梯恩梯/萘共晶初始热分解的反应分子动力学模拟

Reax FF反应力场在冲击起爆、爆轰等问题中的应用多围绕常规含能材料。利用增加了长程修正项Elg的Reax FF/lg反应力场对梯恩梯/萘(TNT/C_(10)H_8)共晶初始高温热分解进行模拟,并通过TNT单晶比较了C_(10)H_8对共晶整体反应特征的影响,利用指数函数及反应速率方程拟合得到共晶初级吸热反应和次级放热反应的活化能分别为35.7 kcal/mol和56.1 kcal/mol.初级吸热反应的活化能与TNT单晶基本相同,而次级放热反应的活化能则远远高于TNT单晶,并且同温度条件下共晶次级反应放热量小于TNT单晶。拟合得到的反应物的衰减速率表明,C_(10)H_8的加入将抑制共晶内TNT的分解。产物识别分析显示初始产物为NO_2、NO和HONO,并且通过NO_2和TNT—NO_2,NO和TNT—NO,HONO和TNT—HONO分布数量的比较论证了固相共晶和TNT单晶的初始反应路径为双分子反应机制。共晶热分解最终主要产物为N_2,H_2O,CO_2和CO.并且由于共晶内C_(10)H_8分子C—C键断裂所需的能量高于C—H键断裂所需的能量,C_(10)H_8分子的初始热分解路径为C—H键断裂,并且形成的H原子将促进共晶内H2O的产率高于TNT单晶内H2O的产率。

Initial Thermal Decomposition of TNT/C10H8 Cocrystal:Reactive Molecular Dynamics Simulations

The discussion of shock initiation and detonation with ReaxFF reactive force field has centered nearly around conventional energetic materials. The comprehensive molecular dynamics of thermal decomposition of condensed phase TNT/C₁₀H₈ cocrystal with the ReaxFF/lg potential function are studied, which adds a long range correction term to the total energy expression of original ReaxFF. The thermal decomposition of TNT single crystal is performed similarly to determine the main effect of C₁₀H₈ on the overall thermal characteristics of cocrystal. Furthermore, the activation energies associated with endothermic and exothermic stages of cocrystal thermal decomposition are found to be 35.7 kcal/mol and 56.1 kcal/mol, respectively. Its activation energy at primary endothermic stage is compatible with that of TNT single crystal, but the activation energy at secondary exothermic stage is higher than the value calculated for TNT. In addition, the heat output calculated during the exothermic step of TNT/C₁₀H₈ cocrystal is less than that of TNT at the same temperature. The decay rate of reactants by curve fitting shows that C₁₀H₈ inhibits the decomposition of TNT in cocrystal. NO₂, NO and HONO are major primary decomposition products by the way of identification analysis. The distribution of NO₂ /TNT_—NO2, NO/TNT_—NO, HONO/TNT_—HONO shows that the decomposition proceeds via bimolecular reaction. Main final products of cocrystal are N₂,H₂O,CO₂, and CO, and the initial decomposition routes of C₁₀H₈ is C—H bond dissociation as a result of C—C bond dissociation energy of C₁₀H₈ in cocrystal is higher than C—H bond, and this process may promote the formation of H₂O.