Gravity settling, rheology and particle-packing structure of aqueous alumina suspensions have been investigated using submicrometer
a-Al2O3 powders with an average particle size 0.2 mm dispersed in pure water. The suspension pH varied from 2 to
11. The interface that separated the supernatant from the sediment appeared to settle linearly with time during the sedimentation
experiment, followed then by a gradual reach toward a minimal sediment height; to which, the height was pH and solids loading
dependent. The suspensions tended to form a continuous particulate network that defined the gravity settling as 50.1 at pH 11.
This resulted in a flocculated suspension structure which barely settled even after 24 h without disturbance. The flocculated suspensions
exhibited correspondingly a shear-thinning flow character over given shear-rate range (g=1–1000 s1) examined, in contrast to an
apparent transition of flow toward shear thickening from the shear thinning for the better-dispersed suspensions (pH=2) at relatively
high shear rates (5100 s1). This finding suggested a breakdown of the particulate network into smaller flow units for the
flocculated suspensions as shear rate was increased. Films made from the flocculated suspensions showed apparent cracking after
drying. Microstructural examinations revealed that a pronounced grain growth occurred in the films made from the pH 2 suspensions
after isothermal sintering.