Effects of powder–liquid states on the grinding efficiency of silica particles by rotating ball milling

Abstract

Grinding is an important and widely applied industrial process for decreasing the size of particles, and it has been most frequently carried out together with liquid medium to improve the efficiency. In this study, the relationship among various grinding times of SiO₂ particles by rotating ball milling, volumes of ethanol used as the medium (corresponding to pendular to slurry states) and types of the liquid medium were systematically investigated in terms of the grinding efficiency. Without ethanol, the SiO₂ particles could never be pulverized even after 48 h of the ball milling, whereas they were pulverized in its presence because the ethanol adsorbed on the particle restricted their adhesion. The highest grinding efficiency was achieved with 1 ml of ethanol against 20 g of SiO₂ particles with polypropylene vessel including 200 g of zirconia balls with a diameter of 5 mm and seven zirconia balls with a diameter of 10 mm under 150 rpm for 24 h. The grinding efficiency increased with decreasing viscosity, because the impact power generated by the milling was efficiently conducted toward the particles due to its high flowability and low concentration in the impact zone. The ratio of the dipole moment to molecular volume in the liquid medium strongly affected the grinding efficiency, in which ethanol could efficiently serve as the medium, because they could easily adsorb to the SiO₂ particle. The overall grinding mechanism and process factors were investigated.