Processing of Concentrated Aqueous Silicon Nitride Slips by Slip Casting

The optimization of concentrated Si3N4 powder aqueous slurry properties to achieve high packing density slipcast compacts and subsequent high sintered densities was investigated. The influence of pH, sintering aid powder (6% Y2O3, 4% Al2O3), NH4PA dispersant, and Si3N4 oxidative thermal treatment was determined for 32 vol% Si3N4 slurries. The results were then utilized to optimize the dispersion properties of 43 vol% solids Si3N4‐sintering aid slurries. Calcination of the Si3N4 powder was observed to result in significantly greater adsorption of NH4PA dispersant and effectively reduced the viscosity of the 32 vol% slurries. Lower viscosities of the optimized dispersion 43 vol% Si3N4‐sintering aid slurries resulted in higher slipcast packing density compacts with smaller pore sizes and pore volumes, and corresponding higher sintered densities.