Comparison of sizing small particles using different technologies

Abstract

Two of the most widely used methods in sizing particulate materials are the electrical sensing zone method (ESZ) and the laser diffraction (LD). In order to deduce size information from a measurement, it is assumed in the LD technology that the particles are spheres. For real industrial materials, only rarely are the particles spherical. The effects of non-sphericity on different technologies vary, causing discrepancies in results and bias from the true characteristics of the sample. Applications in many fields require information about the shape of the particles in addition to their size. Recently, dynamic image analysis (DIA) has been shown to be able to provide both size and shape information of particulate materials. DIA is not subject to restrictions of the spherical assumption and, therefore, provides a means to study the effect of shape in the results obtained using LD and ESZ. In this study, samples of various shapes were characterized using the three technologies (LD, ESZ, and DIA). Laser diffraction yielded progressively larger mean sizes as well as broader distributions as the shape of the particles deviates more and more from that of a sphere. The ESZ and DIA experiments, on the other hand, produced compatible results much less affected by particle shape. The study suggests that DIA is a powerful tool in characterizing nonspherical particles and that caution needs to be taken when evaluating the sizing results of nonspherical particles using laser diffraction.