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The strong explosiveness, toxicity and environmental pollution of picric acid make its sensitive detection important. Recently, LMOF materials are showing great potential toward efficient detection of PA. However, hindered by the weak connections between LMOFs and analytes, a feasible fluorescence selectivity and sensitivity to desired compounds by constructed LMOFs remain challenging. Herein, we propose a new strategy by using the innate adsorption ability of MOFs. We choose NDC−Zn, a highly stable LMOF with unique pore structures. The topology of ligands can capture PAs specifically inside the pores and the selectivities are further elevated. PET effects are boosted due to longer and closer contact between ligands and trapped PAs, thus higher sensitivity is also achieved. Besides, a fluorescence enhancement at a visible wavelength was found as the concentration of PA increased, suggesting a potential application of naked‐eye recognition for PA. NDC−Zn exhibited an outstanding detection sensitivity for PA with a quenching constant of 49657 M−1, as well as distinctive fluorescence quenching among 9 nitro explosives. From DFT calculations, the fluorescence quenching mechanisms such as PET and the complexation between H2NDC and PA were supported. [ABSTRACT FROM AUTHOR]

[Display omitted] • Severe fragmentation of lead styphnate particles occurred after cryogenic storage. • A structural transition of lead styphnate crystal was observed at low temperatures. • The structural information during transition was obtained using AIMD calculations. • The flame sensitivity and friction sensitivity of lead styphnate were deteriorated at low temperatures. • Ignition failure of lead styphnate occurred at −80 °C. As one of the most used pyrotechnic composites in spacecraft pyrotechnic devices, the reliability of lead styphnate (LS) in a cryogenic environment needs an adaptability evaluation before the deployment of new deep space exploration programs. Nonetheless, there is a limited understanding of the effects of low temperatures on LS. Herein, we have designed cryogenic storage experiments with a low-temperature in-situ methodology to explore the effects of low temperatures on the properties and performance of LS. By comparing the experimental data before, after storage, and at low temperatures, LS exhibited unique characteristics and failure behaviors at low temperatures than at high temperatures. After storage, the impact sensitivity of LS increased sharply due to particle fragmentation, whilst the flame sensitivity of LS decreased significantly at low temperatures. Employing in-situ powder x-ray diffraction (PXRD) characterization and ignition tests, the low-temperature ignition failure of LS is thought to be closely related to the distortion of the crystal structure of LS, resulting in a "structural shutdown" at −80 °C. Our study disclosed the properties of LS at low temperatures and provided feasible research methods for other energetic materials, aiming to prevent possible future risks and help to establish test standards at low temperatures. [ABSTRACT FROM AUTHOR]

During storage, lead styphnate (LS) is affected by different environmental stresses. Especially, the dual stress of temperature and humidity has a synergistic aging effect, which degrades or even completely loses the performance of LS, thus seriously affecting the firing reliability and even leading to misfire. Based on this, an accelerated aging test on LS exploring the aging behavior at high temperature and high humidity conditions was reported in this study. At extreme conditions of temperature and humidity, the color of LS had faded and gradually became lighter with the aging time. According to scanning electron microscope results, it indicated that due to long-term erosion, the surface of LS became rough, cracks and many small micropore. Some crystals were broken, and a large amount of debris appeared. Notably, the intensity of some main X-ray diffraction characteristic peaks decreased significantly or even disappeared with the aging time. On the one hand, the thermal stability of LS decreased slightly. On the other hand, its sensitivity performance gradually degraded after hygrothermal aging. Particularly, the flame sensitivity of LS decreased gradually with the aging time. In a word, our findings provide relevant evidence for the reliability of LS in storage conditions. [ABSTRACT FROM AUTHOR]

Metastable intermolecular composites (MICs) typically use Al as fuel and transition metal oxides as oxidizers, while their reactivities are hindered by the inert Al 2 O 3 passivation layer on the surface of Al particles. Recently, transition metal fluorides have emerged as novel fluorine-containing oxidizers for promoting the reactivity of metal fuels through interfacial fluorination of oxide layer. In this work, nanosized CoF 2 and Co 3 O 4 were prepared through pyrolysis of CoF 2 ·4H 2 O precursor using different calcination conditions. To investigate the function of CoF 2 in reaction and the influence of CoF 2 content on reactive performances, a series of MICs composed of n-Al, Co 3 O 4 , and CoF 2 were prepared through ultrasonic dispersion method. Thermal analysis indicated that Al/CoF 2 composite had significantly higher specific heat release (2.30 kJ/g) than that of Al/Co 3 O 4 composite (1.45 kJ/g), and CoF 2 facilitated the occurrence of exothermic reaction at a relatively lower temperature. AlF 3 was found as main reaction products of Al/CoF 2 at 650 °C, and AlF 3 sublimes at the temperature above 850 °C. Although the pressure output and flame intensity of Al/CoF 2 composite is lower than that of Al/Co 3 O 4 composite, hybrid Al/Co 3 O 4 /CoF 2 composites with 20 %–35 % CoF 2 showed significantly enhanced energetic performances compared with sole Al/Co 3 O 4 , suggesting that CoF 2 can function as an effective reaction modifier. [ABSTRACT FROM AUTHOR]