Honeycomb catalyst coating with alumina slurries: The vacuum method

During the flow of fluid on a porous surface particulate materials in the fluid are deposited on the surface. This deposition phenomenon governs the application of several different types of coatings including paint coatings on houses. Ceramic honeycomb catalytic converters for automobiles and industry are sometimes made by catalyst coating processes that utilize such deposition. The inactive ceramic honeycombs are coated by drawing a catalyst liquid through the honeycomb. During the flow the liquid leaves a film of catalyst on the walls. One of the coating methods, the vacuum method, was the focus of this study.; Typically the coat forms a circular cross-section within the square honeycomb channels. Surface active materials were used to minimize the formation of circular cross-section coatings. A second problem is that during the coating process several of the honeycomb channels get clogged by the catalyst liquid, lowering catalytic converter quality. In this study, the flow of catalyst liquid in honeycomb channels was simulated by liquid flowing in both non-porous glass and porous cordierite ceramic tubes. The flow of was investigated visually using a video-camera set-up. Observations of the effects of liquid physical properties and the flow conditions were made. Wave instabilities formed in the catalyst film were found to be the source of the clogging.