bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoelectron Spectroscopic Study of the Adsorption and Co‐adsorption of Hydrogen and Carbon Monoxide on Iron Films
Authors: Wedler G. , Ertel J. 
Published: July 2012

AbstractThe adsorption of carbon monoxide and of hydrogen on evaporated iron films is studied by means of ultra violet photoelectron spectroscopy (UPS) and X‐ray photoelectron spectroscopy (XPS). Both methods indicate that carbon monoxide begins to decompose at 298 K. At 423 K the decomposition is complete. UP spectra of co‐adsorbed hydrogen and carbon monoxide confirm the existence of an interaction between these two gases in the adsorption layer at 298 K. The results are used to correlate earlier thermodynamic and kinetic studies with known literature data about photoelectron spectra of the systems Fe/H2, CO and to discuss the influence of crystal orientation and surface structure on the adsorption of H2 and CO on Fe.
Hydrogen Trapping in β‐NbHx by Lattice Defects
Authors: Baden Wolfgang , Weiss Alarich 
Published: July 2012

Abstract1H NMR was studied in thin foils of β‐NbHx (0.71 ≦ x ≦ 0.86). Three 1H NMR signals, A, B, and C have been observed. Their chemical shift depends on the hydrogen concentration x. The separation of the signals is several ten ppm. A strong dependence of the signal intensity from the pretreatment of the metal foil is found. It is shown that the signal A is most probably due to hydrogen atoms trapped at dislocations and domain boundaries. Signal B belongs to the 1H NMR in the undisturbed lattice of β‐NbHx. Finally signal C is possibly due to hydrogen trapped at interstitial oxygen impurities.
Kinetic Influences on Reaction Processes in the Quasiternary System HgkCd(1‐k)TelSe(1‐l)
Authors: Leute V. , Schmidtke H. M. , Stratmann W. , Kalb A. 
Published: July 2012

AbstractKinetic aspects of the solid state reaction between the binary semiconductors CdTe and HgSe as well as the topochemistry of the reaction zone are investigated by an electron microprobe and by optical microscopy. The reaction path is markedly influenced by intrinsic doping of the binary reaction components. Pronounced regions of uphill diffusion of chalcogens or of metals are essential features of the reaction behaviour in this semiconductor alloy system.
Defects and Cation Diffusion in Magnetite (V): Electrical Conduction, Cation Distribution and Point Defects in Fe3‐δO4
Authors: Dieckmann R. , Witt C. A. , Mason T. O. 
Published: July 2012

AbstractElectrical conductivity in magnetite has been studied experimentally as a function of temperature and oxygen activity between 560 and 1400°C. The results indicate that above TC (=575°C) an octahedral site small polaron mechanism is dominant over the entire temperature range (Ea = 0.1136 eV). By comparing data on electrical conductivity and thermoelectric power, a second (small polaron) mechanism (Ea = 0.714 eV) is detected at elevated temperatures. Additionally, equilibrium constants for the cation vacancy formation are derived from fitting the conductivity isotherms as a function of oxygen activity. These agree well with values determined thermogravimetrically.
Electron Impact Induced Excitation Processes Involving the Sulfur Clusters S2 to S8
Authors: Rosinger W. , Grade M. , Hirschwald W. 
Published: July 2012

AbstractIonization efficiency curves of the gaseous sulfur species Si (i = 2–8) in equilibrium with solid red HgS were obtained by electron impact ionization. Analysis of fine structure of the curves yields energy levels of ground and excited ion states. — For S2 and S8 the experimental values are in good agreement with independent photoionization and photoelectron spectroscopic data from the literature. In the case of S3 to S7 numerous appearance potentials were determined which reflect processes such as direct ionization, autoionization, fragmentation, and predissociation. Extended Hückel calculations were performed for verification of the experimental energies and for spectroscopic assignment of states. — By the second and third law methods the heats of the gas phase reactions Si(g) = i/2 S2(g) (i = 3–8) and average bond energies of the sulfur species were determined.
Internal and External Oxidation of Nonmetallic Compounds and Solid Solutions (I)
Authors: Schmalzried H. 
Published: July 2012

AbstractA formal analysis is given treating the phenomenon of internal and external oxidation of oxide solid solutions. Theoretically, two situations can arise if those oxides are brought in an environment of higher oxygen potential. (1) Demixing and subsequently the formation of an outer layer of the reaction product occurs. (2) The reaction product forms internally; the two‐phase front advances into the interior of the solid solution. Some analogies with the phenomenon of internal alloy oxidation are discussed. Normally, a parabolic reaction kinetics prevails. Depending on the composition of, and the transport coefficients in the solid solution, a change from an internal to an external reaction may occur, and a criterion for this change is deduced. Internal oxidation (and reduction) is a means to disperse a second phase into an oxide matrix. This process may alter electrical, chemical and mechanical properties of the solid in question and thus could be of interest for materials science as well as geochemistry.
ESR of Mn2+ Ions in ZnP2 and Structural Correlations
Authors: Frick B. , Siebert D. 
Published: July 2012

AbstractIn tetragonal ZnP2 paramagnetic Mn2+ substitutes for the Zn2+ ions that are all equivalent. The hyperfine structure constant A of the paramagnetic Mn2+ centre was determined to 53(2) · 10−4 cm−1. Measurements of the optical activity revealed a characteristic twinning of the red, plate‐like crystals. In monoclinic ZnP2 two different Mn2+ centres could be detected in accordance with two different Zn sites. A site assignment was possible by considering a pseudo‐orthorhombic unit. The same assignment was obtained by comparing the orientations of the centres' axes with calculated directions of the axes of crystal field tensors. The agreement of the A values of the two different centres in monoclinic ZnP2 among themselves and with the A value in tetragonal ZnP2 supports a structure without Zn‐Zn bonds for the monoclinic modification.
Improvement of Electrochemical Methods for Studying Metal‐Hydrogen Systems
Authors: Schöneich H.‐G. , Züchner H. 
Published: July 2012

AbstractCorrect diffusion measurements using electrochemical methods must be carried out under careful consideration of the boundary conditions. — It is shown that the diffusion of recombined H‐atoms from the metal surface into the electrolyte does not seem to be the main reason for a loss of hydrogen concentration, but the presence of oxidizing species (generally oxygen), solved in the electrolyte, which lead to an enhanced electrochemical oxidation of hydrogen. In order to avoid this source of systematic errors, deaerated H2SO4was used for measuring time lag curves of hydrogen diffusion in palladium. Measured time lag curves, obtained by the current pulse method, agree very well with theoretical curves, evaluated from the solution of Fick's second law. — When determining diffusion coefficients by measuring the break‐through time one has to take into account the ratio of the amount of hydrogen, discharged on the entry side of the diffusion foil, to the content of hydrogen within the sample from precharging runs.
The Trimethylsulfonium Ion, [(CH3)3S]⊕, in Hexachlorometallate(IV) Complexes, [(CH3)3S]2MCl6 (M = Pt, Se, Te, Sn). 1H NMR, 35Cl NQR, and X‐Ray Diffraction Studies
Authors: Ikeda Ryuichi , Nakamura Daiyu , Kadel Rainer , Weiss Alarich 
Published: July 2012

AbstractThe measurements of 35Cl NQR spectra and X‐ray powder diffraction patterns were carried out in a series of the complexes of trimethylsulfonium hexachlorometallates(IV), (triMS)2MCl6 (M = Pt, Se, Te, Sn). For (triMS)2TeCl6 and (triMS)2SnCl6, 1H NMR second moments were determined at various temperatures between 77 K and 370 K. The temperature dependence of 1H NMR spin‐lattice relaxation times was observed for (triMS)2PtCl6, (triMS)2TeCl6, and (triMS)3SnCl6. From X‐ray powder patterns, it was found that the complexes studied are isomorphous with each other and form cubic crystals belonging to the space group T‐Pa3. The unit cell dimensions were determined. A single 35Cl NQR line was observed for all of the complexes in agreement with the crystal symmetry. From 1H NMR studies, two kinds of motions of (triMS)⊕, namely, the intracationic CH3 group reorientation and the reorientation of the whole cation about its C3 axis, were observed separately in the above three complexes. The activation energies of these motions were evaluated and compared with those of trimethylammonium ions in hexahalometallate(IV) complexes previously reported.
14N Nuclear Quadrupole Resonance in Simple Compounds Containing the Amino Group
Authors: Okuda Tsutomu , Ueda Akinobu , Mishima Kanae , Suzuki Toshinori , Negita Hisao 
Published: July 2012

Abstract14N nuclear quadrupole resonance was observed in acetamide, CH3CONH2, and chloroacetamide, CH2ClCONH2, by pulse technique. The resonance frequencies in both compounds increase with raising from 80 K to 340 K. In acetamide the activation energy was calculated to be 17.6 kJ · mol−1 in the temperature range from 260 K to 320 K and 48.1 kJ · mol−1 above 320 K. The former is thought to be attributed to the reorientation of the amino group and the latter, to the torsional motion of molecule. In the case of chloroacetamide the echo signal is too weak to obtain the correct T1 value, but the relaxation mechanism seems to be similar to that of acetamide. The positive temperature dependence of resonance frequencies is due to the hydrogen bond.
Interaction of Ammonia with Metallic Copper, Nickel and Cobalt Catalysts Studied by Temperature Programmed Desorption
Authors: Baiker Alfons , Monti Daniele 
Published: July 2012

AbstractThe adsorption of ammonia on unsupported and alumina supported copper, nickel and cobalt catalysts was studied employing temperature programmed desorption. No ammonia desorption was observed in the experiments carried out with the unsupported metal powders. Nickel and cobalt showed desorption of nitrogen and hydrogen, whereas with copper only nitrogen desorption was observed. On the alumina supported metal catalysts the desorbing gases were ammonia, hydrogen and nitrogen with ammonia as major desorbing species. The investigations indicate that the adsorption of ammonia at 570 K leads to nitride formation on the metal surfaces. The amount of metal nitride formed increases in the sequence: copper, nickel, cobalt. Hydrogen suppresses the nitride formation. This is shown by comparative desorption experiments on catalyst samples which were exposed to hydrogen after exposure to ammonia. The rate of the metal nitride reduction is larger on nickel and cobalt than on copper. This is ascribed to the lower activity of the copper for hydrogen dissociation.
Rate Coefficients of Elementary Steps in the Inhibited Oxidation of Ethylbenzene, I. Interaction between Peroxy Radicals and Inhibitor Molecules
Authors: Lukács J. , Héberger K. , Gál D. 
Published: July 2012

AbstractThe inhibited oxidation of ethylbenzene has been investigated in the presence of 2,6‐di‐tert‐butyl‐4‐methyl‐phenol (ionol). 1‐Phenylethyl‐hydroperoxide was used as a source of radicals. The time dependence of oxygen consumption was measured at t = 120°C and simulated using a reaction mechanism consisting of 20 elementary steps. Simulation was carried out by changing the value of the rate constant of the reaction

Since the calculated curves are — at a constant rate of initiation — essentially influenced by the value of k5, simulation is a proper method for its determination. The best fit was achieved at k5 = 5 · 105l · mol−1 s−1. — The contribution of the various elementary steps to oxygen consumption has been also determined.
Kinetics and Mechanism of Hydrocarbon Formation in the System C2H2/O/H at Temperatures up to 1300 K
Authors: Homann K. H. , Wellmann Ch. 
Published: July 2012

AbstractThe consumption of O atoms and the formation of CO, C3H4 (Propyne and Propadiene), C4H2 (Butadiyne) and other hydrocarbons in the system C2H2/O with and without added H atoms has been studied in the temperature range 295–1300 K, p = 2.7 mbar. Both the rate of formation and the yield of C3H4 in C2H2‐rich mixtures increases with higher temperature. The rate of C4H2 formation increases but the maximum concentration remains constant up to 500 K. The results can be described quantitatively through a slightly modified mechanism of 30 reactions that had been proposed previously for the reaction at room temperature.
Kinetics of the Reactions of OH‐Radicals with Benzene, Benzene‐d6 and Naphthalene
Authors: Lorenz K. , Zellner R. 
Published: July 2012

AbstractAbsolute rate constants for the reactions of hydroxyl radicals with benzene (1), benzene‐d6 (2), and naphthalene (3) have been obtained using excimer laser photolysis to generate OH and time resolved resonance fluorescence as its monitor. Reaction (1) was studied at total pressures between 1.5 and 112 mbar at 298 K using Ar as a diluent gas. k1 is found to increase with pressure up to –40 mbar, but to be essentially pressure independent at still higher pressures, k (298 K) = (7.0 ± 1.5) 1011 cm3/mol · s. The temperature variation of k1 as studied over the range 244 – 24 K. At temperatures below 330 K normal Arrhenius behaviour with k1 (T) = (3.8 ± 1.0) 1012 exp[‐(500 ± 50) K/T] cm3/mol · s is observed, corresponding to the addition reaction (1) OH + C6H6 → C6H6OH. Between 330 and 420 K a sharp decrease of k1 with increasing temperature is noted, which we attribute to reaction (1) becoming reversible. For the stabilization energy of C6H6OH we derive (79 ± 6) kJ/mol. Above 420 K a transition of k1 to a positive temperature dependence, corresponding to the abstraction reaction (1') OH + C6H6 → H2O + C6H5 is noted. Rate constants for the reaction of OH with benzene‐d6 (2) are essentially identical to those of reaction (1) except for temperatures above 420 K, where k2 falls considerably below k1. This isotope effect is a confirmation of the (1') abstraction route. Reaction (3) was studied at total pressures between 6 and 128 mbar (He) where it is found to be essentially pressure independent. Its temperature variation was studied between 337 and 525 K. Over this region the rate coefficient decreases from (8.8 ± 3.5) 1012 cm3/mol · s to (6.6 ± 2.6) 1011 cm3/mol · s, with the decrease with temperature being relatively weak up to 410 K, k1(T ≤ 410 K) = (2.2 ± 1.0) 1012 exp[(440 ± 50) K/T] cm3/mol · s, and stronger at still higher temperatures. This behaviour is interpreted as to correspond to the addition reaction (3) OH + C10H8 → C10H8OH and its equilibration. The stabilization energy of the OH‐naphthalene adduct is estimated to be (95 ± 6) kJ/mol.
Spectrum and Lifetime of NH(a1Δ → X3Σ'−) in Inert Gas Matrices
Authors: Esser H. , Langen J. , Schurath U. 
Published: July 2012

AbstractMetastable NH(a1Δ) radicals were produced by the photolysis of matrix isolated HN3(HNCO) at 206.2 nm. The (0,0) and (0,1) bands of the forbidden transition to NH(X3Σ−) were observed in emission in the rare gases and in nitrogen, yielding Franck‐Condon factors, ΔG1/2 values, and matrix shifts. The line structure of the (0,0) band in Xe is due to nearly free rotation of the radical in the electronic ground state. Rotation in the other matrices is strongly inhibited or totally suppressed by the presence of the other photofragment N2 in or near the cage. Lifetimes of NH(a1Δ) in Ne, N2, Ar, Kr and Xe are 335 ms, 365 ms, 375 ms, 790 ms and 1020 ms. The strong temperature dependence of the lifetime in Xe is in quantitative agreement with a theoretical model of multiphonon induced inter system crossing to NH(X3Σ−, ν = 4), indicating a fluorescence yield near 80% in the low temperature limit. The shorter lifetimes in the other matrices are believed to be due to enhanced molecule‐medium coupling by the nearby N2 photofragment. Extrapolation of the Xe data yields an estimate of 3.3 s for the radiative lifetime of gaseous NH(a1Δ).
Coexistence Curve of the System Methanol/Carbon Disulfide in the Vicinity of the Critical Point
Authors: Oswald U. , Woermann D. 
Published: July 2012

AbstractThe coexistence curve of the system methanol/carbon disulfide is determined by observing the temperature of phase separation of 32 samples over a narrow range of composition close to the critical point (10−5≤t≤ 10−3;t= (Tc‐Tc)/Tc). The functional form of the difference in order parameter in terms of mass fraction, mole fraction, or volume fraction is consistent with the concept of universality of critical phenomena. The following critical data are obtained: mass fraction of carbon disulfideyc= 0.805 ± 0.005;Tc= (34.281 ± 0.002) °C; β = 0.329 ± 0.005.
The Independent Molecular Interaction Sites Model III. A Monte‐Carlo Study of the Reference Fluid for Hard Dumbbell Systems
Authors: Naumann K.‐H. , Bansal R. , Bruns W. 
Published: July 2012

AbstractThe site‐site pair distribution functions of the Independent‐Molecular‐Interaction‐Sites (IMIS) reference fluid for homonuclear hard dumbbell systems are evaluated by Monte‐Carlo simulation and from the Percus‐Yevick approximation. The good overall agreement with the “exact” pair correlation functions for these systems suggests that the IMIS model provides a reliable route to the structural properties of interaction site model fluids with short‐ranged site‐site potentials.
A Generalized van der Waals Equation of State I. Treatment of Molecular Shape in Terms of the Boublik‐Nezbeda Equation
Authors: Svejda P. , Kohler F. 
Published: July 2012

AbstractA description is given how to construct hard convex bodies to resemble several hydrocarbon molecules. It is shown that this description, when inserted into a generalized van der Waals model, leads to very good agreement in the p‐p‐T properties at low temperatures and high densities. Furthermore, the attractive van der Waals parameters exhibit the property of additivity. The extension of this model to mixtures is presented, though the detailed comparison of some mixing properties is deferred to forthcoming publications.
Additional Comments on the Induced Optical Activity in the Charge‐transfer Complexes of Optically Active Ketones with Tetracyanoethylene
Authors: Tajiri Akio , Gonohe Narishi , Hatano Masahiro 
Published: July 2012

AbstractThe intermolecular electron donor‐acceptor complexes of the optically active ketones with tetracyanoethylene (TCNE) have exhibited circular dichroism (CD) and magnetic circular dichroism in the charge‐transfer absorption region. A possible geometry has been proposed in order to interpret the sign of the observed CD spectrum in each complex. A symmetry consideration for the observed Faraday B term has supported a local structure of the ketone‐TCNE complex where the TCNE plane is rotated around the carbonyl axis. A temperature variation spectrophotometry of the thermodynamic parameters for the selected systems has not given a conclusive evidence for the isomeric 1:1 complexes in these systems.
Recent Developments in the Experimental Determination of Thermodynamic Quantities of Metals and Alloys
Authors: Komarek Kurt L. 
Published: July 2012

AbstractRecent developments of experimental techniques for the measurement of thermodynamic quantities of metals and alloys are reviewed. Special emphasis is placed on calorimetry of reacting and non‐reacting systems, emf methods with liquid and solid electrolytes, and the various Knudsen effusion methods.
Thermodynamics of Compounds with Narrow Ranges of Nonstoichiometry
Authors: Schmalzried H. 
Published: July 2012

AbstractThermodynamic functions of compounds with narrow ranges of homogeneity are calculated with the aid of the concept of defect thermodynamics. In doing so, the irregular structural elements of a crystal are formally treated as quasi‐particles in dilute solution on their respective sublattices. This concept is illustrated with binary and ternary ionic crystals (for example Fe3‐δO4; Ag2+δS; Co1‐δ; (Co,Mg)1‐δO; (Fe,Mg)2‐δSiO4). The nonstoichiometry δ of these compounds is calculated as a function of the independent thermodynamic variables and compared with experimental results.
Electronic and Elastic Influences on the Energetics of Alloy Formation
Authors: Schaller H.‐J. 
Published: July 2012

AbstractPalladium and platinum alloys have turned out to be a useful subject for relating thermodynamic properties with electronic and elastic quantities of the components. The mixing behavior of a number of interstitial and substitutional alloys exhibits analogous characteristics and may be interpreted by means of the same model. – Two effects are discussed to account for nonideal properties. An “electronic” effect is based on the observation that a number of alloy components behave as electron donors with respect to Pd and Pt. The charge transfer gives rise to a bonding contribution which is determined by the Fermi levels of the components and the valency of the solute. Extremely negative deviations from ideal mixing behavior have been predicted and observed upon adding unnoble components such as Al, Zr, Th or rare earth metals. For a number of Pd alloys the rise of the Fermi energy can be described as a function of the valence electron concentration only, irrespective of the particular donor. – An “elastic” effect is associated with the lattice distortion brought about by the dissolved particles. Models based on continuum elastic considerations are discussed in order to estimate the strain energy at infinite dilution. This quantity is correlated to the pair interaction energy in the quasichemical approach, which was used to calculate the concentration dependence of the elastic contribution. – Based on the underlying assumptions, the thermodynamic excess quantities can be separated in an electronic and an elastic part. These ideas are quite general and should be useful in a number of other metallic solutions.
Homogeneous Equilibria in Liquid Alloys and Glass Formation
Authors: Sommer F. 
Published: July 2012

AbstractUsing homogeneous equilibria reactions for the description of chemical short range order tendencies in liquid alloys with compound forming tendency it is possible, with the association model, to describe different kinds of asymmetrical concentration dependences, to calculate the temperature dependences of the thermodynamic mixing functions as well as to extrapolate for multicomponent systems. Some exemplary results are shown. The existence of a chemical short range order is an important factor of influence on the glass formation ability obtained by rapid quenching from the liquid phase. On the one hand, it causes small chemical driving forces for a crystallization and, hereby, a thermodynamic promotion of glass formation. On the other hand, glass formation is additionally kinetically favoured, if the stoichiometric compositions of the associates in the liquid alloys are not in accordance with those of the crystalline equilibrium phases in the glass formation range.
Experimental Aspects of Solid Galvanic Cell Methods for Thermodynamic Studies on Alloys
Authors: Kleykamp H. 
Published: July 2012

AbstractThe phase diagrams of the ZrO2–CaO, ZrO2–Y2O3, ThO2–Y2O3 and ThO2–La2O3 systems are discussed in view of the use of the electrolytes in emf measurements. It is shown that thermodynamic studies on metallic A‐B systems using solid galvanic cells with oxygen and fluorine ion conducting electrolytes require the knowledge of the phase diagrams of the corresponding ternary A‐B‐O and A‐B‐F systems for the cell arrangements. Examples for misleading emf measurements by use of incompatible electrodes are given. Asymmetric cells, side reactions between the electrodes and the electrical leads, and impurities in the cover gas as sources for erroneous emf measurements are demonstrated. The characteristics of reference electrodes for oxide electrolytes in environments with different oxygen partial pressures are outlined. The role of oxygen as an impurity in the electrodes for CaF2 electrolytes is investigated.