PROCESSING EFFECTS ON THE FLOW ORIENTATION PROPERTIES OF A MAGNETIC PARTICLE SUSPENSION

A new rheomagnetic measurement for studying the orientation of magnetic particles in suspension is presented. The apparatus, constructed on the basis of our previous theoretical development and Gedanken experiment on the magnetic particle suspension, is described in detail. The magnetic particles are rod-like gamma-Fe2O3 such as those employed in magnetic recording disk coating formulation. In the apparatus, the magnetic particle suspension flows from a large chamber into a narrow tube which has a coil wound near the entrance. The relationship between the measured coil inductance and the flow rate is established to study the shape of flocs in the suspension. This apparatus is employed to study the dispersion quality of magnetic particle suspension for various conditions: the effects of magnetic particle concentration, surfactant level and milling.