Abstract
The aspect ratios of rod-like and discoidal particles including six clay and two amphibole asbestos materials were evaluated by comparing the particle size distribution data derived from sedimentation measurements with those by a laser scattering method, following the techniques described by Jennings and Parslow (1988). The evaluated values were compared with the geometrical length ratios of individual particles which were determined independently by an image analysis made on transmission electron micrographs.
In the rod-like particles of halloysite and amosite, whose shapes are characterized by the two major and minor lengths of the particle, the aspect ratios evaluated from the two instrumental measurements were nearly consistent with the geometrical length ratios by the imaging method, though the consistency was not good exceptionally in crocidolite. On the other hand, the discoidal particles studied here showed significant deviations between the two ratio values. Their shapes are actually characterized by the three parameters of particle, i.e., the length, the width, and the thickness; the ratios of these three parameters all contribute to the divergence between the different particle size measuring instruments. Taking a geometrical mean of the length/thickness, the width/thickness, and the length/width ratios was satisfactorily consistent with the aspect ratio value evaluated from the instrumental measurements. It is conclusive that the divergence observed between the different particle size distribution measuring instruments is sensitive to the aspect ratio of the particle, as shown by Jennings and Parslow (1988). Nevertheless, if the particles have appreciably three different parameters required to characterize the geometries, the aspect ratio evaluated by instrumental measurements is related to all of the geometrical length ratios of individual particles.
