Search Results (34)

Although oily sludge is an industrial waste and difficult to separate, its calorific value can still reach 6000 cal/g, thus possessing significant recycling value. This study compares various types of non-thermal plasma for refining oily sludge. The pre-treatment technology utilized filtration combined with solvent extraction to extract the oil portion from the oily sludge. Subsequently, two types of non-thermal plasma, DC streamer discharge and dielectric plasma discharge, were used to crack and activate the oily sludge under different operating conditions. The fuel compositions and properties of the refined fuel treated by two types of non-thermal plasma were compared. The elemental carbon and oxygen of the oily sludge after treatment in a direct DBD plasma reactor for 8 min were 1.96 wt.% less and 1.38 wt.% higher than those of commercial diesel. The research results indicate that the pre-treatment process can effectively improve the refined fuel properties. After pre-treatment, the calorific value of the primary product from the oily sludge can reach 10,598 cal/g. However, the carbon residue of the oily sludge after pre-treatment remained as high as 5.58 wt.%, which implied that further refining processes are required. The streamer discharge plasma reactor used a tungsten needle tip as a high-voltage electrode, leading to a rather small treated range. Corona discharge and arc formation are prone to being produced during the plasma action. Moreover, the addition of quartz glass beads can form a protruding area on the surface of the oily sludge, generating an increase in the reacting surface of the oily sludge, and hence an enhancement of treatment efficiency, in turn. The direct treatment of DBD plasma can thus have a wider and more uniform operating range of plasma generation and a superior efficiency of plasma reaction. Therefore, a direct DBD type of non-thermal equilibrium plasma reactor is preferable to treat oily sludge among those three types of plasma reactor designs. Additionally, when the plasma voltage is increased, it effectively enhances fuel properties. Full article

The global coronavirus (COVID-19) pandemic in early 2020 caused the amount of medical waste, especially plastic waste, to increase. The pandemic exacerbated the plastic waste management problem, including the need to find more sustainable treatment methods. This study investigated the sustainable conversion of plastic waste (FFP2-type face masks) to syngas via pure CO₂ plasma gasification to recover energy and reduce environmental pollution. A direct current (DC) thermal arc plasma torch of 40.6–68.4 kW power generated the plasma stream. Carbon dioxide (CO₂), as a greenhouse gas (GHG), was used as the main plasma-forming gas and gasifying agent. The 140_thermal feedstock input plasma gasification system was used in the study. The effect of the CO₂-to-C ratio on the gasification performance efficiency was investigated. The best CO₂ plasma gasification process performance was obtained at a CO₂-to-C ratio of 2.34. In these conditions, the main syngas components (H₂ + CO) comprised 80.46 vol.% (H₂: 24.62 vol.% and CO: 55.84 vol.%) and the following values were seen for the heating value of the syngas (LHV_syngas: 13.88 MJ/Nm³), the syngas yield (3.13 Nm³/kg_FFP2), the tar content in the syngas (23.0 g/Nm³), the carbon conversion efficiency (CCE: 70.6%), and the cold gas efficiency (CGE: 47.8%). Additionally, the plasma gasification process mass and energy balance were evaluated. It was demonstrated that CO₂ plasma gasification could be a promising thermochemical treatment technology for sustainable plastic waste disposal and the simultaneous utilization of greenhouse gases, such as carbon dioxide. Full article

High-quality diamond-like carbon (DLC) films are renowned for their exceptional hardness, low friction coefficient, and superior chemical stability. These properties make DLC films exceptionally suitable for protective coatings in optical, mechanical, aerospace, and military applications. Thick DLC films with outstanding mechanical properties were deposited on DC53 die steel using a mixed energy carbon plasma generated by a filtered cathodic vacuum arc (FCVA) device. The structural, mechanical, tribological, and optical properties of the films were tested by Raman, surface morphology instrument, Vickers Indenter, tribometer, and UV-VIS spectrophotometry. The results indicated that 14 µm tetrahedral amorphous carbon (ta-C) films with a good combination with DC53 die steel substrate were obtained. The hardness was 9415 HV, which is close to that of diamond films. The fracture toughness was 4 MPa·m^1/2. The friction coefficient was 0.0898, and the optical band gap was 3.12 eV. Full article

The imperative to achieve a climate-neutral industry necessitates CO₂-free alternatives for H₂ production. Recent developments suggest that plasma technology holds promise in this regard. This study investigates H₂ production by methane pyrolysis using a lab-scale plasma furnace, with the primary objective of achieving a high H₂ yield through continuous production. The plasma furnace features a DC-transferred thermal plasma arc system. The plasma gas comprises Ar and CH₄, introduced into the reaction zone through the graphite hollow cathode. The off-gas is channeled for further analysis, while the plasma arc is recorded by a camera installed on the top lid. Results showcase a high H₂ yield in the range of up to 100%. A stable process is facilitated by a higher power and lower CH₄ input, contributing to a higher H₂ yield in the end. Conversely, an increased gas flow results in a shorter gas residence time, reducing H₂ yield. The images of the plasma arc zone vividly depict the formation and growth of carbon, leading to disruptive interruptions in the arc, hence declining efficiency. The produced solid carbon exhibits high purity with a fluffy and fine structure. This paper concludes that further optimization and development of the process are essential to achieve stable continuous operation with a high utilization degree. Full article

Nanostructured transition metal nitrides (TMNs) have been considered as a promising substitute for precious metal catalysts toward ORR due to their multi-electron orbitals, metallic properties, and low cost. To design TMN catalysts with high catalytic activity toward ORR, the intrinsic features of the influencing factor on the catalytic activity toward ORR of nanostructured TMNs need to be investigated. In this paper, titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) nanoparticles (NPs) are highly efficient and synthesized in one step by the direct current arc plasma. TiN, ZrN, and HfN NPs with an oxidation layer are applied as the catalysts of hybrid sodium–air batteries (HSABs). The effect of the composition and structural attributes of TMNs on ORR catalysis is defined as follows: (i) composition effect. With the increase in the oxygen content, the catalytic ORR capability of TMNs decreases progressively due to the reduction in oxygen adsorption capacity; (ii) structure effect. The redistribution of the density of states (DOS) of ZrN indicates higher ORR activity than TiN and HfN. HSABs with ZrN exhibit an excellent cyclic stability up to 137 cycles (about 140 h), an outstanding rate performance, and a specific capacity of 2817 mAh·g⁻¹ at 1.0 mA·cm⁻². Full article

Plasma generation by means of electrical discharge requires specialized power supply systems. The applicability of plasma for various plasma processes depends on its parameters, and these, in turn, depend on the parameters of power supply systems. Arc plasma can be unstable, generating a lot of electromagnetic interference, overvoltage and overcurrent. The power system of a plasma reactor must guarantee good plasma control characteristics, be immune to disturbances and ensure good cooperation with the power grid. This article analyzes the cooperation of a three-phase plasma reactor, with a gliding arc discharge and a power supply system of a new type. This system integrates an AC/DC/AC converter and a five-column transformer with a special design in a single device. Using the properties of magnetic circuits, it is possible to integrate the functions of ignition and sustaining the burning of the discharge in the reactor in a single transformer. The proper design of the transformer is crucial to achieve the good cooperation of the AC/DC/AC converter with both the plasma reactor and the power supply network. The presented power supply design shows a number of positive features, predisposing it to powering arc plasma reactors. Full article

Background: The use of nitinol (NiTi) archwires in orthodontic treatment has increased significantly due to unique mechanical properties. The greatest obstacle for safe orthodontic treatment is chemically or microbiologically induced corrosion, resulting in nickel (Ni) release. The aim of this investigation was to enhance corrosion resistance and introduce antibacterial properties to NiTi archwires by coating them with copper (Cu) doper titanium nitride (TiN-Cu). Methods: NiTi archwires were coated with TiN-Cu using cathodic arc evaporation (CAE) and direct current magnetron sputtering (DC-MS). The morphology of the sample was analyzed via field emission scanning electron microscopy (FESEM) and chemical composition was assessed using energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to estimate the ion release. The biocompatibility of samples was investigated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Antibacterial activity was tested against Streptococcus mutans and Streptococcus mitis. Results: Physicochemical characterization revealed well-designed coatings with the presence of TiN phase with incorporated Cu. TiN-Cu-nanocoated archwires showed a statistically lower Ni release (p < 0.05). Relative cell viability was the highest in 28-day eluates of TiN-Cu-nanocoated archwires (p < 0.05). The most remarkable decrease in Streptococcus mitis concentrations was observed in the case of TiN-Cu-coated archwires (p < 0.05). Conclusion: Taking into account biocompatibility and antibacterial tests, TiN-Cu-nanocoated archwires may be considered as a good candidate for further clinical investigations. Full article

The application of direct-current plasma arc furnace technology to the problem of coal gasification is investigated using computational multiphysics models of the plasma arc inside such units. An integrated modelling workflow for the study of DC plasma arc discharges in synthesis gas atmospheres is presented. The thermodynamic and transport properties of the plasma are estimated using statistical mechanics calculations and are shown to have highly non-linear dependencies on the gas composition and temperature. A computational magnetohydrodynamic solver for electromagnetically coupled flows is developed and implemented in the OpenFOAM^® framework, and the behaviour of three-dimensional transient simulations of arc formation and dynamics is studied in response to different plasma gas compositions and furnace operating conditions. To demonstrate the utility of the methods presented, practical engineering results are obtained from an ensemble of simulation results for a pilot-scale furnace design. These include the stability of the arc under different operating conditions and the dependence of voltage–current relationships on the arc length, which are relevant in understanding the industrial operability of plasma arc furnaces used for waste coal gasification. Full article

The fabrication of ZnO nanoparticles (NPs) was monitored and studied in situ by controlling the plasma parameters of the direct current (DC) arc plasma system, such as the current density and chamber pressure. The optical emission signature of nitrogen was spectroscopically studied using optical emission spectroscopy (OES) techniques, and it showed a dependency on the nitrogen concentration in the ZnO nanoparticles in relation to the output of the ZnO NPs-based homojunction light-emitting diodes (LEDs). The synthesized NPs had a good crystalline quality and hexagonal wurtzite structure, and they were characterized by X-ray diffraction (XRD) techniques and scanning electron microscope (SEM). The photoluminescence properties of the ZnO NPs and the optical and electrical parameters of the LEDs were also analyzed and correlated. The results indicate that the nitrogen dopants act as acceptors in the ZnO NPs and are favored in low plasma temperatures during fabrication. We anticipate that the results can provide an effective way to realize reliable nitrogen-doped p-type ZnO and tremendously encourage the development of low-dimensional ZnO homojunction LEDs. Full article

This study has been performed to reveal the main characteristics of operating a direct current (DC) plasma-chemical reactor (PChR) designed for hazardous waste treatment. The PChR employs thermal plasma as the operating environment. The investigations presented in this paper were conducted to study the electrical and energy characteristics of the plasma torch and plasma-chemical reactor during the destruction of inorganic waste. The PChR is equipped with a plasma torch with a nominal capacity of 50 kW and a free-burning arc. The zone of heat release from the atmospheric pressure DC arc cathode and arc anode (melted waste) spot is combined with the area of chemical reactions. The plasma torch (PT) parameters vary in the range of arc current I = 120–180 A, arc voltage U = 250–280 V, arc length x = 0–100 mm, and gas flow rate G = 1–3 g/s at atmospheric pressure, using air as the plasma-forming gas. The experimental results confirmed that plasma technology has several advantages over conventional incineration, including higher temperatures, heat source independence from the waste being processed or additional fuel, and a shorter exposure time in the high-temperature area. It was determined that the arc current increases with increasing arc length. With increasing arc length, the initial part begins to operate in a turbulent regime. This study determines the dependence on the heat flux transferred by electrons to the anode on the arc current. The convective heat flux density distribution over the anode heating spot was measured and discussed. Full article

This paper presents the results of testing and optimization of a plasma-assisted combustion scheme based on a pylon for fuel injection equipped with a plasma actuator. Electrodes were installed behind the stern of the pylon for the creation of Q-DC discharge with voltage U = 200–2500 V and current I = 3–7.5 A. The experiments were performed in the PWT-50 supersonic wind tunnel of the JIHT RAS under the following conditions: Mach number M = 2, static pressure ~200 Torr, stagnation temperature T₀ = 300 K. Gaseous fuel ethylene was used and the fuel mass flow rate was 0.5–4 g/s. The pylon had a streamlined shape that prevented the formation of a stagnant zone; plasma-assisted combustion was performed under more difficult conditions compared to plasma-assisted combustion on a flat wall, where separated flows near the wall are easily formed by discharge. In this work, two new geometries of pylon equipped with electrodes were proposed and experimentally tested. A second version providing a longer discharge length demonstrates stable ignition and intense combustion in a fully discussed fuel mass flow rate. The process of ignition in a supersonic flow and flame front pulsations was described. A reduction in the energy input in comparison with the previously considered configurations of plasma-assisted combustion was also demonstrated. Full article

In this paper, we report the experimental results obtained in slag waste processing by direct current arc discharge initiated in ambient air. The method does not employ vacuum and gas equipment, therefore increasing the energy efficiency of processing. Plasma processing of coal slag was performed at different arc exposure times: 5, 10, 15, 20, and 25 s. The obtained materials contained a significant amount of graphite, which was removed through combustion. The micropowder based on silicon carbide and aluminum nitride was obtained and then sintered by spark plasma. The bulk ceramic samples based on silicon carbide with the hardness of ~10.4 GPa were finally fabricated. Full article

Without the Fluorinert solution and proper pad design, the high–voltage (HV) transistor used during the DC breakdown voltage (V_bk) measurement might be damaged by the partial discharge (PD) in the air if its V_bk is close to one thousand volts or more. From the waveform measurement, the PD in the air occurred at 650 V HV GaN HEMTs during the V_bk measurement, it is ignited by the unipolar arc, and it is not ignited by the avalanche breakdown. This is based on the fact that the current falls below zero ampere to become a negative current, and the voltage rises so that it is higher than the setting voltage of the DC meter at the onset of the PD, thus corresponding with the electrons, leaving the plasma to cathode, and enabling a build–in potential to exist in the plasma. Then, the PD ignites because the current starts to rise in order to allow for a positive spike current; the voltage level subsequently falls and a lower voltage reading is obtained. Full article

This work focuses on detailed descriptions of DC discharge properties in supersonic airflow and its applicability in combustion simulations. Due to the complexity of obtaining most of the data in the experiment, our experimental research was supplemented by a numerical simulation. Two packages, i.e., FlowVision (fast commercial CFD for 3D engineering) and Plasmaero (2D scientific code developed in JIHT RAS for MHD tasks), were used for modeling the arc DC discharge in a supersonic flow at Mach (M) = 2. Both will be considered for further use in plasma-assisted combustion modeling, so it is important to validate both codes using experimental data from the model configuration with discharge. Axisymmetric geometries of experiments with two coaxial electrodes located parallel to the flow were chosen to avoid the appearance of the current channel part perpendicular to the flow and the corresponding discharge pulsations. Such geometries allow performing numerical simulations in 2D formulation, making it possible to compare the results obtained in the experiments and calculations. As a result of this work, two-dimensional distributions involving temperature, current density, chemical composition, and other discharge and flow parameters were obtained for arc DC discharges 0.5–7 A in a supersonic flow (Pst = 22 kPa, T = 170 K, V~500 m/s). Good qualitative agreement between experimental and numerical results was achieved. The production of a significant amount of atomic oxygen, which accelerates combustion, was noted. Full article

A plasma jet-triggered gas switch (PJT-GS) has been developed as an important piece of equipment to operate in an $\pm$800 kV ultra-high voltage direct current transmission system (UHV DC) to achieve grid system protection and control. The crucial factors that would affect its operational performance, such as the current level the PJT-GS could withstand and the gas gap distance between the two rotating electrodes, are comparatively studied in the present work by analysing the arc dynamic characteristics. The rotating electrode used in the PJT-GS is designed with a helical-slotted structure, and the arc can be rotated circularly driven by the produced transverse magnetic field (TMF) along the electrode edge. The objective of such research is to provide a thorough study of the arc dynamic behaviour during the current flowing process of the PJT-GS and also to characterise the physical mechanism that affects the arc rotation and the PJT-GS operation performance. The magnetohydrodynamic-based (MHD) approach is applied by establishing a 3D arc model. Following such a study, the variation of arc characteristics under different operation conditions could be thoroughly determined and it also could provide the guidance for the PJT-GS optimum design reasonably to support its corresponding engineering applications. Full article