Dispersion of nanoparticle clusters by ball milling

The full and complete dispersion of nanoparticles is critical to enabling industry to formulate products which exploit the properties of such materials and hence realize the full economic value of such products. Ball milling is conventionally used for the comminution of particle slurries and, of the various wet milling techniques, is the most effective in producing fine particle sizes. Here we consider the use of a ball mill (also referred to as a stirred media mill) for the dispersion of a slurry of nanoparticle aggregates and compare its performance to a typical rotor-stator device commonly used by industry. The slurry is an aqueous dispersion of Aerosil 200 V that has a primary particle size of about 12 am and comes as a dry powder. On dispersion in water it forms large aggregates which are difficult to fully disperse. Aerosil is readily available in quantity and is used in a number of industrially relevant applications and so is an ideal test material for such trials. A lab scale Fryma Co-Ball mill (0.5 L volume) is used and the effects of bead fill (40-70% flow rate (0.1-1 kg/min) and rotor speed (7.5-18 m/s) are investigated. Specific energy is the most effective ways to correlate performance to particle size suggesting that residence time (i.e., flow rate) is the most important process parameter. Lower rotor speeds are also shown to be more energy efficient. The correlations show that the ball mill provides a significant improvement in dispersion (d[3,2] = 0.61 mu m) over the conventional rotor-stator device.