Origin of strength change in ceramics associated with the alteration of spray dryer

A significant difference of strength was noted in alumina ceramics made through the powder compaction process with spray dryers of two sizes. The origin of the change was examined by new characterization methods involving optical microscopy. The granules were found to have irregular shape. Defects in compacts were formed from these dimples and also from the nonuniform packing of powder particles at the granule boundaries. These defects are responsible for major defects in sintered bodies. The change of strength in the ceramics can be explained by the change of granule size with the spray dryer. The size of granules was found to directly affect the size of defects in the green and sintered bodies. The size of granules, defects in granules, green bodies, and sintered bodies were approximately 20-30% smaller for granules made with the small spray drier. There was a direct correlation between the size of defect and the strength of ceramics.