CL20-TNT共晶高温热解的ReaxFF/lg反应力场分子动力学模拟

摘要

ReaxFF/lg势函数是在ReaxFF的基础上增加了对范德华引力的描述,因此可以更好地用于描述晶体密度和结构,而含能材料密度很大程度上影响着爆轰的宏观性质(如爆速、反应区宽度、能量输出结构等).本文采用ReaxFF/lg反应力场分析了高温条件下凝聚相CL20-TNT共晶的初始分解情况,并通过简单的指数函数拟合势能演化曲线获得了平衡和诱导期以及整体反应时间,随后通过反应速率方程得到了共晶热解的活化能Ea (185.052 kJ/mol). CL20-TNT共晶热解过程中CL20分子均在TNT之前分解完毕,并且随着温度的升高, TNT的分解速率明显加快,温度越高二者完全分解所需的时间越接近.有限时间步长下的产物识别分析显示主要产物为NO2, NO, CO2, N2, H2O, HON, HNO3. NO2是C−NO2和N−NO2键均裂共同贡献的结果,其产量快速地增加,达到峰值后开始减少,此过程伴随着NO2参与其他反应使得NO2中的N原子进入到其他的含N分子中.次要产物主要为CO, N2O, N2O5, CHO. N2O具有很强的氧化能力,使其分布有着剧烈的波动特征.%ReaxFF/lg reactive force field is the extention of ReaxFF by adding a van der Waals attraction term. It can be used to well describe density and structure of crystal, moreover, the macroscopic property of detonation is significantly influenced by the density of energetic material. We report on the initial thermal decomposition of condensed phase CL20-TNT cocrystal under high temperature here. The time evolution curve of the potential energy can be described reasonably well by a single exponential function from which we obtain the initial equilibration and induction time, overall characteristic time of pyrolysis. Afterward, we also obtain the activation energy Ea (185.052 kJ/mol) from these simulations. All the CL20 molecules are completed before TNT decomposition in our simulations. And as the temperature rises, the TNT decomposition rate is significantly accelerated. The higher the temperature at which complete decomposition occurs, the closer to each other the times needed for CL20 and TNT to be completely decomposed will be. Product identification analysis with the limited time steps shows that the main products are NO2, NO, CO2, N2, H2O, HON, HNO3. C−NO2 and N−NO2 bond homolysis jointly contribute to the results of the NO2. The NO2 yield rapid increases to the peak and then decreases subsequently. This process is accompanied with NO2 participating in other reactions so that the N atom of NO2 enters into the other N-containing molecule. Secondary products are mainly CO, N2O, N2O5, CHO. N2O has a strong oxidation ability, so that the distribution has a dramatic fluctuation characteristics.