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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

What predictions can be made on the nature of carbon and carbon-bearing compounds (hydrocarbons) in the interstellar medium based on studies of interplanetary dust particles?

The nature of hydrocarbons and properties of elemental carbon in circumstellar, interstellar, and interplanetary dust is a long standing problem in astronomy and meteorite research. The textures and crystallographical properties of poorly graphitized carbon (PGC) from carbonaceous chondrites and Chondritic Porous Aggregates (CPAs) are comparable with PGCs formed by dehydrogenation and carbonization of hydrocarbon precursors under natural terrestrial and experimental conditions. A multistage model of hydrocarbon diagenesis in CPA and carbonaceous chondrite (proto-) planetary parent bodies was proposed in which hydrocarbons are subjected to low temperature hydrous pyrolysis. Continued efforts to recognize hydrocarbons and elemental phases in CPAs may allow understanding of the multistage hydrocarbon/elemental carbon model.

Rietmeijer, F. J. M.↗
NASA NTRS1988

Insitu measurement and control of processing properties of composite resins in a production tool

An in situ measuring technique for use in automated composite processing and quality control is discussed. Frequency dependent electromagnetic sensors are used to measure processing parameters at four ply positions inside a thick section 192-ply graphite-epoxy composite during cure in an 8 x 4 in. autoclave. Viscosity measurements obtained using the sensors are compared with the viscosities calculated using the Loos-Springer cure process model. Good overall agreement is obtained. In a subsequent autoclave run, the output from the four sensors was used to control the autoclave temperature. Using the 'closed loop' sensor controlled autoclave temperature resulted in a more uniform and more rapid cure cycle.

Kranbuehl, D.↗
NASA NTRS1991

Development of graphite/copper composites utilizing engineered interfaces

In situ measurements of graphite/copper alloy contact angles were made using the sessile drop method. The interfacial energy values obtained from these measurements were then applied to a model for the fiber matrix interfacial debonding phenomenon found in graphite/copper composites. The formation obtained from the sessile drop tests led to the development of a copper alloy that suitably wets graphite. Characterization of graphite/copper alloy interfaces subjected to elevated temperatures was conducted using Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Auger Electron Spectroscopy, and X Ray Diffraction analyses. These analyses indicated that during sessile drop tests conducted at 1130 C for 1 hour, copper alloys containing greater than 0.98 at pct chromium form continuous reaction layers of approx. 10 microns in thickness. The reaction layers are adherent to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 deg or less. X ray diffraction results indicate that the reaction layer is Cr3C2.

Devincent, Sandra M.↗
DOE OSTI2026

Hydrogen uptake in graphite matrix at high temperature

Tritium management is a critical challenge for the next generation of nuclear reactors, such as Fluoride Salt Cooled High Temperature Reactors (FHRs) and High Temperature Gas-cooled Reactors (HTGRs), due to the higher production rate (up to 10,000 times) than conventional Light Water Reactors (LWRs). Graphitic materials employed as moderator, reflector, and fuel pebbles offer a potential pathway for tritium recovery by serving as a sink for tritium. Prediction of uptake capacity under reactor relevant conditions remains a challenge due to a lack of low partial pressure data and significant inter-grade variability of graphite. This study addresses these gaps by providing a comprehensive characterization of hydrogen (as a tritium surrogate) uptake and release behavior in the A3-3 graphite matrix (GM) used in fuel pebbles. Uptake measurements are performed at reactor relevant temperatures of 600- 800 °C, 1-200 Torr hydrogen pressure, and 15-120 min equilibration time, followed by thermal desorption spectroscopy up to 1100 °C. Uptake experiments at different equilibration times demonstrate the role of kinetics in hydrogen uptake, which can be modeled as a diffusion-with-trapping process. In the thermodynamics limit, the Sips adsorption model is shown to capture the uptake in A3-3 GM well. Our campaign provides a set of new results for hydrogen uptake in A3-3, including limiting uptake capacity at 600 °C, apparent diffusion coefficient at 600 °C, and the first estimates of the FHR/HTGR relevant (600 °C, 20 Pa partial pressure) equilibrium uptake capacity and time to saturation. Desorption data highlights a new site for hydrogen uptake, not observed in nuclear graphite, which we attribute to the non-graphitized binder. Using the Kissinger method, we estimate activation energy for release from the desorption peaks, confirming the activation energy for release from the basal planes and providing the first estimate for the activation energy of release from the binder.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Ultra-wide bandgap β-Ga 2 O 3 films: Optical, phonon, and temperature response properties

Optical and phonon interactions of Ga 2 O 3 thin films with nanocrystalline morphology were studied at extreme temperatures. The films were grown using a sputtering technique and analyzed via temperature response transmission, Raman scattering, and high-resolution deep-UV photoluminescence (PL). Raman modes indicated that the structure corresponds to the β-phase. The optical-gap at the range of 77–620 K exhibited a redshift of ~200 meV, with a temperature coefficient of ~0.4 meV/K. The optical-gap at room-temperature is 4.85 eV. The electron–phonon interaction model at that temperature range pointed to a low energy phonon, ~31 meV, that is involved in the thermal properties of the optical-gap. Detailed Urbach energy analysis indicated that defects are the dominant mechanism controlling the band-edge characteristics even at an elevated temperature regime where phonon dominance is usually expected. Defects are attributed to the disordered forms of graphite that were detected via Raman scattering and to the granular morphology of the film. A deep-UV laser with an above bandgap exaction line of 5.1 eV was employed to map the PL of the films. The highly resolved spectra, even at room-temperature, show a strong emission of ~3.56 eV attributed to self-trapped holes (STHs). The STH is discussed and modeled in terms of the self-trapped exciton. Moreover, a very distinct but low-intensity emission was found at 4.85 eV that agrees with the value of the optical-gap and is attributed to bandgap recombination. The intensity ratio between the STH and that of the bandgap was found to be 6:1.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Characterizing the seismic response of a molten salt nuclear reactor

Abstract One Generation IV nuclear reactor, which uses a fluoride salt as a coolant, graphite reflector blocks as a moderator, and circulating buoyant TRISO pebbles as fuel is at an advanced stage of development. To characterize the seismic behavior of components of this reactor, validate numerical models for analysis, and develop recommendations for design, a set of earthquake‐simulator experiments on a scaled model of the reactor vessel and its internals was executed on a six‐degree‐of‐freedom earthquake simulator. The model was seismically isolated at its base using two types of spherical sliding bearings. The scaled model involved representations of the prototype reactor vessel, core barrel, reflector blocks, coolant, and spherical fuel pebbles. The material and geometric properties of different test components were selected based on a dynamic similitude scaling analysis and an approximate length scale of 0.4. Four sets of three‐component earthquake motions were used as inputs for testing. Instrumentation on the test specimen recorded the dynamic responses of the outer vessel, core barrel, and reflector‐block assembly, the hydrodynamic responses (sloshing and hydrodynamic pressure) of the liquid coolant, pebble consolidation under earthquake shaking, and the behavior of the isolation systems. This paper describes the design of the experiments and presents key results from the tests. The dynamic responses of the outer vessel, core barrel, and the reflector blocks revealed that the components responded as a unit for the intense shaking used in the experiments. The sloshing response of the fluid in a thin annulus near the perimeter of the vessel was heavily damped. The change in the packing fraction of the pebble bed under repeated, intense 3D earthquake shaking was less than 3%. Seismically isolating the vessel substantially reduced demands on its internal components.

Engineering↗
NASA NTRS1972

Thermally stable macromolecules.

Man-made polymers are compared with certain naturally occurring polymers which have long been used at elevated temperatures. The pyrolysis of model compounds is discussed together with aspects of thermogravimetric analysis, torsional braid analysis, and questions of chemical and radiation stability. Some structure-property relationships are examined, giving attention to asbestos, mica, graphite, and diamond. Questions of bond strengths are investigated along with the stability of ladder polymers and some fundamental concepts in the synthesis of aromatic and heteroaromatic polymers. The substances considered include aromatic single-strand polymers, heteroaromatic polymers, polymers obtained by addition polymerizations, and nonhydrogen-containing polymers. Future trends are also explored.

Pezdirtz, G. F.↗
NASA NTRS1992

Three-dimensional finite element simulation of intermingled-fiber hybrid composite behavior

Three-dimensional finite element methods and the intraply hybrid micromechanics equations are used to predict composite properties for a unidirectional graphite-epoxy primary composite with S-glass fibers used as hybridizing fibers. The micromechanics equations are embedded in a computer code ICAN (Integrated Composites Analyzer). The three-dimensional finite element model consists of three-by-three unit cell array, with a total fiber volume ratio of 0.54. There is a good agreement between the composite properties and microstresses obtained from both methods. The results indicate that the finite element methods and micromechanics equations can be used to obtain the properties of intermingled hybrid composites needed for analysis/design of hybrid composite structures.

Mital, Subodh K.↗
NASA NTRS2001

Chemical and Flowfield Modeling for Enhanced Analysis of Contamination Experiments

This paper describes the application of a new Direct Simulation Monte Carlo (DSMC) code, the Molecular Beam Simulator (MBS), which is designed to analyze laboratory scale molecular beam-surface (and crossed-beam) experiments. The MBS is primarily intended to model experiments associated with spacecraft contamination effects, but it can also be used to simulate a variety of surface chemistry and reactive flow measurements. The MBS code is fully three-dimensional, includes a wide-range of chemical processes, and can model one or multiple pulsed (non-steady) sources. As an example application of the MBS code, a fast, pulsed, oxygen atom-surface experiment which examines the chemistry behind erosion of graphite by oxygen atoms is analyzed. Unsteady DSMC simulations show that experimental observations of excited molecular states after the pulse has hit the surface are consistent with two distinct chemical mechanisms: a direct one where the excited molecules are formed on the surface, and a two-step mechanism where ground state molecules formed on the surface are collisionally excited after they leave the surface by trailing oxygen atoms in the pulse. Further DSMC calculations suggest experiments which can distinguish between these mechanisms.

Braunstein, Matthew↗
NASA NTRS1998

Ground-based simulations of cosmic ray heavy ion interactions in spacecraft and planetary habitat shielding materials

This paper surveys some recent accelerator-based measurements of the nuclear fragmentation of high energy nuclei in shielding and tissue-equivalent materials. These data are needed to make accurate predictions of the radiation field produced at depth in spacecraft and planetary habitat shielding materials and in the human body by heavy charged particles in the galactic cosmic radiation. Projectile-target combinations include 1 GeV/nucleon 56Fe incident on aluminum and graphite and 600 MeV/nucleon 56Fe and 290 MeV/nucleon 12C on polyethylene. We present examples of the dependence of fragmentation on material type and thickness, of a comparison between data and a fragmentation model, and of multiple fragments produced along the beam axis.

NASA Discipline Radiation Health↗
NASA NTRS2010

Modeling Nucleation and Grain Growth in the Solar Nebula: Initial Progress Report

The primitive solar nebula was a violent and chaotic environment where high energy collisions, lightning, shocks and magnetic re-connection events rapidly vaporized some fraction of nebular dust, melted larger particles while leaving the largest grains virtually undisturbed. At the same time, some tiny grains containing very easily disturbed noble gas signatures (e.g., small, pre-solar graphite or SiC particles) never experienced this violence, yet can be found directly adjacent to much larger meteoritic components (chondrules or CAIs) that did. Additional components in the matrix of the most primitive carbonaceous chondrites and in some chondritic porous interplanetary dust particles include tiny nebular condensates, aggregates of condensates and partially annealed aggregates. Grains formed in violent transient events in the solar nebula did not come to equilibrium with their surroundings. To understand the formation and textures of these materials as well as their nebular abundances we must rely on Nucleation Theory and kinetic models of grain growth, coagulation and annealing. Such models have been very uncertain in the past: we will discuss the steps we are taking to increase their reliability.

Nuth, Joseph A.↗
DOE OSTI2022

Quantifying Graphite Solid-Electrolyte Interphase Chemistry and its Impact on Fast Charging

The solid-electrolyte interphase (SEI) enables the remarkable capacity retention of lithium-ion batteries, yet a comprehensive quantitative description of the SEI composition remains elusive. Using a combination of differential electrochemical mass spectrometry and mass spectrometry titration, we quantify graphite SEI components formed under electrolytes of varying salt concentrations. We find that, regardless of salt concentration, a conversion of initially deposited lithium ethylene dicarbonate to monocarbonates (likely lithium ethylene monocarbonate) and noncarbonate species occurs, and the extent of this conversion increases with electrolyte aging. Here, we additionally demonstrate that as the concentration increases (up to 2.0 M LiPF6), the SEI becomes progressively thinner with more LiF and less solid carbonates deposited. Finally, we reveal that less dead lithium formation and less solid carbonate deposition occur during prolonged fast charging for higher-concentration electrolytes. Because of the advantages imparted by a thinner SEI, the onset state of charge for lithium plating for the 2.0 M electrolyte is later than that predicted by a standard electrochemical model, underscoring the importance of explicit SEI effects in future electrochemical models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Artificial intelligence based analysis of nanoindentation load–displacement data using a genetic algorithm

In this work, we developed an automated tool, Nanoindentation Neo package for the analysis of nanoindentation load–displacement curves using a Genetic Algorithm (GA) applied to the Oliver-Pharr method (Oliver et al.,1992). For some materials, such as polycrystalline isotropic graphites, Least Squares Fitting (LSF) of the unload curve can produce unrealistic fit parameters. These graphites exhibit sharply peaked unloading curves not easily fit using the LSF, which tends to overestimate the indenter tip geometry parameter. To tackle this problem, we extended our general materials characterization tool Neo for EXAFS analysis (Terry et al., 2021) to fit nanoindentation data. Nanoindentation Neo automatically processes and analyzes nanoindentation data with minimal user input while producing meaningful fit parameters. GA, a robust metaheuristic method, begins with a population of temporary solutions using model parameters called chromosomes; from these we evaluate a fitness value for each solution, and select the best solutions to mix with random solutions producing the next generation. A mutation operator then modifies existing solutions by random perturbations, and the optimal solution is selected. We tested the GA method using Silica and Al reference standards. We fit samples of graphite and a high entropy alloy (HEA) consisting of BCC and FCC phases.

42 ENGINEERING↗
DOE OSTI2021

Modeling of the Molten Salt Reactor Experiment with SCALE

A SCALE model was developed for the Molten Salt Reactor Experiment (MSRE) benchmark that was recently added to the International Handbook of Evaluated Reactor Physics Benchmark Experiments. This SCALE model served as a basis for criticality calculations and nuclear data sensitivity and uncertainty analyses with the Monte Carlo code Shift and the TSUNAMI computational capabilities in the SCALE code system. The focus of this work is the assessment of the impact of nuclear data on the calculated eigenvalue results in support of the discussion of differences between the calculated and the experimental eigenvalue result. The differences in the eigenvalues obtained using the ENDF/B-VII.0, ENDF/B-VII.1, and ENDF/B-VIII.0 nuclear data libraries cover a relatively small range of ~230 pcm. Since eigenvalue sensitivity of the MSRE is dominated by the neutron multiplicity and neutron capture of 235 U and elastic scattering in graphite, relevant changes in the ENDF/B libraries for nuclear reactions (such as carbon capture) that caused large differences in other graphite-moderated systems did not have a significant impact. Propagation of nuclear data uncertainty results in an eigenvalue uncertainty of ~700 pcm with the major contributors being 235 U neutron multiplicity, graphite elastic scattering, and 7Li neutron capture. All calculations resulted in large differences of ~2000 pcm in eigenvalue compared to the benchmark experimental value. Several potential contributors to this difference—including uncertainties and gaps in the knowledge of the material, geometry, and nuclear data—were identified. Simplified models of the full MSRE core were developed, and similarity assessments were conduced with the full MSRE core model. It was found that simplified models can serve as adequate surrogates of the full-core model such that they can be used for performing selected nuclear data performance assessments with a lower computational burden.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Competing conduction mechanisms in high performance carbon nanotube fibers

The performance of carbon nanotube (CNT) cables, a contender for copper-wire replacement, is tied to its metallic and semi-conducting-like conductivity responses with temperature; the origin of the semi-conducting-like response however is an underappreciated incongruity in literature. With controlled aspect-ratio and doping-degree, over 61 unique cryogenic experiments including anisotropy and Hall measurements, CNT cable performance is explored at extreme temperatures (65 mK) and magnetic-fields (60 T). A semi-conducting-like conductivity response with temperature becomes temperature-independent approaching absolute-zero, uniquely demonstrating for the first time the necessity of heterogeneous fluctuation induced tunneling; complete de-doping leads to localized hopping, contrasting graphite's pure metallic-like response. High-field magneto-resistance (including novel +22 % longitudinal magneto-resistance near room-temperature) is analyzed with hopping and classical two-band models, both yielding a similar parameter useful for conductor development. Varying field-orientation angle uncovers significant two- and four-fold symmetries that are shown to be from Aharonov-Bohm-like corrections to the curvature-induced bandgap, a first for macroscale CNT fibers. Tight-binding calculations using Green's Function formalism model the largest, coherent transport to-date in commensurate CNT bundles in magnetic-field, revealing non-uniform transmission across bundle cross-sections with doping restoring uniformity; independent of doping, transport in bundle-junction-bundle systems are predominantly from CNTs adjacent to the other bundle—demonstrating that smaller bundles are more efficient for electronic transport. The final impact is predicting the ultimate conductivity of heterogeneous CNT cables using temperature and field-dependent transport, surpassing conductivity of traditional metals.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Parametric analysis of anodic degradation mechanisms for fast charging lithium batteries with graphite anode

In this work, we report the impact of the temperature-driven synergistically-coupled anodic degradation mechanisms on the electrochemical performance of lithium batteries with graphite anode over multiple cycles. Temperature dependence of electrochemical reactions and damage mechanisms, such as solid electrolyte interface (SEI) growth, lithium plating/stripping, dead lithium storage/dissolution, and film cracking are incorporated into the degradation model. Results of a parametric analysis are presented, evaluating the effects of charging rates (1–6 C), operating temperatures (-15 – 45°C) and electrode design parameters, on the relative performance fade in the lithium-ion battery. Thermo-electrochemical process maps are developed to provide insights into the relationship between electrode performance and failure mechanisms. The simulation results predict a severe capacity loss due to lithium plating at low temperatures, which is further aggravated at high charging rates. A common strategy for mitigating lithium plating, through charging at high temperatures, also results in rapid capacity loss due to accelerated SEI formation. Simulation results are used to identify the combination of operating conditions and electrode design parameters that improve the electrochemical performance of the battery. These results demonstrate an opportunity to design safe and high-performance lithium-ion batteries, guided by anodic degradation models.

Battery design↗
NASA NTRS1975

Dynamic sampling of laser-induced vapor plumes by mass spectrometry

Mass spectrometric techniques and instrumentation for the dynamic sampling of laser-induced vapor clouds during their submillisecond expansion periods are discussed. Illustrations are drawn primarily from the results of pulsed-laser heating of some oxides and graphites; these include comparisons of incident laser beam pulses with the resultant pulses of positive ions and selected neutral species. Observed characteristics of vapor pulses from graphite are shown to correlate with calculated surface temperature response. Dynamic velocity measurements of individual vapor species are described and, from these velocities, vaporization temperatures are derived and compared using four gas dynamic models for vapor expansion into vacuum. Additional measurements indicate that the laser beam may interact directly with the neutral vapors to produce ions.

Lincoln, K. A.↗
NASA NTRS1980

Experimental determination of unsteady blade element aerodynamics in cascades. Volume 1: Torsion mode cascade

A two dimensional cascade of harmonically oscillating airfoils was designed to model a near tip section from a rotor which was known to have experienced supersonic torsional flutter. This five bladed cascade had a solidity of 1.17 and a setting angle of 1.07 rad. Graphite epoxy airfoils were fabricated to achieve the realistically high reduced frequency level of 0.44. The cascade was tested over a range of static pressure ratios approximating the blade element operating conditions of the rotor along a constant speed line which penetrated the flutter boundary. The time-steady and time-unsteady flow field surrounding the center cascade airfoil were investigated. The effects of reduced solidity and decreased setting angle on the flow field were also evaluated.

Riffel, R. E.↗