Effect of Mixing of Nanoparticle Agglomerates on Density

Mark Panczyk1, Daniel To1, Sameer Dalvi1, Rajesh Davé1, and Sankaran Sundaresan2. (1) Chemical Engineering, New Jersey Institute of Technology, 138 Warren Street, YCEES 208, Newark, NJ 07102, (2) Chemical Engineering, Princeton University, Princeton, NJ 08544

Nanotechnology is a rapidly growing field that can be used to produce high quality materials while decreasing the processing resources such as time and energy. One area where this is important is the production of composite materials by the heat treatment of powder mixtures. An example is the formation of mullite from mixtures of alumina (dp = 21 nm) and silica (dp =16 nm) nanopowders mixed in the molar ratio of 3:2. Well-mixed powders are required to achieve high mullite conversions, however the scale of mixing tends to be limited by the formation of large fractal agglomerates. Additionally, the highly porous agglomerates result in low relative densities after heat treatment, which leads to poor composite uniformity and diminished material performance. Reducing the size of the agglomerates leads to higher quality materials due to the increase in the interfacial surface area and packing density.

Silica and alumina nanopowders were mixed using Magnetically Assisted Impact Mixing (MAIM), an environmentally benign dry mixing method, where sub-millimeter magnets propelled by an alternating field were used to restructure the agglomerates and mix the powders on the sub-micron scale. The powders were mixed to varying qualities, as determined by Energy Dispersive X-Ray Spectroscopy (EDS), and then correlated to the bulk density of the mixed powder at three different stages of processing: before pressing, after pressing, and after sintering.