(82d) Characterizing Nanoparticle Agglomerates in a Nanopowder Fluidized Bed

Nanoparticles in a gaseous environment agglomerate in a hierarchical fashion; this leads to peculiar hydrodynamics when fluidizing nanopowders. From production until powder processing in the gas phase, nanoparticles typically go from individual particles to aggregates, simple agglomerates, and complex agglomerates. Even though the structures at each level have unique properties, they are commonly assessed as a whole. Additionally, the effect of external factors on the morphology of these structures during gas processing is not well understood and challenging to study due to the limited techniques for in situ analysis of the dynamic phenomena.

Here, we study different ceramic oxide nanoparticles. In our lab, we use such particles to functionalize them via atomic layer deposition in a fluidized bed, e.g. for catalysis. In order to optimize this process, it is important to know the structure of the agglomerates. We describe the structural characteristics of each hierarchical level of complex agglomerate formation obtained from two in situ techniques: small-angle neutron scattering for the smaller scales, and a settling tube coupled with a boroscope for the larger scales. The first scale, namely aggregates, are open structures with a fractal dimension of about 1.5, which then form simple agglomerates with a fractal dimension close to 3, that later cluster into complex agglomerates that present a fractal dimension of about 2. In addition, we characterize the contact mechanics of the nanopowders agglomerates using atomic force microscopy. Finally, we will discuss the entrainment of nanosized clusters from the fluidized bed.