Imparting High Polymorph Transition Resistance to Cyclotetramethylene-tetranitramine via Spherulitic Aggregation Enabled Crystal Shape Constraint
Imparting High Polymorph Transition Resistance to Cyclotetramethylene-tetranitramine via Spherulitic Aggregation Enabled Crystal Shape Constraint
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DOI：
10.1016/j.cej.2022.139602
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发表时间：
2022-10
影响因子：
15.1
通讯作者：
Xin Zhou;Hongzhen Li;Xiaoqing Zhou;Shi-Hai Hao;Mi Yan;Pangangjin Zou;Shiliang Huang;Xuan He;Chaoyang Zhang
中科院分区：
文献类型：
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作者：
Xin Zhou;Hongzhen Li;Xiaoqing Zhou;Shi-Hai Hao;Mi Yan;Pangangjin Zou;Shiliang Huang;Xuan He;Chaoyang Zhang
高熔点炸药(HMX)，即环四亚甲基四硝胺，受到结构不稳定、感度增加和高温下不必要的爆燃等问题的困扰，这些问题与其在160-185°C左右的β-→-δ多晶型转变造成的微结构破坏密切相关。因此，需要扩大β形式的热稳定性。在这里，展示了一种新的策略，通过粒子水平的聚集来调节这种β-→-δ转变。使用聚乙烯吡咯烷酮作为生长添加剂，研究表明，β-HMX单晶可以在颗粒尺寸和致密性得到精细控制的情况下，形成独特的球晶形态。发现相变对球晶聚集很敏感，但与颗粒尺寸的减小高度相关。值得注意的是，β-HMX球晶的起始转变温度高达205°C，与其单晶对应的最高值相比，最大提高了20°C。力学研究表明，受抑制的β-→-δ转变源于球晶聚集体中亚单位晶体的各向异性膨胀受到限制，这种限制是由其反常的径向堆积方式引起的。该策略有望推广到其他多形态炸药领域，从而为未来高性能含能材料的发展带来新的视角。
The high melting explosive (HMX), i.e., cyclotetramethylene-tetranitramine, is plagued by issues such as structural instability, increased sensitivity, and unwanted deflagration at elevated temperatures, which are strongly linked to the microstructural damage generated by its β → δ polymorphic transition around 160–185 °C. An extension of the β form thermal stability is therefore desired. Herein, a new strategy to regulate such β → δ transition via particle-level aggregation is demonstrated. Using polyvinyl pyrrolidone as a growth additive, this study shows that single-crystalline β-HMX can evolve into a unique spherulitic morphology with fine control over particle sizes and compactness. The phase transition is then found sensitive to the spherulitic aggregation while highly correlating with the decrease in particle size. Remarkably, the β-HMX spherulites exhibit an onset transition temperature of up to 205 °C, corresponding to a maximum 20 °C increment as compared with the highest value achieved by its single crystalline counterpart. Mechanistic investigation reveals that the suppressed β → δ transition origins from the restricting of anisotropic expansion of the subunit crystallites in spherulitic aggregates, induced by their unusual radial packing mode. The proposed strategy is expected to be translated to other polymorphic explosives, hence bringing a fresh perspective to future high-performance energetic materials development.