Tunable catalytic activity of energetic multi-metal hexanitro complexes for RDX decomposition and ignition

Abstract

Development of the high energy and low signature propellants with controllable heat releases is always desirable but challenging. Herein, four versatile energetic materials, multi-metal hexanitro complexes (K3[Co(NO2)6], K2Pb[M(NO2)6] (M = Cu2+, Ni2+, Co2+)) as potential catalysts and flash suppressors of the propellants, have been prepared and characterized, and their effects on the non-isothermal and adiabatic decomposition behaviors and kinetics, pyrolysis pathway, heat release, laser ignition and flame propagation properties of RDX have been studied. The results showed that the structure, composition, powder color, and morphology of the hexanitro complexes were transformed due to the substation of transition metal cations, resulting in their different thermal behaviors. The study of the non-isothermal decomposition kinetics showed that the decomposition peak temperature and activation energy (Ea) of RDX was decreased by the addition of hexanitro complexes, and addition of K2Pb[Co(NO2)6] to RDX has the lowest activation energy, while the replacing of the transition metal cations Cu2+ and Ni2+ for Co2+ cannot improve the catalytic activity. The influence of hexanitro complexes on the main pyrolysis pathway of RDX was studied by the TG-FTIR technique, and it is found that the decomposition products (NO and metal oxides) of hexanitro complexes resulted in the transformation of the pyrolysis mechanism of RDX. The adiabatic decomposition results showed that the RDX/K2Pb[Cu(NO2)6] had the largest self-heat rate and the lowest Ea, whereas the RDX/K2Pb[Co(NO2)6] have the shortest time to maximum rate under adiabatic condition. The addition of K2Pb[Cu(NO2)6] to RDX resulted in the largest total heat release, the fastest release rate, and the lowest ignition delay time. The results from the non-isothermal and adiabatic decomposition, heat release and ignition presented that the diverse metal cations in the hexanitro complexes led to the different catalytic performances, which indicated the tunable catalytic activities of hexanitro complex systems to RDX pyrolysis. The hexanitro complexes facilitated the mass and heat transfer in the flame propagation process, owing to the formation of enormous gaseous products and microparticles. Therefore, the tunable characterization of energetic hexanitro complexes demonstrated that these complexes have a large potential application for controlling the heat release of the solid propellants.