Yang Fang, Yang Zongwei, Yu Qian, Li Gang, Zhao Chuande, Tian Yong
Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), P.O. Box 919-311, Mianyang, Sichuan 621999, China.
Phys Chem Chem Phys. 2023 Mar 1;25(9):6838-6846. doi: 10.1039/d2cp04822a.
High-energy, low-sensitivity energetic cocrystals are one successful application of the supramolecular strategy. The practical application of cocrystal explosives requires an in-depth understanding of the stability of their crystal phase structure under long-term heating, but relevant research is rare. In this study, the CL-20/MTNP (2, 4, 6, 8, 10, 12-hexanitrohexaazaisowurtzitane/1-methyl-3,4,5-trinitropyrazole) cocrystal was selected as a representative cocrystal explosive to investigate its crystal phase structure stability under long-term heating. The phase separation of the CL-20/MTNP cocrystal was observed for the first time. It was revealed that the MTNP molecules at crystal defects first underwent molecular rotation, which weakened interactions between CL-20 and MTNP molecules. Then, the MTNP molecules diffused along channels surrounded by CL-20 molecules to the crystal surface and escaped to generate γ-CL-20. We call this process the "thermal escape" of MTNP, whose effect on the safety performance of the CL-20/MTNP cocrystal was studied by comparing the mechanical sensitivity of samples with different degrees of thermal escape. The mechanical sensitivity of the CL-20/MTNP cocrystal did not greatly change during the induction period, but it increased upon the loss of MTNP. Moreover, the thermal escape kinetics for the two stages were obtained to prevent or control their thermal escape. The prediction of the kinetics confirmed the validity of the kinetic analysis. This study promotes the performance evaluation and application of CL-20/MTNP cocrystals and also provides a new perspective in the investigation of cocrystal explosives.
高能、低感度含能共晶体是超分子策略的一项成功应用。共晶炸药的实际应用需要深入了解其晶相结构在长期加热下的稳定性，但相关研究较少。在本研究中，选择CL-20/MTNP（2,4,6,8,10,12-六硝基六氮杂异伍兹烷/1-甲基-3,4,5-三硝基吡唑）共晶体作为代表性共晶炸药，研究其在长期加热下的晶相结构稳定性。首次观察到CL-20/MTNP共晶体的相分离。结果表明，晶体缺陷处的MTNP分子首先发生分子旋转，这削弱了CL-20与MTNP分子之间的相互作用。然后，MTNP分子沿着由CL-20分子包围的通道扩散到晶体表面并逸出，生成γ-CL-20。我们将此过程称为MTNP的“热逸出”，通过比较不同热逸出程度样品的机械感度，研究了其对CL-20/MTNP共晶体安全性能的影响。CL-20/MTNP共晶体的机械感度在诱导期内变化不大，但在MTNP损失后增加。此外，还获得了两个阶段的热逸出动力学，以防止或控制它们的热逸出。动力学预测证实了动力学分析的有效性。本研究促进了CL-20/MTNP共晶体的性能评估和应用，也为共晶炸药的研究提供了新的视角。
