Search NASA⌕ Search

SEARCH · Search NASA

Results for “scanning electron diffraction”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The use of analytical surface tools in the fundamental study of wear

Various techniques and surface tools available for the study of the atomic nature of the wear of materials are reviewed These include chemical etching, x-ray diffraction, electron diffraction, scanning electron microscopy, low-energy electron diffraction, Auger emission spectroscopy analysis, electron spectroscopy for chemical analysis, field ion microscopy, and the atom probe. Properties of the surface and wear surface regions which affect wear, such as surface energy, crystal structure, crystallographic orientation, mode of dislocation behavior, and cohesive binding, are discussed. A number of mechanisms involved in the generation of wear particles are identified with the aid of the aforementioned tools.

Buckley, D. H.↗
NASA NTRS1977

The use of analytical surface tools in the fundamental study of wear

This paper reviews the various techniques and surface tools available for the study of the atomic nature of the wear of materials. These include chemical etching, X-ray diffraction, electron diffraction, scanning electron microscopy, low-energy electron diffraction, Auger emission spectroscopy analysis, electron spectroscopy for chemical analysis, field ion microscopy, and the atom probe. Properties of the surface and wear surface regions which effect wear such as surface energy, crystal structure, crystallographic orientation, mode of dislocation behavior, and cohesive binding are discussed. A number of mechanisms involved in the generation of wear particles are identified with the aid of the aforementioned tools.

Buckley, D. H.↗
NASA NTRS1976

Chemical vapor deposition growth

A chemical vapor deposition (CVD) reactor system with a vertical deposition chamber was used for the growth of Si films on glass, glass-ceramic, and polycrystalline ceramic substrates. Silicon vapor was produced by pyrolysis of SiH4 in a H2 or He carrier gas. Preliminary deposition experiments with two of the available glasses were not encouraging. Moderately encouraging results, however, were obtained with fired polycrystalline alumina substrates, which were used for Si deposition at temperatures above 1,000 C. The surfaces of both the substrates and the films were characterized by X-ray diffraction, reflection electron diffraction, scanning electron microscopy optical microscopy, and surface profilometric techniques. Several experiments were conducted to establish baseline performance data for the reactor system, including temperature distributions on the sample pedestal, effects of carrier gas flow rate on temperature and film thickness, and Si film growth rate as a function of temperature.

Ruth, R. P.↗
NASA NTRS1990

Nature and origin of interstellar diamond from the Allende CV3 meteorite

Data and experimental evidence which support the contention that the C delta diamonds may result from grain-grain collisions in supernova shocks in the interstellar medium are presented. Fragments of the Allende CV3 chondrite were acid-treated. A whitish powder was obtained. For the Analytical Electron Microscopy (AEM) a small drop of ethanol suspension was transferred onto holey carbon support films on 3 mm EM grids. The AEM was performed on transmission-thin fragments of the material which overlay holes in the film, to eliminate interference from the substrate. Electron Spectroscopy for Chemical Analysis (ESCA) was performed on a large aliquot of C. Diamond was identified by selected area electron diffraction. Scanning Transmission Electron Microscope / Energy Dispersive X-ray (STEM-EDS) microanalyses of the C delta diamond, using a light-element detector, show that oxygen and possibly nitrogen are the only impurities consistently present. ESCA spectra from bulk C delta material confirm the presence of N at a level of 0.35 percent or less. Under UV irradiation a yellow-red fluorescence is observed, consistent with that of natural diamonds containing substitutional N. Electron Energy Loss Spectra (EELS) were recorded at 2 eV resolution from the C delta diamond, high pressure synthetic diamond, a diamond film produced in a low pressure plasma by chemical vapor deposition (CVD) on a heated silicon substrate (Roy, 1987), graphite, and amorphous arc sputtered carbon. Comparison of the carbon K edge shape and fine structure shows the Allende C delta phase to be largely diamond, but with a significant pre-edge absorption feature indicative of transitions of C 1s electrons into pi asterisk orbitals which are absent in the purely sp(3)-bonded diamond but present in graphite and amorphous carbon.

Blake, David↗
NASA NTRS1992

Beneficiation of ilmenite from lumar analog

The results reported were obtained on a meteoric eucrite sample called Millbillillie Sample no. 173. Optical microscopy studies of the sample showed it to consist of ilmenite, troilite, and transparent gangue. The transparent gangue consisted of feldspar (anorthite), pyroxenes, olivines, and opaques. Troilite was present in minor quantities. Screen assay analyses of the 30, 100, 200, and 400 US mesh screen fractions showed that minor concentration of titanium occurred in the 200 x 400 and -400 mesh screen fractions. Scanning electron microscopy (SEM) studies of the bulk sample showed the presence of a variety of ilmenite grains, ranging from 50 microns down to less than 1 micron without any evidence of liberation. Electron Diffraction Scans (EDS) confirmed the ratio of Fe to Ti in the ilmenite grains. Dry magnetic separation in a Frantz Isodynamic Separator was found to be effective only at sizes finer than 150 microns (100 US mesh) and more so at 200 mesh (74 microns). In each case, dedusting of the sample to remove -400 mesh (-0.037 microns) fines was required. Liberation size was determined to be 200 mesh and finer. The highest grade concentrate assaying 3.45 percent Ti was produced by magnetic separation of the -200 + 400 mesh screen fraction assaying 0.44 Ti (from a -30 mesh sample) at a current setting of 0.35 AMP. This concentrate contained 21.2 percent of the Ti values in the screen fraction with 2.72 weight percent of feed to test. The results can be projected to a sample stage ground to -200 mesh. Magnetic separation of the 200 + 400 mesh (-0.074 + 0.037 microns) should produce a concentrate accounting for 1.41 weight percent of the feed. This concentrate will analyze 3.45 percent Ti and contain 10.3 percent of the Ti values in the feed. By changing the Frantz Magnetic Separator settings, a lower grade concentrate analyzing 0.98 percent Ti can be produced at an increased recovery of 25.4 percent. The concentrate weight will be 11.7 percent of the feed. It must be emphasized that improved grades and recoveries can be obtained with the -400 mesh fines. However, beneficiation of these extremely fine materials is not possible in a practical process scheme.

Ramadorai, G.↗
NASA NTRS1975

Morphological growth of sputtered MoS2 films

Sputtered MoS2 films from 300 A to 20,000 A thick were deposited on metal and glass surfaces. The substrate effects such as surface temperature, finish, pretreatment and chemistry as they affect the film formation characteristics were investigated by optical, electron transmission, electron diffraction, and scanning electron microscopy. Substrate temperature and surface chemistry were found to be the prime variables as to the formation of a crystalline or amorphous film. The friction characteristics are strictly influenced by the type of film formed. Surface chemistry and surface pretreatment account for compound formation and corresponding grain growth, which directly affect the adhesion characteristics, resulting in poor adherence. The type of surface finish (topography) as related to scratches, impurities, inhomogeneities, etc., are favorable nucleation sites for the growth of isolated and complex nodules within the film, and various complex surface overgrowths on the film. These nodular growth features have progressively more undesirable effects on the film behavior as the film thickness increases.

Spalvins, T.↗
NASA NTRS1975

Hot corrosion evaluation of aluminide coated superalloys in support of an ASTM Round Robin program

Commercial aluminized coatings on substrates were hot corroded at 900 C in a 0.3 Mach burner rig with 5 ppm synthetic sea salt and at two cycling frequencies. Extensive post-exposure examinations were conducted on the corroded specimens such as metallography, X-ray diffraction, scanning electron microscopy, microprobe raster scans, and spectrographic analyses. Thermodynamic calculations were made of the equilibrium burner flame composition and the calculations were compared to the experimental findings. It was found that localized spalling of the coatings preceded coating failure. It is suggested that the spalling of the coatings is due to the formation of localized stresses caused by the depletion of chromium and aluminum in the coating or the enrichment of the coating with sulfur. For the materials and test conditions investigated, it was found that coating life is dependent only upon the initial coating thickness and not on the type of aluminized coating, the substrate, or the cycle frequency.

Santoro, G.↗
NASA NTRS1975

Morphological growth of sputtered MoS2 films

Sputtered MoS2 films from 300 A to 20,000 A thick were deposited on metal and glass surfaces. The substrate effects such as surface temperature, finish, pretreatment, and chemistry as they affect the film formation characteristics were investigated by optical, electron transmission, electron diffraction, and scanning electron microscopy. Substrate temperature and surface chemistry were found to be the prime variables as to the formation of a crystalline or amorphous film. The friction characteristics are strictly influenced by the type of film formed. Surface chemistry and surface pretreatment account for compound formation and corresponding grain growth, which directly affect the adhesion characteristics, resulting in poor adherence. Scratches, impurities, inhomogeneities, etc., are favorable nucleation sites for the growth of isolated and complex nodules within the film.

Spalvins, T.↗
NASA NTRS1977

Microstructural and wear properties of sputtered carbides and silicides

Sputtered Cr3C2, Cr3Si2, and MoSi2 wear-resistant films (0.05 to 3.5 microns thick) were deposited on metal and glass surfaces. Electron transmission, electron diffraction, and scanning electron microscopy were used to determine the microstructural appearance. Strong adherence was obtained with these sputtered films. Internal stresses and defect crystallographic growth structures of various configurations within the film have progressively more undesirable effects for film thicknesses greater than 1.5 microns. Sliding contact and rolling element bearing tests were performed with these sputtered films. Bearings sputtered with a duplex coating (0.1-micron-thick undercoating of Cr3Si2 and subsequently 0.6-micron coating of MoS2) produced marked improvement over straight MoS2 films.

Spalvins, T.↗
NASA NTRS1978

Interaction of hydrogen chloride with alumina

The influence of temperature, pressure, and outgas conditions on the absorption of hydrogen chloride and water vapor on both alpha and gamma alumina was studied. Characterization of the adsorbents was performed using X-ray powder diffraction, scanning electron microscopy (SEM), low temperature nitrogen adsorption desorption measurements, BET nitrogen surface area measurements and electron spectroscopy for chemical analysis (ESCA). Water vapor adsorption isotherms at 30, 40, and 50 C were measured on alpha and gamma alumina after outgassing at 80, 200, and 400 C. Both outgas temperature and adsorption temperature influenced the adsorption of water vapor on the aluminas. The water vapor adsorption was completely reversible. Alpha alumina absorbed more water per unit area than gamma alumina. Differences in the adsorption capacity for water vapor of the two aluminas were explained on the basis of ideal surface models of alpha and gamma alumina. Isosteric heats of adsorption for water vapor on the aluminas were determined over a limited range of surface coverage.

Bailey, R. R.↗
NASA NTRS1977

Microstructural and wear properties of sputtered carbides and silicides

Sputtered Cr3C2, Cr3Si2, and MoSi2 wear-resistant films (0.05 to 3.5 microns thick) were deposited on metal and glass surfaces. Electron transmission, electron diffraction, and scanning electron microscopy were used to determine the microstructural appearance. Strong adherence was obtained with these sputtered films. Internal stresses and defect crystallographic growth structures of various configurations within the film have progressively more undesirable effects for film thicknesses greater than 1.5 microns. Sliding contact and rolling-element bearing tests were also performed with these sputtered films.

Spalvins, T.↗
NASA NTRS1978

The hot corrosion of Co-25Cr-10Ni-5Ta-3Al-0.5Y alloy /S-57/

A cobalt-base alloy, Co-25Cr-10Ni-5Ta-3Al-0.5Y (S-57), was subjected to hot corrosion in Mach 0.3 burner-rig combustion gases at maximum alloy temperatures of 900 and 1000 C. Various salt concentrations were injected into the burner: 0.5, 2,5, and 10 parts per million synthetic sea salt and 4 parts per million sodium sulfate (Na2SO4). The extent of corrosion was determined by measuring the maximum depth of corrosion in the alloy, and the corrosion process was studied by metallography, X-ray diffraction, scanning electron microscopy, and electron microprobe analysis. While S-57 was found to possess only moderate oxidation resistance at these temperatures, this alloy resisted significant hot corrosion attack under all but the most severe test conditions. The process of hot corrosion attack under the most severe conditions of this study was primarily sulfidation.

Santoro, G. J.↗
NASA NTRS1982

Effects of cobalt on the microstructure of Udimet 700

Cobalt, a critical and "strategic" alloying element in many superalloys, was systematically substituted by nickel in experimental alloys Udimet 700 containing 0.1, 4.3, 8.6, 12.8 and the standard 17.0 wt.% cobalt. Electrolytic and chemical extraction techniques, X-ray diffraction, scanning electron and optical microscopy were used for the microstructural studies. The total weight fraction of gamma' was not significantly affected by the cobalt content, although a difference in the size and quantities of the primary and secondary gamma' phases was apparent. The lattice parameters of the gamma' were found to increase with increasing cobalt content while the lattice mismatch between the gamma matrix and gamma' phases decreased. Other significant effects of cobalt on the weight fraction, distribution and formation of the carbide and boride phases as well as the relative stability of the experimental alloys during long-time aging are also discussed.

Engel, M. A.↗
NASA NTRS1983

Interaction of hydrogen chloride and water with oxide surfaces. III - Titanium dioxide

The adsorption of hydrogen chloride and water vapors on five TiO2 powders in both the anatase and rutile crystalline forms was studied as a function of temperature, pressure, and outgas conditions. The adsorbents were characterized utilizing X-ray powder diffraction, scanning electron microscopy, surface area analysis, indicator method, microelectrophoresis, XPS, and infrared spectroscopy. It was found that both outgas temperature and adsorption temperature influenced the adsorption of water vapor on TiO2, while water vapor adsorption on TiO2 was completely reversible. It is argued that the number of hydroxyl groups present on the surface determines the adsorption capacity of water on the different titanium dioxides. It was found that heats of immersion in water were affected significantly by outgas temperature. Hydrogen chloride adsorption isotherms at 30 C measured on TiO2 after outgassing at 100-400 C showed that a part of the total HCl adsorbed was irreversibly adsorbed. The highest HCl adsorption capacity per unit area was exhibited by anatase, while pure rutile exhibited the lowest adsorption capacity.

Siriwardane, R. V.↗
NASA NTRS1983

Surface acoustic wave/silicon monolithic sensor/processor

A new technique for sputter deposition of piezoelectric zinc oxide (ZnO) is described. An argon-ion milling system was converted to sputter zinc oxide films in an oxygen atmosphere using a pure zinc oxide target. Piezoelectric films were grown on silicon dioxide and silicon dioxide overlayed with gold. The sputtered films were evaluated using surface acoustic wave measurements, X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and resistivity measurements. The effect of the sputtering conditions on the film quality and the result of post-deposition annealing are discussed. The application of these films to the generation of surface acoustic waves is also discussed.

Kowel, S. T.↗
NASA NTRS1984

Formation of bulk metallic glass by fluxing

Bulk specimens (0.4-4 g mass) of the alloy Pd40Ni40P20 have been undercooled consistently to the glass state, with no detectable superficial crystallinity, in a molten flux of dehydrated boron oxide. The minimum dimension of the most massive glass specimen, so formed, was 1.0 cm. The absence of crystallinity in the specimens was confirmed by X-ray diffraction, scanning electron microscopy, and calorimetry.

Kui, H. W.↗
NASA NTRS1988

Molecular beam epitaxy and metalorganic chemical vapor deposition growth of epitaxial CdTe on (100) GaAs/Si and (111) GaAs/Si substrates

Epitaxial CdTe has been grown on both (100)GaAs/Si and (111)GaAs/Si substrates. A combination of molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has been employed for the first time to achieve this growth: the GaAs layers are grown on Si substrates by MBE and the CdTe film is subsequently deposited on GaAs/Si by MOCVD. The grown layers have been characterized by X-ray diffraction, scanning electron microscopy, and photoluminescence.

Nouhi, A.↗
NASA NTRS1993

Hot Hydrogen Testing of Refractory Metals and Ceramics

The objective of this investigation is to develop a technique with which refractory metal carbide samples can be exposed to hydrogen containing gases at high temperatures, and to use various microstructural and analytical techniques to determine the chemical and rate processes involved in hydrogen degradation in these materials. Five types of carbides were examined including WC, NbC, HfC, ZrC, and TaC. The ceramics were purchased and were all monolithic in nature. The temperature range investigated was from 850 to 1600 C with a hydrogen pressure of one atmosphere. Control experiments, in vacuum, were also conducted for comparison so that the net effects due to hydrogen could be isolated. The samples were analyzed prior to and after exposure. Gas samples were collected in selected experiments and analyzed using gas chromography. Characterization of the resulting microstructure after exposure to hydrogen was conducted using optical microscopy, x-ray diffraction, scanning electron microscopy, and weight change. The ceramics were purchased and were all monolithic in nature. It was found that all samples lost weight after exposure, both in hydrogen and vacuum. Results from the microstructure analyses show that the degradation processes are different among the five types of ceramics involved. In addition, the apparent activation energy for the degradation process is a function of temperature even within the same material. This indicates that there are more than one mechanism involved in each material, and that the mechanisms are temperature dependent.

Zee, Ralph↗