Zhang Yaping, Li Qikai, He Yuanhang
State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China.
MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, China.
ACS Omega. 2020 Nov 4;5(45):28984-28991. doi: 10.1021/acsomega.0c03133. eCollection 2020 Nov 17.
In this paper, ReaxFF force field combined with molecular dynamics method was used to study the ignition, deflagration, and detonation of pentaerythritol tetranitrate (PETN) induced by hot spots. The hot spot is 5.6% of the total volume. When the hot spot temperature is 1000 K, the deflagration and detonation of PETN cannot be observed in the simulation time of 200 ps. When the hot spot temperature is 2000 K, it corresponds to the heating time of 20 to 50 ps, deflation and detonation were observed. During hot spot ignition, the products of decomposition of the condensed phase PETN are dominated by NO and HONO. The energy required for the C-C bond and C-ONO bond cleavage in PETN is high, resulting in only a small amount of CHO and NO during the reaction. Small nitrogen-containing molecules (such as NO, NO, HONO, HNO, etc.) mainly exist during thermal equilibrium, while the number of N increases sharply during the thermal runaway stage, and a small amount of NH and NH are also produced. HO molecules are formed before CO and N are produced, and the number always dominates. During the thermal runaway, the entire system can maintain a spontaneous reaction, resulting in a sharp rise in temperature of about 2500 K in 20 ps. During this phase, the catalytic effect of HO accelerates the formation of CO and N due to the near Chapman-Jouguet point in the crystal. PETN is a weak oxygen balance explosive that results in a small amount of CO and H production during the thermal instability phase. When the reaction is balanced, the relative molecular mass is close to or exceeds that of PETN. The product is only less than 1% of the total mass fraction, while the small molecule product is as high as 78%, and some relative molecular masses are [75,225]. The intermediates account for about 21%. Rapid and complex reaction events make it difficult to accurately predict the structure of these intermediates by existing experiments and calculations, which will be the focus of future research.
本文采用ReaxFF力场结合分子动力学方法研究了热点引发的季戊四醇四硝酸酯（PETN）的着火、爆燃和爆轰。热点占总体积的5.6%。当热点温度为1000 K时，在200 ps的模拟时间内未观察到PETN的爆燃和爆轰。当热点温度为2000 K时，对应加热时间为20至50 ps，观察到了爆燃和爆轰。在热点点火过程中，凝聚相PETN的分解产物以NO和HONO为主。PETN中C-C键和C-ONO键断裂所需能量较高，导致反应过程中仅产生少量的CHO和NO。小分子含氮化合物（如NO、NO、HONO、HNO等）主要存在于热平衡阶段，而在热失控阶段N的数量急剧增加，同时还产生少量的NH和NH。HO分子在CO和N产生之前形成，且数量始终占主导。在热失控过程中，整个系统能够维持自发反应，导致温度在20 ps内急剧上升约2500 K。在此阶段，由于晶体接近查普曼-朱盖点，HO的催化作用加速了CO和N的形成。PETN是一种氧平衡较弱的炸药，在热不稳定阶段会产生少量的CO和H。当反应达到平衡时，相对分子质量接近或超过PETN的相对分子质量。产物仅占总质量分数的不到1%，而小分子产物高达78%，一些相对分子质量为[75,225]。中间体约占21%。快速而复杂的反应过程使得现有实验和计算难以准确预测这些中间体的结构，这将是未来研究的重点。
