Combustion performance of tannic acid-Fe(III) coated Al-10Li particles with improved chemical stability

Owing to their superior combustion performance, aluminum-lithium particles (Al-Li) are frequently considered as an alternative to aluminum as high-energy metallic fuels. However, the poor chemical stability of Al-10Li particles limits their wide applications. To address this, a core shell structure of tannic acid-Fe(III) (TA-Fe) is fabricated on Al-10Li particles (denoted as Al-10Li@TA-Fe) through a low-cost and one-step self-assembly method. The distribution and morphology of the surface coating are characterized by Fourier-transform infrared spectroscopy, energy-dispersive spectroscopy, and field emission scanning electron microscopy. The chemical stability of the Al-10Li@TA-Fe particles is assessed by mixing with ammonium perchlorate (AP). Results indicate that the TA-Fe coating significantly enhances the chemical stability of the Al-10Li particles by suppressing the reaction between Li and AP, which forms gas species of NH₃. Furthermore, the combustion performance of both the coated and uncoated particles is studied based on a single-particle ignition and combustion platform by comparing the ignition delay time and the micro-explosion delay time. Results indicate that though the surface coating inhibits the heat transfer to the inner particle, it paradoxically facilitates the weakening of the surface oxide shell of Al-10Li through chemical reactions between TA-Fe and Al-10Li as revealed by FTIR and SEM analyses after heat treatment. Therefore, the synergistic effect of these two competing processes enables the Al-10Li@TA-Fe particles to simultaneously retain ignition and micro-explosion delay times comparable to those of uncoated Al-10Li particles at high temperatures. Novelty and significance statement Despite the superior combustion performance, Al-Li particles suffer from low chemical stability. Existing surface coating strategies, primarily developed for low-Li-content particles, often involve complex preparation or high cost. This work presents a low-cost, one-step coating strategy based on tannic acid-Fe(III) (TA-Fe) self-assembly for high-Li-content Al-10Li particles. Experimental results indicate that the coated Al-10Li particles exhibit significantly enhanced chemical stability and compatibility with ammonium perchlorate, even when mixed with the oxidizer of ammonium perchlorate, while maintaining comparable combustion performance to uncoated Al-10Li particles. The coating strategy developed in the present study is critical for the design, preparation, and optimization of advanced solid propellants.