Discharge In Mixture Research Articles

Self-Organization of Dissipative Structures in Gas-Discharge Plasma of Self-Initiated Volume Discharge

It is shown that the features of the development of the self-initiated volume discharge in gas mixtures of a non-chain electrochemical HF laser are caused by self-organizing processes of dissipative structures representing plasma diffusion channels. The formation features of diffusion channels in the gas-discharge plasma of the self-initiated volume discharge are determined.

Langmuir probe measurements in nanodust containing argon-acetylene plasmas

This paper presents the results regarding the influence of cyclic growth of nanoparticles from the gas phase on the parameters of a low-temperature plasma. The measurements were carried out in an asymmetric RF (13.56 MHz) discharge in mixtures of argon and acetylene gases. The main plasma parameters such as the electron temperature, electron density and plasma potential were determined by a Langmuir probe and compared with the discharge self-bias voltage signal. The contamination problem of the electric probe tip in a reactive plasma due to the sticking of nanoparticles and radicals was minimized by applying a rapid “complex” sweep pattern of the probe voltage. The method based on the oscillation of the probe voltage with a frequency higher than the frequency of dust particles. The measurement results show a decrease in the electron density during the cyclic growth due to their absorption on the surface of the nanoparticles. On the contrary, the electron temperature and plasma potential increase. Additionally, a laser light scattering system was used to evidence the presence of the dust particle cloud in the vicinity of the probe position.

Modeling of an Impact of Thin Insulating Film on the Electrode Surface on Discharge Ignition in Mercury Illuminating Lamps at Low Ambient Temperatures

The mixture of argon and mercury vapor with temperature-dependent composition is used as the background gas in different types of gas discharge illuminating lamps. The aim of this work was to develop a model of the low-current discharge in an argon-mercury mixture at presence of a thin insulating film on the cathode and to investigate the influence of film on the discharge ignition voltage at low ambient temperatures. When discharge modeling, we used the obtained earlier expression which describes dependence of the mixture ionization coefficient on temperature. When there was a thin insulating film on the cathode the model took into account that positive charges are accumulated on its surface during the discharge. They generate an electric field in the film sufficient for the field emission of electrons from the metal substrate of the electrode into the insulator and some of them can overcome the potential barrier at the film outer boundary and go out in the discharge volume improving emission characteristics of the cathode.Calculations showed that at a temperature decrease the electric field strengthes in the discharge gap and the voltage in it are increased due to reduction of the saturated mercury vapor density in the mixture followed by the decrease of its ionization coefficient. Existence of a thin insulating film on the cathode surface results in an increase of the cathode effective secondary electron emission yield which compensates the reduction of the mixture ionization coefficient value.The results of discharge characteristics modeling demonstrate that in case of the cathode with an insulating film the discharge ignition becomes possible at a lower inter-electrode voltage. This ensures outdoor mercury lamp turning on at a reduced supply voltage and increases its reliability under low ambient temperatures.

Fourier transform microwave spectroscopy of Criegee intermediates: The conformational behaviour of butyraldehyde oxide.

Four conformers of the n-propyl-substituted Criegee intermediate, CH3CH2CH2CHOO, also named n-butyraldehyde oxide, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodobutane/O2 diluted in Ar or Ne. The observation of only syn species is in contrast to the results of other previous studies of alkyl-substituted Criegee intermediates, in particular, those for the structural isomers, isobutyraldehyde oxide ((CH3)2CHCHOO), and methyl-ethyl-ketone oxide (C2H5C(CH3)OO), for which syn and anti species have been observed coexisting in the gas phase.

A review of thermal processes in the production and their influences on performance of asphalt mixtures with reclaimed asphalt pavement (RAP)

Abstract The use of reclaimed asphalt pavement (RAP) in asphalt mixtures is considered as one of the best sustainable practices in the construction of transportation infrastructures. Extensive efforts have been made to design, produce, and evaluate RAP mixtures produced by the hot recycling technology in asphalt plants. However, the inconsistencies or contradictive conclusions regarding the performance of RAP mixtures reported in the literature impede the use of high percentage of RAP in asphalt mixtures. One of the knowledge gaps for the discrepant behaviors of RAP mixtures is the negligence of the influence of production thermal processes, e.g. mixing time, production temperature, silo storage temperature and time, etc., on the mechanical performance of RAP mixtures. In this context, this paper synthetically reviewed the fundamental thermodynamics and kinematics involved in the plant production of RAP mixtures and the corresponding numerical methodologies to quantify the thermal processes. Three prevailing numerical methods, including overall energy balance method, 1-D thermal-granular model, and coupled computational fluid dynamics and discrete element method, are used to quantify the temperatures of hot gases, virgin aggregates, and RAP particles in the drum dryer. Then, the key production parameters that could influence the performance of RAP mixtures were identified based on the experimental studies. The review results from the experimental studies highlighted the importance of mixing time, mixture discharge temperature, and silo storage time on the mechanical performances of laboratory-produced and plant-produced RAP mixtures. The review findings from this study can be used to guide the best practice of the production of RAP mixtures and further contribute to the energy saving and sustainable construction of using RAP in asphalt mixtures.

Monte Carlo Simulation of the Ion and Fast Atom Energy Spectra at the Cathode Surface in Low-Current Discharge in a Mixture of Argon with Mercury Vapor

Simulation of ion and fast atom motion in the low-current discharge in an argon-mercury mixture used in gas discharge illuminating lamps is performed with the Monte Carlo method. As at the stage of discharge ignition mercury relative content in the mixture is small, only collisions of fast particles with slow argon atoms are taken into account. The energy spectra of the ion and fast atom flows bombarding the cathode surface are calculated. The energy distribution of mercury ions is shown to differ considerably from that found previously from analytical model based on the approximation of mercury ion continuous slowing down in argon. The effective rates of tungsten cathode sputtering by ions and fast atoms are calculated, as well as the flow densities of sputtered atoms, as functions of the reduced electric field strength in the discharge gap. At small mercury content in the mixture of the order of 10–3, the cathode is found to be sputtered mainly by mercury ions. Their contribution to sputtering process decreases with increasing in the reduced electric field strength and decreasing in the mixture temperature.

Самоорганизация газоразрядной плазмы в SF-=SUB=-6-=/SUB=- и смесях на его основе

It was shown that the dynamics of a self-initiated volume discharge in SF6-based mixtures can be explained on the base of the ecton model of the cathode spots birth and the current density limiting effect due to the gas mixture molecular components dissociation.

Features of CS2 conversion in nonequilibrium gas-discharge plasma of multicomponent atmospheric-pressure mixtures

Features of carbon disulfide CS2 conversion in nonequilibrium plasma formed by a pulsed corona discharge in multicomponent atmospheric-pressure mixtures are discussed. A method of standard mixtures is proposed to investigate a mutual influence of CS2 and products of its conversion (sulfur dioxide SO2 and carbonyl sulfide COS) on the efficiency of removal of all three toxic components. Concentration dependencies of toxic impurities on the energy input into the mixture were obtained. Relative reactivities of sulfur-containing components for various mixture compositions were determined.

Numerical Simulation of Plasma Kinetics in a Low-Pressure Inductively Coupled Discharge in Argon and Mercury Mixtures

This paper deals with a model that simulates an electrodeless lamp with argon/mercury chemistry. The plasma kinetics model equations were solved using COMSOL (multiphysics simulation software) with appropriate boundary conditions. The numerical modeling of inductively coupled plasma is of crucial importance to understand the behavior of different physical quantities that characterize the ionized gasses such as electrical parameters. The electric and magnetic fields were handled by the electromagnetic model using the multiturn coil method. Results are in fairly good agreement with the experimental data from the literature and fit well with the expected physics of the discharge plasma.

Diffuse discharges in SF 6 and mixtures of SF 6 with H 2 , formed by nanosecond voltage pulses in non‐uniform electric field

Results of experimental study of nanosecond diffuse discharge in SF6 and gas mixtures of SF6 with H2, D2 and C2H6 are presented. The aim of this work is to study parameters of discharge between two extended electrodes with a small radius of curvature in SF6 and SF6 with additives. It was shown that diffuse discharge can be formed in SF6 at elevated pressure between blade electrodes with length of 30 cm. It was also confirmed that in a sharply non-uniform electric field a beam of runaway electrons is generated and that the gap breakdown occurs due to ionisation waves which begin on electrodes with small radius of curvature. Laser action in the infrared spectral region was obtained in SF6–H2 (D2, C2H6) mixtures. The laser output up to 110 mJ was easily achieved which corresponds to ultimate intrinsic efficiency (with respect to deposited energy) of 10%.

Characteristics of high pressure nanosecond discharge in methane-containing gas mixtures

A nanosecond discharge of voltage up to 240 kV and pulse length of 10÷25 ns in mixtures of CH4 and CO2 at gas pressures up to 6 bar was investigated. For a pulse corona discharge and diffuse discharge from pointed cathodes, the dependences of the energy input in the gas on pressure, gas composition, and electrode geometry were obtained. It is demonstrated that the pulse energy of the diffuse discharge far exceeds the pulse energy of the corona discharge. The maximum specific energy input per pulse for the diffuse discharge was 0.5 J/cm3. The data obtained are necessary to determine the specific energy consumption for methane reforming and correct assessment of the efficiency of discharge technologies for processing natural gas.

The effect of fuel oxidation on electron swarm properties and nanosecond discharge characteristics in combustible mixtures

The results of the calculations of electron transport and rate coefficients in oxidized methane:O2, propane:O2 and H2:O2 mixtures were presented for different temperatures and reduced electric fields E/N from 1 to 3 × 103 Td. The calculations were made for various oxidized fuel fractions. It was shown that fuel oxidation led to a drastic decrease in the average electron energy, electron drift velocity and attachment coefficient for E/N < 60 Td. At higher reduced electric fields, the effect of fuel oxidation on the average electron energy and electron drift velocity was small, whereas the attachment coefficient increased with increasing oxidation degree. In addition, in the hydrocarbon-containing mixtures for E/N ∼ 30 Td, the electron drift velocity varied nonmonotonously with the oxidation degree increase. The critical reduced electric field at which the average rate of electron production in the mixture was equal to the average attachment rate increased with fuel oxidation due to the increased attachment rate and decreased detachment rate. The effect of intermediate species on the electron transport and rate properties in partially oxidized mixtures was small. The calculated results were used to self-consistently simulate fuel oxidation and plasma characteristics for high-voltage nanosecond repetitive discharges in combustible mixtures. Zero-dimensional simulation in a H2:O2 mixture showed that the reduced electric field at the instant when the deposited energy peaked was close to the critical values of E/N and increased with increasing oxidized fuel fraction.

Blistering in Molybdenum Foils under Exposure to the Glow Discharge of D2‒N2 Mixtures

The evolution of indestructible blistering in molybdenum foils with the Mo {100} texture is investigated in dc glow discharge in a D2–N2 mixture with a nitrogen molar fraction in the mixture varying from zero to unity at 100 V potential negative with respect to plasma, a total pressure of 15 Pa, and temperatures of 30–60°C. After the addition of 0.01N2 to the deuterium discharge, the surface area occupied by the blisters increases from 2 to 5% and reaches its maximum of 11% upon exposure to D2−0.04N2 mixture discharge (the fluence is 4 × 1019 cm–2). Afterward, the area decreases, and blistering is absent in the pure N2 discharge. The amount of deuterium desorbed from the samples upon heating also increases with the addition of nitrogen. In accordance with X-ray photoelectron spectroscopy data, a nitride layer about 5 nm thick is formed if small amounts of N2 are added to D2. This layer is assumed to slow both the recombination rate of atomic deuterium coming from the material bulk to the surface and the transfer of D2 molecules into the gas phase. At the same time, the nitride layer increases the diffusion flux of D atoms into the foil bulk, promoting blister growth.

Formation of Nitrogen Oxides (N2O, NO, and NO2) in Typical Plasma and Plasma-Catalytic Processes for Air Pollution Control

Effects of discharge power, O2 content, reaction temperature, catalyst introduction, and presence of NO and dichloromethane (DCM) on the formation of nitrogen oxides (N2O, NO, and NO2) by discharge in N2-O2 mixture have been systematically investigated using a dielectric barrier discharge (DBD) reactor. Results show that discharge in N2-O2 mixture always produces several to hundreds ppm of nitrogen oxides as byproducts. The production of nitrogen oxides increases with the increase of O2 content and the introduction of Al2O3 or RuO2/Al2O3 catalyst. N2O production first increases and then decreases/levels off with increasing discharge power at room temperature, but increases monotonously at 300 °C. NO and NO2 are produced only at relatively high discharge power at room temperature but are produced at all discharge power tested at 300 °C. Increasing the reaction temperature from room temperature to 300 °C significantly reduces the production of N2O but increases that of NO and NO2. The presence of hundreds ppm NO in N2-O2 mixture significantly reduces the production of N2O due to the effective quenching of the vital species for N2O formation (N2(A3Σu+)) by NO. The presence of hundreds ppm DCM, however, hardly affects the production of nitrogen oxides, demonstrating the precedence of nitrogen oxide production over DCM decomposition in N2-O2 plasma.

Simulation of cathode surface sputtering by ions and fast atoms in Townsend discharge in argon-mercury mixture with temperature-dependent composition

The mixture of argon and mercury vapor is used as the background gas in different types of gas discharge illuminating lamps. The aim of this work was development of a model, describing transport of electrons, ions and fast atoms in the one-dimensional low-current gas discharge in argon-mercury mixture, and determination of the dependence of their contributions to the cathode sputtering, limiting the device service time, on the temperature.For simulation of motion of electrons we used the Monte Carlo method of statistical modeling, whereas the ion and metastable excited atom motion, in order to reduce the calculation time, we described on the basis of their macroscopic transport equations, which allowed to obtain their flow densities at the cathode surface. Then, using the Monte Carlo method, we found the energy spectra of ions and fast atoms, generated in collisions of ions with mixture atoms, at the cathode surface and also the effective coefficients of the cathode sputtering by each type of particles.Calculations showed that the flow densities of argon ions and fast argon atoms, produced in collisions of argon ions with slow argon atoms, do not depend on the temperature, while the flow densities of mercury ions and fast argon atoms generated by them grow rapidly with the temperature due to an increase of mercury content in the mixture.There are represented results of modeling of the energy spectra of ions and fast atoms at the cathode surface. They demonstrate that at low mercury content in the mixture of the order of 10–3 the energies of mercury ions exceed that of the other types of particles, so that the cathode is sputtered mainly by mercury ions, and their contribution to sputtering is reduced at a mixture temperature decrease.

Non‐oxidative methane coupling to C2 hydrocarbons in a microwave plasma reactor

Non‐oxidative methane activation is carried out in a microwave plasma reactor for coupling to higher hydrocarbons. Fourier transform infrared spectroscopy (FTIR) was used to measure absolute concentrations of the major hydrocarbon species. Hydrogen concentration was also independently inferred from pressure‐based change in molar flow measurements. By closing both the carbon and hydrogen balance, from stoichiometry of the reactions, the amount of deposits was obtained as well. Additionally, core gas temperatures up to 2500 K were measured with Raman scattering when nitrogen acted as probing molecule in sample mixture discharges. At low gas temperatures, ethane and ethylene were significant products based on plasma chemistry, with ethane selectivities reaching up to 60%. At higher gas temperatures, thermal effects become stronger shifting the selectivity toward acetylene and deposits, resembling more with equilibrium calculations. The energy efficiency of the methane conversion reached up to 15% from which 10% represented coupling efficiency to higher hydrocarbons. It is concluded that there is an interplay between plasma and thermal chemistry where plasma generates radicals and final distribution is set by thermodynamics.

Mode Transition in an Inductively Coupled Argon–Mercury Mixture Discharge Studied by Interferometer and Optical Emission Spectroscopy

The E–H-mode-transition process in an inductively coupled argon–mercury mixture discharge plasma was investigated by an interferometer and a spectrometer. The transition powers upon different natural pressures and mercury content were studied. The electron density versus input power under several discharge conditions in the E mode and H mode was measured detailedly by the interferometer. These results suggested that the nonlinear effects of power absorption and dissipation play a significant role in the mode transition process. In addition, the optical emission system was employed to obtain the intensity ratios of spectral lines at different mercury proportions, which shed light on the mechanism of stepwise ionization and the variability of H-to-E-mode-transition powers in the argon–mercury mixture discharge.

Conformational preferences of Criegee intermediates: Isopropyl substituted carbonyl oxide.

Three conformers of the isopropyl-substituted Criegee intermediate, (CH3)2CHCHOO, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodo-2-methylpropane/O2 diluted in Ar or Ne. The use of different carrier gases in the supersonic expansion reveals the difference of the collisional relaxation process between anti-conformers. The conformational relaxation pathways have been investigated theoretically and are presented as well. In light of these results, the previous study on the ethyl-substituted Criegee intermediate, where the absence of one of the four possible conformers was associated with collisional relaxation processes, has been re-examined. Here we report the detection of a new conformer of the ethyl-substituted Criegee intermediate observed using Ne as the seeding gas.

Plasma-chemical processes under high-power gyrotron’s discharge in the mixtures of metal and dielectric powders

Synthesis of nano- and microstructured materials is a field of high activity in material science. Plasma-chemical processes are effective and versatile tools for this purpose. Plasma can be generated in different ways, in this work we use pulses of high-power gyrotron (75 GHz/550 kW) to initiate a discharge in mixtures of metal and dielectric powders. Depending on the starting composition of mixture it is possible to obtain new materials. It was shown earlier that MgAl2O4 can be prepared from Mg/Al2O3 mixture. Now we demonstrate that organic compounds can also be introduced into the mixture. Using melamine as a source of nitrogen we prepared aluminum oxynitrides (Al11O15N, Al27O39N) starting from Al/Al2O3. An addition of small amount of carborane C2B10H12 makes the process even more intensive, since in this case hydrogen is involved. Proposals on possible mechanism was made basing on observations during the process and composition and morphology of final products.

Self-sustained volume discharge in mixtures of SF6 with hydrocarbons, hydrogen and deuterium for non-chain HF(DF) lasers

This paper reports on the comprehensive studies on a self-sustained volume discharge in SF6-based working media for electrochemical non-chain hydrogen fluoride (deuterium fluoride) lasers. The majority of the experimental results have first been obtained at various values of gas pressure for the discharge gaps with a large interelectrode distance, including plane electrode systems with a strong enhancement of the edge electric field. Some special features of the observed physical phenomena are explained using the developed adequate mathematical models. In particular, a radically new mechanism of the ionization instability in SF6-based mixtures at an intermediate pressure has been first considered and a relevant mathematical theory was developed. On this basis, the experimentally observable break-up of the discharge current into separate filaments in a laser-heated SF6-mixture was qualitatively explained. Some practical applications and recommendations have also been drawn from the performed studies.