高速冲击压缩梯恩梯的分子动力学模拟

采用反应力场分子动力学方法模拟了梯恩梯(2,4,6-trinitrotoluene,TNT) 冲击压缩过程. 冲击压缩完全时,体积压缩至原体积40%,梯恩梯分子分解完毕,体系压力达到峰值. 随后稀疏波反向拉伸致大量原子或分子基团飞溅至下游,同时压力开始卸载. 密度及粒子速度剖面显示压缩波后方密度较大,粒子基本处于静止状态,且压缩波内存在较大的粒子速度梯度. 早期化学反应特征是梯恩梯分子在冲击压缩作用下脱落H,O 原子后残基快速聚合形成较大的分子团簇,此阶段和平动—振动弛豫过程相关,并且分子由平动—振动模态转换的时间尺度为0.5 ps. 产物识别分析显示梯恩梯在高速冲击压缩下致C—H,O＝N 键断裂,脱落的原子部分形成OH,H₂,H₂O,N₂,部分H,O 原子游离在体系中. 含碳团簇分析显示,冲击压缩作用致体系中含碳团簇的摩尔质量逐渐累积. 体系内含碳团簇中O/C,H/C,N/C 原子数量比值逐渐趋于平衡(O/C=0.680,H/C=0.410,N/C=0.284),且均小于初始结构中的比值. 

MOLECULAR DYNAMICS SIMULATIONS OF HIGH VELOCITY SHOCK COMPRESSED TNT

We simulate the shock compression behavior of TNT with ReaxFF-MD. When shock compression is complete, all of the TNT molecules are decomposed, and when volume compression is up to the 40% of original volume, pressure of the system reaches a peak. Close behind is rarefaction wave reverse stretching the compressed energetic materials and leading to a large number of atoms or molecules group splash to the downstream, pressure begin to unload at the same time. Density and particle wave velocity profile show a greater density in the compressed region, and the particles in a stationary state, but sharp velocity gradient in the region of compression wave. In the earlier chemical characteristics, TNT molecules shed the H, O atoms under the effect of shock compression, and then the residues aggregate to the larger clusters, and this phase associated with translational-vibrational relaxation processes. The rotational mode is subsequently transferred into vibrational modes with a time scale of 0.5 ps. Fragment analysis shows that a large number of C-H, O＝N bonds rupture to form the OH, H₂, H₂O, N₂ groups and parts of H, O atoms are free in the system. The molar mass of the carbon-containing clusters under the joint actions of compressional wave ahead and rear compression is accumulating gradually from the analysis. Atomic ratio in the carbon-containing clusters tends to balance (O/C=0.680, H/C=0.410, N/C=0.284), but less than the ratio in the initial structure.