The possibility that there is an equilibrium between aggregate breaking and
formation during aeration has been highlighted by experiments using a tracer
powder. For all the experimental conditions tested, the starting point was obtained by
feeding 30 g of the Al2O3 nanopowder (white powder) and then 5 g of copper oxide
nanopowder (tracer), which forms a black layer on the top of the bed (Fig.7A). The
primary particle average size and density of the tracer powder are 33 nm and 6315
kg/m3 respectively.