Study of the morphology of solidified binder in spray fluidized bed agglomerates by X-ray tomography

Properties of agglomerated products depend on the materials used (primary particles, binder) and on their internal structure. Previous studies have characterized the internal structure of spray fluidized bed agglomerates in terms of the placement of primary particles, but binder morphology has not been investigated until now. Therefore, solidified binder morphology in spray fluidized bed agglomerates is discussed in the present work on data gained by X-ray micro-computed tomography. The main results refer to glass beads as the primary particles and to HPMC with contrast agent as the binder. Gas temperature and drying rate are shown to have a very strong influence not only on the morphology of the bridges that connect primary particles, specifically on the macroscopic porosity (hollowness) of such bridges, but also on the microscopic porosity of seemingly full bridge parts. Individual bridge volume, bridge clustering, binder volume distribution and agglomerate filling ratio with binder are discussed, and a classification is proposed for the various solidified binder elements observed. A critical view to systematic errors stemming from limitations in spatial resolution of the applied imaging technique is provided.