(160j) Effect of Dry Particle Coating on Packing Density of Cohesive Powders under Low Consolidation

Flowability of fine powders is strongly dependent on memory effects such us the effect of previous consolidation stresses on the packing density of the powder. In this work we present measurements of the particle packing density of fine cohesive powders as a function of the consolidation stress previously applied on the sample. Cornstarch particles, with a mean size of around 15 microns are coated with 20nm hydrophobic fumed silica nanoparticles by dry particle coating method to reduce the cohesiveness of the original powder. The weight percentage of additive is varied between 0.025% and 1%, which influences the cohesion of the coated powder. We examine the influence of the cohesion on packing density. Experiments are carried out using a conventional device for measuring the tapped density as well as the Sevilla Powder Tester apparatus, which is based on the use of gas flow either to fluidize to erase memory of the powder or to compress the bed in order to subject it to a controllable consolidation stress. The particle volume fraction is derived from the height of the bed, which is measured by a high-accuracy sensor placed on top of the vessel. It is observed that powders with lower amounts of coated additive have larger cohesion and form larger agglomerate structures and hence show lower packing densities. As amount of coated additive increases, cohesion is reduced and smaller agglomerates are formed which pack better in both fluidized and non-fluidized states. The effect of low consolidation stresses are also examined on the packing density. Some of the experimental results are also compared with DEM simulations.