The properties of particles include particle size, shape, surface structure and pore structure. The shape of the particles can impact on many properties of a powder sample, including specific surface area, flowability, magnetic property, packing property, abrasive property and chemical activity. In order to improve the characteristics and performance of some products, particle shapes have been designed and produced based on their applications by industrial and scientific research.
Particle shape, also named as particle morphology, is currently characterized by measuring and calculating the projected shapes of the particles, including outline contour and roughness. All the methods employ microscopic imaging systems with the function of image analysis. In the calculation of particle shapes, the characterization of irregular shaped particles is common, with important features including particle roundness, the aspect ratio of elongated (or fibrous) particles, and the ratio of thickess-to-diameter for flakes or platelets, etc. The images are taken by microscope and then analyzed by software. The specific analysis methods are:
(1) Roundness: it can be calculated by the circumference of the circle equal to the particle area divided by the actual circumference of the particle (could also be calculated by "the equivalent diameter of the circumference is divided by the area equivalent diameter"). But no matter what algorithm is used , the closer the value is to 1, the better the roundness of the particles.
(2) Aspect ratio: the ratio of the length of the particle circumscribed rectangle to the average width of the particle.
(3) Diameter-thickness ratio: the ratio of the diameter of the particle-equivalent circle to the thickness of the particles.
A detailed description of automated imaging
can be found HERE