1. MECHANICAL SENSITIVITY
Ultrasonic approach to the synthesis of core-shell microparticles with improved mechanical sensitivity
(Ultrasonic Sonochemistry, 2014, 21, 1349–1357.)
Bing Huang, Xiaofei Hao, Haobin Zhang, Zhijian Yang, Zhigang Ma, Hongzhen Li, Fude Nie, Hui Huang
Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang , China
INTRODUCTION
EXPERIMENTAL
Insensitive high explosives have been subjected to extensive research for their desirable characteristics. As a consequence, considerable effort has been devoted to the exploration of the explosive with higher explosive performance and lower sensitivity [1]. Although remarkable progress has been made in maintaining explosion performance and decreasing sensitivity, there is rarely effective work to construct a perfect core–shell structure to further tune the safety–power contradiction. Herein, we demonstrate a facile ultrasonic approach to synthesize core–shell composite microparticles.
Firstly, g TATB nanoparticles were dispersed in 10mL of ultrapure water through high-intensity ultrasonic irradiation with the output acoustic power of 240 W at a frequency of 40 kHz for 30 min. At the same time, 1 g Estane-modified HMX microparticles were put into 20 mL of ultrapure water, which were facilitated by using the ultrasonic apparatus for 30 min. In the next step, a hot suspension of sonicated TATB nanoparticles was immediately added to the above Estane-modified HMX suspension and ultrasonically treated for 15 min. Afterward, a green-yellow product was collected by vacuum filtration and dried in an oven at 60 °C for 8 h.
XPS SURFACE ANALYSIS
SEM PHOTOGRAPHS
The absence of N1s peaks of HMX in the XPS survey scans for core–shell microparticles implies that the surface of HMX were coated successfully by nano-TATB layer with the coverage close to 100%. This result is in good accordance with the SEM analysis.
Before and after decoration with Estane, the surface of the HMX and Estane-modified HMX microparticles are both smooth (Fig. b and d). However, the core–shell structures possess rough surface due to the grainy structure of the outer TATB layer (Fig. f). The inset presents that an obvious coarse layer is continuously distributed over the surface of core layer, and the size is in correspondence with the results of TATB raw material in Fig. h.
GROWTH MECHANISM
MECHANICAL SENSITIVITY
The impact and friction sensitivity of the core–shell obtained with the sheath content of 15% are higher than 112 cm and 0%, respectively, which proves that the core–shell composite is less sensitive to mechanical stimuli due to its unique microstructures.
Under ultrasonic condition, a large number of bubbles can create localized hot spots with an exceedingly high transient temperature (5000 °C) and pressure (500 atm) on a microsecond time scale, which can provide energy to cause chemical and mechanical effects [2].
With the assistance of extraordinary, the groups on the surface of the HMX particles can be activated, thus facilitating the interaction between TATB and Estane-modified HMX.
Physical effects of ultrasonic cavitation can drive particles together for inelastic impact at the point of meeting, leading to
the rapid synthesis of core–shell microparticles.
The reason is likely that the HMX core is protected by insensitive graphite-like nano-TATB, which plays a buffer and lubrication role when external forces are acted on the sample, thus resulting in formation of fewer hot spots and reduction of mechanical sensitivity.
CONCLUSIONS
REFERENCES
A facile ultrasonic approach for fabricating core– shell microparticles has been brought forward. A possible mechanism is proposed to account for the formation of perfect core–shell structures. The corresponding core– shell composites show excellent mechanical sensitivity, and have potential applications in civilian and military areas.
(1) Zhang, Y. Q.; Parrish, D. A.; Shreeve, J. M. Journal of Materials Chemistry A, 2013, 1, 585−593.
(2) Bang, J. H.; Suslick, K.S. Advanced Materials, 2010, 22, 1039−1059.