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Atmospheric Plasmas for Carbon Nanotubes (CNTs)
Published in R. Mohan Sankaran, Plasma Processing of Nanomaterials, 2017
Jae Beom Park, Se Jin Kyung, Geun Young Yeom
The conventional DBD has a high breakdown voltage (30 kV/cm at air) and relatively low plasma density due to a high recombination rate at atmospheric pressure. This makes it difficult to use DBDs for processing applications other than surface treatment [75–79]. To obtain a higher plasma density, a modified DBD system composed of a multi-pin-powered electrode instead of a planar-powered electrode has been developed [80]. The pin shape of the multi-pin electrode was fabricated in the shape of a pyramid by machining the electrode surface. The multi-pin pyramid-shaped electrode resulted in a lower breakdown voltage because of the high localized electric field. In addition, the high density of pins on the electrode and diffusion of the discharge on the electrode surface allowed the microdischarges to merge and form a uniform glow discharge. Thus, the modified DBD not only has a lower breakdown voltage but also a higher plasma density compared to a conventional DBD system under similar discharge conditions.
Introduction
Published in Yong Yang, Young I. Cho, Alexander Fridman, Plasma Discharge in Liquid, 2017
Yong Yang, Young I. Cho, Alexander Fridman
Plasma discharge, especially dielectric barrier discharges (DBD), has been used for the production of ozone for the past several decades for water treatment purposes. Ozone has a lifetime of approximately 10–60 min, which varies depending on the pressure, temperature, and humidity of surrounding conditions. Because of the relatively long lifetime of ozone, ozone gas is remotely produced in air or oxygen, stored in a tank, and injected into water using a compressor. Of note is that hydrogen peroxide is also produced when ozone is produced in a plasma discharge in humid air. However, the half-life of the hydrogen peroxide is much shorter, so it could not be directly used for conventional water treatment systems.
Non-Equilibrium Cold Atmospheric Pressure Discharges
Published in Alexander Fridman, Lawrence A. Kennedy, Plasma Physics and Engineering, 2021
Alexander Fridman, Lawrence A. Kennedy
The corona-to-spark transition at high voltage is prevented in pulsed corona discharges by employing special nano-second pulse power supplies. An alternate approach to avoid formation of sparks and current growth in the channels formed by streamers is to place a dielectric barrier in the discharge gap. This is the principal idea of the dielectric barrier discharges (DBD). The presence of a dielectric barrier in the discharge gap precludes DC operation of DBD and which usually operates at frequencies between 0.5 and 500 kHz. Sometimes dielectric-barrier discharges are also called silent discharges. This is due to the absence of sparks, which are accompanied by local overheating, generation of local shock waves, and noise. an advantage of the DBD is the simplicity of its operation. It can be employed in strongly non-equilibrium conditions at atmospheric pressure and at reasonably high power levels, without using sophisticated pulse power supplies. Today the DBD finds large-scale industrial use for ozone generation (U. Kogelschatz, 1988; U. Kogelschatzs, B. Eliasson, 1995; also see Figure 9.11). These discharges are industrially applied as well in CO2 lasers, and as a UV-source in excimer lamps. DBD application for pollution control and surface treatment is promising, but the largest DBD applications are related to plasma display panels for large-area flat television screens. Contributions to understanding and industrial applications of DBD were made by U. Kogelschatzs, B. Eliasson, and their group at ABB (see, for example, U. Kogelschatzs, B. Eliasson, W. Egli, 1997). The DBD has a long history. It was first introduced by W. Siemens in 1857 to create ozone which determined the main direction for investigations and applications of this discharge for many decades. Important steps in understanding the physical nature of the DBD were made by K. Bussin 1932 and A. Klemenc, H. Hinterberger, H. Hofer in 1937. Their work showed that this discharge occurs in a number of individual tiny breakdown channels, which are referred to as micro-discharges.
Numerical simulation of air DBD under standard atmospheric pressure
Published in Radiation Effects and Defects in Solids, 2022
Xiaobing Wang, Chenyang Zhu, Lu Wang, Jinqiu Liu, An Jin
In 1928, Langmuir first proposed the term ‘plasma’. The plasma followed by solids, liquids and gases was later referred to as an ionized gas of the ‘fourth state of matter’ (1). Plasma is a kind of conductive fluid, which is made up of electrons, ions, neutral substances and free radicals, and the total electric charge of electrons and various negative ions is roughly equal to that of positive ions, so it is generally electrically neutral. Dielectric barrier discharge (DBD) has been known for a long time, also referred to as barrier discharge or silent discharge, and it is a physical phenomenon that generates plasma between the discharge gap formed by two electrodes separated by insulators such as glass, quartz and ceramics (2). The DBD combines high electron energy with a low neutral gas temperature, readily producing many plasma chemical ions and neutral species with low gas heating, the gas heating is low, and it has the advantages of simple operation, high safety and long service life of the equipment, because of these all characteristics, DBDs are widely used in surface treatment, pollution control, agriculture, biomedical applications and many other technological applications (3–11).
Humid air plasma-assisted surface treatment as a green functionalization technique to enhance the multi-walled carbon nanotubes dispersion and stability in aqueous solutions
Published in Journal of Dispersion Science and Technology, 2022
Masoud Tabarsa, Bahman ZareNezhad
Generally, in the dielectric barrier discharge (DBD) method, plasma is formed between two electrodes which at least one of them is covered by a dielectric layer. This discharge occurs by applying an alternating voltage to the electrodes by the instantaneous emission of electrons from the cathode. The DBD is not uniform and consists of numerous micro-discharges that are dispersed in the discharge space. DBD plasma is widely used due to unbalanced atmospheric pressure conditions with various gases such as air. The electrode used for this discharge is copper and has a diameter of 7 cm and a height of 1 cm. One of the electrodes is connected to a high voltage power supply and the other to the ground. Two glass plates are also used as dielectrics, one of which is a sample material. The voltage range of the device is 1-20 kV. An HMEGHM203 oscilloscope was used to determine the output current and phase difference between voltage and current. The gas used to produce plasma is air, which is set at 15 ml/min by a mass flow rate controller for every 100 mg of material. Figure 1 shows a schematic image of the laboratory system used to functionalize nanotubes by humid air plasma. As is shown in Figure 1, by applying the high voltage difference, the humid air between the two poles is ionized and produces a plasma phase. By placing MWCNTs in this space, the interaction of the active particles with the surface of the nanotubes makes them functional.
Experimental study of nitrobenzene degradation in water by strong ionization dielectric barrier discharge
Published in Environmental Technology, 2021
Muhammad Imran Nawaz, Chengwu Yi, Hong Zhao, Prince Junior Asilevi, Lanlan Yin, Rongjie Yi, Qaiser Javed, Huijuan Wang
Dielectric barrier discharge (DBD) plasma technology is a recent approach which has gained rapid attention in last few years due to its distinctive benefits [20]. It is broadly used in the study for surface treatment [21, 22], volatile organic compound (VOC) degradation [23,24], catalyst treatment [25] and in several other areas. The use of DBD technology for the wastewater degradation [26–28] is a novel approach towards wastewater treatment. The DBD apparatus mainly consists of a dielectric barrier made of quartz, ceramics, glass, alumina or mica and a discharge electrode that covers the dielectric barrier. Dielectric barrier uniformly distributes the discharge over the whole electrode. A high voltage is applied between the electrodes and discharge occurs in the DBD that excites the background gas molecules to produce a high range of active species including molecules (H2O2, O3, etc.), radicals (, , •O, •H, •OH), ultraviolet light, electrohydraulic cavitation, and shockwave [27, 29–32]. These active species have robust action and act as powerful oxidizing agents that can prompt chain reactions in pollutant molecules and are expected to sufficiently destruct wastewater pollutants. Because of their high oxidizing ability, several complex and toxic organic pollutants could be transformed into less or even non-toxic products. The degraded NB byproducts formulate into CO2 and H2O, thus giving an eventual solution for wastewater treatment [33]. Compared with other treatment methods, DBD produces a stable, uniform and diffuse discharge. Furthermore, DBD has small footprints to the environment, high treatment efficiency, short processing cycle and no effects of secondary pollution that overcomes the limitations of the existing and traditional methods.