Electric Discharge In Liquid Research Articles

(Invited) Nanosecond Electrical Discharges in Liquids: Applications in the Synthesis of Nanoparticles, Including Nanoalloys

In recent decades, the field of nanotechnology has witnessed rapid growth, fueled by the exceptional physical, chemical, mechanical, and electrical properties of nanoscale materials. Nanomaterials have found applications across various domains, including catalysis, drug delivery, microelectronics, and more. Notably, plasma-based methods have emerged as promising avenues for nanomaterial synthesis, offering versatile approaches through both bottom-up and top-down techniques.One particularly innovative area of research is the plasma-liquid system, which has demonstrated remarkable efficiency in nanomaterial synthesis. This system involves the generation of plasma in a gas phase in contact with a liquid or directly within the liquid, sometimes aided by the introduction of bubbles. This communication has two goals: 1) present an overview of the physics of different discharge mechanisms, with a particular focus on the intriguing phenomena occurring at the interfaces, and 2) show different cases where nanomaterials of interest are produced. For instance, we will show that in-liquid spark discharges prouce nanoparticles through electrode erosion, and notably, the properties of these materials are highly sensitive to both the nature of the electrode and the composition of the liquid. In the second part, we introduce an innovative plasma-liquid system where a discharge can be produced at or close the interface of two immiscible liquids. In specific cases where the system is composed of a conductive solution (e.g. salty water) and a hydrocarbon liquid, spark discharges can be generated between a pin in liquid hydrocarbon and the surface of the conductive solution. This unique configuration facilitates therefore an interaction between a high-density plasma (generated in liquid) and a solution containing metal ions. At this stage, many reactions may occur and lead to the reduction of ions to produce nanomaterials. We found that the particles collected from hydrocarbon liquid are different from those collected from the solution, in terms of composition and size distribution. This finding suggests the triggering of different chemical reactions in each liquid, involving thus species with short- as well as long-lifetime species. Consequently, we adopted this approach to synthesize metal nanoparticles as well as binary and ternary nanoalloys, expanding the scope of possibilities in nanomaterial synthesis.

Graphitic N-doped graphene via solution plasma with a single dielectric barrier

Graphitic nitrogen-doped graphene (g-NG) with significantly high nitrogen content, i.e., 18.79 at.%, could be produced by the electrical discharge in liquid, so-called “solution plasma”, with a single dielectric barrier. The proposed system could reduce the excessive current, resulting in stabilizing the glow plasma and maintaining the overall temperature. It could promote the preservation of nitrogen atoms from evaporation during the synthesis process and the formation of a graphitic carbon framework. Moreover, the influence of the precursors, i.e., six-membered ring organic molecules with and without the substitution of nitrogen atoms and the nitrogen-based functional groups, was also investigated to provide the guideline for the synthesis of g-NG via this proposed method. The substitution of nitrogen atoms in the benzene ring could be used to synthesize g-NG with higher nitrogen dopants, compared to the benzene ring with only nitrogen-based functional groups. • Graphitic nitrogen-doped graphene (g-NG) was successfully synthesized. • The nitrogen doping concentration was incredibly high (18.79 at.%). • The synthesis was conducted by solution plasma with single dielectric barrier. • Lower discharge current in the solution plasma was a key for formation of g-NG.

Role of bubble and impurity dynamics in electrical breakdown of dielectric liquids

Electrical discharges in liquids with and without gas injection was experimentally studied with two circuits (RC and single spark gap). Electrical breakdown could be initiated from the following mechanisms: electrode initiation; impurity initiation; and Taylor cone driven initiation. Discharges initiated by electrodes were observed only with the single spark gap circuit. Impurities and Taylor cones can initiate discharges when using the RC circuit. With the single spark gap circuit, bubbles were nearly stationary in the gap before and during discharges because of the limited time to respond to the electric field growth (dV/dt = 1 kV ns−1). Bubbles and impurities gain significant energy and undergo significant dynamic changes with the RC circuit under a long rising time. Charge relaxation time on bubbles or impurities in the fluids were close to 100 ms, which is comparable with the circuit rising time. Bubble dynamics observed include reduced bubble size, increased bubble speed and shape change. Taylor cones were observed on bubble surface using a high-speed camera during multiple discharge events, and usually led to breakdown. Taylor cones develop on a bubble surface through multiple states over a period of 10–500 μs. State one was typically seen on a bubble surface with a sharp tip caused by the residual charge. A single streamer was initiated on the tip of the cone at state two. State three developed multiple bush-like streamers on the cone and usually triggered a breakdown in the gap. Discharge behaviors in liquids were also investigated with the RC circuit at different pulsing frequencies. At a low pulsing frequency (1 Hz), discharge events are independent from each other. When pulsed above 10 Hz, bubbles created in the gap accumulate and participate in the next discharge event. Bubble accumulation results in a cloud where local secondary discharges are observed with a much higher frequency up to a few kHz for several milliseconds.

Synthesis of nickel and cobalt oxide nanoparticles by pulsed underwater spark discharges

Electrical discharges in liquids are considered an efficient and ecological technique of nanoparticle synthesis via controlled erosion of electrodes. Herein, we use spark discharges between Co–Co, Ni–Ni, Co–Ni, or Ni–Co electrodes immersed in distilled water to synthesize Co and/or Ni nanoparticles, as well as their oxides. When mixed electrodes are used (Co–Ni or Ni–Co), both Co and Ni nanoparticles are produced, and the major species is dictated by the nature of the anode pin. The characteristics of nanoparticles synthesized under varying conditions of pulse width (100 and 500 ns) and voltage amplitude (5 and 20 kV) are analyzed by transmission electron microscopy. Within the investigated discharge conditions, it is not possible to produce Co–Ni nanoalloys; however, core–shell nanoparticles are observed among the Ni and Co nanoparticles. Finally, the direct optical bandgaps of the nanomaterials are determined using UV-visible absorption spectroscopy.

Shock waves in pulsed electrical discharges in liquids: numerical simulation and comparison to experiment

In this paper a computational model for the post-breakdown phase of an electrical discharge in liquids is presented and validated through comparison with data from a high voltage pulsed power discharge in a water-filled crucible. The numerical framework consists of an arc plasma channel modeled by equivalent resistor-inductor-capacitor circuit equations coupled to a computational fluid dynamics (CFD) model (based on OpenFOAM) that solves the compressible fluid equations for describing the shock waves associated with the rapid development of the plasma channel. The circuit model equations evolve the initial discharge plasma expansion which are then used to initialize the pressure pulse in the CFD model. Both single-phase (liquid) and two-phase (gas–liquid) CFD solvers were implemented and compared. The dynamics and magnitude of the simulated pressure pulse perturbations at the boundaries of the crucible were validated with the pressure sensor measurements made in an experiment of a pulsed electrical discharge in liquid water.

Electromagnetic and Thermal Phenomena Modeling of Electrical Discharges in Liquids

Electrical discharges in liquids have received lots of attention with respect to their potential applications in various techniques and technical processes. Exemplary, they are useful for water treatment, chemical and thermal processes acceleration, or nanoparticles production. In this paper the special utility of discharges for cold pasteurization of fruit juices is presented. Development of devices for its implementation is a significant engineering problem and should be performed using modeling and simulation techniques to determine the real parameters of discharges. Unfortunately, there is a lack of clear and uniform description of breakdown phenomena in liquids. To overcome this limitation, new methods and algorithms for streamers propagation and breakdown phase analysis are presented in the paper. All solutions were tested in “active area” in the form of liquid material model, placed between two flat electrodes. Electromagnetic and thermal-coupled field analysis were performed to determine all the factors that affect the discharge propagation. Additionally, some circuit models were used to include the power source cooperation with discharge region. In general, presented solutions can be defined as universal and one can use them for numerical simulation of other types of discharges.

A novel continuous-flow electrohydraulic discharge process for handling high-conductivity wastewaters

Electrical discharge in liquid is a promising technique to remove pollutants from various industrial and agricultural wastewaters; however, using this technique to treat high-organic-strength wastewater has been hindered by its inability to handle wastewaters with high conductivity due possibly to the reactor design. In this study, a novel electrohydraulic discharge reactor was examined to determine the effect of conductivity and liquid flow rate on liquid temperature, power consumption, and H2O2 production. Liquid conductivity was represented by NaCl solutions at different concentrations (from 100 to 700 mg/L), and two groups of liquid flow rates (24, 48, 73, 98, and 122 mL/min and 36, 61, 86, and 122 mL/min) were employed. The results showed that the optimum liquid flow rate was 48 mL/min for the reactor without significantly increasing the liquid temperature. (The corresponding power consumption was 290 W, and the system production efficiency was 0.86 g H2O2/kWh.) A good power relationship was obtained between the final liquid temperature and the liquid flow rate (R = 0.9836). For H2O2 production, a treatment time of 30 min achieved the highest H2O2 concentration in the liquid, and a further increase in treatment times found little improvement. The optimal water conductivity was 467 µS/cm for producing the highest concentration of H2O2 in the treated water (82 mg/L). The novel electrohydraulic discharge reactor appeared to be able to handle wastewater with much higher conductivity than the reactors examined by previous researchers, so it could potentially be developed into a promising technology for treating high-organic-strength wastewaters.

Shock wave release behavior of a pulsed positive streamer discharge in water

We performed experimental observations to distinguish an individual shock front released by a pulsed positive streamer discharge in water. The step length between two adjacent shock wave events was measured and its dependence on water conductivity and applied voltage was investigated. We found that the step length between two adjacent shock wave events is ∼160 μm, independent of both water conductivity and applied voltage, within the range studied. Based on the bubble theory of electrical discharge in liquid, we concluded that the individual shock front is released by the electrical breakdown of a gaseous micro-segment near the head of a streamer filament in water. After launching a shock wave, the filament head pauses and waits for another gaseous micro-segment to form in front of it.

Effect of Dielectric Conductivity on Micro-Electrical Discharge Machining Plasma Characteristics Using Optical Emission Spectroscopy

Electrical conductivity of the dielectric liquid has been shown to play main role in discharge initiation and electrical breakdown as revealed by several modeling and experimental studies on electrical discharges in liquids. However, there has been lack of systematic efforts to evaluate how dielectric conductivity affects the micro-electrical discharge machining (micro-EDM) process, in particular. Experimental investigation has been carried out to understand the effect of dielectric conductivity on micro-EDM plasma characteristics using optical emission spectroscopy. Plasma temperature and electron density estimations have been obtained at five levels of electrical conductivity of water. It is found that while the plasma temperature shows a marginal decrease, electron density of the plasma increases with an increase in the conductivity. At increased electron density, a higher heat flux at anode can be expected resulting in increased material erosion.

Synthesis of Nickel–Carbon Nanoparticles by Electrical Discharge in Liquid

Composite nickel–carbon nanoparticles were synthesized by electrical discharge in liquid. The synthesis was carried out in water and ethanol under various discharge conditions, including purging the discharge gap with argon. In water, electrical discharge was conducted between graphite and nickel electrodes. In ethanol, two nickel electrodes were used with the liquid acting as the carbon supplier. The size of the particles obtained, their composition, and the production rate depend on the type of working fluid and synthesis duration. It was also shown that the particle production rate in water is greater than in ethanol, and purging the electrode gap with argon reduces this rate two or three times.

Influence of composition of electrolyte on electric discharge in liquid

Within this work results of researches of electric discharge with liquid nonmetallic electrodes are presented. Features of formation of electric discharge depending on structure and concentration of electrolyte, electrophysical processes are described, the volt-ampere characteristic of the category is constructed. Distribution of electric field strength along an electrolyte stream is presented.

Sodium Chloride Crystallization by Electric Discharge in Brine

Electrical discharges in liquids are currently used to synthesize nanoparticles. The plasma-liquid interaction is complex, where parameters such as electric field, ion charges and other species present are important. In order to understand the mechanism of crystallization, mother liquor (saturated solution of NaCl, MgCl2 and KCl) was used to study the effectiveness and selectivity of the crystallization caused by the application of plasma. Discharge was applied with the solution at room temperature or during cooling. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and chemical analysis was used to evaluate the structure and composition effects on crystal structure and composition. It was observed that the discharge induces selectively crystallization, and when compared to crystals obtained conventionally by cooling, were smaller and more uniform. We therefore confirm that plasma in liquid can also be used to selectively crystallize materials in atmospheric pressure, where the sizes of the crystals must be dependent on the parameters used.

The effect of electrical conductivity on nanosecond discharges in distilled water and in methanol with argon bubbles

We investigated the effect of a liquid’s electrical conductivity (EC) on the physical characteristics of electrical discharges in liquids with gaseous bubbles. Argon gas was supplied into the liquid to form an array of gaseous bubbles in between two electrodes (a pin-to-hollow electrode setup). Methanol and water were considered as base liquids, representing a low and a high dielectric permittivity (ε) liquid respectively, while potassium chloride (KCl) was added to control the EC of the liquids. When increasing the EC of the liquids, we found that the discharge probability was reduced by 46% for in-water and 38% for in-methanol discharges. We also found that the injected charge decreased by ~4 µC as the EC increased. Moreover, as the gap distance increased from 1 to 2.5 mm, the injected charge decreased by 2 µC for in-water discharge and by 4 µC for in-methanol discharge. The plasma emission is another important parameter in characterizing discharges. With increasing the EC, the plasma emission volume decreased linearly by a factor of ~5. The plasma lifetime was shortened by around 33% for in-water and 20% for in-methanol discharges in the case of d = 1 mm, while the decrease was 40% for in-water and 30% for in-methanol discharges in the case of d = 2.5 mm. Using the broadening characteristics of the Hα line, the electron density was estimated during the first 100 ns by ~3 × 1017 cm−3 for in-water discharges and by ~2 × 1018 cm−3 for in-methanol discharges, and it decreased by about one order of magnitude after 800 ns; note that ne dependence on the EC was not significant. The reported findings provide further understanding of electrical discharges in bubbled liquids and highlight the influence of a liquid’s EC, which are useful in the development and optimization of the applications based on such process.

Luminescence properties of nanoparticles synthesized in electric discharge in liquid under ultrasonic cavitation

The differences in the luminescence intensity of metal oxide nanoparticles synthesized in electric discharges in liquidmedia under intense ultrasonic vibrations in the absence and presence of cavitation are studied.

Effect of ultrasonic cavitation on dynamics and characteristics of electric discharge in liquid

Characteristics of electric discharges in liquid media under intense ultrasonic vibrations are studied. The difference in current dynamics and discharge voltages in the presence and in the absence of cavitation is shown.

Generation of dc pin-hole discharges in liquids: comparison of discharge breakdown in diaphragm and capillary configuration

Electrical discharges in liquids can be generated in several electrode configurations; one of them is called as a pin-hole. The discharge is created inside a small orifice in the dielectric barrier connecting two chambers filled by any conductive solution. Each chamber contains one electrode. Based on the orifice length/diameter ratio, the discharge is called as a capillary or diaphragm discharge. The present paper gives the first detailed observation of the dependence of discharge creation on the orifice shape for selected NaCl solution conductivities (250−1000 µ Sc m �1 ). As a dielectric barrier, ceramic discs with thickness varying from 0.3 to 1.5 mm were used. Diameter of one central pin-hole was in the range of 0.25−1.00 mm. The non-pulsing dc high voltage up to 2 kV with power up to 500 W was used for the presented study. The bubble theory of the discharge generation was confirmed at the set conditions.

Initiation process and propagation mechanism of positive streamer discharge in water

The aim of this study was to clarify the initiation process and the propagation mechanism of positive underwater streamers under the application of pulsed voltage with a duration of 10 μs, focusing on two different theories of electrical discharges in liquids: the bubble theory and the direct ionization theory. The initiation process, which is the time lag from the beginning of voltage application to streamer inception, was found to be related to the bubble theory. In this process, Joule heating resulted in the formation of a bubble cluster at the tip of a needle electrode. Streamer inception was observed from the tip of a protrusion on the surface of this bubble cluster, which acted as a virtual sharp electrode to enhance the local electric field to a level greater than 10 MV/cm. Streak imaging of secondary streamer propagation showed that luminescence preceded gas channel generation, suggesting a mechanism of direct ionization in water. Streak imaging of primary streamer propagation revealed intermittent propagation, synchronized with repetitive pulsed currents. Shadowgraph imaging of streamers synchronized with the light emission signal indicated the possibility of direct ionization in water for primary streamer propagation as well as for secondary streamer propagation.

S0550402 液中プラズマ放電の電気流体力学解析([S055-04]プラズマアクチュエータ(4),流体工学部門)

The electrohydrodynamics due to electrical discharges in liquids are studied by using the finite element modeling method. The thermal and electrical phenomena occurred in electrical discharges are coupled to model the vapor layer formation. The formation and growth of bubbles in liquids is modelled by the interface dynamics, in which the interface is traced by a phase field equation. The results show that the vapor layer insulates the electrode surface possessed of high electrical field from the liquid. The electrode surface is heated to exceed the temperature at the Leidenfrost point to form a film boiling.

Investigation of hydrodynamic processes at multi-pulse power input into the channel of an electric discharge in liquid

The method of numerical experiments has been applied to specify the conditions under which pulsation pressure pulses are realized by combined electrodischarge systems in the plasma channel and the ambient liquid. It is shown that, on the basis of a main fixed power source, it is possible to establish a series of combined power sources ensuring the generation of uniform two-pulsation pressure pulses.

Перспективы получения мелкодисперсных порошков с помощью импульсного электрического разряда в жидкости

Перспективы получения мелкодисперсных порошков с помощью импульсного электрического разряда в жидкости