Pressure Microwave Plasma Research Articles

Volatile Organic Compounds (VOCs) Distribution from PCB Waste and Vitrification by Reacting with Flux Agents

Resin, the part of printed circuit board (PCB) waste, consists of harmful elements and volatile organic compounds (VOCs) and can cause pollution, but it can also be potentially treated through vitrification. Hence, the purpose of this study is to investigate the distribution of VOCs and analyze the effects of different flux agent types, pyrolysis duration, flux agent ratio, and effect of different carrier gases to vitrify resin waste in an atmospheric-pressure microwave plasma reactor. The resins to the flux agents - shell powder, limestone and quartz sand ratio of 50:50 and 25:75 gave the best results for the vitrification compared to the ratio of 75:25 and control (absence of flux agent). Furthermore, the crystalline structures of CaCO3 and SiO2 dominated the final residue, and this confirmed the vitrification of the resin. Flux agents also can reduce the distribution of propylene and benzene from the plasma pyrolysis. A longer duration of the pyrolysis, a higher flux agent ratio and flux agent types can be recommended for plasma pyrolysis applications even though they have no significant impact on the inertization of the elements statistically. Shell powder is thus suggested as a cost-less flux agent which can create vitrification and inertization of the contaminants from resin in plasma discharges.

Volatile Organic Compound (VOC) Reduction from Face Mask Wastes via a Microwave Plasma Reactor

Since the outbreak of the COVID-19 pandemic, the driven of face masks as personal protective equipment has increased significantly. Thus, disposed face masks from users should be handled properly for preventing the contamination of medical waste and the potential spread of viruses to the environment. This study gives information for dealing with face masks and assessing the volatile organic compounds (VOCs) concentrations via an atmospheric-pressure microwave plasma reactor. Face mask samples were mixed with the flux agents, namely cullet/glass, Al2O3, SiO2 and CaCO3. Samples were compared with control (no addition of flux agents) and the addition of only cullet. Moreover, microwave power, gas flow rate and pyrolysis duration were controlled at 1000 W, 9 standard liter per minute (SLM) and 5 min, respectively. The total concentration of VOC with the absence of flux agents was 448.04 ppm. Furthermore, the fuse of cullet and SiO2-Al2O3-cullet in the mask reduced the concentration of VOCs by 314.77 ppm and 54.7 ppm, respectively. Furthermore, the combination of CaCO3-SiO2-Al2O3-cullet creates the vitrification of material with the presence of crystalline structure, where the compositions of Ca and Si were 13.55% and 19.12%, respectively. Moreover, the final composition of carbon from the flux agents was 17.92 ± 10.08%. This study confirms that the fuse of CaCO3-SiO2-Al2O3-glass/cullet reduced the VOC via plasma technology, which is a promising method to be implemented in order to reduce the concentration of VOC from the face mask waste.

Experimental investigation of the methane combustion assisted by atmospheric pressure oxygen microwave plasma torch

The atmospheric-pressure oxygen microwave plasma is employed to enhance the methane combustion in the jet-diffusion combustor. The plasma-assisted combustion (PAC) is compared with natural combustion without plasma application in terms of the flame morphology, flame temperature, and combustion efficiency. It is found experimentally that the oxygen plasma assistance in combustion is prominent in lean oxygen condition, and the active species generated in the microwave plasma torch contribute to the combustion process more dominantly than the flame temperature change caused by heating of oxygen microwave plasma. The combustion degree of CH4 in PAC is much more enhanced in lean oxygen combustion, and the exhaust gas in combustion is effectively controlled with the use of the oxygen microwave plasma torch.

A New Stripline-Based Atmospheric Pressure Microwave Plasma Sheet Source Designed for Surface Modification of Materials.

A new type of microwave plasma source is presented in which plasma at atmospheric pressure is generated inside a quartz rectangular flat box placed in a stripline supplied by a 2.45 GHz coaxial line. The plasma has a sheet shape and is designed for surface modification. Electric field and power flux distributions, tuning characteristics, and power characteristics (ratios of radiated, absorbed, and entering power) are numerically studied for three configurations: open, semi-closed, and closed. The calculations show that near-zero radiation reduction is possible only for the closed configuration, while the ratio of radiated power to entering power is always greater than 30% for the other configurations. The moving plunger is not sufficient for the ratio of reflected to incident power to fall below 20% for both the closed and open configurations. This is possible for the semi-closed configuration, but then the radiated power is the highest. The experiment shows that for the same entering power, the plasma volume is largest for the closed configuration and smallest for the open configuration, which we attribute to the difference in radiated power. The plasma generated using the closed stripline configuration has a larger volume than plasma generated using the rectangular waveguide.

Stable filamentary structures in atmospheric pressure microwave plasma torch

This paper experimentally investigates the processes governing the single- and multi-filament regimes in an atmospheric pressure microwave (MW) torch operated in argon. Optical emission spectroscopy and spectral imaging are the principal diagnostics techniques which are employed. MW power is found to be the main parameter controlling the number of filaments. The single-filament regime exhibits many properties typical for surface wave discharges, e.g. a linear decrease in electron density along the axis or the existence of a central dip in the radial/lateral emission profiles. Simple geometric quantities, such as the length or thickness of the filament(s), vary almost linearly with the input MW power, and exhibit discontinuities at successive filament splitting events. These take place at similar values of filament maximum thickness, and may be due to skin-depth limited power transfer. The presence and chemistry of a low-emission intensity plasma shell surrounding the filament(s) is also investigated. The gas temperature is estimated from the OH band and complemented by Schlieren imaging, which revealed that a much larger cone of gas is being heated by filaments than is their diameter.

Structure-controllable synthesis of ZnO nanowires using water vapor in an atmospheric-pressure microwave plasma system

Although the use of atmospheric-pressure microwave plasma to synthesize ZnO nanowires addresses various issues associated with conventional synthesis methods, it is difficult to obtain nanowires with controlled diameters and lengths. Herein, we investigated the effects of microwave input power and water vapor on the structure of ZnO nanowires grown using an atmospheric-pressure microwave plasma system. It was found that the aspect ratio of ZnO nanowires could be controlled by adjusting the plasma temperature and the amount of OH radicals. This method successfully produced ZnO nanowires in a structure-controllable manner with a wide range of aspect ratios from 10 to 340. Interestingly, we found that the sensitivity of the ZnO nanowires to UV irradiation was closely related to the morphology. In particular, the ZnO nanowires with high aspect ratios and densities showed excellent sensing characteristics.

Investigation on the Microwave Excited Plasma Filament at Atmospheric Pressure

A high-efficiency microwave atmospheric pressure plasma jet (APPJ) has been developed in previous work. Long and stable plasma filament is excited directly in the open air with 2.45-GHz microwave power and double-channel argon flow by a double-coaxial structure. Unlike those plasma jets that strongly rely on a high flow rate to shape the plasma jet, this method produces a stable filamentous plasma jet at a low flow rate whose length and diameter are in a linear relationship with absorbed microwave power. This study aims to investigate the fundamental parameters of this special plasma filament under different power levels and gas flow rates by optical emission spectroscopy (OES), including the electron temperature and the spectrum. The electron temperature is determined to be 0.71–0.81 eV. It decreases slightly as the power increases, which is different from other high-voltage or radio frequency excited plasma jets under high power. The electron temperature does not change significantly with the change of microwave power and argon flow rate, more manifested as a change in the length, which indicates that this special plasma filament is related to the complex interaction of the microwave field and plasma. This study provides basic parameters for further investigation of this kind of plasma jet for theoretical and numerical simulation.

Assessment of two atmospheric-pressure microwave plasma sources for H2 production from ethanol decomposition

H2 is considered as a sustainable fuel despite being obtained from other raw sources. Plasma technology can be used to produce it from alcohol decomposition as an excellent alternative technique to those habitually utilized. In the present study, two atmospheric-pressure microwave plasma sources, namely TorcheàInjection Axiale sur Guide d'Ondes (TIAGO) and surfatron, have been assessed for hydrogen production through ethanol decomposition, including for the first time both an analysis of the influence of operational conditions and energetic performance. Gaseous by-products are studied by Mass Spectrometry in a wide range of experimental conditions, focusing on the discharge capability to withstand and decompose ethanol and produce H2. Surfatron discharges exhibit a good capability to produce H2 with significant selectivity for low Ar flow rates, which is reduced for larger flow rates due to a decrease in the residence time of ethanol in the discharge. Besides, its capability to withstand the alcohol is limited due to the maximum power that can be applied to maintain the plasma. However, TIAGO torch plasmas surpass the performance of surfatron for H2 production, being able to withstand the introduction of larger ethanol flow rates. This fact allows for higher H2 production with higher selectivity, showing an almost complete (>99%) ethanol decomposition in a wide range of working conditions. Furthermore, the torch shows a better energetic performance than the surfatron for larger ethanol flows, providing with larger H2 production rates of 0.61 g kW-1h−1 with relatively low specific energies required for ethanol processing (0.17 kWh g−1).

Experiments and modeling of atmospheric pressure microwave plasma reforming of a methane-carbon dioxide mixture

Atmospheric pressure microwave plasma reforming was conducted on a methane (CH4) and carbon dioxide (CO2) mixture, and characterized by measuring the temperature of the plasma and gas composition of the reforming product via optical emission spectroscopy (OES) and gas chromatographic measurement. The temperature at the plasma reached as high as 5900 K regardless of the specific energy input, while at microwave power of 2 kW and flow rate of 10 slm, nearly all CH4 and CO2 were converted into hydrogen (H2) and carbon monoxide (CO). The plasma temperature higher than the level achievable from uniform gas heating implied that only a part of the flow will enter the plasma region, and the rest will bypass and mix with the plasma stream downstream. Thus, a reactor network-type simulation was performed by modeling the plasma and surrounding streams, each as a series of perfectly-stirred reactors; the reactors at the same downstream locations interacted for the gas diffusion and heat conduction. The simulation reproduced the measured gas compositions well, revealing that the reforming proceeded as the surrounding gas enters and diffuses out of the plasma stream due to the flow mixing, as well as through the heating of the surrounding stream by the plasma stream.

Investigation on Continuous and Modulated Microwave Plasma Filaments at Atmospheric Pressure

Microwave atmospheric pressure plasma jets continue to evolve with the growth of atmospheric plasma’s applications in sterilization, material modification, and cancer treatment. In this article, continuous and modulated microwave plasma filaments were produced by a hand-held microwave plasma jet, and then they were compared in plasma length, electron temperature, and emission spectrum. The electron temperature was measured by the emission spectroscopy diagnostic method, and the regularities of the compared parameters’ change were studied by varying duty cycles and periods of the modulating signal. The results prove that the modulated microwave can generate stable plasma filaments directly in the air without protective tubes, and it is different from the continuous microwave plasma in all compared parameters. Besides, stable dendritic tearing of plasma filaments was observed. These results imply that modulated microwave and continuous microwave plasma filaments cannot be regarded as the same, the changing manner and the reaction on the surface of the medium may be completely different even if they are the same to the naked eye in most cases. These results are helpful for the controlling and understanding of microwave plasma, and the stable tearing could be used to expand the treated area of a single plasma jet.

Direct Growth of Carbon Nanotubes on Aluminum Foil by Atmospheric Pressure Microwave Plasma Chemical Vapor Deposition

This paper is about the research that carbon nanotubes (CNTs) grow on aluminum foils without additional catalysts by atmospheric pressure microwave plasma chemical vapor deposition (AMPCVD) with the precursor of argon-hydrogen-ethanol. At different temperatures, a series of experiments that CNTs grow on aluminum foils were done with and without the alumina layer. The EDS results showed that iron impurities in aluminum foils catalyze the growth of CNTs. By measurements of SEM and HRTEM, tens of microns long and multi-walled CNTs are grown. The CNTs’ content in the sample changes more with the increase in temperature. The Raman measuring shows that CNTs have fewer defects with higher temperature. Finally, by measurements of EDS mapping and XRD on aluminum foil, the growth mechanism of CNTs was discussed.

Decomposition reaction of phosphate rock under the action of microwave plasma* *Project supported by the National Natural Science Foundation of China (Grant No. 21076131).

The decomposition reaction of phosphate rock under the action of microwave plasma was investigated. Phosphate rock and its decomposition products were characterized by x-ray diffraction (XRD), energy disperse spectroscopy (EDS), and chemical analysis. The measurements of electron temperature (T e) and electron density (N e) of plasma plume under atmospheric pressure were carried out using optical emission spectroscopy(OES). The electron temperature (T e) was determined based on the calculation of the relative intensity of the O II (301.91 nm) and O II (347.49 nm) spectral lines. Correspondingly, electron densities were obtained using the Saha ionization equation which was based on the C I (247.86 nm) line and the C II (296.62 nm) line under the assumption of local thermodynamic equilibrium (LTE). The relationship between the relative intensity of the active components and the gas output was studied by the spectrometer. Finally the reaction mechanism of the decomposition of the phosphate rock under the action of the atmospheric pressure microwave plasma was proposed. The results showed that with the increase of CO flow and microwave power, the electron temperature and electron density in the plasma show a decreasing and increasing trend. The CO is dissociated into gaseous carbon ions under the action of microwave plasma, and the presence of gaseous carbon ions promotes the decomposition of the phosphate rock.

One-step Synthesis of Carbon Nanotubes Network with Rich Oxygenated Functional Groups via Microwave Plasma in Atmospheric Pressure

AbstractAn atmospheric pressure microwave plasma tubular furnace apparatus (MPTF) for the rapid synthesis of carbon nanotubes (CNTs) has been developed. CNTs have been synthesized by an Argon-Hydrogen microwave plasma using ethanol vapor as carbon source with the furnace temperature of 800 °C at the atmospheric pressure. The synthesized CNTs have been analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and are shown to be multi-walled and tangled and chemically connected to form a high-density network with the diameter at the range of 25-70 nm. The measurement of X-ray photoelectron spectroscopy (XPS) indicates that a large number of oxygenated functional groups grown on the surface of CNTs. These properties proved that the CNTs could be utilized as nanoscale templates for various applications.

Microwave Plasma System for Continuous Treatment of Railway Track

Braking conditions are a fundamental issue for the railway and have been a limiting factor in network capacity and timetabling. Leaf fall, especially during the autumn season, creates low-adhesion problems on railways, causing braking problems for trains. To address the requirements of the novel plasma industrial applications towards environmental applications, this work developed and tested a 2.45 GHz microwave atmospheric pressure plasma system for in situ removal of the third body layer deposited onto the railway so as to improve braking. The plasma reactor consisted of a 15 kW, 2.45 GHz magnetron-based microwave generator and a plasma reactor (dielectric tube placed in a TE01 monomode microwave cavity); the atmospheric plasma ignited and sustained at different power levels (2–15 kW) in different gases (nitrogen, argon) as well as mixtures of these gases with reactive molecules (water, oxygen) was jetted directly onto the railhead as to change the conditions for the wheel–rail interface. This technology is hoped to be a game-changer in enabling predictable and optimized braking on the railway network. Challenges encountered during the demonstration phase are discussed. Subsequent work should validate the results on a working railway line during the autumn season.

Production of Long-scale Atmospheric-pressure Microwave Plasma and its Applications to Surface Process

Production of Long-scale Atmospheric-pressure Microwave Plasma and its Applications to Surface Process

Impact of Atmospheric Pressure Microwave Plasma Treatment on Quality of Selected Spices

Current industry needs are related to higher awareness of modern consumers. These consumers are looking for products in which properties such as bioactive compounds are preserved as much as possible. Plasma treatment is one of the most promising nonthermal technologies that can decontaminate food and keep its original properties. Therefore, the aim of this work was to examine the usefulness of atmospheric pressure argon microwave plasma on decontamination of black pepper seeds, allspice berries and juniper berries. The samples were irradiated by plasma for 15–60 s and their physicochemical (dry matter content, water activity, color, total phenolic content, antioxidant activity, piperine content in black pepper seeds) and microbial (bacteria and molds count) quality was evaluated afterwards. Results demonstrated that plasma irradiation for 15 s was sufficient for partial inactivation of A. niger but less effective against the Gram-positive bacterium B. subtilis, regardless of the raw material. At the same time, plasma treatment reduced water activity, which can positively affect further storage of spices. Properly selected plasma parameters may also enhance extractability of phenolics or piperine (from black pepper seeds) and improve antioxidant activity with not very great, but visible, color changes.

Computational study of plasma-induced flow instabilities in power modulated atmospheric-pressure microwave plasma jet

This work presents a combined experimental and simulation-based investigation of gas flow perturbations caused by atmospheric-pressure microwave plasma jet with modulated power. These plasma-induced flow instabilities are observed experimentally by schlieren imaging and the mechanism of their formation is explained using a numerical model. The model offers a time-resolved self-consistent solution of plasma dynamics, gas flow, and heat transfer equations. The simulation results are in good agreement with the experimental observations and we conclude that the key mechanism behind the flow perturbations is rapid gas heating at the end of the discharge tube.

Synthesis of Multiwalled Carbon Nanotubes on Stainless Steel by Atmospheric Pressure Microwave Plasma Chemical Vapor Deposition

In this paper, we synthesize carbon nanotubes (CNTs) by using atmospheric pressure microwave plasma chemical vapor deposition (AMPCVD). In AMPCVD, a coaxial plasma generator provides 200 W 2.45 GHz microwave plasma at atmospheric pressure to decompose the precursor. A high-temperature tube furnace provides a suitable growth temperature for the deposition of CNTs. Optical fiber spectroscopy was used to measure the compositions of the argon–ethanol–hydrogen plasma. A comparative experiment of ethanol precursor decomposition, with and without plasma, was carried out to measure the role of the microwave plasma, showing that the 200 W microwave plasma can decompose 99% of ethanol precursor at any furnace temperature. CNTs were prepared on a stainless steel substrate by using the technology to decompose ethanol with the plasma power of 200 W at the temperatures of 500, 600, 700, and 800 °C; CNT growth increases with the increase in temperature. Prepared CNTs, analyzed by SEM and HRTEM, were shown to be multiwalled and tangled with each other. The measurement of XPS and Raman spectroscopy indicates that many oxygenated functional groups have attached to the surface of the CNTs.

Economic and environmental evaluation of flux agents in the vitrification of resin waste: A SWOT analysis

Flux agents play an important role in the pyrolysis treatment of vitrifying hazardous wastes. Among these is plasma jets, a cost-less flux agent derived from shell powder which can be used to create vitrification. It is a promising option to be applied in the vitrification of elements and to remove the VOCs of hazardous waste, namely, resin from PCB scrap in an atmospheric-pressure microwave plasma reactor. In this study, a laboratory scale experiment was conducted. The experiment was performed in the pyrolysis of resin which was added with flux agents. The economic evaluation of the flux agents, and the circular economy concept of the final residue derived from the plasma pyrolysis was then analyzed post treatment. To test the strength and weakness of the experiment, the SWOT analysis was performed. The outcome helped in the understanding of the cost-less flux agent used in the pyrolysis treatment of hazardous waste. Results showed that fusing shell powder in resin was better for improving the removal efficiency of VOCs, such as benzene and toluene as well as toxic metals than compared to other flux agents such as limestone and quartz sand. Moreover, the final residue of resin was found to fulfil the concept of circular economy where it could be reused as an absorbent of methyl blue, thereby indicating good absorption performance, from 1 ppm–100 ppm. The twelve strategies that were derived from the SWOT analysis could be used as information outlining the current internal and external condition for the development and application of shell powder. Shell powder, as a cost-less flux agent, has the potential for enhancing waste management and circular economy when used in the pyrolysis treatment of future hazardous wastes.

Thermocouple and electric probe measurements in a cold atmospheric-pressure microwave plasma jet

A cold atmospheric-pressure plasma jet was studied using the novel microwave plasmatron recently developed. Cold plasma jet was generated in Ar flow by electrode 2.45 GHz discharge of up to 200 W power in the portable plasmatron burner (torch) with 2.5 cm diameter outlet. Oscillograms and floating potential dependences on distance from the torch outlet were measured by planar electric probe. Axial and radial distributions of gas temperature in a cold plasma jet were obtained by means of thermocouple method.