Preparation and characterization of alumina granules via tumbling and agitation granulation

Abstract

Granulation of alumina powder was performed, and the characteristics of the resulting granules and the sintered bodies produced from them were evaluated. The granulation processes were conducted under the following conditions: hand sieving (HS), sieving using a rotating and tapping shaker (Ro-Tap sieving, RTS) which involves a tumbling motion; dry agitation granulation using a high-shear mixer (AD); and semi-wet agitation granulation with binder addition (AB). The granulation effect increased progressively in the order of HS, RTS, AD, and AB. As the granulation effect increased, the granules became larger and more spherical, and their size distribution became narrower with a sharper peak. The loose bulk density increased and the angle of repose decreased, whereas the tapped bulk density showed no significant change due to the collapse of the granules. Although the strength of the granules increased with the progression of granulation, the strength of the sintered bodies decreased. This phenomenon is considered to result from the stronger granules being less prone to collapse during compaction, which led to the formation of residual pores between granules in the green bodies. These pores subsequently became defects in the sintered bodies, which reduced their strength.