Characterization of rod-shape magnetic particles by Sedimentation Field-Flow Fractionation and electron microscopy: Particle size and length distribution

Sedimentation Field-Flow Fractionation (SdFFF) has been applied to the size characterization of nonspherical, rod shaped chromium dioxide particles which are currently being used as magnetic recording media. Retention of the rod shaped particles in SdFFF was largely dependent on flow rates and external field strengths. To obtain an accurate size distribution profile, a proper run condition was chosen at which retention of rods follows the SdFFF theory. While retention of rods at a high field strength was decreased by the role of lift forces, it was shown that retention at a low field strength was increased by the restricted diffusion of rod like particles. At an optimum run condition, where no retention perturbations existed, an apparent diameter distribution of rods was easily obtained and then converted to a length distribution with the application of the average cross-section diameter of rod shaped chromium dioxide particles measured by microscopy.