In situ dynamic light scattering and synchrotron, X-ray powder diffraction study of the early stages of zeolite growth

The synthesis of zeolite LTA from a clear solution of nominal composition 8.6Na(2)O-0.18Al(2)O(3)-SiO2-150H(2)O was investigated using a combination of techniques (Dynamic Light Scattering, DLS, and X-ray Powder Diffraction, XRPD, in situ experiments performed at the BM8 beam line of the ESRF facility in Grenoble, France) to obtain information on the early stages of the nucleation process. The experiments were performed at temperatures ranging between 60 and 100 degreesC. The DLS data clearly show at all temperatures the rapid development of an amorphous phase which consistently precedes the appearance of the LTA crystals. The observation of the amorphous precursor, the delayed formation of the crystalline zeolite, and the analysis of the kinetic parameters of the process indicate that the nucleation process of zeolite LTA from clear solution is heterogeneous and occurs at the interface between the solution and the amorphous precursor.