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At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Carbon catalysis of reactions in the lithium SOCl2 and SO2 systems

Certain hazards associated with lithium batteries have delayed widespread acceptance of these power sources. The reactivity of ground lithium carbon mixtures was examined. The effect of carbon types on this reactivity was determined. The basic reaction involved mixtures of lithium and carbon with battery electrolyte. The various parameters that influenced this reactivity included: the nature and freshness of the carbon; the freshness, the purity, and the conductive salt of the electrolyte; and the effect of Teflon or moisture.

Kilroy, W. P.↗
NASA NTRS1980

Carbon fiber production at low temperatures from polyacrylonitrile

Recent safety considerations have sought to lower the electrical conductivity of carbon fibers. Carbon fibers produced from polyacrylonitrile at low carbonization temperatures (600-900 C) possess low electrical conductivity but do not possess adequate strength. Low-temperature processes are described which improve fiber strength but do not increase electrical conductivity substantially. The processes result in a carbon fiber with nearly twice the tensile strength compared to the old process. Process development and its effect on fiber properties are reported.

Cagliostro, D. E.↗
NASA NTRS1981

The abundance and excitation of the carbon chains in interstellar molecular clouds

Emission lines from the carbon chains HC3N, HC5N, HC7N and HC9N were observed at 3 mm, 7 mm, and 1.4 cm in a number of dark clouds, Orion A and IRC(plus)10216. Non-LTE models were constructed to describe excitation and column densities. Component models for the Taurus dark cloud TMC-1 suggested that relative molecular abundances do not vary substantially along the cloud ridge, whereas the H2 density does by a factor of three. Data available for other dark clouds showed that the decrease in abundance with length from one carbon chain to the next is nearly constant, being close to 2.3. The decline in carbon chain abundance with length is steeper in Orion KL than in dark clouds by a factor of approximately four. Abundance ratios derived for the carbon star IRC(plus)10216 are uncertain, due to difficulties in modeling excitation rates in this environment.

Bujarrabal, V.↗
NASA NTRS1981

A far-infrared emission feature in carbon-rich stars and planetary nebulae

The 16-30 micron spectra of several carbon stars and the planetary nebulae IC 418 and NGC 6572 have been obtained using the NASA C-141 Kuiper Airborne Observatory. A newly observed emission feature appears in the spectrum of IRC +10216 and several other carbon stars at wavelengths greater than 24 microns. The feature is interpreted as resulting from a solid-state resonance in the dust grains which have condensed around these stars. A similar feature appears in the spectra of IC 418 and NGC 6572, implying that the same type of dust is present. Since the dust probably condensed from a carbon-rich gas, this indicates an evolutionary link between carbon stars and these planetary nebulae. No identification for the grain material has been found, but some clues are apparent which could aid in the identification.

Forrest, W. J.↗
NASA NTRS1982

Carbon-catalyzed oxidation of SO2 by NO2 and air

A series of experiments was performed using carbon particles (commercial furnace black) as a surrogate for soot particles. Carbon particles were suspended in water, and gas mixtures were bubbled into the suspensions to observe the effect of carbon particles on the oxidation of SO2 by air and NO2. Identical gas mixtures were bubbled into a blank containing only pure water. After exposure each solution was analyzed for pH and sulfate. It was found that NO2 greatly enhances the oxidation of SO2 to sulfate in the presence of carbon particles. The amount of sulfate found in the blanks was significantly less. Under the conditions of these experiments no saturation of the reaction was observed and SO2 was converted to sulfate even in a highly acid medium (pH or = 1.5).

Rogowski, R. S.↗
NASA NTRS1982

Carbon catalyzed SO2 oxidation by NO2 and O3

The oxidation of SO2 to sulfate on carbon particles by trace quantities of NO2 and O3 was studied. Particulate carbon black was either: (1) directly exposed on the pan of a microbalance to various humidified mixtures of SO2 and oxidant gas and the resultant weight gains monitored, or (2) the gas mixtures were bubbled through aqueous suspensions of carbon black and pure water blanks. In each set of experiments the run times were varied appropriately and the yields of sulfate were determined analytically. Conversion of SO2 to sulfate was thus characterized as a function of exposure time and of oxidant gas. Carbon black was determined to be an excellent catalyst for SO2 oxidation to sulfate by both NO2 and O3. No saturation effects were observed in either experimental approach. Conversions of SO2 to sulfate did not appear pH dependent.

Cofer, W. R., III↗
NASA NTRS1983

Stronger Carbon Fibers for Reinforced Plastics

Process makes fibers 70 percent stronger at lower carbonization temperature. Stronger carbon fibers result from benzoic acid pretreatment and addition of acetylene to nitrogen carbonizing atmosphere. New process also makes carbon fibers of higher electrical resistance -- an important safety consideration.

Cagliostro, D. E.↗
NASA NTRS1983

The study of integrated coal-gasifier molten carbonate fuel cell systems

A novel integration concept for a coal-fueled coal gasifier-molten carbonate fuel cell power plant was studied. Effort focused on determining the efficiency potential of the concept, design, and development requirements of the processes in order to achieve the efficiency. The concept incorporates a methane producing catalytic gasifier of the type previously under development by Exxon Research and Development Corp., a reforming molten carbonate fuel cell power section of the type currently under development by United Technologies Corp., and a gasifier-fuel cell recycle loop. The concept utilizes the fuel cell waste heat, in the form of hydrogen and carbon monoxide, to generate additional fuel in the coal gasifier, thereby eliminating the use of both an O2 plant and a stream bottoming cycle from the power plant. The concept has the potential for achieving coal-pile-to-busbar efficiencies of 50-59%, depending on the process configuration and degree of process configuration and degree of process development requirements. This is significantly higher than any previously reported gasifier-molten carbonate fuel cell system.

Source record↗
NASA NTRS1982

Oxidation of SO2 by NO2 and air in an aqueous suspension of carbon

A series of experiments has been performed using carbon black as a surrogate for soot particles. Carbon black was suspended in water and gas mixtures were bubbled into the suspensions to observe the effect of carbon particles on the oxidation of SO2 by air and NO2. Identical gas mixtures were bubbled into a black containing only pure water. After exposure each solution was analyzed for pH and sulfate. It was found that NO2 greatly enhances the oxidation of SO2 to sulfate in the presence of carbon black. The amount of sulfate in the blanks was significantly less. Under the conditions of the experiments no saturation of the reaction was observed and SO2 was converted to sulfate even in a highly acid medium (pH not less than 1.5).

Rogowski, R. S.↗
NASA NTRS1983

The dust around the carbon star IRC +10216

Mass loss from late-type stars is important both in the evolution of these objects and for replenishment of the interstellar medium with processed material. Because the outflows are cool and dense, grains form. The present investigation is concerned with the nature of the extinction of the grains in the carbon star IRC+10216. The basic method employed involves the study of the extinction as a function of wavelength around IRC+10216. By a comparison with different models, it is then possible to infer which grain model is more likely to be correct. It is concluded that the dust around IRC+10216 is composed of relatively small grains. The grains are either amorphous carbon or graphite similar to that described by Mezger et al. (1982), but not like the graphite described by Mitchell and Robinson (1980). In particular, the grains around IRC + 10216 are relatively efficient emitters in the infrared. If this result is true of carbon stars in general, it means that the carbon grains present in the interstellar medium are much cooler than often believed.

Jura, M.↗
NASA NTRS1982

Residual stress in high modulus carbon fibers

The modulus and residual strain in carbon fibers are measured by successively electrochemically milling away the fiber surface. Electrochemical etching is found to remove the carbon fiber surface very uniformly, in contrast to air and wet oxidation. The precision of fiber diameter measurements is improved by using a laser diffraction technique instead of optical methods. More precise diameter measurements reveal that past correlations of diameter and fiber modulus are largely measurement artifact. The moduli of most carbon fibers decrease after the outer layers of the fibers are removed. Owing to experimental difficulties, the moduli and strengths of the fibers at their centers are not determined, and moduli are estimated on the basis of microstructure. The calculated residual stresses are found to be insensitive to these moduli estimates as well as the exact form of regression equation used to describe the moduli and residual strain distributions. Axial compressive residual stresses are found to be very high for some higher modulus carbon fibers. It is pointed out that the compressive stress makes the fibers insensitive to surface flaws when loaded in tension but it may initiate failure by buckling when loaded in compression.

Chen, K. J.↗
NASA NTRS1984

Discovery of the first carbon star in NGC 6822

A new photometric technique has been developed for detecting carbon and M stars in distant stellar systems, leading to isolation of carbon-star candidates in a number of Local-Group galaxies. One of the brighter candidates in NGC 6822 has been confirmed spectroscopically; at a distance of approximately 0.5 Mpc, it is the first truly extragalactic carbon star to be positively identified. The star has M(I) = about -5.7 mag, placing it near the upper-luminosity end of known carbon stars in the Magellanic Clouds.

Aaronson, M.↗
NASA NTRS1984

The effect of tantalum and carbon on the structure/properties of a single crystal nickel-base superalloy

The microstructure, phase chemistry, and creep and hot tensile properties were studied as a function of tantalum and carbon levels in Mar-M247 type single crystal alloys. Microstructural studies showed that several types of carbides (MC, M23C6 and M5C) are present in the normal carbon (0.10 wt % C) alloys after heat treatment. In general, the composition of the MC carbides changes from titanium rich to tantalum rich as the tantalum level in the alloy increases. Small M23C6 carbides are present in all alloys. Tungsten rich M6C carbides are also observed in the alloy containing no tantalum. No carbides are present in the low carbon (0.01 wt % C) alloy series. The morphology of gamma prime is observed to be sensitive to heat treatment and tantalum level in the alloy. Cuboidal gamma prime is present in all the as cast structures. After heat treatment, the gamma prime precipitates tend to have a more spheroidal like morphology, and this tendency increases as the tantalum level decreases. On prolonged aging, the gamma prime reverts back to a cuboidal morphology or under stress at high temperatures, forms a rafted structure. The weight fraction and lattice parameter of the spheroidal gamma prime increases with increasing tantalum content. Changes in the phase chemistry of the gamma prime matrix and gamma prime have also been analyzed using phase extraction techniques. The partitioning ratio decreases for tungsten and aluminum and increases for tantalum as the tantalum content increases for both alloy series; no significant changes occur in the partitioning ratios of the other alloying elements. A reduction in secondary creep rate and an increase in rupture time result from increasing the tantalum content and decreasing the carbon level.

Nguyen, H. C.↗
NASA NTRS1985

Carbon isotopes in bulk carbonaceous chondrites

The chemical and physical processes involved in the formation of the solar system are examined. Primitive matter has been found on a microscopic scale in a variety of meteorites: fragments of small solar system bodies that were never part of a large planet. This primitive matter has, in most cases, been identified by the presence of anomalous abundances of some isotopes of the chemical elements. Of particular interest for carbon isotope studies are the primitive meteorites known as carbonaceous chondrites. Using a selective oxidation technique to sort out the carbon contained in different chemical forms (graphite, carbonates, and organic matter), four carbonaceous chondrites are analyzed. The presence of the (13) C-rich component was confirmed and additional carbon components with different, but characteristic, isotopic signatures were resolved.

Halbout, J.↗
NASA NTRS1985

Potential spin-offs of the carbon dioxide observational platform system (CO-OPS) for remote sensing opportunities

Alternate remote sensing techniques that could utilize the slight losses of energy from the microwave beam which powers the NASA/MSFC Carbon Dioxide Observational Platform System (CO-OPS) to achieve the objectives of the U.S. Department of Energy (DOE) Carbon Dioxide Research Program's regional observational data requirements, ODRs, are addressed heuristically. The opportunity for regional remote sensing of the carbon dioxide and water vapor constituents in the atmosphere are discussed as a potential spin off of the CO-OPS. The CO-OPS is envisioned as a high altitude (approx. 25 km) observational platform system powered by microwave energy for regional observational use by the DOE in their Carbon Dioxide Research Program.

Stephens, J. B.↗
NASA NTRS1985

The chemistry of Li/SOCl2 cells - An ESR study of carbon electrodes

Carbon electrodes from Li/SOCl2 cells were studied by electron spin resonance after various stages of discharge. Different behavior was observed in the temperature-dependent part of the ESR linewidth, defined as 'intrinsic linewidth', Delta H(int), when two different electrolytes were used. With one electrolyte, 1.5M LiAlCl4/SoCl2, the Delta H(int) value stayed constant or slightly decreased whereas with another electrolyte, 1.0M LiAlCl4/14 percent BrClin SOCl2, the value increased as discharge progressed. The carbon electrodes are modified differently during discharge with these two electrolytes, and it is speculated that this may be due to changes in the carbon matrix functional groups. This difference in the carbon electrodes may explain the claimed differences in safety performance of the cells.

Kim, S. S.↗
NASA NTRS1985

Synthesis and properties of copoly(carbonate imides)

Copoly(carbonate imides) with varying amounts of carbonate in the backbone were prepared by reacting 4,4-prime-diaminodiphenyl carbonate and 4,4-prime diaminodiphenyl ether with benzophenonetetracarboxylic acid dianhydride in dimethylacetamide at room temeprature. Homopolymers of the two diamines as well as of 3,4-prime- and 3,3-prime-diaminodiphenyl carbonate were prepared in a similar procedure and their properties compared with those of the copolymers.

Maudgal, S.↗
NASA NTRS1985

Poorly graphitized carbon as a new cosmothermometer for primitive extraterrestrial materials

A description is presented for the most common carbon phase in carbon-rich chondritic porous (CP) aggregate collected from the stratosphere by NASA researchers as part of the Cosmic Dust Program. An extraterrestrial origin was confirmed for the samples by microscopic examinations. The sample grains contained 45 percent carbon-rich phases and 30 percent low-temperature phases. Studies of the d002 interlayer spacing of the carbon clumps indicated that graphitization occurred at metamorphic temperatures after solar nebular condensation, yet early in solar system formation. Graphitized terrestrial materials served as a useful reference against which the CP materials were compared.

Rietmeijer, F. J. M.↗