Influence of particle size distributions with various geometrical standard deviations on slip-cast forming and sintering behavior in submicron alumina powder compacts

The influence of particle size distributions of submicron high-purity α-alumina powders on forming and sintering behavior in an agglomerate-free condition were investigated. Nine kinds of alumina powders with the same median diameter (d_PM50 = 0.53 μm) and different geometrical standard deviations (σr = 1.2-2.0) in lognormal particle size distributions were prepared by blending spherical-like commercial α-alumina powders, and were also adjusted to near ideal distributions so that a of a mass distribution was comparable with one of the number distribution. In order to prevent the agglomerate and contamination of the impurities, forming was performed by means of the colloid process, i.e., the slip casting method using the porous alumina molds. Relative densities of green compacts and bodies sintered at up to 1300°C increased with increasing σ, but densities of bodies sintered at 1500°C or more increased with decreasing σ. The width of the grain size distributions of those bodies increased with increasing σ. The abnormal grains over 30 μm of the grain size generated at more than 1.7 of σ for alumina bodies sintered at 1700°C and those grains contained many pores. The powder with a narrow distribution in size is better to fabricate a translucent material.