The Stabilization Of Energetic Material α Al Uminum Hydride And Its Combustion Performance

As the power source of rocket engine,solid propellants generally adopt the aluminum powder as the fuel,which has the disadvantages of insufficient combustion and high ignition temperature.Meanwhile,the metal hydride Aluminum hydride（AlH₃）is an ideal energetic material with high energy density,low decomposition temperature and excellent combustion performance in contrast with other metal fuels.The most stable crystal phase α-AlH₃ is commonly used as a fuel for solid rocket propellants and a hydrogen source of portable fuel cells.However,the complex preparation process and poor storage stability of α-AlH₃ affects its combustion performance and safety performance.Herein,this thesis optimized the synthesis process and described the stability of α-AlH₃ and its application in the solid propellants.In addition,we introduced two α-AlH₃ stabilized composite materials to improve the stability and combustion performance of α-AlH₃ and realize the application in the field of propellants.Finally,the change of surface bonding energy of α-AlH₃ before and after stabilization was calculated by density functional theory to study the synthesis mechanism of the composite materials.Firstly,we determined the optimal synthesis scheme of Aluminum hydride with liquid phase synthesis,solid-phase crystal transformation catalyzed by 5 % LiAlH₄,and purification with ether at low temperature,and then obtained the high purity α-AlH₃;Then,the storage stability,humidity stability and thermal stability of α-AlH₃ were studied,in which the surface of α-AlH₃ would form a scaly oxide layer after 14 days of storage,and the humidity seriously affected the stability;Afterwards,α-AlH₃ based solid propellants were prepared and tested,which found that α-AlH₃ could significantly improve the combustion performance of the propellants with the heat of combustion raising to 150 %,and the maximum combustion temperature increasing by about 200 ℃.However,the presence of voids and wrinkles in α-AlH₃ based propellants due to the poor stability and compatibility of α-AlH₃ was not suitable for application.Therefore,the stabilization of α-AlH₃ has an important application value in the field of solid propellants.Secondly,two types of α-AlH₃ stabilized composites were synthesized by chemical adsorption and in-situ polymerization modification to solve the problem of poor stability of α-AlH₃.The synthesis methods,storage stability,humidity stability,thermal stability,and combustion performance of the composites were compared.Among them,the composites modified by acetylacetone had the excellent storage stability and complete coating structure with no oxide layer forming on the surface after 30 days.Unfortunately,the thermal stability was no significant improvement because of the poor thermal decomposition of bonding agent.What’s more,compared with PS@α-AlH₃ and PMA/PS@α-AlH₃ synthesized by in-situ polymerization,the PMA@α-AlH₃ which was received by in-situ polymerization of methyl acrylate exhibited the cross-linking structures,larger particle size,complete cladding,excellent stability,and combustion performance.The humidity decomposition rate decreased to 9.45 % of α-AlH₃,the thermal decomposition rate decreased to 42.72 %,and the ignition delay time decreased from 400 ms to 12 ms.The excellent performance of PMA@AlH₃ made this composite a prospective energetic material with broad application.Finally,the adsorption energy of α-AlH₃ with the coating agent was calculated by density functional theory（DFT）,which confirmed that the composite materials were synthetized separately by chemical adsorption of acetylacetone and methyl acrylate.The coating agents could avoid the adsorption of water molecules and improve the humidity stability by occupying the binding sites on the surface of α-AlH₃.