Combustion performance of composite propellants containing core-shell Al@M(IO₃)_x metastable composites

Aluminum (Al) has been widely used in solid composite propellants (SCPs) to increase the specific impulse. However, Al always subjects to coalescence, sintering to large agglomerations during combustion of SCPs resulting in larger two-phase flow losses. Herein, core-shell μ-Al@M(IO₃)_x composites have designed and synthesized as a replacement for micron-sized Al (μ-Al) in the Al/AP/RDX/HTPB propellant with tunable combustion behavior. The results show the thermal reactivity and heat releases of SCP are largely enhanced by using these novel metal-based composites. With the inclusion of μ-Al@EGCG@Fe(IO₃)₃ (EGCG: Epigallocatechin gallate), the major exothermic peak is reduced by 29.1 °C compared to the reference propellant with a heat release increase up to 5475 J g⁻¹, exceeding that of the reference sample (86 J g⁻¹ higher). The burn rates are increased with the inclusion of μ-Al@(MIO₃)_x, while the pressure exponent is higher. The SCP-1 (0.3), SCP-2 (0.18) and SCP-4 (0.25) that have relatively low pressure exponent and high burn rates are good candidates for future applications. The major condensed combustion products (CCPs) of these SCPs are Al₂O₃, Al_2.81O_3.56N_0.44, Al₄C₃, Al₂OC, AlN and C₇H₁₈ClN. The agglomeration can be reduced with a minor inclusion of μ-Al@M(IO₃)_x due to the enhanced interfacial reactions, and the average CCP sizes (0.5 μm for SCP-1 and SCP-4) are even smaller than that of initial μ-Al (1.2 μm).