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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Raman spectroscopy of graphite in high magnetic fields: Electron-phonon coupling and magnetophonon resonance

The magneto-Raman measurements of graphite were performed in a back-scattering Faraday geometry at temperature 10 K in magnetic fields up to 45 T. The experimental data reveal the rich structure of Raman-active excitations dominated by K-point massive electrons. At high magnetic fields the graphite E{sub 2g} Raman line shows complex multi- component behavior interpreted as magnetophonon resonance coupled electron-phonon modes at graphite’s K-point. Also we found the clear signature of the fundamental, strongly dumped, n=0 magnetophonon resonance associated with H point massless holes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Reductive-expansion synthesis of graphene

Exemplary embodiments provide materials and methods for forming graphene-based exfoliated products with low oxygen contents by a reductive-expansion reaction from a physical mixture containing graphite-based precursor(s) and a chemical agent. Exemplary embodiments also provide materials and methods for forming graphene-based exfoliated products with controllable amounts of nitrogen and/or other impurities incorporated in the material structure as a result of a reductive-expansion reaction from a physical mixture containing graphite-based precursor(s) and a chemical agent.

Luhrs, Claudia Catalina↗
NASA NTRS1992

Method of fabricating lightweight honeycomb structures

A process is disclosed for fabricating lightweight honeycomb type structures out of material such as silicon carbide (SiC) and silicon (S). The lightweight structure consists of a core to define the shape and size of the structure. The core is coated with an appropriate deposit such as SiC or Si to give the lightweight structure strength and stiffness and for bonding the lightweight structure to another surface. The core is fabricated from extremely thin ribs of appropriately stiff and strong material such as graphite. First, a graphite core consisting of an outer hexagonal cell with six inner triangular cells is constructed from the graphite ribs. The graphite core may be placed on the back-up side of a SiC faceplate and then coated with SiC to produce a monolithic structure without the use of any bonding agent. Cores and methods for the fabrication thereof in which the six inner triangular cells are further divided into a plurality of cells are also disclosed.

Goela, Jitendra S.↗
NASA NTRS1989

Effects of silicate-graphite dust in H II regions

Interstellar dust that is present in H II regions will most likely absorb H-ionizing photons more efficiently than He-ionizing photons. Assuming a silicate-graphite dust composition, the effects of such selective absorption on the ionization structure of H, He, O, and N are investigated with emphasis on a blister geometry. Scattering by the dust grains is included in the generalized on-the-spot approximation. For a relatively soft radiation field of effective temperature about 35,000 K, the radiation hardening may cause the He(+) zone to be nearly coextensive with the H(+) zone, and the O(++) volume is strongly increased relative to the N(++) volume. The smaller grains (radii about 0.005 micron) contribute most to the selective absorption. We show that because of a cancellation of effects a simple analytical formula for the fraction of ionizing photons absorbed by the dust given by Petrosian, Silk, and Field is quite accurate in the case of silicate-graphite dust, even for blister regions.

Aannestad, Per A.↗
DOE OSTI2010

The Evolution of Electronic Structure in Few-layerGraphene Revealed by Optical Spectroscopy

The massless Dirac spectrum of electrons in single-layer graphene has been thoroughly studied both theoretically and experimentally. Although a subject of considerable theoretical interest, experimental investigations of the richer electronic structure of few-layer graphene (FLG) have been limited. Here we examine FLG graphene crystals with Bernal stacking of layer thicknesses N = 1,2,3,...8 prepared using the mechanical exfoliation technique. For each layer thickness N, infrared conductivity measurements over the spectral range of 0.2-1.0 eV have been performed and reveal a distinctive band structure, with different conductivity peaks present below 0.5 eV and a relatively flat spectrum at higher photon energies. The principal transitions exhibit a systematic energy-scaling behavior with N. These observations are explained within a unified zone-folding scheme that generates the electronic states for all FLG materials from that of the bulk 3D graphite crystal through imposition of appropriate boundary conditions. Using the Kubo formula, we find that the complete infrared conductivity spectra for the different FLG crystals can be reproduced reasonably well within the framework a tight-binding model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

1D Co- and N-Doped Hierarchically Porous Carbon Nanotubes Derived from Bimetallic Metal Organic Framework for Efficient Oxygen and Tri-iodide Reduction Reactions

Hierarchically porous Co- and N-doped carbon nanotubes are designed as highly efficient electrocatalysts for both oxygen and tri-iodide reduction reactions via a dual-template synthesis approach. Bimetallic Zn/Co-based-zeolitic imidazolate frameworks coated on tellurium nanotubes are pyrolyzed, generating a structure with high surface area, hierarchical pore structure, abundant Co–N x active sites, and a 1D tubular graphitic carbon framework.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Distinct Chemistries Explain Decoupling of Slip and Wettability in Atomically Smooth Aqueous Interfaces

Despite essentially identical crystallography and equilibrium structuring of water, nanoscopic channels composed of hexagonal boron nitride and graphite exhibit an order-of-magnitude difference in fluid slip. We investigate this difference using molecular dynamics simulations, demonstrating that its origin is in the distinct chemistries of the two materials. In particular, the presence of polar bonds in hexagonal boron nitride, absent in graphite, leads to Coulombic interactions between the polar water molecules and the wall. We demonstrate that this interaction is manifested in a large typical lateral force experienced by a layer of oriented hydrogen atoms in the vicinity of the wall, leading to the enhanced friction in hexagonal boron nitride. The fluid adhesion to the wall is dominated by dispersive forces in both materials, leading to similar wettabilities. Finally, our results rationalize recent observations that the difference in frictional characteristics of graphite and hexagonal boron nitride cannot be explained on the basis of the minor differences in their wettabilities.

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

Phase Transition of H 2 in Subnanometer Pores Observed at 75 K

In this paper, we report a phase transition in H 2 adsorbed in a locally graphitic Saran carbon with subnanometer pores 0.5–0.65 nm in width, in which two layers of hydrogen can just barely squeeze, provided they pack tightly. The phase transition is observed at 75 K, temperatures far higher than other systems in which an adsorbent is known to increase phase transition temperatures: for instance, H 2 melts at 14 K in the bulk, but at 20 K on graphite because the solid H 2 is stabilized by the surface structure. Here we observe a transition at 75 K and 77–200 bar: from a low-temperature, low-density phase to a high-temperature, higher density phase. We model the low-density phase as a monolayer commensurate solid composed mostly of para-H 2 (the ground nuclear spin state, S = 0) and the high-density phase as an orientationally ordered bilayer commensurate solid composed mostly of ortho-H 2 (S = 1). We attribute the increase in density with temperature to the fact that the oblong ortho-H 2 can pack more densely. The transition is observed using two experiments. The high-density phase is associated with an increase in neutron backscatter by a factor of 7.0 ± 0.1. Normally, hydrogen produces no backscatter (scattering angle >90°). This backscatter appears along with a discontinuous increase in the excitation mass from 1.2 amu to 21.0 ± 2.3 amu, which we associate with collective nuclear spin excitations in the orientationally ordered phase. Film densities were measured using hydrogen adsorption. Finally, no phase transition was observed in H 2 adsorbed in control activated carbon materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Demonstration of and future perspective on scaling ultrafast-laser-ablation microstructuring of Li-ion battery electrodes to roll-to-roll production and large-format cells

This work demonstrates integration of an ultrafast laser onto a roll-to-roll machine, the laser structuring of a double-sided, 700 m long roll of graphite battery anode and its subsequent manufacture into 27 Ah prismatic cells. The electrode was ablated with a novel hybrid-microstructure composed of both hexagonally arranged pores for enhanced rate performance and channels for fast electrolyte wetting. Subsequently, this anode and a non-ablated baseline anode are paired with an NMC111 cathode for cell building and electrochemical characterization. Compared to the baseline, laser ablated cells demonstrated a reduction in soaking time of at least 60%, an improvement in fast charge capability with >30% more capacity accepted during 6C charging, and an extension of cycle life of >40% during 0.5C cycling. Further, a perspective is provided on scaling ultrafast laser ablation of battery electrodes to industrial throughputs. Additionally, lessons learned from this pilot-scale demonstration are provided in regards to optical architecture, debris removal, and system control. A techno-economic analysis is used to demonstrate that laser ablation can be integrated into existing electrode manufacturing facilities with only ≈$\$$1.3 per kWh increase (≈2%) in manufacturing cost. Preemptive electrode design for laser ablation is discussed as a further method for enhancing performance. Finally, an analysis of available laser systems and beam-scanning architectures is used to determine design requirements to scale process throughput to a state-of-the-art speed of 50 m min −1 . This analysis demonstrates that laser ablating Li-ion battery electrodes has multiple benefits to manufacturing and battery performance, that the technology already exists to achieve high laser-ablation throughputs, and that integrating ultrafast laser ablation to electrode manufacturing will not create a cost or processing bottleneck.

25 ENERGY STORAGE↗
DOE OSTI2026

Unraveling interphase-driven failure pathways in LiMn0.6Fe0.4PO4/graphite pouch cells

LiMnxFe1−xPO4 (LMFP) is a promising high-voltage, thermally stable, and earth-abundant cathode material, yet its practical application is limited by interphase instability and Mn dissolution. In this work, we systematically evaluate LiMn0.6Fe0.4PO4/graphite pouch cells using three electrolyte formulations including control carbonate electrolyte, control + 2 wt% vinylene carbonate (VC), and control + 2 wt% VC + 1 wt% 1,3,2-dioxathiolane 2,2-dioxide (DTD), to establish how electrolyte composition governs interphase chemistry and long-term degradation. Electrochemical testing shows that both additives are preferentially reduced prior to ethylene carbonate (EC) during cell formation, generating robust cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI) layers that suppress gas evolution and raise the first-cycle coulombic efficiency to 89.3%. Additionally, the dual-additive electrolyte delivers the most stable performance, retaining over 85% capacity after 600 cycles while minimizing impedance growth under long-term cycling at C/3 and 40 °C. Soft X-ray absorption spectroscopy confirms that VC + DTD effectively suppresses electrolyte oxidation at the cathode surface, and micro-X-ray fluorescence shows substantially reduced Mn dissolution and deposition on the graphite anode. Density functional theory simulations further provided insights into the structural and energetic influences of alkoxide species on the cathode surface, proposing a Mn2+ extraction mechanism. The combined experimental and computational findings establish a mechanistic link between electrolyte composition and interphase evolution, highlighting the effectiveness of electrolyte engineering for extending the operational lifetime of LMFP-based lithium-ion batteries.

Chak, Chanmonirath Michael↗
DOE OSTI2011

Surface damage on diamond membranes fabricated by ion implantation and lift-off

Thin membranes with excellent optical properties are essential elements in diamond based photonic systems. Due to the chemical inertness of diamond, ion beam processing must be employed to carve photonic structures. One method to realize such membranes is ion-implantation graphitization followed by chemical removal of the sacrificial graphite. The interface revealed when the sacrificial layer is removed has interesting properties. To investigate this interface, we employed the surface sensitive technique of grazing angle channeled Rutherford backscattering spectroscopy. Even after high temperature annealing and chemical etching a thin layer of damaged diamond remains, however, it is removed by hydrogen plasma exposure.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthesis, characterization and conductivity studies of ZnFe{sub 2}O{sub 4} nanoparticles

Transition metal ferrites with general formula AB{sub 2}O{sub 4} (A=Co, Cu, Mn, Zn, B=Fe{sup +3}) could be used as an anode materials in lithium ion battery (LIB), because, lithium ion batteries fabricated using ferrite materials show the high capacity than commonly used graphite. The ZnFe{sub 2}O{sub 4} with cubic spinel structured material was prepared by acrylamide assisted citrate combustion process. Phase, structural coordination and thermal behavior of the prepared ZnFe{sub 2}O{sub 4} were confirmed by powder X-ray diffraction, FTIR spectra and TG/DTA thermogram respectively. Morphology and specific surface area of the ZnFe{sub 2}O{sub 4} were identified by SEM and BET surface analyzer respectively and its conductivity studies were made through impedance spectroscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Fuel Motion Monitoring System at TREAT – FY2017 Instrumentation Summary

This document is a report summarizing FY2017 efforts related to the Transient Reactor Test Facility (TREAT) Fuel Motion Monitoring System, "hodoscope," refurbishment campaign. TREAT is an air-cooled, graphite-moderated, heterogeneous test facility designed to evaluate reactor fuels and structural materials under conditions that simulate various types of transient overpower and under-cooling situations in a nuclear reactor. Fuel meltdowns, metal-water reactions, thermal interaction between overheated fuel and coolant, and the transient behavior of ceramic fuel for high-temperature systems can be studied. A key instrument that monitors fuel motion as these events take place is the fast neutron hodoscope. The hodoscope is designed to allow for pre-, during-, and post- transient imaging of fuel within a test loop in the center of the reactor core. The preferred technique for imaging is detection of fast neutrons produced by fission in the test fuel, travelling unmoderated through an empty row of core fuel assemblies and then through a multi-slot collimator to a 360-detector array. Due to the age of the instrument, a refurbishment of the hodoscope’s fast neutron detection capability is necessary to support real-time, fuel-position experimental data collection. One particular challenge in this regard is related to the refurbishment of the fast-neutron-sensing detector elements in the detector array. This report summarizes major activities and accomplishments related to the FMMS refurbishment in FY2017. Of particular note was work related to identifying options for new proton recoil scintillator wafer and initial examination of the TREAT proton recoil proportional counter detectors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1984

Sealing ceramic material in low melting point glass

A structured device placed in an aerated crucible to pack ceramics molding substance that is to be processed was designed. The structure is wrapped by sealing material made of pyrex glass and graphite foil or sheet with a weight attached on top of it. The crucible is made of carbon; the ceramics material to be treated through heat intervenient press process is molding substance consisting mainly of silicon nitride.

Moritoki, M.↗
NASA NTRS1987

Indirect measurement of N-14 quadrupolar coupling for NH3 intercalated in potassium graphite

A method for indirect measurement of the nuclear quadrupolar coupling was developed and applied to NH3 molecules in the graphite intercalation compound K(NH3)4.3C24, which has a layered structure with alternating carbon and intercalant layers. Three triplets were observed in the H-1 NMR spectra of the compound. The value of the N-14 quadrupolar coupling constant of NH3 (3.7 MHz), determined indirectly from the H-1 NMR spectra, was intermediate between the gas value of 4.1 MHz and the solid-state value of 3.2 MHz. The method was also used to deduce the (H-1)-(H-1) and (N-14)-(H-1) dipolar interactions, the H-1 chemical shifts, and the molecular orientations and motions of NH3.

Tsang, T.↗
NASA NTRS1987

The Large Deployable Reflector (LDR) - Plans and progress

The program history, scientific aims, design, and projected performance of the LDR, a 20-m-primary two-stage four-mirror orbiting sub-mm/FIR astronomical observatory under NASA development, are reviewed. It is shown that the LDR would provide capabilities complementary to those of IRAS, the Kuiper Airborne Observatory, the IRTF, the Hubble Space Telescope, and the planned Space IR Telescope Facility for observations of small-scale background anisotropies, high-redshift galaxies, and objects at temperatures of a few times 10 K or lower. The current design concept is illustrated with extensive drawings, diagrams, and tables of instrument parameters. Particular attention is given to the graphite-epoxy facing and Al-honeycomb core of the primary structure, the focal-plane instruments, and outstanding technological problems.

Swanson, Paul N.↗
NASA NTRS1991

A high-efficiency 59- to 64-GHz TWT for intersatellite communications

The design of a 75-W, 59- to 64- GHz TWT with a predicted overall efficiency in excess of 40 percent is described. This intersatellite communications TWT, designated Model 961HA, employs a coupled-cavity slow-wave structure with a two-step velocity taper and an isotropic graphite multistage depressed collector (MDC). Because the RF efficiency of this TWT is less than 8 percent, an MDC design providing a very high collector efficiency was necessary to achieve the overall efficiency goal of 40 percent.

Wilson, Jeffrey D.↗