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The nano-/microstructured energetic materials (EMs) often display a unique combination of low-sensitivity and high-stability, but their structural control across multiple-length scales has proven difficult. Here, a polyvinyl pyrrolidone (PVP) polymer-directed crystallization method is developed to construct high explosive 1,3,5,7-Tetranitro-1,3,5,7-tetrazacyclooctane (HMX) polycrystalline aggregates with controllable molecular-scale structure (polymorph) and crystal-scale aggregation microstructures. It was found that the polymorph and microstructural characteristics of aggregates show a strong dependence on the initial supersaturation, PVP concentration and feeding rate. In particular, the morphology and the phase composition of the aggregates could be systematically tuned from δ-phase star-like aggregates to γ-phase flake spherulite by simply varying the HMX concentration. A slower feeding rate could lead to more compact spherulites with a well-defined Maltese-cross extinction pattern. According to the process analysis technology (PAT) and Hansen solubility parameters (HSPs) analysis, it was proposed that the preferential absorption of antisolvent and strong interaction between PVP/HMX could disrupt the local solution chemistry, lower the level of supersaturation and increase the induction time, resulting in regulation in the molecular assembly pathway of HMX. Moreover, the HMX spherulitic aggregates are much less sensitive to impact and friction than reported plate-like γ-HMX as well as raw HMX. This work provides a fresh way for the design and preparation of high explosive polycrystalline aggregates with well-defined multi-scale architectural features and reduced mechanical sensitivity.

Sensitivity is one of the greatest concerns in explosive materials, and its underlying mechanism remains ambiguous. In this study, 2,6-diamino-3,5- dinitropyrazine -1-oxide (LLM-105) crystals with different morphologies, such as crosswise, needle, plate, block, diamond, and spherical shapes, were prepared using a solution crystallization method, and their crystal characteristics and sensitivity were investigated. It was found that the H50 values (impact sensitivity) of LLM-105 vary within an extremely wide range of 33.8–112.2 cm and are mainly influenced by the particle morphology, crystal integrity, particle surface defects, and roughness, but are mostly independent of intracrystalline defects and particle sizes. The friction sensitivities of all samples are zero and are unaffected by the crystal characteristics. The G50 values (shock sensitivity) are within the range of 0–6.9 mm, increasing with decreasing particle sizes and the apparent crystal density. Notably, LLM-105 crystals with a spherical shape, good integrity, smooth surface, and fewer defects are insensitive to impact and shock impulse. The relationships between the crystal characteristics and the sensitivity of LLM-105 are extremely complex and show some abnormal phenomena, which can be attributed to the crystal packing style and aggregated microstructures of LLM-105.

The crystal packing style of energetic compounds has a significant impact on their safety. Herein, using Multiwfn, the interactions of ANPZ (2,6-diamino-3,5-dinitropyrazine) and DMDNP (2,6-dimethoxyl-3,5-dinitropyrazine), having the same dinitro-pyrazine ring with different crystal packing styles, were visualized to investigate the assembly of the corresponding crystal packing styles. Via the customization of the molecular structure, A1 and A2 compounds were synthesized to regulate the interactions to achieve the other two crystal packing styles. To further utilize this strategy and balance the contradiction between the energy content and safety of the energetic materials, the compound A3 was customized by the addition of an N–O group into the structure of A1. The crystal was modulated into a more impact-insensitive packing style while maintaining similar energy content as that in A1. All these results confirm that this strategy can be utilized to design and synthesize novel insensitive energetic materials.

A novel strategy to prepare spherical crystals of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) has been developed by introducing polymeric additives into the antisolvent emulsion crystallization. The spherical crystals are induced by modifying the intermolecular hydrogen bonds network of LLM-105. The results show that the concentration of polyvinylpyrrolidone (PVP), which acts as a polymeric additive, is a crucial factor to get quite different morphologies of LLM-105 crystal products. X-like shaped crystals have been produced in the absence of PVP. In contrast, spherical crystals have been obtained in the presence of PVP. Importantly, LLM-105 spherulites with a mean particle size of 78.0 μm can be obtained by adding a proper amount of PVP, which has a narrow size distribution (CV = 31.2). In addition, time-resolved morphological evolution processes of X-like shaped and spherical crystals have been performed. Meanwhile, 1H NMR experiments also have been conducted to understand the intermolecular hydro...

According to statistical and survey data, land use survey data and TM imagines from 2000 to 2008, dynamic changes of quantitative and regional difference of land use in ShangHuang experiment area during the last 8 years are analyzed. Based upon the model of Markov's shift matrix, the land use changes are discussed. The results indicated that the general trend of cultivated land during the past 8 years was decreasing and regional differences of cultivated land was very notable. The dynamic change of cultivated land shows sloping farmland change to forest land and grassland, some good quality of cultivated land change to high economic beneficial garden plot.

LUCC research is the focus of the study of entironment change, according to statistical and survey data, land use survey data and TM imagines from 1982 to 2008, analyzed the dynamic changes of LUCC in ShangHuang experiment area during the last 27 years. Based upon which, the major driving forces that influence the changes of land resources are discussed. The results indicated that throughout the study period, policy factors play a important role in land use change, Under the impact of policy factor, accounting for 74.39 percent of cultivated land change throughout the study period, while to the grassland, especially to the articial grassland, accounting for 31.1 percent of grassland change throughout the study period