Dispersion and consolidation of silicon nitride whisker in aqueous suspension

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Abstract
Characteristics of aqueous silicon nitride whisker suspension and the packing nature of whiskers during consolidation (sedimentation or filtration) were investigated in order to control the microstructure and density of a whisker compact. Silicon nitride whiskers (average size 0.4 μm × 3.7 μm) coated by SiO2 film were well dispersed at pH 10.5 due to the strong repulsion force among negatively charged whiskers. Low viscosity suspension of highly charged whiskers showing Newtonian behavior formed a dense whisker compact with a narrow pore size distribution of small pores. The density increase of green compact was accompanied by the orientation of whiskers where the direction in length of whiskers was perpendicular to the direction of filtration. Application of an external pressure (isostatic pressing) to porous whisker compacts consisting of network structure of randomly packed whiskers or whiskers of low orientation increased the green density.