Nanocrystalline Coating by Electrophoretic Deposition (EPD)

摘要

Alumina coatings using sub-micron and nanosized powders on steel substrates have been produced using electrophoretic deopistion (EPD). The sub-micron powder (d_(v50) 200nm) gave coherent and cohesive films whereas the nanosized powder gave films with macroscopic defects. Large cracks due to capillary forces during the drying step were the predominant defects. A cellulose derived binder was added to the alcohol/alumina suspensions used in order to reduce the effect. The films had layer thickness between 1 to 60μm. The effect of film thickness on the crack formation is also described. For the purpose of comparison the alumina/ethanol dispersion were also slip cast to produce cylindrical pieces. The green densities for the nanosized alumina were very low at 15.9% for both EPD and slip cast bodies. The sintered EPD layer showed a density about 37.1% and the sintered body obtained by slip casting process gave a density about 34.1%. These reasons for these low densities and how to modify them are discussed.