Early stages of MFI film formation

The early stages of MFI (Si-ZSM-5) film formation on a quartz substrate are observed in nanometer scale by a field emission scanning electron microscope, and the crystallization mechanism is discussed. The change in the morphology, the number and the size of particles formed on a substrate surface are carefully studied in the course of the synthesis. Our results indicate that a gel layer, most probably consisting of silica/tetrapropylammonium composites, is formed at first. Then there are two crystallization routes. In one route, spherical composites are formed, enlarged, and aggregated, followed by crystallization. In the other route, the crystallization starts within the gel layer, and the crystals grow out of the gel layer. The effect of the aging process on the crystallization is also studied. (C) 1998 Elsevier Science B.V. All rights reserved.