Nano Aluminum Synthesis with Nonthermal Capacitively Coupled Plasma for Enhanced Yield and Size Control

Aluminum is one of the most prevalent naturally occurring resources on Earth. The characteristics and applications of bulk aluminum have been established, but synthesis of nanoscale aluminum (nAl) with tunable particle size and distribution has been problematic due to the processing limitations imposed by the current state-of-the-art techniques. Limitations to produce metal nanoparticles incentivizes the development of new synthesis methodologies for nAl, particularly if those are capable of providing enhanced size control. We have previously synthesized nAl particles via nonequilibrium, inductively coupled plasmas and successfully identified major improvements to the synthesis rate and the effectiveness of using aluminum trichloride (AlCl₃) as a precursor. This work presents the synthesis of nAl particles with significantly increased batch yield and the capability to tune particle sizes in a wide range via capacitively coupled plasmas. A radiofrequency nonequilibrium plasma was applied to a mixture of argon, hydrogen and AlCl3 to facilitate the nucleation and growth of nAl particles. Our preliminary results demonstrate close to a 10-times higher production yield than our previous work and tunable sizes from 6 to 45 nm through variations of the plasma power. Powder X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy revealed a high degree of metallic aluminum, a reduced occurrence of amorphous Al byproducts such as alumina and AlCl₃, as well as monodisperse particles with a narrow size distribution.<br/>This work was primarily supported by the US Army Combat Capabilities Development Command-Army Research Laboratory under Cooperative Agreement W911NF-19-2-0283.