Nanoscale Etching of Particles in Continuous Flow Reactor

Aluminum(Al)/Aluminum oxide(Al₂O₃) nano-particles are widely used as combustion catalysts for solid and liquid propellants, nano-composites, conductive coatings, nano-energetic materials etc. This necessitates their rapid synthesis with proper size control. Synthesis of these nano-particles can be done by different bottom up or top down approaches although scaling up of such processes may change their physical and chemical properties. In this work, we have used a top down approach of etching through a continuous flow micro-reactor to produce nano-particles. This approach provides a better control on the size distribution of the etched particles in comparison to other fixed volume micro-reactors. We have been able to validate our experimental data through modeling tools which indicate the rapid refluxing of the etchant at the particle interface as the main reason behind this size control. The particle size of 100 nm is reduced to a distribution 9.2 nm (average diameter) ±3 nm. Using similar conditions of the etchant and particles a fixed volume reactor is found to realize a larger average size (52 nm), a higher range and a slower etching rate.