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At least 829 records · Page 46
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NASA NTRS2002

Development of HVOF Sprayed Erosion/Oxidation Resistant Coatings for Composite Structural Components in Propulsion Systems

Thermally sprayed coatings are being studied and developed as methods of enabling lightweight composites to be used more extensively as structural components in propulsion applications in order to reduce costs and improve efficiency through weight reductions. The primary goal of this work is the development of functionally graded material [FGM] polymer/metal matrix composite coatings to provide improved erosion/oxidation resistance to polyimide-based polymer matrix composite [PMC] substrates. The goal is to grade the coating composition from pure polyimide, similar to the PMC substrate matrix on one side, to 100 % WC-Co on the other. Both step-wise and continuous gradation of the loading of the WC-Co reinforcing phase are being investigated. Details of the coating parameter development will be presented, specifically the high velocity oxy-fuel [HVOF] combustion spraying of pure PMR-11 matrix material and layers of various composition PMR-II/WC-Co blends onto steel and PMR-15 composite substrates. Results of the HVOF process optimization, microstructural characterization, and analysis will be presented. The sprayed coatings were evaluated using standard metallographic techniques - optical and scanning electron microscopy [SEM]. An SEM + electron dispersive spectroscopy [EDS] technique has also been used to confirm retention of the PMR-II component. Results of peel/butt adhesion testing to determine adhesion will also be presented.

Knight, R.↗
NASA NTRS2002

High-Temperature Mechanical Properties of Cr(3+) Doped Sapphire Fibers

High-temperature slow-crack growth of single crystal 10 wt% Cr2O3 - Al2O3 (nominal composition) fibers has been studied by tensile rupture experiments at 1400 C, under different stressing rates (0.5 to 41.5 MPa/s). Slow-crack growth (SCG) is less pronounced with increasing Cr2O3. Rupture stresses increased with the stressing rate from 397 MPa to 515 MPa, resulting in a SCG exponent, N=19. The Cr2O3 composition was analyzed by Energy Dispersed X-Ray Spectra (EDS) and fracture surfaces were studied by scanning electron microscopy (SEM). Results are compared with previous studies on 100-300 ppm Cr3(+) doped sapphire fibers and on commercial sapphire fibers.

Sayir, A.↗
NASA NTRS2002

Oxidation of a Silica-Containing Material in a Mach 0.3 Burner Rig

A primarily silica-containing material with traces of organic compounds, as well as aluminum and calcium additions, was exposed to a Mach 0.3 burner rig at atmospheric pressure using jet fuel. The sample was exposed for 5 continuous hours at 1370 C. Post exposure x-ray diffraction analyses indicate formation of cristobalite, quartz, NiO and Spinel (Al(Ni)CR2O4). The rig hardware is composed of a nickel-based superalloy with traces of Fe. These elements are indicated in the energy dispersive spectroscopy (EDS) results. This material was studied as a candidate for high temperature applications under an engine technology program.

Nguyen, QuynhGiao N.↗
NASA NTRS2002

Comparison of a 2D Photochemical Model to Data Using Statistical Trend Analysis

We have analyzed our 23-year merged ozone data set for variability and trends with a statistical time-series model. To assist in that analysis, we have analyzed the Goddard ED photochemical model for the same time period with the same time-series model. Multiple runs of the photochemical model allow us to separate the effects of various terms on ozone, such as solar cycle and volcanic eruptions. We use this to help us separate those signals from each other in the data. We also used a smoothed version of the photochemical model's prediction of global ozone change in place of a simple linear trend. We find a number of interesting results. This particular photochemical model is more sensitive to chlorine perturbations than the atmosphere appears to be. It is less sensitive to solar cycle. It predicts an effect from the Pinatubo eruption that is nearly symmetric in the two hemispheres, but the data appears to have not responded to Pinatubo in the southern mid-latitudes. These results and their uncertainties will be discussed.

Stolarski, Richard S.↗
NASA NTRS2002

A Review of Single Source Precursors for the Deposition of Ternary Chalcopyrite Materials

The development of thin-film solar cells on flexible, lightweight, space-qualified durable substrates (i.e. Kapton) provides an attractive solution to fabricating solar arrays with high specific power, (W/kg). The syntheses and thermal modulation of ternary single source precursors, based on the [{LR}2Cu(SR')2In(SR')2] architecture in good yields are described. Thermogravimetric analyses (TGA) and Low temperature Differential Scanning Caloriometry, (DSC) demonstrate that controlled manipulation of the steric and electronic properties of either the group five-donor and/or chalcogenide moiety permits directed adjustment of the thermal stability and physical properties of the precursors. TGA-Evolved Gas Analysis, confirms that single precursors decompose by the initial extrusion of the sulphide moiety, followed by the loss of the neutral donor group, (L) to release the ternary chalcopyrite matrix. X-ray diffraction studies, EDS and SEM on the non-volatile pyrolized material demonstrate that these derivatives afford single-phase CuInS2/CuInSe2 materials at low temperature. Thin-film fabrication studies demonstrate that these single source precursors can be used in a spray chemical vapor deposition process, for depositing CuInS2 onto flexible polymer substrates at temperatures less than 400 C.

Banger, K. K.↗
NASA NTRS2002

Quantum Dot Solar Cells

We have been investigating the synthesis of quantum dots of CdSe, CuInS2, and CuInSe2 for use in an intermediate bandgap solar cell. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Bawendi, et. al., in the early 1990's. However, unlike previous work in this area we have also utilized single-source precursor molecules in the synthesis process. We will present XRD, TEM, SEM and EDS characterization of our initial attempts at fabricating these quantum dots. Investigation of the size distributions of these nanoparticles via laser light scattering and scanning electron microscopy will be presented. Theoretical estimates on appropriate quantum dot composition, size, and inter-dot spacing along with potential scenarios for solar cell fabrication will be discussed.

Raffaelle, Ryne P.↗
NASA NTRS2002

Microfossils in the Murchison and Rainbow Carbonaceous Meteorites

Astrobiologists are working to develop methodologies for the recognition of bacterial microfossils, biominerals, and chemical biomarkers in terrestrial rocks, to provide a basis for the scientific assessment of possible microfossils in meteorites and other Astromaterials. During the past 5 years, we have conducted electron microscopy investigations to understand the morphology and chemical composition of microfossils in ancient terrestrial rocks and to search for microfossils presence in meteorites. We have detected evidence of indigenous microfossils and biominerals in-situ in every carbonaceous meteorite investigated but have found no evidence for microfossils in the nickel-iron and stony meteorites studied. In this paper, we provide a brief review of prior evidence for microfossils in meteorites and present Scanning and Environmental Scanning Electron Microscope (SEM and ESEM) and Field Emission Scanning Electron Microscope (FESEM) images of microfossils found in-situ in freshly fractured surfaces of the Murchison and Rainbow meteorites. We describe the techniques and methods used to protect the samples from contamination and for the discrimination of indigenous microfossils from recent terrestrial contaminants We provide data from Energy Dispersive Spectroscopy (EDS) and Link microprobe analysis of the chemical elements and 2D x-ray maps as strong evidence that these biogenic forms are indigenous to the meteorites and cannot logically be interpreted as recent bio-contaminants. We show evidence of framboidal magnetites and pyrites and compare them with framboidal magnetites and pyrites found in Cambrian richs from the Siberian Platform.

Hoover, Richard B.↗
NASA NTRS2002

Ternary Precursors for Depositing I-III-VI2 Thin Films for Solar Cells via Spray CVD

The development of thin-film solar cells on flexible, lightweight, space-qualified substrates provides an attractive cost solution to fabricating solar arrays with high specific power (W/kg). Thin-film fabrication studies demonstrate that ternary single source precursors (SSP's) can be used in either a hot or cold-wall spray chemical vapour deposition (CVD) reactor, for depositing CuInS2, CuGaS2, and CuGaInS2 at reduced temperatures (400 to 450 C), which display good electrical and optical properties suitable for photovoltaic (PV) devices. X-ray diffraction studies, energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) confirmed the formation of the single phase CIS, CGS, CIGS thin-films on various substrates at reduced temperatures.

Banger, K. K.↗
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

Expedition 7 Crew Training Clip

This video shows the Expedition 7 crew of the International Space Station (ISS) during various training activities prior to launch. The crew consisted of Commander Yuri Malenchenko and Flight Engineer Ed Lu. At the virtual reality lab, the two astronauts work at a control panel, with Lu operating a joystick and speaking on earphones. Another section of the video shows Lu and Malenchenko inputting data into laptop computers, Lu testing an intercom and a video camera, and Lu using a machine to analyze blood samples from the crew. At the neutral buoyancy lab, the astronauts are helped in suit-up. The attachment of their gloves is shown. The video ends with Lu and Malenchenko lowered into a pool on a platform.

Source record↗
NASA NTRS2003

Flame Spray Strain Gages with Improved Durability and Lifetimes

The focus of this APP research program was to improve the bond coats used in the fabrication of flame sprayed instrumentation. Typically. a bond coat is applied to a superalloy surface prior to the application of a thin dielectric coating onto which instrumentation is placed. After affixing the instrumentation, a much thicker ceramic topcoat is typically applied to protect the instrumentation from harsh environments. The fatigue life of NiCoCrAlY coated superalloys was extended beyond current state-of-the-art by relatively simple and cost effective means. Heat treatment in reduced oxygen partial pressures at 1750 to 1800 F effectively doubled the fatigue life of NiCoCrAlY coated substrates relative to as-sprayed substrates and when used in conjunction with platinum diffusion barriers yielded a four fold increase in the fatigue life of NiCoCrAlY coated substrates. Further improvements in the fatigue life of thermally sprayed coatings were made by employing intermediate coatings, which minimized thermal expansion differences between the bond coat and top coat. Combinatorial chemistry experiments yielded an optimum composition for an intermediate TCE matching coating that showed considerable promise in extending the fatigue life of thermal spray instrumentation. The intermediate coating had two functions: to reduce the surface roughness of the peaks and valleys associated with the as-sprayed NiCoCrAlY bond coat, and to produce a thin layer of a mixture of Al2O3 and NiCoCrAlY that exhibited an intermediate TCE. The optimal composition of the intermediate coating consisted of 60 wt% Al2O3 and 40 wt% NiCoCrAlY, as determined by energy dispersive analysis of x-rays (EDS). Intermediate coatings having this composition were prepared by physical vapor deposition and the resulting coating systems are being evaluated in our test facility.

Fralick, Gustave↗
NASA NTRS2003

MSFC MXER Tether Study

This viewgraph presentation provides an overview of the proposed Momentum-eXchange/Electrodynamic Reboost (MXER) space hardware system. The tether system would be position cart-wheeling cables above the Earth and then, rotating like a giant sling, would capture spacecraft or payloads from space shuttles in low Earth orbits and launch them into higher orbits. This study focuses on system validation and structural design issues for MXER. Topics examined include: tether facility design, ED tether system, payload capture/catch mechanism, payload accomodations assembly (PAA), PAA rendezvous capability, and PAA capability to correct tether misthrows.

Polsgrove, Tara↗
NASA NTRS2003

Cryogenic Properties of Aluminum Beryllium and Beryllium Materials

Ultimate tensile strength, yield strength, and elongation were obtained for the aluminum-beryllium alloy, AlBeMetl62 (38%Al-62%Be), at cryogenic (-195.5 C (-320 F) and (-252.8 C) (-423 F)) temperatures, and for an optical grade beryllium, O-30H (99%Be), at -252.8 C. AlBeMetl62 material was purchased to the requirements of SAE-AMS7912, "Aluminum-Beryllium Alloy, Extrusions." O-30H material was purchased to the requirements of Brush Wellman Inc. specification O-30H Optical Grade Beryllium. The ultimate tensile and yield strengths for extruded AlBeMetl62 material increased with decreasing temperature, and the percent elongation decreased with decreasing temperature. Design properties for the ultimate tensile strength, yield strength, and percent elongation for extruded AlBeMetl62 were generated. It was not possible to distinguish a difference in the room and cryogenic ultimate strength for the hot isostatically pressed (HIP'ed) O-30H material. The O30H elongation decreased with decreasing temperature.

Gamwell, Wayne R.↗
NASA NTRS2003

Oxidation of Ultra-High Temperature Ceramics in Water Vapor

Ultra high temperature ceramics (UHTCs) including HfB2 + SiC (20% by volume), ZrB2 + SiC (20% by volume) and ZrB2 + SiC (14% by volume) + C (30% by volume) have historically been evaluated as reusable thermal protection systems for hypersonic vehicles. This study investigates UHTCs for use as potential combustion and aeropropulsion engine materials. These materials were oxidized in water vapor (90%) using a cyclic vertical furnace at 1 atm. The total exposure time was 10 hours at temperatures of 1200, 1300, and 1400 C. CVD SiC was also evaluated as a baseline comparison. Weight change measurements, X-ray diffraction analyses, surface and cross-sectional SEM and EDS were performed. These results will be compared with tests ran in static air at temperatures of 1327, 1627, and 1927 C. Oxidation comparisons will also be made to the study by Tripp. A small number of high pressure burner rig (HPBR) results at 1100 and 1300 C will also be discussed. Specific weight changes at all three temperatures along with the SIC results are shown. SiC weight change is negligible at such short duration times. HB2 + SiC (HS) performed the best out of all the tested UHTCS for all exposure temperatures. ZrB2 + Sic (ZS) results indicate a slightly lower oxidation rate than that of ZrBl + SiC + C (ZCS) at 1200 and 1400 C, but a clear distinction can not be made based on the limited number of tested samples. Scanning electron micrographs of the cross-sections of all the UHTCs were evaluated. A representative area for HS is presented at 1400 C for 26 hours which was the composition with the least amount of oxidation. A continuous SiO2 scale is present in the outer most edge of the surface. An image of ZCS is presented at 1400 C for 10 hours, which shows the most degradation of all the compositions studied. Here, the oxide surface is a mixture of ZrSiO4, ZrO2 and SO2.

Nguyen, QuynhGiao N.↗
NASA NTRS2003

Testing of RANS Turbulence Models for Stratified Flows Based on DNS Data

In most geophysical flows, turbulence occurs at the smallest scales and one of the two most important additional physical phenomena to account for is strati cation (the other being rotation). In this paper, the main objective is to investigate proposed changes to RANS turbulence models which include the effects of stratifi- cation more explicitly. These proposed changes were developed using a DNS database on strati ed and sheared homogenous turbulence developed by Shih et al. (2000) and are described more fully in Ferziger et al. (2003). The data generated by Shih, et al. (2000) (hereinafter referred to as SKFR) are used to study the parameters in the k- model as a function of the turbulent Froude number, Frk. A modified version of the standard k- model based on the local turbulent Froude number is proposed. The proposed model is applied to a stratified open channel flow, a test case that differs significantly from the flows from which the modified parameters were derived. The turbulence modeling and results are discussed in the next two sections followed by suggestions for future work.

Venayagamoorthy, S. K.↗
NASA NTRS2004

Oxidation of Ultra-High Temperature Ceramics in Water Vapor

Ultra High Temperature Ceramics (UHTCs) including HfB2 + 20% SiC (HS), and ZrB2 + 20% SiC (ZC), and ZrB2 + 30% C + 14% SiC (ZCS) have been investigated for use as potential aeropropolsion engine materials. These materials were oxidized in water vapor (90%) using a cyclic vertical furnace at 1 atm. The total exposure time was 10 hours at temperature of 1200, 1300, and 1400 C. CVD SiC was also evaluate as a baseline for comparison. Weight change, X-ray diffraction analysis, surface and cross-sectional SEM and EDS were performed. These results are compared with tests conducted in a stagnant air furnace at temperatures of 1327 C for 100 minutes, and with high pressure burner rig (HPBR) results at 1100 and 1300 C at 6 atm for 50 h. Total recession measurements are also reported for the two tests environments.

Nguyen, QuynGiao N.↗
NASA NTRS2004

Bringing Up Baby

In 1977, I had just finished eight years on the Viking program, which was just a marvelously rich, fascinating experience, using the most up-to-date, sophisticated management techniques, under an outstanding leader named Jim Martin. After that, you could say the opportunities available to me within NASA in some ways were limitless. I remember quite vividly when I got the phone call from Ed Cortright, who was the Langley Center Director at the time, with news about my next assignment. He asked me to come to the aid of a project that was in trouble, the Rotor Systems Research Aircraft (RSRA).

Guastaferro, Angelo↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Mars: Surface Coatings, Mineralogy, and Surface Properties

The session "Mars: Surface Coatings, Mineralogy, and Surface Properties" contained the following reports:High-Silica Rock Coatings: TES Surface-Type 2 and Chemical Weathering on Mars; Old Desert Varnish-like Coatings and Young Breccias at the Mars Pathfinder Landing Site; Analyses of IR-Stealthy and Coated Surface Materials: A Comparison of LIBS and Reflectance Spectra and Their Application to Mars Surface Exploration; Contrasting Interpretations of TES Spectra of the 2003 Rover:Opportunity-Landing Site: Hematite Coatings and Gray Hematite; A New Hematite Formation Mechanism for Mars; Geomorphic and Diagenetic Analogs to Hematite Regions on Mars: Examples from Jurassic Sandstones of Southern Utah, USA; The Geologic Record of Early Mars: A Layered, Cratered, and "Valley-"ed: Volume; A Simple Approach to Estimating Surface Emissivity with THEMIS; A Large Scale Topographic Correction for THEMIS Data; Thermophysical Properties of Meridiani Planum, Mars; Thermophysical and Spectral Properties of Gusev, the MER-Spirit Landing Site on Mars; Determining Water Content of Geologic Materials Using Reflectance Spectroscopy; and Global Mapping of Martian Bound Water at 6.1 Microns Based on TES Data: Seasonal Hydration.

Source record↗