Search NASA⌕ Search

SEARCH · Search NASA

Results for “active surface area”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Dynamic Model of Basic Oxygen Steelmaking Process Based on Multizone Reaction Kinetics: Modeling of Decarburization

In a previous study by the authors (Rout et al. in Metall Mater Trans B 49:537–557, 2018), a dynamic model for the BOF, employing the concept of multizone kinetics was developed. In the current study, the kinetics of decarburization reaction is investigated. The jet impact and slag–metal emulsion zones were identified to be primary zones for carbon oxidation. The dynamic parameters in the rate equation of decarburization such as residence time of metal drops in the emulsion, interfacial area evolution, initial size, and the effects of surface-active oxides have been included in the kinetic rate equation of the metal droplet. A modified mass-transfer coefficient based on the ideal Langmuir adsorption equilibrium has been proposed to take into account the surface blockage effects of SiO{sub 2} and P{sub 2}O{sub 5} in slag on the decarburization kinetics of a metal droplet in the emulsion. Further, a size distribution function has been included in the rate equation to evaluate the effect of droplet size on reaction kinetics. The mathematical simulation indicates that decarburization of the droplet in the emulsion is a strong function of the initial size and residence time. A modified droplet generation rate proposed previously by the authors has been used to estimate the total decarburization rate by slag–metal emulsion. The model’s prediction shows that about 76 pct of total carbon is removed by reactions in the emulsion, and the remaining is removed by reactions at the jet impact zone. The predicted bath carbon by the model has been found to be in good agreement with the industrially measured data.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synchrotron X-ray studies of model SOFC cathodes, part II: Porous powder cathodes

Infiltrated La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) sintered porous powder cathodes for solid oxide fuel cells have been investigated by synchrotron ultra-small angle x-ray scattering (USAXS). Here, we demonstrated that atomic layer deposition (ALD) is the method for a uniform coating and liquid-phase infiltration for growing nanoscale particles on the porous LSCF surfaces. The MnO infiltrate, grown by ALD, forms a conformal layer with a uniform thickness throughout the pores evidenced by USAXS thickness fringes. The La 0.6 Sr 0.4 CoO 3 (LSC) and La 2 Zr 2 O 7 (LZO) infiltrates, grown by liquid-phase infiltration, were found to form nanoscale particles on the surfaces of LSCF particles resulting in increased surface areas. In conclusion, impedance measurements suggest that the catalytic property of LSC infiltrate, not the increased surface area of LZO, is important for increasing oxygen reduction activities.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthesis of PtCo 3 polyhedral nanoparticles and evolution to Pt 3 Co nanoframes

Bimetallic nanoframes have great potential for achieving new levels of catalytic activity in various heterogeneous reactions due to their high surface area dispersion of expensive noble metals on the exterior and interior surfaces of the structure. PtCo 3 nanoparticles with polyhedral shapes were synthesized by a hot-injection method. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy (EDS) showed that these nanoparticles demonstrated elemental segregation of platinum to the edges of the polyhedron, forming the basis for a framework nanostructure. The process of preferential oxidative leaching which removed cobalt from the interior of the framework was tracked by EDS and inductively coupled plasma optical emission spectroscopy. This evolution procedure left the platinum-rich edges intact to form a Pt 3 Co nanoframe. Finally, this is the first reported synthesis of a platinum-cobalt nanoframe and could have potential applications in catalytic reactions such as oxygen reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Improving the Thermodynamic Stability of Aluminate Spinel Nanoparticles with Rare Earths

Surface energy is a key parameter to understand and predict the stability of catalysts. In this work, the surface energy of MgAl 2 O 4 , an important base material for catalyst support, was reduced by using dopants prone to form surface excess (surface segregation): Y 3+ , Gd 3+ , and La 3+ . The energy reduction was predicted by atomistic simulations of spinel surfaces and experimentally demonstrated by using microcalorimetry. The surface energy of undoped MgAl 2 O 4 was directly measured as 1.65 ± 0.04 J/m 2 and was reduced by adding 2 mol % of the dopants to 1.55 ± 0.04 J/m 2 for Y-doping, 1.45 ± 0.05 J/m 2 for Gd-doping, and 1.26 ± 0.06 J/m 2 for La-doping. Atomistic simulations are qualitatively consistent with the experiments, reinforcing the link between the role of dopants in stabilizing the surface and the energy of segregation. Surface segregation was experimentally assessed using electron energy loss spectroscopy mapping in a scanning transmission electron microscopy image. Finally, the reduced energy resulted in coarsening inhibition for the doped samples and, hence, systematically smaller particle sizes (larger surface areas), meaning increased stability for catalytic applications. Moreover, both experiment and modeling reveal preferential dopant segregation to specific surfaces, which leads to the preponderance of {111} surface planes and suggests a strategy to enhance the area of desired surfaces in nanoparticles for better catalyst support activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Constructing Bifunctional 3D Holey and Ultrathin CoP Nanosheets for Efficient Overall Water Splitting

Pursuing cost-effective water-splitting catalysts is still a significant scientific challenge to produce renewable fuels and chemicals from various renewable feedstocks. The construction of controllable binder-free nanostructures with self-standing holey and ultrathin nanosheets is one of the promising approaches. Herein, by employing a combination of the potentiodynamic mode of electrodeposition and low-temperature phosphidation, three-dimensional (3D) holey CoP ultrathin nanosheets are fabricated on a carbon cloth (PD-CoP UNSs/CC) as bifunctional catalysts. Electrochemical tests show that the PD-CoP UNSs/CC exhibits outstanding hydrogen evolution reaction performance at all pH values with overpotentials of 47, 90, and 51 mV to approach 10 mA cm –2 in acidic, neutral, and alkaline media, respectively. Meanwhile, only a low overpotential of 268 mV is required to drive 20 mA cm –2 for the oxygen evolution reaction in alkaline media. Cyclic voltammetry and impedance studies suggest the enhanced performance is mainly attributed to the unique 3D holey ultrathin nanosheets, which could increase the electrochemically active area, facilitate the release of gas bubbles from electrode surfaces, and improve effective electrolyte diffusion. This work suggests an efficient path to design and fabricate non-noble bifunctional electrocatalysts for water splitting at a large scale.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Porous carbon derived from aniline-modified fungus for symmetrical supercapacitor electrodes

N incorporated carbon materials are proven to be efficient EDLCs electrode materials. In this work, aniline modified fungus served as a raw material, and N-doped porous activated carbon is prepared via an efficient KOH activation method. A porous network with a high specific surface area of 2339 m 2 g -1 is displayed by the prepared carbon material, resulting in a high accessible surface area and low ion diffusion resistance which is desirable for EDLC electrode materials. In assembled EDLCs, the N–AC based electrode exhibits a specific capacitance of 218 F g -1 at a current density of 0.1 A g -1 . Besides, excellent stability is displayed after 5000 continuous cycles at different current densities ranging from 0.1 to 10 A g -1 . Thus, the present work reveals a promising candidate for electrode materials of EDLCs.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Understanding the critical chemistry to inhibit lithium consumption in lean lithium metal composite anodes

Lithium metal has been deemed by many as the “Holy Grail” of anode materials due to its high theoretical capacity (~3860 mA h g -1 ), redox potential of -3.040 V vs. SHE, and light weight. The goal of this work is to investigate the relationship between a lean lithium metal anode and its consumption as a function of host materials, electrochemical protocol and electrolyte composition. With the use of carbon nanofibers, lithium metal has been electrodeposited onto the host matrix and used in a battery with a LiNi 0.6 Mn 0.2 Co 0.2 O 2 cathode. The mass-loading of lithium can be easily controlled and utilized to investigate the practicality of an anode limited battery (i.e., limited lithium with an effective thickness <15 μm) in a high surface area matrix. We then quantify the consumption rate of active lithium using different electrolyte additives and current rates in full cells and observe that the lithium consumption behavior in an anode-limited cell is different from that in an anode-excess cell. Our results highlight the necessity of applying truly lithium-limited cells when evaluating the electrochemical properties of lithium anodes and electrolyte additives. By extending this method to a standard graphite host, full cells can retain 75% of their initial capacities after 1000 cycles. The present study demonstrates the importance of graphitic carbon in increasing the lifespan of limited lithium (<15 μm) for practical lithium metal batteries.

25 ENERGY STORAGE↗
DOE OSTI2023

Synthesis of zirconium-based metal–organic frameworks with iron( ii ) clathrochelate ligands

Zirconium-based metal organic frameworks (MOFs) are of great significance in supramolecular coordination chemistry, mainly as catalysts, due to their chemical stability and structural diversity. We report the synthesis of zirconium-clathrochelate based crystalline MOFs (Zr-GU-1to -4) made from hexanuclear zirconium inorganic nodes and iron(II) clathrochelate-based ditopic carboxylic acid ligands bearing various lateral moieties, namely, butyl, cyclohexyl, phenyl and methyl groups. Among the various iron(II) clathrochelate linkers, the one with butyl side chains, i.e., Zr-GU-1, forms stable crystalline MOFs as confirmed by single-crystal X-ray crystallography and exhibits a promising porosity with a BET surface area of ~650 m 2 g -1 after its activation with supercritical CO 2 (ScCO 2 ) from acetonitrile.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

Monitoring of environmental effects of coal strip mining from satellite imagery

This paper evaluates satellite imagery as a means of monitoring coal strip mines and their environmental effects. The satellite imagery employed is Skylab EREP S-190A and S-190B from SL-2, SL-3 and SL-4 missions; a large variety of camera/film/filter combinations has been reviewed. The investigation includes determining the applicability of satellite imagery for detection of disturbed acreage in areas of coal surface mining as well as the much more detailed monitoring of specific surface-mining operations, including: active mines, inactive mines, highwalls, ramp roads, pits, water impoundments and their associated acidity, graded areas and types of grading, and reclamed areas. Techniques have been developed to enable mining personnel to utilize this imagery in a practical and economic manner, requiring no previous photo-interpretation background and no purchases of expensive viewing or data-analysis equipment. To corroborate the photo-interpretation results, on-site observations were made in the very active mining area near Madisonville, Kentucky.

Brooks, R. L.↗
NASA NTRS1978

Lunar KREEP volcanism - Geologic evidence for history and mode of emplacement

The history of KREEP basalt emplacement in the Fra Mauro and Imbrium basin regions was investigated on the basis of the petrologic and geochemical characteristics of Apollo 14 and 15 samples and data from photogeologic, site geology and remote sensing studies. Results suggest that KREEP emplacement began after the excavation of the South Imbrium basin more than 4.0 to 4.1 billion years ago, continued into early to mid-Imbrium, and was in part sychronous with mare volcanism. Surface KREEP activity appears to be concentrated in a triangular area bounded by the Apollo 15 site, southern Procellarum and the Aristarchus region. Most of the Apollo 15 igneous KREEP basalts are products of post-Imbrium KREEP volcanism within the Imbrium basis, whereas the Apollo 14 KREEP-rich breccias represent extensively reworked KREEP volcanics extruded prior to about 4.0 to 4.1 billion years ago.

Hawke, B. R.↗
NASA NTRS1983

Three Mars years - Viking Lander 1 imaging observations

The Mutch Memorial Station (Viking Lander 1) on Mars acquired imaging and meteorological data over a period of 2245 martian days (3.3 martian years). This article discusses the deposition and erosion of thin deposits (ten to hundreds of micrometers) of bright red dust associated with global dust storms, and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter. Atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds. Erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities. Except for redistribution of thin layers of materials, the surface appears to be remarkably stable, perhaps because of cohension of the undisturbed surface material.

Arvidson, R. E.↗
NASA NTRS1988

A model for intensity profiles of dust jets near the nucleus of Comet Halley

The Giotto spacecraft's Halley Multicolor Camera images have been used to derive intensity profiles of the jetlike dust features that are associated with active regions of the Comet Halley nucleus. An intensity profile's asymptotic behavior at a radius greater than 100 km from the nucleus can be seen as arising from a source located at a hypothetical point below the active source region. Several source distributions are investigated. The extended source model considers divergent dust flow from an active area of arbitrary shape. It is concluded that the surface is neither smooth nor homogeneous, but must instead be characterized by varying curvature and roughness in order to reflect the observed conical dust flow.

Huebner, W. F.↗
DOE OSTI2019

Enhanced Techniques for Concrete Decontamination During Decommissioning - 19005

As the primary material of construction for nuclear power plant structures, concrete naturally represents the largest fraction of contaminated material by surface area. As such, decontamination of concrete is a major activity during decommissioning projects. As reported in EPRI 3002005412, Characterization and Remediation of Contaminated Concrete, currently used techniques for decontamination of contaminated concrete are generally slow and labor-intensive to apply. This report notes that little change to the techniques used for concrete decontamination have been made during the past 20 years. There is a clear need for improvement to the techniques available for decontamination of concrete. Needed enhancements include substantial improvements in efficiency, waste management, industrial safety, and worker radiation exposure. Potential areas for development include increased automation of existing techniques, improvement in delivery systems for decontamination equipment, and further development of alternative techniques such as microwave and laser scabbling, and nitrogen blasting. To address this need, EPRI is conducting a project to develop enhanced techniques for concrete decontamination. The project focuses on two primary areas: 1. Adaption of existing techniques to improve efficiency through automation and/or altering the delivery systems for the decontamination equipment (for example, through use of exiting robotic systems); and 2. Field demonstration of technologies currently in the engineering development stage, such as nitrogen blasting and laser scabbling. This paper will report the initial results of this EPRI project, which includes identification of promising candidate technologies that will be demonstrated during the next project phase. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles

Data from both laboratory studies and atmospheric measurements are used to develop an empirical parameterization for the immersion freezing activity of natural mineral dust particles. Measurements made with the Colorado State University (CSU) continuous flow diffusion chamber (CFDC) when processing mineral dust aerosols at a nominal 105% relative humidity with respect to water (RH w ) are taken as a measure of the immersion freezing nucleation activity of particles. Ice active frozen fractions vs. temperature for dusts representative of Saharan and Asian desert sources were consistent with similar measurements in atmospheric dust plumes for a limited set of comparisons available. The parameterization developed follows the form of one suggested previously for atmospheric particles of non-specific composition in quantifying ice nucleating particle concentrations as functions of temperature and the total number concentration of particles larger than 0.5 μm diameter. Such an approach does not explicitly account for surface area and time dependencies for ice nucleation, but sufficiently encapsulates the activation properties for potential use in regional and global modeling simulations, and possible application in developing remote sensing retrievals for ice nucleating particles. A calibration factor is introduced to account for the apparent underestimate (by approximately 3, on average) of the immersion freezing fraction of mineral dust particles for CSU CFDC data processed at an RH w of 105% vs. maximum fractions active at higher RH w . Instrumental factors that affect activation behavior vs. RH w in CFDC instruments remain to be fully explored in future studies. Nevertheless, the use of this calibration factor is supported by comparison to ice activation data obtained for the same aerosols from Aerosol Interactions and Dynamics of the Atmosphere (AIDA) expansion chamber cloud parcel experiments. Further comparison of the new parameterization, including calibration correction, to predictions of the immersion freezing surface active site density parameterization for mineral dust particles, developed separately from AIDA experimental data alone, shows excellent agreement for data collected in a descent through a Saharan aerosol layer. These studies support the utility of laboratory measurements to obtain atmospherically relevant data on the ice nucleation properties of dust and other particle types, and suggest the suitability of considering all mineral dust as a single type of ice nucleating particle as a useful first-order approximation in numerical modeling investigations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

A Modified P1 Moiety Enhances in vitro Antiviral Activity against Various Multi-Drug-Resistant HIV-1 Variants and in vitro CNS Penetration Properties of a Novel Nonpeptidic Protease Inhibitor, GRL-10413

We here report that GRL-10413, a novel non-peptidic HIV-1 protease inhibitor (PI) containing a modified P1 moiety and a sulfonamide isostere, is highly active against laboratory HIV-1 strains and primary clinical isolates (EC 50 : 0.00035 - 0.0018 μM) with minimal cytotoxicity (CC 50 : 35.7 μM). GRL-10413 blocked the infectivity and replication of HIV-1 NL4-3 variants selected by up to 5 μM concentrations of atazanavir, lopinavir, or amprenavir (EC 50 : 0.0021 - 0.0023 μM). GRL-10413 also maintained its strong antiviral activity against multi-drug-resistant clinical HIV-1 variants isolated from patients, who no longer responded to various antiviral regimens after long-term antiretroviral therapy. The development of resistance against GRL-10413 was significantly delayed compared to that of APV. In addition, GRL-10413 showed a favorable central nervous system (CNS) penetration property as assessed with an in vitro blood brain barrier (BBB) reconstruction system. Analysis of the crystal structure of HIV-1 protease in complex with GRL-10413 demonstrated that the modified P1 moiety of GRL-10413 has a greater hydrophobic surface area and makes greater van der Waals contacts with active-site amino acids of protease than in the case of darunavir. Moreover, the chlorine substituent in the P1 moiety interacts with protease in two distinct configurations. The present data demonstrate that GRL-10413 has desirable features for treating patients infected with wild-type and/or multi-drug-resistant HIV-1 variants with favorable CNS-penetration capability and that the newly modified P1-moiety may confer desirable features in designing novel anti-HIV-1 PIs.

Amano, Masayuki↗
DOE OSTI2018

Controllable synthesis of hydroxyapatite-supported palladium nanoparticles with enhanced catalytic activity

A multi-stage electrochemical method was developed to synthesize palladium (Pd) nanoparticles supported on hydroxyapatite (HA) coatings. In the first stage, a dense coating of HA nanocrystals was synthesized from an aqueous electrolyte solution onto a titanium cathode surface through a galvanostatic process. The HA-coated titanium electrode was then used as the cathode for the electrochemical reduction of Pd2+ from aqueous solution. A synthesis approach using two sequential electrochemical reduction reactions was found to be more e ective in producing uniform coatings of Pd nanoparticles than a single stage reduction. In the first step, a higher voltage was applied to the cathode for a short time to promote the nucleation of Pd nanoparticles. A lower voltage was then applied for a longer time in the second stage to promote the growth of the Pd nanoparticles. The size and size distribution of the Pd nanoparticles were controlled by adjusting the duration of the first and second stages of electrochemical reduction. The resulting HA supported Pd nanoparticles demonstrated significantly higher catalytic activity than commercial Pd nanoparticles in the degradation of methyl orange by NaBH 4 . The high surface area and the complex oxidation states of the HA-supported Pd nanoparticles are believed to account for the enhanced catalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

The effects of hydrothermal temperature on the photocatalytic performance of ZnIn{sub 2}S{sub 4} for hydrogen generation under visible light irradiation

Highlights: • The ZnIn{sub 2}S{sub 4} (120, 140, 160, 180, and 200 °C) was prepared. • The activities splitting water to hydrogen under visible light were evaluated. • The activity achieved the best when hydrothermal temperature was 160 °C. • The activity order is related to the surface morphology and surface defects. - Abstract: A series of ZnIn{sub 2}S{sub 4} photocatalysts were successfully synthesized using the hydrothermal method with different hydrothermal temperatures (120, 140, 160, 180, and 200 °C) and characterized by various analysis techniques, such as UV–vis, XRD, SEM, BET and PL. The results indicated that these photocatalysts had a similar band gap. The hydrothermal temperature had a huge influence on the properties of the photocatalysts such as the BET surface area, the total pore volume, the average pore diameter, the defects and the morphology. The photocatalytic activities of ZnIn{sub 2}S{sub 4} were evaluated based on photocatalytic hydrogen production from water under visible-light irradiation. The activity order is attributed to the coefficient of the surface morphology and the surface defects. The hydrogen production efficiency achieved the best when the hydrothermal temperature was 160 °C. On the basis of the characterization of the catalysts, the effects of the hydrothermal temperature on the photocatalytic activity of ZnIn{sub 2}S{sub 4} were discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A Biomimetic Approach to New Adsorptive Hydrogen Storage Metal-Organic Frameworks

In the past decades, there has been an escalation of interest in the study of MOFs due to their fascinating structures and intriguing application potentials. Their exceptionally high surface areas, uniform yet tunable pore sizes, and well-defined adsorbate-MOF interaction sites make them suitable for hydrogen storage. Various strategies to increase the hydrogen capacity of MOFs, such as constructing pore sizes comparable to hydrogen molecules, increasing surface area and pore volume, utilizing catenation, and introducing coordinatively unsaturated metal centers (UMCs) have been widely explored to increase the hydrogen uptake of the MOFs. MOFs with hydrogen uptake approaching the DOE gravimetric storage goal under reasonable pressure but cryo- temperature (typically 77 K) were achieved. However, the weak interaction between hydrogen molecules and MOFs has been the major hurdle limiting the hydrogen uptake of MOFs at ambient temperature. Along the road, we have realized both high surface area and strong interaction between framework and hydrogen are equally essential for porous materials to be practically applicable in Hydrogen storage. Increasing the isosteric heats of adsorption for hydrogen through the introduction of active centers into the framework could have great potential on rendering the framework with strong interaction toward hydrogen. Approaches on increasing the surface areas and improving hydrogen affinity by optimizing size and structure of the pores and the alignment of active centers around the pores in frameworks have been pursued, for example: (a) the introduction of coordinatively UMC (represents a metal center missing multiple ligands) with potential capability of multiple dihydrogen-binding (Kubas type, non-dissociative) per UMC, (b) the design and synthesis of proton-rich MOFs in which a + H3 binds dihydrogen just like a metal ion does, and (c) the preparation of MOFs and PPNs with well aligned internal electric fields. We believe the accomplishments of this DOE supported research will greatly benefit the future pursuit of hydrogen storage materials. The ultimate goal to increase the gravimetric and volumetric hydrogen storage capacity to meet DOE targets for Light-Duty Vehicles is achievable.

08 HYDROGEN↗