DC Plasma Jet Research Articles

Synthesis of thermally stable carbon nanostructures via ethanol pyrolysis in DC plasma jets

Thermostable graphene and carbon nanotubes (CNTs) obtained by the plasma-chemical method were stable when heated to 1300 K. The peculiarity of the obtained materials is associated with the nature of the precursor (ethanol) containing oxygen. It is shown that the composition of the gas phase and the temperature interval for the formation of gaseous precursors depends on the plasma-forming gas used for the pyrolysis of ethanol in a plasma jet: helium, argon, or nitrogen. According to the results of plasma flow simulation, the temperatures of the onset of carbon condensation for helium plasma (2900–2950 K) and argon plasma (2980–3010 K) are quite close, and in the corresponding gas phase the main components are H, H2 and CO, and at lower concentrations there are radicals COOH and OH and HCO+. The nitrogen plasma contains well-represented cyanopolyins responsible for the rearrangement of the gas phase at lower temperatures of 2240–2250 K. It seems that these temperatures are too low for CNT synthesis, so only graphene is formed here. The influence of the combination of H and O in the high-temperature region of plasma flow on the mechanism of formation of precursors of carbon nanostructures has been found.

Antibacterial activity of silver nanoparticles and lemon peel mixture on E-coli Bacteria

In this work, pulsed laser ablation in liquid (PLAL) technique is used to prepare the Ag nanoparticles in water, and prepare lemon peel extract by plasma discharge in a fabricated DC plasma jet in record time at two intervals (5,15) minutes, using Nd:YAG laser wavelength 532 nm at three energies (500, 700, and 900) mJ. Where mixed the colloidal Ag nanoparticles with lemon peel extract in different conditions and applied it on the antibacterial activity Escherichia coli (E. coli.). The antibacterial activity was performed by the agar disc diffusion method. The study confirmed that there was a significant improvement in bacterial inhibition in the case of mixing. Study the UV before and after mixing we note increases in intensity. the inhibition increasing with energy, the best inhibition take place at 900 mJ, at 15 minutes.

Mechanism of Hydrogen Peroxide Formation by Alternating Current and Direct Current Plasma Jets

In this work, a discharge device is designed to realize the generation of alternative current (ac) and direction current (dc) cold atmospheric plasma (CAP) jet in the same generator for studying the production mechanism of H2O2 induced by plasma in water. The interaction between the plasma jets and deionized water is decomposed into three pathways by using a special reactor system, including electrochemical pathway, gaseous dissolution pathway, and the integrated pathway. Two kinds of ac plasma jets are generated by adjusting the electrode structure of the plasma generator, meanwhile two kinds of dc plasma jets are generated by adjusting the polarity of the discharge electrodes. Stable plasma jets are generated in all four configurations. The aqueous H2O2 as well as its vital precursor hydroxyl radical (OH) produced by the plasma jets is detected. The results show that the producing pathway of aqueous H2O2 depends on the position where the OH recombination reaction takes place during the treatment, and does not depend on whether the plasma is excited by ac or dc electric power.

Effect of the precursor aggregate state on the synthesis of CNTs in a DC plasma jet

The transformation of various carbonaceous substances into ordered carbon nanostructures is a fundamental process in nanotechnology. Since this structural transformation is a common property of various methods for producing CNTs, understanding the mechanism of this process in the bulk of a plasma jet will be extremely important, since no substrates are used here. We present an experimental and numerical study of the synthesis of CNTs with and without external catalysts for the pyrolysis of soot, acetylene, and ethanol in a DC argon plasma at a pressure of 350 Torr. By combining various physical methods, including simultaneous thermal analysis, diffraction analysis, electron microscopy, and energy dispersive analysis, we will show that the aggregation state of the precursor significantly affects the structural and morphological properties of CNTs. Theoretical calculations under the assumption of local thermodynamic equilibrium made it possible to study the gas phase composition of a plasma flow in which the CNT precursor is nucleated. It was found that during the pyrolysis of soot (C), the condensation temperature of solid carbon is 3672 K, with the hydrogen in precursor (C2H2) it is lower and equals 3353 K, with the addition of oxygen (C2H5OH) its value becomes even <3141 K. At the lowest condensation temperature, the most thermally stable CNTs are formed.

Engineering of graphene flakes in the process of synthesis in DC plasma jets.

During the pyrolysis of hydrocarbons in helium plasma jets in a plasma-chemical reactor, graphene flakes of a different structure and resistance were obtained. The presence of hydrogen in these structures was established by physicochemical methods, and its content depends on the pressure in the plasma-chemical reactor and the composition of a plasma-forming system. In addition to hydrogen, a relatively low concentration of oxygen atoms is present in the graphene flakes. Hydrogen is involved in the graphene nucleation, whereas oxygen is absorbed on graphene flakes from the air at low temperatures. It was found that a pressure increase in the reactor (up to 710 Torr) leads to the formation of flakes with a low resistivity (0.12-0.20 kOhm sq-1) and low defect density. In the case of synthesis at a low pressure (350-500 Torr), the resistance of graphene flakes is increased by three orders of magnitude (100-400 kOhm sq-1) with a more complicated defect structure and built-in hydrogen. Moreover, hydrogen is difficult to remove from these flakes, and annealing at relatively high temperatures (up to 300 °C) leads to a weak decrease in the resistance due to flake deformation. Additionally, the functionalization of the graphene flakes synthesized at a low pressure with fluorine atoms is suppressed due to their structural features. In general, the selection of growth parameters (gas pressure in a camera, flow rate and content of impurity atoms) allows one to control the defects in graphene, and its structure and conductivity.

Outside Front Cover: Plasma Process. Polym. 11/2021

Outside Front Cover: Electrochemical treatment (EChT), an effective therapy for tumors, is also one of the physicochemical processes coupled in plasma treatment. In this paper, a comparative study is carried out on the anticancer effect between DC plasma jet and EChT with similar topological structure and average current. It is found that the electrochemical process plays an important role in the immediate anticancer effect during the plasma treatment, but it contributes little on the sustained anticancer effect after the plasma treatment. Further details can be found in the article by Dingxin Liu, Zifeng Wang, Zeyu Chen, Dehui Xu, Min Chen, Jinkun Chen, Mengying Zhu, Hao Zhang, Xiaohua Wang, Michael G. Kong, and Mingzhe Rong (e2100087).

Microwave Plasma Assisted Sol‐Gel Synthesis of TiO2 Photocatalyst for DC Plasma Jet Driven Degradation of Methylene Blue

AbstractA new microwave plasma assisted sol‐gel (MPAS) technique was adopted to produce Titanium dioxide (TiO2) photocatalyst by using pure and mixed stabilizers. The crystalline phases, composition, bandgap energy and surface morphology of TiO2 were studied through SEM, XRD, FT‐IR, UV‐Visible spectroscopy and photoluminescence spectroscopy. The average particle size of MPAS synthesized TiO2 nanoparticles remained smaller than the simple sol‐gel method while bandgap energy increased by 40 %. The rutile content and crystallinity of nanoparticles were also found higher in MPAS synthesized TiO2 than the simple sol‐gel method. The type of stabilizer only effected the particle size but not the phase transformations of TiO2 nanoparticles. TiO2 photocatalyst with band gap of 3.06 eV was used to degrade methylene blue dye in water under the exposure of open atmosphere argon plasma jet. UV radiation intensity of the plasma jet at a distance of 2 cm was 576 μW/cm2, which reduced to 149 μW/cm2 at 10 cm. The plasma jet produced some highly reactive species and UV radiations. The reactive species reacted with dye molecules while UV radiations promoted the activity of TiO2. The dye degradation efficiency of the process, under the combined effect of reactive species and TiO2 activity, reached to 95 % after 30 min of plasma exposure time.

Post-synthesis plasma processing and activation of TiO2 photocatalyst for the removal of synthetic dyes from industrial wastewater

In this study, TiO2 nanopowders were prepared by combining the surfactant assisted sol–gel method with microwave plasma calcination. Plasma calcination was performed just for 20–30 min for reducing the calcination time and ensuring the energy efficient synthesis of photocatalyst. The mixed anatase–rutile phased TiO2 nanoparticles were obtained under these synthesis conditions. The band gap energy of the photocatalyst decreased by 40% on microwave plasma calcination. The surfactants were found to be ineffective on phase transformations of synthesized TiO2. FTIR analysis confirmed the absorption of O–Ti–O band stretching between 415 and 420 cm−1. The hydroxyl bands (OH) were observed to be less stretched after plasma calcination. The conventionally calcined HA–Ti, NA–Ti and MS–Ti samples showed band gap energies of 5.09 eV, 4.88 eV and 5.06 eV, respectively. The band gap energy of plasma calcined MTHA–Ti, MTNNA–Ti and MTMS–Ti samples was calculated about 4.92 eV, 3.11 eV and 4.96 eV, respectively. The combined effect of photocatalyst, plasma reactive species and UV radiations promoted the degradation efficiency of the methylene blue dye. Under DC plasma jet exposure, the maximum degradation efficiency of 95% was achieved after 30 min of plasma exposure time. The catalyst retained about 93–95% degradation efficiency after five cycles of dye degradation.

Numerical and Experimental Study of the Multichannel Nature of the Synthesis of Carbon Nanostructures in DC Plasma Jets

Wide spectrum of carbon nanostructures was synthesized by means of simple plasma chemistry using DC plasma torch: carbon nanotubes, nanowalls, graphene, hydrogenated graphene and a mixture of nanotubes with graphene. The synthesis was performed in the plasma-chemical reactor under the pressure varying in the close range 350–710 Torr with different types of hydrocarbon as an admixture to the helium plasma. Aliphatics (propane, butane methane and acetylene) were used providing a variation of C:H ratio. The plasma-chemical pyrolysis of hydrocarbons in the temperature range 1000–8000 K was analyzed using the thermodynamic and gas dynamic characteristics. It is determined that the main contribution to the formation of predecessors of solid carbon makes the composition of plasma jet in the temperature range 2500–3500 K. In this range the interrelation between atomic hydrogen H and hydrocarbon molecules CH varies dramatically, and the mole fraction of solid carbon Cgr goes upward. The C:H ratio in the carbon feedstock is shown to have an influence on the particularity of processes of formation of condensed carbon.

Catalytic and Non-Catalytic Treatment of Industrial Wastewater under the Exposure of Non-Thermal Plasma Jet

Freshwater is only 2.5% of the total water on the Earth and rest is contaminated or brackish. Various physical and chemical techniques are being used to purify the contaminated water. This study deals with catalytic plasma treatment of contaminated water collected from different sites of Faisalabad-Pakistan. A non-thermal DC plasma jet technique was used to treat the water samples in the presence of TiO2 catalyst. The plasma-assisted catalytic treatment introduced some oxidative species (O3, H2O2, HO2−, OH−) in the water. These species reacted with pollutants and cause the degradation of harmful contaminants, especially dyes. The degradation of dye sample during plasma treatment was more pronounced as compared to other samples. pH, conductivity and TDS of dye containing sample decreased after catalytic plasma treatment. The degradation of organic pollutants increased due to presence of several oxidants, such as TiO2, ferrous ions and hydrogen peroxide. FT-IR analysis revealed the degradation of some functional groups during treatment process and confirmed the effectiveness of the process. The residue of the treated samples was consisted of amines, amides and N-H functional groups. XRD analysis showed the presence of Alite, Ferrite, aluminate, Si, S and some heavy metals in the residue. The effect of plasma treatment on activity of gram-negative Escherichia coli (E. coli) bacteria in water was also checked. The bacterial activity was reduced by almost 50% after 2 min of plasma treatment.

Time-resolved imaging and spectroscopy of atmospheric pressure plasma bullet propagation and RONS production

An atmospheric pressure plasma jet visually appears as a continuous plasma, but is actually comprised of a series of fast moving ionization waves, commonly called plasma bullets. Plasma bullets are the visible front of ionization streamers. Studying their spatiotemporal formation and propagation can help understand the plasma dynamics. In this work, the formation and lifetime of a high voltage pulsed dc plasma jet and the subsequent bullets were observed using time-resolved synchronized measurements with an intensified charge-coupled device (ICCD) camera and an ICCD spectrometer. The operating voltage, helium flow rate, and pulse width were varied to observe changes in bullet behavior. The measured velocities of the plasma bullets largely depended on voltage but showed that flow rate can have an effect. The formation of OH and excited N2 (2+) was measured at the nanosecond timescale. It was seen that the formation of these species begins at the visible bullet, but the peak emission and decay occur ∼50–100 ns after bullet passage, indicating a finite time of reaction, excitation, and emission. Observing the temporal formation of plasma bullets and reactive species provides insight into some of the reactions occurring in the discharge and how to tailor the plasma operating conditions.

Synthesis and characterization of silver nanorods using water coupled atmospheric pressure dc plasma

Non-thermal microplasmas are gaining attention of research community due to their unique physical, chemical, optical and catalytic properties. Due to theses remarkable properties, microplasmas are being used in medicine, electronics, material processing and biotechnology. In this study, silver nanorods (AgNRs) were synthesized by coupling dc plasma with aqueous solution of silver nitrate (AgNO3). Sucrose was added in the solution as a stabilizing agent. AgNRs were produced in aqueous solution by reducing AgNO3 with dc plasma jet of argon at atmospheric pressure. No additional reducing agent was added used during production of AgNRs. Different molar ratios of AgNO3 were used to control the size and dispersion of nanorods. Chemical composition and surface morphology of AgNRs were examined by using different techniques, such as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The EDX spectrum confirmed that nanorods are AgNRs metallic silver with atomic weight of 16.86%. SEM micrographs revealed the formation of AgNRs. The rod length varied from 5 nm to 100 nm, depending on the molarity of solute.

Flattening behavior of micro- and nano-sized yttria-stabilized zirconia particles plasma-sprayed on smooth preheated (610 K) nickel substrate: part I

The work presented in this paper is devoted to the impact on Ni substrates of molten oxide particles (yttria-stabilized zirconia (YSZ)) either in the micrometer-sized range (between 20 and 100 µm) or in the submicrometer range (between 0.3 and 1.1 µm). YSZ was chosen because no oxidation occurs when plasma-spraying it in air. Micrometer-sized particles were injected into a hot plasma stream obtained with a DC plasma torch (Oerlikon Metco F4 torch) working with a mixture of Ar and H2 (Ar 33 slm and H2 10 slm). Correlatively an ethanol suspension of submicrometer-sized particles was injected into an Ar–He (Ar 40 slm and He 20 slm) DC plasma jet. Upon impact on a smooth Ni substrate preheated in air at 610 K both sizes of particles flatten and form splats. To achieve a much better understanding of splat formation, measurements of the velocity and temperature of an in-flight single particle just prior to its impact and at its impact were developed. Unfortunately, with submicrometer-sized particles, in-flight measurements of a single particle become impossible and only mean values resulting from a few particles are measured, making interpretation trickier. This study focused on the flattening on smooth substrates, presented as Part I, and will be followed by another study, to be presented as Part II, concerning splat formation on rough substrates adapted to the size of sprayed particles and then splat layering. Of course, the rough surfaces will also be preheated as the smooth ones at 610 K.

Technical characteristics of a DC plasma jet with Ar/N2 and O2/N2 gaseous mixtures

In this paper, the optical emission spectroscopy technique is used to examine the physical properties and technical characteristics of the plasma discharge in a fabricated DC plasma jet. The background gas is nitrogen molecular gas which is mixed with argon and oxygen gases at various percentages. The emission spectra are analyzed and, the plasma density, rotational, vibrational and excitation temperatures are obtained for the formed plasma discharges with Ar/N2 and O2/N2 mixtures. Moreover, the NO and OH lines from NOγ(A2Σ+→X2Πr), (A2Σ,v=0→X2Π,v′=0) excitation transitions are observed. It is shown that, at the higher argon and oxygen percentages in both the Ar/N2 and O2/N2 gaseous mixture, the emission intensities of argon ions and oxygen atoms are increased. In addition, at the higher Ar and O2 contributions in both the gaseous mixtures, while the rotational, vibrational and excitation temperatures are higher, they are decreased at the O2/N2 gaseous mixture. Moreover, the plasma electron density reduces for O2/N2 and increases for Ar/N2 gaseous mixture. On the other hand, for both the mixtures, the plasma density, rotational, vibrational and excitation temperatures are increased at the higher DC power source currents. Furthermore, it is seen that the N2 dissociation rate increases at the higher DC currents and Ar and O2 percentages in both the mixtures. However, N2 dissociation rate in the formed plasma jet with Ar/N2 gaseous mixture is higher.

Discharge modes of atmospheric pressure DC plasma jets operated with air or nitrogen

The different discharge modes that were observed for a plasma jet operated at atmospheric pressure with air or nitrogen by applying a DC high voltage to a microhollow cathode geometry were investigated. Critical parameters that determine the operation in either a self-pulsing or ‘true’ DC discharge mode were identified based on an electrical circuit model and investigated accordingly. Current limitation by the overall circuit resistance supports either a continuous charging and discharging of stray capacities, together with associated repetitive plasma generation, or a short circuit operation. These different modes can be controlled by gas flow rate and applied high voltage. Consecutive plasma development in the self-pulsing mode resembles characteristics of a transient spark discharge. When the associated memory effects start to last longer than intervals between subsequent electrical breakdowns, eventually a current-limited self-sustained glow-like discharge is supported.

Analysis of the production mechanism of H2O2 in water treated by helium DC plasma jets

In this paper, helium plasma jets are used for water activation to explore the production mechanism of H2O2 in the water. Either positive or negative DC voltage is used for the plasma excitation. It is found that the concentration of aqueous H2O2 induced by the positive plasma jet is ~4 times larger than that by the negative plasma jet with similar average discharge current. Three production pathways of aqueous H2O2 are considered important in literature, including the electrolysis, the dissolution of gaseous H2O2, and the combination of aqueous OH. However, the first two pathways are found to have similar contributions on H2O2 production for the positive and negative plasma jets. It is deduced that the OH combination in the surface layer of the plasma-activated water is most responsible for the concentration difference of aqueous H2O2 between the two plasma jets.

Stability and structures in atmospheric pressure DC non-transferred arc plasma jets of argon, nitrogen, and air

The stability of dc non-transferred arc plasma jets and their internal structures is investigated through fast photography, emission spectroscopy, and arc dynamics under different operating conditions. A novel method to explore structures inside extremely intense hot plasma jet is conceived and applied for the first time to investigate arc plasma jets. The study revealed distinct interesting structures and their evolution inside the plasma jet, apparently not reported earlier. The associated fundamental mechanisms are identified from direct experimental evidences. Respective steady state jet characteristics with and without air entrainment are obtained from computational fluid dynamic simulation. Arc root motion, air entrainment, and interaction between electromagnetic and fluid dynamic body forces are found to result in a variety of interesting dynamics and structures inside the plasma jet under different operating conditions. Observed behaviors are notably different in argon, nitrogen, and air plasma. While no unusual structures are found over a range of lower flow rates, interesting structures evolve at higher flow rates. Statistical behavior of these structures is found to have a significant dependence on the gas flow rate and torch power. Apart from air entrainment in the downstream, observed isolated temperature islands inside the jet in the upstream have potential to affect particle trajectory, physical processes, and process chemistry in a significant manner.

Study of the physical discharge properties of a Ar/O2 DC plasma jet

In this paper, the physical properties of plasma discharge in a manufactured DC plasma jet operating with the Ar/O2 gaseous mixture are studied. Moreover, the optical emission spectroscopy technique is used to perform the experimental measurements. The obtained emission spectra are analyzed and, the plasma density, rotational, vibrational and electronic temperature are calculated. The NO emission lines from $$ {\text{NO }}\upgamma \left( {{\text{A}}^{2} {{\Sigma }}^{ + } \to {\text{X}}^{2} {{\Pi }}_{\text{r}} } \right) $$ electronic transition are observed. It is seen that, at the higher argon contributions in Ar/O2 gaseous mixture, the emission intensities from argon ions will increase. Moreover, while the vibrational and excitation temperatures are increased at the higher input DC currents, they will decrease at the higher Ar percentages in the Ar/O2 gaseous mixture. Furthermore, at the higher DC currents and Ar contributions, both the plasma electron density and dissociation fraction of oxygen atoms are increased.

Experimental study on ignition characteristics of kerosene–air mixtures in V-shaped burner with DC plasma jet igniter

In this paper, we investigate the effects of DC plasma jet igniter on ignition characteristics of the kerosene–air mixtures in V-shaped burner. The primary principles of DC plasma igniter design have been put forward to prolong the igniter life and improve ignition performance. The main characteristic of plasma igniter is that the anode arc root is fixed at anode nozzle outside surface other than the anode inner surface in conventional design. The electric characteristics of the plasma jet igniter including voltage–current characteristics, the arc column propagation, emission spectrum and anode arc root movement in a quiescent environment are investigated with high speed CCD together with a recording of the voltage and current. The entire ignition process of the plasma jet igniter is recorded by high speed CCD and the ignition delay times of the kerosene–air mixtures defined by the interval between the onset of the plasma igniter and the establishment of a stable flame are measured with two photomultipliers with one of 10 mm band pass filter centered at 780 mm (the plasma igniter emission spectrum of OI) and the other of 10 mm band pass filter centered at 430 mm (direct flame emission of CH(A2Δ→X2Π)). Results show that the plasma igniter works in a restrike mode and the anode spot movement is irregular. The plasma igniter jet contains abundance active particles inferred from the emission spectrum. The ignition delay times increase at first and then decrease with the increase of excess air coefficient ranging from 0.91 to 6.38. The delay times increase quickly when the mixtures are extremely lean or rich.

Numerical simulation of DC air plasma torch modes and plasma jet instability for thermal spraying technology

The article is dedicated to nonstationary simulation of DC air plasma torch. The mathematical model for the analysis of plasma jet instability is developed. The proposed 2D axisymmetric model demonstrates the physical processes taking place inside and in the outer region of the plasma torch. The influence of the power source parameters and anode geometry on voltage and plasma jet fluctuation is described. Simplified mathematical model is developed in order to assess the effect of the flow behavior on heat transfer processes. The developed model can be used for the design of plasma torches and their operation modes. The results of mathematical model verification are based on experimental studies.