Inductively Coupled Thermal Plasma Research Articles

Numerical analysis in Ar-H<sub>2</sub> coupled-coil inductively coupled thermal plasma with Si feedstock for stable operation

<span lang="EN-US">In nanopowder synthesis, the starting powder to be evaporated is infused in a plasma torch through the upper coil and the lower coil in the coupled model of inductively coupled thermal plasma (coupled-coil inductively coupled thermal plasma (ICTP)). Mixing these evaporated materials to form the coupled ICTP significantly influences the thermodynamic and transport properties. It is essential to understand these complex interactions between coupled ICTP and feedstock evaporation. This research investigated the thermal interactions between silicon raw material powder (Si) with ICTP in coupled 99%Ar/1%H<sub>2</sub> through the numerical model developed for the synthesis of Si nanopowder. The feed rate of the Si raw material was set at 0.05, 0.1, and 0.5 g/min. This implies that the increased Si feed is too heavy to vaporize all the injected feed.</span>

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.

Fabrication of zinc oxide nano-structures in RF inductively-coupled thermal plasma and their photoluminescence effects

Zinc oxide (ZnO) nanoparticles and nano-structures were synthesized using RF inductively-coupled thermal plasma system. The ZnO nanoparticles synthesized in high enthalpy plasmas showed high purity and extremely small crystalline characteristics with the (30–50) nm size distribution applicable in various areas. The resultant morphology of the ZnO nanoparticles was influenced by process parameters such as chamber pressure, a cooling method and a reactor configuration. Thus, the effects of process conditions were discussed with perspective of the re-crystallization. In addition, by controlling the operational parameters, flower-like shaped ZnO nano-structures consisting of many hexagonal nano-rods with six facets were also obtained. The ZnO nano-structures showed a good optical property in photoluminescence analysis.

Optical Emission Spectroscopy Diagnostics of Atmospheric Pressure Radio Frequency Ar-H2 Inductively Coupled Thermal Plasma

The atmospheric pressure radio frequency (RF) inductively coupled thermal plasma (ICTP) has been extensively used for many industrial processes. In order to understand the physical–chemical mechanism involved in the discharge process of ICTP, in situ optical emission spectroscopy (OES) was carried out to diagnose and determine the active particles and electron excitation temperature in this plasma. Several active particles such as Ar*, $\text{H}_{\alpha }$ , and $\text{H}_{\beta }$ were detected in the emission spectrum of Ar-H2 ICTP. Based on the Boltzmann plot method, the electron excitation temperature and thermal efficiency of ICTP were evaluated. It was obtained that the electron excitation temperatures in Ar-H2 ICTP varied from 9651.70 to 16691.91 K when the applied power was in the range of 8–15 kW, which was significantly higher than the electron excitation temperature in Ar ICTP at the same applied power. Besides, the thermal efficiency was enhanced from 17.19% for the Ar ICTP to 30.69% for the Ar-H2 ICTP. These results may be beneficial for understanding of the discharge process in atmospheric pressure Ar-H2 ICTP.

Spheroidization behavior of water-atomized 316 stainless steel powder by inductively-coupled thermal plasma

In the additive manufacturing process, fine powders having spherical shape are used due to their high flowability and packing density. When powders are produced by the water atomization method, it is advantageous to prepare fine powders, but powders having irregular shape are prepared, which is not suitable for the AM process. Therefore, in this study, 316 stainless steel powder fabricated by water atomization method were spheroidized using inductively-coupled thermal plasma. The initial water atomized 316 stainless steel powders had an irregular shape; however after spheroidization, their morphology was changed to a perfect spherical shape, which results in the drastic improvement of flowability. Examining the composition changes after spheroidizing, it was confirmed that the concentrations of oxygen and Cr were decreased. The reason for the decrease in oxygen concentration was that the temperature in the plasma process is extremely high and the oxygen partial pressure in the plasma chamber is low. The decrease in Cr concentration was caused by the evaporation of Cr during the spheroidization process, and the vapor pressure and evaporation coefficient of Cr in 316 molten liquid were calculated to analyze the reason.

Synthesis of Spherical V-Nb-Mo-Ta-W High-Entropy Alloy Powder Using Hydrogen Embrittlement and Spheroidization by Thermal Plasma

V-Nb-Mo-Ta-W high-entropy alloy (HEA), one of the refractory HEAs, is considered as a next-generation structural material for ultra-high temperature uses. Refractory HEAs have low castability and machinability due to their high melting temperature and low thermal conductivity. Thus, powder metallurgy becomes a promising method for fabricating components with refractory HEAs. Therefore, in this study, we fabricated spherical V-Nb-Mo-Ta-W HEA powder using hydrogen embrittlement and spheroidization by thermal plasma. The HEA ingot was prepared by vacuum arc melting and revealed to have a single body-centered cubic phase. Hydrogen embrittlement which could be achieved by annealing in a hydrogen atmosphere was introduced to get the ingot pulverized easily to a fine powder having an angular shape. Then, the powder was annealed in a vacuum atmosphere to eliminate the hydrogen from the hydrogenated HEA, resulting in a decrease in the hydrogen concentration from 0.1033 wt% to 0.0003 wt%. The angular shape of the HEA powder was turned into a spherical one by inductively-coupled thermal plasma, allowing to fabricate spherical V-Nb-Mo-Ta-W HEA powder with a d50 value of 28.0 μm.

Numerical parametric investigation on the temperature distribution in Ar/O2 induction thermal plasmas with Ti powder injection: Inclusion of particle evaporation

Thermal interaction between titanium feedstock powder and the thermal plasma is calculated using the developed numerical model for an inductively coupled thermal plasma (ICTP) with particle injection. The interaction between titanium powder and thermal plasmas is very important for the stable establishment of the ICTP and effective heating and evaporation of the injected particles, for example, for particle synthesis. The injected particles are heated by the thermal plasma and they melt and evaporate, contaminating the plasma and thus affecting its properties. The developed numerical model solves the mass, momentum, and energy conservation equations of thermal plasmas as well as the mass transport equation for the evaporated materials. In addition, particle motions are derived by solving the Lagrange equation of motion. The temperature distribution inside the particles and the phase transition from solid, through liquid, to gas of the particles are also taken into account. Finally, a parametric study is conducted to show the influence of the important physical parameters such as input power, sheath gas flow rate, and Ti powder feed rate. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Preparation of spherical WTaMoNbV refractory high entropy alloy powder by inductively-coupled thermal plasma

Abstract Spherical WTaMoNbV refractory high entropy alloy powders were fabricated by milling and spheroidizing using inductively-coupled thermal plasma. The WTaMoNbV alloy is brittle at room temperature; therefore, the alloy ingot could be pulverized by jaw-crushing and ball-milling, and the fabricated powders had an irregular shape. After sieving using meshes ranging in size from 25 to 63 μm, the powders were spheroidized using inductively-coupled thermal plasma. Using this process, spherical WTaMoNbV high entropy alloy powders with d50 of 45.1 μm could be fabricated successfully.

Titanium(III) Sulfide Nanoparticles Coated with Multicomponent Oxide (Ti–S–O) as a Conductive Polysulfide Scavenger for Lithium–Sulfur Batteries

In spite of the high specific capacity and energy density of Li–S batteries based on low-cost sulfur as the active material, their practical use has not yet been realized due to the undesirable formation of soluble polysulfides (PS) during electrochemical cycles and their shuttling effect. In order to minimize this serious issue caused by the active material dissolution, transition metal compounds such as oxides, nitrides, and sulfides have alternatively been used to capture the PS and also to provide electron pathways in the S electrode. However, high-performance additive materials having both high affinity to PS and high electronic conductivity have not been developed thus far. Herein, we report the preparation and application of a new additive material—titanium(III) sulfide (Ti2S3) nanoparticles covered with multicomponent (Ti–S–O) oxide (MO–Ti2S3), which can be synthesized on a large scale using an inductively-coupled thermal plasma synthesis method followed by a simple surface oxidation treatment. MO–Ti2S3 shows much higher PS affinity than other titanium compounds and electronic conductivity that is comparable to that of carbon black. Furthermore, MO–Ti2S3 shows much higher resistance to heat and oxidation while having charge–discharge stability when compared with TiS2. Finally, we show that the cyclability and specific capacity of the Li–S battery can be significantly enhanced by incorporating MO–Ti2S3 in the cathode when compared to utilizing C species.

Numerical simulation on thermal plasma temperature field in the torch for different conditions

Numerical simulation was conducted to obtain the temperature and gas flow fields in inductively coupled thermal plasma (ICTP). Influence of gas composition, power supply, quenching gas, carrier gas, pressure and frequencies were investigated on thermal plasma temperature fields. Results indicated that higher oxygen fraction in gas composition makes the shrinkage of the thermal plasmas, which increases power density in local volume. Further, an increase in the quenching gas, the carrier gas and the pressure did not affect the temperature of thermal plasma. On the other hand, the temperature in thermal plasma decreased at axial position along with degradation of frequency.

Spatiotemporal distribution of thermal plasma temperature and precursor formation in a torch during TiO2 nanopowder synthesis

The spatiotemporal distribution of Ti excitation temperature () was determined from two-dimensional optical emission spectroscopy (2D OES) during TiO2 nanopowder synthesis using an inductively coupled thermal plasma (ICTP) torch. The Ti feedstock powder was injected intermittently into the ICTP torch to elucidate the evaporation of the feedstock and the formation of atomic vapour, precursor molecules, and particle nuclei dynamically. The spectroscopic observation results revealed that was estimated as 2500–4000 K around the central axis of the ICTP torch, and more than 4500 K in the off-axis region. In the on-axis region, TiO was detected with a high radiation intensity in the lower temperature region. These results showed that TiO molecules are formed only in the low temperature region around the central axis of the ICTP torch. In addition, TiO molecular density could be high, especially in the downstream region at the central axis of the ICTP torch.

Uniform Surface Oxidation of an Si Substrate by a Planar Modulated Inductively Coupled Thermal Plasma with Molecular Gas Feed

A planar type of inductively coupled thermal plasma (ICTP) with coil current modulation was adopted for large-area rapid surface oxidation of a substrate. The planar ICTP has been developed by the authors for large-area surface modification processing. In addition, coil current modulation was used to control the temperature and chemical reaction fields in the planar ICTP. Firstly, a fundamental study of the operation of the planar modulated ICTP with a substrate was carried out by measuring its electrical properties and the visible light emission in this work. Secondly, spectroscopic observations were carried out to investigate the effect of the coil current modulation on the radiation intensity distribution of spectral lines from the planar ICTP on the substrate. Thirdly, surface oxidation tests were made for Si substrates by irradiation of the planar modulated ICTP at different modulation frequencies and different duty factors. Oxide layer thickness distribution fabricated on the substrate was measured to study the lateral uniformity of the oxidation processing by the modulated planar ICTP. Finally, it was found that adoption of the coil modulation can improve the uniformity of the oxidation processing by the planar modulated ICTP.

Fundamental study of Ti feedstock evaporation and the precursor formation process in inductively coupled thermal plasmas during TiO2 nanopowder synthesis

Two-dimensional spectroscopic observations were conducted for an inductively coupled thermal plasma (ICTP) torch during TiO2 nanopowder synthesis. The feedstock was injected intermittently into the ICTP torch to investigate the Ti feedstock evaporation process clearly and to elucidate the formation process of precursor species. Spatiotemporal distributions of Ti atomic lines and TiO spectra were observed simultaneously inside the plasma torch with the observation system developed. The observation results showed that the injected Ti feedstock was evaporated to form high-density Ti atomic vapour in the torch, and that the generated Ti atomic vapour is transported and diffused by gas flow and the density gradient. In addition, TiO molecular vapour was generated almost simultaneously around the on-axis region in the torch.

Fe–N-doped graphene as a superior catalyst for H2O2 reduction reaction in neutral solution

Fe–N-doped graphene containing 0.3at% of Fe and 1.9 of N with an active specific surface area of 77.5±4m2g−1 is synthesized in two steps: first N-doped graphene is produced by thermal dissociation of methane in an inductively coupled thermal plasma (ICP) reactor and subsequently the product is converted to Fe–N-doped graphene by a wet chemical method. The catalytic activity of this catalyst toward H2O2 reduction reaction (HPRR) is studied by rotating disk electrode for fuel cell applications. Although the mechanism of HPRR on Fe–N-doped graphene, N-doped graphene and graphene is similar, Fe–N-doped graphene shows the highest catalytic activity toward HPRR. The exchange current density based on the active surface area (j0A) of Fe–N-doped graphene in Na2SO4 solution is (4.4±0.2)×10−8Acm−2, which is 5 times greater than j0A of the N-doped graphene. Direct reduction of H2O2, H2O2 decomposition, O2 reduction, and O2 desorption are predicted as the reactions involved in the HPRR while O2 reduction and O2 desorption are negligible at low and high overpotentials, respectively. Investigation of the effect of the electrolyte and catalyst loading reveals that HPRR on Fe–N-doped graphene suffers from kinetic limitations especially at low catalyst lodgings, fast rotation rates, and strong acidic and basic solutions.

Scaled synthesis of boron nitride nanotubes, nanoribbons, and nanococoons using direct feedstock injection into an extended-pressure, inductively-coupled thermal plasma.

A variable pressure (up to 10 atm) powder/gas/liquid injection inductively coupled plasma system has been developed and used to produce high-quality boron nitride nanotubes (BNNTs) at continuous production rates of 35 g/h. Under suitable conditions, collapsed BN nanotubes (i.e., nanoribbons), and closed shell BN capsules (i.e., nanococoons) are also obtained. The process is adaptable to a large variety of feedstock materials.

Investigation of hydrogen peroxide reduction reaction on graphene and nitrogen doped graphene nanoflakes in neutral solution

H2O2 reduction reaction (HPRR) is studied on both graphene (GNF) and nitrogen doped graphene nanoflakes in 0.1 M Na2SO4 solution by rotating disk electrode. The XPS results indicate that N-doped graphene nanoflakes with high nitrogen content, 32 at%N (N-GNF32), are synthesised successfully by an inductively-coupled thermal plasma (ICP) reactor. Pyridinic, pyrrolic and graphitic N species contribute up to 67% of the total nitrogen. Kinetic parameters such as Tafel slope and stoichiometric number suggest that HPRR occurs by the same mechanism on both GNF and N-GNF32. Although nitrogen does not change the mechanism of HPRR, the results indicate that the reaction rate of H2O2 reduction is enhanced on N-GNF32. The exchange current density of H2O2 reduction based on the active surface area of N-GNF32 is (8.3 ± 0.3) × 10−9 A cm−2, which is 6 times higher than the value determined for GNF. The apparent number of electrons involved in the process suggests that H2O2 decomposition competes with H2O2 reduction on both catalysts. Evaluation of the apparent heterogeneous reaction rate constant and the Tafel slope indicate that simultaneous reduction of O2 and H2O2 is negligible on the N-GNF32. On the other hand, the reduction of O2 and H2O2 occurs simultaneously on the GNF surface.

Prompt response and durability of polymer ablation from synthetic fibers irradiated by thermal plasmas for arc resistant clothes

Interactions between thermal plasmas and synthetic fibers such as polyamide, polyester, phenol and aramid were investigated by thermal plasma irradiation technique. Understanding the above interactions is crucial to design effective flame retardant synthetic fiber clothes with arc resistance to protect a human from arc flash accidents. To investigate the interactions, an Ar inductively coupled thermal plasma (ICTP) was used instead of the arc discharge because the ICTP has high controllability and no contamination. The ICTP irradiation raises polymer ablation in case of polyamide and polyester. Two features of the polymer ablation such as prompt response and durability were fundamentally investigated from viewpoint of shielding the heat flux. It was found that polyamide fiber has both a high prompt response and a long durability.

Spallation Particle Ejection From Polymer Surface Irradiated by Thermal Plasmas

In this paper, polymer ablation phenomena are investigated by direct irradiation of an inductively coupled thermal plasma (ICTP) for a fundamental study. Polymer ablation by thermal plasmas can be seen, for example, in a low-voltage circuit breaker in which the arc plasma contacts the insulation polymer material to be ablated during the current interruption. Effective utilization of polymer ablation phenomena is expected as one technique to enhance arc quenching ability of circuit breakers. Direct irradiation of the ICTP to a polymer specimen enables us to observe the spatial distribution of polymer ablated vapor easily. In addition, we distinctively found spallation particles ejected from polyamide material.

Two-temperature non-chemical equilibrium analysis of Ar–CH 4–O 2 ICTP at reduced pressure

In present work, a two-temperature chemically non-equilibrium (2T-NCE) model has been studied for Ar–CH 4–O 2 inductively coupled thermal plasma (ICTP) at reduced pressure from the viewpoint of interaction between plasma and fuel combustion. Chemically non-equilibrium effects have been taken into account by solving mass conservation equations for each of 22 particles considering convection, diffusion and net production effects. Species density of each particle or simply particle composition was also derived from the mass conservation equation of each one taking the non chemical equilibrium effect into account. For the net production term, totally 196 chemical reactions were taken into account including dissociation, ionization and other chemical reactions and their backward reactions. Finally, heat profile due to individual reaction and the total contribution of all reactions to the heat generated has been observed.

Numerical and experimental investigations on thermal interaction between thermal plasma and solid polymer powders using induction thermal plasma technique

The interaction between thermal plasma and polymer solid powders was investigated using the inductively coupled thermal plasma (ICTP) technique. Interaction between thermal plasmas and polymers is extremely important, for example, for design of down-sized circuit breakers, because it fundamentally affects the interruption capability of the circuit breakers. The ICTP technique was used in this work because it presents the advantages of no contamination and good repeatability. Polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyethylene (PE), and polyoxymethylene (POM) were treated as polymer materials. Numerical modelling for injection of polymer solid powders into Ar thermal plasma was also made including thermal interactions between thermal plasmas and polymer powders. Results showed that PMMA-ablated vapour has a higher plasma-quenching efficiency than others; the polymer solid properties affect the plasma-quenching ability indirectly. Comparison of the calculated results with experimental results showed good agreement from the viewpoints of the spatial distribution of ablated vapour concentration and the average solid particle velocity.