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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Tuning of altermagnetism by strain

For all collinear altermagnets, we sort out piezomagnetic free-energy invariants allowed in the nonrelativistic limit and relativistic piezomagnetic invariants bilinear in the Néel vector $\mathbf{L}$ and magnetization $\mathbf{M}$, which include strain-induced Dzyaloshinskii-Moriya interaction. The symmetry-allowed responses are fully determined by the nonrelativistic spin Laue group. In the nonrelativistic limit, two distinct mechanisms are discussed: the band-filling mechanism, which exists in metals and is illustrated using the simple two-dimensional Lieb lattice model, and the temperature-dependent exchange-driven mechanism, which is illustrated using first-principles calculations for transition-metal fluorides. The leading second-order nonrelativistic term in the strain-induced magnetization is also obtained for CrSb. Piezomagnetism due to the strain-induced Dzyaloshinskii-Moriya interaction is calculated from first principles for transition-metal fluorides, MnTe, and CrSb. Finally, we discuss triplet superconducting correlations supported by altermagnets and protected by inversion rather than time-reversal symmetry. We apply the nonrelativistic classification of Cooper pairs to describe the interplay between strain and superconductivity in the two-dimensional Lieb lattice and in bulk rutile structures. Here, we show that triplet superconductivity is, on average, unitary in an unstrained altermagnet, but becomes non-unitary under piezomagnetically active strain.

FOS: Physical sciences↗
DOE OSTI2025

Solid structure of Li 2 BeF 4 (FLiBe) from room temperature to melting studied by neutron and X-ray diffraction

Molten fluoride salts such as Li 2 BeF 4 (FLiBe) are used in molten salt reactors, fluoride-salt-cooled high-temperature reactors and fusion reactors as a fuel solvent, coolant and/or tritium breeding medium. In engineered systems that use molten salt, solid-state material will be present during melting and freezing scenarios, and therefore the temperature-dependent properties of the solid and solid/liquid phase transition merit investigation. To observe the behavior of the solid state of Li 2 BeF 4 from room temperature to melting, this work used neutron and X-ray diffraction to measure the changes in the lattice parameters and volume of the crystalline unit cell and compared the results with prior low-temperature data for solid Li 2 BeF 4 . From neutron diffraction data it is also possible to identify anisotropy: centimetre-scaled crystals align preferentially with the a axes parallel to the direction of freezing front propagation, and the c axes expand 54% more than the a axes. This work provides the lattice constants as a function of temperature, quantifies the thermal expansion, and determines the equation describing the change in density for solid Li 2 BeF 4 from room temperature to 459°C to be ρ solid (kg m −3 ) = 2182 (3) − 0.115 (2) T (°C) and the volume expansion upon melting to be less than 5%. This density changes depending on molecular weight and enrichment.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Characterization of Real-World and Accelerated Exposed PV Module Backsheet Degradation

Backsheet degradation is key to maintaining the lifetime of photovoltaic (PV) modules. Cracking, delamination, bubbling, and discoloration are main types of degradation. PV modules were collected from PV installations in multiple climatic zones. Multiple types of backsheets were obtained with poly(ethylene teraphlate) (PET) and polyamide air side layers being the largest number of backsheets retrieved. Multiple commercial PV backsheets were exposed to multiple accelerated exposures and key degradation mechanisms were identified. Polyamide backsheets showed cracking in retrieved modules and under accelerated exposures. Poly(vinylidene fluoride) (PVDF) and poly(vinyl fluoride) (PVF) showed the highest stability in retrieved and accelerated exposures. While polyamide had the largest amount of large scale degradation.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2021

Distributed electric field sensing using fibre optics in borehole environments

In the past decade, rapid advances in distributed optical fibre sensing technologies have made it possible to record various geophysical data (e.g. strain, temperature and pressure) continuously in both time and space along the fibre, providing an unprecedented quantity and spatial density of data compared to traditional geophysical measurements as well as reducing data acquisition cost. To date, no distributed fibre-based electromagnetic field sensing system has been implemented although electromagnetic sensing could have a broad range of applications to geophysical imaging and monitoring in borehole environments. The goal of this paper is to provide a theoretical feasibility study regarding the design and use of an electromagnetic sensing optical fibre for geophysical applications. First, we present the sensitivity analysis of a ‘hypothetical’ optical fibre coated with polyvinylidene fluoride, a polymer that provides relatively high piezoelectric properties, yet unlike ceramics, is flexible. Next, using a two-dimensional electromagnetic modelling algorithm, we simulate the earth electric-field-to-fibre-strain transfer function and estimate the theoretical sensitivity of the optical fibre to electric fields. Given the state-of-the-art distributed acoustic sensing strain sensitivities in the picometres strain range, our numerical modelling analysis suggests that a perfectly coupled polyvinylidene fluoride–coated optical fibre can measure electric field values in the mV/m to V/m amplitude range. We then apply a cylindrically symmetric modelling algorithm to simulate numerical models demonstrating the applicability of such a fibre in an oilfield environment. Scenarios investigated employ an electric field source and suggest that the measurements can be used to distinguish the oil versus water ratio with a fibre mounted inside a producing steel cased oil well as well as distinguishing between brine and hydrocarbon filled reservoir zones with a fibre located outside of the casing.

58 GEOSCIENCES↗
DOE OSTI2020

Measurement of the Natural Convection Heat Transfer in a Magnesium Oxide Electrolytic Cell Concept

The rate of heat transfer by natural convection between the wall and electrolyte of an electrolytic cell that produces magnesium (Mg) from magnesium oxide (MgO) at temperatures near 1000 °C in a molten fluoride salt electrolyte is presented. An experimental model of the cell was developed that enabled measurements of the heat transfer in the absence of electrolysis and at temperatures less than 100 °C over ranges of Rayleigh numbers from 1 × 10 -7 to 7 × 10 -8 and Prandtl numbers from 2 to 6200, ranges that include those anticipated in the operation of the MgO electrolytic cell. The model avoids the substantial experimental challenges associated with the high-temperature, corrosive molten salt to enable a conservative estimate of the heat transfer at a lower cost and greater accuracy than would otherwise be possible. The results are correlated by the expression Nu = 0.412Ra 0.23 Pr 0.15 with Nusselt numbers spanning 30–80. The application of the correlation shows that the heat transfer between the cell wall and the molten fluoride electrolyte at ≈1000 °C is characterized by convection coefficients between 100 and 600 W/m 2 -K and is fast enough to enable heat fluxes up to 10 W/cm 2 without compromising the structural integrity of the steel cell wall.

Engineering↗
DOE OSTI2023

Large Eddy Simulation of Convective Heat Transfer in a Random Pebble Bed Using the Spectral Element Method

The development of fluoride-cooled high-temperature reactors has drastically increased the demand for an in-depth understanding of the heat transfer (HT) in packed beds cooled by liquid salts. The complex flow fields and space-dependent porosity found in a pebble bed require a detailed understanding to ensure the proper cooling of the reactor core during normal and accident conditions. As detailed experimental data are complicated to obtain for these configurations, high-fidelity simulation such as large eddy simulation and direct numerical simulation (DNS) can be employed to create a high-resolution heat transfer numerical database that can assist in addressing industrial-driven issues associated with the heat transfer behavior of fluoride-cooled high-temperature reactors. In this paper, we performed a series of large eddy simulation using computational fluid dynamics (CFD) code NekRS to investigate the heat transfer for a bed of 1741 pebbles. Further, the characteristics of the flow, such as average, rms, and time series of velocity and temperature, have been analyzed. Porous media averages have also been performed. The simulation results show a good agreement between non-conjugate heat transfer and conjugate heat transfer. The generated data will be used to benchmark heat transfer modeling methods and local maxima/minima of heat transfer parameters. It will also be used for supporting convective heat transfer quantification for Kairos Power and benchmarking lower fidelity models.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2021

Comparison of AlF 3 thin films grown by thermal and plasma enhanced atomic layer deposition

Films of aluminum fluoride (AlF 3 ) deposited by thermal and plasma enhanced atomic layer deposition (PEALD) have been compared using in situ multiwavelength ellipsometry (MWE) and monochromatic x-ray photoelectron spectroscopy (XPS). The AlF 3 films were grown using cyclic exposures of trimethylaluminum, hydrogen fluoride, and H radicals from a remote H 2 inductively coupled plasma. Films were characterized in situ using MWE and XPS for growth rate, film composition, and impurity incorporation. The MWE showed a growth rate of 1.1 and 0.7 Å per cycle, at 100 °C, for thermal and plasma enhanced ALD AlF 3 films, respectively. Carbon incorporation was below the XPS detection limit. The plasma enhanced ALD AlF 3 film showed the presence of Al-Al chemical states, in the Al 2p scans, suggesting the presence of Al-rich clusters with a concentration of 14%. The Al-rich clusters are thought to originate during the hydrogen plasma step of the PEALD process. Finally, the Al-rich clusters were not detected in thermal ALD AlF 3 films using the same precursors and substrate temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Engineering Solid Electrolyte Interphase Composition by Assessing Decomposition Pathways of Fluorinated Organic Solvents in Lithium Metal Batteries

Studies have shown fluorinated electrolyte solvents can form desirable solid electrolyte interphase (SEI) in lithium metal batteries. In this study, we develop a detailed mechanistic understanding of two high performing electrolytes, Fluoroethylene Carbonate (FEC) and Difluoroethylene Carbonate (DFEC) to demonstrate minimal structural variations can lead to different decomposition products, and thereby the nature of the SEI. Using density functional theory (DFT) calculations, we find different initial bond-breaking mechanisms between FEC and DFEC. We develop free energy diagrams for the decomposition pathways including both electrochemical and chemical steps. Using the computational Li electrode, we identify the largest limiting potential of 1.77 V for FEC decomposition, associated with the formation of lithium fluoride, lithium oxide and FEC oligomers, and 1.53 V for DFEC, which correspond to the formation of polymerized vinylene carbonate and lithium fluoride. We suggest the formation of oligomers in the case of FEC instead of long polymers may lead to better SEI compactness. We also demonstrate the SEI components of FEC and DFEC are not stable on typical cathode voltage (3.87 V). This study presents a unified electrocatalytic perspective on SEI formation and decomposition.

25 ENERGY STORAGE↗
DOE OSTI2023

Application of the Solute-Solvent EMF Cell to Measure Activity of NiF 2 in Molten FLiNaK

Electromotive force (emf) measurements made using a combination of solute- and solvent-based electrodes were used to determine the activity of NiF 2 in molten FLiNaK eutectic at 823 K across a concentration range of x NiF2 = 5.2 × 10 –4 –1.0 × 10 –2 . The solute emf values were measured using electrodes consisting of Ni wires immersed in FLiNaK with dissolved NiF 2 contained in graphite crucibles. The measured emf values were then converted to the FLiNaK Eutectic Potassium Electrode (FEKE) potential and used to quantify the activity of dissolved NiF 2 . This quantification was based upon comparative measurements of a reference solvent electrode consisting of a K-Bi alloy immersed in pure FLiNaK contained in a boron nitride crucible and a solute electrode. Short cell lives were characteristic of the measurements due to the corrosive nature of the fluoride salts. Quantifying the activity of NiF 2 will improve the utility of Ni 2+ /Ni reference electrodes in molten fluoride salts, which are notoriously difficult electrolytes to work with because of their reactivity. In conclusion, this work demonstrates the general nature of the solute-solvent approach as a repeatable, easily employed method for measuring the activity values of electroactive species in a variety of molten salts to improve understanding of the electroactive species behavior in these systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Electrochemical Characterization of Dissolved Oxides in Molten FLiNaK

Molten fluoride salts have long been the subject of investigation given their application in a variety of industrial processes. Oxides are a common exogeneous impurity within these systems, and can lead to many operational and regulatory concerns. In recent studies, the electro-oxidation of dissolved metallic oxides has been attributed to a single step oxygen evolution reaction despite voltametric evidence suggesting otherwise. Here, we first use square wave voltammetry to confirm that the oxidation of dissolved oxides in fluorides proceeds via a two-electron transfer reaction and then demonstrate that the presence of a peroxide-mediated redox reaction better explains the electrochemical data. Numerical simulations were then used to support the determination of improved diffusion coefficients to enable electroanalytical measurements of the oxide concentration across at a variety of temperatures. A linear Arrhenius relationship was observed when the experimental data was corrected for ohmic resistance effects. Concentration measurements using the corrected square wave voltammetry data demonstrated high accuracy across a large range of concentrations, while the uncorrected data showed plateauing and high errors. In total, this work serves to rectify previously misconstrued electrochemical data of oxides in molten salts and demonstrate how accurate, in situ concentration measurements can be achieved in real-world systems.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on H5NF2 by Materials Project

NH4HF2 is High Pressure (4-7GPa) Tellurium structured and crystallizes in the orthorhombic Pmna space group. The structure is zero-dimensional and consists of four ammonium molecules and four hydrogen fluoride hydrogen fluoride molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H13C4NF2 by Materials Project

N(CH3)4HF2 is Silicon tetrafluoride-derived structured and crystallizes in the orthorhombic Pmmn space group. The structure is zero-dimensional and consists of two hydrogen fluoride hydrogen fluoride molecules and two tetramethylammonium molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KH(IF6)2 by Materials Project

K(IF5)2HF2 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional and consists of four hydrogen fluoride hydrogen fluoride molecules and one K(IF5)2 framework. In the K(IF5)2 framework, K1+ is bonded in a 8-coordinate geometry to eight equivalent F1- atoms. All K–F bond lengths are 2.69 Å. I5+ is bonded in a 5-coordinate geometry to five F1- atoms. There is one shorter (1.88 Å) and four longer (1.95 Å) I–F bond length. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one I5+ atom. In the second F1- site, F1- is bonded in a distorted linear geometry to one K1+ and one I5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TeH14C3S3(N3F2)2 by Materials Project

C3H13TeS3(N3F)2HF2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four hydrogen fluoride hydrogen fluoride molecules and two C3H13TeS3(N3F)2 clusters. In each C3H13TeS3(N3F)2 cluster, there are three inequivalent C+3.33+ sites. In the first C+3.33+ site, C+3.33+ is bonded in a distorted bent 120 degrees geometry to two N3- and one S2- atom. Both C–N bond lengths are 1.33 Å. The C–S bond length is 1.75 Å. In the second C+3.33+ site, C+3.33+ is bonded in a distorted trigonal planar geometry to two N3- and one S2- atom. Both C–N bond lengths are 1.33 Å. The C–S bond length is 1.74 Å. In the third C+3.33+ site, C+3.33+ is bonded in a distorted trigonal planar geometry to two N3- and one S2- atom. There is one shorter (1.30 Å) and one longer (1.34 Å) C–N bond length. The C–S bond length is 1.79 Å. There are six inequivalent N3- sites. In the first N3- site, N3- is bonded in a trigonal planar geometry to one C+3.33+ and two H1+ atoms. Both N–H bond lengths are 1.03 Å. In the second N3- site, N3- is bonded in a trigonal planar geometry to one C+3.33+ and two H1+ atoms. There is one shorter (1.02 Å) and one longer (1.03 Å) N–H bond length. In the third N3- site, N3- is bonded in a trigonal planar geometry to one C+3.33+ and two H1+ atoms. Both N–H bond lengths are 1.03 Å. In the fourth N3- site, N3- is bonded in a trigonal planar geometry to one C+3.33+ and two H1+ atoms. There is one shorter (1.01 Å) and one longer (1.02 Å) N–H bond length. In the fifth N3- site, N3- is bonded in a trigonal planar geometry to one C+3.33+ and two H1+ atoms. There is one shorter (1.02 Å) and one longer (1.03 Å) N–H bond length. In the sixth N3- site, N3- is bonded in a trigonal planar geometry to one C+3.33+ and two H1+ atoms. There is one shorter (1.02 Å) and one longer (1.25 Å) N–H bond length. There are thirteen inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one S2- and one F1- atom. The H–S bond length is 2.04 Å. The H–F bond length is 0.99 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the tenth H1+ site, H1+ is bonded in a linear geometry to one N3- and one F1- atom. The H–F bond length is 1.17 Å. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the thirteenth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. Te4+ is bonded in a distorted rectangular see-saw-like geometry to four S2- atoms. There are a spread of Te–S bond distances ranging from 2.45–3.27 Å. There are three inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to one C+3.33+, one H1+, and two equivalent Te4+ atoms. In the second S2- site, S2- is bonded in a water-like geometry to one C+3.33+ and one Te4+ atom. In the third S2- site, S2- is bonded in a distorted T-shaped geometry to one C+3.33+, one Te4+, and one F1- atom. The S–F bond length is 2.77 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one H1+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one H1+ and one S2- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H3F2 by Materials Project

H2(HF)4 crystallizes in the triclinic P1 space group. The structure is zero-dimensional and consists of one hydrogen molecule and two hydrogen fluoride hydrogen fluoride molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HXe2F15 by Materials Project

(XeF6)4(HF2)2F2 crystallizes in the orthorhombic Pna2_1 space group. The structure is zero-dimensional and consists of four hydrofluoric acid molecules, four hydrogen fluoride hydrogen fluoride molecules, and four XeF6 clusters. In each XeF6 cluster, there are two inequivalent Xe sites. In the first Xe site, Xe is bonded in a 7-coordinate geometry to seven F atoms. There are a spread of Xe–F bond distances ranging from 1.98–2.51 Å. In the second Xe site, Xe is bonded in a 7-coordinate geometry to seven F atoms. There are a spread of Xe–F bond distances ranging from 1.98–2.48 Å. There are twelve inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one Xe atom. In the second F site, F is bonded in a single-bond geometry to one Xe atom. In the third F site, F is bonded in a single-bond geometry to one Xe atom. In the fourth F site, F is bonded in a single-bond geometry to one Xe atom. In the fifth F site, F is bonded in a single-bond geometry to one Xe atom. In the sixth F site, F is bonded in a single-bond geometry to one Xe atom. In the seventh F site, F is bonded in a single-bond geometry to one Xe atom. In the eighth F site, F is bonded in a single-bond geometry to one Xe atom. In the ninth F site, F is bonded in a bent 120 degrees geometry to two Xe atoms. In the tenth F site, F is bonded in a single-bond geometry to one Xe atom. In the eleventh F site, F is bonded in a bent 120 degrees geometry to two Xe atoms. In the twelfth F site, F is bonded in a single-bond geometry to one Xe atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H25C8IN2(OF2)2 by Materials Project

(N(CH3)4)2HF2I(OF)2 is Silicon tetrafluoride-derived structured and crystallizes in the monoclinic C2/m space group. The structure is zero-dimensional and consists of four hydrogen fluoride hydrogen fluoride molecules, eight tetramethylammonium molecules, and four I(OF)2 clusters. In each I(OF)2 cluster, O2- is bonded in a single-bond geometry to one I1- atom. The O–I bond length is 1.80 Å. I1- is bonded in a distorted rectangular see-saw-like geometry to two equivalent O2- and two F1- atoms. Both I–F bond lengths are 2.08 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one I1- atom. In the second F1- site, F1- is bonded in a single-bond geometry to one I1- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H4NF2 by Materials Project

N2(H2)3(HF2)2 crystallizes in the trigonal R-3m space group. The structure is zero-dimensional and consists of six hydrogen fluoride hydrogen fluoride molecules, six molecular hydrogen molecules, and three nitrogen molecules.

36 MATERIALS SCIENCE↗