Range Of Hydrogen Concentrations Research Articles

Hydride-Induced Responses in the Mechanical Behavior of Zircaloy-4 Sheets

This study aimed to investigate the impact of hydrogen content, up to 1217 ppm, on the mechanical properties of Zircaloy-4, with a particular focus on the formation and impact of hydrides. Tensile specimens were tested across a range of temperatures and hydrogen concentrations. The results revealed a pronounced ductile-to-brittle transition associated with hydride formation. When the hydrogen content in the specimens ranged between 700 and 850 ppm, a ductile-to-brittle transition was observed at temperatures of 25 °C, 50 °C, and 75 °C. At 25 °C, the ultimate tensile strength (UTS) of Zircaloy-4 linearly increased as the hydrogen concentration rose from 0 to 1217 ppm H. However, at higher temperatures, the behavior of UTS became more complex, especially in the hydrogen concentration ranges of 500–850 ppm H. Elongation (EL) in the hydrided specimens was affected by both temperature and hydrogen concentration. As hydrogen concentration increased, there was a noticeable decline in uniform EL, while non-uniform EL showed even more significant reductions. Scanning electron microscopy (SEM) analysis of the fracture surfaces revealed that quasi-cleavage features became evident when the hydrogen content reached 850 ppm H, across all tested temperatures. These findings not only provide a quantitative assessment of the safety implications of Zircaloy-4 in nuclear reactor applications but also highlight the importance of the hydrogen charging process and mechanical testing in understanding its mechanical behavior.

Ab initio study of the structure and properties of amorphous silicon hydride from accelerated molecular dynamics simulations

This paper presents a large-scale ab initio simulation study of amorphous silicon hydride (a-Si1-xHx) with an emphasis on the structure and properties of the material across a range of hydrogen concentration by combining accelerated molecular dynamics (MD) simulations with first-principles density-functional calculations. The accelerated MD scheme relied on classical metadynamics, which enabled the development of 2500+ high-quality structural models of a-Si1-xHx, with system sizes ranging from 150 to 6000 atoms and hydrogen concentrations vary from 6 to 20 at.%. The resulting amorphous networks were found to be completely free from any coordination defects and that they all exhibited a pristine band-gap in their electronic spectrum. The microstructural properties of hydrogen distributions were examined with an emphasis on the presence of isolated and clustered environments of hydrogen atoms. The results were compared with experimental data obtained from X-ray diffraction, infrared spectroscopy and nuclear magnetic resonance studies.

Effect of the variation of oxygen concentration on the laminar burning velocities of hydrogen-enriched methane flames

The combustion properties of hydrogen-containing fuel mixtures and the effect of the variation of the oxygen content of the oxidizer are at the center of recent research interest. Laminar burning velocity measurements with varied oxygen content can help in the validation of reaction mechanisms for better simulations of combustion systems using exhaust gas recirculation (EGR) or oxygen-enriched atmosphere. Such measurements were carried out in hydrogen-enriched methane−air flames using the heat flux method with higher accuracy and a wider range of initial oxygen and hydrogen concentrations compared to the similar studies in the literature. The mole fractions of the hydrogen and oxygen contents of the initial fuel and oxidizer mixtures were varied between xH2 = 0 and 0.20, and xO2 = 0.14 and 0.23, respectively. The initial gas temperature and pressure were 298 K and 1 bar, respectively. It is demonstrated that the increase of combustion rate by the hydrogen enrichment can be compensated with the decrease of the oxygen content. This compensating effect was investigated in detail in a wide range of equivalence ratio (φ). The experimental data were simulated with 11 widely used methane combustion reaction mechanisms. The prediction accuracies of the mechanisms at lean and rich equivalence ratios were significantly different and the important reaction steps were identified using sensitivity analysis for three mechanisms. Mechanisms POLIMI-2014 and Caltech-2015 gave the best overall predictions.

Hydrogen-induced microstructure optimization and mechanical properties enhancement of forged (TiB + TiC)/Ti6Al4V

This study investigates the impact of hydrogen on the mechanical properties and microstructure of forged titanium matrix composites (TMCs) reinforced with 2.5 vol% TiB and 2.5 vol% TiC. Melt hydrogenation technology was used to fabricate the TMCs with different hydrogen contents, which were then forged at 880 °C. Microstructural analysis revealed that hydrogen accelerated atomic diffusion, resulting in an approximate network microstructure. Hydrogen also promoted dynamic recrystallization during forging, leading to grain refinement and reduced dislocation density. Room temperature tensile tests showed that hydrogen significantly improved the strength and ductility of the forged TMCs within a certain range of hydrogen content. The greatest improvement was observed in the forged TMCs with a hydrogen content of 7.87 × 10−2 wt%, which exhibited a 10.48% increase in yield strength and a 31.36% increase in ductility relative to those without hydrogen. The effects of hydrogenation on crack propagation mechanisms are also discussed in detail. Overall, these findings provide valuable insights into the strengthening and toughening of forged titanium matrix composites through hydrogenation.

Preparation and Hydrogen-Sensitive Property of WO3/Graphene/Pd Ternary Composite

Hydrogen (H2) is a renewable energy source that has the potential to reduce greenhouse gas emissions. However, H2 is also highly flammable and explosive, requiring sensitive and safe sensors for its detection. This work presents the synthesis and characterization of WO3/graphene binary and WO3/graphene/Pd (WG-Pd) ternary nanocomposites with varying graphene and Pd contents using the microwave-assisted hydrothermal method. The excellent catalytic efficacy of Pd nanoparticles facilitated the disintegration of hydrogen molecules into hydrogen atoms with heightened activity, consequently improving the gas-sensing properties of the material. Furthermore, the incorporation of graphene, possessing high conductivity, serves to augment the mobility of charge carriers within the ternary materials, thereby expediting the response/recovery rates of gas sensors. Both graphene and Pd nanoparticles, with work functions distinct from WO3, engender the formation of a heterojunction at the interface of these diverse materials. This enhances the efficacy of electron–hole pair separation and further amplifies the gas-sensing performance of the ternary materials. Consequently, the WG-Pd based sensors exhibited the best gas-sensing performance when compared to anther materials, such as a wide range of hydrogen concentrations (0.05–4 vol.%), a short response time and a good selectivity below 100 °C, even at room temperature. This result indicates that WG-Pd ternary materials are a promising room-temperature hydrogen-sensing materials for H2 detection.

High Sensitivity Hydrogen Sensors Based on Optical Micro/Nanofiber Couplers Working at the Dispersion Turning Point

The safe utilization of hydrogen as a clean fuel and industry material requires the reliable detection of gas leakage. Thus, hydrogen sensors with high sensitivity and fast response are in urgent demand. Optical hydrogen sensors are especially attractive among various hydrogen detection techniques because of their intrinsic safety. Herein, a high-sensitivity hydrogen gas sensor is proposed based on optical micro/nanofiber couplers working at the dispersion turning point. The Pd coatings used were deposited on the waist region by magnetron sputtering. Due to the phase transition of palladium in the presence of hydrogen, intensity changes in the optical transmission of the devices are produced. It is demonstrated that the proposed platform provides high sensitivity, good repeatability, and selectivity, together with a fast response time for hydrogen detection below the explosive concentration. The response and recovery times are ~20 and ~28 seconds, respectively. The detected hydrogen concentration range is 0.1-1.5% (in volume). The detection limit of this sensor is below 0.1%.

Passive electrochemical hydrogen recombiner for hydrogen safety systems: prospects

This paper presents the concept of a passive electrochemical hydrogen recombiner (PEHR). The reaction energy of the recombination of hydrogen and oxygen is used as a source of electrical energy according to the operating principle for hydrogen fuel cells to establish forced circulation of the hydrogen mixture as an alternative to natural circulation (as is not utilized in conventional passive autocatalytic hydrogen recombiners currently used in nuclear power plants (NPPs)). The proposed concept of applying the physical operation principles of a PEHR based on a fuel cell simultaneously increases both productivity in terms of recombined hydrogen and the concentration threshold of flameless operation (the ‘ignition’ limit). Thus, it is possible to reliably ensure the hydrogen explosion safety of NPPs under all conditions, including beyond-design accidents. An experimental setup was assembled to test a laboratory sample of a membrane electrode assembly (MEA) at various hydrogen concentrations near the catalytic surfaces of the electrodes, and the corresponding current–voltage characteristics were recorded. The simplest MEA based on the Advent P1100W PBI membrane demonstrated stable performance (delivery of electrical power) over a wide range of hydrogen concentrations.

Flame propagation characteristics of premixed hydrogen–air deflagration with low concentration in a pipeline

This study used a visualized explosion propagation experimental system to investigate the flame propagation and hydroxyl (OH·) spectral radiation characteristics of hydrogen deflagration at the hydrogen concentration range of 7–17 vol%. The experimental results indicated that maximum flame propagation velocity, maximum explosion pressure, maximum flame temperature, and maximum relative spectral intensity of OH· gradually increased with hydrogen concentration. When concentration increased from 13 vol% to 17 vol%, the time to reach the maximum flame propagation velocity, the formation time of tulip flame, and the duration of the spectral radiation signal of OH· decreased by 52.9%, 55.6%, and 48.2%, respectively. In addition, flame propagation velocity oscillated when the tulip flame appeared, and maximum explosion pressure appeared later than the maximum temperature. Maximum flame propagation velocity, maximum explosion pressure, and maximum flame temperature positively correlated with maximum relative spectral intensity in the reaction system. These findings may serve as an essential reference for the safe and effective use of hydrogen and the research and development of radical targeted explosion suppressants.

Chemical inhibition of hydrogen-air explosions: Literature review, simulations and experiments

This paper summarises the first results from the joint industry project (JIP) ‘Risk-reduction for hydrogen installations by partial suppression of explosions’ (HyRISE). The main objective of the project is to develop fundamental knowledge that can support the development of practical solutions for mitigating hydrogen explosions in congested and confined environments by means of active systems for chemical inhibition. The aim is not to extinguish the incipient flame, but rather to lower the reactivity of the fuel-air mixture prior to ignition, and thereby reduce the consequences of an accidental explosion to a tolerable level. The paper consists of three parts: a review of previous work on chemical inhibition of premixed hydrogen-air flames, simulations with the chemical kinetics software Cantera, and experiments conducted in a 20-litre explosion vessel. The results demonstrate that chemical inhibition can be effective for hydrogen-air mixtures. However, it remains to develop efficient inhibitors and practical systems that can be implemented in industrial facilities, with satisfactory performance over a wide range of hydrogen concentrations.

Study on the role of Pd and ZrVFe hydrogen storage alloy in Pd/ ZrVFe catalyst for hydrogen elimination performance

Hydrogen energy has been considered to be one of the most potential clean energy, but its widespread availability is limited by hydrogen safety. Herein, a hydrogen-oxygen combination catalyst is designed based on a ZrVFe hydrogen storage alloy loaded with Pd, which exhibits excellent hydrogen elimination capability at low temperature, broad hydrogen concentration range and other complex working environments. The results show that the activity of the Pd/ZrVFe catalyst is dependent on the Pd loadings, and the 2 wt% Pd/ZrVFe catalyst can initiate the hydrogen-oxygen elimination reaction rapidly at ∼30 °C under above 2 vol% hydrogen concentration and 2 L min−1 inlet gas flow with a 96% hydrogen elimination efficiency. The Pd/ZrVFe catalyst has excellent hydrogen elimination performance at 2–20 vol% hydrogen concentration, especially at hydrogen concentration above 10%, the hydrogen elimination efficiency can reach more than 99%, and the highest hydrogen elimination rate is as high as 182.6 mL min−1· g−1. In addition, the Pd/ZrVFe catalyst is almost unaffected by irradiation and aerosol poisoning, and this catalyst provided better resistance to iodine vapor poisoning compared to other catalysts. This work opens a new window for addressing hydrogen safety issues.

AAO-Assisted Nanoporous Platinum Films for Hydrogen Sensor Application

The effects of the porosity and the thickness on the ability of hydrogen sensing is demonstrated through a comparison of compact and nanoporous platinum film sensors. The synthesis of anodic aluminum oxide (AAO) nanotubes with an average pore diameter of less than 100 nm served as the template for the fabrication of nanoporous Pt films using an anodization method. This was achieved by applying a voltage of 40 V in 0.4 M of a phosphoric acid solution at 20 °C. To compare the film and nanoporous Pt, layers of approximately 3 nm and 20 nm were coated on both glass substrates and AAO templates using a sputtering technique. FESEM images monitored the formation of nanoporosity by observing the Pt layers covering the upper edges of the AAO nanotubes. Despite their low thickness and the poor long-range order, the EDX and XRD measurements confirmed and uncovered the crystalline properties of the Pt films by comparing the bare and the Pt deposited AAO templates. The nanoporous Pt and Pt thin film sensors were tested in the hydrogen concentration range between 10–50,000 ppm H2 at room temperature, 50 °C, 100 °C and 150 °C. The results reveal that nanoporous Pt performed higher sensitivity than the Pt thin film and the surface scattering phenomenon can express the hydrogen sensing mechanism of the Pt sensors.

Direct hydrogen quantification in high-pressure metal hydrides

High-pressure metal hydride (MH) research evolved into a thriving field within condensed matter physics following the realization of metallic compounds showing phonon mediated near room-temperature superconductivity. However, severe limitations in determining the chemical formula of the reaction products, especially with regards to their hydrogen content, impedes a deep understanding of the synthesized phases and can lead to significantly erroneous conclusions. Here, we present a way to directly access the hydrogen content of MH solids synthesized at high pressures in (laser-heated) diamond anvil cells using nuclear magnetic resonance spectroscopy. We show that this method can be used to investigate MH compounds with a wide range of hydrogen content, from MH x with x = 0.15 (CuH0.15) to x ≲ 6.4 (H6±0.4S5).

Revealing the role of hydrogen content on the mechanical behavior and cracking mechanisms of Zircaloy-4 under strain

The mechanical property of zirconium-alloy reactor cladding materials inevitably degrades because of hydrogen absorption and hydride precipitation. In this study, mechanical behavior and delayed hydrogen cracking (DHC) mechanisms of Zircaloy-4 alloys with a broad range of hydrogen contents were investigated. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and a universal testing machine were jointly employed for this purpose. Results showed that the mechanical property of the hydrogenated specimen not only depended on the size and orientation of hydride, but also was affected by the continuity degree of the load-bearing matrix. The relevant microstructural observation indicated that the lower continuity degree of the load-bearing matrix, the less ductility of Zircaloy-4. More importantly, hydride phase transformation from δ-ZrH 1.5 to γ-ZrH occurred around the crack tip and reduced the local strain, while twinning just appeared at the crack bridging sites in the higher hydrogen-content specimens for changing the crystal orientation and mitigating the local stress concentration. Both those effects are expected to be potential mechanisms of the reappearing yield phenomenon because they are closely linked to dislocation movement. Additionally, based on the combination effect of crack blunting of γ-ZrH and the strain accommodation of twinning, the trend of crack propagation is delayed locally as expected. • The hydride phase transformation and twinning phenomenon around cracks were analyzed using EBSD. • The continuity of the load-bearing matrix profoundly influenced the mechanical properties of hydrided zircaloy-4. • The appearance and disappearance of yield-suppression phenomenon in hydrided zircaloy-4 were investigated. • Both γ-ZrH and twins are beneficial to delay the localized crack propagation.

Neutron diffraction study of concentration phases transition in the TiC0.50Hy alloy

The study belongs to the field of hydrogen materials science. A neutron diffraction study of titanium carbohydride TiC0.50Hy was carried out in the range of hydrogen concentration у = 0.50 ÷ 0.60. It is shown that high-temperature titanium carbohydride TiC0·50H0.50 of equiatomic composition has a face-centered cubic lattice (sp. gr. Fm3¯m), where hydrogen atoms are located in tetrahedral interstices. It has been established that in this alloy in vacuum, the phenomenon of hydrogen thermal emission is observed - complete removal of hydrogen with preservation of the FCC lattice of the TiС0.50 interstitial alloy. For the first time in the Ti–C–H system, a first-order concentration phase transition FCC (sp. gr. Fm3¯m) → HCP (sp. gr. Pm3¯1) in TiC0.50Hy carbohydride at a hydrogen concentration y > 0.50 was discovered without changing the octahedral environment of carbon atoms and tetrahedral the surroundings of hydrogen atoms by Ti atoms. The HCP phase in vacuum is heat-resistant at temperatures T < 600 K. The unit cell volume of the hcp phase is two times smaller than the unit cell volume of the FCC phases TiC0.50Hy and TiH2 of equiatomic composition. The results of studying the fcc phase of the equiatomic composition of TiC0·50H0.50 can be used to prepare a high-temperature hydrogen reservoir in hydrogen energy. The HCP phase can be used as a biological protective material in transport nuclear power plants and on nuclear submarines instead of titanium dihydride TiH2.

Influence of temperature and hydrogen content on the transverse mechanical properties of Zircaloy-4 fuel cladding

This paper presents the results of the investigation on the influence of hydrogen on the transverse mechanical properties of the Zircaloy-4 fuel cladding at various temperatures ranging from room temperature to 600οC. Data pertaining to the mechanical properties of the fuel cladding in the hoop direction are required for the analysis of high burn-up fuel behaviour under loss of coolant accident (LOCA) and reactivity initiated accident (RIA) conditions. Using the ring tension test method, the mechanical properties of the Zircaloy-4 fuel cladding in the transverse direction were evaluated as functions of hydrogen concentration and test temperature. The effect of hydrogen on the mechanical properties was observed to be marginal but the effect of temperature was significant in the investigated hydrogen concentration range (47–475 ppmw).

Reflective-Type High Sensitivity Optical Fiber Hydrogen Sensor Based On Enlarged Taper Cascaded With Tilted Fiber Grating

Highly sensitive reflective-type fiber hydrogen sensor based on an enlarged taper cascaded with a tilted fiber grating (TFBG) was proposed. Hydrogen-sensitive Au-Pd nanofilm was coated on the TFBG surface by magnetron sputtering means. By cascading an enlarged taper upstream to the TFBG, cladding modes and Ghost mode of the TFBG could be coupled into the core to form a reflective-type TFBG-based hydrogen sensor. As the hydrogen was absorbed by the Au-Pd nanofilm, the effective refractive index of the cladding of the TFBG will change accordingly, so as to the reflective spectra of the TFBG. The hydrogen concentration was obtained through the intensity changing of the ghost mode in the reflective spectra of TFBG. The proposed sensor showed a high sensitivity of 4.83 dB/% with a calculated LOD of 0.07% for the hydrogen concentration range from 0% to 0.7% at room temperature with the rapid response time of 26 s and recovery time of 40 s, respectively.

Flame propagation regimes and critical conditions for flame acceleration and detonation transition for hydrogen-air mixtures at cryogenic temperatures

A series of more than 100 experiments with hydrogen-air mixtures have been performed at cryogenic temperatures from 90 to 130 K and ambient pressure. A wide range of hydrogen concentrations from 8 to 60%H2 in a shock tube of 5-m long and 54 mm id was tested. Flame propagation regimes were investigated for all hydrogen compositions at three different blockage ratios 0, 30% and 60% as a function of initial temperature. Piezoelectric pressure sensors and InGaAs photo-diodes have been applied to monitor the flame and shock propagation velocity of the combustion process. More than 150 experiments at ambient pressure and temperature were conducted as the reference data for cryogenic experiments. The critical expansion ratio σ∗ for an effective flame acceleration to the speed of sound was experimentally found at cryogenic temperatures. The detonability criteria for smooth and obstructed channels were used to evaluate the detonation cell sizes at cryogenic temperatures as well. The main peculiarities of cryogenic combustion with respect to the safety assessment were that the maximum combustion pressure was several times higher and the run-up-distance to detonation was two times shorter compared to ambient temperature independent of lower chemical reactivity at cryogenic conditions.

Magneto-Electronic Hydrogen Gas Sensors: A Critical Review

Devices enabling early detection of low concentrations of leaking hydrogen and precision measurements in a wide range of hydrogen concentrations in hydrogen storage systems are essential for the mass-production of fuel-cell vehicles and, more broadly, for the transition to the hydrogen economy. Whereas several competing sensor technologies are potentially suitable for this role, ultra-low fire-hazard, contactless and technically simple magneto-electronic sensors stand apart because they have been able to detect the presence of hydrogen gas in a range of hydrogen concentrations from 0.06% to 100% at atmospheric pressure with the response time approaching the industry gold standard of one second. This new kind of hydrogen sensors is the subject of this review article, where we inform academic physics, chemistry, material science and engineering communities as well as industry researchers about the recent developments in the field of magneto-electronic hydrogen sensors, including those based on magneto-optical Kerr effect, anomalous Hall effect and Ferromagnetic Resonance with a special focus on Ferromagnetic Resonance (FMR)-based devices. In particular, we present the physical foundations of magneto-electronic hydrogen sensors and we critically overview their advantages and disadvantages for applications in the vital areas of the safety of hydrogen-powered cars and hydrogen fuelling stations as well as hydrogen concentration meters, including those operating directly inside hydrogen-fuelled fuel cells. We believe that this review will be of interest to a broad readership, also facilitating the translation of research results into policy and practice.

Development of a selective sensor for the determination of hydrogen

The composition of the catalyst (70% ZrO2 and 30% Cu2O) and the optimal conditions for the selectivity of hydrogen oxidation in the presence of combustible ingredients have been developed. Using a selected catalyst and optimal conditions, selective thermocatalytic hydrogen sensors are manufactured. In the range of hydrogen concentrations of 0.11 – 4.10% vol. the dependence of the sensor signal on the concentration is rectilinear. With continuous operation of the sensor for 1000 hours, the signal value remains stable. The presence of carbon monoxide (up to 1.4%), ammonia (up to 1.7%), and methane (up to 1.2%) in the analyzed mixture does not affect the value of the output signal of the hydrogen sensor. The developed sensors can be used as part of automatic gas analyzers and signaling devices.

Hydrate-based separation of the CO2 + H2 mixtures. Phase equilibria with isopropanol aqueous solutions and hydrogen solubility in CO2 hydrate

The gas hydrates' ability to preferentially bind one of the components of a gas mixture into a hydrate state makes it possible to consider hydrate-based technology as promising for the separation of gas mixtures. When a hydrate is obtained from a gas mixture, mixed hydrates with a complex composition inevitably occur. Issue of their composition determination stays apart. This a rather difficult task, which is complicated by the dissolution of small molecules such as hydrogen in the hydrate phase. This, in turn, impedes the analysis of the data obtained. In this work, the solubility of hydrogen in carbon dioxide hydrate in the range of 269.7–275.7 K and at partial H2 pressure up to 4.5 MPa was experimentally determined. Hydrate composition was found to be CO2·(0.01X)H2·6.5H2O at H2 pressure of X MPa. The equilibrium conditions of hydrates formation in the systems of H2O – CO2 – H2 and H2O – 2-propanol – CO2 – H2 were also determined in a wide range of hydrogen concentrations. Hydrogen seems to be an indifferent diluent gas regarding CO2 hydrate equilibrium pressure. The compositions of the equilibrium phases have been determined as well. It was shown that isopropanol does not form a double hydrate with СО2, only sI СО2 hydrate occurred in the studied systems. The obtained dependencies will be useful in analyzing the process of СО2 + Н2 gas mixtures separation by the hydrate-based method.