Progress in Electrohydrodynamic Atomization Preparation of Energetic Materials with Controlled Microstructures.

Constructing ingenious microstructures, such as core-shell, laminate, microcapsule and porous microstructures, is an efficient strategy for tuning the combustion behaviors and thermal stability of energetic materials (EMs). Electrohydrodynamic atomization (EHDA), which includes electrospray and electrospinning, is a facile and versatile technique that can be used to process bulk materials into particles, fibers, films and three-dimensional (3D) structures with nanoscale feature sizes. However, the application of EHDA in preparing EMs is still in its initial development. This review summarizes the progress of research on EMs prepared by EHDA over the last decade. The morphology and internal structure of the produced materials can be easily altered by varying the operation and precursor parameters. The prepared EMs composed of zero-dimensional (0D) particles, one-dimensional (1D) fibers and two-dimensional (2D) films possess precise microstructures with large surface areas, uniformly dispersed components and narrow size distributions and show superior energy release rates and combustion performances. We also explore the reasons why the fabrication of 3D EM structures by EHDA is still lacking. Finally, we discuss development challenges that impede this field from moving out of the laboratory and into practical application.

Blue-red emission color change from a heavily-doped Eu@MOF composite: Synthesis, characterization and application for 2,4,6-trinitrophenol sensing.

2,4,6-trinitrophenol (TPA) natural degradation is nearly impossible and its accumulation threatens ecosystem. Optical sensing is an attractive detection method for TPA with low demand of equipment and data processing, but still needs to be improved. This work was dedicated to increasing probe-loading content so as to improve sensing sensitivity. Three probes derived from Eu(III)-benzimidazole were designed, with their active H atoms replaced by alkyl groups to eliminate the hydrogen bond with supporting host and thus to improve probe-loading content. Their molecular structure, absorption, emission, and excitation spectra were discussed to confirm their sensing potential to TPA. Then these three probes were loaded into host (bio-MOF-1) via ionic exchange method, which was confirmed by XRD, N2 adsorption/desorption, ICP, and SEM. The loading content and sensing performance of these three probes in bio-MOF-1 were compared. It was found that the elimination of active H atoms indeed increased probe loading content from 44% to 78%, with sensing coefficient increased from 0.010 µM-1 to 0.029 µM-1. A ratiometric sensing towards TPA was observed, with blue emission from bio-MOF-1 host increased and red emission from Eu(III) probe decreased, which was detectable by naked eyes. Linear working equations were fitted with high selectivity.

Assembling Hybrid Energetic Materials with Controllable Interfacial Microstructures by Electrospray.

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.

Tuning the Ignition Performance of a Microchip Initiator by Integrating Various Al/MoO3 Reactive Multilayer Films on a Semiconductor Bridge.

Reactive multilayer films (RMFs) can be integrated into semiconducting electronic structures with the use of microelectromechanical systems (MEMS) technology and represent potential applications in the advancement of microscale energy-demanding systems. In this study, aluminum/molybdenum trioxide (Al/MoO3)-based RMFs with different modulation periods were integrated on a semiconductor bridge (SCB) using a combination of an image reversal lift-off process and magnetron sputtering technology. This produced an energetic semiconductor bridge (ESCB)-chip initiator with controlled ignition performance. The effects of the Al/MoO3 RMFs with different modulation periods on ignition properties of the ESCB initiator were then systematically investigated in terms of flame duration, maximum flame area, and the reaction ratio of the RMFs. These microchip initiators achieved flame durations of 60-600 µs, maximum flame areas of 2.85-17.61 mm2, and reaction ratios of ∼14-100% (discharged with 47 µF/30 V) by simply changing the modulation periods of the Al/MoO3 RMFs. This behavior was also consistent with a one-dimensional diffusion reaction model. The microchip initiator exhibited a high level of integration and proved to have tuned ignition performance, which can potentially be used in civilian and military applications.