Investigating the reaction mechanism of zirconium as a fuel in reactive multilayer films via multimodal analysis.

[Display omitted] • First comprehensive examination of the reaction mechanism in nanoZr-based thermite compositions. • Predominance of a low-temperature exothermic event in Zr/CuO redox reaction. • Zr undergoes a sequential three-step oxidation process below 475 °C. • Zr/CuO demonstrates a 400-fold reduction in ignition delay compared to Al/CuO. In this report, we examine the intricate details of the mechanism driving Zr/CuO thermite system, shedding new light on the exceptional reactivity of Zr fuel with oxygen. Magnetron-sputtered Zr/CuO reactive multilayers were deposited, and thermo-physical techniques were employed to characterize the progression of the chemical reaction upon heating. Unlike commonly used Al fuel, Zr/CuO exhibited 100% heat release below 500 °C, contrasting with the ∼5% observed for conventional Al/CuO system. This enhanced reactivity at low temperature is attributed to the rapid oxygen consumption behavior of Zr, due to the poor barrier of ZrO x to oxygen diffusion. The oxidizing behavior of Zr was quantitatively analyzed using electron microscopy and spectroscopy. Our observations reveal a three-step process of Zr oxidation facilitated by a rapid reduction of CuO to metallic Cu accompanied by the formation of an intermediate Cu 2 O phase: (i) a preliminary low-temperature mass transport initiating at 275 °C, (ii) partial Zr oxidation forming ZrO 2 and oxygen enriched Zr and finally (iii) complete conversion to zirconia at 450 °C. Finally, Zr/CuO reactive thin-films demonstrated a very high reactivity with an ignition delay time of 0.04 ± 0.016 ms and a burn rate of 3.5 m.s−1, in stark contrast to the same volume of Al/CuO, which failed to ignite and burn altogether. This study not only deepens our comprehension of Zr-based thermite system but also underscores its potential for diverse applications in energetic materials. [ABSTRACT FROM AUTHOR]