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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Direct observations of shape fluctuation in long-time atomistic simulations of metallic nanoclusters

Metallic nanoclusters are functional materials whose unique physical and chemical properties are sensitively controlled by their shapes and structures. An in-depth understanding of their morphological stability is therefore of crucial importance. It has been well documented by transmission electron microscopy (TEM) studies that metallic nanoclusters can interconvert between different isomers. However, the relevant mechanisms remain elusive because the timescales of such shape fluctuations are too short to be resolved experimentally and yet too long for conventional atomistic simulations. By employing massively parallel accelerated molecular dynamics (AMD) simulations reaching timescales of milliseconds, here we provide a clear description of the dynamical processes leading to shape fluctuation in metallic nanoclusters of platinum, silver, copper, and gold at different sizes and temperatures. In all these materials, direct transformations between face-centered-cubic and fivefold symmetric structures (decahedron or icosahedron) are observed away from the melting point. These transitions occur following either a slip-mediated twinning mechanism or a surface-reconstruction driven process. The identified pathways are shown to be reversible, allowing for genuine shape fluctuation processes that do not involve melting or other external factors.

36 MATERIALS SCIENCE↗
NASA NTRS2014

In Situ Probe Science at Saturn

A fundamental goal of solar system exploration is to understand the origin of the solar sys-tem, the initial stages, conditions, and processes by which the solar system formed, how the formation pro-cess was initiated, and the nature of the interstellar seed material from which the solar system was born. Key to understanding solar system formation and subsequent dynamical and chemical evolution is the origin and evolution of the giant planets and their atmospheres. Several theories have been put forward to explain the process of solar system formation, and the origin and evolution of the giant planets and their atmospheres. Each theory offers quantifiable predictions of the abundances of noble gases He, Ne, Ar, Kr, and Xe, and abundances of key isotopic ratios 4He3He, DH, 15N14N, 18O16O, and 13C12C. Detection of certain dis-equilibrium species, diagnostic of deeper internal pro-cesses and dynamics of the atmosphere, would also help discriminate between competing theories. Measurements of the critical abundance profiles of these key constituents into the deeper well-mixed at-mosphere must be complemented by measurements of the profiles of atmospheric structure and dynamics at high vertical resolution and also require in situ explora-tion. The atmospheres of the giant planets can also serve as laboratories to better understand the atmospheric chem-istries, dynamics, processes, and climates on all planets including Earth, and offer a context and provide a ground truth for exoplanets and exoplanetary systems. Additionally, Giant planets have long been thought to play a critical role in the development of potentially habitable planetary systems. In the context of giant planet science provided by the Galileo, Juno, and Cassini missions to Jupiter and Sat-urn, a small, relatively shallow Saturn probe capable of measuring abundances and isotopic ratios of key at-mospheric constituents, and atmospheric structure in-cluding pressures, temperatures, dynamics, and cloud locations and properties not accessible by remote sens-ing can serve to test competing theories of solar system and giant planet origin, chemical, and dynamical evolution.

Interstellar↗
DOE OSTI2018

Anomalous Shape Evolution of Ag 2 O 2 Nanocrystals Modulated by Surface Adsorbates during Electron Beam Etching

An understanding of nanocrystal shape evolution is significant for the design, synthesis, and applications of nanocrystals with surface-enhanced properties such as catalysis or plasmonics. Surface adsorbates that are selectively attached to certain facets may strongly affect the atomic pathways of nanocrystal shape development. However, it is a great challenge to directly observe such dynamic processes in situ with a high spatial resolution. In this work, we report the anomalous shape evolution of Ag 2 O 2 nanocrystals modulated by the surface adsorbates of Ag clusters during electron beam etching, which is revealed through in situ transmission electron microscopy (TEM). In contrast to the Ag 2 O 2 nanocrystals without adsorbates, which display the near-equilibrium shape throughout the etching process, Ag 2 O 2 nanocrystals with Ag surface adsorbates show distinct facet development during etching by electron beam irradiation. Three stages of shape changes are observed: a sphere-to-a cube transformation, side etching of a cuboid, and bottom etching underneath the surface adsorbates. We find that the Ag adsorbates modify the Ag 2 O 2 nanocrystal surface configuration by selectively capping the junction between two neighboring facets. They prevent the edge atoms from being etched away and block the diffusion path of surface atoms. Finally, our findings provide critical insights into the modulatory function of surface adsorbates on the shape control of nanocrystals.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRSDate not supplied

Overview of Mars Sample Return – Earth Entry System Woven Roughness Heating Augmentation Test in NASA Langley’s Mach 6 Wind Tunnel

The Mars Sample Return Mission (MSR) is a planned NASA flagship mission in which a sample retrieval lander (SRL) with a rover will be flown to Mars to obtain sample tubes on the surface that were dropped by the Mars 2020 rover [1]. After obtaining the sam-ples, the rover will return and ascend back to Martian orbit onboard the Mars Ascent Vehicle (MAV). Upon return to Earth orbit, the samples will perform Entry, Descent, and Landing (EDL) with the Earth Entry Sys-tem (EES) architecture, and land in Utah. The EES vehicle will utilize a HEEET-variant as its TPS, which will be the first time a woven TPS will be used on a flagship NASA mission [2]. This TPS offers a unique challenge for Computational Fluid Dynamics (CFD) modeling of the aerothermal envi-ronment of the vehicle, as woven roughness heating augmentation has not been extensively investigated experimentally. As a result, in order to validate com-putational models for woven roughness heating aug-mentation, a wind tunnel test campaign at NASA Langley Research Center’s Mach 6 wind tunnel was performed in April of 2023. This test campaign consisted of over a hundred runs with Reynolds numbers spanning from 1-7 mil-lion 1/ft and with six separate wind tunnel models used. A second campaign with a suite of new models will be conducted in Summer 2023 as well as a cam-paign with a flat plate model, both of which are of great interest to the MSR-EES project. The data obtained from this test are extremely vital for the MSR mission, as they will validate CFD roughness heating models which will be directly used to design the TPS of the EES portion of MSR and characterize the heating environment that the entry ve-hicle will experience. Further extensions of the MSR-EES test campaign will continue to provide validation data for developing more effective computational tools.

Jonathan Cheatwood↗
DOE OSTI2020

3D Volumetric Structural Hierarchy Induced by Colloidal Polymerization of a Quantum-Dot Ionic Liquid Monomer Conjugate

Hierarchically structured emissive quantum dot (CdS/CdSe) poly(ionic liquid) composites are synthesized through colloidal polymerization within a lyotropic liquid crystal, yielding a solvent-responsive nanoparticle (NP) composite possessing four ordered structural motifs. The composite is prepared by coassembling an amphiphilic ionic liquid (IL) monomer, 3-decyl-1-vinylimidazolium chloride, [C 10 VIm + ][Cl - ], and IL monomer, 3-(10-mercaptodecyl)-1-vinylimidazolium bromide surface-functionalized quantum dots, QD-[SC 10 VIm + ][Br - ], in 30 wt % water. Photo (UV)-initiated free radical polymerization serves to form a colloidal copolymer that collimates pairs of QDs within the core of large cylinders (average diameter = 21 nm and length = 422 nm), as evidenced by ultrasmall-angle X-ray scattering (USAXS). As revealed by continuous wave terahertz multispectral reconstructive 3-D imaging, the subsurface structure along the cylinder axis undergoes dynamic rearrangement between 2D hexagonal and cubic packing. The polymerized ionic liquid sheath surrounding the QDs is composed of concentric hexagonally perforated lamellae (HPL) with an interlamellar repeat distance of 3 nm, as determined by small-angle X-ray scattering (SAXS). The encapsulated QDs retain crystallinity (TEM and WAXS) and emission characteristics (photoluminescence spectroscopy, lambda(EM) = 638 nm). Phenomenological time-dependent Ginzburg-Landau calculations verify the mesoscale cylinders arise from the topological constraints imposed by the in-plane perforations of the polymerized ionic liquid as it wraps around the hard (unmalleable) spherical QDs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Microstructure and mechanical properties of pure copper wire produced by shear assisted processing and extrusion

Shear assisted processing and extrusion (ShAPE) process can consolidate powdered materials and simultaneously extrude wire or tube with improved properties. We successfully produced copper wire extrusions from powder and solid materials for the first time. The extrusion pressure of ShAPE process is at least two times less than that required for conventional extrusion. We used optical microscopy to inspect and validate the integrity of extrudates. It shows that the microstructure was refined and dynamically recrystallized to equiaxial grains. Compared to the annealed copper wire, ShAPE processed wire has 80% higher yield strength, 15% higher ultimate tensile strength and 20% higher ductility. These were correlated with refined grain size and sub-structuring observed via electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM).

Copper, Wire, Shear Assisted Processing and Extrus↗
DOE OSTI2024

Effect of Solvent Composition on Non-DLVO Forces and Oriented Attachment of Zinc Oxide Nanoparticles

Oriented attachment (OA) occurs when nanoparticles in solution align their crystallographic axes prior to colliding and subsequently fuse into single crystals. Traditional colloidal theories such as DLVO provide a framework for evaluating OA but fail to capture key particle interactions due to the atomistic details of both the crystal structure and the interfacial solution structure. Using zinc oxide as a model system, we investigated the effect of the solvent on short-ranged and long-ranged particle interactions and the resulting OA mechanism. In situ TEM imaging showed that ZnO nanocrystals in toluene undergo long-range attraction comparable to 1kT at separations of 10 nm and 3kT near particle contact. These observations were rationalized by considering non-DLVO interactions, namely dipole-dipole forces and torques between the polar ZnO nanocrystals. Langevin dynamics simulations showed stronger interactions in toluene compared to methanol solvents, consistent with the experimental results. Concurrently, we performed atomic force microscopy measurements using ZnO-coated probes for the short-ranged interaction. Our data provided valuable insights into another type of non-DLVO interaction, namely the repulsive solvation force. Specifically, the solvation force was stronger in water compared to ethanol and methanol, due to the stronger hydrogen bonding and denser packing of water molecules at the interface. In conclusion, our results highlight the importance of non-DLVO forces in a general framework for understanding and predicting particle aggregation and attachment.

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

Radioactive Material Inventory Optimization Using the Plutonium-239 Equivalent Curie Methodology

ABSTRACT The purpose of this paper is to provide the technical basis for application of the Plutonium 239 equivalent curies (PEC) concept used to optimize and limit the material-at-risk (MAR) in the Irradiated Materials Characterization Laboratory (IMCL) located at the Materials and Fuels Complex (MFC). The PEC concept offers a method to normalize all radionuclides to a common radiotoxic hazard index that can be summed to a single value. This paper describes the technical approach to applying the PEC concept, documents the weighting factors and specific activities to be utilized in the calculation, and provides an example of the application of the concept to a radionuclide distribution that is representative of materials encountered in the IMCL. The IMCL is operated to provide a dynamic, re-configurable capability to analyze and characterize irradiated or non-irradiated radioactive material samples. The operations unique to the IMCL include sample storage, preparation, and analysis using experiment-specific instrumentation such as, Electron probe micro-analyzer (EPMA), Focused ion beam (FIB), Transmission electron microscope (TEM), and Scanning electron microscope (SEM). The methodology used to characterize the radioactive material inventory enables the IMCL to operate in such a way that complements their capability and program goals without compromising the safety of the worker, co-located worker, or the general public. The PEC concept offers a method in which all radionuclide inventory is normalized to a common radiotoxic hazard index that can be summed to a single value. The PEC concept is useful in the comparison of various material types for hazard categorization and for identifying worst-case and bounding inventory.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2020

Shape-Shifting Peptide Nanomaterials: Surface Asymmetry Enables pH-Dependent Formation and Interconversion of Collagen Tubes and Sheets

The fabrication of dynamic, transformable biomaterials that respond to environmental cues represents a significant step forward in the development of synthetic materials that rival their highly functional, natural counterparts. In this work, we describe the design and synthesis of crystalline supramolecular architectures from charge-complementary heteromeric pairs of collagen-mimetic peptides (CMPs). Under appropriate conditions, CMP pairs spontaneously assemble into either 1D ultraporous (pore diameter >100 nm) tubes or 2D bilayer nanosheets due to the structural asymmetry that arises from heteromeric self-association. Crystalline collagen tubes represent a heretofore unobserved morphology of this common biomaterial. In-depth structural characterization from a suite of biophysical methods, including TEM, AFM, high-resolution cryo-EM, and SAXS/WAXS measurements, reveals that the sheet and tube assemblies possess a similar underlying lattice structure. The experimental evidence suggests that the tubular structures are a consequence of the self-scrolling of incipient 2D layers of collagen triple helices and that the scrolling direction determines the formation of two distinct structural isoforms. Furthermore, we show that nanosheets and tubes can spontaneously interconvert through manipulation of the assembly pH and systematic adjustment of the CMP sequence. Altogether, we establish initial guidelines for the construction of dynamically responsive 1D and 2D assemblies that undergo a structurally programmed morphological transition.

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

AC/AB Stacking Boundaries in Bilayer Graphene

Boundaries, including phase boundaries, grain boundaries, and domain boundaries, are known to have an important influence on material properties. Here, dark-field (DF) transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) imaging are combined to provide a full view of boundaries between AB and AC stacking domains in bilayer graphene across length scales from discrete atoms to the macroscopic continuum. Combining the images with results obtained by density functional theory (DFT) and classical molecular dynamics calculations, we demonstrate that the AB/AC stacking boundaries in bilayer graphene are nanometer-wide strained channels, mostly in the form of ripples, producing smooth low-energy transitions between the two different stackings. Our results provide a new understanding of the novel stacking boundaries in bilayer graphene, which may be applied to other layered two-dimensional materials as well.

Lin, Junhao↗
DOE OSTI2023

Dielectrics Under Extreme Electric Fields: In Situ Studies on Nanoscale Mechanisms (Final Technical Report)

The lack of materials that can function reliably under extreme electric fields is a critical roadblock to achieving higher energy efficiency and extended service lifetime of devices in electricity generation, transmission, and consumption. Materials typically fail at two or three orders of magnitude below their theoretical dielectric breakdown strength. Identifying the origins of premature dielectric breakdown using state-of-the-art characterization tools will, therefore, enable the design and discovery of transformational materials capable of approaching their intrinsic limits. The vast improvement in the resolution power of imaging tools, combined with the recently developed in situ electric biasing technique, has made high resolution observations of dielectric breakdown as it happens possible. The overall goal of the project is to directly image the dynamic processes of defect formation, accumulation, and interaction with preexisting defects (e.g., dislocations, domain walls, and grain boundaries in crystalline dielectric films) under electric fields up to 1,000 MV/m with a temporal resolution better than 5 microseconds. Using the newly acquired, custom-made Hysitron PI95 transmission electron microscopy (TEM) specimen holder, in situ TEM observations of breakdown at the sub nanometer resolution will be made on representative dielectric compounds with progressive complexities: the linear dielectric SiO 2 , CuO, and TiO 2 , the ferroelectric BaTiO 3 nanocrystals and nanocubes. Through direct observation of the breakdown event at high spatial and temporal resolutions, the nanoscale mechanisms for the failure of dielectrics under intense electric fields will be identified. The results of the project will be applied to the design and processing of new dielectric materials with higher efficiency, improved reliability, and a prolonged lifetime. Such new dielectrics are urgently needed for modernizing energy infrastructures.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Assessing dynamic vegetation model parameter uncertainty across Alaskan arctic tundra plant communities

Abstract As the Arctic region moves into uncharted territory under a warming climate, it is important to refine the terrestrial biosphere models (TBMs) that help us understand and predict change. One fundamental uncertainty in TBMs relates to model parameters, configuration variables internal to the model whose value can be estimated from data. We incorporate a version of the Terrestrial Ecosystem Model (TEM) developed for arctic ecosystems into the Predictive Ecosystem Analyzer (PEcAn) framework. PEcAn treats model parameters as probability distributions, estimates parameters based on a synthesis of available field data, and then quantifies both model sensitivity and uncertainty to a given parameter or suite of parameters. We examined how variation in 21 parameters in the equation for gross primary production influenced model sensitivity and uncertainty in terms of two carbon fluxes (net primary productivity and heterotrophic respiration) and two carbon (C) pools (vegetation C and soil C). We set up different parameterizations of TEM across a range of tundra types (tussock tundra, heath tundra, wet sedge tundra, and shrub tundra) in northern Alaska, along a latitudinal transect extending from the coastal plain near Utqiaġvik to the southern foothills of the Brooks Range, to the Seward Peninsula. TEM was most sensitive to parameters related to the temperature regulation of photosynthesis. Model uncertainty was mostly due to parameters related to leaf area, temperature regulation of photosynthesis, and the stomatal responses to ambient light conditions. Our analysis also showed that sensitivity and uncertainty to a given parameter varied spatially. At some sites, model sensitivity and uncertainty tended to be connected to a wider range of parameters, underlining the importance of assessing tundra community processes across environmental gradients or geographic locations. Generally, across sites, the flux of net primary productivity (NPP) and pool of vegetation C had about equal uncertainty, while heterotrophic respiration had higher uncertainty than the pool of soil C. Our study illustrates the complexity inherent in evaluating parameter uncertainty across highly heterogeneous arctic tundra plant communities. It also provides a framework for iteratively testing how newly collected field data related to key parameters may result in more effective forecasting of Arctic change.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Revealing High-Temperature Reduction Dynamics of High-Entropy Alloy Nanoparticles via In Situ Transmission Electron Microscopy

Understanding the behavior of high-entropy alloy (HEA) materials under hydrogen (H 2 ) environment is of utmost importance for their promising applications in structural materials, catalysis, and energy-related reactions. Herein, the reduction behavior of oxidized FeCoNiCuPt HEA nanoparticles (NPs) in atmospheric pressure H-2 environment was investigated by in situ gas-cell transmission electron microscopy (TEM). The reduction reaction front was maintained at the external surface of the oxide. During reduction, the oxide layer expanded and transformed into porous structures where oxidized Cu was fully reduced to Cu NPs while Fe, Co, and Ni remained in the oxidized form. In situ chemical analysis showed that the expansion of the oxide layer resulted from the outward diffusion flux of all transition metals (Fe, Co, Ni, Cu). Revealing the H-2 reduction behavior of HEA NPs facilitates the development of advanced multicomponent alloys for applications targeting H 2 formation and storage, catalytic hydrogenation, and corrosion removal.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

A reactive wetting strategy improves lithium metal reversibility

The cycling of lithium metal (Li 0 ) anode is often accompanied by irregular lithium plating/stripping, leading to poor Li 0 reversibility, and posing a grand challenge to constructing reliable Li 0 batteries. Hereby, we report a reactive wetting strategy to enable conformal and highly reversible Li 0 plating/stripping through a lithium-reactive substrate. In this study, the reactive wetting, smooth nucleation, and conformal growth behaviors of Li 0 are visualized through in-situ transmission electron microscopy, ex-situ scanning electron microscope, and in-situ optical microscope characterizations. Based on the reactive wetting substrate, high average Coulombic efficiencies (99.0% at 0.5 mA cm -2 for 400 cycles) are realized for Li 0 anodes. By pre-plating Li 0 into the reactive wetting substrate as anodes and leveraging LiFePO 4 as cathodes, high capacity retention (76.0% after 200 cycles in low N/P ratio conditions) is also achieved in the as-constructed Li 0 full cells. This work establishes a fundamental understanding of reactive wetting dynamics of Li 0 and provides a drop-in solution to improving Li 0 reversibility.

25 ENERGY STORAGE↗
DOE OSTI2026

In Situ EXAFS Study of Mo–P Bond Dynamics in Molybdenum Phosphide during CO 2 Reduction and Hydrogen Evolution

Transition Metal Phosphides (TMPs) are widely studied as catalysts in reactions like hydrogen evolution, oxygen reduction, and hydrodesulfurization. TMPs have demonstrated remarkable efficiency in accelerating reactions by providing active sites for adsorption and facilitating the transformation of reaction intermediates, a feature that has increased the interest of TMPs in the electrochemical carbon dioxide reduction reaction (eCO 2 RR). Despite their growing use, the potential-dependent structural behavior of TMPs under operating electrochemical conditions remains insufficiently understood. This work investigates the dynamics of the Mo−P bond during eCO 2 RR and hydrogen evolution reaction (HER) using in situ extended X-ray absorption spectroscopy (EXAFS) studies at the Mo−K edge. Structural characterization of the synthesized MoP nanoparticles was performed by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results of the overall electrochemical activity of MoP are presented through linear sweep voltammetry (LSV) experiments in the potential range of 0 to −1.5 V versus Ag/AgCl and chronoamperometry (CA). Liquid products were analyzed by 1 H NMR spectroscopy. The synthesized catalyst showed increasing activity with the highest Faradaic efficiency of 11.75% for C 2+ products at −1.3 V vs Ag/AgCl. In situ EXAFS revealed a change in the average Mo−P bond distance during eCO 2 RR, whereas no such change was observed during the hydrogen evolution reaction (HER). This finding suggests that phosphorus, particularly through modulation of the Mo−P bond length, plays an important role in the eCO 2 RR and demonstrates how in situ EXAFS can track local structural perturbations in MoP catalysts during electrochemical operation, providing complementary structural insight that correlates with electrochemical behavior.

Catalysts↗
DOE OSTI2024

Probing ferroelectric domain structures and their switching dynamics in SrBi2Ta2O9 by in-situ electric biasing in transmission electron microscopy

Abstract Lead-free SrBi 2 Ta 2 O 9 (SBT) has been a promising ferroelectric material for various applications such as electronics and data storage due to its outstanding ferroelectric properties including high fatigue endurance and low leakage current. However, the atomic-scale domain structure and switching dynamics of ferroelectric SBT remain elusive. This study reveals that spontaneous polarization arises from canted bismuth-cation displacements, forming 90° and Ising-type 180° domain walls. Interestingly, topological pairs of ferroelectric vortex and antivortex connect ferroelectric boundaries where three domain walls converge. In situ electrical biasing transmission electron microscopy (TEM) reveals the dominance of 180° switching over 90°, where oxygen octahedral connectivity is protected by ferroelastic energy in the 90° domain wall. Consequently, all 180° domain walls and (anti)vortices are removed, leaving only 90° domain walls in the electrically poled states. Chemical deterioration along domain walls highlights vulnerability of SBT to ferroelectric fatigue. This study provides insight into crucial aspects for practical applications of SBT.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Achieving Grain Refinement and Related Mechanical Property Improvement of an Al-Zn-Mg-Cu Alloy Through Severe Plastic Deformation

Microstructural features and mechanical properties of an Al-Zn-Mg-Cu alloy processed by equal-channel angular pressing (ECAP) have been investigated. The equivalent plastic strain obtained from the simulation agrees well with that from the analytical calculation in a way that both increase with an increase in deformation, but the strain distribution is non-uniform, appearing as a strain gradient along the norm direction. Microstructure investigation shows that grain refinement is achieved in frequency of low-angle grain boundaries fabricated by ECAP. The pole density is reduced by ECAP, during which the Brass and Goss type textures are introduced. TEM results show chain-like recrystallized grains formed at the grain boundaries and broken second-phase particles come into being due to the heavy shear force. After ECAP, the hardness and strength increase significantly while the elongation is reduced. Besides, an extreme strengthening is confirmed because of the balance between dynamic hardening and softening. The microstructure evolution mechanism is revealed in terms of grain refinement, precipitate phase breakage and texture evolution.

36 MATERIALS SCIENCE↗