High-temperature Plasma Jet Research Articles

Enhanced Oxygen Evolution Reaction Performance of NiMoO4/Carbon Paper Electrocatalysts in Anion Exchange Membrane Water Electrolysis by Atmospheric-Pressure Plasma Jet Treatment.

NiMoO4 was grown on carbon paper (CP) by a hydrothermal method. A rapid and high-temperature atmospheric-pressure plasma jet (APPJ) process was used to generate more oxygen-deficient NiMoO4 on the CP surface to serve as an electrode material for the oxygen evolution reaction (OER). After 60 s of APPJ treatment, the overpotential of the electrode at 100 mA/cm2 decreased to 790 mV and that at 10 mA/cm2 decreased to 368 mV. Additionally, the charge transfer resistance decreased from 2.8 to 1.2 Ω, indicating that APPJ treatment effectively reduced the electrode overpotential and impedance. The effect of NiMoO4/CP/APPJ-60 s on the anion exchange membrane water electrolysis (AEMWE) system was also tested. At a system temperature of 70 °C and current density of 100 mA/cm2, the energy efficiency reached 95.1%, and the specific energy consumption decreased from 4.02 to 3.83 kWh/m3. These results demonstrate that the APPJ-treated NiMoO4/CP electrode can effectively enhance the OER performance in water electrolysis and improve the energy efficiency of the AEMWE system. This approach shows promise in replacing precious metal electrodes, thereby potentially reducing the cost and providing an environmentally friendly alternative.

Collapse characteristics and deposition behaviour of PS–PVD powders with different crushing strengths

Plasma spray–physical vapour deposition uses finely agglomerated spherical powders as raw materials; these powders undergo a complex process of dispersing–melting–evaporation–condensation in high-temperature and high-speed plasma jets to attain the desired physical phase and high-performance columnar-like structure thermal barrier coatings. Currently, the interactions between the powders and the jets have not been fully disclosed. The article examines the crushing strength of powders with various particle sizes and properties. To further elaborate the crushing process, discrete element simulation was used. Additionally, powder spray deposition experiments were conducted to disclose the association between powder properties and the efficiency of coating deposition. The findings indicate that the stiffness of the powder and the size of the internal particles have an impact on the crushing strength of the powder. The stronger the bond strength caused by greater powder stiffness, the more effective the dispersion effect becomes. Furthermore, the smaller the particle size, the higher the compressive and collapse strength. Therefore, the greater the crushing strength of the powder, the higher the rate of powder deposition.

Enhanced high temperature ablation resistance of dense ZrB2–Al2TiO5 composite coating by very low-pressure plasma spraying

ZrB2-based composite coatings with addition of Al2TiO5 were prepared via very low-pressure plasma spraying using mechanically mixed powder of ZrB2 and Al2O3-40 wt%TiO2 (AT40). The ablation behavior of the composite coating was investigated using a high temperature plasma jet at a temperature of ∼2500oC. Results demonstrate the addition of AT40 improved the ablation resistance of the ZrB2 coatings at high temperatures. The coating with 17 vol%AT40 addition exhibited the lowest ablation rate, approximately 1.33 μm/s, which is only one-third of that of the pure ZrB2 coating. The added AT40 filled the pores between ZrO2 crystals during ablation, reducing oxygen penetration and lowering the ablation rate. However, excessive addition of AT40 hindered gaseous B2O3 release and thus led to large pore formation, impairing the protective effect. The ZrB2-AT40 coating is a promising candidate for high-temperature applications.

Continuous synthesis of high-entropy alloy nanoparticles by in-flight alloying of elemental metals

High-entropy alloy (HEA) nanoparticles (NPs) exhibit unusual combinations of functional properties. However, their scalable synthesis remains a significant challenge requiring extreme fabrication conditions. Metal salts are often employed as precursors because of their low decomposition temperatures, yet contain potential impurities. Here, we propose an ultrafast (< 100 ms), one-step method that enables the continuous synthesis of HEA NPs directly from elemental metal powders via in-flight alloying. A high-temperature plasma jet ( > 5000 K) is employed for rapid heating/cooling (103 − 105 K s−1), and demonstrates the synthesis of CrFeCoNiMo HEA NPs ( ~ 50 nm) at a high rate approaching 35 g h−1 with a conversion efficiency of 42%. Our thermofluid simulation reveals that the properties of HEA NPs can be tailored by the plasma gas which affects the thermal history of NPs. The HEA NPs demonstrate an excellent light absorption of > 96% over a wide spectrum, representing great potential for photothermal conversion of solar energy at large scales. Our work shows that the thermal plasma process developed could provide a promising route towards industrial scale production of HEA NPs.

Preparation and properties of Al2O3-PF composite functional protective coating on the surface of polymer matrix composites

In this paper, a metal-free ceramic-resin (Al2O3-PF) composite protective coating was prepared on 3240 glass fiber reinforced epoxy resin by high-energy supersonic plasma spraying technology and “double channel and large temperature difference” powder feeding technology. The composite coating not only has good morphology and structure, but also has excellent performance in various properties. It is found that the bond strength of the composite coating can reach 29.60 MPa, and the shear strength can reach 24.24 MPa, far exceeding the research results in related fields at home and abroad. In addition, under the same wear conditions and high temperature ablation, the composite coating can increase the wear resistance and high temperature ablation resistance of the resin matrix by about 2 times, and the insulation resistance of the coating can still reach 2.43 × 1013 Ω after 500 times of high temperature plasma jet ablation, showing excellent insulation performance. However, due to the structural particularity of the composite coating, its erosion resistance and thermal expansion performance need to be further improved.

Heating Behaviors of Carbon-besed and Silicon-based Materials in High-temperature Plasmajets

When a sample return capsule enters into the Earth's atmosphere, a strong shock wave is generated in front of the capsule, and it is subjected to severe aerodynamic heating. One of the thermal protection methods used to protect the capsule from the heating is the ablation method. In the future, the capsule is expected to become larger and the re-entry speed will increase. In this case, the capsule will be exposed to more severe aerodynamic heating. In order to investigate the fundamental heating behaviors of carbon-based and silicon-based materials, the authors have systematically conducted the heating experiments of these materials in high-temperature plasmajets.

Microstructure and Ablation Behavior of Low-Pressure Plasma Sprayed ZrB2 Coatings Down to 100 Pa.

The effect of chamber pressure on the microstructure and ablation behavior of ZrB2 coatings deposited by low-pressure plasma spraying was investigated. The results showed that as the spray chamber pressure further was reduced to less than 50 kPa, the porosity of the coating deposited at the same distance decreased with the chamber pressure, and the coating prepared under 100 Pa presented the lowest porosity of about 0.89%. The ablation performance test subjected to high-temperature plasma jet revealed that the linear ablation rate of ZrB2 coating increased with the porosity of the coating. As a result, among the ZrB2 coatings deposited at chamber pressures of 100 Pa, 5 kPa, 10 kPa and 50 kPa, the dense coating deposited at 100 Pa showed the lowest ablation rate of 0.33 µm/s. The dense ZrB2 coating with a thickness of about 100 μm was able to withstand 300 s ablation by a plasma flame with a net power of 25 kW resulting in an ablating coating surface temperature of about 2000 °C. The ablation mechanism of the coating was also examined.

Silicon nanorod formation from powder feedstock through co-condensation in plasma flash evaporation and its feasibility for lithium-ion batteries

Si nanowires/nanorods are known to enhance the cycle performance of the lithium-ion batteries. However, viable high throughput production of Si nanomaterials has not yet attained as it requires in general expensive gas source and low-rate and multiple-step approach. As one of the potential approaches, in this work, we report the fast-rate Si nanorod synthesis from low-cost powder source by the modified plasma flash evaporation and the fundamental principle of structural formation during gas co-condensation. In this process, while Si vapors are formed in high temperature plasma jet, molten copper droplets are produced separately at the low temperature region as catalysts for growth of silicon nanorods. Si rods with several micrometers long and a few hundred of nanometers in diameter were produced in a single process at rates up to 40 µm s−1. The growth of the Si nanorods from powder source is primarily characterized by the vapor–liquid–solid growth which is accelerated by the heat extraction at the growth point. The battery cells with the Si nanorods as the anode have shown that a higher capacity and better cyclability is achieved for the nanorods with higher aspect ratios.

The design and analysis of a novel low power atmospheric plasma jet torch for optical fabrication

Over the past few years, atmospheric Inductively Coupled Plasma (ICP) has aroused extensive attention in optical fabrication field since its chemical etching-based processing mode does not mechanically damage work-pieces. However, commercial Fassel-type torch are commonly employed in processing, and the high temperature plasma jet generated by commercial Fassel-type torch will cause thermal damage to optical elements. In this paper, an ICP jet torch is developed for optical fabrication, capable of maintaining plasma jet under a low power of 156 W. By reducing the minimum maintenance power of plasma jet, the processing temperature is down-regulated to 112 °C. To explain the low maintenance power principle in this research, the effect of radial confinement and axial pushing-off on the plasma are analyzed by simulation and experiment processes. Moreover, the effect of these two phenomena on the maintenance power is analyzed experimentally. Subsequently, the experiments are performed to verify the processing temperature, removal efficiency and removal stability of the torch. As revealed from the experimental results, the proposed torch exhibits the stability of footprint up to 97.5%.

Unsteady Heating Experiments of Silicon-based Heat-resistant Materials in High-temperature Plasma-jets

Unsteady Heating Experiments of Silicon-based Heat-resistant Materials in High-temperature Plasma-jets

Estimation of Dense Plasma Temperature Formed under Shock Wave Cumulation.

The research was carried out by means of implosion plasma generators with conical and hemispherical compression chambers to conduct a quantitative assessment of the boundary temperature of super dense plasma jets. It was proved experimentally that nuclear transformations in metals are caused by the impact of super dense plasma jets (11, ..., 12) × 103 kg/m3. The boundary temperature of these jets was evaluated. It was estimated that the nominal boundary temperature of the studied implosion plasma generators is 106 К. The pressure in the target at the penetration of the super dense jet (~12,000 kg/m3) at the speed of 28,000 m / sec is more than 30 ТPa. The boundary temperature was estimated and proved to depend on the pre-determined values only slightly. It was experimentally established that stable isotopes of manganese Mn55 (up to 27%) are formed in iron targets as a result of high temperature plasma jet penetration. The appearance of manganese must be related to iron transformation into stable isotopes Fe56 and Fe54. The obtained results may be applied for investigating structural changes in metals under the conditions of impulsive super high temperatures and pressures. This method can be also used as a testing ground for studying the physical conditions of forming chemical elements as well as super dense plasma jets.

Unique Aspects of Thermal Plasma Torches and Reactor Design for Process Applications

Novel features of arc plasma devices with thermionic and thermo-chemical cathodes and development of associated thermal plasma process reactors are investigated from device design and application point of view. Different types of plasma torches and open arcs, their fundamental differences in architecture, jet behavior, operational constraints, and evolution of interesting electromagnetic forces inside them have been probed. Investigation of instabilities in arcs through direct real-time imaging of arc path using fast photography and impact of powder loading on such instabilities are presented. Development of low power air plasma torches delivering large volume high-temperature plasma jet with long penetration depth has been investigated together with an estimation of hazardous NOx, produced from such devices during operation. Interesting attributes of various types of thermal plasma reactors including plasma spray chemical vapor deposition (CVD) reactors for thick and dense coating, reactors for generation of H-OH plasma, radio frequency (RF) thermal plasma reactors for the synthesis of nanostructures, and air plasma gasifier reactors for environment-friendly mitigation of municipal solid waste (MSW) and electronic wastes have been presented. Coke bed air plasma gasifiers are specially investigated for their important technological aspects. Experimental results are presented with simulation supports for enhanced understanding, wherever necessary.

Design and optimization of plasma jet nozzles based on computational fluid dynamics

This study aims at identifying an optimal solution for the design of convergent-divergent nozzles discharging high-temperature plasma jets. Optimized profile parameters (e.g. throat size, depths of convergent and divergent parts) were developed to enhance the processing capability of the inductively coupled plasma torch. The temperature and velocity of the plasma jet are studied both along the axis of the nozzle and onto the impinged substrate surface. Computational fluid dynamics analysis of 55 models with different cross-sectional profiles highlights cases that can be used to enhance plasma figuring processes. The enhanced nozzles are compared with the benchmark nozzle in all selection criteria. This optimization approach is proven to provide an efficient design method of plasma nozzles for future processing activities. The rapid design and optimization of the nozzle are expected to adjust the material removal footprint of plasma process in metre-scale optical fabrication. Experimental results prove that the enhanced nozzle has 5% higher efficiency against the original one.

A Consideration on Radiation Measurements around Silicon-based Heat-resistant Materials in High-temperature Plasma-jets

A Consideration on Radiation Measurements around Silicon-based Heat-resistant Materials in High-temperature Plasma-jets

Heating Experiments of Carbon-based and Silicon-based Heat-resistant Materials in High-temperature Plasmajets

Heating Experiments of Carbon-based and Silicon-based Heat-resistant Materials in High-temperature Plasmajets

Fast inactivation of microbes and degradation of organic compounds dissolved in water by thermal plasma

The multifunctionality and the advantages of thermal plasma for the fast inactivation of viable cells and degradation of organic compounds dissolved in waste water are presented. A complete bacterial inactivation process was observed and studied using a thermal plasma treatment source with very short application times, in particular for Staphylococcus aureus bundle spore survival. The survival curves and analyses of the experimental data of the initial and final densities of S. aureus bacteria show a dramatic inhibitory effect of the plasma discharge on the residual bacteria survival ratio. As the exposure time increased, the inactivation process rate increased for direct exposure more than it did for indirect exposure. The evaluation of direct and indirect exposure was based on the analysis of the ultraviolet spectrum from the absorbance spectra of the organic compound dye called benzene sulfonate (C16H11N2NaO4S) and of viable cells called S. aureus. Organic compounds were degraded and viable cells were killed in a short time by thermal plasma. Moreover, analyses of total carbon, total organic carbon, and total inorganic carbon showed a fast decrease in organically bound carbon, however, this was not as fast as the absorbance spectra revealed by the exposure time increasing more for direct exposure than indirect exposure. After 100 s of exposure to the organic compound dye the removal had a maximun of 40% for samples with indirect exposure to the plasma and a maximum of 90% for samples with the direct exposure. For both samples, where some organic contaminants still remained in treated water, four electrolytes (KCl, NaCl, Na2SO4, and CH3COONa) were added to be effective for complete sterilization, reaching a purity of 100%. A proposal is made for an optimized thermal plasma water purification system (TPWPS) to improve fast inactivation of microbes and the degradation of organic compounds dissolved in water (especially for direct exposure rather than indirect exposure) using a hybrid plasma torch with an electrical power of 125 kW (500 V–250 A) producing a high-temperature (10 000 K–19 000 K) plasma jet with a maximum gas consumption of 28 mg s−1.

TECHNOLOGICAL SPECIFIC FEATURES ON FORMATION OF PLASMA POWDER COATINGS FROM CERAMICS WITH NON-EQUILIBRIUM STRUCTURE

The paper presents investigations on studying the influence of plasma jet parameters (current, sputtering distance, consumption of nitrogen plasma forming gas), fractional composition of an initial powder on characteristics of plasma powder coatings from ceramics with a non-equilibrium structure. Optimization of APS parameters (plasma spraying in air) has been carried out for the following materials: NiAl, Al2O3–Cr2O–TiO2– 15 % (CaF2–Ni) and FeCr30Mo3 – 12 % CaF2– 50 % TiC. The optimization of sputtering parameters has been made on the basis of obtaining maximum coefficient of the material use. Structure of coatings, their chemical and phase compositions have a determining effect on physical and mechanical properties of the coatings, in particular, on porosity, adhesion strength and wear resistance. In its turn, a structure and a composition of the coating formed on the substrate depend on energy characteristics of the plasma sputtering process, an efficiency of heat exchange processes between dispersed and gas phases of high-temperature plasma jet, and also on a composition, a structure, and properties of the used materials. Thus, a stable distribution of a solid oxide phase has been observed in the volumes of sputtered materials and there are no surface zones with a deficiency of such inclusions that positively affects operability of the investigated wear-resistant coatings. While carrying out plasma deposition of Al2O3–Cr2O–TiO2– 15 % (CaF2-Ni) powders, a coating with a higher micro-hardness has been formed in comparison with Al2O3–Cr2O–TiO2– 15 % (MoS2–Ni) powders that is due to a decrease in porosity and an increase in uniformity of coatings. Graininess of the coatings exerts a significant influence on density of coatings, nature of phase distribution and strength characteristics (wear resistance and adhesion strength).

Tribological studies of thin diamond-like films synthesized using high-speed plasma jet

In this paper, the tribological studies of diamond-like films under slip friction conditions are described. The films have been deposited from various materials (steel, aluminum, copper, and others). These films are deposited by the chemical vapor deposition method using a supersonic high-temperature plasma jet generated by a high-enthalpy plasmatron with a sectionalized interelectrode insert and a cold gas curtain for the walls of the discharge chamber. Tribological studies of the deposited films are performed using the friction simulator in the disc–ring system at rotational reverse motion. As a lubricant, 2% carboxymethylcellulose solution is used. Considerable differences in the tribological behavior depending on the substrate material, where the film has been deposited, are noted.

Re-distribution of the planetary material between the Sun and giant planets at the process of the terrestrial planets formation

The mathematical approximation of the relation for the distances of planets from the Sun and distribution of the planet masses in the Solar system are represented. It is shown that the planetary distances from the Sun can be accurately described by the logarithmic spiral equation. The same relation is established for the four biggest satellites of the Jupiter. The relationship between the masses of the terrestrial planets and their distance from the Sun. is described by the parabola equation. This relationship for the outer planets of the Solar system is described by hyperbola equation. These data allow us to conclude, that the big gaseous planets were formed on the terrestrial planets position on the beginning stage. The gaseous components of these planets were redistributed between the Sun and the Jupiter on the next stage and the terrestrial planets were formed from residual material. There are This is the e-book version of the article, published in Russian Journal of Earth Sciences (doi:10.2205/2016ES000563). It is generated from the original source file using LaTeX’s ebook.cls class. three hypotheses, which can be used for the new models of formation of the planetary systems. Hypothesis 1. Besides molecular clouds there is another source of material, from which stars and planet systems forms. Hypothesis 2. Protosolar cloud can have form high temperature plasma jet. Hypothesis 3. The jet of plasma can roll up in the spiral whirl in which a material moves towards the pole of the spiral where the central star forms.

Influence of Oxidation Behavior of Feedstock on Microstructure and Ablation Resistance of Plasma-Sprayed Zirconium Carbide Coating

Plasma spray is one of the suitable technologies to deposit carbide coatings with high melting point, such as ZrC. However, in the spray processes performed under atmosphere, oxidation of the carbide powder is inevitable. To investigate the influence of the oxidation behavior of feedstock on microstructure and ablation resistance of the deposited coating, ZrC coatings were prepared by atmospheric and vacuum plasma spray (APS and VPS) technologies, respectively. SiC-coated graphite was applied as the substrate. The obtained results showed that the oxidation of ZrC powder in APS process resulted in the formation of ZrO and Zr2O phases. Pores and cracks were more likely to be formed in the as-sprayed APS-ZrC coating. The VPS-ZrC coating without oxides possessed denser microstructure, higher thermal diffusivity, and lower coefficients of thermal expansion as compared with the APS-ZrC coating. A dense ZrO2 layer would be formed on the surface of the VPS-ZrC-coated sample during the ablation process and the substrate can be protected sufficiently after being ablated in high temperature plasma jet. However, the ZrO2 layer, formed by oxidation of the APS-ZrC coating having loose structure, was easy to be washed away by the shearing action of the plasma jet.