A shape factor to assess the shape of particles using image analysis

Abstract

Particle shape analysis is one of the most difficult problems in powder technology, and to date there is no general shape factor available which clearly differentiates between all possible kinds of shape. A shape factor for particles has been developed on the basis of two-dimensional particle outlines obtained by image analysis. The proposed shape factor uses the deviations of the two-dimensional particle outline from standard images of a circle, triangle and square, and considers the particle elongation and the number of characteristic corners of the apparent shape. The proposed shape factor has first been evaluated for mathematically defined shapes. A comparison with standard shape factors such as aspect ratio and circularity has shown that the new shape factor can differentiate between these model shapes. Therefore, five test powders with variable shape have been studied. While aspect ratio and circularity failed to identify the underlying particle shape and the differences in shape between the five powders, the proposed shape factor identified both the shape of each particle batch and the sometimes small differences in shape from batch to batch. Although the new shape factor has some limitations, it could improve the definition of shape characteristics of powders.