Kinetics of nucleation and growth of zeolite LTA from clear solution by in situ and ex situ XRPD

Investigations on the nucleation and growth processes of Linde type A zeolite (LTA) from clear solution were performed (1) in situ using synchrotron X-ray powder diffraction (XRPD) on small volume samples contained in capillaries. and (2) ex situ using laboratory XRPD on samples synthesized from large volume vessels. Isothermal experiments were performed in the temperature range 60-90 degreesC. The well known LTA system was selected in order to define the nucleation and growth mechanisms and kinetic parameters, and to critically compare the results of the kinetic analysis obtained by two rather different methods of investigation, The kinetic modeling of the in situ and ex situ isothermal diffraction data indicate that (1) the nucleation mechanisms are the same whether occurring in small-volume or large-volume syntheses; and (2) despite earlier claims of homogeneous nucleation mechanisms, the nucleation process is heterogeneous and invariably involves the formation of an amorphous precursor. All syntheses products associated with zeolite LTA (that is faujasite and hydroxylsodalite type zeolites) have been characterized by XRPD and scanning electron microscopy analyses. (C) 2002 Elsevier Science Inc. All rights reserved.