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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Material Model Parameters Optimization in Liquid Mercury Target Dynamics Simulation With Machine Learning Surrogates

A pulsed spallation target is subjected to very short (∼0.7μs) but intense loads (23.3 kJ) from repeated proton pulses, which knock away neutrons from the mercury atoms’ nuclei for a wide range application in physics, engineering, medicine, petroleum exploration, biology, chemistry, etc. The effect of this pulsed loading on the stainless-steel target module which contains the flowing mercury target material is difficult to predict not only due to its short but intense explosive-like physical reaction, but also the nonlinear material behavior of the liquid mercury in the structure. Injecting small helium bubbles in the mercury has been an efficient method of mitigating the pressure wave at high power level stage. However, prediction of the resultant loading on the target is more difficult when helium gas is intentionally injected into the mercury. A 2-phase material model that incorporates the Rayleigh-Plesset (R-P) model is expected to address this complex multi-physics dynamics problem by including the bubble dynamics in the liquid mercury. A parameter sensitivity study was firstly employed to understand their impact on the simulation strains. The investigated parameters included E, μ, γ, σ, n, VFgas, and gas cumulative volume curve control parameters a and b. Verification and validation results from sparse polynomial expansions (SPE) method and directional Gaussian smoothing (DGS) optimization show that the surrogate model had training error of ∼7% and validation error of ∼15%, indicating that machine learning methods and surrogate models can help optimize the uncertain parameters in the complex 2-phase material model. This approach is expected to fill the knowledge gap between unknown liquid-gas mixture material model and measured vessel strain responses.

Lin, Lianshan↗
NASA NTRS1982

The Blue Angel. I - The mineralogy and petrogenesis of a hibonite inclusion from the Murchison meteorite

Results are presented of a mineralogical and petrological examination of a relatively large hibonite-containing inclusion in the Murchison chondrite called the Blue Angel. Mechanisms of formation and modification of hibonite-rich inclusions are investigated. Evidence is found that modifying processes occurred before the inclusion was incorporated into its present location, which indicates a sequence of aqueous and metamorphic alteration followed by disruption and relithification of the protometeoritic material. The mineral chemistry and petrography of the Blue Angel is consistent with a three stage formation history, and extensive alteration of Ca-Al-rich inclusions may have occurred by aqueous alteration and thermal metamorphism followed by explosive mixing processes on a parent body.

Armstrong, J. T.↗
DOE OSTI2023

Comparative analysis of sublimation and thermal decomposition of TATB

This experimental study investigated the effects of confinement, starting mass, and heating rate on TATB thermal decomposition and sublimation using a combined Thermo-Gravimetric Analyzer and Differential Scanning Calorimetry (TGA/DSC) instrument. The confinement of volatile products was varied using different pinhole sizes with TGA/DSC pans. The measurements showed the open pan experiments without lids/pinholes resulted in complete sublimation of TATB between 320 °C and 360 °C. The heat of sublimation was determined to be 176 kJ/mol (42 kcal /mol), consistent with literature data obtained from other experimental techniques. The use of pinholes suppressed the sublimation of TATB such that the decrease in pinhole size resulted in 1) an increase in the enthalpy of reaction and an increase in the amount of carbonaceous material remaining at the end of decomposition, and 2) convergence of the two peak temperatures corresponding to maximum heat flow and maximum weight loss. Also, a transition from a two-exotherm thermal decomposition behavior towards a single-exotherm occurred as the pinhole size was decreased for a given starting mass or as the starting mass was increased for a given pinhole size. These results indicate the kinetics of TATB sublimation, TATB thermal decomposition, and gas diffusion out of a TGA/DSC pan can all compete and result in significantly different enthalpies, amounts of remaining materials, and peak temperatures depending on the pinhole size and starting mass used in the measurements. Furthermore, the results also indicate precise control of process variables (pinhole size, starting mass, and heating rate) in TGA/DSC measurements is required for thermal safety assessment of explosives.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Intergranular Hotspots: A Molecular Dynamics Study on the Influence of Compressive and Shear Work

Numerous crystal- and microstructural-level mechanisms are at play in the formation of hotspots, which are known to govern high explosives initiation behavior. Most of these mechanisms, including pore collapse, interfacial friction, and shear banding, involve both compressive and shear work done within the material and have thus far remained difficult to separate. Here, we assess hotspots formed at shocked crystal–crystal interfaces using quasi-1D molecular dynamics simulations that isolate effects due to compression and shear. Two high explosive materials are considered (TATB and PETN) that exhibit distinctly different levels of molecular conformational flexibility and crystal packing anisotropy. Temperature and intramolecular strain energy localization in the hotspot are assessed through parametric variation of the crystal orientation and two velocity components that respectively modulate compression and shear work. The resulting hotspots are found to be highly localized to a region within 5–20 nm of the crystal–crystal interface. Compressive work plays a considerably larger role in localizing temperature and intramolecular strain energy for both materials and all crystal orientations considered. Shear induces a moderate increase in energy localization relative to unsheared cases only for relatively weak compressive shock pressures of approximately 10 GPa. These results help isolate and rank the relative importance of hotspot generation mechanisms and are anticipated to guide the treatment of crystal–crystal interfaces in coarse-grained models of polycrystalline high-explosive materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Flammability and dispersion of tritium in confined release scenarios

Ignition of a flammable tritium-air mixture is the most probable means to produce the water form (T 2 O or HTO), which is more easily absorbed by living tissue and is hence ~10,000 times more hazardous to human health when uptake occurs compared to the gaseous form (T 2 or HT; per Mishima and Steele, 2002). Tritium-air mixtures with T 2 concentrations below 4 mol% are considered sub-flammable and will not readily convert to the more hazardous water form. It is therefore desirable from a safety perspective to understand the dispersion behavior of tritium under different release conditions, especially since tritium is often stored in quantities and pressures much lower than is typical for normal hydrogen. The formation of a flammable layer at the ceiling is a scenario of particular concern because the rate of dispersion to nonflammable conditions is slowest in this configuration, which maximizes the time window over which the flammable tritium may encounter an ignition source. This report describes the processes of buoyant rise and dispersion of tritium. Accumulation of flammable concentrations of tritium next to the ceiling is a common safety concern for hydrogen, but this situation can only occur if dispersion rates are slow with respect to rates of release and rise. Theory and simulations demonstrate that buoyancy does not cause regions with flammable concentrations to form within buildings from sources that have previously been mixed to sub-flammable concentrations. A simulated series of tritium release events with their associated dispersion behavior are reported herein; these simulations apply computational fluid dynamics to rooms with three different ceiling heights and a variety of tritium release rates. Safety related quantities from these simulations are reported, including the mass and volume of tritium occurring in a flammable mixture, the presence or absence of a flammable layer at the ceiling, and the time required for dispersion to nonflammable conditions after the end of the tritium release event. These safety metrics are influenced by the magnitude and rate of the tritium release with respect to the air volume in the room and also the momentum of the plume or jet with respect to the ceiling height. Several screening criteria are recommended to assess whether a specific tritium release scenario is likely to form a flammable layer at the ceiling. The methods and results in this modeling study have applicability to explosion safety analysis for other buoyant flammable gases, including the lighter isotopes of hydrogen.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Energetic Materials

Energetic materials comprise explosives, pyrotechnics, and propellants. The science of energetic materials is dedicated to developing a means to predict performance and safety characteristics with high fidelity. This is a particular challenge and is predicated on materials science and engineering, physics, chemistry, and dynamic response in extreme conditions. Fundamental elements of these complicated composite materials remain grand challenges—from the design of high-energy metastable molecules, to the engineering of composite formulations, to the processing parameters that link to safety and performance characteristics in as-yet undetermined ways. Key elements include crystalline mechanics, grain dynamics, multiphase interfaces, thermal and mechanical damage, and failure—all linked to multistep and high-rate chemistry and shock physics. A future revolution in our understanding and predictive capability for energetic materials behavior and responses is dependent upon sustained focus and advances in materials research and development.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spatially-Resolved Characterization Techniques and Their Implications for Nuclear Debris Formation.

Debris from nuclear tests has a complex formation process and can inform multiple fields of study such as geology, atmospheric science, shock physics, and chemistry under extreme conditions. Macroscopic nuclear debris forms as the result of fireball interaction with surrounding materials (e.g., structural and environmental component), which rapidly undergo melting and vaporization followed by condensation, convective/diffusive mixing, and solidification over the course of seconds. In atmospheric events, some of this material may disperse over long distances, but much of the material is deposited close-in to ground zero, often in multicomponent, partially (or entirely) amorphous debris formations. During the U.S. nuclear testing program, this material was collected and analyzed, particularly for radionuclide composition. Fallout formation models were developed from nuclear test data based on such radionuclide compositional analyses. These models were not just used to understand fallout dispersion (i.e. the spread of radioactivity over geographical regions) but also guide radiochemical interpretations of historical nuclear tests.6 Developments in analytical techniques over the past several decades have made it possible to make new analyses on historical debris, some of which may be more than a half-century old. For example, inductively-coupled plasma mass spectrometry (ICP-MS) has been used to look at the trace elements in glassy fallout material from aboveground nuclear tests (including the Trinity test). Advanced analyses using X-ray absorption allowed for the measurement of oxidation state of fallout constituents, including actinides. The ability to measure trace actinides and their subsequent oxidation state is important to understanding how the surrounding environment may have influenced the resultant fallout composition and may have implications for why certain fractionation trends have been observed. Here we present data from historic nuclear test debris illustrating the power of spatially resolved methods to connect interaction of the near-field environment with the explosion and provide new insights into nuclear debris formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Modeling particulate generation during high energy explosive events

Laser produced plasmas are used to simulate high energy events and are useful for a variety of applications e.g. in industrial sectors, such as semi-conductor manufacturing, as well as medical, environmental, and energy sectors. Particulate generation in laser produced plasmas is related to key features of the plasma: temperature and pressure evolution during plume expansion, plasma chemistry etc. Several uncertainties persist in relating initial high energy events (~microseconds) to particulate formation that happens as the plasma cools and evolves (~milliseconds).

42 ENGINEERING↗
NASA NTRS1990

Submillimeter and millimeter observations of solar system objects

Microwave spectroscopy of solar system objects was supported. It necessarily involves millimeter and submillimeter wavelengths where rotational transitions reside. The existing national facilities are at OVRO, the 12-meter at Kitt Peak, UC array at Hat Creek, the Caltech CSO on Mauna Kea, and the 14-meter at the Univ. of Massachusetts, near Amherst. The group used all of these instruments in the last year except the Univ. of Massachusetts 14-meter. This wavelength range (0.3 to 3 mm) is about to enjoy an explosion of interest as submillimeter receivers become better and easier to use. This region of the spectrum is rich in transitions of molecules that exist in the planetary atmospheres which can be studied for temperature-pressure profiles, wind tracers, and atmospheric chemistry. The list of solar system objects that have been recently addressed with these techniques include: (1) Venus: CO studies of T-P profiles, winds, and photochemistry; SO2 detections; Continuum mapping remains to be done at 1 mm; (2) Earth H2O, CO, NO, NO2, O(18)O, etc. as a test bed for other atmospheres; (3) Mars: H2O, CO, O(18)O studies of T-P profiles, winds (fall of 1990), and photochemistry; (4) Saturn: Same as Jupiter plus submillimeter and millimeter mapping of the ring system; (5) Uranus and Neptune: Continuum thermal mapping; and (6) Titan: CO, HCN, and HC3NT-P information and photochemistry. Recent results are given.

Muhleman, Duane O.↗
DOE OSTI2025

Simultaneous imaging of vibrational, rotational, and electronic wave-packet dynamics in a triatomic molecule

Light-induced molecular dynamics often involve the excitation of several electronic, vibrational, and rotational states. Since the ensuing electronic and nuclear motion determines the pathways and outcomes of photoinduced reactions, our ability to monitor and understand these dynamics is crucial for molecular physics, physical chemistry, and photobiology. However, characterizing this complex motion represents a significant challenge when different degrees of freedom are strongly coupled. In this Letter, we demonstrate how the interplay between vibrational, rotational, and electronic degrees of freedom governs the evolution of molecular wave packets in the low-lying states of strong-field-ionized sulfur dioxide. Using time-resolved Coulomb explosion imaging (CEI) and quantum mechanical wave packet simulations, we directly map the bending vibrations of the molecule, show how the vibrational wave packet is influenced by molecular alignment, and elucidate the consequences of nuclear motion for the coupling between the two lowest electronic states of the cation. Furthermore, our results demonstrate that multicoincident CEI can be an efficient experimental tool for characterizing coupled electronic and nuclear motion in polyatomic molecules.

Atomic & molecular processes in external fields↗
NASA NTRS1979

Sulfur and halogen chemistry of the stratosphere and of volcanic eruption plumes

The major eruption of Volcan de Fuego caused an enhancement of 1.6 x 10 to the 9 kg of SO4(-) in the stratosphere 6 months after the eruption. Measurable changes in nitric acid vapor and particulate chloride were not observed. Subsequent data suggests that HCl was not injected into the stratosphere. The first simultaneous measurement of halogen and sulfur content of gases and particles in explosive eruption plumes is reported. The average percents of elements in particles were sulfur, 2.5 + or - 2.1; chlorine, 18 + or - 12; and fluorine, 38 + or - 29. The average molecular ratio of HCl/SO2 and HCl/HF were 0.41 + or - 0.26 and 14 + or - 12 in the Guatemalan eruption plumes.

Lazrus, A. L.↗
DOE OSTI2025

Investigation into the Synthesis of Several TATB-Inspired Energetic Materials

The synthesis and characterization of several TATB-inspired energetic materials was explored. Despite their structural similarity to TATB, their behavior toward traditional synthetic pathways deviates significantly from that of the parent material. This change in expected reactivity is discussed and an efficient alternative synthesis is reported. The development of a simple and effective route to these TATB-type compounds opens the door to a potential new class of insensitive high explosives.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Radiochemistry and Trinity

Forty seconds after Trinity detonated, Noble Laureate Enrico Fermi calculated the bomb’s energy release. By measuring the lateral dispersion of small pieces of paper dropped before, during, and after the blast wave passed him, he calculated an explosive yield of ten kilotons. Although Fermi’s estimate was only half of the official yield, it provided immediate confirmation that nuclear fission could be fashioned into a weapon of war.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS2004

Microphysics of Pyrocumulonimbus Clouds

The intense heat from forest fires can generate explosive deep convective cloud systems that inject pollutants to high altitudes. Both satellite and high-altitude aircraft measurements have documented cases in which these pyrocumulonimbus clouds inject large amounts of smoke well into the stratosphere (Fromm and Servranckx 2003; Jost et al. 2004). This smoke can remain in the stratosphere, be transported large distances, and affect lower stratospheric chemistry. In addition recent in situ measurements in pyrocumulus updrafts have shown that the high concentrations of smoke particles have significant impacts on cloud microphysical properties. Very high droplet number densities result in delayed precipitation and may enhance lightning (Andrew et al. 2004). Presumably, the smoke particles will also lead to changes in the properties of anvil cirrus produces by the deep convection, with resulting influences on cloud radiative forcing. In situ sampling near the tops of mature pyrocumulonimbus is difficult due to the high altitude and violence of the storms. In this study, we use large eddy simulations (LES) with size-resolved microphysics to elucidate physical processes in pyrocumulonimbus clouds.

Jensen, Eric↗