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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Operando XAS/SAXS: Guiding Design of Single-Atom and Subnanocluster Catalysts

Single-atom and subnanocluster catalysts (SSCs) represent a highly promising class of low-cost materials with high catalytic activity and high atom-utilization efficiency. However, SSCs are susceptible to undergo restructuring during the reactions. Exploring the active sites of catalysts through in situ characterization techniques plays a critical role in studying reaction mechanism and guiding the design of optimum catalysts. In situ X-ray absorption spectroscopy/small-angle X-ray scattering (XAS/SAXS) is promising and widely used for monitoring electronic structure, atomic configuration, and size changes of SSCs during real-time working conditions. Unfortunately, there is no detailed summary of XAS/SAXS characterization results of SSCs. The recent advances in applying in situ XAS/SAXS to SSCs are thoroughly summarized in this review, including the atomic structure and oxidation state variations under open circuit and realistic reaction conditions. Furthermore, the reversible transformation of single-atom catalysts (SACs) to subnanoclusters/nanoparticles and the application of in situ XAS/SAXS in subnanoclusters are discussed. To conlcude, the outlooks in modulating the SSCs and developing operando XAS/SAXS for SSCs are highlighted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

From gamma ray line signals of dark matter to the LHC

We explore the relationship between astrophysical gamma-ray signals and LHC signatures for a class of phenomenologically successful secluded dark matter models, motivated by recent evidence for a ~130@?GeV gamma-ray line. We consider in detail scenarios in which interactions between the dark sector and the standard model are mediated by a vev-less scalar field @f, transforming as an N-plet (N >@?3) under SU(2)_L. Since some of the component fields of @f carry large electric charges, loop induced dark matter annihilation to @c@c and @cZ can be enhanced without the need for non-perturbatively large couplings, and without overproduction of continuum gamma-rays from other final states. We discuss prospects for other experimental tests, including dark matter-nucleon scattering and production of @f at the LHC, where future searches for anomalous charged tracks may be sensitive. The first LHC hints could come from the Higgs sector, where loop corrections involving @f lead to significantly modified h ->@?@c@c and h@?->@?@cZ branching ratios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Effect of isochronal annealing on the microstructure, texture and mechanical properties of a cold-rolled high manganese steel

Highlights: • Recrystallised γ grains have similar orientations to reverted/recovered γ grains. • After reversion, γ orientations are correlated to ε and α′-martensite orientations. • γ nucleation at the boundary of reverted/recovered γ grains - Abstract: A Fe-17Mn-3Al-2Si-1Ni-0.06C wt.% steel was subjected to cold-rolling to 42% thickness reduction and isochronally annealed for 300 s between 500 and 850 °C. The high Mn steel was characterised via electron back-scattering diffraction, transmission electron microscopy and uniaxial tensile testing. The reversion of deformation-induced ε and α′-martensite to austenite (γ) was witnessed with the formation of fine twins in reverted/recovered γ grains after annealing to 650 °C. The nucleation of new γ grains at the boundary of reverted/recovered γ grains was also noted. Upon reversion, the γ orientations originated from the ε and α′-martensite orientations by phase transformation via the Shoji-Nishiyama and Kurdjumov-Sachs orientation relationships, respectively. Upon segmenting the γ grains, the recrystallised γ grains were observed to nucleate with orientations similar to those of the reverted/recovered γ grains. Uniaxial tension on a fully recrystallised γ microstructure showed that the initial γ grain size has a more significant effect on the yield strength than the ε and α′-martensite fractions. On the other hand, the initial ε and α′-martensite fractions affect the total elongation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Deciphering Charge Transfer Processes in Transition Metal Complexes from the Perspective of Ultrafast Electronic and Nuclear Motions

Chemical transformations in charge transfer states result from the interplay between electronic dynamics and nuclear reorganization along excited-state trajectories. Here, in this study, we investigate the ultrafast structural dynamics following photoinduced electron transfer from the metal-metal-to-ligand charge transfer state of an electron donor, a Pt dimer complex, to a covalently linked electron acceptor group using ultrafast time-resolved wide-angle X-ray scattering and optical transient absorption spectroscopy methods to disentangle the interdependence of the excited-state electronic and nuclear dynamics. Following photoexcitation, Pt-Pt bond formation and contraction takes up to 1 ps, much slower than the corresponding process in analogous complexes without electron acceptor groups. Because the Pt-Pt distance change is slow with respect to excited-state electron transfer, it can affect the rate of electron transfer. These results have potential impacts on controlling electron transfer rates via structural alterations to the electron donor group, tuning the charge transfer driving force.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Inverse Temperature Dependence of Charge Carrier Hopping in Quantum Dot Solids

In semiconductors, increasing mobility with decreasing temperature is a signature of charge carrier transport through delocalized bands. We show that this behavior can also occur in nanocrystal solids due to temperature-dependent structural transformations. Using a combination of broadband infrared transient absorption spectroscopy and numerical modeling, we investigate the temperature-dependent charge transport properties of well-ordered PbS quantum dot (QD) solids. Contrary to expectations, we observe that the QD-to-QD charge tunneling rate increases with decreasing temperature, while simultaneously exhibiting thermally activated nearest-neighbor hopping behavior. Using synchrotron grazing-incidence small-angle X-ray scattering, we show that this trend is driven by a temperature-dependent reduction in nearest-neighbor separation that is quantitatively consistent with the measured tunneling rate.

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

Enhanced Catalytic Dechlorination of Polyvinyl Chloride (PVC) and H2 Production Enabled by Synergistic Gaδ+/Ga0 Active Sites in Liquid Metal Particles

Polyvinyl chloride (PVC) is ubiquitous yet challenging to recycle due to its tendency to thermally decompose above 250 °C, releasing toxic, corrosive chlorinated compounds, and its inability to melt. Here, we report a catalytic strategy for PVC upcycling at 160 °C using gallium liquid metal particles (Ga-LMP) featuring a dynamic Ga-GaOOH core–shell architecture. These catalysts enable concurrent dechlorination and hydrogen evolution, yielding up to 7% H2 (based on initial hydrogen atoms in PVC) along with a highly dechlorinated (>95%) carbonaceous solid and aqueous HCl. Mechanistic investigations combining X-ray photoelectron spectroscopy, infrared spectroscopy, solid-state NMR, inelastic neutron scattering, and ab initio molecular dynamics reveal a synergistic interplay between Gaδ+ sites in the GaOOH shell and metallic Ga0 in the core. Cationic Ga initiates C–Cl bond activation and HCl formation, while progressive reduction of the shell exposes Ga0 sites that promote C–H activation and H2 evolution. Control experiments with a Ga salt and bulk Ga liquid metal confirmed that neither oxidation state alone can achieve both transformations efficiently. This work establishes a dynamic dual-site paradigm for liquid metal catalysis, in which the in situ evolution and coexistence of oxidized and metallic species enable sequential and cooperative bond activation pathways. These findings provide a general design principle for novel liquid metal catalysts that target challenging polymer transformations under mild conditions.

Zingg, Benjamin [ORNL] (ORCID:0009000914530153)↗
NASA NTRS2006

Dynamic Theory of Relativistic Electrons Stochastic Heating by Whistler Mode Waves with Application to the Earth Magnetosphere

In the Hamiltonian approach an electron motion in a coherent packet of the whistler mode waves propagating along the direction of an ambient magnetic field is studied. The physical processes by which these particles are accelerated to high energy are established. Equations governing a particle motion by group symmetries of the problem were transformed in to a closed pair of nonlinear difference equations. The solutions of these equations have shown there exists the energetic threshold below that the electron motion is regular, and when the initial energy is above the threshold an electron moves stochastically. It is proved that the upper boundary of particle stochastic heating is conditioned by intrinsic property of the particle chaotic motion. Particle energy spectra and pitch angle electron scattering are described by the Fokker-Planck-Kolmogorov equations. It is shown that significant pitch angle diffusion occurs for the Earth radiation belt electrons with energies from a few keV up to a few MeV.

Khazanov, G. V.↗
NASA NTRS1991

A finite element conjugate gradient FFT method for scattering

Validated results are presented for the new 3D body of revolution finite element boundary integral code. A Fourier series expansion of the vector electric and mangnetic fields is employed to reduce the dimensionality of the system, and the exact boundary condition is employed to terminate the finite element mesh. The mesh termination boundary is chosen such that is leads to convolutional boundary operatores of low O(n) memory demand. Improvements of this code are discussed along with the proposed formulation for a full 3D implementation of the finite element boundary integral method in conjunction with a conjugate gradiant fast Fourier transformation (CGFFT) solution.

Collins, Jeffery D.↗
DOE OSTI2013

A HERSCHEL SURVEY OF THE [N II] 205 {mu}m LINE IN LOCAL LUMINOUS INFRARED GALAXIES: THE [N II] 205 {mu}m EMISSION AS A STAR FORMATION RATE INDICATOR

We present, for the first time, a statistical study of [N II] 205 {mu}m line emission for a large sample of local luminous infrared galaxies using Herschel Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) data. For our sample of galaxies, we investigate the correlation between the [N II] luminosity (L{sub [N{sub II]}}) and the total infrared luminosity (L{sub IR}), as well as the dependence of L{sub [N{sub II]}}/L{sub IR} ratio on L{sub IR}, far-infrared colors (IRAS f{sub 60}/f{sub 100}), and the [O III] 88 {mu}m to [N II] luminosity ratio. We find that L{sub [N{sub II]}} correlates almost linearly with L{sub IR} for non-active galactic nucleus galaxies (all having L{sub IR} < 10{sup 12} L{sub Sun }) in our sample, which implies that L{sub [N{sub II]}} can serve as a star formation rate tracer which is particularly useful for high-redshift galaxies that will be observed with forthcoming submillimeter spectroscopic facilities such as the Atacama Large Millimeter/submillimeter Array. Our analysis shows that the deviation from the mean L{sub [N{sub II]}}-L{sub IR} relation correlates with tracers of the ionization parameter, which suggests that the scatter in this relation is mainly due to the variations in the hardness, and/or ionization parameter, of the ambient galactic UV field among the sources in our sample.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Structure/property relationships in copolymers comprising renewable isosorbide, glucarodilactone, and 2,5-bis(hydroxymethyl)furan subunits

Carbohydrates and their derivatives have great potential as building blocks for the development of renewable materials that are cost and performance competitive with conventional petroleum-based materials. To this end, the rigid carbohydrate-derived diols, glucarodilactone and isosorbide were functionalized with a castor oil derivative, 10-undecenoic acid, forming α,ω-dienes suitable for acyclic diene metathesis (ADMET) polymerization. Equimolar copolymerizations of these two monomers, glucarodilactone undecenoate (GDLU) and isosorbide undecenoate (GDLU), transform brittle homopolymers into elastic materials with shape memory capabilities. To understand the source of these properties, a series of copolymers consisting of a range of GDLU and IU compositions (100:0, 77:23, 76:24, 52:48, 48:52, 18:82, 0:100 mol percent GDLU to IU) was synthesized. The material and chemical properties were characterized by uniaxial tensile testing, small-amplitude oscillatory shear rheology, X-ray scattering and hydrolytic degradation testing. Small compositional changes in this family were shown to have a drastic impact on the observed mechanical performance and degradability of these materials. Rheological measurements of GDLU-containing copolymers found evidence for the presence of transient networking within these materials. We posit that the transient network within this material is responsible for the elasticity and shape memory abilities of the GDL-containing materials. In confirmation of these properties, a novel α,ω-diene 2,5-bis(hydroxymethylfuran) undecenoate (BHMFU) was developed and served as a direct replacement for either GDLU or IU in copolymerizations. The replacement of GDLU resulted in a total loss of the elasticity and shape memory of the copolymers, supporting the role of GDLU in the mechanical performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Detection of nonlinear picosecond acoustic pulses by time-resolved Brillouin scattering

In time-resolved Brillouin scattering (also called picosecond ultrasonic interferometry), the time evolution of the spatial Fourier component of an optically excited acoustic strain distribution is monitored. The wave number is determined by the momentum conservation in photon-phonon interaction. For linear acoustic waves propagating in a homogeneous medium, the detected time-domain signal of the optical probe transient reflectivity shows a sinusoidal oscillation at a constant frequency known as the Brillouin frequency. This oscillation is a result of heterodyning the constant reflection from the sample surface with the Brillouin-scattered field. Here, we present an analytical theory for the nonlinear reshaping of a propagating, finite amplitude picosecond acoustic pulse, which results in a time-dependence of the observed frequency. In particular, we examine the conditions under which this information can be used to study the time-evolution of the weak-shock front speed. Depending on the initial strain pulse parameters and the time interval of its nonlinear transformation, our theory predicts the detected frequency to either be monotonically decreasing or oscillating in time. We support these theoretical predictions by comparison with available experimental data. In general, we find that picosecond ultrasonic interferometry of nonlinear acoustic pulses provides access to the nonlinear acoustic properties of a medium spanning most of the GHz frequency range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Studies of Spinons, Majoranas, and Monopoles in Spin Liquid and Quantum Critical Magnets with Neutrons

Quantum and frustrated materials have eminent potential for the future with the promise of transformative properties in energy storage, conversion, and transmission as well as for new types of computing. Many of the new materials being explored are introduced to have highly unusual ground states that show quantum critical behavior or exotic disorder such as spin liquids. Intense interest is focused on the unusual types of fractionalized quasiparticles that these phases can support such as spin-1/2 spinons, Majorana fermions, and magnetic monopoles. Neutron scattering provides a remarkable tool for probing quantum and frustrated states of real magnetic system by measuring the structure and dynamics of atomic spins on the important energy scales involved. Here I review the signatures of these unusual quasiparticles and the evidence for them starting with quasi-1D magnets covering fractionalization of magnons into spinons, confinement effects, and three classes of quantum critical behavior. In 2D I report on the status of quantum spin liquids in triangular and Kagome magnets before considering the current evidence for exotic Majorana fermions in materials that approximate the Kitaev model. Following this I outline the current status of research into magnetic monopoles in 3D spin ice and the potential for emergent electrodynamics in quantum spin ice. Finally, I consider where new developments in materials, experiment, and theory and modeling could lead to new discoveries.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1983

Hue-saturation-intensity split-spectrum processing of Seasat radar imagery

Characteristics of terrain features in orbital radar imagery are investigated on the basis of radar physics and the human visual system. Signal scattering, the dominant factor in radar imagery, is caused by look angle and relief displacement. Power spectra characteristics are explored, noting that surface scattering dominates the low frequencies and slope significantly affects the high frequency tone variations. The maximum human visual response has been identified for achromatic scenes as 7 cycles per degree, whereas in radar imagery the low frequency half-power point occurs near 2.5 cycles/deg. Image feature size at a scale of 1:500,000 has been calculated for the maximum human response at 1.25 km. A hue-saturation-intensity transformation is presented for displaying two or three data sets on the same image and is demonstrated for Seasat SAR imagery. The transformation is shown to restore low spatial frequencies to the SAR imagery in order to identify terrain features which would otherwise not be visually discernible.

Daily, M.↗
DOE OSTI2021

Instrument for in situ hard x-ray nanobeam characterization during epitaxial crystallization and materials transformations

Solid-phase epitaxy (SPE) and other three-dimensional epitaxial crystallization processes pose challenging structural and chemical characterization problems. The concentration of defects, the spatial distribution of elastic strain, and the chemical state of ions each vary with nanoscale characteristic length scales and depend sensitively on the gas environment and elastic boundary conditions during growth. The lateral or three-dimensional propagation of crystalline interfaces in SPE has nanoscale or submicrometer characteristic distances during typical crystallization times. Here, an in situ synchrotron hard x-ray instrument allows these features to be studied during deposition and crystallization using diffraction, resonant scattering, nanobeam and coherent diffraction imaging, and reflectivity. The instrument incorporates a compact deposition system allowing the use of short-working-distance x-ray focusing optics. Layers are deposited using radio-frequency magnetron sputtering and evaporation sources. The deposition system provides control of the gas atmosphere and sample temperature. The sample is positioned using a stable mechanical design to minimize vibration and drift and employs precise translation stages to enable nanobeam experiments. Results of in situ x-ray characterization of the amorphous thin film deposition process for a SrTiO 3 /BaTiO 3 multilayer illustrate implementation of this instrument.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Sodium tungstate-promoted CaMnO 3 as an effective, phase-transition redox catalyst for redox oxidative cracking of cyclohexane

Oxidative cracking, which combines catalytic oxidation and cracking reactions, represents a promising approach to reduce the energy and carbon intensities for light olefin production from naphtha. The need to co-feed gaseous oxygen with hydrocarbons, however, leads to significant CO x formation and safety concerns. The cost and energy consumption associated with air separation also affects its economic attractiveness. In this study, we investigated a redox oxidative cracking (ROC) scheme and evaluated perovskites (La 0.8 Sr 0.2 FeO 3 and CaMnO 3 ) and Na 2 WO 4 -promoted perovskite (La 0.8 Sr 0.2 FeO 3 @Na 2 WO 4 and CaMnO 3 @Na 2 WO 4 ) as the redox catalysts for ROC. CaMnO 3 @Na 2 WO 4 redox catalyst shows high activity, selectivity, and stability for light olefin production from cyclohexane. Operated under a redox oxidative cracking (ROC) scheme, CaMnO 3 @Na 2 WO 4 enhances the catalytic cracking of cyclohexane, while showing high selectivity towards hydrogen combustion with its built-in, active lattice oxygen. Over three-fold increase in olefin yield compared to thermal cracking and 35% yield increase compared to conventional O 2 -cofeed oxidative cracking were achieved. Low energy ion scattering (LEIS), X-ray photoelectric spectroscopy (XPS), and differential scanning calorimetry (DSC) indicated a core-shell structure, where a molten Na 2 WO 4 layer covers the CaMnO 3 core. Na 2 WO 4 modifies the oxygen donation behavior of CaMnO 3 and provides a catalytically active surface for cyclohexane activation. In-situ XRD revealed that CaMnO 3 @Na 2 WO 4 exhibited excellent structural stability and regenerability. The transformation of Mn 4+ ↔ Mn 3+ ↔ Mn 2+ in CaMnO 3 , facilitated by reversible phase transition to (Ca/Mn)O solid solution, is responsible for the lattice oxygen donation and uptake during redox cycles. Electrochemical impedance spectroscopy (EIS) measurements further confirmed that the oxygen species were transported through the molten Na 2 WO 4 layer to participate in ROC. These findings offer mechanistic insights to design effective redox catalysts for hydrocarbon valorization using the chemical looping strategy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

In-situ EBSD study of deformation behavior of retained austenite in a low-carbon quenching and partitioning steel via uniaxial tensile tests

Through using in-situ electron back-scattered diffraction and uniaxial tensile tests, this work mainly focuses on the deformation behavior of retained austenite (RA) in a low-carbon quenching and partitioning (Q&P) steel. In this paper, three different types of RA can be distinguished from different locations, respectively, RA grains at the triple edges, twinned austenite and RA grains positioned between martensite. The results have shown that grains at the triple edges and twinned austenite could transform easily with increasing strain, i.e. are less stable when compared with RA grains distributed between martensite that could resist a larger plastic deformation. Meanwhile, the strain leads to rotations of RA grains distributed at the triple edges and between martensite. Moreover, RA grains with a similar orientation undergone similar rotations with the same true strain. These RA grains rotated along a specific slip plane and slip direction and the grain rotation is taken as a significant factor to improve the ductility of steel. In addition, grain sizes of RA decreased gradually with an increase of true strain and smaller (0–0.2 μm) grains were more capable of resisting the deformation. According to kernel average misorientation (KAM) analysis, it can be found that strain distribution is preferentially localized near martensite–austenite phase boundaries and in the interior of martensite. The average KAM values increased continuously with increasing true strain. - Highlights: •The in-situ and ex-situ tensile specimens differ to some extent in mechanical properties. •Retained austenite grains at the triple edges and twinned austenite transformed easily at the early stage of true strain. •Film-like retained austenite grains only rotated prior to the transformation during straining. •Retained austenite grains having with a similar orientation experienced similar rotations during the same true strain.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Laponite-Incorporated UiO-66-NH2-Polyethylene Oxide Composite Membranes for Protection against Chemical Warfare Agent Simulants

A strategy is developed to enhance the barrier protection of polyethylene oxide (PEO)-metal–organic framework (MOF) composite films against chemical warfare agent simulants. To achieve enhanced protection, an impermeable high-aspect-ratio filler in the form of Laponite RD (LRD) clay platelets was incorporated into a composite PEO film containing MOF UiO-66-NH 2 . The inclusion of the platelets aids in mitigating permeation of inert hydrocarbons (octane) and toxic chemicals (2-chloroethyl ethyl sulfide, 2-CEES) of dimensions/chemistry similar to prominent vesicant threats while still maintaining high water vapor transport rates (WVTR). By utilizing small-angle neutron scattering, small-angle X-ray scattering, and wide-angle X-ray scattering, the LRD platelet alignment of the films was determined, and the structure of the films was correlated with performance as a barrier material. Performance of the membranes against toxic chemical threats was assessed using permeation testing of octane and 2-CEES, a common simulant for the vesicant mustard gas, and breathability of the membranes was assessed using WVTR measurements. To assess their robustness, chemical exposure (in situ diffuse reflectance infrared Fourier transform spectroscopy) and mechanical (tensile strength) measurements were also performed. It was demonstrated that the barrier performance of the film upon inclusion of the LRD platelets exceeds that of other MOF-polymer composites found in the literature and that this approach establishes a new path for improving permselective materials for chemical protection applications.

36 MATERIALS SCIENCE↗