Hydrogen Diffusion Coefficient Research Articles

Effect of partial Ni substitution in V85Ni15 by Ti on microstructure, mechanical properties and hydrogen permeability of V-based BCC alloy membranes

Vanadium-based alloy membranes with body-centred-cubic (BCC) structure are considered as one of the leading alternatives to Pd-based alloys for hydrogen separation applications due to their lower cost and higher permeability. As permeability and mechanical properties depend on what microstructure can be produced mainly by alloy composition under same processing conditions, the effect of alloy composition on microstructure, mechanical properties and hydrogen permeability has been investigated for the V85Ni15 and V85Ni10Ti5 (at%) alloys prepared by a same process route. All Ni atoms dissolve into the V-matrix to form a single highly supersaturated solid solution with dendritic segregation of Ni-solute atoms in the binary alloy. A part of Ni replacement with 5 at% Ti leads to the formation of small interdendritic phases NiTi and NiTi2 in addition to major phase of V-based solid solution. The mechanical property testing shows that the ultimate strength of the ternary alloy is higher than that of the binary alloy, but the elongation and rollability are lower due to a combination of solid solution hardening and particle strengthening effect. The addition of Ti can greatly increase permeability about 4 times greater than the binary alloy at a permeation testing of 400 °C. But the presence of small amounts of interdendritic compounds provides a barrier to hydrogen migration, resulting in a relatively lower hydrogen diffusion coefficient. In theory, the diffusivity and solubility of hydrogen atom in the presence of alloying element Ti is higher than that in the presence of alloying element Ni in vanadium. This is demonstrated using first principles calculation which further explains the mechanism of hydrogen permeation.

Investigation of the Correlation between Hydrogen Cathodic Charging Conditions and Toughness Properties of Longitudinal Submerged Arc Welded X65 Pipeline Steels

This research work focuses on the investigation of the correlation between hydrogen cathodic charging conditions and toughness properties of a welded X65 pipeline steels. The experimental technique which was applied to determine the characteristic parameters associated with toughness was the crack tip open displacement after hydrogen cathodic charging process. The hydrogen cathodic charging process was carried out in an electrolytic cell with applied current densities of 10, 20, 30 mA/cm2 and hydrogen cathodic charging duration 48 h. Through this study, interesting results were provided concerning the diffusion depth and the diffusion coefficient of atomic hydrogen as far as toughness properties. The maximum diffusion depth value is assigned for each current density field in the region of heat-affected zone and the minimum in the area of fusion zone. In addition, the highest diffusion coefficients are attributed to heat-affected zone and the lowest to fusion zone, for all applied current densities. Finally, the fusion zone is considered to be more prone to the occurrence of embrittlement phenomena compared to base metal. The rate of toughness parameters drop is higher for current densities between 0-10 and 20-30 mA/cm2, where the cathodic current promotes the electrochemical reduction in hydrogen cations to atomic hydrogen.

Correlation between the Parameters of Gas-Phase and Electrochemical Hydrogenation Processes of Intermetallic Compounds

The main ways measuring the parameters that characterize processes of the gas-phase and electrochemical hydrogenation of intermetallic compounds—promising materials for metal hydride hydrogen tanks and chemical power sources—are listed and discussed. The general principles of the mathematical treatment of pertinent experimental data and ways of determining the effective diffusion coefficient of hydrogen in metal hydrides are described. It is shown that sorption/desorption isotherms can be constructed for metal−hydrogen systems on the basis of electrochemical measurements.

Theoretical investigation of molybdenum/tungsten-vanadium solid solution alloy membranes: Thermodynamic stability and hydrogen permeation

To improve the resistance to hydrogen embrittlement and hydrogen permeation performance of vanadium (V) membranes, first-principles calculations were employed to study the stability, dissolution, and diffusion properties of H in transition metal (M = Mo, W)-doped V membranes, as well as their mechanical and thermodynamic properties, as alternative candidates for H2 separation. Our results revealed that the doping percentage of Mo/W alloying can significantly improve the mechanical and thermodynamic properties of pure V. The most stable location for adsorbed H atoms is the tetrahedral interstitial site (TIS) in the body-centered cubic structure of the V1-xMx (x = 0.0625, 0.125, 0.1875, and 0.25) alloys. Additionally, the hydrogen migration path should preferentially follow TIS → nearest-neighbor TIS. An M content of 0.25 yields the best anti-hydrogen embrittlement and the highest hydrogen-diffusion properties. The addition of individual Mo or W as doping elements into the V-based system greatly enhanced the hydrogen diffusion coefficient, and the addition of both Mo and W significantly improved the anti-hydrogen embrittlement of V-based alloys. Our results also showed that hydrogen concentration markedly influenced the solubility and diffusivity of hydrogen in V-based alloy membranes. These results provide a basis for the design of V-based alloy hydrogen permeation membranes.

Diffusion behavior of hydrogen in oxygen saturated and unsaturated plutonium dioxide: An ab initio molecular dynamics study

As the plutonium (Pu) oxides are the crucial issue of the Pu surface and corrosion science and some impurities like hydrogen (H) are virtually impossible to exclude from them in realistic environments, understanding the dynamical behaviors of hydrogen (H) in Pu oxides is essential for the protections and applications of Pu. Here we perform systematic ab initio molecular dynamics (AIMD) calculations to reveal the diffusion behaviors of impurity H in the oxygen saturated (OS) and oxygen unsaturated (OU) Pu dioxide (PuO 2 ). The considered variation ranges of the concentration of interstitial H (θ: H to Pu ratio), the concentration of oxygen vacancy (OV) (n ov : OV to O ratio), and the temperature were 1 32 ∼ 14 32 , 0 ∼ 8 64 , and 300 ∼ 800 K, respectively. The root mean square displacements, radial distribution functions, Bader charge, electronic density of states, and the three-dimensional diffusion coefficients were extracted and analyzed in detail. Results indicate that the H diffusion is inhibited mainly due to the formation of hydroxyl with the host O both in the OS and OU PuO 2 . In the OU PuO 2 the O atoms will transport due to the presence of large concentration of H. The octahedral interstitial site in the OS PuO 2 and the OV in the OU PuO 2 provide a metastable and favorable capturing effect to the interstitial H, respectively. The diffusion coefficient in the OU PuO 2 is smaller than that of in the OS PuO 2 and decreases with n ov essentially as the OV plays the role of a trap for H diffusion. Our conclusions may provide potential guidance for Pu surface and corrosion science. • The mechanisms of inhibit hydrogen diffusion in different plutonium dioxides were confirmed. • Two different capturing effects to hydrogen in saturated and unsaturated PuO 2 were found. • The diffusion coefficients of hydrogen in different plutonium dioxides were obtained. • The variation tendencies of the hydrogen diffusion coefficients were discussed.

Investigation of Hydrogen Embrittlement Susceptibility and Fracture Toughness Drop after in situ Hydrogen Cathodic Charging for an X65 Pipeline Steel.

The present research focuses on the investigation of an in situ hydrogen charging effect during Crack Tip Opening Displacement testing (CTOD) on the fracture toughness properties of X65 pipeline steel. This grade of steel belongs to the broader category of High Strength Low Alloy Steels (HSLA), and its microstructure consists of equiaxed ferritic and bainitic grains with a low volume fraction of degenerated pearlite islands. The studied X65 steel specimens were extracted from pipes with 19.15 mm wall thickness. The fracture toughness parameters were determined after imposing the fatigue pre-cracked specimens on air, on a specific electrolytic cell under a slow strain rate bending loading (according to ASTM G147-98, BS7448, and ISO12135 standards). Concerning the results of this study, in the first phase the hydrogen cations’ penetration depth, the diffusion coefficient of molecular and atomic hydrogen, and the surficial density of blisters were determined. Next, the characteristic parameters related to fracture toughness (such as J, KQ, CTODel, CTODpl) were calculated by the aid of the Force-Crack Mouth Open Displacement curves and the relevant analytical equations.

Studies on diffusion of hydrogen in PWR clad material

Zr-1%Nb alloy is used as cladding material in pressurised water reactors (PWR). Diffusion of hydrogen in this material is one of the important input parameters required for simulating the kinetics of hydrogen embrittlement. For this purpose, one end of cut piece of Zr-1%Nb alloy clad tube of PWR was polished, electrochemically charged with hydrogen and then annealed at required temperatures and time. Hydrogen content was determined in cut pieces of clad tube in axial direction employing hot vacuum extraction quadrupole mass spectrometry (HVE-QMS) technique. From the hydrogen profile in axial direction, diffusion coefficient of hydrogen was estimated employing the solution of Fick’s second law of diffusion with semi-infinite system boundary conditions. Activation energy (Ea) for diffusion of hydrogen in Zr-1%Nb was calculated from the slope of the Arrhenius plot between Log DH and 1/T. The obtained D0 and Ea are well in the range of expectations based on the literature data in various Zr based materials by considering micro-constituents in these materials.

Hydrogen diffusion through Ru thin films

In this paper, an experimental measurement of the diffusion constant of hydrogen in ruthenium is presented. By using a hydrogen indicative Y layer, placed under the Ru layer, the hydrogen flux through Ru was obtained by measuring the optical changes in the Y layer. We use optical transmission measurements to obtain the hydrogenation rate of Y in a temperature range from room temperature to 100 °C. We show that the measured hydrogenation rate is limited mainly by the hydrogen diffusion in Ru. These measurements were used to estimate the diffusion coefficient, D, and activation energy of hydrogen diffusion in Ru thin films to be D = 5.9 × 10−14 m2/s ∙ exp (-0.33 eV/kBτ), with kB the Boltzmann constant and τ the temperature.

Time dependence of silica optical properties during the implantation of fast hydrogen ions: Computer modeling

The paper deals with a computer simulation of the creation and chemical annealing behavior of non-bridging oxygen hole centers (NBOHC) in silica exposed to long-time hydrogen implantation. Calculated time dependence of the number of NBOHCs and the intensity of red band luminescence associated with these defects were in a good agreement with experimental data. It allowed estimating the average cross-section of the radiation production of NBOHCs, the radiation-enhanced hydrogen diffusion coefficient and the reaction rate constant for NBOHC’s passivation by implanted hydrogen. We also paid attention to the physical reasons for some discrepancy between simulated dependences and experimental data as well as between calculated parameters and our previous estimations based on some simplifying assumptions.

Influence of Phases Stability on the Hydrogen Diffusion Coefficient in Ti-6Al-4V

For a unique microstructure creation, thermo-hydrogen treatment (THT), using hydrogen as a temporary alloying element within the heat treatment, is applied. This advanced heat treatment requires reliable data about the hydrogen diffusion coefficient (DH) for understanding diffusion kinetics and its effect on the mechanical behavior of the resulted phases. In this research, three different homogeneous microstructures were established for the investigation using different homogenization parameters. After that, the concentration of hydrogen, charged in the half-length of thin titanium rods via electrochemical hydrogenation, is specified. Then, a diffusion annealing heat treatment was carried out at different temperatures, leading to hydrogen diffusion in the hydrogenated specimens. Furthermore, DH was systematically determined using two methods including the explicit finite difference method (EFDM) and Matano technique (MT). For this purpose, Abaqus software was employed for modeling the hydrogen gradient established in the specimens. Additionally, scanning electron microscopy (SEM) was used for the microstructure examination in order to specify the influence of different hydrogen concentrations on the hydrogenated specimens. The experimental outcomes reveal a substantial effect of the β phase stability and grains sizes of the β and α phases on the hydrogen diffusion. Correspondingly, the results confirm that DH was independent of the hydrogen concentration, and obeys an Arrhenius-type temperature dependence. Furthermore, hydrogen diffusion in the α+β titanium alloys Ti-6Al-4V was slower in comparison to the hydrogen diffusion in the metastable β titanium alloys Ti-10V-2Fe-3Al. In conclusion, it was observed that DH is influenced by the previously performed heat treatments that determine the resulted microstructure types, and a slight influence of the volume fraction of the α phase on DH was observed as well.

Hydrogen Permeation Property and Hydrogen Embrittlement Susceptibility of Pipeline Steel with Oxide Film

In this study, the oxide film on X80 steel was fabricated to decrease hydrogen embrittlement of pipeline steel. The microstructures and mechanical properties in 10MPa hydrogen gas and hydrogen permeation properties were investigated. The phase structure of oxide film was mainly composed of Fe2O3. With the increasing of oxidation temperature, surface oxygen content improves gradually. Oxide film plays an important role in resisting hydrogen penetrating. Hydrogen diffusion coefficient decreases from 38.81☓10-7cm2s-1 to 1.26☓10-7 cm2s-1 for oxidation at 450 ℃. The plastic deformation increases obviously after oxidation. HEI decreases from 40.96% to 11.61% for oxidation at 450 ℃.

Determining the effective hydrogen diffusion coefficient in 100Cr6

AbstractIn the present study, the diffusion constant for hydrogen in hardened 100Cr6 was measured in permeation tests. The tests were conducted on samples of different thicknesses. The diffusivity of hydrogen was also measured in prestrained samples to study the influence of plastic strain on the diffusion rate. A finite element‐based diffusion model was applied to confirm the experimental results by computing the concentrations of diffusible hydrogen and trapped hydrogen due to deformation‐induced defects. The results showed that the concentration of trapped hydrogen remained very low throughout the plastic strain regime under consideration. The average effective diffusion coefficient of hydrogen in 100Cr6 at 30°C was found to be Deff = 4.9 × 10−12 m2/s.

Effective hydrogen diffusion coefficient for CoCrFeMnNi high-entropy alloy and microstructural behaviors after hydrogen permeation

Herein, the first observation of the effective hydrogen diffusion coefficient of CoCrFeMnNi high-entropy alloy (HEA) was performed using electrochemical hydrogen permeation; further, it was compared with those of stainless steels (SS) 304 and 316L. HEA and SS 316L showed similar effective hydrogen diffusion coefficient of 1.75 × 10−11 m2/s and 1.91 × 10−11 m2/s, respectively. SS 304 showed the smallest that of 0.58 × 10−11 m2/s in the study. Hydrogen diffusion through the grain boundary was dominant in face-centered cubic metals. Hydrogen permeation resulted in no change in the microstructure of HEA and SS 316L; however, it caused a martensitic transformation in SS 304.

Evaluation of hydrogen-induced cracking in high-strength steel welded joints by acoustic emission technique

Hydrogen-induced cracking behavior in high-strength steel mainly composed of martensite was analyzed by acoustic emission (AE) technique and finite element method (FEM) in slow strain-rate tensile (SSRT) tests and welding tests. The crack initiation was detected by the AE signals, and the time evolution of stress concentration and hydrogen diffusion were calculated by FEM. The effect of hardness and plastic strain on the hydrogen diffusion coefficient was explicitly introduced into the governing equation in FEM. The criterion and indicator parameter for the crack initiation were derived as a function of maximum principal stress and locally accumulated hydrogen concentration. The results showed that the cracking criterion derived by AE and FEM is useful for predicting the cold cracking behavior and determining the critical preheat temperature to prevent hydrogen-induced cracking.

Hydrides of Laves type Ti–Zr alloys with enhanced H storage capacity as advanced metal hydride battery anodes

The present work was focused on the studies of the effect of variation of stoichiometric composition of Ti–Zr based AB2±x Laves phase alloys by changing the ratio between A (Ti + Zr) and B (Mn + V + Fe + Ni) components belonging to both hypo-stoichiometric (AB1.90, AB1.95) and over-stoichiometric (AB2.08) alloys further to the stoichiometric AB2.0 composition to optimize their hydrogen storage behaviours and performances as the alloy anodes of nickel metal hydride batteries.AB2-xLa0.03 Laves type alloys (A = Ti0.15Zr0.85; B = Mn0.64–0.69V0.11–0.119Fe0.11–0.119Ni1.097–1.184; x = 0, 0.05 and 0.1) were arc melted and then homogenized by annealing.The studies involved probing of the phase-structural composition by X-Ray diffraction (XRD), together with studies of the microstructural state, hydrogen absorption–desorption and thermodynamic characteristics of gas–solid reactions and electrochemical charge-discharge performance, further to the impedance spectroscopy characterization. The alloys were probed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and XRD.These studies concluded that the alloys contained the main C15 FCC Laves type AB2 intermetallic co-existing with a secondary C14 hexagonal Laves phase and a small amount of LaNi intermetallic. The gaseous H storage capacity and electrochemical performances were found to be closely dependent on the stoichiometric compositions of the alloys. High discharge capacities approaching 500 mAh/g were achieved for the AB1.95 alloy. At 500 mA/g current density, the discharge capacity was maintained as high as 80%, with very low capacity retention after 500 cycles. The alloy which had the highest capacity retention after 500 cycles was found to be AB2.0 alloy. Furthermore, AB2.0 alloy showed an excellent cyclic stability together with a high hydrogen diffusion coefficient. Studies of hydrogen diffusion coefficients showed that annealing enhanced the H diffusion rates allowing advanced performance at high discharge current densities. This has been related to a higher content of C15 Laves compound which allows to reach a higher H mobility in contrast with higher storage capacity observed for the C14 Laves type polymorph.

Communication—The Mechanism of Hydrogen Permeation Resistance of Ni Coating Enhanced by the Incorporation of Graphene

As suggested in our previous study, graphene containing Ni-based coating possessed a lower diffusion coefficient of hydrogen that pure Ni did. In this study, Pure Ni and Ni-graphene coatings were prepared in the Watts’ bath by electrodeposition, moreover, the enhancing mechanism of graphene on hydrogen permeation resistance of Ni coating was discussed for the first time. By means of various characterization techniques such as EBSD, SEM and TEM, it was revealed that both the refinement of grain size and the increase of special grain boundaries (GBs) fraction played the main roles due to the introduction of graphene into Ni deposits.

Critical assessment of the evaluation of thermal desorption spectroscopy data for duplex stainless steels: A combined experimental and numerical approach

The present study evaluates thermal desorption spectroscopy (TDS) data measured for UNS S32205 duplex stainless steel. Variations in the TDS spectra are obtained by electrochemical hydrogen charging for different times and by applying different heating rates for desorption to evaluate the desorption activation energy. Good agreement is found when comparing the experimental TDS curves with the desorption flux based on a numerical diffusion model using a homogeneous average hydrogen diffusion coefficient for the two-phase (ferrite-austenite) duplex microstructure. Trapping cannot be distinguished from the experimental TDS data since hydrogen diffusion in austenite is the rate-determining process during desorption. An average diffusion activation energy of 43.4 kJ/mol is determined from the experiments. Moreover, similar findings are obtained with a finite-element model that includes the heterogeneous hydrogen-related properties of the two phases of this duplex stainless steel.

Effects of doping with a third element (Pd, Ru, Ta) on the structure and hydrogen permeation properties of V–10Mo solid solutions

Alloying is an effective method for improving the resistance of V metals to hydrogen embrittlement. The effects of the doping with a third element (Pd, Ru, Ta) on the structure and hydrogen permeation properties of V–10Mo solid solutions have been investigated in this study. As-prepared V–5Mo-5TM (TM = Mo, Pd, Ru, Ta) alloy samples composed of V-based solid solution with a bcc structure are hydrogenated into their corresponding solid solutions (α-phase). Structural changes caused by TM-doping have notable effects on the hydrogen permeation properties (particularly the hydrogen solubility) of V–10Mo alloy, and the ability of the doping element in decreasing the hydrogen solubility of the V–10Mo alloy follows the sequence: Pd > Ru > Ta. Their doping causes a slight decrease in the hydrogen diffusion coefficient as well as an increase in the Vickers hardness of the resulting alloys. This work demonstrates that the mechanical property of V–10Mo alloy can be improved via suitable structure control caused by alloying it with an appropriate element. In addition, this approach might be suitable for improving properties of other relevant binary alloys.

Effect of microstructural inhomogeneity on hydrogen diffusion in welded joints

Hydrogen is a main factor in cold cracking or hydrogen-induced cracking. The most crack susceptible region of a steel welded joint is the heat affected zone (HAZ). Formulation and functional-analytical solution of the one-dimensional problem of hydrogen diffusion in an inhomogeneous butt-welded joint taking into account weld and joint dimensions as well as hydrogen diffusion coefficients and solubilities are presented. It is shown that the peak hydrogen concentration in the HAZ of inhomogeneous joints varies in direct proportion to the initial hydrogen concentration in the weld metal. Peak hydrogen concentration is inversely proportional to the ratio of hydrogen solubilities in the weld and HAZ and the square root of diffusion coefficient ratio of the HAZ and weld. The peak hydrogen concentration in the HAZ can exceed 80% of the initial concentration in the weld if martensitic steel is welded using low-carbon low-alloy welding consumables. Utilization of austenitic consumables leads to reduction in hydrogen concentration in the HAZ by 75–85% in comparison with non-austenitic consumables.

On the Estimation of the Diffusion Coefficient and Distribution of Hydrogen in Stainless Steel

In this work, the localisation of hydrogen in an electrochemically charged stainless steel was investigated by Scanning Kelvin Probe Force Microscopy and Glow Discharge Optical Emission Spectroscopy analysis. Both techniques indicated a high hydrogen content at less than 90 micrometres under the charged surface. Thermal Desorption Spectroscopy was used to calibrate the data from both techniques and thus to calculate the hydrogen concentration. Finally, after assuming certain hypotheses, Fick's laws were used to calculate the coefficient of diffusion and subsurface concentration of hydrogen in cathodic charging conditions.