Study On Preparation,characterization And Properties Of TNT Cocrystal Explosives

2,4,6-trinitrotoluene（TNT）is one of the most commonly used energetic materials.Due to its simple synthesis process,low cost,and low sensitivity,TNT-based casting explosives are commonly used in the ammunition field.However,compared with today’s high-energy explosives,TNT has a relatively low density and detonation performances,which cannot meet today’s high demand for high energetic and low sensitive explosive well.At present,the cocrystallization has gradually become a new method to construct new energetic materials and regulate its performances,which is of great significance to the development of energetic materials.In order to improve the energy of TNT and broaden its application in the field of energetic materials,TNT was combined with another two explosives including1-chloro-2,4,6-trinitrobenzene（TNCB）and 2,4,6-trinitrobenzene（TNB）at the molecular level through the cocrystal technology in this study.On the basis of maintaining the low melting point and sensitivity of TNT,its two kinds cocrystal explosives,with good comprehensive performances superior to TNT,were obtained,which has provided a new idea and method for the molecular design of the explosives with high energy,low sensitivity and melting point in the future.The main work of the paper is as follows:（1）Based on the molecular interactions,for example,hydrogen and halogen bonds and by analyzing the structure and main properties of TNT,two TNT-based cocrystal explosives including TNT/TNCB and TNT/TNB cocrystals were designed using the theoretical and empirical methods.The two cocrystals were prepared by solvent evaporation method using anhydrous ethanol as solvent.（2）The structure of two cocrystals were characterized by single crystal X-ray（SXRD）.Results show that both of the crystals belong to monoclinic system,P21/c space group.TheTNT/TNCB cocrystal explosive is a pale yellow columnar crystal with the molecular formula C₁₃H₇ClN₆O₁₂.Its molecular weight is 474.7 g/mol and the density is 1.743 g/cm³.While the TNT/TNB cocrystal is light brown short columnar crystals with molecular formula C₁₃H₈N₆O₁₂.Its molecular weight is 440.25 g/mol and the density is 1.646 g/cm³.Owing to the similar structure of TNCB and TNB,the two cocrystals exhibit wavelike stacking in which bilayers of molecule TNT alternate with the bilayers of conformer molecules.There are several intermolecular forces in cocrystal,mainly including C–H???O hydrogen bonds,the p-π interactions between-NO2 and the benzene ring and the π-πinteractions between the benzene rings.Besides,the interactions of C–Cl???O also exit in the TNT/TNCB cocrystal.These intermolecular interactions act together to form a stable cocrystal structure.（3）The thermal properties of two cocrystals were measured by differential scanning calorimetry（DSC）.Results reveal that the TNT/TNCB and TNT/TNB cocrystal explosives have melting point of 72.7 ℃ and 67.9 ℃,respectively,which are lower than pure components TNT（83.3 ℃）,TNCB（84.1 ℃）and TNB（119.5 ℃）.It can be seen that the cocrystal explosives with melting point lower than pure components were obtained after cocrystallization.What’s more,it has provided possibility in application of explosives with high energy and melting point in cast-melting explosives.（4）The impact sensitivity of these two cocrystals was tested by drop weight impact test devices.Results show that the drop height of 50% explosion probability（h50）for TNT/TNCB cocrystal explosive is 92.9 cm,which is higher than that of the two pure components TNT（83.5 cm）and TNCB（59.6 cm）superior to the raw materials.The TNT/TNB cocrystal explosive has an h50 of 112.2 cm,which is between TNT（83.5 cm）and TNB（118.9 cm）.However,compared to TNT,the sensitivity of TNT/TNB cocrystal has a substantial decrease.（5）The detonation performances of the two cocrystals have been predicted by theoretical methods.Results reveal that the detonation velocity of TNT/TNCB cocrystal is6837 m/s and the detonation pressure is 21.08 GPa.The detonation velocity of TNT/TNBcocrystal is 6961 m/s,and the detonation pressure is 20.87 GPa.Compared with the main explosive TNT（6670 m/s,19.24 GPa）,the detonation performance of the explosive has been improved through cocrystal technology.