3.2MATERIAL COATING PROCESSCatalytic converters are used in automobile and industries for pollution abatement. They usually consist of cordierite ceramic e xtruded to form a structure of honeycomb-like cells that extend as channels along the catalytic converter length. A paint-like liquid containing the precious metal catalyst is coated on the channel walls. During operation, e xhaust gases are conveyed with low pressure drop through the catalytic converter. Coating processes for catalytic converters present several challenges that have been tackled in the visual analysis lab. Catalytic converter manufacturers complained that quality control of catalyst coat thicknesses is difficult. In addition the coating liquid often clogs several of the catalytic converter channels. Usually,the monoliths are sprayed with a non-viscous solution containing dissolved catalyst. Sometimes the monoliths are coated by dipping into catalyst enriched slurry and then blowing out the slurry with air. The air clears the channels leaving a layer of deposited slurry solids on the channel walls. A solid coat of catalyst, called the wash coat, is left alter the liquid components dries out. A third method is to suck the slurry through the monoliths by lowering one end of the monolith into catalyst slurry and applying a vacuum at the other end of the monolith. This vacuum coating method has been the focus of our research and is illustrated below.