日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

We examined the crystalline and microstructures of zeolite beta crystals synthesised without an OSDA using transmission electron microscope (TEM). The HRTEM images obtained allow the associated ring and channel structures to be identified individually and suggest a random stacking of BEA and BEB building units during crystal growth along ‹001› direction. Different layer stackings of various thicknesses can be readily distinguished. The number of contiguous BEB and BEA lamellae can thus be counted directly based on the switch in orientation of these multi-membered ring layers. Using this direct method for a number of micrographs, the ratio of BEA : BEB lamellae was calculated to be 45 : 55. Further, the distribution of number of contiguous BEB and BEA lamellae measured from TEM micrographs is in agreement with distribution theoretically calculated under assumed to be completely random. In other words, the multilayer structure is formed by a simple stochastic process when no OSDA is used. That is, the results suggest that the crystal is grown while maintaining the state where the free energy is minimized (chemical equilibrium state). In this article, we also suggest a hypothesis of the crystal growth mechanism of the SDA-free beta type zeolite based on this result.