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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Circuit for providing variable waveform excitation

A circuit for testing an electronic component, such as a transformer, includes at least two power supplies and at least two H bridge circuits. A first H bridge circuit is conductively coupled in parallel to a first power supply. A second H bridge circuit is conductively coupled in parallel to a second power supply. The second H bridge circuit includes one or more anti-series diodes for preventing current from the first power supply from passing through the second H bridge circuit to the second power supply. The first H bridge circuit and the second H bridge circuit are configured to conductively couple to the electronic component for providing a voltage with a predefined waveform to the electronic component.

Beddingfield, Richard B.↗
DOE OSTI2016

Precipitation of coherent Ni{sub 2}(Cr, W) superlattice in an Ni–Cr–W superalloy

It is demonstrated that a nanometer-sized Ni{sub 2}(Cr, W) superlattice with a Pt{sub 2}Mo-type structure can precipitate in an Ni–Cr–W alloy by means of a simple aging treatment at 550 °C. The dark-field image of short-range order domains has been found for the first time experimentally. The mechanism of short-range order to long-range order transformation has been revealed based on transmission electron microscopy result and static concentration waves theory and found to be continuous ordering. The randomness of the transformation of static concentration waves leads to equiprobable occurrence of the different variants. The transformation of short-range order to long-range order gives rise to the Pt{sub 2}Mo-type Ni{sub 2}(Cr, W) superlattice. The interfaces between Ni{sub 2}(Cr, W) and Ni-based matrix and the different variants of Ni{sub 2}(Cr, W) have been investigated by high resolution transmission electron microscopy. The results reveal that the interfaces between Ni{sub 2}(Cr, W) and surrounding matrix are coherent at the atomic scale. - Highlights: • The DF image of SRO cluster has been found for the first time experimentally. • The transformation of SRO to LRO gives rise to the Pt{sub 2}Mo-type Ni{sub 2}(Cr, W). • Variants of Ni{sub 2}(Cr, W) occur equiprobably. • The interfaces between Ni{sub 2}(Cr, W) and matrix are coherent at the atomic scale.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Carbon microspheres from ethanol at low temperature: Fabrication, characterization and their use as an electrocatalyst support for methanol oxidation

Highlights: ► Carbon microbeads were prepared by the carbonization of ethanol at low temperature. ► The low temperature carbonization of ethanol was catalyzed by iodine. ► Carbon microbeads can serve as ideal candidate for catalyst supports. -- Abstract: Carbon microspheres (CMSs) with a diameter range of 2–3 μm were prepared by the iodine-catalyzed carbonization of ethanol at low temperatures by solvothermal synthesis. The reaction time, concentrations of reactants, temperatures, different alcohols as carbon precursors and reaction environments were systematically altered to determine the optimal synthesis conditions. The size and shape were characterized by scanning and transmission electron microscopy and their structure was characterized by X-ray powder diffraction and Raman spectroscopy. Energy dispersive X-ray spectroscopy, Fourier transform infrared and X-ray photoelectron spectroscopy showed that abundant oxygen-containing functional groups remain on the surface of the carbon spheres. The formation mechanism involves iodine promotion of the oxidation of ethanol, which results in formation of the CMSs. The specific activity of the CMS-supported Pt catalyst is higher than that of a commercial Pt catalyst from E-TEK or the unsupported Pt catalyst.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanisms responsible for the initiation of a fast breakdown in an atmospheric discharge

Here, the initial stage of the fast electrical breakdown of an air gap with a pin-to-plane electrode geometry is studied on a nanosecond time scale using multi-frame laser probing with an exposure time of 70 ps and spatial resolution as high as 3–4 μm. We find that the gap breakdown is associated with the fast (≲1 ns) formation of a micron-sized (~10 μm) cathode spot that appears as a plasma with an electron density of ${n}_{e}\approx {10}^{19}\,{\mathrm{cm}}^{-3}$. The spot is then transformed into a spark channel having an electron density of ${n}_{e}\sim {10}^{19}\mbox{–}{10}^{20}\,{\mathrm{cm}}^{-3}$. Within ~1 ns after the breakdown the dynamics of the highly ionized near-cathode plasma governs the current capacity of the discharge gap as well as the current rise rate.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Mineralogical transformations in polymetallic nodules and the change of Ni, Cu and Co crystal-chemistry upon burial in sediments

Polymetallic nodules from the Clarion and Clipperton Zone of the equatorial Pacific Ocean were studied using X-ray diffraction, X-ray absorption, Fourier-transformed infrared spectroscopy and transmission electron microscopy. Here, this study includes nodules found at the sediment surface as well as subsurface (14–16 cm sediment depth) and deeply buried (530–985 cm sediment depth) nodules. The surface and subsurface nodules are currently under oxic conditions whereas the deeply buried nodules are under suboxic conditions. Surface nodules consist mainly of turbostratic phyllomanganates (7 Å and 10 Å vernadite and Fe-vernadite); todorokite is a minor phase, if present at all. In contrast, subsurface and especially deeply buried nodules predominantly consist of todorokite, which increases in abundance with depth in the sediment. Thus, upon burial of nodules within the shallow sediment, phyllomanganates transform to todorokite, probably through the combined action of time and change in the ambient chemical conditions. Nodules from deeper sediment depth (>500 cm) consist primarily of todorokite and additionally show signs of dissolution. The transformation of phyllomanganates to todorokite and their further dissolution upon nodule burial under suboxic conditions induces modifications in the crystal-chemistry of Ni, Co, and Cu. In surface nodules, Ni and Co are incorporated in the octahedral sheets of phyllomanganates, whereas Cu mainly is located at the edges of those phyllomanganate sheets. In buried nodules Cu and to a lesser extent Ni are incorporated in todorokite by forming outer-sphere complexes within the tunnels. However, Ni is predominantly incorporated within the octahedra of the newly formed todorokite structure. Co is also enriched in the octahedra of todorokite as a result of dissolution of hydrogenetic vernadite and re-incorporation in the more stable Mn-phase formed during the diagenetic transformation. Co enrichment under suboxic conditions after burial within the sediments is noteworthy since Co in surface nodules is characteristic for oxic conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Precursor preparation for Ca-Al layered double hydroxide to remove hexavalent chromium coexisting with calcium and magnesium chlorides

Al(OH){sub 3} and Ca(OH){sub 2} powders are co-ground to prepare a precursor which hydrates into a layered double hydroxide (LDH) phase by agitation in aqueous solution with target hexavalent chromium (Cr(VI)) at room temperature, to achieve an obvious improvement in removal efficiency of Cr(VI) through an easy incorporation into the structure. Although the prepared precursor transforms into LDH phases also when agitated in the solutions of calcium and magnesium chlorides, it incorporates Cr(VI) preferentially to the chloride salts when they coexist. The adsorption isotherm and kinetic studies show that the phenomena occurring on the Al-Ca precursor fit a pseudo-second-order kinetics with a Langmuir adsorption capacity of 59.45 mg/g. Besides, characterizations of the prepared precursor and the samples after adsorption are also performed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Transmission electron microscope (TEM) to understand the reason of the preferential incorporation of Cr(VI) to the coexisting chloride salts during the LDH phase formation. - Graphical abstract: Activated Ca-Al hydroxides (C{sub 3}A) transformed into Ca-Al-OH compound when agitated in water. Ca-Al precursor (C{sub 3}A) was agitated in a hexavalent chromium (Cr(VI)) solution to form Al-Ca-CrO{sub 4} LDH product. Ca-Al-CrO{sub 4} LDH phase occurred preferentially to Ca-Al-MCl{sub 2} LDH phases in the solutions of calcium and magnesium chlorides, it incorporates Cr(VI) preferentially to the chloride salts when they coexist. - Highlights: • Activated Ca-Al hydroxides transformed into LDH when agitated in water with some inorganic substances. • Hexavalent Cr was incorporated in the LDH structure at high adsorption capacity. • Ca-Al-Cr LDH phase occurred preferentially to Ca-Al-MCl{sub 2} LDH phases with coexistence. • The prepared Ca-Al hydroxides had high performance as adsorbent even with high salinity of the solution.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Role of Alloy Chemistry on Stability of Passive Films in Austenitic Stainless Steel

This study dealt with characterizing oxide passive films in austenitic stainless steels with different chemical compositions. Stacking fault energy was estimated, and thermal conductivity at different temperatures (298, 673, 873 and 1073 K) were calculated. Steels specimens were plane strain compressed and subjected to anodic potentiodynamic polarization scan in a different deaerated testing environment. The deformed specimens were characterized using electron backscattered diffraction system and Fourier transform infrared spectroscopy (FTIR)-imaging. The Cr{sub 2}O{sub 3} peak from FTIR-imaging was captured, and area of the peak was calculated after anodic potentiodynamic polarization scan. The intensity of Cr{sub 2}O{sub 3} peak was related to deformed microstructural features.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Fourier Transform Ultraviolet Spectroscopy of the A Pi-2(3/2) Direct Current X Pi-2(3/2) Transition of BrO

The first spectra of the A (2)Pi(sub 3/2) from X (2)Pi(sub 3/2) electronic transition of BrO using Fourier transform ultraviolet spectroscopy are obtained. Broadband vibrational spectra acquired at 298 +/- 2 K and 228 +/- 5 K, as well as high-resolution rotational spectra of the A from X 7,0 and 12,0 vibrational bands are presented. Wavenumber positions for the spectra are obtained with high accuracy, and cross section assignments are made, incorporating the existing literature. With 35 cm(exp -1) (0.40 nm) resolution the absolute cross section at the peak of the 7,0 band is determined to be (1.58 +/- 0.12) x 10(exp -17) sq cm/molecule at 298 +/- 2 K and (1.97 +/- 0.15) x 10(exp -17) sq cm/molecule at 228 +/- 5 K. BrO dissociation energies are determined with a graphical Birge-Sponer technique, using Le Roy-Bernstein theory to place an upper limit on the extrapolation. From the ground-state dissociation energy, D(sub o)" = 231.0 +/- 1.7 kJ/mol, the heat of formation of BrO(g) is calculated, del(sub f)H(0 K) = 133.7 +/- 1.7 kJ/mol and del(sub f)H(298.15 K) = 126.2 +/- 1.7 kJ/mol. Cross sections for the high-resolution 7,0 and 12,0 rotational peaks are the first to be reported. The band structures are modeled, and improved band origins, rotational constants, centrifugal distortion constants, and linewidths are determined. In particular, J-dependent linewidths and lifetimes are observed for the both the 7,0 and 12,0 bands.

Wilmouth, David M.↗
DOE OSTI2019

Mössbauer Studies and Magnetic Properties of Cubic CuFe{sub 2}O{sub 4} Nanoparticles

This study reports the preparation and characterization of nanocrystalline spinel powder of cubic copper ferrite nanoparticles (NPs) which have been fabricated via a cost-effective citrate sol–gel approach. The structural and morphological properties of the nanoparticles are analyzed by X-ray diffraction (XRD), Fourier transform spectroscopy (FT-IR), and scanning electron microscopy (SEM) whereas magnetic properties and Mössbauer analysis were performed using vibrating sample magnetometer (VSM) and Mössbauer spectra, respectively, and were characterized in detail. The empirical aim of this study is to perceive the transition phase of CuFe{sub 2}O{sub 4} as cubic symmetry which was confirmed by SEM images, and a couple of studies reported on the cubic structure of copper ferrite and discussed the magnetic properties. However, the present study gives the detailed information of the formation of cubic structure and magnetic behavior of the CuFe{sub 2}O{sub 4} cubic structure. X-ray diffraction measurements of resulting NPs show that the grain size of the particles is about 42.08 nm while SEM analysis showed that the particles have cubic nanostructured shapes with non-homogeneous sizes in around 80–100 nm. From {sup 57}Fe, Mössbauer parameters consist of one superparamagnetic doublet and superposition of four sextets. VSM result shows the enhanced superparamagnetic nature of the CuFe{sub 2}O{sub 4} NPs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Enhanced catalytic activity of mesoporous graphitic carbon nitride on thermal decomposition of ammonium perchlorate via copper oxide modification

Highlights: • Novel mpg-C{sub 3}N{sub 4}/rod-like CuO nanocomposites were synthesized via a facile precipitation method for the first time. • The BET surface area of as-synthesized mpg-C{sub 3}N{sub 4}/CuO is 111.33 m{sup 2} g{sup −1}, which is beneficial for catalyzing the thermal decomposition process of ammonium perchlorate (AP). • The synergistic effect between mpg-C{sub 3}N{sub 4} and CuO was the origin of the high catalytic activity. • The mpg-C{sub 3}N{sub 4}/CuO nanocomposites were applied in catalyzing the thermal decomposition of AP and the proposed catalytic mechanism was also proposed. - Abstract: Aiming at enhancing the catalytic activity of mpg-C{sub 3}N{sub 4} on thermal decomposition of ammonium perchlorate, mpg-C{sub 3}N{sub 4} was successfully modified by CuO nanorods, via a facile precipitation method. The structure, morphology and composition of mpg-C{sub 3}N{sub 4} and mpg-C{sub 3}N{sub 4}/CuO nanocomposites were characterized by nitrogen adsorption-desorption measurements, transmission electron microscopy, scanning electron microscope, X-ray power diffraction, fourier transform infrared spectroscopy, as well as X-ray photoelectron spectroscopy. The results demonstrated that CuO nanorods (length of 200–300 nm, diameter of 10–15 nm) were uniformly dispersed throughout mpg-C{sub 3}N{sub 4}, efficiently avoiding the agglomeration. Finally, it was demonstrated that the high weight-loss decomposition temperature of AP was decreased up to 118.5 °C in the presence of 2 wt% mpg-C{sub 3}N{sub 4}/CuO nanocomposites, which was higher than that of pure mpg-C{sub 3}N{sub 4} and CuO, respectively, demonstrating the catalytic performances of the nanocomposites was enhanced via the synergistic catalysis between mpg-C{sub 3}N{sub 4} and CuO.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Laser-induced dehydration of graphite oxide coatings on polymer substrates

Nanosized graphite has been oxidized by the Hummers method to give high quality graphite oxide. This reaction is characterized by a very fast kinetic behavior and a high yield. The produced graphite oxide has been conveniently used to pattern graphene by using a standard photolithographic method, and the resulting systems have been characterized by optical microscopy (OM), scanning electron microscopy (SEM) and by Fourier transform infrared spectroscopy (FT-IR) and Visible-Near Infrared spectroscopy (Vis-NIR)

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Sensitivity of energy-packed compounds based on superfine and nanoporous silicon to pulsed electrical treatments

The sensitivity of an energy-packed compound based on nanoporous silicon and calcium perchlorate to a high-current electron beam is studied. The initiation of explosive transformations in a mixture of potassium picrate with a highly dispersed powder of boron-doped silicon by means of a high-voltage discharge is examined. It is shown that explosive transformation modes (combustion and explosion) appear in the energy-packed compound under study upon its treatment with an electron beam. A relationship is established between the explosive transformation modes and the density of the energy-packed compound and between the breakdown (initiation) voltage and the mass fraction of the silicon powder.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Transformation of engineered nanomaterials through the prism of silver sulfidation

Understanding the structure transformation of engineered nanomaterials (ENMs) is a grand measurement challenge, which impacts many aspects of ENMs applications, such as their efficacy, safety, and environmental consequence. To address the significant knowledge gap regarding the fundamental kinetic rate and extent of ENM transformation in the environment, we present a comprehensive and mechanistic structural investigation of the transformation, aggregation, and dissolution behavior of a polyvinylpyrrolidone-coated silver nanoparticle (AgNP) suspension upon sulfidation in moderately reduced hard water with fulvic acid and dissolved Na 2 S. This reaction is among the most prevalent and industrially and environmentally relevant ENMs transformation. Using ex situ transmission electron microscopy (TEM) and both in situ and ex situ synchrotron-based small angle X-ray scattering (SAXS) and X-ray diffraction (XRD), we find that sulfidation of faceted AgNPs strongly depends on the crystallographic orientation of the facets, with nanometer-scale passivation layers developed on {111} and {100} facets and continuous nucleation and growth on {110} facets. Nanobeam electron diffraction and atomic resolution imaging show Ag and Ag2S domains both possess a high degree of crystalline order, contradicting amorphous structures as previously reported. In situ SAXS/XRD allowed simultaneous determination of the morphological changes and extent of sulfidation of AgNPs. SAXS/XRD results strongly indicate sulfidation follows first-order reaction kinetics without any aggregation. Aided by their size monodispersity, for the first time, using direct, in situ morphology and atomic-structure probes whose results mutually corroborate, we unequivocally determined the sulfidation rate constant of AgNPs under an environmentally relevant condition (≈0.013 min –1 for 68 nm diameter AgNPs). A rigorous analysis of the long-term sulfidation product of the AgNPs under different S/Ag ratios using ex situ SAXS/XRD clearly demonstrates that the silver mass in the original AgNP and transformed Ag/Ag 2 S NP is preserved. This result has important environmental implications, strongly suggesting that Ag + ions, a known highly effective antimicrobial agent, are not leached into the solution during sulfidation of AgNPs. The combined nondestructive methodology can be extended to unfold the structure transformation pathway and kinetics in a broad range of ENM systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Facile synthesis of {alpha}-MnO{sub 2} one-dimensional (1D) nanostructure and energy storage ability studies

The dense manganese oxide nanorods with an extremely narrow distribution are synthesized at a low temperature using first cathodic electrodeposition subsequently heat treatment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the nanorods have bar shapes, and their average diameter is less than 50 nm. The Fourier transform infrared (FT-IR) study, the selected area electron diffraction (SAED) pattern in TEM images and the X-ray diffraction (XRD) result show that the nanorods are {alpha}-MnO{sub 2} single crystal. The results of N{sub 2} adsorption-desorption analysis indicate that the BET surface area of the {alpha}-MnO{sub 2} nanorods is 93 m{sup 2} g{sup -1}. By recording the potential-time curve during the electrodeposition process, it is revealed that water reduction reaction has a major role in the electrogeneration of base at the cathode surface under the applied electrochemical conditions. Finally, based on the H{sub 2} bubbling on the cathode surface, the mechanism of the formation and the growth of {alpha}-MnO{sub 2} nanorods are proposed and discussed. For the electrochemical supercapacitor application, electrochemically prepared {alpha}-MnO{sub 2} is found to be stable for a large number of cycles with high specific capacitance, 338 F g{sup -1} at a scan rate of 10 mV s{sup -1}. Finally, the charge-discharge mechanism is discussed. - Graphical abstract: Highlights: Black-Right-Pointing-Pointer New nanostructures of MnO{sub 2} is synthesized by simple method of cathodicelectrodeposition. Black-Right-Pointing-Pointer The product has unique one-dimensional morphology with average diameter size of 50 nm. Black-Right-Pointing-Pointer The experiment conditions (temperature, current density) has not been reported. Black-Right-Pointing-Pointer The one-nanostructures obtained without using of hard template or surfactant.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Highly Al-doped TiO{sub 2} nanoparticles produced by Ball Mill Method: structural and electronic characterization

Highlights: • Highly Al-doped TiO{sub 2} nanoparticles were synthesized using a Ball Mill Method. • Al doping delayed anatase to rutile phase transformation. • Al doping allow controlling the structural and electronic properties of nanoparticles. - Abstract: This study presents an easy method for synthesizing highly doped TiO{sub 2} nanoparticles. The Ball Mill method was used to synthesize pure and Al-doped titanium dioxide, with an atomic percentage up to 15.7 at.% Al/(Al + Ti). The samples were annealed at 773 K, 973 K and 1173 K, and characterized using ICP-AES, XRD, Raman spectroscopy, FT-IR, TG, STEM, XPS, and UV–vis spectroscopy. The effect of doping and the calcination temperature on the structure and properties of the nanoparticles were studied. The results show high levels of internal doping due to the substitution of Ti{sup 4+} ions by Al{sup 3+} in the TiO{sub 2} lattice. Furthermore, anatase to rutile transformation occurs at higher temperatures when the percentage of doping increases. Therefore, Al doping allows us to control the structural and electronic properties of the nanoparticle synthesized. So, it is possible to obtain nanoparticles with anatase as predominant phase in a higher range of temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Visualizing Size-Dependent Dynamics of CeO 2-δ {100}-Supported CoO x Nanoparticles Under CO 2 Hydrogenation Conditions

Carbon dioxide is a major greenhouse gas. In order to optimize processes focused on its chemical valorization, one needs detailed information about the effects of CO 2 and/or CO 2 /H 2 mixtures on the structure and morphology of metal/oxide catalysts. Here, in this study, the evolution of a catalyst with cobalt supported on CeO 2 -cube nanostructures under CO 2 hydrogenation conditions was investigated by using a set of in situ characterization techniques (X-ray absorption fine structure, X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, and environmental transmission electron microscopy (TEM)). The {100} facets of the ceria support displayed an unexpectedly high stability due to strong interactions with the aggregates of cobalt oxide. A significant influence of interfacial bonding between CoO x and CeO 2-δ {100} is evident through a clear preference in the orientation of CoO x nanoparticles (NPs) with respect to the substrate. For initially reduced Co/CeO 2 -cube nanostructures, a kinetically controlled oxidation of cobalt upon the introduction of CO 2 was observed during the early stages of CO 2 hydrogenation. Environmental TEM revealed the size-dependent morphological behavior of cobalt oxide NPs due to strong interactions with the CeO 2 {100} surface. When the environment was switched from H 2 to a mixture of H 2 and CO 2 at 250 °C, small CoO x NPs (in the largest dimension < 2.5 nm) rapidly transformed from a pyramidal three-dimensional (3D) form to a planar, monatomic layer attached to the concurrently oxidized CeO 2-δ {100} surface. This maximizes the number of sites available for the binding of CO 2 or reaction intermediates. The shape transformation reflected the oxophilic character of cobalt and strong metal–support interactions. The removal of CO 2 from the gas phase led to a reduction of the cobalt oxide NPs by hydrogen and a reversible two-dimensional → 3D transformation. In contrast, no significant morphological changes, apart from further oxidation, were observed for big CoO x NPs (in the largest dimension > 3 nm). These trends are not seen for nanoparticles of noble metals. The observed morphological and structural changes in the small CoO x NPs affected the stability of reaction intermediates and modified the selectivity of the CoO x /CeO 2 catalyst system for methane production.

36 MATERIALS SCIENCE↗