Hydrogen Mixed Gas Research Articles

Synthesis of molybdenum carbide superconducting compounds by microwave-plasma chemical vapor deposition

A method to synthesize molybdenum carbides has been developed based on microwave plasma treatment with methane and hydrogen mixed gases, using a microwave-plasma chemical vapor deposition device. The device framework and its mechanism are described in detail. Two-dimensional α-Mo2C has been directly synthesized by a plate-to-plate substrate holder structure with a microwave power of 920 W and a partial pressure of 20 kPa. In-situ optical emission spectroscopy was used to measure the radical types in the plasma ball during glow discharge. The as-grown α-Mo2C samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy to determine their phases, purity and chemical groups. The superconducting transition temperature was measured, and the transition temperatures of the relevant phases are discussed in detail. The results confirmed that this method is an efficient way to obtain molybdenum carbides and inspire new research interest in transition metal carbides, which have many intrinsic local properties and applications.

Using a hydrogen gas torch to seal edges of vacuum glazing panels and analysis of the related characteristic strength according to the sealed edge shapes

The edges of vacuum glazing panels sealed using a hydrogen-mixed gas torch are of various shapes, which affect the strength of vacuum glass. The characteristic strengths were analyzed according to the edge shapes. Specimens with different edge shapes were manufactured to study the characteristic strengths according to the edge shapes. Three shape parameters (thickness, radius, and deflection) were selected to numerically represent the edge shapes, and the cross-sections were measured accordingly. The four-point bending test was employed on the prepared specimens. Furthermore, the Weibull distribution, which is a statistical analysis method commonly used to study product failure and malfunctioning, was employed to analyze the experimental results. The strength and fracture distribution of the sealing shape were confirmed using the shape parameter and scale parameter of the Weibull distribution. In addition, the cross-sectional shape with the maximum strength was determined by taking into account the characteristic strength and safety factors proposed by major countries. Therefore, it can be applied to the production of vacuum glass by sealing the edge of the glass using the hydrogen-mixed gas torch in the cross-sectional shape satisfying the strength performance of the sealing parts.

Membrane dehumidification process using defect-free hollow fiber membrane

Water vapor removal by the polymeric membrane to reduce the energy cost during the water–gas shift reaction in a catalytic membrane reactor was investigated. In this study, polyamideimide (PAI) defect-free hollow fiber membranes were produced by a dry/wet phase inversion method. The purpose of this study was to investigate the water vapor removal efficiency under high pressure and high temperature. The morphologies of the hollow fiber membranes were characterized by SEM. The water vapor and hydrogen mixed gas separation properties were used to verify the performance of a defect-free membrane. The water vapor removal efficiency increased from 54% to 90% (at 120 °C) as a function of the operating conditions because of the enhanced water vapor flux. However, the H2 retention ratio was negatively related to the water removal efficiency.

Temperature-dependent current–voltage characteristics and ultraviolet light detection of heterojunction diodes comprising n-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films and p-type silicon substrates

Heterojunction diodes comprising poorly (1 at. %) nitrogen-doped n-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films and p-type Si substrates were prepared in nitrogen and hydrogen mixed gas atmosphere by coaxial arc plasma deposition. Dark current density–voltage (J–V) characteristics were studied in the temperature range of 200–400 K, in order to investigate the current transport mechanism through the fabricated heterojunctions. The temperature dependence of the ideality factor and reverse saturation current reveals that carrier transport predominantly occurs in the generation–recombination mechanism and, at low temperatures, it accompanies tunneling via weak traps. The heterojunctions surely exhibited photodetection for 254 nm ultraviolet light illumination. It is expected that photocarriers will be generated at UNCD grains and transported through an a-C:H matrix.

Application of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films for ultraviolet detection

Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon (UNCD/a-C:H) films were grown by coaxial arc plasma deposition in the ambient of nitrogen and hydrogen mixed gases. Synthesized films were structurally investigated by X-ray photoemission and near-edge X-ray absorption fine structure spectroscopies. A heterojunction with p-type Si substrate was fabricated to study the ultraviolet photodetection properties of the film. Capacitance–voltage measurements assure the expansion of a depletion region into the film side. Current–voltage curves in the dark showed a good rectifying behaviour in the bias voltages range between ±5 V. Under 254 nm monochromatic light, the heterojunction shows a capability of deep ultraviolet light detection, which can be attribute to the existence of UNCD grains. As the diode was cooled from 300 K down to 150 K, the detectivity has a notable enhancement from 1.94 × 105 cm Hz1/2 W−1 at 300 K to 5.11 × 1010 cm Hz1/2 W−1 at 150 K, which is mainly due to a remarkable reduction in the leakage current at low temperatures. It was experimentally demonstrated that nitrogen-doped UNCD/a-C:H film works as ultraviolet-range photovoltaic material.

Evaluation of polarization and hydrogen production efficiency of solid oxide electrolysis stack with La0.6Sr0.4Co0.2Fe0.8O3−δ- Ce0.9Gd0.1O1.95 oxygen electrode

The 30-cell (10 × 10 cm2) LSCF-GDC (La0.6Sr0.4Co0.2Fe0.8O3−δ − Ce0.9Gd0.1O1.95) oxygen electrode supported planar solid oxide electrolyzer cell (SOEC) stack module is manufactured and tested at different operation conditions (operating temperature, steam content, gas flow rate et al.) in steam electrolysis mode for hydrogen production. The i–v curves of each electrolysis are recorded and fitted according to the electrochemical models, the influences of operation conditions on the polarization loss of high temperature water electrolysis are analyzed, and the electrolysis efficiencies are calculated. High operating temperature gives the reduction of Ohmic and activation polarization, and high steam content results in significantly lowered activation polarization. The flow rates of the gas onto the hydrogen electrode and oxygen electrode have great impact on concentration and activation polarization. The electrolysis efficiency can reach the maximal value of 80.8% (electrolysis voltage 1.273 V) when the system operating at 800 °C, with 6 L min−1 90% humidified hydrogen mixed gas, and the rate of resultant hydrogen is 4.57 L min−1.

Electrical characteristics of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition

Nitrogen-incorporated ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were synthesized in nitrogen and hydrogen mixed gas atmospheres by coaxial arc plasma deposition. The temperature dependence of electrical resistivity implies that carriers are transported in hopping conduction. Heterojunctions comprising 3 at. % nitrogen-doped films and p-Si substrates exhibited a typical rectifying action. The expansion of a depletion region into the film side was confirmed from the capacitance–voltage characteristics, and the built-in potential and carrier concentration were estimated to be 0.51 eV and 7.5 × 1016 cm−3, respectively. It was experimentally demonstrated that nitrogen-doped UNCD/a-C:H is applicable as an n-type semiconductor.

Establishment of regression model for estimating shape parameters for vacuum-sealed glass panel using design of experiments

Presently, the technique of edges sealing of vacuum glass panels is being utilized in a variety of industrial applications, such as in displays and home appliances. The sealing conditions of a vacuum glass panel strongly affect its key performance parameters, such as its insulation and strength. In the present study, edges of two glass panels were melted and sealed using a hydrogen mixed gas torch. The edges were sealed after appropriately setting process parameters that affected the shape of the sealed edges. Regression models were established for estimating the edge thickness, deflection, and maximum radius of the sealed part, which were considered as shape parameters. The effects of the process parameters on the shape parameters, as well as the interactions among the process parameters, were analyzed, and a polynomial regression model that considered these interactions was established. The feasibility of all the regression models was verified through analysis of variance.

Fabrication of heterojunction diodes comprising nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon and p-type silicon

ABSTRACTNitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited in nitrogen and hydrogen mixed gas atmospheres by coaxial arc plasma deposition (CAPD). Nitrogen-doped films with nitrogen contents of 3 and 8 at.% possessed n-type conduction. The electrical conductivity increased with increasing nitrogen content. Heterojunction diodes with p-type Si exhibited typical rectifying action. From the capacitance-voltage measurement, it was confirmed that the carrier density increases with the nitrogen content.

Study of hydrogen mitigation for safe storage of spent cesium adsorption vessels

Hydrogen mitigation is one of the important issues for safe storage of spent cesium adsorption vessels that were used in the contaminated-water treatment facility at the Fukushima Daiichi Nuclear Power Station because the production and accumulation of hydrogen is induced by the radiolysis of residual water in the vessel. In the present study, an experimental examination was performed using a miniature acrylic vessel to simulate an upper section of the vessel using particle image velocimetry to clarify the internal flow of hydrogen-mixed gas and to verify the analytical results by the ANSYS Fluent code. As a result, weak upflow and circulating flow at the stepped section were successfully visualized, and the validity of the analytical results was confirmed by the flow patterns. Additionally, the practicality of a recombination catalyst for hydrogen and oxygen was considered as a passive autocatalytic recombiner in hydrogen mitigation. A catalytic reaction test was conducted to evaluate its effectiveness. The results showed that the catalyst retains activity under the humid condition assumed in the real vessel.

Direct Growth of Graphene Films on Sapphire (0001) and (112̅0) Surfaces by Self-Catalytic Chemical Vapor Deposition

We investigated mechanism of the metal-catalyst-free direct growth of graphene films in chemical vapor deposition on sapphire surfaces using three kinds of substrates, randomly stepped (0001), phase-separated (0001) and randomly stepped (1120). The graphene growth process includes pit formation in the early stage by hydrogen and methane mixed gas flow, appearance of catalytic action inside the pit, nucleation of graphene on the pit surfaces, and expansion and fusion of graphene films. It was found that the quality of graphene films depends on the crystallographic plane. In addition, even on an identical plane, a domain-selective growth mode was observed between domains with different step-terrace structures. This study indicates that morphology of the sapphire surface is crucial in direct growth of graphene films because a certain density of atomic-steps on the surface is favorable to nucleation of graphene films.

Effects of hydrogen mixture into helium gas on deuterium removal from lithium titanate

Lithium titanate (Li2TiO3) pebbles were irradiated with deuterium ions with energy of 1.7keV and then exposed to helium or helium–hydrogen mixed gas at various temperatures, in order to evaluate the effects of gas exposure on deuterium removal from the pebbles. The amounts of residual deuterium in the pebbles were measured by thermal desorption spectroscopy. The mixing of hydrogen gas into helium gas enhanced the removal amount of deuterium. In other words, the amount of residual deuterium after the helium–hydrogen mixed gas exposure at lower temperature was lower than that after the helium gas exposure. In addition, we also evaluated the pebbles exposed to the helium gas with different hydrogen mixture ratio from 0% to 1%, at 573K. Although the amount of residual deuterium in the pebbles after the exposure decreased with increasing the hydrogen mixture ratio, the implanted deuterium partly remained after the exposure. These results suggest that the tritium inventory may occur at low temperature region in the blanket during the operation.

H2–CH4 mixed gas plasma treatment on LP-MOCVD ZnO:B for amorphous silicon thin film solar cells

We present an innovative dry etching method to modify the surface of in-house ZnO:B (BZO) films deposited by the LP-MOCVD technique. With the optimized hydrogen and methane mixed gas plasma post treatment process, we obtain a novel surface texture that constitutes of pyramids with enlarged feature size (>1μm) and shrunken feature size (<0.2μm), which can improve the light trapping capability both in short and long wavelength region. In addition, we also discuss the evolution of optical and electrical properties of BZO films with etching time. When those etched BZO films are used as front contacts in a-Si:H solar cells, the recovery of open circuit voltage and fill factor can be ascribed to the soft sharp edges of the new pyramids texture. The conversion efficiency of single a-Si:H solar cells can reach up to 6.2% for an absorber layer thickness only around 140nm.

공정변수간의 교호작용을 고려한 모서리 접합두께 및 처짐량 예측 회귀식 도출

The thickness and deflection of melting parts of the glass edge reach the biggest effect on the intensity and thermal insulation performance. During the sealing process using a hydrogen mixed gas torch, the thickness and the deflection effect of the edge part are affected by process parameters. In order to analyze the correlative relationship of the thickness prediction and the deflection of the edge part according to the process parameters, data was obtained by conducting sealing experiments. The main effects and interaction effects of process parameters for the thickness and the shape of the glass edge parts were analyzed through the design of experiment. A mathematical experiment equation that can predict the thickness and deflection of the edge part according to the process parameters was developed by conducting multiple regression equations.

Sensitivity Analysis of Edge Sealing Process Parameters of Vacuum Glazing Panel

The edge sealing process of vacuum glazing panel manufacture is one that requires high reliability in order to maintain a vacuum state between two sheets of glass. In this study, a method of melting and sealing two sheets of glass using the hydrogen mixed gas torch during edge sealing was conducted. During melting and sealing, the deflection effect of the edge part is affected by process parameters such as flow rate of hydrogen mixed gas, moving speed of torch, and distance between the torch and the glass, among others. In order to analyze the correlative relationship of the shape prediction and the sealing shape of the edge part according to the process parameters, data was obtained by conducting sealing experiments and setting shape parameters for the lower melting part. A mathematical experiment equation that can predict the shape of the lower edge part according to the process parameters was developed by conducting nonlinear multiple regression analysis based on the data obtained for the shape parameters. In addition, sensitivity analysis according to the changes in the process parameters was carried out and the effects of the process parameters on the edge shape parameters were analyzed by using the developed mathematical equation.

Study of the Thermal Stability of Supported Catalytic Nanoparticles for the Growth of Single-Walled Carbon Nanotubes with Narrow Diameter Distribution by Chemical Vapor Deposition of Methane

The thermal stability of catalytic precursors is of major importance for the synthesis of single-walled carbon nanotubes (SWNTs) with narrow diameter distributions by chemical vapor deposition at high temperature. We report a study of the thermal stability of iron (Fe) and iron oxide (Fe2O3) nanoparticles with narrow size distribution grown onto Si/SiO2 hydroxylated flat substrates. Whereas the Fe2O3 nanoparticles are thermally stable up to 900 °C, above their reducing temperature of ∼700 °C, the size distribution of Fe nanoparticles increases and broadens. An accurate analysis of atomic force microscopy data shows that this instability is due to a diffusion–coalescence mechanism, ruling out a possible Ostwald’s ripening mechanism. The origin of this behavior is attributed to the dewetting of the nanoparticles. Using the thermally stable oxide nanoparticles as catalytic precursors, SWNTs can be successfully grown using a methane–hydrogen mixed gas. Statistical analysis of the SWNTs Raman radial breathing modes measured using four excitation wavelengths indicates that the diameter distribution of the nanotubes is centered at 1.3 ± 0.03 nm with a narrow full width at half-maximum of 0.3 ± 0.05 nm. The analysis of our results compared with other results recently published suggests that the metal–surface interaction could play a key role in the catalytic decomposition of methane and in the growth of SWNTs.

Hydrogen inhalation ameliorates lipopolysaccharide-induced acute lung injury in mice

Acute lung injury (ALI) is a serious illness, the incidence and mortality of which are very high. Free radicals, such as hydroxyl radicals (OH) and peroxynitrite (ONOO−), are considered to be the final causative molecules in the pathogenesis of ALI. Hydrogen, a new antioxidant, can selectively reduce OH and ONOO−. In the present study, we investigated the hypothesis that hydrogen inhalation could ameliorate ALI induced by intra-tracheal lipopolysaccharide (LPS, 5mg/kg body weight). Mice were randomized into three groups: sham group (physiological saline+2% hydrogen mixed gas), control group (LPS+normal air) and experiment group (LPS+2% hydrogen mixed gas). Bronchoalveolar lavage fluid (BALF) was performed to determine the total protein concentrations and pro-inflammatory cytokines. Lung tissues were assayed for oxidative stress variables, wet/dry (W/D) ratio, histological, immunohistochemistry and Western blotting examinations. Our experiments exhibited that hydrogen improved the survival rate of mice and induced a decrease in lung W/D ratio. In addition, hydrogen decreased malonaldehyde and nitrotyrosine content, inhibited myeloperoxidase and maintained superoxide dismutase activity in lung tissues and associated with a decrease in the expression of TNF-α, IL-1β, IL-6 and total protein concentrations in the BALF. Hydrogen further attenuated histopathological alterations and mitigated lung cell apoptosis. Importantly, hydrogen inhibited the activation of P-JNK, and also reversed changes in Bax, Bcl-xl and caspase-3. In conclusion, our data demonstrated that hydrogen inhalation ameliorated LPS-induced ALI and it may be exerting its protective role by preventing the activation of ROS–JNK–caspase-3 pathway.

Fast H in hydrogen mixed gas microwave plasmas when an atomic hydrogen supporting surface was present

Atomic hydrogen is heated to temperatures of up to two orders of magnitude greater than the electron temperature or the temperature of any other species in certain hydrogen mixed gas RF or glow discharge plasmas. A crucial test of energetic hydrogen chemistry regarding a resonant energy transfer or rt-mechanism (RTM) versus field acceleration models (FAM) as the basis of this selective isotropic heating of a population of extraordinarily high-kinetic-energy hydrogen atoms is the observation of fast H in microwave cells proven to lack a high field as shown by the complete absence of fast H (∼0.08 eV) by Jovicevic et al. [S. Jovicevic, N. Sakan, M. Ivkovic, N. Konjevic, J. Appl. Phys. 105, 013306-1 (2009)]. The RTM predicts an enhancement in the production of fast H with the presence of a surface to support a high concentration of hydrogen atoms in order to initiate the energetic hot H source reaction that then propagates isotropically throughout the plasma. In contrast to the prior results, extraordinarily fast H of greater than 4 eV (50 times that observed and deemed possible in the Evenson microwave cell by FAM advocate Jovicevic et al.) and 50% fractional population was observed as predicted for RTM using the catalytic reaction systems of He/H 2, Ar/H 2, pure H 2, and water vapor microwave plasmas when an electrically insulating, but atomic hydrogen supporting material was placed in the plasma region. Increasing concentrations of Xe in the non-catalytic Xe/H 2 system results in a significant decrease in the energy and population of fast excited-state H atoms.

Modeling and Optimization of Nanomechanics of Diamond-Like Carbon by MPCVD Using Response Surface Methodology

Diamond-like carbon (DLC) films have attracted great interest due to their outstanding mechanical, biocompatibility, thermal, optical and electrical properties. The DLC films can be produced by microwave plasma chemical vapor deposition (MPCVD) using Argon, methane and hydrogen mixed gases. The film properties depend strongly on the experimental parameters such as substrate temperatures; microwave power, process pressure and hydrogen concentration (H2/Ar+CH4+H2). In this study, the properties of nanomechanics of DLC films with various experimental parameters are firstly discussed which include hardness and Young’s modulus characterizing by depth-sensing nanoindentation technique. The nanoindentation is an excellent method for measuring nanomechanical properties of both bulk and thin films. The probe was conducted using a Berkovich diamond tip. To find the optimized process parameters, the statistical and mathematical response surface methodology (RSM) is used to model and analyze the effect of substrate temperature (T), microwave power (W), process pressure (P) and hydrogen concentration (H) on the properties of nanomechanics of DLC films. The central composite experimental design (CCD) is used to evaluate the interaction parametric effects of multiple experimental variables on process response (hardness and Young’s modulus). The predictive quadratic model proposed herein considering the analysis of variance (ANOVA) are proved to fit and predict values of the hardness and Young’s modulus close to those readings recorded experimentally. The most significant influential factors for maximizing the hardness and Young’s modulus have been identified from the ANOVA table. The RSM technique is demonstrated to be a powerful tool in exploration of the manufacturing parameters space of complex physical process of DLC films deposition by MPCVD.

팔라듐이 코팅된 단일모드 광섬유 센서를 이용한 수소 경보 시스템 구현

In this paper, a study on a portable hydrogen alarm system based on the palladium coated single mode fiber sensor has been reported. The fabricated hydrogen sensor exhibited 0.14 dB, 0.41 dB and 0.54 dB optical intensity variation when it was exposed by the nitrogen and hydrogen mixed gas containing 0.5 %, 1 % and 4 % of the hydrogen concentration, respectively. The fabricated sensor exhibited 20 second of response time and 120 second of recovery time for 4 % hydrogen containing gas. The fiber optics layout and software algorithm for detection of hydrogen leakage have been presented. The implanted portable hydrogen alarm system successfully generated an alarm signal when a 4 % hydrogen containing gas was leaked out.