Owing to their extremely high energy density, single-bonded polymeric nitrogen and atomic metallic hydrogen are generally regarded as the ultimate energetic materials. Although their syntheses normally require ultrahigh pressures of several hundred gigapascals (GPa), which prohibit direct materials application, research on their stability, metastability, and fundamental properties are valuable for seeking extreme energetic materials through alternative synthetic routes. Various crystalline and amorphous polymeric nitrogens have been discovered between 100 and 200 GPa. Metastability at ambient conditions has been demonstrated for some of these phases. Cubic-gauche and black-phosphorus polymorphs of single-bonded nitrogen are two particularly interesting phases. Their large hystereses warrant further application-inspired basic research of nitrogen. In contrast, although metallic hydrogen contains the highest-estimated energy density, its picosecond lifetime and picogram quantity make its practical material application impossible at present. ″Metallic hydrogen″ remains a curiosity-driven basic research pursuit focusing on the pressure-induced evolution of the molecular hydrogen crystal and its electronic band structure from a low-density insulator with a very wide electronic band gap to a semiconductor with a narrow gap to a dense molecular metal and atomic metal and eventually to a previously unknown exotic state of matter. This great experimental challenge is driving relentless advancement in ultrahighpressure science and technology.
The latest member of the azole family, the pentazolate or cyclo-N5−, has received increased attention since its first mass-spectral detection by Christe et al. in 2002. As it is carbon- and hydrogen-free, the pentazolate anion can release large amounts of energy while simultaneously decomposing to environmentally friendly nitrogen gas. Due to these attractive qualities, cyclo-N5− and related compounds are essential in the advancement of high-energy-density materials (HEDMs) research. This review aims to provide a consolidated report on all research done on cyclo-N5−, with a focus on pentazoles as energetic materials and on their experimental synthesis. Included in this review are the following: ① the historical significance of cyclo-N5−; ② precursors of cyclo-N5−; ③ synthesis routes of cyclo-N5− with a focus on arylpentazole precursors; ④ factors affecting the stability of cyclo-N5−; ⑤ energetic performances of current energetic cyclo-N5−-containing compounds; and ⑥ future possible experimental research. This review is a comprehensive summary of the current understanding of cyclo-N5−, in an effort to further understand the potential of this anion for adoption as a powerful and environmentally friendly next-generation explosive.
Thermomechanical, physical, and chemical processes in energetic materials (EMs) during manufacturing and processing or under external stimuli such as shock compression, involve multiple temporal and spatial scales. Discovering novel phenomena, acquiring new data, and understanding underlying mechanisms all require temporally and spatially resolved diagnostics. Here, we present a brief review of novel diagnostics that are either emerging or have existed but rarely been applied to EMs, including two-dimensional (2D) and three-dimensional (3D) X-ray imaging, X-ray diffraction, coherent X-ray diffraction imaging, small angle X-ray scattering, terahertz and optical absorption/emission spectroscopy, and one-dimensional (1D) and 2D laser-based velocity/displacement interferometry. Typical spatial scales involved are lattice (nanometer and micrometer) and typical temporal scales (femtosecond, picosecond, nanosecond, microsecond, and millisecond). The targeted scientific questions and engineering problems include defects, strengths, deformations, hot spots, phase changes, reactions, and shock sensitivities. Basic principles of measurement and data analysis, and illustrative examples of these are presented. Advanced measurements and experimental complexities also necessitate further development in corresponding data analysis and interpretation methodologies, and multiscale modeling
The creation of high-performance energetic materials with good mechanical sensitivities has been a great challenge over the past decades, since such materials have huge amounts of energy and are thus essentially unstable. Here, we report on a promising fused-ring energetic material with an unusual twodimensional (2D) structure, 4-nitro-7-azido-pyrazol-[3,4-d]-1,2,3 triazine-2-oxide (NAPTO), whose unique 2D structure has been confirmed by single-crystal X-ray diffraction. Experimental studies show that this novel energetic compound has remarkably high energy (detonation velocity D = 9.12 km∙s−1; detonation pressure P = 35.1 GPa), excellent sensitivities toward external stimuli (impact sensitivity IS = 18 J; friction sensitivity FS = 325 N; electrostatic discharge sensitivity EDS = 0.32 J) and a high thermal decomposition temperature (203.2 °C), thus possessing the dual advantages of high energy and low mechanical sensitivities. To our knowledge, NAPTO is the first fused-ring energetic material with 2D layered crystal stacking. The stabilization mechanism toward external stimuli were investigated using molecular simulations, and the theoretical calculation results demonstrate that the ultraflat 2D layered structure can buffer external mechanical stimuli more effectively than other structures by converting the mechanical energy acting on the material into layer sliding and compression. Our study reveals the great promise of the fused-ring 2D layered structure for creating advanced energetic materials.
Designing and synthesizing more advanced high-energetic materials for practical use via a simple synthetic route are two of the most important issues for the development of energetic materials. Through an elaborate design and rationally selected molecular components, two new metal-free hexagonal perovskite compounds, which are named as DAP-6 and DAP-7 with a general formula of (H2dabco)B(ClO4)3 (H2dabco2+ = 1,4-diazabicyclo[2.2.2]octane-1,4-diium), were fabricated via an easily scaled-up synthetic route using NH3OH+ and NH2NH3+ as B-site cations, respectively. Compared with their NH4+ analog ((H2dabco)(NH4)(ClO4)3; DAP-4), which has a cubic perovskite structure, DAP-6 and DAP-7 have higher crystal densities and enthalpies of formation, thus exhibiting higher calculated detonation performances. Specifically, DAP-7 has an ultrahigh thermal stability (decomposition temperatures (Td) = 375.3 °C), a high detonation velocity (D = 8.883 km·s‒1), and a high detonation pressure (P = 35.8 GPa); therefore, it exhibits potential as a heat-resistant explosive. Similarly, DAP-6 has a high thermal stability (Td = 245.9 °C) and excellent detonation performance (D = 9.123 km·s‒1; P = 38.1 GPa). Nevertheless, it also possesses a remarkably high detonation heat (Q = 6.35 kJ·g‒1) and specific impulse (Isp = 265.3 s), which is superior to that of hexanitrohexaazaisowurtzitane (CL-20; Q = 6.23 kJ·g‒1; Isp = 264.8 s). Thus, DAP-6 can serve as a promising high-performance energetic material for practical use.
A new group of energetic metastable intermixed composites (MICs) was designed and fabricated by means of the spray granulation technique. These MICs are composed of aluminum (Al) as the fuel, ammonium perchlorate (AP) and polyvinylidene fluoride (PVDF) as the co oxidizer. The AP/PVDF ratio was optimized by taking the maximum energy release as the criteria. A minor content of graphene oxide (GO) was also doped in the MICs to act as both lubricant and catalyst. It was shown that Al@AP/PVDF with 0.2% GO has the greatest density (2.57 g·cm–3 ) and highest heat of reaction (5999.5 J•g–1). These values are much higher than those of Al@AP/PVDF (2.00 g·cm–3 and 5569.8 J•g–1 ). The inclusion of GO increases the solidstate reaction rate of Al@AP/PVDF and improves the thermal stability. The flame propagation rate was increased up to 4.76 m·s–1 by doping with 0.2% GO, and was about 10.7% higher than that of Al@AP/ PVDF. Al@AP/PVDF-GO has a better interfacial contact and particle distribution, which results in an improved heat-transfer rate, freedom from the agglomeration of nano Al particles, and an improved combustion reaction rate. This work demonstrates a new strategy to improve the energy release rate and combustion efficiency of Al-based MICs.
Gastric signet ring cell carcinoma (SRCC) and colorectal SRCC are the most aggressive histological types of carcinoma related to a poor prognosis, and place a heavy burden on public health. We undertook a population-based study to analyze the metastatic patterns of SRCC and further estimate its contribution to the cancer-specific survival of gastric SRCC and colorectal SRCC. Data from eligible patients diagnosed with gastric or colorectal SRCC between 2010 and 2012 were obtained from the Surveillance, Epidemiology, and End Results (SEER) database. Chi-squared tests were used to clarify the clinical features in patients with metastatic disease compared with those without metastatic disease. Survival differences of patients with different metastatic sites were compared with a Kaplan–Meier analysis, and other prognostic factors were examined by Cox proportional hazards models. A total of 4055 patients with gastric SRCC or colorectal SRCC were included in our cohort. Among them, 2905 were diagnosed with gastric SRCC, and the remaining 1150 patients were diagnosed with colorectal SRCC. In gastric SRCC, distant lymph nodes were the most common metastatic sites. Furthermore, patients with brain metastases had the worst prognosis. In colorectal SRCC, the liver was the most common metastatic site, and patients with distant lymph node metastases had the highest mortality. In summary, metastasis is a major contributor to cancer mortality in SRCC. The results from our study provide some information for developing follow-up strategies in future studies.
Three-dimensional (3D) printing is an additive manufacturing process. Accordingly, four-dimensional (4D) printing is a manufacturing process that involves multiple research fields. 4D printing conserves the general attributes of 3D printing (such as material waste reduction, and elimination of molds, dies, and machining) and further enables the fourth dimension of products to provide intelligent behavior over time. This intelligent behavior is encoded (usually by an inverse mathematical problem) into stimuliresponsive multi-materials during printing, and is enabled by stimuli after printing. The main difference between 3D- and 4D-printed structures is the presence of one additional dimension, which provides for smart evolution over time. However, currently there is no general formula for modeling and predicting this additional dimension. Herein, by starting from fundamentals, we derive and validate a general biexponential formula with a particular format that can model the time-dependent behavior of nearly all 4D (hydro-, photochemical-, photothermal-, solvent-, pH-, moisture-, electrochemical-, electrothermal-, ultrasound-, etc. responsive) structures. We show that two types of time constants are needed to capture the correct time-dependent behavior of 4D multi-materials. We introduce the concept of mismatch-driven stress at the interface of active and passive materials in 4D multi-material structures, leading to one of the two time constants. We develop and extract the other time constant from our unified model of time-dependent behavior of nearly all stimuli-responsive materials. Our results starting from the most fundamental concepts and ending with governing equations can serve as general design principles for future research in the field of 4D printing, where time-dependent behaviors should be properly understood, modeled, and predicted.