bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Density of Ammonia at High Pressures to 723 K and 950 MPa
Authors: Harlow A. , Wiegand G. , Franck E.U. 
Published: March 2014

AbstractHigh pressure‐high temperature procedure and equipment is described to determine the specific volume of ammonia as a function of pressure and temperature. An autoclave consisting of a nickel‐based superalloy and a suitable pressure‐sensitive separator between ammonia and the pressure‐transmitting fluid is used. Ten volume isotherms between 298 and 723 K and at pressures from 10 to 950 MPa have been determined. Previous literature data extend to 950 MPa but only up to 473 or to 723 K at pressures below 500 MPa. Polynomials with up to eleven terms are used to represent each experimental volume isotherm with a maximum average deviation of 0.16%. A table with smoothed density values is presented for the whole range of conditions. A comparison with data calculated earlier by Haar and Gallagher (1978) up to 500 MPa showed deviations between 0.06 and 1.1% with an average of 0.4%. The present isothermal volume data are reasonably well described by Tait equations. Parameters are given.
Concentration‐Dependent Electroacoustic Spectra of Some Simple Alkali‐Halide Aqueous Electrolytes
Authors: Tankovsky N. , Bärner K. 
Published: March 2014

AbstractExcitation of acoustic waves in electrolytes by means of a.c. electric fields has been used to examine the structural and dynamical properties of the solutions. The acoustical signal efficiency depends on the electrolyte concentration and on the frequency of the exciting electric field. Experimental results, obtained in the aqueous solutions of LiCl, NaCl and KCl, are discussed. The influence of the electroacoustic‐cell design on the obtained results is studied as well.
A Time Domain Reflectometer for Dielectric Relaxation Spectroscopy of Electrolyte Solutions
Authors: Buchner R. , Barthel J. 
Published: March 2014

AbstractA time domain reflectometer for dielectric relaxation spectroscopy of electrolyte solutions in the temperature range of −;45 ≤ ϑ /°C ≤ 90 is presented. With a set of cutoff cells differing in their cell constants, pure solvents covering the permittivity range of 7 ≤ ϵ ≤ 228 and their concentrated electrolyte solutions (κ > 1 Ω−1 m−1) can be investigated at frequencies of 0.05 ≤ v/GHz ≤ 9. In combination with the transmission line system of our laboratory (8.5 ≤ v/GHz ≤ 89) dielectric dispersion, ϵ′(v), and total loss, η″(v) = ϵ″(v) + κ/(2π vϵ0) can be determined with 2% accuracy relative to ϵ.
Characterization of Mo Species Supported on SiO2 Modified with Be2+ and Mg2+
Authors: Aroni Phryni 
Published: March 2014

AbstractTwo series of modified carriers (m.c.) have been prepared by doping silica with various amounts of Be2+ and Mg2+. The prepared m.c. have been used as supports for the preparation of supported Mo(VI) oxide catalysts. The magnitude of interactions between SiO2 and Be2+ or Mg2+ nitrates depends on the kind and content of the cation. After calcination at 600°C a greater fraction of cations remains on the support surface as well dispersed M(NO2)2 in the case of Mg2+ m.c. Concerning the Mo containing samples it was found that doping by Be2+ and Mg2+ causes a solid state transformation of octahedral Mo(VI) to tetrahedral Mo(VI). As before, the extent of the effect differs between Be2+ and Mg2+ and it varies with the content of cation. This effect has been attributed to the inhibition of the polymerization of monomeric Mo(VI) species and/or to the formation of molybdate salts.
The Shape of Se‐Precipitates in a CdSxSe1−x‐Doped Glass
Authors: Gorski Nikolai , Kalus Jürgen , Kunze Bernd , Bischof Thomas , Kiefer Wolfgang , Wiedenmann Albrecht 
Published: March 2014

AbstractSmall angle neutron scattering (SANS) experiments have been carried out on a semiconductor‐doped glass in order to determine the average size and shape of CdSxSe1−x precipitates (x ≈ 0.7). The crystallites are of spherical shape with a mean radius of Rp = 3.5 ± 0.1 nm and are rather monodisperse. The polydispersity is lower than ΔR/Rp ∼0.1. Approximately 69% of CdSxSe1−x are bound in the precipitates, the rest is dissolved in the glass matrix.
The Effect of Ion Size on Solution Mechanism and Defect Cluster Geometry
Authors: Grimes Robin W. , Busker Gerdjan , McCoy Michael A. , Chroneos Alexander , Kilner John A. , Chen Shao‐Ping 
Published: March 2014

AbstractAtomistic simulation calculations are used to predict the solution mechanisms and the defect cluster geometries of: M2+ dopant cations in Y2O3, M3+ dopant cations in CoO and M2+ dopant cations in SrTiO3. The interatomic potential parameters were derived by simultaneously fitting the properties of a range of mixed cation materials. The results suggest that although both solution enthalpies and cluster binding energies do scale with ionic radius, the relationships can be quite complex, materials specific and will not necessarily exhibit simple minima when the radius of the host cation equals the dopant cation, as described in previous studies.
First Principles Description of the Valence States in Manganese Oxides
Authors: Mackrodt W. C. , Williamson E.‐A. 
Published: March 2014

AbstractFirst principles periodic Hartree‐Fock calculations of Li:MnO, LixMnO2 and CaMnO3 are reported from which direct evidence is presented to indicate that the valence state of Mn remains essentially d5 throughout the series. The net spin moment on Mn, on the other hand, follows that convential change from ∼5μB to ∼3μB associated with the valence states Mn(II), Mn(III), Mn(IV).
Recent Studies of Localized Modes in Crystals
Authors: Sangster M.J.L. 
Published: March 2014

AbstractSome recent simulations of localized vibrational modes associated with substitutional impurities in crystals are discussed. Most of the examples are for impurities in III–V semiconductors and alkali halides, cases for which improvements in measurement and sample preparation techniques have generated new exacting tests for theoretical models. The displacements of atoms in the modes are revealed by the fine structure from isotopes of both the impurity and the host crystal atoms. Available schemes for modelling these dynamical properties of defects are reviewed.
Migration of Atomic and Molecular Hydrogen in SiO2: A Molecular Dynamics Study
Authors: Bongiorno A. , Colombo L. 
Published: March 2014

AbstractWe present a theoretical investigation on diffusion of atomic and molecular hydrogen in crystalline as well as amorphous silicon dioxide by means of molecular dynamics simulations. We report a characterization of the migration process of atomic hydrogen in quartz and tridymite and we provide an atomistic description of the diffusion of both atomic and molecular hydrogen in silica.
Spectroscopic Studies of High‐Temperature Processes in Oxides
Authors: Becker K.D. 
Published: March 2014

AbstractSpectroscopic studies can provide important information on physico‐chemical processes in solids, like, e.g., order‐disorder processes, the point defect structure and local defect arrangements, and heterogeneous as well as homogeneous chemical reactions of solids. Results will be reported relating to these topics from experiments that have been performed under in situ conditions, i.e. at high temperatures and under defined conditions of oxygen partial pressures. The examples have been chosen from high‐temperature studies using optical spectroscopy and Mössbauer spectroscopy.
FTIR Spectroscopy to Monitor OH‐Impurity Interactions in Insulating Crystals
Authors: Capelletti Rosanna , Beneventi Paola , Ruffini Andrea 
Published: March 2014

AbstractHydroxyl ion is a common impurity in insulating crystals: by interacting with other impurities, it gives rise to new complexes. The OH‐stretching frequency is a very sensitive probe of the hydroxyl environment. High resolution (0.04 cm_1) FTIR spectroscopy in the temperature range 9–300 K was applied to study the OH‐cation impurity interaction in alkali halides, fluoroperovskites, and sillenites, suitable for optoelectronic applications. Proper thermal treatments and isotopic substitutions allowed to assign the stretching mode absorption lines to the defects in which OH– is embedded and to supply possible models for them. Anharmonicity effect of the OH– ‐stretching modes, monitored by weak overtone lines, were well described in the framework of the Morse model. Electric anharmonicity was also detected. The phonon coupling of the OH–‐stretching mode in different defects was studied by analysing the temperature dependence of the line‐position and ‐width: in most cases the single‐phonon coupling model accounted for the experimental data and supplied the coupled phonon frequencies.
Pairing between Radioactive Solutes and Point‐Defects in Semiconductors
Authors: Wichert Thomas 
Published: March 2014

AbstractThe study of solute point‐defect interactions in crystals is performed on an atomic scale by employing radioactive solutes as local observers. Thereby, the presence of a point‐defect next to the solute atom becomes observable via the altered electronic charge distribution about the solute, giving rise to a defect‐specific electric field gradient. Using the perturbed γγ angular correlation technique, this electric field gradient is detected via the hyperfine interaction occurring at the site of the nucleus of the radioactive atom. The sensitivity to solute point‐defect pairs is typically in the order of 1016cm–3. Several properties of these pairs, such as their chemical nature and thermodynamical behaviour are discussed. The point‐defects addressed in this paper are intrinsic, such as lattice vacancies, and extrinsic, such as substitutional and interstitial impurity atoms. Results for the elemental semiconductor Si and different II‐VI compound semiconductors will be discussed.
FTIR Spectroscopy to Monitor Impurities and Impurity‐Interactions in Sillenite Crystals
Authors: Capelletti Rosanna , Beneventi Paola , Kovács László , Ruffini Andrea 
Published: March 2014

AbstractHigh resolution (0.04 cm–1) absorption spectroscopy is applied at 9 K to study the role played on the vibrational spectra by impurities (Im), as Si4+, Ge4+, P5+, V5+, Mn5+, and S6+, in Bi12SiO20 (BSO), Bi12GeO20 (BGO), and Bi12TiO20 (BTO) sillenite single crystals. Up to three‐phonon transitions (overtones of the F mode and combination of F and A modes) are detected for the impurities in ImO4 tetrahedra. Weak anharmonicity effects are monitored. The presence of additional Im impurities modify the lines due to a) the stretching of OH, typical of the undoped material, and b) the multi‐phonon transitions either of the intrinsic MeO4 (Me = Si, Ge, and Ti) and of the ImO4 tetrahedra. New bands are monitored due to the Im‐OH interaction.
Models of Matter Transport: Their Verification and Use for Dilute Systems with the Aid of Statistical Theories
Authors: Allnatt A.R. 
Published: March 2014

AbstractStatistical expressions for the Onsager phenomenological coefficients are now available for several models of matter transport in systems which are dilute in solutes, vacancies and interstitials. They describe transport by unpaired and paired defects, as in the familiar five‐frequency model. The role of atomistic calculations of the parameters of such models in validating, simplifying or improving them is illustrated. In general it may be difficult to convincingly determine from experiment all the parameters of a given model or to distinguish between closely related models, such as between those retaining first or first and second neighbour binding between a solute and a vacancy. Nevertheless, there is particular utility in knowledge of all the Onsager coefficients for models suggested by atomistic calculations and other information, when one interprets phenomena involving coupled fluxes. This is illustrated by the example of coupled fluxes of a solute, vacancies and interstitials in a dilute alloy under steady irradiation by high energy particles. Here, essential contributions to modelling solute segregation to grain boundaries can be made; striking qualitative differences between closely related models can occur in this case. Finally, the limitations of the current statistical results are examined for systems where the solutes and defects carry effective charges. Limitations are suggested at low temperatures by the existence of a phase transition in the restricted primitive model of dilute aqueous electrolytes. The range of concentration and temperature within which the current procedures, stemming from the early work of Teltow and Lidiard, have been properly validated is limited. In the absence of recent theoretical advances Monte Carlo simulation is becoming the method of choice in investigating such limitations and in studying the transition to higher concentrations where there are larger clusters of defects.
Proton Dynamics in Interacting Hydrogen Bonds in the Solid State: Proton Tunneling in the NHO Hydrogen Bonds of N,N′‐Di(2‐Hydroxy‐1‐Naphthylmethylene)‐p‐Phenylenediamine
Authors: Takeda Sadamu , Inabe Tamotsu , Benedict Claudia , Langer Uwe , Limbach Hans‐Heinrich 
Published: March 2014

AbstractCombination of comprehensive investigations of the spin‐lattice relaxation rate of proton and low temperature 15N‐CP/MAS NMR spectrum provides unique information of proton dynamics in two interacting NHO hydrogen bonds of solid N,N′‐di(2‐hydroxy‐1‐naphthylmethylene)‐p‐phenylenediamine (DNP). It was evidenced from the 1H‐NMR relaxation measurement that tunneling mechanism operates for the proton transfer in the hydrogen bonds. The tunneling phenomenon is closely related to the very small energy differences among the four tautomeric states accompanied with the proton transfer in the two NHO hydrogen bonds. The very small values of the energy difference, in spite of the chemically asymmetric NHO hydrogen bond, were revealed by the 15N‐CP/MAS NMR spectrum. This is a unique character of solid DNP. It was also suggested from the derived energy scheme of the four tautomers and activation energies of the proton transfer that an interaction exists between the two NHO hydrogen bonds linked by π‐electronic molecular frame. This means that the information of one NHO hydrogen bond, i.e. OH‐form or NH‐form, propagates to the other hydrogen bond and the proton transfer in the first hydrogen bond induces the change of the potential function for the proton transfer in the second hydrogen bond.
Electrochemistry of Steel Electrodes: A Combined Study by Linear Reflectivity Measurements and Second Harmonic Generation
Authors: Kohring R. , Buck M. , Eisert F. , Grunze M. , Vogelsang J. 
Published: March 2014

AbstractSteel electrodes were investigated under electrochemically controlled conditions at pH 13. The linear reflectivity at 1064 nm and the second harmonic signal (SHG) at 532 nm generated in reflection were measured for different polarizations and recorded simultaneously with cyclovoltammograms. The potential was varied between −1.4 V and 0.5 V vs. SCE and the optical signals were recorded after repetitive cycling. The reflectivity which probes the whole thickness of the electrochemically active layer and the non‐linear optical signal which, in contrast, only probes the electrode surface and its immediately vicinity, exhibit very different behavior with respect to their potential dependence. In a cathodic scan the increase of the respective optical signals is associated with different peaks of the cyclovoltammogram. Furthermore, the SHG signal is strongly dependent on the polarization. The pronounced changes around −1.25/‐1.1 V in the cathodic/anodic scan direction, which are observed for pp‐polarization, are absent in sp‐ and ms‐polarization. The sp‐signal shows features which are paralleled by a decrease in the linear reflectivity. Contrary to the other polarizations, the ms‐polarized signal does not show any particular features correlated with peaks of the cyclovoltammogram. The potential dependence of the surface charge expressed by a simple parabolic model describes the SHG signal over extended parts of the potential range. The differences between the potential dependence of the SHG signal and the change of the linear reflectivity fully agree with the two layer model of electrochemically formed iron oxides.
Thermodynamics of Vanadium Redox Flow Batteries ‐ Electrochemical and Calorimetric Investigations
Authors: Heintz A. , Illenberger Ch. 
Published: March 2014

AbstractThermodynamic properties of the so‐called All‐Vanadium battery used as energy storage system and other vanadium redox systems related to the All‐Vanadium battery have been studied. An electrochemical cell has been constructed to measure the equilibrium cell voltages as function of the degree of charging in the temperature range from 278 K to 323 K. The first system studied is the disproportion reaction of VO2+ ions with the two half cell reactions VO2+ + H2O ⇄ VO+2 + 2H+ + e− and VO2+ + 2H+ + e− ⇄ V3+ + H2O. The second system is the All‐Vanadium battery reaction with the two half cell reactions VO2+ + H2O ⇄ VO+2 + 2H+ + e− and V3+ + e− ⇄ V2+. The third system is the disproportion reaction of V3+ ions with the half cell reactions V3+ + H2O ⇄ VO2+ + 2H+ + e− and V3+ + e− ⇄ V2+. The molar reaction Gibbs energy, the molar reaction enthalpy, and the molar reaction entropy of each system has been obtained from these data. Additionally the molar reaction enthalpy of the two disproportion reactions and of the reaction V2+ + 2VO2+ + 2H+ → 3VO2+ + H2O has been measured directly by titration calorimetry. The results agree with those obtained from the electrochemical data for the disproportion reactions. No direct calorimetric measurements of the molar reaction enthalpy of the All‐Vanadium battery reaction is possible, but the sum of the molar reaction enthalpies of the two disproportion reactions gives the molar reaction enthalpy of the All‐Vanadium battery reaction. Comparison with the electrochemically determined molar reaction enthalpy of the All‐Vanadium battery reaction shows good agreement indicating satisfying thermodynamic consistency of the whole procedure.
Polymer‐Surfactant Interactions: Non Ionic Polymers with SDS and DTABr
Authors: La Mesa Camillo , Persi Livio , D'Aprano Alessandro 
Published: March 2014

AbstractPolymer‐surfactant interactions in water‐SDS‐polyvinylpyrrolidone (PVP), water‐SDS‐polyoxyethylenglycol (PEO), water‐(DTABr)‐(PEO) and in water‐SDS‐polyoxypropylenglycol (PPO), systems have been investigated by ultrasonic relaxation, adiabatic compressibility and viscosity measurements.Both the hydrodynamic and thermodynamic properties show significant changes at the critical association concentration in presence of polymer. As to the kinetic behaviour, investigation on systems containing PEO or PVP indicates the occurrence of a region where relaxation times are nearly constant. For the low molecular weight PPO polymer this effect has not been observed. Such differences have been ascribed to the minimum polymer chain length effect, required for the binding of surfactant aggregates on the polymer backbone. The dynamics of polymer‐surfactant interactions has been discussed in terms of a kinetic model, previously proposed.
Determination of the ortho‐, para‐, and meta‐Interactions in secondary‐Alkylphenols from Thermochemical Measurements
Authors: Verevkin Sergey P. 
Published: March 2014

AbstractThe standard molar enthalpies of formation ΔfH0m, (1 or cr) at the temperature 298.15 K were measured by using combustion calorimetry for 4‐ethylphenol, 2‐iso‐propylphenol, 2‐iso‐propyl‐5‐methylphenol, 2‐sec‐butyl‐phenol, 4‐iso‐propylphenol, 4‐sec‐butylpnenol, and 4‐cyclo‐hexylphenol. The enthalpy of formation ΔfH0m, (1) of 3‐iso‐propylphenol was obtained from the results of calorimetric and equilibrium studies. The standard molar enthalpies of sublimation (or vaporization) of these compounds, and also of phenol, were obtained from the temperature dependence of the vapour pressure measured in a flow system. Molar enthalpies of fusion Δ1crH0m of the solid compounds were measured by d.s.c. Resulting values of ΔfH0m (g) were obtained at the temperature 298.15 K and used to derive strain enthalpies of alkylphenols. The intra‐molecular interactions of the substituents were discussed in terms of deviations of ΔfH0m (g) from the group additivity rules. Ortho‐, para‐, and meta‐interactions of sec‐alkyl substituent with OH‐group in the gaseous phase was found to be equal 3.9 kJ·mol−1. These values provided a further improvement on the group‐contribution methodology for estimation of thermodynamic properties of organic compounds.
Kinetics of the Gas‐Phase Reaction of NO3 Radicals with 1‐Butene, trans‐Butene, 2‐Methyl‐2‐butene and 2,3‐Dimethyl‐2‐butene Using LIF Detection
Authors: Berndt T. , Kind I. , Karbach H.‐J. 
Published: March 2014

AbstractRate constants for the gas‐phase reaction of NO3 radicals with 1‐butene, trans‐butene, 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene have been obtained in a flow system at 298±2 K and a pressure of 3 mbar He using NO3 LIF measurements. NO3 radicals were produced via thermal decomposition of N2O5 at ca. 400 K, i.e. N2O5+M → NO3+NO2+M.Applying pseudo‐first‐order conditions, the rate constants for 1‐butene and trans‐butene were found to be (1.04±0.11)·10−14 and (3.74±0.45)·10−13, respectively. For 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene the rate constants were obtained under second‐order conditions to be (1.03±0.09)·10−11 and (5.49±0.42)·10−11, respectively (unit: cm3 molecule−1 s1).
Contributions to the Spectroscopic‐Kinetic Analysis of Linear Reaction Systems: Systems with Two Linearly Independent Reactions Using the Concept of Parallel Projection
Authors: Polster J. 
Published: March 2014

AbstractMultistep protolysis or metal‐complex systems can be divided into their individual titration equilibria by the concept of projective mapping using diagrams which contain only absorbance data. In this way, the individual equilibria constants and their ratios can be very easily determined. The concept can be transfered to the spectroscopic‐kinetic analysis of linear reaction systems. Reaction systems which are described by two linearly independent concentration variables (s = 2) can be reduced to systems which depend only on one linearly independent concentration variable (s = 1) by replacing the perspective projection by a parallel projection. The new method is demonstrated by application to the spontaneous hydrolysis of Boc‐gly‐ONP (N‐tert.‐Butoxycarbonyl glycine p‐nitrophenylester) and oNPA (o‐nitrophenyl acetate) in borax buffer (pH = 8.7).
Kinetic Studies on Reversible Dimerization of Thianthrene and 2,3,7,8‐Tetramethoxythianthrene Radical Cations
Authors: Hübler Patrick , Heinze Jürgen 
Published: March 2014

AbstractFast scan voltammetry gives kinetic evidence for the reversible dimerization of the radical cations of thianthrene (T) and 2,3,7,8‐tetra‐methoxythianthrene (TMOT) in acetonitrile. At 256 K an equilibrium constant KDim ≈ 900 for TMOT (KDim ≈ 1.1·104 for T) and rate constants kf ≈ 1·107 and kb ≈ 1.2·104 were determined. Using the semi‐empirical PM3 method, the formation of σ‐bonded dimers is indicated. For the dimerization reaction in acetonitrile, enthalpy values of −79 kJ/mol for T and −56 kJ/mol for TMOT respectively were calculated. Despite the folded structure of the neutral T and TMOT systems and their planarization during the radical cation formation, the heterogeneous electron transfer kinetics was found to be very fast in both cases (1.6 cm/s; 298 K). The activation enthalpy was determined to be 14 kJ/mol in the case of TMOT. Calculations of the inner‐sphere reorganization energy using the Marcus theory produced ΔH#(∞) = 4.6 kJ/mol for TMOT and 3.9 kJ/mol for T respectively at infinite temperatures. This explains the fast electron transfer kinetics and their low activation enthalpies.