Search NASA⌕ Search

SEARCH · Search NASA

Results for “Powder Morphology”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Developing Materials and Coating Technologies for Mitigation of Lunar Dust Adhesion and Abrasion

In order to support long duration missions on the Moon’s surface, materials resistant to the harsh lunar environment are critically needed. Lunar dust poses a major threat to the durability of components and vehicles due to its fine, jagged morphology and highly abrasive nature, which enables the particles to adhere and embed into surfaces of components and devices potentially leading to premature failure. Consequently, significant effort within NASA aims to develop novel materials and coating technologies to limit lunar dust adhesion and abrasion by exploring a variety of production routes and examining properties of candidate material systems, including ceramic, metallic and polymeric. Manufacturing methods investigated include traditional powder processing, additive manufacturing and surface modification via laser ablation patterning of bulk materials and coatings. An overview of ongoing NASA materials and coating research and development to enable lunar exploration will be presented.

Materials↗
NASA NTRSDate not supplied

Uncertainty Quantification and Sensitivity Analysis in Process-Structure-Property Simulations for Laser Powder Bed Fusion Additive Manufacturing

Process variations and process-induced defects like porosity cause significant uncertainty in the microstructure and mechanical behavior of additively manufactured metals. Establishing process-structure-property (PSP) relationships and quantifying uncertainty using experiments alone is costly, especially for structural applications where mechanical allowables must be established for qualification and certification. This work presents a PSP simulation framework for laser powder bed fusion with a focus on uncertainty quantification through probabilistic calibration and multi-fidelity uncertainty propagation. Motivated by phenomenological input parameters related to grain nucleation and growth that are difficult to characterize, a global sensitivity analysis (GSA) is completed. Through GSA, the most important input parameters are identified based on their influence on the statistical distributions of microstructural metrics that influence mechanical behavior, including grain size, morphology, and crystallographic texture. The results provide insight on what experiments are necessary to quantify and control PSP uncertainties, particularly those associated with the more challenging input parameters.

additive manufacturing↗
NASA NTRSDate not supplied

Correlations Between Porosity, Spatter, and Process Metrics for Powder Bed Fusion Laser Beam Metallic Additive Manufacturing

Components fabricated using the powder bed fusion laser beam metallic (PBF-LB/M)additive manufacturing process are the result of a multitude of weld passes conducted sequentially. Qualifying components for aerospace applications requires a thorough understanding of the process-structure-properties relationships. Porosity defects are known to have a strong adverse effect on the mechanical properties of a component. In particular, porosity defects created by lack of fusion have high aspect ratio morphologies leading to stress concentrations that become crack initiation sites. In the present work, the occurrence of spatter induced lack of fusion porosity was studied using synchronized in-situ process monitoring, additive manufacturing model-based process metrics, and high-resolution X-ray computed tomography. The results show that lack of fusion porosity is statistically correlated with unremoved welding spatter ejecta of the PBF-LB/M process and process metrics related to the hatching strategy.

Qualification↗
NASA NTRS1980

The relative stress-corrosion-cracking susceptibility of candidate aluminum-lithium alloys for aerospace structural applications

The microstructure and tensile properties of two powder metallurgy processed aluminum-lithium alloys were determined. Strength properties of 480 MPa yield and 550 MPa ultimate tensile strength with 5% strain to fracture were attained. Very little reduction in area was observed and fracture characteristics were brittle. The magnesium bearing alloy exhibited the highest strength and ductility, but fracture was intergranular. Recrystallization and grain growth, as well as coarse grain boundary precipitation, occurred in Alloy 2. The fracture morphology of the two alloys differed. Alloy 1 fractured along a plane of maximum shear stress, while Alloy 2 fractured along a plane of maximum tensile stress. It is found that a fixed orientation relationship exists between the shear fracture plane and the rolling direction which suggests that the PM alloys are strongly textured.

Pizzo, P. P.↗
NASA NTRSDate not supplied

Developing Materials and Coating Technologies for Mitigation of Lunar Dust Adhesion and Abrasion

In order to support long duration missions on the Moon’s surface, materials resistant to the harsh lunar environment are critically needed. Lunar dust poses a major threat to the durability of components and vehicles due to its fine, jagged morphology and highly abrasive nature, enabling the particles to adhere and embed onto surfaces of components and devices and potentially leading to premature failure. There is significant effort within NASA to develop novel materials and coating technologies to mitigate lunar dust adhesion and abrasion. This effort has been exploring a variety of production routes and examining properties of candidate material systems, including ceramic, metallic and polymeric. Manufacturing methods investigated include ceramic powder processing, additive manufacturing and surface modification via laser ablation patterning of bulk materials and coatings. An overview of ongoing NASA materials and coating research and development efforts to enable lunar surface exploration will be presented.

Materials, Coatings, lunar dust mitigation↗
NASA NTRS2006

Pulsed Laser Deposition of High Temperature Protonic Films

Pulsed laser deposition has been used to fabricate nanostructured BaCe(0.85)Y(0.15)O3- sigma) films. Protonic conduction of fabricated BaCe(0.85)Y(0.15)O(3-sigma) films was compared to sintered BaCe(0.85)Y(0.15)O(3-sigma). Sintered samples and laser targets were prepared by sintering BaCe(0.85)Y(0.15)O(3-sigma) powders derived by solid state synthesis. Films 1 to 8 micron thick were deposited by KrF excimer laser on porous Al2O3 substrates. Thin films were fabricated at deposition temperatures of 700 to 950 C at O2 pressures up to 200 mTorr using laser pulse energies of 0.45 - 0.95 J. Fabricated films were characterized by X-ray diffraction, electron microscopy and electrical impedance spectroscopy. Single phase BaCe(0.85)Y(0.15)O(3-sigma) films with a columnar growth morphology are observed with preferred crystal growth along the [100] or [001] direction. Results indicate [100] growth dependence upon laser pulse energy. Electrical conductivity of bulk samples produced by solid state sintering and thin film samples were measured over a temperature range of 100 C to 900 C. Electrical conduction behavior was dependent upon film deposition temperature. Maximum conductivity occurs at deposition temperature of 900 oC; the electrical conductivity exceeds the sintered specimen. All other deposited films exhibit a lower electrical conductivity than the sintered specimen. Activation energy for electrical conduction showed dependence upon deposition temperature, it varied

Dynys, Fred W.↗
NASA NTRS1981

The fracture morphology of nickel-base superalloys tested in fatigue and creep-fatigue at 650 C

The fracture surfaces of compact tension specimens from seven nickel-base superalloys fatigue tested at 650 C were studied by scanning electron microscopy and optical metallography to determine the nature and morphology of the crack surface in the region of stable growth. Crack propagation testing was performed as part of an earlier study at 650 C in air using a 0.33 Hz fatigue cycle and a creep-fatigue cycle incorporating a 900 second dwell at maximum load. In fatigue, alloys with a grain size greater than 20 micrometers, HIP Astroloy, Waspaloy, and MERL 76, exhibited transgranular fracture. MERL 76 also displayed numerous fracture sites which were associated with boundaries of prior powder particles. The two high strength, fine grain alloys, IN 100 and NASA IIB-7, exhibited intergranular fracture. Rene 95 and HIP plus forged Astroloy displayed a mixed failure mode that was transgranular in the coarse grains and intergranular in the fine grains. Under creep-fatigue conditions, fracture was found to be predominantly intergranular in all seven alloys.

Gayda, J.↗
NASA NTRS2006

Pulsed Laser Deposition of BaCe(sub 0.85)Y(sub 0.15)0(sub 3) FILMS

Pulsed laser deposition has been used to grow nanostructured BaCe(sub 0.85)Y(sub 0.15)0(sub 3) films. The objective is to enhance protonic conduction by reduction of membrane thickness. Sintered samples and laser targets were prepared by sintering BaCe(sub 0.85)Y(sub 0.15)O(sub 3) powders derived by solid state synthesis. Films 2 to 6 m thick were deposited by KrF excimer laser on Si and porous Al2O3 substrates. Nanocrystalline films were fabricated at deposition temperatures of 600-800 C deg at O2 pressure of 30 mTorr and laser fluence of 1.2 J/cm square. Films were characterized by x-ray diffraction, scanning electron microscopy and electrical impedance spectroscopy. Dense single phase BaCe(sub 0.85)Y((sub 0.15) 0(sub 3) films with a columnar growth morphology is observed, preferred crystal growth was found to be dependent upon deposition temperature and substrate type. Electrical conductivity of bulk samples produced by solid state sintering and thin film samples were measured over a temperature range of 100 C deg to 900 C deg in moist argon. Electrical conduction of the fabricated films was 1 to 4 orders of magnitude lower than the sintered bulk samples. With respect to the film growth direction, activation energy for electrical conduction is 3 times higher in the perpendicular direction than the parallel direction.

Dynys, F. W.↗
NASA NTRS2016

Polarized Light Microscopy

Polarized light microscopy (PLM) is a technique which employs the use of polarizing filters to obtain substantial optical property information about the material which is being observed. This information can be combined with other microscopy techniques to confirm or elucidate the identity of an unknown material, determine whether a particular contaminant is present (as with asbestos analysis), or to provide important information that can be used to refine a manufacturing or chemical process. PLM was the major microscopy technique in use for identification of materials for nearly a century since its introduction in 1834 by William Fox Talbot, as other techniques such as SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infrared spectroscopy), XPD (X-ray Powder Diffraction), and TEM (Transmission Electron Microscopy) had not yet been developed. Today, it is still the only technique approved by the Environmental Protection Agency (EPA) for asbestos analysis, and is often the technique first applied for identification of unknown materials. PLM uses different configurations in order to determine different material properties. With each configuration additional clues can be gathered, leading to a conclusion of material identity. With no polarizing filter, the microscope can be used just as a stereo optical microscope, and view qualities such as morphology, size, and number of phases. With a single polarizing filter (single polars), additional properties can be established, such as pleochroism, individual refractive indices, and dispersion staining. With two polarizing filters (crossed polars), even more can be deduced: isotropy vs. anisotropy, extinction angle, birefringence/degree of birefringence, sign of elongation, and anomalous polarization colors, among others. With the use of PLM many of these properties can be determined in a matter of seconds, even for those who are not highly trained. McCrone, a leader in the field of polarized light microscopy, often advised, If you cant determine a specific optical property of a particle after two minutes, move onto another configuration. Since optical properties can be seen so very quickly and easily under polarized light, it is only necessary to spend a maximum of two minutes on a technique to determine a particular property, though often only a few seconds are required.

Engineering↗
NASA NTRSDate not supplied

Laboratory Investigation of the Effect of Venusian Weathering on Mineral Spectra

Introduction: The recent selection of two missions to Venus has renewed the importance of deter-mining weathering reactions between minerals and the Venusian atmosphere, and the spectral signatures of minerals before, during, and after these reactions. The rate at which weathering reactions progress also constrain show long unstable minerals will be present on the surface (e.g., [1]), and enables the use of mineralogy as a constraint on surface age(e.g., [2-3]).In order to gain an understanding of how mineral compositions and spectra change with weathering, we have begun conducting experiments in a 1 atm experimental setup at Wesleyan University. This setup exposes minerals to the temperature and most abundant gases of the Venus atmosphere (CO2, SO2, N2).We conducted initial experiments using biotite, calcite, and montmorillonite in order to test our methodology with minerals that may be relevant to recording the history of water on Venus. Methods: Experiments were conducted in Thermo Fisher Scientific Lindberg/Blue M Mini-Mite horizontal tube furnaces at Wesleyan University. Experiments used natural mineral chips and powders, and were conducted at 1 atmosphere and 460 °C under pre-mixed gases provided by Air Gas(Table 1). The furnaces are set up in a flow through configuration so that solid samples are exposed to a fixed gas composition, and quartz glass process tubes were used in all experiments (1/4” diameter for experiment V4, ½” diameter for all others). These conditions were maintained for the du-rations listed in Table 1, at which point the furnace was turned off with gas flowing until the sample was cool enough to extract under N2and be placed in a desiccator for storage. Run products were carbon coated and examined using a Hitachi SU5000 Field Emission Gun Scanning Electron Microscope (SEM) equipped with an EDAX Octane Pro EDS detector located at Wesley-an University. Visible-Near Infrared Spectroscopy (VNIR) analysis was performed on powdered samples under a nitrogen atmosphere using an ASD Fieldspec Proover the 350-2500 nm range. Powdered mineral samples were milled to a particle size of < 45μm and were spiked with an internal standard (Al2O3, corundum) to obtain quantitative mineralogy. Samples were analyzed using a Panalytical X’Pert pro X-ray Diffractometer (XRD), with an X’Celerator high speed detector and Co Kα radiation, with data collected at a step size of 0.02 ̊/minute step counting rate from 2 to 80 degrees 2θ at 45 mA/40kV in the X-ray Diffraction Laboratory located at NASA Johnson Space Center. Materials Data Inc (MDI) software suite, JadeTMv9 was used for Rietveld refinement to determine phase abundances and mineral identification by comparing XRD patterns to International Center for Diffraction Data (ICDD) database patterns. Table 1: Experimental matrix. Experiment Name Duration (Days)Gas Com-position (trace gas)MineralsV487SO2/N2(1.4%)Montmorillonite, biotiteV519SO2/N2(1.4%)CalciteV619CO2/SO2/N2(1.4% SO2, 2.1% N2)Montmorillonite, biotiteV828SO2/N2(1.4%)Biotite, calcite Results: Calcite. In both experiments, calcite was exposed to the SO2/N2gas mixture, and in both experimental run products, XRD analysis detected anhydrite, which is consistent with EDS measurements conducted in the SEM. The XRD analyses show greater amounts of anhydrite present after 28 days than 19, suggesting the calcite reaction progressed further given longer duration. Grain surface morphology as seen in the SEM also shows secondary mineral growth (Fig. 1). VNIR spectra show no change, as expected since anhydrite lacks spectral features in this wavelength range. Montmorillonite. Montmorillonite was exposed to two different gas mixtures, the SO2/N2mix and CO2/SO2/N2mix over different durations (87 and 19 days, respectively). VNIR analyses of both run products show a reduction in the 1441and1910 nm water features as well as a shift of the 1411 and 2011 nm features to shorter wavelengths that may indicate re-structuring in the crystal lattice and the production of amorphous phases [4]. XRD results are consistent with this, showing a shift of the 001 peak from 15Åto 10Åin both run products. The amount of X-ray amorphous material in the montmorillonite run products was greater than that present in the unreacted clay, being the greatest in the 87 day V4 experiment. No other secondary phases were detected in the run products, however sulfur was present in EDS analyses of powder samples.

A R Santos↗
NASA NTRS1993

Protein crystal growth in low gravity

This Final Technical Report for NASA Grant NAG8-774 covers the period from April 27, 1989 through December 31, 1992. It covers five main topics: fluid flow studies, the influence of growth conditions on the morphology of isocitrate lyase crystals, control of nucleation, the growth of lysozyme by the temperature gradient method and graphoepitaxy of protein crystals. The section on fluid flow discusses the limits of detectability in the Schlieren imaging of fluid flows around protein crystals. The isocitrate lyase study compares crystals grown terrestrially under a variety of conditions with those grown in space. The controlling factor governing the morphology of the crystals is the supersaturation. The lack of flow in the interface between the drop and the atmosphere in microgravity causes protein precipitation in the boundary layer and a lowering of the supersaturation in the drop. This lowered supersaturation leads to improved crystal morphology. Preliminary experiments with lysozyme indicated that localized temperature gradients could be used to nucleate crystals in a controlled manner. An apparatus (thermonucleator) was designed to study the controlled nucleation of protein crystals. This apparatus has been used to nucleate crystals of materials with both normal (ice-water, Rochelle salt and lysozyme) and retrograde (horse serum albumin and alpha chymotrypsinogen A) solubility. These studies have lead to the design of an new apparatus that small and more compatible with use in microgravity. Lysozyme crystals were grown by transporting nutrient from a source (lysozyme powder) to the crystal in a temperature gradient. The influence of path length and cross section on the growth rate was demonstrated. This technique can be combined with the thermonucleator to control both nucleation and growth. Graphoepitaxy utilizes a patterned substrate to orient growing crystals. In this study, silicon substrates with 10 micron grooves were used to grow crystals of catalase, lysozyme and canavalin. In all cases, the crystals grew oriented to the substrate. The supersaturation needed for nucleation and growth was lower on the patterned substrates. In some cases, isolated, large crystals were grown.

Feigelson, Robert S.↗
NASA NTRS2000

SEM Characterization of Extinguished Grains from Plasma-Ignited M30 Charges

M30 propellant grains that had been ignited in interrupted closed bomb experiments were characterize by scanning electron microscopy (SEM). Previous chemical analysis of extinguished grains had given no indications of plasma-propellant chemical interactions that could explain the increased burning rates that had been previously observed in full-pressure closed bomb experiments. (This does not mean that there is no unique chemistry occurring with plasma ignition. It may occur very early in the ignition event and then become obscured by the burning chemistry.) In this work, SEM was used to look at grain morphologies to determine if there were increases in the surface areas of the plasma-ignited grains which would contribute to the apparent increase in the burning rate. Charges were made using 30 propellant grains (approximately 32 grams) stacked in two tiers and in two concentric circles around a plastic straw. Each grain was notched so that, when the grains were expelled from the bomb during extinguishment, it could be determined in which tier and which circle each grain was originally packed. Charges were ignited in a closed bomb by either a nickel wire/Mylar-capillary plasma or black powder. The bomb contained a blowout disk that ruptured when the pressure reached 35 MPa, and the propellant was vented into a collection chamber packed with polyurethane foam. SEM analysis of the grains fired with a conventional black powder igniter showed no signs of unusual burning characteristics. The surfaces seemed to be evenly burned on the exteriors of the grains and in the perforations. Grains that had been subjected to plasma ignition, however, had pits, gouges, chasms, and cracks in the surfaces. The sides of the grains closest to the plasma had the greatest amount of damage, but even surfaces facing the outer wall of the bomb had small pits. The perforations contained gouges and abnormally burned regions (wormholes) that extended into the web. The SEM photos indicated that a grain from the top tier, which was farther away from the plasma ignition source, sustained more plasma-induced damage to the perforations and the web than did the grains on the bottom tier.

Kinkennon, A.↗
NASA NTRS2021

Understanding the Space Weathering of Mercury Through Laboratory Experiments

Introduction: Airless surfaces across the solar system are continually modified by energetic particles from solar wind and micrometeoroid bombardment [1,2]. This process is known as space weathering, and it alters the chemical, microstructural, and optical properties of surface regoliths on airless bodies, including Mercury. On the Moon and S-type asteroids, the reflectance spectral signatures of space weathering include reddening (increasing reflectance with increasing wavelength), darkening (lowering of reflectance), and the attenuation of characteristic absorption bands [2]. Such spectral changes are driven by the production of Fe-bearing nanoparticles(npFe) through both solar wind irradiation and micrometeoroid bombardment. While our understanding of space weathering for the Moon and near-Earth S-types asteroids is advanced, insight into how these processes operate on other planetary bodies is limited. In particular, Mercury experiences a uniquely intense space weathering environment than planetary counterparts at 1 AU, including a moreintense solar wind flux and higher velocity micrometeoroid impacts [4]. Additionally, Mercury has a surface composition unique in the inner solar system, including regions of the surface with very low albedo known as the low reflectance material (LRM), which is enriched in carbon, likely graphite, up to 4wt.% [5].In addition, the concentration of Fe across Mercury’s surface islow (<2 wt.%) compared to the Moonor S-type asteroids asteroids[6]. Our understanding of the effects of space weathering on C-rich and Fe-poor phases is limited. Since Fe plays a critical role inthe development of space weathering characteristicson other airless surfaces(e.g., npFe), its limited availability may significantly affect the development of space weathering features in Mercury surface materials. We can simulate space weathering processes in the laboratory to explore their effects on the microstructural, chemical, and spectral characteristics of Mercury surface materials[7]. Here we used pulsed laser irradiation to simulate the short duration, high-temperature events associated with micrometeoroid impacts. We performed coordinated analyses including reflectance spectroscopy and electron microscopy to investigate the spectral, chemical, and microstructural changes in these mercurian analog samples. Methods: For these experiments, we usedforsteritic olivine with varying FeOcontents, a mineral phase proposed to be abundant on the surface of Mercury. We mixed each sample with graphite to simulate LRM regions of the surface. Wesynthesized the olivinesamplesat 1-bar at NASA’s Johnson Space Centerand prepared pressed powder pellets for laser irradiation [8].We prepared three samples, each with a base layer of olivineto maintain structural integrity and topped witha surface layer containing the graphite-olivine mixture: 1) Sample SC-001 San Carlos olivine(Fo90.91),2)Sample F-S-002 with0.05 wt.% FeO olivine, and 3) F-T-004 with 0.53 wt.% FeO olivine. Each sample was mixed with 5 wt.% powdered graphite and had grain sizes ranging from 45to 125μm. We irradiated each sample usinga pulsed Nd-YAG laser, (l=1064 nm, ~6 ns pulse duration, energy of 48 mJ/pulse) while undervacuumat Northern Arizona University. The laser was rastered1x and then 5x over the surfaceof each sample to simulate progressive space weathering. We collected in situreflectance spectra from the samples after each laser pulse witha Nicolet IS50 Fourier-Transform Infrared spectrometer (lfrom 0.65-2.5 μm). We used an FEI Nova NanoSEM200scanning electron microscope (SEM) and a Hitachi TM4000 Plus benchtop SEM at Purdue University to image the surface morphology and topography of the samples. We extracted thin sections for analysis in the transmission electron microscope(TEM)using the FEI Helios NanoLab 660 focused ion beam (FIB) SEM at the University of Arizona.We performed analysis of the microstructural and chemical characteristics of the samples using the 200 keV JEOL 2500 scanning TEM at Johnson Space Center. Reflectance Spectroscopy Results:Reflectance spectra for each sample are shown in Fig. 1.SC-001:The spectrum of the unirradiated sample exhibits a weak 1.0 μm absorption feature, associated with Fe2+in the olivine,and low overall reflectance (Fig. 1a). Thereflectance and the depth of the absorption band increases after 1x laser raster but are at their lowest after 5x laser rasters.F-T-004:The unirradiated sample has a blue-sloped spectrum with low reflectance without identifiable absorption features (Fig. 1b). With progressive laser irradiation, the sample reflectance increases and becomes strongly red-sloped.F-S-002:The unirradiated sample exhibits a dark, blue-slopedspectrum. The brightness of the sample increases significantly from <0.2average reflectance over >0.8 reflectance in the most irradiated sampleand thespectral slope also becomesslightly reddened (Fig. 1c). Microstructural and Chemical Analysis: Two primary alteration textures were observed in the samples exposed to simulated space weathering: 1) fluffy C-rich,and 2) vesiculated melt. The fluffy C-rich texture is composed oflow-densitydeposits distributed across the surface of the sample(Fig. 2A). Analysis of a FIB section extracted from a low-density C-rich region in sample SC-001 reveals multiple globule-type deposits, discrete from stacked graphite, likely produced via melting from the laser irradiation [9].The vesiculated melt textureis smooth and uniformly distributed across isolated regions of the sample surface. The vesicles measure up to 100s of nmin diameter. Analysis of a FIB section from this texture was extracted from sample F-T-004 reveals a layer of amorphous melt material, close to 100 nm thick and uniform across the FIB section (Fig. 2B). Isolated regions of this melt layer contain small nanoparticles, <5 nm in diameter. Chemical analysis through energy dispersive X-ray spectroscopy reveals the composition of this layer is enriched in Si and depleted in Mg and O compared to the underlying sample. Implications for Space Weathering on Mercury: Previous experiments simulating space weathering of Mercury have showndarkening and reddening of spectra[7,10].However, our use of low-Fe materials and graphite to create a sample set more analogous to the mercurian surface. Our results indicate that sample composition plays a significant and important role in the space weathering of Mercury. In particular, our spectral data demonstrates a strong correlation between spectral slope, Fe content, and simulated space weathering. While the variation in FeO content between samples F-S-002 and F-T-004 is <0.6 wt.%, the spectra deviate from flat to strongly red-sloped(F-T-004). This reddeningmay be linked to the presence of very small nanoparticles observed in the melt textures extracted from sample F-T-004. For the SC-001 sample, the fluffy C-rich textures may be developed by the amalgamation of small graphite particles into these unique morphologies. Such observations indicate that space weathering on Mercury may result in both familiar and new microstructural and chemical characteristics. References: [1]Hapke B. (2001) J. Geophys. Res.-Planet.,106,10039–10073. [2]Pieters C.M. and Noble S.K. (2016) J. Geophys. Res-Planet., 121, 1865–1884. [3] Lucey P.G., and Riner, M.A. (2011) Icarus,212, 451-462.[4]CintalaM.J.(1992)J. Geophys. Res.-Planet.,97,947–973.[5]Klima R.L.et al.(2018)Geophys.Res.Letters, 45, 2945–2953. [6]Nittler L.R., et al. (2011) Science 333, 1847-1850.[7]Sasaki S. and Kurahashi E. (2004) Space weathering on Mercury, Adv.Space Res., 33, 2152-2155.[8] Vander KaadenK.E., et al. (2018) LPSCXLIX, Abstract 1230. [9] McGlaun M.L. et al. (2019) LPSCL, Abstract 2019. [10] TrangD.et al. (2018)LPSCXLIX,Abstract2083

M S Thompson↗
NASA NTRS1995

Thermal conductivity of zirconia thermal barrier coatings

Thermal barrier coatings (TBC's) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBC's is of primary importance. Physical vapor deposition (PVD) and plasma spraying (PS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The PS coatings were applied with either standard powder or hollow sphere particles. The hollow sphere particles yielded a lower density and lower thermal conductivity coating. The thermal conductivity of both fully and partially stabilized zirconia, before and after thermal aging, will be compared. The thermal conductivity of the coatings permanently increases upon exposed to high temperatures. These increases are attributed to microstructural changes within the coatings. Sintering of the as-fabricated plasma sprayed lamellar structure is observed by scanning electron microscopy of coatings isothermally heat treated at temperatures greater than 1100 C. During this sintering process the planar porosity between lamella is converted to a series of small spherical pores. The change in pore morphology is the primary reason for the observed increase in thermal conductivity. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the PVD coatings are less susceptible to thermal aging effects, preliminary results suggest that they have a higher thermal conductivity than PS coatings, both before and after thermal aging. The increases in thermal conductivity due to thermal aging for partially stabilized plasma sprayed zirconia have been found to be less than for fully stabilized plasma sprayed zirconia coatings. The high temperature thermal diffusivity data indicate that if these coatings reach a temperature above 1100 C during operation, they will begin to lose their effectiveness as a thermal barrier.

Dinwiddie, R. B.↗
NASA NTRS2010

Chiral Biomarkers in Meteorites

The chirality of organic molecules with the asymmetric location of group radicals was discovered in 1848 by Louis Pasteur during his investigations of the rotation of the plane of polarization of light by crystals of sodium ammonium paratartrate. It is well established that the amino acids in proteins are exclusively Levorotary (L-aminos) and the sugars in DNA and RNA are Dextrorotary (D-sugars). This phenomenon of homochirality of biological polymers is a fundamental property of all life known on Earth. Furthermore, abiotic production mechanisms typically yield recemic mixtures (i.e. equal amounts of the two enantiomers). When amino acids were first detected in carbonaceous meteorites, it was concluded that they were racemates. This conclusion was taken as evidence that they were extraterrestrial and produced by abiologically. Subsequent studies by numerous researchers have revealed that many of the amino acids in carbonaceous meteorites exhibit a significant L-excess. The observed chirality is much greater than that produced by any currently known abiotic processes (e.g. Linearly polarized light from neutron stars; Circularly polarized ultraviolet light from faint stars; optically active quartz powders; inclusion polymerization in clay minerals; Vester-Ulbricht hypothesis of parity violations, etc.). This paper compares the measured chirality detected in the amino acids of carbonaceous meteorites with the effect of these diverse abiotic processes. IT is concluded that the levels observed are inconsistent with post-arrival biological contamination or with any of the currently known abiotic production mechanisms. However, they are consistent with ancient biological processes on the meteorite parent body. This paper will consider these chiral biomarkers in view of the detection of possible microfossils found in the Orgueil and Murchison carbonaceous meteorites. Energy dispersive x-ray spectroscopy (EDS) data obtained on these morphological biomarkers will be presented to show that the elemental compositions of these morphological biomarkers are not consistent with the compositions expected for modern (i.e. post-arrival) biological contaminants.

Hoover, Richard B.↗
NASA NTRS1984

Abrasive tip treatment for use on compressor blades

A co-spray process was used which simultaneously but separately introduces abrasive grits and metal matrix powder into the plasma stream and entraps the abrasive grits within a molten matrix to form an abrasive coating as the matrix material solidifies on test specimen surfaces. Spray trials were conducted to optimize spray parameter settings for the various matrix/grit combinations before actual spraying of the test specimens. Rub, erosion, and bond adhesion tests were conducted on the coated specimens in the as-sprayed condition as well as on coated specimens that were aged for 100 hours at a temperature of 866K (1100 F). Microscopic examinations were performed to determine the coating abrasive-particle content, the size and shape of the adhesive particles in the coating, and the extent of compositional or morphological changes resulting from the aging process. A nickel chromium/aluminum composite with No. 150 size (0.002 to 0.005 inch) silicon carbide grits was selected as the best matrix/abrasive combination of the candidates surveyed for coating compressor blade tips.

Pedersen, H. C.↗
NASA NTRS1994

Crystallization Kinetics of Barium and Strontium Aluminosilicate Glasses of Feldspar Composition

Crystallization kinetics of BaO.Al2O3.2SiO2 (BAS) and SrO.Al2O3.2SiO2 (SAS) glasses in bulk and powder forms have been studied by non-isothermal differential scanning calorimetry (DSC). The crystal growth activation energies were evaluated to be 473 and 451 kJ/mol for bulk samples and 560 and 534 kJ/mol for powder specimens in BAS and SAS glasses, respectively. Development of crystalline phases on thermal treatments of glasses at various temperatures has been followed by powder x-ray diffraction. Powder samples crystallized at lower temperatures than the bulk and the crystallization temperature was lower for SAS glass than BAS. Crystallization in both glasses appeared to be surface nucleated. The high temperature phase hexacelsian, MAl2Si2O8 (M = Ba or Sr), crystallized first by nucleating preferentially on the glass surface. Also, monoclinic celsian does not nucleate directly in the glass, but is formed at higher temperatures from the transformation of the metastable hexagonal phase. In SAS the transformation to monoclinic celsian occurred rapidly after 1 h at 1100 C. In contrast, in BAS this transformation is sluggish and difficult and did not go to completion even after 10 h heat treatment at 1400 C. The crystal growth morphologies in the glasses have been observed by optical microscopy. Some of the physical properties of the two glasses are also reported.

Hyatt, Mark J.↗
NASA NTRS2000

Freely Suspended Smectic Filaments and the Structure of the B7 Phase of MHOBOW

Our recent discovery of the spontaneous formation of chiral domains in fluid smectic phases of achiral bow-shaped molecules opens up a wide variety of possibilities for new liquid crystal phases and phenomena. The basic, spontaneously chiral layer structure of the highest temperature fluid smectic phases, the B2 and B7, are shown. One of the most intriguing aspects of this structure is the plethora of possible phases coming from different stacking sequences of the polar ordering and tilt directions. The four possibilities of next-nearest neighbor alternation are shown. In the original material studied, NOBOW, the ground states found are antiferroelectric, either the racemic SmC(sub S)P(sub A) or the chiral SmC(sub A)P(sub A). We are currently studying MHOBOW, synthesized by D. Walba which, by virtue of its methyl hexyloxy tail has a tendency to form anticlinic layer interfaces, in the hope of finding a phase with a ferroelectric ground state, either SmC(sub A)P(sub S) or SmC(sub S)P(sub A), which can be obtained in NOBOW only by applying a field. Preliminary observations of MHO-BOW have made its study, from the point of view of understanding novel LC structures, extremely high priority. The following truly remarkable characteristics have been revealed: (i) The smectic phase grows out of the isotropic in the form of helical ribbons. The resulting planar aligned textures of focal conics with layers normal to glass plates exhibit bizarre modulations, including stripes and checker-boards. These have also been seen in other materials suggesting that this is a new phase (tentatively called B7), which is a fluid smectic with some kind of in-layer structure. (ii) It is virtually impossible to make freely suspended films of MHOBOW. Rather it makes the freely suspended filaments which preliminary x-ray scattering experiments reveal to have the nested cylinder layer structure indicated; (iii) The powder x-ray diffraction exhibits four resolution-limited smectic layering peaks, very close in layer spacing, which vary continuously with T. This is further evidence for a more complex three dimensional structure than NOBOW, which has a typical single layering reflection. (iv) The x-ray structure factor of the layering peak of the filaments is extraordinarily complex and rich. Varying in qL (the scattering vector component along the filament axis) from a double slit-like pattern to modulated layer-like patterns, as qH (the scattering vector component normal to the filament axis) is varied over the range where the four powder peaks are located. These results suggest some kind of mosaic structure, perhaps with different layer spacings corresponding to the different stacking sequences. Recent x-ray diffraction experiments show that the peaks are modulated in intensity upon translation along a filament, in domains of several hundred microns dimension. These preliminary experiments suggest that the B7 is a fluid smectic with extremely unusual and fascinating structures. Of all of the many hundreds of fluid smectic materials we have attempted to study in the freely suspended film geometry over the years, only a few have failed to form films, and none showed any great tendency to form filaments, although this clearly should be a possible freely suspended smectic LC morphology. On several occasions in the past we have intentionally tried to make filaments from a variety of smectics without success. Thus the smectic filament formation property makes the B7 phase unique. It seems quite likely that the stability of filaments is related to the in-plane structure. The filaments exhibit other interesting structural and optical features. They are birefringent with a local optic axis which is oblique and which can vary continuously along filament and which can be manipulated with an electric field applied normal to the fiber, as if the field were causing a rotation of the optic axis about the fiber axis. Rapid displacement of the ends of the fiber toward one another causes a macroscopic helixing at low T and causes thick regions to transiently appear at high T, a 1D analog of island formation on a rapidly compressed film.

Clark, N.↗