Colloidal zeolites :from nucleation to zoned films by seeded growth
Abstract (Summary)The work presented in this thesis concerns the investigation of nucleation kinetics for colloidal zeolites, especially the determination of the nucleation period during crystallization. It also concerns the use of colloidal TPA-silicalite-1 for the preparation of zoned MFI films. A novel method, a two-stage varying-temperature procedure, involving starting a crystallization at a certain temperature, and then rapidly changing temperature at some point during the crystallization, was developed for the investigation of nucleation kinetics of colloidal zeolites. As the duration of the crystallization at the initial temperature was extended, the ultimate crystal size and crystal concentration varied until they were approximately equal to those obtained for a complete synthesis at the initial temperature. At this point, the nucleation stage during the crystallization was completed. For the synthesis of colloidal TPA-silicalite- 1, the nucleation process occurred over a substantial period of time, extending over the induction period, but was completed before crystal growth was detected, independent of aging time and silica source. For the synthesis of colloidal zeolite Y, the nucleation and crystal growth processes occurred simultaneously and the nucleation period was significantly longer than the induction period. The two-stage varying-temperature synthesis procedure was used to synthesize particularly small colloidal crystals of TPA-silicalite-1 with a high yield for short synthesis time. In addition, midsynthesis addition of sodium after the nucleation of zeolite Y produced pure colloidal zeolite Y with slightly larger crystals (less than 110 nm) and a high yield. Colloidal TPA-silicalite-1 crystals with a size of 60 nm were used as seeds to prepare different types of zoned MFI films on various substrates by a two- step crystallization method. In the first step a type of MFI film was synthesized on the seeded substrate by hydrothermal treatment. In the second step crystallization of another type of MFI film was achieved by further hydrothermal treatment. The structural configuration of the films was characterized by SEM, EDS, XRD and TEM techniques. The channel continuity at the interface between two different layers depended on both the composition and synthesis conditions used and the order of the layers in the film.
School:Luleå tekniska universitet
Source Type:Doctoral Dissertation
Date of Publication:01/01/2002