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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

High‐Resolution Electron Tomography of Ultrathin Boerdijk–Coxeter–Bernal Nanowire Enabled by Superthin Metal Surface Coating

Abstract The rapid advancement of transmission electron microscopy has resulted in revolutions in a variety of fields, including physics, chemistry, and materials science. With single‐atom resolution, 3D information of each atom in nanoparticles is revealed, while 4D electron tomography is shown to capture the atomic structural kinetics in metal nanoparticles after phase transformation. Quantitative measurements of physical and chemical properties such as chemical coordination, defects, dislocation, and local strain have been made. However, due to the incompatibility of high dose rate with other ultrathin morphologies, such as nanowires, atomic electron tomography has been primarily limited to quasi‐spherical nanoparticles. Herein, the 3D atomic structure of a complex core–shell nanowire composed of an ultrathin Boerdijk–Coxeter–Bernal (BCB) core nanowire and a noble metal thin layer shell deposited on the BCB nanowire surface is discovered. Furthermore, it is demonstrated that a new superthin noble metal layer deposition on an ultrathin BCB nanowire could mitigate electron beam damage using an in situ transmission electron microscope and atomic resolution electron tomography. The colloidal coating method developed for electron tomography can be broadly applied to protect the ultrathin nanomaterials from electron beam damage, benefiting both the advanced material characterizations and enabling fundamental in situ mechanistic studies.

Song, Xiaohui↗
NASA NTRS1985

Protective coatings of metal surfaces by cold plasma treatment

The cold plasma techniques for deposition of various types of protective coatings are reviewed. The main advantage of these techniques for deposition of ceramic films is the lower process temperature, which enables heat treating of the metal prior to deposition. In the field of surface hardening of steel, significant reduction of treatment time and energy consumption were obtained. A simple model for the plasma - surface reactions in a cold plasma system is presented, and the plasma deposition techniques are discussed in view of this model.

Manory, R.↗
DOE OSTI2022

Plasmon-Assisted Direct Interfacial Charge Transfer Enables Molecular Photodissociation on Metal Surfaces

Plasmonic photocatalysis is promising for driving reactions out of equilibrium, leading to enhanced rates and selectivity, but the energy and charge transfer mechanism at the interface remains to be explored. Here, we revisit visible-light plasmon-assisted photodissociation of dimethyl disulfide molecules (S–S bond cleavage) over single-crystalline silver and copper surfaces, using density functional theory calculations and the delta self-consistent field method. We investigate different excitation mechanisms and show that the direct intramolecular excitations, as suggested earlier to explain the experimental findings, cannot address the observed catalytic bond activation. Instead, the calculated excitations mediated by the metal Fermi level agree well with the threshold energy and maximum-yield energy in experiments and suggest that the reaction follows a direct interfacial charge transfer mechanism. Furthermore, we show that the excitation energy and the charge transfer can be modulated by introducing excess charges in the systems. Here, this study thus provides a fundamental understanding of interfacial charge transfer for driving plasmonic photocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Size matters: altering the metal-surface coordination in micropores via structural confinement effects

Solid-state NMR experiments were used to investigate the dynamics of supported complexes grafted to a series of silica gel materials of varied pore sizes. Through dipolar recoupling measurements, we found that ligand dynamics were impeded in the more confined environments, as would be expected. A new form of motion involving the complex as a whole, however, appeared in the most restricted environment consisting of 22 Å diameter pores. These motions persisted down to –100 °C at which point the ligands were frozen on the NMR timescale. The newly observed dynamics could only result from the breaking of secondary dative metal–siloxane interactions that otherwise lock the complex in a preferred orientation on the surface. Crucially, these results show that confinement effects alone can be sufficient to reduce a grafted metal's effective coordination number in direct analogy to the synthesis of undercoordinated complexes using bulky ligands. Finally, this finding could have important implications in the synthesis of more active heterogeneous catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

First-principles calculations of metal surfaces. II. Properties of low-index platinum surfaces toward understanding electron emission

The stability of low-index platinum surfaces and their electronic properties is investigated with density functional theory, toward the goal of understanding the surface structure and electron emission, and identifying precursors to electrical breakdown, on nonideal platinum surfaces. Propensity for electron emission can be related to a local work function, which, in turn, is intimately dependent on the local surface structure. The (1×N) missing row reconstruction of the Pt(110) surface is systematically examined. The (1×3) missing row reconstruction is found to be the lowest in energy, with the (1×2) and (1×4) slightly less stable. In the limit of large (1×N) with wider (111) nanoterraces, the energy accurately approaches the asymptotic limit of the infinite Pt(111) surface. Furthermore, this suggests a local energetic stability of narrow (111) nanoterraces on free Pt surfaces that could be a common structural feature in the complex surface morphologies, leading to work functions consistent with those on thermally grown Pt substrates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Electrochemical deposition of N-heterocyclic carbene monolayers on metal surfaces

N-heterocyclic carbenes (NHCs) have been widely utilized for the formation of self-assembled monolayers (SAMs) on various surfaces. The main methodologies for preparation of NHCs-based SAMs either requires inert atmosphere and strong base for deprotonation of imidazolium precursors or the use of specifically-synthesized precursors such as NHC(H)[HCO 3 ] salts or NHC–CO 2 adducts. Herein, we demonstrate an electrochemical approach for surface-anchoring of NHCs which overcomes the need for dry environment, addition of exogenous strong base or restricting synthetic steps. In the electrochemical deposition, water reduction reaction is used to generate high concentration of hydroxide ions in proximity to a metal electrode. Imidazolium cations were deprotonated by hydroxide ions, leading to carbenes formation that self-assembled on the electrode’s surface. SAMs of NO 2 -functionalized NHCs and dimethyl-benzimidazole were electrochemically deposited on Au films. SAMs of NHCs were also electrochemically deposited on Pt, Pd and Ag films, demonstrating the wide metal scope of this deposition technique.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRSDate not supplied

Mitigation of Silver Ion Loss from Solution by Polymer Coating of Metal Surfaces, Part IV

“Spacecraft potable water systems require a biocidal agent that effectively provides both immediate and residual disinfection over long periods of time. Ionic silver (Ag+) is a leading candidate for this application, but suffers from rapid concentration loss due to interactions with the metallic storage containers and tubing. In order to maintain biocidal efficacy in systems with long periods of dormancy and to reduce the required rate of Ag+ injection, it is necessary to develop alternative materials and coatings for certified metal alloys that significantly reduce the Ag+ loss.” In previous reports, we have described our investigations addressing Ag+ loss mitigation and adhesion performance of parylene barrier coatings on coupons of several metal alloys and 316L tubing under static immersion. In such conditions, parylene-C and AF4 coatings have shown excellent Ag+ loss mitigation performance, and mixed long-term adhesion performance, depending on parylene species and substrate surface chemistry/structure. In Part IV of this series, we begin to address the performance of parylene-C barrier coatings under more challenging and realistic conditions, in order to evaluate potential suitability in flight systems. Using two testbeds, we characterized coating performance under dynamic mechanical operation. In the Flow/Pressure Testbed System, Ag+ solution is pumped through internally coated 316L tubing, with optional pressure cycling. In the Bellows Tank Testbed System, an internally coated edge-welded 316L bellows containing Ag+ solution is cyclically extended and compressed, analogous to the operation of bellows tanks used for potable water storage and delivery on the International Space Station. Periodic determinations of Ag+ loss with testbed cycling/time and visual observation of the parylene-C coatings were conducted. In addition, we characterized parylene-C coating resilience and Ag+ loss with 316L tubing and multiple fitting types under long-term immersion and repeated fitting dis/reassembly.

Lance Dean Delzeit↗
NASA NTRS2019

Mitigation of Silver Ion Loss from Solution by Polymer Coating of Metal Surfaces

Spacecraft potable water systems require a biocidal agent that effectively provides both immediate and residual disinfection over long periods of time. Ionic silver (Ag+) is a leading candidate for this application, but suffers from rapid concentration loss due interactions with the metal storage containers and tubing. In order to maintain biocidal efficacy in systems with long periods of dormancy and to reduce the required rate of Ag+ injection, it is necessary to develop alternative materials and coatings for certified metal alloys that significantly reduce the Ag+ loss. In this work, we investigate the performance of two unusual polymers, Teflon AF 2400 and parylene-AF4, as barrier coatings under immersion in 400 ppb Ag+. We show that 25 m-thick parylene-AF4 is a promising coating with Ag+ losses similar to PTFE. Key challenges with this material include maintenance of adhesion under long-term immersion and control of deposition during the internal coating of high-aspect ratio tubing. Solutions to these problems may including surface structuring of substrates for mechanical anchoring or an alternative parylene-C chemistry (with more stable adhesion), and dynamic spatio-temporal control of substrate temperature, respectively.

water↗
DOE OSTI2021

Structure sensitivity of ammonia electro-oxidation on transition metal surfaces: A first-principles study

Ammonia electro-oxidation is a promising catalytic reaction for application in alkaline fuel cells. In this paper we study the trends in this reaction on the (1 0 0) facet of eight fcc transition metals: Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh. We calculate from first-principles (DFT-GGA-PW91) the energetics for two mechanisms: (i) the N + N mechanism and (ii) the Gerischer-Mauerer mechanism. The onset potentials for both mechanisms are provided for both (1 0 0) and (1 1 1) facets. We also calculate the activation energies for the N-N bond-making non-Faradaic events on Cu, Pt, Pd, Ni, Ir, and Rh. We discover that N* – which is considered a poison for Pt(1 1 1) – is a reactive intermediate on Pt(1 0 0), allowing for a facile dimerization to N2 on Pt(1 0 0) at high potentials. We draw similar analyses for the structure sensitivity on the other metals, and we conclude with some general principles to guide catalyst design for this reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2020

Mitigation of Silver Ion Loss from Solution by Polymer Coating of Metal Surfaces, Part II

“Spacecraft potable water systems require a biocidal agent that effectively provides both immediate and residual disinfection over long periods of time. Ionic silver (Ag+) is a leading candidate for this application, but suffers from rapid concentration loss due to interactions with the metal storage containers and tubing. In order to maintain biocidal efficacy in systems with long periods of dormancy and to reduce the required rate of Ag+ injection, it is necessary to develop alternative materials and coatings for certified metal alloys that significantly reduce the Ag+loss.”1In this work, we continue our investigation of vapor-deposited parylene (AF4, and now C) polymers as conformal barrier coatings under long-term (ca. 1-year) immersion in ca. 400 ppb Ag+. The performanceof internal coatings in tubing/two-ferrule fitting systems is characterized. We report successful “aging” and high concentration Ag+pretreatment of parylene coatings for quantitative reduction of Ag+loss rates. In addition, we observe long-term blister-free adhesion of mechanically anchored parylene-AF4 on nano-structured Ti-6Al-4V alloy and chemically bonded parylene-C on 316L stainless steel. Finally, we report preliminary experiments with mechanical and chemical anchoring of laboratory-deposited parylene-C on 316L.

Silver↗
NASA NTRS1984

NiNO - A model for NO on a metal surface

Two different mechanisms for the bonding of NO to Ni have been found; the first is for a linear geometry and involves a 3d-pi(asterisk) bond and has a short Ni-N bond length. The second mechanism, the more weakly bound, involves a Ni4s-N2p bond in a bent structure. The relationship of these two stages to NO chemisorbed on metals is discussed. For both mechanisms, there are no open shell electrons on NO, consistent with the fact that multiplet splitting is not definitely observed in the photoemission spectra of adsorbed NO.

Bauschlicher, C. W., Jr.↗
DOE OSTI2020

Black textile with bottom metallized surface having enhanced radiative cooling under solar irradiation

We discuss the cooling performance of garments can play an important role of enabling comfortable human activities under extreme environments. Imparting extra cooling performance to a garment in a passive way is extremely challenging under the sunlight which provides a huge energy influx to the garment, especially made of black colored textile. In this study, a solar-adaptive-textile (SAT) has been designed and experimentally demonstrated. Near-infrared (NIR) transmittance to the human skin from the solar irradiance has been intercepted by incorporating a nanoscale sputtered thin aluminum metal film underneath the textile layer facing the skin. The high-pressure sputtering employed allows a deep penetration of aluminum into the fabric structure for enhanced solar-energy-blocking effect and film stability. The aluminum layer effectively reduces the solar irradiance as well as the thermal radiation from the textile, which gets heated in lieu of the human skin. The outdoor, under-the-sun measurements with a simulated skin showed an outstanding 2 °C cooling effect compared to the normal textile without the metal film, while preserving most of the given textile properties such as colors, air permeability and wicking behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Corrosion and Enhanced Hydrogen Evolution in Electrochemical Reduction of Ammonium Carbamate on Transition Metal Surfaces

Experiments and theory are combined to search for catalyst activity and stability descriptors for the direct reactive capture and conversion (RCC) of CO 2 in ammonia capture solutions using Cu, Ag, Au, Sn, and Ti electrodes. Two major phenomena emerge in RCC that are not predominant in the electrochemical CO 2 reduction (CO 2 R) reaction, namely, the rapid corrosion and restructuring of the catalyst in the presence of the CO 2 -ammonia adducts and the promotion of the competing hydrogen evolution reaction (HER). The prevalence of HER in RCC is correlated to the electrostatic attraction of the protonated amine to the electrode and the repulsion of the captured CO 2 , using the potential of zero charge (PZC). The stability of catalysts under RCC conditions is a function of the applied potential and cannot be readily predicted using binding energy descriptors commonly used in the prediction of CO 2 R activity. Finally, a direct correlation between calculated binding energies of CO 2 R intermediates, atomic oxygen, hydrogen, and ammonia and the activity and stability of transition metals for RCC cannot be found, highlighting the need for descriptors beyond those known for CO 2 R.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Diffusion-assisted growth of periodic patterns on metal surfaces

Periodic patterns formed on various solid surfaces could seriously affect the properties of materials. Understanding the underlying mechanism is a key step to apply and control pattern formation in many fields. In this work, periodic patterns induced by low energy plasma exposures on tungsten surfaces are observed and related new formation mechanisms are developed. Results from experiments and computer simulations demonstrate that atom diffusion accelerated by low energy and high flux exposures is the dominant mechanism for pattern formation. Additionally, a similar pattern formation has been confirmed by plasma exposure experiments on molybdenum. Based on this mechanism, patterns with controllable size and shape have been successfully prepared on tungsten surface by adjusting plasma exposure parameters, which may provide a new understanding of pattern formation and related surface damage in tungsten induced by plasma exposures.

36 MATERIALS SCIENCE↗