Preparation And Application Of Ultrafine Sphere-like Fe₂O₃@AP Core-shell Composite Particles

At present,the common methods to increase the burning rate of composite solid propellants are to reduce the particle size of ammonium perchlorate(AP)and use nano-combustion catalysts.However,due to the large specific surface area and high surface energy,of ultrafine AP and nano-Fe₂O₃,ultrafine particles may agglomerate or adsorb on other substances,resulting in poor practical performance.In this subject,ultrafine sphere-like AP and ultrafine sphere-like Fe₂O₃@AP core-shell composite particles are prepared and their applications in composite solid propellants are studied.The main research works are as follows:Firstly,ultrafine sphere-like AP is prepared by reverse emulsion-cooling recrystallization method.The optimum preparation conditions are as follows:the water phase is the water solution of AP,in which the mass fraction of AP is 15%of water;the oil phase is cyclohexane;the mass fraction of mixed surfactant sodium dodecylbenzene sulfonate(SDBS)/Span-80(the mass ratio is 1:3)in the oil phase is 1.75%of the mass of water in the water phase;the volume ratio of oil phase and water phase is 5:2.The thermal decomposition characteristics and impact sensitivity of ultrafine sphere-like AP are compared with raw AP and ultrafine AP prepared by air flow pulverization.The results show that compared with raw AP,the low-temperature thermal decomposition process of ultrafine sphere-like AP and ultrafine AP is not obvious,only the high-temperature thermal decomposition process is obvious.The high temperature thermal decomposition exothermic peak temperature of ultrafine sphere-like AP is 4.6?and 4.9?higher than that of raw AP and ultrafine AP,respectively.Compared with raw AP,the apparent activation energy of ultrafine sphere-like AP is increased by 13.6%,and the pre exponential factor is decreased.The results show that the thermal stability of ultrafine sphere-like AP particles is improved after ultrafine and sphere-like.The sensitivity of ultrafine sphere-like AP and ultrafine AP is higher than that of raw material AP,and the sensitivity of ultrafine sphere-like AP is lower than that of ultrafine AP with the same particle size.Secondly,sodium citrate/Fe₂O₃(SC/Fe₂O₃)composite particles are prepared,and then ultrafine sphere-like SC/Fe₂O₃@AP core-shell composite particles are prepared by inverse emulsion-cooling recrystallization method.The thermal decomposition and impact sensitivity of SC/Fe₂O₃@AP,SC/Fe₂O₃-AP common mixtures and ultrafine spherical AP are studied.The results show that in the SC/Fe₂O₃ composite particles,sodium citrate can be well coated on the surface of nano-Fe₂O₃,which improves its dispersion in AP water solution,and the SC/Fe₂O₃@AP core-shell composite particles are prepared.Compared with the ultra-fine spherical AP,the high temperature thermal decomposition exothermic peak temperature of SC/Fe₂O₃@AP and SC/Fe₂O₃-AP are decreased,indicating that the thermal decomposition activity of SC/Fe₂O₃@AP and SC/Fe₂O₃-AP are increased,and the impact sensitivity of SC/Fe₂O₃@AP and SC/Fe₂O₃-AP also increased.Compared with SC/Fe₂O₃-AP,the high temperature thermal decomposition exothermic peak temperature of SC/Fe₂O₃@AP is decreased,the apparent activation energy decreased by about 8.6%,the thermal decomposition activity of SC/Fe₂O₃@AP is increased,and the sensitivity of SC/Fe₂O₃@AP increased by 6.5%.Finally,SC/Fe₂O₃@AP core-shell composite particles and SC/Fe₂O₃-AP mixture are applied to AP/Al/hydroxy terminated polybutadiene(HTPB)composite propellants.The effects of SC/Fe₂O₃@AP and SC/Fe₂O₃-AP on the thermal decomposition characteristics,sensitivity properties,viscosity,mechanical properties and combustion properties of AP/Al/HTPB composite solid propellants are studied.The results show that compared with SC/Fe₂O₃-AP,when SC/Fe₂O₃@AP is applied to AP/Al/HTPB composite solid propellants,the thermal decomposition exothermic peak temperature is advanced,the thermal decomposition reaction activity is increased,and the impact sensitivity is increased by 11.8%;the viscosity of propellant slurry is reduced;At the test temperature of 50?,20?and-50?,the tensile strength of the propellant increased by 10.8%,19.5%and 3.8%,respectively;the elongation at break increased by 4.5%,2.2%and 13.4%,respectively,and the mechanical properties of the propellant improved obviously;the burning rate of the propellant increased by 1.13 mm·s^-1,which is an increase of 2.5%.