The charging efficiency and flow dynamics of micropowder during jet milling/electrostatic dispersion

Jet milling is a highly efficient method for preparing micro-sized powder in many areas of industry. However, aggregation of the micro-sized powder during processing often offsets the advantages of jet milling to a certain extent. In this work, we discuss a new method to prepare micro-sized powder through the combination of jet milling and electrostatic dispersion(J/E). This method helps to achieve the dual goal of producing fine powders and concurrently maintaining the dispersiveness of the powder product. Calcium carbonate (CaCO3) powders with two different mean particle sizes (10.93 and 25.43 μm) were used as raw materials. The effects of the preparation parameters (the charging voltage and the air pressure) on the charging efficiency of the powder were investigated. We have also simulated the flow dynamics of particles in the J/E chamber using COMSOL Multiphysics software. The results indicate that the charge to mass ratio (q/m) of the powder increases with the increase of the charging voltage until it reaches saturation, and the saturation charge of the raw powder with a larger mean size is higher at an air pressure of 0.3 MPa. When the charging voltage was −60 kV, the q/m of the raw powder with a smaller size reached its maximum at 0.2 MPa, whereas that of another type of the powder achieved its maximum at 0.3 MPa. This suggests that the q/m is determined by the competition between the two conflicting factors, i.e. the refined particle size and the charging time, both influenced by the air pressure and the mean particle size of the raw powder at a given charging voltage. In addition, simulation of the flow dynamics reveals that the dispersion of the particles is enhanced during the transport in the J/E chamber, with increases in the jet velocity and the charging voltage. The effect of the charging voltage is more obvious.