SAXS/WAXS study on the formation of precursors and crystallization of silicalite

The formation of colloidal aggregates which can act as precursors in zeolite crystn. was studied using small-angle scattering of x-rays (SAXS). In the same expt. the onset of crystn. and the increase of crystallinity were measured using wide-angle scattering of x-rays (WAXS). To perform in situ time-resolved combined SAXS/WAXS measurements high brilliance synchrotron radiation was applied. The influence of SiO2, template, and OH- concns. on the synthesis of silicalite (MFI structure) from a clear soln. was studied. The alky. of the synthesis mixt. appeared to be decisive for the formation of colloidal aggregates. At relatively low alky. colloidal aggregates were formed prior to the onset of the crystn. At higher alkalinities no colloidal aggregates could be obsd. at any time during the synthesis, suggesting that nucleation and crystal growth occurred directly from the sol