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Under complex temperature variations, the irreversible thermal expansion of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) based polymer bonded explosives (PBXs) results in decreased shape stability, directly impacting mechanical properties, safety performance during storage and use. In recent years, extensive and thorough researches have seen carried out on the thermal expansion characteristics of TATB based explosives. This paper summarizes the thermal expansion characteristics of TATB based PBXs, the influencing factors, as well as their suppression methods. Starting with the distinctive crystal structure of TATB, the thermal expansion mechanism of TATB based PBXs is introduced, the microstructural evolution during the thermal expansion process is summarized, and the effects of thermal expansion on comprehensive performance are analyzed. More attention to the influencing factors of thermal expansion and control methods are paid. Existing challenges are summarized with the recommendation for further exploration into the irreversible expansion mechanism of TATB based PBXs. It point out several key directions for future development: design and control of TATB crystal structure, construction and development of novel composites with integrated structural-functional properties, as well as the application of negative thermal expansion functional materials.

To better understand the structure-activity relationship and enhance the overall performance of polymer-bonded explosives (PBXs), the neutron and X-ray scattering techniques, which utilize neutron or X-ray radiation as probes, are unique and useful methods for quantifying the inherent hierarchical microstructures and components of PBXs. This review focuses on a series of scattering techniques and their typical applications in PBXs and includes a brief introduction of large neutron and X-ray scientific facilities in China. It describes the basic principles, instrumentation, sample environment, and empirical approaches of small-angle scattering (SAS), neutron reflection (NR), and neutron diffraction (ND). Additionally, it reviews common applications of these scattering techniques in the fields of PBXs. Combining the scattering techniques with complementary methods yields several valuable parameters that account for the microstructural features of PBXs. The combination can be used to establish multi-scale structure-activity relationships of PBXs and optimize the preparation process, numerical simulations, and performance prediction of PBXs. More efforts should be made to (1) gather the comprehensive multi-scale microstructural parameters for certain PBXs and add them to corresponding characteristic databases; (2) further investigate the dependence of the microstructural features on the preparation conditions of PBXs; (3) establish multi-factor correlations between the multi-scale microstructural features and the multiple performances obtained from experiments; (4) incorporate the microstructural parameters into various theoretical computational models.

The deuteration of energetic materials contributes to high signal-to-noise ratios (SNRs) in neutron diffraction, thus allowing the structures of energetic materials to be effectively investigated. This study developed the synthesis methods of deuterated energetic materials through chemical synthesis or newly developed one-pot H/D exchange. Using these methods, it synthesized nine deuterated energetic materials in a concise and low-cost manner: deuterated 1,3,5-triamino-2,4,6-trinitrobenzene (TATB-d6, 1), 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX-d8, 2), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX-d6, 3), dihydroxylammonium 5,5′-bis(tetrazole-1-oate) (TKX-50-d8, 4), nitroguanidine (NQ-d4, 5), 1,1-diamino-2,2-dinitroethylene (FOX-7-d4, 6), 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105-d4, 7), trinitrotoluene (TNT-d3, 8), and 3-nitro-1,2,4-triazol-5-one (NTO-d2, 9). Furthermore, the single crystals of HMX-d8 (2) and RDX-d6 (3) were obtained, and the α-, β-, γ-, and δ-polymorphs of HMX-d8 (2) were prepared accordingly. The deuterated energetic materials were characterized and analyzed using infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD), and neutron diffraction. Besides, this study determined the decomposition activation energy (Ea), pre-exponential factor (A), decomposition rate constant (k), and critical explosion temperature (Tb) of TATB-d6 (1), HMX-d8 (2), and RDX-d6 (3) via DSC experiments at different heating rates. The NMR and neutron diffraction data show that these deuterated energetic materials have high deuteration rates of more than 95%. The DSC and TG analyses indicate that the deuterated energetic materials exhibit slightly higher decomposition temperatures than their nondeuterated counterparts. Furthermore, neutron diffraction shows that the deuterated energetic materials feature high SNRs.

The solid-phase ripening of nano explosives leads to the performance degradation of explosives with time, and it has been a long-standing challenge to understand the solid-phase ripening kinetics of small-molecule nanomaterials. Using an in situ atomic force microscope (AFM) and small angle X-ray scattering (SAXS), this study captured the variations in the morphology and specific surface area (SSA), respectively of hexanitrostilbene (HNS) nanoparticles, which have been applied as an advanced brisant explosive, during their ripening. The solid-phase ripening mechanisms and kinetics were discussed. Both Ostwald ripening (OR) and Smoluchowski ripening (SR) of HNS nanoparticles were observed at 60oC. This study established an empirical model to describe the decrease in SSA in 30 days, which yielded the predicted results with root mean square errors (RMSEs) lower than 5%. Moreover, it demonstrated the significant acceleration effects of dimethyl formamide (DMF) vapour on the ripening rate of HNS nanoparticles. Overall, this study may lay the foundation for scientifically predicting the long-term stability and substantially reducing the ripening rate of HNS nanoparticles and provide a methodology for the study of the solid-phase ripening of small-molecule nanomaterials.