Fluidization and agglomerate structure of SiO2 nanoparticles

Fluidization of six kinds of SiO2 powders, with high void fractions and sizes from 7 to 16 nm, was investigated. The quality of fluidization of these nanoparticles is not the Geldart-C expected with these sizes, but has a free, much looser dynamic behavior with an extremely high bed expansion that obeys the Richardson–Zaki equation. The unique fluidization behavior is due to a porous multi-stage agglomerate (MSA) structure. Nanoparticles link into a tridimensional netlike structure, which then coalesce into simple agglomerates of micron size. When fluidized, these agglomerates further form complex agglomerates whose equilibrium hydrodynamic sizes are 230–331μm. Some important parameters, such as expansion exponent, terminal velocity and equilibrium fluidized agglomerate size were evaluated. The fluidization of ultrafines is attractive, and is possible if the agglomerate structure and properties, especially the interactive forces between agglomerates can be artificially controlled.