bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of the Transient Grating Method to the Measurement of Transport Properties for High Pressure Fluids
Authors: Kimura Y. , Kanda D. , Terazima M. , Hirota N. 
Published: July 2012

AbstractWe have applied the transient grating method to the measurement of the transport properties for high pressure fluids, such as carbon dioxide and trifluoromethane from the gaseous‐ to the liquid‐density regions for the first time. Using nitrobenzene and methyl red as probe moolecules, we have made the transient grating in a high pressure fluid by a nanosecond‐pulsed laser. By the analysis of the time profile of the transient grating signal in sub‐microsecond to sub‐millisecond range, we have succeeded in measuring the density and the temperature dependences of various transport properties such as the thermal diffusion constant, the sound velocity, the sound absorption, and the mass diffusion constant under the same experimental condition. The thermal diffusion constant of our measurement is identical with 4% error to the value reported in literature, irrespective of probe molecules. We have determined the sound velocity within 0.5% error in a high frequency region around hundreds of MHz. The mass diffusion constant of methyl red is determined within 5% error in trifluoromethane at high densities. We have also demonstrated that the thermal diffusion obeys the critical exponent near the critical point.
Calculation of the Static Dielectric Constant of Multipolar Mixtures by Perturbation Theory. An Application to Supercritical Water‐Benzene Mixtures
Authors: Goldman Saul , Joslin Chris 
Published: July 2012

AbstractSecond‐order perturbation theory for the molecular pair correlation function, together with a y‐expansion of the static dielectric constant (ϵ) is used to predict and interpret ϵ for supercritical benzene‐water mixtures. Our predictions are compared directly with experimental results. We find that this approach, which was previously found successful provided y<3 for neat multipolar fluids, is also successful here in predicting the excess mixture dielectric constant, λϵ. The results are quantitative to semi‐quantitative in accuracy depending slightly on the model chosen and the composition of the mixture. No adjustable parameters were used. We interpret our results in terms of underlying molecular clusters, and make a comparison with the predictions of another (non‐molecular) theory.
Magnetic Relaxation and Anisotropic Molecular Reorientation of Liquid 3‐Acetylpyridine
Authors: Suchański W. , Peplińska B. , Kempka M. 
Published: July 2012

AbstractThe nuclear spin‐lattice relaxation times of 13C and 4N as well as the nuclear Overhauser enhancement factor have been measured as a function of temperature for liquid 3‐acetylpyridine. Principal components of the rotational diffusion tensor have been determined. The results are discussed in terms of relative influence of molecular shape and attractive dipolar forces on anisotropy of the molecular reorientations.
Adsorption of Anionic and Cationic Dyes in Dilute Solutions onto a SnO2 Surface Measured by Total Internal Reflection Fluorescence
Authors: Nakashima Tetsuto , Fujishima Akira 
Published: July 2012

AbstractTotal internal reflection fluorescence (TIRF) technique was used in measuring the adsoption of anionic and cationic dyes on the interfaces between SnO2 and the dye solutions. The fluorescence intensities of an anionic dye and a cationic dye from their very dilute solutions to an SnO2 surface were measured as functions of time and pH. The site distributions on the SnO2 surface were estimated from the fluorescence intensities. The fluorescence intensity was also measured as a function of the dye concentration. The ratio of the fluorescence attributable to the solution layer to the fluorescence attributable to the adsorbed dyes on the SnO2 surface was determined. The effects of the supporting electrolytes on the measurement results were examined. The specific adsorption of the supporting electrolytes on the interfaces of SnO2 and the dye solutions were studied and directly measured to be in the order of IO3− > Br− > Cl− > I− > ClO4−.
An Optical In‐Situ Study of the Re‐Oxidation Kinetics of Calcia‐Stabilized Zirconia
Authors: He T. , Becker K. D. , Tannhauser D. S. 
Published: July 2012

AbstractThe re‐oxidation kinetics of strongly reduced single crystals of calcia‐stabilized zirconia (black CSZ) have been investigated by an optical in‐situ method at temperatures between 335 and 520°C. The kinetics obey a parabolic rate law. From the analysis of the optical results it follows that the parabolic rate constant, kp, is controlled by the ionic conductivity of the oxygen ions. The temperature dependence of kp can be represented by an Arrhenius‐type equation with an activation energy of 1.05 eV. The nature of the defect center associated with black CSZ is discussed in connection with its oscillator strength.
The Electric Conductivity of Liquid Cesium to High Temperatures
Authors: Keller E. , Franck E. U. 
Published: July 2012

AbstractAn apparatus is used with a thin walled stainless steel cell and a fourpole potentiometric arrangement to perform precise measurements of the electric conductivity s̀ of liquid cesium to high temperatures at equilibrium vapour pressure. Results are given from 200 to 800°C. A five‐parameter equation for use from the melting temperature of 28.4°C to 1200°C is presented. Conductivity values of 17705 and 6435 ohm−1 cm−1 were obtained for 200 and 800°C, respectively. The relative expected error is given in dependence of temperature. A typical value is 0.34%. All data are well within the range of validity of the near‐free‐electron, NFE, model for metallic conductance.
Small Angle Neutron Scattering Experiments with Aqueous Solutions of the Nonionic Surfactant C12E5 with Critical and Noncritical Composition
Authors: Lesemann M. , Belkoura L. , Woermann D. 
Published: July 2012

AbstractResults of small angle neutron scattering experiments with four solutions of the nonionic surfactant C12E5 in D2O with critical and noncritical compositions in the vicinity of the lower critical point are reported (1.11·10−4 ≤x ≤ 2.042·10−3; x, mole fraction of C12E5; xc = 5.74·10−4, critical mole fraction). They were obtained at temperatures away from the liquid/liquid coexistence curve. The observed angular dependence of scattered neutron intensity is assumed to be caused by micelles formed by surfactant molecules. Two characteristic lengths Ξ1 and Ξ2 are calculated from the scattering profiles. Ξ1 has a value of the order of 10 nm. It is attributed to the extension of noncritical concentration fluctuations. Ξ2 has a value of the order of 1 nm and is attributed to the core of micelles. At constant temperature Ξ1 decreases with increasing surfactant concentration, whereas at constant surfactant concentration it increases with increasing temperature weakly (compared with the divergence of the correlation length of local composition fluctuations approaching Tc). ‐ A combination of light scattering and small angle neutron scattering data obtained with the system C12E5/water gives support to the assumption that in the vicinity of the lower critical point a continuous change will take place from a comparatively weak temperature dependence of the length characterizing the structure of the liquid to a strong temperature dependence of the correlation length of the critical concentration fluctuations.
Aqueous Two‐Phase Systems of Poly(ethylene glycol) and Di‐Potassium Hydrogen Phosphate with and without partitioning Biomolecules – Experimental Results and Modeling of Thermodynamic Properties
Authors: Großmann C. , Tintinger R. , Zhu J. , Maurer G. 
Published: July 2012

AbstractExperimental results for thermodynamic properties of aqueous two‐phase systems of poly(ethylene glycol) and di‐potassium hydrogen phosphate with and without partitioning biomolecules (glycine, phenylalanine and lysozyme) are reported for temperatures between 277 and 333 K. The results are used to develop a semiempirical group‐contribution expression for the excess Gibbs energy of dilute aqueous solutions containing polymeric as well as ionic solutes. The model is applied to correlate some of the new experimental data, while other experimental results are used to test its ability for predicting the electrical potential difference between the coexisting phases, the partition coefficient of lysozyme and the influence of polymer molecular weight on the phase behaviour of aqueous two‐phase systems – a field where most previously known methods are often inadequate.
Computation of the Diffusion Coefficients in Aqueous Electrolyte Solutions from Onsager‐Fuoss and Pikal Theories
Authors: Lobo V. M. M. , Ribeiro A. C. F. , Andrade S. G. C. S. 
Published: July 2012

AbstractA comparison of experimental diffusion coefficients in aqueous solutions of electrolytes with those calculated by Onsager‐Fuoss and Pikal theories is presented. The influence of the ion size parameter a, “distance of closest approach” of ions, on the variation of diffusion coefficients with concentration is discussed.
The Excess Molar Gibbs Energy of Nuclidic Liquid Mixtures
Authors: Calado J. C. G. , Deiters U. K. , Lopes J. N. C. , Rebelo L. P. N. 
Published: July 2012

AbstractThe calculation of GmE from VLE measurements has been extended to multicomponent systems including those where chemical reactions can occur. For nuclide mixtures, the methods have to be adapted in order to take into account the similarity of the mixture's components and the pseudo‐multicomponent characteristics of a system with isotopic exchange. Bigeleisen's theory of isotope effects can then be used to calculate self‐exchange equilibrium constants in the liquid phase at low temperatures and the vapour pressure of partially substituted nuclides. The formalism is applied to some relevant cases, namely those of water and ammonia.
Dynamic Light Scattering Experiments with Aqueous Solutions of Polyelectrolytes of Low Charge Density Along the Polymer Chain in the Presence of Salt
Authors: Topp A. , Belkoura L. , Woermann D. 
Published: July 2012

AbstractDynamic light scattering experiments are carried out with aqueous solutions of poly(2‐vinylpyridine) quarternized to small extents with ethyl bromide and dissolved in an aqueous solution of KBr (molar mass, Mw = 3.14·105 g mol−1; Mw/Mn = 2.24; degree of quarternization, αe; 0.079 ≤ αe ≤ 0.461; electrolyte concentration, cs = 1·10−2 c+, c+ = 1 mol dm−3). Apparent diffusion coefficients Dapp(αe,c̄p) are calculated from the data (c̄p, polymer concentration (g dm−3)). They are plotted as a function of the reduced composition variable Λ= αecp*/cs (cp*, molar volume concentration of the repeat unit of the polymer backbone). For Λ <<1 one apparent diffusion coefficient is observed. In the range Λ ≈︁1 the value of the apparent diffusion coefficient increases with increasing values of (αecp*) and a slow diffusive mode gradually appears. For Λ >>1 a fast and a slow diffusive process is found. In the literature such a behaviour has been reported for solutions of highly charged polyelectrolytes.
Contribution to the Interpretation of the Multistep Cathodic Reduction of Oxygen at the Pt/Zirconia Base Electrolyte Interface at High Temperature
Authors: Barbi G. B. 
Published: July 2012

AbstractThe multistep cathodic reduction at high temperature of the oxygen molecule at the porous platinum/yttria stabilized zirconia solid electrolyte interface has been critically analyzed. Steady state polarization experiments showed that for very thin and very porous layers and oxygen mixtures containing 1% or more oxygen the rate of the overall process is apparently governed by the electrode/electrolyte interfacial diffusion of neutral and/or single ionized atoms. This process is probably fed by the formation of single ionized oxygen molecules at the electrolyte surface, particularly in the neighbours of the electrode/electrolyte/gas phase triple phase boundary. At lower oxygen partial pressures and/or for thicker and less porous metal layers the control is probably transferred to the interpores molecular diffusion. The adsorption of oxygen onto the metal surface, as a step for feeding the transport of reducible species to the triple phase boundary, looks hardly consistent with the evident increase of the overall reaction rate with temperature. The role of platinum, however, can not be confined as a pure electron supply. In fact, at very negative overvoltages it enters the process of morphological expansion of the triple phase boundary zone and likely affects the activity of the electrolyte in the primary process of oxygen ionosorption.
Study of the Influence of Ionic Strength on the Ionic Product of Water in Saline Media at 25°C Using the Pitzer Equations
Authors: Brandariz Isabel , Fiol Sarah , De Vicente Manuel Sastre 
Published: July 2012

AbstractWe studied the influence of ionic strength on the stoichiometric equilibrium ionization constant of water in KNO3 at 25°C by applying the Pitzer equations to the activity coefficients for the species in equilibrium. Reported values for NaCl and KCl media are also analysed.
Mechanism of Extraction of Trivalent Europium from Perchlorate Medium by a Chloroform Mixture of Thenoyltrifluoroacetone and 18C6
Authors: Shehata F. A. , Daoud J. A. , Aly H. F. 
Published: July 2012

AbstractThe extraction of Eu(III) from perchlorate medium by a chloroform solution of thenoyltrifluoroacetone (HTTA) and 18‐crown‐6 (18C6) was kinetically studied. The effect of the extractants concentration, interfacial surface area as well as other parameters affecting the rate of extraction was separately investigated. The effect of temperature was also studied and the thermodynamic functions were calculated. A mechanism of extraction of Eu(III) was proposed to account for the experimental results.
Electronic Transitions in Metallocenes by Resonance Raman Scattering. II.*) The Low‐Energy Visible Spectrum of Nickelocene
Authors: Sassi Paola , Ceccarani Maria Letizia , Cataliotti Rosario Sergio 
Published: July 2012

AbstractThe resonance Raman spectra of nickelocene, dissolved in benzene and cyclohexane solutions, have been studied in the excitation range 15000–19000 wavenumbers. Excitation profiles and depolarization dispersion curves have been obtained for two totally‐symmetric motions, corresponding to the Ni‐Cp stretching and the ring‐breathing vibrations.The experimental data have been interpreted in terms of resonating processes of the Franck‐Condon type, and opportune fitting of the experimental excitation profiles and depolarization data has been done, in the framework of this approach, by numerical calculations. The results of our modelling show that the interpretation of the low‐energy electronic absorption spectrum of nickelocene is slightly different from that of the ferrocene molecule, previously studied in our laboratory.
Monte Carlo Simulation of the Rotator Phase of Cyclohexane
Authors: Würflinger A. 
Published: July 2012

AbstractThe reorientational behaviour of cyclohexane molecules in the rotator phase has been investigated with a Monte Carlo simulation on a system of 108 molecules in a cubic box with periodic boundary conditions. Different starting configurations have been tested, including also a special model where the molecules are aligned parallelly to the four cubic threefold axes. This model is characterized by a low potential energy. The discrete molecular orientations of this model are maintained at 195 K, that is, in the immediate neighbourhood to the low‐temperature solid II‐solid I transition. At higher temperatures no preferred orientations can be detected, irrespective of the employed starting set up. Both the molecular three‐fold axes and the angles between them of neighbouring molecules are distributed randomly. Therefore the Frenkel model of a discrete number of preferred orientations is discounted.
A Rate Equation Approach to Nucleation at Solid Surfaces with Application to Diamond Deposition from the Gas Phase
Authors: Tomellini Massimo 
Published: July 2012

AbstractThe particle size distribution function and the total number of stable clusters formed at solid surfaces during the initial stage of the CVD process, have been modeled. This is done on the basis of a kinetic scheme for nucleation in which the elementary steps are the attachment and the detachment of monomers to and from the clusters. The model is solved in terms of the eigenvalues of the associated kinetic matrix. It is shown that the microscopic growth law of the nucleus directly stems from the kinetics through the rate constants for monomer addition to the nucleus. A relationship between the particle size distribution function and the nucleation kinetics is derived that is used to process experimental data on the size distribution of diamond crystallites at the Si substrate. The overall activation energy for nucleation is obtained from the Arrhenius plot of the eigenvalues extracted from the experimental kinetics. The rate equation approach shows that the observed induction period of the nucleation kinetics can indeed be related to the dimension of the nuclei.
A Shock Tube Study of the Thermal Decomposition of Si2H6 Based on Si and SiH2 Measurements
Authors: Mick H.‐J. , Markus M. W. , Roth P. , Smirnov V. N. 
Published: July 2012

AbstractIn the present investigation the thermal dissociation of disilane (Si2H6) mixed with different additives was measured behind reflected shock waves. Atomic Resonance Absorption Spectroscopy (ARAS) was applied for detecting Si atoms and Ring Dye Laser Absorption Spectroscopy (RDLAS) for detecting SiH2 radicals. Three different series of experiments were performed.In the first group of experiments mixtures of 0.1 to 0.25 ppm Si2H6 diluted in Ar were shock heated to temperatures 2000 K≤T≤3135 K and pressures between 0.8 and 1.4 bar. From the Si‐measurements silane and silylene were found to be the main primary products during disilane decomposition. The SiH2 absorption measurements were carried out at temperatures 1070 K ≤T≤ 1381 K and pressures between 0.35 and 1.3 bar. In these experiments the SiH2 formation was found to be mainly caused by the dissociation reaction Si2H6⇌ SiH4+SiH2 (R1). The rate coefficient k1 was determined by fitting SiH2 profiles calculated based on a simplified reaction mechanism to measured profiles with k1 to be a variable parameter. The value obtained was interpreted based on RRKM calculations. For bath gas concentrations of 3.1 × 10−6≤[M]≤ 4.6 × 10−6 mol cm−3 the rate coefficient k1 can be summarized by the Arrhenius expression k1 = 5.2×1010 exp(‐16850 K/T) s−1. For longer reaction times the SiH2 radicals were consumed due to the reaction SiH2+SiH2 ⇌Si2H2 (R4). The rate coefficient k4 was determined to be k4 = 6.5×1014 cm3 mol−1 s−1 (70%).The second group of experiments was carried out in mixtures with molecular hydrogen as an additive. SiH2measurements were performed in the temperature range 1082 K≤T≤1417 K at pressures 0.24 bar ≤p≤ 1.23 bar by using initial mixtures of 15 to 30 ppm Si2H6 and 5 to 50% H2 diluted in Ar. The aim of this part was to increase the influence of the recombination reaction SiH2 + H2→ SiH4 (R‐2) and to measure the dissociation barrier for the silane decomposition via the equilibrium constant. The data evaluation results in a mean value of E0,2 = 244.1 kJ/mol which is in good agreement to previous investigations.In the last part of this study the influence of silane used as an additive during Si2H6 decomposition was investigated. Initial mixtures of 30 ppm Si2H6 and 300 to 1000 ppm SiH4 diluted in Ar were used under conditions 1060 K ≤ T ≤ 1198 K at pressures between 0.36 and 1.3 bar. From SiH2 concentration measurements an estimation for the rate coefficient of the disproportionation reaction SiH2+SiH4 →H3SiSiH+H2 (R5), k5 = 1.3 × 1013 cm3 mol−1 s−1, was found.
The Microwave Spectrum of the Isothiazole‐Argon van der Waals Complex
Authors: Kretschmer U. 
Published: July 2012

AbstractUsing molecular beam Fourier transform microwave spectroscopy I measured and assigned the rotational spectra of the 32S‐ and 34S‐isothiazole‐argon complexes. The rotational constants are A = 3479.53543(15) MHz, B = 1225.68820(9) MHz, and C = 1154.69246(11) MHz for 32S‐isothiazole‐argon and A = 3428.10063(23) MHz, B = 1216.56872 (19) MHz, and C = 1140.87783(24) MHz for the 34S‐isotopomer. The 14N quadrupole coupling constants χaa = 1.3824(17) MHz, χbb = 0.9126(17) MHz, χcc = ‐2.2951(17) MHz, and χbc = 2.804(35) MHz could be extracted from the analysis of the spectra. For the 34S‐isotopomer I derived χaa = 1.3907(17) MHz, χbb = 0.9242(20), χcc = ‐2.3148(20) MHz, and χbc = 2.829(55) MHz. The spectroscopic constants were used to propose a structure of the isothiazole‐argon van der Waals complex. The argon atom is located 3.55 Å above the ring plane.
Anisotropic Structures in Aqueous Solutions of Aggregated Pseudoisocyanine Dyes
Authors: Stegemeyer H. , Stöckel F. 
Published: July 2012

AbstractOn increasing concentration in highly diluted aqueous solutions of pseudoisocyanine dyes an intensive absorption band of extremely small half‐width (Scheibe band) occurs which is attributed to the formation of dye aggregates (Scheibe or J‐aggregates). By polarizing microscopy it is shown that aqueous solutions of pseudoisocyanine diethylchloride at low temperatures and at concentrationsc>0.2 wt% become birefringent and exhibit a Schlieren texture characteristic for nematic liquid crystals. Above a certain clearing temperatureTcthe solution becomes optically isotropic during a discontinuous phase transition as shown by DSC. The Scheibe band vanishes at temperatures some degrees aboveTc. The phase behaviour is displayed in terms of aT‐c diagram. The aggregation numbers have been determined spectroscopically to about 40 to 50 only slightly increasing belowTc. Obviously, the Scheibe aggregates exhibit a long‐range orientational order even at high dilution typically for a nematic lyotropic liquid crystal. The phase diagram indicates that on increasing temperatures the orientational long‐range order vanishes first before the Scheibe aggregates will be thermically decomposed.
Monolayer Model Simulations of Mixtures of Amphiphilic Molecules
Authors: Stettin H. , Mögel H. ‐J. , Care C. M. 
Published: July 2012

AbstractAthermal Monte Carlo simulations for a mixed monolayer built up from flexible molecules with different chain lengths have been carried out within a cubic lattice model. Only excluded volume interactions are taken into account. The number of chain segments per molecule, the head density, and the mole fraction of each component are varied. It is the aim of the work to investigate the orientational order in such mixtures. The calculated correlation lengths and snapshots did not show any evidence for demixing. In order to understand the effect of mixing on ordering some additional properties of the system have been investigated. Results demonstrating the influence of the mole fraction and chain length on the orientational order parameter, the end‐end distance, the end‐end projection, and the density profiles are presented. These quantities exhibit deviations from an ideal mixing rule. The deviations get stronger with increasing relative chain length difference. The shorter chains do not align in the local environment of long chains.