Increasing Hydrogen Content Research Articles

New Cage-Like Cerium Trihydride Stabilized at Ambient Conditions

New Cage-Like Cerium Trihydride Stabilized at Ambient Conditions

Criteria of Material Failure in Relation to Hydrogen Saturation

A steadily rising interest which specialists in various fields show towards the problem of hydrogen affecting metallic materials and causing their failure is connected to all-increasing requirements set on the durability of machines and equipment in operation. Metallic structures are most often surrounded by such environment which contains hydrogenous components or hydrogen itself (in chemical industry, power engineering, etc). And it leads to various types of degradation in metals (hydrogen embrittlement, hydrogen corrosion, and so on), which, in its turn, could cause catastrophic results. Ultimate strength is considered to be a representative parameter of the process of hydrogen degradation in steels. The authors cite the results of testing conducted on hydrogen-saturated specimens made of A516-55 steel which register a significant decrease in the ultimate strength. It is proposed to use a diagram which describes a fall in metal strength and transition of structural materials into their brittle states following an increase in hydrogen concentration. Discussion is made on criteria for hydrogen-saturated materials of metallic structures failing when a momentary overload occurs under default working conditions.

Studying Aluminum Alloy Defects

Aluminum is widely used in various industries in the form of alloys due to its unique properties - lightness, high electrical conductivity, and corrosion resistance. However, when casting alloys, various defects arise, the main of which are nonconformities of the ingot chemical composition, mechanical properties, and internal structure. The RUSAL Bratsk PJSC (, Irkutsk Region) aluminum alloy samples have been examined for pores, cracks, and oxide films. The causes of their occurrence have been analyzed and ways to eliminate these defects proposed. It has been found that, with increasing hydrogen content in the melt, micro-porosity leads to friability and macro-porosity of the alloy structure. According to the study results, the likelihood of cracks in the ingots could be reduced by evenly decreased metal temperature and casting velocity. The oxide film defects have been eliminated by feeding metal into the mold in a steady turbulence-free manner, increasing the metal settling time in a mixer, and reducing the alloy preparation time in a furnace.

Effect of fluidization/gasification parameters on hydrogen generation in syngas during fluidized-bed gasification process

This study discusses the influence of fluidization and gasification parameters on the hydrogen composition in syngas. For gasification conditions, when Stage 1 and Stage 2 gasifier temperature is 900 °C, the hydrogen content in syngas is 35.59 mol.% when the activated carbon is used as bed material. For using zeolite as bed material, the hydrogen content is 38.25 mol.%. The hydrogen content is higher than that under other conditions, but if the Steam/Biomass ratio is increased to 0.6, the hydrogen content resulted from zeolite as bed material is the highest 39.38 mol.%. For fluidization parameters, when Stage 2 bed material size is changed to 0.46 mm, no matter the bed material is activated carbon or zeolite, the hydrogen content in syngas is the best among three particle sizes. In terms of operating gas velocity, when gas velocity is 1.5 Umf, the hydrogen content is higher. For fluidization parameters, the two bed materials can increase hydrogen content in syngas effectively in Stage 2 fluidized bed, and their effects are similar to each other. However, considering the fluidization parameters, the hydrogen content in syngas when activated carbon is used as bed material is better than that when the zeolite is used.

Stress corrosion cracking and fracture behaviors of gaseous-hydrogenated Titanium alloy Ti-6321 during slow strain rate tests

The stress corrosion cracking (SCC) behavior of gaseous-hydrogenated near-alpha titanium alloy Ti-6321 in the range of 20 ∼ 210 wppm (ppm by weight) was investigated using slow strain rate test (SSRT). Optical Microscopy (OM), Scanning Electron Microscopy (SEM), as well as Transmission Electron Microscopy (TEM), were utilized to observe the microstructures of raw materials, fracture surfaces, cross-sectional areas of fracture surfaces, and the microstructures after deformation; Electron Backscattered Diffraction (EBSD) method was used to analyze the grain orientations so as to analyze the fracture behavior. The results showed that the Ti-6321 alloy revealed no SCC susceptibility in this range, and the material exhibited softening effect when hydrogen content was 65wppm and a hardening effect when hydrogen content exceeded 65wppm. With the increase of hydrogen concentration, the elongation increased because the mobility of dislocations and the nucleation of twins were simultaneously enhanced by hydrogen. In addition, microvoids’ growth and nucleation were inhibited by hydrogen in the matrix.

Segmented mandrel tests of as-received and hydrogenated WWER fuel cladding tubes

The mechanical interaction between the fuel pellet and the cladding tube of a nuclear fuel rod is a very important for safety studies as this phenomenon could lead to fuel failure and release of radioactivity. To investigate the ductility of cladding tubes used in WWER type nuclear power plants, several mandrel tests were performed in the Centre for Energy Research (EK). This modified mandrel test was used to model the mechanical interaction between the fuel pellet and the cladding using a segmented tool. The tests were conducted at room temperature and at 300 °C with inactive as-received and hydrogenated cladding ring samples. The results show a gradual decrease in ductility as the hydrogen content increases, the ductile-brittle transition was seen above 1500 ppm hydrogen absorbed.

Experimental investigation of combustion dynamics and NOx/CO emissions from densely distributed lean-premixed multinozzle CH4/C3H8/H2/air flames

Lean-premixed fuel-flexible combustion technology capable of operating on a wide range of fuels, including high or pure hydrogen, is expected to play a crucial role in reducing nitrogen oxides and carbon dioxide emissions from heavy-duty gas turbine engines, ultimately in achieving energy system decarbonization. However, fuel-flexible operations, particularly with high hydrogen content fuels, require a fundamental, drastic change from conventional nozzle architecture. The use of a number of small-scale multitube injectors – also referred to as micromix nozzles – is indispensable to reduce the likelihood of flashback events in ultra-fast premixed hydrogen flames. At present, the vast majority of what is known about the fundamental mechanisms of combustion dynamics and emissions stem from intensive research in large-scale swirl-stabilized flames. The behavior of small-scale multinozzle flames governed by isolated or collective movements of constituent flames remains, however, largely unexplored. To address these questions, we use densely distributed sixty-injector mesoscale flames as a platform to explore the influence of a full range of CH4/C3H8/H2 fuel blends – including all possible combinations of a blend of two different fuels (CH4 + C3H8, CH4 + H2, C3H8 + H2) and three different fuels (CH4 + C3H8 + H2), as well as single-component fuels (CH4, C3H8, H2) – on combustion dynamics and exhaust emissions under a constant adiabatic flame temperature condition. Here, we show that while the nitrogen oxide emissions are almost unaffected by the fuel compositions considered here, the variation of fuel composition has a significant impact on self-excited instabilities, which tend toward higher frequency oscillations with increasing hydrogen concentration. From phase-resolved OH PLIF measurements for a 50/50 mixture of CH4 and H2, we identify the creation, evolution, and annihilation of an array of coherent vortical structures as the mechanism responsible for sound generation and flame surface modulations without strong interactions between adjacent flames. In contrast, the behavior of the 50% C3H8 + 50% H2 case is dictated primarily by periodic merging and separation of neighboring reactant jets, leading to large-scale asymmetric oscillations in the transverse direction. Given the substantial change in transport properties, effective Lewis number-related interpretation provides a reasonable explanation for the different behaviors of a cluster of small-scale flames.

HYDROGEN IN MUNICIPAL ENERGY

The use of hydrogen in the municipal energy sector is currently inappropriate due to its high cost. Production of hydrogen by electrolysis requires more energy than it is emitted during its combustion. Thermophysical properties of hydrogen and natural gas are compared. Heat value of hydrogen in a unit of volume is 3.3 times lower than that of methane. The cost per unit of energy in hydrogen is more than 10 times higher than in natural gas. Distribution gas networks are not suitable for transportation of pure hydrogen. The possibility of transporting hydrogen in mixtures with natural gas is being studied. The efficiency of fuel use in a heating gas boiler decreases with increasing hydrogen concentration in a mixture with natural gas up to 50 %. The concentration of nitrogen oxides does not depend on the hydrogen content in the mixture. Bibl. 4, Table 1.

Determining failure properties of as-received and hydrided unirradiated Zircaloy-4 from ring compression tests

An integrated experimental and computational approach was developed to determine the plastic strain at fracture and to investigate the fracture energy of as-received and hydrided unirradiated Zircaloy-4 nuclear cladding tubes in the hoop direction at room temperature from ring compression testing (RCT). This work builds on previous methods in the literature that were developed to obtain the mechanical properties of nuclear cladding before fracture (Young’s modulus, yield stress, and strain-hardening parameters) from experimental RCT results and extends the characterization of this material class to include material failure properties. A ductile damage approach was developed and implemented in a validated finite element model to predict material failure, evaluate fracture energy, and quantify the plastic strain at fracture initiation. The hydrogen content of the Zircaloy-4 specimens was varied up to 610 wppm when the failure became brittle. As expected, increasing hydrogen content caused embrittlement of the Zircaloy-4 samples tested and the plastic strain at fracture and fracture energy to decrease

In-situ tensile deformation of Zircaloy-4 sheets with different hydrogen contents at RT and 300 °C

In this paper, the in-situ tensile deformation behaviors of Zircaloy-4 sheets with different hydrogen contents were investigated at room temperature (RT) and 300 °C. The results showed that at RT, the ultimate tensile strength (UTS) increased from 407 MPa to 508 MPa and the reduction of area (RA) decreased from 51% to 29% with the hydrogen content increased from 0 ppm to 850 ppm. When the hydrogen content reached 1300 ppm, both the UTS and RA dropped abruptly, showing an obvious ductile-brittle transition. The in-situ observations showed that for the un-hydrided samples, with the increase of tensile deformation, there first appeared slip deformation, then grain distortion and elongation, and finally crack initiation at the grain boundaries. For the hydrided samples, due to the precipitation of hydrides, the slip deformation and grain distortion were reduced, and the cracks trended to initiate around the hydrides. At 300 °C, the UTS increased from 246 MPa to 318 MPa and the RA decreased from 66% to 55.7% with the hydrogen content increased from 0 ppm to 850 ppm. When the hydrogen content reached 1300 ppm, no ductile-brittle transition was observed. The in-situ observations showed that for the un-hydrided and hydrided samples, with the increase of tensile deformation, they both exhibited good plastic deformation except more cracks initiated around the hydrides in the hydrided samples. The transmission electron microscope observations showed that at RT, with the increase of hydrogen content, the number of hydrides increased, and when the hydrogen content reached to a high level, these hydrides would intersect or collide with each other. However, at 300 °C, these hydrides were observed to be twisted or kinked after tensile deformation, which showed a good deformation ability. Based on these observations, the tensile deformation behavior of the hydrided samples was discussed. • A ductile-brittle transition occurs at hydrogen content of 850 ppm at RT. • Plastic deformation is reduced with the increase of hydrogen content at RT. • Intersect between hydrides is the reason for the ductile-brittle transition. • The ductile-brittle transition can be inhibited below 1300 ppm hydrogen at 300 °C.

Superior Hydrogen Sorption Kinetics of Ti0.20Zr0.20Hf0.20Nb0.40 High-Entropy Alloy

High entropy alloys (HEAs) are composed of multiple main metal elements and have attracted wide attention in various fields. In this study, a novel Ti0.20Zr0.20Hf0.20Nb0.40 HEA was synthesized and its hydrogenation properties were studied, including sorption thermodynamics and hydrogen absorption/desorption kinetics. The maximum hydrogen absorption capacity was 1.5 H/atom at 573 K. X-ray diffraction (XRD) analysis indicated that the crystal structure of Ti0.20Zr0.20Hf0.20Nb0.40 HEA transformed from body-centered cubic (BCC) to body-centered tetragonal (BCT) with increasing hydrogen content, and to face-centered cubic (FCC) after hydrogen absorption to saturation. As a multi-principal element alloy, the Ti0.20Zr0.20Hf0.20Nb0.40 HEA possesses unique hydrogen absorption characteristics. The hydrogen absorption platform pressure rises gradually with the increase of the hydrogen absorption amount, which is caused by multiple kinds of BCT intermediate hydrides with consecutively increasing c/a. The full hydrogen absorption of the Ti0.20Zr0.20Hf0.20Nb0.40 HEA was completed in almost 50 s, which is faster than that of the reported hydrogen storage alloys in the literature. The experimental results demonstrate that the Ti0.20Zr0.20Hf0.20Nb0.40 HEA has excellent kinetic properties, unique thermodynamic hydrogen absorption performance, as well as a low plateau pressure at room temperature.

Unusual hydrogen implanted gold with lattice contraction at increased hydrogen content

The experimental evidence for the contraction of volume of gold implanted with hydrogen at low doses is presented. The contraction of lattice upon the addition of other elements is very rare and extraordinary in the solid-state, not only for gold but also for many other solids. To explain the underlying physics, the pure kinetic theory of absorption is not adequate and the detailed interaction of hydrogen in the lattice needs to be clarified. Our analysis points to the importance of the formation of hydride bonds in a dynamic manner and explains why these bonds become weak at higher doses, leading to the inverse process of volume expansion frequently seen in metallic hydrogen containers.

Mechanical failure of high-burnup fuel rods with stress-relieved annealed and recrystallized M-MDA cladding under reactivity-initiated accident conditions

ABSTRACT To evaluate the effects of the hydride morphology and initial temperature of fuel cladding on the pellet-cladding mechanical interaction failure under reactivity-initiated accident (RIA) conditions, RIA-simulated experiments were performed on high-burnup fuels with stress-relieved annealed (SR) and recrystallized (RX) M-MDATM cladding at room and high (~280°C) temperatures. The results demonstrated that the failure-limit trend of RX-cladded fuels being lower than that of SR-cladded fuels for a similar hydrogen content holds up to at least about 700 wtppm. The observation of the fracture surfaces of failed RX cladding suggests a contribution of radially oriented hydrides to the crack formation and/or penetration, which coincides with the aforementioned failure-limit trend. The temperature effect, namely the failure-limit rise at a high temperature, is evident irrespective of the hydride morphology, while the degree of the temperature effect decreases as the hydrogen content increases.

Tensile properties evolution of hydrogen-induced TA10 titanium alloy welded joints

Hydrogen embrittlement of titanium alloy weldments often occur at low hydrogen concentrations. The effect of hydrogen content on tensile properties of titanium alloy welded joints and its mechanism were studied. The results show that with the increase of hydrogen content, the room temperature strength was significantly improved, the plasticity was significantly deteriorated. At 0.05 wt.% H, solid solution hydrogen had a limited effect on tissue strengthening and a slight increase in tensile strength; solid solution hydrogen reduced the pinning effect of solute atom on dislocation movement, yield strength decreased; solid solution hydrogen only depend on the diffusion and accumulation to cause the local micro-region hydrogen concentration to increase, which had a little effect on the plasticity. After 0.12 wt.% H, the pinning effect of the hydride was strengthened, the hydrogen-induced dislocation cross-slip was more difficult, and the strength at room temperature was significantly increased; the brittle hydride itself fractured, precipitated, or accelerated separation from the matrix, resulting in significant plasticity decline. When not charged with hydrogen or 0.05 wt.% H, the ductile fracture occurred in the welded joint; After 0.12 wt.% H, the brittle fracture was the main; solid solution hydrogen and the hydride had a direct effect on fracture mode transformation.

Sonochemical conversion of CO2 into hydrocarbons: The Sabatier reaction at ambient conditions

In this study, we investigated an alternative method for the chemical CO2 reduction reaction in which power ultrasound (488 kHz ultrasonic plate transducer) was applied to CO2-saturated (up to 3%) pure water, NaCl and synthetic seawater solutions. Under ultrasonic conditions, the converted CO2 products were found to be mainly CH4, C2H4 and C2H6 including large amount of CO which was subsequently converted into CH4. We have found that introducing molecular H2 plays a crucial role in the CO2 conversion process and that increasing hydrogen concentration increased the yields of hydrocarbons. However, it was observed that at higher hydrogen concentrations, the overall conversion decreased since hydrogen, a diatomic gas, is known to decrease cavitational activity in liquids. It was also found that 1.0 M NaCl solutions saturated with 2% CO2 + 98% H2 led to maximum hydrocarbon yields (close to 5%) and increasing the salt concentrations further decreased the yield of hydrocarbons due to the combined physical and chemical effects of ultrasound. It was shown that CO2 present in a synthetic industrial flue gas (86.74% N2, 13% CO2, 0.2% O2 and 600 ppm of CO) could be converted into hydrocarbons through this method by diluting the flue gas with hydrogen. Moreover, it was observed that in addition to pure water, synthetic seawater can also be used as an ultrasonicating media for the sonochemical process where the presence of NaCl improves the yields of hydrocarbons by ca. 40%. We have also shown that by using low frequency high-power ultrasound in the absence of catalysts, it is possible to carry out the conversion process at ambient conditions i.e., at room temperature and pressure. We are postulating that each cavitation bubble formed during ultrasonication act as a “micro-reactor” where the so-called Sabatier reaction -CO2+4H2→UltrasonicationCH4+2H2O - takes place upon collapse of the bubble. We are naming this novel approach as the “Islam-Pollet-Hihn process”.

Effects of deuterium content on the thermal stability and deuterium site occupancy of TiZrHfMoNb deuterides

A series of high entropy alloy (HEA) hydrides/deuterides were synthesized and characterized to explore the relationship between thermal stability and the structure of TiZrHfMoNb deuterides. The X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry results reveal that the lattice constant and cell volume of TiZrHfMoNb hydrides increase with the increasing hydrogen content. The desorption temperature decreases with the increasing hydrogen content, indicating that the increased lattice constant arising from the introduction of deuterium atoms will destabilize the HEA deuterides. A density functional theory calculations demonstrate that the binding energies between hydrogen and metals in BCC TiZrHfMoNb hydrides decline with the increasing hydrogen content, meaning that the thermal stability decreases with the increasing hydrogen content. The HEA deuterides are found to be more stable than their hydrides, implying the remarkable isotopic effect of TiZrHfMoNb HEA. Neutron powder diffraction refinements confirm that deuterium atoms prefer to occupy both of the tetrahedral and octahedral interstitials in BCC structure, while a prior occupation of tetrahedral interstitial sites in FCC structure. The deuterium/hydrogen concentrations and the lattice constants are proposed to be the major factor regulating the thermal stability of HEA deuteride, making them suitable for different application field of hydrogen storage.

Can Galaxy Evolution Mimic Cosmic Reionization?

Abstract Lyα emitting galaxies are powerful tools to probe the late stages of cosmic reionization. The observed sudden drop in Lyα fraction at z > 6 is often interpreted as a sign of reionization, since the intergalactic medium (IGM) is more neutral and opaque to Lyα photons. Crucially, this interpretation of the observations is only valid under the assumption that galaxies themselves experience a minimal evolution at these epochs. By modeling Lyα radiative transfer effects in and around galaxies, we examine whether a change in the galactic properties can reproduce the observed drop in the Lyα fraction. We find that an increase in the galactic neutral hydrogen content or a reduction in the outflow velocity toward higher redshift both lead to a lower Lyα escape fraction, and can thus mimic an increasing neutral fraction of the IGM. We furthermore find that this change in galactic properties leads to systematically different Lyα spectra which can be used to differentiate the two competing effects. Using the CANDELSz7 survey measurements which indicate slightly broader lines at z ∼ 6, we find that the scenario of a mere increase in the galactic column density toward higher z is highly unlikely. We also show that a decrease in outflow velocity is not ruled out by existing data but leads to more prominent blue peaks at z > 6. Our results caution using Lyα observations to estimate the IGM neutral fraction without accounting for the potential change in the galactic properties, e.g., by mapping out the evolution of Lyα spectral characteristics.

A model to determine the effects of low proportion of hydrogen and the flame kernel radius on combustion and emission performance of direct injection spark ignition engine

The only product of hydrogen combustion is water, so it is very clean. In this paper, the effects of low hydrogen content and FKR on the performance of the GDI engine are mainly studied. The simulation results show that adding less than 3% hydrogen in the GDI engine can improve the BP and BT of the engine under typical urban conditions such as 1500 rpm and 2000 rpm. As the hydrogen volume fraction and the FKR increase, the LFS of the mixture increases, resulting in a shorter ignition delay, combustion delay, and 10–90 % MFB. However, an increase in FKR results in a decrease in the BP and BT. In terms of fuel economy, the BSFC decreases as the hydrogen content increases, but as FKR increases, the BSFC increases. In terms of emissions, the proportion of hydrogen increases, HC and NOx emissions increase, and CO and CO2 emissions decrease. Therefore, adding hydrogen to the GDI engine while adjusting the FKR can improve the dynamic performance of the engine and reduce CO and CO2 exhaust emissions.

A density functional theory and neutron diffraction study of the ambient condition properties of sub-stoichiometric yttrium hydride

Several mechanical and thermophysical properties are required as a function of non-stoichiometry for the successful implementation of YH2-x for nuclear reactor moderator applications. Density functional theory calculations, in combination with neutron diffraction experiments, were used to study the structural and mechanical properties of YH2-x. Point defect analysis indicated H occupation primarily at the tetrahedral site within an fcc Y sub-lattice, confirming a fluorite YH2 structure. The small positive formation energy for H vacancies under Y-rich conditions predicted that hypo-stoichiometry is accommodated by Y+YH2 at ambient conditions and by H vacancies in the YH2-x single phase that is relevant to high temperatures. Neutron diffraction studies were used to confirm both the occupation of H on tetrahedral sites and the near-stoichiometric composition of the hydride phase in the two-phase Y+YH2 region of the phase diagram that dominates at room temperature. Energy minimized special-quasirandom-structures of H vacancies were used to calculate lattice parameters, elastic constants, and several other properties as a function of composition for the single phase YH2-x. The lattice parameter of YH2-x decreased by only 0.004 Å with increasing H/Y for the range 1.31≤H/Y≤2.0 indicating a negligible effect on lattice parameters due to vacancy formation. In the two-phase region, however, calculations predicted the density of zY+(1−z)YH2−x to increase with decreasing H/Y at lower temperatures due to the increased fraction of high-density Y metal. For the high temperature single phase, decreasing H/Y reduced the density as a consequence of the lattice expansion associated with vacancy formation. All elastic constants and moduli increased with increasing hydrogen content in single-phase YH2-x.

Structural Evolution of Hydrocarbon-Rich Coal of the Late Carboniferous Taiyuan Formation in Dongpu Sag

The coal system of the Taiyuan Formation in the Dongpu Sag is a good source rock. In this paper, the representative hydrogen-rich coal of the Taiyuan Formation is selected for pyrolysis experiments. We used high-resolution transmission electron microscopy and Fourier transform infrared spectroscopy to characterize the structural evolution of coal during thermal simulation, combined with the characteristics of gas and liquid products from low-maturity coal pyrolysis to comprehensively reveal the process of coal of the Taiyuan Formation to hydrocarbon. The results show that the evolution of a hydrogen-rich coal structure is mainly divided into five stages: (1) Before 350 °C: The content of aromatic hydrogen and the distance between aromatic layers are almost unchanged. The aromatic structure is mainly composed of naphthalene and 2 × 2 aromatic rings, indicating that polycondensation does not clearly occur. Liquid hydrocarbons reach their maximum amount due to liptinite cracking. (2) 350–400 °C: The aromatic layer distance rapidly decreases, indicating that considerable polycondensation occurs. The fatty acid hydrogen in vitrinite is gradually reduced, which is caused by cracking of the side chain of the vitrinite fat to generate gaseous hydrocarbons. The rapid decline in liquid hydrocarbons and total hydrocarbons and the rapid increase in the aromatic hydrogen content of vitrinite may be caused by the cyclization and aromatization of the long-chain fatty acid structure, which converts the liquid hydrocarbons back to a solid. (3) 400–450 °C: The aromatic layer distance is almost unchanged. The fatty acid hydrogen in vitrinite slowly decreases, and the aromatic hydrogen in vitrinite gradually increases. The large amount of gaseous hydrocarbon generated at this stage is partly due to the continued cleavage of the fatty acid side chains in vitrinite and partly from the cleavage of the fatty acid side chains from the solid formed by aromatization. (4) 450–550 °C: The aromatic layer distance rapidly decreases to the minimum, and aromatic rings with sizes above 4 × 4 increase rapidly. Aromatic hydrogen rapidly decreases to the minimum, and the fatty acid hydrogen of vitrinite quickly decreases to 0. Considerable polycondensation and demethylation reactions occur in the vitrinite to produce a large amount of gaseous hydrocarbon. (5) 550–600 °C: The aromatic layer distance and contents of fatty acid hydrogen and aromatic hydrogen in vitrinite change slowly. Additionally, the yields of gas and liquid do not change significantly, indicating that the polycondensation intensity decreases and that the vitrinite and liptinite are cracked without producing hydrocarbons.