ON THE PREDICTION OF EXTRUDATE PORE STRUCTURE FROM PARTICLE SIZE

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Abstract
Measurements have been made of the amount of water required to saturate a range of powders made by blending, in different ratios, three narrow-sized fractions of α-alumina. From these results the porosities of the powders have been calculated. Some powder mixtures were formed into pastes with water and various aids to extrusion; the porosities and densities of dried extruded blends of the same three fractions have been measured by mercury injection. Similar measurements have been made on the same extrudates following firing. A simple liquid saturation test provided a guide to the determination of porosity in the whole system. Particle size distribution results on the original powder blends have been related to the pore size distribution of the dried and fired extrudates. In particular, a detailed comparison between the porosity predicted by the method of Ouchiyama and Tanaka from only the porosities of the three primary fractions and the particle size distributions of the blends, and the porosities calculated by the various experimental methods was carried out. Using measured saturation volumes, pore volumes and densities, the porosities showed good agreement with theory for the blended powders and dried extrudates, but the results for fired extrudates correlated less well.

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