Thermal Plasma Processes Research Articles

Thermal Plasma Synthesis of Li2S Nanoparticles for Application in Lithium-Sulfur Batteries

Inductively-coupled thermal plasma processes were used to produce nanosized Li2S. Prior to the syntheses, the feasibility of forming Li2S was first evaluated using FactSage by considering the phase diagrams of sulfur and different lithium precursors in reducing atmospheres; Li2O, LiOH·H2O, Li2CO3 and Li2SO4·H2O all showed promises in producing Li2S nanoparticles, as confirmed by experiments. Argon and hydrogen mixtures were used as plasma gases, and a carbothermal reduction was implemented for Li2SO4·H2O. In addition, carbon-coated Li2S nanoparticles were synthesized with downstream injection of methane. Carbon was shown to stabilize Li2S upon contact with ambient air. The Li2S nanoparticles were electrochemically tested in half-cells using electrolytes containing LiNO3 or Li2S6 as additives. It was found that adding LiNO3 to the electrolyte was detrimental to the electrochemical performance of Li2S, whereas the combination of Li2S6 and LiNO3 as additives doubled the charge and discharge capacities of the half-cell over 10 cycles.

Thermal Plasma Treatment of Medical Waste

The harmless treatments of medical waste have significantly drawn people’s attention owing to their risks to health-care staff, the public, and the environment. The traditional thermal technology for processing medical waste may cause indispensable secondary pollution such as dioxin, furan, and heavy metals, and infectious materials that may remain in the solid residual. Thermal plasma technologies offer advantages of effectively treating medical waste due to its high temperature and energy density, lower pollutant emissions, rapid start-up and shut-down, and smaller size of the installation. These benefits play roles in the treatment of medical waste on-site or off-site, especially when somewhere encounters an abnormally sharp increase in medical waste. This paper mainly introduces the typical thermal plasma processes of medical waste and its central component, plasma furnace. Meanwhile, how process parameters influence the formed gaseous and solid products, the performances of mass and volume reduction, pathogen destruction, and energy recovery, are discussed in detail. Finally, the mechanism of the thermal plasma process is also analyzed.

Carbon forms, carbide yield and impurity-driven nonstoichiometry of plasma-generated β-silicon carbide nanopowders

Silicon carbide nanopowders are chemically complex materials containing various carbon forms and impurities. The current study quantifies the chemical complexity of these nanopowders in terms of their carbide phase nonstoichiometry and yield. The investigated samples include a range of β-silicon carbide nanopowders (BET surface area = 30–160 m2 g−1) produced from thermal plasma processes. The samples were characterized as to their carbon forms (temperature-programmed oxidation, Raman spectroscopy, HRTEM), total carbon content (combustion analysis), oxygen and nitrogen contents (inert gas fusion), surface elemental composition and bonding (XPS), crystallographic phases (XRD). The nanopowders contain widely varying amounts (0.5–19%) of carbon in noncarbidic forms (free and organic). However, the carbide phase of the nanopowders is invariably carbon deficient with the C:Si atomic ratio ranging from 0.89 to 0.95. The extent of carbon deficiency is linked to the level of oxygen and nitrogen impurities that substitute for carbon in the carbide structure. The substitution scenarios involve high temperature dissolution of nitrogen into the carbide lattice and room-temperature oxidation of particle surfaces to form an amorphous oxycarbide. Uncontrolled surface oxidation and contamination by carbonaceous deposits reduce the SiC yield of the nanopowders (76–91%) from those of ultrafine and micrometer-sized counterparts. Since the majority of contamination occurs on the nanopowder surface, the yield tends to decrease with decreasing particle size. The obtained results emphasize the importance of explicit control over the chemical impurities and particle surface conditions for fabricating the stoichiometrically balanced SiC nanopowders in high yield.

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.

Modelación de una antorcha de plasma de arco no transferido

Las antorchas de plasma se usan para producir el plasma en la manufactura de materiales e industria energética, donde las antorchas de arco de corriente directa representan los componentes principales de los procesos con plasma térmico (plasma spraying, soldadura, corte de metales, tratamiento de residuos, producción de biogás, etc.). En una antorcha de plasma de arco no trasferido, se desarrolla un arco eléctrico aplicando una corriente directa entre el cátodo y el ánodo de la antorcha. Sucesivamente, el plasma se produce calentando, ionizando y expandiendo un gas alimentado a la antorcha antes de la región del cátodo. Los trabajos de laboratorio que usan técnicas de observación y de medición son de difícil aplicación, debido a las características físicas de estos fenómenos físicos. Así las técnicas computacionales pueden representar una herramienta valiosa para investigar los procesos con plasma, aunque el trabajo computacional es extremadamente desafiante, pues estos fenómenos son interdependientes y simultáneos. En este trabajo se propone un modelo computacional para simular una antorcha de plasma bidimensional de arco no trasferido en equilibrio termodinámico local. Se modelan condiciones de estado estacionario para las ecuaciones de conservación de mecánica de fluidos, trasferencia de calor y electromagnetismo en el software Comsol Multiphysics® 5.1. En la trasferencia de calor por radiación, el plasma se asume ópticamente fino y con un coeficiente de emisión neta. El flujo laminar de gas se modela con vórtice libre en la entrada para dos tipologías de antorchas axis-simétricas, respectivamente con argón y nitrógeno como gases de trabajo.

Plasma-Assisted Biomass Gasification with Focus on Carbon Conversion and Reaction Kinetics Compared to Thermal Gasification

Compared to conventional allothermal gasification of solid fuels (e.g., biomass, charcoal, lignite, etc.), plasma-assisted gasification offers an efficient method for applying energy to the gasification process to increase the flexibility of operation conditions and to increase the reaction kinetics. In particular, non-thermal plasmas (NTP) are promising, in which thermal equilibrium is not reached and electrons have a substantially higher mean energy than gas molecules. Thus, it is generally assumed that in NTP the supplied energy is utilized more efficiently for generating free radicals initiating gasification reactions than thermal plasma processes. In order to investigate this hypothesis, we compared purely thermal to non-thermal plasma-assisted gasification of biomass in steam in a drop tube reactor at atmospheric pressure. The NTP was provided by means of gliding arcs between two electrodes aligned in the inlet steam flow with an electric power of about 1 kW. Reaction yields and rates were evaluated using measured gas temperatures by the optical technique. The first experimental results show that the non-thermal plasma not only promotes the carbon conversion of the fuel particles, but also accelerates the reaction kinetics. The carbon conversion is increased by nearly 10% using wood powder as the fuel. With charcoal powder, more than 3% are converted into syngas.

Optical Emission Spectroscopic Study of the Synthesis of Titanium Boride Nanoparticles in RF Thermal Plasma Reactor

Thermal plasma processes have been investigated by optical emission spectroscopy during the synthesis of TiBx nanoparticles from TiO2, B and C precursors using argon and helium both as plasma and sheath gases. Line-rich emission spectra were observed both in Ar–He–TiO2–B and Ar–He–TiO2–B–C cases. Emissions detected in the spectral region of 300–1000 nm were attributed to the electronic relaxation of excited Ti(I) and ionic fragments Ti(II), as well as the molecular species of TiO. The plasma temperature was calculated from the vibration–rotation temperature of the A–X electronic transition of TiO molecule by the least-squares fitting of experimental data to theoretical spectra. The temperatures at 100 mm downstream the torch outlet were found to be between 3800 and 2700 K for the Ar–He–TiO2–B system, and between 5100 and 4300 K for the Ar–He–TiO2–B–C system, respectively. The morphology of as-formed nanoparticles was characterized by transmission electron microscopy. Measurements of specific surface area, evaluated on the basis of Brunauer, Emmett and Teller equation, revealed that in all experimental setups titanium boride nanoparticles were formed with a mean particle size of 17–85 nm. On the basis of X-ray diffraction patterns, the solid reaction products were composed of TiB2, boron doped titanium indicated as Ti(B), Ti2O3, H3BO3 and TiC. The actual composition of products depended on the synthesis conditions.

Special Issue on Numerical Modelling of Low‐Temperature Plasmas for Various Applications – Part I: Review and Tutorial Papers on Numerical Modelling Approaches

Special Issue on Numerical Modelling of Low‐Temperature Plasmas for Various Applications – Part I: Review and Tutorial Papers on Numerical Modelling Approaches

A Simulative and Experimental Approach for the Design and Optimization of Atmospheric Pressure Low Power RF Thermal Plasma Processes

Based on the comparison of simulative and experimental data, an approach is presented for the design and optimization of processes assisted by low power atmospheric pressure Radio Frequency (RF) thermal plasmas. High Speed Imaging (HSI), Schlieren Imaging (SI), and temperature measurement on the surface of the substrate are performed to characterize the effect of the interaction of the RF torch effluent with a substrate placed downstream of the torch outlet. The related processes are simulated in 2‐D axisymmetric and 3‐D domains for different operating conditions, for the plasma generation region and for the downstream region, respectively. The comparison of numerical and experimental results is used to in depth characterize and investigate the behavior of the effluent of the RF torch.

Modeling of Thermal Plasma Processes: The Importance of Two‐Way Plasma‐Surface Interactions

Most thermal plasma applications involve interactions between the plasma and solid or liquid surfaces. Computational models of thermal plasma applications typically consider the influence of the plasma on the surface, but often neglect the effect of the surface on the plasma. In many cases, however, it is not possible to accurately model the plasma process without taking the two‐way interactions into account. This is demonstrated using examples from arc welding, plasma cutting, plasm­a‐particle interactions, such as occur in plasma spheroidization, plasma nanoparticle production and plasma spraying, and high‐ and low‐voltage circuit breakers. Vaporization of metal, ceramic and polymer surfaces, transfer of heat and momentum from the plasma to particles and droplets, and changes in the surface shape are all shown to affect the properties of the plasma.

Titanium and zirconium metal powder spheroidization by thermal plasma processes

Titanium and zirconium metal powder spheroidization by thermal plasma processes

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

Liquid and solution treatment by thermal plasma: a review

During two last decades, numerous technologies and approaches are presented for treating contaminants in liquids and solutions. Among them, thermal plasma has shown rapid kinetic and high destruction efficiencies due to very high temperature and highly active radicals. Hence, the use of thermal plasma for treatment of the contaminants in liquids and solutions has received a lot of attention in view of its low environmental impacts. This review focuses on thermal plasma, and it describes the current status of liquid and solution treatment using this technology. A comprehensive analysis of the available scientific and technical literature on liquid and solution plasma treatment is presented, including the treatment of a variety of contaminants in liquids and solutions via different kinds of thermal plasma. The principles of thermal plasma generation and the available plasma technologies with potential applications to generate valuable products from liquid waste are presented. In addition, the results of the thermal plasma processes for the treatment of specific contaminants are investigated. In light of the investigated literature, thermal plasma is found to have a significant potential to treat the liquid wastes.

Transport Coefficients of Ar/C/H/O/N Systems Thermal Plasma at Atmospheric Pressure

The transport coefficients of thermal plasma composed of Ar/C/H/O/N elements are presented in the temperature range from 1000 to 15000 K. Several chemical composition calculations with different proportions of the elements lead us to retain 35 major species. We have characterized 595 interactions the between these species and derived the collision integrals necessary for the calculation of transport coefficients by Chapman-Enskog method. The following approximation orders have been used: 3rd for electrical conductivity and electrons translation thermal conductivity, 2nd for heavy particles translation thermal conductivity and 1st for viscosity, reaction and internal thermal conductivity. The development of thermal plasma processes lead to the use of plasma gases or gases mixtures more and more complexes. If data concerning the transport coefficients of simple gases like argon, hydrogen, oxygen or nitrogen or some binary mixtures like argon-hydrogen, argon-oxygen or oxygen-nitrogen can be early found in literature, those concerning ternary mixtures or more are not available. Ar/H/O and N brought together and C is added permitting to take into account hydrocarbons. First ours results for simple gases or gases mixtures are compared with recently published data of the literature and finally we present the transport coefficients of oxygen-nitrogen-methane, and argon-steam mixtures.

Volatile Compounds Present in Carbon Blacks Produced by Thermal Plasmas

Carbon black nanopowders were produced using two thermal plasma processes based on DC, respectively ICP plasma torches. Although the produced particles were in the nanometer size range, the values obtained for the surface area of the particles using a Brunauer Emmett Teller technique were very small. This indicated the presence of contaminants in the experimental powders, as confirmed by Raman spectroscopy and thermogravimetric Analysis. A thermal treatment process was developed in order to extract these volatile compounds, which were then identified using a Gas Chromatography–Mass Spectrometry method. The experimental powders were analyzed using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy before and after the thermal treatment in order to determine the effect of the heat treatment on the powder structural properties.

Plasma generators for thermal plasma processes

Abstract An overview is given of Plasma Generators developed with the focus on application in thermal spraying, some of which might even find use in other thermal plasma processes. The construction and operation principle of conventional plasma torches as well as of plasma torches with special features are presented. The particular properties and application potential of the innovative plasma generator types “Triplex”, “Delta” and “Large”, each operating with new physical principles, are discussed.

Thermal Plasma Processes for Production of Hollow Spherical Powders: Theory and Experiment

Present paper considers processes of production and treatment of hollow particles in plasma flows. Specifics of agglomerated powders treatment and expansion of hollow droplets are analyzed theoretically. Experimental results on production of hollow micro particles of ZrO2, Ni, CoNiCrAlY alloy, SiO2 are shown here.

Titanium Oxide Film Deposition on Acrylic Resin by Atmospheric TPCVD

A dye-sensitized solar cell (DSC) is a solar cell that uses an anatase film as a photovoltaic device. Since the anatase film and dye play the roles of electron carrier and electron generator, respectively, in the DSC, porous anatase films are desirable. In this paper, in order to develop a low-cost fabrication process for the photovoltaic device of the DSC, photocatalytic titanium oxide film deposition was carried out by atmospheric thermal plasma CVD. Ar gas, which served as the working gas for the plasma jet and substrate, and a 20 × 40 × 3 mm transparent acrylic resin plate were used. Titanium tetra iso butoxide was used as feedstock. Consequently, by cooling the substrate, an anatase-dominant film could be deposited at 773 K in deposition temperature without meltdown of the substrate on the condition of 100 mm in deposition distance, even in the case of acrylic resin substrate use. By wettability and methylene-blue decoloration tests, it was confirmed that the film showed hydrophilic and decolored methylene blue perfectly by 8-h UV irradiation. Furthermore, the DSC in which the titanium oxide film deposited by this technique was included as a photovoltaic device generated a photoelectromotive force of 25 mV. From these results, these thermal plasma processes were found to have high potential for DSC fabrication.

Arc Plasma Torch Modeling

Arc plasma torches are the primary components of various industrial thermal plasma processes involving plasma spraying, metal cutting and welding, thermal plasma CVD, metal melting and remelting, waste treatment and gas production. They are relatively simple devices whose operation implies intricate thermal, chemical, electrical, and fluid dynamics phenomena. Modeling may be used as a means to better understand the physical processes involved in their operation. This paper presents an overview of the main aspects involved in the modeling of DC arc plasma torches: the mathematical models including thermodynamic and chemical non-equilibrium models, turbulent and radiative transport, thermodynamic and transport property calculation, boundary conditions and arc reattachment models. It focuses on the conventional plasma torches used for plasma spraying that include a hot-cathode and a nozzle anode.

Thermodynamic and transport properties in non-equilibrium argon, oxygen and nitrogen thermal plasmas

Thermal plasma processes and devices have been extensively studied and designed using modeling approach in the last two decades. Still, knowledge of thermodynamic and transport properties is one of the major needs in the modeling of thermal plasma processes. Computation of these properties is usually carried out through the approximated solution of the Boltzmann's equation using the Chapman–Enskog's method. While local thermodynamic equilibrium (LTE) was assumed in the past calculations, the development and use of more sophisticated plasma diagnostics have shown that this assumption often fails in thermal plasmas: for thermal non-equilibrium plasmas, the kinetic electron temperature T e is then assumed to be different from that of heavy species T h, chemical equilibrium being achieved. Non-equilibrium thermodynamic and transport property calculations of argon, nitrogen and oxygen plasmas at atmospheric pressure for electron temperature up to 45,000 K are here presented. Transport properties have been obtained using numerical codes developed by the authors which implement the Devoto's electron and heavy particles decoupling approach. Variation of composition, specific volume, specific enthalpy, specific heat, thermal conductivity, electrical conductivity and viscosity as a function of electron temperature and different degrees of non-equilibrium are reported. Results are compared with available data from published reports to check the accuracy of the developed codes.