Abstract: The collapse behavior of nano-particle SiO ₂(R972)is investigated in a 35 mm diameter fluidized bed.This powder can be easily and uniformly fluidized via self-aggregation.Collapse experiments indicate that the bed collapse curve of SiO ₂ particles is different from that of Geldart Group A and C particles.By analyzing the collapsing velocity,the bed collapse process can be clearly divided into two stages:a rapid initial sedimentation stage with constant velocity,and a decelerating stage of solids consolidation for the incompletely supended agglomerates.The bed collapse mechanism of agglomerate particulate fluidization is proposed.