Aeration and mixing behaviours of nano-sized powders under sound vibration

The aeration and mixing behaviours of two nano-sized powders, Al(2)O(3) (40 nm) and CuO (33 nm), have been investigated in a laboratory scale fluidized bed. The fluidization quality of both powders is very poor without application of acoustic fields. Sound intensities larger than 135 dB and frequencies in the range 100-125 Hz improve their fluidization quality resulting into a homogeneous fluidization regime with high bed expansion. Under the effect of sound, mixing between powders has been qualitatively characterized by the visual observation of the bed and the SEM analysis of captured samples. Under the operating conditions tested, mixing between aggregates of the two powders takes only few minutes. However, mixing also occurs inside aggregates but this process requires larger times, of the order of 80-150 min. (C) 2010 Elsevier B.V. All rights reserved.