Preparation Of Graphene/Iron-based Metal Oxides And Catalytic Decomposition For Energetic Components And The Thermite Performance

Solid propellants play an important role in national defense system,which requires high specific impact,high density,high burning rate,etc.Combustion catalyst is one of the essential components.Therefore,the exploration of new catalyst is of great significance to improve the combustion performance of propellants.Graphene has large specific surface area,excellent thermal conductivity and mechanical strength,making it widely concerned in propellants.It can not only be used alone in propellants,but also can be used as carrier material to load nanocatalysts.In this work,we aimed at synthesizing graphene-based catalysts for catalytic decomposition of energetic components,and several graphene-based nanomaterials were prepared.The detailed contents are as follows:(1)A rFe₂O₃/rGO composite with three-dimensional macroporous structure was prepared by self-assembly approach.The prepared materials were characterized via XRD,SEM,TEM and XPS.DSC was used to evaluate the catalytic activities of rFe₂O₃and rFe₂O₃/rGO in the thermal decomposition of hexanitrohexaazaisowurtzitane(CL-20).The results reveal the excellent catalytic activity of rFe₂O₃/rGO on the thermal decomposition of CL-20,the apparent activation energy of CL-20 decreases by 19.69 k J·mol^-1 in the presence of rFe₂O₃/rGO.The thermal decomposition kinetics of CL-20 with or without catalyst were further studied.It is found that the addition of the catalyst does not change the decomposition mechanism of CL-20.The influences of rFe₂O₃ and rFe₂O₃/rGO on the impact sensitivity of CL-20 were further compared.It can be see that the introduction of graphene reduces the impact sensitivity of CL-20 by 2.0 J,and effectively improves its safe performance.(2)The?-Fe₂O₃/rGO composites with flower-like microsphere structure can be synthesized by one-step solvothermal method.By optimizing the preparation conditions,it is found that graphene acts as both carrier and morphological regulator,forming an intimately coupled structure between graphene sheets and?-Fe₂O₃ particles.As the increase of graphene content,the particle size of?-Fe₂O₃ changes from micron-scale sphere to nanoscale flower-like particles.The effects of?-Fe₂O₃/rGO-2 on the thermal decomposition behavior of CL-20 and HMX were studied by DSC,and?-Fe₂O₃/rGO-2decreased their energy barriers by 32.34 and 88.63 k J·mol^-1,respectively.Furthermore,the thermal decomposition kinetic of CL-20 was found to be transformed from random nucleation-subsequent growth to auto catalysis-branch random nucleation model in the precence of?-Fe₂O₃/rGO-2.(3)A subnanometer-sized amorphous iron oxide(am-Fe₂O₃)was prepared via solvothermal method.Three iron oxides with different crystalline states were obtained by regulating the reaction temperature and calcination temperature.And their catalytic activities of amorphous and crystalline iron oxides on the thermolysis of HMX were studied by DSC.With the increase of crystallinity,the exothermic peak temperature decreases from 283.16 to 265.41,268.93 and 273.54?,respectively.Results show that the catalytic effect of amorphous iron oxide is better than crystalline iron oxide.The am-Fe₂O₃/rGO also was synthesized by simple one-step solvothermal route and was used to catalytic decomposition of HMX and CL-20.The optimum ratio of graphene to am-Fe₂O₃ was evaluated through DSC test.It was found that the catalytic activity of am-Fe₂O₃/rGO complex at low graphene concentration was better than that of am-Fe₂O₃.(4)CoFe₂O₄/rGO composites were prepared by one-step solvothermal method with a particles size of?22 nm,which was used to catalytic decomposition of energetic materials(EMs)and prepare thermites.The effect of graphene concentration on the catalytic decomposition efficiency,thermite behavior,energy output and ignition property of CoFe₂O₄/rGO were investigated.DSC results show that graphene concentration plays an important role in regulating the catalytic decomposition efficiency of CoFe₂O₄/rGO on the thermolysis of EMs.With the increase of graphene concentration,the catalytic activity of CoFe₂O₄/rGO decreases gradually.The study of thermite behavior and laser ignition experiment reveal that the lower concentration of graphene can ensure that thermite is easy to ignite,and has a higher energy level.Through the comprehensive analysis,one can see that only a proper concentration of graphene and CoFe₂O₄ play a gretest role in EMs.(5)Bismuth doped hematite(Bi-Fe₂O₃)was prepared by one-step hydrothermal method,and then three-dimensional porous Bi-Fe₂O₃/rGO composites were prepared using a self-assembly approach.These prepared catalysts were used to catalytic decomposition of HMX and applied into thermite.The effects of Bi doping on the catalytic activity,thermite behavior,energy release and ignition property were systematically compared.Bi doping introduces more defects in the lattice of Fe₂O₃,which increases the surface active sites,and the introduction of graphene can inhibit the agglomeration of particles,thus making Bi-Fe₂O₃/rGO shows the optimal catalytic decomposition efficiency.The exothermic decomposition peak temperature and apparent activation energy of HMX decreased by11.37?and 349.53 k J·mol^-1,respectively.Through the study of thermite behavior,it can be found that the reaction rate of Al/Bix-Fe₂O₃ is faster than that of undoped Al/Fe₂O₃,which indicates that doping can improve the energy release rate.Laser ignition experiments show that doping can shorten the laser ignition time of thermite from 31.5 ms to 19 ms,that is,doping can effectively improve the laser stimulation response.However,the flame retardancy of rGO can inhibit the laser ignition performance.(6)Two high-purity K_xBi_1-xFeO₃ and Ce_xBi_1-xFeO₃ can be obtained through the doping regulation of K and Ce.Furthermore,two nanoscale K_xBi_1-xFeO₃/rGO and Ce_xBi_1-xFeO₃/rGO composites were prepared by one-step solvothermal method.DSC was used to evaluate the catalytic effects of BiFeO₃,BiFeO₃/rGO,K_xBi_1-xFeO₃/rGO and Ce_xBi_1-xFeO₃/rGO on the thermal decomposition of HMX and RDX.Results show that metal-doping can improve the catalytic activity of BiFeO₃ on the thermal decomposition of energetic component,and the catalytic activity can be further enhanced after the in-situ coupling with graphene.