Effects of suspension properties on the microstructure of Al2O3 coatings deposited onto macroporous SiC substrate

Abstract

In this paper the effects of the suspension preparation conditions on suspension coating of porous substrates were investigated. Alumina suspensions were prepared using varying types of additives, including non-ionic polyethylene glycol (PEG), cationic polyethylene imine (PEI), and anionic sodium carboxymethyl cellulose (CMC). Prepared suspensions were coated on porous SiC substrates by spin coating. The flow curves of the suspensions were measured, whereas their particle dispersion states were also observed directly using an optical microscope. In addition, the surface and cross-section of each coating were observed by SEM and analysed by EDX. Finally, the air permeability of each coating was measured.For the suspension with PEG, alumina particles dispersed well in the suspension and the added PEG formed a network structure, resulting in a homogeneous coating on the surface of the substrate with less particle penetration into the substrate pores. For the suspension with CMC and the suspension with PEI, since particles flocculated in the suspensions, particle penetration into the substrate pores hardly occurred, however, the formed coating was inhomogeneous.