State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China.
Chongqing Hongyu Precision Industry Group Co., Ltd., Chongqing 402760, China.
Molecules. 2023 Jun 13;28(12):4735. doi: 10.3390/molecules28124735.
In this study, the crystal appearance of industrial grade 2,6-diamino-3,5-dinitropyridine (PYX) was mostly needle-shaped or rod-shaped with an average aspect ratio of 3.47 and roundness of 0.47. According to national military standards, the explosion percentage of impact sensitivity s about 40% and friction sensitivity is about 60%. To improve loading density and pressing safety, the solvent-antisolvent method was used to optimize the crystal morphology, i.e., to reduce the aspect ratio and increase the roundness value. Firstly, the solubility of PYX in DMSO, DMF, and NMP was measured by the static differential weight method, and the solubility model was established. The results showed that the Apelblat equation and Van't Hoff equation could be used to clarify the temperature dependence of PYX solubility in a single solvent. Scanning electron microscopy (SEM) was used to characterize the morphology of the recrystallized samples. After recrystallization, the aspect ratio of the samples decreased from 3.47 to 1.19, and roundness increased from 0.47 to 0.86. The morphology was greatly improved, and the particle size decreased. The structures before and after recrystallization were characterized by infrared spectroscopy (IR). The results showed that no chemical structure changes occurred during recrystallization, and the chemical purity was improved by 0.7%. According to the GJB-772A-97 explosion probability method, the mechanical sensitivity of explosives was characterized. After recrystallization, the impact sensitivity of explosives was significantly reduced from 40% to 12%. A differential scanning calorimeter (DSC) was used to study the thermal decomposition. The thermal decomposition temperature peak of the sample after recrystallization was 5 °C higher than that of the raw PYX. The thermal decomposition kinetic parameters of the samples were calculated by AKTS software, and the thermal decomposition process under isothermal conditions was predicted. The results showed that the activation energy (E) of the samples after recrystallization was higher by 37.9~527.6 kJ/mol than raw PYX, so the thermal stability and safety of the recrystallized samples were improved.
在这项研究中，工业级 2,6-二氨基-3,5-二硝基吡啶（PYX）的晶体外观主要为针状或棒状，平均纵横比为 3.47，圆形度为 0.47。根据国家军用标准，撞击感度 s 的爆炸百分率约为 40%，摩擦感度约为 60%。为了提高装填密度和压药安全性，采用溶剂-非溶剂法优化晶体形貌，即降低纵横比，提高圆形度值。首先，采用静态差重法测定了 PYX 在 DMSO、DMF 和 NMP 中的溶解度，建立了溶解度模型。结果表明，Apelblat 方程和 Van't Hoff 方程均可用于阐明 PYX 在单一溶剂中的温度依赖性溶解度。扫描电子显微镜（SEM）用于表征重结晶样品的形貌。重结晶后，样品的纵横比从 3.47 降低到 1.19，圆形度从 0.47 提高到 0.86。形貌得到了极大改善，粒径减小。通过红外光谱（IR）对重结晶前后的结构进行了表征。结果表明，重结晶过程中没有发生化学结构变化，化学纯度提高了 0.7%。根据 GJB-772A-97 爆炸概率法，对炸药的机械感度进行了表征。重结晶后，炸药的撞击感度从 40%显著降低至 12%。采用差示扫描量热仪（DSC）研究了热分解。重结晶后样品的热分解温度峰值比原 PYX 高 5°C。采用 AKTS 软件计算了样品的热分解动力学参数，并预测了等温条件下的热分解过程。结果表明，重结晶后样品的活化能（E）比原 PYX 高 37.9~527.6 kJ/mol，因此，重结晶样品的热稳定性和安全性得到了提高。
