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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 NTRS1975

Combustion of bulk titanium in oxygen

The combustion of bulk titanium in one atmosphere oxygen is studied using laser ignition and several analytical techniques. These were high-speed color cinematography, time and space resolved spectra in the visible region, metallography (including SEM) of specimens quenched in argon gas, X-ray and chemical product analyses, and a new optical technique, the Hilbert transform method. The cinematographic application of this technique for visualizing phase objects in the combustion zone is described. The results indicate an initial vapor phase reaction immediately adjacent to the molten surface but as the oxygen uptake progresses the evaporation approaches the point of congruency and a much reduced evaporation rate. This and the accumulation of the various soluble oxides soon drive the reaction zone below the surface where gas formation causes boiling and ejection of particles. The buildup of rutile cuts off the oxygen supply and the reaction ceases.

Clark, A. F.↗
NASA NTRS1992

An Extraordinary Accumulation of (-)-Pinoresinol in Cell-Free Extracts of Forsythia intermedia: Evidence for Enantiospecific Reduction of (+)-Pinoresinol

Stereoselective and enantiospecific transformation mechanisms in lignan biogenesis are only now yielding to scientific inquiry: it has been shown that soluble cell-free preparations from Forsythia intermedia catalysis the formation of the enantiomerically pure lignan, (-)-secoisolariciresinol, when incubated with coniferyl alcohol in the presence of NAD(P)H and H2O2. Surprisingly, (-)-pinoresinol also accumulates in this soluble cell-free assay mixture in greater than 96% enantiomeric excess, even though it is not the naturally occurring antipode present in Forsythia sp. But these soluble cell-free preparations do not engender stereoselective coupling; instead, racemic pinoresinols are first formed, catalysed by an H2O2-dependent peroxidase reaction. An enantiospecific NAD(P)H reductase then converts (+)- pinoresinol, and not the (-)-antipode, into (-)-secoisolariciresinol. Stereoselective syntheis of(+)-pinoresinol from E-coniferyl alcohol is, however, catalysed by an insoluble enzyme preparation in F. suspensa, obtained following removal of readily soluble and ionically bound enzymes; no exogenously supplied cofactors were required other than oxygen, although the reaction was stimulated by NAD-malate addition. Thus, the overall biochemical pathway to enantiomerically pure (-)-secoisolariciresinol has been delineated.

Katayama, Takeshi↗
NASA NTRS1979

Fixation of nitrogen in the prebiotic atmosphere

Reactions between nitrogen and water in the air surrounding lightning discharges can provide an important source of nitric oxide even under conditions where oxygen is a minor atmospheric constituent. Estimates are given for the associated source of soluble nitrite and nitrate. It is shown that lightning and subsequent atmospheric chemistry can provide a source of nitrate for the primitive ocean as large as one million tons of nitrogen per year, sufficient to fill the ocean to its present level of nitrate in less than one million years.

Yung, Y. L.↗
NASA NTRS1999

Flight Validation of Atomic Oxygen Resistant Resistant Polymers

Because of its high reactivity, atomic oxygen causes surface erosion on polymeric materials. although the reaction efficiency depends on the chemical structure of the polymer. We have found an organotin compound, bis(triphenyltin) oxide (BTO), which has an unusually high solubility in solutions of a number of commercial high performance polymers. Films of these polymers containing BTO showed a substantial reduction in erosion by atomic oxygen when compared with films of the pure material. Analysis has shown that in the presence of atomic oxygen, erosion of the exposed surfaces of the BTO-containing films leaves a residual protective tin oxide coating . Since the additive is uniformly distributed throughout the polymeric material, any break or puncture in the protective coating is "healed" by the material below. Samples were exposed to the environment of the low earth orbit (LEO) on two Space Shuttle flights, STS-46, in June of 1992, and STS-51 in September of 1993. The analysis of these samples has been reported previously. For both flights, the samples were small (1.3 cm and 1.9 cm respectively) thus limiting the scope of analysis. In the research under this cooperative agreement, films of a polyetherimide, were exposed to the LEO environment on Space Shuttle flight STS-85 in August of 1997 as part of the Evaluation of Space Environment and Effects on Materials (ESEM) experiment. The polyetherimide chosen is available commercially as Ultem, registered to the General Electric Company. Films of pure Ultem, Ultem with 10% BTO by mass, and Ultem with 20% BTO by mass were exposed in the ram direction for 40 hours during STS-85. Ultem has a Tg of 215 deg C and is soluble in common chlorinated solvents. Granules of the polymer were dried at 120 deg C, but otherwise were used as received. Films were cast on a glass plate from a solution of the polymer in a 60/40 (w/w) mixture of chloroform and 1,1,2,2-tetrachloroethane. The plate was placed in a dust-free box for at least 24 hours to allow much of the solvent to evaporate, and then was moved to a vacuum oven and slowly heated from 20 to 220 deg C over a period of two weeks to completely remove all solvent. Each exposed sample was 7.6 cm long and 2.2 cm wide and about 0.025 mm thick. The structures of Ultem and bis(triphenyltin) oxide are shown.

Kiefer, Richard L.↗
NASA NTRS2005

Influence of Silicate Melt Composition on Metal/Silicate Partitioning of W, Ge, Ga and Ni

The depletion of the siderophile elements in the Earth's upper mantle relative to the chondritic meteorites is a geochemical imprint of core segregation. Therefore, metal/silicate partition coefficients (Dm/s) for siderophile elements are essential to investigations of core formation when used in conjunction with the pattern of elemental abundances in the Earth's mantle. The partitioning of siderophile elements is controlled by temperature, pressure, oxygen fugacity, and by the compositions of the metal and silicate phases. Several recent studies have shown the importance of silicate melt composition on the partitioning of siderophile elements between silicate and metallic liquids. It has been demonstrated that many elements display increased solubility in less polymerized (mafic) melts. However, the importance of silicate melt composition was believed to be minor compared to the influence of oxygen fugacity until studies showed that melt composition is an important factor at high pressures and temperatures. It was found that melt composition is also important for partitioning of high valency siderophile elements. Atmospheric experiments were conducted, varying only silicate melt composition, to assess the importance of silicate melt composition for the partitioning of W, Co and Ga and found that the valence of the dissolving species plays an important role in determining the effect of composition on solubility. In this study, we extend the data set to higher pressures and investigate the role of silicate melt composition on the partitioning of the siderophile elements W, Ge, Ga and Ni between metallic and silicate liquid.

Singletary, S. J.↗
NASA NTRS1986

Volatile solubities in magmas - Transport of volatiles from mantles to planet surfaces

The solubility of CO2, CO, CH4, H2, and H2O in melts of NaAlSi3O8 composition was measured at the mantle conditions of pressure (10-20 Kb) and temperature (1200 C). The melt volatiles were found to have dramatically lower H2/H2O and higher CO/CO2 ratios than the fluid, due to large variations in relative solubilities of volatile species in the melt. Partial melting of source regions of either high or low oxygen fugacity (fO2) will result in magmas with intermediate fO2. This means that volcanic gases can be either more, or less reducing than their source regions and that a volcanic gas composition cannot be used to directly estimate either the fO2 or the volatile composition of the source region. The results suggest that volcanic gases will usually lie in the 'neutral' range, with the fO2 values near those of the quartz-fayalite-magnetite buffer. These gases are predominately H2O with minor CO2, CO, CH4, and H2. These conclusions should apply to earth, Mars, and Venus mantles, in which the magmas produced by partial melting have moderate silica contents, but will probably not apply to very low silica magmas, such as kimberlites, because of the very high solubility of CO2 in those magmas.

Holloway, J. R.↗
NASA NTRS1982

Chemistry of uranium in aluminophosphate glasses

The U(VI)-U(V)-U(IV) redox equilibria are investigated in two sodium aluminophosphate base compositions at a variety of melt temperatures, imposed oxygen fugacities, and uranium contents. Results show that the higher redox states of uranium are quite soluble in the phosphate glasses, although U(IV) readily precipitates from the melts as UO2. In addition, comparisons of the uranium redox equilibria established in phosphate melts versus those in silicate melts shows that the coordination sites of the individual uranium species are generally the same in both solvent systems although they differ in detail.

Schreiber, H. D.↗
NASA NTRS1993

Evaporation of LOX under supercritical and subcritical conditions

The evaporation of LOX under supercritical and subcritical conditions was studied experimentally and theoretically. In experiments, the evaporation rate and surface temperature were measured for LOX strand vaporizing in helium environments at pressures ranging from 5 to 68 atmospheres. Gas sampling and chromatography analysis were also employed to profile the gas composition above the LOX surface for the purpose of model validation. A comprehensive theoretical model was formulated and solved numerically to simulate the evaporation process of LOX at high pressures. The model was based on the conservation equations of mass, momentum, energy, and species concentrations for a multicomponent system, with consideration of gravitational body force, solubility of ambient gases in liquid, and variable thermophysical properties. Good agreement between predictions and measured oxygen mole fraction profiles was obtained. The effect of pressure on the distribution of the Lewis number, as well as the effect of variable diffusion coefficient, were further examined to elucidate the high-pressure transport behavior exhibited in the LOX vaporization process.

Yang, A. S.↗
NASA NTRS2004

The Subsurface Ice Probe (SIPR): A Low-Power Thermal Probe for the Martian Polar Layered Deposits

The distinctive layering visible in images from Mars Global Surveyor of the Martian polar caps, and particularly in the north polar cap, indicates that the stratigraphy of these polar layered deposits may hold a record of Martian climate history covering millions of years. On Earth, ice sheets are cored to retrieve a pristine record of the physical and chemical properties of the ice at depth, and then studied in exacting detail in the laboratory. On the Martian north polar cap, coring is probably not a practical method for implementation in an autonomous lander. As an alternative, thermal probes that drill by melting into the ice are feasible for autonomous operation, and are capable of reasonable approximations to the scientific investigations performed on terrestrial cores, while removing meltwater to the surface for analysis. The Subsurface Ice Probe (SIPR) is such a probe under development at JPL. To explore the dominant climate cycles, it is postulated that tens of meters of depth should be profiled, as this corresponds to the vertical separation of the major layers visible in the MOC images [1]. Optical and spectroscopic analysis of the layers, presumably demarcated by embedded dust and possibly by changes in the ice properties, would contribute to the construction of a chronology. Meltwater analysis may be used to determine the soluble chemistry of the embedded dust, and to monitor gradients of atmospheric gases, particularly hydrogen and oxygen, and isotopic variations that reflect atmospheric conditions at the time the layer was deposited. Thermal measurements can be used to determine the geothermal gradient and the bulk mechanical properties of the ice.

Cardell, G.↗
NASA NTRS2001

Novel effects of nitric oxide

Nitric oxide (NO), a simple free radical gas, elicits a surprisingly wide range of physiological and pathophysiological effects. NO interacts with soluble guanylate cyclase to evoke many of these effects. However, NO can also interact with molecular oxygen and superoxide radicals to produce reactive nitrogen species that can modify a number of macromolecules including proteins, lipids, and nucleic acids. NO can also interact directly with transition metals. Here, we have reviewed the non--3',5'-cyclic-guanosine-monophosphate-mediated effects of NO including modifications of proteins, lipids, and nucleic acids.

Non-NASA Center↗
NASA NTRS2006

Iron-Tolerant Cyanobacteria: Ecophysiology and Fingerprinting

Although the iron-dependent physiology of marine and freshwater cyanobacterial strains has been the focus of extensive study, very few studies dedicated to the physiology and diversity of cyanobacteria inhabiting iron-depositing hot springs have been conducted. One of the few studies that have been conducted [B. Pierson, 1999] found that cyanobacterial members of iron depositing bacterial mat communities might increase the rate of iron oxidation in situ and that ferrous iron concentrations up to 1 mM significantly stimulated light dependent consumption of bicarbonate, suggesting a specific role for elevated iron in photosynthesis of cyanobacteria inhabiting iron-depositing hot springs. Our recent studies pertaining to the diversity and physiology of cyanobacteria populating iron-depositing hot springs in Great Yellowstone area (Western USA) indicated a number of different isolates exhibiting elevated tolerance to Fe(3+) (up to 1 mM). Moreover, stimulation of growth was observed with increased Fe(3+) (0.02-0.4 mM). Molecular fingerprinting of unialgal isolates revealed a new cyanobacterial genus and species Chroogloeocystis siderophila, an unicellular cyanobacterium with significant EPS sheath harboring colloidal Fe(3+) from iron enriched media. Our preliminary data suggest that some filamentous species of iron-tolerant cyanobacteria are capable of exocytosis of iron precipitated in cytoplasm. Prior to 2.4 Ga global oceans were likely significantly enriched in soluble iron [Lindsay et al, 2003], conditions which are not conducive to growth of most contemporary oxygenic cyanobacteria. Thus, iron-tolerant CB may have played important physiological and evolutionary roles in Earths history.

Brown, I. I.↗
NASA NTRS1998

Biogeochemical cycling of manganese in Oneida Lake, New York: whole lake studies of manganese

Oneida Lake, New York is a eutrophic freshwater lake known for its abundant manganese nodules and a dynamic manganese cycle. Temporal and spatial distribution of soluble and particulate manganese in the water column of the lake were analyzed over a 3-year period and correlated with other variables such as oxygen, pH, and temperature. Only data from 1988 are shown. Manganese is removed from the water column in the spring via conversion to particulate form and deposited in the bottom sediments. This removal is due to biological factors, as the lake Eh/pH conditions alone can not account for the oxidation of the soluble manganese Mn(II). During the summer months the manganese from microbial reduction moves from the sediments to the water column. In periods of stratification the soluble Mn(II) builds up to concentrations of 20 micromoles or more in the bottom waters. When mixing occurs, the soluble Mn(II) is rapidly removed via oxidation. This cycle occurs more than once during the summer, with each manganese atom probably being used several times for the oxidation of organic carbon. At the end of the fall, whole lake concentrations of manganese stabilize, and remain at about 1 micromole until the following summer, when the cycle begins again. Inputs and outflows from the lake indicate that the active Mn cycle is primarily internal, with a small accumulation each year into ferromanganese nodules located in the oxic zones of the lake.

NASA Discipline Exobiology↗
NASA NTRS1985

Sulfide and sulfate saturation in hydrous silicate melts

A series of hydrothermal experiments was performed over a wide range of pressures, temperatures, oxygen fugacities, and melt FeO content, in order to examine the effects of physical changes on sulfur solubility in fractionated hydrous silicate melts. On the basis of the experimental results, it is concluded that upper crustal oxidation-reduction reactions and crystal fractionation processes may exert considerable influence on the amount of sulfur contained in magmas erupted at the surface. The application of the experimental results to investigations of volatile transport and volcanic degassing processes on the earth, Venus, and Mars is discussed

Carroll, M. R.↗
NASA NTRS1994

Shadowgraphy of transcritical cryogenic fluids

The future of liquid-rocket propulsion depends heavily on continued development of high pressure liquid oxygen/hydrogen systems that operate near or above the propellant critical states; however, current understanding of transcritical/supercritical injection and combustion is yet lacking. The Phillips Laboratory and the United Technologies Research Center are involved in a collaborative effort to develop diagnostics for and make detailed measurements of transcritical droplet vaporization and combustion. The present shadowgraph study of transcritical cryogenic fluids is aimed at providing insight into the behavior of liquid oxygen or cryogenic stimulants as they are injected into a supercritical environment of the same or other fluids. A detailed history of transcritical injection of liquid nitrogen into gaseous nitrogen at reduced pressures of 0.63 (subcritical) to 1.05 (supercritical) is provided. Also, critical point enhancement due to gas phase solubility and mixture effects is investigated by adding helium to the nitrogen system, which causes a distinct liquid phase to re-appear at supercritical nitrogen pressures. Liquid oxygen injection into supercritical argon or nitrogen, however, does not indicate an increase in the effective critical pressure of the system.

Woodward, R. D.↗
NASA NTRS1991

Polyimides containing pendent siloxane groups

The incorporation of siloxane units into the backbone of aromatic polyimides has been shown to impart certain advantages over the unmodified polyimides. These include enhanced solubility, lower moisture adsorption, lower dielectric constant, improved toughness and surface modification. Also, when exposed to an atomic oxygen environment these materials form an in-situ silicate (SiO2) surface coating which protects the underlying material from further erosion. These unique advantages make polyimide-siloxanes useful in a variety of electronic and aerospace applications. As part of an effort on high performance polymeric materials for potential aerospace applications, polyimides containing pendent siloxane groups are under study. These materials were prepared by reacting a functionalized siloxane compound with polyimides containing benzhydrol groups. Thin films of the polymers exhibited glass transition temperatures ranging from 167 to 235 C. Tensile strengths and moduli measured at 23 C ranged from 11 to 14 ksi and 250 to 450 ksi, respectively. The dielectric constant was lowered substantially from that of the unmodified polyimide.

Connell, John W.↗
NASA NTRS1978

Stability of chromium (III) sulfate in atmospheres containing oxygen and sulfur

The stability of chromium sulfate in the temperature range from 880 K to 1040 K was determined by employing a dynamic gas-solid equilibration technique. The solid chromium sulfate was equilibrated in a gas stream of controlled SO3 potential. Thermogravimetric and differential thermal analyses were used to follow the decomposition of chromium sulfate. X-ray diffraction analysis indicated that the decomposition product was crystalline Cr2O3 and that the mutual solubility between Cr2(SO4)3 and Cr2O3 was negligible. Over the temperature range investigated, the decomposition pressure were significantly high so that chromium sulfate is not expected to form on commercial alloys containing chromium when exposed to gaseous environments containing oxygen and sulfur (such as those encountered in coal gasification).

Jacob, K. T.↗
NASA NTRS1996

Final Report: Research Study on Development of Environmental Friendly Spray-on Foam Insulation (SOFI) for the External Tank (ET)

The selection and quantification of four foams using a more environmentally friendly HCFC-141b blowing agent replacing foams that used the CFC-11 blowing agent for the external tank (ET) LWT has been addressed along with problems and solutions that were encountered during verification. The effort on two lower density spray foams for the ET SLWT are presented, but predicted weight savings were not encouraging. Suggestions for possible problem solving are included along with a new approach for selecting foams for qualification as back-up foams for the foams used on the ET LWT. We investigated three resins for use as thermally sprayed coatings for corrosion prevention on metal. The best coating was obtained with a thermoplastic polyimide resin. This coating has a good chance of meeting ET requirements. Possible third generation blowing agents have been shown usable in polyurethane spray and pour foams, and solubility in isocyannate foam components are acceptable. We considered aerogels as insulation materials on space vehicles, and suggested a liner for a liquid oxygen (LOX) composite tank.

Stuckey, James M.↗
NASA NTRS1976

Solubility of Cr, Ti, and Al in co-existing olivine, spinel, and liquid at 1 atm

The partitioning of chromium between olivines, spinels and silicate liquids was studied as a function of temperature, oxygen fugacity, and cooling rate between 1175 and 1300 C and redox states near the Fe-FeO buffer. It is found that the weight ratio of Cr2O3 in olivine to that in the liquid increases slightly as oxygen fugacity decreases, but the effect is very small. The cooling experiments showed that the Cr2O3 content does not re-equilibrate with cooling.

Akella, J.↗