Atmospheres Of Different Gases Research Articles

Sessile droplet evaporation in the atmosphere of different gases under forced convection

The phenomenon of evaporation from the surface of a liquid droplet into a neutral noncondensible gas was numerically studied by taking forced convection gaseous flow into account. The mathematical model considers the effects of surface tension, gravitational force, viscosity of both liquid and gaseous media, as well as the Stefan flow from the droplet surface, possible free gravitational convection, and the Marangoni convection in droplets, and it is designed to describe diffusion-limited evaporation. We consider the diffusion-limited evaporation process when the diffusive gas flux to the droplet surface is compensated by the convective Stefan flow from the surface. The results indicate an interaction of the liquid and gaseous media. Convective gas flows cause the liquid to move and a vortex to occur in the droplet. The flow velocities in a vortex are 103 times less than the characteristic velocity of forced convection flow in air. The droplet surrounded by gaseous flow changes its shape and oscillates, which causes a gas-density wave. Calculations have shown that the diffusion-limited evaporation rate does not change in the presence of forced convection, which contradicts most of the known experimental works. The possible reason for this discrepancy is the presence of non-equilibrium conditions at the liquid–gas interface in experiments. This leads to a consequent change of the evaporation mode to non-diffusive, while the numerical model postulates the Stefan condition and diffusion-limited evaporation.

The Influence of Ultrasound Cavitation on the Process of Degradation of Organic Substances in Wastewater of Pharmaceutical Production

The influence of ultrasound cavitation in the atmosphere of different gases, namely oxygen, air, and nitrogen, on the destruction of impurities of butanol and ethanol found in wastewater from the pharmaceutical plant “Galichpharm” was investigated. The effect of the corresponding gases (oxygen, nitrogen, and air) without ultrasound cavitation on the destruction of ethanol and butanol impurities in wastewater was comparatively investigated. The degree of oxidation of organic matter, effective rate constants, and approximation coefficients were calculated. It was found that the air supply is the least effective for both ethanol and butanol impurities. Degradation of ethanol by air contributed to the reduction in the organic matter content by 14.6 %, while oxidation of butanol was not observed. Ultrasound cavitation enhanced the effect of air and in common action with air the ethanol impurity content reduced by 32.58 %, and butanol impurity by 4.05 %. Nitrogen bubbling produced mediocre results for the destruction of ethanol and butanol impurities giving a decrease by 17.04 % and 0.67 %, respectively. The highest results were obtained with oxygen. Ethanol impurities decreased by 22.47 % and butanol impurities by 1.75 %. With the common action of oxygen and ultrasound, much higher results were obtained, 44.32 % for ethanol impurities and 7.43 % for butanol impurities.

The effect of a gas environment on the fluorescence intensity of quantum-dot composite systems

The fluorescence kinetics of a composite structure based on colloidal CdSe/ZnS core-shell quantum dots deposited on an array of GaAs nanowires in atmospheres of different gases is studied upon excitation by cw laser radiation. It is suggested that the fluorescence enhancement mechanism consists in the transfer of part of the vibrational energy of quantum dots to surrounding gas molecules due to inelastic collisions.

Optical properties of polyimide layers prepared by vacuum deposition in the presence of gas

Thin polyimide (PI) layers were prepared by simultaneous vacuum evaporation of the polyimide precursors pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA). After deposition the layers were thermally treated 1 hour at 170°C followed by 1 hour at 250°C. Precursors were deposited in a residual atmosphere of different gases - argon, nitrogen, helium and air at a pressure 10−2 Pa. Conditions for fabrication of PI layers with reproducible composition, uniform and smooth surface, without mechanical and chemical defects have been established. It was found that the preparation conditions do not significantly affect the optical properties of the layers. The PI layers before and after thermal treatments are transparent over 85% in the studied spectral range (from 350 to 900 nm). The thermal treatment leads to a bathochromic shift, in a consequence of the transmission edge shift to the longer wavelengths, for all the samples, independently of the deposition conditions in the vacuum chamber. The average refractive indices at 633 nm varied from 1.67 towards 1.72 depending on the deposition conditions and thermal treatment.

One-step self-assembly economical synthesis of hierarchical ZnO nanocrystals and their gas-sensing properties

Hierarchical ZnO pine needles were successfully fabricated via a novel economical one-step self-assembly synthesis. The influences of the amount of metallic zinc powder added and reaction time on the size and morphology of the ZnO were studied in detail. The gas-sensing performance of the hierarchical ZnO pine needles was observed carefully, and it indicated that the sensor based on hierarchical ZnO pine needles showed a high selectivity, quick response and stability for a long time for ethanol gas. Furthermore, AC impedance spectroscopy of the sensor was also examined at different temperatures and in atmospheres of different gases to understand the gas-sensing mechanism, and the results indicate that the sensor has the lowest potential barrier height for the transition of space charges and the minimum resistance when it is exposed to ethanol gas at 400 °C.

Possibilities of production of nanopowders with high power ELV electron accelerator

Electron-beam evaporation of various natural and industrial materials in the atmosphere of different gases at atmospheric pressure can be used for the synthesis of nanosize powders. These powders are characterized by high purity and may exhibit unusual properties. In particular, nanopowders of silicon dioxide and oxide (SiO2, SiO), magnesia (MgO), alumina (Al2O3), titania (TiO2), gadolinium oxide (Gd2O3), various metals (tantalum, molybdenum, nickel, aluminium, copper, silver), semiconductor (Si), nitrides (AlN, TiN), and some other substances had been produced. The process of nanopowder synthesis is highly effective; in particular, the yield of oxides can exceed ten kilograms per hour.

Surface-Assisted Transient Displacement Charge Technique. II. Effect of Gases on Photoinduced Charge Transfer in Self-Assembled Monolayers

Surface-assisted photoinduced transient displacement charge (SPTDC) technique was used to study charge transfer in self-assembled monolayers of 7-diethylaminocoumarin covalently linked to an oxide surface in the atmosphere of different gases. The dipole signal was found to be opposite to that in solution and dependent on the nature of the gas and its pressure. The results were explained by collision-induced relaxation that impedes uninhibited tilting of molecules onto the surface. Collisions with paramagnetic oxygen induce intersystem crossing to long-lived triplet dipolar states of coumarin with the rate close to half of that for the collision rate.

Carbon-mineral adsorbents — new type of sorbents part II. Surface properties and methods of their modification

Chemical structure and morphology of carbon deposits contained in complex carbon-mineral adsorbents prepared by pyrolysis of different substances on the surface of mineral adsorbents such as silica gels, aluminium oxide, aluminosilicates, porous glasses, etc. have been discussed. The morphology of the carbon deposit depends on the course of the pyrolysis reaction and determines the surface properties of complex adsorbents and the possibilities of their practical utilization as sorbents and catalysts. The methods of modification of adsorption properties of such adsorbents prepared on technical and laboratory scales were also presented. Thermal properties of carbon-mineral adsorbents in atmospheres of different gases were also discussed.

Laser induced oxygen adsorption and intensity degradation of porous Si

For light-emitting porous Si there has been a severe problem with instability and degradation in the light emission. We performed in situ photoluminescence measurements to monitor the degradation process under ambient atmosphere of different gases and in ultrahigh-vacuum environment. We found that laser induced oxygen adsorption is the major cause for the light emission degradation, while the laser heating effect can be excluded. We also found the degraded intensity can be partially recovered by reducing the surface oxygen concentration.

Excitation of sulfur and chlorine spark spectra in atmospheres of different gases

Excitation of sulfur and chlorine spark spectra in atmospheres of different gases

Ultraviolet irradiation of ZnS single crystals kept in the atmosphere of different gases

This short communication deals with some preliminary results concerning the changes of the transmission spectra of ZnS single crystals irradiated in various gases by UV light.

I. On the influence of carbonic anhydride and other gases on the development of micro-organisms

In consequence of a paper which has appeared in the last number of the ‘Zeitschrift für Hygiene,’ by Dr. Carl Fränkel, entitled “Ueber die Einwirkung der Kohlensäure auf die Lebensthätigkeit der Mikro-organismen,” I have been led to publish the results of some preliminary experiments on the same subject which I made in the spring of 1886, but which, owing to my attention being at that time devoted to investigations in other directions, I was obliged to put on one side. Although the methods which I adopted in my experiments are essentially different from those which Fränkel has employed, yet the results, so far as they can be compared with his, are on the whole concordant. In my experiments I used the ordinary methods of plate-cultivation (Esmarch’s important modification having not yet been published), the plate-cultivations of the various micro-organisms being then submitted to an atmosphere of different gases in the following manner:— A suitable attenuation of a particular micro-organism was employed, and gelatine plates were poured in the usual way; the different plates, resting one above the other on small glass stages, were placed in a flat porcelain dish and covered over with a glass bell-jar.

On the effect of surrounding media on voltaic ignition

The author refers to some experiments of his published in the Philosophical Magazine for December 1845, and in the Bakerian Lecture for 1847, relating to the difference of ignition generated in a platinum wire heated by the voltaic current, when the wire is immersed in atmospheres of different gases. In the present paper these experiments are continued, the current being passed through two platinum wires both in the same voltaic circuit, but immersed in atmospheres of different gases. It appears from these experiments that the heat generated in the wire is less in hydrogen and its compounds than in other gases; and that when the wires and their atmospheres of gas are immersed in given quantities of water, the water surrounding the hydrogenous gases is less heated than that surrounding those which contain no hydrogen.