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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 OSTI2020

Using SF 6 and Xe to Monitor Gas Migration Through Explosion-Generated Fracture Networks

Here we describe a field study where tracer gas was injected into a subsurface cavity created by a small chemical explosion beneath the water table. The main objective of the study is to compare the migration of sulfur hexafluoride (SF 6 ) and xenon (Xe) through an explosion-generated fracture network and to study the influence of ground water on gas transport. A mixture of tracer gases (50% of SF 6 and 50% of Xe) was injected on 31 October 2018 and gas sampling continued until 8 November 2018. We observe similar trends in SF 6 and Xe concentrations at four ground surface sampling sites. The changes in the SF 6 /Xe ratios with time show that more SF 6 than Xe is observed during the barometric pressure lows when the absolute measured concentrations are highest. Conversely, the ratio SF 6 /Xe is less than 1 during the high-pressure intervals when absolute measured concentrations are low. The results of the experiment suggest that during barometric pressure lows the tracer is migrating to the surface primarily by advective gas phase transport, whereas during barometric pressure highs, advection is suppressed and near-surface evaporation of interstitial pore fluid with tracer dissolved in it becomes more important. Thus, the results of the experiment show that the gas concentrations at the surface are controlled by the combined effects of the gas dissolution into pore water and the barometric pressure fluctuations.

58 GEOSCIENCES↗
DOE OSTI2021

Utilizing Environmental Tracers to Reduce Groundwater Flow and Transport Model Parameter Uncertainties

Abstract Non‐uniqueness in groundwater model calibration is a primary source of uncertainty in groundwater flow and transport predictions. In this study, we investigate the ability of environmental tracer information to constrain groundwater model parameters. We utilize a pilot point calibration procedure conditioned to subsets of observed data including: liquid pressures, tritium ( 3 H), chlorofluorocarbon‐12 (CFC‐12), and sulfur hexafluoride (SF 6 ) concentrations; and groundwater apparent ages inferred from these environmental tracers, to quantify uncertainties in the heterogeneous permeability fields and infiltration rates of a steady‐state 2‐D synthetic aquifer and a transient 3‐D model of a field site located near Riverton, Wyoming (USA). To identify the relative data worth of each observation data type, the post‐calibration uncertainties of the optimal parameters for a given observation subset are compared to that from the full observation data set. Our results suggest that the calibration‐constrained permeability field uncertainties are largest when liquid pressures are used as the sole calibration data set. We find significant reduction in permeability uncertainty and increased predictive accuracy when the environmental tracer concentrations, rather than apparent groundwater ages, are used as calibration targets in the synthetic model. Calibration of the Riverton field site model using environmental tracer concentrations directly produces infiltration rate estimates with the lowest uncertainties, however; permeability field uncertainties remain similar between the environmental tracer concentration and apparent groundwater age calibration scenarios. This work provides insight on the data worth of environmental tracer information to calibrate groundwater models and highlights potential benefits of directly assimilating environmental tracer concentrations into model parameter estimation procedures.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Real-space imaging of the electron-pair density hole in molecular Auger–Meitner decay

Electrons in matter can rearrange extremely quickly under external perturbations, underpinning subsequent structural and chemical transformations. Coulomb interactions between neighbouring electrons often shape this response, giving rise to correlated motion and strongly affecting the distribution of electrons in the system. Here we show that non-resonant hard X-ray scattering can directly access changes in the radial electron-pair density during the rapid rearrangement of core and valence electrons. We do this by studying sulfur hexafluoride molecules undergoing Auger–Meitner decay. We exploit a second-order interaction between the X-ray photons and the molecules to trigger and probe the decay dynamics with a single pulse, capturing the electron loss and redistribution before the molecules dissociate. The experiment shows that changes in electron-pair densities can be isolated and measured on ultrafast timescales, providing insight into the real-space evolution of highly excited and short-lived electronic states.

Simmermacher, Mats [University of Oxford (United K↗
DOE OSTI2021

UO 2 F 2 particulate formation in an impinging jet gas reactor

Computational fluid dynamics (CFD), chemical kinetics, and aerosol dynamics were combined to model the formation of uranyl fluoride particles from the hydrolysis of uranium hexafluoride gas. This chemical process has been studied for many decades, however, detailed measurements of aerosol formation have only become available in the past few years which provide a basis for model comparison. Here, CFD simulations predicted complicated flow patterns in the impinging jet gas reactor. Aerosol formation simulations also predicted higher mass concentrations than were observed experimentally. This suggested that experimental data provided a partial representation which was subsequently enhanced by modeling and simulation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Prospects for detecting UF6 hydrolysis intermediates by mass spectrometry, resonance Raman, and NQR spectroscopy

Simulations are performed to consider several spectrometric and spectroscopic candidates for elucidating the mechanism of the hydrolysis of uranium hexafluoride (UF6). This study is among the first to benchmark the def-mTZVP basis sets for actinide-containing molecules, and it is shown to be a suitable basis set for surveying geometrical structures and vibrational spectra when used in conjunction with density functional theory. An experiment is proposed coupling mass spectrometric ion selection with vibrational spectroscopy, and supporting infrared and Raman spectral simulations demonstrate that ionization blue-shifts bands and can change their qualitative features. Ultraviolet resonance Raman is shown to have good prospects for discriminating U–O–U bridged intermediates, evidence for which was observed recently [L. E. McNamara et al., J. Phys. Chem. A 130, 775–786 (2026)]. As a more speculative approach, we also consider the prospect of addressing 233U or 235U nuclei by quadrupole resonance (NQR) spectroscopy for assigning early stage intermediate complexes. In doing so, we provide a first order-of-magnitude estimate for the collision-induced NQR signal for the UF6 dimer, which is of interest for the interpretation of a fast decoherence time observed in liquid-phase nuclear magnetic resonance. Having provided critical insights into the formation and stability of UF6 hydrolysis intermediates in previous studies, this computational spectroscopy survey is expected to help guide and expedite future laboratory campaigns.

Lutz, Jesse J. [Center for Computing Research, San↗
DOE OSTI2026

The Use of Machine Learning Models for Predicting the Dielectric Strength of Gases

Technological advancements in high voltage systems have pushed sulfur hexafluoride (SF6) to its operational limits. Furthermore, this gas has other drawbacks including a high liquefaction temperature and a high global warming potential. Therefore, there has been an urgent need to find alternative gases with high dielectric strength (DS). In this work, density functional theory (DFT) is used to calculate molecular descriptors that are fed into an artificial neural network (ANN) and a random forest (RF). These machine learning (ML) models are then used to predict the DS for hundreds of molecules. A finite element model (FEM) is also used to calculate the electric field profile of multiple simple electrode geometries as the applied voltage to the system is increased. Results indicate that the random forest model has better generalization to unseen data than the neural network. The highest DS value predicted by the RF was 2.16 relative to the experimental DS of SF6. The results also demonstrate how choosing a gas with a higher DS and a geometry with minimal edges and corners can significantly increase the operating voltage of an electrical system. Due to its superior generalization, the RF represents the most promising path toward an accurate DS predictor once sufficient experimental data are available.

Mileski, Matthew [AFIT]↗
DOE OSTI2022

Nucleation and growth of molybdenum disulfide grown by thermal atomic layer deposition on metal oxides

To enable greater control over thermal atomic layer deposition (ALD) of molybdenum disulfide (MoS 2 ), here we report studies of the reactions of molybdenum hexafluoride (MoF 6 ) and hydrogen sulfide (H 2 S) with metal oxide substrates from nucleation to few-layer films. In situ quartz crystal microbalance experiments performed at 150, 200, and 250 °C revealed temperature-dependent nucleation behavior of the MoF 6 precursor, which is attributed to variations in surface hydroxyl concentration with temperature. In situ Fourier transform infrared spectroscopy coupled with ex situ x-ray photoelectron spectroscopy (XPS) indicated the presence of molybdenum oxide and molybdenum oxyfluoride species during nucleation. Density functional theory calculations additionally support the formation of these species as well as predicted metal oxide to fluoride conversion. Residual gas analysis revealed reaction by-products, and the combined experimental and computational results provided insights into proposed nucleation surface reactions. With additional ALD cycles, Fourier transform infrared spectroscopy indicated steady film growth after ~13 cycles at 200 °C. XPS revealed that higher deposition temperatures resulted in a higher fraction of MoS 2 within the films. Deposition temperature was found to play an important role in film morphology with amorphous films obtained at 200 °C and below, while layered films with vertical platelets were observed at 250 °C. Finally, these results provide an improved understanding of MoS 2 nucleation, which can guide surface preparation for the deposition of few-layer films and advance MoS 2 toward integration into device manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2020

More chemical detection through less sampling: amplifying chemical signals in hyperspectral data cubes through compressive sensing

Compressive sensing (CS) is a method of sampling which permits some classes of signals to be reconstructed with high accuracy even when they were sampled at sub-Nyquist rates. In this paper we explore a phenomenon in which bandwise CS sampling of a hyperspectral data cube followed by reconstruction can actually result in amplification of chemical signals contained in the cube. Perhaps most surprisingly, chemical signal amplification generally seems to increase as the level of sampling decreases. In some examples, the chemical signal is significantly stronger in a data cube reconstructed from 10% CS sampling than it is in the raw, 100% sampled data cube. We explore this phenomenon in two real-world datasets including the Physical Sciences Inc. Fabry-Perot interferometer sensor multispectral dataset and the Johns Hopkins Applied Physics Lab FTIR-based longwave infrared sensor hyperspectral dataset. Each of these datasets contains the release of a chemical simulant, such as glacial acetic acid, triethyl phospate, and sulfur hexafluoride, and in all cases we use the adaptive coherence estimator (ACE) to detect a target signal in the hyperspectral data cube. We end the paper by suggesting some theoretical justifications for why chemical signals would be amplified in CS sampled and reconstructed hyperspectral data cubes and discuss some practical implications.

Hyperspectral imagery, Compressive Sensing, single↗
DOE OSTI2024

Monitoring the Reaction Dynamics of UF6 by Cryogenic Layering and FTIR Spectroscopy

Uranium hexafluoride (UF6) is a commonly used material feedstock for uranium enrichment processes. When introduced to water in the atmosphere, it reacts rapidly to form uranyl fluoride (UO2F2). Here, we investigate the UF6 hydrolysis reaction by cryogenically trapping reaction intermediates and characterizing the trapped species by FTIR. The reactant species are sequentially layered onto a diamond substrate held at 10K by a closed cycle liquid helium cryostat. At this temperature, the hydrolysis reaction is not spontaneous and can be catalyzed by the introduction of heat. Upon heating, the reaction moves through several intermediate compounds before proceeding to the final UO2F2 product. Several previously unobserved bands appear while the reaction progresses which may help to elucidate the mechanism behind UF6 hydrolysis.

McNamara, III, Louis E.↗
DOE OSTI2020

Materials Data on OsF6 by Materials Project

OsF6 is beta Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four osmium hexafluoride molecules. Os6+ is bonded in an octahedral geometry to six F1- atoms. All Os–F bond lengths are 1.87 Å. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one Os6+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one Os6+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one Os6+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one Os6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UF6 by Materials Project

UF6 is beta Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four uranium hexafluoride molecules. U6+ is bonded in an octahedral geometry to six F1- atoms. There are five shorter (2.02 Å) and one longer (2.03 Å) U–F bond lengths. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one U6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on WF6 by Materials Project

WF6 is beta Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four tungsten hexafluoride molecules. W6+ is bonded in an octahedral geometry to six F1- atoms. All W–F bond lengths are 1.88 Å. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one W6+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one W6+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one W6+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one W6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoF6 by Materials Project

MoF6 is beta Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four molybdenum hexafluoride molecules. Mo6+ is bonded in an octahedral geometry to six F1- atoms. All Mo–F bond lengths are 1.87 Å. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one Mo6+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one Mo6+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one Mo6+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one Mo6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoF6 by Materials Project

MoF6 is Tungsten structured and crystallizes in the cubic Im-3m space group. The structure is zero-dimensional and consists of two molybdenum hexafluoride molecules. Mo6+ is bonded in an octahedral geometry to six equivalent F1- atoms. All Mo–F bond lengths are 1.87 Å. F1- is bonded in a single-bond geometry to one Mo6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SF6 by Materials Project

SF6 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of three sulfur hexafluoride molecules. S6+ is bonded in an octahedral geometry to six F1- atoms. All S–F bond lengths are 1.59 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one S6+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one S6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UF6 by Materials Project

UF6 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four uranium hexafluoride molecules. U6+ is bonded in an octahedral geometry to six F1- atoms. There are five shorter (2.02 Å) and one longer (2.03 Å) U–F bond lengths. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one U6+ atom. In the sixth F1- site, F1- is bonded in a single-bond geometry to one U6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on OsClF8 by Materials Project

OsF6ClF2 is beta-prime cadmium gold structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of two osmium hexafluoride molecules and two ClF2 clusters. In each ClF2 cluster, Cl is bonded in a distorted rectangular see-saw-like geometry to two equivalent F atoms. Both Cl–F bond lengths are 1.62 Å. F is bonded in a single-bond geometry to one Cl atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SF6 by Materials Project

SF6 is Tungsten structured and crystallizes in the cubic Im-3m space group. The structure is zero-dimensional and consists of two sulfur hexafluoride molecules. S6+ is bonded in an octahedral geometry to six equivalent F1- atoms. All S–F bond lengths are 1.60 Å. F1- is bonded in a single-bond geometry to one S6+ atom.

36 MATERIALS SCIENCE↗