Flow Rate Of Plasma-forming Gas Research Articles

Evaluation of thermal plasma-synthesized cobalt boride nanoparticles as efficient water-splitting catalysts

Herein, cobalt boride nanoparticles are synthesized using the thermal plasma process and investigated in their performance as electrocatalysts for water splitting. The products show efficient electrocatalyst performance for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte (1 M KOH). The size distribution of the products, CoB and Co2B, is between 5 and 15 nm, which is decreased by reducing the flow rate of plasma-forming gas. The results reveal that the size of the particles could be controlled by changing the flow rate of the plasma-forming gas. Furthermore, the cobalt boride nanoparticles with high crystallinity could be synthesized through a one-step process without the post-treatment process. The products achieve an overpotential of 355 mV at a current density of 10 mA/cm2 and a Tafel slope of 49 mV/dec in the OER measurement, and their performance is more efficient than that of the cobalt-based catalysts reported to date. In contrast, the products exhibit a relatively high Tafel slope of 92 mV/dec and a low active surface area of 1.2 mF/cm2 in the HER measurement. However, their long-term stable performance is maintained for OER and HER at ± 10 mA/cm2 for 40 h. Thus, cobalt boride nanoparticles are a promising material for the anode of water-splitting electrodes.

Microplasma-sprayed multilayer coatings for electric heating elements

Abstract The paper presents new results on the application of microplasma spraying (MPS) for manufacturing electric heating elements (EHEs) consisting of a St3 steel plate (the substrate) with a sprayed electrically insulating Al2O3 sublayer (400±50 μm thick) and TiO2 electric heating tracks (4 mm width; 150±50 μm thickness). Measurements of the temperature of the multilayer coating with a thermal imager enabled determination of the temperature distribution over the surface of the EHE. The electric strength and conductivity tests showed the efficiency of the sprayed EHEs up to a temperature of 200°C. The results of analysis of the causes of material losses during MPS of electric heating tracks (TiO2) are presented, and the optimal parameters for efficient MPS of coatings in the form of narrow tracks on steel substrates are determined. Using regression analyses, the equation for the influence of MPS parameters on the coating transfer efficiency (CTE) is obtained. Process parameters such as the electric current and the plasma-forming gas flow rate have been found to have the greatest influence on the CTE. In the experiment, a high efficiency of the sprayed material during MPS of electric heating tracks of TiO2 powder was established (the maximum CTE reached 89%), which indicates the prospects for using MPS technology in the production of EHEs for DC electric heating and for maintaining the temperature of product surfaces up to 200°C.

ПЛАЗМЕННАЯ ТЕХНОЛОГИЯ ПОЛУЧЕНИЯ СТЕКЛОМИКРОШАРИКОВ НА ОСНОВЕ БОЯ ТАРНЫХ И СОРТОВЫХ СТЕКОЛ

A technology – based on the breakage of graded and container glasses – was developed for the production of glass microbeads in a plasma reactor. The regularities of the influence of the flow rate of plasma-forming gas argon and the power of the plasma reactor on the fractional composition of glass microbeads were established. It was shown that with an increase in the flow rate of plasma-forming gas from 1.0 m3/hour to 2,0 m3/hour and the current strength from 300 A to 400 A, the amount of fraction over 630 microns increases due to coagulation processes. It was established that under the influence of high plasma temperatures, about 6000-8000 K, complete melting and sphering of particles occur with the formation of glass microbeads ranging in size from 80 microns to 1250 microns. The microhardness, acid resistance and alkali resistance of glass microbeads were investigated.

Effect of microplasma spraying parameters on the loss of sprayed Zr wire and coating porosity

The article presents new results of studying the causes of material loss during microplasma spraying (MPS) and substantiates the choice of optimal parameters for efficient spraying of zirconium wire coatings on steel substrates and obtaining coatings with the desired porosity up to 20.3% on a titanium alloy. Optimum spraying parameters provide the maximum material utilization coefficient (MUC) - up to 95%, and the minimum material losses when spraying coatings on small parts: 47% when spraying onto a substrate with an average cross-sectional area of ​​2 mm and less than 1% when spraying onto a substrate with an average diameter of 8 mm. The studies were carried out using a multifactorial experiment with fractional replicas 24-1 with varying such spraying parameters as current strength, spraying distance, plasma-forming gas flow rate, and wire flow rate. To study the distribution of the coating material in the spray spot, macro photography of the metallization figures was carried out and analyzed with the construction of approximating curves. Scanning electron microscopy was used to determine the pore size and porosity of zirconium coatings at different parameters of microplasma spraying on a titanium alloy. Using the methods of regression analysis of the experimental results, equations were obtained that make it possible to assess the degree of influence of the parameters of microplasma spraying on the value of the MUC and the porosity of the coatings, and it was found that the greatest influence is exerted by the current strength and the plasma-forming gas flow rate. The choice of the optimal MPS parameters of a zirconium coating with a porosity suitable for medical implant coatings has been substantiated.

Lowtemperature plasma generator for effective processing of materials

Low-temperature plasma is used in metallurgy for steel alloying by nitrogen, deoxidization of magnetic alloys, obtaining of steels with particularly low carbon content, metal cleaning of nonmetallic inclusions, desulfurization and other refining processes. The wide application of those technologies is restrained by absence of reliable generators of low-temperature plasma (GLP) with sufficient resource of continuous operation. As a result of studies, a universal generator of high-enthalpy plasma jet of various working gases was created. The generator has expanding channel of the output electrode with an efficiency of ~60 % for argon working gas and ~80% for nitrogen and air. It was shown that the developed generator of low-temperature plasma ensures formation of a weakly diverging (2α = 12°) plasma jet with a diameter D = 5–12 mm, an enthalpy of 5–50 kJ/g and a mass average temperature of 5–10 kK, at a full electric power of the arc discharge of 5–50 kW and a plasma-forming gas flow rate of 1–3 g/s. Results of the study of propane additions to the plasma-forming gas effect on the state of cathodes with inserts made of pure tungsten, lanthanum tungsten, and hafnium presented. It was shown that a small propane addition (1%) to the plasma-forming gas, results in reducing effect of the insert material. Study of the GLP operation at arc current 100A with addition to the working gas nitrogen maximum possible volume of propane, which don’t disturb stability of arc showed that for the developed plasma generator at the nitrogen flow rate ~0,45 g/s, the propane flow rate was ~0,33 g/s (not more than ~73 % of the plasma-forming gas). The created high-resource GLP with changeable electrodes enables to obtain at the exit a high-enthalpy plasma flow of various gases (argon, nitrogen, air) and can be a prototype of more powerful plasmotrons of various technological application, in particular for plasma metallurgy.

Development of plasma technology for metal powders used in additive technologies

The article describes the main characteristics of plasma technology designed for the production of metal powders, such as voltage, current, plasma-forming gas flow rate, plasma flow temperature. Based on experimental data and theoretical calculations, mathematical models are constructed to refine the defining characteristics, as well as to visualize the process. The mathematical model contains a spray chamber, an electrode rotation mechanism, a gas mixture supply unit, a plasma heating source, and a water cooling system for the chamber walls. The method of a rotating electrode with plasma heating (PREP) was used.

Arc initiation in plasma installations

The paper is devoted to a research of electric arc ignition devices in plasma torch of alternating and direct current. High-voltage alternating current plasma is used as one of ignition devices. Its power is 5–10 kW, the plasma-forming gas flowrate is 2–5 g/s. The plasma flow with electron concentration of 1014–1016 cm−3 sufficient for main arc ignition is set in a zone of the minimum distance between the main electrodes of a plasma torch by injector operation. The second method uses a construction series of the direct current plasma torches. They were designed to transfer ac plasma torches with rail electrodes into a class of electrical installations with a supply voltage less than 1000 V. Their current-voltage characteristics and life tests are received. The cathode erosion is about 10−6 g/C, the anode erosion is 10−7 g/C. The pulse erosion injector is developed for an arc ignition in a direct current plasma torch. The pulsed injector is supplied from the capacitive storage.

Propellant grade ultrafine aluminum powder by RF induction plasma

A continuous process of synthesizing ultrafine aluminum powder (UFAP) having high yield rate using RF induction plasma is reported in the current work. The processing parameters (powder injection probe position; powder feed rate; flow rates of gases for plasma forming, quenching and passivation) were varied systematically to evaluate their influence on the size and distribution, and metallic Al content of the synthesized powder. The UFAP was characterized using X–ray diffraction and, scanning and transmission electron microscopes. The metallic aluminum content of UFAP was evaluated using hydrogen gas evolution technique and its thermal behavior was studied using simultaneous thermo–gravimetric and differential scanning calorimetry under static air. UFAP with an average particle size varying between 220 and 400 nm was obtained under different processing conditions and a maximum metallic Al content of 89.2% was obtained at a high powder feed rate. Among the parameters studied, increased powder feed rate, plasma forming gas flow rate and the position of the powder injection probe had a significant effect on the particle size, distribution and the metallic Al content of the synthesized UFAP.

Generator of chemically active low-temperature plasma

A new generator of high enthalpy (H0 > 40 kJ/g), chemically active nitrogen and air plasmas was designed and constructed. Main feature of the generator is an expanding channel of an output electrode; the generator belongs to the class of DC plasma torches with thermionic cathode with an efficiency of 80%. The generator ensures the formation of a slightly divergent plasma jet (2α = 12°) with a diameter of D = 10-12 mm, an electric arc maximum power of 20-50 kW, plasma forming gas flow rate 1.0-2.0 g/s, and the average plasma temperature at an outlet of 8000-11000 K.

Synthesis of Silicon Nanoparticles and Nanowires by a Nontransferred Arc Plasma System

Silicon nanomaterials were synthesized from solid silicon powder in microsize using a nontransferred arc plasma system. Synthesized silicon nanomaterials were sphere or wire in morphology according to the input power of arc plasma, the flow rate of plasma forming gas, and the collecting position of product. The product was spherical nanoparticles at a high input power for complete evaporation, while it was nanowires at a relatively low input power. The mean diameter of synthesized silicon nanoparticles was increased from 20.52 nm to 40.01 nm by increasing the input power from 9 kW to 13 kW. On the other hand, the diameter of silicon nanowires was controllable by changing the flow rate of plasma forming gas. The mean diameter of silicon nanowires was increased from 16.69 nm to 23.03 nm by decreasing the plasma forming gas flow rate from 15 L/min to 12 L/min.

Heat-power working regimes of a high-frequency (0.44 MHz) 1000-kW induction plasmatron

The energy working regimes of a superpower high-frequency induction (HFI) plasmatron with a high-frequency (HF) generator are studied. The HFI plasmatron with a power of 1000 kVA and a working frequency of 440 kHz, in which air is used as a plasma-forming gas, can be used for treatment of various oxide powder materials. The energy regimes substantially influence finish products and their costs. Various working regimes of the HFI plasma unit and the following characteristics are studied: the dependence of the vibration power on the anode power, the dependence of the power losses on the anode power at various of plasma-forming gas flow rates, and the coefficients of efficiency of the plasmatron and the HFI-plasma unit at various powers. The effect of the plasma-forming gas flow rate on the bulk temperature is determined.

A criterion of similarity and transition to turbulence for electric arc flows

A method is suggested for determining the similarity criterion and the criterion of transition of an electric arc flow in a plasmatron channel from a laminar regime to a turbulent one (equivalent Reynolds number) that does not require using any reference temperature. Application of this method to the available experimental data on the transition to turbulence demonstrates its correctness and efficiency. The critical value of the proposed similarity criterion corresponding to the boundary of the transition from a laminar regime to a turbulent one has been revealed. A marginal curve separating the regions of the laminar and turbulent regimes of the plasma flow has been plotted in the space of the operating plasmatron parameters. A phenomenon of a double change of the electric arc flow regime with electric current rise upon constant plasma-forming gas flow rate has been discovered.

Microwave Plasma Process Optimization to Produce Nano Titania through Design of Experiments

The numerous unique advantages afforded by microwave plasma synthesis have led to its extensive utilization in synthesis of a wide variety of highly pure nanopowders. The present research reports synthesis of commercially important titania nanopowder from low cost titanium tetrachloride using this process. The parametric impact of the process parameters on the conversion efficiency and percentage anatase in titania nanopowder has been studied using statistically designed experiments and analysis. The outcome of this research indicated that low levels of plasma forming gas flow rate (PFR), additional gas flow rate (AFR), and precursor feed rate (FR), along with high level of carrier gas flow rate (CFR) would result in the most efficient conversion process with suitable percentage of anatase for photocatalytic applications.

Effects of Constrictor Geometry, Arc Current, and Gas Flow Rate on Thermal Plasma Characteristics in a Segmented Arc Heater

A numerical simulation on a segmented arc heater which is used to generate high thermal flow environments for the test of heat shield materials, were carried out. In this numerical prediction work, targets level of input power class, minimum enthalpy at the exit of the heater, and maximum pressure inside the heater were set up as 400 kW, 20 MJ/kg, and 4 bar, respectively. In order to produce uniform temperature and velocity characteristics of thermal flow for a successful test, effects of design and operation variables on the thermal plasma characteristics were analyzed. Number of the segments packs and diameter of the constrictor were changed 1 ∼ 3 (105 ∼ 315 mm) and 12 ∼ 20 mm, respectively. As the torch operating variables, arc current was changed from 300 A to 500 A and plasma forming gas flow rate was varied from 6 g/s to 14 g/s. Arc current was adjusted to achieve about 400 kW according to constrictor geometry at fixed gas flow rate of 10 g/s, and optimal design conditions for uniform radial temperature and low pressure profiles with Mach number 1 at the supersonic throat were expected when the constrictor length and diameter were 315 mm and 16 mm, respectively. From the numerical results, diameters of the supersonic nozzle exit which determines test target size were calculated as 55.5 mm and 82.4 mm in the cases of Mach number 2 and 3, respectively.

Effect of critical plasma spray parameter on properties of hollow cathode plasma sprayed alumina coatings

A 20 kW hollow cathode plasma spray torch was manufactured and its performances were examined by spraying alumina coatings on mild steel substrates with different critical plasma spray parameters (CPSP: 0.12, 0.24, 0.36, 0.48). CPSP is defined as the ratio between the torch input power and primary plasma forming gas flow rate. The effects of CPSP on the microstructure, porosity, microhardness, surface roughness, sliding wear and erosive wear properties of the coatings were investigated. The electrothermal efficiency and the excitation temperature of the plasma jet were also investigated for different CPSP. The microstructure and phase composition of the alumina coatings were examined using scanning electron microscope and X-ray diffraction (XRD) analysis respectively. XRD analysis revealed that alumina particles during plasma spraying reach sufficient melting state prior to the impact on the substrate with a velocity comparable to that of conventional plasma spraying. The experimental results have shown that the CPSP has significant influence on the microstructure and other properties of the deposited alumina coating. It also showed that the hollow cathode plasma spray torch is a suitable tool to coat the dense ceramic materials with low input power levels.

Study of Nanodispersed Iron Oxides Produced in Steel Drilling by Contracted Electric-Arc Air Plasma Torch

The optimal conditions on the plasma-forming gas flowrate, discharge current and voltage, distance between the plasma-torch nozzle and the metal plate surface for the process of penetration in and vaporization of steel plates by the contracted electric-arc air plasma torch accompanied by water quenching, were determined. The X-ray structural and phase studies as well as Mössbauer and electron microscope studies on the samples treated were performed. It was demonstrated that the vaporized elemental iron was oxidized by the oxygen present in the air plasma jet to form iron oxides (wüstite, magnetite, hematite), which, depending on their mass ratios, determined the color of the iron oxide pigments, namely, beginning from light yellow, through deep yellow, light brown, deep brown, violet, red-violet, to black. A high degree of dispersity of the iron oxides is thus produced, with an averaged diameter of the particles below 500 nm, and their defective crystal structure form the basis of their potential application as components of iron-containing catalysts and pigments.

The Shunting of Current and the Resultant Variation of Voltage in Channels of Plasmatrons with Self-Adjusting Length of Electric Arc

The characteristics of pulsation processes in dc plasmatrons with the cathode located in the channel center and the anode in the form of a cylindrical or a conical channel wall are investigated in plasmas of argon and nitrogen at atmospheric pressure. The fast Fourier transform of signals and their subsequent computer processing are used to obtain the dependences of the frequency of fluctuations of the arcing voltage on the working parameters of the plasmatron, namely, the electric arc current, the flow rate of plasma-forming gas, and the channel diameter. For plasmatrons with the self-adjusting length of the electric arc, analysis is performed of the mechanism of reclosing of the anode region of the arc, i.e., of the electric arc shunting associated with the stretching of the current filament by a flow of gas and with the electrodynamic interaction of different filament regions. A formula is derived which defines the dependence of the characteristic frequency of fluctuations of the arcing voltage on the external parameters of the problem, namely, the arc current, the flow rate of the working gas, and the characteristic channel diameter. It is demonstrated that the pattern of the dependence of the frequency of voltage fluctuations on the gas flow rate may vary with the values of the parameter of magnetohydrodynamic interaction. The formula generalizes the experimental results of numerous researchers obtained in a wide range of variation of the external parameters.

Plasma generation for the plasma cutting process

This study is an attempt to estimate the overall properties, viz. the thermal power and force, of an intense plasma jet produced by a plasma cutting torch, and to relate the properties of the plasma to the diameter of the nozzle of the plasma torch and the flow rate of plasma-forming gas. For cutting metallic plates using a thermal plasma, a narrow plasma jet is produced by means of a transferred electric are between an electrode in a plasma torch and the material to be cut. The power density and pressure exerted by the plasma jet on the material at the region of cut needs to be high so that a straight cut, without dress at the bottom of the plate, can be obtained. A simple theory to describe the behavior of the arc in a plasma cutting torch has been developed to predict the are radius, pressure, and arc voltage at the nozzle exit as a function of are current for a range of nozzle sizes and air flow rates. The results obtained are in good agreement with the measured values for an air plasma cutting torch nominally rated for 100-A operation. The relationships between the mass flow rate of plasma gas, plasma power, and arc force have been discussed in the light of design of plasma torches for plasma cutting.