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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effects of Mineral Surface Properties on Supercritical CO 2 Wettability in a Siliciclastic Reservoir

Wettability is a key reservoir characteristic influencing geological carbon sequestration (GCS) processes, such as CO 2 transport and storage capacity. Wettability is often determined on a limited number of reservoir samples by measuring the contact angle at the CO 2 /brine/mineral interface, but the ability to predict this value remains a challenge. In this work, minerals comprising a natural reservoir sample were identified, and the influence of their surface roughness and mineralogy on the contact angle was quantified to evaluate predictive models and controlling mechanisms. The natural sample was obtained from the Mount Simon formation, a representative siliciclastic reservoir that is the site of a United States Department of Energy CO 2 injection project. A thin section of the Mount Simon sandstone was examined with compound light microscopy and environmental scanning electron microscopy (ESEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Quartz and feldspar were identified as dominant minerals and were coated with various reddish black precipitates consistent with illite clay and iron oxide hematite. Contact angle (θ) measurements were conducted for the four representative minerals and the Mount Simon sample over a range of pressures (2–25 MPa) at 40 °C. At supercritical conditions, all samples are strongly water-wet, with contact angles between 27° and 45°. Several predictive models for contact angle were evaluated for the mineral and Mount Simon samples, including the Wenzel and Cassie–Baxter models, plus newly proposed modifications of these that account for the fraction of different minerals comprising the reservoir sample surface, the surface roughness, and the extent that roughness pits are filled with brine. Modeling results suggest that the fraction of mineral surfaces containing roughness pits filled with brine is the most important reservoir characteristic that controls wettability in the Mount Simon sandstone, followed by surface mineralogy. Finally, to our knowledge, this is one of the few studies to investigate the effects of individual minerals on the wettability of a natural reservoir sample.

58 GEOSCIENCES↗
NASA NTRS1986

Non-Lambertian effects on remote sensing of surface reflectance and vegetation index

This paper discusses the effects of non-Lambertian reflection from a homogeneous surface on remote sensing of the surface reflectance and vegetation index from a satellite. Remote measurement of the surface characteristics is perturbed by atmospheric scattering of sun light. This scattering tends to smooth the angular dependence of non-Lambertian surface reflectances, an effect that is not present in the case of Lambertian surfaces. This effect is calculated to test the validity of a Lambertian assumption used in remote sensing. For the three types of vegetations considered in this study, the assumption of Lambertian surface can be used satisfactorily in the derivation of surface reflectance from remotely measured radiance for a view angle outside the backscattering region. Within the backscattering region, however, the use of the assumption can result in a considerable error in the derived surface reflectance. Accuracy also deteriorates with increasing solar zenith angle. The angular distribution of the surface reflectance derived from remote measurements is smoother than that at the surface. The effect of surface non-Lambertianity on remote sensing of vegetation index is very weak. Since the effect is similiar in the visible and near infrared part of the solar spectrum for the vegetations treated in this study, it is canceled in deriving the vegetation index. The effect of the diffuse skylight on surface reflectance measurements at ground level is also discussed.

Lee, T. Y.↗
NASA NTRS1977

Effect of evaporative surface cooling on thermographic assessment of burn depth

Differences in surface temperature between evaporating and nonevaporating, partial- and full-thickness burn injuries were studied in 20 male, white guinea pigs. Evaporative cooling can disguise the temperature differential of the partial-thickness injury and lead to a false full-thickness diagnosis. A full-thickness burn with blister intact may retain enough heat to result in a false partial-thickness diagnosis. By the fourth postburn day, formation of a dry eschar may allow a surface temperature measurement without the complication of differential evaporation. For earlier use of thermographic information, evaporation effects must be accounted for or eliminated.

Anselmo, V. J.↗
DOE OSTI2018

Oxygen Reduction on Gold Nanocrystal Surfaces in Alkaline Electrolyte: Evidence for Surface Proton Transfer Effects

Four-electron oxygen reduction reaction (4e-ORR) pathway, as a key high-performance reaction pathway in energy conversion, has been sought after in numerous investigations on metal surfaces over the last decades. Although the surfaces of the most noble metals, including platinum and palladium, demonstrate the fullpotential- range 4e-ORR, this is not the case, for gold (Au) surfaces. The 4e-ORR is only operative on Au surfaces with {100} subfacets, e.g. Au(100), in alkaline solution, however restricted to a certain potential region at low overpotentials, while reverting to a 2e-ORR at high overpotentials. This ORR on Au(100) has been a long-standing puzzle of electrocatalysis. Hereby we review the ORR studies on Au, along with the studies of water effects on Au catalysts, and present our electrochemical results with monofacet Au nanocrystals. Finally, combining with theoretical calculations we demonstrate that surface proton transfer from co-adsorbed water plays the key role in determining the ORR mechanism on Au surfaces in base.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Pretreatment Effects on the Surface Chemistry of Small Oxygenates on Molybdenum Trioxide

Understanding surface reactions of biomass-derived oxygenates on metal oxides is important for designing catalysts for valorization of biomass. As such, This work elucidated the effect of different pretreatments on molybdenum trioxide (MoO 3 ) to understand how surface reactivity is controlled by the surface oxidation state. The catalyst was pretreated in oxidative, inert, and reducing environments. The inert and reducing pretreatments created oxygen vacancies on the catalyst surface that acted as active sites for the adsorption of oxygenated molecules, with the reducing pretreatment yielding a higher density of these active sites. Exposing the catalyst to an alcoholic solvent such as methanol also led to a partial reduction similar to the inert pretreatment. After pretreatment, the catalyst was exposed to ethanol, acetaldehyde, and crotonaldehyde with subsequent characterization by diffuse reflectance infrared spectroscopy (DRIFTS), temperature-programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) was also used to determine adsorption configurations and energies of ethanol, acetaldehyde, and crotonaldehyde. Reduced surfaces were shown to have a stronger affinity for carbonyls, leading to a higher activity for the aldol condensation of acetaldehyde and ethanol to C 4 molecules. Catalysts pretreated in an oxidative environment were completely inactive toward chemisorption and reaction of acetaldehyde.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1985

Effects of deterministic surface distortions on reflector antenna performance

Systematic distortions of reflector antenna surfaces can cause antenna radiation patterns to be undesirably different from those of perfectly smooth reflector surfaces. In this paper, a simulation model for systematic distortions is described which permits an efficient computation of the effects of distortions in the reflector pattern. The model uses a vector diffraction physical optics analysis for the determination of both the co-polar and cross-polar fields. An interpolation scheme is also presented for the description of reflector surfaces which are prescribed by discrete points. Representative numerical results are presented for reflectors with sinusoidally and thermally distorted surfaces. Finally, comparisons are made between the measured and calculated patterns of a slowly-varying distorted offset parabolic reflector.

Rahmat-Samii, Y.↗
NASA NTRS1979

Interaction of high voltage surfaces with the space plasma

Tests were conducted using plasma densities of approximately 10 to the 5th power - 10 to the 6th power/cu cm. Insulating materials tested were polyimide (Dapton), mica and glass. Surface-area effects were found to be substantially reduced from those previously reported at lower plasma densities. The difference in typical plasma density was felt to be the major cause of this change, although a saturation effect may also be involved. At the 10 to the 5th power/cu cm plasma density range, surface effects on collection current appear limited to roughly 1 cm from the hole. A factor of several reduction of collected current was obtained with both surface scribing and a 2 x 2 cm conducting mesh. It appears possible that the effects of surface treatment might be more significant at lower plasma densities. Effects of repeated tests were also noted, with current collection decreasing with successive tests. Depending on the materials involved, the effect appeared due to either the smoothing of the inside of the insulator hole or the sputtering of insulator on the exposed conductor. A general conclusion was made from a variety of observations, that the generation of vapor is a major factor in the enhancement of collected current.

Kaufman, H. R.↗
NASA NTRS1984

Nature of the Surface and Its Effect on Solid-state Interactions

An important aspect of the friction and wear of solids is the nature and the mechanical behavior of the surface films. A description of the mechanical, physical, and chemical behavior of surface films is achieved by an investigation of boundary lubrication. Two major points are demonstrated. First, the sliding of two solid surfaces under boundary lubricating conditions creates third bodies in the interface. Second, the nature and the evolution of the interface are dictated by the colloidal behavior of the products generated. To illustrate these two propositions, some recent work is presented.

Georges, J. M.↗
NASA NTRS1972

Thermal effects in equilibrium surface segregation in a copper/10-atomic-percent-aluminum alloy using Auger electron spectroscopy

Equilibrium surface segregation of aluminum in a copper-10-atomic-percent-aluminum single crystal alloy oriented in the /111/ direction was demonstrated by using Auger electron spectroscopy. This crystal was in the solid solution range of composition. Equilibrium surface segregation was verified by observing that the aluminum surface concentration varied reversibly with temperature in the range 550 to 850 K. These results were curve fitted to an expression for equilibrium grain boundary segregation and gave a retrieval energy of 5780 J/mole (1380 cal/mole) and a maximum frozen-in surface coverage three times the bulk layer concentration. Analyses concerning the relative merits of sputtering calibration and the effects of evaporation are also included.

Ferrante, J.↗
NASA NTRS1973

Oxygen and sulfur interactions with a clean iron surface and the effect of rubbing contact on these interactions

An investigation was conducted to determine the nature of the chemical interactions of oxygen and sulfur with iron when surfaces are stationary and also during sliding in a vacuum environment. Various gases that contained sulfur, oxygen, or both were adsorbed to iron at 23 C. The gases included oxygen, hydrogen sulfide, methyl mercaptan, and sulfur dioxide. Friction experiments were conducted with a hemispherical rider sliding on a rotating disk. An Auger cylindrical mirror analyzer was used to monitor the iron surface chemistry. The results of this study indicate that oxygen will completely displace sulfide films from iron surfaces. Organic thiols containing sulfur, such as methyl mercaptan, adsorb to an iron surface dissociatively. Only sulfur is detected on the iron surface. Sliding inhibits the formation of sulfide films on iron with the adsorption of hydrogen sulfide and methyl mercaptan. With oxygen and sulfur dioxide, the sliding process does not affect adsorption behavior.

Buckley, D. H.↗
NASA NTRS1975

Surface properties and effective resolution from ground-based observations of Mercury

A detailed study to evaluate ground-based photographs of Mercury has been carried out. Models of the surface scattering properties have been assumed and smeared with a Gaussian function for direct comparison with center-to-limb scans along Mercury's intensity equator. Data from a range of phase angles from 31 to 92 deg have been compared with smeared models assuming a Lambert surface, a surface which obeys the Lommel-Seeliger law and one which is Minnaertian, having a variable coefficient. Within the limits of the observations a lunar Minnaert surface yields the most consistent interpretation. An objective evaluation of the resolution of the photographs is obtained in terms of Gaussian half-widths.

Beebe, R. F.↗
NASA NTRS1977

Mars - Photodesorption from mineral surfaces and its effects on atmospheric stability

Kinetic constraints are employed to identify the reactive chemisorbed complexes, to describe the mechanism of UV-accelerated desorption from Fe (+2) on mineral surfaces, and to estimate the photodesorption rate on Mars. In particular, it is proposed that gases such as O2, CO2, CO, H2O and N2 undergo an adsorption-desorption process at octahedrally coordinated Fe (+2) surface sites to produce seven-coordinate transition-state complexes. The ligand field stabilization energy acquired by these complexes lies between 16 and 18 kcal per mole. Published photocatalysis data are used to assess the role of photodesorption in Martian atmospheric chemistry and stability.

Huguenin, R. L.↗
NASA NTRS1994

Computing Incompressible Flows With Free Surfaces

RIPPLE computer program models transient, two-dimensional flows of incompressible fluids with surface tension on free surfaces of general shape. Surface tension modeled as volume force derived from continuum-surface-force model, giving RIPPLE both robustness and accuracy in modeling surface-tension effects at free surface. Also models wall adhesion effects. Written in FORTRAN 77.

Kothe, D.↗
NASA NTRS1981

A study of real jet effects on the surface pressure distribution induced by a jet in a crossflow

A study of jet exit profile, exit Mach number, swirl and turbulence level on jet-induced loadings for jets exhausting from a surface into a crossflow is presented. The importance of each of these real jet characteristics is assessed using available data. Where adequate surface pressure distribution data are available, a correlation method to predict surface pressure for a jet exhausting from an infinite flat plate is used either to attempt to develop a correlation based on the real jet characteristics or to model the effects of that characteristic. Data comparisons are presented for selected cases. Also, a summary of information on surface pressure distribution data for jet exhausting from flat plates into a subsonic crossflow is presented.

Perkins, S. C., Jr.↗
DOE OSTI2015

Nonradiative Plasmon Decay and Hot Carrier Dynamics: Effects of Phonons, Surfaces, and Geometry

The behavior of metals across a broad frequency range from microwave to ultraviolet frequencies is of interest in plasmonics, nanophotonics, and metamaterials. Depending on the frequency, losses of collective excitations in metals can be predominantly classical resistive effects or Landau damping. In this context, we present first-principles calculations that capture all of the significant microscopic mechanisms underlying surface plasmon decay and predict the initial excited carrier distributions so generated. Particularly, we include ab initio predictions of phonon-assisted optical excitations in metals, which are critical to bridging the frequency range between resistive losses at low frequencies and direct interband transitions at high frequencies. In the commonly used plasmonic materials, gold, silver, copper, and aluminum, we find that resistive losses compete with phonon-assisted carrier generation below the interband threshold, but hot carrier generation via direct transitions dominates above threshold. Furthermore, we predict energy-dependent lifetimes and mean free paths of hot carriers, accounting for electron–electron and electron–phonon scattering, to provide insight toward transport of plasmonically generated carriers at the nanoscale.

36 MATERIALS SCIENCE↗