4.1 The myriad array of particle size analysis techniques available to the modern-day powder technologist is both daunting and confusing. Many of the techniques are applicable only to certain types of materials, and all have limited ranges of applicability with respect to powder particle size. This guide is an attempt to describe and define the applicability of each of the available techniques, so that powder technologists, and others interested in powders, may make informed and appropriate choices in characterizing their materials.

4.2 This guide is intended to be used to determine the best and most efficient way of characterizing the particle size distribution of a particular powder material. It may also be used to determine whether a reported powder particle size, or size distribution, was obtained in an appropriate and meaningful way.

4.3 Most particle size analysis techniques report particle size in terms of an "equivalent spherical diameter:" the diameter of an ideal spherical particle of the material of interest that would be detected in the same manner during analysis as the (usually irregular-shaped) actual particle under the same conditions. The different techniques must necessarily use different definitions of the equivalent spherical diameter, based on their different operating principles. However, when analyzing elongated particles, the size parameter most relevant to the intended application should be measured; for example, length (maximum dimension).

4.4 Reported particle size measurement is a function of both the actual dimension or shape factor, or both, as well as the particular physical or chemical properties of the particle being measured. Caution is required when comparing data from instruments operating on different physical or chemical parameters or with different particle size measurement ranges. Sample acquisition, handling, and preparation can also affect reported particle size results.