Oxygen Admixture Research Articles

Current dynamics and mechanisms for the instability of a non-self-sustained glow discharge in nitrogen

The current dynamics in a non-self-sustained glow discharge in atmospheric-pressure nitrogen (with a small admixture of oxygen) at cryogenic and room temperatures is studied experimentally and theoretically. For the first time, the theoretical model incorporates the processes of the decomposition of O2+·N2 and NO+·N2 complex ions in collisions with vibrationally excited nitrogen molecules and the associative ionization reactions with the participation of excited nitrogen and oxygen atoms. The computation results agree quite satisfactorily with the experimental data on the current dynamics and the duration of the stable phase of a non-self-sustained discharge for various applied voltages. Even a small (0.01%) oxygen admixture is found to greatly affect the dynamics of the ion composition and the characteristic duration of the stable phase of a non-self-sustained discharge in atmospheric-pressure nitrogen.

Investigation of the mechanism for rapid heating of nitrogen and air in gas discharges

A rapid heating of nitrogen-oxygen mixtures excited by gas discharges is investigated numerically with allowance for the following main processes: the reactions of predissociation of highly excited electronic states of oxygen molecules (which are populated via electron impact or via the quenching of the excited states of N2 molecules), the reactions of quenching of the excited atoms O(1 D) by nitrogen molecules, the VT relaxation reactions, etc. The calculated results adequately describe available experimental data on the dynamics of air heating in gas-discharge plasmas. It is shown that, over a broad range of values of the reduced electric field E/N, gas heating is maintained by a fixed fraction of the discharge power that is expended on the excitation of the electronic degrees of freedom of molecules (for discharges in air, ηE⋍28%). The lower the oxygen content of the mixture, the smaller the quantity ηE. The question of a rapid heating of nitrogen with a small admixture of oxygen is discussed.

Structural and electrical properties of In 2O 3:Sn films prepared by radio-frequency sputtering

A series of In 2O 3:Sn (ITO) films has been prepared by radio-frequency sputtering at 380°C with the oxygen admixture to the sputter gas being varied systematically. At a low oxygen flux, the (400) grains are much larger than grains with other orientations. With increasing oxygen flux, grain diameter and free electron concentration decrease and the texture of the crystallographic orientations changes from (400) to (622) dominant. It is suggested to estimate the fraction of material with a certain orientation by the product of height and third power of the width of the corresponding X-ray peak. This yields the same total X-ray scattering intensity for all samples. The structural properties are explained by a model of dynamic incorporation and segregation of oxygen during film growth. The electron mobility as a function of the electron density roughly follows a power law similar to that of single crystals, indicating that it is dominated by scattering at ionised donors.

First-principles Raman studies on YBa 2Cu 3O 7

We have investigated all Raman-active phonon modes (A 1 g , B 2 g , and B 3 g symmetry) of YBa 2Cu 3O 7 by first-principles LAPW calculations based on density functional theory. We demonstrate that an excellent overall agreement between measured and calculated phonon frequencies can only be achieved on the basis of a fully optimized crystal structure. The Raman scattering intensities for the A 1 g modes are determined. Due to a strongly decreased admixture of apical oxygen in the eigenvector of the O2-O3 mode with respect to previously published results the discrepancy between theory and experiment in the resonance profile of this mode is lifted.

Electron temperature measurements in medium electron density plasmas

This paper reports the results of the spectroscopic electron temperature ( T e) measurements in plasmas with electron densities ranging (0.3–1.4)×10 17 cm −3. The results of T e measurements obtained from various spectroscopic methods are mutually compared and discussed in relation to the condition for partial local thermodynamic equilibrium (PLTE). For the cases when the application of the spectroscopic techniques for T e measurements cannot be justified on the bases of PLTE criterion, new method for determination of plasma electron temperature is proposed and tested. Measurements of plasma parameters, electron temperature and electron density were performed in a low-pressure pulsed arc in helium with small admixture of nitrogen or oxygen whose ions were used as thermometric species. The electron densities were determined from the width of the He II P α 468.6 nm line.

Influence of admixtures on production rate of atomic nitrogen

In this paper, we present the dependencies of atomic nitrogen concentration in the afterglow on the amount of oxygen admixture added to the main gas. It is observed that until a certain threshold, the concentration of atomic nitrogen rises rapidly with the amount of admixture. If even more of the admixture is added, the concentration of nitrogen atoms decreases again. We suggest the explanation of this phenomenon by two antagonistic processes acting together: (i) decrease of the surface recombination coefficient by blocking of active sites and (ii) chemical reaction between N and O2 in the volume.

Studies of some acid–base equilibria in the molten eutectic mixture KCl–LiCl at 700°C

The reversibility of a membrane oxygen electrode Pt(O 2) ∣ ZrO 2(Y 2O 3) and acid–base reactions in molten LiCl–KCl at 700°C have been studied by the potentiometric method. The calibration plot has been found to consist of three regions — with predominant effect of oxygen admixtures, with the region at pO>2 and (∂ E/∂pO)=2.303 RT/2 F and one region at pO<2 with (∂ E/∂pO)=2.303 RT/ F× F. Solubility products of CoO(p P=4.43+0.11), NiO (p P=5.34±0.2), and MgO (p P=5.87±0.05) at 700°C have been determined. Acidic properties of Cd 2+ and Pb 2+ have been found to be completely levelled to those of Li +. The increase of oxide solubilities and shift of the inflection point on the calibration plot as compared with molten KCl–NaCl and CsCl–KCl–NaCl was caused by the increasing of the acidity of the melt studied. The shift of oxoacidity in Li-based melt has been estimated as ∼3.5 pO units. The possibility of the use of equilibria studied for the determination of acidity indices of molten alkaline halides is discussed.

A physicomathematical model of corrosion of iron in a lead melt with an admixture of oxygen

We propose a physicomathematical model for the corrosion of iron in a lead melt which contains oxygen. The model allows one do describe the distinct features and regularities of the kinetics of corrosion processes taking into account the multiphase, and multicomponent nature of the system and the interaction of components during the processes of adsorption and diffusion. To adequately describe the phenomena under study when formulating the diffusion boundary-value problem, we used nonstationary conditions, which represent correlation surface physicochemical effects, for mass transfer through the interface.

Modelling of Sheath Potential Drop Instabilities in Sol with the Use of PR-2 Mirror Machine

The boost and damping of the level of potential fluctuations are reproduced in imitation experiments with an electron beam driven discharge in the linear open system. The most pronounced instability of the sheath potential drop is observed in hydrogen plasmas in the presence of small admixtures of oxygen for materials which form oxides with enhanced emissivity of secondary electrons. Measurements of the plasma fluctuations level are in a qualitative agreement with analytical analysis of temporal evolution of plasma -surface interaction as function of internal and external electric circuit parameters.The surface currents which appear between zones with different emissivity and are closed by the bulk of the incident plasma flow have been studied with the use of the two-plate collector. It is shown that these currents can crucially influence the plasma turbulence.

Influence of oxygen admixtures on the lifetime of metastable antiprotonic helium atoms

Two experiments have been performed at the CERN Low Energy Antiproton Ring (LEAR) facility to study the lifetime shortening of metastable antiprotonic helium atoms by the presence of ppm admixtures of oxygen. The change in shape and lifetime of the delayed annihilation time spectra can be reproduced fairly well by fitting a simple four-level model to the data and assuming equal quenching cross sections for all metastable levels. From this we deduce a quenching cross section of $(1.35\ifmmode\pm\else\textpm\fi{}0.03)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15} {\mathrm{cm}}^{2}$ at a temperature of 100 K. An analysis of data from a previous experiment gives a value for the quenching cross section at room temperature of $(1.34\ifmmode\pm\else\textpm\fi{}0.07)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15} {\mathrm{cm}}^{2}.$ Resonant laser deexcitation of the levels $(n,l)=(37,34)$ and $(39,35)$ (the lowest metastable levels of the cascades $\ensuremath{\upsilon}=n\ensuremath{-}l\ensuremath{-}1=2$ and $3,$ respectively) was used to examine the time development of the population of these levels. Quenching cross sections of $(1.32\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15} {\mathrm{cm}}^{2}$ and $(1.90\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15} {\mathrm{cm}}^{2}$ were deduced for the $\ensuremath{\upsilon}=2$ and $\ensuremath{\upsilon}=3$ cascades from these studies at 100 K.

An effect of gamma-neutron irradiation and oxygen admixtures on interaction of hydrogen with austenitic 18Cr–10Ni–Ti steel

Experimental data on permeability and diffusion of hydrogen through austenitic 18Cr–10Ni–0.65Ti steel with 0.08 and 0.12 wt.% of carbon have been obtained with special equipment designed and installed at the research reactor IVV-2M. It has been shown that parameters of hydrogen isotope transfer in the steel increased substantially during irradiation by fast neutrons of flux density f fast<1.8×10 18 n m −2 per s, fluence F=9.5×10 24 n m −2 ( E>0.1 MeV) and absorbed gamma dose 3.6 W g −1 at temperatures of 573–1073 K. Under these irradiation conditions, even a small oxygen admixture content in hydrogen allowed creation of reliable surface barriers on the steel, which essentially decreased hydrogen permeability. At the same time, the physico-mechanical properties of the steel under study changed.

Thermal conductivity of solid argon with oxygen admixtures

Thermal conductivity investigations of pure and oxygen doped argon crystals have been carried out over the temperature range 1.3--26 K. Samples with oxygen concentration of 0.008, 0.024, 0.063, 0.225, and 0.390 mol % were measured. The result is that the interaction of phonons with the spin-rotational motion of oxygen molecules in an argon matrix is the most significant among possible mechanisms of phonon scattering by the impurities. In the thermal conductivity of the samples, no mutual interaction of the oxygen impurities has been observed over the investigated impurity concentration range.

Fracture mechanical behaviour of the steel 15 MnNi 6 3 in argon and in high pressure hydrogen gas with admixtures of oxygen

For the low alloyed fine grained ferritic structural steel 15 MnNi 6 3 in a first step J-integral tests were performed at room temperature in argon, pure high pressure hydrogen gas as well as with admixtures of oxygen (10 vpm, 150 vpm) in the single specimen technique. The J R-curve received for pure hydrogen environment is essentially lower than the curve for argon. The J R-curve for hydrogen with 10 vpm oxygen is shifted towards the one for pure hydrogen whereas the admixture of 150 vpm oxygen results in a J R-curve near the argon curve. The J Ic-value for 10 vpm oxygen admixture is approximately twice the one for pure hydrogen, for 150 vpm oxygen admixture about three times that for pure hydrogen. For the specimen fractured in argon a dimpled fracture surface, for the one tested in pure hydrogen a flat quasi-cleavage fracture was observed. With increasing oxygen admixture the portion of ductile fracture grows.

Relaxation of electron polarization for optically pumped rubidium atoms

Relaxation time constants of electron polarization, 〈Sz〉, for optically pumped rubidium atoms in a drifilm coated glass cell have been investigated with the Faraday rotation method. The dependence of the 〈Sz〉 relaxation time on pump cell temperature, rubidium density and applied magnetic field has been determined with high precision. The measurements allow the determination of the local magnetic field on the surface, alkali-wall binding energy and wall-dwell time. Furthermore, the change of relaxation time caused by admixtures of molecular hydrogen, nitrogen and oxygen has been investigated. No influence due to the addition of hydrogen could be detected up to a density of 3.3×1014 cm−3 at typical rubidium densities of several 1011 cm−3. The cross section for depolarizing collisons with molecular oxygen has been determined to be 7.50×10−15 cm2. The corresponding cross section for nitrogen was found to be two orders of magnitude lower. The experimental results are discussed in respect to the performance of spin exchange sources for nuclear polarized hydrogen and deuterium.

Introduction to the Special Issue “Using context in applications”

For the low alloyed fine grained ferritic structural steel 15 MnNi 6 3 in a first step J-integral tests were performed at room temperature in argon, pure high pressure hydrogen gas as well as with admixtures of oxygen (10 vpm, 150 vpm) in the single specimen technique. The JR-curve received for pure hydrogen environment is essentially lower than the curve for argon. The JR-curve for hydrogen with 10 vpm oxygen is shifted towards the one for pure hydrogen whereas the admixture of 150 vpm oxygen results in a JR-curve near the argon curve. The JIc-value for 10 vpm oxygen admixture is approximately twice the one for pure hydrogen, for 150 vpm oxygen admixture about three times that for pure hydrogen. For the specimen fractured in argon a dimpled fracture surface, for the one tested in pure hydrogen a flat quasi-cleavage fracture was observed. With increasing oxygen admixture the portion of ductile fracture grows.

Effect of antihypertensive agents on the arterial partial pressure of oxygen and venous admixture after cardiac surgery

To determine whether stopping nitroglycerin and sodium nitroprusside (both vasodilators) infusions in hypertensive, postcardiac surgical patients requiring a high FIO2 improves PaO2 and venous admixture. Prospective, clinical trial. Intensive care unit in a university-affiliated hospital. Thirty postcardiac surgical patients who, because of high FIO2 requirements, did not meet the criteria for weaning from mechanical ventilation and who were receiving infusions of nitroglycerin and/or sodium nitroprusside to control blood pressure. PaO2, venous admixture, and oxygen transport data were determined at baseline using arterial and mixed venous blood gas samples and hemodynamic values from a pulmonary artery catheter. The nitroglycerin and sodium nitroprusside infusions were stopped, and intravenous boluses of labetalol were administered to maintain a target blood pressure. After the vasodilator infusions were stopped, the baseline measurements were repeated to redetermine PaO2, venous admixture, and oxygen transport values. Results included a mean increase in PaO2 from 79.3 +/- 15 torr (10.5 +/- 2.0 kPa) to 118.3 +/- 38 torr (15.7 +/- 5.1 kPa) and a mean decrease in venous admixture from 26.4 +/- 5.8% to 17.6 +/- 5.6% when the vasodilators were stopped. All 30 patients had an increase in PaO2 and a decrease in venous admixture. Because of the improvement in oxygenation, 28 of the 30 patients met the criteria for weaning from mechanical ventilation once nitroglycerin and sodium nitroprusside were stopped or decreased. Labetalol was well tolerated in this group of patients who had preserved ventricular function. Substituting labetalol for nitroglycerin and sodium nitroprusside improves arterial oxygenation and venous admixture in hypertensive postcardiac surgical patients who require a high FIO2. This change in therapy may allow patients to be weaned from mechanical ventilation sooner.

Effect of admixtures of oxygen on the oxidation of iron and Fe−Cr alloys in lead melts

We study the process of oxidation of Armco iron and Fe−16Cr and Fe−16Cr−1Al model alloys held in lead melts with different concentrations of oxygen for 1000 h at 650°C. It was discovered that the intensity of oxidation, the structure, and phase composition of oxide layers are determined by the activity of oxygen in the liquid metal. By the methods of layer-by-layer X-ray diffraction analysis and microscopic X-ray diffraction analysis, it was shown that, for low concentrations of oxygen in lead (C 0≤10−6 wt.%), a thin (1–5μm) oxide [magnetite (Fe3O4] film is formed on the surface of iron. If alloys are held under the same conditions, then we also observe an increase in the concentration of chromium in the subsurface layers. For higher concentrations of oxygen (up to 10−5 wt.%), a film of magnetite (with inclusions of pure lead) is formed on the surface of unalloyed iron. In alloys, under the layer of magnetite, we detect the formation of oxide layers with the same composition as a solid solution of Fe3O4 and FeCr2O4 and the structure of spinel. These layers efficiently suppress the process of penetration of lead but do not completely terminate the process of diffusion of oxygen into the bulk of the material, which eventually leads to the internal oxidation of alloy.

Broad pressure range PTFE surface modification with slot antenna microwave discharge

A modified slot antenna microwave plasma source (SLAN) was applied for surface modification of PTFE samples. Typical microwave power was 2.0 kW. Argon, and argon with a small admixture of oxygen, were used as discharge gases. A significant change of advancing contact angle (decrease from 120° to 60°) after processing occurs only for pressure below 1 mbar. The receding contact angle varies strongly with pressure, from 10°–25° for 0.5 mbar to 60°–80° for 1 bar. Receding contact angle vs. processing time shows a minimum for 20 s for almost all pressures. Results improve with decreasing distance to the discharge wall. Samples processed at 0.5 mbar are less modified when a small oxygen flow is added. Operating at the pressures of 400 mbar and 1 bar, the admixture of oxygen reduces the receding angle by another 10°–15°. An exceptionally small receding contact angle (30°) is observed when the 100 sccm oxygen gas flow is added just after the process has started. The feasibility of large area surface modification in atmospheric pressure is documented.

Hysteresis effects in the sputtering process using two reactive gases

The reactive sputtering process involving two reactive gases has been investigated. Sputtering titanium in the presence of oxygen and nitrogen in argon was studied by means of optical emission and mass spectrometries. The experiments reveal the mechanism of the mixed target poisoning. Increasing the nitrogen supply in the presence of a constant oxygen supply forces the reactive sputtering system to avalanche from a high-rate metal-sputtering mode to a low-rate compound-sputtering mode at a lower N 2-to-Ar ratio as compared with the single reactive gas Ar N 2 reactive sputtering process. The amount of the oxygen admixture, however, also affects the character of the avalanche and the corresponding hysteresis effect. At a definite level of constant oxygen supply the Ar N 2 processing behaviour becomes irreversible, successive decreasing of the nitrogen supply to zero in this case is not sufficient to force the process to return back to the high-rate metal-sputtering mode. A “process trapping” effect appears. The coupling effect between the consumption of both reactive gases N 2 and O 2 during increase and successive decrease of N 2 in the presence of a constant O 2 supply is reflected in the dependencies of the respective partial pressures. The cause of the observed trapping effect, the shift and the change of the character of the sputtering rate hysteresis curve may be explained in terms of the link between the consumption of the reactive gases and the corresponding target condition. The experimental findings support the theoretical model of the two-gases reactive-sputering process recently presented by the authors.

Population densities and rate coefficients for electron impact excitation in singly ionized oxygen

In non-LTE arc plasmas, O II excited state number densities were measured relative to the O II ground and metastable states. The results were compared with collisional-radiative code calculations on the basis of the JET ADAS programs. Stationary He plasmas with small oxygen admixtures, generated in a 5 mm diameter cascade arc chamber (pressures 13-70 hPa, arc current 150 A), were investigated spectroscopically in the visible and the VUV spectral range. The continuum of a 2 mm diameter pure He arc (atmospheric pressure, current 100 A) served for calibration of the VUV system response. Plasma diagnostics on the basis of H beta Stark broadening yielded electron densities between 2.4*1014 and 2.0*1015 cm-3 for the low-pressure O II mixture plasmas. The intensities of a He II line were analysed with respect to electron temperatures, resulting in values from 3.5 to 8.2 eV. The O II ground and metastable number densities were derived from resonance lines in the VUV on the basis of the corona excitation balance and the relevant rate coefficients. Subsequently, the population of five 3p levels and one 3d level was obtained from lines in the visible spectrum. The agreement of measured and calculated excited state populations is generally very satisfactory, thus confirming the rate coefficients in the code. This is of particular interest in this intermediate region between corona balance and LTE, where many atomic data are required in the simulation. Clear indications were found for the diffusion of metastables lowering their number densities significantly below their statistical values.