Research On The Inner Structure Of Fluidized Agglomerate Formed By Nanoparticles

Nanoparticles, which the diameter are between 0.1nm and 100 nm, are difficult to go on normal fluidization. Because of the strong cohesive force, nanoparticles are easy to aggregate and fluidized in the form of agglomerate. Due to the unknown of the complex porous multi-stage inner structure of fluidized agglomerate, the interactions between agglomerate and fluidization gas are still unknown. Therefore, the kinetic growth model of agglomerate and the factors that influence fluidization cannot be well solved. In this paper, Si O2 nanoparticles are fluidized in a fluidized bed by dry air, and two methods are choose to analysis the inner structure characteristics of fluidized agglomerate formed in the bottom of bed.After summary all the methods to calculate the fractal dimension of agglomerate, a new calculate method which is more accurate is proposed according to the properties of agglomerate. By this method, the fractal dimension is calculate to be over 3 which means that the agglomerates formed in the bottom of bed are not fractal structure and they are grew in different models.In order to obtain the inner structure characteristics of fluidized agglomerate, epoxy resin is used to solidify the inner porous structure. And then it is cut into ultrathin sections of 60 nm for TEM observation, the TEM image clearly showed the structure details of the agglomerate cross-section. For dealing with these images, a new analysis method is proposed. Porosity and pore distribution are chosen as the two parameters to describe the structure characteristics. From the result, multi-stage structure is clearly showed. From the simple to complex, every stage of the agglomerate is nanoparticle, netlike structure, simple agglomerate and fluidized agglomerate, respectively. In the same kinetic growth model, simple agglomerates of different size are formed. And every simple agglomerate is grown uniformly in every direction. The pore structure is similar from the inner to outer space, and the pore volume is rapidly lowering as the pore diameter is growing. The mean porosity of simple agglomerate is 62.18%, and much of the pore are betwenn 25nm~100nm in diameter. The fluidized agglomerates are formed in different kinetic growth model, but every agglomerate is grown uniformly in every direction. The pore structure is also similar from the inner to outer space, and the pore volume is rapidly lowering as the pore diameter is growing. The mean porosity of fluidized agglomerate changes a lot as the diameter of agglomerate is changing, and much of the pore are betwenn 200nm~1000nm in diameter.