Increasing Hydrogen Content Research Articles

Hardening effect of diffusible hydrogen on BCC Fe-based model alloys by in situ backside hydrogen charging

Hydrogen embrittlement is common in metallic materials and a critical issue in industries involving hydrogen-related processes. Here we investigate the mechanical response upon hydrogen loading of ferritic Fe-16Cr, Fe-21Cr and Fe-4Al alloys. We use a novel in situ setup for electrochemical backside hydrogen charging during nanoindentation. Single-phase ferritic Fe-Cr binary alloys with high hydrogen diffusivity and low solubility, are ideal for in situ studies during hydrogen charging, particularly the effect of diffusible and lightly trapped hydrogen is targeted. The hardness increases linearly with increasing hydrogen content until a quasi-equilibrium state between hydrogen absorption and desorption is reached while Young's modulus remains unaffected. Above this transient region, the slope of the absolute hardness experiences a drastic decrease. The hardness variation in Fe-21Cr is anisotropic as determined for (100), (110) and (111) oriented grains. Increasing the Cr content enhances the hardening effect in (100) orientation: a 16.7 % hardness increase is observed in Fe-21Cr, while Fe-16Cr, shows an increment of 10.8 %. A Fe-4Al alloy increases slightly in hardness by only 4.3 % at the applied current density of 3 mA/cm2. The hardening effect is caused by enhancing dislocation density, as revealed by studying the cross-section underneath the nanoindentation imprints.

Effect of hydrostatic pressure on hydrogen behavior on the surface of X70 pipeline steel

Hydrogen embrittlement is a serious phenomenon resulting in severe ductility deterioration of engineering materials due to the presence of hydrogen atoms. The low concentration of dissolved oxygen in deep-sea provide the condition for hydrogen production. Herein, the hydrogen permeation behavior in X70 pipeline steel in acid/alkaline environment under different hydrostatic pressure were investigated via electrochemical hydrogen permeation parameters. The results revealed the different trends of i∞ with increasing hydrostatic pressure. The phenomenon was described from the perspectives of hydrogen generation, absorption/desorption and permeation process by potentiodynamic polarization, linear sweep voltammetry (LSV) and EIS tests. The experimental permeation data were fitted with surface effect model and leads to the conclusion that the hydrostatic pressure greatly enhanced the adsorption rate and restricts the desorption rate of absorbed hydrogen atoms on the metal surface, thereby the process of atomic hydrogen compounding into hydrogen molecules is inhibited, leading to an increase in sub-surface hydrogen concentration (C0).

Hydrogen enriched natural gas as fuel for CHP units

This study investigates the potential benefits and drawbacks of adding hydrogen to natural gas grids on stationary cogeneration plants. Fuel blended with up to 30% hydrogen by volume was tested using a commercial six-cylinder spark ignition engine designed for pure natural gas operation without modifications to the engine. In line with normal practice for cogeneration plant engines, the power output, the lower heating value of the air/fuel mixture, the ignition timing and the engine speed were held constant. Results show that increasing hydrogen concentration led to an earlier peak cylinder pressure, indicating significantly accelerated combustion. As a result, peak pressures were up to 39% higher than with natural gas and up to 10% of fuel burned before top dead center. Despite this, thermal efficiency improved up to 6%. Cycle-by-cycle variation decreased by half, indicating reduced misfires on account of hydrogen. However, nitrogen oxide emissions increased exponentially with increasing hydrogen amounts. Our findings suggest that hydrogen-enriched natural gas is a promising fuel for stationary cogeneration plants, but modifications to engine control settings are necessary to ensure optimal performance and compliance with nitrogen oxide emission regulations. These modifications might include adjustments to the mixture control system and ignition timing.

Hydrogen accumulation and diffusion in cylindrical-shaped pipeline steels with coating defects

The effective diffusion of hydrogen in a cylindrical geometry, mimicking a pipe with a coating defect, was investigated by modelling and verified experimentally. Analytical solutions for the extreme cases of no hydrogen uptake and constant hydrogen uptake were developed. Simulations showed less than 5% error, when compared to two well-documented reference cases for diffusion. The intermediate case of modelling kinetic controlled hydrogen uptake was investigated and the effects of time, position, effective diffusion coefficient, corrosion protection current density and their binary interactions, were reported. Modelling results show, that certain parameter combinations such as effective hydrogen diffusion coefficients between 10−11 - 10−9.5 m2 s−1, particularly in combination with a hydrogen uptake jH of more than 0.1 A m−2, may lead to locally increased hydrogen concentrations in the material.

Occurrence of characteristic defects of grinding balls from rejects of continuously cast billets of rail steel

On the basis of metallographic studies, the authors determined the characteristic defects of grinding balls rolled from the rejects of continuously cast billets of K76F rail steel. Relationship of the presence of internal defects of the balls with their impact resistance was established. Defects in the form of internal cracks with accumulations of non-metallic inclusions in the area of their localization and flocks have the greatest impact on the reduction of balls impact resistance. Such defects are the cause of balls destruction during impact resistance tests in 62 and 17 % of cases, respectively. The effect of internal cracks without significant accumulations of non-metallic inclusions and quenching microcracks located along the boundaries of the phase interface was estimated at 12 and 9 %. The regularities and mechanism of influence of the rejects chemical composition of K76F rail steel billets on the probability of destruction of the balls produced from them during impact resistance tests were established. An increase in sulfur content in the billets of the studied rail steel reduces impact resistance of the balls produced from them, as it contributes to formation of non-plastic sulfides that concentrate in the area of internal cracks. An increase in hydrogen content in rail steel naturally contributes to an increase in probability of formation of the flocks, which significantly reduce the balls stability to shock loads. An increase in carbon content in the initial billets affects the increase in probability of destruction of K76F steel balls during copra tests. It is explained by formation of cementite-type carbides when carbon content corresponding to the eutectoid steel is reached. In general, the relative degree of influence of the K76F rail steel chemical composition on impact resistance of grinding balls is 48 %.

Effects of hydrogen content on laminar burning velocity and Markstein length in outwardly propagating spherical SNG–air premixed flames

As the hydrogen content of the five synthetic natural gas (SNG) fuels fixed with the Wobbe index increases, the unstretched laminar burning velocity and Markstein length also increase. For the addition of hydrogen to natural gas pipelines, an experiment was conducted using up to 19% hydrogen gas (SNG H19). By comparing the error rates with the measured laminar burning velocities and the four reaction mechanisms, Aramco 2.0 was selected as the optimized mechanism for the SNG mixtures. The unstretched laminar burning velocities were compared with those of Aramco 2.0 for SNG–air premixed flames under elevated pressures up to 0.5 MPa for equivalence ratios (ϕ) of 0.7–1.4. The results showed that the measured laminar burning velocities were consistent with the numerical values under lean and stoichiometric conditions; however, the deviations increased under rich conditions as the hydrogen content increased. The laminar burning velocities estimated using the four mixing laws were evaluated under elevated pressure and rich conditions. Consequently, the results predicted by mass-fraction mixing and Q/k models were in good agreement with the measured values. The Markstein length decreases linearly as the hydrogen content increases, but all Markstein lengths are positive; therefore, no instability occurs in the SNG–air premixed flames. The measured Markstein lengths were compared with the theoretical Markstein lengths and reasonably traced well to the isothermal surface at 600 K. When the hydrogen content reaches up to SNG H19, the theoretical Markstein lengths overpredict the results, except for ϕ values of 0.7 and 1.4.

Studies on the Performance of Engines Powered with Hydrogen-Enriched Biogas

Sustainability of energy supply has become a prime concern for energy producers and consumers alike. There is heightened awareness in the global community about the decreasing supply of conventional fossil fuels along with increasing fuel and energy demand and the consequent rise in unit energy cost. In addition to the sustainability aspect, the environmental impact of emissions from fossil fuel combustion is the focus of global targets for emissions reduction. In this context, the research and application of sustainable and non-polluting fuels become significant. Internal combustion (IC) engines are part of a significant energy-consuming sector, and the application of sustainable and non-polluting fuels within IC engines would be impactful. Biogas and hydrogen are viewed as sustainable and non-polluting alternatives to conventional fossil fuels. However, either of these used individually offer certain disadvantages. Experimental results and analysis of the performance and emissions characteristics of an IC engine fueled with biogas blended with 5, 10, and 15% hydrogen volume fractions are studied. An increase in hydrogen content increases the engine’s performance and power and reduces carbon monoxide (CO) and total hydrocarbons (THCs). However, nitrogen oxides (NOx) are found to increase due to higher combustion temperatures attributed to hydrogen. A 17.5% increase in brake power is observed for 15% hydrogen-enriched biogas, compared to plain biogas, at an equivalence ratio of 0.6. Similarly, a 17% increase in BTE, a 50% decrease in CO, a 68% decrease in UHC, but a 71% increase in NOx are observed for 15% hydrogen-enriched biogas.

Effects of H2 addition on the instability characteristics of CO/air and CH4/air in a horizontal narrow channel

ABSTRACT This paper investigates the instability characteristics of CO/H2/air and CH4/H2/air mixtures in a narrow channel under standard temperature and pressure conditions. The CO/H2 mixture exhibits a greater overpressure growth rate and maximum explosion overpressure as compared to the CH4/H2 mixture at the same hydrogen content. As the hydrogen content increases, the maximum explosion overpressure (P max) value increases, while the corresponding time (θ) value gradually decreases. The maximum explosion overpressure of CH4/H2 and CO/H2 mixtures is 28.27 kPa and 25.09 kPa, respectively. The flame wrinkles to form cells due to the Darius-Landau instability, and the interaction between the vortex tube and premixed flame affects the structure of turbulent premixed combustion. The oscillation frequency of the overpressure increases with increasing hydrogen content, and the oscillation belongs to the Helmholtz oscillation. The CO/H2 mixtures exhibit greater flame thickness than CH4/H2 mixtures, resulting in lower Peclet numbers and therefore greater relative importance of heat losses. As the hydrogen content increases, the sensitivity coefficient of R99 (OH + CO <=> H + CO2) in the CO/H2 mixture gradually decreases, while the sensitivity coefficients of R38 (H + O2 <=> O + OH) and R84 (OH + H2 <=> H + H2O) increase. The elementary reaction R38 plays a leading role in increasing the laminar burning velocity of the CH4/H2 mixture. The trend of R38 variation in the two mixtures is opposite with increasing hydrogen content.

Prediction of the Engine Performance and Emission Characteristics of Glycine Max Biodiesel Blends With Nanoadditives and Hydrogen

Abstract This study investigates the Glycine max (soybean oil) biodiesel with hydrogen along with MgO nanoadditives on compression ignition engines. A series of tests were conducted at various loading conditions in a water-cooled, single-cylinder, constant-speed engine. The biodiesel-blended soya oil was used as the primary fuel, and hydrogen was added at a constant volume of 25 LPM. Additionally, MgO nanoparticles were dispersed to the blends at concentrations of 50 ppm. In this study, it was found that the addition of hydrogen to the compression ignition (CI) engine resulted in an increase in combustion performance. In addition, hydrogen and oxygen molecules significantly reduced the exhaust gas temperature and brake-specific fuel consumption of biodiesel samples. An increase in nanoparticle concentration resulted in a reduction in emissions of pollutants such CO2, CO, and HC. Inclusion of the hydrogen in the combustion chamber reduces the carbon content burned. Further, the availability of extra molecules in the MgO aids the fuel to reach higher combustion rates. At higher load conditions, biodiesel blends showed a slight decrease in NOx emissions. Overall, from the findings, it is clear that hydrogen addition and nanoparticles enhanced emission and combustion process, which is attributed due to the increase in hydrogen content in the fuel.

Comparison of combustion characteristics of MILD model combustor and multi-nozzle array model combustor fueled hydrogen-methane mixtures

Key issues facing the development of hydrogen gas turbines include achieving low NOx emissions on hydrogen-enriched fuels, prevention of flashback and thermoacoustic instability. The present experimental investigation shows the fuel feasibility of MILD combustion and multi-nozzle array combustion with hydrogen-enriched fuels. The combustion characteristics, such as the range of combustion stability, NOx/CO emissions, and reaction zone distribution, have been determined for hydrogen contents ranging from 0% to 50% by volume. Compared to the MILD model combustor, the multi-nozzle array model combustor can achieve a broader range of stable combustion up to 40% by volume. As the hydrogen content increases from 0% to 40% by volume, the lean blowout (LBO) temperature of the multi-nozzle array model combustor decreases from 1600 K to 1400 K. When the hydrogen content reaches 50% of the volume, both the MILD model combustor and the multi-nozzle array model combustor exhibit thermoacoustic instability at high equivalence ratios. For the multi-nozzle array model combustor, NOx emissions are less than 20 ppm@15% O2 and CO emissions are less than 30 ppm@15% O2 in the adiabatic temperature range of 1400 K–2100 K. NOx emissions of the multi-nozzle array combustor are higher than that of the MILD combustor, but remain ultra-low due to the flue gas recirculation ratio. With increasing hydrogen content, the reaction zone becomes more concentrated along the axial and radial directions. The lift-off height of the reaction zone is 1.6 nozzle diameters at 40% by volume hydrogen content, which ensures the safety of the nozzles and prevent flashback.

Effects of Coenzyme Q10 on the Biomarkers (Hydrogen, Methane, SCFA and TMA) and Composition of the Gut Microbiome in Rats.

The predominant route of administration of drugs with coenzyme Q10 (CoQ10) is administration per os. The bioavailability of CoQ10 is about 2-3%. Prolonged use of CoQ10 to achieve pharmacological effects contributes to the creation of elevated concentrations of CoQ10 in the intestinal lumen. CoQ10 can have an effect on the gut microbiota and the levels of biomarkers it produces. CoQ10 at a dose of 30 mg/kg/day was administered per os to Wistar rats for 21 days. The levels of gut microbiota biomarkers (hydrogen, methane, short-chain fatty acids (SCFA), and trimethylamine (TMA)) and taxonomic composition were measured twice: before the administration of CoQ10 and at the end of the experiment. Hydrogen and methane levels were measured using the fasting lactulose breath test, fecal and blood SCFA and fecal TMA concentrations were determined by NMR, and 16S sequencing was used to analyze the taxonomic composition. Administration of CoQ10 for 21 days resulted in a 1.83-fold (p = 0.02) increase in hydrogen concentration in the total air sample (exhaled air + flatus), a 63% (p = 0.02) increase in the total concentration of SCFA (acetate, propionate, butyrate) in feces, a 126% increase in butyrate (p = 0.04), a 6.56-fold (p = 0.03) decrease in TMA levels, a 2.4-fold increase in relative abundance of Ruminococcus and Lachnospiraceae AC 2044 group by 7.5 times and a 2.8-fold decrease in relative representation of Helicobacter. The mechanism of antioxidant effect of orally administered CoQ10 can include modification of the taxonomic composition of the gut microbiota and increased generation of molecular hydrogen, which is antioxidant by itself. The evoked increase in the level of butyric acid can be followed by protection of the gut barrier function.

A mathematical model for dehydrogenation of molten steel in the Vacuum degasser

This paper presents a mathematical model of VD dehydrogenation aimed at predicting hydrogen removal during the VD vacuum refining process and investigating the effect of controllable parameters on the dehydrogenation process. Taking into account the behavior of argon bubbles during their uplifting, the model considers that the dehydrogenation reaction occurs at three sites, the surface of the Ar bubbles, the bath surface of the molten steel, and the bulk steel. The calculated results are in good agreement with the industrial production data. The hydrogen content of the molten steel during VD dehydrogenation is observed to vary as an inversely proportional function with the vacuum holding time, decreasing rapidly in the early stage and slowing down in the later stage. Using the model, the contribution of different reaction sites to the dehydrogenation process was investigated. It was found that the internal spontaneous nucleation of the molten steel dominated the dehydrogenation process at the beginning. Then, the internal spontaneous nucleation gradually weakened to disappear as the hydrogen content of the molten steel decreased, followed by the dominance of dehydrogenation on the surface of the Ar bubble. The model also investigated the effect of vacuum pressure and argon flow rate on the VD dehydrogenation process. It was found that the vacuum pressure significantly influenced the dehydrogenation rate on the Ar bubble surface and the bath surface mainly by affecting the equilibrium hydrogen concentration in the gas phase and by influencing the critical nucleation depth, which affected the internal spontaneous dehydrogenation. Moreover, the increase of the argon flow rate not only increases the reaction area of the Ar bubble but also the reaction area at the activation zone on the bath surface. Additionally, the increase of the initial hydrogen content in the molten steel significantly promotes the spontaneous dehydrogenation of the internal nucleation in the bulk steel.

Effect of hydrogen on the microstructure and mechanical properties of high temperature deformation of Ti6Al4V additive manufactured

The additive manufactured Ti6Al4V-xH titanium alloy was compressed at 600°C–750 °C on a Gleeble 3800 testing machine, and the compression rates were 1s−1 and 0.01s−1, respectively. The experimental results show that with the increase of hydrogen content, the flow stress of the alloy decreases firstly and then increases gradually. When the hydrogen content is 0.27 wt%, the flow stress of titanium alloy is the smallest. EBSD and TEM analysis were carried out and show that the α lamellar microstructure became larger at 0.27H, the corresponding flow stress also decreased, and slip bands appeared in the alloy. Dislocation slip was an important deformation mechanism of the alloy. When the hydrogen content continued to increase, the α phase in the alloy gradually decreased, and α″ appeared at 0.81H. Therefore, adding appropriate hydrogen can reduce the alloy flow stress and improve the performance of titanium alloy during hot deformation.

Numerical study on particle distribution characteristics of slush hydrogen in a cryogenic tank

A numerical model considering phase change and heat transfer was established by the Euler-Euler two-fluid method to investigate the storage characteristics and two-phase flow field of slush hydrogen. Numerous numerical simulations were performed to discuss the effect of particle diameter (dp = 0.02–0.5 mm), content of solid hydrogen (αs = 10%–50%), and heat leakage (q = 50–200W·m−2) on the flow field. It was found that particle deposition could occur during the storage process, and there exist moving vortices with contrary directions under specific conditions. The sedimentation characteristics and vortex size are influenced by many factors including particle size, solid hydrogen content, and heat leakage. An increase in particle size could lead to the strengthening of precipitation and the expansion of the counterclockwise vortex region on the right side of the tank. And the increase in solid hydrogen content could result in more deposition and more collisions and friction between particles. Moreover, the increase in heat leakage could increase the area of the counterclockwise vortex. Numerical results of the deposition and flow field characteristics in the storage tank could clearly show the physical law of the slush hydrogen so that the uniform distribution of slush hydrogen could be promoted for efficient storage and application.

Machine learning-assisted tri-objective optimization inspired by grey wolf behavior of an enhanced SOFC-based system for power and freshwater production

In recent years paying attention to the generation of clean and sustainable power and fresh water along with having lower cost and emission has increased. In the present research, a novel scheme for generating efficient power using the flame-assisted fuel cell is introduced, which has higher efficiency than ordinary fuel cells due to increased hydrogen concentration in the flame-rich combustion chamber. The waste heat is then introduced to a multi-effect desalination unit through a heat recovery steam generation unit to generate fresh, drinkable water. In order to make the system have higher efficiency, lower cost, and lower emission, the machine learning techniques are applied to optimize the operational conditions of the system, and find out the best solution point based on the cutting-edge algorithm of the grey wolf. Also, a complete techno-economic analysis and a parametric study are necessary to figure out the best solution point based on the TOPSIS method. The results indicate that the maximum value of exergy efficiency and drinkable water generation is 67.5% and 3.4 kg/s, respectively, while the minimum energy cost is 90.1 $/MWh. Moreover, results show that for the second optimization scenario considering the drinkable water production, energy cost, and pollution index as the objectives, the net produced power, energy efficiency, exergy efficiency, and water mass flowrate improve by around 1059 kW, 5.1%, 1.3%, and 1.6 kg/s than the design condition. Besides, energy cost and emission index are reduced by about 22 $/MWh and 51.9 kg/MWh, respectively.

Investigation of spark ignition processes of laminar strained premixed stoichiometric NH[formula omitted]-H[formula omitted]-air flames

A knowledge of the ignition properties of ammonia (NH3)/hydrogen (H2) mixtures is important because of their abundance in chemical engineering processes, and also because of their prospective role as fuels in future energy systems. In particular, the question arises if and how important characteristics like ignition limits and minimum ignition energies in NH3/H2 mixtures are related to the physical conditions. To address this question, this work studies ignition process in ammonia/hydrogen mixtures by numerical simulations. These track the evolution of ammonia/hydrogen mixtures during and after the deposition of a certain ignition energy, using a detailed treatment of chemical reactions and molecular transport. Studies on the influence of different system parameters on the minimally required ignition energy are performed. These are the strain rate, hydrogen content, pressure and initial (pre-ignition) temperature. Significant findings include a quasi-linear correlation between the transition strain rate, defined as the strain rate below which no external energy is required to initiate successful ignition (auto-ignition) and a characteristic reaction rate, defined as the inverse of ignition delay time in homogeneous, quiescent mixtures. Also, the relative decay of minimum ignition energy with increasing hydrogen content is less pronounced for higher pressures. Analysis of the results supports a knowledge-based approach towards fail-proof ignition devices and reliable prevention of hazards. The simulations are used for assessing the ignitability of ammonia and its mixtures with hydrogen.

Enhancement of hydrogen embrittlement resistance in a Fe-18Mn-0.6C twinning induced plasticity steel by copper alloying

The effect of Cu alloying on hydrogen embrittlement (HE) in TWIP steel was studied using the low-speed linearly increasing stress test (LIST) with simultaneous cathodic hydrogen charging. Cu alloying influenced HE resistance by the following mechanism. (i) Cu alloying increased the stacking fault energy, which canceled out the embrittling effect of hydrogen on promoting local plasticity and mechanical twins/dislocations concentration. (ii) Cu alloying refined the austenite grains, especially after low-temperature (700 °C) annealing and thus delayed mechanical twinning that causes an increased hydrogen concentration. (iii) Cu alloying caused the formation of a Cu-rich surface which reduced the diffusible hydrogen content, particularly for the steel annealed at 900 °C. (iv) Cu alloying dispersed mechanical twins by Cu precipitate/Cu-rich clusters, which homogenized the diffusible hydrogen and decreased the local hydrogen concentration at the HE vulnerable interfaces. Mechanism (iv) in the 700 °C annealed Cu-alloyed TWIP steel produced the greatest increase in HE resistance.

High temperature elastic properties of sub-stoichiometric yttrium dihydrides

Yttrium hydrides are considered as candidate materials for neutron moderation applied in microreactors (akin transportable miniaturized nuclear reactors) owing to their superior thermal stability and hydrogen retention. The evolution of elastic properties of these materials at elevated temperatures, needed for predicting the thermomechanical response and performance of the moderator during in-service reactor conditions, however, is lacking. Here, we report the Young’s and shear elastic moduli of three stoichiometries of bulk yttrium hydride (YHx, x = 1.61, 1.82, and 1.84) from room temperature to 1000 °C. In situ temperature-dependent measurements of the longitudinal and shear wave velocities were performed using a laser ultrasonic technique while heating the sample in a vacuum-pumped heating stage. The elastic moduli increased linearly with increasing hydrogen content and decreased by ∼10 % during heating from room temperature to 1000 °C in the three YHx compositions. The linear relationship between the elastic moduli and the hydrogen content in yttrium hydride was verified by atomistic calculations based on density functional theory (DFT). The absence of abrupt changes in the temperature-dependent measurements of elastic modulus of the YHx samples suggested negligible loss of hydrogen at elevated temperatures. Excellent agreement was found between the measured and calculated dependence of the elastic moduli on the stoichiometry, thereby providing a new approach for investigating the effects of fabrication-induced parameters (such as porosity) on the elastic moduli. This study demonstrates the utility of the combined approach involving DFT-based atomistic calculations and measurements of the elastic moduli for the informative development of metal hydrides and can be used as a metric for novel moderator materials investigations for emerging microreactors and beyond.

The mechanism of hydride formation during electrochemical hydrogen charging of Ti–6Al–4V

The present work studies experimentally the hydrogen uptake and hydride formation in duplex Ti–6Al–4V. Hydrogen is introduced by electrochemical hydrogen charging at room temperature. The effect of the applied charging conditions is evaluated considering the effect of the charging duration and charging current density. Moderate charging conditions induce solute hydrogen in the lattice, resulting in lattice strains, as revealed by X-ray diffraction. More severe hydrogen exposure results in the formation of titanium hydrides when the hydrogen concentration exceeds the solubility limit of the Ti-α phase, as verified by a combined characterization with X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, and hydrogen melt extraction. A progressive mechanism of hydride formation upon increasing hydrogen content is proposed as the charging conditions clearly influence the hydrogen distribution and hydride formation in the material. Controlling the electrochemical hydrogen charging conditions enables to further understand the role of hydrogen and hydrides in hydrogen-induced failure mechanisms, as well as it offers opportunities for sustainable thermohydrogen processing of titanium.

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.