Modelling of high-energy grinding processes

The comminution and tuning of several structural parameters of materials is often accomplished following a top-down route by high energy grinding. The reduced size of the particles constituting the end product and the incorporation of defects cause modified materials properties and increased solid-state chemical reactivity. Among grinding devices, the planetary ball mill features high efficiency and versatility, being suitable for almost any kind of material, from metals and ceramics to organic compounds and pharmaceuticals. While its design and the working principle are rather simple, since grinding occurs by impacts between milling media (balls and jar) and mill charge, the characteristics of the end product strongly depend on a multitude of variables, determining balls trajectories and velocities and, in turn, the nature of impulsive forces exchanged during collisions. Numerical models can enourmously contribute to shed light on the process by providing the time evolution of kinematic and dynamic properties of milling media as well as quantities involved in contact events, permitting to understand the role of each milling variable and to design the characteristics of the end product. This Thesis chiefly proposes the implementation of a multibody dynamics model of the planetary ball milling process, its direct and indirect validation – respectively against movie collected in-operando and properties of the end product revealed by the analysis of X-ray powder diffraction data –, the evaluation of the effect of selected milling variables and the investigation of innovative solutions defining specific collisions features, obtained by the re-design of the jar shape. Some relevant case studies are also presented, namely the exfoliation of a bulk for the production of 2D nanostructured materials and the milling of the pharmaceutical compound Efavirenz, aimed at inducing structural and microstructural transformations enhancing dissolution properties.