Theoretical Studies On Decomposition And Combustion Mechanisms,molecular Design,and Environmental Responses Of Energetic Compounds

In the present thesis,ab initio molecular dynamics(AIMD)and density functional tight-binding(DFTB)molecular dynamics(DFTB-MD)methods were used to systematically study the initial decomposition mechanisms and subsequent decomposition processes of 7 crystalline explosives under extreme conditions.The mechanisms and kinetics of decomposition and combustion reactions of crystalline FOX-7(1,1-diamino-2,2-dinitroethylene)under high temperatures were simulated.Density functional theory(DFT)was used to predict the detonation properties and impact sensitivity of our designed 1,2,3,4-tetrazine-functionalized FOX-7 derivatives and azaoxyadamantanes.The oxidation and reduction abilities,degradation mechanisms in soil,and potential toxicity of some energetic compounds were studied by using DFT.The contents of the dissertation are divided into five parts mainly:1.Decomposition mechanisms of high energy crystals at high temperaturesThe initial decomposition mechanisms and subsequent decomposition processes of isolated and crystal TEX(4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane)at 2160 K were investigated using AIMD.Catalytic reaction paths of hydrogen radical during the crystal decomposition were presented.Releasing mechanisms of nitrogen gas,pyrolysis mechanisms of cycles,and formation mechanisms of long chains and heterocycles were displayed.The time evolution of the population of the main fragments during the decomposition was discussed.The adiabatic decomposition processes of ?-HMX(octogen)at 2400 K,2700 K,and 3000 K were simulated using DFTB-MD.Their detailed initial decomposition mechanisms,subsequent decomposition paths,and main products were displayed.Mutual competitive mechanisms of several initial decomposition mechanisms were discussed.The time evolution of the initial decomposition mechanisms and main products during the decomposition were investigated.2.Decomposition mechanisms of high energy crystals at high pressures coupled with high temperaturesThe decomposition processes of ionic salt DBTD(dihydrazinium 3,3,-dinitro-5,5'-bis-1,2,4-triazole-l,1-diolate),NHN(nickel hydrazine nitrate)with MOF(metal organic frameworks)structure,Cl-20(2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexa-azaisowurtzitane),P-HMX,and a-RDX(hexogeon)were simulated using AIMD.The differences in the decomposition mechanisms of DBTD under five conditions were discussed.We analyzed the influencing factors on its decomposition.The effects of the supercell's size on the decomposition mechanisms were investigated.The influences of different external conditions on the decomposition mechanisms of NHN crystal were discussed.We displayed the formation mechanisms of multi-Ni compounds and H2O and the formation and disintegration mechanisms of polycyclic networks.The initial decomposition mechanisms of CL-20,?-HMX,and a-RDX crystals were presented.We discussed the main decomposition paths after their initiations.The time evolution of the main products during their decomposition was studied.3.Decomposition and combustion mechanisms of FOX-7 at high temperaturesThe decomposition and combustion processes of uni-and multi-molecular FOX-7 at high temperatures were simulated by using DFTB-MD.The differences in the uni-and multi-molecular decomposition and combustion mechanisms of FOX-7 were compared.The competition reaction paths of the intermediates after initiations were presented.The time evolution of the main products during their decomposition and combustion were investigated.We studied the kinetic properties of their decomposition and combustion.4.Molecular design of 1,2,3,4-tetrazole-functionalized FOX-7 derivatives and azaoxyadamantanesN-oxides and nitro groups were introduced into the basic skeletons of 1,2,3,4-tetrazole-functionalized FOX-7 and cage azaadamantane to construct a series of derivatives by using different strategies of molecular design.DFT was used to predict their detonation properties and sensitivity and potential high energy density compounds were selected.5.Environmental responses of energetic compoundsThe oxidation and reduction abilities of 6 1,2,3,4-tetrazine-functionalized FOX-7 derivatives and the degradation mechanisms of the sixth compound among them in soil were studied by using DFT.We investigated the redox properties and acute toxicity of 21 nitro compounds.