Suspension characteristics and rheological properties of TBA-based freeze casting alumina/zirconia slurries

The sedimentation bulk density and rheology of TBA-based alumina and alumina/zirconia mixed suspensions have been studied in terms of oxide loading (20, 30 vol.%), and types of additives (dispersant, dispersant/binder, dispersant/surfactant, dispersant/surfactant/binder). Citric acid, ethoxylated acetylenic diol (Dynol 604), poly(vinyl butyral) (PVB), and tertiary-butyl alcohol (TBA) have been used as the dispersant, surfactant, binder, and liquid medium, respectively. The sedimentation density significantly increased upon adding the dispersant; the effect was more pronounced with an alumina/zirconia suspension most likely due to the high specific surface area of zirconia. With a further addition of the binder, the sedimentation density decreased. The suspension viscosity generally behaved in an opposite manner to the sedimentation density, i.e. a low sedimentation density gave a high low-shear viscosity, indicative of the formation of a highly ordered structure in the suspended particles. The low shear rate rheology showed a shear thinning; in a such case, the degree of shear thinning was greatly increased with a high solid loading (30 to 20 vol.%). TBA-based alumina/zirconia suspension mixed with 5 vol.% zirconia gave an intermediate sedimentation density and the rheological behavior of pure alumina and 15 vol.% zirconia-containing alumina suspensions, implying the alumina and zirconia particles are non-interacting with each other.