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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Synthesis of ZnO:As Films Using Off-Axis Sputtering Deposition

As a novel oxide semiconductor material, ZnO is interesting for use in many applications. For fabricating electronic devices, it is important to have n- and p- type ZnO materials. Arsenic has been proven to be one of the p-type dopants for ZnO materials. However, information in studying the ZnAsO ternary compound films has been scarce. In order to investigate the morphology, structure and electrical properties of ZnAsO ternary compounds, ZnO:As films have been synthesized using off-axis sputtering deposition on various substrates including (100) Si and (0001) sapphire crystals. Films are grown under various growth conditions. ZnO:As targets with the atomic weight ratios of arsenic to zinc from 0.01 to 0.10 are used for film synthesis. The growth temperatures and pressures range from 350 to 550C and 5 to 150 mTorr, respectively. Argon to oxygen gas ratio for film growth is varied to examine the film quality as well. Film surface morphology, crystal structure, and compositions, are characterized using atomic force microscopy, x-ray diffraction, and energy dispersive spectroscopy, respectively. The compositions of target material and ZnO:As films grown under various conditions are then assessed. The electrical properties were also measured. The detail of these measurements will be discussed in the presentation.

Zhu, Shen↗
NASA NTRS1975

Review of electrical and thermal properties of carbon and graphite

Some of the electrical and thermal properties of ordered and partially ordered carbons are reviewed. Earlier and current research areas are discussed relative to electrical properties of pyrolytic and polycrystalline graphite; thermal, electrical, and magnetic properties of graphitizable and glassy carbon with heat treatment temperatures in the range 600-2500 C; Josephson junction-like and switching behavior in carbon films; and some high-conductivity and superconducting compounds made from carbon. Due to the newness and complexity of many of the areas examined, the results are not always completely understood, nor have these areas been completely investigated experimentally. Suggestions for future research are made.

Woollam, J. A.↗
NASA NTRS1986

Sediment-transport (wind) experiments in zero-gravity

The carousel wind tunnel (CWT) can be a significant tool for the determination of the nature and magnitude of interparticlar forces at threshold of motion. By altering particle and drum surface electrical properties and/or by applying electric potential difference across the inner and outer drums, it should be possible to separate electrostatic effects from other forces of cohesion. Besides particle trajectory and bedform analyses, suggestions for research include particle aggregation in zero and subgravity environments, effect of suspension-saltation ratio on soil abrasion, and the effects of shear and shearfree turbulence on particle aggregation as applied to evolution of solar nebula.

Iverson, J.↗
NASA NTRS1988

Effects Of Radiation On Elastomers

Report provides data on effects of radiation on elastomers. Quantifies effects by giving minimum radiation levels to induce changes of 1 percent and 25 percent in given properties. Electrical, mechanical, and chemical properties included in data. Combined effects of heat and radiation briefly considered. Data summarized in graphic form useful to designers.

Bouquet, Frank L.↗
NASA NTRS1995

Reduction, analysis, and properties of electric current systems in solar active regions

The specific attraction and, in large part, the significance of solar magnetograms lie in the fact that they give the most important data on the electric currents and the nonpotentiality of active regions. Using the vector magnetograms from the Marshall Space Flight Center (MSFC), we employ a unique technique in the area of data analysis for resolving the 180 deg ambiguity in order to calculate the spatial structure of the vertical electric current density. The 180 deg ambiguity is resolved by applying concepts from the nonlinear multivariable optimization theory. The technique is shown to be of particular importance in very nonpotential active regions. The characterization of the vertical electric current density for a set of vector magnetograms using this method then gives the spatial scale, locations, and magnitude of these current systems. The method, which employs an intermediate parametric function which covers the magnetogram and which defines the local `preferred' direction, minimizes a specific functional of the observed transverse magnetic field. The specific functional that is successful is the integral of the square of the vertical current density. We find that the vertical electric current densities have common characteristics for the extended bipolar (beta) (gamma) (delta)-regions studied. The largest current systems have j(sub z)'s which maximizes around 30 mA/sq m and have a linear decreasing distribution to a diameter of 30 Mn.

Gary, G. Allen↗
NASA NTRS1995

Reduction, Analysis, and Properties of Electric Current Systems in Solar Active Regions

The specific attraction and, in large part, the significance of solar vector magnetograms lie in the fact that they give the most important data on the electric currents and the nonpotentiality of active regions. Using the vector magnetograms from the Marshall Space Flight Center (MSFC), we employ a unique technique in the area of data analysis for resolving the 180 degree ambiguity in order to calculate the spatial structure of the vertical electric current density. The 180 degree ambiguity is resolved by applying concepts from the nonlinear multivariable optimization theory. The technique is shown to be of particular importance in very nonpotential active regions. The characterization of the vertical electric current density for a set of vector magnetograms using this method then gives the spatial scale, locations, and magnitude of these current systems. The method, which employs an intermediate parametric function which covers the magnetogram and which defines the local "preferred" direction, minimizes a specific functional of the observed transverse magnetic field. The specific functional that is successful is the integral of the square of the vertical current density. We find that the vertical electric current densities have common characteristics for the extended bipolar beta gamma delta-regions studied. The largest current systems have j(sub z)'s which maximizes around 30 mA per square meter and have a linear decreasing distribution to a diameter of 30 Mm.

Gary, G. Allen↗
NASA NTRS1967

Fission-electric cell irradiation

Capsule reactor irradiation experiments on fission electric devices under high radiation intensity to determine electrical properties and materials problems

ELECTRIC PROPERTY↗
NASA NTRS2015

Compatibility of the Radio Frequency Mass Gauge with Composite Tanks

The radio frequency mass gauge (RFMG) is a low-gravity propellant quantity gauge being developed at NASA for possible use in long-duration space missions utilizing cryogenic propellants. As part of the RFMG technology development process, we evaluated the compatibility of the RFMG with a graphite-epoxy composite material used to construct propellant tanks. The key material property that can affect compatibility with the RFMG is the electrical conductivity. Using samples of 8552IM7 graphite-epoxy composite, we characterized the resistivity and reflectivity over a range of frequencies. An RF impedance analyzer was used to characterize the out-of-plane electrical properties (along the sample thickness) in the frequency range 10 to 1800 MHZ. The resistivity value at 500 MHz was 4.8 ohm-cm. Microwave waveguide measurements of samples in the range 1.7 2.6 GHz, performed by inserting the samples into a WR-430 waveguide, showed reflectivity values above 98. Together, these results suggested that a tank constructed from graphite-epoxy composite would produce good quality electromagnetic tank modes, which is needed for the RFMG. This was verified by room-temperature measurements of the electromagnetic modes of a 2.4 m diameter tank constructed by Boeing from similar graphite-epoxy composite material. The quality factor Q of the tank electromagnetic modes, measured via RF reflection measurements from an antenna mounted in the tank, was typically in the range 400 Q 3000. The good quality modes observed in the tank indicate that the RFMG is compatible with graphite-epoxy tanks, and thus the RFMG could be used as a low-gravity propellant quantity gauge in such tanks filled with cryogenic propellants.

Radio frequencies↗
NASA NTRS2015

Compatibility of the Radio Frequency Mass Gauge with Graphite-Epoxy Composite Tanks

The radio frequency mass gauge (RFMG) is a low-gravity propellant quantity gauge being developed at NASA for possible use in long-duration space missions utilizing cryogenic propellants. As part of the RFMG technology development process, we evaluated the compatibility of the RFMG with a graphite-epoxy composite material used to construct propellant tanks. The key material property that can affect compatibility with the RFMG is the electrical conductivity. Using samples of 8552/IM7 graphite-epoxy composite, we characterized the resistivity and reflectivity over a range of frequencies. An RF impedance analyzer was used to characterize the out-of-plane electrical properties (along the sample thickness) in the frequency range 10 to 1800 MHZ. The resistivity value at 500 MHz was 4.8 ohm-cm. Microwave waveguide measurements of samples in the range 1.7 - 2.6 GHz, performed by inserting the samples into a WR-430 waveguide, showed reflectivity values above 98%. Together, these results suggested that a tank constructed from graphite/epoxy composite would produce good quality electromagnetic tank modes, which is needed for the RFMG. This was verified by room-temperature measurements of the electromagnetic modes of a 2.4 m diameter tank constructed by Boeing from similar graphite-epoxy composite material. The quality factor Q of the tank electromagnetic modes, measured via RF reflection measurements from an antenna mounted in the tank, was typically in the range 400 less than Q less than 3000. The good quality modes observed in the tank indicate that the RFMG is compatible with graphite-epoxy tanks, and thus the RFMG could be used as a low-gravity propellant quantity gauge in such tanks filled with cryogenic propellants.

Propellant tanks↗
NASA NTRS1975

Development of a thin film solid state gaseous HCl sensor

The selection of materials to develop a thin film HCl sensor is discussed. Data were primarily concerned with chemical and physical properties of the film and with electrical properties which exhibit and enhance electrical response when HCl is absorbed on the film surface. Techniques investigated for enhancing electrical response include changing conditions for growing films, adding impurities to the film, changing ambient light intensity, and altering the ambient temperature of the sensing element.

Source record↗
NASA NTRS2003

Functionalization of Carbon Nanotubes

These project will explore the functionalization of carbon nanotubes via the formation of molecular complexes with perylene diimide based systems. It is anticipated that these complexes would be soluble in organic solvent and enable the homogenous dispersion of carbon nanotubes in polymer films. Molecular complexes will be prepared and characterized using standard spectroscopic and thermal analytical techniques. Polymer films will be prepared with these complexes and their properties (electrical and thermal conductivity, mechanical properties, stability) evaluated.

Webber, Stephen E.↗
NASA NTRS1991

Effect of lightning strike on bromine intercalated graphite fiber/epoxy composites

Laminar composites were fabricated from pristine and bromine intercalated pitch based graphite fibers. It was found that laminar composites could be fabricated using either pristine or intercalated graphite fibers using standard fabrication techniques. The intercalated graphite fiber composites had electrical properties which were markedly improved over both the corresponding pitch based and polyacrylonitrile (PAN) based composites. Despite composites resistivities more than an order of magnitude lower for pitch based fiber composites, the lightning strike resistance was poorer than that of the Pan based fiber composites. This leads to the conclusion that the mechanical properties of the pitch fibers are more important than electrical or thermal properties in determining the lightning strike resistance. Based on indicated lightning strike tolerance for high elongation to failure materials, the use of vapor grown, rather than pitch based graphite fibers appears promising.

Gaier, James R.↗
NASA NTRS2015

Spacecraft Charging Sensitivity to Material Properties

Evaluating spacecraft charging behavior of a vehicle in the space environment requires knowledge of the material properties relevant to the charging process. Implementing surface and internal charging models requires a user to specify a number of material electrical properties including electrical resistivity parameters (dark and radiation induced), dielectric constant, secondary electron yields, photoemission yields, and breakdown strength in order to correctly evaluate the electric discharge threat posed by the increasing electric fields generated by the accumulating charge density. In addition, bulk material mass density and/or chemical composition must be known in order to analyze radiation shielding properties when evaluating internal charging. We will first describe the physics of spacecraft charging and show how uncertainties in material properties propagate through spacecraft charging algorithms to impact the results obtained from charging models. We then provide examples using spacecraft charging codes to demonstrate their sensitivity to material properties. The goal of this presentation is to emphasize the importance in having good information on relevant material properties in order to best characterize on orbit charging threats.

Minow, Joseph I.↗