Size and shape characterization of oblate and prolate particles

New methodological developments for the characterization of anisometric particles are presented and their application to real particle systems is demonstrated. In the case of oblate particles, using pyrophyllite as an example, a recently developed model relation is applied to extract approximate shape information by comparing laser diffraction and sedimentation results. The LS shape factor, an approximate measure of the average aspect ratio of the system, is found to be approx. 4.3 in the central region of the size distribution. In the case of prolate particles, taking organic crystals (mesalamine) as an example, distributions of different size measures (projected-area diameter, minimal and maximal Feret diameter) and aspect ratios are determined via microscopic image analysis and the sizing results compared with laser diffraction. It is found that the laser diffraction results exhibit a broader distribution, which is shifted in direction of the fine-size region (median diameter 16.9 μm versus 21.0 μm).