bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion of interacting lattice gases on homogeneous surfaces
Authors: Uebing Christian , Gomer Robert 
Published: July 2012

AbstractTracer and chemical surface diffusion coefficients, D* and D respectively, were studied on a homogeneous surface of square symmetry by means of Monte Carlo modeling. D was determined by the fluctuation autocorrelation function method and from the Kubo‐Green equation. Both techniques yield identical results. Simulations were carried out for a lattice gas model with repulsive nearest neighbor interactions affecting both adsorption sites (ϕNN) and saddle points (ϕ*NN) of the periodic potential. The phase diagram of the lattice gas model shows c(2×2) ordering at low temperatures θ≈︁0.5. It was found that both types of interactions, ϕNN and ϕ*NN, strongly affect surface diffusion. The effects are most pronounced at low tempratures T and high surface coverages θ where the adatoms are closely together. It was found that raising the saddle point energies by ϕ*NN counteracts and may totally compensate for the effect of repulsive nearest neighbor interactions ϕNN.
Simultaneous small‐ and wide‐angle X‐ray diffraction during the main transition of dimyristoylphosphatidylethanolamine
Authors: Rappolt Michael , Rapp Gert 
Published: July 2012

AbstractThe main transition of dimyristoylphosphatidylethanolamine (DMPE) dispersed in excess water has been investigated by simultaneous small‐ and wide‐angle X‐ray diffraction during heating and cooling scans. At scan‐rates of 0.6°C/min and 0.1°C/min the transition has at least three components during heating, and four components during cooling. Amplitude and thermal width of these components are similar to those found in calorimetric experiments (B.Z. Chowdhry, G. Lipka, A. W. Dalziel, and J. M. Sturtevant, Biophys. J. 45, 901‐904 (1984); H. Yao, I. Hatta, R. Koynova, and B. Tenchov, Biophys. J. 61, 683‐693 (1992)). It is suggested that the different components of the transition from the gel to the liquid crystalline phase and vice versa are attributed to different steps of a cluster growth mechanism in liposomes. Initially the growth proceeds primarily radially, most likely along defects, and not shell by shell. A model is presented to explain (1) the sequence of steps, (2) their relative width and cooperativity and (3) the hysteresis of the transition.
On the rate constant for non‐steady state nucleation at solid surfaces
Authors: Tomellini Massimo 
Published: July 2012

AbstractThe rate constant for non‐steady state nucleation at solid surfaces has been evaluated in the case of very small size of the critical nucleus. For this purpose a rate equation approach has been employed in which elementary steps are the attachment and the detachment of both ad‐monomers and gas monomers to and from the subcritical clusters. It is shown that if equilibrium is established between gas‐ and ad‐monomers the rate constant can be written in a highly simplified form. In this case a detailed computation indicates the apparent activation energy for nucleation to depend on the ratio between the surface diffusion coefficient of ad‐monomers and the flux of gas atoms incoming at the surface. The rate constant exhibits a power law dependence on the flux of monomers whose exponent is related to the size of the critical cluster. Both the physical cases of weak adsorption and of total condensation of the ad‐atoms at the nucleation sites have been considered.
Some results on the mechanism of the reaction between O(3P)‐atoms and HOCl. An experimental and Ab initio model study
Authors: Schindler Ralph N. , Dethlefs Jan , Schmidt Mark 
Published: July 2012

AbstractThe rate constant for the title reaction was redetermined using discharge flow technique and mass spectrometric measurements of HOCl consumption. The overall rate constant k = (1.7±0.3)×10−13 cm3 molecule−1 s−1 was obtained and found to be practically independent of temperature in the range 213 K≤T≤298 K. In experiments using 18O atoms the time dependence in the formation of the products 18O16O, HC1 and Cl2 was determined. Based on the experimental data available it is proposed that the reaction occurs via an intermediate complex mechanism but it could not be decided by which primary steps the reaction is initiated.Ab initio model calculations were carried out in an attempt to quantify conceived reaction pathways. Structures and energetics of the intermediates were computed. On the basis of these calculations it is suggested that Cl abstraction from HOC1 should be regarded as the preferred initiation step. The O‐atom attack leads to the formation of an intermediate HOClO. Alternative reaction pathways, like H abstraction from HOCl by O‐atom attack, or a mechanism in which HO2 and Cl are formed were found to be less probable. In the present calculations no support could be found for the thermodynamically most preferred reaction route to contribute to product formation. Structure and energy of the intermediate HOC1O are computed.
Surface order induced ferroelectricity in ultrathin films of the smectic a phase of a chiral liquid crystal
Authors: Hoffmann E. , Stegemeyer H. 
Published: July 2012

AbstractIn free standing films of the smectic A phase of a chiral liquid crystal ferroelectric switching has been observed. The polarization charge obtained by the field switching does not depend on the number of smectic A layers. The results confirm the molecular tilt in the boundary layers of the film caused by surface ordering.
Sequential electrodeposition of silver and bismuth on a gold surface
Authors: Schröter C. , Solomun T. 
Published: July 2012

AbstractSequential electrodeposition of Ag and Bi from a single electrolyte on Au (111) was studied by means of voltammetry and ion scattering spectroscopy (ISS). Silver was electrodeposited first under diffusion control. Subsequently, bismuth was deposited under potential sweep conditions. Underpotential deposition of BI on the gold surface modified with five Ag monolayers takes place similar to the deposition on the Ag (111) electrode. The deposited Bi can be electrodissolved completely with Ag remaining on the surface. However, the voltammetric characteristics of this process are different from the one in the case of Bi on the (111) surface of a silver single crystal. The ISS data suggest that this might be due to intermixing at the Ag/Bi interface occurring subsequent to the formation of the initial Bi on Ag structure on Au(111).
Multicomponent diffusion of sodium alginate solutions with added salt. II. Charged vs. Uncharged system
Authors: Paradies H. Henrich , Wagner Dirk , Fischer Wulf R. 
Published: July 2012

AbstractDiffusion coefficients are reported for dilute aqueous solutions of sodium alginate, and for three compositions of the ternary system comprising of sodium alginate/sodium chloride/water at 20°C applying the conductimetric method. From binary transport data the ternary diffusion coefficients for alginate of added salt (NaCl) can be qualitatively calculated. Due to electrostatic interactions between the ions the diffusive flow of the alginate polyelectrolyte and added salt reveal strong coupling. At pH>5.0 (20°C) and ionic strength of 0.015 M NaCl each mole of diffusing alginate cotransports approximately 210 moles of NaCl. Coupled flow of NaCl ceased if the solution pH is approaching pH 5.5, close to the isoelectric point of alginate (pH 5.4). Between pH 4.5–5.0 the coupled transport of NaCl is governed by the diffusion of the protonated alginate concentration gradient due to the diffusion induced electric field along the neutral alginate. At acidic pH (3.5–4.0) diffusing alginate generates a counter flow of NaCl due to additional bound protons, yielding a net positive charge hence the D21‐value is large and positive.
On the uniqueness of stratification‐induced structural transformations in confined films
Authors: Schoen Martin 
Published: July 2012

AbstractThis article is devoted to an investigation of structural transformations which occur in molecularly thin films confined between planar structured and unstructured rigid solid surfaces as the number of fluid strata parallel with the walls changes under conditions of fixed chemical potential μ and temperature T. The transformations become manifest as periodic maxima in the transverse isothermal compressibility k∥ computed in grand canonical ensemble Monte Carlo simulations via fluctuations in film density. The transformation occurs at nearly identical characteristic separations sz of the surfaces regardless of whether these are discrete (i.e., composed of individual atoms) or smooth in transverse dimensions. The transformation is caused mainly by confinement to spaces of molecular dimension and is unique, that is independent of details of the film‐wall interaction. Because of the inhomogeneity of a film between structured surfaces in transverse dimensions a definition of k∥ in terms of density fluctuations is precluded in general. However, by considering only restricted thermodynamic transformations on a length scale defined in units of the lattice constants characterizing the wall structure, such a definition is possible introducing k∥ as a density fluctuation‐related quantity in a coarse‐grained sense. Variations of the local density of the film around the transition points suggest to perceive the phase transition as stratification‐induced, because it happens after the new stratum has begun to form.
Isothermal Switching of conductivity in microemulsions via photodimerization of acridizinium bromide [1]
Authors: Nees Dieter , Cichos Ulrike , Wolff Thomas 
Published: July 2012

AbstractMicroemulsions composed of Aerosol OT (AOT), isooctane, and water in the mass ratio 1:1. 54:0.75 exhibit percolation, i.e., transition from a w/o to an o/w microemulsion, at 33 °C as revealed by the appearance of conductivity. In the presence of 0.01 mol/dm3 of acridizinium bromide the percolation temperature increases to 38 °C. Irradiation of this mixture with glass‐filtered light leads to a further rise of the percolation temperature to 43 °C. Thus, the system can be switched from conducting to non‐conducting upon irradiation at between 38 and 43 °C.
An improved thermodynamic approach to the stability of multi‐component silicate glasses in aqueous solutions
Authors: Conradt Reinhard , Geasee Pisit 
Published: July 2012

AbstractA rate equation is developed by which the dissolution rates of multicomponent silicate glasses in diluted aqueous solutions can be calculated as a function of pH, CO2 partial pressure, and salinity. Gibbs free energies of hydration are derived by treating the aqueous solution as a diluted system of aqueous species of the various cations in the glass, and by treating the glass as a mixture of the constitutional phases taken from its basic phase diagram. Beside the free energies, the amounts of H+ and OH− absorbed at the glass surface are taken into account as rate determining factors. Calculated dissolution rates of silica, A type, E type, rock, and slag glass fibres agree with experimental values within ±30% on a linear scale.
Crystallization processes of cordierite glasses
Authors: Morinaga Kenji , Takebe Hiromichi 
Published: July 2012

AbstractTo prepare α‐cordierite glass ceramics, we demonstrate two types of phase diagrams of a composition 2MgO·2Al2O3·5SiO2 with time courses. One is the continuous‐cooling‐transformation (CCT) diagram; the other is the temperature‐time‐transformation (TTT) diagram. At ∼ 1273 K, μ‐cordierite is crystallized as the primary phase and then it transforms to α‐cordierite with a lath‐like martensite transformation. The volume expansion derived from this transformation results in a lot of cracks in crystallized glasses. Since the addition of MgF2 for the substitution of MgO (ca. 5%) suppresses the μ‐to α‐cordierite transformation but promotes the direct crystallization of α‐cordierite from glass, we can prepare α‐cordierite glass ceramics without cracks. In this paper, we point out the needs and usefulness of CCT and TTT diagrams for glass ceramics processing.
Nucleation sites at cordierite glass surfaces
Authors: Müller R. , Reinsch S. , Völksch G. , Heide K. 
Published: July 2012

AbstractThe nucleation density, N, of high‐quartz solid solution crystals (“μ‐cordierite”) at surfaces of cordierite glass (2 MgO·2Al2O3·5SiO2) was studied by optical and electron microscopy for differently damaged surfaces prepared and thermally treated in controlled ambient atmosphere.(i) Sharp tips and edges are dominating nucleation sites at mechanical damaged cordierite glass surfaces. These sites are privileged due to a substantial reduce of the elastic energy that contributes to the work of forming a critical nucleus within the surrounding glass phase. (ii) Solid foreign particles are dominating nucleation sites at smooth surfaces. Oxide particles, dusted on to the glass surface prior to heat treatment, increase N in most cases. Their nucleating efficiency (ZrO2 (monoclinic)>(ZrO2 (tetragonal)>Al2O3 ≈ Fe2O3>CeO2>MgO) indicate their role as chemically stable nucleating substrates. Non‐oxide particles have no influence (SiC, Si3N4) or even suppress surface nucleation (WC, W) indicating chemical interaction with the glass. (iii) Both, no strong influence of ambient humidity on N and similar minimum values of N, Nmin≈10−8 μm−2, for free air and vacuum experiments indicate minor nucleation activity of flat pristine glass surfaces even in contact with air. On the other hand, N is influenced by the sample‐crucible geometry.
The influence of the iron concentration and the Fe2+/Fe3+ redox ratio on the crystallisation of Bioverit II
Authors: Kasten C. , Carl G. , Rüssel C. 
Published: July 2012

AbstractTransition metal ions do not solely influence the optical properties of glasses but also their crystallisation behavior. In the case of iron in a mica glass ceramic, Fe3+ leads to smaller mica‐aggregates and suppresses the crystallisation of indialith. In glasses melted under reducing conditions, Fe2+ is formed which is incorporated into the indialith and leads to a preferred crystallisation of this phase. Iron does not act as a simple colouring additive but influences the whole nucleation and crystallisation process.
III. Electrochemistry in Glasses and Melts. Glass electrodes: Why and how they function
Authors: Baucke Friedrich G. K. 
Published: July 2012

AbstractSubsurface concentration profiling by Ion Bombardment for Spectrochemical Analysis (IBSCA) and Nuclear Reaction Analysis (NRA) combined with other methods yielded information on the ionic processes at and in glass electrode membranes and results in the mechanism (“dissociation mechanism”) of glass electrodes. The primary step is the formation of a phase boundary equilibrium between functional groups, e.g. siloxy, at the glass surface and hydronium or alkali ions in the solution. It determines the potential of the glass due to the charge density established at the glass surface by the dissociated form of the surface groups, e.g. SiO−, and the surface activities of the acidic or salt forms of the surface groups, e.g. SiOH and SiOM, respectively. This inseparable connection of solution‐dependent potential and “surface coverage” was verified by electrolytic migration experiments. The concentration gradients thus caused below the glass surface lead to an ionic interdiffusion in the subsurface glass range (if the ions attached to the surface groups are not hindered sterically to enter the glass), which is the first step of glass corrosion, and to a diffusion voltage, which is part of the overall membrane potential. Quantitative expressions are given, and it is shown that, in principle, the response of glass electrodes is below “ideal”, i.e. smaller than RT(In 10)/F, which explains the well known sub‐Nernstian response of pH glass electrodes. Two new sodium errors were found. Construction and operation of glass electrodes are briefly sketched as an introductory basis. The reason for the long existence of the purely thermodynamic “ion exchange theory” is analysed.
Voltammetry in silicate and borosilicate melts
Authors: Claußen Olaf , Rüssel Christian 
Published: July 2012

AbstractWith the aid of square‐wave‐voltammetry, redox equilibria of various multivalent elements were studied in a soda‐lime‐silicate and a borosilicate glass melt in the temperature range of 600 to 1300°C. The peaks in the current‐potential curves could be attributed to certain redox couples. The peak potentials measured dependend linearly on temperature proving that both standard enthalpy and standard entropy possess constant values within the temperature range studied. The peak potentials measured in the silicate and the borosilicate melt were in fairly good agreement. A systematic shift caused by the higher alkali content of the borosilicate glass could not be observed.
IV. Transport Phenomena, Properties of Glass Surface and Corrosion. Ion and polaron conducting glasses
Authors: Cramer C. 
Published: July 2012

AbstractConductivity spectra, σ(ω), covering wide frequency ranges up to the mid infrared, have been taken of various glasses at different temperatures. The systems studied include the ion‐conducting glasses 0.30 Na2O·0.70 B2O3, 0.30 Li2O·0.70 B2O3 and B2O3·0.56 Li2O·0.45 LiBr as well as the polaron conducting glass 0.2 P2O5·0.8 (0.89 V2O5·0.11 V2O4). In the case of the ion‐conducting glasses it is possible to separate vibrational and hopping spectra from each other. The resulting hopping spectra display high‐frequency plateaus; in the dispersive regime, two power‐law exponents are observed, one being smaller, the other larger than unity. In contrast, the dispersive conductivity of the polaron conducting glass shows a simple single‐power‐law behavior with an exponent smaller than one. The interpretation of the spectra includes the idea of different “target” sites for the mobile species. A model concept for ion and polaron transport in glasses is proposed.
Oriented crystallization of fresnoite in an electric field
Authors: Keding Ralf , Rüssel Christian 
Published: July 2012

AbstractA glass melt with the composition of Ba2TiSi2O8·0.75 SiO2 was soaked at 1300°C. This did not lead to any crystallization. A current of 50 mA applied between the platinum crucible which acted as the anode and a platinum cylinder inserted to the melt as the cathode led to a potential of 1.2 V. This resulted in a crystallization of fresnoite at the cathode which continues for around 10 min until the crystallites reached the anode. The resulting glass ceramic was highly oriented and the microstructure was composed by fairly long needles consisting of fresnoite crystals. The long axis of the needles is the crystallographic c‐axis of the fresnoite. It is a polar axis and oriented parallel to the electric field. The nucleation process caused by current flow supposedly is an effect of the Ti3+ formed. Here, the viscosity should be decreased in the vicinity of the cathode and therefore the nucleation is enabled.
Sn+‐implantation and radiation‐induced structural modifications in amorphous SiO2
Authors: Angermann T. , Dunken H. H. 
Published: July 2012

AbstractThe structural damage produced by Sn+‐implantation into high purity silica substrates with doses of 1.1–2.0×1017 ions/cm2 at an acceleration voltage of 300keV has been analyzed by infrared reflexion spectroscopy (IRR), UV‐VIS spectroscopy, Rutherford backscattering spectroscopy (RBS), X‐ray diffraction and transmission electron microscopy (TEM). Densification, bond distortion and structural disorder of the implanted samples have been investigated. X‐ray diffractograms and TEM observations proved the formation of nanosize β‐Sn‐colloides.
V. Physicochemical Methods of Glass Characterization. Connectivities and cation distributions in oxide glasses: New results from solid state NMR
Authors: van Wüllen Leo , Gee Becky , Züchner Lars , Bertmer Marko , Eckert Hellmut 
Published: July 2012

AbstractModern solid state nuclear magnetic resonance (NMR) techniques afford powerful experimental strategies for elucidating detailed structural information in noncrystalline materials. While previous research emphasis has been on the identification and quantification of local environments (short‐range‐order), primarily by using the technique of magic‐angle spinning (MAS) NMR, correlations beyond the nearest neighbor coordination sphere (intermediate‐range order) can be studied by more sophisticated methods. This contribution focuses on recent advances made for a variety of oxide glasses, using methods of dipolar spectroscopy: Connectivities among the structural building blocks present in sodium aluminoborate glasses have been exposed using 11B{27Al} and 27Al{11 B} rotational echo double resonance (REDOR) NMR. Similarly, 29Si{31P} and 29Si{7Li} REDOR data form the basis of a structural model integrating six‐coordinated silicon into the network structure of alkali silicophosphate glasses. The spatial cation distributions in sodium silicate glasses are studied by 23Na spin echo decay spectroscopy, offering experimental evidence for inhomogeneous cation distributions at low alkaline contents. Finally, for mixed alkali sodium lithium silicate glasses, 23Na{7Li} spin echo double resonance (SEDOR) and 29Si{23Na} and 29Si{7Li} REDOR spectroscopies provide important experimental criteria for testing hypothesized relative Na‐Li cation ordering scenarios.
Structure of vitreous KPO3 studied by neutron and X‐ray diffraction
Authors: Hoppe U. , Walter G. , Stachel D. , Hannon A. C. 
Published: July 2012

AbstractThe gain of information about the glass structure obtained by RMC simulations on the basis of neutron and X‐ray diffraction results is demonstrated by vitreous KPO3. Details of the first neighbour P‐O peak confirm the existence of ring and chain structures which are formed from two‐fold linked PO4 units. The separation distance of these anionic molecular structures is determined by the dimension of the large K+ cations. The mutual arrangements of the modifier cations in their oxygen polyhedra form an interpenetrating substructure which surrounds the various forms of linked PO4 tetrahedra.
Cation ordering scenarios in mixed alkali silicate glasses. Experimental constraints from 23Na{6Li} spin echo double resonance NMR
Authors: Gee Becky , Eckert Hellmut 
Published: July 2012

AbstractThe spatial arrangement of sodium and lithium ions in mixed‐alkali silicate glasses of composition [(Li2O)1‐y(Na2O)y,]0.4[SiO2]0.6 (y = 0.25, 0.50 and 0.75) is explored by 23Na{6Li} spin echo double resonance (SEDOR) NMR spectroscopy on isotopically labelled materials. The results are discussed within the context of two basic models for the spatial cation distribution, both of which are calculated with the constraint of resulting in the same cation density as experimentally measured for the glasses: The first scenario considers a homogeneous distribution of the cations by arranging them at regular distances on a cubic lattice. For this base model, a statistical mutual arrangement of lithium and sodium is in fairly good agreement with the experimental data. The second scenario models a clustered distribution by fractionally occupying the cation sites of the Na2O lattice in a random fashion. If this base model obtains, the experimental NMR results indicate preferential interactions among like cations. Approximate agreement with the experimental SEDOR decay curves can be obtained by assuming a flat distribution function of MNa‐Li2 values, ranging from zero to M20, the average second moments calculated for a statistical mutual distribution of Li and Na ions. This model also gives satisfactory fits to previously published 23Na{7Li} SEDOR data on compositional analogous glasses with the natural isotope distribution.