Ignition and Combustion Characteristics of Al/TiB₂-Based Nanothermites: Effect of Bifuel Distribution

Aluminum has demonstrated compelling attributes over decades of research, encompassing affordability, abundance, and a high specific energy density when utilized as a fuel in energetic materials such as nanothermites. However, fully realizing the ignition and combustion performance of Al poses a significant challenge, primarily due to its high ignition point and sintering tendency, the latter being hypothesized to be the rate-limiting step in Al-based nanothermite combustion. Herein, we examine the influence of nano-TiB2 addition on the ignition and combustion properties of CuO/Al by adjusting the Al-TiB2 binary fuel distribution. Magnetron-sputtered CuO/Al-TiB2 multilayers were prepared, and their ignition and combustion characteristics were studied. It was found that all configurations of the CuO/Al-TiB2 system outperform CuO/Al. Notably, 62.5% loading demonstrated the most significant improvement in the ignition delay, with a decrease of similar to 100%. Furthermore, each nano-TiB2-loaded CuO/Al thermite exceeded the propagation rate of CuO/Al by a factor of 2. Differential scanning calorimetry, high-speed videography, spectroscopy, and microscopy were instrumental in elucidating the factors contributing to this improvement and understanding the role of TiB2. While low-temperature TiB2 oxidation contributed to shorter ignition delays, the combustion characteristics were found to be highly controlled by a heterogeneous gas condensed-phase reaction rather than the flame temperature and materials' thermal properties. This study demonstrates that the addition of nano-TiB2 to Al-based thermites holds a significant potential in applications where it is necessary to either lower or finely tune the ignition times. From a manufacturing perspective, this integration technique provides a straightforward approach to enhance the ignition and combustion performance of CuO/Al nanothermites.