LAUSR

Abstract Faujasite (FAU) zeolite membranes were prepared by seed growth method. The polycrystalline zeolite membrane became less porous with the growth of zeolite crystals. The microstructure of the membrane was characterized by SEM and TEM after several rates of crystal growth. In addition, Si/Al ratio was analysed by TEM-EDS. Meso-voids existed in the zeolite membrane after 1-h synthesis, and hexagonal shaped FAU crystals were easily distinguished. Twin relations were quite often observed for the connection between FAU crystals, while they were seldom found in the seed crystals. On the other hand, crystals lost hexagonal shape with further synthesis time. Moreover, the density of twin relations became less. While voids could hardly being observed by SEM in the zeolite membrane, there existed intercrystalline boundaries formed by two crystals of different orientation. Microstructures of these boundaries were directly observed by HREM. Si/Al ratio of the zeolite membrane was close to 1, which is smaller than that of seed crystals (Si/Al = 2.5). Step growth at the twin boundary was firstly observed. This growth process is assumed to be the key growth mechanism in densification of the polycrystalline zeolite membrane. Finally, densification process of zeolite membrane is proposed based on the microscopic analysis.