ABSTRACT
Table 2.1 shows many common methods of experiencing the size of irregular particles. The first six of these are obtained from microscopy and image analysis: the sieve diameter from sieving methods, specific surface diameter from permeability measurements, surface diameter from gas adsorption; Stokes’ diameter from sedimentation methods, volume diameter from electrical sensing zone methods, and optical diameters from instruments using optical sensing detectors. Again, for most industrial powders, all these diameters will be different. This is not necessarily a disadvantage if one is aware of the reasons for the differences and is able to convert one equivalent diameter to another. It is used to advantage when one wishes to increase the sensitivity of detection of a change in size distribution of a powder during a processing step. For example, if one is concerned with breakage and the reduction of mass, then a volume-sensitive (e.g., electrical sensing zone instrument or X-ray sensing) instrument will be most useful. Whereas in attrition, where volume is conserved but large numbers of very fine particles are abraded from the surfaces of large particles, number counting or surface methods will have the highest sensitivity to the change.
