Oxygen-argon Gas Mixtures Research Articles

ШУМ КАК УСЛОВИЕ, СПОСОБСТВУЮЩЕЕ АВИАЦИОННЫМ СОБЫТИЯМ

The article provides statistical data on passenger turnover of air transport in comparison with other types of transport in Russia, as well as flight safety indicators over the last decade. The leading types of events leading to aviation accidents have been identified. It has been revealed that the cause of many of the negative aviation events that have occurred are violations of the functional state, loss of performance and errors of crew members, which are facilitated by the conditions of the person’s environment. The authors study the variability of heart rhythms, reflecting changes in the psycho-emotional state of a person during noise. The results of the study confirm that a change in the activity of the sympathetic and parasympathetic parts of the autonomic nervous system of the human operator. This indicates the development of stress under the influence of noise. The authors demonstrate the importance of counteracting the negative effects of noise on aviation personnel to improve flight safety and reduce injuries and propose to use otoprotection with an oxygen-argon gas mixture to concentrate the attention of the crew in extreme situations. Key words: air transport, aviation accidents, human factor, noise, otoprotection, argon.

Focused Plasma- and Pure Water-Enabled, Electrode-Emerged Nanointerfaced NiCo Hydroxide-Oxide for Robust Overall Water Splitting.

Bimetallic, bifunctional electrocatalysts capable of driving both oxygen (OER) and hydrogen (HER) evolution half-reactions on both electrodes in commercial water electrolysis cells are among the most promising materials systems for clean hydrogen energy generation. However, insufficient hydrogen and oxygen production activity at industry-relevant current densities and long-term catalyst stability on the electrode surface prevent this approach from industrial translation. This work resolves these challenges by advancing the promising, yet far-from-successful attempts to sprout bimetallic electrocatalytic nanostructures directly from electrode frames. For the first time, we utilize magnetic-field-focused, atmospheric-pressure plasma jets in oxygen-argon gas mixtures to successfully induce the nanointerfaced bimetallic NiCo hydroxide and oxide catalyst phases. After a simple hydrothermal treatment in pure water, NiCo bimetallic hydroxide nanosheets are densely covered with strongly bonded bimetallic NiCo oxide nanoparticles which ensure high catalytic activity evidenced by the low overpotentials for both HER and OER for delivering a current density of 100 mA cm-2 (j100) of only 306 and 484 mV, respectively. The electrode-emerged nanointerfaced NiCo hydroxide-oxide bimetallic system (NiCo2O4-NiCo(OH)x) shows an ultrastable electrocatalytic performance under a high current density of j200, which only decays 5.8% and 6.3% for HER and OER processes within 100 h. The competitive H2 and O2 production rates are about 1.27 and 0.69 mmol h-1 cm-2 (near to 2:1, under j10 conditions), meeting a nearly 100% Faradaic efficiency. Furthermore, the theory calculation indicates that the Ni and Co sites of NiCo2O4-NiCo(OH)x are the catalytic centers for the HER process. Our new plasma-enabled approach for the controlled production of bimetallic hydroxide-oxide active nanointerfaced systems is generic and is potentially suitable for diverse materials systems and applications well beyond electrocatalysis.

Heterogeneous reaction kinetics for oxidation and combustion of boron

Non-isothermal thermogravimetric (TG) analysis was used to study the oxidation kinetics for 95% pure amorphous boron powder. Commercial boron powders were pre-treated with acetonitrile and water to reduce the thickness of their initial hydrated oxide layer and to achieve a narrower particle size distribution. The samples were oxidized at different heating rates in an oxygen-argon gas mixture. Boron particles comprising aggregates of finer primary particles were modeled as spheres with porous shells and solid cores. Experimental TG traces were split among particles of different sizes. The split was based on the measured particle size distribution and accounted for the fraction of the measured mass gain assigned to different powder particle size bins using the core-shell particle model. Further, the reactive shell was assumed to consist of densely packed spherical primary particles. The reaction kinetics was quantified to obtain both activation energy and pre-factor describing oxidation of the primary particles. The early stage of oxidation is well described with the activation energy of 148 ± 6 kJ/mol. The oxidation rate of boron particle of any size can be obtained considering the rate of oxidation of the primary particle and the introduced core-shell particle structure. The obtained oxidation model was extrapolated to the range of temperatures typical of boron combustion. A change in the particle morphology occurring when boron melts and the aggregates of primary particles coalesce into a single droplet was accounted for. Burn times predicted at different temperatures were close to those measured for boron particles burning in room air. Comparisons suggest that the particle surface temperature varies in the range of 3500–4500 K, approaching boron boiling point. It is concluded that the same heterogeneous kinetics governs both low-temperature oxidation of boron when the oxide film thickness is small and its full-fledged combustion occurring at much higher temperatures.

Implementation of smooth nanocrystalline diamond microstructures by combining reactive ion etching and ion beam etching

Due to its extraordinary properties diamond can be used as mold in a hot embossing process which allows the replication of micro-optical structures. For this application a low surface roughness is indispensable. We investigated the ability of ion beam etching (IBE) to smooth defined rough areas after reactive ion etching (RIE). Simulations based on the influence of the angle dependence of the ion beam etch rate showed the suitability of this approach.Different surface qualities were achieved for nanocrystalline diamond films by RIE with three different oxygen-argon gas mixtures and etch depth, respectively. SEM images displayed the expected increase of surface roughness with the oxygen share of the gas mixture and the achieved etch depth.No masking layers were employed during ion beam post-processing. The comparison of different AFM images confirm that this process enlarged the etch depths corresponding to the initial surface roughness until the rough areas are smoothed completely. With increasing surface roughness the expenditure of time necessary to reach saturation rose. Etch rates measured for reactive ion etching were 5 to 6 times higher than the etch rate measured for IBE. Simply comparing the etch time the combination of RIE and IBE is up to four times faster than only employing IBE for the fabrication of structures despite using low RIE plasma powers.

Influence of the oxygen concentration on the formation of crystalline phases of ZrO2 nanoparticles during the low-pressure arc-discharge plasma synthesis

The synthesis of nanoparticles of zirconium dioxide with different contents of the monoclinic and tetragonal phases has been investigated. The synthesis has been performed by controlling the oxygen content in the gas mixture in the plasma-chemical evaporation–condensation process in low-pressure arc-discharge plasma. The crystal structure of synthesized ZrO2 nanoparticles has been studied using X-ray diffraction. The morphology of the particles has been analyzed using transmission electron microscopy. The nanoparticle growth in arc-discharge plasma has been examined using optical emission spectroscopy. The X-ray powder diffraction analysis has revealed that the content of the monoclinic phase of ZrO2 increases with a decrease in the oxygen content in the oxygen–argon gas mixture.

Influence of thermal diffusion on decarburisation of iron–chromium alloy droplets by oxygen–argon gas mixtures

Using an electromagnetic levitation technique, the kinetics of decarburisation of Fe–Cr–C alloy droplets by oxygen–argon gas mixtures containing up to 10 vol.-% oxygen was investigated at 1873 K. The observed decarburisation rates were less than predicted using conventional formulation of governing mass transport numbers. It is hypothesised that the effects of thermal diffusion caused by the steep temperature gradient (∼1550 degrees) between the incoming gas stream and the surface of the droplet, is responsible for the difference observed between the well established mass transfer model and the experimental data for decarburisation kinetics. This finding has important implications with respect to the application of appropriate mass/heat transport equations when using commercial software to model pyro-metallurgical processes, such as stainless steel refining, where large temperature gradients are an inherent component of the system.

Oxidation and Melting of Aluminum Nanopowders

Recently, nanometer-sized aluminum powders became available commercially, and their use as potential additives to propellants, explosives, and pyrotechnics has attracted significant interest. It has been suggested that very low melting temperatures are expected for nanosized aluminum powders and that such low melting temperatures could accelerate oxidation and trigger ignition much earlier than for regular, micron-sized aluminum powders. The objective of this work was to investigate experimentally the melting and oxidation behavior of nanosized aluminum powders. Powder samples with three different nominal sizes of 44, 80, and 121 nm were provided by Nanotechnologies Inc. The particle size distributions were measured using small-angle X-ray scattering. Melting was studied by differential scanning calorimetry where the powders were heated from room temperature to 750 degrees C in an argon environment. Thermogravimetric analysis was used to measure the mass increase indicative of oxidation while the powders were heated in an oxygen-argon gas mixture. The measured melting curves were compared to those computed using the experimental particle size distributions and thermodynamic models describing the melting temperature and enthalpy as functions of the particle size. The melting behavior predicted by different models correlated with the experimental observations only qualitatively. Characteristic stepwise oxidation was observed for all studied nanopowders. The observed oxidation behavior was well interpreted considering the recently established kinetics of oxidation of micron-sized aluminum powders. No correlation was found between the melting and oxidation of aluminum nanopowders.

Melting and Oxidation of Nanometer Size Aluminum Powders

AbstractRecently, nanometer-sized aluminum powders became available commercially and their use as potential additives to propellants, explosives, and pyrotechnics has attracted significant interest. It has been suggested that very low melting temperatures are expected for nano-sized aluminum powders and that such low melting temperatures could accelerate oxidation and trigger ignition much earlier than for regular, micron-sized aluminum powders. The objective of this work was to investigate experimentally the melting and oxidation behavior of nano-sized aluminum powders. Powder samples with three different nominal sizes of 44, 80, and 121 nm were provided by Nanotechnologies Inc. The particle size distributions were measured using small angle x-ray scattering. Melting was studied by differential scanning calorimetry where the powders were heated from room temperature to 750 °C in argon environment. Thermogravimetric analysis was used to measure the mass increase indicative of oxidation while the powders were heated in an oxygen-argon gas mixture. The measured melting curves were compared to those computed using the experimental particle size distributions and thermodynamic models describing the melting temperature and enthalpy as functions of the particle size. The melting behavior predicted by different models correlated with the experimental observations only qualitatively. Characteristic step-wise oxidation was observed for all studied nanopowders. The observed oxidation behavior was well interpreted considering the recently established kinetics of oxidation of micron-sized aluminum powders. No correlation was found between the melting and oxidation of aluminum nanopowders.

溶融アンチモンの酸化揮発反応速度

In order to elucidate the kinetics and mechanism of liquid antimony oxidation, experiments were conducted with air and oxygen-argon gas mixtures from the view point of an antimony recovery from antimony-bearing materials such as an used lead-battery and InSb, GaSb semiconductors. The experimental condition was in the temperature range between 973 and 1,173 K, in the oxygen partial pressure range between 0.05 and 0.25 atm.The experimental results show that the oxidation rate increases with increasing gas flow rate, oxygen partial pressure and temperature. An evaporation study of pure water into an argon gas stream was then carried out with respect to the mass transfer characteristics in the gas phase in the reactor used for the present work. The Sherwood number is correlated by the following equation : Sh = 1.38Re0.64Sc1/2. Then the equation was applied to analyze the oxidation kinetics of liquid antimony. The kinetic analysis shows that the mass transfer step in the gas phase controls the overall rate in the experimental range studied, except for the condition of 0.05 atm as the oxygen partial pressure.

The Effects of Gas Composition on the Ion Milling of Cross Sectional Tem Samples Containing Carbon Layers

AbstractDuring conventional ion milling of carbon thin films on Si or SiC, the carbon has a much slower milling rate than the Si, SiC, and the epoxy resin. As a result, the substrates were thinned much more rapidly than the carbon films. A solution suggested by several subscribers to the Microscopy Society of America's Microscopy Listserver among others was to reactively ion mill the samples with a 20–25% oxygen-argon gas mixture. Is this the best inert gas to use? Neon has a mass that is between Si and C and therefore should impart a higher energy transfer to the C atoms than Ar. To determine whether the mass of the inert gas is important in balancing the milling rates, four gases were used to ion mill samples of a PLD DLC film with a nominal thickness of 0.5 μm. For improved adhesion of the films to the Si substrate, an initial 2 nm of Ti and a nominal 0.5 μm thick layer of TiC was grown using a combined PLD and magnetron sputtering technique prior to the PLD DLC.1,2 The gases were 100%Ar, 100%Ne, 75%Ar-25%O2, and 75%Ne-25%O2. Using the Tripod Polisher, the samples were polished flat using typical conditions and the surfaces examined by atomic force microscopy and compared. TEM samples prepared by single-sided dimpling prior to ion milling were prepared using the gas composition which gave the best results with respect to the AFM. A methodology is established for determining ion milling conditions for samples having layers of different compositions.

Indium–tin oxide films radio frequency sputtered from specially formulated high density indium–tin oxide targets

High density ITO (indium–tin oxide) targets doped with Al2O3 and SiO2 manufactured in the Tektronix Ceramics Division have been used to rf sputter ITO films of various thicknesses on borosilicate glass substrates. Sputtering in an oxygen–argon gas mixture and annealing in forming gas, resulted in ITO films exhibiting 90% transmission at 550 nm and a sheet resistance of 15 Ω/sq for a thickness of 1100 Å. Sputtering in an oxygen–argon gas mixture and annealing in air increased sheet resistance without a large effect on the transmission. Films sputtered in argon gas alone were transparent in the visible and the sheet resistance was found to be 100–180 Ω/sq for the same thickness, without annealing.

Optical and Electrical Properties of SnO2:F Thin Films Obtained by R.F. Sputtering With Various Targets

Tin oxide films were deposited on glass substrates by reactive and non reactive r.f. sputtering using different types of targets corresponding to various Sn/F atomic ratio: hot pressed Sn–SnF2or SnO2–SnF2mixtures, ceramics obtained by casting either an aqueous SnO2–SnF2slurry or a suspension of tin oxide in molten tin fluoride. The samples were prepared in oxygen-argon gas mixtures in which the oxygen concentration was varied from 0 mole % up to 30 mole% depending on the target. The optical and electrical properties of the obtained thin films have been studied and compared to those of the films obtained by spray technique.

Oxygen-linked binding of halothane to human adult haemoglobin.

The affinity for oxygen of normal human haemoglobin (Hb) solutions was measured in the presence of increasing concentrations of halothane. We observed a maximum increase in P50 of 25% with halothane 40 kPa compared with control (oxygen-argon gas mixtures) indicating the oxygen-linked character of the binding of halothane to the Hb molecule. The effect of halothane on P50 was independent of pH between 7.0 and 8.0 and of chloride concentration between 10 and 100 mmol litre-1. This suggests that halothane-Hb interactions may occur through hydrophobic linkage as occurs with short chain aliphatic hydrocarbons. The oxygen-linked binding of halothane appears of minor importance in altering oxygen binding to Hb in vivo compared with other factors such as chloride ion or 2, 3-DPG.

Efficiency of Sample Transport from the Electrode Cavity to the Excitation Zone of Gas-Stabilized dc Arcs for Spectrochemical Analysis

The transfer of atomized material from the electrode cavity to the discharge region of a dc arc is quantitatively defined in terms of the efficiency with which elements enter the excitation region. Equations inherent in the determination of efficiencies from spectral-line intensities are given. Relative efficiencies were experimentally determined for a synthetic silicate sample containing some 20 test elements as trace or minor constituents. The elements were selected according to volatility and carbide forming properties. The influences of the following variables on the efficiency were investigated: (a) type of element, (b) preliminary fusion of test sample with lithium metaborate, (c) dilution of test sample with lithium carbonate or lithium fluoride, (d) two different types of Stallwood-jet devices for arc stabilization and control of atmosphere, (e) the composition of the stabilizing gas, viz., the oxygen content of an oxygen—argon gas mixture, and (f) the flow rate of the stabilizing gas.

Influences of the physical and chemical processes in the electrode cavity and the gaseous atmosphere in the arc on the emission characteristics of the d.c. arc for spectrochemical analysis—I: Efficiency of particle transport from the electrode cavity to the excitation zone

The transfer of atomized material from the electrode cavity to the discharge region of a d.c. arc is quantitatively defined in terms of the efficiency with which elements enter the excitation region. Equations inherent in the determination of efficiencies from spectral-line intensities are given. Relative efficiencies were experimentally determined for a synthetic silicate sample containing some twenty test elements as trace or minor constituents. The elements were selected according to volatility and carbide forming properties. The influences of the following variables on the efficiency were investigated: (i) type of element; (ii) preliminary fusion of test sample with lithium metaborate; (iii) dilution of test sample with lithium carbonate or lithium fluoride; (iv) two different types of Stallwood-jet device for arc stabilization and control of atmosphere; (v) the composition of the stabilizing gas, viz. the oxygen content of an oxygen-argon gas mixture; (vi) the flow rate of the stabilizing gas. A detailed discussion of the experimental technique includes a description of a new Stallwood-jet device with two independently controlled gas flows permitting both adequate stabilization of the arc and suppression of molecular bands without requiring a chamber.

Thermal conductivities of nitrogen-argon and oxygen-argon gas mixtures

The thermal conductivities of N2-Ar and O2-Ar mixtures have been measured over the temperature range from -183 to 200°c by the hot-wire method. The thermal conductivity against composition curves show a minimum at all temperatures which cannot be explained by the existing theories of heat conductivity. The results confirm the suggestion put forward previously by Mukhopadhyay and Barua in order to explain the similar appearance of a minimum for the H2-He system.