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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 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Studies of the Crystallization Process of Aluminum-Silicon Alloys Using a High Temperature Microscope

It is shown that primary silicon crystals grow polyhedral in super-eutectic AlSi melts and that phosphorus additives to the melt confirm the strong seeding capacity. Primary silicon exhibits strong dendritic seeding effects in eutectic silicon phases of various silicon alloys, whereas primary aluminum does not possess this capacity. Sodium addition also produces a dendritic silicon network growth in the interior of the sample that is attributed to the slower silicon diffusion velocity during cooling.

Justi, S.↗
NASA NTRS1985

Immunocytochemical localization of glial fibrillary acidic protein (GFAP) in the area postrema of the cat - Light and electron microscopic study

Glial fibrillary acidic protein (GFAP) was demonstrated in the cytoplasm and processes of ependymal cells and astroglial components of the area postrema of the cat. These observations differ from the findings in the ependyma of the ventricular cavities which are consistently negative for the protein. Since some studies have suggested sensory functions of the glial cells in this emetic chemoreceptor trigger zone, a careful consideration of morphological and biochemical attributes of these cells seems appropriate.

Damelio, F. E.↗
NASA NTRS1983

The scanning electron microscope as a tool in space biology

Normal erythrocytes are disc-shaped and are referred to here descriptively as discocytes. Several morphologically variant forms occur nomally but in rather small amounts, usually less than one percent of total. It has been shown though, that spiculed variant forms referred to as echinocytes are generated in significant amounts at zero g. Normal red cells have been stressed in vitro in an effort to duplicate the observed discocyte-echinocyte transformation at zero g. The significance of this transformation to extended stay in space and some of the plausible reasons for this transformation are discussed.

Barrett, R. A.↗
NASA NTRS1983

Electron microscopic observations of hydrogen implantation in ilmenites

Hydrogen ion beams were found to form submicrometer, bumpy textures on the surface of ilmenite grains. From this effect, it is believed that similar bumpy textures seen on lunar ilmenite, pyroxene, and olivine grains are likely to be caused by solar wind irradiation. As a consequence, the concentration of bumpy textured grains may be a useful index of surface maturity for lunar soils. An attempt was made to search for grains with these bumpy textures in interplanetary dust and lunar and meteoritic regolith breccias in order to obtain information about the duration of their exposure to the solar wind. Solar wind irradiation was simulated on natural, terrestrial ilmenite. Hydrogen ion beams were directed at small grains and polished sections which were then examined by electron microscopy.

Blanford, G. E.↗
NASA NTRS1986

Electron microscopic determination of the metastable dissociation region in the system Li sub 2SiO3-SiO sub 2

Seven glasses with an alkali oxide content in the range 9.57 to 29.53 mole percent were investigated. The temperature at which the transition of microheterogeneous mixing to the condition of mutual solubility occurs on heating is found. It is found that the altered constituent composition results in the alteration in the percentage amount of the coexisting phases.

Marinov, M.↗
NASA NTRS1986

Emission FTIR analyses of thin microscopic patches of jet fuel residues deposited on heated metal surfaces

The relationship of fuel stability to fuel composition and the development of mechanisms for deposit formation were investigated. Fuel deposits reduce heat transfer efficiency and increase resistance to fuel flow and are highly detrimental to aircraft performance. Infrared emission Fourier transform spectroscopy was chosen as the primary method of analysis because it was sensitive enough to be used in-situ on tiny patches of monolayers or of only a few molecular layers of deposits which generally proved completely insoluble in any nondestructive solvents. Deposits of four base fuels were compared; dodecane, a dodecane/tetralin blend, commercial Jet A fuel, and a broadened-properties jet fuel particularly rich in polynuclear aromatics. Every fuel in turn was provided with and without small additions of such additives as thiophene, furan, pyrrole, and copper and iron naphthenates.

Lauer, J. L.↗
NASA NTRS1986

Transmission electron microscopic examination of phosphoric acid fuel cell components

Transmission electron microscopy (TEM) was used to physically characterize tested and untested phosphoric acid fuel cell (PAFC) components. Those examined included carbon-supported platinum catalysts, carbon backing paper, and Teflon-bonded catalyst layers at various stages of fabrication and after testing in pressurized PAFC's. Applicability of electron diffraction and electron energy loss spectroscopy for identifying the various phases was explored. The discussion focuses on the morphology and size distribution of platinum, the morphology and structural aspects of Teflon in catalyst layers, and the structural evidence of carbon corrosion. Reference is made to other physical characterization techniques where appropriate. A qualitative model of the catalyst layer that emerged from the TEM studies is presented.

Pebler, A.↗
NASA NTRS1987

Microscopic Gas-Flow Controller

Proposed flow-controlling and -measuring device made by batch solid-state microelectronic-fabrication techniques. Device contains ultrasensitive silicon capacitive pressure transducer, gas-flow channels etched in silicon wafer, and integrated microvalves. Used to control and monitor low gas flows at low pressures.

Wise, Kensall D.↗
NASA NTRS1988

In situ fatigue loading stage inside scanning electron microscope

A fatigue loading stage inside a scanning electron microscopy (SEM) was developed. The stage allows dynamic and static high-magnification and high-resolution viewing of the fatigue crack initiation and crack propagation processes. The loading stage is controlled by a closed-loop servohydraulic system. Maximum load is 1000 lb (4450 N) with test frequencies ranging up to 30 Hz. The stage accommodates specimens up to 2 inches (50 mm) in length and tolerates substantial specimen translation to view the propagating crack. At room temperature, acceptable working resolution is obtainable for magnifications ranging up to 10,000X. The system is equipped with a high-temperature setup designed for temperatures up to 2000 F (1100 C). The signal can be videotaped for further analysis of the pertinent fatigue damage mechanisms. The design allows for quick and easy interchange and conversion of the SEM from a loading stage configuration to its normal operational configuration and vice versa. Tests are performed entirely in the in-situ mode. In contrast to other designs, the NASA design has greatly extended the life of the loading stage by not exposing the bellows to cyclic loading. The loading stage was used to investigate the fatigue crack growth mechanisms in the (100)-oriented PWA 1480 single-crystal, nickel-based supperalloy. The high-magnification observations revealed the details of the crack growth processes.

Telesman, Jack↗
NASA NTRS1988

Phase diagrams and microscopic structures of (Hg,Cd)Te, (Hg,Zn)Te, and (Cd,Zn)Te alloys

A cluster theory based on the quasi-chemical approximation has been applied to study the local correlation bond-length distribution, and phase diagrams of the II-VI pseudobinary alloys Hg(1 - x)Cd(x)Te, Hg(1 - x)Zn(x)Te, and Cd(1 - x)Zn(x)Te. The cluster energy is calculated by letting it relax in some effective alloy medium and then considering the contributions from the strain and chemical energies. Two different models are presented to simulate the alloy medium. While both models show that all three alloys have nearly random distributions, the signs of the local correlation prove to be sensitive to the alloy medium chosen for the energy calculation. Good agreement is found between experiment and the bond lengths and phase diagrams in both models.

Patrick, R. S.↗
NASA NTRS1989

Microscopic deformation in a heated unidirectional graphite-epoxy composite

Both in-plane and out-of-plane displacements were determined in patches of the toughened 1962-ERLX epoxy bounded by three closely packed high-modulus P75S graphite fibers. The P75S/1962-ERLX composite was unidirectional, with an average fiber volume of 60 percent. On heating to 44 C from room temperature, the epoxy confined between clusters of three fibers sank in a trough beneath the plane of the fiber ends by 50-120 nm. When the maximum temperature achieved in the prior thermal cycles exceeded 100 C the depth of the trough increased. However, when cycles exceeding 100 C were followed by thermal cycles of decreasing amplitude, chosen to reduce interfacial stress relaxation, the depth of the trough decreased. The results illustrate the feasibility of deducing quantitative data on local deformation from high-resolution strain measurements on cut surfaces.

Morris, W. L.↗
NASA NTRS1989

Automated thin-film analyses of anhydrous interplanetary dust particles in the analytical electron microscope

An AEM apparatus equipped with digital beam control has obtained quantitative point-count analyses of thin sections taken from eight anhydrous chondritic interplanetary dust particles (IDPs); between 200 and 500 X-ray analyses were collected from each thin section and analyzed for Mg, Al, Si, S, Ca, Cr, Mn, Fe, and Ni. Two types of anhydrous chondritic aggregates were observed in the eight IDPs: one highly porous, the other less so. The eight anhydrous IDPs are characterizable as mixtures of fine- and coarse-grained aggregates, large mineral grains, glass, and carbonaceous materials. Their elemental concentrations follow those of solar abundances, suggesting that they are unperturbed by aqueous alteration.

Bradley, J. P.↗
NASA NTRS1990

Matrix mineralogy of the Lance CO3 carbonaceous chondrite - A transmission electron microscope study

Results are presented on electron microprobe analyses of three CO chondrites, all of which are falls: Lance, Kainsaz, and Warrenton. The TEM mineralogy results of Lance chondrite show that Fe-rich matrix olivines have been altered to Fe-bearing serpentine and Fe(3+) oxide; matrix metal was also altered to produce Fe(3+) oxides, leaving the residual metal enriched in Ni. Olivine grains in Lance's matrix contain channels along their 100-line and 001-line directions; the formation and convergence of such channels resulted in a grain-size reduction of the olivine. A study of Kainsaz and Warrenton showed that these meteorites do not contain phyllosilicates in their matrices, although both contain Fe(3+) oxide between olivine grains. It is suggested that, prior to its alteration, Lance probably resembled Kainsaz, an unaltered CO3 chondrite.

Keller, Lindsay P.↗
NASA NTRS1990

Particle acceleration in step function shear flows - A microscopic analysis

The transport of energetic particles in a moving, scattering fluid, which has a large shear in its velocity over a distance small compared with the scattering mean free path is discussed. The analysis is complementary to an earlier paper by Earl, Jokipii, and Morfill (1988), which considered effects of more-gradual shear in the diffusion approximation. The case in which the scattering fluid undergoes a step function change in velocity, in the direction normal to the flow is considered. An analytical, approximate calculation and a Monte Carlo analysis of particle motion are presented. It is found that particles gain energy at a rate proportional to the square of the magnitude of the velocity change.

Jokipii, J. R.↗
NASA NTRS1990

Model gases for the detailed study of microscopic chemical nonequilibrium in diatomic gas flows

It is shown that chlorine (Cl2) and iodine (I2) are suitable model diatomic gases to use in theoretical studies of chemical nonequilibrium that account for rotational and vibrational as well as electronic processes in a gas. Because of the low temperature at which significant dissociation can be achieved in iodine, it is a particularly attractive candidate for the study of relatively low temperature chemically reacting flows, permitting detailed knowledge of the nonequilibrium populations of translational, rotational, vibrational and electronic energy levels. A preliminary investigation indicates that a useful iodine flow facility can be constructed and that diagnostic techniques are available to validate in detail prediction techniques for nonequilibrium flows.

Kunc, Joseph A.↗
NASA NTRS1990

Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si

The quality of GaAs thin films grown via MBE under pulsed excimer laser irradiation on Si substrates is examined in both laser-irradiated and nonirradiated areas using Raman scattering, Rayleigh scattering, and by photoluminescence (PL), as a function of temperature, and by TEM. The temperature dependence of the PL and Raman peak positions indicates the presence of compressive stress in the thin GaAs films in both laser-irradiated and nonirradiated areas. This indicates incomplete homogeneous strain relaxation by dislocations at the growth temperature. The residual compressive strain at the growth temperature is large enough such that even with the introduction of tensile strain arising from the difference in thermal expansion coefficients of GaAs and Si, a compressive strain is still present at room temperature for these thin GaAs/Si films.

Lao, Pudong↗