Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session W02: Thermal Response, Cook-off, Aging, and CompatibilityRecordings Available
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Chair: Brian Little Room: Anaheim Marriott Platinum 6 |
Thursday, July 14, 2022 4:00PM - 4:15PM |
W02.00001: Unified thermal transport in Molecular crystals Zhiyu Liu, Peter W Chung, Gaurav Kumar Phonons play an essential role in heat transport and energy conversion in molecular crystals. Moreover, phonons are vital in understanding the sensitivity and laser-induced properties of energetic materials. However, the phonon transport mechanism in many molecular crystals is still unclear. This work studies the anharmonic phonon properties and thermal transport of molecular crystal RDX and cellulose Iβ using lattice dynamics and molecular dynamics. Both materials have a large number of phonons whose path lengths fall below the Ioffe-Regel limit, where the widely used phonon gas model (PGM) has been shown to break down. The unified thermal transport model, which accounts for the contributions from diagonal and off-diagonal terms of the heat-current operator, is applied to study the thermal conductivity. The unified model shows better agreement with the Green-Kubo method than PGM for both materials. Compared to the diagonal terms (particle-like), the off-diagonal terms (wave-like) dominate the phonon transport in both materials. Our study provides insights into the understanding of thermal transport in complex molecular crystals and paves the way for theoretical study of light matter interactions in complex molecular materials. |
Thursday, July 14, 2022 4:15PM - 4:30PM |
W02.00002: Electromagnetic-Induced Thermal Decomposition of RDX Rosemary S Burritt, Amanda L Duque, Levi A Lystrom, Lee Perry We recently discovered that electromagnetic (EM – 2.45 GHz) energy perturbs the thermal ignition mechanism of a common energetic material. We hypothesize that the EM energy 'pumps' the gas-phase charged species that form as part of the pre-ignition process, resulting in accelerated reactions without uniformly heating the volume. Here, we investigate the behavior of RDX exposed to short pulses of EM energy after heating to temperatures below the threshold for thermal decomposition. We have constructed a temperature-controlled experiment to expose the sample to strong electric fields (~ 1 MV/m). Emission was monitored by visible and infrared sensors. The photonic response time was on the order of milliseconds. A theory-based model developed for a similar system shows a comparable temporal response and suggests a mechanism where EM energy accelerates the gas-phase, heat producing reactions, ultimately increasing the heat feedback to the rate-limiting surface reactions. These observations support our hypothesis and illuminated the heat feedback mechanism. Future work will refine the model specifically for the system presented here and expand to include the explosives. HMX and PETN. |
Thursday, July 14, 2022 4:30PM - 4:45PM |
W02.00003: Pressure and temperature dependent thermal conductivity tensor of high explosive crystals Romain Perriot Modeling and simulation are critical for predicting the performance and safety of high explosives (HE), in particular their response to moderate insults in accident scenarios. Thermal conductivity, notably, is a key component of HE modeling: heat localization leads to the creation of “hot spots” where chemical reactions occur, ultimately causing events such as deflagration of detonation; heat conduction limits the temperatures accessible in hot spots and thus has a major impact on these phenomena. However, experimental information on thermal conductivity is usually scarce, and rarely accounts for temperature, pressure, and orientation dependence, which are critical input to higher-scale simulations. In this work, we use reverse non-equilibrium molecular dynamics (RNEMD) to determine the thermal conductivity of three important HEs: orthorhombic α-1,3,5-trinitro-1,3,5-triazinane (α-RDX), monoclinic β-1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (β-HMX), and tetragonal pentaerythritol tetranitrate (PETN). Importantly, we compute the full thermal conductivity tensor for these compounds, as a function of temperature and pressure, allowing for the determination of heat transport in any direction, and for thermodynamic conditions that span the stability |
Thursday, July 14, 2022 4:45PM - 5:00PM |
W02.00004: Thermal effects of long-term aging on pentaerythritol tetranitrate (PETN): A multi-analytical study over 18 months at 50, 60, and 75 °C. Kyle D Spielvogel, Nicholas Lease, Maria Campbell, Reid T Buckley, Nathan J Burnside, Geoffrey W Brown, Daniel N Preston, Virginia W Manner Widespread use of pentaerythritol tetranitrate (PETN) by civilian and military sectors warrants the investigation of how aging conditions may affect initiation and performance of PETN-based detonators. Powders of PETN held at elevated temperatures result in larger particle size and altered chemical composition that affects detonator performance. Addition of stabilizers to PETN powders can slow the rate of change without affecting explosive performance. However, the effects of long-term storage on stabilized PETN at elevated temperatures have not been studied in a large-scale, statistically significant way. Here we describe an aging study of detonators and powders of pure PETN and TriPEON-stabilized PETN, at sampling times between 1 to 18 months at three different temperatures of 50, 60, and 75 °C. The stabilized powders show a decreasing rate of change up to 60 °C and slowed the rate of change at 75 °C without significantly impacting detonator performance. Supporting Fischer specific surface area analysis, SEM imaging, light scattering particle size, HPLC and detonator performance will be discussed. |
Thursday, July 14, 2022 5:00PM - 5:15PM |
W02.00005: On the use of thermal quadrupole to simulate the response of a high explosive cylinder to a slow thermal aggression Laurent Fieschi, Gérard Baudin, Virginie Le Gallo Slow cook-off is, among other aggressions, one type of solicitation that is highly studied to ensuring ammunition safety. Indeed, under this type of aggression, a high explosive tends to produce a reaction much more violent than under a fast cook-off. |
Thursday, July 14, 2022 5:15PM - 5:30PM |
W02.00006: Radiation Stability of the Nitrate Ester Energetic Functional Group Patricia L Huestis, Nicholas Lease, Christopher E Freye, Virginia W Manner High explosives (HE) are used in a variety of applications that require them to be stable under a wide range of harsh environments, and understanding how HE is altered by ionizing radiation is of particular importance. This talk will focus on the radiolytic degradation of the nitrate ester (-ONO2) functional group (FG) which is the energetic FG responsible for the explosive properties of the commonly used pentaerythritol tetranitrate (PETN). Trace chemical analyses using proton nuclear magnetic resonance (1H-NMR) and ultra high pressure liquid chromatography (UHPLC) were completed on control and γ-irradiated materials containing nitrate esters to assess chemical changes brought about by the ionizing radiation. Results indicate that the nitrate ester FG is the predominantly affected part of the molecule, and the most probable degradation pathway involves the cleavage of the trigger linkage (O-NO2). These results were found to be insufficient to explain changes in small scale sensitivity tests seen by other researchers, and thus other radiolytic changes to the materials will be discussed. |
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