(238b) High Temperature Crystallization of Micronic Powders by Activated Fluidization Processes

A high temperature fluidized bed reactor (HTFBR) has been developed to crystallize Zn2SiO4:Mn2+ microscopic powders between 900 and 1200°C. Because of high interparticle forces existing in such Geldart's group C powders, it was necessary to activate their fluidization. Following previous results, two activated processes of fluidization were used, addition of coarse particles to fine powders and vibrated fluidization. In order to evidence the advantages of the fluidized bed technology over more conventional treatments in static mode, a comparative study of the main particle characteristics after heat treatment in a crucible and in the HTFBR was performed. The X-Ray Diffraction patterns, the size distribution and the FEG SEM morphology of particles before and after thermal treatments were compared for the three processes. The crystallinity of the samples treated was equivalent for the three methods. Massive sintering phenomena occurred in the crucible from 1000°C whereas the original granulometry of particles was maintained in the HTFBR till 1100°C. The interest of activated fluidization processes to post treat microscopic particles is thus fully demonstrated.

KEYWORDS: Gas solid fluidization, Microscopic powders, Vibrated fluidized bed, High temperature crystallization, Particle morphology, Sintering