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1.
Recently, much attention has been paid to gas discharges producing nonthermal plasma because of many potential benefits in industrial applications. Historically, past work focused on Dielectric Barrier (silent) Discharges (DBD) and pulse-periodical corona discharges. Recently, a number of new different discharge techniques succeeded in producing stable gas discharge at atmospheric pressure. Among these are repetitively pulsed glow discharge; continuous glow discharge in a gas flow; hollow-cathode atmospheric pressure discharge; RF and microwave (MW) discharges. Several new variants of the DBD have been demonstrated over a rather wide range of frequencies. All these forms of gas discharge are characterized by a strong nonequilibrium plasma state. We attempt to classify these discharges with respect to their properties, and an overview of possible applications is made. Conditions for the existence of homogenous and filamentary forms of each of the discharge types are discussed.  相似文献   

2.
Langmuir probe studies have been performed on rf (27.1 MHz) discharges in O2 under planar reactor conditions to determine the axial variation of the plasma parameters (positive ion density, electron temperature, and dc space potential) as a function of pressure (20–220 Pa) and power (10–150 W) or current (0.1–2 A). By monitoring the second derivative of the I–V probe characteristics, the suppression of the rf component in the probe circuit can be optimized. Referring to this problem, numerical studies provide relations for the determination of the residual rf component as well as of the dc component of the plasma potential at incomplete rf compensation. The positive ion density is obtained from the ion saturation currents. Here the effect of collisions between ions and neutral particles within the probe sheath (for p> 100 Pa) is considered. The electron energy distribution function is found to be of the Maxwellian type for all discharge conditions investigated here. If the pressure and the power exceed critical values, the axial charge carrier distribution is characterized by a valley formation in the bulk plasma center. This fact demonstrates that secondary electron emission due to ion impact on the electrode surfaces and following ionization by these electrons near the sheaths in front of the electrodes are significant processes for sustaining the discharge. At low pressures (p60 Pa) the dc plasma potential was found to be identical with the half-peak maintaining voltage of the discharge, in agreement with the model idea of a symmetric rf planar discharge where the rf voltage drop across the bulk plasma can be neglected. For growing pressure, however, the plasma system moves gradually toward a situation where the V-I characteristics of the discharge are significantly controlled by processes in the bulk plasma. This transition depends on the current density.  相似文献   

3.
Radiofrequency discharges fed with CCl4-Cl2 mixtures have been studied in the pressure range 0.3 to 0.6 torr by means of emission spectroscopic actinometry with Ar, He, and N2 as actinometers. Two different reactors, a parallel plate and a capacitively coupled tubular one, have been utilized for this study to obtain information for a large range of electron energy distributions. Analysis of the experimental results demonstrates the following: the utilization of actinometry and its range of validity, the importance of electron attachment to CClx species during the plasma decomposition process, and the effects of the presence of chlorine and “glowpolymer” in the discharge medium.  相似文献   

4.
The paper reports on the construction and operating characteristics of a planar dielectric barrier discharge (DBD) plasma generator. The generator was powered from a commercial frequency inverter at 400 Hz through a high voltage transformer. It could be operated up to a specific energy density (power per gas flow) of 20 Wh/m3. The corresponding power density was about 0.5 W per cubic centimeter of discharge volume. Special emphasis was given to a simple and reliable construction, which was easy to assemble and is based on a new, nonexpensive barrier material with excellent electrical, mechanical, and thermal properties. The modular reactor design allows simple plasma power scale-up. The reactor works with undried ambient air without additional cooling. In the range up to 10 Wh/m3 the ozone generation from ambient air was directly proportional to the energy density at a rate of 60 g O3 per kWh or 30 ppm/Wh/m3. Thus the generator can serve as an effective source for chemically active radicals in plasma gas cleaning applications.  相似文献   

5.
The hydrogen atom yield in pure-H2 RF and microwave-sustained discharges is investigated both theoretically and experimentally. A particle balance model is developed that provides the concentrations of the H, H2, H+, H 2 + , and H 3 + species. It is also shown that an approximate solution of this model is adequate for calculating the concentration of H atoms (required, for instance, in diamond film deposition) in the 0.1–10 torr range. Next, the validity of the actinometry technique applied to the determination of the H-atom density in pure-H2 discharges is examined. Using this diagnostic, it is observed that the H-atom concentration decreases when the vessel wall temperature increases, owing to the increased efficiency of atomic hydrogen recombination on the wall. To overcome this effect, the discharge tube wall is cooled off with dimethyl polysiloxane, a low-loss dielectric liquid. It improves significantly the H-atom concentration at 2450 MHz provided the pressure is typically below a few torr and the power density is not too high.  相似文献   

6.
Nanosecond pulsed non-thermal atmospheric-pressure plasmas are promising for numerous applications including air and water purification, ozone synthesis, surface sterilization, material processing, and biomedical care. However, the high cost of the nanosecond pulsed power sources has hindered adaptation of the plasma-based technologies for clinical and industrial use. This paper presents a low cost (<100US$) nanosecond pulsed plasma system that consists of a Cockcroft–Walton high voltage charging circuit, a compact nanosecond pulse generator using a spark gap as switch, and a plasma reactor. The nanosecond pulse power source requires only a 12 V DC input, hence is battery operable. Through the optimization of the experimental parameters, pulses with a peak voltage >10 kV, a 3 ns rise time (10 to 90 %), and a 10 ns pulse duration (full width at half maximum) at a pulse repetition rate of up to 500 Hz were achieved in the present study. It has been successfully tested to power three different plasma reactors to form pulsed corona discharges, dielectric barrier discharges, and sliding discharges. The energy efficiency of such a nanosecond pulsed sliding discharge system was assessed in the context of ozone synthesis using air or oxygen as the feed gas, and was found comparable to a previously reported non-thermal plasma system that used commercial high voltage pulsed power sources. This study demonstrated that this low-cost nanosecond pulsed power source can prove to be an energy efficient and simple supply to drive various non-thermal atmospheric-pressure plasma reactors for environmental, medical and other applications.  相似文献   

7.
Creatore  M.  Favia  P.  Tenuto  G.  Valentini  A.  d'Agostino  R. 《Plasmas and Polymers》2000,5(3-4):201-218
A NH3 plasma process has been studied for enhancing the adhesion of aluminum coatings on polyethyleneterephtalate (PET) films. According to our peel strength results, NH3 plasmas increase markedly the adhesion of aluminum on PET compared to O2 discharges, with a much shorter treatment time. A tentative model of nonhindered growth of Al-coating based on the Lewis basic character of the functionalities grafted by NH3 plasma is proposed for Al-polymer interactions, and for explaining the various steps in the process. The effects of power input and treatment time on the polymer surface chemistry and on the metal-polymer peel strength have been evaluated. Treatment times as short as 0.1 s at 100 W proved to be the best conditions in NH3 plasmas, for a significant increase in Al/PET adhesion, while longer treatments have a detrimental effect. This may explain why most authors have not discovered the benefits of NH3 plasmas for improving the adhesion of metals on PET, and have preferred O2 or air treatments. The relative basicity of PET grafted with N-containing functionalities has been measured by means of X-ray Photoelectron Spectroscopy (XPS) analysis of samples exposed to vapors of trichloromethane, a Lewis acid molecular probe. The Al/PET adhesion was evaluated by means of a 180° Peel Test.  相似文献   

8.
Shielded sliding discharges are nanosecond streamer discharges which develop along a dielectric between metal foil electrodes, with one of the foils extended over the entire rear of the dielectric layer. The electrode configuration not only allowed rearranging discharges in parallel due to the decoupling effect of the metal layer, but also to modify the electric field distribution in such a way that components normal to the surface are enhanced, leading to an increased energy density in the discharge plasma. By varying the electrode gap, the applied voltage, and the repetition rate, it is shown that by keeping the average electric field constant, the discharge voltage can be reduced from tens of kV to values on the order of a few kV, but only at the expense of a reduced energy density of the plasma. Varying the repetition rate from 20 to 500 Hz resulted in a slightly reduced energy per pulse, likely caused by residual charges on the dielectric surface. Measurements of the NO conversion to NO2 and ozone synthesis in dry air showed that the conversion is only dependent on the energy density of the discharge plasma. Although reducing the pulse voltage from the tens of kV range to that of few kV, and possibly even lower, causes a reduction in energy density, this loss can be compensated for by increasing the electrode gap area. This and the possibility to form discharge arrays allows generating large volume discharge reactors for environmental applications, at modest pulsed voltages.  相似文献   

9.
CARS Diagnostic and Modeling of a Dielectric Barrier Discharge   总被引:1,自引:0,他引:1  
Baeva  M.  Dogan  A.  Ehlbeck  J.  Pott  A.  Uhlenbusch  J. 《Plasma Chemistry and Plasma Processing》1999,19(4):445-466
Dielectric barrier discharges (DBD) with planar- and knife-shaped electrodes are operated in N2O2NO mixtures under a pressure of 20 and 98 kPa. They are excited by means of consecutive unipolar or bipolar high-voltage pulse packages of 10 kV at a pulse repetition rate of 1 and 2 kHz. The rotational and vibrational excitation of N 2 molecules and the reduction of nitric oxide (NO) in the discharge have been investigated using coherent anti-Stokes Raman scattering (CARS) technique. Rotational (gas) temperatures near the room temperature and vibrational temperatures of about 800 K at atmospheric pressure and 1400 K at a pressure of 20 kPa are observed. Therefore, chemical reactions of NO with vibrationally excited N 2 are probably insignificant. One-dimensional kinetic models are developed that balance 35 chemical reactions between 10 species and deliver equations for the population density of excited vibrational levels of N 2 together with a solution of the Boltzmann equation for the electrons. A good agreement between measured vibrational temperatures of N 2 , the concentration of NO, and calculated data is achieved. Modeling of the plasma discharge verifies that a DBD operated with a N2NO mixture reduces the NO content, the simultaneous presence of O 2 , already 1%, is enough to prevent the NO reduction.  相似文献   

10.
Energy efficiency of NO removal by pulsed corona discharges   总被引:1,自引:0,他引:1  
Pulsed positive corona discharges are used to remove NO from the flue gas of a methane burner. At low power input this leads to an increase in NO2, which shows that the process is oxidative. Removal efficiency is greatest when discharges are produced with high-voltage pulses, which are shorter in duration than the time required by the primary streamers to cross the discharge gap, in combination with a dc bias. Other important parameters are input power density and residence time. The best result obtained so far is an energy consumption of 20 eV per NO molecule removed, at 50% deNOx i.e., a removal of 150 ppm NOx, using a residence time of 15 s and an input power density, of 3.5 Wh/Nm3. [Wh/Nm3 stands for watt-hour per normal cubic meter, i.e., at normal conditions (273 K and 1 bar). This implies that 1 Nm3 contains 2.505 1025 molecules.] There appears to be room for improvement by the addition of gaseous and particulate chemicals or the use of multiple corona treatment. It is argued front comparison between results from models and experiments that the direct production of OH by the discharge is only the initiation of the cleaning process.  相似文献   

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