Argon Hydrogen Research Articles

Phase Stability and Superconductivity of Compressed Argon–Hydrogen Compounds from First-Principles

We present the phase stability and superconductivity of Ar–H compounds under high pressure predicted by first-principles calculations and a genetic algorithm technique for crystal structure search....

Mathematical Simulation of Processes in ICP/RF Plasma Torch for Plasma Chemical Reactions

This paper presents the results of mathematical simulation of processes in argon–hydrogen inductively coupled plasma/radio frequency induction plasma torch for plasma chemical reactions. This first part starts a series of papers for simulation and study of plasma properties for a variety of gases and mixtures, which could be used for a number of prospective technologies. The results of mathematical simulation allow further research on the mechanisms of chemical reactions in argon–hydrogen plasma to increase effectiveness of obtaining the target product.

Tin-catalyzed oriented array of microropes of silicon oxide nanowires synthesized on different substrates

Silicon oxide (SiOx) nanowires were synthesized from a monosilane–argon–hydrogen mixture on substrates of different materials (monocrystalline silicon (c-Si), glass, stainless steel, copper, and copper with a SiO2 barrier layer) coated with a tin catalyst film 60 nm thick using the gas-jet electron beam plasma chemical vapor deposition (GJ EBP CVD) method. High-density oriented arrays of microropes of SiOx nanowires were obtained on c-Si and glass substrates and a copper substrate with a SiO2 barrier layer. The fabrication of the nanowires included three steps: heating the substrate with the tin catalyst film, hydrogen plasma treatment of it, and synthesis of the structures. Heating and hydrogen plasma treatment of the tin catalyst on c-Si and glass substrates leads to a decrease in the wetting of the substrate material by tin. As a result, the morphology of the tin catalyst particles changes from semi-elliptical to truncated spherical, which leads to a significant decrease in their surface density as a result of coalescence. A condition for obtaining a high-density oriented array of microropes of SiOx nanowires by the GJ EBP CVD method using a tin catalyst is the absence of chemical reaction between tin and the substrate material.

Microwave atmospheric pressure plasma jets for wastewater treatment: Degradation of methylene blue as a model dye

The degradation of methylene blue in aqueous solution as a model dye using a non thermal microwave (2.45 GHz) plasma jet at atmospheric pressure has been investigated. Argon has been used as feed gas and aqueous solutions with different concentrations of the dye were treated using the effluent from plasma jet in a remote exposure. The removal efficiency increased as the dye concentration decreased from 250 to 5 ppm. Methylene blue degrades after different treatment times, depending on the experimental plasma conditions. Thus, kinetic constants up to 0.177 min−1 were obtained. The higher the Ar flow, the faster the degradation rate. Optical emission spectroscopy (OES) was used to gather information about the species present in the gas phase, specifically excited argon atoms. Argon excited species and hydrogen peroxide play an important role in the degradation of the dye. In fact, the conversion of methylene blue was directly related to the density of argon excited species in the gas phase and the concentration of hydrogen peroxide in the aqueous liquid phase. Values of energy yield at 50% dye conversion of 0.296 g/kWh were achieved. Also, the use of two plasma applicators in parallel has been proven to improve energy efficiency.

Hydrogen Plasma Processing of Iron Ore

Iron is currently produced by carbothermic reduction of oxide ores. This is a multiple-stage process that requires large-scale equipment and high capital investment, and produces large amounts of CO2. An alternative to carbothermic reduction is reduction using a hydrogen plasma, which comprises vibrationally excited molecular, atomic, and ionic states of hydrogen, all of which can reduce iron oxides, even at low temperatures. Besides the thermodynamic and kinetic advantages of a hydrogen plasma, the byproduct of the reaction is water, which does not pose any environmental problems. A review of the theory and practice of iron ore reduction using a hydrogen plasma is presented. The thermodynamic and kinetic aspects are considered, with molecular, atomic and ionic hydrogen considered separately. The importance of vibrationally excited hydrogen molecules in overcoming the activation energy barriers, and in transferring energy to the iron oxide, is emphasized. Both thermal and nonthermal plasmas are considered. The thermophysical properties of hydrogen and argon–hydrogen plasmas are discussed, and their influence on the constriction and flow in the of arc plasmas is considered. The published R&D on hydrogen plasma reduction of iron oxide is reviewed, with both the reduction of molten iron ore and in-flight reduction of iron ore particles being considered. Finally, the technical and economic feasibility of the process are discussed. It is shown that hydrogen plasma processing requires less energy than carbothermic reduction, mainly because pelletization, sintering, and cokemaking are not required. Moreover, the formation of the greenhouse gas CO2 as a byproduct is avoided. In-flight reduction has the potential for a throughput at least equivalent to the blast furnace process. It is concluded that hydrogen plasma reduction of iron ore is a potentially attractive alternative to standard methods.

Structural characterization of the interface structure of amorphous silicon thin films after post-deposition argon or hydrogen plasma treatment

The interfaces in silicon thin film solar cells and silicon heterojunction solar cells are considered to be very important for the solar cell conversion efficiency. This work studies the interface properties of hydrogenated amorphous silicon thin films deposited on crystalline silicon wafers after post-deposition hydrogen plasma treatment (HPT) or argon plasma treatment (APT). The investigation extends our previous study by examining the structural changes resulting from the post-deposition plasma treatment on silicon thin film solar cells. We analyzed the ellipsometry and infrared spectra of our samples to gain a deeper understanding of the fundamental plasma treatment effects. By using post-deposition APT and HPT, we were able to reduce the material stress and improve the structure of these layers. Our results show that APT yields a more compact material with fewer voids and less distinct localized tail states. We discuss the effect of APT and HPT on the most crucial interface in silicon heterojunction solar cells, the i-a-Si:H/c-Si interface. We propose to introduce APT as a post-deposition process step in the fabrication of silicon heterojunction solar cells.

Cytocompatibility by MTT Assay and Platelet Adhesion of Ti and Ti-6Al-4V coated with Hydroxyapatite in different Plasma Gas Atmospheres

ABSTRACTAimThis study was performed to evaluate the biocompatibility of pure titanium and Ti-6Al-4V metals coated with hydroxyapatite (HA) by plasma spray using different plasma gas atmospheres.Materials and methodsThe cell viabilities for each HA-coated sample in an atmosphere of argon, argon—hydrogen, nitrogen, and nitrogen—hydrogen were studied using MTT assay and platelet adhesion test.ResultsThe mean cell viabilities by MTT [3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide] assay of samples coated with HA in argon—hydrogen plasma atmosphere showed maximum cell viability at different time intervals compared with other coating atmospheres of argon—hydrogen, nitrogen, and nitrogen—hydrogen. A statistically significant value of cell viability (p < 0.001) was observed between and within the groups of argon, argon—hydrogen, nitrogen, and nitrogen—hydrogen plasma gas atmosphere. The platelet adhesion study showed agglomerates of platelet cells in some isolated regions of HA for all atmospheres.SignificanceThe results obtained in this study can serve as a guide for the development of new Ti-based HA-coated implants in different plasma gas atmospheres.How to cite this articleKotian R, Rao PP, Madhyastha P, Shobha KL, Rao BSS, Ginjupalli K. Cytocompatibility by MTT Assay and Platelet Adhesion of Ti and Ti-6Al-4V coated with Hydroxyapatite in different Plasma Gas Atmospheres. World J Dent 2017;8(1):28-36.

Separating Technology of Pure Zirconia from Zircon-Sand by the Ar-H<sub>2</sub> Arc Plasma Fusion and the Microwave Leaching

Zirconia (ZrO2) has excellent properties such as high toughness, high strength, thermal stability and high corrosion resistance. Thus, recent zirconia has been spotlighted as a dental material. Most of pure zirconia has been separated from zircon sand (ZrSiO4) by wet refining process which is very complex and not an environmental. The arc plasma fusion method has the advantages as a sustainable process that can easily and quickly get very good fine and high pure powders from the original materials compared with traditional wet method. In this study, zircon sand is separated into zirconia and silica by using the Ar-H2(hydrogen) arc plasma refining. And then silica is removed from it by the microwave leaching method to produce a high pure zirconia. Argon gas, hydrogen gas, copper anode and tungsten cathode are used for the plasma arc generation. To facilitate zirconia and silica separation, carbon of 1-3molar ratios are added with zircon sand. Plasma melting were sequentially conducted two processes. After a reduction process using Ar gas only, it was refined using a mixed gas of Ar-H2. After melting and water cooling in chamber, the solid phases composed with zirconia and silica were obtained at 240 ̊C, and 20% sulfuric acid solution was used as the leaching materials to obtain a high purity zirconia (more than 99%).

Modeling of Single and Dual Frequency Capacitive Discharge in Argon Hydrogen Mixture − Dynamic Effects and Ion Energy Distribution Functions

Single (SF) and dual frequency capacitively coupled plasma (DF CCP) in (0–50%) H2/Ar mixtures was studied numerically with 1D hybrid (Particle‐in‐cell with Monte Carlo Collision + fluid) model. In SF (81 MHz) discharge the effect of hydrogen dilution is studied for the fixed discharge input power. Mechanisms of the plasma density decrease and variation of ions composition with H2 percentage are discussed. The effect of low‐frequency voltage on plasma density, ions composition, ions fluxes, and ions energy was studied in DF CCP (1.76–81 MHz) discharge in 5% H2/Ar gas mixture at low (20 mTorr) and high (100 mTorr) pressures.

Efficiency of the plasma-chemical method of preparation of silicon from quartz in an argon-hydrogen flow

A kinetic model of nonequilibrium chemical processes in gas mixtures of Si, O, H, and Ar and a model of the calculation of the main parameters of plasma facilities for the implementation of the plasma-chemical method of the direct preparation of silicon from quartz in argon–hydrogen gas-plasma flows have been formulated. The criteria and general conditions at which the maximal yield of silicon is achieved were determined. The main mode and construction parameters of plasma facilities were determined. It is shown that at the consumed electrical power of a stationary plasmatron of 100 kW the calculated efficiency of the facility (over vapor Si) could be on the order of 10–2 g/s.

Measurement and optimization of atmospheric plasma sprayed CoMoCrSi coatings parameters on Ti-6Al-4V substrates affecting microstructural and properties using hybrid abductor induction mechanism

Abstract A hybrid artificial intelligence method (AIM) is used to optimize the atmospheric plasma spraying (APS) processing parameters for CoMoCrSi coatings deposited on Ti-6Al-4V substrates. In the proposed approach, the Taguchi design method is used to obtain an initial solution for the optimal set of APS parameters. The true optimal values of the spray distance, chamber pressure, current, argon gas flow rate and hydrogen gas flow rate are then obtained using an artificial neural network (ANN) and genetic algorithm (GA). The coatings deposited using the processing parameters determined using the Taguchi design method alone have a porosity of 8.5%. However, following the ANN/GA optimization procedure, the porosity reduces to just 5.6%. The XRD analysis results show that the as-sprayed coatings contain Cr 3 Si phase as a result of the high-temperature plasma flame. In addition, it is shown that the structure of the Ti phase in the coating transforms from a α-Ti crystal structure (i.e., HCP) to a β-Ti crystal structure (i.e., BCC) during thermal treatment at temperatures to 1200 °C. Finally, it is shown that the hardness of the annealed coatings increases with both an increasing annealing time and an increasing annealing temperature. The higher hardness under higher temperature conditions is attributed to the precipitation of Cr 3 Si phase. Overall, the coatings obtained in the present study using the optimal spray-coating parameters have a low porosity, a high hardness and a good thermal stability at high temperatures.

Effect of gamma irradiation on Schottky-contacted vertically aligned ZnO nanorod-based hydrogen sensor

We report the impact of gamma irradiation on the performance of a gold Schottky-contacted ZnO nanorod-based hydrogen sensor. RF-sputtered vertically aligned highly c-axis-oriented ZnO NRs were grown on Si(100) substrate. X-ray diffraction shows no significant change in crystal structure at low gamma doses from 1 to 5 kGy. As gamma irradiation doses increase to 10 kGy, the single crystalline ZnO structure converts to polycrystalline. The photoluminescence spectra also shows suppression of the near-band emission peak and the huge wide-band spectrum indicates the generation of structural defects at high gamma doses. At 1 kGy, the hydrogen sensor response was enhanced from 67% to 77% for 1% hydrogen in pure argon at a 150 °C operating temperature. However, at 10 kGy, the relative response decreases to 33.5%. High gamma irradiation causes displacement damage and defects in ZnO NRs, and as a result, degrades the sensor’s performance as a result. Low gamma irradiation doses activate the ZnO NR surface through ionization, which enhances the sensor performance. The relative response of the hydrogen sensor was enhanced by ∼14.9% with respect to pristine ZnO using 1 kGy gamma ray treatment.

Electrophoretic Deposition Kinetics and Characterization of Ni–La1.95Ca0.05Zr2O7−δ Particulate Thin Films

Suspensions of NiO–La1.95Ca0.05Zr2O7−δ (NiO–LCZ) composite material have been prepared in isopropanol medium using iodine and acetylacetone as dispersants. The effect of iodine concentration on suspension stability, electrical conductivity, and suspension pH are studied in detail to optimize the suspension chemistry. Electrophoretic deposition has been successfully conducted on conducting substrate (steel plate) to fabricate NiO–LCZ thin particulate films. Deposition kinetics have been studied in detail to optimize the process parameters. Good quality particulate films of such composite on steel plates are obtained at an applied voltage of 60 V for 3 min. The optimized suspension chemistry and process parameters thus obtained are then used to fabricate NiO–LCZ composite films onto nonconducting porous ceramic substrate by placing a conducting plate at the reverse side of the porous substrate. The deposited films along with the ceramic substrates are co‐fired at 1400°C for 6 h in reducing atmosphere (5% hydrogen in argon) to produce a good quality dense Ni–LCZ film of thickness ~40 μm. The hydrogen permeation flux of the developed cermet membrane has been measured and it reveals that Ni–LCZ could be used as a potential membrane for hydrogen separation at high temperature.

Experimental Study for Comparison of H2and Ar–H2Gas Mixture Glow Discharge Wall Conditioning in ADITYA Tokamak

Low-temperature glow discharge wall conditioning (GDC) using H2 gas is effective in reduction of oxygen and carbon (low-Z) contained impurities on near surface region of the vacuum vessel wall. The high retention of hydrogen in vessel wall/components due to long operation of H2 GDC increases hydrogen outgassing during plasma operation and affects the production of high-temperature plasma in tokamak. The hydrogen retention can be reduced using inert gas GDC by sputter cleaning for short duration. But, in that case, the outgassing rate of the inert gas increases, which may impair the plasma performance. To overcome above problems, the GDC with hydrogen-inert gas mixture can be used for better removal of C and O surface contaminants and low hydrogen retention in the vacuum vessel surface. In ADITYA tokamak, H2 GDC is carried out regularly after plasma operations, while the GDC with argon–hydrogen (Ar–H2) mixture has been experimentally tested to observe the reduction of the oxygen and carbon impurities along with low hydrogen retention. In Ar–H2 GDC, the formation of the ArH+ hydride ions, which have quite long life and more energy compared with H2+ ions formed in H2 GDC for breaking the bond of wall molecules. A systematic comparative study of H2 GDC and Ar–H2 mixture GDC by changing the mixture ratio has been carried out in ADITYA tokamak. The relative levels of oxygen and carbon contain impurities have been measured using residual gas analyzer in both GDCs. We have observed a substantial reduction in oxygen and carbon impurities with a significant improvement in wall condition with Ar–H2 GDC compared with the H2 GDC. The effect of wall conditioning by Ar–H2 GDC on the performance of high-temperature plasma operation is presented in this paper.

Synthesis and morphology of silicon oxide nanowires from a free jet activated by electron-beam plasma

Silicon oxide nanowires were synthesized from monosilane–argon–hydrogen mixture by the gas-jet electron-beam plasma chemical deposition method with simultaneous oxygen injection into the vacuum chamber. The synthesis was performed on monocrystalline silicon substrates covered with micron and nanometer tin catalyst particles. The nanowires are formed the via vapor–liquid–solid mechanism in the “catalyst-on-bottom” mode, in which many nanowires grow from one catalyst particle. The process of synthesizing nanowires on a substrate with catalyst consists of three stages: heating to synthesis temperature, hydrogen plasma treatment, and nanowire growth. In the substrate region corresponding to the jet axis, different structures are formed depending on the catalyst particle size. For catalyst particles under 100 nm, there are formed structures of chaotically oriented and interlaced bundles of silica nanowires. For catalyst particles of 0.3–1 micron, there are formed oriented arrays of cylindrically shaped nanowire bundles (“microropes”). Cocoon-like structures are formed for catalyst particles of more than 1 micron.We propose a model of nanowire growth by this method, which is based on nonuniform heating of a catalyst particle by a directed plasma flow. It was found that for synthesis of oriented microrope arrays the initial tin film thickness should be less than 100 nm and the synthesis process should include a hydrogen plasma treatment stage.

Synthesis of silicon oxide nanowires by the GJ EBP CVD method using different diluent gases

Nanowires of silicon oxide SiOx (x ≤ 2) were synthesized from a mixture of monosilane and hydrogen (helium, argon) by gas‐jet electron beam plasma chemical vapor deposition (GJ EBP CVD) method with simultaneous supply of oxygen into the vacuum chamber. The synthesis was performed on monocrystalline silicon and glass substrates coated with micron‐sized particles of a tin catalyst. In particular, aligned arrays of nanowire bundles (microropes) were synthesized from a mixture of monosilane and hydrogen (argon). A bundle of amorphous silicon oxide nanowires, each of which is about 15 nm in diameter, grows from a catalyst particle. The growth rate of the microropes is about 25 nm s−1 at a synthesis temperature of 320–330 °C. The morphology of the nanostructures was investigated by transmission and scanning electron microscopy, their composition by X‐ray energy dispersive spectroscopy and optical properties by photoluminescence spectroscopy. The synthesis was carried out using the well‐known vapor–liquid–solid (VLS) mechanism. A model is proposed for the synthesis of the nanostructures by the above method, including the formation of aligned bundles of nanowires (microropes) due to nonuniform heating of the catalyst particle by directed plasma flow. The obtained nanostructures have intense photoluminescence in the visible region of the spectrum at room temperature.

Direct determination of cadmium in foods by solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry using a tungsten coil trap

In this work, a solid sampling device consisting of a tungsten coil trap, porous carbon vaporizer and on-line ashing furnace of a Ni–Cr coil was interfaced with inductively coupled plasma mass spectrometry (ICP-MS). A modified double gas circuit system was employed that was composed of carrier and supplemental gas lines controlled by separate gas mass flow controllers. For Cd determination in food samples using the assembled solid sampling ICP-MS, the optimal ashing and vaporization conditions, flow rate of the argon–hydrogen (Ar/H2) (v:v=24:1) carrier gas and supplemental gas, and minimum sampling mass were investigated. Under the optimized conditions, the limit of quantification was 0.5pg and the relative standard deviation was within a 10.0% error range (n=10). Furthermore, the mean spiked recoveries for various food samples were 99.4%–105.9% (n=6). The Cd concentrations measured by the proposed method were all within the certified values of the reference materials or were not significantly different (P>0.05) from those of the microwave digestion ICP-MS method, demonstrating the good accuracy and precision of the solid sampling ICP-MS method for Cd determination in food samples.

Optimization of catalyst formation conditions for synthesis of carbon nanotubes using Taguchi method

A growth of Carbon Nanotubes (CNTs) suffers many difficulties in finding optimum growth parameters, reproducibility and mass-production, related to the large number of parameters influencing synthesis process. Choosing the proper parameters can be a time consuming process, and still may not give the optimal growth values. One of the possible solutions to decrease the number of the experiments, is to apply optimization methods to the design of the experiment parameter matrix. In this work, Taguchi method of designing experiments is applied to optimize the formation of iron catalyst during annealing process by analyzing average roughness and size of particles. The annealing parameters were: annealing time (tAN), hydrogen flow rate (fH2), temperature (TAN) and argon flow rate (fAr). Plots of signal-to-noise ratios showed that temperature and annealing time have the highest impact on final results of experiment. For more detailed study of the influence of parameters, the interaction plots of tested parameters were analyzed. For the final evaluation, CNT forests were grown on silicon substrates with AlOX/Fe catalyst by thermal chemical vapor deposition method. Based on obtained results, the average diameter of CNTs was decreased by 67% and reduced from 9.1nm (multi-walled CNTs) to 3.0nm (single-walled CNTs).

Study of the surface of GaAs after etching in high-frequency and glow discharge plasma by atomic force microscopy

The quality of the surface of a semiconductor structure after plasma-chemical etching in plasma of HCl/Ar, HCl/Cl2, HCl/H2 mixtures, and freon R12 plasma is studied. It is shown that the optimal combination of the etch rate and surface roughness is achieved in the hydrogen chloride and argon mixture. In mixtures with hydrogen, the etch rates are too low for high surface quality; in mixtures with chlorine, the surface roughness exceeds technologically acceptable values due to high etch rates. The high-frequency discharge in freon R12 can be effectively used to etch semiconductors, providing technologically acceptable interaction rates, while retaining a uniform and clean surface.

Effects of annealing conditions and film thickness on electrical and optical properties of epitaxial Al-doped ZnO films

Epitaxial films of Al-doped ZnO were grown at 400°C on sapphire-R substrates at atmospheric pressure via the aerosol-assisted MOCVD technique. The film microstructure, surface morphology, and electrical and optical properties were investigated in relation to the annealing temperature (300–600°C), gas atmosphere (argon–hydrogen mixture, argon, nitrogen, vacuum, oxygen, and air) and film thickness (~70–1200nm). The annealing influenced the carrier concentration and mobility in the films, producing an enlarged effect at higher temperatures, whereas the crystalline quality and surface morphology of the films were nearly unaffected by annealing. The electrical properties of the films markedly degraded after annealing in oxygen and air, and improved when annealed in other gas environments. The largest improvement of the electrical properties was obtained by annealing of films in the argon–hydrogen mixture. The rapid evolution of film properties with thickness was observed in the range of small thicknesses (~70–170nm). The film properties were nearly unchanged for further increases in the film thickness up to ~800nm, whereas thicker films exhibited degraded electrical properties due to their partial cracking. The effect of the annealing on film electrical properties increased with the decrease in the film thickness. The gas atmosphere (air or nitrogen) during the films cooling to RT after deposition also influenced the electrical properties of films.