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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Rate constant for the reaction between OH and CS2 at 298 and 520 K

In an attempt to resolve discrepancies between published values of the rate constant for the reaction between the hydroxyl radical and carbon disulfide, the reaction has been studied in a discharge flow system by using resonance fluorescence for kinetic measurements and mass spectrometry for product analysis. On the basis of the measured rate constant for disappearance of OH, and measurements of the amount of carbonyl sulfide formed, it was estimated that for the reaction HO + CS2 yields HS + OCS, rate constant values are not greater than 3 x 10 to the -15th/cu cm per sec at 520 K and not greater than 7 x 10 to the -15th/cu cm per sec at 298 K, upper limits are specified because of the inability to isolate exclusively this reaction channel, and because of possible involvement of wall reactions. These results confirm the low values found for this rate constant in two very recent studies.

Leu, M.-T.↗
NASA NTRS1982

Fluorescence yields from photodissociation of OCS at 1060-1240 A

The cross sections for the production of fluorescence (3000-8000 A) from excited photofragments of OCS were determined in order to gain a better understanding of the role of carbonyl sulfide in interstellar photochemistry. Synchrotron radiation was used as the light source for the measurements in the 1060-1240 A region, as it is suitable for measuring the absorption cross section in the structured region. It was found that the quantum yields for the production of various CO triplet states are less than 1.5% at the observed excitation photon wavelengths.

Lee, L. C.↗
NASA NTRS1985

Spectroscopic analysis of radiation-generated changes in tensile properties of a polyetherimide film

The effects of electron radiation on Ultem, a polyetherimide were studied for doses from 2 x 10 to the 9th power to 6 x 10 to the 9th power rad. Specimens were studied for tensile property testing and for electron paramagnetic resonance and infrared spectroscopic measurements of molecular structure. A Faraday cup design and a method for remote temperature measurement were developed. The spectroscopic data show that radiation caused dehydrogenation of methyl groups, rupture of main-chain ether linkage, and opening of imide rings, all to form radicals and indicate that the so-formed atomic hydrogen attached to phenyl radicals, but not to phenoxyl radicals, which would have formed hydroxyls. The observed decays of the radiation-generated phenoxyl, gem-dimethyl, and carbonyl radicals were interpreted as a combining of the radicals to form crosslinking. This crosslinking is the probable cause of the major reduction in the elongation of the tensile specimens after irradiation. Subsequent classical solubility tests indicate that the irradiation caused massive crosslinking.

Long, E. R., Jr.↗
NASA NTRS1986

Effect of impregnation method on cycle life of the nickel electrode

The nickel electrode has been identified as the life limiting component for individual pressure vessel (IPV) nickel-hydrogen cells when cycled under a low earth orbit (LEO) cycle regime at deep depths of discharge. As a part of an overall program to develop a long life nickel electrode for nickel-hydrogen cells, the effect of two different methods of electrochemical impregnation on the cycle life of the nickel electrode was investigated. One method was the Pickett (aqueous/ethanolic) process. The other was the modified Bell (aqueous) process. The plaques for both impregnation methods were made by sintering dry carbonyl nickel powder in a reducing atmosphere. The plaques contain a nickel screen substrate. Electrodes made from both processes were cycle tested in Air Force design IPV nickel-hydrogen cells. The only factor different for this test was the method of plaque impregnation; all other factors were the same. The cells were cycled to failure under a 90 min LEO cycle regime at a deep depth of discharge (80 percent DOD). Failure for this test was defined to occur when the cell voltage degraded to 1.0 V prior to the completion of the 35 min discharge.

Smithrick, J. J.↗
NASA NTRS1985

Analysis of TQCM surface contamination adsorbed during the Spacelab I Mission

The Temperature-Controlled Quartz Crystal Microbalance (TQCM) system was flown on the Spacelab I Mission as part of the Induced Environment Contamination Monitor to monitor surface contamination (SC) in the payload bay. SC on the five sensors of the TQCM was analyzed by means of IR spectroscopy, scanning electron spectroscopy, and energy dispersive X-ray fluorescence. The amount of SC ranged from 1.4 micrograms/sq cm for the -Z sensor to 39.9 micrograms/sq cm for the +X sensor. The IR analysis showed strong CH2, CH3, and carbonyl absorption bands, indicative of ester and polyester compounds found in adhesives, plasticizers, and tape. The particulates (mostly ranging from 1 micron to 20 microns in size) were mainly composed of Mg, Al, Al2O3, and Si, and probably originated in the solid rocket firings.

Mckeown, D.↗
NASA NTRS1986

UV laser deposition of metal films by photogenerated free radicals

A novel photochemical method for liquid-phase deposition of metal films is described. In the liquid phase deposition scheme, a metal containing compound and a metal-metal bonded carbonyl complex are dissolved together in a polar solvent and the mixture is irradiated using a UV laser. The optical arrangement consists of a HeCd laser which provides 7 mW of power at a wavelength of 325 nm in the TEM(OO) mode. The beam is attenuated and may be expanded to a diameter of 5-20 mm. Experiments with photochemical deposition of silver films onto glass and quartz substrates are described in detail. Mass spectrometric analysis of deposited silver films indicated a deposition rate of about 1 A/s at incident power levels of 0.01 W/sq cm. UV laser-induced copper and palladium films have also been obtained. A black and white photograph showing the silver Van Der Pauw pattern of a solution-deposited film is provided.

Montgomery, R. K.↗
NASA NTRS1985

Toward a spartan scenario for use of lunar materials

The present discussion has the objective to identify those raw materials for use in manufacture which can most readily be obtained from lunar materials as they are currently known. The state of lunar exploration is incomplete, and concentrated ores may exist for elements now regarded as rare or dispersed. This paper provides a description of minimum possibilities, based on the notion of making do with the least feasible amounts of separation and processing. The discussion is limited to the most abundant materials observed at lunar sites visited by the Apollo missions. The ground rules for use of lunar products are considered along with the tools required to carry out any significant production of raw materials for manufacture, and lunar surface conditions. Readily available materials include unprocessed regolith and minimally processed regolith. A few examples of processing methods are provided, giving attention to thermal release of gases, hydrogen reduction of ilmenite, carbonyl processing, electrolysis of molten silicate, and destructive distillation.

Haskin, L. A.↗
NASA NTRS1986

Toughening mechanisms in elastomer-modified epoxies. I - Mechanical studies. II - Microscopy studies

Tensile dilatometry at constant displacement rates is presently used to ascertain whether voiding, crazing or shear banding are the deformation mechanisms at work in the toughening of brittle epoxies through the addition of an elastomeric phase. The results obtained for epoxies toughened by various levels of several types of carbonyl-terminated butadiene nitrile liquid rubber indicate that, at low strain rates, the rubber particles simply enhance shear deformation; at sufficiently high strain rates, the particles cavitate and promote further shear deformation. Examinations of these materials are conducted by means of SEM, TEM, and optical microscopy in the second part of this study. Toughening is hypothesized to involve cavitation's relieving of triaxial tension at the crack tip, as well as shear band formation, which creates a plastic zone.

Yee, A. F.↗
NASA NTRS1986

Effect of impregnation method on cycle life of the nickel electrode

The nickel electrode has been identified as the life limiting component for individual pressure vessel (IPV) nickel-hydrogen cells when cycled under a low earth orbit (LEO) cycle regime at deep depths of discharge. As a part of an overall program to develop a long life nickel electrode for nickel-hydrogen cells, the effect of two different methods of electrochemical impregnation on the cycle life of the nickel electrode was investigated. One method was the Pickett (aqueous/ethanolic) process. The other was the modified Bell (aqueous) process. The plaques for both impregnation methods were made by sintering dry carbonyl nickel powder in a reducing atmosphere. The plaques contain a nickel screen substrate. Electrodes made from both processes were cycle tested in Air Force design IPV nickel-hydrogen cells. The only factor different for this test was the method of plaque impregnation; all other factors were the same. The cells were cycled to failure under a 90 min LEO cycle regime at a deep depth of discharge (80 percent DOD). Failure for this test was defined to occur when the cell voltage degraded to 1.0 V prior to the completion of the 35 min discharge.

Smithrick, J. J.↗
NASA NTRS1987

Polyether-polyester graft copolymer

Described is a polyether graft polymer having improved solvent resistance and crystalline thermally reversible crosslinks. The copolymer is prepared by a novel process of anionic copolymerization. These polymers exhibit good solvent resistance and are well suited for aircraft parts. Previous aromatic polyethers, also known as polyphenylene oxides, have certain deficiencies which detract from their usefulness. These commercial polymers are often soluble in common solvents including the halocarbon and aromatic hydrocarbon types of paint thinners and removers. This limitation prevents the use of these polyethers in structural articles requiring frequent painting. In addition, the most popular commercially available polyether is a very high melting plastic. This makes it considerably more difficult to fabricate finished parts from this material. These problems are solved by providing an aromatic polyether graft copolymer with improved solvent resistance and crystalline thermally reversible crosslinks. The graft copolymer is formed by converting the carboxyl groups of a carboxylated polyphenylene oxide polymer to ionic carbonyl groups in a suitable solvent, reacting pivalolactone with the dissolved polymer, and adding acid to the solution to produce the graft copolymer.

Bell, Vernon L.↗
NASA NTRS1987

Ketimine modifications as a route to novel amorphous and derived semicrystalline poly(arylene ether ketone) homo- and copolymers

A series of amine terminal amorphous poly(arylene ether ketone) oligomers of controlled molecular weights (2-15 K) were synthesized. These oligomers have been found to undergo 'self-crosslinking' reactions upon heating above 220 C, via the reaction of the terminal amine groups with the in-chain keto carbonyl functionalities. The resulting networks are ductile, chemically resistant, and nonporous. The networks obtained via generated ketimine functionality were characterized by solid state NMR. They have also been found to be remarkably stable toward hydrolysis. Ketimine functional bishalide monomers have also been synthesized. Such monomers have been utilized to synthesize a wide variety of amorphous poly(arylene ether) ketimine polymers. A high molecular weight hydroquinone functional poly(arylene ether) ketimine has been acid treated to regenerate a poly(arylene ether ketone) backbone in solution. This novel procedure thus allows for the synthesis of important matrix resins under relatively mild conditions.

Mohanty, D. K.↗
NASA NTRS1988

FTIR characterization of thermally cycled PMR-15 composites

Chemical characterization results are presented for a variety of PMR-15/graphite composites, differentiated according to prepreg types and cure cycles, which were subjected to 1000 thermal cycles between 0 and 450 F. Fourier transform IR spectroscopy was used in conjunction with diffuse reflectance sampling to examine whether changes in the matrix resin chemistry due to environmental exposure may have contributed to microcracking. Analysis based on compound spectra revealed behavior associated with the oxidation of methylene groups to carbonyl groups on the composite surface; evidence of crosslinking also emerged, although the two phenomena do not appear to be related.

Young, Philip R.↗
NASA NTRS1989

Advances in lightweight nickel electrode technology

Studies are currently underway to further the development of lightweight nickel electrode technology. Work is focused primarily on the space nickel-hydrogen system and nickel-iron system but is also applicable to the nickel-cadmium and nickel-zinc systems. The goal is to reduce electrode weight while maintaining or improving performance thereby increasing electrode energy density. Two basic electrode structures are being investigated. The first is the traditional nickel sponge produced from sintered nickel-carbonyl powder and the second is a new material for this application which consists of a non-woven mat of nickel fiber. Electrodes are being manufactured, tested and evaluated at the electrode and cell level.

Coates, Dwaine↗
NASA NTRS1989

Advances in lightweight nickel electrode technology

Studies are currently underway to further the development of lightweight nickel electrode technology. Work is focused primarily on the space nickel-hydrogen system and nickel-iron system but is also applicable to the nickel-cadmium and nickel-zinc systems. The goal is to reduce electrode weight while maintaining or improving performance, thereby increasing electrode energy density. Two basic electrode structures are being investigated. The first is the traditional nickel sponge produced from sintered nickel-carbonyl powder. The second is a new material for this application which consists of a non-woven mat of nickel fiber. Electrodes are being manufactured, tested, and evaluated at the electrode and cell level.

Coates, Dwaine↗
NASA NTRS1990

Characterization of the corrosion resistance of several alloys to dilute biologically active solutions

Sulfate reducing bacteria and acid producing bacteria/fungi detected in hygiene waters increased the corrosion rate in aluminum alloy. Biologically active media enhanced the formation of pits on metal coupons. Direct observation of gas evolved at the corrosion sample, coupled with scanning electron microscopy (SEM) and energy dispersive x-ray analysis of the corrosion products indicates that the corrosion rate is increased because the presence of bacteria favor the reduction of hydrogen as the cathodic reaction through the reaction of oxygen and water. SEM verifies the presence of microbes in a biofilm on the surface of corroding samples. The bacterial consortia are associated with anodic sites on the metal surface, aggressive pitting occurs adjacent to biofilms. Many pits are associated with triple points and inclusions in the aluminum alloy microstructure. Similar bacterial colonization was found on the stainless steel samples. Fourier transform Infrared Spectroscopy confirmed the presence of carbonyl groups in pitted areas of samples exposed to biologically active waters.

Walsh, Daniel W.↗
NASA NTRS1991

Coproduction of volatiles and metals from extraterrestrial materials

Two main efforts in support of the general goals of SERC/culpr are presented. Investigations of processes for the coproduction of metals from extra-terrestrial materials in conjunction with plausible schemes for oxygen extraction continue. The principal emphasis was on the extraction and purification of iron from the ilmenite reduction process for oxygen, from the cathode metal deposits made in the magma electrolysis process for oxygen, and from native ferrous metal alloys on the moon and asteroids. All work on the separation and purification of ferrous metals was focussed upon the gaseous carbonyl process, a scheme that involves only temperatures attainable by passive thermal control. The exploration of a variety of schemes was initiated, involving the use of several different propulsion options and both propulsive and aerobraking capture at earth, for return of extraterrestrial resources to earth orbits. In addition, the search for new opportunities in space resource utilization continues. Examples include the continuation of work underway on: (1) the feasibility of locating solar power satellites in highly eccentric earth orbit; (2) the energetics of extracting the potential clean fusion fuel He-3 from the atmosphere for return to earth; and (3) the utility of a nuclear steam rocket (using non-terrestrial water as the working fluid) for transportation in the inner solar system.

Lewis, John S.↗
NASA NTRS1989

NASA Space Engineering Research Center for Utilization of Local Planetary Resources

Progress toward the goal of exploiting extraterrestrial resources for space missions is documented. Some areas of research included are as follows: Propellant and propulsion optimization; Automation of propellant processing with quantitative simulation; Ore reduction through chlorination and free radical production; Characterization of lunar ilmenite and its simulants; Carbothermal reduction of ilmenite with special reference to microgravity chemical reactor design; Gaseous carbonyl extraction and purification of ferrous metals; Overall energy management; and Information management for space processing.

Ramohalli, Kumar↗
NASA NTRS1989

Extraction of volatiles and metals from extraterrestrial ores

Extraterrestrial materials, processes, and products were identified which are associated with the production of propellants in space, including the most complete possible conversion of the feedstocks for propellant production into useful products with the minimum feasible expenditure of energy. Laboratory research was identified and begun on several processes that promise very large increases in the mass of useful products at the cost of only modest increases in energy consumption. Processes for manufacturing propellants then become processes for making propellants plus metals and refractories. It is the overall yield of useful materials per unit expended energy that matters, not simply the yield of propellants. Three tasks have been undertaken to date: (1) Literature search and compilation of a dBase 3 data base on space materials processing; (2) Gaseous carbonyl extraction and purification of ferrous metals; and (3) Characterization of lunar ilmenite and its simulants.

Lewis, John S.↗