Application of electrophoretic deposition for inner surface coating of porous ceramic tubes

The direct coating of a nano-porous alumina layer on the inner surface of micro-porous alumina tubes was performed by electrophoretic deposition (EPD). A thin layer of polypyrrole (Ppy) was synthesized on the inside wall of the porous tubes by the chemical polymerization of pyrrole (Py) to give the wall electric conduction for the EPD electrode. The bimodal suspension of alumina powders with 0.6 μm and 30 nm average particle sizes was selected to control the nano-porous structure. The thickness of the coating layer was controlled by altering the applied voltage and deposition time. The interfacial connection of the coated layer and the substrate was observed by SEM before and after sintering. The pore size of the coated layer was characterized by its pore size distribution.