The crystal morphology of highly explosive cyclotrimethylenetrinitramine (hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)) has been characterized by the crystal-face-indexing method in combination with single-crystal X-ray diffraction and rotation imaging techniques. As a result, the morphology importance of the facets in RDX crystals grown in acetone and dimethyl sulfoxide (DMSO) is on the order of (111) ≈ (210) > (021) ≈ (102) > (001) ≈ (010) ≈ (100) and (111) > (210) > (010) > (001) ≈ (021), respectively. Crystal sizes have also been measured along the a-, b-, and c-axes, which show a less-preferred orientation of RDX crystals than octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystals. In addition, the {111} and {210} facets show good thermodynamic stability, while the appearance of the other facets is dynamically affected by solution conditions during the growth of RDX crystals from the hundred-micrometer scale to the millimeter scale. After crystal face indexing, surface models were built for the dominant {111} and {210} facets as well as the special {010} facet. On the surface of the {111} facet, the outstanding H and O atoms lead to a regular arrangement of positive and negative charges. For the {210} facet, twisted grooves are observed on the surface in the Connelly surface model. More interestingly, large hollows with dimensions of 11.6 × 11.8 Ų are generated on the surface of the {010} facet. The high adsorption ability of the hollows to DMSO molecules plays a key role in the enhanced morphology importance of the {010} facet in DMSO, as evidenced by molecular dynamics simulations. All of these results can be applied to the morphology control of energetic crystals and will be a good reference to the interfacial interaction of the RDX crystal in both polymer-bonded explosives (PBXs) and propellants.

中文翻译：

---

晶面索引法及理论计算研究高爆RDX的暴露面和表面性质

采用晶面索引法结合单晶X射线衍射对高爆炸性环三亚甲基三硝胺（六氢-1,3,5-三硝基-1,3,5-三嗪（RDX））的晶体形貌进行了表征和旋转成像技术。因此，在丙酮和二甲基亚砜 (DMSO) 中生长的 RDX 晶体中晶面的形态重要性约为 (111) ≈ (210) > (021) ≈ (102) > (001) ≈ (010)分别为 ≈ (100) 和 (111) > (210) > (010) > (001) ≈ (021)。还沿着a、b和c轴测量了晶体尺寸，这表明RDX 晶体的取向不如八氢-1,3,5,7-四硝基-1,3,5， 7-四佐辛 (HMX) 晶体。此外，{111}和{210}晶面表现出良好的热力学稳定性，而其他晶面的外观在RDX晶体从百微米级到毫米级的生长过程中受到溶液条件的动态影响。晶面索引后，为主要的{111}和{210}面以及特殊的{010}面建立了表面模型。在{111}面的表面，突出的H和O原子导致正电荷和负电荷的规则排列。对于{210}面，在康纳利表面模型的表面上观察到扭曲的凹槽。更有趣的是， {010}面的表面会产生尺寸为11.6 × 11.8 Å ²的大空洞。分子动力学模拟证明，空穴对 DMSO 分子的高吸附能力对于增强 DMSO 中 {010} 面的形态重要性起着关键作用。所有这些结果都可以应用于含能晶体的形貌控制，并且将为RDX晶体在聚合物粘结炸药（PBX）和推进剂中的界面相互作用提供很好的参考。