Enhancement in Energy Release and Combustion Efficiency of Solid Propellants by Incorporation of MoO_3-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.