(404c) Powder Tribocharging: Measurement, DEM Simulation with Patchy Particles and Process Optimization

When two objects are rubbed against each other, they charge because of the triboelectric effect. It occurs as well between insulators as between metals whether they are made of the same material or not. This effect is predominant in powders which show significant charging due to the large rate of collisions between its constituents.

In this presentation, we first show how to measure the ability of a powder to charge electrostatically during a flow in contact with a selected material. The GranuCharge measurement method is used, and some cases studies will be shown to illustrate the measurement.

Afterward, we consider a theoretical model based on the existence of acceptor and donor sites (also called patches) of charges at the surface of the particles. This model has been implemented in a customized DEM code. The patches at the surface of spherical particles are defined using a Voronoi tessellation. These patches could be donors or acceptors of charges with a donor probability and a uniform distribution to assign the patches’ nature. To test the model, we placed electrically neutral and equal in size particles in a rotating drum and measured the total transferred charge over time while the drum is rotating. The total transferred charge increases rapidly to saturate. Therefore, the patches are charging inducing the formation of agglomerates as observed experimentally. We reproduced also numerically the charging of binary mixtures with small and large grains charging with an opposite charge. One more time, this result is coherent with experimental observations.

Finally, GranuCharge measurement method and the DEM code are combined to better understand powder processing methods influenced by electrostatic charges. In particular, the electrostatic interaction is used to obtain controlled agglomeration processes.