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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Hydrogen migration at restructuring palladium–silver oxide boundaries dramatically enhances reduction rate of silver oxide

Heterogeneous catalysts are complex materials with multiple interfaces. A critical proposition in exploiting bifunctionality in alloy catalysts is to achieve surface migration across interfaces separating functionally dissimilar regions. Herein, we demonstrate the enhancement of more than 10 4 in the rate of molecular hydrogen reduction of a silver surface oxide in the presence of palladium oxide compared to pure silver oxide resulting from the transfer of atomic hydrogen from palladium oxide islands onto the surrounding surface formed from oxidation of a palladium-silver alloy. The palladium-silver interface also dynamically restructures during reduction, resulting in silver-palladium intermixing. This study clearly demonstrates the migration of reaction intermediates and catalyst material across surface interfacial boundaries in alloys with a significant effect on surface reactivity, having broad implications for the catalytic function of bimetallic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Super-Joule heating in graphene and silver nanowire network

Transistors, sensors, and transparent conductors based on randomly assembled nanowire networks lean on multi-component percolation for unique and distinctive applications in flexible electronics, biochemical sensing, and solar cells. Although conduction models for 1-D and 1-D/2-D networks have been developed, typically assuming linear electronic transport and self-heating, the model has not been validated by direct high-resolution characterization of coupled electronic pathways and thermal response. In this letter, we show the occurrence of nonlinear “super-Joule” self-heating at the transport bottlenecks in networks of silver nanowires and silver nanowire/single layer graphene hybrid using high resolution thermoreflectance (TR) imaging. TR images at the microscopic self-heating hotspots within nanowire network and nanowire/graphene hybrid network devices with submicron spatial resolution are used to infer electrical current pathways. The findings encourage a fundamental reevaluation of transport models for network-based percolating conductors.

42 ENGINEERING↗
DOE OSTI2016

Pressure tuning the lattice and optical response of silver sulfide

Binary transition metal chalcogenides have attracted increasing attention for their unique structural and electronic properties. High pressure is a powerful tool for tuning the lattice and electronic structure of transition metal chalcogenides away from their pristine states. In this work, we systematically studied the in situ structural and optical behavior of silver sulfide (Ag{sub 2}S) under pressure by synchrotron X-ray diffraction and infrared spectroscopy measurements in a diamond anvil cell. Upon compression, Ag{sub 2}S undergoes structural symmetrization accompanied by a series of structural transitions while the crystallographic inequivalence of the two Ag sites is maintained. Electronically, pressure effectively tunes the ambient semiconducting Ag{sub 2}S into a metal at ∼22 GPa. Drude model analysis shows that the optical conductivity evolves significantly, reaching the highest value of 100 Ω{sup −1} cm{sup −1} at ∼40 GPa. Our results highlight the structural and electronic tunability of silver chalcogenides as a function of pressure and suggest the potential of Ag{sub 2}S as a platform for developing optical and opto-electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Silver-Containing α-MnO 2 Nanorods: Electrochemistry in Na-Based Battery Systems

Manganese oxides are considered attractive cathode materials for rechargeable batteries due to the high abundance and environmental friendliness of manganese. In particular, cryptomelane and hollandite are desirable due to their ability to host cations within their octahedral molecular sieve (OMS-2) Alpha-MnO 2 structure. In this work, we investigate silver containing Alpha-MnO 2 structured materials (Ag x Mn 8 O 16 , x = 1.22, L-Ag-OMS-2 or 1.66, H-Ag-OMS-2) as host materials for Li ion and Na ion insertion/de-insertion. The results indicate a significant difference in the lithiation versus sodiation process the OMS-2 materials. Initial reduction of Ag 1.22 Mn 8 O 16 to 1.0 V delivered ~370 mAh/g. Cycling of Ag1.22Mn8O16 between voltage ranges of 3.8 - 1.7 V and 3.8 - 1.3 V in a Na battery delivered initial capacities of 113 and 247 mAh/g, respectively. In contrast, Ag1.66Mn8O16 delivered only 15 mAh/g, ~0.5 electron equivalents, to 1.7 and 1.3 volts. Study of the system by electrochemical impedance spectroscopy (EIS) showed a significant decrease in charge transfer resistance from 2029 Omega to 594 Omega after 1.5 electron equivalents per Ag 1.22 Mn 8 O 16 formula unit of Na ion insertion. In contrast, both Ag 1.22 Mn 8 O 16 and Ag 1.66 Mn 8 O 16 exhibited gradual impedance increases during lithiation. The formation of silver metal could be detected only in the sodiated material by X-ray diffraction (XRD). Thus, the impedance of Ag-OMS-2 decreases upon sodiation coincident with the formation of silver metal during the discharge process, consistent with the more favorable formation of silver metal during the sodiation process relative to the lithation process.

25 ENERGY STORAGE↗
DOE OSTI2013

Hypoxia inducible factor-1 (HIF-1)–flavin containing monooxygenase-2 (FMO-2) signaling acts in silver nanoparticles and silver ion toxicity in the nematode, Caenorhabditis elegans

In the present study, nanotoxicity mechanism associated with silver nanoparticles (AgNPs) exposure was investigated on the nematode, Caenorhabditis elegans focusing on the hypoxia response pathway. In order to test whether AgNPs-induced hypoxia inducible factor-1 (HIF-1) activation was due to hypoxia or to oxidative stress, depletion of dissolved oxygen (DO) in the test media and a rescue effect using an antioxidant were investigated, respectively. The results suggested that oxidative stress was involved in activation of the HIF-1 pathway. We then investigated the toxicological implications of HIF-1 activation by examining the HIF-1 mediated transcriptional response. Of the genes tested, increased expression of the flavin containing monooxygenase-2 (FMO-2) gene was found to be the most significant as induced by AgNPs exposure. We found that AgNPs exposure induced FMO-2 activation in a HIF-1 and p38 MAPK PMK-1 dependent manner, and oxidative stress was involved in it. We conducted all experiments to include comparison of AgNPs and AgNO{sub 3} in order to evaluate whether any observed toxicity was due to dissolution or particle specific. The AgNPs and AgNO{sub 3} did not produce any qualitative differences in terms of exerting toxicity in the pathways observed in this study, however, considering equal amount of silver mass, in every endpoint tested the AgNPs were found to be more toxic than AgNO{sub 3}. These results suggest that Ag nanotoxicity is dependent not only on dissolution of Ag ion but also on particle specific effects and HIF-1–FMO-2 pathway seems to be involved in it. - Highlights: • HIF-1 signaling was investigated in C. elegans exposed to AgNPs and AgNO{sub 3}. • HIF-1 and PMK-1 were needed for AgNPs- and AgNO{sub 3}-induced fmo-2 gene expression. • PMK-1–HIF-1–FMO-2 pathway was dependent on oxidative stress. • AgNPs and AgNO{sub 3} did not produce any qualitative differences in HIF-1 signaling. • AgNPs were more toxic than an equal amount of silver mass contained in AgNO{sub 3}.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Formation of an ensemble of silver nanoparticles in the process of surface evaporation of glass optical waveguides doped with silver ions by the radiation of a pulsed CO{sub 2} laser

It is shown that pulsed irradiation (a wavelength of 10.6 μm and an energy density of 0.6 – 8.5 J cm{sup -2}) of glass with a waveguide layer containing silver ion leads to the formation of a ring, surrounding the irradiated zone and consisting of silver nanoparticles deposited on the glass surface. The possible process of formation of silver nanoparticles under laser irradiation is discussed. (optics and technology of nanostructures)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Silver chromate and silver dichromate nanostructures: Sonochemical synthesis, characterization, and photocatalytic properties

Graphical abstract: In this work, Ag{sub 2}CrO{sub 4} and Ag{sub 2}Cr{sub 2}O{sub 7} nanostructures have been sonochemically prepared using silver salicylate. The effect of preparation parameters on the morphology of the products was investigated by SEM images. Highlights: ► Herein, Ag{sub 2}CrO{sub 4} and Ag{sub 2}Cr{sub 2}O{sub 7} nanostructures have been sonochemically prepared. ► The effect of preparation parameters on the morphology of the products was investigated. ► The photocatalytic activity of the as-prepared Ag{sub 2}CrO{sub 4} nanoparticles was tested. ► XPS spectra indicated the high purity of Ag{sub 2}Cr{sub 2}O{sub 7} nanostructures obtained. - Abstract: In this work, Ag{sub 2}CrO{sub 4} and Ag{sub 2}Cr{sub 2}O{sub 7} nanostructures have been produced via a sonochemical method using silver salicylate as precursor. Besides silver salicylate, Na{sub 2}CrO{sub 4} and (NH{sub 4}){sub 2}Cr{sub 2}O{sub 7} as starting reagents were applied. To investigate the effect of preparation parameters on the morphology and particle size of Ag{sub 2}CrO{sub 4} and Ag{sub 2}Cr{sub 2}O{sub 7}, sonication time, type of surfactant and its concentration were changed. The as-produced nanostructures were characterized by techniques like powder X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The scanning electron micrographs showed that particle-like and rod-like nanostructures of Ag{sub 2}CrO{sub 4} and Ag{sub 2}Cr{sub 2}O{sub 7} were produced using different surfactants. To investigate the catalytic properties of Ag{sub 2}CrO{sub 4} nanoparticles, photooxidation of methyl orange (MO) was performed. According to the obtained results, it was found that the methyl orange degradation was about 87.3% after 280 min irradiation of visible light.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis of silver nano-materials from Grevillea robusta A Cunn (Silver-oak tree) leaves extract and shape directing role of cetyltrimethylammonium bromide

Grevillea robusta (Silver-oak tree) tree is a medicinal tree. Conventional UV-visible spectrophotometric and transmission electron microscopic technique were used to determine the morphology of silver nanoplates (AgNP) using Grevillea robusta (Silver-oak tree) aqueous leaves extract for the first time. The visible spectra showed the presence of three well defined surface plasmon absorption (SPR) bands at 500, 550 and 675 nm which was attributed to the anisotropic growth of Ag-nanoplates. Transmission electron microscopic (TEM) analysis of AgNP showed formation of truncated triangular, polyhedral with some irregular shapes nanoplates in the size range 8-20 nm. Cetyltrimethylammonium bromide (CTAB) has no significant effect on the shape of the spectra, position of SPR bands, size and size distribution of AgNP.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Synthesis of silver nanospheroids in silver-containing nanoporous glass under the effect of nanosecond laser pulses

Experimental evidence is presented that nanosecond laser irradiation of nanoporous silicate glass containing subnanometre Ag{sub n} molecular silver clusters leads to the formation of spheroidal silver nanoparticles in the glass pores. Their shape has been confirmed by numerical simulation and electronic-microscopic images. The main processes induced by laser irradiation are local heating and the photoionisation and photofragmentation of the molecular silver clusters, followed by the aggregation of the fragments of the molecular clusters into nanoparticles. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

In-Situ Silver Acetylide Silver Nitrate Explosive Deposition Measurements Using X-Ray Fluorescence.

The Light Initiated High Explosive facility utilized a spray deposited coating of silver acetylide - silver nitrate explosive to impart a mechanical shock into targets of interest. A diagnostic was required to measure the explosive deposition in - situ. An X - ray fluorescence spectrometer was deployed at the facility. A measurement methodology was developed to measure the explosive quantity with sufficient accuracy. Through the use of a tin reference material under the silver based explosive, a field calibration relationship has been developed with a standard deviation of 3.2 % . The effect of the inserted tin material into the experiment configuration has been explored.

Covert, Timothy Todd↗
DOE OSTI2017

Performance of Silver-Exchanged Mordenite and Silver-Functionalized Silica-Aerogel Under Vessel Off-gas Conditions

US regulations 40 CFR 61, 40 CFR 190, and 10 CFR 20 govern release limits for volatile radionuclides contained in the gaseous effluents of used nuclear fuel (UNF) reprocessing facilities. Of the four volatile radionuclides that are restricted by the release limits ( 3 H, 14 C, 85 Kr, and 129 I) 129 I will require the greatest degree of abatement. Previous studies have shown that overall plant decontamination factor (DF) for 129 I must, at minimum, exceed 1,000 to meet regulatory requirements. Iodine-containing off-gas will be present in the dissolver off-gas, the cell off-gas, the vessel off-gas (VOG), the waste off-gas, and the shear off-gas. The VOG will most likely contain 1%–5% of the total iodine at part per billion (ppb) concentrations. A number of studies have examined iodine abatement from the dissolver off-gas, which contains greater than 95% of the iodine inventory of the plant, but very few have examined the recovery of iodine from the VOG stream. Reduced silver-exchanged mordenite (Ag 0 Z) has been considered a promising iodine sorbent for use in UNF reprocessing plants, but recent efforts have identified silver-functionalized silica-aerogel (AgAerogel) as a potential alternative. The testing reported here reflects a substantial increase in the body of work available on iodine adsorption by both silver sorbents under prototypical VOG conditions. Both I2 and methyl iodide (CH 3 I) adsorption tests have been conducted with Ag 0 Z and AgAerogel at a range of concentrations up to 1,000 ppb. These experiments were performed with two specific aims: (1) to assess the effect of iodine concentration on its adsorption by the sorbent and (2) to compare the performance of Ag 0 Z and AgAerogel in the removal of iodine from a prototypical VOG stream.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1995

Measurements of the optical properties of thin films of silver and silver oxide

The optical properties of silver films and their oxides are measured to better characterize such films for use as sensors for atomic oxygen. Good agreement between properties of measured pure silver films and reported optical constants is observed. Similar comparisons for silver oxide have not been possible because of a lack of reported constants, but self-consistencies and discrepancies in our measured results are described.

Peters, Palmer N.↗
NASA NTRS2000

Reflective Silvered Polyimide Films Via In Situ Thermal Reduction Silver (I) Complexes

Self-metallizing. flexible polyimide films with highly reflective surfaces are prepared by an in situ self-metallization procedure involving thermally initiated reduction of polymer-soluble silver(I) complexes. Polyamic acid solutions are doped with silver(I) acetate and solubilizing agents. Thermally curing the silver(I) doped resins leads to flexible. metallized films which have reflectivities as high as 100%. abrasion-resistant surfaces. thermal stability and, in some cases, electrical conductivity, rendering them useful for space applications.

Southward, Robin E.↗
DOE OSTI2016

Structure, electrical characteristics, and high-temperature stability of aerosol jet printed silver nanoparticle films

Printed electronics has emerged as a versatile eco-friendly fabrication technique to create sintered nanoparticle (NP) films on arbitrary surfaces with an excellent control over the film microstructure. While applicability of such films for high-temperature applications is not explored previously, herein we report the high-temperature electrical stability of silver (Ag) metal NP films fabricated using an Aerosol Jet based printing technique and demonstrate that this behavior is dictated by changes in the film microstructure. In-situ high temperature (24–500 °C) impedance spectroscopy measurements show that the real part of the impedance increases with increasing temperature up to 150 °C, at which point a decreasing trend prevails until 300 °C, followed again by an increase in impedance. The electrical behavior is correlated with the in-situ grain growth of the Ag NP films, as observed afterwards by scanning electron microscopy and X-ray diffraction (XRD), and could be tailored by controlling the initial microstructure through sintering conditions. Using combined diffraction and spectroscopic analytical methods, it is demonstrated the Aerosol Jet printed Ag NP films exhibit enhanced thermal stability and oxidation resistance. In addition to establishing the conditions for stability of Ag NP films, the results provide a fundamental understanding of the effect of grain growth and reduction in grain boundary area on the electrical stability of sintered NP films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗