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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Development of superalloys by powder metallurgy for use at 1000 - 1400 F

Consolidated powders of four nickel-base superalloys were studied for potential application as compressor and turbine discs in jet engines. All of the alloys were based on the Rene' 95 chemistry. Three of these had variations in carbon and A12O3 contents, and the fourth alloy was chemically modified to a higher volume fraction. The A12O3 was added by preoxidation of the powders prior to extrusion. Various levels of four experimental factors (1) alloy composition, (2) grain size, (3) thermomechanical processing, and (4) room temperature deformation plus final age were evaluated by tensile and stress rupture testing at 1200 F. Various levels of the four factors were assumed in order to construct the statistically-designed experiment, but the actual levels investigated were established in preliminary studies that preceded the statistical process development study.

Calhoun, C. D.↗
NASA NTRS1978

Chemical aspects of the formation of the solar system

Application of Alfven's theory for the formation of the solar system and the constraints imposed by the chemical composition of space materials are discussed with reference to chemical processes involved in the formation of the solar system. Evidence for the chemical properties of the space medium and the chemical consequences of the postulated physical differentiation processes are outlined, and interpretations based on structure and composition of meteorite material are indicated. A large range of topics, including processes involving chemical differentiation, temperature effects, and isotope fractionation, are examined.

Arrhenius, G.↗
NASA NTRS1992

Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels

Reports of the 13C content of marine particulate organic carbon are compiled and on the basis of GEOSECS data and temperatures, concentrations, and isotopic compositions of dissolved CO2 in the waters in which the related phytoplankton grew are estimated. In this way, the fractionation of carbon isotopes during photosynthetic fixation of CO2 is found to be significantly correlated with concentrations of dissolved CO2. Because ancient carbon isotopic fractionations have been determined from analyses of sedimentary porphyrins [Popp et al., 1989], the relationship between isotopic fractionation and concentrations of dissolved CO2 developed here can be employed to estimate concentrations of CO2 dissolved in ancient oceans and, in turn, partial pressures of CO2 in ancient atmospheres. The calculations take into account the temperature dependence of chemical and isotopic equilibria in the dissolved-inorganic-carbon system and of air-sea equilibria. Paleoenvironmental temperatures for each sample are estimated from reconstructions of paleogeography, latitudinal temperature gradients, and secular changes in low-latitude sea surface temperature. It is estimated that atmospheric partial pressures of CO2 were over 1000 micro atm 160 - 100 Ma ago, then declined to values near 300 micro atm during the next 100 Ma. Analysis of a high-resolution record of carbon isotopic fractionation at the Cenomanian-Turonian boundary suggests that the partial pressure of CO2 in the atmosphere was drawn down from values near 840 micro atm to values near 700 micro atm during the anoxic event.

NASA Discipline Exobiology↗
NASA NTRS2017

Revised Models of Interstellar Nitrogen Isotopic Fractionation

Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of (15)N enrichments found in comets and meteorites. Chemical model calculations indicate that atom-molecular ion and ion-molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense loud chemistry show that the revised (15)N enrichments fail to match observed values. We have investigated the effects of these reaction rate modifications on the chemical model of Wirstrom et al. (2012) for which there are significant physical and chemical differences with respect to other models. We have included (15)N fractionation of CN in neutral-neutral reactions and also updated rate coefficients for key reactions in the nitrogen chemistry. We find that the revised fractionation rates have the effect of suppressing (15)N enrichment in ammonia at all times, while the depletion is even more pronounced, reaching (14)N/(15)N ratios of > 2000. Taking the updated nitrogen chemistry into account, no sigificant enrichment occurs in HCN or HNC, contrary to observational evidence in dark clouds and comets, although the (14)N/(15)N ratio can still be below 100 in CN itself. However, such low CN abundances are predicted that the updated model falls short of explaining the bulk (15)N enhancements observed in primitive materials. It is clear that alternative fractionating reactions are necessary to reproduce observations, so further laboratory and theoretical studies are urgently needed.

Astrochemistry↗
NASA NTRS1994

Lessons from an evolving rRNA: 16S and 23S rRNA structures from a comparative perspective

The 16S and 23S rRNA higher-order structures inferred from comparative analysis are now quite refined. The models presented here differ from their immediate predecessors only in minor detail. Thus, it is safe to assert that all of the standard secondary-structure elements in (prokaryotic) rRNAs have been identified, with approximately 90% of the individual base pairs in each molecule having independent comparative support, and that at least some of the tertiary interactions have been revealed. It is interesting to compare the rRNAs in this respect with tRNA, whose higher-order structure is known in detail from its crystal structure (36) (Table 2). It can be seen that rRNAs have as great a fraction of their sequence in established secondary-structure elements as does tRNA. However, the fact that the former show a much lower fraction of identified tertiary interactions and a greater fraction of unpaired nucleotides than the latter implies that many of the rRNA tertiary interactions remain to be located. (Alternatively, the ribosome might involve protein-rRNA rather than intramolecular rRNA interactions to stabilize three-dimensional structure.) Experimental studies on rRNA are consistent to a first approximation with the structures proposed here, confirming the basic assumption of comparative analysis, i.e., that bases whose compositions strictly covary are physically interacting. In the exhaustive study of Moazed et al. (45) on protection of the bases in the small-subunit rRNA against chemical modification, the vast majority of bases inferred to pair by covariation are found to be protected from chemical modification, both in isolated small-subunit rRNA and in the 30S subunit. The majority of the tertiary interactions are reflected in the chemical protection data as well (45). On the other hand, many of the bases not shown as paired in Fig. 1 are accessible to chemical attack (45). However, in this case a sizeable fraction of them are also protected against chemical modification (in the isolated rRNA), which suggests that considerable higher-order structure remains to be found (although all of it may not involve base-base interactions and so may not be detectable by comparative analysis). The agreement between the higher-order structure of the small-subunit rRNA and protection against chemical modification is not perfect, however; some bases shown to covary canonically are accessible to chemical modification (45).(ABSTRACT TRUNCATED AT 400 WORDS).

Review↗
NASA NTRS1996

An Apollo 15 Mare Basalt Fragment and Lunar Mare Provinces

Lunar sample 15474,4 is a tiny fragment of olivine-augite vitrophyre that is a mare basalt. Although petroraphically distinct from all other Apollo 15 samples, it has been ignored since its first brief description. Our new petrographic and mineral chemical data show that the olivines and pyroxenes are distinct from those in other basalts. The basalt cooled and solidified extremely rapidly; some of the olivine might be cumulate or crystallized prior to extrusion. Bulk-chemical data show that the sample is probably similar to an evolved Apollo 15 olivine-normative basalt in major elements but is distinct in its rare earth element pattern. Its chemical composition and petrography both show that 15474,4 cannot be derived from other Apollo 15 mare basalts by shallow-level crystal fractionation. It represents a distinct extrusion of magma. Nonetheless, the chemical features that 15474,4 has in common with other Apollo 15 mare basalts, including the high FeO/Sc, the general similarity of the rare earth element pattern, and the common (and chondritic) TiO2/Sm ratio, emphasize the concept of a geochemical province at the Apollo 15 site that is distinct from basalts and provinces elsewhere. In making a consistent picture for the derivation of all of the Apollo 15 basalts, both the commonalities and the differences among the basalts must be explained. The Apollo 15 commonalities and differences suggest that the sources must have consisted of major silicate phases with the same composition but with varied amounts of a magma trapped from a contemporary magma ocean. They probably had a high olivine/pyroxene ratio and underwent small and reasonably consistent degrees of partial melting to produce the basalts. These inferences may be inconsistent with models that suggest greatly different depths of melting among basalts, primitive sources for the green glasses, or extensive olivine fractionation during ascent. An integrated approach to lunar mare provinces, of which the Apollo 15 mare basalts constitute only one, offers advances in our understanding of the physical and chemical processes of source formation and mare production but has so far not been utilized.

Ryder, Graham↗
NASA NTRS1986

Volatile components and continental material of planets

It is shown that the continental material of the terrestrial planets varies in composition from planet to planet according to the abundances and composition of true volatiles (H20, CO2, etc.) in the outer shells of the planets. The formation of these shells occurs very early in a planet's evolution when the role of endogenous processes is indistinct and continental materials are subject to melting and vaporizing in the absence of an atmosphere. As a result, the chemical properties of continental materials are related not only to fractionation processes but also to meltability and volatility. For planets retaining a certain quantity of true volatile components, the chemical transformation of continental material is characterized by a close interaction between impact melting vaporization and endogeneous geological processes.

Florenskiy, K. P.↗
NASA NTRS1981

Columbia River volcanism - The question of mantle heterogeneity or crustal contamination

It is found that, although crystal fractionation played an important role in producing the chemical characteristics of Columbia River Province basalts displaying a wide range of chemical and isotopic compositions, the isotopic variability calls for the involvement of at least two isotopically distinct components. The major and trace element characteristics of the main volume of the basalts are not consistent with a metasomatized mantle source region, and the presence of a primordial mantel component is not supported by the chemical data. Models of simple binary mixing between a primary magma and Precambrian sialic crustal materials, while satisfying the observed Nd and Sr isotopic variations, fail to account for major trace element abundances. The combination of crustal assimilation and fractional crystalization is found to give a superior fit to the compositional data.

Carlson, R. W.↗
NASA NTRS2004

Fire Suppression and Response

This report is concerned with the following topics regarding fire suppression:What is the relative effectiveness of candidate suppressants to extinguish a representative fire in reduced gravity, including high-O2 mole fraction, low -pressure environments? What are the relative advantages and disadvantages of physically acting and chemically-acting agents in spacecraft fire suppression? What are the O2 mole fraction and absolute pressure below which a fire cannot exist? What effect does gas-phase radiation play in the overall fire and post-fire environments? Are the candidate suppressants effective to extinguish fires on practical solid fuels? What is required to suppress non-flaming fires (smoldering and deep seated fires) in reduced gravity? How can idealized space experiment results be applied to a practical fire scenario? What is the optimal agent deployment strategy for space fire suppression?

Ruff, Gary A.↗
NASA NTRS1984

Geochemical constraints on magma processes in a peralkaline system - The Paisano volcano, west Texas

Petrographic and trace element data from a continuous stratigraphic sequence of flows from the peralkaline Paisano Volcano in west Texas are used to delineate magnetic processes responsible for the chemical evolution of this volcano. It is shown that crystal fractionation of the phenocrystic assemblage explains the main compositional variation, but magma mixing of a less evolved melt composition also affected the chemical evolution of the volcano.

Mcdonough, W. F.↗
NASA NTRS1980

Fluid dynamics of the unsteady two phase processes leading to DDT in granular solid propellants

Deflagration to Detonation (DDT) was predicted to occur in porous beds of high-energy solid propellants by solving the unsteady fluid mechanical convective heat transfer from hot gas products, obtained from the rapid burning at high pressures, provides the impetus to develop a narrow combustion zone and a resulting strong shock. A parametric study clearly indicates that DDT occurs only when a combination of the solids loading fraction, the burning rate constants, the propellant chemical energy, and the particle size provide for critical energy and gas release to support a detonation wave. Predictions for the run-up length to detonation as a function of these parameters are presented.

Krier, H.↗
NASA NTRS2009

Implementation of Radiation, Ablation, and Free Energy Minimization Modules for Coupled Simulations of Hypersonic Flow

A description of models and boundary conditions required for coupling radiation and ablation physics to a hypersonic flow simulation is provided. Chemical equilibrium routines for varying elemental mass fraction are required in the flow solver to integrate with the equilibrium chemistry assumption employed in the ablation models. The capability also enables an equilibrium catalytic wall boundary condition in the non-ablating case. The paper focuses on numerical implementation issues using FIRE II, Mars return, and Apollo 4 applications to provide context for discussion. Variable relaxation factors applied to the Jacobian elements of partial equilibrium relations required for convergence are defined. Challenges of strong radiation coupling in a shock capturing algorithm are addressed. Results are presented to show how the current suite of models responds to a wide variety of conditions involving coupled radiation and ablation.

Gnoffo, Peter A.↗
NASA NTRS2014

Processing of Packing Foams Using Heat Melt Compaction

Foam is used extensively as packing material for items sent to the International Space Station (ISS). Although lightweight, foam is bulky and can occupy a large fraction of the limited ISS volume. Four chemically distinct foams have been used on the ISS. In descending order of current usage, these are Plastazote Zotek Minicel Pyrell. Processing foam with the Heat Melt Compactor (HMC), a solid waste treatment system, has been proposed to reduce the volume of foams stored on spacecraft. Prior to HMC testing, Thermogravimetric Analyses were conducted on the four foams as a precaution to ensure that the thermal decomposition temperatures were not within range of HMC operation (180C). Pyrell was not tested with the HMC because it is known to release toxic compounds and comprises less than 1.5 of total foam usage on ISS resupply flights. Zotek, Minicel, Plastazote LD24FR (low density), and Plastazote LD45FR (high density) were processed with the HMC at 130, 150 and 170C. Volume was reduced by 82.6 on average (n19; std dev4.88). Hydrocarbons and several other compounds emitted during foam processing were measured using a Total Hydrocarbon Analyzer and FTIR. Effects of process temperature and foam type on exhaust composition are discussed. Feeding of foams into the limited size opening of the HMC compaction chamber is likely to be a challenge, particularly in microgravity. Some suggestions are proposed to facilitate feeding foam into the HMC. Processing packing foam with the HMC has been shown to substantially reduce foam volume, and also has the potential benefit of producing radiation-shielding foam tiles.

Harris, Linden↗
NASA NTRS2022

Reduction of Raman Spectroscopy Data for H2-CO2-Air Tubular Flame Measurements

An approach of reducing spontaneous Raman spectroscopy data, based on the matrix inversion method which logically removes undesired sources of the Raman scattering signals including cross-talk due to the signals from other species, is discussed. The approach contains extensive calibration of temperature-dependent system response. The Raman spectra of several cold and hot calibration flames and their resulting calibration matrix are elaborated. The structure of H2-CO2-air tubular flames, in terms of major species (CO2, O2, N2, H2O, and H2) concentrations and temperature, was successfully measured with the optical technique. The Raman spectra data used in this study are taken from a uniquely designed experimental apparatus – a tubular burner and Raman spectroscopy system at Vanderbilt University. The characteristic uncertainties for chemical species are approximately ±2% by mole fraction for hot products and ±0.5% for room temperature reactants. The approach described here for hydrogen/air tubular flames may be adapted to hydrocarbon/air tubular flames when other necessary major species, for example, CH4 and CO for methane/air tubular flame, are considered in the whole process.

Raman Spectroscopy↗
NASA NTRS1982

The Apollo 14 regolith - Chemistry of cores 14210/14211 and 14220 and soils 14141, 14148, and 14149

Neutron activation analysis was performed on bulk and size fractions from drive tube specimens from 39 cm and 16.5 cm depths, and soil samples taken at the Apollo 14 landing site. Chemical data were obtained for 31 major, minor, and trace elements in the KREEPy soils. The cores were homogeneous in chemical composition, containing 20% LKFM, 15% mare basalt, 6% ANT, and 59% high-K KREEP, according to the classifications of Laul and Papike (1980). The meteoritic fraction was 3-7% for both cores, while the chemical compositions of both cores and soils were similar. Differences were detected in the fractions finer than 10 microns, which were more feldspathic than the coarser samples. The similarities between the grains 1000-90 micron in diam and less than 10 micron in diam, in terms of chemical contents, indicates that the observed agglutinates were derived from fusion of the finest grained fraction. The dominant soil-forming processes were comminution and vertical mixing of the regolith.

Laul, J. C.↗
NASA NTRS2003

Uptake of Organic Vapors by Sulfate Aerosols: Physical and Chemical Processes

While it is known that upper tropospheric sulfate particles contain a significant amount of organic matter, both the source of the organic fraction and its form in solution are unknown. These studies explore how the chemical characteristics of the molecules and surfaces in question affect heterogeneous interactions. The solubilities of acetaldehyde [CH3CHO] and ethanol [CH3CH20H] in cold, aqueous sulfuric acid solutions have been measured by Knudsen cell studies. Henry's law solubility coefficients range from 10(exp 2) to 10(exp 5) M/atm for acetaldehyde, and from 10(exp 4) to 10(exp 9) M/atm for ethanol under upper tropospheric conditions (210-240 K, 40-80 wt. % H2S04). The multiple solvation pathways (protonation, enolization, etc.) available to these compounds in acidic aqueous environments will be discussed. Preliminary results from the interaction of acetaldehyde with solutions of formaldehyde in sulfuric acid will be presented as well. The physical and chemical processes that affect organic uptake by aqueous aerosols will be explored, with the aim of evaluating organic species not yet studied in low temperature aqueous sulfuric acid.

Michelsen, R. R.↗
NASA NTRS1992

On the weathering of Martian igneous rocks

Besides the young crystallization age, one of the first arguments for the martian origin of shergottite, nakhlite, and chassignite (SNC) meteorites came from the chemical similarity of the meteorite Shergotty and the martian soil as measured by Viking XRF analyses. In the meantime, the discovery of trapped rare gas and nitrogen components with element and isotope ratios closely matching the highly characteristic ratios of the Mars atmosphere in the shock glasses of shergottite EETA79001 was further striking evidence that the SNC's are martian surface rocks. The martian soil composition as derived from the Viking mission, with its extremely high S and Cl concentrations, was interpreted as weathering products of mafic igneous rocks. The low SiO2 content and the low abundance of K and other trace elements in the martian soils point to a mafic crust with a considerably smaller degree of fractionation compared to the terrestrial crust. However, the chemical evolution of the martian regolith and soil in respect to surface reaction with the planetary atmosphere or hydrosphere is poorly understood. A critical point in this respect is that the geochemical evidence as derived from the SNC meteorites suggests that Mars is a very dry planet that should have lost almost all its initially large water inventory during its accretion.

Dreibus, G.↗