Enhancement in Energy Release and Combustion Efficiency of Solid Propellants by Incorporation of MoO3–x Quantum Dots into Al@AP Composites

The synergistic regulation of high energy output and low sensitivity has been a persistent research focus in solid propellant development. In this study, oxygen-deficient MoO_3–x quantum dots (QDs)-modified Al@AP core–shell composites were fabricated via spray-drying, with a reference system containing fine AP (s-AP) serving as a control group. Systematic investigations were conducted on the interfacial modification effects and the incorporation of MoO_3–x QDs on the energy release characteristics, ignition-combustion performance, and safety properties of HTPB-based composite propellants. The results indicate that SP4 with Al@AP/MoO_3–x has significantly enhanced energy outputs compared with SP1 containing Al/AP, and the heat of reaction increased from 6270 to 6615 J·g^–1 under identical loading densities. Meanwhile, the ignition delay time of SP4 was shortened from 25.76 to 16.38 ms, and the flame radiation intensity was increased from 1640.8 to 1944.2, indicating a significantly improved ignition property. Furthermore, the higher burning rate at low pressure and suppressed rate surges at high pressure of SP4 result in a reduced burning rate pressure exponent (from 0.57 to 0.39). Safety tests revealed lower impact sensitivity for Al@AP/MoO_3–x versus Al/AP/s-AP systems based on the increased burning rate. Condensed combustion product (CCP) analyses demonstrated that the core–shell structure effectively mitigated Al agglomeration, evidenced by increased fine particles and decreased Al residues, indicating an enhanced combustion efficiency. MoO_3–x QDs further optimized the CCP size distribution, reducing the dominant particle size from 44.7 to 22.3 μm.