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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial & engineering chemistry research 30 (1991), S. 2152-2159 
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2143-2150 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model to investigate a gel-to-zeolite transformation as a possible growth mechanism through association and rearrangements of extended precursor structures is developed and solved via continuum time lattice Monte Carlo simulations. The model is used to study the morphology of zeolite L nanocrystals grown from an initial amorphous microporous precursor gel. The model considers gel dissolution to release growth precursor extended structures, precursor migration, precursor–precursor association, precursor incorporation into zeolite nanoparticles, and zeolite dissolution. It is shown that the gel-to-zeolite transformation can occur when dissolved precursor migration is slow compared to precursor incorporation and zeolite dissolution. Under these conditions, the initial gel microstructure (intraparticle porosity) has a significant effect on the zeolite morphology and on the crystallization kinetics. This transformation proceeds in two stages: A zeolitic framework forms initially without long-range order, followed by slow rearrangement of building units into nanocrystalline particles with possible defects. Finally different growth modes are identified as a function of microkinetic parameters and gel morphology. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Chemistry of materials 7 (1995), S. 1734-1741 
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Zeolites and related crystalline microporous oxides—tetrahedrally coordinated atoms covalently linked into a porous framework—are of interest for applications ranging from catalysis to adsorption and ion-exchange. In some of these materials (such as zeolite rho) adsorbates, ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 3020-3029 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An oriented submicron silicalite membrane has been prepared by growing a layer of oriented silicalite crystals on a composite precursor nanocrystalline silicalite/alumina film using controlled secondary growth. The orientation of the crystals at the surface was such that both straight and sinusoidal channel networks run nearly parallel to the membrane surface. The membrane exhibits ideal selectivities for H2 over N2 as high as 60 at 150°C and O2 over N2 as high as 3.6 at 185°C. H2, N2 and O2 permeances are 2.13, 0.05 and 0.17 cm3(STP)/(cm2·min·atm) at 185°C, respectively, and the corresponding apparent activation energies are 11, 26 and 32 kJ/mol. The permeation characteristics are attributed to the preferred orientation of the molecular sieving layer.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 847-856 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Silica and alumina layers deposited onto the walls of porous Vycor tubes by chloride hydrolysis in an opposing reactants geometry have been characterized by scanning electron microscopy and electron microprobe analysis. The layers are asymmetric, having a long tail toward the side of the chloride flow and a sharp boundary at the other side. The deposit thickness is several tenths of microns, while the totally plugged region is of order of 1 micron.A model has been developed describing reaction, diffusion and evolution of the porous structure in the Vycor substrate due to the accumulation of the solid product. The deposition reaction is described by transient kinetics in terms if the concentrations of silanol and chloride groups in the product layer, as well as the concentrations of the gaseous reactants. The model is capable of generating deposit profiles in good agreement with those measured by electron microprobe analysis.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1849-1860 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model developed for SiO2 deposition in porous Vycor glass using SiCl4 hydrolysis describes reaction, diffusion and evolution of the pore structure due to accumulation of the solid product. The deposition reaction is described by transient heterogeneous kinetics in terms of the concentrations of silanol and chloride groups in the product layer as well as those of the gaseous reactants. For typical deposition conditions the pseudo steady-state approximation for surface species could lead to erroneous predictions. Pore structure evolution is modeled by incorporating results of percolation theory. For this purpose the porous glass is represented by a Bethe lattice with coordination number 3 and alternatively by a decorated Bethe lattice in which each bond is replaced by a composite bond consisting of two bonds in series. The second network can capture the effect of pore radius variation along a single pore. For the decorated lattice, pore connectivity interruption at a higher void fraction leads to thinner deposits and shorter deposition times for pore plugging compared to the corresponding ones for the simple lattice.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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