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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The influence of surface dents and grooves on traction in sliding EHD point contacts

Changes in traction, caused by dents and grooves on a highly polished ball, are investigated as these defects approach and go through sliding elastohydrodynamic point contacts. The contacts are formed with the ball loading against a transparent disk. The ball and thus the topographical features are held stationary at various locations in the vicinity and within the contact while the disk is rotating. These topographical features can cause substantial changes in the traction when compared to traction obtained with smooth surfaces. Previously announced in STAR as N82-32734

Cusano, C.↗
NASA NTRS1983

Diffusion processes in Al2O3 scales - Void growth, grain growth, and scale growth

The internal microstructure and growth kinetics of Al2O3 scales on Ni-15Cr-13Al (wt percent) are investigated by TEM and analyzed in relation to models of diffusivity. Polished arc-melted specimens were oxidized in 1-atm air at 1100 C for 0.1, 1.0, and 20 hours and ion-thinned for TEM at 100 kV. The frequency distribution of void size and grain size is determined for different oxidation times and scale depths. The kinetics of microvoid growth and of grain and scale growth are plotted and related via simplified models to lattice and grain-boundary oxygen diffusivity, respectively. Good agreement is found between model predictions and data obtained by Oishi and Kingery (1960) on oxygen diffusion in bulk Al2O3. The further implications and limitations of these findings are discssed.

Smialek, J. L.↗
NASA NTRS1983

The oxidation behavior of a model molybdenum/tungsten-containing alloy in air alone and in air with trace levels of NaCl(g)

Thermogravimetric, metallographic, and X-ray studies of a model alloy, Ni-(17 a/o)Al-(10 a/o)Mo+W, oxidized in dry air at 600-1200 C and in air with 10 ppm NaCl gas at 900 C, are reported. The alloy was melted under Ar and pretreated in flowing H2 for 24 h at 1300 C. Polished 1.3 x 1.3 x 0.2-cm specimens were washed and degreased prior to oxidation in a quartz tube within a furnace for up to 120 hr. The oxidation activation energy of the alloy is determined to be about 30 kcal/mole. The specimens oxidized at 900 C and hotter exhibited oxidized and nitrided phases covered by complex NiMoO4, NiWO4, and NiAl2O4 scales and a porous, nonprotective outer layer of NiO. The oxidation behavior is found to be determined by the formation and growth of the scale, especially the (Mo,W)O2 component. Al2O3 scale layers were not formed, and further runs with pure O2 or Ar-(20 percent)O2 ruled out an explanation of this phenomenon based on aluminum nitride formation. The oxidation was accelerated by the addition of NaCl gas, a finding attributed to the reaction of NaCl with external locally protective Al2O3 scales and with the internal(Mo, W)O2 layers.

Smeggil, J. G.↗
NASA NTRS1983

Inter-layered clay stacks in Jurassic shales

Scanning electron microscopy in the backscattered electron mode is used together with energy-dispersive X-ray microanalysis to show that Lower Jurassic shales from the North Sea Basin contain large numbers of clay mineral stacks up to 150 microns in size. Polished shale sections are examined to determine the size, shape orientation, textural relationships, and internal compositional variations of the clays. Preliminary evidence that the clay stacks are authigenic, and may have formed at shallow burial depths during early diagenesis, is presented.

Pye, K.↗
NASA NTRS1983

Plasma-enhanced CVD silicon nitride antireflection coatings for solar cells

Multilayer plasma-enhanced chemical vapor deposition (PECVD) silicon nitride antireflection coatings were deposited on space quality silicon solar cells. Preliminary experiments indicated that multilayer coatings decreased the total reflectance of polished silicon from 35 percent to less than 3 percent over the spectral range 0.4-1.0 micron. The solar cell energy conversion efficiency was increased from an average of 8.84 percent to an average of 12.63 percent.

Johnson, C. C.↗
NASA NTRS1984

Ruled and holographic gratings experiment (A0138-5)

The behavior of ruled and holographic gratings with various coatings after extended exposure to the space environments was examined. The coatings and differentiating between the influences of vacuum and solar illumination were examined. In the past, several ruled and holographic gratings with various coatings were successfully flown on rocket experiments. Future utilizations of such gratings are considered for the Space Telescope and for various Spacelab projects under development. The techniques which is used to replicate gratings can also be used to obtain a wide range of lightweight optical components, including sophisticated aspherical, highly polished mirrors.

Moreau, G.↗
NASA NTRS1984

Chemical mechanisms and reaction rates for the initiation of hot corrosion of IN-738

Sodium-sulfate-induced hot corrosion of preoxidized IN-738 was studied at 975 C with special emphasis placed on the processes occurring during the long induction period. Thermogravimetric tests were run for predetermined periods of time, and then one set of specimens was washed with water. Chemical analysis of the wash solutions yielded information about water soluble metal salts and residual sulfate. A second set of samples was cross sectioned dry and polished in a nonaqueous medium. Element distributions within the oxide scale were obtained from electron microprobe X-ray micrographs. Evolution of SO was monitored throughout the thermogravimetric tests. Kinetic rate studies were performed for several pertinent processes; appropriate rate constants were obtained from the following chemical reactions: Cr2O3 + 2 Na2SO4(1) + 3/2 O2 yields 2 Na2CrO4(1) + 2 SO3(g)n TiO2 + Na2SO4(1) yields Na2O(TiO2)n + SO3(g)n TiO2 + Na2CrO4(1) yields Na2O(TiO2)n + CrO3(g).

Fryburg, G. C.↗
NASA NTRS1984

Kasprzyk airfoil. The first wind-tunnel tests

The Kasprzyk slotted flap glider airfoil (the Kasper wing) enabling glider flight at 32 km/h and 0.5 m/sec descent speed was wind tunnel tested in the U.S. The test layout is described and reasons offered for discrepancies between wind tunnel results and Polish in flight data: high induced drag caused by relative size of model wing span and tunnel, by vortex attenuators on the model and their proximity to the tunnel wall, nonsimilarity between flow over a smooth wing and flow over the Kasprzyk wing with bound vortices, obstruction of the tunnel test chamber cross section by the model wing, discrepant Reynolds numbers, and model airfoil aspect ratio much smaller than the prototype. The overall results offer partial confirmation of the Kasprzyk theory, but further in tunnel and in flight studies are recommended.

Wusatowski, T.↗
NASA NTRS1984

Excimer laser annealing to fabricate low cost solar cells

The objective is to show whether or not pulsed excimer laser annealing (PELA) of ion-implanted junctions is a cost effective replacement for diffused junctions in fabricating crystalline silicon solar cells. The preliminary economic analysis completed shows that the use of PELA to fabricate both the front junction and back surface field (BSF) would cost approximately 35 cents per peak watt (Wp), compared to a cost of 15 cents/Wp for diffusion, aluminum BSF and an extra cleaning step in the baseline process. The cost advantage of the PELA process depends on improving the average cell efficiency from 14% to 16%, which would lower the overall cost of the module by about 15 cents/Wp. An optimized PELA process compatible with commercial production is to be developed, and increased cell efficiency with sufficient product for adequate statistical analysis demonstrated. An excimer laser annealing station was set-up and made operational. The first experiment used 248 nm radiation to anneal phosphorus implants in polished and texture-etched silicon.

Source record↗
NASA NTRS1983

Mineralogy and petrology of chondrules and inclusions in the Mokoia CV3 chondrite

The inclusions and chondrules of the Mokoia CV3 chondrite are studied systematically and compared with those in the Allende meteorite. Five polished thin sections of Mokoia were examined by optical microscopy, backscattered scanning electron microscopy, and electronprobe microanalysis, and objects greater than about 100 microns in apparent diameter were measured and classified petrographically. Three major types of olivine chondrules are distinguished: igneous chondrules, which evidently crystallized from droplets of silicate melt; recrystallized chondrules, apparently metamorphosed at relatively high temperatures; and accretional aggregates, which are probably fragments of igneous chondrules. Refractory inclusions in Mokoia are generally similar to those found in Allende, although Mokoia inclusions include phyllosilicates rather than feldspathoids and melilite-rich Ca, Al-rich inclusions (CAIs) are more abundant in Allende. The small, fine-grained CAIs, which are more abundant than coarse-grained CAIs in both meteorites, are observed to represent aggregates of three distinct constituents: concentric objects, chaotic material and inclusion matrix. It is concluded that most of the CAIs probably formed during metamorphism, partial melting, and incomplete distillation of primitive dust aggregates heated in the solar nebula.

Cohen, R. E.↗
NASA NTRS1983

A three-dimensional study of metal grains in equilibrated, ordinary chondrites

Metal particles in Guarena (H6), Colby (L6) and St. Severin (LL6) were studied by optical microscopy and by electron microprobe analysis. Observations from successive polished sections through the metal particles show that kamacite and taenite grains, which often appear to be isolated particles, are connected directly or by intervening sulfides. Also tetrataenite rims are widest when adjacent to sulfide or kamacite. These observations indicate that transfer of Ni during cooling when kamacite-taenite phase growth takes place does not occur through the silicate phases but proceeds through metal and sulfide phases or along grain boundaries. By utilizing the central Ni content of taenite grains from successive sections, metallographic cooling rates were determined more precisely than by using one arbitrary section. Cooling rates determined in this manner for Guarena, Colby, and St. Severin are 4.3 K, 4.0 K, and 1.0 K per million years, respectively.

Willis, J.↗
NASA NTRS1984

'Fluffy' Type A Ca-, Al-rich inclusions in the Allende meteorite

Inclusions called 'fluffy' Type A's or FTA's in the Allende meteorite are examined as possible candidates for relict vapor-solid condensate grains, remaining from the original solar nebula. Type A inclusions are characterized by abundant melilite and absence of primary anorthite and titaniferous pyroxene. Fluffy Type A's were probably loosely bound clumps of crystals drifting in the solar nebula, analogous to dustballs or snowflakes. Polished thin sections of all samples were studied optically and with a JEOL JSM-35 scanning electron microscope. It is reasonably clear that neither whole FTA's nor constituent nodules of the coarser grained ones were ever molten. Despite solid-state recrystallization which has affected these inclusions to varying degrees, the coarser grained material remaining in many of them is probably a relic of vapor-solid condensation in the solar nebula.

Macpherson, G. J.↗
NASA NTRS1984

Free-standing thin film Ge single crystals grown by plasma-enhanced chemical vapor deposition

The films, which are approximately 10 microns in thickness, are grown epitaxially on polished (100) NaCl substrates at 450 C by plasma enhanced chemical vapor deposition. Upon cooling, the films are separated from the substrate by differential shear stress, leaving free-standing films of Ge which can be handled. Growths are attained by nucleating at minimum plasma power for very brief intervals and then raising the power to 65 W to increase the growth rate to approximately 10 microns/h. It is found that substrate exposure to the plasma at too high a power for too long a time sputters and erodes the surface, thereby substantially degrading the nucleation process and the ultimate growths. It is noted that the free-standing films are visually specular and exhibit a high degree of crystalline order when examined by X-ray diffraction. Auger electron spectroscopy and energy dispersive analysis of X-rays reveal no detectable bulk contamination.

Outlaw, R. A.↗
NASA NTRS1984

Experimental results for the scattering of X-rays from smooth surfaces

By utilizing the unique X-ray test facility at NASA's Marshall Space Flight Center, high resolution data have been obtained for the scattering of X-rays from smooth optical flats. Using X-rays with energies in the range from 2.99 keV to 8.06 keV, the resulting reflected images from five state-of-the-art polished mirror flats with various substrate and coating materials are presented and analyzed. Evidence for large angle scattering is shown to exist for some energies and is discussed in terms of theoretical models for surface defects.

Williams, A. C.↗
NASA NTRS1986

Image-Processing Educator

Apple Image-Processing Educator (AIPE) explores ability of microcomputers to provide personalized computer-assisted instruction (CAI) in digital image processing of remotely sensed images. AIPE is "proof-of-concept" system, not polished production system. User-friendly prompts provide access to explanations of common features of digital image processing and of sample programs that implement these features.

Gunther, F. J.↗
NASA NTRS1984

Optical contacting for gravity probe star tracker

A star-tracker telescope, constructed entirely of fused silica elements optically contacted together, has been proposed to provide submilliarc-second pointing accuracy for Gravity Probe. A bibliography and discussion on optical contacting (the bonding of very flat, highly polished surfaces without the use of adhesives) are presented. Then results from preliminary experiments on the strength of optical contacts including a tensile strength test in liquid helium are discussed. Suggestions are made for further study to verify an optical contacting method for the Gravity Probe star-tracker telescope.

Wright, J. J.↗
NASA NTRS1984

Extreme incompatibility of Pb during the crystallization of magmatic iron meteorites

The partitioning behavior of Pb in the three-phase system metal-troilite-sulfide liquid was investigated. Microscopic examination and electron microprobe analysis of a polished section showed three phases--Fe metal, troilite and an Fe-S-Pb-O metallic liquid. The Pb concentration of the metallic liquid was 1.4 wt.%; the Pb contents of both the troilite and the Fe metal were below the detection limit of the electron probe. To better define the Pb concentrations of the solid phases, the same sample was analyzed for Pb and Fe using the M.I.T., Harvard and Brown ion microprobe. Even at this level of precision, some conclusions and speculations are possible: (1) The D(Pb) (troilite/metallic liquid) is low (.01 to .001) and, contrary to expectation, troilite, like metal, excludes Pb very effectively during the crystallization of metallic liquids; (2) Pb in iron meteorites is conceivably concentrated in trace phases which are less susceptible to contamination than metal and troilite; and (3) taken at face value D(Pb)(metal/troilite) is 0.1, but given the Pb and Fe ion yields from simple endmember phases (Fe, FeS, Pb, PbS), this D is more likely to be 0.05 to 0.03.

Jones, J. H.↗
NASA NTRS1985

Characterization of material surfaces exposed to atomic oxygen on space shuttle missions

Material samples prepared for exposure to ambient atomic oxygen encountered during space shuttle flights in low Earth orbit were characterized by the experimental techniques of ELLIPSOMETRY, ESCA, PIXE, and RBS. The first group of samples, which were exposed during the STS-8 mission, exhibited some very interesting results. The second group of samples, which are to be exposed during the upcoming STS-17 mission, have been especially prepared to yield quantitative information on the optical changes, oxygen solution, and surface layer formation on metal films of silver, gold, nickel, chromium, aluminum, platinum, and palladium evaporated onto optically polished silicon wafers.

Fromhold, A. T.↗