Stabilization of aqueous Si3N4 suspensions with ammonium salt of poly(acrylic acid) at various pH

The stabilization of aqueous silicon nitride suspensions with ammonium salt of poly(acrylic acid) at various pH was examined systematically in order to understand the basic mechanism of dispersion. The effects of colloidal structure on particle packing was characterized by sedimentation and equivalent stokes diameter (ESD) of X-ray sedimentation technique. The rheological behavior of silicon nitride in the presence of PAA–NH4 is strongly dependent on pH and three rheological types has been defined. The electrostatic repulsion between the PAA–NH4-modified particle surface was found to be a primary mechanism governing the dispersion in both the neutral and alkaline pH range, on the other hand the steric repulsion of PAA–NH4 in acidic pH range was demonstrated to have a positive contribution to the dispersion.