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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Dissociation of CH4 by electron impact: Production of metastable hydrogen and carbon fragments

Metastable fragments produced by electron impact excitation of CH4 have been investigated for incident electron energies from threshold to 300 eV. Only metastable hydrogen and carbon atoms were observed. Onset energies for the production of metastable hydrogen atoms were observed at electron impact energies of 22.0 + or - .5 eV, 25.5 + or - .6 eV, 36.7 + or - .6 eV and 66 + or - 3 eV, and at 26.6 + or - .6 eV for the production of metastable carbon atoms. Most of the fragments appear to have been formed in high-lying Rydberg states. The total metastable hydrogen cross section reaches a maximum value of approximately 1 X 10 to the minus 18th power sq cm at 100 eV. At the same energy, the metastable carbon cross section is 2 x 10 to the minus 19th power sq cm.

Finn, T. G.↗
NASA NTRS1973

The remote measurement of trace atmospheric species by correlation interferometry. I - Carbon monoxide and methane

A correlation interferometer has been developed for the measurement of carbon monoxide and methane at 2.35 micrometers in the troposphere and in the stratosphere. This instrument has been tested in laboratory tests, solar-looking outdoor tests, and downward-looking airplane-based tests. The aircraft tests were flown on a Falcon fanjet provided by The Canada Centre for Remote Sensing over both polluted and unpolluted regions of North America. The results of these various tests are discussed. Based on the results obtained for carbon monoxide and methane, a study was undertaken to investigate the feasibility of measuring other atmospheric trace species by correlation interferometry. Results of the feasibility study for carbon dioxide, water vapor, ammonia, nitrous oxide, nitric oxide, nitrogen dioxide, sulfur dioxide, and several hydrocarbons are presented.

Goldstein, H. W.↗
NASA NTRS1974

On the relation between carbon star spectral types and colors

Observations of 32 carbon stars are listed in a table, taking into account the spectral classes given by Yamashita (1966) and Richer (1971). The relations between spectral type and color for carbon stars appear consistent with the differences between Yamashita's and Richer's types if carbon star groups I-III lie on a decreasing boundary temperature sequence.

Honeycutt, R. K.↗
NASA NTRS1975

Performance of a hypersonic hot fuselage structure with a carbon dioxide frost projected, nonintegral cryogenic tank

A model which consisted of a hot structure and a nonintegral tank protected by a carbon dioxide frost thermal protection system was tested under the following conditions: (1) room temperature loading and (2) heating and loading corresponding to the Mach 8 flight of an air-breathing launch vehicle. In the simulated flight tests, liquid nitrogen inside the tank was withdrawn at the rate fuel would be consumed. Prior to each simulated flight test, carbon dioxide was cryodeposited in the insulation surrounding the tank; during the tests, subliming CO2 frost absorbed heat and provided a purge gas for the space between the tank and the structure. A method of flame spraying the joints between panels with a nickel-aluminum material was developed to prevent excessive leakage of the purge gas through the outer structure. The tests indicated that the hot structure (with a joint repaired by riveting), the nonintegral tank and suspension system, and the carbon dioxide frost thermal protection system provide a workable concept with predictable performance.

Sharpe, E. L.↗
NASA NTRS1975

Friction and wear of carbon-graphite materials for high energy brakes

Caliper-type brakes simulation experiments were conducted on seven different carbon-graphite material formulations against a steel disk material and against a carbon-graphite disk material. The effects of binder level, boron carbide (B4C) additions, graphite fiber additions, and graphite cloth reinforcement on friction and wear behavior were investigated. Reductions in binder level and additions of B4C each resulted in increased wear. The wear rate was not affected by the addition of graphite fibers. Transition to severe wear and high friction was observed in the case of graphite-cloth-reinforced carbon sliding against a disk of similar composition. This transition was related to the disruption of a continuous graphite shear film that must form on the sliding surfaces if low wear is to occur. The exposure of the fiber structure of the cloth constituent is believed to play a role in the shear film disruption.

Bill, R. C.↗
NASA NTRS1974

Simulation of lunar carbon chemistry. I - Solar wind contribution

Simulation experiments were conducted to identify the role of solar and lunar winds in the evolution of lunar carbon chemistry. Major conclusions are that (1) implantation of solar wind C, D, and N ions in silicates synthesizes small molecules that can be released into vacuum either by ion sputtering or by heating; (2) this synthesis is highly specific when compared to other processes accounting for the formation of molecules in the solar nebula or in interstellar space; (3) the carbon injected by the solar wind in the crystalline component of mature soils should reach a saturation concentration of about 200 ppm; and (4) the carbon chemistry of the crystalline component of mature soils is dominated by solar wind implantation effects.

Bibring, J. P.↗
NASA NTRS1974

Simulation of lunar carbon chemistry. II - Lunar winds contribution

Simulation experiments, computations, and analysis of glassy agglutinates show that a directly condensed lunar wind vapor phase is strongly depleted in carbon and sulfur compounds and may recrystallize rapidly in the lunar thermal cycle and separate from host crystals. Factors preventing identification of low-energy species implanted from the lunar atmosphere are discussed. Computational results indicate that the implanted lunar winds carbon originates both from the vapor phases injected into the lunar atmosphere during thermal metamorphism of mature lunar soil grains and from direct volatization of impacting micrometeorites. It is suggested that microglass splashes and tiny crystalline grains possibly attached to the surface of coarser grains do not affect the characteristics of solar wind carbon chemistry in the lunar soil.

Bibring, J. P.↗
NASA NTRS1975

Dissociation of CH4 and CD4 by electron impact - Production of metastable and high-Rydberg hydrogen and carbon fragments

Production of hydrogen and carbon atoms in metastable and high-lying Rydberg states by electron-impact dissociation of methane and deuterated methane is investigated for incident electron energies ranging from threshold values to 300 eV. Threshold energies for five different processes resulting in metastable hydrogen and carbon atoms are determined in the energy range from 20 to 70 eV, and it is shown that metastable hydrogen atoms are produced in four of these collisional processes while metastable carbon atoms are produced in the other. The nature of each collisional process is described, differential cross sections are derived for the dissociative excitation of both types of atoms to metastable and high-Rydberg states at 100 eV, and the onset energy for UV photon production is measured. Much of the data is interpreted in terms of the ion core model suggested by Kupriyanov (1968) and developed by Freund (1971).

Finn, T. G.↗
NASA NTRS1975

On the lower mass limit for the carbon detonation scenario

The lower mass limit for carbon detonation (about 4 solar masses) is due to an argument by Paczynski (1970) that stars in the range between 1.4 and 3.5 solar masses will lose their envelopes prior to carbon detonation. This argument is based on two criteria for mass loss: (1) the envelope is unstable to adiabatic oscillations, and (2) the total energy of the envelope is positive. Recent hydrodynamic calculations of red-giant envelopes have shown that the envelopes are highly nonadiabatic and that the second criterion is not a sufficient condition for mass loss. Thus, a calculation which takes into account the nonadiabatic nature of the envelope is required in order to determine the lower mass limit for carbon detonation. This lower mass limit is directly related to the formation mechanisms and statistics of supernovae and pulsars.

Endal, A. S.↗
NASA NTRS1977

Less-costly activated carbon for sewage treatment

Lignite-aided sewage treatment is based on absorption of dissolved pollutants by activated carbon. Settling sludge is removed and dried into cakes that are pyrolyzed with lignites to yield activated carbon. Lignite is less expensive than activated carbon previously used to supplement pyrolysis yield.

Ingham, J. D.↗
NASA NTRS1975

A new solar carbon abundance based on non-LTE CN molecular spectra

A detailed non-LTE analysis of solar CN spectra strongly suggest a revised carbon abundance for the sun. We recommend a value of log carbon abundance = 8.35 plus or minus 0.15 which is significantly lower than the presently accepted value of log carbon abundance = 8.55. This revision may have important consequences in astrophysics.

Mount, G. H.↗
NASA NTRS1975

Large diameter carbon-boron fiber

Investigations concerned with a development of large-diameter carbon fibers are considered, taking into account the employment of vapor deposition techniques. In the experiments a carbon monofilament substrate is used together with reacting gases which consist of combinations of hydrogen, methane, and boron trichloride. It is found that the described approach can be used to obtain a large-diameter carbon filament containing boron. The filament has reasonable strength and modulus properties.

Veltri, R. D.↗
NASA NTRS1976

Venus - Microwave detection of carbon monoxide

The 115-gigahertz microwave line of carbon monoxide has been detected in the spectrum of Venus. The measurement proves that the carbon monoxide mixing ratio increases above an altitude of 85 kilometers in the Venus stratosphere and provides quantitative information on carbon monoxide in the altitude region from 80 to 110 kilometers. This altitude region is well above that which has been previously sensed.

Kakar, R. K.↗
NASA NTRS1976

Microwave measurement of mesospheric carbon monoxide

Ground-based observations of atmospheric absorption of solar radiation at a wavelength of 2.6 millimeters has provided the first measurement of mesospheric carbon monoxide. The measurement agrees with photochemical predictions of a carbon monoxide source in the lower thermosphere due to dissociation of carbon dioxide by solar radiation, and has implications for the magnitude of vertical transport in the mesosphere.

Waters, J. W.↗
NASA NTRS1976

The carbon monoxide abundance in interstellar clouds

The steady-state abundance of carbon monoxide in interstellar clouds is calculated as a function of optical depth, density, and temperature. The molecular reactions which lead to CO can be initiated by the following ion-molecule reactions: H(+) + O yields O(+) + H, C(+) + H2 yields CH2(+) + a photon, and H3(+) + C and O. As the ultraviolet radiation field is attenuated, C(+) is transformed primarily into CO and C I. There are characteristic column densities for the transition to CO corresponding to the optical depths for attenuating this field at different wavelengths. For thick, low-temperature clouds the attenuation of the fields which ionize carbon, sulfur, and heavy metals is important for CO production initiated by H3(+). Complete conversion to CO does not necessarily occur, and considerable neutral carbon may be expected even in optically thick clouds. Comparison of integrated column densities of CO with extinction are in reasonable agreement with observations.

Langer, W.↗
NASA NTRS1977

Development of a prototype regeneration carbon dioxide absorber

A prototype regenerable carbon dioxide absorber was developed to maintain the environmental quality of the portable life support system. The absorber works on the alkali metal carbonate-bicarbonate solid-gas reaction to remove carbon dioxide from the atmosphere. The prototype sorber module was designed, fabricated, and tested at simulated extravehicular activity conditions to arrive at optimum design. The unit maintains sorber outlet concentration below 5 mm Hg. An optimization study was made with respect to heat transfer, temperature control, sorbent utilization, sorber life and regenerability, and final size of the module. Important parameters influencing the capacity of the final absorber unit were identified and recommendations for improvement were made.

Patel, P. S.↗
NASA NTRS1978

Friction and wear of carbon-graphite materials for high-energy brakes

Caliper type brake simulation experiments were conducted on seven different carbon graphite materials formulations against a steel disk material and against a carbon graphite disk material. The effects of binder level, boron carbide (B4C) additions, SiC additions, graphite fiber additions, and graphite cloth reinforcement on friction and wear behavior were investigated. Reductions in binder level, additions of B4C, and additions of SiC each resulted in increased wear. The wear rate was not affected by the addition of graphite fibers. Transition to severe wear and high friction was observed in the case of graphite-cloth-reinforced carbon sliding against a disk of similar composition. The transition was related to the disruption of a continuous graphite shear film that must form on the sliding surfaces if low wear is to occur.

Bill, R. C.↗
NASA NTRS1978

Low density bismaleimide-carbon microballoon composites

A process is described for constructing for a composite laminate structure which exhibits a high resistance to heat and flame provides safer interior structures for aircraft and submarine compartments. Composite laminate structures are prepared by the bismaleimide resin preimpregnation of a fiberglass cloth to form a face sheet which is bonded with a bismaleimide hot melt adhesive to a porous core structure selected from the group consisting of polyamide paper and bismaleimide-glass fabric which is filled with carbon microballoons. The carbon microballoons are prepared by pyrolyzing phenolic micro-balloons in the presence of nitrogen. A slurry of the carbon microballoons is prepared to fill the porous core structure. The porous core structure and face sheet are bonded to provide panel structures exhibiting increased mechanical capacities and lower oxygen limit values and smoke density values.

Kourtides, D. A.↗