Condensation of Argon,Monosilane and Their Mixtures in a Pulse Free Jet

Pulse supersonic outflow of Ar, SiH₄ and Ar + SiH₄ gas mixture (where monosilane is a small admixture) was studied experimentally by the method of molecular beam mass-spectrometry. Using argon as an example we have shown that condensation processes at the quasi-stationary region of a pulse flow and within a stationary jet are similar. In the flows of pure gases clusters of argon and silane (hydrogenated silicon) and in the mixture argon – silane complexes were registered. The dependencies of the intensities of monomer and cluster ions on stagnation pressure were investigated. It was shown that in the mixture jet at low stagnation pressures the condensation process with the formation of monosilane clusters takes place and at high pressures mixed argon-silane complexes are formed. The parameters of flow transition into the regime of developed condensation were determined for pure gases and their mixture.     

Formation of silver clusters in nozzle expansions

The first successful experiments to generate continuum silver cluster beams from nozzle expansions are described. A mixture Ar/Ag expands out of a conical nozzle (0.35 mm dia., 10° cone angle, length 17 mm). At 2150 K, total pressure 300 kPa, silver partial pressure 8 kPa the silver intensity measured with a rate meter 479mm away from the source is 1.8 nm/s, or 0.02 g m^?2s^?1. The data for the onset of clustering confirm the predictions of the scaling laws developed to compare condensation in nozzle expansions of metal vapors with that of rare gases.     

Clathrate hydrate formation after CO2-H2O vapour deposition

We study vapour condensation of carbon dioxide and water at 77 K in a high-vacuum apparatus, transfer the sample to a piston-cylinder apparatus kept at 77 K and subsequently heat it at 20 MPa to 200 K. Samples are monitored by in situ volumetric experiments and after quench-recovery to 77 K and 1 bar by powder X-ray diffraction. At 77 K a heterogeneous mixture of amorphous solid water (ASW) and crystalline carbon dioxide is produced, both by co-deposition and sequential deposition of CO(2) and H(2)O. This heterogeneous mixture transforms to a mixture of cubic structure I carbon dioxide clathrate and crystalline carbon dioxide in the temperature range 160-200 K at 20 MPa. However, no crystalline ice is detected. This is, to the best of our knowledge, the first report of CO(2) clathrate hydrate formation from co-deposits of ASW and CO(2). The presence of external CO(2) vapour pressure in the annealing stage is not necessary for clathrate formation. The solid-solid transformation is accompanied by a density increase. Desorption of crystalline CO(2) atop the ASW sample is inhibited by applying 20 MPa in a piston-cylinder apparatus, and ultimately the clathrate is stabilized inside layers of crystalline CO(2) rather than in cubic or hexagonal ice. The vapour pressure of carbon dioxide needed for clathrate hydrate formation is lower by a few orders of magnitude compared to other known routes of CO(2) clathrate formation. The route described here is, thus, of relevance for understanding formation of CO(2) clathrate hydrates in astrophysical environments.     

Production of carbon disulphide dimers by an adiabatic gas expansion method

The production of carbon disulphide dimers by adiabatic gas expansion of a mixture comprised of CS₂ vapour and Ar is studied by using an electron impact ion source and a double focusing sector field mass spectrometer. Results of measurements of the generation of (CS₂)₂⁺ cluster ions versus the stagnation pressure (0–160 kPa) at several stagnation temperatures (267–300 K) are described. An empirical formula describing the carbon disulphide dimer production is proposed.     

Characteristic analysis of cavitation bubbles in carbon dioxide fluid

After analysing the characteristics of bubble cavitation in high-pressure carbon dioxide (CO₂) fluid, cavitation conditions and some correlative physical characteristics are investigated. The results show that the ultrasonic intensity of liquid carbon dioxide to make cavitation occur is affected by the initial radius of the bubbles, hydrostatic pressure, temperature and vapour pressure within the bubbles in liquid CO₂. At the low frequency of ultrasound, the phase-speed of the liquid CO₂ gradually approaches the sound speed of the pure liquid when void fraction increases. At high frequency, the phase-speed is nearly equal to the sound speed in the liquid under different void fractions. The attenuation of ultrasound in liquid carbon dioxide reaches a maximum near the resonance frequency and then decreases when frequency either increases or decreases. At the resonance frequency, the phase-speed and the attenuation increase when the void fraction increases.     

Reactive scattering of a helium seeded oxygen atom beam

A high pressure microwave discharge source operating with a dilute mixture of O₂ in He has been used to produce a supersonic nozzle beam of O atoms seeded in He. This source has been used to study the reactive scattering of O atoms with Cl₂ and CS₂ molecules at an initial translational energy E = 38 kJ mol^?1. Velocity distribution of reactive scattering were measured over a wide angular range by cross-correlation time-of-flight analysis. The O + Cl₂ reaction proceeds via a short-lived collision complex while the O + CS₂ reaction follows a stripping mechanism.     

High pressure solubility data of carbon dioxide in (tri-iso-butyl(methyl)phosphonium tosylate + water) systems

Ionic liquids are attracting great attention nowadays due to their interesting properties which make them useful in a broad range of applications including reaction media or separation/capture of environmentally hazardous gases such as carbon dioxide. In many cases, for practical and/or economical reasons, the use of aqueous solutions of ILs would be preferable to their use as pure compounds.In this work, high pressure equilibrium data for the {carbon dioxide (CO₂) + tri-iso-butyl(methyl)phosphonium tosylate [iBu₃MeP][TOS] + water system were measured at temperatures ranging from (276 to 370) K and pressures up to 100 MPa. Measurements were performed using a high-pressure cell with a sapphire window that allows direct observation of the liquid–vapour transition. Mixtures with different IL concentrations were studied in order to check the influence of the amount of IL on the solubility of CO₂ in the aqueous mixture.The results show that the presence of IL enhances the solubility of CO₂ in the (IL + water) system revealing a salting-in effect of the IL on the solubility of CO₂. The appearance of a three phase region was observed for IL concentrations higher than 4 mol% of IL in water when working at pressures between 4 and 8 MPa and temperatures between (280 and 305) K. In this range, the upper limit of the VLE region observed is shown to increase with the temperature being almost independent of the IL initial concentration in the mixture.     

Double Tetrametaphosphates Ca2-xMx IIP4O12

Abstract

The thermal synthesis of Ca₂-_xM_x ^IIP₄O₁₂ (M^II=Mn, Co; x=0,5 -1,5) starts from a mixture of carbonates of the respective metals and phosphoric acid. Formation of the products has been followed by TA (thermal analyses) under quasi-isothermal-isobaric conditions and compared with that of simple tetrametaphosphates at the same conditions (Refs 1,2). Distinct effect of water vapour pressure on the condensation reaction course is indicated; enhanced pressure retards the reactions and shifts them to higher temperatures, but it favours formation of the desired condensation intermediates and, especially, increases the yield of the double tetrametaphosphate. Monoclinic structure of the microcrystalline products obtained has been confirmed. The lattice parameters have been determined, and their shift to lower values with increasing x has been observed. The TA methods have been used to follow thermal stability of the products and to determine the temperatures of melting and of reversible transition to higher linear phosphates (polyphosphates). For these vitreous products we have determined their softening temperatures, and temperature, heat, and energy of the recrystallization connected with reverse formation of the double tetrametaphosphates. The reversible transition is also used for synthesis of the pure products (Ref. 3) which appear to be promissing as special inorganic pigments (Ref. 4).     

Enhancement of negative ion currents by argon/CO2 mixtures in an electron impact ion source

Argon and mixtures of argon with carbon dioxide in the range of 1–50% have been used as moderator gases for negative ion production in an electron impact ion source of a VG ZAB-2F mass spectrometer. The enhancement of quasi-molecular anion ([M – H]^?) currents of oxygen-containing samples has been studied. It is a function of the composition of moderator gas mixture, moderator gas pressure, and sample pressure in the ion source. Most intensive quasi-molecular anion currents have been observed at a pressure in the ion source of c. 2.5 × 10^?5 Torr (measured by the ion gauge remote from the ion source of the ZAB-2F) using a moderator gas mixture of 10% CO₂ in argon. Fragmentation of the samples may be increased by increasing the concentration of CO₂ in the moderator gas.     

Reactive scattering of a neon seeded oxygen atom beam

A high pressure microwave discharge source operating with a dilute mixture of O₂ in Ne has been used to produce a supersonic nozzle beam of O atoms seeded in Ne. This low energy supersonic O atom beam has been used to study the reactive scattering of O atoms with Cl₂ and CS₂ molecules at an initial translational energy E = 13 kJ mol^?1. The results are compared with rective scattering from the same reactions using a high energy O atom beam formed by seeding O atoms in He. The O + Cl₂ reaction proceeds via a short-lived collision complex where the lifetime of the collision complex depends upon the initial translational energy. However the O + CS₂ reaction follows a stripping mechanism which is unaffected by initial translational energy.     

A predictive approach based on the Simha–Somcynsky free‐volume theory for the effect of dissolved gas on viscosity and glass transition temperature of polymeric mixtures

The gas concentration and pressure effects on the shear viscosity of molten polymers were modeled by using a unified approach based on a free volume theory. A concentration and pressure dependent “shift factor,” which accounts for free volume changes associated with polymer‐gas mixing and with variation of absolute pressure as well as for dilution effects, has been herein used to scale the pure polymer viscosity, as evaluated at the same temperature and atmospheric pressure. The expression of the free volume of the polymer/gas mixture was obtained by using the Simha and Somcynsky equation of state for multicomponent fluids. Experimental shear viscosity data, obtained for poly(ε‐caprolactone) with nitrogen and carbon dioxide were successfully predicted by using this approach. Good agreement with predictions was also found in the case of viscosity data reported in the literature for polystyrene and poly(dimethylsiloxane) with carbon dioxide. Free volume arguments have also been used to predict the T_g depression for polystyrene/carbon dioxide and for poly(methyl methacrylate)/carbon dioxide mixtures, based on calculations performed, again, with the Simha and Somcynsky theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1863–1873, 2006     

Formation of carbon nanoparticles by the condensation of supersaturated atomic vapor obtained by the laser photolysis of C3O2

A new technique is suggested for obtaining nanoparticles from highly supersaturated vapor resulting from the laser photolysis of volatile compounds. The growth of carbon nanoparticles resulting from C₃O₂ photolysis has been studied in detail. Absorbing UV quanta (from an Ar-F excimer laser), C₃O₂ molecules decompose to yield atomic carbon vapor with precisely known and readily controllable parameters. This is followed by the condensation of supersaturated carbon vapor and the formation of carbon nanoparticles. These processes have been investigated by the laser extinction and laser-induced incandescence (LII) methods in wide ranges of experimental conditions (carbon vapor concentration, nature of the diluent gas, and gas pressure). The current and ultimate particle sizes and the kinetic parameters of particle growth have been determined. The characteristic time of particle growth ranges between 20 and 1000 μs, depending on photolysis conditions. The ultimate particle size determined by electron microscopy is 5–12 nm for all experimental conditions. It increases with increasing total gas pressure and carbon vapor partial pressure and depends on the diluent gas. The translational energy accommodation coefficients for the Ar, He, CO, and C₃O₂ molecules interacting with the carbon particle surface have been determined by comparing the LII and electron microscopic particle sizes. A simple model has been constructed to describe the condensation of carbon nanoparticles from supersaturated atomic vapor. According to this model, the main process in nanoparticle formation is surface growth through the addition of separate atoms to the nucleation cluster. The nucleus concentrations for various condensation parameters have been determined by comparing experimental and calculated data.     

Direct temperature measurement in alkali halide cluster beam

The temperature of a sodium fluoride cluster beam produced by laser vaporization is estimated from the rotationally-resolved laser spectroscopy of the Na₂ dimer. The cluster beam is obtained by laser vaporization of a sodium rod in a mixture of helium containing a small amount (1%) of SF₆. Both rotational and vibrational temperatures (respectively 170 K and 400 K) are much higher than expected from a simple theoretical model of a supersonic beam. These temperatures can be lowered to 70 K and 250 K respectively by cooling the nozzle to liquid nitrogen temperature.     

Beam-injection flame furnace AAS: comparison of different nozzle types for beam generation and application of sub-critical liquid carbon dioxide as carrier and gas pressure pump

In beam injection flame furnace AAS (BIFF-AAS) the sample is introduced as a free-flying high-speed liquid beam into an AAS flame-heated nickel tube, resulting in a considerable improvement in the power of detection. For optimization of beam generation different nozzle types (smooth jet nozzles, turbulent working nozzles) have been compared at different pressures. It was found that the type of the nozzle hardly influences the analytical signal. However, the flow rates resulting from the different inner diameters of the nozzles and the applied pressures led to drastic changes in the analytical signal. For these investigations a recently developed 0.6 MPa (84 psig) diaphragm pump system was used. Furthermore, for the first time ever sub-critical liquid carbon dioxide has been used simultaneously as a liquid gas-pressure pump, as carrier in a flow-injection system (FIA), and for the beam generation. Transport of the carrier takes place as a result of the head pressure (6 MPa) of the liquid CO₂ in the gas cylinder. For volatile elements (e.g. Cd, Hg, Pb, and Tl) detection limits between 0.2 µg L^–1 (Cd) and 28 µg L^–1 (Hg) were found, the standard deviation was from 0.6% to 3.2% depending on the element, concentration, and sample volume used. The use of liquid CO₂ as a carrier in FIA systems opens up new possibilities for online sample pretreatment and trace preconcentration.     

Use of x-ray microtomography to visualise dynamic adsorption of organic vapour and water vapour on activated carbon

X-ray microtomography coupled with image analysis was used to quantify the adsorption of vapours on activated carbon beds. This technique was tested using three different challenges: CCl₄, water vapour and a mixture of water- and organic vapour. It is shown that the used technique allows determining the adsorption front progress in the case of organic vapour and mixture of water and organic vapour whereas the existence of this front was not so obvious in the case of water vapour. Experimental results obtained for organic vapours were interpreted on the basis of the Wheeler-Jonas equation: a good agreement was found between experimental and theoretical breakthrough times.     

Reversible isopentane-induced depression of carbon dioxide permeation through polycarbonate

Permeability data are reported for carbon dioxide in Lexan polycarbonate at 35°C. Measurements were made for both pure carbon dioxide and for a mixed feed consisting of carbon dioxide with a 117.8-torr (0.155-atm) Partial pressure of isopentane. The effects of varying upstream CO₂ driving pressure from 1 up to 20 atm were studied. The permeability to CO₂ is reduced significantly in the presence of isopentane; however, the fractional depression of the CO₂ permeability due to the isopentane at low driving pressures is much more significant than at high CO₂ driving pressures. The well-known pressure dependence of carbon dioxide permeabilities in glassy polymers, therefore, is largely diminished by introducing isopentane to the pure carbon dioxide feed. These observations are consistent with a model for transport in glassy polymers which explains the observed trends in terms of competition between the two penetrants for microvoid sorption sites existing in the non-equilibrium glassy polymer. Exclusion of carbon dioxide from microvoid sorption sites by the more condensable isopentane preempts transport through the microvoid regions, resulting in the observed depression of the CO₂ permeability.     

Low pressure solubility and thermodynamics of solvation of oxygen,carbon dioxide,and carbon monoxide in fluorinated liquids

The solubility of oxygen, carbon dioxide, and carbon monoxide in three fluorinated liquids – perfluorohexylethane, perfluorooctane and bromoperfluorooctane – is presented. Mole fraction solubilities were calculated from new experimental Ostwald coefficient data for CO₂ and CO, and from previously published values for O₂, associated with original values of density and vapour pressure for the pure solvents. Carbon dioxide is the most soluble gas with mole fraction solubilities of the order of 10⁻². Oxygen and carbon monoxide are one order of magnitude less soluble. The measurements were done as a function of temperature between (288 and 313) K and from the variation of the calculated Henry’s law constants with temperature, the thermodynamic properties of solvation such as the Gibbs free energy, the enthalpy and the entropy were calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry’s law constants from appropriate smoothing equations is of 1% for carbon dioxide and oxygen and of 3% for carbon monoxide. The data obtained here are judged accurate to within ±5%.     

Molecular dynamics studies to understand the mechanism of heat accommodation in homogeneous condensing flow of carbon dioxide

Using molecular dynamics (MD), we have studied the mechanism of heat accommodation between carbon dioxide clusters and monomers for temperatures and cluster size conditions that exist in homogeneous condensing supersonic expansion plumes. The work was motivated by our meso-scale direct simulation Monte Carlo and Bhatnagar-Gross-Krook based condensation simulations where we found that the heat accommodation model plays a key role in the near-field of the nozzle expansion particularly as the degree of condensation increases [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. The heat released by nucleation and condensation and the heat removed by cluster evaporation can be transferred or removed from either the kinetic or translational modes of the carbon dioxide monomers. The molecular dynamics results show that the time required for gas-cluster interactions to establish an equilibrium from an initial state of non-equilibrium is less than the time step used in meso-scale analyses [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. Therefore, the good agreement obtained between the measured cluster and gas number density and gas temperature profiles with the meso-scale modeling using the second energy exchange mechanism is not fortuitous but is physically based. Our MD simulations also showed that a dynamic equilibrium is established by the gas-cluster interactions in which condensation and evaporation processes take place constantly to and from a cluster.     

Sorption of CO2, C2H4, N2O and their binary mixtures in poly(methyl methacrylate)

Sorption of carbon dioxide, ethylene, and nitrous oxide in poly(methyl methacrylate) (PMMA) at 35°C has been characterized for each gas as a pure component and for mixtures of carbon dioxide/ethylene and carbon dioxide/nitrous oxide. Pressures up to 20 atm were examined. Pure-component sorption isotherms are concave to the pressure axis for each of the gases. This behavior is accurately described by the dual-mode sorption model. Using only the purecomponent dual-mode parameters and the generalization of the model for gas mixtures, one can predict the total concentration of gas sorbed in the polymer to within an average deviation of ±2.01% for the CO₂/C₂H₄/PMMA system and ±0.98% for the CO₂/N₂O/PMMA system. In both systems, for each component of the mixture, sorption levels were lower than corresponding pure-component sorption levels at pressures equal to the partial pressure of the respective components in the mixture. Depression of the sorbed concentration in mixture situations appears to be a general feature of the above systems and can be substantial in some situations. For the CO₂/C₂H₄/PMMA system, use of pure-component sorption data to estimate the total sorbed concentration in the mixture would be in error by as much as 40% if one failed to account for competition phenomena responsible for depression in mixed-gas situations. Mixture pressures as high as 20 atm were studied for both systems and in the CO₂/N₂O/PMMA system sorbed concentrations reach 33.90 [cm³(STP)/cm³ polymer] without any significant deviation from model predictions.