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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Moderate temperature Na cells. III - Electrochemical and structural studies of Cr0.5V0.5S2 and its Na intercalates

Experimental results are reported on the behavior of a rechargeable Na cell incorporating a Cr0.5V0.5S2 cathode. The cell operates at 130 C and uses as electrolyte a 1M solution of NaI in 1,2-bis(2-methoxy-ethoxy)ethane (triglyme). The mechanism of discharge of Cr0.5V0.5S2 involves Na intercalation. It is found that the maximum rechargeable capacity of the Cr0.5V0.5S2 cathode is 0.7 e(overbar)/mol. With an average cell voltage of 1.9 V, the theoretical specific energy of the cathode is 273 W-hr/kg.

Abraham, K. M.↗
NASA NTRS1985

Intercalated-Carbon Low-Resistivity Fibers

Experiments show feasiblity of making lightweight, electrically conductive fibers from graphite intercalation compounds. Fibers thermally stable in air up to 100 degrees C. These materials used as ingredients in composite enclosures for electronic equipment, especially where such equipment must be both light in weight and electrically conductive for electrostatic drainage or radio-frequency suppression.

Yavrouian, A. H.↗
NASA NTRS1985

The 13C nuclear magnetic resonance in graphite intercalation compounds

The (13)C NMR chemical shifts of graphite intercalation compounds were calculated. For acceptor types, the shifts come mainly from the paramagnetic (Ramsey) intra-atomic terms. They are related to the gross features of the two-dimensional band structures. The calculated anisotropy is about -140 ppm and is independent of the finer details such as charge transfer. For donor types, the carbon 2p pi orbitals are spin-polarized because of mixing with metal conduction electrons, thus there is an additional dipolar contribution which may be correlated with the electronic specific heat. The general agreement with experimental data is satisfactory.

Tsang, T.↗
NASA NTRS1984

Diamagnetism and charge transfer in graphite intercalation compounds

The magnetic susceptibilities at 300 K of the acceptor-type intercalation compounds of graphite with Br2 and ICl are calculated; the results are compared with published experimental measurements in graphs; and the charge-transfer parameter f is inferred using a rigid-band model (Loughin et al., 1978; Weinberger et al., 1978; Mattix et al., 1983). Assuming a screening length of 200 pm, the values determined are f = 0.3 for C(8N)Br2 and f = 0.09 for C(13N)ICl.

Tsang, T.↗
NASA NTRS1985

C-13 nuclear magnetic resonance in graphite intercalation compounds

The C-13 NMR chemical shifts of graphite intercalation compounds have been calculated. For acceptor types, the shifts come mainly from the paramagnetic (Ramsey) intra-atomic terms. They are related to the gross features of the two-dimensional band structures. The calculated anisotropy is about - 140 ppm and is independent of the finer details such as charge transfer. For donor types, the carbon 2p pi orbitals are spin-polarized because of mixing with metal-conduction electrons, thus there is an additional dipolar contribution which may be correlated with the electronic specific heat. The general agreement with experimental data is satisfactory.

Tsang, T.↗
NASA NTRS1986

Simultaneous electrical resistivity and mass uptake measurements in bromine intercalated fibers

Changes in mass and electrical resistivity of several types of pitch-based and vapor-grown graphite fibers were monitored during reaction with bromine. The observed threshold pressure dependent reaction suggested that the fibers were intercalated. In the fully brominated compound, the mass was increased by 44 percent and the resistivity was improved by a factor of 17. In the residue compound, the mass was increased by 22 percent and the resistivity was improved by a factor of 5. Fibers possessing different degrees of graphitization had surprisingly similar changes in both mass and resistivity.

Jaworske, D. A.↗
NASA NTRS1988

Production and characterization of CdCl2 intercalated graphite fibers

Graphite fibers were intercalated using CdCl2 as a Cl source and Cl2 as carrier gas. Fibers were synthesized with a resistivity-density figure of merit comparable to that of copper. These fibers can withstand practical electrical current densities as high as 54,000 A/sq cm. Their thermal coefficient of resistivity is 0.0016 C, which is approximately 41 percent of those for copper and aluminum.

Gooden, Clarence E.↗
NASA NTRS1992

Kinetics of intercalation of lithium into NbSe3 and TiS2 cathodes

Titanium disulfide and niobium triselenide are two well-studied candidate materials for positive electrodes in rechargeable lithium cells. A comparative study of the kinetics of intercalation of lithium in both the cathodes is made here based on various electrochemical techniques, i.e., linear polarization, potentiodynamic polarization, and ac impedance under different experimental conditions such as prismatic or disk configuration of fresh, partially discharged, or cycled electrode. Further, the diffusion coefficients of lithium ions in these cathodes are estimated under these conditions using conventional techniques, i.e., ac impedance, chronocoulometry, chronoamperometry, and current pulse relaxation. Based on the values of the diffusion coefficients, the applicability of these methods for the determination of diffusion coefficients is discussed.

Ratnakumar, B. V.↗
NASA NTRS1993

Intercalated hybrid graphite fiber composite

The invention is directed to a highly conductive lightweight hybrid material and methods of producing the same. The hybrid composite is obtained by weaving strands of a high strength carbon or graphite fiber into a fabric-like structure, depositing a layer of carbon onto the structure, heat treating the structure to graphitize the carbon layer, and intercalating the graphitic carbon layer structure. A laminate composite material useful for protection against lightning strikes comprises at least one layer of the hybrid material over at least one layer of high strength carbon or graphite fibers. The composite material of the present invention is compatible with matrix compounds, has a coefficient of thermal expansion which is the same as underlying fiber layers, and is resistant to galvanic corrosion in addition to being highly conductive. These materials are useful in the aerospace industry, in particular as lightning strike protection for airplanes.

Gaier, James R.↗
NASA NTRS2002

The Electrical and Thermal Conductivity of Woven Pristine and Intercalated Graphite Fiber-Polymer Composites

A series of woven fabric laminar composite plates and narrow strips were fabricated from a variety of pitch-based pristine and bromine intercalated graphite fibers in an attempt to determine the influence of the weave on the electrical and thermal conduction. It was found generally that these materials can be treated as if they are homogeneous plates. The rule of mixtures describes the resistivity of the composite fairly well if it is realized that only the component of the fibers normal to the equipotential surface will conduct current. When the composite is narrow with respect to the fiber weave, however, there is a marked angular dependence of the resistance which was well modeled by assuming that the current follows only along the fibers (and not across them in a transverse direction), and that the contact resistance among the fibers in the composite is negligible. The thermal conductivity of composites made from less conductive fibers more closely followed the rule of mixtures than that of the high conductivity fibers, though this is thought to be an artifact of the measurement technique. Electrical and thermal anisotropy could be induced in a particular region of the structure by weaving together high and low conductivity fibers in different directions, though this must be done throughout all of the layers of the structure as interlaminar conduction precludes having only the top layer carry the anisotropy. The anisotropy in the thermal conductivity is considerably less than either that predicted by the rule of mixtures or the electrical resistivity.

Gaier, James R.↗
NASA NTRS1994

Crystal structure of a four-stranded intercalated DNA: d(C4)

The crystal structure of d(C4) solved at 2.3-A resolution reveals a four-stranded molecule composed of two interdigitated or intercalated duplexes. The duplexes are held together by hemiprotonated cytosine-cytosine base pairs and are parallel stranded, but the two duplexes point in opposite directions. The molecule has a slow right-handed twist of 12.4 degrees between covalently linked cytosine base pairs, and the base stacking distance is 3.1 A. This is in general agreement with the NMR studies. A biological role for DNA in this conformation is suggested.

Non-NASA Center↗
NASA NTRSDate not supplied

Intercalation and Exfoliation of Hexagonal Boron Nitride

Innovators at NASA's Glenn Research Center have made several breakthroughs in treating hexagonal boron nitride (hBN) nanomaterials, improving their properties to supplant carbon nanotubes in many applications. These advances have hBN nanomaterials set to transform applications such as heat sinks, electrical insulators, lightweight piezoelectric polymers for satellites and unmanned aerial vehicles, ceramic composites for jet engines, biomedical components, and radiation shielding technology.

Hexagonal Boron Nitride↗
NASA NTRS1986

Anticorrelation of Shubnikov-deHaas amplitudes and negative magnetoresistance magnitudes in intercalated pitch based graphite fibers

In pitch based carbon fibers at low temperatures, simultaneous presence of a negative magnetoresistance and the Shubnikov-deHaas effect are found. The strengths of these effects correlate inversely. These results can be understood in terms of the amount of order vs disorder in the fiber, as described by Guigon and Oberlin from structural studies.

Woollam, John A.↗