Transient Spark Research Articles

On the modes of nanosecond pulsed plasmas for combustion ignition of quiescent CH4-air mixtures

The effect of transient plasma modes on ignition kernel development are discussed here for a quiescent CH4-air combustion model system. A 10 ns high-voltage pulse was applied to a pin-to-pin electrode in lean fuel-air mixtures at room temperature and atmospheric pressure. High-impedance streamer, transient spark and low-impedance spark discharges were identified based on pulse waveforms of voltage and current. A sustained ignition kernel expansion was observed when the plasma discharge transitioned into a transient spark or spark discharge. The minimum ignition energy was obtained at the transient spark mode, which has less than a third of the energy or Coulomb transfer compared to the low-impedance spark. Employing repetitive 10-pulse sequence at 10 kHz, the lean-fuel limit was extended from an equivalence ratio of 0.6 for the single pulse ignition to 0.5. The use of repetitive pulses also allowed streamer breakdown or spark initiation to occur at a lower voltage.

Effect of Transient Spark Discharge and Plasma Activated Water Treatments against Fusarium graminearum Infected Wheat Grains under Laboratory Conditions

Over the last decade, more and more attention has been paid to applications of non-thermal plasma in agriculture, where it is used to decontaminate various microorganisms and to improve the seed germination. In this study, we present the results of a newly developed point-to-ring NTP transient spark discharge apparatus (NTP), plasma activated water (PAW) and their combined treatment on Durum wheat and Common wheat grains under laboratory conditions. Transient spark discharge treatment was used as direct treatment while indirect treatment of wheat grains was performed by PAW produced in point-to-plane NTP transient spark apparatus. We found that the degree of grain surface decontamination was in order NTP > PAW > combined treatment. In the case of Durum wheat grain germination, all treatments increased germination with increasing exposure times, while in the case of Common wheat, PAW treatment and combined treatment did not significantly increase the grain germination. In conclusion, plasma treatment has enormous potential for use in agriculture and its possibilities need to be fully explored.

Inactivation pathways of Escherichia coli and Staphylococcus aureus induced by transient spark discharge in liquids

AbstractCold plasma finds considerable interest in biodecontamination. A major issue is to elucidate the pathways of plasma–bacteria interaction. The present work aims at studying inactivation mechanisms for planktonic bacteria Escherichia coli and Staphylococcus aureus induced by cold plasma generated by a transient spark discharge. Changes in bacterial viability, metabolic activity, membrane integrity, intracellular reactive oxygen species level, and cell morphology reveal different patterns of cellular damage of the bacteria. Our results emphasize the importance of cell membrane integrity and maintenance of intracellular redox balatnce to resist plasma treatment. The physicochemical properties of the plasma‐treated liquid (PTL) are monitored. Acidification and accumulation of various reactive species including •OH, H2O2, ONOOH, and NO3− in PTL play crucial roles in bacterial inactivation.

Molecular dynamics of JUNO-IZUMO1 complexation suggests biologically relevant mechanisms in fertilization

JUNO-IZUMO1 binding is the first known physical link created between the sperm and egg membranes in fertilization, however, how this initiates sperm-egg fusion remains elusive. As advanced structural insights will help to combat the infertility crisis, or advance fertility control, we employed all-atom Molecular Dynamics (MD) to derive dynamic structural insights that are difficult to obtain experimentally. We found that the hydrated JUNO-IZUMO1 interface is composed of a large set of short-lived non-covalent interactions. The contact interface is destabilized by strategically located point mutations, as well as by Zn2+ ions, which shift IZUMO1 into the non-binding “boomerang” conformation. We hypothesize that the latter might explain how the transient zinc spark, as released after sperm entry into the oocyte, might contribute to block polyspermy. To address a second mystery, we performed another set of simulations, as it was previously suggested that JUNO in solution is unable to bind to folate despite it belonging to the folate receptor family. MD now suggests that JUNO complexation with IZUMO1 opens up the binding pocket thereby enabling folate insertion. Our MD simulations thus provide crucial new hypotheses how the dynamics of the JUNO-IZUMO1 complex upon solvation might regulate fertility.

The influence of electric circuit parameters on NOx generation by transient spark discharge

Nitrogen fixation, production of NO and NO2 from N2 and O2 in air, has been investigated with transient spark self-pulsing DC discharges. NO production is boosted by the addition of capacitors and an inductor to the electrical circuit which drives the discharge. The quantity of NO produced per joule of electrical input energy is doubled, though the quantity of NO2 produced drops. The yield of NO is also increased because the modified circuit enables higher discharge currents to be used. NO concentrations as high as 2000 ppm were obtained with input energy densities of around 300 J per liter of input gas, whilst NO2 concentrations were around 150 ppm. This simple modification of the driving circuit may have potential for optimizing the plasma chemistry with other input gas mixtures and for scaling up nitrogen fixation from air.

Temporal evolution characteristics of the excited species in a pulsed needle-water discharge: effect of voltage and frequency

Transient spark discharge has broad application prospects due to its excellent performance in generating reactive oxygen species, but there is currently limited research on transient excited species, which are important precursors for the formation of these species. In this paper, we obtained a transient spark discharge with a needle-water electrode configuration, and then developed an optical detection system based on a photomultiplier to measure the temporal evolution of four excited species. It is observed that N2 (C) is produced mainly in the streamer phase, while H (n = 3), O (3p), and OH (A) are produced mainly in the spark phase, which results from the difference in threshold energy and pathway for generating different species. To investigate the variation mechanism of peak time and peak intensity during the evolution process, the gas temperature T g, electron density n e, and electron excitation temperature T exc were calculated by using the optical emission spectroscopy under different pulse voltage and pulse repetition frequency conditions. The results indicate that the discharge conditions influence the physical parameters of T g, n e, and T exc as well as the output voltage waveform, and then they jointly determine the evolution characteristics of excited species. These insights contribute to understanding the characteristics of excited species which affect the formation of reactive species by influencing the chemical chain reaction in the transient spark discharge.

Study on characteristics of acoustic signals generated by different DC discharge modes

Acoustic signals contain rich discharge information. In this study, the acoustic signal characteristics of transient glow, spark, and glow discharges generated through DC pin–pin discharge were investigated. The signals were analyzed in the time, frequency, and time–frequency domains, and the correlation between the electric and the acoustic signal was studied statistically. The results show that glow discharge does not produce measurable sound signals. For the other modes, with a decrease in the discharge gap, the amplitude of the acoustic signal increases sharply with mode transformation, the short-time average energy becomes higher, and the frequency components are more abundant. Meanwhile, the current pulse and sound pressure pulse have a one-to-one relationship in the transient glow and spark regimes, and they are positively correlated in amplitude. A brief theoretical analysis of the mechanism of plasma sound and the trends of signals in different modes is presented. Essentially, the change in the discharge energy is closely related to the sound generation of the plasma.

Influence of a transient spark plasma discharge on producing high molecular masses of chemical products from l-cysteine

Cold atmospheric pressure plasmas are considered a forthcoming method in many research areas. Plasma modification of biomolecules has received much attention in addition to plasma-treated biomaterials. Hence, in this work, we operated a transient spark plasma (TSP) discharge to study its effect on the l-cysteine chemical structure. the TSP was configured in a pin-to-ring electrode arrangement and flowed by Ar gas. We also investigated the effect of two chemicals; dimethyl sulfoxide (DMSO) and hydrogen peroxide (H2O2) by the bubbling method to show how they can change the creation of new chemical bioproducts. Ultraviolet–Visible absorption spectroscopy, Fourier transform infrared spectroscopy and Liquid chromatography–mass spectroscopy were used to investigate any changes in chemical bonds of cysteine structure and to depict the generation of new biomolecules. Based on the displayed results plasma-generated reactive species had a great role in the chemical structure of the cysteine. Entering DMSO and H2O2 into the plasma caused the creation of new products and the heaviest biomolecule was produced by the simultaneous addition of DMSO and H2O2. The results also predicted that some chemical products and amino acids with a higher value molecular masse produced from the polymerization process of cysteine solution. The strong oxidation process is responsible for the heavy chemical compounds.

Atmospheric air plasma sustainment by semiconductor microwave for hydroxyl radical production and powder metal element analysis

A semiconductor microwave device that generates a series of burst microwaves at a sub-microsecond duration has been successfully used in a breakdown plasma spectrometer in atmospheric conditions. Microwave delivery has been changed to couple the microwave with laser sparks and electric sparks which are typical plasma ignition sources in laser-induced breakdown spectroscopy (LIBS) and spark-induced breakdown spectroscopy (SIBS). A helical antenna was used for the laser spark, while a coaxial antenna was considered more appropriate for the electric spark. The weak and transient sparks in LIBS and SIBS are enlarged by the microwaves which are stably sustained in the air. The microwave's output power and pulse duration are easily controllable, resulting in tunable plasma intensity and sustained production of hydroxyl radicals (OH radicals). Even in continuous-wave operation by microwave, the low-energy system prevented the formation of high-temperature thermal plasma (>10,000 K) without any mechanical cooling system. The microwave-enhanced LIBS (MW-LIBS) and microwave-enhanced SIBS (MW-SIBS) could be applied to optical emission spectroscopy analyses. In analytical applications, MW-SIBS produces no shockwave in contrast with MW-LIBS which is a great advantage in powdered samples. The MW-SIBS successfully analyzed the direct introduction of copper metal powders.

Highly synergistic effect for tetracycline degradation by coupling a transient spark gas–liquid discharge with TiO2 photocatalysis

Water pollution driven by the increasing antibiotic abuse leads to serious ecological impacts and risks to human health. Non-thermal plasma, a sustainable advanced oxidation process, is considered as a promising approach for antibiotic degradation. In this study, a transient spark gas–liquid discharge was developed for the degradation of tetracycline in water and coupled with a photocatalyst (TiO2) to further improve the degradation efficiency. Results show that the discharge was accompanied by intense UV light of up to 28 μW/cm2. The tetracycline degradation performance was strongly dependent on the pulse voltage, working gas, initial concentrations of tetracycline and the catalyst addition. The best degradation performance was achieved in the plasma-TiO2 system with a degradation rate of 90.2% after 10 min treatment. The catalyst exhibits a high efficiency at lower pulse voltages, with the synergetic intensity of plasma and TiO2 showing a decreasing trend with increasing pulse voltage. Radical quenching experiments suggest that hydroxyl radical (∙OH) plays a key role in the tetracycline degradation process. A pathway for tetracycline degradation by the plasma-TiO2 process is deduced according to the analysis of the degradation intermediates. Further, seed germination and plant growth tests for the treated water demonstrated the feasibility of discharging the treated water to irrigate agricultural crops.

Coupled Antibacterial Effects of Plasma-Activated Water and Pulsed Electric Field

In the biomedical applications of cold plasma, the dominant biological effect is most typically attributed to the reactive oxygen and nitrogen species (RONS), while the physical effect of electric fields is sometimes overlooked. Here, we investigated the antibacterial effect of RONS in plasma-activated water (PAW) on the inactivation of E. coli bacteria, coupled with a mild 200-nanosecond pulsed electric field (PEF) treatment. By using transient spark discharge plasma in open atmospheric air and closed air reactors, and by adding hydrogen peroxide (H2O2) into the PAW, different chemical compositions of RONS were obtained. We measured the time evolution of the concentrations of key species in the PAW post-discharge: nitrites (NO2−) and H2O2. PAW rich in both NO2− and H2O2 showed an antibacterial effect, which was enhanced by the PEF, whereas PAW rich in NO2− and poor in H2O2 showed an enhancement of the antibacterial effect by the PEF only when H2O2 was externally added. The presence of sufficient concentrations of both NO2− and H2O2 optimized the formation of peroxynitrous acid (ONOOH), which caused a strong peroxidation of the cell membranes leading to the cell death, but it also made them more vulnerable to the PEF treatment. The results suggest that the interaction with radicals during the bacteria exposure to PAW leads to an antibacterial effect reinforced by the pulsed electric field, hence showing a synergy of the chemical and physical plasma agents. This opens new perspectives for applications both plasma and PEF areas of research.

The Effect of Plasma Activated Water on Maize (Zea mays L.) under Arsenic Stress.

Plasma activated water (PAW) is a source of various chemical species useful for plant growth, development, and stress response. In the present study, PAW was generated by a transient spark discharge (TS) operated in ambient air and used on maize corns and seedlings in the 3 day paper rolls cultivation followed by 10 day hydroponics cultivation. For 3 day cultivation, two pre-treatments were established, “priming PAW” and “rolls PAW”, with corns imbibed for 6 h in the PAW and then watered daily by fresh water and PAW, respectively. The roots and the shoot were then analyzed for guaiacol peroxidase (G-POX, POX) activity, root tissues for their lignification, and root cell walls for in situ POX activity. To evaluate the potential of PAW in the alleviation abiotic stress, ten randomly selected seedlings were hydroponically cultivated for the following 10 days in 0.5 Hoagland nutrient solutions with and without 150 μM As. The seedlings were then analyzed for POX and catalase (CAT) activities after As treatment, their leaves for photosynthetic pigments concentration, and leaves and roots for As concentration. The PAW improved the growth of the 3 day-old seedlings in terms of the root and the shoot length, while roots revealed accelerated endodermal development. After the following 10 day cultivation, roots from PAW pre-treatment were shorter and thinner but more branched than the control roots. The PAW also enhanced the POX activity immediately after the imbibition and in the 3 day old roots. After 10 day hydroponic cultivation, antioxidant response depended on the PAW pre-treatment. CAT activity was higher in As treatments compared to the corresponding PAW treatments, while POX activity was not obvious, and its elevated activity was found only in the priming PAW treatment. The PAW pre-treatment protected chlorophylls in the following treatments combined with As, while carotenoids increased in treatments despite PAW pre-treatment. Finally, the accumulation of As in the roots was not affected by PAW pre-treatment but increased in the leaves.

Inactivation of Acanthamoeba Cysts in Suspension and on Contaminated Contact Lenses Using Non-Thermal Plasma.

Water suspensions of cysts of a pathogenic clinical isolate of Acanthamoeba sp. were prepared, and the cysts were inactivated either in suspension or placed on the surface of contact lenses by the non-thermal plasma produced by the DC corona transient spark discharge. The efficacy of this treatment was determined by cultivation and the presence of vegetative trophozoites indicating non-inactivated cysts. The negative discharge appeared to be more effective than the positive one. The complete inactivation occurred in water suspension after 40 min and on contaminated lenses after 50 min of plasma exposure. The properties of lenses seem to not be affected by plasma exposure; that is, their optical power, diameter, curvature, water content and infrared and Raman spectra remain unchanged.

Chemical and Antimicrobial Effects of Air Non-Thermal Plasma Processing of Fresh Apple Juice with Focus on Safety Aspects.

Freshly squeezed apple juice was subjected to air non-thermal plasma treatment to investigate the capability of this processing method to inactivate microorganisms and to evaluate its safety when applied to liquid food products. Two different configurations of a transient spark discharge in ambient air were tested: an electrospray system with the juice flowing directly through the high voltage needle electrode, and a batch system, where the discharge was generated onto the surface of the juice. The key physico-chemical parameters of the juice, such as pH, conductivity, color, transmittance, and Brix degree, did not significantly change upon treatment. The concentration of nitrate ions formed by the plasma was safe, while that of nitrite ions and hydrogen peroxide was initially higher than the safety limits, but decreased within 24 h post treatment. The plasma effect on individual natural components of the juice, such as sugars, organic acids, and polyphenols, treated in water solutions led to their partial or substantial decomposition. However, when these compounds were plasma-treated altogether in the juice, they remained unaffected. The antimicrobial effect of the plasma processing was evaluated via the inoculation of model microorganisms. A stronger (6 log) decontamination was detected for bacteria Escherichia coli with respect to yeast Saccharomyces cerevisiae. Plasma processing led to a substantial extension of the juice shelf-life by up to 26 days if refrigerated, which represents a promising application potential in food technology.

The Role of HNO2 in the Generation of Plasma-Activated Water by Air Transient Spark Discharge

Transient spark (TS), a DC-driven self-pulsing discharge generating a highly reactive atmospheric pressure air plasma, was employed as a rich source of NOx. In dry air, TS generates high concentrations of NO and NO2, increasing approximately linearly with increasing input energy density (Ed), reaching 1200 and 180 ppm of NO and NO2, at Ed = 400 J/L, respectively. In humid air, the concentration of NO2 decreased down to 120 ppm in favor of HNO2 that reached approximately 100 ppm at Ed = 400 J/L. The advantage of TS is its capability of simultaneous generation of the plasma and the formation of microdroplets by the electrospray (ES) of water directly inside the discharge zone. The TS discharge can thus efficiently generate plasma-activated water (PAW) with high concentration of H2O2−(aq), NO2−(aq) and NO3−(aq), because water microdroplets significantly increase the plasma-liquid interaction interface. This enables a fast transfer of species such as NO, NO2, HNO2 from the gas into water. In this study, we compare TS with water ES in a one stage system and TS operated in dry or humid air followed by water ES in a two-stage system, and show that gaseous HNO2, rather than NO or NO2, plays a major role in the formation of NO2−(aq) in PAW that reached the concentration up to 2.7 mM.

In-situ synthesis and low-temperature fabrication of B4C/TiB2-based multilayer graded composites with B4C and Ti–Al intermetallics mixtures through transient liquid phase sintering

The seven-layer B4C/TiB2-based graded composites was prepared with B4C and Ti–Al intermetallics through stepped laminating processing and transient liquid phase spark plasma sintering. The sintering strategy of the graded composites was proposed based on the sintering products of monolayer materials with different contents of Ti–Al intermetallics from 5 wt% to 60 wt%. The top three layers and bottom three layers were sintered respectively at 1650 °C and 1500 °C, and then the middle layer was used as the binder to joint the as-preserved two sections at 1550 °C. The apparent density of the as-prepared B4C/TiB2-based multilayer graded composites was 2.94 g/cm3, which was lower than that of most advanced ceramics. With the increase in the addition of Ti–Al intermetallics, the hardness of B4C/TiB2-based multilayer graded composites decreased from 31 GPa (B4C-riched) to 25 GPa (TiB2-riched), whereas the fracture toughness increased from 3.8 MPa·m0.5–6.02 MPa·m0.5. The compressive strength was up to 1100 MPa, displaying the jagged stress-strain curve. Crack propagation resistance mechanisms such as deflection and bridging enhanced the fracture toughness. The B4C/TiB2-based multilayer graded composites fabricated at low temperature possess high front hardness, high rear toughness, high overall strength and low density, and has promising applications in impact-resistant fields such as lightweight ceramic armor.

Effect of Plasma Activated Water, Hydrogen Peroxide, and Nitrates on Lettuce Growth and Its Physiological Parameters

Cold plasma generated by atmospheric pressure air discharge is a source of various gaseous reactive oxygen and nitrogen species (RONS). When the plasma is generated in a contact with water, the RONS dissolve into water, change its chemical composition, while producing so-called plasma activated water (PAW). The PAW has the potential to be effectively used in various agricultural applications, as the long lived liquid RONS (H2O2, NO2−, NO3−) may act like signaling molecules in plant metabolism or serve as nutrients. We studied the effect of the PAW on lettuce plants and compared it with the effect of H2O2 and/or NO3− solutions of various concentrations to assess their role in the PAW. The PAW was generated from tap water by DC driven self-pulsing transient spark discharge. Pre-grown lettuce plants were cultivated in pots with soil and irrigated with the PAW or solutions of H2O2 and/or NO3−. After 5 weeks the growth parameters, number and quality of leaves, fresh and dry weight of plants, photosynthetic pigment (chlorophyll a + b) content, photosynthetic rate, and activity of antioxidant enzymes (superoxide dismutase, SOD) were evaluated. Lettuce plants irrigated with the PAW in comparison with chemically equivalent solution of H2O2 and NO3− had similar dry weight; however, the PAW induced higher photosynthetic pigment content, higher photosynthetic rate, and lower activity of SOD. The NO3− mainly contributed to the increase of dry weight, photosynthetic pigment content, photosynthetic rate, and overall better appearance of plants. The H2O2 contributed to an increase of dry weight and induced SOD activity. In general, H2O2 and NO3− in proper concentrations can stimulate plant growth and affect their physiological properties.

Microstructure and mechanical behaviour of transient liquid phase spark plasma sintered B4C–SiC–TiB2 composites from a B4C–TiSi2 system

Almost fully-dense B4C–SiC–TiB2 composites with a high combination of strength and toughness were prepared through in situ reactive spark plasma sintering using B4C and TiSi2 as raw materials. The densification, microstructure, mechanical properties, reaction, and toughening mechanisms were explored. TiSi2 was confirmed as a reactive sintering additive to promote densification via transient liquid-phase sintering. Specifically, Si formed via the reaction between B4C and TiSi2 that served as a transient component contributed to densification when it melted and then reacted with C to yield more SiC. Toughening mechanisms, including crack deflection, branching and bridging, could be observed due to the residual stresses induced by the thermoelastic mismatches. Particularly, the introduced SiC–TiB2 agglomerates composed of interlocked SiC and TiB2 played a critical role in improving toughness. Accordingly, the B4C–SiC–TiB2 composite created with B4C-16 wt% TiSi2 achieved excellent mechanical performance, containing a Vickers hardness of 33.5 GPa, a flexural strength of 608.7 MPa and a fracture toughness of 6.43 MPa m1/2.

Measurement of electron density in transient spark discharge by simple interferometry

In this work, the electron density in an atmospheric-pressure Ar transient spark (TS) discharge was measured using an interferometric method. The discharge was operated in a pin-to-plate electrode configuration by applying DC voltages of 7–10 kV. The TS discharge current occurred within a short duration of less than 100 ns, and the peak current was as high as ~ 3 A. Below 8 kV, the TS discharge had weak, irregular emission, making it difficult to measure the electron density using Stark broadening. Here, we developed a simple He–Ne laser Michelson interferogram method for estimating the electron density of unstable TS discharge. Above 8 kV, the electron density values obtained from Stark broadening and the Michelson interferogram were similar and proportional to the dissipated energy. This interferogram method could be adopted to measure the electron density of unstable discharge plasmas, which was measured to be 1 × 1016 cm−3 at 7.0 kV in this experiment.

The effect of water activated by nonthermal air plasma on the growth of farm plants: Case of maize and barley

AbstractThe effects of plasma‐activated water (PAW) generated by nonthermal air plasmas of transient spark with water electrospray or atmospheric glow discharge were investigated on maize (Zea mays L. var Saccharata) and barley (Hordeum vulgare L.) seedlings. PAW is characterized by measuring concentrations of reactive oxygen and nitrogen species (H2O2, , ). After 4 weeks of plants growth, the effects of PAW are analyzed by measuring plant growth and physiological parameters: plant length and fresh weight, photosynthetic pigments concentration and photosynthesis rate, total soluble proteins, antioxidant enzyme activity, and DNA damage. The results suggest that PAW, depending on chemical composition, has the potential to improve the plant growth and influence the physiological parameters, while causing no harmful DNA damage.