湿热耦合作用下HNIW的多路径相变行为与诱导机制研究

Hexanitrohexaazaisowurtzitane (HNIW) has been widely researched with high expectations as known to be practical application of highest energy density explosives. However, the polymorphic transition behaviors of HNIW in different environments make its safety and reliability significantly reduced, thus restricting its application and popularization in weapon systems. Therefore, exploring the induction factors and inherent mechanism of HNIW phase transition, and seeking a reliable method to control the phase transition behaviors is one of the most pivotal problems in the current study of HNIW. Accordingly, in this project, an investigation will be carried out to aim at understanding the competitive mechanism of HNIW multidirectional phase transitions in hygrothermal environment. Humidity and temperature synchronous loading device will be designed. With advanced in situ characterization techniques, the multidirectional phase transition rules of HNIW with different crystal characteristics (such as purity, particle size, defect etc) as the main parts will be investigated under various humidity/temperature environments. The relationships between the phase transition behaviors and the key microstructure parameters of HNIW will also be obtained. Moreover, with molecular dynamic simulations, the transference and diffusion behaviors of water molecules will be calculated when HNIW crystal structures are rearranging. The relationships between interfacial reaction and molecular cluster size of HNIW will also be explored. In addition, combined with experimental results, the rules and mechanism of HNIW multidirectional phase transition behaviors induced by temperature and humidity will ultimately be revealed. The research results provide basic support for controlling crystal structure stability of HNIW and selecting process techniques of HNIW explosive formulation.

作为目前能量密度最高的硝胺类单质炸药，HNIW一经问世就被寄予厚望，然而其在复杂环境中表现出的多晶型相变行为，使得其安全性和可靠性显著降低，以致其在武器系统中的应用与推广受到制约。因此，探索HNIW相变过程的影响因素，认识其内在的转变机制，对于有效控制其不利相变具有非常重要的作用。本项目以我们近期发现的湿热耦合效应下HNIW的多路径相变现象为入手点，通过设计原位加载实验装置，借助高分辨的在线表征技术，重点考察湿热环境下不同晶体特性（纯度、颗粒度、缺陷等）HNIW的相变规律，探寻关键结构参量与相变行为之间的关联；并通过分子动力学模拟，研究水分子在HNIW晶体结构重排过程中的迁移与扩散行为，寻找界面过程反应与分子团簇大小之间的关系，结合相关实验结果，最终认识HNIW在湿热耦合作用下的多路径相变规律与诱导机制，为HNIW的环境适应性和应用可靠性研究提供支撑。

多晶型炸药的相变现象严重影响其使用性能，HNIW 虽具有很好的潜在应用前景，但其晶体结构稳定性一直制约着它自身的发展。为深入认识HNIW 对于复杂环境的适应性，挖掘其在湿热环境下的多路径相变与诱导机制，本项目以首次发现湿热耦合效应引起HNIW 炸药多路径相变的现象为出发点，搭建了湿热精确可调原位加载装置，并在X-射线粉末衍射仪上进行使用，建立了温湿度精确可调的原位协同加载技术。通过筛选不同晶体特性HNIW晶体，开展了HNIW的晶体特性与热晶变的关联机制研究，发现晶体尺寸效应会改变HNIW热晶变行为，超细HNIW晶体的热晶变起始温度较100μm晶体高，但晶变速率更快，可从晶体缺陷的两面性解释该异常热晶变行为。HNIW固态晶型转变是内部诱导与外部诱导协同作用结果，HNIW晶体的表面缺陷及内部缺陷越多，将降低晶变起始温度，晶变活化能也相对降低，从而促使晶变发生，同时结合纳米尺寸效应揭示了晶体形貌及颗粒尺寸对HNIW晶变的影响机制。研究发现湿热环境下HNIW的颗粒尺寸效应导致其多路径相变行为（ε→γ、ε→α），针对湿热环境下HNIW热晶变温度大幅降低（从135℃降低到80℃）的问题，探索了不同晶体特性HNIW晶体的湿热环境下结构稳定性，发现晶体特性的差异是导致HNIW出现多路径相变的关键因素，在低湿热条件下HNIW的结构相变并不明显，但其微结构损伤将导致晶相结构稳定性变差且相变温度降低。结合理论计算，得出湿热环境会诱导HNIW发生气-固界面反应，使得水分子嵌入HNIW晶体的晶胞中，这种嵌入方式是有一定选择性，提出了水分子通过表面微溶诱导成核生长机理促使炸药发生晶型转变从而嵌入到HNIW晶体内部。本项目属于应用基础研究，对于以HNIW为基的炸药配方研制、加工成型工艺、性能测试方法和弹药贮存方式的选择都具有十分重要的意义。

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