Effect of Small Size Beads on Dispersion of Nanometer-Sized Silica Particle by Wet Beads Mill Process

Abstract

Wet dispersion mechanism of manometer-sized silica powder was investigated in a verticaltype beads mill using fine zirconium oxide (zirconia) beads. Zirconia beads of various sizes were used to disperse coagulated silica powders in nanometer size. The dispersed particles were measured by TEM and a dynamic light scattering technique and the contamination during the dispersion was also evaluated. Fine beads with the average diameters of 20μm and 50μm were found to be very effective for suppressing contamination from the beads as well as for achieving its homodispersity. 300μm-zirconia beads used in the present work had a very rough surface, which resulted in the silica powder contamination with zirconia in the level of 3250ppm. On the contrary, the surface of 20μm-beads was smooth and zirconia-contamination in the silica powder was decreased to 240ppm. The observation of bead surface and the amount of zirconia (impurity) suggested that the surface of large bead is easily worn away due to the collisions between the beads compared to smaller beads. The coagulated silica powder can be dispersed homogeneously using the beads with size smaller than 50μm, whereas coagulated silica particles were observed using the beads with size larger than 100μm. For coagulates of nanoparticles, main dispersion mechanism with large beads is pulverization while that with small beads is deflocculation. It is important not to give excessive energy to the coagulated particles for preventing the recoagulation and the contamination from the beads. Smaller beads (below 100μm) is suitable in this case.