The mutual effects between the interparticle forces and mechanical properties on fluidization of TiO2 nanoparticle agglomerates in a conical fluidized bed: nanoindentation and pressure fluctuation analysis

Abstract

Understanding the agglomeration process of nanoparticles (NPs) can help to decrease their adhesion during fluidization. Herein, the mutual effects between the mechanical properties and interparticle cohesive forces of the TiO2 NPs as well as the fluidization regimes were studied in a conical fluidized bed. Young’s modulus and hardness of the agglomerates were determined by nanoindentation test. The size range of NPs, porous simple-agglomerates, and dense complex-agglomerates were 23 ± 3 nm, ~ 40–80 μm, and ~ 170–270 μm, respectively. Pressure fluctuation analysis exhibited a transition flow regime from a particulate phase to bubbling, slugging, turbulent fluidization, and spouting regime. The ratio of hydrodynamic to interparticle force was applied to describe the bed characteristics, while the granular Bond number obtained from settling experiments was used to find the agglomerates fractal dimension. The laser images showed the size, structure, and number of agglomerates depends on the type of fluidizing gas and fluidization regime. The dependency of the hardness on the fluidization regime showed the interparticle force diminishes with decreasing the asperity radius of agglomerates. The results showed full fluidization takes place, where the primary complex-agglomerates breakdown into simple-agglomerates and re-agglomerate into secondary complex-agglomerates with the fragile structures and irregular shape that simply fluidized at the spouting regime.