Nanopowder Fluidization and Mixing Under the Effect of Acoustic Fields

Gas fluidization is one of the best available techniques to disperse and process large quantities of nanosized powders. Nevertheless, on the basis of their primary particle size and material density, fine powders fall under the Geldart group C (<30 ?m) classification, which means that fluidization is expected to be particularly difficult because of cohesive forces existing between particles. In order to overcome these inter-particle forces and achieve a smooth fluidization regime, externally assisted fluidization can be used, thus involving the application of additional forces. Among all the available techniques, sound assisted fluidization has been indicated as one of the best technological option. The present work is focused on the study of the fluidization and mixing of nanoparticles under sound assisted conditions. All the fluidization tests have been performed at ambient temperature and pressure in a laboratory scale sound assisted apparatus. In particular, the first section of this work presents the results about the fluidization behaviour of four different nanopowders (Al2O3, Fe2O3, CuO and ZrO2) in terms of pressure drops, bed expansion and minimum fluidization velocity as affected by acoustic fields of different intensity (125-150 dB) and frequency (50-300 Hz). The fluidization of binary mixtures of two powders (Al2O3, and Fe2O3) is also investigated under the application of different acoustic fields and varying the amount of the two powders. Then the mixing between two different nanopowders (Al2O3/Fe2O3) has been investigated from both a "global/macroscopic" and "local/microscopic" point of view.