Break-up of nano-particle agglomerates by hydrodynamically limited processes

When dry nano-particulate powders are first added into a liquid, clusters as large as hundreds of microns can be formed. In this study, high shear impellers, such as the sawtooth Ekatomizer and rotor-stator impellers were used to suspend and break-up these agglomerates in a stirred vessel. The high local energy dissipation rates generated by these impeller could slowly break up clusters to sub-micron sizes by an erosional mechanism. In comparison, single and multiple passes through a valve homogeniser could quickly break the nano-particle clusters to sub-micron sizes; single pass operation had the highest breakage efficiency for a given specific energy input. For both equipment types, the rate of fines generation was found to be controlled by the maximum energy dissipation rate. However, the size of the fine aggregates produced was a constant and was not a function of the energy dissipation rate.