Oxygen-containing Gas Mixtures Research Articles

Thermogravimetric/Thermal-Mass Spectroscopy Insight into Oxidation Propensity of Various Mechanochemically Made Kesterite Cu2ZnSnS4 Nanopowders.

Thermogravimetry coupled with thermal analysis and quadrupole mass spectroscopy TGA/DTA-QMS were primarily used to assess the oxidation susceptibility of a pool of nanocrystalline powders of the semiconductor kesterite Cu2ZnSnS4 for prospective photovoltaic applications, which were prepared via the mechanochemically assisted synthesis route from two different precursor systems. Each system, as confirmed by XRD patterns, yielded first the cubic polytype of kesterite with defunct semiconductor properties, which, after thermal annealing at 500 °C under neutral gas atmosphere, was converted to the tetragonal semiconductor polytype. The TGA/DTA-QMS determinations up to 1000 °C were carried out under a neutral argon Ar atmosphere and under a dry, oxygen-containing gas mixture of O2:Ar = 1:4 (vol.). The mass spectroscopy data confirmed that under each of the gas atmospheres, a distinctly different, multistep evolution of such oxygen-bearing gaseous compounds as sulfur oxides SO2/SO3, carbon dioxide CO2, and water vapor H2O was taking place. The TGA/DTA changes in correlation with the nature of evolving gases helped in the elucidation of the plausible chemistry linked to kesterite oxidation, both in the stage of nanopowder synthesis/storage at ambient air conditions and during forced oxidation up to 1000 °C in the dry, oxygen-containing gas mixture.

Influence of Oxygen-containing Filling Gas Mixtures on the Interruption Capability of MV Load Break Switches

Nowadays SF6 is commonly used as filling gas for medium voltage load break switches due to its outstanding insulating and arc-quenching properties. However, due to its high global warming potential the interrupting performance of alternative eco-friendly gases are investigated for such devices. This contribution investigates the thermal interruption capability of a medium voltage load break switch using two different oxygen-containing gas mixtures: dry air and a mixture of nitrogen, oxygen and carbon dioxide. The findings indicate an improved performance in comparison to pure nitrogen when considering an admixture of oxygen. In gas mixtures containing 80\% nitrogen, the addition of oxygen results in an enhanced thermal interruption capability compared to an equivalent proportion of carbon dioxide.

Reaction of Oxygen with Uranium (IV) Chloride in Fused Alkali Chlorides

Reaction of oxygen with solutions of uranium(IV) chloride in fused LiCl and three alkali chloride eutectic mixtures (LiCl–KCl, NaCl–KCl–CsCl, NaCl–CsCl) was investigated at 550–750 °C. Bubbling oxygen or oxygen-containing gas mixtures (O2–H2O, O2–Ar, O2–H2O–Ar) through LiCl–UCl4 melts resulted in significant precipitation of uranium (up to 87%) in the form of oxides and alkali uranates. Increasing mean radius of the solvent melt cations decreased the degree of uranium precipitation and uranyl chloride (soluble in the melt) became the main product of the reaction. High temperature spectroscopy measurements were employed to determine the kinetic parameters of the reaction in LiCl–KCl, NaCl–KCl–CsCl and NaCl–CsCl melts. Reaction rates, order, rate constants and activation energy values were estimated. Increasing temperature led to increased reaction rates but the effect of uranium chloride concentration depended on the cationic melt composition. Oxygen reacts with uranium(IV) containing melts much faster than with the melts containing rare earth chlorides and oxygen sparging can be implemented for separating uranium and rare earth fission products in pyrochemical reprocessing of spent nuclear fuels.

Biostable Fluorine-Containing Coatings on the Surface of Polymers

We considered the formation of the integrated biostable coating on the surface of several polymers using the original gas-phase fluorination technology. The effectiveness of surface modification of low-density polyethylene (LDPE) and polypropylene (PP) was confirmed by corresponding changes in the absorption spectra of infrared radiation with the modified samples. The gas-phase fluorination quality of ultrahigh molecular weight polyethylene (UHMWPE) and nitrile butadiene rubber (NBR) surfaces was evidenced by the results of scanning electron microscopy (SEM) and energy dispersion analysis (EDS). As was shown with the direct measurements of water and ethyleneglycol wetting angles, the properties differences of the polymer materials with modified surfaces from the initial one correlated well with the change in free surface energy induced by the chemical and morphological transformations under the fluorine and oxygen-containing gas mixtures treatment. The developed technique for the bio-contamination degree quantifying, based on the computer analysis of the corresponding images, allowed us to establish that gas-phase fluorination of the surface approximately doubles the time during which the biofouling of LDPE, PP and UHMWPE with the mixed colony of Rivularia and Stigonema Minutum algae occurs under natural conditions. No positive effect from fluorination was observed for NBR, which was explained, from our point of view, by the difference in the mechanisms of biostability for the considered polymer materials.

Adsorption and diffusion behavior of two-component gases in coal particles at different temperatures

Oxygen (O2) plays a crucial role in the occurrence and progression of coal spontaneous combustion (CSC), but the diffusion behaviors of O2 and oxygen-containing gas mixtures (e.g., CO2-O2) in the microchannels of coal under different temperatures have involved little investigation. In this work, isothermal adsorption experiments of two-component gas mixtures at different temperatures (293 K-333 K) were first carried out. A two-component gas mixture adsorption model for coal particles based on the free gas density gradient (FGDG) diffusion was then developed. The cumulative gas adsorption was obtained by numerical solution and the microchannel diffusion coefficients (Fm) of single-component gases in gas mixtures were obtained by comparing the simulation results with the experimental data. The results show that: (i) the equilibrium cumulative adsorption of three types of gas mixtures decreases with the increase of temperature, and their cumulative adsorption satisfies our proposed empirical equation; (ii) the simulation results of strongly adsorbed single-component gases are in high agreement with the experimental data throughout the adsorption period, and the developed model is verified. It also indicates that the model can characterize the migration behavior of single-component gas in coal particles under different temperature conditions; (iii) the Fm of a single-component gas will gradually increase as the temperature increases, leading to further enhancement of diffusion behavior of the gas. This research is expected to provide some theoretical foundations for understanding the mechanisms of gas mixtures flowing in coal matrices under different temperature environments.

Fluorescence characteristics of the fuel tracer 1-methylnaphthalene for the investigation of equivalence ratio and temperature in an oxygen-containing environment

In this work, the fluorescence properties of the fuel tracer 1-methylnaphthalene (1-MN) are investigated in a calibration flow cell at elevated temperatures and pressures. This fuel tracer is well suited to investigate mixture formation in diesel engine applications, as 1-MN is a natural diesel fuel component. A tracer-LIF (laser-induced fluorescence) concept is developed that enables temperature measurements using a two-color approach in oxygen-containing gas mixtures. Furthermore, the potential for simultaneous measurement of equivalence ratio (fuel–air ratio, FAR) is evaluated. First, a picosecond Nd:YLF-laser at 263 nm in combination with a spectrograph and a streak unit was used to investigate the spectral fluorescence emission and fluorescence lifetimes. In addition, a nanosecond Nd:YAG-laser at 266 nm was used for fluorescence calibration with regard to equivalence ratio and temperature. All measurements were performed in an oxygen-containing environment at different equivalence ratios, temperatures up to 800 K and pressures up to 2.5 MPa. The dependency of the fluorescence emission on equivalence ratio was studied for varied fuel amount and air concentrations. The calibration data form the basis for investigations of fuel distribution and temperature under realistic engine conditions in an oxygen-containing environment.

Analysis of the systematic force-transmission error of the magnetic-suspension coupling in single-sinker densimeters and commercial gravimetric sorption analyzers

Here we present an analysis of the force-transmission error for a commercial gravimetric sorption analyzer that applies equally to single-sinker densimeters. Gravimetric sorption analyzers are commonly used for the investigation of gas adsorption on porous materials (e.g., zeolites) with a simultaneous density measurement of the sample gas. The key component of the instrument is a magnetic-suspension coupling; this coupling transmits, without contact, the weight of the “density sinker” and of the sample container with the porous sample (which are both inside a pressurized measuring cell) to a balance at ambient pressure. However, since neither the coupling housing nor the sample gas are magnetically neutral, a small, systematic force-transmission error (FTE) occurs. For the correction of this FTE, an empirical correction model was developed. We show that the FTE can be subdivided into two parts: an apparatus contribution, and a fluid contribution. In the current paper we describe the effect of the FTE on the accuracy of the density measurements; the effect of the FTE on the accuracy of sorption measurements on porous and non-porous materials will be presented in a companion paper. The magnitude of the FTE in case of density measurement is shown by comparing the results of density measurements of four pure gases with values calculated from reference equations of state. The apparatus contribution of the FTE is typically (0.23 kg m−3 + 50 × 10−6·ρfluid), and the fluid contribution can reach values up to 500 × 10−6·ρfluid for diamagnetic fluids; for oxygen-containing gas mixtures it can be much greater.

Infrared gas phase study on plasma-polymer interactions in high-current diffuse dielectric barrier discharge

A roll-to-roll high-current diffuse dielectric barrier discharge at atmospheric pressure was operated in air and Ar/N2/O2 gas mixtures. The exhaust gas from the discharge was studied using a high-resolution Fourier-transform infrared spectrometer in the range from 3000 to 750 cm−1 to unravel the plasma-polymer interactions. The absorption features of HxNyOz, COx, and HCOOH (formic acid) were identified, and the relative densities were deduced by fitting the absorption bands of the detected molecules. Strong interactions between plasma and polymer (Polyethylene-2,6-naphthalate, or PEN) in precursor-free oxygen-containing gas mixtures were observed as evidenced by a high COx production. The presence of HCOOH in the gas effluent, formed through plasma-chemical synthesis of COx, turns out to be a sensitive indicator for etching. By adding tetraethylorthosilicate precursor in the plasma, dramatic changes in the COx production were measured, and two distinct deposition regimes were identified. At high precursor flows, a good agreement with the precursor combustion and the COx production was observed, whereas at low precursor flows an etching-deposition regime transpires, and the COx production is dominated by polymer etching.

Effect of phase separation in an Fe20Ni80/Fe50Mn50 structure with exchange coupling

The effect of heat treatment and partial oxidation of an Fe50Mn50 layer on the structure and magnetic properties of exchange-coupled Fe20Ni80/Fe50Mn50 layers has been investigated. The behavior of the exchange-bias field and coercive force depending on the temperature of annealing upon heat treatment in a vacuum or in an oxygen-containing gas mixture has been studied. It has been shown that, by adjusting the parameters of annealing in the gas mixture, it is possible to increase the field of switching of the exchange-coupled Fe20Ni80/Fe50Mn50 layers.

Liquid ventilation.

Human have lungs to breathe air and they have no gills to breath liquids like fish. When the surface tension at the air-liquid interface of the lung increases as in acute lung injury, scientists started to think about filling the lung with fluid instead of air to reduce the surface tension and facilitate ventilation. Liquid ventilation (LV) is a technique of mechanical ventilation in which the lungs are insufflated with an oxygenated perfluorochemical liquid rather than an oxygen-containing gas mixture. The use of perfluorochemicals, rather than nitrogen as the inert carrier of oxygen and carbon dioxide offers a number of advantages for the treatment of acute lung injury. In addition, there are non-respiratory applications with expanding potential including pulmonary drug delivery and radiographic imaging. It is well-known that respiratory diseases are one of the most common causes of morbidity and mortality in intensive care unit. During the past few years several new modalities of treatment have been introduced. One of them and probably the most fascinating, is of LV. Partial LV, on which much of the existing research has concentrated, requires partial filling of lungs with perfluorocarbons (PFC's) and ventilation with gas tidal volumes using conventional mechanical ventilators. Various physico-chemical properties of PFC's make them the ideal media. It results in a dramatic improvement in lung compliance and oxygenation and decline in mean airway pressure and oxygen requirements. No long-term side-effect reported.

Tempo-spatially Resolved Ozone Characteristics During Single-electrode Dielectric Barrier Discharge (SE-DBD) Operation against Metal and Porcine Skin Surfaces

Ozone is a major component produced by low-temperature plasmas operating in oxygen-containing gas mixtures. For correlation with biological or clinical results of plas- ma medical therapies as well as for evaluation of application security, tempo-spatially resolved ozone concentrations need to be considered. When operating a single-electrode dielectric barrier discharge (SE-DBD), the electric field characteristics are dependent on the geometrical setup as well as the electrical properties of the counter electrode. Thus, the counter electrode also affects the plasma input power and hence the total production of chemical species. Therefore, we studied the power input and the tempo-spatial characteristics of ozone concentrations during operation of a SE-DBD operated at voltage pulses in the µs regime against a clean metal electrode and a metal electrode covered with porcine skin samples. At energy densities of up to 1.85 J/cm 2 , the ozone concentrations in the plasma volume amount to as much as 293 ppm whereas at a distance of 5 and 20 cm, respectively, from the discharge, concentrations have decreased beneath recom- mended safety limits of 0.1 ppm. Furthermore, significantly lower ozone concentrations could be observed when skin samples were used as part of the counter electrode.

Low pressure plasmachemical processing of multi-walled carbon nanotubes for the production of polyurethane composite films with improved mechanical properties

Multiwalled carbon nanotubes (CNTs) were modified in low pressure capacitively coupled discharges (13.56 and 27.12MHz) in Ar/NH3 and oxygen-containing gas mixtures. A direct functionalization by nitrogen groups was not possible but 1–3 percentage of carbon–oxygen bonds increased with the total oxygen content on the expenses of sp2C almost independently on the plasma conditions. The plasma modified CNTs were used as fillers for polyurethane (PU) composites prepared by in situ polymerization. The composites were investigated by depth sensing indentation that revealed the existence of surface harder layer caused probably by different polymerization process in the bulk and at the surface that was in a contact with air. The significant improvement of the hardness and elastic modulus was observed when plasma-modified CNTs with high amount of oxygen were added to PU. It also improved the creep resistance of the PU, whereas the ability to recover from a deformation, i.e. anelastic recovery, did not change much.

Liquid Ventilation

Mammals have lungs to breathe air and they have no gills to breath liquids. When the surface tension at the air-liquid interface of the lung increases, as in acute lung injury, scientists started to think about filling the lung with fluid instead of air to reduce the surface tension and facilitate ventilation. Liquid ventilation (LV) is a technique of mechanical ventilation in which the lungs are insufflated with an oxygenated perfluorochemical liquid rather than an oxygen-containing gas mixture. The use of perfluorochemicals, rather than nitrogen, as the inert carrier of oxygen and carbon dioxide offers a number of theoretical advantages for the treatment of acute lung injury. In addition, there are non-respiratory applications with expanding potential including pulmonary drug delivery and radiographic imaging. The potential for multiple clinical applications for liquid-assisted ventilation will be clarified and optimized in future.

Shielding Gas Oxygen Additions as a Means of Curbing Nitrogen Degassing During the Autogenous Arc Welding of Nitrogen-Alloyed Stainless Steel

This study examined the influence of oxygen additions (0.5% to 2.0%) to argon-rich shielding gas on nitrogen degassing during the autogenous arc welding of a high-manganese nitrogen-alloyed austenitic stainless steel, previously commercially available under the trade name of Cromanite. Autogenous arc welding of this steel in inert shielding gas results in considerable nitrogen losses from the weld pool, characterised by an unstable arc, spattering and violent metal expulsion from the weld pool. Oxygen additions to the shielding gas stabilise the arc and curb nitrogen-induced porosity, but at least 2.0% oxygen (by volume) is required to maintain the weld metal nitrogen content at the level of the parent material prior to welding. The beneficial effect of oxygen additions to the shielding gas is attributed to the formation of a solid MnCr2O4 spinel phase on the weld pool surface during welding, which retards nitrogen degassing by reducing the area available for the adsorption of nitrogen atoms prior to their recombination to form N2. This layer has a granular, irregular appearance and presents a less effective barrier to nitrogen degassing than the continuous, uniform liquid slag layer that forms when the Cr-Ni 300-series austenitic stainless steels are welded in oxygen-containing shielding gas mixtures.

Pulsed electron-beam sustained discharge CO laser on oxygen-containing gas mixtures

It is shown that the addition of molecular oxygen to the working mixture of a pulsed electron-beam sustained-discharge (EBSD) laser CO amplifier leads to the increase in the small-signal gain (SSG) at the fundamental vibrational v+1→v transitions in a CO molecule for v=6–13, which is explained by the increase in the population of vibrational levels. In this case, the temporal parameters of the dynamics decrease at all probed transitions. Variations observed in the SSG dynamics are explained by analysing the kinetic processes of vibrational—vibrational exchange between molecules. The study of lasing parameters of a pulsed CO laser showed that the threshold energy input decreased with increasing the oxygen content in the working mixture. It is found that the CO laser efficiency at fundamental transitions increases with the addition of oxygen, the maximum efficiency being achieved at lower energy inputs. It is shown that the pulsed EBSD CO laser can operate on the air working mixture both at the fundamental transitions and the first vibrational overtone transitions v+2→v.

Gain dynamics in a pulsed laser amplifier on CO–He, CO–N2 and CO–O2 gas mixtures

Small-signal gain (SSG) dynamics G(t) in the active medium of a pulsed laser amplifier operating on the v+1→vP(J) vibrational–rotational transitions of the CO molecule, including high (v > 15) vibrational transitions, is studied experimentally. It is demonstrated that as the vibrational number increases from 7 to 31, G changes with time slower, while Gmax decreases in this case by three times. It is found that at a fixed value of v the rate of the SSG rise increases with increasing the rotational number J > 6. It is shown that in oxygen-containing gas mixtures (CO:O2 = 1:19) the value of Gmax at low vibrational levels (for v < 13) can substantially exceed Gmax in mixtures containing nitrogen (CO:N2 = 1:19) instead of oxygen. It is found that the efficiency (47%) of a CO laser on mixtures with a high concentration of oxygen considerably exceeds the efficiency (30%) of a CO laser operating on a nitrogen-containing mixture.

Survival ofCampylobacter jejuniin different gas mixtures

Campylobacter jejuni in fresh chilled chicken meat is known to be a major risk factor for human gastrointestinal disease. In the present study, the survival under chilled conditions of different C. jejuni strains exposed to different gas mixtures usually used for gas packaging of food was examined. Bolton broth and fresh, skinless chicken fillets were inoculated with six and four strains, respectively, and exposed to the gas mixtures 70/30% O(2)/CO(2), 70/30% N(2)/CO(2), and 100% N(2) (the latter only investigated in broth) at refrigeration temperature (4-5 degrees C). In broth culture, the strains survived significantly longer when exposed to 100% N(2) and 70/30% N(2)/CO(2) than in the oxygen-containing gas mixture, 70/30% O(2)/CO(2) (P<0.0001). For the two anaerobic gas mixtures, the reductions only reached 0.3-0.8 log(10) CFU mL(-1) within the same period. In the presence of oxygen, the numbers of C. jejuni were reduced by a minimum of 4.6 log(10) CFU mL(-1) over 21 days. When inoculated onto chicken fillets, the C. jejuni strains also died significantly faster in the oxygen-containing gas mixture, 70/30% O(2)/CO(2) (P<0.0001), reaching reductions of 2.0-2.6 log(10) CFU g(-1) after 8 days. In the gas mixture without oxygen (70/30% N(2)/CO(2)), no reductions were observed.

Amplification and scintillation properties of oxygen-rich gas mixtures for optical-TPC applications

We studied electron amplification and light emission fromavalanches in oxygen-containing gas mixtures. The mixturesinvestigated in this work included, among others, CO2 and N2Omixed with Triethylamine (TEA) or N2. Double-Step Parallel Gap(DSPG) multipliers and THick Gas Electron Multipliers (THGEM) wereinvestigated. High light yields were measured from CO2 + N2 andCO2 + TEA, though with different emission spectra. We observed thecharacteristic wave-length emission of N2 and of TEA and used apolymer wave-length shifter to convert TEA UV-light into the visiblespectrum. The results of these measurements indicate the applicabilityof optical recording of ionizing tracks in a TPC target-detectordesigned to study the cross-sections of the16O(γ, α)12C reaction, a central problem in nuclearastrophysics.

Discrete-continual model of flame propagation in a gas suspension of metal particles. I. One-dimensional approximation

Experimental data on combustion of magnesium particles in oxygen-containing gas mixtures are analyzed and generalized, which allowed us to develop a semi-empirical mathematical model that takes into account the integral effect of the initial particle size, pressure, and velocity of the oxidizing flow on combustion. Flame propagation in an air suspension of fine magnesium particles is considered in a one-dimensional approximation. For this purpose, a discrete-continual model of flame propagation in a gas suspension of metal particles is developed. The flammability limits in a vessel, caused by heat losses into the ambient medium and by spatial nonuniformity of the distribution of disperse-phase particles, are numerically determined, and the influence of nonuniformity and bidispersion of a one-dimensional ensemble of particles on flame characteristics is studied.

Pulsed electron-beam-sustained discharge in oxygen-containing gas mixtures: electrical characteristics, spectroscopy,and singlet oxygen yield

The electrical and spectroscopic characteristics of electron-beam-sustained discharge (EBSD) in oxygen and oxygen-containing gas mixtures are studied experimentally under gas pressures up to 100 Torr in a large excitation volume (∼18 L). It is shown that the EBSD in pure oxygen and its mixtures with inert gases is unstable and is characterised by a small specific energy contribution. The addition of small amounts (∼1%-10%) of carbon monoxide or hydrogen to oxygen or its mixtures with inert gases considerably improves the stability of the discharge, while the specific energy contribution W increases by more then an order of magnitude, achieving ∼6.5 kJ L-1 atm-1 per molecular component of the gas mixture. A part of the energy supplied to the EBSD is spent to excite vibrational levels of molecular additives. This was demonstrated experimentally by the initiation of a CO laser based on the O2 : Ar : CO = 1 : 1 : 0.1 mixture. Experimental results on spectroscopy of the excited electronic states O2(a1Δg) and O2(b1Σg+), of oxygen formed in the EBSD are presented. A technique was worked out for measuring the concentration of singlet oxygen in the O2(a1Δg) state in the afterglow of the pulsed EBSD by comparing with the radiation intensity of singlet oxygen of a given concentration produced in a chemical generator. Preliminary measurements of the singlet-oxygen yield in the EBSD show that its value ∼3% for W ∼ 1.0 kJ L-1 atm-1 is in agreement with the theoretical estimate. Theoretical calculations performed for W ∼ 6.5 kJ L-1 atm-1 at a fixed temperature show that the singlet-oxygen yield may be ∼20%, which is higher than the value required to achieve the lasing threshold in an oxygen—iodine laser at room temperature.