Rydberg Matter Clusters: Theory of Interaction and Sorption Properties

Sorption capacity of Rydberg matter (RM) clusters is examined for both electronegative and neutral molecules. Sorption isotherm of RM has been determined as a function of gas pressure and time. It is shown that chemisorption is characteristic for electronegative molecules whereas molecules with no affinity to electrons are absorbed by physisorption mechanism. Sorption capacity of RM is shown to be highest for physisorption mechanism. Absorption of molecules by RM clusters can be used either to detect condensed RM formation or both to maintain high vacuum conditions and high purity of noble gas atmospheres. Sorption capacity of RM can significantly exceed conventional getter sorption capacities.     

Vapour permeation and sorption in fluoropolymer gel membrane based on ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide

The emissions of hydrocarbons from fossil fuels into atmosphere entail both an economic loss and an environmental pollution. Membrane separations can be used for vapour recovery and/or vapour removal from the permanent gas stream, given that the appropriate membrane is identified. A neat poly(vinylidene fluoride-co-hexafluoropropylene) membrane is impermeable to both the representatives of aliphatic hydrocarbons and branched hydrocarbons, namely hexane and isooctane, whereas the permeation flux is enhanced by the presence of 80 mass % of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide in the membrane, as detailed in this work. The permeabilities of hydrocarbon vapours were determined from the binary mixture containing hydrocarbon and nitrogen to simulate the real input of an air stream containing a condensable hydrocarbon. The diffusion coefficient determined from sorption measurements was higher for hexane, as would be expected for a smaller molecule, whereas both the sorption isotherms and permeabilities of the hydrocarbons studied were found to be almost identical. It is possible that the sorption effect predominates in the transport mechanism for VOCs/N₂ separations.     

Sorption and dilation of silicone elastomer composites at high gas pressures: The role of interfacial quality

In elastomers the crosslink density, the presence of filler particles, and the volumetric confinement toward sorptive dilation can influence the extent of gas mass uptake. In this study the effects of filler particles on the high-pressure gas mass sorption and the volumetric dilation of a silicone elastomer matrix has been investigated. Glass beads, ca. 30 μm radii, with different surface treatments were incorporated as inclusions in various specimens at relatively low concentrations of ca. 10% by volume. The high-pressure gases used were N₂ and CO₂ up to a maximum ambient pressure of ca. 25 MPa at ca. 20°C and 42°C, respectively. The gas mass sorption was determined by a vibrating reed technique. The sorptive dilation was measured by an ultrasonic transducer operating as a displacement probe. In certain systems the absorbed CO₂ gas was able to disrupt the internal interfaces. This led to an increased gas mass uptake in the corrupted specimen. The N₂ gas did not affect the interfacial bonds. The amount of penetrant uptake was found generally to be reduced when the internal interfaces were not disrupted. The presence of various internal interfaces restrained the sorptive dilation of the elastomeric matrix. These hindrances to the natural sorptive dilation of the elastomer network suppressed the extent of the gas sorption process. This effect has also been investigated separately in detail using model ‘poker chip’ type of specimens of various aspect ratios. The sorptive dilational characteristics have been correlated with the mechanical properties of similar specimens. The influence of an almost complete volumetric confinement on the gas sorption capacity of the silicone elastomer specimen has also been studied. © 1992 John Wiley & Sons, Inc.     

An empirical dependence of frequency in the oscillatory sorption of H2 and D2 in Pd on the first ionization potential of noble gases

Oscillatory heat evolution in sorption of H(2) and D(2) in Pd can be induced by an admixture of ~10 vol.% of an inert gas (He, Ne, Ar, Kr, or N(2)) to either isotope prior to its contact with palladium powder. The oscillations are represented in the form of a calorimetric time series, recorded using a gas flow-through microcalorimeter at the temperatures of 75 °C for D(2) and 106 °C for H(2). For both D(2) and H(2), the oscillation parameters change as a function of the kind of inert gas used: the amplitude increases and the frequency decreases in passing from He to Kr. An empirical dependence of the oscillation frequencies observed for various admixtures and normalized with respect to Kr has been found. Accordingly, the frequency is a function of a product of the first ionization potential and the square root of atomic mass of the inert gas (He, Ne, Ar, Kr, or N(2)). On the other hand, invariance of the thermal effects of sorption is evident from the integrated areas under the calorimetric time series yielding the molar heats of sorption conserved, irrespective of the inert gas admixture. A novel calibration procedure has been devised in order to deal with an instability of calibration factor arising in desorption of H(2) and D(2) from Pd. A method of dynamic calibration factor made it possible to obtain a good agreement between the heats of sorption and desorption of both H(2) and D(2) within individual sorption-desorption cycles for all inert gas admixtures.     

Signal enhancement in desorption nanoelectrospray ionization by custom‐made inlet with pressure regulation

The efficiency of desorption/ionization becomes more critical as the sampled surface area decreases. Desorption electrospray and desorption nanoelectrospray belong to ambient ionizations and enable direct surface analysis including mass spectrometric imaging. Lateral resolution in tens of micrometers was demonstrated for desorption nanoelectrospray previously, but sensitivity of the surface scan can be an issue. For desorption electrospray, the drag force in the source is driven by the flow of used gases and vacuum suction. Ion signal intensity can be improved by controlling the nebulizing gas flow rate or auxiliary pumping of a closed compartment in front of the mass spectrometer inlet. Because nanoelectrospray generates charged droplets without the assistance of a nebulizing gas, only vacuum suction drives the gas flow. In this study, the effect of pressure drop between the atmospheric and evacuated region of a mass spectrometer on the ion signal intensity was investigated for desorption nanoelectrospray. A modification of the commercial inlet was designed. An auxiliary pump was directly connected to an inner compartment of the modified mass spectrometer inlet through a needle valve that enabled the regulation of the reduced pressure. Adjustment of the pressure drop significantly increased signal intensity (more than one order of magnitude in some cases). To a lesser extent, the temperature of a heated capillary (an integral part of the inlet) also influenced the signal intensity. The applicability of desorption nanoelectrospray equipped with pressure regulation was demonstrated by the analysis of synthetic cathinones or a pill of paracetamol. Because pressure in the inlet depends on the diameters of orifices and the power of vacuum systems of mass spectrometers, the effect of the pressure regulation can be different for different instruments. Nevertheless, the presented results confirmed the importance of pressure drop‐driven transport for desorption nanoelectrospray efficiency and can encourage its new applications.     

Determination of total gas content and its composition in Indian PFBR blanket pellets

Total gas content and its composition are important specifications for sintered nuclear fuel pellets particularly in the case of fast breeder reactor fuels. Most commonly, total gas content and its composition is determined by hot vacuum extraction-quadrupole mass spectrometry (HVE-QMS). A number of parameters in this methodology such as temperature, duration of heating for quantitative extraction of evolved gases, total volume of the system, gas analysis conditions etc. need to be optimized for reliable measurements. In addition, sensitivity factors for various gases like H₂, CH₄, N₂, CO, O₂ and CO₂ in quadrupole mass spectrometry required for quantification of results have been determined and validated employing reference gas mixtures of known composition. Employing these optimized conditions total gas content and its composition in blanket pellets (uranium oxide pellets) of Indian prototype fast breeder reactor was determined employing HVE-QMS. The relative expanded uncertainty (at a coverage factor k = 2) in the measurement of total gas content excluding hydrogen was estimated as per ISO guidelines and it was found to be 9.2 %.     

Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures

A sound understanding of any sorption system requires an accurate determination of the enthalpy of adsorption. This is a fundamental thermodynamic quantity that can be determined from experimental sorption data and its correct calculation is extremely important for heat management in adsorptive gas storage applications. It is especially relevant for hydrogen storage, where porous adsorptive storage is regarded as a competing alternative to more mature storage methods such as liquid hydrogen and compressed gas. Among the most common methods to calculate isosteric enthalpies in the literature are the virial equation and the Clausius–Clapeyron equation. Both methods have drawbacks, for example, the arbitrary number of terms in the virial equation and the assumption of ideal gas behaviour in the Clausius–Clapeyron equation. Although some researchers have calculated isosteric enthalpies of adsorption using excess amounts adsorbed, it is arguably more relevant to applications and may also be more thermodynamically consistent to use absolute amounts adsorbed, since the Gibbs excess is a partition, not a thermodynamic phase. In this paper the isosteric enthalpies of adsorption are calculated using the virial, Clausius–Clapeyron and Clapeyron equations from hydrogen sorption data for two materials—activated carbon AX-21 and metal-organic framework MIL-101. It is shown for these two example materials that the Clausius–Clapeyron equation can only be used at low coverage, since hydrogen’s behaviour deviates from ideal at high pressures. The use of the virial equation for isosteric enthalpies is shown to require care, since it is highly dependent on selecting an appropriate number of parameters. A systematic study on the use of different parameters for the virial was performed and it was shown that, for the AX-21 case, the Clausius–Clapeyron seems to give better approximations to the exact isosteric enthalpies calculated using the Clapeyron equation than the virial equation with 10 variable parameters.     

Determination of anabolic steroids with gas chromatography-ion trap mass spectrometry using hydrogen as carrier gas.

Helium is considered to be the ideal carrier gas for gas chromatography/mass spectrometry (GC/MS) in general, and for use with an ion trap in particular. Helium is an inert gas, can be used without special precautions for security and, moreover, it is needed as a damping gas in the trap. A disadvantage of helium is the high viscosity resulting in long GC run times. In this work hydrogen was tested as an alternative carrier gas for GC in performing GC/MS analyses. A hydrogen generator was used as a safe source of hydrogen gas. It is demonstrated that hydrogen can be used as a carrier gas for the gas chromatograph in combination with helium as make-up gas for the trap. The analysis time was thus shortened and the chromatographic performance was optimized. Although hydrogen has proven useful as a carrier gas in gas chromatography coupled to standard detectors such as ECD or FID, its use is not mentioned extensively in the literature concerning gas chromatography-ion trap mass spectrometry. However, it is worth considering as a possibility because of its chromatographic advantages and its advantageous price when using a hydrogen generator.     

小型高分辨电子轰击离子源反射式飞行时间质谱仪的研制

常用的气体分析质谱仪使用四极杆质谱作为分析器,分辨率一般低于300,无法解决同质量数离子带来的干扰问题.本实验自行研制了一种小型高分辨气体分析质谱仪,它采用电子轰击离子源反射式飞行时间质量分析器.仪器腔体总长45 cm,在m/z 28的位置,质量分辨率达到3000(Full width at half maximum,FWHM),实现了CO和N2的半峰谷分离;在m/z 69的位置,仪器分辨率达到5000(FWHM).在直接大气压进样条件下,可以检测到空气中136Xe(含量7.8 μ g/m3)和80Kr(含量2.8 μg/m3).使用ADC采集时,仪器的动态范围为1 06.该仪器将作为高端气体质谱仪,应用于过程监测在线分析、环境有机挥发物研究、热分析质谱及催化反应监测等领域.     

Influence of carbon dioxide in the determination of oxygen in copper by reduction fusion

It has been reported that copper melted in a graphite crucible at high temperature will give off its oxygen content mainly as CO and partially as CO(2). Thus if oxygen in copper is determined by means of apparatus designed to measure only CO as the reaction product, the results are obviously liable to error. Methods of suppressing formation of CO(2) during the fusion process are proposed. When the oxygen is determined by gas chromatography, formation of CO(2) can be suppressed by adding a 0.5% Si-1.5% NiCu bath-alloy together with the copper sample or by inserting a spectrographically pure carbon rod into the graphite crucible used for the fusion. When the oxygen is determined by coulometry, formation of CO(2) can be suppressed by the addition of the SiNiCu bath-alloy or by appropriate modification of the graphite crucible to obtain an optimum working temperature. The results obtained by either method are in agreement with those obtained by a modified vacuum fusion method in which CO and CO(2) can both be measured. These methods have been validated by analysis of two standard reference materials.     

The relative contribution of adsorption to the overall sorption and transport of small molecules in amber

In 1987, Berner and Landis reported that upon vacuum grinding of 80 million year old amber, a gas mixture was released which suggested an oxygen-rich prehistoric environment. Fundamental to their argument was the assumption that amber, an organic glass formed during the fossilization of tree sap, is a perfect sealant. Their assumption was challenged by three technical comments which collectively concluded that gases diffuse readily through amber. In order to defend their key assumption that gases are perfectly trapped in amber, Berner and Landis dismissed the data obtained through gravimetric sorption experiments as only a measure of surface adsorption rather than bulk absorption in and concomitant diffusion through the amber matrix. The validity of interpreting these gravimetric experiments as a measure of bulk diffusion is demonstrated by exploring the physical basis for interpreting gravimetric sorption data. Most importantly, new experimental gravimetric sorption data are presented which demonstrate an explicit separation of adsorption from diffusion-controlled absorption and also reveal that adsorption accounts for a very small fraction of the total sorption in amber.     

Removal of heat of adsorption from adsorbent by forced convection

An analytical mathematical model is used to investigate the effectiveness of forced convection for removal of the heat of adsorption from an adsorbent mass undergoing a differential adsorption process in a flow system. An example of such a process is measurement of gas adsorption kinetics using a differential adsorption bed. Isothermal operation may not be achieved even when a high gas flow rate is used, particularly if the sorption kinetics is relatively fast. Very small changes in the adsorbent temperature can cause significant departure from the isothermal uptake behavior when the heat of adsorption is moderately large. A criterion for validity of isothermal data analysis is given.     

Nachweis und Analyse kleinster Grasmengen in Metallen mit dem Massenfilter

Zusammenfassung Die Bestimmung kleinster Gasgehalte in Metallen nach dem Heißextraktionsverfahren wird an der unteren Nachweisgrenze durch Sorptionseffekte empfindlich gestört. Die hier beschriebene Meßanordnung benutzt daher einen Ultrahochvakuumbehälter als Extraktionskammer. Mit Hilfe von Bayard-Alpert-Vakuummeter und Massenfilter werden Total- und Partialdrucke während der Probenentgasung als Funktion von Zeit und Temperatur fortlaufend registriert, so daß Sorptionseffekte und der Einfluß von Gashäuten auf der Probenoberfläche weitgehend eliminiert werden können.Am Beispiel der Restgasbestimmung in Kupfer wird gezeigt, daß auf diese Weise eine Nachweisgrenze von einigen 10^–3 ppm erreichbar ist und außerdem Aufschlüsse über die Kinetik der Gasabgabe gewonnen werden.

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Summary The detection of very small gas contents in metals according to the hot extraction method is appreciably disturbed by sorption effects at the lower detection limit. The measuring setup described therefore uses an ultra-high vacuum vessel as extraction chamber. With the aid of a Bayard-Alpert vacuum gauge and a mass filter the total and partial pressures during the specimen outgassing process are continously recorded as a function of time and temperature, thus eliminating to a large extent the above sorption effects and the influence of gas films on the surface of the specimen.The example given (detection of the residual gas content in copper) shows that by this method a detection limit of a few 10^–3 ppm is attainable. Information is also gained with respect to the kinetics of gas evolution.

     

Vacuum balance and related studies of cokes used in steel production

The reactivities of cokes derived from coal blends used in the steel industry have been compared. Kinetics and rates of oxidation have been correlated with changes in surface area and porosity determined by gravimetric gas sorption using vacuum microbalances.During the earlier stages of oxidation of the cokes in carbon dioxide at 1000 °C, the surface area increases considerably, reaching a maximum at about 20 % burn-off. This change in surface area is ascribed to formation of pores at the surface, including opening of initially-closed pores as the burning proceeds.At higher percentage burn-offs, the surface area decreases to a very low value as the ash sinters with loss of porosity.     

On the sorption of gas mixtures by polymer glasses

It was realized recently that various phenomena, related to the sorption of small molecules in polymer glasses could be described within the framework of a site distribution (SD) model. According to the SD model, non-equilibrium structure of glassy polymer leads to the distribution of sorption energies within the interchain holes. The parameters of the distribution for the given polymer–gas system could be expressed through the polymer–gas characteristics or evaluated from the experimental pressure–concentration isotherms. In this work we show how these parameters could be used to predict the sorption isotherms for gas mixtures. The suppression of solubility of each component by the other components, which is the main feature of mixed sorption by polymer glasses can be described within the SD model through the competitive occupancy of low-energy sorption sites. The clear physical meaning of the energy distribution parameters allows to analyze the role of different factors on the competitive sorption from gas mixtures. The comparison of SD model with the other theoretical approaches are given and new experiments, which could check the validity of our approach are proposed.     

On the theory of the mechanochemical sorption-striction phenomenon in nanoporous bodies with dispersion forces

The soption-striction phenomenon is a change in the dimensions of a porous body in the course of sorption due to the strain caused by the action of molecular forces. The formulation of the theory of the phenomenon includes the following problems: the statistical-mechanical calculation of the pressure tensor in the pore interior as a function of the pore shape and size; the analysis of the role of surface tension in the mechanical equilibrium condition at the pore wall and producing strain at various mechanisms (physical or chemical) of sorption; the calculation of the body strain within the theory of elasticity. The calculation of the pressure tensor was performed for spherical, cylindrical, and flat (slit-like) pores using asymptotic relations for ordinary dispersion forces (in the context of the nano-scaled pore size) and dispersion forces with electromagnetic retardation (for micropores of larger dimensions), with the pair potential exponents −6 and −7, respectively. The results obtained consider both an initial contraction of a porous body in a vacuum and an additional contraction, if any, or the body expansion on the initial stage of the gas sorption. The exact calculation of strain is given for a cylindrical and spherical pore. The role of surface tension is shown to be reduced, first, to the initial contractive strain of a porous body in a vacuum and, second, to the body dilatation in the course of the gas sorption. A small additional contraction of a porous body on the initial stage of sorption (that, as is shown, cannot be caused by surface tension) is explained by the peculiarities of the sorbate pressure tensor in a pore. The effect is more pronounced the smaller the pore size and the lower the temperature, and is typical for nanoporous bodies. A general consideration based on the Irving-Kirkwood pressure tensor qualitatively confirms the regularities established for any kind of molecular interaction. Original Russian Text A.I. Rusanov, F.M. Kuni, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 3, pp. 404-426.     

真空紫外光电离质谱技术进展及其在快速分析中的应用

真空紫外光电离源(VUV-PI)是一种普适性的质谱软电离源,真空紫外光电离质谱谱图无碎片、易解析、灵敏度高,适合于在线快速分析。真空紫外光电离质谱根据分析对象不同可以直接采用单光子电离或添加掺杂剂实现化学电离,能实现气、液、固体分析,也可实现成像分析。该文介绍了真空紫外光电离源的电离原理、光源类型,分析了光电离质谱灵敏度的影响因素及其技术改进措施,并阐述了真空紫外光电离质谱技术在环境污染物、化工产物在线分析、国家安全分析以及生物医学分析中的相关应用研究。最后,总结了真空紫外光电离源的优缺点,并对真空紫外光电离技术在性能和应用方面的发展前景进行了展望。     

Comparison of three models for permeation of CO2/CH4 mixtures in poly(phenylene oxide)

Two models for the permeability of pure gases have been extended to include binary gas mixtures. The first is an extension of a pure gas permeability model, proposed by Petropoulos, which is based on gradients of chemical potential. This model predicts the permeability of components in a gas mixture solely on the basis of competition for sorption sites within the polymer matrix. The second mixed gas model follows an earlier analysis by Barrer for pure gases which includes the effects of saturation of Langmuir sites on the diffusion as well as the sorption processes responsible for permeation. This generalized “competitive sorption/diffusion” model includes the effect of each gas component on the sorption and diffusion of the other component in the mixture. The flux equations from these two models have been solved numerically to predict the permeability of gas mixtures on the basis of pure gas sorption and transport parameters. Both the mixed gas Petropoulos and competitive sorption/diffusion model predictions are compared with predictions from the earlier simple competitive sorption model based on gradients of concentration. An analysis of all three models is presented for the case of CO₂/CH₄ permeability in poly(phenylene oxide) (PPO). As expected, the competitive sorption/diffusion model predicts lower permeability than either of the models which consider only competitive sorption effects. The permeability depression of both CO₂ and CH₄ predicted by the competitive sorption/diffusion model is roughly twice that predicted by the competitive sorption model, whereas the mixed gas Petropoulos model predictions for both gases lie between the other two model predictions. For the PPO/CO₂/CH₄ system, the methane permeability data lie above the predictions of all three models, whereas CO₂ data lie below the predictions of all models. Consequently, the competitive sorption/diffusion model gives the most accurate prediction for CO₂, while the simple competitive sorption model is best for methane. The effects of mixed gas sorption, fugacity, and CO₂-induced dilation were considered and do not explain the inaccuracies of any of the models. The relatively small errors in mixed gas permeability predictions using either of the three models are likely to be related to “transport plasticization” of PPO owing to high levels of CO₂ sorption and its effect on polymer segmental motions and gas diffusivity.     

Heterogeneous reaction of suspended phosmet particles with NO3 radicals

As an organophosphorous insecticide, phosmet is widely used for plant protection as well as against the ectoparasites on productive livestock. It emits into the atmosphere in both gas and particulate phases via spray drift from treatments and postapplication emissions, but its degradation in the atmosphere is not well-known up to now. In this study, the heterogeneous reaction of phosmet absorbed on the azelaic acid particles with NO(3) radicals is investigated in real-time using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). Two primary products and their nitro-substituted derivates are observed. The apparent reaction rate of phosmet particles with NO(3) radicals is also obtained by a relative rate method with isoprene and 1,4-cyclohexadiene as the reference compounds. The concentrations of the reference substance and phosmet particles are synchronously detected with an atmospheric gas analysis mass spectrometer and the VUV-ATOFMS. Under the experimental conditions, the average apparent reaction rate obtained is (1.92 ± 0.09) × 10(-12) cm(3) molecule(-1) s(-1), and the corresponding atmospheric lifetime toward NO(3) radicals is roughly estimated to be ~0.3 h.     

Rapid characterization of biomaterials by field ionization

The direct application of field ionization to complex biomaterials is described. Volatiles are characterized by gas chromatography mass spectrometry. Complex involatile materials are investigated by thermal degradation in high vacuum. The methodology and typical analytical features of pyrolysis of biopolymers and soft ionization of their pyrolysates in the high electric field are described. The combination of direct, in-source pyrolysis mass spectrometry and pyrolysis gas chromatography mass spectrometry is used in two steps. Firstly, for fast profiling of the complex materials and, secondly, for identification of significant products of the controlled thermal degradation process. In particular, temperature programmed/time-resolved pyrolysis field ionization mass spectrometry has been shown to be an efficient analytical tool as demonstrated for typical examples such as chitin, cellulose, hemicellulose, lignin, wood, peat and coal. Recent results on foodstuffs such as coffee, chocolate, tea and biscuits illustrate the potential of the combined methods for routine work.