Pure Noble Gases Research Articles

Sublimation of volatiles from H2O:CO2 bulk ices in the context of comet 67P/Churyumov–Gerasimenko

Context. The ROSINA instrument on board the Rosetta spacecraft measured, among others, the outgassing of noble gases from comet 67P/Churyumov–Gerasimenko. The interpretation of this dataset and unravelling underlying desorption mechanisms requires detailed laboratory studies. Aims. We aim to improve our understanding of the desorption patterns, trapping, and fractionation of noble gases released from the H2O:CO2-dominated ice of comet 67P. Methods. In the laboratory, ice films of neon, argon, krypton, or xenon (Ne, Ar, Kr, and Xe) mixed in CO2:H2O were prepared at 15 K. Temperature-programmed desorption mass spectrometry is employed to analyse the desorption behaviour of the noble gases. Mass spectrometric ROSINA data of 67P were analysed to determine the fraction of argon associated with CO2 and H2O, respectively. Results. CO2 has a significant effect on noble gas desorption behaviour, resulting in the co-release of noble gases with CO2, decreasing the amount of noble gas trapped within water, shifting the pure phase noble gas peak desorption temperature to lower temperatures, and prolonging the trapping of neon. These effects are linked to competition for binding sites in the water ice and the formation of crystalline CO2. Desorption energies of the pure phase noble gas release were determined and found to be higher than those previously reported in the literature. Enhancement of the Ar/Kr and Ar/Xe ratios are at best 40% and not significantly influenced by the addition of CO2. Analysis of ROSINA mass spectrometric data shows that the fraction of argon associated with H2O is 0.53 ± 0.30, which cannot be explained by our laboratory results. Conclusions. Multicomponent ice mixtures affect the desorption behaviour of volatiles compared to simple binary mixtures and experiments on realistic cometary ice analogues are vital to understanding comet outgassing.

Calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions with accurate thermodynamic models

Determining solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions is essential for various applications of noble gases in geological processes and for understanding the migration and accumulation of helium. This study developed two thermodynamic models for calculations of solubilities of five pure noble gases (i.e. He, Ne, Ar, Kr, and Xe) and He–CO2/CH4/N2 gas mixtures in water and in aqueous NaCl solution. The first model is constructed by extending the improved SAFT-LJ equation of state (EOS) to five binary H2O-noble gas systems and four ternary systems (i.e. H2O–He–NaCl, H2O–He–CO2, H2O–He–CH4, and H2O–He–N2). Both the non-ideality of aqueous phase and that of vapor phase of these systems were described using the improved SAFT-LJ EOS (φ-φ model). The second model is developed by modifying the gas solubility model proposed by Duan and his coworkers (one type of γ-φ model). The Pitzer theory was used to describe the non-ideality of aqueous phase and the improved SAFT-LJ EOS was used to describe the non-ideality of vapor phase. Both binary adjustable parameters of the improved SAFT-LJ EOS and parameters of the modified solubility model for pure gas were evaluated from experimental solubility data for pure gas. Both models are predictive for solubilities of gas mixtures since there is no need to evaluate their parameters from solubility data of gas mixtures.Comparisons of calculations of two models with experimental data show that both models can well represent solubilities and Henry's coefficients of five noble gases in pure water, as well as the solubility of He in aqueous NaCl solutions over a wide P-T range (273–600 K, 1–2000 bar for the solubility of He in water). The absolute average deviation of the improved SAFT-LJ EOS from experimental solubility data for five noble gases in pure water is 3.14% and that of the modified solubility model is 2.21%. Predictions of the improved SAFT-LJ EOS for Henry's coefficients for He in the He–CO2–H2O system are consistent with available experimental data. According to predictions of the improved SAFT-LJ EOS, Henry's coefficient for He in the He–CO2–H2O system is always lower than that in the He–H2O system at the same depth. Within 0–5 km depth, He solubility of He–CO2 gas mixture is much greater than that of pure He at the same depth and He partial pressure, He solubility of He–N2 mixture is a little greater than that of pure He, and He solubility of He–CH4 mixture is between that of He–CO2 mixture and that of He–N2 mixture. A computer program for calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in pure water and in aqueous NaCl solutions can be obtained from the corresponding author via email.

Bulk Viscosity of Dilute Gases and Their Mixtures

In this work, we use the Green–Kubo method to study the bulk viscosity of various dilute gases and their mixtures. First, we study the effects of the atomic mass on the bulk viscosity of dilute diatomic gas by estimating the bulk viscosity of four different isotopes of nitrogen gas. We then study the effects of addition of noble gas on the bulk viscosity of dilute nitrogen gas. We consider mixtures of nitrogen with three noble gases, viz., neon, argon, and krypton at eight different compositions between pure nitrogen to pure noble gas. It is followed by an estimation of bulk viscosity of pure oxygen and mixtures of nitrogen and oxygen for various compositions. In this case, three different composition are considered, viz., 25% N2 + 75% O2, 50% N2 + 50% O2, and 78% N2 + 22% O2. The last composition is aimed to represent the dry air. A brief review of works that study the effects of incorporation of bulk viscosity in analysis of various flow situations has also been provided.

Development of a fully analytical equation of state using ab initio interaction potentials. Application to pure simple fluids: Noble gases Ne, Ar, Kr, and Xe

In this work, we have extended the first-order mean spherical approximation (FMSA) equation of state (EOS) of Tang and Lu [J. Chem. Phys., 99, 9828 (1993)] in order to predict accurately fluid phase diagrams using ab initio potentials. At this level of development, we restricted to simple spherical compounds.The original equation based on hard-core two-Yukawa (HC2Y) was improved by the following:•Adding a new approximate simple correction to include higher orders in the development of Tang and Lu to get an analytical model closer to the full MSA.•Including a term to a better account for the long-range behavior of two-body potentials.•Adding a three-body interaction term (1st order perturbation) based on Axilrod-Teller potential.A general recommendation for setting the hard-sphere diameter value was also given.The predictive capability of the EOS was tested in a systematic manner. First, we checked that various simple theoretical potential (Mie n-6 and Exp n-6) phase diagrams are well reproduced. Second, the EOS was used for predicting fluid phase diagrams of the pure noble gases fluid series Ne, Ar, Kr, and Xe using realistic (i.e. derived from ab initio) two-body and three-body interaction potentials. The model is in good agreement with the experimental phase diagrams.As a conclusion, the simple statistical-mechanics-based fully analytical EOS developed in this work predicts accurately fluid phase diagrams of simple spherical compounds using ab initio potentials. No adjustable parameter was used. This EOS constitutes a strong basis for future development of a predictive model based on ab initio potentials and applicable to more complex compounds.

Extending Noble Gas Solubilities in Water to Higher Temperatures for Environmental Application

Noble gas concentrations in natural waters are widely used to determine ambient temperature conditions during the last intensive contact with the atmosphere (equilibration). Such applications require accurate solubility functions, which so far are available only for the common environmental temperature range between (0 and 35) °C. Nonetheless, environmental scenarios that generate higher surface-water temperatures (such as volcanism) exist. Previous solubility measurements beyond ∼35 °C are sparse or outdated and were determined through equilibration of water with pure noble gases. This can potentially render them not suitable for environmental applications where equilibration with atmospheric air is considered. We therefore conducted new measurements for the solubilities of helium, neon, argon, krypton, and xenon in deionized water equilibrated with atmospheric air at ∼1 bar for temperatures ranging from (25 to 80) °C. These measurements were combined with data from the literature that were obtained in a similar manner and fitted with a commonly used function to determine new noble gas solubility functions valid from (0 to 80) °C. We estimate relative standard uncertainties with a 0.99 level of confidence between 0.015 and 0.030 for the new functions, which are thus suitable for the investigation of environmental high-temperature equilibration scenarios. For temperatures beyond 35 °C, the new functions deviate significantly from previous studies.

Can every substance exist as an amorphous solid?

Many substances can exist as amorphous solids, but it is an open question whether or not all substances can be put into the amorphous form. It has been proposed that the demonstration of pure amorphous argon is the most convincing evidence for the universality of the amorphous state. However, theoretical studies have shown that a non-crystalline structure made by quenching liquid argon is not a solid, for it crystallizes immediately. Here, we demonstrate that amorphous argon model containing triple-shell icosahedral clusters can exist for more than one day below 7 K, supporting the universality of the amorphous state. Our findings open new perspectives not only for making amorphous solids of substances such as pure noble gases and fcc metals which have not yet been put into the amorphous form but also for enhancing the stability of existing amorphous solids.

Optical Emission Spectroscopy as a Diagnostic Tool for Characterization of Atmospheric Plasma Jets

A suitable technique for localized surface treatment of solid materials is an atmospheric pressure plasma jet (APPJ). The properties of the APPJ plasma often depend on small details like the concentration of gaseous impurities what influences the surface kinetics. The simplest and often most useful configuration of the APPJ is presented, characterized by optical emission spectroscopy (OES), and results are discussed in view of various papers. Furthermore, results of additional recent papers on the characterization of the APPJ by OES are presented as well. Because the APPJ is operating at atmospheric pressure, even the water vapor traces may significantly alter the type and concentration of reactive species. The APPJ sustained in noble gases represents a source of vacuum ultraviolet (VUV) radiation that is absorbed in the surface of the treated material, thus causing bond scission. The addition of minute amounts of reactive gases causes significant suppression of VUV radiation and the formation of reactive radicals. These radicals such as OH, O, N, NO, O3, and alike interact chemically with the surface causing its functionalization. Huge gradients of these radicals have been reported, so the surface finish is limited to the area reached by the radicals. Particularly OH radicals significantly prevail in the OES spectra, even when using very pure noble gas. They may cause suppression of other spectral features. OH radicals are especially pronounced in Ar plasmas. Their density decreases exponentially with a distance from the APPJ orifice.

Theoretical investigation of ZIFs as adsorbents or membranes for separating noble gas mixtures: applying a newer method for predicting performances

Zeolitic imidazolate frameworks (ZIFs) possess similar topological structures with zeolites, however a number of characteristic properties of the ZIFs, such as easy incorporation of desired linkers to their structures, tunable pore sizes, high porosities, and large surface areas make them better option for targeted engineering applications. In this respect, cheaper, highly efficient, and selective separation of syngas mixtures using ZIFs has been already shown in the literature. Separation and purification of noble gases, on the other hand, have been achieved using energy demanding cryogenic distillation of air and currently we know little about noble gas separation performances of the ZIFs. Replacing energy intensive gas separation techniques with adsorbent and/or membrane based separation technologies, indeed, have been motivated for decreasing the operational costs, price of the pure noble gases, as well as opening new application areas for the noble gases. In this respect, we theoretically investigate Xe/Kr and Xe/Ar separation performances of eight ZIFs, namely ZIF-6, ZIF-11, ZIF-60, ZIF-67, ZIF-69, ZIF-78, ZIF-79, and ZIF-81 using Grand Canonical Monte Carlo and Molecular Dynamics simulations and calculate Xe permeability and permeation selectivity using a newer method suggested previously by our group. While ZIF-11 shows significant Xe uptake from the noble gas mixtures, ZIF-81 and ZIF-79 show exceptional Xe adsorption selectivities for two gas mixtures at low pressures, 22.5 and 21 for the Xe/Kr and 128 and 120 for the Xe/Ar mixture, respectively. ZIF-69 and ZIF-79 show high Xe permeability (4. $$2\times 1$$ 0 $$^5$$ and 3. $$2\times 1$$ 0 $$^5$$ Barrers) as well as high Xe permeation selectivity (17.35 and 15.85) for the Xe/Ar mixture at 2 bar feed gas pressure. For the Xe/Kr mixture, on the other hand, we observe high Xe permeability and moderate Xe permeation selectivity, especially at low pressures. Comparing with the limited literature available, these ZIFs show promise for selective separation of Xe from its binary mixtures of Kr and Ar at room temperature. We also compare the permeability and permeation selectivity predictions using different approaches, namely the new method and the approximate approach which is commonly used in the literature. Results reveal significant deviations of the approximate approach with respect to the new method, especially for the permeability calculations. Thus, using the new method for determining membrane performances is highly suggested.

Construction of elementary reaction paths of pure and mixed Argon-Xenon clusters : a parallel tempering based study

The problem of studying structural transformation for going from one isomer to another through a transition state is one of considerable interest in chemistry. In this work, we would like to examine the efficiency of the replica exchange Monte Carlo strategy or parallel tempering to search potential energy surface describing the interaction between atoms in noble gas clusters. The systems chosen are both a pure noble gas cluster as well as those formed by two different noble gas entities. Location of minimal structures as well as transition state with the path connecting these three critical points has been carried out for different sizes. To understand the working principles of the parallel tempering method, distribution of structures found in different replicas has been analyzed and insights have been given as to how parallel tempering can be use effectively to handle this problem effectively.

Study of pure and mixed clustered noble gas puffs irradiated with a high intensity (7 × 1019 W/cm2) sub-ps laser beam and achievement of a strong X-ray flash in a laser-generated debris-free X-ray source

AbstractWe present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

A determination of atmospheric helium, neon, argon, krypton, and xenon solubility concentrations in water and seawater

We have determined the concentrations of atmospheric helium, neon, argon, krypton, and xenon in distilled water and seawater equilibrated with moist marine air at one atmosphere over a temperature range from near freezing point to approximately 35 °C and a salinity range of zero to roughly 39.5 PSS78. In all, we made 74 sets of noble gas measurements at 34 distinct temperature and salinity combinations. The experiments included 35 replicate pairs of samples drawn from 35 separate equilibrations, which in turn had three pairs of repeat equilibrations run at close to identical temperatures. We fit the results to an eight-parameter function similar to one commonly used to compute solubility equilibrium concentrations of these gases for environmental waters. Based on an estimate of analytical accuracy, reproducibility of the comparison with secondary atmospheric standards, replicate sample reproducibility, and reproducibility of the repeat equilibrations, we estimate this function to predict equilibrium concentrations at a particular temperature and salinity within this range to overall precisions 0.10% or better. This includes the regression statistics associated with interpolation and analytical errors for fitting the 8-parameter smoothing function. There is an overall systematic uncertainty of 0.15% for all gases, based on our confidence in and experience with the integrity and cross-calibration of our air standards over recent years. Because our methods are calibrated using assumed and explicit atmospheric abundances of these noble gases, any subsequent uncertainties in atmospheric abundances cancel out in the determination, particularly when the oceanographic measurements utilize marine air as a primary standard. Furthermore, measurement at ambient atmospheric abundances avoids any potential co-solvency induced biases introduced by using ~1 atm pure noble gases, as has been done in most previous studies. We compare these determinations to those made by others in the past and find modest but significant systematic differences with those results.

Charge and light production in the charge readout system of a dual phase LAr TPC

For the future neutrino oscillation experiment DUNE, liquid argon time projection chambers with a fiducial mass of 10 kton each are foreseen. The dual phase concept is one of the two implementations considered, wherein electrons produced by ionization in the liquid are extracted to a gaseous region above the liquid where they are amplified. For the amplification, large electron multipliers will be used. The technology was tested in various prototypes, most recently with a 3 × 1 × 1 m3 large setup. An even larger prototype of 6 × 6 × 6 m3 is currently being constructed and will start operation in 2019. An intensive R&D program was carried out with the focus on achieving an effective gain of at least 20. In the simulation study here presented for the first time not only the electron signal is considered but also the ion backflow and the expected production of secondary scintillation light is studied, because the latter might limit the capability of the detector to trigger on low energetic non-beam physics. It is found that the ion backflow and the light yield can be expected to be very large. The results for the effective gain show a discrepancy with experimental data, both in size and shape of the gain curve. Based on literature studies, it is argued that photon feedback might contribute to the gain in detectors filled with pure noble gases, especially in the case of pure argon.

Photoelectron extraction efficiency into Ar-CF4 and Xe-CF4 gas mixtures

Experimental measurements of the extraction efficiency f of the photoelectrons emitted from a reflective CsI photocathode into Ar-CF4 and Xe-CF4 gaseous mixtures are presented, as a function of reduced electric field E/p in the range 0.1 to 3 V cm−1 Torr−1 and as a function of CF4 concentration. The experimental data is compared to Monte Carlo simulation results. The investigation confirms that backdiffusion of low-energy photoelectrons emitted from a photocathode into a gas medium depends strongly on the nature of the gas. The effect is especially significant in pure noble gases, but it can be considerably reduced by the admixture of certain molecular gases, like CF4.

Molecular investigation of gas adsorption, separation, and transport on carbon nanoscrolls: A combined grand canonical Monte Carlo and molecular dynamics study

Carbon nanoscrolls (CNSs), with controllable interlayer distances, have been systematically studied with respect to noble gas adsorption, separation, and transport properties. Grand canonical Monte Carlo simulations were performed on pure noble gases and noble gas mixtures interacting with CNSs at different temperatures. There is separation of gases across a series of CNS interlayer distances at different pressures. The optimal interlayer distance for each noble gas was determined. Selective adsorption was characterized for noble gas mixtures, and the corresponding selectivity was explored. A molecular sieving effect was observed for a certain interlayer gap range, in which the energetically unfavorable smaller gas atoms were better stored in the CNS. In addition, molecular dynamics simulations were conducted to understand the transport properties of noble gases in carbon nanoscrolls in both the cross-sectional and axial directions of the CNS. Gas molecules are found to be captured most strongly when the CNS has the optimal interlayer distance for adsorption.

Predicting stability limits for pure and doped dicationic noble gas clusters undergoing coulomb explosion: A parallel tempering based study.

We have used a replica exchange Monte-Carlo procedure, popularly known as Parallel Tempering, to study the problem of Coulomb explosion in homogeneous Ar and Xe dicationic clusters as well as mixed Ar-Xe dicationic clusters of varying sizes with different degrees of relative composition. All the clusters studied have two units of positive charges. The simulations reveal that in all the cases there is a cutoff size below which the clusters fragment. It is seen that for the case of pure Ar, the value is around 95 while that for Xe it is 55. For the mixed clusters with increasing Xe content, the cutoff limit for suppression of Coulomb explosion gradually decreases from 95 for a pure Ar to 55 for a pure Xe cluster. The hallmark of this study is this smooth progression. All the clusters are simulated using the reliable potential energy surface developed by Gay and Berne (Gay and Berne, Phys. Rev. Lett. 1982, 49, 194). For the hetero clusters, we have also discussed two different ways of charge distribution, that is one in which both positive charges are on two Xe atoms and the other where the two charges are at a Xe atom and at an Ar atom. The fragmentation patterns observed by us are such that single ionic ejections are the favored dissociating pattern. © 2017 Wiley Periodicals, Inc.

Electrons from stable gas crystals lower the threshold in particle detection

A method for growing pure noble gas crystals in an apparatus with high-sensitivity electron detection demonstrates a new approach to low-threshold particle detection with axions in mind.

Piezo-driven valve for disruption mitigation studies in tokamaks

Disruptions are a major issue for the safe operation of tokamaks. Hence the mitigation of disruptive effects is of high priority in view of ITER and DEMO. Previous experiments at ASDEX Upgrade have shown that the injections of massive amounts of gaseous impurities using in-vessel valves mitigate disruptions very efficiently, due to short time of flight of the gas towards the plasma edge and the applicability of pure noble gases. A new valve concept for in-vessel massive gas injection has been developed at ASDEX Upgrade to replace the old valves which suffered from reliability problems. This new valve is a normally closed valve since the valve plate is pressed into the main sealing by a stainless steel bellow (acting as a spring), sealing off the gas reservoir, which can hold 42cm3 of gas at a pressure of up to 5MPa. The valves actuator consists of 4 piezoelectric stacks which are mounted in two parallel pairs into a monolithic titanium frame. This frame is rigidly connected to the valve plate and it amplifies the stroke of the stacks to allow a total stroke of the valve plate of 2.2mm, which is reached after 5ms. The diameter of the straight valve nozzle is 14mm allowing a peak flow rate of 44kPam3/s after 1ms. The valve has a size of 173mm×88mm×70mm.

Pressure effects on the X-ray intrinsic position resolution in noble gases and mixtures

A study of the effect of gas pressure in the position resolution of an interacting X or γ-ray photon in a gas medium is performed. The intrinsic position resolution for pure noble gases (Argon and Xenon) and their mixtures with CO2 and CH4 was calculated for several gas pressures (1–10 bar) and for photon energies between 1 and 60 keV, being possible to establish a linear relation between the intrinsic position resolution and the inverse of the gas pressure in the indicated energy range, as intuitively expected. We show how, at high pressures and low photoelectron energies, this intrinsic 1/P scaling is modified due to the diffusion of the primary ionization in the direction perpendicular to the electric field. In order to evaluate the quality of the method here described, a comparison between the available experimental data and microscopic simulations is presented in this work and discussed. In the majority of cases, a good agreement is observed. The conditions to achieve position resolutions down to 10 μm in a realistic detector are shown and discussed.

A comparative study on the frequency effects of the electrical characteristics of the pulsed dielectric barrier discharge in He/O2 and in Ar/O2 at atmospheric pressure

In this work, a comparative study on the frequency effects of the electrical characteristics of the pulsed dielectric barrier discharges in He/O2 and in Ar/O2 at atmospheric pressure has been performed by means of the numerical simulation based on a 1-D fluid model at frequencies below 100 kHz. The frequency dependences of the characteristic quantities of the discharges in the two gases have been systematically calculated and analyzed under the oxygen concentrations below 2%. The characteristic quantities include the discharge current density, the averaged electron density, the electric field, and the averaged electron temperature. Especially, the frequency effects on the averaged particle densities of the reactive species have also been calculated. This work gives the following significant results. For the two gases, there are two bipolar discharges in one period of applied voltage pulse under the considered frequency range and oxygen concentrations, as occurred in the pure noble gases. The frequency affects the two discharges in He/O2, but in Ar/O2, it induces a strong effect only on the first discharge. For the first discharge in each gas, there is a characteristic frequency at which the characteristic quantities reach their respective minimum, and this frequency appears earlier for Ar/O2. For the second discharge in Ar/O2, the averaged electron density presents a slight variation with the frequency. In addition, the discharge in Ar/O2 is strong and the averaged electron temperature is low, compared to those in He/O2. The total averaged particle density of the reactive species in Ar/O2 is larger than those in He/O2 by about one order of magnitude.

Molecular simulation of adsorption and separation of pure noble gases and noble gas mixtures on single wall carbon nanotubes

Grand Canonical Monte Carlo simulations were performed to systematically study the adsorption and separation of noble gases on single wall carbon nanotube (SWCNT) bundles. Pure noble gases, as well as binary and ternary mixtures, were simulated in carbon nanotube systems under various conditions. Adsorption data was collected at 100K and 300K over a wide range of pressures. Carbon nanotube bundles present distinct adsorption capacities towards different noble gases. In particular, larger and heavier noble gases are easier to be adsorbed at low pressure, while lighter atoms with smaller sizes can be better stored at high pressure. For noble gas mixtures with equal molar loadings, selective adsorption was observed and the selectivity inverted at different pressure ranges according to the choice of mixtures. Furthermore, the influence of loading proportion of the components on the adsorption behavior was investigated by varying the loading partial pressure in binary mixtures from 1% to 99%. The results suggest gas–CNT interactions dominate the adsorption selectivity at low loading conditions, whereas the entropic effect plays a more important role at high loadings.