Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F03: Materials in Extremes: Reactive Chemistry at Extreme ConditionsFocus
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Sponsoring Units: GSCCM Chair: Nithin Mathew, Los Alamos National Laboratory Room: 107 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F03.00001: Elucidating Long Timescale Chemical Events in Reactive Materials Invited Speaker: Nir Goldman Knowledge of the equation of state and chemical kinetics of materials under reactive conditions is needed for a wide number of research areas, including studies of planetary interiors, astrobiology, and high-pressure detonations of energetic materials. In this regard, we have developed a family of atomistic simulation models which yield similar accuracy to higher order quantum approaches (Kohn-Sham DFT) while yielding orders of magnitude increase in computational efficiency. This talk will focus on three different types of models in development in our research group: (1) semi-empirical quantum simulation approaches, (2) reactive force fields for molecular dynamics simulations, and (3) spin lattice models for solid phase reactivity. These efforts will be discussed in the context of corrosion on actinide and other metal surfaces, shock compression of organics and energetic materials, and prebiotic synthesis in impacting astrophysical ices. Our methods provide a straightforward way to conduct computationally efficient and highly accurate simulations over a broad range of conditions, where physical and chemical properties can be difficult to interrogate directly and there is historically a significant reliance on theoretical approaches for interpretation and validation of experimental results. Prepared by LLNL under Contract DE-AC52-07NA27344 |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F03.00002: A multiscale approach: Developing a Molecular Dynamics-informed RDX chemistry model for characterizing hot spot criticality in continuum-level simulations Michael Sakano, Ahmed Hamed, Edward Kober, Brenden Hamilton, Mahbub Islam, Marisol Koslowski, Alejandro H Strachan Reactive molecular dynamics (MD) simulations can describe the complex physical and chemical processes in high energy density materials and ultimately contribute to a predictive understanding of their shock initiation under dynamical loading. However, computational intensity limits MD to the nanoscale, making it difficult to simulate hot spot formation and eventual shock to detonation transition. Thus, we developed a multiscale model that uses MD simulations to inform a continuum model capable of reaching the microstructural scales. We use dimensionality reduction via unsupervised learning to establish a two-step reduced-order chemistry model for the decomposition of RDX. From both homogeneous isothermal and adiabatic simulations, we extract chemical kinetics and heat of reaction parameters. The continuum model, capable of capturing chemistry, thermal transport and mechanics, is verified using homogeneous cook-off simulations and the multiscale approach validated from hot spot calculations. We find good agreement between the predicted critical temperatures from explicit MD simulations and the continuum model for nanoscale hot spots. Finally, we predict critical hot spot temperature as a function of size and quantify the effect of uncertainties for various materials’ parameters. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F03.00003: Ultrafast Detonation of Hydrazoic Acid: Insights from Many-body Molecular Dynamics Force Fields Huy Pham, Nir Goldman, Laurence Fried In this work, we present the development and application of the Chebyshev Interaction Model for Efficient Simulations (ChIMES) to the study of hydrazoic acid (HN3) under detonation. Computational study of HN3 is challenging due to its ultrafast detonation, i.e. the chemical decomposition to stable products is complete in less than 10 ps, and the system evolves through multiple thermodynamics (ambient and extreme conditions) and electronic (metal and insulator) states. We show that ChIMES, a generalized many-body reactive force field machine-learned to density functional theory (DFT) molecular dynamics trajectories, is able to retain the accuracy of DFT simulation in describing structural properties and chemistry for a wide range of thermodynamics states while increasing orders of magnitude in computational efficiency. Shock compression simulations show that the developed ChIMES model can capture the ultrafast chemical reactions of HN3. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F03.00004: Reaction rates in shocked nitromethane from density functional tight binding simulations Romain Perriot, Marc Cawkwell, Enrique Martinez Saez, Edward Kober, Shawn David McGrane The chemistry of energetic materials (EM) is characterized by rapid exothermic reactions that lead to dramatic increase of the pressure and temperature on the pico- to nanosecond timescales. Under these conditions, experiments have struggled to provide detailed insights into early and intermediate processes, and simulations have thus become a valuable tool to help interpret experiments and parameterize mesoscale models. We have performed molecular dynamics (MD) cook-off simulations of nitromethane under pressure with DFTB, a parameterized form of DFT that allows to simulate systems with hundreds of atoms, over hundreds of picoseconds, with explicit treatment of the electronic interactions and an accuracy close to that of DFT. We find drastically different times-to-explosion, even for the same initial T/P conditions, due to multiple complex and competitive chemical pathways. However, a simple effective reaction rate can be extracted, as long as multiple simulations are performed at each T/P to account for the stochastic component of detonation chemistry in EM. We built a two-step model for NM detonation that can be compared to experimental results and used in higher scale models. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F03.00005: UQ-Driven Reactive Burn and EOS Parameterization, along with Particle Force Model Assessment for the Simulation of an Explosive Multiphase Experiment Joshua Garno, Sangjune Bae, Frederick Ouellet, Thomas L Jackson, Nam-Ho Kim, Raphael Haftka, S Balachandar Recent results indicate that the Maxey-Riley-Gatignol (MRG) model is able to predict the force on a particle due to a passing air-shock and compressed flow. This work aims to assess the model’s predictive capability in the high-energy, post-detonation flow regime. Due to the tight coupling between the gas flow and particle motion, the evaluation of the particle force model necessitates high accuracy in the prediction of the gas flow. Therefore, modeling the detonation and rapid expansion of post-detonation product gases requires accurate models of reactive burn and the equation of state (EOS) for products of detonation. Using flow information extracted from experimental high-speed photographs as validation data, we make use of UQ methodologies to optimize the explosive-specific model parameters of the JWL EOS. With quantitative flow agreement between experiments and our finite-volume point-particle simulations, the MRG force model governing the motion of the particles is examined. Experimental X-ray data provides the trajectories of a few Tungsten particles for comparison with simulation results. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F03.00006: Probing Intermediate Formation of Thin Film Explosives Through Ultrafast Broadband Infrared Spectroscopy Michael Powell, Pamela Bowlan, Steven F. Son, Cynthia Bolme, Kathryn E Brown, David Steven Moore, Marc Cawkwell, Alejandro H Strachan, Shawn David McGrane A first step to predicting explosive performance and safety is to understand the chemical pathways taken when high explosive materials are shocked. Unfortunately, there is insufficient data at relevant time and length scales to directly compare experiments to molecular level models. The intention of this work is to link experimental results to molecular dynamics models using ultrafast broadband mid-infrared and visible absorption spectroscopy to probe the chemical changes energetic materials undergo when shocked. PETN, a common HE, was shocked to the reactive regime and showed increased absorption near the anti-symmetric NO2 stretch but not the symmetric NO2 stretch. This change was attributed to absorbance from intermediate formation. These results were compared to molecular dynamics and accelerated chemistry models to interpret the shock chemistry. Comparing to gas phase calculations of the infrared absorption intensities, the intermediate was most likely HONO indicating H-ion and NO2 elimination play an important role in early shock chemistry for PETN. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F03.00007: Amorphous Explosives Rajen Patel, Victor Stepanov Glassy amorphous organic energetics is a new field offering several novel areas for study. While practical application might be limited due to low density and propensity to crystallization of amorphous energetics, the scientific opportunities are fertile. For example, they allow an in depth view of crystallization in real time, even of novel systems such as cocrystals, and the in situ characterization of pores, cracks and other gross defects as they form. Amorphous energetic formulations with relatively low excipient (i.e. polymer used to inhibit crystallization) loadings offer a novel method of examining materials at extreme conditions. They can compared to their crystalline counterparts, and this could shed light on the processes of crystallization, shock induced phase transformations, and mechanically induced chemical reactions. While practical application will be limited for amorphous materials due to their low density, the scientific possibilities are quite exciting. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F03.00008: Mechanical Stimulation of Gasless Reaction in Inorganic Systems: Overview Alexander Mukasyan The phenomenon of a reaction, occurring in inorganic high energy density systems after it is stimulated by a shock wave, has been under investigation for a long time. The first experimental studies on the topic of chemical transformations in the inorganic substance under shock compression dated back to the late 1950s and a lot of work has been accomplished since. In this overview, we primarily consider reactive heterogeneous media that involves a powder mixture of the inorganic solid precursors, which, after mechanical stimulation, resulted in the synthesis of a new material. It is no doubt that such reactions can be initiated by sufficient mechanical impulse, but can they occur in the time scale of the high-pressure shock state? What mechanisms may be responsible for such rapid solid-state transformations? These and related questions are discussed based on the recent experimental findings. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F03.00009: Dance of HMX molecule in conformational space by quasi-static heating: a combined Raman spectroscopy and theoretical study Yangyang Zeng, Chan Gao, guoyang yu, Rucheng Dai, Zhongping Wang, Zengming Zhang, Xianxu Zheng, YanQiang Yang The complexity of HMX polymorphs arises from conformers and molecular packing. In this study, HMX single crystal is heated at rates of 0.1 or 0.2 K/min during phase transitions. The sample is equilibrated at least 15 minutes at every step of increasing temperature to achieve the quasi-static condition. Raman spectroscopy is performed to monitor transitions between conformers by fitting position and full width at half maximum of the observed spectra. Conformers, transition states and IRC are verified at the level of DLPNO-CCSD(T)/cc-pVQZ//M062X-D3(0)/def2-TZVP for single HMX molecule. We attribute the response of spectra to ring puckering and nitro vibrations during phase transitions by analyzing Raman spectra and decomposition and identification of vibrational modes. Our results provide evidence of β-α and subsequent α-δ phase transition, which agree with recent thermodynamic model that α-HMX must be thermodynamically stable in phase diagram. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F03.00010: DETONATION PROPERTIES OF PRESSED AND LIQUID HYDRAZINE NITRATE Alexander Utkin, Valentina Mochalova In this work, the structure of the steady-state detonation waves, the critical diameter, detonation parameters and the dependence of detonation velocity on the charge diameter for pressed hydrazine nitrate (HN) and the HN/water solution were investigated by a VISAR laser interferometer. For pressed HN, it was found that the critical diameter drops with the initial density decrease. For pressed HN, the change of the detonation velocity with variation of the initial density is not monotonic, but has a characteristic s-shape. For the water solution of HN, the detonation velocity decreases linearly with increasing concentration of water. The limits of detonation propagation were found for HN/water solution. It doesn’t detonate at a water concentration exceeding 33 wt % at room temperature. |
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