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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

High temperature regenerative H.sub.2 S sorbents

Efficient, regenerable sorbents for removal of H.sub.2 S from high temperature gas streams comprise porous, high surface area particles. A first class of sorbents comprise a thin film of binary oxides that form a eutectic at the temperature of the gas stream coated onto a porous, high surface area refractory support. The binary oxides are a mixture of a Group VB or VIB metal oxide with a Group IB, IIB or VIII metal oxide such as a film of V-Zn-O, V-Cu-O, Cu-Mo-O, Zn-Mo-O or Fe-Mo-O coated on an alumina support. A second class of sorbents consist of particles of unsupported mixed oxides in the form of highly dispersed solid solutions of solid compounds characterized by small crystallite size, high porosity and relatively high surface area. The mixed oxide sorbents contain one Group IB, IIB or VIIB metal oxide such as copper, zinc or manganese and one or more oxides of Groups IIIA, VIB or VII such as aluminum, iron or molybdenum. The presence of iron or aluminum maintains the Group IB, IIB or VIIB metal in its oxidized state. Presence of molybdenum results in eutectic formation at sulfidation temperature and improves the efficiency of the sorbent.

Flytani-Stephanopoulos, Maria↗
NASA NTRS1983

A survey of ultraviolet interstellar absorption lines

A telescope-spectrometer on the Copernicus spacecraft made possible the measurement of many ultraviolet absorption lines produced by the interstellar gas. The present survey provides data on ultraviolet absorption lines in the spectra of 88 early-type stars. The stars observed are divided into four classes, including reddened stars, unreddened bright stars, moderately reddened bright stars, and unreddened and moderately reddened faint stars. Data are presented for equivalent width, W, radial velocity V, and rms line width, D, taking into account some 10 to 20 lines of N I, O I, Si II, P II, S II, Cl I, Cl II, Mn II, Fe II, Ni II, Cu II, and H2. The data are based on multiple scans for each line. Attention is given to details of observations, the data reduction procedure, and the computation of equivalent width, mean velocity, and velocity dispersion.

Bohlin, R. C.↗
NASA NTRS1974

The electrical properties of low-g processed immiscible alloys

When dispersed or mixed immiscibles are solidified on earth, a large amount of separation of the constituents takes place due to differences in densities. However, when the immiscibles are dispersed and solidified in zero-gravity, density separation does not occur, and unique composite solids can be formed with many new and promising electrical properties. By measuring the electrical resistivity and superconducting critical temperature of zero-g processed Ga-Bi samples, it has been found that the electrical properties of such materials are entirely different from the basic constituents and the ground control samples. The finest dispersions are obtained only in a low-gravity environment. Our results indicate that space-processed immiscible materials may form an entirely new class of electronic materials. The interesting electrical properties of directionally solidified Al-Cu eutectic, a two-component alloy consisting of Al and Al2Cu which was processed on Skylab (M566) are briefly reviewed. The electrical resistivity of directionally solidified eutectics with a lamellar structure are highly anisotropic and have been studied both experimentally and theoretically. The local resistivity of the space-processed samples are compared to a ground control sample and to the expected theoretical results.

Otto, G. H.↗
NASA NTRS1976

Properties of splat-quenched 7075 aluminum type alloys

The 7075 alloy belonging to the Al-Zn-Mg-Cu system, prepared by powder metallurgy techniques, was used in a study of alloys prepared from splat-quenched foils consolidated into bar material by hot extrusion. Ni and Fe were included in one alloy specimen, producing a fine dispersion of FeAl3 type particles which added to the strength of the aged alloy but did not coarsen upon heat treatment. Fine oxide films showing up on air-splatted foils induce finely dispersed oxide stringers (if the foils are not hot-worked subsequently) which in turn promote axial cracking (but longitudinal tensile strength is not seriously impaired). Splatting in a protective atmosphere, or thermomechanical processing, is recommended to compensate for this.

Durand, J. P. H. A.↗
NASA NTRS1982

The 18 May 1980 eruption of Mount St. Helens: The nature of the eruption, with an atmospheric perspective

Mount St. Helens erupted somewhat less than 0.5 cu km of magma (dense rock equivalent) on May 18, 1980. The May 18 event was usually violent. As much 35% of the volume of the airfall material fell outside of the 2.5 mm isopach, which encloses about 88,000 sq km. This extraordinary dispersive power was transmitted by an eruption column which reached heights of more than 20 km. There was a lateral blast (or surge) of unusually large dimensions associated with the onset of the eruption. The magma is dacitic in composition and had a low ( 500 ppm) sulfur content. Distal ashes contain much nonmagmatic (lithic) material, but smaller ( 50 microns m) particles are mostly finely divided magmatic dacite. The grain size distributions of the ash are multimodal, frequently with peaks at 90, 25, and 10 microns. The finer populations fell out faster than their terminal velocities as simple particles would suggest. It is inferred that large proportions of the fine ash fell out as composite particles. This condition greatly reduces the atmospheric burden of silicate particles. Some of the unusual aspects (violence, intense surges, multimodal grain size distributions, lithic content of the ashes) of the eruption may be due to its phreatomagmatic character. The hydrothermal system above the magma may have infiltrated the magma body at the onset of the eruption. An "overprint" of the geochemistry of this hydrothermal system on the geochemistry of the magmatic gas system is likely. One important feature is that reduced gas species may be much more abundant than in many eruptions. Another is that fine ash may form aggregates more readily.

Rose, W. I., Jr.↗
NASA NTRS1975

A study of interstellar lines in the rocket spectrum of delta Scorpii

Ten interstellar lines in the vacuum UV spectrum of delta Sco are analyzed which were recorded on rocket spectrograms. Two cloud components are resolved which have Doppler widths of 1.55 km/sec (larger cloud) and 2.16 km/sec (smaller cloud). Column densities are derived for C I, C II, N I, O I, Al II, Si II, and Fe II, and abundances relative to atomic hydrogen are determined from them. Silicon and iron are found to be slightly overabundant relative to the solar abundances, while the other elements are underabundant by factors ranging from 1.8 to 8.6. Mean cloud densities of 250 and 150 per cu cm (for the larger and smaller clouds, respectively) are determined, and the average ratios of electron density to hydrogen-atom density are derived using the column densities of C I and C II. It is shown that the iron abundance can be decreased to less than the solar abundance by doubling the velocity dispersion of the iron ions.

Smith, A. M.↗
NASA NTRS2005

Mechanical Properties and Microstructure Investigation of Lead Free Solder

While the electronics industry appears to be focusing on Sn-Ag-Cu as the alloy of choice for lead free electronics assembly, ,the exact composition varies by geographic region, supplier and user. Add to that dissolved copper and silver from the printed circuit board traces and surface finish, and there can be significant variation in the final solder joint composition. A systematic study of the mechanical and microstructural properties of Sn-Ag-Cu alloys with Ag varying from 2wt% to 4wt% and Cu varying from 0.5wt% to lSwt%, was undertaken in this research study. Different sample preparation techniques (water quenched, oil quenched and water quenched followed by reflow) were explored and the resulting microstructure compared to that of a typical reflowed lead free chip scale package (CSP) solder joint. Tensile properties (modulus, 0.2% yield strength and the ultimate tensile strength) and creep behavior of selected alloy compositions (Sn-4Ag-1 X u , Sn-4Ag-OSCu, Sn- 2Ag-1 X u , Sn-2Ag-OSCu, Sn-3.5Ag-O.SCu) were determined for three conditions: as- cast; aged for 100 hours at 125OC; and aged for 250 hours at 125OC. There was no significant difference in Young's Modulus as a function of alloy composition. After an initial decrease in modulus after 100 hours at 125"C, there was an insignificant change with further aging. The distribution of 0.2% strain yield stress and ultimate tensile strength as a function of alloy composition was more significant and decreased with aging time and temperature. The microstructures of these alloys were examined using light and scanning electron microscopy (LM and SEM) respectively and SEM based energy dispersive x-ray spectroscopy (EDS). Fracture surface and cross-section analysis were performed on the specimens after creep testing. The creep testing results and the effect of high temperature aging on mechanical properties is presented for the oil quenched samples. In general the microstructure of oil quenched specimen exhibited a eutectic region of Sn with moderately dispersed Ag3Sn intermetallic, surrounded by a dendritic Sn-rich phase. The SEM images of the fracture surface indicated the presence of a tough shear surface at the initial cavity break area and a break line in the middle of specimen along the failure direction. A hyperbolic-sine creep model was adopted and used to fit the creep experiment data. The effect on the mechanical properties by adding the quaternary element bismuth to the Sn-3.5Ag-0.8Cu alloy was measured and compared with the mechanical properties of the ternary alloys. The results of this research study provide necessary data for the modeling of solder joint reliability for a range of Sn-Ag-Cu compositions and a baseline for evaluating the effects of subsequent quaternary additions.

Wang, Qing↗
NASA NTRS1984

Coaxial carbon plasma gun deposition of amorphous carbon films

A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented.

Sater, D. M.↗
NASA NTRS1990

In-situ integrated processing and characterization of thin films of high temperature superconductors, dielectrics and semiconductors by MOCVD

In this strategy of depositing the basic building blocks of superconductors, semiconductors, and dielectric having common elements, researchers deposited superconducting films of Y-Ba-Cu-O, semiconductor films of Cu2O, and dielectric films of BaF2 and Y2O3 by metal oxide chemical vapor deposition (MOCVD). By switching source materials entering the chamber, and by using direct writting capability, complex device structures like three-terminal hybrid semiconductors/superconductors transistors can be fabricated. The Y-Ba-Cu-O superconducting thin films on BaF2/YSZ substrates show a T(sub c) of 80 K and are textured with most of the grains having their c-axis or a-axis perpendicular to the substrate. Electrical characteristics as well as structural characteristics of superconductors and related materials obtained by x-ray defraction, electron microscopy, and energy dispersive x-ray analysis are discussed.

Singh, R.↗
NASA NTRS1991

In-situ integrated processing and characterization of thin films of high temperature superconductors, dielectrics and semiconductors by MOCVD

In this strategy of depositing the basic building blocks of superconductors, semiconductors, and dielectrics having common elements, researchers deposited superconducting films of Y-Ba-Cu-O, semiconductor films of Cu2O, and dielectric films of BaF2 and Y2O3 by metal oxide chemical vapor deposition (MOCVD). By switching source materials entering the chamber, and by using direct writing capability, complex device structures like three terminal hybrid semiconductor/superconductor transistors can be fabricated. The Y-Ba-Cu-O superconducting thin films on BaF2/YSZ substrates show a T(sub c) of 80 K and are textured with most of the grains having their c-axis or a-axis perpendicular to the substrate. Electrical characteristics as well as structural characteristics of superconductors and related materials obtained by x-ray deffraction, electron microscopy, and energy dispersive x-ray analysis are discussed.

Singh, R.↗
NASA NTRS2000

Friction and Wear Properties of Selected Solid Lubricating Films: Magnetron-Sputtered and Plasma-Assisted, Chemical-Vapor-Deposited Diamondlike Carbon Films - Part 3

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of magnetron-sputtered diamondlike carbon (MS DLC) and plasma-assisted, chemical-vapor-deposited diamondlike carbon (PACVD DLC) films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of L-2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7x10(exp -7) Pa), humid air (relative humidity, approx.20 percent), and dry nitrogen (relative humidity, <1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the DLC films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the DLC films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 10(exp -6) cu mm/N-m or less, respectively. MS DLC films and PACVD DLC films met the criteria in humid air and dry nitrogen but failed in ultrahigh vacuum, where the coefficients of friction were greater than the criterion, 0.3. In sliding contact with 440C stainless steel balls in all three environments the PACVD DLC films exhibited better tribological performance (i.e., lower friction and wear) than the MS DLC films. All sliding involved adhesive transfer of wear materials: transfer of DLC wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart DLC film.

Miyoshi, Kazuhisa↗
NASA NTRS2004

Sub-Micrometer Scale Minor Element Mapping in Interplanetary Dust Particles: A Test for Stratospheric Contamination

Combined X-ray microprobe (XRM), energy dispersive x-ray fluorescence using a Transmission Electron Microscope (TEM), and electron microprobe measurements have determined that the average bulk chemical composition of the interplanetary dust particles (IDPs) collected from the Earth s stratosphere is enriched relative to the CI meteorite composition by a factor of 2 to 4 for carbon and for the moderately volatile elements Na, K, P, Mn, Cu, Zn, Ga, Ge, and Se, and enriched to approximately 30 times CI for Br. However, Jessberger et al., who have reported similar bulk enrichments using Proton Induced X-ray Emission (PIXE), attribute the enrichments to contamination by meteor-derived atmospheric aerosols during the several weeks these IDPs reside in the Earth s atmosphere prior to collection. Using scanning Auger spectroscopy, a very sensitive surface analysis technique, Mackinnon and Mogk have observed S contamination on the surface of IDPs, presumably due to the accretion of sulfate aerosols during stratospheric residence. But the S-rich layer they detected was so thin (approximately 100 angstroms thick) that the total amount of S on the surface was too small to significantly perturb the bulk S-content of a chondritic IDP. Stephan et al. provide support for the contamination hypothesis by reporting the enrichment of Br on the edges of the IDPs using Time-of-Flight Secondary-Ion Mass-Spectrometry (TOFSIMS), but TOF-SIMS is notorious for producing false edge-effects, particularly on irregularly-shaped samples like IDPs. Sutton et al. mapped the spatial distribution of Fe, Ni, Zn, Br, and Sr, at the approximately 2 m scale, in four IDPs using element-specific x-ray fluorescence (XRF) computed microtomography. They found the moderately volatile elements Zn and Br, although spatially inhomogeneous, were not concentrated on the surface of any of the IDPs they examined, suggesting that the Zn and the Br enrichments in the IDPs are not due to contamination during stratospheric residence.

Flynn, G. J.↗
NASA NTRS1989

Thrust chamber material technology program

This report covers work performed at Pratt & Whitney on development of copper-based materials for long-life, reusable, regeneratively cooled rocket engine thrust chambers. The program approached the goal of enhanced cyclic life through the application of rapid solidification to alloy development, to introduce fine dispersions to strengthen and stabilize the alloys at elevated temperatures. After screening of alloy systems, copper-based alloys containing Cr, Co, Hf, Ag, Ti, and Zr were processed by rapid-solidification atomization in bulk quantities. Those bulk alloys showing the most promise were characterized by tensile testing, thermal conductivity testing, and elevated-temperature, low-cycle fatigue (LFC) testing. Characterization indicated that Cu- 1.1 percent Hf exhibited the greatest potential as an improved-life thrust chamber material, exhibiting LCF life about four times that of NASA-Z. Other alloys (Cu- 0.6 percent Zr, and Cu- 0.6 percent Zr- 1.0 percent Cr) exhibited promise for use in this application, but needed more development work to balance properties.

Andrus, J. S.↗
NASA NTRS2000

Friction and Wear Properties of Selected Solid Lubricating Films: Ion-Plated Lead Films - Part 2

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of ion-plated lead films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of 1.2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7 x 10(exp -7 Pa), humid air (relative humidity, approx. 20 percent), and dry nitrogen (relative humidity, less then 1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the ion-plated lead films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the ion-plated lead films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 1(exp -6) cu mm/N.m or less, respectively. The ion-plated lead films met both criteria only in ultrahigh vacuum but failed in humid air and in dry nitrogen, where the coefficient of friction was higher than the criterion. Both the lead film wear rate and the ball wear rate met that criterion in all three environments. Adhesion and plastic deformation played important roles in the friction and wear of the ion-plated lead films in contact with 440C stainless steel balls in the three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart lead.

Miyoshi, Kazuhisa↗
NASA NTRS2005

Nano-engineered Multiwall Carbon Nanotube-copper Composite Thermal Interface Material for Efficient Heat Conduction

Efforts in integrated circuit (IC) packaging technologies have recently been focused on management of increasing heat density associated with high frequency and high density circuit designs. While current flip-chip package designs can accommodate relatively high amounts of heat density, new materials need to be developed to manage thermal effects of next-generation integrated circuits. Multiwall carbon nanotubes (MWNT) have been shown to significantly enhance thermal conduction in the axial direction and thus can be considered to be a candidate for future thermal interface materials by facilitating efficient thermal transport. This work focuses on fabrication and characterization of a robust MWNT-copper composite material as an element in IC package designs. We show that using vertically aligned MWNT arrays reduces interfacial thermal resistance by increasing conduction surface area, and furthermore, the embedded copper acts as a lateral heat spreader to efficiently disperse heat, a necessary function for packaging materials. In addition, we demonstrate reusability of the material, and the absence of residue on the contacting material, both novel features of the MWNT-copper composite that are not found in most state-of-the-art thermal interface materials. Electrochemical methods such as metal deposition and etch are discussed for the creation of the MWNT-Cu composite, detailing issues and observations with using such methods. We show that precise engineering of the composite surface affects the ability of this material to act as an efficient thermal interface material. A thermal contact resistance measurement has been designed to obtain a value of thermal contact resistance for a variety of different thermal contact materials.

Ngo, Quoc↗
NASA NTRS1999

Self-Lubricating Composite Containing Chromium Oxide

A self lubricating. friction and wear reducing composite material useful over a wide temperature range of from cryogenic temperature up to about 900 C. contains 60 80 wt. % of particulate Cr2O3, dispersed in a metal binder of a metal alloy containing Cr and at least 50 wt. % of Ni, Cr or a mature of Ni and Cr. It also contains 5-20 wt. % of a fluoride of at least one Group I, Group II or rare earth metal and. optionally, 5-20 wt. % of a low temperature lubricant metal, such as Ag. Au, Pt, Pd, Rh and Cu. This composite exhibits less oxidation instability and less abrasiveness than composites containing chromium carbide, is readily applied using plasma spray and can be ground and polished with a silicon carbide abrasive.

Dellacorte, Christopher↗
NASA NTRS1977

Observations of O VI

A useful spectroscopic tracer for a hot phase of interstellar gas is the O VI ion, which reaches its maximum concentration in collisional ionization between 100,000 and 1 million K. Presently, over 70 stars have been observed for O VI absorption by the Copernicus satellite. Nearly all of the stars show broad weak lines, but no evidence favoring a circumstellar origin for the gas can be found. An overall average for the electron density of the hot gas in the galactic plane is of the order of 0.001 per cu cm. The relative volume in space occupied by the hot-gas regions (and hence their internal density) is uncertain, but a filling factor in the range from 0.02 to 0.2 seems most plausible. Fluctuations in radial velocities and column densities suggest there are roughly 6 regions per kpc, each with an O VI column density of approximately 10 trillion per sq cm. The observed rms dispersion of radial velocities for these regions is 26 km/s.

Jenkins, E. B.↗
NASA NTRS2001

Aerospace Structural Materials Handbook Supplement GRCop-84

GRCop-84 is a high strength-high conductivity copper-based alloy developed at NASA Glenn Research Center for combustion chamber liners of regeneratively cooled rocket engines. It also has promise for other high heat flux applications operating at temperatures up to 700 C (1292 F) and potentially higher. The alloy must be made by powder metallurgy techniques such as gas atomization. Slower cooling rates such as those experienced during casting do not develop a proper microstructure. Once made into powder, the alloy exhibits excellent processability using conventional consolidation and forming techniques, e.g., extrusion and rolling. GRCop-84 is strengthened by a combination of dispersion and precipitation strengthening by fine (50-500 nanometer (2-20 microinch)) Cr2Nb particles and Hall-Petch strengthening from a fine copper grain size. The presence of a high volume fraction of particles prevents grain boundary sliding at high temperatures and contributes to the alloy's overall good high temperature mechanical properties. Maximum thermal conductivity is obtained by using two alloying elements (Cr, Nb) with limited solubility in solid Cu that form a high temperature intermetallic compound with an even lower solid solubility. The resulting matrix of the alloy is nearly pure copper. The limited solubility also minimizes Cr2Nb particle coarsening at elevated temperatures and enhances microstructural and mechanical property stability. Further enhancement of the microstructural stability is obtained by using a high volume fraction (approx. 14 vol.%) of Cr2Nb particles that effectively pin grain growth.

Ellis, David L.↗