梯恩梯(TNT)爆轰初期形成富碳团簇分子及类石墨结构的分子动力学模拟
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摘要
富碳炸药在爆轰过程中可产生团簇分子,而现有的实验手段不能直接观测团簇分子的形成过程.本文采用Reax FF/lg力场对梯恩梯(TNT)在不同温度下的热分解过程进行了模拟.研究发现:团簇分子在反应初始阶段形成缓慢,大约一次增加一个TNT相对分子质量.随着反应进行,团簇分子迅速增大,最大团簇分子相对分子质量可达8000~10000,约占体系质量的18%.分析团簇分子的结构发现,团簇分子中一部分苯环被破坏,形成五元环和夹杂N、O原子的六元环,在3500 K条件下还形成了更为复杂的七元环等结构.通过体积膨胀和直接降温的方法,研究了团簇分子的稳定性:体积膨胀使得团簇分子迅速分解;而直接降温,团簇分子又聚合成更大的团簇.分析类石墨结构的产生过程,发现先膨胀然后降温是必不可少的步骤.比较团簇分子和TNT分子中各原子质量所占比,团簇分子中C原子质量比始终在增加.
The clusters can be seen in carbon-rich explosives during detonation. However, we can't directly observe the formation of clusters by experimental methods. The thermal decomposition of TNT at various temperatures are studied using Reax FF/lg molecular dynamics simulations. The Reax FF/lg force field provides detailed information on the formation of cluster from atomic level, the stability of the clusters and the graphite-like structures. The results show that clusters formed slowly at the initial reaction with increasing the relative molecular mass of a TNT approximately one time. As the reaction proceeding, the mass of clusters increases rapidly, and the molecular weight of max cluster can reach 8000~10000(amu), accounting over about 18% of the system mass. Analysis of the structure of the clusters reveal that some benzene rings in the clusters were broken, and five-membered rings and the six-membered rings which contain N and O atoms were formed, and the more complex seven-membered rings structure were formed under the 3500 K condition. Through the method of linear expansion and direct cooling, the stability of the clusters was studied: the clusters decomposed rapidly by the method of linear expansion, while the clusters aggregated into larger clusters by the method of direct cooling. Through the analysis of graphite-like structures, we obtain that it is an essential step to first expand and the cool down second by analysis the production process of graphite-like structures. The mass ratio of C atoms in the clusters has been increasing during the reaction process by comparing the ratio of the mass of each atom in the clusters and TNT molecules, while the mass ratio of N atoms and H atoms in the clusters decrease and the mass ratio of O atoms show more complicated during the whole reaction. This study can provide a good basis for the preparation of new nanomaterials for detonation of TNT.
The clusters can be seen in carbon-rich explosives during detonation. However, we can't directly observe the formation of clusters by experimental methods. The thermal decomposition of TNT at various temperatures are studied using Reax FF/lg molecular dynamics simulations. The Reax FF/lg force field provides detailed information on the formation of cluster from atomic level, the stability of the clusters and the graphite-like structures. The results show that clusters formed slowly at the initial reaction with increasing the relative molecular mass of a TNT approximately one time. As the reaction proceeding, the mass of clusters increases rapidly, and the molecular weight of max cluster can reach 8000~10000(amu), accounting over about 18% of the system mass. Analysis of the structure of the clusters reveal that some benzene rings in the clusters were broken, and five-membered rings and the six-membered rings which contain N and O atoms were formed, and the more complex seven-membered rings structure were formed under the 3500 K condition. Through the method of linear expansion and direct cooling, the stability of the clusters was studied: the clusters decomposed rapidly by the method of linear expansion, while the clusters aggregated into larger clusters by the method of direct cooling. Through the analysis of graphite-like structures, we obtain that it is an essential step to first expand and the cool down second by analysis the production process of graphite-like structures. The mass ratio of C atoms in the clusters has been increasing during the reaction process by comparing the ratio of the mass of each atom in the clusters and TNT molecules, while the mass ratio of N atoms and H atoms in the clusters decrease and the mass ratio of O atoms show more complicated during the whole reaction. This study can provide a good basis for the preparation of new nanomaterials for detonation of TNT.
引文
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[26]Kuklja,M.M.;Kunz,A.B.J.Phys.Chem.Solids 2001,61,35.
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