Ar-H2 Mixture Research Articles

H2 permeance and surface characterization of a thin (2 μm) Pd-Ni composite membrane prepared by electroless plating

The high cost of palladium membranes limits their widespread use in industrial applications. We report a novel strategy for the preparation of economic hydrogen separation membranes. In this study, a Pd88-Ni12 composite membrane was prepared with a considerable nickel content (>10 wt%) for the first time using the organic–inorganic activation method in the ELP approach. The H2 permeance of the Pd88-Ni12 composite membrane was 4.34 × 10-7 mol m−2 s−1 Pa−1 at 500 °C with infinite selectivity (H2/N2). The membrane exhibited suitable performance when exposed to binary mixtures under various operating conditions. At 500 °C and 100 kPa, with the same concentration of impurity gases, the H2 permeance of the Pd88-Ni12 composite membrane was 3.33 × 10 -7 mol m−2 s−1 Pa−1 for the H2-Ar mixture, 3.12 × 10 -7 mol m−2 s−1 Pa−1 for the H2-N2 mixture, 2.56 × 10 -7 mol m−2 s−1 Pa−1 for the H2-CO2 mixture, and 2.54 × 10 -7 mol m−2 s−1 Pa−1 for the H2-CO mixture. The effect of operating parameters and the amount of impurity concentration in the gas feed on the stage cut in binary gas mixtures was investigated. Increasing operating temperature and pressure enhanced the stage cut for all mixtures while increasing the impurity concentration in the gas feed led to a decrease in the stage cut, independent of operating conditions. The Pd88-Ni12 composite membrane indicated suitable long-time permeance stability for 150 h at a transmembrane pressure range of 100–300 kPa and 500 °C under an H2/N2 gas atmosphere. Finally, the cost investigation demonstrated that the Pd88-Ni12 composite membrane had a 38 % lower specific cost than the pure palladium composite membrane.

Thermodynamic Modeling of Elemental Distributions of Trace Elements in Non-ferrous Iron Residue Hydrogen Reduction

Every year millions of tons of iron residue are generated as a by-product of zinc production. Stabilized landfilled iron residue contains recoverable metals that could be valorized with further processing. Pyrometallurgical processing allows the recovery of valuable metals while simultaneously producing a clean slag that can then be further utilized. A thermodynamic model was developed with FactSage version 8.0. The focus was on minor element behavior and distribution of elements between phases. Calculations were performed at 1200–1400°C and pressure of 1 atm with both pure H2 and H2-Ar mixtures used as a reductant. Also, the concentrations of Pb and Zn in the input were varied. The results showed that a liquid alloy phase forms consisting mostly of either Cu, As and Pb or Fe, As and Cu. It was noted that a higher Ar total gas amount in reduction decreased the mass fraction of the liquid alloy and increased the evaporation of elements into fume dust. S, Bi, Pb, Ge and Zn were observed to evaporate fully, while As, In, Sb and Ag evaporated only partially. The results need to be verified experimentally.

Hydrogen-assisted spark generation of silver nanoparticles: The effect of hydrogen content on the signal intensity in surface-enhanced Raman spectroscopy

We employed the so-called hydrogen-assisted spark generation method to produce silver nanoparticles by means of a repetitive spark discharge in a flowing gas atmosphere. Different compositions of H2–Ar mixtures were used as carrier gas to systematically investigate the effect of the hydrogen content on the signal enhancement obtainable with silver nanoparticles in Raman spectroscopic measurements. To this end, the particles were collected on filters and used as SERS substrates without further preparation. It was shown that a ca. 50-fold signal-increase can be achieved by adding at least 30% H2 to the Ar gas. The potential causes of the enhancement were also investigated, and they were associated partly with more pronounced aggregation on the filter and partly with the increased resilience of the silver particles against surface oxidation. The latter effect was supported by control experiments with non-oxidizable gold nanoparticles, which did not exhibit considerable enhancement-variation regardless of the hydrogen content.

Synthesis of bifunctional Ru–Pd catalysts following a double reduction method: hydrogenation/dehydrogenation of liquid organic hydrogen carriers

Treatment of Ru2.5Pd2.5/H2 catalyst with Ar–H2 mixture exposed strong acid sites, prompting further reduction of Run+ and Pd2+, leading to enhanced interaction of Ru and Pd with carrier, possessing excellent hydrogenation–dehydrogenation activity.

The Influence of Hydrogen Concentration in an Ar–H2 Mixture on the Electrical Properties of Solid Oxide Fuel Cells

The Influence of Hydrogen Concentration in an Ar–H2 Mixture on the Electrical Properties of Solid Oxide Fuel Cells

Reduction of Graphene Oxide by Laser Scribing in Different Atmospheres and Application in Humidity Sensing

Laser scribing, by far proposed as a method for efficiently transforming graphene oxide into reduced graphene, has been employed, using a CW laser beam, to study the modifications of graphene oxide scribed under different controlled atmospheres, including air, N2, Ar, and a 95 : 5 (v/v) Ar/H2 mixture. We have found that laser scribing effects, including chemical composition, order degree, and electrical properties, strongly depend upon the atmosphere during the irradiation. The electrical properties of the various materials, obtained in different atmospheres, have been evaluated with respect to the sensing properties towards humidity, the materials produced in pure Argon yielding the highest sensitivity and the fastest response, while related Raman microspectroscopy measurements showed that both Ar and Ar-H2 mixture produce the highest order among the various samples. The results stress the importance and the potentialities of controlling the irradiation atmosphere in order to tune the composition and electrical properties of the laser-scribed graphene oxide materials.

Evaluation of Corrosion Phenomena of T91 Steel in Stagnant Liquid Lead at High Operational Temperatures

The present study aims to deepen the knowledge on the corrosion behavior of martensitic T91 steel in contact with liquid lead in view of its application in advanced nuclear energy systems. Steel samples have been analyzed after the immersion in stagnant molten lead at different temperatures (550°C to 650°C) and for an exposure time of 550 h. In order to evaluate the influence of different oxidizing conditions, the corrosion tests were performed under both Ar and Ar-H2 mixtures. Within the temperature range applied, the oxygen content in the liquid lead was Co = 6.8±2.7 × 10−2 wt% and Co = 9.2±3.6 × 10−8 wt%, respectively. When the Ar atmosphere was applied, dissolution of iron and chromium has been observed for temperature above 590°C. Conversely, under an Ar-H2 mixture atmosphere, mainly the presence of internal oxidation along the grain boundaries whose depth increases with temperature was detected.

Coexistence of two different atomic structures in the Σ13 pyramidal twin boundary in α-Al2O3

ABSTRACTAn α-Al2O3 bicrystal with a (104)/[110] Σ13 grain boundary was fabricated by joining two pieces of single crystal at 1500°C in an Ar–H2 mixture gas. The resultant grain boundary was characterised by scanning transmission electron microscopy (STEM) at the atomic level. STEM observations revealed that the grain boundary consists of two regions with different atomic structures. These two structures were identified to be the most and second-most stable structures by theoretical calculations and STEM image simulation. The coexistence of two different structures in the Σ13 grain boundary is discussed.

H2 dissociation in Ar–H2 arc discharge of moderate pressure

The line intensity ratio technique for estimation of hydrogen-to-argon density ratio and hydrogen molecule dissociation degree in arc discharge in Ar–H2 mixtures at moderate pressures (2–3 Torr) is analyzed. Intensity ratios of three hydrogen lines of Balmer series (Hα (656.3 nm), Hβ (486.3 nm) and Hγ (434.0 nm)) to ArI 750.4 nm (2p1 → 1 s2) and ArI 811.5 nm (2p9 → 1s5) lines were examined. Effect of Ar fraction in Ar–H2 mixtures on the diagnostic technique and molecular hydrogen dissociation degree in the large-volume high-density moderate-pressure Ar–H2 arc was studied. Using ArI 811 nm line for the intensity ratio diagnostics in the arc discharge is not valid due to great role of the excitation from 1s5 in production of Ar 2p9 level. It is shown that to obtain the correct H density value it is necessary to account quenching of H* excited states by Ar atoms and H2 molecules. Pair of Hα and ArI 750 nm lines is the best choice for determining atomic hydrogen density using HI-to-ArI line intensity ratio technique because of the upper excited state of Hα (n = 3) is less subjected to quenching by Ar atoms and H2 molecules as compared with higher H* levels (n = 4, 5). It is shown increasing Ar fraction in Ar–H2 mixtures results in growth of the molecular hydrogen dissociation degree.

Electrochemical preparation of standard gas mixtures using solid-state electrolyte membrane

A novel electrochemical method of preparation of standard gas mixtures for calibration of gas-analytical equipment with O2, H2 and CO was elaborated. Utilization of solid state electrolyte membrane allows to perform a nearly 100%-efficient electrochemical generation or conversion of the analyte and avoid some problems typical for liquid electrolytes, such as solvent evaporation and condensation at the inner walls of the gas tubes or deviations from the Faraday’s law. Analysis of uncertainties associated with the calibration procedure showed that the lowest systematic errors are achieved when the calibrant is generated during the electrolysis (i.e. anodic evolution of oxygen or cathodic generation of CO), and the major uncertainties are associated with operation of the flow controllers. For calibration with H2, where the calibrant is partially converted during the electrochemical process, the total uncertainty is essentially determined by molar fractions of the components in H2-Ar mixture, instrumental errors of the equipment, primarily by precision of mass-flow controllers or stability of the gas flow, and the initial flow rate of the calibrant-containing gas mixture. The relative total errors of calibration with oxygen are assessed to be 5–6%; similar uncertainties were calculated for analysis of oxygen content in standard gas mixtures by chromatography using the electrochemical method of calibration.

Electromagnetic Performance of CVD Si3N4–SiCN Ceramics Oxidized from 500 to 1000 °C

In this paper, SiCN ceramics are introduced into Si3N4 substrate by chemical vapor deposition (CVD) using SiCl4–C3H6–NH3–H2–Ar mixture gases, and then the as‐prepared Si3N4–SiCN ceramics are oxidized at 500, 800, 1000 °C for 5 h. At 500 °C, the weight and electromagnetic (EM) wave absorbing performance of Si3N4–SiCN ceramics change slightly with the increasing oxidation time, indicating that there is no obvious oxidation occurring for Si3N4–SiCN ceramics. At 800 and 1000 °C, the initial oxidation of SiCN ceramics is controlled by oxidation of carbon, which is transformed into oxidation of SiC with the increasing oxidation time. At 800 °C, the dielectric properties and EM wave absorbing performance of Si3N4–SiCN ceramics decrease finally. The minimal reflection coefficient (RC) is only –3.8 dB at the thickness of 2.65 mm. At 1000 °C, the absorbing agents in Si3N4–SiCN ceramics disappear completely after 5 h, showing EM wave transparent properties. The EM wave absorbing properties of Si3N4–SiCN ceramics are mainly dominated by SiC. In addition, the content of absorbing agents can be calculated by analyzing the weight change of Si3N4–SiCN ceramics at 1000 °C.

Comments on the Langmuir probe measurements of radio-frequency capacitive argon–hydrogen mixture discharge at low pressure

In this paper, the current–voltage graphs of discharge in the chamber of capacitive coupled radio frequency (CCRF) at low pressure were presented for Langmuir probe. The Langmuir probe measurements for estimating the electron density and temperature in capacitive coupled discharges at low pressures were presented and the electron temperatures of the Ar–H2 mixture discharge generated at different conditions were reported using the Langmuir probe. The focus of this study is that the CCRF discharge can be determined and explained using the characteristics of plasma by means of Langmuir probe measurements for the different hydrogen rates in Ar–H2 mixture discharge. The measurement results of Langmuir probe gave values around 1015 m−3 for the electron density. The floating potential depended on the electronegative gas amount. It was found that the increase of hydrogen gas amount in the mixture discharge caused the decrease of the floating potential. Also, a decrease in the argon (Ar) metastable with the increase in hydrogen (H2) content was obtained. When the applied radio frequency (RF) power was increased, the thickness and collisionless sheath occurring at lower RF power could transform to thin sheath.

Influence of Feedstock Powder Modification by Heat Treatments on the Properties of APS-Sprayed Al2O3-40% TiO2 Coatings

The formation and decomposition of aluminum titanate (Al2TiO5, tialite) in feedstock powders and coatings of the binary Al2O3-TiO2 system are so far poorly understood. A commercial fused and crushed Al2O3-40%TiO2 powder was selected as the feedstock for the experimental series presented in this paper, as the composition is close to that of Al2TiO5. Part of that powder was heat-treated in air at 1150 and 1500 °C in order to modify the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including EDS of metallographically prepared cross sections. Only a maximum content of about 45 wt.% Al2TiO5 was possible to obtain with the heat treatment at 1500 °C due to inhomogeneous distribution of Al and Ti in the original powder. Coatings were prepared by plasma spraying using a TriplexPro-210 (Oerlikon Metco) with Ar-H2 and Ar-He plasma gas mixtures at plasma power levels of 41 and 48 kW. Coatings were studied by XRD, SEM including EDS linescans of metallographically prepared cross sections, and microhardness HV1. With the exception of the powder heat-treated at 1500 °C an Al2TiO5-Ti3O5 (tialite–anosovite) solid solution Al2−xTi1+xO5 instead of Al2TiO5 existed in the initial powder and the coatings.

Optical and electrical properties of capacitive coupled radio frequency Ar-H2 mixture discharge at the low pressure

In this study, the electrical and optical properties and plasma's parameters of capacitive radio frequency (RF) discharge for the argon and hydrogen mixture at low pressure are investigated using optical emission spectroscopy (OES) and a Langmuir probe. The wavelengths of spectral lines obtained from OES are between 400 and 950 nm. By using the spectral lines and probe data, the electron temperature for every different RF power, mixture rate and flow rate are determined by the modified Boltzmann curve method. The Langmuir probe gives the electron temperature and other plasma properties for the same discharge parameters.

Electricity production from lignocellulosic biomass by direct coupling of a gasifier and a Nickel/Yttria-stabilized Zirconia-based solid oxide fuel cell. Part 1: From gas production to direct electricity production

This work presents the direct coupling of a gasification pilot according to the patented concept by S3D Company and of a Ni-YSZ-based SOFC. The composition of gas issued from the gasifier is rather stable, with H2 ≈ 15%, CO ≈ 15%, CH4 ≈ 1%, CO2 ≈ 20% and N2 ≈ 49%. Before injecting directly the gas on the cell, a preliminary test of the home-made cell consisting of an industrial Fiaxell Nickel/Yttria-stabilized Zirconia-based anode-electrolyte assembly covered by praseodymium nickelate oxide was performed with H2N2 mixtures. The cell is tested at 750 °C and 850 °C, with a maximum power density of 1.4 W cm−2 at 850 °C when fueled with a 76%–24% H2Ar mixture. The effect of the dilution of the gas is also studied, and validates the use of a bag containing the gas issued from the gasifier. In these conditions, using exclusively the fuel issued from biomass, without any additional purification steps, maximum power densities of 340 mW cm−2 and 113 mW cm−2 can be obtained at 850 °C and 750 °C respectively.

Concentration of atomic hydrogen in a dielectric barrier discharge measured by two-photon absorption fluorescence

Two-photon absorption laser-induced fluorescence (TALIF) was utilized for measuring the concentration of atomic hydrogen in a volume dielectric barrier discharge (DBD) ignited in mixtures of Ar, H2 and O2 at atmospheric pressure. The method was calibrated by TALIF of krypton diluted in argon at atmospheric pressure, proving that three-body collisions had a negligible effect on quenching of excited krypton atoms. The diagnostic study was complemented with a 3D numerical model of the gas flow and a zero-dimensional model of the chemistry in order to better understand the reaction kinetics and identify the key pathways leading to the production and destruction of atomic hydrogen. It was determined that the density of atomic hydrogen in Ar–H2 mixtures was in the order of 1021 m−3 and decreased when oxygen was added into the gas mixture. Spatially resolved measurements and simulations revealed a sharply bordered region with low atomic hydrogen concentration when oxygen was added to the gas mixture. At substoichiometric oxygen/hydrogen ratios, this H-poor region is confined to an area close to the gas inlet and it is shown that the size of this region is not only influenced by the chemistry but also by the gas flow patterns. Experimentally, it was observed that a decrease in H2 concentration in the feeding Ar–H2 mixture led to an increase in H production in the DBD.

Chemical Vapor Deposition of Tantalum Carbide from TaCl5-C3H6-Ar-H2 System

Tantalum carbide, which is one of the ultra-high temperature ceramics, was deposited on graphite by low pressure chemical vapor deposition from a TaCl 5 -C₃H 6 - Ar-H₂ mixture. To maintain a constant TaCl 5 /C₃H 6 ratio during the deposition process, TaCl 5 powders were continuously fed into the sublimation chamber using a screw-driven feeder. Sublimation behavior of TaCl5 powder was measured by thermogravimetric analysis. TaC coatings have various phases such as Ta+α-Ta₂C, α-Ta₂C+TaC 1-x , and TaC 1-x depending on the powder feeding methods, the C₃H 6 /TaCl 5 ratio, and the deposition temperatures. Near-stoichiometric TaC was obtained by optimizing the deposition parameters. Phase compositions were analyzed by XRD, XPS, and Raman analysis.

Isothermal Reduction of Oxide Scale on Hot-Rolled, Low-Carbon Steel in 10 pct H2-Ar

The isothermal reduction of oxide scale on hot-rolled, low-carbon steel strip in 10 pct H2-Ar mixtures in the temperature range of 673 K to 1073 K (400 °C to 800 °C) was investigated by using a thermo-gravimetric analyzer (TGA). During heating under an argon atmosphere, magnetite/iron eutectoid and proeutectoid magnetite in the oxide scale successively transformed into wustite at a temperature above 843 K (570 °C). The kinetic plot of the isothermal reduction assumes a sigmoid shape, including induction, acceleration, and finally the decaying stage. Fitting the kinetic curve to mathematical models, the reaction at 1073 K (800 °C) and 773 K (500 °C) were determined to be controlled by phase-boundary-controlled reaction and three-dimensional growth of nuclei, respectively. The reduction product varies with temperature and itself affects the kinetics. Porous and dense iron were, respectively, obtained below and above 873 K (600 °C). A “rate-minimum” was observed at 973 K (700 °C) due to the formation of dense iron that blocks the gas diffusion. Due to the structural transformation of oxide scale during heating, the reactant depends on the heating process. However, compared with the oxide scale structure, the temperature is more important in determining the reduction kinetics at temperatures above 973 K (700 °C).

Influence of chlorine substitution on adsorption of gaseous chlorinated phenolics on multi-walled carbon nanotubes embedded in SiO2

Multi-walled carbon nanotubes (MWCNTs) embedded in SiO2 particles were prepared through the floating-catalyst chemical vapor deposition method. The parameters reaction time and flow rate of the carbon source (CH4) were studied to obtain optimum conditions for MWCNT synthesis. The obtained MWCNTs were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy to confirm their morphology and crystallinity. The optimum conditions were a CH4 flow rate of 100 ml/min in a H2–Ar mixture at a flow rate of 500 ml/min and a reaction time of 20 min. Under these conditions, MWCNTs with average outer and inner diameters of around 50 and 10 nm, respectively, were obtained. SiO2 particles with embedded MWCNTs were studied for their adsorption of gaseous chlorinated phenolic compounds (CPCs), with emphasis on the effect of number of chlorine substituents. The CPC compounds of 2-chlorophenol (CP) and 2,4-dichlorophenol (DCP) were compared against phenol (P). Adsorption of P and CPCs on the particles fit well the Langmuir isotherm. The adsorption capacities of P, CP, and DCP on SiO2 particles with embedded MWCNTs were found to be 3.12, 13.83, and 44.25 mg/g, respectively. Desorption activation energy was determined by thermogravimetric analysis. Chlorine substitution on P changed the adsorption process from physical to chemical adsorption. The particles showed high potential for use as a pre-concentration unit for solid-phase microextraction.

Experimental Study for Comparison of H2and Ar–H2Gas Mixture Glow Discharge Wall Conditioning in ADITYA Tokamak

Low-temperature glow discharge wall conditioning (GDC) using H2 gas is effective in reduction of oxygen and carbon (low-Z) contained impurities on near surface region of the vacuum vessel wall. The high retention of hydrogen in vessel wall/components due to long operation of H2 GDC increases hydrogen outgassing during plasma operation and affects the production of high-temperature plasma in tokamak. The hydrogen retention can be reduced using inert gas GDC by sputter cleaning for short duration. But, in that case, the outgassing rate of the inert gas increases, which may impair the plasma performance. To overcome above problems, the GDC with hydrogen-inert gas mixture can be used for better removal of C and O surface contaminants and low hydrogen retention in the vacuum vessel surface. In ADITYA tokamak, H2 GDC is carried out regularly after plasma operations, while the GDC with argon–hydrogen (Ar–H2) mixture has been experimentally tested to observe the reduction of the oxygen and carbon impurities along with low hydrogen retention. In Ar–H2 GDC, the formation of the ArH+ hydride ions, which have quite long life and more energy compared with H2+ ions formed in H2 GDC for breaking the bond of wall molecules. A systematic comparative study of H2 GDC and Ar–H2 mixture GDC by changing the mixture ratio has been carried out in ADITYA tokamak. The relative levels of oxygen and carbon contain impurities have been measured using residual gas analyzer in both GDCs. We have observed a substantial reduction in oxygen and carbon impurities with a significant improvement in wall condition with Ar–H2 GDC compared with the H2 GDC. The effect of wall conditioning by Ar–H2 GDC on the performance of high-temperature plasma operation is presented in this paper.