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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Lunar surface chemistry of regions common to the orbital X-ray and gamma-ray experiments

Concentration ratios of Al/Si and Mg/Si have been determined from the orbital X-ray data for twenty-two regions for which the concentrations of Th, K, Fe, and Mg has previously been specified from orbital gamma-ray data. The strong anticorrelation between Fe and Al seen in returned samples is confirmed for large areas of the lunar surface. The natural radioactivity of the large maria increases from east to west whereas an inverse in true for the aluminum concentration. The difficulty in determining Mg concentrations in each experiment is discussed.

Bielefeld, M. J.↗
NASA NTRS1982

Surface chemistry, friction and wear of Ni-Zn and Mn-Zn ferrites in contact with metals

X-ray photoelectron and Auger electron spectroscopy analysis were used in sliding friction experiments. These experiments were conducted with hot-pressed polycrystalline Ni-Zn and Mn-Zn ferrites, and single-crystal Mn-Zn ferrite in contact with various transition metals at room temperature in both vacuum and argon. The results indicate that Ni2O3 and Fe3O4 were present on the Ni-Zn ferrite surface in addition to the nominal bulk constituents, while MnO2 and Fe3O4 were present on the Mn-Zn ferrite surface in addition to the nominal bulk constituents. The coefficients of friction for the ferrites in contact with metals were related to the relative chemical activity of these metals. The more active the metal, the higher is the coefficient of friction. The coefficients of friction for the ferrites were correlated with the free energy of formation of the lowest metal oxide. The interfacial bond can be regarded as a chemical bond between the metal atoms and the oxygen anions in the ferrite surfaces. The adsorption of oxygen on clean metal and ferrite does strengthen the metal-ferrite contact and increase the friction. The ferrites exhibit local cracking and fracture with sliding under adhesive conditions. All the metals transferred to he surfaces of the ferrites in sliding.

Miyoshi, K.↗
NASA NTRS1983

Surface chemistry, friction, and wear of Ni-Zn and Mn-Zn ferrites in contact with metals

X-ray photoelectron and Auger electron spectroscopy analysis were used in sliding friction experiments. These experiments were conducted with hot-pressed polycrystalline Ni-Zn and Mn-Zn ferrites, and single-crystal Mn-Zn ferrite in contact with various transition metals at room temperature in both vacuum and argon. The results indicate that Ni2O3 and Fe3O4 were present on the Ni-Zn ferrite surface in addition to the nominal bulk constituents, while MnO2 and Fe3O4 were present on the Mn-Zn ferrite surface in addition to the nominal bulk constituents. The coefficients of friction for the ferrites in contact with metals were related to the relative chemical activity of these metals. The more active the metal, the higher is the coefficient of friction. The coefficients of friction for the ferrites were correlated with the free energy of formation of the lowest metal oxide. The interfacial bond can be regarded as a chemical bond between the metal atoms and the oxygen anions in the ferrite surfaces. The adsorption of oxygen on clean metal and ferrite does strengthen the metal-ferrite contact and increase the friction. The ferrites exhibit local cracking and fracture with sliding under adhesive conditions. All the metals transferred to the surfaces of the ferrites in sliding. Previously announced in STAR as N83-19901

Miyoshi, K.↗
NASA NTRS1979

Surface chemistry of iron sliding in air and nitrogen lubricated with hexadecane and hexadecane containing dibenzyl-dilsulfide

Wear experiments were conducted on iron sliding in hexadecane and hexadecane plus one weight percent dibenzyl dilsulfide (DBDS) in atmospheres of air and nitrogen at room temperature. The wear scars and the wear debris were analyzed by X-ray photoelectron spectroscopy. The presence of air reduced wear but increased friction, while DBDS reduced friction but had little effect on wear except that the wear increased somewhat when DBDS was used in air. Wear scar analysis indicated that oxygen and sulfur competed chemically for the surface, with the oxide predominating. Low wear was associated with a thick oxide layer and low friction with a thin predominantly sulfide layer. Analysis of the wear debris indicated the presence of a sulfate in the high wear case (hexadecane plus DBDS in air), and showed the presence of an organic sulfide in the low wear case (Hexadecane plus DBDS in nitrogen).

Wheeler, D. R.↗
NASA NTRS1989

A surface chemistry model for the altitude dependence of the N2 Lyman-Birge-Hopfield glow on spacecraft

Low-orbiting spacecraft have been observed to cause UV emission in the N2 Lyman-Birge-Hopfield bands. The chemical processes expected to underlie this emission are examined. Recombination between incident and adsorbed N atoms has been proposed as the source of radiating excited N2. However, the cubic dependence of the intensity, as N2 concentration cubed or N2 concentration squared x O concentration, has not been explained. It is suggested that this can be explained by a model where adsorption of nitrogen on the spacecraft surface is balanced mainly by the removal of N from the surface by atomic oxygen. On the basis of these assumptions a mathematical model for the production of excited N2 is constructed. It is shown that for large enough reaction efficiencies the model predicts a magnitude and altitude dependence for the emission which can explain the measurements reported by other investigators.

Cuthbertson, J. W.↗
NASA NTRS2005

Transient Catalytic Combustor Model With Detailed Gas and Surface Chemistry

In this work, we numerically investigate the transient combustion of a premixed gas mixture in a narrow, perfectly-insulated, catalytic channel which can represent an interior channel of a catalytic monolith. The model assumes a quasi-steady gas-phase and a transient, thermally thin solid phase. The gas phase is one-dimensional, but it does account for heat and mass transfer in a direction perpendicular to the flow via appropriate heat and mass transfer coefficients. The model neglects axial conduction in both the gas and in the solid. The model includes both detailed gas-phase reactions and catalytic surface reactions. The reactants modeled so far include lean mixtures of dry CO and CO/H2 mixtures, with pure oxygen as the oxidizer. The results include transient computations of light-off and system response to inlet condition variations. In some cases, the model predicts two different steady-state solutions depending on whether the channel is initially hot or cold. Additionally, the model suggests that the catalytic ignition of CO/O2 mixtures is extremely sensitive to small variations of inlet equivalence ratios and parts per million levels of H2.

Struk, Peter M.↗
NASA NTRS1984

Fracture mechanics and surface chemistry investigations of environment-assisted crack growth

It is pointed out that environment-assisted subcritical crack growth in high-strength steels and other high-strength alloys (particularly in hydrogen and in hydrogenous environments) is an important technological problem of long standing. This problem is directly related to issues of structural integrity, durability, and reliability. The terms 'hydrogen embrittlement' and 'stress corrosion cracking' have been employed to describe the considered phenomenon. This paper provides a summary of contributions made during the past ten years toward the understanding of environmentally assisted crack growth. The processes involved in crack growth are examined, and details regarding crack growth and chemical reactions are discussed, taking into account crack growth in steels exposed to water/water vapor, the effect of hydrogen, reactions involving hydrogen sulfide, and aspects of fracture surface morphology and composition. Attention is also given to the modeling of crack growth response, crack growth in gas mixtures, and the interaction of solute atoms with the crack-tip stress field.

Wei, R. P.↗
NASA NTRS1985

Effects of surface chemistry on hot corrosion life

Burner rig tests were conducted under the following conditions: 900 C, hourly thermal cycling, 0.5 ppm sodium as MaCl in the gas stream, velocity 0.3 Mach. The alloys are Udiment 700, Rene 80, uncoated and with RT21, Codep, or NiCoCrAlY coatings. These tests were completed for specimens in the as-processed condition and after aging at 1100 C in oxidizing or inert evnivronments for time up to 600 hours. Coil inductance changes used for periodic nondestructive inspection of specimens were useful in following the course of corrosion. Typical sulfidation was observed in all cases, structurally similar to that observed for service-run turbine components. Aging at cuased a severe decrease in hot corrosion life of RT21 and Codep coatings and a significant but less decrease in the life of the NiCoCrAlY coating. The extent of these decreases was much greater for all three coatings on U700 substrates than on Rene 80 substrates. Coating/substrate interdiffusion rather than by surface oxidation.

Fryxell, R. E.↗
NASA NTRS1976

Surface chemistry of selected lunar regions

A completely new analysis has been carried out on the data from the Apollo 15 and 16 gamma ray spectrometer experiments. The components of the continuum background have been estimated. The elements Th, K, Fe and Mg give useful results; results for Ti are significant only for a few high Ti regions. Errors are given, and the results are checked by other methods. Concentrations are reported for about sixty lunar regions; the ground track has been subdivided in various ways. The borders of the maria seem well-defined chemically, while the distribution of KREEP is broad. This wide distribution requires emplacement of KREEP before the era of mare formation. Its high concentration in western mare soils seems to require major vertical mixing.

Bielefeld, M. J.↗
NASA NTRS1976

Surface chemistry of selected lunar regions

A completely new analysis has been carried out on the data from the Apollo 15 and 16 gamma ray spectrometer experiments. The components of the continuum background have been estimated. The elements Th, K, Fe and Mg give useful results; results for Ti are significant only for a few high Ti regions. Errors are given, and the results are checked by other methods. Concentrations are reported for about sixty lunar regions; the ground track has been subdivided in various ways. The borders of the maria seem well-defined chemically, while the distribution of KREEP is broad. This wide distribution requires emplacement of KREEP before the era of mare formation. Its high concentration in western mare soils seems to require major vertical mixing.

Bielefeld, M. J.↗
NASA NTRS1976

Surface chemistry of selected lunar regions

A completely new analysis has been carried out on the data from the Apollo 15 and 16 gamma-ray spectrometer experiments. The components of the continuum background have been estimated. The elements Th, K, Fe, and Mg give useful results; for Ti are significant only for a few high-Ti regions. Errors are given, and the results are checked by other methods. Concentrations are reported for about 60 lunar regions; the ground track has been subdivided in various ways. The borders of the maria seem well-defined chemically, while the distribution of KREEP is broad. This wide distribution requires emplacement of KREEP before the era of mare formation. Its high concentration in western mare soils seems to require major vertical mixing.

Bielefeld, M. J.↗
NASA NTRS1984

Effects of surface chemistry on hot corrosion life

Baseline burner rig hot corrosion with Udimet 700, Rene' 80; uncoated and with RT21, Codep, or NiCoCrAlY coatings were tested. Test conditions are: 900C, hourly thermal cycling, 0.5 ppm sodium as NaCl in the gas stream, velocity 0.3 Mach. The uncoated alloys exhibited substantial typical sulfidation in the range of 140 to 170 hours. The aluminide coatings show initial visual evidence of hot corrosion at about 400 hours, however, there is no such visual evidence for the NiCoCrAlY coatings. The turbine components show sulfidation. The extent of this distress appeared to be inversely related to the average length of mission which may, reflect greater percentage of operating time near ground level or greater percentage of operation time at takeoff conditions (higher temperatures). In some cases, however, the location of maximum distress did not exhibit the structural features of hot corrosion.

Fryxell, R. E.↗
NASA NTRS1982

Effects of surface chemistry on hot corrosion life: Overview

This program concentrates on analyzing a limited number of hot corroded components from the field and the carrying out of a series of controlled laboratory experiments to establish the effects of oxide scale and coating chemistry on hot corrosion life. This is to be determined principally from the length of the incubation period, the investigation of the mechanisms of hot corrosion attack, and the fitting of the data generated from the test exposure experiments to an empirical life prediction model.

Merutka, J.↗
NASA NTRS1985

Environmental Degradation of Materials: Surface Chemistry Related to Stress Corrosion Cracking

Parallel experiments have been performed in order to develop a comprehensive model for stress cracking (SCC) in structural materials. The central objective is to determine the relationship between the activity and selectivity of the microstructure of structural materials to their dissolution kinetics and experimentally measured SCC kinetics. Zinc was chosen as a prototype metal system. The SCC behavior of two oriented single-crystal disks of zinc in a chromic oxide/sodium sulfate solution (Palmerton solution) were determined. It was found that: (1) the dissolution rate is strongly (hkil)-dependent and proportional to the exposure time in the aggressive environment; and (2) a specific slip system is selectively active to dissolution under applied stress and this slip line controls crack initiation and propagation. As a precursor to potential microgrvity experiments, electrophoretic mobility measurements of zinc particles were obtained in solutions of sodium sulfate (0.0033 M) with concentrations of dissolved oxygen from 2 to 8 ppm. The equilibrium distribution of exposed oriented planes as well as their correlation will determine the particle mobility.

Schwarz, J. A.↗