The Yields of Radical Products in Water Decomposition under Discharges with Electrolytic Electrodes

The features of generation, combination, and scavenging of primary radicals under the action of an atmospheric-pressure glow discharge and microdischarges on electrolytic electrodes were compared. A profound difference in chemical effects was revealed at different polarities of the electrolytic electrode. The identity of water decomposition mechanisms was demonstrated for the electrolytic cathode in the case of a stationary discharge over the surface and for the arrays of quasi-stationary microdischarges at the valve anode immersed in the solution. The assumption that the generation of primary water decomposition products in a discharge system with an electrolytic cathode is predominantly due to ionization in the liquid phase at the expense of the kinetic energy of accelerated particles arriving from the discharge to the solution was confirmed.     

A Study of Two-Dimensional Microdischarge Pattern Formation in Dielectric Barrier Discharges

Although microdischarges in dielectric-barrier discharges (DBDs) have been studied for the past century, their mutual interaction was explained only recently. This interaction is responsible for the formation of microdischarge patterns reminiscent of two-dimensional crystals. Depending on the application, microdischarge patterns may have a significant influence on DBD performance, particularly when spatial uniformity is desired. This paper presents the results of study of regular microdischarge pattern formation in DBD in air at atmospheric pressure. Experimental images of DBD (Lichtenberg figures) were obtained using photostimulable phosphors. A new method for analysis of microdischarge patterns that allow measuring the degree of pattern regularity was developed. Simulated and experimental patterns were compared using the newly developed method and comparison indicates the presence of interaction between microdischarges. Analysis of microdischarge patterns shows that regularity of the patterns increases with the number of excitation cycles used to produce the pattern.     

Exploring microdischarges for portable sensing applications

This paper describes the use of microdischarges as transducing elements in sensors and detectors. Chemical and physical sensing of gases, chemical sensing of liquids, and radiation detection are described. These applications are explored from the perspective of their use in portable microsystems, with emphasis on compactness, power consumption, the ability to operate at or near atmospheric pressure (to reduce pumping challenges), and the ability to operate in an air ambient (to reduce the need for reservoirs of carrier gases). Manufacturing methods and performance results are described for selected examples.

Tetragonal to monoclinic phase transition observed during Zr anodisation

Plasma electrolytic oxidation (PEO) is a coating procedure that utilises anodic oxidation in aqueous electrolytes above the dielectric breakdown voltage to produce oxide coatings that have specific properties. These conditions facilitate oxide formation under localised high temperatures and pressures that originate from short-lived microdischarges at sites over the metal surface and have fast oxide volume expansion. Anodic ZrO₂ films were prepared by subjecting metallic zirconium to PEO in acid solutions (H₂C₂O₄ and H₃PO₄) using a galvanostatic DC regime. The ZrO₂ microstructure was investigated in films that were prepared at different charge densities. During the anodic breakdown, an important change in the amplitude of the voltage oscillations at a specific charge density was observed (i.e., the transition charge density (Q ^T)). We verified that this transition charge is a monotonic function of both the current density and temperature applied during the anodisation, which indicated that Q ^T is an intrinsic response of this system. The oxide morphology and microstructure were characterised using SEM and X-ray diffraction experiments (XRD) techniques. X-ray diffraction analysis revealed that the change in voltage oscillation was correlated with oxide microstructure changes during the breakdown process.     

The Water Degradation Yield and Spatial Distribution of Primary Radicals in the Near-Discharge Volume of an Electrolytic Cathode

The features of combination and scavenging reactions of OH radicals were experimentally investigated in comparison with the decomposition of water by the action of anodic microdischarges on an electrolytic cathode. The assumption was proved that the formation of primary water degradation products occurs mainly in the liquid phase in tracks of fast particles entering the solution from the discharge plasma. The local concentration of OH radicals in tracks was estimated at the level of 10^–2 mol/l; although the peripheral regions of tracks can overlap because of the close arrangement of tracks in the near-discharge layer of the solution, the central regions of increased OH concentration may be considered as isolated.     

Pulsed Discharge Regeneration of Diesel Particulate Filters

A novel method for the removal of soot from a diesel particulate filter using pulsed electric discharges is presented. High voltage pulses of between 18 and 25 kV of nano to microsecond duration and with pulse energies of typically 100–200 mJ were applied to the filter via a series spark gap. Initial slow erosion of the soot layer proceeds via the formation of microdischarges. Subsequent spark discharges removed the accumulated soot more effectively from a larger filter volume. Average soot removal rates of ～0.1–0.2 g/min were achieved at 50 Hz breakdown frequency by optimizing both electrode geometry and breakdown voltage. On-engine long term testing of the technology showed soot removal by pulsed discharge to be reliable, efficient and uniform; a total of 100 g of soot was deposited and removed over 18 filter regeneration cycles.     

The role of electrolyte concentration in the decomposition of water and generation of electrons under conditions of anodic microdischarges

The dependence of the yield of water decomposition (from the measured yield of formation of hydrogen peroxide and yield of scavenging of OH radicals by isopropanol), as well as the yield of electron scavenging by a solute (nitrobenzene), on the concentration of aqueous electrolyte (sodium tetraborate and ammonium tetraborate) solutions under the action of anodic microdischarges was determined. Nonmonotonic functions were found, which exhibited maximums at 0.03 and 0.1 M concentrations for water decomposition and electrons, respectively. The results were explained by an increase in the fraction of anionic current through the discharge plasma-liquid cathode interface as the electrolyte concentration was increased.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 140–142.Original Russian Text Copyright © 2005 by Polyakov, Badalyan, Bakhturova.This revised version was published online in April 2005 with a corrected cover date.     

Microdischarge-Induced Decomposition of Ammonia and Reduction of Silver Ions for Formation of Two-Dimensional Network Structure

Microdischarge-induced reaction processes working at atmospheric pressure create fractal-like network structure of metal nano-particles which shows variable electric and optical properties. Due to their smallness, microdischarges or microplasmas can be installed in a gas-tubing system, and they enable us to create a compact chemical reduction reactor which includes decomposers of molecules, gas flows, and aqueous solutions with metallic ions at atmospheric pressure. Ammonia (NH₃) gas is successfully decomposed in this reactor, and its products which include mainly hydrazine (N₂H₄) and flow in the downstream induce reduction reactions for AgNO₃ solution. Various parameters in the reactor trigger formation of functional patterns of silver nano-particles like partially transparent layers whose conductivity is variable. Optical properties of this equivalent films show some absorption spectra coming from structure resonances, which can be an optical metamaterials in this self-assembly process.     

Oxidation of Acetylene in Atmospheric Pressure Pulsed Corona Discharge Cell Working in the Nanosecond Regime

Combined experimental and modeling studies of acetylene oxidation in pulsed corona discharges working in the nanosecond regime are presented. The corona cell was characterized in term of power deposition to provide input data for the model. The concentrations of ozone, CO, CO₂ and residual acetylene were systematically measured for model validation purposes. The model used allows describing the detailed chemistry in the discharge and the mass transfer between the microdischarges and the discharge free regions in the corona cell. Results showed that the model allows a satisfactory prediction of the acetylene residual fraction, CO and CO₂ yields and O₃ concentration for a wide range of conditions. They enabled a precise identification of the product distribution and confirmed the central role of O-atom in the oxidation process. They also revealed that ketene, H₂CCO, plays an important role in the oxidation mechanism and allowed drawing some conclusions on the optimization of the oxidation process.     

Preparation and Application of Ca0.8 Sr0.2 TiO3 for Plasma Activation of CO2

Despite a large interest in plasma-assisted catalytic technology (PACT), very little has been reported about the catalytic effects of different dielectric barriers on a dielectric barrier discharge (DBD) reaction. In the present study, Ca_0.8Sr_0.2TiO₃, that possesses a high permittivity, was prepared by liquid phase sintering and used as a dielectric barrier in a DBD reactor to break CO₂. The mechanical and dielectric properties of Ca_0.8Sr_0.2TiO₃ were greatly enhanced by adding 0.5 wt.% Li₂Si₂O₅. A DBD plasma was successfully generated by using this Ca_0.8Sr_0.2TiO₃ as a dielectric barrier and 18.8% CO₂ conversion was achieved with the residence time of 0.17 s at the frequency of 8 kHz, which was much higher than with those using an alumina or a silica glass barrier. It was found that the plasma power increased with the increasing of the permittivity, and finally very dense and strong microdischarges were initiated to decompose CO₂.     

Plasma Polymerization in a Nitrogen/Ethanol Dielectric Barrier Discharge: A Parameter Study

Plasma Chemistry and Plasma Processing - Plasma polymerization experiments are typically conducted by sustaining a non-thermal plasma in a gas flow containing monomer molecules. Recently, it was...     

Etching Characteristic of Graphite and Metal Substrates by Hydrocarbon Plasma in Closed Cavity

Plasma Chemistry and Plasma Processing - Plasma can be used to effectively remove coke from a metal surface. The plasma etching conditions of coke and emission spectrum characteristics on the metal...     

On the Possibilities of Straightforward Characterization of Plasma Activated Water

Plasma Chemistry and Plasma Processing - Plasma activated deionized water from a hot arc 150 W PAW synthesizer has been analyzed for nitrite, nitrate and peroxide densities. Observed nitrite and...     

Air to H2-N2 Pulse Plasma Jet for In-Vitro Plant Tissue Culture Process: Source Characteristics

Plasma Chemistry and Plasma Processing - Plasma agriculture has been considered as a promising solution for sustainable and safe agri-food production. Its applications include germination...     

Numerical Study of Jet–Target Interaction: Influence of Dielectric Permittivity on the Electric Field Experienced by the Target

Plasma Chemistry and Plasma Processing - This work presents a study of the influence of dielectric permittivity on the interaction between a positive pulsed He plasma jet and a 0.5 mm-thick...     

Temporal Evolution of Polarization Resolved Laser-Induced Breakdown Spectroscopy of Cu

Plasma Chemistry and Plasma Processing - Polarization-resolved laser-induced breakdown spectroscopy based on a temporal investigation of polarized Cu plasma emission is presented by a gated...     

Correction to: Rooting and Related Physiological Characteristics Responses to Stolon Cuttings Pre-treatment by Cold Plasma in Centipedegrass (Eremochloa ophiuroides (Munro.) Hack.)

Plasma Chemistry and Plasma Processing - The article Rooting and Related Physiological Characteristics Responses to Stolon Cuttings Pre?treatment by Cold Plasma in Centipedegrass (Eremochloa...     

Quantitative Analysis of Ozone and Nitrogen Oxides Produced by a Low Power Miniaturized Surface Dielectric Barrier Discharge: Effect of Oxygen Content and Humidity Level

Plasma Chemistry and Plasma Processing - This study presented a quantitative evaluation of the performance of a low power miniaturized SDBD source for the production of ozone and nitrogen oxides as...     

Hydrogen Production via Synthetic Biogas Reforming in Atmospheric-Pressure Microwave (915 MHz) Plasma at High Gas-Flow Output

Plasma Chemistry and Plasma Processing - This paper is a contribution to the development of microwave plasma-based technology for hydrogen (H2) production from a so-called synthetic biogas,...