Arc Plasma Torch Research Articles

Structure and Property Coating Modification by High Energy Density

The paper reviews the results of investigations of the surface layer structure and properties of type 35-L steel and commercially pure titanium modified by plasma flows (arc plasma torch with the powder blown into an arc), electro-explosive alloying of titanium specimens, and high energy electron-beam treatment performed on the vacuum electron-beam plant SOLO. It is shown that the surface treatments under review have lead to a multilayer and multi-phase structure formed by crystalline particles of sub-microsized and nanosized range, mechanical (microhardness) and tribological (wear resistance) properties of which exceed manifold that of the substrate material.

Three-dimensional simulation of an argon–hydrogen DC non-transferred arc plasma torch

Simulations of a DC non-transferred arc plasma torch operating with argon–hydrogen have been performed by using a three-dimensional model. An artificially high electrical conductivity layer is employed to allow the current passing through the low temperature region near the anode wall. A new way by using two equations to describe the current density distribution is developed. Besides, a new method for determining the location of the arc-root attachment is proposed, in which the minimum total heat transfer rate through the anode wall is considered as the criterion for the lowest energy loss. Based on this criterion, the real arc core radius and length are predicted. Moreover, the influences of arc current and mass flow rate on the plasma arc characteristics are also investigated. The results obtained show that the location of the arc-root attachment predicted by the minimum total heat transfer rate principle is in good agreement with the previous work and the experimental data. Additionally, it is found that arc length can be reduced by increasing current or decreasing flow rate. Also, higher current and flow rate lead to higher temperature and velocity inside the plasma torch.

Development of a Submerged Thermal Plasma Process for Combustion of Organic Liquid Waste

A process for the destruction of organic liquid waste has been developed in which a nontransferred arc plasma torch is operated with oxygen as the plasma gas; the originality of this process is that the plasma jet composed by the plasma forming gases and the combustion products is immersed in an aqueous solution: the objective is to convert the organic fraction into CO2 and H2O, to condense the H2O, and to trap in solution the mineral content of the waste. In addition to maintain the process at room temperature, the solution also ensures most of the functions of an off-gas treatment system: cooling, filtration, and neutralization. We describe the development of the experimental setup developed on the basis of extended test results, with particular attention to the head-end stages of the torch designed to improve the combustion efficiency. The results presented here are focused on incineration of a mixture of tributylphosphate and dodecane: mineralization rate is better than 99 % and phosphorus capture is better than 98 %.

Identification of Coherent Flow Structures in Nonequilibrium Plasmas

Nonequilibrium atmospheric-pressure plasmas are at the core of a broad range of energy, medical, environmental, and manufacturing applications. The analysis of coherent flow structures is used in diverse areas of fluids engineering for the study of complex flows, and can lead to greater understanding of nonequilibrium plasma flows, particularly of the dynamics of their degree of thermodynamic nonequilibrium. Three different coherent structure identification criteria are used to analyze simulation results of the flow dynamics from an arc plasma torch obtained using a thermodynamic nonequilibrium model. The results reveal some of the possibilities and challenges of the studied criteria for the analysis of nonequilibrium discharges.

Carbon nanotube surface modification with the attachment of Si nanoparticles in a thermal plasma jet

The nanocomposite of carbon nanotube and silicon is a promising anode material for a high-capacity lithium-ion battery, because it can improve electrode performance by decreasing the pulverization and swelling of the electrode. In this work, the nanocomposite of multiwalled carbon nanotube and silicon (MWCNT–Si) was synthesized by attaching silicon nanoparticles to the surface of MWCNT in a thermal plasma jet generated from a nontransferred arc plasma torch. The effects of the input power of plasma, the injection position of Si feedstock, and the mass ratio of silicon to MWCNT on the characteristics of nanocomposite were examined. The structure of the nanocomposite and the chemical species in the product were analyzed by electron microscopy and X-ray diffraction, respectively. Although a small amount of SiC was found, MWCNT–Si nanocomposite was synthesized at a relatively high input power. The size and content of silicon nanoparticles in MWCNT–Si nanocomposites were controllable by changing the mass ratio of silicon to MWCNT raw materials. On changing the silicon feedstock injection position, MWCNT–Si nanocomposite was found when the feed position of silicon was at the inside of plasma torch due to the high heat flux and the long residence time.

Axial evolution of radial heat flux profiles transmitted by atmospheric pressure nitrogen and argon arcs

Axial evolutions of radial heat flux profiles in argon and nitrogen plasma jets from an atmospheric pressure dc non-transferred arc plasma torch are determined using a double calorimetric technique. Results are presented for power levels suitable for the processing of high temperature ceramic oxides, where the heat flux data reported in the literature is rare. Variations of the profile widths and profile maxima are presented as a function of axial distance as well as power. Relatively uniform profile width over prolonged axial distance for nitrogen plasma compared to argon is an important observation which has the potential to offer a much longer dwell time of the injected particles inside the plasma, avoiding the problem of unmelts, especially for ceramics. A comparative study of the heat flux profiles for argon and nitrogen plasma is presented. The obtained results are compared with the data reported in literature.

Zircon dissociation in air plasma through a low power transferred arc plasma torch

Thermal plasma dissociation offers a convenient and attractive route to prepare zirconium oxide from zircon mineral. Transferred and non-transferred arc plasma torches have been used to study zircon dissociation. The major thrust has been to accomplish complete dissociation and make the process simpler and cost effective. Technologically, this has been attempted in argon-fired plasma reactors using higher electrical power. The present work reports a cost effective low power transferred arc plasma (TAP) processing method for dissociating zircon by using air as the plasma forming gas. Phase composition and microstructure formation of the dissociated zircon were examined by XRD and SEM with EDX. Experimental results showed that the torch input power and processing time strongly influenced the dissociation percentage as well as the microstructure formation. Further, obtained results revealed that the air plasma medium significantly improved the percentage of zircon dissociation rather than argon plasma medium at 10 and 15kW power levels. The air plasma gives complete zircon dissociation at 10kW power with 5min of processing.

Nanocarbon structures formed in a universal plasma reactor

The results of an instrumental study of a deposit formed on the electrodes of an arc plasma torch with propane-butane mixture feeding into the interelectrode gap are presented. The optical, electron, and Raman microscopy techniques have been used in the study. According to Raman spectra, the cathode deposit contains various forms of nanocarbon. It has been found that maleic anhydride is synthesized and covalently grafted to nanographite in the absence of a specialty catalyst during plasma torch operation. Having a large specific surface area, the nanocarbon itself acts as a heterogeneous catalyst in this case. It has been shown that an arc plasma torch of this design with a hydrocarbon feed gas can be considered a mini-reactor for synthesis of different forms of nanocarbon, its surface modification, and alteration of physicochemical properties.

High-rate homoepitaxial growth of CVD single crystal diamond by dc arc plasma jet at blow-down (open cycle) mode

Abstract Growth and applications of large size high quality single crystal diamond is one of the most significant progresses in the field of CVD diamond film research ever made in the past 15 years. However, up to now most of the works were done by microwave plasma CVD operating at high pressures. In the present investigation it is demonstrated that relatively high quality single crystal diamond layer with the FWHM of the diamond Raman peak of less than 2 cm− 1 and the FWHM of the diamond (400) reflection X-ray Rocking Curve of 0.028° can be obtained by the 20 kW dc arc plasma jet operating at blow down (open cycle) mode at a growth rate as high as 36 μm/h. The reason why dc arc plasma jet is also suitable for high quality epitaxial growth of single crystal diamond is that very high concentration of atomic hydrogen can be easily provided by the extremely high gas temperature due to the arc discharging. Detailed results on the effects of the ratio of H2/Ar, the distance between the substrate to the anode nozzle of the arc plasma torch, the concentration of methane, and the substrate temperature on the growth of single crystal diamond are presented, and discussed comprehensively, and compared to that with the MWCVD, and with our previous work on the 30 kW dc arc plasma jet operating at arc root rotation and gas recycling mode.

Diagnostic methods used for atmospheric pressure thermal arc plasma

Diagnostic methods used for atmospheric pressure thermal arc plasmas are presented in this paper. An experimental direct current arc plasma torch was used as a source for plasma generation at atmospheric pressure. Overheated water vapor was employed as a plasma-forming gas with an admixture of argon as a shielding gas. A couple of plasma diagnostic methods were invoked to perform the analysis of the generated plasma jet at the nozzle exhaust of the torch. Firstly, an optical emission spectroscopy method was used to determine the chemical composition of the water vapor plasma, and from the obtained spectra, the rotational and excitation temperatures were calculated roughly. Secondly, an enthalpy probe measurement was performed in order to measure the mean temperature and the velocity lengthwise and crosswise in the plasma stream.

Inertization of Heavy Metals Present in Galvanic Sludge by DC Thermal Plasma

Galvanic sludge results from the treatment of effluents generated by the industrial metal surface treatment of industrial material, which consists in the deposition of a metal on a surface or a metal surface attack, for example, electrodeposition of conductors (metals) and non conductive, phosphate, anodizing, oxidation and/or printed circuit. The treatment proposed here is exposure of the galvanic sludge to the high temperatures provided by thermal plasma, a process which aims to vitrify the galvanic sludge and render metals (iron, zinc, and chromium) inert. Two different plasma reactors were assembled: with a DC transferred arc plasma torch and with a DC nontransferred arc plasma torch. In this way it was possible to verify which reactor was more efficient in the inertization of the metals and also to investigate whether the addition of quartzite sand to the sludge influences the vitrification of the material. Quantification of water content and density of the galvanic raw sludge were performed, as well as analyzes of total organic carbon (TOC) and identify the elements that make up the raw sludge through spectroscopy X-ray fluorescence (XRF). The chemical composition and the form of the pyrolyzed and vitrified sludge were analyzed by scanning electron microscopy with energy-dispersive X-ray spectrometer (SEM-EDS) analysis, which it is a analysis that shows the chemical of the sample surface. The inertization of the sludge was verified in leaching tests, where the leachate was analyzed by flame atomic absorption spectroscopy (FAAS). The results of water content and density were 64.35% and 2.994 g.cm(-3), respectively. The TOC analysis determined 1.73% of C in the sample of galvanic raw sludge, and XRF analysis determined the most stable elements in the sample, and showed the highest peaks (higher stability) were Fe, Zn, and Cr. The efficiency of the sludge inertization was 100% for chromium, 99% for zinc, and 100% for iron. The results also showed that the most efficient reactor was that with the DC transferred arc plasma torch and quartzite sand positively influenced by the vitrification during the pyrolysis of the galvanic sludge.

Characterization of the surface topography of arc-treated aluminum alloys by fractal geometry

Abstract An atmospheric pressure plasma arc discharge creates a complex structure on an aluminum (Al) surface that is a challenging task to characterize by conventional techniques. The solution could be in applying the principles of fractal geometry to characterize the arc-treated aluminum surface while studying profiles obtained by an optical profilometer and SEM (scanning electron microscope) images. The fractal dimension (FD) is determined along with the other conventional surface characteristic parameters (Ra, Rq, Sa, and Sq). The influence of the arc process parameters such as the arc current (I) and plasma torch velocity (v) on the fractal dimension is explored.

Wettability characterization and adhesion enhancement of arc-treated surface of aluminum alloys

The aim of this study is to determine the wettability-enhancing effects of an atmospheric pressure, direct current (DC) plasma arc discharge on the surface of aluminum alloys. Wettability is a critical factor in engineering applications such as biomedical implants, painting, and adhesive bonding. For example, in the realm of adhesive bonding, greater wettability improves a metal substrate's attraction to an adhesive material and results in a higher bond quality. In this study, the contact angle was determined and compared as a measure of the wettability using two different techniques: the sessile drop and the ballistic deposition with water as a test liquid. The effect of different arc discharge process parameters on the wettability, including arc current and plasma torch velocity, was studied. A two-dimensional finite element analysis based on the volume-of-fluid model was carried out to explore the behavior of droplet (e.g., spreading and stabilization) on an ideal surface. Additionally, the values of the dynamic receding contact angle were measured through the simulation by applying the tilted plate method and considering the surface roughness to compare the results with the values obtained from the ballistic deposition method. Studying the wettability alteration of the surface of aluminum alloys subjected to the arc treatment revealed the wettability reduction over time. Additionally, it was found that there was a linear correlation between the contact angle value and the strength of adhesively bonded joints using two structural adhesives. The results of this study in the wettability modification of aluminum subjected to the arc treatment and wettability alteration of the treated substrate over time may be used as a quality assurance tool to design the production process and achieve the desired quality and strength in adhesively bonded joints.

Alternating current-driven non-thermal arc plasma torch working with air medium at atmospheric pressure

This work is devoted to the investigation of the discharge characteristics of high-frequency alternating current (ac) plasma torch working with air medium using electrical and spectroscopic techniques. A simple structure and compact ac plasma torch associated with a resonance power supply allows the generation of low power discharges (lower than 1 kW) with high voltage and low current. The discharge shows a negative resistance characteristic, and its curve shifts up with gas flow increased. The effects of power on the emission intensity of NO (A 2Σ+ → X 2Π), OH (A 2Σ → X 2Π, 0–0), N2(C 3Πu → B 3Πg), Hα and O and their spatial distributions in plasma jet axial direction were investigated. It has been found that the emission intensities of NO, OH, N2, Hα and O rise with an increase in power dissipation. With increasing axial distances of plasma jet from nozzle exit, the emission intensity of OH increases and then decreases, while the emission intensities of other species decrease sharply. The vibrational temperature is much higher than the gas temperature, which demonstrates the ac-driven arc discharge deviation from thermal equilibrium plasma.

Employment of boron-doped carbon materials for the anode materials of lithium ion batteries

Abstract Plasma carbon and boron-doped carbons are prepared by gas phase synthesis technique using a plasma arc torch apparatus. The effects of boron doping on the microstructure and electrochemical performance are investigated. Transmission electron microscopy results indicate that crystalline graphitic sheets are formed when the content of boron in the carbon is higher than around 1.00 wt.% X-ray diffraction (XRD) and Raman analysis also reveal that the increased amount of boron doping results in decreased interlayer spacing and increased crystallite size of the boron-doped carbons. The boron-doped carbons exhibit not only higher reversible capacity, but also better rate capability than undoped plasma carbon, due to the formation of nano-structured carbon composite composed of both spherically shaped amorphous (hard carbon-like) and paper-shaped crystalline (graphite-like) phases. The reversible capacity remained over 390 mAh g −1 even after 200 cycles at a current density of 300 mA g −1 for the 1.00 wt.% boron-doped carbon.

Detoxifying PCDD/Fs and heavy metals in fly ash from medical waste incinerators with a DC double arc plasma torch

Medical waste incinerator (MWI) fly ash is regarded as a highly toxic waste because it contains high concentrations of heavy metals and dioxins, including polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Therefore fly ash from MWI must be appropriately treated before being discharged into the environment. A melting process based on a direct current thermal plasma torch has been developed to convert MWI fly ash into harmless slag. The leaching characteristics of heavy metals in fly ash and vitrified slag were investigated using the toxicity characteristic leaching procedure, while the content of PCDD/Fs in the fly ashes and slags was measured using method 1613 of the US EPA. The experimental results show that the decomposition rate of PCDD/Fs is over 99% in toxic equivalent quantity value and the leaching of heavy metals in the slag significantly decreases after the plasma melting process. The produced slag has a compact and homogeneous microstructure with density of up to 2.8 g/cm3.

Computational study of flow dynamics from a dc arc plasma jet

Plasma jets produced by direct-current (dc) non-transferred arc plasma torches, at the core of technologies ranging from spray coating to pyrolysis, present intricate dynamics due to the coupled interaction of fluid flow, thermal and electromagnetic phenomena. The flow dynamics from an arc discharge plasma jet are investigated using time-dependent three-dimensional simulations encompassing the dynamics of the arc inside the torch, the evolution of the jet through the discharge environment, and the subsequent impingement of the jet over a flat substrate. The plasma is described by a chemical equilibrium and thermodynamic nonequilibrium (two-temperature) model. The numerical formulation of the physical model is based on a monolithic and fully coupled treatment of the fluid and electromagnetic equations using a variational multiscale finite element method. Simulation results uncover distinct aspects of the flow dynamics, including the jet forcing due to the movement of the electric arc, the prevalence of deviations between heavy-species and electron temperatures in the plasma fringes, the development of shear-flow instabilities around the jet, the occurrence of localized regions with high electric fields far from the arc, and the formation and evolution of coherent flow structures.

High Speed Video Camera and Electrical Signal Analyses of Arcs Behavior in a 3-Phase AC Arc Plasma Torch

A 3-phase AC plasma torch has been developed and aims at overcoming some limits of the classical DC torches in terms of efficiency, cost and reliability. However, the arc behavior in 3-phase plasma torch remains poorly explored. This paper is dedicated to the high speed video camera at 100,000 frames per second and electrical signal analyses of arcs behavior in a 3-phase AC arc plasma torch. First, a reference case at 150 A, in nitrogen as working gas, has been deeply analyzed. Afterwards, a parametric study based on current and inter-electrode gap has been carried out. Results show that only one arc can exist at a given time and arcs rotate by switching from a pair of electrodes to another one, following the maximal electrical gap potential. However, a particular “abnormal” arc behavior was sometimes observed. Indeed, the arc motion within the inter-electrode gap increases the heat exchange and stabilizes the 3-phase discharge whereas the system is unbalanced when the arc is in the periphery. The analysis highlights that the arc motion is strongly influenced by the electrode jet velocity and repulsive Lorentz forces. The parametric study shows that the current increases both jet velocity and arc discharge stability. Elsewhere, the increase of the inter-electrode gap can also stabilizes the electrical 3-phase arc discharge. Furthermore, the correlation between arc motion and current waveform is highlighted. This work is likely to open the way toward a better understanding of 3-phase discharges in the perspective of their further optimization.

High-Enthalpy Plasma Facility for Fusion Plasma Material Interaction Studies

A high-enthalpy plasma facility with 0.4 MW power level has been constructed at Chonbuk National University in Korea. A segmented arc plasma torch was adopted as a plasma source for this facility. It is designed to have high thermal efficiency and long life in the production of supersonic plasma flow with enthalpy above 13 MJ/kg at a velocity of Mach 3. Diagnostic systems include enthalpy probe with mass spectrometer for the measurement of enthalpy, plasma composition and plasma temperatures, and heat flux probe for the measurement of heat flux. Visualization systems such as a pyrometer, a fast camera and an emission spectroscopy have been installed to monitor the surface temperature of the substrate, the plasma density and flow patterns.

Numerical design study on a high-powered segmented-type arc plasma torch for a high-enthalpy supersonic plasma wind tunnel

As a high-powered plasma source to produce a specific enthalpy higher than 20 MJ/kg at an air flow rate of 50 g/s for a supersonic plasma wind tunnel, a segmented-type arc plasma torch with an input power level of MW class is characterized in this paper. For this purpose, a numerical parametric study was carried out to determine the main design parameters, such as, the constrictor length LC, the diameter of segmented disk DC, and the diameter of the electrode DE, under the requirements of specific enthalpy and air flow rate. From the results of the numerical study, firstly the plasma power and specific enthalpy are found to increase with increasing LC at the expense of the torch efficiency, which is defined as the ratio of the total exit enthalpy to the plasma power. On the other hand, an increase in DC is observed to improve the torch efficiency by reducing the plasma power at a fixed arc current and gas flow rate. Moreover, an increase in DE is also found to contribute to improvements in the torch efficiency and the specific enthalpy by expanding the high-temperature region of the arc plasma and decreasing plasma velocities at the torch exit. Accordingly, a scale up to MW class for obtaining a high specific enthalpy can be achieved efficiently by inserting segmented disks with relatively large diameters between enlarged electrodes and then increasing the arc currents. For example, if the length of a constrictor consisting of segmented disks with a diameter of DC = 25 mm is extended to LC = 900 mm and then the arc current is increased up to 800 A, it is predicted that a specific enthalpy of 21.2 MJ/kg can be achieved at a plasma power of 2.89 MW and an air flow rate of 50 g/s, which corresponds to a torch efficiency of 36.6%. Based on these numerical parametric study results, we expect that a segmented arc plasma torch can be designed to meet the requirements of a supersonic plasma wind tunnel, such as a specific enthalpy, air flow rate and plasma power.