Argon Flow Rate Research Articles

Effects of Ingested vs. Injected Propellant on Radio-Frequency Discharge Plasma Properties

Radio-frequency (RF) ion thrusters are characterized in vacuum test facilities differentiated by pumping speed and thus subject to varying levels of neutral propellant ingestion that affect plasma plume properties and artificially raise the pressure of neutral propellant available to the thruster. These plasma properties are often used to calculate anticipated thrust values for RF thruster prototypes without consideration of the effects ingested neutral propellant may have beyond increasing the amount of neutral atoms available. This study compares exit plane plasma properties for nominal operation of a replica of the Madison Helicon Experiment operating at a propellant flow rate of 2 standard cm^3/min argon subject to 3.8 cm^3/min ingested argon flow with thruster operation over a range of propellant flow rates (1.3–60 standard cm^3/min argon) subject to a maximum ingested argon flow rate of 0.8 cm^3/min to determine the validity of compensating for neutral ingestion at higher operating pressures by increasing supplied propellant flow rates when operating at lower facility pressures. This study finds that no single operating condition at the 0.8 cm^3/min ingestion condition reproduces all the plasma property values recorded at the nominal flow rate at the 3.8 cm^3/min ingestion condition. The inability of plasma properties to be reproduced at a single adjusted flow rate is a result of the differing magnitudes of influence neutral ingestion effects have on individual plume properties.

Catalytic Growth of 1D ZnO Nanoneedles on Glass Substrates Through Vapor Transport

In this study, one-dimensional (1D) zinc oxide (ZnO) nanoneedles are successfully fabricated on a Ag catalyst-coated glass substrate through simple physical vapor deposition via thermal evaporation of zinc (Zn) powder in the presence of oxygen (O2) gas at a low growth temperature of 450°C. The growth rate and diameter of ZnO nanoneedles increase as a function of varying silver (Ag) film thicknesses and argon (Ar) flow rates. Detailed structural investigations confirm that the synthesized nanoneedles have high crystallinity with a hexagonal wurtzite structure, and they preferentially grow along the c-axis orientation. This approach provides a simple and cost-effective method for the synthesis and controlled growth of 1D nanostructures, which can be useful in solid-state devices and various optoelectronic applications.

Controlled Syntheses of Multi-walled Carbon Nanotubes from Bimetallic Fe–Co Catalyst Supported on Kaolin by Chemical Vapour Deposition Method

Multi-walled carbon nanotubes (MWCNTs) were synthesized via acetylene gas deposition over bimetallic Fe–Co/kaolin catalyst by chemical vapour deposition method. The effects of synthesis parameters such as calcination temperatures, reaction time, argon and acetylene flow rates on the CNTs yield were examined using $$2^{4}$$ full factorial experimental design. The as-prepared nanomaterials were characterized by HRSEM/EDS, HRTEM, TGA, DLS, XRD, XPS and BET. The HRSEM/TGA revealed well dispersion of the metallic particles on the kaolin support with high thermal stability. XRD analysis of the catalyst confirmed the formation of mixed oxides of different intensities which can favour the growth of MWCNTs. The optimum conditions to obtain high catalyst yield of 88.9% were: mixing ratio of 1.6, stirring speed 1000 rpm, calcination temperature $$500\,{^{\circ }}\hbox {C}$$ and calcination time 14 h. The HRSEM, HRTEM and XRD analyses showed that optimal controlled conditions to obtain homogeneous growth of high-quality graphitic MWCNTs of different inner and outer diameters were: reaction temperature of $$700\,{^{\circ }}\hbox {C}$$ , growing time 55 min, argon flow rate 220 mL/min and acetylene flow rate 180 mL/min. The BET analysis showed that the surface area of unpurified MWCNTs was $$275.5~\hbox {m}^{2}/\hbox {g}$$ while pure MWCNTs increased to $$330.6~\hbox {m}^{2}/\hbox {g}$$ after acid treatment. The statistical analysis showed that deposition temperature and acetylene flow rate positively exerted significant influence on the CNTs yield than other synthesis parameters, an evidence of thermodynamic-controlled mechanism. This study demonstrated that kaolin can act as an excellent substrate for MWCNTs growth compared to other commercial supports such as $$\hbox {CaCO}_{3}$$ , MgO, $$\hbox {Al}_{2}\hbox {O}_{3}$$ , $$\hbox {SiO}_{2}$$ .

The deposition of cadmium selenide and cadmium phosphide thin films from cadmium thioselenoimidodiphosphinate by AACVD and the formation of an aromatic species.

Aerosol-assisted chemical vapour deposition (AACVD) of Cd[(SPiPr2)(SePiPr2)N]2 yields hexagonal cadmium selenide and monoclinic cadmium phosphide films on glass substrates between 475 and 525 °C at different argon flow rates. The films were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). All the results of XRD, EDAX and XPS are in agreement with our previous investigations on Cd[(SePiPr2)2N]2. A breakdown mechanism is proposed based on mass spectra and density functional theory calculations. A large peak at m/z 207 in the mass spectra, previously assigned by us as a new aromatic species, is also observed for this complex.

Diamond-like carbon films prepared by high power impulse magnetron sputtering

Abstract Diamond-like carbon (DLC) thin films were prepared by high power impulse magnetron sputtering (HiPIMS) with different deposition conditions. The main variable parameters were the argon flow rate, and deposition time. The carbon films were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The results from the XPS measurements show that the DLC films are composed of two main different carbon species; i.e. carbon with sp3 and sp2 configurations. The XAS measurements reveal that the DLC films contain hydrogen. The present of hydrogen affects the sheet resistivity of the films. The resistance of the DLC films increases exponentially when the temperature decreases.

Controlling the carbon nanotube type with processing parameters synthesized by floating catalyst chemical vapour deposition

Abstract Single and multi-walled carbon nanotubes have been synthesized by floating catalyst chemical vapour deposition technique. Methane, argon, ferrocene and sulphur were used as carbon source, inert gas, catalyst and promoter, respectively. The types of carbon nanotubes (single or multi-walled) were governed by a variety of experimental factors: the ferrocene flow rate, methane flow rate, sulfur flow rate, argon flow rate and reaction temperature. The optimization of the process parameters was carried out to find the parameter 'islands' for the selective formation of single or multiwalled carbon nanotubes. The characterization was carried out by transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. A high hydrogen flow rate, low methane flow rate and high sulfur flow rate were crucial factors for selective synthesis of single walled carbon nanotubes. This work provides methodology for optimization of processing parameters for synthesizing high purity single or multi walled carbon nanotubes

Optical Properties and Microstructure of TiNxOy and TiN Thin Films before and after Annealing at Different Conditions

TiN and TiNxOy thin films share many properties such as electrical and optical properties. In this work, a comparison is conducted between TiN (with and without annealing at 400 °C in air and vacuum) and TiNxOy thin films deposited by using RF magnetron sputtering with the same pure titanium target, Argon (Ar) flow rate, nitrogen flow rates, and deposition time on stainless steel substrates. In the case of TiNxOy thin film, oxygen was pumped in addition. The optical properties of the thin films were characterized by spectrophotometer, and Fourier transform infrared spectroscopy (FTIR). The morphology, topography, and structure were studied by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). The results show that both thin films have metal-like behavior with some similarities in phases, structure, and microstructure and differences in optical absorbance. It is shown that the absorbance of TiN (after vacuum-annealing) and TiNxOy have close absorbance percentages at the visible range of light with an unstable profile, while after air-annealing the optical absorbance of TiN exceeds that of TiNxOy. This work introduces annealed TiN thin films as a candidate solar selective absorber at high-temperature applications alternatively to TiNxOy.

РАЗРАБОТКА ТЕХНОЛОГИЧЕСКОГО РЕГЛАМЕНТА НАУГЛЕРОЖИВАНИЯ ЧУГУНА В 30-т КОВШЕ. ЧАСТЬ 1

The results of numerical simulation of the carbonization of low-carbon iron as a by-product of the production of titanium slag for the designed unit ladle-furnace (LF) installation as applied to the conditions of PJSC Zaporizhzhya Titanium-Magnesium Combine are presented. The technological regulations have been developed and a numerical study has been carried out on the carburization of metal in a 30-ton ladle at the LF. For the production of commercial pig iron, associated iron-containing waste is used. The purpose of the work is to identify factors of the influence of out-of-furnace processing on technology optimization. A numerical simulation was performed of the carburization technology of liquid low-carbon (up to 2% carbon) cast iron with lump (fraction up to 50 mm) graphite and coke introduced onto the surface of a ladle bath (excluding slag cover). The material and energy balances of the process were carried out, the properties of carburizing materials were studied, and the diffusion coefficient of carbon in a liquid metal was estimated. The results of studies of the hydrodynamic and thermal conditions in the bucket bath of the LF are estimated from the contour diagrams of the flow rates and temperature fields for different flow rates of argon supplied through the bottom and submerged tuyeres. The optimal fractions of carbon-containing materials were determined. It has been shown that treatment on LF with lump graphite requires a shorter duration (≈ 45%) compared with lump coke. To accelerate the process of diffusion dissolution of carbon, it is necessary to periodically (every 3 portions of 70 kg of graphite and coke) heat the melt to a temperature of 1520-1530 ° C. Injection of powdered graphite and coke contributes to a more efficient absorption of carbon and a decrease in the duration of the process (≈ by 1/3). Research continues in the direction of using flux-cored wire for carburizing cast iron at LF.

Blood absorption improvement of a naturally derived hemostatic agent by atmospheric pressure plasma jet

Hemostatic capability improvement of a chitosan hemostatic agent was achieved by surface modification using the atmospheric pressure plasma jet experiment. The chitosan hemostatic agent acquired high blood absorption rate, at 4.60 ml/m, when exposed to input power 10 W of the radiofrequency power supply, the argon flow rate of 4 L/m mixture with an oxygen gas of 10 ml/m, and treatment time of 30 s. A significant decreased was observed in the hemoglobin leak value, inducing early blood clotting ability of clotting in 30 s. The strong relation of gas plasma discharge with the OH radical and the atomic oxygen, exhibited an increase in the hydrophilic properties, which lead to the chitosan hemostatic agent being very effective.

Maintenance of cast brass taps by pulsed Nd:YAG LASER welding

During solidification of melted metal in casting process, the volume decreases, resulting in cracks, voids and porosities. These defects, depending on the application and requirements, might result in rejection during quality control. For maintenance of cast brass taps, TIG welding is already employed. Thus, considering the several advantages of laser welding in comparison with conventional welding processes, in this work, the authors analyze the possibility of using laser welding in the maintenance of cast brass taps. A pulsed Nd:YAG laser welding machine was used to weld cast brass taps cracks. Additionally, a parametric study was carried in order to identify and determine the fundamental and best set of parameters to repair cast brass cracks and depressions with laser welding. The parameters are laser power and energy; pulse type and frequency; and laser beam diameter. Additionally, in order to analyze the repair and welding quality, metallographic (macro and micro) analyzes were carried. Both cracks and depressions were successfully repaired with laser welding technique. Therefore, in this work, it was verified the excellent applicability of pulsed Nd:YAG laser welding in repairing defects on cast brass taps. The best set of parameters was: 10 ms rectangular pulse with a frequency of 5 Hz; energy of 34.8 J; 1.2 mm laser beam; and Argon flow rate of 6 l/min.

Empirical relationship between band gap and synthesis parameters of chemical vapor deposition-synthesized multiwalled carbon nanotubes

In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on CaCO3 was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature (700oC), time (55 min), argon flow rate (230.37 mL min–1) and acetylene flow rate (150 mL min–1) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.

Microstructural and in vitro characterization of 45S5 bioactive glass coatings deposited by solution precursor plasma spraying (SPPS)

The present work focused on the development of bioactive glass coatings employing Solution Precursor Plasma Spraying. Precursors of SiO2, CaO, Na2O and P2O5 were mixed in distilled water to prepare concentrated solutions with a composition close to the 45S5 bioactive glass.Solutions were rheologically characterized to assess their stability with time and deposited onto AISI type 304 stainless steel to develop coatings under different parameters related to the thermal spraying technique. The effect of these parameters on coatings microstructure was studied by scanning electron microscopy. Coatings were also analysed by X–ray diffraction and scratch test to complete the microstructural characterization. Moreover, coatings bioactivity was evaluated by immersing them in Simulated Body Fluid.The study showed that using short spraying distances and low argon flow rates, gave rise to the typical microstructure derived from liquid feedstocks whereas some crystallization associated to the long spray distance used occurred. Scratch test revealed that the resulting coating possessed good mechanical properties when compared with similar coatings obtained by other plasma spraying techniques. Moreover, the obtained coating could develop an hydroxycarbonate apatite layer when in contact with Simulated Body Fluid as demonstrated by scanning electron microscopy, X–ray diffraction and Fourier transform infrared spectroscopy.

Research on the Factors Affecting the Growth of Large-Size Monolayer MoS₂ by APCVD.

The transition-metal chalcogenides (TMDs) are gaining increased attention from many scientists recently. Monolayer MoS2 is an emerging layered TMD material with many excellent physical and electrical properties. It can be widely used in catalysis, transistors, optoelectronics and integrated circuits. Here, the large-sized monolayer MoS2 is grown on the silicon substrate with a 285-nm-thick oxide layer by atmospheric pressure chemical vapor deposition (APCVD) of sulfurized molybdenum trioxide. This method is simple and it does not require vacuum treatment. In addition, the effects of growth conditions, such as sulfur source, molybdenum source, growth temperature, and argon flow rate on the quality and area of MoS2 are further studied systematically. These analysis results help to master the morphology and optical properties of monolayer MoS2. The high quality, excellent performance, and large-size monolayer MoS2 under the optimal growth condition is characterized by optical microscopy, AFM, XPS, photoluminescence, and Raman spectroscopy. The Raman spectrum and PL mapping show that the grown MoS2 is a uniform triangular monolayer with a side length of 100 μm, which can pave the way for the applications of photodetectors and transistors.

Preparation and characterization DLC thin films using atmospheric pressure plasma Jet

Diamond-like carbon, amorphous hydrogenated films forms of carbon, were pretreated from cyclohexane (C6H12) liquid using plasma jet which operates with alternating voltage 7.5kv and frequency 28kHz. The plasma Separates molecules of cyclohexane and Transform it into carbon nanoparticles. The effect of argon flow rate (0.5, 1 and 1.5 L/min) on the optical and chemical bonding properties of the films were investigated. These films were characterized by UV–Visible spectrophotometer, X-ray diffractometer (XRD) Raman spectroscopy and scanning electron microscopy (SEM). The main absorption appears around 296, 299 and 309nm at the three flow rate of argon gas. The value of the optical energy gap is 3.37, 3.55 and 3.68 eV at a different flow rate of argon gas. For XRD analysis, The presence of diamond peaks and graphite peaks in the x-ray spectrum for these films Indicates that there is an occurrence of local ordered sp3 and sp2 for carbon domains and graphite respectively. Raman spectroscopy analysis revealed two broad bands D band and G band. The upshift of D band of diamond and downshift of the G band of graphite with is indicative of the presence of DLC films.

Feasibility analysis and simulation of argon recovery in low oxygen-purity cryogenic air separation process with low energy consumption

This paper has discussed and simulated different low oxygen-purity air separation processes with or without argon recovery to find out efficient air separation process using HYSYS platform, and proposed a novel mixing-column process that provides high argon recovery rate based on energy saving effect. For comparison, all the proposed cases are simulated under the same process conditions of 50,000 Nm3/h feed air, 95% gaseous oxygen purity, 0.03 MPa gauge pressure, and 300 Nm3/h liquid oxygen output. Three main performance parameters including oxygen recovery rate, energy consumption and argon recovery rate are compared, and the simulation results show that among five types of processes without argon recovery, the triple-column process, whose energy requirement decreases by 14.9% compared with conventional dual-column process, achieves the lowest energy consumption. Argon production is required in many aspects during air separation process. The feasibility of argon recovery in low oxygen-purity air separation process is studied. The process with argon recovery named mixing-column process is proposed, whose argon recovery rate can reach up to 60.88%, which further increases up to 62.23% with the optimized raw argon flow rate and mixing-ingredient. The energy consumption of the proposed mixing-column process is decreased by 3.5% compared with conventional dual-column process, while the argon recovery rate of the triple-column process can only reach to 4.55% in despite of energy saving by 12%. In addition, more stable argon recovery performance as well as higher argon recovery rate is realized by this novel process when using varied oxygen purity in low oxygen-purity (≤99%) process.

Numerical Simulation of Steel and Argon Gas Two-Phase Flow in Continuous Casting Using LES + VOF + DPM Model

A coupled three-dimensional model, including Large Eddy Simulation model, Lagrangian Discrete Phase Model and VOF multiphase model was developed to investigate the transient two-phase flow and bubble distribution in continuous casting strand. A two-way coupling model including the effect of the drag force, lift force, virtual mass force and pressure gradient force was adopted. The lift force was added via user defined function. A Rosin–Rammler bubble size distribution base on the water model was employed. The results show that the effect of the lift force cannot be ignored during the calculation of the steel and argon gas two-phase flow. Only the bubbles smaller than 2 mm would be brought to near the narrow face. With the increase of the argon flow rate, the transformation of the flow pattern from the double roll to complex flow and single roll was successfully predicted.

Microstructure and properties of a-C films deposited under different argon flow rate on stainless steel bipolar plates for proton exchange membrane fuel cells

Amorphous carbon (a-C) film is deposited to improve the corrosion resistance and interfacial conductivity of stainless steel bipolar plates in proton exchange membrane fuel cells. Argon flow rate significantly influences the atoms free path and bias ions current drawn at the substrate and thus to modify the microstructure of a-C films. Therefore, this study aims to investigate the effects of argon flow rate on compactness, microstructure, corrosion resistance and interfacial contact resistance of a-C films comprehensively. The lowest contact resistance and corrosion current density are 1.3 mΩ cm2 and 0.1 μA/cm2, respectively, which is much lower than the technical target and previous studies. At last, the enhancement of corrosion resistance and interfacial conductivity of a-C films are discussed. The promising results are shedding new light on the deposition mechanism of a-C films applicable for proton exchange membrane fuel cells.

Vertically-oriented graphene nanowalls: Growth and application in Li-ion batteries

Vertically-oriented graphene nanowalls (VGNWs) have been successfully synthesized under different experimental conditions (such as flow rate of argon, growth temperature, plasma power as well as deposition time) on copper foils in the reactive methane and argon environment using a capacitively coupled plasma-enhanced horizontal tube furnace deposition system. It is shown that the morphology and structure of VGNWs can be effectively tailored by experimental conditions. Furthermore, the growth mechanism of VGNWs produced in the plasma-based approach has been investigated. The synthesized VGNWs are used as anode materials in Li-ion batteries and the batteries show outstanding cycle efficiency (~99%). The specific capacity of coin-type cells can be improved by adjusting the experimental parameters and reaches 400 mAh g−1 in the first charge-discharge cycle. This work is particularly important for the development of an advanced process for the synthesis and application of carbon-based nanomaterials.

Catalytic hydrodeoxygenation of bio-oil using in situ generated hydrogen in plasma reactor: Effects of allumina supported catalysts and plasma parameters

Abstract In this study, hydrodeoxygenation of guaiacol, a lignin derived model compound, has been studied experimentally via a combination of dielectric barrier discharge plasma and catalyst. Cracking of methyl groups in the chemical structure of bio-oil is used to provide the hydrogen which is required for hydrodeoxygenation reaction. In order to maximize the degree of deoxygenation and guaiacol conversion, the effects of operating and plasma parameters including applied voltage, guaiacol and argon flow rate have been examined. Furthermore, performance of plasma alone and catalytic plasma has been compared by filling the active volume of the discharge with different commercial catalysts including Ni, Co–Mo, Ni–Mo, Pt–Re and Pt–Cl supported on Al2O3. The highest guaiacol conversion of 92% and deoxygenation degree of 65% are achieved in the presence of Pt–Cl/Al2O3 and Pt–Re/Al2O3 catalysts, respectively. According to the results, the main products were BTX, phenol, methylphenols and dimethylphenols. Unlike previous studies in which catechol was produced as a major product, in our plasma system phenol can be produced selectively through direct demethoxylation rather than demethylation reaction. It is also evident from the results that the hydrogen challenges of hydrodeoxygenation reaction can be overcome by catalytic DBD plasma reactor.

Characterization of Single and Multiphase Hydrodynamics in Continuous Slab Casting Mold in the Presence of Applied Magnetic Field

A numerical investigation has been carried out to characterize both single and multiphase hydrodynamics in a continuous casting mold under the influence of a superimposed magnetic field. Three-dimensional single- and two-phase magnetohydrodynamic flow and turbulence models have been developed for numerical simulation. The computational model results are in agreement with the plant experimental measurements. In a single phase paradigm, with a functional variation in applied magnetic field distributions, the results have been shown for both conducting and non-conducting media. On the other hand, for multiphase flow, based on the actual magnetic field measurement values at the plant, simulations have been carried out at a representative 6 L/min argon flow rate. Overall, the superimposed magnetic field is observed to subdue the flow velocity magnitude and the distribution of turbulence intensity in the continuous casting mold. A similar phenomenon has also been noticed for multiphase flows.