Pulsed Electrical Discharges In Water Research Articles

Atomic scale microscopy unveils the growth mechanism of 2D-like CuO nanoparticle agglomerates produced via electrical discharges in water

In this paper we describe the growth mechanism leading to the selective synthesis of 2D-like CuO nanoparticle agglomerates via pulsed electrical discharges in water. By adjusting the voltage and pulse width, we selected four experimental conditions: 5 kV/100 ns, 5 kV/500 ns, 20 kV/100 ns and 20 kV/500 ns. In these conditions, we obtained agglomerates with dimensions ranging between 40 and 100 nm, formed of CuO nanoparticles having sizes of few nm. While the morphology of the agglomerates and their composition do not change in all the four conditions, the size, the shape and the crystal properties of the CuO nanoparticles can be finely tuned by choosing the coupling between voltage and pulse width. Moreover, the nanoparticles are more densely agglomerated at longer pulse width. Based on our observations, we infer the growth mechanism of the CuO nanoparticle agglomerates. We demonstrate that CuO nanoparticles are formed during the discharge, while their agglomeration can be mainly due to the pressure gradients existing within the plasma formed by the discharge, which encourage nanoparticle agglomeration on one plane.

Shockwaves from pulsed streamer discharge imaged at ultra-high speeds

A high-speed camera system revealed the individual shockwaves created by a pulsed electrical discharge in water, unveiling some of the fundamental physics.

Influence of the Distributed Phase of Gas Bubbles on a Pulsed Electrical Discharge in Water

The development of a pulsed electrical discharge in water with vapor–air microbubbles, the volume distribution of which in water is close to uniform, has been studied experimentally. The presence of volumetric microbubbles with an average diameter of ~50 μm and a bulk gas content of no more than 1% does not change the thermal mechanism of the development of the discharge in water with a conductivity of ~300 μS/cm at overvoltages of 1–1.5, the minimum breakdown voltage being ~9 kV. Under these conditions, the determining role is played by the surface bubbles, which change the observed mechanism of the discharge development. The discharge is initiated in the surface bubbles simultaneously on both electrodes. The growth of the cathode channel at a velocity of ~60 m/s leads to the closure of the 1-cm-long gap during a time of ~160 μs.

Optical properties of polyimides films treated by nanosecond pulsed electrical discharges in water

Fluorinated polyimide films containing cobalt chloride based on hexafluoroisopropylidenediphthalic dianhydride and 4,4′-diamino-3,3′-dimethyl diphenylmethane were treated by nanosecond pulsed electrical discharges generated in distilled water. The polyimide films have been characterized by Fourier transform infrared (FTIR) spectra and contact angle measurements, optical transmission spectroscopy, and fluorescence spectroscopy. Significant changes in some intrinsic fluorescence features, such as the intensity and position of the emission peak, have been observed during exposure to water plasma. These effects have been considered to correlate with the development of specific chemical interactions between the liquid and the macromolecules, including the formation of hydrogen bridges. A slight increase in surface hydrophobicity was observed after plasma treatment. FTIR spectra showed a decrease in the intensity of the absorption band and an opening of the imide ring, depending on the treatment time.

Detailed Investigation of the Electric Discharge Plasma between Copper Electrodes Immersed into Water

A phenomenological picture of pulsed electrical discharge in water is produced by combining electrical, spectroscopic, and imaging methods. The discharge is generated by applying ~350 μs long 100 to 220 V pulses (values of current from 400 to 1000 A, respectively) between the point-to-point copper electrodes submerged into the non-purified tap water. Plasma channel and gas bubble occur between the tips of the electrodes, which are initially in contact with each other. The study includes detailed experimental investigation of plasma parameters of such discharge using the correlation between time-resolved high-speed imaging, electrical characteristics, and optical emission spectroscopic data. Radial distributions of the electron density of plasma is estimated from the analysis of profiles and widths of registered Hα and Hβ hydrogen lines, and Cu I 515.3 nm line, exposed to the Stark mechanism of spectral lines’ broadening. Estimations of the electrodes’ erosion rate and bubbles’ size depending on the electrical input parameters of the circuit are presented. Experimental results of this work may be valuable for the advancement of modeling and the theoretical understanding of the pulse electric discharges in water.

Nanostructuration of polysilane-SiQDs composite by pulsed electrical discharges in water

Pulsed electrical discharges in water were used for nanostructuration of the polysilane-silicon quantum dots (SiQDs) composite dispersed in a cellulose acetate matrix. For this purpose, the polysilane-SiQDs composite was synthesized by chain scission of a poly[diphenyl-co-methyl(H)] oligomer in the presence of molten sodium and catalytic amounts of methyl(H) dichlorosilane. The resulting solid was utilized to prepare free standing thin films using the cellulose acetate matrix as support. Samples of these films were exposed to nanosecond pulsed electrical discharges in water. Through this approach, chemo-mechanical nanostructuration of specific silicon-based structures occurred by removing the excess of polysilane and by oxidative action. Fluorescence measurements of the plasma treated samples showed a higher intensity compared to the untreated ones. The elemental composition and the morphology of the film surface were investigated by TEM, XPS, UHR-SEM and AFM analysis. Such a technique represents a new approach toward a selective processing of the polysilane-SiQDs composite to obtain patterns with different optoelectronic properties on various supports.

Cobalt Containing Polyimide Films Treated by Nanosecond Pulsed Electrical Discharges in Water

This paper describes the effect of nanosecond pulsed electrical discharges generated in distilled water on cobalt-modified fluorinated polyimide (PI) films derived from hexafluoroisopropylidendiphthalic dianhydride and 4,4’-diamino-3,3’-dimethyl diphenylmethane. The PI films have been characterized by dielectric spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction (XRD) measurements. The relative permittivity of the PI films increased after treatment by water plasma. The XRD analysis has shown a slight increase of the degree of intermolecular ordering and stronger $\pi $ – $\pi $ interactions with the increase of the plasma treatment time. Application of nanosecond high-voltage pulses has induced an increase in concentration of CF3 groups at the polymer surface. A decrease of the cobalt and chlorine fractions, due to their migration into water, and an increase of aliphatic C–C bonds at the film surface may be responsible for the relative permittivity modification after exposure to water plasma.

Time-resolved processes in a pulsed electrical discharge in water generated with shock wave assistance in a plate-to-plate configuration

Plate-to-plate geometry is not usually used for a discharge generation in water because of a low electric field that is insufficient for electrical breakdown between electrodes. In the present research, a new method of the generation of electrical discharge in water using plate electrodes is proposed. A high voltage pulse is applied to a pair of disc electrodes at a time when a shock wave is passing between them. This method allows for depositing a higher electrical energy than with the case of pin-to-pin electrodes (or pin-to-plate electrodes) without their destruction. This discharge initiation occurs in numerous cavitation bubbles generated by the shock wave. The discharge evolution was studied using a high-speed framing camera. Two interesting effects have been observed. Firstly, multiple streamers are incepted on a cathode, which is not typical for the symmetrical electrode configuration. Secondly, the plasma in the spark channel reveals not to be homogeneous. The dynamics of a vapour bubble generated by this spark were studied by a shadowgraph method. The bubble’s growth, collapse and rebound are discussed.

Pulsed electrical discharges in water for removal of organic pollutants: a comparative study

In this study, the efficiency of different types of pulsed electrical discharges for the removal of organic pollutants from wastewater has been determined. Three discharge types, either in the water volume or in close proximity to the water surface are studied. The production of hydrogen peroxide in pure water, and the degradation of two typical pollutants (4-chlorophenol and 4-nitrophenol) is measured together with the amount of electrical energy dissipated in discharges. It is shown that the energy yield for the degradation of organic pollutants, expressed in terms of degraded moles per Joule, strongly depends on the discharge type. The highest efficiency is obtained with pulsed corona discharges in humid air above the water surface. A lower efficiency is found with spark discharges in water, and the less efficient process is constituted by streamer discharges in water. The influence of ferrous ions added to solutions is also very different according to the discharge type. This helps to get a better understanding of the degradation processes involved with the different discharge types.

The role of platinum as the high voltage electrode in the enhancement of Fenton's reaction in liquid phase electrical discharge

Pulsed electrical discharges in water produce a variety of oxidative and reductive species including hydroxyl radicals, hydrogen peroxide, and hydrogen. The reaction of ferrous ions with hydrogen peroxide (Fenton's reaction) provides additional hydroxyl radicals. Previous experiments with pulsed electrical discharges in water have shown that when ferrous sulfate is used as an electrolyte with a platinum high voltage electrode significantly higher organic compound degradation can be obtained in comparison to the case with an electrode made of nickel-chromium. In the work presented here, it is shown that particles emitted into solution from the platinum high voltage electrode enhance the production of hydroxyl radicals by forming a catalytic cycle between ferric and ferrous ions. The ferrous ions are converted to ferric ions by the Fenton's reaction utilizing hydrogen peroxide from the electrical discharge and the ferric ions are in turn converted to ferrous ions by reactions on the platinum particles emitted into solution from the high voltage electrode with molecular hydrogen formed by the electrical discharge. Based upon experiments with various scavengers it is concluded that the catalytic effect of the platinum particles is due to the presence of adsorbed hydrogen, while in contrast the nickel-chromium, which does not adsorb hydrogen, high voltage electrode and particles emitted by this electrode have no effect on the ferric ion regeneration.

Quantification of Hydroxyl Radicals Produced in Aqueous Phase Pulsed Electrical Discharge Reactors

High voltage pulsed electrical discharges in water are of interest for a number of applications, for example, in chemistry, water treatment, electrical transmission, and bioengineering, because of the formation of highly reactive molecular and radical species (including the hydroxyl radical). While the existence of hydroxyl radicals in these systems has been demonstrated by emission spectroscopy, accurate quantification of the rates of formation of this species is needed to develop insight into the means by which electrical discharge can promote useful chemical reactions. This paper focuses on quantification of hydroxyl radicals using chemical probes (dimethyl sulfoxide (DMSO) and disodium salt of terephthalic acid (NaTA)).