Gas Mixture Of Helium Research Articles

Detection of atomic oxygen and nitrogen created in a radio-frequency-driven micro-scale atmospheric pressure plasma jet using mass spectrometry

In this paper we show mass spectrometry results for a radio-frequency-driven micro-atmospheric pressure plasma jet (μ-APPJ) discharge obtained using a mass analyzer with triple differential pumping allowing us to sample directly in ambient atmospheric pressure environment (Hiden HPR-60). The flow of the buffer gas (mixture of helium and 1% oxygen) was 2 slm and 3 slm and the excitation frequency was 13.56 MHz. We monitored production of atomic oxygen and nitrogen in the plasma for different flows and powers given by the RF power supply. These measurements were made for energies of electrons emitted from the ionization filament below the threshold for dissociation of O2 and N2. In addition to oxygen and nitrogen atoms, yields for O2, N2, NO and O3 are recorded for different powers and gas flows. It is shown that the μ-APPJ is symmetrical and operates in α-mode. The power transmitted to the discharge was below 5 W in all measurements.

ESR studies of nitrogen atoms stabilized in aggregates of krypton–nitrogen nanoclusters immersed in superfluid helium

Impurity–helium condensates (IHCs) containing nitrogen and krypton atoms immersed in superfluid 4He have been studied via CW electron spin resonance (ESR). The IHCs are gel-like aggregates of nanoclusters composed of impurity species. It was found that the addition of krypton atoms to the nitrogen–helium gas mixture used for preparation of IHCs increases the efficiency of stabilization of nitrogen atoms. We have achieved high average (5 · 1019 cm−3) and local (2 · 1021 cm−3) concentrations of nitrogen atoms in krypton–nitrogen–helium condensates. The analysis of ESR lines shows that in krypton-nitrogen nanoclusters three different sites exist for stabilization of nitrogen atoms. Nitrogen atoms are stabilized in the krypton core of nanoclusters, in the nitrogen molecular layer that covers the Kr core, and on the surface of the nanoclusters. High concentrations of nitrogen atoms achieved in IHCs provide an important step in the search for magnetic ordering effects at low temperatures.

Application of atmospheric pressure nonthermal plasma for thein vitroeradication of bacterial biofilms

The use of atmospheric pressure nonthermal plasma represents an interesting and novel approach for the decontamination of surfaces colonized with microbial biofilms that exhibit enhanced tolerance to antimicrobial challenge. In this study, the influence of an atmospheric pressure nonthermal plasma jet, operated in a helium and oxygen gas mixture under ambient pressure, was evaluated against biofilms of Bacillus cereus, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Within < 4 min of plasma exposure, complete eradication of the two gram-positive bacterial biofilms was achieved. Although gram-negative biofilms required longer treatment time, their complete eradication was still possible with 10 min of exposure. Whilst this study provides useful proof of concept data on the use of atmospheric pressure plasmas for the eradication of bacterial biofilms in vitro, it also demonstrates the critical need for improved understanding of the mechanisms and kinetics related to such a potentially significant approach.

Tris(diethylamino)silane—A new precursor compound for obtaining layers of silicon carbonitride

Silicon carbonitride layers have been obtained by chemical deposition from the gas phase with thermal (LPCVD) and plasma (PECVD) activation of the gas mixture of helium with the new volatile siliconorganic compound tris(diethylamino)silane (Et 2N)3SiH (TDEAS) in the temperature region 373–1173 K. Thermodynamic simulation of the deposition processes from the gas mixture (TDEAS + He) in the temperature interval 300–1300 K and pressure interval P tot 0 from 1 × 10−2 to 10 mm Hg has revealed the possibility of varying the equilibrium composition of the condensed phase depending on the synthesis temperature and the composition of the initial gas mixture. Physicochemical and functional properties of obtained layers were studied by complex of modern methods. It has been established that the chemical composition of the silicon carbonitride layers obtained by the PECVD method, depending on the deposition conditions, approaches that of silicon oxynitride or nitride, and the composition of those obtained by the LPCVD method approaches that of silicon carbide. The presence of nanocrystals with a phase composition close to the standard α-Si3N4 phase and of carbon inclusions has been found in the layers.

Surface modification of closed plastic bags for adherent cell cultivation

In modern medicine human mesenchymal stem cells are becoming increasingly important. However, a successful cultivation of this type of cells is only possible under very specific conditions. Of great importance, for instance, are the absence of contaminants such as foreign microbiological organisms, i.e., sterility, and the chemical functionalization of the ground on which the cells are grown. As cultivation of these cells makes high demands, a new procedure for cell cultivation has been developed in which closed plastic bags are used. For adherent cell growth chemical functional groups have to be introduced on the inner surface of the plastic bag. This can be achieved by a new, atmospheric-pressure plasma-based method presented in this paper. The method which was developed jointly by the Fraunhofer IST and the Helmholtz HZI can be implemented in automated equipment as is also shown in this contribution. Plasma process gases used include helium or helium-based gas mixtures (He + N + H) and vapors of suitable film-forming agents or precursors such as APTMS, DACH, and TMOS in helium. The effect of plasma treatment is investigated by FTIR-ATR spectroscopy as well as surface tension determination based on contact angle measurements and XPS. Plasma treatment in nominally pure helium increases the surface tension of the polymer foil due to the presence of oxygen traces in the gas and oxygen diffusing through the gas-permeable foil, respectively, reacting with surface radical centers formed during contact with the discharge. Primary amino groups are obtained on the inner surface by treatment in mixtures with nitrogen and hydrogen albeit their amount is comparably small due to diffusion of oxygen through the gas-permeable bag, interfering with the plasma-amination process. Surface modifications introducing amino groups on the inner surface turned out to be most efficient in the promotion of cell growth.

Using mixed gases for massive gas injection disruption mitigation on Alcator C-Mod

Mixed gases are used for massive gas injection disruption mitigation on Alcator C-Mod in order to optimize radiation efficiency, halo current reduction and response time. Gas mixtures of helium and argon (argon fraction 0–50%) are investigated in detail, as well as mixtures of deuterium, argon, krypton and helium. Experiments show that injecting He/Ar mixtures leads to faster thermal and current quenches than with pure helium or argon injection, thus improving the time response of the disruption mitigation system and reducing the halo current. Small fractions of argon (∼5–10%) in helium also lead to optimized radiation fractions with large electron density increases in the core plasma. These results are consistent with the expectation that small fractions of argon will be entrained with the faster helium in the early phases of gas flow. The gas mixing allows one to simultaneously exploit the fast particle delivery rate of light helium gas and the large radiation capability of argon.

An automated system for DC and RF plasma characterization by guard double electric probes

Monitoring basic plasma parameters such as temperature (T), density (n), floating potential (Vf) or Debye length (λd) provides vital knowledge during the ion implantation processing of materials immersed in plasmas (PIII or PSII) generated either by DC or (13.56MHz) RF sources. Thus, a fully automated electromechanical system has been designed and constructed on the basis of guard double electric probes in order to prevent both probe erosion and plasma contamination. The electronic components of the system comprise a ±150V triangular and ramp wave form generator capable of supplying ±50μA to ±100mA currents at 1–2000Hz frequencies and a DAQ PCI-6023E data acquisition board with a 12 bit resolution compatible with LabVIEW graphic language. A program has been specifically developed for the latter in order to control the probe position within the discharge vessel and to capture, filter, visualize, process and store the respective information. The system has been experimentally applied to DC and RF plasmas of helium, argon, nitrogen, oxygen, and multiple gas mixtures with great success, inside several PIII reactors. Results are presented free from RF interference from the process itself or other surrounding sources.

Note: Computation of collision-induced absorption by dense deuterium–helium gas mixtures

Note: Computation of collision-induced absorption by dense deuterium–helium gas mixtures

Process Parameters Optimization of an Aluminium Alloy with Pulsed Gas Tungsten Arc Welding (GTAW) Using Gas Mixtures

This paper demonstrates the enhancement of mechanical properties and effective optimization of pulsed GTAW process parameters on aluminium alloy 6061 using sinusoidal AC wave with argon plus helium gas mixtures. Modified Taguchi Method (MTM) was employed to formulate experimental layout and to study effect of process parameter optimization on mechanical properties of the weld joints. Microstructural characterization of weld joint was carried out to understand the structural property correlation with process parameters.

Radiation hardening and IASCC susceptibility of extra high purity austenitic stainless steel

An extra high purity austenitic stainless steel (EHP alloy: Fe–25Cr–35Ni SAR) was developed with countermeasures for irradiation assisted stress corrosion cracking (IASCC). To study the radiation-induced hardening and the susceptibility of IASCC for EHP alloy, EHP alloys were irradiated at 553±20K in a helium and nitrogen gas mixture at the fluence level of 1.5×1025n/m2. After neutron irradiation, tensile tests and slow strain rate tests (SSRTs) of irradiated specimens were conducted in air at 561K and in oxygenated high purity water at 561K, respectively. The fracture surfaces were examined using SEM after tensile tests and SSRTs. The tendency of radiation-induced hardening of EHP alloy was the same as irradiated type 304 and type 316 stainless steels. Though there was a little effect of the countermeasures on the suppression of irradiation hardening. EHP alloy had excellent resistance for IASCC up to 1.5×1025n/m2.

Reconciling the centimeter- and millimeter-wavelength ammonia absorption spectra under jovian conditions: Extensive millimeter-wavelength measurements and a consistent model

Over 1000 laboratory measurements of the 2–4mm-wavelength opacity of ammonia have been made under simulated jovian atmospheric conditions using a high-precision laboratory system developed at Georgia Tech. These laboratory measurements of the opacity of ammonia were made of various gas mixtures of hydrogen (∼77.5–85.5%), helium (∼12.5–13.5%), and ammonia (1–10%) at pressures between 1 and 3 bars and temperatures between 200 and 300K. Laboratory measurements were also made of the opacity of pure ammonia at pressures between 0.05 and 1bar and temperatures between 200 and 300K. Using these millimeter-wavelength measurements and close to 2000cm-wavelength measurements made by Hanley et al. (2009), a new consistent model has been developed to accurately characterize the absorption spectra of ammonia in a hydrogen/helium atmosphere in the 1mm to 30cm wavelength range. This model can be used in the 1–30cm wavelength range at pressures up to 20 bars and temperatures from 200 to 500K and in the 1mm to 1cm wavelength range at pressures up to 3 bars and temperatures from 200 to 300K. These measurements and the accompanying model will enable better interpretation of the centimeter- and millimeter-wavelength emission spectra of the jovian planets.

Chromia-Assisted Decarburization of W-Rich Ni-Based Alloys in Impure Helium at 1273 K (1000 °C)

The microstructure and surface stability of two experimental W-rich Ni-based alloys have been studied at 1273 K (1000 °C) in an impure-He environment containing only CO and CO2 as impurities. The alloy Ni-2.3Al-12Cr-12W contained 0.08 wt pct carbon in solution, whereas the second alloy Ni-2.3Al-3Mo-12Cr-12Co-12W contained M6C carbides at the same carbon level. Both alloys, which were preoxidized with ~2.3 μm Cr2O3 layer, were decarburized completely within 50 hours of exposure to the helium gas mixture at 1273 K (1000 °C) via the following chromia-assisted decarburization reaction: Cr2O3 (s) + 3Calloy (s) → 2Cr (s) + 3CO (g). Microstructural observations, bulk carbon analysis, and microprobe measurements confirmed that the carbon in solid solution reacted with the surface chromium oxide resulting in the simultaneous loss of chromia and carbon. The Cr produced by the decomposition of the Cr2O3 diffused back into the alloy, whereas CO gas was released and detected by a gas chromatograph. Once the alloy carbon content was reduced to negligible levels, subsequent exposure led to the uninterrupted growth of Cr2O3 layer in both alloys. In the preoxidized alloys, chromia-assisted decarburization rates were slower for an alloy containing carbides compared with the alloy with carbon in solid solution only. The formation of Cr2O3 is shown to be the rate-limiting step in the chromia-assisted decarburization reaction. Exposure of as-fabricated alloys to the impure-He environment led to the formation of a thin layer of Al2O3 (<1 μm) between the substrate and surface Cr2O3 oxide that inhibited this decarburization process by acting as a diffusion barrier.

Improvement of In-Flight Alumina Spheroidization Process Using a Small Power Argon DC-RF Hybrid Plasma Flow System by Helium Mixture

For the further improvement of in-flight alumina spheroidization process with a low-power direct-current radiofrequency (DC-RF) hybrid plasma flow system, the effect of a small amount of helium gas mixture in argon main gas and also the effect of increasing DC nozzle diameter on powder spheroidization ratio have been experimentally clarified with correlating helium gas mixture percentage, plasma enthalpy, powder in-flight velocity, and temperature. The alumina spheroidization ratio increases by helium gas mixture as a result of enhancement of plasma enthalpy. The highest spheroidization ratio is obtained by 4% mixture of helium in central gas with enlarging nozzle diameter from 3 to 4 mm, even under the constant low input electric power given to a DC-RF hybrid plasma flow system.

Assessment of Extravascular Lung Water and Cardiac Function in Trimix SCUBA Diving

An increasing number of recreational self-contained underwater breathing apparatus (SCUBA) divers use trimix of oxygen, helium, and nitrogen for dives deeper than 60 m of sea water. Although it was seldom linked to the development of pulmonary edema, whether SCUBA diving affects the extravascular lung water (EVLW) accumulation is largely unexplored. Seven divers performed six dives on consecutive days using compressed gas mixture of oxygen, helium, and nitrogen (trimix), with diving depths ranging from 55 to 80 m. The echocardiographic parameters (bubble grade, lung comets, mean pulmonary arterial pressure (PAP), and left ventricular function) and the blood levels of the N-terminal part of pro-brain natriuretic peptide (NT-proBNP) were assessed before and after each dive. Venous gas bubbling was detected after each dive with mean probability of decompression sickness ranging from 1.77% to 3.12%. After each dive, several ultrasonographically detected lung comets rose significantly, which was paralleled by increased pulmonary artery pressure (PAP) and decreased left ventricular contractility (reduced ejection fraction at higher end-systolic and end-diastolic volumes) as well as the elevated NT-proBNP. The number of ultrasound lung comets and mean PAP did not return to baseline values after each dive. This is the first report that asymptomatic SCUBA dives are associated with accumulation of EVLW with concomitant increase in PAP, diminished left ventricular contractility, and increased release of NT-proBNP, suggesting a significant cardiopulmonary strain. EVLW and PAP did not return to baseline during repetitive dives, indicating possible cumulative effect with increasing the risk for pulmonary edema.

PLASMA SPRAYING OF BORON CARBIDE USING TERNARY GAS MIXTURES

Materials which exhibit high specific heat and melting enthalpy combined with a low density, like boron carbide B4C, are difficult to melt by plasma spraying under standard spray conditions. Moreover, the injection of this low-density powder in the plasma jet is critical, especially when fine particles are used. The optimization of the plasma-forming gas composition may make the penetration of the particles in the gas flow easier, and improve their melting state. This paper presents an investigation of the effect of the composition of ternary gas mixtures of argon, helium and hydrogen on B4C particles heating and acceleration. The particle injection and the resulting spray pattern in the jet were controlled by using a 1D imaging technique. The particle velocity distribution was measured with a laser Doppler anemometer and the particle overall temperature with a high-speed pyrometer.

Characterization of Acetylene Plasma-Polymer Films: Recovery of Surface Hydrophobicity by Aging

Aging phenomena of plasma polymer films were studied by using the surface analysis techniques of contact angle measurement, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOFSIMS), and atomic force microscopy (AFM). The polymer films were grown on an aluminum substrate by using a plasma polymerization method from a gas mixture of acetylene and helium, and the films were subsequently modified to have a hydrophilic surface by oxygen plasma treatment. Aging of the polymer films was examined by exposing the samples to water and air environments. The aging process increased the hydrophobicity of the surface, as revealed by an increase in the advancing contact angle of water. XPS analysis showed that the population of oxygen-containing polar groups increased due to the uptake of oxygen during the aging, whereas TOF-SIMS analysis revealed a decrease in the polar group population in the uppermost surface layer. The results suggest that the change in surface property from hydrophilic to hydrophobic nature results from the restructuring of polymer chains near the surface, rather than compositional change of the surface. Oxidative degradation may enhance the mobility and the restructuring process of polymer chains.

Measurements of transition probabilities for two N I infrared transitions and their application for diagnostics of low temperature plasmas

Spectra emitted from a wall-stabilized arc, running in a gas mixture of helium, argon, nitrogen, oxygen and traces of hydrogen have been studied. Intensities of selected spectral transitions of neutral nitrogen and oxygen have been measured. Applying the Boltzmann plot method and using a reliable set of O I transition probabilities of spectral lines, originating from levels considerably spread in excitation energies, the temperatures of arc plasmas have been determined. Line intensities of two N I infrared transitions, originating from doubly excited terms 3p′ 2F o and 3p′ 2G have been measured. In order to obtain the corresponding transition probabilities ( A ki ) for these lines, intensities of other N I infrared lines, with well known transition probabilities (taken from recently published data by Wiese and Fuhr [W.L. Wiese and J.R. Fuhr, Improved critical compilations of selected atomic transition probabilities for neutral and singly ionized carbon and nitrogen, J. Phys. Chem. Ref. Data 36 (2007) 1287–1345] from National Institute of Standards and Technology — NIST) have been measured. For evaluation of the transition probabilities the temperatures obtained from the above mentioned O I Boltzmann plots have been used. The results agree satisfactorily with older data found in literature. The new A ki values for transitions involving the doubly excited levels, together with A ki values taken from the above mentioned NIST source (used for determination of the new A ki values), are proposed as a convenient set for determining temperatures of plasmas containing nitrogen atoms.

On the Discharge Parameters of a Glow-Mode DBD at Medium and Atmospheric Pressure

In this paper, we report on the behavior of a glow-mode pulsed barrier discharge working at different gas pressure (25-760 torr) in helium and helium-oxygen gas mixture. The experimental setup consists of a plane-parallel geometry of a dielectric barrier discharge (DBD) system, excited by positive monopolar voltage pulses. The discharge properties were characterized by electrical measurements and emission spectroscopy. Our investigations showed that the discharge consists of two current pulses, with different polarities, corresponding to each voltage pulse. The main results referred to the effect of pressure and oxygen percentage on the discharge parameters. The time-resolved spectroscopy of the DBD plasma working at different pressure pointed out the differences between the discharge mechanism at medium pressure and that close to atmospheric pressure. Moreover, at medium pressure (25 torr), the oxygen atoms are efficiently created for about 2% of molecular oxygen added to gas mixture.

Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) based on a Proton Conducting Electrolyte

Single chamber solid oxide fuel cells (SC-SOFCs) are promising for portable power applications because they are simpler than the conventional dual-chamber cells. SC-SOFCs based on the cell Ni/BaCe0.3Zr0.5Y0.2O3-δ (BCZY)/Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) were investigated under gas mixtures of propane (C3H8), oxygen (O2), and helium (He) with different compositions. To enhance the fuel partial oxidation at low temperatures, a porous layer of Ru was added onto the anode surface. Two configurations, finger (with parallel electrodes) and sandwich (with electrodes on opposite sides of the pellets), were analyzed

Surface Modification of Polyimide for Improving Adhesion Strength by Inductively Coupled Plasma

This study examined the effect of an inductively coupled plasma (ICP) treatment using an argon and helium gas mixture on the adhesion between polyimide and a copper film. Optical emission spectroscopy (OES) of the ICP revealed the emission intensity of helium and argon at various intensities with the helium mixing ratio. The treated polyimide surface was analyzed using a contact angle analyzer, Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The contact angle and RMS roughness ranged from 66 to 31° and 2.3 to 4.1 nm, respectively. XPS showed an increase in C–O bonding. The highest peel strength was 0.43 kgf/cm at a 40% of helium mixing ratio, which contained the highest level of activate species. Overall, an ICP treatment of a polyimide surface with a 40% helium gas mixture improves the adhesion strength between copper and polyimide significantly.