bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Micromachining of Stainless Steel by Ultrashort Voltage Pulses
Authors: Cagnon Laurent , Kirchner Viola , Kock Matthias , Schuster Rolf , Ertl Gerhard , Gmelin W. Thomas , Kück Heinz
Published: December 2003

Application of ultrashort voltage pulses to a tiny tool electrode under suitable electrochemical conditions enables precise three-dimensional machining of stainless steel. In order to reach submicrometer precision and high processing speed, the formation of a passive layer on the workpiece surface during the machining process has to be prevented by proper choice of the electrolyte. Mixtures of concentrated hydrofluoric and hydrochloric acid are well suited in this respect and allow the automated machining of complicated three-dimensional microelements. The dependence of the machining precision on pulse duration and pulse amplitude was investigated in detail.
Molecular Structure Effects in the Adsorption Behaviour of some Aromatic Heterocyclic Compounds at High-Area Carbon-Cloth in Relation to Waste-Water Purification
Authors: Conway Brian E. , Ayranci Guler , Ayranci Erol
Published: December 2003

Adsorption behaviours of some structurally related aromatic heterocyclic compounds at an high-area carbon-cloth material have been investigated in relation to waste-water purification. Adsorption processes were followed by monitoring the concentration of adsorbates in a specially designed cell using an in situ UV spectrophotometric method. The rates of adsorption were compared by treating the data according to first-order kinetics. Among the seven heterocyclic compounds studied, thiophene was found to exhibit the highest adsorption rate. This was attributed to the presence of the electron-donative S heteroatom in the structure of this compound. The influences of the dipole moment, the orientation at the C-cloth surface and the size of the heterocyclic adsorbate compound, as well as the type of heteroatom in the ring and the adsorbates’ hydration parameters, on the extent of adsorption of these compounds at the C-cloth were investigated.
Frequency Response Analysis of the Potential Modulated Microwave Reflectivity Response of p-Type Silicon During Anodic Dissolution in Ammonium Fluoride Solutions
Authors: Duffy N. W. , Kirah K. , Peter L. M. , Ushiroda S.
Published: December 2003

Interpretation of the impedance of the silicon electrolyte interface is particularly complicated under conditions in which anodic silicon dissolution occurs. In the present work the frequency-resolved potential modulated microwave reflectivity (PMMR) technique has been combined with electrochemical impedance spectroscopy (EIS) to study the behaviour of low-doped p-type silicon in buffered ammonium fluoride. The EIS response is determined by the total impedance of the system, whereas the PMMR response originates from modulation of the hole density in the silicon space charge region. This difference has led to the development of a novel approach to deconvolution of the interfacial impedance. It involves multiplication of the PMMR and EIS responses to give the space charge impedance. Particular attention is focussed on accumulation conditions in the electropolishing region, where the surface of the silicon is covered by a duplex oxide film. The impedance of the accumulation layer is obtained using the new approach, and the oxide impedance is then derived. Analysis of the PMMR results provides convincing evidence that the hole mobility in the accumulation layer is more than an order of magnitude smaller than in the bulk.
Voltammetry and Impedance of Pt(111) Electrodes in Aqueous KClO4 Solutions
Authors: Pajkossy Tamás
Published: December 2003

The voltammetric behaviour of Pt(111) electrodes in neutral and near-neutral aqueous KClO4 solutions (4 < pH < 9.7) is discussed. In this system, within the ideally polarizable potential region, the only processes affecting voltammetry and impedance are the adsorption and desorption of the H+ and OH− ions. Due to the low bulk concentrations of these ions, the desad processes are diffusion controlled. This situation is analysed using cyclic voltammetry, transient and impedance measurements.
Quantitative Modeling of the Oscillatory Electrooxidation of Hydrogen on Pt in the Presence of Poisons
Authors: Plenge F. , Varela H. , Lübke M. , Krischer K.
Published: December 2003

A quantitative model of oscillations observed during hydrogen oxidation on platinum in the presence of electrosorbing metal ions and specifically adsorbing anions is presented and the model predictions are compared with experiments. Mass and charge balances of all reactants lead in a first step to a seven variable model which is governed by reaction steps that have been widely studied. We demonstrate that attractive interactions between metal and halide ions on the electrode surface, which were recently reported, are crucial for the observed dynamics. The model parameters were almost exclusively taken out of the literature. The model is then reduced to its minimal form without losing dynamic features arriving at a four variable system. Experimental time series of three of the four variables of the model and measured bifurcation diagrams are presented. It is shown that the integrated time evolution and the calculated bifurcation diagrams of the model agree almost quantitatively with the experiment.
The Concept of Dwell Times in a Kinetic Model of Alloy Deposition
Authors: Plieth W.
Published: December 2003

A model of alloy deposition was developed based on a concept of dwell times of atoms in kink site positions. It was shown that the dwell times, together with the deposition rates of the alloy components are the steering parameters deciding, which atom will be deposited in the different kink sites of the growing alloy. The model provides a basis for quantitative modelling of alloy composition and alloy structure.
Hydrogen Evolution at a Single Supported Nanoparticle: A Kinetic Model
Authors: Eikerling M. , Meier J. , Stimming U.
Published: December 2003

A kinetic model of the processes during hydrogen evolution at a single Pd nanoparticle supported on an Au substrate is studied. It builds the theoretical framework for results of currently performed STM measurements on this system. The objective of the theory is to establish relations between measured transients and underlying processes. It, thereby, helps to implement the routines for the determination of kinetic parameters from transient currents and supplements the characterization of the Pd/Au system. The balance of hydrogen involves interfacial processes on the Pd/Au substrate surface, hydrogen diffusion in the bulk electrolyte and hydrogen oxidation at the tip. The key parameter of the model is the rate of hydrogen desorption from the Pd surface. If this rate is small hydrogen will spillover from the Pd particle and diffuse on the Au surface from where it will be subsequently released. Thereby, large amounts of hydrogen can be stored on the surface. It is demonstrated, that this mechanism complies with the high turnover rates at the smallest catalyst particles and characteristic time scales observed in experiment.
Nano-Ionics: Trivial and Non-Trivial Size Effects on Ion Conduction in Solids
Authors: Maier J.
Published: December 2003

The significance of nano-size effects for ion transport in solids is highlighted both experimentally – by presenting various results of recent investigations – and theoretically – by considering expected size effects using a top-down approach. It is helpful to distinguish between trivial size effects (effects that equally occur at single interfaces but are augmented by the high interfacial density) and true size effects (involving local modifications due to the finite boundary conditions). The latter ones essentially include space charge overlap and structural interference leading to two characteristic sizes with respect to defect chemistry. The contribution also briefly touches upon effects of dimensionality and shape as well as of discreteness of carrier distribution.
Spontaneous and Electrodeposition of Pt on Ru(0001)
Authors: Zei M.S. , Lei T. , Ertl Gerhard
Published: December 2003

Pt was deposited onto a Ru(0001) electrode from a PtCl6
2−-containing HClO4 solution either electrochemically or spontaneously (i.e. without external current flow). Composition, structure and morphology of the deposit were studied by means of Auger electron spectroscopy (AES), high energy electron diffraction (RHEED), and scanning electron microscopy (SEM). At first pseudomorphic growth of a 2D-Pt adlayer takes place, while with higher coverages 3D-clusters develop for which the most densely packed [011]-rows of the Pt(111) planes are parallel with the most densely packed [1120]-rows of the Ru(0001) substrate. These Pt-clusters exhibit typical diameters between 2 and 10nm, while their average mutual separation varies with the total amount of deposit. If compared with the bare Ru(0001) surface, the samples with Pt deposits exhibit considerably enhanced activity with respect to electrooxidation of formic acid or methanol.
Structure of Electrochemically Deposited Sulfide Layers on Cu(100)
Authors: Spaenig A. , Broekmann P. , Wandelt K.
Published: December 2003

In-situ EC-STM has been used to examine distinct phases of electrochemically deposited sulfide layers on Cu(100). The observed structures can be clearly assigned to specific ranges of the electrode potential and the sulfide concentration in solution. The scope of the present contribution is to report the various structural phases and their potential dependence. A full description of their concentration dependence will be given in a forthcoming paper. All incipient adsorption processes have been performed exclusively at negative electrode potentials close to the on-set of the hydrogen evolution reaction in order to avoid heavy surface reactions of the copper substrate with sulfide as seen at positive electrode potentials. In a very early stage of the sulfidation first a metastable, transient p(2×2)-S layer with a nominal coverage of Θ = 0.25ML is formed which gets irreversibly replaced by an energetically more stable c(6×2)-S phase with Θ = 0.33ML. This process at constant potential is kinetically hindered and depends on the sulfide supply from the electrolyte of given concentration. All further phase transitions induced by a positive going potential sweep are influenced by the sulfide supply from the electrolyte phase as well. A low sulfide supply from a low concentration electrolyte during a positive going potential sweep provokes a uniaxial compression of the preexisting c(6×2)-S phase ending up with a striped c(4×2)-S phase. Conversely a high sulfide supply from a high concentration solution during a positive going potential sweep causes a massive reorganization of both the atomic structure and the surface morphology on a mesoscopic scale. This latter process involves a massive transport of copper material out of the topmost copper layer and is, hence, identified as an adsorbate induced reconstruction of the copper substrate. The symmetry of the resultant sulfide structure on-top of the reconstructed copper substrate is similar to a square c(2×2) arrangement but on a copper surface whose lattice constants are expanded by 9 with respect to the copper bulk structure. Hence, the atomic surface structure is denoted as a pseudo-c(2×2)-S reconstruction.
The Influence of Halide Ions on the Kinetics of Electrochemical Copper(II) Reduction
Authors: Doblhofer Karl , Wasle Sabine , Soares David M. , Weil Konrad G. , Weinberg Gisela , Ertl Gerhard
Published: December 2003

The cathodic reduction of copper(II) in an electrolyte comparable to technical conditions (2.2M H2SO4 + 0.3M CuSO4) is markedly affected by the presence of small concentrations of halide ions. Chloride ions accelerate the reaction, while it is slowed down by bromide. Experiments in which cyclic voltammetry is combined with an electrochemical quartz-crystal microbalance reveal the deposition and dissolution of crystalline CuCl or CuBr, respectively, on the copper surface. At the technically relevant more negative electrode potentials bulk CuCl and CuBr are unstable, however halide ions are adsorbed on the copper electrode. Although there is evidence for adsorption of the reacting Cu(II) species at the electrode surface, up to a concentration of 0.3M CuSO4 in presence as well as in absence of adsorbed halogenide, there is no evidence for limiation of the reaction rate caused by a limited coverage of the surface with this species.
The Adsorption of 2,3-Dimercaptopropane Sulfonate at the Au〈111〉 Electrode in Alkaline Solution
Authors: Yang Y. , Valet O. , Donner C. , Baumgärtel H.
Published: December 2003

In alkaline solution the sodium salt of 2,3-dimercaptopropanesulfonate (DMPS) is readily adsorbed at the reconstructed Au〈111〉 surface. After determining the PZC of the electrode current transients due to the adsorption have been measured at different electrode potentials. They reveal electronic charge redistribution as well as OH− desorption from the interface. From STM investigations it is concluded that the adsorption involves reorientation in the primarily formed adlayer and slow lifting of the reconstruction. The reductive desorption of DMPS has been observed at −0.97V vs. SCE.
In situ Infrared Reflection Absorption Spectroscopy Studies of the Interaction of Nafion® with the Pt Electrode Surface
Authors: Malevich Dzmitry , Zamlynny Vlad , Sun Shi-Gang , Lipkowski Jacek
Published: December 2003

Infrared Reflection Absorption Spectroscopy (IRRAS) has been applied to study the nature of the co-ordination of Nafion® to a Pt electrode surface. The experiments have been carried out using a Pt electrode coated with a thin film of Nafion® assembled into a thin layer spectroelectrochemical cell. The potential modulation or the subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) experiments have been performed, in order to distinguish between the bulk properties of the Nafion® membrane and the properties of the membrane at the interace with the Pt electrode. The results showed that the interaction between the membrane and a Pt electrode resembles the interaction between a Pt electrode and a sulfuric acid solution.
Stripping Voltammetry and Chronoamperometry of an Adsorbed Species with Repulsive Lateral Interactions
Authors: Koper Marc T. M.
Published: December 2003

In this paper a simple model is considered for the stripping voltammetry and chronoamperometry of an adsorbed species with repulsive lateral interactions. In the limit of strongly repulsive lateral interactions, the chronoamperometric transient is predicted to be hyperbolic, i.e. to have a t
−1 dependence. This dependence is confirmed by both the numerical simulation of the mean-field equations and by the Dynamic Monte Carlo simulations. However, in the analysis of the Dynamic Monte Carlo simulations, inflexion points are found in a log-log plot of the data, corresponding to the formation of ordered configurations on the surface. The stripping voltammetry exhibits broader stripping peaks with increasingly repulsive lateral interactions. An analysis of the peak potential versus the logarithm of the scan rate yields the Tafel slope, irrespective of the strength of the lateral interactions. In the Dynamic Monte Carlo simulations, strong repulsive interactions lead to multiple stripping peaks, the peaks becoming more pronounced with a faster surface diffusion of the adsorbed species. These peaks are related to the existence of ordered configurations on the electrode, whose long-range order is enhanced at faster diffusion rates.
Co-adsorption of Fluoride and Hydroxide Ions on Ag(111) in Alkaline Electrolytes: Electrochemical and SHG Studies
Authors: Danckwerts M. , Savinova E. R. , Horswell S. L. , Pettinger B. , Doblhofer Karl
Published: December 2003

Hydroxide (OH−) adsorption at Ag(111)/alkaline electrolyte interfaces is the initial step leading to the formation of surface oxide. We investigate how OH− anion adsorption is influenced by co-adsorption of supporting electrolyte anions (F−). Pure NaF and NaOH as well as mixed electrolytes ranging from pH=5.8 to 14 are investigated. The rotational anisotropy of the second harmonic generation (SHG) signal is measured to distinguish adsorptive processes from structural changes on the Ag surface. Our results clearly show a cross-over from F−-dominated to OH−-dominated adsorption, while both species remain charged upon adsorption. At more positive potentials, but below the reversible potential of bulk oxide growth, OH is discharged leading to sub-monolayer oxide build-up, whereas in acidic electrolyte, Ag is dissolved. At intermediate pH, the formation of a structured OH−/F− co-adsorbed layer is proposed.
Electronic Properties of LiMo3Se3-Nanowires and Mo3Se3-Nanowire-Networks for Nanoscale Electronic Devices
Authors: Heidelberg A. , Bloeß H. , Schultze J. W. , Booth C. J. , Samulski E. T. , Boland J. J.
Published: December 2003

Nanowires and nanotubes have attracted much interest as potential building blocks for nanotechnology. This interest can be traced to the novel structural and electronic properties of these nanomaterials. Here we describe a study that measures the electronic properties of bare LiMo3Se3-nanowires, together with wires that have been stabilized by alkylammonium- and pyridinium-ligands. The bare LiMo3Se3-nanowires consist of individual wire bundles whereas the stabilized wires form networks with an inter-wire spacing determined by the ligand. The bare wires are shown to be metallic but susceptible to electrical degradation (oxidation) in air. However, conductivity measurements at different temperature and oxidation times show that conduction in the wire networks occurs via a percolation mechanism and is activated. Moreover, the corrosion rate of the Mo3Se3-nanowires is dramatically reduced when the wires are stabilized, demonstrating that the ligands form a protective semi-insulating coating.
Adlayer Structures Probed by Distance Tunnelling Spectroscopy for Au(111)/H2SO4 + Cu2+
Authors: Nagy Gabor , Wandlowski Thomas
Published: December 2003

We performed a series of distance tunnelling characteristics measurements for the system Au(111)/0.05 M H2SO4 + 1 mM Cu2+ to understand, if it is possible to map the liquid part of the double layer perpendicular to the electrode surface. We found that we probed the double layer in a distance range where we do not penetrate into the inner Helmholtz layer. Nevertheless, the tip is sufficiently close to the metal surface to address adlayer features showing sensitivity toward long-range ordered structures. The bias between the STM tip and the sample drops in the inner Helmholtz layer, and electronic overlap exists between the adsorbed layer and the metal surface. Molecular contributions to the electronic structure of ordered adlayers appear to be detectable. At larger distances from the surface the average barrier height was found to be about 1 eV, practically independent on the electrode potential.
ΔS°t – as a Structural Probe – a Critical Analysis of the Method and Determination of Structure of Aquo-Alcoholic Mixtures
Authors: Gumtya S. K. , Bandyopadhyay G. , Lahiri S. C.
Published: December 2003

Attempts were made for a critical examination of the use of ΔS°t as a structural probe to study the ion induced perturbations on aquo-alcoholic solvent mixtures. The division of the thermodynamic properties of TATB (tetraphenyl arsonium tetraphenyl borate) in solution into equal parts is not free from defects. Naturally, the calculation of single ion values based on TATB is also problematic. Dissection of the single ion values like TΔS°t(ion) as suggested by Kundu is full of errors. Analysis shows TΔS°t(ion) to be an insensitive parameter to determine the structural characteristics of aquo-alcoholic mixtures. Structure of aquo-alcoholic mixtures should be determined from the excess thermodynamic properties of mixing, excess dielectric properties of mixing, excess polarizabilities, the correlation parameter “g” etc. Other properties like ultrasonic sound absorption, excess volume and viscosity of mixing were found to be useful. Ion induced perturbations of any solvent system will be dictated by the structure of the particular solvent system. A knowledge of the structure of the aquo-alcoholic mixtures is imperative to develop an idea regarding ion induced perturbations as mirror image relations because of compensation of ΔH° and TΔS° (and of ΔH°t and TΔS°t) will be observed in any solvent system. The thermodynamic measurements provide a summary of all interaction energies over a long time. To comprehend the rational structural details of the solvent systems, accurate thermodynamic measurements alongwith relaxation experiments providing high time and good structural resolutions are necessary.
Viscosity Properties of Electrolytes in Propylene Carbonate Based Lithium Battery Electrolyte Solutions
Authors: Wang Jianji , Zhao Yang , Zhuo Kelei , Lin Ruisen
Published: December 2003

Viscosities of LiClO4 and LiBr have been measured in solvent mixtures of propylene carbonate (PC) with dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile (AN) and methyl formate (MF) at 298.15K. The dependence of viscosity on the composition of the mixed solvents was fitted with an equation without adjustable parameter. Viscosity B-coefficients for lithium salts and the corresponding activation free energies (Δμ0,≠) for viscous flow have been evaluated. At the same time, viscosity B-coefficients were predicted by the dielectric friction theory. The unsuccessful prediction of the composition dependence of the B-coefficients indicates that improvements will be necessary on the theory with taking account of the short-range interaction and molecular nature of the solvents. Furthermore, solute–solvent interactions in these mixed solvents are discussed in terms of the B-coefficients and activation parameters.
Influence of Solubilized Azo Dyes on the C.M.C. Value of Cetyl-Trimethylammonium Bromide
Authors: De Vijlder Michel
Published: December 2003

The spectral changes in the visible absorption range of the two anionic azo dyes Methyl an Ethyl Orange in neutral aqueous solution, induced by the presence of Cetyl-trimethylammonium bromide (CTAB) micelles, are attributed to the partial solubilization of the dyes rather than to the formation of mixed micelles. The same phenomenon is not observed with the larger Orange IV (C6H5NHC6H4N=NC6H4SO3
−Na+). The c.m.c.CTAB values in the presence of dyes were obtained from spectrophotometric as well as from surface tension measurements. The reduction of the electrostatic forces within the micelles due to the presence of dye counterions initially provokes the expected progressive lowering of the c.m.c.CTAB values. In a higher dye concentration range, however, appears a systematical increase denoting a renewed strengthening of the interactions between dye and surfactant monomers that also prevail below the c.m.c. (Buwalda et al.). This assumption is supported by the observed corresponding decrease of the values for the association constant which characterize the interactions existing between the dye monomers and the surfactant micelles. At fixed dye concentrations, increasing amounts of a strong electrolyte (NaBr) lower the c.m.c.CTAB in accordance with the requirements of the Corrin-Harkins relation. Partition coefficient values have been estimated from the spectrophotometric data by using the relation proposed by Kawamura et al.. They depend on the nature and on the concentration of the solubilizate as well as on the ionic strength of the solution but their order of magnitude invariably evidences the importance of the solubilization process.
Electrical Conductivity of Some Copper Manganites
Authors: Ismail F. M. , Hamad F. F. , Faraj H. S.
Published: December 2003

The a.c. conductivity as a function of temperature was measured for ten prepared samples. The measurements were carried out in the temperature range 25–340°C. The sample CuMn2O4 prepared either from oxide or carbonate contains the least impurity content, while the sample Cu1.5Mn1.5O4 from oxide origin and Cu1.6Mn1.4O4 from carbonate origin contain the highest impurity content. The activation energy ΔE
1 values for the oxide origin samples are nearly the same of those obtained from carbonate origin. The variation of ΔE
2 values with concentration of copper content (x) appears to be consistent.
Thermodynamic Excess Properties of the 1-Alkylamine + Alkane and di-n-Alkylamine + Alkane Systems in Terms of an Associated Mixture Model with Equation of State Contribution
Authors: Treszczanowicz Andrzej J. , Treszczanowicz Teresa
Published: December 2003

The model proposed by Treszczanowicz and Benson (1985) is applied for the description and interpretation of excess enthalpyHE, excess volumeVEand excess molar isobaric heat capacityCEpof the binary systems formed by 1-alkylamines and dialkyl-amines withn-alkanes. In the model, the self-association contribution is described by an athermal associated mixture model with the continuous mode of association of the Mecke–Kempter type and the equation of state contribution described by the Flory theory. The three self-association parameters: enthalpy, entropy and volume are valid over the whole homologous series of 1-alkylamines and dialkylamines. The equation of state interaction parameters are correlated for both series of mixtures with the structure of the component molecules by using the Kehiaian–Guggenheim group contribution method. The model predicts reasonably wellHEas well asVEfor both these classes of mixtures.
Temperature Dependence of Viscosity and Density of cis-1,4/trans-1,3-Dimethylcyclohexane and Several other Commonly Used Organic Solvents
Authors: Ruth A. A. , Lesche H. , Nickel B.
Published: December 2003

The dynamic viscosity (η) of the glass-forming 50:50 mixture of cis-1,4/trans-1,3-dimethylcyclohexane (ct-DMCH) was measured from 293 K down to ≈ 126 K where η ~ 1.2 × 106 mPas. The viscosity measurements of several other commonly used solvents cover the range from 293 K down to ≈ 148 K (η ~ 1.4 × 104 mPas) for 1-propanol (1-Prop), to ≈118 K (η ~ 2.5 × 102 mPas) for 2-methylpentane (2-MP), to ≈ 167 K (η ~ 10.0 mPas) for isooctane (Isooct), to ≈ 183 K (η ~ 2.8 mPas) for cyclopentane (CP) and down to ≈ 98 K (η ~ 4.6 × 102 mPas) for the 30:70 mixture of cyclopentane/isopentane (CP/IP). The density (ρ) of all solvents was measured correspondingly over appropriate temperature ranges. For the solvents studied here, the temperature dependence of the viscosity can be represented by a single Arrhenius term down to ~180 K. Over a wider temperature range down to ~118K the sum of two Arrhenius terms is required, and in the low temperature regime a Vogel–Tammann–Fulcher expression is necessary to adequately describe the temperature dependence of the dynamic viscosity.
Activity Coefficients of Potassium Dihydrogen Phosphate in Aqueous Solutions at 25°C and in Aqueous Mixtures of Urea and this Electrolyte in the Temperature Range 20–35°C
Authors: Partanen Jaakko I. , Mori Yuko , Louhi-Kultanen Marjatta , Kallas Juha J.
Published: December 2003

Simple two-parameter Hückel and Pitzer equations were determined for the calculation of the activity and osmotic coefficients of aqueous solutions of potassium dihydrogen phosphate at 25°C up to a molality of the saturated solution (= 1.83 mol kg−1). The isopiestic data measured by Stokes (1945) were used in the parameter estimations. The resulting parameter values were tested with all thermodynamic data found in the literature for this electrolyte at this temperature. In these tests it was observed, that the Hückel equation applies to the data within experimental error up to a molality of 1.0 mol kg−1, and the Pitzer equation applies well to the data in the molality range 1.0–1.83 mol kg−1 but not very well in dilute solutions. Therefore, also a three-parameter Pitzer equation was determined that applies to all data. The activity and osmotic coefficients calculated by these three models were compared to the values suggested by Robinson and Stokes (1959) and to those calculated by the equations of Hamer and Wu (1972) and of Pitzer and Mayorga (1973) for this electrolyte. Solubility measurements of KH2PO4 at 20, 25, 30 and 35°C were made in aqueous urea solutions, and the molality of urea varied in these measurements from 0 to 2.5 mol kg−1. The thermodynamics of these studies were analyzed by using the Pitzer formalism. It was observed that only one interaction parameter between urea molecules and ions (this parameter is linearly dependent on the temperature) was needed to describe almost completely the new solubility data.
Surface Tension of the System LiF-NaF-K2NbF7
Authors: Kubíková B. , Vasiliev R. , Šimko F. , Daněk V.
Published: December 2003

The surface tension of the molten system LiF-NaF-K2NbF7 has been determined using the maximum bubble pressure method. The error in the surface tension measurement was estimated to be ±1%. Based on the obtained data the composition dependence of the surface tension and of the surface tension excess of the investigated system was calculated. The results are discussed in term of the anionic composition. From the surface tension excess results the negative deviation from the ideal behavior of the studied system.
Nuclear Magnetic Resonance in Expanded Fluid Metals
Authors: Warren William W.
Published: December 2003

Adaptation of the internally-heated autoclave technique to nuclear magnetic resonance (NMR) has permitted NMR measurements of electronically-conducting fluids at high temperatures and pressures. The history of NMR experiments on mercury, selenium, and cesium is reviewed briefly with reference to subsequent relevant research on these materials.
Equation of State and Electrical Conductivity of Dense Fluid Hydrogen and Helium
Authors: Redmer Ronald , Juranek H. , Kuhlbrodt S. , Schwarz V.
Published: December 2003

The equation of state of fluid hydrogen, helium, and their mixtures is determined within fluid variational theory. Reactions between the constituents such as dissociation and ionization are considered. Results are given for densities and temperatures relevant for the interior of giant planets. Furthermore, the electrical conductivity is determined within linear response theory. Comparison is performed with available experiments and other theoretical work.
The Transition to the Metallic State in Alkali and Low-Z Fluids
Authors: Nellis W. J. , Chau R. , Edwards Peter P. , Winter Roland
Published: December 2003

We review here experiments that investigate how the electronic properties of five chemically dissimilar fluid elements, hydrogen, nitrogen, oxygen, rubidium and caesium, vary with density beyond their critical points. Remarkably, all five elements in their metallic regime have essentially the same electrical conductivities, close to the predicted minimum metallic conductivity of a high-temperature, disordered metallic fluid. The large differences in their respective metal-nonmetal transition densities are rationalized in terms of each chemical element’s unique atomic properties of size (radial extent of electronic wave function, N.F.Mott) and electronic polarizability (K.F.Herzfeld and D.A.Goldhammer). These experiments thereby highlight the pivotal role of atomic properties in dictating the metallic or nonmetallic status of chemical elements of the periodic classification.
Slow Dynamics Due to the Metal-Nonmetal Transition in Liquids
Authors: Yao Makoto , Kohno Hirotaka , Kajikawa Hiroaki
Published: December 2003

It is well known that the liquid dynamics slows down on approaching the liquid-gas critical point or the liquid-glass transition. Recently we have found by the sound attenuation measurements that the metal-nonmetal (M-NM) transition also induces slow dynamics. In the M-NM transition range of expanded liquid Hg, we have observed anomalous increase in the sound attenuation due to the structural relaxation process. Assuming a simple Debye-type relaxation, we have estimated that the relaxation time should be of the order of nanoseconds and revealed that the relaxation strength has a broad maximum in the M-NM transition range. Moreover, two types of anomalies have been observed also in the semiconductor-metal (S-M) transition range of liquid Te-Se mixtures. We present the recent experimental results of the sound attenuation measurements and discuss briefly the mechanisms of the slow dynamics in the metal-nonmetal transition range of liquids.
Volumetric Properties, Compressibilities and Volume Fluctuations in Phospholipid-Cholesterol Bilayers
Authors: Seemann H. , Winter Roland
Published: December 2003

We conducted detailed measurements of the apparent specific volume of dipalmitoylphosphatidylcholine (DPPC)–cholesterol mixtures in excess water as a function of pressure up to 70MPa (700bar) at 20, 38 and 50°C. The volumetric properties and the isothermal compressibility κ
T of the lipid vesicles were determined at cholesterol concentrations, χchol, ranging up to 50 mol. The thermodynamic data are compared with other physico-chemical properties of phospholipid–cholesterol mixtures. Furthermore, the thermodynamic properties of the system are discussed in the light of the various T, χchol–phase diagrams and computer simulation studies published in the literature.
The Network-Chain Transformation in the Liquid As-Te Mixtures near the Semiconductor-Metal Transition
Authors: Hoshino H. , Endo H. , Maruyama K.
Published: December 2003

The results of neutron diffraction and EXAFS measurements for l-Te and l-As-Te mixtures (10, 20, 30 and 40at. As) are discussed. The g(r) patterns of l-Te show a substantial overlap between the first and second peaks. The first minimum after the first peak of g(r) around 3.2Å is filled up at high temperature. Upon the addition of As to l-Te the first peak of g(r) becomes sharp, implying that As atoms bridge between Te chains and suppress the thermal fluctuations of the inter-chain distances. The filling of the first minimum around 3.2Å observed for l-As-Te mixtures at high temperature is associated with the inter-chain correlation in a densely packed configuration. From the EXAFS analysis of l-As-Te mixtures we conclude that the network structure composed of threefold coordinated As atoms and twofold coordinated Te atoms is transformed into a twofold coordinated chain structure. The network-chain transformation is accompanied by a gradual semiconductor to metal transition. The first sharp diffraction peak observed for l-As20Te80 and l-As40Te60 is related to the Te-Te intermediate range order in -Te-As-Te- or -Te-As-As-Te- chain molecules.
Local Structure of Liquid Te Studied by Neutron Diffraction and EXAFS
Authors: Endo Hirohisa , Maruyama K. , Hoshino H. , Ikemoto H.
Published: December 2003

Neutron diffraction measurements for liquid (l-) Te have been performed. The first minimum after the first peak of g(r) is well above zero and filled up with temperature, while the second peak diminishes substantially and flattens out at high temperature. The temperature variations of g(r) are analyzed combining the structural information available from our EXAFS results. The curve fitting of g(r) for l-Te predicts that two different inter-chain components coexist. The first corresponds to the short-distance inter-chain component around 3.2Å and the second corresponds to the long-distance inter-chain component around 3.8Å. The filling of the first minimum around 3.2Å at high temperature is clearly related to the metallization. EXAFS analysis on the basis of the model g(r) indicates that the short-distance inter-chain component (P2) responsible for the metallic conduction in l-Te as well as the nearest intra-chain component (P1) are required for fitting the oscillatory spectrum in the region of short-range sensitivity of the EXAFS signal. It is concluded that the S-M transition observed for l-Te arises from the transformation to the densely packed configuration composed of shortened chain molecules.
Wetting Transitions in Fluid K
x
KCl1−

x
Revisited
Authors: Dogel S. , Nattland D. , Freyland Werner
Published: December 2003

Spectroscopic ellipsometry and reflectometry were employed to study the wetting behaviour of the metal–molten salt system K
x
(KCl)1−

x
at the interface to an inert sapphire wall. We present new results on the wetting film spectra and on the film thickness at solid–liquid coexistence and in the homogeneous liquid phase. The film spectra clearly show the typical absorption of the liquid state F-centre. The wetting film thickness strongly increases approaching the monotectic temperature along the liquidus line. In the homogeneous regime the film thickness decreases at constant composition with increasing temperature and at constant temperature with decreasing salt concentration in agreement with complete wetting. For the interpretation within the framework of tetra point wetting we have developed a quantitative description of the excess Gibbs energy of the system.
To the Temperature Dependence of Carbon Particle Formation in Shock Wave Pyrolysis Processes
Authors: Emelianov A. , Eremin A. , Jander H. , Wagner H. Gg.
Published: December 2003

In this work the results of numerous experiments on carbon particle formation in combustion and pyrolysis of various carbon bearing molecules behind shock waves in the wide temperature range from 1200K to 3500K are analyzed. It is shown, that the discrepancy in the temperatures of the maximum particle yield could be attributed to the differences in the endothermicy of the pyrolysis of various molecules and the maximum optical density at 633nm in all mixtures can be related to the same temperture T=1600K. Based on this consideration, several statements were formulated. First – particle growth in all mixtures can be described by the uniform dependence of optical density D (at 633 nm) on time D~aτ0.4 indicating, that particle formation proceeds via homogeneous condensation. The second – decrease of the optical density at 633nm with the temperature rise is caused not by the decrease of particle yield, but the decrease of their size resulting in the fall of extinction at the given wavelength. Third – the reason of the fall of the final particle size with the temperature rise is the acceleration of the initial cluster formation process and a corresponding increase of the particle number density. And the last statement – the secondary particle growth, observed at T>2200K is completely determined by the primary clusters (nucleus) formed behind the incident wave and the coagulation of small carbon particles formed behind the reflected shock wave using these clusters.
Thermal Diffusion of Weak Electrolytes: IV. Relationship between the Transported Enthalpies of the Ionic and Molecular Form of the Solute
Authors: Domonkos L. , Liszi J.
Published: December 2003

It is established that during the thermal diffusion of weak electrolytes in dilute aqueous solution the total transported enthalpies of the molecular and ionic form of the solute component are practically identical.
Analysis of Semiconductor Cluster Beam Polarization Taking Small Permanent Dipole Moments into Account
Authors: Schnell M. , Herwig C. , Becker J. A.
Published: December 2003

Deflections of semiconductor cluster beams in an inhomogeneous electric field deliver enhanced polarizabilities for cold isolated Ga
N
As
M
clusters with odd number of atoms n=N+M up to n=17. One speculated that the high polarizabilities result from their electronic open shell structure. This was qualitatively confirmed by optical absorption cross section measurements, but the enhancement of polarizability is too large to be explained through a Kramers–Kronig-relation as purely electronic effect. Moreover, quantum chemical calculations gave permanent dipole moments of some tenths of a Debye for certain compositions. The clusters are too heavy to identify these dipole moments by beam broadening effects, but we will show in the present analytic investigation within classical top theory, that a slight reversible-adiabatic alignment of the clusters dipole moment in the electric field increases the average beam deflection and the derived polarizability values. This effect was up to now not taken into account and it offers a consistent explanation of the Ga
N
As
M
polarizabilities by small permanent dipole moments of some tenths of a Debye and a reasonable rotational temperature between 2 and 12K.
Prediction of Reduced Falloff Curves for Recombination Reactions at Low Temperatures
Authors: Cobos Carlos J. , Troe Jürgen
Published: December 2003

Strong collision falloff curves for barrierless recombination reactions at low temperatures are calculated taking into account transitional modes only. Specific rate constantsk(E,J) from statistical adiabatic channel/classical trajectory (SACM/CT) calculations are used. Broadening factors of the falloff curves are found to depend only weakly on the temperature. A systematic analysis of the influence of the centrifugal barriersE0(J), which are governed by the potential energy surface of the bond energiesE0, and of the number of transitional modes is made. Guidelines for estimating center broadening factors and shape functions for the broadening factors are given.
Phase Separation in Ultracold Boson–Fermion Mixtures under Confinement
Authors: Akdeniz Z. , Tosi M. P.
Published: December 2003

A short review is given of recent progress in understanding the demixing transition in a mesoscopic gaseous cloud of bosonic and fermionic alkali atoms under the effect of their mutual repulsions at zero temperature. The mixture is confined inside a magnetic trap exerting external harmonic potentials on the atoms and the bosonic component is taken in a Bose-Einstein condensed state while the fermions are in a spin-polarized state. Main emphasis is placed on the role of the confinement: in a mesoscopic system (i) the phase transition becomes smooth as a function of the driving parameter, which is the boson-fermion s-wave scattering length; and (ii) various configurations of the phase-separated gaseous cloud are allowed, including some very exotic ones in an anisotropic trap. The transition inside a spherical trap leads to an egg-type structure, with the bosonic condensate being surrounded by a shell of fermions, and is best identified from a sharp upturn of the frequency of low-lying monopolar and dipolar oscillations of fermionic character. This dynamical signature of the transition appears when the overlap between the two components has already started to decrease, but is still quite appreciable. A system of specific experimental interest is the mixture of 6Li and 7Li isotopes, whose parameters could be driven towards the phase transition.
Can Alkali Metal Doped Zeolites be Metallic? – Microwave Conductivity of Rubidium Doped Zeolite Rho
Authors: Edmondson Michael J. , Barker Peter D. , Porch Adrian , Anderson Paul A. , Edwards Peter P.
Published: December 2003

Large crystallites of high purity zeolite rho have been synthesized by controlled monitoring of the aging and heating period of the mother gel. The microwave conductivity of Rb-rho samples doped with up to 20Rb atoms p.u.c. was measured over the temperature range 15–300K. Confirmation that the conductivity was due to rubidium doped zeolite rho and not decomposition products or residual rubidium metal was provided by XRD, TEM, and microwave loss measurements on zeolite supported silver particles, the latter providing the first experimental confirmation of the validity of the quasistatic analysis for highly conducting particles. At low concentrations of rubidium dopant the observed microwave responses were dominated by dielectric effects. In the sample Rb17/Rb-rho, a strongly temperature-dependent electronic contribution to the conductivity was observed above ~150K. In Rb20/Rb-rho, conductivities in the range 1.5–2.3 Sm−1 were observed between 15 and 300K. The residual conductivity at 15K indicates that the sample is indeed metallic, but the values of conductivity measured are low in comparison to conventional metals.
Density Dependence of the Interrelation between Single Particle Motion and the Collective Dynamics in Liquid Sodium
Authors: Pilgrim W.-C. , Morkel C.
Published: December 2003

Over a wide range of densities we have systematically investigated the single particle motion in liquid sodium in a series of quasielastic neutron scattering experiments. Our experimental results are in excellent agreement with predictions from molecular dynamics simulations and Mode-Coupling-Theory. The results allow to determine the microscopic mechanisms that control the single particle motion on atomic time- and length- scale and to relate these mechanisms to the values of the macroscopic diffusion coefficient at different densities. We can clearly distinguish three different density regimes where respectively three different coupling mechanisms between diffusive motion and collective modes dominate: At high density, particle diffusion is hindered and the main contribution to forward motion of a particle comes from a coupling to longitudinal density modes; however, at slightly reduced density the motion of the particle is coupled to transverse shear modes which cause an enhancement of the diffusive motion and hence of the diffusion coefficient. Only at very low density, the system gradually returns to particle dynamics which is controlled by binary collisions as predicted by simple hard sphere theories.
Novel Ionization Mechanisms of Molecular Clusters in Ultraintense Laser Fields
Authors: Last Isidore , Jortner Joshua
Published: December 2003

We explore extreme multielectron ionization of (Xe)
n
molecular clusters resulting in the formation of highly charged Xe
k

+, k=8–32, ions in ultraintense laser fields (intensity I= 1016–1019 W cm−2), which is driven by a compound, sequential-parallel, inner-outer ionization mechanism. A computational and theoretical study is advanced for the three fundamental processes of electron fs dynamics, which involve the barrier suppression of inner ionization of the constituents, the formation of an energetic electron-positive ion charged plasma within the cluster and the outer ionization of unbound electrons from the cluster. New features of the formation, characteristics, response and dynamics of the electron-positive ion charged plasma in molecular clusters in ultraintense laser fields were explored, providing novel information on a transient (1–100 fs) metallic state in finite chemical systems.
The Chemical Potential of Metal Atoms in Small Particles
Authors: Schäfer Rolf
Published: December 2003

The chemical potential of metal atoms in isolated clusters has been investigated in dependence of cluster size by means of molecular beam experiments. For that purpose the heat of condensation, which is released during a cluster deposition experiment, is measured with novel microcalorimeters. The experimentally determined heat of condensation enables one to determine the formation enthalpies of the isolated particles. Additional temperature dependent measurements gives insight in the melting behaviour of the isolated systems. The investigations allow one to discuss the size-dependence of the chemical potential of metal atoms in small particles in comparison to predictions on the basis of a simple thermodynamic droplet model.