Investigation into the Formation of Fluidized Titanium Dioxide Porous Nanoagglomerates in a Conical Fluid Bed and Evaluating Its Physical and Mechanical Properties

In this study, the hydrodynamic behavior of a conical fluid bed containing hydrophilic titanium oxide P25 nanoparticles and the formation of agglomerates were investigated. The particles with an initial diameter of 21 nm were fluidized by nitrogen and airflow at different superficial gas velocities. The size of the agglomerates during fluidization was determined by laser imaging and microscope electron diffraction (SEM) in the range of 40- 250 μm. According to laser images, the average size of agglomerates fluidized by nitrogen gas and airflow was 112 and 131 μm, respectively, while the average size of the complex agglomerates at the end of fluidization with nitrogen gas and airflow were 75 and 95 μm, respectively. The dynamical analysis of the bed showed that the size of the final agglomerates is highly dependent on the fluidization time. Due to the strong attractive forces between the nanoparticles, the size of the primary agglomerates was in the range of approximately 220-120 μm, which, with the continuation of fluidization, was broken down into smaller particles in the range of 145-100 μm. Young's modulus was calculated by fitting the displacement curve obtained from atomic force microscopy to 144 kPa, which corresponded to the Hertz model (141 kPa). The results indicated that increasing the gas velocity and applying airflow can partly increase the mean sphericity of particles (0.82-0.86). According to the experiments, fluidization time had a significant effect on the reduction of particle sphericity (0.58-0.75), which was affected by the failure of large agglomerates with sharp edges. The results showed that the initial agglomerates were fragile and have porosity above 80%, whereas the ultimate porosity was less than 50% with a relatively smooth surface. Unlike particle fluidization in cylindrical fluidized beds, the results of this study can help reduce particle agglomeration and achieve uniform particle size distribution.