In situ synthesis of [Cu(BODN)·5H2O]n@nano-Al composite energetic films with tunable properties in pyro-MEMS

Integrating energetic materials with microelectromechanical systems (MEMS) to achieve miniaturized integrated smart energetic microchips has broad application prospects in miniaturized aerospace systems and civil explosive systems. In this work, MEMS compatible [Cu(BODN)·5H2O]n arrays and [Cu(BODN)·5H2O]n@nano-Al composite energetic films were successfully fabricated on copper substrates by the in situ reaction method and drop-coating method. Single crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, infrared spectroscopy, differential thermal analyses, and pulsed laser ignition were employed to characterize the prepared samples. The results show that [Cu(BODN)·5H2O]n arrays formed by the coordination reaction between the Cu(OH)2 template and the BODN ligand exhibit a porous supramolecular structure with excellent thermal and energy properties. Their morphology and composition on a copper substrate can be effectively regulated by adjusting the reaction time and solution concentration. In addition, adjustable energetic properties of [Cu(BODN)·5H2O]n@nano-Al composite films can be achieved after the encapsulation of nano-Al. Their heat release, flame height and ignition duration can reach as much as 1987.5 J g-1, 13.2 mm, and 5900 μs, respectively, indicating that [Cu(BODN)·5H2O]n@nano-Al can be used as an excellent pyrotechnic agent in MEMS ignition chips. Overall, this work provides a reference for the integration and application of energetic materials in MEMS systems.

Design, preparation, and combustion performance of energetic catalysts based on transition metal ions (Cu2+, Co2+, Fe2+) and 3-aminofurazan-4-carboxylic acid

Development of energetic catalysts with high energy density and strong catalytic activity has become the focus and frontier of research, which is expected to improve the combustion performance and ballistic properties of solid propellants. In this work, three energetic catalysts, M(H2O)4(AFCA)2·H2O (AFCA = 3-aminofurazan-4-carboxylic acid, M = Cu, Co, Fe), are designed and synthesized based on the coordination reaction of transition metal ions and the energetic ligand. The target products are characterized by single crystal X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, optical microscopy, and scanning electron microscopy. The results reveal that Cu(H2O)4(AFCA)2·H2O crystallizes in the monoclinic space group, Dc = 1.918 g cm-3. Co(H2O)4(AFCA)2·H2O, and Fe(H2O)4(AFCA)2·H2O belong to orthorhombic space groups, their density is 1.886 g cm-3 and 1.856 g cm-3, respectively. In addition, the designed catalysts show higher catalytic activity than some reported catalysts such as Co(en)(H2BTI)2]2·en (H3BTI = 4,5-bis(1H-tetrazol-5-yl)-1H-imida-zole), Co-AzT (H2AzT = 5,5'-azotetrazole-1,1'-diol), and [Pb(BTF)(H2O)2]n (BTF = 4,4'-oxybis [3,3'-(1-hydroxy-tetrazolyl)]furazan) for the thermal decomposition of ammonium perchlorate (AP). The high-temperature decomposition peak temperatures of AP/Cu(H2O)4(AFCA)2·H2O, AP/Co(H2O)4(AFCA)2·H2O, and AP/Fe(H2O)4 (AFCA)2·H2O are decreased by 120.3 °C, 151.8 °C and 89.5 °C compared to the case of pure AP, while the heat release of them are increased by 768.8 J g-1, 780.5 J g-1, 750.9 J g-1, respectively. Moreover, the burning rates of solid propellants composed of AP/Cu(AFCA)2(H2O)4·H2O, AP/Co(AFCA)2(H2O)4·H2O and AP/Fe(AFCA)2(H2O)4·H2O are increased by 2.16 mm s-1, 2.53 mm s-1, and 1.57 mm s-1 compared with the case of pure AP. This research shows considerable application prospects in improving the combustion and energy performance of solid propellants, it is also a reference for the design and preparation of other novel energetic catalysts.

A Covalent Organic Framework Membrane with Homo Hierarchical Pores for Confined Reactive Crystallization

Gas-liquid (G-L) reactive crystallization is a major technology for advanced materials construction, which requires a short diffusion path on the interface to ensure the reactant supply and stable crystal nucleation under ultrahigh supersaturation. Herein, a covalent organic framework (COF) membrane with homo hierarchical pore structures was proposed as an effective interfacial material for the regulation of confined reactive crystallization. By combining the ordered nanopores of COFs and micropores of anodic aluminum oxide (AAO), the COF membrane simultaneously provided an excellent nanoscale diffusion-reaction regulation network as the molecular-level confined G-L reactive interface and adjustable submicrometer gas mass transfer channels. The highly selective construction of CaCO₃ superstructures was then achieved. When the submicrometer primary pore size r_p of the constructed COF membrane ranged from 120 to 1.6 nm, the diffusion mechanism of CO₂ varied from viscous flow diffusion to Knudsen diffusion. The growth orientation of CaCO₃ crystals was well confined to obtain spindle-shaped crystals with high selectivity. Meanwhile, the crystal selectivity factor (cube/sphere) increased from 0 to 3.53 under the low interfacial nuclear barrier. Thus, the COF membrane with coupled micro-nanostructures successfully screened the directional preparation conditions for diverse CaCO₃ superstructures, which also paved a meaningful path for the functional application of COFs in accurate mass transfer control and confined chemical reactions.

In situ synthesis of hydrophobic coatings: an effective strategy to reduce hygroscopicity and catalyze decomposition of ammonium perchlorate

An in situ reaction of stearic acid with copper acetate or cobalt acetate was adopted to prepare hydrophobic coatings, which effectively reduced the hygroscopicity and accelerated the thermal decomposition process of ammonium perchlorate.