Ar-H2 Mixture Research Articles

Collision-induced hyper-Rayleigh spectrum of H2–Ar gas mixture

The collision-induced hyper-Rayleigh (CIHR) spectra of the gaseous H(2)-Ar mixture are discussed in the binary regime on the basis of our ab initio computed H(2)-Ar collision-induced (CI) first dipole hyperpolarizability tensor Deltabeta(R). A method for the computation of the spherical, rotationally adapted components Deltabeta(lambdaL) ((s,K))(R) of Deltabeta(R) needed for spectroscopic line shape analysis is proposed. Both the vector and the septor parts of the H(2)-Ar CIHR spectrum are evaluated at room (T=295 K) temperature. The spectra are calculated assuming the full quantum computations based on the Schrodinger equation of the relative translational motion of H(2)-Ar as well as semiclassical methods (classical trajectory approach and Birnbaum-Cohen model translational profiles). The H(2)-Ar pair CIHR septor spectrum has been found stronger than the vector one.

Stability of the H2–(He, Ne, Ar) fluid mixtures

A theory of mixtures based on a statistical mechanical perturbation scheme is used to compute the excess free energy of mixing, the excess entropy of mixing and the concentration fluctuations in the long wavelength limit as functions of composition (c) over a wide range of temperature (T = 150 to 350 K) and pressure (p = 10 MPa to 10 GPa). This has been utilized to investigate the effects of c, T and p on the solubility of H2 (the first element of the periodic table) to He, Ne and Ar (the first three elements of the last group) and the thermodynamic stability of the mixture. The long-range correlations among the constituent species are included through the double Yukawa potential which acts as a perturbation to the hard sphere reference mixture. The non-additivity of the potentials of the constituent species is linked to the second virial coefficients which can be determined from the experimental data. Necessary corrections to the equation of state for dimerisation of H2 molecule and quantum effects are included. At a given T = 150 K and p = 100 MPa, H2–Ar mixture exhibits greater thermodynamic stability than H2–Ne and H2–Ar.

The dissociation of hydrogen molecules in the positive column of a DC glow discharge in an H2-Ar mixture

The dissociation of hydrogen molecules in the positive column of a DC glow discharge in an H2-Ar mixture

Application of Proton Conductors to Hydrogen Monitoring for Liquid Metal and Molten Salt Systems

The chemical control of impurity such as hydrogen and oxygen in coolants is one of the critical issues for the development of liquid metal cooled fast reactors and self-cooled liquid breeder blankets for fusion reactors. Especially, hydrogen (isotopes) level is the key parameter for corrosion and mechanical properties of the in-reactor components. For fission reactors, the monitor of hydrogen level in the melt is important for safety operation. The control of tritium is essential for the tritium breeding performance of the fusion reactors. Therefore, on-line hydrogen sensing is a key technology for these systems. In the present study, conceptual design for the on-line hydrogen sensor to be used in liquid sodium (Na), lead (Pb), lead-bismuth (Pb-Bi), lithium (Li), lead-lithium (Pb-17Li) and molten salt LiF-BeF2 (Flibe) was performed. The cell of hydrogen sensor is made of a solid electrolyte. The solid electrolyte proposed in this study is the CaZrO3-based ceramics, which is well-known as proton conducting ceramics. In this concept, the cell is immersed into the melt which is containing the hydrogen at the activity of PH1 of ambient atmosphere. Then, the cell is filled with Ar-H2 mixture gas at regulated hydrogen activity of PH2. The electromotive force (EMF) is obtained by the proton conduction in the electro chemical system expressed as Pt, Melt(PH1) | Proton conductor | PH2, Pt. The Nernst equation is used for the evaluation of the hydrogen activity from the obtained EMF. The evaluations of expected performance of the sensor in liquid Na, Pb, Pb-Bi, Pb-17Li, Li and Flibe were carried out by means of the measurement test in gas atmosphere at hydrogen activities equivalent to those for the melts in the reactor conditions. In the test, the hydrogen activity in the gas varied from 2.2x10-14 to 1. The sensor exhibited good response, stability and reproducibility.

Numerical Modeling of an Ar–H2 Radio-Frequency Plasma Reactor under Thermal and Chemical Nonequilibrium Conditions

The species densities and the thermal and chemical nonequilibrium phenomena in an Ar–H2 radio frequency inductively coupled plasma reactor used for hydrogenation of materials have been investigated through numerical simulation. The mathematical model consists of a two-temperature fluid dynamics model and a chemical kinetics model that takes into account the effect of local chemical nonequilibrium. Computations are carried out for the rf plasma running at 11.7 kW and 27 kPa for different Ar–H2 mixtures and for pure argon. Predicted results for the electron and heavy-species temperatures, the species densities, as well as the degree of thermal and chemical nonequilibrium, are presented in detail. It is found that the electron and hydrogen atom densities in the reactor and in the near-wall region of the torch are strongly altered by nonequilibrium effects. The hydrogen atom density remains high in the reactor zone, and peaks in a region that has been found to be attractive for material processing. Deviations from thermal and chemical equilibrium are greatly reduced by the addition of hydrogen to an argon plasma.

Hybrid Physical-Chemical Vapor Transport Growth of SiC Bulk Crystals

The effects of H2 addition to the growth ambient during physical vapor transport (PVT) growth of 6H and 4H SiC were investigated using SIMS, DLTS and Hall effect measurements. Using this hybrid physical-chemical vapor transport (HPVT) approach, boules were grown using Ar-H2 and He-H2 mixtures with H2 concentrations up to 50 at%. Thermodynamic modeling suggests that addition of H2 improves the carbon transport in HPVT compared to standard PVT. This should lead to a substantial decrease in the concentration of residual N donors and the concentration of electron traps. This is confirmed by the experimental results. As expected, the source transport rate increased as H2 was added to the growth environment due to increased C transport. The background nitrogen concentration and the free electron density decreased significantly with increasing H2 concentration. The formation of electron traps (activation energies of 0.4 eV, 0.6-0.65 eV, 0.7 eV, 0.9 eV and 1 eV) was also strongly suppressed. These changes were observed for H2 concentrations as low as 4 at%. The decreased N concentration improves the ability to produce high resistivity SiC material, and for H2 concentrations as high as 10-25%, the very first wafers cut from the seed end of the boules have a resistivity exceeding 106 cm.

Interaction-induced dipole moment of the Ar–H2 dimer: Dependence on the H2 bond length

We present ab initio calculations of the interaction-induced dipole moment of the Ar-H2 van der Waals dimer. The primary focus of our calculations is on the H2 bond length dependence of the dipole moment, which determines the intensities of both the collision-induced H2 upsilon = 1 <-- 0 fundamental band in gaseous Ar-H2 mixtures and the dopant-induced H2 upsilon = 1 <-- 0 absorption feature in Ar-doped solid H2 matrices. Our calculations employ large atom-centered basis sets, diffuse bond functions positioned between the two monomers, and a coupled cluster treatment of valence electron correlation; core-valence correlation effects appear to make negligible contributions to the interaction-induced dipole moment for the Ar-H2 configurations considered here.

Micro-crystalline silicon-germanium thin films prepared by the multi-target RF sputtering system

AbstractMicro-crystalline silicon-germanium (μc-SiGe) films were prepared by the multi-target RF sputtering system using Ar and Ar-H2 mixture gases. The crystallization temperature of Si0.3Ge0.7 films is reduced from 600 °C to 400 °C by the introduction of H2 into the sputtering gases. The dark conductivity of 1.7x10-7 S/cm and one order of magnitude of photosensitivity are obtained with the H2/Ar flow ratio of 2. The activation energy of dark conductivity is 0.42 eV, which is a half of the energy gaps of Si0.3Ge0.7, and show that the films have intrinsic nature. Besides, the absorption coefficients are similar to those of single crystalline Si0.3Ge0.7. The results suggest that the H2 introduction is effective both to reduce the dangling bond defects and to decrease the crystallization temperature of the μc-SiGe films.

Poly-crystalline Ge thin films prepared by RF sputtering method for thermo photo voltaic application

AbstractThe poly crystalline Ge films were prepared by the RF sputtering method with Ar and Ar-H2 mixture gases. The crystallization temperature increases from 400 °C to 500 °C due to the H2 introduction into the sputtering gases. On the other hand, the H2 introduction decreases the absorption coefficients in the long wavelength region corresponding to lower energy values than the energy gap of Ge, although much higher absorption coefficients are observed in the case of the Ar sputtering. Probably, the gap state density decreases due to the hydrogen termination of dangling-bonds in the grain-boundaries. The (220) preferential orientation is stressed and the highest Hall mobility is obtained with 75% of the gas flow ratio [Ar/ (Ar+H2)]. The preferential growth probably causes higher quality Ge films.

Quench deposited Kr–H2 and Ar–H2 mixtures: in quest of impurity–hydrogen gels

The structure and morphology of low-temperature quench condensed binary alloys of hydrogen with argon and krypton were studied by powder x-ray diffraction. The nominal hydrogen fraction c in both systems was varied from 0 to 50%; the condensation was performed at 5–6 K; both as-prepared and annealed samples were examined by x-ray diffraction. Few reflections (and often only one) can be unambiguously detected for the as-grown alloy samples. In Kr–H2 condensates with c&amp;lt;10% the x-ray patterns show fine-grain krypton-rich crystallites with a rather high actual hydrogen content as estimated from Vegard’s law. For high nominal hydrogen fractions (c⩾10%) no reflections attributable to the krypton lattice were recorded and the incoherent background showed no characteristic swelling around the position of the (111) reflection from pure Kr; instead, the reflections from a hydrogen-rich hcp phase were distinct. As the temperature was steadily raised the hydrogen reflections disappeared first. Then at a certain temperature the samples underwent an abrupt transformation as a result of which heat was released and larger x-ray detectable textured krypton crystallites were formed. In the as-grown Ar–H2 samples only the (111) reflections from the argon-rich phase were recorded. Warmup led to the same consequences, i.e. hydrogen effusion followed by recrystallization. In both systems the recrystallization onset temperature depends substantially on the nominal hydrogen fraction in the gas. The shift of the lattice parameter in the as-grown argon-based phases suggests strong suppression of the quantum nature of hydrogen in the argon lattice environment. The experimental findings viewed as a whole can be construed as evidence of the fact that quench-condensed hydrogen-containing alloys morphologically resemble helium-impurity solids (gels) whose structure and morphology are currently being studied at Cornell University.

Grain growth in magnetron-sputtered nickel films

Abstract Grain growth and texture development of magnetron-sputtered Na films on thermally oxidized Si wafers were investigated as a function of sputtering and annealing atmospheres. Ni films of 1 μm thickness were sputtered in either pure Ar or an Ar–H2 gas mixture and subsequently annealed in high vacuum or a hydrogen atmosphere at 800°C. The films were characterized by focused ion-beam microscopy and X-ray diffraction. The Ni films had a strong {111} texture after sputtering. Films sputtered in an Ar-H2 mixture and annealed in H2 underwent abnormal grain growth, resulting in a {100} texture. These films had a mean grain diameter of about 50 μm. The unusual abnormal grain growth is believed to be caused by a cleaning of the Ni films during sputtering and annealing in H2.

Transport of ground-state hydrogen atoms in a plasma expansion.

The transport of ground-state atomic hydrogen in the expansion of a thermal plasma generated from an Ar-H2 mixture is studied by means of laser-based diagnostic techniques. The flow of hydrogen atoms is investigated by two-photon excitation laser-induced fluorescence (LIF), whereas Ar atoms are probed by LIF as well as by UV Rayleigh scattering. The transport of Ar atoms can be fully understood in terms of a free jet flow; H atoms on the contrary exhibit an anomalous behavior. In the course of the plasma expansion, hydrogen atoms decouple from the argon fluid by a diffusion process as a direct consequence of recombination of H atoms at the vessel walls. In this contribution it is shown, on the basis of experimental results, how plasma-surface interactions can strongly influence the flow pattern of an atomic radical fluid.

Plasma-assisted boriding of industrial components in a pulsed d.c. glow discharge

The influence of process parameters on plasma-assisted boriding of ferrous materials in a BCl3–H2–Ar atmosphere has been investigated. The elimination of pores in steel substrates is largely influenced by the discharge potential for a fixed BCl3–H2–Ar mixture. The electrical discharge is characterised by the belt of optical emission spectroscopy. Non-porous boride layers have been applied for oil pump drive gears which were then wear tested. The results show excellent wear protection properties of boride layers produced in a plasma-assisted process.

Chemical Kinetic Modelling of Non-Equilibrium Ar-H2 Thermal Plasmas

A chemical kinetic model has been constructed to predict the gas and electron temperature dependence of the neutral and ionic species composition in Ar-H2 mixtures under thermal plasma conditions. The model includes electron impact, thermal impact, ion-molecule, and recombination reactions as well as accounting for diffusion. Important metastable and excited states of species have been accounted for as well as the presence of neutral molecules, radicals, and atoms, positively and negatively charged atoms and molecular ions, and electrons. All relevant electron temperature, gas temperature and pressure terms have been included. Calculations were performed for electron and gas temperatures between 300 and 15000 K and various pressures. Under equilibrium and non-equilibrium conditions, Ar, H2, H, ArH3+, Ar+, H+, H- and electrons were found to be the dominant neutral and charged species. No significant negative ion concentrations are observed.

Velocity Measurements for Arc Jets Produced by a DC Plasma Spray Torch

An optical method was used to determine the axial velocity of plasma jets produced by a DC plasma spray torch. Different experimental conditions were tested in order to systematically study the influence of the working parameters on the plasma velocity. In this way, the arc current ranged between 200 and 600 A, the gas flow rate between 30 and 80 slm, and the internal nozzle diameter between 6 and 10 mm; the plasma gases were either an Ar–H 2 mixture or N 2 . Rather well defined tendencies were observed and at the same time it appeared that the arc stability greatly influenced the fluctuations of the velocity.

Deviation from Local Thermodynamic Equilibrium State in Thermal Plasma.

Spectroscopic analysis of Ar–H2 and Ar–N2 plasmas revealed that the population density of the excited states of each species (Ar, H and N) followed a Boltzmann distribution, but each species had its own respective excitation temperature. The temperature of the argon was lower than that of the hydrogen in the plasma of Ar–H2 mixture. The temperature of the nitrogen was close to that of the argon in the plasma of Ar–N2 mixture under one atmospheric pressure. The estimation of the temperatures defined by the velocity distribution functions from the experimental conditions indicate that there are the possibilities to have higher temperatures for the hydrogen than that for the argon in the plasma. These results suggest that there is a deviation from local thermodynamic equilibrium (LTE) in these plasmas under one atmospheric pressure. The deviations from LTE in these plasmas are explained by the differences in the energy flow in the plasmas. The energy flows of these plasmas are considered as follows from the estimated relaxation times of energy distributions for each species. As for the Ar–H2 plasma, the electric energy is transferred to the electrons and then the energy of electrons is transferred to the hydrogen atoms. The argon atoms are mainly heated by collisions with the hydrogen atoms. In the case of the Ar–N2 plasma, both the argon atoms and the nitrogen atoms are heated by collisions with the electrons which obtain the electric energy. As a result, the temperature state of Te≈TH>TAr and Te>TAr≈TN could exist in the plasma.

Synthesis and characterization of chains composed of nanometer size Fe[sbnd]Cr[sbnd]B particles

Ferromagnetic chains composed of nanometer size FeCrB particles have been synthesized by reducing a mixture of iron and chromium chloride solutions with potassium borohydride at ambient temperature in the presence of an applied magnetic field. The samples are characterized by inductively coupled plasma analysis, transmission electron microscopy, X-ray diffraction and SQUID magnetometer measurements. The particle size could be varied from 28 to 60 nm by varying the ethanol content in the reaction medium. An increasing boron content with increasing ethanol in the reaction medium causes a decrease in crystallinity. The observed magnetic properties are correlated to the degree of crystallinity, chemical composition and particle size. The magnetic properties are improved significantly by annealing the chains at 500°C in ArH2 mixture. The incorporation of about 1 at% Cr into the FeCrB chains enhances significantly the corrosion resistance. The magnetic data are also found to support the chain of spheres model for the magnetization reversal.

Chemical synthesis, microstructure, and magnetic properties of chains composed of ultrafine Fe–Co–B particles

An inexpensive chemical method was used to obtain ferromagnetic chains composed of nanometer size spheres of Fe–Co–B. The method involves a controlled reduction with KBH4 in aqueous as well as water-ethanol media of Fe2+ and Co2+ in the presence of an applied magnetic field. The chemical composition, particle size, crystallinity, and microstructure are characterized by inductively coupled plasma analysis, transmission electron microscopy, and x-ray diffraction. The magnetic properties are evaluated with superconducting quantum interference device magnetometer. The particle size and crystallinity decrease by increasing both the Co content and the amount of ethanol in the reaction medium. The observed magnetic properties are correlated to the degree of crystallinity and chemical composition. The magnetic properties are improved significantly by a subsequent annealing step at 400–500 °C in an Ar–H2 mixture. Moreover, the experiments carried out to verify the magnetization reversal mechanism support the chain of spheres model.

Numerical method and composition in multi-temperature plasmas: Application to an Ar-H2 mixture

To take into account the nonequilibrium between the temperatures (electronic, rotation, vibration, translation) in plasmas, the partition function are modified. Then they are used to determine the concentration in a Gibbs free energy minimization method adopted to a multi-temperature plasma. Their influence oil the results for different temperature hypotheses is quantified. The composition and thermodynamic properties of an Ar-H2 mixture are given and discussed for different temperature nonequilibria.

Electronic structure of anatase TiO2 oxide

Photoemission spectromicroscopy was used to investigate the electronic structure of TiO2 anatase single crystals and polycrystalline thin films. The stoichiometry and the degree of oxidation of as-grown crystals, as-deposited films, as well as of thermally annealed samples in different atmospheres, were analyzed, based on the Ti 2p and O 1s core levels, with an energy resolution of 0.4 eV. The experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals. In reduced samples, the experimental DOS is characterized by intense emission in the region of O 2p bonding orbitals, and does not exhibit an appreciable density of states in the band gap. As-grown crystals exhibit small band gap emission (a few percent of the valence band VB signal) at about 0.8 eV, which is attributed to Ti3+ (3d) defect states. Annealing the crystals at high temperatures in O2 or subsequent thermal reduction in an Ar–H2 mixture (95%–5%) produces nearly stoichiometric surfaces with smaller or undetectable density of Ti3+ states. In addition, some redistribution of the spectral weight is observed in the VB spectra.