Arc Plasma Torch Research Articles

TO HIGHLY PRODUCTIVE SYNTHESIS OF ALUMINUM NANOPARTICLES IN PLASMA FLOW AT ATMOSPHERIC PRESSURE

Purpose. To study the highly productive evaporation of aluminum micron powder in an atmospheric pressure plasma jet for the synthesis of nanoaluminum. Using special plasma technology, nanoparticles can be produced by rapid melting and evaporation of the initial micrometer particles and their subsequent re-nucleation. Research methods. Methods of mathematical and computer modeling of subsonic plasma turbulent jets at atmospheric pressure and experimental studies of two-phase processes during thermal plasma treatment using an arc plasma torch. Results. Based on computer modeling, a special reactor system was designed and developed, which includes a plasma-jet reactor with an electric arc plasma torch for the synthesis of aluminum nanoparticles. Numerical modeling makes it possible to determine the position of the melting point, evaporation and crushing of a molten particle, the evolution of the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the crushing point. An experimental test of the operation of the reactor system was carried out using arc plasma torches with a power of 30 and 150 kW. It has been shown that intensifying the fragmentation of dispersed raw materials in a plasma jet can be useful in technologies for producing nanomaterials. The consequence of the fragmentation process is the redistribution of the fractional composition of the powder along the plasma jet and the accompanying changes in the dynamics of movement, heating and evaporation of particles. It has been determined that when the temperature of the largest aluminum particles reaches 2500 C, the total amount of evaporated mass is theoretically equal to 100%. The main parameters influencing the behavior of particles in a plasma jet are particle diameter, powder injection rate, flow rate, temperature and composition of the plasma gas. Taking these parameters into account will allow the process to operate at increased productivity. Scientific novelty. A mathematical description of the process of fragmentation a polydisperse powder, based on a continuum approach, has been obtained, which makes it possible to determine the position of the crushing point of a molten particle, the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the point of crushing and evaporation. It was shown for the first time that it is possible to carry out a process in which complete evaporation of a molten drop is achieved due to the high enthalpy of the plasma before the end of mixing with steam. Practical value. A special reactor system has been designed and developed, which includes a plasma-jet reactor with an electric arc plasmatron for the synthesis of aluminum nanoparticles. The operating parameters of the reactor system have been determined, which will allow the synthesis of aluminum nanoparticles to be carried out with high productivity.

Controllable preparation of YSZ-STHS in arc plasma spheroidization: Exploring the plasma flow characteristics' impact on powder quality

Yttria-stabilized zirconia hollow spherical powder (YSZ-HOSP) is a widely utilized ceramic material in thermal barrier coatings (TBCs). Within the category of YSZ-HOSP, yttria-stabilized zirconia spherical thin-walled hollow-shell powder (YSZ-STHS) displays immense potential for producing TBCs with minimal inter-lamellar porosity and cracks. Arc plasma torch equipped with flow-shaping nozzle shows promise for preparing YSZ-STHS. However, there is limited research on the impact of the nozzle geometry on plasma flow field characteristics and the resulting effect on the quality of YSZ-HOSP, particularly in terms of spheroidization ratio, hollow-shell powder ratio, and shell thickness. To achieve controllable preparation of YSZ-STHS in arc plasma spheroidization, this paper proposed a novel model for the formation of YSZ-HOSP under different plasma flow characteristics, including high-speed compressing flow field, intermediate-speed critical flow field, and low-speed expanding flow field. These different plasma flow characteristics were achieved by changing the nozzle diameter and investigated by both numerical simulation and experiments in terms of plasma flow characteristics, electro-thermal characteristics, and the quality of the YSZ-HOSP. Results reveal that YSZ-HOSP prepared with high-speed compressing flow field resulted in a low hollow-shell powder ratio, while low-speed expanding flow field led to an over-thick shell. Conversely, the intermediate-speed critical flow field demonstrates relatively high thermal efficiency and enthalpy, along with moderate jet temperature and velocity, resulting in YSZ-STHS with a spheroidization ratio of 96.6 %, a hollow-shell powder ratio of 92.5 %, and a mean shell thickness of 3.49 μm. Therefore, it is evident that manipulating plasma flow characteristics allows for the controlled preparation of YSZ-STHS.

Method of neutralization of nitrogen oxides in area of low-temperature plasma

In the production of 1 ton of oxalic acid, 2000 m3 of gases with an average content of 2–2.5% of nitrogen oxides are emitted into the atmosphere. The existing methods of air purification from nitrous gases have a number of disadvantages and therefore cannot be widely used in industry. Based on theoretical and experimental studies, a new method for the thermal decomposition of nitrogen oxides has been developed, which provides for the sanitary purification of waste gases in the production of oxalic acid, up to the maximum permissible concentrations. The process of thermal decomposition of nitrogen oxides in the temperature range from 500 to approximately 50000С has been studied. To achieve such temperatures, an arc plasma torch with a tungsten cathode and a copper anode was used. The degree of decomposition was determined by measuring the NO concentration at the inlet and outlet by the evacuated flask method. The effects of gaseous (hydrogen, ammonia, methane, natural gas), liquid (kerosene, gasoline, fuel oil), and solid reducing agents (coke, coal, graphite) on the decomposition reaction of nitrogen oxides were also studied.

Experimental study on the life and performance of an improved DC arc plasma torch

A novel DC arc plasma torch is designed in this paper in order to reduce the electrode erosion, and a series of experiments are carried out to investigate how to improve the lifetime and performance of the nitrogen DC arc plasma torch. The analysis of voltage characteristics of the plasma torch indicates that the interelectrode insert can increase the average arc voltage and the sudden expansion structure can reduce the voltage fluctuation, which is helpful to improve the working stability to some extent. The spectrum characteristics at the plasma torch outlet and the cold flow simulations show that the dual shielding gas mainly act near the anode and can effectively cover the entire anode wall. Combining the shielding gas distribution with anode heat transfer processes in argon and nitrogen plasma torch, it is inferred that argon shielding gas plays an important role on reducing the anode heat transfer processes in nitrogen plasma torch, which can effectively suppress the anode erosion. The life testing experimental results find that there is no significant erosion of the cathode, anode, and interelectrode insert after cumulative working time exceeding 20 h. The maximum nitrogen plasma jet length can reach ∼35 mm with the outlet jet temperature of about 20 000 K at the current of 100 A and nitrogen gas flow rate of 10 slm. The maximum average specific enthalpy and thermal efficiency are respectively about 14 MJ kg−1 and 75% in the nitrogen plasma torch. Therefore, this newly designed DC arc plasma torch not only can suppress the electrode erosion but also has good working performance, which is expected to have excellent application prospects.

Keyhole Welding with Hybrid Plasma-Free Arc Source

Improving the keyhole welding process window is challenging work because the force and thermal state in the weld pool are hard to control. A hybrid plasma-free arc source was developed based on a plasma arc torch, sided tungsten was added close to the constraint orifice to form a free arc, and hybrid arcs formed after the free arc was fully absorbed into the constraint arc. In such a one-anode, twocathode hybrid arc system, the added free arc acts in an assistant role to adjust arc heat output without influencing the arc pressure peak, and the constraint arc acts as the guiding arc to control the arc pressure and slightly incline to the free arc side. Bead-on welding experiments were done to test keyhole welding process behavior with the hybrid arc source, including arc column, keyhole state, weld surface performance, and melting state in the weld pool. Results showed that (1) the hybrid arc can enlarge the stable keyhole welding process window in aspects of welding current and welding speed, and a more-obvious improving effect is obtained with the leading-sided tungsten; (2) the hybrid arc with the rear-sided tungsten has a smooth front weld surface; (3) the increased heat will enlarge the weld cross-section area with no obvious influence to the backside weld width; and (4) the leading keyhole wall is related to the outer tungsten position. The research gives a new method for improving keyhole welding stability.

Keyhole Welding with Hybrid Plasma-Free Arc Source

Improving the keyhole welding process window is challenging work because the force and thermal state in the weld pool are hard to control. A hybrid plasma-free arc source was developed based on a plasma arc torch, sided tungsten was added close to the constraint orifice to form a free arc, and hybrid arcs formed after the free arc was fully absorbed into the constraint arc. In such a one-anode, twocathode hybrid arc system, the added free arc acts in an assistant role to adjust arc heat output without influencing the arc pressure peak, and the constraint arc acts as the guiding arc to control the arc pressure and slightly incline to the free arc side. Bead-on welding experiments were done to test keyhole welding process behavior with the hybrid arc source, including arc column, keyhole state, weld surface performance, and melting state in the weld pool. Results showed that (1) the hybrid arc can enlarge the stable keyhole welding process window in aspects of welding current and welding speed, and a more-obvious improving effect is obtained with the leading-sided tungsten; (2) the hybrid arc with the rear-sided tungsten has a smooth front weld surface; (3) the increased heat will enlarge the weld cross-section area with no obvious influence to the backside weld width; and (4) the leading keyhole wall is related to the outer tungsten position. The research gives a new method for improving keyhole welding stability.

Research on the Production of Turquoise Hydrogen from Methane (CH4) through Plasma Reaction

Turquoise hydrogen is produced through a process of separating carbon into solid carbon based on fossil fuels and refers to hydrogen that does not produce carbon dioxide. In this study, the characteristics of turquoise hydrogen production through a methane thermal cracking reaction using an arc plasma torch were investigated. The plasma torch operated stably under high voltage and transport gas flow conditions. The composition of the gas generated from the methane plasma reaction was analyzed using an online IR gas analyzer and GC-FID. The experimental results show that the hydrogen yield decreased to 16.4% as the methane feed rate increased but increased to 58.8% as the plasma power increased. Under these conditions, the yield of solid carbon, a valuable byproduct, was also shown to increase to 62.9%. In addition, solid carbon showed high-temperature heat-treated characteristics based on its generation location. Carbon oxides such as CO and CO2 are rarely generated under any experimental conditions. Consequently, it can be considered that plasma thermal cracking is a promising technology for CO2-free hydrogen production and a valuable solid carbon.

ОЦЕНКА ВЛИЯНИЯ ТЕХНОЛОГИЧЕСКИХ РЕЖИМОВ ПЛАЗМЕННОГО НАНЕСЕНИЯ ПОКРЫТИЙ НА ТОЛЩИНУ ФОРМИРУЕМОГО СЛОЯ

Parts of technological machines, complexes and equipment used in many industries are subject to various types of mechanical wear, which leads to a significant decrease in their durability and an increase in maintenance and operating costs. Promising directions for improving the technologies of plasma application of wear-resistant coatings have been identified. Special attention was paid to the thickness of the functional layer, since when using plasma spraying methods, it has a significant impact on the quality of coatings. (Research purpose) The research purpose is developing mathematical models that make it possible to study the influence of the technological parameters of the plasma application of wear-resistant coatings on the thickness of the functional layer being formed. (Materials and methods) Samples made of 45 steel were used for experimental studies, on which a nickel-based powder PG-CP4 (PR-NH17CP4) was sprayed by plasma method. The current strength of the plasma torch arc, the spraying distance and the consumption of plasma-forming gas were adopted as the main technological modes of plasma spraying of coatings. The thickness of the formed coatings was measured on standardized equipment. Statistical processing of the obtained coating thickness values was carried out using a complete factor experiment using the Box-Wilson method. (Results and discussion). We have developed an experimental mathematical model of the technological process of plasma coating and demonstrated its operability. The criteria used to evaluate the variance of experiments, the adequacy and significance of the obtained regression equations are described. Using the Statistica program, a graphical interpretation of the studied dependencies was given. (Conclusions) Based on the mathematical planning of the experiment, models were obtained that make it possible to establish the relationship between the coating thickness and the specified technological parameters of the plasma spraying process. The results of the analysis of the presented analytical dependencies showed that the thickness of the coating is most influenced by the current strength of the plasma torch arc.

Heat treatment of ground surface using an electric arc plasma generator

The article presents a generalization of the results of experimental and theoretical studies on the intensive thermal effect on the surface of foundations from cohesive soils (as opposed to deep heat treatment) using an electric arc generator of low-temperature plasma (plasmatron). A plasmatron with massive consumable electrodes made of borosilicated graphite and a wide "blurred" plasma torch was used for heat treatment. Physical and mathematical modeling of the thermal effect on the surface of clay soil by a moving high-temperature source has been performed. For the first time, a special installation was manufactured and experimental studies were carried out on the heat treatment of ground surfaces on the site with an electric arc plasma torch. It is established that the effective heat flux density reaches 2.5-.3.5 kW/cm2. The main part of the thermal energy for the used plasmatron enters the material due to radiant heat transfer. An analytical mathematical model of the temperature field of a three-dimensional semi-bounded body in the technological process under consideration is given by an essentially nonlinear boundary value problem for a nonlinear heat equation with nonlinear boundary conditions of the second kind. When solving thermophysical problems, the ground semi-bounded space was considered as a quasi-homogeneous medium having a constant initial temperature and initial thermophysical parameters that change in the process of temperature increase. The effective values of the thermophysical characteristics were determined on the basis of experimental data. Calculations and experiments have shown that the temperature boundary leading to significant changes in the structural properties of soils drops to a depth of 4-6 cm from the surface, despite the boiling of the ground melt with a temperature of 2500 ...2800 K on the ground surface. Therefore, a new technological principle of heat treatment is proposed, which consists in building up the ground melt in layers of 4-5 cm up from the initial surface. The impossibility of obtaining a positive effect even with the use of a powerful high-temperature source of exposure in the case of traditional surface heat treatment technology has been confirmed. The new plasma technology of surface heat treatment of ground surfaces to the stage of silicate melt allows to obtain a common layer of the required thickness. At the same time, the efficiency of surface heat treatment is significantly increased. The new technology of layer-by-layer surface deposition reduces cracking in the layer when the melt cools, but does not eliminate this negative process.

Effect of H2 addition on the preparation of ZrO2 powder from zircon (ZrSiO4) using a plasma torch

In this study, the plasma torch is utilized for the preparation of highly pure ZrO2 from zircon (ZrSiO4). The incorporation of H2 into the discharge gas Ar improves the plasma physical parameters and serves as a reducing agent to promote the irreversibility of the pyrolysis reaction of ZrSiO4. ZrSiO4 powder is fed internally into a DC arc plasma torch through a powder feeder device. The DC torch generates thermal plasma that can fully heat all the ZrSiO4 within a short period for pyrolysis, extraction, and separation, eventually producing high-purity ZrO2. According to the results, the addition of H2 to the working gas increases the material temperature in the flame by increasing the plasma temperature, thereby promoting the pyrolysis of ZrSiO4. The temperature of the material is 2500–2600 °C, which is higher than the boiling point of the pyrolysis product SiO2 while maintaining the high melting points of ZrSiO4 and ZrO2. Furthermore, H2 plasma acts as a reducing agent in the pyrolysis reaction, where it combines with the O of the product to prevent the reversibility of the pyrolysis reaction of ZrSiO4 and retains only ZrO2.

Experimental and numerical investigation of medical waste disposal via plasma gasification

The COVID-19 pandemic has increased global awareness of proper medical waste disposal. Conventional methods like incineration and gasification are insufficient due to low energy efficiency and harmful emissions. Plasma gasification, however, offers significant advantages, including economical benefits, higher efficiency, lower emissions, and greater hydrogen production potential. Hence, plasma gasification can be an influential alternative to conventional methods with further developments. In this study, gasification characteristics of medical waste are investigated in a novel laboratory-scale updraft plasma gasifier. The gasifier utilizes a DC arc plasma torch with a maximum capacity of 5 kWh. Medical waste samples are prepared by mixing various consumables like face masks and cotton bandages, whereas waste capacity of the gasifier is estimated to be 7.0 kg/h for an equivalence ratio (ER) of 0.2. Simulations are conducted for ER values of 0.1, 0.2, 0.3, and 0.4 using ANSYS Fluent software, and the plasma jet is modeled as hot gas. Results demonstrate that integrating the throat configuration to the updraft plasma gasifier and increasing the ER value enhance H2 production and reduce CO content in the syngas. The minimum H2 content is found as 48.5% for ER = 0.1 with 24.1% CO, while the maximum H2 content is 54.7% for ER = 0.4 with 17.1% CO. The gasifier configuration achieves a carbon conversion rate (CCR) of 29.1% and a cold gas efficiency (CGE) of 28.5%.

Welding process with hybrid arc by compositing two free arcs into constraint arc

Controlling heat output and force in the arc source is important to improve the keyhole stability during welding. In this study, a double-layer hybrid arc torch was developed by adding two outer tungsten electrodes symmetrically to the orifice in the plasma arc torch. Two free arcs forming from the two outer tungsten tips are absorbed into the center constraint arc to form a hybrid arc. The arc pressure of the hybrid arc was measured, and welding experiments were carried out to test the application possibility in the keyhole welding process. It was found that: the arc pressure of the hybrid arc with two free arcs is symmetrical. The additional heat input provided by free arcs can be transferred into the keyhole bottom, and a lower constraint arc current is needed to form a stable fully penetrated keyhole. With the left-right arranged outer tungsten electrodes, arc heat is easier to be deposited into the keyhole bottom, and less sum of arc current is needed to form a fully penetrated keyhole. With the leading-rear arranged outer tungsten electrodes, the reflected arc will bridge the weld pool and the rear tungsten, and the coupling state between the free arc and the constraint arc is disturbed. When the constraint arc current is 115A and the free arc current is 40A, a fully penetrated keyhole can be formed with the left-right arranged outer tungsten electrodes but cannot be formed with the leading-rear arranged outer tungsten electrodes. The proposed hybrid arc system has advantages over the previous model in terms of a wider range of usable arc current and symmetrically distributed arc.

Experimental study on the characteristics of V‐type arc plasma torch with four electrodes

AbstractThe arc plasma is widely used in various fields due to its excellent advantages, such as elevated temperature, high enthalpy, and increased energy density. Under this direction, a four‐electrode V‐shaped arc plasma torch was developed to increase both the arc power and plasma volume. The arc dynamic characteristics, the volt‐ampere characteristics, and the thermal efficiency of the arc plasma torch were systematically studied. From the acquired results, a large‐scale, and low‐frequency re‐strike process between the arc channels was demonstrated. Compared with the common twin‐electrode structure, the stability of the four‐electrode structure during the discharging process was improved, exhibiting a wider frequency distribution of the re‐strike events. The electrode layout may also affect the dynamic evolution process of the arc. However, from a statistical point of view, no significant differences in electrical characteristics were recorded. The four‐electrode V‐shaped arc plasma torch presented a typical descending volt‐ampere characteristic, and the re‐strike frequency increased with an increase in the current. A high thermal efficiency (above 83%) was obtained in the range of arc current of 80–200 A. At a current value of 200 A, the jet enthalpy and the average gas temperature can reach 17.41 MJ/kg and 6590 K, and the corresponding jet length was close to 80 cm because of both the high thermal efficiency and enthalpy. The stable discharge process, high thermal efficiency, high jet enthalpy value, and large volume rendered the proposed four‐electrode V‐shaped arc plasma torch to be suitable for various applications including nanomaterial preparation, metal powder spheroidization, etc.

Numerical and experimental investigation of thermal regimes of thermionic cathodes of arc plasma torches

The modelling method based on decoupling the simulation of the cathodic part of the arc (the cathode and the near-cathode non-equilibrium plasma layer) from the simulation of the arc on the whole has been extended to cathodes of arc plasma torches, consisting of an insert with a conical tip, made of pure or doped tungsten, and a surrounding water-cooled copper holder. The method was validated by comparison with the experiment, performed on a 200 A DC arc in atmospheric-pressure argon. Standard work function of polycrystalline tungsten of 4.54 eV was used for modelling of pure-tungsten insert and a good agreement with the experiment was found with respect to both the insert tip shape and the temperature distribution in the tip, recorded in the stable operation mode. There are no unambiguous data on the work function for arc cathodes made of doped tungsten, although in situ measurements of the effective work function of cathodes of high-pressure arc discharges provide useful hints. On the other hand, the experiments reported in this work show that the tip temperatures of inserts made of tungsten doped with of thorium, or lanthanum, or yttrium, recorded during the stable-mode operation at the arc current of 200 A, vary in a rather narrow range 3100–3200 K. This suggests that the work functions of doped tungsten inserts, operated in the stable mode, are close to each other as well. Indeed, the results of modelling with the same value of the work function of 3 eV give a reasonably good agreement with the experiment in all three cases.

Investigation of Upgraded Technology for Plasma Spraying of Bronze Powder Using the Combined Process with Hydrocarbon Additions

The object of the research is thermal spray process for the formation of metal coating from bronze powder in plasma-fuel variant, using direct current (DC) electric arc plasma torch, on steel samples. The aim of the work was to investigate and develop the technology for plasma-fuel spraying of functional coatings (for wear-resistant and antimicrobial applications) on machine-building and medical purpose pieces with increased process capacity and moderate energy consumptions in a comparison with conventional thermal spray technologies with use of inert and oxygen-free gas media. During the study, using experimental and thermodynamic estimation methods, the thermal and chemical parameters of the process under the spraying conditions at ambient pressure were characterized, which made it possible to determine the area of preferred regimes of the developed technology. On the modernized testing unit for plasma spraying of metal powders with power of up to 40 kW, operating using a controlled combination of three types of gases – technical nitrogen and propane-butane (LPG) with compressed air, the measurement and optimization of the operating and constructive/assembling parameters of the system for aluminum bronze coating spraying were established. In this case, the experiments were carried out using the designed fuel intensifier, which is joined with the PP-25 arc plasma torch, as well as additional technological equipment (protective shroud). For samples of the resulting coatings with a thickness of 100 to 450 mm from the bronze material, testing of phase composition and some parameters of the resulting coatings on steel products was carried out. Operating capacity of the proposed process reaches 7–15 kg/h for bronze powder when using a moderate power of the torch – up to 35–40 kW and a limited flow rate of hydrocarbon gas (for example, LPG of the SPBT grade) – 0.1–0.35 kg/h. Analysis of the energy efficiency parameters of the developed technology, as well as its calculated technical characteristics, in a comparison with plasma and combined equipment of a similar purpose, showed that it has an advantage in terms of target indicators, in particular, in terms of energy consumption and total energy efficiency of the spraying unit, not less than 20–30 %. This makes it to proceed later to the stage of application of this technology into production based on a new process for the metal coating formation, in particular with antimicrobial properties, with improved energy efficiency of the process.

Experimental study on a small-scale oxygen-enriched entrained flow biomass gasifier assisted by non-thermal arc plasma

A small-scale oxygen-enriched entrained flow biomass gasifier consisting of a non-thermal arc plasma torch and a stainless steel bellows was developed. The characteristics of the non-thermal arc plasma were diagnosed. The effects of oxygen concentration and bellows length on the gasification process using rice husk powder as feedstock at a feed rate of 27.1 g/min were studied. The results show that increasing the oxygen concentration of gasifying agent and using longer bellows both lead to the improvement of cold gas efficiency, carbon conversion efficiency, and yields of H2 and CO. The cold gas efficiency of the gasifier at a bellows length of 500 mm and oxygen concentration of 34.7% is 65.8%. And benefiting from low auxiliary energy consumption, the gasifier’s energy efficiency reaches 60.5%. The non-thermal arc plasma assists the entrained flow gasification by converting part of the feedstock into activated reactants.

Possibility Study in CO2 Free Hydrogen Production Using Dodecane (C12H26) from Plasma Reaction

Turquoise hydrogen refers to hydrogen produced through a fossil-fuel-based process in which carbon is separated into solid carbon and no carbon dioxide is produced. In this study, dodecane was selected as a simulated oil for waste plastic pyrolysis recovery oil, and the turquoise hydrogen production characteristics through the thermal cracking reaction using an arc plasma torch were investigated. The plasma was stably discharged at 2 to 4 kW. Hydrogen in the produced gas was analyzed through an online IR gas analyzer, and hydrocarbons from C1 to C5 were analyzed through GC-FID. As a result of the experiment, the hydrogen yield tended to increase as the plasma power increased, and a maximum of 11.5% based on mass was obtained. On the other hand, carbon oxides such as CO and CO2 were not generated. Along with hydrogen, the valuable by-products of this process are solid carbon and gaseous hydrocarbons. The solid carbon yields also increased up to 66% as the plasma power increased. On the other hand, the yield of gaseous hydrocarbons showed an opposite trend to that of hydrogen and carbon and consisted mainly of C2 series (average content of 77%) and olefins (average fraction of 0.67). Consequently, it can be considered that the plasma thermal cracking is a promising technology for the CO2-free hydrogen production, as well as solid carbon and C2-olefin.

Сфероидизация нанопорошковых микрогранул вольфрама в термической плазме электродугового разряда

A method for producing tungsten powder consisting of spherical microparticles with dimensions of 20 – 50 µm is considered when processing a granular tungsten nanopowder in a flow of argon electric arc thermal plasma. Experimental studies of plasma chemical synthesis of tungsten nanopowder in a plasma reactor with a limited jet flow during the interaction of tungsten trioxide with a flow of hydrogen-containing plasma generated in an electric arc plasma torch have been carried out. The conditions of spray drying and the properties of a suspension consisting of tungsten nanoparticles have been experimentally determined, ensuring the production of mechanically strong nanopowder microgranules of rounded shape with a homogeneous internal nanostructure that does not contain cavities, with the yield of microgranules with a size of less than 60 µm at the level of 65 %. The influence of the parameters of the plasma processing of nanopowder microgranules in the thermal plasma flow on the degree of spheroidization and the microstructure of the resulting particles has been established.

Ferrite fraction in duplex stainless steel welded with a novel plasma arc torch

Ferrite fraction in duplex stainless steel welded with a novel plasma arc torch

Numerical analysis of direct-current (DC) plasma processing for high-efficient steel surface modification

Nowadays, direct-current (dc) non-transferred arc plasma torch has drawn significant interest from both academia and industry due to the capability to process products in an efficient and convenient way. The core of this technology is to clarify and manipulate the arc behavior at the interior of the dc plasma torch to produce ideal plasma jets for processing. To solve this problem, a quasi-steady axisymmetric model is built to simulate and compare the arc characteristics in different operating conditions and different nozzle structures of the plasma torch. The results uncover distinct aspects of the study on arc characteristics, including the detection of the primary arc attachment region and its spatial features caused by the choking effect of torch structure. The thermal efficiency focused on processing substrate is also calculated in this paper for estimating the performance of plasma processing. The calculated results show that increasing the mass flow rate brings better thermal efficiency and the greatest promotion is at least 6% in the same current value, whereas improving the arc current value causes the opposite result. Meanwhile, two types of nozzle are compared to the original design in thermal efficiency, where the wide nozzle is chosen for torch optimization due to its best power efficiency. The secondary arc attachment on the metal substrate is discovered though its impact scope is only within a radius of 10 mm from the torch axis, its effect on the processing could be ignored for the extremely low electric current value.