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 N _B, and the number of surface silanol groups per unit area, N _A, 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.