Exploiting the Synthesis of Uniform-sized Aluminum Nanocrystals through Low-pressure Nonequilibrium Plasmas (Dusty Plasmas)*

The high specific surface areas and intrinsic reactive properties of aluminum (Al) nanoparticles (nAl) make them attractive for many applications. However, affordable commercial nAl powders are severely hindered by wide particle size distributions ranging from tens of nanometers up to more than several microns and thick inactive oxide passivation shells surrounding the active metal cores. These disadvantages are especially unfavorable for using nAl as high-energy fuels for reactive materials applications. It is crucial to develop scalable methodologies for the synthesis of nAl with tunable crystallinity, particle size and size distribution. Plasma technologies couple matter with energy and thus provide unique opportunities for synthesizing nanoparticles which otherwise would be technically challenging to produce with conventional methods. This work presents our study of nAl nucleation and growth by using different Al-containing precursors in argon in low-pressure nonequilibrium plasmas (dusty plasmas). We found that the properties of nAl, including the particle size, Al crystallinity, chemical composition, and yield are highly dependent on the plasma type and setup, as well as the plasma experimental conditions. These include precursor and gas compositions, flow rate, and plasma power. In this presentation, we will demonstrate our success of synthesizing plasma-tunable uniform nAl using aluminum trichloride (AlCl₃) as a precursor in capacitively coupled plasmas (CCP). Characterization of various techniques confirm the high purity and crystallinity of our CCP-synthesized nAl crystals as opposed to those synthesized via inductively coupled plasmas. This work shows the promise of synthesizing nAl with significantly superior properties to current state-of-art commercial products via scalable dusty plasma techniques.