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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Thick film silicon growth techniques

Thick film silicon ribbons were produced by means of the edge-defined, film-fed growth (EFG) technique. EFG is a process by which single crystals may be grown having a shape controlled by the outside dimensions of a die, the growth taking place from an extremely thin film of liquid fed by capillary action from a crucible below. The principal problem to be overcome in the application of this process to the growth of thick film silicon ribbon relates to the material, such as the shaping die. For the method to operate, this die material must be wet by the liquid silicon. To preserve semiconductor quality, the liquid silicon must not react significantly with the die material. The most promising die material for this application appears to be SiC and SiC-SiO2 admixture. In this case good wetting occurs between the molten silicon and the SiC. C is a relatively unharmful contaminant of Si and additions of quartz to SiC are found to decrease the extent of reaction.

Bates, H. E.↗
NASA NTRS1971

Fractographic observations of Ti-6Al-4V alloy fatigued in vacuum.

These observations were made as part of a study of the influence of temperature and chemical environment on fatigue-crack growth. The results obtained, along with additional fractographic results in other environments, suggest that the mechanism for fatigue-crack growth in the Ti-6Al-4V alloy is basically similar (striations are observed) for a wide range of environments. In addition to ?vacuum,' these environments include distilled water, ?dry' and ?wet' air, ?dry' hydrogen, and ?dry' and ?wet' argon.

Ritter, D. L.↗
NASA NTRS1973

New concept in brazing metallic honeycomb panels

Aluminum oxide coating provides surface which will not be wetted by brazing alloy and which stops metallic diffusion welding of tooling materials to part being produced. This method eliminates loss of tooling materials and parts from braze wetting and allows fall-apart disassembly of tooling after brazing.

Carter, P. D.↗
NASA NTRS1973

Inorganic separator technology program

Testing and failure analyses of silver zinc cells with largely inorganic separators were performed. The results showed that the wet stand and cycle life objective of the silver-zinc cell development program were essentially accomplished and led to recommendations for cell composition, design, and operation that should yield further improvement in wet and cycle life. A series of advanced inorganic materials was successfully developed and formulated into rigid and semiflexible separator samples. Suitable screening tests for evaluation of largely inorganic separators were selected and modified for application to the separator materials. The results showed that many of these formulations are potentially superior to previously used materials and permitted selection of three promising materials for further evaluation in silver-zinc cells.

Smatko, J. S.↗
NASA NTRS1973

Microwave signatures of snow and fresh water ice

During March of 1971, the NASA Convair 990 Airborne Observatory carrying microwave radiometers in the wavelength range 0.8 to 21 cm was flown over dry snow with different substrata: Lake ice at Bear Lake in Utah; wet soil in the Yampa River Valley near Steamboat Springs, Colorado; and glacier ice, firm and wet snow on the South Cascade Glacier in Washington. The data presented indicate that the transparency of the snow cover is a function of wavelength. False-color images of microwave brightness temperatures obtained from a scanning radiometer operating at a wavelength of 1.55 cm demonstrate the capability of scanning radiometers for mapping snowfields.

Schmugge, T.↗
NASA NTRS1974

Preliminary road alinement through the Great Kavir in Iran by repetitive ERTS-1 coverage

Access to the Great Kavir is generally limited to the period August through October when some salt crusts will support limited vehicular movement. The condition of the salt crusts and their parent sediments during the long wet season have been unknown. This absence of information about the surface of the Great Kavir has prevented an intensive study of a possible road alinement which could shorten the present route between northern and central Iran by 760 km. False color diazo composites of bands 4, 5, and 7 were prepared from positives of ERTS-1 MSS images taken of the Great Kavir. These scenes presented a record of the seasonal hydrologic changes that occurred from the dry to the wet season. During the period of maximum inundation and lowest bearing strengths, as inferred from the image of May 12, 1973, it was possible to select a preliminary road alinement that would avoid the wettest or roughest areas and take advantage of the best terrain and shortest distance. The eventual road alinement should be based on a longer record of observation and on-site investigations.

Krinsley, D. B.↗
NASA NTRS1974

Experimental investigation of the braking and cornering characteristics of 30 x 11.5-14.5, type 8, aircraft tires with different tread patterns

An investigation was conducted at the aircraft landing loads and traction facility to study the braking and cornering characteristics, including the drag-force and cornering-force friction coefficients, of 30 by 11.5-14.5, type VIII aircraft tires with five different tread patterns. Test data were obtained on dry, damp, and flooded runway surfaces over a range of yaw angles from 0 deg to 12 deg at ground speeds from 5 knots to 100 knots. The results of this investigation indicate that a tread pattern consisting of transverse cuts across the entire width of the tread slightly improved the tire traction performance on wet surfaces. The braking and cornering capability of the tires was degraded by thin-film lubrication and tire hydroplaning effects on the wet runway surfaces. The braking capability of the tires decreased when the yaw angle was increased.

Dreher, R. C.↗
NASA NTRS1975

Eutectic superalloys by edge-defined, film-fed growth

The feasibility of producing directionally solidified eutectic alloy composites by edge-defined, film-fed growth (EFG) was carried out. The three eutectic alloys which were investigated were gamma + delta, gamma/gamma prime + delta, and a Co-base TaC alloy containing Cr and Ni. Investigations into the compatibility and wettability of these metals with various carbides, borides, nitrides, and oxides disclosed that compounds with the largest (negative) heats of formation were most stable but poorest wetting. Nitrides and carbides had suitable stability and low contact angles but capillary rise was observed only with carbides. Oxides would not give capillary rise but would probably fulfill the other wetting requirements of EFG. Tantalum carbide was selected for most of the experimental portion of the program based on its exhibiting spontaneous capillary rise and satisfactory slow rate of degradation in the liquid metals. Samples of all three alloys were grown by EFG with the major experimental effort restricted to gamma + delta and gamma/gamma prime + delta alloys. In the standard, uncooled EFG apparatus, the thermal gradient was inferred from the growth speed and was 150 to 200 C/cm. This value may be compared to typical gradients of less than 100 C/cm normally achieved in a standard Bridgman-type apparatus. When a stream of helium was directed against the side of the bar during growth, the gradient was found to improve to about 250 C/cm. In comparison, a theoretical gradient of 700 C/cm should be possible under ideal conditions, without the use of chills. Methods for optimizing the gradient in EFG are discussed, and should allow attainment of close to the theoretical for a particular configuration.

Hurley, G. F.↗
NASA NTRS1975

Carbide coated fibers in graphite-aluminum composites

The NASA-supported program at the Los Alamos Scientific Laboratory (LASL) to develop carbon fiber-aluminum matrix composites is described. Chemical vapor deposition (CVD) was used to uniformly deposit thin, smooth, continuous coats of TiC on the fibers of graphite tows. Wet chemical coating of fibers, followed by high-temperature treatment, was also used, but showed little promise as an alternative coating method. Strength measurements on CVD coated fiber tows showed that thin carbide coats can add to fiber strength. The ability of aluminum alloys to wet TiC was successfully demonstrated using TiC-coated graphite surfaces. Pressure-infiltration of TiC- and ZrC-coated fiber tows with aluminum alloys was only partially successful. Experiments were performed to evaluate the effectiveness of carbide coats on carbon as barriers to prevent reaction between alluminum alloys and carbon. Initial results indicate that composites of aluminum and carbide-coated graphite are stable for long periods of time at temperatures near the alloy solidus.

Imprescia, R. J.↗
NASA NTRS1974

Microwave profiling of snowpack free-water content

A microwave system is proposed to measure the amount of liquid-phase water in a snowpack operating in the range of 1 to 10 GHz. Attenuation of the beam between source and receivers is produced by the water in the snow. The relationships of frequency, distance, and volume percent of water are calculated for an assumed detector sensitivity, together with the estimated cost of a representative system. A laboratory test is described that shows the attenuation for snow at maximum wetness at 9.35 GHz. A configuration is proposed that involves a vertical tube containing microwave and radioactive sources and another vertical tube containing microwave and gamma-ray detectors, so that density and wetness profiles are obtained simultaneously over essentially the same path.

Linlor, W. I.↗
NASA NTRS1974

The Skylab concentrated atmospheric radiation project - An overview

An overview is presented of the Skylab Concentrated Atmospheric Radiation Project (SCARP), which was conducted to determine the accuracy and applicability of different models of radiation transfer through air masses of differing characteristics including varying amounts of wet and dry aerosols. Sites surveyed included onshore and offshore areas in the vicinity of Houston, Texas, the White Sands Missile Range in New Mexico, and Phoenix, Arizona, which provided a variety of warm, hot, dry, wet, clean, and dirty atmospheres. A typical exercise is described, and problems encountered during the experiment are discussed. It is noted that ten models of atmospheric scattering were utilized and that available data is being compared with the models.

Whitehead, V. S.↗
NASA NTRS1977

Remote moisture-content balance

Automatic balance monitors wetness of wood samples to determine forest fire hazards. Fuel model consists of four wooden dowels that will absorb precipitation moisture and humidity at rate related to moisture absorption by forest wood. Model wetness is determined from weight changes as monitored by electronic balance.

Blomseth, R. A.↗
NASA NTRS1977

NASA diagonal-braked test vehicle evaluation of traction characteristics of grooved and ungrooved runway surfaces at Miami International Airport, Miami, Florida, 8-9 May 1973

Two runways were evaluated under artificially wetted conditions with the NASA diagonal-braked vehicle (DBV). Results of the evaluation which included a pavement drainage analysis, a pavement skid resistance analysis, and a DBV wet/dry stopping distance ratio analysis indicated that the ungrooved runway surfaces had poor water drainage characteristics and poor skid resistance under wet conditions at high speeds especially in rubbercoated areas of the runways. Grooving runways to a transverse 1-1/4 x 1/4 x 1/4 inch pattern greatly improved both the water drainage and pavement skid resistance capability of these asphaltic concrete surfaces.

Horne, W. B.↗
NASA NTRS1977

Studies of friction and wear characteristics of various wires for wire-brush skids

The friction and wear characteristics of 22 types and sizes of wires for potential use in wire-brush skids were studied. These characteristics were determined by placing brushes made from candidate wires on a belt sander whose moving belt simulated landing roll-out distance. At the same time, the drag force and wear behavior were monitored. Data were obtained over distances up to 3048 m (10,000 ft) at preselected bearing pressures of 172 to 1034 kPa (25 to 150 psi). In general, the friction coefficient developed by the candidate wires was found to be independent of bearing pressure and ranged between 0.4 and 0.6 under the test conditions of this investigation. The friction coefficient was not degraded when the surface was wetted and appears to be independent of wire diameter except perhaps when wire size is relatively large compared with the surface asperities. Generally, the high friction demonstrated by the soft materials was accompanied by high wear rates; conversely, the hard materials provided greater wear resistance but offered lower friction. For all test wires, the wear was shown to increase with increasing bearing pressure, in general, for the same bearing pressure, wear increased with increasing wire diameter and decreased when the surface was wetted.

Dreher, R. C.↗
NASA NTRS1976

Flooding of Monroe County, Michigan - A comparison of three remote sensor data sets

During the spring of 1973, three techniques were used to obtain remotely sensed data pertaining to the flooded shoreline of Monroe County, Michigan. Although digitized data from the Earth Resources Technology Satellite were available on magnetic tapes, analysis was based on interpretation methods normally used for aerial photography, since the black and white IR photography and side-looking airborne radar (SLAR) data were available only as images. Using IR photography as the standard, it was found that ERTS-1 Band 7 imagery had a 93% accuracy in detecting areas in the combined category of open water and flooded fields. X(HH) data from SLAR detected that built-up and wet areas were built-up (89 to 100% accuracy), but not that they were wet. It is suggested that these two sensors used in concert from orbital heights could provide information useful to relief organizations in flooded areas. It is considered likely that SLAR data will improve as higher resolution becomes available.

Bryan, M. L.↗
NASA NTRS1977

Resolution of grass canopy biomass classes

Analysis of variance methods has been applied to in situ grassland spectral reflectance data in order to determine the classes or levels of total wet biomass that can be resolved spectrally by a single narrow band measurement. Ground-truth clipping of blue grama grass plots was performed immediately following spectral reflectance measurements at 91 wavelength intervals which were 0.005 microns apart over the spectral range from 0.350 to 0.800 microns. It was found that the photographic infrared region of 0.750 to 0.800 microns could be used to distinguish three classes or levels of total wet biomass. Four or five classes, particularly at higher biomass levels, could not be distinguished by this technique.

Tucker, C. J.↗
NASA NTRS1978

Guidelines for the selection and application of tantalum electrolytic capacitors in highly reliable equipment

Guidelines are given for the selection and application of three types of tantalum electrolytic capacitors in current use in the design of electrical and electronic circuits for space flight missions. In addition, the guidelines supplement requirements of existing military specifications used in the procurement of capacitors. A need exists for these guidelines to assist designers in preventing some of the recurring, serious problems experienced with tantalum electrolytic capacitors in the recent past. The three types of capacitors covered by these guidelines are; solid, wet foil, and tantalum cased wet slug.

Holladay, A. M.↗
NASA NTRS1978

Spectral Measurement of Watershed Coefficients in the Southern Great Plains

The author has identified the following significant results. It was apparent that the spectra calibration of runoff curve numbers cannot be achieved on watersheds where significant areas of timber were within the drainage area. The absorption of light by wet soil conditions restricts differentiation of watersheds with regard to watershed runoff curve numbers. It appeared that the predominant factor influencing the classification of watershed runoff curve numbers was the difference in soil color and its associated reflectance when dry. In regions where vegetation grown throughout the year, where wet surface conditions prevail or where watersheds are timbered, there is little hope of classifying runoff potential with visible light alone.

Blanchard, B. J.↗