bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acid‐Base Equilibria of Hydrophilic Indicators in Water‐in‐Oil Microemulsions
Authors: Chinelatto Ana M. , Fonseca Maria T. M. , Kiyan Nilo Z. , Seoud Omar A. El 
Published: July 2012

AbstractThe apparent pKa values of the positively charged, hydrophilic indicators 2‐hydroxy‐5‐bromo‐trimethylanilinium chloride (HBTC) and 2‐hydroxy‐5‐nitro‐trimethylanilinium chloride (HNTC) in the presence of water‐in‐oil microemulsion of the surfactants benzylcetyldimethyl ammonium chloride (BCDC) in benzene and polyoxyethylene (4) dodecyl ether (Brij‐30) in heptane were determined spectrophotometrically. The experimental variables were the type of buffer (benzimidazole, phosphate, and tris) and the ratios [water]/[surfactant] and [buffer]/[surfactant]. It is shown that: a) the indicators are confined within the second hydration shell of the nanodroplet, i.e. are not adsorbed at the water/oil interface; b) the use of the starting pH values of the buffer solutions, i.e., those measured outside the micellar domain, to calculate the micellar pKa values of the indicators is inadequate; c) buffer‐independent micellar pKa values can be obtained if the starting pHs of the buffer solutions were corrected for ion exchange with the counter‐ion of the positively charged surfactant, and for the lower polarity of the micelle‐solubilized water (relative to bulk water); d) the micellar ΔpKa (=pKa in the aggregate −pKa in water) ranged from ‐0.45 to ‐0.20 unit for HBTC/BCDC, from ‐0.44 to ‐0.13 unit for HNTC/BCDC, from 0.22 to 0.64 unit for HBTC/Brij‐30, and from 0.27 to 0.59 unit for HNTC/Brij‐30; e) these micelle‐induced pKa shifts can be analyzed in terms of the lower polarity of the micelle‐solubilized water (relative to bulk water) and perturbation of the acid‐base equilibria by the electrostatic effect of the positively charged W/O interface (BCDC); f) the magnitude of latter effect, at the average solubilization site of the indicator was calculated to range from 28 to 67 mV.
Diffusion‐Viscous Flow Coupling and Global Transport Coefficients Symmetry in Matter Transport Through Porous Membranes
Authors: Bartoszkiewicz M. , Miekisz S. 
Published: July 2012

AbstractIf statistical mechanical theory of Bearman and Kirkwood is applied to describe isothermal permeation of an incompressible solution through a porous membrane at mechanical equilibrium and not far from thermodynamic equilibrium and if the pores are homogeneous and cylindrical, the global transport coefficients of the system are symmetric if and only if switching off the short‐ranged membrane‐solution interactions leads to an uncoupling of diffusion and viscous flow.
Eloflux Fuel Cells and Electrolysis Cells
Authors: Winsel August , Führer Oliver , Rühling Klaus , Fischer Christian 
Published: July 2012

AbstractIn recent years in a corporation of the VARTA research and development centre in Kelkheim and the University of Kassel, a new kind of Eloflux fuel cell and electrolysis cell system was developed. This alkaline hydrogen‐oxygen system is a continuation of the VARTA fuel cell system with sinter‐nickel electrodes of the 1960's. The decisive progress, was the development of the new Raney‐Nickel hydrogen electrode with its simple and inexpensive manufacturing technique in 1983. Together with a new oxygen‐electrode of the same kind, we built within the scope of the Hermes fuel cell project different types of Eloflux fuel cells in 1988. First Eloflux electrolysis cells, which have the same design and similar electrodes as the fuel cells, were made last year.—This report deals with the manufacturing and the characteristics of the electrodes, with the principle of Eloflux cells and with the characteristics of the latest fuel cells, electrolysis cells and electrolyte reconcentrators.
On the Electrocatalysis of the Oxygen Reduction in Acid Electrolyte
Authors: Fabjan Ch. , Frithum G. , Hartl H. 
Published: July 2012

AbstractConsiderable electrocatalytic activity for the oxygen reduction in acid electrolytes (HClO4, H2SO4) was obtained with heat treated polypyrrole prepared by anodic polymerization on a carbon substrate‐containing Co and Fe as transition metal ions, comparable to that for Pt loaded electrodes. Apart from structural effects (increase of active area) the activity is attributed to N4‐coordinated transition metal species formed in the pyrolysis process. The electrode performance significantly depends on the nature of the metal ions and temp. of the heat treatment.—A cathodic reaction order of +1 with respect to O2(po2) indicates a mechanism avoiding the formation of peroxide in a potential range in which charge transfer is the rate controlling step. Promising results were obtained in extended time tests up to 400 hrs at 60°C.
Electrochemical Investigation of Amperometric Ammonia Gas Sensors
Authors: Pfenning D.‐M. , Deprez J. , Kitzelmann D. 
Published: July 2012

AbstractResults of potentiodynamic and potentiostatic measurements of the electrooxidation of ammonia traces with platinum as a catalyst in a strong alkaline electrolyte are reported. To improve the performance of a fuel cell, such as an electrochemical gas sensor for ammonia traces, the hydrophobicity of the Teflon‐bonded platinum black gas diffusion working electrode is varied. The expectation that with increasing Teflon content of the catalytic anode the long term characteristics are enhanced could not be confirmed. The weakening of the cell current is influenced much more by effects belonging to the incorporation of carbon dioxide in the electrolyte.—The optimal operating potential for a three‐electrode cell arrangement, which depends also on the cross sensitivities to other gases, is in the range of 1.1 to 1.3 Volts.
The Direct Oxidation of Methanol at Platinum Based Catalytic Electrodes: What is New Since Ten Years?
Authors: Leger J.‐M. , Lamy C. 
Published: July 2012

AbstractMethanol is one of the best candidates as fuel in fuel cell systems for terrestrial applications. However, the development of Direct Methanol Fuel Cell (DMFC) have been limited during a long period by problems mainly related to poisoning phenomena which led to a decrease of the cell performances. Since 10–15 years, significant progresses were made in the understanding of the electrooxidation of methanol. For example, with the availability of new “in situ” spectroscopic methods, it is now well accepted that adsorbed CO is the poisoning species. Electrodes of well‐defined structure (such as single crystals) allow correlations between the activity of the electrode and its surface structure to be made. All these new results bring new insights in the mechanism of methanol electrooxidation and let to think that new improvements in the DMFC could be expected for the next few years.
On the Reaction of CH2(ã1A1) with HF
Authors: Wagener R. , Gg. Wagner H. 
Published: July 2012

AbstractThe insertion reaction of singlet methylene CH2(ã1A1) into the strongest element‐hydrogen bond, H‐F, is investigated. CH2(ã1A1) is generated by pulsed UV‐laser photolysis of CH2CO. Its removal is directly monitored via LIF‐detection. The experiments are carried out under first order reaction conditions at temperatures T = 295, 380, and 485 K. Second order rate constants are determined from plots of first order rate constants versus the partial pressure of HF. The expression k1 = (5.5 ± 1.5)·1013·(T/295 K)(‐0.5±0.5) cm3/mol s is derived for the rate constant of the total depletion of CH2(ã1A1 0,0,0) with HF. Thus at room temperature the reaction is slower than the analogous reactions with NH3, H2O and HCl. For the isotopically substituted CD2(ã1A1 0,0,0) with HF the following rate expression is determined: k2 = (1.0 ± 0.3)·1014 (T/295 K)(‐1.0±1.0) cm3/mol s. The reaction of vibrationally excited CH2(ã1A1 0,0,0) with HF has a room temperature rate constant of k3 = (2.0 ± 0.4)·1014 cm3/mol s. Fluorocarbene CHF is detected as primary reaction product by LIF. Thermochemical considerations show the formation of CHF is the only exothermic reaction pathway besides physical quenching of CH2(ã1A1).
Hydrogenated Amorphous Silicon by Infrared Multiphoton Absorption with a Pulsed CO2‐Laser
Authors: Roth A. , Chiussi S. , Dietrich T. R. , Comes F. J. 
Published: July 2012

AbstractThe following work gives a discussion on hydrogenated amorphous silicon (a‐Si:H) film preparation by laser induced chemical vapor deposition (LICVD) using a pulsed CO2‐laser in a parallel configuration. Deposition rate and initiation of polymerization were studied as a function of total pressure, gas flow, gas mixture (buffer gas, silane and/or disilane), substrate temperature, and radiation flux. The results lead to a reaction model where higher silane homologues play an important role for the film production. The film properties strongly depend on the substrate temperature Ts. The activation energy Ea of the dark conductivity decreases from 1.1 eV to 0.7 eV for films prepared at Ts = 230°C to 450°C. In the same temperature range, the dark conductivity σd increases from ∼10−14 to ∼10−10 (Ω cm)−1, whereas the photo conductivity σph shows a maximum of ∼10−6 (Ω cm)−1 at Ts = 320‐330°C. These values, especially their temperature behaviour, are compared with the results of other CO2‐LICVD works and further production methods. It is shown that the film formation depends on the gas phase chemistry as well as on the substrate temperature.
Evaluation of the Excess Gibbs Energy of Mixing in Binary Alcohol‐Water Mixtures from the Liquid‐Liquid Partition Data in Electrolyte‐Water‐Alcohol Systems
Authors: Apelblat Alexander 
Published: July 2012

AbstractThe excess Gibbs energies of mixing at 298.15 K in fully or partially miscible water‐alcohol mixtures (1‐propanol, 2‐propanol, 1‐butanol, 2‐butanol, 2‐methyl‐1‐propanol (isobutanol), 2‐methyl‐2‐propanol (tert. butanol), 1‐pentanol, 2‐pentanol, 1‐hexanol, 1‐heptanol, 1‐octanol, 2‐octanol and cyclohexanol) are reported. They were calculated from the solubility and partition data by applying the Gibbs‐Duhem relationship and changing the standard state of water from water saturated with alcohols to pure water. In the 1‐propanol‐water, 2‐propanol‐water, 1‐butanol‐water, 2‐butanol‐water, 1‐pentanol‐water and 2‐pentanol‐water systems the excess entropies of mixing were also determined.
Investigations of the Nature of Critical Line Very Close to a Double Critical Point
Authors: Narayanan T. , Prafulla B. V. , Kumar A. , Gopal E. S. R. 
Published: July 2012

AbstractThe curvature of the line of critical points in a reentrant ternary mixture is determined by approaching the double critical point (DCP) extremely closely. The results establish the continuous and quadratic nature of this line. Out study encompasses as small a loop size (ΔT) as 663 mK. The DCP is realized when ΔT becomes zero.
The Relevance of Nonlinear Energy Localization in RNA Self‐Splicing
Authors: Fernández Ariel 
Published: July 2012

AbstractWe implement a ϕ4‐model to analyze the localization of energy in collective modes along the sugar‐phosphate backbone of RNA strands. We focus on the relevance of soliton‐like excitations in the site‐specificity of intramolecular nucleophilic attacks leading to transesterifications in the sugar‐phosphate backbone. We provide evidence supporting the view that hot spots for transesterification of catalytic RNA are caused by a combination of two factors: nonlinear energy transfer and intra‐chain folding. In particular, our results might help understanding the physics of covalent cyclization and cycle‐reopening in the catalytic intervening sequence (IVS) of ribosomal RNA from Tetrahymena and also they might help identifying the nucleophilic agents and cosubstrate in IVS RNA excision from rRNA.
Interferometric Determination of Mean Polarizabilities and Second Density Virial Coefficients of Methane Between 128 K and 890 K
Authors: Hohm Uwe , Kerl Klaus 
Published: July 2012

AbstractMean dynamic dipole polarizabilities α0(λ, T) and second thermodynamic virial coefficients B(T) of meth‐ane have been determined for the first time in the extended temperature range 128 K ≦ T ≦ 890 K by means of only one apparatus using interferometric low‐pressure measurements (p ≦ 03 MPa) of the refractive index n(λ, T, p) in the visible wavelength range (λ = vacuum wavelength). α0(λ, T) is in good accordance with previously measured values, but an obvious small minimum at the critical temperature Tc seems to occur. The B(T)‐data determined in the low‐temperature range ΔT1 (128 K ≦ T ≦ 298 K) are in fair agreement with other published data. The high‐temperature B(T)‐values of the range ΔTII (760 K ≦ T ≦ 890 K) have been measured for the first time. They are in good accordance with extrapolated low‐temperature virial coefficients. The mean standard deviation | ΔB | ≈ 8 cm3 mol−1 of the measured B(T)‐values may be further reduced by means of more precise measurements of pressure p.
Crystal Structure and Hydrogen Bond in Mono‐, Di‐, and Trichloroacetates of 4‐Methylaniline and 3,4‐Dimethylaniline, An X‐Ray and 35Cl NQR Investigation
Authors: Basaran Reha , Dou Shi‐Qi , Weiss Alarich 
Published: July 2012

AbstractThe 35Cl NQR spectra of the mono‐, di‐, and trichloroacetates of 4‐methylaniline and 3,4‐dimethylaniline, [4‐(CH3)C6H4NH3⊕] [Cl3‐nHnCCOO⊖] and [3,4‐(CH3)2C6H3NH3⊕] [Cl3‐nHnCCOO⊖], n = 0, 1, 2, were studied in the range 77 ≦ T/K ≦ Tdecomposition or Tbleaching out. Whereas for the monochloroacetates of both aniline derivatives the 35Cl NQR is observable up to T > 353 K, broadening of the 35Cl NQR lines of both groups, ‐CHCl2 and ‐ CCl3, lead to a bleaching of the NQR signals in the range 114 ≦ T/K ≦ 280, far below the decomposition temperature of the respective compound. The crystal structures of [4‐(CH3)C6H4NH3⊕] [Cl2HCCOO⊖] and of [3,4‐(CH3)2C6H3NH3+] [Cl3‐nHnCCOO⊖], n = 0, 1 were determined at room temperature. The results of both, diffraction experiments and 35Cl NQR are compared and discussed.
The Debye‐Hückel Theory for Hydrated Ions. IV. Activity and Osmotic Coefficients in Aqueous Solutions with a 1:1 Electrolyte and a Hydrophilic Nonelectrolyte
Authors: Schönert Hansjürgen 
Published: July 2012

AbstractTwo thermodynamic models of stepwise hydration of solutes in aqueous solutions are merged: one for 1:1 electrolytes and a another one for hydrophilic nonelectrolytes. The theory is compared with measurements for six systems taken from the literature. Except for: H2O + HCl + glycerol, the agreement is satisfactory.
On the Nature of the Surface Aggregation in Surfactant Adsorption Onto Polar Surfaces
Authors: Narkiewicz‐Michalek J. 
Published: July 2012

AbstractAt a certain surfactant concentration called “critical” or “hemimicelle” concentration a spontaneous aggregation takes place of surfactant molecules adsorbed onto polar surfaces. In spite of many works which have been published, the nature of that surface aggregation is still not understood well. The aim of this paper is to explore to which extent the concept of 2D condensation can explain the observed features of that surface aggregation. To that purpose the recent theoretical approach by Koopal is generalized to take the surface heterogeneity into account. This is because the surface heterogeneity is believed to be an important factor affecting the surface aggregation. Some striking similarities between the observed features of surface aggregation and the theoretical predictions based on the concept of 2D condensation are found. That concept, however, cannot at the present stage of the theory explain yet the finite tangent of the linear sections in the experimental isotherms corresponding to the surface aggregation.
Diffusion Coefficients of Four‐Component Systems from Taylor Dispersion Profiles. Sucrose + LiCl + KCl + Water and NBu4Br + LiBr + KBr + Water
Authors: Leaist Derek G. 
Published: July 2012

AbstractThe Taylor dispersion (peak‐broadening) technique is used to measure the quaternary interdiffusion coefficients of the four‐component systems sucrose + LiCl + KCl + water and tetra‐n‐butylammonium bromide + LiBr + KBr + water at 25°C. The dispersion of the eluted solutes is followed by differential refractometry. Direct least‐squares analysis of the measured peak shapes is used to calculate the interdiffusion coefficients. Equations are developed to describe dispersion in multicomponent systems containing arbitrary numbers of components.
Excess Enthalpy HE of Binary and Ternary Mixtures Containing Methanol, Methyl‐Tert. Butyl Ether (MTBE) and n‐Heptane
Authors: Tusel‐Langer E. , Lichtenthaler R. N. 
Published: July 2012

AbstractMolar excess enthalpies HE have been measured for ternary mixtures of methanol + MTBE + n‐heptane and for the three corresponding binary mixtures of these compounds using a quasi‐isothermal flow calorimeter. The measurements have been performed at atmospheric pressure and at 298.1 and 313.1 K. The experimental results are compared with those calculated using the ERAS‐(Extended Real Associated Solution) model and the NRTL‐equation.
Photo‐sinking Phenomenon: Photodecomposition Rate of Silane Bonded on TiO2 Powders
Authors: Patel K. , Yamagata S. , Fujishima A. , Loo B. H. , Kato T. 
Published: July 2012

AbstractPhotodecomposition of silane from silanized TiO2 powders in contact with water was determined from the change in wettability of surfaces, i.e. hydrophobic to hydrophilic conversion. The decomposition rate of silane, estimated from the amount of powder converted to hydrophilic, was found to correlate with their photocatalytic activity in the oxidation of ethanol. Anodic and cathodic processes in the Photo‐sinking phenomenon were explained from the qualitative effects, for example, addition of anions and cations on photo‐sinking phenomenon respectively indicated that the photo‐excited holes decomposed the bonded silane and the adsorbed oxygen trapped the electrons. The Photo‐sinking phenomenon was applied for the estimation of photocatalytic activities of TiO2 powders and the separation of the photoactive powder from a mixture.
Composition Dependent Electronic Conductivities and Hall Coefficients of Mixed Ionic‐Electronic Conductors. Part IV: The High‐Temperature Phase of Silver Telluride
Authors: Kellers J. , Hock S. , Funke K. 
Published: July 2012

AbstractThe electronic conductivity, σe, and the Hall coefficient, RH, of Ag2+δ Te are experimentally determined at temperatures from 200°C to 480°C and at values of the composition parameter, δ, covering the entire stability range. The composition is varied and monitored by in situ coulometric titration. The evaluation of the experimental data yields a harmonic conduction band, while the anharmonicity of the valence band becomes obvious at higher temperatures. The experimental data are consistent with predominant scattering of electrons and holes at longitudinal acoustic phonons. Accordingly, the electronic relaxation time depends on energy and temperature as τ ∼ ϵ−1/2 · T−1.
Communications On the Temperature of Sputtered Metal Cluster Ions Investigated in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer
Authors: Schnabel Patrick , Irion Manfred P. , Weil Konrad G. 
Published: July 2012

AbstractWe use the initial rates of the reaction of ammonia with iron cluster ions after different storage times in order to characterize their temperature. For well defined times before reaction they are in contact with xenon gas at p ≈ 10−7 mbar. We can show, that they approach the temperature of the heat bath within about 5 s. Immediately after being trapped in the cell, their temperature is higher by not more than 20°C.
Modelling Tropospheric OH; A New Approach
Authors: Herbert A. , Armerding W. , Comes F. J. 
Published: July 2012

AbstractA new fully dynamic model for tropospheric OH has been developed. The model structure is especially designed to comply with the needs of small scale problems and comparison with field data. Using the local character of most measurements providing the boundary conditions to the calculations and the local character of the OH concentration itself, the model is able to simplify the description of transport and deposition processes. Additionally the required initial data set can be reduced thus leading generally to a minimization of the measurement based error of the model results. As a special feature this model can calculate fluxes of atmospheric constituents resulting from emissions and transport which are an input to most models. Combining the photochemical model with budget and sensitivity calculations this system is equipped with testing and self‐correction facilities which help to achieve a strong error reduction in tropospheric modelling. First tests simulating dynamic flux‐reaction systems have shown that this approach is a very promising new way to model fast tropospheric photochemistry.
On the Application of Kramers' Theory to Elementary Chemical Reactions
Authors: Troe J. 
Published: July 2012

AbstractKramers' diffusion model in the energy controlled low viscosity and the momentum controlled high viscosity range is confronted with reality for elementary unimolecular reactions and radical associations in dense media. Collisional energy transfer appears to be much more complicated than described by the idealized model. On the other hand, there are examples where the Kramers‐Smoluchowski equation well describes the transition to high viscosity behavior. In other cases, solvent shifts of the reaction barriers are pronounced and superimposed on the transport effects described by Kramers' model.
High Pressure NMR Studies of the Kramers Turnover for Reactions in Liquid Solutions
Authors: Jonas J. , Peng X. 
Published: July 2012

AbstractAdvantages of NMR techniques to obtain the rate data for simple isomerizations in liquid solutions and advantages of using high pressure to change the viscosity of the solution are discussed. After a brief overview of our experiments on cyclohexane, 1,1‐difluorocyclohexane, and N,N‐dimethyltrichloroacetamide, the discussion focuses on the ethylene rotation in μ‐cyclopentadienylethylenetetrafluoroethylene‐rhodium in several solvents. – The experimental data, as interpreted in terms of stochastic models of isomerization reactions, indicate a Kramers turnover for the pressure dependence of the rotation of coordinated ethylene in the Rh complex in solution. In fact, the observation of the energy‐controlled regime in this system may be the consequence of the so‐called heavy metal atom bottleneck effect which reduces the intramolecular energy transfer within the molecule. The experimental dependences of the rates upon solvent viscosity and/or Enskog collision frequency show that solvent shear viscosity represents only an approximative measure of the coupling of the reaction coordinate to the medium.