(299f) Deagglomeration and Mixing of Nanopowders Using RESS Based Methods

Nano-sized materials are gaining popularity because of their unique properties. The high interfacial area can result in improved interactions and increased reaction rates over micron-sized materials, however these desired properties are often not realized due to the agglomeration of the individual nano-sized constituents limiting the available surface area. A common method to overcome this limitation is by mixing two nano-powders together on the particulate scale, which ensures a high interfacial surface area between the two constituents. This is achieved by first breaking up the individual constituent powders and then mix them together. This method is most commonly performed in liquid solvents, however removal of the suspending fluid can be expensive in terms of both time and resources, and potentially lead to drying based segregation. Additionally these solvents can be harmful to the operators and the environment. Therefore the objective of this work was to use dry mixing methods, which are environmentally friendly, to improve the quality of mixing of alumina (dp = 13 nm) and silica (dp = 16 nm) nano-powders using a RESS based mixing method.

The powders were mixed using Rapid Expansion of High Pressure and Supercritical Suspensions process, where nanopowders suspended in high pressure carbon dioxide were simultaneously deagglomerated and mixed upon expansion through a micron-sized capillary nozzle. Agglomerate sizes were determined using a Scanning Mobility Particle Spectrometer (SMPS), by TSI, Inc, which uses differential mobility analysis, an online technique, as well as collection by diffusion and image analysis performed with field emission scanning electron microscopy (SEM). The mixing quality was determined by electron microscopy in conjunction with Energy Dispersive X-Ray Spectroscopy (SEM-EDS). It was shown that mixing quality was dependent on a variety of factors including deagglomeration efficiency, nozzle diameter and premixing.