Effect of mechanical vibration on the size and microstructure of titania granules produced by auto-granulation

Auto-granulation is the growth of particle clusters of fine, cohesive powders due to agitation of the bed, such as mechanical vibration. This clustering occurs without the addition of any binder to the system and the granules reach an equilibrium size due to the balance between disruptive and adhesive forces experienced by the clusters during process operations. For this reason, it is important in powder processing to be able to characterize this behavior. In this study, a sub-micron titania powder is mechanically vibrated under controlled conditions to induce clustering and promote auto-granulation. The amplitude and frequency of the vibration are varied to view their effect on the equilibrium granule size. Furthermore, imaging of cross-sections of the granules is conducted to provide insight into the internal microstructure and measure the packing fraction of the constituent particles. It is found that under all vibrational conditions investigated the particles exhibit a core–rim microstructure.