Suspension characteristics and rheological properties of mullite/zirconia powder in methyl isobutyl ketone

Particle size and its distribution, sedimentation bulk density and rheology of mullite, zirconia, and mullite/zirconia mixed suspensions have been studied in terms of oxide loading (20, 30 vol%), and types of additives (dispersant, dispersant/plasticizer, dispersant/plasticizer/binder). Polyester/polyamine, dibutyl phthalate, poly(vinyl butyral), and methyl isobutyl ketone have been used as the dispersant, plasticizer, binder, and liquid medium, respectively. Sedimentation density significantly increased upon adding dispersant; the effect was more pronounced with zirconia suspension most likely due to the fine and hence high specific surface area of zirconia. With further addition of plasticizer and plasticizer/binder, the sedimentation density decreased. The suspension viscosity generally behaved in an opposite manner to the sedimentation density, i.e., low sedimentation density gave high low-shear viscosity, indicative of high order structure formation in the suspended particles. High shear rate rheology showed a shear thinning and its onset began at lower shear rate with higher solid loading. Mullite/zirconia mixed suspension gave intermediate sedimentation and rheological behavior, implying the two types of particles are non-interacting.