Multidimensionality in fluidized nanopowder agglomerates

Abstract

In recent years, the interest in fluidization as a mean to process nanoparticles is strongly increasing. Due to the small size of the nanoparticles, which makes van der Waals forces predominate, they do not fluidize as single particles but as agglomerates. Various researchers using settling experiments and bed expansion measurements conclude that fluidized agglomerates are fractal structures with a single fractal dimension of 2.5. Based on microscopy results, Wang et al. "Powder Technology 124, 152-C159 (2002)" propose a hierarchical structure, which seems in contradiction with the use of only one fractal dimension as a descriptor of the whole structure. Moreover, it is not clear whether the structure presented by the agglomerates ex-situ is the same during fluidization. Hence, in this work we have characterized in-situ the internal structure of fluidized agglomerates by means of spin-echo small-angle neutron scattering (SESANS). We show that the structure of the agglomerates present at least two fractal dimensions. One of them is ≃ 2.1 and characterizes the primary strong agglomerates. The second one is ≃ 2.8 and characterizes the larger agglomerates formed by the primary agglomerates. © 2013 AIP Publishing LLC.