ball milling high-energy ball milling CHMO:0001656 HEBM high energy ball milling The mechanical reduction of the particle size of a solid sample by grinding with one or more inert balls (ceramic, flint or stainless steel, 2–8 mm diameter) rotating at high speed (up to 650 rpm) around a horizontal axis. A high-speed agitator is used to increase the speed of the balls which are held in vacuum or in an inert gas (e.g. Ar).