Structural Design Of Chromium Oxygen And Manganese Oxides And Their Catalytic Thermal Decomposition Of Ammonium Perchlorate

Ammonium perchlorate?AP?is an important part of solid rocket propellant,and its research on thermal decomposition process is of great significance.With the continuous exploration of researchers,catalysts such as metal composites,carbon nanomaterials and metal oxides have been developed for the AP thermal decomposition.Among them,metal oxides are widely used in the catalytic process of AP thermal decomposition because of their low cost and good catalytic performance.Based on material synthesis and AP thermal decomposition mechanism,the research on oxide structure design has always been a hotspot in this field.The anion exchange resin was used as a hard template,and a chromium oxide microsphere?Cr₂O₃-MPB?having a porous structure was constructed by controlling the concentration of the impregnation solution?K₂Cr₂O₇?and the calcination temperature.Through SEM,Nitrogen Adsorption-Desorption and TEM characterization,Cr₂O₃-MPB has a spherical morphology?0.2 mm-0.3 mm?macroscopically,and has mesopores/macropores with a pore diameter between 20 nm and 90 nm.According to the study of synthesis mechanism,the mesoporous/macroporous channels of Cr₂O₃-MPB microspheres are formed after the removal of the organic skeleton in the resin.Therefore,the channels of Cr₂O₃-MPB microspheres have the characteristics of 3D continuous penetration.In the AP thermal decomposition,commercial Cr₂O₃ crystals have a catalytic effect on the AP thermal decomposition.The HTD temperature of AP can be reduced to385.1 ^oC and the heat release can be increased to 768.8 J·g^-1.In comparison,the catalytic performance of Cr₂O₃-MPB is much higher than that of commercial Cr₂O₃ crystals.The HTD temperature of AP can be reduced to 337.8 ^oC,and the heat release can be increased to 1203.5 J·g^-1.This is mainly attributed to the 3D inter-connected mesoporous/macroporous channel of Cr₂O₃-MPB,which is conducive to gas mass transfer.Composite oxides containing trivalent manganese and tetravalent manganese were synthesized by using KMnO₄ solution as impregnating solution and anion exchange resin as limiting growth template.The characterization results show that the composite oxide consists of Mn₂O₃ and MnO₂ crystal phases,and the sample exhibits non-porous,dense nanorod structure.In the AP thermal decomposition reaction,commercial Mn₂O₃ and MnO₂ crystals have catalytic effect on the AP thermal decomposition process.The HTD temperature of AP decreases to 340.7 ^oC and 354.9 ^oC,respectively,and the heat release increases to 872.5 J·g^-1 and 874.7 J·g^-1.In comparison,when the ratio of Mn₂O₃ to MnO₂is 1.3,the HTD temperature of AP decomposition catalyzed by composite oxides can be reduced to 320.8 ^oC,and the heat release can be increased to 1450.0 J·g^-1.The catalytic performance is much higher than that of commercial Mn₂O₃ and MnO₂ crystals.Because composite oxides do not have abundant pore structure or high specific surface area,the enhancement of AP thermal decomposition catalysis by composite oxides is independent of pore structure.Through the surface photocurrent test analysis,combined with the redox reaction mechanism in the AP thermal decomposition process,the strong catalytic effect of the composite oxide on AP decomposition is attributed to the existence of the p-n type homo-junction structure between the MnO₂ and Mn₂O₃ in the composite.Enhancement of electronic transmission.