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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 NTRS1973

Volatile element chemistry of selected lunar, meteoritic, and terrestrial samples

Using vacuum pyrolysis and high resolution mass spectrometry, a study is made of the gas release patterns of representative lunar samples, meteorites, terrestrial samples, and synthetic samples doped with various sources of carbon and nitrogen. The pyrolytic gas evolution patterns were intercorrelated, allowing an assessment of the possible sources of the volatilizable material in the lunar samples to be made. Lightly surface adsorbed species and more strongly chemisorbed species are released from ambient to 300 C and from 300 to 500 C, respectively. The low-temperature volatiles (less than 500 C) derived from various chondrites correlate well with the gas evolution patterns of volatile-rich samples, as for example 74220 and 61221. Solar wind entrapped species and molecules derived from reactions probably in the grain surfaces are evolved from about 500 to 700 C, respectively. Solar wind implanted C, N, and S species are generated from 750 to 1150 C, probably by reaction with the mineral matrix during the annealing process. Possible indigenous and/or refractory carbide, nitride, and sulfide C, N, and S are released in the region from 1200 C to fusion.

Simoneit, B. R.↗
NASA NTRS1986

Secondary-electron-emission losses in multistage depressed collectors and traveling-wave-tube efficiency improvements with carbon collector electrode surfaces

Secondary-electron-emission losses in multistage depressed collectors (MDC's) and their effects on overall traveling-wave-tube (TWT) efficiency were investigated. Two representative TWT's and several computer-modeled MDC's were used. The experimental techniques provide the measurement of both the TWT overall and the collector efficiencies. The TWT-MDC performance was optimized and measured over a wide range of operating conditions, with geometrically identical collectors, which utilized different electrode surface materials. Comparisons of the performance of copper electrodes to that of various forms of carbon, including pyrolytic and iisotropic graphites, were stressed. The results indicate that: (1) a significant improvement in the TWT overall efficiency was obtained in all cases by the use of carbon, rather than copper electrodes, and (2) that the extent of this efficiency enhancement depended on the characteristics of the TWT, the TWT operating point, the MDC design, and collector voltages. Ion textured graphite was found to be particularly effective in minimizing the secondary-electron-emission losses. Experimental and analytical results, however, indicate that it is at least as important to provide a maximum amount of electrostatic suppression of secondary electrons by proper MDC design. Such suppression, which is obtained by ensuring that a substantial suppressing electric field exists over the regions of the electrodes where most of the current is incident, was found to be very effective. Experimental results indicate that, with proper MDC design and the use of electrode surfaces with low secondary-electron yield, degradation of the collector efficiency can be limited to a few percent.

Ramins, P.↗
NASA NTRS1987

Design, fabrication and performance of small, graphite electrode, multistage depressed collectors with 200-W, CW, 8- to 18-GHz traveling-wave tubes

Small multistage depressed collectors (MDC's) which used pyrolytic graphite, ion-beam-textured pyrolytic graphite, and isotropic graphite electrodes were designed, fabricated, and evaluated in conjuntion with 200-W, continuous wave (CW), 8- to 18-GHz traveling-wave tubes (TWT's). The design, construction, and performance of the MDC's are described. The bakeout performance of the collectors, in terms of gas evolution, was indistinguishable from that of typical production tubes with copper collectors. However, preliminary results indicate that some additional radiofrequency (RF) and dc beam processing time (and/or longer or higher temperature bakeouts) may be needed beyond that of typical copper electrode collectors. This is particularly true for pyrolytic graphite electrodes and for TWT's without appendage ion pumps. Extended testing indicated good long-term stability of the textured pyrolytic graphite and isotropic graphite electrode surfaces. The isotropic graphite in particular showed considerable promise as an MDC electrode material because of its high purity, low cost, simple construction, potential for very compact overall size, and relatively low secondary electron emission yield characteristics in the as-machined state. However, considerably more testing experience is required before definitive conclusions on its suitability for electronic countermeasure systems and space TWT's can be made.

Ebihara, Ben T.↗
NASA NTRS2012

Composite with In Situ Plenums

A document describes a high-performance thermal distribution panel (TDP) concept using high-conductivity (greater than 800 W/mK) macro composite skin with in situ heat pipes. The processing technologies proposed to build such a panel result in a one-piece, inseparable assembly with high conductance in both the X and Y planes. The TDP configuration can also be used to produce panels with high structural stiffness. The one-piece construction of the TDP eliminates the thermal interface between the cooling plenums and the heat spreader base, and obviates the need for bulky mounting flanges and thick heat spreaders used on baseline designs. The conductivity of the TDP can be configured to exceed 800 W/mK with a mass density below 2.5 grams per cubic centimeter. This material can provide efficient conductive heat transfer between the in situ heat plenums, permitting the use of thinner panel thicknesses. The plenums may be used as heat pipes, loop heat pipes, or liquid cooling channels. The panel technology used in the TDP is a macro-composite comprised of aluminum-encapsulated annealed pyrolytic graphite (APG). APG is highly aligned crystalline graphite with an in-plane thermal conductivity of 1,700 W/mK. APG has low shear strength and does not constrain the encapsulating material. The proposed concept has no thermal interfaces between the heat pipes and the spreader plate, further improving the overall conductance of the system. The in situ plenums can also be used for liquid cooling applications. The process can be used to fabricate structural panels by adding a second thin sheet.

Montesano, Mark↗
NASA NTRS1980

Silicon halide-alkali metal flames as a source of solar grade silicon

The feasibility of using continuous high-temperature reactions of alkali metals and silicon halides to produce silicon in large quantities and of suitable purity for use in the production of photovoltaic solar cells was demonstrated. Low pressure experiments were performed demonstrating the production of free silicon and providing experience with the construction of reactant vapor generators. Further experiments at higher reagent flow rates were performed in a low temperature flow tube configuration with co-axial injection of reagents and relatively pure silicon was produced. A high temperature graphite flow tube was built and continuous separation of Si from NaCl was demonstrated. A larger scaled well stirred reactor was built. Experiments were performed to investigate the compatability of graphite based reactor materials of construction with sodium. At 1100 to 1200 K none of these materials were found to be suitable. At 1700 K the graphites performed well with little damage except to coatings of pyrolytic graphite and silicon carbide which were damaged.

Olson, D. B.↗
NASA NTRS2002

Thermal and Chemical Characterization of Non-Metallic Materials Using Coupled Thermogravimetric Analysis and Infrared Spectroscopy

Thermogravimetric analysis (TGA) is widely employed in the thermal characterization of non-metallic materials, yielding valuable information on decomposition characteristics of a sample over a wide temperature range. However, a potential wealth of chemical information is lost during the process, with the evolving gases generated during thermal decomposition escaping through the exhaust line. Fourier Transform-Infrared spectroscopy (FT-IR) is a powerful analytical technique for determining many chemical constituents while in any material state, in this application, the gas phase. By linking these two techniques, evolving gases generated during the TGA process are directed into an appropriately equipped infrared spectrometer for chemical speciation. Consequently, both thermal decomposition and chemical characterization of a material may be obtained in a single sample run. In practice, a heated transfer line is employed to connect the two instruments while a purge gas stream directs the evolving gases into the FT-IR. The purge gas can be either high purity air or an inert gas such as nitrogen to allow oxidative and pyrolytic processes to be examined, respectively. The FT-IR data is collected realtime, allowing continuous monitoring of chemical compositional changes over the course of thermal decomposition. Using this coupled technique, an array of diverse materials has been examined, including composites, plastics, rubber, fiberglass epoxy resins, polycarbonates, silicones, lubricants and fluorocarbon materials. The benefit of combining these two methodologies is of particular importance in the aerospace community, where newly developing materials have little available data with which to refer. By providing both thermal and chemical data simultaneously, a more definitive and comprehensive characterization of the material is possible. Additionally, this procedure has been found to be a viable screening technique for certain materials, with the generated data useful in the selection of other appropriate analytical procedures for further material characterization.

Huff, Timothy L.↗
NASA NTRS2001

Thermal and Chemical Characterization of Non-metallic Materials Using Coupled Thermogravimetric Analysis and Infrared Spectroscopy

Thermogravimetric analysis (TGA) is widely employed in the thermal characterization of non-metallic materials, yielding valuable information on decomposition characteristics of a sample over a wide temperature range. However, a potential wealth of chemical information is lost during the process, with the evolving gases generated during thermal decomposition escaping through the exhaust line. Fourier Transform-Infrared spectroscopy (FT-IR) is a powerful analytical technique for determining many chemical constituents while in any material state, in this application, the gas phase. By linking these two techniques, evolving gases generated during the TGA process are directed into an appropriately equipped infrared spectrometer for chemical speciation. Consequently, both thermal decomposition and chemical characterization of a material may be obtained in a single sample run. In practice, a heated transfer line is employed to connect the two instruments while a purge gas stream directs the evolving gases into the FT-IR, The purge gas can be either high purity air or an inert gas such as nitrogen to allow oxidative and pyrolytic processes to be examined, respectively. The FT-IR data is collected real-time, allowing continuous monitoring of chemical compositional changes over the course of thermal decomposition. Using this coupled technique, an array of diverse materials has been examined, including composites, plastics, rubber, fiberglass epoxy resins, polycarbonates, silicones, lubricants and fluorocarbon materials. The benefit of combining these two methodologies is of particular importance in the aerospace community, where newly developing materials have little available data with which to refer. By providing both thermal and chemical data simultaneously, a more definitive and comprehensive characterization of the material is possible. Additionally, this procedure has been found to be a viable screening technique for certain materials, with the generated data useful in the selection of other appropriate analytical procedures for further material characterization.

Huff, Timothy L.↗
NASA NTRS2002

Characterization of C/SiC Ceramic Matrix Composites (CMCs) with Novel Interface Fiber Coatings

Ceramic Matrix Composites (CMCs) are attractive candidate aerospace materials due to their high specific strength, low density and high temperature capabilities. The National Aeronautics and Space Administration (NASA) is pursuing the use of CMC components in advanced Reusable Launch Vehicle (RLV) propulsion applications. Carbon fiber-reinforced silicon carbide (C/SiC) is the primary material of interest for a variety of RLV propulsion applications. These composites consist of high-strength carbon fibers and a high modulus, oxidation resistant matrix. For RLV propulsion applications, environmental durability will be critical. Two types of carbon fibers were processed with both standard (pyrolytic carbon) and novel (multilayer and pseudoporous) types of interface coatings as part of a study investigating various combinations of constituents. The benefit of protecting the composites with a surface sealant was also investigated. The strengths, durability in oxidizing environments, and microstructures of these developmental composite materials are presented. The novel interface coatings and the surface sealant show promise for protecting the carbon fibers from the oxidizing environment.

Petko, Jeanne F.↗
NASA NTRS1981

Adhesion and friction of transition metals in contact with nonmetallic hard materials

Sliding friction experiments were conducted with the metals yttrium, titanium, tantalum, zirconium, vanadium, neodymium, iron, cobalt, nickel, tungsten, platinum, rhenium, ruthenium, and rhodium in sliding contact with single crystal diamond, silicon carbide, pyrolytic boron nitride, and ferrite. Auger electron spectroscopy analysis was conducted with the metals and nonmetals to determine the surface chemistry and the degree of surface cleanliness. The results of the investigation indicate the adhesion and friction of the transition metals in contact with diamond, silicon carbide, boron nitride, and ferrite are related to the relative chemical activity of the metals. The more chemically active the metal, the higher the coefficient of friction and the greater amount of transfer to the nonmetals.

Miyoshi, K.↗
NASA NTRS1983

Ion sputter textured graphite electrode plates

A specially textured surface of pyrolytic graphite exhibits extremely low yields of secondary electrons and reduced numbers of reflected primary electrons after impingement of high energy primary electrons. Electrode plates of this material are used in multistage depressed collectors. An ion flux having an energy between 500 iV and 1000 iV and a current density between 1.0 mA/sq cm and 6.0 mA/sq cm produces surface roughening or texturing which is in the form of needles or spires. Such textured surfaces are especially useful as anode collector plates in high tube devices.

Curren, A. N.↗
NASA NTRS1985

Multistage spent particle collector and a method for making same

A description is given of a spent particle collector which maintains structural integrity when raised to a high temperature although constructed of materials having widely different coefficients of expansion. The collector is comprised of one or more axisymmetric stages, each stage comprising a subassembly. A subassembly includes an inner pyrolytic graphite ring, a transition ring, a ceramic insulator ring and an outer metal ring which forms part of the wall of the collector. Each transition is of a ductile metal having high thermal conductivity and is provided with an annular sputter shield wall extending toward the source of spent particles and, where necessary, a trough in the other surface to enclose the sputter shield of the next adjacent transition ring. A plurality of radial extending slots are provided in a transition ring to form segments which are retained in their position by the sputter shield.

Ebihara, B. T.↗
NASA NTRS1992

An isotopic biogeochemical study of the Green River oil shale

Thirty-five different samples from three different sulfur cycles were examined in this stratigraphically oriented study of the Shell 22x-l well (U.S.G.S. C177 core) in the Piceance Basin, Colorado. Carbon isotopic compositions of constituents of Green River bitumens indicate mixing of three main components: products of primary photoautotrophs and their immediate consumers (delta approximately -30% vs PDB), products of methanotrophic bacteria (delta approximately -85%), and products of unknown bacteria (delta approximately -40%). For individual compounds synthesized by primary producers, delta-values ranged from -28 to -32%. 13C contents of individual primary products (beta-carotane, steranes, acyclic isoprenoids, tricyclic triterpenoids) were not closely correlated, suggesting diverse origins for these materials. 13C contents of numerous hopanoids were inversely related to sulfur abundance, indicating that they derived both from methanotrophs and from other bacteria, with abundances of methanotrophs depressed when sulfur was plentiful in the paleoenvironment. gamma-Cerane coeluted with 3 beta(CH3),17 alpha(H),21 beta(H)-hopane, but delta-values could be determined after deconvolution. gamma-Cerane (delta approximately -25%) probably derives from a eukaryotic heterotroph grazing on primary materials, the latter compound (delta approximately -90%) must derive from methanotrophic organisms. 13C contents of n-alkanes in bitumen differed markedly from those of paraffins generated pyrolytically. Isotopic and quantitative relationships suggest that alkanes released by pyrolysis derived from a resistant biopolymer of eukaryotic origin and that this was a dominant constituent of total organic carbon.

Non-NASA Center↗
NASA NTRS1979

Silicon Halide-alkali Metal Flames as a Source of Solar Grade Silicon

A program is presented which was aimed at determining the feasibility of using high temperature reactions of alkali metals and silicon halides to produce low cost solar-grade silicon. Experiments are being conducted to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, and determine the effects of the reactants and/or products on materials of reactor construction. During the current reporting period, the results of heat release experiments were used to design and construct a new type of thick-wall graphite reactor to produce larger quantities of silicon. A reactor test facility was constructed. Material compatibility tests were performed for Na in contact with graphite and several coated graphites. All samples were rapidly degraded at T = 1200K, while samples retained structural strength at 1700K. Pyrolytic graphite coatings cracked and separated from substances in all cases.

Olson, D. B.↗
NASA NTRS1993

Modeling Thermodynamics Of Charring Of A Polymer

Improved method of predicting and of nondestructively analyzing pyrolytic effects in, and thermomechanical properties of, polymers combines theories and techniques from several engineering and scientific disciplines. Evolved in effort to understand charring and erosion of carbon phenolic ablative material in nozzle of rocket engine. Also applicable to other polymers and particularly to nondestructive engineering analysis of specimens heated, charred, or burned.

Funaro, Gregory V.↗
NASA NTRS1972

An evaluation of pyrolytic techniques with regard to the Apollo 11, 12 and 14 lunar samples analyses.

The first technique involved pyrolysis at 700 C under an inert atmosphere in a flowing He system at normal pressure. The products were collected at liquid nitrogen temperature and then allowed to pass instantaneously into a combined capillary gas chromatograph-mass spectrometer. The second technique consisted of a vacuum pyrolysis where the sample was first degassed at 150 C and then pyrolized at 500 C and 1000 C consecutively. The products were again collected at liquid nitrogen temperature and then they were directly introduced to the ion source of the mass spectrometer through a modified gas inlet system. The experiments have shown the importance of taking into account the factors that influence pyrolytic degradation and/or the synthesis of products. Pyrolysis of Apollo 14 lunar fines and scrapings from an astronaut's glove gave different products by mass spectroscopy and showed different looking flaky materials upon scanning electron microscopy.

Nagy, B.↗
NASA NTRS1976

The pyrolytic release experiment - Measurement of carbon assimilation

The pyrolytic release experiment or carbon assimilation experiment is one of the three modules in the biology instrument on the 1976 Viking landers, which aims at detecting microbial life in Martian surface materials. The paper examines this experiment relative to the scientific assumptions in developing the test, the laboratory investigation supporting the experimental concept, and the operation and testing of the flight instrument. The only assumptions made are that the Martian species are adapted to function in their arid environment and that atmospheric CO2 or CO are assimilated by the species. Although the test is primarily designed to measure photoassimilation of CO2 or CO, the assimilation of these gases in heterotrophic or chemolithotrophic metabolism could also be detected. A new possibility for a carbon cycle on Mars is discussed.

Hubbard, J. S.↗
NASA NTRS2001

Detached Bridgman Growth of Germanium and Germanium-Silicon Alloy Crystals

Earth based experiments on the science of detached crystal growth are being conducted on germanium and germanium-silicon alloys (2at% Si average composition) in preparation for a series of experiments aboard the International Space Station (ISS) to differentiate among proposed mechanisms contributing to detachment. Sessile drop measurements were first carried out for a large number of substrates made of potential ampoule materials to determine the contact angles and the surface tension as a function of temperature and composition. The process atmosphere and duration of the experiment (for some cases) were also found to have significant influence on the wetting angle. Growth experiments have used pyrolytic boron nitride (pBN) and fused silica ampoules with the majority of the detached results occurring predictably in the pBN. The contact angles were 173 deg (Ge) and 165 deg (GeSi) for pBN. For fused silica, the contact angle decreases to an equilibrium value with duration of measurement ranging from 150 to 117 deg (Ge), 129 to 100 deg (GeSi). Forming gas (Ar + 2% H2) and vacuum have been used in the growth ampoules. With gas in the ampoule, a variation of the temperature profile during growth has been used to control the pressure difference between the top of the melt and the volume below the melt caused by detachment of the growing crystal. The stability of detachment has been modeled and substantial insight has been gained into the reasons that detachment has most often been observed in reduced gravity but nonetheless has occurred randomly even there. An empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed and will be presented. Methods for determining the nature and extent of detachment include profilometry and optical and electron microscopy. This surface study is the subject of another presentation at this Congress. Results in this presentation will show that we have established the effects of different ampoule materials, temperature profiles, pressure differences, and silicon concentrations and that samples that are nearly completely detached can be grown repeatedly.

Szofran, F. R.↗
NASA NTRS2010

MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis

Atomic oxygen erosion of polymers in low Earth orbit (LEO) poses a serious threat to spacecraft performance and durability. To address this, 40 different polymer samples and a sample of pyrolytic graphite, collectively called the PEACE (Polymer Erosion and Contamination Experiment) Polymers, were exposed to the LEO space environment on the exterior of the International Space Station (ISS) for nearly 4 years as part of the Materials International Space Station Experiment 1 & 2 (MISSE 1 & 2). The purpose of the PEACE Polymers experiment was to obtain accurate mass loss measurements in space to combine with ground measurements in order to accurately calculate the atomic oxygen erosion yields of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time. Error calculations were performed in order to determine the accuracy of the mass measurements and therefore of the erosion yield values. The standard deviation, or error, of each factor was incorporated into the fractional uncertainty of the erosion yield for each of three different situations, depending on the post-flight weighing procedure. The resulting error calculations showed the erosion yield values to be very accurate, with an average error of 3.30 percent.

McCarthy, Catherine E.↗