surface carbon formation: Topics by Science.gov

Sample records for surface carbon formation

Role of carbon impurities on the surface morphology evolution of tungsten under high dose helium ion irradiation

NASA Astrophysics Data System (ADS)

Al-Ajlony, A.; Tripathi, J. K.; Hassanein, A.

2015-11-01

The effect of carbon impurities on the surface evolution (e.g., fuzz formation) of tungsten (W) surface during 300 eV He ions irradiation was studied. Several tungsten samples were irradiated by He ion beam with a various carbon ions percentage. The presence of minute carbon contamination within the He ion beam was found to be effective in preventing the fuzz formation. At higher carbon concentration, the W surface was found to be fully covered with a thick graphitic layer on the top of tungsten carbide (WC) layer that cover the sample surface. Lowering the ion beam carbon percentage was effective in a significant reduction in the thickness of the surface graphite layer. Under these conditions the W surface was also found to be immune for the fuzz formation. The effect of W fuzz prevention by the WC formation on the sample surface was more noticeable when the He ion beam had much lower carbon (C) ions content (0.01% C). In this case, the fuzz formation was prevented on the vast majority of the W sample surface, while W fuzz was found in limited and isolated areas. The W surface also shows good resistance to morphology evolution when bombarded by high flux of pure H ions at 900 °C.
Methane formation from the hydrogenation of carbon dioxide on Ni(110) surface--a density functional theoretical study.

PubMed

Bothra, Pallavi; Periyasamy, Ganga; Pati, Swapan K

2013-04-21

The complete hydrogenation mechanisms of CO2 are explored on Ni(110) surface catalyst using density functional theory. We have studied the possible hydrogenation mechanism to form product methane from the stable adsorption-co-adsorption intermediates of CO2 and H2 on Ni(110) surface. Our computations clearly elucidate that the mechanism for the formation of methyl, methoxy and methane moieties from carbon dioxide on the nickel catalyst. Moreover, our studies clearly show that the methane formation via hydroxyl carbonyl intermediate requires a lower energy barrier than via carbon monoxide and formate intermediates on the Ni(110) surface.
Stepped Single Crystals as Improved Model for Supported Catalysts: Ethylene, Methanol and Assorted Molecules on PLATINUM(511) and PLATINUM(331)

NASA Astrophysics Data System (ADS)

Spaendonk, Vincent Van

Past research has shown unusual activity of the (1 x 1)Pt(110) surface to break carbon-carbon and carbon -oxygen bonds. Methane formation from ethylene or ethane has been reported for supported platinum catalysts. A model for the methane formation on (1 x 1)Pt(110), was proposed by Yagasaki. In this study, the mechanism of methane formation has been further investigated, and Yagasaki's model tested, by studying the decomposition of ethylene and methanol on the stepped surfaces Pt(511) and Pt(331) with Temperature Programmed Desorption. The experiments have been carried out in a Ultra High Vacuum system, equipped with a mass spectrometer, LEED and AES. Hydrogen and carbon monoxide desorption show that on Pt(511) different adsorption sites are available than on Pt(331). Ethylene decomposition on Pt(511) leads to small amounts of methane formation compared to (1 x 1)Pt(110). The metastable (1 x 1) phase of Pt(511) is 2-3 times more active than the stable (hex) phase. When ^{13}C_2H _4 is used, ^{13 }CH_4 is not detected. Methane formation is not seen on the Pt(331) surface. Arguments are given why Pt(511) is a superior model for supported catalysts compared to (1 x 1)Pt(110). The carbon-oxygen bond of methanol is not broken on either Pt(511) or Pt(331), whether the surface is clean or covered with oxygen. Hydrogen saturating the surface, prevents the chemisorption of ethylene and the formation of methane. Postadsorption of hydrogen does not lead to an increase in methane formation. Coadsorption of ethylene with carbon monoxide shows a maximum methane formation at 0.3 L carbon monoxide exposure. Poison experiments with 'oxide' and carbon indicate that the active site for methane formation is located at the step. The amount of carbon deposited during ethylene decomposition, increases in the order (1 x 1)Pt(511) to (hex)Pt(511) to Pt(331). This is also the order for decreasing methane activity. In a new model, it is proposed that in order to be active for methane formation, a surface has to prevent the polymerization of single carbon species to inactive graphite. The model predicts that surfaces with large enough (111) terraces have higher diffusion rates and allow the single carbon species to convert to graphite before the species can be hydrogenated.
Simulating the formation of carbon-rich molecules on an idealized graphitic surface

NASA Astrophysics Data System (ADS)

Marshall, David W.; Sadeghpour, H. R.

2016-01-01

There is accumulating evidence for the presence of complex molecules, including carbon-bearing and organic molecules, in the interstellar medium. Much of this evidence comes to us from studies of chemical composition, photo- and mass spectroscopy in cometary, meteoritic and asteroid samples, indicating a need to better understand the surface chemistry of astrophysical objects. There is also considerable interest in the origins of life-forming and life-sustaining molecules on the Earth. Here, we perform reactive molecular dynamics simulations to probe the formation of carbon-rich molecules and clusters on carbonaceous surfaces resembling dust grains and meteoroids. Our results show that large chains form on graphitic surfaces at low temperatures (100-500 K) and smaller fullerene-like molecules form at higher temperatures (2000-3000 K). The formation is faster on the surface than in the gas at low temperatures but slower at high temperatures as surface interactions prevent small clusters from coagulation. We find that for efficient formation of molecular complexity, mobility about the surface is important and helps to build larger carbon chains on the surface than in the gas phase at low temperatures. Finally, we show that the temperature of the surface strongly determines what kind of structures forms and that low turbulent environments are needed for efficient formation.
Carbon-containing compounds on fusion-related surfaces: Thermal and ion-induced formation and erosion

NASA Astrophysics Data System (ADS)

Linsmeier, Christian

2004-12-01

The deposition of carbon on metals is the unavoidable consequence of the application of different wall materials in present and future fusion experiments like ITER. Presently used and prospected materials besides carbon (CFC materials in high heat load areas) are tungsten and beryllium. The simultaneous application of different materials leads to the formation of surface compounds due to the erosion, transport and re-deposition of material during plasma operations. The formation and erosion processes are governed by widely varying surface temperatures and kinetic energies as well as the spectrum of impinging particles from the plasma. The knowledge of the dependence on these parameters is crucial for the understanding and prediction of the compound formation on wall materials. The formation of surface layers is of great importance, since they not only determine erosion rates, but also influence the ability of the first wall for hydrogen isotope inventory accumulation and release. Surface compound formation, diffusion and erosion phenomena are studied under well-controlled ultra-high vacuum conditions using in-situ X-ray photoelectron spectroscopy (XPS) and ion beam analysis techniques available at a 3 MV tandem accelerator. XPS provides chemical information and allows distinguishing elemental and carbidic phases with high surface sensitivity. Accelerator-based spectroscopies provide quantitative compositional analysis and sensitivity for deuterium in the surface layers. Using these techniques, the formation of carbidic layers on metals is studied from room temperature up to 1700 K. The formation of an interfacial carbide of several monolayers thickness is not only observed for metals with exothermic carbide formation enthalpies, but also in the cases of Ni and Fe which form endothermic carbides. Additional carbon deposited at 300 K remains elemental. Depending on the substrate, carbon diffusion into the bulk starts at elevated temperatures together with additional carbide formation. Depending on the bond nature in the carbide (metallic in the transition metal carbides, ionic e.g. in Be2C), the surface carbide layer is dissolved upon further increased temperatures or remains stable. Carbide formation can also be initiated by ion bombardment, both of chemically inert noble gas ions or C+ or CO+ ions. In the latter case, a deposition-erosion equilibrium develops which leads to a ternary surface layer of constant thickness. A chemical erosion channel is also discussed for the enhanced erosion of thin carbon films on metals by deuterium ions.
Structural, optical and compositional stability of MoS2 multi-layer flakes under high dose electron beam irradiation

NASA Astrophysics Data System (ADS)

Rotunno, E.; Fabbri, F.; Cinquanta, E.; Kaplan, D.; Longo, M.; Lazzarini, L.; Molle, A.; Swaminathan, V.; Salviati, G.

2016-06-01

MoS2 multi-layer flakes, exfoliated from geological molybdenite, have been exposed to high dose electron irradiation showing clear evidence of crystal lattice and stoichiometry modifications. A massive surface sulfur depletion is induced together with the consequent formation of molybdenum nanoislands. It is found that a nanometric amorphous carbon layer, unwillingly deposited during the transmission electron microscope experiments, prevents the formation of the nanoislands. In the absence of the carbon layer, the formation of molybdenum grains proceeds both on the top and bottom surfaces of the flake. If carbon is present on both the surfaces then the formation of Mo grains is completely prevented.
Martian Cryogenic Carbonate Formation: Stable Isotope Variations Observed in Laboratory Studies

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Niles, Paul B.; Sun, Tao; Fu, Qi; Romanek, Christopher S.; Gibson, Everett K. Jr.

2014-01-01

The history of water on Mars is tied to the formation of carbonates through atmospheric CO2 and its control of the climate history of the planet. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms easily from freezing solutions when carbon dioxide degasses quickly from Ca-bicarbonate-rich water, a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lake beds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. A series of laboratory experiments were conducted that simulated cryogenic carbonate formation on Mars in order to understand their isotopic systematics. The results indicate that carbonates grown under martian conditions show variable enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values.
Self-formation of a nanonet of fluorinated carbon nanowires on the Si surface by combined etching in fluorine-containing plasma

NASA Astrophysics Data System (ADS)

Amirov, I. I.; Gorlachev, E. S.; Mazaletskiy, L. A.; Izyumov, M. O.; Alov, N. V.

2018-03-01

In this work, we report a technique of the self-formation of a nanonet of fluorinated carbon nanowires on the Si surface using a combined etching in fluorine-containing C4F8/Ar and SF6 plasmas. Using scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy, we show that after the etching of Si in the C4F8/Ar plasma, a fluorinated carbon film of nanometer-scale thickness is formed on its surface and its formation accelerates at elevated temperatures. After a subsequent short-term etching in the SF6 plasma, the film is modified into a nanonet of self-formed fluorinated carbon nanowires.
Calcium carbonate nucleation in an alkaline lake surface water, Pyramid Lake, Nevada, USA

USGS Publications Warehouse

Reddy, Michael M.; Hoch, Anthony

2012-01-01

Calcium concentration and calcite supersaturation (Ω) needed for calcium carbonate nucleation and crystal growth in Pyramid Lake (PL) surface water were determined during August of 1997, 2000, and 2001. PL surface water has Ω values of 10-16. Notwithstanding high Ω, calcium carbonate growth did not occur on aragonite single crystals suspended PL surface water for several months. However, calcium solution addition to PL surface-water samples caused reproducible calcium carbonate mineral nucleation and crystal growth. Mean PL surface-water calcium concentration at nucleation was 2.33 mM (n = 10), a value about nine times higher than the ambient PL surface-water calcium concentration (0.26 mM); mean Ω at nucleation (109 with a standard deviation of 8) is about eight times the PL surface-water Ω. Calcium concentration and Ω regulated the calcium carbonate formation in PL nucleation experiments and surface water. Unfiltered samples nucleated at lower Ω than filtered samples. Calcium concentration and Ω at nucleation for experiments in the presence of added particles were within one standard deviation of the mean for all samples. Calcium carbonate formation rates followed a simple rate expression of the form, rate (mM/min) = A (Ω) + B. The best fit rate equation "Rate (Δ mM/Δ min) = -0.0026 Ω + 0.0175 (r = 0.904, n = 10)" was statistically significant at greater than the 0.01 confidence level and gives, after rearrangement, Ω at zero rate of 6.7. Nucleation in PL surface water and morphology of calcium carbonate particles formed in PL nucleation experiments and in PL surface-water samples suggest crystal growth inhibition by multiple substances present in PL surface water mediates PL calcium carbonate formation, but there is insufficient information to determine the chemical nature of all inhibitors.
Calcium Carbonate Nucleation in an Alkaline Lake Surface Water, Pyramid Lake, Nevada, USA

USGS Publications Warehouse

Reddy, M.M.; Hoch, A.

2012-01-01

Calcium concentration and calcite supersaturation (??) needed for calcium carbonate nucleation and crystal growth in Pyramid Lake (PL) surface water were determined during August of 1997, 2000, and 2001. PL surface water has ?? values of 10-16. Notwithstanding high ??, calcium carbonate growth did not occur on aragonite single crystals suspended PL surface water for several months. However, calcium solution addition to PL surface-water samples caused reproducible calcium carbonate mineral nucleation and crystal growth. Mean PL surface-water calcium concentration at nucleation was 2.33 mM (n = 10), a value about nine times higher than the ambient PL surface-water calcium concentration (0.26 mM); mean ?? at nucleation (109 with a standard deviation of 8) is about eight times the PL surface-water ??. Calcium concentration and ?? regulated the calcium carbonate formation in PL nucleation experiments and surface water. Unfiltered samples nucleated at lower ?? than filtered samples. Calcium concentration and ?? at nucleation for experiments in the presence of added particles were within one standard deviation of the mean for all samples. Calcium carbonate formation rates followed a simple rate expression of the form, rate (mM/min) = A (??) + B. The best fit rate equation "Rate (?? mM/?? min) = -0.0026 ?? + 0.0175 (r = 0.904, n = 10)" was statistically significant at greater than the 0.01 confidence level and gives, after rearrangement, ?? at zero rate of 6.7. Nucleation in PL surface water and morphology of calcium carbonate particles formed in PL nucleation experiments and in PL surface-water samples suggest crystal growth inhibition by multiple substances present in PL surface water mediates PL calcium carbonate formation, but there is insufficient information to determine the chemical nature of all inhibitors. ?? 2011 U.S. Government.
Reactivity of formic acid (HCOOD and DCOOH) at uranium and UO 2.0 surfaces

NASA Astrophysics Data System (ADS)

Manner, William L.; Lloyd, Jane A.; Paffett, Mark T.

1999-10-01

Interactions of DCOOH and HCOOD with uranium and UO 2.0 surfaces have been examined using surface-specific techniques of thermal desorption mass spectroscopy (TDMS), X-ray photoelectron spectroscopy (XPS), and static secondary ion mass spectroscopy (SSIMS). On the clean uranium surface, formate is the predominant product following formic acid adsorption at 100 K. A wide range of products is observed after annealing to 200 K, including formate, hydroxyl, O ads, and H ads (D ads) groups. Adsorbed formate decomposes by 300 K increasing the concentration of the remaining surface products. Surface-adsorbed carbon following TDMS measurements remains as the carbide, as indicated from XPS and SSIMS measurements. The only gaseous species created in high yields from the clean surface upon annealing are H 2, HD, and D 2. On the oxide surface (UO 2.0), adsorbed formate groups are more stable toward dissociation in comparison with the clean uranium surface. Between 100 and 300 K the predominant species on the UO 2.0 surface are surface formate and hydroxyl groups. Hydroxyl groups react between 300 and 350 K to release water from the surface. Adsorbed formate groups decompose between 400 and 500 K to release CO and H 2CO (D 2CO) groups from the oxide surface. Carbon was not detected on the oxide surface by XPS or SSIMS after annealing to 500 K, indicating that all carbon-containing species either desorb in the form of CO-containing products or migrate into the surface.
Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars.

PubMed

Shaheen, R; Abramian, A; Horn, J; Dominguez, G; Sullivan, R; Thiemens, Mark H

2010-11-23

The debate of life on Mars centers around the source of the globular, micrometer-sized mineral carbonates in the ALH84001 meteorite; consequently, the identification of Martian processes that form carbonates is critical. This paper reports a previously undescribed carbonate formation process that occurs on Earth and, likely, on Mars. We identified micrometer-sized carbonates in terrestrial aerosols that possess excess (17)O (0.4-3.9‰). The unique O-isotopic composition mechanistically describes the atmospheric heterogeneous chemical reaction on aerosol surfaces. Concomitant laboratory experiments define the transfer of ozone isotopic anomaly to carbonates via hydrogen peroxide formation when O(3) reacts with surface adsorbed water. This previously unidentified chemical reaction scenario provides an explanation for production of the isotopically anomalous carbonates found in the SNC (shergottites, nakhlaites, chassignites) Martian meteorites and terrestrial atmospheric carbonates. The anomalous hydrogen peroxide formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir, thus producing mass independently fractionated secondary mineral evaporites. The formation of peroxide via heterogeneous chemistry on aerosol surfaces also reveals a previously undescribed oxidative process of utility in understanding ozone and oxygen chemistry, both on Mars and Earth.
Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars

PubMed Central

Shaheen, R.; Abramian, A.; Horn, J.; Dominguez, G.; Sullivan, R.; Thiemens, Mark H.

2010-01-01

The debate of life on Mars centers around the source of the globular, micrometer-sized mineral carbonates in the ALH84001 meteorite; consequently, the identification of Martian processes that form carbonates is critical. This paper reports a previously undescribed carbonate formation process that occurs on Earth and, likely, on Mars. We identified micrometer-sized carbonates in terrestrial aerosols that possess excess 17O (0.4–3.9‰). The unique O-isotopic composition mechanistically describes the atmospheric heterogeneous chemical reaction on aerosol surfaces. Concomitant laboratory experiments define the transfer of ozone isotopic anomaly to carbonates via hydrogen peroxide formation when O3 reacts with surface adsorbed water. This previously unidentified chemical reaction scenario provides an explanation for production of the isotopically anomalous carbonates found in the SNC (shergottites, nakhlaites, chassignites) Martian meteorites and terrestrial atmospheric carbonates. The anomalous hydrogen peroxide formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir, thus producing mass independently fractionated secondary mineral evaporites. The formation of peroxide via heterogeneous chemistry on aerosol surfaces also reveals a previously undescribed oxidative process of utility in understanding ozone and oxygen chemistry, both on Mars and Earth. PMID:21059939
Gas-solid carbonation as a possible source of carbonates in cold planetary environments

NASA Astrophysics Data System (ADS)

Garenne, A.; Montes-Hernandez, G.; Beck, P.; Schmitt, B.; Brissaud, O.; Pommerol, A.

2013-02-01

Carbonates are abundant sedimentary minerals at the surface and sub-surface of the Earth and they have been proposed as tracers of liquid water in extraterrestrial environments. Their formation mechanism is since generally associated with aqueous alteration processes. Recently, carbonate minerals have been discovered on Mars' surface by different orbitals or rover missions. In particular, the phoenix mission has measured from 1% to 5% of calcium carbonate (calcite type) within the soil (Smith et al., 2009). These occurrences have been reported in area where the relative humidity is significantly high (Boynton et al., 2009). The small concentration of carbonates suggests an alternative process on mineral grain surfaces (as suggested by Shaheen et al., 2010) than carbonation in aqueous conditions. Such an observation could rather point toward a possible formation mechanism by dust-gas reaction under current Martian conditions. To understand the mechanism of carbonate formation under conditions relevant to current Martian atmosphere and surface, we designed an experimental setup consisting of an infrared microscope coupled to a cryogenic reaction cell (IR-CryoCell setup). Three different mineral precursors of carbonates (Ca and Mg hydroxides, and a hydrated Ca silicate formed from Ca2SiO4), low temperature (from -10 to +30 °C), and reduced CO2 pressure (from 100 to 2000 mbar) were utilized to investigate the mechanism of gas-solid carbonation at mineral surfaces. These mineral materials are crucial precursors to form Ca and Mg carbonates in humid environments (0%
Formation and composition of adsorbates on hydrophobic carbon surfaces from aqueous laccase-maltodextrin mixture suspension

NASA Astrophysics Data System (ADS)

Corrales Ureña, Yendry Regina; Lisboa-Filho, Paulo Noronha; Szardenings, Michael; Gätjen, Linda; Noeske, Paul-Ludwig Michael; Rischka, Klaus

2016-11-01

A robust procedure for the surface bio-functionalization of carbon surfaces was developed. It consists on the modification of carbon materials in contact with an aqueous suspension of the enzyme laccase from Trametes versicolor and the lyophilization agent maltodextrin, with the pH value adjusted close to the isoelectric point of the enzyme. We report in-situ investigations applying Quartz Crystal Microbalance with Dissipation (QCM-D) for carbon-coated sensor surfaces and, moreover, ex-situ measurements with static contact angle measurements, X-ray Photoelectron Spectroscopy (XPS) and Scanning Force Microscopy (SFM) for smooth Highly Oriented Pyrolytic Graphite (HOPG) substrates, for contact times between the enzyme formulation and the carbon material surface ranging from 20 s to 24 h. QCM-D studies reveals the formation of rigid layer of biomaterial, a few nanometers thin, which shows a strongly improved wettability of the substrate surface upon contact angle measurements. Following spectroscopic characterization, these layers are composed of mixtures of laccase and maltodextrin. The formation of these adsorbates is attributed to attractive interactions between laccase, the maltodextrin-based lyophilization agent and the hydrophobic carbon surfaces; a short-term contact between the aqueous laccase mixture suspension and HOPG surfaces is shown to merely result in de-wetting patterns influencing the results of contact angle measurements. The new enzyme-based surface modification of carbon-based materials is suggested to be applicable for the improvement of not only the wettability of low energy substrate surfaces with fluid formulations like coatings or adhesives, but also their adhesion in contact with hardened polymers.
Long-term release of antibiotics by carbon nanotube-coated titanium alloy surfaces diminish biofilm formation by Staphylococcus epidermidis.

PubMed

Hirschfeld, Josefine; Akinoglu, Eser M; Wirtz, Dieter C; Hoerauf, Achim; Bekeredjian-Ding, Isabelle; Jepsen, Søren; Haddouti, El-Mustapha; Limmer, Andreas; Giersig, Michael

2017-05-01

Bacterial biofilms cause a considerable amount of prosthetic joint infections every year, resulting in morbidity and expensive revision surgery. To address this problem, surface modifications of implant materials such as carbon nanotube (CNT) coatings have been investigated in the past years. CNTs are biologically compatible and can be utilized as drug delivery systems. In this study, multi-walled carbon nanotube (MWCNT) coated TiAl6V4 titanium alloy discs were fabricated and impregnated with Rifampicin, and tested for their ability to prevent biofilm formation over a period of ten days. Agar plate-based assays were employed to assess the antimicrobial activity of these surfaces against Staphylococcus epidermidis. It was shown that vertically aligned MWCNTs were more stable against attrition on rough surfaces than on polished TiAl6V4 surfaces. Discs with coated surfaces caused a significant inhibition of biofilm formation for up to five days. Therefore, MWCNT-modified surfaces may be effective against pathogenic biofilm formation on endoprostheses. Copyright © 2017 Elsevier Inc. All rights reserved.
Low-energy electron irradiation induced top-surface nanocrystallization of amorphous carbon film

NASA Astrophysics Data System (ADS)

Chen, Cheng; Fan, Xue; Diao, Dongfeng

2016-10-01

We report a low-energy electron irradiation method to nanocrystallize the top-surface of amorphous carbon film in electron cyclotron resonance plasma system. The nanostructure evolution of the carbon film as a function of electron irradiation density and time was examined by transmission electron microscope (TEM) and Raman spectroscopy. The results showed that the electron irradiation gave rise to the formation of sp2 nanocrystallites in the film top-surface within 4 nm thickness. The formation of sp2 nanocrystallite was ascribed to the inelastic electron scattering in the top-surface of carbon film. The frictional property of low-energy electron irradiated film was measured by a pin-on-disk tribometer. The sp2 nanocrystallized top-surface induced a lower friction coefficient than that of the original pure amorphous film. This method enables a convenient nanocrystallization of amorphous surface.
Enhancing the Properties of Carbon and Gold Substrates by Surface Modification

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

Harnisch, Jennifer Anne

2001-01-01

The properties of both carbon and gold substrates are easily affected by the judicious choice of a surface modification protocol. Several such processes for altering surface composition have been published in literature. The research presented in this thesis primarily focuses on the development of on-column methods to modify carbon stationary phases used in electrochemically modulated liquid chromatography (EMLC). To this end, both porous graphitic carbon (PGC) and glassy carbon (GC) particles have been modified on-column by the electroreduction of arenediazonium salts and the oxidation of arylacetate anions (the Kolbe reaction). Once modified, the carbon stationary phases show enhanced chromatographic performancemore » both in conventional liquid chromatographic columns and EMLC columns. Additionally, one may also exploit the creation of aryl films to by electroreduction of arenediazonium salts in the creation of nanostructured materials. The formation of mercaptobenzene film on the surface of a GC electrode provides a linking platform for the chemisorption of gold nanoparticles. After deposition of nanoparticles, the surface chemistry of the gold can be further altered by self-assembled monolayer (SAM) formation via the chemisorption of a second thiol species. Finally, the properties of gold films can be altered such that they display carbon-like behavior through the formation of benzenehexathiol (BHT) SAMs. BHT chemisorbs to the gold surface in a previously unprecedented planar fashion. Carbon and gold substrates can be chemically altered by several methodologies resulting in new surface properties. The development of modification protocols and their application in the analytical arena is considered herein.« less
Carbonate-mediated Mars-van Krevelen mechanism for CO oxidation on cobalt-doped ceria catalysts: facet-dependence and coordination-dependence.

PubMed

Liu, Bing; Li, Wenping; Song, Weiyu; Liu, Jian

2018-06-13

Carbonate intermediates have been reported to play an active role in CO oxidation over ceria-based catalysts in recent experimental studies. However, the detailed CO oxidation mechanism involving carbonate intermediates over ceria-based catalysts remains obscure. In this work, we carried out systematic density functional theory calculations corrected by on-site Coulomb interactions (DFT+U) to investigate the complete CO oxidation mechanism involving carbonate intermediates over cobalt-doped CeO2 catalysts, aiming to unravel how the carbonate participates in CO oxidation and shed light on the underlying factors that control the carbonate-mediated reaction mechanism. A novel carbonate-mediated Mars-van Krevelen (M-vK) mechanism was proposed, in which the carbonate acts as an active intermediate rather than a spectator and can react with CO to form CO2. This carbonate-mediated M-vK mechanism is facet-dependent because it is predominant on the (110) surface whereas the conventional M-vK mechanism is more favorable on (111) and (100) surfaces. The origin of facet-dependence was discussed by analyzing the geometric and electronic structures. It is found that the negatively charged bent CO2- intermediate formed on the (110) surface plays a critical role in the carbonate-mediated M-vK mechanism, whereas the formation of a neutral linear CO2 intermediate on (111) and (100) surfaces hinders the carbonate-mediated M-vK mechanism. The surface oxygen vacancy hinders the formation of carbonate intermediates, indicating that the carbonate-mediated M-vK mechanism is also vacancy-dependent. The formation of carbonate intermediates on different metal (Ti, V, W, Mo and Re) doped CeO2(110) surfaces was studied and the results indicate that the coordination environment of the dopant species is a key factor that determines the carbonate-mediated M-vK mechanism. This study provides atomic-scale insights into the reaction mechanism involving carbonate intermediates and the structure-mechanism relationship for CO oxidation over cobalt-ceria catalysts.
The Potential Role Played by the Fullerene-Like Structures of Interstellar Carbon Dust in the Formation of Molecular Hydrogen in Space

NASA Astrophysics Data System (ADS)

Cataldo, Franco; Iglesias-Groth, Susana

After a general introduction to the problem of formation of molecular hydrogen from atomic hydrogen in the interstellar medium and in the dense molecular clouds in particular, and after the explanation of the key role played by the surfaces on this process, it is proposed that the most suitable carbon surface for the formation of molecular hydrogen (from the radiative association process of atomic hydrogen) can be represented by carbon black rather than by graphite. Furthermore, it is proposed that the fullerene-like structures present in the carbon black graphene sheets are the reaction sites where molecular hydrogen may be formed.

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

Rodenbücher, C.; Hildebrandt, E.; Sharath, S. U.

On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO{sub 2−x}) contaminated with adsorbates of carbon oxides, the formation of hafnium carbide (HfC{sub x}) at the surface during vacuum annealing at temperatures as low as 600 °C is reported. Using X-ray photoelectron spectroscopy the evolution of the HfC{sub x} surface layer related to a transformation from insulating into metallic state is monitored in situ. In contrast, for fully stoichiometric HfO{sub 2} thin films prepared and measured under identical conditions, the formation of HfC{sub x} was not detectable suggesting that the enhanced adsorption of carbon oxides on oxygen deficient films providesmore » a carbon source for the carbide formation. This shows that a high concentration of oxygen vacancies in carbon contaminated hafnia lowers considerably the formation energy of hafnium carbide. Thus, the presence of a sufficient amount of residual carbon in resistive random access memory devices might lead to a similar carbide formation within the conducting filaments due to Joule heating.« less
Co-adsorption of oxygen and formic acid on rutile TiO2 (110) studied by infrared reflection-absorption spectroscopy

NASA Astrophysics Data System (ADS)

Mattsson, Andreas; Österlund, Lars

2017-09-01

Adsorption of formic acid and co-adsorption with oxygen have been investigated on the rutile TiO2(110) surface using p- and s-polarized infrared reflection-absorption spectroscopy (IRRAS) at O2 exposures between 45 L to 8100 L and at temperatures between 273 K and 343 K. On the clean surface formic acid dissociates into a formate ion (formate) and a proton. Formate binds to two five-fold coordinated Ti atoms in the troughs along the [001] direction, and the proton binds to neighboring bridging O atoms. Exposure of adsorbed formate to O2 leads to a decrease in the asymmetric νas(OCO) band at 1532 cm-1 and to the concomitant formation of a new vibration band at 1516 cm-1. From the s-and p-polarized IRRAS measurements performed at different O2 exposures, surface pre-treatments and substrate temperatures, and by comparisons with previous reports, we conclude that the new species is a bidentate surface hydrogen carbonate, which is formed by reaction between formate and oxygen adatoms on the surface. The σv reflection plane of the surface hydrogen carbonate molecule is oriented along the [001] direction, i.e. the same direction as the adsorbed formate molecule. On the clean TiO2(110) surface exposed to O2 prior to formic acid adsorption, similar results are obtained. The reaction rate to form surface hydrogen carbonate from formate is found to follow first-order kinetics, with an apparent activation energy of Er=0.25 eV.
A density functional theory study on the carbon chain growth of ethanol formation on Cu-Co (111) and (211) surfaces

NASA Astrophysics Data System (ADS)

Ren, Bohua; Dong, Xiuqin; Yu, Yingzhe; Wen, Guobin; Zhang, Minhua

2017-08-01

Calculations based on the first-principle density functional theory were carried out to study the most controversial reactions in ethanol formation from syngas on Cu-Co surfaces: CO dissociation mechanism and the key reactions of carbon chain growth of ethanol formation (HCO insertion reactions) on four model surfaces (Cu-Co (111) and (211) with Cu-rich or Co-rich surfaces) to investigate the synergy of the Cu and Co components since the complete reaction network of ethanol formation from syngas is a huge computational burden to calculate on four Cu-Co surface models. We investigated adsorption of important species involved in these reactions, activation barrier and reaction energy of H-assisted dissociation mechanism, directly dissociation of CO, and HCO insertion reactions (CHx + HCO → CHxCHO (x = 1-3)) on four Cu-Co surface models. It was found that reactions on Cu-rich (111) and (211) surfaces all have lower activation barrier in H-assisted dissociation and HCO insertion reactions, especially CH + HCO → CHCHO reaction. The PDOS of 4d orbitals of surface Cu and Co atoms of all surfaces were studied. Analysis of d-band center of Cu and Co atoms and the activation barrier data suggested the correlation between electronic property and catalytic performance. Cu-Co bimetallic with Cu-rich surface allows Co to have higher catalytic activity through the interaction of Cu and Co atom. Then it will improve the adsorption of CO and catalytic activity of Co. Thus it is more favorable to the carbon chain growth in ethanol formation. Our study revealed the factors influencing the carbon chain growth in ethanol production and explained the internal mechanism from electronic property aspect.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, W; Zhou, Yunshen; Hou, Wenjia

Direct formation of graphene with controlled number of graphitic layers on dielectric surfaces is highly desired for practical applications. Despite significant progress achieved in understanding the formation of graphene on metallic surfaces through chemical vapor deposition (CVD) of hydrocarbons, very limited research is available elucidating the graphene formation process via rapid thermal processing (RTP) of solid-state amorphous carbon, through which graphene is formed directly on dielectric surfaces accompanied by autonomous nickel evaporation. It is suggested that a metastable hexagonal nickel carbide (Ni 3C) intermediate phase plays a critical role in transforming amorphous carbon to 2D crystalline graphene and contributing tomore » the autonomous Ni evaporation. Temperature resolved carbon and nickel evolution in the RTP process is investigated using Auger electron spectroscopic (AES) depth profiling and glancing-angle X-ray diffraction (GAXRD). Formation, migration and decomposition of the hexagonal Ni 3C are confirmed to be responsible for the formation of graphene and the evaporation of Ni at 1100 °C. The Ni 3C-assisted graphene formation mechanism expands the understanding of Ni-catalyzed graphene formation, and provides insightful guidance for controlled growth of graphene through the solid-state transformation process.« less
Search for Past Life on Mars: Possible Relict Biogenic Activity in Martian Meteorite ALH84001

NASA Technical Reports Server (NTRS)

McKay, David S.; Gibson, Everett K., Jr.; Thomas-Keprta, Kathie L.; Vali, Hojatollah; Romanek, Christopher S.; Clemett, Simon J.; Chillier, Xavier D. F.; Maechling, Claude R.; Zare, Richard N.

1996-01-01

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest the PAHs are indigenous to the meteorite. High resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-monosulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.
Intrinsic activation: the relationship between biomass inorganic content and porosity formation during pyrolysis.

PubMed

Stratford, James P; Hutchings, Tony R; de Leij, Frans A A M

2014-05-01

The utility of pyrolytic carbons is closely related to their porosity and surface area, there is a clear benefit to the development of biomass pyrolysis processes which produce highly porous carbons. The results presented in this work demonstrate that by using biomass precursors with high inorganic content along with specified process conditions, carbons can be consistently produced with specific surface areas between 900 and 1600 m(2)/g. Results from 12 different source materials show that the formation of increased porosity in pyrolytic carbons is strongly associated with the presence of inorganic elements in the precursors including: magnesium, potassium and sulfur. It was found that pyrolysis of macro-algae can produce especially high specific surface area carbons (mean: 1500 m(2)/g), without externally applied activating agents. Using cheap readily available agricultural residues such as oilseed rape straw, pyrolytic carbons can be produced with specific surface areas of around 950 m(2)/g. Copyright © 2014 Elsevier Ltd. All rights reserved.
Gas-solid carbonation as a current alternative origin for carbonates in Martian regolith

NASA Astrophysics Data System (ADS)

Garenne, A.; Montes-Hernandez, G.; Beck, P.; Schmitt, B.; Brissaud, O.

2011-12-01

Carbonates are abundant sedimentary minerals at the surface and sub-surface of Earth and they have been proposed as tracers of liquid water in extraterrestrial environments (e.g. at Mars surface). Its formation mechanism is since generally associated with aqueous alteration processes. Recently, carbonates minerals have been discovered on Mars surface by different orbital or rovers missions. In particular, the phoenix mission has measured from 1 to 5% of calcium carbonate (calcite type). These occurrences have been reported in area were the relative humidity is significantly high (Boynton et al., 2009). The small concentration of carbonates suggests an alternative process than carbonation in aqueous conditions. Such an observation might rather point toward a possible formation mechanism by dust-gas reaction under current Martian conditions. For this reason, in the present study, we designed an experimental setup consisting of an infrared microscope coupled to a cryogenic reaction cell (IR-CryoCell setup) in order to investigate the gas-solid carbonation of three different mineral precursors for carbonates (Ca and Mg hydroxides, and a hydrated Ca silicate formed from Ca2SiO4) at low temperature (from -10 to 25°C) and at reduced CO2 pressure (from 100 to 1000 mbar). These mineral materials are crucial precursors to form respective Ca and Mg carbonates in humid environments (0 < relative humidity < 100%) at dust-CO2 or dust-water ice-CO2 interfaces. The results have revealed a significant and fast carbonation process for Ca hydroxide and hydrated Ca silicate. Conversely, slight carbonation process was observed for Mg hydroxide. These results suggest that gas-solid carbonation process or carbonate formation at the dust-water ice-CO2 interfaces could be a currently active Mars surface process. We note that the carbonation process at low temperature (<0°C) described in the present study could also have important implications on the dust-water ice-CO2 interactions in cold terrestrial environments (e.g. Antarctic).
Feasibility study of surface-modified carbon cloth electrodes using atmospheric pressure plasma jets for microbial fuel cells

NASA Astrophysics Data System (ADS)

Chang, Shih-Hang; Liou, Jyun-Sian; Liu, Jung-Liang; Chiu, Yi-Fan; Xu, Chang-Han; Chen, Bor-Yann; Chen, Jian-Zhang

2016-12-01

This study investigated the surface and electrochemical properties of carbon cloth electrodes surface-modified by using atmospheric pressure plasma jets (APPJs) for applications involving microbial fuel cells (MFCs). APPJ treatment made the carbon cloth highly hydrophilic and did not introduce any observable cracks or flaws. MFCs configured with APPJ-treated carbon cloth electrodes exhibited electrochemical performance (maximum power density of 7.56 mW m-2) superior to that of MFCs configured with untreated carbon cloth electrodes (maximum power density of 2.38 mW m-2). This boost in performance can be attributed to the formation of abundant carboxyl and ammonium functional groups on the surface of APPJ-treated carbon cloth, which promoted the formation of anodic biofilms and the adhesion of bacteria, while facilitating the transfer of electrons from the bacteria to the electrodes. APPJ surface modification is non-toxic and environmentally friendly (no exogenous chemicals are required), which is particularly beneficial as the introduction of toxins might otherwise inhibit bacterial growth and metabolism. The APPJ surface modification process is rapid, cost-effective, and applicable to substrates covering a large area, making it ideal for the fabrication of large-scale MFCs and bioelectrochemical bioenergy devices.
Catalytic carbide formation at aluminium-carbon interfaces

NASA Technical Reports Server (NTRS)

Maruyama, B.; Rabenberg, L.; Ohuchi, F. S.

1990-01-01

X-ray photoelectron spectroscopy investigations of the reaction of several monolayer-thick films of aluminum with glassy carbon substrates are presented. The influence of molecular oxygen and water vapor on the rate of reaction is examined. It is concluded that water vapor catalyzed the formation of aluminum carbide from aluminum and carbon by forming active sites which weakened carbon-carbon bonds at the glassy carbon surface, thus assisting their cleavage. The rate of carbide formation for undosed and molecular oxygen-dosed examples was less as neither metallic aluminum nor oxygen-formed alumina could bond to the carbon atom with sufficient strength to dissociate it quickly.
Orbital identification of carbonate-bearing rocks on Mars

USGS Publications Warehouse

Ehlmann, B.L.; Mustard, J.F.; Murchie, S.L.; Poulet, F.; Bishop, J.L.; Brown, A.J.; Calvin, W.M.; Clark, R.N.; Des Marais, D.J.; Milliken, R.E.; Roach, L.H.; Roush, T.L.; Swayze, G.A.; Wray, J.J.

2008-01-01

Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering, proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.
Metal organic chemical vapor deposition of environmental barrier coatings for the inhibition of solid deposit formation from heated jet fuel

NASA Astrophysics Data System (ADS)

Mohan, Arun Ram

Solid deposit formation from jet fuel compromises the fuel handling system of an aviation turbine engine and increases the maintenance downtime of an aircraft. The deposit formation process depends upon the composition of the fuel, the nature of metal surfaces that come in contact with the heated fuel and the operating conditions of the engine. The objective of the study is to investigate the effect of substrate surfaces on the amount and nature of solid deposits in the intermediate regime where both autoxidation and pyrolysis play an important role in deposit formation. A particular focus has been directed to examining the effectiveness of barrier coatings produced by metal organic chemical vapor deposition (MOCVD) on metal surfaces for inhibiting the solid deposit formation from jet fuel degradation. In the first part of the experimental study, a commercial Jet-A sample was stressed in a flow reactor on seven different metal surfaces: AISI316, AISI 321, AISI 304, AISI 347, Inconel 600, Inconel 718, Inconel 750X and FecrAlloy. Examination of deposits by thermal and microscopic analysis shows that the solid deposit formation is influenced by the interaction of organosulfur compounds and autoxidation products with the metal surfaces. The nature of metal sulfides was predicted by Fe-Ni-S ternary phase diagram. Thermal stressing on uncoated surfaces produced coke deposits with varying degree of structural order. They are hydrogen-rich and structurally disordered deposits, spherulitic deposits, small carbon particles with relatively ordered structures and large platelets of ordered carbon structures formed by metal catalysis. In the second part of the study, environmental barrier coatings were deposited on tube surfaces to inhibit solid deposit formation from the heated fuel. A new CVD system was configured by the proper choice of components for mass flow, pressure and temperature control in the reactor. A bubbler was designed to deliver the precursor into the reactor for the deposition of metal and metal oxide functional coatings by MOCVD. Alumina was chosen as a candidate for metal oxide coating because of its thermal and phase stability. Platinum was chosen as a candidate to utilize the oxygen spillover process to maintain a self-cleaning surface by oxidizing the deposits formed during thermal stressing. Two metal organic precursors, aluminum trisecondary butoxide and aluminum acetylacetonate, were used as precursors to coat tubes of varying diameters. The morphology and uniformity of the coatings were characterized by electron microscopy and energy-dispersive x-ray spectroscopy. The coating was characterized by x-ray photoelectron spectroscopy to obtain the surface chemical composition. This is the first study conducted to examine the application of MOCVD to coat internal surfaces of tubes with varying diameters. In the third part of the study, the metal oxide coatings, alumina from aluminum acetylacetonate, alumina from aluminum trisecondary butoxide, zirconia from zirconium acetylacetonate, tantalum oxide from tantalum pentaethoxide and the metal coating, platinum from platinum acetylacetonate were deposited by MOCVD on AISI304. The chemical composition and the surface acidity of the coatings were characterized by x-ray photoelectron spectroscopy. The morphology of the coatings was characterized by electron microscopy. The coated substrates were tested in the presence of heated Jet-A in a flow reactor to evaluate their effectiveness in inhibiting the solid deposit formation. All coatings inhibited the formation of metal sulfides and the carbonaceous solid deposits formed by metal catalysis. The coatings also delayed the accumulation of solid carbonaceous deposits. In particular, it has been confirmed that the surface acidity of the metal oxide coatings affects the formation of carbonaceous deposits. Bimolecular addition reactions promoted by the Bronsted acid sites appear to lead to the formation of carbonaceous solid deposits depending on the surface acidity of the coatings. In the last part of the study, the residual carbon was incorporated in the zirconia coating by deposition with and without oxygen. As carbon surface is less active towards coke deposition, presence of residual carbon in the coating was expected to reduce its activity towards carbon deposition. The residual carbon in the coating was characterized by Raman spectroscopy and thermal analysis. However, it has been observed that residual carbon in the coating beyond a certain concentration compromises the integrity of the coating during the process of cooling the substrate from deposition temperature to room temperature. It has been found that residual carbon in the zirconia coating does not appear to affect the activity of the surface towards carbon deposition.
Nature, formation, and distribution of carbonates on Ceres.

PubMed

Carrozzo, Filippo Giacomo; De Sanctis, Maria Cristina; Raponi, Andrea; Ammannito, Eleonora; Castillo-Rogez, Julie; Ehlmann, Bethany L; Marchi, Simone; Stein, Nathaniel; Ciarniello, Mauro; Tosi, Federico; Capaccioni, Fabrizio; Capria, Maria Teresa; Fonte, Sergio; Formisano, Michelangelo; Frigeri, Alessandro; Giardino, Marco; Longobardo, Andrea; Magni, Gianfranco; Palomba, Ernesto; Zambon, Francesca; Raymond, Carol A; Russell, Christopher T

2018-03-01

Different carbonates have been detected on Ceres, and their abundance and spatial distribution have been mapped using a visible and infrared mapping spectrometer (VIR), the Dawn imaging spectrometer. Carbonates are abundant and ubiquitous across the surface, but variations in the strength and position of infrared spectral absorptions indicate variations in the composition and amount of these minerals. Mg-Ca carbonates are detected all over the surface, but localized areas show Na carbonates, such as natrite (Na 2 CO 3 ) and hydrated Na carbonates (for example, Na 2 CO 3 ·H 2 O). Their geological settings and accessory NH 4 -bearing phases suggest the upwelling, excavation, and exposure of salts formed from Na-CO 3 -NH 4 -Cl brine solutions at multiple locations across the planet. The presence of the hydrated carbonates indicates that their formation/exposure on Ceres' surface is geologically recent and dehydration to the anhydrous form (Na 2 CO 3 ) is ongoing, implying a still-evolving body.
Solid-state graphene formation via a nickel carbide intermediate phase [Nickel carbide (Ni 3C) as an intermediate phase for graphene formation

DOE PAGES

Xiong, W; Zhou, Yunshen; Hou, Wenjia; ...

2015-11-10

Direct formation of graphene with controlled number of graphitic layers on dielectric surfaces is highly desired for practical applications. Despite significant progress achieved in understanding the formation of graphene on metallic surfaces through chemical vapor deposition (CVD) of hydrocarbons, very limited research is available elucidating the graphene formation process via rapid thermal processing (RTP) of solid-state amorphous carbon, through which graphene is formed directly on dielectric surfaces accompanied by autonomous nickel evaporation. It is suggested that a metastable hexagonal nickel carbide (Ni 3C) intermediate phase plays a critical role in transforming amorphous carbon to 2D crystalline graphene and contributing tomore » the autonomous Ni evaporation. Temperature resolved carbon and nickel evolution in the RTP process is investigated using Auger electron spectroscopic (AES) depth profiling and glancing-angle X-ray diffraction (GAXRD). Formation, migration and decomposition of the hexagonal Ni 3C are confirmed to be responsible for the formation of graphene and the evaporation of Ni at 1100 °C. The Ni 3C-assisted graphene formation mechanism expands the understanding of Ni-catalyzed graphene formation, and provides insightful guidance for controlled growth of graphene through the solid-state transformation process.« less
Improved adhesion of ultra-hard carbon films on cobalt–chromium orthopaedic implant alloy

PubMed Central

Vaid, Rishi; Diggins, Patrick; Weimer, Jeffrey J.; Koopman, M.; Vohra, Yogesh K.

2010-01-01

While interfacial graphite formation and subsequent poor film adhesion is commonly reported for chemical vapor deposited hard carbon films on cobalt-based materials, we find the presence of O2 in the feedgas mixture to be useful in achieving adhesion on a CoCrMo alloy. Nucleation studies of surface structure before formation of fully coalesced hard carbon films reveal that O2 feedgas helps mask the catalytic effect of cobalt with carbon through early formation of chromium oxides and carbides. The chromium oxides, in particular, act as a diffusion barrier to cobalt, minimizing its migration to the surface where it would otherwise interact deleteriously with carbon to form graphite. When O2 is not used, graphitic soot forms and films delaminate readily upon cooling to room temperature. Continuous 1 μm-thick nanostructured carbon films grown with O2 remain adhered with measured hardness of 60 GPa and show stable, non-catastrophic circumferential micro-cracks near the edges of indent craters made using Rockwell indentation. PMID:21221739
The role of carbon in ion beam nano-patterning of silicon

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

Bhattacharjee, S.; UGC-DAE Consortium for Scientific Research, III/LB-8, Saltlake, Kolkata 700098; Karmakar, P.

2013-10-28

We report a comparative study of nano-pattern formations on a carbon film and a smooth Si(100) surface following inert and chemically active ion bombardment. For the case of carbon film, patterns could be formed both by inert (Ar{sup +}) and self (C{sup +}) ion bombardment with the former producing ripples at relatively lower fluence. In contrast, bombardment by inert Ar{sup +} failed to form the nano patterns on Si surface, while bombardment by the same energy C{sup +} generated the ripples. Thus, impurity induced chemical effect seems to be crucial rather than the Bradley-Harper or Carter-Vishnyakov effects for destabilizing themore » surface for ripple formation.« less
Bifunctional redox tagging of carbon nanoparticles

NASA Astrophysics Data System (ADS)

Poon, Jeffrey; Batchelor-McAuley, Christopher; Tschulik, Kristina; Palgrave, Robert G.; Compton, Richard G.

2015-01-01

Despite extensive work on the controlled surface modification of carbon with redox moieties, to date almost all available methodologies involve complex chemistry and are prone to the formation of polymerized multi-layer surface structures. Herein, the facile bifunctional redox tagging of carbon nanoparticles (diameter 27 nm) and its characterization is undertaken using the industrial dye Reactive Blue 2. The modification route is demonstrated to be via exceptionally strong physisorption. The modified carbon is found to exhibit both well-defined oxidative and reductive voltammetric redox features which are quantitatively interpreted. The method provides a generic approach to monolayer modifications of carbon and carbon nanoparticle surfaces.
Carbon Dioxide Clouds at High Altitude in the Tropics and in an Early Dense Martian Atmosphere

NASA Technical Reports Server (NTRS)

Colaprete, Anthony; Toon, Owen B.

2001-01-01

We use a time dependent, microphysical cloud model to study the formation of carbon dioxide clouds in the Martian atmosphere. Laboratory studies by Glandor et al. show that high critical supersaturations are required for cloud particle nucleation and that surface kinetic growth is not limited. These conditions, which are similar to those for cirrus clouds on Earth, lead to the formation of carbon dioxide ice particles with radii greater than 500 micrometers and concentrations of less than 0.1 cm(exp -3) for typical atmospheric conditions. Within the current Martian atmosphere, CO2 cloud formation is possible at the poles during winter and at high altitudes in the tropics during periods of increased atmospheric dust loading. In both cases, temperature perturbations of several degrees below the CO2 saturation temperature are required to nucleate new cloud particles suggesting that dynamical processes are the most common initiators of carbon dioxide clouds rather than diabatic cooling. The microphysical cloud model, coupled to a two-stream radiative transfer model, is used to reexamine the impact of CO2 clouds on the surface temperature within a dense CO2 atmosphere. The formation of carbon dioxide clouds leads to a warmer surface than what would be expected for clear sky conditions. The amount of warming is sensitive to the presence of dust and water vapor in the atmosphere, both of which act to dampen cloud effects. The radiative warming associated with cloud formation, as well as latent heating, work to dissipate the clouds when present. Thus, clouds never last for periods much longer than several days, limiting their overall effectiveness for warming the surface. The time average cloud optical depth is approximately unity leading to a 5-10 K warming, depending on the surface pressure. However, the surface temperature does not rise about the freezing point of liquid water even for pressures as high as 5 bars, at a solar luminosity of 75% the current value.
Monitoring the Electrochemical Processes in the Lithium–Air Battery by Solid State NMR Spectroscopy

PubMed Central

2013-01-01

A multi-nuclear solid-state NMR approach is employed to investigate the lithium–air battery, to monitor the evolution of the electrochemical products formed during cycling, and to gain insight into processes affecting capacity fading. While lithium peroxide is identified by 17O solid state NMR (ssNMR) as the predominant product in the first discharge in 1,2-dimethoxyethane (DME) based electrolytes, it reacts with the carbon cathode surface to form carbonate during the charging process. 13C ssNMR provides evidence for carbonate formation on the surface of the carbon cathode, the carbonate being removed at high charging voltages in the first cycle, but accumulating in later cycles. Small amounts of lithium hydroxide and formate are also detected in discharged cathodes and while the hydroxide formation is reversible, the formate persists and accumulates in the cathode upon further cycling. The results indicate that the rechargeability of the battery is limited by both the electrolyte and the carbon cathode stability. The utility of ssNMR spectroscopy in directly detecting product formation and decomposition within the battery is demonstrated, a necessary step in the assessment of new electrolytes, catalysts, and cathode materials for the development of a viable lithium–oxygen battery. PMID:24489976
Grafting of diazonium salts on oxides surface: formation of aryl-O bonds on iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Brymora, Katarzyna; Fouineau, Jonathan; Eddarir, Asma; Chau, François; Yaacoub, Nader; Grenèche, Jean-Marc; Pinson, Jean; Ammar, Souad; Calvayrac, Florent

2015-11-01

Combining ab initio modeling and 57Fe Mössbauer spectrometry, we characterized the nature of the chemical linkage of aminoalkyl arenediazonium salt on the surface of iron oxide nanoparticles. We established that it is built through a metal-oxygen-carbon bonding and not a metal-carbon one, as usually suggested and commonly observed in previously studied metal- or carbon-based surfaces.
Formation of cerussite and hydrocerussite during adsorption of lead from aqueous solution on oxidized carbons by cold oxygen plasma

NASA Astrophysics Data System (ADS)

De Velasco Maldonado, Paola S.; Hernández-Montoya, Virginia; Concheso, A.; Montes-Morán, Miguel A.

2016-11-01

A new procedure of elimination of Pb2+ from aqueous solution using carbon adsorbents, in which high amounts of cerussite and hydrocerussite are deposited on the carbon surfaces, is reported. The procedure includes the preparation of carbons from selected lignocellulosic wastes (pecan nut shells and peach stones) by single carbonization and further oxidation with cold oxygen plasma. The materials prior and after the oxidation treatment were characterized using elemental analysis, FT-IR spectroscopy, SEM/EDX analysis, adsorption of N2 at -196 °C and X-ray photoelectron spectroscopy. The adsorption of Pb2+ was carried out in batch systems under constant agitation. The formation of cerussite and hydrocerussite on the spent carbon surfaces was confirmed by XRD, SEM/EDX and FT-IR. A Pb2+ removal mechanism is proposed in which a co-precipitation of lead nitrate and calcium carbonate would render the formation of the lead carbonates. In such mechanism, the occurrence of CaCO3 on the surface of the adsorbents plays a crucial role. The presence of calcium carbonate on the precursors is understood on the basis of the thermal evolution of calcium oxalate originally present in the biomass. The oxygen plasma treatment helps to expose the calcium carbonate nanocrystals thus improving dramatically the removal capacity of Pb2+. Accordingly, retention capacities as high as 63 mg of Pb2+ per gram of adsorbent have been attained.

Enhanced carbon monoxide utilization in methanation process

DOEpatents

Elek, Louis F.; Frost, Albert C.

1984-01-01

Carbon monoxide - containing gas streams are passed over a catalyst to deposit a surface layer of active surface carbon thereon essentially without the formation of inactive coke. The active carbon is subsequently reacted with steam or hydrogen to form methane. Surprisingly, hydrogen and water vapor present in the feed gas do not adversely affect CO utilization significantly, and such hydrogen actually results in a significant increase in CO utilization.
High-surface-area mesoporous TiO2 microspheres via one-step nanoparticle self-assembly for enhanced lithium-ion storage

NASA Astrophysics Data System (ADS)

Wang, Hsin-Yi; Chen, Jiazang; Hy, Sunny; Yu, Linghui; Xu, Zhichuan; Liu, Bin

2014-11-01

Mesoporous TiO2 microspheres assembled from TiO2 nanoparticles with specific surface areas as high as 150 m2 g-1 were synthesized via a facile one-step solvothermal reaction of titanium isopropoxide and anhydrous acetone. Aldol condensation of acetone gradually releases structural H2O, which hydrolyzes and condenses titanium isopropoxide, forming TiO2 nanocrystals. Simultaneous growth and aggregation of TiO2 nanocrystals leads to the formation of high-surface-area TiO2 microspheres under solvothermal conditions. After a low-temperature post-synthesis calcination, carbonate could be incorporated into TiO2 as a dopant with the carbon source coming from the organic byproducts during the synthesis. Carbonate doping modifies the electronic structure of TiO2 (e.g., Fermi level, Ef), and thus influences its electrochemical properties. Solid electrolyte interface (SEI) formation, which is not common for titania, could be initiated in carbonate-doped TiO2 due to elevated Ef. After removing carbonate dopants by high-temperature calcination, the mesoporous TiO2 microspheres showed much improved performance in lithium insertion and stability at various current rates, attributed to a synergistic effect of high surface area, large pore size and good anatase crystallinity.Mesoporous TiO2 microspheres assembled from TiO2 nanoparticles with specific surface areas as high as 150 m2 g-1 were synthesized via a facile one-step solvothermal reaction of titanium isopropoxide and anhydrous acetone. Aldol condensation of acetone gradually releases structural H2O, which hydrolyzes and condenses titanium isopropoxide, forming TiO2 nanocrystals. Simultaneous growth and aggregation of TiO2 nanocrystals leads to the formation of high-surface-area TiO2 microspheres under solvothermal conditions. After a low-temperature post-synthesis calcination, carbonate could be incorporated into TiO2 as a dopant with the carbon source coming from the organic byproducts during the synthesis. Carbonate doping modifies the electronic structure of TiO2 (e.g., Fermi level, Ef), and thus influences its electrochemical properties. Solid electrolyte interface (SEI) formation, which is not common for titania, could be initiated in carbonate-doped TiO2 due to elevated Ef. After removing carbonate dopants by high-temperature calcination, the mesoporous TiO2 microspheres showed much improved performance in lithium insertion and stability at various current rates, attributed to a synergistic effect of high surface area, large pore size and good anatase crystallinity. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr04729j
Monolayer formation of human osteoblastic cells on vertically aligned multiwalled carbon nanotube scaffolds.

PubMed

Lobo, Anderson O; Antunes, Erica F; Palma, Mariana Bs; Pacheco-Soares, Cristina; Trava-Airoldi, Vladimir J; Corat, Evaldo J

2010-03-12

Monolayer formation of SaOS-2 (human osteoblast-like cells) was observed on VACNT (vertically aligned multiwalled carbon nanotubes) scaffolds without purification or functionalization. The VACNT were produced by a microwave plasma chemical vapour deposition on titanium surfaces with nickel or iron as catalyst. Cell viability and morphology studies were evaluated by LDH (lactate dehydrogenase) release assay and SEM (scanning electron microscopy), respectively. The non-toxicity and the flat spreading with monolayer formation of the SaOs-2 on VACNT scaffolds surface indicate that they can be used for biomedical applications.
Synthesis of SnO2 pillared carbon using long chain alkylamine grafted graphene oxide: an efficient anode material for lithium ion batteries

NASA Astrophysics Data System (ADS)

Reddy, M. Jeevan Kumar; Ryu, Sung Hun; Shanmugharaj, A. M.

2015-12-01

With the objective of developing new advanced composite materials that can be used as anodes for lithium ion batteries (LIBs), herein we describe the synthesis of SnO2 pillared carbon using various alkylamine (hexylamine; dodecylamine and octadecylamine) grafted graphene oxides and butyl trichlorotin precursors followed by its calcination at 500 °C for 2 h. While the grafted alkylamine induces crystalline growth of SnO2 pillars, thermal annealing of alkylamine grafted graphene oxide results in the formation of amorphous carbon coated graphene. Field emission scanning electron microscopy (FE-SEM) results reveal the successful formation of SnO2 pillared carbon on the graphene surface. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy characterization corroborates the formation of rutile SnO2 crystals on the graphene surface. A significant rise in the BET surface area is observed for SnO2 pillared carbon, when compared to pristine GO. Electrochemical characterization studies of SnO2 pillared carbon based anode materials showed an enhanced lithium storage capacity and fine cyclic performance in comparison with pristine GO. The initial specific capacities of SnO2 pillared carbon are observed to be 1379 mA h g-1, 1255 mA h g-1 and 1360 mA h g-1 that decrease to 750 mA h g-1, 643 mA h g-1 and 560 mA h g-1 depending upon the chain length of grafted alkylamine on the graphene surface respectively. Electrochemical impedance spectral analysis reveals that the exchange current density of SnO2 pillared carbon based electrodes is higher, corroborating its enhanced electrochemical activity in comparison with GO based electrodes.With the objective of developing new advanced composite materials that can be used as anodes for lithium ion batteries (LIBs), herein we describe the synthesis of SnO2 pillared carbon using various alkylamine (hexylamine; dodecylamine and octadecylamine) grafted graphene oxides and butyl trichlorotin precursors followed by its calcination at 500 °C for 2 h. While the grafted alkylamine induces crystalline growth of SnO2 pillars, thermal annealing of alkylamine grafted graphene oxide results in the formation of amorphous carbon coated graphene. Field emission scanning electron microscopy (FE-SEM) results reveal the successful formation of SnO2 pillared carbon on the graphene surface. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy characterization corroborates the formation of rutile SnO2 crystals on the graphene surface. A significant rise in the BET surface area is observed for SnO2 pillared carbon, when compared to pristine GO. Electrochemical characterization studies of SnO2 pillared carbon based anode materials showed an enhanced lithium storage capacity and fine cyclic performance in comparison with pristine GO. The initial specific capacities of SnO2 pillared carbon are observed to be 1379 mA h g-1, 1255 mA h g-1 and 1360 mA h g-1 that decrease to 750 mA h g-1, 643 mA h g-1 and 560 mA h g-1 depending upon the chain length of grafted alkylamine on the graphene surface respectively. Electrochemical impedance spectral analysis reveals that the exchange current density of SnO2 pillared carbon based electrodes is higher, corroborating its enhanced electrochemical activity in comparison with GO based electrodes. Electronic supplementary information (ESI) available: XPS, FE-SEM, FE-TEM, TGA FT-IR, EIS, CV of and charge discharge profiles of RGO-SnO2 composites. See DOI: 10.1039/c5nr06680h
Interdependency of Subsurface Carbon Distribution and Graphene–Catalyst Interaction

PubMed Central

2014-01-01

The dynamics of the graphene–catalyst interaction during chemical vapor deposition are investigated using in situ, time- and depth-resolved X-ray photoelectron spectroscopy, and complementary grand canonical Monte Carlo simulations coupled to a tight-binding model. We thereby reveal the interdependency of the distribution of carbon close to the catalyst surface and the strength of the graphene–catalyst interaction. The strong interaction of epitaxial graphene with Ni(111) causes a depletion of dissolved carbon close to the catalyst surface, which prevents additional layer formation leading to a self-limiting graphene growth behavior for low exposure pressures (10–6–10–3 mbar). A further hydrocarbon pressure increase (to ∼10–1 mbar) leads to weakening of the graphene–Ni(111) interaction accompanied by additional graphene layer formation, mediated by an increased concentration of near-surface dissolved carbon. We show that growth of more weakly adhered, rotated graphene on Ni(111) is linked to an initially higher level of near-surface carbon compared to the case of epitaxial graphene growth. The key implications of these results for graphene growth control and their relevance to carbon nanotube growth are highlighted in the context of existing literature. PMID:25188018
Catalyst free growth of CNTs by CVD on nanoscale rough surfaces of silicon substrates

NASA Astrophysics Data System (ADS)

Damodar, D.; Sahoo, R. K.; Jacob, C.

2013-06-01

Catalyst free growth of carbon nanotubes (CNT) has been achieved using atmospheric pressure chemical vapor deposition (APCVD) on surface modified Si(111) substrates. The effect of the substrate surface has been observed by partially etching with KOH (potassium hydroxide) solution which is an anisotropic etchant. Scanning electron microscopy (SEM) confirmed the formation of CNTs over most of the area of the substrate where substrates were anisotropically etched. Transmission electron microscopy (TEM) was used to observe the internal structure of the CNTs. Raman spectroscopy further confirmed the formation of the carbon nanostructures and also their graphitic crystallinity.
Initial development and performance evaluation of a process for formation of dense carbon by pyrolysis of methane

NASA Technical Reports Server (NTRS)

Noyes, G. P.; Cusick, R. J.

1985-01-01

The three steps in pyrolytic carbon formation are: (1) gaseous hydrocarbon polymerization and aromatic formation; (2) gas-phase condensation and surface adsorption/impingement of polyaromatic hydrocarbon; and (3) final dehydration to carbon. The structure of the carbon in the various stages of formation is examined. The apparatuses and experimental procedures for the pyrolysis of methane in a 60 cm long quartz reactor tube at temperatures ranging from 1400-1600 K are described. The percentage of carbon converted and its density are calculated and tabularly presented. The results reveal that dense carbon formation is maximized and soot eliminated by this procedure. It is observed that conversion efficiency depends on the composition of the inlet gas and conversion increases with increasing temperature. Based on the experimental data a three-man carbon reactor subsystem (CRS) is developed; the functions of the Sabatier Methanation Reactor, two carbon formation reactors and fluid handling components of the CRS are analyzed. The CRS forms 16 kg of carbon at a rate of 0.8 kg/day for 20 days in a two percent volume density quartz wool packing at temperature of 1500-1600 K.
System and method for controlling hydrogen elimination during carbon nanotube synthesis from hydrocarbons

DOEpatents

Reilly, Peter T. A.

2010-03-23

A system and method for producing carbon nanotubes by chemical vapor deposition includes a catalyst support having first and second surfaces. The catalyst support is capable of hydrogen transport from the first to the second surface. A catalyst is provided on the first surface of the catalyst support. The catalyst is selected to catalyze the chemical vapor deposition formation of carbon nanotubes. A fuel source is provided for supplying fuel to the catalyst.
Impact of surface processes and climate variability on clumped isotope thermometry of soil carbonates, southern Central Andes, Argentina (Invited)

NASA Astrophysics Data System (ADS)

Huntington, K. W.; Peters, N.; Roe, G.; Hoke, G. D.; Eiler, J.

2010-12-01

Soil carbonates archive a potentially rich record of past climate, but rates of pedogenic carbonate formation, erosion, and deposition impact how the isotopic composition and formation temperature of carbonate-bearing paleosols reflect the local environmental conditions under which they form. We investigate these processes using conventional stable isotope (δ18O and δ13C) and clumped isotope thermometry data for Quaternary pedogenic carbonates from the southern Central Andes at ~33°S, Argentina. The study area spans over 2 km of relief in the Río Mendoza and Río de las Cuevas valleys, accessing a range of mean annual temperature conditions and vegetative cover and exhibiting large seasonal variations in temperature, precipitation, and soil moisture. Variations in soil conditions influence carbonate precipitation and dissolution reactions and the rate and depth of pedogenic carbonate formation. Because soil temperature varies predictably as a function of depth in the soil and seasonal and secular variations in air temperature, clumped isotope thermometry of samples collected in soil pits offers a direct way to estimate the seasonality of pedogenic carbonate formation and potential biases in the long-term climate record. We explore potential complications due to the effects of radiative solar heating on the relationship between air and soil temperatures by examining clumped isotope thermometry results in the context of site-to-site variations in vegetative cover. Temperature estimates from clumped isotope thermometry of pedogenic carbonate collected 5-110 cm below geomorphically stable soil surfaces from 1200-3400 m a.s.l. are compared to temperature profiles predicted by simple rule-based models of soil carbonate formation. The models use climate reanalysis daily diagnostic data (soil temperature, soil moisture, and latent heat flux as a proxy for evaporation) and weather station data as input to assess how varying rates of pedogenic carbonate formation integrated over millennial timescales might impact the geologic record of temperature and isotopic composition.
Synthesis of SnO2 pillared carbon using long chain alkylamine grafted graphene oxide: an efficient anode material for lithium ion batteries.

PubMed

Reddy, M Jeevan Kumar; Ryu, Sung Hun; Shanmugharaj, A M

2016-01-07

With the objective of developing new advanced composite materials that can be used as anodes for lithium ion batteries (LIBs), herein we describe the synthesis of SnO2 pillared carbon using various alkylamine (hexylamine; dodecylamine and octadecylamine) grafted graphene oxides and butyl trichlorotin precursors followed by its calcination at 500 °C for 2 h. While the grafted alkylamine induces crystalline growth of SnO2 pillars, thermal annealing of alkylamine grafted graphene oxide results in the formation of amorphous carbon coated graphene. Field emission scanning electron microscopy (FE-SEM) results reveal the successful formation of SnO2 pillared carbon on the graphene surface. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy characterization corroborates the formation of rutile SnO2 crystals on the graphene surface. A significant rise in the BET surface area is observed for SnO2 pillared carbon, when compared to pristine GO. Electrochemical characterization studies of SnO2 pillared carbon based anode materials showed an enhanced lithium storage capacity and fine cyclic performance in comparison with pristine GO. The initial specific capacities of SnO2 pillared carbon are observed to be 1379 mA h g(-1), 1255 mA h g(-1) and 1360 mA h g(-1) that decrease to 750 mA h g(-1), 643 mA h g(-1) and 560 mA h g(-1) depending upon the chain length of grafted alkylamine on the graphene surface respectively. Electrochemical impedance spectral analysis reveals that the exchange current density of SnO2 pillared carbon based electrodes is higher, corroborating its enhanced electrochemical activity in comparison with GO based electrodes.
The formation of the smallest fullerene-like carbon cages on metal surfaces

NASA Astrophysics Data System (ADS)

Ben Romdhane, F.; Rodríguez-Manzo, J. A.; Andrieux-Ledier, A.; Fossard, F.; Hallal, A.; Magaud, L.; Coraux, J.; Loiseau, A.; Banhart, F.

2016-01-01

The nucleation and growth of carbon on catalytically active metal surfaces is one of the most important techniques to produce nanomaterials such as graphene or nanotubes. Here it is shown by in situ electron microscopy that fullerene-like spherical clusters with diameters down to 0.4 nm and thus much smaller than C60 grow in a polymerized state on Co, Fe, or Ru surfaces. The cages appear on the surface of metallic islands in contact with graphene under heating to at least 650 °C and successively cooling to less than 500 °C. The formation of the small cages is explained by the segregation of carbon on a supersaturated metal, driven by kinetics. First principles energy calculations show that the clusters polymerize and can be attached to defects in graphene. Under compression, the polymerized cages appear in a crystalline structure.The nucleation and growth of carbon on catalytically active metal surfaces is one of the most important techniques to produce nanomaterials such as graphene or nanotubes. Here it is shown by in situ electron microscopy that fullerene-like spherical clusters with diameters down to 0.4 nm and thus much smaller than C60 grow in a polymerized state on Co, Fe, or Ru surfaces. The cages appear on the surface of metallic islands in contact with graphene under heating to at least 650 °C and successively cooling to less than 500 °C. The formation of the small cages is explained by the segregation of carbon on a supersaturated metal, driven by kinetics. First principles energy calculations show that the clusters polymerize and can be attached to defects in graphene. Under compression, the polymerized cages appear in a crystalline structure. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08212a
Carbon solids in oxygen-deficient explosives (LA-UR-13-21151)

NASA Astrophysics Data System (ADS)

Peery, Travis

2013-06-01

The phase behavior of excess carbon in oxygen-deficient explosives has a significant effect on detonation properties and product equations of state. Mixtures of fuel oil in ammonium nitrate (ANFO) above a stoichiometric ratio demonstrate that even small amounts of graphite, on the order of 5% by mole fraction, can substantially alter the Chapman-Jouget (CJ) state properties, a central ingredient in modeling the products equation of state. Similar effects can be seen for Composition B, which borders the carbon phase boundary between graphite and diamond. Nano-diamond formation adds complexity to the product modeling because of surface adsorption effects. I will discuss these carbon phase issues in our equation of state modeling of detonation products, including our statistical mechanics description of carbon clustering and surface chemistry to properly treat solid carbon formation. This work is supported by the Advanced Simulation and Computing Program, under the NNSA.
Calcium carbonate scale control, effect of material and inhibitors.

PubMed

Macadam, J; Parsons, S A

2004-01-01

This paper focuses on developing a reproducible method for reducing calcium carbonate scale formation on heated surfaces where scaling can cause serious problems. It is known that calcium carbonate precipitation is sensitive to impurity ions, such as iron and zinc, even at trace concentration levels. In this paper two sets of experiments are reported. The first experiments were undertaken to investigate the effect of zinc, copper and iron dosing on CaCO3 nucleation and precipitation. Results from the experiments showed that the most effective inhibitor of CaCO3 precipitation was zinc and the effect was linked to dose levels and temperature. Copper and iron had little effect on precipitation in the dose range investigated. The second trial was undertaken to translate the precipitation data to scale formation. These tests were undertaken at 70 degrees C. 5 mg x L(-1) zinc dose reduced the scale formation by 35%. The effect of iron on calcium carbonate scaling rate was not significant. The physical nature of the material on which the scale is formed also influences the scaling. The scaling experiment was also used to investigate the effect of different surface material (stainless steel, copper and aluminium) on CaCO3 scale formation. Copper surface scaled the most.
Process for the formation of wear- and scuff-resistant carbon coatings

DOEpatents

Malaczynski, Gerard W.; Qiu, Xiaohong; Mantese, Joseph V.; Elmoursi, Alaa A.; Hamdi, Aboud H.; Wood, Blake P.; Walter, Kevin C.; Nastasi, Michael A.

1995-01-01

A process for forming an adherent diamond-like carbon coating on a workpiece of suitable material such as an aluminum alloy is disclosed. The workpiece is successively immersed in different plasma atmospheres and subjected to short duration, high voltage, negative electrical potential pulses or constant negative electrical potentials or the like so as to clean the surface of oxygen atoms, implant carbon atoms into the surface of the alloy to form carbide compounds while codepositing a carbonaceous layer on the surface, bombard and remove the carbonaceous layer, and to thereafter deposit a generally amorphous hydrogen-containing carbon layer on the surface of the article.
Can environmental conditions trigger cyanobacterial surfaces and following carbonate formation: implication for biomineralization and biotechnology

NASA Astrophysics Data System (ADS)

Paulo, C.; Dittrich, M.; Zhu, T.

2015-12-01

In this presentation we will give an overview what kind of the factors may trigger carbonate formations at the cell surfaces under a variety of environmental conditions. As examples, we will present the results from our recent studies on formation of calcium carbonates, dolomites and bio-cements. The extracellular polymeric substances (EPS) in the Synechococcuscell envelope are recognized key players in the nucleation of carbonates in marine and freshwater environments. Yet, little is known about a nutrient contents control over the molecular composition of Synechococcus cell envelope, and consequently, biomineralization. In the first study, we investigated how a variation of the phosphorus (P) in the growth media can lead to changes in the surface reactivity of the cells and impact their ability to form carbonates. The objective of the second study is to gain insights into the spatial distribution of cyanobacterial EPS and dolomite from different sediment layers of Khor Al-Adaid sabkha (Qatar). Here, we characterized microbial mats on molecular level in respect of organic and inorganic components using in-situ 2D Raman spectroscopy and Atomic Force Microscopy (AFM) were used. Additionally, 2D chemical maps of sediment layers documented spectral characterizations of minerals and organic matter of microbial origins at high spatial resolution. Finally, we will show the results from the experiments with auto-phototrophic cyanobacteria Gloeocapsa PCC73106, which habitat on the monument surfaces, towards its application for bio-concrete, a product of microbial carbonate precipitation. We studied the biomineralization in biofilm forming Gloeocapsa PCC73106 on the concrete surface as a pre-requirement for microbial carbonate precipitation. Biomineralization on the concrete surface by live cells and killed cells were compared with that under the abiotic condition. Our experiments allow us to conclude that environmental conditions play a significant role in the control of the EPS dynamics and synthesis by cyanobacteria cells and, hence, these factors should be considered in biomineralization experiments.
Penetration of carbon-fabric-reinforced composites by edge cracks during thermal aging

NASA Technical Reports Server (NTRS)

Bowles, Kenneth J.; Kamvouris, John E.

1994-01-01

Thermo-oxidative stability (TOS) test results are significantly influenced by the formation and growth or presence of interlaminar and interlaminar cracks in the cut edges of all carbon-fiber-crosslinked high-temperature polymer matrix composites(exp 1-5) (i.e., unidirectional, crossplied, angle-plied, and fabric composites). The thermo-oxidative degradation of these composites is heavily dependent on the surface area that is exposed to the harmful environment and on the surface-to-volume ratio of the structure under study. Since the growth of cracks and voids on the composite surfaces significantly increases the exposed surface areas, it is imperative that the interaction between the aging process and the formation of new surface area as the aging time progresses be understood.
The formation of the smallest fullerene-like carbon cages on metal surfaces.

PubMed

Ben Romdhane, F; Rodríguez-Manzo, J A; Andrieux-Ledier, A; Fossard, F; Hallal, A; Magaud, L; Coraux, J; Loiseau, A; Banhart, F

2016-02-07

The nucleation and growth of carbon on catalytically active metal surfaces is one of the most important techniques to produce nanomaterials such as graphene or nanotubes. Here it is shown by in situ electron microscopy that fullerene-like spherical clusters with diameters down to 0.4 nm and thus much smaller than C60 grow in a polymerized state on Co, Fe, or Ru surfaces. The cages appear on the surface of metallic islands in contact with graphene under heating to at least 650 °C and successively cooling to less than 500 °C. The formation of the small cages is explained by the segregation of carbon on a supersaturated metal, driven by kinetics. First principles energy calculations show that the clusters polymerize and can be attached to defects in graphene. Under compression, the polymerized cages appear in a crystalline structure.
Surface Roughness of Various Diamond-Like Carbon Films

NASA Astrophysics Data System (ADS)

Liu, Dongping; Liu, Yanhong; Chen, Baoxiang

2006-11-01

Atomic force microscopy is used to estimate and compare the surface morphology of hydrogenated and hydrogen-free diamond-like carbon (DLC) films. The films were prepared by using DC magnetron sputtering of a graphite target, pulsed cathodic carbon arcs, electron cyclotron resonance (ECR), plasma source ion implantation and dielectric barrier discharge (DBD). The difference in the surface structure is presented for each method of deposition. The influences of various discharge parameters on the film surface properties are discussed based upon the experimental results. The coalescence process via the diffusion of adsorbed carbon species is responsible for the formation of hydrogen-free DLC films with rough surfaces. The films with surface roughness at an atomic level can be deposited by energetic ion impacts in a highly ionized carbon plasma. The dangling bonds created by atomic hydrogen lead to the uniform growth of hydrocarbon species at the a-C:H film surfaces of the ECR or DBD plasmas.
Carbonate Mineral Formation on Mars: Clues from Stable Isotope Variation Seen in Cryogenic Laboratory Studies of Carbonate Salts

NASA Technical Reports Server (NTRS)

Socki, Richard; Niles, Paul B.; Sun, Tao; Fu, Qi; Romanek, Christopher S.; Gibson, Everett K.

2013-01-01

The geologic history of water on the planet Mars is intimately connected to the formation of carbonate minerals through atmospheric CO2 and its control of the climate history of Mars. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms readily when a rise in pH occurs as a result of carbon dioxide degassing quickly from freezing Ca-bicarbonate-rich water solutions. This is a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lakebeds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. We report here the results of a series of laboratory experiments that were conducted to simulate potential cryogenic carbonate formation on the planet Mars. These results indicate that carbonates grown under martian conditions (controlled atmospheric pressure and temperature) show enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values with average delta13C(DIC-CARB) values of 20.5%0 which exceed the expected equilibrium fractionation factor of [10(sup 3) ln alpha = 13%0] at 0 degC. Oxygen isotopes showed a smaller enrichment with delta18O(H2O-CARB) values of 35.5%0, slightly exceeding the equilibrium fractionation factor of [10(sup 3) ln alpha = 34%0 ] at 0degC. Large kinetic carbon isotope effects during carbonate precipitation could substantially affect the carbon isotope evolution of CO2 on Mars allowing for more efficient removal of 13C from the Noachian atmosphere enriched by atmospheric loss. This mechanism would be consistent with the observations of large carbon isotope variations in martian materials despite the relative paucity of carbonate minerals in the martian crust.
Influence of carbon on the formation of the surface layer in the process of electroerosion alloying of steel with tungsten

NASA Astrophysics Data System (ADS)

Vasil'eva, E. V.; Bochkov, V. E.; Mikheev, É. A.; Lyakishev, V. A.; Afanas'eva, T. N.

1983-10-01

With an increase in carbon content in the steel being treated, the thickness of the alloyed layer increases and its microhardness also increases. The carbon exerts a deoxidizing action on the layer being formed and promotes a reduction in the threshold of deerosion and also additional strengthening of the layer as the result of the formation of binary η-carbides.

Covariant C and O Isotope Trends in Some Terrestrial Carbonates and ALH 84001: Possible Linkage Through Similar Formation Processes

NASA Technical Reports Server (NTRS)

Volk, Kathryn E.; Niles, Paul B.; Socki, Richard A.

2011-01-01

Carbonate minerals found on the surface of Mars and in martian meteorites indicate that liquid water has played a significant role in the planet's history. These findings have raised questions regarding the history of the martian hydrosphere and atmosphere as well as the possibility of life. Sunset Crater, Arizona is a dry environment with relatively high evaporation and brief periods of precipitation. This environment resembles Mars and may make Sunset Crater a good analog to martian carbonates. In this study we sought to identify discrete micro-scale isotopic variation within the carbonate crusts in Sunset Crater to see if they resembled the micro-scale isotope variation found in ALH 84001 carbonates. Sunset Crater carbonate formation may be used as a martian analog and ultimately provide insight into carbonate formation in ALH 84001.
Evidence for Carbonate Surface Complexation during Forsterite Carbonation in Wet Supercritical Carbon Dioxide

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

Loring, John S.; Chen, Jeffrey; Benezeth Ep Gisquet, Pascale

Continental flood basalts are attractive formations for geologic sequestration of carbon dioxide because of their reactive divalent-cation containing silicates, such as forsterite (Mg2SiO4), suitable for long-term trapping of CO2 mineralized as metal carbonates. The goal of this study was to investigate at a molecular level the carbonation products formed during the reaction of forsterite with supercritical CO2 (scCO2) as a function of the concentration of H2O adsorbed to the forsterite surface. Experiments were performed at 50 °C and 90 bar using an in situ IR titration capability, and post-reaction samples were examined by ex situ techniques, including SEM, XPS, FIB-TEM,more » TGA-MS, and MAS-NMR. Carbonation products and reaction extents varied greatly with adsorbed H2O. We show for the first time evidence of Mg-carbonate surface complexation under wet scCO2 conditions. Carbonate is found to be coordinated to Mg at the forsterite surface in a predominately bidentate fashion at adsorbed H2O concentrations below 27 µmol/m2. Above this concentration and up to 76 µmol/m2, monodentate coordinated complexes become dominant. Beyond a threshold adsorbed H2O concentration of 76 µmol/m2, crystalline carbonates continuously precipitate as magnesite, and the particles that form are hundreds of times larger than the estimated thicknesses of the adsorbed water films of about 7 to 15 Å. At an applied level, these results suggest that mineral carbonation in scCO2 dominated fluids near the wellbore and adjacent to caprocks will be insignificant and limited to surface complexation, unless adsorbed H2O concentrations are high enough to promote crystalline carbonate formation. At a fundamental level, the surface complexes and their dependence on adsorbed H2O concentration give insights regarding forsterite dissolution processes and magnesite nucleation and growth.« less
Evidence for Carbonate Surface Complexation during Forsterite Carbonation in Wet Supercritical Carbon Dioxide

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

Loring, John S.; Chen, Jeffrey; Benezeth, Pascale

Continental flood basalts are attractive formations for geologic sequestration of carbon dioxide because of their reactive divalent-cation containing silicates, such as forsterite (Mg2SiO4), suitable for long-term trapping of CO2 mineralized as metal carbonates. The goal of this study was to investigate at a molecular level the carbonation products formed during the reaction of forsterite with supercritical CO2 (scCO2) as a function of the concentration of H2O adsorbed to the forsterite surface. Experiments were performed at 50 °C and 90 bar using an in situ IR titration capability, and post-reaction samples were examined by ex situ techniques, including SEM, XPS, FIB-TEM,more » TGA-MS, and MAS-NMR. Carbonation products and reaction extents varied greatly with adsorbed H2O. We show for the first time evidence of Mg-carbonate surface complexation under wet scCO2 conditions. Carbonate is found to be coordinated to Mg at the forsterite surface in a predominately bidentate fashion at adsorbed H2O concentrations below 27 µmol/m2. Above this concentration and up to 76 µmol/m2, monodentate coordinated complexes become dominant. Beyond a threshold adsorbed H2O concentration of 76 µmol/m2, crystalline carbonates continuously precipitate as magnesite, and the particles that form are hundreds of times larger than the estimated thicknesses of the adsorbed water films of about 7 to 15 Å. At an applied level, the implication of these results is that mineral trapping in scCO2 dominated fluids will be insignificant and limited to surface complexation unless adsorbed H2O concentrations are high enough to promote crystalline carbonate formation. At a fundamental level, the surface complexes and their dependence on adsorbed H2O concentration give insights regarding forsterite dissolution processes and magnesite nucleation and growth.« less
Formation of brucite and cronstedtite-bearing mineral assemblages on Ceres

NASA Astrophysics Data System (ADS)

Zolotov, Mikhail Yu.

2014-01-01

Dwarf planet Ceres is the largest body in the main asteroid belt with a rocky surface and uncertain internal structure. Spectra of Ceres in near- and mid-infrared wavelengths are consistent with the occurrence of brucite, Mg-bearing carbonates, and an Fe-rich phyllosilicate cronstedtite. Spectra of 10 Hygiea and 324 Bamberga imply similar compositions. Here, we considered stabilities of these minerals to constrain their origin. Cronstedtite is most stable at the temperature of ˜0 °C at moderately oxidizing aqueous conditions and at high water/rock ratios. Although cronstedtite could form on planetesimals, the apparent lack of serpentine may indicate its formation by Ceres' temporary surface solutions. Brucite forms at a low activity of dissolved SiO2, at a low fugacity of CO2, and at highly alkaline pH. Brucite and cronstedtite do not form together and may not form deep in the Ceres' interior. The absence of Mg serpentine from Ceres' surface materials and the unlikely occurrence of very olivine-rich rocks do not indicate a formation of brucite through serpentinization of such rocks. Brucite could form by transient near-surface fluids which do not equilibrate with silicates. Temporary fluids could deposit Mg carbonates before, after, or together with brucite at near-surface conditions that favor CO2 degassing. Regardless of Ceres' internal structure, internal thermal and aqueous processes may not affect cold near-surface layers. Percolation of interior fluids is not consistent with the lack of detection of low-solubility salts. However, impacts of ice-rich targets during the Late Heavy Bombardment could account for transient aqueous environments and unusual surface mineralogies of Ceres, Hygiea, and Bamberga. Brucite and Mg carbonates could have formed through hydration and carbonation of MgO evaporated from silicates. Apparently abundant carbonates may indicate an ample impact oxidation of organic matter, and the occurrence of brucite with cronstedtite may reflect turbulent and disequilibrium environments. Clay-like homogeneous surface materials on Ceres could be gravitationally sorted deposits of impact clouds.
Diagnostics of Carbon Nanotube Formation in a Laser Produced Plume: Spectroscopic in situ nanotube detection using spectral absorption and surface temperature measurements by black body emission

NASA Technical Reports Server (NTRS)

DeBoer, Gary D.

2005-01-01

Carbon nanotubes hold great promise for material advancements in the areas of composites and electronics. The advancement of research in these areas is dependent upon the availability of carbon nanotubes to a broad spectrum of academic and industrial researchers. Although there has been much progress made in reducing the costs of carbon nanotubes and increasing the quality and purity of the products, an increase in demand for still less expensive and specific nanotubes types has also grown. This summer's work has involved two experiments that have been designed to further the understanding of the dynamics and chemical mechanisms of carbon nanotube formation. It is expected that a better understanding of the process of formation of nanotubes will aid current production designs and stimulate ideas for future production designs increasing the quantity, quality, and production control of carbon nanotubes. The first experiment involved the measurement of surface temperature of the target as a function of time with respect to the ablation lasers. A peak surface temperature of 5000 K was determined from spectral analysis of black body emission from the target surface. The surface temperature as a function of various changes in operating parameters was also obtained. This data is expected to aid the modeling of ablation and plume dynamics. The second experiment involved a time and spatial measurement of the spectrally resolved absorbance of the laser produced plume. This experiment explored the possibility of developing absorbance and fluorescence to detect carbon nanotubes during production. To attain control over the production of nanotubes with specific properties and reduce costs, a real time in situ diagnostics method would be very beneficial. Results from this summer's work indicate that detection of nanotubes during production may possibly be used for production feed back control.
Molecular-scale characterization of uranium sorption by bone apatite materials for a permeable reactive barrier demonstration

USGS Publications Warehouse

Fuller, C.C.; Bargar, J.R.; Davis, J.A.

2003-01-01

Uranium binding to bone charcoal and bone meal apatite materials was investigated using U LIII-edge EXAFS spectroscopy and synchrotron source XRD measurements of laboratory batch preparations in the absence and presence of dissolved carbonate. Pelletized bone char apatite recovered from a permeable reactive barrier (PRB) at Fry Canyon, UT, was also studied. EXAFS analyses indicate that U(VI) sorption in the absence of dissolved carbonate occurred by surface complexation of U(VI) for sorbed concentrations ??? 5500 ??g U(VI)/g for all materials with the exception of crushed bone char pellets. Either a split or a disordered equatorial oxygen shell was observed, consistent with complexation of uranyl by the apatite surface. A second shell of atoms at a distance of 2.9 A?? was required to fit the spectra of samples prepared in the presence of dissolved carbonate (4.8 mM total) and is interpreted as formation of ternary carbonate complexes with sorbed U(VI). A U-P distance at 3.5-3.6 A?? was found for most samples under conditions where uranyl phosphate phases did not form, which is consistent with monodentate coordination of uranyl by phosphate groups in the apatite surface. At sorbed concentrations ??? 5500 ??g U(VI)/g in the absence of dissolved carbonate, formation of the uranyl phosphate solid phase, chernikovite, was observed. The presence of dissolved carbonate (4.8 mM total) suppressed the formation of chernikovite, which was not detected even with sorbed U(VI) up to 12 300 ??g U(VI)/g in batch samples of bone meal, bone charcoal, and reagent-grade hydroxyapatite. EXAFS spectra of bone char samples recovered from the Fry Canyon PRB were comparable to laboratory samples in the presence of dissolved carbonate where U(VI) sorption occurred by surface complexation. Our findings demonstrate that uranium uptake by bone apatite will probably occur by surface complexation instead of precipitation of uranyl phosphate phases under the groundwater conditions found at many U-contaminated sites.
The Formation of Fe/Mg Smectite Under Mildly Acidic Conditions on Early Mars

NASA Technical Reports Server (NTRS)

Sutter, B.; Golden, D. C.; Ming, Douglas W.; Niles, P. B.

2011-01-01

The detection of Fe/Mg smectites and carbonate in Noachian and early Hesperian terrain of Mars suggests that neutral to mildly alkaline conditions prevailed during the early history of Mars. If early Mars surface geochemical conditions were neutral to moderately alkaline with a denser CO2 atmosphere than today, then large carbonates deposits should be more widely detected in Noachian terrain. Why have so few carbonate deposits been detected compared to Fe/Mg smectites? Fe/Mg smectites on early Mars formed under mildly acidic conditions, which would preclude the extensive formation of carbonate deposits. The goal of the proposed work is to evaluate the formation of Fe/Mg smectites under mildly acidic conditions.
Spent coffee-based activated carbon: specific surface features and their importance for H2S separation process.

PubMed

Kante, Karifala; Nieto-Delgado, Cesar; Rangel-Mendez, J Rene; Bandosz, Teresa J

2012-01-30

Activated carbons were prepared from spent ground coffee. Zinc chloride was used as an activation agent. The obtained materials were used as a media for separation of hydrogen sulfide from air at ambient conditions. The materials were characterized using adsorption of nitrogen, elemental analysis, SEM, FTIR, and thermal analysis. Surface features of the carbons depend on the amount of an activation agent used. Even though the residual inorganic matter takes part in the H(2)S retention via salt formation, the porous surface of carbons governs the separation process. The chemical activation method chosen resulted in formation of large volume of pores with sizes between 10 and 30Å, optimal for water and hydrogen sulfide adsorption. Even though the activation process can be optimized/changed, the presence of nitrogen in the precursor (caffeine) is a significant asset of that specific organic waste. Nitrogen functional groups play a catalytic role in hydrogen sulfide oxidation. Copyright © 2011 Elsevier B.V. All rights reserved.
The effect of carbon chain length of starting materials on the formation of carbon dots and their optical properties

NASA Astrophysics Data System (ADS)

Pan, Xiaohua; Zhang, Yan; Sun, Xiaobo; Pan, Wei; Yu, Guifeng; Si, Shuxin; Wang, Jinping

2018-04-01

Carbon dots (CDs) have attracted increasing attention due to their high performances and potential applications in wide range of areas. However, their emission mechanism is not clear so far. In order to reveal more factors contributing to the emission of CDs, the effect of carbon chain length of starting materials on the formation of CDs and their optical properties was experimentally investigated in this work. In order to focus on the effect of carbon chain length, the starting materials with C, O, N in fully identical forms and only carbon chain lengths being different were selected for synthesizing CDs, including citric acid (CA) and adipic acid (AA) as carbon sources, and diamines with different carbon chain lengths (H2N(CH2)nNH2, n = 2, 4, 6) as nitrogen sources, as well as ethylenediamine (EDA) as nitrogen source and diacids with different carbon chain lengths (HOOC(CH2)nCOOH, n = 0, 2, 4, 6) as carbon sources. Therefore, the effect of carbon chain length of starting materials on the formation and optical properties of CDs can be systematically investigated by characterizing and comparing the structures and optical properties of as-prepared nine types of CDs. Moreover, the density of –NH2 on the surface of the CDs was quantitatively detected by a spectrophotometry so as to elucidate the relationship between the –NH2 related surface state and the optical properties.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Demin, V. A., E-mail: victordemin88@gmail.com; Blank, V. D.; Karaeva, A. R.

A new fully carbon nanocomposite material is synthesized by the immersion of carbon nanotubes in a fullerene solution in carbon disulfide. The presence of a dense layer of fullerene molecules on the outer nanotube surface is demonstrated by TEM and XPS. Fullerenes are redistributed on the nanotube surface during a long-term action of an electron beam, which points to the existence of a molecular bond between a nanotube and fullerenes. Theoretical calculations show that the formation of a fullerene shell begins with the attachment of one C{sub 60} molecule to a defect on the nanotube surface.
Enhanced catalyst stability for cyclic co methanation operations

DOEpatents

Risch, Alan P.; Rabo, Jule A.

1983-01-01

Carbon monoxide-containing gas streams are passed over a catalyst to deposit a surface layer of active surface carbon thereon essentially without the formation of inactive coke. The active carbon is thereafter reacted with steam or hydrogen to form methane. Enhanced catalyst stability for long term, cyclic operation is obtained by the incorporation of an alkali or alkaline earth dopant in a silica binding agent added to the catalyst-support additive composition.
In Situ FT-IR Spectroscopic Study of CO2 and CO Adsorption on Y2O3, ZrO2, and Yttria-Stabilized ZrO2

PubMed Central

2013-01-01

In situ FT-IR spectroscopy was exploited to study the adsorption of CO2 and CO on commercially available yttria-stabilized ZrO2 (8 mol % Y, YSZ-8), Y2O3, and ZrO2. All three oxides were pretreated at high temperatures (1173 K) in air, which leads to effective dehydroxylation of pure ZrO2. Both Y2O3 and YSZ-8 show a much higher reactivity toward CO and CO2 adsorption than ZrO2 because of more facile rehydroxylation of Y-containing phases. Several different carbonate species have been observed following CO2 adsorption on Y2O3 and YSZ-8, which are much more strongly bound on the former, due to formation of higher-coordinated polydentate carbonate species upon annealing. As the crucial factor governing the formation of carbonates, the presence of reactive (basic) surface hydroxyl groups on Y-centers was identified. Therefore, chemisorption of CO2 most likely includes insertion of the CO2 molecule into a reactive surface hydroxyl group and the subsequent formation of a bicarbonate species. Formate formation following CO adsorption has been observed on all three oxides but is less pronounced on ZrO2 due to effective dehydroxylation of the surface during high-temperature treatment. The latter generally causes suppression of the surface reactivity of ZrO2 samples regarding reactions involving CO or CO2 as reaction intermediates. PMID:24009780
Penetration of Solar Radiation into Solid Carbon Dioxide

NASA Astrophysics Data System (ADS)

Chinnery, H. E.; Hagermann, A.; Kaufmann, E.; Lewis, S. R.; Grady, M. M.

2017-09-01

Carbon dioxide ice exists naturally on the surface of Mars. This is a unique environment, with no Earth analogues, and so determining the properties of such a surface is important to further our understanding of the Martian environment. Laboratory experiments have determined the e-folding scale, or absorption scale length, for carbon dioxide slab ice, granular ice and snow. This is a universal measure of how transparent a material is to visible light, and so has implications for the radiative budget of carbon dioxide ice covered surfaces, as well as physical processes, such as the so-called spider formations in the cryptic region near the Martian south pole.
Adsorption, polymerization and decomposition of acetaldehyde on clean and carbon-covered Rh(111) surfaces

NASA Astrophysics Data System (ADS)

Kovács, Imre; Farkas, Arnold Péter; Szitás, Ádám; Kónya, Zoltán; Kiss, János

2017-10-01

The adsorption and dissociation of acetaldehyde were investigated on clean and carbon-covered Rh(111) single crystal surfaces by electron energy loss spectroscopy (EELS), temperature programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS) and work function (Δφ) measurements. Acetaldehyde is a starting material for the catalytic production of many important chemicals and investigation of its reactions motivated by environmental purposes too. The adsorption of acetaldehyde on clean Rh(111) surface produced various types of adsorption forms. η1-(O)-CH3CHOa and η2-(O,C)-CH3CHOa are developing and characterized by HREELS. η1-CH3CHOa partly desorbed at Tp = 150 K, another part of these species are incorporated in trimer and linear 2D polimer species. The desorption of trimers (at amu 132) were observed in TPD with a peak maximum at Tp = 225 K. Above this temperature acetaldehyde either desorbed or bonded as a stable surface intermediate (η2-CH3CHOa) on the rhodium surface. The molecules decomposed to adsorbed products, and only hydrogen and carbon monoxide were analyzed in TPD. Surface carbon decreased the uptake of adsorbed acetaldehyde, inhibited the formation of polymers, nevertheless, it induced the Csbnd O bond scission and CO formation with 40-50 K lower temperature after higher acetaldehyde exposure.
Surface reaction modification: The effect of structured overlayers of sulfur on the kinetics and mechanism of the decomposition of formic acid on Pt(111)

NASA Astrophysics Data System (ADS)

Abbas, N.; Madix, R. J.

The reaction of formic acid (DCOOH) on Pt(111), Pt(111)-(2×2)S and Pt(111)-(√3×√3)R30°S surfaces was examined by temperature programmed reaction spectroscopy. On the clean surface formic acid decomposed to yield primarily carbon dioxide and the hydrogenic species (H 2, HD and D 2) at low coverages. Although the formation of water and carbon monoxide via a dehydration reaction was observed at these coverages, the yield of these products was small when compared to the other products of reaction. The evolution of CO 2 at low temperature was ascribed to the decomposition of the formate intermediate. In the presence of sulfur the amount of molecularly adsorbed formic acid decreased up to a factor of three on the (√3×√3)R30°S surface, and a decline in the reactivity of over an order of magnitude was also observed. The only products formed were the hydrogenic species and carbon dioxide. The absence of carbon monoxide indicated that the dehydration pathway was blocked by sulfur. In addition to the low temperature CO 2 peak a high temperature CO 2-producing path was also evident. It was inferred from both the stoichiometry and the coincident evolution of D 2 and CO 2 in the high temperature states that these products also evolved due to the decomposition of the formate intermediate. On increasing the sulfur coverage to one-third monolayer this intermediate was further stabilized, and a predominance of the decomposition via the high temperature path was observed. Stability of the formate intermediate was attributed to inhibition of the decomposition reaction by sulfur atoms. The activation energy for formate decomposition increased from 15 kcal/gmole on the clean surface to 24.3 kcal/gmol on the (√3×√3)R30°S overlayer.
Electrochemical mineral scale prevention and removal on electrically conducting carbon nanotube--polyamide reverse osmosis membranes.

PubMed

Duan, Wenyan; Dudchenko, Alexander; Mende, Elizabeth; Flyer, Celeste; Zhu, Xiaobo; Jassby, David

2014-05-01

The electrochemical prevention and removal of CaSO4 and CaCO3 mineral scales on electrically conducting carbon nanotube - polyamide reverse osmosis membrane was investigated. Different electrical potentials were applied to the membrane surface while filtering model scaling solutions with high saturation indices. Scaling progression was monitored through flux measurements. CaCO3 scale was efficiently removed from the membrane surface through the intermittent application of a 2.5 V potential to the membrane surface, when the membrane acted as an anode. Water oxidation at the anode, which led to proton formation, resulted in the dissolution of deposited CaCO3 crystals. CaSO4 scale formation was significantly retarded through the continuous application of 1.5 V DC to the membrane surface, when the membrane was operated as an anode. The continuous application of a sufficient electrical potential to the membrane surface leads to the formation of a thick layer of counter-ions along the membrane surface that pushed CaSO4 crystal formation away from the membrane surface, allowing the formed crystals to be carried away by the cross-flow. We developed a simple model, based on a modified Poisson-Boltzmann equation, which qualitatively explained our observed experimental results.
Ammonia modification of activated carbon to enhance carbon dioxide adsorption: Effect of pre-oxidation

NASA Astrophysics Data System (ADS)

Shafeeyan, Mohammad Saleh; Daud, Wan Mohd Ashri Wan; Houshmand, Amirhossein; Arami-Niya, Arash

2011-02-01

A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO2) adsorbent. In general, CO2 adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO2 adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N2 adsorption/desorption at -196 °C. CO2 capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO2 adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 °C) considerably enhanced the CO2 uptake at higher temperatures.
Catalytic conversion of aliphatic alcohols on carbon nanomaterials: The roles of structure and surface functional groups

NASA Astrophysics Data System (ADS)

Tveritinova, E. A.; Zhitnev, Yu. N.; Chernyak, S. A.; Arkhipova, E. A.; Savilov, S. V.; Lunin, V. V.

2017-03-01

Carbon nanomaterials with the structure of graphene and different compositions of the surface groups are used as catalysts for the conversion of C2-C4 aliphatic alcohols. The conversions of ethanol, propanol- 1, propanol-2, butanol-1, butanol-2, and tert-butanol on carbon nanotubes, nanoflakes, and nanoflakes doped with nitrogen are investigated. Oxidized and nonoxidized multiwalled carbon nanotubes, nanoflakes, and nanoflakes doped with nitrogen are synthesized. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning and transmission electronic microscopies, Brunauer-Emmett-Teller method, derivatographic analyses, and the pulsed microcatalytic method are used to characterize comprehensively the prepared catalysts. It was established that all of the investigated carbon nanomaterials (with the exception of nondoped carbon nanoflakes) are bifunctional catalysts for the conversion of aliphatic alcohols, and promote dehydration reactions with the formation of olefins and dehydrogenation reactions with the formation of aldehydes or ketones. Nanoflakes doped with nitrogen are inert with respect to secondary alcohols and tert-butanol. The role of oxygen-containing and nitrogen-containing surface groups, and of the geometrical structure of the carbon matrix of graphene nanocarbon materials in the catalytic conversion of aliphatic alcohols, is revealed. Characteristics of the conversion of aliphatic alcohols that are associated with their structure are identified.
The Effect of Fluoroethylene Carbonate as an Additive on the Solid Electrolyte Interphase on Silicon Lithium-Ion Electrodes

DOE PAGES

Schroder, Kjell; Li, Juchuan; Dudney, Nancy J.; ...

2015-08-03

Fluoroethylene carbonate (FEC) has become a standard electrolyte additive for use with silicon negative electrodes, but how FEC affects solid electrolyte interphase (SEI) formation on the silicon anode’s surface is still not well understood. Herein, SEI formed from LiPF6-based carbonate electrolytes, with and without FEC, were investigated on 50 nm thick amorphous silicon thin film electrodes to understand the role of FEC on silicon electrode surface reactions. In contrast to previous work, anhydrous and anoxic techniques were used to prevent air and moisture contamination of prepared SEI films. This allowed for accurate characterization of the SEI structure and composition bymore » X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry depth profiling. These results show that FEC reduction leads to fluoride ion and LiF formation, consistent with previous computational and experimental results. Surprisingly, we also find that these species decrease lithium-ion solubility and increase the reactivity of the silicon surface. We conclude that the effectiveness of FEC at improving the Coulombic efficiency and capacity retention is due to fluoride ion formation from reduction of the electrolyte, which leads to the chemical attack of any silicon-oxide surface passivation layers and the formation of a kinetically stable SEI comprising predominately lithium fluoride and lithium oxide.« less
Self-organized carbon-rich stripe formation from competitive carbon and aluminium segregation at Fe0.85Al0.15(1 1 0) surfaces

NASA Astrophysics Data System (ADS)

Dai, Zongbei; Borghetti, Patrizia; Mouchaal, Younes; Chenot, Stéphane; David, Pascal; Jupille, Jacques; Cabailh, Gregory; Lazzari, Rémi

2018-06-01

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A2 random alloy Fe0.85Al0.15(1 1 0) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼ 900 K, carbon segregates in the form of self-organized protruding stripes separated by ∼ 5 nm that run along the [ 0 0 1 ] B bulk direction and cover up to 34% of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements.

Persistent free radicals in carbon-based materials on transformation of refractory organic contaminants (ROCs) in water: A critical review.

PubMed

Qin, Yaxin; Li, Guiying; Gao, Yanpeng; Zhang, Lizhi; Ok, Yong Sik; An, Taicheng

2018-06-15

With the increased concentrations and kinds of refractory organic contaminants (ROCs) in aquatic environments, many previous reviews systematically summarized the applications of carbon-based materials in the adsorption and catalytic degradation of ROCs for their economically viable and environmentally friendly behavior. Interestingly, recent studies indicated that carbon-based materials in natural environment can also mediate the transformation of ROCs directly or indirectly due to their abundant persistent free radicals (PFRs). Understanding the formation mechanisms of PFRs in carbo-based materials and their interactions with ROCs is essential to develop their further applications in environment remediation. However, there is no comprehensive review so far about the direct and indirect removal of ROCs mediated by PFRs in amorphous, porous and crystalline carbon-based materials. The review aims to evaluate the formation mechanisms of PFRs in carbon-based materials synthesized through pyrolysis and hydrothermal carbonization processes. The influence of synthesis conditions (temperature and time) and carbon sources on the types as well as the concentrations of PFRs in carbon-based materials are also discussed. In particular, the effects of metals on the concentrations and types of PFRs in carbon-based materials are highlighted because they are considered as the catalysts for the formation of PFRs. The formation mechanisms of reactive species and the further transformation mechanisms of ROCs are briefly summarized, and the surface properties of carbon-based materials including surface area, types and number of functional groups, etc. are found to be the key parameters controlling their activities. However, due to diversity and complexity of carbon-based materials, the exact relationships between the activities of carbon-based materials and PFRs are still uncertain. Finally, the existing problems and current challenges for the ROCs transformation with carbon-based materials are also pointed out. Copyright © 2018 Elsevier Ltd. All rights reserved.
Protolytic carbon film technology

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

Renschler, C.L.; White, C.A.

1996-04-01

This paper presents a technique for the deposition of polyacrylonitrile (PAN) on virtually any surface allowing carbon film formation with only the caveat that the substrate must withstand carbonization temperatures of at least 600 degrees centigrade. The influence of processing conditions upon the structure and properties of the carbonized film is discussed. Electrical conductivity, microstructure, and morphology control are also described.
Nanosized carbon modifier used to control plastic deformations of asphalt concrete

NASA Astrophysics Data System (ADS)

Vysotskaya, M. A.; Shekhovtsova, S. Yu; Barkovsky, D. V.

2018-03-01

Aspects related to plastic track, the formation of which directly depends on the properties of the binder in the composition of asphalt concrete, are considered in this article. The effect of primary carbon nanomaterials on the quality of polymer and bitumen binder in comparison with the traditional binder including cross-linking agent is evaluated. The influence of binders on the resistance to the track formation of type B asphalt concrete is studied. To quantify the service life of surfacing, a calculation method based on the criteria for the resistance of surfacing material to plastic deformations is used.
On the Application of Lithium Additives in the Electrolytic Production of Primary Aluminum

NASA Astrophysics Data System (ADS)

Saitov, A. V.; Bazhin, V. Yu.; Povarov, V. G.

2017-12-01

The behavior of carbon-graphite subjected to treatment in the lithium carbonate Li2CO3 melt without cryolite and alkali-metal fluorides is studied to reliably estimate the influence of lithium on the surface layers of a carbon-containing cathode lining. The chemical composition and the structure of the carbon-graphite material after its interaction with lithium in the Li2CO3 melt have been studied. The high-temperature interaction of the system components in the melt is found to be accompanied by fracture of the operating surface of the carbon-graphite material, while the carbon-graphite surface does not failed upon interacting with lithium vapors. Based on the obtained data, a model for the formation of lithium ions during the reduction of lithium and its interaction with a carbon-graphite sample during the electrolysis of lithium carbonate is proposed.
Effects of Surface Oxygen on the Performance of Carbon as an Anode in Lithium-Ion Batteries

NASA Technical Reports Server (NTRS)

Hung, Ching-Cheh; Clark, Gregory W.

2001-01-01

Carbon materials with similar bulk structure but different surface oxygen were compared for their performance as anodes in lithium-ion battery. The bulk structure was such that the graphene planes were perpendicular to the surface. Three types of surfaces were examined: surface containing C=O type oxygen. surface containing -O-C type oxygen, and surface containing high concentration of active sites. The test involved cycles of lithium insertion into and release from the carbon materials, which was in the half cells of carbon/saturated LiI-50/50 (vol %) EC and DMC/lithium. During the first cycle of lithium insertion, the presence of adsorbed oxygen, -O-C type oxygen, active carbon sites, and C=O type oxygen resulted in the formation of solid-electrolyte interface (SEI) when the carbon's voltage relative to lithium metal was >1.35, 1 to 1.35, 0.5 to 1, and 0.67 to 0.7 V, respectively. An optimum -O-C type oxygen and a minimum C=O type oxygen was found to increase the reversible and decrease the irreversible capacity of carbon. Active sites on the carbon surface result in a large irreversible capacity and a second lithium insertion-release mechanism. However, this new mechanism has a short cycle life.
Non-encapsulation approach for high-performance Li-S batteries through controlled nucleation and growth

NASA Astrophysics Data System (ADS)

Pan, Huilin; Chen, Junzheng; Cao, Ruiguo; Murugesan, Vijay; Rajput, Nav Nidhi; Han, Kee Sung; Persson, Kristin; Estevez, Luis; Engelhard, Mark H.; Zhang, Ji-Guang; Mueller, Karl T.; Cui, Yi; Shao, Yuyan; Liu, Jun

2017-10-01

High-surface-area, nanostructured carbon is widely used for encapsulating sulfur and improving the cyclic stability of Li-S batteries, but the high carbon content and low packing density limit the specific energy that can be achieved. Here we report an approach that does not rely on sulfur encapsulation. We used a low-surface-area, open carbon fibre architecture to control the nucleation and growth of the sulfur species by manipulating the carbon surface chemistry and the solvent properties, such as donor number and Li+ diffusivity. Our approach facilitates the formation of large open spheres and prevents the production of an undesired insulating sulfur-containing film on the carbon surface. This mechanism leads to 100% sulfur utilization, almost no capacity fading, over 99% coulombic efficiency and high energy density (1,835 Wh kg-1 and 2,317 Wh l-1). This finding offers an alternative approach for designing high-energy and low-cost Li-S batteries through controlling sulfur reaction on low-surface-area carbon.
Spatial imaging of carbon reactivity centers in Pd/C catalytic systems† †Electronic supplementary information (ESI) available: Detailed experimental procedures and FE-SEM images. See DOI: 10.1039/c5sc00802f

PubMed Central

Pentsak, E. O.; Kashin, A. S.; Polynski, M. V.; Kvashnina, K. O.; Glatzel, P.

2015-01-01

Gaining insight into Pd/C catalytic systems aimed at locating reactive centers on carbon surfaces, revealing their properties and estimating the number of reactive centers presents a challenging problem. In the present study state-of-the-art experimental techniques involving ultra high resolution SEM/STEM microscopy (1 Å resolution), high brilliance X-ray absorption spectroscopy and theoretical calculations on truly nanoscale systems were utilized to reveal the role of carbon centers in the formation and nature of Pd/C catalytic materials. Generation of Pd clusters in solution from the easily available Pd2dba3 precursor and the unique reactivity of the Pd clusters opened an excellent opportunity to develop an efficient procedure for the imaging of a carbon surface. Defect sites and reactivity centers of a carbon surface were mapped in three-dimensional space with high resolution and excellent contrast using a user-friendly nanoscale imaging procedure. The proposed imaging approach takes advantage of the specific interactions of reactive carbon centers with Pd clusters, which allows spatial information about chemical reactivity across the Pd/C system to be obtained using a microscopy technique. Mapping the reactivity centers with Pd markers provided unique information about the reactivity of the graphene layers and showed that >2000 reactive centers can be located per 1 μm2 of the surface area of the carbon material. A computational study at a PBE-D3-GPW level differentiated the relative affinity of the Pd2 species to the reactive centers of graphene. These findings emphasized the spatial complexity of the carbon material at the nanoscale and indicated the importance of the surface defect nature, which exhibited substantial gradients and variations across the surface area. The findings show the crucial role of the structure of the carbon support, which governs the formation of Pd/C systems and their catalytic activity. PMID:29511504
Isotopic Composition of Carbonates in Antarctic Ordinary Chondrites and Miller Range Nakhlites: Insights into Martian Amazonian Aqueous Alteration

NASA Technical Reports Server (NTRS)

Evans, M. E.; Niles, P. B.; Chapman, P.

2017-01-01

The martian surface contains features of ancient fluvial systems. Stable isotope analysis of carbonates that form in aqueous systems can reveal their formation conditions. The Nakhlite meteorites originally formed on Mars 1.3 Ga and were later exposed to aqueous fluids that left behind carbonate minerals [1], thus analysis of these carbonates can provide data to understand Amazonian climate conditions on Mars. Carbonates found in the Nakhlite meteorites contain a range of delta(sup 13)C values, which may be either martian carbonates or terrestrial contamination. To better under-stand terrestrial weathering products and martian carbonate formation processes, we conducted a set of carbonate isotope analyses on Antarctic meteorites focusing on Miller Range (MIL) Nakhlites as well as Ordinary Chondrites (OCs) (Figure 1)[1-11] [12]. OCs of petrology type H, L, and LL 3-6 were selected since they are not expected to contain preterrestrial carbonates, yet they have visible evaporite minerals on the fusion crust indicating terrestrial alteration. These cryogenically formed terrestrial carbonates may also provide an analog for cryogenic carbonate formation on Mars.
Mineralization of Basalts in the CO 2-H 2O-H 2S System

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

Schaef, Herbert T.; McGrail, B. Peter; Owen, Antionette T.

2013-05-10

Basalt samples representing five different formations were immersed in water equilibrated with supercritical carbon dioxide containing 1% hydrogen sulfide (H2S) at reservoir conditions (100 bar, 90°C) for up to 3.5 years. Surface coatings in the form of pyrite and metal cation substituted carbonates were identified as reaction products associated with all five basalts. In some cases, high pressure tests contained excess H2S, which produced the most corroded basalts and largest amount of secondary products. In comparison, tests containing limited amounts of H2S appeared least reacted with significantly less concentrations of reaction products. In all cases, pyrite appeared to precede carbonation,more » and in some instances, was observed in the absence of carbonation such as in cracks, fractures, and within the porous glassy mesostasis. Armoring reactions from pyrite surface coatings observed in earlier shorter duration tests were found to be temporary with carbonate mineralization observed with all the basalts tested in these long duration experiments. Geochemical simulations conducted with the geochemical code EQ3/6 accurately predicted early pyrite precipitation followed by formation of carbonates. Reactivity with H2S was correlated with measured Fe(II)/Fe(III) ratios in the basalts with more facile pyrite formation occurring with basalts containing more Fe(III) phases. These experimental and modeling results confirm potential for long term sequestration of acid gas mixtures in continental flood basalt formations.« less
Method and apparatus for detecting the presence and thickness of carbon and oxide layers on EUV reflective surfaces

DOEpatents

Malinowski, Michael E.

2005-01-25

The characteristics of radiation that is reflected from carbon deposits and oxidation formations on highly reflective surfaces such as Mo/Si mirrors can be quantified and employed to detect and measure the presence of such impurities on optics. Specifically, it has been shown that carbon deposits on a Mo/Si multilayer mirror decreases the intensity of reflected HeNe laser (632.8 nm) light. In contrast, oxide layers formed on the mirror should cause an increase in HeNe power reflection. Both static measurements and real-time monitoring of carbon and oxide surface impurities on optical elements in lithography tools should be achievable.
Process for producing methane from gas streams containing carbon monoxide and hydrogen

DOEpatents

Frost, Albert C.

1980-01-01

Carbon monoxide-containing gas streams are passed over a catalyst capable of catalyzing the disproportionation of carbon monoxide so as to deposit a surface layer of active surface carbon on the catalyst essentially without formation of inactive coke thereon. The surface layer is contacted with steam and is thus converted to methane and CO.sub.2, from which a relatively pure methane product may be obtained. While carbon monoxide-containing gas streams having hydrogen or water present therein can be used only the carbon monoxide available after reaction with said hydrogen or water is decomposed to form said active surface carbon. Although hydrogen or water will be converted, partially or completely, to methane that can be utilized in a combustion zone to generate heat for steam production or other energy recovery purposes, said hydrogen is selectively removed from a CO--H.sub.2 -containing feed stream by partial oxidation thereof prior to disproportionation of the CO content of said stream.
Synthesis of a conducting SiO2-carbon composite from commercial silicone grease and its conversion to paramagnetic SiO2 particles.

PubMed

Pol, V G; Pol, S V; George, P P; Markovsky, B; Gedanken, A

2006-07-13

The thermal decomposition of commercial silicone grease was carried out in a closed reactor (Swagelok) that was heated at 800 degrees C for 3 h, yielding a SiO2-carbon composite with a BET surface area of 369 m2/g. The bulk conductivity (5.72 x 10(-6) S x cm(-2)) of the SiO2-carbon composite was determined by impedance measurements. The as-prepared SiO2-carbon composite was further annealed at 500 degrees C in air for 2 h, which led to the formation of white paramagnetic silica particles (confirmed by ESR), possessing a surface area of 111 m2/g. The present synthetic technique requires unsophisticated equipment and a low-cost commercial precursor, and the reaction is carried out without a solvent, surfactant, or catalyst. The mechanism for the formation of a porous SiO2-carbon composite from the silicone grease is also presented.
Multi-scale investigation into the mechanisms of fault mirror formation in seismically active carbonate rocks

NASA Astrophysics Data System (ADS)

Ohl, Markus; Chatzaras, Vasileios; Niemeijer, Andre; King, Helen; Drury, Martyn; Plümper, Oliver

2017-04-01

Mirror surfaces along principal slip zones in carbonate rocks have recently received considerable attention as they are thought to form during fault slip at seismic velocities and thus may be a marker for paleo-seismicity (Siman-Tov et al., 2013). Therefore, these structures represent an opportunity to improve our understanding of earthquake mechanics in carbonate faults. Recent investigations reported the formation of fault mirrors in natural rocks as well as in laboratory experiments and connected their occurrence to the development of nano-sized granular material (Spagnuolo et al., 2015). However, the underlying formation and deformation mechanisms of these fault mirrors are still poorly constrained and warrant further research. In order to understand the influence and significance of these fault products on the overall fault behavior, we analysed the micro-, and nanostructural inventory of natural fault samples containing mirror slip surfaces. Here we present first results on the possible formation mechanisms of fault mirrors and associated deformation mechanisms operating in the carbonate fault gouge from two seismically active fault zones in central Greece. Our study specifically focuses on mirror slip surfaces obtained from the Arkitsa fault in the Gulf of Evia and the Schinos fault in the Gulf of Corinth. The Schinos fault was reactivated by a magnitude 6.7 earthquake in 1981 while the Arkitsa fault is thought to have been reactivated by a magnitude 6.9 earthquake in 1894. Our investigations encompass a combination of state-of-the-art analytical techniques including X-ray computed tomography, focused ion beam scanning electron microscopy (FIB-SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Using this multiscale analytical approach, we report decarbonation-reaction structures, considerable calcite twinning and grain welding immediately below the mirror slip surface. Grains or areas indicating decarbonation reactions show a foam-like, grainy texture. Some areas show a lamellar structure of decarbonated and intact calcite, representing former calcite twins. The average grain size of welded grains is between 100 - 200 nm. In addition, we identified the formation of an amorphous calcium-bearing phase that is enriched in Al, Fe, Si and Mg compared to the host calcite. This phase covers the coarser calcite grains as a thin film and welds them together as well as infiltrating cleavage planes, cracks and surface corrugations on top of the principal mirror slip surface. Thus, it contributes to creating a highly smooth slip surface. References: Siman-Tov et al., 2013, Nanograins form carbonate fault mirrors: Geology, v. 41; no. 6; p. 703-706. Spagnuolo et al., 2015, Fast-moving dislocations trigger flash weakening in carbonate bearing faults during earthquakes: Nature Scientific Reports 5:1611
Neon ion beam induced pattern formation on amorphous carbon surfaces

NASA Astrophysics Data System (ADS)

Bobes, Omar; Hofsäss, Hans; Zhang, Kun

2018-02-01

We investigate the ripple pattern formation on amorphous carbon surfaces at room temperature during low energy Ne ion irradiation as a function of the ion incidence angle. Monte Carlo simulations of the curvature coefficients applied to the Bradley-Harper and Cater-Vishnyakov models, including the recent extensions by Harrison-Bradley and Hofsäss predict that pattern formation on amorphous carbon thin films should be possible for low energy Ne ions from 250 eV up to 1500 eV. Moreover, simulations are able to explain the absence of pattern formation in certain cases. Our experimental results are compared with prediction using current linear theoretical models and applying the crater function formalism, as well as Monte Carlo simulations to calculate curvature coefficients using the SDTrimSP program. Calculations indicate that no patterns should be generated up to 45° incidence angle if the dynamic behavior of the thickness of the ion irradiated layer introduced by Hofsäss is taken into account, while pattern formation most pronounced from 50° for ion energy between 250 eV and 1500 eV, which are in good agreement with our experimental data.
Influence of Pore Structure on the Effectiveness of a Biogenic Carbonate Surface Treatment for Limestone Conservation ▿

PubMed Central

De Muynck, Willem; Leuridan, Stijn; Van Loo, Denis; Verbeken, Kim; Cnudde, Veerle; De Belie, Nele; Verstraete, Willy

2011-01-01

A ureolytic biodeposition treatment was applied to five types of limestone in order to investigate the effect of pore structure on the protective performance of a biogenic carbonate surface treatment. Protective performance was assessed by means of transport and degradation processes, and the penetration depth of the treatment was visualized by microtomography. Pore size governs bacterial adsorption and hence the location and amount of carbonate precipitated. This study indicated that in macroporous stone, biogenic carbonate formation occurred to a larger extent and at greater depths than in microporous stone. As a consequence, the biodeposition treatment exhibited the greatest protective performance on macroporous stone. While precipitation was limited to the outer surface of microporous stone, biogenic carbonate formation occurred at depths of greater than 2 mm for Savonnières and Euville. For Savonnières, the presence of biogenic carbonate resulted in a 20-fold decreased rate of water absorption, which resulted in increased resistance to sodium sulfate attack and to freezing and thawing. While untreated samples were completely degraded after 15 cycles of salt attack, no damage was observed in biodeposition-treated Savonnières. From this study, it is clear that biodeposition is very effective and more feasible for macroporous stones than for microporous stones. PMID:21821746
Influence of pore structure on the effectiveness of a biogenic carbonate surface treatment for limestone conservation.

PubMed

De Muynck, Willem; Leuridan, Stijn; Van Loo, Denis; Verbeken, Kim; Cnudde, Veerle; De Belie, Nele; Verstraete, Willy

2011-10-01

A ureolytic biodeposition treatment was applied to five types of limestone in order to investigate the effect of pore structure on the protective performance of a biogenic carbonate surface treatment. Protective performance was assessed by means of transport and degradation processes, and the penetration depth of the treatment was visualized by microtomography. Pore size governs bacterial adsorption and hence the location and amount of carbonate precipitated. This study indicated that in macroporous stone, biogenic carbonate formation occurred to a larger extent and at greater depths than in microporous stone. As a consequence, the biodeposition treatment exhibited the greatest protective performance on macroporous stone. While precipitation was limited to the outer surface of microporous stone, biogenic carbonate formation occurred at depths of greater than 2 mm for Savonnières and Euville. For Savonnières, the presence of biogenic carbonate resulted in a 20-fold decreased rate of water absorption, which resulted in increased resistance to sodium sulfate attack and to freezing and thawing. While untreated samples were completely degraded after 15 cycles of salt attack, no damage was observed in biodeposition-treated Savonnières. From this study, it is clear that biodeposition is very effective and more feasible for macroporous stones than for microporous stones.
Bioactive carbon-PEEK composites prepared by chemical surface treatment.

PubMed

Miyazaki, Toshiki; Matsunami, Chisato; Shirosaki, Yuki

2017-01-01

Polyetheretherketone (PEEK) has attracted much attention as an artificial intervertebral spacer for spinal reconstruction. Furthermore, PEEK plastic reinforced with carbon fiber has twice the bending strength of pure PEEK. However, the PEEK-based materials do not show ability for direct bone bonding, i.e., bioactivity. Although several trials have been conducted for enabling PEEK with bioactivity, few studies have reported on bioactive surface modification of carbon-PEEK composites. In the present study, we attempted the preparation of bioactive carbon-PEEK composites by chemical treatments with H 2 SO 4 and CaCl 2 . Bioactivity was evaluated by in vitro apatite formation in simulated body fluid (SBF). The apatite formation on the carbon-PEEK composite was compared with that of pure PEEK. Both pure PEEK and carbon-PEEK composite formed the apatite in SBF when they were treated with H 2 SO 4 and CaCl 2 ; the latter showed higher apatite-forming ability than the former. It is conjectured that many functional groups able to induce the apatite nucleation, such as sulfo and carboxyl groups, are incorporated into the dispersed carbon phase in the carbon-PEEK composites. Copyright © 2016 Elsevier B.V. All rights reserved.
Surface modification by carbon ion implantation for the application of ni-based amorphous alloys as bipolar plate in proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Kim, Min-Uk; Kim, Do-Hyang; Han, Seung-hee; Fleury, Eric; Seok, Hyun-Kwang; Cha, Pil-Ryung; Kim, Yu-Chan

2011-04-01

Ni-based amorphous alloys with surface modification by carbon ion implantation are proposed as an alternative bipolar plate material for polymer electrolyte membrane fuel cells (PEMFCs). Both Ni60Nb20Ti10Zr10 alloys with and without carbon ion implantation have corrosion resistance as good as graphite as well as much lower contact resistance than 316L stainless steel in the PEMFC environment. The formation of conductive surface carbide due to carbon ion implantation results in a decrease in the contact resistance to a level comparable to that of graphite. This combination of excellent properties indicates that carbon ion implanted Ni-based amorphous alloys can be potential candidate materials for bipolar plates in PEMFCs.
Activated carbon derived from waste coffee grounds for stable methane storage.

PubMed

Kemp, K Christian; Baek, Seung Bin; Lee, Wang-Geun; Meyyappan, M; Kim, Kwang S

2015-09-25

An activated carbon material derived from waste coffee grounds is shown to be an effective and stable medium for methane storage. The sample activated at 900 °C displays a surface area of 1040.3 m(2) g(-1) and a micropore volume of 0.574 cm(3) g(-1) and exhibits a stable CH4 adsorption capacity of ∼4.2 mmol g(-1) at 3.0 MPa and a temperature range of 298 ± 10 K. The same material exhibits an impressive hydrogen storage capacity of 1.75 wt% as well at 77 K and 100 kPa. Here, we also propose a mechanism for the formation of activated carbon from spent coffee grounds. At low temperatures, the material has two distinct types with low and high surface areas; however, activation at elevated temperatures drives off the low surface area carbon, leaving behind the porous high surface area activated carbon.
Activated carbon derived from waste coffee grounds for stable methane storage

NASA Astrophysics Data System (ADS)

Kemp, K. Christian; Baek, Seung Bin; Lee, Wang-Geun; Meyyappan, M.; Kim, Kwang S.

2015-09-01

An activated carbon material derived from waste coffee grounds is shown to be an effective and stable medium for methane storage. The sample activated at 900 °C displays a surface area of 1040.3 m2 g-1 and a micropore volume of 0.574 cm3 g-1 and exhibits a stable CH4 adsorption capacity of ˜4.2 mmol g-1 at 3.0 MPa and a temperature range of 298 ± 10 K. The same material exhibits an impressive hydrogen storage capacity of 1.75 wt% as well at 77 K and 100 kPa. Here, we also propose a mechanism for the formation of activated carbon from spent coffee grounds. At low temperatures, the material has two distinct types with low and high surface areas; however, activation at elevated temperatures drives off the low surface area carbon, leaving behind the porous high surface area activated carbon.

Highly sensitive and simple SERS substrate based on photochemically generated carbon nanotubes-gold nanorods hybrids.

PubMed

Caires, A J; Vaz, R P; Fantini, C; Ladeira, L O

2015-10-01

We report a simple and easy formation of hybrids between multi-wall carbon nanotubes and gold nanorods by one-pot in situ photochemical synthesis. Measurements of surface-enhanced Raman scattering (SERS) through the effect "coffee ring" in visible and near infrared (NIR) show high sensitivity with detection of nanomolar concentrations of aromatic dyes. The formation of nanocomposites between carbon nanotubes and gold nanorods without chemical binders simplifies the preparation. Photochemical synthesis is an advance over the techniques previously published. Copyright © 2015 Elsevier Inc. All rights reserved.
Laser ablation of a silicon target in chloroform: formation of multilayer graphite nanostructures

NASA Astrophysics Data System (ADS)

Abderrafi, Kamal; García-Calzada, Raúl; Sanchez-Royo, Juan F.; Chirvony, Vladimir S.; Agouram, Saïd; Abargues, Rafael; Ibáñez, Rafael; Martínez-Pastor, Juan P.

2013-04-01

With the use of high-resolution transmission electron microscopy, selected area electron diffraction and x-ray photoelectron spectroscopy methods of analysis we show that the laser ablation of a Si target in chloroform (CHCl3) by nanosecond UV pulses (40 ns, 355 nm) results in the formation of about 50-80 nm core-shell nanoparticles with a polycrystalline core composed of small (5-10 nm) Si and SiC mono-crystallites, the core being coated by several layers of carbon with the structure of graphite (the shell). In addition, free carbon multilayer nanostructures (carbon nano-onions) are also found in the suspension. On the basis of a comparison with similar laser ablation experiments implemented in carbon tetrachloride (CCl4), where only bare (uncoated) Si nanoparticles are produced, we suggest that a chemical (solvent decomposition giving rise to highly reactive CH-containing radicals) rather than a physical (solvent atomization followed by carbon nanostructure formation) mechanism is responsible for the formation of graphitic shells. The silicon carbonization process found for the case of laser ablation in chloroform may be promising for silicon surface protection and functionalization.
Sorption of trivalent lanthanides and actinides onto montmorillonite: Macroscopic, thermodynamic and structural evidence for ternary hydroxo and carbonato surface complexes on multiple sorption sites.

PubMed

Fernandes, M Marques; Scheinost, A C; Baeyens, B

2016-08-01

The credibility of long-term safety assessments of radioactive waste repositories may be greatly enhanced by a molecular level understanding of the sorption processes onto individual minerals present in the near- and far-fields. In this study we couple macroscopic sorption experiments to surface complexation modelling and spectroscopic investigations, including extended X-ray absorption fine structure (EXAFS) and time-resolved laser fluorescence spectroscopies (TRLFS), to elucidate the uptake mechanism of trivalent lanthanides and actinides (Ln/An(III)) by montmorillonite in the absence and presence of dissolved carbonate. Based on the experimental sorption isotherms for the carbonate-free system, the previously developed 2 site protolysis non electrostatic surface complexation and cation exchange (2SPNE SC/CE) model needed to be complemented with an additional surface complexation reaction onto weak sites. The fitting of sorption isotherms in the presence of carbonate required refinement of the previously published model by reducing the strong site capacity and by adding the formation of Ln/An(III)-carbonato complexes both on strong and weak sites. EXAFS spectra of selected Am samples and TRLFS spectra of selected Cm samples corroborate the model assumptions by showing the existence of different surface complexation sites and evidencing the formation of Ln/An(III) carbonate surface complexes. In the absence of carbonate and at low loadings, Ln/An(III) form strong inner-sphere complexes through binding to three Al(O,OH)6 octahedra, most likely by occupying vacant sites in the octahedral layers of montmorillonite, which are exposed on {010} and {110} edge faces. At higher loadings, Ln/An(III) binds to only one Al octahedron, forming a weaker, edge-sharing surface complex. In the presence of carbonate, we identified a ternary mono- or dicarbonato Ln/An(III) complex binding directly to one Al(O,OH)6 octahedron, revealing that type-A ternary complexes form with the one or two carbonate groups pointing away from the surface into the solution phase. Within the spectroscopically observable concentration range these complexes could only be identified on the weak sites, in line with the small strong site capacity suggested by the refined sorption model. When the solubility of carbonates was exceeded, formation of an Am carbonate hydroxide could be identified. The excellent agreement between the thermodynamic model parameters obtained by fitting the macroscopic data, and the spectroscopically identified mechanisms, demonstrates the mature state of the 2SPNE SC/CE model for predicting and quantifying the retention of Ln/An(III) elements by montmorillonite-rich clay rocks. Copyright © 2016 Elsevier Ltd. All rights reserved.
Ultrathin Hydrophobic Coatings Obtained on Polyethylene Terephthalate Materials in Supercritical Carbon Dioxide with Co-Solvents

NASA Astrophysics Data System (ADS)

Kumeeva, T. Yu.; Prorokova, N. P.

2018-02-01

The surface properties of ultradisperse polytetrafluoroethylene coatings on polyethylene terephthalate materials modified in a supercritical carbon dioxide medium with co-solvent additions (aliphatic alcohols) were analyzed. An atomic force microscopy study revealed the peculiarities of the morphology of the hydrophobic coatings formed in the presence of co-solvents. The contribution of the co-solvents to the formation of the surface layer with a low surface energy was evaluated from the surface energy components of the modified polyester material. The stability of the coatings against dry friction was analyzed.
Cryogenic Carbonate Formation on Mars: Clues from Stable Isotope Variations Seen in Experimental Studies

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Niles, Paul B.; Fu, Qi; Gibson, Everett K., Jr.

2010-01-01

Discoveries of large deposits of sedimentary materials on the planet Mars by landers and orbiters have confirmed the widely held hypothesis that water has played a crucial role in the development of the martian surface. Recent studies have indicated that both water ice and liquid water may have been present and in the case of water ice perhaps is still present on or near the surface of Mars. However, there remains much controversy about the prevailing atmospheric conditions and climate of Mars during its history and whether liquid water existed on the martian surface simply during discrete geological events or whether this water was present over relatively much longer geologic time periods. The recent identification of Ca-rich carbonate by the Phoenix lander as well as its measurement of the isotopic composition of atmospheric CO2 has shown the importance of understanding the carbonates on Mars as an important sink of atmospheric carbon. This work compliments that of our past experiments where we produced cryogenic calcite in open containers, as analogs for terrestrial aufeis formation, and as a means for evaluating the fractionation of C-13 in CO2 during bicarbonate freezing [13]. Unlike our previous experiments in which carbonates were grown in ambient laboratory condition in open containers (atmospheric pressure and composition), this work attempts to quantify the amount of delta C-13 enrichment possible in both fluids and secondary carbonates formed from freezing of bicarbonate fluids under martian-like atmospheric conditions. Morphologic textures of produced carbonates in these experiments are also examined under SEM in order to identify the effect that the cryogenic freezing process has on the mineral's mineralogy. Understanding the role of kinetic isotope fractionation during formation of carbonates under martian-like conditions will aid in our ability to quantify the isotopic composition of the carbonate sink furthering our ability to model the climate history of Mars.
Effect of carbonic anhydrase on silicate weathering and carbonate formation at present day CO2 concentrations compared to primordial values

PubMed Central

Xiao, Leilei; Lian, Bin; Hao, Jianchao; Liu, Congqiang; Wang, Shijie

2015-01-01

It is widely recognized that carbonic anhydrase (CA) participates in silicate weathering and carbonate formation. Nevertheless, it is still not known if the magnitude of the effect produced by CA on surface rock evolution changes or not. In this work, CA gene expression from Bacillus mucilaginosus and the effects of recombination protein on wollastonite dissolution and carbonate formation under different conditions are explored. Real-time fluorescent quantitative PCR was used to explore the correlation between CA gene expression and sufficiency or deficiency in calcium and CO2 concentration. The results show that the expression of CA genes is negatively correlated with both CO2 concentration and ease of obtaining soluble calcium. A pure form of the protein of interest (CA) is obtained by cloning, heterologous expression, and purification. The results from tests of the recombination protein on wollastonite dissolution and carbonate formation at different levels of CO2 concentration show that the magnitudes of the effects of CA and CO2 concentration are negatively correlated. These results suggest that the effects of microbial CA in relation to silicate weathering and carbonate formation may have increased importance at the modern atmospheric CO2 concentration compared to 3 billion years ago. PMID:25583135
MN Carbonates in the Martian Meteorite Nakhla: Possible Evidence of Brine Evaporation

NASA Technical Reports Server (NTRS)

Bailey, J. V.; McKay, D. S.; Wentworth, S. J.

2003-01-01

The importance of secondary phases in martian meteorites lies in their potential to provide clues about the martian environments responsible for their formation. During this study, we analyzed a number of carbonate-bearing fracture surfaces from the Nakhla meteorite. Here we describe the physical and chemical properties of several manganese-calcium-rich siderites. Additionally, we describe a potential model for the formation and alteration of these carbonates, and we suggest constraints on the conditions responsible for their precipitation. Nakhla is an olivine-bearing clinopyroxenite with minor amounts of feldspar, FeS, and Fe oxides. Secondary mineral assemblages include vein filling clay with embedded iron oxides, a calcium sulfate, amorphous silica, chlorapatite, halite and carbonates. Bridges and Grady suggested that the carbonates in Nakhla formed from brine evaporation. Isotope studies of the Mn rich siderite are also consistent with formation from hydrothermal fluids with an upper T constraint of 170 C.
The long-term carbon cycle, fossil fuels and atmospheric composition.

PubMed

Berner, Robert A

2003-11-20

The long-term carbon cycle operates over millions of years and involves the exchange of carbon between rocks and the Earth's surface. There are many complex feedback pathways between carbon burial, nutrient cycling, atmospheric carbon dioxide and oxygen, and climate. New calculations of carbon fluxes during the Phanerozoic eon (the past 550 million years) illustrate how the long-term carbon cycle has affected the burial of organic matter and fossil-fuel formation, as well as the evolution of atmospheric composition.
Interaction of scandium and titanium atoms with a carbon surface containing five- and seven-membered rings

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

Krasnov, P. O., E-mail: kpo1980@gmail.com; Eliseeva, N. S.; Kuzubov, A. A., E-mail: alex_xx@rambler.ru

2012-01-15

The use of carbon nanotubes coated by atoms of transition metals to store molecular hydrogen is associated with the problem of the aggregation of these atoms, which leads to the formation of metal clusters. The quantum-chemical simulation of cluster models of the carbon surface of a graphene type with scandium and titanium atoms has been performed. It has been shown that the presence of five- and seven-membered rings, in addition to six-membered rings, in these structures makes it possible to strongly suppress the processes of the migration of metal atoms over the surface, preventing their clustering.
The effects of liquid-phase oxidation of multiwall carbon nanotubes on their surface characteristics

NASA Astrophysics Data System (ADS)

Burmistrov, I. N.; Muratov, D. S.; Ilinykh, I. A.; Kolesnikov, E. A.; Godymchuk, A. Yu; Kuznetsov, D. V.

2016-01-01

The development of new sorbents based on nanostructured carbon materials recently became a perspective field of research. Main topic of current study is to investigate the effect of different regimes of multiwall carbon nanotubes (MWCNT) surface modification process on their structural characteristics. MWCNT samples were treated with nitric acid at high temperature. Structural properties were studied using low temperature nitrogen adsorption and acid-base back titration methods. The study showed that diluted nitric acid does not affect MWCNT structure. Concentrated nitric acid treatment leads to formation of 2.8 carboxylic groups per 1 nm2 of the sample surface.
Influence of Carbon interstitials to Ti1-xMexN (Me = Zr, Al, Cr) coatings by pulsed laser ablation on wear resistance

NASA Astrophysics Data System (ADS)

Jeon, Seol; Hong, Eunpyo; Kwon, Se-Hun; Lee, Heesoo

2018-06-01

The wear resistance of Ti1-xMexN (Me = Zr, Al, Cr) coatings by the laser carburization process was investigated in terms of local atomic structural changes. The repeated pulsed laser ablation was performed to the Ti1-xMexN coating surfaces after Graphite paste was covered. The friction coefficients of the coating specimens were decreased from ∼0.7 to 0.2, and the formation of cracks and debris was suppressed by implementing the laser ablation process. ToF-SIMS depth profiles showed that the laser carburization helps Carbon penetrate into the coating layer as deep as ∼20 nm below its surface. XPS and XAFS analyses revealed that the improvement of the wear resistance of the coatings was achieved not by formation of TiC or ZrC lattices on the coatings surfaces but by Carbon interstitials to the Ti1-xMexN lattices.
Fluorine interaction with defects on graphite surface by a first-principles study

NASA Astrophysics Data System (ADS)

Wang, Song; Xuezhi, Ke; Zhang, Wei; Gong, Wenbin; Huai, Ping; Zhang, Wenqing; Zhu, Zhiyuan

2014-02-01

The interaction between fluorine atom and graphite surface has been investigated in the framework of density functional theory. Due to the consideration of molten salt reactor system, only carbon adatoms and vacancies are chemical reactive for fluorine atoms. Fluorine adsorption on carbon adatom will enhance the mobility of carbon adatom. Carbon adatom can also be removed easily from graphite surface in form of CF2 molecule, explaining the formation mechanism of CF2 molecule in previous experiment. For the interaction between fluorine and vacancy, we find that fluorine atoms which adsorb at vacancy can hardly escape. Both pristine surface and vacancy are impossible for fluorine to penetrate due to the high penetration barrier. We believe our result is helpful to understand the compatibility between graphite and fluorine molten salt in molten salt reactor system.
Electron Transfer Strategies Regulate Carbonate Mineral and Micropore Formation

NASA Astrophysics Data System (ADS)

Zeng, Zhirui; Tice, Michael M.

2018-01-01

Some microbial carbonates are robust biosignatures due to their distinct morphologies and compositions. However, whether carbonates induced by microbial iron reduction have such features is unknown. Iron-reducing bacteria use various strategies to transfer electrons to iron oxide minerals (e.g., membrane-bound enzymes, soluble electron shuttles, nanowires, as well as different mechanisms for moving over or attaching to mineral surfaces). This diversity has the potential to create mineral biosignatures through manipulating the microenvironments in which carbonate precipitation occurs. We used Shewanella oneidensis MR-1, Geothrix fermentans, and Geobacter metallireducens GS-15, representing three different strategies, to reduce solid ferric hydroxide in order to evaluate their influence on carbonate and micropore formation (micro-size porosity in mineral rocks). Our results indicate that electron transfer strategies determined the morphology (rhombohedral, spherical, or long-chained) of precipitated calcium-rich siderite by controlling the level of carbonate saturation and the location of carbonate formation. Remarkably, electron transfer strategies also produced distinctive cell-shaped micropores in both carbonate and hydroxide minerals, thus producing suites of features that could potentially serve as biosignatures recording information about the sizes, shapes, and physiologies of iron-reducing organisms.
Dust in brown dwarfs and extrasolar planets. V. Cloud formation in carbon- and oxygen-rich environments

NASA Astrophysics Data System (ADS)

Helling, Ch.; Tootill, D.; Woitke, P.; Lee, G.

2017-07-01

Context. Recent observations indicate potentially carbon-rich (C/O > 1) exoplanet atmospheres. Spectral fitting methods for brown dwarfs and exoplanets have invoked the C/O ratio as additional parameter but carbon-rich cloud formation modeling is a challenge for the models applied. The determination of the habitable zone for exoplanets requires the treatment of cloud formation in chemically different regimes. Aims: We aim to model cloud formation processes for carbon-rich exoplanetary atmospheres. Disk models show that carbon-rich or near-carbon-rich niches may emerge and cool carbon planets may trace these particular stages of planetary evolution. Methods: We extended our kinetic cloud formation model by including carbon seed formation and the formation of C[s], TiC[s], SiC[s], KCl[s], and MgS[s] by gas-surface reactions. We solved a system of dust moment equations and element conservation for a prescribed Drift-Phoenixatmosphere structure to study how a cloud structure would change with changing initial C/O0 = 0.43...10.0. Results: The seed formation efficiency is lower in carbon-rich atmospheres than in oxygen-rich gases because carbon is a very effective growth species. The consequence is that fewer particles make up a cloud if C/O0 > 1. The cloud particles are smaller in size than in an oxygen-rich atmosphere. An increasing initial C/O ratio does not revert this trend because a much greater abundance of condensible gas species exists in a carbon-rich environment. Cloud particles are generally made of a mix of materials: carbon dominates if C/O0 > 1 and silicates dominate if C/O0 < 1. A carbon content of 80-90% carbon is reached only in extreme cases where C/O0 = 3.0 or 10.0. Conclusions: Carbon-rich atmospheres form clouds that are made of particles of height-dependent mixed compositions, sizes and numbers. The remaining gas phase is far less depleted than in an oxygen-rich atmosphere. Typical tracer molecules are HCN and C2H2 in combination with a featureless, smooth continuum due to a carbonaceous cloud cover, unless the cloud particles become crystalline.
Surface Chemistry of Perovskite-Type Electrodes During High Temperature CO2 Electrolysis Investigated by Operando Photoelectron Spectroscopy.

PubMed

Opitz, Alexander K; Nenning, Andreas; Rameshan, Christoph; Kubicek, Markus; Götsch, Thomas; Blume, Raoul; Hävecker, Michael; Knop-Gericke, Axel; Rupprechter, Günther; Klötzer, Bernhard; Fleig, Jürgen

2017-10-18

Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO 2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H 2 ) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO 3-δ and (La,Sr)CrO 3-δ based perovskite-type electrodes was studied during electrochemical CO 2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO 2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO 2 reduction. In contrast to water splitting, the CO 2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view.
Surface Chemistry of Perovskite-Type Electrodes During High Temperature CO2 Electrolysis Investigated by Operando Photoelectron Spectroscopy

PubMed Central

2017-01-01

Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H2) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO3−δ and (La,Sr)CrO3−δ based perovskite-type electrodes was studied during electrochemical CO2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO2 reduction. In contrast to water splitting, the CO2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view. PMID:28933825
Carbonate formation on bioactive glasses.

PubMed

Cerruti, Marta; Morterra, Claudio

2004-07-20

The system termed 58S is a sol-gel-synthesized bioactive glass composed of SiO2, CaO, and P2O5, used in medicine as bone prosthetic because, when immersed in a physiological fluid, a layer of hydroxycarbonate apatite is formed on its surface. The mechanism of bioactive glass 58S carbonation was studied in the vacuum by means of in-situ FTIR spectroscopy with the use of CO2, H2O, and CD3CN as probe molecules. The study in the vacuum was necessary to identify both the molecules specifically involved in the carbonation process and the type of carbonates formed. Bioactive glass 58S was compared to a Ca-doped silica and to CaO. On CaO, ionic carbonates could form by contact with CO2 alone, whereas on 58S and on Ca-doped silica carbonation occurred only if both CO2 and an excess of H2O were present on the sample. The function of H2O was not only to block surface cationic sites, so that CO2 could not manifest its Lewis base behavior, but also to form a liquid-like (mono)layer that allowed the formation of carbonate ions. The presence of H2O is also supposed to promote Ca2+ migration from the bulk to the surface. Carbonates formed at the surface of CaO and of Ca-bearing silicas (thus including bioactive glasses) are of the same type, but are produced through two different mechanisms. The finding that a water excess is necessary to start heavy carbonation on bioactive glasses seemed to imply that the mechanism leading to in-situ carbonation simulates, in a simplified and easy-to-reproduce system, what happens both in solution, when carbonates are incorporated in the apatite layer, and during sample shelf-aging. Copyright 2004 American Chemical Society
Grafting of activated carbon cloths for selective adsorption

NASA Astrophysics Data System (ADS)

Gineys, M.; Benoit, R.; Cohaut, N.; Béguin, F.; Delpeux-Ouldriane, S.

2016-05-01

Chemical functionalization of an activated carbon cloth with 3-aminophthalic acid and 4-aminobenzoic acid groups by the in situ formation of the corresponding diazonium salt in aqueous acidic solution is reported. The nature and amount of selected functions on an activated carbon surface, in particular the grafted density, were determined by potentiometric titration, elemental analysis and X-ray photoelectron spectroscopy (XPS). The nanotextural properties of the modified carbon were explored by gas adsorption. Functionalized activated carbon cloth was obtained at a discrete grafting level while preserving interesting textural properties and a large porous volume. Finally, the grafting homogeneity of the carbon surface and the nature of the chemical bonding were investigated using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) technique.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Arendt, Paul N.; DePaula, Ramond F.; Zhu, Yuntian T.

An array of carbon nanotubes is prepared by exposing a catalyst structure to a carbon nanotube precursor. Embodiment catalyst structures include one or more trenches, channels, or a combination of trenches and channels. A system for preparing the array includes a heated surface for heating the catalyst structure and a cooling portion that cools gas above the catalyst structure. The system heats the catalyst structure so that the interaction between the precursor and the catalyst structure results in the formation of an array of carbon nanotubes on the catalyst structure, and cools the gas near the catalyst structure and alsomore » cools any carbon nanotubes that form on the catalyst structure to prevent or at least minimize the formation of amorphous carbon. Arrays thus formed may be used for spinning fibers of carbon nanotubes.« less
Nanoscale Silicon as a Catalyst for Graphene Growth: Mechanistic Insight from in Situ Raman Spectroscopy

DOE PAGES

Share, Keith; Carter, Rachel E.; Nikolaev, Pavel; ...

2016-06-08

Nanoscale carbons are typically synthesized by thermal decomposition of a hydrocarbon at the surface of a metal catalyst. Whereas the use of silicon as an alternative to metal catalysts could unlock new techniques to seamlessly couple carbon nanostructures and semiconductor materials, stable carbide formation renders bulk silicon incapable of the precipitation and growth of graphitic structures. In this article, we provide evidence supported by comprehensive in situ Raman experiments that indicates nanoscale grains of silicon in porous silicon (PSi) scaffolds act as catalysts for hydrocarbon decomposition and growth of few-layered graphene at temperatures as low as 700 K. Self-limiting growthmore » kinetics of graphene with activation energies measured between 0.32–0.37 eV elucidates the formation of highly reactive surface-bound Si radicals that aid in the decomposition of hydrocarbons. Nucleation and growth of graphitic layers on PSi exhibits striking similarity to catalytic growth on nickel surfaces, involving temperature dependent surface and subsurface diffusion of carbon. Lastly, this work elucidates how the nanoscale properties of silicon can be exploited to yield catalytic properties distinguished from bulk silicon, opening an important avenue to engineer catalytic interfaces combining the two most technologically important materials for modern applications—silicon and nanoscale carbons.« less

Vacancy Mediated Mechanism of Nitrogen Substitution in Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Srivastava, Deepak; Menon, Madhu; Sadanadan, Bindu; Rao, Apparao M.

2003-01-01

Nitrogen substitution reaction in a graphene sheet and carbon nanotubes of different diameter are investigated using the generalized tight-binding molecular dynamics method. The formation of a vacancy in curved graphene sheet or a carbon nanotube is found to cause a curvature dependent local reconstruction of the surface. Our simulations and analysis show that vacancy mediated N substitution (rather than N chemisorption) is favored on the surface of nanotubes with diameter larger than 8 nm. This predicted value of the critical minimum diameter for N incorporation is confirmed by experimental results presented.
Paleoweathering features in the Sergi Formation (Jurassic-Cretaceous), northeastern Brazil, and implications for hydrocarbon exploration

NASA Astrophysics Data System (ADS)

Pierini, Cristina; Mizusaki, Ana M.; Pimentel, Nuno; Faccini, Ubiratan F.; Scherer, Claiton M. S.

2010-03-01

Paleoweathering in the Sergi Formation has been classified and analyzed to ascertain its origin and relationship with stratigraphic evolution. The Sergi Formation belongs to the pre-rift sequence of the Recôncavo Basin (northeastern Brazil) and comprises a complex association of eolian and fluvial sandstones and lacustrine mudstones. This formation can be subdivided into three depositional sequences bounded by regional unconformities. Four paleoweathering types, each one related to a distinct origin, have been described in the Sergi Formation: (1) textural mottling, which is distinguished by alternating rock colors as a result of the iron oxide mobilization within mineral phases that evolved under alternating oxidation (yellowish, brownish and reddish shades) and reduction (grayish or greenish hues) conditions; (2) non-textural mottling, which displays a discoloration pattern that is independent of the original rock texture; (3) carbonate concentrations, usually related to carbonate nodule formation, which display a massive internal structure that reveals their origin through continuous growth or crystallization; and (4) banded carbonates (silicified), associated with the beginning of regular surface formation due to the chemical precipitation of carbonates within lacustrine environments. Both mottling color motifs and carbonate accumulation usually represent groundwater oscillation rather than pedogenesis. Only carbonate intraclasts and banded carbonate (silicified) have their origin ascribed to pedogenesis sensu stricto, although the carbonate intraclasts do not represent soil deposits in situ, but calcretes eroded from areas close to channels, and the banded carbonates (silicified) have strong diagenetic modifications. Therefore, it is reasonable to assume that fluvial and meteoric water have controlled paleoweathering evolution as well as deposition, yet both aspects are ruled by the same mechanisms (relief, sedimentation rate and, above all, climate).
Carbon storage potential of Columbia River flood basalt

NASA Astrophysics Data System (ADS)

Wells, R. K.; Xiong, W.; Giammar, D.; Skemer, P. A.

2017-12-01

Basalt reservoirs are an important option for sequestering carbon through dissolution of host rock and precipitation of stable carbonate minerals. This study seeks to understand the nature of dissolution and surface roughening processes and their influence on the timing and spatial distribution of carbonation, in static experiments at 150 °C and 100 bar CO2. Intact samples and cores with milled pathways from Ca-rich and Fe-rich Columbia River flood basalt formations were reacted for up to 40 weeks. Experimental specimens were analyzed using SEM-EDS, microprobe, and μCT scanning, Raman spectroscopy, and 2D profilometer to characterize changes in composition and surface roughness. ICP-MS was used to examine bulk fluid chemistry. Initial dissolution of olivine grains results in higher Mg2+ and Fe2+ concentrations within the bulk solution in the first week of reaction. However, once available olivine grains are gone, Ca-rich pyroxene becomes the primary contributor of Ca2+, Mg2+, and Fe2+ within the bulk solution. The complete dissolution of olivine grains resulted in pits up to 200 μm deep. Dissolution of other minerals resulted in the formation of microscale textures, primarily along grain boundaries and fractures. The surface roughness increased by factors of up to 42, while surface area increased 20%. Based on these results, pyroxene is the sustaining contributor of divalent metal cations during dissolution of basalt, and the limited connectivity of olivine and pyroxene grains limits the exposure of new reactive surface areas. Within 6 weeks, aragonite precipitated in Ca-rich basalt samples, while Fe-rich samples precipitated of siderite. The highest concentration of carbonates occurs 1/3 into milled pathways, which simulate dead-end fractures, in low porosity basalts, and near the fracture tip in high porosity basalts. Even at elevated temperatures, the fractures are not blocked nor filled within 40 weeks of reaction. When vesicles are present, carbonates can precipitate within these pores even when the pores do not appear to connect to the main fracture pathway. Based on our experimental results, we estimate the carbon storage potential of the Ca-rich formations within the Columbia River flood basalt to be 47 kg CO2/m3, which could be reached in 38 years at a constant carbonation rate of 1.24 ± 0.54 kg CO2/m3yr.
A novel carbon electrode material for highly improved EDLC performance.

PubMed

Fang, Baizeng; Binder, Leo

2006-04-20

Porous materials, developed by grafting functional groups through chemical surface modification with a surfactant, represent an innovative concept in energy storage. This work reports, in detail, the first practical realization of a novel carbon electrode based on grafting of vinyltrimethoxysilane (vtmos) functional group for energy storage in electric double layer capacitor (EDLC). Surface modification with surfactant vtmos enhances the hydrophobisation of activated carbon and the affinity toward propylene carbonate (PC) solvent, which improves the wettability of activated carbon in the electrolyte solution based on PC solvent, resulting in not only a lower resistance to the transport of electrolyte ions within micropores of activated carbon but also more usable surface area for the formation of electric double layer, and accordingly, higher specific capacitance, energy density, and power capability available from the capacitor based on modified carbon. Especially, the effects from surface modification become superior at higher discharge rate, at which much better EDLC performance (i.e., much higher energy density and power capability) has been achieved by the modified carbon, suggesting that the modified carbon is a novel and very promising electrode material of EDLC for large current applications where both high energy density and power capability are required.
Formation of CO2, H2 and condensed carbon from siderite dissolution in the 200-300 °C range and at 50 MPa

NASA Astrophysics Data System (ADS)

Milesi, Vincent; Guyot, François; Brunet, Fabrice; Richard, Laurent; Recham, Nadir; Benedetti, Marc; Dairou, Julien; Prinzhofer, Alain

2015-04-01

Laboratory experiments were conducted to investigate the chemical processes governing the carbon speciation associated to hydrothermal decomposition of siderite. Experiments were carried out in sealed gold capsules using synthetic siderite and deionised water. The samples were reacted at 200 and 300 °C, under a pressure of 50 MPa. Siderite dissolved to reach the 3FeCO3 + H2O = Fe3O4 + 3CO2 + H2 equilibrium and magnetite, Fe3O4, was produced accordingly. The gas phase was dominated by CO2, H2 and CH4, the latter being in strong thermodynamic disequilibrium with CO2. Contrary to the other gas products, H2 concentration was found to decrease with run duration. TEM observations showed the occurrence of condensed carbon phases at the surfaces of magnetite and residual siderite grains. Thermodynamic calculations predict the formation of condensed carbon in the experiments according to the reaction: CO2 + 2H2 ⇒ C + 2H2O, which accounted for the observed H2 concentration decrease up to the point where H2 and CO2 activities were buffered by the graphite-siderite-magnetite assemblage. The well-organized structure of the carbon coating around magnetite emphasizes the high catalytic potential of magnetite surface for carbon reduction and polymerization. The formation of such C-rich phases may represent a potential source of CH4 by hydrogenation. On the other hand, the catalysis of Fischer-Tropsch type reactions may be poisoned by the presence of carbon coating on mineral surfaces. In any case, this study also demonstrates that abiotic H2 generation by water reduction, widely studied in recent years in ultrabasic contexts, can also occur in sedimentary contexts where siderite is present. We show that, in the latter case, natural H2 concentration will be buffered by a condensed carbon phase associated with magnetite.
Carbon nanoscrolls by pyrolysis of a polymer

NASA Astrophysics Data System (ADS)

Yadav, Prasad; Warule, Sambhaji; Jog, Jyoti; Ogale, Satishchandra

2012-12-01

3D network of carbon nanoscrolls was synthesized starting from pyrolysis of poly(acrylic acid-co-maleic acid) sodium salt. It is a catalyst-free process where pyrolysis of polymer leads to formation of carbon form and sodium carbonate. Upon water soaking of pyrolysis product, the carbon form undergoes self-assembly to form carbon nanoscrolls. The interlayer distance between the walls of carbon nanoscroll was found to be 0.34 nm and the carbon nanoscrolls exhibited a surface area of 188 m2/g as measured by the BET method.
Molecular dynamics studies of water deposition on hematite surfaces

NASA Astrophysics Data System (ADS)

Kvamme, Bjørn; Kuznetsova, Tatiana; Haynes, Martin

2012-12-01

The interest in carbon dioxide for enhanced oil recovery is increasing proportional to the decrease in naturally driven oil production and also due to the increasing demand for reduced emission of carbon dioxide to the atmosphere. Transport of carbon dioxide in offshore pipelines involves high pressure and low temperatures which may lead to the formation of hydrate between residual water dissolved in carbon dioxide. The critical question is whether the water at some condition of temperature and pressure will drop out as liquid droplets or as water adsorbed on the surfaces of the pipeline and then subsequently form hydrates heterogeneously. In this work we have used the 6-311G basis set with B3LYP to estimate the charge distribution of different sizes of hematite crystals. The obtained surface charge distribution were kept unchanged while the inner charge distribution where scaled so as to result in an overall neutral crystal. These rust particles were embedded in water and chemical potential for adsorbed water molecules were estimated through thermodynamic integration and compared to similar estimates for same size water cluster. Estimated values of water chemical potentials indicate that it is thermodynamically favorable for water to adsorb on hematite, and that evaluation of potential carbon dioxide hydrate formation conditions and kinetics should be based this sequence of processes.
Red mud carbonation using carbon dioxide: Effects of carbonate and calcium ions on goethite surface properties and settling.

PubMed

Liang, Gaojie; Chen, Wenmi; Nguyen, Anh V; Nguyen, Tuan A H

2018-05-01

Carbonation using CO 2 appears as an attractive solution for disposing of red mud suspensions, an aluminum industry hazardous waste since it also offers an option for CO 2 sequestration. Here we report the novel findings that CO 3 2- together with Ca 2+ can significantly affect the surface properties and settling of goethite, a major component of red mud. Specifically, their effects on the goethite surface chemistry, colloidal interaction forces and settling in alkaline solutions are investigated. The surface potential becomes more negative by the formation of carbonate inner-sphere complexes on goethite surface. It is consistent with the strong repulsion, decreased particle size and settling velocity with increased carbonate concentrations as measured by atomic force microscopy, particle size analysis, and particle settling. Adding Ca 2+ that forms outer-sphere complexes with pre-adsorbed carbonate changes goethite surface charge negligibly. Changing repulsion to the attraction between goethite surfaces by increasing calcium dosage indicates the surface bridging, in accordance with the increased settling velocity. The adverse effect of carbonate on goethite flocculation is probably due to its specific chemisorption and competition with flocculants. By forming outer-sphere complexes together with the flocculant-calcium bridging effect, calcium ions can eliminate the negative influence of carbonate and improve the flocculation of goethite particles. These findings contribute to a better understanding of goethite particle interaction with salt ions and flocculants in controlling the particle behavior in the handling processes, including the red mud carbonation. Copyright © 2018 Elsevier Inc. All rights reserved.
Effect of Ar ion on the surface properties of low density polyethylene

NASA Astrophysics Data System (ADS)

Zaki, M. F.

2016-04-01

In this paper, low-density polyethylene (LDPE) was irradiated by argon ion with different fluences up to 1015ions/cm2. The optical, chemical and hardness properties have been investigated using UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and micro-indentation tester, respectively. The results showed the ion beam bombardment induced decreases in the transmittance of the irradiated polymer samples. This change in transmittance can be attributed to the formation of conjugated bonds i.e. possible formation of defects and/or carbon clusters. The indirect optical band gap decreased from 3.0 eV for the pristine sample to 2.3 eV for that sample irradiated with the highest fluence of the Ar ion beam. Furthermore, the number of carbon atoms and clusters increased with increasing Ar ion fluences. FTIR spectra showed the formation of new bands of the bombarded polymer samples. Furthermore, polar groups were created on the surface of the irradiated samples which refer to the increase of the hydrophilic nature of the surface of the irradiated samples. The Vicker's hardness increased from 4.9 MPa for the pristine sample to 17.9 MPa for those bombarded at the highest fluence. This increase is attributed to the increase in the crosslinking and alterations of the bombarded surface into hydrogenated amorphous carbon, which improves the hardness of the irradiated samples. The bombarded LDPE surfaces may be used in special applications to the field of the micro-electronic devices and shock absorbers.
Study of different carbon materials for their use as bioanodes in microbial fuel cells.

PubMed

González-Nava, Catalina; Godínez, Luis A; Chávez, Abraham U; Cercado, Bibiana; Arriaga, Luis G; Rodríguez-Valadez, Francisco J

2016-01-01

Microbial fuel cells (MFCs) are capable of removing the organic matter contained in water while generating a certain amount of electrical power at the same time. One of the most important aspects in the operation of MFCs is the formation of biofilms on the anode. Here, we report the characterization of different carbon electrodes and biofilm using a rapid and easy methodology for the growth of biofilms. The biofilms were developed and generated a voltage in less than 4 days, obtaining a maximum of 0.3 V in the cells. Scanning electron microscopy images revealed that growth of the biofilm was only on the surface of the electrode, and consequently both carbon cloth Electrochem and carbon cloth Roe materials showed a greater quantity of volatile solids on the surface of the anode and power density. The results suggested that the best support was carbon cloth Electrochem because it generated a power density of 13.4 mW/m(2) and required only a few hours for the formation of the biofilm.
Microscopic Study of Carbon Surfaces Interacting with High Carbon Ferromanganese Slag

NASA Astrophysics Data System (ADS)

Safarian, Jafar; Kolbeinsen, Leiv

2015-02-01

The interaction of carbon materials with molten slags occurs in many pyro-metallurgical processes. In the production of high carbon ferromanganese in submerged arc furnace, the carbothermic reduction of MnO-containing silicate slags yields the metal product. In order to study the interaction of carbon with MnO-containing slags, sessile drop wettability technique is employed in this study to reduce MnO from a molten slag drop by carbon substrates. The interfacial area on the carbon substrate before and after reaction with slag is studied by scanning electron microscope. It is indicated that no Mn metal particles are found at the interface through the reduction of the MnO slag. Moreover, the reduction of MnO occurs through the contribution of Boudouard reaction and it causes carbon consumption in particular active sites at the interface, which generate carbon degradation and open pore growth at the interface. It is shown that the slag is fragmented to many micro-droplets at the reaction interface, potentially due to the effect on the interfacial energies of a provisional liquid Mn thin film. The rapid reduction of these slag micro-droplets affects the carbon surface with making deep micro-pores. A mechanism for the formation of slag micro-droplets is proposed, which is based on the formation of provisional micro thin films of liquid Mn at the interface.
Using in situ synchrotron radiation wide angle X-ray scattering (WAXS) to study CaCO3 scale formation at ambient and elevated temperature.

PubMed

Chen, Tao; Neville, Anne; Sorbie, Ken; Zhong, Zhong

2007-01-01

The formation of calcium carbonate mineral scale is a persistent and expensive problem in oil and gas production, water piping systems, power generator, and batch precipitation. The aim of this paper is to further the understanding of scale formation and inhibition by in situ probing of crystal growth by synchrotron radiation wide angle X-ray scattering (WAXS) at ambient and elevated temperature. This novel technique enables in situ study of mineral scale formation and inhibition and as such, information on the nucleation and growth processes are accessible. This technique studies bulk precipitation and surface deposition in the same system and will be of great benefit to the understanding of an industrial scaling system. It offers an exciting prospect for the study of scaling. It has been shown that the nucleation and growth of various calcareous polymorphs and their individual crystal planes can be followed in real-time and from this the following conclusions are reached. The process of scale deposition on the surface can be divided into an unstable phase and a stable phase. The initial phase of crystallization of calcium carbonate is characterized by instability with individual planes from various vaterite and aragonite polymorphs emerging and subsequently disappearing under the hydrodynamic conditions. After the initial unstable phase, various calcium carbonate crystal planes adhere on the surface and then grow on the surface. At 25 degrees C, the main plane of surface deposit is calcite and a strong (104) peak is detected. The other calcite planes (102), (006), (110) (113) and (202) are hardly detectable under this condition. At 80 degrees C, the main planes in the surface deposit are the (104), (113) and (110) planes of calcite. Stable planes of vaterite and aragonite are also observed. This paper will discuss how surface scale evolves--exploring the power of the synchrotron in situ methodology.
Influence of inoculum type, inorganic salt and nitrogen to carbon ratio on sclerotium formation and carotenoid production in surface culture of Penicillium sp. PT95.

PubMed

Han, Jian-Rong; Xu, Jun; Zhou, Xiao-Mei

2002-01-01

This study examined the respective effect of inoculum type, inorganic salt and nitrogen to carbon ratio on sclerotium formation and carotenoid production in surface culture of Penicillium sp. PT95. Neither the spore inoculum nor the mycelial pellet inoculum could result in the formation of sclerotium on a modified Czapek agar medium after incubation of 28 days, whereas the inoculum in the form of sclerotium caused the formation of numerous orange, sand-shaped sclerotia after incubation of 14 days. Among four inorganic salts tested, K(2)HPO(4) was more essential to the sclerotium formation and carotenoid production of strain PT95 as compared to KCl, MgSO(4) or FeSO(4). It was also shown that the combination of K(2)HPO(4), KCl and MgSO(4) could produce the best positive cooperation and give the highest sclerotia biomass (782 mg/plate) and carotenoid content in sclerotium (420 microg/g of dry sclerotia) as well as pigment yield (328 microg/plate). The medium containing 0.24 approximately 0.48 g/l sodium nitrate-nitrogen was effective to both the sclerotium formation and carotenoid production of strain PT95 when available maltose-carbon concentrations were at 5.26 approximately 21.05 g/l. The optimal N:C ratio was found to be 1:25.
Autothermal reforming of aliphatic and aromatic hydrocarbon liquids

NASA Technical Reports Server (NTRS)

Flytzani-Stephanopoulos, M.; Voecks, G. E.

1983-01-01

Results are presented from a study of the autothermal reforming of paraffins and aromatics over nickel catalysts. The trials were performed to examine the carbon products that appear when steam is passed over hydrocarbon liquids to form H2-rich gases, i.e., the autothermal process (ATR). Attention was given to n-hexane, n-tetradecane, benzene, and benzene solutions of naphthalene with reactant preheat to 1000-1150 F. The carbon-formation limit was sought as a function of the steam-to-carbon and oxygen to carbon molar ratios at constant pressure and the preheat temperatures. The catalyst bed was examined after each trial to identify the locations and types of carbon formed using SEM, thermal gravimetric analysis, and X ray diffraction techniques. The hydrocarbon fuels each had a separate temperature and reaction profile, as well as carbon formation characteristics. No carbon formation was observed in the upper layer of the reactor bed, while both gas phase and surface-grown deposits were present in the lower part. The results are concluded of use in the study of No. 2 fuel oil for ATR feedstock.
Electron Transfer Strategies Regulate Carbonate Mineral and Micropore Formation.

PubMed

Zeng, Zhirui; Tice, Michael M

2018-01-01

Some microbial carbonates are robust biosignatures due to their distinct morphologies and compositions. However, whether carbonates induced by microbial iron reduction have such features is unknown. Iron-reducing bacteria use various strategies to transfer electrons to iron oxide minerals (e.g., membrane-bound enzymes, soluble electron shuttles, nanowires, as well as different mechanisms for moving over or attaching to mineral surfaces). This diversity has the potential to create mineral biosignatures through manipulating the microenvironments in which carbonate precipitation occurs. We used Shewanella oneidensis MR-1, Geothrix fermentans, and Geobacter metallireducens GS-15, representing three different strategies, to reduce solid ferric hydroxide in order to evaluate their influence on carbonate and micropore formation (micro-size porosity in mineral rocks). Our results indicate that electron transfer strategies determined the morphology (rhombohedral, spherical, or long-chained) of precipitated calcium-rich siderite by controlling the level of carbonate saturation and the location of carbonate formation. Remarkably, electron transfer strategies also produced distinctive cell-shaped micropores in both carbonate and hydroxide minerals, thus producing suites of features that could potentially serve as biosignatures recording information about the sizes, shapes, and physiologies of iron-reducing organisms. Key Words: Microbial iron reduction-Micropore-Electron transfer strategies-Microbial carbonate. Astrobiology 18, 28-36.
The role of beaded activated carbon's surface oxygen groups on irreversible adsorption of organic vapors.

PubMed

Jahandar Lashaki, Masoud; Atkinson, John D; Hashisho, Zaher; Phillips, John H; Anderson, James E; Nichols, Mark

2016-11-05

The objective of this study is to determine the contribution of surface oxygen groups to irreversible adsorption (aka heel formation) during cyclic adsorption/regeneration of organic vapors commonly found in industrial systems, including vehicle-painting operations. For this purpose, three chemically modified activated carbon samples, including two oxygen-deficient (hydrogen-treated and heat-treated) and one oxygen-rich sample (nitric acid-treated) were prepared. The samples were tested for 5 adsorption/regeneration cycles using a mixture of nine organic compounds. For the different samples, mass balance cumulative heel was 14 and 20% higher for oxygen functionalized and hydrogen-treated samples, respectively, relative to heat-treated sample. Thermal analysis results showed heel formation due to physisorption for the oxygen-deficient samples, and weakened physisorption combined with chemisorption for the oxygen-rich sample. Chemisorption was attributed to consumption of surface oxygen groups by adsorbed species, resulting in formation of high boiling point oxidation byproducts or bonding between the adsorbates and the surface groups. Pore size distributions indicated that different pore sizes contributed to heel formation - narrow micropores (<7Å) in the oxygen-deficient samples and midsize micropores (7-12Å) in the oxygen-rich sample. The results from this study help explain the heel formation mechanism and how it relates to chemically tailored adsorbent materials. Copyright © 2016 Elsevier B.V. All rights reserved.
Effect of diamond-like carbon thin film coated acrylic resin on candida albicans biofilm formation.

PubMed

Queiroz, José Renato Cavalcanti; Fissmer, Sara Fernanda; Koga-Ito, Cristiane Yumi; Salvia, Ana C R D; Massi, Marcos; Sobrinho, Argermiro Soares da Silva; Júnior, Lafayette Nogueira

2013-08-01

The purpose of this study was to evaluate the effect of diamond-like carbon thin films doped and undoped with silver nanoparticles coating poly(methyl methacrylate) (PMMA) on Candida albicans biofilm formation. The control of biofilm formation is important to prevent oral diseases in denture users. Forty-five PMMA disks were obtained, finished, cleaned in an ultrasonic bath, and divided into three groups: Gc, no surface coating (control group); Gdlc, coated with diamond-like carbon film; and Gag, coated with diamond-like carbon film doped with silver nanoparticles. The films were deposited using a reactive magnetron sputtering system (physical vapor deposition process). The specimens were characterized by optical profilometry, atomic force microscopy, and Rutherford backscattering spectroscopy analyses that determined differences in chemical composition and morphological structure. Following sterilization of the specimens by γ-ray irradiation, C. albicans (ATCC 18804) biofilms were formed by immersion in 2 ml of Sabouraud dextrose broth inoculated with a standardized fungal suspension. After 24 hours, the number of colony forming units (cfu) per specimen was counted. Data concerning biofilm formation were analyzed using ANOVA and the Tukey test (p < 0.05). C. albicans biofilm formation was significantly influenced by the films (p < 0.00001), reducing the number of cfu, while not affecting the roughness parameters (p > 0.05). The Tukey test showed no significant difference between Gdlc and Gag. Films deposited were extremely thin (∼50 nm). The silver particles presented a diameter between 60 and 120 nm and regular distribution throughout the film surface (to Gag). Diamond-like carbon films, doped or undoped with silver nanoparticles, coating the base of PMMA-based dentures could be an alternative procedure for preventing candidosis in denture users. © 2013 by the American College of Prosthodontists.
Hierarchical structures of carbon nanotubes and arrays of chromium-capped silicon nanopillars: formation and electrical properties.

PubMed

Koch, Stefan; Joshi, Ravi K; Noyong, Michael; Timper, Jan; Schneider, Jörg J; Simon, Ulrich

2012-09-10

The formation of stochastically oriented carbon-nanotube networks on top of an array of free-standing chromium-capped silicon nanopillars is reported. The combination of nanosphere lithography and chemical vapor deposition enables the construction of nanostructures that exhibit a hierarchical sequence of structural sizes. Metallic chromium serves as an etching mask for Si-pillar formation and as a nucleation site for the formation of carbon nanotubes through the chemical vapor deposition of ethene, ethanol, and methane, respectively, thereby bridging individual pillars from top to top. Iron and cobalt were applied onto the chromium caps as catalysts for CNT growth and the influence of different carbon sources and different gas-flow rates were investigated. The carbon nanotubes were structurally characterized and their DC electrical properties were studied by in situ local- and ex situ macroscopic measurements, both of which reveal their semiconductor properties. This process demonstrates how carbon nanotubes can be integrated into Si-based semiconductors and, thus, this process may be used to form high-surface-area sensors or new porous catalyst supports with enhanced gas-permeation properties. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Effects of specific surface area of metallic nickel particles on carbon deposition kinetics

NASA Astrophysics Data System (ADS)

Chen, Zhi-yuan; Bian, Liu-zhen; Yu, Zi-you; Wang, Li-jun; Li, Fu-shen; Chou, Kuo-Chih

2018-02-01

Carbon deposition on nickel powders in methane involves three stages in different reaction temperature ranges. Temperature programing oxidation test and Raman spectrum results indicated the formation of complex and ordered carbon structures at high deposition temperatures. The values of I(D)/ I(G) of the deposited carbon reached 1.86, 1.30, and 1.22 in the first, second, and third stages, respectively. The structure of carbon in the second stage was similar to that in the third stage. Carbon deposited in the first stage rarely contained homogeneous pyrolytic deposit layers. A kinetic model was developed to analyze the carbon deposition behavior in the first stage. The rate-determining step of the first stage is supposed to be interfacial reaction. Based on the investigation of carbon deposition kinetics on nickel powders from different resources, carbon deposition rate is suggested to have a linear relation with the square of specific surface area of nickel particles.
Destruction of Refractory Carbon in Protoplanetary Disks

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

Anderson, Dana E.; Blake, Geoffrey A.; Bergin, Edwin A.

The Earth and other rocky bodies in the inner solar system contain significantly less carbon than the primordial materials that seeded their formation. These carbon-poor objects include the parent bodies of primitive meteorites, suggesting that at least one process responsible for solid-phase carbon depletion was active prior to the early stages of planet formation. Potential mechanisms include the erosion of carbonaceous materials by photons or atomic oxygen in the surface layers of the protoplanetary disk. Under photochemically generated favorable conditions, these reactions can deplete the near-surface abundance of carbon grains and polycyclic aromatic hydrocarbons by several orders of magnitude onmore » short timescales relative to the lifetime of the disk out to radii of ∼20–100+ au from the central star depending on the form of refractory carbon present. Due to the reliance of destruction mechanisms on a high influx of photons, the extent of refractory carbon depletion is quite sensitive to the disk’s internal radiation field. Dust transport within the disk is required to affect the composition of the midplane. In our current model of a passive, constant- α disk, where α = 0.01, carbon grains can be turbulently lofted into the destructive surface layers and depleted out to radii of ∼3–10 au for 0.1–1 μ m grains. Smaller grains can be cleared out of the planet-forming region completely. Destruction may be more effective in an actively accreting disk or when considering individual grain trajectories in non-idealized disks.« less

Soldering of Carbon Materials Using Transition Metal Rich Alloys.

PubMed

Burda, Marek; Lekawa-Raus, Agnieszka; Gruszczyk, Andrzej; Koziol, Krzysztof K K

2015-08-25

Joining of carbon materials via soldering has not been possible up to now due to lack of wetting of carbons by metals at standard soldering temperatures. This issue has been a severely restricting factor for many potential electrical/electronic and mechanical applications of nanostructured and conventional carbon materials. Here we demonstrate the formation of alloys that enable soldering of these structures. By addition of several percent (2.5-5%) of transition metal such as chromium or nickel to a standard lead-free soldering tin based alloy we obtained a solder that can be applied using a commercial soldering iron at typical soldering temperatures of approximately 350 °C and at ambient conditions. The use of this solder enables the formation of mechanically strong and electrically conductive joints between carbon materials and, when supported by a simple two-step technique, can successfully bond carbon structures to any metal terminal. It has been shown using optical and scanning electron microscope images as well as X-ray diffraction patterns and energy dispersive X-ray mapping that the successful formation of carbon-solder bonds is possible, first, thanks to the uniform nonreactive dispersion of transition metals in the tin-based matrix. Further, during the soldering process, these free elements diffuse into the carbon-alloy border with no formation of brazing-like carbides, which would damage the surface of the carbon materials.
Controlled growth-reversal of catalytic carbon nanotubes under electron-beam irradiation.

PubMed

Stolojan, Vlad; Tison, Yann; Chen, Guan Yow; Silva, Ravi

2006-09-01

The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni3C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni3C (2-13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes.
Characterization of dissolved organic matter from surface waters with low to high dissolved organic carbon and the related disinfection byproduct formation potential.

PubMed

Li, Angzhen; Zhao, Xu; Mao, Ran; Liu, Huijuan; Qu, Jiuhui

2014-04-30

In this study, the disinfection byproduct formation potential (DBPFP) of three surface waters with the dissolved organic carbon (DOC) content of 2.5, 5.2, and 7.9mg/L was investigated. The formation and distribution of trihalomethanes and haloacetic acids were evaluated. Samples collected from three surface waters in China were fractionated based on molecular weight and hydrophobicity. The raw water containing more hydrophobic (Ho) fraction exhibited higher formation potentials of haloacetic acid and trihalomethane. The DBPFP of the surface waters did not correlate with the DOC value. The values of DBPFP per DOC were correlated with the specific ultraviolet absorbance (SUVA) for Ho and Hi fractions. The obtained results suggested that SUVA cannot reveal the ability of reactive sites to form disinfection byproducts for waters with few aromatic structures. Combined with the analysis of FTIR and nuclear magnetic resonance spectra of the raw waters and the corresponding fractions, it was concluded that the Ho fraction with phenolic hydroxyl and conjugated double bonds was responsible for the production of trichloromethanes and trichloroacetic acids. The Hi fraction with amino and carboxyl groups had the potential to form dichloroacetic acids and chlorinated trihalomethanes. Copyright © 2014. Published by Elsevier B.V.
Study of the adsorption of Cd and Zn onto an activated carbon: Influence of pH, cation concentration, and adsorbent concentration

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

Seco, A.; Marzal, P.; Gabaldon, C.

1999-06-01

The single adsorption of Cd and Zn from aqueous solutions has been investigated on Scharlau Ca 346 granular activated carbon in a wide range of experimental conditions: pH, metal concentration, and carbon concentration. The results showed the efficiency of the activated carbon as sorbent for both metals. Metal removals increase on raising the pH and carbon concentration, and decrease on raising the initial metal concentration. The adsorption processes have been modeled using the surface complex formation (SCF) Triple Layer Model (TLM). The adsorbent TLM parameters were determined. Modeling has been performed assuming a single surface bidentate species or an overallmore » surface species with fractional stoichiometry. The bidentate stoichiometry successfully predicted cadmium and zinc removals in all the experimental conditions. The Freundlich isotherm has been also checked.« less
Pyrolyzed-parylene based sensors and method of manufacture

NASA Technical Reports Server (NTRS)

Tai, Yu-Chong (Inventor); Liger, Matthieu (Inventor); Miserendino, Scott (Inventor); Konishi, Satoshi (Inventor)

2007-01-01

A method (and resulting structure) for fabricating a sensing device. The method includes providing a substrate comprising a surface region and forming an insulating material overlying the surface region. The method also includes forming a film of carbon based material overlying the insulating material and treating to the film of carbon based material to pyrolyzed the carbon based material to cause formation of a film of substantially carbon based material having a resistivity ranging within a predetermined range. The method also provides at least a portion of the pyrolyzed carbon based material in a sensor application and uses the portion of the pyrolyzed carbon based material in the sensing application. In a specific embodiment, the sensing application is selected from chemical, humidity, piezoelectric, radiation, mechanical strain or temperature.
Using Calcium Isotopic Composition of Calcium Carbonate Veins to Assess the Roles of Vein Formation and Seafloor Alteration in Regulation of the Carbon Cycle

NASA Astrophysics Data System (ADS)

Chen, F.; Coggon, R. M.; Teagle, D. A. H.; Turchyn, A. V.

2016-12-01

Calcium carbonate vein formation in the oceanic crust has been proposed as a climate-sensitive feedback mechanism that regulates the carbon cycle on million-year timescales. The suggestion has been that higher pCO2 levels may drive changes in ocean temperature and pH that increase seafloor alteration, releasing more calcium from oceanic basalt. This results in more removal of carbon from Earth's surface through calcium carbonate formation, which includes calcium carbonate vein formation in oceanic crust. The importance of this feedback mechanism remains enigmatic. Measurements of the δ44Ca of calcium carbonate veins in the oceanic crust may constrain the sources of calcium and timing of vein formation. Seawater and basalt are the only sources present shortly after crustal formation, whereas other sources, such as anhydrite dissolution and sedimentary carbonates become available when the crust ages, at which point carbonate veins may form far from the ridge axis. We report the calcium isotopic composition of 65 calcium carbonate veins, ranging from 108 to 1.2 million years old, in hydrothermally altered basalt from the Mid-Atlantic and Juan de Fuca ridges. We also present 43 δ44Ca measurements of 5.9 million year old basalts and dikes from the Costa Rica Rift that have undergone hydrothermal alteration over a range of conditions in upper crust. The δ44Ca of the calcium carbonate veins ranges from -1.59 to 1.01‰ (versus Bulk Silicate Earth), whereas the δ44Ca of altered basalts ranges from -0.18 to 0.28‰. Depth and temperature of formation seem to be major influences on calcium carbonate vein δ44Ca, with veins formed at cool, shallower depths having higher δ44Ca, closer to seawater. In contrast, we note no temporal variation in δ44Ca of calcium carbonate veins when comparing samples from older and younger crust. The majority of veins (54 out of 65) have δ44Ca between that of seawater and basalt, which implies that they may have formed quite soon after crustal formation before other sources of calcium became available. We conclude that calcium carbonate vein formation may derive a significant fraction of calcium from seafloor alteration of basalts. This may cause rates of carbonate vein formation to be sensitive to aspects of ocean chemistry that vary due to changing climate conditions.
Calcium carbonate mineralization mediated by in vitro cultured mantle cells from Pinctada fucata.

PubMed

Kong, Wei; Li, Shiguo; Xiang, Liang; Xie, Liping; Zhang, Rongqing

2015-08-07

Formation of the molluscan shell is believed to be an extracellular event mediated by matrix proteins. We report calcium carbonate mineralization mediated by Pinctada fucata mantle cells. Crystals only appeared when mantle cells were present in the crystallization solution. These crystals were piled up in highly ordered units and showed the typical characteristics of biomineralization products. A thin organic framework was observed after dissolving the crystals in EDTA. Some crystals had etched surfaces with a much smoother appearance than other parts. Mantle cells were observed to be attached to some of these smooth surfaces. These results suggest that mantle cells may be directly involved in the nucleation and remodeling process of calcium carbonate mineralization. Our result demonstrate the practicability of studying the mantle cell mechanism of biomineralization and contribute to the overall understanding of the shell formation process. Copyright © 2015 Elsevier Inc. All rights reserved.
Formation of recent Pb-Ag-Au mineralization by potential sub-surface microbial activity

NASA Astrophysics Data System (ADS)

Tornos, Fernando; Velasco, Francisco; Menor-Salván, César; Delgado, Antonio; Slack, John F.; Escobar, Juan Manuel

2014-08-01

Las Cruces is a base-metal deposit in the Iberian Pyrite Belt, one of the world’s best-known ore provinces. Here we report the occurrence of major Pb-Ag-Au mineralization resulting from recent sub-surface replacement of supergene oxyhydroxides by carbonate and sulphide minerals. This is probably the largest documented occurrence of recent microbial activity producing an ore assemblage previously unknown in supergene mineralizing environments. The presence of microbial features in the sulphides suggests that these may be the first-described natural bacteriomorphs of galena. The low δ13C values of the carbonate minerals indicate formation by deep anaerobic microbial processes. Sulphur isotope values of sulphides are interpreted here as reflecting microbial reduction in a system impoverished in sulphate. We suggest that biogenic activity has produced around 3.1 × 109 moles of reduced sulphur and 1010 moles of CO2, promoting the formation of ca. 1.19 Mt of carbonates, 114,000 t of galena, 638 t of silver sulphides and 6.5 t of gold.
Structural-phase states and wear resistance of surface formed on steel by surfacing

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

Kapralov, Evgenie V.; Raykov, Sergey V.; Vaschuk, Ekaterina S.

2014-11-14

Investigations of elementary and phase structure, state of defect structure and tribological characteristics of a surfacing, formed on a low carbon low-alloy steel by a welding method were carried out. It was revealed that a surfacing, formed on a steel surface is accompanied by the multilayer formation, and increases the wear resistance of the layer surfacing as determined.
Ozonation of 1,2-dihydroxybenzene in the presence of activated carbon.

PubMed

Zaror, C; Soto, G; Valdés, H; Mansilla, H

2001-01-01

This work aims at obtaining experimental data on ozonation of 1,2-dihydroxybenzene (DHB) in the presence of activated carbon, with a view to assessing possible changes in its surface chemical structure and adsorption capacity. Experiments were conducted in a 0.5 L reactor, loaded with 2 g Filtrasorb 400 granular activated carbon, and 1-5 mM DHB aqueous solution at pH 2-8. Ozone gas was generated with an Ozocav generator, and fed into the reactor for a given exposure time, in the range 0.5-240 min, at 25 degrees C and 1 atm. After each run, liquid and activated carbon samples were taken for chemical assays. Soluble organic groups present on the active carbon surface were desorbed and analysed by GC-MS and HPLC. Activated carbon chemical surface properties were analysed using TPD, FT-IR, and XPS techniques. Reactions between ozone and adsorbed DHB were shown to be fast, leading to formation of C-6, C-4 and C-2 by-products. Oxygenated surface groups, particularly, COOH and C = O, increased as a result of ozonation.
Structure, dynamics and stability of water/scCO2/mineral interfaces from ab initio molecular dynamics simulations.

PubMed

Lee, Mal-Soon; Peter McGrail, B; Rousseau, Roger; Glezakou, Vassiliki-Alexandra

2015-10-12

The boundary layer at solid-liquid interfaces is a unique reaction environment that poses significant scientific challenges to characterize and understand by experimentation alone. Using ab initio molecular dynamics (AIMD) methods, we report on the structure and dynamics of boundary layer formation, cation mobilization and carbonation under geologic carbon sequestration scenarios (T = 323 K and P = 90 bar) on a prototypical anorthite (001) surface. At low coverage, water film formation is enthalpically favored, but entropically hindered. Simulated adsorption isotherms show that a water monolayer will form even at the low water concentrations of water-saturated scCO2. Carbonation reactions readily occur at electron-rich terminal Oxygen sites adjacent to cation vacancies that readily form in the presence of a water monolayer. These results point to a carbonation mechanism that does not require prior carbonic acid formation in the bulk liquid. This work also highlights the modern capabilities of theoretical methods to address structure and reactivity at interfaces of high chemical complexity.
Abiotic vs biological sources and fates of organic compounds in a low temperature continental serpentinizing system

NASA Astrophysics Data System (ADS)

Robinson, K.; Noble, S. M.; Shock, E.

2016-12-01

Serpentinization is likely the most common water-rock reaction in our solar system. During this process ultramafic silicates are hydrated, a calcium hydroxide solution is formed, and H2O is reduced to H2 coupled to the oxidation of Fe2+ to Fe3+. The resulting hyper-alkaline, reduced conditions generate thermodynamic drives for numerous carbon compound reactions, including the precipitation of various carbonate minerals and the reduction of inorganic carbonate to organic carbon. Testing the extent to which these thermodynamic drives lead to observable results led to the present study of the flow and transformations of carbon through the active continental serpentinizing system at the Samail Ophiolite in the Sultanate of Oman. Water samples were collected from shallow groundwater (representing system input), hyper-alkaline seeps (system output), boreholes (system intermediate), and surface fluid mixing zones, and analyzed for concentrations of dissolved inorganic carbon (DIC + δ13C), organic carbon (+ δ13C), formate, acetate, H2, methane (+ δ13C), ethane, and an accompanying suite of other geochemical solutes. These analyses indicate that the vast majority of DIC in these serpentinizing fluids precipitates in the subsurface as carbonate minerals; however, a significant amount of DIC is converted into organic acids and light hydrocarbons and expelled at the surface in hyper-alkaline seeps. Based on thermodynamic calculations, it seems most likely that formate last equilibrated with dolomite (CaMg[CO3]2) in the subsurface, acetate last equilibrated with calcite (CaCO3) near the surface, and methane and ethane last equilibrated in a distinct carbon-limited region of the subsurface. As for the fates of these compounds, energetic calculations reveal that a combination of oxidative, reductive, and fermentative metabolisms are thermodynamically favorable. Indeed, δ13C trends record microbial methane oxidation at the surface and cannot rule out methane as biologically sourced from the subsurface.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Xing, Rong; Dagle, Vanessa Lebarbier; Flake, Matthew

In this study we examine feasibility for steam reforming the mixed oxygenate aqueous fraction derived from mildly hydrotreated fast pyrolysis bio-oils. Catalysts selective towards hydrogen formation and resistant to carbon formation utilizing feeds with relatively low steam-to-carbon (S/C) ratios are desired. Rh (5 wt%), Pt (5 wt%), Ru (5 wt%), Ir (5 wt%), Ni (15 wt%), and Co (15 wt%) metals supported on MgAl 2O 4 were evaluated for catalytic performance at 500°C and 1 atm using a complex feed mixture comprising of acids, polyols, cycloalkanes, and phenolic compounds. The Rh catalyst was found to be the most active andmore » resistant to carbon formation. The Ni and Co catalysts were found to be more active than the other noble metal catalysts investigated (Pt, Ru, and Ir). However, Ni was found to form significantly more carbon (coke) on the catalyst surface. Furthermore, Co was found to be the most selective towards H 2 formation. Evaluating the effect of temperature on stability for the Rh catalyst we found that catalyst stability was best when operated at 500°C as compared to the higher temperatures investigated (700, 800°C). When operating at 700°C significantly more graphitic formation was observed on the spent catalyst surface. Operating at 800°C resulted in reactor plugging as a result of thermal decomposition of the reactants. Thus, a concept analogous to the petroleum industries’ use of a pre-reformer, operated at approximately 500°C for steam reforming of the heavier naphtha components, followed by a high temperature methane reforming operated in the 600-850°C temperature range, could be applied in the case of steam reforming biomass derived oxygenates. Moreover, stability evaluations were performed over the Rh, Ni, and Co catalysts at 500°C and 1 atm, under similar initial conversions, reveal the Co catalyst to be the most stable and selective towards H 2 production. Conversion and selectivity to CH 4 over Co remained relatively stable at approximately 80% and 1.2%, respectively. By contrast, the Rh and Ni catalysts CH 4 selectivity’s were approximately 7-8%. Thus suggesting that a Co type catalyst may be more suitable for the steam reforming of biomass derived oxygenates as compared to the more conventional Ni and Rh type steam reforming catalysts. However, deposition of carbon on the surface was observed. High resolution TEM on the spent catalysts revealed the formation of graphitic carbon on the Rh catalyst, and filamentous carbon formation was observed on both the Ni and Co catalysts, albeit less pronounced on Co. Thus there is certainly opportunity for improvement in Co catalyst design and/or with process optimization.« less
Lithium storage in structurally tunable carbon anode derived from sustainable source

DOE PAGES

Lim, Daw Gen; Kim, Kyungho; Razdan, Mayuri; ...

2017-09-01

Here, a meticulous solid state chemistry approach has been developed for the synthesis of carbon anode from a sustainable source. The reaction mechanism of carbon formation during pyrolysis of sustainable feed-stock was studied in situ by employing Raman microspectroscopy. No Raman spectral changes observed below 160°C (thermally stable precursor) followed by color change, however above 280°C characteristic D and G bands of graphitic carbon are recorded. Derived carbon particles exhibited high specific surface area with low structural ordering (active carbons) to low specific surface area with high graphitic ordering as a function of increasing reaction temperature. Carbons synthesized at 600°Cmore » demonstrated enhanced reversible lithiation capacity (390 mAh g -1), high charge-discharge rate capability, and stable cycle life. On the contrary, carbons synthesized at higher temperatures (>1200°C) produced more graphite-like structure yielding longer specific capacity retention with lower reversible capacity.« less
Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors.

PubMed

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J; Mijowska, Ewa

2012-05-29

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.
Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

NASA Astrophysics Data System (ADS)

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J.; Mijowska, Ewa

2012-05-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.
Carbon dioxide-assisted fabrication of highly uniform submicron-sized colloidal carbon spheres via hydrothermal carbonization using soft drink

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

Moon, Gun-Hee; Shin, Yongsoon; Arey, Bruce W.

An eco-friendly and economical method for the formation of uniform-sized carbon spheres by hydrothermal dehydration/condensation of a commercial carbonated beverage at 200 oC is reported. CO2 dissolved in the beverage accelerates the dehydration kinetics of the dissolved sugar molecules leading to production of homogeneous carbon spheres having a diameter less than 850 nm. In the presence of CO2, the rough surface of these carbon spheres likely results from continuous Ostwald ripening of constituent microscopic carbon-containing spheres that are formed by subsequent polymerization of intermediate HMF molecules.
Anthropogenic carbon in the ocean—Surface to interior connections

NASA Astrophysics Data System (ADS)

Groeskamp, Sjoerd; Lenton, Andrew; Matear, Richard; Sloyan, Bernadette M.; Langlais, Clothilde

2016-11-01

Quantifying the surface to interior transport of anthropogenic carbon (CA) is critical for projecting future carbon uptake and for improved understanding of the role of the oceans in the global carbon cycle. Here we develop and apply a diagnostic tool that provides a volumetric stream function in (CA,σ0) coordinates to calculate the total diapycnal CA transport in the ocean, where σ0 is the surface referenced potential density anomaly. We combine this with air-sea fluxes of CA to infer the internal ocean mixing of CA to obtain a closed globally integrated budget analyses of the ocean's CA transport. This diagnostic separates the contribution from the mean flow, seasonal cycles, trend, surface fluxes, and mixing in the distribution and the accumulation of CA in the ocean. We find that the redistribution of CA from the surface to the interior of the ocean is due to an interplay between circulation and mixing. The circulation component is dominated by the mean flow; however, effects due to seasonal cycles are significant for the CA redistribution. The two most important pathways for CA subduction are through the transformation of thermocline water (TW) into subantarctic mode water and by transformation of Circumpolar Deep Water (CDW) into lighter Antarctic Intermediate Water. The results suggest that an accurate representation of intermediate and mode water formation, deep water formation, and spatial and temporal distribution of ocean mixing in ocean models is essential to simulate and project the oceanic uptake of CA.
Graphitic carbon stabilized silver nanoparticles synthesized by a simple chemical precursor method

NASA Astrophysics Data System (ADS)

Soni, Bhasker; Biswas, Somnath

2018-04-01

Monodispersed graphitic carbon stabilized silver nanoparticles (AgNPs) were synthesized following a simple chemical precursor method. The precursor was obtained by a controlled reduction of Ag+ in aqueous solution of poly-vinyl alcohol (PVA) and sucrose. The process allows precise control over the morphology of the AgNPs along with in situ formation of a surface stabilization layer of graphitic carbon.
Methanation of gas streams containing carbon monoxide and hydrogen

DOEpatents

Frost, Albert C.

1983-01-01

Carbon monoxide-containing gas streams having a relatively high concentration of hydrogen are pretreated so as to remove the hydrogen in a recoverable form for use in the second step of a cyclic, essentially two-step process for the production of methane. The thus-treated streams are then passed over a catalyst to deposit a surface layer of active surface carbon thereon essentially without the formation of inactive coke. This active carbon is reacted with said hydrogen removed from the feed gas stream to form methane. The utilization of the CO in the feed gas stream is appreciably increased, enhancing the overall process for the production of relatively pure, low-cost methane from CO-containing waste gas streams.

Microwave-assisted synthesis of porous carbon-titania and highly crystalline titania nanostructures.

PubMed

Parker, Alison; Marszewski, Michal; Jaroniec, Mietek

2013-03-01

Porous carbon-titania and highly crystalline titania nanostructured materials were obtained through a microwave-assisted one-pot synthesis. Resorcinol and formaldehyde were used as carbon precursors, triblock copolymer Pluronic F127 as a stabilizing agent, and titanium isopropoxide as a titania precursor. This microwave-assisted one-pot synthesis involved formation of carbon spheres according to the recently modified Stöber method followed by hydrolysis and condensation of titania precursor. This method afforded carbon-titania composite materials containing anatase phase with specific surface areas as high as 390 m(2) g(-1). The pure nanostructured titania, obtained after removal of carbon through calcination of the composite material in air, was shown to be the anatase phase with considerably higher degree of crystallinity and the specific surface area as high as 130 m(2) g(-1). The resulting titania, because of its high surface area, well-developed porosity, and high crystallinity, is of great interest for catalysis, water treatment, lithium batteries, and other energy-related applications.
Influence of calcareous deposit on corrosion behavior of Q235 carbon steel with sulfate-reducing bacteria

NASA Astrophysics Data System (ADS)

Zhang, Jie; Li, Xiaolong; Wang, Jiangwei; Xu, Weichen; Duan, Jizhou; Chen, Shougang; Hou, Baorong

2017-12-01

Cathodic protection is a very effective method to protect metals, which can form calcareous deposits on metal surface. Research on the interrelationship between fouling organism and calcareous deposits is very important but very limited, especially sulfate-reducing bacteria (SRB). SRB is a kind of very important fouling organism that causes microbial corrosion of metals. A study of the influence of calcareous deposit on corrosion behavior of Q235 carbon steel in SRB-containing culture medium was carried out using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and surface spectroscopy (EDS). The calcareous deposit was formed with good crystallinity and smooth surface under the gradient current density of -30 μA cm-2 in natural seawater for 72 h. Our results can help elucidate the formation of calcareous deposits and reveal the interrelationship between SRB and calcareous deposits under cathodic protection. The results indicate that the corrosion tendency of carbon steel was obviously affected by Sulfate-reducing Bacteria (SRB) metabolic activity and the calcareous deposit formed on the surface of carbon steel under cathodic protection was favourable to reduce the corrosion rate. Calcareous deposits can promote bacterial adhesion before biofilm formation. The results revealed the interaction between biofouling and calcareous deposits, and the anti-corrosion ability was enhanced by a kind of inorganic and organic composite membranes formed by biofilm and calcareous deposits.
In Situ Potentiodynamic Analysis of the Electrolyte/Silicon Electrodes Interface Reactions - A Sum Frequency Generation Vibrational Spectroscopy Study

DOE PAGES

Horowitz, Yonatan; Han, Hui-Ling; Ross, Philip N.; ...

2015-12-11

The key factor in long-term use of batteries is the formation of an electrically insulating solid layer that allows lithium ion transport but stops further electrolyte redox reactions on the electrode surface, hence solid electrolyte interphase (SEI). In this paper, we have studied a common electrolyte, 1.0 M LiPF 6/ethylene carbonate (EC)/diethyl carbonate (DEC), reduction products on crystalline silicon (Si) electrodes in a lithium (Li) half-cell system under reaction conditions. We employed in situ sum frequency generation vibrational spectroscopy (SFG-VS) with interface sensitivity in order to probe the molecular composition of the SEI surface species under various applied potentials wheremore » electrolyte reduction is expected. We found that, with a Si(100)-hydrogen terminated wafer, a Si-ethoxy (Si-OC 2H 5) surface intermediate forms due to DEC decomposition. Our results suggest that the SEI surface composition varies depending on the termination of Si surface, i.e., the acidity of the Si surface. We provide the evidence of specific chemical composition of the SEI on the anode surface under reaction conditions. This supports an electrochemical electrolyte reduction mechanism in which the reduction of the DEC molecule to an ethoxy moiety plays a key role. Finally, these findings shed new light on the formation mechanism of SEI on Si anodes in particular and on SEI formation in general.« less
Effect of Ar ion on the surface properties of low density polyethylene.

PubMed

Zaki, M F

2016-04-15

In this paper, low-density polyethylene (LDPE) was irradiated by argon ion with different fluences up to 10(15) ions/cm(2). The optical, chemical and hardness properties have been investigated using UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and micro-indentation tester, respectively. The results showed the ion beam bombardment induced decreases in the transmittance of the irradiated polymer samples. This change in transmittance can be attributed to the formation of conjugated bonds i.e. possible formation of defects and/or carbon clusters. The indirect optical band gap decreased from 3.0 eV for the pristine sample to 2.3 eV for that sample irradiated with the highest fluence of the Ar ion beam. Furthermore, the number of carbon atoms and clusters increased with increasing Ar ion fluences. FTIR spectra showed the formation of new bands of the bombarded polymer samples. Furthermore, polar groups were created on the surface of the irradiated samples which refer to the increase of the hydrophilic nature of the surface of the irradiated samples. The Vicker's hardness increased from 4.9 MPa for the pristine sample to 17.9 MPa for those bombarded at the highest fluence. This increase is attributed to the increase in the crosslinking and alterations of the bombarded surface into hydrogenated amorphous carbon, which improves the hardness of the irradiated samples. The bombarded LDPE surfaces may be used in special applications to the field of the micro-electronic devices and shock absorbers. Copyright © 2016 Elsevier B.V. All rights reserved.
Polypeptide formation on polar mineral surfaces: possibility of complete chirality

NASA Astrophysics Data System (ADS)

Schrader, Malcolm E.

2017-01-01

In the present work, it is shown that thermodynamically feasible polymerization of cyanomethanol, which can be formed from formaldehyde and hydrogen cyanide, can lead to synthesis of polypeptides as well as to the previously reported synthesis of RNA. If the polymerization takes place on a one-dimensional feature of a mineral, such as for example a crack on its surface, the concept of quasi-chirality is introduced to describe the adsorbed polypeptide. This, in principle, would lead to formation of proteins that are completely homochiral in their alpha carbon groups. The concept of quasi-chirality can also be introduced in the condensation of glycine under similar conditions to form a polypeptide. This again leads to proteins completely chiral in their alpha carbon groups.
Formation of fouling deposits on a carbon steel surface from Colombian heavy crude oil under preheating conditions

NASA Astrophysics Data System (ADS)

Muñoz Pinto, D. A.; Cuervo Camargo, S. M.; Orozco Parra, M.; Laverde, D.; García Vergara, S.; Blanco Pinzon, C.

2016-02-01

Fouling in heat exchangers is produced by the deposition of undesired materials on metal surfaces. As fouling progresses, pressure drop and heat transfer resistance is observed and therefore the overall thermal efficiency of the equipment diminishes. Fouling is mainly caused by the deposition of suspended particles, such as those from chemical reactions, crystallization of certain salts, and some corrosion processes. In order to understand the formation of fouling deposits from Colombian heavy oil (API≈12.3) on carbon steel SA 516 Gr 70, a batch stirred tank reactor was used. The reactor was operated at a constant pressure of 340psi while varying the temperature and reaction times. To evaluate the formation of deposits on the metal surfaces, the steel samples were characterized by gravimetric analysis and Scanning Electron Microscopy (SEM). On the exposed surfaces, the results revealed an increase in the total mass derived from the deposition of salt compounds, iron oxides and alkaline metals. In general, fouling was modulated by both the temperature and the reaction time, but under the experimental conditions, the temperature seems to be the predominant variable that controls and accelerates fouling.
In vitro platelet activation, aggregation and platelet-granulocyte complex formation induced by surface modified single-walled carbon nanotubes.

PubMed

Fent, János; Bihari, Péter; Vippola, Minnamari; Sarlin, Essi; Lakatos, Susan

2015-08-01

Surface modification of single-walled carbon nanotubes (SWCNTs) such as carboxylation, amidation, hydroxylation and pegylation is used to reduce the nanotube toxicity and render them more suitable for biomedical applications than their pristine counterparts. Toxicity can be manifested in platelet activation as it has been shown for SWCNTs. However, the effect of various surface modifications on the platelet activating potential of SWCNTs has not been tested yet. In vitro platelet activation (CD62P) as well as the platelet-granulocyte complex formation (CD15/CD41 double positivity) in human whole blood were measured by flow cytometry in the presence of 0.1mg/ml of pristine or various surface modified SWCNTs. The effect of various SWCNTs was tested by whole blood impedance aggregometry, too. All tested SWCNTs but the hydroxylated ones activate platelets and promote platelet-granulocyte complex formation in vitro. Carboxylated, pegylated and pristine SWCNTs induce whole blood aggregation as well. Although pegylation is preferred from biomedical point of view, among the samples tested by us pegylated SWCNTs induced far the most prominent activation and a well detectable aggregation of platelets in whole blood. Copyright © 2015 Elsevier Ltd. All rights reserved.
Bosch Reactor Development for High Percentage Oxygen Recovery from Carbon Dioxide

NASA Technical Reports Server (NTRS)

Howard, David; Abney, Morgan

2015-01-01

This next Generation Life Support Project entails the development and demonstration of Bosch reaction technologies to improve oxygen recovery from metabolically generated oxygen and/or space environments. A primary focus was placed on alternate carbon formation reactor concepts to improve useful catalyst life for space vehicle applications, and make use of in situ catalyst resources for non-terrestrial surface missions. Current state-of-the-art oxygen recovery systems onboard the International Space Station are able to effectively recover approximately 45 percent of the oxygen consumed by humans and exhausted in the form of carbon dioxide (CO2). Excess CO2 is vented overboard and the oxygen contained in the molecules is lost. For long-duration missions beyond the reaches of Earth for resupply, it will be necessary to recover greater amounts of constituents such as oxygen that are necessary for sustaining life. Bosch technologies theoretically recover 100 percent of the oxygen from CO2, producing pure carbon as the sole waste product. Challenges with this technology revolve around the carbon product fouling catalyst materials, drastically limiting catalyst life. This project successfully demonstrated techniques to extend catalyst surface area exposure times to improve catalyst life for vehicle applications, and demonstrated the use of Martian and lunar regolith as viable catalyst Bosch Reactor Development for High Percentage Oxygen Recovery From Carbon Dioxide materials for surface missions. The Bosch process generates carbon nanotube formation within the regolith, which has been shown to improve mechanical properties of building materials. Production of bricks from post reaction regolith for building and radiation shielding applications were also explored.
Molar tooth structures in calcareous nodules, early Neoproterozoic Burovaya Formation, Turukhansk region, Siberia

NASA Astrophysics Data System (ADS)

Pope, Michael C.; Bartley, Julie K.; Knoll, Andrew H.; Petrov, Peter Yu.

2003-05-01

Molar tooth structures are abundant in large (1-2 m diameter) carbonate nodules within fine-grained, subtidal carbonates of the early Neoproterozoic (lower Upper Riphean) Burovaya Formation along the Sukhaya Tunguska River, Turukhansk Uplift, northwestern Siberia. Although molar tooth structures are regionally abundant in this unit, here they occur only within the nodules. Stable isotopic compositions of molar-tooth-filling dolomicrospar cements and of thinly bedded dolomicrite within and surrounding the nodules are indistinguishable from one another. The carbon isotopic compositions (mean δ13C=+2.8‰ PDB±0.4) reflect mean average oceanic surface water composition during their formation; the light oxygen isotopic compositions (mean δ18O=-6.4‰ PDB±2.2) are generally similar to those of other little-altered Meso- to Neoproterozoic limestones and dolostones. These molar tooth structures have no features that would support a tectonic origin; they more likely formed through bacterial processes. Carbonate cement filling of these voids occurred soon after their formation, but the mechanism responsible for this carbonate precipitation is currently uncertain. Local restriction of molar tooth structures to early diagenetic nodules suggests that penecontemporaneous lithification was required for the formation, or at least preservation, of these widespread Mesoproterozoic to Neoproterozoic features.
Carbonate platform, slope, and basinal deposits of Upper Oligocene, Kalimantan, Indonesia

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

Armin, R.A.; Cutler, W.G.; Mahadi, S.

1987-05-01

Upper Oligocene platform carbonates (Berai Formation) occur extensively on the Barito shelf in southeastern Kalimantan (Borneo) and are flanked northward by coeval slope and basinal deposits (Bongan Formation) which accumulated in the southwestern part of the Kutei basin. Isolated carbonate buildups equivalent to the Berai Formation also occur within the Kutei basin and were probably deposited on basement highs. The distribution of these facies is fairly well constrained by the study of outcrops, wells, and seismic profiles. The Berai Formation consists of diverse limestone types with a wide range of textures and with dominant skeletal components of large foraminifera, redmore » algae, and corals. Deposition of the Berai Formation occurred in moderate- and high-energy shallow-marine conditions. Slope and basin facies occur in extensional basins adjacent to the shelfal carbonates and peripheral to isolated carbonate buildups. Slope deposits consist of hemipelagic claystone, debris-flow conglomerate, calciturbidite, and volcaniclastic intervals. syndepositional downslope transport of slope deposits was an important process, as indicated by intervals containing redeposited debris flows, intraformational truncation surfaces, slide blocks, and associated shear planes. Recurrent movement on basin-margin faults and local volcanism probably perpetuated instability of slope deposits. Basinal deposits consist of calcareous claystone with intercalated thin, distal calciturbidite and volcaniclastic beds.« less
Carbon, oxygen and strontium isotopic constraints on fluid sources, temperatures and biogeochemical processes during the formation of seep carbonates - Secchia River site, Northern Apennines

NASA Astrophysics Data System (ADS)

Viola, Irene; Capozzi, Rossella; Bernasconi, Stefano M.; Rickli, Jörg

2017-07-01

Understanding authigenic seep carbonate formation provides clues for hydrocarbon exploration and insights into contributions to gas budgets of marine environments and the atmosphere. Seep carbonates discovered in the outcropping succession along the Secchia riverbanks (near Modena, Italy) belong to the Argille Azzurre Formation of Early Pleistocene age deposited in an upper shelf environment overlying the Miocene foredeep successions, which include hydrocarbon fields. The fluid migration from the hydrocarbon fields, up to the surface, is presently active on land and started in the marine succession during the Late Miocene. Authigenic globular carbonate concretions and carbonate chimneys are interspersed along the strata throughout the section. A comprehensive geochemical characterisation of the carbonates has been carried out to understand the processes leading to their formation. The carbonate concretions are the record of past hydrocarbon vents linked to the Miocene petroleum system of the Northern Apennines. The samples are composed of > 50% microcrystalline dolomite. The δ13C signatures identify two groups in the samples according to different type of formation processes. Globular concretions have positive values that suggest an influence of CO2 associated to secondary methanogenesis due to microbial degradation of higher hydrocarbons. The analysed chimney, with negative δ13C values, is interpreted as former conduit where carbonate precipitation is promoted by Anaerobic Oxidation of Methane coupled with Sulfate Reduction. The δ18O range, coupled with 87/86Sr signatures, indicate that the contribution of deep connate water from the Miocene reservoirs is up to 23% during the formation of the globular concretions. The connate water occurrence is also documented by higher ambient temperatures. The different isotope signatures in seep carbonates result from the relative contribution of the recognised gas and water components, linked to different plumbing systems and fluid supply from a well-defined hydrocarbon field. The seep carbonate characteristics have enlightened variations in biogeochemical processes, which can be rarely quantified in ancient and present-day marine environments.
Electrochemical synthesis of elongated noble metal nanoparticles, such as nanowires and nanorods, on high-surface area carbon supports

DOEpatents

Adzic, Radoslav; Blyznakov, Stoyan; Vukmirovic, Miomir

2015-08-04

Elongated noble-metal nanoparticles and methods for their manufacture are disclosed. The method involves the formation of a plurality of elongated noble-metal nanoparticles by electrochemical deposition of the noble metal on a high surface area carbon support, such as carbon nanoparticles. Prior to electrochemical deposition, the carbon support may be functionalized by oxidation, thus making the manufacturing process simple and cost-effective. The generated elongated nanoparticles are covalently bound to the carbon support and can be used directly in electrocatalysis. The process provides elongated noble-metal nanoparticles with high catalytic activities and improved durability in combination with high catalyst utilization since the nanoparticles are deposited and covalently bound to the carbon support in their final position and will not change in forming an electrode assembly.
Spatial and temporal control of the diazonium modification of sp2 carbon surfaces.

PubMed

Kirkman, Paul M; Güell, Aleix G; Cuharuc, Anatolii S; Unwin, Patrick R

2014-01-08

Interest in the controlled chemical functionalization of sp(2) carbon materials using diazonium compounds has been recently reignited, particularly as a means to generate a band gap in graphene. We demonstrate local diazonium modification of pristine sp(2) carbon surfaces, with high control, at the micrometer scale through the use of scanning electrochemical cell microscopy (SECCM). Electrochemically driven diazonium patterning is investigated at a range of driving forces, coupled with surface analysis using atomic force microscopy (AFM) and Raman spectroscopy. We highlight how the film density, level of sp(2)/sp(3) rehybridization and the extent of multilayer formation can be controlled, paving the way for the use of localized electrochemistry as a route to controlled diazonium modification.
Surface Ligand Promotion of Carbon Dioxide Reduction through Stabilizing Chemisorbed Reactive Intermediates.

PubMed

Wang, Zhijiang; Wu, Lina; Sun, Kun; Chen, Ting; Jiang, Zhaohua; Cheng, Tao; Goddard, William A

2018-05-23

We have explored functionalizing metal catalysts with surface ligands as an approach to facilitate electrochemical carbon dioxide reduction reaction (CO 2 RR). To provide a molecular level understanding of the mechanism by which this enhancement occurs, we combine in situ spectroscopy analysis with an interpretation based on quantum mechanics (QM) calculations. We find that a surface ligand can play a critical role in stabilizing the chemisorbed CO 2 , which facilitates CO 2 activation and leads to a 0.3 V decrease in the overpotential for carbon monoxide (CO) formation. Moreover, the presence of the surface ligand leads to nearly exclusive CO production. At -0.6 V (versus reversible hydrogen electrode, RHE), CO is the only significant product with a faradic efficiency of 93% and a current density of 1.9 mA cm -2 . This improvement corresponds to 53-fold enhancement in turnover frequency compared with the Ag nanoparticles (NPs) without surface ligands.
MgO-templated carbon as a negative electrode material for Na-ion capacitors

NASA Astrophysics Data System (ADS)

Kado, Yuya; Soneda, Yasushi

2016-12-01

In this study, MgO-templated carbon with different pore structures was investigated as a negative electrode material for Na-ion capacitors. With increasing the Brunauer-Emmett-Teller surface area, the irreversible capacity increased, and the coulombic efficiency of the 1st cycle decreased because of the formation of solid electrolyte interface layers. MgO-templated carbon annealed at 1000 °C exhibited the highest capacity and best rate performance, suggesting that an appropriate balance between surface area and crystallinity is imperative for fast Na-ion storage, attributed to the storage mechanism: combination of non-faradaic electric double-layer capacitance and faradaic Na intercalation in the carbon layers. Finally, a Na-ion capacitor cell using MgO-templated carbon and activated carbon as the negative and positive electrodes, respectively, exhibited an energy density at high power density significantly greater than that exhibited by the cell using a commercial hard carbon negative electrode.
Response to Comment on “Active sites for CO 2 hydrogenation to methanol on Cu/ZnO catalysts”

DOE PAGES

Kattel, Shyam; Ramírez, Pedro J.; Chen, Jingguang G.; ...

2017-09-01

In their Comment on our recent paper, Nakamura et al. argue that our x-ray photoelectron spectroscopy (XPS) analysis was affected by the presence of formate species on the catalyst surface. This argument is not valid because the reactant gases were evacuated at temperatures from 525 to 575 kelvin, conditions under which formate is not stable on the catalyst surface. An analysis of the XPS results obtained after exposing zinc oxide/copper (111) [ZnO/Cu(111)] surfaces to hydrogen (H 2) and mixtures of carbon dioxide (CO 2)/H 2 show an absence of carbon (C) 1s signal, no asymmetries in the oxygen (O) 1smore » peak, and a Zn:O intensity close to 1:1. Thus and finally, the most active phase of these catalysts contained a ZnO-Cu interface.« less
Response to Comment on "Active sites for CO2 hydrogenation to methanol on Cu/ZnO catalysts".

PubMed

Kattel, Shyam; Ramírez, Pedro J; Chen, Jingguang G; Rodriguez, José A; Liu, Ping

2017-09-01

In their Comment on the our recent Report, Nakamura et al argue that our x-ray photoelectron spectroscopy (XPS) analysis was affected by the presence of formate species on the catalyst surface. This argument is not valid because the reactant gases were evacuated at temperatures from 525 to 575 kelvin, conditions under which formate is not stable on the catalyst surface. An analysis of the XPS results obtained after exposing zinc oxide/copper (111) [ZnO/Cu(111)] surfaces to hydrogen (H 2 ) and mixtures of carbon dioxide (CO 2 )/H 2 show an absence of carbon (C) 1s signal, no asymmetries in the oxygen (O) 1s peak, and a Zn:O intensity close to 1:1. Thus, the most active phase of these catalysts contained a ZnO-Cu interface. Copyright © 2017, American Association for the Advancement of Science.
Study of benzotriazole as corrosion inhibitors of carbon steel in chloride solution containing hydrogen sulfide using electrochemical impedance spectroscopy (EIS)

NASA Astrophysics Data System (ADS)

Solehudin, Agus; Nurdin, Isdiriayani

2014-03-01

Corrosion and inhibition studies on API 5LX65 carbon steel in chloride solution containing various concentrations of benzotriazole has been conducted at temperature of 70°C using Electrochemical Impedance Spectroscopy (EIS). Corroded carbon steel surface with and without inhibitor have been observed using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscopy (EDS). The objectives of this research are to study the performance of benzotriazole as corrosion inhibitors. The experimental results of carbon steel corrosion in 3.5% NaCl solution containing 500 mg/l H2S at different BTAH concentrations showed that corrosion rate of carbon steel decreases with increasing of BTAH concentrations from 0 to 10 mmol/l. The inhibition efficiency of BTAH was found to be affected by its concentration. The optimum efficiency obtained of BTAH is 93% at concentration of 5 mmol/l. The result of XRD and EDS analysis reveal the iron sulfide (FeS) formation on corroded carbon steel surface without inhibitor. The EDS spectrum show the Nitrogen (N) bond on carbon steel surface inhibited by BTAH.
Production of activated carbon from rice husk Vietnam

NASA Astrophysics Data System (ADS)

Korobochkin, V. V.; Tu, N. V.; Hieu, N. M.

2016-09-01

This work is dedicated to the production of activated carbon from rice husk from Delta of the Red River in Viet Nam. At the first stage, carbonization of a rice husk was carried out to obtain material containing 43.1% carbon and 25 % silica with a specific surface area of 51.5 m2/g. After separating of silica (the second stage), the specific surface area of the product increased to 204 m2/g and the silica content decreased to 1.23% by weight as well. The most important stage in the formation of the porous structure of the material is the activation. The products with the high specific surface area in the range of 800-1345 m2/g were obtained by activation of carbonized product with water vapour or carbon dioxide at temperatures of 700 °C and 850 °C, with varying the flow rate of the activating agent and activation time. The best results were achieved by activation of carbon material with water vapour at the flow rate of 0.08 dm3/min per 500 g of material and the temperature of 850 °C.
An Impact Origin for Surface Minerals on Ceres

NASA Astrophysics Data System (ADS)

Zolotov, M. Y.

2013-12-01

The dwarf planet Ceres is the largest body in the main asteroid belt with a hydrated dark rocky surface and an uncertain internal structure [1,2]. Spectra of Ceres in the near- and mid-infrared ranges show that surface materials may not contain abundant serpentine, saponite, sulfates, olivine, pyroxenes, and organic matter [2,3], which are common in carbonaceous chondrites. However, brucite, Mg carbonates, cronstedtite, and magnetite could be abundant and indicate aqueous processes [2,3]. The formation of abundant brucite, carbonates, and cronstedtite requires open-system low-temperature conditions characterized by elevated water/rock ratios and low fugacities of hydrogen and carbon dioxide. The observed mineralogy is more consistent with a near-surface origin than with a formation within Ceres or on planetesimals. The instability of aqueous solutions at the surface of Ceres implies mineral deposition during transient events of fluidal activity. But a warming of near-surface rocks by thermal processes in the interior requires dehydration of rocks, which is not consistent with the low density of Ceres. The lack of low-solubility sulfates in surface materials does not indicate percolation of interior fluids. Carbonate-bearing fluids may not percolate to the cold surface, especially if Ceres had undergone water-rock differentiation [1,4]. The lack of serpentine in surface materials does not indicate a formation of brucite through aqueous alteration of olivine-rich rocks. Though, the observed minerals could form in impact collisions of ice-rich targets and/or impactors. OH-bearing phases may condense from water-rich impact plumes [5]. Brucite and Mg carbonates could form through hydrolysis and carbonation of condensed MgO formed through evaporation of silicates. Apparently abundant carbonates may indicate an ample oxidation of organics. Ferric iron in magnetite and cronstedtite agrees with water-rich and oxidizing impact settings [5]. Turbulent and disequilibrium environments in impact plumes and surges could have led to deposition of minerals which typically do not form together (e.g., brucite and cronstedtite). Aqueous minerals could have formed in impact clouds, crater outflows, transient ice-covered crater lakes, and related hydrothermal systems. The observed clay-sized and spatially homogeneous surface materials [2] could be gravitationally sorted deposits of impact clouds and surges. The surface materials could have formed through impacts on an icy shell of a differentiated Ceres during the Late Heavy Bombardment (LHB) in the inner solar system, which affected may other asteroids [6]. However, mineral-forming processes during collisions of an undifferentiated and hydrated Ceres with water-rich bodies during LHB remain a possibility. A detection of fluidized crater outflows together with topography and composition of surface materials with Dawn will test this hypothesis. Refs: [1] McCord, T.B. et al. (2011) Space Sci. Rev. 163, 63-76. [2] Rivkin, A.S. et al. (2011) Space Sci. Rev. 101, 1-22. [3] Milliken, R.E., and Rivkin, A.S. (2009) Nature Geoscience 2, 258-261. [4] Castillo-Rogez, J.C., and McCord, T.B. (2010) Icarus 205, 443-459. [5] Gerasimov, M.V. et al. (2002) Deep-Sea Res. II 49, 995-1009. [6] Marchi, S. et al. (2013) Nature Geoscience, 6, 303-307.

Adsorption of SOx and NOx in activated viscose fibers.

PubMed

Plens, Ana Carolina O; Monaro, Daniel L G; Coutinho, Aparecido R

2015-01-01

SOx and NOx are emissions resulting from combustion processes and are the main agents that contribute to the formation of acid rain, which causes harm to humans and the environment. Several techniques for removing these pollutants are applied in i.e. oil refineries, thermoelectric that use petroleum oils and vehicular pollution. Among these, highlight the adsorption of contaminants by the usage of activated carbon fibers and activated carbon, which are characterized by high surface area and uniform distribution of pores, providing appropriate conditions for application in processes of removing environmental contaminants. In the present work, activated viscose fibers (AVF) were prepared and applied in adsorption experiments of NO and SO2. The materials produced showed high values of surface area, with a predominance of micro pores with diameters in the range of 1.0 nm. The AVF had satisfactory performance in the removal of contaminants and are compatible with other synthetic fibers. Thus, the formation of active sites of carbon provides contaminants adsorption, demonstrating that carbon fibers cloth can be applied for the removal of pollutants.
Nanotube Surface Arrays: Weaving, Bending, and Assembling on Patterned Silicon

NASA Astrophysics Data System (ADS)

Tsukruk, Vladimir V.; Ko, Hyunhyub; Peleshanko, Sergiy

2004-02-01

We report the fabrication of ordered arrays of oriented and bent carbon nanotube on a patterned silicon surface with a micron scale spacing extending over millimeter size surface areas. We suggest that the patterning is controlled by the hydrodynamic behavior of a fluid front and orientation and bending mechanisms are facilitated by the pinned carbon nanotubes trapped by the liquid-solid-vapor contact line. The bending of the pinned nanotubes occurs along the shrinking receding front of the drying microdroplets. The formation of stratified microfluidic layers is vital for stimulating periodic instabilities of the contact line.
Radiocarbon (14C) Constraints On The Fraction Of Refractory Dissolved Organic Carbon In Primary Marine Aerosol From The Northwest Atlantic

NASA Astrophysics Data System (ADS)

Beaupre, S. R.; Kieber, D. J.; Keene, W. C.; Long, M. S.; Frossard, A. A.; Kinsey, J. D.; Duplessis, P.; Chang, R.; Maben, J. R.; Lu, X.; Zhu, Y.; Bisgrove, J.

2017-12-01

Nearly all organic carbon in seawater is dissolved (DOC), with more than 95% considered refractory based on modeled average lifetimes ( 16,000 years) and characteristically old bulk radiocarbon (14C) ages (4000 - 6000 years) that exceed the timescales of overturning circulation. Although this refractory dissolved organic carbon (RDOC) is present throughout the oceans as a major reservoir of the global carbon cycle, its sources and sinks are poorly constrained. Recently, RDOC was proposed to be removed from the oceans through adsorption onto the surfaces of rising bubble plumes produced by breaking waves, ejection into the atmosphere via bubble bursting as a component of primary marine aerosol (PMA), and subsequent oxidation in the atmosphere. To test this mechanism, we used natural abundance 14C (5730 ± 40 yr half-life) to trace the fraction of RDOC in PMA produced in a high capacity generator at two biologically-productive and two oligotrophic hydrographic stations in the Northwest Atlantic Ocean during a research cruise aboard the R/V Endeavor (Sep - Oct 2016). The 14C signatures of PMA separately generated day and night from near-surface (5 m) and deep (2500 m) seawater were compared with corresponding 14C signatures in seawater of near-surface dissolved inorganic carbon (DIC, a proxy for recently produced organic matter), bulk deep DOC (a proxy for RDOC), and near-surface bulk DOC. Results constrain the selectivity of PMA formation from RDOC in natural mixtures of recently produced and refractory DOC. The implications of these results for PMA formation and RDOC biogeochemistry will be discussed.
Measurements of Polyatomic Molecule Formation on an Icy Grain Analog Using Fast Atoms

NASA Technical Reports Server (NTRS)

Chutjian, A.; Madsunkov, S.; Shortt, B. J.; MacAskill, J. A.; Darrach, M. R.

2006-01-01

Carbon dioxide has been produced from the impact of a monoenergetic O(P-3) beam upon a surface cooled to 4.8 K and covered with a CO ice. Using temperature-programmed desorption and mass spectrometer detection, we have detected increasing amounts of CO2 formation with O(P-3) energies of 2, 5, 10, and 14 eV. This is the first measurement of polyatomic molecule formation on a surface with superthermal atoms. The goal of this work is to detect other polyatomic species, such as CH3OH, which can be formed under conditions that simulate the grain temperature, surface coverage, and superthermal atoms present in shock-heated circumstellar and interstellar regions.
The effect of activated carbon support surface modification on characteristics of carbon nanospheres prepared by deposition precipitation of Fe-catalyst

NASA Astrophysics Data System (ADS)

Kristianto, H.; Arie, A. A.; Susanti, R. F.; Halim, M.; Lee, J. K.

2016-11-01

In this study the effect of activated carbon support modification to synthesis of CNSs was observed. Modification of activated carbon was done by using nitric acid. The effect of modification was analyzed from its FTIR spectra. The Fe catalysts were deposited on to the support by using urea deposition precipitation method at various initial catalysts concentration. CNSs was synthesized by utilizing cooking palm oil as renewable carbon source, and pyrolized at 700°C for 1 hour under nitrogen atmosphere. The products obtained then analyzed using SEM-EDS, TEM, XRD, and Raman spectroscopy. The modification of activated carbon support had increased the oxygen functional group. This increase resulted on increase of metal catalysts deposited on activated carbon surface. Peak of C (100) was observed, while ID/IG of samples were obtained around 0.9, which is commonly obtained for CNSs. High catalysts loading on modified activated carbon support caused decomposition of CNSs and formation carbon onion.
Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

PubMed Central

2012-01-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors. PMID:22643113
Correlation study of nanocrystalline carbon doped thin films prepared by a thermionic vacuum arc deposition technique

NASA Astrophysics Data System (ADS)

Dinca-Balan, Virginia; Vladoiu, Rodica; Mandes, Aurelia; Prodan, Gabriel

2017-11-01

The synthesis of Ag, Mg and Si nanocrystalline, embedded in a hydrogen-free amorphous carbon (a-C) matrix, deposited by a high vacuum and free buffer gas technique, were investigated. The films with compact structures and extremely smooth surfaces were prepared using the thermionic vacuum arc method in one electron gun configuration, on glass and silicon substrates. The surface morphology and wettability of the obtained multifunctional thin films were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and free surface energy (FSE) by See System. The results from the TEM measurements show how the Ag, Mg and Si interacted with carbon and the influence these materials have on the thin film structure formation and the grain size distribution. SEM correlated with EDX results reveal a very precise comparative study, regarding the quantity of the elements that morphed into carbides nanostructures. Also, the FSE results prove how different materials in combination with carbon can make changes to the surface properties.
DOE Office of Scientific and Technical Information (OSTI.GOV)

De Yoreo, J; Orme, C; Dove, P

Since the dawn of life on earth, organisms have directed the crystallization of inorganic ions from solution to form minerals that meet specific biological needs. The resulting materials often exhibit remarkable properties, making the processes involved in biomineralization of interest to a wide array of scientific disciplines. From a geochemical standpoint, perhaps the most important consequence is that CaCO{sub 3} biomineral formation occurs in the Oceans on such a large scale that it influences many aspects of seawater chemistry and results in sequestration of carbon in the form of carbonate sediments. In this manner, the products of biomineralization are preservedmore » in the rock record and serve as an extensive chronicle of the interplay between biota and the earth system environment. From the point of view of materials synthesis, biological control over epitaxy is an elegant example of self-organization in complex molecular systems. Through selective introduction of peptides and proteins, living organisms deterministically modify nucleation, step kinetics, surface morphologies, and facet stabilities to produce nanophase materials, topologically complex single-crystals, and multi-layer composite. The resulting materials have biological functions as diverse as structural supports, porous filtration media, grinding and cutting tools, lenses, gravity sensors and magnetic guidance systems. As Table I shows, calcium carbonate minerals are ubiquitous amongst these biomineral structures. In addition , calcium carbonate is a well studied material that is easily crystallized and has known solution chemistry. Consequently, the calcium carbonate system provides an excellent model for investigating biomineralization processes. Surprisingly, in spite of the identification of carbonate biogenesis as a critical contributor to the carbon reservoir mediating climate change, and the enormous potential of biomimetic synthesis for production of tailored, crystalline nano- and micro-structured materials, the fundamental physical controls on carbonate biomineral formation remain poorly understood. Carbonates are formed in diverse environments almost exclusively by living organisms. These naturally occurring marine and fresh water minerals most commonly occur as the polymorphs of calcite, aragonite and vaterite which are nucleated and grown in the exoskeletons and tissues of marine and freshwater organisms ranging from simple bacteria and algae to crustaceans, molluscs, or sponges. It is known that the soluble fraction associated with mineralizing parts of organisms plays a primary role in crystal formation. In the formation of molluscan shells, this fraction is distinguished by the common presence of aspartic acid rich amino acid mixtures. It is also known that carbonates exposed to different polyamino acids exhibit different crystal habits. Belcher et al. showed that exposing growing CaCO{sub 3} crystals alternately to solutions containing polyanionic proteins associated with the aragonitic and calcitic layers of mollusc shells led to sequential switching of the crystal structure of the newly grown material between that of aragonite and calcite. Further work has demonstrated that these protein mixtures alter the morphology of the calcite growth surface and that they contain two fractions effecting growth: a step-binding fraction that inhibits step advancement on calcite surfaces, and a surface binding fraction that appears to lead to the subsequent nucleation of aragonite. Wierzbicki et al. found that polyaspartate molecules (ASP{sub 20}) bind to calcite surfaces. Finally, modeling of ASP{sub 15} binding to calcite planes predicts large binding energies for well defined orientations. This and related evidence shows that systematic relationships between crystal morphology and surface interactions with the reactive groups of the organic molecules must exist. However, the interplay between surface chemistry and the physical processes of nucleation and crystal growth are poorly understood because, until recently only ex situ biochemical studies focusing on the effect of changes in solution chemistry and/or surface stereo-chemistry on macroscopic crystal morphology had been performed.« less
Simultaneous Magnetic and Charge Doping of Topological Insulators with Carbon

NASA Astrophysics Data System (ADS)

Shen, Lei; Zeng, Minggang; Lu, Yunhao; Yang, Ming; Feng, Yuan Ping

2013-12-01

A two-step doping process, magnetic followed by charge or vice versa, is required to produce massive topological surface states (TSS) in topological insulators for many physics and device applications. Here, we demonstrate simultaneous magnetic and hole doping achieved with a single dopant, carbon, in Bi2Se3 by first-principles calculations. Carbon substitution for Se (CSe) results in an opening of a sizable surface Dirac gap (up to 82 meV), while the Fermi level remains inside the bulk gap and close to the Dirac point at moderate doping concentrations. The strong localization of 2p states of CSe favors spontaneous spin polarization via a p-p interaction and formation of ordered magnetic moments mediated by surface states. Meanwhile, holes are introduced into the system by CSe. This dual function of carbon doping suggests a simple way to realize insulating massive TSS.
Modulation of Protein Fouling and Interfacial Properties at Carbon Surfaces via Immobilization of Glycans Using Aryldiazonium Chemistry

PubMed Central

Zen, Federico; Angione, M. Daniela; Behan, James A.; Cullen, Ronan J.; Duff, Thomas; Vasconcelos, Joana M.; Scanlan, Eoin M.; Colavita, Paula E.

2016-01-01

Carbon materials and nanomaterials are of great interest for biological applications such as implantable devices and nanoparticle vectors, however, to realize their potential it is critical to control formation and composition of the protein corona in biological media. In this work, protein adsorption studies were carried out at carbon surfaces functionalized with aryldiazonium layers bearing mono- and di-saccharide glycosides. Surface IR reflectance absorption spectroscopy and quartz crystal microbalance were used to study adsorption of albumin, lysozyme and fibrinogen. Protein adsorption was found to decrease by 30–90% with respect to bare carbon surfaces; notably, enhanced rejection was observed in the case of the tested di-saccharide vs. simple mono-saccharides for near-physiological protein concentration values. ζ-potential measurements revealed that aryldiazonium chemistry results in the immobilization of phenylglycosides without a change in surface charge density, which is known to be important for protein adsorption. Multisolvent contact angle measurements were used to calculate surface free energy and acid-base polar components of bare and modified surfaces based on the van Oss-Chaudhury-Good model: results indicate that protein resistance in these phenylglycoside layers correlates positively with wetting behavior and Lewis basicity. PMID:27108562
Modulation of Protein Fouling and Interfacial Properties at Carbon Surfaces via Immobilization of Glycans Using Aryldiazonium Chemistry

NASA Astrophysics Data System (ADS)

Zen, Federico; Angione, M. Daniela; Behan, James A.; Cullen, Ronan J.; Duff, Thomas; Vasconcelos, Joana M.; Scanlan, Eoin M.; Colavita, Paula E.

2016-04-01

Carbon materials and nanomaterials are of great interest for biological applications such as implantable devices and nanoparticle vectors, however, to realize their potential it is critical to control formation and composition of the protein corona in biological media. In this work, protein adsorption studies were carried out at carbon surfaces functionalized with aryldiazonium layers bearing mono- and di-saccharide glycosides. Surface IR reflectance absorption spectroscopy and quartz crystal microbalance were used to study adsorption of albumin, lysozyme and fibrinogen. Protein adsorption was found to decrease by 30-90% with respect to bare carbon surfaces; notably, enhanced rejection was observed in the case of the tested di-saccharide vs. simple mono-saccharides for near-physiological protein concentration values. ζ-potential measurements revealed that aryldiazonium chemistry results in the immobilization of phenylglycosides without a change in surface charge density, which is known to be important for protein adsorption. Multisolvent contact angle measurements were used to calculate surface free energy and acid-base polar components of bare and modified surfaces based on the van Oss-Chaudhury-Good model: results indicate that protein resistance in these phenylglycoside layers correlates positively with wetting behavior and Lewis basicity.
Highly Microporous Nitrogen-doped Carbon Synthesized from Azine-linked Covalent Organic Framework and its Supercapacitor Function.

PubMed

Kim, Gayoung; Yang, Jun; Nakashima, Naotoshi; Shiraki, Tomohiro

2017-12-11

Porous carbons with nitrogen-doped (N-doped) structures are promising materials for advanced energy conversion and storage applications, including supercapacitors and fuel cell catalysts. In this study, microporous N-doped carbon was successfully fabricated through carbonization of covalent organic frameworks (COFs) with an azine-linked two-dimensional molecular network (ACOF1). In the carbonized ACOF1, micropores with diameters smaller than 1 nm are selectively formed, and a high specific surface area (1596 cm 2 g -1 ) is achieved. In addition, the highly porous structure with N-doped sites results in enhancement of the electrochemical capacitance. Detailed investigation for the micropore-forming process reveals that the formation of nitrogen gas during the thermal degradation of the azine bond contributes to the microporous structure formation. Therefore, the present direct carbonization approach using COFs allows the fabrication of microporous heteroatom-doped carbons, based on molecularly designed COFs, toward future electrochemical and energy applications. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Density-functional theory study of dimethyl carbonate synthesis by methanol oxidative carbonylation on single-atom Cu1/graphene catalyst

NASA Astrophysics Data System (ADS)

Sun, Wei; Shi, Ruina; Wang, Xuhui; Liu, Shusen; Han, Xiaoxia; Zhao, Chaofan; Li, Zhong; Ren, Jun

2017-12-01

The mechanism for dimethyl carbonate (DMC) synthesis by oxidation carbonylation of methanol on a single-atom Cu1/graphene catalyst was investigated by density-functional theory calculations. Carbon vacancies in graphene can significantly enhance the interaction between Cu atoms and graphene supports, and provide an increased transfer of electrons from Cu atoms to the graphene sheet. Compared with Cu-doped divacancy graphene (Cu/DG), Cu-doped monovacancy graphene (Cu/MG) provides a stronger interaction between adsorbents and the catalyst surface. Among the reaction processes over Cu1/graphene catalysts, CO insertion into methoxide was more favorable than dimethoxide. The rate-limiting step on the Cu/DG surface is the carbomethoxide reaction with methoxide, which is exothermic by 164.6 kJ mol-1 and has an activation barrier of 190.9 kJ mol-1 energy. Compared with that on the Cu crystal surface, Cu4 and Cu3Rh clusters, and the Cu2O(111) surface, the rate-determining step for DMC formation on Cu/MG, which is CO insertion into methoxide, needs to overcome the lowest barrier of 73.5 kJ mol-1 and is exothermic by 44.6 kJ mol-1. Therefore, Cu/MG was beneficial to the formation of DMC as a single-atom catalyst.
Graphite-Conjugated Rhenium Catalysts for Carbon Dioxide Reduction

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

Oh, Seokjoon; Gallagher, James R.; Miller, Jeffrey T.

2016-02-17

Condensation of fac-Re(5,6-diamino-1,10-phenanthroline)(CO)(3)Cl to o-quinone edge defects on graphitic carbon surfaces generates graphite-conjugated rhenium (GCC-Re) catalysts that are highly active for CO2 reduction to CO in acetonitrile electrolyte. X-ray photo-electron and X-ray absorption spectroscopies establish the formation of surface-bound Re centers with well-defined coordination environments. GCC-Re species on glassy carbon surfaces display catalytic currents greater than 50 mA cm(-2) with 96 +/- 3% Faradaic efficiency for CO production. Normalized for the number of Re active sites, GCC-Re catalysts exhibit higher turnover frequencies than that of a soluble molecular analogue, fac-Re(1,10-phenanthroline)(CO)(3)Cl, and turnover numbers greater than 12,000. In contrast to themore » molecular analogue, GCC-Re surfaces display a Tafel slope of 150 mV/decade, indicative of a catalytic mechanism involving rate-limiting one-electron transfer. This work establishes graphite conjugation as a powerful strategy for generating well-defined, tunable, heterogeneous electrocatalysts on ubiquitous graphitic carbon surfaces.« less
Planktic foraminifera form their shells by attachment of metastable carbonate particles

NASA Astrophysics Data System (ADS)

Wirth, R.; Jacob, D. E.; Eggins, S.

2016-12-01

Planktic foraminifera shells contribute up to half the inorganic carbon exported from the surface ocean to the seafloor. Their tiny calcium carbonate shells are preserved in sediments as calcite, and provide our most valuable geochemical archive of changes surface ocean conditions and climate spanning the last 100 million years. Here we show the shells of living planktic foraminifers Orbulina universa and Neogloboquadrina dutertrei consist of nano-particulate vaterite and amorphous calcium carbonate. This indicates formation via a non-classical crystallization pathway involving metastable carbonate intermediate phases before transforming to calcite, and requires a new perspective on how geochemical proxies are incorporated into planktic foraminifer shells. Our findings indicate planktic foraminifer shells could be far more susceptible to dissolution and ocean acidification than previously thought, and account for unexpected shell dissolution above the calcite saturation horizon in the ocean, which is a major uncertainty in modelling oceanic carbon fluxes.
Cooked Food Waste-An Efficient and Less Expensive Precursor for the Generation of Activated Carbon.

PubMed

Krithiga, Thangavelu; Sabina, Xavier Janet; Rajesh, Baskaran; Ilbeygi, Hamid; Shetty, Adka Nityananda; Reddy, Ramanjaneya; Karthikeyan, Jayabalan

2018-06-01

Activated carbon was synthesized from cooked food waste, especially dehydrated rice kernels, by chemical activation method using NaOH and KOH as activating agents. It was then characterized by ultimate and proximate analysis, BET surface analysis, XRD, FTIR, Raman and SEM. The XRD patterns and Raman spectra confirmed the amorphous nature of the prepared activated carbons. Ultimate analysis showed an increase in the carbon content after activation of the raw carbon samples. Upon activation with NaOH and KOH, the surface area of the carbon sample was found to have increased from 0.3424 to 539.78 and 306.83 m2g-1 respectively. The SEM images revealed the formation of heterogeneous pores on the surface of the activated samples. The samples were then tested for their adsorption activity using acetic acid and methylene blue. Based on the regression coefficients, the adsorption kinetics of methylene blue dye were fitted with pseudo-second order model for both samples. Similarly, the Freundlich isotherm was found to be a better fit than Langmuir isotherm for both samples. The activity of thus prepared activated carbons was found to be comparable with the commercial carbon.
A new mechanism for selective adsorption of rubber on carbon black surface caused by nano-confinement in SBR/NBR solution

NASA Astrophysics Data System (ADS)

Kawazoe, Masayuki

A novel mechanism of selective adsorption of rubber molecules onto carbon black surface in a binary immiscible rubber blend solution has been proposed in this dissertation. The phenomenon leads to uneven distribution of carbon black to the specific polymer in the blend and the obtained electrically conductive composite showed drastic reduction of percolation threshold concentration (PTC). The mechanism and the feature of conductive network formation have much potential concerning both fundamental understanding and industrial application to improve conductive polymer composites. In chapter I, carbon black filled conductive polymer composites are briefly reviewed. Then, in chapter II, a mechanism of rubber molecular confinement into carbon black aggregate structure is introduced to explain the selective adsorption of a specific rubber onto carbon black surface in an immiscible rubber solution blend (styrene butadiene rubber (SBR) and acrylonitrile butadiene rubber (NBR) with toluene or chloroform). Next, in chapters III and IV, polymers with various radius of gyration (Rg) and carbon blacks with various aggregate structure are examined to verify the selective adsorption mechanism. Finally, in chapter V, the novel mechanism was applied to create unique meso-/micro-unit conductive network in carbon black dispersed SBR/NBR composites.
Carbon/ λ-MnO 2 composites for supercapacitor electrodes

NASA Astrophysics Data System (ADS)

Malak-Polaczyk, A.; Matei-Ghimbeu, C.; Vix-Guterl, C.; Frackowiak, E.

2010-04-01

In the present work a composite of carbon with λ-MnO 2 have been synthesized by a simple two-step route. In the first step, to obtain LiMn 2O 4/carbon material, mesoporous activated carbon was impregnated with the solution of precursor metal salts and heated subsequently. As-prepared materials were acid treated which resulted in the formation of λ-MnO 2/carbon. Physical properties, structure and specific surface area of electrode materials were studied by TEM, X-ray diffraction and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. TEM images confirmed well dispersed λ-MnO 2 particles on the surface of carbon material. The carbon in the composite plays an important role as the surface area enhancing component and a support of pseudocapacitive material. Furthermore, the through-connected porosity serves as a continuous pathway for electrolyte transport. A synergetic effect of the porous carbon framework and of the redox properties of the λ-MnO 2 is at the origin of improvement of specific capacitance values which has been observed for composites after delithiation.
Autolytic hydrolases affect sexual and asexual development of Aspergillus nidulans.

PubMed

Emri, Tamás; Vékony, Viktória; Gila, Barnabás; Nagy, Flóra; Forgács, Katalin; Pócsi, István

2018-03-30

Radial growth, asexual sporulation, and cleistothecia formation as well as extracellular chitinase and proteinase formation of Aspergillus nidulans were monitored in surface cultures in order to study the physiological role of extracellular hydrolase production in carbon-stressed cultures. We set up carbon-stressed and carbon-overfed experimental conditions by varying the starting glucose concentration within the range of 2.5 and 40 g/L. Glucose starvation induced radial growth and hydrolase production and enhanced the maturation of cleistothecia; meanwhile, glucose-rich conditions enhanced mycelial biomass, conidia, and cleistothecia production. Double deletion of chiB and engA (encoding an extracellular endochitinase and a β-1,3-endoglucanase, respectively) decreased conidia production under carbon-stressed conditions, suggesting that these autolytic hydrolases can support conidia formation by releasing nutrients from the cell wall polysaccharides of dead hyphae. Double deletion of prtA and pepJ (both genes encode extracellular proteases) reduced the number of cleistothecia even under carbon-rich conditions except in the presence of casamino acids, which supports the view that sexual development and amino acid metabolism are tightly connected to each other in this fungus.
By-products of the serpentinization process on the Oman ophiolite : chemical and isotopic composition of carbonate deposits in alkaline springs, and associated secondary phases

NASA Astrophysics Data System (ADS)

Sissmann, O.; Martinez, I.; Deville, E.; Beaumont, V.; Pillot, D.; Prinzhofer, A.; Vacquand, C.; Chaduteau, C.; Agrinier, P.; Guyot, F. J.

2014-12-01

The isotopic compositions (d13C, d18O) of natural carbonates produced by the alteration of basic and ultrabasic rocks on the Oman ophiolite have been measured in order to better understand their formation mechanisms. Fossil carbonates developed on altered peridotitic samples, mostly found in fractures, and contemporary carbonates were studied. The samples bear a large range of d13C. Those collected in veins are magnesian (magnesite, dolomite) and have a carbon signature reflecting mixing of processes and important fractionation (-11‰ to 8‰). Their association with talc and lizardite suggests they are by-products of a serpentinization process, that must have occurred as a carbon-rich fluid was circulating at depth. On the other hand, the carbonates are mostly calcic when formed in alkaline springs, most of which are located in the vicinity of lithological discontinuities such as the peridotite-gabbro contact (Moho). Aragonite forms a few meters below the surface of the ponds in Mg-poor water, and is systematically associated with brucite (Mg(OH)2). This suggests most of the Mg dissolved at depth has reprecipitated during the fluid's ascension through fractures or faults as carbonates and serpentine. Further up, on the surface waters of the ponds (depleted in Mg and D.I.C.), thin calcite films precipitate and reach extremely negative d13C values (-28‰), which could reflect either a biological carbon source, or kinetic fractionation from pumping atmospheric CO2. Their formation represent an efficient and natural process for carbon dioxide mineral sequestration. The d18O signature from all samples confirm the minerals crystallized from a low-temperature fluid. The hyperalkaline conditions (pH between 11 and 12) allowing for these fast precipitation kinetics are generated by the serpentinization process occurring at depth, as indicated by the measured associated H2-rich gas flows (over 50%) seeping out to the surface.

Carbon mediated reduction of silicon dioxide and growth of copper silicide particles in uniform width channels

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

Pizzocchero, Filippo; Bøggild, Peter; Booth, Timothy J.

We show that surface arc-discharge deposited carbon plays a critical intermediary role in the breakdown of thermally grown oxide diffusion barriers of 90 nm on a silicon wafer at 1035 °C in an Ar/H{sub 2} atmosphere, resulting in the formation of epitaxial copper silicide particles in ≈ 10 μm wide channels, which are aligned with the intersections of the (100) surface of the wafer and the (110) planes on an oxidized silicon wafer, as well as endotaxial copper silicide nanoparticles within the wafer bulk. We apply energy dispersive x-ray spectroscopy, in combination with scanning and transmission electron microscopy of focusedmore » ion beam fabricated lammelas and trenches in the structure to elucidate the process of their formation.« less
Electrocatalytic Production of C3-C4 Compounds by Conversion of CO2 on a Chloride-Induced Bi-Phasic Cu2O-Cu Catalyst.

PubMed

Lee, Seunghwa; Kim, Dahee; Lee, Jaeyoung

2015-12-01

Electrocatalytic conversion of carbon dioxide (CO2) has recently received considerable attention as one of the most feasible CO2 utilization techniques. In particular, copper and copper-derived catalysts have exhibited the ability to produce a number of organic molecules from CO2. Herein, we report a chloride (Cl)-induced bi-phasic cuprous oxide (Cu2O) and metallic copper (Cu) electrode (Cu2OCl) as an efficient catalyst for the formation of high-carbon organic molecules by CO2 conversion, and identify the origin of electroselectivity toward the formation of high-carbon organic compounds. The Cu2OCl electrocatalyst results in the preferential formation of multi-carbon fuels, including n-propanol and n-butane C3-C4 compounds. We propose that the remarkable electrocatalytic conversion behavior is due to the favorable affinity between the reaction intermediates and the catalytic surface. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Natural oil slicks fuel surface water microbial activities in the northern Gulf of Mexico

PubMed Central

Ziervogel, Kai; D'souza, Nigel; Sweet, Julia; Yan, Beizhan; Passow, Uta

2014-01-01

We conducted a series of roller tank incubations with surface seawater from the Green Canyon oil reservoir, northern Gulf of Mexico, amended with either a natural oil slick (GCS-oil) or pristine oil. The goal was to test whether bacterial activities of natural surface water communities facilitate the formation of oil-rich marine snow (oil snow). Although oil snow did not form during any of our experiments, we found specific bacterial metabolic responses to the addition of GCS-oil that profoundly affected carbon cycling within our 4-days incubations. Peptidase and β-glucosidase activities indicative of bacterial enzymatic hydrolysis of peptides and carbohydrates, respectively, were suppressed upon the addition of GCS-oil relative to the non-oil treatment, suggesting that ascending oil and gas initially inhibits bacterial metabolism in surface water. Biodegradation of physically dispersed GCS-oil components, indicated by the degradation of lower molecular weight n-alkanes as well as the rapid transformation of particulate oil-carbon (C: N >40) into the DOC pool, led to the production of carbohydrate- and peptide-rich degradation byproducts and bacterial metabolites such as transparent exopolymer particles (TEP). TEP formation was highest at day 4 in the presence of GCS-oil; in contrast, TEP levels in the non-oil treatment already peaked at day 2. Cell-specific enzymatic activities closely followed TEP concentrations in the presence and absence of GCS-oil. These results demonstrate that the formation of oil slicks and activities of oil-degrading bacteria result in a temporal offset of microbial cycling of organic matter, affecting food web interactions and carbon cycling in surface waters over cold seeps. PMID:24847314
Natural oil slicks fuel surface water microbial activities in the northern Gulf of Mexico.

PubMed

Ziervogel, Kai; D'Souza, Nigel; Sweet, Julia; Yan, Beizhan; Passow, Uta

2014-01-01

We conducted a series of roller tank incubations with surface seawater from the Green Canyon oil reservoir, northern Gulf of Mexico, amended with either a natural oil slick (GCS-oil) or pristine oil. The goal was to test whether bacterial activities of natural surface water communities facilitate the formation of oil-rich marine snow (oil snow). Although oil snow did not form during any of our experiments, we found specific bacterial metabolic responses to the addition of GCS-oil that profoundly affected carbon cycling within our 4-days incubations. Peptidase and β-glucosidase activities indicative of bacterial enzymatic hydrolysis of peptides and carbohydrates, respectively, were suppressed upon the addition of GCS-oil relative to the non-oil treatment, suggesting that ascending oil and gas initially inhibits bacterial metabolism in surface water. Biodegradation of physically dispersed GCS-oil components, indicated by the degradation of lower molecular weight n-alkanes as well as the rapid transformation of particulate oil-carbon (C: N >40) into the DOC pool, led to the production of carbohydrate- and peptide-rich degradation byproducts and bacterial metabolites such as transparent exopolymer particles (TEP). TEP formation was highest at day 4 in the presence of GCS-oil; in contrast, TEP levels in the non-oil treatment already peaked at day 2. Cell-specific enzymatic activities closely followed TEP concentrations in the presence and absence of GCS-oil. These results demonstrate that the formation of oil slicks and activities of oil-degrading bacteria result in a temporal offset of microbial cycling of organic matter, affecting food web interactions and carbon cycling in surface waters over cold seeps.
Room Temperature Halogenation of Polyimide Film Surface using Chlorine Trifluoride Gas

NASA Astrophysics Data System (ADS)

Habuka, Hitoshi; Kosuga, Takahiro; Koike, Kunihiko; Aida, Toshihiro; Takeuchi, Takashi; Aihara, Masahiko

2004-02-01

In order to develop a new application of chlorine trifluoride gas, the halogenation of a polyimide film surface at room temperature and at atmospheric pressure is studied for the first time. The polyimide film surface after exposure to the chlorine trifluoride gas shows a decreased water contact angle with increasing chlorine trifluoride gas concentration and exposure period. Since both X-ray photoelectron spectroscopy and infrared absorption spectroscopy simultaneously showed the formation of a carbon-chlorine bond and carbon-fluorine bond, it is concluded that the chlorine trifluoride gas can easily and safely perform the halogenation of the polyimide film surface under the stated conditions using a low-cost process and equipment.
Growth of carbon structured over Pd, Pt and Ni: A comparative DFT study

NASA Astrophysics Data System (ADS)

Quiroga, Matías Abel

2013-03-01

To elucidate the graphene-like structures mechanisms growth over the M(1 1 1) surface (M = Pd, Pt and Ni) we performed ab initio calculus in the frame of density functional theory with the exchange-correlation functional treated according to the Generalized Gradient Approximation (GGA). In order to avoid the problem that represent the complex interaction between the well formed graphene layer and the metallic surface, we recreate the carbon rings formation initial steps, by adding one by one carbon atoms over M(1 1 1) surface. With this strategy, the chemical bonding is always present until the graphene layer is well formed, in which case the GGA neglects van der Waals dispersive forces. We investigate the electronic properties by studying the band structure and the density of states.
Microporous novolac-derived carbon beads/sulfur hybrid cathode for lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Choudhury, Soumyadip; Krüner, Benjamin; Massuti-Ballester, Pau; Tolosa, Aura; Prehal, Christian; Grobelsek, Ingrid; Paris, Oskar; Borchardt, Lars; Presser, Volker

2017-07-01

Novolac-derived nanoporous carbon beads were used as conductive matrix for lithium-sulfur battery cathodes. We employed a facile self-emulsifying synthesis to obtain sub-micrometer novolac-derived carbon beads with nanopores. After pyrolysis, the carbon beads showed already a specific surface area of 640 m2 g-1 which was increased to 2080 m2 g-1 after physical activation. The non-activated and the activated carbon beads represent nanoporous carbon with a medium and a high surface area, respectively. This allows us to assess the influence of the porosity on the electrochemical performance of lithium-sulfur battery cathodes. The carbon/sulfur hybrids were obtained from two different approaches of sulfur infiltration: melt-infusion of sulfur (annealing) and in situ formation of sulfur from sodium thiosulfate. The best performance (∼880 mAh gsulfur-1 at low charge rate; 5th cycle) and high performance stability (>600 mAh gsulfur-1 after 100 cycles) were found for the activated carbon beads when using melt infusion of sulfur.
Water-wetting surfaces as hydrate promoters during transport of carbon dioxide with impurities.

PubMed

Kuznetsova, Tatiana; Jensen, Bjørnar; Kvamme, Bjørn; Sjøblom, Sara

2015-05-21

Water condensing as liquid drops within the fluid bulk has traditionally been the only scenario accepted in the industrial analysis of hydrate risks. We have applied a combination of absolute thermodynamics and molecular dynamics modeling to analyze the five primary routes of hydrate formation in a rusty pipeline carrying dense carbon dioxide with methane, hydrogen sulfide, argon, and nitrogen as additional impurities. We have revised the risk analysis of all possible routes in accordance with the combination of the first and the second laws of thermodynamics to determine the highest permissible content of water. It was found that at concentrations lower than five percent, hydrogen sulfide will only support the formation of carbon dioxide-dominated hydrate from adsorbed water and hydrate formers from carbon dioxide phase rather than formation in the aqueous phase. Our results indicate that hydrogen sulfide leaving carbon dioxide for the aqueous phase will be able to create an additional hydrate phase in the aqueous region adjacent to the first adsorbed water layer. The growth of hydrate from different phases will decrease the induction time by substantially reducing the kinetically limiting mass transport across the hydrate films. Hydrate formation via adsorption of water on rusty walls will play the decisive role in hydrate formation risk, with the initial concentration of hydrogen sulfide being the critical factor. We concluded that the safest way to eliminate hydrate risks is to ensure that the water content of carbon dioxide is low enough to prevent water dropout via the adsorption mechanism.
Formation of Amorphous Carbon Nanoparticles by the Laser Electrodispersion Method

NASA Astrophysics Data System (ADS)

Gurevich, S. A.; Gorokhov, M. V.; Kozhevin, V. M.; Kukushkin, M. V.; Levitskii, V. S.; Markov, L. K.; Yavsin, D. A.

2018-03-01

Experimental results on the laser ablation of the highly oriented pyrolytic graphite by using light pulses of an Nd:YAG laser (pulse width 25 ns, pulse energy 220 mJ) are presented. Analysis of the surface profile of the carbon target shows that the target material melts in the course of the laser ablation. As a result of ablation, a coating consisting of carbon nanoparticles about 10 nm in size is formed on the substrate placed at a distance of 4 cm from the target. It is assumed that such particles are formed as a result of the electrodispersion of carbon droplets detached from the target surface and charged to an unstable state in the laser plasma plume. Raman spectra of the coatings indicate that the carbon nanoparticles being formed have an amorphous structure.
Surface segregation on Fe3%Si0.04%VC(100) single crystal surfaces

NASA Astrophysics Data System (ADS)

Uebing, C.; Viefhaus, H.

1990-10-01

Surface segregation phenomena on (100) oriented single crystal surfaces of the ferritic Fe-3%Si-0.04%V-C alloy were investigated by AES and LEED. At temperatures below 635 °C vanadium and carbon cosegregation is observed after prolonged heating. At thermodynamic equilibrium the substrate surface is saturated with the binary surface compound VC. The two-dimensional VC is epitaxially arranged on the substrate surface as indicated by LEED investigations. Its structure corresponds to the (100) plane of the three-dimensional VC with rocksalt structure. Sharp above 635 °C the surface compound VC is dissolved into the bulk. At higher temperatures the substrate surface is covered with segregated silicon forming a c(2 × 2) structure. This surface phase transition is reversible. Because of the low concentration and slow diffusion of vanadium, non-equilibrium surface states are formed as intermediates upon segregation of silicon and carbon. Below 500 °C a disordered graphite layer with a characteristical asymmetrical C Auger peak is observed on the substrate surface. Above 500 °C carbon segregation leads to the formation of an ordered c(2 × 2) structure with a symmetrical C Auger peak being characteristic for carbidic or atomically adsorbed species. At increasing temperatures silicon segregation takes place leading to a c(2 × 2) structure. Between silicon and carbon site competition is effective.
Carbon cycle history through the Middle Jurassic (Aalenian - Bathonian) of the Mecsek Mountains, Southern Hungary

NASA Astrophysics Data System (ADS)

Price, Gregory D.; Főzy, István; Galácz, András

2018-04-01

A carbonate carbon isotope curve from the Aalenian-Bathonian interval is presented from the Óbánya valley, of the Mecsek Mountains, Hungary. This interval is certainly less well constrained and studied than other Jurassic time slices. The Óbánya valley lies in the eastern part of the Mecsek Mountains, between Óbánya and Kisújbánya and provides exposures of an Aalenian to Lower Cretaceous sequence. It is not strongly affected by tectonics, as compared to other sections of eastern Mecsek of the same age. In parts, a rich fossil assemblage has been collected, with Bathonian ammonites being especially valuable at this locality. The pelagic Middle Jurassic is represented by the Komló Calcareous Marl Formation and thin-bedded limestones of the Óbánya Limestone Formation. These are overlain by Upper Jurassic siliceous limestones and radiolarites of the Fonyászó Limestone Formation. Our new data indicate a series of carbon isotope anomalies within the late Aalenian and early-middle Bajocian. In particular, analysis of the Komló Calcareous Marl Formation reveals a negative carbon isotope excursion followed by positive values that occurs near the base of the section (across the Aalenian-Bajocian boundary). The origin of this carbon-isotope anomaly is interpreted to lie in significant changes to carbon fluxes potentially stemming from reduced run off, lowering the fertility of surface waters which in turn leads to lessened primary production and a negative δ13C shift. These data are comparable with carbonate carbon isotope records from other Tethyan margin sediments. Our integrated biostratigraphy and carbon isotope stratigraphy enable us to improve stratigraphic correlation and age determination of the examined strata. Therefore, this study of the Komló Calcareous Marl Formation confirms that the existing carbon isotope curves serve as a global standard for Aalenian-Bathonian δ13C variation.
Spatial Distributions of Metal Atoms During Carbon SWNTs Formation: Measurements and Modelling

NASA Technical Reports Server (NTRS)

Cau, M.; Dorval, N.; Attal-Tretout, B.; Cochon, J. L.; Loiseau, A.; Farhat, S.; Hinkov, I.; Scott, C. D.

2004-01-01

Experiments and modelling have been undertaken to clarify the role of metal catalysts during single-wall carbon nanotube formation. For instance, we wonder whether the metal catalyst is active as an atom, a cluster, a liquid or solid nanoparticle [1]. A reactor has been developed for synthesis by continuous CO2-laser vaporisation of a carbon-nickel-cobalt target in laminar helium flow. The laser induced fluorescence technique [2] is applied for local probing of gaseous Ni, Co and CZ species throughout the hot carbon flow of the target heated up to 3500 K. A rapid depletion of C2 in contrast to the spatial extent of metal atoms is observed in the plume (Fig. 1). This asserts that C2 condenses earlier than Ni and Co atoms.[3, 4]. The depletion is even faster when catalysts are present. It may indicate that an interaction between metal atoms and carbon dimers takes place in the gas as soon as they are expelled from the target surface. Two methods of modelling are used: a spatially I-D calculation developed originally for the arc process [5], and a zero-D time dependent calculation, solving the chemical kinetics along the streamlines [6]. The latter includes Ni cluster formation. The peak of C2 density is calculated close to the target surface where the temperature is the highest. In the hot region, C; is dominant. As the carbon products move away from the target and mix with the ambient helium, they recombine into larger clusters, as demonstrated by the peak of C5 density around 1 mm. The profile of Ni-atom density compares fairly well with the measured one (Fig. 2). The early increase is due to the drop of temperature, and the final decrease beyond 6 mm results from Ni cluster formation at the eutectic temperature (approx.1600 K).
An Evaluation of the Corrosion and Mechanical Performance of Interstitially Surface Hardened Stainless Steel

DTIC Science & Technology

2013-05-10

Performance of Interstitially Surface Hardened Stainless Steel 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Jones, Jennifer Lynn...interstitial carbon atoms into stainless steel surfaces without the formation of carbides. Surface hardening of machine elements such as impellors or...the corrosion resistance of the stainless steel is retained, rather than degraded, is of particular interest for marine applications. This project
Ion irradiation induced surface modification studies of polymers using SPM

NASA Astrophysics Data System (ADS)

Tripathi, A.; Kumar, Amit; Singh, F.; Kabiraj, D.; Avasthi, D. K.; Pivin, J. C.

2005-07-01

Various types of scanning probe microscopy (SPM) techniques: atomic force microscopy (AFM) (contact and tapping in height and amplitude mode), scanning tunnelling microscopy (STM) and conducting atomic force microscopy (C-AFM) are used for studying ion beam induced surface modifications, nanostructure/cluster formation and disintegration in polymers and similar soft carbon based materials. In the present study, the results of studies on four materials, namely, (A) methyltriethoxysilane/phenyltriethoxysilane (MTES/PTES) based gel, (B) triethoxisilane (TH) based gel, (C) highly oriented pyrolytic graphite (HOPG) bulk and (D) fullerene (C60) thin films are discussed. In the case of Si based gels prepared from pre-cursors containing organic groups (MTES/PTES), hillocks are observed at the surface and their size decreases from 70 to 25 nm with increasing fluence, whereas, in the case of a gel with a stoichiometry SiO1.25H1, prepared from TH, an increases in the size of hillocks is observed. Hillocks are also formed at the surface of HOPG irradiated with 120 MeV Au beam at a low fluence, whereas, formation of craters and a re-organisation of surface features is observed at a higher fluence. In the case of C60 films, 120 MeV Au ion irradiation induces the formation of conducting ion tracks, which is attributed to the transformation from insulating C60 to conducting graphite like carbon.
Optimizing pentacene thin-film transistor performance: Temperature and surface condition induced layer growth modification.

PubMed

Lassnig, R; Hollerer, M; Striedinger, B; Fian, A; Stadlober, B; Winkler, A

2015-11-01

In this work we present in situ electrical and surface analytical, as well as ex situ atomic force microscopy (AFM) studies on temperature and surface condition induced pentacene layer growth modifications, leading to the selection of optimized deposition conditions and entailing performance improvements. We prepared p ++ -silicon/silicon dioxide bottom-gate, gold bottom-contact transistor samples and evaluated the pentacene layer growth for three different surface conditions (sputtered, sputtered + carbon and unsputtered + carbon) at sample temperatures during deposition of 200 K, 300 K and 350 K. The AFM investigations focused on the gold contacts, the silicon dioxide channel region and the highly critical transition area. Evaluations of coverage dependent saturation mobilities, threshold voltages and corresponding AFM analysis were able to confirm that the first 3-4 full monolayers contribute to the majority of charge transport within the channel region. At high temperatures and on sputtered surfaces uniform layer formation in the contact-channel transition area is limited by dewetting, leading to the formation of trenches and the partial development of double layer islands within the channel region instead of full wetting layers. By combining the advantages of an initial high temperature deposition (well-ordered islands in the channel) and a subsequent low temperature deposition (continuous film formation for low contact resistance) we were able to prepare very thin (8 ML) pentacene transistors of comparably high mobility.
Optimizing pentacene thin-film transistor performance: Temperature and surface condition induced layer growth modification

PubMed Central

Lassnig, R.; Hollerer, M.; Striedinger, B.; Fian, A.; Stadlober, B.; Winkler, A.

2015-01-01

In this work we present in situ electrical and surface analytical, as well as ex situ atomic force microscopy (AFM) studies on temperature and surface condition induced pentacene layer growth modifications, leading to the selection of optimized deposition conditions and entailing performance improvements. We prepared p++-silicon/silicon dioxide bottom-gate, gold bottom-contact transistor samples and evaluated the pentacene layer growth for three different surface conditions (sputtered, sputtered + carbon and unsputtered + carbon) at sample temperatures during deposition of 200 K, 300 K and 350 K. The AFM investigations focused on the gold contacts, the silicon dioxide channel region and the highly critical transition area. Evaluations of coverage dependent saturation mobilities, threshold voltages and corresponding AFM analysis were able to confirm that the first 3–4 full monolayers contribute to the majority of charge transport within the channel region. At high temperatures and on sputtered surfaces uniform layer formation in the contact–channel transition area is limited by dewetting, leading to the formation of trenches and the partial development of double layer islands within the channel region instead of full wetting layers. By combining the advantages of an initial high temperature deposition (well-ordered islands in the channel) and a subsequent low temperature deposition (continuous film formation for low contact resistance) we were able to prepare very thin (8 ML) pentacene transistors of comparably high mobility. PMID:26543442
The formation of nanostructured carbon material on a ferrocene-containing polymer surface induced by a high-power ion beam

NASA Astrophysics Data System (ADS)

Kovivchak, V. S.; Kryazhev, Yu. G.; Zapevalova, E. S.

2016-02-01

The surface morphology and the composition of polymer layers based on chlorinated polyvinylchloride with addition of ferrocene (up to 10% of the polymer mass) subject to the action of a nanosecond high-power ion beam are studied. It is demonstrated that carbon material in the form of nanofibers with an average diameter of 80 nm and a length of up to 10 μm is formed on a surface singly irradiated by such beam with a current density of ˜100 A/cm2. A possible mechanism of the observed phenomenon is discussed.
Carbonates in the Martian meteorite Allan Hills 84001 formed at 18 ± 4 °C in a near-surface aqueous environment

PubMed Central

Halevy, Itay; Fischer, Woodward W.; Eiler, John M.

2011-01-01

Despite evidence for liquid water at the surface of Mars during the Noachian epoch, the temperature of early aqueous environments has been impossible to establish, raising questions of whether the surface of Mars was ever warmer than today. We address this problem by determining the precipitation temperature of secondary carbonate minerals preserved in the oldest known sample of Mars’ crust—the approximately 4.1 billion-year-old meteorite Allan Hills 84001 (ALH84001). The formation environment of these carbonates, which are constrained to be slightly younger than the crystallization age of the rock (i.e., 3.9 to 4.0 billion years), has been poorly understood, hindering insight into the hydrologic and carbon cycles of earliest Mars. Using “clumped” isotope thermometry we find that the carbonates in ALH84001 precipitated at a temperature of approximately 18 °C, with water and carbon dioxide derived from the ancient Martian atmosphere. Furthermore, covarying carbonate carbon and oxygen isotope ratios are constrained to have formed at constant, low temperatures, pointing to deposition from a gradually evaporating, subsurface water body—likely a shallow aquifer (meters to tens of meters below the surface). Despite the mild temperatures, the apparently ephemeral nature of water in this environment leaves open the question of its habitability. PMID:21969543
Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential

NASA Astrophysics Data System (ADS)

Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

2015-12-01

To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results.To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06016h
Oxidative Attack of Carbon/Carbon Substrates through Coating Pinholes

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.; Leonhardt, Todd; Curry, Donald; Rapp, Robert A.

1998-01-01

A critical issue with oxidation protected carbon/carbon composites used for spacecraft thermal protection is the formation of coating pinholes. In laboratory experiments, artificial pinholes were drilled through SiC-coatings on a carbon/carbon material and the material was oxidized at 600, 1000, and 1400 C at reduced pressures of air. The attack of the carbon/carbon was quantified by both weight loss and a novel cross-sectioning technique. A two-zone, one dimensional diffusion control model was adapted to analyze this problem. Agreement of the model with experiment was reasonable at 1000 and 1400 C; however results at lower temperatures show clear deviations from the theory suggesting that surface reaction control plays a role.

Conversion of 1,2-Propylene Glycol on Rutile TiO2(110)

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

Chen, Long; Li, Zhenjun; Smith, R. Scott

2014-07-17

We have studied the reactions of 1,2-propylene glycol (1,2-PG), DOCH(CH3)CH2OD, on partially reduced, hydroxylated and oxidized TiO2(110) surfaces using temperature programmed desorption. On reduced TiO2(110), propylene, propanal, and acetone are identified as primary carbon-containing products. While the propylene formation channel dominates at low 1,2-PG coverages, all of the above-mentioned products are observed at high coverages. The carbon-containing products are accompanied by the formation of D2O and D2. The observation of only deuterated products shows that the source of hydrogen (D) is from the 1,2-PG hydroxyls. The role of bridging oxygen vacancy (VO) sites was further investigated by titrating them viamore » hydroxylation and oxidation. The results show that hydroxylation does not change the reactivity because the VO sites are regenerated at 500 K, which is a temperature lower than the 1,2-PG product formation temperature. In contrast, surface oxidation causes significant changes in the product distribution, with increased acetone and propanal formation and decreased propylene formation. Additionally D2 is completely eliminated as an observed product at the expense of D2O formation.« less
Evaluation of Contrail Reduction Strategies Based on Environmental and Operational Costs

NASA Technical Reports Server (NTRS)

Chen, Neil Y.; Sridhar, Banavar; Ng, Hok K.; Li, Jinhua

2013-01-01

This paper evaluates a set of contrail reduction strategies based on environmental and operational costs. A linear climate model was first used to convert climate effects of carbon dioxide emissions and aircraft contrails to changes in Absolute Global Temperature Potential, a metric that measures the mean surface temperature change due to aircraft emissions and persistent contrail formations. The concept of social cost of carbon and the carbon auction price from recent California's cap-and-trade system were then used to relate the carbon dioxide emissions and contrail formations to an environmental cost index. The strategy for contrail reduction is based on minimizing contrail formations by altering the aircraft's cruising altitude. The strategy uses a user-defined factor to trade off between contrail reduction and additional fuel burn and carbon dioxide emissions. A higher value of tradeoff factor results in more contrail reduction but also more fuel burn and carbon emissions. The strategy is considered favorable when the net environmental cost benefit exceeds the operational cost. The results show how the net environmental benefit varies with different decision-making time-horizon and different carbon cost. The cost models provide a guidance to select the trade-off factor that will result in the most net environmental benefit.
Probing surface sites of TiO2: reactions with [HRe(CO)5] and [CH3Re(CO)5].

PubMed

Lobo-Lapidus, Rodrigo J; Gates, Bruce C

2010-10-04

Two carbonyl complexes of rhenium, [HRe(CO)(5)] and [CH(3)Re(CO)(5)], were used to probe surface sites of TiO(2) (anatase). These complexes were adsorbed from the gas phase onto anatase powder that had been treated in flowing O(2) or under vacuum to vary the density of surface OH sites. Infrared (IR) spectra demonstrate the variation in the number of sites, including Ti(+3)-OH and Ti(+4)-OH. IR and extended X-ray absorption fine structure (EXAFS) spectra show that chemisorption of the rhenium complexes led to their decarbonylation, with formation of surface-bound rhenium tricarbonyls, when [HRe(CO)(5)] was adsorbed, or rhenium tetracarbonyls, when [CH(3)Re(CO)(5)] was adsorbed. These reactions were accompanied by the formation of water and surface carbonates and removal of terminal hydroxyl groups associated with Ti(+3) and Ti(+4) ions on the anatase. Data characterizing the samples after adsorption of [HRe(CO)(5)] or [CH(3)Re(CO)(5)] determined a ranking of the reactivity of the surface OH sites, with the Ti(+3)-OH groups being the more reactive towards the rhenium complexes but the less likely to be dehydroxylated. The two rhenium pentacarbonyl probes provided complementary information, suggesting that the carbonate species originate from carbonyl ligands initially bonded to the rhenium and from hydroxyl groups of the titania surface, with the reaction leading to the formation of water and bridging hydroxyl groups on the titania. The results illustrate the value of using a family of organometallic complexes as probes of oxide surface sites.
Post-formation copper-nitrogen species on carbon black: their chemical structures and active sites for oxygen reduction reaction.

PubMed

Xie, Xin; Liu, Jingjun; Li, Tuanfeng; Song, Ye; Wang, Feng

2018-05-16

Note that 3d transition metal and nitrogen co-doped carbon materials (TM-N-C) are considered as the most promising next-generation electrocatalysts alternative to precious Pt for oxygen reduction reaction (ORR). Herein, we have fabricated a Cu-N-C catalyst through directly grafting copper-nitrogen complexes composed by cuprous chloride and ammonia water onto the surface of an industrial carbon black at 500℃. In an alkaline environment, the synthesized catalyst exhibits excellent ORR catalytic activity, which is comparable to the state-of-the-art Pt/C catalyst but far exceeding that obtained by the original carbon. Moreover, the catalyst displays much better stability than the Pt/C. The enhanced ORR performance is proven to originate from the post-formation Cu(I)-N2 and Cu(II)-N4 sites at the carbon surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The possible ORR process catalyzed by these Cu-Nx species is discussed at atomic level. This work provides a simple and fast synthesis strategy for efficient TM-N-C catalysts on a large scale for energy storage and conversion systems. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Study of benzotriazole as corrosion inhibitors of carbon steel in chloride solution containing hydrogen sulfide using electrochemical impedance spectroscopy (EIS)

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

Solehudin, Agus, E-mail: asolehudin@upi.edu; Nurdin, Isdiriayani

2014-03-24

Corrosion and inhibition studies on API 5LX65 carbon steel in chloride solution containing various concentrations of benzotriazole has been conducted at temperature of 70°C using Electrochemical Impedance Spectroscopy (EIS). Corroded carbon steel surface with and without inhibitor have been observed using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscopy (EDS). The objectives of this research are to study the performance of benzotriazole as corrosion inhibitors. The experimental results of carbon steel corrosion in 3.5% NaCl solution containing 500 mg/l H{sub 2}S at different BTAH concentrations showed that corrosion rate of carbon steel decreases with increasing of BTAHmore » concentrations from 0 to 10 mmol/l. The inhibition efficiency of BTAH was found to be affected by its concentration. The optimum efficiency obtained of BTAH is 93% at concentration of 5 mmol/l. The result of XRD and EDS analysis reveal the iron sulfide (FeS) formation on corroded carbon steel surface without inhibitor. The EDS spectrum show the Nitrogen (N) bond on carbon steel surface inhibited by BTAH.« less
Making Activated Carbon for Storing Gas

NASA Technical Reports Server (NTRS)

Wojtowicz, Marek A.; Serio, Michael A.; Suuberg, Eric M.

2005-01-01

Solid disks of microporous activated carbon, produced by a method that enables optimization of pore structure, have been investigated as means of storing gas (especially hydrogen for use as a fuel) at relatively low pressure through adsorption on pore surfaces. For hydrogen and other gases of practical interest, a narrow distribution of pore sizes <2 nm is preferable. The present method is a variant of a previously patented method of cyclic chemisorption and desorption in which a piece of carbon is alternately (1) heated to the lower of two elevated temperatures in air or other oxidizing gas, causing the formation of stable carbon/oxygen surface complexes; then (2) heated to the higher of the two elevated temperatures in flowing helium or other inert gas, causing the desorption of the surface complexes in the form of carbon monoxide. In the present method, pore structure is optimized partly by heating to a temperature of 1,100 C during carbonization. Another aspect of the method exploits the finding that for each gas-storage pressure, gas-storage capacity can be maximized by burning off a specific proportion (typically between 10 and 20 weight percent) of the carbon during the cyclic chemisorption/desorption process.
Influence of plasma treatment of carbon blacks on electrochemical activity of Pt/carbon blacks catalysts for DMFCs

NASA Astrophysics Data System (ADS)

Kim, Seok; Cho, Mi-Hwa; Lee, Jae-Rock; Park, Soo-Jin

In this work, in order to improve the dispersion of platinum catalysts deposited on carbon materials, the effects of surface plasma treatment of carbon blacks (CBs) were investigated. The surface characteristics of the CBs were determined by fourier transformed-infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and Boehm's titration method. The electrochemical properties of the plasma-treated CBs-supported Pt (Pt/CBs) catalysts were analyzed by linear sweep voltammetry (LSV) experiments. From the results of FT-IR and acid-base values, N 2-plasma treatment of the CBs at 300 W intensity led to a formation of a free radical on the CBs. The peak intensity increased with increase of the treatment time, due to the formation of new basic functional groups (such as C-N, C dbnd N, -NH 3 +, -NH, and dbnd NH) by the free radical on the CBs. Accordingly, the basic values were enhanced by the basic functional groups. However, after a specific reaction time, N 2-plasma treatment could hardly influence on change of the surface functional groups of CBs, due to the disappearance of free radical. Consequently, it was found that optimal treatment time was 30 s for the best electro activity of Pt/CBs catalysts and the N 2-plasma treated Pt/CBs possessed the better electrochemical properties than the pristine Pt/CBs.
High temperature surface effects of He + implantation in ICF fusion first wall materials

NASA Astrophysics Data System (ADS)

Zenobia, Samuel J.; Radel, R. F.; Cipiti, B. B.; Kulcinski, Gerald L.

2009-06-01

The first wall armor of the inertial confinement fusion reactor chambers must withstand high temperatures and significant radiation damage from target debris and neutrons. The resilience of multiple materials to one component of the target debris has been investigated using energetic (20-40 keV) helium ions generated in the inertial electrostatic confinement device at the University of Wisconsin. The materials studied include: single-crystalline, and polycrystalline tungsten, tungsten-coated tantalum-carbide 'foams', tungsten-rhenium alloy, silicon carbide, carbon-carbon velvet, and tungsten-coated carbon-carbon velvet. Steady-state irradiation temperatures ranged from 750 to 1250 °C with helium fluences between 5 × 10 17 and 1 × 10 20 He +/cm 2. The crystalline, rhenium alloyed, carbide foam, and powder metallurgical tungsten specimens each experienced extensive pore formation after He + irradiation. Flaking and pore formation occurred on silicon carbide samples. Individual fibers of carbon-carbon velvet specimens sustained erosion and corrugation, in addition to the roughening and rupturing of tungsten coatings after helium ion implantation.
Tuning Product Selectivity for Aqueous CO2 Reduction with a Mn(bipyridine)-pyrene Catalyst Immobilized on a Carbon Nanotube Electrode

PubMed Central

2017-01-01

The development of high-performance electrocatalytic systems for the controlled reduction of CO2 to value-added chemicals is a key goal in emerging renewable energy technologies. The lack of selective and scalable catalysts in aqueous solution currently hampers the implementation of such a process. Here, the assembly of a [MnBr(2,2′-bipyridine)(CO)3] complex anchored to a carbon nanotube electrode via a pyrene unit is reported. Immobilization of the molecular catalyst allows electrocatalytic reduction of CO2 under fully aqueous conditions with a catalytic onset overpotential of η = 360 mV, and controlled potential electrolysis generated more than 1000 turnovers at η = 550 mV. The product selectivity can be tuned by alteration of the catalyst loading on the nanotube surface. CO was observed as the main product at high catalyst loadings, whereas formate was the dominant CO2 reduction product at low catalyst loadings. Using UV–vis and surface-sensitive IR spectroelectrochemical techniques, two different intermediates were identified as responsible for the change in selectivity of the heterogenized Mn catalyst. The formation of a dimeric Mn0 species at higher surface loading was shown to preferentially lead to CO formation, whereas at lower surface loading the electrochemical generation of a monomeric Mn-hydride is suggested to greatly enhance the production of formate. These results emphasize the advantages of integrating molecular catalysts onto electrode surfaces for enhancing catalytic activity while allowing excellent control and a deeper understanding of the catalytic mechanisms. PMID:28885841
Formation of dysprosium carbide on the graphite (0001) surface

DOE PAGES

Lii-Rosales, Ann; Zhou, Yinghui; Wallingford, Mark; ...

2017-07-12

When using scanning tunneling microscopy, we characterize a surface carbide that forms such that Dy is deposited on the basal plane of graphite. In order to form carbide islands on terraces, Dy is first deposited at 650–800 K, which forms large metallic islands. Upon annealing at 1000 K, these clusters convert to carbide. Deposition directly at 1000 K is ineffective because nucleation on terraces is inhibited. Reaction is signaled by the fact that each carbide cluster is partially or totally surrounded by an etch pit. The etch pit is one carbon layer deep for most carbide clusters. Carbide clusters aremore » also identifiable by striations on their surfaces. Based on mass balance, and assuming that only the surface layer of carbon is involved in the reaction, the carbide has stoichiometry D y 2 C . This is Dy-rich compared with the most common bulk carbide Dy C 2 , which may reflect limited surface carbon transport to the carbide.« less
The short-term reduction of uranium by nanoscale zero-valent iron (nZVI): role of oxide shell, reduction mechanism and the formation of U( v )-carbonate phases

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

Tsarev, Sergey; Collins, Richard N.; Ilton, Eugene S.

Nanoscale zero-valent iron (nZVI) is a potential remediation agent for uranium-contaminated groundwaters, however, a complete mechanistic understanding of the processes that lead to uranium immobilization has yet to be achieved. In this study, the short-term anoxic reaction of U(VI) with fresh, (anoxic) aged and corroded nZVI particles was investigated under aqueous conditions conducive to the formation of thermodynamically stable U(VI)-Ca-CO3 ternary aqueous complexes. The first stage of the reaction between U(VI) and nZVI was assigned to sorption processes with the formation of surface U(VI)-carbonate complexes. Aged nZVI removed U(VI) faster than either fresh or corroded nZVI and it is hypothesizedmore » that U reduction initially occurs through the transfer of one electron from Fe(II) in the nZVI surface oxide layer. Evidence for reduction to U(V) was obtained through X-ray photoelectron spectroscopy and by determination of U-O bond distances of ~2.05 Å and 2.27 Å by U LIII-edge X-ray absorption spectroscopy detection of U-O bond distances at ~2.05 Å and 2.27 Å with these distances , similar to thoseat observed for the U(V) site in the mixed U(V)/U(VI) carbonate mineral wyartite. Scanning transmission electron microscopy also demonstrated that U was present as a nanoparticulate phase after one day of reaction, rather than a surface complex. Further reduction to U(IV), as observed in previous studies, would appear to be rate-limiting and coincident with the transformation of this meta-stable U-carbonate phase to uraninite (UO2).« less
The evolution of organic matter in space.

PubMed

Ehrenfreund, Pascale; Spaans, Marco; Holm, Nils G

2011-02-13

Carbon, and molecules made from it, have already been observed in the early Universe. During cosmic time, many galaxies undergo intense periods of star formation, during which heavy elements like carbon, oxygen, nitrogen, silicon and iron are produced. Also, many complex molecules, from carbon monoxide to polycyclic aromatic hydrocarbons, are detected in these systems, like they are for our own Galaxy. Interstellar molecular clouds and circumstellar envelopes are factories of complex molecular synthesis. A surprisingly high number of molecules that are used in contemporary biochemistry on the Earth are found in the interstellar medium, planetary atmospheres and surfaces, comets, asteroids and meteorites and interplanetary dust particles. Large quantities of extra-terrestrial material were delivered via comets and asteroids to young planetary surfaces during the heavy bombardment phase. Monitoring the formation and evolution of organic matter in space is crucial in order to determine the prebiotic reservoirs available to the early Earth. It is equally important to reveal abiotic routes to prebiotic molecules in the Earth environments. Materials from both carbon sources (extra-terrestrial and endogenous) may have contributed to biochemical pathways on the Earth leading to life's origin. The research avenues discussed also guide us to extend our knowledge to other habitable worlds.
Effect of surface Fe-S hybrid structure on the activity of the perfect and reduced α-Fe2O3(001) for chemical looping combustion

NASA Astrophysics Data System (ADS)

Xiao, Xianbin; Qin, Wu; Wang, Jianye; Li, Junhao; Dong, Changqing

2018-05-01

Sulfurization of the gradually reduced Fe2O3 surfaces is inevitable while Fe2O3 is used as an oxygen carrier (OC) for coal chemical looping combustion (CLC), which will result in formation of Fe-S hybrid structure on the surfaces. The Fe-S hybrid structure will directly alter the reactivity of the surfaces. Therefore, detailed properties of Fe-S hybrid structure over the perfect and reduced Fe2O3(001) surfaces, and its effect on the interfacial interactions, including CO oxidization and decomposition on the surfaces, were investigated by using density functional theory (DFT) calculations. The S atom prefers to chemically bind to Fe site with electron transfer from the surfaces to the S atom, and a deeper reduction of Fe2O3(001) leads to an increasing interaction between S and Fe. The formation of Fe-S hybrid structure alters the electronic properties of the gradually reduced Fe2O3(001) surfaces, promoting CO oxidation on the surfaces ranging from Fe2O3 to FeO, but depressing carbon deposition on the surfaces ranging from FeO to Fe. The sulfurized FeO acts as a watershed to realize relatively high CO oxidation rate and low carbon deposition. Results provided a fundamental understanding for controlling and optimizing the CLC processes.
Mechanisms and efficiency of the simultaneous removal of metals and cyanides by using ferrate(VI): crucial roles of nanocrystalline iron(III) oxyhydroxides and metal carbonates.

PubMed

Filip, Jan; Yngard, Ria A; Siskova, Karolina; Marusak, Zdenek; Ettler, Vojtech; Sajdl, Petr; Sharma, Virender K; Zboril, Radek

2011-08-29

The reaction of potassium ferrate(VI), K(2)FeO(4), with weak-acid dissociable cyanides--namely, K(2)[Zn(CN)(4)], K(2)[Cd(CN)(4)], K(2)[Ni(CN)(4)], and K(3)[Cu(CN)(4)]--results in the formation of iron(III) oxyhydroxide nanoparticles that differ in size, crystal structure, and surface area. During cyanide oxidation and the simultaneous reduction of iron(VI), zinc(II), copper(II), and cadmium(II), metallic ions are almost completely removed from solution due to their coprecipitation with the iron(III) oxyhydroxides including 2-line ferrihydrite, 7-line ferrihydrite, and/or goethite. Based on the results of XRD, Mössbauer and IR spectroscopies, as well as TEM, X-ray photoelectron emission spectroscopy, and Brunauer-Emmett-Teller measurements, we suggest three scavenging mechanisms for the removal of metals including their incorporation into the ferrihydrite crystal structure, the formation of a separate phase, and their adsorption onto the precipitate surface. Zn and Cu are preferentially and almost completely incorporated into the crystal structure of the iron(III) oxyhydroxides; the formation of the Cd-bearing, X-ray amorphous phase, together with Cd carbonate is the principal mechanism of Cd removal. Interestingly, Ni remains predominantly in solution due to the key role of nickel(II) carbonate, which exhibits a solubility product constant several orders of magnitude higher than the carbonates of the other metals. Traces of Ni, identified in the iron(III) precipitate, are exclusively adsorbed onto the large surface area of nanoparticles. We discuss the relationship between the crystal structure of iron(III) oxyhydroxides and the mechanism of metal removal, as well as the linear relationship observed between the rate constant and the surface area of precipitates. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Cyclic process for producing methane with catalyst regeneration

DOEpatents

Frost, Albert C.; Risch, Alan P.

1980-01-01

Carbon monoxide-containing gas streams are passed over a catalyst capable of catalyzing the disproportionation of carbon monoxide so as to deposit a surface layer of active surface carbon on the catalyst essentially without formation of inactive coke thereon. The surface layer is contacted with steam and is thus converted to methane and CO.sub.2, from which a relatively pure methane product may be obtained. For practical commercial operations utilizing the two-step process of the invention of a cyclic basis, nickel, cobalt, ruthenium, thenium and alloys thereof are especially prepared for use in a metal state, with CO disproportionation being carried out at temperatures up to about 350.degree. C. and with the conversion of active surface carbon to methane being carried out by reaction with steam. The catalyst is employed in such cyclic operations without the necessity for employing a regeneration step as part of each processing cycle. Inactive carbon or coke that tends to form on the catalyst over the course of continuous operations utilizing such cyclic process is effectively and advantageously removed, on a periodic basis, in place of conventional burn off with an inert stream containing a low concentration of oxygen.
Clumped Isotope Thermometry Reveals Variations in Soil Carbonate Seasonal Biases Over >4 km of Relief in the Semi-Arid Andes of Central Chile

NASA Astrophysics Data System (ADS)

Burgener, L. K.; Huntington, K. W.; Hoke, G. D.; Schauer, A. J.; Ringham, M. C.; Latorre Hidalgo, C.; Díaz, F.

2015-12-01

The application of carbonate clumped isotope thermometry to soil carbonates has the potential to shed new light on questions regarding terrestrial paleoclimate. In order to better utilize this paleoclimate tool, outstanding questions regarding seasonal biases in soil carbonate formation and the relationship between soil carbonate formation temperatures (T(Δ47)) and surface temperatures must be resolved. We address these questions by comparing C, O, and clumped isotope data from Holocene/modern soil carbonates to modern meteorological data. The data were collected along a 170 km transect with >4 km of relief in central Chile (~30°S). Previous studies have suggested that soil carbonates should record a warm season bias and form in isotopic equilibrium with soil water and soil CO2. We identify two discrete climate zones separated by the local winter snow line (~3200 m). Below this boundary, precipitation falls as rain and soil carbonate T(Δ47) values at depths >40 cm resemble summer soil temperatures; at higher elevations, precipitation falls as snow and T(Δ47) values resemble mean annual soil temperatures. Soil carbonates from the highest sample site (4700 m), which is devoid of vegetation and located near perennial snow fields, yield anomalous δ18O, δ13C, and T(Δ47) values, indicative of kinetic isotope effects that we attribute to cryogenic carbonate formation. Our results suggest that soil carbonates from depths <40 cm are affected by large, high frequency variations in temperature and precipitation, and should not be used as paleotemperature proxies. These findings (1) highlight the role of soil moisture in modulating soil carbonate formation and the resulting T(Δ47) values, (2) underscore the importance of understanding past soil moisture conditions when attempting to reconstruct paleotemperatures using carbonate clumped isotope thermometry, and (3) suggest that soil carbonates from high elevation or high latitude sites may form under non-equilibrium conditions.
South Polar Spiders on Mars

NASA Image and Video Library

2007-04-27

NASA Mars Reconnaissance Rover spied these spider-like formations, likely caused as carbon dioxide ice changes from a solid to a gas; the gas moves through channels until it reaches the surface and vents out.
Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene.

PubMed

Burls, Natalie J; Fedorov, Alexey V; Sigman, Daniel M; Jaccard, Samuel L; Tiedemann, Ralf; Haug, Gerald H

2017-09-01

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, the world's largest ocean, where relatively fresh surface waters inhibit North Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400-ppmv (parts per million by volume) CO 2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanying pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redox-sensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming.
Karst geomorphology and hydrology of the Shenandoah Valley near Harrisonburg, Virginia

USGS Publications Warehouse

Doctor, Daniel H.; Orndorff, Wil; Maynard, Joel; Heller, Matthew J.; Casile, Gerolamo C.

2014-01-01

The karst of the central Shenandoah Valley has characteristics of both shallow and deep phreatic formation. This field guide focuses on the region around Harrisonburg, Virginia, where a number of these karst features and their associated geologic context can be examined. Ancient, widespread alluvial deposits cover much of the carbonate bedrock on the western side of the valley, where shallow karstification has resulted in classical fluviokarst development. However, in upland exposures of carbonate rock, isolated caves exist atop hills not affected by surface processes other than exposure during denudation. The upland caves contain phreatic deposits of calcite and fine-grained sediments. They lack any evidence of having been invaded by surface streams. Recent geologic mapping and LIDAR (light detection and ranging) elevation data have enabled interpretive association between bedrock structure, igneous intrusions, silicification and brecciation of host carbonate bedrock, and the location of several caves and karst springs. Geochemistry, water quality, and water temperature data support the broad categorization of springs into those affected primarily by shallow near-surface recharge, and those sourced deeper in the karst aquifer. The deep-seated karst formation occurred in the distant past where subvertical fracture and fault zones intersect thrust faults and/or cross-strike faults, enabling upwelling of deep-circulating meteoric groundwater. Most caves formed in such settings have been overprinted by later circulation of shallow groundwater, thus removing evidence of the history of earliest inception; however, several caves do preserve evidence of an earlier formation.
Controls on the methane released through ebullition affected by permafrost degradation

Treesearch

S.J. Klapstein; M.R. Turetsky; A.D. McGuire; J.W. Harden; C.I. Czimczik; X. Xu; J.P. Chanton; J.M. Waddington

2014-01-01

Permafrost thaw in peat plateaus leads to the flooding of surface soils and the formation of collapse scar bogs, which have the potential to be large emitters of methane (CH4) from surface peat as well as deeper, previously frozen, permafrost carbon (C). We used a network of bubble traps, permanently installed 20 cm and 60 cm beneath the moss surface, to examine...

Impact of UV irradiation on multiwall carbon nanotubes in nanocomposites: formation of entangled surface layer and mechanisms of release resistance

PubMed Central

Nguyen, Tinh; Petersen, Elijah J.; Pellegrin, Bastien; Gorham, Justin M.; Lam, Thomas; Zhao, Minhua; Sung, Lipiin

2017-01-01

Multiwall carbon nanotubes (MWCNTs) are nanofillers used in consumer and structural polymeric products to enhance a variety of properties. Under weathering, the polymer matrix will degrade and the nanofillers may be released from the products potentially impacting ecological or human health. In this study, we investigated the degradation of a 0.72 % (by mass) MWCNT/amine-cured epoxy nanocomposite irradiated with high intensity ultraviolet (UV) light at various doses, the effects of UV exposure on the surface accumulation and potential release of MWCNTs, and possible mechanisms for the release resistance of the MWCNT surface layer formed on nanocomposites by UV irradiation. Irradiated samples were characterized for chemical degradation, mass loss, surface morphological changes, and MWCNT release using a variety of analytical techniques. Under 295 nm to 400 nm UV radiation up to a dose of 4865 MJ/m2, the nanocomposite matrix underwent photodegradation, resulting in formation of a dense, entangled MWCNT network structure on the surface. However, no MWCNT release was detected, even at very high UV doses, suggesting that the MWCNT surface layer formed from UV irradiation of polymer nanocomposites resist release. Four possible release resistance mechanisms of the UV-induced MWCNT surface layer are presented and discussed. PMID:28603293
Highly porous activated carbons from resource-recovered Leucaena leucocephala wood as capacitive deionization electrodes.

PubMed

Hou, Chia-Hung; Liu, Nei-Ling; Hsi, Hsing-Cheng

2015-12-01

Highly porous activated carbons were resource-recovered from Leucaena leucocephala (Lam.) de Wit. wood through combined chemical and physical activation (i.e., KOH etching followed by CO2 activation). This invasive species, which has severely damaged the ecological economics of Taiwan, was used as the precursor for producing high-quality carbonaceous electrodes for capacitive deionization (CDI). Carbonization and activation conditions strongly influenced the structure of chars and activated carbons. The total surface area and pore volume of activated carbons increased with increasing KOH/char ratio and activation time. Overgasification induced a substantial amount of mesopores in the activated carbons. In addition, the electrochemical properties and CDI electrosorptive performance of the activated carbons were evaluated; cyclic voltammetry and galvanostatic charge/discharge measurements revealed a typical capacitive behavior and electrical double layer formation, confirming ion electrosorption in the porous structure. The activated-carbon electrode, which possessed high surface area and both mesopores and micropores, exhibited improved capacitor characteristics and high electrosorptive performance. Highly porous activated carbons derived from waste L. leucocephala were demonstrated to be suitable CDI electrode materials. Copyright © 2015 Elsevier Ltd. All rights reserved.
Microscopic insight into the bilateral formation of carbon spirals from a symmetric iron core

PubMed Central

Shiozawa, Hidetsugu; Bachmatiuk, Alicja; Stangl, Andreas; Cox, David C.; Silva, S. Ravi P.; Rümmeli, Mark H.; Pichler, Thomas

2013-01-01

Mirrored carbon-spirals have been produced from pressured ferrocene via the bilateral extrusion of the spiral pairs from an iron core. A parametric plot of the surface geometry displays the fractal growth of the conical helix made with the logarithmic spiral. Electron microscopy studies show the core is a crystalline cementite which grows and transforms its shape from spherical to biconical as it extrudes two spiralling carbon arms. In a cross section along the arms we observe graphitic flakes arranged in a herringbone structure, normal to which defects propagate. Local-wave-pattern analysis reveals nanoscale defect patterns of two-fold symmetry around the core. The data suggest that the bilateral growth originates from a globular cementite crystal with molten surfaces and the nano-defects shape emerging hexagonal carbon into a fractal structure. Understanding and knowledge obtained provide a basis for the controlled production of advanced carbon materials with designed geometries. PMID:23670649
Three-dimensional polypyrrole-derived carbon nanotube framework for dye adsorption and electrochemical supercapacitor

NASA Astrophysics Data System (ADS)

Xin, Shengchang; Yang, Na; Gao, Fei; Zhao, Jing; Li, Liang; Teng, Chao

2017-08-01

Three-dimensional carbon nanotube frameworks have been prepared via pyrolysis of polypyrrole nanotube aerogels that are synthesized by the simultaneous self-degraded template synthesis and hydrogel assembly followed by freeze-drying. The microstructure and composition of the materials are investigated by thermal gravimetric analysis, Raman spectrum, X-ray photoelectron spectroscopy, transmission electron microscopy, and specific surface analyzer. The results confirm the formation of three-dimensional carbon nanotube frameworks with low density, high mechanical properties, and high specific surface area. Compared with PPy aerogel precursor, the as-prepared three-dimensional carbon nanotube frameworks exhibit outstanding adsorption capacity towards organic dyes. Moreover, electrochemical tests show that the products possess high specific capacitance, good rate capability and excellent cycling performance with no capacitance loss over 1000 cycles. These characteristics collectively indicate the potential of three-dimensional polypyrrole-derived carbon nanotube framework as a promising macroscopic device for the applications in environmental and energy storages.
Effect of Silane Coupling Agent on the Creep Behavior and Mechanical Properties of Carbon Fibers/Acrylonitrile Butadiene Rubber Composites.

PubMed

Choi, Woong-Ki; Park, Gil-Young; Kim, Byoung-Shuk; Seo, Min-Kang

2018-09-01

In this study, we investigated the effect of the silane coupling agent on the relationship between the surface free energy of carbon fibers (CFs) and the mechanical strength of CFs/acrylonitrile butadiene rubber (NBR) composites. Moreover, the creep behavior of the CF/NBR composites at surface energetic point of view were studied. The specific component of the surface free energy of the carbon fibers was found to increase upon grafting of the silane coupling agent, resulting in an increase in the tensile strength of the CF/NBR composites. On the other hand, the compressive creep strength was found to follow a slightly different trend. These results indicate the possible formation of a complex interpenetrating polymer network depending on the molecular size of the organic functional groups of the silane coupling agent.
New catalyst supports prepared by surface modification of graphene- and carbon nanotube structures with nitrogen containing carbon coatings

NASA Astrophysics Data System (ADS)

Oh, Eun-Jin; Hempelmann, Rolf; Nica, Valentin; Radev, Ivan; Natter, Harald

2017-02-01

We present a new and facile method for preparation of nitrogen containing carbon coatings (NCC) on the surface of graphene- and carbon nanotubes (CNT), which has an increased electronic conductivity. The modified carbon system can be used as catalyst support for electrocatalytic applications, especially for polymer electrolyte membrane fuel cells (PEMFC). The surface modification is performed by impregnating carbon structures with a nitrogen containing ionic liquid (IL) with a defined C:N ratio, followed by a thermal treatment under ambient conditions. We investigate the influence of the main experimental parameters (IL amount, temperature, substrate morphology) on the formation of the NCC. Additionally, the structure and the chemical composition of the resulting products are analyzed by electron microscopic techniques (SEM, TEM), energy disperse X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS) and hot extraction analysis. The modified surface has a nitrogen content of 29 wt% which decreases strongly at temperatures above 600 °C. The new catalyst supports are used for the preparation of PEMFC anodes which are characterized by polarization measurements and electrochemical impedance spectroscopy (EIS). Compared to unmodified graphene and CNT samples the electronic conductivity of the modified systems is increased by a factor of 2 and shows improved mass transport properties.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Suuberg, E.M.; Lilly, W.D.; Aarna, I.

This project is concerned with the mechanism of reduction of both NO and N{sub 2}O by carbons. It was recognized some years ago that NO formed during fluidized bed coal combustion can be heterogeneously reduced in-situ by the carbonaceous solid intermediates of combustion. This has been recently supplemented by the knowledge that heterogeneous reaction with carbon can also play an important role in reducing emissions of N{sub 2}, but that the NO-carbon reactions might also contribute to formation of N{sub 2}. The precise role of carbon in N{sub 2} reduction and formation has yet to be established. Interest in themore » N{sub 2} and N{sub 2}O-char reactions has been significant in connection with both combustor modeling, as well as in design of post-combustion NO{sub x} control strategies. In our studies, a DuPont thermogravimetric analyzer (TGA) is used for the char reactivity studies. The temperature and mass are recorded as function of time, using a Macintosh computer and software for simultaneous apparatus control and data acquisition. Specific surface areas of char samples were determined by the N{sub 2} BET method at 77 K. A standard flow-type adsorption device (Quantasorb) was used for the measurements. Prior to surface area analysis, all samples were outgassed in a flow of nitrogen at 573 K for 3 hours. The carbonaceous solids used were resin char, graphite, coconut char and a Wyodak coal char. As was noted in the last report, carbons derived from different original materials show quite similar behaviors, in terms of the trends, but there are significant differences in actual reaction rates. It was shown that the spread of the reaction rate data from different studies, when expressed on a mass of carbon reactant- or surface area-basis, was almost the same.« less
Insights into Metal Oxide and Zero-Valent Metal Nanocrystal Formation on Multiwalled Carbon Nanotube Surfaces during Sol-Gel Process.

PubMed

Das, Dipesh; Sabaraya, Indu V; Sabo-Attwood, Tara; Saleh, Navid B

2018-06-05

Carbon nanotubes are hybridized with metal crystals to impart multifunctionality into the nanohybrids (NHs). Simple but effective synthesis techniques are desired to form both zero-valent and oxides of different metal species on carbon nanotube surfaces. Sol-gel technique brings in significant advantages and is a viable technique for such synthesis. This study probes the efficacy of sol-gel process and aims to identify underlying mechanisms of crystal formation. Standard electron potential (SEP) is used as a guiding parameter to choose the metal species; i.e., highly negative SEP (e.g., Zn) with oxide crystal tendency, highly positive SEP (e.g., Ag) with zero-valent crystal-tendency, and intermediate range SEP (e.g., Cu) to probe the oxidation tendency in crystal formation are chosen. Transmission electron microscopy and X-ray diffraction are used to evaluate the synthesized NHs. Results indicate that SEP can be a reliable guide for the resulting crystalline phase of a certain metal species, particularly when the magnitude of this parameter is relatively high. However, for intermediate range SEP-metals, mix phase crystals can be expected. For example, Cu will form Cu₂O and zero-valent Cu crystals, unless the synthesis is performed in a reducing environment.
Pyrolytic carbon-coated stainless steel felt as a high-performance anode for bioelectrochemical systems.

PubMed

Guo, Kun; Hidalgo, Diana; Tommasi, Tonia; Rabaey, Korneel

2016-07-01

Scale up of bioelectrochemical systems (BESs) requires highly conductive, biocompatible and stable electrodes. Here we present pyrolytic carbon-coated stainless steel felt (C-SS felt) as a high-performance and scalable anode. The electrode is created by generating a carbon layer on stainless steel felt (SS felt) via a multi-step deposition process involving α-d-glucose impregnation, caramelization, and pyrolysis. Physicochemical characterizations of the surface elucidate that a thin (20±5μm) and homogenous layer of polycrystalline graphitic carbon was obtained on SS felt surface after modification. The carbon coating significantly increases the biocompatibility, enabling robust electroactive biofilm formation. The C-SS felt electrodes reach current densities (jmax) of 3.65±0.14mA/cm(2) within 7days of operation, which is 11 times higher than plain SS felt electrodes (0.30±0.04mA/cm(2)). The excellent biocompatibility, high specific surface area, high conductivity, good mechanical strength, and low cost make C-SS felt a promising electrode for BESs. Copyright © 2016 Elsevier Ltd. All rights reserved.
Reactivity of NO2 and CO2 with hardened cement paste containing activated carbon

NASA Astrophysics Data System (ADS)

Horgnies, M.; Dubois-Brugger, I.; Krou, N. J.; Batonneau-Gener, I.; Belin, T.; Mignard, S.

2015-07-01

The development of building materials to reduce the concentration of NO2 is growing interest in a world where the air quality in urban areas is affected by the car traffic. The main binder in concrete is the cement paste that is partly composed of calcium hydroxide. This alkaline hydrate composing the hardened cement paste shows a high BET surface area (close to 100 m2.g-1) and can absorb low-concentrations of NO2. However, the presence of CO2 in the atmosphere limits the de-polluting effect of reference cement paste, mainly due to carbonation of the alkaline hydrates (reaction leading to the formation of calcium carbonate). The results established in this paper demonstrate that the addition of activated carbon in the cement paste, because of its very high BET surface area (close to 800 m2.g-1) and its specific reactivity with NO2, can significantly improve and prolong the de-polluting effect in presence of CO2 and even after complete carbonation of the surface of the cement paste.
230Th/U dating of a late Pleistocene alluvial fan along the southern San Andreas fault

USGS Publications Warehouse

Fletcher, Kathryn E.K.; Sharp, Warren D.; Kendrick, Katherine J.; Behr, Whitney M.; Hudnut, Kenneth W.; Hanks, Thomas C.

2010-01-01

U-series dating of pedogenic carbonate-clast coatings provides a reliable, precise minimum age of 45.1 ± 0.6 ka (2σ) for the T2 geomorphic surface of the Biskra Palms alluvial fan, Coachella Valley, California. Concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238U-234U-230Th system has remained closed since carbonate formation. The U-series minimum age is used to assess previously published 10Be exposure ages of cobbles and boulders. All but one cobble age and some boulder 10Be ages are younger than the U-series minimum age, indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine-grained matrix to expose them on the present fan surface. A comparison of U-series and 10Be ages indicates that the interval between final alluvial deposition on the T2 fan surface and accumulation of dateable carbonate is not well resolved at Biskra Palms; however, the “time lag” inherent to dating via U-series on pedogenic carbonate can be no larger than ∼10 k.y., the uncertainty of the 10Be-derived age of the T2 fan surface. Dating of the T2 fan surface via U-series on pedogenic carbonate (minimum age, 45.1 ± 0.6 ka) and 10Be on boulder-top samples using forward modeling (preferred age, 50 ± 5 ka) provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development.
230Th/U dating of a late pleistocene alluvial fan along the southern san andreas fault

USGS Publications Warehouse

Fletcher, K.E.K.; Sharp, W.D.; Kendrick, K.J.; Behr, W.M.; Hudnut, K.W.; Hanks, T.C.

2010-01-01

U-series dating of pedogenic carbonate-clast coatings provides a reliable, precise minimum age of 45.1 ?? 0.6 ka (2??) for the T2 geomorphic surface of the Biskra Palms alluvial fan, Coachella Valley, California. Concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238U-234U-230Th system has remained closed since carbonate formation. The U-series minimum age is used to assess previously published 10Be exposure ages of cobbles and boulders. All but one cobble age and some boulder 10Be ages are younger than the U-series minimum age, indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine-grained matrix to expose them on the present fan surface. A comparison of U-series and 10Be ages indicates that the interval between final alluvial deposition on the T2 fan surface and accumulation of dateable carbonate is not well resolved at Biskra Palms; however, the "time lag" inherent to dating via U-series on pedogenic carbonate can be no larger than ~10 k.y., the uncertainty of the 10Be-derived age of the T2 fan surface. Dating of the T2 fan surface via U-series on pedogenic carbonate (minimum age, 45.1 ?? 0.6 ka) and 10Be on boulder-top samples using forward modeling (preferred age, 50 ?? 5 ka) provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development. ?? 2010 Geological Society of America.
Immobilization of natural anti-oxidants on carbon nanotubes and aging behavior of ultra-high molecular weight polyethylene-based nanocomposites

NASA Astrophysics Data System (ADS)

Dintcheva, Nadka Tzankova; Arrigo, Rossella; Gambarotti, Cristian; Guenzi, Monica; Carroccio, Sabrina; Cicogna, Francesca; Filippone, Giovanni

2014-05-01

The use of natural antioxidants is an attractive way to formulate nanocomposites with extended durability and with potential applications in bio-medical field. In this work, Vitamin E (VE) in the form of α-tocopherol and Quercetin (Q) are physically immobilized on the outer surface of multi-walled carbon nanotubes (CNTs). Afterward, the CNTs-VE and CNTs-Q are used to formulate thermally stable ultra high molecular weight polyethylene based nanocomposites. The obtained results in the study of the thermo-oxidation behavior suggest a beneficial effect of the natural anti-oxidant carbon nanotubes systems. The unexpected excellent thermo-resistance of the nanocomposites seems to be due to a synergistic effect of the natural anti-oxidant and carbon nanotubes, i.e. strong interaction between CNT surface and anti-oxidant molecules. Particularly, these interactions cause the formation of structural defects onto outer CNT surfaces, which, in turn, increase the CNT radical scavenging activity.
Carbon dioxide hydrogenation on Ni(110).

PubMed

Vesselli, Erik; De Rogatis, Loredana; Ding, Xunlei; Baraldi, Alessandro; Savio, Letizia; Vattuone, Luca; Rocca, Mario; Fornasiero, Paolo; Peressi, Maria; Baldereschi, Alfonso; Rosei, Renzo; Comelli, Giovanni

2008-08-27

We demonstrate that the key step for the reaction of CO 2 with hydrogen on Ni(110) is a change of the activated molecule coordination to the metal surface. At 90 K, CO 2 is negatively charged and chemically bonded via the carbon atom. When the temperature is increased and H approaches, the H-CO 2 complex flips and binds to the surface through the two oxygen atoms, while H binds to the carbon atom, thus yielding formate. We provide the atomic-level description of this process by means of conventional ultrahigh vacuum surface science techniques combined with density functional theory calculations and corroborated by high pressure reactivity tests. Knowledge about the details of the mechanisms involved in this reaction can yield a deeper comprehension of heterogeneous catalytic organic synthesis processes involving carbon dioxide as a reactant. We show why on Ni the CO 2 hydrogenation barrier is remarkably smaller than that on the common Cu metal-based catalyst. Our results provide a possible interpretation of the observed high catalytic activity of NiCu alloys.
Biofunctionalization of silicone rubber with microgroove-patterned surface and carbon-ion implantation to enhance biocompatibility and reduce capsule formation.

PubMed

Lei, Ze-Yuan; Liu, Ting; Li, Wei-Juan; Shi, Xiao-Hua; Fan, Dong-Li

Silicone rubber implants have been widely used to repair soft tissue defects and deformities. However, poor biocompatibility can elicit capsule formation, usually resulting in prosthesis contracture and displacement in long-term usage. To overcome this problem, this study investigated the properties of silicone rubber materials with or without a microgroove-patterned surface and with or without carbon (C)-ion implantation. Atomic force microscopy, X-ray photoelectron spectroscopy, and a water contact angle test were used to characterize surface morphology and physicochemical properties. Cytocompatibility was investigated by a cell adhesion experiment, immunofluorescence staining, a Cell Counting Kit-8 assay, and scanning electron microscopy in vitro. Histocompatibility was evaluated by studying the inflammatory response and fiber capsule formation that developed after subcutaneous implantation in rats for 7 days, 15 days, and 30 days in vivo. Parallel microgrooves were found on the surfaces of patterned silicone rubber (P-SR) and patterned C-ion-implanted silicone rubber (PC-SR). Irregular larger peaks and deeper valleys were present on the surface of silicone rubber implanted with C ions (C-SR). The silicone rubber surfaces with microgroove patterns had stable physical and chemical properties and exhibited moderate hydrophobicity. PC-SR exhibited moderately increased dermal fibroblast cell adhesion and growth, and its surface microstructure promoted orderly cell growth. Histocompatibility experiments on animals showed that both the anti-inflammatory and antifibrosis properties of PC-SR were slightly better than those of the other materials, and there was also a lower capsular contracture rate and less collagen deposition around implants made from PC-SR. Although the surface chemical properties, dermal fibroblast cell growth, and cell adhesion were not changed by microgroove pattern modification, a more orderly cell arrangement was obtained, leading to enhanced biocompatibility and reduced capsule formation. Thus, this approach to the modification of silicone rubber, in combination with C-ion implantation, should be considered for further investigation and application.
Silk-regulated hierarchical hollow magnetite/carbon nanocomposite spheroids for lithium-ion battery anodes.

PubMed

Sheng, Weiqin; Zhu, Guobin; Kaplan, David L; Cao, Chuanbao; Zhu, Hesun; Lu, Qiang

2015-03-20

Hierarchical olive-like structured carbon-Fe3O4 nanocomposite particles composed of a hollow interior and a carbon coated surface are prepared by a facile, silk protein-assisted hydrothermal method. Silk nanofibers as templates and carbon precursors first regulate the formation of hollow Fe2O3 microspheres and then they are converted into carbon by a reduction process into Fe3O4. This process significantly simplifies the fabrication and carbon coating processes to form complex hollow structures. When tested as anode materials for lithium-ion batteries, these hollow carbon-coated particles exhibit high capacity (900 mAh g(-1)), excellent cycle stability (180 cycles) and rate performance due to their unique hierarchical hollow structure and carbon coating.
Competitive sorption of carbonate and arsenic to hematite: combined ATR-FTIR and batch experiments.

PubMed

Brechbühl, Yves; Christl, Iso; Elzinga, Evert J; Kretzschmar, Ruben

2012-07-01

The competitive sorption of carbonate and arsenic to hematite was investigated in closed-system batch experiments. The experimental conditions covered a pH range of 3-7, arsenate concentrations of 3-300 μM, and arsenite concentrations of 3-200 μM. Dissolved carbonate concentrations were varied by fixing the CO(2) partial pressure at 0.39 (atmospheric), 10, or 100 hPa. Sorption data were modeled with a one-site three plane model considering carbonate and arsenate surface complexes derived from ATR-FTIR spectroscopy analyses. Macroscopic sorption data revealed that in the pH range 3-7, carbonate was a weak competitor for both arsenite and arsenate. The competitive effect of carbonate increased with increasing CO(2) partial pressure and decreasing arsenic concentrations. For arsenate, sorption was reduced by carbonate only at slightly acidic to neutral pH values, whereas arsenite sorption was decreased across the entire pH range. ATR-FTIR spectra indicated the predominant formation of bidentate binuclear inner-sphere surface complexes for both sorbed arsenate and sorbed carbonate. Surface complexation modeling based on the dominant arsenate and carbonate surface complexes indicated by ATR-FTIR and assuming inner-sphere complexation of arsenite successfully described the macroscopic sorption data. Our results imply that in natural arsenic-contaminated systems where iron oxide minerals are important sorbents, dissolved carbonate may increase aqueous arsenite concentrations, but will affect dissolved arsenate concentrations only at neutral to alkaline pH and at very high CO(2) partial pressures. Copyright © 2012 Elsevier Inc. All rights reserved.
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
Formation and decomposition of siderite for CO2 treatment

NASA Astrophysics Data System (ADS)

Y Mora, E.; Sarmiento, A.; Vera, E.; Drozd, V.; Durigyn, A.; Saxena, S.

2017-12-01

In this research work, we studied the conditions for formation and decomposition of siderite FeCO3 from hematite Fe2O3 along with carbon dioxide CO2 at suitable thermodynamic conditions. As reductant agents were used mixtures of two elements, metallic iron and graphite. Best levels of carbonation were found in mixtures with bigger amounts of metallic iron. It was demonstrated that CO2 capture capacity by hematite depends of temperature, CO2 pressure, and reaction time. Temperatures between 100 and 150°C, pressures between 10 and 30bar and reaction times between 1 and 4h were adjusted for analyse the carbonation behaviour; siderite formation was improved by increases of these three variables. There was no carbonation without water in the mixtures, due to kinetic limitations. CO2 capture capacity was calculated from Rietveld refinement results. Using vacuum system and Dielectric Barrier Discharge, DBD plasma, the siderite was decomposed at 300°C, and 320°C respectively. Techniques as X-ray diffraction, and surface area analysis were employed to study the material.
Mixed material formation and erosion

NASA Astrophysics Data System (ADS)

Linsmeier, Ch.; Luthin, J.; Goldstraß, P.

2001-03-01

The formation of mixed phases on materials relevant for first wall components of fusion devices is studied under well-defined conditions in ultra-high vacuum (UHV). This is necessary in order to determine fundamental parameters governing the basic processes of chemical reaction, material mixing and erosion. We examined the binary systems comprising of the wall materials beryllium, silicon, tungsten and titanium and carbon, the latter being both a wall material and a plasma impurity. Experiments were carried out to study the interaction of carbon in the form of a vapor-deposited component on clean, well-defined elemental surfaces. The chemical composition and the binding state are measured by X-ray photoelectron spectroscopy (XPS) after annealing treatments. For all materials, a limited carbide formation is found at room temperature. Annealing carbon films on elemental substrate leads to a complete carbidization of the carbon layer. The carbide layers on Be and Si are stable even at very high temperatures, whereas the carbides of Ti and W dissolve. The erosion of these two metals by sputtering is then identical to the pure metals, whereas for Be and Si a protective carbide layer can reduce the sputtering yields.

Chemical State of Surface Oxygen on Carbon and Its Effects on the Capacity of the Carbon Anode in a Lithium-Ion Battery Investigated

NASA Technical Reports Server (NTRS)

Hung, Ching-Cheh

2001-01-01

In a lithium-ion battery, the lithium-storage capacity of the carbon anode is greatly affected by a surface layer formed during the first half cycle of lithium insertion and release into and out of the carbon anode. The formation of this solid-electrolyte interface, in turn, is affected by the chemistry of the carbon surface. A study at the NASA Glenn Research Center examined the cause-and-effect relations. Information obtained from this research could contribute in designing a high-capacity lithium-ion battery and, therefore, small, powerful spacecraft. In one test, three types of surfaces were examined: (1) a surface with low oxygen content (1.5 at.%) and a high concentration of active sites, (2) a surface with 4.5 at.% -OH or -OC type oxygen, and (3) a surface with 6.5 at.% O=C type oxygen. The samples were made from the same precursor and had similar bulk properties. They were tested under a constant current of 10 mA/g in half cells that used lithium metal as the counter electrode and 0.5 M lithium iodide in 50/50 (vol%) ethylene carbonate and dimethyl carbonate as the electrolyte. For the first cycle of the electrochemical test, the graph describes the voltage of the carbon anode versus the lithium metal as a function of the capacity (amount of lithium insertion or release). From these data, it can be observed that the surface with low oxygen and a high concentration of active sites could result in a high irreversible capacity. Such a high irreversible capacity could be prevented if the active sites were allowed to react with oxygen in air, producing -OH or -OC type oxygen. The O=C type oxygen, on the other hand, could greatly reduce the capacity of lithium intercalation and, therefore, needs to be avoided during battery fabrication.
Gas evolution from cathode materials: A pathway to solvent decomposition concomitant to SEI formation.

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

Browning, Katie L; Baggetto, Loic; Unocic, Raymond R

This work reports a method to explore the catalytic reactivity of electrode surfaces towards the decomposition of carbonate solvents [ethylene carbonate (EC), dimethyl carbonate (DMC), and EC/DMC]. We show that the decomposition of a 1:1 wt% EC/DMC mixture is accelerated over certain commercially available LiCoO2 materials resulting in the formation of CO2 while over pure EC or DMC the reaction is much slower or negligible. The solubility of the produced CO2 in carbonate solvents is high (0.025 grams/mL) which masks the effect of electrolyte decomposition during storage or use. The origin of this decomposition is not clear but it ismore » expected to be present on other cathode materials and may affect the analysis of SEI products as well as the safety of Li-ion batteries.« less
Reversible interconversion of carbon dioxide and formate by an electroactive enzyme

PubMed Central

Reda, Torsten; Plugge, Caroline M.; Abram, Nerilie J.; Hirst, Judy

2008-01-01

Carbon dioxide (CO2) is a kinetically and thermodynamically stable molecule. It is easily formed by the oxidation of organic molecules, during combustion or respiration, but is difficult to reduce. The production of reduced carbon compounds from CO2 is an attractive proposition, because carbon-neutral energy sources could be used to generate fuel resources and sequester CO2 from the atmosphere. However, available methods for the electrochemical reduction of CO2 require excessive overpotentials (are energetically wasteful) and produce mixtures of products. Here, we show that a tungsten-containing formate dehydrogenase enzyme (FDH1) adsorbed to an electrode surface catalyzes the efficient electrochemical reduction of CO2 to formate. Electrocatalysis by FDH1 is thermodynamically reversible—only small overpotentials are required, and the point of zero net catalytic current defines the reduction potential. It occurs under thoroughly mild conditions, and formate is the only product. Both as a homogeneous catalyst and on the electrode, FDH1 catalyzes CO2 reduction with a rate more than two orders of magnitude faster than that of any known catalyst for the same reaction. Formate oxidation is more than five times faster than CO2 reduction. Thermodynamically, formate and hydrogen are oxidized at similar potentials, so formate is a viable energy source in its own right as well as an industrially important feedstock and a stable intermediate in the conversion of CO2 to methanol and methane. FDH1 demonstrates the feasibility of interconverting CO2 and formate electrochemically, and it is a template for the development of robust synthetic catalysts suitable for practical applications. PMID:18667702
Facile preparation of hierarchically porous carbon using diatomite as both template and catalyst and methylene blue adsorption of carbon products.

PubMed

Liu, Dong; Yuan, Peng; Tan, Daoyong; Liu, Hongmei; Wang, Tong; Fan, Mingde; Zhu, Jianxi; He, Hongping

2012-12-15

Hierarchically porous carbons were prepared using a facile preparation method in which diatomite was utilized as both template and catalyst. The porous structures of the carbon products and their formation mechanisms were investigated. The macroporosity and microporosity of the diatomite-templated carbons were derived from replication of diatom shell and structure-reconfiguration of the carbon film, respectively. The macroporosity of carbons was strongly dependent on the original morphology of the diatomite template. The macroporous structure composed of carbon plates connected by the pillar- and tube-like macropores resulted from the replication of the central and edge pores of the diatom shells with disk-shaped morphology, respectively. And another macroporous carbon tubes were also replicated from canoe-shaped diatom shells. The acidity of diatomite dramatically affected the porosity of the carbons, more acid sites of diatomite template resulted in higher surface area and pore volume of the carbon products. The diatomite-templated carbons exhibited higher adsorption capacity for methylene blue than the commercial activated carbon (CAC), although the specific surface area was much smaller than that of CAC, due to the hierarchical porosity of diatomite-templated carbons. And the carbons were readily reclaimed and regenerated. Copyright © 2012 Elsevier Inc. All rights reserved.
Following the Interstellar History of Carbon: From the Interiors of Stars to the Surfaces of Planets.

PubMed

Ziurys, L M; Halfen, D T; Geppert, W; Aikawa, Y

2016-12-01

The chemical history of carbon is traced from its origin in stellar nucleosynthesis to its delivery to planet surfaces. The molecular carriers of this element are examined at each stage in the cycling of interstellar organic material and their eventual incorporation into solar system bodies. The connection between the various interstellar carbon reservoirs is also examined. Carbon has two stellar sources: supernova explosions and mass loss from evolved stars. In the latter case, the carbon is dredged up from the interior and then ejected into a circumstellar envelope, where a rich and unusual C-based chemistry occurs. This molecular material is eventually released into the general interstellar medium through planetary nebulae. It is first incorporated into diffuse clouds, where carbon is found in polyatomic molecules such as H 2 CO, HCN, HNC, c-C 3 H 2 , and even C 60 + . These objects then collapse into dense clouds, the sites of star and planet formation. Such clouds foster an active organic chemistry, producing compounds with a wide range of functional groups with both gas-phase and surface mechanisms. As stars and planets form, the chemical composition is altered by increasing stellar radiation, as well as possibly by reactions in the presolar nebula. Some molecular, carbon-rich material remains pristine, however, encapsulated in comets, meteorites, and interplanetary dust particles, and is delivered to planet surfaces. Key Words: Carbon isotopes-Prebiotic evolution-Interstellar molecules-Comets-Meteorites. Astrobiology 16, 997-1012.
Simulating CO2 Leakage and Seepage From Geologic Carbon Sequestration Sites: Implications for Near-Surface Monitoring

NASA Astrophysics Data System (ADS)

Oldenburg, C. M.; Lewicki, J. L.; Zhang, Y.

2003-12-01

The injection of CO2 into deep geologic formations for the purpose of carbon sequestration entails risk that CO2 will leak upward from the target formation and ultimately seep out of the ground surface. We have developed a coupled subsurface and atmospheric surface layer modeling capability based on TOUGH2 to simulate CO2 leakage and seepage. Simulation results for representative subsurface and surface layer conditions are used to specify the requirements of potential near-surface monitoring strategies relevant to both health, safety, and environmental risk assessment as well as sequestration verification. The coupled model makes use of the standard multicomponent and multiphase framework of TOUGH2 and extends the model domain to include an atmospheric surface layer. In the atmospheric surface layer, we assume a logarithmic velocity profile for the time-averaged wind and make use of Pasquill-Gifford and Smagorinski dispersion coefficients to model surface layer dispersion. Results for the unsaturated zone and surface layer show that the vadose zone pore space can become filled with pure CO2 even for small leakage fluxes, but that CO2 concentrations above the ground surface are very low due to the strong effects of dispersion caused by surface winds. Ecological processes such as plant photosynthesis and root respiration, as well as biodegradation in soils, strongly affect near-surface CO2 concentrations and fluxes. The challenge for geologic carbon sequestration verification is to discern the leakage and seepage signal from the ecological signal. Our simulations point to the importance of subsurface monitoring and the need for geochemical (e.g., isotopic) analyses to distinguish leaking injected fossil CO2 from natural ecological CO2. This work was supported by the Office of Science, U.S. Department of Energy under contract No. DE-AC03-76SF00098.
Rare isotope studies involving catalytic oxidation of CO over platinum-tin oxide

NASA Technical Reports Server (NTRS)

Upchurch, Billy T.; Wood, George M., Jr.; Hess, Robert V.; Hoyt, Ronald F.

1987-01-01

Results of studies utilizing normal and rare oxygen isotopes in the catalytic oxidation of carbon monoxide over a platinum-tin oxide catalyst substrate are presented. Chemisorption of labeled carbon monoxide on the catalyst followed by thermal desorption yielded a carbon dioxide product with an oxygen-18 composition consistent with the formation of a carbonate-like intermediate in the chemisorption process. The efficacy of a method developed for the oxygen-18 labeling of the platinum-tin oxide catalyst surface for use in closed cycle pulsed care isotope carbon dioxide lasers is demonstrated for the equivalent of 10 to the 6th power pulses at 10 pulses per second.
Fractography of the high temperature hydrogen attack of a medium carbon steel

NASA Technical Reports Server (NTRS)

Melson, H. G.; Moorhead, R. D.

1975-01-01

Microscopic fracture processes were studied which are associated with hydrogen attack of a medium carbon steel in a well-controlled, high-temperature, high-purity hydrogen environment. Exposure to a hydrogen pressure and temperature of 3.5 MN/m2 and 575 C was found to degrade room temperature tensile properties with increasing exposure time. After 408 hr, yield and ultimate strengths were reduced by more than 40 percent and elongation was reduced to less than 2 percent. Initial fissure formation was found to be associated with manganese rich particles, most probably manganese oxide, aligned in the microstructure during the rolling operation. Fissure growth was found to be associated with a reduction in carbide content of the microstructure and was inhibited by the depletion of carbon. The interior surfaces of sectioned fissures or bubbles exhibit both primary and secondary cracking by intergranular separation. The grain surfaces were rough and rounded, suggesting a diffusion-associated separation process. Specimens that failed at room temperature after exposure to hydrogen were found to exhibit mixed mode fracture having varying amounts of intergranular separation, dimple formation, and cleavage, depending on exposure time.
Stabilizing platinum in phosphoric acid fuel cells

NASA Technical Reports Server (NTRS)

Remick, R. J.

1981-01-01

The cathode of the phosphoric acid fuel cell uses a high surface area platinum catalyst supported on a carbon substrate. During operation, the small platinum crystallites sinter, causing loss in cell performance. A support was developed that stabilizes platinum in the high surface area condition by retarding or preventing the sintering process. The approach is to form etch pits in the carbon by oxidizing the carbon in the presence of a metal oxide catalyst, remove the metal oxide by an acid wash, and then deposit platinum in these pits. Results confirm the formation of etch pits in each of the three supports chosen for investigation: Vulcan XC-72R, Vulcan XC-72 that was graphized at 2500 C, and Shawinigan Acetylene Black.
The Diversity of Carbon in Cometary Refractory Dust Particles

NASA Technical Reports Server (NTRS)

Wooden, D. H.

2018-01-01

When comparing the dark icy surfaces of outer solar system small bodies and the composition of carbonaceous chondrites derived from dark asteroids we find a significant discrepancy in the assessed amounts of elemental carbon: up to 80% amorphous carbon is used to model the dark surfaces of Kuiper Belt Objects and Centaurs whereas at most 5% of elemental carbon is found in carbonaceous chondrites. If we presume that regimes of comet nuclei formation are analogous to disk regimes where other outer solar system ice-rich bodies formed then we can turn to comet dust to gain insights into the diversity in the concentration and forms of carbon available in the outer disk. Comet dust offers important insights into the diversity in the amounts and forms of carbon that were incorporated into aggregate dust particles in the colder parts of the protoplanetary disk out of which comet nuclei accreted. Comet nuclei are amongst the most primitive bodies because they have remained cold and unequilibrated. Comet dust particles reveal the presence of forms of elemental carbon and of soluble and insoluble organic matter, and in a great diversity of concentrations from very little, e.g., Stardust samples of comet 81P/Wild 2, to 80% by volume for Ultra Carbonaceous Antarctic Micro Meteorites (UCAMMs). Cometary outbursts and/or jet activity also demonstrate variations in the concentration of carbon in the grains at different grain sizes within a single comet. We review the diversity of carbon-bearing dust grains in cometary samples, flyby measurements and deduced from remote-sensing to enrich the discussion about the diversity of carbonaceous matter available in the outer ice-rich disk at the time of comet nuclei formation.
The formation of weathering products on the LEW 85320 ordinary chondrite - Evidence from carbon and oxygen stable isotope compositions and implications for carbonates in SNC meteorites

NASA Technical Reports Server (NTRS)

Grady, Monica M.; Wright, I. P.; Pillinger, C. T.; Gibson, E. K., Jr.

1989-01-01

Isotopic analysis of nesquehonite recovered from the surface of the LEW 85320 H5 ordinary chondrite shows that the delta C-13 and delta O-18 values of the two generations of bicarbonate (Antarctic and Texas) are different: delta C-13 = + 7.9 per mil and + 4.2 per mil; delta O-18 = + 17.9 per mil and + 12.1 per mil, respectively. Carbon isotopic compositions are consistent with equilibrium formation from atmospheric carbon dioxide at - 2 + or - 4 C (Antarctic) and + 16 + or - 4 C (Texas). Oxygen isotopic data imply that the water required for nesquehonite precipitation was derived from atmospheric water vapor or glacial meltwater which had locally exchanged with silicates, either in the meteorite or in underlying bedrock. Although carbonates with similar delta C-13 values have been identified in the SNC meteorites EETA 79001 and Nakhla, petrographic and temperature constraints argue against their simply being terrestrial weathering products.
Photoassisted carbon dioxide reduction and formation of twoand three-carbon compounds. [prebiological photosynthesis

NASA Technical Reports Server (NTRS)

Halmann, M.; Aurian-Blajeni, B.; Bloch, S.

1981-01-01

The photoassisted reduction of aqueous carbon dioxide in the presence of naturally occurring minerals is investigated as a possible abiotic precursor of photosynthesis. Aqueous carbon dioxide saturated suspensions or surfaces of the minerals nontronite, bentonite, anatase, wolframite, molybdenite, minium, cinnabar and hematite were irradiated with high-pressure mercury lamps or sunlight. Chemical analyses reveal the production of formic acid, formaldehyde, methanol and methane, and the two and three-carbon compounds glyoxal (CHOCHO) and malonaldehyde (CH2(CHO)2). It is suggested that such photosynthetic reactions with visible light in the presence of semiconducting minerals may provide models for prebiological carbon and nitrogen fixation in both oxidized and reduced atmospheres.
Mars brine formation experiment

NASA Technical Reports Server (NTRS)

Moore, Jeffrey M.; Bullock, Mark A.; Stoker, Carol R.

1992-01-01

Evaporites, particularly carbonates, nitrates, and sulfates, may be major sinks of volatiles scavenged from the martian atmosphere. Mars is thought to have once had a denser, warmer atmosphere that permitted the presence of liquid surface water. The conversion of atmospheric CO2 into carbonate is hypothesized to have degraded the martian climate to its present state of a generally subfreezing, desiccated desert. The rate for such a conversion under martian conditions is poorly known, so the time scale of climate degradation by this process cannot be easily evaluated. If some models are correct, carbonate formation may have been fast at geological time scales. The experiments of Booth and Kieffer also imply fast (10(exp 6) - 10(exp 7) yr) removal of the missing CO2 inventory, estimated to be 1 - 5 bar, by means of carbonate formation. The timing of formation of many of the fluvial features observed on Mars is, in large part, dependent on when and how fast the atmosphere changed. A knowledge of the rate at which carbonates and nitrates formed is also essential for assessing the probability that life, or its chemical precursors, could have developed on Mars. No previous experiments have quantitatively evaluated the rate of solution for a suite of mobile anions and cations from unaltered minerals and atmospheric gases into liquid water under Mars-like conditions. Such experiments are the focus of this task.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Gromov, D. G.; Dubkov, S. V., E-mail: sv.dubkov@gmail.com; Pavlov, A. A.

It is shown that it is possible to grow carbon nanotubes on the surface of an amorphous Ni–Ta–N metal alloy film with a low Ni content (~25 at %) by chemical deposition from acetylene at temperature 400–800°C. It is established that the addition of nitrogen into the Ni–Ta alloy composition is favorable for the formation of tantalum nitride and the expulsion of Ni clusters, which act as a catalyst of the growth of carbon nanotubes, onto the surface. From Raman spectroscopy studies, it is found that, as the temperature of synthesis is raised, the quality of nanotubes is improved.
Integrated approaches to terminal Proterozoic stratigraphy: an example from the Olenek Uplift, northeastern Siberia

NASA Technical Reports Server (NTRS)

Knoll, A. H.; Grotzinger, J. P.; Kaufman, A. J.; Kolosov, P.

1995-01-01

In the Olenek Uplift of northeastern Siberia, the Khorbusuonka Group and overlying Kessyusa and Erkeket formations preserve a significant record of terminal Proterozoic and basal Cambrian Earth history. A composite section more than 350 m thick is reconstructed from numerous exposures along the Khorbusuonka River. The Khorbusuonka Group comprises three principal sedimentary sequences: peritidal dolomites of the Mastakh Formation, which are bounded above and below by red beds; the Khatyspyt and most of the overlying Turkut formations, which shallow upward from relatively deep-water carbonaceous micrites to cross-bedded dolomitic grainstones and stromatolites; and a thin upper Turkut sequence bounded by karst surfaces. The overlying Kessyusa Formation is bounded above and below by erosional surfaces and contains additional parasequence boundaries internally. Ediacaran metazoans, simple trace fossils, and vendotaenids occur in the Khatyspyt Formation; small shelly fossils, more complex trace fossils, and acritarchs all appear near the base of the Kessyusa Formation and diversify upward. The carbon-isotopic composition of carbonates varies stratigraphically in a pattern comparable to that determined for other terminal Proterozoic and basal Cambrian successions. In concert, litho-, bio-, and chemostratigraphic data indicate the importance of the Khorbusuonka Group in the global correlation of terminal Proterozoic sedimentary rocks. Stratigraphic data and a recently determined radiometric date on basal Kessyusa volcanic breccias further underscore the significance of the Olenek region in investigations of the Proterozoic-cambrian boundary.
Integrated approaches to terminal Proterozoic stratigraphy: an example from the Olenek Uplift, northeastern Siberia.

PubMed

Knoll, A H; Grotzinger, J P; Kaufman, A J; Kolosov, P

1995-01-01

In the Olenek Uplift of northeastern Siberia, the Khorbusuonka Group and overlying Kessyusa and Erkeket formations preserve a significant record of terminal Proterozoic and basal Cambrian Earth history. A composite section more than 350 m thick is reconstructed from numerous exposures along the Khorbusuonka River. The Khorbusuonka Group comprises three principal sedimentary sequences: peritidal dolomites of the Mastakh Formation, which are bounded above and below by red beds; the Khatyspyt and most of the overlying Turkut formations, which shallow upward from relatively deep-water carbonaceous micrites to cross-bedded dolomitic grainstones and stromatolites; and a thin upper Turkut sequence bounded by karst surfaces. The overlying Kessyusa Formation is bounded above and below by erosional surfaces and contains additional parasequence boundaries internally. Ediacaran metazoans, simple trace fossils, and vendotaenids occur in the Khatyspyt Formation; small shelly fossils, more complex trace fossils, and acritarchs all appear near the base of the Kessyusa Formation and diversify upward. The carbon-isotopic composition of carbonates varies stratigraphically in a pattern comparable to that determined for other terminal Proterozoic and basal Cambrian successions. In concert, litho-, bio-, and chemostratigraphic data indicate the importance of the Khorbusuonka Group in the global correlation of terminal Proterozoic sedimentary rocks. Stratigraphic data and a recently determined radiometric date on basal Kessyusa volcanic breccias further underscore the significance of the Olenek region in investigations of the Proterozoic-cambrian boundary.
Effects of Surface-Modified MgO Nanoparticles on Inclusion Characteristics and Microstructure in Carbon Structural Steel

NASA Astrophysics Data System (ADS)

Guo, Hao; Yang, Shufeng; Li, Jingshe; Zhao, Mengjing; Chen, Zhengyang; Zhang, Xueliang; Li, Jikang

2018-05-01

An innovative approach involving chemical modification of the surface of MgO nanoparticles (NPs) for steelmaking and application of NPs to carbon structural steel has been investigated. The results show that the inclusions in the test steels were completely converted to MgAl2O4 spinel or MnS complex inclusions. The mean inclusion size decreased with increasing NP content from 0.01% to 0.03%, but increased at 0.05% because of NP aggregation. Addition of NPs increased the amount of intragranular ferrite and prevented polygonal ferrite formation, thereby enhancing the impact toughness. Impact tests showed that the dimple fractures in steel with 0.05% NP content were deeper than those in the other samples because the MgAl2O4 inclusions were larger. The surface-modified MgO NPs had a major effect on the inclusion characteristics and microstructure of carbon structural steel.
Oxalate minerals on Mars?

NASA Astrophysics Data System (ADS)

Applin, D. M.; Izawa, M. R. M.; Cloutis, E. A.; Goltz, D.; Johnson, J. R.

2015-06-01

Small amounts of unidentified organic compounds have only recently been inferred on Mars despite strong reasons to expect significant concentrations and decades of searching. Based on X-ray diffraction and reflectance spectroscopic analyses we show that solid oxalic acid and its most common mineral salts are stable under the pressure and ultraviolet irradiation environment of the surface of Mars, and could represent a heretofore largely overlooked reservoir of organic carbon in the martian near-surface. In addition to the delivery to Mars by carbonaceous chondrites, oxalate minerals are among the predicted breakdown products of meteoritic organic matter delivered to the martian surface, as well as any endogenic organic carbon reaching the martian surface from the interior. A reinterpretation of pyrolysis experiments from the Viking, Phoenix, and Mars Science Laboratory missions shows that all are consistent with the presence of significant concentrations of oxalate minerals. Oxalate minerals could be important in numerous martian geochemical processes, including acting as a possible nitrogen sink (as ammonium oxalate), and contributing to the formation of “organic” carbonates, methane, and hydroxyl radicals.
Carbon vacancy-induced enhancement of the visible light-driven photocatalytic oxidation of NO over g-C3N4 nanosheets

NASA Astrophysics Data System (ADS)

Li, Yuhan; Ho, Wingkei; Lv, Kangle; Zhu, Bicheng; Lee, Shun Cheng

2018-02-01

g-C3N4 (gCN) with carbon vacancy has been extensively investigated and applied in (photo)catalysis. Engineering the carbon vacancy in gCN is of great importance, but it remains a challenging task. In this work, we report for the first time the fabrication of gCN with carbon vacancy (Cv-gCN) via thermal treatment of pristine gCN in CO2 atmosphere. The photocatalytic performance of Cv-gCN is evaluated on the basis of NO oxidization under visible light irradiation (λ > 400 nm) in a continual reactor. The successful formation of carbon vacancy in gCN is confirmed through electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). The photocatalytic oxidation removal rate of NO over Cv-gCN is 59.0%, which is two times higher than that over pristine gCN (24.2%). The results of the quenching experiment show that superoxide radicals (O2rad -) act as the main reactive oxygen species, which is responsible for the oxidation of NO. The enlarged BET surface areas and negatively shifted conduction band (CB) potential enhance the photocatalytic activity of Cv-gCN, which facilitates the efficient electron transfer from the CB of Cv-gCN to the surface adsorbed oxygen, resulting in the formation of O2rad - that can oxidize NO.
Submicron magnetite grains and carbon compounds in Martian meteorite ALH84001: inorganic, abiotic formation by shock and thermal metamorphism.

PubMed

Treiman, Allan H

2003-01-01

Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe(3)O(4), reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered).

Carbon Disulfide (CS2) Mechanisms in Formation of Atmospheric Carbon Dioxide (CO2) Formation from Unconventional Shale Gas Extraction and Processing Operations and Global Climate Change.

PubMed

Rich, Alisa L; Patel, Jay T

2015-01-01

Carbon disulfide (CS2) has been historically associated with the production of rayon, cellophane, and carbon tetrachloride. This study identifies multiple mechanisms by which CS2 contributes to the formation of CO2 in the atmosphere. CS2 and other associated sulfide compounds were found by this study to be present in emissions from unconventional shale gas extraction and processing (E&P) operations. The breakdown products of CS2; carbonyl sulfide (COS), carbon monoxide (CO), and sulfur dioxide (SO2) are indirect greenhouse gases (GHGs) that contribute to CO2 levels in the atmosphere. The heat-trapping nature of CO2 has been found to increase the surface temperature, resulting in regional and global climate change. The purpose of this study is to identify five mechanisms by which CS2 and the breakdown products of CS2 contribute to atmospheric concentrations of CO2. The five mechanisms of CO2 formation are as follows: Chemical Interaction of CS2 and hydrogen sulfide (H2S) present in natural gas at high temperatures, resulting in CO2 formation;Combustion of CS2 in the presence of oxygen producing SO2 and CO2;Photolysis of CS2 leading to the formation of COS, CO, and SO2, which are indirect contributors to CO2 formation;One-step hydrolysis of CS2, producing reactive intermediates and ultimately forming H2S and CO2;Two-step hydrolysis of CS2 forming the reactive COS intermediate that reacts with an additional water molecule, ultimately forming H2S and CO2. CS2 and COS additionally are implicated in the formation of SO2 in the stratosphere and/or troposphere. SO2 is an indirect contributor to CO2 formation and is implicated in global climate change.
Decrypting the Formation Conditions of the Basement Carbonate-Bearing Rocks at Nili Fossae

NASA Astrophysics Data System (ADS)

Brown, A. J.

2015-12-01

The Nili Fossae region is the site of a number of proposed Landing Sites for the Mars 2020 Rover. A distinguishing feature of many of these sites is the access to large exposures of carbonate (Ehlmann et al. 2008). Serpentinization has been proposed as a formation mechanism of these carbonates, including carbonated (Brown et al. 2010, Viviano, et al. 2013) and low temperature, near surface serpentinization. The potential for carbonated serpentization at Nili Fossae links the region to Earth analogs in terrestrial greenstone belts such as the Pilbara in Western Australia, where talc-carbonate bearing komatiite cumulate units of the Dresser Formation overlie the siliceous, stromatolite-bearing Strelley Pool Chert unit (Van Kranendonk and Pirajno, 2004). If a similar relationship exists on Mars, investigations of rocks stratigraphically beneath the carbonate-bearing units at Nili Fossae ("the basement rocks") may provide the best chance to examine well preserved organic material from the Noachian. This hypothesis is testable by Mars 2020. In preparation for the the Mars 2020 landing site, we are examining the thermodynamic relationships that favor formation of serpentine and talc-carbonate and different pressures and temperatures in the crust (Barnes 2007). This will allow us to constrain the low grade metamorphism required to replicate the proposed models of serpentinisation and help us understand the regional metamophic gradient that is critical to furthering our knowledge of the ancient rocks of Nili Fossae. Refs:Barnes, S. J. "Komatiites: Petrology, Volcanology, Metamorphism, and Geochemistry." S.E.G. 13 (2007): 13. Brown, A. J., et al.. "Hydrothermal Formation of Clay-Carbonate Alteration Assemblages in the Nili Fossae Region of Mars." EPSL 297 (2010): 174-82. Ehlmann, B. L. et al. "Orbital Identification of Carbonate-Bearing Rocks on Mars." Science 322, no. 5909 1828-32. Van Kranendonk, M.J., and F. Pirajno. "Geochemistry of Metabasalts and Hydrothermal Alteration Zones Associated with Ca. 3.45 Ga Chert+/- Barite Deposits" GEEA 4, no. 3 (2004): 253-78. Viviano, C. E., et al. "Implications for Early Hydrothermal Environments on Mars through the Spectral Evidence for Carbonation and Chloritization Reactions in the Nili Fossae Region." JGR 118, no. 9 (2013): 1858-72.
Mechanisms of Enhanced Hemoglobin Electroactivity on Carbon Electrodes upon Exposure to a Water-Miscible Primary Alcohol.

PubMed

Tom, Justin; Jakubec, Philip J; Andreas, Heather A

2018-05-01

Exposing a carbon electrode to hemoglobin (Hb) and alcoholic solvents, such as methanol, ethanol or 1-propanol, drastically changes Hb electroactivity, but until this work, the important underlying mechanisms were unclear. For the first time, we show that these alcohols impact Hb electroactivity via three mechanisms: modification of the carbon surface oxides on the glassy carbon (GC) electrode, Hb film formation, and structural changes to Hb. C 1s X-ray photoelectron spectroscopy provided evidence for significant alcohol-induced modification of the carbon surface oxides, and differential pulse voltammetry showed links between these modifications and Hb electroactivity. Spectroscopic ellipsometry showed that Hb films formed during exposure to Hb- and alcohol-containing electrolytes increased in thickness with increasing alcohol content, although film thickness played only a minor role in Hb electroactivity. Alcohol-induced structural changes in Hb are confirmed with UV-visible absorption and fluorescence data, showing that Hb denaturation also was a significant factor in increasing Hb electroactivity. Carbon-surface-oxide modification and Hb denaturation worked in tandem to maximally increase the Hb electroactivity in 60% methanol. While in ethanol and 1-propanol, the significant increases in Hb electroactivity caused by Hb denaturation were offset by an increase in Hb-inhibiting carbon surface oxides. Knowledge of these mechanisms shows the impact of alcohols on both Hb and carbon electrodes, allows for thoughtful design of the Hb-sensing system, is vital for proper analysis of Hb electroactivity in the presence of these alcohols (e.g., when used as binder solvents for immobilizing Hb into films), and provides fundamental understanding of the Hb-carbon interactions.
Protein-free formation of bone-like apatite: New insights into the key role of carbonation

PubMed Central

Deymier, Alix C.; Nair, Arun K.; Depalle, Baptiste; Qin, Zhao; Arcot, Kashyap; Drouet, Christophe; Yoder, Claude H.; Buehler, Markus J.; Thomopoulos, Stavros; Genin, Guy M.; Pasteris, Jill D.

2017-01-01

The nanometer-sized plate-like morphology of bone mineral is necessary for proper bone mechanics and physiology. However, mechanisms regulating the morphology of these mineral nanocrystals remain unclear. The dominant hypothesis attributes the size and shape regulation to organic-mineral interactions. Here, we present data supporting the hypothesis that physicochemical effects of carbonate integration within the apatite lattice control the morphology, size, and mechanics of bioapatite mineral crystals. Carbonated apatites synthesized in the absence of organic molecules presented plate-like morphologies and nanoscale crystallite dimensions. Experimentally-determined crystallite size, lattice spacing, solubility and atomic order were modified by carbonate concentration. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations predicted changes in surface energy and elastic moduli with carbonate concentration. Combining these results with a scaling law predicted the experimentally observed scaling of size and energetics with carbonate concentration. The experiments and models describe a clear mechanism by which crystal dimensions are controlled by carbonate substitution. Furthermore, the results demonstrate that carbonate substitution is sufficient to drive the formation of bone-like crystallites. This new understanding points to pathways for biomimetic synthesis of novel, nanostructured biomaterials. PMID:28279923
Escape of carbon element in surface ablation of cobalt cemented tungsten carbide with pulsed UV laser

NASA Astrophysics Data System (ADS)

Li, Tiejun; Lou, Qihong; Dong, Jingxing; Wei, Yunrong; Liu, Jingru

2001-03-01

Surface ablation of cobalt cemented tungsten carbide hardmetal has been carried out in this work using a 308 nm, 30 ns XeCl excimer laser. The surface phase transformation on different pulse number of laser shots has been investigated by means of XRD and microphotography as well as AES at laser fluence of 2.5 J/cm 2. The experimental results showed that the phase structure of irradiated area has partly transformed from original WC to β-WC 1- x, then to α-W 2C and CW 3, and finally to W crystal. It is suggested that the formation of non-stoichiometric tungsten carbide should result from the escaping of carbon element due to accumulated heating of surface by pulsed laser irradiation.
Collisions of slow ions C3Hn+ and C3Dn+ (n = 2-8) with room temperature carbon surfaces: mass spectra of product ions and the ion survival probability.

PubMed

Pysanenko, Andriy; Zabka, Jan; Feketeová, Linda; Märk, Tilmann D; Herman, Zdenek

2008-01-01

Collisions of C3Hn+ (n = 2-8) ions and some of their per- deuterated analogs with room temperature carbon (HOPG) surfaces (hydrocarbon-covered) were investigated over the incident energy range 13-45 eV in beam scattering experiments. The mass spectra of product ions were measured and main fragmentation paths of the incident projectile ions, energized in the surface collision, were determined. The extent of fragmentation increased with increasing incident energy. Mass spectra of even-electron ions C3H7+ and C3H5+ showed only fragmentations, mass spectra of radical cations C3H8*+ and C3H6*+ showed both simple fragmentations of the projectile ion and formation of products of its surface chemical reaction (H-atom transfer between the projectile ion and hydrocarbons on the surface). No carbon-chain build-up reaction (formation of C4 hydrocarbons) was detected. The survival probability of the incident ions, S(a), was usually found to be about 1-2% for the radical cation projectile ions C3H8*+, C3H6*+, C3H4*+ and C3H2*+ and several percent up to about 20% for the even-electron projectile ions C3H7+, C3H5+, C3H3+. A plot of S(a) values of C1, C2, C3, some C7 hydrocarbon ions, Ar+ and CO2+ on hydrocarbon-covered carbon surfaces as a function of the ionization energies (IE) of the projectile species showed a drop from about 10% to about 1% and less at IE 8.5-9.5 eV and further decrease with increasing IE. A strong correlation was found between log S(a) and IE, a linear decrease over the entire range of IE investigated (7-16 eV), described by log S(a) = (3.9 +/- 0.5)-(0.39 +/- 0.04) IE.
Significance of hypoburrow nodule formation associated with large biogenic sedimentary structures in open-marine bay siliciclastics of the Upper Eocene Birket Qarun Formation, Wadi El-Hitan, Fayum, Egypt

NASA Astrophysics Data System (ADS)

Abdel-Fattah, Zaki A.; Gingras, Murray K.; Pemberton, S. George

Unusually large biogenic sedimentary structures from the shallow quiescent-marine siliciclastics of the Upper Eocene Birket Qarun Formation in the Fayum area of Egypt display pronounced concretion formation around the trace fossils. The structures are massive, and vary morphologically, forming branched pillars (up to dm-scale), vertical (up to 180 cm height) amphora-like masses, and 3-D box-work "maze". Bioturbation, mainly Thalassinoides attributable to the Glossifungites ichnofacies, mediated and modified the physical and chemical microenvironments influencing early diagenesis; i.e., burrows promote the precipitation of pervasive calcite-dominated cement. The inferred paragenesis, combined with the negative (light) carbon and oxygen stable-isotopic values of the bulk calcite (δ 13C PDB from -0.94 to -4.98‰ and δ 18O PDB from -4.63 to -7.22‰) and bulk dolomite (δ 13C PDB from -2.05 to -8.23‰ and δ 18O PDB from -1.41 to -11.20‰), imply that the pore-water carbon was derived directly from seawater and dissolution of metastable carbonate, which was mediated by bacterial decomposition of organic matter and mixing of meteoric ground water. Thereby, the carbonate cement precipitated mostly under eodiagenetic conditions near the sediment/water interface (<~3 m in depth). The distribution of these structures is confined to parasequence-bounding flooding surfaces (generally expressed as transgressive surfaces of erosion). Notably, sedimentological, ichnological and paragenetic data can be related to stratigraphic evolution such that geochemical and textural evidence is distinctly associated with (1) early cementation of the host sandstone during highstands of relative sea level, (2) the formation of firmgrounds during low relative sea level, (3) the development of a Glossifungites-demarcated discontinuity during initial relative sea-level rise, and (4) continued cementation with rising relative sea level. This was followed by burial diagenesis, evidence for which is derived from petrographic and isotopic data.
Amending the Structure of Renewable Carbon from Biorefinery Waste-Streams for Energy Storage Applications.

PubMed

Ho, Hoi Chun; Goswami, Monojoy; Chen, Jihua; Keum, Jong K; Naskar, Amit K

2018-05-29

Biorefineries produce impure sugar waste streams that are being underutilized. By converting this waste to a profitable by-product, biorefineries could be safeguarded against low oil prices. We demonstrate controlled production of useful carbon materials from the waste concentrate via hydrothermal synthesis and carbonization. We devise a pathway to producing tunable, porous spherical carbon materials by modeling the gross structure formation and developing an understanding of the pore formation mechanism utilizing simple reaction principles. Compared to a simple hydrothermal synthesis from sugar concentrate, emulsion-based synthesis results in hollow spheres with abundant microporosity. In contrast, conventional hydrothermal synthesis produces solid beads with micro and mesoporosity. All the carbonaceous materials show promise in energy storage application. Using our reaction pathway, perfect hollow activated carbon spheres can be produced from waste sugar in liquid effluence of biomass steam pretreatment units. The renewable carbon product demonstrated a desirable surface area of 872 m 2 /g and capacitance of up to 109 F/g when made into an electric double layer supercapacitor. The capacitor exhibited nearly ideal capacitive behavior with 90.5% capacitance retention after 5000 cycles.
Ablation properties of carbon/carbon composites with tungsten carbide

NASA Astrophysics Data System (ADS)

Yin, Jian; Zhang, Hongbo; Xiong, Xiang; Huang, Baiyun; Zuo, Jinlv

2009-02-01

The ablation properties and morphologies of carbon/carbon (C/C) composites with tungsten carbide (WC) filaments were investigated by ablation test on an arc heater and scanning electron microscopy. And the results were compared with those without tungsten carbide (WC) filaments tested under the same conditions. It shows that there is a big difference between C/C composites with and without WC filaments on both macroscopic and microscopic ablation morphologies and the ablation rates of the former are higher than the latter. It is found that the ablation process of C/C composites with WC filaments includes oxidation of carbon fibers, carbon matrices and WC, melting of WC and WO 3, and denudation of WC, WO 3 and C/C composites. Oxidation and melting of WC leads to the formation of holes in z directional carbon fiber bundles, which increases the coarseness of the ablation surfaces of the composites, speeds up ablation and leads to the higher ablation rate. Moreover, it is further found that the molten WC and WO 3 cannot form a continuous film on the ablation surface to prevent further ablation of C/C composites.
One-pot synthesis of transition metal ion-chelating ordered mesoporous carbon/carbon nanotube composites for active and durable fuel cell catalysts

NASA Astrophysics Data System (ADS)

Dombrovskis, Johanna K.; Palmqvist, Anders E. C.

2017-07-01

Development of non-precious metal catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells with high activity and durability and with optimal water management properties is of outmost technological importance and highly challenging. Here we study the possibilities offered through judicious selection of small molecular precursors used for the formation of ordered mesoporous carbon-based non-precious metal ORR catalysts. By combining two complementary precursors, we present a one-pot synthesis that leads to a composite material consisting of transition metal ion-chelating ordered mesoporous carbon and multi-walled carbon nanotubes (TM-OMC/CNT). The resulting composite materials show high specific surface areas and a carbon structure that exhibits graphitic signatures. The synthesis procedure allows for tuning of the carbon structure, the surface area, the pore volume and the ratio of the two components of the composite. The TM-OMC/CNT composites were processed into membrane electrode assemblies and evaluated in single cell fuel cell measurements where they showed a combination of good ORR activity and very high durability.
Effect of carbon supports on RhRe bifunctional catalysts for selective hydrogenolysis of tetrahydropyran-2-methanol

DOE PAGES

Karanjkar, Pranav U.; Burt, Samuel P.; Chen, Xiaoli; ...

2016-09-12

Tetrahydropyran-2-methanol undergoes selective C–O–C hydrogenolysis to produce 1,6-hexanediol using a bifunctional RhRe (reducible metal with an oxophilic promoter) catalyst supported on Vulcan XC-72 carbon (VXC) with >90% selectivity. This RhRe/VXC catalyst is stable over 40 h of reaction in a continuous flow fixed bed reactor. The hydrogenolysis activity of RhRe/VXC is two orders-of-magnitude higher than that of RhRe supported on Norit Darco 12X40 activated carbon (NDC). STEM–EDS analysis reveals that, compared to the RhRe/VXC catalyst, the Re and Rh component metals are segregated on the surface of the low activity RhRe/NDC catalyst, suggesting that Rh and Re in close proximitymore » (“bimetallic” particles) are required for an active hydrogenolysis catalyst. Differences in metal distribution on the carbon surfaces are, in turn, linked to the properties of the carbons: NDC has both a higher surface area and surface oxygen content. Thus, the low areal density of Rh and Re precursors on the high area NDC and/or interactions of the precursors with its O functional groups may interfere with the formation of the bimetallic species required for an active catalyst.« less
Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene

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

Burls, Natalie J.; Fedorov, Alexey V.; Sigman, Daniel M.

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, theworld’s largest ocean,where relatively fresh surface waters inhibitNorth Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400–ppmv (parts per million by volume) CO 2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanyingmore » pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redoxsensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming.« less
Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene

PubMed Central

Burls, Natalie J.; Fedorov, Alexey V.; Sigman, Daniel M.; Jaccard, Samuel L.; Tiedemann, Ralf; Haug, Gerald H.

2017-01-01

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, the world’s largest ocean, where relatively fresh surface waters inhibit North Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400–ppmv (parts per million by volume) CO2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanying pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redox-sensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming. PMID:28924606
Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene

DOE PAGES

Burls, Natalie J.; Fedorov, Alexey V.; Sigman, Daniel M.; ...

2017-09-13

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, theworld’s largest ocean,where relatively fresh surface waters inhibitNorth Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400–ppmv (parts per million by volume) CO 2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanyingmore » pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redoxsensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming.« less
Mechanisms and kinetics study on the trihalomethanes formation with carbon nanoparticle precursors.

PubMed

Du, Tingting; Wang, Yingying; Yang, Xin; Wang, Wei; Guo, Haonan; Xiong, Xinyu; Gao, Rui; Wuli, Xiati; Adeleye, Adeyemi S; Li, Yao

2016-07-01

With lots of carbon nanoparticles (CNPs) applied in the industry, the possibilities of their environmental release have received much attention. As the CNPs may enter drinking water systems, and persist in water and wastewater treatment systems, their possible reaction with disinfectants should be studied. In this study, the formation of trihalomethanes (THMs) with 5 types of carbon nanotubes (CNTs), graphene oxide (GO) and reduced graphene oxide (rGO) was investigated. All CNPs could act as precursors of THMs in aqueous phase. Total concentrations of THMs formed with CNPs varied from 0.24 to 0.95 μM, much lower than that formed from chlorinated Suwannee River Natural Organic Matter (SRNOM) (approximately 9 μM). The kinetics of THMs formation with GO was 0.0814 M(-1) s(-1), which is higher than most of the chlorinated humic acid obtained from different natural waters. The study indicates that during chlorination, C-Cl bond could be formed on the surface of CNPs. However, carbon atoms at the middle of two meta-positioned OH groups on the benzene ring are more active and may prefer to form THMs with chlorine oxidation. The influences of pH and reactant doses on the formation of THMs were also discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.
Synthesis of flat sticky hydrophobic carbon diamond-like films using atmospheric pressure Ar/CH4 dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Rincón, R.; Hendaoui, A.; de Matos, J.; Chaker, M.

2016-06-01

An Ar/CH4 atmospheric pressure dielectric barrier discharge (AP-DBD) was used to synthesize sticky hydrophobic diamond-like carbon (DLC) films on glass surface. The film is formed with plasma treatment duration shorter than 30 s, and water contact angles larger than 90° together with contact angle hysteresis larger than 10° can be achieved. According to Fourier transform infrared spectroscopy and atomic force microscopy analysis, hydrocarbon functional groups are created on the glass substrate, producing coatings with low surface energy (˜35 mJ m-2) with no modification of the surface roughness. To infer the plasma processes leading to the formation of low energy DLC surfaces, optical emission spectroscopy was used. From the results, a direct relationship between the CH species present in the plasma and the carbon concentration in the hydrophobic layer was found, which suggests that the CH species are the precursors of DLC film growth. Additionally, the plasma gas temperature was measured to be below 350 K which highlights the suitability of using AP-DBD to treat thermo-sensitive surfaces.
Growth of vertically aligned multiwalled carbon nanotubes forests on metal alloy Ni-Nb-N with low content of catalyst

NASA Astrophysics Data System (ADS)

Dubkov, S.; Trifonov, A.; Shaman, Yu; Pavlov, A.; Shulyat'ev, A.; Skorik, S.; Kirilenko, E. P.; Rygalin, B.

2016-08-01

This research shows the possibility of carbon nanotubes (CNTs) formation on the surface of low nickel (∼ 10 at.%) Ni-Nb-N amorphous metal alloy film by CVD method at 550 °C of the gas mixture based on acetylene. The structure of CNT were studied by transmission and scanning-electron microscopy, energy-dispersive X-ray and the Raman spectroscopy.
Nanostructured LiMPO4 (M = Fe, Mn, Co, Ni) - carbon composites as cathode materials for Li-ion battery

NASA Astrophysics Data System (ADS)

Dimesso, L.; Spanheimer, C.; Nguyen, T. T. D.; Hausbrand, R.; Jaegermann, W.

2012-10-01

Nanostructured materials are considered to be strong candidates for fundamental advances in efficient storage and/or conversion. In nanostructured materials transport kinetics and surface processes play determining roles. This work describes recent developments in the synthesis and characterization of composites which consist of lithium metal phosphates (LiMPO4, M = Fe, Mn, Co, Ni) coated on nanostructured carbon supports (unordered nanofibers, foams). The composites have been prepared by coating the carbon structures in aqueous (or polyols) solutions containing lithium, metal ions and phosphates. After drying out, the composites have been thermally treated at different temperatures (between 600-780°C) for 5-12 hours under nitrogen. The formation of the olivine structured phase was confirmed by the X-ray diffraction analysis on powders prepared under very similar conditions. The surface investigation revealed the formation of an homogeneous coating of the olivine phase on the carbon structures. The electrochemical performance on the composites showed a dramatic improvement of the discharge specific capacity (measured at a discharge rate of C/25 and room temperature) compared to the prepared powders. The delivered values were 105 mAhg-1 for M = Fe, 100 mAhg-1 for M = Co, 70 mAhg-1 for M = Mn and 30 mAhg-1 for M = Ni respectively.
Deposition And Characterization Of Ultra Thin Diamond Like Carbon Films

NASA Astrophysics Data System (ADS)

Tomcik, B.

2010-07-01

Amorphous hydrogenated and/or nitrogenated carbon films, a-C:H/a-C:N, in overall thickness up to 2 nm are materials of choice as a mechanical and corrosion protection layer of the magnetic media in modern hard disk drive disks. In order to obtain high density and void-free films the sputtering technology has been replaced by different plasma and ion beam deposition techniques. Hydrocarbon gas precursors, like C2H2 or CH4 with H2 and N2 as reactive gases are commonly used in Kaufman DC ion and RF plasma beam sources. Optimum incident energy of carbon ions, C+, is up to 100 eV while the typical ion current densities during the film formation are in the mA/cm2 range. Other carbon deposition techniques, like filtered cathodic arc, still suffer from co-deposition of fine nanosized carbon clusters (nano dust) and their improvements are moving toward arc excitation in the kHz and MHz frequency range. Non-destructive film analysis like μ-Raman optical spectroscopy, spectroscopic ellipsometry, FTIR and optical surface analysis are mainly used in the carbon film characterization. Due to extreme low film thicknesses the surface enhanced Raman spectroscopy (SERS) with pre-deposited layer of Au can reduce the signal collection time and minimize photon-induced damage during the spectra acquisition. Standard approach in the μ-Raman film evaluation is the measurement of the position (shift) and area of D and G-peaks under the deconvoluted overall carbon spectrum. Also, a slope of the carbon spectrum in the 1000-2000 cm-1 wavenumber range is used as a measure of the hydrogen intake within a film. Diamond like carbon (DLC) film should possess elasticity and self-healing properties during the occasional crash of the read-write head flying only couple of nanometers above the spinning film. Film corrosion protection capabilities are mostly evaluated by electrochemical tests, potentio-dynamic and linear polarization method and by business environmental method. Corrosion mechanism, seen as a build-up of cobalt compounds on the top of DLC film, can be minimized with higher carbon film density (above 2.2g/cm3), voidfree film formation and lower film surface nano-roughness. Also, the carbide forming flash layer of Cr or Ti, with typical thicknesses of 0.5 nm may precede the DLC film deposition. Plasma beam sources should be cleaned periodically in oxygen or hydrogen gas flow to prevent incorporation of carbon sooth particles and nano-dust into the film. DLC film susceptibility to cobalt migration from the magnetic layer can be estimated using different techniques: by counting the number of corrosion spots per disk surface area, measuring the amount of cobalt on the surface with inductively coupled plasma or Rutherford backscattering spectroscopy.
Oil/water/rock wettability: Influencing factors and implications for low salinity water flooding in carbonate reservoirs

DOE PAGES

Chen, Yongqiang; Xie, Quan; Sari, Ahmad; ...

2017-11-21

Wettability of the oil/brine/rock system is an essential petro-physical parameter which governs subsurface multiphase flow behaviour and the distribution of fluids, thus directly affecting oil recovery. Recent studies [1–3] show that manipulation of injected brine composition can enhance oil recovery by shifting wettability from oil-wet to water-wet. However, what factor(s) control system wettability has not been completely elucidated due to incomplete understanding of the geochemical system. To isolate and identify the key factors at play we used in this paper SO 4 2—free solutions to examine the effect of salinity (formation brine/FB, 10 times diluted formation brine/10 dFB, and 100more » times diluted formation brine/100 dFB) on the contact angle of oil droplets at the surface of calcite. We then compared contact angle results with predictions of surface complexation by low salinity water using PHREEQC software. We demonstrate that the conventional dilution approach likely triggers an oil-wet system at low pH, which may explain why the low salinity water EOR-effect is not always observed by injecting low salinity water in carbonated reservoirs. pH plays a fundamental role in the surface chemistry of oil/brine interfaces, and wettability. Our contact angle results show that formation brine triggered a strong water-wet system (35°) at pH 2.55, yet 100 times diluted formation brine led to a strongly oil-wet system (contact angle = 175°) at pH 5.68. Surface complexation modelling correctly predicted the wettability trend with salinity; the bond product sum ([>CaOH 2 +][–COO -] + [>CO 3 -][–NH +] + [>CO 3 -][–COOCa +]) increased with decreasing salinity. Finally, at pH < 6 dilution likely makes the calcite surface oil-wet, particularly for crude oils with high base number. Yet, dilution probably causes water wetness at pH > 7 for crude oils with high acid number.« less

Oil/water/rock wettability: Influencing factors and implications for low salinity water flooding in carbonate reservoirs

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

Chen, Yongqiang; Xie, Quan; Sari, Ahmad

Wettability of the oil/brine/rock system is an essential petro-physical parameter which governs subsurface multiphase flow behaviour and the distribution of fluids, thus directly affecting oil recovery. Recent studies [1–3] show that manipulation of injected brine composition can enhance oil recovery by shifting wettability from oil-wet to water-wet. However, what factor(s) control system wettability has not been completely elucidated due to incomplete understanding of the geochemical system. To isolate and identify the key factors at play we used in this paper SO 4 2—free solutions to examine the effect of salinity (formation brine/FB, 10 times diluted formation brine/10 dFB, and 100more » times diluted formation brine/100 dFB) on the contact angle of oil droplets at the surface of calcite. We then compared contact angle results with predictions of surface complexation by low salinity water using PHREEQC software. We demonstrate that the conventional dilution approach likely triggers an oil-wet system at low pH, which may explain why the low salinity water EOR-effect is not always observed by injecting low salinity water in carbonated reservoirs. pH plays a fundamental role in the surface chemistry of oil/brine interfaces, and wettability. Our contact angle results show that formation brine triggered a strong water-wet system (35°) at pH 2.55, yet 100 times diluted formation brine led to a strongly oil-wet system (contact angle = 175°) at pH 5.68. Surface complexation modelling correctly predicted the wettability trend with salinity; the bond product sum ([>CaOH 2 +][–COO -] + [>CO 3 -][–NH +] + [>CO 3 -][–COOCa +]) increased with decreasing salinity. Finally, at pH < 6 dilution likely makes the calcite surface oil-wet, particularly for crude oils with high base number. Yet, dilution probably causes water wetness at pH > 7 for crude oils with high acid number.« less
Studies of carbon incorporation on the diamond [100] surface during chemical vapor deposition using density functional theory.

PubMed

Cheesman, Andrew; Harvey, Jeremy N; Ashfold, Michael N R

2008-11-13

Accurate potential energy surface calculations are presented for many of the key steps involved in diamond chemical vapor deposition on the [100] surface (in its 2 x 1 reconstructed and hydrogenated form). The growing diamond surface was described by using a large (approximately 1500 atoms) cluster model, with the key atoms involved in chemical steps being described by using a quantum mechanical (QM, density functional theory, DFT) method and the bulk of the atoms being described by molecular mechanics (MM). The resulting hybrid QM/MM calculations are more systematic and/or at a higher level of theory than previous work on this growth process. The dominant process for carbon addition, in the form of methyl radicals, is predicted to be addition to a surface radical site, opening of the adjacent C-C dimer bond, insertion, and ultimate ring closure. Other steps such as insertion across the trough between rows of dimer bonds or addition to a neighboring dimer leading to formation of a reconstruction on the next layer may also contribute. Etching of carbon can also occur; the most likely mechanism involves loss of a two-carbon moiety in the form of ethene. The present higher-level calculations confirm that migration of inserted carbon along both dimer rows and chains should be relatively facile, with barriers of approximately 150 kJ mol (-1) when starting from suitable diradical species, and that this step should play an important role in establishing growth of smooth surfaces.
Activated Biomass-derived Graphene-based Carbons for Supercapacitors with High Energy and Power Density.

PubMed

Jung, SungHoon; Myung, Yusik; Kim, Bit Na; Kim, In Gyoo; You, In-Kyu; Kim, TaeYoung

2018-01-30

Here, we present a facile and low-cost method to produce hierarchically porous graphene-based carbons from a biomass source. Three-dimensional (3D) graphene-based carbons were produced through continuous sequential steps such as the formation and transformation of glucose-based polymers into 3D foam-like structures and their subsequent carbonization to form the corresponding macroporous carbons with thin graphene-based carbon walls of macropores and intersectional carbon skeletons. Physical and chemical activation was then performed on this carbon to create micro- and meso-pores, thereby producing hierarchically porous biomass-derived graphene-based carbons with a high Brunauer-Emmett-Teller specific surface area of 3,657 m 2 g -1 . Owing to its exceptionally high surface area, interconnected hierarchical pore networks, and a high degree of graphitization, this carbon exhibited a high specific capacitance of 175 F g -1 in ionic liquid electrolyte. A supercapacitor constructed with this carbon yielded a maximum energy density of 74 Wh kg -1 and a maximum power density of 408 kW kg -1 , based on the total mass of electrodes, which is comparable to those of the state-of-the-art graphene-based carbons. This approach holds promise for the low-cost and readily scalable production of high performance electrode materials for supercapacitors.
Temperature-dependent Study of Isobutanol Decomposition

DTIC Science & Technology

2012-11-01

dimensional Al2O3 alumina CO2 carbon dioxide FTIR Fourier transform infrared Pd palladium Rh rhodium TPD temperature-programmed desorption TPO...that increasing temperature promotes aldehyde formation on the surface of each catalyst. In addition, it is shown that palladium (Pd) activates the...formation of aldehydes and CO2 at a lower temperature than a rhodium (Rh) catalyst. 15. SUBJECT TERMS Isobutanol, FTIR, spectroscopy 16. SECURITY
Investigating CO2 Reservoirs at Gale Crater and Evidence for a Dense Early Atmosphere

NASA Technical Reports Server (NTRS)

Niles, P. B.; Archer, P. D.; Heil, E.; Eigenbrode, J.; McAdam, A.; Sutter, B.; Franz, H.; Navarro-Gonzalez, R.; Ming, D.; Mahaffy, P. R.;

2015-01-01

One of the most compelling features of the Gale landing site is its age. Based on crater counts, the formation of Gale crater is dated to be near the beginning of the Hesperian near the pivotal Hesperian/Noachian transition. This is a time period on Mars that is linked to increased fluvial activity through valley network formation and also marks a transition from higher erosion rates/clay mineral formation to lower erosion rates with mineralogies dominated by sulfate minerals. Results from the Curiosity mission have shown extensive evidence for fluvial activity within the crater suggesting that sediments on the floor of the crater and even sediments making up Mt. Sharp itself were the result of longstanding activity of liquid water. Warm/wet conditions on early Mars are likely due to a thicker atmosphere and increased abundance of greenhouse gases including the main component of the atmosphere, CO2. Carbon dioxide is minor component of the Earth's atmosphere yet plays a major role in surface water chemistry, weathering, and formation of secondary minerals. An ancient martian atmosphere was likely dominated by CO2 and any waters in equilibrium with this atmosphere would have different chemical characteristics. Studies have noted that high partial pressures of CO2 would result in increased carbonic acid formation and lowering of the pH so that carbonate minerals are not stable. However, if there were a dense CO2 atmosphere present at the Hesperian/Noachian transition, it would have to be stored in a carbon reservoir on the surface or lost to space. The Mt. Sharp sediments are potentially one of the best places on Mars to investigate these CO2 reservoirs as they are proposed to have formed in the early Hesperian, from an alkaline lake, and record the transition to an aeolian dominated regime near the top of the sequence. The total amount of CO2 in the Gale crater soils and sediments is significant but lower than expected if a thick atmosphere was present at the Hesperian/Noachian boundary. Likewise, the absence of carbonates suggests that CO2- weathering processes similar to those present on Earth were not dominant. Instead it is possible that more exotic CO2 deposition has occurred driven by atmospheric photochemistry and/or degradation of organic carbon.

Integrated foraminiferal biostratigraphy and chemostratigraphy of the querecual formation (Cretaceous), Eastern Venezuela

USGS Publications Warehouse

Crespo De Cabrera, S.; Sliter, W.V.; Jarvis, I.

1999-01-01

An integrated foraminiferal biostratigraphy and chemostratigraphy is presented for the Lower to Upper Cretaceous Querecual Formation exposed on Chimana Grande Island, Eastern Venezuela. The formation consists of >450 m alternating foraminiferal and organic-rich carbonates and laminated mudrocks, and is considered the main hydrocarbon source rock for the eastern Venezuela Basin. Biostratigraphic resolution within the Querecual Formation is poor, due to a paucity of keeled planktonic foraminifera and impoverished benthic faunas. Deposition occurred in a bathyal environment, with dysaerobic or anoxic bottom waters resulting from high rates of surface productivity associated with an upwelling environment. Biostratigraphic evidence indicates that the Querecual Formation ranges from the upper Albian Rotalipora ticinensis Zone to the Santonian Dicarinella asymetrica Zone. Iron and Al contents fall through the Albian-Cenomanian indicating a progressive decrease in the detrital supply, driven by rising eustatic sea level. A Ca profile demonstrates variations in carbonate production and dissolution. High total organic carbon (TOC) intervals occur in the upper Albian to mid-Cenomanian and Turonian, and high Ba/Al and Si/Al ratios characterize mid-Cenomanian and younger sediments. Variations in these elements primarily reflect changes in marine productivity, but are also affected by diagenetic processes. A stable carbon isotope curve established from analysis of organic matter (??13Corg) correlates well with published ??13C curves for carbonates from England and Italy. The Cenomanian/Turonian boundary cannot be identified using planktonic foraminifera, because key taxa are absent, but the base of the Turonian is clearly indicated by a sharp fall in ??13C immediately above a major positive excursion. The bottom of the Coniacian is placed below a ??13C minimum, towards the base of the Dicarinella concavata Zone. Combined with the foraminiferal data, the isotopic data enable much improved stratigraphic resolution compared to previous investigations of the formation.
Formation of a highly doped ultra-thin amorphous carbon layer by ion bombardment of graphene.

PubMed

Michałowski, Paweł Piotr; Pasternak, Iwona; Ciepielewski, Paweł; Guinea, Francisco; Strupiński, Włodek

2018-07-27

Ion bombardment of graphene leads to the formation of defects which may be used to tune properties of the graphene based devices. In this work, however, we present that the presence of the graphene layer on a surface of a sample has a significant impact on the ion bombardment process: broken sp 2 bonds react with the incoming ions and trap them close to the surface of the sample, preventing a standard ion implantation. For an ion bombardment with a low impact energy and significant dose (in the range of 10 14 atoms cm -2 ) an amorphization of the graphene layer is observed but at the same time, most of the incoming ions do not penetrate the sample but stop at the surface, thus forming a highly doped ultra-thin amorphous carbon layer. The effect may be used to create thin layers containing desired atoms if no other technique is available. This approach is particularly useful for secondary ion mass spectrometry where a high concentration of Cs at the surface of a sample significantly enhances the negative ionization probability, allowing it to reach better detection limits.
Formation of a highly doped ultra-thin amorphous carbon layer by ion bombardment of graphene

NASA Astrophysics Data System (ADS)

Piotr Michałowski, Paweł; Pasternak, Iwona; Ciepielewski, Paweł; Guinea, Francisco; Strupiński, Włodek

2018-07-01

Ion bombardment of graphene leads to the formation of defects which may be used to tune properties of the graphene based devices. In this work, however, we present that the presence of the graphene layer on a surface of a sample has a significant impact on the ion bombardment process: broken sp2 bonds react with the incoming ions and trap them close to the surface of the sample, preventing a standard ion implantation. For an ion bombardment with a low impact energy and significant dose (in the range of 1014 atoms cm‑2) an amorphization of the graphene layer is observed but at the same time, most of the incoming ions do not penetrate the sample but stop at the surface, thus forming a highly doped ultra-thin amorphous carbon layer. The effect may be used to create thin layers containing desired atoms if no other technique is available. This approach is particularly useful for secondary ion mass spectrometry where a high concentration of Cs at the surface of a sample significantly enhances the negative ionization probability, allowing it to reach better detection limits.
Insights into electrodeposition of an inhibitor film and its inhibitive effects on calcium carbonate deposition.

PubMed

Morizot, Arnaud P; Neville, Anne

2002-01-01

Polycarboxylic acid (PAA), a common scale inhibitor has demonstrated adsorption properties on stainless steel surfaces. An electrochemically based technique has been used to assess the extent of film formation. The presence of calcium and magnesium ions in the solution and the cathodic electrochemical activity at the metal surface have been shown to enhance the inhibitor film formation by promoting the transport of the inhibitor from the solution to the metal surface. The effect of the inhibitor film in retarding scale deposition is assessed using measurement of the deposition onto metal electrodes immersed in a supersaturated solution of CaCO(3). The practical implications of these findings are discussed.
Statistical characterization of surface features from tungsten-coated divertor inserts in the DIII-D Metal Rings Campaign

NASA Astrophysics Data System (ADS)

Adams, Jacob; Unterberg, Ezekial; Chrobak, Christopher; Stahl, Brian; Abrams, Tyler

2017-10-01

Continuing analysis of tungsten-coated inserts from the recent DIII-D Metal Rings Campaign utilizes a statistical approach to study carbon migration and deposition on W surfaces and to characterize the pre- versus post-exposure surface morphology. A TZM base was coated with W using both CVD and PVD and allowed for comparison between the two coating methods. The W inserts were positioned in the lower DIII-D divertor in both the upper (shelf) region and lower (floor) region and subjected to multiple plasma shots, primarily in H-mode. Currently, the post-exposure W inserts are being characterized using SEM/EDX to qualify the surface morphology and to quantify the surface chemical composition. In addition, profilometry is being used to measure the surface roughness of the inserts both before and after plasma exposure. Preliminary results suggest a correlation between the pre-exposure surface roughness and the level of carbon deposited on the surface. Furthermore, ongoing in-depth analysis may reveal insights into the formation mechanism of nanoscale bumps found in the carbon-rich regions of the W surfaces that have not yet been explained. Work supported in part by US DoE under the Science Undergraduate Laboratory Internship (SULI) program and under DE-FC02-04ER54698.
Oxygen vacancy formation characteristics in the bulk and across different surface terminations of La (1₋x)Sr xFe (1₋y)Co yO (3₋δ) perovskite oxides for CO 2 conversion

DOE PAGES

Maiti, Debtanu; Daza, Yolanda A.; Yung, Matthew M.; ...

2016-03-07

Density functional theory (DFT) based investigation of two parameters of prime interest -- oxygen vacancy and surface terminations along (100) and (110) planes -- has been conducted for La (1-x)Sr xFe(1-y)Co yO (3-more » $$\\delta$$) perovskite oxides in view of their application towards thermochemical carbon dioxide conversion reactions. The bulk oxygen vacancy formation energies for these mixed perovskite oxides are found to increase with increasing lanthanum and iron contents in the 'A' site and 'B' site, respectively. Surface terminations along (100) and (110) crystal planes are studied to probe their stability and their capabilities to accommodate surface oxygen vacancies. Amongst the various terminations, the oxygen-rich (110) surface and strontium-rich (100) surface are the most stable, while transition metal-rich terminations along (100) revealed preference towards the production of oxygen vacancies. The carbon dioxide adsorption strength, a key descriptor for CO 2 conversion reactions, is found to increase on oxygen vacant surfaces thus establishing the importance of oxygen vacancies in CO 2 conversion reactions. Amongst all the surface terminations, the lanthanum-oxygen terminated surface exhibited the strongest CO 2 adsorption strength. Finally, the theoretical prediction of the oxygen vacancy trends and the stability of the samples were corroborated by the temperature-programmed reduction and oxidation reactions and in situ XRD crystallography.« less
Stretchable and flexible thermoelectric polymer composites

NASA Astrophysics Data System (ADS)

Slobodian, P.; Riha, P.; Matyas, J.; Olejnik, R.

2018-03-01

Polymer composites were manufactured from pristine and oxidized multi-walled carbon nanotubes and ethylene-octene copolymer. The composites had thermoelectric properties and exhibit thermoelectric effect, that is, the conversion of temperature differences into electricity. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy of the multi-walled carbon nanotubes in ethylene-octene copolymer matrix showed that the oxidation with HNO3 or KMnO4 enhanced its p-type electrical conductivity and that the thermoelectric power increase was proportional to the formation of new oxygen-containing functional groups on the surface of carbon nanotubes.
Zero-valent iron particles embedded on the mesoporous silica-carbon for chromium (VI) removal from aqueous solution

NASA Astrophysics Data System (ADS)

Xiong, Kun; Gao, Yuan; Zhou, Lin; Zhang, Xianming

2016-09-01

Nanoscale zero-valent iron (nZVI) particles were embedded on the walls of mesoporous silica-carbon (MSC) under the conditions of high-temperature carbonization and reduction and used to remove chromium (VI) from aqueous solution. The structure and textural properties of nZVI-MSC were characterized by the powder X-ray diffraction, transmission electron microscopy and N2 adsorption and desorption. The results show that nZVI-MSC has highly ordered mesoporous structure and large surface area, indistinguishable with that of MSC. Compared with the support MSC and iron particles supported on the activated carbon (nZVI/AC), nZVI-MSC exhibited much higher Cr(VI) removal efficiency with about 98 %. The removal process obeys a pseudo first-order model. Such excellent performance of nZVI-MSC could be ascribed to the large surface and iron particles embedded on the walls of the MSC, forming an intimate contact with the MSC. It is proposed that this feature might create certain micro-electrode on the interface of iron particles and MSC, which prevented the formation of metal oxide on the surface and provided fresh Fe surface for Cr(VI) removal.
Facilitation of NADH Electrooxidation at Treated Carbon Nanotubes

PubMed Central

Wooten, Marilyn; Gorski, Waldemar

2010-01-01

The relationship between the state of the surface of carbon nanotubes (CNT) and their electrochemical activity was investigated using the enzyme cofactor dihydronicotinamide adenine dinucleotide (NADH) as a redox probe. The boiling of CNT in water, while nondestructive, activated them toward the oxidation of NADH as indicated by a shift in the anodic peak potential of NADH (ENADH) from 0.4 to 0.0 V. The shift in ENADH was due to the redox mediation of NADH oxidation by traces of quinone species that were formed on the surface of treated CNT. The harsher treatment that comprised of microwaving of CNT in concentrated nitric acid had a similar effect on the ENADH and, additionally, it increased the anodic peak current of NADH. The latter correlated with the formation of defects on the surface of acid-microwaved CNT as indicated by their Raman spectra. The increase in current was discussed considering a role of surface mediators on the buckled graphene sheets of acid-microwaved CNT. The other carbon allotropes including the edge plane pyrolytic graphite, graphite powder, and glassy carbon did not display a comparable activation toward the oxidation of NADH. PMID:20088562
Observation of chemical erosion of carbon based wall materials in the TEXTOR tokamak

NASA Astrophysics Data System (ADS)

Philipps, V.; Pospieszczyk, A.; Erdweg, M.; Schweer, B.; Vietzke, E.; Winter, J.

1996-01-01

Mass spectroscopy and optical spectroscopy have been used to measure the formation of methane, higher hydrocarbons and of CO during the interaction of limiters with the boundary plasma and of special carbon targets with the scrape-off-layer plasma (SOL) of TEXTOR. Mass spectroscopic data are obtained by the Sniffer probe in the SOL under carbon, boronized and siliconized wall conditions. At target temperatures <=100 °C, methane yields range typically between 0.7 and 1.2%. They vary only little with changing plasma conditions. C2-hydrocarbon formation dominates the overall carbon erosion under many conditions. Their yields increase with decreasing plasma temperature. Siliconization of the walls reduces the methane formation only little but suppresses the formation of higher hydrocarbons significantly. CO formation is dominated by the actual oxygen impurity fluxes and ranges between 0.2% up to 1.5% depending on the wall conditioning. Supporting data on hydrocarbon and CO formation are obtained from the outgassing after the discharge. Optical spectroscopy has been used to determine methane formation yields from CH band emission in front of graphite test limiters positioned at the last closed flux surface. The yields are typically in the range between 1.5 and 5% and are generally a factor 2-3 higher compared to those from mass spectroscopy. The CH4 formation is nearly constant between 200 °C up to 700 °C and decreases beyond 800-1000 °C. It decreases with increasing flux density. C2 hydrocarbon emission from the limiters has not been observed by molecular band emission within the range of normal plasma conditions. They show up only for detached plasma conditions.
Effective Removal of Tetracycline Antibiotics from Water using Hybrid Carbon Membranes

NASA Astrophysics Data System (ADS)

Liu, Ming-Kai; Liu, Ying-Ya; Bao, Dan-Dan; Zhu, Gen; Yang, Guo-Hai; Geng, Jun-Feng; Li, Hai-Tao

2017-03-01

Antibiotic residues in drinking water have become a global problem, especially in developing countries. However, effective purification of water contaminated by antibiotics remains a great challenge. Here, we investigated the removing of tetracycline by carbon nanomaterials with different structures and surface functionalities. The result shows that a membrane of thick graphene oxide (GO) and activated carbon (AC) with a thickness of 15 μm can effectively remove 98.9% of tetracycline hydrochloride (TCH) from water by vacuum filtration. Structural analysis indicated that the AC nanoparticles were uniformly inserted into the GO interstitial sites without any aggregations. Also, GO sheets were loosened by the encapsulated AC nanoparticles, leading to the formation of numerous tiny pores (3-10 nm) that acted as channels for fluid passage, whereas the carbons and chemical groups on the GO surface adsorbed TCH. GO/AC membrane exhibits the best adsorption efficiency among the investigated materials, including pure GO, AC, carbon nanotube (CNT), and CNT/AC and GO/CNT hybrids.
Surface protection of austenitic steels by carbon nanotube coatings

NASA Astrophysics Data System (ADS)

MacLucas, T.; Schütz, S.; Suarez, S.; Mücklich, F.

2018-03-01

In the present study, surface protection properties of multiwall carbon nanotubes (CNTs) deposited on polished austenitic stainless steel are evaluated. Electrophoretic deposition is used as a coating technique. Contact angle measurements reveal hydrophilic as well as hydrophobic wetting characteristics of the carbon nanotube coating depending on the additive used for the deposition. Tribological properties of carbon nanotube coatings on steel substrate are determined with a ball-on-disc tribometer. Effective lubrication can be achieved by adding magnesium nitrate as an additive due to the formation of a holding layer detaining CNTs in the contact area. Furthermore, wear track analysis reveals minimal wear on the coated substrate as well as carbon residues providing lubrication. Energy dispersive x-ray spectroscopy is used to qualitatively analyse the elemental composition of the coating and the underlying substrate. The results explain the observed wetting characteristics of each coating. Finally, merely minimal oxidation is detected on the CNT-coated substrate as opposed to the uncoated sample.
Investigation of the interfacial properties of polyurethane/carbon nanotube hybrid composites: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Goclon, Jakub; Panczyk, Tomasz; Winkler, Krzysztof

2018-03-01

Considering the varied applications of hybrid polymer/carbon nanotube composites and the constant progress in the synthesis methods of such materials, we report a theoretical study of interfacial layer formation between pristine single-wall carbon nanotubes (SWCNTs) and polyurethane (PU) using molecular dynamic simulations. We vary the SWCNT diameter and the number of PU chains to examine various PU-SWCNT interaction patterns. Our simulations indicate the important role of intra-chain forces in PU. No regular polymeric structures could be identified on the carbon nanotube surface during the simulations. We find that increasing the SWCNT diameter results in stronger polymer binding. However, higher surface loadings of PU lead to stronger interpenetration by the polymeric segments; this effect is more apparent for SWCNTs with small diameters. Our core finding is that the attached PU binds most strongly to the carbon nanotubes with the largest diameters. Polymer dynamics reveal the loose distribution of PU chains in these systems.
Bulk and surface structural investigations of diesel engine soot and carbon black.

PubMed

Müller, J-O; Su, D S; Wild, U; Schlögl, R

2007-08-14

The microstructure and electronic structure of environmentally relevant carbons such as Euro IV heavy duty diesel engine soot, soot from a black smoking diesel engine, spark discharge soot as model aerosol, commercial furnace soot and lamp black are investigated by transmission electron microscopy, electron energy-loss spectroscopy and X-ray photoelectron spectroscopy. The materials exhibit differences in the predominant bonding, which influences microstructure as well as surface functionalization. These chemical and physical properties depend on the formation history of the investigated carbonaceous materials. In this work, a correlation of the microstructure of the samples to the predominant bonding and incorporation of oxygen into the carbons is obtained. It is shown that a high amount of defects and the deviation of the carbons from a perfect graphitic structure results in a increased incorporation of oxygen and hydrogen. A correlation between the length and curvature of graphene layers with the bonding state of carbon atoms and incorporation of oxygen and hydrogen is established.
Morphological, structural, and chemical effects in response of novel carbide derived carbon sensor to NH3, N2O, and air.

PubMed

Adu, Kofi W; Li, Qixiu; Desai, Sharvil C; Sidorov, Anton N; Sumanasekera, Gamini U; Lueking, Angela D

2009-01-06

The response of two carbide derived carbons (CDCs) films to NH(3), N(2)O, and room air is investigated by four probe resistance at room temperature and pressures up to 760 Torr. The two CDC films were synthesized at 600 (CDC-600) and 1000 degrees C (CDC-1000) to vary the carbon morphology from completely amorphous to more ordered, and determine the role of structure, surface area, and porosity on sensor response. Sensor response time followed kinetic diameter and indicated a more ordered carbon structure slowed response due to increased tortuosity caused by the formation of graphitic layers at the particle fringe. Steady state sensor response was greater for the less-ordered material, despite its decreased surface area, decreased micropore volume, and less favorable surface chemistry, suggesting carbon structure is a stronger predictor of sensor response than surface chemistry. The lack of correlation between adsorption of the probe gases and sensor response suggests chemical interaction (charge transfer) drive sensor response within the material; N(2)O response, in particular, did not follow simple adsorption behavior. Based on Raman and FTIR characterization, carbon morphology (disorder) appeared to be the determining factor in overall sensor response, likely due to increased charge transfer between gases and carbon defects of amorphous or disordered regions. The response of the amorphous CDC-600 film to NH(3) was 45% without prior oxidation, showing amorphous CDCs have promise as chemical sensors without additional pretreatment common to other carbon sensors.

Ground penetrating radar imaging of cap rock, caliche and carbonate strata

USGS Publications Warehouse

Kruse, S.E.; Schneider, J.C.; Campagna, D.J.; Inman, J.A.; Hickey, T.D.

2000-01-01

Field experiments show ground penetrating radar (GPR) can be used to image shallow carbonate stratigraphy effectively in a variety of settings. In south Florida, the position and structure of cap rock cover on limestone can be an important control on surface water flow and vegetation, but larger scale outcrops (tens of meters) of cap rock are sparse. GPR mapping through south Florida prairie, cypress swamp and hardwood hammock resolves variations in thickness and structure of cap rock to ~3 m and holds the potential to test theories for cap rock-vegetation relationships. In other settings, carbonate strata are mapped to test models for the formation of local structural anomalies. A test of GPR imaging capabilities on an arid caliche (calcrete) horizon in southeastern Nevada shows depth penetration to ~2 m with resolution of the base of caliche. GPR profiling also succeeds in resolving more deeply buried (~5 m) limestone discontinuity surfaces that record subaerial exposure in south Florida. (C) 2000 Elsevier Science B.V. All rights reserved.Field experiments show ground penetrating radar (GPR) can be used to image shallow carbonate stratigraphy effectively in a variety of settings. In south Florida, the position and structure of cap rock cover on limestone can be an important control on surface water flow and vegetation, but larger scale outcrops (tens of meters) of cap rock are sparse. GPR mapping through south Florida prairie, cypress swamp and hardwood hammock resolves variations in thickness and structure of cap rock to approx. 3 m and holds the potential to test theories for cap rock-vegetation relationships. In other settings, carbonate strata are mapped to test models for the formation of local structural anomalies. A test of GPR imaging capabilities on an arid caliche (calcrete) horizon in southeastern Nevada shows depth penetration to approx. 2 m with resolution of the base of caliche. GPR profiling also succeeds in resolving more deeply buried (approx. 5 m) limestone discontinuity surfaces that record subaerial exposure in south Florida.
Reversible control of biofilm formation by Cellulomonas spp. in response to nitrogen availability.

PubMed

Young, Jenna M; Leschine, Susan B; Reguera, Gemma

2012-03-01

The microbial degradation of cellulose contributes greatly to the cycling of carbon in terrestrial environments and feedbacks to the atmosphere, a process that is highly responsive to nitrogen inputs. Yet how key groups of cellulolytic microorganisms adaptively respond to the global conditions of nitrogen limitation and/or anthropogenic or climate nitrogen inputs is poorly understood. The actinobacterial genus Cellulomonas is of special interest because it incorporates the only species known to degrade cellulose aerobically and anaerobically. Furthermore, despite their inability to fix nitrogen, they are active decomposers in nitrogen-limited environments. Here we show that nitrogen limitation induced biofilm formation in Cellulomonas spp., a process that was coupled to carbon sequestration and storage in a curdlan-type biofilm matrix. The response was reversible and the curdlan matrix was solubilized and used as a carbon and energy source for biofilm dispersal once nitrogen sources became available. The biofilms attached strongly to cellulosic surfaces and, despite the growth limitation, produced cellulases and degraded cellulose more efficiently. The results show that biofilm formation is a competitive strategy for carbon and nitrogen acquisition and provide valuable insights linking nitrogen inputs to carbon sequestration and remobilization in terrestrial environments. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.
Reaction of methyl formate with VC(1 0 0) and TiC(1 0 0) surfaces

NASA Astrophysics Data System (ADS)

Frantz, Peter; Kim, Hyun I.; Didziulis, Stephen V.; Li, Shuang; Chen, Zhiying; Perry, Scott S.

2005-12-01

The chemistry of the (1 0 0) surface of the tribologically important materials vanadium carbide (VC) and titanium carbide (TiC) with methyl formate (CH 3OCHO) has been studied with X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). The molecule reacts with each surface at temperatures below 150 K, although the extent of reaction is greater on the TiC surface. XPS and HREELS results indicate that the first step in this chemistry is the cleavage of the CH 3O-CHO bond, generating surface methoxy groups (CH 3O-) and either carbon monoxide on VC or a formyl (CHO) group on TiC. The methoxy group reacts further on both surfaces via pathways expected based on previous methanol adsorption studies, primarily decomposing through a formyl intermediate on VC to generate formaldehyde and evolving methanol on TiC. The formyl group formed directly from methyl formate on TiC enables the production and evolution of formaldehyde, and also appears to break down further to the elements. These results indicate a propensity for these carbides to react with esters, leading potentially to the beneficial formation of friction lowering surface films or the deleterious degradation of ester-based lubricants.
Structure of the Clean and Oxygen-Covered Cu(100) Surface at Room Temperature in the Presence of Methanol Vapor in the 10-200 mTorr Pressure Range.

PubMed

Eren, Baran; Kersell, Heath; Weatherup, Robert S; Heine, Christian; Crumlin, Ethan J; Friend, Cynthia M; Salmeron, Miquel B

2018-01-18

Using ambient pressure X-ray photoelectron spectroscopy (APXPS) and high pressure scanning tunneling microscopy (HPSTM), we show that in equilibrium with 0.01-0.2 Torr of methanol vapor, at room temperature, the Cu(100) surface is covered with methoxy species forming a c(2 × 2) overlayer structure. In contrast, no methoxy is formed if the surface is saturated with an ordered oxygen layer, even when the methanol pressure is 0.2 Torr. At oxygen coverages below saturation, methanol dissociates and reacts with the atomic oxygen, producing methoxy and formate on the surface, and formaldehyde that desorbs to the gas phase. Unlike the case of pure carbon monoxide and carbon dioxide, methanol does not induce the restructuring of the Cu(100) surface. These results provide insight into catalytic anhydrous production of aldehydes.
Covalent enzyme immobilization onto carbon nanotubes using a membrane reactor

NASA Astrophysics Data System (ADS)

Voicu, Stefan Ioan; Nechifor, Aurelia Cristina; Gales, Ovidiu; Nechifor, Gheorghe

2011-05-01

Composite porous polysulfone-carbon nanotubes membranes were prepared by dispersing carbon nanotubes into a polysulfone solution followed by the membrane formation by phase inversion-immersion precipitation technique. The carbon nanotubes with amino groups on surface were functionalized with different enzymes (carbonic anhydrase, invertase, diastase) using cyanuric chloride as linker between enzyme and carbon nanotube. The composite membrane was used as a membrane reactor for a better dispersion of carbon nanotubes and access to reaction centers. The membrane also facilitates the transport of enzymes to active carbon nanotubes centers for functionalization (amino groups). The functionalized carbon nanotubes are isolated by dissolving the membranes after the end of reaction. Carbon nanotubes with covalent immobilized enzymes are used for biosensors fabrications. The obtained membranes were characterized by Scanning Electron Microscopy, Thermal analysis, FT-IR Spectroscopy, Nuclear Magnetic Resonance, and functionalized carbon nanotubes were characterized by FT-IR spectroscopy.
Dioctahedral Phyllosilicates Versus Zeolites and Carbonates Versus Zeolites Competitions as Constraints to Understanding Early Mars Alteration Conditions

NASA Astrophysics Data System (ADS)

Viennet, Jean-Christophe; Bultel, Benjamin; Riu, Lucie; Werner, Stephanie C.

2017-11-01

Widespread occurrence of Fe,Mg-phyllosilicates has been observed on Noachian Martian terrains. Therefore, the study of Fe,Mg-phyllosilicate formation, in order to characterize early Martian environmental conditions, is of particular interest to the Martian community. Previous studies have shown that the investigation of Fe,Mg-smectite formation alone helps to describe early Mars environmental conditions, but there are still large uncertainties in terms of pH range, oxic/anoxic conditions, etc. Interestingly, carbonates and/or zeolites have also been observed on Noachian surfaces in association with the Fe,Mg-phyllosilicates. Consequently, the present study focuses on the dioctahedral/trioctahedral phyllosilicate/carbonate/zeolite formation as a function of various CO2 contents (100% N2, 10% CO2/90% N2, and 100% CO2), from a combined approach including closed system laboratory experiments for 3 weeks at 120°C and geochemical simulations. The experimental results show that as the CO2 content decreases, the amount of dioctahedral clay minerals decreases in favor of trioctahedral minerals. Carbonates and dioctahedral clay minerals are formed during the experiments with CO2. When Ca-zeolites are formed, no carbonates and dioctahedral minerals are observed. Geochemical simulation aided in establishing pH as a key parameter in determining mineral formation patterns. Indeed, under acidic conditions dioctahedral clay minerals and carbonate minerals are formed, while trioctahedral clay minerals are formed in basic conditions with a neutral pH value of 5.98 at 120°C. Zeolites are favored from pH ≳ 7.2. The results obtained shed new light on the importance of dioctahedral clay minerals versus zeolites and carbonates versus zeolites competitions to better define the aqueous alteration processes throughout early Mars history.
IMPACT OF OXYGEN MEDIATED OXIDATIVE COUPLING ON ADSORPTION KINETICS

EPA Science Inventory

The presence of molecular oxygen in the test environment promotes oxidative coupling (polymer formation) of phenolic compounds on the surface of granular activated carbon (GAC). Both adsorption equilibria and adsorption kinetics are affected by these chemical reactions. Lack of...
Ultrasound-assisted synthesis and processing of carbon materials

NASA Astrophysics Data System (ADS)

Fortunato, Maria E.

2011-12-01

Part I: Porous carbons are of interest in many applications because of their high surface areas and other physicochemical properties, and much effort has been directed towards developing new methods for controlling the porosity of carbons. Ultrasonic spray pyrolysis (USP) is an aerosol method suitable for large-scale, continuous synthesis of materials. Ultrasound is used to create aerosol droplets of a precursor solution which serve as micron-sized spherical reactors for materials synthesis. This work presents a precursor system for the template-free USP synthesis of porous carbons using low-cost precursors that do not evolve or require hazardous chemicals: sucrose was used as the carbon source, and sodium carbonate, sodium bicarbonate, or sodium nitrate was added as a decomposition catalyst and porogen. The USP carbons had macroporous interiors and microporous shells with surface areas as high as 800 m2/g and a narrow pore size distribution. It was determined that the interior porosity was a result of the gas evolution from salt decomposition and not from the presence of a salt template. Porous carbon is frequently used as a catalyst support because it provides high surface area and it is chemically and physically stable under many anoxic reaction conditions. Typically, the preparation of supported catalysts requires multiple steps for carbonization and metal impregnation. In this work, iron-impregnated porous carbon microspheres (Fe-C) were prepared by a one-step USP process by incorporating both the carbon and metal sources into the precursor solution. Carbonization, pore formation, metal impregnation, and metal activation occurred simultaneously to produce Fe-C materials with surface areas as high as 800 m2/g and up to 10 wt% Fe incorporated as nanoparticles < 20 nm in diameter. Fe-C was used as a catalyst to reduce aqueous hexavalent chromium, which demonstrated the accessibility of the iron nanoparticles despite the fact that they are likely encapsulated in the porous carbon support. Part II: The effects of high intensity ultrasound arise from acoustic cavitation: the formation, growth, and collapse of bubbles in a liquid. Bubble collapse produces intense localized heating (˜5000 K), high pressures (˜300 atm), and enormous heating and cooling rates (>109 K/sec). In solid-liquid slurries, surface erosion and particle fracture occur due to the shockwaves and microjets formed from asymmetric bubble collapse at extended surfaces. The chemical and physical effects of ultrasound have been studied as an adjunct to the traditional chemical pretreatment of lignocellulosic biomass for ethanol production. Lignocellulosic biomass consists of cellulose, hemicellulose, and lignin. The surface effects of ultrasound were used in this work to increase the accessibility of the cellulose, which can be converted to glucose and then fermented into ethanol. The lignocellulosic biomass used in this work was Miscanthus x giganteus (Mxg) which was grown at the University of Illinois at Urbana-Champaign. The chemical effects of NaOH pretreatment on Mxg were enhanced by ultrasound: greater delignification and a significant increase in the amount of pores >5 nm were observed. ˜ 70% of the theoretical glucose yield was obtained by enzymatic saccharification of the ultrasound-assisted NaOH-pretreated Mxg; this is comparable to the yields that can be obtained by traditional alkaline pretreatments, but it was achieved in a shorter time and at a lower temperature. Because the apparatus used for laboratory studies is not a likely device for scale-up, the economics of ultrasound with regards to energy balance are not yet resolved.
Research of Adhesion Bonds Between Gas-Thermal Coating and Pre-Modified Base

NASA Astrophysics Data System (ADS)

Kovalevskaya, Z.; Zaitsev, K.; Klimenov, V.

2016-08-01

Nature of adhesive bonds between gas-thermal nickel alloy coating and carbon steel base was examined using laser profilometry, optical metallography, transmission and scanning electron microscopy. The steel surface was plastically pre-deformed by an ultrasonic tool. Proved that ultrasound pre-treatment modifies the steel surface. Increase of dislocation density and formation of sub micro-structure are base elements of surface modification. While using high-speed gas-flame, plasma and detonation modes of coatings, surface activation occurs and durable adhesion is formed. Ultrasonic pre-treatment of base material is effective when sprayed particles and base material interact through physical-chemical bond formation. Before applying high-speed gas flame and plasma sprayed coatings, authors recommend ultrasonic pretreatment, which creates periodic wavy topography with a stroke of 250 microns on the steel surface. Before applying detonation sprayed coatings, authors recommend ultrasound pretreatment that create modified surface with a uniform micro-topography.
Electrical and galvanomagnetic properties of nanoporous carbon samples impregnated with bromine

NASA Astrophysics Data System (ADS)

Danishevskii, A. M.; Popov, V. V.; Kyutt, R. N.; Gordeev, S. K.

2013-07-01

Nanoporous carbon samples with a large specific surface area can be filled with heavier elements or their compounds, which makes it possible to investigate the interaction of their electronic subsystems with carbon. One of the elements convenient for filling pores of carbon materials is bromine. Impregnation of nanoporous carbon samples with bromine causes the occurrence of the processes of micropore filling, monolayer adsorption, and intercalation. It has been found that samples impregnated with bromine substantially change their electrical and galvanomagnetic properties, and these changes depend on the structure of the samples. It has been shown that, if in the skeleton of a porous carbon sample there is a fraction of graphite clusters, the impregnation of the sample with bromine increases the concentration of charged carriers (holes). But when the sample has a quasi-amorphous structure, the injection of bromine into the sample leads to the appearance of a certain concentration of electrons in addition to charged mobile holes of the initial sample; i.e., the electrical conductivity becomes bipolar. In the former case, bromine molecules intercalate graphite clusters and, since bromine is an acceptor during intercalation of graphite, the hole concentration in the carbon skeleton network increases. In the latter case, bromine molecules can only be adsorbed on pore walls. As a result, the adsorption interaction between the electron shells of bromine molecules and the carbon surface leads to the formation of a donor layer near the surface and to the generation of electrons in the carbon skeleton network.
Carbothermal transformation of a graphitic carbon nanofiber/silica aerogel composite to a SiC/silica nanocomposite.

PubMed

Lu, Weijie; Steigerwalt, Eve S; Moore, Joshua T; Sullivan, Lisa M; Collins, W Eugene; Lukehart, C M

2004-09-01

Carbon nanofiber/silica aerogel composites are prepared by sol-gel processing of surface-enhanced herringbone graphitic carbon nanofibers (GCNF) and Si(OMe)4, followed by supercritical CO2 drying. Heating the resulting GCNF/silica aerogel composites to 1650 degrees C under a partial pressure of Ar gas initiates carbothermal reaction between the silica aerogel matrix and the carbon nanofiber component to form SiC/silica nanocomposites. The SiC phase is present as nearly spherical nanoparticles, having an average diameter of ca. 8 nm. Formation of SiC is confirmed by powder XRD and by Raman spectroscopy.
Hydrogeothermal Convective Circulation Model for the Formation of the Chicxulub Ring of Cenotes in the Yucatan Peninsula, Mexico.

NASA Astrophysics Data System (ADS)

Monroy-Rios, E.; Beddows, P. A.

2015-12-01

Despite being deeply buried, the topography and geophysical characteristics of the multi-ring Chicxulub impact structure are reflected on the now subaerial Yucatan Peninsula with aligned arcs of cenotes (sinkholes), forming the "Ring of Cenotes". A pending question is the determination of the geological, geochemical, structural features and associated processes that have led to void development, and the upwards propagation of the voids, cross cutting over 1000 m of super-deposited carbonate sequences. Drawing from the published literature on drill core and geophysical surveys undertaken by Pemex, UNAM, and IODP/ICDP, numerical modeling, and general carbonate platform hydrothermal reactive transport models, we provide a conceptual model for the genesis of the Ring of Cenotes. In horizontally bedded carbonate platforms, geothermal gradients will drive convective flow, with strong vertical components specifically in the platform center. In the Yucatan Platform, a high occurrence of anhydrite and dolomite at depth evokes early burial dolomitization and anhydritization, sourcing Mg from seawater. The Chicxulub impact near the center of the platform produced a low permeability and high thermal conductivity melt rock that arguably extends to the basement rock at 3.5 km below surface. Heat of impact enforced the pre-existing geothermal circulation pattern, and even with depletion of the heat of impact, the high thermal conductivity of the crystalline melt would lead to enhanced geothermal gradients in the center of the platform. The cenotes overlying the crater are deep (150+ m) vertical shafts with most (but not all) breaching the surface. The pit geomorphology suggests a bottom-up formation. Excess Si in the shallow groundwater points to a convective circulation with strong vertical components geochemically linking the granodioritic basement rock to the surface. Water temperature and conductivity profiles support ongoing vertical flux in some deep pit cenotes. Within this framework, we argue for the formation of the Ring of Cenotes by hydrogeothermal convective circulation in the post-impact carbonate sequences, leading to spatially focused dissolution at depth, with voids initiated along the crater edge effectively propagating upwards, often breaching the surface.
Experimental investigation of CO2-brine-rock interactions at simulated in-situ conditions

NASA Astrophysics Data System (ADS)

Słomski, Piotr; Lutyński, Marcin; Mastalerz, Maria; Szczepański, Jacek; Derkowski, Arkadiusz; Topór, Tomasz

2017-04-01

Geological sequestration of carbon dioxide (CO2) in deep formations (e.g. saline aquifers, oil and gas reservoirs and coalbeds) is one of the most promising options for reducing concentration of this anthropogenic greenhouse gas in the atmosphere. CO2 injected into the rock formations can be trapped by several mechanisms including structural and stratigraphic trapping, capillary CO2 trapping, dissolution trapping and mineral trapping. During dissolution trapping, CO2 dissolves in the formation brine and sinks in the reservoir as the CO2-enriched brine has an increased density. In comparison, in mineral trapping, CO2 is bound by precipitating new carbonate minerals. The latter two mechanisms depend on the temperature, pressure, and the mineralogy of the reservoir rock and the chemical composition of the brine. This study discusses laboratory scale alterations of Ordovician and Silurian shale rocks from potential CO2 sequestration site B1 in the Baltic Basin. In the reported experiment, rocks submerged in brine in specially constructed reactors were subjected to CO2 pressure of 30-35 MPa for 30-45 days at temperature of 80 oC. Shale samples were analyzed in terms of mineral composition and mesopore surface area and volume, before and after experiments, by means of X-ray diffraction and N2 low-pressure adsorption, respectively, for possible CO2 induced changes. Comparison of mineral composition before and after experiments demonstrated subtle mineral changes. The most conspicuous was a release of Fe in the form of Fe-oxyhydroxides, most probably related to the decomposition of Fe-bearing minerals like pyrite, chlorite and, less frequently, ankerite. With regard to porosity, interestingly, the most significant increase in mesopore surface area and mesopore volume was observed in samples with the largest drop of chlorite amount. The less significant mineral changes were associated with formation of kaolinite related to breakdown of feldspars and dissolution of carbonate minerals represented by calcite, dolomite, and ankerite. In the analyzed samples, no new carbonate minerals were formed during the experiments. An increase of carbonates was recorded only in three out of 13 samples. However, concentration of carbonates in these three samples is too low to conclude CO2 mineral trapping in new carbonate phases. Acknowledgments: the study was supported from grant SHALESEQ (No PL12-0109) funded by the National Centre for Research and Development.
Atomic force microscopy and X-ray photoelectron spectroscopy study of NO2 reactions on CaCO3 (1014) surfaces in humid environments.

PubMed

Baltrusaitis, Jonas; Grassian, Vicki H

2012-09-13

In this study, alternating current (AC) mode atomic force microscopy (AFM) combined with phase imaging and X-ray photoelectron spectroscopy (XPS) were used to investigate the effect of nitrogen dioxide (NO2) adsorption on calcium carbonate (CaCO3) (101̅4) surfaces at 296 K in the presence of relative humidity (RH). At 70% RH, CaCO3 (101̅4) surfaces undergo rapid formation of a metastable amorphous calcium carbonate layer, which in turn serves as a substrate for recrystallization of a nonhydrated calcite phase, presumably vaterite. The adsorption of nitrogen dioxide changes the surface properties of CaCO3 (101̅4) and the mechanism for formation of new phases. In particular, the first calcite nucleation layer serves as a source of material for further island growth; when it is depleted, there is no change in total volume of nitrocalcite, Ca(NO3)2, particles formed whereas the total number of particles decreases. This indicates that these particles are mobile and coalesce. Phase imaging combined with force curve measurements reveals areas of inhomogeneous energy dissipation during the process of water adsorption in relative humidity experiments, as well as during nitrocalcite particle formation. Potential origins of the different energy dissipation modes within the sample are discussed. Finally, XPS analysis confirms that NO2 adsorbs on CaCO3 (101̅4) in the form of nitrate (NO3(-)) regardless of environmental conditions or the pretreatment of the calcite surface at different relative humidity.
Efficient surface formation route of interstellar hydroxylamine through NO hydrogenation. II. The multilayer regime in interstellar relevant ices

NASA Astrophysics Data System (ADS)

Fedoseev, G.; Ioppolo, S.; Lamberts, T.; Zhen, J. F.; Cuppen, H. M.; Linnartz, H.

2012-08-01

Hydroxylamine (NH2OH) is one of the potential precursors of complex pre-biotic species in space. Here, we present a detailed experimental study of hydroxylamine formation through nitric oxide (NO) surface hydrogenation for astronomically relevant conditions. The aim of this work is to investigate hydroxylamine formation efficiencies in polar (water-rich) and non-polar (carbon monoxide-rich) interstellar ice analogues. A complex reaction network involving both final (N2O, NH2OH) and intermediate (HNO, NH2O., etc.) products is discussed. The main conclusion is that hydroxyl-amine formation takes place via a fast and barrierless mechanism and it is found to be even more abundantly formed in a water-rich environment at lower temperatures. In parallel, we experimentally verify the non-formation of hydroxylamine upon UV photolysis of NO ice at cryogenic temperatures as well as the non-detection of NC- and NCO-bond bearing species after UV processing of NO in carbon monoxide-rich ices. Our results are implemented into an astrochemical reaction model, which shows that NH2OH is abundant in the solid phase under dark molecular cloud conditions. Once NH2OH desorbs from the ice grains, it becomes available to form more complex species (e.g., glycine and β-alanine) in gas phase reaction schemes.
Formation of Platinum Catalyst on Carbon Black Using an In-Liquid Plasma Method for Fuel Cells.

PubMed

Show, Yoshiyuki; Ueno, Yutaro

2017-01-31

Platinum (Pt) catalyst was formed on the surface of carbon black using an in-liquid plasma method. The formed Pt catalyst showed the average particle size of 4.1 nm. This Pt catalyst was applied to a polymer electrolyte membrane fuel cell (PEMFC). The PEMFC showed an open voltage of 0.85 V and a maximum output power density of 216 mW/cm2.
Formation of Platinum Catalyst on Carbon Black Using an In-Liquid Plasma Method for Fuel Cells

PubMed Central

Show, Yoshiyuki; Ueno, Yutaro

2017-01-01

Platinum (Pt) catalyst was formed on the surface of carbon black using an in-liquid plasma method. The formed Pt catalyst showed the average particle size of 4.1 nm. This Pt catalyst was applied to a polymer electrolyte membrane fuel cell (PEMFC). The PEMFC showed an open voltage of 0.85 V and a maximum output power density of 216 mW/cm2. PMID:28336864
Application of Multiple Regression and Design of Experiments for Modelling the Effect of Monoethylene Glycol in the Calcium Carbonate Scaling Process.

PubMed

Kartnaller, Vinicius; Venâncio, Fabrício; F do Rosário, Francisca; Cajaiba, João

2018-04-10

To avoid gas hydrate formation during oil and gas production, companies usually employ thermodynamic inhibitors consisting of hydroxyl compounds, such as monoethylene glycol (MEG). However, these inhibitors may cause other types of fouling during production such as inorganic salt deposits (scale). Calcium carbonate is one of the main scaling salts and is a great concern, especially for the new pre-salt wells being explored in Brazil. Hence, it is important to understand how using inhibitors to control gas hydrate formation may be interacting with the scale formation process. Multiple regression and design of experiments were used to mathematically model the calcium carbonate scaling process and its evolution in the presence of MEG. It was seen that MEG, although inducing the precipitation by increasing the supersaturation ratio, actually works as a scale inhibitor for calcium carbonate in concentrations over 40%. This effect was not due to changes in the viscosity, as suggested in the literature, but possibly to the binding of MEG to the CaCO₃ particles' surface. The interaction of the MEG inhibition effect with the system's variables was also assessed, when temperature' and calcium concentration were more relevant.
Two-Dimensional Porous Carbon: Synthesis and Ion-Transport Properties.

PubMed

Zheng, Xiaoyu; Luo, Jiayan; Lv, Wei; Wang, Da-Wei; Yang, Quan-Hong

2015-09-23

Their chemical stability, high specific surface area, and electric conductivity enable porous carbon materials to be the most commonly used electrode materials for electrochemical capacitors (also known as supercapacitors). To further increase the energy and power density, engineering of the pore structures with a higher electrochemical accessible surface area, faster ion-transport path and a more-robust interface with the electrolyte is widely investigated. Compared with traditional porous carbons, two-dimensional (2D) porous carbon sheets with an interlinked hierarchical porous structure are a good candidate for supercapacitors due to their advantages in high aspect ratio for electrode packing and electron transport, hierarchical pore structures for ion transport, and short ion-transport length. Recent progress on the synthesis of 2D porous carbons is reported here, along with the improved electrochemical behavior due to enhanced ion transport. Challenges for the controlled preparation of 2D porous carbons with desired properties are also discussed; these require precise tuning of the hierarchical structure and a clarification of the formation mechanisms. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Coeval Formation of Aqueous Minerals on Mars

NASA Astrophysics Data System (ADS)

Fairen, A.; Uceda, E.; Gil, C.; Palmero Rodriguez, A.; Gago-Duport, L.

2015-12-01

Understanding the geochemical conditions on early Mars requires an explanation for the presence of sulfates and phyllosilicates, which must be also consistent with the absence of widespread sedimentary carbonates. In addition, sulfates and phyllosilicates do not generally occur together on Mars, which has been interpreted as a marker for detached mineral formation due to differing planetary environmental conditions separated dramatically, either in time or in space. Here, thermodynamic equilibrium calculations are used to determine the stability boundaries for phyllosilicates, ferrous and ferric sulfates, carbonates and iron oxyhydroxides precipitation on early Mars, at different atmospheric CO2 pressures and both under reducing and oxidizing conditions. Results suggest that phyllosilicates formed in mildly acidic to alkaline aqueous solutions, with a pH>4 for nontronite and a pH>6 for other smectites with low content in Fe and Mg (montmorillonite, saponite). Sulfate deposition dominates in solutions moderately to highly acidic, with a pH<6 conducive to the synthesis of kieserite. In the overlapping phyllosilicates/sulfates pH range, between 4 and 6, a competition for Mg between nontronite and kieserite is expected, and the formation of nontronite would be favored in areas where SiO2 activity in surface waters was high as a result of intense weathering of the early basaltic crust. Carbonates formed at pH>6, overlapping with the synthesis of low-Fe-Mg smectites. Model calculations anticipate the co-precipitation of smectites and siderite or any alteration product that could have resulted from the later substitution of Fe in siderite, such as Mg- or Mn-carbonate, triggering a competition for Mg between magnesite and low-Fe-Mg smectites. As expected, the model does not predict coeval synthesis of carbonates and sulfates. Goethite and other oxyhydroxides precipitate at pH below 2, a range at which jarosite and goethite are the expected iron-bearing phases. These results suggest that the major water-alteration products on the Martian surface were deposited simultaneously in space and in time, creating diverse geochemical conditions over the entire surface of a cold Mars during the wet Noachian/Hesperian times.

Characterization of Cracking Mechanisms of Carbon Anodes Used in Aluminum Industry by Optical Microscopy and Tomography

NASA Astrophysics Data System (ADS)

Amrani, Salah; Kocaefe, Duygu; Kocaefe, Yasar; Bhattacharyay, Dipankar; Bouazara, Mohamed; Morais, Brigitte

2016-10-01

The objective of this work is to understand the different mechanisms of crack formation in dense anodes used in the aluminum industry. The first approach used is based on the qualitative characterization of the surface cracks and the depth of these cracks. The second approach, which constitutes a quantitative characterization, is carried out by determining the distribution of the crack width along its length as well as the percentage of the surface containing cracks. A qualitative analysis of crack formation was also carried out using 3D tomography. It was observed that mixing and forming conditions have a significant effect on crack formation in green anodes. The devolatilization of pitch during baking causes the formation and propagation of cracks in baked anodes in which large particles control the direction of crack propagation.
A recipe to create nano-grains on dolomite

NASA Astrophysics Data System (ADS)

Røyne, Anja; Pluymakers, Anne

2017-04-01

Advances in imaging techniques in recent years have allowed for easy microstructure visualization at nano-resolution, and many studies have observed nano-grains in different materials, including rocks. An important example in geological systems is their seemingly ubiquitous occurrence on so-called mirror-like slip surfaces, produced in natural and experimental earthquakes of both carbonate and silicate rocks. It is, however, not yet clear whether these nano-grains can indeed be used as a reliable indicator of seismic slip. Since carbonates are prone to decarbonation at temperatures exceeding 550 - 600 °C, nano-grain formation may be formed due to heating rather than shear. In this study, we have investigated the effect of elevated temperatures on carbonate fault rocks. We used hand-polished mirror-like dolomite protolith, as well as natural fault mirror surfaces, obtained from the Foiana Fault Zone from the Southern Alps in Italy. The samples were heated to 200 to 800 degC in a 5 hour heating cycle, followed by slow cooling ( 12 h) to room temperature. Subsequently, we imaged the samples using SEM and AFM. Nano-grain formation on the surfaces of hand-polished samples starts around 400 ° C, and is pervasive at and above 600 ° C. Fault mirror samples are initially coated with naturally formed nano-grains and only very local patches on these surfaces display obvious morphological changes due to heating. Exposing both types of sample heated to 600 °C to DI water under the AFM shows rapid recrystallization and the formation of a more porous and blade-like crystal layer on the entire surface. This happens both in hand-polished and naturally polished surfaces. Fault mirror samples that have not been heated do not change when exposed to water. We have shown that nano-grains can form as a result of heating without shear, but that samples that have experienced high shear strain have a water- and heat-resistant coating composed of otherwise morphologically indistinguishable nano-grains. These results show that caution is needed when interpreting laboratory and field microstructures, since there is more than one way to cook up a nano-grain.
Fabrication of transition metal-containing nanostructures via polymer templates for a multitude of applications

NASA Astrophysics Data System (ADS)

Lu, Jennifer Qing

Nanostructures such as carbon nanotubes and semiconducting nanowires offer great technological promise due to their remarkable properties. The lack of a rational synthesis method prevents fabricating these nanostructures with desirable and consistent properties at predefined locations for device applications. In this thesis, employing polymer templates, a variety of highly ordered catalytically active transition metal nanostructures, ranging from single metallic nanoparticles of Fe, Co, Ni, Au and bimetallic nanoparticles of Ni/Fe and Co/Mo to Fe-rich silicon oxide nanodomains with uniform and tunable size and spacing have been successfully synthesized. These nanostructures have been demonstrated to be excellent catalyst systems for the synthesis of carbon nanotube and silicon nanowire. High quality, small diameter carbon nanotubes and nanowires with narrow size distribution have been successfully attained. Because these catalytically active nanostructures are uniformly distributed and do not agglomerate at the growth temperatures, uniform, high density and high quality carbon nanotube mats have been obtained. Since this polymer template approach is fully compatible with conventional top-down photolithography, lithographically selective growth of carbon nanotubes on a surface or suspended carbon nanotubes across trenches have been produced by using existing semiconductor processing. We have also shown the feasibility of producing carbon nanotubes and silicon nanowires at predefined locations on a wafer format and established a wafer-level carbon nanotube based device fabrication process. The ability of the polymer template approach to control catalyst systems at the nano-, micro- and macro-scales paves a pathway for commercialization of these 1D nanostructure-enabled devices. Beside producing well-defined, highly ordered discrete catalytically active metal-containing nanostructures by the polymer template approach, Au and Ag nanotextured surfaces have also been attained by using a self-assembled ferrocenylsilane-based inorganic block copolymer template. These Au and Ag nanotextured surfaces exhibit different surface plasmon behavior than the nanotextured surface. Greatly enhanced and uniform Raman scattering have been observed on Ag nanotextured surfaces. Highly sensitive Au nanotextured surfaces suggest their potential application as sensing surfaces for SPR-based biodetection. This simple fabrication technique of producing inorganic nanostructures with adjustable properties such as size, spacing and composition offers great promise for both fundamental research and technological development.
Reaction of silanes in supercritical CO2 with TiO2 and Al2O3.

PubMed

Gu, Wei; Tripp, Carl P

2006-06-20

Infrared spectroscopy was used to investigate the reaction of silanes with TiO2 and Al2O3 using supercritical CO2 (Sc-CO2) as a solvent. It was found that contact of Sc-CO2 with TiO2 leads to partial removal of the water layer and to the formation of carbonate, bicarbonate, and carboxylate species on the surface. Although these carbonate species are weakly bound to the TiO2 surface and can be removed by a N2 purge, they poison the surface, resulting in a lower level of reaction of silanes with TiO2. Specifically, the amount of hexamethyldisilazane adsorbed on TiO2 is about 10% of the value obtained when the reaction is performed from the gas phase. This is not unique to TiO2, as the formation of carbonate species also occurs upon contact of Al2O3 with Sc-CO2 and this leads to a lower level of reaction with hexamethyldisilazane. This is in contrast to reactions of silanes on SiO2 where Sc-CO2 has several advantages over conventional gaseous or nonaqueous methods. As a result, caution needs to be applied when using Sc-CO2 as a solvent for silanization reactions on oxides other than SiO2.
Using hydrogeology to identify the source of groundwater to Montezuma Well, a natural spring in central Arizona: part 1

USGS Publications Warehouse

Johnson, Raymond H.; DeWitt, Ed H.; Arnold, L. Rick

2012-01-01

Montezuma Well is a natural spring located within a “sinkhole” in the desert environment of the Verde Valley in Central Arizona. It is managed by the National Park Service as part of Montezuma Castle National Monument. Because of increasing development of groundwater in the area, this research was undertaken to better understand the sources of groundwater to Montezuma Well. The use of well logs and geophysics provides details on the geology in the area around Montezuma Well. This includes characterizing the extent and position of a basalt dike that intruded a deep fracture zone. This low permeability barrier forces groundwater to the surface at the Montezuma Well “pool” with sufficient velocity to entrain sand-sized particles from underlying bedrock. Permeable fractures along and above the basalt dike provide conduits that carry deep sourced carbon dioxide to the surface, which can dissolve carbonate minerals along the transport path in response to the added carbon dioxide. At the ground surface, CO2 degasses, depositing travertine. Geologic cross sections, rock geochemistry, and semi-quantitative groundwater flow modeling provide a hydrogeologic framework that indicates groundwater flow through a karstic limestone at depth (Redwall Limestone) as the most significant source of groundwater to Montezuma Well. Additional groundwater flow from the overlying formations (Verde Formation and Permian Sandstones) is a possibility, but significant flow from these units is not indicated.
Nano-Welding of Multi-Walled Carbon Nanotubes on Silicon and Silica Surface by Laser Irradiation.

PubMed

Yuan, Yanping; Chen, Jimin

2016-02-24

In this study, a continuous fiber laser (1064 nm wavelength, 30 W/cm²) is used to irradiate multi-walled carbon nanotubes (MWCNTs) on different substrate surfaces. Effects of substrates on nano-welding of MWCNTs are investigated by scanning electron microscope (SEM). For MWCNTs on silica, after 3 s irradiation, nanoscale welding with good quality can be achieved due to breaking C-C bonds and formation of new graphene layers. While welding junctions can be formed until 10 s for the MWCNTs on silicon, the difference of irradiation time to achieve welding is attributed to the difference of thermal conductivity for silica and silicon. As the irradiation time is prolonged up to 12.5 s, most of the MWCNTs are welded to a silicon substrate, which leads to their frameworks of tube walls on the silicon surface. This is because the accumulation of absorbed energy makes the temperature rise. Then chemical reactions among silicon, carbon and nitrogen occur. New chemical bonds of Si-N and Si-C achieve the welding between the MWCNTs and silicon. Vibration modes of Si₃N₄ appear at peaks of 363 cm -1 and 663 cm -1 . There are vibration modes of SiC at peaks of 618 cm -1 , 779 cm -1 and 973 cm -1 . The experimental observation proves chemical reactions and the formation of Si₃N₄ and SiC by laser irradiation.
From Black Hole to Hydrate Hole: Gas hydrates, authigenic carbonates and vent biota as indicators of fluid migration at pockmark sites of the Northern Congo Fan

NASA Astrophysics Data System (ADS)

Kasten, S.; Schneider, R.; Spiess, V.; Cruise Participants Of M56b

2003-04-01

A recent high-resolution seismic, echosounder and video survey combined with detailed geological and geochemical sampling of pockmark sites on the Northern Congo Fan was carried out with RV Meteor in November/December 2002 in the frame of the project "CONGO" (BMBF/BEO "Geotechnologien"). These investigations revealed the extensive occurrence of surface and sub-surface gas hydrates as well as characteristic features of fluid venting such as clams (Calyptogena), tube worms (Pogonophera) and huge amounts of authigenic carbonates. In a first approach the patchyness in the occurrence of these features was mapped in relation to pockmark structure and seismic reflectors. Detailed sampling of three pockmarks by gravity corer showed that gas hydrates are present at and close to the sediment surface and often occur as several distinct layers and/or veins intercalated with hemipelagic muds. The depth of the upper boundary of these hydrate-bearing sediments increases from the center towards the edge of the pockmark structures. Pore water concentration profiles of sulfate and methane document the process of anaerobic methane oxidation above the hydrate-bearing layers. For those cores which contained several gas hydrate layers preliminary pore water profiles suggest the occurrence of more than one zone of anaerobic methane oxidation. Authigenic carbonates are found in high abundance, irregularly distributed within the pockmarks close to the sediment surface. These carbonates occur in a wide variety with respect to size, shape, structure and mineralogy. Their formation is associated with high amounts of bicarbonate released by the process of anaerobic methane oxidation. In the gravity cores authigenic carbonates are always present above hydrate-bearing sections. However, the quantities and characteristics of these authigenic minerals in relation to venting and microbial activity as well as to gas hydrate dissociation are not clear yet. Unraveling this relationship will be a major target of further investigation. By means of detailed studies of the sedimentary solid-phase, authigenic carbonates, clam layers and molecular biomarkers we will also try to reconstruct the history of venting and the dynamics of gas hydrate formation and decomposition in the Northern Congo fan area.
Formation of Nanosized Defective Lithium Peroxides through Si-Coated Carbon Nanotube Cathodes for High Energy Efficiency Li-O2 Batteries.

PubMed

Lin, Qi; Cui, Zhonghui; Sun, Jiyang; Huo, Hanyu; Chen, Cheng; Guo, Xiangxin

2018-06-06

The formation and decomposition of lithium peroxides (Li 2 O 2 ) during cycling is the key process for the reversible operation of lithium-oxygen batteries. The manipulation of such products from the large toroidal particles about hundreds of nanometers to the ones in the scale of tens of nanometers can improve the energy efficiency and the cycle life of the batteries. In this work, we carry out an in situ morphology tuning of Li 2 O 2 by virtue of the surface properties of the n-type Si-modified aligned carbon nanotube (CNT) cathodes. With the introduction of an n-type Si coating layer on the CNT surface, the morphology of Li 2 O 2 formed by discharge changes from large toroidal particles (∼300 nm) deposited on the pristine CNT cathodes to nanoparticles (10-20 nm) with poor crystallinity and plenty of lithium vacancies. Beneficial from such changes, the charge overpotential dramatically decreases to 0.55 V, with the charge plateau lying at 3.5 V even in the case of a high discharge capacity (3450 mA h g -1 ) being delivered, resulting in the high electrical energy efficiency approaching 80%. Such an improvement is attributed to the fact that the introduction of the n-type Si coating layer changes the surface properties of CNTs and guides the formation of nanosized amorphous-like lithium peroxides with plenty of defects. These results demonstrate that the cathode surface properties play an important role in the formation of products formed during the cycle, providing inspiration to design superior cathodes for the Li-O 2 cells.
Chemical reaction CO+OH • → CO 2+H • autocatalyzed by carbon dioxide: Quantum chemical study of the potential energy surfaces

DOE PAGES

Masunov, Artem E.; Wait, Elizabeth; Vasu, Subith S.

2016-06-28

The supercritical carbon dioxide medium, used to increase efficiency in oxy combustion fossil energy technology, may drastically alter both rates and mechanisms of chemical reactions. Here we investigate potential energy surface of the second most important combustion reaction with quantum chemistry methods. Two types of effects are reported: formation of the covalent intermediates and formation of van der Waals complexes by spectator CO 2 molecule. While spectator molecule alter the activation barrier only slightly, the covalent bonding opens a new reaction pathway. The mechanism includes sequential covalent binding of CO 2 to OH radical and CO molecule, hydrogen transfer frommore » oxygen to carbon atoms, and CH bond dissociation. This reduces the activation barrier by 11 kcal/mol at the rate-determining step and is expected to accelerate the reaction rate. The finding of predicted catalytic effect is expected to play an important role not only in combustion but also in a broad array of chemical processes taking place in supercritical CO 2 medium. Furthermore, tt may open a new venue for controlling reaction rates for chemical manufacturing.« less
Microbial Fuel Cell-driven caustic potash production from wastewater for carbon sequestration.

PubMed

Gajda, Iwona; Greenman, John; Melhuish, Chris; Santoro, Carlo; Ieropoulos, Ioannis

2016-09-01

This work reports on the novel formation of caustic potash (KOH) directly on the MFC cathode locking carbon dioxide into potassium bicarbonate salt (kalicinite) while producing, instead of consuming electrical power. Using potassium-rich wastewater as a fuel for microorganisms to generate electricity in the anode chamber, has resulted in the formation of caustic catholyte directly on the surface of the cathode electrode. Analysis of this liquid has shown to be highly alkaline (pH>13) and act as a CO2 sorbent. It has been later mineralised to kalicinite thus locking carbon dioxide into potassium bicarbonate salt. This work demonstrates an electricity generation method as a simple, cost-effective and environmentally friendly route towards CO2 sequestration that perhaps leads to a carbon negative economy. Moreover, it shows a potential application for both electricity production and nutrient recovery in the form of minerals from nutrient-rich wastewater streams such as urine for use as fertiliser in the future. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.
Relation of trihalomethane-formation potential to water-quality and physical characteristics of small water-supply lakes, eastern Kansas

USGS Publications Warehouse

Pope, L.M.; Arruda, J.A.; Fromm, C.H.

1988-01-01

The formation of carcinogenic trihalomethanes during the treatment of public surface water supplies has become a potentially serious problem. The U. S. Geological Survey, in cooperation with the Kansas Department of Health and Environment , investigated the potential for trihalomethane formation in water from 15 small, public water supply lakes in eastern Kansas from April 1984 through April 1986 in order to define the principal factors that affect or control the potential for trihalomethane formation during the water treatment process. Relations of mean concentrations of trihalomethane-formation potential to selected water quality and lake and watershed physical characteristics were investigated using correlation and regression analysis. Statistically significant, direct relations were developed between trihalomethanes produced in unfiltered and filtered lake water and mean concentrations of total and dissolved organic carbon. Correlation coefficients for these relations ranged from 0.86 to 0.93. Mean values of maximum depth of lake were shown to have statistically significant inverse relations to mean concentrations of trihalomethane-formation potential and total and dissolved organic carbon. Correlation coefficients for these relations ranged from -0.76 to -0.81. (USGS)
Comparison of caprock pore networks which potentially will be impacted by carbon sequestration projects.

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

McCray, John; Navarre-Sitchler, Alexis; Mouzakis, Katherine

Injection of CO2 into underground rock formations can reduce atmospheric CO2 emissions. Caprocks present above potential storage formations are the main structural trap inhibiting CO2 from leaking into overlying aquifers or back to the Earth's surface. Dissolution and precipitation of caprock minerals resulting from reaction with CO2 may alter the pore network where many pores are of the micrometer to nanometer scale, thus altering the structural trapping potential of the caprock. However, the distribution, geometry and volume of pores at these scales are poorly characterized. In order to evaluate the overall risk of leakage of CO2 from storage formations, amore » first critical step is understanding the distribution and shape of pores in a variety of different caprocks. As the caprock is often comprised of mudstones, we analyzed samples from several mudstone formations with small angle neutron scattering (SANS) and high-resolution transmission electron microscopy (TEM) imaging to compare the pore networks. Mudstones were chosen from current or potential sites for carbon sequestration projects including the Marine Tuscaloosa Group, the Lower Tuscaloosa Group, the upper and lower shale members of the Kirtland Formation, and the Pennsylvanian Gothic shale. Expandable clay contents ranged from 10% to approximately 40% in the Gothic shale and Kirtland Formation, respectively. During SANS, neutrons effectively scatter from interfaces between materials with differing scattering length density (i.e., minerals and pores). The intensity of scattered neutrons, I(Q), where Q is the scattering vector, gives information about the volume and arrangement of pores in the sample. The slope of the scattering data when plotted as log I(Q) vs. log Q provides information about the fractality or geometry of the pore network. On such plots slopes from -2 to -3 represent mass fractals while slopes from -3 to -4 represent surface fractals. Scattering data showed surface fractal dimensions for the Kirtland formation and one sample from the Tuscaloosa formation close to 3, indicating very rough surfaces. In contrast, scattering data for the Gothic shale formation exhibited mass fractal behavior. In one sample of the Tuscaloosa formation the data are described by a surface fractal at low Q (larger pores) and a mass fractal at high Q (smaller pores), indicating two pore populations contributing to the scattering behavior. These small angle neutron scattering results, combined with high-resolution TEM imaging, provided a means for both qualitative and quantitative analysis of the differences in pore networks between these various mudstones.« less
Reconstruction of limnology and microbialite formation conditions from carbonate clumped isotope thermometry.

PubMed

Petryshyn, V A; Lim, D; Laval, B L; Brady, A; Slater, G; Tripati, A K

2015-01-01

Quantitative tools for deciphering the environment of microbialite formation are relatively limited. For example, the oxygen isotope carbonate-water geothermometer requires assumptions about the isotopic composition of the water of formation. We explored the utility of using 'clumped' isotope thermometry as a tool to study the temperatures of microbialite formation. We studied microbialites recovered from water depths of 10-55 m in Pavilion Lake, and 10-25 m in Kelly Lake, spanning the thermocline in both lakes. We determined the temperature of carbonate growth and the (18)O/(16)O ratio of the waters that microbialites grew in. Results were then compared to current limnological data from the lakes to reconstruct the history of microbialite formation. Modern microbialites collected at shallow depths (11.7 m) in both lakes yield clumped isotope-based temperatures of formation that are within error of summer water temperatures, suggesting that clumped isotope analyses may be used to reconstruct past climates and to probe the environments in which microbialites formed. The deepest microbialites (21.7-55 m) were recovered from below the present-day thermoclines in both lakes and yield radioisotope ages indicating they primarily formed earlier in the Holocene. During this time, pollen data and our reconstructed water (18)O/(16)O ratios indicate a period of aridity, with lower lake levels. At present, there is a close association between both photosynthetic and heterotrophic communities, and carbonate precipitation/microbialite formation, with biosignatures of photosynthetic influences on carbonate detected in microbialites from the photic zone and above the thermocline (i.e., depths of generally <20 m). Given the deeper microbialites are receiving <1% of photosynthetically active radiation (PAR), it is likely these microbialites primarily formed when lower lake levels resulted in microbialites being located higher in the photic zone, in warm surface waters. © 2014 John Wiley & Sons Ltd.
Surface modification of Ti alloy by electro-explosive alloying and electron-beam treatment

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

Gromov, Victor, E-mail: gromov@physics.sibsiu.ru; Kobzareva, Tatiana, E-mail: kobzarevatanya@mail.ru; Budovskikh, Evgeniy, E-mail: budovskih-ea@physics.sibsiu.ru

2016-01-15

By methods of modern physical metallurgy the analysis of structure phase states of titanium alloy VT6 is carried out after electric explosion alloying with boron carbide and subsequent irradiation by pulsed electron beam. The formation of an electro-explosive alloying zone of a thickness up to 50 µm, having a gradient structure, characterized by decrease in the concentration of carbon and boron with increasing distance to the treatable surface has been revealed. Subsequent electron-beam treatment of alloying zone leads to smoothing of the alloying area surface and is accompanied by the multilayer structure formation at the depth of 30 µm withmore » alternating layers with different alloying degrees having the structure of submicro - and nanoscale level.« less
Tracing iron-carbon redox from surface to core

NASA Astrophysics Data System (ADS)

McCammon, C. A.; Cerantola, V.; Bykova, E.; Kupenko, I.; Bykov, M.; Chumakov, A. I.; Rüffer, R.; Dubrovinsky, L. S.

2017-12-01

Numerous redox reactions separate the Earth's oxidised surface from its reduced core. Many involve iron, the Earth's most abundant element and the mantle's most abundant transition element. Most iron redox reactions (although not all) also involve other elements, including carbon, where iron-carbon interactions drive a number of important processes within the Earth, for example diamond formation. Many of the Earth's redox boundaries are sharp, much like the seismic properties that define them, for example between the lower mantle and the core. Other regions that appear seismically homogeneous, for example the lower mantle, harbour a wealth of reactions between oxidised and reduced phases of iron and carbon. We have undertaken many experiments at high pressure and high temperature on phases containing iron and carbon using synchrotron-based X-rays to probe structures and iron oxidation states. Results demonstrate the dominant role that crystal structures play in determining the stable oxidation states of iron and carbon, even when oxygen fugacity (and common sense) would suggest otherwise. Iron in bridgmanite, for example, occurs predominantly in its oxidised form (ferric iron) throughout the lower mantle, despite the inferred reducing conditions. Newly discovered structures of iron carbonate also stabilise ferric iron, while simultaneously reducing some carbon to diamond to balance charge. Other high-pressure iron carbonates appear to be associated with the emerging zoo of iron oxide phases, involving transitions between ferrous and ferric iron through the exchange of oxygen. The presentation will trace redox relations between iron and carbon from the Earth's surface to its core, with an emphasis on recent experimental results.
Combined wet and dry cleaning of SiGe(001)

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

Park, Sang Wook; Kaufman-Osborn, Tobin; Kim, Hyonwoong

Combined wet and dry cleaning via hydrofluoric acid (HF) and atomic hydrogen on Si{sub 0.6}Ge{sub 0.4}(001) surface was studied at the atomic level using ultrahigh vacuum scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy to understand the chemical transformations of the surface. Aqueous HF removes native oxide, but residual carbon and oxygen are still observed on Si{sub 0.6}Ge{sub 0.4}(001) due to hydrocarbon contamination from post HF exposure to ambient. The oxygen contamination can be eliminated by shielding the sample from ambient via covering the sample in the HF cleaning solution until the sample is introduced tomore » the vacuum chamber or by transferring the sample in an inert environment; however, both processes still leave carbon contaminant. Dry in-situ atomic hydrogen cleaning above 330 °C removes the carbon contamination on the surface consistent with a thermally activated atomic hydrogen reaction with surface hydrocarbon. A postdeposition anneal at 550 °C induces formation of an atomically flat and ordered SiGe surface observed by STM. STS verifies that the wet and dry cleaned surface has an unpinned Fermi level with no states between the conduction and valence band edge comparable to sputter cleaned SiGe surfaces.« less
Water electrolysis with a conducting carbon cloth: subthreshold hydrogen generation and superthreshold carbon quantum dot formation.

PubMed

Biswal, Mandakini; Deshpande, Aparna; Kelkar, Sarika; Ogale, Satishchandra

2014-03-01

A conducting carbon cloth, which has an interesting turbostratic microstructure and functional groups that are distinctly different from other ordered forms of carbon, such as graphite, graphene, and carbon nanotubes, was synthesized by a simple one-step pyrolysis of cellulose fabric. This turbostratic disorder and surface chemical functionalities had interesting consequences for water splitting and hydrogen generation when such a cloth was used as an electrode in the alkaline electrolysis process. Importantly, this work also gives a new twist to carbon-assisted electrolysis. During electrolysis, the active sites in the carbon cloth allow slow oxidation of its surface to transform the surface groups from COH to COOH and so forth at a voltage as low as 0.2 V in a two-electrode system, along with platinum as the cathode, instead of 1.23 V (plus overpotential), which is required for platinum, steel, or even graphite anodes. The quantity of subthreshold hydrogen evolved was 24 mL cm(-2) h(-1) at 1 V. Interestingly, at a superthreshold potential (>1.23 V+overpotential), another remarkable phenomenon was found. At such voltages, along with the high rate and quantity of hydrogen evolution, rapid exfoliation of the tiny nanoscale (5-7 nm) units of carbon quantum dots (CQDs) are found in copious amounts due to an enhanced oxidation rate. These CQDs show bright-blue fluorescence under UV light. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
IR femtochemistry on the surface of wide-gap ionic crystals

NASA Astrophysics Data System (ADS)

Laptev, V. B.; Chekalin, S. V.; Dorofeyev, I. A.; Kompanets, V. O.; Pigulsky, S. V.; Ryabov, E. A.

2018-02-01

We have found and studied a phenomenon of the growth of films resulting from decomposition of some organic and silicon-containing molecules adsorbed on the surface of ionic crystals under the action of IR (1.4-5.4 µm) femtosecond radiation of a moderate intensity, ~1011 W cm-2. In the gas phase, these molecules do not decompose. Microstructured films consisting of amorphous carbon, graphite oxide, and silicon dioxide have been obtained. The formation of carbon films was accompanied by the appearance of different hydrocarbons in the gas phase. The extensive films of graphite oxide have been obtained. The decomposition of molecules on the surface is apparently caused by non-resonant ionization and subsequent deep fragmentation. The mechanisms of ionization at relatively low intensities of the femtosecond IR radiation have been discussed.
Carbide coated fibers in graphite-aluminum composites

NASA Technical Reports Server (NTRS)

Imprescia, R. J.; Levinson, L. S.; Reiswig, R. D.; Wallace, T. C.; Williams, J. M.

1975-01-01

The study of protective-coupling layers of refractory metal carbides on the graphite fibers prior to their incorporation into composites is presented. Such layers should be directly wettable by liquid aluminum and should act as diffusion barriers to prevent the formation of aluminum carbide. Chemical vapor deposition was used to uniformly deposit thin, smooth, continuous coats of ZrC on the carbon fibers of tows derived from both rayon and polyacrylonitrile. A wet chemical coating of the fibers, followed by high-temperature treatment, was used, and showed promise as an alternative coating method. Experiments were performed to demonstrate the ability of aluminum alloys to wet carbide surfaces. Titanium carbide, zirconium carbide and carbide-coated graphite surfaces were successfully wetted. Results indicate that initial attempts to wet surfaces of ZrC-coated carbon fibers appear successful.
Features of Wear-Resistant Cast Iron Coating Formation During Plasma-Powder Surfacing

NASA Astrophysics Data System (ADS)

Vdovin, K. N.; Emelyushin, A. N.; Nefed'ev, S. P.

2017-09-01

The structure of coatings deposited on steel 45 by plasma-powder surfacing of white wear-resistant cast iron is studied. The effects of surfacing regime and additional production effects on the welding bath during surfacing produced by current modulation, accelerated cooling of the deposited beads by blowing with air, and accelerated cooling of the substrate with running water on the structure, are determined. A new composition is suggested for powder material for depositing wear-resistant and corrosion-resistant coatings on a carbon steel by the plasma-powder process.

Hydrocarbon Deposition Attenuates Osteoblast Activity on Titanium

PubMed Central

Hayashi, R.; Ueno, T.; Migita, S.; Tsutsumi, Y.; Doi, H.; Ogawa, T.; Hanawa, T.; Wakabayashi, N.

2014-01-01

Although the reported percentage of bone-implant contact is far lower than 100%, the cause of such low levels of bone formation has rarely been investigated. This study tested the negative biological effect of hydrocarbon deposition onto titanium surfaces, which has been reported to be inevitable. Osteogenic MC3T3-E1 cells were cultured on titanium disks on which the carbon concentration was experimentally regulated to achieve carbon/titanium (C/Ti) ratios of 0.3, 0.7, and 1.0. Initial cellular activities such as cell attachment and cell spreading were concentration-dependently suppressed by the amount of carbon on the titanium surface. The osteoblastic functions of alkaline phosphatase activity and calcium mineralization were also reduced by more than 40% on the C/Ti (1.0) surface. These results indicate that osteoblast activity is influenced by the degree of hydrocarbon contamination on titanium implants and suggest that hydrocarbon decomposition before implant placement may increase the biocompatibility of titanium. PMID:24868012
Characterization of Light Non-Methane Hydrocarbons, Surface Water DOC, and Aerosols over the Nordic Seas

NASA Astrophysics Data System (ADS)

Hudson, E. D.; Ariya, P. A.

2006-12-01

Whole air, size-fractionated marine aerosols, and surface ocean water DOC were sampled together during June-July 2004 on the Nordic seas, in order to explore factors leading to the formation of volatile organic compounds (VOCs) at the sea surface and their transfer to the atmosphere. High site-to-site variability in 19 non-methane hydrocarbon concentrations suggests highly variable, local sources for these compounds. Acetone, C5 and C6 hydrocarbons, and dimethylsulfide were identified in the seawater samples using solid-phase microextraction/GC-MS. The aerosols were analysed by SEM-EDX and contained primarily inorganic material (sea salt, marine sulfates, and carbonates) and little organic matter. However, a culturable bacterium was isolated from the large (9.9 - 18 μ m) fraction at one site, and identified as Micrococcus luteus. We will discuss the implication of these results on potential exchange processes at the ocean-atmosphere interface and the impact of bioaerosols in transferring marine organic carbon to atmospheric organic carbon.
Amending the Structure of Renewable Carbon from Biorefinery Waste-Streams for Energy Storage Applications

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

Ho, Hoi Chun; Goswami, Monojoy; Chen, Jihua

Biorefineries produce impure sugar waste streams that are being underutilized. By converting this waste to a profitable by-product, biorefineries could be safeguarded against low oil prices. We demonstrate controlled production of useful carbon materials from the waste concentrate via hydrothermal synthesis and carbonization. We devise a pathway to producing tunable, porous spherical carbon materials by modeling the gross structure formation and developing an understanding of the pore formation mechanism utilizing simple reaction principles. Compared to a simple hydrothermal synthesis from sugar concentrate, emulsion-based synthesis results in hollow spheres with abundant microporosity. In contrast, conventional hydrothermal synthesis produces solid beads withmore » micro and mesoporosity. All the carbonaceous materials show promise in energy storage application. Using our reaction pathway, perfect hollow activated carbon spheres can be produced from waste sugar in liquid effluence of biomass steam pretreatment units. As a result, the renewable carbon product demonstrated a desirable surface area of 872 m 2/g and capacitance of up to 109 F/g when made into an electric double layer supercapacitor. The capacitor exhibited nearly ideal capacitive behavior with 90.5% capacitance retention after 5000 cycles.« less
Geochemical distinctions between igneous carbonate, calcite cements, and limestone xenoliths (Polino carbonatite, Italy): spatially resolved LAICPMS analyses

NASA Astrophysics Data System (ADS)

Rosatelli, G.; Wall, F.; Stoppa, F.; Brilli, M.

2010-11-01

Petrography-controlled laser ablation inductively coupled plasma mass spectrometry (LAICPMS) analyses of carbonate in fresh shallow level sub-volcanic Polino monticellite calcio-carbonatite tuffisite have been performed to assess the geochemical differences between fresh igneous, epigenetic carbonates and sedimentary accidental fragments. Igneous calcite has consistently high LREE/HREE ratios (La/Yb N , 15-130) due to high LREE (ΣLREE, 425-1,269 ppm). Secondary calcite cements are characterized by progressively lower and more variable trace element contents, with lower LREE/HREE ratios. A distinguishing geochemical feature is progressively increasing negative Ce anomalies observed through coarse secondary calcite that can be related to the surface environment processes. The limestone accidental fragments in the tuffisite have trace element contents almost two orders of magnitude lower than igneous carbonate and low LREE (ΣLREE < 9.5 ppm) with low LREE/HREE fractionation (La/Yb N ratios < 18). The stable isotope composition of different carbonate types is consistent with their formation in different environments. The tuffisitization processes during diatreme formation under high CO2-OH fugacity conditions may account for the differences noted in the igneous carbonates.
Amending the Structure of Renewable Carbon from Biorefinery Waste-Streams for Energy Storage Applications

DOE PAGES

Ho, Hoi Chun; Goswami, Monojoy; Chen, Jihua; ...

2018-05-29

Biorefineries produce impure sugar waste streams that are being underutilized. By converting this waste to a profitable by-product, biorefineries could be safeguarded against low oil prices. We demonstrate controlled production of useful carbon materials from the waste concentrate via hydrothermal synthesis and carbonization. We devise a pathway to producing tunable, porous spherical carbon materials by modeling the gross structure formation and developing an understanding of the pore formation mechanism utilizing simple reaction principles. Compared to a simple hydrothermal synthesis from sugar concentrate, emulsion-based synthesis results in hollow spheres with abundant microporosity. In contrast, conventional hydrothermal synthesis produces solid beads withmore » micro and mesoporosity. All the carbonaceous materials show promise in energy storage application. Using our reaction pathway, perfect hollow activated carbon spheres can be produced from waste sugar in liquid effluence of biomass steam pretreatment units. As a result, the renewable carbon product demonstrated a desirable surface area of 872 m 2/g and capacitance of up to 109 F/g when made into an electric double layer supercapacitor. The capacitor exhibited nearly ideal capacitive behavior with 90.5% capacitance retention after 5000 cycles.« less
Interaction between aggrading geomorphic surfaces and the formation of a late pleistocene paleosol in the palouse loess of eastern Washington state

NASA Astrophysics Data System (ADS)

McDonald, Eric V.; Busacca, Alan J.

1990-09-01

Variable rates of loess deposition contributed to dramatic regional variation in a soil-stratigraphic unit, the Washtucna Soil, in the Palouse loess deposits in the Channeled Scabland of eastern Washington state. Throughout most of the Channeled Scabland, the morphology of the Washtucna Soil is that of a single buried soil, but it bifurcates into two well-developed and pedologically distinct buried soils in areas immediately downwind of the major source of loessial sediment. Regional loess stratigraphy confirms that the two well-developed soils formed during the same interval of time during which only one soil formed in areas that are distal to loess source areas. The variable and perhaps rapid rates of soil formation suggested by the stratigraphy resulted from an interaction between variable rates of loess deposition and the formation of superimposed calcic soils. Petrocalcic horizons with weak Stage IV morphology formed as the zone of carbonate accumulation moved up into former A and cambic horizons that had been profusely burrowed by cicadas. The development of cicada burrows in one phase of soil development that were subsequently engulfed by pedogenic carbonate under a rising land surface seems to have greatly accelerated the development of the petrocalcic horizons. Accelerated rates of formation of the petrocalcic horizons occurred when extrinsic (pulses of loess deposition) and intrinsic (engulfment of burrowed horizons) thresholds were exceeded. Stratigraphic evidence suggests that the soil formation that accompanied the rise in the land surface due to additional loess deposition may have occurred during the late Wisconsin glaciation when giant glacial outburst floods in the channeled Scabland triggered a new cycle of loess deposition.
Controlling surface property of K2SiF6:Mn4+ for improvement of lighting-emitting diode reliability

NASA Astrophysics Data System (ADS)

Kim, Juseong; Jang, Inseok; Song, Gwang Yeom; Kim, Wan-Ho; Jeon, Sie-Wook; Kim, Jae-Pil

2018-05-01

The surface property of moisture-sensitive K2SiF6:Mn4+ (KSF) as a red-emitting phosphor was controlled through dry-type surface modification in order to improve the photo-performance and reliability of lighting-emitting diode (LED). The phosphor surface was modified with silane coupling agents having different carbon chain length by plasma-assisted method. Comparing between as-prepared and modified KSF, water-resistance and photo-emission efficiency were enhanced due to the formation of hydrophobic shell and the elimination of surface quenching sites. Moreover, the dispersibility of phosphor was increased as increasing the carbon chain length of silane because the interfacial affinity between phosphor and encapsulant was improved. After fabricating LED device, the enhancement of photo-performance and long-term reliability could be successfully achieved in LED device with modified phosphor. It is attributed to that the degradation of phosphor efficiency by moisture was suppressed and heat dissipation in LED PKG was improved through the surface modification.
Rapid prototyping of three-dimensional microstructures from multiwalled carbon nanotubes

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

Hung, W.H.; Kumar, Rajay; Bushmaker, Adam

The authors report a method for creating three-dimensional carbon nanotube structures, whereby a focused laser beam is used to selectively burn local regions of a dense forest of multiwalled carbon nanotubes. Raman spectroscopy and scanning electron microscopy are used to quantify the threshold for laser burnout and depth of burnout. The minimum power density for burning carbon nanotubes in air is found to be 244 {mu}W/{mu}m{sup 2}. We create various three-dimensional patterns using this method, illustrating its potential use for the rapid prototyping of carbon nanotube microstructures. Undercut profiles, changes in nanotube density, and nanoparticle formation are observed after lasermore » surface treatment and provide insight into the dynamic process of the burnout mechanism.« less
Electron-spectroscopy studies of clean thorium and uranium surfaces. Chemisorption and initial stages of reaction with O2, CO, and CO2

NASA Astrophysics Data System (ADS)

McLean, W.; Colmenares, C. A.; Smith, R. L.; Somorjai, G. A.

1982-01-01

The adsorption of O2, CO, and CO2 on the thorium (111) crystal face and on polycrystalline α-uranium has been investigated by x-ray photoelectron spectroscopy, Auger electron spectroscopy (AES), and secondary-ion mass spectroscopy (SIMS) at 300 K. Oxygen adsorption on both metals resulted in the formation of the metal dioxide. CO and CO2 adsorption on Th(111) produced species derived from atomic carbon and oxygen; the presence of molecular CO was also detected. Only atomic carbon and oxygen were observed on uranium. Elemental depth profiles by AES and SIMS indicated that the carbon produced by the dissociation of CO or CO2 diffused into the bulk of the metals to form a carbide, while the oxygen remained on their surfaces as an oxide.
EPR spin trapping evidence of radical intermediates in the photo-reduction of bicarbonate/CO2 in TiO2 aqueous suspensions.

PubMed

Molinari, Alessandra; Samiolo, Luca; Amadelli, Rossano

2015-05-01

Using the EPR spin trapping technique, we prove that simultaneous reactions take place in illuminated suspensions of TiO2 in aqueous carbonate solutions (pH ≈ 7). The adsorbed HCO3(-) is reduced to formate as directly made evident by the detection of formate radicals (˙CO2(-)). In addition, the amount of OH˙ radicals from the photo-oxidation of water shows a linear dependence on the concentration of bicarbonate, indicating that electron scavenging by HCO3(-) increases the lifetime of holes. In a weakly alkaline medium, photo-oxidation of HCO3(-)/CO3(2-) to ˙CO3(-) interferes with the oxidation of water. A comparative analysis of different TiO2 samples shows that formation of ˙CO2(-) is influenced by factors related to the nature of the surface, once expected surface area effects are accounted for. Modification of the TiO2 surface with noble metal nanoparticles does not have unequivocal benefits: the overall activity improves with Pd and Rh but not with Ru, which favours HCO3(-) photo-oxidation even at pH = 7. In general, identification of radical intermediates of oxidation and reduction reactions can provide useful mechanistic information that may be used in the development of photocatalytic systems for the reduction of CO2 also stored in the form of carbonates.
Hydrogeology of south-central St Croix, US Virgin Islands

USGS Publications Warehouse

Graves, R.P.

1995-01-01

The subsurface geology of south-central St. Croix consists of alluvium and underlying carbonate rocks. The alluvial deposits consist of sand and gravel with cobbles and boulders and, locally, thin lenses of silt and clay. The carbonate rocks consist of the Oligocene to Middle Miocene age Jealousy formation, the Miocene and Pliocene are Kingshill Limestone, and the Pliocene and younger age Post-Kingshill Carbonates. Ground water occurs under water-table conditions in the alluvial, Post-Kingshill Carbonates, and Kingshill Limestone deposits. These deposits are hydraulically connected and are considered to be a single hydrologic unit. The top of the water-table aquifer can range from 5 to 68 feet below land surface. The top of the Jealousy Formation is considered to be the bottom of the water- table aquifer and generally is from 85 to greater than 120 feet below land surface. Aquifer yields in south- central St. Croix can range from less than 5 gallons per minute to 80 gallons per minute. The ground- water in the study area is of the sodium-chloride type. Ground-water samples collected from selected wells had chloride concentrations ranging from 64 to 4,400 milligrams per liter, and dissolved solid concen- trations ranging from 619 to 7,540 milligrams per liter. Connate water is suspected as being the source of sodium chloride in the ground water.
Physical defect formation in few layer graphene-like carbon on metals: influence of temperature, acidity, and chemical functionalization.

PubMed

Schumacher, Christoph M; Grass, Robert N; Rossier, Michael; Athanassiou, Evagelos K; Stark, Wendelin J

2012-03-06

A systematical examination of the chemical stability of cobalt metal nanomagnets with a graphene-like carbon coating is used to study the otherwise rather elusive formation of nanometer-sized physical defects in few layer graphene as a result of acid treatments. We therefore first exposed the core-shell nanomaterial to well-controlled solutions of altering acidity and temperature. The release of cobalt into these solutions over time offered a simple tool to monitor the progress of particle degradation. The results suggested that the oxidative damage of the graphene-like coatings was the rate-limiting step during particle degradation since only fully intact or entirely emptied carbon shells were found after the experiments. If ionic noble metal species were additionally present in the acidic solutions, the noble metal was found to reduce on the surface of specific, defective particles. The altered electrochemical gradients across the carbon shells were however not found to lead to a faster release of cobalt from the particles. The suggested mechanistic insight was further confirmed by the covalent chemical functionalization of the particle surface with chemically inert aryl species, which leads to an additional thickening of the shells. This leads to reduced cobalt release rates as well as slower noble metal reduction rates depending on the augmentation of the shell thickness.
Living in Salt: The formation and development of extremophile habitats and biosignatures within salt crusts of the hyperarid Atacama Desert

NASA Astrophysics Data System (ADS)

Finstad, K. M.; Amundson, R.

2013-12-01

It has become increasing apparent that salt-rich deposits are present on the Martian surface and that aqueous alteration has occurred sometime during the planet's past. In the hyperarid Atacama Desert in Chile, an important Earth-based analogue to Mars, microbial life has been discovered inhabiting halite (NaCl) surface crust deposits. Is it possible that similar salt deposits on Mars once harbored microbial life? If so, what adaptations were likely necessary for survival in such an environment and what biosignatures are expected to remain? Although this fascinating ecosystem in the Atacama Desert has been recognized, neither the physical processes of halite crust formation, nor the microorganisms residing within the salts have been extensively studied. To better understand the formation and geochemical dynamics of this unique habitat, we chose two sites within the Atacama Desert which exhibit both active crust formation as well as the presence of microbial communities: one site is on a dry Holocene age lake bed, while the other is of Pleistocene age. At each site soil profiles were excavated and total geochemical analyses were performed. Field observations clearly showed that the soils exhibited transitions of carbonate to sulfate to chloride salt deposition with decreasing depth, and that the thickness and mass of halite in the surficial crust was related to the age of the soil. Isotope profiles of carbon, nitrogen, and sulfur from these soils were also analyzed. Once exposed to the atmosphere, the halite crusts reside in a dynamic state of dissolution and erosion by wind and fog, and reformation due to fog and dew. In the crust nodules, microbial communities were sampled, in centimeter increments from the surface, for carbon, nitrogen, and sulfur isotope/concentration profiles. Our analyses help elucidate the physical and geochemical processes linked to the formation and evolution of these dynamic salt crusts, and the imprint of microbial life within them. A detailed examination of this habitat provides guidelines for interpreting and understanding similar data from hyperarid environments, such as Mars, and planning for future Mars exploration.
Photocatalysis and the origin of life: synthesis of nucleoside bases from formamide on TiO2(001) single surfaces.

PubMed

Senanayake, S D; Idriss, H

2006-01-31

We report the conversion of a large fraction of formamide (NH(2)CHO) to high-molecular-weight compounds attributed to nucleoside bases on the surface of a TiO(2) (001) single crystal in ultra-high vacuum conditions. If true, we present previously unreported evidence for making biologically relevant molecules from a C1 compound on any single crystal surface in high vacuum and in dry conditions. An UV light of 3.2 eV was necessary to make the reaction. This UV light excites the semiconductor surface but not directly the adsorbed formamide molecules or the reaction products. There thus is no need to use high energy in the form of photons or electrical discharge to make the carbon-carbon and carbon-nitrogen bonds necessary for life. Consequently, the reaction products may accumulate with time and may not be subject to decomposition by the excitation source. The formation of these molecules, by surface reaction of formamide, is proof that some minerals in the form of oxide semiconductors are active materials for making high-molecular-weight organic molecules that may have acted as precursors for biological compounds required for life in the universe.
One Step Assembly of Thin Films of Carbon Nanotubes on Screen Printed Interface for Electrochemical Aptasensing of Breast Cancer Biomarker.

PubMed

Nawaz, Muhammad Azhar Hayat; Rauf, Sajid; Catanante, Gaelle; Nawaz, Mian Hasnain; Nunes, Gilvanda; Marty, Jean Louis; Hayat, Akhtar

2016-10-06

Thin films of organic moiety functionalized carbon nanotubes (CNTs) from a very well-dispersed aqueous solution were designed on a screen printed transducer surface through a single step directed assembly methodology. Very high density of CNTs was obtained on the screen printed electrode surface, with the formation of a thin and uniform layer on transducer substrate. Functionalized CNTs were characterized by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and Brunauer-Emmett- Teller (BET) surface area analyzer methodologies, while CNT coated screen printed transducer platform was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The proposed methodology makes use of a minimum amount of CNTs and toxic solvents, and is successfully demonstrated to form thin films over macroscopic areas of screen printed carbon transducer surface. The CNT coated screen printed transducer surface was integrated in the fabrication of electrochemical aptasensors for breast cancer biomarker analysis. This CNT coated platform can be applied to immobilize enzymes, antibodies and DNA in the construction of biosensor for a broad spectrum of applications.
One Step Assembly of Thin Films of Carbon Nanotubes on Screen Printed Interface for Electrochemical Aptasensing of Breast Cancer Biomarker

PubMed Central

Nawaz, Muhammad Azhar Hayat; Rauf, Sajid; Catanante, Gaelle; Nawaz, Mian Hasnain; Nunes, Gilvanda; Louis Marty, Jean; Hayat, Akhtar

2016-01-01

Thin films of organic moiety functionalized carbon nanotubes (CNTs) from a very well-dispersed aqueous solution were designed on a screen printed transducer surface through a single step directed assembly methodology. Very high density of CNTs was obtained on the screen printed electrode surface, with the formation of a thin and uniform layer on transducer substrate. Functionalized CNTs were characterized by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface area analyzer methodologies, while CNT coated screen printed transducer platform was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The proposed methodology makes use of a minimum amount of CNTs and toxic solvents, and is successfully demonstrated to form thin films over macroscopic areas of screen printed carbon transducer surface. The CNT coated screen printed transducer surface was integrated in the fabrication of electrochemical aptasensors for breast cancer biomarker analysis. This CNT coated platform can be applied to immobilize enzymes, antibodies and DNA in the construction of biosensor for a broad spectrum of applications. PMID:27782067
40 CFR 60.641 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... formations beneath the earth's surface. The principal hydrocarbon constituent is methane. Onshore means all... sulfur compounds means H2S, carbonyl sulfide (COS), and carbon disulfide (CS2). Sulfur production rate... efficiency achieved in percent, carried to one decimal place. SThe sulfur production rate, kilograms per hour...
40 CFR 60.641 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... formations beneath the earth's surface. The principal hydrocarbon constituent is methane. Onshore means all... sulfur compounds means H2S, carbonyl sulfide (COS), and carbon disulfide (CS2). Sulfur production rate... efficiency achieved in percent, carried to one decimal place. SThe sulfur production rate, kilograms per hour...
Irreversible Capacities of Graphite in Low Temperature Electrolytes for Lithium-Ion Batteries

NASA Technical Reports Server (NTRS)

Ratnakumar, B.; Smart, M.; Surampudi, S.; Wang, Y.; Zhang, X.; Greenbaum, S.; Hightower, A.; Ahn, C.; Fultz, B.

1999-01-01

Carbonaceous anode materials in lithium ion rechargeable cells experience irreversible capacity, mainly due to a consumption of lithium in the formation of surface passive films. The stability and kinetics of lithium intercalation into the carbon anodes are dictated by these films.
Carbonate-shelf depositional environments of the Ordovician Viola formation in South-Central Kansas

USGS Publications Warehouse

Newell, K.D.

2000-01-01

The Upper Ordovician Viola Formation, an important petroleum reservoir in the Midcontinent, is a carbonate unit present over much of the subsurface in Kansas. The Viola is composed of two fining-upward sedimentary packages that are separated from each other by a minor karstic surface representing a brief period of exposure. Each package represents a third-order sedimentary cycle and consists of an echinoderm-rich packstone overlain by a thicker lime mudstone. The echinoderm-rich packstone was deposited nearshore in agitated waters, but subsequently was bioturbated. The overlying lime mudstone was deposited in deeper, quiet waters, and locally contains storm-deposited carbonate sands. Subtle growth of the Central Kansas Arch and Pratt Anticline (structures transecting the depositional shelf) is indicated by packstones and grainstones being thicker over these arches, whereas finer grained lithologies dominate in basinal areas on the arch flanks. Structureless lime mudstones, probably intensely bioturbated, grade into laminated lime mudstones farther basinward.

Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene

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

Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong

Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzagmore » directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. Lastly, the correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.« less
Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene

DOE PAGES

Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong; ...

2014-12-01

Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzagmore » directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. Lastly, the correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.« less
Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene.

PubMed

Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong; Son, Young-Woo; Park, Yeonggu; Lee, Mi Jung; Byun, Ik-Su; Kim, Jin-Soo; Choi, Choon-Gi; Bostwick, Aaron; Rotenberg, Eli; Park, Bae Ho

2014-12-01

Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzag directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. The correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.
Novel phase of carbon, ferromagnetism, and conversion into diamond

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

Narayan, Jagdish, E-mail: narayan@ncsu.edu; Bhaumik, Anagh

2015-12-07

We report the discovery of a new phase of carbon (referred to as Q-carbon) and address fundamental issues related to direct conversion of carbon into diamond at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon is formed as result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. It is shown thatmore » nanosecond laser heating of diamond-like amorphous carbon on sapphire, glass, and polymer substrates can be confined to melt carbon in a super undercooled state. By quenching the carbon from the super undercooled state, we have created a new state of carbon (Q-carbon) from which nanodiamond, microdiamond, microneedles, and single-crystal thin films are formed depending upon the nucleation and growth times allowed for diamond formation. The Q-carbon quenched from liquid is a new state of solid carbon with a higher mass density than amorphous carbon and a mixture of mostly fourfold sp{sup 3} (75%–85%) with the rest being threefold sp{sup 2} bonded carbon (with distinct entropy). It is expected to have new and improved mechanical hardness, electrical conductivity, chemical, and physical properties, including room-temperature ferromagnetism (RTFM) and enhanced field emission. Here we present interesting results on RTFM, enhanced electrical conductivity and surface potential of Q-carbon to emphasize its unique properties. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g{sup −1}. From the Q-carbon, diamond phase is nucleated and a variety of micro- and nanostructures and large-area single-crystal diamond sheets are grown by allowing growth times as needed. Subsequent laser pulses can be used to grow nanodiamond into microdiamond and nucleate other nanostructures of diamond on the top of existing microdiamond and create novel nanostructured materials. The microstructural details provide insights into the mechanism of formation of nanodiamond, microdiamond, nanoneedles, microneedles, and single-crystal thin films. This process allows carbon-to-diamond conversion and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp{sup 3} bonding for diamond formation.« less
Novel phase of carbon, ferromagnetism, and conversion into diamond

NASA Astrophysics Data System (ADS)

Narayan, Jagdish; Bhaumik, Anagh

2015-12-01

We report the discovery of a new phase of carbon (referred to as Q-carbon) and address fundamental issues related to direct conversion of carbon into diamond at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon is formed as result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. It is shown that nanosecond laser heating of diamond-like amorphous carbon on sapphire, glass, and polymer substrates can be confined to melt carbon in a super undercooled state. By quenching the carbon from the super undercooled state, we have created a new state of carbon (Q-carbon) from which nanodiamond, microdiamond, microneedles, and single-crystal thin films are formed depending upon the nucleation and growth times allowed for diamond formation. The Q-carbon quenched from liquid is a new state of solid carbon with a higher mass density than amorphous carbon and a mixture of mostly fourfold sp3 (75%-85%) with the rest being threefold sp2 bonded carbon (with distinct entropy). It is expected to have new and improved mechanical hardness, electrical conductivity, chemical, and physical properties, including room-temperature ferromagnetism (RTFM) and enhanced field emission. Here we present interesting results on RTFM, enhanced electrical conductivity and surface potential of Q-carbon to emphasize its unique properties. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g-1. From the Q-carbon, diamond phase is nucleated and a variety of micro- and nanostructures and large-area single-crystal diamond sheets are grown by allowing growth times as needed. Subsequent laser pulses can be used to grow nanodiamond into microdiamond and nucleate other nanostructures of diamond on the top of existing microdiamond and create novel nanostructured materials. The microstructural details provide insights into the mechanism of formation of nanodiamond, microdiamond, nanoneedles, microneedles, and single-crystal thin films. This process allows carbon-to-diamond conversion and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp3 bonding for diamond formation.
Morphology and topography study of graphene synthesized from plant oil

NASA Astrophysics Data System (ADS)

Robaiah, M.; Rusop, M.; Abdullah, S.; Khusaimi, Z.; Azhan, H.; Laila, M. O.; Salifairus, M. J.; Asli, N. A.

2018-05-01

The graphene is material consists of bonded atom carbon atoms in sheet form one atom thick. The different types of carbon sources which are refined corn oil, palm oil and waste cooking palm oil were used as carbon feedstock to supply carbon atom for synthesizing graphene on the nickel substrate by thermal chemical vapour deposition. The substrate and carbon sources were placed in double zone furnaces. The carbon sources and the substrate were heated at 300 °C and 900 °C respectively. The both furnaces were switched off after synthesis time for cooling process finish. The formation of the graphene on the Ni surface appears due to segregation and precipitation of a high amount of carbon from the source material during the cooling process. FESEM, AFM, UV-VIS Spectroscopy and Raman Spectroscopy were used to characterize and synthesized graphene.
Continuously increasing δ98Mo values in Neoarchean black shales and iron formations from the Hamersley Basin

NASA Astrophysics Data System (ADS)

Kurzweil, Florian; Wille, Martin; Schoenberg, Ronny; Taubald, Heinrich; Van Kranendonk, Martin J.

2015-09-01

We present Mo-, C- and O-isotope data from black shales, carbonate- and oxide facies iron formations from the Hamersley Group, Western Australia, that range in age from 2.6 to 2.5 billion years. The data show a continuous increase from near crustal δ98Mo values of around 0.50‰ for the oldest Marra Mamba and Wittenoom formations towards higher values of up to 1.51‰ for the youngest sample of the Brockman Iron Formation. Thereby, the trend in increasing δ98Mo values is portrayed by both carbonate facies iron formations and black shales. Considering the positive correlation between Mo concentration and total organic carbon, we argue that this uniformity is best explained by molybdate adsorption onto organic matter in carbonate iron formations and scavenging of thiomolybdate onto sulfurized organic matter in black shales. A temporal increase in the seawater δ98Mo over the period 2.6-2.5 Ga is observed assuming an overall low Mo isotope fractionation during both Mo removal processes. Oxide facies iron formations show lowest Mo concentrations, lowest total organic carbon and slightly lower δ98Mo compared to nearly contemporaneous black shales. This may indicate that in iron formation settings with very low organic matter burial rates, the preferential adsorption of light Mo isotopes onto Fe-(oxyhydr)oxides becomes more relevant. A similar Mo-isotope pattern was previously found in contemporaneous black shales and carbonates of the Griqualand West Basin, South Africa. The consistent and concomitant increase in δ98Mo after 2.54 billion years ago suggests a more homogenous distribution of seawater molybdate with uniform isotopic composition in various depositional settings within the Hamersley Basin and the Griqualand West Basin. The modeling of the oceanic Mo inventory in relation to the Mo in- and outflux suggests that the long-term build-up of an isotopically heavy seawater Mo reservoir requires a sedimentary sink for isotopically light Mo. The search for this sink (i.e. adsorption onto Mn-oxides in well oxygenated surface oceans and/or subaerial environments or incomplete thiomolybdate formation in weakly sulfidic settings) remains debated, but its relevance becomes more important closer to the Great Oxidation Event and is probably related to already weakly oxidizing conditions even prior to the 2.5 Ga "whiff of oxygen".
Identification of Fragile Microscopic Structures during Mineral Transformations in Wet Supercritical CO2

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

Arey, Bruce W.; Kovarik, Libor; Qafoku, Odeta

2013-04-01

In this study we examine the nature of highly fragile reaction products that form in low water content super critical carbon dioxide (scCO2) using a combination of scanning electron microscopy/focus ion beam (SEM/FIB), confocal Raman spectroscopy, helium ion microscopy (HeIM), and transmission electron microscopy (TEM). HeIM images show these precipitates to be fragile rosettes that can readily decompose even under slight heating from an electron beam. Using the TEM revealed details on the interfacial structure between the newly formed surface precipitates and the underlying initial solid phases. The detailed microscopic analysis revealed that the growth of the precipitates either followedmore » a tip growth mechanism with precipitates forming directly on the forsterite surface if the initial solid was non-porous (natural forsterite) or growth from the surface of the precipitates where fluid was conducted through the porous (nanoforsterite) agglomerates to the growth center. The mechanism of formation of the hydrated/hydroxylated magnesium carbonate compound (HHMC) phases offers insight into the possible mechanisms of carbonate mineral formation from scCO2 solutions which has recently received a great deal of attention as the result of the potential for CO2 to act as an atmospheric greenhouse gas and impact overall global warming. The techniques used here to examine these fragile structures an also be used to examine a wide range of fragile material surfaces. SEM and FIB technologies have now been brought together in a single instrument, which represents a powerful combination for the studies in biological, geological and materials science.« less
Viability of pyrite pulled metabolism in the ‘iron-sulfur world’ theory: Quantum chemical assessment

NASA Astrophysics Data System (ADS)

Michalkova, Andrea; Kholod, Yana; Kosenkov, Dmytro; Gorb, Leonid; Leszczynski, Jerzy

2011-04-01

The viability of pyrite-pulled metabolism in the 'iron-sulfur world' theory was assessed using a simple model of iron-nickel sulfide (Fe-Ni-S) surface and data obtained from quantum chemical calculations. We have investigated how the individual reactions in the carbon fixation cycle (carboxylic acids formation) on an Fe-Ni-S surface could have operated to produce carboxylic acids from carbon oxide and water. The proposed model cycle reveals how the individual reactions might have functioned and provides the thermodynamics of each step of the proposed pathway. The feasibility of individual reactions, as well the whole cycle was considered. The reaction of acetic acid production from CH 3SH and CO on an Fe-Ni sulfide surface was revealed to be endergonic with a few partial steps having positive Gibbs free energy. On the other hand, the pyrite formation was found to be slightly exergonic. The significance of the catalytic activity of transition metal sulfides in generation of acetic acid was shown. The Gibbs free energy values indicate that the acetic acid synthesis is unfavorable to proceed on the studied Fe-Ni-S model under simulated conditions. The importance of these results in terms of a primordial chemistry on iron-nickel sulfide surfaces is discussed.
Sedimentology and taphonomy of the upper Karoo-equivalent Mpandi Formation in the Tuli Basin of Zimbabwe, with a new 40Ar/ 39Ar age for the Tuli basalts

NASA Astrophysics Data System (ADS)

Rogers, Raymond R.; Rogers, Kristina Curry; Munyikwa, Darlington; Terry, Rebecca C.; Singer, Bradley S.

2004-10-01

Karoo-equivalent rocks in the Tuli Basin of Zimbabwe are described, with a focus on the dinosaur-bearing Mpandi Formation, which correlates with the Elliot Formation (Late Triassic-Early Jurassic) in the main Karoo Basin. Isolated exposures of the Mpandi Formation along the banks of the Limpopo River consist of red silty claystones and siltstones that preserve root traces, small carbonate nodules, and hematite-coated prosauropod bones. These fine-grained facies accumulated on an ancient semi-arid floodplain. Widespread exposures of quartz-rich sandstone and siltstone representing the upper Mpandi Formation crop out on Sentinel Ranch. These strata preserve carbonate concretions and silicified root casts, and exhibit cross-bedding indicative of deposition via traction currents, presumably in stream channels. Prosauropod fossils are also preserved in the Sentinel Ranch exposures, with one particularly noteworthy site characterized by a nearly complete and articulated Massospondylus individual. An unconformity caps the Mpandi Formation in the study area, and this stratigraphically significant surface rests on a laterally-continuous zone of pervasive silicification interpreted as a silcrete. Morphologic, petrographic, and geochemical data indicate that the Mpandi silcrete formed by intensive leaching near the ground surface during prolonged hiatus. Chert clasts eroded from the silcrete are intercalated at the base of the overlying Samkoto Formation (equivalent to the Clarens Formation in the main Karoo Basin), which in turn is overlain by the Tuli basalts. These basalts, which are part of the Karoo Igneous Province, yield a new 40Ar/ 39Ar plateau age of 186.3 ± 1.2 Ma.
Ubiquitylation Functions in the Calcium Carbonate Biomineralization in the Extracellular Matrix

PubMed Central

Fang, Dong; Pan, Cong; Lin, Huijuan; Lin, Ya; Xu, Guangrui; Zhang, Guiyou; Wang, Hongzhong; Xie, Liping; Zhang, Rongqing

2012-01-01

Mollusks shell formation is mediated by matrix proteins and many of these proteins have been identified and characterized. However, the mechanisms of protein control remain unknown. Here, we report the ubiquitylation of matrix proteins in the prismatic layer of the pearl oyster, Pinctada fucata. The presence of ubiquitylated proteins in the prismatic layer of the shell was detected with a combination of western blot and immunogold assays. The coupled ubiquitins were separated and identified by Edman degradation and liquid chromatography/mass spectrometry (LC/MS). Antibody injection in vivo resulted in large amounts of calcium carbonate randomly accumulating on the surface of the nacreous layer. These ubiquitylated proteins could bind to specific faces of calcite and aragonite, which are the two main mineral components of the shell. In the in vitro calcium carbonate crystallization assay, they could reduce the rate of calcium carbonate precipitation and induce the calcite formation. Furthermore, when the attached ubiquitins were removed, the functions of the EDTA-soluble matrix of the prismatic layer were changed. Their potency to inhibit precipitation of calcium carbonate was decreased and their influence on the morphology of calcium carbonate crystals was changed. Taken together, ubiquitylation is involved in shell formation. Although the ubiquitylation is supposed to be involved in every aspect of biophysical processes, our work connected the biomineralization-related proteins and the ubiquitylation mechanism in the extracellular matrix for the first time. This would promote our understanding of the shell biomineralization and the ubiquitylation processes. PMID:22558208
Functionalized granular activated carbon and surface complexation with chromates and bi-chromates in wastewater.

PubMed

Singha, Somdutta; Sarkar, Ujjaini; Luharuka, Pallavi

2013-03-01

Cr(VI) is present in the aqueous medium as chromate (CrO4(2-)) and bi-chromate (HCrO4(-)). Functionalized granular activated carbons (FACs) are used as adsorbents in the treatment of wastewaters containing hexavalent chromium. The FACs are prepared by chemical modifications of granular activated carbons (GACs) using functionalizing agents like HNO3, HCl and HF. The Brunauer, Emmett and Teller surface areas of FAC-HCl (693.5m(2)/g), FAC-HNO3 (648.8m(2)/g) and FAC-HF (726.2m(2)/g) are comparable to the GAC (777.7m(2)/g). But, the adsorption capacity of each of the FAC-HNO3, FAC-HCl and FAC-HF is found to be higher than the GAC. The functional groups play an important role in the adsorption process and pH has practically no role in this specific case. The FACs have hydrophilic protonated external surfaces in particular, along with the functional surface sites capable to make complexes with the CrO4(2-) and HCrO4(-) present. Surface complex formation is maximized in the order FAC-HNO3>FAC-HF>FAC-HCl, in proportion to the total surface acidity. This is also confirmed by the well-known pseudo second-order kinetic model. Physi-sorption equilibrium isotherms are parameterized by using standard Freundlich and Langmuir models. Langmuir fits better. The formation of surface complexes with the functional groups and hexavalent chromium is also revealed in the images of field emission scanning electron micrograph; energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy analysis after adsorption. The intra-particle diffusion is not the only rate-controlling factor. The Boyd's film diffusion model fits very well with R(2) as high as 98.1% for FAC-HNO3. This result demonstrates that the functionalization of the GAC by acid treatments would increase the diffusion rate, predominantly with a boundary layer diffusion effect. Copyright © 2013 Elsevier B.V. All rights reserved.
Clustering of water molecules in ultramicroporous carbon: In-situ small-angle neutron scattering

DOE PAGES

Bahadur, Jitendra; Contescu, Cristian I.; Rai, Durgesh K.; ...

2016-10-19

The adsorption of water is central to most of the applications of microporous carbon as adsorbent material. We report early kinetics of water adsorption in the microporous carbon using in-situ small-angle neutron scattering. It is observed that adsorption of water occurs via cluster formation of molecules. Interestingly, the cluster size remains constant throughout the adsorption process whereas number density of clusters increases with time. The role of surface chemistry of microporous carbon on the early kinetics of adsorption process was also investigated. Lastly, the present study provides direct experimental evidence for cluster assisted adsorption of water molecules in microporous carbonmore » (Do-Do model).« less
Influence of feedstock chemical composition on product formation and characteristics derived from the hydrothermal carbonization of mixed feedstocks.

PubMed

Lu, Xiaowei; Berge, Nicole D

2014-08-01

As the exploration of the carbonization of mixed feedstocks continues, there is a distinct need to understand how feedstock chemical composition and structural complexity influence the composition of generated products. Laboratory experiments were conducted to evaluate the carbonization of pure compounds, mixtures of the pure compounds, and complex feedstocks comprised of the pure compounds (e.g., paper, wood). Results indicate that feedstock properties do influence carbonization product properties. Carbonization product characteristics were predicted using results from the carbonization of the pure compounds and indicate that recovered solids energy contents are more accurately predicted than solid yields and the carbon mass in each phase, while predictions associated with solids surface functional groups are more difficult to predict using this linear approach. To more accurately predict carbonization products, it may be necessary to account for feedstock structure and/or additional feedstock properties. Copyright © 2014 Elsevier Ltd. All rights reserved.
Spatial characterization of soil properties and influence in soil formation in oak-grassland of Sierra Morena, S Spain

NASA Astrophysics Data System (ADS)

Román-Sánchez, Andrea; Cáceres, Francisco; Pédèches, Remi; Giráldez Cervera, Juan Vicente; Vanwalleghem, Tom

2016-04-01

The Mediterranean oak-grassland ecosystem is very important for the rural economy and for the biodiversity of south-western European countries like Spain and Portugal. Nevertheless these ecosystems are not well characterized especially their soils. In this report soil carbon has been evaluated and related to other properties. The principal factors controlling the structure, productivity and evolution of forest ecosystems are bedrock, climate, relief, vegetation and time. Soil carbon has an important influence in the soil and ecosystem structures. The purpose of this study is to determine the relationship between relief, soil properties, spatial distribution of soil carbon and their influence in soil formation and geomorphology. This work is part of another study which aims to elucidate the processes involved in the soil formation and to examine their behaviour on long-term with a modelling. In our study area, located in oak-grassland of Sierra Morena, in Cordoba, S Spain, have been studied 67 points at 6 depths in 262 hectares in order to determine carbon content varying between 0-6%, soil properties such as soil depth between 0-4 m, horizon depth and the rocks amount in surface. The relationship between the soil carbon, soil properties and the relief characteristic like slope, aspect, curvature can shed light the processes that affect the mechanisms of bedrock weathering and their interrelationship with geomorphological processes.
Effect of hydrodynamics and surface roughness on the electrochemical behaviour of carbon steel in CSG produced water

NASA Astrophysics Data System (ADS)

Eyu, Gaius Debi; Will, Geoffrey; Dekkers, Willem; MacLeod, Jennifer

2015-12-01

The influence of fluid flow, surface roughness and immersion time on the electrochemical behaviour of carbon steel in coal seam gas produced water under static and hydrodynamic conditions has been studied. The disc electrode surface morphology before and after the corrosion test was characterized using scanning electron microscopy (SEM). The corrosion product was examined using X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD).The results show that the anodic current density increased with increasing surface roughness and consequently a decrease in corrosion surface resistance. Under dynamic flow conditions, the corrosion rate increased with increasing rotating speed due to the high mass transfer coefficient and formation of non-protective akaganeite β-FeO(OH) and goethite α-FeO(OH) corrosion scale at the electrode surface. The corrosion rate was lowest at 0 rpm. The corrosion rate decreased in both static and dynamic conditions with increasing immersion time. The decrease in corrosion rate is attributed to the deposition of corrosion products on the electrode surface. SEM results revealed that the rougher surface exhibited a great tendency toward pitting corrosion.
Surface nucleation and independent growth of Ce(OH)4 within confinement space on modified carbon black surface to prepare nano-CeO2 without agglomeration

NASA Astrophysics Data System (ADS)

Zhang, Xinyue; Xia, Chunhui; Li, Kaitao; Lin, Yanjun

2018-06-01

Highly dispersed negative carboxyl groups can be formed on carbon black (CB) surface modified with strong nitric acid. Therefore positive cations can be uniformly absorbed by carboxyl groups and precipitated within a confinement space on modified CB surface to prepare highly dispersed nanomaterials. In this paper, the formation and dispersion status of surface negative carboxyl groups, adsorption status of Ce3+, surface confinement nucleation, crystallization and calcination process were studied by EDS, SEM, and laser particle size analysis. The results show that the carboxyl groups formed on modified CB surface are highly dispersed, and Ce3+ cations can be uniformly anchored by carboxyl groups. Therefore, highly dispersed Ce3+ can react with OH- within a confinement surface region to form positive nano-Ce(OH)4 nuclei which also can be adsorbed by electrostatic attraction. After independent growth of Ce(OH)4 without agglomeration, highly dispersed CeO2 nanoparticles without agglomeration can be prepared together with the help of effectively isolates by CO2 released in the combustion of CB.
Surface nucleation and independent growth of Ce(OH)4 within confinement space on modified carbon black surface to prepare nano-CeO2 without agglomeration

NASA Astrophysics Data System (ADS)

Zhang, Xinyue; Xia, Chunhui; Li, Kaitao; Lin, Yanjun

2018-04-01

Highly dispersed negative carboxyl groups can be formed on carbon black (CB) surface modified with strong nitric acid. Therefore positive cations can be uniformly absorbed by carboxyl groups and precipitated within a confinement space on modified CB surface to prepare highly dispersed nanomaterials. In this paper, the formation and dispersion status of surface negative carboxyl groups, adsorption status of Ce3+, surface confinement nucleation, crystallization and calcination process were studied by EDS, SEM, and laser particle size analysis. The results show that the carboxyl groups formed on modified CB surface are highly dispersed, and Ce3+ cations can be uniformly anchored by carboxyl groups. Therefore, highly dispersed Ce3+ can react with OH- within a confinement surface region to form positive nano-Ce(OH)4 nuclei which also can be adsorbed by electrostatic attraction. After independent growth of Ce(OH)4 without agglomeration, highly dispersed CeO2 nanoparticles without agglomeration can be prepared together with the help of effectively isolates by CO2 released in the combustion of CB.
Carbon Isotopes of Alkanes in Hydrothermal Abiotic Organic Synthesis Processes at High Temperatures and Pressures: An Experimental Study

NASA Technical Reports Server (NTRS)

Fu, Qi; Socki, Richard A.; Niles, Paul B.

2010-01-01

Observation of methane in the Martian atmosphere has been reported by different detection techniques [1-4]. With more evidence showing extensive water-rock interaction in Martian history [5-7], abiotic formation by Fischer-Tropsch Type (FTT) synthesis during serpentization reactions may be one possible process responsible for methane generation on Mars [8, 9]. While the experimental studies performed to date leave little doubt that chemical reactions exist for the abiotic synthesis of organic compounds by mineral surface-catalyzed reactions [10-12], little is known about the reaction pathways by which CO2 and/or CO are reduced under hydrothermal conditions. Carbon and hydrogen isotope measurements of alkanes have been used as an effective tool to constrain the origin and reaction pathways of hydrocarbon formation. Alkanes generated by thermal breakdown of high molecular weight organic compounds have carbon and hydrogen isotopic signatures completely distinct from those formed abiotically [13-15]. Recent experimental studies, however, showed that different abiogenic hydrocarbon formation processes (e.g., polymerization vs. depolymerization) may have different carbon and hydrogen isotopic patterns [16]. Results from previous experiments studying decomposition of higher molecular weight organic compounds (lignite) also suggested that pressure could be a crucial factor affecting fractionation of carbon isotopes [17]. Under high pressure conditions, no experimental data are available describing fractionation of carbon isotope during mineral catalyzed FTT synthesis. Thus, hydrothermal experiments present an excellent opportunity to provide the requisite carbon isotope data. Such data can also be used to identify reaction pathways of abiotic organic synthesis under experimental conditions.
Surface-initiated graft polymerization on multiwalled carbon nanotubes pretreated by corona discharge at atmospheric pressure.

PubMed

Xu, Lihua; Fang, Zhengping; Song, Ping'an; Peng, Mao

2010-03-01

Surface-initiated graft polymerization on multi-walled carbon nanotubes pretreated with a corona discharge at atmospheric pressure was explored. The mechanism of the corona-discharge-induced graft polymerization is discussed. The results indicate that MWCNTs were encapsulated by poly(glycidyl methacrylate) (PGMA), demonstrating the formation of PGMA-grafted MWCNTs (PGMA-g-MWCNTs), with a grafting ratio of about 22 wt%. The solubility of PGMA-g-MWCNTs in ethanol was dramatically improved compared to pristine MWCNTs, which could contribute to fabricating high-performance polymer/MWCNTs nanocomposites in the future. Compared with most plasma processes, which operate at low pressures, corona discharge has the merit of working at atmospheric pressure.

Studies of Scale Formation and Kinetics of Crofer 22 APU and Haynes 230 in Carbon Oxide-Containing Environment for SOFC Applications

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

Ziomek-Moroz, M.; Covino, B.S., Jr.; Holcomb, G.R.

2006-01-01

Significant progress in reducing the operating temperature of SOFCs below 800oC may allow the use of chromia-forming metallic interconnects at a substantial cost savings. Hydrogen is the main fuel for all types of fuel cells except direct methanol fuel cells. Hydrogen can be generated from fossil fuels, including coal, natural gas, diesel, gasoline, other hydrocarbons, and oxygenates (e.g., methanol, ethanol, butanol, etc.). Carbon oxides present in the hydrogen fuel can cause significant performance problems due to carbon formation (coking). Also, literature data indicate that in CO/CO2 gaseous environments, metallic materials that gain their corrosion resistance due to formation of Cr2O3,more » could form stable chromium carbides. The chromium carbide formation causes depletion of chromium in these alloys. If the carbides oxidize, they form non-protective scales. Considering a potential detrimental effect of carbon oxides on iron- and nickel-base alloy stability, determining corrosion performance of metallic interconnect candidates in carbon oxide-containing environments at SOFC operating temperatures is a must. In this research, the corrosion behavior of Crofer 22 APU and Haynes 230 was studied in a CO-rich atmosphere at 750°C. Chemical composition of the gaseous environment at the outlet was determined using gas chromatography (GC). After 800 h of exposure to the gaseous environment the surfaces of the corroded samples were studied by scanning electron microscopy (SEM) equipped with microanalytical capabilities. X-ray diffraction (XRD) analysis was also used in this study.« less
Derivation of the midinfrared (5.0-25.0 micron) optical constants of hydrous carbonate and sulfate

NASA Technical Reports Server (NTRS)

Roush, Ted L.; Orenberg, James B.; Pollack, James B.

1993-01-01

There is ample theoretical and observational evidence suggesting liquid water was once stable at the surface of Mars. Because water is essential to the evolution of life, it is important to understand the types of environments in which the liquid water was present. For example, if water were present early in Mars' history, then this raises the possibility that biological activity may have evolved only to eventually become extinct as liquid water became scarce. Alternatively, if liquid water were stable only later in Mars' history, then it becomes problematic to envision mechanisms by which biological activity evolved and remained viable without water until more favorable conditions existed. Even without biological activity, atmospheric carbon dioxide dissolved in water can assist the chemical weathering of primary igneous minerals producing common secondary phases such as hydartes, carbonates, and sulfates. While the identification of hydrates, carbonates, and sulfates on Mars cannot provide direct evidence of biological activity, it can provide significant information regarding the presence and duration of an environment that would support the presence of liquid water at the surface. The specific mineralogy of these secondary phases can provide insight into the environments of their formation. For example, the slow precipitation that occurs in large standing bodies of water, e.g. oceans or lakes, commonly results in the formation of calcite, magnesite, dolomite, siderite, and rhodochrosite. Rapid precipitation that occurs in ephemeral bodies of water, e.g. hypersaline lakes or playas, can result in the formation of all of the above phases as well as aragonite, vaterite, hydrated carbonates, alkali carbonates, bicarbonates, and other poorly ordered phases. Absorption features identified in recent near-infrared spectra of Mars have been interpreted as being due to bicarbonate and bisulfate located in the mineral scaplite. Spectral data returned by the Mariner 6 and 7 spacecraft have been inerpreted as remaining consistent with the presence of hydrated carbonates. Additional, airborne thermal infrared spectra of Mars have been interpreted as implying the presence of carbonates, sulfates, and hydrates. Modeling of the thermal infrared data relied upon the optical constants of calcite anhydrite and a mixture of water in basalt because of their availability. The derived abundances of carbonate and sulfate were 1-3 percent and 10-15 percent by volume. However, the observed complexity and positions of the bands suggested other carbonate-, and sulfate-bearing species. We have already derived optical constants for hydrous and anhydrous silicates, and we are now applying these techniques to the derivation of the optical constants of hydrous carbonate and sulfate.
A mild, near-surface aqueous environment on Noachian Mars preserved in ALH84001

NASA Astrophysics Data System (ADS)

Halevy, I.; Fischer, W. W.; Eiler, J. M.

2011-12-01

Despite widespread evidence for liquid water at the surface of Mars during parts of the Noachian epoch, the temperature of early aqueous environments has been impossible to establish, raising questions of whether Mars' surface was ever warmer than today. This has hindered insight into aqueous alteration processes, which, on the basis of orbital spectroscopy, appear to have been prevalent on Noachian Mars. It is important to understand such processes, as they link the observed secondary mineral assemblages to interactions between primary igneous silicates and the surface environment (atmosphere-hydrosphere). We have addressed this problem by determining the precipitation temperatures of secondary carbonate minerals preserved in the oldest known sample of Mars' crust-the meteorite Allan Hills 84001 (ALH84001). Using carbonate 'clumped' isotope thermometry we have found that the carbonates in ALH84001, which are 3.9-4.0 billion years old, formed at a temperature of ~18±4°C. With temperature known, we used the carbon and oxygen isotopic composition of the carbonates, as constrained by both our measurements and previous acid digestion and ion microprobe studies, to develop a model for their formation process and environment. The observed isotopic variation is best explained by carbonate precipitation out of a gradually evaporating, shallow subsurface aqueous solution (e.g. a regolith aquifer) at near-constant temperatures. Furthermore, on the basis of the isotopic composition of the earliest precipitated carbonates in ALH84001, the volatiles from which they formed (H2O and CO2) came not from depth, but from the early Martian surface. The occurrence of carbonates in other SNC meteorites and as a minor component of Martian dust implies that environments analogous to the one we studied may have been important in generating some of the observed secondary mineral assemblages by interaction between Mars' igneous crust and its atmosphere-hydrosphere.
Theoretical modeling to study the impact of different oxidizers (etchants) on the plasma-assisted catalytic carbon nanofiber growth

NASA Astrophysics Data System (ADS)

Gupta, Ravi; Sharma, Suresh C.

2017-07-01

An analytical model based on the various surface deposition processes and plasma sheath kinetics of the plasma species (electrons, positively charged ions, radicals, and neutrals) has been developed to investigate the effects of different plasmas (different etchants) on the catalyzed plasma aided growth of carbon nanofibers (CNFs). In particular, the model accounts the poisoning of the catalyst nanoparticle, i.e., the formation of the amorphous carbon layer on the catalyst active surface due to the continuous dissociation of incoming hydrocarbon species from the plasma. It is observed that oxidizers (H2O and O2) in the typical hydrocarbon/hydrogen (C2H2 + H2) plasma act as the dominant etchants and remove the amorphous carbon layer from the catalyst surface and, thus, preserve and enhance the catalyst activity. However, the growth rate of CNFs is much higher when O2 is added as an etchant in the reactive plasma as compared to H2O. This is due to the dual role played by the oxygen, i.e., (i) removal of amorphous carbon from the catalyst active surface, (ii) removal of hydrogen radicals that interact with the carbon species generated on the catalyst surface and suppress their diffusion through the catalyst nanoparticles. The CNF grows much longer in the presence of O2, therefore, etching of CNF tip and deformation of catalyst nanoparticle is the maximum, and hence, the CNF tip diameter is least. Moreover, in the present investigation, we also found that the relative concentrations of H2O or O2 species in the reactive plasma have significant effects on the CNF growth. Our theoretical results are in good agreement with the experimental observations.
Overhead Projector Demonstrations: Some Ideas from the Past.

ERIC Educational Resources Information Center

Kolb, Doris

1987-01-01

Describes nine chemistry demonstrations that can be done using an overhead projector. Includes demonstrations on common ion effect, crystal formation from supersaturated solutions, making iron positive with nitric acid, optical activity, carbon dioxide in human breath, amphoteric hydroxides, the surface tension of mercury, and natural acid-base…
Aqueous aerosol SOA formation: impact on aerosol physical properties.

PubMed

Woo, Joseph L; Kim, Derek D; Schwier, Allison N; Li, Ruizhi; McNeill, V Faye

2013-01-01

Organic chemistry in aerosol water has recently been recognized as a potentially important source of secondary organic aerosol (SOA) material. This SOA material may be surface-active, therefore potentially affecting aerosol heterogeneous activity, ice nucleation, and CCN activity. Aqueous aerosol chemistry has also been shown to be a potential source of light-absorbing products ("brown carbon"). We present results on the formation of secondary organic aerosol material in aerosol water and the associated changes in aerosol physical properties from GAMMA (Gas-Aerosol Model for Mechanism Analysis), a photochemical box model with coupled gas and detailed aqueous aerosol chemistry. The detailed aerosol composition output from GAMMA was coupled with two recently developed modules for predicting a) aerosol surface tension and b) the UV-Vis absorption spectrum of the aerosol, based on our previous laboratory observations. The simulation results suggest that the formation of oligomers and organic acids in bulk aerosol water is unlikely to perturb aerosol surface tension significantly. Isoprene-derived organosulfates are formed in high concentrations in acidic aerosols under low-NO(x) conditions, but more experimental data are needed before the potential impact of these species on aerosol surface tension may be evaluated. Adsorption of surfactants from the gas phase may further suppress aerosol surface tension. Light absorption by aqueous aerosol SOA material is driven by dark glyoxal chemistry and is highest under high-NO(x) conditions, at high relative humidity, in the early morning hours. The wavelength dependence of the predicted absorption spectra is comparable to field observations and the predicted mass absorption efficiencies suggest that aqueous aerosol chemistry can be a significant source of aerosol brown carbon under urban conditions.
Controllable synthesis of nitrogen-doped hollow mesoporous carbon spheres using ionic liquids as template for supercapacitors

NASA Astrophysics Data System (ADS)

Chen, Aibing; Li, Yunqian; Liu, Lei; Yu, Yifeng; Xia, Kechan; Wang, Yuying; Li, Shuhui

2017-01-01

We have demonstrated a facile and controllable synthesis of monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) using resorcinol/formaldehyde resin as a carbon precursor, tetraethyl orthosilicate as a structure-assistant agent, ionic liquids (ILs) as soft template, partial carbon sources, and nitrogen sources. The sizes and the architectures including hollow and yolk-shell of resultant carbon spheres can be efficiently controlled through the adjustment of the content of ILs. Alkyl chain length of the ILs also has an important effect on the formation of N-HMCSs. With proper alkyl chain length and content of ILs, the resultant N-HMCSs show monodispersed hollow spheres with high surface areas (up to 1158 m2 g-1), large pore volumes (up to 1.70 cm3 g-1), and uniform mesopore size (5.0 nm). Combining the hollow mesoporous structure, high porosity, large surface area, and nitrogen functionality, the as-synthesized N-HMCSs have good supercapacitor performance with good capacitance (up to 159 F g-1) and favorable capacitance retention (88% capacitive retention after 5000 cycles).
Surface properties of CNTs and their interaction with silica.

PubMed

Sobolkina, Anastasia; Mechtcherine, Viktor; Bellmann, Cornelia; Khavrus, Vyacheslav; Oswald, Steffen; Hampel, Silke; Leonhardt, Albrecht

2014-01-01

In order to improve the embedding of carbon nanotubes (CNTs) in cement-based matrices, silica was deposited on the sidewall of CNTs by a sol-gel method. Knowledge of the conditions of CNTs' surfaces is a key issue in understanding the corresponding interaction mechanisms. In this study various types of CNTs synthesized using acetonitrile, cyclohexane, and methane were investigated with regard to their physicochemical surface properties. Significant differences in surface polarity as well as in the wetting properties of the CNTs, depending on the precursors used, were revealed by combining electro-kinetic potential and contact angle measurements. The hydrophobicity of CNTs decreases by utilising the carbon sources in the following order: cyclohexane, methane, and finally acetonitrile. The XPS analysis, applied to estimate the chemical composition at the CNT surface, showed nitrogen atoms incorporated into the tube structure by using acetonitrile as a carbon source. It was found that the simultaneous presence of nitrogen- and/or oxygen-containing sites with different acid-base properties increased the surface polarity of the CNTs, imparting amphoteric characteristics to them and improving their wetting behaviour. Regarding the silica deposition, strong differences in adsorption capacity of the CNTs were observed. The mechanism of silica adsorption through interfacial bond formation was discussed. Copyright © 2013 Elsevier Inc. All rights reserved.
Contribution of Organic Material to the Stable Isotope Composition of Some Terrestrial Carbonates as Analogs for Martian Processes

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Gibson, Everett K., Jr.; Bissada, K. K.

2005-01-01

Understanding the isotopic geochemistry of terrestrial carbonate formation is essential to understanding the evolution of the Martian atmosphere, hydrosphere, and potential biosphere. Carbonate minerals, in particular, are important secondary minerals for interpreting past aqueous environments, as illustrated by the carbonates present in ALH84001 [1]. Models for the history of Mars suggest that the planet was warmer, wetter, and possessed a greater atmospheric pressure within the first billion years as compared to present conditions [2],[3],[4], and likely had an active hydrologic cycle. Morse and Marion [5] point out that associated with this hydrologic cycle would be the active chemical weathering of silicate minerals and thus consumption of atmospheric CO2 and deposition of carbonate and silica. It is during this warmer and wetter period of Martian history that surface and/or near-surface conditions would be most favorable for harboring possible microbiological life. Carbonates within ALH84001 offer evidence that fluids were present at 3.9 Gy on Mars [6]. A more through understanding of the effects of aqueous weathering and the potential contribution of organic compounds on the isotopic composition of Martian carbonate minerals can be gained by studying some terrestrial occurrences of carbonate rocks.
Investigation of quartz diagenesis in mudstones of the Spraberry and Wolfcamp Formations

NASA Astrophysics Data System (ADS)

Eakin, A.; Reece, J. S.

2016-12-01

Here we present preliminary core analysis of the diagenetic variability existing within a siliceous mudstone facies of the Permian Spraberry and Wolfcamp Formations in the Midland Basin, Texas. Within this mudstone facies, the carbonate content varies from absent in several Wolfcamp Formation samples to >40 wt. % in the Spraberry Formation. A normalized ratio of quartz to clay content with carbonate removed reveals a systematic decrease in quartz content with increasing clay content. This relationship is typical of rocks with variable amounts of detrital quartz content. However, in this siliceous mudstone facies, the abundance of detrital quartz silt grains does not vary widely. Additionally, for the same clay content, the Wolfcamp Formation shows a higher concentration of quartz than the Spraberry Formation. Scanning electron microscopy (SEM) reveals the presence of microcrystalline quartz cement that likely accounts for the increased quartz content in the Wolfcamp Formation. This research tests the hypothesis that the increased quartz cement in the Wolfcamp Formation may occur at the expense of the carbonate cement present in the overlying Spraberry Formation. Furthermore, the deviation in quartz content for the same clay concentration only occurs once the ratio of quartz to clay content increases beyond 1.2. This ratio may represent a threshold of detrital quartz in the clay matrix required to have enough porosity and nucleation surface area for authigenic quartz growth. The presence of matrix cement may impact the mechanical properties to favor fracturing and cataclasis over more ductile deformation. This would enhance development of secondary porosity, while also increasing permeability through the connection of primary pores. Acquiring a fundamental understanding of diagenesis in the Spraberry and Wolfcamp Formations will aid in better prediction of mechanical behavior during drilling and optimized resource recovery.
Surface martensitization of Carbon steel using Arc Plasma Sintering

NASA Astrophysics Data System (ADS)

Wahyudi, Haris; Dimyati, Arbi; Sebayang, Darwin

2018-03-01

In this paper new technology of surface structure modification of steel by short plasma exposure in Arc Plasma Sintering (APS) device is presented. APS is an apparatus working based on plasma generated by DC pulsed current originally used for synthesizing materials via sintering and melting. Plasma exposure in APS was applied into the specimens for 1 and 3 seconds which generate temperature approximately about 1300-1500°C. The SUP9, pearlitic carbon steel samples were used. The hardness, hardening depth and microstructure of the specimens have been investigated by Vickers micro hardness test and Scanning Electron Microscopy (SEM) supported by Energy Dispersive X-Ray Spectroscopy (EDX). The results have showed that the mechanical property was significantly improved due to the formation of single martensitic structures as identified by SEM. The hardness of treated surface evaluated by Vickers hardness test showed significant improvement nearly three time from 190 VHN before to 524 VHN after treatment. Furthermore, EDX confirmed that the formation of martensite layer occurred without altering its composition. The APS also produced uniform hardened layer up to 250 μm. The experiment has demonstrated that arc plasma process was successfully improved the mechanical properties of steel in relatively very short time.
Spontaneous formation of non-uniform double helices for elastic rods under torsion

NASA Astrophysics Data System (ADS)

Li, Hongyuan; Zhao, Shumin; Xia, Minggang; He, Siyu; Yang, Qifan; Yan, Yuming; Zhao, Hanqiao

2017-02-01

The spontaneous formation of double helices for filaments under torsion is common and significant. For example, the research on the supercoiling of DNA is helpful for understanding the replication and transcription of DNA. Similar double helices can appear in carbon nanotube yarns, cables, telephone wires and so forth. We noticed that non-uniform double helices can be produced due to the surface friction induced by the self-contact. Therefore an ideal model was presented to investigate the formation of double helices for elastic rods under torque. A general equilibrium condition which is valid for both the smooth surface and the rough surface situations is derived by using the variational method. By adding further constraints, the smooth and rough surface situations are investigated in detail respectively. Additionally, the model showed that the specific process of how to twist and slack the rod can determine the surface friction and hence influence the configuration of the double helix formed by rods with rough surfaces. Based on this principle, a method of manufacturing double helices with designed configurations was proposed and demonstrated. Finally, experiments were performed to verify the model and the results agreed well with the theory.
Integrated Experimental and Modeling Studies of Mineral Carbonation as a Mechanism for Permanent Carbon Sequestration in Mafic/Ultramafic Rocks

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

Wang, Zhengrong; Qiu, Lin; Zhang, Shuang

2014-09-30

A program of laboratory experiments, modeling and fieldwork was carried out at Yale University, University of Maryland, and University of Hawai‘i, under a DOE Award (DE-FE0004375) to study mineral carbonation as a practical method of geologic carbon sequestration. Mineral carbonation, also called carbon mineralization, is the conversion of (fluid) carbon dioxide into (solid) carbonate minerals in rocks, by way of naturally occurring chemical reactions. Mafic and ultramafic rocks, such as volcanic basalt, are natural candidates for carbonation, because the magnesium and iron silicate minerals in these rocks react with brines of dissolved carbon dioxide to form carbonate minerals. By trappingmore » carbon dioxide (CO 2) underground as a constituent of solid rock, carbonation of natural basalt formations would be a secure method of sequestering CO 2 captured at power plants in efforts to mitigate climate change. Geochemical laboratory experiments at Yale, carried out in a batch reactor at 200°C and 150 bar (15 MPa), studied carbonation of the olivine mineral forsterite (Mg 2SiO 4) reacting with CO 2 brines in the form of sodium bicarbonate (NaHCO 3) solutions. The main carbonation product in these reactions is the carbonate mineral magnesite (MgCO 3). A series of 32 runs varied the reaction time, the reactive surface area of olivine grains and powders, the concentration of the reacting fluid, and the starting ratio of fluid to olivine mass. These experiments were the first to study the rate of olivine carbonation under passive conditions approaching equilibrium. The results show that, in a simple batch reaction, olivine carbonation is fastest during the first 24 hours and then slows significantly and even reverses. A natural measure of the extent of carbonation is a quantity called the carbonation fraction, which compares the amount of carbon removed from solution, during a run, to the maximum amount that could have been removed if the olivine initially present had fully dissolved and the cations released had subsequently precipitated in carbonate minerals. The carbonation fractions observed in batch experiments with olivine grains and powders varied significantly, from less than 0.01 (1%) to more than 0.5 (50%). Over time, the carbonation fractions reached an upper limit after about 24 to 72 hours of reaction, then stayed constant or decreased. The peak Final Scientific/Technical Report DE-FE0004275 | Mineral Carbonation | 4 coincided with the appearance of secondary magnesium-bearing silicate minerals, whose formation competes for magnesium ions in solution and can even promote conditions that dissolve magnesite. The highest carbonation fractions resulted from experiments with low ratios of concentrated solution to olivine, during which amorphous silica spheres or meshes formed, instead of secondary silicate minerals. The highest carbonation fractions appear to result from competing effects. Precipitation of silica layers on olivine reduces the reactive surface area and, thus, the rate of olivine dissolution (which ultimately limits the carbonation rate), but these same silica layers can also inhibit the formation of secondary silicate minerals that consume magnesite formed in earlier stages of carbonation. Simulation of these experiments with simple geochemical models using the software program EQ3/6 reproduces the general trends observed—especially the results for the carbonation fraction in short-run experiments. Although further experimentation and better models are needed, this study nevertheless provides a framework for understanding the optimal conditions for sequestering carbon dioxide by reacting CO 2-bearing fluids with rocks containing olivine minerals. A series of experiments at the Rock Physics Laboratory at the University of Maryland studied the carbonation process during deformation of thermally cracked olivine-rich rock samples (dunite) saturated with CO 2 brines of varying compositions. A goal of these geomechanical experiments was to see if flow and deformation processes, which accompany natural carbonation reactions in underground settings, work to enhance or inhibit the reactions. The experiments involved hydrostatic compaction, followed by deformation at a constant rate of strain. Sample permeability was monitored during the reactions. Comparison of the samples’ volume changes to their axial strains (shortening) during deformation indicates that samples reacted with CO 2-saturated brines accommodate more axial compaction, before the onset of dilation (a swelling that precedes rock failure), than samples reacted with distilled water. Analyses of the reacted samples with scanning electron microscope (SEM) images indicate, first, that dissolution of olivine occurring in the initial stages of carbonation can provide pathways to fluid flow that sustain the reaction, and, second, that carbonate minerals precipitated along existing fractures in the rocks may serve as asperities, or roughness on a crack’s surface that restricts its closure. Final Scientific/Technical Report DE-FE0004275 | Mineral Carbonation | 5 In a related study undertaken by one of the principal investigators as a spin-off of the main project, a simple model of (magnesite) crystal growth in the pore space of basalts undergoing carbonation was developed. The model suggests that, under a carefully controlled program of CO 2 injection, carbonate mineral growth can harden the rock formation against earthquakes that might otherwise be induced by the injection of large fluid volumes (Yarushina and Bercovici, 2013). The overall conclusion of the research project is that mineral carbonation of underground mafic and ultramafic rock formations is a viable candidate for long-term sequestration of man-made carbon dioxide. No results obtained during the project indicate that the method is inherently intractable in its implementation; moreover, enormous volumes of basalt near Earth’s surface are candidate locations for large-scale injection programs. The geochemical experiments do indicate, however, that there will be significant engineering challenges in maintaining high rates of carbonation, by delaying the onset of chemical conditions that promote formation of secondary silicate minerals and, therefore, slow down, or even reverse, the carbonation process. It remains an open question as to whether carbonation processes can be sustained for many years in an engineered system operating on a large scale—a scale capable of accommodating millions of tons of CO 2 annually. The development of realistic theoretical models that can systematically describe the combined effects of reactive flow, precipitation and geomechanical deformation is a major barrier to further understanding of the practical viability of mineral carbonation as large-scale method of carbon sequestration.« less
Outbursts formation on low carbon and trip steel grades during hot-dip galvanisation

NASA Astrophysics Data System (ADS)

Petit, E. J.; Lamm, L.; Gilles, M.

2004-12-01

Low carbon and TRIP grade steels have been hot dip galvanised in order to study outbursts formation. Microstructure and texture of intermetallic phases have been observed after selective electrochemical etching by scanning electron microscopy. Potential versus time (chronopotentiometric) characteristics were recorded in order to monitor surface modifications. This combination of techniques enable to quantify and observe intermetallic phase one by one. The overall thickness of coating on both substrates are similar. However, microstructures of Fe-Zn intermetallic phases are very different on both grades. In particular, the V phase is dense on standard steel but develops a highly branched filament structure on TRIP steel. The transformation of V phase to d and G1 are limited on TRIP steel. Differences of texture provide clues for understanding mechanisms of formation of outbursts. They can account for the differences of mechanical properties and corrosion resistance. Silicon from the substrate influences the reactivity of TRIP steels due to capping and local reactions. La formation des outbursts a été étudiée sur un acier bas carbone et sur un acier TRIP galvanisés. Les épaisseurs des revêtements sont similaires. Néanmoins, les observations microscopiques et les érosions électrochimiques montrent que la répartition des phases intermétalliques et leurs microstructures diffèrent sensiblement en fonction de la nature du substrat. Ces différences expliquent les propriétés mécaniques et anticorrosions. L’encapsulation de la surface par les oxydes de silicium freine la transformation de la phase dzêta en delta et gamma sur l’acier TRIP.
Sedimentology and paleogeography of the Natih carbonate platform in the Oman mountains

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

Philip, J.M.; Borgomano, J.R.; Al Maskiry, S.

1993-09-01

Field study of the Natih Formation in the Jebel Akhdar and the Oman foothills allows us to establish a new stratigraphical and sedimentological model of this important hydrocarbon reservoir unit. Thanks to the study of rudists and the discovery of ammonites, a new precisions can be given to the chronostratigraphy of the Natih Formation. It was especially demonstrated by the presence of Hippuritids (rudists) that the top of the Natih Formation matches the Cenomanian/Turonian boundary and corresponds to either rudist-rich layers or hard grounds and condensed levels. The stratigraphical correlations between several outcrop section allow one to establish a conceptualmore » sequence stratigraphic model which can be compared to the subsurface by using the Natih subdivisions [open quotes]A to G.[close quotes] The recognition of sequence boundaries, maximum flooding surfaces, and system tracts might help to understand the seismo-stratigraphic expression of the Natih interval in the subsurface. Furthermore, this sequence stratigraphic model clearly illustrates the interfingering of the carbonate reservoir intervals and the organic-rich units (Fitri Mb) at the top of the Natih Formation. We also have identified a clear zonation from deeper marine to shallow-marine carbonate deposits, the most significant of which are the rudistid facies. They form banks, thickets, and biostroms and do not constitute anomalous build ups such as bioherms. Good leaching potentials generally are related to these rudistid facies, especially when they are very rich in skeletal aragonite from the Caprinids shells. Significant primary porosity may be related also to the Hippuritid skeletal cavities at the top of the Natih. Reservoir potentials can be enhanced if these Caprinid-rich intervals are related to exposure surfaces such as the top Natih E and the top Natih A.« less
Hurricanes and Climate: the U.S. CLIVAR Working Group on Hurricanes

NASA Technical Reports Server (NTRS)

Walsh, Kevin; Camargo, Suzana J.; Vecchi, Gabriel A.; Daloz, Anne Sophie; Elsner, James; Emanuel, Kerry; Horn, Michael; Lim, Young-Kwon; Roberts, Malcolm; Patricola, Christina;

2015-01-01

While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. The idealized experiments of the Hurricane Working Group of U.S. CLIVAR, combined with results from other model simulations, have suggested relationships between tropical cyclone formation rates and climate variables such as mid-tropospheric vertical velocity. Systematic differences are shown between experiments in which only sea surface temperature is increases versus experiments where only atmospheric carbon dioxide is increased, with the carbon dioxide experiments more likely to demonstrate a decrease in numbers. Further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols.

Tribolayer Formation in a Metal-on-Metal (MoM) Hip Joint: An Electrochemical Investigation

PubMed Central

Mathew, MT; Nagelli, C; Pourzal, R; Fischer, A; Laurent, MP; Jacobs, JJ; Wimmer, MA

2013-01-01

The demand for total hip replacement (THR) surgery is increasing in the younger population due to faster rehabilitation and more complete restoration of function. Up to 2009, metal-on-metal (MoM) hip joint bearings were a popular choice due to their design flexibility, post-operative stability and relatively low wear rates. The main wear mechanisms that occur along the bearing surface of MoM joints are tribochemical reactions that deposit a mixture of wear debris, metal ions and organic matrix of decomposed proteins known as a tribolayer. No in-depth electrochemical studies have been reported on the structure and characteristics of this tribolayer or about the parameters involved in its formation. In this study, we conducted an electrochemical investigation of different surfaces (bulk-like: control, nano-crystalline: new implant and tribolayer surface: retrieved implant) made out of two commonly used hip CoCrMo alloys (high-carbon and low-carbon). As per ASTM standard, cyclic polarization tests and electrochemical impedance spectroscopy tests were conducted. The results obtained from electrochemical parameters for different surfaces clearly indicated a reduction in corrosion for the tribolayer surface (Icorr: 0.76 μA/cm2). Further, polarization resistance (Rp:2.39±0.60MΩ/cm2) and capacitance (Cdl:15.20±0.75 μF/cm2) indicated variation in corrosion kinetics for the tribolayer surface, that attributed to its structure and stability in a simulated body environment. PMID:24099949
Preparation and Electrocatalytic Activity of Gold Nanoparticles Immobilized on the Surface of 4-Mercaptobenzoyl-Functionalized Multiwalled Carbon Nanotubes

DTIC Science & Technology

2010-12-20

thiolate -Au bonds,30 and so GNP/MB-MWCNT hybrids were synthesized using a modified literature procedure.31 The SEM images show sequential...4 The electrocatalytic stability of GNP/MB-MWCNT supposes to be originated from the formation of stable thiolate -Au bonds that prevent aggregation of...Moon, K.-S.; Wong, C. P. Carbon 2007, 45, 655–661. (19) Sandler, J.; Shaffer, M. S. P.; Prasse, T.; Bauhofer, W.; Schulte, K.; Windle, A. H. Polymer
Low density, resorcinol-formaldehyde aerogels

DOEpatents

Pekala, Richard W.

1991-01-01

The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer "Clusters". The covalent crosslinking of these "clusters" produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density.ltoreq.100 mg/cc; cell size .ltoreq.0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100.circle.. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.
Low density, resorcinol-formaldehyde aerogels

DOEpatents

Pekala, Richard W.

1989-01-01

The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer "clusters". The covalent crosslinking of these "clusters" produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density .ltoreq.100 mg/cc; cell size .ltoreq.0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100 .ANG.. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.

Low density, resorcinol-formaldehyde aerogels

DOEpatents

Pekala, R.W.

1989-10-10

The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer clusters. The covalent crosslinking of these clusters produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density [<=]100 mg/cc; cell size [<=]0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100 [angstrom]. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.
Synthesis of Stacked-Cup Carbon Nanotubes in a Metal Free Low Temperature System

NASA Technical Reports Server (NTRS)

Kimura, Yuki; Nuth, Joseph A.; Johnson, Natasha M.; Farmer, Kevin D.; Roberts, Kenneth P.; Hussaini, Syed R.

2011-01-01

Stacked-cup carbon nanotubes were formed by either Fischer-Tropsch type or Haber Bosch type reactions in a metal free system. Graphite particles were used as the catalyst. The samples were heated at 600 C in a gas mixture of CO 75 Torr, N2 75 Torr and H2 550 Torr for three days. Trans mission electron microscope analysis of the catalyst surface at the completion of the experiment recognized the growth of nanotubes. They were 10-50 nm in diameter and approximately 1 micrometer in length. They had a hollow channel of 5-20 nm in the center. The nanotubes may have grown on graphite surfaces by the CO disproportionation reaction and the surface tension of the carbon nucleus may have determined the diameter. Although, generally, the diameter of a carbon nanotube depends on the size of the cataly1ic particles, the diameter of the nanotubes on graphite particles was independent of the particle size and significantly confined within a narrow range compared with that produced using catalytic amorphous iron-silicate nanoparticles. Therefore, they must have an unknown formation process that is different than the generally accepted mechanism.
The Formation of Formaldehyde on Interstellar Carbonaceous Grain Analogs by O/H Atom Addition

NASA Astrophysics Data System (ADS)

Potapov, Alexey; Jäger, Cornelia; Henning, Thomas; Jonusas, Mindaugas; Krim, Lahouari

2017-09-01

An understanding of possible scenarios for the formation of astrophysically relevant molecules, particularly complex organic molecules, will bring us one step closer to the understanding of our astrochemical heritage. In this context, formaldehyde is an important molecule as a precursor of methanol, which in turn is a starting point for the formation of more complex organic species. In the present experiments, for the first time, following the synthesis of CO, formaldehyde has been produced on the surface of interstellar grain analogs, hydrogenated fullerene-like carbon grains, by O and H atom bombardment. The formation of H2CO is an indication for a possible methanol formation route in such systems.
Altering wettability to recover more oil from tight formations

DOE PAGES

Brady, Patrick V.; Bryan, Charles R.; Thyne, Geoffrey; ...

2016-06-03

We describe here a method for chemically modifying fracturing fluids and overflushes to chemically increase oil recovery from tight formations. Oil wetting of tight formations is usually controlled by adhesion to illite, kerogen, or both; adhesion to carbonate minerals may also play a role. Oil-illite adhesion is sensitive to salinity, dissolved divalent cation content, and pH. We measure oil-rock adhesion with middle Bakken formation oil and core to verify a surface complexation model of reservoir wettability. The agreement between the model and experiments suggests that wettability trends in tight formations can be quantitatively predicted and that fracturing fluid and overflushmore » compositions can be individually tailored to increase oil recovery.« less
Altering wettability to recover more oil from tight formations

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

Brady, Patrick V.; Bryan, Charles R.; Thyne, Geoffrey

We describe here a method for chemically modifying fracturing fluids and overflushes to chemically increase oil recovery from tight formations. Oil wetting of tight formations is usually controlled by adhesion to illite, kerogen, or both; adhesion to carbonate minerals may also play a role. Oil-illite adhesion is sensitive to salinity, dissolved divalent cation content, and pH. We measure oil-rock adhesion with middle Bakken formation oil and core to verify a surface complexation model of reservoir wettability. The agreement between the model and experiments suggests that wettability trends in tight formations can be quantitatively predicted and that fracturing fluid and overflushmore » compositions can be individually tailored to increase oil recovery.« less
Recognition and delineation of Paleokarst zones by the use of wireline logs in the bitumen-saturated upper Devonian Grosmont formation of Northeastern Alberta, Canada

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

Dembicki, E.A.; Machel, H.G.

1996-05-01

The Upper Devonian Grosmont Formation in northeastern Alberta, Canada, is a shallow-marine carbonate platform complex that was subaerially exposed for hundreds of millions of years between the Mississippian(?) and Cretaceous. During this lengthy exposure period, an extensive karst system developed that is characterized by an irregular erosional surface, meter-size (several feet) dissolution cavities, collapse breccias, sinkholes, paleosols, and fractures. The karsted Grosmont Formation, which contains giant reserves of bitumen, sub-crops beneath Cretaceous clastic sediments of the giant Athabasca tar sands deposit. The paleokarst in the Grosmont Formation can be recognized on wireline logs in relatively nonargillaceous carbonate intervals (<30 APImore » units on the gamma-ray log) as excursions of the caliper log, off-scale neutron-density porosity readings, and severe cycle skipping of the acoustic log. The paleokarst is more prevalent in the upper units of the Grosmont Formation, and the effects of karstification decrease toward stratigraphically older and deeper units. The paleokarst usually occurs within 35 m (115 ft) of the erosional surface. The reservoir properties of the Grosmont Formation (e.g., thickness, porosity, permeability, and seal effectiveness) are significantly influenced by karstification. Depending upon the location, karstification has either benefited or degraded the reservoir characteristics. Benefits include porosity values greater than 40% (up to 100% in caverns) and permeability values of 30,000 md in severely fractured intervals. Detrimental reservoir characteristics include erosion, porosity and permeability reduction, and seal ineffectiveness.« less
Hurricanes and Climate: The U.S. CLIVAR Working Group on Hurricanes

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

Walsh, Kevin J. E.; Camargo, Suzana J.; Vecchi, Gabriel A.

While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and to understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. This article summarizes published research from the idealized experiments of the Hurricane Working Group of U.S. Climate and Ocean: Variability, Predictability and Change (CLIVAR). This work, combined with results frommore » other model simulations, has strengthened relationships between tropical cyclone formation rates and climate variables such as midtropospheric vertical velocity, with decreased climatological vertical velocities leading to decreased tropical cyclone formation. Systematic differences are shown between experiments in which only sea surface temperature is increased compared with experiments where only atmospheric carbon dioxide is increased. Experiments where only carbon dioxide is increased are more likely to demonstrate a decrease in tropical cyclone numbers, similar to the decreases simulated by many climate models for a future, warmer climate. Experiments where the two effects are combined also show decreases in numbers, but these tend to be less for models that demonstrate a strong tropical cyclone response to increased sea surface temperatures. Lastly, further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols.« less
Hurricanes and Climate: The U.S. CLIVAR Working Group on Hurricanes

DOE PAGES

Walsh, Kevin J. E.; Camargo, Suzana J.; Vecchi, Gabriel A.; ...

2015-06-01

While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and to understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. This article summarizes published research from the idealized experiments of the Hurricane Working Group of U.S. Climate and Ocean: Variability, Predictability and Change (CLIVAR). This work, combined with results frommore » other model simulations, has strengthened relationships between tropical cyclone formation rates and climate variables such as midtropospheric vertical velocity, with decreased climatological vertical velocities leading to decreased tropical cyclone formation. Systematic differences are shown between experiments in which only sea surface temperature is increased compared with experiments where only atmospheric carbon dioxide is increased. Experiments where only carbon dioxide is increased are more likely to demonstrate a decrease in tropical cyclone numbers, similar to the decreases simulated by many climate models for a future, warmer climate. Experiments where the two effects are combined also show decreases in numbers, but these tend to be less for models that demonstrate a strong tropical cyclone response to increased sea surface temperatures. Lastly, further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols.« less
Forsterite Carbonation in Wet Supercritical CO2 and Sodium Citrate

NASA Astrophysics Data System (ADS)

Qiu, L.; Schaef, T.; Wang, Z.; Miller, Q.; McGrail, P.

2013-12-01

Lin Qiu1*, Herbert T. Schaef2, Zhengrong Wang1, Quin R.S. Miller3, BP McGrail2 1. Yale University, New Haven, CT, USA 2. Pacific Northwest National Laboratory, Richland, WA, USA 3. University of Wyoming, Laramie, WY, USA Geologic reservoirs for managing carbon emissions (mostly CO2) have expanded over the last 5 years to include unconventional formations including basalts and fractured shales. Recently, ~1000 metric tons of CO2 was injected into the Columbia River Basalt (CRB) in Eastern Washington as part of the Wallula Pilot Project, Big Sky Regional Carbon Partnership. Based on reservoir conditions, the injected CO2 is present as a supercritical fluid that dissolves into the formation water over time, and reacts with basalt components to form carbonate minerals. In this paper, we discuss mineral transformation reactions occurring when the forsterite (Mg2SiO4) is exposed to wet scCO2 in equilibrium with pure water and sodium citrate solutions. Forsterite was selected as it is an important olivine group mineral present in igneous and mafic rocks. Citrate was selected as it has been shown to enhance mineral dissolution and organic ligands are possible degradation products of the microbial communities present in the formational waters of the CRB. For the supercritical phase, transformation reactions were examined by in situ high pressure x-ray diffraction (HXRD) in the presence of supercritical carbon dioxide (scCO2) in contact with water and sodium citrate solutions at conditions relevant to carbon sequestration. Experimental results show close-to-complete dissolution of forsterite in contact with scCO2 equilibrated with pure water for 90 hours (90 bar and 50°C). Under these conditions, thin films of water coated the mineral surface, providing a mechanism for silicate dissolution and transport of cations necessary for carbonate formation. The primary crystalline component initially detected with in situ HXRD was the hydrated magnesium carbonate, nesquehonite [MgCO3-3H2O], which reached a maximum concentration of 85 wt% within ~30 hours of the experiment before decreasing below detection limit. Detection of the anhydrous magnesium carbonate, magnesite [MgCO3], first occurred at 15 hours, but increased dramatically over the remaining course of the experiment to levels near 90 wt%. In contrast, the presence of sodium citrate solutions in the reactor could eliminate the formation of nesquehonite. Based on the in situ HXRD results, nesquehonite did not form during experiments having sodium citrate solutions of 0.1 M, and the forsterite carbonation proceeded directly to magnesite at a concentration 90 wt% after 80 hours. Testing with less or more concentrated sodium citrate solutions (0.01 or 0.5 M), the nesquehonite formation was not attenuated or overall carbonation rates were decreased, respectively. These results indicate the possibility of organic compounds to dissolve into wet supercritical CO2 fluids and impact the formation of hydrated crystalline carbonates (often considered as transitional phases in carbonation routes to more stable minerals). Likely processes under consideration include the formation of organic complexes with metal cations in the thin water film. These results also have implications for ex situ carbonation processes and highlight the possibility of utilizing organic additives to enhance mineral dissolution prior to carbonation.
Experimental evidence for glycolaldehyde and ethylene glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions

NASA Astrophysics Data System (ADS)

Fedoseev, G.; Cuppen, H. M.; Ioppolo, S.; Lamberts, T.; Linnartz, H.

2015-04-01

This study focuses on the formation of two molecules of astrobiological importance - glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) - by surface hydrogenation of CO molecules. Our experiments aim at simulating the CO freeze-out stage in interstellar dark cloud regions, well before thermal and energetic processing become dominant. It is shown that along with the formation of H2CO and CH3OH - two well-established products of CO hydrogenation - also molecules with more than one carbon atom form. The key step in this process is believed to be the recombination of two HCO radicals followed by the formation of a C-C bond. The experimentally established reaction pathways are implemented into a continuous-time random-walk Monte Carlo model, previously used to model the formation of CH3OH on astrochemical time-scales, to study their impact on the solid-state abundances in dense interstellar clouds of glycolaldehyde and ethylene glycol.
Origin of ultramafic-hosted magnesite on Margarita Island, Venezuela

NASA Astrophysics Data System (ADS)

Abu-Jaber, N. S.; Kimberley, M. M.

1992-06-01

Ultramafic-hosted deposits of magnesite (MgCO3) have been studied on Margarita Island, Venezuela, to elucidate the source of carbon and conditions of formation for this type of ore. Petrographic, mineralogic, and δ18O data indicate that magnesite precipitated on Margarita in near-surface environments at low P and T. δ13C ranges from -9 to -16‰ PDB within the magnesite and -8 to -10‰ PDB within some calcite and dolomite elsewhere on the island. The isotopically light dolomite fills karst and the calcite occurs as stock-work veins which resemble the magnesite deposits. These carbon isotopic ratios are consistent with a deep-seated source rather than an overlying source from a zone of surficial weathering. However, there is not much enrichment of precious metals and no enrichment of heavy rare-earth elements, as would be expected if the carbon had migrated upward as aqueous carbonate ions. The carbon probably has risen as a gaseous mixture of CO2 and CH4 which partially dissolved in near-surface water before leaching cations and precipitating as magnesite and other carbonates. The process probably is ongoing, given regional exhalation of carbonaceous gases.
Facile formation of metallic bismuth/bismuth oxide heterojunction on porous carbon with enhanced photocatalytic activity.

PubMed

Zhang, Liping; Ghimire, Pramila; Phuriragpitikhon, Jenjira; Jiang, Baojiang; Gonçalves, Alexandre A S; Jaroniec, Mietek

2018-03-01

Bismuth/bismuth oxide heterojunction on porous carbon (Bi 0 /Bi 2 O 3 @C) was successfully prepared by a surfactant-assisted sol-gel method. This composite photocatalyst was fabricated by depositing Bi 2 O 3 and metallic bismuth nanoparticles (NPs) on porous carbon sheets. Bi NPs were created by in-situ reduction of Bi 2 O 3 with amorphous carbon. During the synthesis, bismuth and carbon precursors were mixed in different ratios, resulting in distinct amounts of metallic bismuth in the composites. The composites showed large specific surface area and pore volume as well as strong light absorption ability due to the existing carbon. In addition, the plasmonic bismuth NPs were found to behave as a noble metal, which is able to generate hot charge carriers under visible light irradiation. Photocatalytic performance of the Bi 0 /Bi 2 O 3 @C composites was investigated by degradation of methylene blue. It turned out that the composites showed much higher efficiency as compared to bare Bi 2 O 3 , which may be attributed to the synergistic effects of porous structures, improved optical absorption, and surface plasmon resonance. Copyright © 2017 Elsevier Inc. All rights reserved.
Microscopic Fuel Particles Produced by Self-Assembly of Actinide Nanoclusters on Carbon Nanomaterials

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

Na, Chongzheng

2016-10-17

Many consider further development of nuclear power to be essential for sustained development of society; however, the fuel forms currently used are expensive to recycle. In this project, we sought to create the knowledge and knowhow that are needed to produce nanocomposite materials by directly depositing uranium nanoclusters on networks of carbon- based nanomaterials. The objectives of the proposed work were to (1) determine the control of uranium nanocluster surface chemistry on nanocomposite formation, (2) determine the control of carbon nanomaterial surface chemistry on nanocomposite formation, and (3) develop protocols for synthesizing uranium-carbon nanomaterials. After examining a wide variety ofmore » synthetic methods, we show that synthesizing graphene-supported UO 2 nanocrystals in polar ethylene glycol compounds by polyol reduction under boiling reflux can enable the use of an inexpensive graphene precursor graphene oxide in the production of uranium-carbon nanocomposites in a one-pot process. We further show that triethylene glycol is the most suitable solvent for producing nanometer-sized UO 2 crystals compared to monoethylene glycol, diethylene glycol, and polyethylene glycol. Graphene-supported UO 2 nanocrystals synthesized with triethylene glycol show evidence of heteroepitaxy, which can be beneficial for facilitating heat transfer in nuclear fuel particles. Furthermore, we show that graphene-supported UO 2 nanocrystals synthesized by polyol reduction can be readily stored in alcohols, preventing oxidation from the prevalent oxygen in air. Together, these methods provide a facile approach for preparing and storing graphene-supported UO nanocrystals for further investigation and development under ambient conditions.« less
Effects of Pedogenic Fe Oxides on Soil Aggregate-Associated Carbon

NASA Astrophysics Data System (ADS)

Asefaw Berhe, A.; Jin, L.

2017-12-01

Carbon sequestration is intimately related to the soil structure, mainly soil aggregate dynamics. Carbon storage in soil aggregates has been recognized as an important carbon stabilization mechanism in soils. Organic matter and pedogenic Fe oxides are major binding agents that facilitate soil aggregate formation and stability. However, few studies have investigated how different forms of pedogenic Fe oxides can affect soil carbon distribution in different aggregate-size fractions. We investigated sequentially extracted pedogenic Fe oxides (in the order of organically complexed Fe extracted with sodium pyrophosphate, poorly-crystalline Fe oxides extracted with hydroxylamine hydrochloride, and crystalline Fe oxides extracted with dithionite hydrochloride) and determined the amount and nature of C in macroaggregates (2-0.25mm), microaggregates (0.25-0.053mm), and two silt and clay fractions (0.053-0.02mm, and <0.02mm) in Musick soil from Sierra Nevada mountain in California. We also determined how pedogenic Fe oxides affect soil carbon distribution along soil depth gradients. Findings of our study revealed that the proportion of organic matter complexed Fe decreased, but the proportion of crystalline Fe increased with increasing soil depths. Poorly crystalline Fe oxides (e.g. ferrihydrite) was identified as a major Fe oxide in surface soil, whereas crystalline Fe oxides (e.g. goethite) were found in deeper soil layers. These results suggest that high concentration of organic matter in surface soil suppressed Fe crystallization. Calcium cation was closely related to the pyrophosphate extractable Fe and C, which indicates that calcium may be a major cation that contribute to the organic matter complexed Fe and C pool. Increasing concentrations of extractable Fe and C with decreasing aggregate size fractions also suggests that Fe oxides play an important role in formation and stability of silt and clay fractions, and leading to further stabilization of carbon in soil. Our findings provide mechanistic understanding of how pedogenic Fe oxides play important role in carbon stabilization in different aggregate-size fractions in soil.
Biogeochemical Controls on Authigenic Carbonate Formation at the Chapopote "Asphalt Volcano", Bay of Campeche

NASA Astrophysics Data System (ADS)

Naehr, T. H.; Bohrmann, G.; Birgel, D.; MacDonald, I. R.

2007-12-01

Unusual hydrocarbon seep features, so-called "asphalt volcanoes" were explored in the Bay of Campeche, southern Gulf of Mexico, in the spring of 2006. Guided by data from satellite imagery that showed evidence for persistent oil seeps in the region, we investigated lava-like flows of solidified asphalt along the rim of a dissected salt dome at a water depth of about 3000 m. Fresh asphalt contains copious thermogenic gas and gas hydrate. Slabs of authigenic carbonate form surface crusts with layers of oil pooled beneath. Sediments are anoxic with H2S concentrations of 8 to 13 mM. Gas hydrate forms layers and mounds in the surface sediments. Alkalinity profiles show values from 29 to 35 mM, indicating oxidation of hydrocarbons by reduction of seawater sulfate. Molecular and isotopic compositions of gas hydrate and sediment headspace indicate moderately mature, thermogenic gas. Oily sediment extracts and asphalt pieces are composed of a degraded mixture of hydrocarbons with a peak at n-C30 and a few resolved C29 to C32 hopanes. Authigenic carbonate crusts from Chapopote are porous, aragonite-cemented mudstones. Peloidal textures are common, as are bivalve shells and at least two generations of aragonite-cemented intraclasts. The carbon isotopic composition of the authigenic aragonite cements varies between -28.6 ‰ and -17.9 ‰ (PDB), indicating a contribution of carbon from non-methane liquid hydrocarbons to the total pool of dissolved CO2. δ18O values of the carbonates range from +3.2 ‰ to +4.5 ‰ (PDB), suggesting aragonite formation under near-equilibrium conditions in the shallow subsurface. Molecular fossils extracted from one carbonate sample contain abundant 13C-depleted archeal lipids, derived from anaerobic methanotrophs, suggesting that organisms mediating the anaerobic oxidation of methane are closely associated with carbonate authigenesis at the Chapopote asphalt seep site.
ORCHIDEE-CNP: Site-Scale Evaluation against Observations from a Soil Formation Chronosequence in Hawaii

NASA Astrophysics Data System (ADS)

Goll, D. S.; Vuichard, N.; Maignan, F.; Jornet-Puig, A.; Sardans, J.; Peng, S.; Sun, Y.; Kvakić, M.; Guimberteau, M.; Guenet, B.; Zaehle, S.; Penuelas, J.; Jannssens, I.; Ciais, P.

2017-12-01

Land surface models rarely incorporate the terrestrial phosphorus cycle and its interactions with the carbon cycle, despite the extensive scientific debate about the importance of nitrogen and phosphorus supply for future land carbon uptake. We describe a representation of the terrestrial phosphorus cycle for the land surface model ORCHIDEE, and evaluate it with data from nutrient manipulation experiments along a soil formation chronosequence in Hawaii. ORCHIDEE accounts for influence of nutritional state of vegetation on tissue nutrient concentrations, photosynthesis, plant growth, biomass allocation, biochemical (phosphatase-mediated) mineralization and biological nitrogen fixation. Changes in nutrient content (quality) of litter affect the carbon use efficiency of decomposition and in return the nutrient availability to vegetation. The model explicitly accounts for root zone depletion of phosphorus as a function of root phosphorus uptake and phosphorus transport from soil to the root surface. The model captures the observed differences in the foliage stoichiometry of vegetation between an early (300yr) and a late stage (4.1 Myr) of soil development. The contrasting sensitivities of net primary productivity to the addition of either nitrogen, phosphorus or both among sites are in general reproduced by the model. As observed, the model simulates a preferential stimulation of leaf level productivity when nitrogen stress is alleviated, while leaf level productivity and leaf area index are stimulated equally when phosphorus stress is alleviated. The nutrient use efficiencies in the model are lower as observed primarily due to biases in the nutrient content and turnover of woody biomass.
Facile synthesis of efficient visible active C-doped TiO{sub 2} nanomaterials with high surface area for the simultaneous removal of phenol and Cr(VI)

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

Mani, A.Daya; Reddy, P.Manoj Kumar; Srinivaas, M.

2015-01-15

Highlights: • Facile synthesis of C-doped TiO{sub 2} nanomaterials with high surface area. • Utilization of citric acid and ascorbic acid as fuels based on evolution of gases. • Enhanced visible activity for the oxidation of phenol and reduction of Cr(VI). • Study of simultaneous oxidation of phenol and reduction of Cr(VI) for the first time. • Proposed plausible mechanism for the simultaneous removal of phenol and Cr(VI). - Abstract: A single step synthesis of carbon doped TiO{sub 2} (anatase) nanomaterials have been reported by using combustion synthesis using ascorbic acid and citric acid fuels. X-ray diffraction studies indicated themore » formation of nanosized anatase titania, whereas, transmission electron microscopy confirmed the formation of nanosized TiO{sub 2} anatase. The carbon doping into TiO{sub 2} matrix was identified by X-ray photoelectron spectroscopy, whereas, thermogravimetric study quantified the carbon doping. Diffuse reflectance UV–vis spectra indicated the band gap of less than 3 eV, a prerequisite for the photocatalytic activity under visible light irradiation. The N{sub 2} adsorption studies revealed the high surface area (upto 290 m{sup 2}/g) of the synthesized photocatalysts. Typical photocatalytic activity data indicated that the simultaneous removal of Cr(VI) and phenol is advantageous than degradation of the individual pollutants.« less
Nano-Welding of Multi-Walled Carbon Nanotubes on Silicon and Silica Surface by Laser Irradiation

PubMed Central

Yuan, Yanping; Chen, Jimin

2016-01-01

In this study, a continuous fiber laser (1064 nm wavelength, 30 W/cm2) is used to irradiate multi-walled carbon nanotubes (MWCNTs) on different substrate surfaces. Effects of substrates on nano-welding of MWCNTs are investigated by scanning electron microscope (SEM). For MWCNTs on silica, after 3 s irradiation, nanoscale welding with good quality can be achieved due to breaking C–C bonds and formation of new graphene layers. While welding junctions can be formed until 10 s for the MWCNTs on silicon, the difference of irradiation time to achieve welding is attributed to the difference of thermal conductivity for silica and silicon. As the irradiation time is prolonged up to 12.5 s, most of the MWCNTs are welded to a silicon substrate, which leads to their frameworks of tube walls on the silicon surface. This is because the accumulation of absorbed energy makes the temperature rise. Then chemical reactions among silicon, carbon and nitrogen occur. New chemical bonds of Si–N and Si–C achieve the welding between the MWCNTs and silicon. Vibration modes of Si3N4 appear at peaks of 363 cm−1 and 663 cm−1. There are vibration modes of SiC at peaks of 618 cm−1, 779 cm−1 and 973 cm−1. The experimental observation proves chemical reactions and the formation of Si3N4 and SiC by laser irradiation. PMID:28344293
Hyper-localized carbon mineralization in diffusion-limited basalt fractures

NASA Astrophysics Data System (ADS)

Menefee, A. H.; Giammar, D.; Ellis, B. R.

2017-12-01

Basalt formations could enable secure carbon sequestration through mineral trapping. CO2 injection acidifies formation brines and drives dissolution of the host rock, which releases divalent metal cations that combine with dissolved carbonate ions to form stable carbonate minerals. Here, a series of high-pressure flow-through experiments was conducted to evaluate how transport limitations and geochemical gradients drive microscale carbonation reactions in fractured basalts. To isolate advection- and diffusion-controlled zones, surfaces of saw-cut basalt cores were milled to create one primary flow channel adjoined by four dead-end fracture pathways. In the first experiment, a representative basalt brine (6.3 mM NaHCO3) equilibrated with CO2 (100ºC, 10 MPa) was injected at 1 mL/h under 20 MPa confining stress. The second experiment was conducted under the same physical conditions but [NaHCO3] was elevated to 640 mM, and in the third, temperature was also raised to 150ºC. Effluent chemistry was monitored via ICP-MS to infer dissolution trends and calibrate reactive transport models. Reacted cores were characterized using x-ray computed tomography (xCT), optical microscopy, scanning electron microscopy, and Raman spectroscopy. Carbonation occurred in all experiments but increased in experiments with higher alkalinity and higher temperature. At low [NaHCO3], secondary precipitate coatings formed distinct reaction fronts that varied with distance into dead-end fractures. Reactive transport modeling demonstrated that these reactions fronts were due to sharp gradients in pH and dissolved inorganic carbon. Carbonation was restricted to transport-limited vugs and pores between the confined core surfaces and was highly localized on reactive primary mineral grains (e.g. pyroxene) that contributed major divalent cations. Increasing [NaHCO3] by two orders of magnitude significantly enhanced carbonation and promoted Mg and Fe uptake into carbonates. While xCT scans revealed clays filling the advective path, no permeability changes were measured. Our coupled experiment-modeling approach further elucidates the geochemical conditions controlling carbonation reactions and extends unique microstructural observations to implications for long-term CO2 mineralization in basalt reservoirs.
The Impact of Sonication on the Surface Quality of Single-Walled Carbon Nanotubes.

PubMed

Koh, Byumseok; Cheng, Wei

2015-08-01

Sonication process is regularly adopted for dispersing single-walled carbon nanotubes (SWCNTs) in an aqueous medium. This can be achieved by either covalent functionalization of SWCNTs with strong acid or by noncovalent functionalization using dispersants that adsorb onto the surface of SWCNTs during dispersion. Because the dispersion process is usually performed using sonication, unintentional free radical formation during sonication process may induce covalent modification of SWCNT surface. Herein, we have systematically investigated the status of SWCNT surface modification under various sonication conditions using Raman spectroscopy. Comparing ID /IG (Raman intensities between D and G bands) ratio of SWCNTs under various sonication conditions suggests that typical sonication conditions (1-6 h bath sonication with sonication power between 3 and 80 W) in aqueous media do not induce covalent modification of SWCNT surface. In addition, we confirm that SWCNT dispersion with single-stranded DNA (ssDNA) involves noncovalent adsorption of ssDNA onto the surface of SWCNTs, but not covalent linkage between ssDNA and SWCNT surface. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Transglutaminase-induced crosslinking of gelatin-calcium carbonate composite films.

PubMed

Wang, Yuemeng; Liu, Anjun; Ye, Ran; Wang, Wenhang; Li, Xin

2015-01-01

The effects of transglutaminase (TGase) on the rheological profiles and interactions of gelatin-calcium carbonate solutions were studied. In addition, mechanical properties, water vapour permeability and microstructures of gelatin-calcium carbonate films were also investigated and compared. Fluorescence data suggested that the interaction of TGase and gelation-calcium carbonate belonged to a static quenching mechanism, and merely one binding site between TGase and gelatin-calcium carbonate was identified. Moreover, differential scanning calorimetry (DSC), the mechanical properties and the water vapour permeability studies revealed that TGase favoured the strong intramolecular polymerisation of the peptides in gelatin. The microstructures of the surfaces and cross sections in gelatin-calcium carbonate films were shown by scanning electron microscope (SEM) micrographs. The results of the fourier transform infrared spectroscopy (FTIR) indicated that TGase caused conformational changes in the proteins films. Therefore, TGase successfully facilitated the formation of gelatin-calcium carbonate composite films. Copyright © 2014 Elsevier Ltd. All rights reserved.
Study on the formation of graphene by ion implantation on Cu, Ni and CuNi alloy

NASA Astrophysics Data System (ADS)

Kim, Janghyuk; Kim, Hong-Yeol; Jeon, Jeong Heum; An, Sungjoo; Hong, Jongwon; Kim, Jihyun

2018-09-01

This study identifies the details for direct synthesis of graphene by carbon ion implantation on Cu, Ni and CuNi alloy. Firstly, diffusion and concentration of carbon atoms in Cu and Ni are estimated separately. The concentrations of carbon atoms near the surfaces of Cu and Ni after carbon ion implantation and subsequent thermal annealing were correlated with the number of atoms and with the coverage or thickness of graphene. Systematic experiments showed that the Cu has higher carbon diffusivity and graphene coverage than Ni but higher temperatures and longer annealing times are required to synthesize graphene, similar to those in chemical vapor deposition method. The CuNi system shows better graphene coverage and quality than that on a single metal catalyst even after a short annealing time, as it has larger carbon diffusivity and lower carbon solubility than Ni and shows lower activation energy than Cu.
Dissolution-Assisted Pattern Formation During Olivine Carbonation

NASA Astrophysics Data System (ADS)

Lisabeth, Harrison; Zhu, Wenlu; Xing, Tiange; De Andrade, Vincent

2017-10-01

Olivine and pyroxene-bearing rocks in the oceanic crust react with hydrothermal fluids producing changes in the physical characteristics and behaviors of the altered rocks. Notably, these reactions tend to increase solid volume, reducing pore volume, permeability, and available reactive surface area, yet entirely hydrated and/or carbonated rocks are commonly observed in the field. We investigate the evolution of porosity and permeability of fractured dunites reacted with CO2-rich solutions in laboratory experiments. The alteration of crack surfaces changes the mechanical and transport properties of the bulk samples. Analysis of three-dimensional microstructural data shows that although precipitation of secondary minerals causes the total porosity of the sample to decrease, an interconnected network of porosity is maintained through channelized dissolution and coupled carbonate precipitation. The observed microstructure appears to be the result of chemo-mechanical coupling, which may provide a mechanism of porosity maintenance without the need to invoke reaction-driven cracking.
Investigation of the H2S poisoning process for sensing composite material based on carbon nanotubes and metal oxides

PubMed Central

Duan, Yichen; Pirolli, Laurent; Teplyakov, Andrew V.

2016-01-01

The poisoning of H2S sensing material based on the mixture of acid-treated carbon nanotubes, CuO and SnO2 was investigated by exposing the material to high doses of H2S (1% in volume) and following the changes spectroscopically. The presence of metal sulfides (CuS and SnS2), sulfates and thiols was confirmed on the surface of this material as the result of H2S poisoning. Further study revealed that leaving this material in air for extended period of time led to reoxidation of metal sulfides back to metal oxides. The formation of thiols and sulfates directly on carbon nanotubes is not reversible under these conditions; however, the extent of the overall surface reaction in this case is substantially lower than that for the composite material. PMID:27812240
Dissolution-Assisted Pattern Formation During Olivine Carbonation

DOE PAGES

Lisabeth, Harrison; Zhu, Wenlu; Xing, Tiange; ...

2017-08-31

Olivine and pyroxene bearing rocks in the oceanic crust react with hydrothermal fluids producing changes in the physical characteristics and behaviors of the altered rocks. Notably, these reactions tend to increase solid volume, reducing pore volume, permeability and available reactive surface area; yet, entirely hydrated and/or carbonated rocks are commonly observed in the field. We investigate the evolution of porosity and permeability of fractured dunites reacted with CO 2-rich solutions in laboratory experiments. The alteration of crack surfaces changes the mechanical and transport properties of the bulk samples. Analysis of three-dimensional microstructural data shows that although precipitation of secondary mineralsmore » causes the total porosity of the sample to decrease, an interconnected network of porosity is maintained through channelized dissolution and coupled carbonate precipitation. Lastly, the observed microstructure appears to be the result of chemo-mechanical coupling, which may provide a mechanism of porosity maintenance without the need to invoke reaction-driven cracking.« less
Vitreous carbon mask substrate for X-ray lithography

DOEpatents

Aigeldinger, Georg [Livermore, CA; Skala, Dawn M [Fremont, CA; Griffiths, Stewart K [Livermore, CA; Talin, Albert Alec [Livermore, CA; Losey, Matthew W [Livermore, CA; Yang, Chu-Yeu Peter [Dublin, CA

2009-10-27

The present invention is directed to the use of vitreous carbon as a substrate material for providing masks for X-ray lithography. The new substrate also enables a small thickness of the mask absorber used to pattern the resist, and this enables improved mask accuracy. An alternative embodiment comprised the use of vitreous carbon as a LIGA substrate wherein the VC wafer blank is etched in a reactive ion plasma after which an X-ray resist is bonded. This surface treatment provides a surface enabling good adhesion of the X-ray photoresist and subsequent nucleation and adhesion of the electrodeposited metal for LIGA mold-making while the VC substrate practically eliminates secondary radiation effects that lead to delamination of the X-ray resist form the substrate, the loss of isolated resist features, and the formation of a resist layer adjacent to the substrate that is insoluble in the developer.
Investigation of the H2S poisoning process for sensing composite material based on carbon nanotubes and metal oxides.

PubMed

Duan, Yichen; Pirolli, Laurent; Teplyakov, Andrew V

2016-11-01

The poisoning of H 2 S sensing material based on the mixture of acid-treated carbon nanotubes, CuO and SnO 2 was investigated by exposing the material to high doses of H 2 S (1% in volume) and following the changes spectroscopically. The presence of metal sulfides (CuS and SnS 2 ), sulfates and thiols was confirmed on the surface of this material as the result of H 2 S poisoning. Further study revealed that leaving this material in air for extended period of time led to reoxidation of metal sulfides back to metal oxides. The formation of thiols and sulfates directly on carbon nanotubes is not reversible under these conditions; however, the extent of the overall surface reaction in this case is substantially lower than that for the composite material.
THE POTENTIAL INFLUENCES OF FACE VELOCITY ON PM ARTIFACT LOSSES FOR EXPOSURE SAMPLERS USING TEFLON FILTER COLLECTION SUBSTRATES

EPA Science Inventory

The influences of artifact formations and losses on Particulate Matter (PM) sampler collection surfaces are well documented, especially for nitrates (Hering and Cass, 1999), and SVOC's (McDow, 1999), and more recently for speciated carbon (Turpin and Lim, 2001). These artifact...
Dissolved organic carbon concentrations and compositions, and trihalomethane formation potentials in waters from agricultural peat soils, Sacramento-San Joaquin Delta, California; implications for drinking-water quality

USGS Publications Warehouse

Fujii, Roger; Ranalli, Anthony J.; Aiken, George R.; Bergamaschi, Brian A.

1998-01-01

Water exported from the Sacramento-San Joaquin River delta (Delta) is an important drinking-water source for more than 20 million people in California. At times, this water contains elevated concentrations of dissolved organic carbon and bromide, and exceeds the U.S. Environmental Protection Agency's maximum contaminant level for trihalomethanes of 0.100 milligrams per liter if chlorinated for drinking water. About 20 to 50 percent of the trihalomethane precursors to Delta waters originates from drainage water from peat soils on Delta islands. This report elucidates some of the factors and processes controlling and affecting the concentration and quality of dissolved organic carbon released from peat soils and relates the propensity of dissolved organic carbon to form trihalomethanes to its chemical composition.Soil water was sampled from near-surface, oxidized, well-decomposed peat soil (upper soil zone) and deeper, reduced, fibrous peat soil (lower soil zone) from one agricultural field in the west central Delta over 1 year. Concentrations of dissolved organic carbon in the upper soil zone were highly variable, with median concentrations ranging from 46.4 to 83.2 milligrams per liter. Concentrations of dissolved organic carbon in samples from the lower soil zone were much less variable and generally slightly higher than samples from the upper soil zone, with median concentrations ranging from 49.3 to 82.3 milligrams per liter. The dissolved organic carbon from the lower soil zone had significantly higher aromaticity (as measured by specific ultraviolet absorbance) and contained significantly greater amounts of aromatic humic substances (as measured by XAD resin fractionation and carbon-13 nuclear magnetic resonance analysis of XAD isolates) than the dissolved organic carbon from the upper soil zone. These results support the conclusion that more aromatic forms of dissolved organic carbon are produced under anaerobic conditions compared to aerobic conditions. Dissolved organic carbon concentration, trihalomethane formation potential, and ultraviolet absorbance were all highly correlated, showing that trihalomethane precursors increased with increasing dissolved organic carbon and ultraviolet absorbance for whole water samples. Contrary to the generally accepted conceptual model for trihalomethane formation that assumes that aromatic forms of carbon are primary precursors to trihalomethanes, results from this study indicate that dissolved organic carbon aromaticity appears unrelated to trihalomethane formation on a carbon-normalized basis. Thus, dissolved organic carbon aromaticity alone cannot fully explain or predict trihalomethane precursor content, and further investigation of aromatic and nonaromatic forms of carbon will be needed to better identify trihalomethane precursors.
Formation of porous networks on polymeric surfaces by femtosecond laser micromachining

NASA Astrophysics Data System (ADS)

Assaf, Youssef; Kietzig, Anne-Marie

2017-02-01

In this study, porous network structures were successfully created on various polymer surfaces by femtosecond laser micromachining. Six different polymers (poly(tetrafluoroethylene) (PTFE), poly(methyl methacrylate) (PMMA), high density poly(ethylene) (HDPE), poly(lactic acid) (PLA), poly(carbonate) (PC), and poly(ethylene terephthalate) (PET)) were machined at different fluences and pulse numbers, and the resulting structures were identified and compared by lacunarity analysis. At low fluence and pulse numbers, porous networks were confirmed to form on all materials except PLA. Furthermore, all networks except for PMMA were shown to bundle up at high fluence and pulse numbers. In the case of PC, a complete breakdown of the structure at such conditions was observed. Operation slightly above threshold fluence and at low pulse numbers is therefore recommended for porous network formation. Finally, the thickness over which these structures formed was measured and compared to two intrinsic material dependent parameters: the single pulse threshold fluence and the incubation coefficient. Results indicate that a lower threshold fluence at operating conditions favors material removal over structure formation and is hence detrimental to porous network formation. Favorable machining conditions and material-dependent parameters for the formation of porous networks on polymer surfaces have thus been identified.
Changes in the formation of AAIW and storage of anthropogenic carbon in the South Atlantic in the 1990s and 2000s

NASA Astrophysics Data System (ADS)

Kieke, Dagmar; Steinfeldt, Reiner; Rhein, Monika; Huhn, Oliver

2017-04-01

Antarctic Intermediate Water (AAIW) is the most abundant intermediate water mass originating in the southern hemisphere and is easily recognized by its low salinity tongue located at depths between 500 m to 1500 m. As AAIW contributes to the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), knowledge regarding its formation, associated variability, and its vulnerability with respect to the uptake of anthropogenic carbon (Cant) is of high relevance in a world facing increasing atmospheric Cant concentrations and global warming with direct impact on the AMOC strength and variability. We have used transient tracer data (chlorofluorocarbon, CFC) covering the period 1982-2005 to calculate CFC inventories and to derive rates of AAIW formation in the South Atlantic. Tracer data collected prior to 1995 have been referenced to 1990 and data from 1995 onwards to the year 2000. This allows to assess the changes in formation between these two periods. As a major result, we find a significant decrease in the formation of AAIW in the South Atlantic. Based on the tracer data and applying the transit time distribution (TTD) method, we have furthermore estimated changes in the inventories and storage of Cant within the AAIW. We find that the reduction of AAIW formation has severe implications for the uptake of Cant within this layer in the South Atlantic. Our results are discussed in the light of long-term changes regarding the strength of the surface forcing over the western South Atlantic and variations in the phase of the Southern Annular Mode (SAM). A decrease in the AAIW formation can partly be attributed to a weakening in the surface forcing that correlates to variations in the SAM.
Maleimide-activated aryl diazonium salts for electrode surface functionalization with biological and redox-active molecules.

PubMed

Harper, Jason C; Polsky, Ronen; Wheeler, David R; Brozik, Susan M

2008-03-04

A versatile and simple method is introduced for formation of maleimide-functionalized surfaces using maleimide-activated aryl diazonium salts. We show for the first time electrodeposition of N-(4-diazophenyl)maleimide tetrafluoroborate on gold and carbon electrodes which was characterized via voltammetry, grazing angle FTIR, and ellipsometry. Electrodeposition conditions were used to control film thickness and yielded submonolayer-to-multilayer grafting. The resulting phenylmaleimide surfaces served as effective coupling agents for electrode functionalization with ferrocene and the redox-active protein cytochrome c. The utility of phenylmaleimide diazonium toward formation of a diazonium-activated conjugate, followed by direct electrodeposition of the diazonium-modified DNA onto the electrode surface, was also demonstrated. Effective electron transfer was obtained between immobilized molecules and the electrodes. This novel application of N-phenylmaleimide diazonium may facilitate the development of bioelectronic devices including biofuel cells, biosensors, and DNA and protein microarrays.
Reducing Ice Adhesion on Nonsmooth Metallic Surfaces: Wettability and Topography Effects.

PubMed

Ling, Edwin Jee Yang; Uong, Victor; Renault-Crispo, Jean-Sébastien; Kietzig, Anne-Marie; Servio, Phillip

2016-04-06

The effects of ice formation and accretion on external surfaces range from being mildly annoying to potentially life-threatening. Ice-shedding materials, which lower the adhesion strength of ice to its surface, have recently received renewed research attention as a means to circumvent the problem of icing. In this work, we investigate how surface wettability and surface topography influence the ice adhesion strength on three different surfaces: (i) superhydrophobic laser-inscribed square pillars on copper, (ii) stainless steel 316 Dutch-weave meshes, and (iii) multiwalled carbon nanotube-covered steel meshes. The finest stainless steel mesh displayed the best performance with a 93% decrease in ice adhesion relative to polished stainless steel, while the superhydrophobic square pillars exhibited an increase in ice adhesion by up to 67% relative to polished copper. Comparisons of dynamic contact angles revealed little correlation between surface wettability and ice adhesion. On the other hand, by considering the ice formation process and the fracture mechanics at the ice-substrate interface, we found that two competing mechanisms governing ice adhesion strength arise on nonplanar surfaces: (i) mechanical interlocking of the ice within the surface features that enhances adhesion, and (ii) formation of microcracks that act as interfacial stress concentrators, which reduce adhesion. Our analysis provides insight toward new approaches for the design of ice-releasing materials through the use of surface topographies that promote interfacial crack propagation.
Wollastonite Carbonation in Water-Bearing Supercritical CO2: Effects of Particle Size.

PubMed

Min, Yujia; Li, Qingyun; Voltolini, Marco; Kneafsey, Timothy; Jun, Young-Shin

2017-11-07

The performance of geologic CO 2 sequestration (GCS) can be affected by CO 2 mineralization and changes in the permeability of geologic formations resulting from interactions between water-bearing supercritical CO 2 (scCO 2 ) and silicates in reservoir rocks. However, without an understanding of the size effects, the findings in previous studies using nanometer- or micrometer-size particles cannot be applied to the bulk rock in field sites. In this study, we report the effects of particle sizes on the carbonation of wollastonite (CaSiO 3 ) at 60 °C and 100 bar in water-bearing scCO 2 . After normalization by the surface area, the thickness of the reacted wollastonite layer on the surfaces was independent of particle sizes. After 20 h, the reaction was not controlled by the kinetics of surface reactions but by the diffusion of water-bearing scCO 2 across the product layer on wollastonite surfaces. Among the products of reaction, amorphous silica, rather than calcite, covered the wollastonite surface and acted as a diffusion barrier to water-bearing scCO 2 . The product layer was not highly porous, with a specific surface area 10 times smaller than that of the altered amorphous silica formed at the wollastonite surface in aqueous solution. These findings can help us evaluate the impacts of mineral carbonation in water-bearing scCO 2 .
Late Precambrian-Cambrian sediments of Huqf group, Sultanate of Oman

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

Gorin, G.E.; Racz, L.G.; Walter, M.R.

1982-12-01

The Huqf Group is the oldest known sedimentary sequence overlying crystalline basement in the Sultanate of Oman. It crops out on a broad regional high, the Huqf Axis, which forms a dominating structural element on the southeastern edge of the Arabian peninsula. Subsurface and outcrop evidence within and outside of Oman suggests that the sediments of the Huqf Group lie within the age span of late Precambrian to Early-Middle Cambrian. The Huqf Group is subdivided into five formations corresponding to an alternation of clastics (Abu Mahara and Shuram Formations) and carbonates (Khufai and Buah Formations) deposited in essentially shallow marinemore » to supratidal (or fluviatile) conditions and terminated by an evaporitic sequence (Ara Formation). Evaporites are absent on the Huqf Axis, but they are thickly developed to the west over a large part of southern and central Oman, where they acted as the major structure former of most of Oman's fields, and even locally pierced up to the surface. Regional correlations suggest that the predominantly carbonate-evaporitic facies of the Huqf Group was widely distributed in late Precambrian-Early Cambrian time: the Huqf basin is tentatively considered part of a belt of evaporitic basins and intervening carbonate platforms, which stretched across the Pangea landmass from the Indian subcontinent (Salt Range of Pakistan) through South Yemen, Oman, and Saudi Arabia into the gulf states and Iran (Hormuz Series and carbonate platform north of the Zagros).« less
Impact of Desulfovibrio alaskensis biofilms on corrosion behaviour of carbon steel in marine environment.

PubMed

Wikieł, Agata J; Datsenko, Iaryna; Vera, Mario; Sand, Wolfgang

2014-06-01

Sulfate reducing prokaryotes are associated with the steel deterioration. They build heterogeneous biofilms, capable of accelerating corrosion processes. In this study metabolic activity and the biofilm development of Desulfovibrio alaskensis were correlated to electrochemical response of carbon steel surface. In the exponential growth phase sulfide concentration reached its maximum of about 10mM. This phenomenon was responsible for the parallel increase in the corrosion potential (Ecorr) up to -720mV (vs. SCE). Subsequently, during the intensive biofilm formation and development another Ecorr peak (-710mV vs. SCE) occurred. Decrease in Ecorr was registered during the biofilm maturation and kept stable, being 20mV lower than in the control. While carbon steel was protected from the microbial attachment and exposed to metabolic products, only one potential maximum (-730mV vs. SCE) was recorded. Here Ecorr variations coincided with sulfide concentration changes and kept at 120mV lower vs. the control. Weight loss examinations revealed corrosion rates, which did not exceed 0.05mm/y. Confocal microscopy suggested the importance of extracellular proteins in the biofilm formation. Above 150 proteins were detected in the EPS matrix. Surface effects of biofilm and metabolic products were visualised, revealing the role of attached microorganisms in the localised corrosion. © 2013.
Methane Decomposition and Carbon Growth on Y2O3, Yttria-Stabilized Zirconia, and ZrO2

PubMed Central

2014-01-01

Carbon deposition following thermal methane decomposition under dry and steam reforming conditions has been studied on yttria-stabilized zirconia (YSZ), Y2O3, and ZrO2 by a range of different chemical, structural, and spectroscopic characterization techniques, including aberration-corrected electron microscopy, Raman spectroscopy, electric impedance spectroscopy, and volumetric adsorption techniques. Concordantly, all experimental techniques reveal the formation of a conducting layer of disordered nanocrystalline graphite covering the individual grains of the respective pure oxides after treatment in dry methane at temperatures T ≥ 1000 K. In addition, treatment under moist methane conditions causes additional formation of carbon-nanotube-like architectures by partial detachment of the graphite layers. All experiments show that during carbon growth, no substantial reduction of any of the oxides takes place. Our results, therefore, indicate that these pure oxides can act as efficient nonmetallic substrates for methane-induced growth of different carbon species with potentially important implications regarding their use in solid oxide fuel cells. Moreover, by comparing the three oxides, we could elucidate differences in the methane reactivities of the respective SOFC-relevant purely oxidic surfaces under typical SOFC operation conditions without the presence of metallic constituents. PMID:24587591
Formation of continuous activated carbon fibers for barrier fabrics

NASA Astrophysics Data System (ADS)

Liang, Ying

1997-08-01

Commercial protective suits made of active carbon granules or nonwoven fabrics are heavy, have low moisture vapor transport rate, and are uncomfortable. Inherent problems due to construction of barrier fabrics lead to severe heat stress when worn for even short time in warm environments. One proposed method to eliminate these problems is to facilitate the construction of a fabric made of continuous activated carbon fibers (CACF). This study is directed toward investigating the possibility of developing CAFC from two precursors: aramid and fibrillated PAN fiber. It was shown in this study that Kevlar-29 fibers could be quickly carbonized and activated to CACF with high adsorptivity and relatively low weight loss. CACF with high surface area (>500 msp2/g) and reasonable tenacity (≈1g/denier) were successfully prepared from Kevlar fibers through a three-step process: pretreatment, carbonization, and activation. X-ray diffraction, Fourier Transform Infrared Spectroscopy (FTIR), and thermal analysis were conducted to understand the evolution of physical and chemical properties during pretreatment. The influence of temperature, heating rate, and pyrolysis environment on the thermal behavior was determined by DSC and TGA/DTA and used as an indicator for optimizing the pyrolysis conditions. Surface analysis by nitrogen isotherms indicated that the resultant fibers had micropores and mesopores on the surface of CACF. This was also inferred by studies on the surface morphology through Scanning Electron Microscopy (SEM) and Scanning Tunneling Microscopy (STM). An investigation of the surface chemical structure by X-ray photoelectron spectroscopy (XPS) before and after activation and elemental analysis confirmed that adsorption of Kevlar based CACF mainly arises due to the physisorption instead of chemisorption. A multistep stabilization along with carbonization and activation was used to prepare active carbon fiber from fibrillated PAN fiber. The resultant fiber retained its fibrillar structure and provided a very high surface area, up to 1400 msp2/g, but was brittle. The characterization of the thermal behavior, mechanical properties, and surface structure of the pyrolyzed fiber at each processing step was also carried out by using various techniques, such as DSC and TGA, Instron, and SEM. These studies provide directions for preparation of CACF from novel precursors.
Influence of culture media on the physical and chemical properties of Ag-TiCN coatings

NASA Astrophysics Data System (ADS)

Carvalho, I.; Escobar Galindo, R.; Henriques, M.; Palacio, C.; Carvalho, S.

2014-08-01

The aim of this study was to verify the possible physical and chemical changes that may occur on the surface of Ag-TiCN coatings after exposure to the culture media used in microbiological and cytotoxic assays, respectively tryptic soy broth (TSB) and Dulbecco's modified eagle's medium (DMEM). After sample immersion for 24 h in the media, analyses were performed by glow discharge optical emission spectroscopy discharge radiation (GDOES), Rutherford backscattering spectroscopy (RBS) and x-ray photoelectron spectroscopy (XPS). The results of GDOES profile, RBS and XPS spectra, of samples immersed in TSB, demonstrated the formation of a thin layer of carbon, oxygen and nitrogen that could be due to the presence of proteins in TSB. After 24 h of immersion in DMEM, the results showed the formation of a thin layer of calcium phosphates on the surface, since the coatings displayed a highly oxidized surface in which calcium and phosphorus were detected. All these results suggested that the formation of a layer on the coating surface prevented the release of silver ions in concentrations that allow antibacterial activity.
Studying Antarctic Ordinary Chondrite (OC) and Miller Range (MIL) Nakhlite Meteorites to Assess Carbonate Formation on Earth and Mars

NASA Astrophysics Data System (ADS)

Evans, Michael Ellis

Carbonates are found in meteorites collected from Antarctica. The stable isotope composition of these carbonates records their formation environment on either Earth or Mars. The first research objective of this dissertation is to characterize the delta18O and delta 13C values of terrestrial carbonates formed on Ordinary Chondrites (OCs) collected in regions near known martian meteorites. The second objective is to characterize the delta18O and delta13C values of martian carbonates from Nakhlites collected from the Miller Range (MIL). The third objective is to assess environmental changes on Mars since the Noachian period. The OCs selected had no pre-terrestrial carbonates so any carbonates detected are presumed terrestrial in origin. The study methodology is stepped extraction of CO2 created from phosphoric acid reaction with meteorite carbonate. Stable isotope results show that two distinct terrestrial carbonate species (Ca-rich and Fe/Mg-rich) formed in Antarctica on OCs from a thin-film of meltwater containing dissolved CO2. Carbon isotope data suggests the terrestrial carbonates formed in equilibrium with atmospheric CO2 delta 13C = -7.5‰ at >15°C. The wide variation in delta 18O suggests the carbonates did not form in equilibrium with meteoric water alone, but possibly formed from an exchange of oxygen isotopes in both water and dissolved CO2. Antarctica provides a model for carbonate formation in a low water/rock ratio, near 0°C environment like modern Mars. Nakhlite parent basalt formed on Mars 1.3 billion years ago and the meteorites were ejected by a single impact approximately 11 million years ago. They traveled thru space before eventually falling to the Earth surface 10,000-40,000 years ago. Nakhlite samples for this research were all collected from the Miller Range (MIL) in Antarctica. The Nakhlite stable isotope results show two carbonate species (Ca-rich and Fe/Mg-rich) with a range of delta18O values that are similar to the terrestrial OC carbonates. The Nakhlite carbonates have distinctly different, heavier delta13C values from a presumed martian carbon reservoir. These carbonates cannot form in equilibrium at 15°C with the modern Mars atmospheric CO2 (measured by the Curiosity rover) delta13C = 46‰, but may reflect kinetic carbonate formation from a high pH fluid. Alternatively, the Nakhlite carbonates may have formed with a lighter, early Amazonian atmosphere of delta 13C ≈ 30‰. Assuming the martian carbonates formed in a thin-film environment like the OC terrestrial carbonates, an oxygen mixing model predicts early Amazonian martian meteoric water delta18O = -30‰.

Controlling the set of carbon-fiber embedded cement with electric current

DOEpatents

Mattus, Alfred J.

2004-06-15

A method for promoting cement or concrete set on demand for concrete that has been chemically retarded by adding carbon fiber to the concrete, which enables it to become electrically conductive, sodium tartrate retardant, and copper sulfate which forms a copper tartrate complex in alkaline concrete mixes. Using electricity, the concrete mix anodically converts the retarding tartrate to an insoluble polyester polymer. The carbon fibers act as a continuous anode surface with a counter electrode wire embedded in the mix. Upon energizing, the retarding effect of tartrate is defeated by formation of the polyester polymer through condensation esterification thereby allowing the normal set to proceed unimpeded.
Ethylene decomposition over Pt(100): A mechanism study from first principle calculation

NASA Astrophysics Data System (ADS)

Wang, Yuchun; Dong, Xiuqin; Yu, Yingzhe; Zhang, Minhua

2016-12-01

First principle based density functional theory was used to calculate the complete step-by-step decomposition network of ethylene (C2H4) over Pt(100) as a model for understanding the carbon deposition of olefin hydrocarbon over transition metal surface. We discussed the structural and energetic properties of all the Csbnd H and Csbnd C bond cleavage reactions in order to fully understand the formation pathway of carbon monomer. It is easier for Csbnd H bond cleavage reactions to take place, as the activation barrier of these reactions is relatively lower than that of Csbnd C bond cleavage as a whole. However, vinyl (CH2CH) is likely to be the precursor of Csbnd C bond scission, as the activation barrier of Csbnd C bond cleavage reaction of CH2CH is much lower than that of CH2CH dehydrogenation and the reaction is exothermic by 0.15 eV. CC was another form of depositional carbon on Pt(100), as it is easy to form but difficult to decompose. Finally we proposed six possible routes of carbon monomer formation.
The effect of fluoroethylene carbonate additive content on the formation of the solid-electrolyte interphase and capacity fade of Li-ion full-cell employing nano Si-graphene composite anodes

NASA Astrophysics Data System (ADS)

Bordes, Arnaud; Eom, KwangSup; Fuller, Thomas F.

2014-07-01

When fluoroethylene carbonate (FEC) is added to the ethylene carbonate (EC)-diethyl carbonate (DEC) electrolyte, the capacity and cyclability of full-cells employing Si-graphene anode and lithium nickel cobalt aluminum oxide cathode (NCA) cathode are improved due to formation of a thin (30-50 nm) SEI layer with low ionic resistance (∼2 ohm cm2) on the surface of Si-graphene anode. These properties are confirmed with electrochemical impedance spectroscopy and a cross-sectional image analysis using Focused Ion Beam (FIB)-SEM. Approximately 5 wt.% FEC in EC:DEC (1:1 wt.%) shows the highest capacity and most stability. This high capacity and low capacity fade is attributed to a more stable SEI layer containing less CH2OCO2Li, Li2CO3 and LiF compounds, which consume cyclable Li. Additionally, a greater amount of polycarbonate (PC), which is known to form a more robust passivation layer, thus reducing further reduction of electrolyte, is confirmed with X-ray photoelectron spectroscopy (XPS).
Morphological transformations of BNCO nanomaterials: Role of intermediates

NASA Astrophysics Data System (ADS)

Wang, B. B.; Qu, X. L.; Zhu, M. K.; Levchenko, I.; Baranov, O.; Zhong, X. X.; Xu, S.; Ostrikov, K.

2018-06-01

Highly controllable structural transformation of various doped carbon and boron nitride nanomaterials have been achieved with the perspective of their application in microelectronics, optoelectronics, energy devices and catalytic reactions. Specifically, the syntheses of one-dimensional (1D) boron and nitrogen co-doped tube-like carbon nanorods and 2D vertical carbon and oxygen co-doped boron nitride nanosheets on silicon coated with gold films in N2-H2 plasma was demonstrated. During the synthesis of nanomaterials, boron carbide was used as carbon and boron sources. The results of characterizations by scanning and transmission electron microscopes, as well as micro-Raman and X-ray photoelectron spectroscopes indicate that the formation of different nanomaterials relates to the growth temperature and quantity of boron carbide. Specifically, 1D tube-like carbon nanorods doped with boron and nitrogen are formed at ∼910 °C using a small quantity of boron carbide, while 2D vertical boron nitride nanosheets doped with carbon and oxygen are grown at ∼870 °C using a large quantity of boron carbide. These studies indicate that the behaviors of a reactive intermediate product B2O3 on surfaces of Au nanoparticles play an important role in the formation of different nanomaterials, i.e., whether the B2O3 molecules deposited on Au nanoparticles are desorbed mainly determines the formation of different nanomaterials. The formation of 2D vertical carbon and oxygen co-doped boron nitride nanosheets is related to the high growth rate of edges of nanosheets. Furthermore, the photoluminescence (PL) properties of 1D boron and nitrogen co-doped tube-like carbon nanorods and 2D vertical carbon and oxygen co-doped boron nitride nanosheets were studied at room temperature. The PL results show that all the nanomaterials generate the ultraviolet, blue, green and red PL bands, but the 2D vertical carbon and oxygen co-doped boron nitride nanosheets emit more and stronger PL bands than the 1D boron and nitrogen co-doped tube-like carbon nanorods. The significant differences in the PL properties can be attributed to different carbon structures in these nanomaterials. These achievements can be used to synthesize and control the structures of nanomaterials and contribute to the development of the next generation optoelectronic nanodevices based on 1D and 2D nanomaterials.
Gallium(III) adsorption on carbonates and oxides: X-ray absorption fine structure spectroscopy study and surface complexation modeling.

PubMed

Pokrovsky, O S; Pokrovski, G S; Schott, J

2004-11-15

Adsorption of Ga on calcite, magnesite, amorphous silica, and manganese oxide as a function of pH and gallium concentration in solution was studied using a batch adsorption technique. Adsorbed complexes of Ga on calcite, magnesite, and delta-MnO2 were further characterized using XAFS spectroscopy. At high surface loadings from supersaturated solutions, Ga is likely to form a polymeric network at the surface (edge- and corner-sharing octahedra). At low surface loadings, Ga presents as isolated octahedra, probably attached to the Me-O sites on the surface, and coordinated by water molecules and hydroxide groups at 1.90-1.94 A. At pH>6, Ga therefore changes its coordination from 4 to 6 when adsorbing from solution (Ga(OH)(-)4(aq)) onto metal surface sites (MeOGa(OH)n(H2O)2-n(5-n), Me = Ca, Mg, or Mn, and n=1 and 2 for carbonate minerals and MnO2, respectively). Because the EXAFS is not capable of seeing hydrogen atoms, the protonation of surface complexes was determined by fitting the experimental pH-dependent Ga adsorption edge. A surface complexation model which assumes the constant capacitance of the electric double layer (CCM) and postulates the formation of positively charged, neutral and negatively charged surface complexes for carbonates, manganese oxide and silica, respectively, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Ga concentration.
Carbon Textile Decorated with Pseudocapacitive VC/Vx Oy for High-Performance Flexible Supercapacitors.

PubMed

Van Lam, Do; Shim, Hyung Cheoul; Kim, Jae-Hyun; Lee, Hak-Joo; Lee, Seung-Mo

2017-11-01

It is demonstrated that, via V 2 O 5 coating by low temperature atomic layer deposition and subsequent pyrolysis, ubiquitous cotton textile can readily turn into high-surface-area carbon textile fully decorated with pseudocapacitive V x O y /VC widely usable as electrodes of high-performance supercapacitor. It is found that carbothermic reduction of V 2 O 5 (C + V 2 O 5 → C' + VC + CO/CO 2 (g)) leads to chemical/mechanical activation of carbon textile, thereby producing high-surface-area conductive carbon textile. In addition, sequential phase transformation and carbide formation (V 2 O 5 → V x O y → VC) occurred by carbothermic reduction trigger decoration of the carbon textile with redox-active V x O y /VC. Thanks to the synergistic effect of electrical double layer and pseudocapacitance, the supercapacitors made of the hybrid carbon textile exhibit far better energy density (over 30-fold increase) with excellent cycling stability than the carbon textile simply undergone pyrolysis. The method can open up a promising and facile way to synthesize hybrid electrode materials for electrochemical energy storages possessing advantages of both electrical double layer and pseudocapacitive material. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Highly crystalline carbon dots from fresh tomato: UV emission and quantum confinement.

PubMed

Liu, Weijian; Li, Chun; Sun, Xiaobo; Pan, Wei; Yu, Guifeng; Wang, Jinping

2017-12-01

In this article, fresh tomatoes are explored as a low-cost source to prepare high-performance carbon dots by using microwave-assisted pyrolysis. Given that amino groups might act as nucleophiles for cleaving covalent bridging ester or ether in the crosslinked macromolecules in the biomass bulk, ethylenediamine (EDA) and urea with amino groups were applied as nucleophiles to modulate the chemical composites of the carbon nanoparticles in order to tune their fluorescence emission and enhance their quantum yields. Very interestingly, the carbon dots synthesized in the presence of urea had a highly crystalline nature, a low-degree amorphous surface and were smaller than 5 nm. Moreover, the doped N contributed to the formation of a cyclic form of core that resulted in a strong electron-withdrawing ability within the conjugated C plane. Therefore, this type of carbon dot exhibited marked quantum confinement, with the maximum fluorescence peak located in the UV region. Carbon nanoparticles greater than 20 nm in size, prepared using pristine fresh tomato and in the presence of EDA, emitted surface state controlled fluorescence. Additionally, carbon nanoparticles synthesized using fresh tomato pulp in the presence of EDA and urea were explored for bioimaging of plant pathogenic fungi and the detection of vanillin.
Highly crystalline carbon dots from fresh tomato: UV emission and quantum confinement

NASA Astrophysics Data System (ADS)

Liu, Weijian; Li, Chun; Sun, Xiaobo; Pan, Wei; Yu, Guifeng; Wang, Jinping

2017-12-01

In this article, fresh tomatoes are explored as a low-cost source to prepare high-performance carbon dots by using microwave-assisted pyrolysis. Given that amino groups might act as nucleophiles for cleaving covalent bridging ester or ether in the crosslinked macromolecules in the biomass bulk, ethylenediamine (EDA) and urea with amino groups were applied as nucleophiles to modulate the chemical composites of the carbon nanoparticles in order to tune their fluorescence emission and enhance their quantum yields. Very interestingly, the carbon dots synthesized in the presence of urea had a highly crystalline nature, a low-degree amorphous surface and were smaller than 5 nm. Moreover, the doped N contributed to the formation of a cyclic form of core that resulted in a strong electron-withdrawing ability within the conjugated C plane. Therefore, this type of carbon dot exhibited marked quantum confinement, with the maximum fluorescence peak located in the UV region. Carbon nanoparticles greater than 20 nm in size, prepared using pristine fresh tomato and in the presence of EDA, emitted surface state controlled fluorescence. Additionally, carbon nanoparticles synthesized using fresh tomato pulp in the presence of EDA and urea were explored for bioimaging of plant pathogenic fungi and the detection of vanillin.
Surface bioactivity modification of titanium by CO 2 plasma treatment and induction of hydroxyapatite: In vitro and in vivo studies

NASA Astrophysics Data System (ADS)

Hu, Xixue; Shen, Hong; Shuai, Kegang; Zhang, Enwei; Bai, Yanjie; Cheng, Yan; Xiong, Xiaoling; Wang, Shenguo; Fang, Jing; Wei, Shicheng

2011-01-01

Since metallic biomaterials used for orthopedic and dental implants possess a paucity of reactive functional groups, bioactivity modification of these materials is challenging. In the present work, the titanium discs and rods were treated with carbon dioxide plasma and then incubated in a modified simulated body fluid 1.5SBF to obtain a hydroxyapatite layer. Surface hydrophilicity of samples, changes of surface chemistry, surface morphologies of samples, and structural analysis of formed hydroxyapatite were investigated by contact angle to water, X-ray photoelectron spectrometer (XPS), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The results demonstrated that hydrophilicity of titanium surface was improved and hydroxyl groups increased after modification with carbon dioxide plasma treatment. The hydroxyl groups on the surface of titanium were the richest after carbon dioxide plasma treatment under the condition of 20 W for less than 30 s. The hydroxyapatite formability of titanium surface was enhanced by carbon dioxide plasma pretreatment, which was attributed to the surface chemistry. MC3T3-E1 cell as a model cell was cultured on the Ti, CPT-Ti and CPT/SBF-Ti discs in vitro, and the results of the morphology and differentiation of the cell showed that CPT/SBF-Ti was the highest bioactive. The relative parameters of the new bone around the Ti and CPT/SBF-Ti rods including bone mineral density (BMD), a ratio of bone volume to total volume (BV/TV), trabecular thickness (Tb.Th.) and trabecular number (Tb.N.) were analyzed by a micro-computed tomography (micro-CT) after 4-, 8- and 12-week implantation periods in vivo. The results indicated that the CPT/SBF-Ti was more advantageous for new bone formation.
The role of iron-sulfides on cycling of organic carbon in the St Lawrence River system: Evidence of sulfur-promoted carbon sequestration?

NASA Astrophysics Data System (ADS)

Balind, K.; Barber, A.; Gélinas, Y.

2017-12-01

The biogeochemical cycle of sulfur is intimately linked with that of carbon, as well as with that of iron through the formation of iron-sulfur complexes. Iron-sulfide minerals such as mackinawite (FeS) and greigite (Fe3S4) form below the oxic/anoxic redox boundary in marine and lacustrine sediments and soils. Reactive iron species, abundant in surface sediments, can undergo reductive dissolution leading to the formation of soluble Fe(II) which can then precipitate in the form of iron sulfur species. While sedimentary iron-oxides have been thoroughly explored in terms of their ability to sorb and sequester organic carbon (OC) (Lalonde et al.; 2012), the role of FeS in the long-term preservation of OC remains undefined. In this study, we present depth profiles for carbon, iron, and sulfur in the aqueous-phase, along with data from sequential extractions of sulfur speciation in the solid-phase collected from sediment cores from the St Lawrence River and estuarine system, demonstrating the transition from fresh to saltwater sediments. Additionally, we present synthetic iron sulfur sorption experiments using both model and natural organic molecules in order to assess the importance of FeS in sedimentary carbon storage.
Biochar from Coffee Residues: A New Promising Sorbent

NASA Astrophysics Data System (ADS)

Fotopoulou, Kalliopi; Karapanagioti, Hrissi; Manariotis, Ioannis

2014-05-01

Biochar is a carbon-rich material produced by heating biomass in an oxygen-limited environment. Biochar is mainly used as an additive to soils to sequester carbon and improve soil fertility as well as a sorbent for environmental remediation processes. Surface properties such as point of zero charge, surface area and pore volume, surface topography, surface functional groups and acid-base behavior are important factors, which affect sorption efficiency. Understanding the surface alteration of biochars increases our understanding of the pollutant-sorbent interaction. The objective of the present study was to characterize the surface properties of biochar produced, and to investigate the effect of thermal treatment conditions on key characteristics that affect sorptive properties. The espresso coffee residue was obtained after the coffee was brewed through espresso machines in coffee shops. The coffee residue was dried and kept in an oven at 50oC until its pyrolysis at 850oC. Pyrolysis with different coffee mass and containers were tested in order to find optimum biochar characteristics. Detailed characterization techniques were carried out to determine the properties of the produced biochar. The surface area, the pore volume, and the average pore size of the biochars were determined using gas (N2) adsorption-desorption cycles using the Brunauer, Emmett, and Teller (BET) equation. Open surface area and micropore volume were determined using the t-plot method and the Harkins & Jura equation. Total organic carbon was also determined because it is an important factor that affects sorption. The results were compared with the corresponding properties of activated carbons. The biochar produced exhibited a wide range of surface area from 21 to 770 m2/g and open surface area from 21 to 65 m2/g. It is obvious that the surface area results from the formation of pores. Actually it was calculated that up to 90% of the porosity is due to the micropores. More specifically the average size of the pores for the high surface area biochars was 32 A. Finally, the organic carbon content of the produced biochar ranged from 45 to 75%.
Thermodynamics of a phase transition of silicon nanoparticles at the annealing and carbonization of porous silicon

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

Nagornov, Yu. S., E-mail: Nagornov.Yuri@gmail.com

2015-12-15

The formation of SiC nanocrystals of the cubic modification in the process of high-temperature carbonization of porous silicon has been analyzed. A thermodynamic model has been proposed to describe the experimental data obtained by atomic-force microscopy, Raman scattering, spectral analysis, Auger spectroscopy, and X-ray diffraction spectroscopy. It has been shown that the surface energy of silicon nanoparticles and quantum filaments is released in the process of annealing and carbonization. The Monte Carlo simulation has shown that the released energy makes it possible to overcome the nucleation barrier and to form SiC nanocrystals. The processes of laser annealing and electron irradiationmore » of carbonized porous silicon have been analyzed.« less
Investigating the Basis of Biogenic Calcium Carbonate Formation from an Amorphous Precursor: Nature of the Transformation to Calcite on Hydroxyl Functionalized Surfaces

NASA Astrophysics Data System (ADS)

Wang, D.; Lee, J. R.; Talley, C. E.; Murphy, K. E.; Han, T. Y.; Deyoreo, J. J.; Dove, P. M.

2006-12-01

Calcium carbonate biominerals are particularly significant because of their direct role in regulating the global carbon cycle, as well as their ubiquitous occurrence across earth environments. Biogenic carbonates are further distinguished by their broad phlyogenetic distribution; hence it has been suggested that unrelated eukaryotes must have used similar biochemical strategies to control mineralization. Recent studies have shown that an amorphous calcium carbonate (ACC) phase potentially plays a key role in the initial formation of carbonate minerals and in "shaping" them into complex morphologies widely seen in biominerals. Echinoderms, mollusks, and possibly many other organisms use ACC as a precursor phase that is first nucleated in cellularly controlled environments such as vesicles and subsequently transforms into a fully crystalline material. Recent studies on sea urchin embryos have shown that during transformation ACC develops short range that resembles calcite before fully crystallizing and serve as inspiration for our studies in synthetic systems. Self-assembled monolayers (SAM) on gold and silver have been used as simple model systems that approximate biological surfaces. Many studies have shown that thiol monolayers with hydroxyl termination stabilize a transitory ACC film that with prolonged exposure to aqueous solution transforms into calcite nucleated on {104} faces. Using Near Edge X-ray Absorption Fine Structure (NEXAFS) we studied SAM/mineral interactions with well ordered mercaptophenol monolayers showed that when these films are first exposed to calcium carbonate solutions, they become disordered and remain so after subsequent deposition of an ACC over-layer. Yet calcite nucleates and grows from the surface bound ACC with predominantly {104} orientation, which suggests a dynamic structural relationship between the SAMs and the mineral phase. While the monolayer/mineral phase interaction has been characterized, the mechanism for nucleating calcite from ACC on these SAMs remains unknown and is the objective of this research. Our preliminary observations of the transforming ACC film with in situ Raman spectroscopy have shown a strengthening of the symmetric mode of the carbonate ion suggesting ordering of the ACC. To fully determine the structural evolution of the mineral phase we will use both Raman and Extended X-Ray Absorption Fine Structure (EXAFS) measurements, coupled with morphological analysis using SEM.
Nano- to Formation-Scale Estimates of Mineral-Specific Reactive Surface Area

NASA Astrophysics Data System (ADS)

Cole, D. R.; Swift, A.; Sheets, J.; Anovitz, L. M.

2017-12-01

Predictions of changes in fluid composition, coupled with the evolution of the solid matrix, include the generation and testing of reactive transport models. However, translating a heterogeneous natural system into physical and chemical model parameters, including the critical but poorly-constrained metric of fluid-accessible surface area, continues to challenge Earth scientists. Studies of carbon storage capacity, permeability, rock strain due to mineral dissolution and precipitation, or the prediction of rock evolution through diagenesis and weathering each consider macroscale outcomes of processes that often are critically impacted by rock surface geometry at the nanoscale. The approach taken here is to consider the whole vertical extent of a saline reservoir and then to address two questions. First, what is the accessible surface area for each major mineral, and for all adjacent pore sizes from <2 nm on up, within each major lithofacies in that formation? Second, with the formation thus divided into units of analysis, parameterized, and placed into geologic context, what constraints can be placed on reactive surface area as a function of mineral composition? A complex sandstone covering a substantial fraction of the quartz-K-feldspar-illite ternary is selected and mineral-specific surface area quantified using neutron scattering, nitrogen and mercury porosimetry, multi-signal high-resolution mineral mapping, and other techniques. For neutron scattering, scale-specific pore geometries enable more accurate translation of volume into surface area. By applying this workflow to all end-member lithologies of this reservoir formation, equations and maps of surface area as a function of position on a quartz-feldspar-clay ternary plot are developed for each major mineral. Results from this work therefore advance our ability to parameterize models not just for the particular formation studied, but for similar geologic units as well.
Spectral identification of chemisorbed CO2 and application to Mars analog materials

NASA Technical Reports Server (NTRS)

Zent, A. P.; Roush, T. L.

1992-01-01

The goal of this work is to identify the spectral signature of chemisorbed CO2, to test the efficacy of carbonate formation on Mars-analog materials via CO2 chemisorption, and to identify the surface-chemical characteristics of good chemisorbents, with the intent of assessing the possible geochemical importance of CO2 chemisorption as a quasipermanent CO2 sink in the Martian environment. Our approach is to search for infrared spectral bands that result from chemisorption of CO2 molecules onto chemical reagents and Mars-analog materials, and to identify the salient differences in adsorbents that favor strong, permanent CO2 chemisorption. The total amount of CO2 in the early Martian atmosphere, and consequent surface temperatures, are unknown. A CO2 greenhouse may not have been an adequate mechanism under any circumstances; however, it if were, then most of that CO2 must still be in the near-surface environment; no escape mechanism that could remove it after the decline of channeling has been identified. The only plausible reservoir is carbonate, and there are various remote sensing techniques that can be used to search for it. We are investigating CO2 chemisorption as a permanent CO2 sink, and to aid in interpretation of remotely sensed IR spectra of Mars. A common effect reported in CO2 adsorption studies is the formation of a layer of carbonate or bicarbonate anions on adsorbents that have OH- groups available on their surfaces. Inorganic hydroxyls occur on phyllosilicates, amorphous silicates, metal oxides and hydroxides; it is the most abundant and reactive surface functional group on the surfaces of terrestrial silicates. The process responsible for the reaction is chemisorption. Chemisorption is distinguished from physical adsorption in that there is a transfer of electrons between species, and the formation of a chemical bond. The heat of chemisorption is typically of the same order as heats of chemical reaction (i.e., a few hundred to a few thousand kJ/mole), as opposed to heats of physical adsorption (a few kJ per mole). Chemisorption is an activated process that is promoted by an increase in temperature - quite the opposite of physical adsorption. Chemisorption is not reversible in the sense that physical adsorption is.
Influence of surface vacancy defects on the carburisation of Fe 110 surface by carbon monoxide

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

Chakrabarty, Aurab, E-mail: aurab.chakrabarty@qatar.tamu.edu; Bouhali, Othmane; Mousseau, Normand

Adsorption and dissociation of gaseous carbon monoxide (CO) on metal surfaces is one of the most frequently occurring processes of carburisation, known as primary initiator of metal dusting corrosion. Among the various factors that can significantly influence the carburisation process are the intrinsic surface defects such as single surface vacancies occurring at high concentrations due to their low formation energy. Intuitively, adsorption and dissociation barriers of CO are expected to be lowered in the vicinity of a surface vacancy, due to the strong attractive interaction between the vacancy and the C atom. Here the adsorption energies and dissociation pathways ofmore » CO on clean and defective Fe 110 surface are explored by means of density functional theory. Interestingly, we find that the O adatom, resulting from the CO dissociation, is unstable in the electron-deficit neighbourhood of the vacancy due to its large electron affinity, and raises the barrier of the carburisation pathway. Still, a full comparative study between the clean surface and the vacancy-defected surface reveals that the complete process of carburisation, starting from adsorption to subsurface diffusion of C, is more favourable in the vicinity of a vacancy defect.« less
Multi-Scale Investigation of the Formation and Breakdown of Passive Films on Carbon Steel Rebar in Concrete

NASA Astrophysics Data System (ADS)

Ghods, Pouria

The multi-scale investigation presented in this thesis was carried out to understand better the mechanisms of passivation and chloride-induced depassivation of carbon steel reinforcement in concrete. The study consisted of electrochemical experiments (electrochemical impedance spectroscopy, linear polarization resistance, free corrosion potential, anodic polarization), microscopic examinations (scanning electron microscopy, transmission electron microscopy, selected area diffraction, convergent beam electron diffraction), numerical modeling (finite element method), and spectroscopic studies (x-ray photoelectron, energy dispersed x-ray, electron energy loss). Electrochemical and microscopic studies showed that the composition of the pore solution and the surface conditions of the rebar affect the passivity and depassivation of carbon steel in concrete. It was demonstrated that crevices between mill scale and steel may become potential sites for depassivation and pit nucleation. The numerical investigation that was carried out to test this hypothesis confirmed that the ratio of chloride to hydroxide concentrations, Cl-/OH-, in crevices increased to levels higher than that of the bulk pore solution, making crevices more vulnerable to depassivation. Therefore, it was concluded that the variability associated with reported chloride thresholds might be attributed, at least in part, to the variability in mill scale properties resulting from the variability in manufacturing. The nano-scale microscopic and spectroscopic studies indicated the formation of 4-10 nm-thick passive oxide films on carbon steel in simulated concrete pore solutions, and these films consisted of two layers separated with an indistinct border. The inner layer was mainly composed of protective Fe2+-rich oxides that are in epitaxial relationship with the underlying steel surface; while the outer layer mostly consisted of (possibly porous) Fe3+-rich oxides, through which chlorides can penetrate. It was proposed that, in the presence of chlorides, Fe+2-rich oxides in the inner layer transform into Fe+3-rich oxides and potentially become un-protective. Although how this transformation occurs is still subject of future research, there are evidences showing that the process most likely leads to the formation of local anodic and cathodic sites on the steel surface.
Co-precipitation of dissolved organic matter by calcium carbonate in Pyramid Lake, Nevada

USGS Publications Warehouse

Leenheer, Jerry A.; Reddy, Michael M.

2008-01-01

Our previous research has demonstrated that dissolved organic matter (DOM) influences calcium carbonate mineral formation in surface and ground water. To better understand DOM mediation of carbonate precipitation and DOM co-precipitation and/or incorporation with carbonate minerals, we characterized the content and speciation of DOM in carbonate minerals and in the lake water of Pyramid Lake, Nevada, USA. A 400-gram block of precipitated calcium carbonate from the Pyramid Lake shore was dissolved in 8 liters of 10% acetic acid. Particulate matter not dissolved by acetic acid was removed by centrifugation. DOM from the carbonate rock was fractionated into nine portions using evaporation, dialysis, resin adsorption, and selective precipitations to remove acetic acid and inorganic constituents. The calcium carbonate rock contained 0.23% DOM by weight. This DOM was enriched in polycarboxylic proteinaceous acids and hydroxy-acids in comparison with the present lake water. DOM in lake water was composed of aliphatic, alicyclic polycarboxylic acids. These compound classes were found in previous studies to inhibit calcium carbonate precipitation. DOM fractions from the carbonate rock were 14C-age dated at about 3,100 to 3,500 years before present. The mechanism of DOM co-precipitation and/or physical incorporation in the calcium carbonate is believed to be due to formation of insoluble calcium complexes with polycarboxylic proteinaceous acids and hydroxy-acids that have moderately large stability constants at the alkaline pH of the lake. DOM co-precipitation with calcium carbonate and incorporation in precipitated carbonate minerals removes proteinaceous DOM, but nearly equivalent concentrations of neutral and acidic forms of organic nitrogen in DOM remain in solution. Calcium carbonate precipitation during lime softening pretreatment of drinking water may have practical applications for removal of proteinaceous disinfection by-product precursors.
Influence of surface oxygenated groups on the formation of active Cu species and the catalytic activity of Cu/AC catalyst for the synthesis of dimethyl carbonate

NASA Astrophysics Data System (ADS)

Zhang, Guoqiang; Li, Zhong; Zheng, Huayan; Hao, Zhiqiang; Wang, Xia; Wang, Jiajun

2016-12-01

Activated carbon (AC) supported Cu catalysts are employed to study the influence of surface oxygenated groups on the formation of active Cu species and the catalytic activity of Cu/AC catalyst for oxidative carbonylation of methanol to dimethyl carbonate (DMC). The AC supports are thermal treated under different temperatures in order to adjust the levels of surface oxygenated groups. The AC supports are characterized by BET, TPD-MS and XRD, and the Cu/AC catalysts are characterized by BET, XRD, TEM, XPS, AAS, CH3OH-TPD and N2O chemisorption. The results show that as the treatment temperature is below 800 °C, the BET surface area of the corresponding AC supports are nearly unchanged and close to that of the original AC (1529.6 m2/g). But as the thermal treatment temperature is elevated from 1000 to 1600 °C, the BET surface area of AC supports gradually decreases from 1407.6 to 972.2 m2/g. After loading of Cu, the BET surface area of copper catalysts is in the range of 834.4 to 1545.3 m2/g, which is slightly less than that of the respective supports. When AC is thermal treated at 400 and 600 °C, the unstable carboxylic acid and anhydrides groups are selectively removed, which has weakened the mobility and agglomeration of Cu species during the calcination process, and thus improve the Cu species dispersion over AC support. But as the treatment temperature is elevated from 600 °C to 1200 °C, the Cu species dispersion begins to decline suggesting further removal of stable surface oxygenated groups is unfavorable for Cu species dispersion. Moreover, higher thermal treatment temperature (above 1200 °C) promotes the graphitization degree of AC and leds to the decrease of Cu loading on AC support. Meanwhile, the removal of surface oxygenated groups by thermal treatment is conducive to the formation of more π-sites, and thus promote the reduction of Cu2+ to Cu+ and Cu0 as active centers. The specific surface area of (Cu+ + Cu0) is improved by thermal treatment of AC, however, the space time yield of DMC on unit specific surface area of (Cu+ + Cu0) is in the range of 23.1-49.1 mg h-1 m-2, which is much less than that (77.6 mg h-1 m-2) of the original catalyst. The possible reason is that the removal of surface oxygenated groups results in AC support transforms from hydrophilicity to hydrophobicity, which is detrimental for the adsorption of CH3OH resulting in the decreased local concentration of CH3OH on active Cu species.
Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite

PubMed Central

Benzerara, Karim; Menguy, Nicolas; Guyot, François; Dominici, Christian; Gillet, Philippe

2003-01-01

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation. PMID:12792020

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite.

PubMed

Benzerara, Karim; Menguy, Nicolas; Guyot, Francois; Dominici, Christian; Gillet, Philippe

2003-06-24

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.
Metabolic Reconstruction and Modeling Microbial Electrosynthesis.

PubMed

Marshall, Christopher W; Ross, Daniel E; Handley, Kim M; Weisenhorn, Pamela B; Edirisinghe, Janaka N; Henry, Christopher S; Gilbert, Jack A; May, Harold D; Norman, R Sean

2017-08-21

Microbial electrosynthesis is a renewable energy and chemical production platform that relies on microbial cells to capture electrons from a cathode and fix carbon. Yet despite the promise of this technology, the metabolic capacity of the microbes that inhabit the electrode surface and catalyze electron transfer in these systems remains largely unknown. We assembled thirteen draft genomes from a microbial electrosynthesis system producing primarily acetate from carbon dioxide, and their transcriptional activity was mapped to genomes from cells on the electrode surface and in the supernatant. This allowed us to create a metabolic model of the predominant community members belonging to Acetobacterium, Sulfurospirillum, and Desulfovibrio. According to the model, the Acetobacterium was the primary carbon fixer, and a keystone member of the community. Transcripts of soluble hydrogenases and ferredoxins from Acetobacterium and hydrogenases, formate dehydrogenase, and cytochromes of Desulfovibrio were found in high abundance near the electrode surface. Cytochrome c oxidases of facultative members of the community were highly expressed in the supernatant despite completely sealed reactors and constant flushing with anaerobic gases. These molecular discoveries and metabolic modeling now serve as a foundation for future examination and development of electrosynthetic microbial communities.
TOWARD THE FORMATION OF CARBONACEOUS REFRACTORY MATTER IN HIGH TEMPERATURE HYDROCARBON-RICH ATMOSPHERES OF EXOPLANETS UPON MICROMETEOROID IMPACT

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

Dangi, Beni B.; Kim, Yong S.; Krasnokutski, Serge A.

2015-05-20

We report on laboratory simulation experiments mimicking the chemical processing of model atmospheres of exoplanets containing C3 and C4 hydrocarbons at moderate temperatures of 400 K upon interaction of catalytic surfaces of micrometeoroids. By utilizing an ultrasonic levitator device and heating singly levitated particles under simulated microgravity conditions, Raman spectroscopy is utilized as a non-invasive tool to probe on line and in situ the conversion of C3 and C4 hydrocarbons to refractory carbonaceous matter on the surfaces of levitated particles. Secondary Ion Mass Spectrometry and electron microscopic imaging were also conducted to gain further insight into the elementary composition andmore » structures of the refractories formed. Our results provide compelling evidence that in the presence of a catalytic surface, which can be supplied in the form of micrometeoroids and atmospheric dust particles, hydrocarbon gases present in the atmospheres of exoplanets can be converted to refractory, carbon-rich carbonaceous matter of mainly graphitic structure with a carbon content of at least 90% at elevated temperatures. This finding might explain the low methane to carbon monoxide (CH{sub 4}–CO) ratio in the hot Neptune GJ 436b, where the abundant methane photochemically converts to higher order hydrocarbons and ultimately to refractory graphite-like carbon in the presence of a silicon surface.« less
The Ordovician Sebree Trough: An oceanic passage to the Midcontinent United States

USGS Publications Warehouse

Kolata, Dennis R.; Huff, W.D.; Bergstrom, Stig M.

2001-01-01

The Sebree Trough is a relatively narrow, shale-filled sedimentary feature extending for several hundred kilometers across the Middle and Late Ordovician carbonate platform of the Midcontinent United States. The dark graptolitic shales within the trough stand in contrast to the coeval bryozoan-brachiopod-echinodermrich limestones on the flanking platforms. We infer from regional stratal patterns, thickness and facies trends, and temporal relations established by biostratigraphy and K-bentonite stratigraphy that the Sebree Trough initially began to develop during late Turinian to early Chatfieldian time (Mohawkian Series) as a linear bathymetric depression situated over the failed late Precambrian-Early Cambrian Reelfoot Rift. Rising sea level and positioning of a subtropical convergence zone along the southern margin of Laurentia caused the rift depression to descend into cool, oxygen-poor, phosphate-rich oceanic waters that entered the southern reaches of the rift from the Iapetus Ocean. The trough apparently formed in a system of epicontinental estuarine circulation marked by a density-stratified water column. Trough formation was accompanied by cessation of carbonate sedimentation, deposition of graptolitic shales, development of hardground omission surfaces, substrate erosion, and local phosphogenesis. The carbonate platforms on either side of the trough are dominated by bryozoan-brachiopod-echinoderm grainstones and packstones that were deposited in zones of mixing where cool, nutrient-rich waters encountered warmer shelf waters. Concurrently, lime mudstone and wackestone were deposited shoreward (northern Illinois, Wisconsin, Iowa, Minnesota, Michigan) in warmer, more tropical shallow seas. Coeval upward growth of the flanking carbonate platforms sustained and enhanced development of the trough shale facies. Five widespread diachronous late Mohawkian and Cincinnatian omission surfaces are present in the carbonate facies of the Midcontinent. These surfaces include sub-Deicke K-bentonite, DSI; top of Black River Limestone, DS2; base and top of the Guttenberg Limestone Member of the Decorah Formation, DS3 and DS4; and top of the Trenton Limestone, DS5. Some of the surfaces correspond to previously described depositional sequence boundaries. All five surfaces, which embody deepening phases on top of high-stand-systems tracts, converge in the Sebree Trough, indicating that the trough was a long-lived feature and was the source of eutrophic waters that episodically spread across the adjacent platforms, terminating carbonate production. Late Turinian and early Chatfieldian incipient drowning episodes were followed by a final drowning event that began in the Sebree Trough during the late Chatfieldian (Climacograptus spiniferus Zone) and reached southernmost Minnesota and other regions far within the platform interior by Richmondian time (Amorphognathus ordovicicus Zone).
Chabazite and dolomite formation in a dolocrete profile: An example of a complex alkaline paragenesis in Lanzarote, Canary Islands

NASA Astrophysics Data System (ADS)

Alonso-Zarza, Ana M.; Bustamante, Leticia; Huerta, Pedro; Rodríguez-Berriguete, Álvaro; Huertas, María José

2016-05-01

This paper studies the weathering and soil formation processes operating on detrital sediments containing alkaline volcanic rock fragments of the Mirador del Río dolocrete profile. The profile consists of a lower horizon of removilised weathered basalts, an intermediate red sandy mudstones horizon with irregular carbonate layers and a topmost horizon of amalgamated carbonate layers with root traces. Formation occurred in arid to semiarid climates, giving place to a complex mineralogical association, including Mg-carbonates and chabazite, rarely described in cal/dolocretes profiles. Initial vadose weathering processes occurred in the basalts and in directly overlying detrital sediments, producing (Stage 1) red-smectites and dolomicrite. Dominant phreatic (Stage 2) conditions allowed precipitation of coarse-zoned dolomite and chabazite filling porosities. In Stages 3 and 4, mostly pedogenic, biogenic processes played an important role in dolomite and calcite accumulation in the profile. Overall evolution of the profile and its mineralogical association involved initial processes dominated by alteration of host rock, to provide silica and Mg-rich alkaline waters, suitable for chabazite and dolomite formation, without a previous carbonate phase. Dolomite formed both abiogenically and biogenically, but without a previous carbonate precursor and in the absence of evaporites. Dominance of calcite towards the profile top is the result of Mg/Ca decrease in the interstitial meteoric waters due to decreased supply of Mg from weathering, and increased supply of Ca in aeolian dust. Meteoric origin of the water is confirmed by C and O isotope values, which also indicate lack of deep sourced CO2. The dolocrete studied and its complex mineral association reveal the complex interactions that occur at surface during weathering and pedogenesis of basalt-sourced rocks.
Effects of Extensive Beetle-Induced Forest Mortality on Aromatic Organic Carbon Loading and Disinfection Byproduct Formation Potential

NASA Astrophysics Data System (ADS)

Brouillard, B.; Mikkelson, K. M.; Dickenson, E.; Sharp, J.

2015-12-01

Recent drought and warmer temperatures associated with climate change have caused increased pest-induced forest mortality with impacts on biogeochemical and hydrologic processes. To better understand the seasonal impacts of bark beetle infestation on water quality, samples were collected regularly over two overlapping snow free seasons at surface water intakes of six water treatment facilities in the Rocky Mountain region of Colorado displaying varying levels of bark beetle infestation (high >40%, moderate 20-40%, and low <20%). Organic carbon concentrations were typically 3 to 6 times higher in waters sourced from high beetle-impacted watersheds compared to moderate and low impact watersheds, revealing elevated specific ultraviolet absorbance, fluorescence, and humic-like intensity indicative of elevated aromatic carbon signatures. Accordingly, an increase in disinfection byproduct (DBP) formation potential of 400 to 600% was quantified when contrasted with watersheds containing less tree mortality. Beetle impact exasperated seasonal increases in carbon loading and DBP formation potential following both runoff and precipitation events indicating windows when enhanced water treatment may be utilized by water providers in highly infested regions. Additionally, elevated carbon concentrations throughout the summer and fall along with peaks following precipitation events provide evidence of shifting hydrologic flow paths in areas experiencing high forest mortality from decreased tree water uptake and interception. Collectively, these results demonstrate the need for continued watershed protection and monitoring with a changing climate as the resultant perturbations can have adverse effects on biogeochemistry and water quality in heavily impacted areas.
4-Vinyl-1,3-Dioxolane-2-One as an Additive for Li-Ion Cells

NASA Technical Reports Server (NTRS)

Smart, Marshall; Bugga, Ratnakumar

2006-01-01

Electrolyte additive 4-vinyl-1,3-dioxolane-2-one has been found to be promising for rechargeable lithium-ion electrochemical cells. This and other additives, along with advanced electrolytes comprising solutions of LiPF6 in various mixtures of carbonate solvents, have been investigated in a continuing effort to improve the performances of rechargeable lithium-ion electrochemical cells, especially at low temperatures. In contrast to work by other researchers who have investigated the use of this additive to improve the high-temperature resilience of Li-ion cells, the current work involves the incorporation of 4-vinyl-1,3-dioxolane-2-one into quaternary carbonate electrolyte mixtures, previously optimized for low-temperature applications, resulting in improved low-temperature performance. The benefit afforded by 4-vinyl-1,3- dioxolane-2-one can be better understood in the light of relevant information from a number of prior NASA Tech Briefs articles about electrolytes and additives for such cells. To recapitulate: The loss of performance with decreasing temperature is attributable largely to a decrease of ionic conductivity and the increase in viscosity of the electrolyte. What is needed to extend the lower limit of operating temperature is a stable electrolyte solution with relatively small lowtemperature viscosity, a large electric permittivity, adequate coordination behavior, and appropriate ranges of solubilities of liquid and salt constituents. Whether the anode is made of graphitic or non-graphitic carbon, a film on the surface of the anode acts as a solid/electrolyte interface (SEI), the nature of which is critical to low-temperature performance. Desirably, the surface film should exert a chemically protective (passivating) effect on both the anode and the electrolyte, yet should remain conductive to lithium ions to facilitate intercalation and de-intercalation of the ions into and out of the carbon during discharging and charging, respectively. The additives investigated previously include alkyl pyrocarbonates. Those additives help to improve low-temperature performances by giving rise to the formation of SEIs having desired properties. The formation of the SEIs is believed to be facilitated by products (e.g., CO2) of the decomposition of these additives. These decomposition products are believed to react to form Li2CO3-based films on the carbon electrodes. The present additive, 4-vinyl-1,3-dioxolane-2-one, also helps to improve lowtemperature performance by contributing to the formation of SEIs having desired properties, but probably in a different manner: It is believed that, as part of the decomposition process, the compound polymerizes on the surfaces of carbon electrodes.
Effects of ozonation pretreatment on natural organic matter and wastewater derived organic matter - Possible implications on the formation of ozonation by-products.

PubMed

Papageorgiou, Alexandros; Stylianou, Stylianos K; Kaffes, Pavlos; Zouboulis, Anastasios I; Voutsa, Dimitra

2017-03-01

The aim of this study was to investigate possible implications of natural and wastewater derived organic matter in river water that is subsequently used following treatment for drinking purposes. River water was subjected to lab-scale ozonation experiments under different ozone doses (0.1, 0.4, 0.8, 1.0 and 2.0 mgO 3 /mgC) and contact times (1, 3, 5, 8 and 10 min). Mixtures of river water with humic acids or wastewaters (sewage wastewater and secondary effluents) at different proportions were also ozonated. Dissolved organic carbon and biodegradable dissolved organic carbon concentrations as well as spectroscopic characteristics (UV absorbance and fluorescence intensities) of different types of dissolved organic matter and possible changes due to the ozonation treatment are presented. River water, humic substances and wastewater exhibited distinct spectroscopic characteristics that could serve for pollution source tracing. Wastewater impacted surface water results in higher formation of carbonyl compounds. However, the formation yield (μg/mgC) of wastewaters was lower than that of surface water possibly due to different composition of wastewater derived organic matter and the presence of scavengers, which may limit the oxidative efficiency of ozone. Copyright © 2016 Elsevier Ltd. All rights reserved.
Flame oxidation of stainless steel felt enhances anodic biofilm formation and current output in bioelectrochemical systems.

PubMed

Guo, Kun; Donose, Bogdan C; Soeriyadi, Alexander H; Prévoteau, Antonin; Patil, Sunil A; Freguia, Stefano; Gooding, J Justin; Rabaey, Korneel

2014-06-17

Stainless steel (SS) can be an attractive material to create large electrodes for microbial bioelectrochemical systems (BESs), due to its low cost and high conductivity. However, poor biocompatibility limits its successful application today. Here we report a simple and effective method to make SS electrodes biocompatible by means of flame oxidation. Physicochemical characterization of electrode surface indicated that iron oxide nanoparticles (IONPs) were generated in situ on an SS felt surface by flame oxidation. IONPs-coating dramatically enhanced the biocompatibility of SS felt and consequently resulted in a robust electroactive biofilm formation at its surface in BESs. The maximum current densities reached at IONPs-coated SS felt electrodes were 16.5 times and 4.8 times higher than the untreated SS felts and carbon felts, respectively. Furthermore, the maximum current density achieved with the IONPs-coated SS felt (1.92 mA/cm(2), 27.42 mA/cm(3)) is one of the highest current densities reported thus far. These results demonstrate for the first time that flame oxidized SS felts could be a good alternative to carbon-based electrodes for achieving high current densities in BESs. Most importantly, high conductivity, excellent mechanical strength, strong chemical stability, large specific surface area, and comparatively low cost of flame oxidized SS felts offer exciting opportunities for scaling-up of the anodes for BESs.
The atomic nature of polymer-metal interactions in adhesion, friction and wear

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Brainard, W. A.

1973-01-01

Adhesion experiments with polytetra-fluoroethylene (PTFE) and polyimide contacting tungsten indicate that the polymers bond chemically to the clean metal surface. Polymer chain fragments which transfer to the surface of tungsten in field ion microscopy adhesion studies are highly oriented. Auger emission spectroscopy of PTFE transfer films to various metal surfaces indicates that the PTFE is bonded to the metal surface via the carbon atom. With PTFE in sliding contact with different orientations of aluminum, metal orientation is found to influence surfaces in sliding. The lowest friction and least amount of surface damage is detected on the highest atomic density (111) plane. The friction process itself can initiate polymer film formation from simple organic molecules.
The Influence of Calcium Carbonate Composition and Activated Carbon in Pack Carburizing Low Carbon Steel Process in The Review of Hardness and Micro Structure

NASA Astrophysics Data System (ADS)

Hafni; Hadi, Syafrul; Edison

2017-12-01

Carburizing is a way of hardening the surface by heating the metal (steel) above the critical temperature in an environment containing carbon. Steel at a temperature of the critical temperature of affinity to carbon. Carbon is absorbed into the metal form a solid solution of carbon-iron and the outer layer has high carbon content. When the composition of the activator and the activated charcoal is right, it will perfect the carbon atoms to diffuse into the test material to low carbon steels. Thick layer of carbon Depending on the time and temperature are used. Pack carburizing process in this study, using 1 kg of solid carbon derived from coconut shell charcoal with a variation of 20%, 10% and 5% calcium carbonate activator, burner temperature of 950 0C, holding time 4 hours. The test material is low carbon steel has 9 pieces. Each composition has three specimens. Furnace used in this study is a pack carburizing furnace which has a designed burner box with a volume of 1000 x 600 x 400 (mm3) of coal-fired. Equipped with a circulation of oxygen from the blower 2 inches and has a wall of refractory bricks. From the variation of composition CaCO3, microstructure formed on the specimen with 20% CaCO3, better diffusion of carbon into the carbon steel, it is seen by the form marten site structure after quenching, and this indicates that there has been an increase of or adding carbon to in the specimen. This led to the formation of marten site specimen into hard surfaces, where the average value of hardness at one point side (side edge) 31.7 HRC
The production of oxidants in Europa's surface.

PubMed

Johnson, R E; Quickenden, T I; Cooper, P D; McKinley, A J; Freeman, C G

2003-01-01

The oxidants produced by radiolysis and photolysis in the icy surface of Europa may be necessary to sustain carbon-based biochemistry in Europa's putative subsurface ocean. Because the subduction of oxidants to the ocean presents considerable thermodynamic challenges, we examine the formation of oxygen and related species in Europa's surface ice with the goal of characterizing the chemical state of the irradiated material. Relevant spectral observations of Europa and the laboratory data on the production of oxygen and related species are first summarized. Since the laboratory data are incomplete, we examine the rate equations for formation of oxygen and its chemical precursors by radiolysis and photolysis. Measurements and simple rate equations are suggested that can be used to characterize the production of oxidants in Europa's surface material and the chemical environment produced by radiolysis. Possible precursor molecules and the role of radical trapping are examined. The possibility of oxygen reactions on grain surfaces in Europa's regolith is discussed, and the earlier estimates of the supply of O(2) to the atmosphere are increased.
Modern terrestrial analogues for the carbonate globules in Martian meteorite ALH84001.

PubMed

Kazmierczak, Józef; Kempe, Stephan

2003-04-01

Modern carbonate globules, located in cracks of submerged volcanic rocks and in calcareous pinnacles in alkaline (sodic) Lake Van, Turkey, appear to be analogues for the approximately 3.9 billion-year-old carbonate globules in Martian meteorite ALH84001. These terrestrial globules have similar diameters and are chemically and mineralogically zoned. Furthermore, they display surface and etching structures similar to those described from ALH84001, which were interpreted as fossilized microbial forms. These terrestrial carbonates formed at low temperatures where Ca-rich groundwaters enter the lake. Chemical, mineralogical, microbiological, and biomolecular methods were used in an attempt to decipher the process responsible for the genesis of these structures. Although the exact mode of formation of Lake Van carbonates remains an enigma, their similarity to the Martian globules indicates that the ALH84001 carbonates may have formed in similar setting on ancient Mars.
The Formation of Formaldehyde on Interstellar Carbonaceous Grain Analogs by O/H Atom Addition

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

Potapov, Alexey; Jäger, Cornelia; Henning, Thomas

An understanding of possible scenarios for the formation of astrophysically relevant molecules, particularly complex organic molecules, will bring us one step closer to the understanding of our astrochemical heritage. In this context, formaldehyde is an important molecule as a precursor of methanol, which in turn is a starting point for the formation of more complex organic species. In the present experiments, for the first time, following the synthesis of CO, formaldehyde has been produced on the surface of interstellar grain analogs, hydrogenated fullerene-like carbon grains, by O and H atom bombardment. The formation of H{sub 2}CO is an indication formore » a possible methanol formation route in such systems.« less
An atomic carbon source for high temperature molecular beam epitaxy of graphene.

PubMed

Albar, J D; Summerfield, A; Cheng, T S; Davies, A; Smith, E F; Khlobystov, A N; Mellor, C J; Taniguchi, T; Watanabe, K; Foxon, C T; Eaves, L; Beton, P H; Novikov, S V

2017-07-26

We report the use of a novel atomic carbon source for the molecular beam epitaxy (MBE) of graphene layers on hBN flakes and on sapphire wafers at substrate growth temperatures of ~1400 °C. The source produces a flux of predominantly atomic carbon, which diffuses through the walls of a Joule-heated tantalum tube filled with graphite powder. We demonstrate deposition of carbon on sapphire with carbon deposition rates up to 12 nm/h. Atomic force microscopy measurements reveal the formation of hexagonal moiré patterns when graphene monolayers are grown on hBN flakes. The Raman spectra of the graphene layers grown on hBN and sapphire with the sublimation carbon source and the atomic carbon source are similar, whilst the nature of the carbon aggregates is different - graphitic with the sublimation carbon source and amorphous with the atomic carbon source. At MBE growth temperatures we observe etching of the sapphire wafer surface by the flux from the atomic carbon source, which we have not observed in the MBE growth of graphene with the sublimation carbon source.
Resolving the inconsistency between the ice giants and cometary D/H ratios

NASA Astrophysics Data System (ADS)

Ali-Dib, M.; Mousis, O.; Petit, J.-M.; Lunine, J. I.

2014-12-01

The properties and chemical compositions of giant planets strongly depend on their formation locations. The formation mechanisms of the ice giants Uranus and Neptune, and their elemental and isotopic compositions, have long been debated. The density of solids in the outer protosolar nebula is too low to explain their formation within a timescale consistent with the presence of the gaseous protoplanetary disk, and spectroscopic observations show that both planets are highly enriched in carbon, very poor in nitrogen, and the ices from which they originally formed might had deuterium-to-hydrogen ratios lower than the predicted cometary value, unexplained properties observed in no other planets. Here we show that all these properties can be explained naturally if Uranus and Neptune both formed at the carbon monoxide iceline location, namely the region where this gas condensates in the protosolar nebula. This outer region of the protosolar nebula intrinsically has enough surface density to form both planets from carbon-rich solids but nitrogen-depleted gas, in abundances consistent with their observed values. Water rich interiors originating mostly from transformed CO ices reconcile the D/H value observed in Uranus and Neptune with the cometary value.
Elemental geochemistry and strontium-isotope stratigraphy of Cenomanian to Santonian neritic carbonates in the Zagros Basin, Iran

NASA Astrophysics Data System (ADS)

Navidtalab, Amin; Rahimpour-Bonab, Hossain; Huck, Stefan; Heimhofer, Ulrich

2016-12-01

A Neo-Tethyan upper Cenomanian-Santonian neritic carbonate ramp succession (Sarvak and Ilam formations), drilled in the Zagros Basin in southwest Iran, was investigated via detailed sedimentology, microfacies analysis, elemental geochemistry and Sr-isotope stratigraphy (SIS). The succession contains two exposure surfaces, which are known as the CT-ES and mT-ES (Cenomanian-Turonian and middle Turonian, respectively), and associated prominent negative carbon-isotope excursions that represent important regional stratigraphic marker horizons. Precise knowledge about the onset of platform exposure and the duration of the exposure-related hiatus, however, is currently lacking due to a rather low-resolved shallow-water biostratigraphic framework and a bulk carbonate carbon-isotope pattern that clearly differs from global Late Cretaceous reference curves. Therefore, the existing bio-chemostratigraphic framework was complemented by bulk carbonate strontium-isotope stratigraphy (SIS). As bulk carbonate material is in particular prone to diagenetic alteration, a careful selection of least altered samples has been carried out by means of elemental geochemistry and petrography. In contrast to what could be expected, the meteoric alteration of limestones beneath both exposure surfaces is not clearly expressed by increasing iron and manganese and coeval decreasing strontium contents. On the contrary, the impact of meteoric diagenesis is well illustrated via pronounced increases in Rb concentrations and concomitant prominent positive shifts to radiogenic strontium-isotope values, an observation that clearly reflects the decay of continentally derived 87Rb into 87Sr. Rubidium corrected strontium-isotope values place the CT-ES around the Cenomanian-Turonian boundary and point to an exposure duration of less than 0.4 Myr. This rather short-term CT-ES related hiatus is supported by petrographic evidence, which indicates a youth karstification stage of strata beneath the CT-ES. Following SIS, the Ilam-Sarvak transition at the top of Nezzazatinella-Dicyclina interval zone coincides with the mT-ES. Carbonates placing above this transition (Ilam Formation) are ascribed to the earliest to latest early Santonian, while carbonates immediately beneath the mT-ES (Sarvak Formation) are dated as late Turonian. SIS thus indicates a long-lasting hiatus of 4.5 Myr associated with the mT-ES. Emergence represented by the CT-ES is here proposed as harbinger of the mT-ES in the Zagros Basin, which most likely resulted from stepwise peripheral bulging due to ophiolite obduction in combination with a small-scale global sea level fall around 94 Ma.
Susceptibility of Granite Rock to scCO2/Water at 200 degrees C and 250 degrees C

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

Sugama, T.; Gill, S., Ecker, L., Butcher, T., Warren, J.

Granite rock comprising anorthoclase-type albite and quartz as its major phases and biotite mica as the minor one was exposed to supercritical carbon dioxide (scCO{sub 2})/water at 250 C and 13.78 MPa pressure for 104 hours. For comparison purpose, four other rocks, albite, hornblende, diorite, and quartz, also were exposed. During the exposure of granite, ionic carbonic acid, known as the wet carbonation reactant, preferentially reacted with anorthoclase-type albite and biotite, rather than with quartz. The susceptibility of biotite to wet carbonation was higher than that of anorthoclase-type albite. All the carbonation by-products of anorthoclase-type albite were amorphous phases includingmore » Na- and K-carbonates, a kaolinite clay-like compound, and silicon dioxide, while wet carbonation converted biotite into potassium aluminum silicate, siderite, and magnesite in crystalline phases and hydrogen fluoride (HF). Three of these reaction by-products, Na- and K-carbonates and HF, were highly soluble in water. Correspondingly, the carbonated top surface layer, about 1.27 mm thick as carbonation depth, developed porous microstructure with numerous large voids, some of which have a size of {>=} 10 {mu}m, reflecting the erosion of granite by the leaching of these water-soluble reaction by-products. Comparing with this carbonation depth, its depth of other minerals was considerable lower, particularly, for hornblende and diorite with 0.07 and 0.02 mm, while no carbonate compound was detected in quartz. The major factor governing these low carbonation depths in these rocks was the formation of water-insensitive scale-like carbonate by-products such as calcite (CaCO{sub 3}), siderite (FeCO{sub 3}), and magnesite (MgCO{sub 3}). Their formation within the superficial layer of these minerals served as protective barrier layer that inhibits and retards further carbonation of fresh underlying minerals, even if the exposure time was extended. Thus, the coverage by this barrier layer of the non-carbonated surfaces of the underlying rock was reason why the hornblende and diorite exhibited a minimum depth of carbonation. Under exposure to the scCO{sub 2}/water at 200 C and 10.34 MPa pressure for up to 42 days, the ranking of the magnitude of erosion caused by wet carbonation was in the following order; granite > albite > hornblende > diorite > quartz. The eroding-caused weight loss of granite (0.88 %) was {approx}2.4, {approx}5.2, {approx}9.8, and {approx}17.6 times greater than that of albite, hornblends, diorite, and quartz, respectively.« less
Development of nanomaterial-enabled advanced oxidation techniques for treatment of organic micropollutants

NASA Astrophysics Data System (ADS)

Oulton, Rebekah Lynn

Increasing demand for limited fresh water resources necessitates that alternative water sources be developed. Nonpotable reuse of treated wastewater represents one such alternative. However, the ubiquitous presence of organic micropollutants such as pharmaceuticals and personal care products (PPCPs) in wastewater effluents limits use of this resource. Numerous investigations have examined PPCP fate during wastewater treatment, focusing on their removal during conventional and advanced treatment processes. Analysis of influent and effluent data from published studies reveals that at best 1-log10 concentration unit of PPCP removal can generally be achieved with conventional treatment. In contrast, plants employing advanced treatment methods, particularly ozonation and/or membranes, remove most PPCPs often to levels below analytical detection limits. However, membrane treatment is cost prohibitive for many facilities, and ozone treatment can be very selective. Ozone-recalcitrant compounds require the use of Advanced Oxidation Processes (AOPs), which utilize highly reactive hydroxyl radicals (*OH) to target resistant pollutants. Due to cost and energy use concerns associated with current AOPs, alternatives such as catalytic ozonation are under investigation. Catalytic ozonation uses substrates such as activated carbon to promote *OH formation during ozonation. Here, we show that multi-walled carbon nanotubes (MWCNTs) represent another viable substrate, promoting *OH formation during ozonation to levels exceeding activated carbon and equivalent to conventional ozone-based AOPs. Via a series of batch reactions, we observ a strong correlation between *OH formation and MWCNT surface oxygen concentrations. Results suggest that deprotonated carboxyl groups on the CNT surface are integral to their reactivity toward ozone and corresponding *OH formation. From a practical standpoint, we show that industrial grade MWCNTs exhibit similar *OH production as their research-grade counterparts. Accelerated aging studies indicate that MWCNTs maintain surface reactivity for an extended period during ozonation treatment. Further, *OH generation is essentially unaffected in complex water matrices containing known radical scavengers, and is effective for degradation of the ozone-recalcitrant herbicide atrazine. A proof-of-concept study verified that results from batch systems can be replicated in a flow-through reactor utilizing MWCNTs immobilized on a ceramic membrane support. Collective, results suggest that CNT-enhanced ozonation may provide a viable treatment alternative for emerging organic micropollutants.
BioMig--A Method to Evaluate the Potential Release of Compounds from and the Formation of Biofilms on Polymeric Materials in Contact with Drinking Water.

PubMed

Wen, Gang; Kötzsch, Stefan; Vital, Marius; Egli, Thomas; Ma, Jun

2015-10-06

In contact with water, polymeric materials (plastics) release compounds that can support suspended microbial growth and/or biofilm formation. The different methods presently used in the European Union to test plastics take 7-16 weeks to obtain a result. In industry, this delays material and product development as well as quality testing. Therefore, we developed a method package (BioMig) that allows testing of plastic materials with high reproducibility in 2 weeks for their potential biofilm (or biomass) formation and release of carbonaceous migration products when in contact with water. BioMig consists of (i) an extended migration potential test (seven times for 24 h at 60 °C), based on the European norm EN 12873-1 and the German UBA (Umweltbundesamt) guideline, and (ii) a biomass formation potential (BFP) test (14 days at 30 °C), which is a modified version of the Dutch biofilm production potential test. In the migration potential test, the amount of carbon released into water by the specimen is quantified by monitoring total and assimilable organic carbon over time; furthermore, the modular design of the test also allows one to assess additional parameters such as pathogen growth potential on the migration water or toxic effects on microbial growth. Flow cytometry (FCM)-based total cell counting (TCC) is used to quantify microbial growth in suspension and on surfaces after removal with mild sonication without affecting cell integrity. The BFP test allows one to determine both the planktonic (pBFP) and the sessile (sBFP) cell fractions. The sBFP consists of surface-attached cells after removal (>90% efficiency). Results for four standard test materials (PE-Xa, PE-Xc, EPDM 2%, and EPDM 20%), plus positive (PVC-P) and negative (glass) controls are presented. FCM-based TCC demonstrates that the release of growth-supporting carbon and proliferation of surface-attached cells stops increasing and stabilizes after 14 days of incubation; this allows for faster assessment of growth-supporting properties of plastics with BioMig compared to established tests.

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