Connectivity in binary mixtures of spherical particles

Mono- and poly-disperse assemblies of spherical particles are investigated in terms of their average and partial coordination numbers by means of X-ray microtomography using a novel morphology-based image processing method to statistically distinguish true contacting particles from very close ones having apparent contacts arising from image artefacts. This technique is shown to reduce overestimations given by the laborious liquid-bridge method while corroborating theoretical predictions such as $\overline{Z}\le 6$ for random beds of mono-sized spheres and trends of the partial coordination numbers in binary mixtures of spheres. This method also provides a detailed and unbiased visualization of the long-range connectivity between similar particles which suggests that for partial coordination numbers ${\overline{Z}}_{ii}>3$, chains of particular contact-category are formed throughout the assembly.