A Molecular Dynamics Simulation Study On The Influence Of Nanocrystallization And Atmospheric Environment On The Thermal Decomposition Of RDX

Cyclotrimethylene trinitramine(RDX)is an energetic material which could instantaneously release plenty of gas and heat under the stimulation of extermal energy,and therefore RDX is widely used in the military field and civilian field.The thermal decomposition of RDX is closely related to its combustion,detonation and stability,and the thermal decomposition of RDX is a vital indicator to ensure its investigation,production and application.Meanwhile,the thermal decomposition of RDX is also a process affected by many factors,such as nanominiaturization and atmospheres.However,due to the extreme experimental conditions and complex reaction mechanism,the influence of nanominiaturization and atmospheres on the thermal decomposition of RDX has not been completely clarified at present,and the details of the thermal decomposition process and reaction mechanism is lacking.Fortunately,these research difficulties could be solved by reaction molecular dynamics,which could capture the details of chemical reaction,microstructure change and other dynamic processes,and which could also clarify the reaction mechanism of RDX under extreme conditions such as high temperature,high pressure and impact.Therefore,the reaction molecular dynamics was used to investigate the influence of nanominiaturization and atmospheres on the thermal decomposition of RDX.In this paper,we established different RDX models and simulated their thermal decomposition under the different heating conditions,which includes programmed heating and constant temperature heating,and then we compared their potential energy evolution,thermal decomposition process and decomposition reaction pathway.By investigating the influence of nanominiaturization on the thermal decomposition of RDX,we have obtained the following conclusions.Firstly,the nanominiaturization makes RDX have higher potential energy and stronger thermal effect than the original RDX in the thermal decomposition process.Secondly,under the condition of programmed heating,the initial therlal decomposition of bulk phase RDX occurs in the form of solid phase,while the initial thermal decomposition of RDX nanoparticles occurs on the surface of particles in the form of amorphous phase.Thirdly,the nanominiaturization makes RDX enter the stage of rapid thermal decomposition at lower temperature than the original R)X,which means that the nanominiaturization accelerates the thermal decomposition of RDX.Finally,the initial thermal decomposition reaction pathway of bulk RDX and RDX nanoparticles are both mainly N-N bond fission.A large amount of RDX reacts with the NO2 which from decomposed RDX due to the strong cage effect in bulk RDX.Nevertheless,there is no cage effect in RDX nanoparticles,and therefore the number of reactions between RDX and NO2 is very few.In addition,the RDR,which is an intermediate product in thermal decomposition of RDX,will be decomposed in the form of ring fracture in RDX nanoparticles.By investigating the influence of atmospheres on the thermal decomposition of RDX.we have obtained the following conclusions.NH3 can strongly proinote the thermal decomposition of RDX through its unique reaction with RDX,and NO,CO,NO2 can also obviously promote the thermal decomposition of RDX by seizing O atoms from RDX.Since CO2,HZ,H2O and NZ do not react with RDX and its intermediate products,and their hindering effect on the reaction,they slightly inhibit the thermal decomposition of RDX.However,02 strongly inhibited the thermal decomposition of RDX due to the reason that 02 can consume a large amount of promoter of RDX thermal decomposition.We also found that the number of ONDNTA molecules,which are generated during the thermal decomposition of RDX under atmosphere,may be used to judge whether the influence of this atmosphere on the thermal decomposition of RDX is promoted or inhibited.