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Boron (B) has potential applications in energetic materials as additive fuel. In order to understand the combustion mechanism of B with various scales, the ignition and combustion characteristics of micro- and nano-sized B under different pressures (0.4 MPa, 0.8 MPa and 1.2 MPa) and atmospheres (60% O 2 + 40% N 2 , 80% O 2 + 20% N 2 and 100% O 2) were studied by a laser ignition and combustion experimental system. The evolution images and specialized parameters of ignition and combustion under different conditions were obtained, and the effects of atmosphere and pressure on the ignition and combustion characteristics of micro- and nano-sized B were discussed. Meanwhile, the crystal structure and morphology of condensed combustion products were observed by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM), and then the compositions in micro-areas were analyzed by energy dispersive X-ray spectroscopy (EDX). The results show that, the burning of micro-sized B is relatively slow, while the burning of nano-sized B is intensified, and a deflagration-like phenomenon is observed for nano-sized B in pure oxygen with pressures of 0.8 and 1.2 MPa. The ignition delay time, combustion time and maximum flame temperature of nano-sized B are smaller than those of micro-sized B, while the maximum characteristic spectral intensity of nano-sized B is stronger. Besides, B 2 O 3 , B 6 O and BN exist in condensed combustion products of micro-sized B, but only B 2 O 3 is detected for nano-sized B, and products agglomerating is observed for nano-sized B. In general, nano-sized B has significant advantages than micro-sized B in the ignition and combustion characteristics, especially under conditions of high oxygen concentrations and high pressures. [ABSTRACT FROM AUTHOR]

Reactive materials consisting of aluminum (Al) and fluorine-containing oxidizers have been extensively developed owing to high energy density and potential applications in propellants and explosives. Herein, graphite fluoride (CF) as a new fluorine-containing oxidizer was introduced to construct nano-Al based reactive materials. Systematic investigation and comparison were executed on exothermic reaction behavior and combustion performance of nano-Al/CF and nano-Al/polytetrafluoroethylene (PTFE) based reactive materials. The energy output and exothermic peak of nano-Al/CF were approximately 2367 J/g and 641 °C, which were 300 J/g and 85 °C higher than those of nano-Al/PTFE, respectively. The effects of nano-Al/CF mass ratio and packing density on burning rates were examined to fully understand combustion reaction and flame propagation behavior. Nano-Al/CF exhibited excellent burning rate (1670 m/s), much higher than that of nano-Al/PTFE (930 m/s). More interestingly, flame splitting phenomenon including three distinct flame regions was observed on the critical position with the highest burning rate for nano-Al/CF with the mass ratios of 25/70 and 30/75. The burning rate of nano-Al/CF increased and then decreased with the packing densities ranging from 20.87% to 53.47% TMD. The dominating combustion reaction products (AlF 3 and C) were further determined to figure out the reaction mechanism. These results demonstrated that CF as fluorine-containing oxidizer to construct reactive materials has potential applications in propellants, explosives and pyrotechnics. [ABSTRACT FROM AUTHOR]

The incorporation of aluminum (Al) into explosives represents a facility and efficient way to enhance the energy output through the secondary reaction between Al and the detonation products of explosive. The Al/O ratio and microstructure of HMX/Al play critical roles in combustion performance and energy output. Herein, a gradient structured HMX/Al composite has been designed and fabricated via 3D printing technology using well-dispersed HMX/Al-based ink. For HMX/Al lines, the second reaction heat increases from 196.5 J/g to 1644.8 J/g and the burning rate would decrease from 14.6 to 12.0 mm/s with Al content increased from 10 to 30 wt%. For gradient structured HMX/Al, the burning rate could be controlled by varying the component ratio and the burning rate of each component in the gradient structure was higher than that of the normal HMX/Al counterpart. Furthermore, a gradient evolution of pressure output was monitored for gradient structured HMX/Al cylinder ignited by the laser. These results indicate that the gradient structure as an effective approach can tune combustion performance and energy output of HMX/Al. [ABSTRACT FROM AUTHOR]

The multilayer nanostructured FG/Al (MN-FG/Al) energetic materials with particle mosaic have been rapidly assembled by the intercalation-like method, and the energy output performance of these MN-FG/Al energetic materials can be effectively regulated by changing the ratio of FG and nAl. [Display omitted] • Propose an efficient strategy towards the design of energetic materials. • Multilayer nanostructured have assembled by the intercalation-like method. • Energy output can be effectively regulated by changing the ratio of FG and Al. • Oxygen content determines the reaction and obtains different pressure outputs. Fluorinated reactive materials as new energetic materials are widely studied because of their high combustion heat and the ability to release large amounts of gaseous products. In order to further improve combustion reaction and the energy release efficiency, structural processing strategy is usually adopted to construct unique microstructures for fluorinated reactive materials. In this work, it is found that fluorinated graphene (FG) and nano-aluminum (nAl) can be rapidly assembled by the intercalation-like method to form multilayer nanostructured energetic materials with particle mosaic. Based on this, the energy output performance of these multilayer nanostructured energetic materials can be effectively regulated by changing the ratio of FG to nAl. The shortest laser ignition delay time (8 ms) and the longest burning time (56 ms) can be achieved for the multilayer nanostructured energetic material with proper FG/Al ratio, while the burning rate of the sample spline can reach 14.83 cm/s. In addition, the reaction process of multilayer nanostructured FG/Al energetic materials depends upon oxygen content that participates in the reaction in different atmospheres, leading to the different pressure output performance. This study provides a promising strategy for the further application of fluorinated reactive materials in the field of energetic materials. [ABSTRACT FROM AUTHOR]

To improve and adjust the combustion and energy output of HMX/Al, graphite fluoride (CF) as oxidizer was introduced in HMX/Al and gradient structured HMX/Al/CF was prepared by additive manufacturing technology. For HMX/Al added with CF, a significantly exothermic peak is observed ranging from 860 to 950 °C due to the reaction of Al and fluorine derived from CF decomposition, and the heat release increases by 106.63% compared to that of HMX/Al. The fourth exothermic heat increases from 161.48 to 955.25 J/g with the increased Al content from 10 to 30 wt%. Moreover, the combustion rate and pressure output of HMX/Al have been improved by introducing CF. For HMX/Al added with CF, the combustion time decreases from 10.3 to 2.5 s, which is dependent on the Al content from 10 to 30 wt%. And the highest peak pressure is 1712.2 kPa when Al content is 20 wt% in HMX/Al/CF composites. Furthermore, gradient structured HMX/Al/CF consisting of three layers with Al content of 10, 20 and 30 wt% was prepared to improve combustion and pressure output. The combustion rate and peak pressure of gradient structured HMX/Al/CF are higher than those of single structured HMX/Al/CF. The highest peak pressure (∼2.24 MPa) is obtained when the Al content of the middle layer and outer layer is 30 wt% and 20 wt% in the gradient structured HMX/Al/CF cylinder, respectively. Finally, the reaction intermediates and combustion reaction products were fully characterized to understand the enhanced effect of CF in HMX/Al. This work provides a promoting way to improve and regulate the combustion reaction performance and pressure output of HMX/Al. [ABSTRACT FROM AUTHOR]

A micro-sized B-Al alloy has application potential to be an energetic material for metal fuel. To understand the combustion mechanism of micro-sized B-Al compound powder and explosives containing B-Al (30 wt.%), the ignition and combustion characteristics of B-Al compound powder without and with HMX (cyclotetramethylenetetranitramine) under different pressures (0.4, 0.8, 1.2, 1.5 and 1.8 MPa) and atmospheres (60% O + 2 40 % N 2 , 80% O + 2 20 % N 2 and 100% O 2) were studied via a laser ignition experimental system. The images and characteristic parameters of the ignition and combustion process with different conditions for the B-Al compound powder without and with HMX were obtained. The effects of atmosphere and pressure on the ignition and combustion characteristics of the B-Al compound powder without and with HMX were discussed through a comparative analysis. For the condensed combustion products (CCPs), the phase crystal structures were analysed with X-ray diffraction (XRD), the micro-morphology of the surface was observed with scanning electron microscopy (SEM), and the micro-area elementary composition was analysed with X-ray energy dispersive spectrum (EDS). The results show that whether the increase in pressure or oxygen concentration, the ignition delay time (t id) and combustion time (t ct) of samples without and with HMX decrease, while the maximum spectral intensity (I max) and the maximum combustion temperature (T max) increase. According to the flame morphology, the combustion of the B-Al compound powder is weaker, while that of the B-Al powder with HMX is more intense, and the flame area is larger, which produces a large amount of smoke and presents a deflagration phenomenon. Specially, for various B-Al powder (B/Al = 3/7, 1/1 and 7/3) with HMX under high pressures (1.2, 1.5 and 1.8 MPa), the higher ratio of B leads to shorter combustion time and stronger spectral intensity. Unreacted B, Al and their final oxides, B 2 O 3 and Al 2 O 3 , were detected in the CCPs of both samples without and with HMX. In addition, the CCPs like BN, AlN and Al 5 O 6 N were also detected. The experimental results can help us better understand the chemical reaction mechanism and energy release characteristics of HMX-based explosives containing B-Al. [ABSTRACT FROM AUTHOR]