Thermal Plasma Source Research Articles

Evaluation of process conditions for methane pyrolysis applying the triple thermal plasma system

Among various thermal plasma sources for CH4 pyrolysis, singular direct current (DC) thermal plasma has limited capacity, erosion, and efficiency. However, the triple thermal plasma system has been applied for nanomaterial synthesis and exhibited results overcoming these limitations. This study used the triple thermal plasma system to investigate the most suitable conditions for CH4 pyrolysis. CH4 conversion rate and selectivity of H2 and C2H2 were analyzed by varying the CH4 flow rate and quenching conditions at a fixed power supply of approximately 30 kW, and the specific energy requirement (SER) per 1 kg H2 was compared with that of previous works. The maximum conversion rate was 97% at 50 L/min of CH4, which is approximately 7% higher than earlier studies under conditions with similar process enthalpy. In addition, the conversion of CH4 to C2H2 and further to heavier hydrocarbons proceeded one order of magnitude faster than the reaction time expected by the gas-phase reaction. This result is attributed to the easy penetration of CH4 into the core region with the highest temperature and the strong interaction between the processing gas and graphite surface due to the arrangement of the torches in the triple plasma system. C2H2 selectivity was relatively high, while it was less affected by the increase in the quenching gas than generally expected. This finding was attributed to the naturally fast quenching rate without quenching gas due to the structure expanding from the first to the second graphite. While quenching can enhance selectivity by stabilizing the radicals as intermediates such as H2 or C2H2, it depressed the following reaction with dehydrogenation. Thus, the quenching conditions must be optimized. Finally, we demonstrated that the triple thermal plasma enhanced CH4 pyrolysis regarding H2 production efficiency.

Investigation of Temperature Fluctuation of Diode-Rectified Multiphase AC Arc by High-Speed Visualization

An innovative multiphase AC arc was drastically improved by diode-rectification technique with bipolar electrode. Temperature fields and arc behaviour of the diode-rectified multiphase AC was successfully visualized on the basis of the high-speed camera technique with appropriate band-pass filter optics. Arc temperature was measured by Boltzmann plot method with two line emissions from atomic argon at 675.2834 nm and 794.8176 nm. Arc temperature fluctuates in the range from 7,000 to 13,000 K. The arc temperature near the cathode was higher than 13,000 K, while that near the anode was about 10,000 K. Arc temperature in the centre region in the furnace was about 7,000–9,000 K, which is sufficiently high to melt and evaporate the refractory metals or ceramics. Obtained results suggested the diode-rectified multiphase AC arc is a promising thermal plasma source for material processing at high productivity.

High-speed visualization of metal oxide precursor in multiphase AC arc during nanoparticle formation

The purpose of the present work is to elucidate the formation mechanism of metal oxide nanoparticles in a multiphase AC arc, which is one of the most attractive thermal plasma sources. Lanthanum oxide nanoparticles were focused on, on the basis of spectroscopic diagnostics and thermodynamic considerations. The dynamic behavior of lanthanum vapor and lanthanum monoxide in a multiphase AC arc was visualized by a high-speed camera through band-pass filter optics. Furthermore, the two-dimensional temperature field of the multiphase AC arc was successfully estimated by the same camera system based on the relative intensity method, which included the emissions from the lanthanum atom and lanthanum ion. The obtained temperature profile and intensity profile of lanthanum and lanthanum monoxide suggest that the oxidation from lanthanum to lanthanum monoxide occurred following thermodynamic equilibrium. Understanding these fundamental phenomena in the thermal plasma nanofabrication process enables one to expand the capability of thermal plasma for innovative material processing.

A Remarkably Narrow RHESSI X-Ray Flare on 2011 September 25

Abstract The unusually narrow X-ray source imaged with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during an impulsive spike lasting for ∼10 s during the Geostationary Operational Environmental Satellite C7.9 flare on 2011 September 25 (SOL2011-09-25T03:32) was only ∼2″ wide and ∼10″ long. Comparison with Helioseismsic and Magnetic Imager magnetograms and Atmospheric Imaging Assembly images at 1700 Å shows that the X-ray emission was primarily from a long ribbon in the region of positive polarity with little if any emission from the negative polarity ribbon. However, a thermal plasma source density of ∼1012 cm−3 estimated from the RHESSI-derived emission measure and source area showed that this could best be interpreted as a coronal hard X-ray source in which the accelerated electrons with energies less than ∼50 keV were stopped by Coulomb collisions in the corona, thus explaining the lack of the more usual bright X-ray footpoints. Analysis of RHESSI spectra shows greater consistency with a multi-temperature distribution and a low-energy cutoff to the accelerated electron spectrum of 22 keV compared to 12 keV if a single-temperature distribution is assumed. This leads to a change in the lower limit on the total energy in electrons by an order of magnitude, given the steepness of the best-fit electron spectrum with a power-law index of ∼6.

Nonequilibrium Phenomena in (Quasi-)thermal Plasma Flows

Thermal plasmas are utilized in diverse applications that require high power densities or throughputs, such as metal cutting, welding, spraying, metallurgy, and materials synthesis. Thermal plasma applications involve interactions between the highly energetic plasma and working gas streams, confining devices, or processing materials. Whereas thermal plasma implies a state of equilibrium (i.e. Local Thermodynamic Equilibrium, LTE), due to the above interactions, thermal plasma flows depict nonequilibrium phenomena of two types: kinetic and dissipative. Kinetic nonequilibrium manifests microscopically and is caused by localized imbalances between particles and fields interactions. Its occurrence is evidenced, for example, as deviations from thermal equilibrium between heavy-species and electrons or from mass-action laws. In contrast, dissipative nonequilibrium reveals macroscopically and is produced by external driving forces that incite distributed responses, such as the growth of instabilities, the occurrence of self-organization, or the establishment of turbulence. Although kinetic nonequilibrium has been increasingly incorporated in thermal plasma flow models (e.g. finite-rate chemistry, two-temperature models), it is the great advances in numerical computing that is enabling the exploration of dissipative nonequilibrium (e.g. pattern formation, small-scale turbulent features). Both types of nonequilibrium are reviewed, including their estimation and incidence, within the context of computational models and their relevance to thermal plasma sources and processes.

Generation of Plasma Activated Water by a Hybrid Plasma Source

Recently, plasma activated water (PAW) has drawn huge attention because it is considered to be useful for biomedical and agricultural applications. Because the PAW contains several nitrogen compounds such as nitrate, it can be used as a natural fertilizer. In this article, we report the comparative test results of PAW production by combining nonthermal plasma, thermal plasma, and hybrid methods. As a thermal plasma source, gas-jet assisted pulsed discharge (GAPD) under water was used, and the coaxial cylindrical dielectric barrier discharge (DBD) was adopted as the nonthermal plasma source. The difference in the radical generation rate between the two methods was identified. Some synergy effects in the formation of nitrate ion by the hybrid system were also confirmed. It is considered that the surface discharge through the air channel in GAPD formed by the gas jet stabilized more rapidly by increasing the conductivity of water by relatively high power DBD. This combination can greatly improve the energy efficiency of nitric acid production at relatively low input energies.

Tunable Core-Shell Nanowire Active Material for High Capacity Li-Ion Battery Anodes Comprised of PECVD Deposited aSi on Directly Grown Ge Nanowires.

Herein, we report the formation of core@shell nanowires (NWs) comprised of crystalline germanium NW cores with amorphous silicon shells (Ge@aSi) and their performance as a high capacity Li-ion battery anode material. The Ge NWs were synthesized directly from the current collector in a solvent vapor growth (SVG) system and used as hosts for the deposition of the Si shells via a plasma-enhanced chemical vapor deposition (PECVD) process utilizing an expanding thermal plasma (ETP) source. The secondary deposition allows for the preparation of Ge@aSi core@shell structures with tunable Ge/Si ratios (2:1 and 1:1) and superior gravimetric and areal capacities, relative to pure Ge. The binder-free anodes exhibited discharge capacities of up to 2066 mAh/g and retained capacities of 1455 mAh/g after 150 cycles (for the 1:1 ratio). The 2:1 ratio showed a minimal ∼5% fade in capacity between the 20th and 150th cycles. Ex situ microscopy revealed a complete restructuring of the active material to an interconnected Si1- xGe x morphology due to repeated lithiation and delithiation. In full-cell testing, a prelithiation step counteracted first cycle Li consumption and resulted in a 2-fold improvement to the capacity of the prelithiated cell versus the unconditioned full-cells. Remarkable rate capability was also delivered where capacities of 750 mAh/g were observed at a rate of 10 C.

Inhibition of cervical cancer cell growth by non-thermal atmospheric plasma application utilizing a thermal argon plasma source

Inhibition of cervical cancer cell growth by non-thermal atmospheric plasma application utilizing a thermal argon plasma source

Ex vivo characterization of thermal argon plasma sources for potential cold atmospheric plasma application in medicine

Ex vivo characterization of thermal argon plasma sources for potential cold atmospheric plasma application in medicine

Schlieren imaging: a powerful tool for atmospheric plasma diagnostic

Schlieren imaging has been widely used in science and technology to investigate phenomena occurring in transparent media. In particular, it has proven to be a powerful tool in fundamental studies and process optimization for atmospheric pressure plasma diagnostics, providing qualitative and (in some cases) also quantitative information on the fluid-dynamic characteristics of plasmas generated by many different types of sources. However, obtaining significant and reliable results by schlieren imaging can be challenging, especially when considering the variety of geometries and applications of atmospheric pressure plasma sources. Therefore, it is necessary to adopt solutions that can address the specific issues of different plasma-assisted processes. In this paper, an overview on the use of the schlieren imaging technique for atmospheric pressure plasma characterization is presented. In the first part, the physical principles behind this technique and the different setups that can be adopted to perform it are presented. In the second part, examples of schlieren imaging applied to different kinds of atmospheric pressure plasmas (non-equilibrium plasma jets, plasma actuators for flow control and thermal plasma sources) are presented, showing how it was used to characterize the fluid-dynamic behavior of plasma-assisted processes and reporting best practices in performing this diagnostic technique.

SOIL-WASHING AND THERMAL PLASMA TREATMENT FOR DECONTAMINATION OF DREDGED MARINE SEDIMENTS FROM THE MIDIA PORT - ROMANIA

The aim of this paper is to show the results of two methodological approaches applied for decontamination of the Midia Port dredged sediment to assess their potential reusability. Firstly, the sediment samples were defined in physical, chemical, microbiological and ecotoxicological terms. The results were compared to the limit values established by environmental regulations for dredged sediment management. Some sediment samples exposed a very high concentration of hydrocarbons; the sediments were classified in three categories on the basis of their level of organic/inorganic pollutants. The polluted sediment samples were subjected to the soil-washing treatment. The post treatment analysis revealed that the coarse silty and sandy fractions resulted unpolluted. The soil-washing induced the physical concentration of pollutants (i.e. C>12) in the silty-clay fraction. The wastewater from the treatment plant, once treated, showed no critical issues. After soil-washing treatment, the sediment samples were exposed to a laboratory scale 30kW RF thermal plasma source. Two types of plasma assisted treatments have been performed: the carbothermal process (to evaluate the technical feasibility of silicon extraction during material inertization) and the vitrification process (only for material inertization). Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) withal X-ray fluorescence (XRF) and leaching tests were used to investigate the obtained material. The acquired results revealed a decontamination of the collected sediments with leaching test results below legal limits. EDS analysis showed the increment of silica (SiO2) content by about 5-7 % after the plasma treatment and that the localized extraction of silicon by the carbothermal reduction process has been obtained.

Suitability of thermal plasmas for large-area bacteria inactivation on temperature-sensitive surfaces – first results with Geobacillus stearothermophilus spores

The application of thermal plasma for large-area bacteria inactivation on temperature-sensitive surfaces is not a common one. Nonetheless, there are thermal plasma generators which offer a high sheath homogeneity and have proven to be suitable for treatment of thermally sensitive materials in the past. To investigate the suitability of such plasmas, agar dishes plated with endospores of Geobacillus stearothermophilus have been treated with a long arc plasma generator called LARGE. The achieved results have been compared with a commercially available non-thermal plasma generator. A significant inactivation of the endospores could be observed only after 60 s of treatment with the thermal plasma source. This was not possible with the non-thermal generator. Moreover, no temperature damage or increase of the specimen could be detected. An attempt to determine the main agents responsible for the microbicidal effects have been made – the influence of plasma gas composition, discharge current and treatment time has been investigated. Significant improvements in the disinfection rates after adding small amounts of nitrogen to the plasma gas could be observed. A first discussion regarding the suitability of thermal plasmas for bacteria inactivation has been given.

Implosive Thermal Plasma Source for Energy Conversion

<em></em><p>Laboratory scale thermal plasma source for magnetohydrodynamic or magnetocumulative generator was developed. The thermal plasma is created from combustible stochiometric mixture of hydrogen and oxygen by spherical implosion of convergent detonation wave. Resulting high velocity plasma is observed by capturing emitted light by hi-speed camera to determine plasma velocity and also spectroscopically in order to estimate of plasma temperatures. Construction of the implosion plasma source is discussed.</p>

多相交流アーク中の酸化物ナノ粒子前駆体の動的挙動

The purpose of this study is to investigate the formation mechanism of aluminum oxide nanoparticles in thermal plasma. A multiphase AC arc was utilized as thermal plasma source to synthesize oxide nanoparticles. Dynamic behavior of the metal oxide vapor which is a precursor of oxide nanoparticles was successfully visualized by high-speed camera with appropriate band-pass filter system. According to spectroscopic measurements, transmission wavelength of band-pass filters were selected to be 670 nm for Al atomic line and 514.5 nm for AlO molecular spectra, respectively. The obtained results indicated that Al vapor was distributed in only upstream of plasma tail while AlO vapor was generated in downstream. These results experimentally elucidated that Al oxide nucleates at first and then Al oxide condenses to form Al2O3 nanoparticles.

Investigation of the antimicrobial activity at safe levels for eukaryotic cells of a low power atmospheric pressure inductively coupled plasma source.

Low power atmospheric pressure inductively coupled thermal plasma sources integrated with a quenching device (cold ICP) for the efficient production of biologically active agents have been recently developed for potential biomedical applications. In the present work, in vitro experiments aimed at assessing the decontamination potential of a cold ICP source were carried out on bacteria typically associated with chronic wounds and designed to represent a realistic wound environment; further in vitro experiments were performed to investigate the effects of plasma-irradiated physiological saline solution on eukaryotic cells viability. A thorough characterization of the plasma source and process, for what concerns ultraviolet (UV) radiation and nitric oxide production as well as the variation of pH and the generation of nitrates and nitrites in the treated liquid media, was carried out to garner fundamental insights that could help the interpretation of biological experiments. Direct plasma treatment of bacterial cells, performed at safe level of UV radiation, induces a relevant decontamination, both on agar plate and in physiological saline solution, after just 2 min of treatment. Furthermore, the indirect treatment of eukaryotic cells, carried out by covering them with physiological saline solution irradiated by plasma, in the same conditions selected for the direct treatment of bacterial cells does not show any noticeable adverse effect to their viability. Some considerations regarding the role of the UV radiation on the decontamination potential of bacterial cells and the viability of the eukaryotic ones will be presented. Moreover, the effects of pH variation, nitrate and nitrite concentrations of the plasma-irradiated physiological saline solution on the decontamination of bacterial suspension and on the viability of eukaryotic cells subjected to the indirect treatment will be discussed. The obtained results will be used to optimize the design of the ICP source for an effective production of reactive species, while keeping effluent temperature and UV radiation at values compatible with biomedical treatments.

Special Issue on Perspectives on Thermal Plasma Research for Industrial Applications: Introduction

Thermal plasmas have very useful properties that are not easily achievable using other means, in particular high power densities, high temperatures, high-velocity flows, high fluxes of active species and intense radiative emission. Moreover they are available in a wide range of configurations (direct-current transferred arcs, direct-current non-transferred arcs or plasma torches, alternating-current arcs, radio-frequency inductively-coupled plasmas, microwave plasmas and laser-produced plasmas) and powers (from hundreds of watts to a hundred megawatts). It is therefore not surprising that they find application in many industrial processes, including those for joining, melting, cutting, coating and deposition, refining, waste treatment, chemical analysis, lighting, propulsion and circuit interruption. It is these many applications that underlie all thermal plasma research; even when arcane questions such as the extent of deviations from local thermodynamic equilibrium in an arc are being investigated, the ultimate goal is to develop better thermal plasma processes for industry. This special issue brings together eight articles written by leading researchers from universities, industry and government research laboratories, presenting their perspectives on particular aspects of thermal plasma research. Each author was asked to present their views on important topics for research and development, outstanding scientific questions, and barriers to future success. The aim is not to present a comprehensive overview of the subject. Rather, the intention is that the special issue will guide researchers towards the important topics that warrant their close attention, and that are critical for future progress in the field. Three of the articles take a wider view, looking at thermal plasma sources, diagnostics and modelling respectively, across a range of applications. The first article considers plasma torches and inductively-coupled plasmas in particular, the second looks mainly at diagnostics of transferred arcs, while the third examines modelling issues that relate to

Thermal Plasma Sources: How Well are They Adopted to Process Needs?

Thermal plasma devices have evolved over the years from an aerospace R&D tool for the simulation of re-entry of space vehicles into powerful sources for a wide range of applications including materials processing, nano-powder synthesis and deposition of functional coatings, waste treatment and biomass gasification. With the development of full scale industrial applications, it is increasingly apparent that the plasma source is an integral part of the process, and that the success of a technology depends to a large extent on the way the plasma source satisfies the process needs. In this paper, a short review is presented of a selected number of commercially available plasma sources that are using DC and/or RF inductively coupled plasma torch technologies.

Using Helium-Generated Cold Plasma to Control Infection and Healing

Cold atmospheric pressure plasma has been proposed for sterilization of inert surfaces and disinfection of living tissues. Our recent studies reveal that chemically active species such as reactive oxygen species generated by a low-power atmospheric pressure non- thermal plasma source obtained by ionizing helium gas mixed with ambient air are mandatory for their antimicrobial effects. In addition, they also initiate intracellular signaling pathways required for wound healing in eukaryotic cells. Thus, exposure to plasma sustains healing of tissue injuries both indirectly through microbicidal effects and directly by action on cells such as fibroblasts involved in tissue regeneration.

Thermal plasma source for processing of MoO3 crystals

Simple original technique for fabrication of molybdenum trioxide MoO3 crystals during electric arc discharge directly from metallic molybdenum was proposed. The vertically oriented free-burning arc was ignited between the end surfaces of metallic molybdenum non- cooled electrodes. Molybdenum oxide crystals were deposited on side surface of bottom electrode (anode). Observation of crystals formation zone was used for determination of main process stages. The resulting products were studied by X-rays diffraction and optical microscopy methods. Investigations indicate, that self-organizing vapor-deposition process of MoO3 crystals formation has place. The resulting product is colorless sparkling prisms and platelets, which mainly consist of orthorhombic a-MoO3 phase. Optical microscopy indicates formation of closely packed feather-like pins structures by vapor-solid process.

Active plasma layer manipulation scheme during hypersonic flight

During hypersonic flight, a vehicle experiences major difficulties in communication and heating, which are known as communication blackout and aerodynamic heating, respectively. Previously, an MHD based system is investigated to solve these difficulties using a Lorentz force which are called an ExB mitigation scheme and MHD heat shield. The capability of an MHD based system is limited by the strength of an applied magnetic field. In order to enhance an MHD effect, it is necessary to increase an electrical conductivity which can be achieved by increasing electron density through plasma source. However, most of thermal plasma sources are not suitable for aerospace applications due to the power consumption. To overcome this technical limitation, thermal ionization methods can be replaced by low-temperature plasma generation system using dielectric barrier discharge (DBD). In this study, the feasibility of a non-thermal plasma jet as a plasma source with the combination of an MHD system is investigated in hypersonic flows in terms of heat flux manipulation and signal attenuation.