PREPARATION OF ANCHORED CERAMIC COATINGS ON METAL SUBSTRATES - A MODIFIED SOL-GEL TECHNIQUE USING COLLOIDAL SILICA SOL

A single-step dip-coating technique was developed to produce stable fi lms or washcoats of controlled thickness, surface area and pore-size d istribution on alumina whisker-covered metal substrates (both flat pla tes and monoliths). Dip-coating slurries were prepared by dispersing f ine porous powder in a colloidal silica sol. The method provided contr ol over coating thickness and coating properties, such as pore-size di stribution and surface area. The coating thickness could be varied bet ween approximately 2 and 40 mu m by selecting slurry composition and w ithdrawal speed in the dipping procedure. The pore-size distribution a nd surface area could be varied by changing type and amount of porous filler material in the dipping slurry. Uniform and bimodal pore-size d istributions were obtained using silica and ZSM-5 molecular sieves, re spectively, yielding coatings with surface areas between 60 and 400 m( 2) g(-1).