How Metal Oxides Change the Reaction Characteristics of Nanothermites

Nanothermites are an emerging energetic material with increasing potential in engineering applications. However, their reaction mechanisms, especially during rapid combustion, are not well understood. This knowledge gap hinders the optimal design and tailoring of nanothermites for specific applications. In this work, several nanothermite composite reactions are investigated through the analysis of reaction characteristics and varying microstructures before and after combustion. The aluminum copper oxide (Al/CuO), aluminum iron oxide (Al/Fe2O3), or aluminum bismuth oxide (Al/Bi2O3) particles are loaded with graphene sheets and ethylenediamine into a direct ink writing system which prints the porous aerogel structure with closely packed nanoenergetic clusters, confirmed by scanning electron microscopy and energy dispersive spectroscopy images. Combustion tests recorded on high-speed and thermal cameras demonstrated the distinct propagation rates and temperature profiles of the three nanothermite composites. After combustion, the products were directly collected, enabled by the remaining graphene structure of the aerogel, and analyzed by scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. The final microstructures, being distinguished by varying size and morphology of the alumina and metal particles in different samples, give valuable insight into the reaction mechanism of each thermite pair. The choice of metal oxide is found to play a crucial role in determining the reaction temperature at the flame front and thus controlling the local reactions of the material. At different temperatures, the occurrence of vapor condensation processes, the condensed phase reaction, and reactive sintering are analyzed and discussed, summarized as key reaction mechanisms during the combustion.