bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Situ High Temperature SERS Study of Oxygen Adsorbed on Ag: Support and Electrochemical Promotion Effects
Authors: Kondarides D. I. , Papatheodorou G. N. , Vayenas C. G. , Verykios X. E. 
Published: July 2012

AbstractIn situ surface enhanced Raman spectra (SERS) of adsorbed oxygen were obtained during oxygen adsorption and ethylene epoxidation on Ag catalyst surfaces at temperatures between 25 and 400 °C and atmospheric total pressure. Three types of Ag catalysts were investigated: (I) Ag supported on a‐Al2O3, (II) Ag films deposited on quartz and (III) Ag films deposited on the O2‐ conducting solid electrolyte Y2O3‐stabilized ZrO2 (YSZ). In the last case the effect of the application of external voltages (‐2 V to +2 V) on the SERS was also examined “in situ” in order to investigate the effect of Non‐Faradaic Electrochemical Modification of Catalytic Activity (NEMCA). Bands at 240, 345, 815, 870, 980 and 1630 cm−1 were observed for the oxygen‐Ag/YSZ system. The 815 and 980 cm−1 bands were also observed for the Ag/quartz and Ag/a‐Al2O3 samples. The intense band at 815 cm−1, assigned to the O‐O stretching vibration of a molecularly adsorbed oxygen species, exhibited an isotope shift of 20 cm−1 upon replacing 16O2 with 18O2. This band is present during ethylene epoxidation at temperatures up to 350 °C and its relative Raman intensity decreases with decreasing O2 to C2H4 ratio. The excitation profile of the 815 cm−1 band and the existence of the overtone at 1630 cm−1 indicate that preresonance Raman enhancement is also responsible for the high intensity spectra obtained. In the case of Ag/YSZ it was found that increasing catalyst potential strengthens the O‐O bond and increases the band intensity, while decreasing catalyst potential causes a decrease in bond strength and band intensity. These observations can be accounted for within the framework of previous NEMCA studies. However the change in relative band intensity can also be due to the effect of applied voltage and changing Fermi level and work function on the enhancing mechanism of SERS.
A Conductance Study of the Binding of Methyl Orange, o‐Methyl Red and p‐Methyl Red Anions by β‐Cyclodextrin in Water
Authors: Tawarah Khalid M. , Wazwaz Aref A. 
Published: July 2012

AbstractA conductance study concerning the binding of methyl orange (MO), o‐methyl red (o‐MR) and p‐methyl red (p‐MR) anions by β‐cyclodextrin (β‐CD) in water has been carried out at 25 °C. The observed molar conductivities (Λs) were found to decrease significantly for mole ratios of cyclodextrin/azo dye less than unity. A model involving 1:1 stoichiometry has been used to analyze the conductance data. The stability constant (K) and the molar conductivity (Λc) for each 1:1 inclusion complex were determined from the conductance data by using a nonlinear least squares curve fitting procedure. The binding sequence, based on the value of K at 25 °C, is found to be p‐MR > MO > o‐MR. The values of the ionic molar conductivities of the free and complexed anions at infinite dilution are reported.
Impedance Spectroscopic Investigation of the Reduction Mechanism of Tantalumhalides During Electrodeposition in Molten Salts
Authors: Bachtler M. , Freyland W. 
Published: July 2012

AbstractThe mechanism of electrochemical reduction of TaCl5 dissolved in molten alkalihalides or their mixtures has been investigated by impedance spectroscopy in the frequency range 10 mHz≤ω≤100 kHz at various cathodic and anodic potentials and temperatures up to 1100 K. From a quantitative interpretation of the diffusion controlled impedance various reduction steps are resolved to better than ±10 mV. This is demonstrated here for a few selected examples. Besides this, the most important observation reported here for the first time is that electronic contributions can become dominant. Only with appropriate consideration of the electronic conduction a quantitative description of the impedance spectra over the whole potential range is found.
On the Stability Range of Microemulsions: From the Tricritical Point to the Lamellar Phase in Water/Formamide‐Octane‐CiEj Systems
Authors: Strey R. 
Published: July 2012

AbstractSymmetric microemulsions containing equal volume fractions of water/formamide, n‐octane and a sufficient amount of n‐alkyl polyglycol ether (CiEj) were studied for various surfactant chain lengths ranging from C4E1 to C14E5 in pure water, as well as for given C4E1 with increasing relative amounts of formamide in the water/formamide mixture (ψ in wt%). In both cases the amphiphilic strength (the amphiphilicity) is changed. Increasing the amphiphilicity one observes, as is well known, the occurrence of the lamellar phase. For the balanced state the lamellar phase occupies a large portion of the isothermal Gibbs triangle as is demonstrated with C10E5. We argue that with further increasing amphiphilicity the three phase body disappears at a four phase point. Decreasing the amphiphilicity the three phase body disappears passing a sequence of lines. First a nonwetting‐wetting transition can macroscopically be observed. Then, a disorder line is passed at which the behavior of the real space correlation function changes from a damped oscillatory behavior to a monotonically decreasing one. We determined previously that this line has been passed by small‐angle neutron scattering. Further, a Lifshitz line as predicted by Landau‐Ginzburg theories occurs until, as the amphiphilicity is even further reduced, a tricritical point is reached at which the three phase body disappears altogether. The results presented may serve as a basis for further experimental research and also stimulate the theoretical description of such systems.
O−2 Decay Catalyzed by Cu2+ and Cu+ Ions in Aqueous Solutions: A Pulse Radiolysis Study for Atmospheric Chemistry
Authors: Piechowski Magnus Von , Nauser Thomas , Hoignè Jürg , Bühler Rolf E. 
Published: July 2012

AbstractThe catalytic decay of O2− radicals due to Cu+ and Cu2+ ions in O2 saturated solutions of low ionic strength was studied by pulse radiolysis and computer simulation of the entire reaction mechanism. Phosphate was used as buffer and formate was used to convert OH radicals into O2−. At pH ≈︁ 6, the very low solubility products of Cu2+ with OH− and PO43‐ limited the copper concentration to the order of μM. In experiments with [Cu2+] > [O2−], the rate constant k (Cu2++O2−) = (8.0±0.5)·109 M−1 s−1 was determined. In systems with [O2−]>[Cu]tot, steady state for the copper ions is attained with apparent first‐order kinetics, which correlates k (Cu2++O2−) with k (Cu++O2−). The O2− decay rate decreased with increasing pH due to Cu2+ complexation with HPO42‐. Correspondingly the pK(CuHPO4) was found to be ‐4.0±0.2 under the assumption that k (CuHPO4+O2−)≤0.01·k (Cu2++O2−. With this value, k (Cu++O2−) could be determined as (9.4±0.8)·109 M−1 s−1 by an iterative procedure. The consequences for the chemistry of atmospheric waters are discussed.
NMR Studies on Dynamics of the Crystallization Water in 12‐Heteropoly Compounds, Na3PMo12O40·nH2O
Authors: Ishimaru Shin'Ichi , Nakamura Nobuo 
Published: July 2012

AbstractThe water dynamics in Na3PMo12O40·nH2O and Na3PMo12O40·nD2O with different n was studied by 1H, 2H, and 23Na NMR spectra and relaxation time measurements over a wide temperature range. The water molecules in hydrate with n = 29 and deuterated hydrate with n = 20 behave like those in bulk water at room temperature. Below room temperature four phase transitions occur in these substances and the degrees of motional freedom of water molecules are lost successively on cooling through the transition points. The mode of the water motions in each phase was assigned by the spectral and the relaxation data analysis: The activation energies for the water motions are 25.9 kJ mol−1 for isotropic rotation and 12.4 kJ mol−1 for translational diffusion in hydrate with n = 29. In the hexahydrate and deuterated hexahydrate only a restricted motion occurs below room temperature down to 120 K, suggesting that the water molecules are far separated from each other and there is no significant interaction between them.
The Constitution of the Silicon‐Carbon System
Authors: Kleykamp H. , Schumacher G. 
Published: July 2012

AbstractThe constitution of the Si‐C system was re‐investigated between 1400 and 3000°C using an arc‐melting furnace and a 350 kHz induction furnace with two pyrometric temperature measurement devices. The experiments were performed in specially designed graphite crucibles in order to avoid the falsification of temperature measurements by the arising vapour species. The samples were further characterized by high temperature DTA and by X‐ray diffraction and X‐ray microanalysis. One intermediate compound, SiC, occurs in the system. Si and SiC form a degenerate eutectic system; the eutectic temperature and composition are 1413°C and 0.02 at.% C, resp. Peritectic formation of SiC was observed at 2830°C according to the reaction [Si0.87C0.13]+ 〈C〉 = 〈SiC〉. The melt boils incongruently under 1 bar pressure at about 3000°C. The condensed vapour consists of Si and SiC containing altogether 40 at.% C. SiC is monotropic. Metastable, cubic β‐SiC is formed from the gas phase and from the melt according to Ostwald's rule. Hexagonal α‐SiC seems to be the stable modification in the overall temperature range.
Dielectric Properties of BAT Collagen in the Temperature Range of Thermal Denaturation
Authors: Jaroszyk F. , Marzec E. 
Published: July 2012

AbstractThe measurements of dielectric properties of collagen BAT in the solid state were made over a frequency of the electric field range of 10 Hz to 10 kHz and at temperatures from 298 to 503 K. The temperature dependence of the dielectric constant ε and the dielectric loss factor ε″ of collagen show that thermal denaturation involves two stages. The first one corresponds to the removal of loosely bound water. The second stage is related to the release of structural bound water and probably to the beginning of the thermal transition from triple helix to coil. The observed frequency dependence of the constants ε″ and ε″ may be due to Maxwell‐Wagner‐Sillars polarization and a lesser degree to dipolar polarization of water molecules. The method of time‐temperature superposition was used to calculate the energy of activation from dielectric date of collagen.
Molecular Dynamics and Self‐Diffusion in Supercritical Water
Authors: Kalinichev A. G. 
Published: July 2012

AbstractThe dynamics of the hindered molecular translations and librations and their dependence on temperature and density has been investigated for supercritical water in the range 630<T<780 K and 0.166<ϱ< 1.284 g/cm3 in terms of velocity autocorrelation functions obtained from molecular dynamics simulations. Calculated self‐diffusion coefficients of supercritical water agree well with available experimental data and results of other simulations. The validity of the Stokes‐Einstein relation has been tested using the experimental data on viscosity of supercritical water.
Unimolecular Fragmentation Kinetics and Binding Energies of Mass Selected Benzene Cluster Ions
Authors: Ernstberger B. , Krause H. , Neusser H. J. 
Published: July 2012

AbstractIn this work the unimolecular decay of cluster ions is investigated in order to deduce energetic and structural information on clusters as a function of size. The dissociation behavior of benzene cluster ions (C6H6)+n with n = 4 to n = 200 is observed after multiphoton ionization of a neutral benzene cluster beam within a reflectron mass spectrometer. With a pulsed deflection technique of undesired ions the metastable decay of mass‐selected cluster sizes within the drift region was observed. The metastable decay efficiency is monotonically increasing in this mass range but pronounced anomalies are found at n = 14, 20, 24, and 27. Using an evaporative ensemble ansatz and an RRKM model with a phase space restricted to the intermolecular cluster modes we were able to determine the dissociation energies for clusters up to n = 23 from a fit of the calculated metastable decay ratios to the measured ones. For this fit the size dependent sequential evaporation of two benzene molecules is important. The dissociation energy is largest for the dimer cation and found to decrease for clusters up to n = 5. For larger clusters it begins to increase with a step‐like behavior after n = 14 and n = 20. This is interpreted in terms of shell filling achieved for icosahedral structures about a center dimer cation.
On the Thermodynamics of Higher Solid Nickel Oxocompounds
Authors: Balej Jan , Divisek Jiri 
Published: July 2012

AbstractOn the basis of the qualitative reevaluation [1] of critically selected data from various authors on the equilibrium or rest potentials of solid nickel oxocompounds it was concluded that the so called “α‐Ni(OH)2/γ‐NiOOH” systems form sufficiently stable solid solutions of Ni(II) and Ni(IV) components in the whole studied range of the oxidation number, zNi = 2.0–3.6, without any participation of Ni(III) compounds. A quantitative reevaluation was based on the model of an uninterrupted series of solid solutions of completely undissociated Ni(OH)2, for NiO2·xH2O a complete dissociation into H+ and NiO2·(x‐1)H2O·OH− was considered. A satisfactory correlation of all experimental data in the entire range of zNi was achieved using empirical Margules' relation of the concentration dependence of activity coefficients of individual components of the solid redox systems. The correlation led to the following standard data at 25°C: E0 = 1.3250±0.0167 V, ΔG0f(NiO2·xH2O) = ‐202.02‐x·237.141±3.21 kJ‐mol−1. With the aid of the empirical relation between ΔH0f and ΔG0f after Karapet'jants the following values were estimated: ΔH0f(NiO2 = ‐257.4±5 kJ mol−1 and ΔH0f(NiO2·2H2O) = ‐844±5 kJ mol−1, S°(NiO2) = 49.2±17 J mol−1 K−1 and S0(NiO2·2H2O) = 139±17 J mol−1 K−1. The calculations were carried out using a corrected value for ΔG0f(Ni(OH)2) = ‐457.7 kJ mol−1 leading to ΔG0f(Ni2+, aq) = ‐45.03 kJ mol−1 and E0 = ‐0.2334 V at 25 °C.
On‐line Determination via Differential Electrochemical Mass Spectroscopy (DEMS) of Chemical Products Formed in Photoelectrocatalytical Systems
Authors: Bogdanoff P. , Alonso‐Vante N. 
Published: July 2012

AbstractThe evolution of oxygen in acid aqueous solution on thin porous titanium dioxide (anatase) electrodes under illumination was monitored with DEMS. By adding Cl− in the electrolyte, a Cl2 mass signal is additionally observed. This latter increases as a function of Cl− concentration while O2 mass signal decreases, although the photocurrent‐potential characteristics remain unchanged. This example illustrates a competitive oxidation which cannot be discriminated by only recording photocurrent‐potential curves.
The Effect of Short‐Range Hydrogen‐Bonded Interactions on the Nature of the Critical Point of Ionic Fluids. Part I: General Properties of the New System Ethylammonium Nitrate+n‐Octanol with an Upper Consolute Point Near Room Temperature
Authors: Weingärtner H. , Merkel T. , Käshammer S. , Schröer W. , Wiegand S. 
Published: July 2012

AbstractWe report on an unusual liquid‐liquid miscibility gap with an upper consolute point at 315.2 K in the ionic system ethylammonium nitrate+n‐octanol at a mole fraction x1 = 0.773 of the salt. Similar phase separations of 1:1‐electrolytes in solvents of low dielectric constant were only found in the solvent‐rich regime at low ion densities, as predicted for charged hard spheres in a dielectric continuum. In analogy to other low‐dielectric constant systems the equivalent conductance exhibits a minimum at low salt concentrations due to the specific features of the ion distribution under these conditions. The pair association constant is however one to two orders of magnitude larger than predicted theoretically and expected by comparison with data for similar systems. This additional stability of the ion pair may be due to hydrogen‐bonds between C2H5NH+3 and NO−3. Possible mechanisms for phase separation are discussed.
The Effect of Three Organic Additives on the Structure and Growth of Electrodeposited Copper: An In‐Situ Scanning Probe Microscopy Study
Authors: Nichols R. J. , Bach C. E. , Meyer H. 
Published: July 2012

AbstractThe growth morphology of copper crystallites and the influence of tris‐aminophenyl and benzothiazolium (BT) derivatives, have been studied in‐situ using scanning probe microscopy (SPM). We have examined the very initial stages of deposition, following copper nucleation at defects in the substrate, up until the formation of relatively thick copper layers. The substrates onto which bulk copper was deposited were Au(111) precovered with UPD copper. Additive BT‐B was the most effective at surpressing the perpendicular growth of the copper crystallites and favoured instead their lateral spreading. 2‐(4‐Dimethylaminophenyl)‐6‐methylbenzothiazole (BT‐A) and crystal violet only showed effective surpression of the crystallites vertical growth for low deposition rates from very dilute Cu2+ solutions. In the case of the quasi‐2D growth, layer deposition occurred via a “birth‐and‐spread” mechanism, with defects in the underlying layer providing favourable nucleation sites for the next one. A pronounced substrate effect was seen in the case of copper deposition under effective additive influence. In this case the first quasi‐two‐dimensional copper layer reached a thickness equivalent to between 4‐7 monolayers, while subsequent 2‐D layers were typically one monolayer high. Models for the copper electrocrystallization, in the absence and presence of additives, are proposed. The importance of 2‐D nucleation in determining the crystallites external shape is discussed.
Modeling of Forward and Reverse Bias Conditions in Bipolar Membranes
Authors: Sokirko A. V. , Ramírez P. , Manzanares J. A. , Mafés S. 
Published: July 2012

AbstractWe present a set of analytical solutions to the problem of ion transport and field enhanced water dissociation in bipolar membranes. Most of the simplifying assumptions introduced in previous models have now been removed. Particular attention is paid to the effects caused by a non‐abrupt, smooth junction at the cation layer/anion layer interface, the forward bias characteristics of the current‐voltage curve, and the membrane electrical resistance. Despite of the coupling between ion transport and the chemical reaction responsible of the field enhanced water dissociation, the solutions derived are simple, and can readily find application in multidisciplinary fields like the biophysical modeling of biological membranes and the separation processes involving synthetic bipolar ion exchange membranes.
Ligand Effects on the Reactivity of Iron (II) Cations FeX+ in the Gas Phase
Authors: Schröder Detlef , Hrusak Jan , Schwarz Helmut 
Published: July 2012

AbstractThe ion‐molecule reactions of ligated iron(II) cations FeX+ (X = H, CH3, C3H5, NH2, OH, F, Cl, Br, I) with acetone are examined by means of Fourier‐Transform Ion Cyclotron Resonance (FTICR) mass spectrometry Three major reactions are observed: i) CH‐bond activation of acetone leading to the loss of HX and concurrent formation of the corresponding iron(II) enolate cation Fe(OC3H5)+, ii) CC‐bond activation accompanied by methanide transfer to yield an acetyl cation and neutral H3CFeX, and iii) association of the reactands to form an adduct complex. For the iron halide cations as a minor process, loss of a neutral water molecule is observed. Whereas CC‐bond activation is restricted to the iron(II) halide cations (X = F, Cl, Br, I), CH‐bond activation is the exclusive process for X = H and also dominates the reactions for X = CH3, C3H5, NH2, OH, and F. The reactivity of the iron(II) fluoride cation, FeF+, is such that both CH‐ and CC‐bond activation occur. The relative reactivities of the FeX+‐cations towards acetone are compared with each others and correlated with thermochemical and electronic properties of the substituents X.
An Optical In‐Situ Method to Study Redox‐Kinetics in SrTiO3
Authors: Bieger T. , Maier J. , Waser R. 
Published: July 2012

AbstractThe optical absorption properties of Fe‐impurity centers in SrTiO3 can be used to probe in‐situ the oxygen activity in the sample. The response of the absorbance upon a sudden change the oxygen partial pressure allows the precise investigation of the kinetics of oxygen incorporation (excorporation). In contrast to electrical measurements no auxiliary contact phases (electrodes) are necessary and also — as shown — valence changes of the impurity ion do not complicate the evaluation. The investigations indicate a change from diffusion control to surface control when lowering the temperature or decreasing the sample thickness. Effective rate constants and chemical diffusion coefficients are determined. It is shown that the chemical diffusion coefficient cannot be understood in terms of charge carrier mobilities and concentrations unless the effect of internal defect‐chemical reactions (here valence changes of the Fe‐ions) is taken into account as previously described by one of us. Using this approach, however, the values can be quantitatively described without any adjustable parameter.
Diffusion Coefficients, Viscosities and Densities in the Binary Subsystems of Methyl isopropyl ketone‐n‐Butyl acetate‐Water
Authors: Thiel Peter , Paschke Albrecht , Winkelmann Jochen 
Published: July 2012

AbstractThe concentration dependence of mutual diffusion coefficients, kinematic viscosities and densities in the binary systems Methyl isopropyl ketone (Mipk)‐n‐Butyl acetate (Buac), Buac‐Water and Mipk‐Water is determined at 288.15 K, 293.15 K and 298.16 K. Diffusion coefficients at infinite dilution were extrapolated from the experimental data.Only in the completely miscible system Mipk‐Buac were the heat of mixing at 297.76 K and vapour‐liquid equilibrium data at 323.15 K and 343.15 K measured and parameters for the NRTL‐equation calculated. In the system Mipk‐water with limited miscibility, the NRTL‐parameters were obtained from liquid‐liquid equilibrium data. Using our values at infinite dilution the concentration dependence of the mutual diffusion coefficients can be satisfactorily predicted by the Caldwell/Babb correlation.
Phase Transitions of Highly Chiral Liquid Crystals in the Region of Metastable Blue Phase I
Authors: Schumacher M. , Demikhov E. , Stegemeyer H. 
Published: July 2012

AbstractThe properties of the supercooled blue phases are investigated. In the case of highly chiral materials with a short range cholesteric phase and a smectic A phase anomalous metastable blue phases are observed. The structural transformations are seen by decreasing the temperature (BPI — metastable BPS) and by applying the electric field as well (BPS — metastable electric field induced BPES).
Nichtlineare Optik in Flüssigkristallen. Fortschrittsbericht
Authors: Eich Manfred 
Published: July 2012

AbstractCalamitic liquid crystalline molecules may exhibit very high electronic hyperpolarizabilities what makes them attractive as NLO chromophores for second order NLO applications (χ(2)). Due to their cooperative alignment behavior liquid crystalline molecules can be very effectively oriented in external electrical fields. Compared to their non liquid crystalline analogs the macroscopic noncentrosymmetrical orientation that is necessary for χ(2)‐activity can be induced much easier. In addition, chiral smectic C phases exhibit a noncentrosymmetrical point symmetry as do LC‐molecules in monolayers at boundaries. In this article recent research results are reported on electric field poling of nematic phases, phasematched second harmonic generation in ferroelectric LC and the use of NLO techniques in understanding how orientational layers induce homogenous bulk alignment in LCDs.