TNT Crystals Research Articles

Mechanism of the Impact-Sensitivity Reduction of Energetic CL-20/TNT Cocrystals: A Nonequilibrium Molecular Dynamics Study

High-energy low-sensitivity explosives are research objectives in the field of energetic materials, and the formation of cocrystals is an important method to improve the safety of explosives. However, the sensitivity reduction mechanism of cocrystal explosives is still unclear. In this study, CL-20/TNT, CL-20 and TNT crystals were taken as research objects. On the basis of the ReaxFF-lg reactive force field, the propagation process of the wave front in the crystals at different impact velocities was simulated. The molecular dynamics data were used to analyze the molecular structure changes and initial chemical reactions, and to explore the sensitivity reduction mechanism of the CL-20/TNT cocrystal. The results showed that the chemical reaction of the CL-20/TNT cocrystal, compared with the CL-20 single crystal, is different under different impact velocities. At an impact velocity of 2 km/s, polymerization and separation of the component molecules weakened the decomposition of CL-20. At an impact velocity of 3 km/s, the decay rates of CL-20 and TNT in the cocrystal decreased, and the intermediate products were enhanced, such as nitrogen oxides. At an impact velocity of 4 km/s, the cocrystal had little effect on the decay rates of the molecules and formation of CO2, but it enhanced formation of N2 and H2O. This may explain the reason for the impact-sensitivity reduction of the CL-20/TNT cocrystal.

Sublimation and Diffusion Kinetics of 2,4,6-Trinitrotoluene (TNT) Single Crystals by Atomic Force Microscopy (AFM).

In this article, we report the in-situ nanoscale experimental measurement of sublimation rates, activation energy of sublimation, and diffusion coefficients of 2,4,6-trinitrotoluene (TNT) single crystals in air using atomic force microscopy (AFM). The crystals were prepared by slow evaporation at 5 °C using acetone-dissolved TNT. The mass loss was calculated by monitoring the shrinkage of the surface area of layered islands formed on the surface of the TNT crystals due to sublimation upon isothermal heating at temperatures below the melting point. The results suggest the sublimation process occurs via two-dimensional detachment of TNT molecules from the non-prominent facets on the crystal surface which imitates the nucleation and crystal growth process. Sublimation rates are one order of magnitude smaller than previously reported values. However, the calculated activation energy (112.15 ± 3.2 kJ/mol) and temperature-dependent sublimation rates agree well with the reported values for TNT thin films and microcrystals determined by UV-vis absorbance spectroscopy and quartz crystal microscopy (QCM) (90–141 kJ/mol). The average diffusion coefficient is (4.35 × 10–6 m2/s) which is within the range of the reported theoretical values with an average of 5.59 × 10–6 m2/s, and about 25% less than that determined using thermogravimetric analysis for powder TNT.

Fundamental studies of the adhesion of explosives to textile and non-textile surfaces

This paper describes the use of atomic force microscopy (AFM) to investigate the interactions between explosives crystals and different surfaces. Crystals of TNT, PETN and RDX were mounted onto tipless AFM cantilevers and repeatedly brought into contact with a range of surfaces (n=15), including textile and non-textile surfaces. The adhesion force during each contact was measured, and the results are presented in this work. The results suggest that explosives crystals display a higher adhesion to smoother, non-textile surfaces, particularly glass. This finding may be of use for forensic explosives investigators when deciding the best types of debris to target for explosives recovery.

The crystal growth and perfection of 2,4,6-trinitrotoluene

Large crystals of TNT were grown from ethyl acetate solution by both temperature lowering and solvent evaporation. The perfection of crystals grown from seeds under carefully controlled conditions was generally higher than those prepared by uncontrolled solvent evaporation. Examination by X-ray topography revealed the crystals to have a characteristic growth induced defect structure comprising growth sectors and boundaries, growth banding, solvent inclusions and dislocations. Twins and stacking faults (SF) were also observed. Many of the defects noted in the topographs can be attributed to impurities. The influence of the highly anisotropic crystal structure on the nature of growth defects is discussed. A structural model proposed to explain twinning and SF formation is partially supported by topographic evidence.

Nucleation of 2,4,6-trinitrotoluene by 2,2′,4,4′,6,6′-hexanitrostilbene

Abstract Nucleation of solidification of 2,4,6,-trinitrotoluene (TNT) by 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) is described. Precipitation of HNS from TNT solution occurs on solidification of the TNT; this precipitation is epitaxial on the most rapid growth front of the TNT crystals and appears in regular bands. The exceptional ability of HNS in nucleating TNT may be related to the close molecular similarity of host and guest.

The microstructures of some amatols

AbstractFusion‐cast amatols contained ammonium nitrate grains included in TNT crystals. Some TNT crystals were prisms elongated on [c] and approximately perpendicular to the wall of the mould. Ammonium nitrate grains were mono‐ or poly‐crystalline and some showed evidence of aggregation prior to incorporation with fused TNT; aggregation during fusion casting was rarely indicated. Segregation of the grains by pressure from growing TNT prisms was seen in a few castings unusually poor in ammonium nitrate.At least some proportion of added wax appeared as segregations in TNT. Added aluminium grains were found in or between TNT crystals. Parallel layers of ammonium nitrate and TNT occurred in parts of test‐pieces of pressed amatol.Completely fused mixtures of TNT with eutectic proportions of ammonium, calcium and sodium nitrates, were simple or multiple emulsions; the structures of these emulsions became ‘frozen’ when the melt solidified.

The microstructures of some fusion‐cast mixtures of pentaerythritol tetranitrate and 2:4:6‐trinitrotoluene

AbstractMolecular compounds or solid solutions of PETN and TNT were not observed. The reported eutectic contained approx. 13% by weight of PETN but, in fusion‐cast 50/50 mixtures containing much undissolved PETN, eutectic‐like intergrowths were either absent or anomalously rich in PETN. The eutectic mixture itself solidified as crystals of TNT with interstitial intergrowths of TNT and excess PETN. A 50/50 mixture, completely fused and then chilled, crystallized as a eutectic‐like intergrowth.In solidified 50/50 mixtures, fusion‐cast at 90–94°, the PETN crystals retained their original shape‐characteristics because little PETN had been dissolved at such temperatures. These crystals were enclosed by crystals of TNT.Added wax caused no obvious changes in the microstructures of the castings and at least some of it persisted as segregations.TNT crystals, elongated on [c], tended to point inwards from the walls of the mould unless their crystallization had been disturbed.The microstructures resembled those of fusion‐cast RDX‐TNT; further, PETN resembled RDX in recrystallizing during prolonged contact with melted TNT.