The Effect Of Particle Shape On Particle Size Measurement

Particle size analysis has a broad range of applications encompassing virtually all industries. Numerous automated techniques exist for measuring particle size distribution and virtually all report particle size in units of equivalent spherical diameter. This is necessary because of the ambiguity of describing the diameter of an irregularly shaped particle, and of constraints inherent in the instrument detection system.

Different measurement techniques that report in equivalent spherical diameter produce somewhat different particle size distributions when particles are nonspherical. Understanding what each particle size technique actually measures, how it performs the measurement, and how it transforms the quantity measured into equivalent spherical diameters are crucial when selecting the most appropriate particle sizing technique for your sample or application. To demonstrate this, we analyzed samples of glass beads, garnet, and wollastonite (because of their shape differences). The analytical techniques employed are static laser light scattering, electrical sensing zone (Coulter Principle), X-ray sedimentation, and dynamic image analysis. The effect particle shape has on the reported particle size is discussed for each of these materials and techniques.