Dispersion mechanisms of aqueous silicon nitride suspensions at high solid loading

A poly(acrylic acid) ammonium was used as dispersant for highly concentrated aqueous silicon nitride suspensions. The aim was to increase the stabilization efficiency of the dispersants at normal processing conditions (pH 10–11) through rheological and sediment measurements, and to correlate this to stabilizing mechanisms by means of ζ-potential and X-ray photoelectron energy spectrometer measurements. Rheological properties of suspensions stabilized with poly(acrylic acid) ammonium were optimized by using the wetting reagent PEG400, especially at solids loadings above 50 vol.%. XPS measurements showed 39% of SiO2 existed in Si3N4 particles would contribute to the wetting ability and dispersibility of the powder in aqueous solvent. Zeta-potential and sedimentation character show that the dispersant adsorbed on silicon nitride for efficient stabilization at high solids loadings. Efficient wetting ability was obtained for highly concentrated Si3N4 suspensions of up to 60 vol.% solids loadings with the PEG400 as wetting reagent. Finally the shrinkage and strength of green bodies formed by different solid loading slurry were characterized and the feature of the green bodies was shown out.