Hydrogen evolution reaction (HER) was intensified to produce bubbles as dynamic templates for the preparation of foamed porous copper (FPCu) in acidic cupric electrolyte. The macroscopic morphologies of FPCu, including pore size distribution and pore density, were determined by the bubble diameter. Bubble assemble behavior was the most important in overall process of gas evolution. Growth of hydrogen bubbles caused coalescence of bubbles and resulted in size increment of the templates. Furthermore, bubble behavior was in tight relation with residence time and current density. Results showed that the morphologies were dependent on deposition time and current density. Small pores in FPCu were attributed to the un-coalesced bubbles and large pores were ascribed to the coalesced bubbles. The embedding and nesting of small holes by the large ones contributed to the formation of hierarchical porous framework. A “stack up layers” model was proposed to illuminate the morphological transformation of FPCu from two-dimensional structure to 3-dimensional framework. Understanding of this model facilitated the preparation of macroporous copper with favorable morphologies.

No abstract

Nanothermites are attracting much attention because of the high energy density, self-sustained exothermic reaction, and high combustion temperature. However, they suffer from sintering and incomplete combustion, leading to poor reactivity and low energy utilization efficiency. In order to enhance the energy output and combustion performance of nanothermites, ammonium perchlorate (AP) was introduced into the Al/CuO nanothermites. The nanothermites with varied content of AP were prepared by electrospray. The morphological characterization of the nanothermites confirms that the nanoparticles are homogeneously mixed without agglomeration. Heat release, specific impulse, and peak pressure of gaseous products exhibit remarkable enhancement with increasing AP content. Specifically, the nanothermites with 7.5 wt % AP produce specific impulse and heat energy of ∼2.7 and ∼1.4 times higher than those of Al/CuO-based nanothermites without AP. In addition, the ignition delay time of the nanothermites containing AP is not greatly increased, enabling fast response during practical applications. Thermal analysis implies that the thermite reaction between Al and CuO can be divided into two steps in the presence of AP: solid−solid phase and liquid−solid phase diffusion reaction. These results provide facile strategy to enhance the output performance of nanothermites, which may facilitate the practical propulsion and combustion applications of nanothermites.

Constructing hybrid energetic materials (HEMs) consisting of nanothermites and organic high explosives is an efficient strategy to regulate the reactivity of energetic composites. To investigate the role of interfacial microstructures in determining the reactivity of HEMs, we employ electrospray, one ramification of electrohydrodynamic atomization, to assemble Al/CuO and hexanitrohexaazaisowurtzitane (CL-20) into composites with various morphologies from different solvent systems. The morphology and compositional information of the assembled clay-like or granular HEMs, which are obtained from ketone, ester, or mixtures of alcohol and ether, are confirmed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The phase transition of CL-20 due to the fast evaporation of charged droplets and insufficient time for recrystallization is studied by Fourier transform infrared spectroscopy (FTIR). Thermogravimetric-differential scanning calorimetry (TG-DSC) is applied to investigate the thermodynamic behaviors and synergistic effect of the nanothermite and high explosive. Enhancements in combustion performance and pressurization characteristics of the as-sprayed HEMs have been observed through open burn tests and pressure cell tests. Granular HEMs show high gas generation and high pressurization rate, while nitrocellulose (NC) fibers existing in the clay-like HEMs would weaken the reactivity to a certain extent. HEMs obtained from the mixture of n-propanol and diethyl ether, in which nano-CL-20 exists as independent particles rather than a matrix, exhibit high gas generation but low pressurization rate. The results indicate that the energy releasing performance of the prepared HEMs can be readily regulated by constructing various interfacial microstructures to satisfy the broad requirements of energy sources.