Dispersion of Si3N4 powders in aqueous media

The stability of Si3N4 suspensions was studied and characterized in terms of zeta potential, sedimentation, apparent viscosity and rheology measurements. Zeta potential measurement showed that the isoelectric point (IEP) of the as-treated Si3N4 particles was pH ∼ 4.6. The ratio between the number of surface amine groups per unit area NB, and the number of surface silanol groups per unit area, NA, was calculated as 0.007. As silanol groups are expected to show acidic behavior, a cationic polymer, PEI was selected as dispersant. After the adsorption of PEI, The IEP of Si3N4 particles shifted to pH 10.4. The surface dissociation behavior of Si3N4 particles in aqueous media was also studied and related to the slurry stability. Based on the sedimentation, apparent viscosity and rheological measurements, the optimal slurry for tape-casting process can be obtained at pH 9.3 with 1 wt.% PEI as dispersant. It was shown that PEI is an effective dispersant for Si3N4 particles in aqueous media.