Barrier Discharge In Nitrogen Research Articles

Optical emission characterization of an atmospheric pressure dielectric barrier discharge in nitrogen: Evolution of CN emissions during PTFE etching

AbstractThe present work investigates the etching of coated polytetrafluoroethylene (PTFE) films using an atmospheric pressure dielectric barrier discharge operating in nitrogen in a filamentary regime. For different treatment durations, the optical emission spectra were recorded over time. Most of the emissions are attributed to the N2 second positive system. The presence of CN is also observed, and its emissions rise with the exposure time of PTFE. This rise is attributed to the density of CN produced. The X‐ray photoelectron spectroscopy surface characterization suggests two etching regimes. This is linked with a change in slope in the intensity evolution of the optical emissions of the CN. At longer times, a fluorinated deposit on the electrode is observed, confirming a different nature of the etched material.

Influence of pulsed gas injections on the stability of Townsend dielectric barrier discharges in nitrogen at atmospheric pressure

This work investigates the effects of pulsed nitrogen gas injections on the stability of Townsend dielectric barrier discharges operated in continuous nitrogen gas flows at atmospheric pressure. For single-pulse injections with pulse durations lower than the continuous gas residence time (∼50 ms), current–voltage characteristics reveal homogeneous discharges with a single current peak per half-cycle of the applied voltage. However, a sudden decrease of the discharge power over time combined with a temporary transition from homogeneous to filamentary discharge is observed for longer pulses at fixed pulsed gas flows and for higher pulsed gas flows at fixed pulse duration. In addition, for multiple pulsed gas injections with repetition frequencies between 0.1 and 10 Hz, discharge destabilisation increases with the number of pulses. Time-resolved optical emission spectroscopy reveals that, over the single pulse time scale, temporal variations of the emission intensities are longer than the expected residence times of the continuous and pulsed gas flows. Furthermore, a rise of oxygen impurities can be seen over both single and multiple-pulses time scales. Two-dimensional gas flow simulations reveal that pulsed injections introduce sharp and narrow temporal gas velocity profiles over the range of experimental conditions investigated, with no cumulative effects in the discharge cell from one pulse to the other. However, pulsed operation introduces significant changes in the neutral gas composition with time scales comparable to those revealed by electrical and optical diagnostics. In such conditions, the outgassing of impurities adsorbed on surfaces located upstream of the discharge cell plays a vital role in Townsend discharges’ physics and characteristics.

Refined analysis of current–voltage characteristics in Townsend dielectric barrier discharges in nitrogen at atmospheric pressure

A refined method is proposed to analyze surface spreading phenomena along the gas flow lines in plane-to-plane Townsend dielectric barrier discharges (TDBDs) in nitrogen at atmospheric pressure. Current–voltage characteristics are recorded as a function of gas residence time using a recently-developed, fragmented-electrode system and the results are analyzed using an equivalent circuit model using dielectric, gas and parasitic capacitances as adjustable parameters. The results show that the capacitance values are directly correlated to the surface spreading of the TDBD, which in turn, influences the shape of the discharge current and gas voltage curves for each half-cycle of the applied voltage. This highlights the importance of a good determination of the effective discharge surface area and therefore of the capacitance values in electrical analysis of TDBD.

The Effect of TiO2 Catalyst on the NO Reduction by Barrier Discharge in Nitrogen

The study investigated NO reduction by N radicals produced by barrier discharge in nitrogen and the possible effect of TiO2 catalyst on this reaction. The experiments for NO reduction were carried out at temperatures ranging from room temperature to 140 °C and at NO concentrations ranging from 200 to 800 ppm. The experimental results were described by a model which was based on six main reactions for the calculation of the NO and NO2 concentrations. The analysis of model suggested two simple methods for the estimation of nitrogen radical production efficiency which in present study was 2 ppm/(J/L). The model also confirmed that N radicals are used very efficiently in the reduction of NO and this process can’t be improved by the catalyst. Nonetheless, experiments showed that the presence of TiO2 catalyst improved the removal of NO. The experimental results can be explained by surface processes taking place with NO2 with the help of other plasma produced nitrogen species.

Particle densities of the pulsed dielectric barrier discharges in nitrogen at atmospheric pressure

Pulsed dielectric barrier discharges (DBDs) have become a promising solution to generate atmospheric-pressure non-equilibrium plasmas. In this work, a one-dimensional fluid model is carried out to research particle densities of the pulsed nitrogen DBDs at atmospheric pressure. Averaged particle densities, time evolutions of axial distributions of particle densities and influences of discharge gap distance dg on the particle densities are systematically illustrated and discussed. The calculation results show that averaged electron densities are lower than averaged N2+ densities, but higher than other averaged ion densities. Time evolutions of axial distributions of electron, N+ and N2+ densities show two peaks during rising and falling phases of applied voltage when dg is 0.2 cm but present gradual increases during pulse width when dg is 0.6 cm, which are similar to those of N2(a′) and N2(B). Maximums of N3+ densities are close to the momentary cathode under dg of 0.2 cm but locate near the grounded electrode under dg of 0.6 cm, which are alike to those of N2(A) and N2(C). Besides, N4+ densities nearby the momentary anode are higher than those nearby the momentary cathode when dg is 0.2 cm. N(2D) has low averaged particle densities and complex time evolutions compared to N.

A diffuse plasma generated by bipolar nanosecond pulsed dielectric barrier discharge in nitrogen

In this study, a bipolar high-voltage pulse with 20 ns rising time is employed to generate diffuse dielectric barrier discharge plasma using wire-plate electrode configuration in nitrogen at atmospheric pressure. The gas temperature of the plasma is determined by comparing the experimental and the best fitted optical emission spectra of the second positive bands of N2(C3Πu → B3 Πg, 0-2) and the first negative bands of N2 + (B2 Σu + → X2 Σg +, 0-0). The effects of the concentration of argon and oxygen on the emission intensities of N2 (C3Πu → B3Πg, 0-0, 337.1 nm), OH (A 2Σ → X2Π, 0-0) and N2 + (B2 Σu + → X2 Σg +, 0-0, 391.4 nm) are investigated. It is shown that the plasma gas temperature keeps almost constant with the pulse repetition rate and pulse peak voltage increasing. The emission intensities of N2 (C3Πu → B3Πg, 0-0, 337.1 nm), OH(A2Σ → X2Π, 0-0) and N2 + (B2 Σu + → X2 Σg +, 0-0, 391.4 nm) rise with increasing the concentration of argon, but decrease with increasing the concentration of oxygen, and the influences of oxygen concentration on the emission intensities of N2(C3Πu → B3Πg, 0-0, 337.1 nm) and OH (A2Σ → X2Π, 0-0) are more greater than that on the emission intensity of N2 + (B2 Σu + → X2 Σg +, 0-0, 391.4 nm).

Novel insights into the development of barrier discharges by advanced volume and surface diagnostics

The comprehensive characterization of microdischarges (MDs) requires complementary diagnostics of volume and surface processes at the same discharge configuration under identical conditions. This contribution summarizes the results from optical, spectroscopic and electric investigations as well as the determination of surface charges and metastable nitrogen molecules in filamentary and diffuse barrier discharges. The feasibility of such an approach is demonstrated on selected examples.Fast optical and spectroscopic methods are reviewed for the example of a pulsed driven single filament dielectric barrier MD. It is demonstrated that the methods of streak recording and cross-correlation spectroscopy can complement one another for a comprehensive study of the MD development. Using these techniques it is shown that the so-called prephase is present also in sub-microsecond pulsed barrier discharges. The excitation starts directly with the voltage increase. In the case of diffuse barrier discharges in nitrogen, the combination of spectroscopic and electrical characterization, surface charge measurement by the Pockels effect, and the determination of nitrogen metastables N2(A) by laser-induced fluorescence provides detailed knowledge about the time-integrated surface charge which correlates with the discharge current for each half cycle, whereas the temporal maximum of the metastables of the order of few 1013 cm−3 is delayed in relation to the current maximum. The spatial (axial) maximum of the metastable density is located near the anode like the emission maximum from N2 second positive system at λ = 337 nm. Furthermore, the lifetime of surface charges beyond a typical discharge period has been investigated.

Nitrogen Plasma Modification and Chemical Derivatization of Polyethylene Surfaces – An In Situ Study Using FTIR‐ATR Spectroscopy

AbstractChemical derivatization reactions of nitrogen plasma‐treated surfaces with aromatic aldehydes, such as the prototypic 4‐trifluoromethyl‐benzaldehyde (TFBA), have for a long time been considered selective for primary amines. Results of an in situ study using FTIR‐ATR spectroscopy challenge the validity of this assumption: Modification of polyethylene surfaces by afterglows of dielectric barrier discharges in nitrogen–hydrogen mixtures with subsequent hydrogen/deuterium exchange or TFBA derivatization suggests that the latter does not follow the commonly assumed reaction scheme.

Spatiotemporal Distribution of a Monofilamentary Dielectric Barrier Discharge in Pure Nitrogen

Time-resolved and spatially resolved ICCD images of the breakdown phase of a monofilamentary dielectric barrier discharge in nitrogen are reported.

Optical study of diffuse bi-directional nanosecond pulsed dielectric barrier discharge in nitrogen

In this study, a bi-directional high voltage pulse with 20 ns rising time is employed to generate diffuse glow-like dielectric barrier discharge plasma with very low gas temperature in N 2 using needle-plate electrode configuration at atmospheric pressure. Both the diffuse nanosecond pulsed dielectric barrier discharge images and the optical emission spectra of the discharge are recorded successfully under severe electromagnetic interference. The effects of pulse peak voltage, pulse repetition rate, and the concentrations of Ar and O 2 on the emission intensities of NO (A 2Σ → X 2Π), OH (A 2Σ → X 2Π, 0-0), N 2 (C 3Π u → B 3Π g, 0-0, 337.1 nm), and N 2 + (B 2Σ u + → X 2Σ g +, 0-0, 391.4 nm) are investigated. The effects of the concentrations of Ar and O 2 on the discharge diffuse performance are also studied. It is found that the emission intensities of NO (A 2Σ → X 2Π), OH (A 2Σ → X 2Π, 0-0), N 2 (C 3Π u → B 3Π g, 0-0, 337.1 nm), and N 2 + (B 2Σ u + → X 2Σ g +, 0-0, 391.4 nm) rise with increasing pulse peak voltage, pulse repetition rate, and the concentration of Ar, but decrease with increasing the concentration of O 2. The main physicochemical processes involved are also discussed.

Homogeneous dielectric barrier discharge in nitrogen at atmospheric pressure

A dielectric barrier discharge in nitrogen at atmospheric pressure was investigated by means of the electrical measurement, the fast photography and the time-resolved spectroscopy. By addition of a nitrogen flow, a stable homogeneous discharge was produced in a gap not longer than 3 mm and it was identified with a Townsend discharge. It was found that the discharge was extinguished while the voltage of the gas gap continued to increase. This extraordinary manner of discharge extinction was explained by the limited number of trapped electrons on the dielectric surface that could not provide a long-lasting Townsend discharge with sufficient secondary electrons. Due to the ‘memory effects’ the lowest breakdown voltage for a Townsend discharge in a 2 mm gap is only 4.9 kV in contrast to the streamer breakdown voltage of 8.2 kV. The working domain of the Townsend discharge is dependent on the frequency and the amplitude of the applied voltage. When the flow velocity increases from 0 to 140 cm s−1, the discharge current decreases from 2.9 to 2.3 mA and the breakdown voltage increases from 5.3 to 5.9 kV, which is attributed to the nitrogen pressure in the gap increasing with the flow velocity. With the gas flow, the intensities of the spectral lines from the second positive system of N2 are almost unchanged, whereas those from NOγ systems are significantly reduced. From this phenomenon, it may be inferred that the density of oxygen as impurity in the discharge gap decreases with the gas flow. This result is in agreement with the existing theory that less oxygen leads to more metastables N2(A) surviving to produce more seed electrons for initiating a Townsend discharge in nitrogen at atmospheric pressure.

大气压下氮气介质阻挡微放电中分子振动温度的时间分辨

大气压下氮气介质阻挡微放电中分子振动温度的时间分辨

Influences of gas flow on gas temperature and discharge mode in dielectric barrier discharge of nitrogen at atmospheric pressure

Dielectric barrier discharge in nitrogen at atmospheric pressure is studied with the spectroscopy and the fast photography of the discharge. By the introduction of a nitrogen flow into the discharge gap, the homogeneous discharge in a 2 mm gap can be maintained. Based on the waveform of the discharge current characterized by a current pulse per half cycle of the applied voltage and the 1 μs exposure discharge photograph showing a luminous layer covering the entire surface of the anode, the homogeneous discharge is identified with a Townsend discharge. The instrumental broadening of the spectrometer used in the experiment is calibrated with a helium-neon laser. The data relevant to the instrumental broadening are input into a code called Specair for calculating the spectrum profiles of 0—2 band in the second positive system of nitrogen molecules at different gas temperatures. By fitting the calculated spectrum profiles to the experimental one, the rotational temperature of the nitrogen molecules is determined. The results show that the dielectric barrier Townsend discharge in nitrogen at atmospheric pressure cannot heat the nitrogen to a high temperature (ΔTg≤50 K) and the small rising in temperature does not induce the thermal instability that leads to the transition of the Townsend discharge to a filamentary discharge. By the addition of a gas flow into the discharge gap, the nitrogen is indeed cooled down to a lower temperature. However, it is not the reason for the Townsend discharge to be maintained. By comparing the discharge spectra with and without the gas flow, it could be concluded that the gas flow much reduces the density of the impurity oxygen desorbed from the dielectric by the discharge and makes it possible for more nitrogen metastables to survive to the beginning time of the next discharge and to provide sufficient seed electrons which are necessary for Townsend discharge.

Parametric study of afterglows issued from Dielectric Barrier Discharges in nitrogen and air and applied on Aureobasidium fungi

This article is devoted to the study of afterglows issued from two Dielectric Barrier Discharge reactors driven by two distinct High Voltage generators. The obtained afterglows are applied on Aureobasidium pullulans fungi in view of a curative treatment. In a first part, the electrical characteristics of the discharges obtained with both systems are studied and in a second part are presented the results of the fungi treatment efficiency.

The influence of electrode gap width on plasma properties of diffuse coplanar surface barrier discharge in nitrogen

In this work we have studied the influence of electrode gap width (inter-electrode distance) on plasma properties of the diffuse coplanar surface barrier discharge. The outer conditions and discharge configuration can substantially influence properties of the discharge. Better understanding of these effects can lead to optimization of the discharge parameters for industrial applications. In this work the discharge was operated in nitrogen at atmospheric pressure. The electrode gap width was varied in the range from 0.6 to 2.2 mm. The input voltage, electrode temperature and gas flow was kept constant for all cases. Plasma parameters were studied by the means of time and space resolved optical emission spectroscopy and oscilloscopic measurements. These measurements gave us time and space distribution of discharge luminosity (e.g. intensities of second positive and first negative systems of nitrogen) and 1D-spatial profiles of rotational and vibrational temperature of nitrogen.

Density measurement in a dielectric barrier discharge in N2 and N2 with small O2 admixtures

This paper deals with the measurement of metastable state density in a dielectric barrier discharge in nitrogen and nitrogen with small admixtures of oxygen, operating in a Townsend-like discharge regime. The measurement is made by optical–optical double resonance-LIF, calibrated by a method based on the measurement of the ratio of nitrogen second positive system and NO-γ emissions, and of NO density by LIF. A metastable density of the order of 1013 cm−3 was found in a nitrogen diffuse discharge. Addition of small oxygen concentrations to the discharge drives a transition to the filamentary regime that appears to be caused not by a marked decrease of the metastable density in the discharge but rather by a considerable increase of its quenching rate. Such an increase, due to collision quenching by O2 and O, strongly reduces the survival of the metastable between two discharge pulses. These observations are consistent with the idea that the diffuse regime can be due to a space charge memory effect due to the nitrogen triplet metastable, which is cancelled by the introduction of oxygen in the gas feed.

Modelling of atmospheric pressure dielectric barrier discharges with emphasis on stability issues

The properties of a barrier discharge in nitrogen near the transition from the Townsend mode to the filamentary mode are studied on the basis of a two-dimensional fluid model. The formation of an intermediate mode (multipeak Townsend discharge) is discussed. The surface processes (ion–electron emission and photoemission) and the positive volume charge are proposed as the mechanisms of formation of a multipeak mode. It is shown that the Townsend mode is stable relative to radial fluctuations, whereas the glow mode is unstable and turns into a filamentary mode. The development of a radial fluctuation into a filament is demonstrated. The homogeneity of the barrier discharge depends on the barrier material. In particular, the widening of the stability region for the discharge with low-permittivity barriers is proved.

Effect of the barrier material in a Townsend barrier discharge in nitrogen at atmospheric pressure

A Townsend-like barrier discharge in nitrogen at 7 kHz frequency is studied experimentally and theoretically. The discharge is homogeneous under a certain range of parameters, which depends on the material of the barriers. The higher the dielectric permittivity of barriers is, the narrower is this range. It is shown that the discharge properties do not only depend on the total capacitance of barriers but they also explicitly depend on the permittivity of a dielectric sheath near the surface. Measured ranges of existence of a Townsend discharge agree with the calculations based on a self-consistent model. Also, the two-dimensional simulations of the barrier discharge show that the stability of the discharge relative to radial fluctuations may depend on the permittivity of barriers. The effect of barrier material is interpreted as the influence of dielectric permittivity on the electric field induced by surface charges.

Diffuse barrier discharges in nitrogen with small admixtures of oxygen: discharge mechanism and transition to the filamentary regime

Diffuse barrier discharges (BDs) are characterized by the periodicity of their discharge current and by the uniform coverage of the entire electrode surface by the plasma. Up to now the discharge development, their appearance and dynamics cannot be adequately explained by elementary processes. Different processes are discussed in the literature controversially, in particular the importance of volume and surface processes on the pre-ionization (Penning-ionization, secondary (γ-) processes, role of surface charges). Diffuse BDs in nitrogen with small admixtures of oxygen are investigated by plasma diagnostics (current/voltage-oscillography, optical emission spectroscopy) and numerical modelling. Special attention is paid to the transition to the usual filamentary mode, characterized by the presence of micro-discharges and caused by the admixture of oxygen in the range of 0–1200 ppm (parts-per-million). This transition starts at low values of O2 (about 450 ppm) and is introduced by an oscillative multi-peak mode. At higher admixtures (about 1000 ppm) the micro-discharges are generated. According to the results of numerical modelling, secondary electron emission by N2(A 3Σu) metastable states plays a major role in discharge maintenance. Due to the much more effective quenching of these states by O2 and NO than by N2 the subsequent delivery of electrons will be decreased when the oxygen amount is increased.

On the Homogeneity of the Glow‐Like Barrier Discharge at Atmospheric Pressure

AbstractSummary: The transition of the barrier discharge in nitrogen in a space‐charge (glow) phase and the evolution of radial inhomogeneities are investigated on the basis of a two‐dimensional hydrodynamic model. At medium frequencies, when the primary mechanism of electron emission from the cathode is desorption of electrons, the final stage of the discharge is a filament. When the frequency of the external voltage is low and the electrons are emitted via UV photons, the initial perturbation significantly expands in a radial direction and a homogeneous glow‐like discharge covering the whole surface of the electrodes is observed.Electron density in the Townsend phase of the discharge at low frequency.magnified imageElectron density in the Townsend phase of the discharge at low frequency.