Identifying the apparent and true grinding limit

Comminution in stirred media mills enables the production of ultrafine particles down to the nanometer range. The grinding results are mainly determined by two contrary mechanisms: particle breakage and agglomeration of the so-created fragments. These competing phenomena often lead to a plateau in particle size above a certain energy input. The degree of agglomeration and therefore the final aggregate size can be controlled by the addition of stabilizers and by the applied shear forces. In this paper the agglomeration behavior of silica particles under different milling and stability conditions is presented. Furthermore the particle breakage behavior in the nanometer range as the other size-determining mechanism will be discussed. In long term grinding experiments with different materials the kinetics of particle breakage as well as the grinding limit as the minimal achievable particle size could be obtained.

In wet grinding processes most materials show after certain milling time no further grinding progress and a plateau in particle size is reached. One can distinguish between the apparent grinding limit, which is an agglomerate size strongly depending on the stability of the suspension, and the true grinding limit. This true grinding limit is determined by microstructural changes inside the particles and can be influenced by material and process parameters.Figure optionsDownload as PowerPoint slide