Abstract
Rheological properties under steady shear were studied with a rotational viscometer for the 30vol% aqueous suspensions of titanium dioxide stabilized with different amounts of sodium pyrophosphate. The apparent viscosity at any given shear rate showed a minimum at 2mg/gTiO2 of Na4 P2O7·10H2O. By a shifting procedure, a composite flow curve was obtained from the shear-rate dependence of the apparent viscosity for suspensions stabilized with different amounts of Na4P2O7·10H2O. The characteristic shear rate at which the pseudoplastic flow appeared was also found to show a minimum at 2mg/gTiO2 of Na4P2O7·10H2O. From the sedimentation tests, the rheological properties of suspensions were revealed to be closely associated with the flocculation of suspended particles. The effects of the amount of Na4P2O7·10H2O on both the sedimentation and the rheological properties were discussed on the basis of the theory of the stability of lyophobic colloids (DLVO theory). It has been concluded that the dependence of apparent viscosity at a fixed shear rate on the amount of Na4P2O7·10H2O can be attributed to the difference in the degree of dispersion in suspensions resulted from the changes in the colloidal forces between the suspended particles. On the other hand, the characteristic shear rate can be elucidated to be closely correlated with the hydrodynamic forces required to attain the same degree of dispersion for the suspensions with different colloidal stabilities.
