摘要:

AbstractThe hydrogenation of CO2on a precipitated Fe‐catalyst and the formation of oxidic and carbidic iron phases were investigated. The hydrogenation reaction was studied by transient‐ and synthesis‐experiments, changes in the structure of the catalyst were followed by X‐ray‐diffraction and Mößbauer‐spectroscopy. In pure CO2the iron is converted to magnetite. In CO2‐H2‐mixtures the catalyst is completely converted to cementite. In the initial state of this reaction small amounts of magnetite are formed in the pores of the catalyst. Methane is the main product of

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980502

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractTransport of matter and charge in ionic crystals is only possible by the existence of irregular structure elements (defects) which are often charged relative to the crystal lattice. A comparison between the transport behaviour of a crystalline matrix containing such charged defects and a liquid electrolyte containing dissolved ions shows a lot of similarities. As is well known the transport properties of liquid electrolytes are strongly affected by interactions between the dissolved ions. We have applied the well elaborated concept of mixed electrolytes by Onsager and Fuoss which was originally devoted to liquid electrolytes to ionic crystals containing charged point defects. The equations of Onsager and Fuoss allow in principle the calculation of the concentration dependence of the phenomenological transport coefficientsLijof all charge carriers of n‐component electrolytes. We will use these equations to predict the transport behaviour of ionic crystals containing differently charged point defects.As examples we have calculated transport coefficients for electrolyte systems which can be regarded as models for the transition metal oxides Co1‐δO and Cu2‐δO. One major result concerns the magnitude of the cross effect between the ionic and electronic fluxes in those materials. The implications of these results with respect to experimental observations are di

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980503

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractA microscopic model of electrotransport in semiconducting ionic crystals is described, which is based on electrostatically interacting hopping charge carriers (cation vacancies and electron holes). Formulating rate equations for the thermally activated motion of electronic and ionic defects in external fields allows for the calculation of stationary charge distributions. In the case of large differences in the mobilities of both defects an adiabatic approximation can be introduced which allows to separate the motion of electron holes and vacancies. The formal problem is identical to the solution of the Poisson‐Boltzmann equation for large defect concentrations. An expression for the charge of transport is derived which is equivalent to the Debye‐Huckel expression for the relaxation effect but includes distinct geometrical positions around a central point cha

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980504

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractThe current/voltage curves of crystalline (100)‐ and (111)‐oriented surfaces of n‐pyrite/electrolyte and n‐pyrite/Pt junctions in darkness and under illumination are strongly influenced by cathodic hydrogen evolution before junction formation. Higher dark current and lower photocurrent on n‐pyrite (111)‐oriented surfaces in comparison to (100)‐oriented surfaces were obtained. The junction properties of the untreated surfaces change from a metal‐like behaviour to a rectifying one. During electrochemical treatment different etching patterns develop according to the exposed surface orientation. In the case of (111)‐oriented crystals these patterns are identified as new (100)‐surfaces. Quantum yields of ca. 0.7 at photon energies of 1.4 eV and almost similar photocurrent action spectra are obtained on n‐pyrite/electrolyte and n‐pyrite/metal junctions. The energetical position of the subbandgap response at 0.68 eV is not changed during etching. The increase of the quantum yield for photon energies higher than 1.4 eV on both types of junction points towards a reduction of surface recombination centers on etched samples. EBIC analysis on previously etched n‐pyrite in contact to vacuum deposited platinum films of 120 to 1000 Å thickness (Schottky barriers) indicate that the charge carrier collection efficiency is higher on etched areas. The role of surface recombination processes for photocurrent generation is

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980505

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractRaman spectra of the “molecular” polycrystalline solids HgCl2(D 2h16), HgBr2(C 2ν16) and of the yellow form of HgI2(C 2ν12) were measured from LN2up to premelting temperatures. Polarized Raman spectra of molten HgX2(X = Cl, Br, I) were measured at temperatures up to 950 K. The pure rotational band contour and the vibrational rotational contour of the HgX2vapors were also measured. Upon melting the vibrational modes of the high temperature solid appear to be preserved. The spectra of the three liquids are similar and are best correlated to the spectra of the D 2h16(HgCl2) solid and the vibrational modes of the HgX2molecules. Reduced Raman spectra of the liquids show splitting of the stretching mode to a doublet, ν1(A1) and ν1(B2g), which is attributed to strong intermolecular coupling. The ν2and ν3internal modes of the solid are also transferred into the melt. The predominant features of the low frequency reduced spectra is a band, VR, which is assigned to the rotatory modes of the HgX2molecules and can be correlated to both the rotational band contour of the vapor and the librational modes of the solid. With increasing temperature the spectra of the liquid show softening of the rotatory modes and a blue shift of the ν1mode, both implying weakening of the intermolecular coupling. An overall decrease in the Raman intensity of the liquid spectra with increasing temperature is attributed to the rapid mol

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980506

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractMeasurements of the electrical conductivity, magnetic susceptibility and thermoelectric power in liquid Cu‐CuTlTe2and Ag‐AgTlTe2systems have been carried out over wide temperature and composition ranges. These liquid systems exhibit the compound‐forming behavior in the vicinity of stoichiometric compositions, Cu3TlTe2and Ag3TlTe2, such as the conductivity minimum, diamagnetic maximum and reverse in the sign of the thermoelectric power. Radial distribution analyses of the stoichiometric compositions, Cu3TlTe2and Ag3TlTe2, by X‐ray and neutron diffractions indicate that the bonding nature of Cu‐Te and Ag‐Te in both alloys is rather covalent, differing from the ionic nature of Tl‐Te in liquid Tl2Te which is well‐known as a typical compound

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980507

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractGeometries of clusters formed by the group‐V‐atoms As, Sb and alkali metals M = Na, K, Cs are studied by extended Hückel (EH) calculations supplemented by a repulsive two‐body interaction and a geometry optimization of the Fletcher‐Powell‐type. The computational results are compared with available ab initio and pseudopotential data as well as experimental findings. The improved EH formalism allows a straightforward analysis of geometric preferences of clusters as a function of the alkali coordination. These findings are then interpreted in terms of qualitative orbital pictures. For clusters containing four group‐V‐atoms, e.g. As4, Sb4, M2As4, M2Sb4, M4As4, M4Sb4, M6As4, M6Sb4, it is shown that the geometry of the central As4(Sb4) unit depends on the number of valence electrons. The bare As4and Sb4clusters have a tetrahedral Tdminimum, while the metal‐to‐group‐V‐atom electron transfer in the alkali coordinated systems stabilizes a square‐planar As4(Sb4) ar

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980508

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractOxygen, modelled as a 2‐center Lennard‐Jones fluid, is studied along three isochores‐spanning the liquid region. Eleven different thermodynamic properties are obtained from simulations in the classical molecular dynamics ensemble. It is shown that most of them agree with experimental data within the combined uncertainty of experiment and simul

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980509

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractPermeabilities of tartrazine for different composite membranes were obtained by tracer diffusion experiments.14C‐labeled tartrazine was synthesized from14C‐aniline hemisulfate and tartaric acid. The composite membranes under investigation consisted of cellulose acetate or polyethersulfone supported by polypropylene membrane backi

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980510

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractThe micellar structure of the cationic surfactant benzethonium chloride (BZC1) was analysed by small‐angle x‐ray scattering techniques. The shape, size and characteristics of the internal structure of BZC1 was studied by the contrast variation method at 20°C (CMC = 5.35 × 10−4Mol/l) by changing the electron density of the solvent through addition of polyols, e.g. sucrose or glycerol. The obtained scattering data were converted to absolute intensities, and analysed for intermicellar interference effects, by applying the rescaled mean spherical approximation method. The morphological parameters, micellar volume, average electron density, ϱ1, radius of gyration, Rν, second moment of the electron density distribution,“a”, and square average of the electron distribution, (Δϱ12), were determined from scattering data in the range of 0.001

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980511

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY