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Showing papers on "Atmospheric pressure published in 2018"


Journal ArticleDOI
TL;DR: Cold-atmospheric plasma clinical use strongly needs the development of standardized reliable protocols, to determine the more efficient type of plasma for each type of cancer, and its combination with conventional treatments.
Abstract: Background:Cold-atmospheric plasma (CAP) is an ionized gas produced at an atmospheric pressure. The aim of this systematic review is to map the use of CAP in oncology and the implemented methodolog...

146 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the onset temperature where reduction in terms of exfoliation takes place, which is determined to be 325 °C at standard atmospheric pressure, and the study leads to achieving highest content with a minimum defect in the graphene lattice at the optimum temperature.
Abstract: Among various methods used for the reduction of graphene oxide (GO) into a purer form of graphene, the thermal reduction method provides a simpler, safer, and economic alternative, compared to other techniques. Thermal reduction of GO causes significant weight loss and volume expansion of the material. Current work investigates the onset temperature where reduction in terms of exfoliation takes place, which is determined to be 325 °C at standard atmospheric pressure. Reduction temperature plays the most crucial role as it controls the quality of reduced graphene oxide in terms of weight percentage of carbon and lattice defect. The study leads to achieving highest content with a minimum defect in the graphene lattice at the optimum temperature, which is found to be 350 °C at standard atmospheric pressure. The thermal reduction process has been analyzed with the help of Fourier transform infrared spectroscopy, thermogravimetric analysis, and thermal degradation kinetics. From thermal degradation kinetics of GO, the rate of reaction has been found to be independent of concentration and is a sole function of temperature.

145 citations



Journal ArticleDOI
TL;DR: In this paper, an evaluation of the error induced by neglecting the effect of air compressibility in modelling Oscillating Water Column (OWC) wave energy converters is presented.

76 citations


Journal ArticleDOI
TL;DR: In this paper, a membrane-covered closed cell is used as a pressure barrier between the enclosed cell at atmospheric pressure and the electron analyzer at vacuum while allowing transmission of photoelectrons.
Abstract: Photoelectron spectroscopy is an excellent technique to explore chemically complex systems in catalysis. However, due to a small mean free path of photoelectrons in gas, liquid and solid media, the study of the gas-solid, liquid-gas, solid-liquid interfaces as well as liquid homogeneous systems are a serious challenge. With differentially pumped analyzers this limitation ceases to exist and no longer restricts photoelectron spectroscopy only to ultra-high vacuum conditions. Presently, photoemission studies at tens of mbar of pressure are possible. To reach atmospheric pressure and even higher, membrane-covered closed cells have been developed. Graphene membranes are impermeable to molecules and almost transparent to photoelectrons. They are used as a pressure barrier between the enclosed cell at atmospheric pressure and the electron analyzer at vacuum while allowing transmission of photoelectrons. By accessing to atmospheric pressure range, with this kind of cell, photoemission studies will become a versatile in situ and operando tool for catalysis. Studies involving liquids in static conditions are an important aspect in this direction, which can be extended to homogeneous catalytic systems. Liquids are presently accessible using micro-jets. Another aspect which is of paramount interest to investigate catalysts is time resolution. By improving the time resolution of photoemission measurements to the sub-second regime it is possible to follow the kinetic changes that are crucial of a catalytic reaction, the changes that occur during catalyst pretreatment and activation, and notably to differentiate active species from spectator ones, which may be the dominating species in a classical experiment.

73 citations


Journal ArticleDOI
TL;DR: Investigating the formation and kinetics of O and OH in a He–H2O plasma jet using absorption spectroscopy and 0D modelling.
Abstract: Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultra-violet high-resolution Fourier-transform absorption spectroscopy and ultra-violet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H2O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 × 1014 cm−3 for OH and 3 × 1013 cm−3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH+ by proton transfer to H2O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H2O+ by proton transfer to H2O and by electron impact dissociation of H2O. It is lost by reactions with other OH molecules to form either H2O + O or H2O2. Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications.

60 citations


Journal ArticleDOI
01 Jan 2018-Icarus
TL;DR: In this paper, the history of the loss and replenishment of the Martian atmosphere using elemental and isotopic compositions of nitrogen and noble gases was examined by taking into consideration various processes, such as impact erosion, replenishment by asteroids and comets, atmospheric escape induced by solar radiation and wind, volcanic degassing, and gas deposition by interplanetary dust particles.

58 citations


Journal ArticleDOI
TL;DR: In this article, high-speed imaging and schlieren imaging were used to investigate the interaction of the laser beam with the powder bed at pressures up to 5 bar, in argon and helium atmospheres.
Abstract: High-speed imaging and schlieren imaging were used to investigate the interaction of the laser beam with the powder bed at pressures up to 5 bar, in argon and helium atmospheres. The entrainment of powder particles in the flow of shielding gas generated by the laser plume, and hence denudation, was reduced at high pressure for both gases. However, for argon, high pressure increased the temperature of both the melt pool and the laser plume, which significantly increased the generation of spatter and ionisation of the metal vapour with degraded surface smoothness and continuity. For helium, the formation of spatter and plasma did not increase with the increase in pressure above that observed at atmospheric pressure: its higher thermal conductivity and thermal diffusivity limited the laser plume temperature. Layers built at 5 bar in helium had a surface smoothness and continuity comparable to those built in argon at atmospheric pressure, but achieved at a higher laser scan speed, suggesting that a high-pressure helium atmosphere may be used to enhance the build rate.

55 citations


Journal ArticleDOI
TL;DR: A helium-based CAP setup equipped with a shielding-gas device, which allows the control of plasma-air interactions and the liquid chemistry developed after CAP treatment is developed, demonstrating clearly that for physical, chemical and biomedical applications, which are usually achieved in ambient air environments, it is necessary to realize an effective control of Plasma- air interactions.
Abstract: The understanding of plasma–liquid interactions is of major importance, not only in physical chemistry, chemical engineering and polymer science, but in biomedicine as well as to better control the biological processes induced on/in biological samples by Cold Atmospheric Plasmas (CAPs). Moreover, plasma–air interactions have to be particularly considered since these CAPs propagate in the ambient air. Herein, we developed a helium-based CAP setup equipped with a shielding-gas device, which allows the control of plasma–air interactions. Thanks to this device, we obtained specific diffuse CAPs, with the ability to propagate along several centimetres in the ambient air at atmospheric pressure. Optical Emission Spectroscopy (OES) measurements were performed on these CAPs during their interaction with a liquid medium (phosphate-buffered saline PBS 10 mM, pH 7.4) giving valuable information about the induced chemistry as a function of the shielding gas composition (variable O2/(O2 + N2) ratio). Several excited species were detected including N2+(First Negative System, FNS), N2(Second Positive System, SPS) and HO˙ radical. The ratios between nitrogen/oxygen excited species strongly depend on the O2/(O2 + N2) ratio. The liquid chemistry developed after CAP treatment was investigated by combining electrochemical and UV-visible absorption spectroscopy methods. We detected and quantified stable oxygen and nitrogen species (H2O2, NO2−, NO3−) along with Reactive Nitrogen Species (RNS) such as the peroxynitrite anion ONOO−. It appears that the RNS/ROS (Reactive Oxygen Species) ratio in the treated liquid depends also on the shielding gas composition. Eventually, the composition of the surrounding environment of CAPs seems to be crucial for the induced plasma chemistry and consequently, for the liquid chemistry. All these results demonstrate clearly that for physical, chemical and biomedical applications, which are usually achieved in ambient air environments, it is necessary to realize an effective control of plasma–air interactions.

54 citations


Journal ArticleDOI
TL;DR: An experimental and theoretical study on microwave plasma enabled assembly of carbon nanostructures, such as multilayer graphene sheets and nanoparticles, was performed and an insight into the physical chemistry ofcarbon nanostructure formation in a high energy density microwave plasma environment is presented.
Abstract: An experimental and theoretical study on microwave (2.45 GHz) plasma enabled assembly of carbon nanostructures, such as multilayer graphene sheets and nanoparticles, was performed. The carbon nanostructures were fabricated at different Ar–CH4 gas mixture composition and flows at atmospheric pressure conditions. The synthesis method is based on decomposition of the carbon-containing precursor (CH4) in the “hot” microwave plasma environment into carbon atoms and molecules, which are further converted into solid carbon nuclei in the “colder” plasma zones. By tailoring of the plasma environment, a controlled synthesis of graphene sheets and diamond-like nanoparticles was achieved. Selective synthesis of graphene flakes was achieved at a microwave power of 1 kW, Ar and methane flow rates of 600 sccm and 2 sccm respectively, while the predominant synthesis of diamond-like nanoparticles was obtained at the same power, but with higher flow rates, i.e. 1000 and 7.5 sccm, respectively. Optical emission spectroscopy was applied to detect the plasma emission related to carbon species from the ‘hot’ plasma zone and to determine the main plasma parameters. Raman spectroscopy and scanning electron microscopy have been applied to characterize the synthesized nanostructures. A previously developed theoretical model was further updated and employed to understand the mechanism of CH4 decomposition and formation of the main building units, i.e. C and C2, of the carbon nanostructures. An insight into the physical chemistry of carbon nanostructure formation in a high energy density microwave plasma environment is presented.

52 citations


Journal ArticleDOI
TL;DR: In this article, high-speed imaging was used to investigate the interaction of the laser beam with the powder bed at sub-atmospheric pressures, where the laser plume produces a flow in the ambient atmosphere that entrains particles toward the melt pool.
Abstract: The perceived advantages of laser powder bed fusion (PBF) at reduced pressure include a more stable melt pool and reduced porosity. In this study, high-speed imaging was used to investigate the interaction of the laser beam with the powder bed at sub-atmospheric pressures. At atmospheric pressure, the laser plume produces a flow in the ambient atmosphere that entrains particles toward the melt pool. As the pressure decreases, this hydrodynamic entrainment increases but eventually the expansion of the laser plume prevents the particles reaching the melt pool: profiles and cross-sections of the track reveal a drastic reduction in its cross-sectional area. As the pressure decreases further, into the molecular flow regime, particles are only repelled by the plume away from the melt pool. The regime between 1 bar and ∼50 mbar (the threshold pressure at which the penetration depth no longer increases) could provide a window for successful processing but might require a pre-sinter to maintain the integrity of the powder bed. Lower pressures would definitely require a pre-sinter, for which the additional processing time and increase in process complexity might be justified for porosity-critical applications.

Journal ArticleDOI
TL;DR: In this paper, the effect of heat release in reactions with charged and electronically excited species, or so-called fast gas heating (FGH), in nanosecond surface dielectric barrier discharge (nSDBD) in atmospheric pressure air is studied.
Abstract: The effect of heat release in reactions with charged and electronically excited species, or so-called fast gas heating (FGH), in nanosecond surface dielectric barrier discharge (nSDBD) in atmospheric pressure air is studied. Two-dimensional numerical simulations based on the PArallel Streamer Solver with KinEtics code are conducted. The code is based on the direct coupling of a self-consistent fluid model with detailed kinetics, an efficient photoionization model, and Euler equations. The choice of local field approximation for nSDBD modeling with simplified kinetics is discussed. The reduced electric field and the electron density are examined at both polarities for identical high-voltage pulses 24 kV in amplitude on a high-voltage electrode and 20 ns full width at half maximum. The distribution of the FGH energy and the resulting gas temperature field are studied and compared with findings in the literature. The input of different reactions to the appearance of hydrodynamic perturbations is analyzed.

Journal ArticleDOI
Xunchen Liu1, Guoyong Zhang1, Yan Huang1, Yizun Wang1, Fei Qi1 
TL;DR: In this paper, a multi-line flame thermometry technique based on mid-infrared direct absorption spectroscopy of carbon dioxide at its $$v_3$$ vibrational fundamental around 4.2μm was presented.
Abstract: We present a multi-line flame thermometry technique based on mid-infrared direct absorption spectroscopy of carbon dioxide at its $$v_3$$ fundamental around 4.2 μm that is particularly suitable for sooting flames. Temperature and concentration profiles of gas phase molecules in a flame are important characteristics to understand its flame structure and combustion chemistry. One of the standard laboratory flames to analyze polycyclic aromatic hydrocarbons (PAH) and soot formation is laminar non-premixed co-flow flame, but PAH and soot introduce artifact to most non-contact optical measurements. Here we report an accurate diagnostic method of the temperature and concentration profiles of CO2 in ethylene diffusion flames by measuring its $$v_3$$ vibrational fundamental. An interband cascade laser was used to probe the R-branch bandhead at 4.2 μm, which is highly sensitive to temperature change, free from soot interference and ambient background. Calibration measurement was carried out both in a low-pressure Herriott cell and an atmospheric pressure tube furnace up to 1550 K to obtain spectroscopic parameters for high-temperature spectra. In our co-flow flame measurement, two-dimensional line-of-sight optical depth of an ethylene/N2 laminar sooting flame was recorded by dual-beam absorption scheme. The axially symmetrical attenuation coefficient profile of CO2 in the co-flow flame was reconstructed from the optical depth by Abel inversion. Spatially resolved flame temperature and in situ CO2 volume fraction profiles were derived from the calibrated CO2 spectroscopic parameters and compared with temperature profiles measured by two-line atomic fluorescence.

Journal ArticleDOI
TL;DR: In this paper, a kinetic mechanism was proposed based on recently computed kinetic parameters from literature, which showed good performances for representing the present experimental data as well as experimental data found in literature consisting of ignition delay times, laminar flame speeds and flame structure.


Journal ArticleDOI
TL;DR: Results are not in good accordance with state-of-the-art drop formation models, which are based on oil-only experiments at atmospheric pressure, and therefore show the need for a modification of such models which incorporates effects of hydrostatic pressure and dissolved gases for the modeling of deep-sea oil spills and blowouts.
Abstract: To date, experimental investigations to determine the droplet size distribution (DSD) of subsea oil spills were mostly conducted at surface conditions, i.e. at atmospheric pressure, and with dead, i.e. purely liquid, oils. To investigate the influence of high hydrostatic pressure and of gases dissolved in the oil on the DSD, experiments with a downscaled blowout are conducted in a high-pressure autoclave at 150 bar hydrostatic pressure. Jets of “live”, i.e. methane-saturated, crude oil and n-decane are compared to jets of “dead” hydrocarbon liquids in artificial seawater. Experiments show that methane dissolved in the liquid oil increases the volume median droplet diameter significantly by up to 97%. These results are not in good accordance with state-of-the-art drop formation models, which are based on oil-only experiments at atmospheric pressure, and therefore show the need for a modification of such models which incorporates effects of hydrostatic pressure and dissolved gases for the modeling of deep-s...

Journal ArticleDOI
TL;DR: In this paper, the main condensation regimes at sub-atmospheric pressure conditions were identified and a comparison was done between the condensation regime experimentally determined and those available in the literature, which were obtained at atmospheric pressure.

Journal ArticleDOI
TL;DR: In this paper, a simple and available novel approach for the oxygen-assisted preparation of ZnS:Mn particles by solid-state reaction at atmospheric pressure without the formation of the corresponding oxides.
Abstract: Mechanoluminescent materials that convert mechanical stimuli to light emission have attracted extensive attention for potential applications in human-machine interactions. Here, we report a simple and available novel approach for the oxygen-assisted preparation of ZnS:Mn particles by solid-state reaction at atmospheric pressure without the formation of the corresponding oxides. The existence of O2 has a positive impact on the formation of S vacancies in wurtzite-phase ZnS, leading to the introduction of Mn2+ ion luminescent centers and shallow donor levels, which can improve the electron-hole recombination rate. The O2 ratio and Mn2+ ion doping concentration have significant effects on the luminous efficiency, which is optimal at 1%–20% and 1 at.%–2 at.% respectively. In addition, a device based on the piezo-photonic effect with excellent pressure sensitivity of 0.032 MPa−1 was fabricated, which can map the two-dimensional pressure distribution ranging from 2.2 to 40.6 MPa in situ. This device can be applied to real-time pressure mapping, smart sensor networks, high-level security systems, human-machine interfaces, and artificial skins.

Journal ArticleDOI
TL;DR: In this paper, the effect of pressure on the response of methane and propane flames to acoustic excitation of the flow is analyzed on the basis of the flame transfer function (FTF) formalism, experimentally determined from velocity and global OH* chemiluminescence measurements at pressures up to 5 bar.

Journal ArticleDOI
TL;DR: In this paper, two sub-atmospheric humidification processes (process-I and II) utilizing solar heat are proposed and assessed theoretically, and the desalinated water production rate, gained output ratio and an economical comparison between processes are made subject to similar operating conditions.

Journal ArticleDOI
TL;DR: In this paper, the corrosion behavior of a Fe48Mo14Cr15Y2C15B6 amorphous coating was examined under high hydrostatic pressure (80 atm), and compared to that at atmospheric pressure (1※atm).

Journal ArticleDOI
TL;DR: In this paper, the effect of low-molecular weight alcohols (methanol and ethanol) and carboxylic acids (formic acid and acetic acid) added to the FLA solution on the morphology of the spectra and spectroscopic parameters of both discharge systems was studied.
Abstract: Atmospheric pressure glow discharge operated in contact with a flowing liquid anode (FLA-APGD), with the solution pH adjusted to pH 6.0 or pH 1.0, was performed to elucidate plasma-chemical processes and reactions occurring in the discharge and the liquid phase. The morphologies in the emission spectra of both FLA-APGD systems in reference to molecular (NO, OH, N2, and N2+) and atomic (H and O) excited species in addition to selected spectroscopic parameters, including the rotational, vibrational, and excitation temperatures and electron number density, were assessed for both discharge systems and compared with those evaluated for APGD operated in contact with a flowing liquid cathode (FLC-APGD). The effect of low-molecular weight (LMW) alcohols (methanol and ethanol) and carboxylic acids (formic acid and acetic acid) added to the FLA solution on the morphology of the spectra and spectroscopic parameters of both discharge systems was studied as well. The analytical performance of both FLA-APGD systems, compliant with the intensities of the atomic lines of Ag, Cd, and Pb, the signal-to-background ratios of these lines, and the detection limits of Ag, Cd, and Pb, under conditions of the absence and presence of the aforementioned LMW organic compounds was determined and compared. It was established that APGD operated in contact with FLA solutions acidified to pH 1.0 or buffered to pH 6.0 conferred a unique set of advantages as compared to the case of the FLC-APGD system. Both FLA-APGD systems were characterized by a large population of high energy electrons and molecular and atomic excited states not quenched by H2O vapor, as in the case of FLC-APGD. Particularly, for the FLA-APGD (pH 1.0) system, the addition of LMW organic compounds resulted in an improvement in its analytical performance for the detection and determination of Ag, Cd, and Pb.

Journal ArticleDOI
TL;DR: In this paper, the phase equilibrium temperature and dissociation heat measurements were performed in the range of the mass fraction of TBPAce aqueous solution from 0.10 to 0.42.
Abstract: This paper reports the experimental study on measuring the phase equilibrium temperatures and the dissociation heats of ionic semiclathrate hydrate formed with tetrabutylphosphonium acetate (TBPAce) under atmospheric pressure. The phase equilibrium temperature and the dissociation heat measurements were performed in the range of the mass fraction of TBPAce aqueous solution from 0.10 to 0.42. The highest phase equilibrium temperature was 11.0 °C at the mass fraction range from 0.35 to 0.39. The largest dissociation heat of pure TBPAce hydrate was 192.0 kJ kg–1 at the mass fraction 0.36. The obtained results indicate that TBPAce hydrate would be suitable for a new thermal energy storage medium for general air conditioning systems.

Journal ArticleDOI
TL;DR: The in-situ CO2 removal pyrolysis of Chinese herb residue was studied by thermodynamic equilibrium simulation and experimental methods and results indicate that the heating value of product gas increases with the increase of Ca/H and pressure, and slightly decreases with the increasing of temperature.

Journal ArticleDOI
TL;DR: In this article, the effect of pressure on the flash point of various fuels (methanol, ethanol, acetone, ethyl acetate, nhexane, n-octane, benzene, toluene) and their binary mixtures was quantified.

Journal ArticleDOI
TL;DR: In this article, a subnanosecond breakdown of atmospheric-pressure air in a nonuniform electric field was studied and it was shown that the ionization waves (streamers) formed in the pre-breakdown stage have a nearly spherical or conical shape.
Abstract: Results are presented from experimental and computational studies of a subnanosecond breakdown of atmospheric-pressure air in a nonuniform electric field. It is shown that the ionization waves (streamers) formed in the prebreakdown stage have a nearly spherical or conical shape. The diameter of the streamer in its widest part is found to increase with increasing voltage and discharge gap length. For a rise time of the voltage pulse of ≈0.5 ns and its amplitude of ≈250 kV, streamers about 8 cm in diameter were observed in a 7-cm-long gap.

Journal ArticleDOI
TL;DR: In this paper, the nanosecond repetitively pulsed discharge to the micrometer scale, in a 200 µm discharge gap in air at atmospheric pressure and room temperature, focusing on measurements of the electron number density and electron temperature, was confined.
Abstract: We confine the nanosecond repetitively pulsed discharge to the micrometer scale, in a 200 µm discharge gap in air at atmospheric pressure and room temperature, focusing on measurements of the electron number density and electron temperature. The Stark broadening of H, O and N atomic lines and electrical conductivity both show that the electron number density reaches a maximum value of 1 × 1019 cm−3. Boltzmann plots show the electron temperature to be 72 kK several nanoseconds after the end of the pulse of applied electric field. We will use these results to determine the mechanism responsible for electron loss during the early recombination phase (t < 500 ns) and comment on the degree of ionization and dissociation.

Journal ArticleDOI
TL;DR: In this paper, a Non-Homogeneous Equilibrium Model (NHEM) was used, and validated by a large scale LH2 spill experiment, and the predicted data displayed good agreement with the experiment.

Journal ArticleDOI
TL;DR: This work designs a new hybrid ion funnel-ion carpet (FUNPET) interface that transmits a broad mass range with a single set of instrument conditions and incorporates a virtual jet disruptor where pressure buildup and counter flow dissipate the supersonic jet that results from gas flow into the interface.

Journal ArticleDOI
TL;DR: In this paper, the plasma decomposition of ammonia was studied as a function of applied voltage/power, residence time including length of an inner electrode and flow rate of reactant gases, partial pressure of ammonia, and amount and the metal species of the inner electrodes.