Importance of the gas phase role to the prediction of energetic material behavior: An experimental study

Abstract

Various thermal ͑radiative, conductive, and convective͒ initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials ͑EM͒. A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine ͑HMX͒ and 2,4,6-trinitrotoluene ͑TNT͒. Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6 mm± 0.4 mm exists below which ignition by CO 2 laser is not possible at the tested irradiances of 29 W / cm 2 and 38 W / cm 2 for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.

Conformations and charge distributions of diazocyclopropanes

“…They are subjected to complicated ignition and combustion processes since they involve several phases, are time–dependent, and their reactions follows multiple, branching paths. The importance of the gas phase to the prediction of energetic material behavior is experimentally established 2, 3. A great goal of the theoretical energetic materials research has been to acquire knowledge to predict various properties of this type of material associated with performance and sensitivity before its frequently expensive, and often hazardous, synthesis is carried out 4.…”

A Multireference Configuration Interaction Study of the Photodynamics of Nitroethylene

“…The study of gas phase energetic molecules can unveil their properties and reactions at the molecular level, and determine decomposition features as a function of the electronic and vibrational excitations. 7 However, the experimental measurements of decomposition processes and their interpretation are very complex, a picture asking for theoretical investigations. Moreover, in spite of the importance of excited states in energetic materials research, only few studies have been carried out in this field.…”

“…Most of the energetic molecules have diffuse electronic spectra and propensity to dissociate and rearrange . In the detonation initiation of these materials, photochemical processes are very important. − In particular, as has been increasingly recognized in the field of photochemical reactions, , nonradiative decomposition processes of energetic molecules through conical intersections play an important and even dominant role. − Therefore, investigations of nonadiabatic processes occurring in energetic molecules are especially interesting.…”

Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles

“…1 In particular, aluminum and boron exhibit considerable promise as high-energy-density species in the presence of oxidizers, 2 and the increasingly economical availability of aluminum nanoparticles, along with a variety of readily tunable physical properties, such as particle diameter and composition of passivation layer, make aluminum nanoparticles particularly attractive for further study. 1,[3][4][5][6][7] When used as an additive in solid-rocket propellants or high explosives, aluminum particles are rapidly ejected into the gas phase following the initial impulsive combustion event; these particles then continue to react with oxidants present in that gas-phase mixture produced by the initial impulsive event. 8 The dynamics of aluminum-particle reactions in such gas-phase environments have been studied in depth by several groups, and a notable dependence of these reaction dynamics on particle size has been observed.…”