Silicalite crystal growth investigated by atomic force microscopy

Jonathan R. Agger, Noreen Hanif, Colin S. Cundy, Andrew P. Wade, Sally Dennison, Paul A. Rawlinson, Michael W. Anderson

    Research output: Contribution to journalArticlepeer-review


    Atomic force microscopy has been used to image the various facets of two morphologically distinct samples of silicalite. The smaller (20 μm) sample A crystals show 1 nm high radial growth terraces. The larger (240 μm) sample B crystals show growth terraces 1 to 2 orders of magnitude higher than the terraces on sample A with growth edges parallel to the crystallographic axes. Moreover, the terraces on the (010) face are significantly higher than the terraces on the (100) face - inconsistent with the previously proposed 90° intergrowth structure. Sample A highlights that under certain synthetic conditions, silicalite grows in a manner akin to zeolites Y and A, via the deposition of layers comprising, in the case of silicalite, pentasil chains. It is probable that the rate of terrace advance is identical on the (010) and (100) faces, and it is the rate of terrace nucleation that dictates the overall growth rate of each facet and hence the relative size expressed in the final crystal morphology. Analysis of the growth terraces of sample B and detailed consideration of the structures of both MFI, and a closely related material MEL, lead to the proposal of a generalized growth mechanism for silicalite including the incorporation of defects within the structure. These defects are thought to be responsible for both the relative and the absolute terrace heights observed and may also explain the hourglass phenomenon observed by optical microscopy. The implications of this growth mechanism, supported by results of infrared microscopy, generate a new dimension to the continuing debate on the existence of intergrowths within one of the most important structures relevant to zeolite catalysis.
    Original languageEnglish
    Pages (from-to)830-839
    Number of pages9
    JournalJournal of the American Chemical Society
    Issue number3
    Publication statusPublished - 22 Jan 2003


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