In-Situ Thermochemical Shock-Induced Stress at the Metal/Oxide Interface Enhances Reactivity of Aluminum Nanoparticles

Although aluminum (Al) nanoparticles have been widely explored as fuels in energetic applications, researchers are still exploring approaches for tuning their energy release profile via microstructural alteration. In this study, we show that a nanocomposite (similar to 70 nm) of a metal ammine complex, such as tetraamine copper nitrate (Cu(NH3)(4)(NO3)(2)/TACN), coated Al nanoparticles containing only 10 wt. % TACN, demonstrates a similar to 200 K lower reaction initiation temperature coupled with an order of magnitude enhancement in the reaction rate. Through time/temperature-resolved mass spectrometry and ignition onset measurements at high heating rates, we show that the ignition occurs due to a condensed phase reaction between Al and copper oxide (CuO) crystallized on TACN decomposition. TEM and XRD analyses on the nanoparticles at an intermediate stage show that the rapid heat release from TACN decomposition in-situ enhances the strain on the Al core with induction of nonuniformities in the thickness of its AlOx shell. The thinner region of the nonuniform shell enables rapid mass transfer of Al ions to the crystallized CuO, enabling their condensed phase ignition. Hence, the thermochemical shock from TACN coating induces stresses at the Al/AlOx interface, which effectively switches the usual gas phase O-2 diffusion-limited ignition process of Al nanoparticles to become condensed phase Al ion transfer controlled, thereby enhancing their reactivity.

Automated summary

This study demonstrates that coating aluminum nanoparticles with a metal ammine complex can lower the reaction initiation temperature and enhance the reaction rate. The ignition occurs due to a condensed phase reaction between the metal ammine complex and copper oxide. The rapid heat release induces strain on the aluminum core, resulting in a nonuniform thickness of the aluminum oxide shell, which enables rapid mass transfer and enhances reactivity.