Showing papers on "Atmospheric pressure published in 2017"

Electrocatalytic Synthesis of Ammonia at Room Temperature and Atmospheric Pressure from Water and Nitrogen on a Carbon-Nanotube-Based Electrocatalyst.

Abstract: Ammonia is synthesized directly from water and N2 at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half-cell for the NH3 synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half-cell. A rate of ammonia formation of 2.2×10−3 gNH3 m−2 h−1 was obtained at room temperature and atmospheric pressure in a flow of N2, with stable behavior for at least 60 h of reaction, under an applied potential of −2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH3 electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N2, making it more reactive towards hydrogenation.

Perspective: The physics, diagnostics, and applications of atmospheric pressure low temperature plasma sources used in plasma medicine

Abstract: Low temperature plasmas have been used in various plasma processing applications for several decades. But it is only in the last thirty years or so that sources generating such plasmas at atmospheric pressure in reliable and stable ways have become more prevalent. First, in the late 1980s, the dielectric barrier discharge was used to generate relatively large volume diffuse plasmas at atmospheric pressure. Then, in the early 2000s, plasma jets that can launch cold plasma plumes in ambient air were developed. Extensive experimental and modeling work was carried out on both methods and much of the physics governing such sources was elucidated. Starting in the mid-1990s, low temperature plasma discharges have been used as sources of chemically reactive species that can be transported to interact with biological media, cells, and tissues and induce impactful biological effects. However, many of the biochemical pathways whereby plasma affects cells remain not well understood. This situation is changing rather ...

Foundations of atmospheric pressure non-equilibrium plasmas

Abstract: Non-equilibrium plasmas have been intensively studied over the past century in the context of material processing, environmental remediation, ozone generation, excimer lamps and plasma display panels. Research on atmospheric pressure non-equilibrium plasmas intensified over the last two decades leading to a large variety of plasma sources that have been developed for an extended application range including chemical conversion, medicine, chemical analysis and disinfection. The fundamental understanding of these discharges is emerging but there remain a lot of unexplained phenomena in these intrinsically complex plasmas. The properties of nonequilibrium plasmas at atmospheric pressure span over a huge range of electron densities as well as heavy particle and electron temperatures. This paper provides an overview of the key underlying processes that are important for the generation and stabilization of atmospheric pressure non-equilibrium plasmas. The unique physical and chemical properties of theses discharges are also summarized.

Plasma‐driven dissociation of CO2 for fuel synthesis

Abstract: Power-to-gas is a storage technology aiming to convert surplus electricity from renewable energy sources like wind and solar power into gaseous fuels compatible with the current network infrastructure. Results of CO2 dissociation in a vortexstabilized microwave plasma reactor are presented. The microwave field, residence time, quenching, and vortex configuration were varied to investigate their influence on energy- and conversion efficiency of CO2 dissociation. Significant deterioration of the energy efficiency is observed at forward vortex plasmas upon increasing pressure in the range of 100 mbar towards atmospheric pressure, which is mitigated by using a reverse vortex flow configuration of the plasma reactor. Data from optical emission shows that under all conditions covered by the experiments the gas temperature is in excess of 4000 K, suggesting a predominant thermal dissociation. Different strategies are proposed to enhance energy and conversion efficiencies of plasma-driven dissociation of CO2.

Modeling of CO2 Splitting in a Microwave Plasma: How to Improve the Conversion and Energy Efficiency

Abstract: Microwave plasmas are one of the most promising techniques for CO2 conversion into value-added chemicals and fuels since they are very energy efficient. Nevertheless, experiments show that this high energy efficiency is only reached at low pressures and significantly drops toward atmospheric pressure, which is a clear limitation for industrial applications. In this paper, we use a zero-dimensional reaction kinetics model to simulate a CO2 microwave plasma in a pressure range from 50 mbar to 1 bar, in order to evaluate the reasons for this decrease in energy efficiency at atmospheric pressure. The code includes a detailed description of the vibrational kinetics of CO2, CO, and O2 as well as the energy exchanges between them because the vibrational kinetics is known to be crucial for energy efficient CO2 splitting. First, we use a self-consistent gas temperature calculation in order to assess the key performance indicators for CO2 splitting, i.e., the CO2 conversion and corresponding energy efficiency. Our ...

Routes to increase the conversion and the energy efficiency in the splitting of CO2 by a dielectric barrier discharge

Abstract: Here, we present routes to increase CO2 conversion into CO using an atmospheric pressure dielectric-barrier discharge. The change in conversion as a function of simple plasma parameters, such as power, flow rate, but also frequency, on-and-off power pulse, thickness and the chemical nature of the dielectric, wall and gas temperature, are described. By means of an in-depth electrical characterization of the discharge (effective plasma voltage, dielectric voltage, plasma current, number and lifetime of the microdischarges), combined with infrared analysis of the walls of the reactor, optical emission spectroscopy for the gas temperature, and mass spectrometry for the CO2 conversion, we propose a global interpretation of the effect of all the experimental parameters on the conversion and efficiency of the reaction.

CO2-CH4 conversion and syngas formation at atmospheric pressure using a multi-electrode dielectric barrier discharge

Abstract: The conversion of CO2 and CH4 into value-added chemicals is studied in a new geometry of a dielectric barrier discharge (DBD) with multi-electrodes, dedicated to the treatment of high gas flow rates. Gas chromatography is used to define the CO2 and CH4 conversion as well as the yields of the products of decomposition (CO, O2 and H2) and of recombination (C2H4, C2H6 and CH2O). The influence of three parameters is investigated on the conversion: the CO2 and CH4 flow rates, the plasma power and the nature of the carrier gas (argon or helium). The energy efficiency of the CO2 conversion is estimated and compared with those of similar atmospheric plasma sources. Our DBD reactor shows a good compromise between a good energy efficiency and the treatment of a large CO2 flow rate.

The effect of the gap distance between an atmospheric-pressure plasma jet nozzle and liquid surface on OH and N2 species concentrations

Abstract: An argon plasma jet at atmospheric pressure was operated at various gap distances between the nozzle of the plasma jet and the water surface in order to study the formation of OH and N2 species in the vicinity of the water surface. Plasma was generated using a 24 kHz sinusoidal power supply at a steady gas flow-rate of 200 sccm. The electron temperature and rotational temperature of gas species were measured using optical emission spectroscopy and found to decrease with increasing gap distance. Meanwhile, the electron density calculated from jet current measurement increased with increasing gap distance. The average OH concentration reduced from 6.10 × 1015 cm−3 to 1.35 × 1015 cm−3, as the gap distance increased from 1 to 4 mm. The 337 nm N2 second positive system studied by optical emission spectroscopy and temporal emission signals increased with increasing gap distance. Plasma activated water was also made from various gap distances in order to confirm the presence of particular reactive oxygen or nitr...

Nanosecond surface dielectric barrier discharge in atmospheric pressure air: I. measurements and 2D modeling of morphology, propagation and hydrodynamic perturbations

Abstract: A parallel 2D code for modeling nanosecond surface dielectric barrier discharge (nSDBD), combining a discharge description, detailed kinetics and hydrodynamics, is developed and validated. A series of experiments and numerical modeling for a single pulse nSDBD in atmospheric pressure air at a voltage amplitude of 24 kV have been performed. The measured and calculated velocity of the discharge front, electrical current, 2D map of N2 () emission and hydrodynamic perturbations caused by the discharge on the time scale μs are compared. The data are presented and analyzed for the negative and positive polarity of the streamers. A set of parametric calculations with different dielectric permittivities and different dielectric thicknesses is presented.

Critical evaluation of recent achievements in low power glow discharge generated at atmospheric pressure between a flowing liquid cathode and a metallic anode for element analysis by optical emission spectrometry

Abstract: Atmospheric pressure glow discharge (APGD) sustained in air between a metallic pin anode and the surface of a flowing liquid cathode (FLC) solution is a small and compact excitation source, in which the analytes are inherently transported to the discharge during its normal operation through electro-spray-like generation of tiny solution droplets and/or sputtering of the FLC solution surface. This survey is devoted to recent development of FLC–APGD in respect to basic researches and its applications in element analysis by optical emission spectrometry (OES). Particular attention is paid to the latest modifications in the construction of the discharge cells and the composition of the FLC solution and their implications for analytical performance of FLC–APGD–OES.

Combustion and ignition characteristics of ammonia/air mixtures in a micro flow reactor with a controlled temperature profile

Abstract: Combustion and ignition characteristics of a stoichiometric ammonia/air mixture were investigated by a micro flow reactor with a controlled temperature profile from ambient temperature to 1300 K at atmospheric pressure. Three kinds of flame dynamics depending on inlet mean flow velocities, namely, normal flames in the high velocity regime, flames with repetitive extinction and ignition (FREI) in the intermediate velocity regime, and weak flames in the low velocity regime, which have also been observed for hydrocarbons in previous studies, were observed for ammonia by the direct observation with a digital still camera in this study. The existence of ammonia weak flames at 1270 K was confirmed. Special attention was paid to weak flames to examine ignition characteristics of an ammonia/air mixture at low temperature because ignition experiments of ammonia have been conducted only at very high temperatures (around 2000 K). Species measurement for a stoichiometric ammonia/air weak flame at 10 cm/s was made using and a mass spectrometer and a T-shaped reactor fused with a micro-probe. The present species measurement elucidated the structure of the ammonia/air weak flame and complete combustion was confirmed at 1290 K. Five reaction mechanisms were used for computations of weak flames and the four of them did not predict complete combustion within the given computational domain. One reaction mechanism predicted complete combustion but the weak flame position in computation was located in a temperature region lower than that in the experiment. The order of reactivity evaluations among the five mechanisms using weak flames in the micro flow reactor agreed with that using ignition delay times at low temperatures which are generally difficult to be taken by ignition experiments. The capability of weak flame methodology to validate ignition properties of reaction mechanisms for low reactivity fuels like ammonia was successfully demonstrated in this study.

Large-Area WS2 Film with Big Single Domains Grown by Chemical Vapor Deposition.

Abstract: High-quality WS2 film with the single domain size up to 400 μm was grown on Si/SiO2 wafer by atmospheric pressure chemical vapor deposition. The effects of some important fabrication parameters on the controlled growth of WS2 film have been investigated in detail, including the choice of precursors, tube pressure, growing temperature, holding time, the amount of sulfur powder, and gas flow rate. By optimizing the growth conditions at one atmospheric pressure, we obtained tungsten disulfide single domains with an average size over 100 μm. Raman spectra, atomic force microscopy, and transmission electron microscopy provided direct evidence that the WS2 film had an atomic layer thickness and a single-domain hexagonal structure with a high crystal quality. And the photoluminescence spectra indicated that the tungsten disulfide films showed an evident layer-number-dependent fluorescence efficiency, depending on their energy band structure. Our study provides an important experimental basis for large-area, controllable preparation of atom-thick tungsten disulfide thin film and can also expedite the development of scalable high-performance optoelectronic devices based on WS2 film.

Streamer-to-spark transition initiated by a nanosecond overvoltage pulsed discharge in air

Abstract: This study is focused on the streamer-to-spark transition generated by an overvoltage nanosecond pulsed discharge under atmospheric pressure air in order to provide a quantitative insight into plasma-assisted ignition. The discharge is generated in atmospheric pressure air by the application of a positive high voltage pulse of 35 kV to pin-to-pin electrodes and a rise time of 5 ns. The generated discharge consists of a streamer phase with high voltage and high current followed by a spark phase characterized by a low voltage and a decreasing current in several hundreds of nanosecond. During the streamer phase, the gas temperature measured by optical emission spectroscopy related to the second positive system of nitrogen shows an ultra-fast gas heating up to 1200 K at 15 ns after the current rise. This ultra-fast gas heating, due to the quenching of electronically excited species by oxygen molecules, is followed by a quick dissociation of molecules and then the discharge transition to a spark. At this transition, the discharge contracts toward the channel axis and evolves into a highly conducting thin column. The spark phase is characterized by a high degree of ionization of nitrogen and oxygen atoms shown by the electron number density and temperature measured from optical emission spectroscopy measurements of N+ lines. Schlieren imaging and optical emission spectroscopy techniques provide the time evolution of the spark radius, from which the initial pressure in the spark is estimated. The expansion of the plasma is adiabatic in the early phase. The electronic temperature and density during this phase allows the determination of the isentropic coefficient. The value around 1.2-1.3 is coherent with the high ionization rate of the plasma in the early phase. The results obtained in this study provide a database and the initial conditions for the validation of numerical simulations of the ignition by plasma discharge. © 2017 IOP Publishing Ltd.

Mini Mass Spectrometer Integrated with a Miniature Ion Funnel

Abstract: Previously, a continuous atmospheric pressure interfaced miniature mass spectrometer was developed in our lab. The continuous atmospheric pressure interface improves system robustness, stability, and scan speed, but it also results in limited ion transfer efficiency and reduced mass resolution. To solve these problems, a miniature ion funnel was designed and integrated into the miniature mass spectrometer for the first time. Besides ion transfer efficiency, dimension and power consumption of the ion funnel also need to be considered throughout the design process. After a systematic optimization, the designed miniature ion funnel could increase ion transfer efficiency by more than 10 times, while lowering the background pressure of ion trap by ∼2 times. As a result, sensitivity and mass resolution of the second generation miniature mass spectrometer were improved by 20 times and ∼2 times, respectively, while maintaining its high scan speed and stability. A sensitive and robust mini-MS, capable of coupling ...

Thomson scattering on non-thermal atmospheric pressure plasma jets

Abstract: To characterize non-thermal atmospheric pressure plasmas experimentally, a large variety of methods and techniques is available, each having its own specific possibilities and limitations. A rewarding method to investigate these plasma sources is laser Thomson scattering. However, that is challenging. Non-thermal atmospheric pressure plasmas (gas temperatures close to room temperature and electron temperatures of a few eV) have usually small dimensions (below 1 mm) and a low degree of ionization (below 10−4). Here an overview is presented of how Thomson scattering can be applied to such plasmas and used to measure directly spatially and temporally resolved the electron density and energy distribution. A general description of the scattering of photons and the guidelines for an experimental setup of this active diagnostic are provided. Special attention is given to the design concepts required to achieve the maximum signal photon flux with a minimum of unwanted signals. Recent results from the literature are also presented and discussed.

The GTC exoplanet transit spectroscopy survey - VI. Detection of sodium in WASP-52b’s cloudy atmosphere

Abstract: We report the first detection of sodium absorption in the atmosphere of the hot Jupiter WASP-52b. We observed one transit of WASP-52b with the low-resolution Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at the 10.4 m Gran Telescopio Canarias (GTC). The resulting transmission spectrum, covering the wavelength range from 522 nm to 903 nm, is flat and featureless, except for the significant narrow absorption signature at the sodium doublet, which can be explained by an atmosphere in solar composition with clouds at 1 mbar. A cloud-free atmosphere is stringently ruled out. By assessing the absorption depths of sodium in various bin widths, we find that temperature increases towards lower atmospheric pressure levels, with a positive temperature gradient of 0.88 ± 0.65 K km-1 , possibly indicative of upper atmospheric heating and a temperature inversion.

Estimations of the Seismic Pressure Noise on Mars Determined from Large Eddy Simulations and Demonstration of Pressure Decorrelation Techniques for the Insight Mission

Abstract: The atmospheric pressure fluctuations on Mars induce an elastic response in the ground that creates a ground tilt, detectable as a seismic signal on the InSight seismometer SEIS. The seismic pressure noise is modeled using Large Eddy Simulations (LES) of the wind and surface pressure at the InSight landing site and a Green’s function ground deformation approach that is subsequently validated via a detailed comparison with two other methods: a spectral approach, and an approach based on Sorrells’ theory (Sorrells,Geophys. J. Int. 26:71–82, 1971; Sorrells et al., Nat. Phys. Sci. 229:14–16, 1971). The horizontal accelerations as a result of the ground tilt due to the LES turbulence-induced pressure fluctuations are found to be typically ∼ 2–40 nm/s2 in amplitude, whereas the direct horizontal acceleration is two orders of magnitude smaller and is thus negligible in comparison. The vertical accelerations are found to be ∼ 0.1–6 nm/s2 in amplitude. These are expected to be worst-case estimates for the seismic noise as we use a half-space approximation; the presence at some (shallow) depth of a harder layer would significantly reduce quasi-static displacement and tilt effects. We show that under calm conditions, a single-pressure measurement is representative of the large-scale pressure field (to a distance of several kilometers), particularly in the prevailing wind direction. However, during windy conditions, small-scale turbulence results in a reduced correlation between the pressure signals, and the single-pressure measurement becomes less representative of the pressure field. The correlation between the seismic signal and the pressure signal is found to be higher for the windiest period because the seismic pressure noise reflects the atmospheric structure close to the seismometer. In the same way that we reduce the atmospheric seismic signal by making use of a pressure sensor that is part of the InSight Auxiliary Payload Sensor Suite, we also the use the synthetic noise data obtained from the LES pressure field to demonstrate a decorrelation strategy. We show that our decorrelation approach is efficient, resulting in a reduction by a factor of ∼ 5 in the observed horizontal tilt noise (in the wind direction) and the vertical noise. This technique can, therefore, be used to remove the pressure signal from the seismic data obtained on Mars during the InSight mission.

Sensitive Determination of Cd in Small-Volume Samples by Miniaturized Liquid Drop Anode Atmospheric Pressure Glow Discharge Optical Emission Spectrometry.

Abstract: A novel liquid drop anode (LDA) direct current atmospheric pressure glow discharge (dc-APGD) system was applied for direct determination of Cd in liquid microsamples (50 μL) by optical emission spectrometry (OES). The microdischarge was generated in open-to-air atmosphere between a solid pin type tungsten cathode and a liquid drop placed on a graphite disk anode. The arrangement of the graphite disk placed on a PTFE chip platform as well as the solid pin type cathode was simple and robust. The limit of detection (LOD) of Cd for the developed LDA-APGD-OES method was 0.20–0.40 μg L–1, while precision (as the relative standard deviation for the repeated measurements) was within 2–5%. By using the liquid drop of 50 μL, the linearity range of 1–1000 μg L–1 was achieved. The effect of addition of the low-molecular weight (LMW) organic compounds, easily ionized elements (EIEs), i.e., Ca, K, Mg, and Na, as well as the foreign ions (Al, Cu, Fe, Mn, Zn) to the solution on the in situ atomization and excitation proc...

The GTC exoplanet transit spectroscopy survey. VII. Detection of sodium in WASP-52b's cloudy atmosphere

Abstract: We report the first detection of sodium absorption in the atmosphere of the hot Jupiter WASP-52b. We observed one transit of WASP-52b with the low-resolution Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at the 10.4 m Gran Telescopio Canarias (GTC). The resulting transmission spectrum, covering the wavelength range from 522 nm to 903 nm, is flat and featureless, except for the significant narrow absorption signature at the sodium doublet, which can be explained by an atmosphere in solar composition with clouds at 1 mbar. A cloud-free atmosphere is stringently ruled out. By assessing the absorption depths of sodium in various bin widths, we find that temperature increases towards lower atmospheric pressure levels, with a positive temperature gradient of 0.88 +/- 0.65 K/km, possibly indicative of upper atmospheric heating and a temperature inversion.

Monolayer WxMo1−xS2 Grown by Atmospheric Pressure Chemical Vapor Deposition: Bandgap Engineering and Field Effect Transistors

Abstract: Monolayer WxMo1−xS2-based field effect transistors are demonstrated for the first time on the monolayer WxMo1−xS2 flake, which is grown by the chemical vapor deposition method under an atmospheric pressure. Detailed material studies using Raman and photoluminescence measurements have been carried out on the as-grown monolayer WxMo1−xS2. Electronic band structure of monolayer WxMo1−xS2 has been calculated using first-principle theory. The thermal stability of monolayer WxMo1−xS2 has been evaluated using Raman-temperature measurement. Carrier transport study on the fabricated WxMo1−xS2 FETs has been analyzed using temperature-dependent current measurement, and a field effect mobility of ≈30 cm2 V−1 s−1 at 300 K is obtained.

The case for in situ resource utilisation for oxygen production on Mars by non-equilibrium plasmas

Abstract: Herein, it is argued that Mars has nearly ideal conditions for CO2 decomposition by non-equilibrium plasmas. It is shown that the pressure and temperature ranges in the CO2 Martian atmosphere favour the vibrational excitation and subsequent up-pumping of the asymmetric stretching mode, which is believed to be a key factor for an efficient plasma dissociation, at the expense of the excitation of the other modes. Therefore, gas discharges operating at atmospheric pressure on Mars are extremely strong candidates to produce O2 efficiently from the locally available resources.

126 264 Assigned Chemical Formulas from an Atmospheric Pressure Photoionization 9.4 T Fourier Transform Positive Ion Cyclotron Resonance Mass Spectrum

Abstract: Here, we present atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance (FTICR) mass analysis of a volcanic asphalt sample by acquiring data for 20 Da wide mass segments across a 1000 Da range, stitched into a single composite mass spectrum, and compare to a broad-band mass spectrum for the same sample. The segmented spectrum contained 170 000 peaks with magnitude greater than 6σ of the root-mean-square (rms) baseline noise, for which 126 264 unique elemental compositions could be assigned. Approximately two-thirds of those compositions represent monoisotopic (i.e., chemically different) species. That complexity is higher than that for any previously reported mass spectrum and almost 3 times greater than that obtained from the corresponding broad-band spectrum (59 015). For the segmented mass spectrum, the signal-to-noise ratio (S/N) was significantly higher throughout the spectrum, but especially at the lower and upper ends of mass distribution relative to that of the near-...

Atmospheric Pressure Non-Thermal Plasma Activation of CO2 in a Packed-Bed Dielectric Barrier Discharge Reactor.

Abstract: Direct conversion of CO2 into CO and O2 was carried out in a packed-bed dielectric barrier discharge (DBD) non-thermal plasma reactor at low temperatures and atmospheric pressure. The maximum CO2 conversion of 22.6% was achieved when BaTiO3 pellets were fully packed into the discharge gap. The introduction of γ-Al2O3 or 10 wt.% Ni/γ-Al2O3 into the BaTiO3 packed DBD reactor increased both CO2 conversion and energy efficiency of the plasma process. Packing γ-Al2O3 or 10 wt.% Ni/γ-Al2O3 in the upstream of the BaTiO3 bed showed higher CO2 conversion and energy efficiency compared to that using middle or downstream packing modes as the reverse reaction of CO2 conversion - the recombination of CO and O to form CO2 is more likely to happen in the middle and downstream modes. Compared to the γ-Al2O3 support, the coupling of the DBD with the Ni catalysts showed a higher CO2 conversion which can be attributed to the presence of Ni active species on the catalyst surface. The argon plasma treatment of the reacted Ni catalyst provided extra evidence to confirm the role of Ni active species in the conversion of CO2