Construction and Modification of Nitrogen-Rich Polycyclic Frameworks: A Promising Fused Tricyclic Host-Guest Energetic Material with Heat Resistance, High Energy, and Low Sensitivity

The construction and modification of novel energetic frameworks to achieve an ideal balance between high energy density and good stability are a continuous pursuit for researchers. In this work, a fused [5,6,5]-tricyclic framework was utilized as the energetic host to encapsulate the oxidant molecules for the first time. A series of new pyridazine-based [5,6] and [5,6,5] fused polycyclic nitrogen-rich skeletons and their derivatives were designed and synthesized. Two strategies, amino oxidation and host-guest inclusion, were used to modify the skeleton in only one step. All compounds exhibit good comprehensive properties (Td (onset) > 200 °C, ρ > 1.85 g cm-3, Dv > 8400 m s-1, IS > 20 J, FS > 360 N). Benefiting from the pyridazine-based fused tricyclic structure with more hydrogen bonding units and larger conjugated systems, the first example of [5,6,5]-tricyclic host-guest energetic material triamino-9H-pyrazolo[3,4-d][1,2,4]triazolo[4,3-b]pyridazine-diperchloric acid (10), shows high decomposition temperature (Td (onset) = 336 °C), high density and heats of formation (ρ = 1.94 g cm-3, ΔHf = 733.4 kJ mol-1), high detonation performance (Dv = 8820 m s-1, P = 36.2 GPa), high specific impulse (Isp = 269 s), and low sensitivity (IS = 30 J, FS > 360 N). The comprehensive performance of 10 is superior to that of high-energy explosive RDX and heat-resistant explosives such as HNS and LLM-105. 10 has the potential to become a comprehensive advanced energetic material that simultaneously satisfies the requirements of high-energy and low-sensitivity explosives, heat-resistant explosives, and solid propellants. This work may give new insights into the construction and modification of a nitrogen-rich polycyclic framework and broaden the applications of fused polycyclic framework for the development of host-guest energetic materials.

Host-Guest Technique for Designing Highly Energetic Compounds with the Nitroamino Group

A new energetic material, 2-azido-4,7-nitroamino-1H-imidazo[4,5-d]pyridazine (ANIP) with a highly sensitive azido group and its host-guest compounds (ANIP/H2O and ANIP/H2O2), and energetic salts were obtained. With the guest and protons in host molecules, an abundant hydrogen bond system can be formed. This results in high crystal density and good sensitivity, which suggests that the host-guest strategy is a promising way to balance the contradiction between energy and sensitivity and provides a new path to obtain a new generation of high energetic materials.

Effects of Different Guests on Pyrolysis Mechanism of α-CL-20/Guest at High Temperatures by Reactive Molecular Dynamics Simulations at High Temperatures

The host-guest inclusion strategy has the potential to surpass the limitations of energy density and suboptimal performances of single explosives. The guest molecules can not only enhance the detonation performance of host explosives but also can enhance their stability. Therefore, a deep analysis of the role of guest influence on the pyrolysis decomposition of the host-guest explosive is necessary. The whole decomposition reaction stage of CL-20/H₂O, CL-20/CO₂, CL-20/N₂O, CL-20/NH₂OH was calculated by ReaxFF-MD. The incorporation of CO₂, N₂O and NH₂OH significantly increase the energy levels of CL-20. However, different guests have little influence on the initial decomposition paths of CL-20. The E_a1 and E_a2 values of CL-20/CO₂, CL-20/N₂O, CL-20/NH₂OH systems are higher than the CL-20/H₂O system. Clearly, incorporation of CO₂, N₂O, NH₂OH can inhibit the initial decomposition and intermediate decomposition stage of CL-20/H₂O. Guest molecules become heavily involved in the reaction and influence on the reaction rates. k₁ of CL-20/N₂O and CL-20/NH₂OH systems are significantly larger than that of CL-20/H₂O at high temperatures. k₁ of CL-20/CO₂ system is very complex, which can be affected deeply by temperatures. k₂ of the CL-20/CO₂, CL-20/N₂O systems is significantly smaller than that of CL-20/H₂O at high temperatures. k₂ of CL-20/NH₂OH system shows little difference at high temperatures. For the CL-20/CO₂ system, the k₃ value of CO₂ is slightly higher than that for CL-20/H₂O, CL-20/N₂O, CL-20/NH₂OH systems, while the k₃ values of N₂ and H₂O are slightly smaller than that for the CL-20/H₂O, CL-20/N₂O, CL-20/NH₂OH systems. For the CL-20/N₂O system, the k₃ value of CO₂ is slightly smaller than that for CL-20/H₂O, CL-20/CO₂, CL-20/NH₂OH systems. For the CL-20/NH₂OH system, the k₃ value of H₂O is slightly larger than that for CL-20/H₂O, CL-20/CO₂, CL-20/N₂O systems. These mechanisms revealed that CO₂, N₂O and NH₂OH molecules inhibit the early stages of the initial decomposition of CL-20 and play an important role for the decomposition subsequently.

Modulation of Crystal Growth of an Energetic Metal-Organic Framework on the Surfaces of Graphene Derivatives for Improved Detonation Performance

Energetic materials are a special class of energy materials composed of C, H, O, and N. Their safety always deteriorates with increasing energy. Regulating the properties of energetic materials to meet application requirements is one of the focuses of research in this field. Energetic metal-organic frameworks (EMOFs) are good candidates as primary explosives to replace lead azide (LA) and other explosives containing toxic metal elements. However, safety remains the biggest concern in applications. In this paper, crystal morphology modulation of EMOF was carried out by stepwise coordination of metal ions and energetic ligands on surfaces of graphene oxide (GO) and amino-functionalized graphene oxide (AGO). Two energetic composite materials, Cu-AFTO@GO and Cu-AFTO@AGO, were successfully synthesized and also the EMOF (Cu-AFTO). The structures and morphologies of these materials were fully characterized. The thermal decomposition behaviors, mechanical sensitivity, and electrostatic discharge sensitivity were investigated in detail. The electric ignition ability of EMOF and two composite materials was tested. This study shows that it is possible to reduce the diameter of EMOF crystals from hundreds of microns to tens of nanometers by a stepwise coordination method. The high electrical conductivity and sensitivity-reducing effect of GO and/or AGO allow the nanosized EMOF crystals to have a lower ignition threshold and lower sensitivity.