Argon Flow Research Articles

Numerical Study on Characteristic Positions and Transition of Flow Patterns in a Slab Continuous Casting Mold

The flow pattern in an opaque mold cannot be readily visible, and worker experience plays a major role in controlling it, even though it has a significant impact on slab quality in a continuous casting (CC) mold. An Eulerian–Eulerian two‐fluid model is used to comprehensively study the two‐phase flow of argon and molten steel in a slab CC mold. The positions of vortex centers in upper/lower recirculation zones and the impingement point of jet flow on the narrow face of mold are identified and their distribution is analyzed. The interactive effects of casting speed, argon flow rate, and immersion depth of the submerged entry nozzle (SEN) on the flow pattern inside the mold are revealed. 2D and 3D flow pattern regimes are plotted and the boundary lines and boundary surfaces are fit with exponential functions and ternary functions, respectively. To obtain a double roll flow in the slab CC mold investigated, the relation among argon flow rate (), casting speed (), and the immersion depth of the SEN () should satisfy, .

New approaches to the synthesis of substituted derivatives of the [B<sub>3</sub>H<sub>8</sub>]<sup>−</sup> anion

Objectives. To develop methods for the synthesis of substituted derivatives of the octahydrotriborate anion. Such compounds can be considered as hydrogen storage, components of ionic liquids, precursors for the production of boride coatings using the traditional chemical vapor deposition method, and also as a building material for the production of higher boron hydrogen clusters.Methods. Since substitution reactions are sensitive to moisture and atmospheric oxygen, the syntheses were carried out in a direct flow of argon or in a dry, sealed SPEKS GB02M glove box with a double gas purification unit and two airlocks. The reaction was initiated by cooling to 0°C, in order to avoid the formation of by-products. All the results were characterized using infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies.Results. The study presents a detailed study of the known methods for preparing substituted derivatives of the octahydrotriborate(1−) anion using dry hydrogen chloride as an electrophilic inductor and makes recommendations for improvement. In this method it is advisable to use cesium octahydrotriborate which facilitates the yield of the target product. New methods were proposed to initiate the substitution reaction in the [B3H8]−-anion using N-chlorosuccinimide and bromine. Using these inductors, new substituted derivatives of the octahydrotriborate anion with N-nucleophiles were obtained and defined by means of IR and NMR spectroscopies: [B3H7NCR], (R = Et, i-Pr, Ph) and [B3H7NH2R], (R = C9H19 (INA), Bn), [B3H7NHEt2], as well as Bu4N[B3H7Hal], Bu4N[B3H6Hal2], where Hal = Сl, Br. It was also established that hydrogen bromide is released during the reaction with bromine and amines. This immediately protonates the amine which requires additional heating of the reaction mixture. The study also established that the reaction mechanism with N-chlorosuccinimide is not radical.Conclusions. The main factors influencing the course of the substitution reaction are the possible occurrence of side interactions between the nucleophile and the inducer, steric possibilities, and subsequent isolation of the reactive reaction products.

Experimental design using the Taguchi method for the development of conductive textiles used in flexible thermoelectric generators

This paper presents several aspects of the robust experimental design methodology using the Taguchi method to develop electrically conductive textiles. These conductive textiles will be used to make thermoelectric generators based on the Seebeck effect. Since the experimental development involves the use of the magnetron sputtering method with more than three variables, the Taguchi method was selected to observe how different parameters (5 independent variables such as argon flow, power, pressure, deposition surface area and metal type used for solid targets) influence the mean and variance of the process performance defined by the thickness of the metal film deposited (dependent variable). In the experimental design framework, the analysis using the Taguchi method, followed by optimisation, helped select the optimal experiments from the set of possible experiments. This methodology reduced the number of experiments by 21–42% and minimised resource consumption (e.g., metal targets, argon, energy).

Ultra-strength of Ti films via (002) texture optimization and nanocolumnar strengthening

This paper focused on the correlation between the (002) texture, columnar grain size and mechanical properties of Ti films prepared by magnetron sputtering. The (002) texture and columnar grain evolution were controlled under a combination of substrate bias voltage and argon flow rate. It was found that the substrate bias voltage was the key factor to dominate the (002) texture and columnar grain size. At constant substrate bias voltage of −100 V, all of Ti films showed a strong (002) texture. The micropillar compression test indicated that the Ti film with a strong (002) texture and nanocolumnar grain obtained an ultra-strength of 3838.2 MPa and an ultra-high work hardening exponent of 0.64 at substrate bias voltage of −100 V and argon flow rate of 20 sccm. The ultra-strength of Ti film stemmed from the fact that the nano-sized grain inhibited the generation of deformation twin and the (002) texture inhibited the activation of <a> slips, and finally the <c+a> slips with high Peierls-Nabarro stress were forced to be activated. Moreover, based on the TEM observation, the source of the ultra-strength of Ti film was explained by the proposed strength formula. Texture optimization and nanocolumnar strengthening are effective methods to improving the strength of pure Ti films. These results provided a new perspective of designing ultra-strength of Ti film materials.

The Impact of Argon Flow Rates on Plasma Behavior in Plasma Jet Systems for Medical Applications

This research presents a thorough spectroscopic investigation of atmospheric- plasma generated by a plasma jet. The study examines the plasma behavior under varying flow rates of argon gas. A primary objective is to identify the optimal flow rate that facilitates the application of the generated plasma in sterilization and bacterial eradication operations. The findings establish a correlation between argon flow and critical plasma parameters, specifically noting variations in electron temperature (Te) &amp; electron number density (ne). Crucially, the study demonstrates that lower argon flow rates are more effective in generating active species such as hydroxyl and NO reactive species. The results of this investigation hold significant promise for advancing our comprehension of plasma jet technology's utility in sterilization or medical treatment processes, emphasizing the importance of gas flow optimization for these applications.

Bacterial Decontamination of Water-Containing Objects Using Piezoelectric Direct Discharge Plasma and Plasma Jet.

Cold atmospheric plasma has become a widespread tool in bacterial decontamination, harnessing reactive oxygen and nitrogen species to neutralize bacteria on surfaces and in the air. This technology is often employed in healthcare, food processing, water treatment, etc. One of the most energy-efficient and universal methods for creating cold atmospheric plasma is the initiation of a piezoelectric direct discharge. The article presents a study of the bactericidal effect of piezoelectric direct discharge plasma generated using the multifunctional source "CAPKO". This device allows for the modification of the method of plasma generation "on the fly" by replacing a unit (cap) on the working device. The results of the generation of reactive oxygen and nitrogen species in a buffer solution in the modes of direct discharge in air and a plasma jet with an argon flow are presented. The bactericidal effect of these types of plasma against the bacteria E. coli BL21 (DE3) was studied. The issues of scaling the treatment technique are considered.

Electron cyclotron resonance (ECR) enhanced diverging magnetic field for controlled particle flux in a microwave-excited plasma column – a numerical investigation

The present work is an investigation of the effect of an externally applied diverging magnetic field on a surface microwave-sustained plasma column. Microwaves (2.45 GHz) are allowed to propagate through a tapered waveguide system containing a discharge tube made up of quartz. Argon gas flows down the tube from top to bottom maintaining a pressure of 1 Torr and a plasma is ignited within the tube owing to the surface microwave propagation. In the absence of a magnetic field, the plasma column exhibits discrete regions of overdense plasma near its center where the electric field of the incident microwaves is observed to be high. As the gas flows down the tube, the plasma density is also found to decrease and the resulting plasma profile is asymmetric about its length. However, in the presence of an axially applied diverging magnetic field , an axial force acts on the plasma, and the discrete overdense plasma regions are found to get symmetrically arranged along the plasma axis. Interesting results are observed when the diverging magnetic field includes a region of electron cyclotron resonance (ECR) corresponding to the microwave frequency. In the presence of an ECR, the electrons are expected to experience resonant heating by microwaves other than the direct heating by these waves. Under such conditions, the discharge dynamics are governed by the resonance mechanism, and the bright spots of overdense plasma regions get shifted to the ECR positions. As the magnetic field strength increases, the overdense plasma moves axially away from the center. These results are a clear indication of a magnetically controlled particle flux over a target and can be exploited in various material processing applications, particularly for surface cleaning applications in the semiconductor industries.

Numerical Investigation on Coalescence Behavior of Liquid Inclusion Particles in Argon Bubble Wake Flow

Microinclusions in steel will significantly affect mechanical performance of final products and therefore require serious concern during metallurgical process. Herein, the collision, coalescence as well as floatation of bubble–inclusion coexisting system is fully studied through a new mathematical model. It comes to the following conclusions: as bubbles rise, they induce a flow of liquid steel from their upper surface to their lower surface, and inclusion droplets rise and collide in the wake of the bubble. The velocity of the bubbles is affected by their deformation, with deformation rates being linked to the Weber number. The coalescence time of these inclusions is primarily influenced by viscosity and surface tension. Coalescence accelerates with higher surface tension or reduced viscosity, and this phenomenon can be described by a formula, which is developed by simulation results. According to this formula, coalescence time of 3CaO·Al2O3 is 20% longer than that of 12CaO7·Al2O3. Consequently, 12CaO7·Al2O3 is more prone to coalescence. The movement of inclusions can be controlled by adjusting gas volume and flow rate. Moreover, promoting coalescence can be achieved by altering the viscosity of inclusions and the surface tension coefficient, making it easier to remove these unwanted inclusions.

In-situ formation of ultra-hard titanium-based composite coatings on carbon steel through electro-spark deposition in different gas media

In the current study, ultra-hard TiC, TiN, and Ti(C,N) layers were in-situ formed on carbon steel substrate using pure titanium electrode via electro-spark deposition (ESD) in argon, nitrogen, argon/nitrogen, and air atmospheres. The synthesized coatings were characterized using various techniques, including FE-SEM/EDS, X-ray diffractometry, Raman spectroscopy, microhardness and nanoindentation tests, and surface roughness measurement. Also, a thermodynamic simulation was executed to estimate the phase-stability. Fe5C2, TiN, Fe3N, and Ti2O3 were determined as the major phases formed under the argon, nitrogen, Ar/N2, and air atmospheres, respectively. The formation of martensite at the interface of the coating and substrate in all atmospheres indicates the capability of the ESD process for surface hardening. The observed discrepancies between the empirically formed phases and the thermodynamics prediction can be related to the non-equilibrium conditions of the ESD process. It was revealed that gaseous media such as argon and nitrogen serve as a protective/active environment in the titanium/steel system. It is proposed that the electro-sparking of titanium under the active nitrogen medium follows an avalanche plasma regime. Under the argon flow, FeTi intermetallic layer is formed. Whilst, electro-sparking in ambient air leads to the formation of various Fe-Ti-O compounds, as well as different TiOn oxides. On the other hand, the utilization of nitrogen gas during the ESD increases the surface roughness and the thickness of the coating, rather than the deposition under the argon flow, due to the extra heat of reactions. The dynamic reactions occur between pure titanium, nitrogen, carbon, and oxygen, leading to the initial formation of Ti(C,N) at the top surface, followed by the production of titanium oxides in the middle layer. The coexistence of the super-hard Ti(C,N) with a hardness of 3130 HV at the top surface and titanium nitrides beneath it in a gradient mode effectively impedes the crack propagation.

Experimental study on the influence of gas flow rate on the plasma plume of N-APPJ

In order to explore the effect of the gas flow rate on the plasma plume, a quantitative study of the effect of the gas flow rate on the atmospheric pressure non-equilibrium plasma plume length was carried out using two different electrode structures. The results show that plasma plume length of up to 80.2 mm can be achieved in atmospheric condition outside the tube. The plasma plume length of the indented tube is smaller than that of the straight tube for the same argon gas flow rate, discharge voltage and axial distance between electrodes, and the effect of the argon flow rate on the plasma plume length is more obvious for the straight tube than for the indented tube. The plasma plume length of the straight-through tube tends to increase and then decrease as the argon flow rate increases, and the variation of the plasma plume length at an axial electrode distance of 0 mm is significantly greater than that of other electrode distance conditions. At the same argon flow rate, the maximum plasma plume length tends to increase and then decrease with the argon flow rate and increases with the axial distance of the electrodes.

Investigating the temperature distribution behavior and flow parameters of argon fluid in a nanochannel with changing dimensions of the obstacle using the molecular dynamics (MD) method

This article, examines the flow of argon inside a nanochannel with respect to the molecular dynamics (MD) in the free molecular flow regime using LAMMPS software. The nanochannel is made of copper featuring a square cross-section and obstacles of varying dimensions and values. In this study, the flow of argon fluid is three-dimensional. To gain a deeper understanding of the effect of solid walls within the nanochannel and their influence on flow behavior, the research is simulated in a nanochannel with all side walls for the 3D model and without side walls for the 2D model. This research assesses the effect of the obstacles’ dimensions and values on the nanochannel wall surface and areas above the wall surface. The total dimensions of all simulated two- and three-dimensional atomic structures with a square cross-section are assumed to be 60 × 60 × 100 Å3. and the presence of square obstacles (with dimensions of 8 × 8 × 8 Å3) and rectangular obstacles (with dimensions of 8 × 18 × 8 Å3) is examined. This study seeks to understand the influence on flow behavior, temperature distribution, density, heat flux, velocity, and thermal conductivity coefficient. This study is simulated using a time step of 1 fs for 10,000 time steps, involving approximately 10,000–15,000 argon and copper atoms. The results of this research indicate that obstacles with structures of P and R and larger dimensions increase the number of solid atoms exhibiting stronger attractive forces. Compared to a smooth nanochannel, the thermal exchange between fluid and solid atoms results in a density increase of 17.5 % and 17.3 %, respectively. On the other hand, in the 3D nanochannel, the sidewalls of the nanochannel have reduced the effect of the presence of R and P obstacles with larger dimensions, which comparing to a smooth nanochannel, have increased the density by 8.21 % and 7.53 %, respectively. The obstacles with different spatial positions (P and R structures) in the two-dimensional nanochannel cause a rise in the thermal conductivity coefficient. The P structure obstacles have a better effect on the thermal conductivity coefficient in the 2D nanochannel compared to the R structure. In the three-dimensional nanochannel, utilizing smaller obstacles proves to be more effective because it results in better atom distribution or temperature distribution due to increased atomic collisions in the central region compared to the wall regions.

Influence of Argon and Helium Purging Flow Rates on the Fusion Zone in Autogenous Stationary TIG Arc Welding of 316L Stainless Steel

Influence of Argon and Helium Purging Flow Rates on the Fusion Zone in Autogenous Stationary TIG Arc Welding of 316L Stainless Steel

EXPERIMENTAL AND THEORETICAL STUDY OF THE BEHAVIOR OF GALLIUM IN A DISCHARGE PLASMA AT ICP-AES DETERMINATION

In the case of inductively coupled plasma atomic emission determination of gallium in metallurgical materials, matrix components can have a significant influence on the determination results. In addition to matrix spectral interference, there may also be non-spectral interference from macrocomponents. The element present in the discharge plasma at high concentrations can lead to a change in the conditions for excitation of the emission spectra, which will lead to a distortion of the intensity of the spectral lines of gallium. It has been established that the spectral lines of gallium are not free from spectral overlap from macrocomponents (iron, chromium, molybdenum, tungsten, nickel and cobalt). As a result, experimental study of non-spectral interference using gallium spectral lines is impossible. Using thermodynamic modeling, a quasi-analyte element was selected, which was proposed to be used to study the non-spectral matrix effect on the analytical signal of gallium during its atomic emission determination with inductively coupled plasma. Indium was proposed as a quasi-analyte. Based on the results of thermodynamic modeling, it was established that when varying the operating parameters of the atomic emission spectrometer (plasma temperature, argon and aerosol flow rate), the spectral behavior of gallium and the proposed indium quasi-analyte in argon plasma is similar. In this case, there is no spectral interference from the quasi-analyte on the spectral lines of gallium, and the increase in the value of the matrix interference estimate observed in some cases is random, which may be due to the time drift of the operating parameters of the atomic emission spectrometer. Thus, it is proposed to use indium as a quasi-analyte for the experimental study of non-spectral interference from matrix components (iron, chromium, molybdenum, tungsten, nickel and cobalt) instead of detectable gallium in metallurgical materials.

Optimum pyrolysis conditions to prepare the most crystalline boron carbide powder from boric acid-mannitol complex ester.

A weak acidic complex ester (CE) in solid form was prepared by a condensation reaction between very weak boric acid (BA: H3BO3) and (D)-mannitol (MA: C6H14O6) by the molar ratio of BA/MA = 2. A boron carbide (B4C) precursor was obtained from heating of the CE at 400 °C for 4 h. The precursor was pyrolyzed under argon flow in the interval of 1300-1550 °C for 4 h and at 1400 °C for 1-4 h, respectively. The materials were examined using several techniques such as X-ray diffraction analysis, thermal analysis, scanning electron microscopy, particle size distribution, and nitrogen adsorption/desorption. The optimum pyrolysis temperature and duration were 1400 °C and 4 h, respectively. The most crystalline B4C particles were distributed between 1 and 100 μm with a mean particle size of 20 μm. The specific surface area and specific pore volume were 13.5 m2 g-1 and 0.09 cm3 g-1, respectively. The size of the pores was between 2 and 36 nm with a mean size of 14 nm.

Straightforward Design Strategy toward 3D Near-Net-Shape Stoichiometric SiC Parts.

Fused deposition modeling (FDM), traditionally reserved for thermoplastics, is modified here with a granule-based extrusion head to be extended to advanced nonoxide ceramics via a straightforward design strategy that considers the shaping opportunities and the chemical richness offered by preceramic polymers. Specifically, 3D near-net-shape stoichiometric silicon carbide (SiC) objects are designed by manipulating the key features of a commercially available polycarbosilane (fusibility, high carbon content, relatively high SiC yield). In the early stage of the process, the carbon-rich polycarbosilane is first mixed with Si and SiC fillers and then thermolyzed at 120 °C to increase polymer branching while offering tailored rheological properties during the subsequent extrusion process at 90 °C and adequate shape retention once extruded. This allows for the design of tailored and complex 3D complex polycarbosilane-based architectures with features down to 400µm. Polymer-based parts are further converted into 3D stoichiometric SiC objects with quasi-near-net-shape-a volume shrinkage reduced to 9.1% is measured-by heat treatment at a temperature as low as 1400 °C (argon flow). Given the flexibility to tune the preceramic polymer chemical and rheological properties, a new combined design approach is leveraged to generate bespoke advanced ceramics with a high freedom in geometry complexity.

Improving the Cyclic Reversibility of Layered Li-Rich Cathodes by Combining Oxygen Vacancies Introduction and Surface Fluorination

Layered-type Li-rich cathode materials have attracted significant attention for the next generation Li-ion batteries, but their poor reversibility in terms of both voltage and capacity upon cycling are as prominent as their high capacity. Irreversible oxygen redox activity and surface deterioration have been deemed as the root cause and direct cause for their poor performance, respectively. To mitigate those issues, we introduce substantial amounts of oxygen vacancies into layered-type Li1.2Ni0.2Co0.2Mn0.4O2 by using CaH2 as a reduction agent. Reduced samples show higher reversible capacity due to the increased cation redox participation, but still sustain poor cyclic performance. With further fluorination to reduced Li1.2Ni0.2Co0.2Mn0.4O2-x by using NH4HF2, the reversible capacity reached 270 mAh/g and maintained its 99% after 100 cycles. STEM-EELS detects deeper F signals rather than just on surface as direct fluorination methods show, and HAXPES patterns indicate there are both ionic and covalent fluorine coordination. These results demonstrate that by the combination of oxygen deficiency introduction and surface fluorination, some F- ions could occupy the sites of oxygen vacancies near the surface rather than sole LiF generation on the surface, which illuminates a new strategy to modify the cathode materials for Li-ion batteries. The Ni0.2Co0.2Mn0.4(OH)1.6 precursor was prepared by the coprecipitation of NiSO4, CoSO4 and MnSO4, and then mixed with LiOH. The mixture was calcined with oxygen flow at 900 ℃ to obtain pristine Li1.2Ni0.2Co0.2Mn0.4O2. The pristine Li1.2Ni0.2Co0.2Mn0.4O2 was reduced by the appropriate amount of CaH2 in a vacuumed glass tube at 260 ℃, then the reduced Li1.2Ni0.2Co0.2Mn0.4O1.85 was mixed with various amounts of NH4HF2 and sintered at 450 ℃ with argon flow. Hard X-ray photoemission spectroscopy (HAXPES, at BL46XU in SPring-8) was used to investigate the coordination state of fluorine ions. The electrodes of different samples were prepared by slurrying the active material, acetylene black, and PVDF with a weight ratio of 8:1:1, then coating on the Al foil. The 2032-type coin cells were assembled for the electrochemical test. The counter electrode was lithium metal and the electrolyte was 1 M LiPF6 in EC and EMC solvent (3:7 by volume). The charge-discharge test was operated on an automatic cycling and data recording system (HJ1001SD8, Hokuto Denko). Fig. 1a shows the F 1s HAXPES spectra of fluorinated samples which were synthesized by subjecting reduced Li1.2Ni0.2Co0.2Mn0.4O1.85 to chemical fluorination using NH4HF2. When F is 0.1 stoichiometry, F ions are more covalent which implies they could mainly occupy the oxygen vacancy sites near surface. Further fluorination increased the intensity of LiF on surface. The cyclic performance of four samples is shown in Fig. 1b. The pristine sample suffered from the severe capacity decay whose drastic oxygen redox activity is deemed to cause various deterioration [1]. Direct fluorination of pristine sample had some positive effect to the cyclic performance because of the reported interface stabilization [2]. The initial capacity of the reduced sample is higher than pristine sample owing to the increased cation redox contribution, but its cyclability is still poor especially after long cycles. The important point to note is the combination of reduction and fluorination significantly improved both the capacity and cyclic performance upon 100 cycles, and the coordination and role of fluorine ions could be different from the conventional fluorination strategy. Figure 1

Turbostratic Carbon Nano Onion Electrode for High Power Density Vanadium Redox Flow Battery

The redox flow battery (RFB) is one of the most promising technologies for stationary energy storage. It consists of a voltaic cell whose electrolytes are stored in tanks outside the system. Whilst the chemistries of the anodic and cathodic electrolytes define the energy density of a RFB system, its power density is determined primarily by its electrodes. These are typically porous carbon media on the surface of which the redox reactions occur. They are a critical component since they require a detailed engineering of electrocatalytically active surface area and mass transport. Still today, they remain the main cause of RFB low power density. In this work, we are showing a novel deposition method to improve the performance of commercially available carbon paper already used in RFB.The gain is thanks to the deposition of turbostratic carbon nano-onion (TCNO) nanoparticles on the carbon fibers of the paper. This process is performed with a proprietary technology called NanoJeD: a CVD in supersonic flow, which promises easy industrial scalability and a fine tunability of the nanoparticle properties. Moreover, with this system is possible to deposit over any substrate.NanoJeD consists in two chambers separated by a high aspect ratio slit. A precursor gas is injected through a porous plug from the top and a vacuum system is connected from the bottom. The slit allows the establishment of a high-pressure ratio between the two chambers and hence the formation of a supersonic jet. The precursor gas, a mixture of Argon (98.4%) and Acetylene (1.6%) flows between two electrodes where a radio frequency (RF) signal is fed (13.56 MHz). The RF ignites a non-thermal plasma in which the precursor molecules are ionized and dissociated into radicals, which polymerize forming hydrogenated carbon clusters and nanoparticles (NPs) of different sizes. Once formed, NPs are dragged through the slit by the gas stream and finally impact on the substrate. Therefore, it is possible to achieve a high throughput (500 mg h-1) and to deposit on a large area of 100 cm2 while precisely controlling the properties of the film. The resulting film has hundreds of squared meters per gram of surface area. For TCNO formation, the NP film is further annealed in vacuum at 1000°C for 2 hours. Using in situ transmission electron microscopy (TEM) and energy electron loss spectroscopy (EELS), we were able to visualize the progression of graphitization and changes in structural properties during annealing. The graphitization process starts in the outer layer and proceeds into the interior of the particle. The geometrical constrains of the NP (average diameter of 20nm) and shrinkage of the NP, allow the formation of curved, turbostratic, defective graphitic sheets. UV photoelectron spectroscopy (UPS) and Raman spectroscopy performed ex-situ allow the analysis of valence bands and structural defects. The high presence of defects and general disorder structure are accompanied with a remarkable increase in catalytic activity. Moreover, the annealing process leads to the sintering of the nanoparticles and the formation of an interface between the carbon fibre and the nanoparticles, as demonstrated by the increased thermal stability tested by. Both phenomena improve the adhesion between nanoparticles and with the surface, making the electrode suitable to be adopted in fluxed systems.The TCNO deposited on a carbon paper was tested as electrode in a Vanadium RFB. The kinetic activity and electrochemical properties were tested via in-situ Raman and in a three-electrode cell set-up. The results reveal an increased kinetic activity with respect to the untreated paper. Using in situ Raman we were able to show differences in redox mechanism between TCNO and bare carbon paper. A chronoamperometry test was used to obtain the transfer coefficient from a Tafel plot. These studies allow the correlation of the catalytic activity with the defectiveness of the TCNO nanoparticle. Vanadium RFB full cell measurements of the TCNO electrode show a drastic increase in performance, reaching an energy efficiency of 70.8% and 86.2% at current densities of 600 mA cm-2 and 200 mA cm-2, respectively. The electrolyte utilisation for these current densities is 59% for the former and 80% for the latter. To investigate the chemical and mechanical stability a stability test was performed. Results showed a low degradation rate of 0.004% EE per cycle. Moreover, TCNO can be used for other electrochemical applications only by adjusting the deposition and annealing parameters.

Microstructure, phase formation, and properties of melt-quenched CoCr0.8Cu0.64FeNi high-entropy alloy

This paper explores the CoCr0.8Cu0.64FeNi high-entropy alloy. Different criteria, such as the valence electron concentration, the Ω parameter, and the atomic size difference δ, are used to estimate the phase composition of the alloy. As-cast samples of the alloy are made by melting the components in a high-temperature Tamman furnace in an argon flow and solidifying them in a copper mold. The weight loss during the ingot production is minimal, and the average cooling rate is about 102 K/s. Melt-quenched samples are made by remelting the cast ingot and rapidly cooling the melt droplets on the inner surface of a fast rotating (about 8000 rpm) hollow copper cylinder. The cooling rate, estimated from the film thickness, is about 106 K/s. X-ray diffraction is used to analyze the structure of the samples on a DRON-2.0 diffractometer with monochromatic Cu Kα radiation. Magnetometry is used to measure the magneticproperties of the samples at room temperature. The results confirm the theoretical predictions that the structure of the alloy, in both states, is an FCC solid solution. The lattice parameters in the as-cast and melt-quenched states are 0.3593 nm and 0.3589 nm, respectively. The results also show that the CoCr0.8Cu0.64FeNi alloy is a soft magnetic material, but its coercivity and microhardness increase after quenching due to internal stresses.

Studying the effect of the argon flow introduced into the arc discharge in the atomic-emission spectrometry of powdered samples using the spillage-injection method

Atomic emission spectral analysis of a powder sample by the method of spillage-injection into the plasma of an arc discharge burning in air is accompanied by the formation of cyanide, nitride and oxide compounds which form molecular bands in the spectrum thus impeding measuring the intensity of the analytical lines of the elements to be determined. Feeding an argon flow into the arc discharge can reduce the amount of spectral interference and increase the plasma temperature, which promotes more a complete evaporation of the analyzed sample injected into the arc discharge and, accordingly, increases the degree of ionization of the elements and the intensity of ion spectral lines. The aim of the study was to develop a device for argon introduction into the arc discharge zone and simultaneous sample delivery by a spillage-injection method, as well as to study the effect of argon consumption on arc discharge parameters and emission spectra of powder samples. The argon input device (up to 2.25 L/min) is developed on the basis on glass funnels, the geometric dimensions of which are selected with the goal of gaining the maximum intensity of spectral lines and reduced intensity of molecular bands at the minimal argon consumption. The study carried out on a «Grand Potok» spectrometer demonstrated that with an increase in argon consumption, the intensity of SiO molecular bands decreases, the plasma temperature increases by 350 – 540 K, and the intensity of ion and atomic lines with the ionization energy above 8 eV increases by more than 4.7 and 2.9 times, respectively. The developed device can be used in analysis of geological materials to improve the metrological characteristics of the results of atomic emission spectral analysis.

Numerical Simulation of Flow and Argon Bubble Distribution in a Continuous Casting Slab Mold under Different Argon Injection Modes

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases.