bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamic parameters of liquid cobalt‐palladium alloys by computer‐aided Knudsen cell mass spectrometry
Authors: Tomiska J. , Belegratis M. S. , Wang H. 
Published: July 2012

AbstractThe computer‐aided Knudsen cell mass spectrometry has been applied for the determination of the molar thermodynamic excess properties of liquid binary Co‐Pd alloys. Thermodynamic evaluation followed the “Digital Intensity‐Ratio” (D.I.R.)‐method. Two‐parameter thermodynamically adapted power (TAP) series are used for the algebraic representation of the molar excess properties. Liquid Co‐Pd alloys are characterized by exothermic molar heats of mixing HE, slight negative molar excess entropies, and negative molar excess Gibbs energies GE. At 1850 K the minimum HE value is −13000 J/mol (55.1 at.% Pd), the minimum SE value is −4 J/(mol K) (52.7 at.% Pd), and the minimum GE value is −5700 J/mol (57.9 at.% Pd). At 1850 K the thermodynamic activities of both components, Pd and Co, show slight negative deviations from Raoult's law over the entire range of composition. The Co activities of the Co‐richest alloys (xPd<0.14) are nearly ideal.
Spatial and functional organization. Coupled models for spatial organization in development
Authors: Maini P. K. 
Published: July 2012

AbstractSeveral simple models have been proposed to account for spatial organization in early development. Recently, a number of models have been proposed in which such patterning mechanisms are coupled. Here, we present a review of some of the latest theoretical results on such systems. In particular, we consider two cases: in one, the coupling of two mechanisms greatly enhances the robustness of the patterns produced; in the other, a hierarchical model exhibits spatially asymmetric patterns that are consistent with certain experimental observations.
Synthetische Polymere: Von der Empirie zum Design von Makromolekülen
Authors: Cherdron Harald 
Published: July 2012

AbstractIntensive studies at both, academic and industrial, laboratories have led to a much better understanding of the relationships between structure/morphology and properties of synthetic polymers. Hence, it became possible in many cases to predict what structures and/or morphologies macromolecules should have in order to meet certain property requirements. This will be demonstrated with four examples: Temperature resistant polymers, alternating copolymers, polymers with liquid crystalline main chains, and highly ordered polymers with nonlinear optical properties.
Properties of liquids at the boiling point: Equation of state, internal pressure and vaporization entropy
Authors: Matyushov Dmitry V. , Schmid Roland 
Published: July 2012

AbstractLiquids at their respective boiling points are considered in the framework of factorization of density and temperature dependencies in the attraction term of the liquid equation of state. The factorization functions Ψ(η) and a(T) are expressed through the vaporization enthalpy and the liquid packing density η. The latter is computed from the compressibility of the liquid with correcting for dipole‐dipole interactions in the framework of the mean‐spherical approximation. On the basis of the functional dependencies of Ψ(η) and a(T), derived from experimental data for a number of liquids, the applicability of equations of state to dense liquids at the boiling point can be analyzed. The function of η determined in this way relates the internal pressure to the cohesive energy. Upon decomposing the entropy of vaporization into the contributions from repulsions and attractions, the famous Trouton constant is shown to be largely determined by the unpacking of molecular hard spheres.
Thermodynamics of iron‐chromium alloys: Mass spectrometric determination of the excess properties in the bbc phase and calculation of the phase diagram
Authors: Vrestal J. , Broz P. , Tomiska J. 
Published: July 2012

AbstractThermodynamic excess properties of iron‐chromium alloys in the bcc phase have been investigated by Knudsen cell mass spectrometry in the temperature range 1470–1750K. The molar excess Gibbs energies, entropies and heats of mixing as well as the thermodynamic activities were determined from the ion intensities as a function of composition by fitting to a sub‐regular solution model (2 parameter T.A.P.‐series; C in J/mol: C = 16800, C = 4490; C in J/(mol·K): C = 4.155, C = 2.065). Solid Fe‐Cr alloys in the bcc phase are characterized by positive molar excess Gibbs energy GE, positive molar excess entropies SE and endothermic molar heat of mixing HE. The following maximum excess properties result at 1725K: HE = 4780 J/mol (53.1 at.‐% Cr), SE = 1.31 J/mol·K (54.7 at.‐% Cr), and GE = 2525 J/mol (51 at.‐% Cr). The phase diagram has been recalculated by using these data. The optimized new sets of T.A.P.‐parameter resulted as: C = −7800, C = 3500 (C in J/mol), C = −6.8, C = 3.8 (C in J/mol·K) for the liquid phase; as well as C = 7800, C = 4500 (C in J/mol), C = 3.1, C = 3.5 (C in J/mol·K) for the fcc phase.
Investigation of Charge Transport Across the Ag | AgI‐interface: (I) Occurrence of Periodic Phenomena During Anodic Dissolution of Silver
Authors: Janek J. , Majoni S. 
Published: July 2012

AbstractBy drawing a constant electric current through a symmetric electrochemical cell of the type Ag|a‐AgI|Ag we observed, under certain experimental conditions, strong periodic oscillations of the voltage across the cell. Depending on current density and applied mechanical force, these oscillations show either periodic or irregular behaviour.Further experiments show that these strong voltage oscillations are caused by the anodic interface at which Ag‐metal is dissolved electrochemically into the solid electrolyte. The phenomenon itself is reproducible, but the appearance of the oscillations is very sensitive to the experimental conditions. We present experimental results for different experimental conditions and cell types and discuss a possible mechanism for the observed phenomenon. An important element of the attempt to find a microscopic explanation is the basic process of forming lattice vacancies in the metal at the anodic interface. The behaviour of these vacancies is crucial for the kinetic properties of the metal‐solid electrolyte interface under non‐equilibrium conditions.
Viscosity of the System KF–K2MoO4–B2O3
Authors: Silný A. , Danêk V. , Chrenkovå M. 
Published: July 2012

AbstractThe viscosity of the melts of the system KF–K2MoO4–B2O3 has been measured by means of the computerised torsional pendulum method.The viscosity of the melts increases both with the increased content of K2MoO4 and B2O3. In the binary system KF–K2MoO4 the simple additivity of the viscosity has been found. In the ternary system strong deviation from the additive behaviour was found which is possible to ascribe to the chemical reactions between the components.From the obtained results it follows, that the binary interaction in the KF‐B203 system corresponds to the chemical reaction8KF+7B2O3 = 3K2B4O7 + 2KBF4, while the interaction in the K2MoO4–B2O3 system corresponds most probably to the formation of the heteropolyanion of the type [BMo6O24]9‐ according to the chemical reaction: 6K2MoO4 + B2O3 = K9[BMo6O24] + 3 KBO2.Statistically significant ternary interaction may be explained as the entrance of the fluorine atoms into the coordination sphere of the molybdenum in the heteropolyanions.
A Modification of the Knudsen Method for Determining the Molecular Weight of Vapors
Authors: Schönherr E. , Freiberg M. 
Published: July 2012

AbstractTwo Knudsen cells, which evaporate condensed material in opposite vertical directions, are hung to the arms of a vacuum beam microbalance. The molecular weight of the effused vapor is computed from the recoil force and individual evaporation rates of the two cells. The recoil force of the cells is determined from the mass change which appears when the evaporation under high vacuum conditions is abruptly suppressed by the inlet of an inert vapor. The method is presented with water as an example.
Solvent and Temperature Effects on the Intramolecular Fluorescence Quenching in Dipeptide Model Compounds [1]
Authors: Sakurai Tadamitsu , Miyoshi Kenichiro , Obitsu Mitsuhiro , Inoue Hiroyasu 
Published: July 2012

AbstractThe mechanism of fluorescence quenching through intramolecular electron transfer (ET) was investigated in the dipeptide model compounds DL‐N‐[4‐(diethylamino)alkyl]‐2‐acetylamino‐3‐(1‐naphthyl)propionamides (1) by stationary and time‐resolved fluorescence spectroscopy in non‐polar and polar solvents. An analysis of the observed singlet‐exciplex fluorescence and the biexponential decay of monomer fluorescence established that emission quenching in non‐polar solvents proceeds through the singlet‐exciplex intermediate with a strong charge‐transfer character, and that the quenching rate constant increases with a decrease in free‐energy change for ET (ΔGet) but it is not very sensitive to the variation of methylene chain length in 1. The observations of biexponential emission decay and very weak exciplex emission in polar solvents suggest that a singlet exciplex and/or a solvent‐separated radical ion pair become a key intermediate in the quenching process. The finding that the magnitude of ΔGet, being regarded as a measure of the stability of an intermediate formed, linearly correlates with the logarithm of solvent viscosity is explained in terms of a short‐lived singlet exciplex that serves as a precursor of the radical ion pair intermediate. Thus, solvent viscosity effects on the biexponential emission decay processes of 1 with small ΔGet in protic polar solvents provide a good criterion for the exclusive operation of a singlet‐exciplex mechanism in the case that a short‐lived exciplex and a long‐lived radical ion pair are produced. It was also found that any of activation parameters for ET fluorescence quenching process in acetonitrile is comparable to the corresponding parameter obtained in methylcyclohexane. This finding may present kinetic evidence for the participation of a singlet‐exciplex mechanism in the aprotic polar solvent, acetonitrile.
Nanocrystalline Palladium by Pulsed Electrodeposition
Authors: Natter H. , Hempelmann R. , Krajewski T. 
Published: July 2012

AbstractA pulsed electrochemical deposition technique is developed which allows to produce large amounts of nanocrystalline palladium with very low porosity. By an appropriate choice of the deposition parameters the shape and the size of the crystallites can be varied.
Solution of Hydrogen in Cold‐Worked Pd‐Ni, Pd‐Pt, and Pd‐Ni‐Ag Alloys
Authors: Kishimoto S. , Yoshida N. , Masui T. , Ibaragi T. , Nakano A. , Hiratsuka T. 
Published: July 2012

AbstractThe effect of cold‐working on hydrogen solubilities in the dilute region (α phase) has been investigated for Pd1‐xNix(x≤0.2), Pd1‐xPtx(x≤0.19), and Pd1‐xNi(1/2)xAg(1/2)x(x≤0.2) alloys by measuring pressure‐composition isotherms between 273 and 348 K. The enhancement of hydrogen solubility in Pd‐Ni alloys resulting from dislocation‐hydrogen interaction tends to increase with increasing Ni content, in contrast to the case of Pd‐Ag and Pd‐Au alloys. On the other hand, the solubility enhancements in Pd‐Pt and Pd‐Ni‐Ag alloys did not change significantly with alloying metal contents. These results can be qualitatively explained by the interactions between the alloying elements with different sizes and the stress fields of dislocations. The hydrogen trapping at defects such as vacancies was also predicted from the observation of the initial region of the isotherms for cold‐worked alloys. It was found that the extent of pressure hysteresis in the isotherm for Pd0.9Ni0.1 alloy which has been initially cold‐worked is less than for the well‐annealed alloy and in the case of Pd0.85Ni0.075Ag0.075 alloy the hysteresis disappears completely.
Measurements of Interaction Second Virial Coefficients of Binary Mixtures of Inert Gases and Gases
Authors: Vatter K. , Schmidt H. J. , Elias E. , Schramm B. 
Published: July 2012

AbstractThe interaction second virial coefficients of the mixtures Ar/CO, Ar/N2, Ar/O2, Ne/CO, Ne/N2, and Ne/O2were measured from 296 K to 463 K, utilizing the expansion method and the temperature changing method. Improvements in the previously described apparatuses reduced systematical errors and provided more accurate measurements of the coefficients. The experimental data were compared to calculations of interaction second virial coefficients based on modern potential energy surfaces. None of the previously reported potential energy surfaces was sufficient to account for the measured interaction second virial coefficients over our experimental temperature range from 296 K to 463 K.
Electronic Structure of Molten Salts: A Numerical Approach
Authors: Koslowski Thorsten 
Published: July 2012

AbstractWe present a numerical study of the electronic structure of a simple model of molten salts, with application to alkali halides. The geometry of the model is simulated using the primitive model of charged hard spheres, the electronic structure is described by a tight‐binding Hamiltonian. We study the influence of the topological and Madelung potential disorder on the evolution of the density of states upon melting and the optical absorption, the latter directly comparable to experiments. A population analysis of the cationic conduction band is performed, the results are discussed with respect to the possible formation of dipolar atoms in the corresponding metal‐molten salt solutions.
Curvature Elasticity Models of Microemulsions
Authors: Safran S. A. , Tlusty T. 
Published: July 2012

AbstractWe review the theory of curvature elasticity of thin, fluid films starting with a phenomenological formalism motivated by microscopic, physical examples. The effects of finite compressibility of the layer, exchange of molecules between the film and the solution, and the intrinsic bending stiffness of the film are taken into account; these degrees of freedom account for all the important molecular modes of the system. The effects of fluctuations of the number of molecules in the film (which is in equilibrium with surfactant molecules or micelles in solution) and in the area per molecule about its equilibrium value is shown to soften the curvature elastic moduli. The relationship of the bending moduli to the pressure distribution in the film is discussed and it is demonstrated that isotropic liquid films have no bending modulus, in the continuum limit. The bending moduli for charged membranes and for block copolymers and estimated. Finally, some recent experimental measure of curvature elasticity are discussed and compared with the theory.
FTIR‐Spectroscopic Study of Reactions of FCO and FC(O)OO Radicals in the Presence of O2 and NO2
Authors: Bednarek G. , Argüello G. A. , Zellner R. 
Published: July 2012

AbstractSteady‐state photolysis of oxalylfluoride (FC(O)C(O)F) together with FTIR‐spectroscopy has been used to investigate the reactions of FCO and FC(O)OO radicals in the presence of O2 and NO2. Formation of FCO radicals has been identified as the main photodissociation process of oxalylfluoride at λ = 254 nm. However, a quantum yield of ø = 0.11±0.02 was attributed to the direct formation of CF2O and CO in this process. In the presence of O2, the products of reactions of FC(O)Ox(x = 0, 1, 2) radicals were bis‐fluoroformylperoxide (FC(O)OOC(O)F) and bis‐fluoroformyltrioxide (FC(O)OOOC(O)F), as well as CF2O, CO and CO2. Addition of NO2 to the reaction system led to the formation of fluoroformylperoxynitrate (FC(O)OONO2). The rate constant for the thermal decomposition of fluoroformylperoxynitrate in the temperature range 275–307 K was measured to be k(T) = 3.5 × 1016 exp (‐13 900+1700−2600/T) s−1. For bis‐fluoroformyltrioxide, a rate constant for thermal decomposition of 6.0×10−4 s−1 was measured at temperatures around 250 K. The thermal stability of bisfluoroformyltrioxide and fluoroformylperoxynitrate is discussed in terms of a comparison with the stability of similar molecules.
Molecular Motions in a Molecular Crystal: Tetrachloro‐m‐Xylene
Authors: Moura Ramos Joaquim J. , Sousa Rui J. Cândido , Correia Natália T. , Dionísio Madalena S. C. 
Published: July 2012

AbstractIn the present work we report a study of the molecular relaxation processes in tetrachloro‐m‐xylene in the solid state. The techniques of dielectric relaxation spectroscopy and thermally stimulated discharge currents were used in order to identify and characterise the different relaxation processes and it was found that a solid rotator phase appears on heating at a temperature of ∼−125°C. It was also observed by thermally stimulated currents that a higher temperature relaxation occurs above ∼−15°C. The attribution, at the molecular level, of this relaxation is not straightforward and it was suggested that it probably corresponds to the onset of the self‐diffusional motions in the solid.
The Role of Surface Oxides in the Electrooxidation of Methanol, Formic Acid and CO on Pt, Ru and Codeposited Pt‐Ru
Authors: Frelink T. , Visscher W. , Cox A. P. , van Veen J. A. R. 
Published: July 2012

AbstractThe growth of an oxide layer on Pt, Ru and codeposited Pt‐Ru was monitored ellipsometrically during the electrooxidation of CH3OH, HCOOH and adsorbed CO. In the potential region where these molecules or their intermediates are oxidized at the Pt‐Ru surface, the Ru‐oxide is no longer observed. This supports the bifunctional mechanism that has been proposed for the promoting role of Ru on Pt. PtO is not involved in the HCOOH and COads oxidation. The adsorbed CO layer on Pt and on Pt‐Ru could also be observed with ellipsometry.
The Role of Solvent Permittivity in Estimation of Electrolyte Activity Coefficients for Systems with Ion Pairing on the Basis of the Mean Spherical Approximation
Authors: Tikanen Alex C. , Fawcett W. Ronald 
Published: July 2012

AbstractMean ionic activity coefficient for aqueous solutions of CdCl2, CuCl2, MgCl2, Na2SO4, MgSO4 and CdSO4, systems for which dielectric relaxation data have recently been obtained, can be estimated accurately on the basis of a modified version of the mean spherical approximation (MSA) for electrolyte solutions with consideration of ion pairing. The modification makes use of the actual solution permittivity rather than the permittivity of the pure solvent. Reasonable ion pairing association constants, Kas, have been determined by fitting the theoretically determined mean ionic activity coefficients to experimentally measured values in the range of concentration for which the dielectric permittivity data exist using one additional adjustable parameter, namely, the restricted diameter for all species involved.
Solvatochromism in Pure Solvents: Effects of the Molecular Structure of the Probe
Authors: Novaki Luzia P. , El Seoud Omar A. 
Published: July 2012

AbstractThe following solvatochromic probes were synthesized: 1‐methyl‐8‐oxyquinolinium betaine (QB), sodium 1‐methyl‐8‐oxyquinolinium betaine‐5‐sulphonate (QBS), and 1‐methyl‐3‐oxypyridinium betaine (PB). Their solvatochromic behavior in 28 protic and aprotic solvents was investigated, and the data compared to those of 2,6‐diphenyl‐4‐(2,4,6‐triphenyl‐1‐pyridinio)‐1‐phenolate, (RB). Solvent polarity scales based on QB, QBS, and PB correlate linearly with the ET(30) scale of RB. The Taft‐Kamlet‐Abboud equation satisfactorily applies to the solvatochromic data of RB, QB, QBS and PB. The multiparameter regression coefficients (a) and (s) of the above mentioned equation show that the sensitivity of the probe to solvent dipolarity/polarizability, and hydrogen bond donation is clearly dependent on its molecular structure. This dependence was tested for a total of 26 probes of widely different structures. It is shown that this is a general behavior, i.e., log |a| and |s| are linearly dependent on the pKa and the dipole moment of the probe, respectively.
Time‐dependent processes in polyelectrolyte solutions
Authors: Reed Wayne F. 
Published: July 2012

AbstractMost theoretical and experimental efforts in polyelectrolyte science have been aimed at understanding equilibrium properties. The purpose of this chapter is to call attention to the wide array of kinetic phenomena which occur in polyelectrolyte solutions on their way to equilibrium. Such time‐dependent processes include dissolution of dry powders, phase separation, aggregation, gelation, and degradation. Because equilibration times in polyelectrolyte solutions can be quite long, polyelectrolyte solutions may often be used and studied, wittingly or not, in non‐equilibrium states. After a brief review of some of the equilibrium properties of polyelectrolyte solutions, a few simple ideas and examples are given to illustrate non‐equilibrium processes. A larger emphasis is given to the degradation problem, simply because it is the area of time‐dependent phenomena where the author and co‐workers have so far made the most quantitative headway.
Viscoelastic properties of polyelectrolyte solutions
Authors: Noda Ichiro , Takahashi Yoshiaki 
Published: July 2012

AbstractViscoelastic properties of polyelectrolyte solutions were studied in the absence and presence of added salt over a wide range of polymer concentration in comparison with those of non‐ionic polymers in good solvents.In the semidilute region where the polymer concentration C is higher than the overlap concentration for viscosity C*v, but lower than C** (ca. 0.3 kg/dm3), the polymer concentration dependence of specific viscosity at zero‐shear rate η increases with increasing added‐salt concentration Cs and at high Cs it almost agrees with that of non‐ionic polymers in good solvents. In the concentrated and entangled region where C>C and C>C**, η more steeply increases with C even in salt‐free solutions, implying the screening of electrostatic interaction and the increase of local frictional coefficients as considered in concentrated non‐ionic polymer solutions.In the dilute region where C is lower than the overlap concentration for steady‐state compliance C, the steady‐state compliance Je more strongly depends on molecular weight and C than in non‐ionic polymer solutions. In the semidilute region where C>C, but C<C**, the polymer concentration dependence of Je is lower than that of non‐ionic polymer solutions. In the concentrated and entangled region where C>C and C>C**, the polymer concentration dependence becomes similar to that of non‐ionic polymer solutions. In the concentrated and non‐entangled region where C<C and C>C**, the frequency dependences of storage and loss moduli are well explained by the modified Rouse model like non‐ionic polymer systems in the same region.The experimental results in the semidilute region are well explained by our theory of viscoelastic properties of polyelectrolyte solutions based on the reptation model with electrostatic interactions.
Viscometric behavior of dilute polyelectrolytes. Role of electrostatic interactions
Authors: Roure I. , Rinaudo M. , Milas M. 
Published: July 2012

AbstractThis paper deals with the investigation of the electroviscous effects on sodium hyaluronate aqueous solutions. Dilution of a polyelectrolyte in water or low salt concentration solvent gives a reduced viscosity passing through a maximum whose position corresponds to a polymer concentration directly related to the ionic concentration. Independently of the molecular weight when isoionic dilution is performed, the conformation is preserved and the intrinsic viscosity corresponding to the adopted ionic concentration is obtained as soon as the concentration range corresponds to the dilute domain.At end the model previously proposed to take into account the role of the electrostatic interactions on the conformation is adopted to interpret, with a good agreement, the data of intrinsic viscosity versus ionic concentration.