Controlled flow of smart powders.

The flow properties of powders are mainly due to the interplay of cohesive forces and intergrain frictional forces. We have experimentally investigated a "smart granular system" for which the interparticle cohesion can be tuned by a magnetic field B[over ] . We show that the rheological features of such a system can be controlled. Indeed, the granular flow can be controlled or even stopped by the magnetic field. Depending on the orientation of B[over ] , different dynamical regimes can be obtained like a "dry liquid state" forming conical droplets as well as a "layered soft state." Scaling laws are given for the flow rate outside a funnel as a function of B and for the stopping threshold of the flow as a function of the funnel output diameter D . From this analysis, it appears that the flowing properties are related to the dimensionality of the magnetic aggregates.