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

Abstract

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-TiB 2 addition on the ignition and combustion properties of CuO/Al by adjusting the Al-TiB 2 binary fuel distribution. Magnetron-sputtered CuO/Al-TiB 2 multilayers were prepared, and their ignition and combustion characteristics were studied. It was found that all configurations of the CuO/Al-TiB 2 system outperform CuO/Al. Notably, 62.5% loading demonstrated the most significant improvement in the ignition delay, with a decrease of ∼100%. Furthermore, each nano-TiB 2 -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 TiB 2 . While low-temperature TiB 2 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-TiB 2 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.

Design and Fabrication of a Fast-Response and Low-Energy Input Micro-Igniter

“…Reducing ignition time can be achieved either by increasing the input current [28] which is not desirable in miniaturized and embedded systems, or, by modifying the composition or properties of the thermite film [30,37,38]. We explored the replacement of Al by Ti in the first bilayer of CuO/Al multilayer films owing to the high reactivity of Ti as a fuel [30,49].…”

“…A typical RMFB comprises of a metallic thin film (such as Ni-Cr [22,34], Cr [35], Au-Ti [26], Ti [28,30,31]) onto which a reactive multilayer film is deposited. This latter is composed of alternating nanolayers (tens to hundreds of nm) of metal (Al [29,36], Ti [30], TiB2 [37,38]) and oxidizer (CuO [39,40], MoO3 [27]). Aluminum is often the chosen metal for the reactive multilayer films due to its high availability, low cost and well-developed deposition process [29].…”

Synergistic Enhancement on Ignition and Combustion Properties of Boron via Viton Core–Shell Coating

“…To improve the ignition and combustion characteristics of boron, many groups have carried out research on the modification of boron, such as metals (Al, , Fe, Ti, Mg, and Ni), which are more reducible and reactive compared to boron powder and can form metal borides with boron at lower ignition temperatures, thus enhancing the ignition and combustion of boron. For example, 1% Ni increases the total heat release and average combustion intensity of boron by 7.7 and 19.5%, respectively .…”