Oxygen Admixture Research Articles

Controlled synthesis of NO in an atmospheric pressure plasma by suppressing NO destruction channels by plasma catalysis

NO synthesis using plasma catalysis is analyzed in a parallel-plate atmospheric pressure RF plasma from N2/O2 admixed to helium exposed to Fe and Pt catalysts on a SiO2 support. The NO x species are measured by Fourier-transform infrared spectroscopy in a multi-pass cell. The trends in species densities can be well explained by air chemistry reactions, where NO’s progressive oxidation occurs with increasing oxygen admixture and ozone generation. The sequence can be controlled by the state of the surface that preferentially quenches O3 and allows for an optimum NO production. The maximum production of NO is found at 70% N2/(N2+O2) mixture ratio at 120 ∘C using sandblasted glass, with a conversion rate of 0.085%.

Oxygen isotopic compositions of fresh rooftop micrometeorites from the Budel collection—Insights into the contemporary cosmic dust flux

AbstractCosmic dust particles originate from a wide variety of solar system and interstellar objects, including sources not identified among meteorite collections. Particles that survive atmospheric entry are retrieved on the Earth's surface as micrometeorites. The recovery of these micrometeorites has recently advanced to rooftop sites. Here, we present the results of an extensive isotopic study on this type of rooftop micrometeorite from the Budel collection, the Netherlands, accreted to the Earth between October 31, 2018 and June 16, 2021. The triple oxygen isotopic compositions of 80 silica‐dominated cosmic spherules (CSs) with diameters ranging between 105 and 515 μm are obtained relying on 213 in situ spot analyses determined using ion microprobe. Our analyzed population spans a large range of isotopic compositions and is dominated by carbonaceous chondritic sources. In situ measurements on several CSs support a possible continuum between 16O‐rich and 16O‐poor compositions following the CM mixing line, showing that 16O‐poor CSs may be genetically related to aqueously altered carbonaceous chondrites. We demonstrate that weathering in the terrestrial environment has negligible effects on the isotopic compositions of the studied CSs and attempt to quantify the effects of kinetic mass‐dependent fractionation and admixture of terrestrial oxygen during atmospheric entry. The results further corroborate previously suggested relations between CS texture and the duration and intensity of the heating pulse experienced during atmospheric deceleration. Finally, the young and well‐constrained terrestrial age of the collection provides insights into the most recent flux of cosmic dust. Our results indicate no major recent changes in the global flux compared with collections sampled over thousand‐ to million‐year time scales and demonstrate that 16O‐poor material is still represented in the modern‐day cosmic dust flux at a relative abundance of ~13%–15%. As such, rooftop micrometeorites represent a valuable reservoir to study the characteristics of the contemporary cosmic dust flux.

A new 2D fluid-MC hybrid approach for simulating nonequilibrium atmospheric pressure plasmas: density distribution of atomic oxygen in radio-frequency plasma jets in He/O2 mixtures

A spatially two dimensional fluid-MC hybrid (fluid-kinetic) simulation method is developed and applied to the COST reference microplasma jet operated in helium with an oxygen admixture of 0.5%, excited by a single frequency voltage waveform with f = 13.56 MHz and ϕrms=275 V. The simulation approach is based on a fluid model augmented by a Monte Carlo module that generates electron impact rates for the continuity equations solved by the fluid module. This method is capable of providing the same level of accuracy as PIC/MCC simulations with an agreement within 5%–10% at atmospheric pressure, while being significantly faster (with a speedup factor of 30 for serial to 50 for parallel implementation). The simulation results are compared to previous measurements of atomic oxygen densities (Steuer et al 2021 J. Phys. D: Appl. Phys. 54 355204), and show a very good agreement. It is found that the buildup and saturation of the atomic oxygen density distribution along the jet are due to the interplay of chemical and electron impact reactions as well as of the gas flow. Comparing the simulation results to that of Liu et al 2021 J. Phys. D: Appl. Phys. 54 275204, it is inferred that fluid models where a 2-term BE solver is used, fail to describe the COST jet in an accurate manner due to the underestimation of the electron impact rates.

Influence of shielding gas on filler wire mixing at laser hybrid welding of thick high strength steels

The laser hybrid welding process offers many advantages during welding of thick-walled steels, such as the increased penetration depth and, thus, reduced number of layers, reduced heat input and decreased distortion compared to arc-based welding processes. Especially, when welding high-strength steels (HSS), the reduced heat input plays an essential role. However, a major challenge when laser hybrid welding of thick-walled steels is the limited filler wire mixing over the entire seam thickness, which can lead to changed mechanical properties over the depth. To overcome this issue, the add of oxygen into the shielding gas and its influence on the filler wire mixing and finally to the mechanical properties were investigated within this work. Therefore, 20 mm thick S690QL steels were laser hybrid welded in a single-pass. A contactless electromagnetic backing was used to avoid sagging. The admixture of oxygen was performed by a gas mixer, where the oxygen content was varied between 0 % and 7.2 %. The experiments were also accompanied by laser beam welding tests in steel/glass configuration, where the melt pool geometry as well as the melt flow characteristics were captured by a high-speed camera. It can be concluded, that adding of approx. 4 % oxygen into the shielding gas had a positive effect on the filler wire mixing, were up to a depth of 18 mm elements of the filler wire could be observed.

Investigation of the Al-Mo-B(CN) Coatings Deposited Using Magnetron Sputtering of Al-Mo-B4C Target Produced by Detonation Spray Coating

In this work, a metal–ceramic composite target for magnetron sputtering was manufactured by a robotic complex for detonation spraying of coatings equipped with a multi-chamber detonation accelerator. The powder composition (30Mo-30Al-40B4C) was sprayed onto the copper plate base of the composite target cathode. The obtained cathode target with Al-Mo-B4C coating (thickness 280–300 μm) was used to deposit the Al-Mo-B(CN) coating (DC mode) on flat specimens of AISI 316 steel and silicon using equipment for magnetron sputtering UNICOAT 200. The Al-Mo-B4C coating has a lamella-type structure with inclusions of boron carbide particles. The structure and morphology of the coatings were studied using methods of optical analysis, scanning electron microscopy, atomic force microscopy, X-ray analysis, and X-ray photoelectron spectroscopy. Mechanical and tribological properties of the Al-Mo-B(CN) thin coatings were studied using a nanoindenter, a scratch tester, and a tribometer under a fluid-free friction regime at room temperature. The Al-Mo-B(CN) coating (thickness ~1 μm) exhibited a dense homogeneous fine-grained design without columnar elements and had an amorphous structure. The formation of the MoB2 and AlN phase with an admixture of oxygen in the form of aluminum oxide, molybdenum oxide, and boron oxide was determined using XPS analysis. The Al-Mo-B(CN) coating possessed a hardness of 13 GPa, an elasticity modulus of 114 GPa, an elastic recovery of 45%, a friction coefficient of 0.8 against a steel 100 Cr6 ball, and an adhesion strength of 11 N.

MODELING OF TEMPERATURE FIELDS AND GAS-DYNAMIC FLOWS IN THE ZONE OF PLACEMENT OF LITHIUM CERAMICS SAMPLES DURING TGA STUDIES

Modeling of thermogravimetric experiments is an essential tool for understanding the physical and chemical processes that occur during research. This approach helps improve data quality and gain a better understanding of what is going on during thermogravimetric analysis.This paper describes the procedure for modeling a TGA experiment on a Mettler Toledo TGA/DSC 3+ gravimeter, which, together with a mass spectrometer, a humidity generator, and an analytical balance, is part of the TiGRа analytical complex (NNC RK, Kurchatov, Kazakhstan). A description is given of the problem of modeling heat transfer processes in a gravimeter, the process of mass transfer of the reaction gas and reaction products in the gravimeter chamber, as well as the processes of chemical interaction of lithium ceramics with the reaction gas during TGA experiments. Helium with an admixture of oxygen and water vapor was considered as the purge gas.Calculations carried out using the developed model show that at a purge gas supply rate of 100 ml/s, the temperature gradient across the samples will be 2–2.5 ℃, and the gas velocity in the pebble bed will not exceed 0.5 mm/s. It has been established that the concentrations of CO2 carried away by the helium flow above the backfill and in the exit zone (in the sampling zone of the mass analyzer) at different temperatures can differ up to 22 times. Thus, using the developed model, it is possible to calculate the concentrations of CO2, CO, and H2 at any point of the thermogravimeter furnace directly above the test sample, inside and/or outside the pebble bed, in the area of the reaction mixture inlet and in the sampling area of the mass analyzer, etc. Also, if necessary, it is possible to determine the coefficients for recalculating concentrations in different sections of the pebble bed relative to the measured value. Using this model, it is possible to determine the parameters of chemical reactions – the initial concentration of carbon in the pebble bed, the activation energy of the reactions, and the concentration of O2 and H2O impurities in the purge helium, achieving the coincidence of the calculated and recorded curves using a mass analyzer. The developed model has a practical potential for further expansion of its analytical capabilities by refining the list of chemical reactions.

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.

Effect of argon cold plasma composition on orthodontic bonding-new insights into input parameters and protocols.

Cold atmospheric plasma can functionalize enamel without damaging the substrate morphology. It therefore has the potential to be agentle alternative to conventional acid etching. To realize the full potential of cold atmospheric plasma in orthodontic bonding, the input parameters and protocols that are most beneficial to surface modification must first be identified. We aimed to clarify how the admixture of oxygen to cold atmospheric plasma and the rewetting of the enamel affect the conditioning properties for orthodontic bonding. First, we illustrated the morphological effects of different plasma compositions on the enamel surface by means of scanning electron microscopy. Then, we measured the shear bond strength resulting from different conditioning techniques on bovine enamel specimens: conventional acid etching; no conditioning; pure argon plasma; argon plasma plus 0.5% oxygen admixture; argon plasma plus 0.5% oxygen and rewetting after plasma application. Brackets were bonded using light cured adhesive; all specimens were subjected to thermocycling. The shear bond strength of each specimen was measured in auniversal testing machine and compared using Welch one-way analysis of variance (ANOVA) and Games-Howell post hoc test. Specimens conditioned with argon plasma plus 0.5% oxygen and rewetting showed asignificantly higher shear bond strength than specimens conditioned with conventional acid etching. Conditioning with pure argon plasma and argon plasma plus 0.5% oxygen without rewetting yielded significantly lower shear bond strength. Admixing 0.5% oxygen and rewetting the enamel after plasma application are crucial steps that could help make cold atmospheric plasma agentle conditioning technique in orthodontic bonding.

Modelling of Nonthermal Dielectric Barrier Discharge Plasma at Atmospheric Pressure and Role of Produced Reactive Species in Surface Polymer Microbial Purification

A nonthermal atmospheric plasma reactor was used to sterilize polymer surfaces and satisfy safety constraints in a biological medium. A 1D fluid model was developed using COMSOL Multiphysics software® 5.4 with a helium-oxygen mixture at low temperature for the decontamination of bacteria on polymer surfaces. An analysis of the evolution of the homogeneous dielectric barrier discharge (DBD) was carried out through studying the dynamic behavior of the discharge parameters including the discharge current, the consumed power, the gas gap voltage, and transport charges. In addition, the electrical characteristics of a homogeneous DBD under different operating conditions were studied. The results shown that increasing voltage or frequency caused higher ionization levels and maximum increase of metastable species' density and expanded the sterilization area. On the other hand, it was possible to operate plasma discharges at a low voltage and a high density of plasma using higher values of the secondary emission coefficient or permittivity of the dielectric barrier materials. When the discharge gas pressure increased, the current discharges declined, which indicated a lower sterilization efficiency under high pressure. A short gap width and the admixture of oxygen were needed for sufficient bio-decontamination. Plasma-based pollutant degradation devices could therefore benefit from these results.

Spatially and temporally resolved atomic oxygen densities in a micro cavity plasma array

Micro cavity plasma arrays have numerous applications, such as the treatment of volatile organic compounds or the generation of new species. In recent years, the focus has also shifted to plasma catalysis, in which catalytic surfaces are combined with plasmas. The key to all of these applications is the generation of reactive species such as atomic oxygen within the plasma. Typically, atomic oxygen densities can be measured by laser spectroscopic methods. In the case of a micro plasma array, which consists of thousands of cavities with a diameter between 50 and 200 µm, optical access is limited. For this reason, an optical emission spectroscopy approach, helium state enhanced actinometry, is used. 2D resolved narrow bandwidth measurements are performed by using an ICCD camera in combination with a tunable bandpass filter (550–1000 nm). The discharge is operated in helium with an oxygen admixture of 0.1%. An argon admixture of 0.05% is used as actinometer gas. The triangular excitation voltage is varied between amplitudes of 400 and 800 V at a frequency of 15 kHz. Very high dissociation degrees up to nearly complete dissociation are observed. Time resolved measurements show significant differences in oxygen density between the increasing and the decreasing potential phase.

The effect of Penning ionization reactions on the evolution of He with O2 admixtures plasma jets

In this study, the effect of the O2 and N2 Penning ionization reactions on the evolution a capillary helium atmospheric pressure plasma jet (APPJ) with and without the presence of oxygen admixtures is investigated numerically using a two dimensional axi-symmetric model. In order to better understand potential applications of plasma surface interaction, the He and He + O2 (1000 ppm) APPJ is launched into a dielectric target. Moreover, the numerical model is compared with experimental measurements showing that the model captures the right physics and can elucidate the discharge dynamics. The comparison is realized for axial and radial measurements in order to have a complete picture of the plasma jet evolution. In this paper, the velocity and the shape of the plasma guided streamer were chosen as indicators of plasma jet evolution. In particular, the investigation is accomplished experimentally by tracking the spatio-temporal resolved emission of 706.5 nm (3s3S → 2p3P) line and numerically by calculating the reaction rate for the same transition. The O2 and N2 Penning reactions are then independently considered in the numerical model in order to isolate their contribution to the plasma evolution. It is shown that for the pure helium plasma, the N2 Penning reactions are more important to the plasma evolution. However, when oxygen admixtures are added to the plasma gas, the O2 Penning reactions become more important than the N2 ones.

Behaviour of single-crystal nickel alloy in the conditions of high-temperature hydrogen corrosion

This study presents the results of the investigation of the behaviour of ZhS32-VI single-crystal nickel alloy in hydrogen environment or argon atmosphere at 850°C. The microstructure and chemical composition of corrosion deposits were studied by scanning electron microscopy and X-ray energy-dispersive analysis. It has been established that in argon containing an admixture of oxygen a dense scale rich in cobalt and nickel oxides is formed. At atmosphere containing 65% hydrogen and 35% argon an increased content of aluminum in the surface composition was noted. The influence of 100% hydrogen leads to segregation of tungsten and rhenium with the formation of convex growths. The data of simultaneous thermal analysis revealed that the amount of desorbed hydrogen can be from 0.08 to 0.14%.

The influence of oxygen concentration on the hollow cathode discharge in He/O2 mixed gas

Hollow cathode discharge in He/O2 mixed gas is simulated using a two-dimensional fluid model for the first time. The model contains 15 particles and 66 reactions. The evolutions of discharge current, electric field, charged and reactive particles with different oxygen concentrations are obtained. The primary mechanisms of generation and loss for particles under different oxygen concentrations are discussed. The results show that the added O2 in helium has both positive and negative effects on the discharge. The discharge does not monotonically change with the increasing oxygen concentration. When the oxygen concentration is low, oxygen admixture could enhance the discharge, that is, the discharge current, radial electric field, electron density, density, O density, and the O(1D) density increase with the increase of oxygen concentration. When the oxygen concentration is high, it will weaken discharge, that is, the discharge current, radial electric field, electron density, density, O density, and the O(1D) density decrease with the increase of oxygen concentration. The main reactive particles in discharge are O and O(1D). These densities are much higher than the density of charged particles. The optimal oxygen concentration for O and O(1D) is 0.5% and 0.4%, and the corresponding maximum density is 4.34 × 1013 cm−3 and 1.50 × 1013 cm−3. The generation and loss rates for these particles at different oxygen concentrations are calculated, which contributes to the change in particle densities.

Effect of Negative Ion Generation on Complex Plasma Structure Properties.

We propose a low-density discharge plasma model that takes into account the impact of oxygen admixture in typical conditions of complex (dusty) plasmas. Numerical simulations based on this model show that the concentration of negative ions turns out to be very high, and they play an important role in the overall kinetics in this particular range of plasma conditions. The ambipolar diffusion electric field drags these negative ions into the center of the plasma. The density of negative ions is high enough to push the negatively charged dust component out of the center, both by weakening the radial electric field and by increasing the thermophoretic force. This phenomenon was observed in the published experiment and qualitatively supports the proposed model. Additionally, the proposed model allows an alternative explanation of the experiment.

Non-linear etch process of MF particles embedded in an rf plasma with oxygen admixture

Commonly used melamine formaldehyde micro-particles exposed to an rf discharge are known to be etched by a plasma as soon as an admixture of oxygen is present. By means of in situ high precision size measurements, the plasma–surface interaction is investigated. A comparison of experimental data, advanced Mie-scattering techniques, and a reaction rate model allows, for the first time, to quantitatively describe the etch process.

Characterization of an atmospheric pressure plasma jet producing the auroral transition O(1S) to O(1D)

We present a detailed characterization of an atmospheric pressure plasma jet that produces the metastable oxygen states O(1S) and OD) with emission of the ‘auroral’ green line. The device used 99.999 pure argon as a working gas for the plasma generation. Optical emission spectroscopy was used to understand the active species present in the plasma jet and to infer the mechanism of O(1S) creation and destruction. The continuum spectrum was used in conjunction with a method based on machine learning for determining the arbitrary electron probability distribution function. Discharge and plasma properties were estimated from Lissajous plots and using calculations with the BOLSIG+ software. The metastable oxygen forms for all operating parameters of the plasma jet system in a linear electrode configuration. The camera images provided information of the overall plasma jet behavior as parameters were altered. While the metastable oxygen was produced for every iteration, the plasma jet behavior changed considerably when the powered and grounded electrodes are switched. Small admixtures of oxygen and nitrogen were introduced in the plasma jet to understand the kinetic processes of metastable oxygen destruction and the 557.7 nm auroral line. This behavior has implications for plasma reactive chemistry in fundamental areas such as auroral physics as well as technological applications of plasmas.

RF-driven atmospheric-pressure capillary plasma jet in a He/O2 gas mixture: Multi-diagnostic approach to energy transport

Atmospheric-pressure plasma jets operated in noble gases with an oxygen admixture have high application potential in industry and medicine. In this paper, we report on an extension of the well-studied RF-driven plasma jet from the European Cooperation in Science and Technology (COST-Jet), which has shown to deliver stable and reproducible discharge conditions but is limited to the α-discharge mode at low input powers. The so-called capillary-jet features the same discharge geometry as the COST-Jet, but the plasma is ignited inside a capillary with a square cross section acting as a dielectric in front of the electrodes. This prevents a glow-to-arc-transition at high input powers and allows stable operation in the γ-mode. We performed a set of measurements on the capillary-jet in the α- and γ-mode and compared the α-mode results to data obtained for the COST-Jet showing that the discharges are indeed similar and that the capillary-jet extends the accessible parameter range to high input powers. The presented results include power characteristics, temperature measurements, atomic oxygen densities from helium state enhanced actinometry, and molecular beam mass spectrometry (MBMS) as well as ozone densities from MBMS as functions of input power and molecular oxygen admixture. The results are summarized into an energy balance with most of the power dissipated into heating of the plasma feed gas.

Comparison of gaseous contamination of thin tungsten and gold coatings deposited from ablated plasma generated by Intense Pulsed Ion Beams

The paper presents experimental results on C, N and O contamination in thin tungsten and gold coatings deposited on GaAs substrates from ablated plasma generated by intense pulsed ion beams accelerated in a magnetically insulated diode. The coating thickness was controlled by energy-dispersive X-Ray Fluorescence analysis. Depth profiles of C, N and O concentrations in the coatings were determined using quantitative Auger Electron Spectroscopy (AES) with ion sputtering. Non-destructive charged particle activation analysis via the nuclear reactions 12C(d,n)13N, 14N(d,n)15O and 16O(d,n)17F, induced by 3 MeV deuterons of extracted from a cyclotron was used to calibrate the AES determination of C, N and O. The gold coating was found to be devoid of detectable amounts of all gases, while carbon dominated by an order of magnitude over nitrogen and oxygen in tungsten coatings. Carbon contamination increased linearly with an increase in the number of ion shots applied. It was concluded that the main source of gas contamination is the residual atmosphere of the working chamber and the purest coatings can be obtained at the highest deposition rates per shot. A significant increase of oxygen admixture was found in the tungsten coatings after the samples were stored in the ambient atmosphere for 25 years. The storage did not affect the purity of the gold coating, but carbon seemed to diffuse from the Au/GaAs interface to the coating surface.

Numerical study on peak current in pulse-modulated radio-frequency discharges with atmospheric helium–oxygen admixtures

Atmospheric pressure pulse-modulated radio-frequency (rf) plasmas have drawn growing attention due to their potential in applications. By selecting appropriate modulation parameters, the diffused and large-volume plasma can be generated in the pulse-modulated rf plasma with plenty of reactive oxygen species, which is essential for the biomedical application of helium–oxygen plasmas. In this paper, by means of a fluid model, the formation of the peak current in the first period (PCFP) in a pulse-modulated rf helium–oxygen discharge driven by a sinusoidal voltage is discussed, the existence of a reverse field near the anode caused by the negative and positive charges contributes greatly to the mechanism of PCFP. In the simulation, as oxygen admixture increases, the negative ions of O− and become dominative anions in the sheath region, which can’t be driven to the anode very quickly to build a reverse field, thus the PCFP eventually disappears. This study can effectively enhance the understanding of different transportation behavior of heavy negative ions and electrons, and further optimize pulse-modulated rf discharges with helium–oxygen mixtures in various applications.

Numerical study of singlet delta oxygen (O2(a1Δg)) generation and transport in the He/O2 atmospheric pressure plasma jet

This paper investigates the spatial-temporal evolution and the transport of the singlet delta oxygen (O2(a1Δg)) of an atmospheric pressure plasma jet using a 2D fluid modeling. The plasma jet is produced in pure helium or helium with small oxygen admixtures (no bigger than 2%), by applying a constant DC voltage of +5 kV on the annular electrode. It is found that, at the 0.7% O2 admixture, a higher O2(a1Δg) density is obtained inside the tube before the jet impacts the substrate. After the jet propagates along the substrate surface, the peak O2(a1Δg) density is transferred from the tube to the gap. Varying the O2 admixtures percentage in the working gas changes the O2(a1Δg) spatial distribution. The O2(a1Δg) with two thinner edges is dominantly produced in the helium–air mixing layer for pure helium. The addition of O2 in the working gas leads to O2(a1Δg) production in the tube. Meanwhile, the thickness of the O2(a1Δg) edges increases in the helium–air mixing layer. But the radius of the O2(a1Δg) density channel continuously reduces with the O2 admixture. The O2(a1Δg) density and its surface flux first increase within the 0.7% O2 admixture and then decreases with the further augment of the O2 admixture. The influence of the gas flow velocity on the production and transport of O2(a1Δg) is also studied. Increasing the gas flow velocity changes the spatial distribution of the O2(a1Δg) density from the solid structure to the annular structure in the gap. At the same time, lower volume average density and instantaneous flux are obtained at larger gas flow velocity.