Use of horizontal mechanical vibrations to fluidize micrometric powders

The fluidization hydrodynamics of titanium oxide TiO2 powders, 700 nm in mean Sauter diameter, has been studied in order to perform Chemical Vapor Deposition (CVD) on their surface. A horizontally vibrating fluidization column, 5 cm in internal diameter and 80 cm in height has been used; the characteristics of vibration have been monitored by an accelerometer and the fluidization hydrodynamics has been analysed from gas pressure drop, bed expansion and mean agglomerates size measurements. First, fully reproducible results have been obtained only after the application of an operating protocol aiming to confer to powders an initial state of compaction before beginning the fluidization experiments. The distributor porosity appeared to modify the fluidization quality; the maximum porosity tested (40%) has been retained since it allowed to not plug-in the distributor. When building the pressure drop and bed expansion curves, the initial fluidization velocity revealed to modify the measured values for a given gas velocity and only the highest initial fluidization velocity studied (25 cm/s) allowed reaching a full fluidization. Such a high value indicates that these were stable agglomerates of hundreds of microns in diameter that were fluidized and not individual micronic grains. A large range of vibration frequencies and amplitudes have then been tested, corresponding to vibration intensities between 0.4 and 13. The best results have been obtained for intermediate values which may correspond to a maximum breaking up of the agglomerates. Long fluidization experiments (1 h) performed at fixed gas velocity and vibration intensity have shown that a fine tuning of the fluidization velocity is of major importance to find stable vibro fluidization conditions with minimized sizes of agglomerates. The high velocity retained (25 cm/s) and the low percentage of elutriation observed (