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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 259-264 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bipolar membranes consist of a layered ion-exchange structure composed of a cation selective membrane joined to an anion selective membrane. They are analogous to semiconductor p-n devices as both of them present current-voltage curves exhibiting similar rectification properties. In this article, we present some current-voltage curves obtained for different bipolar membranes at several temperatures. The results can be interpreted in terms of a simple model for ion transport and field-enhanced water dissociation previously developed. The mechanism responsible for water splitting is assumed to be a catalytic proton transfer reaction between the charged groups and the water at the membrane interface. The effects of temperature are taken into account by introducing an Arrhenius-type relationship for the dependence of the forward rate constant of the reaction on temperature. Finally, comparison between theory and experiments provides reasonable values for the parameters introduced in the theoretical model. The analysis aims at developing a better physical understanding of a process in which chemical reactions and transport phenomena are coupled in such a way that the potential technological applications depend strongly on this coupling.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 76 (1972), S. 238-242 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Trends in Biotechnology 3 (1985), S. 112-118 
    ISSN: 0167-7799
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Inorganica Chimica Acta 202 (1992), S. 119 
    ISSN: 0020-1693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 246 (1971), S. 669-678 
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Summary The formation mechanism of asymmetric cellulose acetate membranes, which are suited for reverse osmosis desalination, is studied. The main parameters in the membrane preparation technique, i.e., the casting solution composition, the wash bath temperature, and the annealing time and temperature, are discussed and rationalized. The actual membrane formation is interpreted as precipitation of the polymer from a multicomponent system which is only partially miscible. The observed asymmetric membrane structure is related to the kinetics of precipitation from supersaturated solutions. The phase diagram of the system cellulose acetate-acetone-formamide-water is presented. Membranes are made according to a recipe given in the literature. Their transport properties are determined in filtration tests with a 1% sodium chloride solution at an applied hydrostatic pressure of 100 atm. X-ray diffraction and electron microscopy are used to study their structures.
    Notes: Zusammenfassung Der Bildungsmechanismus von asymmetrischen Zelluloseazetatmembranen, die zur Wasserentsalzung nach dem Prinzip der umgekehrten Osmose geeignet sind, wird untersucht. Die wichtigsten Herstellungsparameter wie Zusammensetzung der Membranlösung, Fällungstemperatur, Anlaßzeit- und Anlaßtemperatur werden diskutiert und interpretiert. Es wird davon ausgegangen, daß die eigentliche Bildung der Membran auf einer Fällungsreaktion aus einem Mehrkomponentensystem mit Mischungslücke beruht und die asymmetrische Struktur auf die Kinetik der Fällung aus einer stark übersättigten Lösung zurückzuführen ist. Hierzu wird das Mischungsdiagramm des Systems Zelluloseazetat-Aceton-Formamid-Wasser aufgenommen. Die Membranen werden nach Literaturvorschrift hergestellt, ihre Transporteigenschaften in Filtrationsversuchen mit einer l-gew.%igen NaCl-Lösung bei 100 atm hydrostatischem Druck bestimmt und ihre Struktur röntgenologisch und elektronenmikroskopisch untersucht.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 1405-1421 
    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 alcohol permeability and permselectivity properties as well as the morphology of membranes made of a newly developed AB-cross-linked copolymer system composed of elastomeric and glassy components were investigated. The copolymer was synthesized by a hydrosilylation reaction between poly(styrene-stat-isoprenes) (Mn from 40,000 to 100,000 g/mol) with high content in unsaturated side groups (≈ 60% of entire isoprene content) and polyhydrogen polysiloxanes with varying SiH content (0.75 10.7 mol %) and molecular mass, Mn, from 2,500 to 36,000 g/mol. A two-track approach was taken to determine the morphology of the copolymer system. The first employed the usual polymer characterization methods such as electron microscopy, DSC, IR spectroscopy, the density gradient method, and mechanical measurements. For the second approach, different copolymer permeability models were tested so as to give an insight into the copolymer morphology. As a final step, the permeability and permselectivity properties were correlated with the morphological structure of the copolymer system. It was observed that the respective continuous microphase dominated the copolymer's physical properties, as, e.g., permeability, permselectivity, and mechanical properties. The microphase inversion in the copolymer system was proved by the permeability/permselectivity as well as by the mechanical measurements. © 1993 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 15 (1971), S. 811-828 
    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: An attempt has been made to rationalize the variables in the preparation procedure of Loeb-Sourirajan-type reverse-osmosis membranes. The quaternary phase diagram of the system cellulose acetate-acetone-formamide-water was determined and has proved a useful tool in the discussion of membrane structures and properties. A mechanism based on differences in the precipitation rate of the polymer during the membrane formation process has been suggested to explain the observed asymmetry in the membrane structure. The porosity of the membrane has been ascribed to the relative rates of water entering and solvent leaving the cast film. The effects of the casting solution composition, the evaporation time, the wash bath temperature, and the annealing procedure have been studied. X-Ray diffraction and electron microscopy were used to supplement flux and retention data of membranes made from a cellulose acetate-formamide-acetone casting solution.
    Additional Material: 14 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 14 (1970), S. 1197-1214 
    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: Batch and flow recirculation cells were used to study the properties of high-flux ultrafiltration membranes with different macromolecular solutions. At low pressures, solutions of completely retained macromolecular solutes have a flux which is approximately the same as the flux of pure solvent. At higher pressures, the solution flux levels off. The flux, at the leveling-off period, is approximately inversely proportional to the solution concentration. In this plateau region the flux increases with temperature and agitation of the solution but decreases with time. These results are explained by the formation of a gel layer on the membrane surface during the filtration of macromolecular solutions. In ultrafiltration, in contrast to dialysis and GPC, a linear polymer penetrates the selective barrier more readily than does a globular protein of the same molecular weight. The difference may arise from the liquid shear stresses within the barrier medium due to the movement of fluid relative to the pore walls, which is large only in ultrafiltration. Also, retention of polymers was found to decrease with pressure and to increase with agitation of the solution.
    Additional Material: 13 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 40 (1974), S. 391-404 
    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: The key to a successful application of the ‘membrane filtration technique&’ is the development of synthetic polymer membranes with the particular transport properties suited to a specific separation problem, i.e. a membrane which rejects molecules of a certain size or chemical nature while being permeable to others. Recent progress in polymer chemistry has led to development of tailor made membranes with high filtration rates and high specific separation characteristics and which also show good chemical, mechanical and thermal stability. These membranes generally are of asymmetric structure and are prepared by a phase inversion process. This membrane preparation technique is described and the main process parameters with their effect on the membrane separation characteristics are discussed in detail.
    Notes: Für die erfolgreiche Anwendung der Membranfiltrationstechnik ist die Entwicklung von Membranen aus synthetischen Polymeren erforderlich, die für ein spezifisches Trennproblem geeignet sind, d. h. man benötigt Membranen, die Moleküle einer bestimmten Größe oder bestimmten chemischen Art zurückhalten, für die anderen aber durchlässig sind. Neuere Fortschritte auf diesem Gebiet führten zu Membranen mit hoher Filtrationsgeschwindigkeit und guter chemischer, mechanischer und thermischer Stabilität. Diese Membranen besitzen generell eine asymmetrische Struktur und werden durch einen Phasenumkehrprozeß erzeugt. Die Herstellungstechnik wird beschrieben und die wichtigsten Prozeßparameter werden in bezug auf ihren Einfluß auf die Membran diskutiert.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 73 (1978), S. 1-23 
    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: It is possible to make asymmetric reverse osmosis membranes from aromatic polyamides and polyamidhydrazides. Polyamide-membranes demonstrate better than 99% NaCl rejection during pressure filtration at 100 bar, while polyamidhydrazide-membranes under the same conditions demonstrate quantitative retention of MgSO4 but only 90 to 98% for NaCl. The preparation and properties of these membranes are described.
    Notes: Aus aromatischen Polyamiden und Polyamid-Hydraziden lassen sich asymmetrische Umkehrosmose-Membranen herstellen. Polyamid-Membranen weisen bei Druckfitration bei 100 bar Kochsalz zu mehr als 99% zurück, während Polyamid-Hydrazid Membranen unter gleichen Bedingungen, bei quantitativem Rückhaltevermögen für MgSO4, Kochsalz nur zu 90 bis 98% zurückweisen. Herstellung und Eigenschaften dieser Membranen werden beschrieben.
    Additional Material: 2 Ill.
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