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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Profiling microcraters using stereomicrographs.

The determination of the population, shape, and size of microcraters on lunar rocks enables space scientists to study cosmic erosion, survival times of rocks on the lunar surface, and the flux of primary cosmic particles. A graphical method of profiling and contouring microcraters on lunar rocks from a pair of stereomicrographs obtained by a scanning electron microscope was developed. The graphical method utilizes the simple geometry of photography generated by a parallel bundle of rays, orthogonal to the image plane.

Malhotra, R. C.↗
NASA NTRS1973

Role of Hf and Zr in the hydrogen embrittlement of Ta and Cb alloys

The hydrogen embrittlement of aged T-111 and similar Ta and Cb alloys is characterized and the mechanisms believed responsible for the increased sensitivity of T-111 to low temperature hydrogen embrittlement after aging for 1000 hours or longer near 1040 C are described. A total of eight Ta base alloys and two Cb base alloys were investigated. The effects of pre-age annealing temperature, aging time, temperature and environment, and alloy composition on the susceptibility to hydrogen embrittlement were investigated. The primary method of determining the effects of these variables on the ductility of T-111 was by bend testing at 25 and -196 C. Fractured specimens were examined by the scanning electron microscope, electron microprobe, metallography and X-ray diffration.

Stephens, J. R.↗
NASA NTRS1973

Examination of oxide scales in the SEM using backscattered electron images

The complementary use of the scanning electron microscope in the backscattered electron mode with the more usual secondary electron mode results in a significant increase in the versatility of the instrument, since regions of different chemical composition can be readily detected, and their morphology examined. The use of this technique to examine complex oxide scales formed on heat-resistant alloys is described, and in particular the location of thoria particles in the scale formed on a Ni-20 wt pct Cr-2.3 wt pct ThO2 alloy, and the examination of the behavior of yttrium during the high-temperature oxidation of a Co-Cr-Al-Y alloy are discussed.

Price, C. W.↗
NASA NTRS1973

X ray analysis of balloon-collected particles erroneously considered as an October influx into the lower stratosphere

Individual particles were analyzed on the collection screens in a Jeolco scanning electron microscope using a Kevex Li-drifted silicon energy dispersive X ray detector. It was found that the bulk of the stratospheric samples studied comes from explosive squib devices. It is pointed out that this finding does not invalidate the extensive results obtained by Bigg et al. (1970, 1971) in previous sampling experiments.

Farlow, N. H.↗
NASA NTRS1974

Role of HF and Zr in the hydrogen embrittlement of Ta and Cb alloys

An attempt is made to characterize the hydrogen embrittlement of aged T-111 and similar Ta and Cb alloys and to describe the mechanisms believed responsible for the increased sensitivity of T-111 to low temperature hydrogen embrittlement after aging for 1000 hr or longer near 1040 C. A total of eight Ta-base alloys and two Cb-base alloys were investigated. The effects of pre-age annealing temperature, aging time, temperature and environment, and alloy composition on the susceptibility to hydrogen embrittlement were investigated. The primary method of determining the effects of these variables on the ductility of T-111 was by bend testing at 25 and -196 C. Fractured specimens were examined by the scanning electron microscope, electron microprobe, metallography, and X-ray diffraction.

Stephens, J. R.↗
NASA NTRS1974

Cathodoluminescence of regolith returned by Luna 16 automatic station

Observations of local variations in the intensity and spectral composition of the cathodoluminescence of lunar regolith are described. These variations are caused by structural features, by the kind and quantity of the material, and by the admixtures. In addition, cathodoluminescent emission is also associated with a change in the temperature of the lunar surface. Periodic diurnal illumination and darkening of the moon is responsible for a temperature gradient normal to the lines of longitude. These observations made of regolith, using a scanning electron microscope with an attachment for temperature variation, simulate the indicated thermal changes of the cathodoluminescent properties of lunar material.

Spivak, G. V.↗
NASA NTRS1975

Dynamic SEM wear studies of tungsten carbide cermets

Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examined, and etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the tungsten carbide (WC) and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation, and the wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation, and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk.

Brainard, W. A.↗
NASA NTRS1975

Study of the thermal degradation mechanism of a composite propellant

The current experimental program was designed to systematically investigate the role of the oxidizer in the thermal degradation process of composite propellants. The scanning electron microscope (SEM) was used to examine the failure sites in thermally degraded propellant samples. The formulation variables tested were oxidizer purity, oxidizer particle size, and oxidizer to binder bonding agent. The binder, a saturated hydrocarbon, was kept constant throughout the experiments. The oxidizers were: AP, chlorate-doped AP, arsenate-doped AP, and phosphate-doped AP. The oxidizer particle size distribution was 60% of the large fraction and 40% of the small fraction. The bonding agent, when present, was used at the 0.15% level. The data showed that both the oxidizer purity and particle size had an important affect on the thermal degradation process. The affect of the oxidizer particle size was more noticeable at the higher temperature and stress levels. An examination of the failure site, by SEM, of propellants subject to these latter conditions indicated that the fracturing of the large oxidizer particles led to the propellant cracking.

Schmidt, W. G.↗
NASA NTRS1975

Scanning electron microscopy of a pink inclusion from the Allende meteorite

A scanning electron microscope study of a fine-grained, pin, Ca-rich inclusion from the Allende meteorite has revealed strong evidence for direct condensation of its constituent minerals from a vapor. This observation extends to the alkali-bearing phases in addition to the Ca-, Al-silicates and suggests that the feldspathoids as well as the refractory silicates are solar nebular condensates.

Grossman, L.↗
NASA NTRS1975

Investigation and simulation of metallic spherules from lunar soils

The microstructure and chemical composition of metallic spherules from the lunar soil were studied by optical, electron-probe, and scanning-electron-microscope techniques. Metallic spherules produced experimentally were compared to the lunar spherules with respect to structure, chemistry, and cooling rates. The structure of the lunar spherules indicates an origin by solidification of molten globules of metal. The spherules are probably produced from both lunar and meteoric sources, the major source being the metal phase present in lunar rocks and soil.

Blau, P. J.↗
NASA NTRS1974

Microcircuit failure analysis using the SEM

The scanning electron microscope adds a new dimension to the knowledge that can be obtained from a failed microcircuit. When used with conventional techniques, SEM assists and clarifies the analysis, but it does not replace light microscopy. The most advantageous features for microcircuit analysis are long working distances and great depth of field. Manufacturer related failure modes of microcircuits are metallization defects, poor bonding, surface and particle contamination, and design and fabrication faults. User related failure modes are caused by abuse, such as overstress. The Physics of Failure Procedure followed by the Astrionics Laboratory in failure analysis is described, which is designed to obtain maximum information available from each step.

Nicolas, D. P.↗
NASA NTRS1975

An investigation of the compressive strength of Kevlar 49/epoxy composites

Tests were performed to evaluate the effect of a wide range of variables including matrix properties, interface properties, fiber prestressing, secondary reinforcement, and others on the ultimate compressive strength of Kevlar 49/epoxy composites. Scanning electron microscopy is used to assess the resulting failure surfaces. In addition, a theoretical study is conducted to determine the influence of fiber anisotropy and lack of perfect bond between fiber and matrix on the shear mode microbuckling. The experimental evaluation of the effect of various constituent and process characteristics on the behavior of these unidirectional composites in compression did not reveal any substantial increase in strength. However, theoretical evaluations indicate that the high degree of fiber anisotropy results in a significant drop in the predicted stress level for internal instability. Scanning electron microscope data analysis suggests that internal fiber failure and smooth surface debonding could be responsible for the measured low compressive strengths.

Kulkarni, S. V.↗
NASA NTRS1975

Dynamic SEM wear studies of tungsten carbide cermets

Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examined. Etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the WC and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation. The wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk.

Brainard, W. A.↗
NASA NTRS1975

The grape cluster, metal particle 63344,1

The grape cluster metal particle 63344,1 found in lunar coarse fines is examined using the scanning electron microscope (SEM), electron microprobe, and an optical microscope. This metal particle is approximately 0.5 cm in its largest dimension and consists of hundreds of metallic globules welded together to form a structure somewhat like a bunch of grapes. Electron microprobe analysis for Fe, Ni, Co, P, and S in the metal was carried out using wavelength dispersive detectors. No primary solidification structure is observed in the globules, and the particle is slow cooled from the solidification temperature (nearly 1300 C) taking days to probably months to reach 600 C. Two mechanisms for the formation of globules are proposed. One mechanism involves the primary impact of an iron meteorite which produces a metallic liquid and vapor phase. The second mechanism involves the formation of a liquid pool of metal after impact of an iron meteorite projectile followed by a secondary impact in the liquid metal pool.

Goldstein, J. I.↗
NASA NTRS1976

Determination of surface recombination velocity in heavily doped silicon

A method was developed and successfully tested for the determination of the effective surface recombination velocity of silicon layers doped by diffusion of phosphorus to a level of 10 to the 19th to 10 to the 21st per cu cm. The effective recombination velocity was obtained from the dependence of the electron-beam-induced current on the penetration of the electron beam of a scanning electron microscope. A special silicon diode was constructed which permitted the collection at the p-n junction of the carriers excited by the electron beam. This diode also permitted the study of the effects of surface preparation on the effective surface recombination velocity.

Watanabe, M.↗
NASA NTRS1977

Analysis of ablation debris from natural and artificial iron meteorites

Artificial ablation studies were performed on iron and nickel-iron samples using an arc-heated plasma of ionized air. Experiment conditions simulated a meteoroid traveling about 12 km/sec at an altitude of 70 km. The artificially produced fusion crusts and ablation debris show features very similar to natural fusion crusts of the iron meteorites Boguslavka, Norfork, and N'Kandhla and to magnetic spherules recovered from Mn nodules. X-ray diffraction, electron microprobe, optical, and scanning electron microscope analyses reveal that important mineralogical, elemental, and textural changes occur during ablation. Some metal is melted and ablated. The outer margin of the melted rind is oxidized and recrystallizes as a discontinuous crust of magnetite and wustite. Adjacent to the oxidized metallic ablation zone is an unoxidized metallic ablation zone in which structures such as Widmannstatten bands are obliterated as the metal is transformed to unequilibrated alpha 2 nickel-iron. Volatile elements are vaporized and less volatile elements undergo fractionation.

Blanchard, M. B.↗
NASA NTRS1976

Lithification of vitric- and clastic-matrix breccias - SEM petrography

A scanning electron microscope was used in a petrographic investigation of the matrix textures of 41 lunar breccias ranging from very friable soil clods through coherent microbreccias and tough vitric breccias to tough, fine-grained crystalline breccias. It was found that as their coherence increases, the matrices display a gradual increase in the content of glass from 1 or 2% as filaments less than 1 micron across through 5-50% as irregularly shaped patches up to 200 microns across to over 50% as continuous networks.

Phinney, W. C.↗
NASA NTRS1979

SEM probe of IC radiation sensitivity

Scanning Electron Microscope (SEM) used to irradiate single integrated circuit (IC) subcomponent to test for radiation sensitivity can localize area of IC less than .03 by .03 mm for determination of exact location of radiation sensitive section.

Gauthier, M. K.↗