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At least 271 records · Page 15

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NASA NTRS1993

Chemical stability of titanium diboride reinforcement in nickel aluminide matrices

Chemical stability of TiB2 reinforcement in NiAl (45 at percent Al) and Ni3Al (24 at percent Al) matrices has been theoretically and experimentally investigated. Calculations were made using thermodynamic properties of the systems to predict behavior at temperatures between 1173 and 1573 K. Experimental investigation of hot-press consolidated TiB2 particulate/prealloyed matrix powder blends were conducted using energy dispersive X-ray analysis, XRD, AES, and TEM. The theoretical and experimental analyses suggest that TiB2 is chemically stable in both matrices up to 1573 K; however, TiB2 was found to be less active in NiAl than in Ni3Al due to lower nickel activity in NiAl.

Rigney, J. D.↗

NASA NTRS1993

Development of a recursion RNG-based turbulence model

Reynolds stress closure models based on the recursion renormalization group theory are developed for the prediction of turbulent separated flows. The proposed model uses a finite wavenumber truncation scheme to account for the spectral distribution of energy. In particular, the model incorporates effects of both local and nonlocal interactions. The nonlocal interactions are shown to yield a contribution identical to that from the epsilon-renormalization group (RNG), while the local interactions introduce higher order dispersive effects. A formal analysis of the model is presented and its ability to accurately predict separated flows is analyzed from a combined theoretical and computational stand point. Turbulent flow past a backward facing step is chosen as a test case and the results obtained based on detailed computations demonstrate that the proposed recursion -RNG model with finite cut-off wavenumber can yield very good predictions for the backstep problem.

Zhou, YE↗

NASA NTRS1995

Natural and orbital debris particles on LDEF's trailing and forward-facing surfaces

Approximately 1000 impact craters on the Chemistry of Meteoroid Experiment (CME) have been analyzed by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDXA) to determine the compositional make-up of projectile residues. This report completes our systematic survey of gold and aluminum surfaces exposed at the trailing-edge (A03) and forward-facing (A11) LDEF sites, respectively. The major categories for the projectile residues were (1) natural, with diverse subgroups such as chondritic, monomineralic silicates, and sulfides, and (2) man made, that were classified into aluminum (metallic or oxide) and miscellaneous materials (such as stainless steel, paint flakes, etc). On CME gold collectors on LDEF's trailing edge approximately 11 percent of all craters greater than 100 micron in diameter were due to man-made debris, the majority (8.6 percent) caused by pure aluminum, approximately 31.4 percent were due to cosmic dust, while the remaining 58 percent were indeterminate via the analytical techniques utilized in this study. The aluminum surfaces located at the A11 forward-facing site did not permit analysis of aluminum impactors, but approximately 9.4 percent of all craters were demonstratably caused by miscellaneous debris materials and approximately 39.2 percent were the result of natural particles, leaving approximately 50 percent which were indeterminate. Model considerations and calculations are presented that focus on the crater-production rates for features greater than 100 micron in diameter, and on assigning the intermediate crater population to man-made or natural particles. An enhancement factor of 6 in the crater-production rate of natural impactors for the 'forward-facing' versus the 'trailing-edge' CME collectors was found to best explain all observations (i.e., total crater number(s), as well as their computational characteristics). Enhancement factors of 10 and 4 are either too high or too low. It is also suggested that approximately 45 percent of all craters greater than 100 micron in diameter are caused by man-made impactors on the A11 surfaces. This makes the production rate for craters greater than 100 micron in diameter, resulting from orbital debris, a factor of 40 higher on the forward-facing sides as opposed to the trailing-edge direction.

Hoerz, Friedrich↗

NASA NTRS1995

A diagnostic analysis of the VVP single-doppler retrieval technique

A diagnostic analysis of the VVP (volume velocity processing) retrieval method is presented, with emphasis on understanding the technique as a linear, multivariate regression. Similarities and differences to the velocity-azimuth display and extended velocity-azimuth display retrieval techniques are discussed, using this framework. Conventional regression diagnostics are then employed to quantitatively determine situations in which the VVP technique is likely to fail. An algorithm for preparation and analysis of a robust VVP retrieval is developed and applied to synthetic and actual datasets with high temporal and spatial resolution. A fundamental (but quantifiable) limitation to some forms of VVP analysis is inadequate sampling dispersion in the n space of the multivariate regression, manifest as a collinearity between the basis functions of some fitted parameters. Such collinearity may be present either in the definition of these basis functions or in their realization in a given sampling configuration. This nonorthogonality may cause numerical instability, variance inflation (decrease in robustness), and increased sensitivity to bias from neglected wind components. It is shown that these effects prevent the application of VVP to small azimuthal sectors of data. The behavior of the VVP regression is further diagnosed over a wide range of sampling constraints, and reasonable sector limits are established.

Boccippio, Dennis J.↗

NASA NTRS1995

Narrow-field imaging of the lunar sodium exosphere

We present the first results of a new technique for imaging the lunar Na atmosphere. The technique employs high resolution, a narrow bandpass, and specific observing geometry to suppress scattered light and image lunar atmospheric Na I emission down to approximately 50 km altitude. Analysis of four latitudinally dispersed images shows that the lunar Na atmosphere exhibits intersting latitudinal and radial dependencies. Application of a simple Maxwellian collisionless exosphere model indicates that: (1) at least two thermal populations are required to adequately fit the soldium's radial intensity behavior, and (2) the fractional abundances and temperatures of the two components vary systematically with latitude. We conclude that both cold (barometric) and hot (suprathermal) Na may coexist in the lunar atmosphere, either as distinct components or as elements of a continuum of populations ranging in temperature from the local surface temperature up to or exceeding escape energies.

Stern, S. Alan↗

NASA NTRS1997

Development of Processing Techniques for Advanced Thermal Protection Materials

Thermal Protection Materials Branch (TPMB) has been involved in various research programs to improve the properties and structural integrity of the existing aerospace high temperature materials. Specimens from various research programs were brought into the analytical laboratory for the purpose of obtaining and refining the material characterization. The analytical laboratory in TPMB has many different instruments which were utilized to determine the physical and chemical characteristics of materials. Some of the instruments that were utilized by the SJSU students are: Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDX), X-ray Diffraction Spectrometer (XRD), Fourier Transform-Infrared Spectroscopy (FTIR), Ultra Violet Spectroscopy/Visible Spectroscopy (UV/VIS), Particle Size Analyzer (PSA), and Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). The above mentioned analytical instruments were utilized in the material characterization process of the specimens from research programs such as: aerogel ceramics (I) and (II), X-33 Blankets, ARC-Jet specimens, QUICFIX specimens and gas permeability of lightweight ceramic ablators. In addition to analytical instruments in the analytical laboratory at TPMB, there are several on-going experiments. One particular experiment allows the measurement of permeability of ceramic ablators. From these measurements, physical characteristics of the ceramic ablators can be derived.

Selvaduray, Guna↗

NASA NTRS1998

Alteration Products and Secondary Minerals in Martian Meteorite Allan Hills 84001

The martian meteorites contain alteration products and secondary minerals that are a critical part of understanding their near-surface histories on both Mars and Earth. In some martian meteorites, suspected martian preterrestrial alteration products can be distinguished from terrestrial weathering effects Using scanning electron microscopy (SEM), field emission SEM (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray analysis (EDS), we are studying natural fracture surfaces of ALH 84001 chips, including samples from both the interior and the exterior of the meteorite. Exterior samples include fusion crust surfaces, which are important in determining the extent of terrestrial weathering of meteorites. The focus of this study is weathering features and secondary minerals other than the distinctive carbonate globules that continue to be studied by many researchers.

Wentworth, S. J.↗

NASA NTRS2001

Development of an Innovative Algorithm for Aerodynamics-Structure Interaction Using Lattice Boltzmann Method

The lattice Boltzmann equation (LBE) is a kinetic formulation which offers an alternative computational method capable of solving fluid dynamics for various systems. Major advantages of the method are owing to the fact that the solution for the particle distribution functions is explicit, easy to implement, and the algorithm is natural to parallelize. In this final report, we summarize the works accomplished in the past three years. Since most works have been published, the technical details can be found in the literature. Brief summary will be provided in this report. In this project, a second-order accurate treatment of boundary condition in the LBE method is developed for a curved boundary and tested successfully in various 2-D and 3-D configurations. To evaluate the aerodynamic force on a body in the context of LBE method, several force evaluation schemes have been investigated. A simple momentum exchange method is shown to give reliable and accurate values for the force on a body in both 2-D and 3-D cases. Various 3-D LBE models have been assessed in terms of efficiency, accuracy, and robustness. In general, accurate 3-D results can be obtained using LBE methods. The 3-D 19-bit model is found to be the best one among the 15-bit, 19-bit, and 27-bit LBE models. To achieve desired grid resolution and to accommodate the far field boundary conditions in aerodynamics computations, a multi-block LBE method is developed by dividing the flow field into various blocks each having constant lattice spacing. Substantial contribution to the LBE method is also made through the development of a new, generalized lattice Boltzmann equation constructed in the moment space in order to improve the computational stability, detailed theoretical analysis on the stability, dispersion, and dissipation characteristics of the LBE method, and computational studies of high Reynolds number flows with singular gradients. Finally, a finite difference-based lattice Boltzmann method is developed for inviscid compressible flows.

Mei, Ren-Wei↗

NASA NTRS1998

Atomic force microscopy imaging of fragments from the Martian meteorite ALH84001

A combination of scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM) techniques, as well as atomic force microscopy (AFM) methods has been used to study fragments of the Martian meteorite ALH84001. Images of the same areas on the meteorite were obtained prior to and following gold/palladium coating by mapping the surface of the fragment using ESEM coupled with energy-dispersive X-ray analysis. Viewing of the fragments demonstrated the presence of structures, previously described as nanofossils by McKay et al. (Search for past life on Mars--possible relic biogenic activity in martian meteorite ALH84001. Science, 1996, pp. 924-930) of NASA who used SEM imaging of gold-coated meteorite samples. Careful imaging of the fragments revealed that the observed structures were not an artefact introduced by the coating procedure.

Carbonates/analysis↗

NASA NTRS2007

Microbial Extremophiles in Evolutionary Aspect

Pikuta, Elena V.↗

NASA NTRS2007

Astrobiological Significance of Microbial Extremophiles

The microflora of the cryosphere of planet Earth provides the best analogs for life forms that might be found in the permafrost or polar ice caps of Mars, near the surface of the cometary nuclei, or in the liquid water beneath and the ice crusts of icy moons of Jupiter and Saturn. The importance of study alkaliphilic microorganisms for astrobiology was enhanced by the findings of abundant carbonates and carbonate globules rimmed with possibly biogenic magnetites in association with the putative microfossils in the ALH84001 meteorite. Although the ALH84001 "nanofossils" were to small and simple to be unambiguously recognized as biogenic, they stimulated Astrobiology research and studies of microbial extremophiles and biomarkers in ancient rocks and meteorites. Recent studies of CI and CM carbonaceous meteorites have resulted in the detection of the well-preserved mineralized remains of coccoidal and filamentous microorganisms in cyanobacterial mats. Energy Dispersive X-ray Analysis has shown anomalous biogenic element ratios clearly indicating they are not recent biological contaminants. This paper reviews microbial extremophiles in context of their significance to Astrobiology. The study of halophilic microorganisms was started from work with saline soils and lakes, and one of the record of good growth for Haloferax mediterranei was shown at 30 percent NaC1. Although alkali-tolerant nitrifying bacteria had previously been reported, the first described alkaliphilic microorganism was the bacterium Streptococcus faecalis. Halophilic and alkaliphilic forms are relevant to conditions that might be found in closed impact basins and craters on Mars filled with evaporite deposits. The first obligately acidophilic bacterium described was Acidithiobacillus ferrooxydans (formally Thiobacillus ferrooxidans). Later thermophilic lithotrophic acidophiles were found, and the hyperacidophilic moderately thermophilic species of the genus Picrophilus were found to grow at negative pH. The epoch of study of thermophilic microorganisms starts with the discovery of Thermus aquaticus, and presently the maximum temperature for growth at 113 C was found for Pyrolobus fumarii. The microorganisms capable of growth at high temperatures and in hyperacidic environments on Earth are good analogs for life that might be able to survive in hot acidic droplets in the upper regimes of the atmosphere of Venus. The study of barophiles was made possible by engineering achievements leading to the development of the submersible crafts used to study the Black Smokers of the Deep-sea Hydrothermal vents. The first described radioresistant bacterium Deinococcus radiodurans can survive ionizing irradiation and other DNA-damaging assaults at doses that are lethal to all other organisms. These microbes are models for life that might endure high radiation environments in the ice near the surface of comets or on the icy moons of Jupiter and Saturn and in the seafloor deep beneath icy crusts Europa and Enceladus. This paper presents ESEM and FESEM images showing intact microbes preserved in the deep ice cores extracted from just above Lake Vostok, Antarctica that are considered analogs for life forms that might survive on comets and icy moons.

Pikuta, Elena V.↗

NASA NTRS2000

Scanning Electron Microscopy Investigation of a Sample Depth Profile Through the Martian Meteorite Nakhla

The ongoing scientific debate as to whether or not the Martian meteorite ALH84001 contained evidence of possible biogenic activities showed the need to establish consistent methods to ascertain the origin of such evidence. To distinguish between terrestrial organic material/microbial contaminants and possible indigenous microbiota within meteorites is therefore crucial. With this in mind a depth profile consisting of four samples from a new sample allocation of Martian meteorite Nakhla was investigated using scanning electron microscopy (SEM) and energy dispersive X-ray analysis. SEM imaging of freshly broken fractured chips revealed structures strongly recent terrestrial microorganisms, in some cases showing evidence of active growth. This conclusion was supported by EDX analysis, which showed the presence of carbon associated with these structures, we concluded that these structures represent recent terrestrial contaminants rather than structures indigenous to the meteorite. Page

Toporski, Jan↗

NASA NTRS2011

The Formation of Wassonite: A New Titanium Monosulfide Mineral in the Yamato 691 Enstatite Chondrite

Wassonite, ideally stoichiometric TiS, is a titanium monosulfide not previously observed in nature, that was discovered within the Yamato 691 EH3 enstatite chondrite [1]. Because of the submicrometer size of the wassonite grains, it was not possible to determine conventional macroscopic properties. However, the chemical composition and crystal structure were well constrained by extensive quantitative energy dispersive x-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for wassonite is rhombohedral (a = 3.42 plus or minus 0.07, c = 26.50 plus or minus 0.53 Angstroms) with space group: R(sup 3 raised bar) m (R9 type), cell volume: 268.4 plus or minus 0.53 Angstroms(sup 3), Z=9, density (calculated): 4.452 grams per cubic centimeter, empirical formula: (Ti(sub 0.93), Fe(sub 0.06), Cr(sub 0.01))S. In this study, we discuss possible formation mechanisms of wassonite and its associated minerals based on the petrology, mineralogy, crystallography, thermodynamic calculations, Al/Mg isotopic systematics and the O-isotopic composition of the wassonite-bearing BO chondrule.

Nakamura-Messenger, K.↗

NASA NTRS2015

Methodology for Producing a Uniform Distribution of UO2 in a Tungsten Matrix

Current work at NASA's Marshall Space Flight Center (MSFC) is focused on the development CERMET fuel materials for Nuclear Thermal Propulsion (NTP). The CERMETs consist of uranium dioxide (UO2) fuel particles embedded in a tungsten (W) metal matrix. Initial testing of W-UO2 samples fabricated from fine angular powders performed reasonably well, but suffered from significant fuel loss during repeated thermal cycling due to agglomeration of the UO2 (1). The blended powder mixtures resulted in a non-uniform dispersion of the UO2 particles in the tungsten matrix, which allows rapid vaporization of the interconnected UO2 from the sample edges into the bulk material. Also, the angular powders create areas of stress concentrations due to thermal expansion mismatch, which eventually cracks the tungsten matrix. Evenly coating spherical UO2 particles with chemical vapor deposited (CVD) tungsten prior to consolidation was previously demonstrated to provide improved performance. However, the CVD processing technology is expensive and not currently available. In order to reduce cost and enhance performance, a powder coating process has been developed at MSFC to produce a uniform distribution of the spherical UO2 particles in a tungsten matrix. The method involves utilization of a polyethylene binder during mixing which leads to fine tungsten powders clinging to the larger UO2 spherical particles. This process was developed using HfO2 as a surrogate for UO2. Enough powder was mixed to make 8 discs (2cm diameter x 8mm thickness) using spark plasma sintering. A uniaxial pressure of 50 MPa was used at four different temperatures (2 samples at each temperature). The first two samples were heated to 1400C and 1500C respectively for 5 minutes. Densities for these samples were less than 85% of theoretical, so the time at temperature was increased to 20 minutes for the remaining samples. The highest densities were achieved for the two samples sintered at 1700C (approx. 92% of theoretical). Scanning electron microscopy (SEM) of the mixed powders and the sintered samples along with energy dispersive x-ray analysis was obtained. The SEM of the powders clearly show the fine W powder adhered to the larger HfO2 particles and a uniform distribution of HfO2 particles in a tungsten matrix upon densification. Vicker's Microhardness testing was also performed on all samples using 0.5, 1.0 and 2.0 kg loads. Five indents were made at each load level. All indents were placed in the tungsten matrix to assist as a proxy in measuring densification. The highest hardness value was obtained for the 1700C specimens. The hardness average for these samples was 312.14 MPa. This powder processing method has been applied to W/UO2 powders with the SEM of the powders appearing similar to the W/HfO2 powder images.

Tucker, Dennis S.↗

NASA NTRS2017

Characterization of Biological Fallout Particles of Cleanrooms to Measure Spacecraft Cleanliness

NASA cleanrooms are humidity, temperature-regulated, and particle contaminant-controlled environments used for spacecraft assembly. Microorganisms, which are crucial contaminants shed from humans and transported through the environment, can adapt to the oligotrophic cleanroom conditions. These biogenic particles need to be identified to extend our knowledge of biological contamination for future NASA mission use. Here, we devised an aluminum coupon with polycarbonate filter setup to collect fallout particles from an ISO 5 and an ISO 7 cleanroom. We demonstrated the presence of microbial particles, as standalone entities and associated with inert particles in cleanroom environments. The contamination was confirmed as biogenic in virtue of estimating the elemental composition of individual and aggregated particles using an epifluorescence and Field Emission Scanning Electron Microscopy (FESEM) coupled with an energy dispersive X-ray analysis (EDX). Epifluorescence microscopy showed that the particles were stained less (25%) with SYTO 9 and more (75%) with propidium iodide, suggesting that the suspected biogenic particles are membrane-compromised. Remarkably, biological particles such as bacteria and fungal spores/hyphae were observed at sizes ranging from 2 to 70 µm, with abundant C and O elemental signatures and essential tracers (Na, Mg, K, Ca and Cl). Inert particles (2 to 500 µm) that were characterized included compositions such as silica (SiO2), aluminosilicates (Al, Si), and carbonaceous fibers. Furthermore, we designed and illustrated a unique correlative epifluorescence and FE-SEM method to strengthen this approach by acquiring the same biogenic particles in the same filter coupon for a one-to-one comparison. Interestingly, the SYTO 9 stained particles showed abundant C and O elemental signature implying that they are viable microbial particles. Constant evaluation of cleanroom biological and inert particles will help to characterize biological contamination for future NASA missions (e.g. Mars 2020).

Malli Mohan, Ganesh Babu↗

NASA NTRSDate not supplied

Quick and Correlative TOF-SIMS Analysis of Dispersoid Content in Powder Feedstock and Printed Oxide Dispersion Strengthened Alloys

Oxide dispersion strengthening (ODS) of metal alloys, when combined with additive manufacturing (AM), can be used to solve high-temperature material application problems. The performance of ODS materials is dependent on nano-scale oxide being distributed uniformly throughout the metal matrix; a homogenous distribution is critical to the creep and yield strength. Therefore, quantifying and analyzing these oxide nanoparticles is essential for ODS alloy development. Assessing the chemistry and morphology of dispersoids in a material can be conducted using a variety of X-ray and electron-based methods. Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), which assesses chemical concentrations from ion masses, provides the necessary spatial resolution and avoids potential spectral overlap of all elements present. In this work, preparing ODS powder feedstock and Laser Powder Bed Fusion AM was conducted with a NiCoCr alloy and yttria dispersoid, mixed with a Resodyn resonance mixer and printed on an EOS M100 3D printer at NASA Glenn. TOF-SIMS was performed on a Physical Electronics NanoTOF TRIFT V TOF-SIMS at Case Western Reserve University. The TOF-SIMS results collected on the feedstock powder samples correspond to the qualitative interpretation of the homogeneity of the oxide coating on the metal powder from SEM images. This provides quantitative support to the qualitative microscopy images collected earlier in the process design phase. The variance in the yttrium distribution on the powder feedstock samples also correlated with the variance of the yttrium distribution detected in the printed samples. This correlation supported the hypothesis that an even coating of yttria on the metal powders contributes to an even distribution of yttria in the printed material.

Laura G. Wilson↗

NASA NTRSDate not supplied

Contamination, Transportation or Transmutation in LENR Material Analyses

LENR experiments using various loading and triggering mechanisms rely on a variety of elemental and isotopic assays to determine LENR effects. These assays include optical microscopy, Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM/EDX), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). All of these methods observe the surface of a material. By dissolving or vaporizing the sample, Inductively Coupled Plasma Optical Element Spectroscopy (ICP-OES) can determine elemental composition (ppb) or with mass spectroscopy, isotopes (ICP/MS). One can use a focused ion beam (FIB) to cut open a sample and observe the “cut” with either SEM/EDX, or Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). High Purity Gamma Ray Spectroscopy (HPGe) and alpha/ beta Liquid Scintillator spectroscopy can be used. We’ve employed these assay methods in our NASA GRC research under both the Advanced Energy Conversion and Lattice Confinement Fusion Projects. However, there are limitations associated with each of these methods ranging from handling contamination, instrumental limitations including sensitivity and field of view, and sample preparation.

Low Energy Nuclear Reactions↗

NASA NTRS1994

Direct calculations of waves in fluid flows using high-order compact difference scheme

The solution of the unsteady Euler equations by a sixth-order compact difference scheme combined with a fourth-order Runge-Kutta method is investigated. Closed-form expression for the amplification factors and their corresponding dispersion correlations are obtained by Fourier analysis of the fully discretized, two-dimensional Euler equations. The numerical dissipation, dispersion, and anisotropic effects are assessed. It is found that the Courant-Friedrichs-Lewy (CFL) limit for stable calculations is about 0.8. For a CFL number equal to 0.6, the smallest wavelength which is resolved without numerical damping is about six - eight grid nodes. For phase speeds corresponding to acoustic waves, the corresponding time period is resolved by about 200 - 300 time steps. Three numerical examples of waves in compressible flow are included: (1) sound propagation in a duct with linear shear, (2) linear wave growth in a compressible free shear layer, and (3) vortex pairing in a compressible free shear layer perturbed at two frequencies.

Yu, Sheng-Tao↗