A. Yu. Nikiforov

The influence of water vapor content on electrical and spectral properties of an atmospheric pressure plasma jet

An atmospheric pressure plasma jet generated in Ar with water vapor is investigated. It is shown that an increase in the water content results in a decrease in the input power and asymmetry of the current waveform on positive and negative half-periods of the applied voltage. Space-resolved spectroscopy with a resolution of 1?mm and an imaging technique are applied for the characterization of the afterglow and investigation of the influence of water content on plasma properties. The rotational temperature of the jet is determined by simulation of the OH radical emission spectrum, transition A?2?+(v = 0) ? X?2?(v = 0). It is revealed that the temperature of the discharge increases from 450?K (Ar) up to 850?K with an increase in the water content up to 7600?ppm. Generation of the discharge in mixtures of argon with water vapor at a concentration of 350?ppm results in a maximal yield of OH radicals that can be useful in plasma jet applications. Preliminary tests of polypropylene surface modification are carried out in order to estimate the influence of water content on the results of treatment.

Electron density measurement in atmospheric pressure plasma jets: Stark broadening of hydrogenated and non-hydrogenated lines

Electron density is one of the key parameters in the physics of a gas discharge. In this contribution the application of the Stark broadening method to determine the electron density in low temperature atmospheric pressure plasma jets is discussed. An overview of the available theoretical Stark broadening calculations of hydrogenated and non-hydrogenated atomic lines is presented. The difficulty in the evaluation of the fine structure splitting of lines, which is important at low electron density, is analysed and recommendations on the applicability of the method for low ionization degree plasmas are given. Different emission line broadening mechanisms under atmospheric pressure conditions are discussed and an experimental line profile fitting procedure for the determination of the Stark broadening contribution is suggested. Available experimental data is carefully analysed for the Stark broadening of lines in plasma jets excited over a wide range of frequencies from dc to MW and pulsed mode. Finally, recommendations are given concerning the application of the Stark broadening technique for the estimation of the electron density under typical conditions of plasma jets.

Surface Modification of Poly-ε-Caprolactone with an Atmospheric Pressure Plasma Jet

In this work, poly-ε-caprolactone samples are modified by an atmospheric pressure plasma jet in pure argon and argon/water vapour mixtures. In a first part of the paper, the chemical species present in the plasma jet are identified by optical emission spectroscopy and it was found that plasmas generated in argon/0.05xa0% water vapour mixtures show the highest emission intensity of OH (A–X) at 308xa0nm. In a subsequent section, plasma jet surface treatments in argon and argon/water vapour mixtures have been investigated using contact angle measurements and X-ray photoelectron spectroscopy. The polymer samples modified with the plasma jet show a significant decrease in water contact angle due to the incorporation of oxygen-containing groups, such as C–O, C=O and O–C=O. The most efficient oxygen inclusion was however found when 0.05xa0% of water vapour is added to the argon feeding gas, which correlates with the highest intensity of OH (X) radicals. By optimizing the OH (X) radical yield in the plasma jet, the highest polymer modification efficiency can thus be obtained.

Influence of capillary geometry and applied voltage on hydrogen peroxide and OH radical formation in ac underwater electrical discharges

The generation of hydroxyl (OH) radicals and hydrogen peroxide (H2O2) in underwater capillary discharges with different geometries is studied. It is found that the efficiency of the production of these active species depends on the input power and on the length of the capillary. A maximal rate of H2O2 generation of 3.6 × 10−3u2009mmolu2009lu2009s−1 has been measured in a 1u2009mm capillary at a discharge power level of 77u2009W. The hydrogen peroxide yield is lower for the 1u2009mm capillary than for the 5u2009mm capillary . The kinetics of OH formation is investigated by recording emission spectra in the UV range (280–400u2009nm). It is shown that the rate of OH formation sharply decreases with increasing capillary length, for capillaries longer than 3u2009mm. A comparison of the efficiency of different plasma-solution reactors for the generation of active species has been carried out. In the investigated capillary discharge the hydrogen peroxide yield is higher than the values reported for a diaphragm discharge and for a glow discharge with the electrolyte cathode at atmospheric pressure.

Physical properties and chemical efficiency of an underwater dc discharge generated in He, Ar, N2 and air bubbles

A dc excited discharge generated in bubbles (He, Ar, Air, N2) in liquid phase is investigated in this work. Voltage/current characteristics and emission spectra of the discharge are recorded in the current range 10?30?mA. Electron density in the discharge is measured from Stark broadening of the H? line and is of the order of 2?6 ? 1020?m?3, depending on the feed gas. Estimation of electron temperature is carried out based on the balance of charged particles. Gas temperature is estimated by the slope of the Boltzmann plot and by the simulation of the OH band with different , and Tvib. Rotation temperature in the He discharge is 1200?K at I = 10?mA and linearly increases with current up to 1600?K. In the plasma of molecular gases the temperature is higher and almost constant at different currents. Chemical efficiency of the plasma is measured by the production of H2O2 and by the destruction of Direct Blue 106 dye. The highest energy consumption of H2O2 generation is achieved in the air discharge and it decreases up to 50% in the He plasma. Maximal efficiency of dye destruction is observed in the N2 plasma characterized by an energy consumption of dye decomposition of 0.86?g?kWh?1.

Plasma sputtering of water molecules from the liquid phase by low-energy ions: Molecular dynamics simulation

The ion bombardment-assisted transfer of the components of a solution to the plasma zone in an atmospheric-pressure glow discharge with a liquid cathode plays an important role. The dynamics of the impact of a 50–500 eV ion on the surface of liquid water was studied by molecular dynamics simulation. Data on the amount of water molecules transferred by ion impact to the gas phase are presented. It was shown that the sputtering yield of water can reach 450 molecules per ion at an energy consumption of 0.75 eV for sputtering. Structural changes occurring in the liquid phase under ion bombardment were analyzed on the basis of the dynamics of degradation of hydrogen bonds.

Comparison of plasma and plasma-solution modifications of polymer materials in the liquid phase

The capabilities of atmospheric-pressure gas-discharge plasma and plasma-solution systems as applied to enhancement of industrial processes in solutions, such as flax bleaching and wood delignification, were analyzed. It was shown that the set of active species generated in the plasma systems corresponds to that required for the processes in question. According to estimates, the efficiency of plasma-solution systems is higher than that of cold atmospheric-pressure plasma. A kinetic scheme for the bleaching processes activated in the plasma-solution systems is discussed.

Effect of the Products of Plasma-Chemical Transformations on the Properties of a Plasma and Its Dynamic Behavior

A glow-discharge plasma bounded by a chemically reactive surface is studied. It is shown that the investigation of the properties of such systems must take into account heterogeneous reactions and chemical feedback. A study is undertaken to explore the dynamics of attaining the steady-state values of the discharge current and the plasma glow intensity in a case where there is gas desorption from the boundary surface. A formal model of the process is proposed that takes into account the accumulation of negative ions in the bulk of the positive column of the discharge. This model enables one to qualitatively explain the experimentally observed dynamic features of a plasma.

Electrical and optical properties of a diaphragm-type underwater discharge

The electric and spectral properties of diaphragm discharge excited at a frequency of 50 Hz in a sodium sulfate solution were studied. It was found that the emission of hydrogen atoms, OH radicals, and Na atoms is characterized by an initial spike coinciding with a current pulse and afterglow that lasts over a few hundred microseconds, which can be associated with gas discharge-induced chemiluminescence in the solution. Preliminary estimates of the discharge characteristics have been made.