Particle shape is a very important property in many fields of research, and with many practical, diverse, and commercially important applications including pharmaceuticals, civil engineering, metallurgy, health, and food processing. Many of the methods used to evaluate the shapes of solid particles employ a plane section through the particles. This mode may be termed Plane of Section. Plane of Section abstracts three-dimensional (3D) objects to two dimensions (2D).
This algorithm and imaging technique obtains the boundaries of each particle in a polished thin section using imagery obtained using a petrographic microscope in reflected light mode. Two images, each composited from numerous overlapping high-resolution images, are used — one in focus and one with the stage brought slightly toward the objective lens. By comparing the energy diffracted in the latter with the former, the particles on the front surface are identified. Then the algorithm identifies individual particles at the front surface of the section, followed by filling of cracks and holes in the outlines of the particles. For each particle, various geometric characteristics are measured. For subsequent work, area, perimeter, max Feret diameter, and orthogonal Feret diameter are retained. These values can then be used to compute aspect ratio and Heywood factor of each particle for analysis. The tabulated aspect ratio and Heywood factor values for a thin section form a highly informative probability description of the sampled material’s particle shape. Use of an optical microscope is faster and cheaper than alternative imaging technologies such as SEM (scanning electron microscope), although SEM offers higher ultimate resolution.
The major novel aspect of this technology is the use of two images at different planes to greatly simplify identification of material on the front surface of the sample. Other unusual features include the relatively easy creation of high-resolution panoramas that are perfectly registered, and the repair of cracks in the particles.