Tatb Crystal Shape Control And Orientation

As the only insensitive high explosive sanctified by the American Energy Department, 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is very insensitive to the outside stimulations, such as heat, light, shock wave, friction, and impact. Therefor, TATB has been applied widely in the military and civil applications where insensitive explosives are required and become an important material in the insensitivation engineering of armaments and ammunitions. However, the TATB based PBXs commonly present anisotropic expansion, deformation and an unstable shape, which restrict the applications of PBXs greatly. The previous works show that the anisotropic expansion has something to do with the commonly existed phenomena, the preferred orientation. As for the die pressed X-0219 cylinders, more than 19% of crystal will take place preferred orientation. By controlling the crystal morphology of TATB, the preferred orientation and anisotropic expansion can be restricted, and the influence of preferred orientation on the shape change of TATB based PBXs can be investigated, which will provide some guide for improving the shape stability of TATB based explosives.This paper prepared TATB crystals with different morphology, and discussed the effect of some factors on TATB crystal morphology. By means of high temperature anti-solvent recrsytallization, three kinds of anti-solvents, which can mainly form intramolecular hydrogen bond,π-πstacking interaction and intramolecular interaction with TATB molecules, respectively, are added to different solvents to investigate the influence of anti-solvents on the crystal morphology of TATB. It is shown that the anti-solvents that can form hydrogen bond with TATB molecules lead to near-spherical crystals, anti-solvents with big conjugatedπ-bonds lead to platy crystals, while anti-solvents that can form intermolecular interaction mainly lead to more irregular crystals with more defects.This paper concluded the way how to prepare near-spherical and plate TATB crystal. Under fast stirring (>300 rpm), add water or other anti-solvents that can form hydrogen bond with TATB to make TATB precipitate at high temperature, and cool for a farther precipitate, near-spherical crystal can be gained. To the contrast, under slow stirring (<100 rpm), adding no anti-solvent or anti-solvents that can formπ-πstacking interaction with TATB molecules will make plate crystals.This paper tested the apparent density, purity and thermal properties of TATB samples with different crystal morphology. The results of density gradient method show that the densities of crystallized TATB samples are higher than that of TATB materials (1.915 g.cm-3), even reach to 1.9367±0.0011 g.cm-3, which is much higher than the highest value in literature (1.9276 g.cm-3) and is close to the theory density of TATB crystal. So, by the high temperature anti-solvent recrsytallization, we can prepare high quality TATB crystals and improve the energy density of TATB based explosives. The recrystallized TATB with different crystal morphology showed DSC exothermal peak at 364.3±2.7℃and the initial temperature of decomposition was at 378.9±1.7℃. It can be concluded that TATB with different morphology have approximate exothermal peak, so recrsytallization does not change the thermal stability of TATB. What's more, the crystallization can also improve the purity and crystal quality of TATB, which may have much influence on the application of TATB crystals.This paper also investigated the preferred orientation of TATB powder and cylinders. The crystal morphology has much influence on the preferred orientation of TATB and the degree of preferred orientation of platy crystals is much bigger than that of TATB materials and near-spherical crystals at the same condition. So, spheroidizing can help to control the preferred orientation, even anisotropic expansion of TATB based PBXs. What's more, the pressing way also has something to do with the preferred orientation, the die pressed cylinders has obvious anisotropic preferred orientation, but the isotropic pressed has less. It's clear that the pressure, pressing temperature, different locations along the same direction has little effect on the preferred orientation.Finally, this paper investigated the anisotropic expansion of TATB cylinders. Cycle between the temperature range -54℃to 74℃, all the TATB cylinders expand a lot. But with the times of thermal cycle increase, the degree of expansion decrease. Affected by the preferred orientation of TATB, the irreversible expansion of TATB cylinders is different with TATB crystal morphology and particle size, as well as the directions. The irreversible expansions of materials and platy TATB present abvious anisotropy, but for the cylinders pressed with near-spherical crystals, irreversible expansions alonge different direction are equal and small. In addition, the cylinders pressed under the same condition with different morphology TATB have different density. Material cylinders have the lowest density, far lower than that of cylinder with near-spherical and platy TATB. On the contrary, cylinders with large near-spherical TATB particles have the highest density. So, cylinders with recrystallized TATB have higher density and contain more energy in the same unit. That means recrystallization can help to control the anisotropic expansion as well as to improve the energy density of TATB based PBXs.