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Nanoparticles can be produced by wet grinding in stirred‐media mills. In the lower nanometer range a true grinding limit exists, where the transferred energy from the grinding media is no longer sufficient to induce further breakage of the particles even after stressing events with high stress energies. Variations in process conditions lead to the conclusion that the grinding limit is hardly affected by most of the investigated process parameters. However, at high solids concentrations and/or small particle sizes, a drastic increase in suspension viscosity occurs, which leads to a dampening of the grinding media motion and to a reduction in the transferred stress energy. Hence, the rheological behavior can limit the grinding process, and a viscous dampening‐related grinding limit can be reached prior to the true grinding limit.

The influence of several process parameters like milling time, ball‐to‐beaker volume ratio, diameter of milling balls, and rotation frequency on the Knoevenagel condensation of vanillin and barbituric acid in planetary ball mills was investigated. These parameters determine the amount of energy provided for the reaction. Additionally, numerical simulations were carried out to describe the stress conditions in detail and to compute the drive power and energy transfer which cannot be measured directly. The mill and experimental parameters were modeled by the discrete element method with adequate coefficients of friction and restitution required to describe the powder behavior in the system. The coefficients were determined by correlation of experiments and simulations.

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