Mechanism investigation for remarkable decreases in sensitivities from micron to nano nitroamine

Raw hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was pulverized to nano RDX by mechanical milling, and their micron morphology and surface elements were probed by transmission electronmicroscope and X-ray photoelectron spectroscopy analyses. Thermal analysis was employed to take a kinetic evaluation on thermal decomposition of raw and nano RDX. The result indicated that activation energy for thermal decomposition of nano RDXis closed to the value of raw RDX, which means nano RDX had similar thermal reactivity as raw RDX. However, the sensitivity tests showed that when raw RDX was pulverized to nanoparticles, its mechanical and shock sensitivities decreased by more than 45%. Since it was impossible to use kinetic evaluation to explain the reason why the difference on sensitivities between raw and nano RDX was so distinct, we recruited classic detonation models to solve the problem. By combining the models of Khasainov's and Merzhanov's, we related the detonation parameters such as temperature of hot spots, critical temperature of hot spots (T-C), critical size of hot spots (delta(C)), and mean size of explosive particles, and concluded that: (a) under the same condition, mean size of hot spot in nano RDX charge was much smaller than that of raw RDX charge; (b) at the same delta(C), T-C of nano RDX (776 K) was higher than that of raw RDX (459 K); and (c) particle size was not an important factor to affect sensitivities of explosives unless size of explosive particles was less than 400 nm. These results must base on a steady thermal reactivity from micron to nano RDX.