A model based uniquely on condensed phase reactions coupled with the thermal equation is developed to study the initiation and early stage of the redox reaction in Al/CuO nanothermites. It considers the effect of a wetting contact angle between Al and CuO particles, which may be induced by sintering mechanisms and/or the synthesis method. In order to validate the model, two published experiments are reproduced in silico. Results provide the first quantification of: (i) how sintering affects the initiation of Al/CuO nanoparticle mixtures, depending on experimental conditions, (ii) the extent to which condensed phase mechanisms dominate gas-mediated reactions in the initiation process, two subjects that have been highly debated in the literature. It was found that initiation appears more strongly affected by sintering when particles are exposed to an ultra-short and intense heat pulse (∼1011 K s−1) than those exposed to a lower heating rate (∼105 K s−1). Additionally, calculations show that sintering may cause a drastic decrease in the initiation delay (down to the ns regime) when using CuO nanoparticles below 50 nm in diameter that can be brought to melting temperature through optical absorption. Finally, the role of gas-surface versus condensed phase reactions in the Al/CuO initiation process is evaluated theoretically. Initiation through condensed phase reactions, while slightly faster and more efficient, exhibits a comparable timescale (∼1–2 ms) to initiation through gas-surface reactions, providing clear evidence for the contribution of both during the initiation phase.
This paper describes a kinetic model dedicated to thermite nanopowder combustion, in which core equations are based on condensed phase mechanisms only. We explore all combinations of fuels/oxidizers, namely Al, Zr, B/CuO, Fe2O3, WO3, and Pb3O4, with 60 % of the theoretical maximum density packing, at which condensed phase mechanisms govern the reaction. Aluminothermites offer the best performances, with initiation delays in the range of a few tens of microseconds, and faster burn rates (60 cm s−1 for CuO). B and Zr based thermites are primarily limited by diffusion characteristics in their oxides that are more stringent than the common Al2O3 barrier layer. Combination of a poor thermal conductivity and efficient oxygen diffusion towards the fuel allows rapid initiation, while thermal conductivity is essential to increase the burn rate, as evidenced from iron oxide giving the fastest burn rates of all B- and Zr-based thermites (16 and 32 cm·s−1, respectively) despite poor mass transport properties in the condensed phase; almost at the level of Al/CuO (41 versus 61 cm·s−1). Finally, formulations of the effective thermal conduction coefficient are provided, from pure bulk, to nanoparticular structured material, giving light to the effects of the microstructure and its size distribution on thermite performances.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.