Enhancing the reactivity and combustion efficiency of Al@AP by precise catalysis of MoO_3-x quantum dots with oxygen vacancy

Aluminum (Al) can significantly improve the energy density and specific impulse (I_sp) of solid rocket propellants as the primary metal fuel, but its incomplete combustion results in an undesirable energy release performance. The strategy of fuel/oxidizer interfacial control has been proved to effectively enhance the reaction efficiency of Al-based composites and thus improving the combustion properties of solid propellants. Ammonium perchlorate (AP) is commonly used as a high-energy oxidizer in solid propellant, and its thermal decomposition behavior directly affects the combustion characteristics of propellants. The addition of combustion catalysts can decrease thermal decomposition temperature and increase thermal reactivity of AP. As an emerging catalytic material, MoO_3-x quantum dots (QDs) with oxygen vacancies possess a high specific surface and strong charge adsorption capacity, which renders it a great potential for catalyzing AP. In this study, MoO_3-x QDs were introduced as catalyst and compared with traditional nano-metal oxides (M_xO_y), the spherical Al@AP/M_xO_y composites with polydopamine as interfacial layer were prepared by spray drying method. The particle morphology, thermal decomposition kinetics and ignition properties of Al@AP/M_xO_y were investigated. The phase composition, morphology and particle size distribution for the condensed combustion products of composites were further analyzed. The decreased particle size and less unreacted Al content in CCPs indicated the increase of combustion efficiency between Al and AP. In particular, Al@AP/MoO_3-x has the higher heat of reaction, lower thermal decomposition temperature and small CCPs particle size distribution, which collectively suggested that the MoO_3-x is capable to improve the thermal reactivity of Al@AP composites with a higher combustion efficiency.