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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Nanoscale insights into the structure of solution-processed graphene by x-ray scattering

Abstract Chemical exfoliation is an attractive approach for the synthesis of graphene due to its low cost and simplicity. However, challenges still remain in the characterization of solution-processed graphene, in particular with atomic resolution. Through this work we demonstrate the x-ray pair distribution function as a novel approach to study solution-processed graphene or other 2D materials with atomic resolution, directly in solution, produced by liquid-phase and electrochemical exfoliations. The results show the disappearance of long-range atomic correlations, in both cases, confirming the production of single and few-layer graphene. In addition, a considerable ring distortion has been observed as compared to graphite, irrespective of the solvent used: the normal surface angle to the sheet of the powder sample should be less than 6°, compatible with ripples formation observed in suspended graphene. We attribute this effect to the interaction of solvent molecules with the graphene nanosheets.

36 MATERIALS SCIENCE↗
NASA NTRS2017

Wear Trends of the HERMeS Thruster as a Function of Throttle Point

A series of short-duration (200 hour) wear tests were conducted with two Hall Effect Rocket with Magnetic Shielding (HERMeS) technology demonstration units (TDU). Front pole covers, cathode keeper, and discharge channel wear were characterized as a function of discharge voltage, magnetic field strength, and chamber pressure. No discharge channel erosion was observed. Inner pole cover erosion was shown to be a weak function of discharge voltage with most erosion occurring at the lowest value, 300 volts. The TDU-3 keeper electrode eroded with each operating condition, with high magnetic field yielding the greatest erosion rate. The TDU-1 keeper electrode exhibited net deposition suggesting its configuration is more consistent with meeting overall HERMeS service life requirements. Ratios of molybdenum to graphite erosion rates suggests, with high uncertainty, that the sputtering ions are originating downstream of the thruster exit plane, striking the surface with small angles of incidence.

life (durability)↗
DOE OSTI2020

Coefficient of Thermal Expansion during Ratchet Growth of TATB Compactions

Triamino trinitrobenzene (TATB) is an insensitive high explosive, meaning that it is quite immune from accidental detonation and only performs in appropriately engineered configurations. While this is advantageous for applications, the TATB crystal is graphitic and possesses significant thermal and mechanical anisotropy. Compactions of TATB crystals, with or without binder, have been shown to have oriented TATB crystals that relate to the pressing geometry and process, and this TATB texture necessarily imparts microscale and macroscale anisotropy to the compaction. By a mechanism not fully understood, thermal cycling results in irreversible volume expansion (also called ratchet growth) of the compaction likely by creating stress points on the microscale. Changes in density caused by thermal cycling can certainly effect the explosive performance. Our past characterization of the ratchet growth phenomenon has focused on the magnitude of the irreversible strain as measured before and after a thermal cycle. Finally, in the work presented here, we analyze the evolving thermal expansion behavior during the ascending and descending temperature ramps, providing further insight into the material changes taking place during the ratchet growth phenomenon.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2022

Coefficient of Thermal Expansion Evolution during Ratchet Growth of PBX 9502 and Neat TATB

The Plastic-Bonded Explosive (PBX) 9502 is comprised of the insensitive high explosive TATB (triamino trinitrobenzine) crystals coated in FK-800 polymer binder and isostatically pressed. The TATB crystals have a graphitic, plate-like morphology and possess significant thermal and mechanical anisotropy. Compactions of neat TATB or TATB-based composites (like PBX 9502) have been shown to have TATB crystals that are oriented during the pressing process giving rise to TATB texture and resulting in micro- and macro-scale anisotropy of the compaction. Thermal cycling of the compactions results in irreversible volume expansion (or ratchet growth) likely by creating stress points on the microscale. However, the actual mechanism behind this expansion is not fully understood. Previous characterization of the ratchet growth phenomenon has focused on the magnitude of the irreversible strain as measured before and after a thermal cycle. In the work presented here, we analyze the evolving thermal expansion behavior during the ascending and descending temperature ramps and compare differences observed due to the presence/absence of binder in the compaction.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2019

Plasma-enabled healing of graphene nano-platelets layer

Graphene platelet networks (GPNs) were deposited onto silicon substrates by means of anodic arc discharge ignited between two graphite electrodes. Here, substrate temperature and pressure of helium atmosphere were optimized for the production of the carbon nanomaterials. The samples were modified or destroyed with different methods to mimic typical environments responsible of severe surface degradation. The emulated conditions were performed by four surface treatments, namely thermal oxidation, substrate overheating, exposition to glow discharge, and metal coating due to arc plasma. In the next step, the samples were regenerated on the same substrates with identical deposition technique. Damaging and re-growth of GPN samples were systematically characterized by scanning electron microscopy and Raman spectroscopy. Furthermore, the full regeneration of the structural and morphological properties of the samples has proven that this healing method by arc plasma is adequate for restoring the functionality of 2D nanostructures exposed to harsh environments.

42 ENGINEERING↗
DOE OSTI2024

Laser-induced graphene gas sensors for environmental monitoring

Artemesia tridentatais a foundational plant taxon in western North America and an important medicinal plant threatened by climate change. Low-cost fabrication of sensors is critical for developing large-area sensor networks for understanding and monitoring a range of environmental conditions. However, the availability of materials and manufacturing processes is still in the early stages, limiting the capacity to develop cost-effective sensors at a large scale. In this study, we demonstrate the fabrication of low-cost flexible sensors using laser-induced graphene (LIG); a graphitic material synthesized using a 450-nm wavelength bench top laser patterned onto polyimide substrates. We demonstrate the effect of the intensity and focus of the incident beam on the morphology and electrical properties of the synthesized material. Raman analyses of the synthesized LIG show a defect-rich graphene with a crystallite size in the tens of nanometers. This shows that the high level of disorder within the LIG structure, along with the porous nature of the material provide a good surface for gas adsorption. The initial characterization of the material has shown an analyte response represented by a change in resistance of up to 5% in the presence of volatile organic compounds (VOCs) that are emitted and detected byArtemisiaspecies. Bend testing up to 100 cycles provides evidence that these sensors will remain resilient when deployed across the landscapes to assess VOC signaling in plant communities. The versatile low-cost laser writing technique highlights the promise of low-cost and scalable fabrication of LIG sensors for gas sensor monitoring.

Chemistry↗
NASA NTRS1985

Environmental stability graphite/PMR-15 composites

During the past few years the Boeing Company was screening graphite composites for use in hot areas of engine nacelle structure. Structural and thermal analyses have shown that there is the potential for a 25 to 30 percent weight savings by using a graphite polyimide (Gr/PI) composite material in this type of structure. Work conducted on the NASA CASTS program (Composites for Advanced Space Transportation Systems) amply demonstrated the capability of Graphite/PMR-15 for short term service (125 hours) at temperatures up to 589 K (600 F). In addition, the CASTS program demonstrated that large structures could be fabricated using Gr/PMR-15. In commercial applications, however, the requirement exists for long term service capability (tens of thousands of hours) at temperatures ranging upwards from 449 K (350 F). The results of Graphite/PMR-15 materials characterization efforts conducted at Boeing are presented with emphasis on materials properties after isothermal aging at temperatures of 449 K (350 F) and above.

Sheppard, C. H.↗
DOE OSTI2024

Probing Basal and Prismatic Planes of Graphitic Materials for Metal Single Atom and Subnanometer Cluster Stabilization

Abstract Supported metal single atom catalysis is a dynamic research area in catalysis science combining the advantages of homogeneous and heterogeneous catalysis. Understanding the interactions between metal single atoms and the support constitutes a challenge facing the development of such catalysts, since these interactions are essential in optimizing the catalytic performance. For conventional carbon supports, two types of surfaces can contribute to single atom stabilization: the basal planes and the prismatic surface; both of which can be decorated by defects and surface oxygen groups. To date, most studies on carbon‐supported single atom catalysts focused on nitrogen‐doped carbons, which, unlike classic carbon materials, have a fairly well‐defined chemical environment. Herein we report the synthesis, characterization and modeling of rhodium single atom catalysts supported on carbon materials presenting distinct concentrations of surface oxygen groups and basal/prismatic surface area. The influence of these parameters on the speciation of the Rh species, their coordination and ultimately on their catalytic performance in hydrogenation and hydroformylation reactions is analyzed. The results obtained show that catalysis itself is an interesting tool for the fine characterization of these materials, for which the detection of small quantities of metal clusters remains a challenge, even when combining several cutting‐edge analytical methods.

Vidal, Mathieu↗
DOE OSTI2016

Helical Poly(5-alkyl-2,3-thiophene)s: Controlled Synthesis and Structure Characterization

Whereas Poly(3-alkyl-2,5-thiophene)s (P3AT), with many potential applications, have been extensively investigated, their ortho-connected isomers, poly(5-alkyl-2,3-thiophene)s (P5AT), have never been reported because of the difficulty in their syntheses. We herein present the first synthesis of regioregular P5AT via controlled Suzuki cross-coupling polymerization with PEPPSI-IPr as catalyst, affording the polymers with tunable molecular weight, narrow polydispersity (PDI) and well-defined functional end groups at the gram scale. The helical geometry of P5AT was studied by a combination of NMR, small angle x-ray scattering (SAXS) and scanning tunneling microscopy (STM). Particularly, the single polymer chain of poly(5- 2 butyl-2,3-thiophene) (P5BT) on highly oriented pyrolytic graphite (HOPG) substrates with either M or P helical conformation was directly observed by STM. The comparison of UV-vis absorption between poly(5-hexyl-2,3-thiophene) (P5HT) (λ = 345 nm) and poly(3-hexyl-2,5- thiophene) (P3HT) (λ = 450 nm) indicated that the degree of conjugation of the backbone in P5HT is less than in P3HT, which may be a consequence of the helical geometry of the former compared to the more planar geometry of the latter. Moreover, we found that P5HT can emit green fluorescence under UV (λ = 360 nm) irradiation

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Graphite fiber textile preform/copper matrix composites

This project has the objective of exploring the use of graphite fiber textile preform/copper matrix composites in spacecraft heat transmitting and radiating components. The preforms are to be fabricated by braiding of tows and when infiltrated with copper will result in a 3-D reinforced, near net shape composite with improved specific properties such as lower density and higher stiffness. It is anticipated that the use of textile technology will result in a more robust preform and consequently better final composite; it is hard to anticipate what performance tradeoffs will result, and these will be explored through testing and characterization.

Filatovs, G. J.↗
DOE OSTI2016

High temperature oxidation of PCD coated Zr alloy

Polycrystalline diamond (PCD) coating is a promising possibility for prevention, or reduction of high temperature oxidation of zirconium alloys and decrease corrosion rate of zirconium alloy during standard operation. Zirconium alloys are widely used as cladding and construction material in almost all types of nuclear reactors, where usually creates a barrier between nuclear fuel and cooling water in the primary circuit. Hydrogen and considerable amount of heat is released during steam oxidation that may occur in an eventual accident. In this paper zirconium alloy was covered by polycrystalline diamond layer using Plasma Enhanced Linear Antennas Microwave Chemical Vapor Deposition system reactor. X-Ray Diffraction and Raman spectroscopy measurements confirmed coverage of the surface area with crystalline and amorphous carbon layer. Characterizations (Raman spectroscopy) were done for zirconium alloy covered with polycrystalline diamond layer before and after high temperature steam exposure. Weight increase and hydrogen release were measured during steam exposure. The results show that the oxidation kinetics of PCD coated samples is similar to kinetics of uncoated samples at almost all temperatures, but with lower hydrogen production and lower weight gains. Most important difference is in later beginning of breakaway oxidation at 1000 Celsius degrees, when breakaway oxidation starts on PCD coated sample 15 minutes later. Raman spectroscopy revealed graphitization of the PCD layer and the diamond sp{sup 3} bounds are lost and the Raman signal consists only from the two graphite-related D bounds. It implies conversion of PCD layer to the homogeneous non-crystalline carbon layer with a large content of graphitic phase. Overall hydrogen production and weight gain values are generally lower then for uncoated samples.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Revisiting Discharge Mechanism of CF x as a High Energy Density Cathode Material for Lithium Primary Battery

Lithium/fluorinated graphite (Li/CFx) primary batteries show great promise for applications in a wide range of energy storage systems due to their high energy density (>2100 Wh kg –1 ) and low self-discharge rate (<0.5% per year at 25 °C). While the electrochemical performance of the CF x cathode is indeed promising, the discharge reaction mechanism is not thoroughly understood to date. In this article, a multiscale investigation of the CF x discharge mechanism is performed using a novel cathode structure to minimize the carbon and fluorine additives for precise cathode characterizations. Titration gas chromatography, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, cross-sectional focused ion beam, high-resolution transmission electron microscopy, and scanning transmission electron microscopy with electron energy loss spectroscopy are utilized to investigate this system. Results show no metallic lithium deposition or intercalation during the discharge reaction. Crystalline lithium fluoride particles uniformly distributed with <10 nm sizes into the CF x layers, and carbon with lower sp2 content similar to the hard-carbon structure are the products during discharge. This article deepens the understanding of CF x as a high energy density cathode material and highlights the need for future investigations on primary battery materials to advance performance.

25 ENERGY STORAGE↗
DOE OSTI2021

Progress of Divertor Heat and Particle Flux Control in EAST for Advanced Steady-State Operation in the Last 10 Years

Active control of the excessively high heat and particle fluxes on the divertor target plates is of fundamental importance to the steady state operation of tokamaks, especially for fusion reactors. A series of experiments have been carried out on this critical issue to relieve the plasma-wall interactions in the experimental advanced superconducting tokamak (EAST) in the last ten years, not only contributing to the long pulse operation of EAST itself, but also providing physical understandings and potential techniques to the next-generation devices like ITER. Here we have characterized the power deposition pattern and broadened the divertor footprint width effectively. The plasma-wetted area is actively handled using either 3-dimentional edge magnetic topology or advanced plasma equilibrium, thereby peak heat flux around the strike point is reduced. Active control of detachment or radiation compatible with core plasma performance has progressed significantly in very recent years, with a series of active feedback control modules developed and utilized successfully, based on the divertor physics advances with both experiments and simulation. The upper divertor of EAST was upgraded from graphite to active water-cooling ITER-like tungsten in 2014, exhibiting much enhanced heat removal capability. As for the particle exhaust including both fueling and impurity particles, in addition to wall conditioning and impurity source control, the efficiency of particle flux exhaust is optimized by making full use of the divertor closure and the plasma drifts in both scrape-off layer and divertor volume. These heat and particle exhaust advances contribute greatly to a series of EAST achievements like H-mode operation over 100 s. A brief near-term plan on the integrated control of divertor plasma-wall interactions in long-time scale will also be introduced, aiming to provide favorable divertor operation solution for ITER and CFETR.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Towards a mechanistic understanding of the sol–gel syntheses of ternary carbides

Sol–gel chemistry, while being extremely established, is to this day not fully understood, and much of the underlying chemistry and mechanisms are yet to be unraveled. Here, in this work, we elaborate on the sol–gel chemistry of Cr 2 GaC, the first layered ternary carbide belonging to the MAX phase family to ever be synthesized using this wet chemical approach. Leveraging a variety of both in- and ex situ characterization techniques, including X-ray and neutron powder diffraction, X-ray absorption fine structure analyses, total scattering analyses, and differential scanning calorimetry coupled with mass spectrometry, in-depth analyses of the local structures and reaction pathways are elucidated. While the metals first form tetrahedrally and octahedrally coordinated oxidic structures, that subsequently grow and crystallize into oxides, the carbon source citric acid sits on a separate reaction pathway, that does not merge with the metals until the very end. In fact, after decomposing it remains nanostructured and disordered graphite until the temperature allows for the reduction of the metal oxides into the layered carbide. Based on this, we hypothesize that the method is mostly applicable to systems where the needed metals are reducible by graphite around the formation temperature of the target phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Refinement of the composition and structure of YBaCo{sub 4-x}Al{sub x}O{sub 7+{delta}} crystals

YBa(Co{sub 4-x}Al{sub x})O{sub 7+{delta}} (114Y) crystals have been grown in the Y-Ba-Co-O system by spontaneous crystallization from a slowly cooled nonstoichiometric melt. To change the oxygen content, the crystals were isothermally annealed in air in the range of 280-490 Degree-Sign C. The crystals grown were characterized by scanning electron microscopy and powder X-ray diffraction. According to the data of an X-ray spectroscopic quantitative microprobe analysis, the average compositions of 'as-grown' and oxygen-saturated crystals were Y{sub 1.04}Ba{sub 1}Co{sub 3.54}Al{sub 0.50}O{sub 7.8} and Y{sub 1.02}Ba{sub 1}Co{sub 3.55}Al{sub 0.51}O{sub 8.4}, respectively. The refinement of the crystal structure after saturation on an automatic Bruker X8APEX diffractometer with a CCD detector (MoK{alpha} radiation, graphite monochromator, {theta}{sub max} = 32.54 Degree-Sign , sp. gr. P6{sub 3}mc, a = 6.2746(9), c = 10.257(3) Angstrom-Sign , V = 349.71(13) Angstrom-Sign {sup 3}, Z = 2, d{sub calcd} = 5.220 g/cm{sup 3}) reveals the location of Al in two independent positions of Co atoms and yields the general formula of the compound as YBaCo{sub 3.26}Al{sub 0.74}O{sub 7}. Problems related to the difference in the compositions obtained by different methods are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2019

Wear Trends of the HERMeS Thruster as a Function of Throttle Point

A series of short-duration (200 h) wear tests were conducted with two Hall Effect Rocket with Magnetic Shielding (HERMeS) technology demonstration units. Front pole covers, cathode keeper, and discharge channel wear were characterized as a function of discharge voltage, magnetic field strength, and chamber pressure. No discharge channel erosion was observed. Inner pole cover erosion was shown to be a weak function of discharge voltage with most erosion occurring at the lowest value, 300 V. The Technology Demonstration Unit (TDU) 3 keeper electrode eroded with each operating condition, with high magnetic field yielding the greatest erosion rate. The TDU-1 keeper electrode exhibited net deposition suggesting its configuration is more consistent with meeting overall HERMeS service life requirements. Ratios of molybdenum to graphite erosion rates suggests, with high uncertainty, that the sputtering ions are originating downstream of the thruster exit plane, striking the surface with small angles of incidence.

Williams, George J., Jr.↗
DOE OSTI2018

Microstructure Characterization and Modeling for Improved Electrode Design

As part of DOE's Computer-Aided Engineering of Batteries Program, the National Renewable Energy Laboratory is developing detailed models capturing the influence of lithium-ion battery electrode design, recipe and processing on the electrode's microstructure and relating that microstructure to device-level performance. Given the difficulty in obtaining 3D microstructural images of the electrode's inert components, team member Purdue University developed an algorithm to computationally generate the so-called carbon-binder domain (CBD) for any given recipe. Mesoscale models explore the device-level impact of the CBD phase on multiple idealized and actual electrode geometries. With the inclusion of this CBD phase, microstructure models are used to predict the tortuosity of 14 different graphite and NMC electrode designs. Tortuosity predictions are shown in good agreement with experimental direct measurement and electrochemical rate studies.

25 ENERGY STORAGE↗
DOE OSTI2016

Spectroscopic investigations on oxidized multi-walled carbon nanotubes

The pristine multi-walled carbon nanotubes (MWCNTs) were oxidized by the ultrasonication process. The oxidized MWCNTs were characterized by the X-ray diffraction (XRD), ultraviolet–visible (UV-Vis) and Fourier transform -Raman (FT-Raman) spectroscopic techniques. The XRD analysis confirms that the oxidized MWCNTs exist in a hexagonal structure and the sharp XRD peak corresponds to the (002) Bragg’s reflection plane, which indicates that the MWCNTs have higher crystalline nature. The UV-Vis analysis confirms that the MWCNTs functionalized with the carboxylic acid. The red shift was observed corresponds to the D band in the Raman spectrum, which reveals that the reduced disordered graphitic structure of oxidized MWCNTs. The strong Raman peak was observed at 2563 cm{sup -1} corresponds to the overtone of the D band, which is the characteristic vibrational mode of oxidized MWCNTs. The carboxylic acid functionalization of MWCNTs enhances the dispersibility, which paves the way for potential applications in the field of biosensors and targeted drug delivery.

77 NANOSCIENCE AND NANOTECHNOLOGY↗