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  • X-ray diffraction  (2)
  • 36.40  (1)
  • 74.62.Fj  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    On the relation between catalytic performance and microstructure of polycrystalline silver in the partial oxidation of methanol (1995)
    Springer
    Catalysis letters 33 (1995), S. 305-319 
    Details
    ISSN: 1572-879X
    Keywords: methanol oxidation ; conversion to formaldehyde ; silver ; surface oxygen ; STM ; IMR-MS ; adsorption-induced restructuring ; atomic structure ; texture ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Electrolytic silver was investigated as partial oxidation catalyst for the conversion of methanol to formaldehyde. Using the mass spectrometric technique as on-line detector the relation between feed composition and temperature was determined allowing us to conclude that two simultaneous reaction pathways operate under steady state conditions. The microstructure was analysed by XRD and STM. A pronounced restructuring of the surface on the mesoscopic scale was detected. The atomic structure of the γ oxygen phase was determined on the (111) face of facets grown during reaction. The two reaction pathways find their counterparts in two distinctly different surface microstructures providing different geometries for the respective active sites. After prolonged time on stream the high surface mobility of the silver atoms removes all mesoscopic restructuring without changing the conversion characteristics. The observed restructuring is thus considered as a frozen large scale image of the continuously changing surface under reaction conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00814233
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of C60/C70 ratios in fullerene mixtures and film characterization by scanning tunneling microscopy (1993)
    Springer
    Applied physics 56 (1993), S. 197-205 
    Details
    ISSN: 1432-0630
    Keywords: 36.40 ; 61.1.P ; 68.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Fullerene powder mixtures with different C60/C70 ratios have been analyzed by a variety of techniques, and results have been compared. The fullerence mixtures have been characterized as solutions in n-hexane by high-pressure liquid chromatography (HPLC) and UV-VIS spectroscopy. Thin films of fullerenes on Au(111) have been prepared from the mixtures by sublimation. The sublimation process has been studied by simultaneous thermogravimetric and differential thermal analyses. Thin fullerene films on Au(111) have been investigated by scanning tunneling microscopy (STM). The STM images show primarily two types of ballshaped molecules arranged in a lattice with hexagonal symmetry (fcc(111) face, nearest neighbour distance: 1 nm). The two species differ in diameter. STM images of films made of mixtures of different C60/C70 ratios show that C70 molecules display a larger apparent diameter (0.8 nm) and corrugation than C60 molecules (0.7 nm). The C60/C70 ratios obtained by counting the corresponding molecular species in the STM images of the thin films are compared to the C60/C70 ratios determined by HPLC on hexane solutions of the mixtures. The observed differences might be explained by different rates of sublimation for the two species. The STM images reveal film defects (vacancies and boundaries) and dynamic processes (displacement of C70 molecules and vacancies). In films prepared to have a C60 coverage of less than one monolayer, stable structural units of the C60(111) surface consisting of three or seven C60 molecules are revealed by STM. Occasionally, substructure within individual fullerene molecules is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539474
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  • 3
    Electronic Resource
    Electronic Resource
    Pressure dependence of superconductivity in Ba4C60 (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1703-1708 
    Details
    ISSN: 1573-7357
    Keywords: 74.62.Fj ; 74.70.Wz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In BaxC60 superconductivity (sc) at Tc=(6.8±0.2) K is associated with the x=4 phase. Here we present pressure studies of Tc of a BaxC60 sample (dTc/dp= −1.9 K/GPa) which exhibits a large volume fraction of the x=4 phase. In the alkali-fullerides K60C60 and Rb3C60 Tc is governed by the electronic density of states N(EF) (Tc ∝exp{−1/N(EF)V}). The dependence of N(EF) on volume can be approximated by N(EF)=N0 d eff 3, where deff is the surface to surface distance of neighboured C60-molecules. This relationship is corroborated by (TC,d)-data of various compounds of the form A3−xBxC60 (A: K, Rb; B: K, Rb, Cs; x≤2). Strong deviation from this behavior is found for the alkaline-fulleride superconductor Ba4C60. This deviation is attributed to the hybridization of alkaline-metal s-, d-states and C60 π-states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00753944
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  • 4
    Electronic Resource
    Electronic Resource
    On the structure of the activated iron catalyst for ammonia synthesis (1994)
    Springer
    Topics in catalysis 1 (1994), S. 195-214 
    Details
    ISSN: 1572-9028
    Keywords: ammonia synthesis ; micro structure ; X-ray diffraction ; promoters ; iron ; reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The contribution focuses on a brief account of the activation of iron oxide precursors to ammonia synthesis catalysts and discusses the question as to why “normal iron” is so inferior in catalytic performance compared to “ammonia iron”. The combination of microstructural analysis with kinetic observations allows the conclusion that the microtexture of ammonia iron is with a platelet morphology different from isotropic iron. The role of all additives in the generation of the platelet form is examined. The presence of oxygen, which was speculated to be beneficial for the reaction under certain conditions, was found to be detrimental for the catalytic performance under the present testing conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01492276
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