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  • 1995-1999  (5)
  • 1970-1974  (3)
  • Polymer and Materials Science  (6)
  • Snow bands  (2)
  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192056
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation and properties of composites of kevlar-nomex copolymer and boehmite (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 139-151 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein neuartiges organisch-anorganisches Hybridmaterial wurde durch den Einbau des Minerals Böhmit mittels eines Sol-Gel-Prozesses in ein Kevlar-Nomex-Copolymeres hergestellt. Durch Reaktion eines Gemisches aus m- und p-Phenylendiamin mit Terephthaloylchlorid und anschließender Umsetzung mit Aminophenyltrimethoxysilan wurden Poly(phenylenterephthalamid)-Ketten mit Aminophenyltri-methoxysilan-Endgruppen synthetisiert. In dieser Polymermatrix wurde die Hydrolyse der Alkoxygruppen einer Lösung von Aluminium-sec-butanolat in Butanol durchgeführt. Dadurch wurde ein chemisch an die Aramid-Ketten gebundenes anorganisches Netzwerk aufgebaut. Aus den hergestellten Hybridmaterialien mit unterschiedlichen Böhmit-Gehalten in der Aramidmatrix wurden Filme gegossen. Die Filme aus Hybridmaterial mit bis zu 15 Gew.-% Böhmit waren transparent gelb, während bei 20 und mehr Gew.-% Böhmit opake Filme erhalten wurden. Die mechanischen Eigenschaften dieser Filme wurden untersucht. Zugfestigkeit, Zugmodul, Härte und maximale Bruchdehnung nahmen mit steigendem Böhmitgehalt zunächst zu, vemngerten sich jedoch bei weiterer Erhöhung des Mineralanteils wieder. Der Zugmodul des Hybridmaterials bei 25°C lag zwischen 3,0 und 4,5 GPa. Die Materialien hielten einer maximalen Zugspannung von 252 MPa stand und zeigten Zersetzungstemperaturen von etwa 450°C. Die rnit DMTA ermittelten Werte für den Speichemodul lagen im Bereich 7,6-18,9 GPa. Das tan δ-Signal verbreiterte sich mit zunehmendem Böhmitanteil und ging bei hohen Böhmitgehalten in eine Schulter über. Die Signalpositionen des Verlustfaktors wurden infolge der zunehmenden sterischen Einschränkung der Segmentbewegungen rnit steigendem anorganischen Anteil zu höheren Temperaturen verschoben.
    Notes: A new organic-inorganic hybrid material was prepared by incorporating boehmite into a Kevlar-Nomex copolymer via a sol-gel process. Poly(phenylene-terephthalamide) chains having aminophenyltrimethoxysilane end groups were prepared by reacting a mixture of m-and p-phenylenediamine with terephthaloyl chloride, followed by end-capping with aminophenyltrimethoxysilane. The hydrolysis of the alkoxy groups of an aluminium sec-butoxide solution in butanol was carried out in the polymer matrix, thus creating an inorganic network structure combined chemically with the aramid chains. Hybrid materials containing different proportions of boehmite in aramid were thus produced and films were cast by solvent evaporation technique. These films with up to 15 wt.-% of boehmite were yellow and transparent, whereas the films with 20 wt.-% or more contents of boehmite were opaque. Mechanical properties of these films were analyzed. The values of tensile strength, initial modulus, toughness and maximum strain at rupture were initially found to increase and then decrease with further addition of boehmite. The tensile modulus of the hybrid material was found to be in the range of 3.0-4.5 GPa at 25°C. These ceramers were found to withstand maximum tensile stress of the order of 252 MPa, and the thermal decomposition temperature was around 450°C. The storage modulus as measured using DMTA was in the range of 7.6-18.9 GPa. The tan δ peak which in general became broader with increasing boehmite content showed a shoulder for composites containing large amounts of boehmite. The position of the peaks shifted towards high temperature with the increase in the inorganic contents showing hindrance in motion with increasing boehmite contents.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052480109
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  • 3
    Electronic Resource
    Electronic Resource
    Morphological instabilities in pattern formation by precipitation and crystallization processes (1996)
    Springer
    Geologische Rundschau 85 (1996), S. 19-28 
    Details
    ISSN: 0016-7835
    Keywords: Key words Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192056
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The columnar growth angle in obliquely evaporated Thin filmsHerrn Professor Karl Heinz Kloos aus Anlaß seines 65. Geburtstages zugeeignet (1995)
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 26 (1995), S. 22-26 
    Details
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Die Orientierung der Säulen in der Mikrostruktur schräg aufgedampfter dünner SchichtenSchräg aufgedampfte dünne Schichten entwickeln gewöhnlich eine Mikrostruktur aus Sälen, deren Wachstumswinkel relativ zur Substratnormalen, β, nicht mit dem Einfallswinkel α übereinstimmt. Hier wird gezeigt, daß der funktionale Zusammenhang β(α) durch die Gleichung tan β=tan α + ρ-1(dρ/δα) in universeller Weise mit der Winkelabhängigkeit der Schichtdichte ρ verknüpft ist. Ein Vergleich mit numerischen Daten aus Simulationen der ballistischen Abscheidung von Scheiben und Kugeln bestätigt die Theorie.
    Notes: Vapor-deposited thin films grown under conditions of oblique incidence commonly develop a microstructure of columns, inclined at an angle β relative to the substrate normal, which differs from the angle of incidence α. Here it is shown that the functional relation β(α) is universally linked to the dependence of the film density ρ on the angle of incidence, through the equation tan β=tan α + ρ-1(dρ/dα). The theory is supported by an analysis of published numerical data obtained from simulations of ballistic deposition of disks and spheres.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mawe.19950260107
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  • 5
    Electronic Resource
    Electronic Resource
    Lokaler Korrosionsangriff unter Wasserstoffblasen, die an der Oberfläche von Zink haften (1971)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 22 (1971), S. 309-311 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Pitting corrosion under hydrogen bubbles, adherent to the surface of zincInvestigation zinc alloys in acid solutions, it could be determined that under hydrogen bubbles which has adhered on the surface, annuker pitting corrosion took place. The types of corrosion attack were examined under a microscope during and after the corrosion test and in some cases under scanning electron microscope. The formation of the annular pittings can be interpreted as an impoverishment of hydrogen ions in the boundary layer between the hydrogen bubble and the surface of the specimen.
    Notes: Bei Korrosionsuntersuchungen an Zinklegierungen im sauren Korrosionsmedium konnte festgestellt werden, daß an Stellen anhaftender Wasserstoffblasen auf der Probenoberfläche ringförmiger Lochfraß entsteht. Diese Korrosionserscheinungen wurden während und nach dem Korrosionsversuch mit dem Lichtmikroskop und dem Rasterelektronenmikroskop untersucht. Das Entstehen dieser ringförmigen Lochfraßnarben kann durch die Verarmung von Wasserstoffionen in der Grenzschicht zwischen Wasserstoffblase und Probenoberfläche erklärt werden.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19710220407
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  • 6
    Electronic Resource
    Electronic Resource
    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
    Keywords: nanocomposites ; sol-gel ; heteropolymetallates ; photochromics ; holographic data storage ; amplitude grating ; two-wave-mixing recording ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: 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.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 7
    Electronic Resource
    Electronic Resource
    Thermomechanical behavior of a systematic series of poly(L-alpha-alkylamino acids) in dry and moist nitrogen (1973)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 17 (1973), S. 2089-2096 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The solid-state thermomechanical behavior of polyglycine, poly-L-alanine, poly-L-valine, and poly-L-leucine was investigated throughout the temperature range -180° to 500°C in dry and moist nitrogen atmospheres at about 1 cps using torsional braid analysis. Transitions of the dry polymers and complexities introduced by the presence of water were investigated by temperature cycling.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1973.070170710
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  • 8
    Electronic Resource
    Electronic Resource
    Die Beeinflussung der Korrosion von Zink durch Metalle, die im Korrosionsmedium als Kationen enthalten sind (1971)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 22 (1971), S. 125-134 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Influence on zinc corrosion by metals being present as cations in the corrosive mediumAddition of cations of nobler metals may accelerate or inhibit corrosion of zinc in acid media, depending on the hydrogen overvoltage of the metal deposits being formed. In the case of low hydrogen overvoltage corrosion is accelerated. This accelerating effect decreases in the following order: As-III, Sb-III, Ni-II, Cu-II, Co-II, Fe-II, Cd-II, Ga-III, In-III, Pb-II, Tl-I and Hg-II. This fact also goes to show that Pb contents in the zinc or preliminary amalgamation reduce the influecne of the deposits. On the other hand, Cd contents in zinc have a negligible effect and Fe contents tend to surprisingly accelerate corrosion.
    Notes: Zusatz von Kationen edlerer, Metalle kann die Korrosion von Zn in sauren Medien beschleunigen oder hemmen, je nachdem, ob die entstehenden Metallniederschläge niedrige bzw. hohe Wasserstoffüberspannung aufweisen: im ersten Falle wird die Korrosion beschleunigt. Die korrosionsfördernde Wirkung nimmt dabei in der folgenden Reihe ab: As-III, Sb-III, Ni-II, Cu-II, Co-II, Fe-II, Cd-II, Ga-III, In-III, Pb-II, Tl-I und Hg-II. Daraus ist auch zu erklären, daß Pb-Gehalte im Zn sowie vorheriges Amalgamieren den Einfluß der Niederschläge verringern. Cd-Gehalte im Zn wirken sich hingegen kaum aus und Fe führt überraschend zu starker Zunahme der Korrosion.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19710220204
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