Electromagnetically induced localized ignition in secondary high explosives

Abstract

A model for electromagnetically induced hot spots is developed from the well-established theories of dielectric mixtures, microwave absorption, heat transfer, and thermal ignition. This mathematical model is used to elucidate the interplay among these theories for a microwave heated system of secondary high explosive within which isolated electromagnetically lossy spheres are randomly distributed. Results are shown in this article for the specific case of pentaerythritol tetranitrate with embedded spheres of varying diameter and conductivity illuminated by a uniform time harmonic electromagnetic field of 1, 8, and 15 GHz. It is shown that for a given frequency and electric field strength internal to a particle embedded in a secondary high explosive, there exists a range of values for the particle’s diameter and conductivity for which electromagnetically induced hot-spot ignition of the high explosive is possible. By providing an accurate estimate for the range of necessary geometric and electrical properties of the system, this idealized model can be used to guide potentially complex and otherwise less tractable computational and experimental studies of microwave-induced hot spots. We found that the condition of relatively large particles, with semiconductorlike conductivity, exposed to the highest possible frequency is most favorable for hot-spot ignition.

Analyzing the Effects of Electromagnetic Exposure on Energetic Compositions

“…Exposure of energetic materials to electromagnetic waves has been investigated previous for a multitude of purposes across various frequencies. There have been studies that investigate how lasers ignite nanocomposite thermites [3], microwave ignition studies in combustion synthesis [4][5][6], ignition in secondary explosives by localized microwave [7], and hazard studies of microwave irradiation on explosives [8]. Frequencies used in previous studies were limited to 2.45 GHz or higher frequencies such as 75 GHz.…”

X‐Band Microwave Properties and Ignition Predictions of Neat Explosives

“…Consequently, recent approaches to enhance heating have focused on the intentional inclusion of absorptive particles such as SiC and carbon nanotubes [14][15][16][17]. The focus of these studies, however, has been primarily to study localized hot spot formation and ignition within these materials rather than to develop a fundamental understanding of the response of neat explosives to electromagnetic energy.…”

Microscale Electromagnetic Heating in Heterogeneous Energetic Materials Based on X-ray Computed Tomography

“…Modeling and simulation tools are therefore a valuable route towards understanding and predicting the behavior of heterogeneous energetic materials under electromagnetic stimuli. Previous works along this direction have used simple semi-analytical models based on homogenization theory [3], or continuum models of idealized mesoscale geometries to mimic real complex structures [2,5]. Although useful, these approaches cannot unequivocally determine the spatial and temporal behavior of hot spots in real heterogeneous energetic materials.…”