Size and shape characterization of polydisperse short-fiber systems

Two wollastonites, polydisperse with respect to size and shape, are characterized by image analysis. Aspect ratios are calculated for individual particles (1000–1500 objects) from the minimum and maximum Feret diameters measured. Although scatter is large (approximately 50%), average aspect ratios are well reproducible and approximately size-invariant, approximately 5 and 16 for wollastonite WM 45 and HSV 45, respectively. A transformation procedure is proposed and applied to transform the number-weighted size distributions obtained via image analysis into volume-weighted size distributions that can be compared with laser diffraction. The laser diffraction medians (21.6 μm and 29.1 μm for WM 45 and HSV 45, respectively) are close to the medians of the minimum Feret diameter distributions (20.6 μm and 29.9 μm for WM 45 and HSV 45, respectively). This is clear evidence of the fact that laser diffraction results need not at all correspond to projected area diameters determined by image analysis.