Processing of Concentrated Aqueous Silicon Nitride Slips by Slip Casting

Abstract

The optimization of concentrated Si 3 N 4 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% Y 2 O 3 , 4% Al 2 O 3 ), NH 4 PA dispersant, and Si 3 N 4 oxidative thermal treatment was determined for 32 vol% Si 3 N 4 slurries. The results were then utilized to optimize the dispersion properties of 43 vol% solids Si 3 N 4 ‐sintering aid slurries. Calcination of the Si 3 N 4 powder was observed to result in significantly greater adsorption of NH 4 PA dispersant and effectively reduced the viscosity of the 32 vol% slurries. Lower viscosities of the optimized dispersion 43 vol% Si 3 N 4 ‐sintering aid slurries resulted in higher slipcast packing density compacts with smaller pore sizes and pore volumes, and corresponding higher sintered densities.