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The structure and properties of nano-carbon materials formed in explosives detonation are always a challenge, not only for the designing and manufacturing of these materials but also for clearly understanding the detonation performance of explosives. Herein, we study the dynamic evolution process of condensed-phase carbon involved in 2,4,6-Triamino-1,3,5-trinitrobenzene (TATB) detonation using the quantum-based molecular dynamics method. Various carbon structures such as, graphene-like, diamond-like, and "diaphite", are obtained under different pressures. The transition from a C sp2- to a sp3-hybrid, driven by the conversion of a hexatomic to a non-hexatomic ring, is detected under high pressure. A tightly bound nucleation mechanism for diamond-like carbon dominated by a graphene-like carbon layer is uncovered. The graphene-like layer is readily constructed at the early stage, which would connect with surrounding carbon atoms or fragments to form the tetrahedral structure, with a high fraction of sp3-hybridized carbon. After that, the deformed carbon layers further coalesce with each other by bonding between carbon atoms within the five-member ring, to form the diamond-like nucleus. The complex "diaphite" configuration is detected during the diamond-like carbon nucleation, which illustrates that the nucleation and growth of detonation nano-diamond would accompany the intergrowth of graphene-like layers. [ABSTRACT FROM AUTHOR]

Plastic-bonded explosives (PBXs) consisting of explosive grains and a polymer binder are commonly synthesized to improve mechanical properties and reduce sensitivity, but their intrinsic chemical behaviors while subjected to stress are not sufficiently understood yet. Here, we construct three composites of β-HMX bonded with the HTPB binder to investigate the reaction characteristics under shock loading using the quantum-based molecular dynamics method. Six typical interactions between HMX and HTPB molecules are detected when the system is subjected to pressure. Although the initial electron structure is modified by the impurity states from HTPB, the metallization process for HMX does not significantly change. The shock decompositions of HMX/HTPB along the (100) and (010) surface are initiated by molecular ring dissociation and hydrogen transfer. The initial oxidations of C and H within HTPB possess advantages. As for the (001) surface, the dissociation is started with alkyl dehydrogenation oxidation, and a stronger hydrogen transfer from HTPB to HMX is detected during the following process. Furthermore, considerable fragment aggregation is observed, which mainly derives from the formation of new C−C and C−N bonds under high pressure. The effect of cluster evolution on the progression of the following reaction is further studied by analyzing the bonded structure and displacement rate. [ABSTRACT FROM AUTHOR]

The phase transition mechanism is always the challenge in energetic material fields, but it is crucial for understanding the microscopic ignition and detonation reaction performance. Here, we investigate the phase transition process of β-HMX under high temperature, using ab initio molecular dynamics simulation. The microscopic structure deformation and corresponding spectral characteristic is systematically studied. The corresponding relationship between microscopic structure and spectral signal is established through the partial spectra calculation. The results show that the equatorial C N bonds and axial N N bonds of HMX molecule have the most obvious shrinkage. It is the fundamental origination for the deformation of molecular ring and N-NO 2 group, which would further induce the initial phase transition. The axial N-NO 2 group plays the major role both in the β → α and β → δ phase transitions, while the deformation of equatorial NO 2 group also closely affects the β → δ phase transition. [ABSTRACT FROM AUTHOR]

[Display omitted] • The significant acceleration of new-formed H 2 on AB metallization is identified. • The H H bond is efficiently polarized by interaction of H H⋯H B between H 2 and AB. • The special H 2 -couples deriving from the trapped effect of AB are detected. • The synergetic metallization mechanism of AB and H 2 subjected to pressure is uncovered. Ammonia borane (NH 3 BH 3 , AB), as a typical hydrogen-rich compound, is expected to be a promising hydrogen source for low-pressure metallization materials. However, its microscopic electronic properties subjected to pressure are not sufficiently understood yet. In this study, we systematically investigate the pressurization process of AB and its complex with H 2 to uncover their metallization mechanism, using ab initio molecular dynamics method. As pressure increase, AB first undergoes partial dehydrogenation to liberate some H 2 molecules. The metallization progress is effectively promoted via H H⋯H B interaction between new-formed H 2 and -BH x group, with the metallization pressure of 450 GPa. As to AB H 2 compound, the electron states of AB are first activated through the enhanced interaction of H H⋯H B deriving from the additional H 2. In turn, the H H bonds within the corresponding H 2 molecules are partially polarized. The special H 2 -couples are formed through the H H⋯H H interaction, promoting the electron dispersion with each other. The whole electron channel of AB H 2 system is threaded together by the synergistic interactions of H H⋯H B and H H⋯H H, which significantly accelerate the pressurization metallization progress, resulting in a really lower metallization pressure of 250 GPa. Our study elucidate the synergistic metallization mechanism of AB and H 2 system for the first time, which would provide a great inspiration for low-pressure metallization studies of hydrogen or hydrogen-rich materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermolysis mechanisms of β-HMX under different thermodynamics states are investigated. • The special hydrogen transfer mechanism induced by NO 3 molecule is uncovered. • The reaction kinetics properties are compared with different reaction conditions. The thermolysis of β-HMX under different thermodynamics states are investigated using quantum-based molecular dynamics method. The reaction is mainly initiated with molecular ring breaking and alkyl dehydrogenation. The cleavages of N-N and C-N bonds are impeded under high pressure, while that of C-H bond is significantly enhanced. NO 3 is more favorably produced under low pressure, which can promote the hydrogen transfer to form H 2 O or OH. The reaction kinetics constants reflect that the initial endothermic reaction is really slower under high pressure, but the following exothermic reaction is significantly accelerated with a larger reaction heat of 368.05 cal·g−1. [ABSTRACT FROM AUTHOR]

The thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is studied using a quantum-based molecular dynamics (MD) method at several temperatures, to uncover its fundamental reaction mechanism and kinetic properties. The primary decomposition pathways, key intermediate products and their population evolutions are systematically investigated. For the first time, we uncover four sequential reaction stages during the thermal dissociation of TATB: (1) C–NO2 bond cleavage and amino dehydrogenation; (2) hydrogen transfer to nitro or NO2, with further conversion to NO and H2O; (3) carbon oxidation and molecular ring deep fission to generate CO and small –CN fragments; (4) final formation of gaseous N2 and CO2. The fission and formation rate constants and reaction energy barriers of the main chemical bonds are obtained by exploring the kinetic process. We confirm that C–NH2 bond breaking is the rate-controlling step for carbon oxidation, while N–N bond formation is the rate-controlling step for N2 generation. Besides, we obtain the global exothermic reaction rate and reaction heat based on an analysis of the changes in potential energy. The results not only give a deep insight into the chemical performance of TATB, but also provide prerequisite parameters for improving the macroscopic physical models for explosive reactivity. [ABSTRACT FROM AUTHOR]

We have systematically studied the high-pressure (up to 100 GPa) behavior of ammonia borane at 0 K using particle optimization algorithm combined with the first principles calculation. The long-unsolved high-pressure structures and a complete phase transition sequence were obtained: P6 3 mc → Pmn2 1 → P2 1 (Z = 2) → P2 1 (Z = 4) → C2/m → P2 1 /m, and the phase transition pressures are 1.23, 2.77, 11.9, 13.8, 22.34 GPa, respectively. The lack of imaginary phonon frequency effectively proves the rationality and dynamic stability of the above structures. The Raman modes calculated by density functional theory (DFT) reveals the evolution of the vibration mode under pressure, which is in good agreement with the experiment results. The analysis of dihydrogen bonds in ammonia borane shows the bonding mechanism of different high-pressure phase structures. Our research not only enriches the high-pressure phase structure of the ammonia borane system but also provides essential information for hydrogen storage materials. Image 1 • The high-pressure phase structures by structure search. • A complete phase transition sequence of ammonia borane at high pressure. • The structures of the experiment were confirmed by the comparison of Raman spectra. [ABSTRACT FROM AUTHOR]