A Contact Model for the Effect of Particle Coating on Improving the Flowability of Cohesive Powders

Abstract

Coating or blending of fine particles on the surface of primary powder particles is often applied to improve and control the flow behavior of the powder. The effect of coating primary powder particles with fine particles on the cohesion force between primary powder particles is quantitatively examined. The JKR theory is extended to include the effect of particle coating on the force-displacement relationship due to surface energy and elastic deformation. It is shown that the cohesion force between two primary particles in the presence of a fine coating particle is directly proportional to the size ratio of the coating particle to the host powder particle and results in a drastic reduction in the cohesion force. Through discrete element simulation of powder flow, which uses the force-displacement relationship based on the extended JKR theory, the improved flowability is demonstrated. Competing effects of the coating and shear induced migration on the macroscopic behavior of the power flow are discussed. The effect of coating on improving the flowability is also experimentally demonstrated by comparing the measured angles of repose at a static condition and the flow rates of the gravity driven flow through a funnel for powders with and without particle coating.