Coordination measurements in compacted NaCl irregular powders using X-ray microtomography

X-ray microtomography and three-dimensional (3D) image analysis are used to quantify the structural evolution during cold isostatic compaction of two irregularly shaped NaCl powders having different mean particle sizes (75 and 400 μm) and somewhat different aspect ratios. Varying the compaction pressure to vary the powder packing density, the structure of the different packings is quantified in terms of the mean coordination number and of the mean contact area between contacting particles. These parameters are extracted using a 3D image analysis algorithm that is tested beforehand for consistency with compacted monosized sphere packings generated numerically. It is found that the mean area of contact between the irregular particles, which have been studied here, varies, as a function of relative density, according to the same relationship as that derived for spherical particles. The number of contacts, and hence the total contact area, per particle are on the other hand roughly 50% higher than for compacted monomodal spheres.