Pressure DC Discharge Research Articles

GAS DISCHARGES AS A TOOL FOR CLEANING GAS AND SOLUTION MEDIUMS AND SYNTHESIS OF INORGANIC MATERIALS

The article provides an overview of the results of research of the purification processes of gas and solution media from organic (tetrachloromethane, 1,4-dichlorobenzene and 2,4-di-chlorophenol, etc.) and inorganic (Cr(VI), Mn(VII), Cu2+, Fe2+3+, Zn2+, Cd2+, Ni2+, etc.) substances, as well as the synthesis of oxide materials based on the above metals under the action of a dielectric barrier discharge (DBD) and atmospheric pressure DC discharge. The work was carried out in joint research conducted at the Departments of Industrial Ecology and Microelectronic Devices and Materials of the ISUCT over the past 10 years. As a result of the research, the kinetic regularities of decomposition of the above organic substances were revealed, i.e. the rate and effective rate constants of the decomposition reactions and their dependences on the DBR parameters (power, gas and solution flow rates) were determined. On the basis of these data, the energy efficiency of decomposition processes was found. The main decomposition products and their dependence on the discharge parameters are determined. Probable mechanisms of the ongoing processes were proposed. It is shown that the action of a direct current discharge on aqueous solutions leads to the reduction of Cr(VI) and Mn(VII) in the composition of Cr2O72- and MnO4- to Cr3+ and Mn2+ ions. When the same discharge acts on solutions of salts containing Cu2+, Fe2+3+, Zn2+, Cd2+, Ni2+ ions, the formation of colloidal solutions of hydroxo compounds of these ions is observed. The sizes of resulting particles, their phase and chemical composition were determined by DLS, SEM, EDX, TGA, XRD, DSC methods. It is shown that the calcination of the obtained particles leads to the formation of crystalline oxides of the corresponding metals. Thus, the action of the discharge ensures the purification of aqueous solutions from heavy metals with the formation of oxide materials of the nanoscale range, which have semiconductor and catalytic properties. For citation: Guschin A.A., Grinevich V.I., Kvitkova E.Yu., Gusev G.I., Shutov D.A., Ivanov A.N., Manukyan A.S., Rybkin V.V. Gas discharges as a tool for cleaning gas and solution mediums and synthesis of inorganic materials. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 7. P. 120-131. DOI: 10.6060/ivkkt.20236607. 6835j.

Numerical study of various scenarios for the formation of atmospheric pressure DC discharge characteristics in argon: from glow to arc discharge

In this work, on the basis of a unified model from the point of view of describing the gas discharge gap and electrodes for 2D geometry, numerical calculations were carried out to study various modes of direct current discharges in argon at atmospheric pressure. The influence of the cooling conditions of the electrodes on the current–voltage characteristic of the discharge is shown: the transition from normal glow to arc discharge with the formation of an abnormal glow mode and without it. It is shown that, depending on the cooling conditions of the electrodes, two forms of arc discharge can be obtained: with a diffuse or contracted current spot. In the low-current mode, current and voltage oscillations were obtained during the transition from the Townsend to the normal glow discharge.

Chromium Ion Redox Processes in Aqueous Solution during Treatment with Atmospheric Pressure Direct-Current Discharge in Oxygen

The kinetic features of the oxidation–reduction processes of chromium ions during the treatment of potassium dichromate aqueous solutions with concentrations of 0.092–0.39 mmol/L in atmospheric-pressure dc discharge in oxygen at currents of 20–60 mA have been investigated. The solution served as the cathode of the discharge. It has been found that the discharge induces reversible Cr6+ ↔ Cr3+ redox reactions of chromium ions. The limiting degree of reduction of Cr6+ ions slightly depends on the discharge current and decreases with an increase in the initial concentration of the solution. The apparent rate constants of oxidation and reduction have been found, and the energy efficiency of the process has been evaluated. The obtained data are compared with previously obtained results for electric discharge in air and argon. It has been shown that the discharge in argon is the most effective for carrying out the reduction process.

Reduction–Oxidation of Chromium Ions in Aqueous Solution by Treatment with Atmospheric-Pressure Direct-Current Discharge in Argon

Kinetic features of the oxidation–reduction processes of chromium ions in a potassium dichromate aqueous solution subjected to treatment in argon atmospheric-pressure dc discharge have been investigated in the discharge current range of 20–80 mA and the dichromate concentration range of 0.1–0.5 mmol/L. The solution served as the discharge cathode. It has been revealed that the discharge treatment stimulates the reduction reactions of Cr6+ to Cr3+ ions and the reverse reactions of oxidation of Cr3+ to Cr6+ ions; i.e., the oxidation–reduction reactions are reversible. The limiting degree of reduction of Cr6+ ions has been found to depend on the discharge current and the initial concentration of the solution. The apparent rate constants of oxidation and reduction have been determined, and the energy efficiency of the process has been evaluated. The data are compared with the results obtained earlier for a discharge in air.

Experimental Study of Heating of a Liquid Cathode and Transfer of Its Components into the Gas Phase under the Action of a DC Discharge

An atmospheric-pressure dc discharge in air (i = 10–50 mA) with metal and liquid electrolyte electrodes was studied experimentally. An aqueous solution of sodium chloride (0.5 mol/L) was used as the cathode or anode. The electric field strength in the plasma and the cathode (anode) voltage drops were obtained from the measured dependences of the discharge voltage on the electrode gap length. The gas temperature was deduced from the spectral distribution of nitrogen emission in the band N2(C3Π u → B3Π g , 0–2). The time dependences of the temperatures of the liquid electrolyte electrodes during the discharge and in its afterglow, as well as the evaporation rate of the solution, were determined experimentally. The contributions of ion bombardment and heat flux from the plasma to the heating of the liquid electrode and transfer of solvent (water) into the gas phase are discussed using the experimental data obtained.

Modification of polypropylene in the afterglow of the atmospheric pressure discharges in air and argon

Polypropylene films were modified in the flowing afterglow of the atmospheric pressure DC discharge in argon and in air. The modification was carried out at a discharge current of 15 mA, a gas flow rate of 24 and 105 m/s and a treatment time of 3 - 30 s. Polymer samples were placed on the distance of 5 - 15 mm downstream the plasma Contact angles for water and ATR-FTIR spectra were used for the film surface characterization. Concentrations of oxygen containing groups in modified polymer layer were estimated on the base of ATR-FTIR data. Modification in the both plasma forming gases results in the decrease of the contact angles and in the formation of oxygen containing groups in the polymer surface layer. Dependencies of contact angles on treatment time, gas flow rate and plasma - polymer distance were obtained. Increasing the treatment time and the gas flow rate results in a higher oxidation degree of the PP. Treatment in the afterglow of the argon plasma has been shown to give the less water contact angles and more densities of oxygen containing groups in polypropilene at the gas flow rate of 105 m/s and the treatment time of 30 s.

Transfer of Liquid Cathode Components to the Gas Phase and Their Effect on the Parameters of the Atmospheric Pressure DC Discharge

The transfer of solvent and components of dissolved substances from aqueous solutions to the gas phase under the action of atmospheric pressure air glow discharge was experimentally studied. solutions of NaCl, KCl, CuCl2, MgCl2, CaCl2, SrCl2, BaCl2, NaNO3, KNO3, Ba(NO3)2, Na2SO4, K2SO4, CuSO4 with concentrations of 0.1–0.5 mol/L were used as the cathodes of DC discharge at a current of 10–70 mA. The influence of the solution composition on cathode voltage drop and the electric field strength in plasma has been shown. Plasma emission spectra showed the appearance of metal atoms in the plasma requires threshold discharge current or threshold power input to the liquid cathode by ion bombardment. The threshold power values depend on the mass of hydrated cations and their concentration in solution. The efficiency of the transfer processes was characterized by transfer coefficients—the number of particles transferred from the liquid to the gas phase per one ion bombarding the cathode. Dependences of the transfer coefficients on the power dissipated in the cathode region and on the hydration energy of the cations were obtained. Experimental data on the rate of condensate accumulation in the special trap were used to estimate the concentrations of water molecules in the plasma.

IMPACT OF TRANSFER PROCESSES OF LIQIUD CATHODE COMPONENTS ON PHYSICAL-CHEMICAL PARAMETERS OF ATMOSPHERIC PRESSURE DC DISCHARGE

Experimental data on glow discharge parameters of atmospheric pressure in air with cathodes from distilled water and water containing ions of potassium, sodium and copper (II) are obtained. Chlorides of the corresponding salts were used. The current range was 20-60 mA, and the solution concentrations were -0.1-0.4 mol/l. The cathode drops of the potential and the electric fields in the plasma are determined by the mobile anode method. With emission spectroscopy by modeling the unresolved rotational structure of the emission bands of the second positive system of nitrogen molecules, gas temperatures were found. On the basis of these data, the total concentrations of the particles, the reduced electric field strengths, were found. It is found that the increase in the discharge current leads to a decrease in the cathode drops of the potential, the strengths of the electric fields, and the reduced field strengths. At the same time, the temperature of the gas was practically independent on the discharge current and it was 1600 ± 150 K. By numerical solution of the Boltzmann equation for electrons, electron energy distribution functions, mean energies and electron concentrations and rate constants of the processes occurring under the action of electron impact were determined. An estimate is made of the contribution to the formation of charged particles in the plasma of ionization processes of metal atoms that appear in the gas phase as a result of non-equilibrium transfer from the liquid cathode. It is shown that for molar fractions of metal atoms of 10-4 and higher, ionization is completely determined by collisions of electrons with metal atoms, rather than with molecules of the main plasma-forming gas. It is also shown that discharges with cathodes containing salt solutions have smaller values of cathode potential drops.Forcitation:Kuletsan A.L., Shutov D.A., Rybkin V.V. Impact of transfer processes of liqiud cathode components on physical-chemical parameters of atmospheric pressure dc discharge. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 6. P. 52-58.

Dynamic transition in the discharge current between gas-dominant discharge and self-sputtering in high-power impulse magnetron sputtering

Abstract An unstable stage is observed from the discharge current during the transition from gas-dominant discharge to the self-sputtering dominant regime in high-power impulse magnetron sputtering (HiPIMS). The phenomenon and the formation mechanism are time dependent and there is a dynamic transition between the two stable stages. The threshold of the high stable discharge is investigated at different pressure and hybrid DC discharge. According to the derivation of the discharge current, the temperature in the discharge is found to play a major role in the dynamic transition at moderate voltage.

Kinetics and Mechanism of Cr(VI) Reduction in a Water Cathode Induced by Atmospheric Pressure DC Discharge in Air

The process of reduction of Cr6+ ions (solution of potassium dichromate, K2Cr2O7) in a water cathode was studied during a DC discharge in air. The concentration range of Cr6+ was (5.7–19) ×10−5 mol/l and discharge current range was 20–80 mA. Cr6+ ions were shown to be reversibly reduced under a discharge action. The equilibrium degree of reduction increased with increasing initial concentration of the solution at fixed discharge current. At fixed initial concentration the reduction degree increased with increasing discharge current. The reduction degrees so obtained were 0.34–0.84. A kinetic scheme of the processes taking place in a solution was proposed. The calculated data obtained as a result of application of this scheme described well the experimental results on Cr6+ kinetics. The main processes of Cr6+ reduction and Cr3+ oxidation were revealed. HO2· radicals and hydrogen peroxide were shown to be responsible for Cr6+ reduction whereas ·OH radicals and O2 molecules provide the reverse process of Cr3+ oxidation to Cr6+. The mechanism of action of phenol additives improving the process efficiency is discussed. The efficiency of phenol action as a radical scavenger was shown to be determined with its mass-transfer to the reaction area rather than chemical reaction rate.

Reduction of chromium(VI) in aqueous solution by treatment with direct-current discharge at atmospheric-pressure in air

The kinetics of reduction of Cr(VI) by treating its aqueous solution in atmospheric pressure dc discharge in air has been studied at the discharge current range of 20–80 mA and the concentration range of 1.25–12.5 mg/L. The solution has served as the discharge cathode. It has been shown that the discharge treatment leads to a decrease in the Cr(VI) concentration to its steady-state value, with the latter depending on the discharge current and the initial concentration of the solution. The effective rate constants of the forward and reverse processes have been determined, the energy efficiency of the process has been evaluated, and possible mechanisms of the reactions involved have been discussed.

Experimental Study of the Liquid Cathode Components Transfer to the DC Discharge Plasma at Atmospheric Pressure

The transfer processes of solvent and dissolved substances in gas phase from aqueous solutions used as cathodes under the action of atmospheric pressure DC discharge were investigated.The electric field strength in plasma (E), cathode voltage drop (Uc) and rates of solution evaporation were measured. The transfer coefficients were calculated. The effect of transfer processes on plasma physical properties was experimentally studied. The threshold characteristics of cations transfer process were determined.

Characteristics of atmospheric pressure DC discharge above sulfonol water solutions

The electrophysical characteristics of the plasma of the contact DC discharge in the air above sulfonol (C12H25C6H4SO3Na) water solutions, within the concentration range of 5 × 10−3−10 g/L, at a discharge current within the range 20–100 mA are investigated. The input discharge power, the electric current density, the cathode potential drop, and the electric field strength depending on the solution concentration have been measured. The radiation spectra of the discharges are investigated and the emitting components are established. The regularities of the radiation intensity behavior of the excited atoms and molecules in the discharge, the vibrational temperatures of the vibration excited nitrogen molecules, and the neutral particle temperatures are determined. Also, the reduced electric field strengths for the whole range of the investigated sulfonol concentrations is calculated.

Destruction of sodium lauryl sulfate in its aqueous solutions by contact glow discharge treatment

Degradation of the anionic surfactant sodium lauryl sulfate (C12H25SO4Na, SLS) in its aqueous solutions with concentrations of 0.02–1.1 mmol/L acting as a liquid cathode of atmospheric-pressure dc discharge in air at a discharge current ranging within 20–100 mA has been studied. The products of degradation in the liquid phase have been identified, and the kinetic characteristics of their formation at an initial SLS concentration of 5 × 10−3 g/L (∼0.02 mmol/L) and a discharge current of 40 mA have been determined.

Modeling Chemical Composition for an Atmospheric Pressure DC Discharge in Air with Water Cathode by 0-D model

This paper reports the results of the chemical composition modeling for an atmospheric pressure DC air discharge with water cathode. The modeling was based on the combined solution of Boltzmann equation for electrons, equations of vibrational kinetics for ground states of N2, O2, H2O and NO molecules, equations of chemical kinetics and plasma conductivity equation. Calculations were carried out using experimental values of E/N and gas temperatures for the discharge currents range of 20–50 mA. The effect of H2O concentration on the plasma composition was studied. The main particles of plasma were shown to be O2(a1Δ, b1Σ), O(3P), NO, NO2, HNO3, H2O2 and OH. Effective vibrational temperatures of molecules were higher than gas temperature and they did not depend on the discharge current. Distribution functions on vibrational levels for N2, O2, H2O and NO ground states were non-equilibrium ones.

Destruction of sulfonol in its aqueous solutions by contact glow discharge treatment: 2. Mechanisms and kinetic simulation

A mechanism for the degradation of Sulfonol in its aqueous solutions acting as a liquid cathode of atmospheric-pressure dc discharge in air and for the formation of the products has been proposed, and the chemical kinetics of the degradation processes has been numerically simulated.

Destruction of sulfonol in its aqueous solutions by contact glow discharge treatment: 1. Product formation kinetics

Degradation of the anionic surfactant Sulfonol (sodium alkylbenzenesulfonate) in its aqueous solutions acting as a liquid cathode of atmospheric-pressure dc discharge in air has been studied. The products of plasma-chemical decomposition of Sulfonol in the liquid phase have been identified. The kinetic characteristics of the formation of products of plasma-chemical reactions at a substrate concentration of 5 × 10−3 g/L (0.014 mmol/L) and a discharge current of 40 mA have been determined.

Deposition of cathode carbon films in the plasma of a low-current gas discharge at atmospheric pressure

Plasma-chemical deposition of carbon films is carried out under the conditions of an atmospheric-pressure dc discharge from a mixture of hydrocarbons (methane and butane–propane) with helium on substrates (Ni and Cu) that serve as the cathode in the process of discharge. The formation of predominantly disordered films from graphite crystallites is observed at small deposition times. An array of carbon nanotubes coated with structured carbon is formed, as the duration of deposition increases; layers of graphitized scales are formed along the film’s edges.

The characteristics of electrons and vibrational distributions of molecules in an atmospheric-pressure liquid-cathode dc discharge in air

Results are given of the calculation of vibrational distribution of N2, O2, and H2O molecules and of electron energy distribution functions in the plasma of atmospheric-pressure dc discharge with a distilled-water cathode. The system of equations of vibrational kinetics is solved simultaneously with the Boltzmann equation using the measured values of reduced electric-field strength, of discharge current density, of gas temperature, and of band intensities of the second positive system of N2 molecules.