THE FLOCCULATION OF AQUEOUS SUSPENSIONS OF TITANIA INDUCED BY SURFACENUCLEATION OF CALCIUM PHOSPHATES

Titanium oxide aqueous Suspensions have been destabilized by a navel m echanism; the nucleation of octacalcium phosphate on the particle surf aces, using the constant composition technique. The results suggest th at the potential energies resulting from the electric double layers ar ound the titania particles play only secondary roles in the flocculati on, in that a decrease in S-potential of titania colloids from -47 mV to -13 mV does not in itself cause the titania suspension to flocculat e, in contrast to the predictions of the classical DLVO theory. Howeve r, in the process df;nucleation of the moderately hydrophobic octacalc ium phosphate phase (gamma(S)(-) = 19.7 mJ m(-2)) onto titania particl e surfaces, the latter become more hydrophobic with gamma(S)(-) values ranging from 52 to 23.4 mi m(-2). This change is sufficient to cause the particles to flocculate since the energies of attraction result fr om hydrophobic interactions (90%) and van der Waals forces (10%).