Arc Plasma Method Research Articles

Significant Improvement in Magnetorheological Performance by Controlling Micron Interspaces with High Permeability Submicron Particles.

The shear yield strength, sedimentation stability and zero-field viscosity of magnetorheological fluids (MRFs) are crucial for practical vibration damping applications, yet achieving a balanced combination of these performances remains challenging. Developing MRFs with excellent comprehensive performance is key to advancing smart vibration damping technologies further. Theoretically, incorporating a multiscale particle system and leveraging synergistic effects between their can somewhat enhance MRFs' performance. However, this approach often faces issues such as insignificant increases in shear yield strength and excessive rise in zero-field viscosity. In response, this study employs a DC arc plasma method to synthesize a high magnetic permeability, low coercivity submicron FeNi particles, and further develops a novel CIPs-FeNi bidisperse MRFs. The introduction of submicron FeNi particles not only significantly enhances the shear2019 yield strength of MRFs under low magnetic fields but also promotes improvements in sedimentation stability and redispersibility without excessively increasing viscosity. Comprehensive performance analysis is conducted to explore the optimal content ratio, and detailed mechanisms for the enhancement of performance are elucidated through analysis of parameters such as chain-like structure, magnetic flux density and friction coefficient. Most importantly, the superior comprehensive performance combined with straightforward fabrication methods significantly enhances the engineering applicability of the CIPs-FeNi bidisperse MRFs.

Molecular dynamics simulation study of graphene synthesis by rotating arc plasma

The rotating arc plasma method, based on its unique characteristics, provides a simple, efficient, and catalyst-free approach for graphene material synthesis. This study employs molecular dynamics simulations to theoretically investigate the detailed growth process of graphene at the atomic scale using plasma. During the growth process, different radicals serve as dissociation precursors within the plasma. Simulation results indicate that the growth process of graphene clusters involves three stages: extension of carbon clusters, cyclization of carbon chains, and coalescence of clusters into sheets. Firstly, the precursor concentration affects the size of graphene clusters; increasing the precursor concentration enlarges the cluster size but also increases the likelihood of curling. Secondly, increasing the hydrogen content in the precursor can reduce the growth rate of clusters, decrease dangling bonds at the periphery of clusters, thereby slowing down cluster closure and maintaining a well-defined sheet structure. Lastly, appropriately elevating the simulation temperature can enhance the reaction rate during the simulation process without altering the reaction pathway. These research findings establish the foundation for understanding the growth mechanism of graphene.

Synthesis of chromium carbide powder by vacuum-free electric arc plasma method

Chromium carbide powders were synthesized by vacuum-free electric arc method using pure chromium and carbon powder as starting components. The powders obtained in the experimental series were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), laser diffraction and differential thermal analysis. In the experiments, electrical parameters were recorded, and the thermal field generated in the reaction zone was measured using an infrared camera and tungsten‑rhenium thermocouples. The study results show the feasibility of plasma arc discharge synthesis of chromium carbide compounds Cr3C2 and Cr7C3 within 60 s at current intensity of 200 A. SEM analysis of the resulting powder shows that it consists of acute-angled particles of ∼9 to ∼50 μm in size. An updated design of the discharge circuit employed in the study significantly increases the purity of the final product. Vacuum-free electric arc synthesis of chromium carbide has been studied for the first time.

A modified Fe–Ni alloy coating in pure iron combined of surface mechanical attrition treatment and spark plasma sintering approach

To overcome the shortage of long processing time, high energy consumption, and complex controlling in fabricating Fe–Ni alloy coating, this paper was modified Fe–Ni alloy coating based on the mechanical alloying, electrodeposition, laser cladding and DC arc plasma method. Here, Surface Mechanical Attrition Treatment (SMAT) had been chosen as a pre-treatment to fabricate uniform Fe–Ni alloy coating by Spark Plasma Sintering (SPS). After the well-designed coating approach of SMAT + SPS, a homogeneous and continuous Fe–Ni alloy coating was fabricated on a pure iron plate. During study of the effect of SMAT and the subsequent process of SPS on microstructure and mechanical properties of Fe–Ni alloy coating, a valid set of process parameters were investigated. The results show that the thickness of Fe–Ni interface layer was enhanced significantly by SMAT. In comparison, the depth on the SMAT-sample was approximately twice as thick as on the untreated coarse-grained (CG) sample. The relative densification, microhardness and friction and wear performance are significantly related to the sintering temperature, which also affects the microstructure of interface between iron matrix and alloy coating. It has been evidently proved that, the sintering temperature just within 800–900 °C, the optimum performance Fe–Ni alloy coating on the SMATed iron matrix could be obtained, which has higher density, better wear resistance and tighter bonding.

Pt–Ni Thin-Film Catalyst for the Hydrogen Oxidation Reaction under Alkaline Conditions

Improving the catalysts of the hydrogen oxidation reaction (HOR) in alkaline conditions is necessary for developing anion exchange membrane fuel cells as alternatives to conventional proton-exchange-membrane fuel cells. Previous studies have demonstrated Pt catalyst improvement by forming coordinatively saturated surface sites (i.e., plane surfaces) as well as by combining Pt with other metals. In this study, Pt–Ni thin-film catalysts, which exhibited an enhanced activity compared to Pt monometal thin-film and nanoparticle catalysts, were prepared by a pulsed arc plasma method. Additionally, the prepared catalysts were heated to form Pt–Ni alloy catalysts with further improved activity. Thus, Pt–Ni alloy thin films were demonstrated as highly active structures in an alkaline HOR.

Preparation of silver nanopowders and its application in low temperature electrically conductive adhesive

Printable electrically conductive adhesive with high electrical conductivity and good mechanical properties has a broad application prospect in electronic devices. In order to explore the preparation method of high-purity nanometal conductive filler for conductive adhesive, silver nanopowders were prepared by DC arc plasma method. The silver nanopowders present a spherical structure and the average particle size is 55 nm. In this paper, a high performance electrically conductive adhesive (ECA) was prepared. This ECA was fabricated by mixing silver nanopowders with epoxy resin and screen-printed to a required shape. It was found that the ECA can be solidified through a low temperature sintering method in the air at 150 °C for 10 min. The electrical and mechanical properties of above ECA were investigated and characterized. The ECA filled with 75 % silver nanopowders exhibits excellent performances, including high electrical conductivity (9.8 × 10−3 Ω·cm) and high bonding strength (8.3 MPa). Based on the performance characteristics, the ECA applications in flexible printed electrodes and interconnecting materials are demonstrated.

Insights into thermodynamic destabilization in Mg-In-D hydrogen storage system: A combined synchrotron X-ray and neutron diffraction study

In this study, ultrafine Mg(In) solid-solution particles were successfully prepared through an arc plasma method and their deuterium uptake/release performances were systematically estimated with respect to the identically processed pure Mg particles. Thermodynamic destabilization and kinetic enhancement of Mg-In-D system were achieved simultaneously with lower deuterium ab/desorption enthalpies and decreased desorption temperatures. For the first time, an in-situ synchrotron X-ray diffraction (ISXRD) coupled with neutron powder diffraction (NPD) technique and density functional theory (DFT) calculations clearly substantiated that an indium diffusion-dominated phase transition is the driving force for the evolution from mixture of MgD2 and Mg-In intermetallic to Mg-based solid solution during the deuterium release (DR). The ISXRD results clarified the real-time phase transition from MgIn to Mg3In at 515 K and the interreaction of MgD2 and Mg3In at 640 K, by which the matrix could be destabilized to trigger an indium-diffusion governed DR reaction in deuteride. Moreover, with the aid of NPD experiment, the microstructure evolution of Mg-In-D system demonstrated the continuous diffusion of indium into Mg/MgD2 upon desorption. The solubilized indium in MgD2 effectively reduced the D-migration energy barrier and stabilized the lattice structure to restrain the constriction of Mg-D bonds, through which the noticeable improvement on both thermodynamic and kinetic performances of the Mg-In system was achieved. The combination of synchrotron X-ray and neutron diffraction offers a high-efficiency strategy to fathom the hydrogen discharging mechanism from the viewpoint of real-time phase transitions and crystalline structure evolutions.

Machine learning-driven synthesis of TiZrNbHfTaC5 high-entropy carbide

Synthesis of high-entropy carbides (HEC) requires high temperatures that can be provided by electric arc plasma method. However, the formation temperature of a single-phase sample remains unknown. Moreover, under some temperatures multi-phase structures can emerge. In this work, we developed an approach for a controllable synthesis of HEC TiZrNbHfTaC5 based on theoretical and experimental techniques. We used Canonical Monte Carlo (CMC) simulations with the machine learning interatomic potentials to determine the temperature conditions for the formation of single-phase and multi-phase samples. In full agreement with the theory, the single-phase sample, produced with electric arc discharge, was observed at 2000 K. Below 1200 K, the sample decomposed into (Ti-Nb-Ta)C, and a mixture of (Zr-Hf-Ta)C, (Zr-Nb-Hf)C, (Zr-Nb)C, and (Zr-Ta)C. Our results demonstrate the conditions for the formation of HEC and we anticipate that our approach can pave the way towards targeted synthesis of multicomponent materials.

Local Structural Analysis of Carbon Supported Pt Catalysts Synthesized by an Arc Plasma Method

Local Structural Analysis of Carbon Supported Pt Catalysts Synthesized by an Arc Plasma Method

Measurement of re-entry plasma density using microwave reflectometer in laboratory.

A laboratory-scale experiment was conducted to reproduce plasma with properties similar to re-entry plasma and measure the plasma density using a microwave reflectometer system. To reproduce a similar re-entry plasma, a high-temperature refractory anode vacuum arc plasma method was used among arc plasma discharge methods, and arc plasma having high temperature, high speed, and high-density plasma characteristics was discharged inside a vacuum chamber. A hot refractory anode made of tungsten was used to show high-temperature plasma characteristics, and high-density plasma characteristics were demonstrated using re-evaporation around the anode. In addition, high-speed plasma characteristics were exhibited using a brass cathode. This kind of arc plasma discharge has a high temperature and is characterized by high fluctuation. It was determined that a microwave reflectometer system with good spatial resolution and non-invasiveness would be suitable to measure plasma with these characteristics. The reflection coefficient was measured using a reflector system by comparing the voltage between the traveling wave applied to the plasma and the reflected wave reflected by the plasma, and the technique of analyzing the plasma density using the difference between these reflection coefficients was used. In this study, the plasma density according to the pressure change was typically measured as 1012-1013cm-3, which showed a similar tendency to the result of measuring the actual re-entry plasma density.

Ce-modified Rh overlayer for a three-way catalytic converter with oxygen storage/release capability

A nanometric Rh overlayer exhibits excellent three-way catalytic activity under stoichiometric conditions. However, dynamic changes in the air-to-fuel (A/F) ratio under experimental conditions deteriorates the catalytic activity caused by the lack of oxygen storage/release capability of Rh. In this study, we first report that the surface modification of the Rh overlayer by a small amount of Ce using a sequential metal deposition technique based on the pulsed arc-plasma method enhances its three-way catalytic activity under A/F perturbation conditions. X-ray photoelectron spectroscopy and X-ray absorption fine structure measurements revealed that the redox behavior of the surface Ce contributed to an oxygen storage/release and buffered the A/F change. The Ce-modified Rh overlayer with a metal honeycomb structure exhibited high activity for the three-way catalytic reaction even under A/F perturbation conditions at high space velocity. This novel catalytic converter is expected to be significantly process and energy saving compared to the conventional catalytic converter. Thus, the oxygen storage/release performance, heat resistance, and low-temperature activity can be improved by controlling the surface composition.

Hydrogen arc plasma promotes the purification and nanoparticle preparation of tungsten

As an important refractory metal, tungsten (W) has unique physical-chemical properties, and the applications of high-quality tungsten NPs with uniform particle size, high purity, and good particle dispersion in industrial fields are highly desirable. Herein, the integration of tungsten metallurgical purification and nanoparticle preparation is achieved by the hydrogen arc plasma method. In the process of purification, on the condition of arc current of 250 A, hydrogen concentrations of 30 vol%, purification time of 40 min, and gas pressure of 60 kPa, the highest impurity removal rate is achieved. The active H+ is able to react with impurities to generate metal hydride (MH, M = Al, Cr, Mg, and Fe), which promotes the removal rate of impurity elements. During the preparation of nanoparticles (NPs), the as-prepared tungsten NPs with an average particle size of 44.1 nm have a regular spherical structure, high purity, and a relatively uniform particle size distribution. When the hydrogen concentration is controlled at 50 vol%, the extremely high temperature promotes the evaporation of tungsten. Meanwhile, the active H+ reacts with tungsten to form tungsten hydride (WH), further increasing the evaporation rate of tungsten. According to the above results, the hydrogen arc plasma promotes the simplification of the production process steps of high purity tungsten NPs and reduces the industrialized production cost of high-quality refractory metal NPs.

Large-Scale Synthesis of Molybdenum Carbide Based Catalyst by Vacuum-Free DС Arc Plasma Method

The paper presents experimental studies on the synthesis of materials based on molybdenum carbide, which can be used as a catalyst for hydrogen production by water splitting. We successfully carried out experiments to scale up the process, namely, the amount of the synthesized product was increased by 4 times with the same parameters of the experimental setup. In this case, the specific energy decreases taking into account the increase in the mass of the product. The energy intensity of the material obtained has been reduced from 520 kJ/g to 130 kJ/g.

Influence of Plasma on the Combustion Mode in a Scramjet

To examine the plasma-assisted combustion of a scramjet, a microwave-enhanced gliding arc plasma method was proposed in this study, and the flame structure and combustion instability were observed. The mechanism of plasma-assisted combustion was obtained via a Bunsen experiment, and then the influence on supersonic combustion was obtained on a direct-connected scramjet. The active species of the flame was determined via optical emission spectroscopy, and the flame temperature was measured with a thermocouple. The luminous intensity of the OH radicals in the flame increased ninefold when the flame temperature was increased to 1573 K, but the luminous intensity of CH* and C2 was not obviously changed with the excitation of arc plasma. Moreover, the DC arc plasma had no effect on the rotation and the vibration temperature of OH radicals under these experimental conditions. In the range of microwave energy less than 800 W, there was no typical change in the intensity of the radicals; however, when the microwave power was up to 1000 W, the effect became obvious. When plasma was applied to the scramjet, the plasma caused the pre-combustion shock train to move forward, and the initial and stable position of the flame was transferred from the cavity shear layer to the front of the fuel jet. These results clearly show that plasma free radical mechanisms cause changes to combustion modes.

Plastic anisotropy and compressive deformation behavior of Zinc prepared by sintering using fine particles

In recent years, Zn can potentially be applied as biomaterials owing to its excellent biocompatibility and biocorrosion resistance. However, Zn has poor strength and large plastic anisotropy due to its hexagonal close-packed (HCP) structure. In this study, to increase the strength and plastic isotropy, fine-grained Zn polycrystal was produced by spark plasma sintering from Zn fine particles prepared by arc plasma method. Yield strength and the plastic anisotropy of the sintered Zn were evaluated by compression tests and Vickers indentation. The yield strength of the sintered Zn was significantly higher than the as-cast Zn. Moreover, the plastic anisotropy of the sintered Zn was small because of its fine grain and random texture.

Modelling of a Non-Transferred Plasma Torch Used for Nano-Silica Powders Production

In this study, a two-dimensional numerical model was developed to simulate operation conditions in the non-transferred plasma torch, used to synthesis nanosilica powder. The turbulent magnetohydrodynamic model was presented to predict the nitrogen plasma flow and heat transfer characteristics inside and outside the plasma torch. The continuity, momentum, energy, current continuity equations, and the turbulence model were expressed in cylindrical coordinates and numerically solved by COMSOL Multiphysics software with a finite element method. The operation conditions of the mass flow rate of ionized gas ranging from 78 sccm to 240 sccm and the current varying between 50 A to 200 A were systematically analyzed. The variation in the electrothermal efficiency with the gas flow rate, the plasma current, and the enthalpy was also reported. The results revealed that the increase in working current lead to a raise in the effective electric power and then an increase in the distribution of plasma velocity and temperature. The efficiency of the torch was found to be between 36% and 75%. The plasma jet exited the nozzle torch with a larger fast and hot core diameter with increasing current. The numerical results showed good correlation and good trends with the experimental measurement. This study allowed us to obtain more efficient control of the process conditions and a better optimization of this process in terms of the production rate and primary particle size. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the primary nanosilica powder that was experimentally collected. The arc plasma method enabled us to produce a spherical silicon ultra-fine powder of about 20 nm in diameter.

Effects of different concentrations of artificial joint prosthesis nanoparticles on cytotoxicity and osteogenic differentiation of bone marrow stromal cell (BMSCs) in vivo

To explore the effects of artificial joint prosthesis nanoparticles on cytotoxicity and osteogenic differentiation of Bone Marrow Stromal Cell (BMSCs). SD rats were used to isolate cells and titanium metal obtained from artificial joint revision surgery was prepared into nanoparticles by the direct current arc plasma method. The SD rats were then divided into control group, blank group (group A: D-MEM medium+10% FBS), low concentration group (group B: 0.01 mg/mL titanium alloy particles), medium concentration group (group C: 0.05 mg/mL titanium alloy particles), high concentration group (group D: 0.1 mg/mL titanium alloy particles plus D-MEM complete medium+10% FBS), followed by analysis of cytotoxicity and osteogenic differentiation of BMSCs. Among the three test groups, group B showed highest percentage of viable cells and group D had lowest. The percentages of viable cells in three test groups were significantly lower and cell death rate were higher than those in the control group (P < 0.05). Titanium alloy metal particles inhibited osteogenic differentiation of BMSCs in a dose dependent manner. The cells in control group were stained and dark brown nuclei were visible. The stained cells were almost invisible in group A, and less red-stained areas in group B, and with a small amount of cell nuclei. Artificial joint prosthesis particles had certain effects on cytotoxicity and osteogenic differentiation of BMSCs in vivo. Among them, the high concentration of titanium alloy nanoparticles test group had the highest percentage of viable cells.

Effect of passivation treatment and arc current on the properties of Zn fine particles prepared by arc plasma method

In this study, the effects of the passivation treatment and arc current on the properties of Zn fine particles, prepared by the arc plasma method, were investigated to obtain particles with a minimum amount of oxide impurities for application in powder metallurgy. The average particle size of the Zn fine particles, prepared by this method, increased with the increasing arc current, and a minimum average particle size of 236.2 nm was achieved at an arc current of 40 A. The particle size distribution could be better fitted with a lognormal distribution function than with a normal distribution function. Further, the O concentration of the Zn fine particles, upon exposure to air, could be controlled by passivation treatment in 1% O2/Ar atmosphere. Thus, Zn fine particles, with low quantities of oxides, could be efficiently produced by this method.

Direct observations of diffusion controlled microstructure transition in Mg-In/Mg-Ag ultrafine particles with enhanced hydrogen storage and hydrolysis properties

In this work, Mg(In) and Mg(Ag) solid-solution ultrafine particles were successfully synthesized by using a direct current (DC) arc-plasma method and their hydrogen storage and hydrolysis behaviors were thoroughly investigated. In particular, microstructural analyses clearly reveal that MgH2@MgIn and MgH2@MgAg composites are autogenerated upon hydrogenation via the formation of nano MgIn or MgAg intermetallic phase on MgH2: Mg(In/Ag) + H2 ⟷ MgH2 + MgIn/MgAg. Upon dehydrogenation, in-situ TEM observations confirm that the reverse reaction occurs through the diffusion of In/Ag from the MgIn/MgAg phase to MgH2. Such a diffusion process is coupled with the decomposition of MgH2, leading to the microstructural transition from MgH2@MgIn or MgH2@MgAg to corresponding solid solutions. For Mg-In system, the discovery of the intermediate phase Mg3In through in-situ TEM observation indicates that the dehydrogenation process is a two-step reaction dominated by the diffusion of In. Meantime, the improved hydrolysis performances of the MgH2@MgIn and MgH2@MgAg composites are primarily attributed to the direct participation of MgIn/MgAg in the hydrolysis reaction, providing more active sites for accelerating hydrogen yield. Therefore, the introduction of In or Ag into Mg has provided with noticeable improvements in the hydrogen storage as well as the hydrolysis properties of MgH2.

HAXPES Characterization of Carbon Supported Pt Catalysts Synthesized by an Arc Plasma Method

HAXPES Characterization of Carbon Supported Pt Catalysts Synthesized by an Arc Plasma Method