COATING OF SOL PARTICLES FOR MEMBRANE APPLICATIONS

For improving chemical and thermal stability of gamma-Al2O3 membranes boehmite (AlOOH) sol-particles are coated with Zr4+-species with two t echniques. These techniques are heterogeneous precipitation (HP-method ) and ''surface-reaction-foIlowed-by-polycondensation'' (SRPC-method). A continuous coating layer is formed at relative low Zr4+-concentrati on, about one monolayer coverage of boehmite particles, and with the H P-method. For larger concentrations and for the SRPC-method small part icles (order 1 nm) of Zr4+-species are formed on the surface of the bo ehmite particles. After drying and calcination up to 1000 degrees C no continuous layer of a zirconia phase could be detected for all sample s. However the thermal stability of the porous structure is improved. Phase transitions of alumina occur at temperatures of 1100 degrees C a nd the porous structure of the membrane material is then destabilized.