Temperature-dependent selective oxidation processes for Ni-5Cr and Ni-4Al

DOE PAGES

Kruska, Karen; Schreiber, Daniel K.; Olszta, Matthew J.; ...

2018-05-09

The selective oxidation of Ni-5Cr and Ni-4 Al alloys is evaluated during high (800 °C) and low (420 °C) temperature exposures with the oxygen partial pressure moderated by a Ni/NiO powder buffer. Internal oxidation of Cr and Al is observed throughout the matrix and at grain boundaries at 800 °C accompanied by the ejection of Ni onto the surface for both. At 420 °C, matrix internal oxidation was eliminated and only Ni-4 Al exhibited intergranular (IG) oxidation. Surprisingly, a protective surface oxide rapidly formed for Ni-5Cr blocking IG oxidation. Finally, this is contradictory to results in 330–360 °C hydrogenated watermore » environments where both alloys show IG oxidation.« less

Temperature-dependent selective oxidation processes for Ni-5Cr and Ni-4Al

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruska, Karen; Schreiber, Daniel K.; Olszta, Matthew J.

The selective oxidation of Ni-5Cr and Ni-4 Al alloys is evaluated during high (800 °C) and low (420 °C) temperature exposures with the oxygen partial pressure moderated by a Ni/NiO powder buffer. Internal oxidation of Cr and Al is observed throughout the matrix and at grain boundaries at 800 °C accompanied by the ejection of Ni onto the surface for both. At 420 °C, matrix internal oxidation was eliminated and only Ni-4 Al exhibited intergranular (IG) oxidation. Surprisingly, a protective surface oxide rapidly formed for Ni-5Cr blocking IG oxidation. Finally, this is contradictory to results in 330–360 °C hydrogenated watermore » environments where both alloys show IG oxidation.« less

Detection of lack of fusion using opaque additives

NASA Technical Reports Server (NTRS)

Cook, J. L.

1973-01-01

Reliable nondestructive inspection for incomplete weldment penetration and rapid oxidation of aluminum surfaces when exposed to the atmosphere are currently two major problems in welded aluminum spacecraft structure. Incomplete-penetration defects are extremely difficult to detect and can lead to catastrophic failure of the structure. The moisture absorbed by aluminum oxide on the surface can cause weldment porosity if the surface is not cleaned before welding. The approach employed in this program to solve both problems was to employ copper as a coating to prevent oxidation of the aluminum. Also, copper was used as an opaque additive in the weldment to enhance X-ray detection in the event of incomplete penetration.

40 CFR 98.208 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... GREENHOUSE GAS REPORTING Magnesium Production § 98.208 Definitions. All terms used in this subpart have the... the surface of molten magnesium from rapid oxidation and burning in the presence of air. The molten magnesium may be the surface of a casting or ingot production operation or the surface of a crucible of...

40 CFR 98.208 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... GREENHOUSE GAS REPORTING Magnesium Production § 98.208 Definitions. All terms used in this subpart have the... the surface of molten magnesium from rapid oxidation and burning in the presence of air. The molten magnesium may be the surface of a casting or ingot production operation or the surface of a crucible of...

40 CFR 98.208 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... GREENHOUSE GAS REPORTING Magnesium Production § 98.208 Definitions. All terms used in this subpart have the... the surface of molten magnesium from rapid oxidation and burning in the presence of air. The molten magnesium may be the surface of a casting or ingot production operation or the surface of a crucible of...

40 CFR 98.208 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... GREENHOUSE GAS REPORTING Magnesium Production § 98.208 Definitions. All terms used in this subpart have the... the surface of molten magnesium from rapid oxidation and burning in the presence of air. The molten magnesium may be the surface of a casting or ingot production operation or the surface of a crucible of...

As(III) oxidation by MnO2 during groundwater treatment.

PubMed

Gude, J C J; Rietveld, L C; van Halem, D

2017-03-15

The top layer of natural rapid sand filtration was found to effectively oxidise arsenite (As(III)) in groundwater treatment. However, the oxidation pathway has not yet been identified. The aim of this study was to investigate whether naturally formed manganese oxide (MnO 2 ), present on filter grains, could abiotically be responsible for As(III) oxidation in the top of a rapid sand filter. For this purpose As(III) oxidation with two MnO 2 containing powders was investigated in aerobic water containing manganese(II) (Mn(II)), iron(II) (Fe(II)) and/or iron(III) (Fe(III)). The first MnO 2 powder was a very pure - commercially available - natural MnO 2 powder. The second originated from a filter sand coating, produced over 22 years in a rapid filter during aeration and filtration. Jar test experiments showed that both powders oxidised As(III). However, when applying the MnO 2 in aerated, raw groundwater, As(III) removal was not enhanced compared to aeration alone. It was found that the presence of Fe(II)) and Mn(II) inhibited As(III) oxidation, as Fe(II) and Mn(II) adsorption and oxidation were preferred over As(III) on the MnO 2 surface (at pH 7). Therefore it is concluded that just because MnO 2 is present in a filter bed, it does not necessarily mean that MnO 2 will be available to oxidise As(III). However, unlike Fe(II), the addition of Fe(III) did not hinder As(III) oxidation on the MnO 2 surface; resulting in subsequent effective As(V) removal by the flocculating hydrous ferric oxides. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nonlinear electronic transport and enhanced catalytic behavior caused by native oxides on Cu nanowires

NASA Astrophysics Data System (ADS)

Hajimammadov, Rashad; Csendes, Zita; Ojakoski, Juha-Matti; Lorite, Gabriela Simone; Mohl, Melinda; Kordas, Krisztian

2017-09-01

Electrical transport properties of individual nanowires (both in axial and transversal directions) and their random networks suggest rapid oxidation when Cu is exposed to ambient conditions. The oxidation process is elucidated by thorough XRD, XPS and Raman analyzes conducted for a period of 30 days. Based on the obtained experimental data, we may conclude that first, cuprous oxide and copper hydroxide form that finally transform to cupric oxide. In electrical applications, oxidation of copper is not a true problem as long as thin films or bulk metal is concerned. However, as highlighted in our work, this is not the case for nanowires, since the oxidized surface plays quite important role in the contact formation and also in the conduction of percolated nanowire networks. On the other hand, by taking advantage of the mixed surface oxide states present on the nanowires along with their large specific surface area, we tested and found excellent catalytic activity of the oxidized nanowires in phenol oxidation, which suggests further applications of these materials in catalysis.

Hydrogen passivation of silicon(100) used as templates for low-temperature epitaxy and oxidation

NASA Astrophysics Data System (ADS)

Atluri, Vasudeva Prasad

Epitaxial growth, oxidation and ohmic contacts require surfaces as free as possible of physical defects and chemical contaminants, especially, oxygen and hydrocarbons. Wet chemical cleaning typically involves a RCA clean to remove contaminants by stripping the native oxide and regrowing a chemical oxide with only trace levels of carbon and metallic impurities. Low temperature epitaxy, T<800sp° C, limits the thermal budget for the desorption of impurities and surface oxides, and can be performed on processed structures. But, silicon dioxide cannot be desorbed at temperatures lower than 800sp°C. Recently, hydrogen passivation of Si(111) has been reported to produce stable and ordered surfaces at low temperatures. Hydrogen can then be desorbed between 200sp°C and 600sp°C prior to deposition. In this work, Si(100) is passivated via a solution of hydrofluoric acid in alcohol (methanol, ethanol, or isopropyl alcohol) with HF concentrations between 0.5 to 10%. A rinse in water or alcohol is performed after etching to remove excess fluorine. This work investigates wet chemical cleaning of Si(100) to produce ordered, hydrogen-terminated, oxygen- and carbon-free surfaces to be used as templates for low temperature epitaxial growth and rapid thermal oxidation. Ion beam analysis, Tapping mode atomic force microscopy, Fourier transform infrared spectroscopy, Secondary ion mass spectroscopy, Chemical etching, Capacitance-voltage measurements and Ellipsometry are used to measure, at the surface and interface, impurities concentration, residual disorder, crystalline order, surface topography, roughness, chemical composition, defects density, electrical characteristics, thickness, and refractive index as a function of cleaning conditions for homoepitaxial silicon growth and oxidation. The wetting characteristics of the Si(100) surfaces are measured with a tilting plate technique. Different materials are analyzed by ion beam analysis for use as hydrogen standards in elastic recoil detection of hydrogen on sample surfaces. The results obtained in this study provide a quantitative optimization of passivation of Si(100) surfaces and their use as templates for low temperature epitaxy and rapid thermal oxidation. Ion beam analysis shows that the total coverage of H increases during passivation of Si(100) via HF in alcohol, while Fourier transform infrared spectroscopy indicates that more complex termination than the formation of simple silicon hydrides occurs.

Passivation of uranium towards air corrosion by N 2+ and C + ion implantation

NASA Astrophysics Data System (ADS)

Arkush, R.; Mintz, M. H.; Shamir, N.

2000-10-01

The passivation of uranium surfaces against air corrosion, by ion implantation processes was studied, using surface analysis methods. Implanting 45 keV N +2 and C + ions produces thin modified surface layers with gradual gradients of the corresponding compounds (i.e., nitrides and carbides, respectively), which avoid the formation of discontinuous interfaces typical to coatings. Such gradual interfaces impart excellent mechanical stability and adhesion to the modified layers, in spite of the large misfit between the metal substrate and the implantation on induced compounds. It turns out that these layers provide an almost absolute protection against air corrosion. A rapid initial stage of oxidation of the modified surface layers takes place, forming very thin protective oxidation zones (1-4 nm thick), which practically stop further air oxidation for years. The mechanism of the initial oxidation stage of the modified layers seems to vary with the type of surface (i.e., either nitrides or carbides). However, in any case the protection ability of the formed oxidation products is excellent, probably due to the close match between these compounds and the underlying nitrides or carbides.

ESCA study of oxidation and hot corrosion of nickel-base superalloys. [Electron Spectroscopy for Chemical Analysis

NASA Technical Reports Server (NTRS)

Smith, S. R.; Carter, W. J., III; Mateescu, G. D.; Kohl, F. J.; Fryburg, G. C.; Stearns, C. A.

1980-01-01

A study of the high-temperature oxidation and Na2SO4-induced hot corrosion of nickel-base superalloys has been accomplished by using ESCA to determine the surface composition of the oxidized or corroded samples. Oxidation was carried out at 900 or 1000 C in slowly flowing O2 for samples of B-1900, NASA-TRW VIA, 713C, and IN-738. Hot corrosion of B-1900 was induced by applying a coating of Na2SO4 to preoxidized samples, then heating to 900 C in slowly flowing O2. For oxidized samples, the predominant type of scale formed by each superalloy showed a marked surface enrichment of Ti. For corroded samples, the transfer of significant amounts of material from the oxide layer to the surface of the salt layer was observed before the onset of rapidly accelerating weight gain. Marked changes in surface composition coincided with the beginning of accelerating corrosion, the most striking of which were a tenfold decrease in the sulfur to sodium ratio and an increase in the Cr(VI) to Cr(III) ratio.

Corrosion resistance of the microarc oxidation coatings prepared on magnesium alloy

NASA Astrophysics Data System (ADS)

Lv, Ying; Li, Jun Gang; Wu, Ming Zhong; Ma, Zhen; Zhang, Jing Qiang; Wang, Le Le

2018-06-01

Ceramic coatings were prepared on the surface of AZ91D magnesium alloy by microarc oxidation technology. The effects of different voltages on morphology, phase composition and thickness of the coatings were characterized by SEM and XRD. The corrosion resistance of the coatings was measured by electrochemical workstation. Results indicated that the microarc oxidation coatings prepared in sodium silicate electrolyte exhibited porous surface and mainly comprised MgO, Mg2SiO4 and a small amount of MgAl2O4. The thickness of the oxide coatings increased rapidly with the increase of voltage. The coating prepared at 400V voltage had good electrochemical corrosion resistance in 3.5wt% NaCl solution.

Rapid Evaporation of Water on Graphene/Graphene-Oxide: A Molecular Dynamics Study.

PubMed

Li, Qibin; Xiao, Yitian; Shi, Xiaoyang; Song, Shufeng

2017-09-07

To reveal the mechanism of energy storage in the water/graphene system and water/grapheme-oxide system, the processes of rapid evaporation of water molecules on the sheets of graphene and graphene-oxide are investigated by molecular dynamics simulations. The results show that both the water/graphene and water/grapheme-oxide systems can store more energy than the pure water system during evaporation. The hydroxyl groups on the surface of graphene-oxide are able to reduce the attractive interactions between water molecules and the sheet of graphene-oxide. Also, the radial distribution function of the oxygen atom indicates that the hydroxyl groups affect the arrangement of water molecules at the water/graphene-oxide interface. Therefore, the capacity of thermal energy storage of the water/graphene-oxide system is lower than that of the water/graphene system, because of less desorption energy at the water/graphene-oxide interface. Also, the evaporation rate of water molecules on the graphene-oxide sheet is slower than that on the graphene sheet. The Leidenfrost phenomenon can be observed during the evaporation process in the water/grapheme-oxide system.

Rapid Evaporation of Water on Graphene/Graphene-Oxide: A Molecular Dynamics Study

PubMed Central

Li, Qibin; Xiao, Yitian; Shi, Xiaoyang; Song, Shufeng

2017-01-01

To reveal the mechanism of energy storage in the water/graphene system and water/grapheme-oxide system, the processes of rapid evaporation of water molecules on the sheets of graphene and graphene-oxide are investigated by molecular dynamics simulations. The results show that both the water/graphene and water/grapheme-oxide systems can store more energy than the pure water system during evaporation. The hydroxyl groups on the surface of graphene-oxide are able to reduce the attractive interactions between water molecules and the sheet of graphene-oxide. Also, the radial distribution function of the oxygen atom indicates that the hydroxyl groups affect the arrangement of water molecules at the water/graphene-oxide interface. Therefore, the capacity of thermal energy storage of the water/graphene-oxide system is lower than that of the water/graphene system, because of less desorption energy at the water/graphene-oxide interface. Also, the evaporation rate of water molecules on the graphene-oxide sheet is slower than that on the graphene sheet. The Leidenfrost phenomenon can be observed during the evaporation process in the water/grapheme-oxide system. PMID:28880207

Pure and Oxidized Copper Materials as Potential Antimicrobial Surfaces for Spaceflight Activities.

PubMed

Hahn, C; Hans, M; Hein, C; Mancinelli, R L; Mücklich, F; Wirth, R; Rettberg, P; Hellweg, C E; Moeller, R

2017-12-01

Microbial biofilms can lead to persistent infections and degrade a variety of materials, and they are notorious for their persistence and resistance to eradication. During long-duration space missions, microbial biofilms present a danger to crew health and spacecraft integrity. The use of antimicrobial surfaces provides an alternative strategy for inhibiting microbial growth and biofilm formation to conventional cleaning procedures and the use of disinfectants. Antimicrobial surfaces contain organic or inorganic compounds, such as antimicrobial peptides or copper and silver, that inhibit microbial growth. The efficacy of wetted oxidized copper layers and pure copper surfaces as antimicrobial agents was tested by applying cultures of Escherichia coli and Staphylococcus cohnii to these metallic surfaces. Stainless steel surfaces were used as non-inhibitory control surfaces. The production of reactive oxygen species and membrane damage increased rapidly within 1 h of exposure on pure copper surfaces, but the effect on cell survival was negligible even after 2 h of exposure. However, longer exposure times of up to 4 h led to a rapid decrease in cell survival, whereby the survival of cells was additionally dependent on the exposed cell density. Finally, the release of metal ions was determined to identify a possible correlation between copper ions in suspension and cell survival. These measurements indicated a steady increase of free copper ions, which were released indirectly by cells presumably through excreted complexing agents. These data indicate that the application of antimicrobial surfaces in spaceflight facilities could improve crew health and mitigate material damage caused by microbial contamination and biofilm formation. Furthermore, the results of this study indicate that cuprous oxide layers were superior to pure copper surfaces related to the antimicrobial effect and that cell density is a significant factor that influences the time dependence of antimicrobial activity. Key Words: Contact killing-E. coli-S. cohnii-Antimicrobial copper surfaces-Copper oxide layers-Human health-Planetary protection. Astrobiology 17, 1183-1191.

Reactions of singlet oxygen with pine pollen.

NASA Technical Reports Server (NTRS)

Dowty, B.; Laseter, J. L.; Griffin, G. W.; Politzer, I. R.; Walkinshaw, C. H.

1973-01-01

A study was initiated to determine whether viable atmospheric particles such as plant pollens and fungal spores containing unsaturated lipids can interact with singlet oxygen to give oxygenated products that are potentially toxic. The results obtained confirm that surface and near surface components of common viable particulate matter in the atmosphere may be subject to rapid oxidation by singlet oxygen, leading to products which are probably allylic hydroperoxides. In connection with increasing atmospheric pollution, it is important to note that materials toxic to mammalian lung tissue may be oxidatively produced on the surfaces of viable particulate matter.

Native oxide formation on pentagonal copper nanowires: A TEM study

NASA Astrophysics Data System (ADS)

Hajimammadov, Rashad; Mohl, Melinda; Kordas, Krisztian

2018-06-01

Hydrothermally synthesized copper nanowires were allowed to oxidize in air at room temperature and 30% constant humidity for the period of 22 days. The growth of native oxide layer was followed up by high-resolution transmission electron microscopy and diffraction to reveal and understand the kinetics of the oxidation process. Copper oxides appear in the form of differently oriented crystalline phases around the metallic core as a shell-like layer (Cu2O) and as nanoscopic islands (CuO) on the top of that. Time dependent oxide thickness data suggests that oxidation follows the field-assisted growth model at the beginning of the process, as practically immediately an oxide layer of ∼2.8 nm thickness develops on the surface. However, after this initial rapid growth, the local field attenuates and the classical parabolic diffusion limited growth plays the main role in the oxidation. Because of the single crystal facets on the side surface of penta-twinned Cu nanowires, the oxidation rate in the diffusion limited regime is lower than in polycrystalline films.

Influence of growth conditions on subsequent submonolayer oxide decomposition on Si(111)

NASA Astrophysics Data System (ADS)

Shklyaev, A. A.; Aono, Masakazu; Suzuki, Takanori

1996-10-01

The decomposition kinetics of oxide with a coverage between 0.1 and 0.5 ML, grown by oxidation of the Si(111)-7×7 surface at temperatures between 550 and 800 °C for oxygen pressures (Pox) between 3×10-8 and 2×10-6 Torr, is investigated with optical second-harmonic generation. Through the analysis of the pressure dependence of the initial oxide-growth rate, we separate the conditions for a slow oxide growth at Pox near Ptr(T) and for a rapid oxide growth at Pox>3Ptr(T), where Ptr(T) is the transition pressure to Si-etching regime without oxide growth. For the rapidly grown oxide, the oxide decomposition rate decreases with increasing oxide coverage, whereas the activation energy of about 3 eV does not change significantly. While in the case when the oxide is desorbed at the same temperature as are used for oxide growth, the oxide decomposition is described by an apparent activation energy of 1.5 eV. For the slowly grown oxide of 0.1 ML coverage, the oxide desorption kinetics shows a rapid decomposition stage followed by a slow stage. For the slowly grown oxide of 0.3 ML coverage, the slow stage with a large activation energy of 4.1 eV becomes dominant in the latter part of decomposition. The dependence of the desorption kinetics on the oxide-growth conditions described here could be a reason for the scattering of the kinetic parameters in the literature for O2 interaction with silicon at elevated temperatures.

Control of grown-in defects and oxygen precipitates in silicon wafers with DZ-IG structure by ultrahigh-temperature rapid thermal oxidation

NASA Astrophysics Data System (ADS)

Maeda, Susumu; Sudo, Haruo; Okamura, Hideyuki; Nakamura, Kozo; Sueoka, Koji; Izunome, Koji

2018-04-01

A new control technique for achieving compatibility between crystal quality and gettering ability for heavy metal impurities was demonstrated for a nitrogen-doped Czochralski silicon wafer with a diameter of 300 mm via ultra-high temperature rapid thermal oxidation (UHT-RTO) processing. We have found that the DZ-IG structure with surface denuded zone and the wafer bulk with dense oxygen precipitates were formed by the control of vacancies in UHT-RTO process at temperature exceeding 1300 °C. It was also confirmed that most of the void defects were annihilated from the sub-surface of the wafer due to the interstitial Si atoms that were generated at the SiO2/Si interface. These results indicated that vacancies corresponded to dominant species, despite numerous interstitial silicon injections. We have explained these prominent features by the degree of super-saturation for the interstitial silicon due to oxidation and the precise thermal properties of the vacancy and interstitial silicon.

Single-layered graphene oxide nanosheet/polyaniline hybrids fabricated through direct molecular exfoliation.

PubMed

Chen, Guan-Liang; Shau, Shi-Min; Juang, Tzong-Yuan; Lee, Rong-Ho; Chen, Chih-Ping; Suen, Shing-Yi; Jeng, Ru-Jong

2011-12-06

In this study, we used direct molecular exfoliation for the rapid, facile, large-scale fabrication of single-layered graphene oxide nanosheets (GOSs). Using macromolecular polyaniline (PANI) as a layered space enlarger, we readily and rapidly synthesized individual GOSs at room temperature through the in situ polymerization of aniline on the 2D GOS platform. The chemically modified GOS platelets formed unique 2D-layered GOS/PANI hybrids, with the PANI nanorods embedded between the GO interlayers and extended over the GO surface. X-ray diffraction revealed that intergallery expansion occurred in the GO basal spacing after the PANI nanorods had anchored and grown onto the surface of the GO layer. Transparent folding GOSs were, therefore, observed in transmission electron microscopy images. GOS/PANI nanohybrids possessing high conductivities and large work functions have the potential for application as electrode materials in optoelectronic devices. Our dispersion/exfoliation methodology is a facile means of preparing individual GOS platelets with high throughput, potentially expanding the applicability of nanographene oxide materials. © 2011 American Chemical Society

Iron Oxide Films Prepared by Rapid Thermal Processing for Solar Energy Conversion

PubMed Central

Wickman, B.; Bastos Fanta, A.; Burrows, A.; Hellman, A.; Wagner, J. B.; Iandolo, B.

2017-01-01

Hematite is a promising and extensively investigated material for various photoelectrochemical (PEC) processes for energy conversion and storage, in particular for oxidation reactions. Thermal treatments during synthesis of hematite are found to affect the performance of hematite electrodes considerably. Herein, we present hematite thin films fabricated via one-step oxidation of Fe by rapid thermal processing (RTP). In particular, we investigate the effect of oxidation temperature on the PEC properties of hematite. Films prepared at 750 °C show the highest activity towards water oxidation. These films show the largest average grain size and the highest charge carrier density, as determined from electron microscopy and impedance spectroscopy analysis. We believe that the fast processing enabled by RTP makes this technique a preferred method for investigation of novel materials and architectures, potentially also on nanostructured electrodes, where retaining high surface area is crucial to maximize performance. PMID:28091573

Rapid oxidation of geothermal arsenic(III) in streamwaters of the eastern Sierra Nevada

USGS Publications Warehouse

Wilkie, J.A.; Hering, J.G.

1998-01-01

Arsenic redox cycling was examined in source waters of the Los Angeles Aqueduct, specifically at Hot Creek, a tributary of the Owens River. Elevated arsenic concentrations in Hot Creek result from geothermal inputs. Total arsenic and As(III) concentrations were determined in the creek and in hot spring pools along its banks. Samples were processed in the field using anion-exchange columns to separate inorganic As(III) and As(V) species. Downstream of the geothermal inputs, decreasing contributions of As(III) to total arsenic concentrations indicated rapid in-stream oxidation of As(III) to As(V) with almost complete oxidation occurring within 1200 m. Based on assumed plug flow transport and a flow velocity of about 0.4 m/s, the pseudo- first-order half-life calculated for this reaction was approximately 0.3 h. Conservative transport of total dissolved arsenic was observed over the reach. Pseudo-first-order reaction rates determined for As(III) oxidation in batch studies conducted in the field with aquatic macrophytes and/or macrophyte surface matter were comparable to the in-stream oxidation rate observed along Hot Creek. In batch kinetic studies, oxidation was not observed after sterile filtration or after the addition of antibiotics, which indicates that bacteria attached to submerged macrophytes are mediating the rapid As(III) oxidation reaction.Arsenic redox cycling was examined in source waters of the Los Angeles Aqueduct, specifically at Hot Creek, a tributary of the Owens River. Elevated arsenic concentrations in Hot Creek result from geothermal inputs. Total arsenic and As(III) concentrations were determined in the creek and in hot spring pools along its banks. Samples were processed in the field using anion-exchange columns to separate inorganic As(III) and As(V) species. Downstream of the geothermal inputs, decreasing contributions of As(III) to total arsenic concentrations indicated rapid in-stream oxidation of As(III) to As(V) with almost complete oxidation occurring within 1200 m. Based on assumed plug flow transport and a flow velocity of about 0.4 m/s, the pseudo-first-order half-life calculated for this reaction was approximately 0.3 h. Conservative transport of total dissolved arsenic was observed over the reach. Pseudo-first-order reaction rates determined for As(III) oxidation in batch studies conducted in the field with aquatic macrophytes and/or macrophyte surface matter were comparable to the in-stream oxidation rate observed along Hot Creek. In batch kinetic studies, oxidation was not observed after sterile filtration or after the addition of antibiotics, which indicates that bacteria attached to submerged macrophytes are mediating the rapid As(III) oxidation reaction.

Microstructure of rapidly solidified Nb-based pre-alloyed powders for additive manufacturing

NASA Astrophysics Data System (ADS)

Guo, Yueling; Jia, Lina; Kong, Bin; Zhang, Shengnan; Zhang, Fengxiang; Zhang, Hu

2017-07-01

For powder-based additive manufacturing, sphere-shaped Nb-37Ti-13Cr-2Al-1Si pre-alloyed powders were prepared by plasma rotating electrode processing (PREP). The microstructure, surface oxidation and microhardness of the pre-alloyed powders were systematically investigated. Results showed that the main phases were Nb solid solution (Nbss) and Cr2Nb. The Cr2Nb phases were further determined using transmission electron microscopy (TEM). Fine dendrite structures were observed in the as-fabricated pre-alloyed powders, which transformed to large grains after heat treatment (HT) at 1450 °C for 3 h. With the increase of powder size, the secondary dendrite arm spacing (SDAS) increased and the microhardness (HV) decreased. A clean powder surface free of oxide particles was obtained by PREP and an oxide layer with 9.39 nm in thickness was generated on the powder surface. Compared with Cr- and Nb-oxides, more Ti-oxides were formed on outmost powder surface with a higher content of Ti (up to 47.86 at.%). The differences upon the microstructure and microhardness of the pre-alloyed powders with different sizes were discussed.

Surface Modifications of Materials by Electrochemical Methods to Improve the Properties for Industrial and Medical Applications

NASA Astrophysics Data System (ADS)

Benea, Lidia

2018-06-01

There are two applied electrochemical methods in our group in order to obtain advanced functional surfaces on materials: (i) direct electrochemical synthesis by electro-codeposition process and (ii) anodization of materials to form nanoporous oxide layers followed by electrodeposition of hydroxyapatite or other bioactive molecules and compounds into porous film. Electrodeposition is a process of low energy consumption, and therefore very convenient for the surface modification of various types of materials. Electrodeposition is a powerful method compared with other methods, which led her to be adopted and spread rapidly in nanotechnology to obtain nanostructured layers and films. Nanoporous thin oxide layers on titanum alloys as support for hydroxyapatite or other biomolecules electrodeposition in view of biomedical applications could be obtained by electrochemical methods. For surface modification of titanium or titanium alloys to improve the biocompatibility or osseointegration, the two steps must be fulfilled; the first is controlled growth of oxide layer followed by second being biomolecule electrodeposition into nanoporous formed titanium oxide layer.

Sunken wood habitat for thiotrophic symbiosis in mangrove swamps.

PubMed

Laurent, Mélina C Z; Gros, Olivier; Brulport, Jean-Pierre; Gaill, Françoise; Bris, Nadine Le

2009-03-01

Large organic falls to the benthic environment, such as dead wood or whale bones, harbour organisms relying on sulfide-oxidizing symbionts. Nothing is known however, concerning sulfide enrichment at the wood surface and its relation to wood colonization by sulfide-oxidizing symbiotic organisms. In this study we combined in situ hydrogen sulfide and pH measurements on sunken wood, with associated fauna microscopy analyses in a tropical mangrove swamp. This shallow environment is known to harbour thiotrophic symbioses and is also abundantly supplied with sunken wood. A significant sulfide enrichment at the wood surface was revealed. A 72h sequence of measurements emphasized the wide fluctuation of sulfide levels (0.1->100muM) over time with both a tidal influence and rapid fluctuations. Protozoans observed on the wood surface were similar to Zoothamnium niveum and to vorticellids. Our SEM observations revealed their association with ectosymbiotic bacteria, which are likely to be sulfide-oxidizers. These results support the idea that sunken wood surfaces constitute an environment suitable for sulfide-oxidizing symbioses.

Metallic copper corrosion rates, moisture content, and growth medium influence survival of copper-ion resistant bacteria

PubMed Central

Elguindi, Jutta; Moffitt, Stuart; Hasman, Henrik; Andrade, Cassandra; Raghavan, Srini; Rensing, Christopher

2013-01-01

The rapid killing of various bacteria in contact with metallic copper is thought to be influenced by influx of copper ions into the cells but the exact mechanism is not fully understood. This study showed that the kinetics of contact-killing of copper surfaces depended greatly on the amount of moisture present, copper content of alloys, type of medium used, and type of bacteria. We examined antibiotic- and copper-ion resistant strains of Escherichia coli and Enterococcus faecium isolated from pig farms following the use of copper sulfate as feed supplement. The results showed rapid killing of both copper-ion resistant E. coli and E. faecium strains when samples in rich medium were spread in a thin, moist layer on copper alloys with 85% or greater copper content. E. coli strains were rapidly killed under dry conditions while E. faecium strains were less affected. Electroplated copper surface corrosion rates were determined from electro-chemical polarization tests using the Stern-Geary method and revealed decreased corrosion rates with benzotriazole and thermal oxide coating. Copper-ion resistant E. coli and E. faecium cells suspended in 0.8% NaCl showed prolonged survival rates on electroplated copper surfaces with benzotriazole coating and thermal oxide coating compared to surfaces without anti-corrosion treatment. Control of surface corrosion affected the level of copper ion influx into bacterial cells which contributed directly to bacterial killing. PMID:21085951

Friction and wear of some ferrous-base metallic glasses

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1983-01-01

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminum oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

Friction and wear of some ferrous-base metallic glasses

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1984-01-01

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminium oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

The Cross-Sectional Investigation of Oxide Scale FeCr Alloys and Commercial Ferritic Steel Implanted with Lanthanum and Titanium Dopants after Oxidation Test at 900°C

NASA Astrophysics Data System (ADS)

Saryanto, Hendi; Sebayang, Darwin; Untoro, Pudji; Sujitno, Tjipto

2018-03-01

The cross-sectional examinations of oxide scales formed by oxidation on the surface of FeCr alloys and Ferritic Steel that implanted with lanthanum and titanium dopants were observed and investigated. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) has been used to study the cross-sectional oxides produced by specimens after oxidation process. X-ray diffraction (XRD) analysis was used to strengthen the analysis of the oxide scale morphology, oxide phases and oxidation products. Cross-sectional observations show the effectiveness of La implantation for improving thinner and stronger scale/substrate interface during oxidation process. The result shows that the thickness of oxide scales formed on the surface of La implanted FeCr alloy and ferritic steel was found less than 3 μm and 300 μm, respectively. The oxide scale formed on the surface of La implanted specimens consisted roughly of Cr2O3 with a small amount of FeO mixture, which indicates that lanthanum implantation can improve the adherence, reduce the growth of the oxide scale as well as reduce the Cr evaporation. On the other side, the oxide scale formed on the surface of FeCr alloys and ferritic steel that implanted with titanium dopant was thicker, indicating that significant increase in oxidation mass gain. It can be noticed that titanium implantation ineffectively promotes Cr rich oxide. At the same time, the amount of Fe increased and diffused outwards, which caused the formation and rapid growth of FeO.

Pure and Oxidized Copper Materials as Potential Antimicrobial Surfaces for Spaceflight Activities

NASA Astrophysics Data System (ADS)

Hahn, C.; Hans, M.; Hein, C.; Mancinelli, R. L.; Mücklich, F.; Wirth, R.; Rettberg, P.; Hellweg, C. E.; Moeller, R.

2017-12-01

Microbial biofilms can lead to persistent infections and degrade a variety of materials, and they are notorious for their persistence and resistance to eradication. During long-duration space missions, microbial biofilms present a danger to crew health and spacecraft integrity. The use of antimicrobial surfaces provides an alternative strategy for inhibiting microbial growth and biofilm formation to conventional cleaning procedures and the use of disinfectants. Antimicrobial surfaces contain organic or inorganic compounds, such as antimicrobial peptides or copper and silver, that inhibit microbial growth. The efficacy of wetted oxidized copper layers and pure copper surfaces as antimicrobial agents was tested by applying cultures of Escherichia coli and Staphylococcus cohnii to these metallic surfaces. Stainless steel surfaces were used as non-inhibitory control surfaces. The production of reactive oxygen species and membrane damage increased rapidly within 1 h of exposure on pure copper surfaces, but the effect on cell survival was negligible even after 2 h of exposure. However, longer exposure times of up to 4 h led to a rapid decrease in cell survival, whereby the survival of cells was additionally dependent on the exposed cell density. Finally, the release of metal ions was determined to identify a possible correlation between copper ions in suspension and cell survival. These measurements indicated a steady increase of free copper ions, which were released indirectly by cells presumably through excreted complexing agents. These data indicate that the application of antimicrobial surfaces in spaceflight facilities could improve crew health and mitigate material damage caused by microbial contamination and biofilm formation. Furthermore, the results of this study indicate that cuprous oxide layers were superior to pure copper surfaces related to the antimicrobial effect and that cell density is a significant factor that influences the time dependence of antimicrobial activity.

A method of treating the non-grey error in total emittance measurements

NASA Technical Reports Server (NTRS)

Heaney, J. B.; Henninger, J. H.

1971-01-01

In techniques for the rapid determination of total emittance, the sample is generally exposed to surroundings that are at a different temperature than the sample's surface. When the infrared spectral reflectance of the surface is spectrally selective, these techniques introduce an error into the total emittance values. Surfaces of aluminum overcoated with oxides of various thicknesses fall into this class. Because they are often used as temperature control coatings on satellites, their emittances must be accurately known. The magnitude of the error was calculated for Alzak and silicon oxide-coated aluminum and was shown to be dependent on the thickness of the oxide coating. The results demonstrate that, because the magnitude of the error is thickness-dependent, it is generally impossible or impractical to eliminate it by calibrating the measuring device.

Competitive adsorption of dopamine and rhodamine 6G on the surface of graphene oxide.

PubMed

Ren, Hui; Kulkarni, Dhaval D; Kodiyath, Rajesh; Xu, Weinan; Choi, Ikjun; Tsukruk, Vladimir V

2014-02-26

Competitive adsorption-desorption behavior of popular fluorescent labeling and bioanalyte molecules, Rhodamine 6G (R6G) and dopamine (DA), on a chemically heterogeneous graphene oxide (GO) surface is discussed in this study. Individually, R6G and DA compounds were found to adsorb rapidly on the surface of graphene oxide as they followed the traditional Langmuir adsorption behavior. FTIR analysis suggested that both R6G and DA molecules predominantly adsorb on the hydrophilic oxidized regions of the GO surface. Thus, when R6G and DA compounds were adsorbed from mixed solution, competitive adsorption was observed around the oxygen-containing groups of GO sheets, which resulted in partial desorption of R6G molecules from the surface of GO into the solution. The desorbed R6G molecules can be monitored by fluorescence change in solution and was dependent on the DA concentration. We suggest that the efficient competitive adsorption of different strongly bound bioanalytes onto GO-dye complex can be used for the development of sensitive and selective colorimetric biosensors.

Detection of creatinine enriched on a surface imprinted polystyrene film using FT-ATR-IR.

PubMed

Sreenivasan, K

2006-01-01

The surface of polystyrene (PS) was chemically modified by coating a thin layer of polyaniline (PANI) by oxidizing aniline using ammonium persulfate. Affinity sites for creatinine, a clinically relevant molecule, were created in the coated layer by adding creatinine as print molecules during the oxidation. The imprinted layer adsorbed creatinine was compared to non-imprinted surface reflecting the creation of creatinine-specific sites on the surface. The equilibrium was attained rapidly, indicating that a material of this kind is suitable for sensing applications. The adsorbed creatinine on the surface was detected using the technique of Fourier transform attenuated total internal reflection infra red spectroscopy (FT-ATR-IR). The results show that molecularly imprinted surface can enrich molecules of interest and the enriched molecules can be detected using FT-IR.

Zirconium-based conversion film formation on zinc, aluminium and magnesium oxides and their interactions with functionalized molecules

NASA Astrophysics Data System (ADS)

Fockaert, L. I.; Taheri, P.; Abrahami, S. T.; Boelen, B.; Terryn, H.; Mol, J. M. C.

2017-11-01

Zirconium-based conversion treatment of zinc, aluminium and magnesium oxides have been studied in-situ using ATR-FTIR in a Kretschmann geometry. This set-up was coupled to an electrochemical cell, which allowed to obtain chemical and electrochemical information simultaneously as a function of conversion time. This elucidated the strong relation between physico-chemical surface properties and zirconium-based conversion kinetics. Whereas the surface hydroxyl density of zinc and aluminium increased during conversion, magnesium (hydr)oxide was shown to dissolve in the acid solution. Due to this dissolution, strong surface alkalization can be expected, explaining the rapid conversion kinetics. AES depth profiling was used to determine the final oxide thickness and elemental composition. This confirmed that magnesium is most active and forms a zirconium oxide layer approximately 10 times thicker than zinc. On the other hand, the presence of zirconium oxide on aluminium is very low and can be considered as not fully covering the metal oxide. Additionally, the converted oxide chemistry was related to the bonding mechanisms of amide functionalized molecules using ATR-FTIR and XPS. It was shown that inclusion of zirconium altered the acid-base properties, increasing the substrate proton donating capabilities in case of magnesium oxide and increasing hydrogen bonding and Bronsted interactions due to increased surface hydroxide fractions on zinc and aluminium substrates.

Investigating the oxidation mechanism of tantalum nanoparticles at high heating rates

NASA Astrophysics Data System (ADS)

DeLisio, Jeffery B.; Wang, Xizheng; Wu, Tao; Egan, Garth C.; Jacob, Rohit J.; Zachariah, Michael R.

2017-12-01

Reduced diffusion length scales and increased specific surface areas of nanosized metal fuels have recently demonstrated increased reaction rates for these systems, increasing their relevance in a wide variety of applications. The most commonly employed metal fuel, aluminum, tends to oxidize rapidly near its melting point (660 °C) in addition to undergoing a phase change of the nascent oxide shell. To further expand on the understanding of nanosized metal fuel oxidation, tantalum nanoparticles were studied due to their high melting point (3017 °C) in comparison to aluminum. Both traditional slow heating rate and in-situ high heating rate techniques were used to probe the oxidation of tantalum nanoparticles in oxygen containing environments in addition to nanothermite mixtures. When oxidized by gas phase oxygen, the oxide shell of the tantalum nanoparticles rapidly crystallized creating cracks that may attribute to enhanced oxygen diffusion into the particle. In the case of tantalum based nanothermites, oxide shell crystallization was shown to induce reactive sintering with the metal oxide resulting in a narrow range of ignition temperatures independent of the metal oxide used. The oxidation mechanism was modeled using the Deal-Grove model to extract rate parameters, and theoretical burn times for tantalum based nanocomposites were calculated.

Surface chemistry, microstructure and friction properties of some ferrous-base metallic glasses at temperatures to 750 C

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

X-ray photoelectron spectroscopy analysis, transmission electron microscopy, diffraction studies, and sliding friction experiments were conducted with ferrous-base metallic glasses in sliding contact with aluminum oxide at temperatures from room to 750 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on the friction properties, surface chemistry, and microstructure of metallic glasses. The relative concentrations of the various constituents at the surface of the sputtered specimens were very different from the normal bulk compositions. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and silicon oxide at 350 C and boron nitride above 500 C. The coefficient of friction increased with increasing temperature to 350 C. Above 500 C the coefficient of friction decreased rapidly. The segregation of contaminants may be responsible for the friction behavior.

Toward optimizing dental implant performance: Surface characterization of Ti and TiZr implant materials.

PubMed

Murphy, M; Walczak, M S; Thomas, A G; Silikas, N; Berner, S; Lindsay, R

2017-01-01

Targeting understanding enhanced osseointegration kinetics, the goal of this study was to characterize the surface morphology and composition of Ti and TiZr dental implant substrates subjected to one of two surface treatments developed by Straumann. These two treatments are typically known as SLA and SLActive, with the latter resulting in more rapid osseointegration. A range of techniques was applied to characterize four different substrate/surface treatment combinations (Ti SLA , Ti SLActive , TiZr SLA , and TiZr SLActive ). Contact angle measurements established their hydrophilic/hydrophobic nature. Surface morphology was probed with scanning electron microscopy. X-ray diffraction, Raman μ-spectroscopy, and X-ray photoelectron spectroscopy were used to elucidate the composition of the near-surface region. Consistent with previous work, surface morphology was found to differ only at the nanoscale, with both SLActive substrates displaying nano-protrusions. Spectroscopic data indicate that all substrates exhibit surface films of titanium oxide displaying near TiO 2 stoichiometry. Raman μ-spectroscopy reveals that amorphous TiO 2 is most likely the only phase present on Ti SL A , whilst rutile-TiO 2 is also evidenced on Ti SLActive , TiZr SLA , and TiZr SLActive . For TiZr alloy substrates, there is no evidence of discrete phases of oxidized Zr. X-ray photoelectron spectra demonstrate that all samples are terminated by adventitious carbon, with it being somewhat thicker (∼1nm) on Ti SL A and TiZr SLA . Given previous in vivo studies, acquired data suggest that both nanoscale protrusions, and a thinner layer of adventitious carbon contribute to the more rapid osseointegration of SLActive dental implants. Composition of the surface oxide layer is apparently less important in determining osseointegration kinetics. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Fabrication of oxidation-resistant Ge colloidal nanoparticles by pulsed laser ablation in aqueous HCl

NASA Astrophysics Data System (ADS)

Hamanaka, Yasushi; Iwata, Masahiro; Katsuno, Junichi

2017-06-01

Spherical Ge nanoparticles with diameters of 20-80 nm were fabricated by laser ablation of a Ge single crystal in water and in aqueous HCl using sub-picosecond laser pulses (1040 nm, 700 fs, 100 kHz, and a pulse energy of 10 µJ). We found that the as-synthesized nanoparticles suffered rapid oxidization followed by dissolution when laser ablation was conducted in pure water. In contrast, oxidation of Ge nanoparticles produced in dilute HCl and stored intact was minimal, and colloidal dispersions of the Ge nanoparticles remained stable up to 7 days. It was elucidated that dangling bonds on the surfaces of the Ge nanoparticles were terminated by Cl, which inhibited oxidation, and that such hydrophilic surfaces might improve the dispersibility of nanoparticles in aqueous solvent.

Hydrogen retention in lithium and lithium oxide films

NASA Astrophysics Data System (ADS)

Buzi, L.; Yang, Y.; Domínguez-Gutiérrez, F. J.; Nelson, A. O.; Hofman, M.; Krstić, P. S.; Kaita, R.; Koel, B. E.

2018-04-01

Pure lithium (Li) surfaces are difficult to maintain in fusion devices due to rapid oxide formation, therefore, parameterizing and understanding the mechanisms of hydrogen (H, D) retention in lithium oxide (Li2O) in addition to pure Li is crucial for Li plasma-facing material applications. To compare H retention in Li and Li2O films, measurements were made as a function of surface temperature (90-520 K) under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD). In both cases, the total retention dropped with surface temperature, from 95% at 90 K to 35% at 520 K Li2O films retained H in similar amounts as pure Li. Molecular Dynamics (MD) modeling was used to elucidate the mechanisms of H retention, and results were consistent with experiments in terms of both retention fraction and the drop of retention with temperature.

Simple combination of oxidants with zero-valent-iron (ZVI) achieved very rapid and highly efficient removal of heavy metals from water.

PubMed

Guo, Xuejun; Yang, Zhe; Dong, Haiyang; Guan, Xiaohong; Ren, Qidong; Lv, Xiaofang; Jin, Xin

2016-01-01

This study, for the first time, demonstrated a continuously accelerated Fe(0) corrosion driven by common oxidants (i.e., NaClO, KMnO4 or H2O2) and thereby the rapid and efficient removal of heavy metals (HMs) by zero-valent iron (ZVI) under the experimental conditions of jar tests and column running. ZVI simply coupled with NaClO, KMnO4 or H2O2 (0.5 mM) resulted in almost complete As(V) removal within only 10 min with 1000 μg/L of initial As(V) at initial pH of 7.5(±0.1) and liquid solid ratio of 200:1. Simultaneous removal of 200 μg/L of initial Cd(II) and Hg(II) to 2.4-4.4 μg/L for Cd(II) and to 4.0-5.0 μg/L for Hg(II) were achieved within 30 min. No deterioration of HM removal was observed during the ten recycles of jar tests. The ZVI columns activated by 0.1 mM of oxidants had stably treated 40,200 (NaClO), 20,295 (KMnO4) and 40,200 (H2O2) bed volumes (BV) of HM-contaminated drinking water, but with no any indication of As breakthrough (<10 μg/L) even at short empty bed contact time (EBCT) of 8.0 min. The high efficiency of HMs removal from both the jar tests and column running implied a continuous and stable activation (overcoming of iron passivation) of Fe(0) surface by the oxidants. Via the proper increase in oxidant dosing, the ZVI/oxidant combination was applicable to treat highly As(V)-contaminated wastewater. During Fe(0) surface corrosion accelerated by oxidants, a large amount of fresh and reactive iron oxides and oxyhydroxides were continuously generated, which were responsible for the rapid and efficient removal of HMs through multiple mechanisms including adsorption and co-precipitation. A steady state of Fe(0) surface activation and HM removal enabled this simply coupled system to remove HMs with high speed, efficiency and perdurability. Copyright © 2015 Elsevier Ltd. All rights reserved.

Manganese oxide helices, rings, strands, and films, and methods for their preparation

DOEpatents

Suib, Steven L.; Giraldo, Oscar; Marquez, Manuel; Brock, Stephanie

2003-01-07

Methods for the preparation of mixed-valence manganese oxide compositions with quaternary ammonium ions are described. The compositions self-assemble into helices, rings, and strands without any imposed concentration gradient. These helices, rings, and strands, as well as films having the same composition, undergo rapid ion exchange to replace the quaternary ammonium ions with various metal ions. And the metal-ion-containing manganese oxide compositions so formed can be heat treated to form semi-conducting materials with high surface areas.

Stabilizing Nanocrystalline Oxide Nanofibers at Elevated Temperatures by Coating Nanoscale Surface Amorphous Films.

PubMed

Yao, Lei; Pan, Wei; Luo, Jian; Zhao, Xiaohui; Cheng, Jing; Nishijima, Hiroki

2018-01-10

Nanocrystalline materials often exhibit extraordinary mechanical and physical properties but their applications at elevated temperatures are impaired by the rapid grain growth. Moreover, the grain growth in nanocrystalline oxide nanofibers at high temperatures can occur at hundreds of degrees lower than that would occur in corresponding bulk nanocrystalline materials, which would eventually break the fibers. Herein, by characterizing a model system of scandia-stabilized zirconia using hot-stage in situ scanning transmission electron microscopy, we discover that the enhanced grain growth in nanofibers is initiated at the surface. Subsequently, we demonstrate that coating the fibers with nanometer-thick amorphous alumina layer can enhance their temperature stability by nearly 400 °C via suppressing the surface-initiated grain growth. Such a strategy can be effectively applied to other oxide nanofibers, such as samarium-doped ceria, yttrium-stabilized zirconia, and lanthanum molybdate. The nanocoatings also increase the flexibility of the oxide nanofibers and stabilize the high-temperature phases that have 10 times higher ionic conductivity. This study provides new insights into the surface-initiated grain growth in nanocrystalline oxide nanofibers and develops a facile yet innovative strategy to improve the high-temperature stability of nanofibers for a broad range of applications.

Modified rare earth semiconductor oxide as a new nucleotide probe.

PubMed

Shrestha, S; Mills, C E; Lewington, J; Tsang, S C

2006-12-28

Recent rapid developments in biological analysis, medical diagnosis, pharmaceutical industry, and environmental control fuel the urgent need for recognition of particular DNA sequences from samples. Currently, DNA detection techniques use radiochemical, enzymatic, fluorescent, or electrochemiluminescent methods; however, these techniques require costly labeled DNA and highly skilled and cumbersome procedure, which prohibit any in-situ monitoring. Here, we report that hybridization of surface-immobilized single-stranded oligonucleotide on praseodymium oxide (evaluated as a biosensor surface for the first time) with complimentary strands in solution provokes a significant shift of electrical impedance curve. This shift is attributed to a change in electrical characteristics through modification of surface charge of the underlying modified praseodymium oxide upon hybridization with the complementary oligonucelotide strand. On the other hand, using a noncomplementary single strand in solution does not create an equivalent change in the impedance value. This result clearly suggests that a new and simple electrochemical technique based on the change in electrical properties of the modified praseodymium oxide semiconductor surface upon recognition and transduction of a biological event without using labeled species is revealed.

Efficient oxidation and sorption of arsenite using a novel titanium(IV)-manganese(IV) binary oxide sorbent.

PubMed

Zhang, Wei; Liu, Caihong; Zheng, Tong; Ma, Jun; Zhang, Gaosheng; Ren, Guohui; Wang, Lu; Liu, Yulei

2018-04-19

Owing to the high toxicity and mobility, the removal of arsenite (As(III)) is significantly more difficult than arsenate (As(V)), thus representing a major challenge in arsenite-contaminated water treatment. For efficient elimination of As(III), we successfully fabricated a novel Ti-Mn binary oxide via a simultaneous oxidation and coprecipitation process. The amorphous oxide was aggregated from nanosized particles with a high specific surface area of 349.5 m 2 /g. It could effectively oxidize As(III) to As(V) and had a high As(III) sorption capacity of 107.0 mg/g. As(III) sorption occurred rapidly and equilibrium was achieved within 24 h. The kinetic data was well fitted by the pseudo-second-order equation, indicating a chemical sorption process. The material was almost independent upon the presence of competitive ions. The As(III) removal by the sorbent is a combined process coupled oxidation with sorption, where the MnO 2 content is mainly responsible for oxidizing As(III) to As(V) and the formed As(V) is then adsorbed onto the surface of amorphous TiO 2 content, through replacing the surface hydroxyl group or the adsorbed As(III) and forming inner-sphere surface complexes. Furthermore, the arsenic-containing oxide could be effectively regenerated and reused. The bi-functional sorbent could be used as a potentially attractive sorbent for As(III) removal in drinking water treatment and environmental remediation. Copyright © 2018. Published by Elsevier B.V.

Microwave-assisted routes for rapid and efficient modification of layered perovskites.

PubMed

Akbarian-Tefaghi, S; Wiley, J B

2018-02-27

Recent advances in exploiting microwave radiation in the topochemical modification of layered oxide perovskites are presented. Such methods work well for rapid bulk synthetic steps used in the production of novel inorganic-organic hybrids (protonation, grafting, intercalation, and in situ click reactions), exfoliation to produce dispersed nanosheets, and post-exfoliation processing to rapidly vary nanosheet surface groups. Compared to traditional methods that often take days, microwave methods can produce quality products in as little as 1-2 h.

Shallow gas off the Rhône prodelta, Gulf of Lions

USGS Publications Warehouse

Garcia-Garcia, Ana; Orange, Daniel L.; Lorenson, T.; Radakovitch, Olivier; Tesi, Tommaso; Miserocchi, Stefano; Berne, Serge; Friend, P.L.; Nittrouer, Chuck; Normand, Alain

2006-01-01

In areas unaffected by the high flux of organic matter and rapid/thick flood deposition, or in between flood events, the conditions for methanogenesis and gas accumulation have not been met; in these areas, the physical and biological reworking of the surficial sediment may effectively oxidize and mineralize organic matter and limit bacterial methanogenesis in the sub-surface. We propose that in the Rhône prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried, effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial.

Enzymatically enhanced collisions on ultramicroelectrodes for specific and rapid detection of individual viruses

PubMed Central

Dick, Jeffrey E.; Hilterbrand, Adam T.; Strawsine, Lauren M.; Upton, Jason W.; Bard, Allen J.

2016-01-01

We report the specific collision of a single murine cytomegalovirus (MCMV) on a platinum ultramicroelectrode (UME, radius of 1 μm). Antibody directed against the viral surface protein glycoprotein B functionalized with glucose oxidase (GOx) allowed for specific detection of the virus in solution and a biological sample (urine). The oxidation of ferrocene methanol to ferrocenium methanol was carried out at the electrode surface, and the ferrocenium methanol acted as the cosubstrate to GOx to catalyze the oxidation of glucose to gluconolactone. In the presence of glucose, the incident collision of a GOx-covered virus onto the UME while ferrocene methanol was being oxidized produced stepwise increases in current as observed by amperometry. These current increases were observed due to the feedback loop of ferrocene methanol to the surface of the electrode after GOx reduces ferrocenium methanol back to ferrocene. Negative controls (i) without glucose, (ii) with an irrelevant virus (murine gammaherpesvirus 68), and (iii) without either virus do not display these current increases. Stepwise current decreases were observed for the prior two negative controls and no discrete events were observed for the latter. We further apply this method to the detection of MCMV in urine of infected mice. The method provides for a selective, rapid, and sensitive detection technique based on electrochemical collisions. PMID:27217569

Differential proteomics analysis of the surface heterogeneity of dextran iron oxide nanoparticles and the implications for their in vivo clearance

PubMed Central

Simberg, Dmitri; Park, Ji-Ho; Karmali, Priya P.; Zhang, Wan-Ming; Merkulov, Sergei; McCrae, Keith; Bhatia, Sangeeta; Sailor, Michael; Ruoslahti, Erkki

2009-01-01

In order to understand the role of plasma proteins in the rapid liver clearance of dextran-coated superparamagnetic iron oxide (SPIO) in vivo, we analyzed the full repertoire of SPIO-binding blood proteins using novel two-dimensional differential mass spectrometry approach. The identified proteins showed specificity for surface domains of the nanoparticles: mannan-binding lectins bound to the dextran coating, histidine-rich glycoprotein and kininogen bound to the iron oxide part, and the complement lectin and contact clotting factors were secondary binders. Nanoparticle clearance studies in knockout mice suggested that these proteins, as well as several previously identified opsonins, do not play a significant role in the SPIO clearance. However, both the dextran coat and the iron oxide core remained accessible to specific probes after incubation of SPIO in plasma, suggesting that the nanoparticle surface could be available for recognition by macrophages, regardless of protein coating. These data provide guidance to rational design of bioinert, long-circulating nanoparticles. PMID:19394687

Differential proteomics analysis of the surface heterogeneity of dextran iron oxide nanoparticles and the implications for their in vivo clearance.

PubMed

Simberg, Dmitri; Park, Ji-Ho; Karmali, Priya P; Zhang, Wan-Ming; Merkulov, Sergei; McCrae, Keith; Bhatia, Sangeeta N; Sailor, Michael; Ruoslahti, Erkki

2009-08-01

In order to understand the role of plasma proteins in the rapid liver clearance of dextran-coated superparamagnetic iron oxide (SPIO) in vivo, we analyzed the full repertoire of SPIO-binding blood proteins using novel two-dimensional differential mass spectrometry approach. The identified proteins showed specificity for surface domains of the nanoparticles: mannan-binding lectins bound to the dextran coating, histidine-rich glycoprotein and kininogen bound to the iron oxide part, and the complement lectin and contact clotting factors were secondary binders. Nanoparticle clearance studies in knockout mice suggested that these proteins, as well as several previously identified opsonins, do not play a significant role in the SPIO clearance. However, both the dextran coat and the iron oxide core remained accessible to specific probes after incubation of SPIO in plasma, suggesting that the nanoparticle surface could be available for recognition by macrophages, regardless of protein coating. These data provide guidance to rational design of bioinert, long-circulating nanoparticles.

The Dye Sensitized Photoelectrosynthesis Cell (DSPEC) for Solar Water Splitting and CO2 Reduction

NASA Astrophysics Data System (ADS)

Meyer, Thomas; Alibabaei, Leila; Sherman, Benjamin; Sheridan, Matthew; Ashford, Dennis; Lapides, Alex; Brennaman, Kyle; Nayak, Animesh; Roy, Subhangi; Wee, Kyung-Ryang; Gish, Melissa; Meyer, Jerry; Papanikolas, John

The dye-sensitized photoelectrosynthesis cell (DSPEC) integrates molecular level light absorption and catalysis with the bandgap properties of stable oxide materials such as TiO2 and NiO. Excitation of surface-bound chromophores leads to excited state formation and rapid electron or hole injection into the conduction or valence bands of n or p-type oxides. Addition of thin layers of TiO2 or NiO on the surfaces of mesoscopic, nanoparticle films of semiconductor or transparent conducting oxides to give core/shell structures provides a basis for accumulating multiple redox equivalents at catalysts for water oxidation or CO2 reduction. UNC EFRC Center for Solar Fuels, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001011.

Aqueous Assembly of Oxide and Fluoride Nanoparticles into 3D Microassemblies.

PubMed

Cui, Shanying; Guan, Xin N; Ghantous, Eliana; Vajo, John J; Lucas, Matthew; Hsiao, Ming-Siao; Drummy, Lawrence F; Collins, Joshua; Juhl, Abigail; Roper, Christopher S; Gross, Adam F

2018-06-28

We demonstrate rapid [∼mm 3 /(h·L)] organic ligand-free self-assembly of three-dimensional, >50 μm single-domain microassemblies containing up to 10 7 individual aligned nanoparticles through a scalable aqueous process. Organization and alignment of aqueous solution-dispersed nanoparticles are induced by decreasing their pH-dependent surface charge without organic ligands, which could be temperature-sensitive or infrared light absorbing. This process is exhibited by transforming both dispersed iron oxide hydroxide nanorods and lithium yttrium fluoride nanoparticles into high packing density microassemblies. The approach is generalizable to nanomaterials with pH-dependent surface charge (e.g., oxides, fluorides, and sulfides) for applications requiring long-range alignment of nanostructures as well as high packing density.

Hydrogen retention in lithium and lithium oxide films

DOE PAGES

Buzi, L.; Yang, Y.; Dominguez-Gutierrez, F. J.; ...

2018-02-09

Pure lithium (Li) surfaces are difficult to maintain in fusion devices due to rapid oxide formation, therefore, parameterizing and understanding the mechanisms of hydrogen (H, D) retention in lithium oxide (Li 2O) in addition to pure Li is crucial for Li plasma-facing material applications. To compare H retention in Li and Li 2O films, measurements were made as a function of surface temperature (90–520 K) under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD). In both cases, the total retention dropped with surface temperature, from 95% at 90 K to 35% at 520 K Li 2O films retained Hmore » in similar amounts as pure Li. Finally, Molecular Dynamics (MD) modeling was used to elucidate the mechanisms of H retention, and results were consistent with experiments in terms of both retention fraction and the drop of retention with temperature.« less

Hydrogen retention in lithium and lithium oxide films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buzi, L.; Yang, Y.; Dominguez-Gutierrez, F. J.

Pure lithium (Li) surfaces are difficult to maintain in fusion devices due to rapid oxide formation, therefore, parameterizing and understanding the mechanisms of hydrogen (H, D) retention in lithium oxide (Li 2O) in addition to pure Li is crucial for Li plasma-facing material applications. To compare H retention in Li and Li 2O films, measurements were made as a function of surface temperature (90–520 K) under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD). In both cases, the total retention dropped with surface temperature, from 95% at 90 K to 35% at 520 K Li 2O films retained Hmore » in similar amounts as pure Li. Finally, Molecular Dynamics (MD) modeling was used to elucidate the mechanisms of H retention, and results were consistent with experiments in terms of both retention fraction and the drop of retention with temperature.« less

Synthesis and improved explosion behaviors of aluminum powders coated with nano-sized nickel film

NASA Astrophysics Data System (ADS)

Kim, Kyung Tae; Kim, Dong Won; Kim, Soo Hyung; Kim, Chang Kee; Choi, Yoon Jeong

2017-09-01

Nickel (Ni) materials with a thickness of a few hundred nm were homogeneously coated on the surfaces of aluminum (Al) powders by an electroless plating process. The Ni-coated Al powders show characteristic interfacial structures mixed of Ni, Al and O instead of densely packed Al oxide at the surface. The explosion test of the Ni-coated Al powders utilizing flame ignition showed that the powders had a 3.6 times enhanced pressurization rate of 405 kPa/ms compared to 111 kPa/ms of uncoated Al powders. It was found that this is due to a feasible diffusion of oxygen atoms into the Al powders through the thin and rough interfacial layers present at the Ni/Al interface. These results clearly indicate that nano-sized Ni film introduced instead of surface oxide acts as a very profitable layer to achieve efficient combustion behaviors by a rapid oxidation of Al powders.

Superplasticity. Revision

DTIC Science & Technology

1989-09-01

angle to the applied tension and failure rapidly follows, as the volume of metal now deforming is small. Local necking Contributes virtually nothing...into components. It is thought that the 9 phase may be responsible for grain refinement, but it may be due to minute traces of oxide on the original...order to minimize oxidation and related detrimental surface degradation due to the reactivity of titanium. The use of such protective gases is not

Oxidative Processing of Latent Fas in the Endoplasmic Reticulum Controls the Strength of Apoptosis

PubMed Central

Anathy, Vikas; Roberson, Elle; Cunniff, Brian; Nolin, James D.; Hoffman, Sidra; Spiess, Page; Guala, Amy S.; Lahue, Karolyn G.; Goldman, Dylan; Flemer, Stevenson; van der Vliet, Albert; Heintz, Nicholas H.; Budd, Ralph C.; Tew, Kenneth D.

2012-01-01

We recently demonstrated that S-glutathionylation of the death receptor Fas (Fas-SSG) amplifies apoptosis (V. Anathy et al., J. Cell Biol. 184:241–252, 2009). In the present study, we demonstrate that distinct pools of Fas exist in cells. Upon ligation of surface Fas, a separate pool of latent Fas in the endoplasmic reticulum (ER) underwent rapid oxidative processing characterized by the loss of free sulfhydryl content (Fas-SH) and resultant increases in S-glutathionylation of Cys294, leading to increases of surface Fas. Stimulation with FasL rapidly induced associations of Fas with ERp57 and glutathione S-transferase π (GSTP), a protein disulfide isomerase and catalyst of S-glutathionylation, respectively, in the ER. Knockdown or inhibition of ERp57 and GSTP1 substantially decreased FasL-induced oxidative processing and S-glutathionylation of Fas, resulting in decreased death-inducing signaling complex formation and caspase activity and enhanced survival. Bleomycin-induced pulmonary fibrosis was accompanied by increased interactions between Fas-ERp57-GSTP1 and S-glutathionylation of Fas. Importantly, fibrosis was largely prevented following short interfering RNA-mediated ablation of ERp57 and GSTP. Collectively, these findings illuminate a regulatory switch, a ligand-initiated oxidative processing of latent Fas, that controls the strength of apoptosis. PMID:22751926

Dependence of LTX plasma performance on surface conditions as determined by in situ analysis of plasma facing components

NASA Astrophysics Data System (ADS)

Lucia, M.; Kaita, R.; Majeski, R.; Bedoya, F.; Allain, J. P.; Abrams, T.; Bell, R. E.; Boyle, D. P.; Jaworski, M. A.; Schmitt, J. C.

2015-08-01

The Materials Analysis and Particle Probe (MAPP) diagnostic has been implemented on the Lithium Tokamak Experiment (LTX) at PPPL, providing the first in situ X-ray photoelectron spectroscopy (XPS) surface characterization of tokamak plasma facing components (PFCs). MAPP samples were exposed to argon glow discharge conditioning (GDC), lithium evaporations, and hydrogen tokamak discharges inside LTX. Samples were analyzed with XPS, and alterations to surface conditions were correlated against observed LTX plasma performance changes. Argon GDC caused the accumulation of nm-scale metal oxide layers on the PFC surface, which appeared to bury surface carbon and oxygen contamination and thus improve plasma performance. Lithium evaporation led to the rapid formation of a lithium oxide (Li2O) surface; plasma performance was strongly improved for sufficiently thick evaporative coatings. Results indicate that a 5 h argon GDC or a 50 nm evaporative lithium coating will both significantly improve LTX plasma performance.

Probing Interfacial Processes on Graphene Surface by Mass Detection

NASA Astrophysics Data System (ADS)

Kakenov, Nurbek; Kocabas, Coskun

2013-03-01

In this work we studied the mass density of graphene, probed interfacial processes on graphene surface and examined the formation of graphene oxide by mass detection. The graphene layers were synthesized by chemical vapor deposition method on copper foils and transfer-printed on a quartz crystal microbalance (QCM). The mass density of single layer graphene was measured by investigating the mechanical resonance of the QCM. Moreover, we extended the developed technique to probe the binding dynamics of proteins on the surface of graphene, were able to obtain nonspecific binding constant of BSA protein of graphene surface in aqueous solution. The time trace of resonance signal showed that the BSA molecules rapidly saturated by filling the available binding sites on graphene surface. Furthermore, we monitored oxidation of graphene surface under oxygen plasma by tracing the changes of interfacial mass of the graphene controlled by the shifts in Raman spectra. Three regimes were observed the formation of graphene oxide which increases the interfacial mass, the release of carbon dioxide and the removal of small graphene/graphene oxide flakes. Scientific and Technological Research Council of Turkey (TUBITAK) grant no. 110T304, 109T209, Marie Curie International Reintegration Grant (IRG) grant no 256458, Turkish Academy of Science (TUBA-Gebip).

Rapid solid-state metathesis route to transition-metal doped titanias

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coleman, Nathaniel; Perera, Sujith; Gillan, Edward G., E-mail: edward-gillan@uiowa.edu

2015-12-15

Rapid solid-state metathesis (SSM) reactions are often short-lived highly exothermic reactions that yield a molten alkali halide salt that aids in product growth and crystallization. SSM reactions may also produce kinetically stabilized structures due to the short (seconds) reaction times. This report describes the investigation of rapid SSM reactions in the synthesis of transition-metal doped titanias (M–TiO{sub 2}). The dopant targeted compositions were ten mol percent and based on elemental analysis, many of the M–TiO{sub 2} samples were close to this targeted level. Based on surface analysis, some samples showed large enrichment in surface dopant content, particularly chromium and manganesemore » doped samples. Due to the highly exothermic nature of these reactions, rutile structured TiO{sub 2} was observed in all cases. The M–TiO{sub 2} samples are visible colored and show magnetic and optical properties consistent with the dopant in an oxide environment. UV and visible photocatalytic experiments with these visibly colored rutile M–TiO{sub 2} powders showed that many of them are strongly absorbent for methylene blue dye and degrade the dye under both UV and visible light illumination. This work may open up SSM reactions as an alternate non-thermodynamic reaction strategy for dopant incorporation into a wide range of oxide and non-oxides.« less

A catalytic surface for amyloid fibril formation

NASA Astrophysics Data System (ADS)

Hammarström, P.; Ali, M. M.; Mishra, R.; Svensson, S.; Tengvall, P.; Lundström, I.

2008-03-01

A hydrophobic surface incubated in a solution of protein molecules (insulin monomers) was made into a catalytic surface for amyloid fibril formation by repeatedly incubate, rinse and dry the surface. The present contribution describes how this unexpected transformation occurred and its relation to rapid fibrillation of insulin solutions in contact with the surface. A tentative model of the properties of the catalytic surface is given, corroborated by ellipsometric measurements of the thickness of the organic layer on the surface and by atomic force microscopy. The surfaces used were spontaneously oxidized silicon made hydrophobic through treatment in dichlorodimethylsilane.

Rapid Surface Functionalization of Hydrogen-Terminated Silicon by Alkyl Silanols.

PubMed

Escorihuela, Jorge; Zuilhof, Han

2017-04-26

Surface functionalization of inorganic semiconductor substrates, particularly silicon, has focused attention toward many technologically important applications, involving photovoltaic energy, biosensing and catalysis. For such modification processes, oxide-free (H-terminated) silicon surfaces are highly required, and different chemical approaches have been described in the past decades. However, their reactivity is often poor, requiring long reaction times (2-18 h) or the use of UV light (10-30 min). Here, we report a simple and rapid surface functionalization for H-terminated Si(111) surfaces using alkyl silanols. This catalyst-free surface reaction is fast (15 min at room temperature) and can be accelerated with UV light irradiation, reducing the reaction time to 1-2 min. This grafting procedure leads to densely packed organic monolayers that are hydrolytically stable (even up to 30 days at pH 3 or 11) and can display excellent antifouling behavior against a range of organic polymers.

Rapid Surface Functionalization of Hydrogen-Terminated Silicon by Alkyl Silanols

PubMed Central

2017-01-01

Surface functionalization of inorganic semiconductor substrates, particularly silicon, has focused attention toward many technologically important applications, involving photovoltaic energy, biosensing and catalysis. For such modification processes, oxide-free (H-terminated) silicon surfaces are highly required, and different chemical approaches have been described in the past decades. However, their reactivity is often poor, requiring long reaction times (2–18 h) or the use of UV light (10–30 min). Here, we report a simple and rapid surface functionalization for H-terminated Si(111) surfaces using alkyl silanols. This catalyst-free surface reaction is fast (15 min at room temperature) and can be accelerated with UV light irradiation, reducing the reaction time to 1–2 min. This grafting procedure leads to densely packed organic monolayers that are hydrolytically stable (even up to 30 days at pH 3 or 11) and can display excellent antifouling behavior against a range of organic polymers. PMID:28409624

Paralinear Oxidation of CVD SiC in Water Vapor

NASA Technical Reports Server (NTRS)

Opila, Elizabeth J.; Hann, Raiford E., Jr.

1997-01-01

The oxidation kinetics of CVD SiC were monitored by thermogravimetric analysis (TGA) in a 50% H2O/50% O2 gas mixture flowing at 4.4 cm/s for temperatures between 1200 and 1400 C. Paralinear weight change kinetics were observed as the water vapor oxidized the SiC and simultaneously volatilized the silica scale. The long-term degradation rate of SiC is determined by the volatility of the silica scale. Rapid SiC surface recession rates were estimated from these data for actual aircraft engine combustor conditions.

Surface oxidation of GaN(0001): Nitrogen plasma-assisted cleaning for ultrahigh vacuum applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gangopadhyay, Subhashis; Schmidt, Thomas, E-mail: tschmidt@ifp.uni-bremen.de; Kruse, Carsten

The cleaning of metal-organic vapor-phase epitaxial GaN(0001) template layers grown on sapphire has been investigated. Different procedures, performed under ultrahigh vacuum conditions, including degassing and exposure to active nitrogen from a radio frequency nitrogen plasma source have been compared. For this purpose, x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and scanning tunneling microscopy have been employed in order to assess chemical as well as structural and morphological surface properties. Initial degassing at 600 °C under ultrahigh vacuum conditions only partially eliminates the surface contaminants. In contrast to plasma assisted nitrogen cleaning at temperatures as low as 300 °C, active-nitrogen exposure at temperaturesmore » as high as 700 °C removes the majority of oxide species from the surface. However, extended high-temperature active-nitrogen cleaning leads to severe surface roughening. Optimum results regarding both the removal of surface oxides as well as the surface structural and morphological quality have been achieved for a combination of initial low-temperature plasma-assisted cleaning, followed by a rapid nitrogen plasma-assisted cleaning at high temperature.« less

Effect of rapid oxidation on optical and electrical properties of silicon nanowires obtained by chemical etching

NASA Astrophysics Data System (ADS)

Karyaoui, M.; Bardaoui, A.; Ben Rabha, M.; Harmand, J. C.; Amlouk, M.

2012-05-01

In the present work, we report the investigation of passivated silicon nanowires (SiNWs) having an average radius of 3.7 μm, obtained by chemical etching of p-type silicon (p-Si). The surface passivation of the SiNWs was performed through a rapid oxidation conducted under a controlled atmosphere at different temperatures and durations. The morphology of the SiNWs was examined using a scanning electron microscope (SEM) that revealed a wave-like structure of dense and vertically aligned one-dimensional silicon nanostructures. On the other hand, optical and electrical characterizations of the SiNWs were studied using a UV-Vis-NIR spectrometer, the Fourier transform infrared spectroscopy (FTIR) and I-V measurements. The reflectance of SiNWs has been dropped to approximately 2% in comparison to that of bare p-Si. This low reflectance slightly increased after carrying out the rapid thermal annealing. The observed behavior was attributed to the formation of a SiO2 layer, as confirmed by FTIR measurements. Finally, the electrical measurements have shown that the rapid oxidation, at certain conditions, contributes to the improvement of the electrical responses of the SiNWs, which can be of great interest for photovoltaic applications.

Nanoscale assembly of high-temperature oxidation-resistant nanocomposites.

PubMed

Peng, Xiao

2010-02-01

Structural considerations for designing a high-temperature oxidation-resistant metallic material are proposed, based on the dependence of the material structure on a promotion of the development of a protective scale of chromia or alumina. The material should have numerous sites on its surface for nucleating the protective oxides at the onset of oxidation and abundant grain boundaries in deeper areas for simultaneously supplying sufficient flux of the protective-oxide-forming elements toward the surface for a rapid linkage of the oxide nuclei through their lateral growth. Based on these considerations, we fabricated, using an electrochemical deposition method, novel nanocomposites which have a nanocrystalline metal matrix containing Cr and/or Al nanoparticles dispersed at the nano length scale. The validity of the design considerations is verified by comparing the high-temperature oxidation of a typical Ni-Cr nanocomposite system with two types of conventional Ni-Cr materials having similar or higher Cr content but different structure: one is a composite having a nanocrystalline Ni matrix containing Cr microparticles dispersed at the microscale and the other are micron-grained Ni-Cr alloys with the Cr distribution at the atomic length scale.

Nanoscale assembly of high-temperature oxidation-resistant nanocomposites

NASA Astrophysics Data System (ADS)

Peng, Xiao

2010-02-01

Structural considerations for designing a high-temperature oxidation-resistant metallic material are proposed, based on the dependence of the material structure on a promotion of the development of a protective scale of chromia or alumina. The material should have numerous sites on its surface for nucleating the protective oxides at the onset of oxidation and abundant grain boundaries in deeper areas for simultaneously supplying sufficient flux of the protective-oxide-forming elements toward the surface for a rapid linkage of the oxide nuclei through their lateral growth. Based on these considerations, we fabricated, using an electrochemical deposition method, novel nanocomposites which have a nanocrystalline metal matrix containing Cr and/or Al nanoparticles dispersed at the nano length scale. The validity of the design considerations is verified by comparing the high-temperature oxidation of a typical Ni-Cr nanocomposite system with two types of conventional Ni-Cr materials having similar or higher Cr content but different structure: one is a composite having a nanocrystalline Ni matrix containing Cr microparticles dispersed at the microscale and the other are micron-grained Ni-Cr alloys with the Cr distribution at the atomic length scale.

Oxidation of ammonia and methane in an alkaline, saline lake

USGS Publications Warehouse

Joye, S.B.; Connell, T.L.; Miller, L.G.; Oremland, R.S.; Jellison, R.S.

1999-01-01

The oxidation of ammonia (NH3) and methane (CH4) was investigated in an alkaline saline lake, Mono Lake, California (U.S.A.). Ammonia oxidation was examined in April and July 1995 by comparing dark 14CO2 fixation rates in the presence or absence of methyl fluoride (MeF), an inhibitor of NH3 oxidation. Ammonia oxidizer-mediated dark 14CO2 fixation rates were similar in surface (5-7 m) and oxycline (11-15 m) waters, ranging between 70-340 and 89-186 nM d-1, respectively, or 1-7% of primary production by phytoplankton. Ammonia oxidation rates ranged between 580-2,830 nM d-1 in surface waters and 732-1,548 nM d-1 in oxycline waters. Methane oxidation was examined using a 14CH4 tracer technique in July 1994, April 1995, and July 1995. Methane oxidation rates were consistently higher in July, and rates in oxycline and anaerobic bottom waters (0.5-37 and 7-48 nM d-1, respectively) were 10-fold higher than those in aerobic surface waters (0.04-3.8 nM d-1). The majority of CH4 oxidation, in terms of integrated activity, occurred within anoxic bottom waters. Water column oxidation reduced the potential lake-atmosphere CH4 flux by a factor of two to three. Measured oxidation rates and water column concentrations were used to estimate the biological turnover times of NH3 and CH4. The NH3 pool turns over rapidly, on time scales of 0.8 d in surface waters and 10 d within the oxycline, while CH4 is cycled on 103-d time scales in surface waters and 102-d time scales within oxycline and bottom waters. Our data suggest an important role for NH3 oxidation in alkaline, saline lakes since the process converts volatile NH3 to soluble NO2-, thereby reducing loss via lake-atmosphere exchange and maintaining nitrogen in a form that is readily available to phytoplankton.

Characteristics of oxide scale formed on Cu-bearing austenitic stainless steel during early stages of high temperature oxidation

NASA Astrophysics Data System (ADS)

Swaminathan, Srinivasan; Krishna, Nanda Gopala; Kim, Dong-Ik

2015-10-01

Oxide scale evolution on Cu-bearing austenitic stainless steel 304H at 650 °C, in ambient air, for exposure times 100, 300, 500 and 1000 h, has been investigated. Surface morphology and chemistry of the oxide scale grown were examined using SEM/EDX and XPS. The oxidation kinetics was determined by measuring the weight change using an electronic balance. At the initial stage, up to 500 h of exposure time, the oxidation rate was rapid due to surface reactions governed primarily by oxygen ingress, and then, dropped to a low rate after prolonged oxidation for 1000 h. The diffusion of reactants through the initially formed oxide scale limits the oxidation rate at longer times, thus, the progress of reaction followed the parabolic kinetics. The formed oxide scale was enriched significantly with segregation and subsequent oxidation of Nb, and finely dispersed metallic Cu particles. Within the time frame of oxidation, the oxide scale was mainly composed of mixed oxides such as FeCr2O4 and MnCr2O4 along with the binary oxides of Fe, Cr and Mn. Moreover, the precipitation fraction of Cu-rich particles on the oxide scale increased markedly with increase of exposure times. The chemical heterogeneity of oxide scale suggests that the oxidation occurred in a non-selective manner.

Laser method for forming low-resistance ohmic contacts on semiconducting oxides

DOEpatents

Narayan, Jagdish

1981-01-01

This invention is a new method for the formation of high-quality ohmic contacts on wide-band-gap semiconducting oxides. As exemplified by the formation of an ohmic contact on n-type BaTiO.sub.3 containing a p-n junction, the invention entails depositing a film of a metallic electroding material on the BaTiO.sub.3 surface and irradiating the film with a Q-switched laser pulse effecting complete melting of the film and localized melting of the surface layer of oxide immediately underlying the film. The resulting solidified metallic contact is ohmic, has unusually low contact resistance, and is thermally stable, even at elevated temperatures. The contact does not require cleaning before attachment of any suitable electrical lead. This method is safe, rapid, reproducible, and relatively inexpensive.

Method for forming low-resistance ohmic contacts on semiconducting oxides

DOEpatents

Narayan, J.

1979-10-01

The invention provides a new method for the formation of high-quality ohmic contacts on wide-band-gap semiconducting oxides. As exemplified by the formation of an ohmic contact on n-type BaTiO/sub 3/ containing a p-n junction, the invention entails depositing a film of a metallic electroding material on the BaTiO/sub 3/ surface and irradiating the film with a Q-switched laser pulse effecting complete melting of the film and localized melting of the surface layer of oxide immediately underlying the film. The resulting solidified metallic contact is ohmic, has unusually low contact resistance, and is thermally stable, even at elevated temmperatures. The contact does not require cleaning before attachment of any suitable electrical lead. This method is safe, rapid, reproducible, and relatively inexpensive.

The Preparation, Characterization, Mechanical and Antibacterial Properties of GO-ZnO Nanocomposites with a Poly(l-lactide)-Modified Surface

PubMed Central

Yuan, Mingwei; Xiong, Chengdong; Jiang, Lin; Li, Hongli

2018-01-01

Graphene oxide (GO) was employed for the preparation of GO-zinc oxide (ZnO). The hydroxyl group on the surface was exploited to trigger the l-lactide ring-opening polymerization. A composite material with poly(l-lactide) (PLLA) chains grafted to the GO-ZnO surface, GO-ZnO-PLLA, was prepared. The results demonstrated that the employed method allowed one-step, rapid grafting of PLLA to the GO-ZnO surface. The chemical structure of the GO surface was altered by improved dispersion of GO-ZnO in organic solvents, thus enhancing the GO-ZnO dispersion in the PLLA matrix and the interface bonding with PLLA. Subsequently, composite films, GO-ZnO-PLLA and GO-ZnO-PLLA/PLLA, were prepared. The changes in interface properties and mechanical properties were studied. Furthermore, the antibacterial performance of nano-ZnO was investigated. PMID:29473891

Non-Metallic Ti Oxides and MnS/FeS2 Complex Precipitation in Ti-Killed Steel

NASA Astrophysics Data System (ADS)

Chen, Jieyun; Zhao, Dan; Li, Huigai; Zheng, Shaobo

Titanium deoxidized experiments can be carried in vacuum induction furnace by adding Ti-Fe alloy in molten steel to simulate strip casting. Sub-rapid solidification samples were obtained in the method of suing copper mold. The morphology, the chemical composition and the structures of nanometer precipitations were carried out to investigate by transmission electron microscope (TEM) with Energy Dispersive X ray Spectrum (EDX) and by collecting diffraction patterns with carbon extraction specimens. It has been found that titanium oxides were TiO monoclinic, Ti4O7 anorthic and TiO2 orthogonal structure in one nanometer inclusion, as the composite oxide was precipitated MnS/FeS2 cubic structure during sub-rapid solidification. Thermodynamic calculation analysis showed that it was possible to precipitate different kinds of nonstoichiometric TiOx. The solid solution between MnS/FeS2 will precipitate on the surface of titanium oxides because of good coherency relationship.

Effect of Er{sup 3+} ions on the phase formation and properties of In{sub 2}O{sub 3}nanostructures crystallized upon microwave heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemos, Samantha C.S.; Romeiro, Fernanda C.; Paula, Leonardo F. de

Regular sized nanostructures of indium oxide (In{sub 2}O{sub 3}) were homogeneously grown using a facile route, i.e. a microwave-hydrothermal method combined with rapid thermal treatment in a microwave oven. The presence of Er{sup 3+} doping plays an important role in controlling the formation of cubic (bcc) and rhombohedral (rh) In{sub 2}O{sub 3} phases. The samples presented broad photoluminescent emission bands in the green-orange region, which were attributed to the recombination of electrons at oxygen vacancies. The photocatalytic activities of pure bcc-In{sub 2}O{sub 3} and a bcc-rh-In{sub 2}O{sub 3} mixture towards the UVA degradation of methylene blue (MB) were also evaluated.more » The results showed that Er{sup +3} doped In{sub 2}O{sub 3} exhibited the highest photocatalytic activity with a photonic efficiency three times higher than the pure oxide. The improved performance was attributed to the higher surface area, the greater concentration of electron traps due the presence of the dopant and the possible formation of heterojunctions between the cubic and rhombohedral phases. - Graphical abstract: Photodegradation curves as a function of irradiation time of the samples obtained upon rapid microwave heating. - Highlights: • Efficient and rapid microwave heating to obtain Er{sup 3+} doped In{sub 2}O{sub 3} nanostructures. • Er{sup 3+} ions doping is fundamental to stabilizing the crystalline rhombohedral phase. • Symmetry breaking induced by vacancies in the lattice leads to photoluminescence. • Surface area of doped sample was two times higher than the surface of pure oxide. • The presence of defects in the lattice structure favors photocatalytic activity.« less

Opposing effects of humidity on rhodochrosite surface oxidation.

PubMed

Na, Chongzheng; Tang, Yuanzhi; Wang, Haitao; Martin, Scot T

2015-03-03

Rhodochrosite (MnCO3) is a model mineral representing carbonate aerosol particles containing redox-active elements that can influence particle surface reconstruction in humid air, thereby affecting the heterogeneous transformation of important atmospheric constituents such as nitric oxides, sulfur dioxides, and organic acids. Using in situ atomic force microscopy, we show that the surface reconstruction of rhodochrosite in humid oxygen leads to the formation and growth of oxide nanostructures. The oxidative reconstruction consists of two consecutive processes with distinctive time scales, including a long waiting period corresponding to slow nucleation and a rapid expansion phase corresponding to fast growth. By varying the relative humidity from 55 to 78%, we further show that increasing humidity has opposing effects on the two processes, accelerating nucleation from 2.8(±0.2) × 10(-3) to 3.0(±0.2) × 10(-2) h(-1) but decelerating growth from 7.5(±0.3) × 10(-3) to 3.1(±0.1) × 10(-3) μm(2) h(-1). Through quantitative analysis, we propose that nanostructure nucleation is controlled by rhodochrosite surface dissolution, similar to the dissolution-precipitation mechanism proposed for carbonate mineral surface reconstruction in aqueous solution. To explain nanostructure growth in humid oxygen, a new Cabrera-Mott mechanism involving electron tunneling and solid-state diffusion is proposed.

Rapid Grafting of Azido-labeled Oligo(ethylene glycol)s onto an Alkynyl-terminated Monolayer on Non-oxidized Silicon via Microwave-assisted “Click” Reaction

PubMed Central

Li, Yan; Wang, Jun; Cai, Chengzhi

2011-01-01

Microwave (MW) irradiation was used for the grafting of azido-labeled oligo(ethylene oxide) (OEG) on alkynyl-terminated non-oxidized silicon substrates via copper-catalyzed “click” reaction. The “clickable” monolayers were prepared by photografting of an α,ω-alkynene, where the alkynyl terminus was protected by a trimethylgermanyl (TMG) group, onto hydrogen-terminated Si(111) surfaces. X-ray photoelectron spectroscopy (XPS) was primarily employed to characterize the monolayers, and the data obtained were utilized to calculate the surface density of the TMG-alkynyl-functionalized substrate. MW-assisted one-pot deprotection/click reaction was optimized on the surfaces using azido-tagged OEG derivatives. Using MW instead of conventional heating led to a substantial improvement on the rate of the reaction while suppressing the oxidation of the silicon interface and OEG degradation. The antifouling property of the resulting substrates was evaluated using fibrinogen as a model protein. Results show that the OEG-modification reduced the protein adsorption by >90%. PMID:21306165

Rapid assessment of oxidation via middle-down LCMS correlates with methionine side-chain solvent-accessible surface area for 121 clinical stage monoclonal antibodies.

PubMed

Yang, Rong; Jain, Tushar; Lynaugh, Heather; Nobrega, R Paul; Lu, Xiaojun; Boland, Todd; Burnina, Irina; Sun, Tingwan; Caffry, Isabelle; Brown, Michael; Zhi, Xiaoyong; Lilov, Asparouh; Xu, Yingda

Susceptibility of methionine to oxidation is an important concern for chemical stability during the development of a monoclonal antibody (mAb) therapeutic. To minimize downstream risks, leading candidates are usually screened under forced oxidation conditions to identify oxidation-labile molecules. Here we report results of forced oxidation on a large set of in-house expressed and purified mAbs with variable region sequences corresponding to 121 clinical stage mAbs. These mAb samples were treated with 0.1% H 2 O 2 for 24 hours before enzymatic cleavage below the hinge, followed by reduction of inter-chain disulfide bonds for the detection of the light chain, Fab portion of heavy chain (Fd) and Fc by liquid chromatography-mass spectrometry. This high-throughput, middle-down approach allows detection of oxidation site(s) at the resolution of 3 distinct segments. The experimental oxidation data correlates well with theoretical predictions based on the solvent-accessible surface area of the methionine side-chains within these segments. These results validate the use of upstream computational modeling to predict mAb oxidation susceptibility at the sequence level.

Oxidation of pyrite in an anoxic atmosphere

USGS Publications Warehouse

Thorpe, A.N.; Senftle, F.E.; Alexander, Corrine; Dulong, F.T.; LaCount, R.B.; Friedman, S.

1987-01-01

Pyrite (FeS2) inclusions in coal, when heated in an oxygen deficient atmosphere (approximately 1% oxygen), become coated with magnetic Fe3O4 due to oxidation. Most of the FeS2 can thus be removed from the coal by magnetic separation to reduce the sulphur concentration. The oxidation products have been studied in greater detail by measuring the SO2 and O2 in the effluent gas during the heating process and by performing further magnetic measurements. At 582 K, the pyrite surface was oxidized to FeSO4. Significant oxidation of FeSO4 and FeS2 to Fe3O4 was observed starting at 677 K. At about 681 K, the Fe3O4 is further oxidized to ??-Fe2O3. At 681 K, under isothermal conditions, the oxidation is impeded by the ??-Fe2O3 formed on the surfaces of the grains. If the temperature is rapidly increased, the oxygen penetrates the ??-Fe2O3 veneer to the FeS2 core of the pyrite grains and oxidizes essentially the whole pyrite mass to Fe3O4 before ??-Fe2O3 can be formed. ?? 1987.

Iron and manganese removal: Recent advances in modelling treatment efficiency by rapid sand filtration.

PubMed

Vries, D; Bertelkamp, C; Schoonenberg Kegel, F; Hofs, B; Dusseldorp, J; Bruins, J H; de Vet, W; van den Akker, B

2017-02-01

A model has been developed that takes into account the main characteristics of (submerged) rapid filtration: the water quality parameters of the influent water, notably pH, iron(II) and manganese(II) concentrations, homogeneous oxidation in the supernatant layer, surface sorption and heterogeneous oxidation kinetics in the filter, and filter media adsorption characteristics. Simplifying assumptions are made to enable validation in practice, while maintaining the main mechanisms involved in iron(II) and manganese(II) removal. Adsorption isotherm data collected from different Dutch treatment sites show that Fe(II)/Mn(II) adsorption may vary substantially between them, but generally increases with higher pH. The model is sensitive to (experimentally) determined adsorption parameters and the heterogeneous oxidation rate. Model results coincide with experimental values when the heterogeneous rate constants are calibrated. Copyright © 2016 Elsevier Ltd. All rights reserved.

Rapid vapor deposition of highly conformal silica nanolaminates.

PubMed

Hausmann, Dennis; Becker, Jill; Wang, Shenglong; Gordon, Roy G

2002-10-11

Highly uniform and conformal coatings can be made by the alternating exposures of a surface to vapors of two reactants, in a process commonly called atomic layer deposition (ALD). The application of ALD has, however, been limited because of slow deposition rates, with a theoretical maximum of one monolayer per cycle. We show that alternating exposure of a surface to vapors of trimethylaluminum and tris(tert-butoxy)silanol deposits highly conformal layers of amorphous silicon dioxide and aluminum oxide nanolaminates at rates of 12 nanometers (more than 32 monolayers) per cycle. This process allows for the uniform lining or filling of long, narrow holes. We propose that these ALD layers grow by a previously unknown catalytic mechanism that also operates during the rapid ALD of many other metal silicates. This process should allow improved production of many devices, such as trench insulation between transistors in microelectronics, planar waveguides, microelectromechanical structures, multilayer optical filters, and protective layers against diffusion, oxidation, or corrosion.

Oxidative dissolution of pyrite surfaces by hexavalent chromium: Surface site saturation and surface renewal

NASA Astrophysics Data System (ADS)

Graham, Andrew M.; Bouwer, Edward J.

2012-04-01

In-situ reduction of toxic Cr(VI) to nontoxic Cr(III) represents an important natural attenuation process for Cr(VI)-impacted environments. This study investigates the stoichiometry and kinetics of Cr(VI) reduction by pyrite, a reduced iron-sulfur mineral ubiquitous in recent estuarine and marine sediments. Pyrite suspensions at surface loadings of 0.28-2.10 m2/L (typical of estuarine or marine sediments) were capable of completely reducing 7-120 μM Cr(VI) on the timescale of minutes to days, with the time to reaction completion decreasing with increasing pyrite loading, decreasing initial Cr(VI) concentration, and decreasing suspension pH. Analysis of metal species (Cr and Fe) and sulfur species in solution and at the mineral surface indicated that Cr(VI) oxidatively dissolved the pyrite surface, releasing ferrous iron and sulfate into solution as the reaction progressed. Surface disulfide groups were postulated as the Cr(VI)-reactive surface entity. Net production or consumption of aqueous Fe(II) was shown to depend upon the relative rates of proton-promoted Fe(II) release, Fe(II) release due to oxidative dissolution of pyrite in the presence of Cr(VI), and Fe(II) consumption due to homogeneous reaction with Cr(VI). Kinetics of Cr(VI) reduction by pyrite displayed a biphasic pattern, and the time to reaction completion increased dramatically with increasing initial Cr(VI) concentration. Rapid Cr(VI) removal occurred early in the reaction progress, attributable to Cr(VI) loss under an adsorption-limited regime. Slow, approximately zero-order, Cr(VI) removal occurred over the bulk of the time courses, and corresponded to Cr(VI) removal under surface site saturation conditions. Stoichiometric Cr(VI) reduction was able to proceed under surface site limited conditions owing to regeneration of reactive surface sites following desorption/dissolution of oxidized surface products, as demonstrated in repeat Cr(VI)-spiking experiments. The role of surface passivation was evaluated by comparing rates of Cr(VI) reduction in the presence and absence of the Cr(III)-complexing agent citrate. While citrate addition significantly enhanced Cr(III) solubility, rates of Cr(VI) reduction were only marginally accelerated, suggesting that Cr(OH)3(s) coatings did not completely block access of Cr(VI) to reactive surface sites on pyrite. Given the rapid rates of Cr(VI) reduction with pyrite under pH and surface coverage conditions typical of natural environments, we propose that Cr(VI) reduction by pyrite be considered in fate and transport models for Cr in contaminated sediments.

Sorption of carbamazepine by commercial graphene oxides: a comparative study with granular activated carbon and multiwalled carbon nanotubes.

PubMed

Cai, Nan; Larese-Casanova, Philip

2014-07-15

Graphene nanosheet materials represent a potentially new high surface area sorbent for the treatment of endocrine disrupting compounds (EDCs) in water. However, sorption behavior has been reported only for laboratory graphene prepared by a laborious and hazardous graphite exfoliation process. A careful examination of commercially available, clean, high-volume produced graphene materials should reveal whether they are appropriate for sorbent technologies and which physicochemical properties most influence sorption performance. In this study, three commercially available graphene oxide powders of various particle sizes, specific surface areas, and surface chemistries were evaluated for their sorption performance using carbamazepine and nine other EDCs and were compared to that of conventional granular activated carbon (GAC) and multi-walled carbon nanotubes (MWCNTs). Sorption kinetics of carbamazepine on graphene oxide powders was rapid and reversible with alcohol washing, consistent with π-π interactions. The various sorption extents as described by Freundlich isotherms were best explained by available surface area, and only the highest surface area graphene oxide (771 m(2)/g) out-performed GAC and MWCNTs. Increasing pH caused more negative surface charge, a twofold decrease in sorption of anionic ibuprofen, a onefold increase in sorption of cationic atenolol, and no change for neutral carbamazepine, highlighting the role of electrostatic interactions. Copyright © 2014 Elsevier Inc. All rights reserved.

System for rapid biohydrogen phenotypic screening of microorganisms using a chemochromic sensor

DOEpatents

Seibert, Michael; Benson, David K.; Flynn, Timothy Michael

2002-01-01

Provided is a system for identifying a hydrogen gas producing organism. The system includes a sensor film having a first layer comprising a transition metal oxide or oxysalt and a second layer comprising a hydrogen-dissociative catalyst metal, the first and second layers having an inner and an outer surface wherein the inner surface of the second layer is deposited on the outer surface of the first layer, and a substrate adjacent to the outer surface of the second layer, the organism isolated on the substrate.

Method and apparatus for rapid biohydrogen phenotypic screening of microorganisms using a chemochromic sensor

DOEpatents

Seibert, Michael; Benson, David K.; Flynn, Timothy Michael

2001-01-01

The invention provides an assay system for identifying a hydrogen-gas-producing organism, including a sensor film having a first layer comprising a transition metal oxide or oxysalt and a second layer comprising hydrogen-dissociative catalyst metal, the first and second layers having an inner and an outer surface wherein the inner surface of the second layer is deposited on the outer surface of the first layer, and a substrate disposed proximally to the outer surface of the second layer, the organism being isolated on the substrate.

An Investigation of the Hot Corrosion Protectivity Behavior of Platinum Modified Aluminide Coatings on Nickel-Based Superalloys

DTIC Science & Technology

1987-03-01

is unlimited. WCRT LAIISIPIcaiIo IP THIS P431 IEPORT DOCUMENTATION PAGE* is REIPOT SECURilY CLASSIFICATION 1b RISTRtC7IVI MARKINGS la FURITY... grow until it forms a continuous surface layer. At this point, there is a parabolic decrease in the rate of oxidation and the surface stabilizes. If...surface as PtA1 2 and Pt 2 A13. Consequently, the platinum concentration gradient that develops is highest at the surface, but, rapidly diminishes as the

Rapid antibiotic efficacy screening with aluminum oxide nanoporous membrane filter-chip and optical detection system.

PubMed

Tsou, Pei-Hsiang; Sreenivasappa, Harini; Hong, Sungmin; Yasuike, Masayuki; Miyamoto, Hiroshi; Nakano, Keiyo; Misawa, Takeyuki; Kameoka, Jun

2010-09-15

We have developed a filter-chip and optical detection system for rapid antibiotic efficacy screening. The filter-chip consisted of a 1-mL reservoir and an anodic aluminum oxide (AAO) nanoporous membrane. Sample solution with liquid growth media, bacteria, and antibiotics was incubated in the reservoir for a specific period of time. The number of live bacteria on the surface of membrane was counted after the incubation with antibiotics and filtration. Using this biosensing system, we have demonstrated a 1-h antibiotic screening for patients' clinical samples, significantly faster than the conventional antibiotic susceptibility tests that typically take more than 24h. This rapid screening nature makes the filter-chip and detection system ideal for tailoring antibiotic treatment to individual patients by reducing the microbial antibiotic resistance, and improving the survival rate for patients suffering from postoperative infections. Published by Elsevier B.V.

Enhanced Formation of Oxidants from Bimetallic Nickel-Iron Nanoparticles in the Presence of Oxygen

PubMed Central

Lee, Changha; Sedlak, David L.

2009-01-01

Nanoparticulate zero-valent iron (nZVI) rapidly reacts with oxygen to produce strong oxidants, capable of transforming organic contaminants in water. However, the low yield of oxidants with respect to the iron added normally limits the application of this system. Bimetallic nickel-iron nanoparticles (nNi-Fe; i.e., Ni-Fe alloy and Ni-coated Fe nanoparticles) exhibited enhanced yields of oxidants compared to nZVI. nNi-Fe (Ni-Fe alloy nanoparticles with [Ni]/[Fe] = 0.28 and Ni-coated Fe nanoparticles with [Ni]/[Fe] = 0.035) produced approximately 40% and 85% higher yields of formaldehyde from the oxidation of methanol relative to nZVI at pH 4 and 7, respectively. Ni-coated Fe nanoparticles showed a higher efficiency for oxidant production relative to Ni-Fe alloy nanoparticles based on Ni content. Addition of Ni did not enhance the oxidation of 2-propanol or benzoic acid, indicating that Ni addition did not enhance hydroxyl radical formation. The enhancement in oxidant yield was observed over a pH range of 4 – 9. The enhanced production of oxidant by nNi-Fe appears to be attributable to two factors. First, the nNi-Fe surface is less reactive toward hydrogen peroxide (H2O2) than the nZVI surface, which favors the reaction of H2O2 with dissolved Fe(II) (the Fenton reaction). Second, the nNi-Fe surface promotes oxidant production from the oxidation of ferrous ion by oxygen at neutral pH values. PMID:19068843

The effects of iron(II) on the kinetics of arsenic oxidation and sorption on manganese oxides.

PubMed

Wu, Yun; Li, Wei; Sparks, Donald L

2015-11-01

In this study, As(III) oxidation kinetics by a poorly-crystalline phyllomanganate (δ-MnO2) in the presence and absence of dissolved Fe(II) was investigated using stirred-flow and batch experiments. Chemically synthetic δ-MnO2 was reacted with four influent solutions, containing the same As(III) concentration but different Fe(II) concentrations, at pH 6. The results show an initial rapid As(III) oxidation by δ-MnO2, which is followed by an appreciably slow reaction after 8h. In the presence of Fe(II), As(III) oxidation is inhibited due to the competitive oxidation of Fe(II) as well as the formation of Fe(III)-(hydr)oxides on the δ-MnO2 surface. However, the sorption of As(III), As(V) and Mn(II) are increased, for the newly formed Fe(III)-(hydr)oxides provide additional sorption sites. This study suggests that the competitive oxidation of Fe(II) and consequently the precipitation of Fe(III) compounds on the δ-MnO2 surface play an important role in As(III) oxidation and As sequestration. Understanding these processes would be helpful in developing in situ strategies for remediation of As-contaminated waters and soils. Copyright © 2015 Elsevier Inc. All rights reserved.

Periodic disruptions induced by high repetition rate femtosecond pulses on magnesium-oxide-doped lithium niobate surfaces

NASA Astrophysics Data System (ADS)

Zhang, Shuanggen; Kan, Hongli; Zhai, Kaili; Ma, Xiurong; Luo, Yiming; Hu, Minglie; Wang, Qingyue

2017-02-01

In this paper, we demonstrate the periodic disruption formation on magnesium-oxide-doped lithium niobate surfaces by a femtosecond fiber laser system with wavelength and repetition rate of 1040 nm and 52 MHz, respectively. Three main experimental conditions, laser average power, scanning speed, and orientation of sample were systematically studied. In particular, the ablation morphologies of periodic disruptions under different crystal orientations were specifically researched. The result shows that such disruptions consisting of a bamboo-like inner structure appears periodically for focusing on the surface of X-, Y- and Z-cut wafers, which are formed by a rapid quenching of the material. Meanwhile, due to the anisotropic property, the bamboo-like inner structures consist of a cavity only arise from X- and Z-cut orientation.

Decomposition of poly(amide-imide) film enameled on solid copper wire using atmospheric pressure non-equilibrium plasma.

PubMed

Sugiyama, Kazuo; Suzuki, Katsunori; Kuwasima, Shusuke; Aoki, Yosuke; Yajima, Tatsuhiko

2009-01-01

The decomposition of a poly(amide-imide) thin film coated on a solid copper wire was attempted using atmospheric pressure non-equilibrium plasma. The plasma was produced by applying microwave power to an electrically conductive material in a gas mixture of argon, oxygen, and hydrogen. The poly(amide-imide) thin film was easily decomposed by argon-oxygen mixed gas plasma and an oxidized copper surface was obtained. The reduction of the oxidized surface with argon-hydrogen mixed gas plasma rapidly yielded a metallic copper surface. A continuous plasma heat-treatment process using a combination of both the argon-oxygen plasma and argon-hydrogen plasma was found to be suitable for the decomposition of the poly(amide-imide) thin film coated on the solid copper wire.

A Study on Factors Affecting the Degradation of Magnesium and a Magnesium-Yttrium Alloy for Biomedical Applications

PubMed Central

Johnson, Ian; Liu, Huinan

2013-01-01

Controlling degradation of magnesium or its alloys in physiological saline solutions is essential for their potential applications in clinically viable implants. Rapid degradation of magnesium-based materials reduces the mechanical properties of implants prematurely and severely increases alkalinity of the local environment. Therefore, the objective of this study is to investigate the effects of three interactive factors on magnesium degradation, specifically, the addition of yttrium to form a magnesium-yttrium alloy versus pure magnesium, the metallic versus oxide surfaces, and the presence versus absence of physiological salt ions in the immersion solution. In the immersion solution of phosphate buffered saline (PBS), the magnesium-yttrium alloy with metallic surface degraded the slowest, followed by pure magnesium with metallic or oxide surfaces, and the magnesium-yttrium alloy with oxide surface degraded the fastest. However, in deionized (DI) water, the degradation rate showed a different trend. Specifically, pure magnesium with metallic or oxide surfaces degraded the slowest, followed by the magnesium-yttrium alloy with oxide surface, and the magnesium-yttrium alloy with metallic surface degraded the fastest. Interestingly, only magnesium-yttrium alloy with metallic surface degraded slower in PBS than in DI water, while all the other samples degraded faster in PBS than in DI water. Clearly, the results showed that the alloy composition, presence or absence of surface oxide layer, and presence or absence of physiological salt ions in the immersion solution all influenced the degradation rate and mode. Moreover, these three factors showed statistically significant interactions. This study revealed the complex interrelationships among these factors and their respective contributions to degradation for the first time. The results of this study not only improved our understanding of magnesium degradation in physiological environment, but also presented the key factors to consider in order to satisfy the degradation requirements for next-generation biodegradable implants and devices. PMID:23799028

General facile approach to transition-metal oxides with highly uniform mesoporosity and their application as adsorbents for heavy-metal-ion sequestration.

PubMed

Seisenbaeva, Gulaim A; Daniel, Geoffrey; Kessler, Vadim G; Nedelec, Jean-Marie

2014-08-18

Mesoporous powders of transition-metal oxides, TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5, pure from organic impurities were produced by a rapid single-step thermohydrolytic approach. The obtained materials display an impressively large active surface area and sharp pore-size distribution, being composed of partially coalesced uniform nanoparticles with crystalline cores and amorphous shells. They reveal extremely high adsorption capacity in removal of Cr(VI) anions from solutions (25.8 for TiO2, 73.0 for ZrO2, and 74.7 mg g(-1) for Nb2O5 in relation to the Cr2O7(2-) anion), making them very attractive as adsorbents in water remediation applications. The difference in adsorption capacities for the studied oxides may be explained by variation in surface hydration and surface-charge distribution. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synergistic effect of sunlight induced photothermal conversion and H2O2 release based on hybridized tungsten oxide gel for cancer inhibition

NASA Astrophysics Data System (ADS)

Wang, Cong; Gao, Yibo; Gao, Xinghua; Wang, Hua; Tian, Jingxuan; Wang, Li; Zhou, Bingpu; Ye, Ziran; Wan, Jun; Wen, Weijia

2016-10-01

A highly efficient photochromic hydrogel was successfully fabricated via casting precursor, which is based on amorphous tungsten oxide and poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide). Under simulated solar illumination, the hydrogel has a rapid and controlled temperature increasing ratio as its coloration degree. Localized electrons in the amorphous tungsten oxide play a vital role in absorption over a broad range of wavelengths from 400 nm to 1100 nm, encompassing the entire visible light and infrared regions in the solar spectrum. More importantly, the material exhibits sustainable released H2O2 induced by localized electrons, which has a synergistic effect with the rapid surface temperature increase. The amount of H2O2 released by each film can be tuned by the light irradiation, and the film coloration can indicate the degree of oxidative stress. The ability of the H2O2-releasing gels in vitro study was investigated to induce apoptosis in melanoma tumor cells and NIH 3T3 fibroblasts. The in vivo experimental results indicate that these gels have a greater healing effect than the control in the early stages of tumor formation.

Synergistic effect of sunlight induced photothermal conversion and H2O2 release based on hybridized tungsten oxide gel for cancer inhibition

PubMed Central

Wang, Cong; Gao, Yibo; Gao, Xinghua; Wang, Hua; Tian, Jingxuan; Wang, Li; Zhou, Bingpu; Ye, Ziran; Wan, Jun; Wen, Weijia

2016-01-01

A highly efficient photochromic hydrogel was successfully fabricated via casting precursor, which is based on amorphous tungsten oxide and poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide). Under simulated solar illumination, the hydrogel has a rapid and controlled temperature increasing ratio as its coloration degree. Localized electrons in the amorphous tungsten oxide play a vital role in absorption over a broad range of wavelengths from 400 nm to 1100 nm, encompassing the entire visible light and infrared regions in the solar spectrum. More importantly, the material exhibits sustainable released H2O2 induced by localized electrons, which has a synergistic effect with the rapid surface temperature increase. The amount of H2O2 released by each film can be tuned by the light irradiation, and the film coloration can indicate the degree of oxidative stress. The ability of the H2O2-releasing gels in vitro study was investigated to induce apoptosis in melanoma tumor cells and NIH 3T3 fibroblasts. The in vivo experimental results indicate that these gels have a greater healing effect than the control in the early stages of tumor formation. PMID:27775086

The missing organic molecules on Mars

NASA Technical Reports Server (NTRS)

Benner, S. A.; Devine, K. G.; Matveeva, L. N.; Powell, D. H.

2000-01-01

GC-MS on the Viking 1976 Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This result suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the rate at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzenecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS. Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is generated by oxidation of organic matter known to come to Mars, is rather stable to further oxidation, and would not have been easily detected by the Viking experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m(2) of Martian surface over 3 billion years. How much remains depends on decomposition rates under Martian conditions. As available data do not require that the surface of Mars be very strongly oxidizing, some organic molecules might be found near the surface of Mars, perhaps in amounts sufficient to be a resource. Missions should seek these and recognize that these complicate the search for organics from entirely hypothetical Martian life.

The missing organic molecules on Mars

PubMed Central

Benner, Steven A.; Devine, Kevin G.; Matveeva, Lidia N.; Powell, David H.

2000-01-01

GC-MS on the Viking 1976 Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This result suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the rate at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzenecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS. Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is generated by oxidation of organic matter known to come to Mars, is rather stable to further oxidation, and would not have been easily detected by the Viking experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m2 of Martian surface over 3 billion years. How much remains depends on decomposition rates under Martian conditions. As available data do not require that the surface of Mars be very strongly oxidizing, some organic molecules might be found near the surface of Mars, perhaps in amounts sufficient to be a resource. Missions should seek these and recognize that these complicate the search for organics from entirely hypothetical Martian life. PMID:10706606

The missing organic molecules on Mars.

PubMed

Benner, S A; Devine, K G; Matveeva, L N; Powell, D H

2000-03-14

GC-MS on the Viking 1976 Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This result suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the rate at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzenecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS. Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is generated by oxidation of organic matter known to come to Mars, is rather stable to further oxidation, and would not have been easily detected by the Viking experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m(2) of Martian surface over 3 billion years. How much remains depends on decomposition rates under Martian conditions. As available data do not require that the surface of Mars be very strongly oxidizing, some organic molecules might be found near the surface of Mars, perhaps in amounts sufficient to be a resource. Missions should seek these and recognize that these complicate the search for organics from entirely hypothetical Martian life.

Ab Initio Density Functional Calculations and Infra-Red Study of CO Interaction with Pd Atoms on θ-Al2O3 (010) Surface.

PubMed

Narula, Chaitanya K; Allard, Lawrence F; Wu, Zili

2017-07-24

The ab initio density functional theoretical studies show that energetics favor CO oxidation on single Pd atoms supported on θ-alumina. The diffuse reflectance infra-red spectroscopy (DRIFTS) results show that carbonates are formed as intermediates when single supported Pd atoms are exposed to a gaseous mixture of CO + O 2 . The rapid agglomeration of Pd atoms under CO oxidation conditions even at 6 °C leads to the presence of Pd particles along with single atoms during CO oxidation experiments. Thus, the observed CO oxidation has contributions from both single Pd atoms and Pd particles.

Plutonium(IV) and (V) sorption to goethite at sub-femtomolar to micromolar concentrations: Redox transformations and surface precipitation

DOE PAGES

Zhao, Pihong; Begg, James D.; Zavarin, Mavrik; ...

2016-06-06

Here, Pu(IV) and Pu(V) sorption to goethite was investigated over a concentration range of 10 –15–10 –5 M at pH 8. Experiments with initial Pu concentrations of 10 –15 – 10 –8 M produced linear Pu sorption isotherms, demonstrating that Pu sorption to goethite is not concentration-dependent across this concentration range. Equivalent Pu(IV) and Pu(V) sorption Kd values obtained at 1 and 2-week sampling time points indicated that Pu(V) is rapidly reduced to Pu(IV) on the goethite surface. Further, it suggested that Pu surface redox transformations are sufficiently rapid to achieve an equilibrium state within 1 week, regardless of themore » initial Pu oxidation state. At initial concentrations >10 –8 M, both Pu oxidation states exhibited deviations from linear sorption behavior and less Pu was adsorbed than at lower concentrations. NanoSIMS and HRTEM analysis of samples with initial Pu concentrations of 10 –8 – 10 –6 M indicated that Pu surface and/or bulk precipitation was likely responsible for this deviation. In 10 –6 M Pu(IV) and Pu(V) samples, HRTEM analysis showed the formation of a body centered cubic (bcc) Pu 4O 7 structure on the goethite surface, confirming that reduction of Pu(V) had occurred on the mineral surface and that epitaxial distortion previously observed for Pu(IV) sorption occurs with Pu(V) as well.« less

Internal oxidation phenomenon in pure copper

NASA Astrophysics Data System (ADS)

Rudolf, Rebeka; Anžel, Ivan

2009-04-01

This paper presents two special kinds of internal oxidation phenomenon that can take place in pure metals containing a high concentration of non-equilibrium defects. These processes are Internal Oxidation (IO) and Internal Carbonisation (IC). Both processes start with the dissolution of oxidant (O or C) into the pure metal at the free surfaces, and continue with the diffusion of oxidant atoms into the metal matrix volume, where they are trapped at numerous defects within the crystal lattice. Increasing oxidant activity at these places causes local oxidation of the matrix and, consequently, precipitation of fine oxide or graphite particles. The IO and IC processes were tested on the rapidly solidified pure copper which was produced by the Chill-Block Melt Spinning Technique. Analysis of the IO process showed the formation of Cu-Cu2O, and the formation of Cu-C composite from the IC process.

Characterizations of Ca- and Mg-incorporating micro/nano-structured surfaces on titanium fabricated by microarc oxidation and hydrothermal treatments

NASA Astrophysics Data System (ADS)

Ko, Sang-Hoon; Hwang, Moon-Jin; Moon, Won-Jin; Park, Yeong-Joon; Song, Ho-Jun

2015-12-01

The micro/nano-surface characteristics of magnesium- and calcium-incorporating titanium oxide layers fabricated on titanium metal using microarc oxidation (MAO) and hydrothermal (HT) treatments were investigated. Calcium acetate monohydrate (CA), magnesium acetate monohydrate (MA), and β-glycerophosphoric acid disodium salt pentahydrate were used as electrolytes for MAO treatment of titanium disks. CA/MA electrolyte concentrations (all in M) were 0.2/0.0 (CA20-MAO), 0.15/0.05 (CA15MA5-MAO), 0.1/0.1 (CA10MA10-MAO), 0.05/0.15 (CA5MA15-MAO), and 0.0/0.2 (MA20-MAO). MAO-HT groups were prepared by hydrothermal treatment of MAO groups. The porous surface morphology was consistent even after HT treatment. The incorporation of Mg ions in the oxide layer during MAO treatment was more favorable than incorporation of Ca ions. However, Mg ions were released more rapidly than Ca ions after HT treatment. The anatase TiO2 structure was dominant for all the groups and an increase in the rutile TiO2 structure was observed with an increase in MA concentration. Nano-sized crystallites were observed on the porous surface for all MAO-HT groups. Nano-needle-like crystallites were observed on the surface of CA20-MAO-HT. The crystallites exhibited shorter and thicker characteristics with an increase in Mg concentration.

Oxidation and hot corrosion of hot-pressed Si3N4 at 1000 deg C

NASA Technical Reports Server (NTRS)

Fielder, W. L.

1985-01-01

The oxidation and hot corrosion of a commercial, hot-pressed Si3N4 were investigated at 1000 C under an atmosphere of flowing O2. For the hot corrosion studies, thin films of Na2SO4 were airbrushed on the Si3N4 surface. The hot corrosion attack was monitored by the following techniques: continuous weight measurements, SO2 evolution, film morphology, and chemical analyses. Even though the hot corrosion weight changes after 25 hr were relatively small, the formation of SiO2 from oxidation of Si3N4 was an order of magnitude greater in the presence of molten Na2SO4. The formation of a protective SiO2 phase at the Si3N4 surface is minimized by the fluxing action of the molten Na2SO4 thereby allowing the oxidation of the Si3N4 to proceed more rapidly. A simple process is proposed to account for the hot corrosion process.

Rapid cycling of reactive nitrogen in the marine boundary layer.

PubMed

Ye, Chunxiang; Zhou, Xianliang; Pu, Dennis; Stutz, Jochen; Festa, James; Spolaor, Max; Tsai, Catalina; Cantrell, Christopher; Mauldin, Roy L; Campos, Teresa; Weinheimer, Andrew; Hornbrook, Rebecca S; Apel, Eric C; Guenther, Alex; Kaser, Lisa; Yuan, Bin; Karl, Thomas; Haggerty, Julie; Hall, Samuel; Ullmann, Kirk; Smith, James N; Ortega, John; Knote, Christoph

2016-04-28

Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

High Useful Yield and Isotopic Analysis of Uranium by Resonance Ionization Mass Spectrometry

DOE PAGES

Savina, Michael R.; Isselhardt, Brett H.; Kucher, Andrew; ...

2017-05-09

Useful yields from resonance ionization mass spectrometry can be extremely high compared to other mass spectrometry techniques, but uranium analysis shows strong matrix effects arising from the tendency of uranium to form strongly bound oxide molecules that do not dissociate appreciably on energetic ion bombardment. Here, we demonstrate a useful yield of 24% for metallic uranium. Modeling the laser ionization and ion transmission processes shows that the high useful yield is attributable to a high ion fraction achieved by resonance ionization. We quantify the reduction of uranium oxide surface layers by Ar + and Ga + sputtering. The useful yieldmore » for uranium atoms from a uranium dioxide matrix is 0.4% and rises to 2% when the surface is in sputter equilibrium with the ion beam. The lower useful yield from the oxide is almost entirely due to uranium oxide molecules reducing the neutral atom content of the sputtered flux. We also demonstrate rapid isotopic analysis of solid uranium oxide at a precision of <0.5% relative standard deviation using relatively broadband lasers to mitigate spectroscopic fractionation.« less

High Useful Yield and Isotopic Analysis of Uranium by Resonance Ionization Mass Spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Savina, Michael R.; Isselhardt, Brett H.; Kucher, Andrew

Useful yields from resonance ionization mass spectrometry can be extremely high compared to other mass spectrometry techniques, but uranium analysis shows strong matrix effects arising from the tendency of uranium to form strongly bound oxide molecules that do not dissociate appreciably on energetic ion bombardment. Here, we demonstrate a useful yield of 24% for metallic uranium. Modeling the laser ionization and ion transmission processes shows that the high useful yield is attributable to a high ion fraction achieved by resonance ionization. We quantify the reduction of uranium oxide surface layers by Ar + and Ga + sputtering. The useful yieldmore » for uranium atoms from a uranium dioxide matrix is 0.4% and rises to 2% when the surface is in sputter equilibrium with the ion beam. The lower useful yield from the oxide is almost entirely due to uranium oxide molecules reducing the neutral atom content of the sputtered flux. We also demonstrate rapid isotopic analysis of solid uranium oxide at a precision of <0.5% relative standard deviation using relatively broadband lasers to mitigate spectroscopic fractionation.« less

Surface oxidation and thermoelectric properties of indium-doped tin telluride nanowires.

PubMed

Li, Zhen; Xu, Enzhi; Losovyj, Yaroslav; Li, Nan; Chen, Aiping; Swartzentruber, Brian; Sinitsyn, Nikolai; Yoo, Jinkyoung; Jia, Quanxi; Zhang, Shixiong

2017-09-14

The recent discovery of excellent thermoelectric properties and topological surface states in SnTe-based compounds has attracted extensive attention in various research areas. Indium doped SnTe is of particular interest because, depending on the doping level, it can either generate resonant states in the bulk valence band leading to enhanced thermoelectric properties, or induce superconductivity that coexists with topological states. Here we report on the vapor deposition of In-doped SnTe nanowires and the study of their surface oxidation and thermoelectric properties. The nanowire growth is assisted by Au catalysts, and their morphologies vary as a function of substrate position and temperature. Transmission electron microscopy characterization reveals the formation of an amorphous surface in single crystalline nanowires. X-ray photoelectron spectroscopy studies suggest that the nanowire surface is composed of In 2 O 3 , SnO 2 , Te and TeO 2 which can be readily removed by argon ion sputtering. Exposure of the cleaned nanowires to atmosphere leads to rapid oxidation of the surface within only one minute. Characterization of electrical conductivity σ, thermopower S, and thermal conductivity κ was performed on the same In-doped nanowire which shows suppressed σ and κ but enhanced S yielding an improved thermoelectric figure of merit ZT compared to the undoped SnTe.

Patterning of a-C DLC films: exploration of an aqueous electro-oxidative mechanism

NASA Astrophysics Data System (ADS)

Mühl, Thomas; Myhra, Sverre

2007-06-01

Conducting ion-beam assisted CVD deposited a-C type DLC films can be patterned electro-oxidatively by masked and maskless probe-induced STM-based lithography. The former constitutes a parallel rapid processing technology, with the tip acting as a distant stationary electrode. The latter is a higher spatial resolution serial technology, with the tip defining a travelling local electro-chemical cell. The mechanism is based on electro-oxidative conversion of solid carbon to gaseous CO or CO2 in the presence of an aqueous phase, either as a bulk fluid or as a thin adsorbed film. The process is constrained kinetically in the early stages by limitations on charge transport through the surface barrier at the fluid-to-solid interface and subsequently by the availability of oxidants and by their transport to reactive sites. The as-received surface is terminated by chemisorbed oxygen, leading to the formation of an insulating surface barrier. The threshold potential for initiation of conversion depends on the width of the barrier. The results may have implications for new technologies exploiting the properties of carbon-based materials, but may also add to the present understanding of the electrochemistry of carbon solids.

Sulfur Dioxide Capture by Heterogeneous Oxidation on Hydroxylated Manganese Dioxide.

PubMed

Wu, Haodong; Cai, Weimin; Long, Mingce; Wang, Hairui; Wang, Zhiping; Chen, Chen; Hu, Xiaofang; Yu, Xiaojuan

2016-06-07

Here we demonstrate that sulfur dioxide (SO2) is efficiently captured via heterogeneous oxidation into sulfate on the surface of hydroxylated manganese dioxide (MnO2). Lab-scale activity tests in a fluidized bed reactor showed that the removal efficiency for a simulated flue gas containing 5000 mg·Nm(-3) SO2 could reach nearly 100% with a GHSV (gas hourly space velocity) of 10000 h(-1). The mechanism was investigated using a combination of experimental characterizations and theoretical calculations. It was found that formation of surface bound sulfate proceeds via association of SO2 with terminal hydroxyls. Both H2O and O2 are essential for the generation of reactive terminal hydroxyls, and the indirect role of O2 in heterogeneous SO2 oxidation at low temperature was also revealed. We propose that the high reactivity of terminal hydroxyls is attributed to the proper surface configuration of MnO2 to adsorb water with degenerate energies for associative and dissociative states, and maintain rapid proton dynamics. Viability analyses suggest that the desulfurization method that is based on such a direct oxidation reaction at the gas/solid interface represents a promising approach for SO2 capture.

Combined catalysts for the combustion of fuel in gas turbines

DOEpatents

Anoshkina, Elvira V.; Laster, Walter R.

2012-11-13

A catalytic oxidation module for a catalytic combustor of a gas turbine engine is provided. The catalytic oxidation module comprises a plurality of spaced apart catalytic elements for receiving a fuel-air mixture over a surface of the catalytic elements. The plurality of catalytic elements includes at least one primary catalytic element comprising a monometallic catalyst and secondary catalytic elements adjacent the primary catalytic element comprising a multi-component catalyst. Ignition of the monometallic catalyst of the primary catalytic element is effective to rapidly increase a temperature within the catalytic oxidation module to a degree sufficient to ignite the multi-component catalyst.

Overlay metallic-cermet alloy coating systems

NASA Technical Reports Server (NTRS)

Gedwill, M. A.; Levine, S. R.; Glasgow, T. K. (Inventor)

1984-01-01

A substrate, such as a turbine blade, vane, or the like, which is subjected to high temperature use is coated with a base coating of an oxide dispersed, metallic alloy (cermet). A top coating of an oxidation, hot corrosion, erosion resistant alloy of nickel, cobalt, or iron is then deposited on the base coating. A heat treatment is used to improve the bonding. The base coating serves as an inhibitor to interdiffusion between the protective top coating and the substrate. Otherwise, the protective top coating would rapidly interact detrimentally with the substrate and degrade by spalling of the protective oxides formed on the outer surface at elevated temperatures.

Dynamic measurements of the spreading of liquid metals in controlled atmospheres with in situ surface preparation and analysis

NASA Astrophysics Data System (ADS)

Peebles, D. E.; Peebles, H. C.; Ohlhausen, J. A.; Hurst, M. J.

1996-02-01

A specially designed ultrahigh vacuum in situ surface analysis and wetting system has been constructed to study the spreading of liquid metal solders on carefully prepared and well-characterized solid substrates. The system consists of a standard ultrahigh vacuum surface analysis chamber linked to a reaction chamber for wetting or other experiments at pressures up to atmospheric. A sophisticated video system allows real-time monitoring of the spreading of the liquid metal through both side and top views. An infrared imaging system allows accurate remote temperature measurements. Sample surfaces are prepared and spreading experiments performed without intermediate exposure of the surfaces to the contaminating atmospheres. Solder spreading is performed under 50 Torr of highly purified helium gas to allow for adequate thermal coupling between the solder and the substrate. Initial studies have been completed for the spreading of pure tin solder on copper substrates in the absence of any fluxing agent. Three types of copper substrate surfaces were investigated in these experiments: the sputter-cleaned, air-exposed, and the as-received surface. Surface chemical analysis by x-ray photoelectron spectroscopy showed the air-exposed surface to consist of about 3 nm of Cu2O, while the as-received surface consisted of about 8 nm of Cu2O. The sputter-cleaned surface contained less than one monolayer (0.3 nm) of Cu2O. Spreading experiments utilizing a linear temperature ramp show that pure tin solder spreads readily on oxidized copper surfaces at elevated temperatures. The initiation temperature for rapid tin spreading on the as-received copper surface was 325 °C. Decreasing the thickness of the oxide on the surface lowered the observed temperature for the initiation of spreading and increased the rate of spreading. On the sputter-cleaned copper surface, rapid solder spreading was observed immediately upon melting of the solder.

Impact of Interfacial Composition on Lipid and Protein Co-Oxidation in Oil-in-Water Emulsions Containing Mixed Emulisifers.

PubMed

Zhu, Zhenbao; Zhao, Cui; Yi, Jianhua; Liu, Ning; Cao, Yuangang; Decker, Eric A; McClements, David Julian

2018-05-02

The impact of interfacial composition on lipid and protein co-oxidation in oil-in-water emulsions containing a mixture of proteins and surfactants was investigated. The emulsions consisted of 5% v/v walnut oil, 0.5% w/v whey protein isolate (WPI), and 0 to 0.4% w/v Tween 20 (pH 3 and pH 7). The protein surface load, magnitude of the ξ-potential, and mean particle diameter of the emulsions decreased as the Tween 20 concentration was increased, indicating the whey proteins were displaced by this nonionic surfactant. The whey proteins were displaced from the lipid droplet surfaces more readily at pH 3 than at pH 7, which may have been due to differences in the conformation or interactions of the proteins at the droplet surfaces at different pH values. Emulsions stabilized by whey proteins alone had relatively low lipid oxidation rates when incubated in the dark at 45 °C for up to 8 days, as determined by measuring lipid hydroperoxides and 2-thiobarbituric acid-reactive substances (TBARS). Conversely, the whey proteins themselves were rapidly oxidized, as shown by carbonyl formation, intrinsic fluorescence, sulfhydryl group loss, and electrophoresis measurements. Displacement of whey proteins from the interface by Tween 20 reduced protein oxidation but promoted lipid oxidation. These results indicated that the adsorbed proteins were more prone to oxidation than the nonadsorbed proteins, and therefore, they could act as better antioxidants. Protein oxidation was faster, while lipid oxidation was slower at pH 3 than at pH 7, which was attributed to a higher antioxidant activity of whey proteins under acidic conditions. These results highlight the importance of interfacial composition and solution pH on the oxidative stability of emulsions containing mixed emulsifiers.

Design Principles for Metal Oxide Redox Materials for Solar-Driven Isothermal Fuel Production.

PubMed

Michalsky, Ronald; Botu, Venkatesh; Hargus, Cory M; Peterson, Andrew A; Steinfeld, Aldo

2015-04-01

The performance of metal oxides as redox materials is limited by their oxygen conductivity and thermochemical stability. Predicting these properties from the electronic structure can support the screening of advanced metal oxides and accelerate their development for clean energy applications. Specifically, reducible metal oxide catalysts and potential redox materials for the solar-thermochemical splitting of CO 2 and H 2 O via an isothermal redox cycle are examined. A volcano-type correlation is developed from available experimental data and density functional theory. It is found that the energy of the oxygen-vacancy formation at the most stable surfaces of TiO 2 , Ti 2 O 3 , Cu 2 O, ZnO, ZrO 2 , MoO 3 , Ag 2 O, CeO 2 , yttria-stabilized zirconia, and three perovskites scales with the Gibbs free energy of formation of the bulk oxides. Analogously, the experimental oxygen self-diffusion constants correlate with the transition-state energy of oxygen conduction. A simple descriptor is derived for rapid screening of oxygen-diffusion trends across a large set of metal oxide compositions. These general trends are rationalized with the electronic charge localized at the lattice oxygen and can be utilized to predict the surface activity, the free energy of complex bulk metal oxides, and their oxygen conductivity.

Linking Precursor Alterations to Nanoscale Structure and Optical Transparency in Polymer Assisted Fast-Rate Dip-Coating of Vanadium Oxide Thin Films

PubMed Central

Glynn, Colm; Creedon, Donal; Geaney, Hugh; Armstrong, Eileen; Collins, Timothy; Morris, Michael A.; Dwyer, Colm O’

2015-01-01

Solution processed metal oxide thin films are important for modern optoelectronic devices ranging from thin film transistors to photovoltaics and for functional optical coatings. Solution processed techniques such as dip-coating, allow thin films to be rapidly deposited over a large range of surfaces including curved, flexible or plastic substrates without extensive processing of comparative vapour or physical deposition methods. To increase the effectiveness and versatility of dip-coated thin films, alterations to commonly used precursors can be made that facilitate controlled thin film deposition. The effects of polymer assisted deposition and changes in solvent-alkoxide dilution on the morphology, structure, optoelectronic properties and crystallinity of vanadium pentoxide thin films was studied using a dip-coating method using a substrate withdrawal speed within the fast-rate draining regime. The formation of sub-100 nm thin films could be achieved rapidly from dilute alkoxide based precursor solutions with high optical transmission in the visible, linked to the phase and film structure. The effects of the polymer addition was shown to change the crystallized vanadium pentoxide thin films from a granular surface structure to a polycrystalline structure composed of a high density of smaller in-plane grains, resulting in a uniform surface morphology with lower thickness and roughness. PMID:26123117

Deciphering ligands' interaction with Cu and Cu2O nanocrystal surfaces by NMR solution tools.

PubMed

Glaria, Arnaud; Cure, Jérémy; Piettre, Kilian; Coppel, Yannick; Turrin, Cédric-Olivier; Chaudret, Bruno; Fau, Pierre

2015-01-12

The hydrogenolysis of [Cu2{(iPrN)2(CCH3)}2] in the presence of hexadecylamine (HDA) or tetradecylphosphonic acid (TDPA) in toluene leads to 6-9 nm copper nanocrystals. Solution NMR spectroscopy has been used to describe the nanoparticle surface chemistry during the dynamic phenomenon of air oxidation. The ligands are organized as multilayered shells around the nanoparticles. The shell of ligands is controlled by both their intermolecular interactions and their bonding strength on the nanocrystals. Under ambient atmosphere, the oxidation rate of colloidal copper nanocrystals closely relies on the chemical nature of the employed ligands (base or acid). Primary amine molecules behave as soft ligands for Cu atoms, but are even more strongly coordinated on surface Cu(I) sites, thus allowing a very efficient corrosion protection of the copper core. On the contrary, the TDPA ligands lead to a rapid oxidation rate of Cu nanoparticles and eventually to the re-dissolution of Cu(II) species at the expense of the nanocrystals. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design and Fabrication of N-Alkyl-Polyethylenimine-Stabilized Iron Oxide Nanoclusters for Gene Delivery

PubMed Central

Liu, Gang; Wang, Zhiyong; Lee, Seulki; Ai, Hua; Chen, Xiaoyuan

2013-01-01

With the rapid development of nanotechnology, inorganic magnetic nanoparticles, especially iron oxide nanoparticles (IOs), have emerged as great vehicles for biomedical diagnostic and therapeutic applications. In order to rationally design IO-based gene delivery nanovectors, surface modification is essential and determines the loading and release of the gene of interest. Here we highlight the basic concepts and applications of nonviral gene delivery vehicles based on low molecular weight N-alkyl polyethylenimine-stabilized IOs. The experimental protocols related to these topics are described in this chapter. PMID:22568910

Defect Chemistry and Plasmon Physics of Colloidal Metal Oxide Nanocrystals.

PubMed

Lounis, Sebastien D; Runnerstrom, Evan L; Llordés, Anna; Milliron, Delia J

2014-05-01

Plasmonic nanocrystals of highly doped metal oxides have seen rapid development in the past decade and represent a class of materials with unique optoelectronic properties. In this Perspective, we discuss doping mechanisms in metal oxides and the accompanying physics of free carrier scattering, both of which have implications in determining the properties of localized surface plasmon resonances (LSPRs) in these nanocrystals. The balance between activation and compensation of dopants limits the free carrier concentration of the most common metal oxides, placing a ceiling on the LSPR frequency. Furthermore, because of ionized impurity scattering of the oscillating plasma by dopant ions, scattering must be treated in a fundamentally different way in semiconductor metal oxide materials when compared with conventional metals. Though these effects are well-understood in bulk metal oxides, further study is needed to understand their manifestation in nanocrystals and corresponding impact on plasmonic properties, and to develop materials that surpass current limitations in free carrier concentration.

Morphologically manipulated Ag/ZnO nanostructures as surface enhanced Raman scattering probes for explosives detection

NASA Astrophysics Data System (ADS)

Shaik, Ummar Pasha; Hamad, Syed; Ahamad Mohiddon, Md.; Soma, Venugopal Rao; Ghanashyam Krishna, M.

2016-03-01

The detection of secondary explosive molecules (e.g., ANTA, FOX-7, and CL-20) using Ag decorated ZnO nanostructures as surface enhanced Raman scattering (SERS) probes is demonstrated. ZnO nanostructures were grown on borosilicate glass substrates by rapid thermal oxidation of metallic Zn films at 500 °C. The oxide nanostructures, including nanosheets and nanowires, emerged over the surface of the Zn film leaving behind the metal residue. We demonstrate that SERS measurements with concentrations as low as 10 μM, of the three explosive molecules ANTA, FOX-7, and CL-20 over ZnO/Ag nanostructures, resulted in enhancement factors of ˜107, ˜107, and ˜104, respectively. These measurements validate the high sensitivity of detection of explosive molecules using Ag decorated ZnO nanostructures as SERS substrates. The Zn metal residue and conditions of annealing play an important role in determining the detection sensitivity.

Mach 1 oxidation of thoriated nickel chromium at 1204 C /2200 F/.

NASA Technical Reports Server (NTRS)

Lowell, C. E.; Sanders, W. A.

1972-01-01

Electropolished and ground samples of TD-NiCr were exposed to a 1-atm, Mach 1 gas stream at 1204 C for times up to 50 hr. The samples were subjected to both cyclic and isothermal exposure. Weight change, metal loss, X-ray diffraction, metallographic, and electron microprobe analyses were performed. Neither surface preparation nor cyclic-against-isothermal-exposure conditions had a strong effect on the oxidation behavior of the alloy. Initially, a Cr2O3 layer was formed whose volatilization resulted in a very rapid loss of metal - more than 40 microns in the first hour. At about 1 hr, the Cr2O3 layer broke down and NiO began to cover the surface. By 5 hr, the NiO had covered the surface and the rate of loss slowed. The rate-controlling step was diffusion of Cr through NiO.

UV stabilization of wood by nano metal oxides dispersed in propylene glycol.

PubMed

Nair, Sreeja; Nagarajappa, Giridhar B; Pandey, Krishna K

2018-06-01

Nanoparticles of some of the metal oxides are known to have high UV protective efficiency. The UV filtering efficiency of nanoparticles invariably depends on their size and stability in the dispersion. In the present work, a stable dispersion of nanoparticles of three metal oxides, zinc oxide (ZnO), cerium oxide (CeO 2 ) and titanium dioxide (TiO 2 ), was prepared in propylene glycol (PG) using ultrasonication. The method is easy and useful as no additional surfactant or dispersant is needed. The particle size and its distribution was confirmed by Scanning Electron Microscopy and Dynamic Light Scattering. The stability of dispersion was assessed by UV-visible absorption spectroscopy. The UV stability of wood surfaces of Wrightia tinctoria coated with nanodispersions of ZnO, CeO 2 and TiO 2 was evaluated under laboratory conditions in an accelerated weathering tester. Changes in the colour and FTIR spectra of exposed specimens were measured periodically. Rapid colour darkening (yellowing) was observed in uncoated and PG coated specimens. In contrast, nanodispersion coated specimens prevented photo-yellowing considerably with significant reduction in colour changes examined by CIE L*, a*, b* and ΔE*. Increase in concentration of nanoparticles in the dispersion imparted higher resistance to UV induced degradation. However, increased concentration of nanoparticles reduced the transparency of the coating. FTIR analysis indicated rapid degradation of lignin in uncoated and PG coated specimens due to UV exposure. Coating of wood surfaces with nanodispersions restricted lignin degradation. The study also demonstrates the potential of propylene glycol as a dispersant for developing stable and efficient UV protective nanodispersions for wood coating. Copyright © 2018 Elsevier B.V. All rights reserved.

Preparation of well-distributed titania nanopillar arrays on Ti6Al4V surface by induction heating for enhancing osteogenic differentiation of stem cells

NASA Astrophysics Data System (ADS)

Li, Ning-Bo; Sun, Sheng-Jun; Bai, Han-Ying; Xiao, Gui-Yong; Xu, Wen-Hua; Zhao, Jun-Han; Chen, Xin; Lu, Yu-Peng; Zhang, Yi-Lin

2018-01-01

Great effort has recently been devoted to the preparation of nanoscale surfaces on titanium-based implants to achieve clinically fast osteoinduction and osseointegration, which relies on the unique characteristics of the nanostructure. In this work, we used induction heating treatment (IHT) as a rapid oxidation method to fabricate a porous nanoscale oxide layer on the Ti6Al4V surface for better medical application. Well-distributed vertical nanopillars were yielded by IHT for 20-35 s on the alloy surface. The composition of the oxides contained rutile/anatase TiO2 and a small amount of Al2O3 between the TiO2 grain boundaries (GBs). This technology resulted in a reduction and subsequent increase of surface roughness of 26-32 nm when upregulating the heating time, followed by the successive enhancement of the thickness, wettability and adhesion strength of the oxidation layer to the matrix. The surface hardness also distinctly rose to 554 HV in the IHT-35 s group compared with the 350 HV of bare Ti6Al4V. The massive small-angle GBs in the bare alloy promoted the formation of nanosized oxide crystallites. The grain refinement and deformation texture reduction further improved the mechanical properties of the matrix after IHT. Moreover, in vitro experiments on a mesenchymal stem cell (BMSC) culture derived from human bone marrow for 1-7 days indicated that the nanoscale layers did not cause cytotoxicity, and facilitated cell differentiation in osteoblasts by enhancing the gene and osteogenesis-related protein expressions after 1-3 weeks of culturing. The increase of the IHT time slightly advanced the BMSC proliferation and differentiation, especially during long-term culture. Our findings provide strong evidence that IHT oxidation technology is a novel nanosurface modification technology, which is potentially promising for further clinical development.

Xenon-Ion Drilling of Tungsten Films

NASA Technical Reports Server (NTRS)

Garner, C. E.

1986-01-01

High-velocity xenon ions used to drill holes of controlled size and distribution through tungsten layer that sheaths surface of controlled-porosity dispenser cathode of traveling wave-tube electron emitter. Controlled-porosity dispenser cathode employs barium/calcium/ aluminum oxide mixture that migrates through pores in cathode surface, thus coating it and reducing its work function. Rapid, precise drilling technique applied to films of other metals and used in other applications where micron-scale holes required. Method requires only few hours, as opposed to tens of hours by prior methods.

Joint services electronics program

NASA Astrophysics Data System (ADS)

Flynn, George W.; Osgood, Richard M., Jr.

1988-05-01

Several milestones have been reached in GaAs research. The first active GaAs device, a 1 micrometer channel width MESFET, has been made at Columbia. This device is a basic building block in the GaAs CCD program. GaAs surface studies have also born fruit. UV light has been found to oxidize rapidly the surface of GaAs in an UHV environment containing traces of water vapor and O2. The mechanism appears to be related to the generation of hot photocarriers.

X-Ray Photoelectron Study of the Oxides Formed on Nickel Metal and Nickel-Chromium 20% Alloy Surfaces Under Reducing and Oxidizing Potentials in Basic, Neutral and Acidic Solutions

NASA Astrophysics Data System (ADS)

Payne, Brad P.; Keech, Peter G.; McIntyre, N. Stewart

The corrosion products produced on polycrystalline Ni metal and Ni-Cr (20%) (NiCr) alloy surfaces exposed to aqueous environments chosen to emulate possible solution conditions in the steam generator (SG) tubing of pressurized water reactors (PWR) were studied using XPS. Additional measurements modelling the distribution of oxidized Ni and Cr species on select alloy specimens were carried out using ToF SIMS. Exposure of Ni metal and NiCr alloy samples to mildly oxidizing potentials in basic solutions resulted in the preferential growth of a β-Ni(OH)2 phase; driven by the dissolution of metallic Ni at both 25°C and 150°C. The presence of β-Ni(OH)2, Cr(OH)3 and small amounts of a Cr6+-containing oxide on NiCr specimens oxidized under mildly oxidizing conditions at 150°C in neutral solutions suggested that the dissolution of both metallic Ni and Cr followed by the back deposition of the corresponding corrosion products was responsible for oxide growth under these conditions. In acidic media oxide nucleation at 150°C under mildly oxidizing potentials was determined to occur via the dissolution of both Ni and Cr species on NiCr specimens as well. The increased stability of Ni2+ in acidic solution led to a limited precipitation of β-Ni(OH)2 resulting in the formation of very thin oxides containing higher levels of Cr(OH)3. Reactions on metallic Ni and NiCr surfaces under highly oxidizing potentials resulted in an increase in the NiO content of these films compared to similar exposures carried out at milder oxidation conditions attributed to accelerated dehydration of the β-Ni(OH)2 phase. In addition, an increase in the Cr(OH)3 contribution on the alloy surface oxidized at a more oxidative potential suggested a more rapid dissolution of Cr under these conditions; overall, uneven films were formed from these conditions. The composition of the corrosion product formed after an exposure to a highly oxidizing potential was found to be unchanged following a subsequent reaction of equivalent length at a much lower oxidizing potential in basic solution.

Long-term stabilization of sprayed zinc oxide thin film transistors by hexafluoropropylene oxide self assembled monolayers

NASA Astrophysics Data System (ADS)

Ortel, Marlis; Kalinovich, Nataliya; Röschenthaler, Gerd-Volker; Wagner, Veit

2013-09-01

Surface functionalization of solution processed zinc oxide layers was studied in transistors with bottom-gate bottom-contact configuration aiming at suppression of trapping processes to increase device stability. Saturation of electrically active surface sites and formation of a moisture barrier to decrease the impact of humid atmosphere was successfully shown by binding hexafluoropropylene oxide (HFPO) on the metal oxide semiconductor. Deep trap level related electrical parameters, i.e., stability, hysteresis, and on-set voltage, improved rapidly within 60 s of exposure which was attributed to occupation of sites characterized by low adsorption energies, e.g., at edges. In contrast, shallow trap level related parameters, i.e., mobility, showed a much slower process of improvement. Identical behavior was determined for the contact angle. A physical model is presented by applying first order reaction kinetics equation to Young's law and multiple trapping and release model which relates the dependence of the contact angle and the mobility to the hexafluoropropylene oxide deposition time. Consistent time constants of τ = ≪1 min, 2 min, and 250 min were extracted for mobility and contact angle which implies a direct dependence on the surface coverage. Mobility decreased at short deposition times, recovered at medium deposition times and improved strongly by 2.4 cm2 V-1 s-1 for long deposition times of 1400 min. A microscopic model of these phenomena is given with interpretation of the different time constants found in the experiment.

Crystalline mesoporous tungsten oxide nanoplate monoliths synthesized by directed soft template method for highly sensitive NO{sub 2} gas sensor applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoa, Nguyen Duc, E-mail: ndhoa@itims.edu.vn; Duy, Nguyen Van; Hieu, Nguyen Van, E-mail: hieu@itims.edu.vn

2013-02-15

Graphical abstract: Display Omitted Highlights: ► Mesoporous WO{sub 3} nanoplate monoliths were obtained by direct templating synthesis. ► Enable effective accession of the analytic molecules for the sensor applications. ► The WO{sub 3} sensor exhibited a high performance to NO{sub 2} gas at low temperature. -- Abstract: Controllable synthesis of nanostructured metal oxide semiconductors with nanocrystalline size, porous structure, and large specific surface area is one of the key issues for effective gas sensor applications. In this study, crystalline mesoporous tungsten oxide nanoplate-like monoliths with high specific surface areas were obtained through instant direct-templating synthesis for highly sensitive nitrogen dioxidemore » (NO{sub 2}) sensor applications. The copolymer soft template was converted into a solid carbon framework by heat treatment in an inert gas prior to calcinations in air to sustain the mesoporous structure of tungsten oxide. The multidirectional mesoporous structures of tungsten oxide with small crystalline size, large specific surface area, and superior physical characteristics enabled the rapid and effective accession of analytic gas molecules. As a result, the sensor response was enhanced and the response and recovery times were reduced, in which the mesoporous tungsten oxide based gas sensor exhibited a superior response of 21,155% to 5 ppm NO{sub 2}. In addition, the developed sensor exhibited selective detection of low NO{sub 2} concentration in ammonia and ethanol at a low temperature of approximately 150 °C.« less

Reduction of aqueous transition metal species on the surfaces of Fe(II)-containing oxides

USGS Publications Warehouse

White, A.F.; Peterson, M.L.

1996-01-01

Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1-7 at 25??C. For an aqueous transition metal m, such reactions are 3[Fe2+Fe3+2]O4(magnetite) + 2/nmz ??? 4[Fe3+2]O3(maghemite) + Fe2+ + 2/nmz-n and 3[Fe2+Ti]O3(ilmenite) + 2/nmz ??? Fe3+2Ti3O9(pseudorutile) + Fe2+ + 2/nmz-n, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] ??? [Fe(III)] is -0.34 to -0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe2+ (-0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 ?? 10-10 mol m-2 s-1. Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe2+ is oxidized homogeneously in solution to Fe3+. X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental solution. In contrast, magnetite weathered under oxidizing vadose conditions show minimum reactivity toward chromate ions. The ability of Fe(II) oxides to reduce transition metals in soils and groundwaters will be strongly dependent on the redox environment.

Reduction of aqueous transition metal species on the surfaces of Fe(II) -containing oxides

NASA Astrophysics Data System (ADS)

White, Art F.; Peterson, Maria L.

1996-10-01

Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1-7 at 25°C. For an aqueous transition metal m, such reactions are 3[FeFe23+]O+2/nm→4[Fe23+]O+Fe+2/nm and 3[FeTi]O+→Fe23+TiO+Fe+2/nm, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] → [Fe(III)] is -0.34 to -0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe 2+ (-0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 × 10 -10 mol m -2 s -1. Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe 2+ is oxidized homogeneously in solution to Fe 3+. X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental solution. In contrast, magnetite weathered under oxidizing vadose conditions show minimum reactivity toward chromate ions. The ability of Fe(II) oxides to reduce transition metals in soils and groundwaters will be strongly dependent on the redox environment.

Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour.

PubMed

Martin, T L; Coe, C; Bagot, P A J; Morrall, P; Smith, G D W; Scott, T; Moody, M P

2016-07-12

Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.

Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour

NASA Astrophysics Data System (ADS)

Martin, T. L.; Coe, C.; Bagot, P. A. J.; Morrall, P.; Smith, G. D. W.; Scott, T.; Moody, M. P.

2016-07-01

Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.

Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour

PubMed Central

Martin, T. L.; Coe, C.; Bagot, P. A. J.; Morrall, P.; Smith, G. D. W; Scott, T.; Moody, M. P.

2016-01-01

Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour. PMID:27403638

Possible roles of manganese redox chemistry in the sulfur cycle

NASA Technical Reports Server (NTRS)

Nealson, K. H.

1985-01-01

Sulfate reducing bacteria (SRB) are very potent MnO2 reducers by virtue of their sulfide production: H2S reacts rapidly with MnO2 to yield Mn(2), elemental sulfur, and water. In manganese rich zones, Mn cycles rapidly if sulfate is present to drive the reduction and the MnO2 precipitates and sinks into anaerobic zones. The production of sulfide (by organisms requiring organic carbon compounds) to reduce manganese oxides might act to couple the carbon and sulfur cycles in water bodies in which the two cycles are physically separated. Iron has been proposed for this provision of reducing power by (Jorgensen, 1983), but since MnS is soluble and FeS is very insoluble in water, it is equally likely that manganese rather than iron provides the electrons to the more oxidized surface layers.

Photoacoustic Spectroscopy of Chemically Modified Surfaces.

DTIC Science & Technology

1981-08-01

Science.4 In that I 2 paper he told of the accidental discovery of the optoacoustic effect in solids. He observed that a rapidly modulated beam of...0L - -LJ Lii Lnf cobr 0D CDV 214 Figure 17. Photoacoustic spectrum of (I) Co 304 ground with y-alumina and (II) CoO-enhanced cobalt oxide ground with y

Rapid Determination of Endospore Viability by Hyperspectral Reflectance Following Surface Decontamination

DTIC Science & Technology

2008-12-01

Alexandria, VA ABSTRACT Bacterial spores , or endospores, such as those of Bacillus anthracis, are an asymmetrical threat. Decontamination... Bacillus subtilis spores by hypochlorite and chlorine dioxide, J. Appl Microbiol., 95(1), 54-67. ...have the ability to distinguish viable from non-viable endospores. In the laboratory, we have exploited the oxidative alteration of the spore coat

Electrocatalytic performance of Pt nanoparticles sputter-deposited on indium tin oxide toward methanol oxidation reaction: The particle size effect

NASA Astrophysics Data System (ADS)

Ting, Chao-Cheng; Chao, Chih-Hsuan; Tsai, Cheng Yu; Cheng, I.-Kai; Pan, Fu-Ming

2017-09-01

We sputter-deposited Pt nanoparticles with an average size ranging from 2.0 nm to 8.5 nm on the indium-tin oxide (ITO) glass substrate, and studied the effect of the size of Pt nanoparticles on electrocatalytic activity of the Pt/ITO electrode toward methanol oxidation reaction (MOR) in acidic solution. X-ray photoelectron spectroscopy (XPS) reveals an interfacial oxidized Pt layer present between Pt nanoparticles and the ITO substrate, which may modify the surface electronic structure of Pt nanoparticles and thus influences the electrocatalytic properties of the Pt catalyst toward MOR. According to electrochemical analyses, smaller Pt nanoparticles exhibit slower kinetics for CO electrooxidation and MOR. However, a smaller particle size enables better CO tolerance because the bifunctional mechanism is more effective on smaller Pt nanoparticles. The electrocatalytic activity decays rapidly for Pt nanoparticles with a size smaller than 3 nm and larger than 8 nm. The rapid activity decay is attributed to Pt dissolution for smaller nanoparticles and to CO poisoning for larger ones. Pt nanoparticles of 5-6 nm in size loaded on ITO demonstrate a greatly improved electrocatalytic activity and stability compared with those deposited on different substrates in our previous studies.

ZnO nanorod arrays and direct wire bonding on GaN surfaces for rapid fabrication of antireflective, high-temperature ultraviolet sensors

NASA Astrophysics Data System (ADS)

So, Hongyun; Senesky, Debbie G.

2016-11-01

Rapid, cost-effective, and simple fabrication/packaging of microscale gallium nitride (GaN) ultraviolet (UV) sensors are demonstrated using zinc oxide nanorod arrays (ZnO NRAs) as an antireflective layer and direct bonding of aluminum wires to the GaN surface. The presence of the ZnO NRAs on the GaN surface significantly reduced the reflectance to less than 1% in the UV and 4% in the visible light region. As a result, the devices fabricated with ZnO NRAs and mechanically stable aluminum bonding wires (pull strength of 3-5 gf) showed higher sensitivity (136.3% at room temperature and 148.2% increase at 250 °C) when compared with devices with bare (uncoated) GaN surfaces. In addition, the devices demonstrated reliable operation at high temperatures up to 300 °C, supporting the feasibility of simple and cost-effective UV sensors operating with higher sensitivity in high-temperature conditions, such as in combustion, downhole, and space exploration applications.

One-pot wet-chemical co-reduction synthesis of bimetallic gold-platinum nanochains supported on reduced graphene oxide with enhanced electrocatalytic activity

NASA Astrophysics Data System (ADS)

Chen, De-Jun; Zhang, Qian-Li; Feng, Jin-Xia; Ju, Ke-Jian; Wang, Ai-Jun; Wei, Jie; Feng, Jiu-Ju

2015-08-01

In this work, a simple, rapid and facile one-pot wet-chemical co-reduction method is developed for synthesis of bimetallic Au-Pt alloyed nanochains supported on reduced graphene oxide (Au-Pt NCs/RGO), in which caffeine is acted as a capping agent and a structure-directing agent, while no any seed, template, surfactant or polymer involved. The as-prepared nanocomposites display enlarged electrochemical active surface area, significantly enhanced catalytic activity and better stability for methanol and ethylene glycol oxidation, compared with commercial Pt-C (Pt 50 wt%), PtRu-C (Pt 30 wt% and Ru 15 wt%) and Pt black.

Coating with overlay metallic-cermet alloy systems

NASA Technical Reports Server (NTRS)

Gedwill, M. A.; Levine, S. R.; Glasgow, T. K. (Inventor)

1984-01-01

A base layer of an oxide dispersed, metallic alloy (cermet) is arc plasma sprayed onto a substrate, such as a turbine blade, vane, or the like, which is subjected to high temperature use. A top layer of an oxidation, hot corrosion, erosion resistant alloy of nickel, cobalt, or iron is then arc plasma sprayed onto the base layer. A heat treatment is used to improve the bonding. The base layer serves as an inhibitor to interdiffusion between the protective top layer and the substrate. Otherwise, the 10 protective top layer would rapidly interact detrimentally with the substrate and degrade by spalling of the protective oxides formed on the outer surface at elevated temperatures.

Synthesis of mesoscale, crumpled, reduced graphene oxide roses by water-in-oil emulsion approach

NASA Astrophysics Data System (ADS)

Sharma, Shruti; Pham, Viet H.; Boscoboinik, Jorge A.; Camino, Fernando; Dickerson, James H.; Tannenbaum, Rina

2018-05-01

Mesoscale crumpled graphene oxide roses (GO roses) were synthesized by using colloidal graphene oxide (GO) variants as precursors for a hybrid emulsification-rapid evaporation approach. This process produced rose-like, spherical, reduced mesostructures of colloidal GO sheets, with corrugated surfaces and particle sizes tunable in the range of ∼800 nm to 15 μm. Excellent reproducibility for particle size distribution is shown for each selected speed of homogenizer rotor among different sample batches. The morphology and chemical structure of these produced GO roses was investigated using electron microscopy and spectroscopy techniques. The proposed synthesis route provides control over particle size, morphology and chemical properties of the synthesized GO roses.

An electrochemical label-free and sensitive thrombin aptasensor based on graphene oxide modified pencil graphite electrode.

PubMed

Ahour, F; Ahsani, M K

2016-12-15

In this work, we tactfully constructed a novel label-free electrochemical aptasensor for rapid and facile detection of thrombin using graphene oxide (GO) and thrombin binding aptamer (TBA). The strategy relies on the preferential adsorption of single-stranded DNA (ssDNA) to GO over aptamer-target complexes. The TBA-thrombin complex formation was monitored by differential pulse voltammetry (DPV) using the guanine oxidation signal. In the absence of thrombin, the aptamers adsorbed onto the surface of GO leading to a strong background guanine oxidation signal. Conversely, in the presence of thrombin, the conformational transformation of TBA after incubating with the thrombin solution and formation of the aptamer-thrombin complexes which had weak binding ability to GO, leads to the desorption of TBA-thrombin complex from electrode surface and significant oxidation signal decrease. The selectivity of the biosensor was studied using other biological substances. The biosensor's signal was proportional to the thrombin concentration from 0.1 to 10nM with a detection limit of 0.07nM. Particularly, the proposed method could be widely applied to the aptamer-based determination of other target analytes. Copyright © 2016 Elsevier B.V. All rights reserved.

Silver decorated polymer supported semiconductor thin films by UV aided metalized laser printing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halbur, Jonathan C.; Padbury, Richard P.; Jur, Jesse S., E-mail: jsjur@ncsu.edu

2016-05-15

A facile ultraviolet assisted metalized laser printing technique is demonstrated through the ability to control selective photodeposition of silver on flexible substrates after atomic layer deposition pretreatment with zinc oxide and titania. The photodeposition of noble metals such as silver onto high surface area, polymer supported semiconductor metal oxides exhibits a new route for nanoparticle surface modification of photoactive enhanced substrates. Photodeposited silver is subsequently characterized using low voltage secondary electron microscopy, x-ray diffraction, and time of flight secondary ion mass spectroscopy. At the nanoscale, the formation of specific morphologies, flake and particle, is highlighted after silver is photodeposited onmore » zinc oxide and titania coated substrates, respectively. The results indicate that the morphology and composition of the silver after photodeposition has a strong dependency on the morphology, crystallinity, and impurity content of the underlying semiconductor oxide. At the macroscale, this work demonstrates how the nanoscale features rapidly coalesce into a printed pattern through the use of masks or an X-Y gantry stage with virtually unlimited design control.« less

Mesoporous MnCeO x solid solutions for low temperature and selective oxidation of hydrocarbons

DOE PAGES

Zhang, Pengfei; Lu, Hanfeng; Zhou, Ying; ...

2015-10-15

The development of noble-metal-free heterogeneous catalysts that can realize the aerobic oxidation of C–H bonds at low temperature is a profound challenge in the catalysis community. Here we report the synthesis of a mesoporous Mn 0.5Ce 0.5O x solid solution that is highly active for the selective oxidation of hydrocarbons under mild conditions (100–120 °C). Notably, the catalytic performance achieved in the oxidation of cyclohexane to cyclohexanone/cyclohexanol (100 °C, conversion: 17.7%) is superior to those by the state-of-art commercial catalysts (140–160 °C, conversion: 3-5%). Finally, the high activity can be attributed to the formation of a Mn 0.5Ce 0.5O xmore » solid solution with an ultrahigh manganese doping concentration in the CeO 2 cubic fluorite lattice, leading to maximum active surface oxygens for the activation of C–H bonds and highly reducible Mn 4+ ions for the rapid migration of oxygen vacancies from the bulk to the surface.« less

Amperometric Biosensor Based on Zirconium Oxide/Polyethylene Glycol/Tyrosinase Composite Film for the Detection of Phenolic Compounds.

PubMed

Ahmad, Nor Monica; Abdullah, Jaafar; Yusof, Nor Azah; Ab Rashid, Ahmad Hazri; Abd Rahman, Samsulida; Hasan, Md Rakibul

2016-06-29

A phenolic biosensor based on a zirconium oxide/polyethylene glycol/tyrosinase composite film for the detection of phenolic compounds has been explored. The formation of the composite film was expected via electrostatic interaction between hexacetyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG), and zirconium oxide nanoparticles casted on screen printed carbon electrode (SPCE). Herein, the electrode was treated by casting hexacetyltrimethylammonium bromide on SPCE to promote a positively charged surface. Later, zirconium oxide was mixed with polyethylene glycol and the mixture was dropped cast onto the positively charged SPCE/CTAB. Tyrosinase was further immobilized onto the modified SPCE. Characterization of the prepared nanocomposite film and the modified SPCE surface was investigated by scanning electron microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Cyclic voltamogram (CV). The developed biosensor exhibits rapid response for less than 10 s. Two linear calibration curves towards phenol in the concentrations ranges of 0.075-10 µM and 10-55 µM with the detection limit of 0.034 µM were obtained. The biosensor shows high sensitivity and good storage stability for at least 30 days.

Mesoporous MnCeOx solid solutions for low temperature and selective oxidation of hydrocarbons

PubMed Central

Zhang, Pengfei; Lu, Hanfeng; Zhou, Ying; Zhang, Li; Wu, Zili; Yang, Shize; Shi, Hongliang; Zhu, Qiulian; Chen, Yinfei; Dai, Sheng

2015-01-01

The development of noble-metal-free heterogeneous catalysts that can realize the aerobic oxidation of C–H bonds at low temperature is a profound challenge in the catalysis community. Here we report the synthesis of a mesoporous Mn0.5Ce0.5Ox solid solution that is highly active for the selective oxidation of hydrocarbons under mild conditions (100–120 °C). Notably, the catalytic performance achieved in the oxidation of cyclohexane to cyclohexanone/cyclohexanol (100 °C, conversion: 17.7%) is superior to those by the state-of-art commercial catalysts (140–160 °C, conversion: 3-5%). The high activity can be attributed to the formation of a Mn0.5Ce0.5Ox solid solution with an ultrahigh manganese doping concentration in the CeO2 cubic fluorite lattice, leading to maximum active surface oxygens for the activation of C–H bonds and highly reducible Mn4+ ions for the rapid migration of oxygen vacancies from the bulk to the surface. PMID:26469151

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

PubMed Central

Perry, Nicola H.; Ishihara, Tatsumi

2016-01-01

Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic), and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance. Insights into aspects of bulk point defect chemistry, electronic structure, crystal structure, and cation choice that impact carrier concentrations and mobilities, surface exchange kinetics, and chemical expansion coefficients are emerging. At the same time, an understanding of the relationship between bulk and surface chemistry is being developed that may assist design of electrodes with more robust surface chemistries, e.g., impurity tolerance or limited surface segregation. Ion scattering techniques (e.g., secondary ion mass spectrometry, SIMS, or low energy ion scattering spectroscopy, LEIS) with high surface sensitivity and increasing lateral resolution are proving useful for measuring surface exchange kinetics, diffusivity, and corresponding outer monolayer chemistry of electrodes exposed to typical operating conditions. Beyond consideration of chemical composition, the use of strain and/or a high density of active interfaces also show promise for enhancing performance. PMID:28773978

Enhancement of methane gas sensing characteristics of graphene oxide sensor by heat treatment and laser irradiation.

PubMed

Assar, Mohammadreza; Karimzadeh, Rouhollah

2016-12-01

The present study uses a rapid, easy and practical method for cost-effective fabrication of a methane gas sensor. The sensor was made by drop-casting a graphene oxide suspension onto an interdigital circuit surface. The electrical conductivity and gas-sensing characteristics of the sensor were determined and then heat treatment and in situ laser irradiation were applied to improve the device conductivity and gas sensitivity. Real-time monitoring of the evolution of the device current as a function of heat treatment time revealed significant changes in the conductance of the graphene oxide sensor. The use of low power laser irradiation enhanced both the electrical conductivity and sensing response of the graphene oxide sensor. Copyright © 2016 Elsevier Inc. All rights reserved.

Comparative study on polyvinyl chloride film as flexible substrate for preparing free-standing polyaniline-based composite electrodes for supercapacitors.

PubMed

Wang, Hongxing; Liu, Dong; Du, Pengcheng; Wei, Wenli; Wang, Qi; Liu, Peng

2017-11-15

The free-standing polyaniline (PANI)-based composite film electrodes were prepared with polyvinyl chloride (PVC) and the aniline modified PVC (PVC-An) films as flexible substrates for supercapacitors, via facile in-situ chemical oxidative polymerization of aniline, with conventional chemical oxidative polymerization or rapid-mixing chemical oxidative polymerization technique. Owing to the grafting of PANI from the PVC-An film as substrate and the suppression of the secondary growth of the primary PANI particles in the rapid-mixing chemical oxidative polymerization, the PVC-g-PANI-2 composite film with loose surface possessed better comprehensive performance, accompanying the high specific capacitance (645.3F/g at a current density of 1A/g), good rate capacitance (retaining 63.2% of original value at a current density of 10A/g and 52.0% at a scan rate of 100mV/s), good cycle stability (retaining 83.1% after 1000 cycles) and the improved internal resistance. Besides its excellent flexibility, it could retain 61.2% of its original specific capacitance under the stress of 8.66MPa for 1h, demonstrating a good tensile-resistance. Copyright © 2017 Elsevier Inc. All rights reserved.

Stabilization and functionalization of iron oxide nanoparticles for biomedical applications

NASA Astrophysics Data System (ADS)

Amstad, Esther; Textor, Marcus; Reimhult, Erik

2011-07-01

Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface presentation of functionalities. This review is focused on different aspects of the stability of superparamagnetic iron oxide NPs, from its practical definition to its implementation by molecular design of the dispersant shell around the iron oxide core and further on to its influence on the magnetic properties of the superparamagnetic iron oxide NPs. Special attention is given to the selection of molecular anchors for the dispersant shell, because of their importance to ensure colloidal and functional stability of sterically stabilized superparamagnetic iron oxide NPs. We further detail how dispersants have been optimized to gain close control over iron oxide NP stability, size and functionalities by independently considering the influences of anchors and the attached sterically repulsive polymer brushes. A critical evaluation of different strategies to stabilize and functionalize core-shell superparamagnetic iron oxide NPs as well as a brief introduction to characterization methods to compare those strategies is given.Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface presentation of functionalities. This review is focused on different aspects of the stability of superparamagnetic iron oxide NPs, from its practical definition to its implementation by molecular design of the dispersant shell around the iron oxide core and further on to its influence on the magnetic properties of the superparamagnetic iron oxide NPs. Special attention is given to the selection of molecular anchors for the dispersant shell, because of their importance to ensure colloidal and functional stability of sterically stabilized superparamagnetic iron oxide NPs. We further detail how dispersants have been optimized to gain close control over iron oxide NP stability, size and functionalities by independently considering the influences of anchors and the attached sterically repulsive polymer brushes. A critical evaluation of different strategies to stabilize and functionalize core-shell superparamagnetic iron oxide NPs as well as a brief introduction to characterization methods to compare those strategies is given. This article was submitted as part of a collection of articles on surface nanotechnology for biological applications. Other papers on this topic can be found in issue 2 of vol. 3 (2011). This issue can be found from the Nanoscale homepage [http://www.rsc.org/nanoscale].

A Novel Method to Assess Wear Rates of Retrieved Tibial Inserts Following in-vivo Use

NASA Astrophysics Data System (ADS)

Paniogue, Tanille J.

Ultra-high molecular weight polyethylene (UHMWPE) on cobalt chrome is the bearing couple of choice for total knee arthroplasty. The number of patients undergoing total knee arthroplasty has been steadily growing and is projected to continue increasing rapidly in the near future. Many of these patients are younger and more active and therefore need a longer lasting device. However, many of these devices fail prematurely and often the primary reason for failure and ultimately revision is due to wear related issues. Therefore, examining how wear rates of the UHMWPE tibial insert change during in-vivo use can help elucidate the mechanisms of accelerated wear and hopefully aid in finding solutions to combat wear related failures. Different crosslinking treatments have been employed by manufacturers to improve wear resistance of the polyethylene. While this has been shown to be an effective way to reduce wear, crosslinking has led to other issues such as oxidative instability and a decline in mechanical properties. The purpose of this body of work is to examine how changes in oxidation, after in-vivo use, affect wear resistance. A novel testing method was developed to test the native articular surface from retrieved tibial inserts in a laboratory Pin-on-Disk (POD) simulator. The method was validated using short-duration implant articular surfaces and non-articular control pins. In the absence of high surface oxidation or severe surface damage, the articular surface pins had comparable steady state wear rates to their bulk counterparts. Tests of devices with longer in-vivo service show chemical changes consistent with a free-radical mediated oxidation mechanism. Tribological assessment of the articular surfaces shows increasing wear rates as a function of oxidation. While this relationship has been hypothesized in the literature, these experiments represent the first physical demonstration of the phenomenon. The wear mechanism is further explored through infrared spectroscopy, assessment of the wear scar, and documentation of evolution of the contact surfaces in the articulation.

Enhancing the protein resistance of silicone via surface-restructuring PEO-silane amphiphiles with variable PEO length

PubMed Central

Rufin, M. A.; Gruetzner, J. A.; Hurley, M. J.; Hawkins, M. L.; Raymond, E. S.; Raymond, J. E.

2015-01-01

Silicones with superior protein resistance were produced by bulk-modification with poly(ethylene oxide) (PEO)-silane amphiphiles that demonstrated a higher capacity to restructure to the surface-water interface versus conventional non-amphiphilic PEO-silanes. The PEO-silane amphiphiles were prepared with a single siloxane tether length but variable PEO segment lengths: α-(EtO)3Si(CH2)2-oligodimethylsiloxane13-block-poly(ethylene oxide)n-OCH3 (n = 3, 8, and 16). Conventional PEO-silane analogues (n = 3, 8 and 16) as well as a siloxane tether-silane (i.e. no PEO segment) were prepared as controls. When surface-grafted onto silicon wafer, PEO-silane amphiphiles produced surfaces that were more hydrophobic and thus more adherent towards fibrinogen versus the corresponding PEO-silane. However, when blended into a silicone, PEO-silane amphiphiles exhibited rapid restructuring to the surface-water interface and excellent protein resistance whereas the PEO-silanes did not. Silicones modified with PEO-silane amphiphiles of PEO segment lengths n = 8 and 16 achieved the highest protein resistance. PMID:26339488

Bacterial Phosphating of Mild (Unalloyed) Steel

PubMed Central

Volkland, Hans-Peter; Harms, Hauke; Müller, Beat; Repphun, Gernot; Wanner, Oskar; Zehnder, Alexander J. B.

2000-01-01

Mild (unalloyed) steel electrodes were incubated in phosphate-buffered cultures of aerobic, biofilm-forming Rhodococcus sp. strain C125 and Pseudomonas putida mt2. A resulting surface reaction leading to the formation of a corrosion-inhibiting vivianite layer was accompanied by a characteristic electrochemical potential (E) curve. First, E increased slightly due to the interaction of phosphate with the iron oxides covering the steel surface. Subsequently, E decreased rapidly and after 1 day reached −510 mV, the potential of free iron, indicating the removal of the iron oxides. At this point, only scattered patches of bacteria covered the surface. A surface reaction, in which iron was released and vivianite precipitated, started. E remained at −510 mV for about 2 days, during which the vivianite layer grew steadily. Thereafter, E increased markedly to the initial value, and the release of iron stopped. Changes in E and formation of vivianite were results of bacterial activity, with oxygen consumption by the biofilm being the driving force. These findings indicate that biofilms may protect steel surfaces and might be used as an alternative method to combat corrosion. PMID:11010888

Size and surface functionalization of iron oxide nanoparticles influence the composition and dynamic nature of their protein corona.

PubMed

Ashby, Jonathan; Pan, Songqin; Zhong, Wenwan

2014-09-10

Nanoparticles (NPs) adsorb proteins when in the biological matrix, and the resulted protein corona could affect NP-cell interactions. The corona has a dynamic nature with the adsorbed proteins constantly exchanging with the free proteins in the matrix at various rates. The rapidly exchanging proteins compose the soft corona, which responds more dynamically to environment changes than the hard corona established by the ones with slow exchange rates. In the present study, the corona formed on the superparamagnetic iron oxide NPs (SPIONs) in human serum was studied by flow field-flow fractionation and ultracentrifugation, which rapidly differentiated the corona proteins based on their exchange rates. By varying the surface hydrophobicity of the SPIONs with a core size around 10 nm, we found out that, the more hydrophobic surface ligand attracted proteins with higher surface hydrophobicity and formed a more dynamic corona with a larger portion of the involved proteins with fast exchange rates. Increasing the core diameter of the SPIONs but keeping the surface ligand the same could also result in a more dynamic corona. A brief investigation of the effect on the cellular uptake of SPIONs using one selected corona protein, transferrin, was conducted. The result showed that, only the stably bound transferrin could significantly enhance cellular uptake, while transferrin bound in a dynamic nature had negligible impact. Our study has led to a better understanding of the relationship between the particle properties and the dynamic nature of the corona, which can help with design of nanomaterials with higher biocompatibility and higher efficacy in biosystems for biomedical applications.

Size and Surface Functionalization of Iron Oxide Nanoparticles Influence the Composition and Dynamic Nature of Their Protein Corona

PubMed Central

2015-01-01

Nanoparticles (NPs) adsorb proteins when in the biological matrix, and the resulted protein corona could affect NP-cell interactions. The corona has a dynamic nature with the adsorbed proteins constantly exchanging with the free proteins in the matrix at various rates. The rapidly exchanging proteins compose the soft corona, which responds more dynamically to environment changes than the hard corona established by the ones with slow exchange rates. In the present study, the corona formed on the superparamagnetic iron oxide NPs (SPIONs) in human serum was studied by flow field-flow fractionation and ultracentrifugation, which rapidly differentiated the corona proteins based on their exchange rates. By varying the surface hydrophobicity of the SPIONs with a core size around 10 nm, we found out that, the more hydrophobic surface ligand attracted proteins with higher surface hydrophobicity and formed a more dynamic corona with a larger portion of the involved proteins with fast exchange rates. Increasing the core diameter of the SPIONs but keeping the surface ligand the same could also result in a more dynamic corona. A brief investigation of the effect on the cellular uptake of SPIONs using one selected corona protein, transferrin, was conducted. The result showed that, only the stably bound transferrin could significantly enhance cellular uptake, while transferrin bound in a dynamic nature had negligible impact. Our study has led to a better understanding of the relationship between the particle properties and the dynamic nature of the corona, which can help with design of nanomaterials with higher biocompatibility and higher efficacy in biosystems for biomedical applications. PMID:25144382

Nucleation and growth of dielectric films on III-V semiconductors during atomic layer deposition

NASA Astrophysics Data System (ADS)

Granados Alpizar, Bernal

In order to continue with metal-oxide-semiconductors (CMOS) transistor scaling and to reduce the power density, the channel should be replaced with a material having a higher electron mobility, such as a III-V semiconductor. However, the integration of III-V's is a challenge because these materials oxidize rapidly when exposed to air and the native oxide produced is characterized by a high density of defects. Deposition of high-k materials on III-V semiconductors using Atomic Layer Deposition (ALD) reduces the thickness of these oxides, improving the semiconductor/oxide interface quality and the transistor electrical characteristics. In this work, ALD is used to deposit two dielectrics, Al 2O3 and TiO2, on two III-V materials, GaAs and InGaAs, and in-situ X-ray photoelectron spectroscopy (XPS) and in-situ thermal programmed desorption (TPD) are used for interface characterization. Hydrofluoric acid (HF) etching of GaAs(100) and brief reoxidation in air produces a 9.0 ±1.6 Å-thick oxide overlayer containing 86% As oxides. The oxides are removed by 1 s pulses of trimethylaluminum (TMA) or TiCl4. TMA removes the oxide overlayer while depositing a 7.5 ± 1.6 Å thick aluminum oxide. The reaction follows a ligand exchange mechanism producing nonvolatile Al-O species that remain on the surface. TiCl4 exposure removes the oxide overlayer in the temperature range 89°C to 300°C, depositing approximately 0.04 monolayer of titanium oxide for deposition temperatures from 89°C to 135°C, but no titanium oxide is present from 170 °C to 230 °C. TiCl4 forms a volatile oxychloride product and removes O from the surface while leaving Cl atoms adsorbed to an elemental As layer, chemically passivating the surface. The native oxide of In0.53Ga0.47As(100) is removed using liquid HF and gas phase HF before deposition of Al2O3 using TMA and H2O at 170 °C. An aluminium oxide film with a thickness of 7.2 ± 1.2 Å and 7.3 ± 1.2 Å is deposited during the first pulse of TMA on liquid and gas phase HF treated samples, respectively. After three complete ALD cycles the thickness of the aluminum oxide film is 10.0 ± 1.2 Å on liquid HF treated and 6.6 ± 1.2 Å on gas phase HF treated surfaces. Samples treated with gas phase HF inhibit growth. Inhibition is caused by residual F atoms that passivate the surface and by surface poisoning due to the thicker carbon film deposited during the first pulse of TMA. On InGaAs covered by native oxide, the first TMA pulse deposits 9 Å of aluminum oxide, and reaches saturation at 13 Å after 15 pulses of TMA. The film grows by scavenging oxygen from the substrate oxides. Substrate oxides are reduced by the first pulse of TMA even at 0°C. At 0°C, on a 9 Å thick Ga-rich oxide surface, 1 pulse of TMA mainly physisorbs and a limited amount of aluminum oxide is deposited. At 0°C, 110°C, and 170°C, more aluminum oxide is deposited on surfaces initially containing As oxide, and larger binding energy (BE) shifts of the O 1s peak are observed compared to surfaces that contain Ga oxides only, showing that As oxides improve the nucleation of Al2O 3.

Advanced Oxidation Protein Products-Modified Albumin Induces Differentiation of RAW264.7 Macrophages into Dendritic-Like Cells Which Is Modulated by Cell Surface Thiols.

PubMed

Garibaldi, Silvano; Barisione, Chiara; Marengo, Barbara; Ameri, Pietro; Brunelli, Claudio; Balbi, Manrico; Ghigliotti, Giorgio

2017-01-10

Local accumulation of Advanced Oxidation Protein Products (AOPP) induces pro-inflammatory and pro-fibrotic processes in kidneys and is an independent predictor of renal fibrosis and of rapid decline of eGFR in patients with chronic kidney disease (CKD). In addition to kidney damage, circulating AOPP may be regarded as mediators of systemic oxidative stress and, in this capacity, they might play a role in the progression of atherosclerotic damage of arterial walls. Atherosclerosis is a chronic inflammatory disease that involves activation of innate and adaptive immunity. Dendritic cells (DCs) are key cells in this process, due to their role in antigen presentation, inflammation resolution and T cell activation. AOPP consist in oxidative modifications of proteins (such as albumin and fibrinogen) that mainly occur through myeloperoxidase (MPO)-derived hypochlorite (HOCl). HOCl modified proteins have been found in atherosclerotic lesions. The oxidizing environment and the shifts in cellular redox equilibrium trigger inflammation, activate immune cells and induce immune responses. Thus, surface thiol groups contribute to the regulation of immune functions. The aims of this work are: (1) to evaluate whether AOPP-proteins induce activation and differentiation of mature macrophages into dendritic cells in vitro; and (2) to define the role of cell surface thiol groups and of free radicals in this process. AOPP-proteins were prepared by in vitro incubation of human serum albumin (HSA) with HOCl. Mouse macrophage-like RAW264.7 were treated with various concentrations of AOPP-HSA with or without the antioxidant N -acetyl cysteine (NAC). Following 48 h of HSA-AOPP treatment, RAW264.7 morphological changes were evaluated by microscopic observation, while markers of dendritic lineage and activation (CD40, CD86, and MHC class II) and allogeneic T cell proliferation were evaluated by flow cytometry. Cell surface thiols were measured by AlexaFluor-maleimide binding, and ROS production was assessed as DCF fluorescence by flow cytometry. HSA-AOPP induced the differentiation of RAW264.7 cells into a dendritic-like phenotype, as shown by morphological changes, by increased CD40, CD86 and MHC class II surface expression and by induction of T cell proliferation. The cell surface thiols dose dependently decreased following HSA-AOPP treatment, while ROS production increased. NAC pre-treatment enhanced the amount of cell surface thiols and prevented their reduction due to treatment with AOPP. Both ROS production and RAW264.7 differentiation into DC-like cells induced by HSA-AOPP were reduced by NAC. Our results highlight that oxidized plasma proteins modulate specific immune responses of macrophages through a process involving changes in the thiol redox equilibrium. We suggest that this mechanism may play a role in determining the rapid progression of the atherosclerotic process observed in CKD patients.

Rapid Sediment Accumulation Results in High Methane Effluxes from Coastal Sediments

PubMed Central

Lenstra, Wytze; Jong, Dirk; Meysman, Filip J. R.; Sapart, Célia J.; van der Veen, Carina; Röckmann, Thomas; Gonzalez, Santiago; Slomp, Caroline P.

2016-01-01

Globally, the methane (CH4) efflux from the ocean to the atmosphere is small, despite high rates of CH4 production in continental shelf and slope environments. This low efflux results from the biological removal of CH4 through anaerobic oxidation with sulfate in marine sediments. In some settings, however, pore water CH4 is found throughout the sulfate-bearing zone, indicating an apparently inefficient oxidation barrier for CH4. Here we demonstrate that rapid sediment accumulation can explain this limited capacity for CH4 removal in coastal sediments. In a saline coastal reservoir (Lake Grevelingen, The Netherlands), we observed high diffusive CH4 effluxes from the sediment into the overlying water column (0.2–0.8 mol m-2 yr-1) during multiple years. Linear pore water CH4 profiles and the absence of an isotopic enrichment commonly associated with CH4 oxidation in a zone with high rates of sulfate reduction (50–170 nmol cm-3 d-1) both suggest that CH4 is bypassing the zone of sulfate reduction. We propose that the rapid sediment accumulation at this site (~ 13 cm yr-1) reduces the residence time of the CH4 oxidizing microorganisms in the sulfate/methane transition zone (< 5 years), thus making it difficult for these slow growing methanotrophic communities to build-up sufficient biomass to efficiently remove pore water CH4. In addition, our results indicate that the high input of organic matter (~ 91 mol C m-2 yr-1) allows for the co-occurrence of different dissimilatory respiration processes, such as (acetotrophic) methanogenesis and sulfate reduction in the surface sediments by providing abundant substrate. We conclude that anthropogenic eutrophication and rapid sediment accumulation likely increase the release of CH4 from coastal sediments. PMID:27560511

Metal-oxide assisted surface treatment of polyimide gate insulators for high-performance organic thin-film transistors.

PubMed

Kim, Sohee; Ha, Taewook; Yoo, Sungmi; Ka, Jae-Won; Kim, Jinsoo; Won, Jong Chan; Choi, Dong Hoon; Jang, Kwang-Suk; Kim, Yun Ho

2017-06-14

We developed a facile method for treating polyimide-based organic gate insulator (OGI) surfaces with self-assembled monolayers (SAMs) by introducing metal-oxide interlayers, called the metal-oxide assisted SAM treatment (MAST). To create sites for surface modification with SAM materials on polyimide-based OGI (KPI) surfaces, the metal-oxide interlayer, here amorphous alumina (α-Al 2 O 3 ), was deposited on the KPI gate insulator using spin-coating via a rapid sol-gel reaction, providing an excellent template for the formation of a high-quality SAM with phosphonic acid anchor groups. The SAM of octadecylphosphonic acid (ODPA) was successfully treated by spin-coating onto the α-Al 2 O 3 -deposited KPI film. After the surface treatment by ODPA/α-Al 2 O 3 , the surface energy of the KPI thin film was remarkably decreased and the molecular compatibility of the film with an organic semiconductor (OSC), 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C 10 ), was increased. Ph-BTBT-C 10 molecules were uniformly deposited on the treated gate insulator surface and grown with high crystallinity, as confirmed by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis. The mobility of Ph-BTBT-C 10 thin-film transistors (TFTs) was approximately doubled, from 0.56 ± 0.05 cm 2 V -1 s -1 to 1.26 ± 0.06 cm 2 V -1 s -1 , after the surface treatment. The surface treatment of α-Al 2 O 3 and ODPA significantly decreased the threshold voltage from -21.2 V to -8.3 V by reducing the trap sites in the OGI and improving the interfacial properties with the OSC. We suggest that the MAST method for OGIs can be applied to various OGI materials lacking reactive sites using SAMs. It may provide a new platform for the surface treatment of OGIs, similar to that of conventional SiO 2 gate insulators.

A review of recent progress in coatings, surface modifications and alloy developments for solid oxide fuel cell ferritic stainless steel interconnects

NASA Astrophysics Data System (ADS)

Shaigan, Nima; Qu, Wei; Ivey, Douglas G.; Chen, Weixing

Ferritic stainless steels have become the standard material for solid oxide fuel cell (SOFC) interconnect applications. The use of commercially available ferritic stainless steels, not specifically designed for interconnect application, however, presents serious issues leading to premature degradation of the fuel cell stack, particularly on the cathode side. These problems include rapidly increasing contact resistance and volatilization of Cr from the oxide scales, resulting in cathode chromium poisoning and cell malfunction. To overcome these issues, a variety of conductive/protective coatings, surface treatments and modifications as well as alloy development have been suggested and studied over the past several years. This paper critically reviews the attempts performed thus far to mitigate the issues associated with the use of ferritic stainless steels on the cathode side. Different approaches are categorized and summarized and examples for each case are provided. Finally, directions and recommendations for the future studies are presented.

Pulsed photonic fabrication of nanostructured metal oxide thin films

NASA Astrophysics Data System (ADS)

Bourgeois, Briley B.; Luo, Sijun; Riggs, Brian C.; Adireddy, Shiva; Chrisey, Douglas B.

2017-09-01

Nanostructured metal oxide thin films with a large specific surface area are preferable for practical device applications in energy conversion and storage. Herein, we report instantaneous (milliseconds) photonic synthesis of three-dimensional (3-D) nanostructured metal oxide thin films through the pulsed photoinitiated pyrolysis of organometallic precursor films made by chemical solution deposition. High wall-plug efficiency-pulsed photonic irradiation (xenon flash lamp, pulse width of 1.93 ms, fluence of 7.7 J/cm2 and frequency of 1.2 Hz) is used for scalable photonic processing. The photothermal effect of subsequent pulses rapidly improves the crystalline quality of nanocrystalline metal oxide thin films in minutes. The following paper highlights pulsed photonic fabrication of 3-D nanostructured TiO2, Co3O4, and Fe2O3 thin films, exemplifying a promising new method for the low-cost and high-throughput manufacturing of nanostructured metal oxide thin films for energy applications.

Probing Selenium-Ion Distributions and Changes in Redox-State at Biofilm/Mineral Interfaces by Coupling Long-period X-ray Standing Wave and XANES Measurements

NASA Astrophysics Data System (ADS)

Templeton, A. S.; Trainor, T. P.; Spormann, A. M.; Brown, G. E.

2002-12-01

Metal sorption and precipitation reactions at biological as well as mineral surfaces are important controls on metal speciation and bioavailability in natural environments. When highly hydrated biofilms form on mineral surfaces, numerous competitive and synergistic effects are predicted to occur. Experimentally, it is challenging to determine where the sorbed metal ions are localized, the relative affinity of the biological vs. mineral surface sites, or to monitor biomineralization reactions or changes in metal speciation that may also occur. A large part of the difficulty is due to the low concentrations of sorbed ions, the small length-scale of the biofilm-mineral interface, and the complex interplay between microbially-catalayzed redox transformations vs. sorption and/or transport processes. Long-period x-ray standing wave (XSW) techniques are well-suited to determining the vertical distribution of metal(oid) species within biofilms overlying mineral surfaces. We will discuss experiments where Se fluorescence yield profiles are used to compare the affinity of Burkholderia cepacia biofilms for binding Se(IV) and Se(VI) species relative to underlying alpha-Al2O3 substrates over three orders of magnitude in [Se]. In addition, we will discuss how coupling the XSW experiments to grazing-incidence, spatially-resolved Se K-edge XANES spectroscopy can be used to differentiate between the oxidation state of the Se complexes localized within the biofilm vs. the mineral surface. This approach is used to monitor changes in the relative distributions of Se(VI), Se(IV) and Se(0) species as a function of time and proximity to the mineral surface. The long-period XSW data show that selenite preferentially binds to the oxide surfaces, particularly at low [Se]. When B. cepacia is metabolically active, B. cepacia rapidly reduces a fraction of the Se(IV) to the red elemental Se form. In contrast, selenate is preferentially partitioned into the B. cepacia biofilms at all [Se] tested due to a lower affinity for binding to the mineral surface. XANES spectra show that rapid reduction of selenate by B. cepacia to Se(IV) and Se(0) species subsequently results in a vertical segregation of Se species at the B. cepacia/alpha-Al2O3 interface. Elemental Se accumulates within the biofilm with the Se(VI), whereas selenite intermediates preferentially sorb to the underlying oxide surface.

Electrochemical Micromachining with Fiber Laser Masking for 304 Stainless Steel

NASA Astrophysics Data System (ADS)

Li, Xiaohai; Wang, Shuming; Wang, Dong; Tong, Han

2017-10-01

In order to fabricate micro structure, the combined machining of electrochemical micro machining (EMM) and laser masking for 304 stainless steel was studied. A device of composite machining of EMM with laser masking was developed, and the experiments of EMM with laser masking were carried out. First, by marking pattern with fiber laser on the surface of 304 stainless steel, the special masking layer can be formed. Through X ray photoelectron spectroscopy (XPS), the corrosion resistance of laser masking layer was analyzed. It is proved by XPS that the iron oxide and chromium oxide on the surface of stainless steel generates due to air oxidation when laser scanning heats. Second, the localization and precision of EMM are improved, since the marking patterns forming on the surface of stainless steel by laser masking play a protective role in the process of subsequent EMM when the appropriate parameters of EMM are selected. At last, the shape and the roughness of the machined samples were measured by SEM and optical profilometer and analyzed. The results show that the rapid fabrication of micro structures on the 304 stainless steel surface can be achieved by EMM with fiber laser masking, which has a good prospect in the field of micro machining.

Influence of oxygenation on chromium redox reactions with manganese sulfide (MnS(s)).

PubMed

Wadhawan, Amar R; Livi, Kenneth J; Stone, Alan T; Bouwer, Edward J

2015-03-17

Manganese sulfide (MnS(s)) minerals exist in sulfidic environments and can have unique reactive abilities because of sulfide, which is a known reductant, and Mn, the oxyhydroxides of which are known oxidants. This study elucidated the role of MnS(s) in controlling Cr speciation with implications on its fate and toxicity in the natural environment, specifically sulfidic sediments that undergo biogeochemical changes due to sediment resuspension during dredging, bioturbation, and flood events. In continuously mixed batch reaction experiments, aqueous CrVI reduction under anaerobic conditions occurred primarily on the surface of MnS(s) displaying a biphasic behavior- the initial rapid removal of CrVI from solution was followed by a slow decline due to surface passivation by reaction products, mainly sorbed or precipitated CrIII. The reaction progress increased with MnS(s) surface area loading but decreased on increasing CrVI concentration and pH, suggesting that surface site regeneration through product desorption was the rate-controlling mechanism. Below circum-neutral pH, higher solubility of MnS(s) resulted in additional CrVI reduction by reduced sulfur species in solution, whereas increased CrIII solubility lowered surface passivation allowing for more reactive sites to participate in the reaction. Aeration of MnS(s) at pH≥7 caused the formation of a heterogeneous MnIII(hydr)oxide that was composed of hausmanite and manganite. CrVI reoccurrence was observed on aeration of CrVI-spiked MnS(s) from the oxidation of product CrIII. The reoccurrence at pH≥7 was attributed to the oxidation of product CrIII by MnIII(hydr)oxide, whereas the reoccurrence at pH<7 was hypothesized from the oxidation of product CrIII by intermediate aqueous MnIII and/or sulfur species. Just as with Cr, MnS(s) may play an important role in speciation, fate, and transport of other environmental contaminants.

Flux observations of isoprene oxidation products above a South East US forest point to chemical conversions on leaf canopy surface

NASA Astrophysics Data System (ADS)

Misztal, P. K.; Su, L.; Park, J.; Holzinger, R.; Nguyen, T.; Teng, A.; St Clair, J. M.; Wennberg, P. O.; Crounse, J.; Seco, R.; Karl, T.; Kaser, L.; Hansel, A.; Canaval, E.; Keutsch, F. N.; Mak, J. E.; Guenther, A. B.; Goldstein, A. H.; Mentler, B.; Lepesant, B.; Schnitzler, J. P.; Partoll, E.

2016-12-01

Isoprene is globally the dominant biogenic VOC (BVOC) emitted by the biosphere. Isoprene rapidly reacts with hydroxyl radicals in the atmosphere, forming oxidized carbonaceous gases some of which further react to form secondary organic aerosol. Isoprene oxidation proceeds simultaneously via NO and HO2 oxidation pathways with relative proportions depending mainly on the amount of available NOx (NO +NO2). Recent SOA modeling of HO2 oxidation of isoprene peroxides and epoxides reveal different SOA yields but few field studies are available to investigate these processes. Understanding of the fundamental chemical and physical processes controlling the fate of isoprene oxidation products is needed to improve SOA modeling under highly variable NOx concentrations and with the branching ratio between HO2 and NO pathways changing as a function of time of day. Plants are an important sink for many atmospheric chemicals formed in the atmosphere but the role of canopy surfaces is not typically accounted for when modeling atmospheric chemistry. Based on simultaneous flux measurements of isoprene carbonyls (MVK+MAC) by proton transfer reaction mass spectrometry and isoprene hydroxy hydroperoxides and epoxy diols (ISOPOOH+IEPOX) by tandem chemical ionization mass spectrometry, we show that the relative proportions of concentrations of these first-order isoprene products exhibit different diurnal patterns, dependent on NOx. Furthermore, a different diurnal flux pattern observed for first order products of NO and HO2 reactions reveals the occurrence of peroxide conversions to carbonyls at the canopy surface resulting in observed positive net emission flux of MVK+MAC in the afternoon. We hypothesize that the plant canopy provides an active surface which can catalyze chemical conversion. This hypothesis is supported by observation of consistent flux patterns at multiple different sites in the US and by a controlled ISOPOOH fumigation experiment of a plant in an enclosure chamber. In the chamber, we observe transformation of ISOPOOH to MVK+MAC on leaf surfaces even under dark conditions when the stomata are closed.

Thermodynamics of Manganese Oxides at Bulk and Nanoscale: Phase Formation, Transformation, Oxidation-Reduction, and Hydration

NASA Astrophysics Data System (ADS)

Birkner, Nancy R.

Natural manganese oxides are generally formed in surficial environments that are near ambient temperature and water-rich, and may be exposed to wet-dry cycles and a variety of adsorbate species that influence dramatically their level of hydration. Manganese oxide minerals are often poorly crystalline, nanophase, and hydrous. In the near-surface environment they are involved in processes that are important to life, such as water column oxygen cycling, biomineralization, and transport of minerals/nutrients through soils and water. These processes, often involving transformations among manganese oxide polymorphs, are governed by a complex interplay between thermodynamics and kinetics. Manganese oxides are also used in technology as catalysts, and for other applications. The major goal of this dissertation is to examine the energetics of bulk and nanophase manganese oxide phases as a function of particle size, composition, and surface hydration. Careful synthesis and characterization of manganese oxide phases with different surface areas provided samples for the study of enthalpies of formation by high temperature oxide melt solution calorimetry and of the energetics of water adsorption on their surfaces. These data provide a quantitative picture of phase stability and how it changes at the nanoscale. The surface energy of the hydrous surface of Mn3O4 is 0.96 +/- 0.08 J/m2, of Mn2O3 is 1.29 +/- 0.10 J/m2, and of MnO2 is 1.64 +/- 0.10 J/m2. The surface energy of the anhydrous surface of Mn3O4 is 1.62 +/- 0.08 J/m 2, of Mn2O3 is 1.77 +/- 0.10 J/m 2, and of MnO2 is 2.05 +/- 0.10 J/m2. Supporting preliminary findings (Navrotsky et al., 2010), the spinel phase (Mn3O4) has a lower surface energy (more stabilizing) than bixbyite, while the latter has a smaller surface energy than pyrolusite. These differences significantly change the positions in oxygen fugacity---temperature space of the redox couples Mn3O4-Mn2O 3 and Mn2O3-MnO2 favoring the lower surface enthalpy phase (the spinel Mn3O4) for smaller particle size and in the presence of surface hydration. Chemisorption of water onto anhydrous nanophase Mn2O 3 surfaces promotes rapidly reversible redox phase changes at room temperature as confirmed by calorimetry, X-ray diffraction, and titration for manganese average oxidation state. Water adsorption microcalorimetry (in situ) at room temperature measured the strongly exothermic integral enthalpy of water adsorption (-103.5 kJ/mol) and monitored the energetics of the redox phase transformation. Hydration-driven redox transformation of anhydrous nanophase Mn(III) 2O3, (high surface enthalpy of anhydrous surfaces 1.77 +/- 0.10 J/m2) to Mn(II,III)3O4 (lower surface enthalpy 0.96 +/- 0.08 J/m2) occurred during the first few doses of water vapor. Surface reduction of nanoparticle bixbyite (Mn 2O3) to hausmannite (Mn3O4) occurs under conditions where no such reactions are seen or expected on grounds of bulk thermodynamics in coarse-grained materials. Layered structure manganese oxides contain alkali or alkaline earth cations and water, are generally fine-grained, and have considerable thermodynamic stability. The surface enthalpies (SE) of layered and tunnel structure complex manganese oxides are significantly lower than those of the binary manganese oxide phases. The SE for hydrous surfaces and overall manganese average oxidation state (AOS) (value in parentheses) are: cryptomelane 0.77 +/- 0.10 J/m 2 (3.78), sodium birnessite 0.69 +/- 0.13 J/m2 (3.56), potassium birnessite 0.55 +/- 0.11 J/m2 (3.52), and calcium birnessite 0.41 +/- 0.11 J/m2 (3.50). Surface enthalpies of hydrous surfaces of the calcium manganese oxide nanosheets are: deltaCa 0.39MnO2.3nH2O 0.75 +/- 0.10 J/m2 (3.89) and deltaCa0.43MnO2.3nH2O 0.57 +/- 0.12 J/m2 (3.68). The surface enthalpy of the complex manganese oxides appears to decrease with decreasing manganese average oxidation state, that is, with greater mixed valence manganese (Mn 3+/4+). Low surface energy suggests loose binding of H2O on the internal and external surfaces and may be critical to catalysis in both natural and technological settings.

Simultaneous determination of environmental estrogens: Diethylstilbestrol and estradiol using Cu-BTC frameworks-sensitized electrode.

PubMed

Ji, Liudi; Wang, Yanying; Wu, Kangbing; Zhang, Weikang

2016-10-01

It is quite important to monitor environmental estrogens in a rapid, sensitive, simple and cost-effective manner due to their wide existence and high toxicity. Using 1,3,5-Benzenetricarboxylic acid (H3BTC) as the ligand and copper ions as the center, Cu-BTC frameworks with surface area of 654.6m(2)/g were prepared, and then used to construct a novel electrochemical sensing platform for diethylstilbestrol (DES) and estradiol (E2). On the surface of Cu-BTC frameworks, two oxidation waves at 0.26V and 0.45V are observed for DES and E2, and the oxidation signals are improved greatly. The prepared Cu-BTC frameworks not only enhance the accumulation efficiency of DES and E2, but also improve their electron transfer ability. The influences of pH value, modification amount of Cu-BTC and accumulation time were examined. As a result, a highly-sensitive, rapid and convenient electrochemical method was developed for the simultaneous determination of DES and E2, with detection limit of 2.7nM and 1.1nM. The practical applications manifest this new sensing system is accurate and feasible. Copyright © 2016 Elsevier B.V. All rights reserved.

Design and fabrication of N-alkyl-polyethylenimine-stabilized iron oxide nanoclusters for gene delivery.

PubMed

Liu, Gang; Wang, Zhiyong; Lee, Seulki; Ai, Hua; Chen, Xiaoyuan

2012-01-01

With the rapid development of nanotechnology, inorganic magnetic nanoparticles, especially iron oxide nanoparticles (IOs), have emerged as great vehicles for biomedical diagnostic and therapeutic applications. In order to rationally design IO-based gene delivery nanovectors, surface modification is essential and determines the loading and release of the gene of interest. Here we highlight the basic concepts and applications of nonviral gene delivery vehicles based on low molecular weight N-alkyl polyethylenimine-stabilized IOs. The experimental protocols related to these topics are described in this chapter. Copyright © 2012 Elsevier Inc. All rights reserved.

Opportunities offered by the interaction of plasma and droplets to elaborate nanostructured oxide materials

NASA Astrophysics Data System (ADS)

Nikravech, Mehrdad; Rahmani, Abdelkader

2016-09-01

The association of plasma and spray will permit to process materials where organometallic precursors are not available or economically non-reliable. The injection of aerosols in low pressure plasma results in the rapid evaporation of solvent and the rapid transformation of small amounts of precursors contained in each droplet leading to form nanoscale oxide particles. We developed two configurations of this technique: one is Spray Plasma that permits to deposit this layers on flat substrates; the second one is Fluidized Spray Plasma that permits to deposit thin layers on the surface of solid beads. The aim of this presentation is to describe the principles of this new technique together with several applications. The influence of experimental parameters to deposit various mixed metal oxides will be demonstrated: thin dense layers of nanostructured ZnO for photovoltaic applications, porous layers of LaxSr1-x MnO3 as the cathode for fuel cells, ZnO-Cu, NiO layers on solid pellets in fluidized bed for catalysis applications. Aknowledgement to Programme interdisciplinaire SPC Énergies de Demain.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Binh T; Lehmann, Johannes C; Kinyangi, James

Black carbon (BC) is a quantitatively important C pool in the global carbon cycle due to its relative recalcitrance against decay compared with other C pools. However, how rapidly BC is oxidized and in what way the molecular structure changes during decomposition over decadal time scales, is largely unknown. In the present study, the long-term dynamics in quality and quantity of BC were investigated in cultivated soil using X-ray Photoelectron Spectroscopy (XPS), Fourier-Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) techniques. BC particles, obtained from soil samples at 8 conversion ages stretching over 100 years and from a forest soilmore » sample from Kenya, were manually picked under a light microscope for characterization and quantification. BC contents rapidly decreased from 12.7 to 3.8 mg C g⁻¹ soil during the first 30 years since conversion, after which they slowly decreased to a steady state at 3.51 mg C g ⁻¹soil. BC-derived C losses over 100 years were estimated at 6000 kg C ha⁻¹ to a depth of 0.1 m. The initial rapid changes in BC stocks resulted in a mean residence time of only around 8.3 years, which was likely a function of both decomposition as well as transport processes. The molecular properties of BC changed more rapidly on surfaces than in the interior of BC particles and more rapidly during the first 30 years than during the following 70 years. The Oc/C ratios (Oc is O bound to C) and carbonyl groups (C=O) increased over time by 133 and 192 %, respectively, indicating oxidation was an important degradation process controlling BC quality. Al, Si, polysaccharides, and to a lesser extent Fe were rapidly adsorbed on BC particle surfaces within the first few years after BC deposition to soil. The protection by physical and chemical stabilization was apparently sufficient to not only minimize decomposition below detection between 30 and 100 years after deposition, but also physical export by erosion and vertical transport below 0.1 m.« less

Graphene nanosheet mediated MALDI-MS (GN-MALDI-MS) for rapid, in situ detection of intact incipient biofilm on material surfaces.

PubMed

Wu, Bo Sgum; Gopal, Judy; Hua, Pei-Yang; Wu, Hui-Fen

2016-09-01

Detection is the first step to efficient treatment, therefore early detection of biofilm gains paramount importance for the initiation of mitigation protocols. A systematic study was conducted to detect the biofilm formation (1h to 2month period) on aluminium, titanium surfaces and their corresponding oxide film surfaces. The limit of detection (LOD) in case of traditional MALDI-MS was limited to a 6h old biofilm. Whereas, in case of the Graphene nanosheet mediated MALDI-MS (GN-MALDI-MS) approach, early detection of the biofilm was demonstrated to be 1h on titanium surfaces and 3h for Al surfaces. Copyright © 2016 Elsevier B.V. All rights reserved.

Rapid Deposition of Oxidized Biogenic Compounds to a Temperate Forest

NASA Technical Reports Server (NTRS)

Nguyen, Tran B.; Crounse, John D.; Teng, Alex P.; St. Clair, Jason M.; Paulot, Fabien; Wolfe, Glenn M.; Wennberg, Paul O.

2015-01-01

We report fluxes and dry deposition velocities for 16 atmospheric compounds above a southeastern United States forest, including: hydrogen peroxide (H2O2), nitric acid (HNO3), hydrogen cyanide (HCN), hydroxymethyl hydroperoxide, peroxyacetic acid, organic hydroxy nitrates, and other multifunctional species derived from the oxidation of isoprene and monoterpenes. The data suggest that dry deposition is the dominant daytime sink for small, saturated oxygenates. Greater than 6 wt %C emitted as isoprene by the forest was returned by dry deposition of its oxidized products. Peroxides account for a large fraction of the oxidant flux, possibly eclipsing ozone in more pristine regions. The measured organic nitrates comprise a sizable portion (15%) of the oxidized nitrogen input into the canopy, with HNO3 making up the balance. We observe that water-soluble compounds (e.g., strong acids and hydroperoxides) deposit with low surface resistance whereas compounds with moderate solubility (e.g., organic nitrates and hydroxycarbonyls) or poor solubility (e.g., HCN) exhibited reduced uptake at the surface of plants. To first order, the relative deposition velocities of water-soluble compounds are constrained by their molecular diffusivity. From resistance modeling, we infer a substantial emission flux of formic acid at the canopy level (approx. 1 nmol m(exp.-2)·s(exp.-1)). GEOS-Chem, awidely used atmospheric chemical transport model, currently underestimates dry deposition for most molecules studied in this work. Reconciling GEOS-Chem deposition velocities with observations resulted in up to a 45% decrease in the simulated surface concentration of trace gases.

Rapid deposition of oxidized biogenic compounds to a temperate forest

PubMed Central

Nguyen, Tran B.; Crounse, John D.; Teng, Alex P.; St. Clair, Jason M.; Paulot, Fabien; Wolfe, Glenn M.; Wennberg, Paul O.

2015-01-01

We report fluxes and dry deposition velocities for 16 atmospheric compounds above a southeastern United States forest, including: hydrogen peroxide (H2O2), nitric acid (HNO3), hydrogen cyanide (HCN), hydroxymethyl hydroperoxide, peroxyacetic acid, organic hydroxy nitrates, and other multifunctional species derived from the oxidation of isoprene and monoterpenes. The data suggest that dry deposition is the dominant daytime sink for small, saturated oxygenates. Greater than 6 wt %C emitted as isoprene by the forest was returned by dry deposition of its oxidized products. Peroxides account for a large fraction of the oxidant flux, possibly eclipsing ozone in more pristine regions. The measured organic nitrates comprise a sizable portion (15%) of the oxidized nitrogen input into the canopy, with HNO3 making up the balance. We observe that water-soluble compounds (e.g., strong acids and hydroperoxides) deposit with low surface resistance whereas compounds with moderate solubility (e.g., organic nitrates and hydroxycarbonyls) or poor solubility (e.g., HCN) exhibited reduced uptake at the surface of plants. To first order, the relative deposition velocities of water-soluble compounds are constrained by their molecular diffusivity. From resistance modeling, we infer a substantial emission flux of formic acid at the canopy level (∼1 nmol m−2⋅s−1). GEOS−Chem, a widely used atmospheric chemical transport model, currently underestimates dry deposition for most molecules studied in this work. Reconciling GEOS−Chem deposition velocities with observations resulted in up to a 45% decrease in the simulated surface concentration of trace gases. PMID:25605913

Oxygen plasma ashing effects on aluminum and titanium space protective coatings

NASA Technical Reports Server (NTRS)

Synowicki, R.; Kubik, R. D.; Hale, J. S.; Peterkin, Jane; Nafis, S.; Woollam, John A.; Zaat, S.

1991-01-01

Using variable angle spectroscopic ellipsometry and atomic force microscopy (AFM), the surface roughness and oxidation of aluminum and titanium thin films have been studied as a function of substrate deposition temperature and oxygen plasma exposure. Increasing substrate deposition temperatures affect film microstructure by greatly increasing grain size. Short exposures to an oxygen plasma environment produce sharp spikes rising rapidly above the surface as seen by AFM. Ellipsometric measurements were made over a wide range of plasma exposure times, and results at longer exposure times suggest that the surface is greater than 30% void. This is qualitatively verified by the AFM images.

Ultra-fast self-assembly and stabilization of reactive nanoparticles in reduced graphene oxide films

PubMed Central

Chen, Yanan; Egan, Garth C.; Wan, Jiayu; Zhu, Shuze; Jacob, Rohit Jiji; Zhou, Wenbo; Dai, Jiaqi; Wang, Yanbin; Danner, Valencia A.; Yao, Yonggang; Fu, Kun; Wang, Yibo; Bao, Wenzhong; Li, Teng; Zachariah, Michael R.; Hu, Liangbing

2016-01-01

Nanoparticles hosted in conductive matrices are ubiquitous in electrochemical energy storage, catalysis and energetic devices. However, agglomeration and surface oxidation remain as two major challenges towards their ultimate utility, especially for highly reactive materials. Here we report uniformly distributed nanoparticles with diameters around 10 nm can be self-assembled within a reduced graphene oxide matrix in 10 ms. Microsized particles in reduced graphene oxide are Joule heated to high temperature (∼1,700 K) and rapidly quenched to preserve the resultant nano-architecture. A possible formation mechanism is that microsized particles melt under high temperature, are separated by defects in reduced graphene oxide and self-assemble into nanoparticles on cooling. The ultra-fast manufacturing approach can be applied to a wide range of materials, including aluminium, silicon, tin and so on. One unique application of this technique is the stabilization of aluminium nanoparticles in reduced graphene oxide film, which we demonstrate to have excellent performance as a switchable energetic material. PMID:27515900

Acidic attack of perfluorinated alkyl ether lubricant molecules by metal oxide surfaces

NASA Technical Reports Server (NTRS)

Zehe, Michael J.; Faut, Owen D.

1990-01-01

The reactions of linear perfluoropolyalkylether (PFAE) lubricants with alpha-Fe203 and Fe203-based solid superacids were studied. The reaction with alpha-Fe203 proceeds in two stages. The first stage is an initial slow catalytic decomposition of the fluid. This reaction releases reactive gaseous products which attach the metal oxide and convert it to FeF3. The second stage is a more rapid decomposition of the fluid, effected by the surface FeF3. A study of the initial breakdown step was performed using alpha-Fe203, alpha-Fe203 preconverted to FeF3, and sulfate-promoted alpha-Fe203 superacids. The results indicate that the breakdown reaction involves acidic attack at fluorine atoms on acetal carbons in the linear PFAE. Possible approaches to combat the problem are outlined.

Dioxygen activation by non-adiabatic oxidative addition to a single metal center [O 2 activation by non-adiabatic oxidative addition to a single metal center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akturk, Eser S.; Yap, Glenn P. A.; Theopold, Klaus H.

2015-10-16

A chromium(I) dinitrogen complex reacts rapidly with O 2 to form the mononuclear dioxo complex [Tp tBu,MeCr V(O) 2] (Tp tBu,Me=hydrotris(3- tert-butyl-5-methylpyrazolyl)borate), whereas the analogous reaction with sulfur stops at the persulfido complex [Tp tBu,MeCr III(S 2)]. The transformation of the putative peroxo intermediate [Tp tBu,MeCr III(O 2)] (S= 3/ 2) into [Tp tBu,MeCr V(O) 2] (S= 1/ 2) is spin-forbidden. The minimum-energy crossing point for the two potential energy surfaces has been identified. Finally, although the dinuclear complex [(Tp tBu,MeCr) 2(μ-O) 2] exists, mechanistic experiments suggest that O 2 activation occurs on a single metal center, by an oxidativemore » addition on the quartet surface followed by crossover to the doublet surface.« less

First results on plasma-surface interactions in the tokamak de varennes

NASA Astrophysics Data System (ADS)

Terreault, B.; Boucher, C.; Paynter, R. W.; Ross, G. G.; ThÉriault, D.; Abel, G.; Boivin, R.; Bolton, R. A.; Castracane, J.; Chevalier, G.; Couture, P.; Décoste, R.; Demers, Y.; Dimoff, K.; Glaude, V.; Gregory, B. C.; Haddad, E.; Janicki, C.; Kalnavarns, J.; Lachambre, J. L.; Mai, H. H.; Neufeld, C. R.; Pacher, H. D.; Pacher, G. W.; Richard, N.; Saint-Jacques, R. G.; Saint-Onge, M.; Simm, C.; Stansfield, B. L.; Veilleux, G.; Whyte, D.; Zuzak, W.

1989-04-01

Results of plasma-surface interaction studies made during the early phases of operation of the Tokamak de Varennes are summarized. It was found that the desorption of molecules from the internal walls by UV radiation can be used to reduce the base pressure. Auger depth profiling of stainless steel (SS) samples exposed to hydrogen discharge cleaning has been performed. Glow discharges at about 0.1 mbar etch the surface carbon and oxide at a rate of 0.5 nm/h. RF-glow discharges at 10 -3 mbar result in a rapid reduction of the oxide and its replacement by a carbide layer (the graphite limiters being the source of the carbon). Long-term wall samples of SS and Si have been profiled by Auger and nuclear analysis. The SS sample has a similar composition to that exposed to the RF-glow conditioning. The Si sample is covered by a 3 nm deposit of metals, C and O, and contains 10 16 H/cm 2 within 30 nm of the surface; this dose and width are consistent with the history of the sample.

Convective forcing of mercury and ozone in the Arctic boundary layer induced by leads in sea ice.

PubMed

Moore, Christopher W; Obrist, Daniel; Steffen, Alexandra; Staebler, Ralf M; Douglas, Thomas A; Richter, Andreas; Nghiem, Son V

2014-02-06

The ongoing regime shift of Arctic sea ice from perennial to seasonal ice is associated with more dynamic patterns of opening and closing sea-ice leads (large transient channels of open water in the ice), which may affect atmospheric and biogeochemical cycles in the Arctic. Mercury and ozone are rapidly removed from the atmospheric boundary layer during depletion events in the Arctic, caused by destruction of ozone along with oxidation of gaseous elemental mercury (Hg(0)) to oxidized mercury (Hg(II)) in the atmosphere and its subsequent deposition to snow and ice. Ozone depletion events can change the oxidative capacity of the air by affecting atmospheric hydroxyl radical chemistry, whereas atmospheric mercury depletion events can increase the deposition of mercury to the Arctic, some of which can enter ecosystems during snowmelt. Here we present near-surface measurements of atmospheric mercury and ozone from two Arctic field campaigns near Barrow, Alaska. We find that coastal depletion events are directly linked to sea-ice dynamics. A consolidated ice cover facilitates the depletion of Hg(0) and ozone, but these immediately recover to near-background concentrations in the upwind presence of open sea-ice leads. We attribute the rapid recoveries of Hg(0) and ozone to lead-initiated shallow convection in the stable Arctic boundary layer, which mixes Hg(0) and ozone from undepleted air masses aloft. This convective forcing provides additional Hg(0) to the surface layer at a time of active depletion chemistry, where it is subject to renewed oxidation. Future work will need to establish the degree to which large-scale changes in sea-ice dynamics across the Arctic alter ozone chemistry and mercury deposition in fragile Arctic ecosystems.

The rapid formation of functional monolayers on silicon under mild conditions.

PubMed

Ciampi, Simone; Luais, Erwann; James, Michael; Choudhury, Moinul H; Darwish, Nadim A; Gooding, J Justin

2014-05-07

We report on an exceedingly mild chemical functionalization of hydrogen-terminated Si(100) with unactivated and unprotected bifunctional α,ω-dialkynes. Monolayer formation occurs rapidly in the dark, and at room temperature, from dilute solutions of an aromatic-conjugated acetylene. The method addresses the poor reactivity of p-type substrates under mild conditions. We suggest the importance of several factors, including an optimal orientation for electron transfer between the adsorbate and the Si surface, conjugation of the acetylenic function with a π-system, as well as the choice of a solvent system that favors electron transfer and screens Coulombic interactions between surface holes and electrons. The passivated Si(100) electrode is amenable to further functionalization and shown to be a viable model system for redox studies at non-oxide semiconductor electrodes in aqueous solutions.

Bench-scale synthesis of nanoscale materials

NASA Technical Reports Server (NTRS)

Buehler, M. F.; Darab, J. G.; Matson, D. W.; Linehan, J. C.

1994-01-01

A novel flow-through hydrothermal method used to synthesize nanoscale powders is introduced by Pacific Northwest Laboratory. The process, Rapid Thermal Decomposition of precursors in Solution (RTDS), uniquely combines high-pressure and high-temperature conditions to rapidly form nanoscale particles. The RTDS process was initially demonstrated on a laboratory scale and was subsequently scaled up to accommodate production rates attractive to industry. The process is able to produce a wide variety of metal oxides and oxyhydroxides. The powders are characterized by scanning and transmission electron microscopic methods, surface-area measurements, and x-ray diffraction. Typical crystallite sizes are less than 20 nanometers, with BET surface areas ranging from 100 to 400 sq m/g. A description of the RTDS process is presented along with powder characterization results. In addition, data on the sintering of nanoscale ZrO2 produced by RTDS are included.

Vacuum ultraviolet trimming of oxygenated functional groups from oxidized self-assembled hexadecyl monolayers in an evacuated environment

NASA Astrophysics Data System (ADS)

Soliman, Ahmed I. A.; Utsunomiya, Toru; Ichii, Takashi; Sugimura, Hiroyuki

2017-09-01

Vacuum ultraviolet light irradiation in dry air generates active oxygen species, which have powerful oxidation abilities. These active oxygen species (O) can oxidize the alkyl moieties of polymers, and generate new oxygenated groups such as OH, CHO and COOH groups. Reducing the oxygen content in the exposure environment decreases the rate of oxidation processes. In this study, we examined the influences of the 172 nm VUV irradiation in a high vacuum (HV, < 10-3 Pa) environment on the chemical constituents, surface properties and morphological structure of well-defined VUV/(O)-modified hexadecyl (HD-) self-assembled monolayer (SAM) prepared on hydrogen-terminated silicon (H-Si) substrate. After VUV light irradiation in a HV environment (HV-VUV), the chemical constituents and surface properties were changed in two distinct stages. At short irradiation time (the first stage), the Csbnd O and COO groups decreased rapidly, while the Cdbnd O groups slightly changed. The dissociation of nonderivatizable groups (such as ether (Csbnd Osbnd C) and ester (Csbnd COOsbnd C) groups) compensated the dissociated OH, CHO, Csbnd COsbnd C and COOH groups. With further irradiation (the second stage), the quantities of the oxygenated groups slightly decreased. The carbon skeleton (Csbnd C) of SAM was scarcely dissociated during the HV-VUV treatment. These chemical changes affected the surface properties, such as wettability and morphology.

Ultra-small (r<2 nm), stable (>1 year) copper oxide quantum dots with wide band gap

NASA Astrophysics Data System (ADS)

Talluri, Bhusankar; Prasad, Edamana; Thomas, Tiju

2018-01-01

Practical use of quantum dots (QDs) will rely on processes that enable (i) monodispersity, (ii) scalability, (iii) green approaches to manufacturing them. We demonstrate, a green, rapid, soft chemical, and industrial viable approach for obtaining quasi-spherical, ultra-small (size ∼2.4 ± 0.5 nm), stable (>1 yr), and monodispersed copper oxide QDs (r < 2 nm) based on digestive ripening (DR). These QDs show wide band gap (Eg∼5.3 eV), this substantial band gap increase is currently inexplicable using Brus' equation, and is likely due to surface chemistry of these strongly confined QDs. Capping with triethanolamine (TEA) results in reduction in the average particle diameter from 9 ± 4 nm to 2.4 ± 0.5 nm and an increase of zeta potential (ξ) from +12 ± 2 mV to +31 ± 2 mV. XPS and electron diffraction studies indicate that capped copper oxide QDs which have TEA chemisorbed on its surface are expected to partly stabilize Cu (I) resulting in mixed phase in these QDs. This result is likely to inform efforts that involve achieving monodisperse microstructures and nano-structures, of oxides with a tendency for multivalency.

Amperometric Biosensor Based on Zirconium Oxide/Polyethylene Glycol/Tyrosinase Composite Film for the Detection of Phenolic Compounds

PubMed Central

Ahmad, Nor Monica; Abdullah, Jaafar; Yusof, Nor Azah; Ab Rashid, Ahmad Hazri; Abd Rahman, Samsulida; Hasan, Md. Rakibul

2016-01-01

A phenolic biosensor based on a zirconium oxide/polyethylene glycol/tyrosinase composite film for the detection of phenolic compounds has been explored. The formation of the composite film was expected via electrostatic interaction between hexacetyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG), and zirconium oxide nanoparticles casted on screen printed carbon electrode (SPCE). Herein, the electrode was treated by casting hexacetyltrimethylammonium bromide on SPCE to promote a positively charged surface. Later, zirconium oxide was mixed with polyethylene glycol and the mixture was dropped cast onto the positively charged SPCE/CTAB. Tyrosinase was further immobilized onto the modified SPCE. Characterization of the prepared nanocomposite film and the modified SPCE surface was investigated by scanning electron microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Cyclic voltamogram (CV). The developed biosensor exhibits rapid response for less than 10 s. Two linear calibration curves towards phenol in the concentrations ranges of 0.075–10 µM and 10–55 µM with the detection limit of 0.034 µM were obtained. The biosensor shows high sensitivity and good storage stability for at least 30 days. PMID:27367738

Subsurface transport of orthophosphate in five agricultural watersheds, USA

USGS Publications Warehouse

Domagalski, Joseph L.; Johnson, Henry M.

2011-01-01

Concentrations of dissolved orthophosphate (ortho P) in the unsaturated zone, groundwater, tile drains, and groundwater/stream water interfaces were assessed in five agricultural watersheds to determine the potential for subsurface transport. Concentrations of iron oxides were measured in the aquifer material and adsorption of ortho P on oxide surfaces was assessed by geochemical modeling. Attenuation of ortho P in these aquifers was attributed primarily to sorption onto iron oxides, and in one location onto clay minerals. Only one location showed a clear indication of phosphorus transport to a stream from groundwater discharge, although groundwater did contribute to the stream load elsewhere. Subsurface ortho P movement at a site in California resulted in a plume down gradient from orchards, which was attenuated by a 200 m thick riparian zone with natural vegetation. Iron oxides had an effect on phosphorus movement and concentrations at all locations, and groundwater chemistry, especially pH, exerted a major control on the amount of phosphorus adsorbed. Groundwater pH at a site in Maryland was below 5 and that resulted in complete sequestration of phosphorus and no movement toward the stream. Geochemical modeling indicated that as the surfaces approached saturation, groundwater concentrations of ortho P rise rapidly.

Microstructure and high-temperature oxidation resistance of TiN/Ti3Al intermetallic matrix composite coatings on Ti6Al4V alloy surface by laser cladding

NASA Astrophysics Data System (ADS)

Zhang, Xiaowei; Liu, Hongxi; Wang, Chuanqi; Zeng, Weihua; Jiang, Yehua

2010-11-01

A high-temperature oxidation resistant TiN embedded in Ti3Al intermetallic matrix composite coating was fabricated on titanium alloy Ti6Al4V surface by 6kW transverse-flow CO2 laser apparatus. The composition, morphology and microstructure of the laser clad TiN/Ti3Al intermetallic matrix composite coating were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). In order to evaluate the high-temperature oxidation resistance of the composite coatings and the titanium alloy substrate, isothermal oxidation test was performed in a conventional high-temperature resistance furnace at 600°C and 800°C respectively. The result shows that the laser clad intermetallic composite coating has a rapidly solidified fine microstructure consisting of TiN primary phase (granular-like, flake-like, and dendrites), and uniformly distributed in the Ti3Al matrix. It indicates that a physical and chemical reaction between the Ti powder and AlN powder occurred completely under the laser irradiation. In addition, the microhardness of the TiN/Ti3Al intermetallic matrix composite coating is 844HV0.2, 3.4 times higher than that of the titanium alloy substrate. The high-temperature oxidation resistance test reveals that TiN/Ti3Al intermetallic matrix composite coating results in the better modification of high-temperature oxidation behavior than the titanium substrate. The excellent high-temperature oxidation resistance of the laser cladding layer is attributed to the formation of the reinforced phase TiN and Al2O3, TiO2 hybrid oxide. Therefore, the laser cladding TiN/Ti3Al intermetallic matrix composite coating is anticipated to be a promising oxidation resistance surface modification technique for Ti6Al4V alloy.

Surface reaction of SnII on goethite (α-FeOOH): surface complexation, redox reaction, reductive dissolution, and phase transformation.

PubMed

Dulnee, Siriwan; Scheinost, Andreas C

2014-08-19

To elucidate the potential risk of (126)Sn migration from nuclear waste repositories, we investigated the surface reactions of Sn(II) on goethite as a function of pH and Sn(II) loading under anoxic condition with O2 level < 2 ppmv. Tin redox state and surface structure were investigated by Sn K edge X-ray absorption spectroscopy (XAS), goethite phase transformations were investigated by high-resolution transmission electron microscopy and selected area electron diffraction. The results demonstrate the rapid and complete oxidation of Sn(II) by goethite and formation of Sn(IV) (1)E and (2)C surface complexes. The contribution of (2)C complexes increases with Sn loading. The Sn(II) oxidation leads to a quantitative release of Fe(II) from goethite at low pH, and to the precipitation of magnetite at higher pH. To predict Sn sorption, we applied surface complexation modeling using the charge distribution multisite complexation approach and the XAS-derived surface complexes. Log K values of 15.5 ± 1.4 for the (1)E complex and 19.2 ± 0.6 for the (2)C complex consistently predict Sn sorption across pH 2-12 and for two different Sn loadings and confirm the strong retention of Sn(II) even under anoxic conditions.

The kinetics of influenza-virus adsorption on iron oxide in the process of viral purification and concentration

PubMed Central

Larin, N. M.; Gallimore, P. H.

1971-01-01

This paper reports a study carried out to clarify the mechanisms involved in adsorption of influenza A and B viruses on iron oxide. Accordingly, the amounts of virus that are adsorbed from virus suspensions of varying concentrations per unit surface area of magnetic or non-magnetic oxide at fixed temperature and time have been determined. The principles involved are clearly the same as those involved in multiple equilibria during the interaction of particles with a large number of combining sites with different intrinsic affinity. Consequently, the amount of virus that is adsorbed per unit mass of iron oxide depends on the size of the adsorbent area, not on its magnetic property. Owing to a significant difference between the affinities of influenza A and B particles for the binding sites on iron oxide, unit surface area of the adsorbent is invariably capable of adsorbing significantly greater amounts of influenza A than B particles. The practical implications of these findings are that a better understanding of the mechanisms involved in virus adsorption on iron oxide will permit a more efficient separation of virus particles from impurities. The simplicity and the rapidity of the technique and the cheapness of the equipment required suggest that the iron oxide method is of great value for both small- or large-scale viral purification, whether it is used as a single step procedure or as a primary step followed by zonal separation. PMID:5291749

Development of PEGylated KMnF3 nanoparticles as a T1-weighted contrast agent: chemical synthesis, in vivo brain MR imaging, and accounting for high relaxivity

NASA Astrophysics Data System (ADS)

Liu, Zhi-Jun; Song, Xiao-Xia; Tang, Qun

2013-05-01

Magnetic nanoparticles consisting of manganese-based T1-weighted contrast agents have rapidly achieved clinical application, however low proton relaxivity impedes further development. In this report, by analyzing nanoparticles' surface oxidation states we propose the possible reason for the low r1 relaxivity of common MnO nanoparticles and develop PEGylated fluoroperovskite KMnF3 nanoparticles as new T1-weighted contrast agents, which exhibit the highest longitudinal relaxivity (r1 = 23.15 mM-1 s-1) among all the reported manganese-based T1-weighted contrast agents. We, for the first time, illustrate a typical example showing that the surface oxidation states of metal ions exposed on the nanoparticles' surfaces are able to influence not only the optical, magnetic, electronic or catalytic properties but also water proton longitudinal relaxivity when applied as an MRI contrast agent. Cytotoxicity tests demonstrate that the PEGylated KMnF3 nanoparticles are free from toxicity. Further in vivo MRI experiments distinctively depict fine anatomical features in brain imaging at a low dose of 5 mg of Mn per kg and possible removal from the kidneys due to their small size and biocompatibility.Magnetic nanoparticles consisting of manganese-based T1-weighted contrast agents have rapidly achieved clinical application, however low proton relaxivity impedes further development. In this report, by analyzing nanoparticles' surface oxidation states we propose the possible reason for the low r1 relaxivity of common MnO nanoparticles and develop PEGylated fluoroperovskite KMnF3 nanoparticles as new T1-weighted contrast agents, which exhibit the highest longitudinal relaxivity (r1 = 23.15 mM-1 s-1) among all the reported manganese-based T1-weighted contrast agents. We, for the first time, illustrate a typical example showing that the surface oxidation states of metal ions exposed on the nanoparticles' surfaces are able to influence not only the optical, magnetic, electronic or catalytic properties but also water proton longitudinal relaxivity when applied as an MRI contrast agent. Cytotoxicity tests demonstrate that the PEGylated KMnF3 nanoparticles are free from toxicity. Further in vivo MRI experiments distinctively depict fine anatomical features in brain imaging at a low dose of 5 mg of Mn per kg and possible removal from the kidneys due to their small size and biocompatibility. Electronic supplementary information (ESI) available: Experimental procedure for two types of MnO nanoparticles, T1-weighted mapping. See DOI: 10.1039/c3nr00721a

A sonochemical approach to the direct surface functionalization of superparamagnetic iron oxide nanoparticles with (3-aminopropyl)triethoxysilane.

PubMed

Sodipo, Bashiru Kayode; Aziz, Azlan Abdul

2014-01-01

We report a sonochemical method of functionalizing superparamagnetic iron oxide nanoparticles (SPION) with (3-aminopropyl)triethoxysilane (APTES). Mechanical stirring, localized hot spots and other unique conditions generated by an acoustic cavitation (sonochemical) process were found to induce a rapid silanization reaction between SPION and APTES. FTIR, XPS and XRD measurements were used to demonstrate the grafting of APTES on SPION. Compared to what was reported in literature, the results showed that the silanization reaction time was greatly minimized. More importantly, the product displayed superparamagnetic behaviour at room temperature with a more than 20% higher saturation magnetization.

Fabrication of free-standing, electrochemically active, and biocompatible graphene oxide-polyaniline and graphene-polyaniline hybrid papers.

PubMed

Yan, Xingbin; Chen, Jiangtao; Yang, Jie; Xue, Qunji; Miele, Philippe

2010-09-01

In this work, we report a low-cost technique via simple rapid-mixture polymerization of aniline using graphene oxide (GO) and graphene papers as substrates, respectively, to fabricate free-standing, flexible GO-polyaniline (PANI) and graphene-PANI hybrid papers. The morphology and microstructure of the obtained papers were characterized by FESEM, FTIR, Raman, and XRD. As results, nanostructural PANI can be deposited on the surfaces of GO and graphene papers, forming thin, lightweight, and flexible paperlike hybrid papers. The hybrid papers display a remarkable combination of excellent electrochemical performances and biocompatibility, making the paperlike materials attractive for new kinds of applications in biosciences.

Investigation of the oxidation behavior of dispersion stabilized alloys when exposed to a dynamic high temperature environment

NASA Technical Reports Server (NTRS)

Tenney, D. R.

1974-01-01

The oxidation behavior of TD-NiCr and TD-NiCrAlY alloys have been studied at 2000 and 2200 F in static and high speed flowing air environments. The TD-NiCrAlY alloys preoxidized to produce an Al2O3 scale on the surface showed good oxidation resistance in both types of environments. The TD-NiCr alloy which had a Cr2O3 oxide scale after preoxidation was found to oxidize more than an order of magnitude faster under the dynamic test conditions than at comparable static test conditions. Although Cr2O3 normally provides good oxidation protection, it was rapidly lost due to formation of volatile CrO3 when exposed to the high speed air stream. The preferred oxide arrangement for the dynamic test consisted of an external layer of NiO with a porous mushroom type morphology, an intermediate duplex layer of NiO and Cr2O3, and a continuous inner layer of Cr2O3 in contact with the alloy substrate. An oxidation model has been developed to explain the observed microstructure and overall oxidation behavior of all alloys.

Plasma Oxidation Of Silver And Zinc In Low-Emissivity Stacks

NASA Astrophysics Data System (ADS)

Ross, R. C.; Sherman, R.,; Bunger, R. A.; Nadel, S. J.

1987-11-01

The oxidation of silver and zinc films was studied by exposing metallic films to low-power 02 plasmas and analyzing the reacted films. This type of oxidation is an important phenomenon near the barrier layer in sputter-deposited metal-oxide/Ag/metal-oxide low-emissivity (low-e) coatings. Barrier layers generally are deposited on the Ag layer to prevent its degradation during subsequent 02 reactive sputtering. Both individual layers and complete stacks were studied. In addition, the thermal stability of plasma-oxidized Ag was examined. There are several important findings for the individual layers. Ag oxidizes rapidly in the plasma, forming Ag≍1.70 after complete reaction. Relative to the original Ag, the 9ide has -l.7 times greater thick-ness, >10 times higher electrical resistiv-ity (p), and increased surface roughness. Zn oxidizes slowly, at only -1% to 0.1% times the rate for Ag, and is thus more difficult to characterize. The results for individual layers are discussed as they relate to practical pro-perties of low-e stacks: the difficulty of obtaining complete barrier layer oxidation without partially degrading the Ag layer as well as the effects of heat treatment and aging.

Titanium dental implant surfaces obtained by anodic spark deposition - From the past to the future.

PubMed

Kaluđerović, Milena R; Schreckenbach, Joachim P; Graf, Hans-Ludwig

2016-12-01

Commercial titanium-based dental implants are obtained applying various methods such as machining, acid etching, anodization, plasma spraying, grit blasting or combination techniques yielding materials with smooth or micro-roughened surfaces. Those techniques are used to optimize the surface properties and to maximize biocompatibility and bioactivity with bone tissue. Present review is focused on the material surfaces obtained by anodic spark deposition (ASD). From the early 1980s till present, the results of numerous studies have shown that anodically oxidized surfaces with different dopants express a positive effect on osteoblasts behavior in vitro and osseointegration in vivo. Those surfaces demonstrated a high biocompatibility and rapid osseointegration in clinical application. This paper provides an overview of the preparation of implant surfaces by employing ASD process. Moreover, reviewed are clinically used ASD implant surfaces (Ticer, TiUnite, Osstem, etc.). The electrolyte variations in ASD process and their influence on surface properties are given herein. Using different electrolytes, anode voltages and temperatures, the above fabrication process can yield various surface morphologies from smooth to rough, porous surfaces. Furthermore, ASD enables thickening of oxide layers and enrichment with different dopands from used electrolyte, which hinder release of potentially toxic titanium ions in surrounding tissue. Particularly exciting results were achieved by calcium and phosphorus doping of the oxide layer (Ticer, ZL Microdent; TiUnite, Nobel Biocare Holding AB) which significantly increased the osteocompatibility. Ticer, a dental implant with anodically oxidized surface and the first among similar materials employed in clinical practice, was found to promote fast osteoblast cell differentiation and mineralization processes. Moreover, Ticer accelerate the integration with the bone, increase the bone/implant contact and improve primary and secondary stability of the implants. Additionally, potential innovations in this field such as fabrication of nanotubes on the implant surfaces as well as novel approaches (e.g. coating with proteins, nanostructured topography; combining implant body and surface derived from titanium and zirconia) are elaborated in this review. Besides, biochemical aspects on implant surface cell/tissue interaction are summarized. From the clinical point of view implant surfaces fabricated by ASD technology possess fast and improved osseointegration, high healing rates and long term prognosis. Copyright © 2016 Elsevier B.V. All rights reserved.

Swept Away: Resuspension of Bacterial Mats Regulates Benthic-Pelagic Exchange of Sulfur

NASA Astrophysics Data System (ADS)

Grant, Jonathan; Bathmann, Ulrich V.

1987-06-01

Filaments and extracellular material from colorless sulfur bacteria (Beggiatoa spp.) form extensive white sulfur mats on surface sediments of coastal, oceanic, and even deep-sea environments. These chemoautotrophic bacteria oxidize soluble reduced sulfur compounds and deposit elemental sulfur, enriching the sulfur content of surface sediment fivefold over that of deeper sediments. Laboratory flume experiments with Beggiatoa mats from an intertidal sandflat (Nova Scotia) demonstrated that even slight erosion of sediment causes a flux of 160 millimoles of sulfur per square meter per hour, two orders of magnitude greater than the flux produced by sulfur transformations involving either sulfate reduction or sulfide oxidation by benthic bacteria. These experiments indicate that resuspension of sulfur bacterial mats by waves and currents is a rapid mechanism by which sediment sulfur is recycled to the water column. Benthic communities thus lose an important storage intermediate for reduced sulfur as well as a high-quality bacterial food source for benthic grazers.

Acidic attack of perfluorinated alkyl ether lubricant molecules by metal oxide surfaces

NASA Technical Reports Server (NTRS)

Zehe, Michael J.; Faut, Owen D.

1989-01-01

The reactions of linear perfluoropolyalkylether (PFAE) lubricants with alpha-Fe2O3 and Fe2O3-based solid superacids were studied. The reaction with alpha-Fe2O3 proceeds in two stages. The first stage is an initial slow catalytic decomposition of the fluid. This reaction releases reactive gaseous products which attach the metal oxide and convert it to FeF3. The second stage is a more rapid decomposition of the fluid, effected by the surface FeF3. A study of the inital breakdown step was performed using alpha-Fe2O3, alpha-Fe2O3 preconverted to FeF3, and sulfate-promoted alpha-Fe2O3 superacids. The results indicate that the breakdown reaction involves acidic attack at fluorine atoms on acetal carbons in the linear PFAE. Possible approaches to combat the problem are outlined.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mihaela Grigore; Richard Sakurovs; David French

Gasification of coke contributes to its degradation in the blast furnace. In this study, the effect of gasification on the inherent catalytic minerals in cokes and their reciprocal influence on gasification are investigated. The catalytic mineral phases identified in the cokes used in this study were metallic iron, iron sulfides, and iron oxides. Metallic iron and pyrrhotite were rapidly oxidized during gasification to iron oxide. The catalysts had a strong influence on the apparent rates at the initial stages of reaction. As gasification proceeds, their effect on the reaction rate diminishes as a result of reducing the surface contact betweenmore » catalyst and carbon matrix because of carbon consumption around the catalyst particles; with extended burnout the reactivity of the coke becomes increasingly dependent on surface area. The reaction rate in the initial stages was also influenced by the particle size of the catalytic minerals; for a given catalytic iron level, the cokes whose catalytic minerals were more finely dispersed had a higher apparent reaction rate than cokes containing larger catalytic particles. Iron, sodium, and potassium in the amorphous phase did not appear to affect the reaction rate. 40 refs., 16 figs., 6 tabs.« less

Using Temperature-Dependent Phenomena at Oxide Surfaces for Species Recognition in Chemical Sensing.

NASA Astrophysics Data System (ADS)

Semancik, Steve; Meier, Douglas; Evju, Jon; Benkstein, Kurt; Boger, Zvi; Montgomery, Chip

2006-03-01

Nanostructured films of SnO2 and TiO2 have been deposited on elements in MEMS arrays to fabricate solid state conductometric gas microsensors. The multilevel platforms within an array, called microhotplates, are individually addressable for localized temperature control and measurement of sensing film electrical conductance. Temperature variations of the microhotplates are employed in thermally-activated CVD oxide film growth, and for rapid temperature-programmed operation of the microsensors. Analytical information on environmental gas phase composition is produced temporally as purposeful thermal fluctuations provide energetic and kinetic control of surface reaction and adsorption/desorption phenomena. Resulting modulations of oxide adsorbate populations cause changing charge transfer behavior and measurable conductance responses. Rich data streams from different sensing films in the arrays have been analyzed by Artificial Neural Networks (ANN) to successfully recognize low concentration species in mixed gases. We illustrate capabilities of the approach and technology in the homeland security area, where dangerous chemicals (TICs, CWSs and CWAs) have been detected at 10-100 ppb levels in interference-spiked air backgrounds.

Stabilization of Titanium Dioxide Nanoparticles at the Surface of Carbon Nanomaterials Promoted by Microwave Heating.

PubMed

Zhang, Rui; Santangelo, Saveria; Fazio, Enza; Neri, Fortunato; D'Arienzo, Massimiliano; Morazzoni, Franca; Zhang, Yihe; Pinna, Nicola; Russo, Patrícia A

2015-10-12

TiO2 is frequently combined with carbon materials, such as reduced graphene oxide (RGO), to produce composites with improved properties, for example for photocatalytic applications. It is shown that heating conditions significantly affect the interface and photocatalytic properties of TiO2 @C, and that microwave irradiation can be advantageous for the synthesis of carbon-based materials. Composites of TiO2 with RGO or amorphous carbon were prepared from reaction of titanium isopropoxide with benzyl alcohol. During the synthesis of the TiO2 nanoparticles, the carbon is involved in reactions that lead to the covalent attachment of the oxide, the extent of which depends on the carbon characteristics, heating rate, and mechanism. TiO2 is more efficiently stabilized at the surface of RGO than amorphous carbon. Rapid heating of the reaction mixture results in a stronger coupling between the nanoparticles and carbon, more uniform coatings, and smaller particles with narrower size distributions. The more efficient attachment of the oxide leads to better photocatalytic performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fabrication of highly textured lithium cobalt oxide films by rapid thermal annealing

DOEpatents

Bates, John B.

2003-04-29

Systems and methods are described for fabrication of highly textured lithium cobalt oxide films by rapid thermal annealing. A method of forming a lithium cobalt oxide film includes depositing a film of lithium cobalt oxide on a substrate; rapidly heating the film of lithium cobalt oxide to a target temperature; and maintaining the film of lithium cobalt oxide at the target temperature for a target annealing time of at most, approximately 60 minutes. The systems and methods provide advantages because they require less time to implement and are, therefore less costly than previous techniques.

Fabrication of highly textured lithium cobalt oxide films by rapid thermal annealing

DOEpatents

Bates, John B.

2002-01-01

Systems and methods are described for fabrication of highly textured lithium cobalt oxide films by rapid thermal annealing. A method of forming a lithium cobalt oxide film includes depositing a film of lithium cobalt oxide on a substrate; rapidly heating the film of lithium cobalt oxide to a target temperature; and maintaining the film of lithium cobalt oxide at the target temperature for a target annealing time of at most, approximately 60 minutes. The systems and methods provide advantages because they require less time to implement and are, therefore less costly than previous techniques.

Fabrication of highly textured lithium cobalt oxide films by rapid thermal annealing

DOEpatents

Bates, John B.

2003-05-13

Systems and methods are described for fabrication of highly textured lithium cobalt oxide films by rapid thermal annealing. A method of forming a lithium cobalt oxide film includes depositing a film of lithium cobalt oxide on a substrate; rapidly heating the film of lithium cobalt oxide to a target temperature; and maintaining the film of lithium cobalt oxide at the target temperature for a target annealing time of at most, approximately 60 minutes. The systems and methods provide advantages because they require less time to implement and are, therefore less costly than previous techniques.

Rapid and controllable perforation of carbon nanotubes by microwave radiation

NASA Astrophysics Data System (ADS)

Ojaghi, Neda; Mokhtarifar, Maryam; Sabaghian, Zahra; Arab, Hamed; Maghrebi, Morteza; Baniadam, Majid

2018-05-01

This study presents a new controlled approach to deep perforation of millimeter-long carbon nanotube arrays (CNTAs) by fast oxidative cutting. The approach is based on decorating CNTAs with silver (Ag) nanoparticles, followed by heating Ag-decorated CNTAs with microwave radiation (2.48 GHz, 300 W). The perforation was evaluated using different techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller method. The results of the oxidation of carbonaceous materials indicated that the relative amount of oxygen functional groups increased without total oxidation of carbon up to 60 s. After 60 s, the amount of functional groups decreased as the total oxidation started suddenly. Afterwards, at around 120 and 420 s, the oxidation of Ag-decorated CNTAs reached the point of total perforation and total cutting, respectively. Though carbon decomposition terminated at around 420 s, the total pore volume and surface area increased continuously. This was attributed to the steady growth of Ag nanoparticles located between CNTAs.

Dopants Diffusion in Silicon during Molecular Oxygen/nitrogen Trifluoride Oxidation and Related Phenomena

NASA Astrophysics Data System (ADS)

Kim, U. S.

1990-01-01

To date, chlorine has been used as useful additives in silicon oxidation. However, rapid scaling of device dimensions motivates the development of a new dielectric layer or modification of the silicon dioxide itself. More recently, chemically enhanced thermal oxidation by the use of fluorine containing species has been introduced to verify the potential of fluorine in the silicon oxidation process. In this study, gaseous nitrogen trifluoride (NF _3) was selected as the fluorine oxidizing source based on ease of use and was compared with the dichlorofluoroethane (C_2H _3Cl_2F) source. Two different kinds of boron marker samples were prepared and oxidized in O_2/NF_3 ambient for the comparison of surface vs bulk oxidation enhanced/retarded diffusion (OED/ORD). The phosphorus, arsenic and antimony diffusion in silicon during fluorine oxidation has been studied using the various covering layers such as SiO_2, Si_3 N_4, and SiO_2 + Si_3N_4 layers. The oxidation related phenomena, i.e. enhanced silicon and silicon nitride oxidation in fluorine ambient were studied and correlated with the point defect balance at the oxidizing interface. The results of this investigation were discussed with special emphasis on the effect of fluorine on enhanced oxidation and dopant diffusion.

Sprayed zinc oxide films: Ultra-violet light-induced reversible surface wettability and platinum-sensitization-assisted improved liquefied petroleum gas response.

PubMed

Nakate, Umesh T; Patil, Pramila; Bulakhe, R N; Lokhande, C D; Kale, Sangeeta N; Naushad, Mu; Mane, Rajaram S

2016-10-15

We report the rapid (superhydrophobic to superhydrophilic) transition property and improvement in the liquefied petroleum gas (LPG) sensing response of zinc oxide (ZnO) nanorods (NRs) on UV-irradiation and platinum (Pt) surface sensitization, respectively. The morphological evolution of ZnO NRs is evidenced from the field emission scanning electron microscope and atomic force microscope digital images and for the structural elucidation X-ray diffraction pattern is used. Elemental survey mapping is obtained from energy dispersive X-ray analysis spectrum. The optical properties have been studied by UV-Visible and photoluminescence spectroscopy measurements. The rapid (120sec) conversion of superhydrophobic (154°) ZnO NRs film to superhydrophilic (7°) is obtained under UV light illumination and the superhydrophobicity is regained by storing sample in dark. The mechanism for switching wettability behavior of ZnO NRs has thoroughly been discussed. In second phase, Pt-sensitized ZnO NRs film has demonstrated considerable gas sensitivity at 260ppm concentration of LPG. At 623K operating temperature, the maximum LPG response of 58% and the response time of 49sec for 1040ppm LPG concentration of Pt- sensitized ZnO NRs film are obtained. This higher LPG response of Pt-sensitized ZnO NRs film over pristine is primarily due to electronic effect and catalytic effect (spill-over effect) caused by an additional of Pt on ZnO NRs film surface. Copyright © 2016 Elsevier Inc. All rights reserved.

Superhydrophobic Ceramic Coatings by Solution Precursor Plasma Spray

PubMed Central

Cai, Yuxuan; Coyle, Thomas W.; Azimi, Gisele; Mostaghimi, Javad

2016-01-01

This work presents a novel coating technique to manufacture ceramic superhydrophobic coatings rapidly and economically. A rare earth oxide (REO) was selected as the coating material due to its hydrophobic nature, chemical inertness, high temperature stability, and good mechanical properties, and deposited on stainless steel substrates by solution precursor plasma spray (SPPS). The effects of various spraying conditions including standoff distance, torch power, number of torch passes, types of solvent and plasma velocity were investigated. The as-sprayed coating demonstrated a hierarchically structured surface topography, which closely resembles superhydrophobic surfaces found in nature. The water contact angle on the SPPS superhydrophobic coating was up to 65% higher than on smooth REO surfaces. PMID:27091306

Remedial Investigation Addendum Report Data Item A009. Volume 1: Report Test

DTIC Science & Technology

1993-12-01

depending on chemical form and oxidation state. Environmentally, chromium exists primarily as trivalent and hexavalent compounds. Hexavalent forms are...intracellularly (Goyer, 1991). Hexavalent chromium compounds are found to predominate in air, surface waters, and groundwaters, while the trivalent forms dominate...in sediments and soils (USEPA, 1984b). Chromium in biological samples and foods exists almost exclusively in the trivalent state because of the rapid

Pulsed sonication for alumina coatings on high-capacity oxides: Performance in lithium-ion cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pol, Vilas G.; Li, Yan; Dogan, Fulya

2014-07-01

High-capacity xLi2MnO3•(1-x)LiMO2 (M=Ni, Mn, Co) oxides show relatively rapid performance degradation when cycled at voltages >4.5V vs. Li/Li+. Previous research has indicated that modifying the oxide surfaces with coatings, such as alumina, reduces cell impedance rise and improves capacity retention. In this article, we demonstrate pulsed-sonication as a rapid and effective approach for coating alumina on Li1.2Ni0.175Mn0.525Co0.1O2 (0.5Li2MnO3•0.5LiNi0.44Mn0.31Co0.25O2) particles. Oxide integrity and morphology is maintained after the sonochemical process and subsequent heat-treatment. Energy dispersive spectroscopy (EDS) X-ray elemental maps show uniform coating of all secondary particles. 27Al Magic Angle Spinning (MAS) NMR data confirm the presence of alumina and mainlymore » indicate octahedral aluminum occupancy in a six-coordinate environment with oxygen. Full cells containing electrodes with the alumina-coated particles demonstrate lower initial impedance rise and better capacity retention during extended cycling to high voltages. However, the coating has a negligible effect on the voltage hysteresis and voltage fade behavior displayed by these oxides. The various data indicate that the pulsed sonochemical technique is a viable approach for coating oxide particles. The methodology described herein can easily be extended beyond alumina to include coatings such as AlF3, MgO, and MgF2.« less

Activated Carbon Fibers "Thickly Overgrown" by Ag Nanohair Through Self-Assembly and Rapid Thermal Annealing

NASA Astrophysics Data System (ADS)

Yan, Xuefeng; Xu, Sijun; Wang, Qiang; Fan, Xuerong

2017-11-01

Anisotropic nanomaterial-modified carbon fibers attract increasing attention because of their superior properties over traditional ones. In this study, activated carbon fibers (ACFs) "thickly overgrown" by Ag nanohair were prepared through self-assembly and rapid thermal annealing. Viscose fibers with well-dispersed silver nanoparticles (AgNPs) on surfaces were first prepared through self-assembly of hyperbranched poly(amino-amine) (HBPAA)-capped AgNPs on viscose surfaces. HBPAA endowed the AgNP surfaces with negative charges and abundant amino groups, allowing AgNPs to monodispersively self-assemble to fiber surfaces. Ag nanohair-grown ACFs were prepared by sequential pre-oxidation and carbonization. Because the carbonization furnace was open-ended, ACFs are immediately transferrable to the outside of the furnace. Therefore, the Ag liquid adsorbed by ACF pores squeezed out to form Ag nanowires through thermal contraction. FESEM characterization indicated that Ag nanohairs stood on ACF surface and grew from ACF caps. XPS and XRD characterization showed that Ag successfully assembled to fiber surfaces and retained its metallic state even after high-temperature carbonization. TG analysis suggested that Ag nanohair-grown ACFs maintained their excellent thermal stabilities. Finally, the fabricated ACFs showed excellent and durable antibacterial activities, and the developed method may provide a potential strategy for preparing metal nanowire-grown ACFs.

Metal fires and their implications for advanced reactors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nowlen, Steven Patrick; Figueroa, Victor G.; Olivier, Tara Jean

This report details the primary results of the Laboratory Directed Research and Development project (LDRD 08-0857) Metal Fires and Their Implications for Advance Reactors. Advanced reactors may employ liquid metal coolants, typically sodium, because of their many desirable qualities. This project addressed some of the significant challenges associated with the use of liquid metal coolants, primary among these being the extremely rapid oxidation (combustion) that occurs at the high operating temperatures in reactors. The project has identified a number of areas for which gaps existed in knowledge pertinent to reactor safety analyses. Experimental and analysis capabilities were developed in thesemore » areas to varying degrees. In conjunction with team participation in a DOE gap analysis panel, focus was on the oxidation of spilled sodium on thermally massive surfaces. These are spills onto surfaces that substantially cool the sodium during the oxidation process, and they are relevant because standard risk mitigation procedures seek to move spill environments into this regime through rapid draining of spilled sodium. While the spilled sodium is not quenched, the burning mode is different in that there is a transition to a smoldering mode that has not been comprehensively described previously. Prior work has described spilled sodium as a pool fire, but there is a crucial, experimentally-observed transition to a smoldering mode of oxidation. A series of experimental measurements have comprehensively described the thermal evolution of this type of sodium fire for the first time. A new physics-based model has been developed that also predicts the thermal evolution of this type of sodium fire for the first time. The model introduces smoldering oxidation through porous oxide layers to go beyond traditional pool fire analyses that have been carried out previously in order to predict experimentally observed trends. Combined, these developments add significantly to the safety analysis capabilities of the advanced-reactor community for directly relevant scenarios. Beyond the focus on the thermally-interacting and smoldering sodium pool fires, experimental and analysis capabilities for sodium spray fires have also been developed in this project.« less

Rapid Detection of Escherichia coli O157:H7 in Fresh Lettuce Based on Localized Surface Plasmon Resonance Combined with Immunomagnetic Separation.

PubMed

Lee, Nari; Choi, Sung-Wook; Chang, Hyun-Joo; Chun, Hyang Sook

2018-05-01

This study presents a method for rapid detection of Escherichia coli O157:H7 in fresh lettuce based on the properties of target separation and localized surface plasmon resonance of immunomagnetic nanoparticles. The multifunctional immunomagnetic nanoparticles enabling simultaneous separation and detection were prepared by synthesizing magnetic nanoparticles (ca. 10 nm in diameter) composed of an iron oxide (Fe 3 O 4 ) core and gold shell and then conjugating these nanoparticles with the anti- E. coli O157:H7 antibodies. The application of multifunctional immunomagnetic nanoparticles for detecting E. coli O157:H7 in a lettuce matrix allowed detection of the presence of <1 log CFU mL -1 without prior enrichment. In contrast, the detection limit of the conventional plating method was 2.74 log CFU mL -1 . The method, which requires no preenrichment, provides an alternative to conventional microbiological detection methods and can be used as a rapid screening tool for a large number of food samples.

Aerobic cometabolic degradation of trichloroethene by methane and ammonia oxidizing microorganisms naturally associated with Carex comosa roots.

PubMed

Powell, C L; Nogaro, G; Agrawal, A

2011-06-01

The degradation potential of trichloroethene by the aerobic methane- and ammonia-oxidizing microorganisms naturally associated with wetland plant (Carex comosa) roots was examined in this study. In bench-scale microcosm experiments with washed (soil free) Carex comosa roots, the activity of root-associated methane- and ammonia-oxidizing microorganisms, which were naturally present on the root surface and/or embedded within the roots, was investigated. Significant methane and ammonia oxidation were observed reproducibly in batch reactors with washed roots incubated in growth media, where methane oxidation developed faster (2 weeks) compared to ammonia oxidation (4 weeks) in live microcosms. After enrichment, the methane oxidizers demonstrated their ability to degrade 150 μg l(-1) TCE effectively at 1.9 mg l(-1) of aqueous CH(4). In contrast, ammonia oxidizers showed a rapid and complete inhibition of ammonia oxidation with 150 μg l(-1) TCE at 20 mg l(-1) of NH(4)(+)-N, which may be attributed to greater sensitivity of ammonia oxidizers to TCE or its degradation product. No such inhibitory effect of TCE degradation was detected on methane oxidation at the above experimental conditions. The results presented here suggest that microorganisms associated with wetland plant roots can assist in the natural attenuation of TCE in contaminated aquatic environments.

Depth profiles of oxygen precipitates in nitride-coated silicon wafers subjected to rapid thermal annealing

NASA Astrophysics Data System (ADS)

Voronkov, V. V.; Falster, R.; Kim, TaeHyeong; Park, SoonSung; Torack, T.

2013-07-01

Silicon wafers, coated with a silicon nitride layer and subjected to high temperature Rapid Thermal Annealing (RTA) in Ar, show—upon a subsequent two-step precipitation anneal cycle (such as 800 °C + 1000 °C)—peculiar depth profiles of oxygen precipitate densities. Some profiles are sharply peaked near the wafer surface, sometimes with a zero bulk density. Other profiles are uniform in depth. The maximum density is always the same. These profiles are well reproduced by simulations assuming that precipitation starts from a uniformly distributed small oxide plates originated from RTA step and composed of oxygen atoms and vacancies ("VO2 plates"). During the first step of the precipitation anneal, an oxide layer propagates around this core plate by a process of oxygen attachment, meaning that an oxygen-only ring-shaped plate emerges around the original plate. These rings, depending on their size, then either dissolve or grow during the second part of the anneal leading to a rich variety of density profiles.

Layer-by-Layer Assembly of a Self-Healing Anticorrosion Coating on Magnesium Alloys.

PubMed

Fan, Fan; Zhou, Chunyu; Wang, Xu; Szpunar, Jerzy

2015-12-16

Fabrication of self-healing anticorrosion coatings has attracted attention as it has the ability to extend the service life and prevent the substrate from corrosive attack. However, a coating system with a rapid self-healing ability and an improved corrosion resistance is rarely reported. In this work, we developed a self-healing anticorrosion coating on a magnesium alloy (AZ31). The coating comprises a cerium-based conversion layer, a graphene oxide layer, and a branched poly(ethylene imine) (PEI)/poly(acrylic acid) (PAA) multilayer. We incorporated the graphene oxide as corrosion inhibitors and used the PEI/PAA multilayers to provide the self-healing ability to the coating systems. X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the composition of the multilayers, and scanning electron microscopy (SEM) was used to analyze the surface morphology. The electrochemical impedance spectroscopy (EIS) results illustrate the improved corrosion resistance of the coating. The proposed coating also has a rapid self-healing ability in the presence of water.

Unlocking Chain Exchange in Highly Amphiphilic Block Polymer Micellar Systems: Influence of Agitation.

PubMed

Murphy, Ryan P; Kelley, Elizabeth G; Rogers, Simon A; Sullivan, Millicent O; Epps, Thomas H

2014-11-18

Chain exchange between block polymer micelles in highly selective solvents, such as water, is well-known to be arrested under quiescent conditions, yet this work demonstrates that simple agitation methods can induce rapid chain exchange in these solvents. Aqueous solutions containing either pure poly(butadiene- b -ethylene oxide) or pure poly(butadiene- b -ethylene oxide- d 4 ) micelles were combined and then subjected to agitation by vortex mixing, concentric cylinder Couette flow, or nitrogen gas sparging. Subsequently, the extent of chain exchange between micelles was quantified using small angle neutron scattering. Rapid vortex mixing induced chain exchange within minutes, as evidenced by a monotonic decrease in scattered intensity, whereas Couette flow and sparging did not lead to measurable chain exchange over the examined time scale of hours. The linear kinetics with respect to agitation time suggested a surface-limited exchange process at the air-water interface. These findings demonstrate the strong influence of processing conditions on block polymer solution assemblies.

Thermal gelation and tissue adhesion of biomimetic hydrogels

PubMed Central

Burke, Sean A; Ritter-Jones, Marsha; Lee, Bruce P; Messersmith, Phillip B

2008-01-01

Marine and freshwater mussels are notorious foulers of natural and manmade surfaces, secreting specialized protein adhesives for rapid and durable attachment to wet substrates. Given the strong and water-resistant nature of mussel adhesive proteins, significant potential exists for mimicking their adhesive characteristics in bioinspired synthetic polymer materials. An important component of these proteins is L-3,4-dihydroxylphenylalanine (DOPA), an amino acid believed to contribute to mussel glue solidification through oxidation and crosslinking reactions. Synthetic polymers containing DOPA residues have previously been shown to crosslink into hydrogels upon the introduction of oxidizing reagents. Here we introduce a strategy for stimuli responsive gel formation of mussel adhesive protein mimetic polymers. Lipid vesicles with a bilayer melting transition of 37 °C were designed from a mixture of dipalmitoyl and dimyristoyl phosphatidylcholines and exploited for the release of a sequestered oxidizing reagent upon heating from ambient to physiologic temperature. Colorimetric studies indicated that sodium-periodate-loaded liposomes released their cargo at the phase transition temperature, and when used in conjunction with a DOPA-functionalized poly(ethylene glycol) polymer gave rise to rapid solidification of a crosslinked polymer hydrogel. The tissue adhesive properties of this biomimetic system were determined by in situ thermal gelation of liposome/polymer hydrogel between two porcine dermal tissue surfaces. Bond strength measurements showed that the bond formed by the adhesive hydrogel (mean = 35.1 kPa, SD = 12.5 kPa, n = 11) was several times stronger than a fibrin glue control tested under the same conditions. The results suggest a possible use of this biomimetic strategy for repair of soft tissues. PMID:18458476

Rare earth element partitioning between hydrous ferric oxides and acid mine water during iron oxidation

USGS Publications Warehouse

Verplanck, P.L.; Nordstrom, D. Kirk; Taylor, Howard E.; Kimball, B.A.

2004-01-01

Ferrous iron rapidly oxidizes to Fe (III) and precipitates as hydrous Fe (III) oxides in acid mine waters. This study examines the effect of Fe precipitation on the rare earth element (REE) geochemistry of acid mine waters to determine the pH range over which REEs behave conservatively and the range over which attenuation and fractionation occur. Two field studies were designed to investigate REE attenuation during Fe oxidation in acidic, alpine surface waters. To complement these field studies, a suite of six acid mine waters with a pH range from 1.6 to 6.1 were collected and allowed to oxidize in the laboratory at ambient conditions to determine the partitioning of REEs during Fe oxidation and precipitation. Results from field experiments document that even with substantial Fe oxidation, the REEs remain dissolved in acid, sulfate waters with pH below 5.1. Between pH 5.1 and 6.6 the REEs partitioned to the solid phases in the water column, and heavy REEs were preferentially removed compared to light REEs. Laboratory experiments corroborated field data with the most solid-phase partitioning occurring in the waters with the highest pH. ?? 2004 Elsevier Ltd. All rights reserved.

Electrochemical label-free and sensitive nanobiosensing of DNA hybridization by graphene oxide modified pencil graphite electrode.

PubMed

Ahour, F; Shamsi, A

2017-09-01

Based on the strong interaction between single-stranded DNA (ss-DNA) and graphene material, we have constructed a novel label-free electrochemical biosensor for rapid and facile detection of short sequences ss-DNA molecules related to hepatitis C virus 1a using graphene oxide modified pencil graphite electrode. The sensing mechanism is based on the superior adsorption of single-stranded DNA to GO over double stranded DNA (ds-DNA). The intrinsic guanine oxidation signal measured by differential pulse voltammetry (DPV) has been used for duplex DNA formation detection. The probe ss-DNA adsorbs onto the surface of GO via the π- π* stacking interactions leading to a strong background guanine oxidation signal. In the presence of complementary target, formation of helix which has weak binding ability to GO induced ds-DNA to release from the electrode surface and significant variation in differential pulse voltammetric response of guanine bases. The results indicated that the oxidation peak current was proportional to the concentration of complementary strand in the range of 0.1 nM-0.5 μM with a detection limit of 4.3 × 10 -11  M. The simple fabricated electrochemical biosensor has high sensitivity, good selectivity, and could be applied as a new platform for a range of target molecules in future. Copyright © 2017 Elsevier Inc. All rights reserved.

A general strategy for the ultrafast surface modification of metals.

PubMed

Shen, Mingli; Zhu, Shenglong; Wang, Fuhui

2016-12-07

Surface modification is an essential step in engineering materials that can withstand the increasingly aggressive environments encountered in various modern energy-conversion systems and chemical processing industries. However, most traditional technologies exhibit disadvantages such as slow diffusion kinetics, processing difficulties or compatibility issues. Here, we present a general strategy for the ultrafast surface modification of metals inspired by electromigration, using aluminizing austenitic stainless steel as an example. Our strategy facilitates the rapid formation of a favourable ductile surface layer composed of FeCrAl or β-FeAl within only 10 min compared with several hours in conventional processes. This result indicates that electromigration can be used to achieve the ultrafast surface modification of metals and can overcome the limitations of traditional technologies. This strategy could be used to aluminize ultra-supercritical steam tubing to withstand aggressive oxidizing environments.

Potassium ions in SiO2: electrets for silicon surface passivation

NASA Astrophysics Data System (ADS)

Bonilla, Ruy S.; Wilshaw, Peter R.

2018-01-01

This manuscript reports an experimental and theoretical study of the transport of potassium ions in thin silicon dioxide films. While alkali contamination was largely researched in the context of MOSFET instability, recent reports indicate that potassium ions can be embedded into oxide films to produce dielectric materials with permanent electric charge, also known as electrets. These electrets are integral to a number of applications, including the passivation of silicon surfaces for optoelectronic devices. In this work, electric field assisted migration of ions is used to rapidly drive K+ into SiO2 and produce effective passivation of silicon surfaces. Charge concentrations of up to ~5  ×  1012 e cm-2 have been achieved. This charge was seen to be stable for over 1500 d, with decay time constants as high as 17 000 d, producing an effectively passivated oxide-silicon interface with SRV  <  7 cm s-1, in 1 Ω cm n-type material. This level of charge stability and passivation effectiveness has not been previously reported. Overall, this is a new and promising methodology to enhance surface passivation for the industrial manufacture of silicon optoelectronic devices.

Formation mechanism and adhesive strength of a hydroxyapatite/TiO2 composite coating on a titanium surface prepared by micro-arc oxidation

NASA Astrophysics Data System (ADS)

Liu, Shimin; Li, Baoe; Liang, Chunyong; Wang, Hongshui; Qiao, Zhixia

2016-01-01

A hydroxyapatite (HA)/TiO2 composite coating was prepared on a titanium surface by one-step micro-arc oxidation (MAO). The formation mechanism of the composite coating was investigated and the adhesion of the coating to the substrate was also measured. The results showed that flocculent structures could be obtained during the early stages of treatment. As the treatment period extended, increasing amounts of Ca-P precipitate appeared on the surface, and the flocculent morphology transformed into a plate-like morphology. Then the plate-like calcium and phosphate salt self-assembled to form flower-like apatite. The Ca/P atomic ratio gradually decreased, indicating that the amounts of Ca2+ ions which diffused into the coating decreased more rapidly than that of PO43- or HPO42-. The adhesive strength between the apatite and TiO2 coating was improved. This improvement is attributed to the interlocking effect between the apatite and TiO2 layer which formed simultaneously during the early stages of the one-step MAO. This study shows that it is a promising method to prepare bioactive coating on a titanium surface.

Surface modifications of dental implants.

PubMed

Stanford, C M

2008-06-01

Dental implant surface technologies have been evolving rapidly to enhance a more rapid bone formation on their surface and hold a potential to increase the predictability of expedited implant therapy. While implant outcomes have become highly predictable, there are sites and conditions that result in elevated implant loss. This paper reviews the impact of macro-retentive features which includes approaches to surface oxide modification, thread design, press-fit and sintered-bead technologies to increase predictability of outcomes. Implant designs that lead to controlled lateral compression of the bone can improve primary stability as long as the stress does not exceed the localized yield strength of the cortical bone. Some implant designs have reduced crestal bone loss by use of multiple cutting threads that are closely spaced, smoothed on the tip but designed to create a hoop-stress stability of the implant as it is completely seated in the osteotomy. Following the placement of the implant, there is a predictable sequence of bone turnover and replacement at the interface that allows the newly formed bone to adapt to microscopic roughness on the implant surface, and on some surfaces, a nanotopography (<10(-9) m scale) that has been shown to preferably influence the formation of bone. Newly emerging studies show that bone cells are exquisitely sensitive to these topographical features and will upregulate the expression of bone related genes for new bone formation when grown on these surfaces. We live in an exciting time of rapid changes in the modalities we can offer patients for tooth replacement therapy. Given this, it is our responsibility to be critical when claims are made, incorporate into our practice what is proven and worthwhile, and to continue to support and provide the best patient care possible.

Corrosion of bare carbon steel as a passive sensor to assess moisture availability for biological activity in Atacama Desert soils.

PubMed

Cáceres, Luis; Davila, Alfonso F; Soliz, Alvaro; Saldivia, Jessica

2018-02-28

Here we consider that the corrosion of polished bared metal coupons can be used as a passive sensor to detect or identify the lower limit of water availability suitable for biological activity in Atacama Desert soils or solid substrates. For this purpose, carbon steel coupons were deposited at selected sites along a west-east transect and removed at predetermined times for morphological inspection. The advantage of this procedure is that the attributes of the oxide layer (corrosion extent, morphology and oxide phases) can be considered as a fingerprint of the atmospheric moisture history at a given time interval. Two types of coupons were used, long rectangular shaped ones that were half-buried in a vertical position, and square shaped ones that were deposited on the soil surface. The morphological attributes observed by SEM inspection were found to correlate to the so-called humectation time which is determined from local meteorological parameters. The main finding was that the decreasing trend of atmospheric moisture along the transect was closely related to corrosion behaviour and water soil penetration. For instance, at the coastal site oxide phases formed on the coupon surface rapidly evolve into well-crystallized species, while at the driest inland site Lomas Bayas only amorphous oxide was observed on the coupons.

Corrosion of Bare Carbon Steel as a Passive Sensor to Assess Moisture Availability for Biological Activity in Atacama Desert Soils

NASA Technical Reports Server (NTRS)

Caceres, Luis; Davila, Alfonso F.; Soliz, Alvaro; Saldivia, Jessica

2018-01-01

In this work we suggest the corrosion of polished bared metal coupons as a passive sensor to detect or identify the lower limit of water availability that could be suitable for biological activity in the Atacama Desert on soil or solid substrates. For this purpose, carbon steel coupons were deposited in selected sites along a west-east transect and removed at predetermined times for morphological inspection. The advantage of this procedure is that the attributes of the oxide layer (corrosion extent, morphology and oxide phases) can be considered as a fingerprint of the atmospheric moisture history at a given time interval. Two types of coupons were used, a long rectangular shape that are half-buried in a vertical position, and square shape that are deposited on the soil surface. The morphological attributes observed by SEM inspection is correlated to the so-called humectation time which is determined from local meteorological parameters. The main result is that the decreasing trend of atmospheric moisture along the transect is closely related to corrosion behavior and water soil penetration. For instance, while in the coastal site oxide phases formed on the coupon surface rapidly evolve to well- crystallized species, in the driest inland site Lomas Bayas only amorphous oxide is observed.

Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals

PubMed Central

White, Gaye F.; Shi, Zhi; Shi, Liang; Wang, Zheming; Dohnalkova, Alice C.; Marshall, Matthew J.; Fredrickson, James K.; Zachara, John M.; Butt, Julea N.; Richardson, David J.; Clarke, Thomas A.

2013-01-01

The mineral-respiring bacterium Shewanella oneidensis uses a protein complex, MtrCAB, composed of two decaheme cytochromes, MtrC and MtrA, brought together inside a transmembrane porin, MtrB, to transport electrons across the outer membrane to a variety of mineral-based electron acceptors. A proteoliposome system containing a pool of internalized electron carriers was used to investigate how the topology of the MtrCAB complex relates to its ability to transport electrons across a lipid bilayer to externally located Fe(III) oxides. With MtrA facing the interior and MtrC exposed on the outer surface of the phospholipid bilayer, the established in vivo orientation, electron transfer from the interior electron carrier pool through MtrCAB to solid-phase Fe(III) oxides was demonstrated. The rates were 103 times higher than those reported for reduction of goethite, hematite, and lepidocrocite by S. oneidensis, and the order of the reaction rates was consistent with those observed in S. oneidensis cultures. In contrast, established rates for single turnover reactions between purified MtrC and Fe(III) oxides were 103 times lower. By providing a continuous flow of electrons, the proteoliposome experiments demonstrate that conduction through MtrCAB directly to Fe(III) oxides is sufficient to support in vivo, anaerobic, solid-phase iron respiration. PMID:23538304

Enhanced wet air oxidation : synergistic rate acceleration upon effluent recirculation

Treesearch

Matthew J. Birchmeier; Charles G. Hill; Carl J. Houtman; Rajai H. Atalla; Ira A. Weinstock

2000-01-01

Wet air oxidation (WAO) reactions of cellobiose, phenol, and syringic acid were carried out under mild conditions (155°C; 0.93MPa 02; soluble catalyst, Na5[PV2Mo10O40]). Initial oxidation rates were rapid but decreased to small values as less reactive oxidation products accumulated. Recalcitrant oxidation products were consumed more rapidly, however, if additional...

Inhibition of Sulfide Mineral Oxidation by Surface Coating Agents: Batch

NASA Astrophysics Data System (ADS)

Choi, J.; Ji, M. K.; Yun, H. S.; Park, Y. T.; Gee, E. D.; Lee, W. R.; Jeon, B.-H.

2012-04-01

Mining activities and mineral industries have impacted on rapid oxidation of sulfide minerals such as pyrite (FeS2) which leads to Acid Mine Drainage (AMD) formation. Some of the abandoned mines discharge polluted water without proper environmental remediation treatments, largely because of financial constraints in treating AMD. Magnitude of the problem is considerable, especially in countries with a long history of mining. As metal sulfides become oxidized during mining activities, the aqueous environment becomes acid and rich in many metals, including iron, lead, mercury, arsenic and many others. The toxic heavy metals are responsible for the environmental deterioration of stream, groundwater and soils. Several strategies to remediate AMD contaminated sites have been proposed. Among the source inhibition and prevention technologies, microencapsulation (coating) has been considered as a promising technology. The encapsulation is based on inhibition of O2 diffusion by surface coating agent and is expected to control the oxidation of pyrite for a long time. Potential of several surface coating agents for preventing oxidation of metal sulfide minerals from both Young-Dong coal mine and Il-Gwang gold mine were examined by conducting batch experiments and field tests. Powdered pyrite as a standard sulfide mineral and rock samples from two mine outcrops were mixed with six coating agents (KH2PO4, MgO and KMnO4 as chemical agents, and apatite, cement and manganite as mineral agents) and incubated with oxidizing agents (H2O2 or NaClO). Batch experiments with Young-Dong coal mine samples showed least SO42- production in presence of KMnO4 (16% sulfate production compared to no surface coating agents) or cement (4%) within 8 days. In the case of Il-Gwang mine samples, least SO42- production was observed in presence of KH2PO4 (8%) or cement (2%) within 8 days. Field-scale pilot tests at Il-Gwang site also showed that addition of KH2PO4 decreased sulfate production from 200 to 13 mg L-1 and reduced Cu and Mn from 8 and 3 mg L-1 to below the detection limits, respectively. The experimental results suggested that the amendment of surface coating agents can be a promising alternative for inhibition of sulfide oxidation at AMD sites.

Effect of N2 annealing on AlZrO oxide

NASA Astrophysics Data System (ADS)

Pétry, J.; Richard, O.; Vandervorst, W.; Conard, T.; Chen, J.; Cosnier, V.

2003-07-01

In the path to the introduction of high-k dielectric into integrated circuit components, a large number of challenges has to be solved. Subsequent to the film deposition, the high-k film is exposed to additional high-temperature anneals for polycrystalline Si activation but also to improve its own electrical properties. Hence, concerns can be raised regarding the thermal stability of these stacks upon annealing. In this study, we investigated the effect of N2 annealing (700 to 900 °C) of atomic layer chemical vapor deposition AlZrO layers using x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOFSIMS), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The effect of the Si surface preparation [H-Si, 0.5 nm rapid thermal oxide (RTO), Al2O3] on the modification of the high-k oxide and the interfacial layer upon annealing was also analyzed. Compositional changes can be observed for all temperature and surface preparations. In particular, we observe a segregation of Al(oxide) toward the surface of the mixed oxide. In addition, an increase of the Si concentration in the high-k film itself can be seen with a diffusion profile extending toward the surface of the film. On the other hand, the modification of the interfacial layer is strongly dependent on the system considered. In the case of mixed oxide grown on 0.5 nm RTO, no differences are observed between the as-deposited layer and the layer annealed at 700 °C. At 800 °C, a radical change occurs: The initial RTO layer seems to be converted into a mixed layer composed of the initial SiO2 and Al2O3 coming from the mixed oxide, however without forming an Al-silicate layer. A similar situation is found for anneals at 900 °C, as well. When grown on 1.5 nm Al2O3 on 0.5 nm RTO, the only difference with the previous system is the observation of an Al-silicate fraction in the interfacial layer for the as-deposited and 700 °C annealed samples, which disappears at higher temperatures. Finally, considering layers deposited on a H-Si surface, we observe a slight increase of the interfacial thickness after annealing at 700 °C and no further changes for a higher annealing temperature.

Iron oxidation stimulates organic matter decomposition in humid tropical forest soils.

PubMed

Hall, Steven J; Silver, Whendee L

2013-09-01

Humid tropical forests have the fastest rates of organic matter decomposition globally, which often coincide with fluctuating oxygen (O2 ) availability in surface soils. Microbial iron (Fe) reduction generates reduced iron [Fe(II)] under anaerobic conditions, which oxidizes to Fe(III) under subsequent aerobic conditions. We demonstrate that Fe (II) oxidation stimulates organic matter decomposition via two mechanisms: (i) organic matter oxidation, likely driven by reactive oxygen species; and (ii) increased dissolved organic carbon (DOC) availability, likely driven by acidification. Phenol oxidative activity increased linearly with Fe(II) concentrations (P < 0.0001, pseudo R(2)  = 0.79) in soils sampled within and among five tropical forest sites. A similar pattern occurred in the absence of soil, suggesting an abiotic driver of this reaction. No phenol oxidative activity occurred in soils under anaerobic conditions, implying the importance of oxidants such as O2 or hydrogen peroxide (H2 O2 ) in addition to Fe(II). Reactions between Fe(II) and H2 O2 generate hydroxyl radical, a strong nonselective oxidant of organic compounds. We found increasing consumption of H2 O2 as soil Fe(II) concentrations increased, suggesting that reactive oxygen species produced by Fe(II) oxidation explained variation in phenol oxidative activity among samples. Amending soils with Fe(II) at field concentrations stimulated short-term C mineralization by up to 270%, likely via a second mechanism. Oxidation of Fe(II) drove a decrease in pH and a monotonic increase in DOC; a decline of two pH units doubled DOC, likely stimulating microbial respiration. We obtained similar results by manipulating soil acidity independently of Fe(II), implying that Fe(II) oxidation affected C substrate availability via pH fluctuations, in addition to producing reactive oxygen species. Iron oxidation coupled to organic matter decomposition contributes to rapid rates of C cycling across humid tropical forests in spite of periodic O2 limitation, and may help explain the rapid turnover of complex C molecules in these soils. © 2013 John Wiley & Sons Ltd.

Nano-scale investigation of the association of microbial nitrogen residues with iron (hydr)oxides in a forest soil O-horizon

NASA Astrophysics Data System (ADS)

Keiluweit, Marco; Bougoure, Jeremy J.; Zeglin, Lydia H.; Myrold, David D.; Weber, Peter K.; Pett-Ridge, Jennifer; Kleber, Markus; Nico, Peter S.

2012-10-01

Amino sugars in fungal cell walls (such as chitin) represent an important source of nitrogen (N) in many forest soil ecosystems. Despite the importance of this material in soil nitrogen cycling, comparatively little is known about abiotic and biotic controls on and the timescale of its turnover. Part of the reason for this lack of information is the inaccessibility of these materials to classic bulk extraction methods. To address this issue, we used advanced visualization tools to examine transformation pathways of chitin-rich fungal cell wall residues as they interact with microorganisms, soil organic matter and mineral surfaces. Our goal was to document initial micro-scale dynamics of the incorporation of 13C- and 15N-labeled chitin into fungi-dominated microenvironments in O-horizons of old-growth forest soils. At the end of a 3-week incubation experiment, high-resolution secondary ion mass spectrometry imaging of hyphae-associated soil microstructures revealed a preferential association of 15N with Fe-rich particles. Synchrotron-based scanning transmission X-ray spectromicroscopy (STXM/NEXAFS) of the same samples showed that thin organic coatings on these soil microstructures are enriched in aliphatic C and amide N on Fe (hydr)oxides, suggesting a concentration of microbial lipids and proteins on these surfaces. A possible explanation for the results of our micro-scale investigation of chemical and spatial patterns is that amide N from chitinous fungal cell walls was assimilated by hyphae-associated bacteria, resynthesized into proteinaceous amide N, and subsequently concentrated onto Fe (hydr)oxide surfaces. If confirmed in other soil ecosystems, such rapid association of microbial N with hydroxylated Fe oxide surfaces may have important implications for mechanistic models of microbial cycling of C and N.

Inherent substrate-dependent growth initiation and selective-area atomic layer deposition of TiO{sub 2} using “water-free” metal-halide/metal alkoxide reactants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atanasov, Sarah E.; Kalanyan, Berç; Parsons, Gregory N., E-mail: gnp@ncsu.edu

2016-01-15

Titanium dioxide atomic layer deposition (ALD) is shown to proceed selectively on oxidized surfaces with minimal deposition on hydrogen-terminated silicon using titanium tetrachloride (TiCl{sub 4}) and titanium tetra-isopropoxide [Ti(OCH(CH{sub 3}){sub 2}){sub 4}, TTIP] precursors. Ex situ x-ray photoelectron spectroscopy shows a more rapid ALD nucleation rate on both Si–OH and Si–H surfaces when water is the oxygen source. Eliminating water delays the oxidation of the hydrogen-terminated silicon, thereby impeding TiO{sub 2} film growth. For deposition at 170 °C, the authors achieve ∼2 nm of TiO{sub 2} on SiO{sub 2} before substantial growth takes place on Si–H. On both Si–H and Si–OH, themore » surface reactions proceed during the first few TiCl{sub 4}/TTIP ALD exposure steps where the resulting products act to impede subsequent growth, especially on Si–H surfaces. Insight from this work helps expand understanding of “inherent” substrate selective ALD, where native differences in substrate surface reaction chemistry are used to promote desired selective-area growth.« less

Transfer RNAs Mediate the Rapid Adaptation of Escherichia coli to Oxidative Stress

PubMed Central

Du, Gaofei; Sun, Xuesong; He, Qing-Yu; Zhang, Gong

2015-01-01

Translational systems can respond promptly to sudden environmental changes to provide rapid adaptations to environmental stress. Unlike the well-studied translational responses to oxidative stress in eukaryotic systems, little is known regarding how prokaryotes respond rapidly to oxidative stress in terms of translation. In this study, we measured protein synthesis from the entire Escherichia coli proteome and found that protein synthesis was severely slowed down under oxidative stress. With unchanged translation initiation, this slowdown was caused by decreased translation elongation speed. We further confirmed by tRNA sequencing and qRT-PCR that this deceleration was caused by a global, enzymatic downregulation of almost all tRNA species shortly after exposure to oxidative agents. Elevation in tRNA levels accelerated translation and protected E. coli against oxidative stress caused by hydrogen peroxide and the antibiotic ciprofloxacin. Our results showed that the global regulation of tRNAs mediates the rapid adjustment of the E. coli translation system for prompt adaptation to oxidative stress. PMID:26090660

Graphene Oxide-Promoted Reshaping and Coarsening of Gold Nanorods and Nanoparticles

PubMed Central

Pan, Hanqing; Low, Serena; Weerasuriya, Nisala; Shon, Young-Seok

2015-01-01

This paper describes thermally induced reshaping and coarsening behaviors of gold nanorods and nanoparticles immobilized on the surface of graphene oxide. Cetyltrimethylammonium bromide-stabilized gold nanorods with an aspect ratio of ~3.5 (54:15 nm) and glutathione-capped gold nanoparticles with an average core size of ~3 nm were synthesized and self-assembled onto the surface of graphene oxide. The hybrid materials were then heated at different temperatures ranging from 50 to 300 °C. The effects of heat treatments were monitored using UV–vis spectroscopy and transmission electron microscopy (TEM). These results were directly compared with those of heat-treated free-standing gold nanorods and nanoparticles without graphene oxide to understand the heat-induced morphological changes of the nanohybrids. The obtained results showed that the gold nanorods would undergo a complete reshaping to spherical particles at the temperature of 50 °C when they are assembled on graphene oxide. In comparison, the complete reshaping of free-standing gold nanorods to spherical particles would ultimately require a heating of the samples at 200 °C. In addition, the spherical gold nanoparticles immobilized on graphene oxide would undergo a rapid coarsening at the temperature of 100–150 °C, which was lower than the temperature (150–200 °C) required for visible coarsening of free-standing gold nanoparticles. The results indicated that graphene oxide facilitates the reshaping and coarsening of gold nanorods and nanoparticles, respectively, during the heat treatments. The stripping and spillover of stabilizing ligands promoted by graphene oxide are proposed to be the main mechanism for the enhancements in the heat-induced transformations of nanohybrids. PMID:25611371

Complement proteins bind to nanoparticle protein corona and undergo dynamic exchange in vivo

NASA Astrophysics Data System (ADS)

Chen, Fangfang; Wang, Guankui; Griffin, James I.; Brenneman, Barbara; Banda, Nirmal K.; Holers, V. Michael; Backos, Donald S.; Wu, Linping; Moghimi, Seyed Moein; Simberg, Dmitri

2017-05-01

When nanoparticles are intravenously injected into the body, complement proteins deposit on the surface of nanoparticles in a process called opsonization. These proteins prime the particle for removal by immune cells and may contribute toward infusion-related adverse effects such as allergic responses. The ways complement proteins assemble on nanoparticles have remained unclear. Here, we show that dextran-coated superparamagnetic iron oxide core-shell nanoworms incubated in human serum and plasma are rapidly opsonized with the third complement component (C3) via the alternative pathway. Serum and plasma proteins bound to the nanoworms are mostly intercalated into the nanoworm shell. We show that C3 covalently binds to these absorbed proteins rather than the dextran shell and the protein-bound C3 undergoes dynamic exchange in vitro. Surface-bound proteins accelerate the assembly of the complement components of the alternative pathway on the nanoworm surface. When nanoworms pre-coated with human plasma were injected into mice, C3 and other adsorbed proteins undergo rapid loss. Our results provide important insight into dynamics of protein adsorption and complement opsonization of nanomedicines.

Advancing the frontiers in nanocatalysis, biointerfaces, and renewable energy conversion by innovations of surface techniques.

PubMed

Somorjai, Gabor A; Frei, Heinz; Park, Jeong Y

2009-11-25

The challenge of chemistry in the 21st century is to achieve 100% selectivity of the desired product molecule in multipath reactions ("green chemistry") and develop renewable energy based processes. Surface chemistry and catalysis play key roles in this enterprise. Development of in situ surface techniques such as high-pressure scanning tunneling microscopy, sum frequency generation (SFG) vibrational spectroscopy, time-resolved Fourier transform infrared methods, and ambient pressure X-ray photoelectron spectroscopy enabled the rapid advancement of three fields: nanocatalysts, biointerfaces, and renewable energy conversion chemistry. In materials nanoscience, synthetic methods have been developed to produce monodisperse metal and oxide nanoparticles (NPs) in the 0.8-10 nm range with controlled shape, oxidation states, and composition; these NPs can be used as selective catalysts since chemical selectivity appears to be dependent on all of these experimental parameters. New spectroscopic and microscopic techniques have been developed that operate under reaction conditions and reveal the dynamic change of molecular structure of catalysts and adsorbed molecules as the reactions proceed with changes in reaction intermediates, catalyst composition, and oxidation states. SFG vibrational spectroscopy detects amino acids, peptides, and proteins adsorbed at hydrophobic and hydrophilic interfaces and monitors the change of surface structure and interactions with coadsorbed water. Exothermic reactions and photons generate hot electrons in metal NPs that may be utilized in chemical energy conversion. The photosplitting of water and carbon dioxide, an important research direction in renewable energy conversion, is discussed.

Evolutionary Optimization of a Charge Transfer Ionic Potential Model for Ta/Ta-Oxide Heterointerfaces

DOE PAGES

Sasikumar, Kiran; Narayanan, Badri; Cherukara, Mathew; ...

2017-03-19

Heterostructures of tantalum and its oxide are of tremendous technological interest for a myriad of technological applications, including electronics, thermal management, catalysis and biochemistry. In particular, local oxygen stoichiometry variation in TaO x memristors comprising of thermodynamically stable metallic (Ta) and insulating oxide (Ta 2O 5) have been shown to result in fast switching on the subnanosecond timescale over a billion cycles. This rapid switching opens up the potential for advanced functional platforms such as stateful logic operations and neuromorphic computation. Despite its broad importance, an atomistic scale understanding of oxygen stoichiometry variation across Ta/TaO x heterointerfaces, such as duringmore » early stages of oxidation and oxide growth, is not well understood. This is mainly due to the lack of a unified interatomic potential model for tantalum oxides that can accurately describe metallic (Ta), ionic (TaO x) as well as mixed (Ta/TaO x interfaces) bonding environments simultaneously. To address this challenge, we introduce a Charge Transfer Ionic Potential (CTIP) model for Ta/Ta-oxide system by training against lattice parameters, cohesive energies, equations of state (EOS), elastic properties, and surface energies of the various experimentally observed Ta 2O 5 polymorphs (hexagonal, orthorhombic and monoclinic) obtained from density functional theory (DFT) calculations. The best CTIP parameters are determined by employing a global optimization scheme driven by genetic algorithms followed by local Simplex optimization. Our newly developed CTIP potential accurately predicts structure, thermodynamics, energetic ordering of polymorphs, as well as elastic and surface properties of both Ta and Ta 2O 5, in excellent agreement with DFT calculations and experiments. We employ our newly parameterized CTIP potential to investigate the early stages of oxidation and atomic scale mechanisms associated with oxide growth on Ta surface at various temperatures. Furthermore, the CTIP potential developed in this work is an invaluable tool to investigate atomic-scale mechanisms and transport phenomena underlying the response of Ta/TaO x interfaces to external stimuli (e.g, temperature, pressure, strain, electric field etc.), as well as other interesting dynamical phenomena including the physics of switching dynamics in TaO x based memristors and neuromorphic devices.« less

Platinum nanoparticles decorated dendrite-like gold nanostructure on glassy carbon electrodes for enhancing electrocatalysis performance to glucose oxidation

NASA Astrophysics Data System (ADS)

Jia, Hongmei; Chang, Gang; Lei, Ming; He, Hanping; Liu, Xiong; Shu, Honghui; Xia, Tiantian; Su, Jie; He, Yunbin

2016-10-01

Platinum nanoparticles decorated dendrite-like gold nanostructure, bimetal composite materials on glassy carbon electrode (Pt/DGNs/GC) for enhancing electrocatalysis to glucose oxidation was designed and successfully fabricated by a facile two-step deposition method without any templates, surfactants, or stabilizers. Dendrite-like gold nanostructure was firstly deposited on the GC electrode via the potentiostatic method, and then platinum nanoparticles were decorated on the surface of gold substrate through chemical reduction deposition. X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) were applied to characterize the evolution of morphology and structure of the as-prepared Pt/DGNs/GC. Based on electrochemical measurements such as cyclic voltammetry, linear voltammetry and chronoamperometry, Pt/DGNs/GC exhibited significantly enhanced electrocatalytic performance to glucose oxidation compared those of pure dendrite-like Au nanoparticles in our previous report. Controlling chemical reduction deposition time, the amount of platinum nanoparticles on Au surface could be regulated, which further tuned electrocatalytic properties toward glucose oxidation. The dendrite-like gold surface partially covered by platinum nanoparticles dramatically enhanced the electrocatalytic performance for the oxidation of glucose because of excellent synergetic effects between gold and platinum species and the increased electrochemical active area from Pt nanoparticles loading. The non-enzymatic glucose biosensor based on Pt/DGNs/GC showed a rapid respond time (within 2 s), wide linear range (from 0.1 mM to 14 mM), low detection limit (0.01 mM), supernal sensitivity (275.44 μA cm-2 mM-1, R = 0.993), satisfactory reproducibility and good stability for glucose sensing. It was demonstrated that Pt/DGNs/GC could work as promising candidate for factual non-enzymatic glucose detection.

Preparation and Oxidation Performance of Y and Ce-Modified Cr Coating on open-cell Ni-Cr-Fe Alloy Foam by the Pack Cementation

NASA Astrophysics Data System (ADS)

Pang, Q.; Hu, Z. L.; Wu, G. H.

2016-12-01

Metallic foams with a high fraction of porosity, low density and high-energy absorption capacity are a rapidly emerging class of novel ultralight weight materials for various engineering applications. In this study, Y-Cr and Ce-Cr-coated Ni-Cr-Fe alloy foams were prepared via the pack cementation method, and the effects of Y and Ce addition on the coating microstructure and oxidation performance were analyzed in order to improve the oxidation resistance of open-cell nickel-based alloy foams. The results show that the Ce-Cr coating is relatively more uniform and has a denser distribution on the surface of the nickel-based alloy foam. The surface grains of the Ce-Cr-coated alloy foam are finer compared to those of the Y-Cr-coated alloy foam. An obvious Ce peak appears on the interface between the coating and the alloy foam strut, which gives rise to a "site-blocking" effect for the short-circuit transport of the cation in the substrate. X-ray diffraction analysis shows that the Y-Cr-coated alloy foam mainly consists of Cr, (Fe, Ni) and (Ni, Cr) phases in the surface layer. The Ce-Cr-coated alloy foam is mainly composed of Cr and (Ni, Cr) phases. Furthermore, the addition of Y and Ce clearly lead to an improvement in the oxidation resistance of the coated alloy foams in the temperature range of 900-1000 °C. The addition of Ce is especially effective in enhancing the diffusion of chromium to the oxidation front, thus, accelerating the formation of a Cr2O3 layer.

Rapid non-genomic effects of glucocorticoids on oxidative stress in a guinea pig model of asthma.

PubMed

Long, Fei; Wang, Yan; Qi, Hui-Hui; Zhou, Xin; Jin, Xian-Qiao

2008-03-01

Glucocorticoids (GC) may exert therapeutic effects in asthma by a rapid non-genomic mechanism. The lungs of asthmatic patients are exposed to oxidative stress, which is believed to be critical in the pathogenesis of asthma. The aim of this study was to investigate whether GC exert a rapid non-genomic effect on oxidative stress in asthmatic guinea pigs. The guinea pig asthma model was used to assess inhibitory effects of budesonide (BUD) on oxidative stress. BAL fluid (BALF), trolox equivalent antioxidant capacity and lung manganese superoxide dismutase (MnSOD) activity were measured by spectrophotometry. Superoxide anion production was measured by cytochrome c reduction assay. Oxidative stress occurred within minutes following antigen challenge and BUD reduced the severity of oxidative stress in asthmatic guinea pigs within 15 min. BUD significantly decreased BALF trolox equivalent antioxidant capacity and lung MnSOD activity, as compared with those of vehicle-treated asthmatic guinea pigs (P < 0.05). Additionally, BUD rapidly inhibited in vitro superoxide anion production by BALF cells and bronchi harvested from sensitized animals. These rapid effects were not blocked by the GC receptor antagonist RU486 and/or the protein synthesis inhibitor cycloheximide. BUD reduced oxidative stress in a guinea pig model of asthma by a rapid non-genomic mechanism. These data suggest new mechanisms whereby GC treatments may benefit asthma.

Rapid recipe formulation for plasma etching of new materials

NASA Astrophysics Data System (ADS)

Chopra, Meghali; Zhang, Zizhuo; Ekerdt, John; Bonnecaze, Roger T.

2016-03-01

A fast and inexpensive scheme for etch rate prediction using flexible continuum models and Bayesian statistics is demonstrated. Bulk etch rates of MgO are predicted using a steady-state model with volume-averaged plasma parameters and classical Langmuir surface kinetics. Plasma particle and surface kinetics are modeled within a global plasma framework using single component Metropolis Hastings methods and limited data. The accuracy of these predictions is evaluated with synthetic and experimental etch rate data for magnesium oxide in an ICP-RIE system. This approach is compared and superior to factorial models generated from JMP, a software package frequently employed for recipe creation and optimization.

Evaluation of support matrices for immobilization of anaerobic consortia for efficient carbon cycling in waste regeneration.

PubMed

Chauhan, Ashvini; Ogram, Andrew

2005-02-18

Efficient metabolism of fatty acids during anaerobic waste digestion requires development of consortia that include "fatty acid consuming H(2) producing bacteria" and methanogenic bacteria. The objective of this research was to optimize methanogenesis from fatty acids by evaluating a variety of support matrices for use in maintaining efficient syntrophic-methanogenic consortia. Tested matrices included clays (montmorillonite and bentonite), glass beads (106 and 425-600mum), microcarriers (cytopore, cytodex, cytoline, and cultispher; conventionally employed for cultivation of mammalian cell lines), BioSep beads (powdered activated carbon), and membranes (hydrophilic; nylon, polysulfone, and hydrophobic; teflon, polypropylene). Data obtained from headspace methane (CH(4)) analyses as an indicator of anaerobic carbon cycling efficiency indicated that material surface properties were important in maintenance and functioning of the anaerobic consortia. Cytoline yielded significantly higher CH(4) than other matrices as early as in the first week of incubation. 16S rRNA gene sequence analysis from crushed cytoline matrix showed the presence of Syntrophomonas spp. (butyrate oxidizing syntrophs) and Syntrophobacter spp. (propionate oxidizing syntrophs), with Methanosaeta spp. (acetate utilizing methanogen), and Methanospirillum spp. (hydrogen utilizing methanogen) cells. It is likely that the more hydrophobic surfaces provided a suitable surface for adherence of cells of syntrophic-methanogenic consortia. Cytoline also appeared to protect entrapped consortia from air, resulting in rapid methanogenesis after aerial exposure. Our study suggests that support matrices can be used in anaerobic digestors, pre-seeded with immobilized or entrapped consortia on support matrices, and may be of value as inoculant-adsorbents to rapidly initiate or recover proper system functioning following perturbation.

Effect of RE (Nd3+, Sm3+) oxide on structural, optical properties of Na2O-Li2O-ZnO-B2O3 glass system

NASA Astrophysics Data System (ADS)

Hivrekar, Mahesh M.; Bhoyar, D. N.; Mande, V. K.; Dhole, V. V.; Solunke, M. B.; Jadhav, K. M.

2018-05-01

Zinc borate glass activated with rare earth oxide (Nd2O3, Sm2O3) of Na2O-Li2O-ZnO-B2O3 quaternary system has been prepared successfully by melt quenching method. The nucleation and growth of RE oxide were controlled temperature range 950-1000° C and rapid cooling at room temperature. The physical, structural and optical properties were characterized by using X-ray diffraction (XRD), SEM, Ultraviolet-visible spectroscopy (UV-Vis). XRD and SEM studies confirmed the amorphous nature, surface morphology of prepared zinc borate glass. The physical parameters like density, molar volume, molar mass of Nd3+, Sm3+ doped borate glass are summarized in the present article. The optical absorption spectra along with tauc's plot are presented. The optical energy band gap increases due to the addition of rare earth oxide confirming the role of network modifier.

The tortoise versus the hare - Possible advantages of microparticulate zerovalent iron (mZVI) over nanoparticulate zerovalent iron (nZVI) in aerobic degradation of contaminants.

PubMed

Ma, Jinxing; He, Di; Collins, Richard N; He, Chuanshu; Waite, T David

2016-11-15

A comparative study of the ability of microparticulate zerovalent iron (mZVI) and nanoparticulate zerovalent iron (nZVI) to oxidize a target compound (in this study, 14 C-labelled formate) under aerobic conditions has been conducted with specific consideration given to differences in reaction mechanisms. Results of Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy showed that mZVI underwent a slow transformation to ferrihydrite while nZVI, in contrast, rapidly transformed into lepidocrocite. The behavior of mZVI (compared to nZVI) could be attributed to either (i) a lower reactivity with oxygen and/or water, (ii) surface passivation by ferrihydrite resulting in reduced electron conductivity, and/or (iii) the relatively low concentration of Fe(II) which, in the case of nZVI, catalyzed the transformation of ferrihydrite to lepidocrocite. The influence of these structural transformations on contaminant removal was profound with the ferrihydrite that formed on mZVI inducing rapid adsorption of formate and moderating reactions of mZVI with oxygen and/or water. Although surface passivation of mZVI was significant, the effectiveness of the ensuing heterogeneous redox reactions in the mZVI/O 2 system, as characterized by the molar ratio of oxidized formate to consumed Fe(0) (i.e., 13.7 ± 0.8 μM/M), was comparable to that for nZVI (16.5 ± 1.4 μM/M). The results of this study highlight the potential of mZVI for the oxidative degradation of target organics in preference to nZVI despite its lower intrinsic reactivity though some means (either natural or engineered) of inducing continual depassivation of the iron oxyhydroxide-coated mZVI would be required in order to maintain ongoing oxidant production. Copyright © 2016 Elsevier Ltd. All rights reserved.

A general strategy for the ultrafast surface modification of metals

PubMed Central

Shen, Mingli; Zhu, Shenglong; Wang, Fuhui

2016-01-01

Surface modification is an essential step in engineering materials that can withstand the increasingly aggressive environments encountered in various modern energy-conversion systems and chemical processing industries. However, most traditional technologies exhibit disadvantages such as slow diffusion kinetics, processing difficulties or compatibility issues. Here, we present a general strategy for the ultrafast surface modification of metals inspired by electromigration, using aluminizing austenitic stainless steel as an example. Our strategy facilitates the rapid formation of a favourable ductile surface layer composed of FeCrAl or β-FeAl within only 10 min compared with several hours in conventional processes. This result indicates that electromigration can be used to achieve the ultrafast surface modification of metals and can overcome the limitations of traditional technologies. This strategy could be used to aluminize ultra-supercritical steam tubing to withstand aggressive oxidizing environments. PMID:27924909

Effect of Rapid Thermal Annealing on the Electrical Characteristics of ZnO Thin-Film Transistors

NASA Astrophysics Data System (ADS)

Remashan, Kariyadan; Hwang, Dae-Kue; Park, Seong-Ju; Jang, Jae-Hyung

2008-04-01

Thin-film transistors (TFTs) with a bottom-gate configuration were fabricated with an RF magnetron sputtered undoped zinc oxide (ZnO) channel layer and plasma-enhanced chemical vapor deposition (PECVD) grown silicon nitride as a gate dielectric. Postfabrication rapid thermal annealing (RTA) and subsequent nitrous oxide (N2O) plasma treatment were employed to improve the performance of ZnO TFTs in terms of on-current and on/off current ratio. The RTA treatment increases the on-current of the TFT significantly, but it also increases its off-current. The off-current of 2×10-8 A and on/off current ratio of 3×103 obtained after the RTA treatment were improved to 10-10 A and 105, respectively, by the subsequent N2O plasma treatment. The better device performance can be attributed to the reduction of oxygen vacancies at the top region of the channel due to oxygen incorporation from the N2O plasma. X-ray photoelectron spectroscopy (XPS) analysis of the TFT samples showed that the RTA-treated ZnO surface has more oxygen vacancies than as-deposited samples, which results in the increased drain current. The XPS study also showed that the subsequent N2O plasma treatment reduces oxygen vacancies only at the surface of ZnO so that the better off-current and on/off current ratio can be obtained.

Oxide-free aC/Zr0.65Al0.075Cu0.275/aC phase plates for transmission electron microscopy.

PubMed

Dries, M; Obermair, M; Hettler, S; Hermann, P; Seemann, K; Seifried, F; Ulrich, S; Fischer, R; Gerthsen, D

2018-06-01

Thin-film phase plates (PP) have become a valuable tool for the imaging of organic objects in transmission electron microscopy (TEM). The thin film usually consists of amorphous carbon (aC), which undergoes rapid aging under intense illumination with high-energy electrons. The limited lifetime of aC film PPs calls for alternative PP materials with improved material stability. This work presents thin-film PPs fabricated from the metallic glass alloy Zr 0.65 Al 0.075 Cu 0.275 (ZAC), which was identified as a promising PP material with beneficial properties, such as a large inelastic mean free path. An adverse effect of the ZAC alloy is the formation of a surface oxide layer in ambient air, which reduces the electrical conductivity and causes electrostatic charging in the electron beam. To avoid surface oxidation, the ZAC alloy is enclosed by thin aC layers. The resulting aC/ZAC/aC layer system is used to fabricate Zernike and Hilbert PPs. Phase-contrast TEM imaging is demonstrated for a sample of carbon nanotubes, which show strong contrast enhancement in PP TEM images. Copyright © 2018 Elsevier B.V. All rights reserved.

Nonthermal dielectric-barrier discharge plasma-induced inactivation involves oxidative DNA damage and membrane lipid peroxidation in Escherichia coli.

PubMed

Joshi, Suresh G; Cooper, Moogega; Yost, Adam; Paff, Michelle; Ercan, Utku K; Fridman, Gregory; Friedman, Gary; Fridman, Alexander; Brooks, Ari D

2011-03-01

Oxidative stress leads to membrane lipid peroxidation, which yields products causing variable degrees of detrimental oxidative modifications in cells. Reactive oxygen species (ROS) are the key regulators in this process and induce lipid peroxidation in Escherichia coli. Application of nonthermal (cold) plasma is increasingly used for inactivation of surface contaminants. Recently, we reported a successful application of nonthermal plasma, using a floating-electrode dielectric-barrier discharge (FE-DBD) technique for rapid inactivation of bacterial contaminants in normal atmospheric air (S. G. Joshi et al., Am. J. Infect. Control 38:293-301, 2010). In the present report, we demonstrate that FE-DBD plasma-mediated inactivation involves membrane lipid peroxidation in E. coli. Dose-dependent ROS, such as singlet oxygen and hydrogen peroxide-like species generated during plasma-induced oxidative stress, were responsible for membrane lipid peroxidation, and ROS scavengers, such as α-tocopherol (vitamin E), were able to significantly inhibit the extent of lipid peroxidation and oxidative DNA damage. These findings indicate that this is a major mechanism involved in FE-DBD plasma-mediated inactivation of bacteria.

Nonthermal Dielectric-Barrier Discharge Plasma-Induced Inactivation Involves Oxidative DNA Damage and Membrane Lipid Peroxidation in Escherichia coli▿

PubMed Central

Joshi, Suresh G.; Cooper, Moogega; Yost, Adam; Paff, Michelle; Ercan, Utku K.; Fridman, Gregory; Friedman, Gary; Fridman, Alexander; Brooks, Ari D.

2011-01-01

Oxidative stress leads to membrane lipid peroxidation, which yields products causing variable degrees of detrimental oxidative modifications in cells. Reactive oxygen species (ROS) are the key regulators in this process and induce lipid peroxidation in Escherichia coli. Application of nonthermal (cold) plasma is increasingly used for inactivation of surface contaminants. Recently, we reported a successful application of nonthermal plasma, using a floating-electrode dielectric-barrier discharge (FE-DBD) technique for rapid inactivation of bacterial contaminants in normal atmospheric air (S. G. Joshi et al., Am. J. Infect. Control 38:293-301, 2010). In the present report, we demonstrate that FE-DBD plasma-mediated inactivation involves membrane lipid peroxidation in E. coli. Dose-dependent ROS, such as singlet oxygen and hydrogen peroxide-like species generated during plasma-induced oxidative stress, were responsible for membrane lipid peroxidation, and ROS scavengers, such as α-tocopherol (vitamin E), were able to significantly inhibit the extent of lipid peroxidation and oxidative DNA damage. These findings indicate that this is a major mechanism involved in FE-DBD plasma-mediated inactivation of bacteria. PMID:21199923

A study of the switching mechanism and electrode material of fully CMOS compatible tungsten oxide ReRAM

NASA Astrophysics Data System (ADS)

Chien, W. C.; Chen, Y. C.; Lai, E. K.; Lee, F. M.; Lin, Y. Y.; Chuang, Alfred T. H.; Chang, K. P.; Yao, Y. D.; Chou, T. H.; Lin, H. M.; Lee, M. H.; Shih, Y. H.; Hsieh, K. Y.; Lu, Chih-Yuan

2011-03-01

Tungsten oxide (WO X ) resistive memory (ReRAM), a two-terminal CMOS compatible nonvolatile memory, has shown promise to surpass the existing flash memory in terms of scalability, switching speed, and potential for 3D stacking. The memory layer, WO X , can be easily fabricated by down-stream plasma oxidation (DSPO) or rapid thermal oxidation (RTO) of W plugs universally used in CMOS circuits. Results of conductive AFM (C-AFM) experiment suggest the switching mechanism is dominated by the REDOX (Reduction-oxidation) reaction—the creation of conducting filaments leads to a low resistance state and the rupturing of the filaments results in a high resistance state. Our experimental results show that the reactions happen at the TE/WO X interface. With this understanding in mind, we proposed two approaches to boost the memory performance: (i) using DSPO to treat the RTO WO X surface and (ii) using Pt TE, which forms a Schottky barrier with WO X . Both approaches, especially the latter, significantly reduce the forming current and enlarge the memory window.

A DFT Investigation of the Mechanism of Propene Ammoxidation over α-Bismuth Molybdate

DOE PAGES

Licht, Rachel B.; Bell, Alexis T.

2016-11-17

We investigated the mechanisms and energetics for the propene oxidation and ammoxidation occurring on the (010) surface of Bi 2 Mo 3 O 12 using density functional theory (DFT). An energetically feasible sequence of elementary steps for propene oxidation to acrolein, propene ammoxidation to acrylonitrile, and acrolein ammoxidation to acrylonitrile is proposed. Consistent with experimental findings, the rate-limiting step for both propene oxidation and ammoxidation is the initial hydrogen abstraction from the methyl group of propene, which is calculated to have an apparent activation energy of 27.3 kcal/mol. The allyl species produced in this reaction is stabilized as an allylmore » alkoxide, which can then undergo hydrogen abstraction to form acrolein or react with ammonia adsorbed on under-coordinated surface Bi 3+ cations to form allylamine. Dehydrogenation of allylamine is shown to produce acrylonitrile, whereas reaction with additional adsorbed ammonia leads to the formation of acetonitrile and hydrogen cyanide. The dehydrogenation of allyalkoxide species is found to have a significantly higher activation barrier than reaction with adsorbed ammonia, consistent with the observation that very little acrolein is produced when ammonia is present. Finally, we found that rapid reoxidation of the catalyst surface to release wate the driving force for all reactions involving the cleavage of C-H or N-H bonds, because practically all of these steps are endothermic. (Chemical Equation Presented).« less

A strontium-incorporated nanoporous titanium implant surface for rapid osseointegration

NASA Astrophysics Data System (ADS)

Zhang, Wenjie; Cao, Huiliang; Zhang, Xiaochen; Li, Guanglong; Chang, Qing; Zhao, Jun; Qiao, Yuqin; Ding, Xun; Yang, Guangzheng; Liu, Xuanyong; Jiang, Xinquan

2016-02-01

Rapid osseointegration of dental implants will shorten the period of treatment and enhance the comfort of patients. Due to the vital role of angiogenesis played during bone development and regeneration, it might be feasible to promote rapid osseointegration by modifying the implant surface to gain a combined angiogenesis/osteogenesis inducing capacity. In this study, a novel coating (MAO-Sr) with strontium-incorporated nanoporous structures on titanium implants was generated via a new micro-arc oxidation, in an attempt to induce angiogenesis and osteogenesis to enhance rapid osseointegration. In vitro, the nanoporous structure significantly enhanced the initial adhesion of canine BMSCs. More importantly, sustained release of strontium ions also displayed a stronger effect on the BMSCs in facilitating their osteogenic differentiation and promoting the angiogenic growth factor secretion to recruit endothelial cells and promote blood vessel formation. Advanced mechanism analyses indicated that MAPK/Erk and PI3K/Akt signaling pathways were involved in these effects of the MAO-Sr coating. Finally, in the canine dental implantation study, the MAO-Sr coating induced faster bone formation within the initial six weeks and the osseointegration effect was comparable to that of the commercially available ITI implants. These results suggest that the MAO-Sr coating has the potential for future use in dental implants.Rapid osseointegration of dental implants will shorten the period of treatment and enhance the comfort of patients. Due to the vital role of angiogenesis played during bone development and regeneration, it might be feasible to promote rapid osseointegration by modifying the implant surface to gain a combined angiogenesis/osteogenesis inducing capacity. In this study, a novel coating (MAO-Sr) with strontium-incorporated nanoporous structures on titanium implants was generated via a new micro-arc oxidation, in an attempt to induce angiogenesis and osteogenesis to enhance rapid osseointegration. In vitro, the nanoporous structure significantly enhanced the initial adhesion of canine BMSCs. More importantly, sustained release of strontium ions also displayed a stronger effect on the BMSCs in facilitating their osteogenic differentiation and promoting the angiogenic growth factor secretion to recruit endothelial cells and promote blood vessel formation. Advanced mechanism analyses indicated that MAPK/Erk and PI3K/Akt signaling pathways were involved in these effects of the MAO-Sr coating. Finally, in the canine dental implantation study, the MAO-Sr coating induced faster bone formation within the initial six weeks and the osseointegration effect was comparable to that of the commercially available ITI implants. These results suggest that the MAO-Sr coating has the potential for future use in dental implants. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08580b

The effect of surface tension, superheat and surface films on the rate of heat transfer from an iron droplet to a water cooled copper mold

NASA Astrophysics Data System (ADS)

Phinichka, Natthapong

In strip casting the cast surface forms during the initial stage of solidification and the phenomenon that occurs during the first 50 milliseconds of contact time between the liquid steel and the mold define the cast surface and its quality. However the exact mechanism of the initial solidification and the process variables that affect initial solidification phenomena during that time are not well understood. The primary goal of this work is to develop a fundamental understanding of factors controlling strip casting. The purpose of the experimental study is to better understand the role of processing parameters on initial solidification phenomena, heat transfer rate and the formation of the cast steel surface. An investigation was made to evaluate the heat transfer rate of different kinds of steels. The experimental apparatus was designed for millisecond resolution of heat transfer behavior. A novel approach of simultaneous in-situ observation and measurement of rapid heat transfer was developed and enabled a coupling between the interfacial heat transfer rate and droplet solidification rate. The solidification rate was estimated from the varying position of the solidification front as captured by a CCD camera. The effects of experimental parameters such as melt superheat, sulfur content and oxide accumulation at the interface on measured heat flux were studied. It was found that the heat flux increased slightly when the percent of sulfur and increased significantly when superheat increased. The oxide accumulation at the interface was found to be manganese and silicon based oxide. When the liquid steel droplets were ejected onto the copper substrate repeatedly, without cleaning the substrate surface between the ejections, a large increase in the interfacial heat flux was observed. The results of the film study indicated that a liquid oxide film existed at the interface. The surface roughness measurement of the solidified specimen decreased with repeated experimentation and better contact between the droplet and the mold was found to be the cause of the improved heat transfer rate.

Burner Rig Hot Corrosion of a Single Crystal Ni-48Al-Ti-Hf-Ga Alloy

NASA Technical Reports Server (NTRS)

Nesbitt, James A.; Darolia, Ram; Cuy, Michael D.

1998-01-01

The hot corrosion resistance of a single crystal Ni-48Al-1Ti-0.5Hf-0.2Ga alloy was examined in a Mach 0.3 burner rig at 900 C for 300 hours. The combustion chamber was doped with 2 ppmw synthetic sea salt. The hot corrosion attack produced a random mound morphology on the surface. Microstructurally, the hot corrosion attack appeared to initiate with oxide-filled pits which were often broad and shallow. At an intermediate stage, the pits increased in size to incorporate unoxidized Ni islands in the corrosion product. The rampant attack stage, which was observed only at sharp sample corners, was characterized by rapid inward growth of alumina in finger-like protrusions incorporating significant amounts of Al-depleted Ni islands. Aluminum consumption in the oxide fingers resulted in the growth of a gamma' layer ahead of the advancing oxide fingers.

Transpassive Dissolution of Copper and Rapid Formation of Brilliant Colored Copper Oxide Films

NASA Astrophysics Data System (ADS)

Fredj, Narjes; Burleigh, T. David; New Mexico Tech Team

2014-03-01

This investigation describes an electrochemical technique for growing adhesive copper oxide films on copper with attractive colors ranging from gold-brown to pearl with intermediate colors from red violet to gold green. The technique consists of anodically dissolving copper at transpassive potentials in hot sodium hydroxide, and then depositing brilliant color films of Cu2O onto the surface of copper after the anodic potential has been turned off. The color of the copper oxide film depends on the temperature, the anodic potential, the time t1 of polarization, and the time t2, which is the time of immersion after potential has been turned off. The brilliant colored films were characterized using glancing angle x-ray diffraction, and the film was found to be primarily Cu2O. Cyclic voltammetry, chronopotentiometry, scanning electron microscopy, and x-ray photoelectron spectroscopy were also used to characterize these films.

Atmospheric-pressure glow plasma synthesis of plasmonic and photoluminescent zinc oxide nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bilik, N., E-mail: bilik006@umn.edu, E-mail: kortshagen@umn.edu; Greenberg, B. L.; Yang, J.

In this paper, we present a large-volume (non-micro) atmospheric pressure glow plasma capable of rapid, large-scale zinc oxide nanocrystal synthesis and deposition (up to 400 μg/min), whereas in the majority of the literature, nanoparticles are synthesized using micro-scale or filamentary plasmas. The reactor is an RF dielectric barrier discharge with a non-uniform gap spacing. This design encourages pre-ionization during the plasma breakdown, making the discharge uniform over a large volume. The produced zinc oxide nanocrystals typically have diameters ranging from 4 to 15 nm and exhibit photoluminescence at ≈550 nm and localized surface plasmon resonance at ≈1900 cm{sup −1} due to oxygen vacancies. Themore » particle size can be tuned to a degree by varying the gas temperature and the precursor mixing ratio.« less

A Comparative Study of Cyclic Oxidation and Sulfates-Induced Hot Corrosion Behavior of Arc-Sprayed Ni-Cr-Ti Coatings at Moderate Temperatures

NASA Astrophysics Data System (ADS)

Guo, Wenmin; Wu, Yuping; Zhang, Jianfeng; Hong, Sheng; Chen, Liyan; Qin, Yujiao

2015-06-01

The cyclic oxidation and sulfates-induced hot corrosion behaviors of a Ni-43Cr-0.3Ti arc-sprayed coating at 550-750 °C were characterized and compared in this study. In general, all the oxidation and hot corrosion kinetic curves of the coating followed a parabolic law, i.e., the weight of the specimens showed a rapid growth initially and then reached the gradual state. However, the initial stage of the hot corrosion process was approximately two times longer than that of the oxidation process, indicating a longer preparation time required for the formation of a protective scale in the former process. At 650 °C, the parabolic rate constant for the hot corrosion was 7.2 × 10-12 g2/(cm4·s), approximately 1.7 times higher than that for the oxidation at the same temperature. The lower parabolic rate constant for the oxidation was mainly attributed to the formation of a protective oxide scale on the surface of corroded specimens, which was composed of a mixture of NiO, Cr2O3, and NiCr2O4. However, as the liquid molten salts emerged during the hot corrosion, these protective oxides would be dissolved and the coating was corrupted acceleratedly.

Wood-Graphene Oxide Composite for Highly Efficient Solar Steam Generation and Desalination.

PubMed

Liu, Keng-Ku; Jiang, Qisheng; Tadepalli, Sirimuvva; Raliya, Ramesh; Biswas, Pratim; Naik, Rajesh R; Singamaneni, Srikanth

2017-03-01

Solar steam generation is a highly promising technology for harvesting solar energy, desalination and water purification. We introduce a novel bilayered structure composed of wood and graphene oxide (GO) for highly efficient solar steam generation. The GO layer deposited on the microporous wood provides broad optical absorption and high photothermal conversion resulting in rapid increase in the temperature at the liquid surface. On the other hand, wood serves as a thermal insulator to confine the photothermal heat to the evaporative surface and to facilitate the efficient transport of water from the bulk to the photothermally active space. Owing to the tailored bilayer structure and the optimal thermo-optical properties of the individual components, the wood-GO composite structure exhibited a solar thermal efficiency of ∼83% under simulated solar excitation at a power density of 12 kW/m 2 . The novel composite structure demonstrated here is highly scalable and cost-efficient, making it an attractive material for various applications involving large light absorption, photothermal conversion and heat localization.

Coating effects on thermal properties of carbon carbon and carbon silicon carbide composites for space thermal protection systems

NASA Astrophysics Data System (ADS)

Albano, M.; Morles, R. B.; Cioeta, F.; Marchetti, M.

2014-06-01

Many are the materials for hot structures, but the most promising one are the carbon based composites nowadays. This is because they have good characteristics with a high stability at high temperatures, preserving their mechanical properties. Unfortunately, carbon reacts rapidly with oxygen and the composites are subjected to oxidation degradation. From this point of view CC has to be modified in order to improve its thermal and oxidative resistance. The most common solutions are the use of silicon carbide into the carbon composites matrix (SiC composites) to make the thermal properties increase and the use of coating on the surface in order to protect the composite from the space plasma effects. Here is presented an experimental study on coating effects on these composites. Thermal properties of coated and non coated materials have been studied and the thermal impact on the matrix and surface degradation is analyzed by a SEM analysis.

Investigations into the structure of PEO-layers for understanding of layer formation

NASA Astrophysics Data System (ADS)

Friedemann, A. E. R.; Thiel, K.; Haßlinger, U.; Ritter, M.; Gesing, Th. M.; Plagemann, P.

2018-06-01

Plasma electrolytic oxidation (PEO) is a type of high-voltage anodic oxidation process capable of producing a thick oxide layer with a wide variety of structural and chemical properties influenced by the electrolytic system. This process enables the combined adjustment of various characteristics, i.e. the morphology and chemical composition. The procedure facilitates the possibility of generating an individual structure as well as forming a crystalline surface in a single step. A highly porous surface with a high crystalline content consisting of titanium dioxide phases is ensured through the process of plasma electrolytic oxidizing pure titanium. In the present study plasma electrolytic oxidized TiO2-layers were investigated regarding their crystallinity through the layer thickness. The layers were prepared with a high applied voltage of 280 V to obtain a PEO-layer with highly crystalline anatase and rutile amounts. Raman spectroscopy and electron backscatter diffraction (EBSD) were selected to clarify the structure of the oxide layer with regard to its crystallinity and phase composition. The composition of the TiO2-phases is more or less irregularly distributed as a result of the higher energy input on the uppermost side of the layer. Scanning transmission electron microscopy (STEM) provided a deeper understanding of the structure and the effects of plasma discharges on the layer. It was observed that the plasma discharges have a strong influence on crystallite formation on top of the oxide layer and also at the boundary layer to the titanium substrate. Therefore, small crystallites of TiO2 could be detected in these regions. In addition, it was shown that amorphous TiO2 phases are formed around the characteristic pore structures, which allows the conclusion to be drawn that a rapid cooling from the gas phase had to take place in these areas.

MPQ-cytometry: a magnetism-based method for quantification of nanoparticle-cell interactions

NASA Astrophysics Data System (ADS)

Shipunova, V. O.; Nikitin, M. P.; Nikitin, P. I.; Deyev, S. M.

2016-06-01

Precise quantification of interactions between nanoparticles and living cells is among the imperative tasks for research in nanobiotechnology, nanotoxicology and biomedicine. To meet the challenge, a rapid method called MPQ-cytometry is developed, which measures the integral non-linear response produced by magnetically labeled nanoparticles in a cell sample with an original magnetic particle quantification (MPQ) technique. MPQ-cytometry provides a sensitivity limit 0.33 ng of nanoparticles and is devoid of a background signal present in many label-based assays. Each measurement takes only a few seconds, and no complicated sample preparation or data processing is required. The capabilities of the method have been demonstrated by quantification of interactions of iron oxide nanoparticles with eukaryotic cells. The total amount of targeted nanoparticles that specifically recognized the HER2/neu oncomarker on the human cancer cell surface was successfully measured, the specificity of interaction permitting the detection of HER2/neu positive cells in a cell mixture. Moreover, it has been shown that MPQ-cytometry analysis of a HER2/neu-specific iron oxide nanoparticle interaction with six cell lines of different tissue origins quantitatively reflects the HER2/neu status of the cells. High correlation of MPQ-cytometry data with those obtained by three other commonly used in molecular and cell biology methods supports consideration of this method as a prospective alternative for both quantifying cell-bound nanoparticles and estimating the expression level of cell surface antigens. The proposed method does not require expensive sophisticated equipment or highly skilled personnel and it can be easily applied for rapid diagnostics, especially under field conditions.Precise quantification of interactions between nanoparticles and living cells is among the imperative tasks for research in nanobiotechnology, nanotoxicology and biomedicine. To meet the challenge, a rapid method called MPQ-cytometry is developed, which measures the integral non-linear response produced by magnetically labeled nanoparticles in a cell sample with an original magnetic particle quantification (MPQ) technique. MPQ-cytometry provides a sensitivity limit 0.33 ng of nanoparticles and is devoid of a background signal present in many label-based assays. Each measurement takes only a few seconds, and no complicated sample preparation or data processing is required. The capabilities of the method have been demonstrated by quantification of interactions of iron oxide nanoparticles with eukaryotic cells. The total amount of targeted nanoparticles that specifically recognized the HER2/neu oncomarker on the human cancer cell surface was successfully measured, the specificity of interaction permitting the detection of HER2/neu positive cells in a cell mixture. Moreover, it has been shown that MPQ-cytometry analysis of a HER2/neu-specific iron oxide nanoparticle interaction with six cell lines of different tissue origins quantitatively reflects the HER2/neu status of the cells. High correlation of MPQ-cytometry data with those obtained by three other commonly used in molecular and cell biology methods supports consideration of this method as a prospective alternative for both quantifying cell-bound nanoparticles and estimating the expression level of cell surface antigens. The proposed method does not require expensive sophisticated equipment or highly skilled personnel and it can be easily applied for rapid diagnostics, especially under field conditions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03507h

Evidence of Aerosols as a Media for Rapid Daytime HONO Production over China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Zhen; Wang, Yuhang; Costabile, Francesa

Current knowledge of daytime HONO sources remains incomplete. A large missing daytime HONO source has been found in many places around the world, including polluted regions in China. Conventional understanding and recent studies attributed this missing source mainly to ground surface processes or gas-phase chemistry, while assuming aerosols to be an insignificant media for HONO production. We analyze in situ observations of HONO and its precursors at an urban site in Beijing, China, and report an apparent dependence of the missing HONO source strength on aerosol surface area and solar ultraviolet radiation. Based on extensive correlation analysis and process-modeling, wemore » propose that the rapid daytime HONO production in Beijing can be explained by enhanced hydrolytic disproportionation of NO2 on aqueous aerosol surfaces due to catalysis by dicarboxylic acid anions. The combination of high abundance of NO2, aromatic hydrocarbons, and aerosols over broad regions in China likely leads to elevated HONO levels, rapid OH production, and enhanced oxidizing capacity on a regional basis. Our findings call for attention to aerosols as a media for daytime heterogeneous HONO production in polluted regions like Beijing. This study also highlights the complex and uncertain heterogeneous chemistry in China, which merits future efforts of reconciling regional modeling and laboratory experiments, in order to understand and mitigate the regional particulate and O3 pollutions over China.« less

Magnesium-phosphate-glass cements with ceramic-type properties

DOEpatents

Sugama, T.; Kukacka, L.E.

1982-09-23

Rapid setting magnesium phosphate (Mg glass) cementitious materials consisting of magnesium phosphate cement paste, polyborax and water-saturated aggregate, exhibits rapid setting and high early strength characteristics. The magnesium glass cement is prepared from a cation-leachable powder and a bivalent metallic ion-accepting liquid such as an aqueous solution of diammonium phosphate and ammonium polyphosphate. The cation-leachable powder includes a mixture of two different magnesium oxide powders processed and sized differently which when mixed with the bivalent metallic ion-accepting liquid provides the magnesium glass cement consisting primarily of magnesium ortho phosphate tetrahydrate, with magnesium hydroxide and magnesium ammonium phosphate hexahydrate also present. The polyborax serves as a set-retarder. The resulting magnesium mono- and polyphosphate cements are particularly suitable for use as a cementing matrix in rapid repair systems for deteriorated concrete structures as well as construction materials and surface coatings for fireproof structures.

Magnesium phosphate glass cements with ceramic-type properties

DOEpatents

Sugama, Toshifumi; Kukacka, Lawrence E.

1984-03-13

Rapid setting magnesium phosphate (Mg glass) cementitious materials consisting of magnesium phosphate cement paste, polyborax and water-saturated aggregate exhibiting rapid setting and high early strength characteristics. The magnesium glass cement is prepared from a cation-leachable powder and a bivalent metallic ion-accepting liquid such as an aqueous solution of diammonium phosphate and ammonium polyphosphate. The cation-leachable powder includes a mixture of two different magnesium oxide powders processed and sized differently which when mixed with the bivalent metallic ion-accepting liquid provides the magnesium glass cement consisting primarily of magnesium ortho phosphate tetrahydrate, with magnesium hydroxide and magnesium ammonium phosphate hexahydrate also present. The polyborax serves as a set-retarder. The resulting magnesium mono- and polyphosphate cements are particularly suitable for use as a cementing matrix in rapid repair systems for deteriorated concrete structures as well as construction materials and surface coatings for fireproof structures.

Molecular and dissociative adsorption of DMMP, Sarin and Soman on dry and wet TiO2(110) using density functional theory

NASA Astrophysics Data System (ADS)

Quintero, Yenny Cardona; Nagarajan, Ramanathan

2018-09-01

Titania, among the metal oxides, has shown promising characteristics for the adsorption and decontamination of chemical warfare nerve agents, due to its high stability and rapid decomposition rates. In this study, the adsorption energy and geometry of the nerve agents Sarin and Soman, and their simulant dimethyl methyl phosphonate (DMMP) on TiO2 rutile (110) surface were calculated using density functional theory. The molecular and dissociative adsorption of the agents and simulant on dry as well as wet metal oxide surfaces were considered. For the wet system, computations were done for the cases of both molecularly adsorbed water (hydrated conformation) and dissociatively adsorbed water (hydroxylated conformation). DFT calculations show that dissociative adsorption of the agents and simulant is preferred over molecular adsorption for both dry and wet TiO2. The dissociative adsorption on hydrated TiO2 shows higher stability among the different configurations considered. The dissociative structure of DMMP on hydrated TiO2 (the most stable one) was identified as the dissociation of a methyl group and its adsorption on the TiO2 surface. For the nerve agents Sarin and Soman on hydrated TiO2 the dissociative structure was by the dissociation of the F atom from the molecule and its interaction with a Ti atom from the surface, which could indicate a reduction in the toxicity of the products. This study shows the relevance of water adsorption on the metal oxide surface for the stability and dissociation of the simulant DMMP and the nerve agents Sarin and Soman on TiO2.

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

PubMed Central

Dickey, Michael D.

2016-01-01

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension. Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries. Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude (~500 mN/m to near zero). Furthermore, this method requires only a very modest potential (< 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests. PMID:26863045

A rapid and low energy consumption method to decolorize the high concentration triphenylmethane dye wastewater: operational parameters optimization for the ultrasonic-assisted ozone oxidation process.

PubMed

Zhou, Xian-Jiao; Guo, Wan-Qian; Yang, Shan-Shan; Ren, Nan-Qi

2012-02-01

This research set up an ultrasonic-assisted ozone oxidation process (UAOOP) to decolorize the triphenylmethane dyes wastewater. Five factors - temperature, initial pH, reaction time, ultrasonic power (low frequency 20 kHz), and ozone concentration - were investigated. Response surface methodology was used to find out the major factors influencing color removal rate and the interactions between these factors, and optimized the operating parameters as well. Under the experimental conditions: reaction temperature 39.81 °C, initial pH 5.29, ultrasonic power 60 W and ozone concentration 0.17 g/L, the highest color removals were achieved with 10 min reaction time and the initial concentration of the MG solution was 1000 mg/L. The optimal results indicated that the UAOOP was a rapid, efficient and low energy consumption technique to decolorize the high concentration MG wastewater. The predicted model was approximately in accordance with the experimental cases with correlation coefficients R(2) and R(adj)(2) of 0.9103 and 0.8386. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

Structure-property-composition relationships in doped zinc oxides: enhanced photocatalytic activity with rare earth dopants.

PubMed

Goodall, Josephine B M; Illsley, Derek; Lines, Robert; Makwana, Neel M; Darr, Jawwad A

2015-02-09

In this paper, we demonstrate the use of continuous hydrothermal flow synthesis (CHFS) technology to rapidly produce a library of 56 crystalline (doped) zinc oxide nanopowders and two undoped samples, each with different particle properties. Each sample was produced in series from the mixing of an aqueous stream of basic zinc nitrate (and dopant ion or modifier) solution with a flow of superheated water (at 450 °C and 24.1 MPa), whereupon a crystalline nanoparticle slurry was rapidly formed. Each composition was collected in series, cleaned, freeze-dried, and then characterized using analytical methods, including powder X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area measurement, X-ray photoelectron spectroscopy, and UV-vis spectrophotometry. Photocatalytic activity of the samples toward the decolorization of methylene blue dye was assessed, and the results revealed that transition metal dopants tended to reduce the photoactivity while rare earth ions, in general, increased the photocatalytic activity. In general, low dopant concentrations were more beneficial to having greater photodecolorization in all cases.

Development of Enterobacter aerogenes fuel cells: from in situ biohydrogen oxidization to direct electroactive biofilm.

PubMed

Zhuang, Li; Zhou, Shungui; Yuan, Yong; Liu, Tinglin; Wu, Zhifeng; Cheng, Jiong

2011-01-01

This study described an Enterobacter aerogenes-catalyzed microbial fuel cell (MFC) with a carbon-based anode that exhibited a maximum power density of 2.51 W/m(3) in the absence of artificial electron mediators. The MFC was started up rapidly, within hours, and the current generation in the early stage was demonstrated to result from in situ oxidation of biohydrogen produced by E. aerogenes during glucose fermentation. Over periodic replacement of substrate, both planktonic biomass in the culture liquid and hydrogen productivity decreased, while increased power density and coulombic efficiency and decreased internal resistance were unexpectedly observed. Using scanning electron microscopy and cyclic voltammetry, it was found that the enhanced MFC performance was associated with the development of electroactive biofilm on the anodic surface, proposed to involve an acclimation and selection process of E. aerogenes cells under electrochemical tension. The significant advantage of rapid start-up and the ability to develop an electroactive biofilm identifies E. aerogenes as a suitable biocatalyst for MFC applications. Copyright © 2010 Elsevier Ltd. All rights reserved.

Substantiating In Vivo Magnetic Brain Tumor Targeting of Cationic Iron Oxide Nanocarriers via Adsorptive Surface Masking

PubMed Central

Chertok, Beata; David, Allan E.; Moffat, Bradford A.; Yang, Victor C.

2009-01-01

Cationic magnetic nanoparticles are attractive as potential vehicles for tumor drug delivery due to their favorable interactions with both the tumor milieu and the therapeutic cargo. However, systemic delivery of these nanoparticles to the tumor site is compromised by their rapid plasma clearance. We developed a simple method for in vivo protection of cationic nanocarriers, using non-covalent surface masking with a conjugate of low molecular weight heparin and polyethylene glycol. Surface masking resulted in an 11-fold increase in plasma AUC and a 2-fold increase in the magnetic capture of systemically injected nanoparticles in orthotopic rodent brain tumors. Overall, the described methodology could expand the prospective applications for cationic magnetic nanoparticles in magnetically-mediated gene/drug delivery. PMID:19782394

Facile fabrication of Ag dendrite-integrated anodic aluminum oxide membrane as effective three-dimensional SERS substrate

NASA Astrophysics Data System (ADS)

Zhang, Cong-yun; Lu, Ya; Zhao, Bin; Hao, Yao-wu; Liu, Ya-qing

2016-07-01

A novel surface enhanced Raman scattering (SERS)-active substrate has been successfully developed, where Ag-dendrites are assembled on the surface and embedded in the channels of anodic aluminum oxide (AAO) membrane, via electrodeposition in AgNO3/PVP aqueous system. Reaction conditions were systematically investigated to attain the best Raman enhancement. The growth mechanism of Ag dendritic nanostructures has been proposed. The Ag dendrite-integrated AAO membrane with unique hierarchical structures exhibits high SERS activity for detecting rhodamine 6G with a detection limit as low as 1 × 10-11 M. Furthermore, the three-dimensional (3D) substrates display a good reproducibility with the average intensity variations at the major Raman peak less than 12%. Most importantly, the 3D SERS substrates without any surface modification show an outstanding SERS response for the molecules with weak affinity for noble metal surfaces. The potential application for the detection of polycyclic aromatic hydrocarbons (PAHs) was evaluated with fluoranthene as Raman target molecule and a sensitive SERS detection with a limit down to 10-8 M was reached. The 3D SERS-active substrate shows promising potential for rapid detection of trace organic pollutants even weak affinity molecules in the environment.

Nanotubular surface modification of metallic implants via electrochemical anodization technique.

PubMed

Wang, Lu-Ning; Jin, Ming; Zheng, Yudong; Guan, Yueping; Lu, Xin; Luo, Jing-Li

2014-01-01

Due to increased awareness and interest in the biomedical implant field as a result of an aging population, research in the field of implantable devices has grown rapidly in the last few decades. Among the biomedical implants, metallic implant materials have been widely used to replace disordered bony tissues in orthopedic and orthodontic surgeries. The clinical success of implants is closely related to their early osseointegration (ie, the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant), which relies heavily on the surface condition of the implant. Electrochemical techniques for modifying biomedical implants are relatively simple, cost-effective, and appropriate for implants with complex shapes. Recently, metal oxide nanotubular arrays via electrochemical anodization have become an attractive technique to build up on metallic implants to enhance the biocompatibility and bioactivity. This article will thoroughly review the relevance of electrochemical anodization techniques for the modification of metallic implant surfaces in nanoscale, and cover the electrochemical anodization techniques used in the development of the types of nanotubular/nanoporous modification achievable via electrochemical approaches, which hold tremendous potential for bio-implant applications. In vitro and in vivo studies using metallic oxide nanotubes are also presented, revealing the potential of nanotubes in biomedical applications. Finally, an outlook of future growth of research in metallic oxide nanotubular arrays is provided. This article will therefore provide researchers with an in-depth understanding of electrochemical anodization modification and provide guidance regarding the design and tuning of new materials to achieve a desired performance and reliable biocompatibility.

Nanotubular surface modification of metallic implants via electrochemical anodization technique

PubMed Central

Wang, Lu-Ning; Jin, Ming; Zheng, Yudong; Guan, Yueping; Lu, Xin; Luo, Jing-Li

2014-01-01

Due to increased awareness and interest in the biomedical implant field as a result of an aging population, research in the field of implantable devices has grown rapidly in the last few decades. Among the biomedical implants, metallic implant materials have been widely used to replace disordered bony tissues in orthopedic and orthodontic surgeries. The clinical success of implants is closely related to their early osseointegration (ie, the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant), which relies heavily on the surface condition of the implant. Electrochemical techniques for modifying biomedical implants are relatively simple, cost-effective, and appropriate for implants with complex shapes. Recently, metal oxide nanotubular arrays via electrochemical anodization have become an attractive technique to build up on metallic implants to enhance the biocompatibility and bioactivity. This article will thoroughly review the relevance of electrochemical anodization techniques for the modification of metallic implant surfaces in nanoscale, and cover the electrochemical anodization techniques used in the development of the types of nanotubular/nanoporous modification achievable via electrochemical approaches, which hold tremendous potential for bio-implant applications. In vitro and in vivo studies using metallic oxide nanotubes are also presented, revealing the potential of nanotubes in biomedical applications. Finally, an outlook of future growth of research in metallic oxide nanotubular arrays is provided. This article will therefore provide researchers with an in-depth understanding of electrochemical anodization modification and provide guidance regarding the design and tuning of new materials to achieve a desired performance and reliable biocompatibility. PMID:25258532

Aligned carbon nanotube, graphene and graphite oxide thin films via substrate-directed rapid interfacial deposition

NASA Astrophysics Data System (ADS)

D'Arcy, Julio M.; Tran, Henry D.; Stieg, Adam Z.; Gimzewski, James K.; Kaner, Richard B.

2012-05-01

A procedure for depositing thin films of carbon nanostructures is described that overcomes the limitations typically associated with solution based methods. Transparent and conductively continuous carbon coatings can be grown on virtually any type of substrate within seconds. Interfacial surface tension gradients result in directional fluid flow and film spreading at the water/oil interface. Transparent films of carbon nanostructures are produced including aligned ropes of single-walled carbon nanotubes and assemblies of single sheets of chemically converted graphene and graphite oxide. Process scale-up, layer-by-layer deposition, and a simple method for coating non-activated hydrophobic surfaces are demonstrated.A procedure for depositing thin films of carbon nanostructures is described that overcomes the limitations typically associated with solution based methods. Transparent and conductively continuous carbon coatings can be grown on virtually any type of substrate within seconds. Interfacial surface tension gradients result in directional fluid flow and film spreading at the water/oil interface. Transparent films of carbon nanostructures are produced including aligned ropes of single-walled carbon nanotubes and assemblies of single sheets of chemically converted graphene and graphite oxide. Process scale-up, layer-by-layer deposition, and a simple method for coating non-activated hydrophobic surfaces are demonstrated. Electronic supplementary information (ESI) available: Droplet coalescence, catenoid formation, mechanism of film growth, scanning electron micrographs showing carbon nanotube alignment, flexible transparent films of SWCNTs, AFM images of a chemically converted graphene film, and SEM images of SWCNT free-standing thin films. See DOI: 10.1039/c2nr00010e

Superhydrophobic ceramic coating: Fabrication by solution precursor plasma spray and investigation of wetting behavior.

PubMed

Xu, Pengyun; Coyle, Thomas W; Pershin, Larry; Mostaghimi, Javad

2018-08-01

Superhydrophobic surfaces are often created by fabricating suitable surface structures from low-surface-energy organic materials using processes that are not suitable for large-scale fabrication. Rare earth oxides (REO) exhibit hydrophobic behavior that is unusual among oxides. Solution precursor plasma spray (SPPS) deposition is a rapid, one-step process that can produce ceramic coatings with fine scale columnar structures. Manipulation of the structure of REO coatings through variation in deposition conditions may allow the wetting behavior to be controlled. Yb 2 O 3 coatings were fabricated via SPPS. Coating structure was investigated by scanning electron microscopy, digital optical microscopy, and x-ray diffraction. The static water contact angle and roll-off angle were measured, and the dynamic impact of water droplets on the coating surface recorded. Superhydrophobic behavior was observed; the best coating exhibited a water contact angle of ∼163°, a roll-off angle of ∼6°, and complete droplet rebound behavior. All coatings were crystalline Yb 2 O 3 , with a nano-scale roughness superimposed on a micron-scale columnar structure. The wetting behaviors of coatings deposited at different standoff distances were correlated with the coating microstructures and surface topographies. The self-cleaning, water flushing and water jetting tests were conducted and further demonstrated the excellent and durable hydrophobicity of the coatings. Copyright © 2018 Elsevier Inc. All rights reserved.

Polysaccharide-thickened aqueous fluoride solutions for rapid destruction of the nerve agent VX. Introducing the opportunity for extensive decontamination scenarios.

PubMed

Elias, Shlomi; Saphier, Sigal; Columbus, Ishay; Zafrani, Yossi

2014-01-01

Among the chemical warfare agents, the extremely toxic nerve agent VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate) is a target of high importance in the development of decontamination methods, due to its indefinite persistence on common environmental surfaces. Liquid decontaminants are mostly characterized by high corrosivity, usually offer poor coverage, and tend to flow and accumulate in low areas. Therefore, the development of a noncorrosive decontaminant, sufficiently viscous to resist dripping from the contaminated surface, is necessary. In the present paper we studied different polysaccharides-thickened fluoride aqueous solutions as noncorrosive decontaminants for rapid and efficient VX degradation to the nontoxic product EMPA (ethyl methylphosphonic acid). Polysaccharides are environmentally benign, natural, and inexpensive. Other known decontaminants cannot be thickened by polysaccharides, due to the sensitivity of the latter toward basic or oxidizing agents. We found that the efficiency of VX degradation in these viscous solutions in terms of kinetics and product identity is similar to that of KF aqueous solutions. Guar gum (1.5 wt %) with 4 wt % KF was chosen for further evaluation. The benign nature, rheological properties, adhering capabilities to different surfaces, and decontamination from a porous matrix were examined. This formulation showed promising properties for implementation as a spray decontaminant for common and sensitive environmental surfaces.

Development of PEGylated KMnF3 nanoparticles as a T1-weighted contrast agent: chemical synthesis, in vivo brain MR imaging, and accounting for high relaxivity.

PubMed

Liu, Zhi-jun; Song, Xiao-xia; Tang, Qun

2013-06-07

Magnetic nanoparticles consisting of manganese-based T1-weighted contrast agents have rapidly achieved clinical application, however low proton relaxivity impedes further development. In this report, by analyzing nanoparticles' surface oxidation states we propose the possible reason for the low r1 relaxivity of common MnO nanoparticles and develop PEGylated fluoroperovskite KMnF3 nanoparticles as new T1-weighted contrast agents, which exhibit the highest longitudinal relaxivity (r1 = 23.15 mM(-1) s(-1)) among all the reported manganese-based T1-weighted contrast agents. We, for the first time, illustrate a typical example showing that the surface oxidation states of metal ions exposed on the nanoparticles' surfaces are able to influence not only the optical, magnetic, electronic or catalytic properties but also water proton longitudinal relaxivity when applied as an MRI contrast agent. Cytotoxicity tests demonstrate that the PEGylated KMnF3 nanoparticles are free from toxicity. Further in vivo MRI experiments distinctively depict fine anatomical features in brain imaging at a low dose of 5 mg of Mn per kg and possible removal from the kidneys due to their small size and biocompatibility.

Oxidation of atomically thin MoS2 on SiO2

NASA Astrophysics Data System (ADS)

Yamamoto, Mahito; Cullen, William; Einstein, Theodore; Fuhrer, Michael

2013-03-01

Surface oxidation of MoS2 markedly affects its electronic, optical, and tribological properties. However, oxidative reactivity of atomically thin MoS2 has yet to be addressed. Here, we investigate oxidation of atomic layers of MoS2 using atomic force microscopy and Raman spectroscopy. MoS2 is mechanically exfoliated onto SiO2 and oxidized in Ar/O2 or Ar/O3 (ozone) at 100-450 °C. MoS2 is much more reactive to O2 than an analogous atomic membrane of graphene and monolayer MoS2 is completely etched very rapidly upon O2 treatment above 300 °C. Thicker MoS2 (> 15 nm) transforms into MoO3 after oxidation at 400 °C, which is confirmed by a Raman peak at 820 cm-1. However, few-layer MoS2 oxidized below 400 °C exhibits no MoO3 Raman mode but etch pits are formed, similar to graphene. We find atomic layers of MoS2 shows larger reactivity to O3 than to O2 and monolayer MoS2 transforms chemically upon O3 treatment even below 100 °C. Work supported by the U. of Maryland NSF-MRSEC under Grant No. DMR 05-20741.

Nanometer-scale modification and welding of silicon and metallic nanowires with a high-intensity electron beam.

PubMed

Xu, Shengyong; Tian, Mingliang; Wang, Jinguo; Xu, Jian; Redwing, Joan M; Chan, Moses H W

2005-12-01

We demonstrate that a high-intensity electron beam can be applied to create holes, gaps, and other patterns of atomic and nanometer dimensions on a single nanowire, to weld individual nanowires to form metal-metal or metal-semiconductor junctions, and to remove the oxide shell from a crystalline nanowire. In single-crystalline Si nanowires, the beam induces instant local vaporization and local amorphization. In metallic Au, Ag, Cu, and Sn nanowires, the beam induces rapid local surface melting and enhanced surface diffusion, in addition to local vaporization. These studies open up a novel approach for patterning and connecting nanomaterials in devices and circuits at the nanometer scale.

Detection of chemical residues in food oil via surface-enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Sun, Kexi; Huang, Qing

2016-05-01

Highly ordered hexagonally patterned Ag-nanorod (Ag-NR) arrays for surface-enhanced Raman scattering (SERS) detection of unhealthy chemical residues in food oil was reported, which was obtained by sputtering Ag on the alumina nanotip arrays stuck out of conical-pore anodic aluminum oxide (AAO) templates. SERS measurements demonstrate that the as-fabricated large-scale Ag-nanostructures can serve as highly sensitive and reproducible SERS substrates for detection of trace amount of chemicals in oil with the lower detection limits of 2×10-6 M for thiram and 10-7 M for rhodamine B, showing the potential of application of SERS in rapid trace detection of pesticide residues and illegal additives in food oils.

A rapid room temperature chemical route for the synthesis of graphene: metal-mediated reduction of graphene oxide.

PubMed

Dey, Ramendra Sundar; Hajra, Saumen; Sahu, Ranjan K; Raj, C Retna; Panigrahi, M K

2012-02-07

A rapid and facile route for the synthesis of reduced graphene oxide sheets (rGOs) at room temperature by the chemical reduction of graphene oxide using Zn/acid in aqueous solution is demonstrated. This journal is © The Royal Society of Chemistry 2012

Epitaxial GeSn film formed by solid phase epitaxy and its application to Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor capacitors with sub-nm equivalent oxide thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ching-Wei; Wu, Yung-Hsien; Hsieh, Ching-Heng

2014-11-17

Through the technique of solid phase epitaxy (SPE), an epitaxial Ge{sub 0.955}Sn{sub 0.045} film was formed on a Ge substrate by depositing an amorphous GeSn film followed by a rapid thermal annealing at 550 °C. A process that uses a SiO{sub 2} capping layer on the amorphous GeSn film during SPE was proposed and it prevents Sn precipitation from occurring while maintaining a smooth surface due to the reduced surface mobility of Sn atoms. The high-quality epitaxial GeSn film was observed to have single crystal structure, uniform thickness and composition, and tiny surface roughness with root mean square of 0.56 nm. Withmore » a SnO{sub x}-free surface, Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor (MOS) capacitors with equivalent oxide thickness (EOT) of 0.55 nm were developed. A small amount of traps inside the Yb{sub 2}O{sub 3} was verified by negligible hysteresis in capacitance measurement. Low leakage current of 0.4 A/cm{sup 2} at gate bias of flatband voltage (V{sub FB})-1 V suggests the high quality of the gate dielectric. In addition, the feasibility of using Yb{sub 2}O{sub 3} to well passivate GeSn surface was also evidenced by the small interface trap density (D{sub it}) of 4.02 × 10{sup 11} eV{sup −1} cm{sup −2}, which can be attributed to smooth GeSn surface and Yb{sub 2}O{sub 3} valency passivation. Both leakage current and D{sub it} performance outperform other passivation techniques at sub-nm EOT regime. The proposed epitaxial GeSn film along with Yb{sub 2}O{sub 3} dielectric paves an alternative way to enable high-performance GeSn MOS devices.« less

Ni-base superalloy powder-processed porous layer for gas cooling in extreme environments

DOE PAGES

White, Emma M. H.; Heidloff, Andrew J.; Byrd, David J.; ...

2016-05-26

Extreme high temperature conditions demand novel solutions for hot gas filters and coolant access architectures, i.e., porous layers on exposed components. These high temperatures, for example in current turbine engines, are at or exceeding current material limits for high temperature oxidation/corrosion, creep resistance, and, even, melting temperature. Thus novel blade designs allowing greater heat removal are required to maintain airfoil temperatures below melting and/ or rapid creep deformation limits. Gas atomized Ni-base superalloy powders were partially sintered into porous layers to allow full-surface, transpirational cooling of the surface of airfoils. Furthermore, these powder-processed porous layers were fully characterized for surface,more » morphology, cross-sectional microstructure, and mechanical strength characteristics. A sintering model based on pure Ni surface diffusion correlated well with the experimental results and allowed reasonable control over the partial sintering process to obtain a specified level of porosity within the porous layer.« less

Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles.

PubMed

Braniste, Tudor; Tiginyanu, Ion; Horvath, Tibor; Raevschi, Simion; Cebotari, Serghei; Lux, Marco; Haverich, Axel; Hilfiker, Andres

2016-01-01

Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle-cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO) nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN.

Ni-base superalloy powder-processed porous layer for gas cooling in extreme environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, Emma M. H.; Heidloff, Andrew J.; Byrd, David J.

Extreme high temperature conditions demand novel solutions for hot gas filters and coolant access architectures, i.e., porous layers on exposed components. These high temperatures, for example in current turbine engines, are at or exceeding current material limits for high temperature oxidation/corrosion, creep resistance, and, even, melting temperature. Thus novel blade designs allowing greater heat removal are required to maintain airfoil temperatures below melting and/ or rapid creep deformation limits. Gas atomized Ni-base superalloy powders were partially sintered into porous layers to allow full-surface, transpirational cooling of the surface of airfoils. Furthermore, these powder-processed porous layers were fully characterized for surface,more » morphology, cross-sectional microstructure, and mechanical strength characteristics. A sintering model based on pure Ni surface diffusion correlated well with the experimental results and allowed reasonable control over the partial sintering process to obtain a specified level of porosity within the porous layer.« less

Indium tin oxide-coated glass modified with reduced graphene oxide sheets and gold nanoparticles as disposable working electrodes for dopamine sensing in meat samples

NASA Astrophysics Data System (ADS)

Yang, Jiang; Strickler, J. Rudi; Gunasekaran, Sundaram

2012-07-01

Sensitive, rapid, and accurate detection of dopamine (DA) at low cost is needed for clinical diagnostic and therapeutic purposes as well as to prevent illegal use of DA in animal feed. We employed a simple approach to synthesize reduced graphene oxide sheets (rGOS) and gold nanoparticles (AuNPs) at room temperature on indium tin oxide-coated glass (ITO) slides as disposable working electrodes for sensing DA. Graphene oxide (GO) was directly reduced on ITO to remove oxygenated species via a rapid and green process without using chemical reducing reagents. AuNPs were electrochemically deposited in situ on rGOS-ITO with fairly uniform density and size. The sensitivity of the AuNPs-rGOS-ITO sensor for DA detection is 62.7 μA mM-1 cm-2 with good selectivity against common electrochemically interfering species such as ascorbic acid (AA) and uric acid (UA), and the detection limit measured by differential pulse voltammetry (DPV), at a signal-noise ratio of 3, was 6.0 × 10-8 M. The electrochemical catalysis of DA was proven to be a surface process with an electron transfer coefficient (α) of 0.478 and a rate constant (ks) of 1.456 s-1. It correlates well with the conventional UV-vis spectrophotometric approach (R = 0.9973) but with more than thrice the dynamic range (up to 4.5 mM). The sensor also exhibited good stability and capability to detect DA in beef samples, and thus is a promising candidate for simple and inexpensive sub-nanomolar detection of DA, especially in the presence of UV-absorbing compounds.

THE EFFECTS OF POLARIZATION UPON THE STEEL WIRE-NITRIC ACID MODEL OF NERVE ACTIVITY.

PubMed

Bishop, G H

1927-11-20

The active process in a short length of steel wire passivated by 65 per cent nitric acid has been observed under the influence of a polarizing current, and the form of the potential recorded by the cathode ray oscillograph. In the passive wire, 80 per cent of the total potential drop takes place at the anode, 20 per cent at the cathode. The change from active to passive states, as measured by the potential change, is very abrupt compared to the duration of activity and the potential curve at a point on the wire is probably almost rectangular. The duration of the refractory state is decreased at the anode and increased at the cathode, as in nerve. This fact is against the idea that reactivity after passivation results from a partial reduction of an oxide layer. Soft iron wire passivated by anodal polarization repassivates after activation in acid of a dilution that fails to passivate it initially. It soon becomes rhythmic with a very short refractory phase, and then reacts continuously. Such a wire exhibits a very sharp alternation between a dark brown oxide coat during activity, and a bright clean surface during passivation. A passive steel wire in nitric acid shows many of the characteristics of an inert electrode such as platinum, and it may be inferred that, superposed upon the primary passivation potential, there exists an electrode or oxidation-reduction potential equilibrium between the effects of the various constituents of the solution. It is suggested that the phenomena of nerve-like reactivity in this system may involve an alternation between two protective coatings of the steel wire. During activity, the surface becomes mechanically coated with a brown oxide. If this coating does not adhere, due to gas convection or to rapid solution of the oxide, passivation does not result. Under sufficiently intense oxidizing conditions, a second oxide coat may form in the interstices of the first, and cover the surface as the first coating dissolves off. This furnishes the electrochemical protection of passivation, which is followed by the gradual attainment of electrode equilibrium with the solution.

THE EFFECTS OF POLARIZATION UPON THE STEEL WIRE-NITRIC ACID MODEL OF NERVE ACTIVITY

PubMed Central

Bishop, George H.

1927-01-01

The active process in a short length of steel wire passivated by 65 per cent nitric acid has been observed under the influence of a polarizing current, and the form of the potential recorded by the cathode ray oscillograph. In the passive wire, 80 per cent of the total potential drop takes place at the anode, 20 per cent at the cathode. The change from active to passive states, as measured by the potential change, is very abrupt compared to the duration of activity and the potential curve at a point on the wire is probably almost rectangular. The duration of the refractory state is decreased at the anode and increased at the cathode, as in nerve. This fact is against the idea that reactivity after passivation results from a partial reduction of an oxide layer. Soft iron wire passivated by anodal polarization repassivates after activation in acid of a dilution that fails to passivate it initially. It soon becomes rhythmic with a very short refractory phase, and then reacts continuously. Such a wire exhibits a very sharp alternation between a dark brown oxide coat during activity, and a bright clean surface during passivation. A passive steel wire in nitric acid shows many of the characteristics of an inert electrode such as platinum, and it may be inferred that, superposed upon the primary passivation potential, there exists an electrode or oxidation-reduction potential equilibrium between the effects of the various constituents of the solution. It is suggested that the phenomena of nerve-like reactivity in this system may involve an alternation between two protective coatings of the steel wire. During activity, the surface becomes mechanically coated with a brown oxide. If this coating does not adhere, due to gas convection or to rapid solution of the oxide, passivation does not result. Under sufficiently intense oxidizing conditions, a second oxide coat may form in the interstices of the first, and cover the surface as the first coating dissolves off. This furnishes the electrochemical protection of passivation, which is followed by the gradual attainment of electrode equilibrium with the solution. PMID:19872388

An Efficient and Rapid Method to Monitor the Oxidative Degradation of Protein Pharmaceuticals: Probing Tyrosine Oxidation with Fluorogenic Derivatization.

PubMed

Bommana, Rupesh; Mozziconacci, Olivier; John Wang, Y; Schöneich, Christian

2017-07-01

The loss of potency of protein therapeutics can be linked to the oxidation of specific amino acid residues leading to a great variety of oxidative modifications. The comprehensive identification of these oxidative modifications requires high-resolution mass spectrometry analysis, which requires time and expensive resources. Here, we propose a fluorogenic derivatization method of oxidized Tyr and Phe yielding benzoxazole derivatives, as an orthogonal technique for the rapid screening of protein oxidation. Four model proteins, IgG1, human growth hormone (hGH), insulin and bovine serum albumin (BSA) were exposed to oxidation via peroxyl radicals and metal-catalyzed reactions and efficiently screened by fluorogenic derivatization of Tyr and Phe oxidation products. Complementary LC-MS analysis was done to identify the extent of methionine oxidation in oxidized proteins. The Fluorogenic derivatization technique can easily be adapted to a 96-well plate, in which several protein formulations can be screened in short time. Representatively for hGH, we show that the formation of benzoxazole parallels the oxidation of Met to methionine sulfoxide which enables estimation of Met oxidation by just recording the fluorescence. Our rapid fluorescence based screening allows for the fast comparison of the stability of multiple formulations.

Photo-stability and time-resolved photoluminescence study of colloidal CdSe/ZnS quantum dots passivated in Al{sub 2}O{sub 3} using atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Chih-Yi; Mao, Ming-Hua, E-mail: mhmao@ntu.edu.tw; Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan

2016-08-28

We report photo-stability enhancement of colloidal CdSe/ZnS quantum dots (QDs) passivated in Al{sub 2}O{sub 3} thin film using the atomic layer deposition (ALD) technique. 62% of the original peak photoluminescence (PL) intensity remained after ALD. The photo-oxidation and photo-induced fluorescence enhancement effects of both the unpassivated and passivated QDs were studied under various conditions, including different excitation sources, power densities, and environment. The unpassivated QDs showed rapid PL degradation under high excitation due to strong photo-oxidation in air while the PL intensity of Al{sub 2}O{sub 3} passivated QDs was found to remain stable. Furthermore, recombination dynamics of the unpassivated andmore » passivated QDs were investigated by time-resolved measurements. The average lifetime of the unpassivated QDs decreases with laser irradiation time due to photo-oxidation. Photo-oxidation creates surface defects which reduces the QD emission intensity and enhances the non-radiative recombination rate. From the comparison of PL decay profiles of the unpassivated and passivated QDs, photo-oxidation-induced surface defects unexpectedly also reduce the radiative recombination rate. The ALD passivation of Al{sub 2}O{sub 3} protects QDs from photo-oxidation and therefore avoids the reduction of radiative recombination rate. Our experimental results demonstrated that passivation of colloidal QDs by ALD is a promising method to well encapsulate QDs to prevent gas permeation and to enhance photo-stability, including the PL intensity and carrier lifetime in air. This is essential for the applications of colloidal QDs in light-emitting devices.« less

Oxidation-driven surface dynamics on NiAl(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Hailang; Chen, Xidong; Li, Liang

Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling upmore » of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). As a result, by comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps, we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps.« less

Oxidation-driven surface dynamics on NiAl(100)

DOE PAGES

Qin, Hailang; Chen, Xidong; Li, Liang; ...

2014-12-29

Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling upmore » of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). As a result, by comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps, we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps.« less

Characterization of the LTC catalyst: Performance against common air pollutants

NASA Astrophysics Data System (ADS)

Collins, Marcia F.

1987-04-01

One of the important qualities of the Low-Temperature Catalyst (LTC) is the rapid oxidation of carbon monoxide to carbon dioxide under a wide variety of conditions. The catalytic material is a palladium-copper activated complex which reacts with various contaminant molecules through a continuous oxidation/reduction cycle. The alumina substrate enhances LTC activity with its favorable surface chemistry and very high surface area. About 10 percent surface water is necessary to facilitate the oxidation of CO. This reaction shows a log-log dependence on contact time, suggesting a Langmuir-Hinshelwood mechanism. In the tube tests, LTC removed 90 to 100 percent of contaminating carbon monoxide in the temperature region of 20 to 4000 C, and at ambient over a range of 25 to 65 percent relative humidity. In contrast, NO2 is chemisorbed by the LTC/alumina material--the amount strongly dependent on temperature increases but independent of humidity. The LTC catalyst has demonstrated excellent capability to remove an important variety of hazardous pollutant gases which are common factors to poor indoor air quality. The Instapure Air Filtration System incorporates the LTC catalyst in a 50:50 mixture with activated carbon to effectively remove particulate, odors, and hazardous gases at room temperature and humidities. The ability to remove hazardous gases is unique for the category of portable air filtration equipment. The wide variety of pollutant gases that LTC removes suggests that catalytic technology is adaptable to a considerable range of commercial and industrial applications.

Characterization of the LTC catalyst: Performance against common air pollutants

NASA Technical Reports Server (NTRS)

Collins, Marcia F.

1987-01-01

One of the important qualities of the Low-Temperature Catalyst (LTC) is the rapid oxidation of carbon monoxide to carbon dioxide under a wide variety of conditions. The catalytic material is a palladium-copper activated complex which reacts with various contaminant molecules through a continuous oxidation/reduction cycle. The alumina substrate enhances LTC activity with its favorable surface chemistry and very high surface area. About 10 percent surface water is necessary to facilitate the oxidation of CO. This reaction shows a log-log dependence on contact time, suggesting a Langmuir-Hinshelwood mechanism. In the tube tests, LTC removed 90 to 100 percent of contaminating carbon monoxide in the temperature region of 20 to 4000 C, and at ambient over a range of 25 to 65 percent relative humidity. In contrast, NO2 is chemisorbed by the LTC/alumina material--the amount strongly dependent on temperature increases but independent of humidity. The LTC catalyst has demonstrated excellent capability to remove an important variety of hazardous pollutant gases which are common factors to poor indoor air quality. The Instapure Air Filtration System incorporates the LTC catalyst in a 50:50 mixture with activated carbon to effectively remove particulate, odors, and hazardous gases at room temperature and humidities. The ability to remove hazardous gases is unique for the category of portable air filtration equipment. The wide variety of pollutant gases that LTC removes suggests that catalytic technology is adaptable to a considerable range of commercial and industrial applications.

Protective actions of progesterone in the cardiovascular system: potential role of membrane progesterone receptors (mPRs) in mediating rapid effects.

PubMed

Thomas, Peter; Pang, Yefei

2013-06-01

The protective functions of progesterone in the cardiovascular system have received little attention even though evidence has accumulated that progesterone lowers blood pressure, inhibits coronary hyperactivity and has powerful vasodilatory and natriuretic effects. One possible reason why potential beneficial actions of progesterone on cardiovascular functions have not been extensively studied is that divergent effects to those of progesterone have been observed in many clinical trials with synthetic progestins such as medroxyprogesterone acetate which are associated with increased risk of coronary disease. Evidence that progesterone exerts protective effects on cardiovascular functions is briefly reviewed. The finding that progesterone administration decreases blood vessel vasoconstriction in several animal models within a few minutes suggests that rapid, nongenomic progesterone mechanisms are of physiological importance in regulating vascular tone. Rapid activation of second messenger pathways by progesterone has been observed in vascular endothelial and smooth muscle cells, resulting in alterations in endothelial nitric oxide synthase (eNOS) activity and calcium influx, respectively. Both nuclear progesterone receptors (PRs) and novel membrane progesterone receptors (mPRs) are candidates for the intermediaries in these rapid, cell-surface initiated progesterone actions in endothelial and smooth muscle vascular cells. PRs have been detected in both cell types. New data are presented showing mPRα, mPRβ and mPRγ are also present in human endothelial and smooth muscle vascular cells. Preliminary evidence suggests mPRs mediate rapid progestin signaling in these endothelial cells, resulting in down-regulation of cAMP production and increased nitric oxide synthesis. The role of mPRs in progesterone regulation of cardiovascular functions warrants further investigation. Copyright © 2013 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zarzycki, Piotr; Rosso, Kevin M.

Understanding Fe(II)-catalyzed transformations of Fe(III)- (oxyhydr)oxides is critical for correctly interpreting stable isotopic distributions and for predicting the fate of metal ions in the environment. Recent Fe isotopic tracer experiments have shown that goethite undergoes rapid recrystallization without phase change when exposed to aqueous Fe(II). The proposed explanation is oxidation of sorbed Fe(II) and reductive Fe(II) release coupled 1:1 by electron conduction through crystallites. Given the availability of two tracer exchange data sets that explore pH and particle size effects (e.g., Handler et al. Environ. Sci. Technol. 2014, 48, 11302-11311; Joshi and Gorski Environ. Sci. Technol. 2016, 50, 7315-7324), wemore » developed a stochastic simulation that exactly mimics these experiments, while imposing the 1:1 constraint. We find that all data can be represented by this model, and unifying mechanistic information emerges. At pH 7.5 a rapid initial exchange is followed by slower exchange, consistent with mixed surface- and diffusion-limited kinetics arising from prominent particle aggregation. At pH 5.0 where aggregation and net Fe(II) sorption are minimal, that exchange is quantitatively proportional to available particle surface area and the density of sorbed Fe(II) is more readily evident. Our analysis reveals a fundamental atom exchange rate of ~10-5 Fe nm-2 s-1, commensurate with some of the reported reductive dissolution rates of goethite, suggesting Fe(II) release is the rate-limiting step in the conduction mechanism during recrystallization.« less

Stochastic Simulation of Isotopic Exchange Mechanisms for Fe(II)-Catalyzed Recrystallization of Goethite.

PubMed

Zarzycki, Piotr; Rosso, Kevin M

2017-07-05

Understanding Fe(II)-catalyzed transformations of Fe(III)-(oxyhydr)oxides is critical for correctly interpreting stable isotopic distributions and for predicting the fate of metal ions in the environment. Recent Fe isotopic tracer experiments have shown that goethite undergoes rapid recrystallization without phase change when exposed to aqueous Fe(II). The proposed explanation is oxidation of sorbed Fe(II) and reductive Fe(II) release coupled 1:1 by electron conduction through crystallites. Given the availability of two tracer exchange data sets that explore pH and particle size effects (e.g., Handler et al. Environ. Sci. Technol. 2014 , 48 , 11302 - 11311 ; Joshi and Gorski Environ. Sci. Technol. 2016 , 50 , 7315 - 7324 ), we developed a stochastic simulation that exactly mimics these experiments, while imposing the 1:1 constraint. We find that all data can be represented by this model, and unifying mechanistic information emerges. At pH 7.5 a rapid initial exchange is followed by slower exchange, consistent with mixed surface- and diffusion-limited kinetics arising from prominent particle aggregation. At pH 5.0 where aggregation and net Fe(II) sorption are minimal, that exchange is quantitatively proportional to available particle surface area and the density of sorbed Fe(II) is more readily evident. Our analysis reveals a fundamental atom exchange rate of ∼10 -5 Fe nm -2 s -1 , commensurate with some of the reported reductive dissolution rates of goethite, suggesting Fe(II) release is the rate-limiting step in the conduction mechanism during recrystallization.

Dark ambient degradation of Bisphenol A and Acid Orange 8 as organic pollutants by perovskite SrFeO₃-δ metal oxide.

PubMed

Leiw, Ming Yian; Guai, Guan Hong; Wang, Xiaoping; Tse, Man Siu; Ng, Chee Mang; Tan, Ooi Kiang

2013-09-15

Current advanced oxidation processes (AOPs) are chemically and energetically intensive processes, which are undesirable for cost-effective and large-scale system water treatment and wastewater recycling. This study explored the Strontium Ferrite (SFO) metal oxide on the degradation of highly concentrated organic pollutants under dark ambient condition without any external stimulants. The SFO particles with single perovskite structure were successfully synthesized with a combined high temperature and high-energy ball milling process. An endocrine disruptor, Bisphenol A (BPA) and an azo dye, Acid Orange 8 (AO8) were used as probe organic pollutants. BPA was completely degraded with 83% of mineralization in 24 h while rapid decoloration of AO8 was achieved in 60 min and complete breakdown into primary intermediates and aliphatic acids occurred in 24 h under the treatment of dispersed SFO metal oxide in water. Such efficient degradation could be attributed to the enhanced adsorption of these anionic pollutants on positively charged ball-milled SFO metal oxide surface, resulted in higher degradation activity. Preliminary degradation mechanisms of BPA and AO8 under the action of SFO metal oxide were proposed. These results showed that the SFO metal oxide could be an efficient alternative material as novel advanced oxidation technology for low cost water treatment. Copyright © 2013 Elsevier B.V. All rights reserved.

In situ REM and ex situ SPM studies of silicon (111) surface

NASA Astrophysics Data System (ADS)

Aseev, A. L.; Kosolobov, S. S.; Latyshev, A. V.; Song, Se Ahn; Saranin, A. A.; Zotov, A. V.; Lifshits, V. G.

2005-09-01

Combination of experimental methods, including ultrahigh vacuum in situ reflection electron microscopy, scanning tunnelling microscopy and atomic force microscopy, has been applied for analysis of surface structure and dynamic processes on silicon (111) surfaces during sublimation, rapid temperature cooling, oxygen reactions and metal-silicon surface phase formation. From analysis of triangular negative islands, 0.08 nm in depth, which were forming during quenching, it was deduced the effective activation energy of the island generation is equalled to 0.35 eV and made conclusion that the (1 × 1) (7 × 7) phase transition on Si(111) assumes to be responsible for the negative island nucleation. On the base of the in situ REM study, the dependence of step motion, initiated by surface vacancies generation during oxygen-silicon interaction, on the terrace width was measured. Peculiarities of the initial stages of silicon surface oxidation at low pressures were considered. From precision measurements, the top silicon atom density was determined for the metal-silicon surface phase formed during Na, Ca, Mg and Ag deposition on clean silicon (111) surface.

Gas Sensors Based on Tin Oxide Nanoparticles Synthesized from a Mini-Arc Plasma Source

DOE PAGES

Lu, Ganhua; Huebner, Kyle L.; Ocola, Leonidas E.; ...

2006-01-01

Minimore » aturized gas sensors or electronic noses to rapidly detect and differentiate trace amount of chemical agents are extremely attractive. In this paper, we report on the fabrication and characterization of a functional tin oxide nanoparticle gas sensor. Tin oxide nanoparticles are first synthesized using a convenient and low-cost mini-arc plasma source. The nanoparticle size distribution is measured online using a scanning electrical mobility spectrometer (SEMS). The product nanoparticles are analyzed ex-situ by high resolution transmission electron microscopy (HRTEM) for morphology and defects, energy dispersive X-ray (EDX) spectroscopy for elemental composition, electron diffraction for crystal structure, and X-ray photoelectron spectroscopy (XPS) for surface composition. Nonagglomerated rutile tin oxide ( SnO 2 ) nanoparticles as small as a few nm have been produced. Larger particles bear a core-shell structure with a metallic core and an oxide shell. The nanoparticles are then assembled onto an e-beam lithographically patterned interdigitated electrode using electrostatic force to fabricate the gas sensor. The nanoparticle sensor exhibits a fast response and a good sensitivity when exposed to 100 ppm ethanol vapor in air.« less

LaCrO3/CuFe2O4 Composite-Coated Crofer 22 APU Stainless Steel Interconnect of Solid Oxide Fuel Cells

NASA Astrophysics Data System (ADS)

Hosseini, Seyedeh Narjes; Enayati, Mohammad Hossein; Karimzadeh, Fathallah; Dayaghi, Amir Masoud

2017-07-01

Rapidly rising contact resistance and cathode Cr poisoning are the major problems associated with unavoidable chromia scale growth on ferritic stainless steel (FSS) interconnects of solid oxide fuel cells. This work investigates the performance of the novel screen-printed composite coatings consisting of dispersed conductive LaCrO3 particles in a CuFe2O4 spinel matrix for Crofer 22 APU FSS, with emphasis on the oxidation behavior and electrical conductivity of these coatings. The results show that the presence of protective spinel coating, accompanied by the effective role of LaCrO3 particle incorporation, prevents the Cr2O3 subscale growth as well as chromium migration into the coating surface at the end of 400 hours of oxidation at 1073 K (800 °C) in air. In addition, the composite coatings decreased the area specific resistance (ASR) from 51.7 and 13.8 mΩ cm2 for uncoated and spinel-coated samples, respectively, to a maximum of 7.7 mΩ cm2 for composite-coated samples after 400 hours of oxidation.

Synchrotron speciation of silver and zinc oxide nanoparticles aged in a kaolin suspension.

PubMed

Scheckel, Kirk G; Luxton, Todd P; El Badawy, Amro M; Impellitteri, Christopher A; Tolaymat, Thabet M

2010-02-15

Assessments of the environmental fate and mobility of nanoparticles must consider the behavior of nanoparticles in relevant environmental systems that may result in speciation changes over time. Environmental conditions may act on nanoparticles to change their size, shape, and surface chemistry. Changing these basic characteristics of nanoparticles may result in a final reaction product that is significantly different than the initial nanomaterial. As such, basing long-term risk and toxicity on the initial properties of a nanomaterial may lead to erroneous conclusions if nanoparticles change upon release to the environment. The influence of aging on the speciation and chemical stability of silver and zinc oxide nanoparticles in kaolin suspensions was examined in batch reactors for up to 18 months. Silver nanoparticles remained unchanged in sodium nitrate suspensions; however, silver chloride was identified with the metallic silver nanoparticles in sodium chloride suspensions and may be attributed to an in situ silver chloride surface coating. Zinc oxide nanoparticles were rapidly converted via destabilization/dissolution mechanisms to Zn(2+) inner-sphere sorption complexes within 1 day of reaction and these sorption complexes were maintained through the 12 month aging processes. Chemical and physical alteration of nanomaterials in the environment must be examined to understand fate, mobility, and toxicology.

Surface Organometallic Chemistry of Supported Iridium(III) as a Probe for Organotransition Metal–Support Interactions in C–H Activation

DOE PAGES

Kaphan, David M.; Klet, Rachel C.; Perras, Frederic A.; ...

2018-05-11

Systematic study of the interactions between organometallic catalysts and metal oxide support materials is essential for the realization of rational design in heterogeneous catalysis. Herein we describe the stoichiometric and catalytic chemistry of a [Cp*(PMe 3)Ir(III)] complex chemisorbed on a variety of acidic metal oxides as a multifaceted probe for stereoelectronic communication between the support and organometallic center. Electrophilic bond activation was explored in the context of stoichiometric hydrogenolysis as well as catalytic H/D exchange. Further information was obtained from the observation of processes related to dynamic exchange between grafted organometallic species and those in solution. The supported organometallic speciesmore » were characterized by a variety of spectroscopic techniques including dynamic nuclear polarization-enhanced solid-state NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray absorption spectroscopy. Finally, strongly acidic modified metal oxides such as sulfated zirconia engender high levels of activity toward electrophilic bond activation of both sp 2 and sp 3 C–H bonds, including the rapid deuteration of methane at room temperature; however, the global trend for the supports studied here does not suggest a direct correlation between activity and surface Brønsted acidity.« less

Novel 2D RuPt core-edge nanocluster catalyst for CO electro-oxidation

NASA Astrophysics Data System (ADS)

Grabow, Lars C.; Yuan, Qiuyi; Doan, Hieu A.; Brankovic, Stanko R.

2015-10-01

A single layer, bi-metallic RuPt catalyst on Au(111) is synthesized using surface limited red-ox replacement of underpotentially deposited Cu and Pb monolayers though a two-step process. The resulting 2D RuPt monolayer nanoclusters have a unique core-edge structure with a Ru core and Pt at the edge along the perimeter. The activity of this catalyst is evaluated using CO monolayer oxidation as the probe reaction. Cyclic voltammetry demonstrates that the 2D RuPt core-edge catalyst morphology is significantly more active than either Pt or Ru monolayer catalysts. Density functional theory calculations in combination with infra-red spectroscopy data point towards oscillating variations (ripples) in the adsorption energy landscape along the radial direction of the Ru core as the origin of the observed behavior. Both, CO and OH experience a thermodynamic driving force for surface migration towards the Ru-Pt interface, where they adsorb most strongly and react rapidly. We propose that the complex interplay between epitaxial strain, ligand and finite size effects is responsible for the formation of the rippled RuPt monolayer cluster, which provides optimal conditions for a quasi-ideal bi-functional mechanism for CO oxidation, in which CO is adsorbed mainly on Pt, and Ru provides OH to the active Pt-Ru interface.

Ground-Based Testing of TiB2 and Al2O3/TiB2 Response to Space Environment

NASA Technical Reports Server (NTRS)

Jefferies, Sharon A.; Logan, Kathryn V.

2007-01-01

Two materials, titanium diboride and an alumina/titanium diboride composite, exhibit characteristics favorable for use in multiple space applications. These characteristics include low mass (4.52 gm/cc), high strain rate impact resistance, high temperature use (3000oC M.P.), thermal and electrical conductivity, thermal shock resistance, and high visible-range reflectivity. Additionally, the presence of boron in these materials gives them the potential to shield against neutron radiation as well as charged radiation. These materials are flying on MISSE 6 to assess material changes resulting from exposure to the space environment. This study provides a preliminary, ground-based examination of these materials' interactions with individual components of the space environment, in particular atomic oxygen (AO) and neutron radiation, in order to better predict and understand post-flight results. Individual specimens are exposed to ground state AO and surface oxidation is measured. Equivalent exposures of up to 13 months show no rapid oxidation, however evidence indicates some surface oxidation occurring. Other samples are placed near a polyethylene moderated, one Ci Am/Be neutron source to determine their shielding capability. Comparisons between exposed and shielded indium foil, which is activated by transmitted neutrons, measure each material's ability to shield neutrons. Preliminary results indicate a significant shielding benefit provided by both materials.

Surface Organometallic Chemistry of Supported Iridium(III) as a Probe for Organotransition Metal–Support Interactions in C–H Activation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaphan, David M.; Klet, Rachel C.; Perras, Frederic A.

Systematic study of the interactions between organometallic catalysts and metal oxide support materials is essential for the realization of rational design in heterogeneous catalysis. Herein we describe the stoichiometric and catalytic chemistry of a [Cp*(PMe 3)Ir(III)] complex chemisorbed on a variety of acidic metal oxides as a multifaceted probe for stereoelectronic communication between the support and organometallic center. Electrophilic bond activation was explored in the context of stoichiometric hydrogenolysis as well as catalytic H/D exchange. Further information was obtained from the observation of processes related to dynamic exchange between grafted organometallic species and those in solution. The supported organometallic speciesmore » were characterized by a variety of spectroscopic techniques including dynamic nuclear polarization-enhanced solid-state NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray absorption spectroscopy. Finally, strongly acidic modified metal oxides such as sulfated zirconia engender high levels of activity toward electrophilic bond activation of both sp 2 and sp 3 C–H bonds, including the rapid deuteration of methane at room temperature; however, the global trend for the supports studied here does not suggest a direct correlation between activity and surface Brønsted acidity.« less

Polyethylene glycol promotes autoxidation of cytochrome c.

PubMed

Sato, Wataru; Uchida, Takeshi; Saio, Tomohide; Ishimori, Koichiro

2018-06-01

Cytochrome c (Cyt c) was rapidly oxidized by molecular oxygen in the presence, but not absence of PEG. The redox potential of heme c was determined by the potentiometric titration to be +236 ± 3 mV in the absence of PEG, which was negatively shifted to +200 ± 4 mV in the presence of PEG. The underlying the rapid oxidation was explored by examining the structural changes in Cyt c in the presence of PEG using UV-visible absorption, circular dichroism, resonance Raman, and fluorescence spectroscopies. These spectroscopic analyses suggested that heme oxidation was induced by a modest tertiary structural change accompanied by a slight shift in the heme position (<1.0 Å) rather than by partial denaturation, as is observed in the presence of cardiolipin. The near-infrared spectra showed that PEG induced dehydration from Cyt c, which triggered heme displacement. The primary dehydration site was estimated to be around surface-exposed hydrophobic residues near the heme center: Ile81 and Val83. These findings and our previous studies, which showed that hydrated water molecules around Ile81 and Val83 are expelled when Cyt c forms a complex with CcO, proposed that dehydration of these residues is functionally significant to electron transfer from Cyt c to CcO. Copyright © 2018 Elsevier B.V. All rights reserved.

Influence of corrosive solutions on microhardness and chemistry of magnesium oxide /001/ surfaces

NASA Technical Reports Server (NTRS)

Ishigaki, H.; Miyoshi, K.; Buckley, D. H.

1982-01-01

X-ray photoelectron spectroscopy analyses and hardness experiments were conducted on cleaved magnesium oxide /001/ surfaces. The magnesium oxide bulk crystals were cleaved to specimen size along the /001/ surface, and indentations were made on the cleaved surface in corrosive solutions containing HCl, NaOH, or HNO3 and in water without exposing the specimen to any other environment. The results indicated that chloride (such as MgCl2) and sodium films are formed on the magnesium oxide surface as a result of interactions between an HCl-containing solution and a cleaved magnesium oxide surface. The chloride films soften the magnesium oxide surface. In this case microhardness is strongly influenced by the pH value of the solution. The lower the pH, the lower the microhardness. Sodium films, which are formed on the magnesium oxide surface exposed to an NaOH containing solution, do not soften the magnesium oxide surface.

Defect states at organic-inorganic interfaces: Insight from first principles calculations for pentaerythritol tetranitrate on MgO surface

NASA Astrophysics Data System (ADS)

Tsyshevsky, Roman V.; Rashkeev, Sergey N.; Kuklja, Maija M.

2015-07-01

Light-responsive organic-inorganic interfaces offer experimental opportunities that are otherwise difficult to achieve. Since laser light can be manipulated very precisely, it becomes possible to engineer selective, predictive, and highly controlled interface properties. Photochemistry of organic-inorganic energetic interfaces is a rapidly emerging research field in which energy absorption and interface stability mechanisms have yet to be established. To explore the interaction of the laser irradiation with molecular materials, we performed first principle calculations of a prototype organic-inorganic interface between a nitroester (pentaerythritol tetranitrate, PETN, C5H8N4O12) and a magnesium oxide (MgO) surface. We found that the light absorption is defined by the band alignment between interface components and interfacial charge transfer coupled with electronic states in the band gap, generated by oxide surface defects. Hence the choice of an oxide substrate and its morphology makes the optical absorption tunable and governs both the energy accumulation and energy release at the interface. The obtained results offer a possible consistent interpretation of experiments on selective laser initiation of energetic materials, which reported that the presence of metal oxide additives triggered the photoinitiation by excitation energy much lower than the band gap. We suggest that PETN photodecomposition is catalyzed by oxygen vacancies (F0 centers) at the MgO surface. Our conclusions predict ways for a complete separation of thermo- and photo-stimulated interface chemistry of molecular materials, which is imperative for highly controllable fast decomposition and was not attainable before. The methodology described here can be applied to any type of molecular material/wide band gap dielectric interfaces. It provides a solid basis for novel design and targeted improvements of organic-inorganic interfaces with desired properties that promise to enable vastly new concepts of energy storage and conversion, photocatalysis, and molecular electronics.

Chemical states of surface oxygen during CO oxidation on Pt(1 1 0) surface revealed by ambient pressure XPS

DOE PAGES

Yu, Youngseok; Koh, Yoobin Esther; Lim, Hojoon; ...

2017-10-20

Here, the study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure conditions, both the α-phase of PtO 2 oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to the exothermic nature of CO oxidation, the temperature of the Pt surface increases as CO oxidation takes place. As the CO/O 2 ratio increases, the production of CO 2 increases continuously and the surface temperature also increases. Interestingly, within the diffusion limited regions, the amount of surface oxide changes littlemore » while the chemisorbed oxygen is reduced.« less

Chemical states of surface oxygen during CO oxidation on Pt(1 1 0) surface revealed by ambient pressure XPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Youngseok; Koh, Yoobin Esther; Lim, Hojoon

Here, the study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure conditions, both the α-phase of PtO 2 oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to the exothermic nature of CO oxidation, the temperature of the Pt surface increases as CO oxidation takes place. As the CO/O 2 ratio increases, the production of CO 2 increases continuously and the surface temperature also increases. Interestingly, within the diffusion limited regions, the amount of surface oxide changes littlemore » while the chemisorbed oxygen is reduced.« less

UV-Enhanced Ethanol Sensing Properties of RF Magnetron-Sputtered ZnO Film.

PubMed

Huang, Jinyu; Du, Yu; Wang, Quan; Zhang, Hao; Geng, Youfu; Li, Xuejin; Tian, Xiaoqing

2017-12-26

ZnO film was deposited by the magnetron sputtering method. The thickness of ZnO film is approximately 2 μm. The influence of UV light illumination on C₂H₅OH sensing properties of ZnO film was investigated. Gas sensing results revealed that the UV-illuminated ZnO film displays excellent C₂H₅OH characteristics in terms of high sensitivity, excellent selectivity, rapid response/recovery, and low detection limit down to 0.1 ppm. The excellent sensing performance of the sensor with UV activation could be attributed to the photocatalytic oxidation of ethanol on the surface of the ZnO film, the planar film structure with high utilizing efficiency of UV light, high electron mobility, and a good surface/volume ratio of of ZnO film with a relatively rough and porous surface.

Compositional transformations in ion implanted polymers

NASA Astrophysics Data System (ADS)

Abdul-Kader, A. M.; Turos, A.; Grambole, D.; Jagielski, J.; Piątkowska, A.; Madi, N. K.; Al-Maadeed, M.

2005-10-01

Changes of surface layer composition produced by ion bombardment of polyethylene and polypropylene samples were studied. These materials are under consideration for load bearing surfaces in biological and technical applications. To improve their tribological properties, surface layers are usually modified by ionizing radiation. Therefore, to study the mechanism of transformations induced by ion beam bombardment selected polymers were implanted with H, He and Ar ions to the fluences ranging from 1 × 1013 to 2 × 1016/cm2. RBS and NRA techniques were applied for sample analysis. Important hydrogen release was observed with increasing ion dose and was correlated with the ion stopping power. Another important effect observed was the rapid oxidation of samples, which apparently occurs after exposure of implanted samples to the air. Up to 10 at.% of oxygen can be incorporated in the implanted layer.

Atomic-scale visualization of oxide thin-film surfaces.

PubMed

Iwaya, Katsuya; Ohsawa, Takeo; Shimizu, Ryota; Okada, Yoshinori; Hitosugi, Taro

2018-01-01

The interfaces of complex oxide heterostructures exhibit intriguing phenomena not observed in their constituent materials. The oxide thin-film growth of such heterostructures has been successfully controlled with unit-cell precision; however, atomic-scale understandings of oxide thin-film surfaces and interfaces have remained insufficient. We examined, with atomic precision, the surface and electronic structures of oxide thin films and their growth processes using low-temperature scanning tunneling microscopy. Our results reveal that oxide thin-film surface structures are complicated in contrast to the general perception and that atomically ordered surfaces can be achieved with careful attention to the surface preparation. Such atomically ordered oxide thin-film surfaces offer great opportunities not only for investigating the microscopic origins of interfacial phenomena but also for exploring new surface phenomena and for studying the electronic states of complex oxides that are inaccessible using bulk samples.

Tungsten carbide/porous carbon composite as superior support for platinum catalyst toward methanol electro-oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Liming; Fu, Honggang, E-mail: fuhg@vip.sina.com; Key Laboratory of Functional Inorganic Material Chemistry, Heilongjiang University, Harbin 150080

2014-01-01

Graphical abstract: The WC nanoparticles are well dispersed in the carbon matrix. The size of WC nanoparticles is about 30 nm. It can be concluded that tungsten carbide and carbon composite was successfully prepared by the present synthesis conditions. - Highlights: • The WC/PC composite with high specific surface area was prepared by a simple way. • The Pt/WC/PC catalyst has superior performance toward methanol electro-oxidation. • The current density for methanol electro-oxidation is as high as 595.93 A g{sup −1} Pt. • The Pt/WC/PC catalyst shows better durability and stronger CO electro-oxidation. • The performance of Pt/WC/PC is superiormore » to the commercial Pt/C (JM) catalyst. - Abstract: Tungsten carbide/porous carbon (WC/PC) composites have been successfully synthesized through a surfactant assisted evaporation-induced-assembly method, followed by a thermal treatment process. In particular, WC/PC-35-1000 composite with tungsten content of 35% synthesized at the carbonized temperature of 1000 °C, exhibited a specific surface area (S{sub BET}) of 457.92 m{sup 2} g{sup −1}. After loading Pt nanoparticles (NPs), the obtained Pt/WC/PC-35-1000 catalyst exhibits the highest unit mass electroactivity (595.93 A g{sup −1} Pt) toward methanol electro-oxidation, which is about 2.6 times as that of the commercial Pt/C (JM) catalyst. Furthermore, the Pt/WC/PC-35-1000 catalyst displays much stronger resistance to CO poisoning and better durability toward methanol electrooxidation compared with the commercial Pt/C (JM) catalyst. The high electrocatalytic activity, strong poison-resistivity and good stability of Pt/WC/PC-35-1000 catalyst are attributed to the porous structures and high specific surface area of WC/PC support could facilitate the rapid mass transportation. Moreover, synergistic effect between WC and Pt NPs is favorable to the higher catalytic performance.« less

Remediation of Cu metal-induced accelerated Fenton reaction by potato peels bio-sorbent.

PubMed

Azmat, Rafia; Moin, Sumeira; Saleem, Ailyan

2016-12-01

This article has allied exposure to Ecological Particulate Matter (EPM) and its remediation using potato peel surface (PPC) bio-sorbent on two important edible crops Spinacia oleracea and Luffa acutangula. Fenton reaction acceleration was one of the major stress oxidation reactions as a consequence of iron and copper toxicity, which involve in the formation of hydroxyl radical (OH) through EPM. Results showed that the oxidative stress encouraged by Cu in both species that recruits the degradation of photosynthetic pigments, initiating decline in growth, reduced leaf area and degrade proteins. The plants were cultivated in natural environmental condition in three pots with three replicates like (a) control, (b) Cu treated and (c) treated water. Oxidative stress initiated by metal activity in Cu accumulated plant (b) were controlled, through bio-sorption of metal from contaminated water using PPC; arranged at laboratory scale. The acceleration of Fenton reaction was verified in terms of OH radical generation. These radicals were tested in aqueous extract of leaves of three types of plants via benzoic acid. The benzoic acid acts as a scavenger of OH radical due to which the decarboxylation of benzoic acid cured. Observation on (b) showed more rapid decarboxylation as compared to other plants which showed that Cu activity was much higher in (b) as compared to (a) and (c). The rapid decarboxylation of benzoic acid and lower chlorophyll contents in (b) suggest that Fenton reaction system was much enhanced by Cu-O and Fe-O chemistry that was successfully controlled by PPC which results in restoring the metabolic pathway and nullifying oxidative stress in (c).

Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics.

PubMed

Hutchins, Daniel O; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E; Castner, David G; Ma, Hong; Jen, Alex K-Y

2012-11-15

Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlO x (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10 -8 A cm -2 and capacitance density of 0.62 µF cm -2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm 2 V -1 s -1 .

Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics

PubMed Central

Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.

2013-01-01

Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlOx (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10−8 A cm−2 and capacitance density of 0.62 µF cm−2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm2 V−1 s−1. PMID:24288423

CHO cell enlargement oscillates with a temperature-compensated period of 24 min

NASA Technical Reports Server (NTRS)

Pogue, R.; Morre, D. M.; Morre, D. J.

2000-01-01

The rate of increase in cell area of CHO cells when measured at intervals of 1 min using a light microscope equipped with a video measurement system, oscillated with a minimum period of about 24 min. The pattern of oscillations paralleled those of the 24 min period observed with the oxidation of NADH by an external cell surface or plasma membrane NADH oxidase. The increase in cell area was non-linear. Intervals of rapid increase in area alternated with intervals of rapid decrease in area. The length of the 24 min period was temperature-compensated (approximately the same when measured at 14 degrees C, 24 degrees C or 34 degrees C) while the rate of cell enlargement increased with temperature over this same range of temperatures.

Method of adhesion between an oxide layer and a metal layer

DOEpatents

Jennison, Dwight R.; Bogicevic, Alexander; Kelber, Jeffry A.; Chambers, Scott A.

2004-09-14

A method of controlling the wetting characteristics and increasing the adhesion between a metal and an oxide layer. By introducing a negatively-charged species to the surface of an oxide layer, layer-by-layer growth of metal deposited onto the oxide surface is promoted, increasing the adhesion strength of the metal-oxide interface. The negatively-charged species can either be deposited onto the oxide surface or a compound can be deposited that dissociates on, or reacts with, the surface to form the negatively-charged species. The deposited metal adatoms can thereby bond laterally to the negatively-charged species as well as vertically to the oxide surface as well as react with the negatively charged species, be oxidized, and incorporated on or into the surface of the oxide.

In Situ Atomic Scale Visualization Of Surface Kinetics Driven Dynamics Of Oxide Growth On A Ni–Cr Surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Langli; Zou, Lianfeng; Schreiber, Daniel K.

2016-01-20

We report in situ atomic-scale visualization of the dynamical three-dimensional (3D) growth of NiO during initial oxidation of Ni-10at%Cr using environmental transmission electron microscopy (ETEM). Despite the thermodynamic preference for Cr2O3 formation, cubic NiO oxides nucleated and grew epitaxially as the dominating oxide phase on the Ni-Cr (100) surface during initial oxidation. The growth of NiO islands proceeds through step-by-step adatom mechanism in 3D, which is sustained by surface diffusion of Ni and O atoms. Although the shapes of oxide islands are controlled by strain energy between oxide and alloy substrate, local surface kinetic variations can lead to the changemore » of surface planes of oxide islands. These results demonstrate that surface diffusion dominates initial oxidation of Ni-Cr in these test conditions.« less

Tobacco smoke aging in the presence of ozone: A room-sized chamber study

NASA Astrophysics Data System (ADS)

Petrick, Lauren M.; Sleiman, Mohamad; Dubowski, Yael; Gundel, Lara A.; Destaillats, Hugo

2011-09-01

Exposure to tobacco pollutants that linger indoors after smoking has taken place ( thirdhand smoke, THS) can occur over extended periods and is modulated by chemical processes involving atmospheric reactive species. This study investigates the role of ozone and indoor surfaces in chemical transformations of tobacco smoke residues. Gas and particle constituents of secondhand smoke (SHS) as well as sorbed SHS on chamber internal walls and model materials (cotton, paper, and gypsum wallboard) were characterized during aging. After smoldering 10 cigarettes in a 24-m 3 room size chamber, gas-phase nicotine was rapidly removed by sorption to chamber surfaces, and subsequently re-emitted during ventilation with clean air to a level of ˜10% that during the smoking phase. During chamber ventilation in the presence of ozone (180 ppb), ozone decayed at a rate of 5.6 h -1 and coincided with a factor of 5 less nicotine sorbed to wallboard. In the presence of ozone, no gas phase nicotine was detected as a result of re-emission, and higher concentrations of nicotine oxidation products were observed than when ventilation was performed with ozone-free air. Analysis of the model surfaces showed that heterogeneous nicotine-ozone reaction was faster on paper than cotton, and both were faster than on wallboard. However, wallboard played a dominant role in ozone-initiated reaction in the chamber due to its large total geometric surface area and sink potential compared to the other substrates. This study is the first to show in a room-sized environmental chamber that the heterogeneous ozone chemistry of sorbed nicotine generates THS constituents of concern, as observed previously in bench-top studies. In addition to the main oxidation products (cotinine, myosmine and N-methyl formamide), nicotine-1-oxide was detected for the first time.

Experimental demonstration of single electron transistors featuring SiO{sub 2} plasma-enhanced atomic layer deposition in Ni-SiO{sub 2}-Ni tunnel junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karbasian, Golnaz, E-mail: Golnaz.Karbasian.1@nd.edu; McConnell, Michael S.; Orlov, Alexei O.

The authors report the use of plasma-enhanced atomic layer deposition (PEALD) to fabricate single-electron transistors (SETs) featuring ultrathin (≈1 nm) tunnel-transparent SiO{sub 2} in Ni-SiO{sub 2}-Ni tunnel junctions. They show that, as a result of the O{sub 2} plasma steps in PEALD of SiO{sub 2}, the top surface of the underlying Ni electrode is oxidized. Additionally, the bottom surface of the upper Ni layer is also oxidized where it is in contact with the deposited SiO{sub 2}, most likely as a result of oxygen-containing species on the surface of the SiO{sub 2}. Due to the presence of these surface parasitic layersmore » of NiO, which exhibit features typical of thermally activated transport, the resistance of Ni-SiO{sub 2}-Ni tunnel junctions is drastically increased. Moreover, the transport mechanism is changed from quantum tunneling through the dielectric barrier to one consistent with thermally activated resistors in series with tunnel junctions. The reduction of NiO to Ni is therefore required to restore the metal-insulator-metal (MIM) structure of the junctions. Rapid thermal annealing in a forming gas ambient at elevated temperatures is presented as a technique to reduce both parasitic oxide layers. This method is of great interest for devices that rely on MIM tunnel junctions with ultrathin barriers. Using this technique, the authors successfully fabricated MIM SETs with minimal trace of parasitic NiO component. They demonstrate that the properties of the tunnel barrier in nanoscale tunnel junctions (with <10{sup −15} m{sup 2} in area) can be evaluated by electrical characterization of SETs.« less

Effect of inflammatory conditions and H2O2 on bare and coated Ti-6Al-4V surfaces: Corrosion behavior, metal ion release and Ca-P formation under long-term immersion in DMEM

NASA Astrophysics Data System (ADS)

Höhn, Sarah; Virtanen, Sannakaisa

2015-12-01

The surface oxide film and calcium-phosphate (Ca-P) formation on Ti-6Al-4V during long-term immersion in biological environments play a decisive role for the biocompatibility of the implant. Hence, the aim of the study was to evaluate the corrosion resistance, metal ion release and Ca-P formation in DMEM under physiological conditions at pH values of 7.4 and in comparison under simulated inflammatory conditions with pH 5 and in presence of H2O2. Furthermore, the influence of the immersion conditions was investigated on different surface treatments: on bare Ti-6Al-4V, after anodization, and for TiO2 nanoparticle (NP) and hydroxyapatite (HA)-incorporated TiO2-NP coatings. In the absence of H2O2, the impedance response indicated a stable thin oxide film and Ca-P formation after 28 days or 56 days depending on the coating, while under inflammatory conditions the Ca-P formation on the surface is time-delayed and dissolution of the anodized oxide layer as well as selective etching of the β-phase and phase boundaries in case of the bare alloy occur. Electrochemical impedance spectroscopy (EIS), however, indicates a good general corrosion behavior in all cases. The quantities of Ti, Al and V released from the bare and coated Ti-6Al-4V alloy markedly increased with decreasing pH (pH ≤ 5). Although the rapid increase of metal release was observed for all samples at pH 5, the quantities were significantly higher for the bare and anodized alloy than after coating with TiO2-NP or HA.

Surface modification of nitrogen-doped carbon nanotubes by ozone via atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lushington, Andrew; Liu, Jian; Tang, Yongji

The use of ozone as an oxidizing agent for atomic layer deposition (ALD) processes is rapidly growing due to its strong oxidizing capabilities. However, the effect of ozone on nanostructured substrates such as nitrogen-doped multiwalled carbon nanotubes (NCNTs) and pristine multiwalled carbon nanotubes (PCNTs) are not very well understood and may provide an avenue toward functionalizing the carbon nanotube surface prior to deposition. The effects of ALD ozone treatment on NCNTs and PCNTs using 10 wt. % ozone at temperatures of 150, 250, and 300 °C are studied. The effect of ozone pulse time and ALD cycle number on NCNTs and PCNTsmore » was also investigated. Morphological changes to the substrate were observed by scanning electron microscopy and high resolution transmission electron microscopy. Brunauer-Emmett-Teller measurements were also conducted to determine surface area, pore size, and pore size distribution following ozone treatment. The graphitic nature of both NCNTs and PCNTs was determined using Raman analysis while x-ray photoelectron spectroscopy (XPS) was employed to probe the chemical nature of NCNTs. It was found that O{sub 3} attack occurs preferentially to the outermost geometric surface of NCNTs. Our research also revealed that the deleterious effects of ozone are found only on NCNTs while little or no damage occurs on PCNTs. Furthermore, XPS analysis indicated that ALD ozone treatment on NCNTs, at elevated temperatures, results in loss of nitrogen content. Our studies demonstrate that ALD ozone treatment is an effective avenue toward creating low nitrogen content, defect rich substrates for use in electrochemical applications and ALD of various metal/metal oxides.« less

Tribological Behavior of Mg97Zn1Y2 Alloy at Elevated Temperatures of 50-200 °C

NASA Astrophysics Data System (ADS)

An, J.; Feng, J. H.; Yan, X. H.; Li, R. G.

2017-10-01

The tribological behavior of Mg97Zn1Y2 alloy was investigated using a pin-on-disk wear machine at wear temperatures of 50-200 °C. Morphologies and chemical compositions of worn surfaces were analyzed using scanning electron microscope and energy-dispersive x-ray spectrometer. The microstructural evolution and hardness change in subsurfaces were examined by optical microscopy and hardness tester. The results showed that the wear temperature had significant influence on the coefficient of friction and wear rate. At wear temperatures of 50-200 °C, with increasing applied load, the coefficient of friction went down rapidly then turned to decrease slowly in the mild wear regime, and continuously decreased modestly until the largest applied load in the severe wear regime. Increasing wear temperature from 50 to 200 °C decreased the mild to severe wear transition load linearly from 120 to 60 N. In the mild wear regime, the main wear mechanisms were identified as abrasion + oxidation and delamination + surface oxidation at 50-150 °C, and delamination at 200 °C, while in the severe wear regime, the main wear mechanisms were identified as severe plastic deformation + spallation of oxide layer and surface melting at 50-150 °C, and severe plastic deformation and surface melting at 200 °C. The microstructural transformation from the deformed to the dynamically recrystallized (DRX), and hardness change from the strain hardening to softening were found in the subsurfaces before and after mild to severe transition. The DRX softening mechanism was determined for mild to severe wear transition at 50-200 °C. A wear transition map was constructed for Mg97Zn1Y2 alloy on applied load versus wear temperature.

Low-cost optical fabrication of flexible copper electrode via laser-induced reductive sintering and adhesive transfer

NASA Astrophysics Data System (ADS)

Back, Seunghyun; Kang, Bongchul

2018-02-01

Fabricating copper electrodes on heat-sensitive polymer films in air is highly challenging owing to the need of expensive copper nanoparticles, rapid oxidation of precursor during sintering, and limitation of sintering temperature to prevent the thermal damage of the polymer film. A laser-induced hybrid process of reductive sintering and adhesive transfer is demonstrated to cost-effectively fabricate copper electrode on a polyethylene film with a thermal resistance below 100 °C. A laser-induced reductive sintering process directly fabricates a high-conductive copper electrode onto a glass donor from copper oxide nanoparticle solution via photo-thermochemical reduction and agglomeration of copper oxide nanoparticles. The sintered copper patterns were transferred in parallel to a heat-sensitive polyethylene film through self-selective surface adhesion of the film, which was generated by the selective laser absorption of the copper pattern. The method reported here could become one of the most important manufacturing technologies for fabricating low-cost wearable and disposable electronics.

A green synthetic strategy of nickel hexacyanoferrate nanoparticals supported on the graphene substrate and its non-enzymatic amperometric sensing application

NASA Astrophysics Data System (ADS)

xue, Zhonghua; He, Nan; Rao, Honghong; Hu, Chenxian; Wang, Xiaofen; Wang, Hui; Liu, Xiuhui; Lu, Xiaoquan

2017-02-01

Rapid glucose detection is a key requirement for both diagnosis and treatment of diabetes. A facile and green strategy to achieve spherical-shaped nickel hexacyanoferrate (NiHCF) nanoparticals supported on electrochemical reduction graphene oxide by using electrochemical cyclic voltammetry is explored. As a sensing substrate, electrochemical reduction graphene oxide deposited on a glassy carbon electrode surface exhibited obvious positive effect on the electrodeposition of NiHCF nanoparticals with spherical structure and thus effectively improved the electrical conductivity and electrochemical sensing of the proposed amperometric sensor. Proof-concept experiments demonstrated that the proposed nanocomposites modified electrode exhibited excellent sensitivity toward glucose oxidation as well as with a satisfying detection limit of 0.11 μM. More importantly, we also explore that as a simple, green and facile method, electrochemical technology can be employed and provide a new strategy for developing GO and metal hexacyanoferrate based amperometric sensing platform toward glucose and other biomolecules.

Laser welding of fused quartz

DOEpatents

Piltch, Martin S.; Carpenter, Robert W.; Archer, III, McIlwaine

2003-06-10

Refractory materials, such as fused quartz plates and rods are welded using a heat source, such as a high power continuous wave carbon dioxide laser. The radiation is optimized through a process of varying the power, the focus, and the feed rates of the laser such that full penetration welds may be accomplished. The process of optimization varies the characteristic wavelengths of the laser until the radiation is almost completely absorbed by the refractory material, thereby leading to a very rapid heating of the material to the melting point. This optimization naturally occurs when a carbon dioxide laser is used to weld quartz. As such this method of quartz welding creates a minimum sized heat-affected zone. Furthermore, the welding apparatus and process requires a ventilation system to carry away the silicon oxides that are produced during the welding process to avoid the deposition of the silicon oxides on the surface of the quartz plates or the contamination of the welds with the silicon oxides.

Detection of Nitric Oxide by the Sample Analysis at Mars (SAM) Instrument Implications for the Presence of Nitrates

NASA Technical Reports Server (NTRS)

Navarro-Gonzalez, R.; Stern, J.; Freissinet, C.; Franz, H. B.; Eigenbrode, J. L..; McKay, C. P.; Coll, P.; Sutter, B.; Archer, D.; McAdam, A.;

Phenolic Modified Ceramic Coating on Biodegradable Mg Alloy: The Improved Corrosion Resistance and Osteoblast-Like Cell Activity.

PubMed

Lee, Hung-Pang; Lin, Da-Jun; Yeh, Ming-Long

2017-06-25

Magnesium alloys have great potential for developing orthopedic implants due to their biodegradability and mechanical properties, but the rapid corrosion rate of the currently-available alloys limits their clinical applications. To increase the corrosion resistance of the substrate, a protective ceramic coating is constructed by a micro-arc oxidation (MAO) process on ZK60 magnesium alloy. The porous ceramic coating is mainly composed of magnesium oxide and magnesium silicate, and the results from cell cultures show it can stimulate osteoblastic cell growth and proliferation. Moreover, gallic acid, a phenolic compound, was successfully introduced onto the MAO coating by grafting on hydrated oxide and chelating with magnesium ions. The gallic acid and rough surface of MAO altered the cell attachment behavior, making it difficult for fibroblasts to adhere to the MAO coating. The viability tests showed that gallic acid could suppress fibroblast growth and stimulate osteoblastic cell proliferation. Overall, the porous MAO coating combined with gallic acid offered a novel strategy for increasing osteocompatibility.

Synthesis of sintering-resistant sorbents for CO2 capture.

PubMed

Liu, Wenqiang; Feng, Bo; Wu, Yueqin; Wang, Guoxiong; Barry, John; da Costa, João C Diniz

2010-04-15

Sorbents for high temperature CO2 capture are under intensive development owing to their potential applications in advanced zero emission power, sorption-enhanced steam methane reforming for hydrogen production and energy storage systems in chemical heat pumps. One of the challenges in the development is the prevention of sintering of the sorbent (normally a calcium oxide derivative) which causes the CO2 capture capacity of the material to deteriorate rapidly after a few cycles of utilization. Here we show that a simple wet mixing method can produce sintering-resistant sorbents from calcium and magnesium salts of d-gluconic acid. It was found that calcium oxide was well distributed in the sorbents with metal oxide nanoparticles on the surface acting as physical barriers, and the CO2 capture capacity of the sorbents was largely maintained over multiple cycles of utilization. This method was also applied to other organometallic salts of calcium and magnesium/aluminum and the produced sorbents showed similarly high reversibility.

Phenolic Modified Ceramic Coating on Biodegradable Mg Alloy: The Improved Corrosion Resistance and Osteoblast-Like Cell Activity

PubMed Central

Lee, Hung-Pang; Lin, Da-Jun; Yeh, Ming-Long

2017-01-01

Magnesium alloys have great potential for developing orthopedic implants due to their biodegradability and mechanical properties, but the rapid corrosion rate of the currently-available alloys limits their clinical applications. To increase the corrosion resistance of the substrate, a protective ceramic coating is constructed by a micro-arc oxidation (MAO) process on ZK60 magnesium alloy. The porous ceramic coating is mainly composed of magnesium oxide and magnesium silicate, and the results from cell cultures show it can stimulate osteoblastic cell growth and proliferation. Moreover, gallic acid, a phenolic compound, was successfully introduced onto the MAO coating by grafting on hydrated oxide and chelating with magnesium ions. The gallic acid and rough surface of MAO altered the cell attachment behavior, making it difficult for fibroblasts to adhere to the MAO coating. The viability tests showed that gallic acid could suppress fibroblast growth and stimulate osteoblastic cell proliferation. Overall, the porous MAO coating combined with gallic acid offered a novel strategy for increasing osteocompatibility. PMID:28773055

The chemical reactivity of the Martian soil and implications for future missions

NASA Technical Reports Server (NTRS)

Zent, Aaron P.; Mckay, Christopher P.

1994-01-01

Possible interpretations of the results of the Viking Biology Experiments suggest that greater than 1 ppm of a thermally labile oxidant, perhaps H2O2, and about 10 ppm of a thermally stable oxidant are present in the martian soil. We reexamine these results and discuss implications for future missions, the search for organics on Mars, and the possible health and engineering effects for human exploration. We conclude that further characterization of the reactivity of the martian regolith materials is warrented-although if our present understanding is correct the oxidant does not pose a hazard to humans. There are difficulties in explaining the reactivity of the Martian soil by oxidants. Most bulk phase compounds that are capable of oxidizing H2O to O2 per the Gas Exchange Experiment (GEx) are thermally labile or unstable against reduction by atmospheric CO2. Models invoking trapped O2 or peroxynitrates (NOO2(-)) require an unlikely geologic history for the Viking Lander 2 site. Most suggested oxidants, including H2O2, are expected to decompose rapidly under martian UV. Nonetheless, we conclude that the best model for the martian soil contains oxidants produced by heterogeneous chemical reactions with a photochemically produced atmospheric oxidant. The GEx results may be due to catalytic decomposition of an unstable oxidizing material by H2O. We show that interfacial reaction sites covering less than 1% of the available soil surfaces could explain the Viking Biology Experiments results.

Efficient simultaneous adsorption-biodegradation of high-concentrated N,N-dimethylformamide from water by Paracoccus denitrificans-graphene oxide microcomposites

NASA Astrophysics Data System (ADS)

Zheng, Yuan; Chen, Dongyun; Li, Najun; Xu, Qingfeng; Li, Hua; He, Jinghui; Lu, Jianmei

2016-02-01

Water contamination becomes one of the most pervasive environmental issues all over the world in recent years. In this paper, the functionalization of graphene oxide (GO) with copolymers containing methacrylic acid (MAA) and butyl methacrylate (BMA) was investigated to prepare a new microcomposite material (PGO) via free radical solution polymerization. PGO was used for the adsorption of N,N-dimethylformamide (DMF) from aqueous solution by utilizing the characteristics of ultralarge surface and the Van der Waals force between DMF molecules and polymers on the surface of PGO. Besides, PGO was used not only a high-capable adsorbent but also a carrier for the immobilization of Paracoccus denitrificans cells in the treatment of high-concentrated DMF. Bacterial cells could immobilized on the PGO (PGO@P. denitrificans) stably by covalent coupling process after acclimatization and high-concentrated DMF (2000 mg/L) could be removed completely and relatively rapidly from aqueous solutions by the simultaneous adsorption-biodegradation (SAB) process of PGO@P. denitrificans. Furthermore, the excellent recycle performance of PGO@P. denitrificans made the whole process more economical and practical.

Gold-nanofève surface-enhanced Raman spectroscopy visualizes hypotaurine as a robust anti-oxidant consumed in cancer survival.

PubMed

Shiota, Megumi; Naya, Masayuki; Yamamoto, Takehiro; Hishiki, Takako; Tani, Takeharu; Takahashi, Hiroyuki; Kubo, Akiko; Koike, Daisuke; Itoh, Mai; Ohmura, Mitsuyo; Kabe, Yasuaki; Sugiura, Yuki; Hiraoka, Nobuyoshi; Morikawa, Takayuki; Takubo, Keiyo; Suina, Kentaro; Nagashima, Hideaki; Sampetrean, Oltea; Nagano, Osamu; Saya, Hideyuki; Yamazoe, Shogo; Watanabe, Hiroyuki; Suematsu, Makoto

2018-04-19

Gold deposition with diagonal angle towards boehmite-based nanostructure creates random arrays of horse-bean-shaped nanostructures named gold-nanofève (GNF). GNF generates many electromagnetic hotspots as surface-enhanced Raman spectroscopy (SERS) excitation sources, and enables large-area visualization of molecular vibration fingerprints of metabolites in human cancer xenografts in livers of immunodeficient mice with sufficient sensitivity and uniformity. Differential screening of GNF-SERS signals in tumours and those in parenchyma demarcated tumour boundaries in liver tissues. Furthermore, GNF-SERS combined with quantum chemical calculation identified cysteine-derived glutathione and hypotaurine (HT) as tumour-dominant and parenchyma-dominant metabolites, respectively. CD44 knockdown in cancer diminished glutathione, but not HT in tumours. Mechanisms whereby tumours sustained HT under CD44-knockdown conditions include upregulation of PHGDH, PSAT1 and PSPH that drove glycolysis-dependent activation of serine/glycine-cleavage systems to provide one-methyl group for HT synthesis. HT was rapidly converted into taurine in cancer cells, suggesting that HT is a robust anti-oxidant for their survival under glutathione-suppressed conditions.

NiO nanoparticles anchored on P-doped α-Fe2O3 nanoarrays: an efficient hole extraction p-n heterojunction photoanode for water oxidation.

PubMed

Li, Feng; Li, Jing; Zhang, Jie; Gao, Lili; Long, Xuefeng; Hu, Yiping; Li, Shuwen; Jin, Jun; Ma, Jiantai

2018-05-16

The photoelectrochemical (PEC) water splitting efficiency of hematite-based photoanode is still far from the theoretical value due to its poor surface reaction kinetics and high density of surface trapping states. To solve these drawbacks, a photoanode consisting of NiO nanoparticles anchored on a gradient P-doped α-Fe2O3 nanorod (NR) array (NiO/P-α-Fe2O3) was fabricated to achieve optimal light absorption and charge separation, and rapid surface reaction kinetic. Specifically, the photoanode with the NR arrays structure allowed high mass transport rate to be achieved while the P-doping effectively decreased surface trapping sites and improved the electrical conductivity of α-Fe2O3. Furthermore, the p-n junction formed between the NiO and P-α-Fe2O3 can further improve the PEC performance due to the efficient hole extraction property and water oxidization catalytic activity of NiO. Consequently, the NiO/P-α-Fe2O3 NR photoanode produced a high photocurrent density of 2.08 mA cm-2 at 1.23V vs. RHE and a 110 mV cathodic shift of the onset potential. This rational design of structure offers a new perspective in exploring high performance PEC photoanodes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nano-graphene in biomedicine: theranostic applications.

PubMed

Yang, Kai; Feng, Liangzhu; Shi, Xiaoze; Liu, Zhuang

2013-01-21

Owing to their unique physical and chemical properties, graphene and its derivatives such as graphene oxide (GO), reduced graphene oxide (RGO) and GO-nanocomposites have attracted tremendous interest in many different fields including biomedicine in recent years. With every atom exposed on its surface, single-layered graphene shows ultra-high surface area available for efficient molecular loading and bioconjugation, and has been widely explored as novel nano-carriers for drug and gene delivery. Utilizing the intrinsic near-infrared (NIR) optical absorbance, in vivo graphene-based photothermal therapy has been realized, achieving excellent anti-tumor therapeutic efficacy in animal experiments. A variety of inorganic nanoparticles can be grown on the surface of nano-graphene, obtaining functional graphene-based nanocomposites with interesting optical and magnetic properties useful for multi-modal imaging and imaging-guided cancer therapy. Moreover, significant efforts have also been devoted to study the behaviors and toxicology of functionalized nano-graphene in animals. It has been uncovered that both surface chemistry and sizes play key roles in controlling the biodistribution, excretion, and toxicity of nano-graphene. Biocompatibly coated nano-graphene with ultra-small sizes can be cleared out from body after systemic administration, without rendering noticeable toxicity to the treated mice. In this review article, we will summarize the latest progress in this rapidly growing field, and discuss future prospects and challenges of using graphene-based materials for theranostic applications.

Method for Localizing and Differentiating Bacteria within Biofilms Grown on Indium Tin Oxide: Spatial Distribution of Exoelectrogenic Bacteria within Intact ITO Biofilms via FISH

DTIC Science & Technology

2017-11-01

404938, “Microbe-surface Interactions in Biofouling and Corrosion” ERDC/CERL TR-17-42 ii Abstract With a limited supply of fossil fuel, there has been...TR-17-42 iv Figures and Tables Figures Figure 1. DFR system used to rapidly form biofilms on ITO-coated glass substrates; (a) bioreactor with ITO...There is a finite amount of fossil fuel remaining in the world, and at cur- rently predicted rates of consumption, it is estimated that strategic re

Development of Transparent Materials Which Reduce Effects of Precipitation Static in Aircraft

DTIC Science & Technology

1952-03-01

36 7 Hydrolysis - MC1 4 + 4H20--- M(OH) 4 + 4HC1 Condensation - M(OH) 4 + heat -_-MO2 + 2H120 The oxide, M02 , is of high molecular weight and...insoluble, and, therefore, potentially of use as a film composition. In some cases the dehydration reaction proceeds rapidly enough at room temperature so... hydrolysis can thereby be controlled. In fact it is possible to let the hydrolysis proceed part way in solution rather than on the treated surface and

Indoor chemistry: research opportunities and challenges.

PubMed

Nazaroff, W W; Goldstein, A H

2015-08-01

In this editorial, we have highlighted key research opportunities and challenges in four topical themes for indoor chemistry: human occupants as agents influencing indoor chemistry; oxidative chemistry; surface phenomena; and semivolatile organic compounds. In each case, enough prior work has been done to demonstrate the importance of the theme and to create a foundation for future studies. Extensive achievements and ongoing progress in (outdoor) atmospheric chemistry—both in the analytical methods developed and in the scientific knowledge created—also contribute to a strong foundation from which to achieve rapid research progress in this exciting new domain.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Franklin

Two main categories of heterogeneous catalysts are metal and metal oxide which catalyze 80% chemical reactions at solid-gas and solid-liquid interfaces. Metal oxide catalysts are much more complicated than metal catalysts. The reason is that the cations of the metal atoms could exhibit a few different oxidation states on surface of the same catalyst particle such as Co 3O 4 or change of their oxidation states under different reactive environments. For a metal catalyst, there is only one oxidation state typically. In addition, surface of a metal oxide can be terminated with multiple surface functionalities including O atoms with differentmore » binding configurations and OH group. For metal, only metal atoms are exposed typically. Obviously, the complication of surface chemistry and structure of a metal oxide makes studies of surface of an oxide catalyst very challenging. Due to the complication of surface of a meal oxide, the electronic and geometric structures of surface of a metal oxide and the exposed species have received enormous attention since oxide catalysts catalyze at least 1/3 chemical reactions in chemical and energy industries. Understanding of catalytic reactions on early transition metal oxide-based catalysts is fundamentally intriguing and of great practical interest in energy- and environment-related catalysis. Exploration of surface chemistry of oxide-based catalysts at molecular level during catalysis has remained challenging though it is critical in deeply understanding catalysis on oxide-based catalysts and developing oxide-based catalysts with high activity and selectivity. Thus, the overall objective of this project is to explore surface chemistry and structure of early transition metal oxide-based catalysts through in-situ characterization of surface of catalysts, measurements of catalytic performances, and then build an intrinsic correlation of surface chemistry and structure with their catalytic performances in a few important catalytic reactions, and essentially fundamentally understand catalytic mechanism. Furthermore, this correlation will guide the design of catalysts with high activity and selectivity.« less

Rapid assessment of singlet oxygen-induced plasma lipid oxidation and its inhibition by antioxidants with diphenyl-1-pyrenylphosphine (DPPP).

PubMed

Morita, Mayuko; Naito, Yuji; Yoshikawa, Toshikazu; Niki, Etsuo

2016-01-01

Recent studies suggesting the involvement of singlet oxygen in the pathogenesis of multiple diseases have attracted renewed attention to lipid oxidation mediated by singlet oxygen. Although the rate constants for singlet oxygen quenching by antioxidants have been measured extensively, the inhibition of lipid oxidation mediated by singlet oxygen has received relatively less attention, partly because a convenient method for measuring the rate of lipid oxidation is not available. The objective of this study was to develop a convenient method to measure plasma lipid oxidation mediated by singlet oxygen which may be applied to a rapid assessment of the antioxidant capacity to inhibit this oxidation using a conventional microplate reader. Singlet oxygen was produced from naphthalene endoperoxide, and lipid hydroperoxide production was followed by using diphenyl-1-pyrenylphosphine (DPPP). Non-fluorescent DPPP reacts stoichiometrically with lipid hydroperoxides to give highly fluorescent DPPP oxide. It was found that plasma oxidation by singlet oxygen increased the fluorescence intensity of DPPP oxide, which was suppressed by antioxidants. Fucoxanthin suppressed the oxidation more efficiently than β-carotene and α-tocopherol, while ascorbic acid and Trolox were not effective. The present method may be useful for monitoring lipid oxidation and also for rapid screening of the capacity of dietary antioxidants and natural products to inhibit lipid oxidation in a biologically relevant system.

Oxide surfaces and metal/oxide interfaces studied by grazing incidence X-ray scattering

NASA Astrophysics Data System (ADS)

Renaud, Gilles

Experimental determinations of the atomic structure of insulating oxide surfaces and metal/oxide interfaces are scarce, because surface science techniques are often limited by the insulating character of the substrate. Grazing incidence X-ray scattering (GIXS), which is not subject to charge effects, can provide very precise information on the atomic structure of oxide surfaces: roughness, relaxation and reconstruction. It is also well adapted to analyze the atomic structure, the registry, the misfit relaxation, elastic or plastic, the growth mode and the morphology of metal/oxide interfaces during their growth, performed in situ. GIXS also allows the analysis of thin films and buried interfaces, in a non-destructive way, yielding the epitaxial relationships, and, by variation of the grazing incidence angle, the lattice parameter relaxation along the growth direction. On semi-coherent interfaces, the existence of an ordered network of interfacial misfit dislocations can be demonstrated, its Burger's vector determined, its ordering during in situ annealing cycles followed, and sometimes even its atomic structure can be addressed. Careful analysis during growth allows the modeling of the dislocation nucleation process. This review emphasizes the new information that GIXS can bring to oxide surfaces and metal/oxide interfaces by comparison with other surface science techniques. The principles of X-ray diffraction by surfaces and interfaces are recalled, together with the advantages and properties of grazing angles. The specific experimental requirements are discussed. Recent results are presented on the determination of the atomic structure of relaxed or reconstructed oxide surfaces. A description of results obtained during the in situ growth of metal on oxide surfaces is also given, as well as investigations of thick metal films on oxide surfaces, with lattice parameter misfit relaxed by an array of dislocations. Recent work performed on oxide thin films having important physical properties such as superconductivity or magnetism is also briefly reviewed. The strengths and limitations of the technique, such as the need for single crystals and surfaces of high crystalline quality are discussed. Finally, an outlook of future prospects in the field is given, such as the study of more complex oxide surfaces, vicinal surfaces, reactive metal/oxide interfaces, metal oxidation processes, the use of surfactants to promote wetting of a metal deposited on an oxide surface or the study of oxide/liquid interfaces in a non-UHV environment.

In-situ Polymerization of Polyaniline/Polypyrrole Copolymer using Different Techniques

NASA Astrophysics Data System (ADS)

Hammad, A. S.; Noby, H.; Elkady, M. F.; El-Shazly, A. H.

2018-01-01

The morphology and surface area of the poly(aniline-co-pyrrole) copolymer (PANPY) are important properties which improve the efficiency of the copolymer in various applications. In this investigation, different techniques were employed to produce PANPY in different morphologies. Aniline and pyrrole were used as monomers, and ammonium peroxydisulfate (APS) was used as an oxidizer with uniform molar ratio. Rapid mixing, drop-wise mixing, and supercritical carbon dioxide (ScCO2) polymerization techniques were appointed. The chemical structure, crystallinity, porosity, and morphology of the composite were distinguished by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET) analysis, and transmission electron microscopy (TEM) respectively. The characterization tests indicated that the polyaniline/polypyrrole copolymer was successfully prepared with different morphologies. Based on the obtained TEM, hollow nanospheres were formed using rapid mixing technique with acetic acid that have a diameter of 75 nm and thickness 26 nm approximately. Also, according to the XRD, the produced structures have a semi- crystalline structure. The synthesized copolymer with ScCO2-assisted polymerization technique showed improved surface area (38.1 m2/g) with HCl as dopant.

An Autopsy of Nanofiltration Membrane Used for Landfill Leachate Treatment

PubMed Central

Demir, Ibrahim; Koyuncu, Ismail; Guclu, Serkan; Yildiz, Senol; Balahorli, Vahit; Caglar, Suphi; Turken, Turker; Pasaoglu, Mehmet E.; Kaya, Recep; Sengur-Tasdemir, Reyhan

2015-01-01

Komurcuoda leachate treatment plant, Istanbul, which consists of membrane bioreactor (MBR) and nanofiltration (NF) system, faced rapid flux decline in membranes after 3-year successful operation. To compensate rapid flux decline in membranes, the fouled membranes were renewed but replacement of the membranes did not solve the problem. To find the reasons and make a comprehensive analysis, membrane autopsy was performed. Visual and physical inspection of the modules and some instrumental analysis were conducted for membrane autopsy. Membranes were found severely fouled with organic and inorganic foulants. Main foulant was iron which was deposited on surface. The main reason was found to be the changing of aerator type of MBR. When surface aerators were exchanged with bottom diffusers which led to increasing of dissolved oxygen (DO) level of the basin, iron particles were oxidized and they converted into particulate insoluble form. It was thought that probably this insoluble form of the iron particles was the main cause of decreased membrane performance. After the diagnosis, a new pretreatment alternative including a new iron antiscalant was suggested and system performance has been recovered. PMID:26137593

A PDMS/paper/glass hybrid microfluidic biochip integrated with aptamer-functionalized graphene oxide nano-biosensors for one-step multiplexed pathogen detection.

PubMed

Zuo, Peng; Li, XiuJun; Dominguez, Delfina C; Ye, Bang-Ce

2013-10-07

Infectious pathogens often cause serious public health concerns throughout the world. There is an increasing demand for simple, rapid and sensitive approaches for multiplexed pathogen detection. In this paper we have developed a polydimethylsiloxane (PDMS)/paper/glass hybrid microfluidic system integrated with aptamer-functionalized graphene oxide (GO) nano-biosensors for simple, one-step, multiplexed pathogen detection. The paper substrate used in this hybrid microfluidic system facilitated the integration of aptamer biosensors on the microfluidic biochip, and avoided complicated surface treatment and aptamer probe immobilization in a PDMS or glass-only microfluidic system. Lactobacillus acidophilus was used as a bacterium model to develop the microfluidic platform with a detection limit of 11.0 cfu mL(-1). We have also successfully extended this method to the simultaneous detection of two infectious pathogens - Staphylococcus aureus and Salmonella enterica. This method is simple and fast. The one-step 'turn on' pathogen assay in a ready-to-use microfluidic device only takes ~10 min to complete on the biochip. Furthermore, this microfluidic device has great potential in rapid detection of a wide variety of different other bacterial and viral pathogens.

A PDMS/paper/glass hybrid microfluidic biochip integrated with aptamer-functionalized graphene oxide nano-biosensors for one-step multiplexed pathogen detection

PubMed Central

Zuo, Peng; Dominguez, Delfina C.; Ye, Bang-Ce

2014-01-01

Infectious pathogens often cause serious public health concerns throughout the world. There is an increasing demand for simple, rapid and sensitive approaches for multiplexed pathogen detection. In this paper we have developed a polydimethylsiloxane (PDMS)/paper/glass hybrid microfluidic system integrated with aptamer-functionalized graphene oxide (GO) nano-biosensors for simple, one-step, multiplexed pathogen detection. The paper substrate used in this hybrid microfluidic system facilitated the integration of aptamer biosensors on the microfluidic biochip, and avoided complicated surface treatment and aptamer probe immobilization in a PDMS or glass-only microfluidic system. Lactobacillus acidophilus was used as a bacterium model to develop the microfluidic platform with a detection limit of 11.0 cfu mL−1. We have also successfully extended this method to the simultaneous detection of two infectious pathogens - Staphylococcus aureus and Salmonella enterica. This method is simple and fast. The one-step ‘turn on’ pathogen assay in a ready-to-use microfluidic device only takes ~10 min to complete on the biochip. Furthermore, this microfluidic device has great potential in rapid detection of a wide variety of different other bacterial and viral pathogens. PMID:23929394

Liquid-phase exfoliated graphene as highly-sensitive sensor for simultaneous determination of endocrine disruptors: diethylstilbestrol and estradiol.

PubMed

Hu, Lintong; Cheng, Qin; Chen, Danchao; Ma, Ming; Wu, Kangbing

2015-01-01

It is quite important to develop convenient and rapid analytical methods for trace levels of endocrine disruptors because they heavily affect health and reproduction of humans and animals. Herein, graphene was easily prepared via one-step exfoliation using N-methyl-2-pyrrolidone as solvent, and then used to construct an electrochemical sensor for highly-sensitive detection of diethylstilbestrol (DES) and estradiol (E2). On the surface of prepared graphene film, two independent and greatly-increased oxidation waves were observed at 0.28V and 0.49V for DES and E2. The remarkable signal enlargements indicated that the detection sensitivity was improved significantly. The influences of pH value, amount of graphene and accumulation time on the oxidation signals of DES and E2 were discussed. As a result, a highly-sensitive and rapid electrochemical method was newly developed for simultaneous detection of DES and E2. The values of detection limit were evaluated to be 10.87 nM and 4.9 nM for DES and E2. Additionally, this new method was successfully used in lake water samples and the accuracy was satisfactory. Copyright © 2014 Elsevier B.V. All rights reserved.

A highly sensitive and selective aptasensor based on graphene oxide fluorescence resonance energy transfer for the rapid determination of oncoprotein PDGF-BB.

PubMed

Liang, Junfei; Wei, Ran; He, Shuai; Liu, Yikan; Guo, Lin; Li, Lidong

2013-03-21

Oncoprotein platelet derived growth factor-BB (PDGF-BB) is one of the most critical growth factors that regulates tumor growth and division. In this work, a highly sensitive and selective fluorescence resonance energy transfer (FRET) aptasensor for PDGF-BB detection based on the assembly of dye-labeled aptamer and graphene oxide (GO) is developed for the first time. Due to the non-covalent assembly between aptamer and GO, fluorescence quenching of the dye takes place because of FRET. In the presence of PDGF-BB, the binding between aptamer and PDGF-BB will disturb the interaction between aptamer and GO, and release the dye-labeled aptamer from the GO surface, resulting in restoration of the fluorophore fluorescence. Because of the high fluorescence quenching efficiency, unique structure, and electronic properties of GO, the GO aptasensor exhibits extraordinarily high sensitivity. We also demonstrate that two highly related molecular variants of PDGF (AA, AB) can be distinguished from PDGF-BB, which indicates the aptasensor has excellent selectivity. Such an aptasensor opens a rapid, selective and sensitive route for the detection of PDGF-BB and provides a promising strategy for other cancer-related proteins detections.

Rapid adsorption of 2,4-dichlorophenoxyacetic acid by iron oxide nanoparticles-doped carboxylic ordered mesoporous carbon.

PubMed

Tang, Lin; Zhang, Sheng; Zeng, Guang-Ming; Zhang, Yi; Yang, Gui-De; Chen, Jun; Wang, Jing-Jing; Wang, Jia-Jia; Zhou, Yao-Yu; Deng, Yao-Cheng

2015-05-01

The ordered mesoporous carbon composite functionalized with carboxylate groups and iron oxide nanoparticles (Fe/OMC) was successfully prepared and used to adsorb 2,4-dichlorophenoxyacetic acid (2,4-D) from wastewater. The resultant adsorbent possessed high degree of order, large specific surface area and pore volume, and good magnetic properties. The increase in initial pollutant concentration and contact time would make the adsorption capacity increase, but the pH and temperature are inversely proportional to 2,4-D uptake. The equilibrium of adsorption was reached within 120 min, and the equilibrated adsorption capacity increased from 99.38 to 310.78 mg/g with the increase of initial concentration of 2,4-D from 100 to 500 mg/L. Notablely, the adsorption capacity reached 97% of the maximum within the first 5 min. The kinetics and isotherm study showed that the pseudo-second-order kinetic and Langmuir isotherm models could well fit the adsorption data. These results indicate that Fe/OMC has a good potential for the rapid adsorption of 2,4-D and prevention of its further diffusion. Copyright © 2014 Elsevier Inc. All rights reserved.

Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils

NASA Astrophysics Data System (ADS)

Hemingway, Jordon D.; Hilton, Robert G.; Hovius, Niels; Eglinton, Timothy I.; Haghipour, Negar; Wacker, Lukas; Chen, Meng-Chiang; Galy, Valier V.

2018-04-01

Lithospheric organic carbon (“petrogenic”; OCpetro) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO2) to the atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 ± 11% of the OCpetro initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO2 emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OCpetro remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO2 emission fluxes that increase with erosion rate, thereby counteracting CO2 drawdown by silicate weathering and biospheric OC burial.

Characterization of Iridium Coated Rhenium Used in High-Temperature, Radiation-Cooled Rocket Thrusters

NASA Technical Reports Server (NTRS)

Stulen, R. H.; Boehme, D. R.; Clift, W. M.; McCarty, K. F.

1990-01-01

Materials used for radiation-cooled rocket thrusters must be capable of surviving under extreme conditions of high-temperatures and oxidizing environments. While combustion efficiency is optimized at high temperatures, many refractory metals are unsuitable for thruster applications due to rapid material loss from the formation of volatile oxides. This process occurs during thruster operation by reaction of the combustion products with the material surface. Aerojet Technical Systems has developed a thruster cone chamber constructed of Re coated with Ir on the inside surface where exposure to the rocket exhaust occurs. Re maintains its structural integrity at high temperature and the Ir coating is applied as an oxidation barrier. Ir also forms volatile oxide species (IrO2 and IrO3) but at a considerably slower rate than Re. In order to understand the performance limits of Ir-coated Re thrusters, we are investigating the interdiffusion and oxidation kinetics of Ir/Re. The formation of iridium and rhenium oxides has been monitored in situ by Raman spectroscopy during high temperature exposure to oxygen. For pure Ir, the growth of oxide films as thin as approximately 200 A could be easily detected and the formation of IrO2 was observed at temperatures as low as 600 C. Ir/Re diffusion test specimens were prepared by magnetron sputtering of Ir on Re substrates. Concentration profiles were determined by sputter Auger depth profiles of the heat treated specimens. Significant interdiffusion was observed at temperatures as low as 1000 C. Measurements of the activation energy suggest that below 1350 C, the dominant diffusion path is along defects, most likely grain boundaries, rather than bulk diffusion through the grains. The phases that form during interdiffusion have been examined by x ray diffraction. Analysis of heated test specimens indicates that the Ir-Re reaction produces a solid solution phase of Ir dissolved in the HCP structure of Re.

Application of X-ray photoelectron spectroscopy to the analysis of stainless-steel welding aerosols

NASA Astrophysics Data System (ADS)

Tandon, R. K.; Payling, R.; Chenhall, B. E.; Crisp, P. T.; Ellis, J.; Baker, R. S.

1985-02-01

Aerosol particles ("fume") from manual metal arc welding of stainless steel with E316L-16 electrodes were analysed by X-ray photoelectron spectroscopy. The inherent complexity of the particles required the use of a wide range of experimental techniques. These included IR spectrophotometry, TGA/DTA, XRF, XRD, AAS and electron microprobe analysis. The surface of the fume particles comprised ≈ 50 at% NaF and KF, ≈ 8 at.% soluble (probably K) chromate, ≈ 30 at% SiO 2 and several at.% transition-metal oxides, hydroxides or silicates. The fluorides and chromates were removed by washing to reveal a surface which was predominantly SiO 2 (≈ 60 at%) with the remainder comprising of transition-metal oxides, silicates and fluorides. Approximately 6 at% F remained on the surface of the water-washed particles, presumably as transition-metal fluoro-complexes. The water-soluble fraction of the fume contained K +, Na +, F - and CrO 2-4 ions in the mole ratio 5:5:4:3. When aerosol particles are deposited in lung tissues, water-soluble constituents would be expected to dissolve rapidly. In view of the suspected carcinogenicity of stainless steel welding fume, a bio-medical study of the combined effects of F - and CrO 2-4 ions on lung tissue is warranted.

Density functional theory studies of TiO2 for photocatalysis and Li storage applications

NASA Astrophysics Data System (ADS)

Kim, Yong-Hoon; Lee, Ji Il; Lee, Dong Ki; Lee, Gyu Heon; Kang, Jeung Ku

We present two theory-experiment collaboration studies of anatase TiO2 for energy applications. First, we discuss a hydrogen-nitrogen co-doped TiO2 (HN-TiO2) as a photocatalyst, and show that the interstitially introduced HN contributes to the increase of solar-to-fuel conversion efficiency. We find that the variation of valence band maximum (VBM) of NH-TiO2 extends the photoactive spectrum to the visible light, and argue that created mid-gap states produce efficient electron and hole conduction channels. Next, we consider experimentally fabricated hierarchical TiO2 nanocrystals integrated with binder-free porous graphene (PG) network foam for a Li storage application. It was found that the TiO2-PG facilitated rapid ionic transfer during the Li-ion insertion/extraction process. We clarify the mechanisms by showing that Li ion migration into the TiO2-PG interface stabilize the binder-free oxide-graphene interface. Atomistic mechanism of Li ion insertion and migration is discussed by comparing cases between an isolated Li ion, when the crowding effect is included, and when the surface Li ions are present. We found that the supply of additional surface Li ions significantly reduce the Li insertion barrier, driving a spontaneous domino-like concerted Li insertion at the oxide surface region.

New oxidation treatment of NiTi shape memory alloys to obtain Ni-free surfaces and to improve biocompatibility.

PubMed

Michiardi, A; Aparicio, C; Planell, J A; Gil, F J

2006-05-01

Various oxidation treatments were applied to nearly equiatomic NiTi alloys so as to form a Ni-free protective oxide on the surface. Sample surfaces were analyzed by X-ray Photoelectron Spectroscopy, and NiTi transformation temperatures were determined by differential scanning calorimetry (DSC) before and after the surface treatment. An ion release experiment was carried out up to one month of immersion in SBF for both oxidized and untreated surfaces. The results show that oxidation treatment in a low-oxygen pressure atmosphere leads to a high surface Ti/Ni ratio, a very low Ni surface concentration and a thick oxide layer. This oxidation treatment does not significantly affect the shape memory properties of the alloy. Moreover, the oxide formed significantly decreases Ni release into exterior medium comparing with untreated surfaces. As a consequence, this new oxidation treatment could be of great interest for biomedical applications, as it could minimize sensitization and allergies and improve biocompatibility and corrosion resistance of NiTi shape memory alloys. (c) 2005 Wiley Periodicals, Inc.

Influence of adsorption versus coprecipitation on the retention of rice straw-derived dissolved organic carbon and subsequent reducibility of Fe-DOC systems

NASA Astrophysics Data System (ADS)

Sodano, Marcella; Lerda, Cristina; Martin, Maria; Celi, Luisella; Said-Pullicino, Daniel

2016-04-01

The dissimilatory reduction of Fe oxides is the main organic C-consuming process in paddy soils under anoxic conditions. The contribution of Fe(III) reduction to anaerobic C mineralization depends on many factors, but most importantly on the bioavailability of labile organic matter and a reducible Fe pool as electron donors and acceptors, respectively. On the other hand, the strong affinity of these minerals for organic matter and their capability of protecting it against microbial decomposition is well known. Natural Fe oxides in these soils may therefore play a key role in determining the C source/sink functions of these agro-ecosystems. Apart from contributing to C stabilization, the interaction between Fe oxides and dissolved organic C (DOC) may influence the structure and reactivity of these natural oxides, and selectively influence the chemical properties of DOC. Indeed, Fe-DOC associations may not only reduce the availability of DOC, but may also limit the microbial reduction of Fe oxides under anoxic conditions. In fact, the accessibility of these minerals to microorganisms, extracellular enzymes, redox active shuttling compound or reducing agents may be impeded by the presence of sorbed organic matter. In soils that are regularly subjected to fluctuations in redox conditions the interaction between DOC and Fe oxides may not only involve organic coatings on mineral surfaces, but also Fe-DOC coprecipitates that form during the rapid oxidation of soil solutions containing important amounts of DOC and Fe(II). However, little is known on how these processes influence DOC retention, and the structure and subsequent reducibility of these Fe-DOC associations. We hypothesized that the nature and extent of the interaction between DOC and Fe oxides may influence the accessibility of the bioavailable Fe pool and consequently its reducibility. We tested this hypothesis by synthesizing a series of Fe-DOC systems with increasing C:Fe ratios prepared by either surface adsorption or coprecipitation, DOC was obtained by incubating a suspension of rice straw in water (straw-solution ratio of 1:30) under oxic conditions at 25° C for 30 days to simulate the decomposition of rice straw in the field. Increasing amounts of DOC were equilibrated (pH = 6) with a known mass of ferrihydrite (initial molar C:Fe ratios of 1, 5 and 10) to obtain surface coated Fe-DOC systems with increasing C loading. On the other hand, coprecipitates with similar initial C:Fe ratios were obtained by oxidation of a Fe(II) solution in the presence of increasing amounts of DOC at pH = 6. A natural Fe-DOC coprecipitate was also obtained by in situ sampling of a paddy soil solution from the topsoil during a cropping season, and subsequent oxidation in the laboratory. The surface and chemical properties of all substrates were subsequently evaluated and compared. We hereby present the first results of the influence of adsorption vs coprecipitation on the selective retention of DOC, structure and surface charge, as well as their susceptibility to chemical reduction with ascorbic acid.

Rapid aqueous phase SO2 oxidation in winter fog in the Indo-Gangetic Plain

NASA Astrophysics Data System (ADS)

Sachan, Himanshu; Sarkar, Chinmoy; Sinha, Baerbel

2013-04-01

Sulphate and sulphur dioxide play an important role in environmental chemistry and climate. The majority of anthropogenic sulphur is released directly as SO2, and a significant fraction of biogenic and natural sulphur emissions are also either directly released as SO2 or oxidised to SO2 in the atmosphere (e.g. H2S, OCS, DMS). Around 50% of global atmospheric sulphur dioxide is then oxidised to sulphate, while the rest is lost through dry and wet deposition. The pathway by which SO2 is oxidised to sulphate is critical in determining the climate forcing and environmental effects of sulphate. Gas-phase oxidation of SO2 by OH radicals or criegee intermediates produces H2SO4 (g), which plays an important role in controlling new particle formation in the troposphere and also modifies the surface properties of hydrophobic particles such as soot and mineral dust. Heterogeneous oxidation of SO2 is considered to occur primarily in cloud droplets, although oxidation on sea salt aerosols and mineral dust surfaces are considered to be regionally important. Heterogeneous oxidation leads to the formation of fewer and larger particles with shorter atmospheric lifetime. The major oxidation pathways which are considered to contribute to sulphate formation in the aqueous phase are oxidation by H2O2 and oxidation by O3 and the lifetime of SO2 with respect to all known loss processes combined is considered to be 1-2 days. Here we report measurements of SO2 measurements from IISER Mohali - Ambient Air Quality Station (30.67°N, 76.73°E), a station located at a suburban site in the Indo Gangetic Basin (IGB) during wintertime (10th Dec. 2011 to 29th Feb. 2012). We use a strong point source of SO2 with known SO2/CO emission ratio (brick kiln) located 6.5 km east of our measurement site to estimate the loss rate of SO2 in wintertime fog in the IGB. We consider the transport from the source to the receptor site to be Lagrangian and use the measured CO concentration at the receptors site to account for changes in the emission intensity (activity pattern) and the dilution of the plume during transport. We see a linear correlation between the measured SO2/CO ratio and the transport time. Binning the data on the basis of relative humidity and applying first order kinetics to SO2 loss within each humidity bin we find the SO2 loss rate with respect to aqueous phase oxidation at our sites varies between > 2.2 x 10-3 mol/cm3/s at 96 % RH and 3.8 x 10-4 mol/cm3/s at 47 % RH. Simple box model calculations reveal that neither oxidation by H2O2 nor oxidation by O3 can account for such rapid SO2 oxidation in the fog water. Considering the high mineral dust loadings are our station (PM 10 typically > 300 μg/m3) we propose that transition metal catalysis by TMI leached from natural mineral dust and resuspended road dust may be responsible for the rapid oxidation of SO2 in the fog water. However, the observed lifetime with respect to aqueous phase oxidation in wintertime fog is a factor 150-800 times shorter than the lifetime of SO2 with respect to TMI catalyzed oxidation currently implemented in global atmospheric chemistry models. During 2012-2013 winter season we will measure TMI concentrations in the fog water and verify the rates coefficients estimated from the ambient observation by conducting controlled experiments both using collected fog water and different TMI mixtures. If confirmed through laboratory studies our findings have major implications for the SO2 lifetime over the IGP (and possibly other regions with high mineral dust loadings) and will significantly alter the regional direct and indirect aerosol forcing estimates due to anthropogenic SO2 emissions. Acknowledgement: We thank the IISER Mohali Atmospheric Chemistry Facility for data and the Ministry of Human Resource Development (MHRD), India and IISER Mohali for funding the facility. Himanshu acknowledges the DST-INSPIRE Fellowship program. Chinmoy Sarkar thanks the Max Planck-DST India Partner Group on Tropospheric OH reactivity and VOCs for funding the research.

Membrane Lipid Peroxidation in Copper Alloy-Mediated Contact Killing of Escherichia coli

PubMed Central

Hong, Robert; Kang, Tae Y.; Michels, Corinne A.

2012-01-01

Copper alloy surfaces are passive antimicrobial sanitizing agents that kill bacteria, fungi, and some viruses. Studies of the mechanism of contact killing in Escherichia coli implicate the membrane as the target, yet the specific component and underlying biochemistry remain unknown. This study explores the hypothesis that nonenzymatic peroxidation of membrane phospholipids is responsible for copper alloy-mediated surface killing. Lipid peroxidation was monitored with the thiobarbituric acid-reactive substances (TBARS) assay. Survival, TBARS levels, and DNA degradation were followed in cells exposed to copper alloy surfaces containing 60 to 99.90% copper or in medium containing CuSO4. In all cases, TBARS levels increased with copper exposure levels. Cells exposed to the highest copper content alloys, C11000 and C24000, exhibited novel characteristics. TBARS increased immediately at a very rapid rate but peaked at about 30 min. This peak was associated with the period of most rapid killing, loss in membrane integrity, and DNA degradation. DNA degradation is not the primary cause of copper-mediated surface killing. Cells exposed to the 60% copper alloy for 60 min had fully intact genomic DNA but no viable cells. In a fabR mutant strain with increased levels of unsaturated fatty acids, sensitivity to copper alloy surface-mediated killing increased, TBARS levels peaked earlier, and genomic DNA degradation occurred sooner than in the isogenic parental strain. Taken together, these results suggest that copper alloy surface-mediated killing of E. coli is triggered by nonenzymatic oxidative damage of membrane phospholipids that ultimately results in the loss of membrane integrity and cell death. PMID:22247141

The effect of molten salt on high temperature behavior of stainless steel and titanium alloy with the presence of water vapor

NASA Astrophysics Data System (ADS)

Baharum, Azila; Othman, Norinsan Kamil; Salleh, Emee Marina

2018-04-01

The high temperature oxidation experiment was conducted to study the behavior of titanium alloy Ti6A14V and stainless steel 316 in Na2SO4-50%NaCl + Ar-20%O2 (molten salt) and Na2SO4-50%NaCl + Ar-20%O2 + 12% H2O (molten salt + water vapor) environment at 900°C for 30 hours using horizontal tube furnace. The sample then was investigated using weight change measurement analysis and X-ray diffraction (XRD) analysis to study the weight gained and the phase oxidation that occurred. The weight gained of the titanium alloy was higher in molten salt environment compared to stainless steel due to the rapid growth in the oxide scale but showed almost no change of weight gained upon addition of water vapor. This is due to the alloy was fully oxidized. Stainless steel showed more protection and better effect in molten salt environment compared to mixed environment showed by slower weight gain and lower oxidation rate. Meanwhile, the phase oxidation test of the samples showed that the titanium alloy consist of multi oxide layer of rutile (TiO2) and Al2O3 on the surface of the exposed sample. While stainless steel show the formation of both protective Cr-rich oxide and non-protective Fe-rich oxide layer. This can be concluded that stainless steel is better compared to Ti alloy due to slow growing of chromia oxide. Therefore it is proven that stainless steel has better self-protection upon high temperature exposure.

Decontamination of adsorbed chemical warfare agents on activated carbon using hydrogen peroxide solutions.

PubMed

Osovsky, Ruth; Kaplan, Doron; Nir, Ido; Rotter, Hadar; Elisha, Shmuel; Columbus, Ishay

2014-09-16

Mild treatment with hydrogen peroxide solutions (3-30%) efficiently decomposes adsorbed chemical warfare agents (CWAs) on microporous activated carbons used in protective garments and air filters. Better than 95% decomposition of adsorbed sulfur mustard (HD), sarin, and VX was achieved at ambient temperatures within 1-24 h, depending on the H2O2 concentration. HD was oxidized to the nontoxic HD-sulfoxide. The nerve agents were perhydrolyzed to the respective nontoxic methylphosphonic acids. The relative rapidity of the oxidation and perhydrolysis under these conditions is attributed to the microenvironment of the micropores. Apparently, the reactions are favored due to basic sites on the carbon surface. Our findings suggest a potential environmentally friendly route for decontamination of adsorbed CWAs, using H2O2 without the need of cosolvents or activators.

Mosaic-shaped cathode for highly durable solid oxide fuel cell under thermal stress

NASA Astrophysics Data System (ADS)

Joo, Jong Hoon; Jeong, Jaewon; Kim, Se Young; Yoo, Chung-Yul; Jung, Doh Won; Park, Hee Jung; Kwak, Chan; Yu, Ji Haeng

2014-02-01

In this study, we propose a novel "mosaic structure" for a SOFC (solid oxide fuel cell) cathode with high thermal expansion to improve the stability against thermal stress. Self-organizing mosaic-shaped cathode has been successfully achieved by controlling the amount of binder in the dip-coating solution. The anode-supported cell with mosaic-shaped cathode shows itself to be highly durable performance for rapid thermal cycles, however, the performance of the cell with a non-mosaic cathode exhibits severe deterioration originated from the delamination at the cathode/electrolyte interface after 7 thermal cycles. The thermal stability of an SOFC cathode can be evidently improved by controlling the surface morphology. In view of the importance of the thermal expansion properties of the cathode, the effects of cathode morphology on the thermal stress stability are discussed.

Friction and oxidative wear of 440C ball bearing steels under high load and extreme bulk temperatures

NASA Technical Reports Server (NTRS)

Chaudhuri, Dilip K.; Slifka, Andrew J.; Siegwarth, James D.

1993-01-01

Unlubricated sliding friction and wear of 440C steels in an oxygen environment have been studied under a variety of load, speed, and temperature ranging from approximately -185 to 675 deg C. A specially designed test apparatus with a ball-on-flat geometry has been used for this purpose. The observed dependencies of the initial coefficient of friction, the average dynamic coefficient of friction, and the wear rate on load, speed, and test temperatures have been examined from the standpoint of existing theories of friction and wear. High contact temperatures are generated during the sliding friction, causing rapid oxidation and localized surface melting. A combination of fatigue, delamination, and loss of hardness due to tempering of the martensitic structure is responsible for the high wear rate observed and the coefficient of friction.

Deposition of conductive TiN shells on SiO2 nanoparticles with a fluidized bed ALD reactor

NASA Astrophysics Data System (ADS)

Didden, Arjen; Hillebrand, Philipp; Wollgarten, Markus; Dam, Bernard; van de Krol, Roel

2016-02-01

Conductive TiN shells have been deposited on SiO2 nanoparticles (10-20 nm primary particle size) with fluidized bed atomic layer deposition using TDMAT and NH3 as precursors. Analysis of the powders confirms that shell growth saturates at approximately 0.4 nm/cycle at TDMAT doses of >1.2 mmol/g of powder. TEM and XPS analysis showed that all particles were coated with homogeneous shells containing titanium. Due to the large specific surface area of the nanoparticles, the TiN shells rapidly oxidize upon exposure to air. Electrical measurements show that the partially oxidized shells are conducting, with apparent resistivity of approximately 11 kΩ cm. The resistivity of the powders is strongly influenced by the NH3 dose, with a smaller dose giving an order-of-magnitude higher resistivity.

Electropolymerization of Uniform Polyaniline Nanorod Arrays on Conducting Oxides as Counter Electrodes in Dye-Sensitized Solar Cells.

PubMed

He, Ziming; Liu, Jing; Khoo, Si Yun; Tan, Timothy Thatt Yang

2016-01-01

Conventional techniques for the synthesis of oriented polyaniline (PANI) nanostructures are often complex or time consuming. Through an innovative reduced graphene oxide (rGO) modified FTO and a low-potential electropolymerization strategy, the rapid and template-free growth of a highly ordered PANI nanorod array on the FTO substrate is realized. The highly ordered nanostructure of the PANI array leads to a high electrocatalytic activity and chemical stability. The importance of the polymerization potential and rGO surface modification to achieve this nanostructure is revealed. Compared to platinum, the PANI nanorod array exhibits an enhanced performance and stability as counter electrodes in dye-sensitized solar cells, with a 17.6 % enhancement in power conversion efficiency. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Anodic behavior of uranium in AlCl3-1-ethyl-3-methyl-imidazolium chloride ionic liquid

NASA Astrophysics Data System (ADS)

Jiang, Yidong; Luo, Lizhu; Wang, Shaofei; Bin, Ren; Zhang, Guikai; Wang, Xiaolin

2018-01-01

The oxidation state of metals unambiguously affects its anodic behavior in ionic liquid. We systematically investigated the anodic behavior of uranium with different surface oxidation states by electrochemical measurements, spectroscopic methods and surface analysis techniques. In the anodic process, metal uranium can be oxidized to U3+. The corresponding products accumulated on the metal/ILs interface will form a viscous layer. The anodic behavior of uranium is also strongly dependent upon the surface oxide states including thickness and homogeneity of the oxide film. With an increase in the thickness of oxide film, it will be breached at potentials in excess of a critical value. A uniform oxide on uranium surface can be breached evenly, and then the underlying metal starts to dissolve forming a viscous layer which can facilitate uniformly stripping of oxide, thus giving an oxide-free surface. Otherwise, a nonuniform oxide can result in a severe pitted surface with residue oxygen.

Method for forming a potential hydrocarbon sensor with low sensitivity to methane and CO

DOEpatents

Mukundan, Rangachary; Brosha, Eric L.; Garzon, Fernando

2003-12-02

A hydrocarbon sensor is formed with an electrolyte body having a first electrolyte surface with a reference electrode depending therefrom and a metal oxide electrode body contained within the electrolyte body and having a first electrode surface coplanar with the first electrolyte surface. The sensor was formed by forming a sintered metal-oxide electrode body and placing the metal-oxide electrode body within an electrolyte powder. The electrolyte powder with the metal-oxide electrode body was pressed to form a pressed electrolyte body containing the metal-oxide electrode body. The electrolyte was removed from an electrolyte surface above the metal-oxide electrode body to expose a metal-oxide electrode surface that is coplanar with the electrolyte surface. The electrolyte body and the metal-oxide electrode body were then sintered to form the hydrocarbon sensor.

Surface Coatings for Gas Detection via Porous Silicon

NASA Astrophysics Data System (ADS)

Ozdemir, Serdar; Li, Ji-Guang; Gole, James

2009-03-01

Nanopore covered microporous silicon interfaces have been formed via an electrochemical etch for gas sensor applications. Rapid reversible and sensitive gas sensors have been fabricated. The fabricated porous silicon (PS) gas sensors display the advantages of operation at room temperature as well as at a single, readily accessible temperature with an insensitivity to temperature drift; operation in a heat-sunk configuration, ease of coating with gas-selective materials; low cost of fabrication and operation, and the ability to rapidly assess false positives by operating the sensor in a pulsed mode. The PS surface has been modified with unique coatings on the basis of a general theory in order to achieve maximum sensitivity and selectivity. Sensing of NH3, NOx and PH3 at or below the ppm level have been observed. A typical PS nanostructure coated microstructured hybrid configuration when coated with tin oxide (NOx, CO) and gold nanostructures (NH3) provides a greatly increased sensitivity to the indicated gases. Al2O3 coating of the porous silicon using atomic layer deposition and its effect on PH3 sensing has been investigated. 20-100 nm TiO2 nanoparticles have been produced using sol-gel methods to coat PS surfaces and the effects on the selectivity and the sensitivity have been studied.

A new experimental apparatus for emissivity measurements of steel and the application of multi-wavelength thermometry to continuous casting billets

NASA Astrophysics Data System (ADS)

Wang, Peng; Hu, Zhenwei; Xie, Zhi; Yan, Ming

2018-05-01

An experimental apparatus has been designed for measuring the emissivity of a steel surface in both vacuum and oxidation atmosphere. The sample is heated with the method of electromagnetic induction in order to ensure the temperature uniformity. The radiance emitted from a sample is measured using a fiber-optic Fourier transform infrared spectrometer. Using this unique apparatus, we investigated the spectral (2-6 μm) and directional (0°-86°) emissivity of stainless steel 304 with different degrees of surface oxidation at temperatures ranging from 800 to 1100 °C. The experimental results show that the emissivity increases slightly with increasing temperature, which accords with the Hagen-Rubens relation. The emissivity increases rapidly at the initial stage of oxidation, but gradually reaches to a constant value after 20 min. In addition, the directional emissivity has a maximum value at the measuring angle of about 75°. The maximum uncertainty of emissivity is only 3.0% over all the measuring ranges, indicating that this experimental apparatus has a high reliability. In order to measure the surface temperature of casting billets based on multi-wavelength thermometry, the bivariate emissivity function with the two variables, wavelength and temperature, is determined. Temperature measurement results based on our technique are compared with those from common dual-wavelength radiation thermometry. Our approach reduces the measured temperature fluctuation from ±20.7 °C to ±2.8 °C and reflects the temperature variation with the changes of production parameters in real time.

Reconciling "Whiffs" of O2 with the Archean MIF S Record: Insights from Sulfide Oxidation Experiments

NASA Astrophysics Data System (ADS)

Johnson, A.; Reinhard, C. T.; Romaniello, S. J.; Greaney, A. T.; Garcia-Robledo, E.; Revsbech, N. P.; Canfield, D. E.; Lyons, T. W.; Anbar, A. D.

2016-12-01

The Archean-Proterozoic transition is marked by the first appreciable accumulation of O2 in Earth's oceans and atmosphere at 2.4 billion years ago (Ga). However, this Great Oxidation Event (GOE) is not the first evidence for O2 in Earth's surface environment. Paleoredox proxies preserved in ancient marine shales (Mo, Cr, Re, U) suggest transient episodes of oxidative weathering before the GOE, perhaps as early as 3.0 Ga. One marine shale in particular, the 2.5 Ga Mount McRae Shale of Western Australia, contains a euxinic interval with Mo enrichments up to 50 ppm. This enrichment is classically interpreted as the result of oxidative weathering of sulfides on the continental surface. However, prior weathering models based on experiments suggested that sulfides require large amounts of O2 [>10-4 present atmospheric level (PAL) pO2] to produce this weathering signature, in conflict with estimates of Archean pO2 from non-mass-dependent (NMD) sulfur isotope anomalies (<10-5 PAL pO2). To reconcile these datasets, we conducted aqueous oxidation experiments of pyrite and molybdenite from 3 - 700 nM O2 (equivalent at equilibrium to 10-5 - 10-3 PAL) to measure oxidation kinetics as a function of the concentration of dissolved O2. We measured rates by injecting oxygenated water at a steady flow rate and monitoring dissolved O2 concentrations with LUMOS sensors. Our data extend the O2 range explored in pyrite oxidation experiments by three orders of magnitude and provide the first rates for molybdenite oxidation at O2 concentrations potentially analogous to those characteristic of the Archean atmosphere. Our results show that pyrite and molybdenite oxidize significantly more rapidly at lower O2 levels than previously thought. As a result, our revised weathering model demonstrates that the Mo enrichments observed in late Archean marine shales are potentially attainable at extremely low atmospheric pO2 values (e.g., <10-5 PAL), reconciling large sedimentary Mo enrichments with co-occurring NMD sulfur isotope anomalies.

Oxidation of SiC/BN/SiC Composites in Reduced Oxygen Partial Pressures

NASA Technical Reports Server (NTRS)

Opila, Elizabeth J.; Boyd, Meredith

2010-01-01

SiC fiber-reinforced SiC composites with a BN interphase are proposed for use as leading edge structures of hypersonic vehicles. The durability of these materials under hypersonic flight conditions is therefore of interest. Thermogravimetric analysis was used to characterize the oxidation kinetics of both the constituent fibers and composite coupons at four temperatures: 816, 1149, 1343, and 1538 C (1500, 2100, 2450, and 2800 F) and in oxygen partial pressures between 5% and 0.1% (balance argon) at 1 atm total pressure. One edge of the coupons was ground off so the effects of oxygen ingress into the composite could be monitored by post-test SEM and EDS. Additional characterization of the oxidation products was conducted by XPS and TOF-SIMS. Under most conditions, the BN oxidized rapidly, leading to the formation of borosilicate glass. Rapid initial oxidation followed by volatilization of boria lead to protective oxide formation and further oxidation was slow. At 1538C in 5% oxygen, both the fibers and coupons exhibited borosilicate glass formation and bubbling. At 1538C in 0.1% oxygen, active oxidation of both the fibers and the composites was observed leading to rapid SiC degradation. BN oxidation at 1538C in 0.1% oxygen was not significant.

Method of physical vapor deposition of metal oxides on semiconductors

DOEpatents

Norton, David P.

2001-01-01

A process for growing a metal oxide thin film upon a semiconductor surface with a physical vapor deposition technique in a high-vacuum environment and a structure formed with the process involves the steps of heating the semiconductor surface and introducing hydrogen gas into the high-vacuum environment to develop conditions at the semiconductor surface which are favorable for growing the desired metal oxide upon the semiconductor surface yet is unfavorable for the formation of any native oxides upon the semiconductor. More specifically, the temperature of the semiconductor surface and the ratio of hydrogen partial pressure to water pressure within the vacuum environment are high enough to render the formation of native oxides on the semiconductor surface thermodynamically unstable yet are not so high that the formation of the desired metal oxide on the semiconductor surface is thermodynamically unstable. Having established these conditions, constituent atoms of the metal oxide to be deposited upon the semiconductor surface are directed toward the surface of the semiconductor by a physical vapor deposition technique so that the atoms come to rest upon the semiconductor surface as a thin film of metal oxide with no native oxide at the semiconductor surface/thin film interface. An example of a structure formed by this method includes an epitaxial thin film of (001)-oriented CeO.sub.2 overlying a substrate of (001) Ge.

Understanding oxygen adsorption on 9.375 at. % Ga-stabilized δ-Pu (111) surface: A DFT study

DOE PAGES

Hernandez, Sarah C.; Wilkerson, Marianne P.; Huda, Muhammad N.

2015-08-30

Plutonium (Pu) metal reacts rapidly in the presence of oxygen (O), resulting in an oxide layer that will eventually have an olive green rust appearance over time. Recent experimental work suggested that the incorporation of gallium (Ga) as an alloying impurity to stabilize the highly symmetric high temperature δ-phase lattice may also provide resistance against corrosion/oxidation of plutonium. In this paper, we modeled a 9.375 at. % Ga stabilized δ-Pu (111) surface and investigated adsorption of atomic O using all-electron density functional theory. Key findings revealed that the O bonded strongly to a Pu-rich threefold hollow fcc site with amore » chemisorption energy of –5.06 eV. Migration of the O atom to a Pu-rich environment was also highly sensitive to the surface chemistry of the Pu–Ga surface; when the initial on-surface O adsorption site included a bond to a nearest neighboring Ga atom, the O atom relaxed to a Ga deficient environment, thus affirming the O preference for Pu. Only one calculated final on-surface O adsorption site included a Ga-O bond, but this chemisorption energy was energetically unfavorable. Chemisorption energies for interstitial adsorption sites that included a Pu or Pu-Ga environment suggested that over-coordination of the O atom was energetically unfavorable as well. Electronic structure properties of the on-surface sites, illustrated by the partial density of states, implied that the Ga 4p states indirectly but strongly influenced the Pu 6d states strongly to hybridize with the O 2p states, while also weakly influenced the Pu 5f states to hybridize with the O 2p states, even though Ga was not participating in bonding with O.« less

Facile and rapid synthesis of Pd nanodendrites for electrocatalysis and surface-enhanced Raman scattering applications

NASA Astrophysics Data System (ADS)

Kannan, Palanisamy; Dolinska, Joanna; Maiyalagan, Thandavarayan; Opallo, Marcin

2014-09-01

Numerous properties from metal nanostructures can be tuned by controlling both their size and shape. In particular, the latter is extremely important because the type of crystalline surface affects the surface electronic density. This paper describes a simple approach to the synthesis of highly-structured, anisotropic palladium nanostructured dendrites. They were obtained using an eco-friendly biomolecule 5-hydroxytryptophan, which acts as both a reducing and stabilizing agent. The growth mechanism is proposed for the evolution of dendrites morphology. It was found that the concentration of 5-hydroxytryptophan played a vital role on the morphology of the nanostructured Pd dendrites. This nanomaterial shows enhanced electrocatalytic performance towards the oxidation of formic acid, and it exhibits surface-enhanced Raman scattering properties towards the prostate specific antigen. These properties may be explored in fuel cells and biosensors, respectively.Numerous properties from metal nanostructures can be tuned by controlling both their size and shape. In particular, the latter is extremely important because the type of crystalline surface affects the surface electronic density. This paper describes a simple approach to the synthesis of highly-structured, anisotropic palladium nanostructured dendrites. They were obtained using an eco-friendly biomolecule 5-hydroxytryptophan, which acts as both a reducing and stabilizing agent. The growth mechanism is proposed for the evolution of dendrites morphology. It was found that the concentration of 5-hydroxytryptophan played a vital role on the morphology of the nanostructured Pd dendrites. This nanomaterial shows enhanced electrocatalytic performance towards the oxidation of formic acid, and it exhibits surface-enhanced Raman scattering properties towards the prostate specific antigen. These properties may be explored in fuel cells and biosensors, respectively. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02896a

Understanding oxygen adsorption on 9.375 at. % Ga-stabilized δ-Pu (111) surface: A DFT study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez, Sarah C.; Wilkerson, Marianne P.; Huda, Muhammad N.

Plutonium (Pu) metal reacts rapidly in the presence of oxygen (O), resulting in an oxide layer that will eventually have an olive green rust appearance over time. Recent experimental work suggested that the incorporation of gallium (Ga) as an alloying impurity to stabilize the highly symmetric high temperature δ-phase lattice may also provide resistance against corrosion/oxidation of plutonium. In this paper, we modeled a 9.375 at. % Ga stabilized δ-Pu (111) surface and investigated adsorption of atomic O using all-electron density functional theory. Key findings revealed that the O bonded strongly to a Pu-rich threefold hollow fcc site with amore » chemisorption energy of –5.06 eV. Migration of the O atom to a Pu-rich environment was also highly sensitive to the surface chemistry of the Pu–Ga surface; when the initial on-surface O adsorption site included a bond to a nearest neighboring Ga atom, the O atom relaxed to a Ga deficient environment, thus affirming the O preference for Pu. Only one calculated final on-surface O adsorption site included a Ga-O bond, but this chemisorption energy was energetically unfavorable. Chemisorption energies for interstitial adsorption sites that included a Pu or Pu-Ga environment suggested that over-coordination of the O atom was energetically unfavorable as well. Electronic structure properties of the on-surface sites, illustrated by the partial density of states, implied that the Ga 4p states indirectly but strongly influenced the Pu 6d states strongly to hybridize with the O 2p states, while also weakly influenced the Pu 5f states to hybridize with the O 2p states, even though Ga was not participating in bonding with O.« less

Preparation of Janus Particles and Alternating Current Electrokinetic Measurements with a Rapidly Fabricated Indium Tin Oxide Electrode Array.

PubMed

Chen, Yu-Liang; Jiang, Hong-Ren

2017-06-23

This article provides a simple method to prepare partially or fully coated metallic particles and to perform the rapid fabrication of electrode arrays, which can facilitate electrical experiments in microfluidic devices. Janus particles are asymmetric particles that contain two different surface properties on their two sides. To prepare Janus particles, a monolayer of silica particles is prepared by a drying process. Gold (Au) is deposited on one side of each particle using a sputtering device. The fully coated metallic particles are completed after the second coating process. To analyze the electrical surface properties of Janus particles, alternating current (AC) electrokinetic measurements, such as dielectrophoresis (DEP) and electrorotation (EROT)- which require specifically designed electrode arrays in the experimental device- are performed. However, traditional methods to fabricate electrode arrays, such as the photolithographic technique, require a series of complicated procedures. Here, we introduce a flexible method to fabricate a designed electrode array. An indium tin oxide (ITO) glass is patterned by a fiber laser marking machine (1,064 nm, 20 W, 90 to 120 ns pulse-width, and 20 to 80 kHz pulse repetition frequency) to create a four-phase electrode array. To generate the four-phase electric field, the electrodes are connected to a 2-channel function generator and to two invertors. The phase shift between the adjacent electrodes is set at either 90° (for EROT) or 180° (for DEP). Representative results of AC electrokinetic measurements with a four-phase ITO electrode array are presented.

Clay-mediated reactions of HCN oligomers - The effect of the oxidation state of the clay

NASA Technical Reports Server (NTRS)

Ferris, J. P.; Alwis, K. W.; Edelson, E. H.; Mount, N.; Hagan, W. J., Jr.

1981-01-01

Montmorillonite clays which contain Fe(III) inhibit the oligomerization of aqueous solutions of HCN. The inhibitory effect is due to the rapid oxidation of diaminomaleonitrile, a key intermediate in HCN oligomerization, by the Fe(III) incorporated into the aluminosilicate lattice of the clay. The Fe(III) oxidizes diaminomaleonitrile to diiminosuccinonitrile, a compound which is rapidly hydrolyzed to HCN and oxalic acid derivatives. Diaminomaleonitrile is not oxidized when Fe(III) in the montmorillonite is reduced with hydrazine. The oxidation state of the clay is an important variable in experiments designed to simulate clay catalysis on the primitive earth.

Method for the rapid synthesis of large quantities of metal oxide nanowires at low temperatures

DOEpatents

Sunkara, Mahendra Kumar [Louisville, KY; Vaddiraju, Sreeram [Mountain View, CA; Mozetic, Miran [Ljubljan, SI; Cvelbar, Uros [Idrija, SI

2009-09-22

A process for the rapid synthesis of metal oxide nanoparticles at low temperatures and methods which facilitate the fabrication of long metal oxide nanowires. The method is based on treatment of metals with oxygen plasma. Using oxygen plasma at low temperatures allows for rapid growth unlike other synthesis methods where nanomaterials take a long time to grow. Density of neutral oxygen atoms in plasma is a controlling factor for the yield of nanowires. The oxygen atom density window differs for different materials. By selecting the optimal oxygen atom density for various materials the yield can be maximized for nanowire synthesis of the metal.

Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles

PubMed Central

Braniste, Tudor; Tiginyanu, Ion; Horvath, Tibor; Raevschi, Simion; Cebotari, Serghei; Lux, Marco; Haverich, Axel

2016-01-01

Summary Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle–cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO) nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN. PMID:27826507

An ordered array of hierarchical spheres for surface-enhanced Raman scattering detection of traces of pesticide

NASA Astrophysics Data System (ADS)

Hu, Xiaoye; Zheng, Peng; Meng, Guowen; Huang, Qing; Zhu, Chuhong; Han, Fangming; Huang, Zhulin; Li, Zhongbo; Wang, Zhaoming; Wu, Nianqiang

2016-09-01

An ordered array of hierarchically-structured core-nanosphere@space-layer@shell-nanoparticles has been fabricated for surface-enhanced Raman scattering (SERS) detection. To fabricate this hierarchically-structured chip, a long-range ordered array of Au/Ag-nanospheres is first patterned in the nano-bowls on the planar surface of ordered nanoporous anodic titanium oxide template. A ultra-thin alumina middle space-layer is then conformally coated on the Au/Ag-nanospheres, and Ag-nanoparticles are finally deposited on the surface of the alumina space-layer to form an ordered array of Au/Ag-nanosphere@Al2O3-layer@Ag-nanoparticles. Finite-difference time-domain simulation shows that SERS hot spots are created between the neighboring Ag-nanoparticles. The ordered array of hierarchical nanostructures is used as the SERS-substrate for a trial detection of methyl parathion (a pesticide) in water and a limit of detection of 1 nM is reached, indicating its promising potential in rapid monitoring of organic pollutants in aquatic environment.

A self-assembled microbonded germanium/silicon heterojunction photodiode for 25 Gb/s high-speed optical interconnects

PubMed Central

Tseng, Chih-Kuo; Chen, Wei-Ting; Chen, Ku-Hung; Liu, Han-Din; Kang, Yimin; Na, Neil; Lee, Ming-Chang M.

2013-01-01

A novel technique using surface tension to locally bond germanium (Ge) on silicon (Si) is presented for fabricating high performance Ge/Si photodiodes. Surface tension is a cohesive force among liquid molecules that tends to bring contiguous objects in contact to maintain a minimum surface energy. We take advantage of this phenomenon to fabricate a heterojunction optoelectronic device where the lattice constants of joined semiconductors are different. A high-speed Ge/Si heterojunction waveguide photodiode is presented by microbonding a beam-shaped Ge, first grown by rapid-melt-growth (RMG) method, on top of a Si waveguide via surface tension. Excellent device performances such as an operating bandwidth of 17 GHz and a responsivity of 0.66 and 0.70 A/W at the reverse bias of −4 and −6 V, respectively, are demonstrated. This technique can be simply implemented via modern complementary metal-oxide-semiconductor (CMOS) fabrication technologies for integrating Ge on Si devices. PMID:24232956

Soft-Template Synthesis of Mesoporous Anatase TiO₂ Nanospheres and Its Enhanced Photoactivity.

PubMed

Li, Xiaojia; Zou, Mingming; Wang, Yang

2017-11-10

Highly crystalline mesoporous anatase TiO₂ nanospheres with high surface area (higher than P25 and anatase TiO₂) are prepared by a soft-template method. Despite the high specific surface area, these samples have three times lower equilibrium adsorption (<2%) than Degussa P25. The rate constant of the mesoporous anatase TiO₂ (0.024 min -1 ) reported here is 364% higher than that of P25 (0.0066 min -1 ), for the same catalytic loading. The results of oxidation-extraction photometry using several reactive oxygen species (ROS) scavengers indicated that mesoporous anatase TiO₂ generates more ROS than P25 under UV-light irradiation. This significant improvement in the photocatalytic performance of mesoporous spherical TiO₂ arises from the following synergistic effects in the reported sample: (i) high surface area; (ii) improved crystallinity; (iii) narrow pore wall thicknesses (ensuring the rapid migration of photogenerated carriers to the surface of the material); and (iv) greater ROS generation under UV-light.

Effect of low thermal budget annealing on surface passivation of silicon by ALD based aluminum oxide films.

PubMed

Vandana; Batra, Neha; Gope, Jhuma; Singh, Rajbir; Panigrahi, Jagannath; Tyagi, Sanjay; Pathi, P; Srivastava, S K; Rauthan, C M S; Singh, P K

2014-10-21

Thermal ALD deposited Al2O3 films on silicon show a marked difference in surface passivation quality as a function of annealing time (using a rapid thermal process). An effective and quality passivation is realized in short anneal duration (∼100 s) in nitrogen ambient which is reflected in the low surface recombination velocity (SRV <10 cm s(-1)). The deduced values are close to the best reported SRV obtained by the high thermal budget process (with annealing time between 10-30 min), conventionally used for improved surface passivation. Both as-deposited and low thermal budget annealed films show the presence of positive fixed charges and this is never been reported in the literature before. The role of field and chemical passivation is investigated in terms of fixed charge and interface defect densities. Further, the importance of the annealing step sequence in the MIS structure fabrication protocol is also investigated from the view point of its effect on the nature of fixed charges.

X-ray photoelectron spectroscopic study of the interaction of xanthate with coal pyrite and mineral pyrite surfaces

NASA Astrophysics Data System (ADS)

Khan, S. U. M.; Baltrus, J. P.; Lai, R. W.; Richardson, A. G.

1991-06-01

Coal pyrite and mineral pyrite surfaces were examined by X-ray photoelectron spectroscopy (XPS) before and after treatment in acidic and basic solutions of sodium ethyl xanthate (NaEtX). XPS showed that the degree of oxidation of coal and mineral pyrite surfaces increased when these pyrites were conditioned in basic solutions. However, conditioning in acidic solutions led to partial removal of surface oxidation from the pyrites. Addition of NaEtX to the acidic and basic solutions enhanced the removal of oxidation from pyrite surfaces. Pretreatment with sulfur dioxide further enhanced the removal of surface oxidation in the presence of NaEtX. Surface oxidation was typically less on mineral pyrite than coal pyrite surfaces following identical treatments. The flotation recoveries of the pyrites in the presence of NaEtX are greatest for the pyrites with the least amount of surface oxidation.

Optimization of NO oxidation by H2O2 thermal decomposition at moderate temperatures.

PubMed

Zhao, Hai-Qian; Wang, Zhong-Hua; Gao, Xing-Cun; Liu, Cheng-Hao; Qi, Han-Bing

2018-01-01

H2O2 was adopted to oxidize NO in simulated flue gas at 100-500°C. The effects of the H2O2 evaporation conditions, gas temperature, initial NO concentration, H2O2 concentration, and H2O2:NO molar ratio on the oxidation efficiency of NO were investigated. The reason for the narrow NO oxidation temperature range near 500°C was determined. The NO oxidation products were analyzed. The removal of NOx using NaOH solution at a moderate oxidation ratio was studied. It was proven that rapid evaporation of the H2O2 solution was critical to increase the NO oxidation efficiency and broaden the oxidation temperature range. the NO oxidation efficiency was above 50% at 300-500°C by contacting the outlet of the syringe needle and the stainless-steel gas pipe together to spread H2O2 solution into a thin film on the surface of the stainless-steel gas pipe, which greatly accelerated the evaporation of H2O2. The NO oxidation efficiency and the NO oxidation rate increased with increasing initial NO concentration. This method was more effective for the oxidation of NO at high concentrations. H2O2 solution with a concentration higher than 15% was more efficient in oxidizing NO. High temperatures decreased the influence of the H2O2 concentration on the NO oxidation efficiency. The oxidation efficiency of NO increased with an increase in the H2O2:NO molar ratio, but the ratio of H2O2 to oxidized NO decreased. Over 80% of the NO oxidation product was NO2, which indicated that the oxidation ratio of NO did not need to be very high. An 86.7% NO removal efficiency was obtained at an oxidation ratio of only 53.8% when combined with alkali absorption.

Optimization of NO oxidation by H2O2 thermal decomposition at moderate temperatures

PubMed Central

Wang, Zhong-hua; Gao, Xing-cun; Liu, Cheng-hao; Qi, Han-bing

2018-01-01

H2O2 was adopted to oxidize NO in simulated flue gas at 100–500°C. The effects of the H2O2 evaporation conditions, gas temperature, initial NO concentration, H2O2 concentration, and H2O2:NO molar ratio on the oxidation efficiency of NO were investigated. The reason for the narrow NO oxidation temperature range near 500°C was determined. The NO oxidation products were analyzed. The removal of NOx using NaOH solution at a moderate oxidation ratio was studied. It was proven that rapid evaporation of the H2O2 solution was critical to increase the NO oxidation efficiency and broaden the oxidation temperature range. the NO oxidation efficiency was above 50% at 300–500°C by contacting the outlet of the syringe needle and the stainless-steel gas pipe together to spread H2O2 solution into a thin film on the surface of the stainless-steel gas pipe, which greatly accelerated the evaporation of H2O2. The NO oxidation efficiency and the NO oxidation rate increased with increasing initial NO concentration. This method was more effective for the oxidation of NO at high concentrations. H2O2 solution with a concentration higher than 15% was more efficient in oxidizing NO. High temperatures decreased the influence of the H2O2 concentration on the NO oxidation efficiency. The oxidation efficiency of NO increased with an increase in the H2O2:NO molar ratio, but the ratio of H2O2 to oxidized NO decreased. Over 80% of the NO oxidation product was NO2, which indicated that the oxidation ratio of NO did not need to be very high. An 86.7% NO removal efficiency was obtained at an oxidation ratio of only 53.8% when combined with alkali absorption. PMID:29668672

Thermal oxidation of single crystal aluminum antimonide and materials having the same

DOEpatents

Sherohman, John William; Yee, Jick Hong; Coombs, III, Arthur William; Wu, Kuang Jen J.

2012-12-25

In one embodiment, a method for forming a non-conductive crystalline oxide layer on an AlSb crystal includes heat treating an AlSb crystal in a partial vacuum atmosphere at a temperature conducive for air adsorbed molecules to desorb, surface molecule groups to decompose, and elemental Sb to evaporate from a surface of the AlSb crystal and exposing the AlSb crystal to an atmosphere comprising oxygen to form a crystalline oxide layer on the surface of the AlSb crystal. In another embodiment, a method for forming a non-conductive crystalline oxide layer on an AlSb crystal includes heat treating an AlSb crystal in a non-oxidizing atmosphere at a temperature conducive for decomposition of an amorphous oxidized surface layer and evaporation of elemental Sb from the AlSb crystal surface and forming stable oxides of Al and Sb from residual surface oxygen to form a crystalline oxide layer on the surface of the AlSb crystal.

Ternary Au/ZnO/rGO nanocomposites electrodes for high performance electrochemical storage devices

NASA Astrophysics Data System (ADS)

Chaudhary, Manchal; Doong, Ruey-an; Kumar, Nagesh; Tseng, Tseung Yuen

2017-10-01

The combination of metal and metal oxide nanoparticles with reduced graphene oxides (rGO) is an active electrode material for electrochemical storage devices. Herein, we have, for the first time, reported the fabrication of ternary Au/ZnO/rGO nanocomposites by using a rapid and environmentally friendly microwave-assisted hydrothermal method for high performance supercapacitor applications. The ZnO/rGO provides excellent electrical conductivity and good macro/mesopore structures, which can facilitate the rapid electrons and ions transport. The Au nanoparticles with particle sizes of 7-12 nm are homogeneously distributed onto the ZnO/rGO surface to enhance the electrochemical performance by retaining the capacitance at high current density. The Au/ZnO/rGO nanocomposites, prepared with the optimized rGO amount of 100 mg exhibit a high specific capacitance of 875 and 424 F g-1 at current densities of 1 and 20 A g-1, respectively, in 2 M KOH. In addition, the energy and power densities of ternary Au/ZnO/rGO can be up to 17.6-36.5 Wh kg-1 and 0.27-5.42 kW kg-1, respectively. Results obtained in this study clearly demonstrate the excellence of ternary Au/ZnO/rGO nanocomposites as the active electrode materials for electrochemical pseudocapacitor performance and can open an avenue to fabricate metal/metal oxide/rGO nanocomposites for electrochemical storage devices with both high energy and power densities.

Gas atomized precursor alloy powder for oxide dispersion strengthened ferritic stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rieken, Joel

Gas atomization reaction synthesis (GARS) was employed as a simplified method for producing precursor powders for oxide dispersion strengthened (ODS) ferritic stainless steels (e.g., Fe-Cr-Y-(Ti,Hf)-O), departing from the conventional mechanical alloying (MA) process. During GARS processing a reactive atomization gas (i.e., Ar-O 2) was used to oxidize the powder surfaces during primary break-up and rapid solidification of the molten alloy. This resulted in envelopment of the powders by an ultra-thin (t < 150 nm) metastable Cr-enriched oxide layer that was used as a vehicle for solid-state transport of O into the consolidated microstructure. In an attempt to better understand themore » kinetics of this GARS reaction, theoretical cooling curves for the atomized droplets were calculated and used to establish an oxidation model for this process. Subsequent elevated temperature heat treatments, which were derived from Rhines pack measurements using an internal oxidation model, were used to promote thermodynamically driven O exchange reactions between trapped films of the initial Cr-enriched surface oxide and internal Y-enriched intermetallic precipitates. This novel microstructural evolution process resulted in the successful formation of nano-metric Y-enriched dispersoids, as confirmed using high energy X-ray diffraction and transmission electron microscopy (TEM), equivalent to conventional ODS alloys from MA powders. The thermal stability of these Y-enriched dispersoids was evaluated using high temperature (1200°C) annealing treatments ranging from 2.5 to 1,000 hrs of exposure. In a further departure from current ODS practice, replacing Ti with additions of Hf appeared to improve the Y-enriched dispersoid thermal stability by means of crystal structure modification. Additionally, the spatial distribution of the dispersoids was found to depend strongly on the original rapidly solidified microstructure. To exploit this, ODS microstructures were engineered from different powder particle size ranges, illustrating microstructural control as a function of particle solidification rate. The consolidation of ultra-fine powders (dia. ≤ 5μm) resulted in a significant reduction in dispersoid size and spacing, consistent with initial scanning electron microscopy studies on as-atomized cross-sectioned particles that suggested that these powders solidified above the threshold velocity to effectively solute trap Y within the α-(Fe,Cr) matrix. Interestingly, when the solidification velocity as a function of particle size was extracted from the aforementioned theoretical particle cooling curves, it could be offered as supporting evidence for these microstructure observations. Thermal-mechanical treatments also were used to create and evaluate the stability of a dislocation substructure within these alloys, using microhardness and TEM analysis of the alloy sub-grain and grain structure. Moreover, elevated temperature tensile tests up to 800°C were used to assess the initial mechanical strength of the ODS microstructure.« less

Multiscale Investigations of the Early Stage Oxidation on Cu Surfaces

NASA Astrophysics Data System (ADS)

Zhu, Qing; Xiao, Penghao; Lian, Xin; Yang, Shen-Che; Henkelman, Grame; Saidi, Wissam; Yang, Judith; University of Pittsburgh Team; University of Texas at Austin Team

Previous in situ TEM experiments have shown that the oxidation of the three low index Cu surfaces (100), (110) and (111) exhibit different oxide nucleation rates, and the resulting oxides have 3-dimensional (3D) island shapes or 2D rafts under different conditions. In order to better understand these results, we have investigated the early stages of Cu oxidation using a multiscale computational approach that employs density functional theory (DFT), reactive force field (ReaxFF), and kinetic Mote Carlo (KMC). With DFT calculation, we have compared O2 dissociation barriers on Cu (100), (110) and (111) surfaces at high oxygen coverage to evaluate the kinetic barrier of sublayer oxidization. We found that O2 dissociation barriers on Cu(111) surface are all lower than those on (110) and (100) surfaces. This trend agrees with experimental observations that (111) surface is easier to oxidize. These DFT calculated energy barriers are then incorporated into KMC simulations. The large scale ReaxFF molecular dynamics and KMC simulations detail the oxidation dynamics of the different Cu surfaces, and show the formation of various oxide morphologies that are consistent with experimental observations.

Real-time photoelectron spectroscopy study of the oxidation reaction kinetics on p-type and n-type Si (001) surfaces

NASA Astrophysics Data System (ADS)

Yu, Zhou

Silicon oxides thermally grown on Si surface are the core gate materials of metal-oxide-semiconductor field effect transistor (MOSFET). This thin oxide layer insulates the gate terminals and the transistors substrate which make MOSFET has certain advantages over those conventional junctions, such as field-effect transistor (FET) and junction field effect transistor (JFET). With an oxide insulating layer, MOSFET is able to sustain higher input impedance and the corresponding gate leakage current can be minimized. Today, though the oxidation process on Si substrate is popular in industry, there are still some uncertainties about its oxidation kinetics. On a path to clarify and modeling the oxidation kinetics, a study of initial oxidation kinetics on Si (001) surface has attracted attentions due to having a relatively low surface electron density and few adsorption channels compared with other Si surface direction. Based on previous studies, there are two oxidation models of Si (001) that extensively accepted, which are dual oxide species mode and autocatalytic reaction model. These models suggest the oxidation kinetics on Si (001) mainly relies on the metastable oxygen atom on the surface and the kinetic is temperature dependent. Professor Yuji Takakuwa's group, Surface Physics laboratory, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, observed surface strain existed during the oxidation kinetics on Si (001) and this is the first time that strain was discovered during Si oxidation. Therefore, it is necessary to explain where the strain comes from since none of previous model research included the surface strain (defects generation) into considerations. Moreover, recent developing of complementary metal-oxide-semiconductor (CMOS) requires a simultaneous oxidation process on p- and n-type Si substrate. However, none of those previous models included the dopant factor into the oxidation kinetic modeling. All of these points that further work is necessary to update and modify the traditional Si (001) oxidation models that had been accepted for several decades. To update and complement the Si (001) oxidation kinetics, an understanding of the temperature and dopant factor during initial oxidation kinetics on Si (001) is our first step. In this study, real-time photoelectron spectroscopy is applied to characterize the oxidized (001) surface and surface information was collected by ultraviolet photoelectron spectroscopy technique. By analyzing parameters such as O 2p spectra uptake, change of work function and the surface state in respect of p- and n- type Si (001) substrate under different temperature, the oxygen adsorption structure and the dopant factor can be determined. In this study, experiments with temperature gradients on p-type Si (001) were conducted and this aims to clarify the temperature dependent characteristic of Si (001) surface oxidation. A comparison of the O 2p uptake, change of work function and surface state between p-and n-type Si (001) is made under a normal temperature and these provides with the data to explain how the dopant factor impacts the oxygen adsorption structure on the surface. In the future, the study of the oxygen adsorption structure will lead to an explanation of the surface strain that discovered; therefore, fundamental of the initial oxidation on Si (001) would be updated and complemented, which would contribute to the future gate technology in MOSFET and CMOS.

Oxidation behavior and electrical property of ferritic stainless steel interconnects with a Cr-La alloying layer by high-energy micro-arc alloying process

NASA Astrophysics Data System (ADS)

Feng, Z. J.; Zeng, C. L.

Chromium volatility, poisoning of the cathode material and rapidly decreasing electrical conductivity are the major problems associated with the application of ferritic stainless steel interconnects of solid oxide fuel cells operated at intermediate temperatures. Recently, a novel and simple high-energy micro-arc alloying (HEMAA) process is proposed to prepare LaCrO 3-based coatings for the type 430 stainless steel interconnects using a LaCrO 3-Ni rod as deposition electrode. In this work, a Cr-La alloying layer is firstly obtained on the alloy surface by HEMAA using Cr and La as deposition electrode, respectively, followed by oxidation treatment at 850 °C in air to form a thermally grown LaCrO 3 coating. With the formation of a protective scale composed of a thick LaCrO 3 outer layer incorporated with small amounts of Cr-rich oxides and a thin Cr 2O 3-rich sub-layer, the oxidation rate of the coated steel is reduced remarkably. A low and stable electrical contact resistance is achieved with the application of LaCrO 3-based coatings, with a value less than 40 mΩ cm 2 during exposure at 850 °C in air for up to 500 h.

Ozone and alkyl nitrate formation from the Deepwater Horizon oil spill atmospheric emissions

NASA Astrophysics Data System (ADS)

Neuman, J. A.; Aikin, K. C.; Atlas, E. L.; Blake, D. R.; Holloway, J. S.; Meinardi, S.; Nowak, J. B.; Parrish, D. D.; Peischl, J.; Perring, A. E.; Pollack, I. B.; Roberts, J. M.; Ryerson, T. B.; Trainer, M.

2012-05-01

Ozone (O3), alkyl nitrates (RONO2), and other photochemical products were formed in the atmosphere downwind from the Deepwater Horizon (DWH) oil spill by photochemical reactions of evaporating hydrocarbons with NOx (=NO + NO2) emissions from spill response activities. Reactive nitrogen species and volatile organic compounds (VOCs) were measured from an instrumented aircraft during daytime flights in the marine boundary layer downwind from the area of surfacing oil. A unique VOC mixture, where alkanes dominated the hydroxyl radical (OH) loss rate, was emitted into a clean marine environment, enabling a focused examination of O3 and RONO2 formation processes. In the atmospheric plume from DWH, the OH loss rate, an indicator of potential O3 formation, was large and dominated by alkanes with between 5 and 10 carbons per molecule (C5-C10). Observations showed that NOx was oxidized very rapidly with a 0.8 h lifetime, producing primarily C6-C10 RONO2 that accounted for 78% of the reactive nitrogen enhancements in the atmospheric plume 2.5 h downwind from DWH. Both observations and calculations of RONO2 and O3 production rates show that alkane oxidation dominated O3 formation chemistry in the plume. Rapid and nearly complete oxidation of NOx to RONO2 effectively terminated O3 production, with O3 formation yields of 6.0 ± 0.5 ppbv O3 per ppbv of NOx oxidized. VOC mixing ratios were in large excess of NOx, and additional NOx would have formed additional O3 in this plume. Analysis of measurements of VOCs, O3, and reactive nitrogen species and calculations of O3 and RONO2 production rates demonstrate that NOx-VOC chemistry in the DWH plume is explained by known mechanisms.

Heat transfer from an oxidized large copper surface to liquid helium: Dependence on surface orientation and treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iwamoto, A.; Mito, T.; Takahata, K.

Heat transfer of large copper plates (18 x 76 mm) in liquid helium has been measured as a function of orientation and treatment of the heat transfer surface. The results relate to applications of large scale superconductors. In order to clarify the influence of the area where the surface treatment peels off, the authors studied five types of heat transfer surface areas including: (a) 100% polished copper sample, (b) and (c) two 50% oxidized copper samples having different patterns of oxidation, (d) 75% oxidized copper sample, (e) 90% oxidized copper sample, and (f) 100% oxidized copper sample. They observed thatmore » the critical heat flux depends on the heat transfer surface orientation. The critical heat flux is a maximum at angles of 0{degrees} - 30{degrees} and decreases monotonically with increasing angles above 30{degrees}, where the angle is taken in reference to the horizontal axis. On the other hand, the minimum heat flux is less dependent on the surface orientation. More than 75% oxidation on the surface makes the critical heat flux increase. The minimum heat fluxes of the 50 and 90% oxidized Cu samples approximately agree with that of the 100% oxidized Cu sample. Experiments and calculations show that the critical and the minimum heat fluxes are a bilinear function of the fraction of oxidized surface area.« less

Enhanced dopamine detection sensitivity by PEDOT/graphene oxide coating on in vivo carbon fiber electrodes.

PubMed

Taylor, I Mitch; Robbins, Elaine M; Catt, Kasey A; Cody, Patrick A; Happe, Cassandra L; Cui, Xinyan Tracy

2017-03-15

Dopamine (DA) is a monoamine neurotransmitter responsible for regulating a variety of vital life functions. In vivo detection of DA poses a challenge due to the low concentration and high speed of physiological signaling. Fast scan cyclic voltammetry at carbon fiber microelectrodes (CFEs) is an effective method to monitor real-time in vivo DA signaling, however the sensitivity is somewhat limited. Electrodeposition of poly(3,4-ethylene dioxythiophene) (PEDOT)/graphene oxide (GO) onto the CFE surface is shown to increase the sensitivity and lower the limit of detection for DA compared to bare CFEs. Thicker PEDOT/GO coatings demonstrate higher sensitivities for DA, but display the negative drawback of slow adsorption and electron transfer kinetics. The moderate thickness resulting from 25 s electrodeposition of PEDOT/GO produces the optimal electrode, exhibiting an 880% increase in sensitivity, a 50% decrease in limit of detection and minimally altered electrode kinetics. PEDOT/GO coated electrodes rapidly and robustly detect DA, both in solution and in the rat dorsal striatum. This increase in DA sensitivity is likely due to increasing the electrode surface area with a PEDOT/GO coating and improved adsorption of DA's oxidation product (DA-o-quinone). Increasing DA sensitivity without compromising electrode kinetics is expected to significantly improve our understanding of the DA function in vivo. Copyright © 2016 Elsevier B.V. All rights reserved.

Enhanced Dopamine Detection Sensitivity by PEDOT/Graphene Oxide Coating on in vivo Carbon Fiber Electrodes

PubMed Central

Taylor, I. Mitch; Robbins, Elaine M.; Catt, Kasey A.; Cody, Patrick A.; Weaver, Cassandra L.; Cui, Xinyan Tracy

2016-01-01

Dopamine (DA) is a monoamine neurotransmitter responsible for regulating a variety of vital life functions. In vivo detection of DA poses a challenge due to the low concentration and high speed of physiological signaling. Fast scan cyclic voltammetry at carbon fiber microelectrodes (CFEs) is an effective method to monitor real-time in vivo DA signaling, however the sensitivity is somewhat limited. Electrodeposition of poly(3,4-ethylene dioxythiophene) (PEDOT)/graphene oxide (GO) onto the CFE surface is shown to increase the sensitivity and lower the limit of detection for DA compared to bare CFEs. Thicker PEDOT/GO coatings demonstrate higher sensitivities for DA, but display the negative drawback of slow adsorption and electron transfer kinetics. The moderate thickness resulting from 25 s electrodeposition of PEDOT/GO produces the optimal electrode, exhibiting an 880% increase in sensitivity, a 50% decrease in limit of detection and minimally altered electrode kinetics. PEDOT/GO coated electrodes rapidly and robustly detect DA, both in solution and in the rat dorsal striatum. This increase in DA sensitivity is likely due to increasing the electrode surface area with a PEDOT/GO coating and improved adsorption of DA’s oxidation product (DA-o-quinone). Increasing DA sensitivity without compromising electrode kinetics is expected to significantly improve our understanding of the DA function in vivo. PMID:27268013

Vertically aligned carbon nanotubes/carbon fiber paper composite to support Pt nanoparticles for direct methanol fuel cell application

NASA Astrophysics Data System (ADS)

Zhang, Jing; Yi, Xi-bin; Liu, Shuo; Fan, Hui-Li; Ju, Wei; Wang, Qi-Chun; Ma, Jie

2017-03-01

Vertically aligned carbon nanotubes (VACNTs) grown on carbon fiber paper (CFP) by plasma enhanced chemical vapor deposition is introduced as a catalyst support material for direct methanol fuel cells (DMFCs). Well dispersed Pt nanoparticles on VACNTs surface are prepared by impregnation-reduction method. The VACNTs on CFP possess well-maintained alignment, large surface area and good electrical conductivity, which leading to the formation of Pt particles with a smaller size and enhance the Pt utilization rate. The structure and nature of resulting Pt/VACNTs/CFP catalysts for methanol oxidation are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and scanning electron microscope (SEM). With the aid of VACNTs, well-dispersed Pt catalysts enable the reversibly rapid redox kinetic since electron transport efficiently passes through a one-dimensional pathway, which leads to enhance the catalytic activity and Pt utilization rate. Compared with the Pt/XC-72/CFP electrode, the electrochemical measurements results display that the Pt/VACNTs/CFP catalyst shows much higher electrocatalytic activity and better stability for methanol oxidation. In addition, the oxidation current from 200 to 1200 s decayed more slowly for the Pt/VACNTs/CFP than that of the Pt/XC-72/CFP catalysts, indicating less accumulation of adsorbed CO species. All those results imply that the Pt/VACNTs/CFP has a great potential for applications in DMFCs.

SO2 adsorption on silica supported iridium.

PubMed

Bounechada, Djamela; Anderson, David P; Skoglundh, Magnus; Carlsson, Per-Anders

2017-02-28

The interaction of SO 2 with Ir/SiO 2 was studied by simultaneous in situ diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry, exposing the sample to different SO 2 concentrations ranging from 10 to 50 ppm in the temperature interval 200-400 °C. Evidences of adsorption of sulfur species in both absence and presence of oxygen are found. For a pre-reduced sample in the absence of oxygen, SO 2 disproportionates such that the iridium surface is rapidly saturated with adsorbed S while minor amounts of formed SO 3 may adsorb on SiO 2 . Adding oxygen to the feed leads to the oxidation of sulfide species that either (i) desorb as SO 2 and/or SO 3 , (ii) remain at metal sites in the form of adsorbed SO 2 , or (iii) spillover to the oxide support and form sulfates (SO 4 2- ). Notably, significant formation of sulfates on silica is possible only in the presence of both SO 2 and O 2 , suggesting that SO 2 oxidation to SO 3 is a necessary first step in the mechanism of formation of sulfates on silica. During the formation of sulfates, a concomitant removal/rearrangement of surface silanol groups is observed. Finally, the interaction of SO 2 with Ir/SiO 2 depends primarily on the temperature and type of gas components but only to a minor extent on the inlet SO 2 concentration.

SO2 adsorption on silica supported iridium

NASA Astrophysics Data System (ADS)

Bounechada, Djamela; Anderson, David P.; Skoglundh, Magnus; Carlsson, Per-Anders

2017-02-01

The interaction of SO2 with Ir/SiO2 was studied by simultaneous in situ diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry, exposing the sample to different SO2 concentrations ranging from 10 to 50 ppm in the temperature interval 200-400 °C. Evidences of adsorption of sulfur species in both absence and presence of oxygen are found. For a pre-reduced sample in the absence of oxygen, SO2 disproportionates such that the iridium surface is rapidly saturated with adsorbed S while minor amounts of formed SO3 may adsorb on SiO2. Adding oxygen to the feed leads to the oxidation of sulfide species that either (i) desorb as SO2 and/or SO3, (ii) remain at metal sites in the form of adsorbed SO2, or (iii) spillover to the oxide support and form sulfates (SO42-). Notably, significant formation of sulfates on silica is possible only in the presence of both SO2 and O2, suggesting that SO2 oxidation to SO3 is a necessary first step in the mechanism of formation of sulfates on silica. During the formation of sulfates, a concomitant removal/rearrangement of surface silanol groups is observed. Finally, the interaction of SO2 with Ir/SiO2 depends primarily on the temperature and type of gas components but only to a minor extent on the inlet SO2 concentration.

Oxygen-induced Al surface segregation in Al(x)Ga(1-x)As and the effect of Y overlayers on the oxidation of the Y/Al(x)Ga(1-x)As interface

NASA Technical Reports Server (NTRS)

Mesarwi, A.; Ignatiev, A.

1992-01-01

The oxidation of Al(x)Ga(1-x)As (x = 0.15, AlGaAs) was studied by AES and XPS at 350 C and different oxygen exposures (up to 5 x 10 exp 4 L). Also studied were the effects of yttrium overlayers (theta = 3 ML) on the oxidation of the AlGaAs surface. Substantial oxygen-induced Al surface segregation has been observed for both yttriated and nonyttriated AlGaAs surfaces which increased with increasing oxygen exposure. Also observed is a significant Y-enhanced oxidation of the AlGaAs surface. Oxidation of the yttriated AlGaAs surface was found to be a factor of 4 greater than that of the nonyttriated surface. Also, while oxidation of the nonyttriated AlGaAs yielded mainly Al2O(x) (x less than 3) and only little Ga2O3, the yttriated AlGaAs surface oxide layer was principally Ga2O3 and stoichiometric Al2O3. However, both the yttriated and nonyttriated surfaces were found to contain metallic As within the oxide layer.

Experimental Study of Floating-Gate-Type Metal-Oxide-Semiconductor Capacitors with Nanosize Triangular Cross-Sectional Tunnel Areas for Low Operating Voltage Flash Memory Application

NASA Astrophysics Data System (ADS)

Liu, Yongxun; Guo, Ruofeng; Kamei, Takahiro; Matsukawa, Takashi; Endo, Kazuhiko; O'uchi, Shinichi; Tsukada, Junichi; Yamauchi, Hiromi; Ishikawa, Yuki; Hayashida, Tetsuro; Sakamoto, Kunihiro; Ogura, Atsushi; Masahara, Meishoku

2012-06-01

The floating-gate (FG)-type metal-oxide-semiconductor (MOS) capacitors with planar (planar-MOS) and three-dimensional (3D) nanosize triangular cross-sectional tunnel areas (3D-MOS) have successfully been fabricated by introducing rapid thermal oxidation (RTO) and postdeposition annealing (PDA), and their electrical characteristics between the control gate (CG) and FG have been systematically compared. It was experimentally found in both planar- and 3D-MOS capacitors that the uniform and higher breakdown voltages are obtained by introducing RTO owing to the high-quality thermal oxide formation on the surface and etched edge regions of the n+ polycrystalline silicon (poly-Si) FG, and the leakage current is highly suppressed after PDA owing to the improved quality of the tetraethylorthosilicate (TEOS) silicon dioxide (SiO2) between CG and FG. Moreover, a lower breakdown voltage between CG and FG was obtained in the fabricated 3D-MOS capacitors as compared with that of planar-MOS capacitors thanks to the enhanced local electric field at the tips of triangular tunnel areas. The developed nanosize triangular cross-sectional tunnel area is useful for the fabrication of low operating voltage flash memories.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okamura, M., E-mail: okamura@bnl.gov; Nishina Center for Accelerator-Based Science, RIKEN, Saitama; Palm, K.

Calcium and lithium ion beams are required by NASA Space Radiation Laboratory at Brookhaven National Laboratory to simulate the effects of cosmic radiation. To identify the difficulties in providing such highly reactive materials as laser targets, both species were experimentally tested. Plate shaped lithium and calcium targets were fabricated to create ablation plasmas with a 6 ns 1064 nm neodymium-doped yttrium aluminum garnet laser. We found significant oxygen contamination in both the Ca and Li high charge state beams due to the rapid oxidation of the surfaces. A large spot size, low power density laser was used to create lowmore » charge state beams without scanning the targets. The low charge state Ca beam did not have any apparent oxygen contamination, showing the potential to clean the target entirely of oxide with a low power beam once in the chamber. The Li target was clearly still oxidizing in the chamber after each low power shot. To measure the rate of oxidation, we shot the low power laser at the target repeatedly at 10 s, 30 s, 60 s, and 120 s interval lengths, showing a linear relation between the interval time and the amount of oxygen in the beam.« less

Hole hopping through tyrosine/tryptophan chains protects proteins from oxidative damage

PubMed Central

Gray, Harry B.; Winkler, Jay R.

2015-01-01

Living organisms have adapted to atmospheric dioxygen by exploiting its oxidizing power while protecting themselves against toxic side effects. Reactive oxygen and nitrogen species formed during oxidative stress, as well as high-potential reactive intermediates formed during enzymatic catalysis, could rapidly and irreversibly damage polypeptides were protective mechanisms not available. Chains of redox-active tyrosine and tryptophan residues can transport potentially damaging oxidizing equivalents (holes) away from fragile active sites and toward protein surfaces where they can be scavenged by cellular reductants. Precise positioning of these chains is required to provide effective protection without inhibiting normal function. A search of the structural database reveals that about one third of all proteins contain Tyr/Trp chains composed of three or more residues. Although these chains are distributed among all enzyme classes, they appear with greatest frequency in the oxidoreductases and hydrolases. Consistent with a redox-protective role, approximately half of the dioxygen-using oxidoreductases have Tyr/Trp chain lengths ≥3 residues. Among the hydrolases, long Tyr/Trp chains appear almost exclusively in the glycoside hydrolases. These chains likely are important for substrate binding and positioning, but a secondary redox role also is a possibility. PMID:26195784

A Comprehensive Review of One-Dimensional Metal-Oxide Nanostructure Photodetectors

PubMed Central

Zhai, Tianyou; Fang, Xiaosheng; Liao, Meiyong; Xu, Xijin; Zeng, Haibo; Yoshio, Bando; Golberg, Dmitri

2009-01-01

One-dimensional (1D) metal-oxide nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications. The construction and integration of photodetectors or optical switches based on such nanostructures with tailored geometries have rapidly advanced in recent years. Active 1D nanostructure photodetector elements can be configured either as resistors whose conductions are altered by a charge-transfer process or as field-effect transistors (FET) whose properties can be controlled by applying appropriate potentials onto the gates. Functionalizing the structure surfaces offers another avenue for expanding the sensor capabilities. This article provides a comprehensive review on the state-of-the-art research activities in the photodetector field. It mainly focuses on the metal oxide 1D nanostructures such as ZnO, SnO2, Cu2O, Ga2O3, Fe2O3, In2O3, CdO, CeO2, and their photoresponses. The review begins with a survey of quasi 1D metal-oxide semiconductor nanostructures and the photodetector principle, then shows the recent progresses on several kinds of important metal-oxide nanostructures and their photoresponses and briefly presents some additional prospective metal-oxide 1D nanomaterials. Finally, the review is concluded with some perspectives and outlook on the future developments in this area. PMID:22454597

Effect of Ge surface termination on oxidation behavior

NASA Astrophysics Data System (ADS)

Lee, Younghwan; Park, Kibyung; Cho, Yong Soo; Lim, Sangwoo

2008-09-01

Sulfur-termination was formed on the Ge(1 0 0) surface using (NH 4) 2S solution. Formation of Ge-S and the oxidation of the S-terminated Ge surface were monitored with multiple internal reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. In the 0.5, 5, or 20% (NH 4) 2S solution, H-termination on the Ge(1 0 0) surface was substituted with S-termination in 1 min. When the S-terminated Ge(1 0 0) surface was exposed in air ambient, the oxidation was retarded for about 3600 min. The preservation time of the oxide layer up to one monolayer of S-terminated Ge(1 0 0) surface was about 120 times longer than for the H-terminated Ge(1 0 0) surface. However, the oxidation of S-terminated Ge(1 0 0) surface drastically increased after the threshold time. There was no significant difference in threshold time between S-terminations formed in 0.5, 5, and 20% (NH 4) 2S solutions. With the surface oxidation, desorption of S on the Ge surface was observed. The desorption behavior of sulfur on the S-terminated Ge(1 0 0) surface was independent of the concentration of the (NH 4) 2S solution that forms S-termination. Non-ideal S-termination on Ge surfaces may be related to drastic oxidation of the Ge surface. Finally, with the desulfurization on the S-terminated Ge(1 0 0) surface, oxide growth is accelerated.

Metal oxide nanorod arrays on monolithic substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Pu-Xian; Guo, Yanbing; Ren, Zheng

A metal oxide nanorod array structure according to embodiments disclosed herein includes a monolithic substrate having a surface and multiple channels, an interface layer bonded to the surface of the substrate, and a metal oxide nanorod array coupled to the substrate surface via the interface layer. The metal oxide can include ceria, zinc oxide, tin oxide, alumina, zirconia, cobalt oxide, and gallium oxide. The substrate can include a glass substrate, a plastic substrate, a silicon substrate, a ceramic monolith, and a stainless steel monolith. The ceramic can include cordierite, alumina, tin oxide, and titania. The nanorod array structure can includemore » a perovskite shell, such as a lanthanum-based transition metal oxide, or a metal oxide shell, such as ceria, zinc oxide, tin oxide, alumina, zirconia, cobalt oxide, and gallium oxide, or a coating of metal particles, such as platinum, gold, palladium, rhodium, and ruthenium, over each metal oxide nanorod. Structures can be bonded to the surface of a substrate and resist erosion if exposed to high velocity flow rates.« less

Roll-to-roll-compatible, flexible, transparent electrodes based on self-nanoembedded Cu nanowires using intense pulsed light irradiation

NASA Astrophysics Data System (ADS)

Zhong, Zhaoyang; Woo, Kyoohee; Kim, Inhyuk; Hwang, Hyewon; Kwon, Sin; Choi, Young-Man; Lee, Youngu; Lee, Taik-Min; Kim, Kwangyoung; Moon, Jooho

2016-04-01

Copper nanowire (Cu NW)-based flexible transparent conductive electrodes (FTCEs) have been investigated in detail for use in various applications such as flexible touch screens, organic photovoltaics and organic light-emitting diodes. In this study, hexadecylamine (HDA) adsorbed onto the surface of NWs is changed into polyvinylpyrrolidone (PVP) via a ligand exchange process; the high-molecular-weight PVP enables high dispersion stability. Intense pulsed light (IPL) irradiation is used to remove organic species present on the surface of the NWs and to form direct connections between the NWs rapidly without any atmospheric control. NWs are self-nanoembedded into a plastic substrate after IPL irradiation, which results in a smooth surface, strong NW/substrate adhesion, excellent mechanical flexibility and enhanced oxidation stability. Moreover, Cu NW FTCEs with high uniformities are successfully fabricated on a large area (150 mm × 200 mm) via successive IPL irradiation that is synchronized with the motion of the sample stage. This study demonstrates the possibility of roll-to-roll-based, large-scale production of low-cost, high-performance Cu NW-based FTCEs.Copper nanowire (Cu NW)-based flexible transparent conductive electrodes (FTCEs) have been investigated in detail for use in various applications such as flexible touch screens, organic photovoltaics and organic light-emitting diodes. In this study, hexadecylamine (HDA) adsorbed onto the surface of NWs is changed into polyvinylpyrrolidone (PVP) via a ligand exchange process; the high-molecular-weight PVP enables high dispersion stability. Intense pulsed light (IPL) irradiation is used to remove organic species present on the surface of the NWs and to form direct connections between the NWs rapidly without any atmospheric control. NWs are self-nanoembedded into a plastic substrate after IPL irradiation, which results in a smooth surface, strong NW/substrate adhesion, excellent mechanical flexibility and enhanced oxidation stability. Moreover, Cu NW FTCEs with high uniformities are successfully fabricated on a large area (150 mm × 200 mm) via successive IPL irradiation that is synchronized with the motion of the sample stage. This study demonstrates the possibility of roll-to-roll-based, large-scale production of low-cost, high-performance Cu NW-based FTCEs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00444j

NANOSIZED MAGNESIUM OXIDE AS CATALYST FOR THE RAPID AND GREEN SYNTHESIS OF SUBSTITUTED 2-AMINO-2-CHROMENES

EPA Science Inventory

A nanosized magnesium oxide catalyzed three-component condensation reaction of aldehyde, malononitrile and ¿-naphthol proceeded rapidly in water/PEG to afford corresponding 2-amino-2-chromenes in high yields at room temperature. The greener protocol was found to be fairly general...

Intelligent design of multifunctional lipid-coated nanoparticle platforms for cancer therapy.

PubMed

Ramishetti, Srinivas; Huang, Leaf

2012-12-01

Nanotechnology is rapidly evolving and dramatically changing the paradigms of drug delivery. The small sizes, unique chemical properties, large surface areas, structural diversity and multifunctionality of nanoparticles prove to be greatly advantageous for combating notoriously therapeutically evasive diseases such as cancer. Multifunctional nanoparticles have been designed to enhance tumor uptake through either passive or active targeting, while also avoiding reticuloendothelial system uptake through the incorporation of PEG onto the surface. First-generation nanoparticle systems, such as liposomes, are good carriers for drugs and nucleic acid therapeutics, although they have some limitations. These lipid bilayers are now being utilized as excellent carriers for drug-loaded, solid core particles such as iron oxide, mesoporus silica and calcium phosphate. In this article, their design, as well as their multifunctional role in cancer therapy are discussed.

On-stack two-dimensional conversion of MoS2 into MoO3

NASA Astrophysics Data System (ADS)

Yeoung Ko, Taeg; Jeong, Areum; Kim, Wontaek; Lee, Jinhwan; Kim, Youngchan; Lee, Jung Eun; Ryu, Gyeong Hee; Park, Kwanghee; Kim, Dogyeong; Lee, Zonghoon; Lee, Min Hyung; Lee, Changgu; Ryu, Sunmin

2017-03-01

Chemical transformation of existing two-dimensional (2D) materials can be crucial in further expanding the 2D crystal palette required to realize various functional heterostructures. In this work, we demonstrate a 2D ‘on-stack’ chemical conversion of single-layer crystalline MoS2 into MoO3 with a precise layer control that enables truly 2D MoO3 and MoO3/MoS2 heterostructures. To minimize perturbation of the 2D morphology, a nonthermal oxidation using O2 plasma was employed. The early stage of the reaction was characterized by a defect-induced Raman peak, drastic quenching of photoluminescence (PL) signals and sub-nm protrusions in atomic force microscopy images. As the reaction proceeded from the uppermost layer to the buried layers, PL and optical second harmonic generation signals showed characteristic modulations revealing a layer-by-layer conversion. The plasma-generated 2D oxides, confirmed as MoO3 by x-ray photoelectron spectroscopy, were found to be amorphous but extremely flat with a surface roughness of 0.18 nm, comparable to that of 1L MoS2. The rate of oxidation quantified by Raman spectroscopy decreased very rapidly for buried sulfide layers due to protection by the surface 2D oxides, exhibiting a pseudo-self-limiting behavior. As exemplified in this work, various on-stack chemical transformations can be applied to other 2D materials in forming otherwise unobtainable materials and complex heterostructures, thus expanding the palette of 2D material building blocks.

Operation of mixed conducting metal oxide membrane systems under transient conditions

DOEpatents

Carolan, Michael Francis [Allentown, PA

2008-12-23

Method of operating an oxygen-permeable mixed conducting membrane having an oxidant feed side, an oxidant feed surface, a permeate side, and a permeate surface, which method comprises controlling the differential strain between the permeate surface and the oxidant feed surface at a value below a selected maximum value by varying the oxygen partial pressure on either or both of the oxidant feed side and the permeate side of the membrane.

Mechanical Properties of Degraded PMR-15 Resin

NASA Technical Reports Server (NTRS)

Tsuji, Luis C.; McManus, Hugh L.; Bowles, Kenneth J.

1998-01-01

Thermo-oxidative aging produces a non-uniform degradation state in PMR-15 resin. A surface layer, usually attributed to oxidative degradation, forms. This surface layer has different properties from the inner material. A set of material tests was designed to separate the properties of the oxidized surface layer from the properties of interior material. Test specimens were aged at 316 C in either air or nitrogen, for durations of up to 800 hours. The thickness of the oxidized surface layer in air aged specimens, and the shrinkage and Coefficient of Thermal Expansion (CTE) of nitrogen aged specimens were measured directly. Four-point-bend tests were performed to determine modulus of both the oxidized surface layer and the interior material. Bimaterial strip specimens consisting of oxidized surface material and unoxidized interior material were constructed and used to determine surface layer shrinkage and CTE. Results confirm that the surface layer and core materials have substantially different properties.

Superconducting composite with multilayer patterns and multiple buffer layers

DOEpatents

Wu, X.D.; Muenchausen, R.E.

1993-10-12

An article of manufacture is described including a substrate, a patterned interlayer of a material selected from the group consisting of magnesium oxide, barium-titanium oxide or barium-zirconium oxide, the patterned interlayer material overcoated with a secondary interlayer material of yttria-stabilized zirconia or magnesium-aluminum oxide, upon the surface of the substrate whereby an intermediate article with an exposed surface of both the overcoated patterned interlayer and the substrate is formed, a coating of a buffer layer selected from the group consisting of cerium oxide, yttrium oxide, curium oxide, dysprosium oxide, erbium oxide, europium oxide, iron oxide, gadolinium oxide, holmium oxide, indium oxide, lanthanum oxide, manganese oxide, lutetium oxide, neodymium oxide, praseodymium oxide, plutonium oxide, samarium oxide, terbium oxide, thallium oxide, thulium oxide, yttrium oxide and ytterbium oxide over the entire exposed surface of the intermediate article, and, a ceramic superconductor. 5 figures.

Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils.

PubMed

Hemingway, Jordon D; Hilton, Robert G; Hovius, Niels; Eglinton, Timothy I; Haghipour, Negar; Wacker, Lukas; Chen, Meng-Chiang; Galy, Valier V

2018-04-13

Lithospheric organic carbon ("petrogenic"; OC petro ) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO 2 ) to the atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 ± 11% of the OC petro initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO 2 emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OC petro remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO 2 emission fluxes that increase with erosion rate, thereby counteracting CO 2 drawdown by silicate weathering and biospheric OC burial. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Cubic mesoporous Ag@CN: a high performance humidity sensor.

PubMed

Tomer, Vijay K; Thangaraj, Nishanthi; Gahlot, Sweta; Kailasam, Kamalakannan

2016-12-01

The fabrication of highly responsive, rapid response/recovery and durable relative humidity (%RH) sensors that can precisely monitor humidity levels still remains a considerable challenge for realizing the next generation humidity sensing applications. Herein, we report a remarkably sensitive and rapid %RH sensor having a reversible response using a nanocasting route for synthesizing mesoporous g-CN (commonly known as g-C 3 N 4 ). The 3D replicated cubic mesostructure provides a high surface area thereby increasing the adsorption, transmission of charge carriers and desorption of water molecules across the sensor surfaces. Owing to its unique structure, the mesoporous g-CN functionalized with well dispersed catalytic Ag nanoparticles exhibits excellent sensitivity in the 11-98% RH range while retaining high stability, negligible hysteresis and superior real time %RH detection performances. Compared to conventional resistive sensors based on metal oxides, a rapid response time (3 s) and recovery time (1.4 s) were observed in the 11-98% RH range. Such impressive features originate from the planar morphology of g-CN as well as unique physical affinity and favourable electronic band positions of this material that facilitate water adsorption and charge transportation. Mesoporous g-CN with Ag nanoparticles is demonstrated to provide an effective strategy in designing high performance %RH sensors and show great promise for utilization of mesoporous 2D layered materials in the Internet of Things and next generation humidity sensing applications.

Predictive Finite Rate Model for Oxygen-Carbon Interactions at High Temperature

NASA Astrophysics Data System (ADS)

Poovathingal, Savio

An oxidation model for carbon surfaces is developed to predict ablation rates for carbon heat shields used in hypersonic vehicles. Unlike existing empirical models, the approach used here was to probe gas-surface interactions individually and then based on an understanding of the relevant fundamental processes, build a predictive model that would be accurate over a wide range of pressures and temperatures, and even microstructures. Initially, molecular dynamics was used to understand the oxidation processes on the surface. The molecular dynamics simulations were compared to molecular beam experiments and good qualitative agreement was observed. The simulations reproduced cylindrical pitting observed in the experiments where oxidation was rapid and primarily occurred around a defect. However, the studies were limited to small systems at low temperatures and could simulate time scales only of the order of nanoseconds. Molecular beam experiments at high surface temperature indicated that a majority of surface reaction products were produced through thermal mechanisms. Since the reactions were thermal, they occurred over long time scales which were computationally prohibitive for molecular dynamics to simulate. The experiments provided detailed dynamical data on the scattering of O, O2, CO, and CO2 and it was found that the data from molecular beam experiments could be used directly to build a model. The data was initially used to deduce surface reaction probabilities at 800 K. The reaction probabilities were then incorporated into the direct simulation Monte Carlo (DSMC) method. Simulations were performed where the microstructure was resolved and dissociated oxygen convected and diffused towards it. For a gas-surface temperature of 800 K, it was found that despite CO being the dominant surface reaction product, a gas-phase reaction forms significant CO2 within the microstructure region. It was also found that surface area did not play any role in concentration of reaction products because the reaction probabilities were in the diffusion dominant regime. The molecular beam data at different surface temperatures was then used to build a finite rate model. Each reaction mechanism and all rate parameters of the new model were determined individually based on the molecular beam data. Despite the experiments being performed at near vacuum conditions, the finite rate model developed using the data could be used at pressures and temperatures relevant to hypersonic conditions. The new model was implemented in a computational fluid dynamics (CFD) solver and flow over a hypersonic vehicle was simulated. The new model predicted similar overall mass loss rates compared to existing models, however, the individual species production rates were completely different. The most notable difference was that the new model (based on molecular beam data) predicts CO as the oxidation reaction product with virtually no CO2 production, whereas existing models predict the exact opposite trend. CO being the dominant oxidation product is consistent with recent high enthalpy wind tunnel experiments. The discovery that measurements taken in molecular beam facilities are able to determine individual reaction mechanisms, including dependence on surface coverage, opens up an entirely new way of constructing ablation models.

The Importance of pH, Oxygen, and Bitumen on the Oxidation and Precipitation of Fe(III)-(oxy)hydroxides during Hydraulic Fracturing of Oil/Gas Shales

NASA Astrophysics Data System (ADS)

Jew, A. D.; Dustin, M. K.; Harrison, A. L.; Joe-Wong, C. M.; Thomas, D.; Maher, K.; Brown, G. E.; Bargar, J.

2016-12-01

Due to the rapid growth of hydraulic fracturing in the United States, understanding the cause for the rapid production drop off of new wells over the initial months of production is paramount. One possibility for the production decrease is pore occlusion caused by the oxidation of Fe(II)-bearing phases resulting in Fe(III) precipitates. To understand the release and fate of Fe in the shale systems, we reacted synthesized fracture fluid at 80oC with shale from four different geological localities (Marcellus Fm., Barnett Fm., Eagle Ford Fm., and Green River Fm.). A variety of wet chemical and synchrotron-based techniques (XRF mapping and x-ray absorption spectroscopy) were used to understand Fe release and solid phase Fe speciation. Solution pH was found to be the greatest factor for Fe release. Carbonate-poor Barnett and Marcellus shale showed rapid Fe release into solution followed by a plateau or significant drop in Fe concentrations indicating mineral precipitation. Conversely, in high carbonate shales, Eagle Ford and Green River, no Fe was detected in solution indicating fast Fe oxidation and precipitation. For all shale samples, bulk Fe EXAFS data show that a significant amount of Fe in the shales is bound directly to organic carbon. Throughout the course of the experiments inorganic Fe(II) phases (primarily pyrite) reacted while Fe(II) bound to C showed no indication of reaction. On the micron scale, XRF mapping coupled with μ-XANES spectroscopy showed that at pH < 4.0, Fe(III) bearing phases precipitated as diffuse surface precipitates of ferrihydrite, goethite, and magnetite away from Fe(II) point sources. In near circum-neutral pH systems, Fe(III)-bearing phases (goethite and hematite) form large particles 10's of μm's in diameter near Fe(II) point sources. Idealized systems containing synthesized fracturing fluid, dissolved ferrous chloride, and bitumen showed that bitumen released during reaction with fracturing fluids is capable of oxidizing Fe(II) to Fe(III) at pH's 2.0 and 7.0. This indicates that bitumen can play a large role in Fe oxidation and speciation in the subsurface. This work shows that shale mineralogy has a significant impact on the morphology and phases of Fe(III) precipitates in the subsurface which in turn can significantly impact subsurface solution flow.

Soot Surface Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix I

NASA Technical Reports Server (NTRS)

Xu, F.; El-Leathy, A. M.; Kim, C. H.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

2003-01-01

Soot surface oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round fuel jets burning in coflowing dry air considering acetylene-nitrogen, ethylene, propyiene-nitrogen, propane and acetylene-benzene-nitrogen in the fuel stream. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2, C2H6, C3H6, C3H8, and C6H6) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption and flow velocities by laser velocimetry. For present test conditions, it was found that soot surface oxidation rates were not affected by fuel type, that direct rates of soot surface oxidation by O2 estimated from Nagle and Strickland-Constable (1962) were small compared to observed soot surface oxidation rates because soot surface oxidation was completed near the flame sheet where O2 concentrations were less than 3% by volume, and that soot surface oxidation rates were described by the OH soot surface oxidation mechanism with a collision efficiency of 0.14 and an uncertainty (95% confidence) of +/- 0.04 when allowing for direct soot surface oxidation by O2, which is in reasonably good agreement with earlier observations of soot surface oxidation rates in both premixed and diffusion flames at atmospheric pressure.

Efficient peroxydisulfate activation process not relying on sulfate radical generation for water pollutant degradation.

PubMed

Zhang, Tao; Chen, Yin; Wang, Yuru; Le Roux, Julien; Yang, Yang; Croué, Jean-Philippe

2014-05-20

Peroxydisulfate (PDS) is an appealing oxidant for contaminated groundwater and toxic industrial wastewaters. Activation of PDS is necessary for application because of its low reactivity. Present activation processes always generate sulfate radicals as actual oxidants which unselectively oxidize organics and halide anions reducing oxidation capacity of PDS and producing toxic halogenated products. Here we report that copper oxide (CuO) can efficiently activate PDS under mild conditions without producing sulfate radicals. The PDS/CuO coupled process is most efficient at neutral pH for decomposing a model compound, 2,4-dichlorophenol (2,4-DCP). In a continuous-flow reaction with an empty-bed contact time of 0.55 min, over 90% of 2,4-DCP (initially 20 μM) and 90% of adsorbable organic chlorine (AOCl) can be removed at the PDS/2,4-DCP molar ratio of 1 and 4, respectively. Based on kinetic study and surface characterization, PDS is proposed to be first activated by CuO through outer-sphere interaction, the rate-limiting step, followed by a rapid reaction with 2,4-DCP present in the solution. In the presence of ubiquitous chloride ions in groundwater/industrial wastewater, the PDS/CuO oxidation shows significant advantages over sulfate radical oxidation by achieving much higher 2,4-DCP degradation capacity and avoiding the formation of highly chlorinated degradation products. This work provides a new way of PDS activation for contaminant removal.

High Concentration of Red Clay as an Alternative for Antibiotics in Aquaculture.

PubMed

Jung, Jaejoon; Jee, Seung Cheol; Sung, Jung-Suk; Park, Woojun

2016-01-01

The use of antibiotics in aquaculture raises environmental and food safety concerns because chronic exposure of an aquatic ecosystem to antibiotics can result in the spread of antibiotic resistance, bioaccumulation of antibiotics in the organisms, and transfer of antibiotics to humans. In an attempt to overcome these problems, high-concentration red clay was applied as an alternative antibiotic against the following common fish pathogens: Aeromonas salmonicida, Vibrio alginolyticus, and Streptococcus equinus. The growth of A. salmonicida and V. alginolyticus was retarded by red clay, whereas that of S. equinus was promoted. Phase contrast and scanning electron microscopy analyses confirmed the attachment of red clay on cell surfaces, resulting in rapid gravitational removal and cell surface damage in both A. salmonicida and V. alginolyticus, but not in S. equinus. Different cell wall properties of grampositive species may explain the unharmed cell surface of S. equinus. Significant levels of oxidative stress were generated in only the former two species, whereas significant changes in membrane permeability were found only in S. equinus, probably because of its physiological adaptation. The bacterial communities in water samples from Oncorhynchus mykiss aquacultures supplemented with red clay showed similar structure and diversity as those from oxytetracycline-treated water. Taken together, the antibiotic effects of high concentrations of red clay in aquaculture can be attributed to gravitational removal, cell surface damage, and oxidative stress production, and suggest that red clay may be used as an alternative for antibiotics in aquaculture.

Surface stoichiometry modification and improved DC/RF characteristics by plasma treated and annealed AlGaN/GaN HEMTs

NASA Astrophysics Data System (ADS)

Upadhyay, Bhanu B.; Takhar, Kuldeep; Jha, Jaya; Ganguly, Swaroop; Saha, Dipankar

2018-03-01

We demonstrate that N2 and O2 plasma treatment followed by rapid thermal annealing leads to surface stoichiometry modification in a AlGaN/GaN high electron mobility transistor. Both the source/drain access and gate regions respond positively improving the transistor characteristics albeit to different extents. Characterizations indicate that the surface show the characteristics of that of a higher band-gap material like AlxOy and GaxOy along with N-vacancy in the sub-surface region. The N-vacancy leads to an increased two-dimensional electron gas density. The formation of oxides lead to a reduced gate leakage current and surface passivation. The DC characteristics show increased transconductance, saturation drain current, ON/OFF current ratio, sub-threshold swing and lower ON resistance by a factor of 2.9, 2.0, 103.3 , 2.3, and 2.1, respectively. The RF characteristics show an increase in unity current gain frequency by a factor of 1.7 for a 500 nm channel length device.

Influence of Surface Chemistry on the Release of an Antibacterial Drug from Nanostructured Porous Silicon.

PubMed

Wang, Mengjia; Hartman, Philip S; Loni, Armando; Canham, Leigh T; Bodiford, Nelli; Coffer, Jeffery L

2015-06-09

Nanostructured mesoporous silicon possesses important properties advantageous to drug loading and delivery. For controlled release of the antibacterial drug triclosan, and its associated activity versus Staphylococcus aureus, previous studies investigated the influence of porosity of the silicon matrix. In this work, we focus on the complementary issue of the influence of surface chemistry on such properties, with particular regard to drug loading and release kinetics that can be ideally adjusted by surface modification. Comparison between drug release from as-anodized, hydride-terminated hydrophobic porous silicon and the oxidized hydrophilic counterpart is complicated due to the rapid bioresorption of the former; hence, a hydrophobic interface with long-term biostability is desired, such as can be provided by a relatively long chain octyl moiety. To minimize possible thermal degradation of the surfaces or drug activity during loading of molten drug species, a solution loading method has been investigated. Such studies demonstrate that the ability of porous silicon to act as an effective carrier for sustained delivery of antibacterial agents can be sensitively altered by surface functionalization.

Development and Application of Operando TEM to a Ruthenium Catalyst for CO Oxidation

NASA Astrophysics Data System (ADS)

Miller, Benjamin Kyle

Operando transmission electron microscopy (TEM) is an extension of in-situ TEM in which the performance of the material being observed is measured simultaneously. This is of great value, since structure-performance relationships lie at the heart of materials science. For catalyst materials, like the SiO2-supported Ru nanoparticles studied, the important performance metric, catalyst activity, is measured inside the microscope by determining the gas composition during imaging. This is accomplished by acquisition of electron energy loss spectra (EELS) of the gas in the environmental TEM while catalysis is taking place. In this work, automated methods for rapidly quantifying low-loss and core-loss EELS of gases were developed. A new sample preparation method was also established to increase catalytic conversion inside a differentially-pumped environmental TEM, and the maximum CO conversion observed was about 80%. A system for mixing gases and delivering them to the environmental TEM was designed and built, and a method for locating and imaging nanoparticles in zone axis orientations while minimizing electron dose rate was determined. After atomic resolution images of Ru nanoparticles observed during CO oxidation were obtained, the shape and surface structures of these particles was investigated. A Wulff model structure for Ru particles was compared to experimental images both by manually rotating the model, and by automatically determining a matching orientation using cross-correlation of shape signatures. From this analysis, it was determined that most Ru particles are close to Wulff-shaped during CO oxidation. While thick oxide layers were not observed to form on Ru during CO oxidation, thin RuO2 layers on the surface of Ru nanoparticles were imaged with atomic resolution for the first time. The activity of these layers is discussed in the context of the literature on the subject, which has thus far been inconclusive. We conclude that disordered oxidized ruthenium, rather than crystalline RuO2 is the most active species.

Rapidly curable electrically conductive clear coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowman, Mark P.; Anderson, Lawrence G.; Post, Gordon L.

2018-01-16

Rapidly curable electrically conductive clear coatings are applied to substrates. The electrically conductive clear coating includes to clear layer having a resinous binder with ultrafine non-stoichiometric tungsten oxide particles dispersed therein. The clear coating may be rapidly cured by subjecting the coating to infrared radiation that heats the tungsten oxide particles and surrounding resinous binder. Localized heating increases the temperature of the coating to thereby thermally cure the coating, while avoiding unwanted heating of the underlying substrate.

Biocompatilibity-related surface characteristics of oxidized NiTi.

PubMed

Danilov, Anatoli; Tuukkanen, Tuomas; Tuukkanen, Juha; Jämsä, Timo

2007-09-15

In the present study, we examined the effect of NiTi oxidation on material surface characteristics related to biocompatibility. Correspondence between electron work function (EWF) and adhesive force predicted by electron theory of adsorption as well as the effect of surface mechanical stress on the adhesive force were studied on the nonoxidized and oxidized at 350, 450, and 600 degrees C NiTi alloy for medical application. The adhesive force generated by the material surface towards the drops of alpha-minimal essential medium (alpha-MEM) was used as a characteristic of NiTi adsorption properties. The study showed that variations in EWF and mechanical stress caused by surface treatment were accompanied by variations in adhesive force. NiTi oxidation at all temperatures used gave rise to decrease in adhesive force and surface stress values in comparison to the nonoxidized state. In contrary, the EWF value revealed increase under the same condition. Variations in surface oxide layer thickness and its phase composition were also followed. The important role of oxide crystallite size in EWF values within the range of crystallite dimensions typical for NiTi surface oxide as an instrument for the fine regulation of NiTi adsorption properties was demonstrated. The comparative oxidation of pure titanium and NiTi showed that the effect of Ni on the EWF value of NiTi surface oxide is negligible. Copyright 2007 Wiley Periodicals, Inc.

Ab initio atomistic thermodynamics study on the oxidation mechanism of binary and ternary alloy surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Shi-Yu, E-mail: buaasyliu@gmail.com; Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong; Liu, Shiyang

Utilizing a combination of ab initio density-functional theory and thermodynamics formalism, we have established the microscopic mechanisms for oxidation of the binary and ternary alloy surfaces and provided a clear explanation for the experimental results of the oxidation. We construct three-dimensional surface phase diagrams (SPDs) for oxygen adsorption on three different Nb-X(110) (X = Ti, Al or Si) binary alloy surfaces. On the basis of the obtained SPDs, we conclude a general microscopic mechanism for the thermodynamic oxidation, that is, under O-rich conditions, a uniform single-phase SPD (type I) and a nonuniform double-phase SPD (type II) correspond to the sustainedmore » complete selective oxidation and the non-sustained partial selective oxidation by adding the X element, respectively. Furthermore, by revealing the framework of thermodynamics for the oxidation mechanism of ternary alloys through the comparison of the surface energies of two separated binary alloys, we provide an understanding for the selective oxidation behavior of the Nb ternary alloy surfaces. Using these general microscopic mechanisms, one could predict the oxidation behavior of any binary and multi-component alloy surfaces based on thermodynamics considerations.« less

Effects of Solar Ultraviolet Radiation on Biogeochemical Dynamics in Aquatic Environments: Report of a Workshop Held in Woods Hole, Massachusetts on 23-26 October 1989

DTIC Science & Technology

1990-01-01

V’V for aqluatic organismls call be calclltteli wit Ii kmlowle’lle oIi 11151’ fatcto(rs. HIowI’ver , ai ke ,N un cert ainty remains in tile choice of...of the rapid rate of oxidation of Fe(II) at such pH and, possibly more importantly, the tendency of reduced iron to remain sorbed to particuiate iron...surface-located metal-organic complexes appears the most reasonable explanation for the ability of light to enhance colloid dissolution, much remains

Solid-binding peptides: smart tools for nanobiotechnology.

PubMed

Care, Andrew; Bergquist, Peter L; Sunna, Anwar

2015-05-01

Over the past decade, solid-binding peptides (SBPs) have been used increasingly as molecular building blocks in nanobiotechnology. These peptides show selectivity and bind with high affinity to the surfaces of a diverse range of solid materials including metals, metal oxides, metal compounds, magnetic materials, semiconductors, carbon materials, polymers, and minerals. They can direct the assembly and functionalisation of materials, and have the ability to mediate the synthesis and construction of nanoparticles and complex nanostructures. As the availability of newly synthesised nanomaterials expands rapidly, so too do the potential applications for SBPs. Copyright © 2015 Elsevier Ltd. All rights reserved.

Superhydrophilicity and antibacterial property of a Cu-dotted oxide coating surface

PubMed Central

2010-01-01

Background Aluminum-made settings are widely used in healthcare, schools, public facilities and transit systems. Frequently-touched surfaces of those settings are likely to harbour bacteria and be a potential source of infection. One method to utilize the effectiveness of copper (Cu) in eliminating pathogens for these surfaces would be to coat the aluminum (Al) items with a Cu coating. However, such a combination of Cu and Al metals is susceptible to galvanic corrosion because of their different electrochemical potentials. Methods In this work, a new approach was proposed in which electrolytic plasma oxidation (EPO) of Al was used to form an oxide surface layer followed by electroplating of Cu metal on the top of the oxide layer. The oxide was designed to function as a corrosion protective and biocompatible layer, and the Cu in the form of dots was utilized as an antibacterial material. The antibacterial property enhanced by superhydrophilicity of the Cu-dotted oxide coating was evaluated. Results A superhydrophilic surface was successfully prepared using electrolytic plasma oxidation of aluminum (Al) followed by electroplating of copper (Cu) in a Cu-dotted form. Both Cu plate and Cu-dotted oxide surfaces had excellent antimicrobial activities against E. coli ATCC 25922, methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300 and vancomycin-resistant Enterococcus faecium (VRE) ATCC 51299. However, its Cu-dotted surface morphology allowed the Cu-dotted oxide surface to be more antibacterial than the smooth Cu plate surface. The enhanced antibacterial property was attributed to the superhydrophilic behaviour of the Cu-dotted oxide surface that allowed the bacteria to have a more effective killing contact with Cu due to spreading of the bacterial suspension media. Conclusion The superhydrophilic Cu-dotted oxide coating surface provided an effective method of controlling bacterial growth and survival on contact surfaces and thus reduces the risk of infection and spread of bacteria-related diseases particularly in moist or wet environments. PMID:20843373

Articles including thin film monolayers and multilayers

DOEpatents

Li, DeQuan; Swanson, Basil I.

1995-01-01

Articles of manufacture including: (a) a base substrate having an oxide surface layer, and a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, (b) a base substrate having an oxide surface layer, a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, and a metal species attached to the multidentate ligand, (c) a base substrate having an oxide surface layer, a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, a metal species attached to the multidentate ligand, and a multifunctional organic ligand attached to the metal species, and (d) a base substrate having an oxide surface layer, a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, a metal species attached to the multidentate ligand, a multifunctional organic ligand attached to the metal species, and a second metal species attached to the multifunctional organic ligand, are provided, such articles useful in detecting the presence of a selected target species, as nonliear optical materials, or as scavengers for selected target species.

Improve oxidation resistance at high temperature by nanocrystalline surface layer

NASA Astrophysics Data System (ADS)

Xia, Z. X.; Zhang, C.; Huang, X. F.; Liu, W. B.; Yang, Z. G.

2015-08-01

An interesting change of scale sequence occurred during oxidation of nanocrystalline surface layer by means of a surface mechanical attrition treatment. The three-layer oxide structure from the surface towards the matrix is Fe3O4, spinel FeCr2O4 and corundum (Fe,Cr)2O3, which is different from the typical two-layer scale consisted of an Fe3O4 outer layer and an FeCr2O4 inner layer in conventional P91 steel. The diffusivity of Cr, Fe and O is enhanced concurrently in the nanocrystalline surface layer, which causes the fast oxidation in the initial oxidation stage. The formation of (Fe,Cr)2O3 inner layer would inhabit fast diffusion of alloy elements in the nanocrystalline surface layer of P91 steel in the later oxidation stage, and it causes a decrease in the parabolic oxidation rate compared with conventional specimens. This study provides a novel approach to improve the oxidation resistance of heat resistant steel without changing its Cr content.

Comparative surface studies on wet and dry sacrificial thermal oxidation on silicon carbide

NASA Astrophysics Data System (ADS)

Koh, A.; Kestle, A.; Wright, C.; Wilks, S. P.; Mawby, P. A.; Bowen, W. R.

2001-04-01

A comparative study on the effect of wet and dry thermal oxidation on 4H-silicon carbide (SiC) and on sacrificial silicon (Si) thermal oxidation on 4H-SiC surface has been conducted using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM images show the formation of 'nano-islands' of varying density on the SiC surface after the removal of thermal oxide using hydrofluoric (HF) acid etch. These nano-islands are resistant to HF acid and have been previously linked to residual carbon [1-3] resulting from the oxidation process. This paper presents the use of a sacrificial silicon oxidation (SSO) step as a form of surface preparation that gives a reproducible clean SiC surface. XPS results show a slight electrical shift in binding energy between the wet and dry thermal oxidation on the standard SiC surface, while the surface produced by the SSO technique shows a minimal shift.

Frost-weathering on Mars: experimental evidence for peroxide formation.

PubMed

Huguenin, R L; Miller, K J; Harwood, W S

1979-12-01

A laboratory study of the interaction of H2O frost with samples of the minerals olivine (Mg,Fe)2SiO4 and pyroxene (Mg,Fe)SiO3 at -11 degrees C to -22 degrees C revealed that an acidic oxidant was produced. Exposure of the frost-treated minerals to liquie H2O produced a sudden drop in pH and resulted in the production of copious O2(g) (as much as approximately 10(20) molecules g-1). Exposure of frost-treated samples to 5 ml of 0.1M HCOONa solution resulted in the rapid oxidation of up to 43% of the formate to CO2(g). These reactions were qualitatively similar to the chemical activity observed during the active cycles of the Viking lander Gas Exchange and Labeled Release Biology experiments. Attempts to identify the oxidant by chemical indicators were inconclusive, but they tentatively suggested that chemisorbed hydrogen peroxide may have formed. The formation of chemisorbed peroxide could be explained as a byproduct of the chemical reduction of the mineral. The following model was proposed. H+ was incorporated into the mineral from surface frost. This would have left behind a residual of excess OH-(ads) (relative to surface H+). Electrons were then stripped from the surface OH-(ads) (due to the large repulsive potential between neighboring OH-(ads)) and incorporated into the crystal to restore charge balance and produce a chemical reduction of the mineral. The resultant surface hydroxyl radicals could then have combined to form the more stable chemisorbed hydrogen peroxide species. While the chemisorbed peroxide should be relatively stable at low temperatures, it should tend to decay to O(ads)+ H2O(g) at higher temperatures with an activation energy of greater than or approximately 34 kcal mole-1. This is consistent with the long-term storage and sterilization behavior of the Viking soil oxidants. It is possible that as little as 0.1--1% frost-weathered material in the martian soil could have produced the unusual chemical activity that occurred during the Viking Gas Exchange and Labeled Release experiments.

NOTE: Measuring oxidative gelation of aqueous flour suspensions using the Rapid Visco Analyzer

USDA-ARS?s Scientific Manuscript database

The Rapid Visco Analyzer (RVA) was investigated as a tool to measure oxidative gelation capacity (OGC) of aqueous wheat-flour suspensions. One, club-wheat patent flour was used to determine optimal hydration time and 33 straight-grade flours (representing 12 hard and 31 soft varieties) were used to ...

Ultraflexible and robust graphene supercapacitors printed on textiles for wearable electronics applications

NASA Astrophysics Data System (ADS)

Abdelkader, Amr M.; Karim, Nazmul; Vallés, Cristina; Afroj, Shaila; Novoselov, Kostya S.; Yeates, Stephen G.

2017-09-01

Printed graphene supercapacitors have the potential to empower tomorrow’s wearable electronics. We report a solid-state flexible supercapacitor device printed on textiles using graphene oxide ink and a screen-printing technique. After printing, graphene oxide was reduced in situ via a rapid electrochemical method avoiding the use of any reducing reagents that may damage the textile substrates. The printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate. The unique hierarchical porous structure of the electrodes facilitated ionic diffusion and maximised the surface area available for the electrolyte/active material interface. The obtained device showed outstanding cyclic stability over 10 000 cycles and maintained excellent mechanical flexibility, which is necessary for wearable applications. The simple printing technique is readily scalable and avoids the problems associated with fabricating supercapacitor devices made of conductive yarn, as previously reported in the literature.

Pulse laser ablation of Au, Ag, and Cu metal targets in liquid for nanoparticle production

NASA Astrophysics Data System (ADS)

Herbani, Y.; Irmaniar; Nasution, R. S.; Mujtahid, F.; Masse, S.

2018-03-01

We have fabricated metal and oxide nanoparticles using pulse laser ablation of Au, Ag, and Cu metal targets immersed in water. While laser ablation of Au and Ag targets in water produced metal nanoparticles which were stable for a month even without any dispersant, we found CuO nanoparticles for Cu target due to rapid oxidation of Cu in water resulted in its poor stability. Au, Ag, and CuO nanoparticles production were barely identified by naked eyes for their distinctive colour of red, yellow, and dark green colloidal suspensions, respectively. It was also verified using UV-Vis spectrometer that Au, Ag, and CuO colloidal nanoparticles have their respective surface plasmon resonance at 520, 400, and 620 nm. TEM observation showed that particle sizes for all the fabricated nanoparticles were in the range of 20 – 40 nm with crystalline structures.

Peripheral Hole Acceptor Moieties on an Organic Dye Improve Dye‐Sensitized Solar Cell Performance

PubMed Central

Hao, Yan; Gabrielsson, Erik; Lohse, Peter William; Yang, Wenxing; Johansson, Erik M. J.; Hagfeldt, Anders

2015-01-01

Investigation of charge transfer dynamics in dye‐sensitized solar cells is of fundamental interest and the control of these dynamics is a key factor for developing more efficient solar cell devices. One possibility for attenuating losses through recombination between injected electrons and oxidized dye molecules is to move the positive charge further away from the metal oxide surface. For this purpose, a metal‐free dye named E6 is developed, in which the chromophore core is tethered to two external triphenylamine (TPA) units. After photoinduced electron injection into TiO2, the remaining hole is rapidly transferred to a peripheral TPA unit. Electron–hole recombination is slowed down by 30% compared to a reference dye without peripheral TPA units. Furthermore, it is found that the added TPA moieties improve the electron blocking effect of the dye, retarding recombination of electrons from TiO2 to the cobalt‐based electrolyte. PMID:27722076

Recyclable graphene oxide grafted with poly(N-isopropylacrylamide) and its enhanced selective adsorption for phenols

NASA Astrophysics Data System (ADS)

Gong, Zailin; Li, Shujin; Han, Weifang; Wang, Jiaping; Ma, Jun; Zhang, Xiangdong

2016-01-01

The graphene oxide (GO) was synthesized with Brodie's method and grafted with poly (N-isopropylacrylamide) (NIPAM) in aqueous solution at ambient temperature. Compared with the initial GO, the PNIPAM graft GO (GO-PNIPAM) has larger surface area, pore volume and self-flocculation effect with rapid response to temperature. Moreover, the GO-PNIPAM also has selective adsorptions with different phenol pollutants because of the different interactions of hydrogen bonds and the molecule structure of the adsorbates. Compared with phenol and bisphenol A, hydroquinone has better adsorption on GO-PNIPAM because of the ample phenolic hydroxyl group and the appropriate molecule structure. The adsorption performance of hydroquinone on GO-PNIPAM is also temperature sensitive because of the thermoresponsive transition of the hydrogen bond. The thermoresponsive adsorption and self-flocculation will make the GO-PNIPAM recyclable in the potential water remediation.

Nanoscale oxidation and complex oxide growth on single crystal iron surfaces and external electric field effects.

PubMed

Jeon, Byoungseon; Van Overmeere, Quentin; van Duin, Adri C T; Ramanathan, Shriram

2013-02-14

Oxidation of iron surfaces and oxide growth mechanisms have been studied using reactive molecular dynamics. Oxide growth kinetics on Fe(100), (110), and (111) surface orientations has been investigated at various temperatures and/or an external electric field. The oxide growth kinetics decreases in the order of (110), (111), and (100) surfaces at 300 K over 1 ns timescale while higher temperature increases the oxidation rate. The oxidation rate shows a transition after an initial high rate, implying that the oxide formation mechanism evolves, with iron cation re-ordering. In early stages of surface oxide growth, oxygen transport through iron interstitial sites is dominant, yielding non-stoichiometric wüstite characteristics. The dominant oxygen inward transport decreases as the oxide thickens, evolving into more stoichiometric oxide phases such as wüstite or hematite. This also suggests that cation outward transport increases correspondingly. In addition to oxidation kinetics simulations, formed oxide layers have been relaxed in the range of 600-1500 K to investigate diffusion characteristics, fitting these results into an Arrhenius relation. The activation energy of oxygen diffusion in oxide layers formed on Fe(100), (110), and (111) surfaces was estimated to be 0.32, 0.26, and 0.28 eV, respectively. Comparison between our modeling results and literature data is then discussed. An external electric field (10 MV cm(-1)) facilitates initial oxidation kinetics by promoting oxygen transport through iron lattice interstitial sites, but reaches self-limiting thickness, showing that similar oxide formation stages are maintained when cation transport increases. The effect of the external electric field on iron oxide structure, composition, and oxide activation energy is found to be minimal, whereas cation outward migration is slightly promoted.

Oxide driven strength evolution of silicon surfaces

DOE PAGES

Grutzik, Scott J.; Milosevic, Erik; Boyce, Brad L.; ...

2015-11-19

Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations showmore » that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Lastly, combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.« less

Analytical electron tomography mapping of the SiCporeoxidation at the nanoscale

NASA Astrophysics Data System (ADS)

Florea, Ileana; Ersen, Ovidiu; Hirlimann, Charles; Roiban, Lucian; Deneuve, Adrien; Houllé, Matthieu; Janowska, Izabela; Nguyen, Patrick; Pham, Charlotte; Pham-Huu, Cuong

2010-12-01

Silicon carbide is a ceramic material that has been widely studied because of its potential applications, ranging from electronics to heterogeneous catalysis. Recently, a new type of SiC materials with a medium specific surface area and thermal conductivity, called β-SiC, has attracted overgrowing interest as a new class of catalyst support in several catalytic reactions. A primary electron tomography study, performed in usual mode, has revealed a dual surface structure defined by two types of porosities made of networks of connected channels with sizes larger than 50 nm and ink-bottled pores with sizes spanning from 4 to 50 nm. Depending on the solvent nature, metal nanoparticles could be selectively deposited inside one of the two porosities, a fact that illustrates a selective wetting titration of the two types of surfaces by different liquids. The explaining hypothesis that has been put forward was that this selectivity against solvents is related to the pore surface oxidation degree of the two types of pores. A new technique of analytical electron tomography, where the series of projections used to reconstruct the volume of an object is recorded in energy filtered mode (EFTEM), has been implemented to map the poreoxidation state and to correlate it with the morphology and the accessibility of the porous network. Applied, for the first time, at a nanoscale resolution, this technique allowed us to obtain 3D elemental maps of different elements present in the analysed porous grains, in particular oxygen; we found thus that the interconnected channelpores are more rapidly oxidized than the ink-bottled ones. Alternatively, our study highlights the great interest of this method that opens the way for obtaining precise information on the chemical composition of a 3D surface at a nanometer scale.Silicon carbide is a ceramic material that has been widely studied because of its potential applications, ranging from electronics to heterogeneous catalysis. Recently, a new type of SiC materials with a medium specific surface area and thermal conductivity, called β-SiC, has attracted overgrowing interest as a new class of catalyst support in several catalytic reactions. A primary electron tomography study, performed in usual mode, has revealed a dual surface structure defined by two types of porosities made of networks of connected channels with sizes larger than 50 nm and ink-bottled pores with sizes spanning from 4 to 50 nm. Depending on the solvent nature, metal nanoparticles could be selectively deposited inside one of the two porosities, a fact that illustrates a selective wetting titration of the two types of surfaces by different liquids. The explaining hypothesis that has been put forward was that this selectivity against solvents is related to the pore surface oxidation degree of the two types of pores. A new technique of analytical electron tomography, where the series of projections used to reconstruct the volume of an object is recorded in energy filtered mode (EFTEM), has been implemented to map the poreoxidation state and to correlate it with the morphology and the accessibility of the porous network. Applied, for the first time, at a nanoscale resolution, this technique allowed us to obtain 3D elemental maps of different elements present in the analysed porous grains, in particular oxygen; we found thus that the interconnected channelpores are more rapidly oxidized than the ink-bottled ones. Alternatively, our study highlights the great interest of this method that opens the way for obtaining precise information on the chemical composition of a 3D surface at a nanometer scale. Electronic supplementary information (ESI) available: SI-1-SI-4. See DOI: 10.1039/c0nr00449a

Kinetic multi-layer model of the epithelial lining fluid (KM-ELF): Reactions of ozone and OH with antioxidants and surfactant molecules

NASA Astrophysics Data System (ADS)

Lakey, Pascale; Pöschl, Ulrich; Shiraiwa, Manabu

2015-04-01

Oxidants cause damage to biosurfaces such as the lung epithelium unless they are effectively scavenged. The respiratory tract is covered in a thin layer of fluid which extends from the nasal cavity to the alveoli and contain species that scavenge ozone and other incoming oxidants. The kinetic multi-layer model of the epithelial lining fluid (KM-ELF) has been developed in order to investigate the reactions of ozone and OH with antioxidants (ascorbate, uric acid, glutathione and α-tocopherol) and surfactant lipids and proteins within the epithelial lining fluid (ELF). The model incorporates different processes: gas phase diffusion, adsorption and desorption from the surface, bulk phase diffusion and known reactions at the surface and in the bulk. The ELF is split into many layers: a sorption layer, a surfactant layer, a near surface bulk layer and several bulk layers. Initial results using KM-ELF indicate that at ELF thicknesses of 80 nm and 1 × 10-4cm the ELF would become rapidly saturated with ozone with saturation occurring in less than a second. However, at an ELF thickness of 1 × 10-3cm concentration gradients were observed throughout the ELF and the presence of antioxidants reduced the O3 reaching the lung cells and tissues by 40% after 1 hour of exposure. In contrast, the antioxidants were efficient scavengers of OH radicals, although the large rate constants of OH reacting with the antioxidants resulted in the antioxidants decaying away rapidly. The chemical half-lives of the antioxidants and surface species were also calculated using KM-ELF as a function of O3 and OH concentration and ELF thickness. Finally, the pH dependence of the products of reactions between antioxidants and O3 were investigated. The KM-ELF model predicted that a harmful ascorbate ozonide product would increase from 1.4 × 1011cm-3at pH 7.4 to 1.1 × 1014 cm-3 at pH 4after 1 hour although a uric acid ozonide product would decrease from 2.0 × 1015cm-3to 5.9 × 1012cm-3.

Simultaneous enzymatic and SERS properties of bifunctional chitosan-modified popcorn-like Au-Ag nanoparticles for high sensitive detection of melamine in milk powder.

PubMed

Li, Junrong; Zhang, Guannan; Wang, Lihua; Shen, Aiguo; Hu, Jiming

2015-08-01

In this work, we suggest a chitosan-modified popcorn-like Au-Ag nanoparticles (CSPNPs) based assay for high sensitive detection of melamine, in which CSPNPs not only provide with an intrinsic peroxidase-like activity but also act as surface enhanced Raman scattering (SERS) substrates. CSPNPs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to the charge transfer complex (CTC), which contributes to a tremendous surface-enhanced resonant Raman scattering (SERRS) signals with 632.8 nm laser excitation. The target molecule melamine can generate an additional compound with H2O2, which means the available amount of H2O2 for the oxidation of TMB reduced. Correspondingly, the SERRS intensity of CTC is decreased. The decreased Raman intensity is proportional to the concentration of melamine over a wide range from 10 nM to 50 μM (R(2)=0.989), with a limit of detection (LOD) of 8.51 nM. Moreover, the proposed highly selective method is fully capable of rapid, separation-free detection of melamine in milk powder. Copyright © 2015 Elsevier B.V. All rights reserved.

Oxidation behavior of a thermal barrier coating

NASA Technical Reports Server (NTRS)

Miller, R. A.

1984-01-01

Thermal barrier coatings, consisting of a plasma sprayed calcium silicate ceramic layer and a CoCrAlY or NiCrAlY bond coat, were applied on B-1900 coupons and cycled hourly in air in a rapid-response furnace to maximum temperatures of 1030, 1100, or 1160 C. Eight specimens were tested for each of the six conditions of bond-coat composition and temperature. Specimens were removed from test at the onset of failure, which was taken to be the formation of a fine surface crack visible at 10X magnification. Specimens were weighed periodically, and plots of weight gain vs time indicate that weight is gained at a parabolic rate after an initial period where weight was gained at a much greater rate. The high initial oxidation rate is thought to arise from the initially high surface area in the porous bond coat. Specimen life (time to first crack) was found to be a strong function of temperature. However, while test lives varied greatly with time, the weight gain at the time of specimen failure was quite insensitive to temperature. This indicates that there is a critical weight gain at which the coating fails when subjected to this test.

Criteria for selecting electrodes for electrical stimulation: theoretical and practical considerations.

PubMed

Brummer, S B; Robblee, L S; Hambrecht, F T

1983-01-01

Smaller, more charge-intensive electrodes are needed for "safe" stimulation of the nervous system. In this paper we review critical concepts and the state of the art in electrodes. Control of charge density and charge balance are essential to avoid tissue electrolysis. Chemical criteria for "safe" stimulation are reviewed ("safe" is equated with "chemically reversible"). An example of a safe, but generally impractical, charge-injection process is double-layer charging. The limit here is the onset of irreversible faradaic processes. More charge can be safely injected with so-called "capacitor" electrodes, such as porous intermixtures of Ta/Ta2O5. BaTiO3 has excellent dielectric properties and may provide a new generation of capacitor electrodes. Faradaic charge injection is usually partially irreversible since some of the products escape into the solution. With Pt, up to 400 muc/cm2 real area can be absorbed by faradaic reactions of surface-adsorbed species, but a small part is lost due to metal dissolution. The surface of "activated" Ir is covered with a multilayer hydrated oxide. Charge injection occurs via rapid valence change within this oxide. Little or no metal dissolution is observed, and gassing limits are not exceeded even under stringent conditions.

Anti-Oxidative and Antibacterial Self-Healing Edible Polyelectrolyte Multilayer Film in Fresh-Cut Fruits.

PubMed

Liu, Xuefan; Han, Wei; Zhu, Yanxi; Xuan, Hongyun; Ren, Jiaoyu; Zhang, Jianhao; Ge, Liqin

2018-04-01

The consumption of fresh-cut fruits is limited because of the oxidation browning and pathogenic bacteria's growth on the fruit surface. Besides, crack of the fresh-keeping film may shorten the preservation time of fruit. In this work, polyelectrolyte multilayer (PEM) film was fabricated by layer-by-layer (LBL) electrostatic deposition method. The film was made by carboxy methylcellulose sodium (CMC) and chitosan (CS). The as-prepared PEM film had good anti-oxidative and antibacterial capability. It inhibited the growth of Gram-negative bacteria and the antibacterial rate was more than 95%. The stratified structure and linear increase of the absorbance in the film verified a linear increase of film thickness. The slight scratched film could self-heal rapidly after the stimulation of water whatever the layer number was. Moreover, the film could heal cracks whose width was far bigger than the thickness. The application of PEM film on fresh-cut apples showed that PEM film had good browning, weight loss and metabolic activity inhibition ability. These results showed that the PEM film is a good candidate as edible film in fresh-cut fruits applications.

The Reduction of Aqueous Metal Species on the Surfaces of Fe(II)-Containing Oxides: The Role of Surface Passivation

USGS Publications Warehouse

White, A.F.; Peterson, M.L.

1998-01-01

The reduction of aqueous transition metal species at the surfaces of Fe(II)- containing oxides has important ramifications in predicting the transport behavior in ground water aquifers. Experimental studies using mineral suspensions and electrodes demonstrate that structural Fe(II) heterogeneously reduces aqueous ferric, cupric, vanadate and chromate ions on magnetite and ilmenite surfaces. The rates of metal reduction on natural oxides is strongly dependent on the extent of surface passivation and redox conditions in the weathering environment. Synchrotron studies show that surface oxidation of Fe(II)-containing oxide minerals decreases their capacity for Cr(VI) reduction at hazardous waste disposal sites.

Ground-water hydrology and subsurface migration of radioisotopes at a low-level solid radioactive-waste disposal site, West Valley, New York

USGS Publications Warehouse

Prudic, David E.; Randall, Allan D.

1977-01-01

Burial trenches for disposal of solid radioactive waste at West Valley, N.Y., are excavated in till that has very low hydraulic conductivity (about 5 x 10 to the minus 8th power centimeters per second). Fractures and root tubes with chemically oxidized and (or) reduced soil in their walls extend to 3 to 4.5 meters below natural land surface. Preliminary simulations of pressure heads with a digital model suggest that hydraulic conductivity is an order of magnitude greater in the fractured till near land surface than at greater depth. Hydraulic gradients are predominantly downward, even beneath small valleys. The upper part of a body of underlying lacustrine silt is unsaturated; in the lower, saturated part, slow lateral flow may occur. In the older trenches, water began to build up in 1971, overflowed briefly in 1975, and was pumped out in 1975-76. Water levels rose abruptly during major rainstorms in mid-1975, indicating rapid infiltration through cracks in the cover material. The new trenches have maintained low, stable water levels, perhaps because of thicker, more compact cover and less waste settlement; pressure heads near these trenches are low, locally approaching zero, perhaps because of slight infiltration and limited near-surface storage. Peak tritium concentrations in test-hole cores (generally 0.00001 to 0.001 microcuries per milliliter) were found within 3 meters of land surface and are attributed to surface contamination. Concentrations declined rapidly with depth within the fractured till; secondary peaks found at about 9 meters in three holes are attributed to lateral migration from trenches. Other radioisotopes were detected only near land surface. Samples from the walls of shallow fractures revealed no accumulation of radioisotopes. (Woodard-USGS)

The Otto Aufranc Award: enhanced biocompatibility of stainless steel implants by titanium coating and microarc oxidation.

PubMed

Lim, Young Wook; Kwon, Soon Yong; Sun, Doo Hoon; Kim, Yong Sik

2011-02-01

Stainless steel is one of the most widely used biomaterials for internal fixation devices, but is not used in cementless arthroplasty implants because a stable oxide layer essential for biocompatibility cannot be formed on the surface. We applied a Ti electron beam coating, to form oxide layer on the stainless steel surface. To form a thicker oxide layer, we used a microarc oxidation process on the surface of Ti coated stainless steel. Modification of the surface using Ti electron beam coating and microarc oxidation could improve the ability of stainless steel implants to osseointegrate. The ability of cells to adhere to grit-blasted, titanium-coated, microarc-oxidated stainless steel in vitro was compared with that of two different types of surface modifications, machined and titanium-coated, and microarc-oxidated. We performed energy-dispersive x-ray spectroscopy and scanning electron microscopy investigations to assess the chemical composition and structure of the stainless steel surfaces and cell morphology. The biologic responses of an osteoblastlike cell line (SaOS-2) were examined by measuring proliferation (cell proliferation assay), differentiation (alkaline phosphatase activity), and attraction ability (cell migration assay). Cell proliferation, alkaline phosphatase activity, migration, and adhesion were increased in the grit-blasted, titanium-coated, microarc-oxidated group compared to the two other groups. Osteoblastlike cells on the grit-blasted, titanium-coated, microarc-oxidated surface were strongly adhered, and proliferated well compared to those on the other surfaces. The surface modifications we used (grit blasting, titanium coating, microarc oxidation) enhanced the biocompatibility (proliferation and migration of osteoblastlike cells) of stainless steel. This process is not unique to stainless steel; it can be applied to many metals to improve their biocompatibility, thus allowing a broad range of materials to be used for cementless implants.

Quantitative X-ray photoelectron spectroscopy-based depth profiling of bioleached arsenopyrite surface by Acidithiobacillus ferrooxidans

NASA Astrophysics Data System (ADS)

Zhu, Tingting; Lu, Xiancai; Liu, Huan; Li, Juan; Zhu, Xiangyu; Lu, Jianjun; Wang, Rucheng

2014-02-01

In supergene environments, microbial activities significantly enhance sulfide oxidation and result in the release of heavy metals, causing serious contamination of soils and waters. As the most commonly encountered arsenic mineral in nature, arsenopyrite (FeAsS) accounts for arsenic contaminants in various environments. In order to investigate the geochemical behavior of arsenic during microbial oxidation of arsenopyrite, (2 3 0) surfaces of arsenopyrite slices were characterized after acidic (pH 2.00) and oxidative decomposition with or without an acidophilic microorganism Acidithiobacillus ferrooxidans. The morphology as well as chemical and elemental depth profiles of the oxidized arsenopyrite surface were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. With the mediation of bacteria, cell-shaped and acicular pits were observed on the reacted arsenopyrite surface, and the concentration of released arsenic species in solution was 50 times as high as that of the abiotic reaction after 10 days reaction. Fine-scale XPS depth profiles of the reacted arsenopyrite surfaces after both microbial and abiotic oxidation provided insights into the changes in chemical states of the elements in arsenopyrite surface layers. Within the 450 nm surface layer of abiotically oxidized arsenopyrite, Fe(III)-oxides appeared and gradually increased towards the surface, and detectable sulfite and monovalent arsenic appeared above 50 nm. In comparison, higher contents of ferric sulfate, sulfite, and arsenite were found in the surface layer of approximately 3 μm of the microbially oxidized arsenopyrite. Intermediates, such as Fe(III)-AsS and S0, were detectable in the presence of bacteria. Changes of oxidative species derived from XPS depth profiles show the oxidation sequence is Fe > As = S in abiotic oxidation, and Fe > S > As in microbial oxidation. Based on these results, a possible reaction path of microbial oxidation was proposed in a concept model.

Studies of high coverage oxidation of the Cu(100) surface using low energy positrons

NASA Astrophysics Data System (ADS)

Fazleev, N. G.; Maddox, W. B.; Weiss, A. H.

2012-02-01

The study of oxidation of single crystal metal surfaces is important in understanding the corrosive and catalytic processes associated with thin film metal oxides. The structures formed on oxidized transition metal surfaces vary from simple adlayers of chemisorbed oxygen to more complex structures which result from the diffusion of oxygen into subsurface regions. In this work we present the results of theoretical studies of positron surface and bulk states and annihilation probabilities of surface-trapped positrons with relevant core electrons at the oxidized Cu(100) surface under conditions of high oxygen coverage. Calculations are performed for various high coverage missing row structures ranging between 0.50 and 1.50 ML oxygen coverage. The results of calculations of positron binding energy, positron work function, and annihilation characteristics of surface trapped positrons with relevant core electrons as function of oxygen coverage are compared with experimental data obtained from studies of oxidation of the Cu(100) surface using positron annihilation induced Auger electron spectroscopy (PAES).

Mechanical Properties of Degraded PMR-15 Resin

NASA Technical Reports Server (NTRS)

Tsuji, Luis C.

2000-01-01

Thermo-oxidative aging produces a nonuniform degradation state in PMR-15 resin. A surface layer, usually attributed to oxidative degradation, forms. This surface layer has different properties from the inner material. A set of material tests was designed to separate the properties of the oxidized surface layer from the properties of interior material. Test specimens were aged at 316 C in either air or nitrogen, for durations of up to 800 hr. The thickness of the oxidized surface layer in air aged specimens, and the shrinkage and coefficient of thermal expansion (CTE) of nitrogen aged specimens were measured directly. The nitrogen-aged specimens were assumed to have the same properties as the interior material in the air-aged specimens. Four-point-bend tests were performed to determine modulus of both the oxidized surface layer and the interior material. Bimaterial strip specimens consisting of oxidized surface material and unoxidized interior material were constructed and used to determine surface layer shrinkage and CTE. Results confirm that the surface layer and core materials have substantially different properties.

Rapid immobilization of simulated radioactive soil waste by microwave sintering.

PubMed

Zhang, Shuai; Shu, Xiaoyan; Chen, Shunzhang; Yang, Huimin; Hou, Chenxi; Mao, Xueli; Chi, Fangting; Song, Mianxin; Lu, Xirui

2017-09-05

A rapid and efficient method is particularly necessary in the timely disposal of seriously radioactive contaminated soil. In this paper, a series of simulated radioactive soil waste containing different contents of neodymium oxide (3-25wt.%) has been successfully vitrified by microwave sintering at 1300°C for 30min. The microstructures, morphology, element distribution, density and chemical durability of as obtained vitrified forms have been analyzed. The results show that the amorphous structure, homogeneous element distribution, and regular density improvement are well kept, except slight cracks emerge on the magnified surface for the 25wt.% Nd 2 O 3 -containing sample. Moreover, all the vitrified forms exhibit excellent chemical durability, and the leaching rates of Nd are kept as ∼10 -4 -10 -6 g/(m 2 day) within 42days. This demonstrates a potential application of microwave sintering in radioactive contaminated soil disposal. Copyright © 2017 Elsevier B.V. All rights reserved.

Rapid growth and photoluminescence properties of doped ZnS one-dimensional nanostructures

NASA Astrophysics Data System (ADS)

Zhuo, R. F.; Feng, H. T.; Yan, D.; Chen, J. T.; Feng, J. J.; Liu, J. Z.; Yan, P. X.

2008-06-01

In this paper we report the synthesis of doped ZnS one-dimensional (1D) nanostructures by well-established technique of chemical vapor deposition using Zn and S powder as precursors. The ZnS 1D nanostructures were grown on the surface of Au particle-filled anodic aluminum oxide templates, catalyst-free graphite sheets and silicon substrates. ZnS 1D nanostructures with Mn, Cu and Fe as dopants were prepared via a rapid process of 15-20 min. The morphologies of ZnS nanostructures synthesized on different substrates and at different growth temperatures have distinct dissimilarities. The size of ZnS nanowires originated from the Au catalysts could be varied by altering the size of membrane nanopores as well as the embedded Au particles. Room-temperature photoluminescence measurements reveal strong blue, green and yellow-orange light emissions from the doped ZnS 1D nanostructures.

Landslide-induced weathering: insight from a deep bedrock tunnel in Taiwan and implications for the carbon cycle

NASA Astrophysics Data System (ADS)

Martin, C. E.; Galy, A.; Calmels, D.; Hovius, N.; Bickle, M.; Chen, M.

2012-12-01

We present new groundwater chemistry data from inside a 520 m-long, un-cased bedrock tunnel in Taroko Gorge, Taiwan. The tunnel cuts through a ~ 250 m ridge of steeply-dipping meta-sediments (schists and marbles) and exhibits water flow characteristic of deep groundwater and slow surface runoff as defined by Calmels et al. (2011). For comparison, surface runoff from the tunnel face is also presented. In October 2009, catastrophic failure resulted in a landslide, removing ~ 10 m-deep of bedrock from the entire ridge face directly above the tunnel entrance. Groundwater was collected from several drip sites in September 2009 and from the same drip sites in May, June, July and August 2010. The chemistry of the water dripping close to the tunnel entrance disrupted by the landslide implies that the post-landslide groundwater was from a meteoric source with negligible evapotranspiration demonstrating that the geomorphic perturbation allowed for the relatively rapid flushing of underlying bedrock fractures. The drop in [Cl-] of ~ 60 % was associated with a rise in the [SO42-] by a factor of ~ 4 and a positive shift in δ13C of the dissolved inorganic carbon (DIC) of ~ 12 ‰. This could imply that weathering products in the fresh post-landslide groundwater resulted from sulphuric acid weathering associated with a rise in the carbonate-derived DIC. The rise in the [SO42-] suggests that the landslide-induced exposure of fresh mineral surfaces resulted in the relatively rapid oxidation of pyrite, generating sulphuric acid, which then acted as the primary weathering agent. Given that [Ca2+] and [HCO3-] remained constant, secondary carbonate precipitation also took place and the rise in the [Na+] by a factor of >7 associated with a rise in [Mg2+] and [K+] suggest that silicate dissolution had also been enhanced by the oxidation of pyrite. These results imply that landslides provide a mechanism for weathering in the deep critical zone, which in this case constitutes a net output of CO2 to the atmosphere. Calmels, D., Galy, A., Hovius, N., Bickle, M., West, J.A., Chen, M-C., Chapman, H. Contribution of deep groundwater to the weathering budget in a rapidly eroding mountain belt, Taiwan. 2011. Earth and Planetary Science Letters 303: 48-58.

Submarine Basaltic Glass Colonization by the Heterotrophic Fe(II)-Oxidizing and Siderophore-Producing Deep-Sea Bacterium Pseudomonas stutzeri VS-10: The Potential Role of Basalt in Enhancing Growth

PubMed Central

Sudek, Lisa A.; Wanger, Greg; Templeton, Alexis S.; Staudigel, Hubert; Tebo, Bradley M.

2017-01-01

Phylogenetically and metabolically diverse bacterial communities have been found in association with submarine basaltic glass surfaces. The driving forces behind basalt colonization are for the most part unknown. It remains ambiguous if basalt provides ecological advantages beyond representing a substrate for surface colonization, such as supplying nutrients and/or energy. Pseudomonas stutzeri VS-10, a metabolically versatile bacterium isolated from Vailulu’u Seamount, was used as a model organism to investigate the physiological responses observed when biofilms are established on basaltic glasses. In Fe-limited heterotrophic media, P. stutzeri VS-10 exhibited elevated growth in the presence of basaltic glass. Diffusion chamber experiments demonstrated that physical attachment or contact of soluble metabolites such as siderophores with the basaltic glass plays a pivotal role in this process. Electrochemical data indicated that P. stutzeri VS-10 is able to use solid substrates (electrodes) as terminal electron donors and acceptors. Siderophore production and heterotrophic Fe(II) oxidation are discussed as potential mechanisms enhancing growth of P. stutzeri VS-10 on glass surfaces. In correlation with that we discuss the possibility that metabolic versatility could represent a common and beneficial physiological trait in marine microbial communities being subject to oligotrophic and rapidly changing deep-sea conditions. PMID:28344573

Formation and Growth of New Organic Aerosol Particles over the Deepwater Horizon Oil Spill

NASA Astrophysics Data System (ADS)

Brock, C. A.; Murphy, D. M.; Bahreini, R.; Middlebrook, A. M.; De Gouw, J. A.

2011-12-01

Aerosol size distributions were measured in June 2010 downwind of the surface oil slick produced by the Deepwater Horizon oil spill in the Gulf of Mexico. Rapid condensation of partially oxidized hydrocarbons was responsible for formation of a plume of secondary organic aerosol downwind of the spill region. New particles were nucleated upwind of the freshest surface oil but downwind of oil that surfaced less than 100 hours previously. These new particles grew by condensation at rates of ~20 nm hr-1; preexisting accumulation mode particles grew by ~10 nm hr-1. The gas-phase concentration of a condensing species necessary to support the observed growth rate assuming irreversible adsorption with unit accommodation coefficient is estimated to be ~0.04-0.09 μg m-3 (~3-8 pptv). The ratio of growth rates for newly formed particles to accumulation mode particles was consistent within error limits with irreversible condensation. Because new particle formation did not occur in areas away from the <100 hr-old oil slick, these results indicate that the oxidation products of VOC species, probably C14-C16 compounds, were directly involved in the growth of the new particles. While a unique and extreme environment, the oil spill plume provides insight into similar processes that may occur in urban and industrial areas where petrochemical products are produced and consumed.

Superparamagnetic iron oxide coated on the surface of cellulose nanospheres for the rapid removal of textile dye under mild condition

NASA Astrophysics Data System (ADS)

Qin, Yunfeng; Qin, Zongyi; Liu, Yannan; Cheng, Miao; Qian, Pengfei; Wang, Qian; Zhu, Meifang

2015-12-01

Magnetic composite nanoparticles (MNPs) were prepared by anchoring iron oxide (Fe3O4) on the surface of carboxyl cellulose nanospheres through a facile chemical co-precipitation method. The as-prepared MNPs were characterized by atomic force microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction measurement, thermal gravity analysis and vibrating sample magnetometry. These MNPs were of a generally spherical shape with a narrow size distribution, and exhibited superparamagnetic behaviors with high saturation magnetization. High efficient removal of Navy blue in aqueous solution was demonstrated at room temperature in a Fenton-like system containing the MNPs and H2O2, which benefited from small particle size, large surface area, high chemical activity, and good dispersibility of the MNPs. The removal efficiency of Navy blue induced by the MNPs prepared at a weight ratio of cellulose to iron of 1:2 were 90.6% at the first minute of the degradation reaction, and 98.0% for 5 min. Furthermore, these MNPs could be efficiently recycled and reused by using an external magnetic field. The approach presented in this paper promotes the use of renewable natural resources as templates for the preparation and stabilization of various inorganic nanomaterials for the purpose of catalysis, magnetic resonance imaging, biomedical and other potential applications.

A rational design approach to nanostructured catalysts for the oxidation of carbon monoxide

NASA Astrophysics Data System (ADS)

Karwacki, Christopher

The extraordinary energetic properties of subnanometer (<10 nm) structures consisting of reduced metals, metal oxides, and graphitic carbons are emerging as the principal technologies involving catalytic reactions at ambient temperatures, for such applications as respiratory protection, pollution abatement, chemical synthesis, sensors, and energy conversion. Gold nanoparticles (Au NP) possess unique reactive properties not present in the bulk state and have served in the past decade as a model for the nanosciences, where molecular species are synthesized, scaled, and engineered into functional materials. Gold nanoparticles as isolated structures are not useful as real catalysts and must co-exist with supports that provide enhanced stability and activity. Support oxides such as TiO2, Fe2O 3, CeO2, SiO2, Al2O3, ZrO 2, and graphitic (active) carbons have been shown to increase the active nature of AuNP and have been the subject of several thousand publications in the past decade. Zirconia compared to titania as a support for Au NP catalysis has been studied with limited success. In fact, the majority of observations show that zirconia is one of the lowest performing metal oxide supports involving Au NP oxidation catalysis. The likely reason for these observations is a lack of understanding of the relationship between structure and surface functionality as it pertains to ambient temperature oxidation catalysis (ATOC). Furthermore, virtually all substrate and catalyst preparations in earlier work were performed at high temperatures, typically 400--900°C, thus forming progressively monomorphic structures containing larger crystals with reduced surface functionality and porosity. In this research, I established the hypothesis based on a structural model that surface functional hydroxides are important to sustained hydrolytic reactions, such as those involving Au NP for the oxidation of CO to CO 2. Theoretical calculations by Ignatchenko, Vittadini, et al. show that zirconia readily dissociates adsorbed water on the most active and stable crystal structures (111) compared to other metal oxides, such as the common anatase (101) form of titania. Also, the support must provide a source of activated oxygen as a means to oxidize intermediate carbonates with CO 2 formation. The role of the support is to provide lattice oxygen in an activated state (O2-) for oxidation of adsorbed CO the Au NP:support interface. Furthermore, the primary interest is the energy associated Au NP in proximity to the support surface. Advancing the understanding of this region is believed to be crucial to the future design of active nanostructured materials that function under ambient conditions. The proposed model involves a structure consisting of properly sized and highly dispersed Au NP supported on a hydroxylated form of nanocrystalline zirconia. This type of zirconia is in a highly polymorphic form consisting of aggregates of small crystals less than 10 nm. The structure is highly porous, containing undercoordinated zirconium atoms, and provides an environment for rapid dissociation of molecular water. In this research and in collaboration with Mogilevsky et al., 37 I introduce a novel method for quantifying the surface concentration of two major forms of hydroxide that form on zirconia. Furthermore, in this research I show how both the porosity of the zirconia support and the size of the crystalline aggregates affect the type and surface concentration of hydroxyl groups. This relationship is thus directly related to the oxidation activity of the catalyst consisting of Au NP supported on hydroxylated ZrO 2. These phenomena are exemplified by a reduction in structural porosity and surface hydroxyl groups with increasing temperature treatments of the zirconia support. Gold NP and ZrO2 supports were extended to studies that included interactions with activated carbons. This work was done on the premise that graphitic carbons, based on their tunable porosities and surface chemistries, can enhance or stabilize the catalytic activity of neighboring Au NP. Gold dispersed on active carbon and hybrid structures consisting of Au/ZrO 2/C shows interesting properties, which lend themselves to catalytic particle stabilization and to the advancement of multifunctional material design.

Surface Area, and Oxidation Effects on Nitridation Kinetics of Silicon Powder Compacts

NASA Technical Reports Server (NTRS)

Bhatt, R. T.; Palczer, A. R.

1998-01-01

Commercially available silicon powders were wet-attrition-milled from 2 to 48 hr to achieve surface areas (SA's) ranging from 1.3 to 70 sq m/g. The surface area effects on the nitridation kinetics of silicon powder compacts were determined at 1250 or 1350 C for 4 hr. In addition, the influence of nitridation environment, and preoxidation on nitridation kinetics of a silicon powder of high surface area (approximately equals 63 sq m/g) was investigated. As the surface area increased, so did the percentage nitridation after 4 hr in N2 at 1250 or 1350 C. Silicon powders of high surface area (greater than 40 sq m/g) can be nitrided to greater than 70% at 1250 C in 4 hr. The nitridation kinetics of the high-surface-area powder compacts were significantly delayed by preoxidation treatment. Conversely, the nitridation environment had no significant influence on the nitridation kinetics of the same powder. Impurities present in the starting powder, and those accumulated during attrition milling, appeared to react with the silica layer on the surface of silicon particles to form a molten silicate layer, which provided a path for rapid diffusion of nitrogen and enhanced the nitridation kinetics of high surface area silicon powder.

Low-temperature CO oxidation on Ni(111) and on a Au/Ni(111) surface alloy.

PubMed

Knudsen, Jan; Merte, Lindsay R; Peng, Guowen; Vang, Ronnie T; Resta, Andrea; Laegsgaard, Erik; Andersen, Jesper N; Mavrikakis, Manos; Besenbacher, Flemming

2010-08-24

From an interplay between scanning tunneling microscopy, temperature programmed desorption, X-ray photoelectron spectroscopy, and density functional theory calculations we have studied low-temperature CO oxidation on Au/Ni(111) surface alloys and on Ni(111). We show that an oxide is formed on both the Ni(111) and the Au/Ni(111) surfaces when oxygen is dosed at 100 K, and that CO can be oxidized at 100 K on both of these surfaces in the presence of weakly bound oxygen. We suggest that low-temperature CO oxidation can be rationalized by CO oxidation on O(2)-saturated NiO(111) surfaces, and show that the main effect of Au in the Au/Ni(111) surface alloy is to block the formation of carbonate and thereby increase the low-temperature CO(2) production.

Ammonium Uptake by Phytoplankton Regulates Nitrification in the Sunlit Ocean

PubMed Central

Smith, Jason M.; Chavez, Francisco P.; Francis, Christopher A.

2014-01-01

Nitrification, the microbial oxidation of ammonium to nitrate, is a central part of the nitrogen cycle. In the ocean’s surface layer, the process alters the distribution of inorganic nitrogen species available to phytoplankton and produces nitrous oxide. A widely held idea among oceanographers is that nitrification is inhibited by light in the ocean. However, recent evidence that the primary organisms involved in nitrification, the ammonia-oxidizing archaea (AOA), are present and active throughout the surface ocean has challenged this idea. Here we show, through field experiments coupling molecular genetic and biogeochemical approaches, that competition for ammonium with phytoplankton is the strongest regulator of nitrification in the photic zone. During multiday experiments at high irradiance a single ecotype of AOA remained active in the presence of rapidly growing phytoplankton. Over the course of this three day experiment, variability in the intensity of competition with phytoplankton caused nitrification rates to decline from those typical of the lower photic zone (60 nmol L−1 d−1) to those in well-lit layers (<1 nmol L−1 d−1). During another set of experiments, nitrification rates exhibited a diel periodicity throughout much of the photic zone, with the highest rates occurring at night when competition with phytoplankton is lowest. Together, the results of our experiments indicate that nitrification rates in the photic zone are more strongly regulated by competition with phytoplankton for ammonium than they are by light itself. This finding advances our ability to model the impact of nitrification on estimates of new primary production, and emphasizes the need to more strongly consider the effects of organismal interactions on nutrient standing stocks and biogeochemical cycling in the surface of the ocean. PMID:25251022

Ammonium uptake by phytoplankton regulates nitrification in the sunlit ocean.

PubMed

Smith, Jason M; Chavez, Francisco P; Francis, Christopher A

2014-01-01

Nitrification, the microbial oxidation of ammonium to nitrate, is a central part of the nitrogen cycle. In the ocean's surface layer, the process alters the distribution of inorganic nitrogen species available to phytoplankton and produces nitrous oxide. A widely held idea among oceanographers is that nitrification is inhibited by light in the ocean. However, recent evidence that the primary organisms involved in nitrification, the ammonia-oxidizing archaea (AOA), are present and active throughout the surface ocean has challenged this idea. Here we show, through field experiments coupling molecular genetic and biogeochemical approaches, that competition for ammonium with phytoplankton is the strongest regulator of nitrification in the photic zone. During multiday experiments at high irradiance a single ecotype of AOA remained active in the presence of rapidly growing phytoplankton. Over the course of this three day experiment, variability in the intensity of competition with phytoplankton caused nitrification rates to decline from those typical of the lower photic zone (60 nmol L-1 d-1) to those in well-lit layers (<1 nmol L-1 d-1). During another set of experiments, nitrification rates exhibited a diel periodicity throughout much of the photic zone, with the highest rates occurring at night when competition with phytoplankton is lowest. Together, the results of our experiments indicate that nitrification rates in the photic zone are more strongly regulated by competition with phytoplankton for ammonium than they are by light itself. This finding advances our ability to model the impact of nitrification on estimates of new primary production, and emphasizes the need to more strongly consider the effects of organismal interactions on nutrient standing stocks and biogeochemical cycling in the surface of the ocean.

Oxidants at the Surface of Mars: A Review in Light of Recent Exploration Results.

PubMed

Lasne, J; Noblet, A; Szopa, C; Navarro-González, R; Cabane, M; Poch, O; Stalport, F; François, P; Atreya, S K; Coll, P

2016-12-01

In 1976, the Viking landers carried out the most comprehensive search for organics and microbial life in the martian regolith. Their results indicate that Mars' surface is lifeless and, surprisingly, depleted in organics at part-per-billion levels. Several biology experiments on the Viking landers gave controversial results that have since been explained by the presence of oxidizing agents on the surface of Mars. These oxidants may degrade abiotic or biological organics, resulting in their nondetection in the regolith. As several exploration missions currently focus on the detection of organics on Mars (or will do so in the near future), knowledge of the oxidative state of the surface is fundamental. It will allow for determination of the capability of organics to survive on a geological timescale, the most favorable places to seek them, and the best methods to process the samples collected at the surface. With this aim, we review the main oxidants assumed to be present on Mars, their possible formation pathways, and those laboratory studies in which their reactivity with organics under Mars-like conditions has been evaluated. Among the oxidants assumed to be present on Mars, only four have been detected so far: perchlorate ions (ClO 4 - ) in salts, hydrogen peroxide (H 2 O 2 ) in the atmosphere, and clays and metal oxides composing surface minerals. Clays have been suggested as catalysts for the oxidation of organics but are treated as oxidants in the following to keep the structure of this article straightforward. This work provides an insight into the oxidizing potential of the surface of Mars and an estimate of the stability of organic matter in an oxidizing environment. Key Words: Mars surface-Astrobiology-Oxidant-Chemical reactions. Astrobiology 16, 977-996.

Ultrasonic assisted rapid synthesis of high uniform super-paramagnetic microspheres with core-shell structure and robust magneto-chromatic ability

NASA Astrophysics Data System (ADS)

Zhang, Wenyan; Chen, Jiahua; Wang, Wei; Lu, GongXuan; Hao, Lingyun; Ni, Yaru; Lu, Chunhua; Xu, Zhongzi

2017-03-01

Super-paramagnetic core-shell microspheres were synthesized by ultrasonic assisted routine under low ultrasonic irradiation powers. Compared with conventional routine, ultrasonic effect could not only improve the uniformity of the core-shell structure of Fe3O4@SiO2, but shorten the synthesis time in large scale. Owing to their hydrophilicity and high surface charge, the Fe3O4@SiO2 microspheres could be dispersed well in distilled water to form homogeneous colloidal suspension. The suspensions have favorable magneto-chromatic ability that they sensitively exhibit brilliant colorful ribbons by magnetic attraction. The colorful ribbons, which distributed along the magnetic lines, make morphology of the magnetic fields become "visible" to naked eyed. Those colorful ribbons originate from strong magnetic interaction between the microspheres and magnetic fields. Furthermore, the magneto-chromatic performance is reversible as the colorful ribbons vanished rapidly with the removing of magnetic fields. The silica layer effectively enhanced the acid resistance and surface-oxidation resistance of theFe3O4@SiO2 microspheres, so they could exhibit stable magnetic nature and robust magneto-chromatic property in acid environment.

A novel method for qualitative analysis of edible oil oxidation using an electronic nose.

PubMed

Xu, Lirong; Yu, Xiuzhu; Liu, Lei; Zhang, Rui

2016-07-01

An electronic nose (E-nose) was used for rapid assessment of the degree of oxidation in edible oils. Peroxide and acid values of edible oil samples were analyzed using data obtained by the American Oil Chemists' Society (AOCS) Official Method for reference. Qualitative discrimination between non-oxidized and oxidized oils was conducted using the E-nose technique developed in combination with cluster analysis (CA), principal component analysis (PCA), and linear discriminant analysis (LDA). The results from CA, PCA and LDA indicated that the E-nose technique could be used for differentiation of non-oxidized and oxidized oils. LDA produced slightly better results than CA and PCA. The proposed approach can be used as an alternative to AOCS Official Method as an innovative tool for rapid detection of edible oil oxidation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Gas phase condensation of superparamagnetic iron oxide-silica nanoparticles - control of the intraparticle phase distribution

NASA Astrophysics Data System (ADS)

Stötzel, C.; Kurland, H.-D.; Grabow, J.; Müller, F. A.

2015-04-01

Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs consisting of a γ-Fe2O3 and a SiO2 hemisphere to γ-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple γ-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis.Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs consisting of a γ-Fe2O3 and a SiO2 hemisphere to γ-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple γ-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis. Electronic supplementary information (ESI) available: Infrared absorption of the raw powders hematite and quartz (section S1), TEM investigation of the spatial distribution of the γ-Fe2O3 inclusions (section S2), particle size distributions of the Fe2O3@SiO2 nanopowder samples (section S3), ζ-potentials of aqueous dispersions of all γ-Fe2O3@SiO2 nanopowder samples (section S4), silanization of Fe2O3@SiO2 composite nanopowders with [3-(2,3-epoxypropoxy)-propyl]trimethoxysilane (section S5), and animation composed of TEM micrographs of Fe2O3@SiO2 NPs recorded at incrementally altered tilt angles (``Rotating Fe2O3@SiO2 NP.avi''). See DOI: 10.1039/c5nr00845j

Surface modification of polyethylene by radiation-induced grafting for adhesive bonding. V. Comparison with other surface treatments. [Gamma radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamakawa, S.; Yamamoto, F.

1980-01-01

Helium gas plasma treatment of low-density polyethylene (LDPE) yields much lower peel strength than oxidative treatment using chromic acid and oxygen gas plasma. The practical adhesion, the bondability retention, and the bond durability of oxidatively treated LDPE sheets, bonded with epoxy adhesives, have been compared with those of partially hydrolyzed LDPE-methyl acrylate surface grafts. The oxidized surfaces easily lose the bondability by light rubbing with tissue paper, solvent extraction, heat aging, and artificial weathering, whereas the grafted surfaces retain the bondability. The bondability loss is due to removal of the oxidized layer, and the bondability retention is due to retentionmore » of the surface homopolymer layer. Conventional antioxidants stabilize the grafted but not the oxidized surfaces against thermal oxidative degradation. The grafted LDPE joints have much higher bond durability in humid environments than those of the oxidized LDPE joints. The dry and wet peel strengths of oxidized LDPE joints are greatly improved by application of primers consisting of a base epoxy resin and organic solvents. An adhesion mechanism involving penetration of epoxy adhesives into the oxidized layers and subsequent reinforcement of the layers by curing of the penetrated epoxy is proposed. 5 figures, 5 tables.« less

Oxidation of Cyclohexene Catalyzed by Nanoporous Au(Ag) in Liquid Phase

DOE PAGES

Dou, Jian; Tang, Yu; Nguyen, Luan; ...

2016-12-22

Nanoporous gold with minor silver content has been identified as a new type of gold based catalyst for selective oxidation of cyclohexene with molecular oxygen in liquid. By oxidation of the leached nanoporous gold foils in ozone, the minor silver content was oxidized in this paper to form silver oxide nanoclusters on the surface of nanoporous gold. With further treatment in methanol, the surface silver oxide was reduced and surface alloy was formed on gold ligaments. Both nanoporous gold treated with ozone only and the one with ozone and then methanol are very active for selective oxidation of cyclohexene withmore » molecular oxygen in liquid of cyclohexene with a turn-over-frequency (TOF) of 0.55–0.99 molecules per surface Au atom per second under a solvent-free and initiator- free condition. The total selectivity for production of 2-cyclohexene-1-one, 2-cyclohexene-1-ol, and cyclohexene oxide was increased from 57.5 % to 80.8 % by an additional treatment of nanoporous gold in methanol after activation in zone. Finally, the correlation of catalytic selectivity for the production of the three products and corresponding surface chemistry of ligament suggests that (1) the formed Au–Ag alloy surface is favorable for the formation of 2-cyclohexen-1-one, 2-cyclohexene-1-ol, and cyclohexene oxide and (2) the surface silver oxide is favorable for the production of cyclohexenyl hydroperoxide.« less

Oxidation of Cyclohexene Catalyzed by Nanoporous Au(Ag) in Liquid Phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dou, Jian; Tang, Yu; Nguyen, Luan

Nanoporous gold with minor silver content has been identified as a new type of gold based catalyst for selective oxidation of cyclohexene with molecular oxygen in liquid. By oxidation of the leached nanoporous gold foils in ozone, the minor silver content was oxidized in this paper to form silver oxide nanoclusters on the surface of nanoporous gold. With further treatment in methanol, the surface silver oxide was reduced and surface alloy was formed on gold ligaments. Both nanoporous gold treated with ozone only and the one with ozone and then methanol are very active for selective oxidation of cyclohexene withmore » molecular oxygen in liquid of cyclohexene with a turn-over-frequency (TOF) of 0.55–0.99 molecules per surface Au atom per second under a solvent-free and initiator- free condition. The total selectivity for production of 2-cyclohexene-1-one, 2-cyclohexene-1-ol, and cyclohexene oxide was increased from 57.5 % to 80.8 % by an additional treatment of nanoporous gold in methanol after activation in zone. Finally, the correlation of catalytic selectivity for the production of the three products and corresponding surface chemistry of ligament suggests that (1) the formed Au–Ag alloy surface is favorable for the formation of 2-cyclohexen-1-one, 2-cyclohexene-1-ol, and cyclohexene oxide and (2) the surface silver oxide is favorable for the production of cyclohexenyl hydroperoxide.« less

Water Vapor Effects on the Oxidation Behavior of Fe-Cr and Ni-Cr Alloys in Atmospheres Relevant to Oxy-fuel Combustion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mu, N.; Jung, K. Y.; Yanar, N. M.

2011-10-01

The oxidation behavior of a number of Fe–Cr- and Ni–Cr-based alloys was studied in atmospheres relevant to oxyfuel combustion at 650 °C. Oxidation was greatly enhanced in ferritic model alloys exposed in low p(O{sub 2}) CO{sub 2} + 30%H{sub 2}O and Ar + 30%H{sub 2}O gases. Rapidly growing iron oxides appear to be porous and gas permeable. Transition from non-protective to protective oxidation occurs on alloys with higher Cr contents between 13.5 and 22 wt% in H{sub 2}O. Excess oxygen, usually found in the actual oxyfuel combustion environments, disrupts the selective oxidation of Fe–Cr alloys by accelerating vaporization of early-formedmore » Cr{sub 2}O{sub 3} in combination with accelerated chromia growth induced by the H{sub 2}O. Rapid Cr consumption leads to the nucleation and rapid growth of iron oxides. On the contrary, Ni–Cr alloys are less affected by the presence of H{sub 2}O and excess O{sub 2}. The difference between Fe–Cr and Ni–Cr alloys is not clear but is postulated to involve less acceleration of chromia growth by water vapor for the latter group of alloys.« less

Influence of the physico-chemical properties of CeO 2-ZrO 2 mixed oxides on the catalytic oxidation of NO to NO 2

NASA Astrophysics Data System (ADS)

Atribak, Idriss; Guillén-Hurtado, Noelia; Bueno-López, Agustín; García-García, Avelina

2010-10-01

Commercial and home-made Ce-Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N 2 adsorption at -196 °C and XPS, and were tested for NO oxidation to NO 2. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce-Zr catalysts. As a general trend, Ce-Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce-Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t'' for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce-Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio.

The rapidly metabolized 32,000-dalton polypeptide of the chloroplast is the "proteinaceous shield" regulating photosystem II electron transport and mediating diuron herbicide sensitivity.

PubMed Central

Mattoo, A K; Pick, U; Hoffman-Falk, H; Edelman, M

1981-01-01

Mild trypsin treatment of Spirodela oligorrhiza thylakoid membranes leads to partial digestion of the rapidly metabolized, surface-exposed, 32,000-dalton protein. Under these conditions, photoreduction of ferricyanide becomes insensitive to diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], an inhibitor of photosystem II electron transport. Preincubation of thylakoids with diuron leads to a conformational change in the 32,000-dalton protein, modifying its trypsin digestion and preventing expression of diuron insensitivity. Finally, light affects the susceptibility of the 32,000-dalton protein to digestion by trypsin. In other experiments, thylakoids specifically depleted in the 32,000-dalton protein were found to be deficient in electron transport at the reducing side of photosystem II but not at the oxidizing side or in photosystem I activities. Thus, the rapidly metabolized 32,000-dalton thylakoid protein in Spirodela chloroplasts fulfills the requirements of the hypothesized "proteinaceous shield" [Renger, G. (1976) Biochim. Biophys. Acta 440, 287-300] regulating electron flow through photosystem II and mediating diuron sensitivity. Images PMID:6940173

Water-driven micromotors for rapid photocatalytic degradation of biological and chemical warfare agents.

PubMed

Li, Jinxing; Singh, Virendra V; Sattayasamitsathit, Sirilak; Orozco, Jahir; Kaufmann, Kevin; Dong, Renfeng; Gao, Wei; Jurado-Sanchez, Beatriz; Fedorak, Yuri; Wang, Joseph

2014-11-25

Threats of chemical and biological warfare agents (CBWA) represent a serious global concern and require rapid and efficient neutralization methods. We present a highly effective micromotor strategy for photocatalytic degradation of CBWA based on light-activated TiO2/Au/Mg microspheres that propel autonomously in natural water and obviate the need for external fuel, decontaminating reagent, or mechanical agitation. The activated TiO2/Au/Mg micromotors generate highly reactive oxygen species responsible for the efficient destruction of the cell membranes of the anthrax simulant Bacillus globigii spore, as well as rapid and complete in situ mineralization of the highly persistent organophosphate nerve agents into nonharmful products. The water-driven propulsion of the TiO2/Au/Mg micromotors facilitates efficient fluid transport and dispersion of the photogenerated reactive oxidative species and their interaction with the CBWA. Coupling of the photocatalytic surface of the micromotors and their autonomous water-driven propulsion thus leads to a reagent-free operation which holds a considerable promise for diverse "green" defense and environmental applications.

Induction and expression of GluA1 (GluR-A)-independent LTP in the hippocampus

PubMed Central

Romberg, Carola; Raffel, Joel; Martin, Lucy; Sprengel, Rolf; Seeburg, Peter H; Rawlins, J Nicholas P; Bannerman, David M; Paulsen, Ole

2009-01-01

Long-term potentiation (LTP) at hippocampal CA3–CA1 synapses is thought to be mediated, at least in part, by an increase in the postsynaptic surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptors induced by N-methyl-d-aspartate (NMDA) receptor activation. While this process was originally attributed to the regulated synaptic insertion of GluA1 (GluR-A) subunit-containing AMPA receptors, recent evidence suggests that regulated synaptic trafficking of GluA2 subunits might also contribute to one or several phases of potentiation. However, it has so far been difficult to separate these two mechanisms experimentally. Here we used genetically modified mice lacking the GluA1 subunit (Gria1−/− mice) to investigate GluA1-independent mechanisms of LTP at CA3–CA1 synapses in transverse hippocampal slices. An extracellular, paired theta-burst stimulation paradigm induced a robust GluA1-independent form of LTP lacking the early, rapidly decaying component characteristic of LTP in wild-type mice. This GluA1-independent form of LTP was attenuated by inhibitors of neuronal nitric oxide synthase and protein kinase C (PKC), two enzymes known to regulate GluA2 surface expression. Furthermore, the induction of GluA1-independent potentiation required the activation of GluN2B (NR2B) subunit-containing NMDA receptors. Our findings support and extend the evidence that LTP at hippocampal CA3–CA1 synapses comprises a rapidly decaying, GluA1-dependent component and a more sustained, GluA1-independent component, induced and expressed via a separate mechanism involving GluN2B-containing NMDA receptors, neuronal nitric oxide synthase and PKC. PMID:19302150

Enhanced in vitro biological activity generated by surface characteristics of anodically oxidized titanium--the contribution of the oxidation effect.

PubMed

Wurihan; Yamada, A; Suzuki, D; Shibata, Y; Kamijo, R; Miyazaki, T

2015-05-20

Anodically oxidized titanium surfaces, prepared by spark discharge, have micro-submicron surface topography and nano-scale surface chemistry, such as hydrophilic functional groups or hydroxyl radicals in parallel. The complexity of the surface characteristics makes it difficult to draw a clear conclusion as to which surface characteristic, of anodically oxidized titanium, is critical in each biological event. This study examined the in vitro biological changes, induced by various surface characteristics of anodically oxidized titanium with, or without, release of hydroxyl radicals onto the surface. Anodically oxidized titanium enhanced the expression of genes associated with differentiating osteoblasts and increased the degree of matrix mineralization by these cells in vitro. The phenotypes of cells on the anodically oxidized titanium were the same with, or without, release of hydroxyl radicals. However, the nanomechanical properties of this in vitro mineralized tissue were significantly enhanced on surfaces, with release of hydroxyl radicals by oxidation effects. In addition, the mineralized tissue, produced in the presence of bone morphogenetic protein-2 on bare titanium, had significantly weaker nanomechanical properties, despite there being higher osteogenic gene expression levels. We show that enhanced osteogenic cell differentiation on modified titanium is not a sufficient indicator of enhanced in vitro mineralization. This is based on the inferior mechanical properties of mineralized tissues, without either being cultured on a titanium surface with release of hydroxyl radicals, or being supplemented with lysyl oxidase family members.

Surface modification of Cu metal particles by the chemical reaction between the surface oxide layer and a halogen surfactant

NASA Astrophysics Data System (ADS)

Yokoyama, Shun; Takahashi, Hideyuki; Itoh, Takashi; Motomiya, Kenichi; Tohji, Kazuyuki

2014-01-01

Surface oxides on small (2-5 μm) copper metal particles can be removed by chemical reaction with tris(2,3-dibromopropyl) isocyanurate (TIC) in diethylene glycol mono-n-hexyl ether (DGHE) solution under mild conditions where metal particles are not damaged. Surface oxides convert to copper bromide species and subsequently dissolve into the solvent. It was found that resultant surface species are resistant to re-oxidation due to remaining surface bromides. This finding opens up a possibility to create microclines based on cheap copper nanoparticles.

Substrate specificity and copper loading of the manganese-oxidizing multicopper oxidase Mnx from Bacillus sp. PL-12.

PubMed

Butterfield, Cristina N; Tebo, Bradley M

2017-02-22

Manganese(ii) oxidation in the environment is thought to be driven by bacteria because enzymatic catalysis is many orders of magnitude faster than the abiotic processes. The heterologously purified Mn oxidase (Mnx) from marine Bacillus sp. PL-12 is made up of the multicopper oxidase (MCO) MnxG and two small Cu and heme-binding proteins of unknown function, MnxE and MnxF. Mnx binds Cu and oxidizes both Mn(ii) and Mn(iii), generating Mn(iv) oxide minerals that resemble those found on the Bacillus spore surface. Spectroscopic techniques have illuminated details about the metallo-cofactors of Mnx, but very little is known about their requirement for catalytic activity, and even less is known about the substrate specificity of Mnx. Here we quantify the canonical MCO Cu and persistent peripheral Cu bound to Mnx, and test Mnx oxidizing ability toward different substrates at varying pH. Mn(ii) appears to be the best substrate in terms of k cat , but its oxidation does not follow Michaelis-Menten kinetics, instead showing a sigmoidal cooperative behavior. Mnx also oxidizes Fe(ii) substrate, but in a Michaelis-Menten manner and with a decreased activity, as well as organic substrates. The reduced metals are more rapidly consumed than the larger organic substrates, suggesting the hypothesis that the Mnx substrate site is small and tuned for metal oxidation. Of biological relevance is the result that Mnx has the highest catalytic efficiency for Mn(ii) at the pH of sea water, especially when the protein is loaded with greater than the requisite four MCO copper atoms, suggesting that the protein has evolved specifically for Mn oxidation.

Mercury Underpotential Deposition to Determine Iridium and Iridium Oxide Electrochemical Surface Areas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alia, Shaun M.; Hurst, Katherine E.; Kocha, Shyam S.

Determining the surface areas of electrocatalysts is critical for separating the key properties of area-specific activity and electrochemical surface area from mass activity. Hydrogen underpotential deposition and carbon monoxide oxidation are typically used to evaluate iridium (Ir) surface areas, but are ineffective on oxides and can be sensitive to surface oxides formed on Ir metals. Mercury underpotential deposition is presented in this study as an alternative, able to produce reasonable surface areas on Ir and Ir oxide nanoparticles, and able to produce similar surface areas prior to and following characterization in oxygen evolution. Reliable electrochemical surface areas allow for comparativemore » studies of different catalyst types and the characterization of advanced oxygen evolution catalysts. Lastly, they also enable the study of catalyst degradation in durability testing, both areas of increasing importance within electrolysis and electrocatalysis.« less

Mercury Underpotential Deposition to Determine Iridium and Iridium Oxide Electrochemical Surface Areas

DOE PAGES

Alia, Shaun M.; Hurst, Katherine E.; Kocha, Shyam S.; ...

2016-06-02

Determining the surface areas of electrocatalysts is critical for separating the key properties of area-specific activity and electrochemical surface area from mass activity. Hydrogen underpotential deposition and carbon monoxide oxidation are typically used to evaluate iridium (Ir) surface areas, but are ineffective on oxides and can be sensitive to surface oxides formed on Ir metals. Mercury underpotential deposition is presented in this study as an alternative, able to produce reasonable surface areas on Ir and Ir oxide nanoparticles, and able to produce similar surface areas prior to and following characterization in oxygen evolution. Reliable electrochemical surface areas allow for comparativemore » studies of different catalyst types and the characterization of advanced oxygen evolution catalysts. Lastly, they also enable the study of catalyst degradation in durability testing, both areas of increasing importance within electrolysis and electrocatalysis.« less

Evaluation of hydrogen radical treatment for indium surface oxide removal and analysis of re-oxidation behavior

NASA Astrophysics Data System (ADS)

Furuyama, Kohta; Yamanaka, Kazuyuki; Higurashi, Eiji; Suga, Tadatomo

2018-02-01

Indium is a commonly used metal for sealing, bonding, and soldering due to its good malleability and ductility even at cryogenic temperatures. The effects of hydrogen radical treatment on indium surface oxide removal were evaluated by the spreading ratio test of indium balls (diameter, 300 µm purity, 99.99%). It was found that hydrogen radical treatment longer than 20 s at temperatures higher than 170 °C results in successful surface oxide removal. X-ray photoelectron spectroscopy analysis was carried out to study the re-oxidation behavior after treatment, and it was found that hydrogen radical treatment slows down the re-oxidation of indium compared with surface oxide removal realized by physical bombardment with an argon fast atom beam.

Intelligent design of multifunctional lipid-coated nanoparticle platforms for cancer therapy

PubMed Central

Ramishetti, Srinivas; Huang, Leaf

2013-01-01

Nanotechnology is rapidly evolving and dramatically changing the paradigms of drug delivery. The small sizes, unique chemical properties, large surface areas, structural diversity and multifunctionality of nanoparticles prove to be greatly advantageous for combating notoriously therapeutically evasive diseases such as cancer. Multifunctional nanoparticles have been designed to enhance tumor uptake through either passive or active targeting, while also avoiding reticuloendothelial system uptake through the incorporation of PEG onto the surface. First-generation nanoparticle systems, such as liposomes, are good carriers for drugs and nucleic acid therapeutics, although they have some limitations. These lipid bilayers are now being utilized as excellent carriers for drug-loaded, solid core particles such as iron oxide, mesoporus silica and calcium phosphate. In this article, their design, as well as their multifunctional role in cancer therapy are discussed. PMID:23323560