Influence of mechanical properties on impact fracture: Prediction of the milling behaviour of pharmaceutical powders by nanoindentation

The impact grinding behaviour of materials can be characterized by the two breakage parameters fMat and xWm,min [Vogel and Peukert, Powder Technol. 129 (2003) 101–110]. These parameters are usually determined by single particle milling tests. The parameters are useful for predicting the selection function and the breakage function and thus enable modelling of impact milling processes. So far, no detailed correlations have been established between the breakage parameters fMat and xWm,min and intrinsic material properties. In this work, we study the correlation between the breakage parameters of pharmaceutical powders and their mechanical properties (hardness, Youngʹs modulus and fracture toughness) that are determined from indentation experiments. It will be shown that fMat and xWm,min can be expressed in terms of the brittleness index (defined as the ratio of hardness to fracture toughness H/Kc). This correlation allows the prediction of the breakage probability of a material by using only a small number of crystals.