Direct observation of aggregates and agglomerates in alumina granules

Aggregates and agglomerates in granules prepared from milled alumina powder were studied with new confocal laser scanning fluorescence microscopy (CLSFM) using the liquid immersion method. Two kinds of ground powders were prepared by agitation bead milling and conventional ball milling and spray drying. The observation by CLSFM was very effective for detecting aggregates and agglomerates of very low amounts in alumina granules. Aggregates and agglomerates were absent in the granule made from powder milled by agitation bead milling, whereas they remained in the granule made from powder milled by ball milling. The volume fractions of these particles were about 2.0 vol.% and under 0.1 vol.% for the granules made from ball-milled and bead-milled powders, respectively.