Ren Chunxing, Liu Han, Li Xiaoxia, Guo Li
State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, P. R. China.
Phys Chem Chem Phys. 2020 Feb 7;22(5):2827-2840. doi: 10.1039/c9cp06102a. Epub 2020 Jan 22.
Understanding the similarities and differences of decomposition mechanisms of CL-20 and its cocrystals is of great interest for practical applications of CL-20 cocrystals. The responses of CL-20 cocrystals to thermal stimulus were investigated using ReaxFF molecular dynamics simulations of two representative cocrystals, CL-20/HMX and CL-20/TNT, under adiabatic conditions and comparing to the baseline system of pure CL-20. The comprehensive chemical details were revealed with the aid of the unique code of VARxMD. The three CL-20-involved reactive systems all exhibit a distinct three-stage character during adiabatic decomposition when using the double peaks of the major intermediate NO amount as the boundary. By taking advantage of the three-stage classification, a clear scenario for the similar stimulus-response of the CL-20 cocrystals can be elucidated for the dominant primary decomposition of CL-20 in stage I and the transition of favored chemical mechanisms from the generation of intermediates/radicals in stage II into their consumption to form stable products in stage III. The similar chemical behaviors are rooted in the dominance of CL-20 chemistry in the initial response of its cocrystals to thermal stimulus. The prolonged reaction zone uncovers the slowed decomposition kinetics of CL-20/HMX and CL-20/TNT, which is associated with the altered kinetics of CL-20 decomposition specifically by N-NO bond scission and CL-20 skeleton decay. The retarded CL-20 decomposition in its cocrystals consequently results in more moderate self-heating and less violent exothermic reactions that agrees with the experimental observations of improved stability and damaged detonation performance of CL-20 cocrystals, particularly for CL-20/TNT. The results obtained in this work suggest that ReaxFF MD simulations can provide useful insight for the modulated chemical properties of varied CL-20 cocrystals.
了解六硝基六氮杂异伍兹烷（CL-20）及其共晶体分解机制的异同，对CL-20共晶体的实际应用具有重要意义。通过对两种代表性共晶体CL-20/奥克托今（HMX）和CL-20/三硝基甲苯（TNT）在绝热条件下进行反应分子动力学（ReaxFF MD）模拟，并与纯CL-20的基线系统进行比较，研究了CL-20共晶体对热刺激的响应。借助VARxMD的独特编码揭示了全面的化学细节。当以主要中间体一氧化氮（NO）量的双峰为边界时，这三个涉及CL-20的反应系统在绝热分解过程中均呈现出明显的三阶段特征。利用这一阶段分类，可以阐明CL-20共晶体类似刺激响应的清晰情景，即第一阶段CL-20的主要初级分解，以及第二阶段中间体/自由基生成到第三阶段其消耗以形成稳定产物过程中有利化学机制的转变。相似的化学行为源于CL-20化学在其共晶体对热刺激初始响应中的主导地位。延长的反应区揭示了CL-20/HMX和CL-20/TNT分解动力学的减缓，这与CL-20分解动力学的改变有关，特别是通过N-NO键断裂和CL-20骨架衰变。CL-20在其共晶体中的分解延迟，导致自热更温和，放热反应更不剧烈，这与CL-20共晶体稳定性提高和爆轰性能受损的实验观察结果一致，但CL-20/TNT尤其如此。这项工作获得的结果表明，ReaxFF MD模拟可为不同CL-20共晶体的化学性质调控提供有用的见解。
