bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relaxation and Reconstruction of Solid Surfaces
Authors: Müller K. 
Published: July 2012

AbstractIt has long been known from LEED (low energy electron diffraction) experiments that semiconductor surface structures differ from those of simple truncations of the bulk solid. Unexpected and sometimes complicated diffraction patterns of a growing number of semiconductor as well as metal surfaces indicate a selvedge region of altered structure. This is uow recognized as a common phenomenon.—The selvedge consists of several atomic layers with modified two‐dimensional periodicity in the outermost layer(s), reconstruction, and with interlayer distances altered with respect to the bulk, relaxation. Structure determinations reveal for monoatomic surfaces a damped oscillatory multilayer relaxation, alloys may even show a rippled relaxation of their surfaces. The kind of reconstruction can be merely displacive where bond lengths are slightly changed. The more dramatic form of reconstruction involves considerable mass transport, broken bonds, formation of steps and domains, etc. In every case the static order and (as a consequence) electronic and dynamic properties as well as the reactivity of the surface are changed.—Structure determinations by LEED and other methods are all but easy. Recent experimental improvements and developments in computational schemes led to rather sophisticated methods which revealed surface models with detailed structural parameters. The reliability and accuracy of different methods are still being discussed. Some results, however, seem to be widely accepted by now.—Adsorption generally affects reconstruction and relaxation. Therefore adsorption sites can no longer be assumed as fixed positions. Phase transitions between ordered phases can be studied as a function of independent parameters such as coverage or temperature. Relaxation and reconstruction trends as well as stability considerations for different model surfaces are now being developed from theoretical studies of the surface energy.
On the Kinetics and Mechanism of the Oxygen Induced (2 × 1) Reconstruction of Ni(HO)
Authors: Behm R. J. , Ertl G. , Wintterlin J. 
Published: July 2012

AbstractThe kinetics for the formation of the reconstructed (2 × 1) structure of O/Ni(110) from a nonreconstructed phase were investigated by LEED and work function measurements. The rates fit well to an “Avrami” type kinetics, which can be interpreted in terms of a nucleation and growth process. An activation barrier of 24 kj/mole is derived, the mechanism and energetic driving force are discussed in this picture and compared to other adsorbate induced surface phase transformations.
Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide
Authors: Tinnemans Oxide A. H. A. , Koster T. P. M. , Thewissen D. H. M. W. , Mackor A. , Schoonman J. 
Published: July 2012

AbstractPolycrystalline Mg‐doped (0.1–5 at. %) Fe2O3 photoelectrodes have been prepared by annealing at 1573 K followed by slow cooling in air to ambient temperature. These materials are essentially single‐phase at Mg concentrations not exceeding 0.5 at. %. Disk‐shaped (photo)‐electrodes were prepared, and their electric and photoelectrochemical (PEC) properties were measured. The positive sign of the photovoltage and of the thermoelectric power θ, confirmed the materials to be p‐type semiconducting.—Carrier concentrations calculated from θ, revealed each Mg2+ to introduce one electron‐hole up to about 0.1 at. % Mg. The a.c. conductivities, showing conductivity activation enthalpies of about 0.5 eV in the temperature region 300–800 K, are affected by grain growth and porosity.—The current‐voltage characteristics in the dark and under illumination, the spectral response, and the flatband potential (Vfb = +2.2 V vs. SCE pH = 10) have also been determined.—PEC photocurrents in the visible region correspond to very low (∼0.1%) monochromatic quantum efficiency which is due to the low electron‐hole mobility. The electronic transition in the visible region is indirect, and evidence has been found for this transition to be Fe‐Fe charge transfer. Surface pretreatment is found to have a major effect on the photoelectrochemical properties as deduced from current‐voltage curves. The stability of the α‐Fe2O3 electrode in alkaline solution is discussed.
An Improved Quartz Microbalance. Applications to the Electrocrystallization and ‐dissolution of Nickel
Authors: Benje Michael , Eiermann Matthias , Pittermann Udo , Weil Konrad G. 
Published: July 2012

AbstractA transistorized Pierce‐Miller‐oscillator is described which can be used to excite a quartz vibrator in contact with a solution. Changes of the resonance frequency of the quartz induced by deposition or dissolution of substances on one of its surfaces can be measured. We also describe a simple teflon holder which allows fixation of the crystal in a position in which only one of its faces is in contact with the solution.—The influence of simultaneous gas evolution on the performance of the balance is discussed. Preliminary results on the role of hydrides during nickel deposition and dissolution are presented and compared with literature data.
Dielectric Properties of Polyelectrolyte Solutions II. Behaviour of Aqueous Solutions of Carboxymethylcellulose with Divalent Counterions
Authors: Bordi F. , Cametti C. 
Published: July 2012

AbstractThe dielectric properties of well‐characterized Carboxymethylcellulose samples of different molecular weights in aqueous solutions of 2:1 valent electrolytes (BaCl2 and CaCl2) have been measured in the frequency range from 1 KHz to 10 MHz at the temperature of 20.0°C.—The results are discussed in comparison with those reported in a previous paper for univalent counterions on the basis of rod‐like Polyelectrolyte dielectric models and the effects of Ba++ and Ca++ counterions on the conformation of the polyion in aqueous solution have been investigated.
The Goldman Constant Field Assumption: Significance and Applicability Conditions
Authors: Mafé S. , Pellicer J. , Aguilella V. M. 
Published: July 2012

AbstractIonic transport phenomena in simple, porous membranes can be approximately represented by the Nernst‐Planck flux equations and Poisson's equation. In order to solve this set of equations for each particular case, the Goldman constant field assumption is one of the most widely used. In the present paper the significance and the applicability conditions of the above hypothesis is critically examined. and the particular situations where it is exact are shown. These conditions are later verified by solving numerically the electrodiffusion equations. The analysis carried out shows that some of the earlier studies based on asymptotic expansions and numerical solutions should be partially revised.
Excess Enthalpies of Binary Liquid Mixtures Containing Oxiranes Part 1: HE (298.15 K, 101.3 kPa) of the Four Systems Chloromethyl‐ and Bromomethyl‐Oxirane + n‐Hexane and n‐Heptane
Authors: Kramer U. , Koçak M. , Steiger A. , Becker F. 
Published: July 2012

AbstractThe excess enthalpies of the four systems chloromethyl‐ and bromomethyl‐oxirane + n‐hexane and + n‐heptane at 298.15 K and 101.3 kPa have been determined by continuous isothermal mixing calorimetry at constant volume using the overflow method. The HE data were evaluated with equilibrium models assuming that the strong endothermic heat effect on mixing is governed by two types of intermolecular interactions, (1) the unspecific mutual solvation of the components, (2) the self‐association of the oxiranes via CH…O interactions. The latter interactions, for which an energy parameter of ‐10 kJ mol−1 is calculated, are enhanced by the electron‐attracting substituents at the oxirane ring.
The Optical Properties of Liquid Se and Se1‐xTex Alloys
Authors: Seyer H.‐P. , Tamura K. , Hoshino H. , Endo H. , Hensel F. 
Published: July 2012

AbstractThe temperature and pressure dependence of the optical properties of liquid Se and Se1‐xTex alloys have been determined by means of normal incident reflectivity measurements between 0.5 and 5.0 eV. The optical conductivity σ(ω) and the real part of the dielectric function ε1(ω) have been derived by means of a modified Kramers‐Kronig analysis. The reported results give useful information about the electronic structure of liquid Se and Se1‐xTex alloys. In particular, the results provide the first direct experimental evidence for coordination driven changes in the electronic structure of these liquids in course of the transition from a nonmetallic to a metal‐like state.
Interstitial Transition Metal Impurities as a Possible Cause of Enhanced Reactivities
Authors: Behner T. , Elbers G. , Remme S. , Prissok F. , Stegger P. , Lehmann G. 
Published: July 2012

AbstractTrivalent ions of Fe, Cr and Mo are easily incorporated into CsCl‐type lattices. Evidently their geometries partly derive from those for divalent ions by exchange of a neutral molecule by hydroxyl or halide. In the ammonium halides hydrogen bonding manifests itself in predominance of low site symmetries and dynamic effects. Evidence for interstitial incorporation of di‐ and trivalent ions in quartz and isomorphous ABO4 compounds is also presented. EPR data for Fe3+ indicate simultaneous incorporation of O2− or OH− in the c‐axis channels. A kinetic reason for preferred interstitial incorporation is proposed. Enhanced mobilities of these as well as certain main constituents may also enhance the reactivities.
Order‐Disorder in Solid 1,2,3‐Trichlorobenzene. A Single Crystal 35CI NQR Study
Authors: Sharma Surendra , Weiden Norbert , Weiss Alarich 
Published: July 2012

AbstractBy single crystal Zeeman split NQR spectroscopy the nuclear quadrupole coupling tensors, NQCT, of 35CI in magnitude, orientation, and symmetry were studied in the range 140 ≦ T/K ≦ 250. Neither the asymmetry parameters nor the orientations of the NQCTs depend significantly on temperature. The disappearance of the 35CI NQR signal well below the melting point was investigated by studying the line width Δv and the spin lattice relaxation time T1 as a function of temperature. From Δv = f(T) an activation energy of 31 kj mol−1 and 36 kJ mol−1, respectively, was found for the two crystallographically inequivalent molecules in the unit cell. The onset of static order‐disorder or the creation of lattice vacancies may be responsible for the line broadening and the change in T1.
Densitometric Characterization of the Main Phase Transition of Dimyristoyl‐Phosphatidylcholine between 0.1 and 40 MPa
Authors: Vennemann Norbert , Lechner M. Dieter , Henkel Thomas , Knoll Wolfgang 
Published: July 2012

AbstractDensitometric measurements employing the mechanical oscillator technique have been performed with dilute aqueous dispersions of dimyristoyllecithin at different temperatures and pressures up to 400 · 105 Pa. Isothermal compressibilities of xLα = 4.5 · 10−10 Pa−1 for the fluid phase and xPβ' = 2.9 · 10−10 Pa−1 for the ordered phase, respectively, are obtained. It is demonstrated that the first order main phase transition from the fluid to the condensed phase can be induced isothermally by increasing the hydrostatic pressure in the measuring cell. The coexistence of the two phases is limited to a narrow pressure range of about 10 · 105 Pa which corresponds to the intrinsic width of the transition. The volume change associated with the phase transition decreases with increasing pressure. The slope of the transition pressure‐temperature relationship increases with increasing pressure. From the limiting slope for p → 105 Pa a transition enthalpy of ΔH = 24.6 kJ·mol−1 is derived.
A Kinetic Study of the Diazotization of Substituted 1‐Naphthylamines
Authors: Castro Albino , Iglesias Emilia , Ram Leis J. ÓN , Peña M. Elena 
Published: July 2012

AbstractThe diazotization of various substituted naphthylamines has been found to be catalysed by the nucleophiles Cl−, Br−, SCN− and thiourea due to the formation of the corresponding nitrosyl salts. The rate controlling steps depend on the concentration of catalyst, with respect to which the order of the reaction varies between 1 and 0. The theoretical rate constants deduced from the proposed reaction mechanism are discussed in terms of the basicity of the amines and the nucleophilicity of the catalysts. The reaction rate's dependence on ionic strength and acidity in the absence of catalysts is also reported and discussed.
Statistical Fluctuations of Temperature and Conversion at the Catalytic CO Oxidation in an Adiabatic Packed Bed Reactor
Authors: Onken H. U. , Wicke E. 
Published: July 2012

AbstractThe oxidation of CO with air at a Pt/γ‐Al2O3 supported catalyst employed in an adiabatic fixed‐bed reactor, is accompanied by nonperiodic variations of CO2 concentration and temperature at the reactor exit. The occurrence of these variations is confined to the region of bifurcation from monostable to bistable behaviour of the fixed‐bed reactor. The variations originate from small temporal and local fluctuations of the reaction rate—and hence the temperature—in the entrance cross‐section of the catalyst bed. In the bifurcation region the temperature humps of these fluctuations (ΔT ≈ 0.5 K) are strongly amplified and finally form reaction zones (ΔT ≈ 120 K) which move to the reactor exit with velocities of 3.5 to 11 mm/min. Measurements at a cluster of 10 catalyst pellets exposed to the CO/air gas stream showed that the fluctuations at the entrance of the fixed bed can be attributed to kinetic oscillations occurring in the regime of descending reaction rate with increasing CO feed. By periodic variations of the CO feed the reaction can be forced to show harmonic or subharmonic resonance. In the latter case, the quasiperiodic Fourier spectrum of the unperturbed reaction turns to a spectrum with a sextet at the subharmonic frequency.
A New Model for Oscillatory Behaviour in Closed Systems: The Autocatalator
Authors: Gray Peter , Scott Stephen K. 
Published: July 2012

AbstractIn closed systems, chemical oscillations cannot go on for ever, but must die away. This paper presents a new/simple, self consistent prototype for such non‐stationary behaviour. No self‐heating is involved: conditions are isothermal. Matter is conserved. The model scheme is:

It is centred on cubic autocatalysis (I), in which the catalyst itself decays slowly (2); there is a small contribution from a direct step (3). There is a precursor, initially in excess, that slowly generates the intermediate A.—This scheme describes a reaction that begins and ends in a monotonic way yet has a finite set of oscillatory excursions in between. There is no multiplicity and no stationary state until reaction is completed, and there are no limit cycles. Reaction follows a unique path.
Modelling of Turbulent Methane‐Air Diffusion Flames: The Laminar‐Flamelet Model
Authors: Rogg B. , Behrendt F. , Warnatz J. 
Published: July 2012

AbstractAn extended laminar diffusion flamelet model of turbulent non‐premixed combustion is applied to an open methane‐air jet diffusion flame. The structure of the laminar flamelets is determined numerically in the counterflow geometry using a detailed mechanism for the methane‐air system consisting of more than 250 elementary reactions of 39 chemical species. The results of the laminar‐flamelet calculations are incorporated into a detailed computation of the turbulent flow field using a k–ε turbulence model. Results from both the laminar and the turbulent flame predictions are compared to experimental data available from the literature.
Comparison of CARS Measurements and Calculations of the Structure of Laminar Methane‐Air Counterflow Diffusion Flames
Authors: Dreier T. , Lange B. , Wolfrum J. , Zahn M. , Behrendt F. , Warnatz J. 
Published: July 2012

AbstractInformation on the structure of laminar diffusion flames under the influence of the strain of an inhomogeneous velocity field is essential for the understanding of turbulent diffusion flames.—To simulate the structure of the stagnation‐point flame the corresponding governing equations for enthalpy, momentum, and chemical species are to be solved. By boundary layer approximations and a coordinate transformation these equations are transformed into a one dimensional form, which is integrated with a finite differences method. Transport is described by a simplified multicomponent model. The detailed reaction mechanism consists of more than 250 elementary steps and 39 chemical species.—For comparison with the numerical results Coherent Anti‐Stokes Raman Scattering (CARS) is used to determine temperature and concentration profiles in an atmospheric pressure CH4/air counterflow diffusion flame. First a comparison between thermocouple and CARS measurements is done in a high temperature furnace up to 2000 K. The temperature dependent CARS spectra of N2 and O2 are evaluated by a computer program. Agreement between both techniques is obtained within 40 K over the complete temperature range. The same procedure is done with oxygen CARS spectra giving a temperature uncertainty of ± 80 K.—The comparison between the experimental and simulated temperature profiles shows satisfactory agreement on the fuel rich side but deviates significantly on the fuel lean side of the mixing layer. This discrepancy is ascribed to shortcomings in the model underlying the numerical simulation. Further ejaculations should therefore replace the use of boundary layer approximations by true two‐dimensional representations of the flow field.
Electrochemistry at Ultramicroelectrodes—Simulation of Heterogeneous and Homogeneous Kinetics by an Improved ADI—Technique
Authors: Heinze Jürgen , Störzbach Michael 
Published: July 2012

AbstractElectrochemistry at Ultramicroelectrodes has become a promising method for measurement and evaluating of electrode kinetics. However, its theoretical treatment is a challenging problem on account of the unusual diffusive mass transport connected with such small electroactive areas. To simplify the computation and to open the way for the use of personal computers an improved alternating direction implicit (ADI) technique based on an implicit Crank‐Nicolson scheme has been developed. The numerical approach allows modelling of all types of electrode reactions including coupled homogeneous processes at ultramicroelectrodes. Numerical results for the reversible and the quasireversible charge transfer as well as first‐ and second‐order follow‐up reactions are presented.
Transport Properties of Liquids VII. Viscosity, Excess Volumes, and Self‐Diffusion of Binary Mixtures of Donor‐Acceptor and of CCl4‐Carboxylic Acid Systems
Authors: Fischer Jens , Weiss Alarich 
Published: July 2012

AbstractIn liquid binary systems C6F6—X, X = C6H6, 1,3,5‐(CH3)3C6H3, 1,3,5‐(i‐CH(CH3)2)3C6H3,C6H12 and in systems CCl4—Y, Y = CF3COOH, CH3COOH, (CH3)3CCOOH the dynamic viscosity η and the self‐diffusion coefficient D of the hydrogen carrying molecules and C6F6 have been measured as a function of the composition at p = 1 bar in the range 285 ≤ T/K ≤ 345. For each of these systems the excess volume VE as a function of composition was determined at a fixed temperature. The phase diagram of the system C6F6‐1,3,5‐(i‐CH(CH3)2)3,C6H3 was studied. ‐ The “charge transfer” interaction between the acceptor molecule C6F6 and the donor molecule 1,3,5‐(CH3)3C6H3 is reflected in the viscosity, in the self‐diffusion coefficients, in VE, and in the excess activation energies (E)E and (E)E In the mixtures C6F6‐X, X = C6H6,1,3,5‐(i‐CH(CH3)2)3C6H3, and C6H12 the viscosity, VE, and the self‐diffusion coefficients D are governed by structure building and structure breaking effects.—In the liquid systems CCl4‐carboxylic acid VE, the logarithmic excess viscosity ln ηE, and the excess activation energy (Eaη)E depends on the pKa, value of the carboxylic acid. The self‐diffusion coefficients measured are discussed in the magnitudes at infinite dilution within the frame of the free volume model.
Demixing in oxygen potential gradients: Two‐phase systems and the morphological stability of the interface
Authors: Ueshima Y. , Schmalzried H. , Koepke J. 
Published: July 2012

AbstractIn order to complement previous investigations on the demixing of one‐phase oxide solid solutions on oxygen potential gradients, solid solutions in two‐phase regions were exposed in an analogous way. The demixing under (quasi‐) steady state conditions is basically the same as found in the one‐phase mixtures. However, in the case of (Mn,Fe)O (wustite)‐(Mn,Fe)3O4 (spinel) solid solutions, the phase boundary between the lower (w) and the higher (sp) oxidized solid solution was not stable morphologically. In fact, a zone of phase mixtures developed in which wustite and spinel with continuously changing composition coexisted locally. This unique behaviour can be explained theoretically in the framework of linear transport theory.
The vibronic spectrum of IrCl2‐6 in low symmetry environments
Authors: Schmidtke Hans‐Herbert , Göttges Dan 
Published: July 2012

AbstractThe low temperature (7–15 K) absorption spectrum of IrCl2‐6 doped in single crystals of potassium and ethylammonium hexachloro‐Sn(IV) salts, A2SnCl6, recorded at high resolution supplies further contributions to solving the assignment problem of vibrational progressions of charge transfer and ligand field spin‐orbit states. The vibrational fine structure indicates differences in vibronic coupling compared to the cubic systems.
Direct determination of CH2(ã1A1) removal rates by olefinic and aromatic hydrocarbons
Authors: Hack W. , Koch M. , Wagener R. , Gg. Wagner H. 
Published: July 2012

AbstractAbsolute rates of CH2(ã1A1) removal by the olefins ethene (C2H4), propene (C3H6), isobutene (i‐C4H8), butadiene (C4H6), allene (C3H4) and the aromatic hydrocarbons toluene (C6H5CH3), p‐xylene (C6H4(CH3)2), ethylbenzene (C6H5C2H5) and cumene (C6H5–(i‐C3H7)) have been determined at low pressures and room temperature. CH2(ã1A1) was produced by pulsed laser photolysis of CH2CO. Concentration profiles of CH2(ã1A1) were recorded using laser induced fluorescence with a variable time delay between the probe laser and the photolysis laser. —The contributions of physical deactivation to the removal of CH2(ã1A1) in the reactions with C2H4, C3H6, C3H4 and C6H5CH3 were investigated quantitatively via the formation of CH2(X̄3B1), detected by LMR. —1CH2 is removed very efficiently by all the reactants, with second order rate constants in units of 1014 cm3/mol s k(C2H4) = 1.4, k(C3H6) = 2.0, k(i‐C4H8) = 2.0, k(C4H6) = 2.1, k(C3H4) = 1.9 and k(C6H5CH3) = 2.3, k(C6H4(CH3)2) = 2.2, k(C6H5C2H5) = 2.5, k(C6H5(i‐C3H7)) = 2.6. The branching ratios of physical deactivation versus total removal for C2H4, C3H6, C3H4, C6H5CH3 were 0.20, 0.24, 0.30, 0.29. The dependence of reaction rates on alkylic substitution of the olefinic and aromatic II bonding systems is small.