Fengdan Zhu,Chang Liu,Desheng Yang,Chaofei Bai,Xinlong Zeng,Ziteng Niu,Guoping Li,Yunjun Luo
Nitro complexes (NCs) have been selected as combustion catalysts for propellants due to their synergistic behavior. However, NCs prepared by traditional methods suffer from poor dispersion and irregular shape, which limit their catalytic potential. Hence, a polymer-assisted anti-solvent crystallization (PAASC) strategy was developed to fabricate potassium barium hexanitronickelate (K 2 Ba[Ni(NO 2 ) 6 ], PBHNN) crystals. In this method, emulsion particles created by mixing the solvent with the poor solvent serve as spherical templates. The particle size and monodispersity of PBHNN are controlled by PVP content. With 0.042 mol/L PVP, PBHNN were monodisperse with a particle size of 1.05±0.03 μm, which showed the best catalytic behavior for increasing the exothermic amount of hexanitrohexaazaisowurtzitane (HNIW) by 100.6 %. The high catalytic performance is due to the large specific surface area and improved contact efficiency. The in-situ TG-FTIR-MS test revealed that the procedure of PBHNN enhanced the pyrolysis of HNIW. The N-NO 2 bonds of HNIW are weakened by the strong attraction of metal oxides to electrons, which accelerates the formation of NO 2 . Consequently, increased NO 2 promotes subsequent oxidation reactions and improves the pyrolysis efficiency of individual HNIW. Therefore, the PAASC method is crucial for the fabrication of spherical monodisperse NCs with uniform particle size and high catalytic activity.
Hexanitro complex K 2 Ba[Ni(NO 2 ) 6 ] was prepared via the co-precipitation method, and its composition and morphology were characterized by XRD , SEM , XPS and FT-IR techniques. The catalytic performances of K 2 Ba[Ni(NO 2 ) 6 ] for CL-20, FOX-7 and TKX-50 thermolysis were also discussed and studied by using DSC and TG-DTG-MS. After K 2 Ba[Ni(NO 2 ) 6 ] were mixed with CL-20, the activation energy ( E a ) of thermolysis reaction was increased, while the heat release was greatly improved, and the transformation from NH 3 to NO occurred. It is attributed to that the decomposition products of K 2 Ba[Ni(NO 2 ) 6 ] have strong effects on the oxidation of the radicals and the electrons transfer . Besides, the thermolysis E a of FOX-7 by addition of the K 2 Ba[Ni(NO 2 ) 6 ] was increased by 81.03 kJ mol −1 , and the heat release was greatly increased. In addition to that the two-step separate thermolysis processes of pure FOX-7 was almost replaced by a one-step exothermic reaction for the FOX-7/K 2 Ba[Ni(NO 2 ) 6 ] mixture, which was due to that Ni 2+ cations could effectively increase the activity of amino groups in the FOX-7 thermolysis process. Finally, K 2 Ba[Ni(NO 2 ) 6 ] scarcely has the thermolysis catalytic activity of TKX-50 owing to the influence of metal cations on the decomposition of the hydroxylamine . Furtherly, the characteristics of ignition and flame propagation on the three energetic mixtures were strongly correlated to their thermolysis pathway and mechanism. The comparative study on the effects of K 2 Ba[Ni(NO 2 ) 6 ] to the CL-20, FOX-7 and TKX-50 thermolysis and ignition showed that the hexanitro complex has great significance on promoting the heat release efficiency of solid propellants for future study.
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