Breakage Behaviors Of Ceramic Particles In A Fluidized Bed Jet Mill

Fluidized bed jet mills are widely used for industrial production of ultrafine powders with high hardness and high purity. However, some problems of the jet-milling process that have not been solved are a) incomprehensive understanding of the breakage mechanism of fluidized bed jet mills and b) simple control of the grinding process and product quality just according to the routine experience without any technical analysis database. For the optimization of operating parameters in the grinding process in a fluidized bed jet mill, this dissertation concerned: a) modeling of kinetics of grinding two ceramic particles (i.e., silicon carbide and alumina) through the population balance model and b) investigation of parameter effects on product characteristics, grinding process and breakage mechanism of the ceramic particles in the jet mill.The Kapur function model was utilized to describe the kinetics of grinding the ceramic particles in a fluidized bed jet mill. The detailed batch-grinding experiments of different ceramic (silicon carbide and alumina) particles in the jet mill were performed to obtain the products with various particle size distributions (PSD) and particle morphologies at different operating parameters (i.e., feed load, work pressure, distance between nozzle outlet and jet meeting point and rotational speed of classifier). Selection and breakage functions were calculated by the Kapur function model. The selection functions (or Kapur functions) and the PSDs could be simulated by some proposed equations via an optimization analysis method. It is indicated that the simulated PSDs are similar to the experimental PSDs.The breakage probability and mechanism of the ceramic particles were apparently affected by the operating parameters in the jet mill. Feed load and work pressure both had a dominant effect on the breakage probability, thus could be correlated to the grinding efficiency and the energy consumption in the mill. The results indicate that there coexist different grinding mechanisms (i.e., impact, abrasion and chipping) at different operating parameters during the grinding process. The breakage probability and mechanism could be also affected by the characteristics of ceramic particles (i.e., particle size, density and crytsal structure). It was found that there was the so-called―optimum grinding size‖corresponding to the greatest breakage probability. When the size of particles to be ground was much greater than the―optimum grinding size‖, particles could not be suspended in a fluidized bed mode for the effective grinding. The brittle ceramic particles ground in a fluidized bed jet mill could follow the breakage mechanisms with impact, abrasion and chipping events.