bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrasound Propagation and the Volume Expansion Minimum in Potassium‐Ammonia solutions
Authors: Parker M. H. , Bowen D. E. 
Published: March 2014

AbstractThe volume expansion minimum reported by Evers and co‐workers was not seen when the measurements were repeated by Gunn and Green. In an attempt to detect this minimum, careful measurements of the velocity of ultrasound waves in potassium‐ammonia solutions have been performed. These measurements were made as a function of both temperature and metal concentration in the region of the reported minimum using a pulse superposition technique accurate to within one part in 104. The velocity is a linear function of the temperature and can be expressed by the equation:.

A minimum in C1 at the same concentration as the volume expansion minimum was seen; however, the relative errors present in C1 are such as to make confirmation of the volume expansion minimum doubtful.
Pressure and Temperature Dependence of Optical Properties of Potassium‐Ammonia and of Potassium Iodide‐Ammonia solutions
Authors: Vogelsgesang R. , Schindewolf U. 
Published: March 2014

AbstractThe absorption spectra of dilute potassium‐ammonia solutions, in which solvated electrons are present, and of potassium iodide‐ammonia solutions (ctts‐spectrum) are in a restricted temperature range shifted with increasing temperature to longer wave‐lengths and with increasing pressure to shorter wave‐lengths. These shifts are interpreted in terms of thermal expansion and of compression resp. of the solvation shells around the electrons and the iodide ions resp. (cavities) the size of which determines the wave‐length of light absorption. At higher temperature however the effects reverse their signs, indicating that the relationship between cavity size and position of the absorption maximum is not unambiguous.The reflectivity of concentrated potassium ammonia solutions increases with temperature but decreases with pressure. The reflectivity behaviour of the solutions therefore parallels their behaviour of electrical conductivity.
Organic Dye Laser Properties and Orientational Relaxation Processes
Authors: Gronau B. , Lippert E. , Rapp W. 
Published: March 2014

AbstractThe system 2‐amino‐7‐nitrofluorene/1,2‐dichlorobenzene was found to show laser action. Contrary to hitherto known dye lasers this system exhibits a blue shift of the dye laser spectrum with increasing dye laser intensity, dye concentration and resonator Q. During emission of a single pulse, the dye laser spectrum shows a blue shift with proceeding time. These effects are explained by orientational relaxation processes of the polar solvent molecules.
Messungen der scheinbaren Molwärme von Wasser in Zeolithen vom Faujasit‐Typ
Authors: Basler W. D. , Lechert H. 
Published: March 2014

AbstractDie scheinbare Molwärme von Wasser, welches in Poren verschiedener Zeolithe vom Faujasit‐Typ adsorbiert war, wurde im Bereich 90‐300 K für verschiedene Belegungen gemessen. Die Ergebnisse zeigen, daβ das adsorbierte Wasser sich bei 300 K wie eine Flüssigkeit verhält. Beim Abkühlen wird keine Kristallisationswärme beobachtet, sondern das Wasser erstarrt bei 200 ‐ 220 K zu einem amorphen Festkörper. Die Übergangstemperatur flüssig‐fest kann mit der Annahme berechnet werden, daβ sie der Sorptionsenergie proportional ist. Der Einfluß der Kationen auf das Verhalten der intrakristallinen Flüssigkeit ist nur gering.
Nachweis und thermisches Verhalten von CdOgas über festem CdO
Authors: Grade M. , Hirschwald W. , Stolze F. 
Published: March 2014

AbstractDie Existenz einer gasförmigen CdO‐Molekel wurde massenspektrometrisch mit Hilfe eines empfindlichen, hochauflösenden Massenspektrometers mit integrierter Knudsenzelle nachgewiesen und ihre Konzentration im Gleichgewicht mit festem Cadmiumoxid als Funktion der Temperatur gemessen. — Zwei gekoppelte Bildungsgleichgewichte werden zur näherungsweisen Berechnung der Dissoziationsenergie D0CdO der CdOgas‐Molekel aus der gemessenen Temperaturabhängigkeit in Betracht gezogen, in Analogie zu früheren Berechnungen für gasförmiges Zinkoxid [1]. Als Mittelwert für D0 ergibt sich:
Stress Induced Drift Diffusion in Grain Boundaries – Application to Creep and to the Growth of Grain Boundary Voids
Authors: Trinkaus Helmut 
Published: March 2014

AbstractThe diffusional matter transport in grain boundaries under the influence of stress fields is discussed. The most important relations, connected with the scaling behaviour of the basic equations, can be deduced from simple estimates. On this basis it is shown (1) that the range of a matter inhomogeneity in a grain boundary and that of the related stress field develop in time as t1/3, (2) that in the early stage the diffusional creep deformation goes with t2/3, (3) that under constant stress isolated grain‐boundary voids grow with constant volume growth rate. The time to brittle fracture caused by simultaneous nucleation and growth of grain‐boundary voids is discussed.
Physico‐Chemical Interaction between Biominerals and their Environment
Authors: Driessens F. C. M. 
Published: March 2014

AbstractA reconsideration of literature data reveals that the incorporation of vacancies, Na, K, Sr, Cl, and CO3 into hydroxyapatite increases its apparent solubility product, whereas that of F decreases it. It is further shown that the composition of saliva is regulated so that a steady state is reached for erupted teeth whereby equilibrium between mineral and saliva is close to the two‐phase boundary of apatite and dicalciumphosphatedihydrate (DCPD). The theory explains qualitatively why and how gradients occur of F, Na, and CO3 in surface enamel, why the surface layer remains nearly intact during caries and why calcifications occur in the arteries and not in the veins. – It is assumed that the incorporation of Mg and citrate ions can increase the apparent solubility product of tricalciumphosphate (TCP) and octacalciumphosphate (OCP) respectively. On this basis an estimate is made of the relative position of the stability fields of apatite, DCPD, TCP, and OCP. This estimate indicates why these calcium phosphates may occur simultaneously in dental calculus, bone, dentine and pathological calcifications. If both the effect of crystal size and that of incorporation of foreign ions are taken into consideration, it can be presumed that calcified tissues are in momentary physico‐chemical equilibrium with the body fluids bathing them.
The Influence of H – H Pairing on the Diffusional Behaviour of Hydrogen in Niobium
Authors: Boes N. , Wicke E. 
Published: March 2014

AbstractThe energy of interaction of neighbouring H atoms is estimated by a simple model for the elastic strain on the metal lattice by interstitial hydrogen. This energy is compared with results obtained by the measurement of thermodynamic equilibrium data in the system Nb/H. – A jump model considering this interaction is proposed for the diffusion of paired H atoms. It explains the observed anomalous temperature dependence of the diffusion coefficient of hydrogen in niobium. – On the basis of this novel process of diffusion the elimination of the anomaly by additionally solved impurities like oxygen or nitrogen can be understood.
Two Routes in the Formation of Hydrogen Halides from OH Adducts of Halogenated Anisoles in Aqueous Solution
Authors: Latif N. , O'Neill P. , Schulte‐Frohlinde D. , Steenken S. 
Published: March 2014

AbstractUsing pulse radiolysis with conductivity detection and steady state γ‐radiolysis it is shown that in aqueous solution the reaction of OH radicals with 2,3‐ and 4‐monohalo (X = F, Cl, Br) anisoles leads to the production of hydrogen halides (HX). The G‐values for production of hydrogen halides measured 10 μs after the pulse are large for the 2‐ and 4‐haloanisoles (G(HX) = 0.5‐1.45) and small for the 3‐haloanisoles (G(HX) = 0.1‐0.3). These yields reflect the amount of OH addition to ring positions substituted by X. The differences in these amounts reflect an ortho‐para directing activity of the methoxy group. – In the case of the OH adducts of 3‐haloanisoles – in contrast to those of 2‐ and 4‐haloanisoles – in addition to the prompt a second order elimination of HX is observed which occurs on the ms time‐scale. This shows that the distribution of OH addition cannot always be obtained from product studies using γ‐radiolysis. The G(HX) values measured using steady state γ‐radiolysis agree with those determined in the ms range using pulse radiolysis.
Two‐ and Three‐Dimensional Reactions of Ag+2 Radical Cations in Aqueous Solutions of Anionic Tensides
Authors: Henglein A. , Proske Th. 
Published: March 2014

AbstractAg+2 radical cations were produced in aqueous 1 · 10−4 molar Ag2SO4 solutions containing micelles of sodium hexadecyl trioxiethylene sulfate and of sodium dodecylsulfate by a short pulse of high energy electrons. The disappearance of Ag+2 and the appearance of Ag2 were followed by optical measurements in the 10−6 to 10−2 s range. – A fraction of the Ag+2 radicals decayed within 1 to 2 microseconds, and the remaining radicals disappeared in a second order process within 10−4 to 10−2 s. These decay processes are attributed to(a) intramicellar or two‐dimensional radical‐radical reaction at the surface of doubly occupied micelles, and(b) intramicellar or three‐dimensional reaction between radicals that are singly adsorbed at micelles. The fraction of (a) increases with increasing concentration ratio of radicals to micelles as expected from statistical considerations. Deviations at low concentration ratios are attributed to the initial formation of some of the radicals in spurs. The observed 100 fold acceleration of the radical‐radical reaction by the reduction in the dimensionality of reaction space is also compared to similar effects in fast biochemical reactions on large carrier molecules.It is concluded from an analysis of the dependence of the bimolecular rate constant of reaction (b) on the tenside concentration that Ag+2 cations reside longer than milliseconds at micelles and can be exchanged directly between two anionic micelles. The rate constants are given for the two tensides.
Substitution Reactions of Beryllium (II) Ion in Mixed Solvents. I. The Beryllium Sulphate Complex in Water‐Formamide Mixtures
Authors: Lachmann R. , Wagner I. , Devia D. H. , Strehlow H. 
Published: March 2014

AbstractThe formation of the inner‐sphere complex of BeSO4 in mixtures of water and formamide has been investigated using the pressure‐jump relaxation method. Whereas in the two pure solvents the reaction is characterized by a single relaxation time in the solvent mixtures two relaxation processes superimpose and which are attributed to the replacement of a water or a formamide molecule, respectively, in the inner‐sphere by the entering sulphate ion. – The multistep association mechanism proposed by Eigen and Tamm [1] prevails also in the solvent mixtures. With increasing mole fraction of formamide the dielectric constant increases and in accordance with Fuoss equation [2] the association constants of the outer‐sphere complexes decrease. However, the inner‐sphere stability constants increase sharply so that the total association constants of BeSO4. increase with the formamide content. The ligand assisted dissociative process (Id [3]) outer‐sphere r̊ inner‐sphere complex is discussed in terms of a concerted mechanism proposed earlier for aqueous solutions [4].
Diffusion Limited Oxygen Quenching of Photo‐Induced Electrochemical Reactions in Sandwich Systems with Molecular Crystals
Authors: Killesreiter Hermann 
Published: March 2014

AbstractPhotoelectrochemical reactions in sandwich systems with the dye 3,3′‐distearyl‐oxacarbocyanine chlorate adsorbed in monolayer assemblies on p‐chloranil single crystals have been used to demonstrate the quenching action of paramagnetic oxygen on sensitized as well as on triplet exciton induced photocurrents. Simultaneously, the presented measurements are a method to study the lateral diffusion of oxygen into monolayer assemblies between the crystal surface and an evaporated aluminum electrode by photoelectrical detection. From the functional time dependence of a reciprocal square‐root law and together with the discussion of a kinetic scheme the rate constants for the quenching of excited dye molecules and of n‐π*‐triplet excitons at the phase boundary could be evaluated to be kq = 2.5 · 1012 M−1 s−1 and 3kq = 1012 M−1 s−1, respectively, on the basis of an estimated upper limit for the diffusion coefficient D = 4 · 10−6 cm2 s−1 for oxygen diffusion into the slab with a bilayer structure. – The method has been extended to sandwich systems with rhodamine B on the surface of anthracene and p‐chloranil crystals that showed no effect due to oxygen, whereas the systems cyanine dye/anthracene revealed less marked photocurrent enhancements as well as decreasings. These results are discussed in terms of hindered oxygen access and of an extended reaction scheme that involves the well‐known oxidizing action of oxygen in sensitization.
1H and 19F Nuclear Spin‐Lattice Relaxation in Solid [X(CH3)4]2SiF6, X = N, P, As and Sb
Authors: Rager H. , Weiss Alarich 
Published: March 2014

AbstractThe spin‐lattice relaxation times T1(1H) and T1(19F) in the solid compounds [X(CH3)4]2SiF6, X = N, P, As, and Sb, were studied in the temperature range 125 K ⩽ T ⩽ 460 K at a NMR frequency of 34 MHz. In the low temperature region protons and fluorine nuclei are coupled by dipole‐dipole interactions and both spin systems relax mainly through the motions of the methyl groups. The activation energy of the methyl group reorientation, Va, decreases with increasing size of the cation. With increasing temperature both T1(1H) and T1(19F) are influenced by the reorientation of the cations as a whole. The activation energy Va1 of the reorientation of [X(CH3)4]+ was determined. From the linewidths of the free induction decays it is concluded that the dynamical behavior of the compounds is mainly determined by the size of the cations. The influence of the anion on T1, is small causing a slight increase of the activation energy Va compared to Va in [X(CH3)4]I. From the Raman spectrum of [N(CH3)4]2SiF6 a 90° reorientation mechanism of the cation seems most probable.
The Influence of Amphiphilic Substances on the Mutual Solubilities in Binary Liquid Systems (Microemulsions)
Authors: Herrmann C.‐U. , Würz U. , Kahlweit M. 
Published: March 2014

AbstractThis paper summarizes the first results of an investigation on the influence of amphiphilic substances on the mutual solubilities of two partially miscible liquids. In the first part, the ternary system C6H6–H2O – Alcohol are studied and in the second part, the quarternary systems C6H6 – H2O – Alcohol – NaDS. The effectivity of different alcohols is discussed as well as the influence of the surfactant on the shape of the phase diagram. The microscopic structure of the solutions was investigated by means of light scattering, small angle X‐ray scattering, and conductivity measurements. The structure of the micelles in different regions of the phase diagram is discussed. The results indicate the existence of a critical composition for the formation of inverse micelles in the C6H6 rich region.
A Proton Magnetic Resonance Investigation of Molecular Motion and Phase Transition in Solid Diamminesilver Dinitroargentate, [Ag(NH3)2]Ag(NO2)2
Authors: Maurer H. M. , Ragle J. L. , Weiss Alarich 
Published: March 2014

AbstractThe second moment and the spin‐lattice relaxation time, T1, of the proton magnetic resonance have been studied in a polycrystalline sample of diamminesilver dinitroargentate. The broadline measurements indicate that the ammine groups reorientate rapidly around their triad axes. A phase transition has been detected by differential thermal analysis at −91°C. Activation energies for the reorientation of 7.20 ± 0.38 kJ mol−1 and 9.96 ± 0.30 kJ mol−1 are derived from the T1‐measurements for the room temperature phase (I) and the low temperature phase (II), respectively. The results are discussed on the basis of the crystal structure. The phase transition can be described by a change from an ordered to an orientationally disordered arrangement of the nitrite ions.
Spectroscopy of Minerals
Authors: Lehmann Gerhard 
Published: March 2014

AbstractExamples for the application of five spectroscopic methods to mineralogical problems which exceed a mere characterization are discussed. In addition in some examples results of infrared and optical absorption as classical spectroscopic tools are also used. In many cases the nonideal compositions and structures of the minerals are of decisive influence upon the results, and sometimes they even generate the observed phenomena.
Picosecond Polarization Spectroscopy of Dye Molecules
Authors: Reiser D. , Laubereau A. 
Published: March 2014

AbstractTheoretical and experimental data are presented on the propagation of picosecond pulses in weakly excited dye solutions. We report a new version of the pump and probe technique, measuring induced dichroism at variable probe pulse frequency. It is shown that the so‐called “coherence peak” in experiments with equal pump and probe frequencies depends on the vibronic relaxation and excited state absorption of the dye molecules. Measurements with different pump and probe frequencies allow to distinguish rotational relaxation times in different electronic states. Interpretation of the experimental data is considerably facilitated at the low excitation intensities used here. Experimental results for vibronic and rotational time constants on phenoxazone 9 and rhodamine 6G are presented.
From Micellar Solutions to Liquid Crystalline Phases
Authors: Hoffmann H. 
Published: March 2014

AbstractThe types of micelles and their sizes which exist in surfactant solutions in the isotropic concentration range in between the critical micelle concentration (Ccmc) and the concentration for liquid crystal formation (Cl.c.) are discussed. Four different types of ionic surfactants are treated:
single chain surfactants with a cubic phase as the first l.c. phase
single chain surfactants with a hexagonal phase as the first l.c. phase
double chain surfactants with a lamellar phase as the first l.c. phase
perfluoro‐surfactants.
Vergleich der Perturbed‐Hard‐Chain‐Theorie mit der Freien‐Volumen‐Theorie und der Flory‐Huggins‐Theorie zur Berechnung von Phasengleichgewichten von Ethylen/Polyethylen‐Mischungen unter Hochdruck
Authors: Jungermann Georg , Luft Gerhard 
Published: March 2014

AbstractThe perturbed‐hard‐chain theory, the free‐volume‐theory and the well known Flory‐Huggins lattice theory of polymer solutions were applied to phase‐equilibrium calculations for mixtures of ethylene and low density polyethylene. The parameters required for the calculations were determined from a large number of experiments under high pressure. By comparison of calculated and measured phase‐equilibrium data it is shown that the perturbed‐hard‐chain‐theory can be applied to predict accurately composition of phases as well as the molar mass of the polymer in the ethylene‐ and in the polyethylene‐rich phases from ambient to high pressure. The free‐volume‐theory failed for pressures near the critical. The solubility of ethylene in the polymer‐rich dense phase could be calculated by means of Flory‐Huggins‐Theory only for low to medium pressures up to 300 bar in good agreement with the experimental data. By means of the perturbed‐hard‐chain‐theory engineers may interpolate and extrapolated limited experimental data with confidence for optimal design of large scale polymerization reactors and separators.
Slit length correction of slowly decaying small‐angle X‐ray scattering‐patterns using a formal extrapolation of the pinhole curve searched for
Authors: Ledent J. , Fontaine F. , Reynaers H. 
Published: March 2014

AbstractStarting from the desmearing method used in small‐angle X‐ray scattering (SAXS) investigations which is based on the processing of a set of linear equations, a procedure is proposed to compute in a single step the pinhole curve as well as an extrapolation curve of the latter towards the wide angles. To this end a small number of parameters are added to the unknowns of the problem to fix some known boundary conditions towards the wide angles. Before solving the equations the added parameters are expressed in terms of the intensity‐unknowns in order not to increase their number. The procedure is presented in the frame of the analysis of SAXS‐data recorded from samples the structure of which can be described by the two‐phase concept.
The influence of water and of alkali promotor on the carbon number distribution of fischer‐tropsch products formed over iron catalysts
Authors: König L. , Gaube J. , Meisel W. , Gütlich P. , Gerhard W. , Plog C. 
Published: March 2014

AbstractThe carbon number distribution of Fischer‐Tropsch products formed over an alkalized precipitated iron catalyst has been studied as a function of the water vapor pressure of the synthesis gas. The carbon number distribution of formed hydrocarbons is characterized by a bimodal Schulz‐Flory distribution of growth probabilities P1 ≈ 0.6 and P2 ≈ 0.87 attributed to unpromoted and promoted (alkalized) sites on the catalyst surface. Promoted sites are more stable with respect to oxidation (deactivation) by water than unpromoted sites. The growth probability of unpromoted sites decreases with increasing ratio P/P — Studies using Mössbauer spectroscopy have shown that iron foils treated with water containing some K2CO3 yield smaller fractions of iron oxides at the surface than those treated with pure water. Also studies on reduced precipitated iron catalysts using SIMS have shown that alkaline treatment reduces the oxidation of iron by water. These results are interpreted in terms of electronic effects.
Analysis of “two‐electron” transfer processes by cyclic voltammetry
Authors: Hinkelmann Klaus , Heinze Jürgen 
Published: March 2014

AbstractThe cyclic voltammetric response for “two‐electron” transfer processes is studied for magnified image. Evaluation of the EE mechanism has been generalized to those cases where the standard heterogeneous rate constants k01 and k02 of both charge transfer steps may take any value between the reversible and irreversible limits and differ by one to two orders of magnitude. A correct interpretation of the cyclic voltammograms demands that the homogeneous disproportionation reaction: 2B ⇋ A + C be included (EE‐DISP). Simulated voltammograms and working curves are presented. Their use opens a way for the quantitative determination of the thermodynamic and heterogeneous kinetic parameters of “two‐electron” transfer reactions.
The jellium model in electrochemistry
Authors: Badiali J. P. 
Published: March 2014

AbstractWe examine the direct contribution of the metal to the differential capacitance of an ideally polarizable electrode. We discuss the extension of the jellium model to the case of noble metals. A simple and rather realistic model is proposed for describing the electronic structure of these metals. We check this model by investigating the electronic work function and its variation with the cristallographic orientation of the surface. Satisfactory results are obtained. As a first step in the calculation of the capacitance we study the response of the metal to an external charge. We may conclude that the metal has certainly a large contribution to the capacitance. Moreover, the correct variation of the capacitance with the orientation of the surface is predicted although the absolute determination of the capacitance seems to be extremely difficult.