Production Of Hydrogen Atoms Research Articles

Photocatalytic reduction of nitroarene derivatives by impressive visible-light active Co3O4-QDs/Mn3O4 nanocomposite

A visible light active Co3O4-quantum dots (QDs)/Mn3O4 nanocomposite was successfully synthesized by a straightforward precipitation approach. Notably, the formation of Mn3O4 nanosheets in composite structure was evidenced by different physicochemical techniques especially transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and N2 sorption analyses, which indicated the uniform distribution of Co3O4-QDs with small size of around 5 nm on the surface of Mn3O4 nanosheets along with the enhancement of specific surface area for final composite. Also, the persistence of Co3O4-QDs during nanocomposite synthesis was analyzed by X-ray diffraction (XRD), FT-IR and TEM techniques. The diffuse reflectance UV–Vis and electrochemical impedance spectroscopies revealed the reduction of band gap energy and enhanced charge separation efficiency for Co3O4-QDs/Mn3O4 nanocomposite, respectively, which consequently led to improved photocatalytic response in comparison with bare Co3O4-QDs and Mn3O4 nanosheets. The as-prepared nanocomposite exhibited excellent photocatalytic activity in the reduction of a wide range of substituted nitroarenes with the yields of higher than 80 % relative to the corresponding arylamines, using N2H4·H2O as the hydrogen source and ethanol as green solvent at 25 °C and ambient pressure under visible light illumination. The synergistic effect could improve the production of active hydrogen atoms, therefore, the reasons for this transformation over the prepared nanocomposite under benign conditions are fully discussed. Furthermore, the nanocomposite could be easily recycled without decay in photocatalytic activity for at least five successive cycles.

Atomic hydrogen production in a cold plasma for application in a metal foil pump

Any good design of fuel cycles for thermonuclear fusion reactors, which operate on deuterium-tritium fusion, comes with minimized tritium inventory. The direct internal recycling concept can significantly reduce the tritium inventory of a fusion power plant by introducing a bypass for most of the unburned fuel from the torus exhaust. It requires a technology that can sharply separate hydrogen isotopes from other gases in the given environment in the reactor's pump duct. The prime candidate for this task is a metal foil pump (MFP) using plasma-driven permeation. A workflow toward a performance predicting modeling tool of a MFP is introduced. It is based on the characterization of the employed cold plasma by using a plasma simulation, which is experimentally validated using optical emission spectroscopy and the actinometry method. The used approach accounts for the radial inhomogeneity of the linearly extended plasma. We determine the atomic hydrogen content down to pressures of 1 Pa and condense the complex processes that contribute to the hydrogen atom production into a single excitation probability. This value can be used in Monte Carlo based modeling approaches to determine the particle exhaust performance of the vacuum pump.

Electrochemical reductive removal of trichloroacetic acids by a three-dimensional binderless carbon nanotubes/ CoP/Co foam electrode: Performance and mechanism

Numerous chlorinated disinfection by-products (DBPs) are produced during the chlorination disinfection of water. Among them, chloroacetic acids (CAAs) are of great concern due to their potential human carcinogenicity. In this study, effective electrocatalytic dechlorination of trichloroacetic acids (TCAA), a typical CAAs, was achieved in the electrochemical system with the three-dimensional (3D) self-supported CoP on cobalt foam modified by carbon nanotubes (CNT/CoP/CF) as the cathode. At a 10 mA cm−2 current density, 74.5% of TCAA (500 μg L−1) was converted into AA within 100 min. In-situ growth of CoP increased the effective electrochemical surface area of the electrode. Electrodeposited CNT promoted electron transfer from the electrode surface to TCAA. Therefore, the production of surface-adsorbed atomic hydrogen (H*) on CNT/CoP/CF was improved, further resulting in excellent electrochemical dechlorination of TCAA. The dechlorination pathway of TCAA proceeded into acetic acids via direct electronic transfer and H*-mediated reduction on CNT/CoP/CF electrode. Additionally, the electroreduction efficiency of CNT/CoP/CF for TCAA exceeded 81.22% even after 20 cycles. The highly efficient TCAA reduction performance (96.57%) in actual water revealed the potential applicability of CNT/CoP/CF in the complex water matrix. This study demonstrated that the CNT/CoP/CF is a promising non-noble metal cathode to remove chlorinated DBPs in practice.

Unveiling the effect of different dissolved organic matter (DOM) on catalytic dechlorination of nFe/Ni particles: Corrosion and passivation effect

Dissolved organic matter (DOM), which is ubiquitously distributed in groundwater, has a crucial role in the fate and reactivity of iron materials. However, there is a lack of direct evidence on how different DOMs interact with nFe/Ni in promoting or inhibiting the dechlorination efficiency of chlorinated aromatic contaminants. By comparing humic acid (HA), fulvic acid (FA), and biochar-derived dissolved organic matter (BDOM) at different pyrolysis temperatures, we first demonstrated that the dechlorination effect of nFe/Ni on 2,4-dichlorophenol (2,4-DCP) depended on the nature of DOMs and their adsorption on nFe/Ni. HA showed an enhancing effect on the dechlorination of 2,4-DCP by nFe/Ni, while the inhibition effect of other DOMs resulted in the following dechlorination order: BDOM300 ≈FA>BDOM700 ≈BDOM500. The C2 component with higher aromaticity and molecular weight promoted the corrosion of nFe/Ni and the production of reactive hydrogen atoms (H*). The effects of different DOMs on nFe/Ni include that (1) HA accelerates the corrosion and H* production of nFe/Ni, (2) FA and BDOM300 enhance the corrosion but inhibit H* production, and (3) Both nFe/Ni corrosion and H* formation are suppressed by BDOM500/BDOM700. Therefore, this study will provide a reference for understanding the nature of DOM-nFe/Ni interaction and improving the catalytic activity of nFe/Ni when different DOMs coexist in practical applications.

Low-pressure inductively coupled plasmas in hydrogen: impact of gas heating on the spatial distribution of atomic hydrogen and vibrationally excited states

Non-equilibrium inductively coupled plasmas (ICPs) operating in hydrogen are of significant interest for applications including large-area materials processing. Increasing control of spatial gas heating, which drives the formation of neutral species density gradients and the rate of gas-temperature-dependent reactions, is critical. In this study, we use 2D fluid-kinetic simulations with the Hybrid Plasma Equipment Model to investigate the spatially resolved production of atomic hydrogen in a low-pressure planar ICP operating in pure hydrogen (10–20 Pa or 0.075–0.15 Torr, 300 W). The reaction set incorporates self-consistent calculation of the spatially resolved gas temperature and 14 vibrationally excited states. We find that the formation of neutral-gas density gradients, which result from spatially non-uniform electrical power deposition at constant pressure, can drive significant variations in the vibrational distribution function and density of atomic hydrogen when gas heating is spatially resolved. This highlights the significance of spatial gas heating on the production of reactive species in relatively high-power-density plasma processing sources.

Unravelling the bifunctional role of biochar in promoting nZVI/Ni towards complete dechlorination of trichloroethylene: Not only a carbonouces support

Trichloroethylene (TCE) is a widely recognized persistent groundwater pollutant, and the majority of dechlorination processes for its reduction yield hazardous by-products with low levels of chlorination. Herein, highly reactive catalysts (BCs@FN) were developed using bifunctional biochar (BC) loaded with nZVI/Ni (FN) nanoparticles for the complete dechlorination of trichloroethylene (TCE). BC plays bifunctional roles in promoting TCE dechlorination by facilitating FN dispersion and enhancing the conductivity of bimetallic FN, thereby promoting the production of dominant reactive atomic hydrogen. Moreover, both the reaction rate constant (kobs) of dechlorination and the amount of essential reduction species of atomic hydrogen exhibited a positive correlation with the conductivities of BCs@FN. Specifically, BC900@FN achieved complete dechlorination of 20 mg/L TCE within 3 h at a kobs value of 1.4 h−1. Analysis regarding carbon balance and Cl existence form disclosed all C-Cl bonds could be broken and 100 % TCE was transformed into ethylene (4.1 %) and ethane (95.9 %). Furthermore, the proposed BC900@FN catalyst demonstrates remarkable TCE degradation efficiencies ranging from 71.2 % to 91.8 % in tap water, municipal water and groundwater samples. These findings highlight the potential application of bifunctional BCs in synthesizing bimetallic catalysts and their practical use for remediating chlorinated contaminants.

Development and commissioning of a hydrogen ion source for the CERN ALPHA experiment

The CERN ALPHA experiment makes precision measurements of antihydrogen atoms held in a superconducting magnetic minimum trap. Recent studies of the antihydrogen spectrum have provided unique tests of fundamental physics, and to improve on these studies ALPHA is now proposing upgrades to directly compare hydrogen and antihydrogen within their existing atom trap. One route towards producing cold, neutral hydrogen atoms is the integration of a hydrogen ion source into the experiment. Ideally, this should provide both positive (H+, H2 +, H3 +) and negative (H-) ions to facilitate different schemes for producing and trapping hydrogen atoms. For compatibility with ALPHA's existing beamlines, the source must produce modest (∼ 10 μA) beam currents at very low final energies (<100 eV). PELLIS, previously developed at JYFL, is a filament-driven ion source that generates 5–10 keV H- beams with small emittances and tens of microamps of beam current. Here, we present a modified PELLIS design to provide both positive and negative hydrogen ions for ALPHA. The use of an electromagnet filter field in PELLIS allows for the optimisation of H- volume production, and also tuning of the positive ion species fraction. We present simulations of H- (and similarly H+) transport through the initial extraction optics, which have been configured for a lower beam energy of 5 keV and designed to match a proposed beamline to interface with ALPHA. We present the results of detailed vacuum simulations that were used to guide the optics design, allowing the source (at 10-2 mbar) to interface with a transport beamline ∼ 0.5 m downstream that has strict vacuum requirements of < 10-9 mbar. We present experimental results from commissioning of the source, and show that it broadly performs as designed for both positive and negative hydrogen ions.

In Situ Measurement of Hydrogen Absorption into Copper-Coated Titanium Using Neutron Reflectometry and Electrochemical Impedance Spectroscopy

We set out to investigate the possibility that a small amount of hydrogen, generated by sulfide-driven corrosion or radiolytic processes, might be absorbed into the copper coating proposed for use as corrosion protection for the used nuclear fuel containers (UFCs) to be stored in a deep geological repository (DGR) in Canada. Hydrogen absorption may have the potential to alter the mechanical properties of the copper coating. This contribution discusses our initial study, using in situ neutron reflectometry (NR) and electrochemical impedance spectroscopy (EIS), of hydrogen absorption into a 50-nm layer of copper coated onto 4 nm of Ti on a Si single-crystal substrate. In situ NR-EIS experiments detected no increase in the hydrogen content within the copper layer of the copper-titanium thin film following 55 h of polarization in deoxygenated 0.1 M NaCl solution at pH 9, at potentials ranging from −444 mV/SCE to −1300 mV/SCE (detection limit ~2 at.%). However, these NR results showed that hydrogen can be absorbed into copper when the latter is cathodically polarized below about ─900 mV/SCE, which is the experimentally measured potential threshold for the hydrogen evolution reaction (HER) under these conditions. Although hydrogen did not accumulate in the outer Cu layer, our experiments revealed that the absorbed hydrogen quickly traversed the Cu layer to concentrate in the underlying titanium layer, which favours absorbed hydrogen. This observation is consistent with hydrogen uptake measured using inert gas fusion analysis on oxygen-free, phosphorus-doped (OFP) copper, which showed that in the absence of hydrogen recombination inhibitors (e.g., As(III)), only a small increase of 22 wt. ppm hydrogen was absorbed into the copper after 24 h at E = −1300 mV/SCE, and no increase in absorbed hydrogen occurred at potentials of −1100 mV/SCE or more positive. The initial absorption efficiency for electrolytically produced hydrogen atoms at the copper surface was determined to be 3.2%, suggesting that there may be an upper limit for hydrogen uptake by the copper coating of the UFC, although studies on 3 mm copper-coated steel samples representative of UFC materials will be required to confirm that. This result supports the prediction that hydrogen absorption is unlikely to lead to any failure of the copper barrier within a proposed DGR, in which it will not be possible to achieve such negative electrochemical potentials. Intended future research using in situ NR-EIS to study hydrogen absorption during the corrosion of copper thin films by HS⁻ ions and further studies on hydrogen absorption into 3-mm-thick copper-coated steel samples will help to validate these conclusions.

H i in Molecular Clouds: Irradiation by FUV Plus Cosmic Rays

We extend the analytic theory presented by Sternberg et al. and Bialy & Sternberg for the production of atomic hydrogen (H i) via far-ultraviolet (FUV) photodissociation at the boundaries of dense interstellar molecular (H2) clouds to also include the effects of penetrating (low-energy) cosmic rays (CRs) for the growth of the total H i column densities. We compute the steady-state abundances of the H i and H2 in one-dimensional gas slabs in which the FUV photodissociation rates are reduced by depth-dependent H2 self-shielding and dust absorption and the CR ionization rates are either constant or reduced by transport effects. The solutions for the H i and H2 density profiles and the integrated H i columns depend primarily on the ratios I UV/Rn and ζ/Rn, where I UV is the intensity of the photodissociating FUV field, ζ is the H2 CR ionization rate, n is the hydrogen gas density, and R is the dust surface H2 formation rate coefficient. We present computations for a wide range of FUV field strengths, CR ionization rates, and dust-to-gas ratios. We develop analytic expressions for the growth of the H i column densities. For Galactic giant molecular clouds (GMCs) with multiphased (warm/cold) H i envelopes, the interior CR zones will dominate the production of the H i only if s−1, where M GMC is the GMC mass, and including attenuation of the CR fluxes. For most Galactic GMCs and conditions, FUV photodissociation dominates over CR ionization for the production of the H i column densities. Furthermore, the CRs do not affect the H i-to-H2 transition points.

Kinetic Study of the Gas-Phase Reaction between Atomic Carbon and Acetone: Low-Temperature Rate Constants and Hydrogen Atom Product Yields

Kinetic Study of the Gas-Phase Reaction between Atomic Carbon and Acetone: Low-Temperature Rate Constants and Hydrogen Atom Product Yields

Nonthermal Hydrogen Loss at Mars: Contributions of Photochemical Mechanisms to Escape and Identification of Key Processes

AbstractHydrogen loss to space is a key control on the evolution of the Martian atmosphere and the desiccation of the red planet. Thermal escape is thought to be the dominant loss process, but both forward modeling studies and remote sensing observations have indicated the presence of a second, higher‐temperature “nonthermal” or “hot” hydrogen component, some fraction of which also escapes. Exothermic reactions and charge/momentum exchange processes produce hydrogen atoms with energy above the escape energy, but H loss via many of these mechanisms has never been studied, and the relative importance of thermal and nonthermal escape at Mars remains uncertain. Here we estimate hydrogen escape fluxes via 47 mechanisms, using newly developed escape probability profiles. We find that HCO+ dissociative recombination is the most important of the mechanisms, accounting for 30%–50% of the nonthermal escape. The reaction + H2 is also important, producing roughly as much escaping H as momentum exchange between hot O and H. Total nonthermal escape from the mechanisms considered amounts to 39% (27%) of thermal escape, for low (high) solar activity. Our escape probability profiles are applicable to any thermospheric hot H production mechanism and can be used to explore seasonal and longer‐term variations, allowing for a deeper understanding of desiccation drivers over various timescales. We highlight the most important mechanisms and suggest that some may be important at Venus, where nonthermal escape dominates and much of the literature centers on charge exchange reactions, which do not result in significant escape in this study.

Atomic hydrogen-mediated enhanced electrocatalytic hydrodehalogenation on Pd@MXene electrodes

In this study, a Pd@MXene catalyst was synthesized to enhance the electrocatalytic hydrodehalogenation (ECH) of emerging halogenated organic pollutants (HOPs) by improving the dispersibility, catalytic activity, and stability of palladium (Pd). The average size of Pd nanoparticles (NPs) was reduced to 3.62 ± 0.34 nm with a more intensive peak of Pd (111), which facilitated atomic hydrogen (H*) production. The Pd@MX/CC electrode demonstrated superior ECH activity for diclofenac (DCF) degradation, with a reaction rate constant (kobs) 2.48 times higher than that of Pd/CC (without MXene). The satisfactory ECH performance of Pd@MX/CC remained consistent within a wide range of initial DCF concentrations (5–100 mg/L), and no significant ECH attenuation was observed even after up to 10 batches. Furthermore, the high activity of Pd@MX/CC was also observed in the ECH of other halogenated organic pollutants (levofloxacin, tetrabromobisphenol A, and diatrizoate). Density functional theory (DFT) calculations revealed that electronic configuration modulation of the Pd@MXene catalyst optimized binging energies to H* , DCF, and dechlorinated products, thereby enhancing the ECH efficiency of DCF.

Excited State Nonadiabatic Molecular Dynamics of Hot Electron Addition to Water Clusters in the Ultrafast Femtosecond Regime

Dissociative electron attachment (DEA) reactions of water result in the production of hydrogen atoms and hydroxide anions. This has been studied for a long time and is relatively slow in liquid water for thermalized hydrated electrons but much faster with a higher-energy electron. Here, we probe the nonadiabatic molecular dynamics after the addition of a hot electron (6-7 eV) to a neutral water cluster (H2O)n, where n = 2-12, considering the 0-100 fs time scale using the fewest switches surface hopping method, in conjunction with ab initio molecular dynamics and the Tamm-Dancoff approximation density functional theory method. The nonadiabatic DEA occurs within 10-60 fs, and with high probability, giving H + OH- above an energy threshold. This is faster than time scales estimated previously for autoionization or adiabatic DEA. The change in threshold energy with cluster size is modest, ranging from 6.6 to 6.9 eV. Dissociation on a femtosecond time scale is consistent with pulsed radiolysis experiments.

Tritium Breeding Performance Analysis of HCLL Blanket Fusion Reactor Employing Vanadium Alloy (V-5Cr-5Ti) as First Wall Material

Neutronic analysis in the HCLL blanket module has been established, and the calculation was performed by the ITER team, including the first wall (FW). In this study, seven materials have been investigated for FW material by considering characteristics such as high neutron fluence capability, low degradation, under irradiation, and high compatibility for blanket material. A three-dimensional configuration simulated in MCNP5 program codes was performed to investigate the neutronic performance and radiation damage effect. Employing seven candidates are vanadium carbide (VC), titanium carbide (TiC), vanadium alloy (V-5Cr-5Ti), graphite (C), tungsten alloy (W-CuCrZr), ceramic alloy (SiC), and HT-9 to study optimization of FW materials configurated in the HCLL blanket module. This novelty study concludes that vanadium alloy (V-5Cr-5Ti) is becoming a promising material candidate. This alloy has the highest number of neutronic performing for 1.27 TBR and 1.26 in multiplication energy factor in all investigations. Meanwhile, the amount of atomic displacement, hydrogen, and helium production are around 22.31 appm, 765.55 appm, and 281.57 appm, respectively. Even though vanadium alloy has a reasonably high radiation damage effect, it is still tolerable compared to several thresholds of DPA. So, it is considered excellent material for FW. Nevertheless, this alloy can replace after 13.45 years for radiation damage.

Ultrafast plasma method allows rapid immobilization of monatomic copper on carboxyl-deficient g-C3N4 for efficient photocatalytic hydrogen production.

Transition-metal monometallic photocatalysts have received extensive attention owing to the maximization of atomic utilization efficiency. However, in previous related works, single-atom loading and stability are generally low due to limited anchor sites and mechanisms. Recently, adding transition-metal monatomic sites to defective carbon nitrides has a good prospect, but there is still lack of diversity in defect structures and preparation techniques. Here, a strategy for preparing defect-type carbon-nitride–coupled monatomic copper catalysts by an ultrafast plasma method is reported. In this method, oxalic acid and commercial copper salt are used as a carboxyl defect additive and a copper source, respectively. Carbon nitride samples containing carboxyl defects and monatomic copper can be processed within 10 min by one-step argon plasma treatment. Infrared spectroscopy and nuclear magnetic resonance prove the existence of carboxyl defects. Spherical aberration electron microscopy and synchrotron radiation analysis confirm the existence of monatomic copper. The proportion of monatomic copper is relatively high, and the purity is high and very uniform. The Cu PCN as-prepared shows not only high photo-Fenton pollutant degradation ability but also high photocatalytic hydrogen evolution ability under visible light. In the photocatalytic reaction, the reversible change of Cu+/Cu2+ greatly promotes the separation and transmission of photogenerated carriers and improves the utilization of photoelectrons. The photocatalytic hydrogen evolution rate of the optimized sample is 8.34 mmol g−1·h−1, which is 4.54 times that of the raw carbon nitride photocatalyst. The cyclic photo-Fenton experiment confirms the catalyst has excellent repeatability in a strong oxidation environment. The synergistic mechanism of the photocatalyst obtained by this plasma is the coordination of single-atom copper sites and carboxyl defect sites. The single copper atoms incorporated can act as an electron-rich active center, enhancing the h+ adsorption and reduction capacity of Cu PCN. At the same time, the carboxyl defect sites can form hydrogen bonds to stabilize the production of hydrogen atoms and subsequently convert them to hydrogen because of the unstable hydrogen bond structure. This plasma strategy is green, convenient, environment-friendly, and waste-free. More importantly, it has the potential for large-scale production, which brings a new way for the general preparation of high-quality monatomic catalysts.

Planet‐Wide Ozone Destruction in the Middle Atmosphere on Mars During Global Dust Storm

AbstractThe Nadir and Occultation for MArs Discovery (NOMAD)/UV‐visible (UVIS) spectrometer on the ExoMars Trace Gas Orbiter provided observations of ozone (O3) and water vapor in the global dust storm of 2018. Here we show in detail, using advanced data filtering and chemical modeling, how Martian O3 in the middle atmosphere was destroyed during the dust storm. In data taken exactly 1 year later when no dust storm occurred, the normal situation had been reestablished. The model simulates how water vapor is transported to high altitudes and latitudes in the storm, where it photolyzes to form odd hydrogen species that catalyze O3. O3 destruction is simulated at all latitudes and up to 100 km, except near the surface where it increases. The simulations also predict a strong increase in the photochemical production of atomic hydrogen in the middle atmosphere, consistent with the enhanced hydrogen escape observed in the upper atmosphere during global dust storms.

Reappraising the Production and Transfer of Hydrogen Atoms From the Middle to the Upper Atmosphere of Mars at Times of Elevated Water Vapor

AbstractWater escape on Mars has recently undergone a paradigm shift with the discovery of unexpected seasonal variations in the population of hydrogen atoms in the exosphere where thermal escape occurs and results in water lost to space. This discovery led to the hypothesis that, contradicting the accepted pathway, atomic hydrogen in the exosphere was not only produced by molecular hydrogen but mostly by high altitude water vapor. Enhanced presence of water at high altitude during southern spring and summer, due to atmospheric warming and intensified transport, favors production of H through photon‐induced ion chemistry of water molecules and thus appears to be the main cause of the observed seasonal variability in escaping hydrogen. This hypothesis is supported by the observation of large concentrations of water vapor between 50 and 150 km during the southern summer solstice and global dust events. Using a simplified yet representative air parcel transport model, we show that in addition to the formation of atomic hydrogen from water photolysis above 80 km, a major fraction of the exospheric hydrogen is formed at altitudes as low as 60 km and is then directly advected to the upper atmosphere. Comparing the injection modes of a variety of events (global dust storm, perihelion periods, and regional storm), we conclude that southern spring/summer controls H production and further ascent into the upper atmosphere on the long term with direct implication for water escape.

Laser-assisted charge transfer in positronium collisions with protons and antiprotons

We study the process of laser-assisted charge transfer in collisions of positronium atoms with protons (antiprotons) with formation of Rydberg hydrogen (antihydrogen) atoms by the use of classical trajectories Monte Carlo simulations of Ps-$p$ dynamics in a linearly polarized infrared field. We do not observe a drastic enhancement of the cross sections similar to that predicted before in laser-assisted electron bremsstrahlung and electron recombination since in the present charge-transfer process the Coulomb focusing effect is absent. Still we see a substantial enhancement up to a factor of 3 in the energy range between ${10}^{\ensuremath{-}4}$ and 0.1 eV for the field of intensity between 10 $\mathrm{MW}/{\mathrm{cm}}^{2}$ and 10 $\mathrm{GW}/{\mathrm{cm}}^{2}$. The effect depends weakly on the orientation of the incident Ps velocity relative to the field polarization vector. Rydberg states of the produced hydrogen atoms whose orbits are close to circular can survive against ionization by laser field and decay spontaneously to lower states. This is favorable for spectroscopic studies of antihydrogen atoms.

Role of H2 and Ar as the diluent gas in continuous hot-wire CVD synthesis of SiC fiber

W-core SiC fiber was synthesized with CH3SiCl3 as the precursor by continuous hot-wire CVD approach. Using H2 and Ar as the diluent gas, the temperature profile and the production of atomic hydrogen (H) in high-speed deposition process were studied by computational flow dynamics (CFD) simulation, and the growth kinetics and microstructure of the deposit were systematically investigated. H2 significantly increases the H production, which reduces the formation of amorphous phase and structural defects (e.g. stacking faults and twins) during SiC growth. Ar could establish a steep thermal gradient in reactor, which enhances the deposit’s surface quality. The mean tensile strength of SiC fiber reaches its peak value (3.15 GPa) with H2 at 1200 sccm, and a high Weibull modulus (14.7) is achieved with Ar at 1600 sccm. These findings indicate H2 is crucial to promote the mechanical performance of SiC fiber, while Ar is beneficial to improving its uniformity.

Macroscopic production of spin-polarised hydrogen atoms from the IR-excitation and photodissociation of molecular beams

We describe methods for the production of spin-polarised H and D atoms from the IR-excitation and photodissociation of molecular beams of HBr, HI, and NH3 isotopes, including optical excitation schemes with partial hyperfine resolution. We discuss the extent to which the production rates may approach the IR-laser production rates of , and how the production rates of conventional methods of may be surpassed significantly.