Mesoscopic structuring and yield stress of magnetofluidized fine particles

Abstract

The fluidization behavior of a bed of fine magnetizable particles excited by an externally applied magnetic field is found to depend on the aggregative nature of the particles before the field was applied. Usually nonaggregated particles organize in quasivertical local linear chains when the field is applied. In contrast, naturally aggregated particles form large-scale branched structures when magnetized by an external field. As a consequence the yield stress of magnetically stabilized beds of naturally aggregated particles is relatively increased and the bed can be stabilized at smaller field intensities. As expected from the magnetic cohesive force between magnetized particles, the yield stress is proportional to the square of the magnetic-field intensity, with a proportionality constant that depends on the mesoscopic organization on the magnetic particles. Remarkably, it is found that quasivertical chainlike structures are stable in spite of the fact that the magnetic field is applied in the horizontal direction.