Efficient construction of Al/F microspheres in Pickering emulsion to regulate combustion reactivity

Reducing the formation of large carbon clusters during the combustion of energetic materials (EMs) and improving their comprehensive performance hold great significance. With fluororubber (F2604) as a binder, this study prepared HNS/n-Al microspheres with different n-Al contents (5%, 10%, and 15%) using droplet microfluidic technology. Then, it characterized and tested the morphology, particle size distribution, dispersibility, crystal structure, thermal properties, mechanical sensitivity, and combustion behavior of the microspheres. The results show that the prepared microspheres had regular shapes, uniform particle sizes, and excellent dispersibility and contained more homogeneous components than physically mixed samples. Furthermore, the microspheres retained the crystal structures of the raw materials, enjoying high safety performance. The thermal analysis shows that HNS/n-Al microspheres had high heat resistance (thermal decomposition temperature: over 354 °C) and that a higher n-Al content was associated with more thorough thermal decomposition reactions of HNS (HNS: 83%, HNS/n-Al: 84%, 86%, and 93%). The ignition experiments show that the HNS/n-Al microspheres possessed excellent and stable combustion performance, as evidenced by more complete combustion reactions and significantly elevated energy release efficiency. Therefore, it is expected to achieve high-energy and high-speed responses of carbon-rich EMs and promote their practical applications. 

Preparing HNS/n-Al heat-resistant microspheres with enhanced combustion performance using droplet microfluidic technology

Efficient energy release and the large-scale preparation of thermite with high energy density are currently crucial issues in the field of explosive systems. In this study, we focused on the utilization of porous metal oxides (pMxOy) prepared through urea co-precipitation and high-temperature annealing to enhance the ignition and combustion performance of nanothermites. We compared the thermochemical reactivity, ignition, and combustion performance of nAl/pMxOy with those of nanothermites composed of nano metal oxides. We found that the use of pMxOy resulted in significantly increased the reaction exergy and reduced the activation energy of nanothermites, the energy released by the nanothermite containing pMxOy increased by up to 33.4%, while the activation energy decreased by up to 34.8%. Furthermore, the ignition and combustion results show that better semiconductor bridge ignition, pressurization, and combustion performance of nanothermites consisting of high free oxygen ratio and high porosity pMxOy. This improvement can be attributed to the enhanced contact between nAl and pMxOy, as well as the improved oxygen ionic conductivity of pMxOy. We believe that this high-performance nanothermite, which utilizes porous metal oxides exhibiting high interfacial activity, can be extensively employed in various initiating explosive devices. Notably, the simplicity of the batched preparation process further enhances its potential for practical application. 

Enhancing the energy release performance of nanothermites through metal oxides free oxygen and pores

Owing to its hydrogen storage capacity, aluminum hydride (AlH3) has been proposed as a potential fuel additive in solid rocket propellants to achieve a higher specific impulse and cooler combustion. In this experimental investigation, we examine the effects of AlH3 loading and particle size on the thermal decomposition, ignition, agglomeration and combustion of high-energy solid propellants at pressures up to 9.1 MPa. We use a variety of diagnostics, including thermogravimetry, differential scanning calorimetry, energy dispersive X-ray spectroscopy, scanning electron microscopy and so on. The results show that adding AlH3 can enhance the thermal decomposition of the propellants. As the loading of fine-grained AlH3 increases, the combustion intensity drops, but the ignition delay time drops as well (by 60 %). When the AlH3 particle size increases, the ignition delay time rises, but it remains shorter than that of a baseline propellant containing Al instead of AlH3. Although AlH3 is found to lower the gas-phase flame temperature and temperature gradient, it enhances the burning rate and lowers the pressure exponent from 0.58 to 0.50. Fine-grained AlH3 is also found to shrink the near-burning surface agglomerates and condensed combustion products, increasing the combustion efficiency from 81.9 % to 94.7 %. However, coarse-grained AlH3 shows the opposite effect, decreasing the combustion efficiency to 63.3 %. Overall, this study sheds new light on the influence of AlH3 addition on high-energy propellants, facilitating the application of this promising fuel additive in solid rocket motors. 

Effects of AlH3 particle size and loading on the combustion and agglomeration of solid propellants

To solve the problem of nano-aluminum (nAl) powder easy agglomeration and improve its thermal reaction, nAl was combined with adhesive (Viton A, F2602) and oxidizer (Ammonium perchlorate, AP) forming microspheres by electrostatic spray method. The morphology and structure were analyzed by SEM, EDS and XPS. The results showed that the microspheres (diameter≈Φ10∼15 μm) were hollow structures formed by winding of fluoropolymer fibers, while AP and nano aluminum particles were embedded on the fibers. By controlling the electric spray process, the well-dispersed AP and nAl nanocrystals were assembled on the fiber. Thermal analysis indicated that the gas phase products decomposed by AP were absorbed by porous microspheres, and part of the heat was stored in polymer fibers, thus promoting the breakdown of the alumina shell and accelerating the pre-ignition reaction. The combustion and laser ignition experiments proved hollow heterogeneous microspheres have excellent thermodynamic properties. The assembled microspheres not only solved the problem of poor rheology caused by the agglomeration of nAl, but also improved the insufficient combustion of nAl and the condensation of products. 

Construction of hollow heterogeneous microspheres containing energy storage fibers by electric spray to promote combustion of nano aluminum

µAl-based reactive materials with improved energy efficiency by using the fluorine-containing oxidizer perfluoropolyether as an interfacial layer

Preparation and characterization of Al@TKX-50@NC composite microspheres by electrospray

Interface Interactions of epsilon-CL-20 and Polymers: from Simulation to Experiment

Dihydroxylammonium 5, 5′-bistetrazole-1, 1′-diolate (TKX-50) is a promising new nitrogen-rich energetic material with considerable properties and low sensitivity, but unfortunately inadequate energy release may restrict its application. To enhance the reactivity of TKX-50 in the energetic materials, TKX-50/CL-20 composite material was constructed by using a facile fabrication method. Further, thermal decomposition analysis, constant-volume combustion cell test and laser ignition experiment were conducted to study the thermal behavior. The results showed that the incorporation of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12 -hexaazaisowurtzi-tane (CL-20) advanced the exothermic peak temperature for the decomposition of TKX-50, and significantly reduced the apparent activation energy obtained by the thermal decomposition kinetic methods. Moreover, CL-20 could promote the combustion and energy release rate of TKX-50 that is reflected on the increased pressurization rate, as well as the stronger and brighter flame that appeared during the combustion process. The obtained results indicated that CL-20 participated in the thermal behavior of TKX-50 and improved its overall reactivity. 

Incorporation of CL-20 into TKX-50 to improve thermal reactivity

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Papers

µAl-based reactive materials with improved energy efficiency by using the fluorine-containing oxidizer perfluoropolyether as an interfacial layer

Preparation and characterization of Al@TKX-50@NC composite microspheres by electrospray

Interface Interactions of epsilon-CL-20 and Polymers: from Simulation to Experiment

Incorporation of CL-20 into TKX-50 to improve thermal reactivity