Search

This work provides a comparative analysis of the sensitivity of the two most widely used kinetic schemes in helium when simulating various modes of direct current discharges in helium: glow and arc. In particular, a kinetic scheme with the formation of three excited atomic states and one molecular state, as well as a scheme with five excited atomic states and two molecular states, are considered. It is shown that the two models yield different results in the glow discharge mode and similar results in the transition from glow to arc and in the arc mode. A study was carried out of the influence of recombination constants from various databases on the discharge characteristics. [ABSTRACT FROM AUTHOR]

Plasma decomposition reactions are used for various gas phase chemical processes including the decomposition of ammonia. In this work we show that pure ammonia can be effectively decomposed at atmospheric pressure and ambient temperature using a packed-bed plasma reactor moderated with BaTiO3 ferroelectric pellets without catalyst. The decomposition rate and energy efficiency of this ferroelectric barrier discharge reactor have been monitored as a function of applied voltage (up to a maximum value of 2.5 kV) and flow rate. For each operating condition reaction efficiencies have been correlated with the parameters defining the electrical response of the reactor. It is found that plasma current and volume inside the reactor and hence the energy efficiency of the process and the decomposition rate vary with the applied voltage and the flow of ammonia (a maximum decomposition rate of 14% and an energy efficiency of 150 LH2/kWh has been determined under optimized operation conditions). The role of back reactions (i.e. N2 + 3H2 → 2NH3) in decreasing reactor performance is another key effect affecting the overall efficiency for the ammonia decomposition. The possibilities of ferroelectric barrier discharge reactors to induce the decomposition of ammonia and the importance of keeping the operating temperature below the Curie temperature of the ferroelectric material are highlighted. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge (DBD) is used for many important applications in various sectors of science and technology. For example, for ozone generation, surface modification of polymers, in plasma medicine, and for decomposition of heavy volatile organic compounds. Nowadays, one of the actual problems is getting of uniformity of discharge distribution for high quality treatment of materials surfaces. To achieve uniform distribution of the discharge, several methods are available, one is to use different types of noble gases, and another is to use AC power supply with frequency varied in wide range. But besides this, another of the potential methods for obtaining a uniformly distributed discharge is to blow through the discharge gap flow of air. This method was used in this paper to conduct experiments which consisted of oscilloscoping voltage and current values, high-speed imaging, also gas flow simulation for comparison with the experiments. The obtained results show the dynamics of microdischarge motion in laminar and turbulent flow regimes, which supported by flow simulation. [ABSTRACT FROM AUTHOR]

The use of low‐temperature plasmas for bio‐decontamination and sterilization has been gaining increased attention. In this study, a two‐dimensional array of integrated coaxial microhollow micro‐discharges generated in dry air at atmospheric pressure is used to treat metal surfaces (gas‐phase) and solution (liquid‐phase) contaminated with a known concentration of feline calicivirus (FCV). FCV acts as a surrogate for human norovirus, which is responsible for causing outbreaks of acute gastroenteritis in humans. The decontamination efficacy as well as the primary chemical pathways leading to virus inactivation in both the treatments are studied and compared. It is found that the humidity of the bio‐sample for gas‐phase treatment in dry air is required to achieve >5 log10 reduction in FCV titer within 3 min. The gas‐phase FCV inactivation is found to be due to a combination of ozone (O3) and reactive nitrogen species (RNS), most likely NOx. The liquid‐phase FCV inactivation mechanism is pH‐dependent and is primarily due to RNS, most likely acidified nitrites. O3 has a negligible effect on FCV suspended in solution. Previous studies performed in a batch reactor have shown that the inactivation pathways through O3 and RNS are mutually exclusive due to ozone poisoning at high NxOy concentrations. The present study employs a flow‐through system which avoids accumulation of reactive species and allows for the coexistence of NOx and O3 for the gas residence times used in this study, giving rise to these specific inactivation pathways. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet (VUV) emissions from 115 to 200 nm from the effluent of an RF (1.2 MHz) capillary jet fed with pure argon and binary mixtures of argon and xenon or krypton (up to 20%) are analyzed. The feed gas mixture is emanating into air at normal pressure. The Ar excimer second continuum, observed in the region of 120-135 nm, prevails in the pure Ar discharge. It decreases when small amounts (as low as 0.5%) of Xe or Kr are added. In that case, the resonant emission of Xe at 147 nm (or 124 nm for Kr, respectively) becomes dominant. The Xe second continuum at 172 nm appears for higher admixtures of Xe (10%). Furthermore, several N I emission lines, the O I resonance line, and H I line appear due to ambient air. Two absorption bands (120.6 and 124.6 nm) are present in the spectra. Their origin could be unequivocally associated to O2 and O3. The radiance is determined end-on at varying axial distance in absolute units for various mixtures of Ar/Xe and Ar/Kr and compared to pure Ar. Integration over the entire VUV wavelength region provides the integrated spectral distribution. Maximum values of 2.2 mW·mm-2·sr-1 are attained in pure Ar and at a distance of 4 mm from the outlet nozzle of the discharge. By adding diminutive admixtures of Kr or Xe, the intensity and spectral distribution is effectively changed. [ABSTRACT FROM AUTHOR]

Emission spectroscopy of plasma-excited chemical species is widely used for generalized chemical analyses in bench-top systems. This paper explores the use of pulsed microdischarges between two and three electrode microstructures, which operate in air at atmospheric pressure, for use in handheld chemical analyzers. Pulsed microdischarges are fired between two-electrodes spaced apart by 0.2-2 mm. Synchronized optical sampling and time resolved spectroscopy are performed to capture the emission spectra from the microdischarge and its afterglow. The discharge spectra in air consist mainly of wide-band background spectra and line spectra from the nitrogen, and water vapor in air. The detection of vapors in air is limited by the relative strengths of representative lines compared to background spectra rather than by their absolute strength. The separate temporal characteristics of the line and background spectra present opportunities to improve detection. This concept is evaluated using isopropyl alcohol vapors (100 ppm) for which lines corresponding to CH fragments are detected with a handheld spectrometer despite the presence of air spectra. This paper also introduces a three-electrode (flashFET) configuration, which further reduces power consumption and electrode wear. Occupying an active area < 1 mm2, it employs a strategically located high-impedance gate electrode that permits the use of pulses < 100 V between the source and drain. The device consumes only 2.5 muJ/pulse at 140 Torr and 22.5 muJ/pulse at atmosphere, as compared to 470 muJ/pulse for two-electrode discharges. The operation of the flashFET as a gas sensor is evaluated using acetone vapors in air ambient. A response curve is obtained by measuring the 388.1 nm emission from acetone fragments for acetone concentrations ranging from 50 to 1000 ppm. [ABSTRACT FROM PUBLISHER]

It has been recently demonstrated that microcathode sustained discharges (MCSD) are very efficient for the production of large fluxes of singlet delta oxygen (SDO). In this paper, a comparison between MCSD operation in \Ar/O2 and in \He/O2 mixtures is done. It is shown that, even if SDO production efficiency is theoretically much higher in \Ar/O2 mixtures, atmospheric pressure operation is only possible in He-based mixtures. [ABSTRACT FROM AUTHOR]