A Theoretical Research On The Sensitivity Of Solid Nitromethane And Its Regulation

Energetic materials have been attracted much attention under high pressure conditions.It is of great scientific significance to explore the influences of pressure on energetic materials from micro perspectives,which enables us to investigate the changes of basic physical properties of energetic materials.The changes due to compression can be studied and discussed around the structural,mechanical,and electronic properties to further understand the complex reaction process of energetic materials.The stability and safety of energetic materials are closely related to the impact sensitivity.In practical application,the energetic materials have been restricted for the contradictions between the high energy density and the stability performance.In order to find energetic materials with excellent detonation performance and high safe capability,it is necessary to study the impact sensitivity so that people can adjust the impact sensitivity of energetic materials by changing the external conditions and realize the maneuverability operation on the impact sensitivity of the energetic materials.Based on the above mentioned issues,the first-principles method has been used to study the basic physical properties of nitromethane(NM)which is the simplest structure of nitro energetic materials.The introduced doping defects have been studied to explore the effects on the impact sensitivity of the solid nitromethane.And surface models have been built to study the influences of different surfaces on the anisotropy of the impact sensitivity for NM.It was found that the obtained structural parameters based on the GGA-PBE+G calculations were in good agreement with the theoretical and experimental results.The methyl groups of nitromethane molecules have obviously rotated under low pressure.With the increasing pressure,methyl rotation of the methyl groups was more and more difficult;we also found that the elastic constants and various mechanical parameters of the nitromethane crystal,such as the bulk modulus,shear modulus,Young's modulus and Poisson's ratio all increased with the increasing pressure,which indicated that the mechanical properties of NM were enhanced under compression.The enhanced impact sensitivity of NM with the increasing pressure has also been discussed.The effects of vacancy defects,water molecule / Ethylenediamine molecule substitution defects have also been studied.The results shown that the band gap values decreased in the vacancy,water molecule and ethylenediamine molecule substitution crystal structures.In which,the crystal with substitution of the ethylenediamine molecule was particularly prominent,indicating that the ethylenediamine has sensitized NM.Besides,the mechanical performances of defective structures were greatly weakened.We introduced dopant atoms in the interstitial sites of the nitromethane lattice,aiming to study the effects of metallic element-doping on the structural properties,electronic properties and sensitivity characteristics.The obtained results indicated that doped defects obviously affected the neighboring nitromethane molecules.And the modification of electronic properties showed that the band gaps were significantly reduced by doped defects.Partial density of states and population analysis further revealed the mechanism for sensitivity reduction of nitromethane.It was suggested that new electronic states have produced in the forbidden bands,thus increasing the impact sensitivity of NM.Finally,the influences of different surfaces for nitromethane have been studied,including(100),(001),(101),(110)and(111)surfaces.There was an obviously great anisotropy in electronic parameters,especially the band gaps of these different surfaces,which indicated the great anisotropic impact sensitivity along different directions of NM.And the value for(111)surface,2.687 eV,was the smaller than other surfaces,showing a higher anisotropy of the impact sensitivity in this surface for NM.And the calculated surface energy indicated that the larger the surface energy was,the more sensitive the NM crystal would be.According to the different paths of the easiest transition of electrons in different surface models,it was shown that the impact sensitivity of NM depended on the orientations.