Dielectric-barrier discharges (silent discharges) are used on a large industrial scale. They combine the advantages of non-equilibrium plasma properties with the ease of atmospheric-pressure operation. A prominent feature is the simple scalability from small laboratory reactors to large industrial installations with megawatt input powers. Efficient and cost-effective all-solid-state power supplies are available. The preferred frequency range lies between 1 kHz and 10 MHz, the preferred pressure range between 10 kPa and 500 kPa. Industrial applications include ozone generation, pollution control, surface treatment, high power CO2 lasers, ultraviolet excimer lamps, excimer based mercury-free fluorescent lamps, and flat large-area plasma displays. Depending on the application and the operating conditions the discharge can have pronounced filamentary structure or fairly diffuse appearance. History, discharge physics, and plasma chemistry of dielectric-barrier discharges and their applications are discussed in detail.

https://www3.nd.edu/~sst/teaching/AME60637/reading/2003_PCPP_Kogelschatz_dbd_review.pdf

Dielectric-barrier Discharges: Their History, Discharge Physics, and Industrial Applications

Atmospheric-pressure plasmas are used in a variety of materials processes. Traditional sources include transferred arcs, plasma torches, corona discharges, and dielectric barrier discharges. In arcs and torches, the electron and neutral temperatures exceed 3000/spl deg/C and the densities of charge species range from 10/sup 16/-10/sup 19/ cm/sup -3/. Due to the high gas temperature, these plasmas are used primarily in metallurgy. Corona and dielectric barrier discharges produce nonequilibrium plasmas with gas temperatures between 50-400/spl deg/C and densities of charged species typical of weakly ionized gases. However, since these discharges are nonuniform, their use in materials processing is limited. Recently, an atmospheric-pressure plasma jet has been developed, which exhibits many characteristics of a conventional, low-pressure glow discharge. In the jet, the gas temperature ranges from 25-200/spl deg/C, charged-particle densities are 10/sup 11/-10/sup 12/ cm/sup -3/, and reactive species are present in high concentrations, i.e., 10-100 ppm. Since this source may be scaled to treat large areas, it could be used in applications which have been restricted to vacuum. In this paper, the physics and chemistry of the plasma jet and other atmospheric-pressure sources are reviewed.

/pdf/the-atmospheric-pressure-plasma-jet-a-review-and-comparison-4n3xn1jiyb.pdf

The atmospheric-pressure plasma jet: a review and comparison to other plasma sources

During the last two decades atmospheric (or high) pressure non-thermal plasmas in and in contact with liquids have received a lot of attention in view of their considerable environmental and medical applications. The simultaneous generation of intense UV radiation, shock waves and active radicals makes these discharges particularly suitable for decontamination, sterilization and purification purposes. This paper reviews the current status of research on atmospheric pressure non-thermal discharges in and in contact with liquids. The emphasis is on their generation mechanisms and their physical characteristics.

http://iopscience.iop.org/article/10.1088/0022-3727/42/5/053001/pdf

Non-thermal plasmas in and in contact with liquids

There is a continuing need for the development of effective, cheap and environmentally friendly processes for the disinfection and degradation of organic pollutants from water. Ozonation processes are now replacing conventional chlorination processes because ozone is a stronger oxidizing agent and a more effective disinfectant without any side effects. However, the fact that the cost of ozonation processes is higher than chlorination processes is their main disadvantage. In this paper recent developments targeted to make ozonation processes cheaper by improving the efficiency of ozone generation, for example, by incorporation of catalytic packing in the ozone generator, better dispersion of ozone in water and faster conversion of dissolved ozone to free radicals are described. The synthesis of ozone in electrical discharges is discussed. Furthermore, the generation and plasma chemical reactions of several chemically active species, such as H2O2, O•, OH•, HO2•, O3*, N2*, e-, O2-, O-, O2+, etc, which are produced in the electrical discharges are described. Most of these species are stronger oxidizers than ozone. Therefore, water treatment by direct electrical discharges may provide a means to utilize these species in addition to ozone. Much research and development activity has been devoted to achieve these targets in the recent past. An overview of these techniques and important developments that have taken place in this area are discussed. In particular, pulsed corona discharge, dielectric barrier discharge and contact glow discharge electrolysis techniques are being studied for the purpose of cleaning water. The units based on electrical discharges in water or close to the water level are being tested at industrial-scale water treatment plants.}

https://iopscience.iop.org/article/10.1088/0963-0252/10/1/311/pdf

Water purification by electrical discharges

Non-thermal plasma technologies: new tools for bio-decontamination.

Applications of corona discharge induced plasmas and unipolar ions are reviewed. Corona process applications emphasize one of two aspects of the discharge: the ions produced or the energetic electrons producing the plasma. The ion identities depend on the polarity of the discharge and the characteristics of the gas mixture, specifically on the electron attaching species. The electron energies depend on the gas characteristics and on the method of generating the corona. In general, in an application using ions, the corona induced plasma zone will occupy a small fraction of the total process volume, while a process using the electrons will fill most of the volume with the plasma. Current state-of-the knowledge of ionized environments and the function of corona discharge processes are discussed in detail. >

/pdf/corona-discharge-processes-358i8a0sc0.pdf

Corona discharge processes

Ceramic dielectric material pellet shape effects on the performance of perfluoroethane (C/sub 2/F/sub 6/) gas removal from simulated semiconductor process gas using packed-bed reactor are experimentally investigated The bench-scale cylindrical shaped (plasma part: 30-mm inner diameter and 20-mm length) plasma reactor consists of two metal mesh electrodes packed with spherical, cylindrical, or hollow cylindrical shaped ferro-electric pellets with various dielectric constants The 60-Hz ac high voltage was applied to the mesh electrode The 3000 ppm C/sub 2/F/sub 6/ gas diluted with nitrogen was used as simulated gas with flow rate of 30 mL/min The C/sub 2/F/sub 6/ concentration was monitored using Fourier transform Infrared absorption spectroscopy measurements The results show that the packed-bed plasma reactor with the hollow cylindrical-shaped pellets removed the C/sub 2/F/sub 6/ gas with energy efficiency of 37 g/kWh This value was almost 15 times higher than the efficiency 25 g/kWh in case of the spherical pellets The discharge characteristics in the reactor were also changed with the pellet shape The discharge onset voltage decreases by changing the pellets shape from sphere to hollow cylinder The quantity of charges accumulated with the microdischarge currents increases by changing the pellet shape from sphere to hollow cylinder in spite of fact that the energy consumed in the reactor decreases

Ferro-electric pellet shape effect on C/sub 2/F/sub 6/ removal by a packed-bed-type nonthermal plasma reactor

For pt.I see ibid.(vol.11 no.3 p.481-90, 2004). In order to validate a nonthermal plasma model using nitrogen in a ferroelectric packed-bed reactor, the number density of the excited nitrogen molecules has been investigated by spectroscopic measurements. Experiments were conducted at applied voltages from 0 to 20 kV, 60 Hz and gas flow rates from 1 to 5 L/min in pure nitrogen gas. The results show that the number density for excited N/sub 2/ molecules increases with increasing applied voltage and dielectric constant and agrees qualitatively with the numerical modeling results at lower applied voltage. The vibrational temperature of the C/sup 3//spl Pi//sub u/ (v') state of N/sub 2/ has been calculated from the light intensity emitted by the 2nd positive band. The vibrational temperature decreases with increasing gas flow rate and no significant effects of the applied voltage and dielectric constant were observed.

Atmospheric pressure of nitrogen plasmas in a ferroelectric packed-bed barrier discharge reactor. Part II. Spectroscopic measurements of excited nitrogen molecule density and its vibrational temperature

An experimental investigation has been conducted to study the morphology of high-frequency electrohydraulic discharge for a liquid-solution plasma, where the liquid-solution plasma is currently investigated for the fabrication of nanometer-size metal particles and inactivation of bacteria. The fundamental nature and basic characteristics of this new type of plasma is relatively not well investigated. In this paper, this type of liquid-solution plasma was experimentally investigated along with discharge morphology.

J.S. Chang

Papers

Corona discharge processes

Ferro-electric pellet shape effect on C/sub 2/F/sub 6/ removal by a packed-bed-type nonthermal plasma reactor

Atmospheric pressure of nitrogen plasmas in a ferroelectric packed-bed barrier discharge reactor. Part II. Spectroscopic measurements of excited nitrogen molecule density and its vibrational temperature

Morphology of High-Frequency Electrohydraulic Discharge for Liquid-Solution Plasmas

Scale-up of ferro-electric packed bed reactor for C2F6 decomposition