3 - Particle size analysis by image analysis

Abstract

This chapter discusses various methods of image analysis for particle size analysis. As microscopy is the only method in which the individual particles are observed and measured, it is often used as an absolute method of particle size analysis. Some of the methods discussed are optical microscopy, measurement of plane sections through packed beds, experimental techniques, determination of particle size distribution by number, quantitative image analysis, electron microscopy, and scanning electron microscopy. Optical microscopy is often used for the examination of particles from about 3 μm to 150 μm in size, although a lower limit of 0.8 μm is often quoted. The most severe limitation of optical transmission microscopy is its small depth of focus. When the size distribution of particles embedded in a continuous solid phase is required, the general approach is to deduce the distribution from the size of particle cross-section in a plane cut through the particle bed. Manual methods of obtaining data from images are slow and tedious and this can give rise to considerable error. The introduction of fully automated image analysis systems has virtually eliminated manual methods and supplanted semi-automatic systems. All image analysis systems use scanning techniques for converting images into electrical signals that are processed to yield data on the images.