On the motion of aggregates composed of different numbers of particles through a non-uniform magnetic field

The influence of a magnetic field on the motion of iron particles located in a viscous fluid was investigated in this study. A magnetic field gradient was formed by orienting the poles of the magnet to produce a variable gap between the poles. The non-uniform magnetic field caused magnetisable particles to travel along the direction of the field gradient. The particles were found to undergo a process of aggregation, which in turn produced larger particles. The particles were also found to align in the direction of the field and hence in a direction perpendicular to the field gradient. Upon aggregation the new entity continued to move along the direction of the field gradient, but at a velocity distinctly higher than that of the aggregating units. When further aggregation occurred the entity increased to an even higher velocity, though the rate of increase in the velocity decreased, leading to an asymptotic velocity for very large aggregates. This behaviour was examined for spherical particles of different diameter and for rod shaped particles. This work shows the effective magnetisation of the iron particles is governed by the aspect ratio of the particles, indeed the mass distribution of the particles within the magnetic field