Hydrogen-rich Environment Research Articles

Tunable Hydrogen-Related Defects in ZnO Nanowires Using Oxygen Plasma Treatment by Ion Energy Adjustment.

The chemical bath deposition (CBD) process enables the deposition of ZnO nanowires (NWs) on various substrates with customizable morphology. However, the hydrogen-rich CBD environment introduces numerous hydrogen-related defects, unintentionally doping the ZnO NWs and increasing their electrical conductivity. The oxygen-based plasma treatment can modify the nature and amount of these defects, potentially tailoring the ZnO NW properties for specific applications. This study examines the impact of the average ion energy on the formation of oxygen vacancies (VO) and hydrogen-related defects in ZnO NWs exposed to low-pressure oxygen plasma. Using X-ray photoelectron spectroscopy (XPS), 5 K cathodoluminescence (5K CL), and Raman spectroscopy, a comprehensive understanding of the effect of the oxygen ion energy on the formation of defects and defect complexes was established. A series of associative and dissociative reactions indicated that controlling plasma process parameters, particularly ion energy, is crucial. The XPS data suggested that increasing the ion energy could enhance Fermi level pinning by increasing the amount of VO and favoring the hydroxyl group adsorption, expanding the depletion region of charge carriers. The 5K CL and Raman spectroscopy further demonstrated the potential to adjust the ZnO NW physical properties by varying the oxygen ion energy, affecting various donor- and acceptor-type defect complexes. This study highlights the ability to tune the ZnO NW properties at low temperature by modifying plasma process parameters, offering new possibilities for a wide variety of nanoscale engineering devices fabricated on flexible and/or transparent substrates.

Designing Dual-Site Catalysts for Selectively Converting CO2 into Methanol.

The variability of CO2 hydrogenation reaction demands new potential strategies to regulate the fine structure of the catalysts for optimizing the reaction pathways. Herein, we report a dual-site strategy to boost the catalytic efficiency of CO2-to-methanol conversion. A new descriptor, τ, was initially established for screening the promising candidates with low-temperature activation capability of CO2, and sequentially a high-performance catalyst was fabricated centred with oxophilic Mo single atoms, who was further decorated with Pt nanoparticles. In CO2 hydrogenation, the obtained dual-site catalysts possess a remarkably-improved methanol generation rate (0.27 mmol gcat. -1 h-1). For comparison, the singe-site Mo and Pt-based catalysts can only produce ethanol and formate acid at a relatively low reaction rate (0.11 mmol gcat. -1 h-1 for ethanol and 0.034 mmol gcat. -1 h-1 for formate acid), respectively. Mechanism studies indicate that the introduction of Pt species could create an active hydrogen-rich environment, leading to the alterations of the adsorption configuration and conversion pathways of the *OCH2 intermediates on Mo sites. As a result, the catalytic selectivity was successfully switched.

Competitive adsorption mechanism of SiHCl3 with BCl3 under a hydrogen atmosphere: Boron impurities introduction into polysilicon

The primary method for electronic-grade (EG) polysilicon production is the modified Siemens process. Unfortunately, the EG polysilicon produced through this method contains excessive levels of boron impurities (> 0.2 ppb), thereby diminishing the product quality. This issue impedes the large-scale production of EG polysilicon. This study establishes the structure of the Si (100) surface within a hydrogen-rich environment under the BCl3-SiHCl3-H2 system and investigates the adsorption mechanisms of BCl3 and SiHCl3, as well as the competitive adsorption mechanism of BCl3-SiHCl3, on the Si (100) surface. The results indicate that the adsorption energy barriers for BCl3 and SiHCl3 on the Si (100) surface are 7.8383 kJ·mol−1 and 229.6970 kJ·mol−1, respectively, so that the preferential adsorption of BCl3 onto the Si (100) surface over SiHCl3. The B atom and the Si atom are competing for adsorption on the Si (100) surface and creating an ab-B-Si-ab structure, and the optimal adsorption path is as follows: ab-BCl3→ab-BCl2→ab-BCl2-SiHCl3→ab-BCl-SiHCl3→ab-B-SiHCl3→ab-B-SiHCl2→ab-B-SiHCl→ab-B-SiH-ab→ab-B-Si-ab.

Laser chemical vapor deposition of TiC fibers and tubes

Laser Chemical Vapor Deposition (LCVD) is a process in which fibers are deposited from a gaseous precursor to a solid phase under a traversing laser focal point. Here, we grow titanium carbide (TiC) fibers and tubes dependent upon a hyperbaric hydrogen-rich, hydrogen-balanced, and hydrogen-lean environment referenced to a titanium tetrachloride and ethylene gas mixture under three different laser intensities. X-ray diffraction confirms the deposition of TiC with energy dispersive spectroscopy noting a radial compositional gradient of titanium and carbon in the diameter of the deposit. Depending on the hydrogen concentration, the TiC encased a core carbon-rich fiber or formed a hollow tube, with these formations explained by thermophoresis. Furthermore, depending on the gas mixture and laser intensity, the carbon-rich interior and TiC outer shell exhibited different morphologies that are discussed in terms of growth rate regimes. The collective outcomes demonstrate the complex processing space in forming ceramic materials by LCVD.

Hydrogen-enhanced densified deformation twins in 304L austenitic stainless steel fabricated by selective laser melting

Twin boundaries are the preferred site for crack nucleation and propagation in a hydrogen-rich environment. The relationship among hydrogen, cellular structure, and deformation twins is significant in further enhancing the resistance to hydrogen embrittlement of austenitic stainless steels produced by SLM. It has been demonstrated that cellular structures with high dislocation densities play a positive role in increasing stress above a critical level for deformation twin formation. The cellular structure affects the distribution of hydrogen, with hydrogen presence at cellular boundaries reducing its accumulation at grain boundaries. Hydrogen increases the density of deformation twins and reduces the thickness of individual deformation twins. This phenomenon can be attributed to an increase in nucleation sites for the deformation twin, which is closely related to the decrease in stacking fault energy and the increase in dislocation density caused by hydrogen. Both cellular structure and deformation twins play a positive role in improving the hydrogen embrittlement resistance of austenitic stainless steels.

Effect of long reaction distance on gas composition from organic-rich shale pyrolysis under high-temperature steam environment

When high-temperature steam is used as a medium to pyrolyze organic-rich shale, water steam not only acts as heat transfer but also participates in the chemical reaction of organic matter pyrolysis, thus affecting the generation law and release characteristics of gas products. In this study, based on a long-distance reaction system of organic-rich shale pyrolysis via steam injection, the effects of steam temperature and reaction distance on gas product composition are analyzed in depth and compared with other pyrolysis processes. The advantages of organic-rich shale pyrolysis via steam injection are then evaluated. The volume concentration of hydrogen in the gas product obtained via the steam injection pyrolysis of organic-rich shale is the highest, which is more than 60%. The hydrogen content increases as the reaction distance is extended; however, the rate of increase changes gradually. Increasing the reaction distance from 800 to 4000 mm increases the hydrogen content from 34.91% to 69.68% and from 63.13% to 78.61% when the steam temperature is 500 °C and 555 °C, respectively. However, the higher the heat injection temperature, the smaller the reaction distance required to form a high concentration hydrogen pyrolysis environment (hydrogen concentration > 60%). When the steam pyrolysis temperature is increased from 500 °C to 555 °C, the reaction distance required to form a high concentration of hydrogen is reduced from 3800 to 800 mm. Compared with the direct retorting process, the volume concentration of hydrogen obtained from high-temperature steam pyrolysis of organic-rich shale is 8.82 and 10.72 times that of the commonly used Fushun and Kivite furnaces, respectively. The pyrolysis of organic-rich shale via steam injection is a pyrolysis process in a hydrogen-rich environment.

Synthesis and nitrogen content regulation of diamond in a high-pressure hydrogen-rich environment

The regulating nitrogen content of diamond in a hydrogen-rich high-temperature and high-pressure (HPHT) growth environment was systematically investigated in this work by developing three growth systems, namely, “FeNi+Ti”, “FeNi+C3N6H6”, and “FeNi+Ti+C3N6H6”. Optical microscopy, infrared spectroscopy, and photoluminescence (PL) spectroscopy measurements were conducted to analyze the spectroscopic characteristics of diamonds grown in these three systems. From our analysis, it was demonstrated that the presence of hydrogen in the sp3 hybrid C–H does not directly affect the color of the diamond and facilitates the increase of the nitrogen-vacancy (NV) center concentration in a high-nitrogen-content diamond. In addition, titanium plays an important role in nitrogen removal, while its impact on hydrogen doping within the diamond lattice is insignificant. Most importantly, by regulating the ratio of nitrogen impurities that coexist in the nitrogen and hydrogen HPHT environment, the production of hydrogenous IIa-type diamond, hydrogenous Ib-type diamond, and hydrogenous high-nitrogen-type diamonds was achieved with a nitrogen content of less than 1 ppm to 1600 ppm.

On Decorating a Honeycomb AlN Monolayer with Hydrogen and Fluorine Atoms: Ab Initio and Experimental Aspects.

Mono- and few-layer hexagonal AlN (h-AlN) has emerged as an alternative "beyond graphene" and "beyond h-BN" 2D material, especially in the context of its verification in ultra-high vacuum Scanning Tunneling Microscopy and Molecular-beam Epitaxy (MBE) experiments. However, graphitic-like AlN has only been recently obtained using a scalable and semiconductor-technology-related synthesis techniques, such as metal-organic chemical vapor deposition (MOCVD), which involves a hydrogen-rich environment. Motivated by these recent experimental findings, in the present work, we carried out ab initio calculations to investigate the hydrogenation of h-AlN monolayers in a variety of functionalization configurations. We also investigated the fluorination of h-AlN monolayers in different decoration configurations. We find that a remarkable span of bandgap variation in h-AlN, from metallic properties to nar-row-bandgap semiconductor, and to wide-bandgap semiconductor can be achieved by its hy-drogenation and fluorination. Exciting application prospects may also arise from the findings that H and F decoration of h-AlN can render some such configurations magnetic. We complemented this modelling picture by disclosing a viable experimental strategy for the fluorination of h-AlN.

The effect of atomic hydrogen on the behavior of a single dislocation of 〈111〉{112} in bcc tungsten: Atomistic study

Tungsten (W) has been widely studied and spotlighted as a plasma-facing material (PFM) in the extreme environment of nuclear fusion due to its excellent physical properties. It is important to investigate the effect of hydrogen on the material behavior of tungsten as it was used in the hydrogen-rich fusion environment. Solute hardening is a typical phenomenon and it is traditionally understood by dragging or pinning effect when hydrogen atoms act like solute atoms that impede dislocation motion. On the other hand, there were several experimental studies reporting softening associated with enhanced dislocation activity, either by easy nucleation or increased mobility, or both. In order to better understand how the effect of hydrogen on mechanical behavior of W, the authors conducted molecular dynamics simulations on dislocation mobility with different dislocation types, hydrogen concentrations, stress, and temperature. At high concentration of 1 at.%, H atoms are often strongly clustered around a dislocation core and produce a super-pinning effect in that both edge and screw started to move at a stress far beyond Peierls stress. This critical stress reduces with temperature increase, and thermally assisted kink or jog formation helps a dislocation escape from the H-cloud trapping. At a low concentration of 0.01-0.1 at.% or a high concentration of 1 at.% without super-pinning, hydrogen dragging barely appeared with a screw dislocation, and the intrinsic lattice resistance dominated the motion of a screw. For an edge dislocation under the same condition, an appreciable reduction in mobility was observed with the increase of H concentration at a low temperature of 300 K and this change in mobility becomes inconspicuous for higher temperatures. In conclusion, this study predicts the hardening of W at a high H concentration of 1 at.% due to dislocation trapping at the H cluster.

Synergistic Catalysis of Reservoir Minerals and Exogenous Catalysts on Aquathermolysis of Heavy Oil

In this study, based on existing heavy oil extraction technology, combined with the mineral composition in a reservoir, the synergistic catalytic effect of reservoir minerals and exogenous catalysts under the reaction system of a hydrogen-rich environment not only reduces the viscosity of thick oil but also reduces the extraction cost and further improves the recovery rate of heavy oil. In this study, the impacts of different reservoir minerals and exogenous catalysts on the aquathermolysis of heavy oil were investigated. The research results showed that the sodium montmorillonite within the reservoir minerals exhibited an optimal catalytic effect, and the synergistic catalytic effect of sodium montmorillonite and catalyst C-Fe (catechol iron) resulted in a viscosity reduction rate of 60.47%. Furthermore, the efficiency of different alcohols as hydrogen donors was screened, among which ethanol had the best catalytic effect. Under the optimal reaction conditions, the viscosity reduction rate after the addition of ethanol was 75.25%. Infrared spectroscopy, elemental analysis, thermogravimetry, and differential scanning calorimetry were used to study the changes in heavy oil before and after hydrothermal cracking. Element analysis showed that the synergistic catalytic effect of sodium-based montmorillonite and catalyst C-Fe increased the hydrocarbon ratio from 0.116 to 0.117, and the content of S and N elements decreased. This fully confirms the catalytic effect of sodium-based montmorillonite and C-Fe catalyst for he hydrogenation reaction of the unsaturated carbon in heavy oil.

Capacitively coupled nonthermal plasma synthesis of aluminum nanocrystals for enhanced yield and size control

Uniform-size, non-native oxide-passivated metallic aluminum nanoparticles (Al NPs) have desirable properties for fuel applications, battery components, plasmonics, and hydrogen catalysis. Nonthermal plasma-assisted synthesis of Al NPs was previously achieved with an inductively coupled plasma (ICP) reactor, but the low production rate and limited tunability of particle size were key barriers to the applications of this material. This work focuses on the application of capacitively coupled plasma (CCP) to achieve improved control over Al NP size and a ten-fold increase in yield. In contrast with many other materials, where NP size is controlled via the gas residence time in the reactor, the Al NP size appeared to depend on the power input to the CCP system. The results indicate that the CCP reactor assembly, with a hydrogen-rich argon/hydrogen plasma, was able to produce Al NPs with diameters that were tunable between 8 and 21 nm at a rate up ∼ 100 mg h−1. X-ray diffraction indicates that a hydrogen-rich environment results in crystalline metal Al particles. The improved synthesis control of the CCP system compared to the ICP system is interpreted in terms of the CCP’s lower plasma density, as determined by double Langmuir probe measurements, leading to reduced NP heating in the CCP that is more amenable to NP nucleation and growth.

Efficiently Removing Hydrogen of H-Supersaturated Liquid Steel in the Vacuum Degasser with Various Gas Injection Modes

Hydrogen removal of H-supersaturated liquid steel produced in a hydrogen-rich environment in an industrial vacuum degasser (VD) is simulated here using a two-phase (argon–steel) Eulerian model. The dehydrogenation efficiency is evaluated for a series of ladle plug layouts and argon-purging modes. Increasing the plug number from the prototype double-plug of the ladle to four or slightly prolonging the degassing time of a triple-plug ladle enables to obtain the specified dehydrogenation efficiency and the end-point hydrogen level. Varying the plug position of the triple-plug ladle makes no significant difference in the dehydrogenation efficiency, which, however, is improved by adjusting the plug angle. For the triple-plug ladle, the non-uniform argon-purging mode improves the melt hydrodynamic conditions, but the optimal dehydrogenation performance is achieved in the uniform mode. The plug number has the greatest impact on the dehydrogenation efficiency compared to the other ladle designs considered. The high-efficiency dehydrogenation of H-supersaturated liquid steel in the VD can be achieved through using the quadruple plugs, or by using the triple plugs positioned at 0.57R, 0.57R, and 0.41R and the angles of 108.6° and 71.4°, with the uniform argon-purging flow rate.

Multi-Mode Total Focusing Method (MTFM) to Detect High-Temperature Hydrogen Attack (HTHA) – A Review

High temperature hydrogen attack (HTHA) is a commonly observed harm component in carbon steels exposed to high temperature and pressure in a hydrogen-rich environment. Hydrogen together with carbon responds to produce methane. The formation of methane bubbles in steel can lead to loss of fracture toughness and lead to intergranular cracking. The main challenge of this problem lies in early warning systems that can detect these bubble clusters before they reach the advanced stage. Several advanced ultrasonic inspections have been developed over the years due to the challenges of inspecting materials for defects and discontinuities. These cover time-of-flight diffraction (ToFD), phased array ultrasonic testing (PAUT), total focusing method (TFM), multi-mode total focusing method (MTFM), and others. However, these ultrasonic techniques used are typically used to detect all possible material defects. This paper briefly discusses the advantages and disadvantages of these techniques. MTFM has been successfully applied to characterize isolated or clustered signs, whether tilted or not, using high-frequency probes. The defects grouped in this paper are believed to be methane bubbles or HTHA. ToFD defect screening before aims to save time and money.

A multi-scale diffusional-mechanically coupled model for super-elastic NiTi shape memory alloy wires in hydrogen-rich environment

The functional devices made by NiTi shape memory alloys (SMAs) are often serviced in hydrogen (H)-rich environment. Recently experimental results showed that the martensite transformation (MT) of NiTi SMA changed strongly after charging H, which originates from the H diffusion in the material and an additional transformation resistance caused by the absorbed H atoms. In this work, a multi-scale diffusional-mechanically coupled constitutive model is constructed to describe the super-elastic deformation of NiTi SMA wires in H-rich environment. In the grain scale, a crystal plasticity-based constitutive model is developed within the framework of irreversible thermodynamics. Four deformation mechanisms, i.e., elasticity, MT, transformation-induced plasticity (TRIP) and H expansion are taken into account. Since the H atoms can be trapped by the lattice defects, the total H concentration is further decomposed into two parts, i.e., the lattice hydrogen concentration and the trapped one. The generalized thermodynamic forces of MT and TRIP are derived from the Gibbs free energy and Clausius-Duhem inequality. The evolution of H concentration field is derived by combining the chemical potential, diffusion balance equation and the Fick's law. In the polycrystalline aggregate scale, in order to measure the interaction among the grains and obtain the overall response of the polycrystalline aggregate, a diffusional-mechanically coupled self-consistent homogenization method is developed. Meanwhile, the finite volume method is employed to calculate the H concentration in each grain. An assumption of uniform stress field in the macroscopic scale is adopted to achieve the scale transition from the polycrystalline aggregate to the whole wire. To validate the prediction capability of the proposed model, the predictions are compared with the experiments. Moreover, the influences of loading rate on the deformation of the wires in the process of in-situ charging H are predicted and discussed.

Selective Catalytic Behavior Induced by Crystal-Phase Transformation in Well-Defined Bimetallic Pt-Sn Nanocrystals.

The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt-Sn phase. Colloidal chemistry offers a route for the synthesis of Pt-Sn bimetallic nanoparticles(NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2nm Pt, PtSn, and Pt3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonalclosepacking(hcp) PtSn and fcc Pt3 Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, facecentredcubic(fcc) Pt3 Sn/Al2 O3 , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L12 -ordered superlattice. Contrary to PtSn, H2 cofeeding has no effect on the Pt3 Sn deactivation rate. The results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure-performance relationship on emerging bimetallic systems.

Fatigue Properties and Life Prediction of GS80A Steel Under the Effect of Hydrogen-Rich Environment

Fatigue Properties and Life Prediction of GS80A Steel Under the Effect of Hydrogen-Rich Environment

In-situ catalytic hydro-liquefaction of Delonix regia lignocellulosic biomass waste in hydrogen-donor solvent

Wastes from forestry residues and tree felling have been a major waste management concern since a long time. This issue had been addressed in this work where utilization of waste Delonix regia biomass by hydro-liquefaction in a hydrogen-donor solvent (methanol) and in presence of Ni–Al co-precipitation catalyst at different temperatures and a fixed pressure have seen to provide synergistic results not only in terms of yield of liquid products but also their higher heating values. To the best of authors’ knowledge, no studies have been testified in the literature using such co-precipitation catalyst for Delonix regia biomass liquefaction. The hydrogen donating capability of alcoholic methanol solvent in the hydro-liquefaction process along with existence of hydrogen rich environment, caused by supply of initial external hydrogen pressure, explained high yield of liquid products. A maximum higher heating value (HHV) of 26.31 MJ/kg for biocrude, obtained at 200 °C and 80 bar final reactor pressure for 60 min reaction time, depicted the potentiality of Ni–Al catalyst in reducing oxygen content of biocrude by partial hydrogenation during the liquefaction process. Apart from this, biocrude showed presence of long chain alkanes, esters, aldehydes and ketones in them. The low phenol content of the biocrude as found from Gas Chromatography-Mass Spectrometry (GC-MS) results were an indication of its less hazardous and toxic nature. The free-flowability and porous nature of solid biochar from this hydro-liquefaction process was a sign of their effectiveness in soil remediation processes and wastewater treatment. Finally, physical properties and fuel potential of biocrude obtained in this process were superior compared to those of bio-oil obtained by catalytic, non-catalytic and hydro-catalytic pyrolysis of same biomass conducted at elevated temperature of 600 °C.

Borophene reinforcing copper matrix composites: Preparation and mechanical properties

The excellent mechanical properties that combine strength, flexibility and toughness make borophene a highlighted material system for innovative applications of nanoelectronic devices and promising for reinforcing metal matrix composites. However, the experiments have not been reported so far due to the difficulty of macroscale preparation of borophene sheets. Recently, large-scale, free-standing, ultrastable hydrogenated borophene sheets have been synthesized in our group using an in-situ multi-step thermal decomposition method of sodium borohydride. Here, borophene reinforcing copper matrix composites were prepared by in-situ thermal decomposition of sodium borohydride powder in hydrogen rich environment. The corresponding bulk three-dimensional borophene sheets network/copper composites were prepared by spark plasma sintering. The structure of borophene in the samples before and after sintering is well consistent with that of triangular borophene. The mechanical properties of the composites are significantly improved by the introduction of borophene. The yield strength and ultimate tensile strength of the composites are close to the reported highest values of graphene in copper matrix and far beyond those of boron nitride in copper matrix. The change of fracture mode from ductile fracture to brittle fracture is ascribed to the stronger interfacial affinity between borophene and copper compared with that between graphene and copper. This study paves the way for the practical application of borophene in high-performance metal matrix composites.

Effect of Interstitial Hydrogen on Elastic Behavior of Metals: An Ab-Initio Study

Abstract A comprehensive assessment of interstitial hydrogen on the elastic behavior across different metals (Al, Ni, Fe, Nb, Ti, and Zr) was carried out using first-principles calculations. The volumetric strain introduced by interstitial hydrogen had a key role in the observed variation in elastic constants. However, in Nb, Ti, and Zr, the host and hydrogen atoms interact strongly which had a significant contribution towards the variation in elastic response due to the presence of hydrogen. The addition of hydrogen reduced the resistance to shear deformation along respective active slip systems for all the metals, except Nb. Similarly, the homogenized macroscopic approximation of Young’s and shear moduli also demonstrated a drop with increasing hydrogen concentration across all the metals, apart from Nb. Finally, these findings accurately quantify the variation in elastic behavior of various metals when exposed to a hydrogen rich environment.

Donor doping of corundum (AlxGa1−x)2O3

Corundum (AlxGa1−x)2O3 alloys have been proposed as a candidate ultrawide-bandgap oxide for a number of applications, but doping is unexplored. We examine the prospects for n-type doping with H, Si, Ge, Sn, Hf, Zr, and Ta in corundum (AlxGa1−x)2O3 alloys using first-principles calculations. All of the dopants are shallow donors in corundum Ga2O3. In the (AlxGa1−x)2O3 alloy, they transition from shallow to deep donors at Al compositions that are unique to each donor. Si and Hf remain shallow donors up to the highest Al contents in corundum (AlxGa1−x)2O3 alloys and are still shallow even as the (AlxGa1−x)2O3 bandgap exceeds 6.5 eV. Finally, we address the detrimental role of cation vacancies as compensating deep acceptors and suggest that doping in a hydrogen-rich environment under cation-rich conditions can be used to overcome this problem.