Shape analysis of synthetic diamond

Two-dimensional images of synthetic industrial diamond particles were obtained using a camera, framegrabber and PC-based image analysis software. Various methods for shape quantification were applied, including two-dimensional shape factors, Fourier series expansion of radius as a function of angle, boundary fractal analysis, polygonal harmonics, and comer counting methods. The shape parameter found to be the most relevant was axis ratio, defined as the ratio of the minor axis to the major axis of the ellipse with the same second moments of area as the particle. Axis ratio was used in an analysis of the sorting of synthetic diamonds on a vibrating table. A model was derived based on the probability that a particle of a given axis ratio would travel to a certain bin. The model described the sorting of bulk material accurately but it was found not to be applicable if the shape mix of the feed material changed dramatically. This was attributed to the fact that the particle-particle interference was not taken into account. An expert system and a neural network were designed in an attempt to classify particles by a combination of four shape parameters. These systems gave good results when discriminating between particles from bin 1 and bin 9 but not for neighbouring bins or for more than two classes. The table sorting process was discussed in light of the findings and it was demonstrated that the shape distributions of sorted diamond fractions can be quantified in a useful and meaningful way. (author)