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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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An Exceptionally Mild and Scalable Solution-Phase Synthesis of Molybdenum Carbide Nanoparticles for Thermocatalytic CO[subscript 2] Hydrogenation
Abstract not provided
Simultaneous Iron and Nickel Isotopic Analyses of Presolar Silicon Carbide Grains.
Aside from recording stellar nucleosynthesis, a few elements in presolar grains can also provide insights into the galactic chemical evolution (GCE) of nuclides. We have studied the carbon, silicon, iron, and nickel isotopic compositions of presolar silicon carbide (SiC) grains from asymptotic giant branch (AGB) stars to better understand GCE. Since only the neutron-rich nuclides in these grains have been heavily influenced by the parent star, the neutron-poor nuclides serve as GCE proxies. Using CHILI, a new resonance ionizationmass spectrometry (RIMS) instrument, we measured 74 presolar SiC grains for all iron and nickel isotopes. With the CHARISMA instrument, 13 presolar SiC grains were analyzed for iron isotopes. All grains were also measured by NanoSIMS for their carbon and silicon isotopic compositions. A comparison of the measured neutron-rich isotopes with models for AGB star nucleosynthesis shows that our measurements are consistent with AGB star predictions for low-mass stars between half-solar and solar metallicity. Furthermore, our measurements give an indication on the Ne-22(alpha, n)Mg-25 reaction rate. In terms of GCE, we find that the GCE-dominated iron and nickel isotope ratios, Fe-54/Fe-56 and Ni-60/Ni-58, correlate with their GCE-dominated counterpart in silicon, Si-29/Si-28. The measured GCE trends include the Solar System composition, showing that the Solar System is not a special case. However, as seen in silicon and titanium, many presolar SiC grains are more evolved for iron and nickel than the Solar System. This confirms prior findings and agrees with observations of large stellar samples that a simple age-metallicity relationship for GCE cannot explain the composition of the solar neighborhood. (C) 2017 Elsevier Ltd. All rights reserved.
Formation of uranium oxy-carbide and uranium carbide via conversion of polymer covered uranium dioxide by laser-based thermal processing
Conventional formation of carbonaceous uranium compounds requires bulk processing using furnace-based approaches. Here, a methodology employing polymer covered uranium dioxide and laser-based heating is explored to enable rapid, localized formation of carbonaceous uranium compounds. Specifically, heating of poly(methyl methacrylate) covered uranium dioxide powder to high temperatures using laser irradiation in argon and methane gaseous environments was investigated. Decomposition of material and reactions induced by laser irradiation were probed in situ by residual gas analysis using a benchtop mass spectrometer. In this study, to determine the effect on the resultant material phase, three different process parameters were varied: gaseous atmosphere, laser power, and laser irradiation time. Material processed under varying conditions was analyzed using powder X-ray diffraction and scanning electron microscopy. This work realized the conversion of uranium dioxide into uranium oxy-carbide(s) and uranium carbide(s) phases, at over 60 wt.%, via the polymer surface application and laser-based thermal decomposition methodology.
High capacitance of coarse-grained carbide derived carbon electrodes
Abstract not provided
Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers
In this paper, a transition from metallic to semiconducting-like behavior has been demonstrated in two-dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M 3 C 2 and M 4 C 3 MXenes. The MXene structure consists of n + 1 layers of near-close packed M layers with C or N occupying the octahedral site between them in an [MX] n M arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M' 2 M"C 2 and M' 2 M" 2 C 3 – where M' and M" are two different early transition metals, such as Mo, Cr, Ta, Nb, V, and Ti. The M' atoms only occupy the outer layers and the M" atoms fill the middle layers. In other words, M' atomic layers sandwich the middle M"–C layers. Using X-ray atomic pair distribution function (PDF) analysis on Mo 2 TiC 2 and Mo 2 Ti 2 C 3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC] n M structures. The electronic properties of these Mo-containing MXenes are compared with their Ti 3 C 2 counterparts, and are found to be no longer metallic-like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo–Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo 2 TiC 2 T x exhibits semiconductor-like transport behavior, while Ti 3 C 2 T x is a metal. Finally, this finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in which semiconducting properties are required.
Reactions of water and C1 molecules on carbide and metal-modified carbide surfaces
The formation of carbides can significantly modify the physical and chemical properties of the parent metals. In the current review, we summarize the general trends in the reactions of water and C1 molecules over transition metal carbide (TMC) and metal-modified TMC surfaces and thin films. Although the primary focus of the current review is on the theoretical and experimental studies of reactions of C1 molecules (CO, CO 2 , CH 3 OH, etc.), the reactions of water will also be reviewed because water plays an important role in many of the C1 transformation reactions. This review is organized by discussing separately thermal reactions and electrochemical reactions, which provides insights into the application of TMCs in heterogeneous catalysis and electrocatalysis, respectively. In thermal reactions, we discuss the thermal decomposition of water and methanol, as well as the reactions of CO and CO 2 over TMC surfaces. In electrochemical reactions, we summarize recent studies in the hydrogen evolution reaction, electrooxidation of methanol and CO, and electroreduction of CO 2 . Lastly, future research opportunities and challenges associated with using TMCs as catalysts and electrocatalysts are also discussed.
Synthesis of highly-active Fe–N–C catalysts for PEMFC with carbide-derived carbons
We study the physico-chemical properties and electrocatalytic activity towards oxygen reduction of two Fe–N–C catalysts based on carbide derived carbon.
Atomic and microstructural origins of stored energy release in neutron-irradiated silicon carbide
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A High-Density, High-Efficiency, Isolated On-Board Vehicle Battery Charger Utilizing Silicon Carbide Power Devices
This paper presents an isolated on-board vehicular battery charger that utilizes silicon carbide (SiC) power devices to achieve high density and high efficiency for application in electric vehicles (EVs) and plug-in hybrid EVs (PHEVs). The proposed level 2 charger has a two-stage architecture where the first stage is a bridgeless boost ac-dc converter and the second stage is a phase-shifted full-bridge isolated dc-dc converter. The operation of both topologies is presented and the specific advantages gained through the use of SiC power devices are discussed. The design of power stage components, the packaging of the multichip power module, and the system-level packaging is presented with a primary focus on system density and a secondary focus on system efficiency. In this work, a hardware prototype is developed and a peak system efficiency of 95% is measured while operating both power stages with a switching frequency of 200 kHz. A maximum output power of 6.1 kW results in a volumetric power density of 5.0 kW/L and a gravimetric power density of 3.8 kW/kg when considering the volume and mass of the system including a case.
Properties of tantalum carbide-graphite and niobium carbide-graphite composites
Mechanical and thermodynamic properties of hot pressed tantalum carbide-graphite and niobium carbide-graphite composites
X-Ray photoelectron spectroscopy study of radiofrequency-sputtered titanium, carbide, molybdenum carbide, and titanium boride coatings and their friction properties
Radiofrequency sputtered coatings of titanium carbide, molybdenum carbide and titanium boride were tested as wear resistant coatings on stainless steel in a pin on disk apparatus. X-ray photoelectron spectroscopy (XPS) was used to analyze the sputtered films with regard to both bulk and interface composition in order to obtain maximum film performance. Significant improvements in friction behavior were obtained when properly biased films were deposited on deliberately preoxidized substrates. XPS depth profile data showed thick graded interfaces for bias deposited films even when adherence was poor. The addition of 10 percent hydrogen to the sputtering gas produced coatings with thin poorly adherent interfaces. Results suggest that some of the common practices in the field of sputtering may be detrimental to achieving maximum adherence and optimum composition for these refractory compounds.
Process for making silicon carbide reinforced silicon carbide composite
A process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.
Silicon carbide reinforced silicon carbide composite
This invention relates to a process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.
Diffusion bonded silicon carbide having iridium and hermetic silicon carbide-iridium bonds
Disclosed is a hermetic bond for a joint including a first layer of silicon carbide; a second layer of silicon carbide; and a bonding layer positioned between the first layer and the second layer, wherein the bonding layer includes an iridium layer, a first reaction zone positioned between the iridium foil layer and the first layer, and a second reaction zone positioned between the iridium foil layer and the second layer, wherein the first reaction zone and the second reaction zone include iridium silicides.
Na-Ion Intercalation and Charge Storage Mechanism in 2D Vanadium Carbide
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Coupled electronic and atomic effects on defect evolution in silicon carbide under ion irradiation
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