Mechanochemical aspects in wet stirred media milling

Abstract

Wet comminution in stirred media mills is a frequently applied fully scalable top-down method towards the production of micron- and submicron particles. Despite the vast field of mechanochemistry which encompasses an increase in reactivity due to the effect of mechanical energy input, there is still no clear picture of the involved mechanisms. In ultra-fine wet grinding the situation is further complicated due to the presence of the solvent: reactions of the stressed solid with the surrounding liquid phase can occur. In this paper several aspects of mechanochemistry occurring in stirred media mills are outlined through suitable experiments. Main focus lies on the comprehensive product characterization and on the role of the liquid phase. It is shown that the liquid phase influences product properties like particle size, porosity, particle shape, structure, chemical composition and the molecular termination of the surface. An increase in the reactivity of ground solids is manifested by a significant increase in dissolution in the aqueous phase during processing in water. Altogether, the liquid dispersion medium which can act as solvent is thus introduced as a new process parameter in stirred media milling and offers new prospects for innovative product design by top-down approaches.