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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Novel Pt/Mg(In)(Al)O catalysts for ethane and propane dehydrogenation

Catalysts for the dehydrogenation of light alkanes were prepared by dispersing Pt on the surface of a calcined hydrotalcite-like support containing indium, Mg(In)(Al)O. Upon reduction in H{sub 2} at temperatures above 673 K, bimetallic particles of PtIn are observed by TEM, which have an average diameter of 1 nm. Analysis of Pt LIII-edge extended X-ray absorption fine structure (EXAFS) data shows that the In content of the bimetallic particles increases with increasing bulk In/Pt ratio and reduction temperature. Pt LIII-edge X-ray absorption near edge structure (XANES) indicates that an increasing donation of electronic charge from In to Pt occurs with increasing In content in the PtIn particles. The activity and selectivity of the Pt/Mg(In)(Al)O catalysts for ethane and propane dehydrogenation reactions are strongly dependent on the bulk In/Pt ratio. For both reactants, maximum activity was achieved for a bulk In/Pt ratio of 0.48, and at this In/Pt ratio, the selectivity to alkene was nearly 100%. Coke deposition was observed after catalyst use for either ethane or propane dehydrogenation, and it was observed that the alloying of Pt with In greatly reduced the amount of coke deposited. Characterization of the deposit by Raman spectroscopy indicates that the coke is present as highly disordered graphite particles <30 nm in diameter. While the amount of coke deposited during ethane and propane dehydrogenation are comparable, the effects on activity are dependent on reactant composition. Coke deposition had no effect on ethane dehydrogenation activity, but caused a loss in propane dehydrogenation activity. This difference is attributed to the greater ease with which coke produced on the surface of PtIn nanoparticles migrates to the support during ethane dehydrogenation versus propane dehydrogenation.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2017

The role of ozone in the formation and structural evolution of graphene oxide obtained from nanographite

Chemical exfoliation of graphite under strong oxidizing conditions yields graphene oxide nanosheets with oxy functional groups on the carbon basal plane. The importance of ozone in the chemical oxidation mechanism of graphite by the widely-used Hummers' method has been largely overlooked. Herein we demonstrate that the ozonolysis of graphite leads to the formation of secondary epoxy and perox-ymonosulfate ester functional groups arising from a rotationally hindered Criegee intermediate and sulfuric acid, in a strongly favored thermodynamic process. This mechanistic step is followed by formation of adjacent epoxy and hydroxy groups as major functionalities on graphene oxides via a radical process, and leaves a significant amount of unreacted peroxides well above levels previously recognized. The thermal decomposition of graphene releases sulfur oxygen species (SO 2 and SO), but does not appear to release ozone even if this reaction pathway is moderately favored thermodynamically. Here we propose anew structural model for graphene oxide based on detailed chemical and spectroscopic data that provides insight into observed chemical reactivity and physical properties, including the antimicrobial activity and protein deactivation.

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

A Comparison of Solid Electrolyte Interphase Formation and Evolution on Highly Oriented Pyrolytic and Disordered Graphite Negative Electrodes in Lithium–Ion Batteries

The presence and stability of solid electrolyte interphase (SEI) on graphitic electrodes is vital to the performance of lithium-ion batteries (LIBs). However, the formation and evolution of SEI remain the least understood area in LIBs due to its dynamic nature, complexity in chemical composition, heterogeneity in morphology, as well as lack of reliable in situ/operando techniques for accurate characterization. In addition, chemical composition and morphology of SEI are not only affected by the choice of electrolyte, but also by the nature of the electrode surface. While introduction of defects into graphitic electrodes has promoted their electrochemical properties, how such structural defects influence SEI formation and evolution remains an open question. In this work, utilizing nondestructive operando electrochemical atomic force microscopy (EChem-AFM) the dynamic SEI formation and evolution on a pair of representative graphitic materials with and without defects, namely, highly oriented pyrolytic and disordered graphite electrodes, are systematically monitored and compared. Complementary to the characterization of SEI topographical and mechanical changes during electrochemical cycling by EChem-AFM, chemical analysis and theoretical calculations are conducted to provide mechanistic insights underlying SEI formation and evolution. The results provide guidance to engineer functional SEIs through design of carbon materials with defects for LIBs and beyond.

25 ENERGY STORAGE↗
DOE OSTI2016

Characterization of thin film deposits on tungsten filaments in catalytic chemical vapor deposition using 1,1-dimethylsilacyclobutane

Metal filament plays a key role in the technique of catalytic chemical vapor deposition (Cat-CVD) as it serves as a catalyst in dissociating the source gas to form reactive species. These reactive species initiate the gas-phase reaction chemistry and final thin film and nanostructure formation. At the same time, they also react with the metal itself, leading to the formation of metal alloys and other deposits. The deposits on the tungsten filaments when exposed to 1,1-dimethylsilacyclobutane (DMSCB), a single-source precursor for silicon carbide thin films, in the process of Cat-CVD were studied in this work. It has been demonstrated that a rich variety of deposits, including tungsten carbides (W{sub 2}C and WC), tungsten silicide (W{sub 5}Si{sub 3}), silicon carbide, amorphous carbon, and graphite, form on the W filament surfaces. The structural and morphological changes in the tungsten filaments depend strongly on the DMSCB pressure and filament temperature. At 1000 and 2000 °C, the formation of WC and W{sub 2}C dominates. In addition, a thin amorphous carbon layer has been found at 1500 °C with the 0.12 and 0.24 Torr of DMSCB and a lower temperature of 1200 °C with the 0.48 Torr of DMSCB. An increase in the DMSCB sample pressure gives rise to higher Si and C contents. As a result, the formation of SiC and W{sub 5}Si{sub 3} has been observed with the two high-pressure DMSCB samples (i.e., 0.24 and 0.48 Torr). The rich decomposition chemistry of DMSCB on the W surfaces is responsible for the extensive changes in the structure of the W filament, providing support for the close relationship between the gas-phase decomposition chemistry and the nature of alloy formation on the metal surface. The understanding of the structural changes obtained from this work will help guide the development of efficient methods to solve the filament aging problem in Cat-CVD and also to achieve a controllable deposition process.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Development of mesopores in superfine grain graphite neutron-irradiated at high fluence

Microstructural changes induced by neutron irradiation of superfine grain graphite G347A (Tokai Carbon, Japan) were examined by nitrogen adsorption at 77K and by three microscopy techniques (SEM, TEM and FIB-SEM tomography). The specimens were irradiated at doses of up to 30 dpa, covering stages before and after the turnaround fluence at three temperatures (300, 450, 750 °C) of their irradiation envelope. The initial graphite densification at low fluences did not produce any detectable effect in the pore size range (<350 nm) measured by gas adsorption. However, graphite irradiated at high fluences, after turnaround, showed severe structural changes. At all three temperatures and high irradiation fluences, gas adsorption revealed significant increase of the volume of narrow mesopores (<5–20nm) and up to five times increase of BET surface area, both in linear relationship with the relative volume expansion. Analysis of microscopy images showed multiplication of fine macropores (>50 nm) at high irradiation fluences and more structural changes on multiple scales, from nanometers to microns. This work demonstrates the unique ability of gas adsorption techniques to analyze open pores with sizes between sub-nanometer and sub-micron in bulk nuclear graphite, with supporting microscopy results.

I. Contescu, Cristian↗
NASA NTRS1986

The development of advanced technology blades for tilt-rotor aircraft

The paper discusses the development and ground testing of blades for the XV-15 tilt-rotor demonstrator aircraft. This work was performed under contract NAS2-11250 with NASA Ames Research Center. These blades, known as the Advanced Technology Blades (ATB), replace the rectangular, steel blades which were part of the XV-15 original design. The materials used in the primary structure of the ATB are fiberglass and high strain graphite epoxy laminates. This facilitates the use of 43 deg of nonlinear twist, a nonuniform tapered planform and thin airfoils required for aerodynamic efficiency. Instrumentation life is extended by encapsulating gages and wiring in the composite structure. Tip shells and cuff fairings are removable to provide access to tip weights and retention hardware; they are also replaceable with alternate research configurations. Extensive laboratory testing has validated predicted strength characteristics. Hover testing has demonstrated performance significantly superior to that predicted by contemporary methodology. Key elements of the test rig used for rotor performance measurement were developed as an ancillary part of the present program. The performance testing included measurement of near- and far-field noise. Induced inflow velocity distributions were also determined and photographs of tip vortex condensation trails were taken. These are providing guidance for modifications to hover peformance codes.

Alexander, Harold R.↗
DOE OSTI2014

Effects of Stone-Wales and vacancy defects in atomic-scale friction on defective graphite

Graphite is an excellent solid lubricant for surface coating, but its performance is significantly weakened by the vacancy or Stone-Wales (SW) defect. This study uses molecular dynamics simulations to explore the frictional behavior of a diamond tip sliding over a graphite which contains a single defect or stacked defects. Our results suggest that the friction on defective graphite shows a strong dependence on defect location and type. The 5-7-7-5 structure of SW defect results in an effectively negative slope of friction. For defective graphite containing a defect in the surface, adding a single vacancy in the interior layer will decrease the friction coefficients, while setting a SW defect in the interior layer may increase the friction coefficients. Our obtained results may provide useful information for understanding the atomic-scale friction properties of defective graphite.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Codes and standards for ceramic composite core materials for High Temperature Reactor applications

Fiber-reinforced ceramic matrix composites are attractive for high-temperature nuclear applications due to excellent thermal and mechanical properties as well as reasonable-to-outstanding radiation resistance. Over the past 20 years, the use of ceramic matrix composite applications expanded to many commercial non-nuclear industries as fabrication and application of the technologies mature. The ASME Boiler Pressure Vessel Code, under Section III Division 5, provides the design and construction rules for High Temperature Reactor components. It published the first rules for ceramic matrix composites to be used for reactor core components. The rules lay out the quality requirements together with the design and materials criteria for the use and application of silicon carbide- and carbon-based matrix material technologies. As with the established graphite rules, the ceramic composite material rules are structured in Subsection HH (from Section III), that addresses the criteria for class SN nonmetallic core components. The code rules rely heavily on the development and publication of standards for composite specification, classification, and testing of mechanical, thermal, and other properties. These test methods are developed in ASTM Committee C28 on Advanced Ceramics, with a current focus on ceramic composite tubes. This article describes the detail of the composites code, the design methodology and similarities to the graphite code, the guidance for the development of specifications for ceramic composites (for nuclear applications) including recent standard developments, and it mentions the next steps to support licensing aspects by validating the code with benchmarking data.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

A stable graphite electrode in superconcentrated LiTFSI-DME/DOL electrolyte and its application in lithium-sulfur full battery

Graphical abstract: In superconcentrated ether-based solutions, the formed SEI film inhibits electrolyte decomposition and graphite exfoliation caused by co-intercalation of solvents. Thus, reversible lithium intercalation and de-intercalation at a graphite electrode has been realized. - Highlights: • Prelithiated graphite anodes are coupled with sulfur composite cathodes to form a Li–S full cell in superconcentrated LiTFSI-DME/DO electrolyte. • The introduced superconcentrated ether-based electrolyte permits reversible lithium intercalation and de-intercalation at a graphite electrode. • The assembled Li–S full battery exhibits better cycle performance and coulombic efficiencies. - Abstract: Herein, prelithiated graphite anodes are coupled with sulfur composite cathodes to form a Li–S full cell in superconcentrated ether electrolyte. This novel system is effective in avoiding sever corrosion of Li-metal anode and significantly improving the safety of present Li–S cell, owing to the replacement of Li-metal anode with graphite. The introduced superconcentrated ether electrolyte has a unique networking structure of Li cations and TFSI anions with Li{sup +}-solvating DME/DOL solvents, which is conducive to form a stable TFSI-derived surface film on the graphite electrode. The stable and dense TFSI-derived film inhibits further electrolyte decomposition and graphite exfoliation caused by co-intercalation of solvents, allowing reversible lithium intercalation and de-intercalation at a graphite electrode. Besides, the severe polysulfides shuttle is also suppressed by the concentrated ether-based solutions. Consequently, the assembled graphite-sulfur full battery retains outstanding capacity of 686 mAh g{sup −1}{sub sulfur} at 0.1C rate after 105 cycles, along with high Coulombic efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Development of mesopores in superfine grain graphite neutron-irradiated at high fluence

Microstructural changes induced by neutron irradiation of superfine grain graphite G347A (Tokai Carbon, Japan) were examined by nitrogen adsorption at 77 K and by three microscopy techniques (SEM, TEM and FIB-SEM tomography). The specimens were irradiated at doses of up to 30 dpa, covering stages before and after the turnaround fluence at three temperatures (300, 450, 750 °C) of their irradiation envelope. The initial graphite densification at low fluences did not produce any detectable effect in the pore size range (<350 nm) measured by gas adsorption. However, graphite irradiated at high fluences, after turnaround, showed severe structural changes. At all three temperatures and high irradiation fluences, gas adsorption revealed significant increase of the volume of narrow mesopores (<5–20 nm) and up to five times increase of BET surface area, both in linear relationship with the relative volume expansion. Analysis of microscopy images showed multiplication of fine macropores (>50 nm) at high irradiation fluences and more structural changes on multiple scales, from nanometers to microns. As a result, this work demonstrates the unique ability of gas adsorption techniques to analyze open pores with sizes between sub-nanometer and sub-micron in bulk nuclear graphite, with supporting microscopy results.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Formation mechanism and optimization of highly luminescent N-doped graphene quantum dots

Photoluminescent graphene quantum dots (GQDs) have received enormous attention because of their unique chemical, electronic and optical properties. Here a series of GQDs were synthesized under hydrothermal processes in order to investigate the formation process and optical properties of N-doped GQDs. Citric acid (CA) was used as a carbon precursor and self-assembled into sheet structure in a basic condition and formed N-free GQD graphite framework through intermolecular dehydrolysis reaction. N-doped GQDs were prepared using a series of N-containing bases such as urea. Detailed structural and property studies demonstrated the formation mechanism of N-doped GQDs for tunable optical emissions. Hydrothermal conditions promote formation of amide between –NH2 and –COOH with the presence of amine in the reaction. The intramoleculur dehydrolysis between neighbour amide and COOH groups led to formation of pyrrolic N in the graphene framework. Further, the pyrrolic N transformed to graphite N under hydrothermal conditions. N-doping results in a great improvement of PL quantum yield (QY) of GQDs. By optimized reaction conditions, the highest PL QY (94%) of N-doped GQDs was obtained using CA as a carbon source and ethylene diamine as a N source. The obtained N-doped GQDs exhibit an excitation-independent blue emission with single exponential lifetime decay.

NANOPARTICLES↗
DOE OSTI2014

Ab initio prediction of SiC nanotubes with negative strain energy

Single-layer SiC nanotubes (SiCNTs) are known to be metastable structures that is why only nanotubular fibers or polygrained nanotubes have been obtained experimentally. In this study, we report on how hydrogen helps to overcome the metastability of SiCNTs. Starting from SiC graphitic sheets, we analyzed the impact of either partial or full hydrogenation on the electronic properties and structural stability of SiCNTs. It is shown that, in general, hydrogenation widens the band gap of both SiC graphitic sheets and nanotubes and, irrespective of the difference in chirality and diameter, leads to the formation of energetically stable SiCNTs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Graphite Material Behavior: NRC Graphite Behavior Model

Introduction to graphite Fabrication of graphite Unique features of nuclear grade graphite Providing the properties As-fabricated material properties of interest Thermal diff, thermal stability, mechanical strength, etc. General graphite behavior and degradation Microstructure: key to behavior Crystallographic structure Basal plane (covalent) bonding Porosity and pore microstructure Degradation Irradiation behavior Oxidation behavior Molten salt issues

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

Polyelectrolyte-Induced Reduction of Exfoliated Graphite Oxide: A Facile Route to Synthesis of Soluble Graphene Nanosheets

Here we report that poly(diallyldimethylammonium chloride) (PDDA) acts as both a reducing agent and a stabilizer to prepare soluble graphene nanosheets from graphite oxide. The results of transmission electron microscopy, X-ray diffraction, X-ray photoeletron spectroscopy, atomic force microscopy, and fourier transform infrared indicated that graphite oxide was successfully reduced to graphene nanosheets which exhibited single-layer structure and high dispersion in various solvents. The reaction mechanism for PDDA-induced reduction of exfoliated graphite oxide was proposed. Furthermore, PDDA facilitated the in-situ growth of highly-dispersed Pt nanoparticles on the surface of graphene nanosheets to form Pt/graphene nanocomposites, which exhibited excellent catalytic activity towards formic acid oxidation. This work presents a facile and environmentally friendly approach to the synthesis of graphene nanosheets, opens up new possibility for preparing graphene and graphene-based nanomaterials for large-scale applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1985

Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites

In an effort to elucidate the changes in molecular structural and mechanical properties of epoxy/graphite fiber composites upon exposure to ionizing radiation in a simulated space environment, spectroscopic and surface properties of tetraglycidyl-4,4'-diamino diphenyl methane (TGDDM) red with diamino diphenyl sulfone (DDS) and T-300 graphite fiber were investigated following exposure to ionizing radiation. Cobalt-60 gamma radiation and 1/2 MeV electrons were used as radiation sources. The system was studied using electron spin resonance (ESR) spectroscopy, infrared absorption spectroscopy, contact angle measurements, and electron spectroscopy for chemical analysis.

Fornes, R. E.↗
NASA NTRS2017

Fully Coupled Aero-Thermochemical-Elastic Simulations of an Eroding Graphite Nozzle

A multiphysics simulation capability has been developed that incorporates mutual interactions between aerodynamics, structural response from aero/thermal loading, ablation/pyrolysis, heating, and surface-to-surface radiation to perform high-fidelity, fully coupled aerothermoelastic ablation simulations, which to date had been unattainable. The multiphysics framework couples CHAR (a 3-D implicit charring ablator solver), Loci/CHEM (a computational fluid dynamics solver for high-speed chemically reacting flows), and Abaqus (a nonlinear structural dynamics solver) to create a fully coupled aerothermoelastic charring ablative solver. The solvers are tightly coupled in a fully integrated fashion to resolve the effects of the ablation pyrolysis and charring process and chemistry products upon the flow field, the changes in surface geometry due to recession upon the flow field, and thermal-structural analysis of the body from the induced aerodynamic heating from the flow field. The multiphysics framework was successfully demonstrated on a solid rocket motor graphite nozzle erosion application. Comparisons were made with available experimental data that measured the throat erosion during the motor firing. The erosion data is well characterized, as the test rig was equipped with a windowed nozzle section for real-time X-ray radiography diagnostics of the instantaneous throat variations for deducing the instantaneous erosion rates. The nozzle initially undergoes a nozzle contraction due to thermal expansion before ablation effects are able to widen the throat. A series of parameters studies were conducted using the coupled simulation capability to determine the sensitivity of the nozzle erosion to different parameters. The parameter studies included the shape of the nozzle throat (flat versus rounded), the material properties, the effect of the choice of turbulence model, and the inclusion or exclusion of the mechanical thermal expansion. Overall, the predicted results match the experiment very well, and the predictions were able to bound the data within acceptable limits.

Blades, E. L.↗
NASA NTRS1997

Experimental indication of a naphthalene-base molecular aggregate for the carrier of the 2175 angstroms interstellar extinction feature

Experiments where the simple polycyclic aromatic hydrocarbon (PAH) naphthalene (C10H8) is subjected to the energetic environment of a plasma have resulted in the synthesis of a molecular aggregate that has ultraviolet spectral characteristics that suggest it provides insight into the nature of the carrier of the 2175 angstroms interstellar extinction feature and may be a laboratory analog. Ultraviolet, visible, infrared, and mass spectroscopy, along with gas chromatography, indicate that it is a molecular aggregate in which an aromatic double ring ("naphthalene") structural base serves as the electron "box" chromophore that gives rise to the envelope of the 2175 angstroms feature. This chromophore can also provide the peak of the feature or function as a mantle in concert with another peak provider such as graphite. The molecular base/chromophore manifests itself both as a structural component of an alkyl-aromatic polymer and as a substructure of hydrogenated PAH species. Its spectral and molecular characteristics are consistent with what is generally expected for a complex molecular aggregate that has a role as an interstellar constituent.

NASA Discipline Exobiology↗