Time-resolved measurements of near infrared emission spectra from explosions: Pure pentaerythritol tetranitrate and its mixtures containing silver and aluminum particles

Abstract

Measurements of chemical transients and thermodynamic conditions are difficult to obtain yet fundamentally important in understanding the behavior of explosives. We have constructed a fast near infrared (NIR) spectrometer and have made temporally and spectrally-resolved emission measurements during postdetonation combustion of pure pentaerythritol tetranitrate (PETN) charges and PETN charges doped with 10 wt % microparticles composed of silver (Ag) and aluminum (Al). We have observed postdetonation PETN emission spectra between 750 and 1500 nm at rates up to 46 992 spectra/s. The instrument captures the highly structured spectra immediately following breakout as well as the longer-lived broadband NIR emission signals from hot particles. The early spectra reveal spectral signatures related to PETN and the reacting constituents of the particles. The later spectra provide a means to infer the gray-body temperature history of the particles.

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.…”

“…The chief disadvantages of the method are the difficulty of the data analysis if temperatures are to be extracted, the care that must be taken to avoid confusing thermal and chemiluminescent emissions, and the fact that like all electronic emission spectroscopies, elevated temperatures are required. Temperatures in the vicinity of ~2000 K are generally required to generate strong emission signals [15][16][17][18].…”