Showing papers on "Atmospheric pressure published in 2005"

Non-thermal atmospheric pressure discharges

Abstract: There has been considerable interest in non-thermal atmospheric pressure discharges over the past decade due to the increased number of industrial applications. Diverse applications demand a solid physical and chemical understanding of the operational principals of such discharges. This paper focuses on the four most important and widely used varieties of non-thermal discharges: corona, dielectric barrier, gliding arc and spark discharge. The physics of these discharges is closely related to the breakdown phenomena. The main players in electrical breakdown of gases: avalanches and streamers are also discussed in this paper. Although non-thermal atmospheric pressure discharges have been intensively studied for the past century, a clear physical picture of these discharges is yet to be obtained.

Room-temperature atmospheric pressure plasma plume for biomedical applications

Abstract: As low-temperature nonequilibrium plasmas come to play an increasing role in biomedical applications, reliable and user-friendly sources need to be developed. These plasma sources have to meet stringent requirements such as low temperature (at or near room temperature), no risk of arcing, operation at atmospheric pressure, preferably hand-held operation, low concentration of ozone generation, etc. In this letter, we present a device that meets exactly such requirements. This device is capable of generating a cold plasma plume several centimeters in length. It exhibits low power requirements as shown by its current-voltage characteristics. Using helium as a carrier gas, very little ozone is generated and the gas temperature, as measured by emission spectroscopy, remains at room temperature even after hours of operations. The plasma plume can be touched by bare hands and can be directed manually by a user to come in contact with delicate objects and materials including skin and dental gum without causing any heating or painful sensation.

Asymmetric surface dielectric barrier discharge in air at atmospheric pressure: electrical properties and induced airflow characteristics

Abstract: The electrical properties of an asymmetric surface dielectric barrier discharge in atmospheric air have been investigated experimentally. The discharge is used for airflow production close to the dielectric surface, and the time-averaged flow velocity spatial profiles have been measured. Velocities of up to 3.5 m s−1 at heights of 1–2 mm are reached when filamentary discharges with current peaks up to 20 mA are produced along the surface. In terms of powers, mechanical powers (output) of a few milliwatts are obtained for electrical powers (input) up to 10 W. Variation laws or behaviour with several discharge parameters (applied voltage waveform, distance between electrodes, dielectric thickness and permittivity) have been experimentally determined.

Temperature and pressure dependence of the viscosity of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Abstract: New measurements have been made for the viscosity of the room-temperature ionic liquid 1-butyl- 3-methylimidazolium hexafluorophosphate ([BMIM]PF6) between (0 and 80) °C with a falling-body viscometer. High-pressure measurements were made at (25, 35, 50, 60, and 70) °C. The overall uncertainty is estimated at ± (2 to 3) %. Atmospheric pressure densities obtained with a vibrating tube densimeter are also reported for temperatures between (0 and 90) °C with an overall uncertainty estimated at ± 0.00005 g·cm-3. The viscosity behavior is qualitatively different from that of molecular liquids, with isotherms being best fitted as functions of the applied pressure rather than as functions of the molar volume. Modified Litovitz and Vogel−Fulcher−Tammann equations have been used to incorporate both the temperature and pressure dependence. Interestingly, the T0 parameter of the VFT equation appears to be independent of pressure within the state point range of the data, but the Angell strength parameter increases wi...

Characterization of a dc atmospheric pressure normal glow discharge

Abstract: Atmospheric pressure dc glow discharges were generated between a thin cylindrical anode and a flat cathode. Voltage?current characteristics, visualization of the discharge and estimations of the current density indicate that the discharge is operating in the normal glow regime. Emission spectroscopy and gas temperature measurements using the 2nd positive band of N2 indicate that the discharge forms a non-equilibirum plasma. Rotational temperatures are 700?K and 1550?K and vibrational temperatures are 5000?K and 4500?K for a 0.4?mA and 10?mA discharge, respectively. The discharge was studied for inter-electrode gap spacing in the range of 20??m?1.5?cm. It is possible to distinguish a negative glow, Faraday dark space and positive column regions of the discharge. The radius of the primary column is about 50??m and is relatively constant with changes in electrode spacing and discharge current. Estimations show that this radial size is important in balancing heat generation and diffusion and in preventing thermal instabilities and the transition to an arc.

Absolute atomic oxygen density measurements by two-photon absorption laser-induced fluorescence spectroscopy in an RF-excited atmospheric pressure plasma jet

Abstract: The atmospheric pressure plasma jet is a capacitively coupled radio frequency discharge (13.56 MHz) running with a high helium flux (2 m3 h−1) between concentric electrodes. Small amounts (0.5%) of admixed molecular oxygen do not disturb the homogeneous plasma discharge. The jet effluent leaving the discharge through the ring-shaped nozzle contains high concentrations of radicals at a low gas temperature—the key property for a variety of applications aiming at treatment of thermally sensitive surfaces. We report on absolute atomic oxygen density measurements by two-photon absorption laser-induced fluorescence (TALIF) spectroscopy in the jet effluent. Calibration is performed with the aid of a comparative TALIF measurement with xenon. An excitation scheme (different from the one earlier published) providing spectral matching of both the two-photon resonances and the fluorescence transitions is applied.

Atmospheric pressure plasma deposition of thin films by Townsend dielectric barrier discharge

Abstract: The aim of this study is to contribute to the understanding of the thin film growth mechanism using an Atmospheric Pressure Townsend-like Discharge (APTD). Films obtained in dielectric barrier discharges fed with N2 and small admixtures of hexamethyldisiloxane (HMDSO) and nitrous oxide (N2O) as oxidizer gas have been investigated. Results are compared to those obtained with SiH4, in similar conditions. The discharge dissipated power and the feed composition ([N2O]/[HMDSO] ratio) on film properties have been investigated by means of Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Ellipsometry. The film thickness homogeneity and deposition rate have been measured by means of a profilometer and an ellipsometer at the same time. Then silicon oxide thin film properties obtained with SiH4 and HMDSO containing APTD are compared. Concerning chemical composition results are similar. In the two cases, a rather low adding of N2O allows to get SiOx layer without N and C incorporation. Si–OH bounds are always observed. The relative contribution of homogeneous and heterogeneous growth mechanisms is very dependent on the nature of the precursor. Because of its high reactivity, SiH4 induces particles formation in the plasma. These particles are efficiently included in the coating, decreasing drastically the layer density. Thin films made with HMDSO are always dense.

Synthesis of blue luminescent si nanoparticles using atmospheric-pressure microdischarges.

Abstract: Silicon nanoparticles are synthesized from a mixture of argon/silane in a continuous flow atmospheric-pressure microdischarge reactor. Particles nucleate and grow to a few nanometers (1−3 nm) in diameter before their growth is abruptly terminated in the short residence time microreactor. Narrow size distributions are obtained as inferred from size classification and imaging. As-grown Si nanoparticles collected in solution exhibit room-temperature photoluminescence that peaks at 420 nm with a quantum efficiency of 30%; the emission is stable for months in ambient air.

Non-thermal atmospheric pressure discharges for surface modification

Abstract: A series of different discharge configurations suitable for surface treatment at atmospheric pressure is discussed, including a non-thermal modular radio frequency (13.56, 27.12 or 40.78 MHz) jet plasma.The capacitively coupled configuration allows the operation with both rare gases (e.g. Ar) and reactive gases (N2, air, reactive admixtures of silicon-containing compounds). Several capillaries are arranged in an array to allow plasma assisted treatment of surfaces including non-flat geometries. Optical emission spectroscopy, mass spectrometry and measurements of the axial and radial temperature profiles are used to characterize the discharge.The surface energy of different polymer materials is significantly enhanced after plasma treatment. Many applications are possible, such as plasma activation of surfaces for adhesion control, surface cleaning, plasma enhanced CVD, plasma cleaning, plasma activation and biomedical applications.

Burning velocity correlation of methane/air turbulent premixed flames at high-pressure and high-temperature

Abstract: Turbulent burning velocities for methane/air mixtures at pressures ranging from atmospheric pressure up to 1.0 MPa and mixture temperatures of 300 and 573 K were measured, which covers the typical operating conditions of premixed-type gas-turbine combustors. A bunsen-type flame stabilized in a high-pressure chamber was used, and OH-PLIF visualization was performed with the pressure and mixture temperature being kept constant. In addition to a burner with an outlet diameter of 20 mm for the high-pressure experiments, a large-scale burner with an outlet diameter of 60 mm was used at atmospheric pressure to extend the turbulence Reynolds number based on the Taylor microscale, Rλ, as a common parameter to compare the pressure and temperature effects. It was confirmed that Rλ over 100 could be attained and that u′/SL could be extended even at atmospheric pressure. Based on the contours of the mean progress variable 〈c〉 = 0.1 determined using OH-PLIF images, turbulent burning velocity was measured. ST/SL was also found to be greatly affected by pressure for preheated mixtures at 573 K. The bending tendency of the ST/SL curves with u′/SL was seen regardless of pressure and mixture temperature and the Rλ region where the bending occurs corresponded well to the region where the smallest scale of flame wrinkling measured as a fractal inner-cutoff approaches the characteristic flame instability scale and becomes almost constant. A power law of ST/SL with (P/P0)(u′/SL) was clearly seen when ST was determined using 〈c〉 = 0.1 contours, and the exponent was close to 0.4, indicating agreement with the previous results using the mean flame cone method and the significant pressure effects on turbulent burning velocity.

Mass Spectrometric Identification of Si–O–H(g) Species from the Reaction of Silica with Water Vapor at Atmospheric Pressure

Abstract: A high-pressure sampling mass spectrometer was used to detect the volatile species formed from SiO2 at temperatures between 1200C and 1400C in a flowing water vapor/oxygen gas mixture at 1 bar total pressure. The primary vapor species identified was Si(OH)4. The fragment ion Si(OH)3+,' was observed in quantities 3 to 5 times larger than the parent ion Si(OH)4+. The Si(OH)3+ intensity was found to have a small temperature dependence and to increase with the water vapor partial pressure as expected. In addition, SiO(OH)+ believed to be a fragment of SiO(OH)2, was observed. These mass spectral results were compared to the behavior of silicon halides.

Investigation of the filamentary and diffuse mode of barrier discharges in N 2 /O 2 mixtures at atmospheric pressure by cross-correlation spectroscopy

Abstract: The techniques of spatially resolved cross-correlation spectroscopy (CCS) and current pulse oscillography were used to carry out systematic investigations of the barrier discharge (BD) in the binary gas mixtures N2/O2 at atmospheric pressure. At very low oxygen concentrations (<500 ppm), the BD was observed in a so-called diffuse mode (also referred to as atmospheric pressure glow discharge, glow silent discharge or homogeneous BD). In the case of the BD filamentary mode, the spatio-temporal distributions of the BD radiation intensities were recorded for the spectral bands of the 0–0 transitions of the second positive (λ = 337 nm) and first negative system of molecular nitrogen (λ = 391 nm). In the case of the diffuse mode, the spectral bands λ = 337 nm, λ = 260 nm (0–3 transition of the γ -system of NO) and λ = 557 nm (radiation of ON2 excimer) were used for this purpose. The velocities of the cathode-directed ionizing waves as well as the effective lifetimes of the excited states N2(C 3 � u)υ� =0 and N + (B 2 � + u )υ � =0 were evaluated from the CCS data. Special attention was devoted to the investigation of the transition between the filamentary and diffuse modes of the BD, this transition being caused by the variation of oxygen content within the range 500–1000 ppm. (Some figures in this article are in colour only in the electronic version)

Plasma sterilization using glow discharge at atmospheric pressure

Abstract: Recent development of atmospheric pressure glow discharge was compared with the performance of an apparatus used in the first APG experiment, in terms of sterilization of newly classified biological indicator: Bacillus atrophaeus, former Bacillus subtilis var. niger and Geobacillus stearothermophilus. Stabilization was attained by controlling the experimental conditions, at low frequency: 100 kHz and Radio Frequency: 13.56 MHz, water vapor/He dilution. Large volume of meta-stable atomic helium is responsible for the result that aids generation of hydroxyl radicals. D 2004 Elsevier B.V. All rights reserved.

Spatially resolved diagnostics of an atmospheric pressure direct current helium microplasma

Abstract: Optical emission spectroscopy measurements were performed with added trace probe gases in an atmospheric pressure direct current helium microplasma. Spatially resolved measurements (resolution ~6 µm) were taken across a 200 µm slot-type discharge. Gas temperature profiles were determined from N2 emission rotational spectroscopy. Stark splitting of the hydrogen Balmer-β line was used to investigate the electric field distribution in the cathode sheath region. Electron densities were evaluated from the analysis of the spectral line broadening of Hβ emission. The gas temperature was between 350 and 550 K, peaking nearer the cathode and increasing with power. The electron density in the bulk plasma was in the range (4–7) × 1013 cm−3. The electric field peaked at the cathode (~60 kV cm−1) and decayed to small values over a distance of ~50 µm (sheath edge) from the cathode. These experimental data were generally in good agreement with a self-consistent one-dimensional model of the discharge.

Investigations of an atmospheric pressure plasma jet by optical emission spectroscopy

Abstract: A plasma jet, which works under atmospheric pressure, has been developed for surface treatment. The plasma stream is generated with a dielectric barrier discharge (DBD) and a process gas of Ar flowing out into the environmental air. The DBD plasma jet features a cold gas temperature. Furthermore, the plasma stream is harmless for humans because of its low voltage. In order to characterize the plasma jet, its electron temperature and its composition have been determined by means of optical emissions spectroscopy.

Surface characteristics of polypropylene film treated by an atmospheric pressure plasma

Abstract: After the atmospheric pressure plasma treatment of polypropylene (PP) film surface, we measured the contact angle of the surface by using polar solvent (water) and nonpolar solvent (diiodomethane). We also calculated the surface free energy of PP film by using the measured values of contact angles. And then we analyzed the change of the contact angle and surface free energy with respect to the conditions of atmospheric pressure plasma treatment. Upon each condition of atmospheric pressure plasma treatment, the contact angle and surface free energy showed optimum value or leveled off. Through AFM analysis, we also observed the change of surface morphology and roughness before and after plasma treatment. The surface roughness of PP film showed the highest value when the plasma treatment time was 90 s. Finally, we analyzed the change of chemical compositions on the PP film surface through XPS. As the result of analysis, we observed that polar functional groups, such as –CO, –C=O, and –COO were introduced on the PP film surface after atmospheric pressure plasma treatment.

Comparison of an atmospheric pressure, radio-frequency discharge operating in the α and γ modes

Abstract: The α and γ modes of an atmospheric pressure, radio-frequency plasma have been investigated. The plasma source consisted of two parallel electrodes that were fed with helium and 0.4 vol% nitrogen. The transition from α to γ was accompanied by a 40% drop in voltage, a 12% decrease in current and a surge in power density from 25 to 2083 W cm−3. Optical emission confirmed that sheath breakdown occurred at the transition point. The maximum light intensity shifted from a position 0.25 mm above the electrodes to right against the metal surfaces. The average density of ground-state nitrogen atoms produced in the atmospheric plasma was determined from the temporal decay of N2(B) emission in the afterglow. It was found that 5.2% and 15.2% of the N2 fed were dissociated into atoms when the plasma was operated in the α and γ modes, respectively. The lower efficiency of the γ discharge may be attributed to the non-uniform distribution of the discharge between the electrodes.

Direct measurement of electron density in microdischarge at atmospheric pressure by Stark broadening

Abstract: We present a method and results for measurement of electron density in atmospheric-pressure dielectric barrier discharge. The electron density of microdischarge in atmospheric pressure argon is measured by using the spectral line profile method. The asymmetrical deconvolution is used to obtain Stark broadening. The results show that the electron density in single filamentary microdischarge at atmospheric pressure argon is 3.05×1015cm−3 if the electron temperature is 10 000 K. The result is in good agreement with the simulation. The electron density in dielectric barrier discharge increases with the increase of applied voltage.

Improved algorithm for calculations of Rayleigh-scattering optical depth in standard atmospheres.

Abstract: Precise calculations of the total Rayleigh-scattering optical depth have been performed at 88 wavelengths ranging from 0.20 to 4.00 microm for the six well-known standard atmosphere models by integrating the volume Rayleigh-scattering coefficient along the vertical atmospheric path from sea level to a 120-km height. The coefficient was determined by use of an improved algorithm based on the Ciddor algorithm [Appl. Opt. 35, 1566 (1996)], extended by us over the 0.20-0.23-microm wavelength range to evaluate the moist air refractive index as a function of wavelength, air pressure, temperature, water-vapor partial pressure, and CO2 volume concentration. The King depolarization factor was also defined taking into account the moisture conditions of air. The results indicate that the influence of water vapor on Rayleigh scattering cannot be neglected at tropospheric altitudes: for standard atmospheric conditions represented in terms of the U.S. Standard Atmosphere (1976) model, the relative variations produced by water vapor in the Rayleigh scattering parameters at a 0.50-microm wavelength turn out to be equal to -0.10% in the moist air refractivity at sea level (where the water-vapor partial pressure is equal to approximately 7.8 hPa), -0.04% in the sea-level King factor, -0.24% in the sea-level Rayleigh-scattering cross section, and -0.06% in the Rayleigh-scattering optical depth.

Integrated coaxial-hollow micro dielectric-barrier-discharges for a large-area plasma source operating at around atmospheric pressure

Abstract: An integrated structure of coaxial-hollow micro dielectric-barrier-discharges has been developed by stacking two metal meshes covered with insulating material. The test panel has an effective area of 50?mm diameter in which hundreds of hollow structures are assembled with a unit hollow area of 0.2 ? 1.7?mm2. He or N2 was used as the discharge gas in the pressure range from 20 to 100?kPa and the firing voltage was less than 2?kV, even at the maximum pressure. The intensity of each microdischarge was observed to be uniform over the whole area throughout the pressure range, and its time evolution during one discharge pulse was analysed through two-dimensional microscopic observation with a gated CCD camera. In a gas flow regime through the coaxial hollow structures, several significant changes of the discharge properties were observed, such as impurity reduction, decrease in discharge voltage and cooling of the neutral gas. The fundamental plasma parameters were measured using a single probe in the downstream region of microdischarges using an auxiliary flat electrode set apart from the mesh electrode plane. The occurrence of an extended glow with a length of some millimetres was observed in He but not in N2. The electron density derived by the probe data in He at 100?kPa was ~3 ? 1011?cm?3, suggesting a value of more than 1012?cm?3 in the active microdischarge region.

Supershort electron beam from air filled diode at atmospheric pressure

Abstract: The properties of an electron beam (e-beam) formed in air under atmospheric pressure are reported. The nanosecond generators RADAN-303 (two devices) and RADAN-220, producing nanosecond voltage pulses with amplitude of up to 400 kV and subnanosecond rise time were used in the experiments. It was shown for the first time that the duration of e-beam current of gas diode behind the foil does not exceed 0.1 ns. The maximum amplitude of current of a supershort avalanche electron beam (SAEB) behind the foil was ∼400 A. The data on the influence of various parameters on e-beam current amplitude measured behind the foil were obtained. An electron beam with energy less than 60 keV and powerful X-ray radiation were formed in discharge gap simultaneously with SAEB.

Sterilization of Escherichia coli and MRSA using microwave-induced argon plasma at atmospheric pressure

Abstract: The use of microwave plasma for sterilization is a relatively new method. The advantages of this method include relatively low temperature, time-saving and nontoxicity compared to the known techniques, such as dry heat, steam autoclave and ethylene oxide (EtO) gas. The aim of this study was to investigate the sterilization effects on Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA) using self-designed, low-cost and reliable, 2.45 GHz, wave guide-based applicator to generate microwave plasma at atmospheric pressure. The results of this study confirmed that the sterilization effect of microwave-induced argon plasma at atmospheric pressure was caused by free radicals and UV light generated during the plasma treatment and the etching process. The microwave plasma system used in this study required much less exposure time than the previous study on bacterial strains of E. coli and MRSA, because of the high plasma density, the large number of free radicals, and the strong UV intensity.