Three new energetic 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) cocrystals, HNS/4,4′-bipyridine, HNS/trans-1,2bis(4-pyridyl)ethylene, and HNS/1,2-bis(4-pyridyl)ethane have been synthesized. A good geometric match and rich Hbonds have been observed between the selected coformer and HNS molecules in all three cocrystals. According to similar configuration and arrangement of HNS−coformer H-bonds, coformer−coformer π-stacking, and HNS−HNS H-bonding interactions, the three cocrystals have a common cocrystal architecture and show high thermal stability and improved sensitivity. This study is helpful for understanding the formation mechanism of energetic cocrystals and the design of new energetic cocrystals.

Abstract:The ε→γ phase transition of HNIW induced by heat was investigated with in situ X-ray powder diffraction (PXRD). The effects of purity, particle size, insensitive additives and the time of isothermal heat treatment on the phase transition were evaluated. It was found that the phase transition is irreversible with changes in temperature, and the two phases can coexist in a certain temperature range. Moreover, the initial phase transition temperature increases with increasing purity and decreasing particle size of HNIW, and thus with the approximate crystal density. The addition of graphite and paraffin wax to HNIW as insensitive additives leads to a decrease in the initial phase transition temperature, but the addition of TATB does not affect the initial phase transition temperature. Thus, TATB is a suitable insensitive additive. Moreover, at the critical temperature, the isothermal time determined the efficiency of the ε-to γ-phase transition. This work lays the foundations for the choice of molding technologies, performance test methods, ammunition storage options, as well as the manufacture of HNIWbased explosive formulations.

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Triple‐base gun propellants composed of nitrocellulose (NC), triethylene glycol dinitrate (TEGDN) and cyclotrimethylenetrinitramine (RDX) with carbon nanofibers (CNFs) were studied to explore the effects of CNFs on the thermal and mechanical properties. The results indicated that CNFs with less than 0.50 wt % were evenly and randomly dispersed in the propellant, otherwise there existed obvious aggregation. Temperatures of initial decomposition and exothermic peak reduced with the increase of NCFs from 0.00 to 3.00 wt %. Decomposition enthalpy of the composites with 0.50 wt % NCFs was 1214.6 J g−1, increased by ∼131.4 J g−1 compared to that of NC‐TEGDN‐RDX propellants. Moreover, the mechanical properties were effectively tailored by varying the amount of CNFs added to the composition. Decomposition enthalpy of the propellant with 0.25 wt % CNFs were hardly compromised for achieving enhancement in the compressive and impact properties, while the tensile strengths decreased slightly compared to that of the propellants.

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