Environmentally benign dry mechanical mixing of nano-particles using magnetically assisted impaction mixing process

The effectiveness of magnetically assisted impaction mixing (MAIM), an environmentally benign mechanical process, in mixing SiO₂+TiO₂ and SiO₂+Al₂O₃ nanoparticle mixtures has been examined. Experiments were carried out at different magnet-to-sample weight ratios, processing times, and magnet sizes. The homogeneity of mixing (HoM) was evaluated at the micron scale using field-emission scanning electron microscopy and energy dispersive X-ray spectroscopy, and at sub-micron scale through electron energy loss spectroscopy and transmission electron microscopy. The HoM improved with an increase in the magnet-to-sample weight ratio and processing time, and a decrease in the magnet size; over the range of conditions tested, the HoM was found to depend on the product of processing time and the number of magnets per unit powder mass. Optimized MAIM process achieved HoM values that were comparable to those attained with Rapid Expansion of Supercritical or High-Pressure Suspensions and sonication of a suspension of the nanoparticles in supercritical CO₂.