Comparison of post-detonation combustion in explosives incorporating aluminum nanoparticles: Influence of the passivation layer

Abstract

Aluminum nanoparticles and explosive formulations that incorporate them have been a subject of ongoing interest due to the potential of aluminum particles to dramatically increase energy content relative to conventional organic explosives. We have used time-resolved atomic and molecular emission spectroscopy to monitor the combustion of aluminum nanoparticles within the overall chemical dynamics of post-detonation fireballs. We have studied the energy release dynamics of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) charges incorporating three types of aluminum nanoparticles: commercial oxide-passivated nanoparticles, oleic acid-capped aluminum nanoparticles (AlOA), and nanoparticles in which the oxide shell of the particle has been functionalized with an acrylic monomer and copolymerized into a fluorinated acrylic matrix (AlFA). The results indicate that the commercial nanoparticles and the AlFA nanoparticles are oxidized at a similar rate, while the AlOA nanoparticles combust more quickly. This is most likely due to the fact that the commercial nano-Al and the AlFA particles are both oxide-passivated, while the AlOA particles are protected by an organic shell that is more easily compromised than an oxide layer. The peak fireball temperatures for RDX charges containing 20 wt. % of commercial nano-Al, AlFA, or AlOA were ∼3900 K, ∼3400 K, and ∼4500 K, respectively.

Time-Dependent Temperature Measurements in Post-Detonation Combustion: Current State-of-the-Art Methods and Emerging Technologies

“…Many subsequent investigations using emission spectroscopy have utilized spectral features in the UV/visible/near-IR to interrogate the temporal dynamics [14][15][16][17][18][19][20]. This region of the spectrum corresponds to electronic transitions of both atomic and molecular species, although we note that vibrational overtones and combination bands can be observed in the near-IR.…”

“…In this approach, the emission spectrum is analyzed qualitatively but chemical dynamics are tracked quantitatively; that is the various peaks and bands in the spectrum are identified and their intensities are plotted as a function of time in order to obtain kinetics information about chemical processes occurring in the fireball [14,15]. This approach has been used in a number of investigations to examine chemical dynamics in fireballs produced following detonation of explosive charges containing aluminum [14][15][16][18][19][20] or silver [16] by tracking the time dependence of atomic Al lines, AlO bands, and atomic Ag lines.…”

“…Large broadband emissions from particulates are also common. One consequence of all this is that the spectrum, while information-rich, can often be quite complex with multiple overlapping bands, large broadband emissions, and strong signals from trace impurities [14,[16][17][18][19][20].…”

“…This complexity, combined with the presence of strong signals from impurities and broadband emissions can make interpretation of the spectrum difficult, particularly when the goal is to extract temperatures from the vibronic bands observed. An alternative approach that has been developed is to utilize atomic emissions for the temperature measurements [16][17][18][19][20], with the molecular emission bands optionally employed to simultaneously track chemical dynamics as described in Section 3.2.2. This approach for measuring temperatures can be employed even in the most congested and difficult-to-assign spectra since the atomic emissions are simply superimposed on top of the other spectral features.…”

Chemical and Morphological Inhomogeneity of Aluminum Metal and Oxides from Soft X-ray Spectromicroscopy

“…42,43 These analytes were specifically chosen because they provided a range of particle sizes, compositions, surface chemistries, and reactivities. [44][45][46][47] For example, previous studies have shown that protecting agents including organic ligands 40,[48][49][50][51][52][53][54] and polymer [55][56][57] or metal coatings 44,58,59 enhanced reactivity properties and provided chemical control over structural attributes like particle size and monodispersity. The STXM-XAS results were consistent with earlier spectromicroscopy studies, 26,55,60 and also revealed new differences in the surface and micron-scale speciation of Al nanoparticles.…”