Showing papers on "Atmospheric pressure published in 2020"

Impact of Lithium Salts on the Combustion Characteristics of Electrolyte under Diverse Pressures

Abstract: The electrolyte is one of the components that releases the most heat during the thermal runaway (TR) and combustion process of lithium-ion batteries (LIBs). Therefore, the thermal hazard of the electrolyte has a significant impact on the safety of LIBs. In this paper, the combustion characteristics of the electrolyte such as parameters of heat release rate (HRR), mass loss rate (MLR) and total heat release (THR) have been investigated and analyzed. In order to meet the current demand of plateau sections with low-pressure and low-oxygen areas on LIBs, an electrolyte with the most commonly used lithium salts, LiPF6, was chosen as the experimental sample. Due to the superior low-temperature performance, an electrolyte containing LiBF4 was also selected to be compared with the LiPF6 sample. Combustion experiments were conducted for electrolyte pool fire under various altitudes. According to the experimental results, both the average and peak values of MLR in the stable combustion stage of the electrolyte pool fire had positive exponential relations with the atmospheric pressure. At the relatively higher altitude, there was less THR, and the average and peak values of HRR decreased significantly, while the combustion duration increased remarkably when compared with that at the lower altitude. The average HRR of the electrolyte with LiBF4 was obviously lower than that of solution containing LiPF6 under low atmospheric pressure, which was slightly higher for LiBF4 electrolyte at standard atmospheric pressure. Because of the low molecular weight (MW) of LiBF4, the THR of the corresponding electrolyte was larger, so the addition of LiBF4 could not effectively improve the safety of the electrolyte. Moreover, the decrease of pressure tended to increase the production of harmful hydrogen fluoride (HF) gas.

Mantle redox state drives outgassing chemistry and atmospheric composition of rocky planets.

Abstract: Volcanic degassing of planetary interiors has important implications for their corresponding atmospheres. The oxidation state of rocky interiors affects the volatile partitioning during mantle melting and subsequent volatile speciation near the surface. Here we show that the mantle redox state is central to the chemical composition of atmospheres while factors such as planetary mass, thermal state, and age mainly affect the degassing rate. We further demonstrate that mantle oxygen fugacity has an effect on atmospheric thickness and that volcanic degassing is most efficient for planets between 2 and 4 Earth masses. We show that outgassing of reduced systems is dominated by strongly reduced gases such as [Formula: see text], with only smaller fractions of moderately reduced/oxidised gases ([Formula: see text], [Formula: see text]). Overall, a reducing scenario leads to a lower atmospheric pressure at the surface and to a larger atmospheric thickness compared to an oxidised system. Atmosphere predictions based on interior redox scenarios can be compared to observations of atmospheres of rocky exoplanets, potentially broadening our knowledge on the diversity of exoplanetary redox states.

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N2

Abstract: Spatially resolved tunable diode-laser absorption measurements of the absolute densities of He-I (23S1) metastables in a micro atmospheric pressure plasma jet operated in He/N2 and driven by "peaks"- and "valleys"-type tailored voltage waveforms are presented. The measurements are performed at different nitrogen admixture concentrations and peak-to-peak voltages with waveforms that consist of up to four consecutive harmonics of the fundamental frequency of 13.56 MHz. Comparisons of the measured metastable densities with those obtained from Particle-in-Cell/Monte Carlo collisions simulations show a good quantitative agreement. The density of helium metastables is found to be significantly enhanced by increasing the number of consecutive driving harmonics. Their generation can be further optimized by tuning the peak-to-peak voltage amplitude and the concentration of the reactive gas admixture. These findings are understood based on detailed fundamental insights into the spatio-temporal electron dynamics gained from the simulations, which show that Voltage Waveform Tailoring allows to control the electron energy distribution function to optimize the metastable generation. A high degree of correlation between the metastable creation rate and the electron impact excitation rate from the helium ground state into the He-I ((3s)3S1) level is observed for some conditions which may facilitate an estimation of the metastable densities based on Phase Resolved Optical Emission Spectroscopy measurements of the 706.5 nm He-I line originating from the above level and metastable density values at proper reference conditions.

Measurements of electric field in an atmospheric pressure helium plasma jet by the E-FISH method

Abstract: Temporal and spatial distributions of the electric field in an atmospheric pressure, ns pulse, positive and negative polarity helium plasma jets are measured by ps electric field induced second harmonic generation. The measurements have been done in a quasi-two-dimensional plasma jet impinging on liquid water, using a laser sheet and a focused laser beam positioned at different heights above the water surface. Absolute calibration of the electric field is obtained by measuring a known Laplacian electric field distribution for the same geometry and at the same flow conditions. The vertical component of the electric field is determined by isolating the second harmonic signal with the vertical polarization. The measured electric field is averaged over the span of the plasma jet, in the direction of the laser sheet or the focused laser beam. The spatial resolution of the laser sheet measurements is approximately 15 μm across the sheet, with the temporal resolution of 10 ns. The spatial resolution of the focused laser beam measurements is approximately 180 μm across the beam, with the temporal resolution of 2.5 ns. The results show non-monotonous electric field distribution across the jet, with two maxima produced by the surface ionization waves propagating over water. Considerable electric field enhancement is detected near the surface. Residual charge accumulation on the water surface is detected only in the negative polarity pulse discharge. The results provide new insight into the charge species kinetics and transport in atmospheric pressure plasma jets, and produce data for detailed validation of high-fidelity kinetic models.

Implications of thermo-chemical instability on the contracted modes in CO2 microwave plasmas

Abstract: Understanding and controlling contraction phenomena of plasmas in reactive flows is essential to optimize the discharge parameters for plasma processing applications such as fuel reforming and gas conversion. In this work, we describe the characteristic discharge modes in a CO2nmicrowave plasma and assess the impact of wave coupling and thermal reactivity on the contraction dynamics. The plasma shape and gas temperature are obtained from the emission profile and the Doppler broadening of the 777 nm O(5S ←n5P) oxygen triplet, respectively. Based on these observations, three distinct discharge modes are identified in the pressure range of 10 mbar to atmospheric pressure. We find that discharge contraction is suppressed by an absorption cut-off of the microwave field at the critical electron density, resulting in a homogeneous discharge mode below the critical transition pressure of 85 mbar. Further increase in the pressure leads to two contracted discharge modes, one emerging at a temperature of 3000 K to 4000 K and one at a temperature of 6000 K to 7000 K, which correspond to the thermal dissociation thresholds of CO2nand CO respectively. The transition dynamics are explained by a thermo-chemical instability, which arises from the coupling of the thermal-ionization instability to heat transfer resulting from thermally driven endothermic CO2ndissociation reactions. These results highlight the impact of thermal chemistry on the contraction dynamics of reactive molecular plasmas.

Pressure effects on the SEIS‐InSight instrument, improvement of seismic records and characterization of long period atmospheric waves from ground displacements

Abstract: Mars atmospheric pressure variations induce ground displacements through elastic deformations. The various sensors of the InSight mission were designed in order to be able to understand and correct for these ground deformations induced by atmospheric effects. Particular efforts were made on one hand to avoid direct pressure and wind effects on the seismometer, and on the other hand to have a high performance pressure sensor operating in the same frequency range as the seismometer. As a consequence of these technical achievements and the low background seismic noise of Mars, the InSight mission is opening a new science domain in which the ground displacements can be used to perform atmospheric science. This study presents an analysis of pressure and seismic signals and the relations between them. After a short description of the pressure and seismic sensors, we present an analysis of these signals as a function of local time at the InSight location. Then, the coherent signals recorded by both pressure and seismic sensors are described and interpreted in terms of atmospheric signals and ground deformation processes. Two different methods to remove the pressure effects recorded by SEIS sensors are presented, and their efficiency is estimated and compared. These decorrelation methods allow the pressure generated noise to be reduced by a factor of two during the active day time period. Finally, an analysis of SEIS signals induced by gravity waves demonstrates the interest of ground displacement measurements to characterize their arrival azimuth.

Sustainable nitrogen fixation from synergistic effect of photo-electrochemical water splitting and atmospheric pressure N2 plasma

Abstract: In this study, nitrogen fixation in the electrolyte was achieved by atmospheric pressure non-thermal plasma generated by a sinusoidal power supply (with an applied voltage of 10 kV and frequency of 33 kHz). Ammonia measurements on plasma exposed electrolyte at several working gas and purging gas conditions revealed that nitrogen plasma in the same gas environment is more favourable for plasma-assisted ammonia synthesis. In addition, photo-electrochemical water splitting was performed by irradiating UV light on a titanium dioxide semiconductor photo-anode to generate hydrogen donor in nitrogen reduction reaction. The amount of ammonia synthesized by this synergistic process of photo-electrochemical water splitting and nitrogen plasma is six times higher than that obtained by nitrogen plasma alone. An increase in the co-synthesized NOX concentrations and background contamination at reaction site reduces the ammonia synthesis rate and Faraday efficiency. However, the ammonia production efficiency was increased up to 72% by using a proton-exchange membrane which prevents the diffusion of oxygen evolved from water splitting into the plasma, and by reducing the axial distance between the plasma electrode and reaction site. The sustainable nitrogen fixation process reported herein can be performed at atmospheric pressure conditions without a direct input of hydrogen gas or any catalyst.

Characterization of a kHz atmospheric pressure plasma jet: comparison of discharge propagation parameters in experiments and simulations without target

Abstract: This paper quantitatively characterizes a kHz atmospheric pressure He plasma jet without target powered by a pulse of positive applied voltage. It focuses on a quantitative comparison between experimental measurements and numerical results of a two-dimensional fluid model using the same configuration, for different values of magnitude and width of pulsed applied voltage. Excellent agreement is obtained between experiments and simulations on the gas mixture distribution, the length and velocity of discharge propagation and the electric field in the discharge front. For the first time in the same jet, the experimentally measured increase of the electric field in the plume is confirmed by the simulations. The electron density and temperature, measured behind the high field front, are found to agree qualitatively. Moreover, the comparison with simulations shows that discharge propagation stops when the potential in the discharge head is lower than a certain threshold. Hence, pulse width and magnitude allow to control propagation length. For long pulses (≥1000 ns), the threshold potential in the discharge front is reached during the pulse. For shorter pulses, propagation is determined by the pulse shape, as the threshold is reached around 90-130 ns after the fall of the pulse. The results suggest that this threshold is defined by the gas mixture at the position of the front.

Specific energy cost for nitrogen fixation as NO x using DC glow discharge in air

Abstract: We report on factors influencing specific energy cost of producing NOx from pin-to-pin DC glow discharges in air at atmospheric pressure. Discharge current, gap distance, gas flowrate, exterior tube wall temperature and the presence and position of activated Al2O3 catalyst powder were examined. Presence of heated catalyst adjacent to the plasma zone improved energy efficiency by as much as 20% at low flows, but the most energy efficient conditions were found at the highest flowrates that allowed a stable discharge (about 10-15 L/min). Under those conditions, catalyst had no effect on efficiency in the present study. The lowest specific energy cost was observed to be between about 200-250 GJ/tN. Transport of active chemical species and energy are likely key factors controlling the specific energy cost of NOx production in the presence of catalyst. Air plasma device design and operating conditions must ensure that plasma-generated active intermediate chemical species transport is optimally coupled with catalytically active surfaces.

Influence of Cold Atmospheric Pressure Plasma on Pea Seeds: DNA Damage of Seedlings and Optical Diagnostics of Plasma

Abstract: Cold atmospheric pressure plasma treatment is currently being explored as an alternative way to improve the germination and growing parameters of plant seeds. However, it is important to pay attention to the effect of plasma treatment on DNA damage of the seeds as well as detailed characteristics of plasma composition and parameters. The aim of this work was to study the DNA damage of plasma-treated pea seeds (Pisum sativum L.) and plasma parameters such as the chemical composition of plasma gaseous compounds and plasma radiation. Seeds were treated with plasma using the diffuse coplanar surface barrier discharge generated in different working gases (ambient air, nitrogen, oxygen and different mixtures of oxygen and nitrogen) at atmospheric pressure and at 60 s, 180 s and 300 s exposure times. DNA damage was studied using the single cell-gel electrophoresis called the comet assay and the plasma parameters were investigated by Fourier transform infrared spectroscopy and optical emission spectroscopy. Experiments in different ratios of oxygen and nitrogen were realized in order to understand the reaction mechanism between the ambient air plasma and the treated seeds. Based on our results, ambient air plasma appears to be the most advantageous for the plasma treatment due to no significant DNA damage because of the proper combination of plasma composition in combination with water vapor present in ambient air.

High-κ dielectric ε-Ga2O3 stabilized in a transparent heteroepitaxial structure grown by mist CVD at atmospheric pressure

Abstract: The dielectric constant of metastable e-Ga2O3 was evaluated for the first time by using a transparent heteroepitaxial structure of e-Ga2O3/indium tin oxide/yttria-stabilized zirconia. The dielectric e-Ga2O3 layer was grown by the facile solution route of mist chemical vapor deposition at atmospheric pressure. The highest dielectric constant of nearly 32 (at an AC frequency of 10 kHz) was about three times larger than that of the most stable β-Ga2O3 phase. This high dielectric constant is attributed to the polar structure of e-Ga2O3 unlike β-Ga2O3, and is comparable to those of the so-called high-κ dielectric oxides. The combination of a wide bandgap and a high dielectric constant would be beneficial for the future development of optoelectrical devices.

Unravelling discharge and surface mechanisms in plasma assisted ammonia reactions

Abstract: Current studies on ammonia synthesis by means of atmospheric pressure plasmas respond to the urgent need of developing less environmentally aggressive processes than the conventional Haber–Bosch ca...

Turbulence and entrainment in an atmospheric pressure dielectric barrier plasma jet

Abstract: Particle image velocimetry, laser‐induced fluorescence, and computational modeling are used to quantify the impact of plasma generation on air entrainment into a helium plasma jet. It is demonstrated that discharge generation yields a minor increase in the exit velocity of the gas. In contrast, the laminar to turbulent transition point is strongly affected, attributed to an increase in plasma‐induced perturbations within the jet shear layer. The temporal decay of laser‐induced fluorescence from OH is used as an indicator of humid air within the plasma. The results show that plasma‐induced perturbations increase the quenching rate of the OH‐fluorescent state; indicating that shear‐layer instabilities play a major role in determining the physicochemical characteristics of the plasma.

Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring

Abstract: Crustal pore pressure, which controls the activities of earthquakes and volcanoes, varies in response to rainfall. The status of pore pressure can be inferred from observed changes in seismic velocity. In this study, we investigate the response of crustal pore pressure to rainfall in southwestern Japan based on time series of seismic velocity derived from ambient noise seismic interferometry. To consider the heterogeneity of the area, rainfall and seismic velocity obtained at each location were directly compared. We used a band-pass filter to distinguish the rainfall variability from sea level and atmospheric pressure, and then calculated the cross-correlation between rainfall and variations in S-wave velocity (Vs). A mostly negative correlation between rainfall and Vs changes indicates groundwater recharge by rainfall, which increases pore pressure. The correlations differ between locations, where most of the observation stations with clear negative cross-correlations were located in areas of granite. On the other hand, we could not observe clear correlations in steep mountain areas, possibly because water flows through river without percolation. This finding suggests that geographical features contribute to the imprint of rainfall on deep formation pore pressure. We further modelled pore pressure change due to rainfall based on diffusion mechanism. A strong negative correlation between pore pressure estimated from rainfall and Vs indicates that the Vs variations are triggered by pore pressure diffusion in the deep formation. Our modelling results show a spatial variation of diffusion parameter which controls the pore pressure in deep formation. By linking the variations in seismic velocity and crustal pore pressure spatially, this study shows that seismic monitoring may be useful in evaluating earthquake triggering processes or volcanic activity.

CrossTalk opposing view: Barometric pressure, independent of , is not the forgotten parameter in altitude physiology and mountain medicine

Abstract: A debate about a possible specific effect of barometric pressure has been introduced, for various reasons, into the domains of exercise and altitude physiology, as well as sports training. Economic considerations may have promoted normobaric methods since normobaric conditions are less expensive to simulate than hypobaric ones, either natural or simulated, in hypobaric chambers. Countries without mountains may well need to train their athletes in hypoxia without the cost of travelling far from home. A debate then arose because scientists challenged the idea that the two methods were equivalent. Medical aspects may arise, especially in the context of high altitude-related diseases (acute mountain sickness, high altitude pulmonary or cerebral oedema). Is the occurrence of these diseases more or less frequent in normobaric or hypobaric conditions?

Dissociation of tetramethylsilane for the growth of SiC nanocrystals by atmospheric pressure microplasma

Abstract: We report on mass spectrometry of residual gases after dissociation of tetramethylsilane (TMS) during the synthesis of silicon carbide (SiC) nanocrystals (NCs) by an atmospheric pressure microplasma. We use these results to provide details that can contribute to the understanding of the formation mechanisms of NCs. Mass spectrometry reveals the presence of high‐mass polymerization products supporting the key role of neutral fragments and limited atomization. On this basis, we found that the loss of methyl groups from TMS, together with hydrogen abstraction, represents important paths leading to nucleation and growth. The combination of TMS concentration and NC residence time controls the NC mean size and the corresponding distributions. For higher precursor concentrations, the reaction kinetics is sufficiently fast to promote coalescence.

Dual-vortex plasmatron: A novel plasma source for CO2 conversion

Abstract: Atmospheric pressure gliding arc (GA) discharges are gaining increasing interest for CO2 conversion and other gas conversion applications, due to their simplicity and high energy efficiency. However, they are characterized by some drawbacks, such as non-uniform gas treatment, limiting the conversion, as well as the development of a hot cathode spot, resulting in severe electrode degradation. In this work, we built a dual-vortex plasmatron, which is a GA plasma reactor with innovative electrode configuration, to solve the above problems. The design aims to improve the CO2 conversion capability of the GA reactor by elongating the arc in two directions, to increase the residence time of the gas inside the arc, and to actively cool the cathode spot by rotation of the arc and gas convection. The measured CO2 conversion and corresponding energy efficiency indeed look very promising. In addition, we developed a fluid dynamics non-thermal plasma model with argon chemistry, to study the arc behavior in the reactor and to explain the experimental results. Keywords: Plasma; Modeling; Reactor; CO2 conversion, CFD, Vortex, Argon, Atmospheric pressure

Oxidation of 5-[(formyloxy)methyl]-furfural to maleic anhydride with atmospheric oxygen using α-MnO2/Cu(NO3)2 as catalysts

Abstract: A novel approach to produce renewable maleic anhydride (MA) from bio-based platform chemical 5-[(formyloxy)methyl]furfural (FMF) was developed with air or pure oxygen at atmospheric pressure using ...

Microwave plasma-based direct synthesis of free-standing N-graphene

Abstract: Free-standing N-graphene was synthesized using a microwave plasma-based method at atmospheric pressure conditions through a single step and in a controllable manner. Using ethanol and ammonia as precursors, N-graphene with low relative amount of bonded oxygen and low level of saturated sp3 carbon bonds was produced. Adjusting the injection position of the nitrogen precursor in the plasma medium leads to selectivity in terms of doping level, nitrogen configuration and production yield. A previously developed theoretical model, based on plasma thermodynamics and chemical kinetics, was further updated to account for the presence of nitrogen precursor. The important role of HCN attachment to the graphene sheets as the main process of N-graphene formation is elucidated. The model predictions were validated by experimental results. Optical Emission Spectroscopy was used to detect the emission of plasma generated “building units” and to determine the gas temperature. The plasma outlet gas was analyzed by Fourier-Transform Infrared Spectroscopy to detect the generated gaseous by-products. The synthesized N-graphene was characterized by Scanning Electron Microscopy, Raman and X-ray photoelectron spectroscopies.

Reproducibility of Crude Oil Spectra Obtained with Ultrahigh Resolution Mass Spectrometry.

Abstract: In this study, the reproducibility of crude oil analyzed with (+) atmospheric pressure photoionization ultrahigh resolution mass spectrometry was evaluated. Three sets of data were obtained at inte...