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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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Baseline Graphite Characterization: Purpose of Baseline, Mechanical Baseline Tests, Physical Properties Tests, Methodology, Baseline progress, Density, Ultimate Tensile Strength, PCEA Ultimate Tensile Strength, Split Disc Tests, Compression Tests, Flexural Tests, and Coefficient of Thermal Expansion.
Graphite overview: Material science, supply chain facts, nuclear material science, licensing thoughts
Abstract The formation of a stable solid electrolyte interphase (SEI) at graphite electrode is necessary for lithium‐ion batteries (LIB) to prevent excessive degradation of electrolytes. Until now, the exact organic composition of SEI has not been decisively determined with lithium ethylene mono‐carbonate (LEMC) being one of the debated components. An air‐tight ambient mass spectrometry (MS) platform is developed to directly characterize the air‐sensitive organic components present in SEI. Ionization occurs via a solvent‐free field‐induced process at atmospheric pressure. Our experimental data, based on tandem MS analysis, revealed LEMC to be the major organic component in SEI. This result resolves a long‐standing mystery surrounding the composition of native SEI in LIB, where no trace of the other debated compound, lithium ethylene dicarbonate, was detected. The energetics of fragmentation of LEMC and the corresponding stabilities of various ionic species detected during the air‐tight ambient MS analysis were calculated using density functional theory (DFT). Our findings confirmed favorable protonation energies and suggested the molecular structures for many of the detected species. Solvent (i. e., ethylene carbonate)‐induced stabilization effects observed during the ionization process were also confirmed by DFT. The reported study encourages the routine use of ambient mass spectrometry to characterize both anodic and cathodic electrodes of all battery types as well as to study other air‐sensitive materials in their native state.
The aim of the present work is mathematical modeling of the heat and mass transfer of {sup 137}Cs under the action of low-temperature equilibrium plasma flow on sections of graphite contaminated by radionuclides. The methods of investigation are calculation of the temperature and mass rate of evaporation of radiocesium by solving a system of quasi-homogeneous nonstationary heat conduction equations with boundary conditions of the first and third kind, which take account of mass transfer, by means of finite-difference elements using the ANSYS package.
Computational and experimental validation of the serviceability of zirconium channels in the reactor core according to strength criteria was conducted in order to ensure safe operation of the RBMK reactor facility under graphite stack deformation conditions. A complex of computational and experimental studies confirmed that the requirements of the operative federal norms and regulations for objects using nuclear power are met.
The results of computational and experimental studies performed at NIKIET to validate the serviceability of the actuating mechanisms of the safety-and-control system in terms of assuring the passability of the absorbing working rods in the case of channel bending under conditions of RMMK-1000 graphite stack distortion are presented. The results of this work were used for the power-generating units with RBMK-1000. They can be used for other types of reactors, in which the working absorbing rods of the SCS move in channels, as well as in other areas of industry where the passability of solid elements is important.
Parameters of the erosive laser plasma of a graphite target on exposure to Nd{sup 3+}:YAG-laser pulses with a wavelength λ = 1064 nm and a pulse duration τ ~ 20 ns have been investigated. Two zones of glow have been found. One zone is quiescent and is located at the target surface at the site of exposure to laser radiation. The other glow zone moves opposite to a laser beam with a velocity of ~10 km/s. A method to control charged-particle fluxes in the erosive laser torch has been proposed.
Effects of core electrons on total energy, correlation energy, and binding energy of graphene, graphite, and diamond have been investigated along with density functional theory (DFT) calculations at the PBE level of theory using all electron and frozen-core calculations. For these calculations, correlation-consistent basis sets cc-pVXZ and cc-pCVXZ have been used where X is the cardinal number that represents the maximum angular momentum number in the basis set. By taking the difference between all electron and frozen-core calculations, core-electron binding energy contribution for each basis set has been obtained. It has been shown that to reduce the effects of core electrons, large basis sets should be used.
Microwave absorbers of cobalt ferrite and graphite composite have been fabricated to investigate the broadening of absorption frequency by mixing small and large particles and comparing single- and double-layer composites in order to broaden the absorption frequency and to enhance multireflection and scattering of electromagnetic wave. CoO and Fe{sub 2}O{sub 3} precursors were mechanically alloyed and sintered at 800, 900, 1000 and 1100 {sup ∘}C in order to synthesise various particle sizes and shapes. A mixed sample of powders sintered at the above mentioned temperatures was also formed. The morphological, phase, and magnetic properties of these samples were studied. Two series of samples have been synthesised which were single- and double-layer composites. Single-layer composite consisted of mixed particles, and their thickness parameters were varied. Double-layer composite was also prepared with various particle sizes of CoFe{sub 2}O{sub 4} as a layer and graphene as another layer. The effect of these layers as matching and absorbing layer was studied. The degree of crystallinity of CoFe{sub 2}O{sub 4} was increased with increase of sintering temperature. Microstructural study showed the evolution of particle size and shape subjected to sintering temperature. Arrhenius plot showed two stages of growth process with activation energy calculated at 26.85 and 83.091 kJ/mol. The critical size of single domain of this sample plotted from the coercivity against particle size was 63.44 nm. Single-layer composite with mixed particle size was not able to show good electromagnetic (EM)-wave absorption; however double-layer composite showed good return loss. The mechanism of the EM-wave absorption of double-layer composite was discussed in this paper.
The preparation and study of electrochemical properties of a graphite screen-printed electrode (SPE) modified with the GO/Fe{sub 3}O{sub 4}@SiO{sub 2} (GO is graphene oxide) nanocomposites are described. The morphologies of the GO/Fe{sub 3}O{sub 4}@SiO{sub 2} nanocomposites were examined by scanning electron microscopy. The electrochemical oxidation of vitamin B{sub 6} (pyridoxine) on SPE modified with the GO/Fe{sub 3}O{sub 4}@SiO{sub 2} nanocomposite was investigated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. Under optimum conditions (pH 7.0), the vitamin B{sub 6} oxidation at the surface of the modified SPE occurs at a potential about 190 mV less positive than that at the unmodified SPE. A linear voltammetric response for vitamin B{sub 6} was obtained in the concentration range 1.0•10 {sup 6}—9.0•10 {sup 4} mol L{sup –1} with a detection limit of 5.2•10 {sup 7} mol L{sup –1} using differential pulse voltammetry. The developed sensor was also successfully applied for determination of trace level of vitamin B{sub 6} in both the standard vitamin B{sub 6} sample and biological samples (urine).
The kinetics for O 2 oxidation of individual graphite and graphene platelet nanoparticles (NPs) were studied as a function of temperature (1200 to 2200 K) at varying oxygen partial pressures, using a single nanoparticle mass spectrometry method. NP temperature (TNP) was measured by measuring the NP thermal emission spectra during the kinetics studies. The initial oxidation efficiency is found to peak in the 1200 to 1500 K range, dropping by an order of magnitude as TNP was increased above 2000 K. There were large NP-to-NP variations in the oxidation rates, attributed to variations in the NP surface structure. In addition, the oxidation efficiencies evolved, non-monotonically, as the NPs reacted, decreasing by factors of between 10 and 300. This evolution of reactivity is attributed to changes in the NP surface structure due to the combination of oxidation and annealing. In conclusion, the optical properties, including wavelength dependence of the emissivity and the absorption cross section for the 532 nm heating laser, also tended to evolve as the NPs oxidized, but differently for each individual NP, presumably reflecting differences in the initial structures and their evolution.
This study evaluates the effects of two types of graphite nanoplatelet (GNP-C and GNP-M) and one type of carbon nanofiber (CNF) on rheological properties, hydration kinetics, autogenous shrinkage, and pore structure of ultra-high-performance concrete (UHPC). The dispersion method was optimized to secure uniform dispersion of the nanomaterials in the UHPC. The plastic viscosity decreased with the nanomaterials content as the content was increased from 0 to 0.05%. As the nanomaterials content increased from 0 to 0.3%, the duration of induction period was extended by the addition of CNF, but shortened by use of GNP-C or GNP-M; cumulative hydration heat release was increased by introduction of nanomaterials; the autogenous shrinkage of UHPC with CNF, GNP-C, and GNP-M was increased by 30%, 20%, and 20%, respectively. The use of 0.3% CNFs reduced the total porosity of the UHPC by approximately 35%, indicating that the presence of CNFs refined the microstructure of UHPC.
In the present study, carbon nanotube (CNT), thermally reduced graphite oxide (TRGO), and CNT-TRGO were functionalized with p-sulfonatocalix[4]arene (SC4) and then investigated for fluorescent detection of cholesterol in the presence of rhodamine 6G (R6G). All of the composite samples show effective quenching of R6G fluorescent intensity without cholesterol, but the fluorescence intensity significantly increases with the addition of cholesterol. The results indicate a strong interaction between SC4 composites and cholesterol rather than between the SC4 composites and R6G, increasing R6G fluorescence intensity in the presence of cholesterol due to the release of R6G from the SC4 composites. Formation of the complex, made of the SC4 composite plus the cholesterol, enables the detection of cholesterol in the wide range of cholesterol concentration up to 109 µM. The binding constant between SC4 and cholesterol has been calculated, indicating that the SC4 composites display the maximum binding constant of 1.9 × 10 4 M -1 with cholesterol.
The electrochemical performance of vanadium redox flow batteries (VRFBs) was enhanced via laser-patterned graphite felt (GF) electrodes. The laser-structured GF electrodes engineered via preparing a series of well-ordered microscopic channel structures with an average width of 200 μm, creating a three-dimensional carbon framework. The ultrafast laser patterning increased the porosity by 10%, as compared to pristine electrode. The analysis of the overpotential distribution using electrochemical impedance spectroscopy revealed that the electrode polarization involving charge transfer and diffusion resistance is strongly alleviated with the aid of carbon micro-perforation. The advanced design of laser-structured GF electrode also exhibits high rate capability, low internal resistance, and excellent cyclability. The improved performance was attributed to the synergistic effect involving (i) high electrochemically active surface area for rapid electrochemical reactions (i.e., V(II)/V(III) and V(IV)/V(V) redox couples) and (ii) excellent transport properties for facile electron/ion/species transport. The micro-scale channels created with the laser-ablation technique act as capillary structures and enabled homogeneous and rapid wetting of GF electrodes as formulated with the classical Washburn equation. The VRFB equipped with the laser-structured GF electrodes delivered a high discharge capacity with exceptional capacity retention upon extended cycling (>84.9%). In conclusion, accordingly, the design of laser-structured electrode paves the pathway towards finely tuning the electrode internal microstructure for improved cyclability, durability, and capacity retention in various electrochemical energy storage/conversion devices (e.g. all-vanadium redox flow batteries).
Harvesting solar energy, preventing hot spots in electronics, transport of temperature-sensitive materials, and capture and repurposing of thermal energy require a latent heat thermal energy storage (TES) system to store/discharge heat repeatedly. For the practical application of phase change material (PCM) composites within TES systems, reliable thermal performance throughout its operational lifetime is essential. Nevertheless, the reliability of thermal conductivity in multi-phase composites over relevant numbers (>10 3 ) of melt/freeze cycles has barely been studied, particularly for composites containing fillers for thermal conductivity enhancement. Here, we introduce a preform-type expanded graphite (EG)/paraffin wax composite possessing highly robust heat transfer and storage properties even after 10,000 melt/freeze cycles. To achieve such excellent reliability, comparative studies on the combined influence of fabrication process, particle size, EG vol%, binder amount, and compaction on both magnitude and robustness of thermal conductivity were undertaken. Our parametric study has yielded a trade-off between thermal conductivity and latent heat. Based on our modeling, 20 vol% EG approaches the case where all EG particles are well-connected thermally while 10 vol% EG is close to loosely connected fillers in the matrix. Thermal conductivity of our paraffin composites containing 20 vol% EG (25.1 W·m -1 ·K -1 ) is highest among other EG/paraffin composites without aligned EG in the literature. After 10,000 thermal cycling, negligible conductivity fading was observed for the 10 vol% EG composite, while reduction in latent heat remained within 10% for all 10, 14, 17 and 20 vol% EG samples. Here we anticipate this work provides insight on suitable recipe for desirable magnitude and robustness of thermal conductivity of EG/paraffin composites.
Solar-driven photocatalytic generation of H 2 O 2 over metal-free catalysts is a sustainable approach for value-added chemical production. Here, we synthesized chlorine-doped graphitic carbon nitride (Cl-doped g-C 3 N 4 ) through a solvothermal method to effectively produce H 2 O 2 with a rate of 1.19 ± 0.06 µM min –1 under visible light irradiation, which was improved by 104 times compared to pristine g-C 3 N 4 . Continuous net production of H 2 O 2 was realized at a rate of 2.78 ± 0.10 µM min –1 up to 54 h with isopropanol as the hole scavenger, whereas H 2 O 2 production was only sustained for ~ 6 h without scavengers. Both molecular simulations and advanced spectroscopic characterizations elucidated that the Cl dopant increased the charge transfer rate, decreased the bandgap, and reduced the activation energy of the rate-limiting step of O 2 reduction, all of which favored H 2 O 2 production. Furthermore, this work implemented a novel metal-free photocatalyst for sustainable H 2 O 2 production and elucidated the mechanism for promoting H 2 O 2 production that can guide future photoreactive nanomaterial design.
This study explores low molecular weight polymers with the same chemical repeat structure as high molecular weight poly acrylic acid (PAA) and lithium poly acrylic acid (LiPAA) binders which act as a dispersant to improve the silicon-graphite electrode performance. The electrodes which utilize LiPAA as a dispersant perform, on average, the best with respect to the maximum capacity (compared to theoretical), rate performance, and capacity retention with time. These electrodes also have the poorest dispersion of binder, indicating that the poor binder dispersion is essential to electrode performance. In contrast, this study shows that electrodes formulated using PAA had good dispersion and performs the worst in cycling. Finally, this work demonstrates that the binder is not uniformly distributed in the electrode, but rather resides in local regions. Overall, the results indicate these regions accommodate volume expansion during cycling.
A color-tunable luminescent material was prepared based on the composition of functionalized graphitic carbon nitride (g-C{sub 3}N{sub 4}) and europium (III). The functionalized g-C{sub 3}N{sub 4} layers not only behave as multifunctional supports including ligand coordinated with europium (III) and a support structure for the formation of the luminescent material, but exhibit excitation wavelength-dependent luminescence, thus the energy transfer between the functionalized g-C{sub 3}N{sub 4} and europium (III) can match very well by controlling the emission wavelength of functionalized g-C{sub 3}N{sub 4}. The as-prepared materials was comprehensively characterized via X-ray photoelectron spectroscopy, Fourier Transform Infrared spectroscopy, X-ray scattering techniques, Ultraviolet and Visible spectrophotometer, fluorescence spectrophotometer, thermogravimetric analysis, etc. The luminescent material exhibits multi-color emissions which are consistent with the characteristic emissions of europium (III) and functionalized g-C{sub 3}N{sub 4}, and the photoluminescence quality and density of the europium (III) can be greatly enhanced. The brilliant optical properties of the materials make them suiting for multipurpose applications in practical fields. - Graphical abstract: Schematic illustration of the synthesis and basic composition of the luminescent material. Inset figures were luminescence emission spectra of g-C{sub 3}N{sub 4} (A), europium (III) complex (a) and luminescent material (b) with the same concentration in (B) (K{sub ex}=350 nm) and photographs of (left) H{sub 2}O and (right) the H{sub 2}O dispersion of luminescence emission spectra under 350 nm UV radiation. The energy transfer in the luminescent material matchs very well and it exhibits multi-color emissions simultaneously. The enhanced photoluminescence quality and density of the europium (III) makes them suiting for multipurpose applications in practical fields. - Highlights: • Luminescent material exhibits multi-color emissions when excited by single wavelength. • The energy trsnsfer between functionalized g-C{sub 3}N{sub 4} and europium matches very vell. • Functionalized g-C{sub 3}N{sub 4} exhibits excitation wavelength-depengdent bright blue luminescence. • Functionalized g-C{sub 3}N{sub 4} layer provided as multifunctional supports.