THE INFLUENCE OF PH AND TEMPERATURE ON THE RHEOLOGY AND STABILITY OF AQUEOUS TITANIUM-DIOXIDE DISPERSIONS

The effects of pH and temperature on the rheology and stability of aqu eous dispersions of rutile (titanium dioxide) were investigated system atically. The dispersions exhibit shear-thinning behaviour, conforming to the Herschel-Bulkley or the Casson-type models in the shear rate r ange investigated. Extreme sensitivity with pH was observed, whereby t he dispersion viscosity can be changed by as much as an order of magni tude with pH variation at constant volume fraction. The temperature ef fect study indicates that the relative contribution of Brownian motion and shear flow to the viscosity is dependent on the flocculation stat e of the dispersion. The rheological behaviour of the dispersions in t his study has been explained in terms of hydrodynamic interactions bet ween particles as well as non-hydrodynamic interactions. These observa tions have important implications in crossflow microfiltration of thes e dispersions. (C) 1997 Elsevier Science S.A.