Editorial

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4 pages, 184 KiB

Open AccessEditorial

Plasma: From Materials to Emerging Technologies

by Mirosław Dors

Appl. Sci. 2021, 11(18), 8311; https://0-doi-org.brum.beds.ac.uk/10.3390/app11188311 - 08 Sep 2021

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Abstract

Interest in plasma as a tool in various technological processes has been growing for several decades [...] Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

Research

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25 pages, 922 KiB

Open AccessFeature PaperArticle

The Helical Resonator: A Scheme for Radio Frequency Plasma Generation

by Emilio Martines, Roberto Cavazzana, Luigi Cordaro and Matteo Zuin

Appl. Sci. 2021, 11(16), 7444; https://0-doi-org.brum.beds.ac.uk/10.3390/app11167444 - 13 Aug 2021

Cited by 1 | Viewed by 3848

Abstract

The helical resonator is a scheme for the production of high voltage at radio frequency, useful for gas breakdown and plasma sustainment, which, through a proper design, enables avoiding the use of a matching network. In this work, we consider the treatment of [...] Read more.

The helical resonator is a scheme for the production of high voltage at radio frequency, useful for gas breakdown and plasma sustainment, which, through a proper design, enables avoiding the use of a matching network. In this work, we consider the treatment of the helical resonator, including a grounded shield, as a transmission line with a shorted end and an open one, the latter possibly connected to a capacitive load. The input voltage is applied to a tap point located near the shorted end. After deriving an expression for the velocity factor of the perturbations propagating along the line, and in the special case of the shield at infinity also of the characteristic impedance, we calculate the input impedance and the voltage amplification factor of the resonator as a function of the wave number. Focusing on the resonance condition, which maximizes the voltage amplification, we then discuss the effect of the tap point position, dissipation and the optional capacitive load, in terms of resonator performance and matching to the power supply. Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

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27 pages, 12914 KiB

Open AccessFeature PaperArticle

Carbon Microstructures Synthesis in Low Temperature Plasma Generated by Microdischarges

by Arkadiusz T. Sobczyk and Anatol Jaworek

Appl. Sci. 2021, 11(13), 5845; https://0-doi-org.brum.beds.ac.uk/10.3390/app11135845 - 23 Jun 2021

Cited by 5 | Viewed by 1569

Abstract

The aim of this paper is to investigate the process of growth of different carbon deposits in low-current electrical microdischarges in argon with an admixture of cyclohexane as the carbon feedstock. The method of synthesis of carbon structures is based on the decomposition [...] Read more.

The aim of this paper is to investigate the process of growth of different carbon deposits in low-current electrical microdischarges in argon with an admixture of cyclohexane as the carbon feedstock. The method of synthesis of carbon structures is based on the decomposition of hydrocarbons in low-temperature plasma generated by an electrical discharge in gas at atmospheric pressure. The following various types of microdischarges generated at this pressure were tested for both polarities of supply voltage with regard to their applications to different carbon deposit synthesis: Townsend discharge, pre-breakdown streamers, breakdown streamers and glow discharge. In these investigations the discharge was generated between a stainless-steel needle and a plate made of a nickel alloy, by electrode distances varying between 1 and 15 mm. The effect of distance between the electrodes, discharge current and hydrocarbon concentration on the obtained carbon structures was investigated. Carbon nanowalls and carbon microfibers were obtained in these discharges. Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

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11 pages, 12476 KiB

Open AccessArticle

Selective Plasma Etching of Polymer-Metal Mesh Foil in Large-Area Hydrogen Atmospheric Pressure Plasma

by Richard Krumpolec, Jana Jurmanová, Miroslav Zemánek, Jakub Kelar, Dušan Kováčik and Mirko Černák

Appl. Sci. 2020, 10(20), 7356; https://0-doi-org.brum.beds.ac.uk/10.3390/app10207356 - 21 Oct 2020

Cited by 6 | Viewed by 2600

Abstract

We present a novel method of surface processing of complex polymer-metal composite substrates. Atmospheric-pressure plasma etching in pure H₂, N₂, H₂/N₂ and air plasmas was used to fabricate flexible transparent composite poly(methyl methacrylate) (PMMA)-based polymer film/Ag-coated [...] Read more.

We present a novel method of surface processing of complex polymer-metal composite substrates. Atmospheric-pressure plasma etching in pure H₂, N₂, H₂/N₂ and air plasmas was used to fabricate flexible transparent composite poly(methyl methacrylate) (PMMA)-based polymer film/Ag-coated Cu metal wire mesh substrates with conductive connection sites by the selective removal of the thin (~10–100 nm) surface PMMA layer. To mimic large-area roll-to-roll processing, we used an advanced alumina-based concavely curved electrode generating a thin and high-power density cold plasma layer by the diffuse coplanar surface barrier discharge. A short 1 s exposure to pure hydrogen plasma, led to successful highly-selective etching of the surface PMMA film without any destruction of the Ag-coated Cu metal wires embedded in the PMMA polymer. On the other hand, the use of ambient air, pure nitrogen and H₂/N₂ plasmas resulted in undesired degradation both of the polymer and the metal wires surfaces. Since it was found that the etching efficiency strongly depends on the process parameters, such as treatment time and the distance from the electrode surface, we studied the effect and performance of these parameters. Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

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16 pages, 7456 KiB

Open AccessArticle

Study on the Effect of Structure Parameters on NO Oxidation in DBD Reactor under Oxygen-Enriched Condition

by Yunkai Cai, Lin Lu and Peng Li

Appl. Sci. 2020, 10(19), 6766; https://0-doi-org.brum.beds.ac.uk/10.3390/app10196766 - 27 Sep 2020

Cited by 9 | Viewed by 1879

Abstract

To improve NO oxidation and energy efficiency, the effect of dielectric barrier discharge reactor structure on NO oxidation was studied experimentally in simulated diesel exhaust at atmospheric pressure. The mixture of 15% O₂/N₂ (balance)/860 ppm NO_X (92% NO + [...] Read more.

To improve NO oxidation and energy efficiency, the effect of dielectric barrier discharge reactor structure on NO oxidation was studied experimentally in simulated diesel exhaust at atmospheric pressure. The mixture of 15% O₂/N₂ (balance)/860 ppm NO_X (92% NO + 8% NO₂) was used as simulated diesel exhaust. The results show that DBD reactor with 100-mm electrode length has the highest oxidation degree of NO_X and energy efficiency. NO oxidation efficiency is promoted and the generation of NO is inhibited significantly by increasing the inner electrode diameter. Increasing the inner electrode diameter not only improve the E/N, but also makes the distribution of E/N more concentrated in the gas gap. The secondary electron emission coefficient (γ) of electrode material is closely related to electron energy and cannot be considered as a constant, which causes the different performance of electrode material for NO oxidation under different gas gap conditions. Compared with the rod electrode, the screw electrode has a higher electric field strength near the top of the screw, which promotes the generation of N radicals and inhibits the generation of O radicals. Rod electrode has a higher NO oxidation and energy efficiency than screw electrode under oxygen-enriched condition. Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

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15 pages, 1858 KiB

Open AccessArticle

Effect of Coulomb Focusing on the Electron–Atom Bremsstrahlung Cross Section for Tungsten and Iron in Nonthermal Lorentzian Plasmas

by Myoung-Jae Lee, Naoko Ashikawa and Young-Dae Jung

Appl. Sci. 2020, 10(14), 4832; https://0-doi-org.brum.beds.ac.uk/10.3390/app10144832 - 14 Jul 2020

Cited by 1 | Viewed by 1607

Abstract

The Coulomb focusing effect on the electron–atom bremsstrahlung spectrum is investigated in nonthermal Lorentzian plasmas. The universal expression of the cross section of nonrelativistic electron–atom bremsstrahlung process is obtained by the solution of the Thomas-Fermi equation with the effective atomic charge. The effective [...] Read more.

The Coulomb focusing effect on the electron–atom bremsstrahlung spectrum is investigated in nonthermal Lorentzian plasmas. The universal expression of the cross section of nonrelativistic electron–atom bremsstrahlung process is obtained by the solution of the Thomas-Fermi equation with the effective atomic charge. The effective Coulomb focusing for the electron–atom bremsstrahlung cross section near the threshold domain is also investigated by adopting the modified Elwert-Sommerfeld factor with the mean effective charge for the bremsstrahlung process. In addition, the bremsstrahlung emission rates are obtained by considering encounters between nonthermal electrons and atoms such as Fe and W atoms. We found that the bremsstrahlung emission rates for nonthermal electron–atoms are lower than those for thermal plasmas. Various nonthermal effects on the bremsstrahlung emission rates in Lorentzian plasmas are also discussed. Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

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10 pages, 4258 KiB

Open AccessArticle

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

by Dashuai Li, Ling Tong and Bo Gao

Appl. Sci. 2020, 10(13), 4468; https://0-doi-org.brum.beds.ac.uk/10.3390/app10134468 - 28 Jun 2020

Cited by 6 | Viewed by 2893

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

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11 pages, 3386 KiB

Open AccessArticle

A Practical Method for Controlling the Asymmetric Mode of Atmospheric Dielectric Barrier Discharges

by Ling Luo, Qiao Wang, Dong Dai, Yuhui Zhang and Licheng Li

Appl. Sci. 2020, 10(4), 1341; https://0-doi-org.brum.beds.ac.uk/10.3390/app10041341 - 16 Feb 2020

Cited by 5 | Viewed by 1687

Abstract

Atmospheric pressure dielectric barrier discharges (DBDs) have been applied in a very broad range of industries due to their outstanding advantages. However, different discharge modes can influence the stability of atmospheric DBDs, such as the density and composition of active species in discharge [...] Read more.

Atmospheric pressure dielectric barrier discharges (DBDs) have been applied in a very broad range of industries due to their outstanding advantages. However, different discharge modes can influence the stability of atmospheric DBDs, such as the density and composition of active species in discharge plasmas, thereby impacting the effect of related applications. It is necessary and valuable to investigate the control of nonlinear modes both in theoretical and practical aspects. In this paper, we propose a practical, state-controlling method to switch the discharge mode from asymmetry to symmetry through changing frequencies of the applied voltage. The simulation results show that changing frequencies can effectively alter the seed electron level at the beginning of the breakdown and then influence the subsequent discharge mode. The higher controlling frequency is recommended since it can limit the dissipative process of residual electrons and is in favor of the formation of symmetric discharge in the after-controlling section. Under our simulation conditions, the discharges with an initial driving frequency of 14 kHz can always be converted to the symmetric period-one mode when the controlling frequency is beyond 30 kHz. Full article

(This article belongs to the Special Issue Plasma: From Materials to Emerging Technologies)

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