Hydrogen Saturation Research Articles

Positron Spectroscopy of Nanodiamonds after Hydrogen Sorption.

The structure and defects of nanodiamonds influence the hydrogen sorption capacity. Positronium can be used as a sensor for detecting places with the most efficient capture of hydrogen atoms. Hydrogenation of carbon materials was performed from gas atmosphere. The concentration of hydrogen absorbed by the sample depends on the temperature and pressure. The concentration 1.2 wt % is achieved at the temperature of 243 K and the pressure of 0.6 MPa. The hydrogen saturation of nanodiamonds changes the positron lifetime. Increase of sorption cycle numbers effects the positron lifetime, as well as the parameters of the Doppler broadening of annihilation line. The electron-positron annihilation being a sensitive method, it allows detecting the electron density fluctuation of the carbon material after hydrogen saturation.

Comparison of resistance to damage of unalloyed carbon steels under the influence of hydrogen

One of the most commonly used construction material in industry is unalloyed steel S235 and S355. These types of steel are used for construction of ships, bridges, coastal construction, welded tanks, and in buildings. Due to the operating conditions, these types of steel may undergo hydrogen degradation in the process of manufacturing of welded structures or when operating the structures. This paper presents the results of study into resistance of selected types of non-alloy structural steels to hydrogen degradation. Tests were carried out to determine changes in mechanical properties in the static trials of stretching without hydrogen, and after saturation with hydrogen. Parallel fractographic and electrochemical studies were carried out. Hydrogen saturation was carried out at the time from 3. up to 24. hours in a solution of 0.1N H2SO4 with the addition of 2 mg/dm3 arsenic oxide (III) at an electric current density of 20 mA/cm2. The results of the tests have shown that the impact of hydrogen on the tested steels S235JR and S355J2 leads to a significant deterioration in their mechanical and electrochemical properties. At comparable concentrations of hydrogen, steel S235JR is less susceptible to hydrogen degradation and has greater corrosive resistance measured in 3% NaCl solution, in comparison with steel S355J2.

Dominant Kinetic Pathways of Graphene Growth in Chemical Vapor Deposition: The Role of Hydrogen

The most popular way to produce graphene nowadays is chemical vapor deposition, where, surprisingly, H$_2$ gas is routinely supplied even though it is a byproduct itself. In this study, by identifying dominant growing pathways via multiscale simulations, we unambiguously reveal the central role hydrogen played in graphene growth. Hydrogen can saturate the edges of a growing graphene island to some extent, depending on the H$_2$ pressure. Although graphene etching by hydrogen has been observed in experiment, hydrogen saturation actually stabilizes graphene edges by reducing the detachment rates of carbon-contained species. Such a new picture well explains some puzzling experimental observations and is also instrumental in growth protocol optimization for two-dimensional atomic crystal van der Waals epitaxy.

Density functional theory study of the interaction of hydrogen with TMC2H2(TM=Sc-Ni)

Different aspects of the hydrogen storage properties of TMC2H2 (TM = Sc-Ni) were evaluated using density functional theory and ab initio molecular dynamics calculations. Hydrogen saturation conformations indicate that the hydrogen gravimetric density of TMC2H2 (TM = Sc-Ni) is 4.54–12.43%. The free energy profiles and first-principles molecular-dynamics (MD) simulations showed that when the first H2 molecule attaches to TMC2H2 (TM = Sc, Ti), the H2 molecule is first dissociated over Ti/Sc, and then, one of the H atoms goes to a carbon atom, forming a CH2 group. That is, there are two types of hydrogen bonding in TiC2H2 and ScTiC2H2: the first set of hydrogen binds to C, and the subsequent set of hydrogen binds to Ti/Sc. Importantly, TiC2H2 is able to bind five H2 molecules with the hydrogen gravimetric density of 12.00%, regardless of CH2 group formation. However, ScC2H3H can bind only three H2 molecules, reducing the gravimetric uptake capacity of ScC2H2 from 12.43% to 10.13%. For TMC2H2 (TM = V, Cr, Mn), the first hydrogen molecule is dissociated, but there is no “spillover effect”. For TMC2H2 (TM = Fe, Co, Ni), the first hydrogen molecule is bound quasi-molecularly. Most of our findings, such as those regarding H2 dissociation and TMC2H3H formation, should be valid for other TM-decorated nanostructures.

Hydrogen Flux through Size Selected Pd Nanoparticles into Underlying Mg Nanofilms

AbstractThe application of Mg for hydrogen storage is hindered due to the slow absorption of hydrogen in Mg films. Herein, the hydrogenation process is explored theoretically using density functional theory calculations, and energy barriers are compared for hydrogen diffusion through Pd nanoparticle/Mg film interfaces and their variations, i.e., Pd(H)/Mg(O). Decomposing the mechanism into basic steps, it is shown that Pd undergoes a strain‐induced crystallographic phase transformation near the interface, and indicated that hydrogen saturation of Pd nanoparticles enhances their efficiency as nanoportals. Using energetic arguments, it is explained why hydrogen diffusion is practically prohibited through native Mg oxide and seriously suppressed through existing hydride domains. Hydrogen flux is experimentally investigated through the nanoportals in Pd‐nanoparticle decorated Mg films by pressure‐composition isotherm measurements. An r ≈ t1/3 relationship is theoretically calculated for the radial growth of hemispherical hydride domains, and this relationship is confirmed by atomic force microscopy. The diffusion constant of hydrogen in Mg films is estimated as DHfilm ≈ 8 × 10−18 m2 s−1, based on transmission electron microscopy characterization. The unique nanoportal configuration allows direct measurement of hydride domain sizes, thus forming a model system for the experimental investigation of hydrogenation in any material.

Luminescence in germania-silica fibers in a 1-2μm region.

We analyze the origins of the luminescence in germania-silica fibers with high germanium concentration (about 30mol.% GeO2) in the region of 1-2μm with a laser pump at the wavelength 532nm. We show that such fibers demonstrate the high level of luminescence which unlikely allows the observation of photon triplets, generated in a third-order spontaneous parametric downconversion process in such fibers. The only efficient approach to the luminescence reduction is the hydrogen saturation of fiber samples; however, even in this case, the level of residual luminescence is still too high for three-photon registration.

Positron Spectroscopy of Defects in Hydrogen-Saturated Zirconium

Zirconium alloys, such as Zr-1Nb are widely used as cladding materials for nuclear fuel elements of light water reactors. Hydrogen embrittlement problem causes degradation of these parts of nuclear reactors. It is known, that hydrogen uptake causes changes in microstructure and defect structure of metals. The aim of this work is study of Zr-1Nb alloys’ defect structure after hydrogen saturation up to the concentration of 600 ppm. Saturation of hydrogen was carried out from the gas phase under high temperature and pressure. This study reveals the increase of average positron lifetime with the increase of hydrogen concentration. Value of the average positron lifetime achieves plateau when the concentration of hydrogen is about 600 ppm. Also the following effects were detected in the material after hydrogen uptake up to different concentrations: crystal lattice expansion, dislocations and vacancy-like defects formation, as well as the defect-hydrogen complexes formation.

Hydrogen saturation and permeation barrier performance of yttrium oxide coatings

In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel inventory. Moreover, the tritium permeation barrier is necessary to avoid that the situation the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Er2O3 and Y2O3, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for Y2O3 due to its favorably low activation behavior compared to the other candidates. Y2O3 thin films are deposited on the reduced activation steel Eurofer97 by means of magnetron sputtering. To quantify the permeation reduction factor of the Y2O3 thin films a new gas-driven deuterium permeation measurement setup was constructed. Comparing the permeation flux through a bare substrate and a coated Eurofer97 substrate, the permeation reduction factor can be determined. The measurement results suggest that the permeation reduction factor is in the same range as for Er2O3. Moreover, the morphological analysis and the permeation measurements indicate that the long term stability of the permeation barrier performance depends on the deuterium saturation in the Y2O3 thin film.

Oxygen effects on the structure and hydrogenation activity of the MoS2 active site: A mechanism study by DFT calculation

Density functional theory (DFT) calculation with numerical atomic functions is used to study oxygen effects on MoS2 hydrotreating active sites. The optimal form of oxygen on active sites is first investigated by experimentation and calculation. Then, the fine structures of a MoS2 nanocluster (S-Mo-S) and an oxygen containing MoS2 nanocluster (O-Mo-S) under reaction conditions, as well as their hydrodesulfurization (HDS) selectivity towards thiophene, are calculated. The results show that bent MoS2 nanoclusters in supported hydrotreating catalysts are more thermodynamically stable when oxygen is substituted for sulfur on the basal plane. Oxygen also reduces the electron density and unoccupied d-orbital energy levels of Mo atoms. The S atoms on the Mo-edge are also more readily substituted by H on O-Mo-S. During thiophene HDS, O-Mo-S has a stronger thiophene adsorption ability than S-Mo-S. Hydrogen transfer has a higher energy requirement along the Mo-edge on O-Mo-S than on S-Mo-S. The hydrogenation saturation activity to CC is lower on the Mo-edge of O-Mo-S than of S-Mo-S, whereas the hydrogenolysis activity at the CS bond is promoted by oxygen. It is predicted that the oxygen can increase the hydrogenolysis selectivity of a MoS2 active nanocluster.

К проблеме водородного охрупчивания стали при каплеударной эрозии

Introduction. The work is devoted to the problem of the hydrogen saturation of steel parts skin at their high-speed impacts with a water-drop flow. A hypothesis of the water molecules dissociation at high-speed drop impacts was suggested in a number of papers. This hypothesis was confirmed by some experimental data. The effect of this dissociation is hydrogen embrittlement of the metal surface layer. The work objective is the calculation and experimental verification of the given mechanism of the erosion destruction of the steel surface. Materials and Methods. Energy equations of various ways of the water molecules dissociation are considered for the calculation-analytical estimates. The Tate and van der Waals equations are used with allowance for the change in the phase states of water at impact. Experimental data are obtained on the basis of spectral analysis using visible monochromatic (qualitative analysis) and infrared (quantitative analysis) emissions. Research Results. An improved calculation apparatus is proposed to determine the energy level of the water molecules dissociation and free hydrogen release with account for the compressibility of water at achievable impact speeds. The results of spectral studies of bubble tracks formed on the experimental steel samples under the bench erosion tests are presented. The spectral analysis shows that the tracks are composed of air bubbles. Free hydrogen is not detected in them. Discussion and Conclusions. The calculated and experimental data obtained in this paper do not give grounds for confirming the hypothesis of hydrogen dissociation under the water-drop impacts with a steel surface in the impact velocity range of 200-600 m / s. Therefore, the mechanism of hydrogen embrittlement, apparently, should be excluded from the number of additive components of the droplet impingement erosive wear.

Influence of tensile stresses on the corrosion resistance of titanium alloy VT22 in aqueous solution of NaCl

How tensile stresses and pH value influence the passivation, corrosion, and structure of a protective film of two-phase titanium alloy VT22 in 3% solution of NaCl is investigated with the help of potentiometry, potential and dynamical analysis, and electrical and chemical impedance spectroscopy. We simulate the process of electrical transfer through the protective film and we reveal that its structure is two-layered. The film consists of a layer based on titanium hydroxide under which there is a titanium oxide layer adjacent to the alloy and primarily it protects the alloy against corrosion. How tensile stresses and pH value influence the hydrogen saturation process and delayed fracture of titanium in an aqueous NaCl solution is investigated.

Effect of hydrogenation on mechanical properties and tensile fracture mechanism of a high-nitrogen austenitic steel

Austenitic stainless steels are frequently used for hydrogen applications due to their high ductility at low temperatures and lower hydrogen environment embrittlement compared to ferritic steels. We study the effect of electrochemical hydrogen saturation up to 40 h on tensile behavior and fracture mechanisms in high-nitrogen austenitic 17Cr–24Mn–1.3V–0.2C–1.3N steel. Hydrogen saturation weakly influences the characteristic of stress–strain curves, but decreases steel ductility, yield stress, and ultimate tensile stress. Hydrogenation provides a change in steel fracture peculiarities—a hydrogen-assisted thin brittle surface layer of ≈5 μm and ductile subsurface layer of 50–150 μm in width in hydrogen-saturated specimens. The subsurface layer shows ductile transgranular fracture with elongated dimples and flat facets. The central parts of fracture surfaces for hydrogenated specimens show ductile fracture mode similar to hydrogen-free state, but they include numerous secondary cracks both for central part and for transition zone between ductile central part and subsurface layer associated with highest hydrogen saturation. The possible reasons of decrease in hydrogen-associated ductility and change in fracture character are discussed.

Фізико-технологічна аналіза наводнення титану у різних станах

Фізико-технологічна аналіза наводнення титану у різних станах

Effect of titanium ion implantation and deposition on hydrogenation behavior of Zr-1Nb alloy

In order to study the effect of titanium ion implantation and deposition on hydrogenation behavior of Zr–1Nb alloy, the samples were subjected to plasma immersion implantation and deposition (PIII&D) of titanium ions at the bias voltage of 0.5–1.5kV using a filtered metal vapor vacuum arc source. The crystalline structure, surface morphology and depth distributions of elements in the surface layer of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and glow-discharge optical emission spectroscopy (GD-OES), respectively. Hydrogen saturation was performed from hydrogen atmosphere at 673K temperature and 2atm. pressure. It was found that hydrogen absorption rate by Zr–1Nb alloy decreased after PIII&D. The modified layers contained a mixing zone of titanium and zirconium, which decreases with increasing bias voltage. Hydrogenation causes the formation of titanium hydrides and lattice distortions of α–Zr at the low bias voltage that does not occur at higher bias voltages. The hydrogenation behavior of modified zirconium alloy was discussed.

Gas release from an E125 zirconium alloy under hydrogenation and deformation conditions

The degassing from a hydrogen-saturated E125 zirconium alloy is studied as a function of its deformation. Zirconium alloy samples are subjected to tension at a relative elongation of 2.5, 5, and 10%. Undeformed and deformed samples were saturated with hydrogen by a galvanic method at a current density of 0.5 A/cm2; that is, they are hydrogen saturated and then deformed. As a result, the defects at which hydrogen is trapped in zirconium are identified. The quantity of hydrogen trapped by defects depends on the strain and the sequence of deformation and hydrogen saturation. This is a technical result of the investigations, which can be used to find optimum operation conditions for hydrogen-saturated zirconium articles.

High stability of palladium/kieselguhr composites during absorption/desorption cycling for hydrogen isotope separation

Palladium/kieselguhr (Pd/K) composites with 57wt.% of Pd were prepared by an improved dipping and thermal decomposition method and heated at elevated temperature to reduce breakdown during hydrogenation-dehydrogenation cycles. The hydrogen absorption kinetic properties of the samples heated at different temperatures were tested under the condition of 20°C with 100kPa hydrogen pressure. The 1300°C heated Pd/K composites were repeated up to 4010 absorption and desorption cycles at temperature ranges between −40°C and 200°C. The results show that the phase structure, hydrogen absorption capacity and hydrogen saturation time of the Pd/K were not affected by the change of heat-treated temperatures. And after heat treatment at 1300°C, the Pd/K particles were strengthened and fraction of larger than 80mesh were as high as 93.4%.

Refinery oil upgrading under methane environment over PdOx/H-ZSM-5: Highly selective olefin cyclization

Olefin content minimization is critical for the long-term storage and long-distance transportation of oil product, which is commonly achieved through hydrogen saturation at high pressure to form paraffin. In this study, a novel catalytic process is reported to convert olefin to cycloalkane under methane environment with high selectivity. The main components of the product oil collected over Pd/ZSM-5 catalysts during olefin model compound (i.e., 1-decene) upgrading are cyclopentane, 1-methylbutyl- and cyclopentane, hexyl- while there are more than 46 species identified in the liquid product from the run with H-ZSM-5 support engaged. The total selectivity of the aforementioned cycloalkane products is up to 91.3% when 0.27wt% Pd/ZSM-5 catalyst is charged, thus making the product oil more profitable. The HRTEM and XPS data reveal that the highly dispersed palladium particles are in the form of PdOx. The results from pyridine FT-IR and NH3-TPD indicate that these PdOx species anchored onto the surface acidic sites exhibit the moderate acidic feature of Lewis acidic sites, which enhances the formation and stabilization of carbenium ion intermediates generated from 1-decene cracking. The strong interaction between PdOx species and surface acidic sites could not only stabilize the particle size and modify the electronic structure of Pd species but also modulate the acidic properties of ZSM-5 support, leading to promoted methane activation which would not only release sufficient hydrogen donors for preventing olefin aromatization, but also inhibit the over-cracking of carbenium ions. As a result, the selectivity of catalyst assisted olefin cyclization under methane environment is greatly enhanced.

Influence of the Electrization of Wet Steam Flow and Electric Fields on a Change in Mechanical Properties of the Materials of Turbine Rotor Blades

This scientific paper gives consideration to experimental data obtained for the influence produced by electrically charged wet steam flow and electric fields on the mechanical properties of materials used for rotor blades. It was established that the charge sign of the steam flow affects a change in microhardeness and a degree of the hydrogen saturation of blade material. The microhardness and the degree of hydrogen saturation of the blade material are affected not only by the flow charge but also by the availability of the electric charge on the specimen and its sign. A linear correlation between the degree of change in the concentration of hydrogen in the metal and the degree of change in its microhardness in test conditions is not observed. This scientific paper gives the analysis of experimental data and it also studies possible mechanisms of changes in the mechanical properties of test materials.

Exceptional Thermal Conductance across Hydrogen‐Bonded Graphene/Polymer Interfaces

Ineffective heat transfer between dissimilar materials of drastically different properties is a challenge for many areas including nanoelectronics and nanocomposites. Here, using atomistic simulations, it is demonstrated that the thermal conductance across the interfaces between graphene and poly(methyl methacrylate) (PMMA) can be improved by 273% by introducing hydrogen‐bond‐capable hydroxyl groups to the interfaces. Stronger than van der Waals interactions, the hydrogen bonds are found to improve the interfacial association, thereby enhancing the coupling of low‐frequency vibrational modes. Using the integrated autocorrelation of interfacial heat power, it is shown directly that the hydrogen bond donors, i.e., oxygen atoms in the hydroxyl groups, build the most effective thermal transport pathways at the graphene/PMMA interfaces. The enhanced interfacial thermal conductance is tunable in a wide range by varying the degree of functionalization, with an upper limit imposed by the saturation of hydrogen bonding. All these results suggest the design of “hydrogen‐bonded material interfaces” for drastically improving interfacial thermal transport toward a wide range of applications.

Recommendations on Alleviating the Saturation of Slab Metal by Hydrogen Based on the Results of Physical Modeling

This article discusses reducing the hydrogen content of low-alloy steels for oil and gas line pipe and shipbuilding and improving these steel’s ductility. In addition to the saturation of the liquid steel with hydrogen, it is also possible for the steel’s hydrogen content to increase after it has solidified. For example, this could occur when slabs are heated in furnaces that are fired with certain types of fuel and have different atmospheres. When a furnace is fired with coke-oven gas and the internal pressure in the furnace is positive, the high hydrogen content of this gas helps saturate the steel with hydrogen. That in turn increases the steel’s contents of discontinuities and nonmetallic inclusions, which leads to the formation of structural stress concentrators and a decrease in ductility. Results are presented from physical modeling of the saturation of pipe steel with hydrogen during the heating of slabs made of the above-indicated types of steel. Aspects of the steel’s saturation in different furnaces atmospheres are examined, the degree of contamination of the steel by hydrogen is determined, and the formation of its structure and hydrogenation are studied. It is definitively established that an increase in the moisture content of the furnace atmosphere increases the degree of saturation of the steel by hydrogen. Recommendations are given on alleviating the hydrogen saturation of steel. It is noted in particular that it is necessary to replace coke-oven gas by natural gas for the slab-heating operation, shorten the heating time to an acceptable extent, and establish the correct values for gas pressure and the gas/air ratio in the furnace.