Synthesis and mechanistic exploration of interfacial control and enhanced catalysis for improving thermal decomposition of AP in Al@AP-Fe₂O₃ composites

Ammonium perchlorate (AP) is commonly used as an oxidant in composite solid propellants (CSPs). The thermal behavior of AP has a significant impact on CSP combustion. This study investigates the thermal behavior of Al-AP-Fe₂O₃ and Al@AP-Fe₂O₃ particles, which were produced using a recrystallization method, under various pressures. The ability of Fe₂O₃ to regulate the decomposition rate of AP and the reasons for the reduced ignition delay under enhanced Fe₂O₃ catalysis are also explored by using density functional theory (DFT) calculations. The results indicate that Fe₂O₃ with a large catalytic contact area has a strong ability to regulate the decomposition rate of AP. The decreasing trend of the temperature difference between low- and high-temperature decomposition peaks belonging to the Al@AP-Fe₂O₃ (32 °C (0.1 MPa) → 19 °C (1.0 MPa) → 14 °C (4.0 MPa)) is weaker than that of the Al-AP-Fe₂O₃ (60 °C (0.1 MPa) → 25 °C (1.0 MPa) → 0 °C (4.0 MPa)) under various pressures. Additionally, the low activation energy of ∗NH₄ClO₄ → ∗NH₃ + ∗H (∗O_3b) + ∗ClO₄ (300 °C: 0.207 eV) is the main reason for the initial decomposition of AP to accelerate and the ignition delay to be reduced under the more adequate α-Fe₂O₃ catalysis. Furthermore, the catalysis of α-Fe₂O₃ with a large contact area can further facilitate or control the oxidation of NH₃ under various pressures or temperatures, influencing the decomposition of AP and enabling its regulation. This study therefore highlights the importance of understanding the catalytic properties of Fe₂O₃ for improving the performance of CSPs and optimizing their combustion behavior.