Rheophysical study of dispersed alumina suspensions

This paper studies the rheological behavior of aqueous suspensions of fine grained (d50 = 200 nm) alumina. Rheological measurements were performed on suspensions containing various amounts of solid and 0.26 wt% of ammonium polymethacrylate in order to ensure a good state of dispersion. Brownian motions, colloidal interactions and hydrodynamic interactions dictate the behavior. The viscosity is mainly influenced by the shear rate and by the solid volume fraction. A Maron and Pierce model was used to describe this last effect in the hydrodynamic regime. The maximum packing fraction was found to be 40 vol%. This value is related to the colloidal stability as described by the DLVO theory. In fact, the maximum packing fraction leads to a surface-to-surface separation distance of about 46 nm because of the repulsive potential. Finally, a dimensionless approach was achieved to quantitatively identify, on the rheogram, the different flow regimes associated to each dominant interaction type.