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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Modeling of High-Temperature Corrosion of Zirconium Alloys Using the eXtended Finite Element Method (X-FEM)

Oxidation modeling in modern nuclear fuel performance codes is currently limited by the lack of coupling with mechanics, thus preventing proper description of how high-temperature oxidation impacts mechanical properties. This is mostly due to the fact that the finite difference formalism adopted in corrosion models is incompatible with the direct coupling with mechanics in the finite element modeling employed in modern nuclear fuel performance codes. In this study, a physically based zirconium alloy corrosion model called the Coupled-Current Charge Compensation (C4) model, which was initially developed for operating temperature conditions, has been updated to include high-temperature corrosion in order to provide additional critical information (e.g., oxygen concentration profile) under loss-of-coolant accident (LOCA) conditions—information lacking in existing empirical models. The C4 model was implemented in the MOOSE finite-element framework developed at Idaho National Laboratory, enabling it to be used in the BISON nuclear fuel performance code based on the MOOSE framework. To precisely track the different interfaces at a relatively low computational cost, the eXtended Finite Element Method (X-FEM) was applied in MOOSE. The model’s results were compared to those of existing empirical models as well as metallographic analysis of high-temperature oxidized Zircaloy-4 coupons. Oxygen diffusivities in the a and ß phases resulting from this comparison closely agree with those found in the literature. The C4 model implemented with X-FEM in MOOSE now has the capability to accurately predict oxide, oxygen-stabilized a, and prior ß phase layer growth kinetics under isothermal exposure at high temperature (1000–1500°C). Furthermore, in contrast with the empirical models, the C4 model accounts for the finite thickness of the fuel cladding. It can predict the oxygen concentration profile evolution through the whole cladding, enabling evaluation of the remaining ductile thickness—a crucial variable for modeling the mechanical behavior of the fuel cladding under LOCA. Furthermore, this implementation allows direct coupling with mechanics, at a low computing cost, using finite-element-based nuclear fuel performance codes such as BISON.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Unraveling Anisotropic and Pulsating Etching of ZnO Nanorods in Hydrochloric Acid via Correlative Electron Microscopy

Despite much technical progress achieved so far, the exact surface and shape evolution during wet chemical etching is less unraveled, especially in ionically bonded ceramics. Herein, by using in situ liquid cell transmission electron microscopy, a repeated two-stage anisotropic and pulsating periodic etching dynamic is discovered during the pencil shape evolution of a single crystal ZnO nanorod in aqueous hydrochloric acid. Specifically, the nanopencil tip shrinks at a slower rate along [0001̅] than that along the $\langle$101̅0$\rangle$ directions, resulting in a sharper ZnO pencil tip. Afterward, rapid tip dissolution happens due to accelerated etching rates along various crystal directions. Concurrently, the vicinal base region of the original nanopencil tip emerges as a new tip followed by the repeated sequence of tip shrinking and removal. The high-index surfaces, such as {101̅m} (m = 0, 1, 2, or 3) and {21̅1̅n} (n = 0, 1, 2, or 3), are found to preferentially expose in different ratios. Our 3D electron tomography, convergent beam electron diffraction, middle-angle bright-field STEM, and XPS results indicate the dissociative Cl – species were bound to the Zn-terminated tip surfaces. Furthermore, DFT calculation suggests the preferential Cl – passivation over the {101̅1} and (0001) surfaces of lower energy than others, leading to preferential surface exposures and the oscillatory variation of different facet etching rates. The boosted reactivity due to high-index nanoscale surface exposures is confirmed by comparatively enhanced chemical sensing and CO 2 hydrogenation activity. In conclusion, these findings provide an in-depth understanding of anisotropic wet chemical etching of ionic nanocrystals and offer a design strategy for advanced functional materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nitrogen evolution, NO X formation and reduction in pressurized oxy coal combustion

Oxy-combustion is one of the most prominent solutions for reducing CO 2 emissions from coal-fired power plants using carbon-capture-and-utilization technology. However, when compared to air combustion at atmospheric pressure, oxy-combustion is very expensive, owing to the significant efficiency penalties associated with air separation, flue gas recirculation (FGR), treatment, compression, and storage or transit of CO 2 . In comparison, pressurized oxy-combustion (POC) is more efficient as it recovers a significant amount of heat energy from the flue gas moistures. Nevertheless, CO 2 derived from pressurized oxy coal combustion has impurities, e.g., acid gases (NO X and SO X ) that can corrode the plant equipment, transport lines as well as deteriorating effect on the environment. Fortunately, in pressurized combustion systems, both NO X and SO X can be scrubbed by a single-column direct contact cooler (DCC), but this requires a minimum ratio of NO X to SO X at the inlet to be efficiently removed. Therefore, NOx is one of the important hindering parameters in commercializing the pressurized oxy-combustion. Although NOx evolution during oxy-coal combustion has been explored extensively at 1 atm, higher pressure studies are rare. Much still needs to be done to better understand the NO X mechanism and the effects of different parameters on NO X emissions under these conditions. Here, this paper reviews the published literature on nitrogen evolution, NO X formation and reduction in pressurized oxy-coal combustion. At higher pressures, the NO X from fuel-bound nitrogen is generated through volatiles, tar and char, all of which are discussed. Where literature is not available, the effect of pressure on NOx evolution in different stages of coal combustion is predicted through CHEMKIN simulation. Homogeneous and heterogeneous pathways of NO X formation and their destruction in pressurized oxy-coal combustion are evaluated. Additionally, the effect of pressure on a few mature and commercialized NOx abatement methods is explored. In the last, the future perspective and recommendation are given. This review will aid in the provision of basic knowledge about NOx evolution and control in pressurized fuel combustion, as well as the identification of new research areas to pursue.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2025

Acoustic misalignment mechanism for axion dark matter

A rotation in the field space of a complex scalar field corresponds to a Bose-Einstein condensation of U(1) charges. We point out that fluctuations in this rotating condensate exhibit sound-wave modes, which can be excited by cosmic perturbations and identified with axion fluctuations once the U(1) charge condensate has been sufficiently diluted by cosmic expansion. We consider the possibility that these axion fluctuations constitute dark matter and develop a formalism to compute its abundance. We carefully account for the growth of fluctuations during the epoch where the complex scalar field rotates on the body of the potential and possible nonlinear evolution when the fluctuations become non-relativistic. We find that the resultant dark matter abundance can exceed the conventional and kinetic misalignment contributions if the radial direction of the complex scalar field is sufficiently heavy. The axion dark matter may also be warm enough to leave imprints on structure formation. We discuss the implications of this novel dark matter production mechanism — acoustic misalignment mechanism — for the axion rotation cosmology, including kination domination and baryogenesis from axion rotation, as well as for axion searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Ultrafast multi-cycle terahertz measurements of the electrical conductivity in strongly excited solids

Key insights in materials at extreme temperatures and pressures can be gained by accurate measurements that determine the electrical conductivity. Free-electron laser pulses can ionize and excite matter out of equilibrium on femtosecond time scales, modifying the electronic and ionic structures and enhancing electronic scattering properties. The transient evolution of the conductivity manifests the energy coupling from high temperature electrons to low temperature ions. Here we combine accelerator-based, high-brightness multi-cycle terahertz radiation with a single-shot electro-optic sampling technique to probe the evolution of DC electrical conductivity using terahertz transmission measurements on sub-picosecond time scales with a multi-undulator free electron laser. Our results allow the direct determination of the electron-electron and electron-ion scattering frequencies that are the major contributors of the electrical resistivity.

36 MATERIALS SCIENCE↗
DOE OSTI2024

eReaxFF force field development for BaZr 0.8 Y 0.2 O 3-δ solid oxide electrolysis cells applications

The use of solid-oxide materials in electrocatalysis applications, especially in hydrogen-evolution reactions, is promising. However, further improvements are warranted to overcome the fundamental bottlenecks to enhancing the performance of solid-oxide electrolysis cells (SOECs), which is directly linked to the more-refined fundamental understanding of complex physical and chemical phenomena and mass exchanges that take place at the surfaces and in the bulk of electrocatalysis materials. Here, we developed an eReaxFF force field for barium zirconate doped with 20 mol% of yttrium, BaZr 0.8 Y 0.2 O 3-δ (BZY20) to enable a systematic, large-length-scale, and longer-timescale atomistic simulation of solid-oxide electrocatalysis for hydrogen generation. All parameters for the eReaxFF were optimized to reproduce quantum-mechanical (QM) calculations on relevant condensed phase and cluster systems describing oxygen vacancies, vacancy migrations, electron localization, water adsorption, water splitting, and hydrogen generation on the surfaces of the BZY20 solid oxide. Using the developed force field, we performed both zero-voltage (excess electrons absent) and non-zero-voltage (excess electrons present) molecular dynamics simulations to observe water adsorption, water splitting, proton migration, oxygen-vacancy migrations, and eventual hydrogen-production reactions. Based on investigations offered in the present study, we conclude that the eReaxFF force field-based approach can enable computationally efficient simulations for electron conductivity, electron leakage, and other non-zero-voltage effects on the solid oxide materials using the explicit-electron concept. Moreover, we demonstrate how the eReaxFF force field-based atomistic-simulation approach can enhance our understanding of processes in SOEC applications and potentially other renewable-energy applications.

08 HYDROGEN↗
DOE OSTI2026

Chirality-induced spin selectivity as a mechanism to control product selectivity during electrochemical CO 2 reduction

Electrocatalytic CO 2 reduction often suffers from competition with the hydrogen evolution reaction (HER), which lowers efficiency and limits product selectivity. Recent studies suggest that electron spin, when controlled at an electrode surface, can influence reaction pathways, but direct evidence linking spin effects to suppressed HER has been limited. Here, in this work, we show that helical chiral copper (Cu) electrodes reduce competing HER during CO 2 reduction, consistent with spin polarization induced via the chiral-induced spin selectivity effect. The helically structured Cu electrodes are fabricated by electrodeposition with a chiral templating reagent. Time-resolved Kerr ellipticity measurements, which track spin-polarized carriers generated by an ultrafast Seebeck current, confirm spin accumulation at the chiral Cu surface. This spin polarization disfavours H—H bond formation, thereby suppressing HER and enabling formate production alongside CO. These findings demonstrate that chirality-based spin control offers a strategy for steering selectivity in CO 2 reduction and other reactions where HER is an undesired competitor.

14 SOLAR ENERGY↗
DOE OSTI2024

Prediction challenge: First principles simulation of the ultrafast electron diffraction spectrum of cyclobutanone

Computer simulation has long been an essential partner of ultrafast experiments, allowing the assignment of microscopic mechanistic detail to low-dimensional spectroscopic data. However, the ability of theory to make a priori predictions of ultrafast experimental results is relatively untested. Herein, as a part of a community challenge, we attempt to predict the signal of an upcoming ultrafast photochemical experiment using state-of-the-art theory in the context of preexisting experimental data. Specifically, we employ ab initio Ehrenfest with collapse to a block mixed quantum–classical simulations to describe the real-time evolution of the electrons and nuclei of cyclobutanone following excitation to the 3s Rydberg state. The gas-phase ultrafast electron diffraction (GUED) signal is simulated for direct comparison to an upcoming experiment at the Stanford Linear Accelerator Laboratory. Following initial ring-opening, dissociation via two distinct channels is observed: the C3 dissociation channel, producing cyclopropane and CO, and the C2 channel, producing CH2CO and C2H4. Direct calculations of the GUED signal indicate how the ring-opened intermediate, the C2 products, and the C3 products can be discriminated in the GUED signal. We also report an a priori analysis of anticipated errors in our predictions: without knowledge of the experimental result, which features of the spectrum do we feel confident we have predicted correctly, and which might we have wrong?

Chemistry↗
DOE OSTI2024

Fluorescence-mediated postcollision interaction in x-ray photoionization of the Xe 𝐾 edge

Postcollision interaction (PCI) in near-threshold photoionization of the K shell of atomic Xe is investigated with hard-x-ray synchrotron radiation. Applying Auger electron spectroscopy, line-shape distortion is monitored in the K-L 2 → L 2 M 4,5 M 4,5 decay channel, where the initial K-L 2 (Kα 2 ) x-ray-emission step mediates the emission of the two continuum electrons. The K-edge result is compared to similar data obtained on direct L 2 M 4,5 M 4,5 decay at the L 2 edge without x-ray-emission. In conclusion, it is found that the evolution of the PCI shift with excess photon energy is very similar at both edges, but a subtle decrease in the PCI shift is observable at the K edge due to the effect of the ultrafast x-ray emission step delaying the PCI energy exchange by a few attoseconds.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Tunable competing magnetic anisotropies and spin reconfigurations in ferrimagnetic Fe 100– x Gd x alloy films

Here, we report a comprehensive study of the temperature evolution of in-plane (IP) and out-of-plane (OOP) effective magnetic anisotropies in compensated ferrimagnetic Fe 100– x Gd x alloy films by employing direct current magnetometry and radiofrequency (RF) transverse susceptibility (TS) measurements. We suggest that our Fe 100– x Gd x system is chemically inhomogeneous and phase segregates into Fe- and Gd-enriched regions. Our IP and OOP magnetometry results indicate that the system undergoes a temperature-driven transformation from an IP-spin-configuration-dominated state to an OOP-spin-configuration-dominated state below a certain temperature (spin reorientation temperature). A two-step reversal behavior emerges in the OOP $\textit{M(H)}$ loop near compensation, which we attribute to the sequential magnetization reversals of Fe- and Gd-enriched domains. Field-induced spin-flop transitions were also observed near the compensation. Our RF TS measurements indicate that the effective magnetic anisotropy for the OOP configuration dominates over that for the IP configuration below a certain spin reorientation temperature. Both IP and OOP anisotropy fields determined from our TS measurement exhibit a minimum around the compensation temperature, which has been explained in the framework of the Stoner-Wohlfarth model.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Self-Generated Plasma Rotation in a Z-Pinch Implosion with Preembedded Axial Magnetic Field

Using detailed spectroscopic measurements, highly resolved in both time and space, a self-generated plasma rotation is demonstrated using a cylindrical implosion with a preembedded axial magnetic field (B z0 ). The rotation direction is found to depend on the direction of B z0 and its velocity is found comparable to the peak implosion velocity, considerably affecting the force and energy balance throughout the implosion. Moreover, the evolution of the rotation is consistent with magnetic flux surface isorotation, a novel observation in a Z pinch, which is a prototypical time dependent system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Back-Stress and Its Evolution during Primary Creep in Particle Strengthened Nickel Superalloys

According to Eshelby’s theory, inelastically inhomogeneous inclusions in a metallic matrix give rise to a distribution of internal stresses. In the case of particle strengthened materials, such as nickel base superalloys, the presence and evolution of this back-stress leads to various observable effects, such as primary creep, back-flow upon loading, and memory of prior deformation. This article presents the background of the concept of back-stress and how it applies to the scenario of creep. A derivation of an evolution equation for back-stress in the context of primary creep is also presented. The results from neutron diffraction with in-situ creep experiments on directionally solidified nickel superalloys are presented in order to demonstrate the validity of the proposed equation and the corollaries derived therefrom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Search for Magnetic Accretion in SW Sextantis Systems

SW Sextantis systems are nova-like cataclysmic variables that have unusual spectroscopic properties, which are thought to be caused by an accretion geometry having part of the mass flux trajectory out of the orbital plane. Accretion onto a magnetic white dwarf is one of the proposed scenarios for these systems. To verify this possibility, we analyzed photometric and polarimetric time-series data for a sample of six SW Sex stars. We report possible modulated circular polarization in BO Cet, SW Sex, and UU Aqr with periods of 11.1, 41.2, and 25.7 minutes, respectively, and less significant periodicities for V380 Oph at 22 minutes and V442 Oph at 19.4 minutes. We confirm previous results that LS Peg shows variable circular polarization. However, we determine a period of 18.8 minutes, which is different from the earlier reported value. We interpret these periods as the spin periods of the white dwarfs. Our polarimetric results indicate that 15% of the SW Sex systems have direct evidence of magnetic accretion. We also discuss SW Sex objects within the perspective of being magnetic systems, considering the latest findings about the demography, formation, and evolution of cataclysmic variables.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

A second order yield-temperature relation for accurate inference of burn-averaged quantities in multi-species plasmas

Measured yields and ion temperatures inferred from the fusion product energy spectra can be used as metrics for the performance of an ICF implosion. This can be to infer species separation, thermal decoupling, flows or other effects that can cause the inferred ion temperatures to deviate from the true underlying thermal temperature and the yield ratio to deviate from the expected value. Direct inference of the impact of these effects on observed temperatures and yields can be difficult to uncover due to underlying dependence on the shape and time evolution of the temperature and density proles of the fusing plasma. Due to differences in the temperature dependence of the reactivities, different fusion products are emitted from different regions and times within the implosion. In order to properly account for this, a second order analytic expression relating the apparent temperatures and yield ratios is developed. This expression can be coupled to models of yield and/or temperature altering effects to infer their burn-averaged impact on an implosion. The second order expression shows significant improvement over lower order expressions in synthetic data studies. Demonstrations of its applications to synthetic data coupled with models of ion thermal decoupling and radial flows are presented. In the case of thermal decoupling both first and second order expressions show reasonable levels of accuracy. To consistently infer the amplitude of radial flow with <10% error the second order equation is required.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Revealing the Latent Atomic World Through Data-Driven Microscopy

Many emerging technologies depend on the precise design of materials structure, chemistry, and defects. As devices shrink, manufacturing tolerances tighten, and performance envelopes improve, we must increasingly measure and manipulate materials at or near the single atom level. Here we describe how transmission electron microscopy (TEM) underpins our ability to see and direct the latent atomic world. We review a selection of our recent high-resolution TEM studies of the synthesis of oxide-based nanomaterials and their evolution in extreme environments. We then discuss powerful new artificial intelligence (AI) and machine learning (ML) approaches we have developed for rich, reproducible, and scalable experimentation. Furthermore, we conclude by discussing future developments that will enable new materials for breakthrough technologies.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Birth of the Hydrated Electron via Charge-Transfer-to-Solvent Excitation of Aqueous Iodide

A primary means to generate hydrated electrons in laboratory experiments is excitation to the charge-transfer-to-solvent (CTTS) state of a solute such as I – (aq), but this initial step in the genesis of e – (aq) has never been simulated directly using ab initio molecular dynamics. Here, we report the first such simulations, combining ground- and excited-state simulations of I – (aq) with a detailed analysis of fluctuations in the Coulomb potential experienced by the nascent solvated electron. What emerges is a two-step picture of the evolution of e – (aq) starting from the CTTS state: I – (aq) + hν → I –* (aq) → I • (aq) + e – (aq). Notably, the equilibrated ground state of e – (aq) evolves from I –* (aq) without any nonadiabatic transitions, simply as a result of solvent reorganization. The methodology used here should be applicable to other photochemical electron transfer processes in solution, an important class of problems directly relevant to photocatalysis and energy transfer.

Carter-Fenk, Kevin↗
DOE OSTI2021

Mutations in artificial self-replicating tiles: A step toward Darwinian evolution

Significance In nature, mutation is the first step of evolution, where it provides the genetic variation for the natural selection to act. Here we take a system of artificial self-replicating tiles, DNA origami, that exhibit templated reproduction. We can generate a small fraction of mutations by introducing a mismatch in hybridization between parent and daughter. We can modify the origami functionality to affect the growth rate of the mutated species, giving it less or more evolutionary advantage, and to become dominant in several generations. The introduction of mutations into an artificial self-replicating system provides new directions for research into self-assembly processes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Tetrahedral Zn 2+ doping LiNi 0.6 Mn 0.2 Co 0.2 O 2 improves discharge capacity retention by altering surface Ni valence during cycling and preventing oxygen evolution

5 mol-% Zn 2+ was added to the co-precipitation synthesis of LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) to understand Zn's effect on the structural and electronic properties of NMC622. Zn is determined to successfully dope into the NMC crystal lattice as there is an increase in d-spacing along the [003], [104], and [110] directions and an increase in molar volume (100.75 cm 3 mol -1 for NMC622 and 101.00 cm 3 mol -1 for Zn-NMC). Through XPS, Zn is determined to dope on the tetrahedral 6c Wyckoff site in the NMC structure and TEM-EDS reveals that despite a slight ZnO impurity phase, 1.4 mol-% Zn successfully dopes into the crystal structure. Furthermore, cyclic voltammetry shows a suppressed anodic wave associated with oxygen evolution and EIS demonstrates that Zn-doped NMC decreases charge transfer resistance and increases Li diffusion by an order of magnitude. After the formation cycles, NMC has a higher 1 C accessible capacity, 141 mAh/g, over Zn-NMC (132 mAh/g), but after long term cycling Zn-NMC has a higher accessible capacity (117 mAh/g compared to 96 mAh/g for NMC) and increases discharge capacity retention by 18% leading to longer cycle life.

Electrochemistry↗