Research On Carbon And Silver Comodified ZnO Catalysts For Thermal Decomposition Performanc Of Ammonium Perchlorate

The thermal decomposition performance of oxidizer directly determines the thrust and specific impulse properties of solid propellant.ZnO has the characteristics of high catalytic activity and good stability,which can improve the heat release and decomposition temperature of the oxidant,and then improve the energy performance of the propellant.Therefore,the development of high-performance ZnO catalyst is of great significance.In this thesis,through the design,preparation and modification of ZnO catalyst and the integrated research on the catalytic performance for the thermal decomposition of ammonium perchlorate,high-performance carbon and silver co modified ZnO catalyst was obtained,which provides theoretical and technical support for the material selection and application of solid propellants.According to the mechanism of grain boundary scattering,ohmic contact barrier model and heterogeneous catalytic reaction theory,a ZnO/carbon black composite catalyst with hierarchical structure was designed,in which carbon black?CB?as the modified support material realized the rapid transfer of conduction band electrons in ZnO,the hierarchical structure profited the diffusion of reactants and products.Then the synergistic effect improved the catalytic performance.ZnO/CB composites were prepared by atomic layer deposition.The influences of deposition cycles on the structure and catalytic performance of the composites were investigated.When the number of deposition cycles was 100,the ZnO/CB composite showed the relatively good catalytic performance,which reduced the peak temperature of ammonium perchlorate thermal decomposition from 432? to 295?,increased the heat release from 369 J/g to 1692 J/g and changed the thermal decomposition process of ammonium perchlorate from two steps to one step.The ZnO in ZnO/CB composite was used as self template to induce the synthesis of metal organic framework compound ZIF-8,which was then pyrolyzed to ZnO/CB composite with hierarchical structure in air atmosphere.The hierarchical ZnO/CB composite further improved the catalytic performance,leading the thermal decomposition temperature reduced to 281? and heat release increased to 1758 J/g.The reason was that the C-O-Zn bond at the interface of ZnO/CB composite provided a fast transfer channel for the conduction band electrons of ZnO,improving the electron utilization.And the hierarchical nanosheet structure and high energy?002?plane of ZnO in ZnO/CB composite were beneficial to the adsorption and decomposition of reactants.Thus the catalytic performance of ZnO/CB composite was improved.In order to further improve the catalytic performance,the ZnO/CB composite was modified by Ag through the chemical impregnation and pyrolysis method.The Ag-ZnO/CB ternary composition was obtained,and the relationship among the chemical composition,microstructure and catalytic performance was investigated.The results showed that the Ag modified ZnO/CB composite reduced the decomposition temperature of ammonium perchlorate to 274? and increased the heat release to 1811 J/g.The improvement of catalytic performance was due to the adsorption of Ag+ ions on the surface and internal pores of ZIF-8,which made Ag nanoparticles were embedded into the hierarchical nanosheet structure of ZnO after pyrolysis.Consequently,the rich and stable interface contact between the two components enhanced the synergistic catalytic effect.The catalytic mechanism of the thermal decomposition of ammonium perchlorate was discussed through the analysis of the variation of product during the catalytic thermal decomposition process of ammonium perchlorate.According to the mechanism of electron transfer,when ZnO is used as catalyst,its conduction band electrons can be trapped by HClO₄,forming HClO_x?x=0,1,2,3?and ionized oxygen?O-?,then the high active O-can oxidize NH₃ to form nitrogen oxides.When ZnO catalyst modified by carbon black,the conduction band electrons are transferred to carbon black rapidly.The positive holes at valence band can be used as the "bridge" between NH₄⁺ and ClO₄^-,accelerating the formation of NH₃ and HClO₄.Then,the increased electrons deepen the decomposition of HClO₄ and the oxidation degree of NH₃ to generate HCl and NO₂.After the ZnO/CB composite was modified by Ag,the Cl-O bond in HClO₄ could be broken to form atomic oxygen?O?by the chemical sensitization of Ag,then the atomic oxygen?O?reacted with NH₃ to form the N₂O.ZnO based composite catalyst was applied to AP/HTPB propellant to study its effect on combustion and energy performance.The results showed that ZnO,ZnO/CB and Ag-ZnO/CB catalysts can increase the burning rate of propellant?5 MPa?from 5.75 mm/s to 6.68,8.64 and 9.46 mm/s,the burning rate pressure index reduced from 0.572 to 0.538,0.369 and 0.427,and the thrust of MEMS micro thruster increased from 58.72 to 111.4,168.8 and 254.9 ?N,respectively.These results indected that the catalyst played a significant role in improving the performance of solid propellants and provided theoretical support for the development of high energy solid propellants.