Boehmite Coating as a Consolidation and Forming Aid in Aqueous Silicon Nitride Processing

Silicon nitride powders were coated by boehmite via a solgel process to improve the consolidation and forming of aqueous silicon nitride suspensions. The coated silicon nitride suspensions had a significantly higher solids loading than the pure silicon nitride in water. Viscosity measurements and centrifugation showed that the coating changed the long‐range interaction between the silicon nitride particles, whereas the pressure filtration study indicated that the oxide coating modified the short‐range interaction at particle contacts. Preliminary rheological studies indicated that at pH 3, the boehmite‐coated silicon nitride suspensions can gel, as indicated by a wide linear viscoelastic region in dynamic rheological tests. The gelation of coated silicon nitride at pH 3 offers the potential for net‐shape forming. Our study establishes a water‐based green body consolidation and forming technique of silicon nitride without polymeric additives or organic solvents.