THE HYDROTHERMAL SYNTHESIS OF SILICALITE - AN IN-SITU SMALL-ANGLE NEUTRON-SCATTERING STUDY

Small-angle neutron scattering has been used to study in situ the gel transformations occurring in the amorphous zeolite reaction mixture during the so-called induction period and subsequent crystallization. The synthesis of silicalite was studied at various temperatures (130, 150, 170, 190-degrees-C). The size of the primary units in the precursor reaction mixture is approximately 45 angstrom. These units grow during the synthesis. The largest particle sizes were obtained at the lowest temperatures owing to the smaller nucleation rate. Before crystallization can occur, a reorganization of the gel phase occurs. During the induction period as well as during the crystallization the gel units have a surface fractal structure. It is concluded that crystallization starts in or on the growing amorphous gel particles.