxies and H i decrease with time at all scales. We demonstrate that processes associated with quenching contribute to this trend. The complex interplay between H i and galaxies underscores the importance of understanding baryonic effects when interpreting the large-scale clustering of H i, blue, and red galaxies at z ≤ 1.

Distribution of hydrogen atoms at a notch on X52 steel under various loads and displacements studied by scanning Kelvin probe and finite element modeling

Abstract In this work, the distribution of hydrogen (H) atoms at a notch on an X52 pipeline steel under various applied loads or displacements were investigated by Volta potential measurements using a scanning Kelvin probe (SKP) and finite element modeling. The stress concentration at the notch is elastic under the test condition. The H atom diffusion and distribution is driven by stress, rather than strain, in the steel. However, when displacements are applied on the steel specimen, the strain dominates the H atom distribution. As the local stress or strain increases, the H atom concentration increases, as indicated by negative shifts of the Volta potential. By establishing the quantitative relationships among Volta potential, von Mises stress, and H atom distribution, this work attempts to provide a novel method for H atom detection in steels through the Volta potential measurement.

Predicting hydrogen segregation energy distributions in strained regions of tungsten using artificial neural network

Employing the smooth overlap of atomic position (SOAP) descriptors, we established an artificial neural network (ANN) model with the ability to effectively and accurately predict the segregation energy Eseg distributions of hydrogen (H) atoms in various strained regions of tungsten (W). The model is verified to have comparable accuracy with the molecular statics (MS) relaxations, as quantitively evidenced by the root mean square error (RMSE) values of 0.018 eV for the homogeneously strained regions, averagely 0.025 eV for regions near different dislocations, and 0.032 eV for regions surrounding an interstitial H cluster. Besides, the predictions yield no systematic bias at both high and low Eseg extremes, which is a common issue in the elastic theory (ET) calculations. Moreover, Eseg values are precisely predicted with the RMSE value of 0.041 eV surrounding an interstitial H cluster that is not encountered during the learning phase of the model, demonstrating the model’s robust generalization capability. Considering its markedly enhanced computation speed, this accurate ANN model holds promising prospects in circumstances that require massive Eseg calculations.

Hydrogen diffusion simulation of the X80 pipeline steel girth weld zone considering the synergistic effect of the structure–stress–concentration field

Hydrogen embrittlement failure, caused by hydrogen permeation and diffusion in the girth weld zone of pipelines, is the main obstacle to large-scale hydrogen blending transportation. Accordingly, a three-dimensional model of the girth weld zone of X80 pipeline steel was established. Considering the influence of structural inhomogeneity in the weld zone, multi-field sequential coupling simulation technology was used to analyze the diffusion process of hydrogen under the combined action of the residual stress and hydrogen concentration fields. A synergistic mechanism between hydrogen enrichment, structural characteristics, and residual stress in the weld zone was revealed. The results indicated that the structural inhomogeneity in the girth weld zone and residual stress field significantly influenced the hydrogen concentration distribution. Moreover, for the hydrogen diffusion process at the grain boundaries, the impact of the residual stress was greater than that of the structural inhomogeneity. This study further clarifies the spatial distribution of hydrogen atoms induced by multi-field coupling in the weld zone and provides a reference for the safety assessment of girth weld layers from an engineering perspective.

Energy distribution of fragments from H2 and H2 + dissociation by electron impact for the use in numerical models applied to negative ion sources

In negative hydrogen ion sources, the kinetic energy of the atoms is directly related to the negative ion yield at the caesiated converter, with a larger contribution from hot atoms. The energy distribution of hydrogen atoms is related to the formation process: either the kinetic energy release, resulting from dissociation of the hydrogen molecules or molecular ions, or the proton neutralization either in the volume or during reflection at walls. The interpretation of recent experimental measurements related to the translational energy distribution of atoms or positive ions could profit from accurate inclusion of the initial energy distribution in numerical models. In this work, we focus on the calculation of the kinetic energy release for the various dissociation channels due to electron impact on H2 and H2 +, in the Franck-Condon and delta approximation. Since in negative ion sources non-equilibrium vibrational distributions of H2 are found, the energy distribution of fragments is calculated for all vibrational levels. The inverse cumulative distribution functions related to the main dissociation processes are given, as well as the cumulative distributions for all dissociation channels by electron impact, for simple implementation in Monte Carlo numerical simulations. Finally, the application of the method to few cases of interest for negative ion sources is discussed.

Low-pressure inductively coupled plasmas in hydrogen: impact of gas heating on the spatial distribution of atomic hydrogen and vibrationally excited states

Non-equilibrium inductively coupled plasmas (ICPs) operating in hydrogen are of significant interest for applications including large-area materials processing. Increasing control of spatial gas heating, which drives the formation of neutral species density gradients and the rate of gas-temperature-dependent reactions, is critical. In this study, we use 2D fluid-kinetic simulations with the Hybrid Plasma Equipment Model to investigate the spatially resolved production of atomic hydrogen in a low-pressure planar ICP operating in pure hydrogen (10–20 Pa or 0.075–0.15 Torr, 300 W). The reaction set incorporates self-consistent calculation of the spatially resolved gas temperature and 14 vibrationally excited states. We find that the formation of neutral-gas density gradients, which result from spatially non-uniform electrical power deposition at constant pressure, can drive significant variations in the vibrational distribution function and density of atomic hydrogen when gas heating is spatially resolved. This highlights the significance of spatial gas heating on the production of reactive species in relatively high-power-density plasma processing sources.

Modeling nuclear quantum effects on long-range electrostatics in nonuniform fluids

Nuclear quantum effects play critical roles in a variety of molecular processes, especially in systems that contain hydrogen and other light nuclei, such as water. For water under ambient conditions, nuclear quantum effects are often interpreted as local effects resulting from a smearing of the hydrogen atom distribution. However, the orientational structure of water at interfaces determines long-range effects, such as electrostatics, through the O–H bond ordering that is impacted by nuclear quantum effects. In this work, I examine nuclear quantum effects on long-range electrostatics of water confined between hydrophobic walls using path integral simulations. To do so, I combine concepts from local molecular field theory with path integral methods at varying levels of approximation to develop efficient and physically intuitive approaches for describing long-range electrostatics in nonuniform quantum systems. Using these approaches, I show that quantum water requires larger electrostatic forces to achieve interfacial screening than the corresponding classical system. This work highlights the subtleties of electrostatics in nonuniform classical and quantum molecular systems, and the methods presented here are expected to be of use to efficiently model nuclear quantum effects in large systems.

On the role of vacancy-hydrogen complexes on dislocation nucleation and propagation in metals

New insights are provided into the role of vacancy-hydrogen (VaH) complexes, compared to the hydrogen atoms alone, on hydrogen embrittlement of nickel. The effect of the concentration of hydrogen atoms and VaH complexes is investigated in different crystal orientations on dislocation emission and propagation in single crystal of nickel using atomistic simulations. At first, embrittlement is studied on the basis of unstable and stable stacking fault energies as well as fracture energy to quantify the embrittlement ratio (unstable stacking fault energy/fracture energy). It is found that VaH complexes lead to high embrittlement compared to H atoms alone. Next, dislocation emission and propagation at pre-cracked single crystal crack-tip are investigated under Mode-I loading. Depending upon the elastic interaction energy and misfit volume, high local concentrations at the crack front lead to the formation of nickel-hydride and nickel-hydride with vacancies phases. These phases are shown to cause softening due to earlier and increased dislocation emission from the interface region. On the other hand, dislocation propagation under the random distribution of hydrogen atoms and VaH complexes at the crack front or along the slip plane shows that VaH complexes lead to hardening that corroborates well with the increased shear stresses observed along the slip plane. Further, VaH complexes lead to the disintegration of partial dislocation and a decrease in dislocation travel distance with respect to time. The softening during emission and hardening during propagation and disintegration of partial dislocation loops due to VaH complexes fit the experimental observations of various dislocation structures on fractured surfaces in the presence of hydrogen, as reported in literature.

Graphite Separation in Sunflower Oil and a Possible Food Monitoring Sensor via Near-infrared Spectroscopy

Introduction: As a quick and non-destructive testing method, Fourier transform infrared (FTIR) spectroscopy has become more popular for identifying food adulteration, manipulation, and deception. Sunflower oil is a widely used food item that may be contaminated or even adulterated with potentially harmful chemical substances associated with health issues. Methods: In this regard, this study was carried out to examine the applicability of near- and midinfrared spectroscopy to identify modifications in the pure sunflower oil and sunflower oil dispersed with graphite. The dispersion of graphite powder in sunflower oil was achieved using the ultrasonic technique. The samples were analyzed using FTIR spectroscopy and transmission electron microscopy. Results: Changes in the FTIR signal were observed, indicating changes in the hydrogen atoms distribution within the solution. The flattened peak at 3470 cm-1 was associated with the overtone of glyceride ester carbonyl absorption compared to pure SO. Additionally, the stretching vibration of carbonyl groups of triglyceride esters occurred as a significant absorption band at 1754 cm-1, and the FTIR absorption at 1447 cm-1 was absent. Transmission electron microscopy (TEM) analysis showed transparent layers of graphene sandwiched with sunflower oil with a distinct flake-like shape Conclusion: These findings support dispersed graphite in sunflower oil to check the food quality.

Reconsideration of Temperature Determined by the Excited-State Population Distribution of Hydrogen Atoms Based on Tsallis Entropy and Its Statistics in Hydrogen Plasma in Non-Equilibrium State.

In non-equilibrium plasmas, the temperature cannot be uniquely determined unless the energy-distribution function is approximated as a Maxwell-Boltzmann distribution. To overcome this problem, we applied Tsallis statistics to determine the temperature with respect to the excited-state populations in non-equilibrium state hydrogen plasma, which enables the description of its entropy that obeys q-exponential population distribution in the non-equilibrium state. However, it is quite difficult to apply the q-exponential distribution because it is a self-consistent function that cannot be solved analytically. In this study, a self-consistent iterative scheme was adopted to calculate q-exponential distribution using the similar algorithm of the Hartree-Fock method. Results show that the excited-state population distribution based on Tsallis statistics well captures the non-equilibrium characteristics in the high-energy region, which is far from the equilibrium-Boltzmann distribution. The temperature was calculated using the partial derivative of entropy with respect to the mean energy based on Tsallis statistics and using the coefficient of q-exponential distribution. An analytical expression was derived and compared with Boltzmann statistics, and the distribution was discussed from the viewpoint of statistical physics.

Distribution of hydrogen atoms at metallurgical microphases of X52 pipeline steel studied by scanning Kelvin probe force microscopy and finite element modelling

The work combined scanning Kelvin probe force microscopy measurements and finite element modelling to study the diffusion and distribution of hydrogen (H) atoms at metallurgical microphases contained in X52 pipeline steel. Results show that the pearlite contained in the steel is more stable than the ferrite during electropolishing, as indicated by the measured topographic profiles and Volta potentials. The hydrogen (H)-charging enhances the electrochemical activity of both pearlite and ferrite, as shown by increased Volta potential and thus the decreased work function. As the H-charging time increases, the Volta potentials of both phases further increase, implying that their activities increase with the H-charging time. The pearlite has a greater Volta potential and thus a lower work function than the ferrite. This is associated with more H atoms accumulating at the pearlite than at the ferrite. The H atom diffusion and accumulation are affected by H diffusivity at phase boundaries, H-trap binding energy and the number of traps in the steel.

The effect of V8C7 size on hydrogen diffusion behavior and hydrogen induced cracking in pipeline steel

This study revealed the relationship between V8C7 size and hydrogen diffusion behavior as well as hydrogen induced cracking (HIC) in pipeline steel. Hydrogen permeation and HIC susceptibility tests were implemented on five conditions with different V8C7 sizes but identical volume fractions. The results proved that with increasing of V8C7 size, the hydrogen effective diffusivity was first decreased and then increased. Increasing the proportion of small size (coherent and semi-coherent) V8C7 increased the effective hydrogen trapping densities, decreased hydrogen diffusion coefficient, improved the distribution of diffusible hydrogen atoms and then the HIC susceptibility of steels was decreased.

Finite element modeling of the distribution of hydrogen atoms at a dent on pipelines for hydrogen transport under cyclic loading

Finite element modeling of the distribution of hydrogen atoms at a dent on pipelines for hydrogen transport under cyclic loading

Adiabatic energy change in the inner heliosheath: how does it affect the distribution of pickup protons and energetic neutral atom fluxes?

ABSTRACT The hydrogen atoms penetrate the heliosphere from the local interstellar medium, and while being ionized, they form the population of pickup protons. The distribution of pickup protons is modified by the adiabatic heating (cooling) induced by the solar wind plasma compression (expansion). In this study, we emphasize the importance of the adiabatic energy change in the inner heliosheath that is usually either neglected or considered improperly. The effect of this process on the energy and spatial distributions of pickup protons and energetic neutral atoms (ENAs), which originate in the charge exchange of pickup protons, has been investigated and quantified using a kinetic model. The model employs the global distributions of plasma and hydrogen atoms in the heliosphere from the simulations of a kinetic-magnetohydrodynamic model of solar wind interaction with the local interstellar medium. The findings indicate that the adiabatic energy change is responsible for the broadening of the pickup proton velocity distribution and the significant enhancement of ENA fluxes (up to ∼5 and ∼20 times in the upwind and downwind directions at energies ∼1–2 keV for an observer at 1 au). It sheds light on the role of adiabatic energy change in explaining the discrepancies between the ENA flux observations and the results of numerical simulations.

Leptothrix biofilms and the formation of oxygen and hydrogen molecules in structure

In this work, the crystal structure of Leptothrix biosamples was studied using positron annihilation lifetime spectroscopy, MIKA modeling package and X-ray diffraction method. The structural analysis results showed that free cubic and orthorhombic phase Fe and trigonal Fe2O3 and cubic Fe3O4 phases were detected in Leptothrix biosamples. It has been determined that the concentration of cubic Fe3O4 phases in biosamples is higher than other phases. The theoretical bases of the regularity of distribution of hydrogen and oxygen atoms in the form of free and vacancies in the trigonal Fe2O3 and cubic Fe3O4 phases were calculated. On the other hand, the lifetime of vacancies in Fe, Fe2O3 and Fe3O4 structures has been determined.

SARA Characterization and Comparison for the Ultra-Heavy Oil via Combined Analyses

Abstract Structure characterization and comparison of the ultra-heavy oil and its four components are fundamental and crucial. In this work, nuclear magnetic resonance analyses were employed to quantitatively investigate carbon and hydrogen atom distributions. Combined with the gel permeation chromatography, elemental analysis, and X-ray diffraction results, average molecular structure parameters were determined for four components. Besides, an improved Brown–Ladner method was adopted to identify and adjust corresponding structural parameters, which considered influences of both heteroatoms (O, S, and N), and katacondensed and/or pericondensed system assumption on aromatic structures, compared with conventional methods. Moreover, molecular architectures of four components were, respectively, speculated and reconstructed based on this improved method, and the specific comparison reflected a higher accuracy. From this study, it could provide updated understandings of specific component structural information for the ultra-heavy oil to facilitate subsequent oil reactivity and simulation studies.

Study by finite element modeling of hydrogen atom diffusion and distribution at a dent on existing pipelines for hydrogen transport

Pipelines, especially existing natural gas pipelines, provide an efficient and economical means for hydrogen transport, accelerating realization of a full-scale hydrogen economy. However, the existing aged pipelines usually contain dents, which serve as effective traps to accumulate hydrogen atoms, potentially causing hydrogen embrittlement and pipeline failures. To date, there has been a strong interest in development techniques for assessment of hydrogen atom distribution at a dent on pipelines. In this work, a three-dimensional nonlinear finite element-based model was developed to investigate the hydrogen atom diffusion and distribution at a constrained dent on an X52 steel pipe. Parametric effects, including dent depth and internal pressure, were determined. The presence of a dent on pipelines drastically changes the local stress and strain distributions, facilitating diffusion and accumulation of hydrogen atoms at the dent. The minimum hydrogen atom concentration at the crystalline lattice sites, (i.e., 3.8 mol/m3) is located on the outer surface of the dent center, and the maximum hydrogen atom concentration (i.e., 12.1 mol/m3) is found on both sides of the dent with 103 mm from the dent center in the circumferential direction. The hydrogen atom concentration at trap sites at the dent is much lower than that at the lattice sites. The diffusion and accumulation of hydrogen atoms at the dent area is affected by two competitive mechanisms, i.e., hydrostatic stress and plastic strain, depending on the initial concentration of hydrogen atoms entering the interior of the pipe steel. At a low initial concentration such as 0.001 mol/m3, the equivalent plastic strain dominates the distribution of hydrogen atoms at the dent, and the hydrogen atom concentration at the lattice sites is much lower than the concentration at the trap sites. At high initial hydrogen atom concentrations such as 0.1 and 1 mol/m3, the hydrostatic stress is the dominant factor to determine the distribution of hydrogen atoms, which mainly accumulate at the lattice sites. With an increased depth of the dent, both the von Mises stress and plastic strain concentrations increase, and so is the hydrogen atom concentration. The increase of internal pressure from 5 MPa to 15 MPa only slightly elevates the von Mises stress, equivalent plastic strain and the hydrogen atom concentration.

In-situ visualization of hydrogen atom distribution at micro-indentation in a carbon steel by scanning Kelvin probe force microscopy

Abstract In this work, a scanning Kelvin probe force microscope was used to in-situ visualize distribution of hydrogen atoms at micro-indentation and metallurgical phases contained in a carbon steel. Topographic profiles and Volta potentials of the steel upon various times of hydrogen-charging were measured. The hydrogen atom distribution at the micro-indentation was analyzed. Results demonstrate that the micro-indentation can serve as a preferential site to accumulate hydrogen atoms. Particularly, the vertex of the indention shows the greatest hydrogen atom enrichment, while the indentation bottom possesses a slightly lower hydrogen atom concentration. More hydrogen atoms accumulate in ferrite than in pearlite in the steel.

Measurements by SKPFM and Finite‐Element Modeling of Hydrogen Atom Diffusion and Distribution in Ferrite and Bainite Contained in X80 Steel

Herein, the diffusion and distribution of hydrogen (H) atoms in ferrite and bainite contained in an X80 pipeline steel is studied by both scanning Kelvin probe force microscopy and finite‐element modeling. The effect of metallurgical microphases on H‐atom accumulation in the steel is analyzed. The results show that H‐charging elevates the electrochemical dissolution activity of both ferrite and bainite contained in the steel, as indicated by the increased Volta potential and thus the decreased work function. The H atoms tend to accumulate at ferrite, making the local H‐atom concentration much greater than the concentration at bainite. The results imply that, compared with bainite, ferrite is the location to accumulate more H atoms initiating hydrogen‐induced cracks once the local H‐atom concentration reaches a threshold value.