Glow Discharge In Air Research Articles

DC discharges in atmospheric air for bio-decontamination – spectroscopic methods for mechanism identification

Three types of DC electrical discharges in atmospheric air (streamer corona, transient spark and glow discharge) were tested for bio-decontamination of bacteria and yeasts in water solution, and spores on surfaces. Static vs. flowing treatment of contaminated water were compared, in the latter the flowing water either covered the grounded electrode or passed through the high voltage needle electrode. The bacteria were killed most efficiently in the flowing regime by transient spark. Streamer corona was efficient when the treated medium flew through the active corona region. The spores on plastic foil and paper surfaces were successfully inactivated by negative corona. The microbes were handled and their population evaluated by standard microbiology cultivation procedures. The emission spectroscopy of the discharges and TBARS (thiobarbituric acid reactive substances) absorption spectrometric detection of the products of lipid peroxidation of bacterial cell membranes indicated a major role of radicals and reactive oxygen species among the bio-decontamination mechanisms.

Aging and annealing behavior of polycarbonate surfaces modified by direct‐current glow discharge in air

AbstractAging and annealing a polycarbonate (PC) polymer surface treated by direct‐current (dc) glow discharge tend to revert it back to its virgin (pristine) state existing before surface modification by glow discharge. This structural recovery during aging and annealing has been studied in terms of the contact angles of test liquids and surface energy and correlated to the parameters of surface treatment such as the treatment time and power. Samples stored in hydrophobic environments such as air and treated by dc glow discharge at higher power levels show less recovery during aging than those treated at lower power levels. Similarly, a longer exposure time at a power level of 2.04 W decreases the extent of structural recovery in terms of surface energy during aging in air. At higher power levels, the higher kinetic energy of plasma species involved during dc glow discharge results in greater thickness of the damaged layer of the polymer surface, and so a PC sample exposed to dc glow discharge at a higher temperature also recovers at a slower rate during the initial phase of aging, whereas samples with surfaces modified by dc glow discharge at room temperature but annealed at a higher temperature show a relatively rapid recovery during the initial phase of aging. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Dc excited glow discharges in atmospheric pressure air in pin-to-water electrode systems

Electrical and optical emission properties of non-equilibrium atmospheric air discharges between a metal pin and a tap water anode/cathode are presented. With a water anode the discharges are of the glow type as is derived from short-exposure time plasma imaging and electrical characteristics. Additionally, the validity of extrapolated scaling laws of low pressure glow discharge supports these findings.In the case of a water cathode the plasma is filamentary in nature at the water surface. In the case of a water anode, the plasma is diffuse down to 10 ns. The timescales on which the filaments are visible in the near water cathode region and estimates of the electrical field in the cathode layer are consistent with the assumption that these filaments occur due to the electrical instability of the water surface.Spatially resolved rotational temperature measurements and dependence of the rotational temperature on current are discussed in detail. The rotational temperatures of OH and N2 in the positive column of the plasma are identical and equal to 3250 ± 250 K. A 2500 K temperature drop in the near anode region clearly shows that the water anode acts as an effective heat sink for the discharge. This indicates that apart from the electrical stabilization of the discharge by the water electrode due to its distributed resistance, a water anode also thermally stabilizes the discharge. The rotational temperature of nitrogen near the metal anode is typically two times smaller.

Inactivation of Escherichia Coli Using Remote Low Temperature Glow Discharge Plasma

Low-temperature plasma is distinguished as a developing approach for sterilization which can deal with and overcome those problems such as thermal sensitivity and destruction by heat, formation of toxic by-products, higher costs and inefficiency in performances, caused by conventional methods. In this study, an experimental investigation was undertaken to characterize the effects of the operational parameters, such as treating time, discharge power and gas flow rate, of remote glow discharge air plasma. The results show that the inactivation of Escherichia coli can reach above 99.99% in less than 60 seconds and the optimal operational conditions for treating time, discharge power and gas flow rate were: 40 s, 80 W and 60 cm3/min, respectively. The contribution of UV radiation during plasma germ deactivation is very limited.

Images of Pulsed Glow Discharge in Air at Different Pressures

This paper illustrates the formation of a volume pulsed glow discharge in air stressed by a single pulse with tens of nanosecond rise time in a nonuniform electric field gap. The images presented here show that diffuse discharges can be obtained in air with no filamentation at different pressures. With the increase of air pressure, the transform appears from diffuse discharge channels to discrete discharge channels because of the inhibiting effect of electron avalanches.

Physico-chemical characterization of a polycarbonate (PC) surface modified by exposure to dc glow discharge in air

The present investigation describes the changes in the wetting characteristics of a polycarbonate (PC) surface modified by exposure to dc glow discharge at 2.04 W, as observed by contact angle measurement. The contact angle of droplets of test liquids of deionized water and formamide on PC surface decreases rapidly with increasing time of exposure to dc glow discharge and attains a minimum. Thereafter, the contact angle increases slightly to show a small hump before saturating finally at longer times of exposure. The lowering of contact angle is primarily due to the increasing polar component of surface energy. Fourier transform infrared spectroscopy and electron spectroscopy for chemical analysis indicate that increasing polar surface energy is accompanied by increased oxidized functional groups such as C–O and C=O, thus showing increasing O/C ratio with increasing exposure time. Atomic force microscopy shows increasing adhesion force with increasing exposure time, consistent with the observed adhesion energy estimated from 2.04 W contact angle measurement.

The effect of glow discharge plasma on the surface properties of Poly (ethylene terephthalate) (PET) film

In the present work, Poly (ethylene terephthalate) films have been exposed to glow discharge air plasma to improve their surface properties for technical applications. Surface energy values have been estimated using contact angle value for different exposure times and different test liquids. Surface composition and morphology of the films were analyzed by XPS and AFM. Crystallinity of the plasma treated samples were studied by XRD analysis. The improvement in adhesive strength was studied by measuring T-peel strength and lap shear strength tests. It was found that the plasma treatment modified the surfaces both in chemical composition and morphology. Change of chemical composition made the polymer surfaces to be highly hydrophilic, which mainly depends on the increase in oxygen-containing groups. The AFM and XRD observation showed that the surface roughness and crystallinity of the PET film increased due to plasma treatment.

Ozone production by nanoporous dielectric barrier glow discharge in atmospheric pressure air

This study is aimed at demonstrating plasma-chemical ozone production based on low temperature atmospheric pressure glow discharge through nanoporous dielectric barriers. The 20kHz ac driven discharge is formed in air or oxygen gas flowing in the axial direction of the cylindrical plasma reactor containing four parallel aluminum rods covered with nanoporous alumina films. The discharge utilizing nanoporous dielectric barrier is more uniform and more energy efficient in ozone generation than the discharge through smooth-surface dielectric barriers.

Images of Pulsed Glow Discharge in Air at Different Pressures

Images of Pulsed Glow Discharge in Air at Different Pressures

Measurement of gas temperature and convection velocity profiles in a dc atmospheric glow discharge

Gas temperature and convective velocity distributions are presented for an unconfined glow discharge in air at atmospheric pressure, with electric currents ranging between 30 and 92 mA. The vertically oriented discharge was formed between a pin anode (top) and an extended cathode. The temperature and velocity profiles were measured using laser-induced Rayleigh scattering and laser Doppler anemometry techniques, respectively. The temperature field exhibited a conical shape with the radius of hot temperature zone increasing toward the anode. A maximum temperature of 2470 K was observed on the discharge axis with the discharge current of 92 mA. Air velocity measurements around the discharge demonstrated that the shape and magnitude of the temperature field are strongly affected by natural convection. Estimates indicate that convective losses may account for more than 50% of the power input into the positive column of the discharge. The measured temperature fields and convective velocity profiles provide a set of data that is important for the evaluation of dc atmospheric glow discharges in various applications such as sound manipulation and acoustic noise mitigation.

Three-dimensional Reconstruction Using Transmission Electron Microscopy Reveals a Swollen, Bell-shaped Structure of Transient Receptor Potential Melastatin Type 2 Cation Channel

Transient receptor potential melastatin type 2 (TRPM2) is a redox-sensitive, calcium-permeable cation channel activated by various signals, such as adenosine diphosphate ribose (ADPR) acting on the ADPR pyrophosphatase (ADPRase) domain, and cyclic ADPR. Here, we purified the FLAG-tagged tetrameric TRPM2 channel, analyzed it using negatively stained electron microscopy, and reconstructed the three-dimensional structure at 2.8-nm resolution. This multimodal sensor molecule has a bell-like shape of 18 nm in width and 25 nm in height. The overall structure is similar to another multimodal sensor channel, TRP canonical type 3 (TRPC3). In both structures, the small extracellular domain is a dense half-dome, whereas the large cytoplasmic domain has a sparse, double-layered structure with multiple internal cavities. However, a unique square prism protuberance was observed under the cytoplasmic domain of TRPM2. The FLAG epitope, fused at the C terminus of the ADPRase domain, was assigned by the antibody to a position close to the protuberance. This indicates that the agonist-binding ADPRase domain and the ion gate in the transmembrane region are separately located in the molecule.

Non-thermal plasma treatment for hydrophilicity improvement of grey cotton fabrics

Abstract In this paper the hydrophilic improvement of the grey cotton fabric by low pressure dc glow discharge air plasma is investigated. The fabrics were treated for different exposure times, discharge potentials and pressure levels. Effect of plasma treatment on the wettability of the fabric was studied by measuring contact angle and dynamic wicking rate. The surface energy values have been estimated using contact angle measurements and effective mean pore radius of the plasma-treated fabrics were estimated by modified Washburn equation via dynamic wicking technique. Degradation and dyeability of the fabrics were determined by weight loss percentage and computer colour matching procedure. Characterization of the functional changes due to the plasma treatment has been carried out by means of Fourier transform infrared spectroscopy (FTIR–ATR). The surface morphology of the untreated and plasma-treated fabrics were analyzed by scanning electron microscopy (SEM).

Transition from Spark Discharge to Constricted Glow Discharge in Atmospheric Air by Capacitor Coupled Discharge

The transition from a spark discharge to a constricted glowdischarge in atmospheric air was studied with a capacitor coupledpin-to-water plasma reactor. The reason of the transition isconsidered to be of various factors, namely the change of the airgap due to the polarization of water molecules by the electricfield, the feedback effect of the capacitors, and the ion trappingmechanism. The effects of the frequency of the power supply,inter-electrode gap, and coupled capacitance on the dischargetransition were also investigated.

Excited Electron Temperature and Molecular Vibration Temperature During Transition from Filamentary Discharge to Glow Discharge in Surface Discharge in Air

A dielectric barrier surface discharge device was used toinvestigate the transition from a filamentary discharge to a glowdischarge in air at different gas pressures. Discharge images andwaveforms of the applied voltage and discharge current were recordedsimultaneously, and it was found that the discharge could transitfrom filamentary to glow with the decrease in pressure. Opticalemission spectra during the transition from a filamentary dischargeto a glow one were recorded. Excited electron temperature can bedetermined from the ratios of the relative intensities of spectrallines while molecular vibration temperature can be measured byanalysing spectral lines of the N2 second positive band system.The results show that both the excited temperature and molecularvibration temperature increase with the decrease in the gaspressure. Qualitative explanations are given.

Propagation of sound in glow discharge plasma

Propagation of sound in a medium where the rate of local heat addition is a function of gas density is analysed theoretically and the results are applied for modelling the experimentally observed effect of amplification of acoustic waves by an extended glow discharge in air. The model adequately describes the experimental dependences of the gain on the wave frequency and discharge power density and predicts that the amplification of sound by an unconfined glow discharge in air increases with discharge current density but does not change noticeably with gas pressure when the current density is kept constant. Quantitative estimates indicate that a gain of as high as 1 m−1 (or 9 dB for a 60 dB wave passing through 1 m of plasma) could be realized using a discharge in air with a current density of 100 mA cm−2.

Shock velocity in weakly ionized nitrogen, air, and argon

The goal of this research was to determine the principal mechanism(s) for the shock velocity increase in weakly ionized gases. This paper reports experimental data on the propagation of spark-generated shock waves (1<Mach<3) into weakly ionized nitrogen, air, and argon glow discharges (1<p<20Torr). In order to distinguish between effects due solely to the presence of electrons and effects due to heating of the background gas via elastic collisions with electrons, the weakly ionized discharge was pulsed on/off. Laser deflection methods determined the shock velocity, and the electron number density was collected using a microwave hairpin resonator. In the afterglow of nitrogen, air, and argon discharges, the shock velocity first decreased, not at the characteristic time for electrons to diffuse to the walls, but rather at the characteristic time for the centerline gas temperature to equilibrate with the wall temperature. These data support the conclusion that the principal mechanism for the increase in shock velocity in weakly ionized gases is thermal heating of the neutral gas species via elastic collisions with electrons.

Simulation of convection-stabilized low-current glow and arc discharges in atmospheric-pressure air

A two-dimensional model of stationary convection-stabilized low-current glow and arc discharge columns in atmospheric-pressure air is developed which accounts for deviation of the plasma state from the local thermodynamic equilibrium (LTE). In addition to equations of energy, continuity and momentum (analogous to those used in LTE arc models), the non-LTE model includes balance equations for plasma species and for the vibrational energy of nitrogen molecules. The kinetic scheme is used which was developed recently for the simulation of low-current wall-stabilized discharges in air. Results of calculation of discharge parameters over a wide current range are presented. It is shown that the non-equilibrium effects are substantial at currents lower than ∼ 100 mA. The calculated plasma parameters agree with available experimental data.

Comparison of Dielectric Barrier Discharge and Atmospheric Pressure Glow Discharge for Surface Modification of PET Film

Non-equilibrium plasmas under atmospheric pressure are of great interest in polymer surface processing because of their convenience, effectiveness and low cost. In the present work polyethylene terephthalate (PET) film surface is modified using the non-equilibrium plasma generated by the atmospheric pressure glow discharge (APGD) and dielectric barrier discharge (DBD) in ambient air. The differences in discharge characteristics between APGD and DBD are shown by measurement of their electrical discharge parameters and observation of light-emission phenomena. The effects of APGD and DBD on PET surface modification are studied by comparing their surface properties, which are characterized by contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM). It is found that the APGD is quite homogeneous and stable in the whole gas gap, which differs from the filamentary micro-discharge of the DBD. It is concluded that the APGD and DBD treatments modify the PET surface in both morphology and composition, but APGD is more effective in PET surface modification than DBD as it can modify the surface more uniformly and make the contact angle decline to a lower level.

Active stabilization of low-current arc discharges in atmospheric-pressure air

Low-current (∼250 mA), high-voltage (∼700 V), dc discharges are observed to operate in air at atmospheric pressure when a closed loop is included for current regulation on the power supply. A dynamic process might control the discharge steadiness more efficiently than the conventional stability criterion that compares the slope of the static volt-ampere characteristic to the value of the external ballast resistor. To check the validity of the inferred stabilization process, a typical 4.7 cm long plasma filament operates in ambient air. Optical and electrical diagnostics are performed to investigate the discharge properties. Measurements then reveal most typical features of an actual arc discharge in air. Consequently, a numerical simulation based on a time-dependent Elenbaas–Heller equation allows calculation of the time-evolution of the plasma in the discharge. Finally, electron density measurements using a specific microwave absorption device confirm the high rate of ionization of the plasma: almost two orders of magnitude higher than for a typical glow discharge in free air.

Influence of Plasma Treatment on the Electroless Deposition of Copper on Carbon Fibers

Air and nitrogen glow discharge were used to replace chromic acid pretreatment to deposit copper film on carbon fiber surfaces from an CuSO4‐HCHO electroless system. A greater copper uptake and a more uniformly coated copper film were obtained for plasma‐treated carbon fibers. The adhesion between the copper film and the carbon fibers was also improved. An orthogonal table L9(34) was used to study the effects of discharge pressure, discharge power, time and gas type on the copper uptake. Scanning electron microscopy (SEM), reflection absorption infrared spectroscopy (RAIR) and X‐ray photoelectron spectroscopy (XPS) at different depths were applied to characterize the physical and chemical changes of the surface of the carbon fibers. The results showed that after plasma treatment, the carbon fiber surface became rough and several types of polar oxygen groups, such as carboxylic acid COOH, esters COOC, quinones Ph˭O, etc., were introduced into the carbon fiber surface. A mechanism of plasma treatment effects on copper electroless deposition on the carbon fiber surface is also suggested.