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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Wide-temperature-spectrum self-lubricating coatings prepared by plasma spraying

Self-lubricating, multicomponent coatings, which lubricate over a wide range of operating conditions, are described. The coatings have been successfully applied by plasma-spraying mixed powders onto superalloy substrates. They have been evaluated in friction and wear experiments, and in sliding contact bearing tests. These coatings are wear resistant by virtue of their self-lubricating characteristics rather than because of extreme hardness; a further benefit is low friction. Experiments with simple pin on disk sliding specimens and oscillating plain cylindrical bearing tests were performed to evaluate the tribological properties of the coatings. It was shown that coatings of nichrome, glass and calcium fluoride are self-lubricating from about 500 to 900 C, but give high friction at the lower temperatures. The addition of silver to the coating composition improved the low temperature bearing properties and resulted in coatings which are self-lubricating from cryogenic temperatures to at least 870 C; they are therefore 'wide temperature spectrum,' self-lubricating compositions.

Sliney, H. E.↗
NASA NTRS1979

In situ oxygen conditioning of /001/ MgO thin film substrates for film growth studies by electron microscopy

It was found that the in situ treatment of 001-plane single-crystal films of MgO (prepared by epitaxial growth from the vapor phase) at high temperatures with a jet of oxygen will produce a surface that is almost equivalent, for epitaxial studies, to surfaces with the same orientation prepared by vacuum cleavage of bulk single crystals. The effectiveness of the process is demonstrated by its impact on the epitaxy of silver.

Moorhead, R. D.↗
NASA NTRS1979

Linear ruby scale and one megabar

The accuracy and validity of certain techniques used in studying high-pressure transitions have been investigated. Experiments which place upper limits of about 20 GPa and about 50 GPa on pressures practically attainable using uniaxial supported opposed anvil devices with tungsten carbide pistons and uniaxial opposed flat anvil diamond devices, respectively, are reported. Direct static determinations of the transition pressures of GaP by two different methods are described. The values obtained indicate that the linear ruby scale increasingly overestimates the transition pressure as the pressure rises above 10 GPa. It is further shown that the use of shock-based marker materials, such as silver, as the basis of pressure measurement in X-ray diffraction studies leads to bulk moduli of cubic carbides which are in extreme disagreement with expected values.

Ruoff, A. L.↗
NASA NTRS1980

Ion-beam cleaning for cold welds

1000 eV beam bombarding metal surfaces to be joined removes oxides and contaminants at rate of several atomic layers per second for current density of 1 mA/squ. cm. Clean surfaces can then be joined by squeezing them together. With ion-beam cleaning, mating force for strong bond is low enough to cause only 1% deformation. Conventional cold-welding requires about 70% deformation for bonding. Technique was tested successfully on aluminum to aluminum welds, copper to copper, copper to aluminum, copper to nickel, and silver to iron. Base metals failed before welds in tear test.

Slater, B. L.↗
NASA NTRS1980

Easily-assembled helical heater

Rugged, compact heater is made from 0.1 mm diameter Inconel wire (125 ohms per meter). Heating element is enclosed in PTFE heat-shrink sleeve. Ends of coal pass through small ceramic spools and are silver-brazed to lead wires. Junctions are potted in epoxy or silicon and covered with crimp sleeves and heat-shrink tubing.

Pizzeck, D. E.↗
NASA NTRS1980

Preliminary study of a solar selective coating system using black cobalt oxide for high temperature solar collectors

Black cobalt oxide coatings (high solar absorptance layer) were deposited on thin layers of silver or gold (low emittance layer) which had been previously deposited on oxidized (diffusion barrier layer) stainless steel substrates. The reflectance properties of these coatings were measured at various thicknesses of cobalt for integrated values of the solar and infrared spectrum. The values of absorptance and emittance were calculated from the measured reflectance values, before and after exposure in air at 650 C for approximately 1000 hours. Absorptance and emittance were interdependent functions of the weight of cobalt oxide. Also, these cobalt oxide/noble metal/oxide diffusion barrier coatings have absorptances greater than 0.90 and emittances of approximately 0.20 even after about 1000 hours at 650 C.

Mcdonald, G.↗
NASA NTRS1979

Development of economical improved thick film solar cell contact

Metal screened electrodes were investigated with base metal pastes and silver systems being focused upon. Contact resistance measurements were refined. A facility allowing fixing in hydrogen and other atmospheres was acquired. Several experiments were made applying screenable pastes to solar cells. Doping investigations emphasized eutectic alloys reduced to powders. Metal systems were reviewed and base metal experiments were done with nickel and copper using lead and tin as the frit metals. Severe adhesion problems were experienced with hydrogen atmospheres in all metal systems. A two step firing schedule was devised. Aluminum-silicon and aluminum-germanium eutectic doping additions to copper pastes were tried on 2 1/4 in diameter solar cell back contacts, both with good results.

Ross, B.↗
NASA NTRS1979

A new method of metallization for silicon solar cells

The new metallization process based on Mo-Sn system was studied. The reaction mechanism of MoO3 and its mixture with Sn was examined. The basic ink composition was modified in order to obtain a low ohmic contact to the cell. The electrical characteristics of the cells were comparable with the existing metallization processes. However, in comparison with the standard processes using silver as the contacting metal, the saving obtained by the use of the new process was substantial.

Macha, M.↗
NASA NTRS1980

Overview of NASA battery technology program

Highlights of NASA's technology program in batteries for space applications are presented. Program elements include: (1) advanced ambient temperature alkaline secondaries, which are primarily nickel-cadmium cells in batteries; (2) a toroidal nickel cadmium secondaries with multi-kilowatt-hour storage capacity primarily for lower orbital applications; (3) ambient temperature lithium batteries, both primary and secondaries, primarily silver hydrogen and high-capacity nickel hydrogen.

Riebling, R. W.↗
NASA NTRS1980

Update, comparing different plate treatments and design

Eight electrochemical cells were tested for precycling capacity and compared. The cell design variables included teflon treatment, silver treatment, light loading, and a polypropylene separator. Data are presented in tabular form.

Baer, D.↗
NASA NTRS1979

High resolution, low cost solar cell contact development

The experimental work demonstrating the feasibility of the MIDFILM process as a low cost means of applying solar cell collector metallization as reported. Cell efficiencies of above 14% (AMl, 28 C) were achieved with fritted silver metallization. Environmental tests suggest that the metallization is slightly humidity sensitive and degradation is observed on cells with high series resistance. The major yield loss in the fabrication of cells was due to discontinuous grid lines, resulting in high series resitance. Standard lead-tin solder plated interconnections do not appear compatible with the MIDFILM contact. Copper, nickel and molybdemun base powder were investigated as low cost metallization systems. The copper based powder degraded the cell response. The nickel and molybdenum base powders oxidized when sintered in the oxidizing atmosphere necessary to ash the photoresin.

Mardesich, N.↗
NASA NTRS1980

A study on various methods of supplying propellant to an orbit insertion rocket engine

Various types of pumps and pump drives were evaluated to determine the lightest weight system for supplying propellants to a planetary orbit insertion rocket engine. From these analyses four candidate propellant feed systems were identified. Systems Nos. 1 and 2 were both battery powered (lithium-thionyl-chloride or silver-zinc) motor driven pumps. System 3 was a monopropellant gas generator powered turbopump. System 4 was a bipropellant gas generator powered turbopump. Parameters considered were pump break horsepower, weight, reliability, transient response and system stability. Figures of merit were established and the ranking of the candidate systems was determined. Conceptual designs were prepared for typical motor driven pumps and turbopump configurations for a 1000 lbf thrust rocket engine.

Boretz, J. E.↗
NASA NTRS1979

Post-development image intensification by autoradiography

A method of post-development intensification of photographic images using a newly developed autoradiographic procedure is described. Radioactive Thiourea-S35 is combined with silver in the developed emulsion, which is then contact printed with a receiver emulsion. The beta decay from S35 produces an enhanced autoradiographic image. The laboratory technique is described and results of astronomical applications are presented.

Askins, B. S.↗
NASA NTRS1979

Measurements of particle emission from discharge sites in Teflon irradiated by high energy electron beams

Anomalous behavior of synchronous orbit satellites manifested by overall degradation of system performance and reduced operating life is associated with electrical discharges resulting from differential charging of the spacecraft surface by fluxes of high energy electrons. During a laboratory simulation silver-backed Teflon samples have been irradiated by electron beams having energies in the range 16-26 keV. Charged particles emitted from the resultant electrical discharges have been measured with a biased Faraday cup and retarding potential analyser. Measurements indicate the presence of two distinct fluxes of particles, the first being an early pulse (0-600ns) of high energy (about 7keV) electrons, while the second is a late pulse (1-5 microseconds) of low energy electrons (less than 1eV) and ions (70eV) leaving the discharge site as a quasi plasma. Calculations indicate an electrostatic field as the dominant accelerating mechanism for charged particles.

Hazelton, R. C.↗
NASA NTRS1980

Pioneer Venus spacecraft design and operation

The Pioneer Venus Orbiter and Multiprobe spacecraft design and operation enabled both remote and in-situ measurements of the Venusian environment from the outermost fringes of the atmosphere all the way to the surface. Both spacecraft were spin-stabilized and solar-cell powered from launch to Venus. Since orbit insertion, the Orbiter has been transmitting measurements from a highly elliptical 24-h orbit with periapsis altitudes down to about 150 km. Data rates up to 2048 bits/s have been utilized through a despun high-gain antenna transmitting at S-band frequency. Spacecraft attitudes, orbit periods, and periapsis altitudes are being maintained as required with a hydrazine propulsion system. The Multiprobe spacecraft (Bus with all four Probes attached) performed the necessary Probe checkouts and deployed the Probes to achieve the desired Probe and Bus targeting. Silver-zinc batteries provided the necessary power on each of the four Probes from separation from the Bus through the entry/descent sequence. Data rates of 256 and 128 bits/s on the Large Probe were maintained with 40-W radiated power, and 64 and 16 bits/s on the Small Probes were maintained with 10-W radiated power, through omni antennas directly to Earth-based stations. Each Probe's entry/descent sequence was controlled with a hardwired entry sequence programmer to achieve the desired scientific and spacecraft operations.

Nothwang, G. J.↗
NASA NTRS1980

The role of cesium suboxides in low-work-function surface layers studied by X-ray photoelectron spectroscopy - Ag-O-Cs

The oxidation of cesium on silver substrates has been studied using photoyield measurements and X-ray photoelectron spectroscopy. The occurrence of two O1s peaks in the core-level spectrum at 527.5 and 531.5-eV binding energy for cesium and oxygen exposures giving the optimum photoyield proves that two oxides of cesium exist in high-photoyield surfaces, and not Cs2O alone as previously thought. From the shape and position of the cesium peaks and the Auger parameter, the assignment of the O1s peaks at 527.5- and 531.5-eV binding energies to oxygen in Cs2O and Cs11O3, respectively, can be made. Hence the total cesium-oxygen layer is a mixed phase consisting of Cs2O + Cs11O3, approximately 20-40 A thick.

Yang, S.-J.↗
NASA NTRS1980

Investigation of titanium-nitride layers for solar-cell contacts

Reactively sputtered titanium-nitride layers have been incorporated as diffusion barriers in a titanium-silver metallization scheme on silicon. Backscattering analysis (2-MeV He/+/, RBS) indicates that the integrity of the system is basically preserved during annealing at 600 C for 10 min. Electrical properties were determined for titanium-nitride layers prepared under different deposition conditions. Resistivity and Hall mobility appear to depend on the oxygen contamination of the deposited material. For the lowest oxygen concentration (less than 5 at %) a resistivity of 170 microohms/cm has been found.

Von Seefeld, H.↗