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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Application of X-ray microcomputed tomography in the characterization of irradiated nuclear fuel and material specimens

X-ray microcomputed tomography (µCT) was applied in characterizing the internal structures of a number of irradiated materials, including carbon-carbon fibre composites, nuclear-grade graphite and tristructural isotropic-coated fuel particles. Local cracks in carbon-carbon fibre composites associated with their synthesis process were observed with µCT without any destructive sample preparation. Pore analysis of graphite samples was performed quantitatively, and qualitative analysis of pore distribution was accomplished. It was also shown that high-resolution µCT can be used to probe internal layer defects of tristructural isotropic-coated fuel particles to elucidate the resulting high release of radioisotopes. Layer defects of sizes ranging from 1 to 5 µm and up could be isolated by to-mography. As an added advantage, µCT could also be used to identify regions with high densities of radioisotopes to deter-mine the proper plane and orientation of particle mounting for further analytical characterization, such as materialographic sectioning followed by optical and electron microscopy. Lastly, in fully ceramic matrix fuel forms, despite the highly absorbing matrix, characterization of tristructural isotropic-coated particles embedded in a silicon carbide matrix was accomplished usingµCT and related advanced image analysis techniques.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
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 OSTI2021

Characterization of zirconium carbide microspheres synthesized via internal gelation

Microspheres of zirconium carbide with grain size 40-320 nm were synthesized using internal gelation techniques and characterized by scanning electron microscopy, synchrotron X-ray diffraction, and neutron total scattering. Compared with a polycrystalline benchmark ZrC sample prepared by plasma vapor phase deposition, the microspheres display lower variance in grain size and considerably lower microstrain representative of a more homogenous internal microstructure. However, excess carbon was present in the microspheres, evident in both the X-ray and neutron diffraction data as well as a corresponding hypostoichiometric ZrC phase. Furthermore, the excess carbon phase is assumed to be pockets of carbon that remained unreacted through the combined internal gelation and subsequent carbothermic reduction synthesis process. Atomic-scale structural characterization with neutron PDF analysis confirmed the presence of localized nano-sized domains of graphite-like carbon material.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Modeling of infrared flux spectra from disk-shaped interstellar dust clouds

Although there is growing observational and theoretical evidence for many disk-shaped objects of astrophysical interest, spherical geometry is assumed in most radiative transfer models. Recently we generalized the quasi-diffusion method developed by Leung (1975, 1976) for spherical geometry to solve the problem of scattering, absorption, and reemission by dust grains in a medium of disk geometry. The method is applicable to a variety of astronomical sources whose dynamics are angular-momentum dominated and hence not accurately treated by spherical geometry, e.g., protoplanetary nebulae, circumstellar disks, bipolar-flow molecular clouds, accretion disks and disk galaxies. Using this technique and realistic grain opacities we construct theoretical models to determine self-consistently the dust temperature distribution and infrared emission from disk-shaped, quiescent dark globules heated externally by the intersteller radiation field. The effects of the following parameters on the temperature structure and the emergent spectrum are studied: grain type (graphite and silicate), optical depth, density inhomogeneity, and degree of disk flattening. The disk models are characterized by an aspect ratio and an optical depth at 0.55 microns. For inhomogeneous models, a gaussian density distribution is assumed such that the ratio of central to surface density is 100. To study the effects of source geometry, we also compare results for models with spherical and disk geometry. In this case both models have the same radius and central optical depth, the disk models having a 1:1 aspect ratio. While the dust temperature distributions in the two cases are very similar, the emergent flux for the disk model depends sensitively on the viewing angle. For clouds which are unresolved, one would expect, since the thermal emission is isotropic in the neighborhood of an emitting grain, and since the emission (in the far infrared) is optically thin, that the emergent flux spectrum should be characteristic only of the dust temperature, and independent of viewing angle. However, because of the lack of complete symmetry and the resulting radiation anisotropy, this is found not to be the case for the disk models. Angle is that it implies a large uncertainty in estimating the radiation dust mass.

Spagna, G. F., Jr.↗
NASA NTRS2011

Nanoparticle Filtration in a RTM Processed Epoxy/Carbon Fiber Composite

Several epoxy matrix composite panels were fabricated by resin transfer molding (RTM) E862/W resin onto a triaxially braided carbon fiber pre-form. Nanoparticles including carbon nanofiber, synthetic clay, and functionalized graphite were dispersed in the E862 matrix, and the extent of particle filtration during processing was characterized. Nanoparticle dispersion in the resin flashing on both the inlet and outlet edges of the panel was compared by TEM. Variation in physical properties such as Tg and moisture absorption throughout the panel were also characterized. All nanoparticle filled panels showed a decrease in Tg along the resin flow path across the panel, indicating nanoparticle filtration, however there was little change in moisture absorption. This works illustrates the need to obtain good nano-particle dispersion in the matrix resin to prevent particle agglomeration and hence particle filtration in the resultant polymer matrix composites (PMC).

Miller, Sandi G.↗
NASA NTRS2016

The Effect of Electrolyte Composition on Lithium Plating During Low Temperature Charging of Li-Ion Cells

In the present work, a number of additives have been investigated for their effect on the charge characteristics of cells containing low temperature, high ester content electrolytes (1.0 M LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + methyl propionate (MP) 20:20:60 vol % + X additive). These experimental three-electrode cells are composed of graphite anodes, LiNiCoAlO2 cathodes, and a lithium metal reference electrode. Cells were first subjected to electrochemical characterization at various temperatures, consisting of performing Electrochemical Impedance Spectroscopy (EIS), linear micropolarization and Tafel polarization measurement to determine the kinetic parameters for both the anodes and cathodes. Following electrochemical characterization, the cells were subjected to charging at decreasing temperatures using C/5 rates to 4.10V, with a constant potential C/50 current taper. Analysis of the C/20 discharge following the charge at low temperature revealed either the presence or absence of a high voltage plateau during the initial stages of the discharge. This plateau has been linked to the presence of lithium metal on the anode previously and was used as a measure for the extent of lithium plating in the cell. Differential analysis (dV/dQ) was applied as well to more clearly visualize the position of the high voltage plateau and use the peak position (x-axis) in the dV/dQ plot as a gauge for the amount of plating which took place in the cell on the prior charge. Most additives investigated increased the resistance of the anode and decreased the resistance of the cathode, thereby leading to an overall increase in plating observed at low temperature. One additive, LiFSI, was found to be beneficial during low temperature charging, however studies of electrode kinetics from the cell containing LiFSI did not reveal significant improvements compared to the baseline.

Jones, John-Paul↗
DOE OSTI2018

Growth Kinetics and Microstructure of PbTe Films Produced on Si and BaF{sub 2} Substrates by a Modified Hot-Wall Method

Lead telluride films have been grown on Si (100) and BaF{sub 2} (100) substrates by a modified hot-wall method using a graphite reaction chamber. According to X-ray diffraction, X-ray microanalysis, and scanning electron microscopy characterization results, the average growth rate of PbTe films having compositions within the homogeneity range of lead telluride increases with increasing lead vapor partial pressure and decreases with increasing tellurium vapor partial pressure, independent of the nature of the substrate. The rate of PbTe film growth has been shown to be maximal in the initial stage of the process and decrease monotonically over time, independent of the nature of the substrate. Independent of the growth time, the average growth rate of the PbTe films on the Si (100) substrates is considerably higher than that on the BaF{sub 2} (100) substrates. Reflection high-energy electron diffraction data indicate that the texture of the PbTe films on Si (100) corresponds to the substrate orientation and that the misorientation angle of the mosaic blocks does not exceed 20°. On the BaF{sub 2} (100) substrates, we observe epitaxial PbTe film growth with the orientation relationship (100), [011] PbTe ║ (100), [011] BaF{sub 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Estimating the Diffusion Coefficient of Lithium in Graphite: Extremely Fast Charging and a Comparison of Data Analysis Techniques

Galvanostatic intermittent titration experiments were performed in three-electrode cells to characterize the effect of C/2, 2-C and 4-C charge rates on the observed lithium diffusion coefficient. As part of the data analysis process, we compared the classic Weppner-Huggins analysis of polarization data with a newer (Wang et al.) analysis method for depolarization data. At low values of x in Li x C 6 , both analysis methods showed the same general trend in the apparent lithium diffusion coefficient, 4-C > 2-C > C/2. The two techniques differed in the magnitude of the estimated diffusion coefficient by about a factor of 100. The observed increase in diffusion coefficient does not last over a large compositional range. Since the estimates from the method of Weppner and Huggins may contain artifacts due to the use of particulate electrodes and high charge rates, the method of Wang et al. may produce better values.

25 ENERGY STORAGE↗
DOE OSTI2016

Coordinated analysis of two graphite grains from the CO3.0 LAP 031117 meteorite: first identification of a CO nova graphite and a presolar iron sulfide subgrain

Presolar grains constitute the remnants of stars that existed before the formation of the solar system. In addition to providing direct information on the materials from which the solar system formed, these grains provide ground-truth information for models of stellar evolution and nucleosynthesis. Here we report the in situ identification of two unique presolar graphite grains from the primitive meteorite LaPaz Icefield 031117. Based on these two graphite grains, we estimate a bulk presolar graphite abundance of 5{sub −3}{sup +7} ppm in this meteorite. One of the grains (LAP-141) is characterized by an enrichment in {sup 12}C and depletions in {sup 33,34}S, and contains a small iron sulfide subgrain, representing the first unambiguous identification of presolar iron sulfide. The other grain (LAP-149) is extremely {sup 13}C-rich and {sup 15}N-poor, with one of the lowest {sup 12}C/{sup 13}C ratios observed among presolar grains. Comparison of its isotopic compositions with new stellar nucleosynthesis and dust condensation models indicates an origin in the ejecta of a low-mass CO nova. Grain LAP-149 is the first putative nova grain that quantitatively best matches nova model predictions, providing the first strong evidence for graphite condensation in nova ejecta. Our discovery confirms that CO nova graphite and presolar iron sulfide contributed to the original building blocks of the solar system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Plasma exposures of a high-conductivity graphitic foam for plasma facing components

The plasma-surface interactions from samples of high-conductivity graphitic foam biased to 120 V and placed in 6–8 eV deuterium plasmas with densities as high as 10 19 m -3 were investigated at the PSI-2 linear plasma device in Jülich. Graphitic foam-plasma interactions were also studied at the Wendelstein 7-X (W7-X) stellarator in Greifswald by exposure to hydrogen and helium plasmas using the Jülich multi-purpose manipulator. The purpose was to explore the possibility of using the material in a plasma facing component, and initial results were encouraging. In W7-X, no measurable erosion or cracking was observed. The PSI-2 samples received a deuterium fluence of 5 × 10 25 m -2 resulting in an average erosion of 43 µm or about 5 mg per sample. Residual gas analysis (RGA) data were acquired to monitor sample outgassing. Laser-induced Breakdown Spectroscopy (LIBS) was used to measure deuterium retention in the porous foam. After exposure, the surfaces were characterized with scanning electron microscopy, energy dispersive x-ray analysis and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The graphitic foam has a thermal conductivity as high as 287 W/mK and is considered as a replacement to more exotic carbon fiber composites such as SepCarb NB31 or isotropic graphites like ATJ that are no longer produced but used in present-day tokamak experiments. Actively cooled monoblocks were made from the foam and underwent extensive materials characterization including infrared response studies at Oak Ridge National Laboratory. This material is under consideration for the proposed actively-cooled W7-X divertor scraper element.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

TREAT reactor LEU fuel-clad chemical interaction empirical modeling analysis

DOE is converting TREAT (Transient Reactor Test) facility from its existing highly enriched uranium (HEU) core to a low-enriched uranium (LEU) core. In order to assess the magnitude of chemical interaction between fuel and cladding materials during physical contact under expected TREAT operational limits, planned transients tests, and reactivity accident scenarios, a combination of experimental testing and thermodynamic modeling was performed to predict the expected chemical interactions among fuel and cladding chemical constituents. Thermodynamic calculations were then validated with empirical data from experiments that emulate TREAT's expected upper operational limits. Pellet samples composed of LEU oxide powder dispersed in a graphite matrix had intimate contact with zirconium-based alloy cladding. The samples were subjected to long-term isothermal heating under high vacuum. Specimen characterization consisted of scanning electron microscopy, x-ray diffraction analysis, and x-ray tomography. ThermoCalc software and Ellingham's diagrams were used for thermodynamic calculations. The X-ray tomography and SEM analysis of the pellets showed a homogeneous distribution of UO{sub 2} particles within the graphite matrix with isolated larger UO{sub 2} agglomerates. The SEM analysis showed the formation of a lamellar structure between the large UO{sub 2} agglomerate and the graphite matrix. This is an indication that diffusion is taking place at a rather moderate temperature and reaction time during the pellet fabrication. Secondary phases, with high Al and Mg content, were detected inside a UO{sub 2} agglomerate using SEM in SE/EBSD mode and chemical analysis with EDS. LEU feedstock impurities, as Al and Mg, seem to promote the chemical reactivity between UO{sub 2} particles and graphite matrix. XRD analysis of a pellet sample showed the presence of UO{sub 2} and graphite, but no other crystalline phases were detected with this technique. Thermodynamic analysis through the use of Ellingham diagrams showed that within TREAT's operational to reactivity accident temperature (278-820 Celsius degrees), UO{sub 2} can be reduced to U metal by Zr due to a more favorable ΔG for the oxidation of Zr.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Quantitative measurement of pebble fuel anisotropy using generalized ellipsometry

The renewed development of high-temperature gas-cooled reactors has created a need to modernize pebble fuel quality control methods. One important specification in these methods is the coefficient of thermal expansion (CTE) anisotropy, which reflects graphite grain alignment and affects fuel performance. This study investigates the feasibility of using two-modulator generalized ellipsometry microscopy (2-MGEM) as a potential surrogate metric for CTE anisotropy. Graphite matrix compacts with controlled levels of anisotropy were fabricated by varying pre-pressures during forming and were subsequently characterized using both optical dilatometry and 2-MGEM. Measured responses were compared to an isotropic reference pebble produced using an industrial manufacturing process to provide a practical baseline. The resulting measurements revealed a strong quantitative correlation between the CTE anisotropy ratio and the corresponding diattenuation ratio. However, propagated measurement uncertainties in the optical method were found to limit definitive pass/fail discrimination, highlighting the need for improved precision before qualification as a quality control tool. Still, the results establish a quantitative relationship between optical and CTE anisotropy and support further development of 2-MGEM as a potential surrogate method for evaluating graphite matrix anisotropy in pebble fuel manufacturing.

Raftery, Alicia [ORNL] (ORCID:0000000259076427)↗
DOE OSTI2011

Formation, characterization and dynamics of onion like carbon structures from nanodiamonds using reactive force-fields for electrical energy storage

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbon nanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core of the nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbon nanostructure appears, with a shell-shell spacing of about {approx}3.4 {angstrom} for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large ({approx}29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Synthesis and characterization of lignin-based carbon materials with tunable microstructure

Lignin-based carbons can be used as a low-cost alternative to graphite and petroleum-based carbons enabling the production of sustainable, functional carbon materials for various applications. The microstructure development of these carbons can be controlled through chemical modification of the lignin precursor and choice of carbonization parameters. In this work, microstructured carbon materials are synthesized from lignin using a combination of chemical modification and carbon fiber processing techniques. Lignin is modified by incorporating different ester groups which results in a precursor highly compatible with melt processing using the fiber extrusion technique and conversion into microstructured carbons by oxidative stabilization and subsequent carbonization. Furthermore, the impact of esterifications on precursor chemistry and carbonizations is investigated. A nuclear magnetic resonance study of modified lignins shows characteristic spectral changes as a result of esterifications. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry shows the modification process does not affect the polymeric character of the lignin backbone. Esterifications result in moderate shifts in O:C and H:C ratios. Thermogravimetric analysis of lignins reveals distinct differences in mass loss trends during oxidations and carbonizations.

anode↗
DOE OSTI2011

Stability and phase evolution of mullite in reducing atmosphere

The aim of this study is to investigate the stability of mullite and its phase evolution when heated at 1600-1650 deg. C in reducing atmosphere created by a carbon bed. The stoichiometric mullite (3Al{sub 2}O{sub 3}.2SiO{sub 2}) was synthesized by reacting the proper precursors at 1400 deg. C in air atmosphere. Samples containing the primary mullite and graphite or carbon were prepared by pressing the mix and heated at 1600-1650 deg. C. Products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the stoichiometric mullite could decompose to corundum and alumina-rich mullite. During firing under reducing atmosphere, the stoichiometric mullite became richer in Al{sup 3+} cations. The gaseous SiO compound was found to be released from the sample and reacting with C to form SiC phase. Comparison of general mullite solid solution (Al{sub 4+2x}Si{sub 2-2x}O{sub 10-x}) with alumina-rich mullite obtained from decomposition revealed that x would take different values depending on temperature and atmosphere. The ultimate decomposition product was found to be corundum. - Research Highlights: {yields} This method is a new route for investigation of thermochemical stability of stoichimetric mullite under reducing condition which have done by the authors. {yields} This research has got very good results for stability of mullite at different conditions. {yields} This work has also studied the mechanism of stability of mullite under reducing atmosphere.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Study on re-sputtering during CN{sub x} film deposition through spectroscopic diagnostics of plasma

A nitrogen-carbon plasma was generated during the deposition of carbon nitride (CN{sub x}) thin films by pulsed laser ablation of a graphite target in a discharge nitrogen plasma, and the optical emission of the generated nitrogen-carbon plasma was measured for the diagnostics of the plasma and the characterization of the process of CN{sub x} film deposition. The nitrogen-carbon plasma was recognized to contain various species including nitrogen molecules and molecular ions excited in the ambient N{sub 2} gas, carbon atoms and atomic ions ablated from the graphite target and CN radicals. The temporal evolution and spatial distribution of the CN emission and their dependence on the substrate bias voltage show two groups of CN radicals flying in opposite directions. One represents the CN radicals formed as the products of the reactions occurring in the nitrogen-carbon plasma, revealing the reactive deposition of CN{sub x} film due to the reactive expansion of the ablation carbon plasma in the discharge nitrogen plasma and the effective formation of gaseous CN radicals as precursors for CN{sub x} film growth. The other one represents the CN radicals re-sputtered from the growing CN{sub x} film by energetic plasma species, evidencing the re-sputtering of the growing film accompanying film growth. And, the re-sputtering presents ion-induced sputtering features.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Excess Surface Area in Bioelectrochemical Systems Causes ion Transport Limitations

We investigated ion transport limitations on 3D graphite felt electrodes by growing Geobacter sulfurreducens biofilms with advection to eliminate external mass transfer limitations. We characterized ion transport limitations by: (i) showing that serially increasing NaCl concentration up to 200mM increased current linearly up to a total of þ273% vs. 0mM NaCl under advective conditions; (ii) growing the biofilm with a starting concentration of 200mM NaCl, which led to a maximum current increase of 400% vs. current generation without NaCl, and (iii) showing that un-colonized surface area remained even after steadystate current was reached. After accounting for iR effects, we confirmed that the excess surface area existed despite a non-zero overpotential. The fact that the biofilm was constrained from colonizing and producing further current under these conditions confirmed the biofilms under study here were ion transport-limited. Our work demonstrates that the use of high surface area electrodes may not increase current density when the system design allows ion transport limitations to become dominant.

Environmental Molecular Sciences Laboratory↗