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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Zinc Adsorption and Hydration Structures at Yttria-Stabilized Zirconia Surfaces

Zinc adsorption and interfacial hydration on yttria-stabilized zirconia (YSZ) surfaces in contact with aqueous zinc solutions at room temperature and neutral pH have been probed, with combined specular high-resolution X-ray reflectivity and element-specific (Zn) resonant anomalous X-ray reflectivity techniques. The total and partial zinc-Specific electron density profiles in the surface normal direction show the detailed interfacial hydration structures with zinc adsorption: Strongly depending on its crystallographic orientations, the YSZ (110) surface adsorbs zinc species only within adsorbed water layers above the terminal plane, while on (111) surface, zinc further-penetrates the substrate (below the terminal plane). Considering that both surfaces are enriched with oxygen vacancies and metal-depleted sites; on which chemisorbed water species are expected, the observed contrast indicates that specific zinc adsorption is controlled strongly by the intrinsic surface chemistry that results from orientation-dependent interfacial structures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Relationships between Water’s Structure and Solute Affinity at Polypeptoid Brush Surfaces

Excellent antifouling surfaces are generally thought to create a tightly bound layer of water that resists solute adsorption, and highly hydrophilic surfaces such as those with zwitterionic functionalities are of significant current interest as antifoulant strategies. Furthermore, despite significant proofs-of-concept, we still lack a fundamental understanding of how the nanoscopic structure of this hydration layer translates to reduced fouling, how surface chemistry can be tuned to achieve antifouling through hydration water, and why, in particular, zwitterionic surfaces seem so promising. Here, we use molecular dynamics simulations and free energy calculations to investigate the molecular relationships among surface chemistry, hydration water structure, and surface–solute affinity across a variety of surface-decorated chemistries. Specifically, we consider polypeptoid-decorated surfaces that display well-known experimental antifouling capabilities and that can be synthesized sequence specifically, with precise backbone positioning of, e.g., charged groups. Through simulations, we calculate the affinities of a range of small solutes to polypeptoid brush surfaces of varied side-chain chemistries. We then demonstrate that measures of the structure of surface hydration water in response to a particular surface chemistry signal solute–surface affinity; specifically, we find that zwitterionic chemistries produce solute–surface repulsion through highly coordinated hydration water while suppressing tetrahedral structuring around the solute, in contrast to uncharged surfaces that show solute–surface affinity. Based on the relationship of this structural perturbation to the affinity of small-molecule solutes, we propose a molecular mechanism by which zwitterionic surface chemistries enhance solute repulsion, with broader implications for the design of antifouling surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Solvent–Adsorbate Interactions and Adsorbate-Specific Solvent Structure in Carbon Dioxide Reduction on a Stepped Cu Surface

In this work, the structure of water and its interactions with various carbon dioxide reduction intermediates adsorbed on a Cu(211) surface is investigated using density functional theory. We find that the presence of adsorbates has a significant and adsorbate-specific effect on the local water structure and that solvation can stabilize adsorbate conformations different from those found in vacuum. We describe relationships between the hydrogen bonding capability of an adsorbate, the dipole moment of the adsorbate, the energetic strength of water–adsorbate interactions, and the change induced in the local water orientation by the adsorbate. Mechanistic implications are discussed. Here, we investigate and quantify the error associated with using arbitrary locally optimized solvent structures in calculations of relevant physical quantities, such as solvated binding energies and work functions. Possible effects of thermal motion on calculations of the work function are investigated using ab initio molecular dynamics.

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

Tuning the electrocatalytic activity of Pt by structurally ordered PdFe/C for the hydrogen oxidation reaction in alkaline media

Tuning the hydrogen adsorption energy (E H ) by controlling the surface electronic structure of Pt is essential for enhancing the hydrogen oxidation reaction (HOR) performance in alkaline media. This could be achieved by forming a Pt skin on PdFe/C nanoparticles with structurally ordered intermetallic (O-PdFe@Pt/C) or disordered alloy (D-PdFe@Pt/C). The HOR activity on O-PdFe@Pt/C exhibits an exchange current density of 1.49 A mg Pt -1 , which is 3.87 and 7.56 times higher than that on D-PdFe@Pt/C (0.385 A mg Pt -1 ) and Pt/C (0.197 A mg Pt -1 ), respectively. The excellent electrocatalytic HOR performance on O-PdFe@Pt/C can be ascribed to the attenuation of E H on the Pt shell induced by the structurally ordered PdFe core, where the E H on O-PdFe@Pt surface is 0.18 eV smaller than that on Pt according to DFT calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Tuning the Outward to Inward Swelling in Lithiated Silicon Nanotubes via Surface Oxide Coating

The electrochemically-induced mechanical degradation hinders the application of Si anodes in advanced lithium-ion batteries. Hollow structures and surface coatings have been often used to mitigate the degradation of Si-based anodes. However, the structural change and degradation mechanism during lithiation/delithiation of hollow Si structures with coatings remain unclear. Here, we combine in situ TEM experiment and chemomechanical modeling to study the electrochemically induced swelling of amorphous-Si (a-Si) nanotubes with different thicknesses of surface SiOx layers. Surprisingly, we find that no inward expansion occurs at the inner surface during lithiation of a-Si nanotubes with native oxides. In contrast, inward expansion can be induced by increasing the thickness of SiOx on the outer surface. Moreover, both the sandwich lithiation mechanism and two-stage lithiation process in a-Si nanotubes remain unchanged with the increasing thickness of surface coatings. Our chemomechanical modeling reveals the mechanical confinement effects in lithiated a-Si nanotubes with and without SiOx coatings. This work not only provides insights into the degradation of nanotube anodes with surface coatings, but also sheds light onto the optimal design of hollow anodes for high-performance lithium-ion batteries.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2024

Small, solubilized platinum nanocrystals consist of an ordered core surrounded by mobile surface atoms

In situ structures of Platinum (Pt) nanoparticles (NPs) can be determined with graphene liquid cell transmission electron microscopy. Atomic-scale three-dimensional structural information about their physiochemical properties in solution is critical for understanding their chemical function. We here analyze eight atomic-resolution maps of small (<3 nm) colloidal Pt NPs. Their structures are composed of an ordered crystalline core surrounded by surface atoms with comparatively high mobility. 3D reconstructions calculated from cumulative doses of 8500 and 17,000 electrons/pixel, respectively, are characterized in terms of loss of atomic densities and atomic displacements. Less than 5% of the total number of atoms are lost due to dissolution or knock-on damage in five of the structures analyzed, whereas 10–16% are lost in the remaining three. Less than 5% of the atomic positions are displaced due to the increased electron irradiation in all structures. The surface dynamics will play a critical role in the diverse catalytic function of Pt NPs and must be considered in efforts to model Pt NP function computationally.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Method of assembling a thermal expansion compensator

A thermal expansion compensator is provided and includes a first electrode structure having a first surface, a second electrode structure having a second surface facing the first surface and an elastic element bonded to the first and second surfaces and including a conductive element by which the first and second electrode structures electrically and/or thermally communicate, the conductive element having a length that is not substantially longer than a distance between the first and second surfaces.

Determan, William↗
DOE OSTI2015

Role of crystallographic anisotropy in the formation of surface layers of single NiTi crystals after ion-plasma alloying

The structure of the surface and near-surface layers of single crystals of NiTi, differently oriented relative to the direction of ion beam treatment was investigated. The role of the crystallographic orientation in formation of structure of surface layers after ion-plasma alloying was revealed. It was found that the orientation effects of selective sputtering and channeling determine the thickness of the oxide and amorphous layers, the depth of penetration of ions and impurities, the distribution of Ni with depth.

36 MATERIALS SCIENCE↗
NASA NTRS2007

Integral Radiator and Storage Tank

A simplified, lightweight system for dissipating heat of a regenerative fuel- cell system would include a heat pipe with its evaporator end placed at the heat source and its condenser end integrated into the wall of the regenerative fuel cell system gas-storage tanks. The tank walls act as heat-radiating surfaces for cooling the regenerative fuel cell system. The system was conceived for use in outer space, where radiation is the only physical mechanism available for transferring heat to the environment. The system could also be adapted for use on propellant tanks or other large-surface-area structures to convert them to space heat-radiating structures. Typically for a regenerative fuel cell system, the radiator is separate from the gas-storage tanks. By using each tank s surface as a heat-radiating surface, the need for a separate, potentially massive radiator structure is eliminated. In addition to the mass savings, overall volume is reduced because a more compact packaging scheme is possible. The underlying tank wall structure provides ample support for heat pipes that help to distribute the heat over the entire tank surface. The heat pipes are attached to the outer surface of each gas-storage tank by use of a high-thermal conductance, carbon-fiber composite-material wrap. Through proper choice of the composite layup, it is possible to exploit the high longitudinal conductivity of the carbon fibers (greater than the thermal conductivity of copper) to minimize the unevenness of the temperature distribution over the tank surface, thereby helping to maximize the overall heat-transfer efficiency. In a prototype of the system, the heat pipe and the composite wrap contribute an average mass of 340 g/sq m of radiator area. Lightweight space radiator panels have a mass of about 3,000 g/sq m of radiator area, so this technique saves almost 90 percent of the mass of separate radiator panels. In tests, the modified surface of the tank was found to have an emissivity of 0.85. The composite wrap remained tightly bound to the surface of the tank throughout the testing in thermal vacuum conditions.

Burke, Kenneth A.↗
DOE OSTI2015

Effect of chlorination on the TlBr band edges for improved room temperature radiation detectors: Effect of chlorination on the TlBr band edges for radiation detectors

Thallium bromide (TlBr) crystals subjected to hydrochloric acid (HCl) chemical treatments have been shown to advantageously affect device performance and longevity in TlBr-based room temperature radiation detectors, yet the exact mechanisms of the improvements remain poorly understood. Here in this paper, we investigate the influence of several HCl chemical treatments on device-grade TlBr and describe the changes in the composition and electronic structure of the surface. Composition analysis and depth profiles obtained from secondary ion mass spectrometry (SIMS) identify the extent to which each HCl etch condition affects the detector surface region and forms of a graded TlBr/TlBr 1-x CL x surface heterojunction. Using a combination of X-ray photoemission spectroscopy (XPS) and hybrid density functional calculations, we are able to determine the valence band offsets, band gaps, and conduction band offsets as a function of Cl content over the entire composition range of TIBr 1-x C1 X . This study establishes a strong correlation between device process conditions, surface chemistry, and electronic structure with the goal of further optimizing the long-term stability and radiation response of TlBr-based detectors.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Existence of electron and hole pockets and partial gap opening in the correlated semimetal Ca 3 Ru 2 O 7

The electronic band structure of correlated Ca 3 Ru 2 O 7 featuring an antiferromagnetic (AFM) as well as a structural transition has been determined theoretically at high temperatures, which has led to the understanding of the remarkable properties of Ca 3 Ru 2 O 7 , such as the bulk spin-valve effects. However, its band structure and Fermi surface (FS) below the structural transition have not been resolved, even though a FS consisting of electron pockets was found experimentally. Here we report magnetoelectrical transport and thermoelectric measurements with the electric current and temperature gradient directed along the a and b axes, respectively, of an untwined single crystal of Ca 3 Ru 2 O 7 . The thermopowers obtained along the two crystal axes were found to show opposite signs at low temperatures, demonstrating the presence of both electron and hole pockets on the FS. In addition, how the FS evolves across T* = 30K at which a distinct transition from coherent to incoherent behavior occurs was also inferred: the Hall and Nernst coefficient results suggest a temperature- and momentum-dependent partial gap opening in Ca 3 Ru 2 O 7 below the structural transition with a possible Lifshitz transition occurring at T*. In conclusion, the experimental demonstration of a correlated semimetal ground state in Ca 3 Ru 2 O 7 calls for further theoretical studies of this remarkable material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2009

Fiber Optic Thermal Health Monitoring of Aerospace Structures and Materials

A new technique is presented for thermographic detection of flaws in materials and structures by performing temperature measurements with fiber Bragg gratings. Individual optical fibers with multiple Bragg gratings employed as surface temperature sensors were bonded to the surfaces of structures with subsurface defects or thickness variations. Both during and following the application of a thermal heat flux to the surface, the individual Bragg grating sensors measured the temporal and spatial temperature variations. The investigated structures included a 10-ply composite specimen with subsurface delaminations of various sizes and depths. The data obtained from grating sensors were further analyzed with thermal modeling to reveal particular characteristics of the interested areas. These results were found to be consistent with those from conventional thermography techniques. Limitations of the technique were investigated using both experimental and numerical simulation techniques. Methods for performing in-situ structural health monitoring are discussed.

Wu, Meng-Chou↗
DOE OSTI2014

A search for planetary Nebulae with the Sloan digital sky survey: the outer regions of M31

We have developed a method to identify planetary nebula (PN) candidates in imaging data of the Sloan Digital Sky Survey (SDSS). This method exploits the SDSS's five-band sampling of emission lines in PN spectra, which results in a color signature distinct from that of other sources. Selection criteria based on this signature can be applied to nearby galaxies in which PNe appear as point sources. We applied these criteria to the whole area of M31 as scanned by the SDSS, selecting 167 PN candidates that are located in the outer regions of M31. The spectra of 80 selected candidates were then observed with the 2.2 m telescope at Calar Alto Observatory. These observations and cross-checks with literature data show that our method has a selection rate efficiency of about 90%, but the efficiency is different for the different groups of PN candidates. In the outer regions of M31, PNe trace different well-known morphological features like the Northern Spur, the NGC 205 Loop, the G1 Clump, etc. In general, the distribution of PNe in the outer region 8 < R < 20 kpc along the minor axis shows the {sup e}xtended disk{sup —}a rotationally supported low surface brightness structure with an exponential scale length of 3.21 ± 0.14 kpc and a total mass of ∼10{sup 10} M {sub ☉}, which is equivalent to the mass of M33. We report the discovery of three PN candidates with projected locations in the center of Andromeda NE, a very low surface brightness giant stellar structure in the outer halo of M31. Two of the PNe were spectroscopically confirmed as genuine PNe. These two PNe are located at projected distances along the major axis of ∼48 Kpc and ∼41 Kpc from the center of M31 and are the most distant PNe in M31 found up to now. With the new PN data at hand we see the obvious kinematic connection between the continuation of the Giant Stream and the Northern Spur. We suggest that 20%-30% of the stars in the Northern Spur area may belong to the Giant Stream. In our data we also see a possible kinematic connection between the Giant Stream and PNe in Andromeda NE, suggesting that Andromeda NE could be the core or remnant of the Giant Stream. Using PN data we estimate the total mass of the Giant Stream progenitor to be ≈10{sup 9} M {sub ☉}. About 90% of its stars appear to have been lost during the interaction with M31.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Study of the Structural Properties of Silicon-on-Sapphire Layers in Hydride-Chloride Vapor-Phase Epitaxy

The surface of silicon-on-sapphire (SOS) epitaxial layers is studied by atomic-force microscopy and the UV (ultraviolet) scattering method. X-Ray diffraction analysis of the SOS layers is carried out. The silicon-sapphire transition region is studied by the photovoltage method. The problem of the accumulation of by-products formed during the synthesis of silicon from monosilane is considered and experimentally confirmed. It is found that the addition of chlorine-containing reagents to the epitaxial process makes it possible to exclude the influence exerted by these products on the growing layer and also to modify the surface microprofile. Analysis of the surface and structure of the SOS layers demonstrates that film growth occurs by the Stranski–Krastanov mechanism. It is shown that a combined method in which a 30–60-nm-thick SOS layer is preliminarily grown from pure SiH{sub 4} and then a layer is additionally grown at a 2SiH{sub 4}:1SiC1{sub 4} ratio of gas component flow rates is the most preferable method for the fabrication of SOS structures with layer thicknesses of 300 nm and more.

36 MATERIALS SCIENCE↗