Agglomeration on drying of yttria-stabilised-zirconia slurry on a metal substrate

Drying behaviour of aqueous yttria-stabilised-zirconia (YSZ) slurry on a metal substrate has been investigated by examining drying kinetics, shrinkage rate and cracking behaviour as a function of agglomeration degree. The agglomeration behaviour of the slurry was varied by changing its pH value, and evaluated by measuring both zeta-potential and viscosity. The drying kinetics of the slurries on substrates was characterized with weight loss and classified as an initial constant rate period (CRP) followed by a falling rate period (FRP). Uneven thickness reduction, measured using optical microscope, occurred in the CRP stage due to lateral flow, and became more uniform with increase in agglomeration degree. Tensile stresses developed within the coating because of the substrate constraint and resulted in crack formation and propagation. Cracking behaviour was controlled by the agglomeration degree of the slurry.