Process engineering with planetary ball mills

Abstract

Planetary ball mills are well known and used for particle size reduction on laboratory and pilot scales for decades while during the last few years the application of planetary ball mills has extended to mechanochemical approaches. Processes inside planetary ball mills are complex and strongly depend on the processed material and synthesis and, thus, the optimum milling conditions have to be assessed for each individual system. The present review focuses on the insight into several parameters like properties of grinding balls, the filling ratio or revolution speed. It gives examples of the aspects of grinding and illustrates some general guidelines to follow for modelling processes in planetary ball mills in terms of refinement, synthesis' yield and contamination from wear. The amount of energy transferred from the milling tools to the powder is significant and hardly measurable for processes in planetary ball mills. Thus numerical simulations based on a discrete-element-method are used to describe the energy transfer to give an adequate description of the process by correlation with experiments. The simulations illustrate the effect of the geometry of planetary ball mills on the energy entry. In addition the imaging of motion patterns inside a planetary ball mill from simulations and video recordings is shown.

Temperature progression in a mixer ball mill

“…For values of U MB \0.36, the increase of milling balls number resulted in more ball-ball and ball-wall collisions and therefore led to a higher energy input and heat dissipation. The ball movement for U MB [0.36 is hindered because of the reduced space for acceleration and less energy is dissipated, which justifies the lower final temperature [28,29]. A similar result was reported by Fang et al for the temperature that was generated in a lysis mill [30].…”

“…By adding even small amounts of quartz sand, the temperature decreased considerably [13]. The grinding stock influences the elasticity of the collisions; the velocity and motion of the milling balls are reduced and as a consequence less energy is dissipated as heat [29]. Thus, with grinding stock a ''damping effect'' can be observed.…”

In situ X-ray diffraction monitoring of a mechanochemical reaction reveals a unique topology metal-organic framework

“…However, despite significant and rapid advances in synthetic scope and methoodology [5][6][7] , the mechanistic understanding of mechanochemical reactions has remained elusive [8][9][10] , creating a major obstacle for the development and optimization of attractive proof-of-principle laboratory experiments into viable large scale processes 11 . It has been proposed that continuous mechanical stress and impact in a mechanochemical reaction environment can give rise to unusual reactivity or intermediate phases different than those normally accessible using conventional chemistry 12 .…”

Process parameter dependent growth phenomena of naproxen nanosuspension manufactured by wet media milling

“…Accordingly, the grinding behavior of a mill is determined by the type of stress events, the number of stress events supplied by the mill per unit time (stress frequency, SF) and the magnitude of the energy supplied to the product particles by the mill (stress energy, SE). As the parameters SF and SE cannot be accessed via direct measurements, numerical methods like discrete-element-methods are currently used to estimate those values inside a planetary ball mill [22]. According to Kwade, the mean stress energy in a stirred media mill is proportional to the stress energy of the grinding media SE GM , which can be calculated according to Eq.…”