Particle size characterization: comparison of laser difraction (LD) and scanning electron microscopy (SEM)

Abstract

Two of the most significant properties of particles are size and shape; they often have direct influence on the materials behavior. Since the particulate systems are constituted by 3D particles of different size, the characterization of this property has to be given by a particle size distribution (PSD) . Among the most popular techniques for PSDs measurement, the image analysis (IA) presents some disadvantages: sampling errors, the analysis of only hundred or a few thousand particles to represent the whole population, the use a 2-D projected image of a 3-D particle and long analysis times. In contrast, the laser diffraction technique allows fast particulate systems characterization, processes a high number of particles per assay and provides highly reproducible results. However, LD provides no details about the particle morphology. Both techniques can be considered complementary, however several data interpretation problems appear whe n the results are compared. To do so, it is necessary to understand the meaning of the size descriptors given by each technique and under which conditions the comparison of results from different size analyzers can be done. In this sense, this work explores first the number of particles required to obtain reproducible PSDs by SEM. Then, it presents a comprehensive characterization of PVC particles by assessing a set of size and shape descriptors. The PSDs obtained by IA-SEM and LD were mathematically transformed to be compared. Finally, IA-SEM data was used to evaluate the convenience of using more than one size descriptor to represent the particles volume.