bluuebunny/crossref_metadata_2025 huggingface dataset:
The Chemical Bond in Amorphous Solids: Localization on Continuous Random Networks
Authors: Koslowski Th. , Von Niessen W.
Published: July 2012

We report numerical results for localization induced by disorder on continuous random networks. The density of states and localization properties of simple tight‐binding Hamiltonians are computed. A scaling method is used to decide about the localized or extended character of eigenstates. For a model system in two dimensions and for models of amorphous Si and Ge, the influence of electron localization on transport properties is discussed. The localization properties are interpreted from a quantum chemical point of view, using the concept of population analysis.
Strukturelle, elektronische und magnetische Eigenschaften komplexer intermetallischer Verbindungen Progress Report
Authors: Hafner J.
Published: July 2012

In recent years, the theory of alloys has progressed on three different levels. On the first level, favoured by physicists, the properties of alloys are calculated by solving the Schrödinger equation in the local‐spindensity (LSD) approximation. Given the high accuracy that is required, such calculations can be performed only for systems with a maximum of hundred nonequivalent atomic sites, even on the most powerful computers. On the second level, chemists describe bonding in terms of the σ, π and δ transfer integrals resulting from the angular‐dependent valence orbitals. Chemical intuition allows to introduce simplifications, and at the reduced accuracy of a Tight‐Binding‐Hückel equation, systems with up to a few thousand atoms may be modelled quite successfully. The third level corresponds to the reasoning traditional in metallurgy: atoms are considered as soft spheres interacting through pair – or embedded‐atom potentials. The simplicity of the interatomic force law allows to simulate the properties of ensembles with up to a hundred thousand atoms. – Progress on all three levels will be illustrated at the example of crystalline and liquid Zintl phases, of crystalline and amorphous magnetic alloys, and of quasicrystalline alloys.
Crystal Structure and Thermodynamic Analysis of the New Semiconducting Chevrel Phase Re6S8Cl2
Authors: Fischer C. , Fiechter S. , Tributsch H. , Reck G. , Schultz B.
Published: July 2012

Re6S8Cl2 single crystals have been synthesized by chemical vapour transport with chlorine as transporting agent. Structure analysis revealed that the material is isomorphous with Re6S8Br2 and Re6Se8Br2 but not with the lamellar Re6Se8Cl2. The thermal stability of this semiconducting rhenium cluster compound was simulated as a function of vapour phase composition by thermochemical calculations in the ternary system Re–S–Cl at temperatures 1000, 1200 and 1400 K. Predominance‐area phase diagrams indicate that Re6S8Cl2 can coexist with Re and ReS2 depending on the vapour pressure ratios of S2/S2Cl2 and Cl2/Re3Cl9.
Chemical Activities in the Solid Solution of Hf in Ni3Al
Authors: Albers M. , Sai Baba M. , Kath D. , Miller M. , Hilpert K.
Published: July 2012

The vaporization of the alloy samples of the compositions (Ni3Al)1‐xHfx, x = 0, 0.010, 0.030, 0.052, 0.070, 0.089, and 0.100, as well as Ni0.75Al0.25‐xHfx, x = 0.020, 0.040, 0.060, 0.080, and 0.100, was investigated at temperatures between 1361 and 1680 K in order to obtain information on the chemical bond in the solid solution of the γ' phase of the type Ni3Al. The partial pressures of Ni and Al were determined by calibration with pure nickel. Chemical activities and excess chemical potentials were evaluated for the solid alloys below the temperature of incipient melting and also in part for the melt. The excess chemical potentials obtained for the γ' phase indicate the substitution of Hf for Al in the γ' or Ni3Al phase.
Elektronische und magnetische Eigenschaften von Alkalidithioferraten(III)
Authors: Bauer M. , Meyer M. , Nagorny K.
Published: July 2012

The isomeric shift of KFeS2, RbFeS2 and Kx Rb1‐x FeS2 is δ = 0.16 mm/s. This value can only be explained with partial occupation of the 4s‐niveau of iron which results from covalent parts of the Fe–S‐bonding as well as the transfer of electron density from sulfur into the 3d‐orbital of iron. – These effects must lead to spin pairing which is besides the additional occupation of the 4s‐niveau and the zero point spin fluctuations responsible for the low hyperfine fields. – The unusually high ordering temperatures could be identified as transition temperatures to antiferromagnetic long distance order. The one‐dimensional interactions remain up to the decomposition temperatures.
35Cl NQR and Crystal Structure Studies of Dimeric Trichloroalcoxystannane Alcoholates
Authors: Sinsel Bernd , Dou Shi‐Qi , Weiss Alarich
Published: July 2012

The 35Cl NQR spectra of the dimeric complexes bis‐[μ‐methoxytrichloromethanolatostannane] (a) and bis‐[μ‐ethoxy‐trichloroethanolatostannane] (b) have been recorded as a function of temperature in the range 77 ≤ T/K ≤ 389 for (a) and 77 ≤ T/K ≤ 363 for (b). The crystal structure of the methanolato stannane (a) [1] was refined by 4‐circle X‐ray diffractometry. [H3COSnCl3·CH3OH]2 (a): C–P21/c, Z = 2; a = 726.2 (3) pm, b = 1247.2 (4) pm, c = 1143.2 (4) pm, β = 126.76 (1)°. (a) undergoes a phase transition in the range 146 K ± 161 K. Three 35Cl NQR lines are observed in the high temperature phase (I). The low temperature phase (II) shows four 35Cl NQR lines. In both phases of (a) the temperature coefficient of the lowest frequency 35Cl NQR line is positive. – No phase transition in (b), [H5C2‐OSnCl3·C2H5OH]2, isomorphous [2] to phase (I) of (a), was observed in the temperature region covered by the 35Cl NQR experiment. A 35Cl NQR triplet was observed and the three frequencies showed normal “Bayer‐type” temperature dependence. – The correlation between Sn–Ci bond lengths and 35Cl NQR frequencies is discussed for both compounds as is the influence of intramolecular R–O–HCl–Sn hydrogen bonding. (R = CH3, C2H5).
Proton Conductivity: Compounds and their Structural and Chemical Peculiarities
Authors: Kreuer K. D. , Dippel Th. , Hainovsky N. G. , Maier J.
Published: July 2012

The problem of proton conductivity in condensed matter is summarized from a phenomenological point of view. Different families of compounds with proton conductivity are distinguished with particular emphazise on their conduction mechanism. Finally some structural peculiarities typically occuring with proton conductivity are extracted from the comparison of data from good and poor proton conductors.
Anomalous H Mobility in NbHxDy and Other Metal‐Hydrogen Systems: Protonic Coherent‐Dissipative Structures
Authors: Chatzidimitriou‐Dreismann C. A.
Published: July 2012

The possibility of protonic quantum effects in metal‐hydrogen systems is discussed, in connection with current theoretical (Complex Scaling Method (CSM), Einstein‐Podolsky‐Rosen (EPR) correlations, coherent‐dissipative structures) and experimental work (on detection of coherent‐dissipative structures of protons in water at room temperature). The following two effects are considered:

The measurement of the diffusion coefficient DH of H in NbHxDy, with x+y = const. (e.g. = 0.60) with NMR, shows a striking decrease of DH (up to one order of magnitude) with decreasing H‐concentration.

The comparison of mobilities of H and μ+ in different metal hydrides reveals the surprising feature that muons (as measured by μSR) apparently diffuse slower than hydrogen (as measured in the absence of muons by neutron scattering) in a large temperature regime.

These effects are interpreted in a natural way within the framework of the CSM‐theory, where broken EPR correlations between protons in the presence of other particles (muons or deuterons) are taken into consideration. As a result, the characteristic length of the protonic coherent‐dissipative structures is shown to be about (1–3)X(lattice constant). – A new prediction of the CSM‐theory concerning neutron scattering on metalhydrogen systems is stated explicitly.
Theoretical Investigation on the Luminescence Transition Probabilities in the Phosphor ZnO:Cu
Authors: Nedelmann L. P. , Mishra K. C. , Sticht J. , Schmidt P. C.
Published: July 2012

Optical properties of ZnO:Cu have been studied using the ASW (augmented spherical wave) band structure method and a supercell approximation to simulate copper impurities. The imaginary part of the dielectric function ϵ2(ω) is calculated in two different ways. In the first calculation, it is assumed that ϵ2(ω) is proportional to the joint density j(E) whereas in a second calculation the dependence of the dipole transitions on the wave vector is taken into account. The comparison of both calculations gives relative oscillator strengths for the different dipole transitions. Furthermore the influence of the choice of atomic sphere radii on the calculated j(E) is studied.
Modelling the Oscillating Electrochemical Reduction of Peroxodisulfate
Authors: Wolf W. , Ye J. , Purgand M. , Eiswirth M. , Doblhofer K.
Published: July 2012

We present a dynamic model for the oscillatory reduction of anions such as S2O82− on different electrodes. The model is solely based on well known electrochemical formulae so that the mechanism can be well understood. The central mechanistic feature is a region of negative differential resistance in the cathodic current/overvoltage curve. It is caused by the repulsive electrostatic interaction between the anions and the negative electrode surface, which counteracts the effect of increasing overvoltage. The model is investigated with numerical techniques from the theory of nonlinear dynamics. The calculations turn out to be in good agreement with experiment.
Diffusion Coefficients for Binary Mixtures of Neon with Argon, Krypton and Xenon from 220 to 400 K
Authors: Dunlop Peter J. , Bignell C. M.
Published: July 2012

Diffusion coefficients are reported for binary mixtures of neon with argon, krypton and xenon from 220 to 400 K. Potential functions are derived from these diffusion coefficients and the second virial coefficients in the literature.
Thermal Variation of the EPR Linewidth of new Phosphoniumyl Free Radicals for NMR Magnetometers
Authors: Ferroud‐Plattet M. P. , Belorizky E. , Berchadsky Y. , Tordo P.
Published: July 2012

The temperature dependence of the EPR linewidth of two phosphoniumyl radicals is investigated between 193K and 353K. The observed behaviour is interpreted through a simple model which assumes that the main contribution to the EPR linewidth arises from the anisotropic component of the large hyperfine coupling of the unpaired electron with the phosphorus nucleus. However the non resolved hyperfine coupling with the protons of the ortho methyl substituents is shown to contribute significantly to the broadening of the EPR linewidths in the high temperature range. The EPR features of the two radicals are discussed to evaluate their usefulness in low field NMR magnetometers.
Solvent Density Dependence of the Dissociation Rates of 2‐Methyl‐2‐Nitrosopropane Dimer in Simple and Molecular Fluids
Authors: Kimura Y. , Yoshimura Y.
Published: July 2012

The dissociation rate constants of 2‐methyl‐2‐nitrosopropane dimer are studied in argon, xenon, carbon dioxide (CO2) chlorotrifluoromethane (CClF3), and trifluoromethane (CHF3) from the gaseous to liquid state at 25.0 and 35.0°. In all solvent fluids, the dissociation rate constant is a decreasing function of solvent density. In argon, xenon, and CClF3, the rate constant at 35° gradually decreases by about 50% with increasing solvent density from ρr ≈︁ 0.0 up to 2.5, where ρr is a reduced density by the critical density of the solvent. In CO2 and CHF3, however, the rate constant shows a large and nonmonotonic dependence on solvent density; the solvent density dependence is large in the low‐ (ρr < 0.5) and high‐(ρr > 2.0) density regions, and is small in the medium‐density region (0.5 < ρr < 1.7). The density dependence of the rate constant in argon and xenon is well reproduced by the Lennard‐Jones fluid model on the basis of the transition state theory. The change in the charge distribution of the reactant molecule is a key to explain the large and nonmonotonical density dependence of the rate constant in CO2 and CHF3.
Adsorption of CO, H2, and O2 on Co3O4
Authors: Gamboa Mutuberría I. , Guil J. M. , Paniego Ruiz
Published: July 2012

Samples of cobalt oxide, Co3O4, have been prepared by calcination in air of cobalt nitrate, Co(NO3)2 · 6H2O. Samples with different surface areas have been obtained by sintering at several temperatures. The adsorption of carbon monoxide, hydrogen, and oxygen on these samples have been measured in a volumetric apparatus in a temperature range from 77 to 373 K. Two kinds of adsorption experiments have been carried out: normal isotherms and kinetic measurements in which the evolution of pressure is monitored as a function of time. In all cases, total and reversible adsorption are measured and irreversible adsorption is calculated. Kinetic results have been analyzed with the aid of the Elovich equation. Isosteric heats of adsorption have been calculated and calorimetric heats have been measured for the system COCO3O4 with a Tian‐Calvet microcalorimeter. From these results it is possible to draw conclusions concerning the nature of the interaction of Co3O4 with the three adsorbates.
An Experimental and Theoretical Investigation on the Solubility of Carbon Dioxide in Aqueous Solutions of Strong Electrolytes
Authors: Rumpf B. , Maurer G.
Published: July 2012

As part of an ongoing project dealing with the measurement and correlation of phase equilibria in aqueous solutions containing a weak base like ammonia and acid gases like carbon dioxide, sulfur dioxide and hydrogen cyanide, the solubility of carbon dioxide was measured in aqueous solutions containing the single salts sodium sulfate and ammonium sulfate as well as in a solution containing both salts. The temperature ranged from 313.15 K to 433.15 K and pressures up to 10 MPa. Pitzer's semiempirical model is used to correlate the new data. From the results for the solubility of carbon dioxide in the single salt aqueous solutions, interaction parameters were determined. With these parameters the solubility of carbon dioxide in an aqueous mixture containing both salts is predicted quantitatively.
Efficiency of the Generation of Protons and Hydroxyl Ions in Bipolar Membranes by Electric Field Enhanced Water Dissociation
Authors: Dang Ngoc‐Ty , Woermann D.
Published: July 2012

The efficiency of the production of protons and hydroxyl ions generated by electric field enhanced water dissociation within bipolar membranes is studied as function of the electrolyte concentration. Two types of bipolar membranes are used for the experiments: (a) A bipolar membrane formed by an anion and a cation exchange membrane which are held together by adhesion. The volume of the transition region between the two ion exchange membranes is varied systematically by inserting stacks of Nucleopore membranes. (b) A bipolar membrane formed by an anion and a cation exchange membrane are bound together permanently. The results are discussed in terms of the model of the membrane with narrow pores. The space charge model proposed in the literature to describe the electrochemical properties of bipolar membranes is modified to interprete the properties of the bipolar membranes of type (a) with a stack of Nucleopore membranes in the enlarged transition zone between the anion and the cation exchange membrane.
CO Hydrogenation on Supported Cobalt Catalysts Studied by in situ FTIR‐Spectroscopy
Authors: Fredriksen G. R. , Blekkan E. A. , Schanke D. , Holmen A.
Published: July 2012

CO hydrogenation on silica and alumina supported Co catalysts has been studied using in situ IR spectroscopy at 473–523 K, 6 bar and H2/CO=2. Bands corresponding to linearly adsorbed CO appeared at 2072 cm−1 on 4.7% Co/SiO2 and 2062 cm−1 on 4.6% Co/γ‐Al2O3, while a pair of bands at 1996 and 1952 cm−1 is observed on the alumina supported Co catalyst. Infrared bands in the 3100–2700 cm−1 and 1700–1200 cm−1 regions are attributed to adsorbed hydrocarbons, surface formate and carbonate species. The variation of the band intensities with time during CO hydrogenation and subsequent treatment in He or H2, indicates that these structures represent reaction products, apparently adsorbed on the support.
The Effect of 2,6‐Dimethylpyridine Poisoning on the Activity in n‐Hexane Cracking of Dealuminated HY Zeolites
Authors: Jolly S. , Saussey J. , Lavalley J. C. , Zanier N. , Benazzi E. , Joly J. F.
Published: July 2012

The use of an IR cell as a flow reactor shows that the activity of dealuminated HY zeolites in n‐hexane cracking at 673 K can be related to hydroxyl groups giving rise to a band at 3600 cm−1. Their presence is connected to extraframework Al species and they are strongly acidic. Specific poisoning experiments with 2,6‐dimethylpyridine evidence their heterogeneity, only a part of them being responsible for the observed activity.
In‐situ Raman Studies of Ethylene Oxidation at Ag(111) and Ag(110) under Catalytic Reaction Conditions
Authors: Bao X. , Pettinger B. , Ertl G. , Schlögl R.
Published: July 2012

In this report we present, to our knowledge, the first Raman investigations at single crystalline Ag(111), Ag(110) and microfacetted Ag(110) samples, which were exposed to N2 or N2 + reactive gases (oxygen and ethylene). The pressure and temperature ranges are close to those used for industrial oxidation of ethylene using Ag‐catalysts. Depending on the orientation of the Ag‐surface and on the history its preparation and temperature cycling (300–900 K), three Raman lines for three Ag—O species were found, assigned to Ag—Oads., —Ag—O—Ag— with oxygen located in the sub‐surface position and oxygen dissolved in the bulk of silver. The disappearence of the Raman line for sub‐surface oxygen in the course of ethylene epoxidation indicates its participation in this reaction.
In‐situ Positron Emission of CO Oxidation
Authors: Vonkeman K. A. , Jonkers G. , van Der Wal S. W. A. , van Santen R. A.
Published: July 2012

Using a Neuro ECAT positron tomograph the Positron Emission computed Tomography (PET) has been utilized to image the catalytic oxidation of CO by using CO and CO2, labelled with short lived positron emitting nuclides. Studies were performed over highly dispersed ceria/γ‐alumina supported platinum and rhodium catalysts. With a mathematical model of the reaction kinetics, based on the elementary steps of the catalytic reaction and partially on literature surface science data, the effect of CeO2promotion and the presence of NO were quantified in terms of the number of adsorption sites and adsorption equilibrium constants. Oxygen atoms of CO2remain much longer in the catalyst bed than the carbon atoms, which is due to carbonate formation at the ceria surface and exchange of the oxygen atoms of these carbonate groups with the ceria lattice oxygen atoms. The heat of desorption of CO from the noble metal surface at low temperatures was found to be increased due to the presence of NO molecules at the surface. At higher temperatures NO dissociates, the adsorbed N and O atoms have a repulsive interaction with adsorbed CO molecules.
In Situ AC Electrical Conductivity Measurement on Bi3FeMo2O12
Authors: Cäldararu Monica , Sprinceana Dan , Ionescu Niculae I.
Published: July 2012

The dynamic evolution of the defect structure of the Bi3FeMo2O12 surface determined by processes frequently encountered in heterogeneous catalysis (e.g. heating‐cooling cycles, adsorption and/or reaction of reactive gases with solid surfaces) can be followed either by direct in situ measurement of the AC electrical conductance, or by comparing the electrical conductance data of successive experiments on the same sample, in standard reference conditions, after various in situ treatments.
In situ ESR‐Untersuchungen an elektrochemischen Systemen
Authors: Dunsch L. , Petr A.
Published: July 2012

The combination of ESR‐spectroscopic measurements with electrochemical techniques is described using a new ESR‐electrochemical cell for studies of solid working electrodes and a computer‐driven system for both the electrochemical and the spectroscopic technique. The variation of the cell construction for different applications as well as the use of signal accumulation after potentiostatic pulses is shown. In the case of a triazine the existence of two radical products in an electrode reaction is proved using the rapid scan ESR‐technique.
The Adsorption of Unsaturated Organic Species at Single Crystal Electrodes Studied by Differential Electrochemical Mass Spectrometry
Authors: Baltruschat H. , Schmiemann U.
Published: July 2012

Using a thin layer cell for differential electrochemical mass spectrometry, we studied the influence of the crystallographic surface orientation of Pt single crystals on the adsorption of benzene, ethene and perchloroethylene. Whereas on Pt(110), adsorbed benzene is completely desorbed at negative potentials under hydrogenation to cyclohexane, it is desorbed as such from the (111) face. — Several adsorbate states are found when ethene is adsorbed on these surfaces. Only part of the adsorbate can be desorbed under hydrogenation to ethane and also dimerization to butane; the extent of this hydrogenative desorption being much higher in the case of the (110) surface. The remaining part of the adsorbate can be oxidized to CO2 at potentials where oxygen is coadsorbed. In addition, at the (110) face and, at higher adsorption potentials also at the (111) face, some CO‐like adsorbate is formed during adsorption. — In the case of perchloroethylene, the adsorption is reductive, i.e. the C—Cl‐bonds dissociate upon adsorption. Cathodic desorption also yields methane besides ethane pointing also to a C—C bond dissociation.
Processes at Interfaces between Solid Electronic, Ionic and Mixed Conductors — Characterization by Voltage and Frequency Dependent Electrical Measurements
Authors: Wiemhöfer H.‐D.
Published: July 2012

Examples are discussed for the electrical characterization of interfaces with solid electronic, ionic and mixed conductors by steady‐state current voltage relations and impedance spectroscopy. Polarization measurements are presented with electron and ion conducting point contacts on mixed conducting solids. Examples for the use of impedance spectroscopy concern the effect of fast grain boundary transport on diffusion impedances in mixed conductors and the impedance of electrodes on solid electrolytes. The experimental realization of in‐situ investigations with XPS and UPS are discussed for oxygen electrodes with yttria‐stabilized zirconia as solid electrolyte.
Impedance Analysis of the Quartz Micro‐Balance Signal
Authors: Fruböse Christian , Doblhofer Karl , Soares David M.
Published: July 2012

During measurements of mass‐changes with the electrochemical quartz‐microbalance (E‐QMB) changes of the visco‐elastic properties of the contacting medium (liquids and/or films) can occur. If such changes are not taken into account in the evaluation of the observed frequency‐changes, erroneous results will normally be obtained. The problem is analyzed on the basis of the system's impedance. Methods for correcting results obtained with impedance‐analyzers and with feedback‐driver circuits are presented.
Probing Electrochemical Adsorbate Structure and Reactions with In‐Situ Atomic‐Resolution Scanning Microscopy: Some Progress and Prospects
Authors: Gao Xiaoping , Weaver Michael J.
Published: July 2012

Some prospects for applying scanning tunneling microscopy (STM) as an in‐situ atomic‐resolution probe of adlayer structure at ordered metal‐solution interfaces are considered with respect to both equilibrium and reactive adsorbate systems. Illustrative results of the former type are presented for the potential‐dependent adsorption of iodide at low‐index gold electrodes. The virtues of acquiring “composite‐domain” STM images, where the electrode potential is altered during data acquisition so to form or remove the adsorbed adlayer, are noted. By generating temporally and spatially adjacent domains featuring substrate and adlayer images in this fashion, the registry between the former and latter atomic arrangements can be deduced with high precision. The suitability of in‐situ STM for examining real‐space dynamics of surface physical and chemical processes is illustrated for potential‐induced reconstruction of Au (100) and for the electrooxidative polymerization of iodide and sulfide. Some limitations as well as strengths of in‐situ STM for these purposes are briefly outlined with regard to its anticipated role in the development of in‐situ electrochemical surface science.
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

In 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

A 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

The 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

Symmetric 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

The 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

The 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

The 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

The 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

The 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

In 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

On 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

The 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

We 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

The 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

We 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

The 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

The 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

The 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

The 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

Calamitic 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.