Plasma parameter diagnosis using hydrogen emission spectra of a quartz-chamber 2.45 GHz ECRIS at Peking University

A quartz-chamber 2.45 GHz electron cyclotron resonance ion source(ECRIS) was designed for diagnostic purposes at Peking University [Patent Number: ZL 201110026605.4]. This ion source can produce a maximum 84 m A hydrogen ion beam at 50 k V with a duty factor of 10%. The root-mean-square(RMS) emittance of this beam is less than 0.12π mm mrad. In our initial work,the electron temperature and electron density inside the plasma chamber had been measured with the line intensity ratio of noble gases. Based on these results, the atomic and molecular emission spectra of hydrogen were applied to determine the dissociation degree of hydrogen and the vibrational temperature of hydrogen molecules in the ground state, respectively. Measurements were performed at gas pressures from 4×10~(-4) to 1×10~(-3) Pa and at input peak RF power ranging from 1000 to 1800 W. The dissociation degree of hydrogen in the range of 0.5%-10% and the vibrational temperature of hydrogen molecules in the ground state in the range of 3500-8500 K were obtained. The plasma processes inside this ECRIS chamber were discussed based on these results.     

Electrical resistivity of fluid methane multiply shock compressed to 147 GPa

Shock wave experiments were carried out to measure the electrical resistivity of fluid methane. The pressure range of 89–147?GPa and the temperature range from 1800 to 2600?K were achieved with a two-stage light-gas gun. We obtained a minimum electrical resistivity value of 4.5?×?10^?2?Ω?cm at pressure and temperature of 147?GPa and 2600?K, which is two orders of magnitude higher than that of hydrogen under similar conditions. The data are interpreted in terms of a continuous transition from insulator to semiconductor state. One possibility reason is chemical decomposition of methane in the shock compression process. Along density and temperature increase with Hugoniot pressure, dissociation of fluid methane increases continuously to form a H₂-rich fluid.     

Phonon spectrum of a naphthalene crystal at a high pressure: Influence of shortened distances on the lattice and intramolecular vibrations

The Raman spectra of a naphthalene crystal have been measured at room temperature in the pressure range up to 20 GPa. The pressure shift and Grüneisen parameters for intermolecular and intramolecular phonons have been determined. The maximum rate of the pressure shift for intermolecular phonons is 44 cm^?1/GPa, and the rate of the pressure shift for intramolecular phonons lies in the range from 1 to 11 cm^?1/GPa for different modes. The pressure dependence of the phonon frequencies for direct and inverse pressure variations has a hysteresis in the pressure range from 2.5 to 16.5 GPa. It has been shown that the linear dependence of the intermolecular phonon frequency on the crystal density has a peculiarity, which indicates a possible phase transition at a pressure of 3.5 GPa. The pressure dependence of intramolecular phonons related to the stretching vibrations of hydrogen atoms exhibits features that are characteristic of intermolecular phonons, which is associated with the influence of shortened distances between the hydrogen atoms of the neighboring molecules on the intermolecular interaction potential.     

Diagnosis of negative hydrogen ions and rovibrational distribution of H<Subscript>2</Subscript> molecule in non-thermal plasmas

Rovibrational excited hydrogen molecule plays an important role for the production of H^- ions. The correlation between H^- ion density and rovibrational distribution of H₂ molecules has been investigated in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry and molecular beam mass spectrometry. The relative vibrational distribution of molecular hydrogen in the electronic ground state has been determined by the best fitting to the Fulcher-α band emission lines. It is shown that the ratio of the Q_(0-0)(1) to Q_(1-1)(1) line is very suitable and simple for the diagnosis of vibrational temperature in the range of 1500 to 7500 K. At certain discharge conditions (ac 40 kHz, 14 kV), the vibrational temperature decreases from 3600 to 2400 K as the pressure increases from 100 to 200 Pa and the negative ions density near the ground electrode also decreases as the pressure increases. Both the hydrogen ions density and the vibrational temperature increase with the increasing of discharge voltage. It is found that the evolution of negative atomic hydrogen ions density greatly depends on the vibrational temperature.     

Nitrogen dissociation and its excitation/vibrational temperature with hydrogen admixture in 50 Hz DC discharge

Trace rare gas optical emission spectroscopy (TRG-OES) is carried out to determine the excitation temperature, vibrational temperature, dissociation fraction and nitrogen (N) atom density in 50?Hz active screen cage nitrogen plasma, as a function of discharge parameters (current density and fill pressure) and hydrogen concentrations. The excitation temperature is determined from Ar–I emission lines and is found to increase with hydrogen mixing. In a similar fashion, the vibrational temperature of second positive system is determined and found to have increasing trend with hydrogen addition. The dissociation fraction increases with hydrogen concentration up to 40% H₂ in the nitrogen plasma, so as the nitrogen atom density.     

Temperature and concentration measurements of molecular hydrogen in a filamentary discharge by coherent anti-stokes raman spectroscopy (CARS)

Coherent anti-Stokes Raman Spectroscopy (CARS) is applied to a filamentary discharge in H₂. Temperature and density profiles of molecular hydrogen are determined. The maximum temperature observed on the discharge axis is 5685 K. Vibrational and rotational transitions are analyzed and a difference in the evaluated temperatures is found which increases with pressure. In addition, the reactive thermal conductivity associated with dissociation is determined and compared with earlier work.     

Metallization of fluid hydrogen at 140 GPa (1.4Mbar) by shock compression

Abstract

The minimum electrical conductivity of a metal was produced in dense hydrogen using shock compression. Metallization occurs at 140 GPa (1.4 Mbar), 0.6 g/cm³ (ninefold compression of initial liquid-H₂ density), and 3000 K. The relatively modest temperature generated by a reverberating shock wave produced the metallic state in a warm quantum fluid at a lower pressure than expected previously for the crystallographically ordered solid at low temperatures. Future research directions are discussed. Possible scientific and technological uses of metastable solid metallic hydrogen are speculated upon in the unlikely event that the metallic fluid can be quenched to this state at ambient pressure and temperature.     

High temperature equation of state of metallic hydrogen

The equation of state of liquid metallic hydrogen is solved numerically. Investigations are carried out at temperatures from 3000 to 20 000 K and densities from 0.2 to 3 mol/cm³, which correspond both to the experimental conditions under which metallic hydrogen is produced on earth and the conditions in the cores of giant planets of the solar system such as Jupiter and Saturn. It is assumed that hydrogen is in an atomic state and all its electrons are collectivized. Perturbation theory in the electron-proton interaction is applied to determine the thermodynamic potentials of metallic hydrogen. The electron subsystem is considered in the randomphase approximation with regard to the exchange interaction and the correlation of electrons in the local-field approximation. The proton-proton interaction is taken into account in the hard-spheres approximation. The thermodynamic characteristics of metallic hydrogen are calculated with regard to the zero-, second-, and third-order perturbation theory terms. The third-order term proves to be rather essential at moderately high temperatures and densities, although it is much smaller than the second-order term. The thermodynamic potentials of metallic hydrogen are monotonically increasing functions of density and temperature. The values of pressure for the temperatures and pressures that are characteristic of the conditions under which metallic hydrogen is produced on earth coincide with the corresponding values reported by the discoverers of metallic hydrogen to a high degree of accuracy. The temperature and density ranges are found in which there exists a liquid phase of metallic hydrogen.     

Reduction of oxidized Fe(100) by hydrogen

The interaction of hydrogen with the oxide layer on Fe(100) has been studied with ellipsometry, AES and LEED. The oxide layer formed at room temperature on Fe(100) rearranges at elevated temperatures, resulting in a reconstructed oxide phase in deeper layers, plus a single monolayer of oxygen on top of the surface. This monolayer is unchanged upon heating. These surfaces are exposed to hydrogen pressures up to 2 × 10⁻² Torr at crystal temperatures between 473 and 643 K. The reduction proceeds via a mechanism of dissociative adsorption of hydrogen on an oxygen filled site. A continuous transport of oxygen from deeper layers to the surface region occurs on a time scale which is fast in comparison with the observed reaction rate. These oxygen containing reaction sites are related to the reconstructed oxide, since a single monolayer of oxygen on Fe(100) is inactive to hydrogen in the pressure range measured. The apparent activation energy for the reaction between the oxide overlayer on Fe(100) and hydrogen is 59 ± 4 kJ/mol at the initial oxygen coverage.     

Hydrogen permeation of tungsten phosphate glass thin films

Thin films of tungsten phosphate glasses were deposited on a Pd substrate by a pulsed laser deposition method and the flux of hydrogen passed thorough the glass film was measured with a conventional gas permeation technique in the temperature range 300–500 °C. The glass film deposited at low oxygen pressure was inappropriate for hydrogen permeation because of reduction of W ions due to oxygen deficiency. The membrane used in the hydrogen permeation experiment was a 3-layered membrane and consisted of Pd film (~ 20 nm), the glass film (≤ 300 nm) and the Pd substrate (250 µm). When the pressure difference of hydrogen and thickness of the glass layer were respectively 0.2 MPa and ~ 100 nm, the permeation rate through the membrane was 2.0 × 10^? 6 mol cm^? 2 s^? 1 at 500 °C. It was confirmed that the protonic and electronic mixed conducting glass thin film show high hydrogen permeation rate.     

Acoustic cavitation in 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide based ionic liquid

In this work, a comparison between the temperatures/pressures within acoustic cavitation bubble in an imidazolium-based room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide ([BMIM][NTf₂]), and in water has been made for a wide range of cavitation parameters including frequency (140–1000 kHz), acoustic intensity (0.5–1 W cm⁻²), liquid temperature (20–50 °C) and external static pressure (0.7–1.5 atm). The used cavitation model takes into account the liquid compressibility as well as the surface tension and the viscosity of the medium. It was found that the bubble temperatures and pressures were always much higher in the ionic liquid compared to those predicted in water. The valuable effect of [BMIM][NTf₂] on the bubble temperature was more pronounced at higher acoustic intensity and liquid temperature and lower frequency and external static pressure. However, confrontation between the predicted and the experimental estimated temperatures in ionic liquids showed an opposite trend as the temperatures measured in some pure ionic liquids are of the same order as those observed in water. The injection of liquid droplets into cavitation bubbles, the pyrolysis of ionic liquids at the bubble-solution interface as well as the lower number of collapsing bubbles in the ionic liquid may be the responsible for the lower measured bubble temperatures in ionic liquids, as compared with water.     

The Hydrogen Dissociator

A performance analysis is presented for the hydrogen dissociator used in hydrogen masers to provide a beam of atomic hydrogen. An analysis of the discharge characteristics yields relations for electron temperature as a function of vessel size and gas pressure and for plasma density as a function of power input. Also a relation between ion impact energy at the wall and electron temperature is derived. For a typical dissociator (2" diameter, 0.1 Torr hydrogen pressure, and 4 watt input power) these relationships yield an electron temperature of 39,000°K, a plasma density of 1011 cm-3 and an ion impact energy of 20 volts. The dissociation rate is calculated using published cross-sections. Assuming a recombination rate of 4 × 10-3, the analysis yields an atomic hydrogen density of about 1014 cm-3, a degree of dissociation of 2%, and an atomic beam flux of 1.3 × 1018 cm-2 × sec-1 for the example quoted. This beam flux is in good agreement with estimated values for hydrogen masers. A coefficient for performance ? is derived for the hydrogen dissociator, defined as the ratio of atomic beam flux to discharge power consumption. It is shown that ? is a function of the electron temperature and has a maximum at 87,000°K. It is concluded from this analysis that the discharge in presently used hydrogen dissociators is well optimized given the pressure constraints of the system.     

Single crystalline graphene synthesized by thermal annealing of humic acid over copper foils

Production of graphene by thermal annealing on copper foil substrates has been studied with different sources of carbon. The three carbon sources include humic acid derived from leonardite, graphenol, and activated charcoal. Hexagonal single crystalline graphene has been synthesized over the copper foil substrates by thermal annealing of humic acid, derived from leonardite, in argon and hydrogen atmosphere (Ar/H₂=20). The annealing temperature was varied between 1050 °C and 1100 °C at atmospheric pressure. Samples have been investigated using scanning electron microscope (SEM) and Raman spectroscopy. At lower temperatures the thermal annealing of the three carbon sources used in this study produces pristine graphene nanosheets which cover almost the whole substrate. However when the annealing temperature has been increased up to 1100 °C, hexagonal single crystalline graphene have been observed only in the case of the humic acid. Raman analysis showed the existence of 2D band around 2690 cm⁻¹.     

Sequence of phase transitions in the thermal dissociation and hydrogen reduction of YMn2O5 Compound

The sequence of phase transitions in the thermal dissociation and hydrogen reduction of YMn₂O₅ compound in the temperature range of 973–1123 K at pressures of 10³-10^-16 Pa is determined by the static method on a vacuum circulation system with subsequent X-ray diffraction analysis of the quenched solid phases. A fragment of the isothermal cross section of the Y-Mn-O system phase diagram is constructed in composition-oxygen pressure coordinates at 1173 K.     

Optical emission spectroscopy of 50 Hz pulsed dc nitrogen–hydrogen plasma in the presence of active screen cage

The N₂-H₂ plasma gas mixture, generated in a 50?Hz pulsed dc discharge system with active screen cage, is characterized by optical emission spectroscopy (OES), as a function of gas pressure, the fractions of hydrogen and current density. The N₂ dissociation degree and N atomic density was measured with actinometery where argon gas is used as actinometer. It was shown that the increase in hydrogen fraction enhances the dissociation of N₂, until the maximum of 40%. The excitation temperature is determined from Ar-I emission line intensities by using the simple Boltzmann plot method. The dissociation fraction and excitation temperature is found to increase with hydrogen mixing in nitrogen plasma.     

High-resolution transmission measurements of CO2 at high temperatures for industrial applications

High-resolution transmission spectra of CO₂ in the 2.7, 4.3 and 15 μm regions at temperatures up to 1773 K and at approximately atmospheric pressure (1.00±0.01 atm) are measured and compared with line-by-line calculations based on the HITEMP-1995, HITEMP-2010, CDSD-HITEMP and CDSD-4000 databases. The spectra have been recorded in a high-temperature flow gas cell and using a Fourier transform infrared (FTIR) spectrometer at a nominal resolution of 0.125 cm^?1. The volume fractions of CO₂ in the measurements were 1, 10 and 100%. The measurements have been validated by comparison with medium-resolution data obtained by Bharadwaj and Modest [6]. The deviations between the experimental spectra and the calculations at 1773 K and the vibrational energy exchange and thermal dissociation of CO₂ at high temperatures are discussed.     

Ferromagnetism, variable range hopping and anomalous Hall effect in epitaxial Co:ZnO thin film

A series of high quality single crystalline epitaxial Zn_0.95Co_0.05O thin films is prepared by molecular beam epitaxy. Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a range of 10¹⁸ cm^-3-10²⁰ cm^-3 by changing the oxygen partial pressure during film growth. The conduction shows variable range hopping at low temperature and thermal activation conduction at high temperature. The ferromagnetism can be maintained up to room temperature. However, the anomalous Hall effect is observed only at low temperature and disappears above 160 K. This phenomenon can be attributed to the local ferromagnetism and the decreased optimal hopping distance at high temperatures.     

Inhibition of hydrogen chemisorption on uranium surfaces by traces of water vapor

Traces of about 2% water vapor are sufficient to inhibit hydrogen dissociation and chemisorption on uranium surfaces, under low pressure exposures, at room temperature. The efficiency of the inhibition increases with temperature in the range of 200 - 400 K. The inhibition effect is also influenced by the extent of residual strain of the sample, with increasing inhibition efficiencies exhibited by a less strained surface. O₂, in contrast to H₂O, is not an inhibitor to surface adsorption and dissociation of hydrogen. Three types of mechanisms are discussed in order to account for the above inhibition effect of water. It is concluded that the most probable mechanism involves the reversible adsorption of water molecules on hydrogen dissociation sites causing their “blocking”.     

A high temperature and atmospheric pressure experimental and detailed chemical kinetic modelling study of 2-methyl furan oxidation

An experimental ignition delay time study for the promising biofuel 2-methyl furan (2MF) was performed at equivalence ratios of 0.5, 1.0 and 2.0 for mixtures of 1% fuel in argon in the temperature range 1200–1800 K at atmospheric pressure. Laminar burning velocities were determined using the heat-flux method for mixtures of 2MF in air at equivalence ratios of 0.55–1.65, initial temperatures of 298–398 K and atmospheric pressure. A detailed chemical kinetic mechanism consisting of 2059 reactions and 391 species has been constructed to describe the oxidation of 2MF and is used to simulate experiment. Accurate reproduction of the experimental data has been obtained over all conditions with the developed mechanism. Rate of production and sensitivity analyses have been carried out to identify important consumption pathways of the fuel and key kinetic parameters under these conditions. The reactions of hydrogen atom with the fuel are highlighted as important under all experimental conditions studied, with abstraction by the hydrogen atom promoting reactivity and hydrogen atom addition to the furan ring inhibiting reactivity. This work, to the authors knowledge, is the first to combine theoretical and experimental work to describe the oxidation of any of the alkylated furans. The mechanism developed herein to describe 2MF combustion should also function as a sub-mechanism to describe the oxidation of 2,5-dimethyl furan whilst also providing key insights into the oxidation of this similar biofuel candidate.     

Thermally stable hydrogen compounds obtained under high pressure on the basis of carbon nanotubes and nanofibers

Compounds containing 6.3–6.5 wt % H and thermally stable in vacuum up to 500°C were obtained by annealing graphite nanofibers and single-walled carbon nanotubes in hydrogen atmosphere under a pressure of 9 GPa at temperatures up to 45°C. A change in the X-ray diffraction patterns indicates that the crystal lattice of graphite nanofibers swells upon hydrogenation and that the structure is recovered after the removal of hydrogen. It was established by IR spectroscopy that hydrogenation enhances light transmission by nanomaterials in the energy range studied (400–5000 cm^?1) and results in the appearance of absorption bands at 2860–2920 cm^?1 that are characteristic of the C–H stretching vibrations. The removal of about 40% of hydrogen absorbed under pressure fully suppresses the C–H vibrational peaks. The experimental results are evidence of two hydrogen states in the materials at room temperature; a noticeable portion of hydrogen forms C–H bonds, but the most of the hydrogen is situated between the graphene layers or inside the nanotubes.