INFLUENCE OF SOLID-STATE TRANSFORMATION TIME ON THE NUCLEATION AND GROWTH OF SILICALITE-1 PREPARED FROM LAYERED SILICATE

The nucleation and crystal growth of silicalite 1 precursors synthesiz ed by solid-state transformation were studied using X-ray diffraction, thermal analysis, IR spectroscopy, Si-29 and C-13 NMR and electron mi croscopy. Silicalite 1 was obtained after 16 h at 130 degrees C in a c losed glass ampoule. Comparison with hydrothermal synthesis showed tha t the characterization of the precursors presents some similarities, h owever, nucleation and crystal growth were much shorter for solid-stat e transformation. Si-29 NMR showed that nucleation started during the first stage (cation exchange) for solid-state transformation, but only during the second stage for solid-state transformation. It was also o bserved that the major changes occurred during the beginning of crysta l growth for solid-state transformation but during nucleation for hydr othermal synthesis. The results were explained by the fact that the st arting materials were completely different: single layered silicate fo r solid-state transformation and colloidal silica for hydrothermal syn thesis.