Theory and experiments for evaluating the number and the dimensions of solid particles dispersed in a liquid medium. Application to the system Si3N4/H2O(I)

Abstract

Titration measurements have been made using a MOS-pH meter device to follow the adsorption processes of H⁺ and OH^– ions onto Si₃N₄ fine particles dispersed in water at different concentrations and pH values. A thermodynamic method has been developed to determine the number of agglomerates per mm³ in the dispersion medium and the corresponding average dimensions of the solid particles under steady-state adsorption conditions. At any fixed solid-phase concentration, the density of the agglomerates reaches a minimum value, and the corresponding average dimensions reach a minimum value, when the pH of the slurries is equal to 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 measurements of the number of ions introduced into the dispersion medium and of the number of ions adsorbed onto the solid particles. The density of the agglomerates and their average diameter have been found to be 6 × 10⁵ mm^–3 and 15 µm, 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 relate the density and the dimensions of the agglomerates to the yield stress of the slurry.