Concentration Of Hydrogen Atoms Research Articles

Elemental carbon and hydrogen concentrations as the main factors in gas-phase graphene synthesis: Quantitative fourier-transform infrared spectroscopy study

Gas-phase microwave plasma-assisted synthesis of freestanding graphene is a promising route to produce high-quality graphene flakes. However, a comprehensive understanding of the gas-phase kinetics that is required to advance production rates and yields is still lacking. Here, we use line-of-sight Fourier-transform infrared (FTIR) absorption spectroscopy as an in situ diagnostic to measure gaseous species formed during graphene synthesis, thereby elucidating the chemical kinetics mechanism. Different carbonaceous precursors that lead to the formation of either few-layer graphene flakes or soot-like particles are examined, and the results are compared with numerical simulations and mass spectrometry measurements. Quantitative FTIR measurements show a correlation between concentration of atomic carbon and hydrogen in the post-plasma region and particle morphology. Lower carbon and higher hydrogen concentrations lead to graphene formation, while higher carbon and lower hydrogen concentrations shift the reaction toward soot-like particles. We also investigate how the precursor chemical composition, precursor flowrate, and delivered microwave power affect the carbon concentration in the post-plasma region, thus enabling to control particle morphology.

Numerical and Experimental Investigation of the Effect of Current Density on the Anomalous Codeposition of Ternary Fe-Co-Ni Alloy Coatings.

Gradient-structured ternary Fe-Co-Ni alloy coatings electrodeposited on steel substrates at various current densities from chloride baths were numerically and experimentally investigated. The electrodeposition process, considering hydrogen evolution and hydrolysis reaction, was modelled using the finite element method (FEM) and was based on the tertiary current distribution. The experimentally tested coating thickness and elemental contents were used to verify the simulation model. Although there was a deviation between the simulation and experiments, the numerical model was still able to predict the variation trend of the coating thickness and elemental contents. The influence of the current density on the coating characterization was experimentally studied. Due to hydrogen evolution, the coating surface exhibited microcracks. The crack density on the coating surface appeared smaller with increasing applied current density. The XRD patterns showed that the deposited coatings consisted of solid-solution phases α-Fe and γ (Fe, Ni) and the metallic compound Co3Fe7; the current density in the present studied range had a small influence on the phase composition. The grain sizes on the coating surface varied from 15 nm to 20 nm. The microhardness of the deposited coatings ranged from 625 HV to 655 HV. Meanwhile, the average microhardness increased slightly as the current density increased from 5 A/dm2 to 10 A/dm2 and then decreased as the current density further increased. Finally, the degree of anomaly along with the metal ion and hydrogen atom concentrations in the vicinity of the cathodic surface were calculated to investigate the anomalous codeposition behaviour.

Elastic deformation and elastic wave velocity of iron and its binary interstitial alloys: Temperature, pressure and interstitial atom concentration dependences

Based on the BCC binary interstitial alloy model with the condition that the interstitial atom concentration is very small compared to the main metal atom concentration and the elastic deformation theory of this alloy obtained on the basis of statistical moment method, we perform numerical calculations for elastic deformation quantities such as the elastic moduli E, K, G, the elastic constants C11, C12, C44, the longitudinal wave velocity Vd and the transverse wave velocity Vn of metal Fe and alloys FeSi, FeC, FeH. Numerical results for Fe are in good agreement with experiments and other calculations. The temperature and pressure dependence of the elastic deformation quantities for FeSi, FeC, FeH are similar to those for Fe. The elastic deformation quantities of FeSi, FeC, FeH in the range from 0 to 1000 K, from 0 to 10 GPa and from 0 to 5% of silicon (carbon, hydrogen) atom concentrations predict experimental results.

Effect of uniaxial tensile strain on binding energy of hydrogen atoms to vacancy-carbon-hydrogen complexes in α-iron

• The hydrogen binding energy to vacancies under uniaxial tensile strain was calculated. • The binding energy of hydrogen atoms to vacancies decreased with increasing strain. • The binding energy of hydrogen to vacancy-C complexes increased with increasing strain. • The hydrogen retention was estimated under uniaxial tensile strain. The hydrogen binding energy to vacancies or vacancy-carbon complexes in α -Fe under uniaxial tensile strain was calculated using the density functional theory. The solution energies of hydrogen and carbon decreased with an increase in the uniaxial tensile strain. With increasing strain, the binding energy of hydrogen atoms to vacancies also decreases; however, the binding energy of the vacancy-carbon complexes increases. The hydrogen retention was estimated under exposure to hydrogen gas. In the strained area, both the hydrogen concentration of the interstitial hydrogen atoms and the number of hydrogen atoms trapped in the vacancies increased. Therefore, hydrogen retention increased with increasing strain; however, the change in the hydrogen binding energy did not have a strong impact on the hydrogen retention. The presence of vacancies affects hydrogen retention more strongly. Although the binding energy of hydrogen atoms to vacancy-carbon complexes increased, the hydrogen retention in the Fe-C alloy was lower than that in pure Fe.

Effect of tensile stress on the hydrogen adsorption of X70 pipeline steel

The effect of stress on the cathodic hydrogen evolution behavior of X70 pipeline steel was investigated by electrochemical tests, tensile tests, and microstructural characterization. The results indicated that the tensile stress enhanced the activity of hydrogen adsorption sites on the metal surface, which was considered as the dominating factor affecting generation, adsorption, and permeation of hydrogen atoms. The subsurface hydrogen atom concentrations quantified by Cyclic voltammetry (CV) tests and the data calculated by hydrogen permeation experiments showed a good correspondence. The results indicated that the tensile stress enhanced the adsorption of hydrogen atoms on the surface and an inhibitory effect on the Tafel and Heyrovsky reaction, thereby leading to the increase of the subsurface hydrogen atom concentration, enhance the hydrogen embrittlement susceptibility of the X70 steel material as demonstrated by plasticity loss in the tensile tests.

Significant suppression of residual nitrogen incorporation in diamond film with a novel susceptor geometry employed in MPCVD

This work proposed to change the structure of the sample susceptor of the microwave plasma chemical vapor deposition (MPCVD) reaction chamber, that is, to introduce a small hole in the center of the susceptor to study its suppression effect on the incorporation of residual nitrogen in the MPCVD diamond film. By using COMSOL multiphysics software simulation, the plasma characteristics and the concentration of chemical reactants in the cylindrical cavity of MPCVD system were studied, including electric field intensity, electron number density, electron temperature, the concentrations of atomic hydrogen, methyl, and nitrogenous substances, etc. After introducing a small hole in the center of the molybdenum support susceptor, we found that no significant changes were found in the center area of the plasma, but the electron state in the plasma changed greatly on the surface above the susceptor. The electron number density was reduced by about 40%, while the electron temperature was reduced by about 0.02 eV, and the concentration of atomic nitrogen was decreased by about an order of magnitude. Moreover, we found that if a specific lower microwave input power is used, and a susceptor structure without the small hole is introduced, the change results similar to those in the surface area of the susceptor will be obtained, but the spatial distribution of electromagnetic field and reactant concentration will be changed.

Molecular dynamics simulations of the hydrogen embrittlement base case: atomic hydrogen in a defect free single crystal

ABSTRACT While significant research has been conducted on the various mechanisms of hydrogen embrittlement, there remains a lack of quantitative understanding on the effect of atomic hydrogen concentration on mechanical properties. Previous work suggests that an increased hydrogen concentration will degrade both the elastic modulus and yield stress. However, experimental samples often contain other atomistic defects that make it difficult to determine the role hydrogen alone plays on material behaviour. Further, experimental studies are often unable to directly quantify the effect of hydrogen concentration on modulus. The purpose of this study was to use molecular dynamics simulations to quantify the effect of interstitial hydrogen on the mechanical properties of iron. The potential type used was shown to significantly affected predicted results. Atomic hydrogen was shown to linearly degrade the elastic modulus and stress to initiate dislocations at all temperatures considered. Increasing hydrogen concentration was shown to promote the formation of dislocations at a lower stress, resulting in a higher density of dislocations and shorter slip distances. This study provides a foundation for better understanding of the role of hydrogen on the degradation of mechanical properties during loading.

Study of Hydrogen Embrittlement in Pipelines and Nuclear Power Plants: Estimates for Durability

Due to the increasing need to further develop the world gas and oil industry and the increased public attention to clean energy sources, studying and preventing Hydrogen Induced Cracking is one of the main safety concerns in nuclear power plants, oil pipelines and platforms. In this article, the growth and incubation times for internal Hydrogen Induced Cracks (HIC) are examined. Specifically, these times are modeled in two separate phases - the first phase (I) is a long time approximation, when the crack growth is believed to be slow such that the equilibrium state for gas concentration establishes instantaneously, and the stationary diffusion problem can be solved for each moment of time. The second phase (II) is a short time approximation, when the crack growth is rapid and the concentration of atomic hydrogen is dependent on time. Closed-form solutions are obtained in both cases and are then coupled using a Padé approximation.

Room-temperature coherence boosting of molecular graphenoids by environmental spectral decomposition

We explore the usage of pulse sequence optimization to boost the quantum properties of topological defects in molecular graphenoids at high temperatures. We reach spin-lattice relaxation times on the same order as those of the best quantum devices in the literature, $\ensuremath{\sim}1$ ms at room temperature. The coherence time is shown to be heavily affected by the hyperfine interaction and by the high concentration of hydrogen atoms in particular. We test and compare the applicability and performance of different decoupling sequences in enhancing the coherence, identifying the best-performing sequences for the purposes of robust state initialization and coherence optimization. Coherence times up to $30 \ensuremath{\mu}\mathrm{s}$ are reached, and we provide insight into the system-environment interaction mechanisms, with a semiclassical model that considers the nuclear bath as a source of a classical random noise and the dynamical decoupling as a filter function. Full deconvolution of the noise spectrum of the bath is obtained, and we show the noise density has a Lorentzian shape whose parameters describe the nuclear-bath dynamics.

On the effects of texture and microstructure on hydrogen transport towards notch tips: A CPFE study

Hydrogen embrittlement is an important degradation mechanism affecting the lifetime of engineering components. The diffusion of hydrogen atoms into the metal lattice can be affected by the localized stresses that develop around service-induced flaws. In addition, the magnitudes of flaw tip stresses are affected by the flaw geometry, as well as the texture and microstructure of the metal. Microstructural effects can be significant, particularly in metals such as zirconium with a high degree of elastic and plastic anisotropy. This study uses a coupled diffusion-crystal plasticity finite element approach to conduct a comprehensive study on the redistribution of hydrogen atoms in the vicinity of service-induced flaws in zirconium polycrystals. The effects of texture, grain size, and notch tip geometry on the concentration of hydrogen atoms in the lattice sites are investigated. The results indicate that material texture can significantly affect the distribution of hydrogen atoms as well as the location of maximum hydrostatic stress and maximum hydrogen concentration. The modeled highly textured microstructures have connected regions of peak hydrogen concentration. It is shown that as the notch tip becomes sharper, the effects of texture on the hydrogen localization near the notch become less significant. It is also shown that with changing grain orientations, it is possible to move the location of peak hydrogen concentration away from the notch tip.

The effect of hydrogen on the mechanical properties of metals under conditions of high-speed deformation

The movement of an ensemble of edge dislocations in metals with a high hydrogen content under conditions of high-speed deformation (high strain rate deformation) is theoretically analyzed. Within the framework of the theory of dynamic interaction of defects (DVD) (DID), an analytical expression is obtained for the dependence of the dynamic yield strength on the concentration of hydrogen atoms. Keywords: dislocations, hydrogen, high-speed deformation, metals.

Bottom-Up Evolution of Diamond-Graphite Hybrid Two-Dimensional Nanostructure: Underlying Picture and Electrochemical Activity.

The diamond-graphite hybrid thin film with low-dimensional nanostructure (e.g., nitrogen-included ultrananocrystalline diamond (N-UNCD) or the alike), has been employed in many impactful breakthrough applications. However, the detailed picture behind the bottom-up evolution of such intriguing carbon nanostructure is far from clarified yet. Here, the authors clarify it, through the concerted efforts of microscopic, physical, and electrochemical analyses for a series of samples synthesized by hot-filament chemical vapor deposition using methane-hydrogen precursor gas, based on the hydrogen-dependent surface reconstruction of nanodiamond and on the substrate-temperature-dependent variation of the growth species (atomic hydrogen and methyl radical) concentration near substrate. The clarified picture provides insights for a drastic enhancement in the electrochemical activities of the hybrid thin film, concerning the detection of important biomolecule, that is, ascorbic acid, uric acid, and dopamine: their limits of detections are 490, 35, and 25nm, respectively, which are among the best of the all-carbon thin film electrodes in the literature. This work also enables a simple and effective way of strongly enhancing AA detection.

Pd–Pb nanoscale films as surface modifiers of Pd,Cu alloy membranes used for hydrogen ultrapurification

The purpose of the article is to reveal the role of the thickness of the layer of the lead-palladium alloy deposited on a copper-palladium membrane in the processes of cathodic injection and the anodic extraction of atomic hydrogen.The objects of the study were ~ 4 μm thick copper-palladium film electrodes obtained by magnetron sputtering of a target with a composition of 56 at. % Cu and 44 at. % Pd. The studies were carried out by cyclic voltammetry and double step anodic-cathodic chronoamperometry in a deaerated 0.1 М H2SO4 aqueous solution. The calculation of the parameters of hydrogen permeability for samples of finite thickness was carried out by mathematical modelling.Cathodic injection and anodic extraction of atomic hydrogen were used to study the effect of the surface modification of the foil membrane of a Pd-Cu solid solution on the diffusion and kinetic parameters of hydrogen permeability. It was found that even a small addition of Pd-Pb (a 2 nm thick film) leads to a decrease in the concentration of atomic hydrogen and the diffusion coefficient in the foil. With an increase in the thickness of the coating there is an increase in the diffusion parameters of the hydrogen injection and extraction processes. However, the hydrogen permeability does not reach the level of the unmodified alloy. The main kinetic parameter, the hydrogen extraction rate constant, changes nonlinearly with an increase in the thickness of the coating.

Study on the characteristics of atomic hydrogen cleaning carbon contamination on multilayers

Mo/Si multilayers are widely used in synchrotron radiation beam-lines and extreme ultraviolet lithography machines. With the increasing power of light source, the problem of carboncontamination on multilayers becomes more and more serious. In-situ efficient and non-damage removal of carbon contamination becomes very necessary. Atomic hydrogen has been proved an effective particle to cleaning carbon without damage. However, the mechanism of atomic hydrogen cleaning carbon contamination is not completely understood now and the cleaning rate is slowly. In order to realize efficient and in situ cleaning of carbon contamination by atomic hydrogen, the influence of different conditions on the process of atomic hydrogen cleaning carbon contamination was researched with experiment firstly. Then, the characteristic relationship of working distance, temperature and atomic hydrogen concentration on the cleaning rate was identified to study the mechanism. The cleaning rate could reach 0.0347 nm/min. In the end, the change of optical properties and surface roughness of multilayer after cleaning were analyzed. The result was shown that the reflectivity of the samples could be effectively recovered and the surface roughness of the samples had little change after cleaning. The workhas great significance for realizing the efficient atomic hydrogen cleaning carbon contamination in-situ.

Influence of freezing and thawing on drainage behaviour for porous asphalt pavement based on molecular dynamics simulation

ABSTRACT To explore the influence of freezing and thawing on drainage behaviour for porous asphalt pavement (PA), molecular dynamics simulation was applied to study the interaction between asphalt and water. Based on the establishment and verification of micro models for asphalt (virgin and aged) and water (ice, ice–water mixture and water), the micro behaviour of interfacial transition zone was intuitively observed. Combined with the multi-gradient experiment results, the micro influence mechanism of freezing and thawing on drainage behaviour of porous asphalt pavement was revealed. The results show that the interaction energy of asphalt–water changes with the occurrence of freeze–thaw. The interaction energy (attraction) between aged asphalt and water is enhanced, which leads to water-induced distress more easily. In addition, with the occurrence of freeze–thaw, the relative concentration of hydrogen atoms at the interfacial transition zone gradually increases, while the fluctuation of carbon atoms increases. The results provide a micro-mechanism for the study of drainage behaviour of porous asphalt pavement under freezing and thawing, which has certain theoretical significance and practical value.

Study of Atomic Hydrogen Concentration in Grain Boundaries of Polycrystalline Diamond Thin Films

This paper describes research focused on investigating the effect of hydrogen (H) atom insertion into the grain boundaries of polycrystalline diamond (PCD) films. This is required in order to understand the key morphological, chemical, physical, and electronic properties of the films. The PCD films were grown using the hot filament chemical vapor deposition (HFCVD) process, with flowing Ar gas mixed with CH4 and H2 gases to control film growth into microcrystalline diamond (MCD, 0.5–3 µm grain sizes), nanocrystalline diamond (NCD, 10–500 nm grain sizes), and ultrananocrystalline diamond (UNCD, 2–5 nm grain sizes) films depending on the Ar/CH4/H2 flow ratios. This study focused on measuring the H atom concentration of the PCD films to determine the effect on the properties indicated above. A simple model is presented, including a hypothesis that the two dangling bonds per unit cell of C atoms serve as the site of hydrogen incorporation. This correlates well with the observed concentration of H atoms in the films. Dangling bonds which are not passivated by hydrogen are postulated to form surface structures which include C double bonds. The Raman peak from these surface structures are the same as observed for transpolyacetyline (TPA). The data reveal that the concentration of H atoms at the grain boundaries is around 1.5 × 1015 atoms/cm2 regardless of grain size. Electrical current measurements, using a conductive atomic force microscopy (CAFM) technique, were performed using an MCD film, showing that the current is concentrated at the grain boundaries. Ultraviolet photo electron spectroscopy (UPS) confirmed that all the PCD films exhibited a metallic behavior. This is to be expected if the nature of grain boundaries is the same regardless of grain size.

Experiments on tritium generation and yield from lithium ceramics during neutron irradiation

The vacuum extraction method with a mass spectrometry registration of tritium is presented in paper. It can provide a full-range analysis of gas phase composition in the chamber with samples under neutron irradiation. Lithium ceramics Li2TiO3 in the form of pebbles with lithium enrichment on 6Li isotope of 96% was examined.The paper shows the results of reactor experiments on study the extraction of tritium-containing molecules from lithium ceramics Li2TiO3 at various temperatures and reactor power levels at the WWR-K research reactor (Almaty, Kazakhstan). The time dependences of tritium yield from the ampoule with ceramics during reactor irradiation were obtained. Near-surface concentrations of tritium and hydrogen atoms on the ceramics surface under reactor irradiation were estimated.

Optical emission spectroscopy of radio frequency inductively coupled plasma for cold hydrogenation of nanoparticles

The radio frequency inductively coupled plasma (ICP) offers an alternative “cold” way to affect the size, composition, structure, and surface functionality of nanoparticles (NPs), such as metal oxide NPs, providing further adjustment of their physical and chemical properties. The ICP was monitored in-situ by optical emission spectroscopy (OES). In particular, hydrogen, oxygen, argon, and nitrogen plasma was studied. OES data show that despite the decrease of the optical emission intensity with increasing gas pressure, the concentration of atomic hydrogen increases with pressure and radio frequency power.

Detailed experimental and kinetic modeling study of toluene/C2 pyrolysis in a single-pulse shock tube

Abstract A combined experimental and kinetic modeling study is carried out to explore the influences of acetylene and ethylene addition on the species formation from toluene pyrolysis. Experiments are conducted separately with four different argon-diluted binary toluene/C2 mixtures in a single pulse shock tube at a nominal pressure of 20 bar over a temperature range of 1150−1650 K. All the experimental mixtures contain about 100 ppm toluene and different amounts of C2 fuels (50, 216, 459 ppm acetylene and 516 ppm ethylene). Species concentrations as a function of the temperature are probed from the post-shock gas mixtures and analyzed through the gas chromatography/gas chromatography-mass spectrometry techniques. A kinetic model is developed, which successfully predicts the absolute species concentration measurements as well as the changes brought by the varied fuel compositions. With the neat fuel decomposition profiles as a reference, both fuel components exhibit increased reactivity in the pyrolysis of all studied binary mixtures, indicating the existence of obvious synergistic effects. In particular, such effects become more remarkable when increasing the initial acetylene concentration. This essentially results from the addition-elimination reaction of a toluene fuel radical and a C2 fuel molecule leading to a C9 molecule and a hydrogen atom. Indene is identified as the predominant C9 product in all studied cases, and its peak concentrations sharply increase with the initial acetylene contents in toluene-acetylene pyrolysis. On the other hand, indane, produced from the addition-elimination reaction between benzyl and ethylene, is only detected at trace levels in toluene/ethylene pyrolysis. This indicates a relatively weaker interaction between benzyl and ethylene, compared to that of benzyl and acetylene. Apart from the increased concentrations of hydrogen atoms and C9 aromatics, interactions between toluene and C2 fuels also directly result in a reduced level of C7 radicals in the reaction system. Overall, PAH species can be divided into two groups according to the way their peak concentrations varying with the initial fuel compositions. For those largely depending on benzyl reactions, such as bibenzyl, biphenylmethane, fluorene and phenanthrene, the peak concentrations decrease with the added C2 fuels. In contrast, increasing trends are observed in the peak concentrations of the PAHs which rely on indenyl as a precursor, including naphthalene, methyl-indene, benzofulvene and acenaphthalene.

Secondary-Ion Mass Spectroscopy for Analysis of the Implanted Hydrogen Profile in Silicon and Impurity Composition of Silicon-on-Insulator Structures

Theoretical and experimental data are reported for the distribution of hydrogen in silicon in SiO2–Si structures after the implantation of hydrogen. Hydrogen is implanted under conditions used in preparing silicon-on-insulator structures by the hydrogen transfer technology. A technique for quantitative estimation of implanted hydrogen high concentrations in silicon using secondary-ion mass spectrometry is suggested. It includes the quantitative calibration of the hydrogen atom concentration and normalization of the depth of analysis from sputtering time. Data for the implanted hydrogen depth distribution in silicon and in Si–SiO2 structures are presented. The lateral uniformity and temporal stability of implanted structures have been monitored.