Particle Shape Factors

The most common approach to describe and differentiate particle shapes has been the use of qualitative concepts. Two fundamental concepts have been used: (a) the dimensionality of the particle and (b) the surface contour of the particle. By the use of these concepts, a model system of shape characterization is presented in Fig. 21. Photomicrographs of several types of loose powders described in the International Standards Organization standard ISO 3252 are shown in Fig. 22. Basic shapes are:

• One-dimensional particles (Fig. 22a and 22d). Two different types of one-dimensional particles can be considered on the basis of their surface contour. One particle is smooth and the other particle is roughened with an irregular type of surface.

• Two-dimensional particles. These are very flat in nature and the surface contour of such particles is usually irregular. The dendritic type (Fig. 22c) is characterized by a tree-like shape and is often associated with electrolytic powders. However, secondary mechanical treatments often destroy such a shape. Flake particles (Fig. 22e) are also considered two-dimensional particles.

• Three-dimensional particles. Most powders are three dimensional in nature. These powders can be equiaxed and nodular. The simplest type of particle in this category is the spherical type (Fig. 22i). By departing from this perfect shape and contour, irregular particles (Fig. 22g) and nodular types (Fig. 22h) are obtained.

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