bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamic Properties of the Melt of the NaI — DyI3 System
Authors: Hilpert K. , Miller M. , Gerads H. , Saha B. 
Published: July 2012

AbstractThe vaporization of the phases of the NaI — DyI3 system present at a temperature of 1000 K, DyI3(s) + melt for 0 < xNaI < 0.53 and melt for 0.53 ≤ xNaI ≤ 1, has been investigated by Knudsen effusion mass spectrometry. The species NaI(g), (NaI)2(g), DyI3(g), NaDyI4(g), and Na2DyI5(g) were identified in the vapour and their partial pressures determined over the entire concentration range of the system. Chemical activities of NaI and DyI3 and excess chemical potentials of NaI were evaluated. The integral excess Gibbs energies of the melt were determined as negative and showed a minimum near the composition xNaI = 0.75 which may indicate the presence of short‐range ordering states of the composition 3NaI:DyI3 caused by the ionic complex [DyI6]3−. The partial pressures are discussed with respect to their significance for chemical vapour transport in metal halide lamps.
Thermodynamic Study of the Liquid and Solid Alloys of the Nickel‐Rich Part of the Al — Ni Phase Diagram Including the AlNi3 Phase
Authors: Hilpert K. , Miller M. , Gerads H. , Nickel H. 
Published: July 2012

AbstractThe vaporization of liquid and solid alloys of the Al — Ni system in the range xNi = 0.7 to 1 has been extensively investigated by the use of Knudsen effusion mass spectrometry in the temperature range between 1389 and 1734 K. 15 alloy samples of different compositions of the complete concentration range were studied in the course of 25 runs and their Al and Ni partial pressures determined. The vapour pressure measurements in the course of the individual runs were carried out over temperature ranges of up to about 300 K covering the solid and the liquid state for many of the alloys investigated. Chemical activities and chemical potentials for Al and Ni as well as Gibbs energies were evaluated at 1600 K for the solid and at 1728 K for the liquid state. Two independent methods were used for the determination of Ni activities of the solid alloys yielding consistent results. The large temperature range of the partial pressure measurement for the solid AlNi3 phase with xNi = 0.750 rendered possible the determination of a complete set of partial and integral thermodynamic functions (ΔG, ΔH, ΔS) for the formation of this phase. The values obtained are discussed. The partial and integral enthalpies of formation are compared with the enthalpies of dissociation of the gaseous species Ni2(g), Al2(g), and AlNi(g). The integral enthalpy of formation, obtained for the first time by vapour pressure measurements, agrees well with the results of a recent calorimetric study.
Thermophysical Properties of Alkali Metal Vapours, Part I — Theoretical Calculation of the Properties of Monatomic Systems
Authors: Nieto Castro C. A. De , Fareleira J. M. N. A. , Matias P. M. , Ramires M. L. V. , Pais A. A. C. Canelas , Varandas A. J. C. 
Published: July 2012

AbstractTheoretical calculations of the second virial coefficients, self‐diffusion, viscosity and thermal conductivity of monatomic alkali metal vapours, lithium, sodium, potassium, cesium and rubidium are presented. The calculations have been carried out using reliable analytical two body interaction potential energy functions for the ground singlet 1Σ+g and the excited triplet 3Σ+g molecular states of the alkali dimers. The results are compared with previously calculated values. — The interpretation of experimental data on the thermophysical properties of alkali metal vapours is complicated by the formation of dimers. It follows that theoretical calculations for the monatomic species should thus provide an independent information on the zero density limits for the experimental properties. Full utilization of this principle is tried in Part II of this paper where an assessment of the available experimental data is attempted.
Extraction Kinetics of Europium(III) by Thenoyltrifluoroacetone and its Mixture with Triphenylphosphine Oxide in Chloroform from Perchlorate Medium
Authors: Daoud J. A. , Khalifa S. M. , Aly H. F. 
Published: July 2012

AbstractThe rate of extraction of Eu(III) from aqueous perchlorate solutions at constant ionic strength of 0.1 (H+, NaClO4) by thenoyltrifluoroacetone (HTTA) or its mixture with triphenylphosphine oxide (Ph3PO) in chloroform was studied using a stirred Lewis cell. The rate of extraction was measured at different [H+], [HTTA] and [Ph3PO]. For the chelate and adduct systems, the rate increased with the increase in [HTTA] and decreased with the increase in [H+]. The rate of extraction increased slightly with the increase in [Ph3PO]. The results were interpreted by a reaction mechanism where the 1 : 1 chelate formation steps in the aqueous phase are the rate‐determining steps. The rate constant kHL (HL = HTTA) and kL were found to be 9.20 ± 0.02 M−1 min−1 and 2.23 ± 0.04 · 103 M−1 min−1, respectively, for the extraction of Eu(III) by HTTA alone and 10.86 ± 0.03 M−1 min−1 and 1.41 ± 0.01 · 104 M−1 min−1 for the extraction by HTTA — Ph3PO mixture. Activation parameters were determined for both systems and discussed.
The Investigation of Near — Critical Mixtures by Means of the Nonlinear Dielectric Effect
Authors: Śliwińska‐Bartkowiak M. 
Published: July 2012

AbstractNonlinear dielectric effect (NDE) occurring in classical critical mixtures of o‐nitrotoluene with alkanes as well as mixtures m‐nitrotoluene with alkanes showing a formally similar NDE course was studied. The magnitude of the measured effect in critical mixtures is proportional to
equation image
where Φ ∼ 1/3. A similar dependence with the same exponent Φ was obtained for the other group of mixtures. — On the grounds of this analogy we conclude that a precritical effect occurs in the m‐nitrotoluene mixtures formally similar to the critical ones and we determine a hypothetical critical temperature for these mixtures.
Influence of Ni Deposits on the Catalytic CO Oxidation on Pt(110)
Authors: Ladas S. , Imbihl R. 
Published: July 2012

AbstractThe influence of Ni deposits in the submonolayer range on the activity of a Pt(110) surface in catalytic CO oxidation has been investigated in the 10−5 and 10−4 Torr range by means of reaction rate, LEED, AES and work function measurements. The presence of Ni on the surface led to an overall reduction of the CO2 production rate with the exception of the low temperature regime where an increase in the reaction rate could be observed for T ≦ 470 K. The increase in catalytic activity at low temperature could be traced back to a change in the CO adsorption properties caused by Ni which reduces the inhibitive effect of a CO adlayer on oxygen adsorption. With oxygen a ternary Pt/Ni/O phase could be observed characterized by a c(4 × 2) pattern in LEED. The reactivity of the oxygen in the ternary phase towards CO is at an intermediate level between the high reactivity of chemisorbed oxygen and the low reactivity of an oxide.
Sorption Kinetics of Xenon on MFI‐Type Zeolite Molecular Sieves
Authors: Bülow M. , Härtel U. , Müller U. , Unger K. K. 
Published: July 2012

AbstractKinetic uptake data for xenon adsorbed onto large and uniform silicalite‐I crystals are presented over a temperature range of 121 K to 296 K. — Adsorption isotherms and corrected diffusion coefficients derived from the uptake curves are given. The heat of adsorption and activation energy of diffusion were estimated from the plots of reciprocal temperature against the logarithm of equilibrium pressure and corrected diffusion coefficients, respectively. — While the corrected diffusion coefficient is independent of coverage for the higher temperatures, it decreases significantly at the lower temperatures investigated (<170 K) when the limiting adsorption capacity has been reached. — Comparing the sorption diffusion data with self‐diffusion coefficients obtained by NMR‐pulsed field gradient techniques, the room‐temperature mobility of xenon in silicalite‐I derived from sorption measurements is lowered by one order of magnitude. However, this result should not be considered necessarily as a discrepancy, due to uncertainties inherent in both techniques.
Potential Energy for the CO2‐NaCl(100) and the Lateral Adsorbate Interaction
Authors: Heidberg J. , Kampshoff E. , Schönekäs O. , Stein H. , Weiss H. 
Published: July 2012

AbstractAn empirical adsorption potentialVADof a single CO2molecule on the (100) face of NaCl is reported. The molecule‐surface interaction is calculated for different orientations of the adsorbed molecule. The lowest energy minimum is found for a molecule parallel to the surface above the cell center, having an energy of adsorption in good agreement with the measured value in the low coverage limit. Using the potential the vibrationalv2‐splitting is calculated for the different orientations of the molecule. — To determine the structure of the CO2‐monolayer on NaCl(100), intermolecular Coulomb and van der Waals terms are added to the molecule‐surface potential. Two basic overlayer structures, namely (2 × 2) and (2 x 1), are investigated and the potential minima determined under variation of the adsorbate configuration. In both cases we find an angle ϕ 90° between neighbouring molecules and a tilt angle ϑ of 30–40 between the CO2molecular axis and the NaCl(100) plane for adsorption sites above Na+. The deepest potential energy minimum for a (2 x 1) structure with 2D space group pg is found for CO2shifted by 0.07 Å from the center of the line between adjacent Na+and Cl−towards Cl−and ϕ = 85.6°,ϑ= 26.2°. According to our spectral line shape analysis and LEED measurements [12] the adsorbate has the (2 x 1) structure.
A Molecular Dynamics Study of the Interface between a Membrane and Water
Authors: Schlenkrich Michael , Nicklas Kai , Brickmann Jürgen , Bopp Philippe 
Published: July 2012

AbstractThe interface between a membrane, modelled by an ensemble of COO− functional groups with rotational and translational degrees of freedom, and liquid water, represented by the TIP4P model, is studied by molecular dynamics (MD) computer simulations. The structure of the bare membrane and of the membrane in the presence of water are studied by means of pair correlation functions. The influence of the membrane on the structure of the water is similarly discussed in terms of density profiles and distribution functions. Three ordered layers of water are found above the membrane, followed by a transition region to the bulk structure. Finally, the single molecule dynamics is examined. The translational self‐diffusion of the water is lowered by one order of magnitude in the vicinity of the membrane and remains anisotropic even above the layered water.
Hydrogen Bond Formation and Molecular Motion in Solutions of Aniline with Nitroxide Free Radicals
Authors: Stark U. , Müller‐Warmuth W. 
Published: July 2012

Abstract1H NMR spin‐lattice relaxation rates and paramagnetic contact shifts have been measured at various temperatures and frequencies in solutions of aniline, aniline‐d2, and aniline‐d5 containing nitroxide free radicals. The data can be explained in terms of transient hydrogen bond formation between the amino protons and the NO group of the radical. Detailed information about the intermolecular transfer of electron spin density and the steric arrangement of the complex have been obtained. Molecular motions and interactions have been probed by relaxation measurements over a large frequency range between 100 kHz and 300 MHz. Relaxation is induced by dipolar interactions of the aniline protons with the unpaired electron spin and rotational tumbling of the associated system. The results are compared with other hydrogen‐bonded complexes of nitroxide radicals and proton donor solvent molecules.
Calculation of the Dielectric Constant of Water to 1000°C and Very High Pressures
Authors: Franck E. U. , Rosenzweig S. , Christoforakos M. 
Published: July 2012

AbstractMeasured data for the dielectric constant of water exist to 550°C and 5000 bar and to 400°C and 3000 bar (critical temperature: 374°C). The present calculations extend to 1000°C and a density of 1 g cm−3 (16000 bar). Results are given for densities between 0.1 and 1 g cm−3 and for temperatures to 1000°C. From 400 to 1000°C at densities of 0.1, 0.5 and 1.0 g cm−3 the dielectric constant varies from 2.04 to 1.50, from 10.45 to 4.69 and from 29.4 to 11.06 respectively. The calculation is based on a hard‐sphere with dipole moment molecular interaction model and an approximate equation of Patey et al. based on a linearized hypernetted chain procedure. The effective hard sphere diameter of 2.68 Å has been derived from fitting to existing PVT data to 1000°C by a suitable equation of state. The effective dipole moment of 2.33 D was obtained from fitting to existing experimental dielectric constant values to 550°C and high densities with the Patey equation. Analogous calculations of the dielectric constants of supercritical, dense HCl, NH3 and CH3F are presented.
The Glass Transition of Hard Spherical Colloids
Authors: Pusey P. N. , van Megen W. 
Published: July 2012

AbstractWhen suspended in a liquid, hard spherical colloidal particles can show fluid, crytalline and glassy phases. A light scattering study of the dynamics of the metastable fluid and glassy phases is reported. Comparison is made with the predictions of mode‐coupling theories applied to the glass transition of simple atomic systems.
Particle Transport in Pores Bounded by Permeable Walls
Authors: Clark A. T. , Lal M. , Jones R. B. 
Published: July 2012

AbstractParticle transport in pores bounded by a pair of parallel, semi‐infinite absorbing boundaries, ideally permeable to the suspending medium, is studied theoretically by solving the classical convective‐diffusive transport equation both for the first passage times and for the particle number versus time profiles. The initial transient appearing in the profiles is ascribed to the initial condition specifying the particle distribution in the pore before the onset of transport and absorption. At small convective flows, the post‐transient period in the profile is characterised by first‐order kinetics, but at large flow rates this period splits into two distinct regimes, one exhibiting zero‐order and the other first‐order kinetic behaviour. The rate constants obtained from the profiles are compared with those derived from the first passage times.
Response of (Poly)Atomic Fluids to Various Flows with Homogeneous Velocity Gradients
Authors: Ryckaert J. P. 
Published: July 2012

AbstractIn this paper a transient non‐equilibrium method based on the so called Sllod equations of motions is developed to study polyatomic fluids in flows with a homogeneous velocity gradient in space. Various flows like pure deformational, pure rotational or elongational flows can be imposed and accommodated with periodic boundary conditions in order to avoid surface effects. The method is illustrated on an atomic fluid, on liquid butane and on liquid chlorine subject respectively to a planar Couette flow, a purely deformational flow and a pure rotational flow.
Recollision Dynamics in the Hard Sphere Fluid
Authors: Vesely Franz J. , Evans Glenn T. 
Published: July 2012

AbstractGiven that two out of N hard spheres have collided at time t = 0, the probability of a recollision, as a function of time, was evaluated by molecular dynamics simulation. Using this conditional probability, certain time correlation functions of interest in the kinetic theory of the hard sphere fluid (and in theories of recombination processes) were computed. The initial values of all these tcf's could be reproduced independently as certain canonical averages. A decomposition of the recollision probability and the various tcf's in terms of first and second recollision functions is given. The first recollision functions in turn can be traced back to sequences of binary collisions involving 3, 4 or more hard spheres.
Non‐Markovian Effect on Diffusion‐Controlled Reactions
Authors: Dong W. , Baros F. , André J. C. 
Published: July 2012

AbstractRecently we have carried out a molecular dynamics simulation of a model of diffusion‐controlled reactions in which the solvent is treated on an equal footing with reactants [8]. It is found that the rate of reactive encounter is larger at short times than that given by the Smoluchowski theory. In the present note it will be shown that the enhanced rate is due to a non‐Markovian effect. The theoretical approach for taking into account the non‐Markovian effect is a generalized diffusion equation, neglecting the mean force, with a time‐dependent diffusion coefficient which is related to the memory function of the velocity auto‐correlation function. By using the relaxation‐time approximation for the memory function, it can be shown that the motion of the mutual approach of the reactants is faster at short times than predicted by the classic Fick's law. It is this enhanced transport which is the physical origin of the enhanced reaction rate. Subjected to the absorbing boundary condition for reactivity, the generalized diffusion equation can still be solved analytically. The results have mathematical expressions as simple as those of the classic Smoluchowski theory.
Canonical Molecular Dynamics of Molecules with Internal Degrees of Freedom
Authors: Toxvaerd S. , Olsen O. H. 
Published: July 2012

AbstractCanonical molecular dynamics simulations of molecules with internal degrees of freedom have been analysed by simulating alkanes at different temperatures and densities. The dynamics of a single thermostated butane molecule is not fully chaotic, even at high temperatures, and it tends to behave regular for large thermostat relaxation times. When the thermostat is applied to a fluid of butane molecules we only obtain a biased sampling for a low fluid density and only for thermostat relaxation times close to the fast intramolecular bond‐ and angle vibration times. The overall behaviour indicates that the anharmonic energy terms play a crucial role for the efficiency of the thermostat.
Dynamics of Liquids and Supercooled Water Studied by High Pressure Pulse NMR
Authors: Lüdemann H.‐D. 
Published: July 2012

AbstractData of the self diffusion coefficient for unpolar, polar, hydrogen bonded liquids and water are discussed and compared to existing molecular theories. — The liquids analyzed are a series of halomethanes (CF4, CF3H, CH3F), some monohydric alcohols (CH3OH, C2H5OH) and light and heavy water. They were studied at temperatures between their melting pressure curves and 450 K to pressures of 200 MPa. For methanol and water the data were extended into the supercooled range.
Multi‐Nuclear Relaxation Time Studies in Undercooled Aqueous Electrolytes
Authors: Lang E. W. , Fink W. , Radkowitsch H. , Girlich D. 
Published: July 2012

AbstractThe dynamic properties of water molecules coordinated to simple ions (alkali‐, alkali earth halides) in undercooled solutions have been investigated with NMR. Relaxation time studies at low temperatures provide details of molecular motions as well as certain features of the local arrangement in the coordination sphere of these ions.
Viscosities, Electric Conductivities and Self Diffusion Coefficients of Tetraalkylammonium‐tetraalkylborides
Authors: Weiden Norbert , Wittekopf Burghard , Weil Konrad G. 
Published: July 2012

AbstractA number of salts of the type R3R'N+ · R3R'B− were prepared, with R, R' = aliphatic groups from methyl to octyl. Most of them are liquid at room temperature. The densities, electric conductivities, and viscosities of these salts were measured as functions of the temperature. Both transport properties correlate strongly with the molar volume, even with unsymmetric salts, where R and R' are different for anion and cation. — For a number of these salts, self diffusion coefficients of anions and cations could be determined by a spin‐echo NMR technique. For this purpose, the NMR signal of a proton from a methylene group adjacent to the central N or B atoms was used. In all investigated cases, the self diffusion coefficients of both constituents of a salt were identical. This finding excludes the applicability of concepts of individual contribution of ions to the transport processes in molten salts. — This is corroborated by the fact, that the Nernst‐Einstein equation does not quantitatively describe the relation between diffusion coefficients and conductivities: The experimental conductivities are in all cases smaller than those calculated from the self diffusion coefficients by use of the Nernst‐Einstein equation.
Ternary Diffusion in the Aqueous Solutions of MgCl2 + KCl, CdCl2 + KCl, ZnCl2 + KCl and Onsager's Reciprocity Relations
Authors: Spallek M. , Hertz H. G. , Funsch M. , Herrmann H. , Weingärtner H. 
Published: July 2012

AbstractThe diffusion coefficients D11, D12, D21, and D22 of the three systems MgCl2(1) + KCl(2) + H2O(3), CdCl2(1) + KCl(2) + H2O(3), and ZnCl2(1) + KCl(2) + H2O(3) have been measured at 25°C. The diaphragm cell method was applied. Diffusion coefficients for the following concentrations were obtained c1 = c2 = 0.25, 0.5, 0.75 M, and c1 = 0.25, 0.5, 0.75 M, c2 = 2c1 = 0.5, 1.0, 1.5 M. The Dij values which refer to the cell fixed system were transformed to the D'ij referring to the solvent fixed coordinate system. By the aid of thermodynamic data taken from the literature and from measurements with cells involving the solutions studied the derivatives of the partial chemical potentials δμi/δcj were determined. From all these data the phenomenological coefficients Ω'ij were calculated and we found the result that for MgCl2 + KCl + H2O Ω'12 = Ω'21 is valid whereas for the complex forming systems CdCl2 + KCl and ZnCl2 + KCl our study yielded phenomenological coefficients Ω'12 ≠ Ω'21.
Mass Transport Coefficients from Liquid Thermal Diffusion Columns
Authors: Ecenarro O. , Madariaga J. A. , Navarro J. L. , Santamaría C. M. , Carrión J. A. , Savirón J. M. 
Published: July 2012

AbstractExperimental data on ordinary diffusion coefficient and thermal diffusion for binary liquid systems containing hexane, heptane, benzene, toluene and carbon tetrachloride are obtained from steady and non‐steady separation measurements in a thermal diffusion column. The data extraction uses a time evolution theory previously developed by the authors that accounts for density effects (the “forgotten effect”). The comparison of the diffusion data with those of the literature provides a powerful test of the derived thermal diffusion factors.
Pressure‐Temperature‐Dependence of Mass Density and Self‐Diffusion Coefficients in the Binary Liquid System n‐Hexane/Benzene
Authors: Brüsewitz Michael , Weiss Alarich 
Published: July 2012

AbstractThe self‐diffusion coefficients of n‐hexane and benzene have been measured in the temperature and pressure range 253.15 ≤ T/K ≤ 368.15; 1 ≤ P/bar ≤ 2000. The mol fraction x of benzene was varied over the range 0 ≤ x ≤ 1 in six steps. — The densities of the liquid mixtures and the pure substances were measured in the given Pressure (P)‐Temperature(T)‐range and the molar volumes were fitted to the Tait‐equation. — The P, T‐dependence of the self‐diffusion coefficients can be described in a phenomenological way by a polynomial. The self‐diffusion coefficients of benzene and n‐hexane in the liquid state vary at constant temperature by factors of 3.0 to 3.5 in the given P‐range. — The temperature dependence of the self‐diffusion coefficients is described by an Arrhenius‐type equation, which leads to activation energies EDa of both components in the binary system. EDa was studied in dependence of concentration and pressure. EDa increases for both compounds with increasing pressure and does not exceed 15 kJ mol−1. — EDa (benzene) depends stronger on the benzene‐concentration in the given P‐range than EDa (n‐hexane). — The free volume model for the transport properties in the liquid mixtures is applied to describe the self‐diffusion coefficients at constant molar volume Dv̄ = D(P,T).