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NASA NTRS2001

Soot Formation in Laminar Premixed Ethylene/Air Flames at Atmospheric Pressure

Soot formation was studied within laminar premixed ethylene/air flames (C/O ratios of 0.78-0.98) stabilized on a flat-flame burner operating at atmospheric pressure. Measurements included soot volume fractions by both laser extinction and gravimetric methods, temperatures by multiline emission, soot structure by thermophoretic sampling and transmission electron microscopy, major gas species concentrations by sampling and gas chromatography, concentrations of condensable hydrocarbons by gravimetric sampling. and velocities by laser velocimetry. These data were used to find soot surface growth rates and primary soot particle nucleation rates along the axes of the flames. Present measurements of soot surface growth rates were correlated successfully by predictions based on typical hydrogen-abstraction/carbon-addition (HACA) mechanisms of Frenklach and co-workers and Colket and Hall. These results suavest that reduced soot surface growth rates with increasing residence time seen in the present and other similar flames were mainly caused by reduced rates of surface activation due to reduced H atom concentrations as temperatures decrease as a result of radiative heat losses. Primary soot particle nucleation rates exhibited variations with temperature and acetylene concentrations that were similar to recent observations for diffusion flames; however, nucleation rates in the premixed flames were significantly lower than in, the diffusion flames for reasons that still must be explained. Finally, predictions of yields of major gas species based on mechanisms from both Frenklach and co-workers and Leung and Lindstedt were in good agreement with present measurements and suggest that H atom concentrations (relevant to HACA mechanisms) approximate estimates based on local thermodynamic equilibrium in the present flames.

Xu, F.↗
NASA NTRS2001

Soot Oxidation in Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure

Soot oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round jets burning in coflowing air considering acetylene, ethylene, propylene and propane as fuels. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation mainly occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of stable major gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2,C2H4, C2H6, C3H6, and C3H8) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by the deconvoluted Li/LiOH atomic absorption technique and flow velocities by laser velocimetry. It was found that soot surface oxidation rates are not particularly affected by fuel type for laminar diffusion flames and are described reasonably well by the OH surface oxidation mechanism with a collision efficiency of 0.10, (standard deviation of 0.07) with no significant effect of fuel type in this behavior; these findings are in good agreement with the classical laminar premixed flame measurements of Neoh et al. Finally, direct rates of surface oxidation by O2 were small compared to OH oxidation for present conditions, based on estimated O2 oxidation rates due to Nagle and Strickland-Constable (1962), because soot oxidation was completed near the flame sheet where O2 concentrations were less than 1.2% by volume.

Xu, F.↗
NASA NTRS2001

Soot Optical Property Study

Recent past studies of soot reaction processes in laminar premixed and nonpremixed flames generally have used the intrusive technique of thermophoretic sampling and analysis by transmission electron microscopy (TEM) to observe soot structure and obtain important fundamental information about soot particle properties, such as soot primary particle diameters, the rate of change of soot primary particle diameter as a function of time (or rate of soot surface growth or oxidation), the amount of soot particle reactive surface area per unit volume, the number of primary soot particles per unit volume, and the rate of formation of primary soot particles (or the rate of soot primary particle nucleation). Given the soot volume per unit volume of the flame (or the soot volume fraction), all these properties are readily found from a measurement of the soot primary particle diameter (which usually is nearly a constant for each location within a laminar flame). This approach is not possible within freely propagating flames, however, because soot properties at given positions in such flames vary relatively rapidly as a function of time in the soot formation and oxidation regions compared to the relatively lengthy sampling times needed to accumulate adequate soot samples and to minimize effects of soot collected on the sampling grid as it moves to and from the sampling position through other portions of the flame. Thus, nonintrusive optical methods must be used to find the soot primary particle diameters needed to define the soot surface reaction properties mentioned earlier. Unfortunately, approximate nonintrusive methods used during early studies of soot reaction properties in flames, found from laser scattering and absorption measurements analyzed assuming either Rayleigh scattering or Mie scattering from polydisperse effective soot particles having the same mass of soot as individual soot aggregates, have not been found to be an effective way to estimate the soot surface reaction area per unit volume. Thus, alternative nonintrusive optical methods of finding these properties must be sought, which was the objective of this phase of the investigation. The alternative method used here involves use of the Rayleigh-Debye-Gans-Polydisperse-Fractal-Aggregate (RDG-PFA) scattering approximation for soot aggregates in flames. Thus, the development of this method will be discussed next before describing its evaluation as a means of nonintrusively measuring soot primary particle diameters in soot-containing flames.

Aung, K. T.↗
NASA NTRS2003

Soot Surface Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure

Soot surface oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round fuel jets burning in coflowing dry air considering acetylene-nitrogen, ethylene, propyiene-nitrogen, propane and acetylene-benzene-nitrogen in the fuel stream. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2, C2H6, C3H6, C3H8, and C6H6) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption and flow velocities by laser velocimetry. For present test conditions, it was found that soot surface oxidation rates were not affected by fuel type, that direct rates of soot surface oxidation by O2 estimated from Nagle and Strickland-Constable (1962) were small compared to observed soot surface oxidation rates because soot surface oxidation was completed near the flame sheet where O2 concentrations were less than 3% by volume, and that soot surface oxidation rates were described by the OH soot surface oxidation mechanism with a collision efficiency of 0.14 and an uncertainty (95% confidence) of +/- 0.04 when allowing for direct soot surface oxidation by O2, which is in reasonably good agreement with earlier observations of soot surface oxidation rates in both premixed and diffusion flames at atmospheric pressure.

Xu, F.↗
NASA NTRS2003

Defect Clustering and Nano-Phase Structure Characterization of Multi-Component Rare Earth Oxide Doped Zirconia-Yttria Thermal Barrier Coatings

Advanced oxide thermal barrier coatings have been developed by incorporating multi-component rare earth oxide dopants into zirconia-yttria to effectively promote the creation of the thermodynamically stable, immobile oxide defect clusters and/or nano-scale phases within the coating systems. The presence of these nano-sized defect clusters has found to significantly reduce the coating intrinsic thermal conductivity, improve sintering resistance, and maintain long-term high temperature stability. In this paper, the defect clusters and nano-structured phases, which were created by the addition of multi-component rare earth dopants to the plasma-sprayed and electron-beam physical vapor deposited thermal barrier coatings, were characterized by high-resolution transmission electron microscopy (TEM). The defect cluster size, distribution, crystallographic and compositional information were investigated using high-resolution TEM lattice imaging, selected area diffraction (SAD), electron energy-loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) analysis techniques. The results showed that substantial defect clusters were formed in the advanced multi-component rare earth oxide doped zirconia- yttria systems. The size of the oxide defect clusters and the cluster dopant segregation was typically ranging from 5 to 50 nm. These multi-component dopant induced defect clusters are an important factor for the coating long-term high temperature stability and excellent performance.

Zhu, Dongming↗
NASA NTRS2003

Structural Evolution and Mechanical Properties of PMR-15/Layered Silicate Nanocomposites

In the first year of this research, we successfully synthesized and characterized Polymer/ Layered Silicate nanocomposite using the polyimide PMR-15 as the polymer and several layered silicate nanoparticles. We have scaled up the process to allow fabrication of monoliths using these nanocomposites. The morphology of these systems was found to evolve during processing to an exfoliated structure for one system and intercalated for the rest. Correlation with Transmission Electron Microscopy studies is underway. Dynamic mechanical analysis (DMA) results showed a significant increase in the thermomechanical properties (E' and E'') of 2.5 wt.% clay loaded nanocomposites in comparison to the neat polyimide. Increasing the clay loading to 5 wt.% decreased these properties. Higher glass transition temperatures were observed for 2.5 wt.% nanocomposites compared to the neat polyimide. A lower coefficient of thermal expansion was observed only for the PGV/PMR-15 nanocomposite. An improvement in the flexural properties (modulus, strength and elongation) was observed for the 2.5 wt.% nanocomposite but not for the 5 wt.% nanocomposites. The improved barrier properties polymer/ silicate nanocomposites suggest that moisture uptake should be decreased for PMR-15 nanocomposites. The results of some recent experiments to examine delineate the ability of the silicate nanoparticles in improving the hydrolytic degradation of PMR-15 will be discussed.

Campbell, Sandi↗
NASA NTRS2003

Laboratory Simulation of Space Weathering: ESR Measurements of Nanophase Metallic Iron in Laser-irradiated Olivine and Pyroxene Samples

S-type asteroids are believed to be parent bodies of ordinary chondrites. Although both S-type asteroids and ordinary chondrites contain the same mineral assemblage, mainly olivine and pyroxene, the reflectance spectra of the asteroids exhibit more overall depletion (darkening) and reddening, and more weakening of absorption bands relative to the meteorites. This spectral mismatch is explained by space weathering process, where high-velocity dust particle impacts should change the optical properties of the uppermost regolith surface of asteroids. In order to simulate the space weathering, we irradiated nanosecond pulse laser beam onto pellet samples of olivine (8.97wt% FeO) and pyroxene (enstatite: 9.88wt% FeO, hypersthene: 16.70wt%). We got spectral changes in our samples similar to that by space weathering on asteroids and confirmed nanophase alpha-metallic iron particles, which were theoretically predicted, not only on olivine but also on pyroxene samples by Transmission Electron Microscopy (TEM). Nanophase metallic iron particles were widely scattered throughout the amorphous rims developed along the olivine grains, whereas they were embedded in aggregates of amorphous in enstatite samples. Recently, we also measured laser-irradiated samples by ESR (Electron Spin Resonance). Strong ESR signals, characteristic to nanophase iron particles, are observed on irradiated olivine samples. In this paper, we report the quantities of nanophase metallic iron particles in pyroxene samples by ESR observations in addition to olivine samples.

Kurahashi, E.↗
NASA NTRS2003

HRTEM and EFTEM Observations of Matrix in the Oxidized CV3 Chondrite ALH 84028: Implications for the Origins of Matrix Olivines

The determination of the nature, distribution, and origin of organic material in carbonaceous chondrites is fundamental to understanding early solar nebular conditions and the origin of life. Using a variety of extraction techniques, followed by detailed chemical analysis, an extensive suite of organic compounds has been identified in carbonaceous chondrites. These data have provided key information on the diversity and isotopic composition of the organic component in chondrites. However, one disadvantage of extraction techniques is that all information regarding the spatial distribution of the organics on a fine scale is lost. This is especially important for the insoluble macromolecular carbon, which constitutes approximately 70% of the carbon in carbonaceous chondrites such as Murchison. The distribution and mineralogical associations may provide important constraints on the possible origins of the carbonaceous material. Our previous studies of the CV3 chondrites Allende and Vigarano have demonstrated that energy filtered transmission electron microscopy (EFTEM), combined with high resolution TEM (HRTEM) are powerful tools for the in situ characterization of insoluble organic matter in carbonaceous chondrites. In this study, we have used SEM and TEM techniques to characterize the matrix mineralogy of the CV3 chondrite ALH 84028 and examine the distribution and mineralogical associations of carbon. We are especially interested in establishing whether the occurrence of poorly graphitized carbon (PGC), observed in Allende matrix olivines, is common to all oxidized CV3 chondrites or is a unique feature of Allende.

Abreu, Neyda M.↗
NASA NTRS2003

Characterization of the Effects of Precursor Mineralogy on Hematite Spectra: Application to Martian Hematite Mineralization

The Thermal Emission Spectrometer (TES) instrument aboard Mars Global Surveyor discovered several isolated deposits of gray, crystalline hematite in Sinus Meridiani, Aram Chaos, and Valles Marineris. A variety of formation mechanisms has been proposed for the martian hematite deposits, including aqueous and nonaqueous processes. Comparison of the average Sinus Meridiani hematite spectrum measured by TES to laboratory emissivity spectra for a variety of naturally occurring hematites shows small but potentially important differences. In particular, the emissivity minimum at 300 and 445/cm in the Sinus Meridiani (SM) spectrum is displaced 10-25/cm to lower frequencies compared to some natural hematite samples. In addition, these bands in the TES data are narrower than the broad bands seen in many natural hematite spectra. These differences may imply that the natural variability of hematite spectra has not been fully characterized, especially with respect to the reaction pathway (precursor mineralogy and temperature of hematite formation) and crystal morphology. Here, we describe the thermal infrared spectral characteristics of several series of synthetic hematite samples derived by direct precipitation, dehydroxylation of fine-grained goethite and the oxidation of magnetite. Several natural hematite sample spectra are also presented for comparison. Transmission electron microscopy (TEM) and Mossbauer spectral analyses of selected samples were performed in order to help determine the causes of the changes seen in the infrared spectra.

Glotch, Timothy D.↗
NASA NTRS2003

High Resolution, Single-Step Patterning of Silica Aerogels

Three-dimensional metallic structures are fabricated with high spatial resolution in silica aerogels. In our method, silica hydrogels are prepared with a standard base-catalyzed route, and exchanged with an aqueous solution typically containing Ag' ions (1 M) and 2-propanol (0.2 M). The metal ions are reduced photolytically with a table-top ultraviolet lamp, or radiolytically, with a focused X-ray beam. We fabricated dots and lines as small as 30 x 70 km, protruding for several mm into the bulk of the materials. The hydrogels are eventually supercritically dried to yield aerogels, without any measurable change in the shape and spatial resolution of the lithographed structures. Transmission electron microscopy shows that illuminated regions are composed of Ag clusters with a size of several pm, separated by thin layers of silica.

Bertino, M. F.↗
NASA NTRS2003

Observations of Glide and Decomposition of a<101> Dislocations at High Temperatures in Ni-Al Single Crystals Deformed along the Hard Orientation

Ni-44at.% Al and Ni-50at.% single crystals were tested in compression in the hard (001) orientations. The dislocation processes and deformation behavior were studied as a function of temperature, strain and strain rate. A slip transition in NiAl occurs from alpha(111) slip to non-alphaaaaaaaaaaa9111) slip at intermediate temperatures. In Ni-50at.% Al single crystal, only alpha(010) dislocations are observed above the slip transition temperature. In contrast, alpha(101)(101) glide has been observed to control deformation beyond the slip transition temperature in Ni-44at.%Al. alpha(101) dislocations are observed primarily along both (111) directions in the glide plane. High-resolution transmission electron microscopy observations show that the core of the alpha(101) dislocations along these directions is decomposed into two alpha(010) dislocations, separated by a distance of approximately 2nm. The temperature window of stability for these alpha(101) dislocations depends upon the strain rate. At a strain rate of 1.4 x 10(exp -4)/s, lpha(101) dislocations are observed between 800 and 1000K. Complete decomposition of a alpha(101) dislocations into alpha(010) dislocations occurs beyond 1000K, leading to alpha(010) climb as the deformation mode at higher temperature. At lower strain rates, decomposition of a alpha(101) dislocations has been observed to occur along the edge orientation at temperatures below 1000K. Embedded-atom method calculations and experimental results indicate that alpha(101) dislocation have a large Peieris stress at low temperature. Based on the present microstructural observations and a survey of the literature with respect to vacancy content and diffusion in NiAl, a model is proposed for alpha(101)(101) glide in Ni-44at.%Al, and for the observed yield strength versus temperature behavior of Ni-Al alloys at intermediate and high temperatures.

Srinivasan, R.↗
NASA NTRS2004

Defect Clustering and Nano-phase Structure Characterization of Multicomponent Rare Earth-Oxide-Doped Zirconia-Yttria Thermal Barrier Coatings

Advanced thermal barrier coatings (TBCs) have been developed by incorporating multicomponent rare earth oxide dopants into zirconia-based thermal barrier coatings to promote the creation of the thermodynamically stable, immobile oxide defect clusters and/or nanophases within the coating systems. In this paper, the defect clusters, induced by Nd, Gd, and Yb rare earth dopants in the zirconia-yttria thermal barrier coatings, were characterized by high-resolution transmission electron microscopy (TEM). The TEM lattice imaging, selected area diffraction (SAD), and electron energy-loss spectroscopy (EELS) analyses demonstrated that the extensive nanoscale rare earth dopant segregation exists in the plasma-sprayed and electron-physical-vapor-deposited (EB PVD) thermal barrier coatings. The nanoscale concentration heterogeneity and the resulting large lattice distortion promoted the formation of parallel and rotational defective lattice clusters in the coating systems. The presence of the 5-to 100-nm-sized defect clusters and nanophases is believed to be responsible for the significant reduction of thermal conductivity, improved sintering resistance, and long-term high temperature stability of the advanced thermal barrier coating systems.

Zhu, Dongming↗
NASA NTRS2003

Attachment of Single-wall Carbon Nanotubes (SWNTs) on Platinum Surfaces by Self-Assembling Techniques

Single-wall carbon nanotubes (SWNTs) are very interesting materials because of their morphology, electronic and mechanical properties. Its morphology (high length-to-diameter ratio) and electronic properties suggest potential application of SWNTs as anode material for lithium ion secondary batteries. The introduction of SWNTs on these types of sources systems will improve their performance, efficiency, and capacity to store energy. A purification method has been applied for the removal of iron and amorphous carbon from the nanotubes. Unpurified and purified SWNTs were characterized by transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). In order to attach carbon nanotubes on platinum electrode surfaces, a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) was deposited over the electrodes. The amino-terminated SAM obtained was characterized by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and Fourier-transforms infrared (FTIR) spectroscopy. Carbon nanotubes were deposited over the amino-terminated SAM by an amide bond formed between SAM amino groups and carboxylic acid groups at the open ends of the carbon nanotubes.This deposition was characterized using Raman spectroscopy and Scanning Electron microscopy (SEM).

Rosario-Castro, Belinda I.↗
NASA NTRS2003

Experiments And Model Development For The Investigation Of Sooting And Radiation Effects In Microgravity Droplet Combustion

This study involves flight experiments (for droplets between 1.5 to 5 mm) and supportive ground-based experiments, with concurrent numerical model development and validation. The experiments involve two fuels: n-heptane, and ethanol. The diagnostic measurements include light extinction for soot volume fraction, two-wavelength pyrometry and thin-filament pyrometry for temperature, spectral detection for OH chemiluminescence, broadband radiometry for flame emission, and thermophoretic sampling with subsequent transmission electron microscopy for soot aerosol property calculations.

Yozgatligil, Ahmet↗
NASA NTRS2004

In Situ Location and Characterization of Carbon-bearing Phases in Carbonaceous Chondrites: Insights from Yamato 791198, a Weakly-altered CM2 Chondrite

Intense studies of carbonaceous chondrites have provided remarkable insights into the behavior of carbon during the earliest stages of our solar system. This research has demonstrated that carbonaceous meteorites contain a diverse array of organic compounds, whose origins are probably the result of multiple processes that occurred in different locations including interstellar space, the solar nebula and asteroidal parent bodies [1-3]. The most abundant organic carbon component in CI1 and CM2 carbonaceous chondrites is so-called macromolecular carbon, a high molecular weight material that has some affinities to terrestrial kerogen and constitutes approximately 60-70% of the organic material in these meteorites. Although recent studies e.g. [3] have radically improved our understanding of the structural and compositional characteristics of this material, a number of key questions remain to be addressed. In particular, our knowledge of where this macromolecular material is distributed at the fine-scale within carbonaceous chondrites is scant. [4] have shown that organic material is associated with phyllosilicate-rich matrix in CM chondrites, but the detailed mineralogical associations are not well-known. Over the past 2 years, we have begun to address this question by using energy filtered transmission electron microscopy (EFTEM) to locate carbon-bearing materials in situ, focusing specifically on the CM2s. To date we have reported data on the Murchison CM2 chondrite [5], a meteorite that has experienced a modest degree of aqueous alteration. To extend our observations to other CM2 chondrites, we have examined the occurrence of carbon-bearing phases in Yamato 791198. Our recent studies [5] have shown that Y-791198 is among the most weakly-altered CM chondrite currently known and hence is likely to preserve a quite primitive distribution of carbonaceous material. In this study, we present initial observations on the distribution of these materials in one fine-grained rim and compare them with our results from Murchison. Such information may provide important insights into the origins of the carbonaceous material and how it was distributed in nebular and perhaps presolar dust.

Brearley, Adrian J.↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Astrobiology

The presentations in this session are: 1. A Prototype Life Detection Chip 2. The Geology of Atlantis Basin, Mars, and Its Astrobiological Interest 3. Collecting Bacteria Together with Aerosols in the Martian Atmosphere by the FOELDIX Experimental Instrument Developed with a Nutrient Detector Pattern: Model Measurements of Effectivity 4. 2D and 3D X-ray Imaging of Microorganisms in Meteorites Using Complexity Analysis to Distinguish Field Images of Stromatoloids from Surrounding Rock Matrix in 3.45 Ga Strelley Pool Chert, Western Australia 4. Characterization of Two Isolates from Andean Lakes in Bolivia Short Time Scale Evolution of Microbiolites in Rapidly Receding Altiplanic Lakes: Learning How to Recognize Changing Signatures of Life 5. The Effect of Salts on Electrospray Ionization of Amino Acids in the Negative Mode 6. Determination of Aromatic Ring Number Using Multi-Channel Deep UV Native Fluorescence 7. Microbial D/H Fractionation in Extraterrestrial Materials: Application to Micrometeorites and Mars 8. Carbon Isotope Characteristics of Spring-fed Iron-precipitating Microbial Mats 9. Amino Acid Survival Under Ambient Martian Surface UV Lighting Extraction of Organic Molecules from Terrestrial Material: Quantitative Yields from Heat and Water Extractions 10. Laboratory Detection and Analysis of Organic Compounds in Rocks Using HPLC and XRD Methods 11. Thermal Decomposition of Siderite-Pyrite Assemblages: Implications for Sulfide Mineralogy in Martian Meteorite ALH84001 Carbonate Globules 12. Determination of the Three-Dimensional Morphology of ALH84001 and Biogenic MV-1 Magnetite: Comparison of Results from Electron Tomography and Classical Transmission Electron Microscopy 13. On the Possibility of a Crypto-Biotic Crust on Mars Based on Northern and Southern Ringed Polar Dune Spots 14. Comparative Planetology of the Terrestrial Inner Planets: Implications for Astrobiology 15. A Possible Europa Exobiology 16. A Possible Biogeochemical Model for Titan

Source record↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Interplanetary Dust and Aerogel

Contents include the following: Isotopically Primitive Interplanetary Dust Particles of Cometary Origin: Evidence from Nitrogen Isotopic Compositions. The Solar Nebula s First Accretionary Particles (FAPs) Are They Preserved in Collected Interplanetary Dust Samples? On the Origin of GEMS. An Analytical SuperSTEM for Extraterrestrial Materials Research. Sub-Micrometer Scale Minor Element Mapping in Interplanetary Dust Particles: A Test for Stratospheric Contamination. First Report of Taenite in an Asteroidal Interplanetary Dust Particle: Flash-heating Simulates Nebular Dust Evolution. FTIR Analyses of IDPs: Comparison with the InfraRed Spectra of the Interstellar Medium. Mineralogical Study of Hydrated IDPs: X-Ray Diffraction and Transmission Electron Microscopy. Focused Ion Beam Recovery and Analysis of Interplanetary Dust Particles (IDPs) and Stardust Analogues. Technique for Concentration of Carbonaceous Material from Aerogel Collectors Using HF-Vapor Etching. Synchrotron X-Ray Analysis of Captured Particle Residue in Aerogel. In-Situ Analyses of Earth Orbital Grains Trapped in Aerogel, Using Synchrotron X-Ray Microfluorescence Techniques. Igneous Rims on Micrometeorites and the Sizes of Chondrules in Main Belt Asteroids.

Source record↗
NASA NTRS2004

Detailed Microstructural Characterization of the Disk Alloy ME3

The advanced powder metallurgy disk alloy ME3 was designed using statistical screening and optimization of composition and processing variables in the NASA/General Electric/Pratt & Whitney HSR/EPM disk program to have extended durability for large disks at maximum temperatures of 600 to 700 C. Scaled-up disks of this alloy were then produced at the conclusion of that program to demonstrate these properties in realistic disk shapes. The objective of the present study was to assess the microstructural characteristics of these ME3 disks at two consistent locations, in order to enable estimation of the variations in microstructure across each disk and across several disks of this advanced alloy. Scaled-up disks processed in the HSR/EPM Compressor/Turbine Disk program had been sectioned, machined into specimens, and tested in tensile, creep, fatigue, and fatigue crack growth tests by NASA Glenn Research Center, in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. For this study, microstructures of grip sections from tensile specimens in the bore and rim were evaluated from these disks. The major and minor phases were identified and quantified using transmission electron microscopy (TEM). Particular attention was directed to the .' precipitates, which along with grain size can predominantly control the mechanical properties of superalloy disks.

Gabb, Timothy P.↗