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  • Self organization  (2)
  • electron microscopy  (2)
  • sol-gel  (2)
  • 1
    Digitale Medien
    Digitale Medien
    Morphological instabilities in pattern formation by precipitation and crystallization processes (1996)
    Springer
    International journal of earth sciences 85 (1996), S. 19-28 
    Details
    ISSN: 1437-3262
    Schlagwort(e): Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00192056
    Standort Signatur Erwartet Verfügbarkeit
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    Artikel (Nationallizenzen)
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  • 2
    Digitale Medien
    Digitale Medien
    Characterization of Electrochromic WO3-Layers Prepared by Sol-Gel Nanotechnology (1998)
    Springer
    Journal of sol gel science and technology 13 (1998), S. 673-678 
    Details
    ISSN: 1573-4846
    Schlagwort(e): electrochromism ; sol-gel ; tungsten oxide ; peroxotungstic acid ; nanocrystalline
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Stable tungsten oxide coating sols suitable for electrochromic applications were prepared by a modified peroxotungstic acid route. Layers up to 250 nm thickness could be deposited on ITO-coated and/or FTO-coated glass substrates in a single dip-coating process. Optoelectrochemical measurements were employed to determine the variation of the electrochromic properties (change in optical density (ΔOD) and switching times) of WO3-layers, investigated as a function of coating parameters, such as chamber humidity and the temperature of heat treatment. High resolution transmission electron microscopy (HR-TEM) has shown that the optimized layers possess a partially crystalline morphology with nanocrystalline regions 2–3 nm in size.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008684720378
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Mechanical Properties of Copolymers from Methacrylate Functionalized Silanes and Bifunctional Methacrylate Monomers (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 625-627 
    Details
    ISSN: 1573-4846
    Schlagwort(e): composite materials ; sol-gel-process ; methacrylate copolymers ; dynamic-mechanical-analysis ; electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Sol gel derived composite materials were prepared from methacryloxypropyltrimethoxysilane (MPTS) and tetraethyleneoxidedimethacrylate (TEGDMA). The amount of MPTS in the composites was varied from 0 to 50 mole%. MPTS was prehydrolyzed at room temperature with 0,1 mole/l HCl/H2O. After complete removal of solvent calculated amounts of TEGDMA were added to the reaction mixture of the prehydrolyzed MPTS. Thermically initiated free radical copolymerization of the methacrylate endgroups was performed in the resulting mixture under nitrogen atmosphere using azobisisobutyronitril (AIBN) as initiator. The composites were investigated by high resolution transmission electronmicroscopy in order to investigate the morphology. The thermomechanical properties as storage, loss modulus, tan δ as well as the glass transition temperature (T g ) of the composites were estimated by dynamic mechanical thermal analysis (DMTA).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018364024805
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Mechanical properties of copolymers from methacrylate functionalized silanes and bifunctional methacrylate monomers (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 625-627 
    Details
    ISSN: 1573-4846
    Schlagwort(e): composite materials ; sol-gel-process ; methacrylate copolymers ; dynamic-mechanical-analysis ; electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Sol gel derived composite materials were prepared from methacryloxypropyltrimethoxysilane (MPTS) and tetraethyleneoxidedimethacrylate (TEGDMA). The amount of MPTS in the composites was varied from 0 to 50 mole%. MPTS was prehydrolyzed at room temperature with 0,1 mole/l HCl/H2O. After complete removal of solvent calculated amounts of TEGDMA were added to the reaction mixture of the prehydrolyzed MPTS. Thermically initiated free radical copolymerization of the methacrylate endgroups was performed in the resulting mixture under nitrogen atmosphere using azobisisobutyronitril (AIBN) as initiator. The composites were investigated by high resolution transmission electronmicroscopy in order to investigate the morphology. The thermomechanical properties as storage, loss modulus, tan-as well as the glass transition temperature (T g ) of the composites were estimated by dynamic mechanical thermal analysis (DMTA).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02436912
    Standort Signatur Erwartet Verfügbarkeit
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    Artikel (Nationallizenzen)
    Volltext
  • 5
    Digitale Medien
    Digitale Medien
    Morphological instabilities in pattern formation by precipitation and crystallization processes (1996)
    Springer
    Geologische Rundschau 85 (1996), S. 19-28 
    Details
    ISSN: 0016-7835
    Schlagwort(e): Key words Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00192056
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 6
    Digitale Medien
    Digitale Medien
    Photochromic Organic-Inorganic Nanocomposites as Holographic Storage Media (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 7 (1997), S. 123-133 
    Details
    ISSN: 1057-9257
    Schlagwort(e): nanocomposites ; sol-gel ; heteropolymetallates ; photochromics ; holographic data storage ; amplitude grating ; two-wave-mixing recording ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: This paper describes the properties of some new organic-inorganic photochromic layers. They are based on a hybrid organic-inorganic matrix in which tungsten heteropolyoxometallates (SiW12O4-40, PW12O3-40) are entrapped in a network obtained from the reaction of 3-glycidoxy-propyltrimethoxysilane. The high homogeneity of these materials on the nanoscale leads to transparent monoliths and layers of controlled thicknesses up to 40 μm. The optical properties of the blend are emphasised and the construction of amplitude gratings in the materials by two-wave-mixing experiments is described. The results of the optical experiments and the comparison with the theoretical background are used as a model for photochromic holographic storage processes. © 1997 John Wiley & Sons, Ltd.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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    Artikel (Nationallizenzen)
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