THEORY AND EXPERIMENTS FOR EVALUATING THE NUMBER AND THE DIMENSIONS OF SOLID PARTICLES DISPERSED IN A LIQUID-MEDIUM - APPLICATION TO THE SYSTEM SI3N4 H2O(1)/

Titration measurements have been made using a MOS-pH meter device to f ollow the adsorption processes of H+ and OH- ions onto Si3N4 fine part icles dispersed in water at different concentrations and pH values. A thermodynamic method has been developed to determine the number of agg lomerates per mm(3) in the dispersion medium and the corresponding ave rage dimensions of the solid particles under steady-state adsorption c onditions. At any fixed solid-phase concentration, the density of the agglomerates reaches a minimum value, and the corresponding average di mensions reach a maximum value, when the pH of the slurries is equal t o the pH at the isoelectric point. The method allows one to obtain the isoelectric point at a pH value of 8.0 +/- 0.1 by following directly the evolution of the particle surface charges through experimental mea surements of the number of ions introduced into the dispersion medium and of the number of ions adsorbed onto the solid particles. The densi ty of the agglomerates and their average diameter have been found to b e 6 x 10(5) mm(-3) and 15 mu m, respectively. The effects of the solid -particle concentration and of the pH value of the dispersed system on these variables have been investigated. The results allow one to rela te the density and the dimensions of the agglomerates to the yield str ess of the slurry.