Effect of hydroxyl groups in PVB on the microstructure of electrophoretically deposited green bodies for thermal barrier coatings

The effect of hydroxyl groups in polyvinyl butyral (PVB) on the microstructure of electrophoretically deposited green bodies for the fabrication of thermal barrier coatings was investigated. Suspensions of yttria-stabilized zirconia (YSZ) particles were prepared with phosphate ester and PVB in a toluene/ethanol mixed solvent. Dispersion properties of YSZ particles were characterized using adsorption isotherms and electrokinetic measurements at two different hydroxyl group contents in PVB. A correlation was made between dispersion characteristics and the microstructure of the electrophoretically deposited green body. A higher hydroxyl value (B-98) resulted in higher adsorption of PVB on YSZ particles compared to a lower hydroxyl value (B-79). The higher adsorption of B-98 resulted in low dynamic mobility of YSZ particulates and led to the formation of a porous green microstructure. The YSZ suspension prepared with B-98 showed a thicker and more porous green microstructure than the suspension prepared with B-79.