Microstructural characterization of the cycling behavior of electrodeposited manganese oxide supercapacitors using 3D electron tomography

NASA Astrophysics Data System (ADS)

Dalili, N.; Clark, M. P.; Davari, E.; Ivey, D. G.

2016-10-01

Manganese oxide has been investigated extensively as an electrochemical capacitor or supercapacitor electrode material. Manganese oxide is inexpensive to fabricate and exhibits relatively high capacitance values, i.e., in excess of 200 F g-1 in many cases; the actual value depends very much on the fabrication method and test conditions. The cycling behavior of Mn oxide, fabricated using anodic electrodeposition, is investigated using slice and view techniques, via a dual scanning electron microscope (SEM) and focused ion beam (FIB) instrument to generate three-dimensional (3D) images, coupled with electrochemical characterization. The initial as-fabricated electrode has a rod-like appearance, with a fine-scale, sheet-like morphology within the rods. The rod-like structure remains after cycling, but there are significant morphological changes. These include partial dissolution of Mn oxide followed by redeposition of Mn oxide in regions close to the substrate. The redeposited material has a finer morphology than the original as-fabricated Mn oxide. The Mn oxide coverage is also better near the substrate. These effects result in an increase in the specific capacitance.

Plasmonic Properties of Silicon Nanocrystals Doped with Boron and Phosphorus.

PubMed

Kramer, Nicolaas J; Schramke, Katelyn S; Kortshagen, Uwe R

2015-08-12

Degenerately doped silicon nanocrystals are appealing plasmonic materials due to silicon's low cost and low toxicity. While surface plasmonic resonances of boron-doped and phosphorus-doped silicon nanocrystals were recently observed, there currently is poor understanding of the effect of surface conditions on their plasmonic behavior. Here, we demonstrate that phosphorus-doped silicon nanocrystals exhibit a plasmon resonance immediately after their synthesis but may lose their plasmonic response with oxidation. In contrast, boron-doped nanocrystals initially do not exhibit plasmonic response but become plasmonically active through postsynthesis oxidation or annealing. We interpret these results in terms of substitutional doping being the dominant doping mechanism for phosphorus-doped silicon nanocrystals, with oxidation-induced defects trapping free electrons. The behavior of boron-doped silicon nanocrystals is more consistent with a strong contribution of surface doping. Importantly, boron-doped silicon nanocrystals exhibit air-stable plasmonic behavior over periods of more than a year.

The Influence of Fabrication Process on the Initial Stages of Steam Oxidation Performed on Haynes® 282® Alloy at 760 °C

NASA Astrophysics Data System (ADS)

Dudziak, T.; Boron, L.; Homa, M.; Nowak, R.; Horton, N.; Sheppard, R.; Purgert, R. M.; Siewiorek, A.; Sobczak, N.; Sobczak, J. J.

2017-01-01

This work presents results observed after the first 5 h of oxidation of Haynes® 282® alloy. The steam oxidation tests have been carried out in pure water at 760 °C for 1, 2 and 5 h, respectively, using an accurate thermogravimetric balance technique. The alloy used for comparison in this work was fabricated using three different methods. The initial steam oxidation performance of the commercially wrought alloy Haynes® 282® was compared with a fabricated cast alloy and a HIP/PM alloy. The results show that in terms of corrosion resistance, fabrication techniques appear to have little impact on steam oxidation performance and behavior. The exposed Ni-based alloys all developed the oxide scales consisting mainly of Cr2O3 phase mixed with some TiO2, while internal Al and Ti precipitations along the grain boundaries were observed both in Haynes® 282® wrought and HIP/PM alloy.

Influence of deformation behavior, oxydation, and temperature on the long time cyclic stress behavior of high temperature steels

NASA Technical Reports Server (NTRS)

Maile, K.

1982-01-01

The influence of different parameters on the creep-fatigue behavior of several steel alloys was investigated. The higher the temperature the lower the crack initiation value. Pauses during the cycle reduce the damage. Oxidation reduces and protective gas increases the lifetime. Prior loading and prior deformation reduce the lifetime. Short annealing slightly affects the cycle stress behavior. The test results do not satisfactorily agree with methods of extrapolation and damage accumulation.

Effect of Iron(II) on Arsenic Sequestration by δ-MnO 2 : Desorption Studies Using Stirred-Flow Experiments and X-Ray Absorption Fine-Structure Spectroscopy

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

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

2015-10-18

Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese (Mn) and iron (Fe) oxides are ubiquitous solids in terrestrial systems and have high sorptive capacities for many trace metals, including As. Although numerous studies have studied the effects of As adsorption and desorption onto Fe and Mn oxides individually, the fate of As within mixed systems representative of natural environments has not been resolved. In this research, As(III) was initially reacted with a poorly crystalline phyllomanganate (δ-MnO 2) in the presence of Fe(II)more » prior to desorption. This initial reaction resulted in the sorption of both As(III) and As(V) on mixed Fe/Mn-oxides surfaces. A desorption study was carried out using two environmentally significant ions, phosphate (PO 4 3–) and calcium (Ca 2+). Both a stirred-flow technique and X-ray absorption fine-structure spectroscopy (XAFS) analysis were used to investigate As desorption behavior. Results showed that when As(III)/Fe(II) = 1:1 in the initial reaction, only As(V) was desorbed, agreeing with a previous study showing that As(III) is not associated with the Fe/Mn-oxides. When As(III)/Fe(II) = 1:10 in the initial reaction, both As(III) and As(V) can be desorbed from the Fe/Mn-oxide surface, and more As(III) is desorbed than As(V). Neither of the desorbents used in this study completely removed As(III) or As(V) from the Fe/Mn-oxides surface. However, the As desorption fraction decreases with increasing Fe(II) concentration in the initial reactions.« less

Effect of Iron(II) on Arsenic Sequestration by δ-MnO2: Desorption Studies Using Stirred-Flow Experiments and X-Ray Absorption Fine-Structure Spectroscopy.

PubMed

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

2015-11-17

Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese (Mn) and iron (Fe) oxides are ubiquitous solids in terrestrial systems and have high sorptive capacities for many trace metals, including As. Although numerous studies have studied the effects of As adsorption and desorption onto Fe and Mn oxides individually, the fate of As within mixed systems representative of natural environments has not been resolved. In this research, As(III) was initially reacted with a poorly crystalline phyllomanganate (δ-MnO2) in the presence of Fe(II) prior to desorption. This initial reaction resulted in the sorption of both As(III) and As(V) on mixed Fe/Mn-oxides surfaces. A desorption study was carried out using two environmentally significant ions, phosphate (PO4(3-)) and calcium (Ca(2+)). Both a stirred-flow technique and X-ray absorption fine-structure spectroscopy (XAFS) analysis were used to investigate As desorption behavior. Results showed that when As(III)/Fe(II) = 1:1 in the initial reaction, only As(V) was desorbed, agreeing with a previous study showing that As(III) is not associated with the Fe/Mn-oxides. When As(III)/Fe(II) = 1:10 in the initial reaction, both As(III) and As(V) can be desorbed from the Fe/Mn-oxide surface, and more As(III) is desorbed than As(V). Neither of the desorbents used in this study completely removed As(III) or As(V) from the Fe/Mn-oxides surface. However, the As desorption fraction decreases with increasing Fe(II) concentration in the initial reactions.

Tribological properties of structural ceramics

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Miyoshi, K.

1985-01-01

The tribological and lubricated behavior of both oxide and nonoxide ceramics are reviewed in this chapter. Ceramics are examined in contact with themselves, other harder materials and metals. Elastic, plastic and fracture behavior of ceramics in solid state contact is discussed. The contact load necessary to initiate fracture in ceramics is shown to be appreciably reduced with tangential motion. Both friction and wear of ceramics are anisotropic and relate to crystal structure as has been observed with metals. Grit size effects in two and three body abrasive wear are observed for ceramics. Both free energy of oxide formation and the d valence bond character of metals are related to the friction and wear characteristics for metals in contact with ceramics. Surface contaminants affect friction and adhesive wear. For example, carbon on silicon carbide and chlorine on aluminum oxide reduce friction while oxygen on metal surfaces in contact with ceramics increases friction. Lubrication increases the critical load necessary to initiate fracture of ceramics both in indentation and with sliding or rubbing. Ceramics compositions both as coatings and in composites are described for the high temperature lubrication of both alloys and ceramics.

Long-Term Cyclic Oxidation Behavior of Uncoated and Coated Re-108 and In-939 at 980 and 870 C

NASA Technical Reports Server (NTRS)

Lee, K. N.; Barrett, C. A.; Smith, J.

1999-01-01

Very long-term cyclic oxidation behavior of Re-108 and ln-939 with and without a protective coating was evaluated at 980 and 870 C, respectively. Re-108 and ln-939 without a protective coating began to show rapid weight loss at 3000 h due to scale spallation, indicating the need for an oxidation protective coating for longer than thousands of hours of oxidative life. NiAl-base coatings of a vapor phase aluminide (VPA), a pack aluminide (CODEP), and a slurry paint aluminide (SERMALOY J) were applied on Re-108 and ln-939. VPA and CODEP on Re-108 and all three coatings on ln-939 showed excellent cyclic oxidation resistance out to 10000 hr. Coated alloys were annealed in an inert atmosphere to determine the loss of Al from the coating into the alloy substrate through diffusion. The Al loss from the coating through diffusion was twice as great as the Al loss through oxidation after 10000 h of cyclic exposure. Oxidation life of VPA-coated Re-108 was estimated by calculating the amount of Al initially available for protective oxidation and the amount of Al lost through oxidation and diffusion.

Effect of reducing system on capacitive behavior of reduced graphene oxide film: Application for supercapacitor

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

Akbi, Hamdane; Yu, Lei; Wang, Bin

2015-01-15

To determine the best chemical reduction of graphene oxide film with hydriodic acid that gives maximum energy and power density, we studied the effect of two reducing systems, hydriodic acid/water and hydriodic acid/acetic acid, on the morphology and electrochemical features of reduced graphene oxide film. Using acetic acid as solvent results in high electrical conductivity (5195 S m{sup −1}), excellent specific capacitance (384 F g{sup −1}) and good cyclic stability (about 98% of its initial response after 4000 cycles). Using water as a solvent, results in an ideal capacitive behavior and excellent cyclic stability (about 6% increase of its initialmore » response after 2100 cycles). - Graphical abstract: The choice of reducing system determines the morphology and structure of the chemically reduced graphene film and, as a result, affects largely the capacitive behavior. - Highlights: • The structure of the graphene film has a pronounced effect on capacitive behavior. • The use of water/HI as reducing system results in an ideal capacitive behavior. • The use of acetic acid/HI as reducing system results in a high specific capacitance.« less

Comparison of the reactivity of alkyl and alkyl amine precursors with native oxide GaAs(100) and InAs(100) surfaces

NASA Astrophysics Data System (ADS)

Henegar, A. J., , Dr.; Gougousi, T., , Prof.

2016-12-01

In this manuscript we compare the interaction of alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titanium) precursors during thermal atomic layer deposition with III-V native oxides. For that purpose we deposit Al2O3 and TiO2, using H2O as the oxidizer, on GaAs(100) and InAs(100) native oxide surfaces. We find that there are distinct differences in the behavior of the two films. For the Al2O3 ALD very little native oxide removal happens after the first few ALD cycles while the interaction of the alkyl amine precursor for TiO2 and the native oxides continues well after the surface has been covered with 2 nm of TiO2. This difference is traced to the superior properties of Al2O3 as a diffusion barrier. Differences are also found in the behavior of the arsenic oxides of the InAs and GaAs substrates. The arsenic oxides from the InAs surface are found to mix more efficiently in the growing dielectric film than those from the GaAs surface. This difference is attributed to lower native oxide stability as well as an initial diffusion path formation by the indium oxides.

From nucleation to coalescence of Cu2O islands during in situ oxidation of Cu(001)

NASA Astrophysics Data System (ADS)

Yang, J. C.; Evan, D.; Tropia, L.

2002-07-01

The nucleation, growth, and coalescence of Cu2O islands due to oxidation of Cu(001) films were visualized by in situ ultrahigh-vacuum transmission electron microscopy. We have previously demonstrated that the nucleation and initial growth of copper oxides is dominated by oxygen surface diffusion. These surface models have been extended to quantitatively represent the coalescence behavior of copper oxidation in the framework of the Johnson-Mehl-Avrami-Kolmogorov theory. An excellent agreement exists between the experimental data of nucleation to coalescence with the surface model. The implication could be an alternate paradigm for passivation and oxidation, since classic theories assume uniform film growth.

Oxidation of Alloy 600 and Alloy 690: Experimentally Accelerated Study in Hydrogenated Supercritical Water

NASA Astrophysics Data System (ADS)

Moss, Tyler; Cao, Guoping; Was, Gary S.

2017-04-01

The objective of this study is to determine whether the oxidation of Alloys 600 and 690 in supercritical water occurs by the same mechanism in subcritical water. Coupons of Alloys 690 and 600 were exposed to hydrogenated subcritical and supercritical water from 633 K to 673 K (360 °C to 400 °C) and the oxidation behavior was observed. By all measures of oxide character and behavior, the oxidation process is the same above and below the supercritical line. Similar oxide morphologies, structures, and chemistries were observed for each alloy across the critical point, indicating that the oxidation mechanism is the same in both subcritical and supercritical water. Oxidation results in a multi-layer oxide structure composed of particles of NiO and NiFe2O4 formed by precipitation on the outer surface and a chromium-rich inner oxide layer formed by diffusion of oxygen to the metal-oxide interface. The inner oxide on Alloy 600 is less chromium rich than that observed on Alloy 690 and is accompanied by preferential oxidation of grain boundaries. The inner oxide on Alloy 690 initially forms by internal oxidation before a protective layer of chromium-rich MO is formed with Cr2O3 at the metal-oxide interface. Grain boundaries in Alloy 690 act as fast diffusion paths for chromium that forms a protective Cr2O3 layer at the surface, preventing grain boundary oxidation from occurring.

Oxidation feature and diffusion mechanism of Zr-based metallic glasses near the glass transition point

NASA Astrophysics Data System (ADS)

Hu, Zheng; Lei, Xianqi; Wang, Yang; Zhang, Kun

2018-03-01

The oxidation behaviors of as-cast, pre-deformed, and crystallized Zr47.9Ti0.3Ni3.1Cu39.3Al9.4 metallic glasses (MGs) were studied near the glass transition point. The oxidation kinetics of the crystallized MGs followed a parabolic-rate law, and the as-cast and pre-deformed MGs exerted a typical two-stage behavior above the glass transition temperature (T g). Most interesting, pre-deformed treatment can significantly improve the oxidation rate of MGs, as the initial oxidation appeared earlier than for the as-cast MGs, and was accompanied by much thicker oxide scale. The EDS and XPS results showed that the metal Al acted as the preferred scavenger that absorbed intrinsic oxygen in the near-surface region of as-cast MGs. However, a homogeneous mixed layer without Al was observed in the pre-deformed MGs. We speculated the accelerated diffusion of other elements in the MGs was due to the local increase in the free volume and significant shear-induced dilation of the local structure. The results from this study demonstrate that MGs exhibit controllable atomic diffusion during the oxidation process, which can facilitate use in super-cooled liquid region applications.

Kinetics of Cyclic Oxidation and Cracking and Finite Element Analysis of MA956 and Sapphire/MA956 Composite System

NASA Technical Reports Server (NTRS)

Lee, Kang N.; Arya, Vinod K.; Halford, Gary R.; Barrett, Charles A.

1996-01-01

Sapphire fiber-reinforced MA956 composites hold promise for significant weight savings and increased high-temperature structural capability, as compared to unreinforced MA956. As part of an overall assessment of the high-temperature characteristics of this material system, cyclic oxidation behavior was studied at 1093 C and 1204 C. Initially, both sets of coupons exhibited parabolic oxidation kinetics. Later, monolithic MA956 exhibited spallation and a linear weight loss, whereas the composite showed a linear weight gain without spallation. Weight loss of the monolithic MA956 resulted from the linking of a multiplicity of randomly oriented and closely spaced surface cracks that facilitated ready spallation. By contrast, cracking of the composite's oxide layer was nonintersecting and aligned nominally parallel with the orientation of the subsurface reinforcing fibers. Oxidative lifetime of monolithic MA956 was projected from the observed oxidation kinetics. Linear elastic, finite element continuum, and micromechanics analyses were performed on coupons of the monolithic and composite materials. Results of the analyses qualitatively agreed well with the observed oxide cracking and spallation behavior of both the MA956 and the Sapphire/MA956 composite coupons.

Long-Term Cyclic Oxidation Behavior of Uncoated and Coated Re-108 and In-939 at 980 and 870 C

NASA Technical Reports Server (NTRS)

Lee, K. N.; Barrett, C. A.; Smith, J.

2000-01-01

Very long-term cyclic oxidation behavior of Re108 and In939 with and without a protective coating was evaluated at 980 and 870 C, respectively. Re-108 and In-939 without a protective coating began to show a rapid weight loss at 3000 h due to scale spallation, indicating the need for an oxidation protective coating for longer than thousands of hours of oxidative life. NiAl-base coatings of a vapor phase aluminide (VPA), a pack aluminide (CODEP), and a slurry paint aluminide (SERMALOY J) were applied on Re-108 and In-939. The VPA and CODEP on Re-108 and all three coatings on In-939 showed excellent cyclic oxidation resistance out to 10,000 h. Coated alloys were annealed in an inert atmosphere to determine the loss of Al from the coating into the alloy substrate through diffusion. The Al loss from the coating through diffusion was twice as great as the Al loss through oxidation after 10,000 h of cyclic exposure. The oxidation life of VPA-coated Re-108 was estimated by calculating the amount of Al initially available for protective oxidation and the amount of Al lost through oxidation and diffusion.

Very high-cycle fatigue failure in micron-scale polycrystalline silicon films: Effects of environment and surface oxide thickness

NASA Astrophysics Data System (ADS)

Alsem, D. H.; Timmerman, R.; Boyce, B. L.; Stach, E. A.; De Hosson, J. Th. M.; Ritchie, R. O.

2007-01-01

Fatigue failure in micron-scale polycrystalline silicon structural films, a phenomenon that is not observed in bulk silicon, can severely impact the durability and reliability of microelectromechanical system devices. Despite several studies on the very high-cycle fatigue behavior of these films (up to 1012cycles), there is still an on-going debate on the precise mechanisms involved. We show here that for devices fabricated in the multiuser microelectromechanical system process (MUMPs) foundry and Sandia Ultra-planar, Multi-level MEMS Technology (SUMMiT V™) process and tested under equi-tension/compression loading at ˜40kHz in different environments, stress-lifetime data exhibit similar trends in fatigue behavior in ambient room air, shorter lifetimes in higher relative humidity environments, and no fatigue failure at all in high vacuum. The transmission electron microscopy of the surface oxides in the test samples shows a four- to sixfold thickening of the surface oxide at stress concentrations after fatigue failure, but no thickening after overload fracture in air or after fatigue cycling in vacuo. We find that such oxide thickening and premature fatigue failure (in air) occur in devices with initial oxide thicknesses of ˜4nm (SUMMiT V™) as well as in devices with much thicker initial oxides ˜20nm (MUMPs). Such results are interpreted and explained by a reaction-layer fatigue mechanism. Specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure of the entire device. The entirety of the evidence presented here strongly indicates that the reaction-layer fatigue mechanism is the governing mechanism for fatigue failure in micron-scale polycrystalline silicon thin films.

Growth behavior of anodic porous alumina formed in malic acid solution

NASA Astrophysics Data System (ADS)

Kikuchi, Tatsuya; Yamamoto, Tsuyoshi; Suzuki, Ryosuke O.

2013-11-01

The growth behavior of anodic porous alumina formed on aluminum by anodizing in malic acid solutions was investigated. High-purity aluminum plates were electropolished in CH3COOH/HClO4 solutions and then anodized in 0.5 M malic acid solutions at 293 K and constant cell voltages of 200-350 V. The anodic porous alumina grew on the aluminum substrate at voltages of 200-250 V, and a black, burned oxide film was formed at higher voltages. The nanopores of the anodic oxide were only formed at grain boundaries of the aluminum substrate during the initial stage of anodizing, and then the growth region extended to the entire aluminum surface as the anodizing time increased. The anodic porous alumina with several defects was formed by anodizing in malic acid solution at 250 V, and oxide cells were approximately 300-800 nm in diameter.

Creep Behavior of Oxide/Oxide Composites with Monazite Fiber Coating at 1100 deg C in Air and in Steam Environments

DTIC Science & Technology

2008-09-01

monolithic ceramics initiates at small defects formed during processing. Minimization of such defects may improve performance, but thermal shock and cyclic...fiber tows are used in CMCs, where the use of small -diameter fibers causes a reduction in scale of microstructural defects associated with the fibers [7... Small Diameter · Improves matrix strength and facilitates fab- rication of thin and complex-shaped CMCs. · Low Density · Improves CMC specific properties

Steam Oxidation Testing in the Severe Accident Test Station

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

Pint, Bruce A.

After the March 2011 accident at Fukushima Daiichi, Oak Ridge National Laboratory (ORNL) began conducting high temperature steam oxidation testing of candidate materials for accident tolerant fuel (ATF) cladding in August 2011 [1-11]. The ATF concept is to enhance safety margins in light water reactors (LWR) during severe accident scenarios by identifying materials with 100× slower steam oxidation rates compared to current Zr-based alloys. In 2012, the ORNL laboratory equipment was expanded and made available to the entire ATF community as the Severe Accident Test Station (SATS) [4,12]. Compared to the current UO2/Zr-based alloy fuel system, an ATF alternative wouldmore » significantly reduce the rate of heat and hydrogen generation in the core during a coolant-limited severe accident [13-14]. The steam oxidation behavior of candidate materials is a key metric in the evaluation of ATF concepts and also an important input into models [15-17]. However, initial modeling work of FeCrAl cladding has used incomplete information on the physical properties of FeCrAl. Also, the steam oxidation data being collected at 1200°-1700°C is unique as no prior work has considered steam oxidation of alloys at such high temperatures. Also, because many accident scenarios include steadily increasing temperatures, the required data are not traditional isothermal exposures but exposures with varying “ramp” rates. In some cases, the steam oxidation behavior has been surprising and difficult to interpret. Thus, more fundamental information continues to be collected. In addition, more work continues to focus on commercially-manufactured tube material. This report summarizes recent work to characterize the behavior of candidate alloys exposed to high temperature steam, evaluate steam oxidation behavior in various ramp scenarios and continue to collect integral data on FeCrAl compared to conventional Zr-based cladding.« less

Photo-oxidation of Polymers Synthesized by Plasma and Initiated CVD

DOE PAGES

Baxamusa, Salmaan H.; Suresh, Aravind; Ehrmann, Paul; ...

2015-11-09

Plasma polymers are often limited by their susceptibility to spontaneous and photo-oxidation. We show that the unusual photoluminescence (PL) behavior of a plasma polymer of trans-2-butene is correlated with its photoluminescence strength. These photo-processes occur under blue light illumination (λ=405 nm), distinguishing them from traditional ultraviolet degradation of polymers. These photo-active defects are likely formed during the plasma deposition process and we show that a polymer synthesized using initiated (i)CVD, non-plasma method, has 1000× lower PL signal and enhanced photo-stability. In conclusion, non-plasma methods such as iCVD may therefore be a route to overcoming material aging issues that limit themore » adoption of plasma polymers.« less

Oxidation behavior of FeAl+Hf,Zr,B

NASA Technical Reports Server (NTRS)

Smialek, James L.; Doychak, Joseph

1988-01-01

The oxidation behavior of Fe-40Al-1Hf, Fe-40Al-1Hf-0.4B, and Fe-40Al-0.1Zr-0.4B (at. percent) alloys was characterized after 900, 1000, and 100 C exposures. Isothermal tests revealed parabolic kinetics after a period of transitional theta-alumina scale growth. The parabolic growth rates for the subsequent alpha-alumina scales were about five times higher than those for NiAl+0.1Zr alloys. The isothermally grown scales showed a propensity toward massive scale spallation due to both extensive rumpling from growth stresses and to an inner layer of HfO2. Cyclic oxidation for 200 1-hr cycles produced little degradation at 900 or 1000 C, but caused significant spallation at 1100 C in the form of small segments of the outer scale. The major difference in the cyclic oxidation of the three FeAl alloys was increased initial spallation for FeAl+Zr,B. Although these FeAl alloys showed many similarities to NiAl alloys, they were generally less oxidation resistant. It is believed that this resulted from nonoptimal levels of dopants and larger thermal expansion mismatch stresses.

Furnace Cyclic Oxidation Behavior of Multicomponent Low Conductivity Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Zhu, Dongming; Nesbitt, James A.; Barrett, Charles A.; McCue, Terry R.; Miller, Robert A.

2004-03-01

Ceramic thermal barrier coatings (TBCs) will play an increasingly important role in advanced gas turbine engines due to their ability to further increase engine operating temperatures and reduce cooling, thus helping achieve future engine low emission, high efficiency, and improved reliability goals. Advanced multicomponent zirconia (ZrO2)-based TBCs are being developed using an oxide defect clustering design approach to achieve the required coating low thermal conductivity and high-temperature stability. Although the new composition coatings were not yet optimized for cyclic durability, an initial durability screening of the candidate coating materials was conducted using conventional furnace cyclic oxidation tests. In this paper, furnace cyclic oxidation behavior of plasma-sprayed ZrO2-based defect cluster TBCs was investigated at 1163°C using 45 min hot-time cycles. The ceramic coating failure mechanisms were studied using scanning electron microscopy (SEM) combined with x-ray diffraction (XRD) phase analysis after the furnace tests. The coating cyclic lifetime is also discussed in relation to coating processing, phase structures, dopant concentration, and other thermo-physical properties.

Preparation of ceramic coating on Ti substrate by Plasma electrolytic oxidation in different electrolytes and evaluation of its corrosion resistance

NASA Astrophysics Data System (ADS)

Shokouhfar, M.; Dehghanian, C.; Baradaran, A.

2011-01-01

Ceramic oxide coatings (titania) were produced on Ti by micro-arc oxidation in different aluminate and carbonate based electrolytes. This process was conducted under constant pulsed DC voltage condition. The effect of KOH and NaF in aluminate based solution was also studied. The surface morphology, growth and phase composition of coatings were investigated using scanning electron microscope and X-ray diffraction. Corrosion behavior of the coatings was also examined by potentiodynamic polarization and electrochemical impedance spectroscopy. It was found that the sparking initiation voltage (spark voltage) had a significant effect on the form and properties of coatings. Coatings obtained from potassium aluminate based solution had a lower spark voltage, higher surface homogeneity and a better corrosion resistance than the carbonate based solution. Addition of NaF instead of KOH had improper effects on the homogeneity and adhesion of coatings which in turn caused a poor corrosion protection behavior of the oxide layer. AC impedance curves showed two time constants which is an indication of the coatings with an outer porous layer and an inner compact layer.

Furnace Cyclic Oxidation Behavior of Multi-Component Low Conductivity Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dong-Ming; Nesbitt, James A.; Barrett, Charles A.; McCue, Terry R.; Miller, Robert A.

2004-01-01

Ceramic thermal barrier coatings will play an increasingly important role in advanced gas turbine engines because of their ability to further increase engine operating temperatures and reduce cooling, thus helping achieve future engine low emission, high efficiency and improved reliability goals. Advanced multi-component zirconia-based thermal barrier coatings are being developed using an oxide defect clustering design approach to achieve the required coating low thermal conductivity and high temperature stability. Although the new composition coatings were not yet optimized for cyclic durability, an initial durability screening of the candidate coating materials was conducted using conventional furnace cyclic oxidation tests. In this paper, furnace cyclic oxidation behavior of plasma-sprayed zirconia-based defect cluster thermal barrier coatings was investigated at 1163 C using 45 min hot cycles. The ceramic coating failure mechanisms were studied using scanning electron microscopy (SEM) combined with X-ray diffraction (XRD) phase analysis after the furnace tests. The coating cyclic lifetime is also discussed in relation to coating processing, phase structures, dopant concentration, and other thermo-physical properties.

Metal Doped Manganese Oxide Thin Films for Supercapacitor Application.

PubMed

Tung, Mai Thanh; Thuy, Hoang Thi Bich; Hang, Le Thi Thu

2015-09-01

Co and Fe doped manganese oxide thin films were prepared by anodic deposition at current density of 50 mA cm(-2) using the electrolyte containing manganese sulfate and either cobalt sulfate or ferrous sulfate. Surface morphology and crystal structure of oxides were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD). Chemical composition of materials was analyzed by X-ray energy dispersive spectroscope (EDS), iodometric titration method and complexometric titration method, respectively. Supercapacitive behavior of Co and Fe doped manganese oxide films were characterized by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The results show that the doped manganese oxides are composed of nano fiber-like structure with radius of 5-20 nm and remain amorphous structure after heat treatment at 100 degrees C for 2 hours. The average valence of manganese increases from +3.808 to +3.867 after doping Co and from +3.808 to +3.846 after doping Fe. The doped manganese oxide film electrodes exhibited preferably ideal pseudo-capacitive behavior. The specific capacitance value of deposited manganese oxide reaches a maximum of 175.3 F/g for doping Co and 244.6 F/g for doping Fe. The thin films retained about 84% of the initial capacity even after 500 cycles of charge-discharge test. Doping Co and Fe decreases diffusion and charge transfer resistance of the films. The electric double layer capacitance and capacitor response frequency are increased after doping.

A Review of In Situ Observations of Crystallization and Growth in High Temperature Oxide Melts

NASA Astrophysics Data System (ADS)

Wang, Zhanjun; Sohn, Il

2018-05-01

This review summarizes the significant results of high-temperature confocal laser scanning microscopy (CLSM) and single hot thermocouple technology (SHTT) and its application in observing the crystallization and growth in high-temperature oxide melts from iron- and steel-making slags to continuous casting mold fluxes. Using in situ observations of CLSM and SHTT images of high-temperature molten oxides with time, temperature, and composition, the crystallization behavior, including crystal morphology, crystallization temperature, initial nucleation and growth rate, could be obtained. The broad range of applications using in situ observations during crystallization have provided a wealth of opportunities in pyrometallurgy and is provided in this review.

Evaluating electrically insulating films deposited on V-4% Cr-4% Ti by reactive CVD

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

Park, J.H.; Cho, W.D.

1997-04-01

Previous CaO coatings on V-4%Cr-4%Ti exhibited high-ohmic insulator behavior even though a small amount of vanadium from the alloy was incorporated in the coating. However, when the vanadium concentration in the coatings is > 15 wt%, the coating becomes conductive. When the vanadium concentration is high in localized areas, a calcium vanadate phase that exhibits semiconductor behavior can form. To explore this situation, CaO and Ca-V-O coatings were produced on vanadium alloys by chemical vapor deposition (CVD) and by a metallic-vapor process to investigate the electrical resistance of the coatings. Initially, the vanadium alloy specimens were either charged with oxygenmore » in argon that contained trace levels of oxygen, or oxidized for 1.5-3 h in a 1% CO-CO{sub 2} gas mixture or in air to form vanadium oxide at 625-650{degrees}C. Most of the specimens were exposed to calcium vapor at 800-850{degrees}C. Initial and final weights were obtained to monitor each step, and surveillance samples were removed for examination by optical and scanning electron microscopy and electron-energy-dispersive and X-ray diffraction analysis; the electrical resistivity was also measured. The authors found that Ca-V-O films exhibited insulator behavior when the ratio of calcium concentration to vanadium concentration R in the film was > 0.9, and semiconductor or conductor behavior for R < 0.8. However, in some cases, semiconductor behavior was observed when CaO-coated samples with R > 0.98 were exposed in liquid lithium. Based on these studies, the authors conclude that semiconductor behavior occurs if a conductive calcium vanadate phase is present in localized regions in the CaO coating.« less

[Effect of SO2 volume fraction in flue gas on the adsorption behaviors adsorbed by ZL50 activated carbon and kinetic analysis].

PubMed

Gao, Ji-xian; Wang, Tie-feng; Wang, Jin-fu

2010-05-01

The influence of SO2 dynamic adsorption behaviors using ZL50 activated carbon for flue gas desulphurization and denitrification under different SO2 volume fraction was investigated experimentally, and the kinetic analysis was conducted by kinetic models. With the increase of SO2 volume fraction in flue gas, the SO2 removal ratio and the activity ratio of ZL50 activated carbon decreased, respectively, and SO2 adsorption rate and capacity increased correspondingly. The calculated results indicate that Bangham model has the best prediction effect, the chemisorption processes of SO2 was significantly affected by catalytic oxidative reaction. The adsorption rate constant of Lagergren's pseudo first order model increased with the increase of inlet SO, volume fraction, which indicated that catalytic oxidative reaction of SO2 adsorbed by ZL50 activated carbon may be the rate controlling step in earlier adsorption stage. The Lagergren's and Bangham's initial adsorption rate were deduced and defined, respectively. The Ho's and Elovich's initial adsorption rate were also deduced in this paper. The Bangham's initial adsorption rate values were defined in good agreement with those of experiments. The defined Bangham's adsorptive reaction kinetic model can describe the SO2 dynamic adsorption rate well. The studied results indicated that the SO2 partial order of initial reaction rate was one or adjacent to one, while the O2 and water vapor partial order of initial reaction rate were constants ranging from 0.15-0.20 and 0.45-0.50, respectively.

NO3 and OH initiated secondary aerosol formation from aliphatic amines - salt formation and effect of water vapor

USDA-ARS?s Scientific Manuscript database

Aliphatic amines enter the atmosphere from a variety of sources, and have been detected existing in gas and particle phases in the atmosphere. Similar to ammonia, amines can form inorganic salt through acid-base reactions. However, the atmospheric behavior of amines with atmospheric oxidants (e.g. n...

Effects of soluble flavin on heterogeneous electron transfer between surface-exposed bacterial cytochromes and iron oxides

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

Wang, Zheming; Shi, Zhi; Shi, Liang

2015-08-25

Dissimilatory iron-reducing bacteria can utilize insoluble Fe(Mn)-oxides as a terminal electron acceptor under anaerobic conditions. For Shewanella species specifically, some evidence suggests that iron reduction is associated with the secretion of flavin mononucleotide (FMN) and riboflavin that are proposed to mediate electron transfer (Marsili et al., 2008). In this work, we used methyl viologen (MV•+)-encapsulated, porin-cytochrome complex (MtrCAB) embedded liposomes (MELs) as a synthetic model of the Shewanella outer membrane to investigate the proposed mediating behavior of secreted flavins. The reduction kinetics of goethite, hematite and lepidocrocite (200 µM) by MELs ([MV•+] ~ 42 µM and MtrABC ≤ 1 nM)more » were determined in the presence FMN at pH 7.0 in N2 atmosphere by monitoring the concentrations of MV•+ and FMN through their characteristic UV-visible absorption spectra. Experiments were performed where i) FMN and Fe(III)-oxide were mixed and then reacted with the reduced MELs and ii) FMN was reacted with the reduced MELs followed by addition of Fe(III)-oxide. The redox reactions proceeded in two steps: a fast step that was completed in a few seconds, and a slower one lasting over 400 seconds. For all three Fe(III)-oxides, the initial reaction rate in the presence of a low concentration of FMN (≤ 1 µM) was at least a factor of five faster than those with MELs alone, and orders of magnitude faster than those by FMNH2, suggesting that FMN may serve as a co-factor that enhances electron transfer from outer-membrane c-cytochromes to Fe(III)-oxides. The rate and extent of the initial reaction followed the order of lepidocrocite > hematite > goethite, the same as their reduction potentials, implying thermodynamic control on reaction rate. However, at higher FMN concentrations (> 1 µM), the reaction rates for both steps decreased and varied inversely with FMN concentration, indicating that FMN inhibited the MEL to Fe(III)-oxide electron transfer reaction. The implications of the observed kinetic behaviors to flavin-mediated Fe(III) oxide reduction in natural environments are discussed.« less

Field Effect Transistor Behavior in Electrospun Polyaniline/Polyethylene Oxide Nanofibers

NASA Technical Reports Server (NTRS)

Miranda, Felix A.; Theofylaktos, Noulie; Mueller, Carl H.; Pinto, Nicholas J.

2004-01-01

Novel transistors and logic devices based on nanotechnology concepts are under intense development. The potential for ultra-low-power circuitry makes nanotechnology attractive for applications such as digital electronics and sensors. For NASA applications, nanotechnology offers tremendous opportunities for increased onboard data processing, and thus autonomous decision-making ability, and novel sensors that detect and respond to environmental stimuli with little oversight requirements. Polyaniline (PANi) is an intriguing material because its electrical conductivity can be changed from insulating to metallic by varying the doping levels and conformations of the polymer chain, and when combined with polyethylene oxide (PEO), can be formed into nanofibers with diameters ranging from approximately 50 to 500 nm (depending on the deposition conditions). The initial goal of this work was to demonstrate transistor behavior in these nanofibers, thus creating a foundation for future logic devices.

The short- and long-term effects of orally administered high-dose reduced graphene oxide nanosheets on mouse behaviors.

PubMed

Zhang, Ding; Zhang, Zheyu; Liu, Yayun; Chu, Maoquan; Yang, Chengyu; Li, Wenhao; Shao, Yuxiang; Yue, Yan; Xu, Rujiao

2015-11-01

Reduced graphene oxide (rGO), a carbon-based nanomaterial, has enormous potential in biomedical research, including in vivo cancer therapeutics. Concerns over the toxicity remain outstanding and must be investigated before clinical application. The effect of rGO exposure on animal behaviors, such as learning and memory abilities, has not been clarified. Herein, we explored the short- and long-term effects of orally administered rGO on mouse behaviors, including general locomotor activity level, balance and neuromuscular coordination, exploratory and anxiety behaviors, and learning and memory abilities using open-field, rotarod, and Morris water maze tests. Compared with mice administered buffer-dispersed mouse chow or buffer alone, mice receiving a high dose of small or large rGO nanosheets showed little change in exploratory, anxiety-like, or learning and memory behaviors, although general locomotor activity, balance, and neuromuscular coordination were initially affected, which the mechanisms (e.g. the influence of rGO exposure on the activity of superoxide dismutase in mouse serum) were discussed. The results presented in this work look to provide a deep understanding of the in vivo toxicity of rGO to animals, especially its effect on learning and memory and other behaviors. Copyright © 2015 Elsevier Ltd. All rights reserved.

Corrosion Behavior of Alloy 625 in PbSO4-Pb3O4-PbCl2-ZnO-10 Wt Pct CdO Molten Salt Medium

NASA Astrophysics Data System (ADS)

Mohammadi Zahrani, E.; Alfantazi, A. M.

2012-08-01

Corrosion behavior and degradation mechanisms of alloy 625 under a 47.288 PbSO4-12.776 Pb3O4-6.844PbCl2-23.108ZnO-10CdO (wt pct) molten salt mixture under air atmosphere were studied at 873 K, 973 K, and 1073 K (600 °C, 700 °C, and 800 °C). Electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) measurements, and potentiodynamic polarization techniques were used to evaluate the degradation mechanisms and characterize the corrosion behavior of the alloy. Morphology, chemical composition, and phase structure of the corrosion products and surface layers of the corroded specimens were studied by scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) and X-ray map analyses. Results confirmed that during the exposure of alloy 625 to the molten salt, chromium was mainly dissolved through an active oxidation process as CrO3, Cr2O3, and CrNbO4, while nickel dissolved only as NiO in the system. Formation of a porous and nonprotective oxide layer with low resistance is responsible for the weak protective properties of the barrier layer at high temperatures of 973 K and 1073 K (700 °C and 800 °C). There were two kinds of attack for INCONEL 625, including general surface corrosion and pitting. Pitting corrosion occurred due to the breakdown of the initial oxide layer by molten salt dissolution of the oxide or oxide cracking.

Cellobiose Dehydrogenase Inhibition of Polymerization of Phenolic Compounds and Enhancing Lignin Degradation by Lignina.

PubMed

Fang, Jing; Liu, Wen; Gao, Pei-Ji

1999-01-01

The kinetic behavior of cellobiose dehydrogenase (CDH) was investigated by steady-state initial velocity studies. Variation in the concentration of one substrate led to changes in K(m) and V(max) of the other substrate. The results were consistent with a ping-pong mechanism. In the presence of cellobiose, CDH could reduce many oxidized products catalyzed by soybean hull peroxidase (SHP). The oxidation product of 1-hydroxybenzotriazole (HBT) catalyzed by SHP inactivated the enzyme itself however, CDH could prevent SHP from inactivation by reducing the oxidation product of HBT. CDH could also inhibit the polymerization of phenolic compounds catalyzed by SHP. It was found that the addition of CDH could enhance kraft pulp lignin degradation by ligninases.

Inhibition effect in supercritical water oxidation of hydroquinone

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

Thammanayakatip, C.; Oshima, Yoshito; Koda, Seiichiro

1998-05-01

In the oxidation reactions of hydroquinone under a supercritical conditions (temperature of 683 K and pressure of 24.5 MPa), the conversion was found to become saturated despite the very fast initial reaction. This behavior was quite different from that under a subcritical condition (temperature of 633 K and pressure of 24.5 MPa). Under both conditions, p-benzoquinone was found to be an important intermediate. The yield of CO{sub 2} was very small, which indicates a strong inhibition effect of hydroquinone and/or its derivatives. These inhibition phenomena should be taken into account very carefully in the application of supercritical water oxidation formore » treating waste organic materials where a complete decomposition is very important.« less

Forming-free colossal resistive switching effect in rare-earth-oxide Gd2O3 films for memristor applications

NASA Astrophysics Data System (ADS)

Cao, Xun; Li, Xiaomin; Gao, Xiangdong; Yu, Weidong; Liu, Xinjun; Zhang, Yiwen; Chen, Lidong; Cheng, Xinhong

2009-10-01

The reproducible forming-free resistive switching (RS) behavior in rare-earth-oxide Gd2O3 polycrystalline thin film was demonstrated. The characteristic of this forming-free RS was similar to that of other forming-necessary binary RS materials except that its initial resistance starts from not the high resistance state (HRS) but the low resistance state (LRS). An ultrahigh resistance switching ratio from HRS to LRS of about six to seven orders of magnitude was achieved at a bias voltage of 0.6 V. Mechanism analysis indicated that the existence of metallic Gd in the Gd2O3 films plays an important role in the forming-free RS performance. Our work provides a novel material with interesting RS behavior, which is beneficial to deepen our understanding of the origin of RS phenomenon.

Microstructural effects on the room and elevated temperature low cycle fatigue behavior of Waspaloy. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Lerch, B. A.

1982-01-01

Longitudinal specimens of Waspaloy containing either coarse grains with small gamma or fine grains with large gamma were tested in air at a frequency of 0.33 Hz or 0.50 Hz. The coarse grained structures exhibited planar slip on (III) planes and precipitate shearing at all temperatures. Cracks initiated by a Stage 1 mechanism and propagated by a striation forming mechanism. At 700 C and 800 C, cleavage and intergranular cracking were observed. Testing at 500 C, 700 C, and 800 C caused precipitation of grain boundary carbides. At 700 C, carbides precipitated on slip bands. The fine grained structures exhibited planar slip on (111) planes. Dislocations looped the large gamma precipitates. This structure led to stress saturation and propagation was observed. Increasing temperatures resulted in increased specimen oxidation for both heat treatments. Slip band and grain boundary oxidation were observed. At 800 C, oxidized grain boundaries were cracked by intersecting slip bands which resulted in intergranular failure. The fine specimens had crack initiation later in the fatigue life, but with more rapid propagation crack propagation.

Elucidating the oxide growth mechanism on platinum at the cathode in PEM fuel cells.

PubMed

Redmond, Erin L; Setzler, Brian P; Alamgir, Faisal M; Fuller, Thomas F

2014-03-21

Simulations of platinum oxidation in literature have yet to fully replicate an experimental cyclic voltammogram. In this manuscript a mechanism for platinum oxidation is proposed based upon the results of in operando X-ray absorption spectroscopy, where it was found that PtO2 is present at longer hold times. A new method to quantify extended X-ray absorption fine structure data is presented, and the extent of oxidation is directly compared to electrochemical data. This comparison indicated that PtO2 was formed at the expense of an initial oxide species. From previous literature studies it can be concluded that the rate of platinum oxidation is not a function of only potential and coverage. To that end, the concept of a heterogeneous oxide layer was introduced into the model, whereby place-exchanged PtO2 structures of varying energy states are formed through a single transition state. This treatment allowed, for the first time, the simulation of the correct current-potential behavior at varying scan rates and upper potential limits.

Accelerated aging studies of UHMWPE. I. Effect of resin, processing, and radiation environment on resistance to mechanical degradation.

PubMed

Edidin, A A; Herr, M P; Villarraga, M L; Muth, J; Yau, S S; Kurtz, S M

2002-08-01

The resin and processing route have been identified as potential variables influencing the mechanical behavior, and hence the clinical performance, of ultra-high molecular weight polyethylene (UHMWPE) orthopedic components. Researchers have reported that components fabricated from 1900 resin may oxidize to a lesser extent than components fabricated from GUR resin during shelf aging after gamma sterilization in air. Conflicting reports on the oxidation resistance for 1900 raise the question of whether resin or manufacturing method, or an interaction between resin and manufacturing method, influences the mechanical behavior of UHMWPE. We conducted a series of accelerated aging studies (no aging, aging in oxygen or in nitrogen) to systematically examine the influence of resin (GUR or 1900), manufacturing method (bulk compression molding or extrusion), and sterilization method (none, in air, or in nitrogen) on the mechanical behavior of UHMWPE. The small punch testing technique was used to evaluate the mechanical behavior of the materials, and Fourier transform infrared spectroscopy was used to characterize the oxidation in selected samples. Our study showed that the sterilization environment, aging condition, and specimen location (surface or subsurface) significantly affected the mechanical behavior of UHMWPE. Each of the three polyethylenes evaluated seem to degrade according to a similar pathway after artificial aging in oxygen and gamma irradiation in air. The initial ability of the materials to exhibit post-yield strain hardening was significantly compromised by degradation. In general, there were only minor differences in the aging behavior of molded and extruded GUR 1050, whereas the molded 1900 material seemed to degrade slightly faster than either of the 1050 materials. Copyright 2002 Wiley Periodicals, Inc.

Effect of solution treatment on the fatigue behavior of an as-forged Mg-Zn-Y-Zr alloy

NASA Astrophysics Data System (ADS)

Wang, S. D.; Xu, D. K.; Wang, B. J.; Han, E. H.; Dong, C.

2016-04-01

Through investigating and comparing the fatigue behavior of an as-forged Mg-6.7Zn-1.3Y-0.6Zr (wt.%) alloy before and after solid solution treatment (T4) in laboratory air, the effect of T4 treatment on fatigue crack initiation was disclosed. S-N curves illustrated that the fatigue strength of as-forged samples was 110 MPa, whereas the fatigue strength of T4 samples was only 80 MPa. Observations to fracture surfaces demonstrated that for as-forged samples, fatigue crack initiation sites were covered with a layer of oxide film. However, due to the coarse grain structure and the dissolution of MgZn2 precipitates, the activation and accumulation of {10-12} twins in T4 samples were much easier, resulting in the preferential fatigue crack initiation at cracked twin boundaries (TBs). Surface characterization demonstrated that TB cracking was mainly ascribed to the incompatible plastic deformation in the twinned area and nearby α-Mg matrix.

Competitive Adsorption and Oxidation Behavior of Heavy Metals on nZVI Coated with TEOS.

PubMed

Eglal, Mahmoud M; Ramamurthy, Amruthur S

2015-11-01

Zero valent iron nanoparticle (nanofer ZVI) is a powerful substance due to its coating with tetraethyl orthosilicate (TEOS). Tetraethyl orthosilicate imparts higher reactivity and decreases particle agglomeration. The competitive removal and displacement of multi-metals are influenced by time, pH, and initial concentration, the presence and properties of competing metals ion in the solution. For both the isotherm and kinetic studies performed for multi-metal removal experiments, compared to Pb II and Cd II, Cu II experienced a higher removal rate during the initial 5 minutes. After 120 minutes, all metals achieved removal efficiency in the range of 95 to 99%. The results of single and competitive kinetic tests for all three metals during the initial 5 minutes indicated that the presence of other metals generally reduce removal efficiency of metals. Both kinetic test and electron dispersive spectroscope (EDS) studies found that Cu II gets removed faster than the other metals. Pseudo-second order behavior was noted for the multi-metal removal systems.

Moderate treadmill exercise prevents oxidative stress-induced anxiety-like behavior in rats.

PubMed

Salim, Samina; Sarraj, Nada; Taneja, Manish; Saha, Kaustuv; Tejada-Simon, Maria Victoria; Chugh, Gaurav

2010-04-02

Recent work has suggested correlation of oxidative stress with anxiety-like behavior. There also is evidence for anxiolytic effects of physical exercise. However, a direct role of oxidative stress in anxiety is not clear and a protective role of physical exercise in oxidative stress-mediated anxiety has never been addressed. In this study, we have utilized rats to test direct involvement of oxidative stress with anxiety-like behavior and have identified oxidative stress mechanisms likely involved in anxiolytic effects of physical exercise. Intraperitoneal injections at non-toxic dose of l-buthionine-(S,R)-sulfoximine (BSO), an agent that increases oxidative stress markers, increased anxiety-like behavior of rats compared to vehicle-treated control rats. Prior 2 weeks treatment with the antioxidant, tempol attenuated BSO-induced anxiety-like behavior of rats suggesting a role of oxidative stress in this phenomenon. Moreover, moderate treadmill exercise prevented BSO-induced anxiety-like behavior of rats and also prevented BSO-mediated increase in oxidative stress markers in serum, urine and brain tissue homogenates from hippocampus, amygdala and locus coeruleus. Thus increasing oxidative stress increases anxiety-like behavior of rats. Moreover, antioxidant or treadmill exercise training both reduce oxidative stress in the rat brain regions implicated in anxiety response and prevent anxiety-like behavior of rats. Published by Elsevier B.V.

High Temperature Mechanical Behavior of Polycrystalline Alumina from Mixed Nanometer and Micrometer Powders

NASA Technical Reports Server (NTRS)

Goldsby, Jon C.

2001-01-01

Sintered aluminum oxide materials were formed using commercial methods from mechanically mixed powders of nano-and micrometer alumina. The powders were consolidated at 1500 and 1600 C with 3.2 and 7.2 ksi applied stress in argon. The conventional micrometer sized powders failed to consolidate. While 100 percent nanometer-sized alumina and its mixture with the micrometer powders achieved less than 99 percent density. Preliminary high temperature creep behavior indicates no super-plastic strains. However high strains (less than 0.65 percent) were generated in the nanometer powder, due to cracks and linked voids initiated by cavitation.

Holographic investigation of solid propellant particulates

NASA Astrophysics Data System (ADS)

Gillespie, T. R.

1981-12-01

The investigation completed the development process to establish a technique to obtain holographic recordings of particulate behavior during the combustion process of solid propellants in a two-dimensional rocket motor. Holographic and photographic recordings were taken in a crossflow environment using various compositions of metallized propellants. The reconstructed holograms are used to provide data on the behavior of aluminum/aluminum oxide particulates in a steady state combustion environment as a function of the initial aluminum size cast into the propellant. High speed, high resolution motion pictures were taken to compare the cinematic data with that available from the holograms.

Oxidation behavior of U-Si compounds in air from 25 to 1000 C

NASA Astrophysics Data System (ADS)

Sooby Wood, E.; White, J. T.; Nelson, A. T.

2017-02-01

The air oxidation behavior of U3Si2, USi, and U3Si5 is studied from room temperature to 1000 C. The onsets of breakaway oxidation for each compound are identified during synthetic air ramps to 1000 C using thermogravimetric analysis. Isothermal air oxidation tests are performed below and above the breakaway oxidation onset to discern the oxidation kinetic behavior of these candidate accident tolerant fuel forms. Uranium metal is tested in the same manner to provide a reference for the oxidation behavior. Thermogravimetric, x-ray diffraction, and scanning electron microscopy analysis are presented here along with a discussion of the oxidation behavior of these materials and the impact of the lack of oxidation resistance to their deployment as accident tolerant nuclear fuels.

Corrosion Behavior of Detonation Gun Sprayed Fe-Al Type Intermetallic Coating

PubMed Central

Senderowski, Cezary; Chodala, Michal; Bojar, Zbigniew

2015-01-01

The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior of Fe-Al type coatings under air atmosphere. The oxide layer ensures satisfying oxidation resistance, even at 950 and 1100 °C. Hematite, α-Al2O3 and metastable alumina phases were noticed on the coatings top surface, which preserves its initial thickness providing protection to the underlying substrate. In general, only negligible changes of the phase composition of the coatings were noticed with simultaneous strengthening controlled in the micro-hardness measurements, even after 10-hours of heating at 1100 °C. On the other hand, the electrochemical corrosion tests, which were carried out in 200 ppm Cl− (NaCl) and pH ~4 (H2SO4) solution to simulate the acid-rain environment, reveal higher values of the breakdown potential for D-gun sprayed Fe-Al type coatings than the ones for the bulk Fe-Al type alloy and Cr21Mn9Ni4 austenitic valve steel. This enables these materials to be used in structural and multifunctional applications in aggressive environments, including acidic ones. PMID:28787991

Oxidation behavior of U-Si compounds in air from 25 to 1000 C

DOE PAGES

Wood, E. Sooby; White, J. T.; Nelson, A. T.

2016-12-18

The air oxidation behavior of U 3Si 2, USi, and U 3Si 5 is studied from room temperature to 1000 C. Moreover, the onsets of breakaway oxidation for each compound are identified during synthetic air ramps to 1000 C using thermogravimetric analysis. Isothermal air oxidation tests are performed below and above the breakaway oxidation onset to discern the oxidation kinetic behavior of these candidate accident tolerant fuel forms. Uranium metal is tested in the same manner to provide a reference for the oxidation behavior. We present thermogravimetric, x-ray diffraction, and scanning electron microscopy analysis here along with a discussion ofmore » the oxidation behavior of these materials and the impact of the lack of oxidation resistance to their deployment as accident tolerant nuclear fuels.« less

Complete and simultaneous removal of ammonium and m-cresol in a nitrifying sequencing batch reactor.

PubMed

Zepeda, Alejandro; Ben-Youssef, Chérif; Rincón, Susana; Cuervo-López, Flor; Gómez, Jorge

2013-06-01

The kinetic behavior, oxidizing ability and tolerance to m-cresol of a nitrifying sludge exposed to different initial concentrations of m-cresol (0-150 mg C L(-1)) were evaluated in a sequencing batch reactor fed with 50 mg NH4 (+)-N L(-1) and operated during 4 months. Complete removal of ammonium and m-cresol was achieved independently of the initial concentration of aromatic compound in all the assays. Up to 25 mg m-cresol-C L(-1) (C/N ratio of 0.5), the nitrifying yield (Y-NO3 (-)) was 0.86 ± 0.05, indicating that the nitrate was the main product of the process; no biomass growth was detected. From 50 to 150 mg m-cresol-C L(-1) (1.0 ≤ C/N ≤ 3.0), simultaneous microbial growth and partial ammonium-to-nitrate conversion were obtained, reaching a maximum microbial total protein concentration of 0.763 g L(-1) (247 % of its initial value) and the lowest Y-NO3 (-) 0.53 ± 0.01 at 150 mg m-cresol-C L(-1). m-Cresol induced a significant decrease in the values of both specific rates of ammonium and nitrite oxidation, being the ammonium oxidation pathway the mainly inhibited. The nitrifying sludge was able to completely oxidize up to 150 mg m-cresol-C L(-1) by SBR cycle, reaching a maximum specific removal rate of 6.45 g m-cresol g(-1) microbial protein-N h(-1). The number of SBR cycles allowed a metabolic adaptation of the nitrifying consortium since nitrification inhibition decreased and faster oxidation of m-cresol took place throughout the cycles.

Oxidation Resistance of Materials Based on Ti3AlC2 Nanolaminate at 600 °C in Air

NASA Astrophysics Data System (ADS)

Ivasyshyn, Andrij; Ostash, Orest; Prikhna, Tatiana; Podhurska, Viktoriya; Basyuk, Tatiana

2016-08-01

The oxidation behavior of Ti3AlC2-based materials had been investigated at 600 °C in static air for 1000 h. It was shown that the intense increase of weight gain per unit surface area for sintered material with porosity of 22 % attributed to oxidation of the outer surface of the specimen and surfaces of pores in the bulk material. The oxidation kinetics of the hot-pressed Ti3AlC2-based material with 1 % porosity remarkably increased for the first 15 h and then slowly decreased. The weight gain per unit surface area for this material was 1.0 mg/cm2 after exposition for 1000 h. The intense initial oxidation of Ti3AlC2-based materials can be eliminated by pre-oxidation treatment at 1200 °C in air for 2 h. As a result, the weight gain per unit surface area for the pre-oxidized material did not exceed 0.11 mg/cm2 after 1000 h of exposition at 600 °C in air. It was demonstrated that the oxidation resistance of Ti3AlC2-based materials can be significantly improved by niobium addition.

Impact of Microstructure on MoS 2 Oxidation and Friction

DOE PAGES

Curry, John F.; Wilson, Mark A.; Luftman, Henry S.; ...

2017-07-31

In this work, we demonstrate the role of microstructure in the friction and oxidation behavior of the lamellar solid lubricant molybdenum disulfide (MoS 2). We report on systematic investigations of oxidation and friction for two MoS 2 films with distinctively different microstructures—amorphous and planar/highly-ordered—before and after exposure to atomic oxygen (AO) and high-temperature (250 °C) molecular oxygen. A combination of experimental tribology, molecular dynamics simulations, X-ray photoelectron spectroscopy (XPS), and high-sensitivity low-energy ion scattering (HS-LEIS) was used to reveal new insights about the links between structure and properties of these widely utilized low-friction materials. Initially, ordered MoS 2 films showedmore » a surprising resistance to both atomic and molecular oxygens (even at elevated temperature), retaining characteristic low friction after exposure to extreme oxidative environments. Finally, XPS shows comparable oxidation of both coatings via AO; however, monolayer resolved compositional depth profiles from HS-LEIS reveal that the microstructure of the ordered coatings limits oxidation to the first atomic layer.« less

The influence of interfacial defects on fast charge trapping in nanocrystalline oxide-semiconductor thin film transistors

NASA Astrophysics Data System (ADS)

Kim, Taeho; Hur, Jihyun; Jeon, Sanghun

2016-05-01

Defects in oxide semiconductors not only influence the initial device performance but also affect device reliability. The front channel is the major carrier transport region during the transistor turn-on stage, therefore an understanding of defects located in the vicinity of the interface is very important. In this study, we investigated the dynamics of charge transport in a nanocrystalline hafnium-indium-zinc-oxide thin-film transistor (TFT) by short pulse I-V, transient current and 1/f noise measurement methods. We found that the fast charging behavior of the tested device stems from defects located in both the front channel and the interface, following a multi-trapping mechanism. We found that a silicon-nitride stacked hafnium-indium-zinc-oxide TFT is vulnerable to interfacial charge trapping compared with silicon-oxide counterpart, causing significant mobility degradation and threshold voltage instability. The 1/f noise measurement data indicate that the carrier transport in a silicon-nitride stacked TFT device is governed by trapping/de-trapping processes via defects in the interface, while the silicon-oxide device follows the mobility fluctuation model.

Oxidation- and Creep-Enhanced Fatigue of Haynes 188 Alloy-Oxide Scale System Under Simulated Pulse Detonation Engine Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.

2002-01-01

The development of the pulse detonation engine (PDE) requires robust design of the engine components that are capable of enduring harsh detonation environments. In this study, a high cycle thermal fatigue test rig was developed for evaluating candidate PDE combustor materials using a CO2 laser. The high cycle thermal fatigue behavior of Haynes 188 alloy was investigated under an enhanced pulsed laser test condition of 30 Hz cycle frequency (33 ms pulse period, and 10 ms pulse width including 0.2 ms pulse spike). The temperature swings generated by the laser pulses near the specimen surface were characterized by using one-dimensional finite difference modeling combined with experimental measurements. The temperature swings resulted in significant thermal cyclic stresses in the oxide scale/alloy system, and induced extensive surface cracking. Striations of various sizes were observed at the cracked surfaces and oxide/alloy interfaces under the cyclic stresses. The test results indicated that oxidation and creep-enhanced fatigue at the oxide scale/alloy interface was an important mechanism for the surface crack initiation and propagation under the simulated PDE condition.

Impact of Microstructure on MoS 2 Oxidation and Friction

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

Curry, John F.; Wilson, Mark A.; Luftman, Henry S.

In this work, we demonstrate the role of microstructure in the friction and oxidation behavior of the lamellar solid lubricant molybdenum disulfide (MoS 2). We report on systematic investigations of oxidation and friction for two MoS 2 films with distinctively different microstructures—amorphous and planar/highly-ordered—before and after exposure to atomic oxygen (AO) and high-temperature (250 °C) molecular oxygen. A combination of experimental tribology, molecular dynamics simulations, X-ray photoelectron spectroscopy (XPS), and high-sensitivity low-energy ion scattering (HS-LEIS) was used to reveal new insights about the links between structure and properties of these widely utilized low-friction materials. Initially, ordered MoS 2 films showedmore » a surprising resistance to both atomic and molecular oxygens (even at elevated temperature), retaining characteristic low friction after exposure to extreme oxidative environments. Finally, XPS shows comparable oxidation of both coatings via AO; however, monolayer resolved compositional depth profiles from HS-LEIS reveal that the microstructure of the ordered coatings limits oxidation to the first atomic layer.« less

Oxidation characteristics of porous-nickel prepared by powder metallurgy and cast-nickel at 1273 K in air for total oxidation time of 100 h.

PubMed

Mohamed, Lamiaa Z; Ghanem, Wafaa A; El Kady, Omayma A; Lotfy, Mohamed M; Ahmed, Hafiz A; Elrefaie, Fawzi A

2017-11-01

The oxidation behavior of two types of inhomogeneous nickel was investigated in air at 1273 K for a total oxidation time of 100 h. The two types were porous sintered-nickel and microstructurally inhomogeneous cast-nickel. The porous-nickel samples were fabricated by compacting Ni powder followed by sintering in vacuum at 1473 K for 2 h. The oxidation kinetics of the samples was determined gravimetrically. The topography and the cross-section microstructure of each oxidized sample were observed using optical and scanning electron microscopy. X-ray diffractometry and X-ray energy dispersive analysis were used to determine the nature of the formed oxide phases. The kinetic results revealed that the porous-nickel samples had higher trend for irreproducibility. The average oxidation rate for porous- and cast-nickel samples was initially rapid, and then decreased gradually to become linear. Linear rate constants were 5.5 × 10 -8  g/cm 2  s and 3.4 × 10 -8  g/cm 2  s for the porous- and cast-nickel samples, respectively. Initially a single-porous non-adherent NiO layer was noticed on the porous- and cast-nickel samples. After a longer time of oxidation, a non-adherent duplex NiO scale was formed. The two layers of the duplex scales were different in color. NiO particles were observed in most of the pores of the porous-nickel samples. Finally, the linear oxidation kinetics and the formation of porous non-adherent duplex oxide scales on the inhomogeneous nickel substrates demonstrated that the addition of new layers of NiO occurred at the scale/metal interface due to the thermodynamically possible reaction between Ni and the molecular oxygen migrating inwardly.

Fatigue crack growth and low cycle fatigue of two nickel base superalloys

NASA Technical Reports Server (NTRS)

Stoloff, N. S.; Duquette, D. J.; Choe, S. J.; Golwalkar, S.

1983-01-01

The fatigue crack growth and low cycle fatigue behavior of two P/M superalloys, Rene 95 and Astroloy, in the hot isostatically pressed (HIP) condition, was determined. Test variables included frequency, temperature, environment, and hold times at peak tensile loads (or strains). Crack initiation sites were identified in both alloys. Crack growth rates were shown to increase in argon with decreasing frequency or with the imposition of hold times. This behavior was attributed to the effect of oxygen in the argon. Auger analyses were performed on oxide films formed in argon. Low cycle fatigue lives also were degraded by tensile hold, contrary to previous reports in the literature. The role of environment in low cycle fatigue behavior is discussed.

Oxidation of high-temperature intermetallics; Proceedings of the Workshop, Cleveland, OH, Sept. 22, 23, 1988

NASA Technical Reports Server (NTRS)

Grobstein, Toni (Editor); Doychak, Joseph (Editor)

1989-01-01

The present conference on the high-temperature oxidation behavior of aerospace structures-applicable intermetallic compounds discusses the influence of reactive-element additions on the oxidation of Ni3Al base alloys, the effect of Ni3Al oxidation below 850 C on fracture behavior, the oxidation of FeAl + Hf, Zr, and B, the synergistic effect of Al and Si on the oxidation resistance of Fe alloys, and pack cementation coatings of Cr-Al on Fe, Ni, and Co alloys. Also discussed are the formation of alumina on Nb- and Ti-base alloys, the oxidation behavior of titanium aluminide alloys, silicide coatings for refractory metals, the oxidation of chromium disilicide, and the oxidation behavior of nickel beryllides.

Role of Nitric Oxide in Stress-Induced Anxiety: From Pathophysiology to Therapeutic Target.

PubMed

Kumar, A; Chanana, P

2017-01-01

Stress is often marked by a state of hyperarousal to aid the initiation of necessary stress response for the successful management of stressful stimuli. It can be manifested as a challenge (stimulus) that requires behavioral, psychological, and physiological adaptations for the maintenance of a state of homeostasis in response to stressful stimuli. In an organism, miscellaneous stressors trigger a wide spectrum of alterations in hormonal and neuronal physiologies, resulting in behavioral (anxiety and depression disorders, diminished food intake and gastrointestinal dysfunctions, decline in sexual behavior, diabetes, and loss of cognitive function) and other physiological responses. Stress serves as a potent etiological link to development of several neuropsychiatric diseases such as depression, anxiety, and cognitive impairments. Exposure to stressful stimuli has been found to be associated with activation of nitric oxide synthase and generation of NO which reacts with spontaneous oxygen species to aid formation of active nitrogen radicals. High concentrations of reactive nitrogen radicals may cause damage to intracellular proteins, in addition to causing impairment to components of the mitochondrial transport chain, leading to cellular energy deficiency. This may further serve as an etiological link to the development of secondary neurological diseases associated with chronic stress. Also, during stress exposure, pharmacological inhibition of nitric oxide production displays reduction in indicators of anxiety- and depressive-like behavior in animal models. Therefore, the purpose of this chapter is to present an overview on the role of NO in stress-evoked emergence of secondary neurological disorders like anxiety as well as citing examples where NO has been used as a therapeutic target for the management of stress-induced anxiety-like behavior. © 2017 Elsevier Inc. All rights reserved.

Mitochondrial capacity, oxidative damage and hypoxia gene expression are associated with age-related division of labor in honey bee (Apis mellifera L.) workers.

PubMed

Cervoni, Mário S; Cardoso-Júnior, Carlos A M; Craveiro, Giovana; Souza, Anderson de O; Alberici, Luciane C; Hartfelder, Klaus

2017-11-01

During adult life, honey bee workers undergo a succession of behavioral states. Nurse bees perform tasks inside the nest, and when they are about 2-3 weeks old they initiate foraging. This switch is associated with alterations in diet, and with the levels of juvenile hormone and vitellogenin circulating in hemolymph. It is not clear whether this behavioral maturation involves major changes at the cellular level, such as mitochondrial activity and the redox environment in the head, thorax and abdomen. Using high-resolution respirometry, biochemical assays and RT-qPCR, we evaluated the association of these parameters with this behavioral change. We found that tissues from the head and abdomen of nurses have a higher oxidative phosphorylation capacity than those of foragers, while for the thorax we found the opposite situation. As higher mitochondrial activity tends to generate more H 2 O 2 , and H 2 O 2 is known to stabilize HIF-1α, this would be expected to stimulate hypoxia signaling. The positive correlation that we observed between mitochondrial activity and hif-1α gene expression in abdomen and head tissue of nurses would be in line with this hypothesis. Higher expression of antioxidant enzyme genes was observed in foragers, which could explain their low levels of protein carbonylation. No alterations were seen in nitric oxide (NO) levels, suggesting that NO signaling is unlikely to be involved in behavioral maturation. We conclude that the behavioral change seen in honey bee workers is reflected in differential mitochondrial activities and redox parameters, and we consider that this can provide insights into the underlying aging process. © 2017. Published by The Company of Biologists Ltd.

Improvement of Bipolar Switching Properties of Gd:SiOx RRAM Devices on Indium Tin Oxide Electrode by Low-Temperature Supercritical CO2 Treatment.

PubMed

Chen, Kai-Huang; Chang, Kuan-Chang; Chang, Ting-Chang; Tsai, Tsung-Ming; Liang, Shu-Ping; Young, Tai-Fa; Syu, Yong-En; Sze, Simon M

2016-12-01

Bipolar switching resistance behaviors of the Gd:SiO2 resistive random access memory (RRAM) devices on indium tin oxide electrode by the low-temperature supercritical CO2-treated technology were investigated. For physical and electrical measurement results obtained, the improvement on oxygen qualities, properties of indium tin oxide electrode, and operation current of the Gd:SiO2 RRAM devices were also observed. In addition, the initial metallic filament-forming model analyses and conduction transferred mechanism in switching resistance properties of the RRAM devices were verified and explained. Finally, the electrical reliability and retention properties of the Gd:SiO2 RRAM devices for low-resistance state (LRS)/high-resistance state (HRS) in different switching cycles were also measured for applications in nonvolatile random memory devices.

Furnace Cyclic Behavior of Plasma-Sprayed Zirconia-Yttria and Multi-Component Rare Earth Oxide Doped Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Nesbitt, James A.; McCue, Terry R.; Barrett, Charles A.; Miller, Robert A.

2002-01-01

Ceramic thermal barrier coatings will play an increasingly important role in advanced gas turbine engines because of their ability to enable further increases in engine temperatures. However, the coating performance and durability become a major concern under the increasingly harsh thermal cycling conditions. Advanced zirconia- and hafnia-based cluster oxide thermal barrier coatings with lower thermal conductivity and improved thermal stability are being developed using a high-heat-flux laser-rig based test approach. Although the new composition coatings were not yet optimized for cyclic durability, an initial durability screening of numerous candidate coating materials was carried out using conventional furnace cyclic tests. In this paper, furnace thermal cyclic behavior of the advanced plasma-sprayed zirconia-yttria-based thermal barrier coatings that were co-doped with multi-component rare earth oxides was investigated at 1163 C using 45 min hot cycles. The ceramic coating failure mechanisms were studied by using scanning electron microscopy combined with X-ray diffraction phase analysis after the furnace tests. The coating cyclic lifetime will be discussed in relation to coating phase structures, total dopant concentrations, and other properties.

Reverse Stability Kinetics of Meat Pigment Oxidation in Aqueous Extract from Fresh Beef.

PubMed

Frelka, John C; Phinney, David M; Wick, Macdonald P; Heldman, Dennis R

2017-12-01

The use of kinetic models is an evolving approach to describing quality changes in foods during processes, including storage. Previous studies indicate that the oxidation rate of myoglobin is accelerated under frozen storage conditions, a phenomenon termed reverse stability. The goal of this study was to develop a model for meat pigment oxidation to incorporate the phenomenon of reverse stability. In this investigation, the model system was an aqueous extract from beef which was stored under a range of temperatures, both unfrozen and frozen. The kinetic analysis showed that in unfrozen solutions, the temperature dependence of oxidation rate followed Arrhenius kinetics. However, under in frozen solutions the rate of oxidation increased with decreasing temperature until reaching a local maximum around -20 °C. The addition of NaCl to the model system increased oxidation rates at all temperatures, even above the initial freezing temperature. This observation suggests that this reaction is dependent on the ionic strength of the solution as well as temperature. The mechanism of this deviant kinetic behavior is not fully understood, but this study shows that the interplay of temperature and composition on the rate of oxidation of meat pigments is complicated and may involve multiple mechanisms. A better understanding of the kinetics of quality loss in a meat system allows for a re-examination of the current recommendations for frozen storage. The deviant kinetic behavior observed in this study indicates that the relationship between quality loss and temperature in a frozen food is not as simple as once thought. Product-specific recommendations could be implemented in the future that would allow for a decrease in energy consumption without a significant loss of quality. © 2017 Institute of Food Technologists®.

The simple preparation of birnessite-type manganese oxide with flower-like microsphere morphology and its remarkable capacity retention

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

Zhu, Gang; Deng, Lingjuan; Wang, Jianfang

Graphical abstract: Flower-like birnessite-type manganese oxide microspheres with large specific surface area and excellent electrochemical properties have been prepared by a facile hydrothermal method. Highlights: ► Birnessite-type manganese oxide with flower-like microsphere morphology and large specific surface area. ► A facile low-temperature hydrothermal method. ► Novel flower-like microsphere consists of the thin nano-platelets. ► Birnessite-type manganese oxide exhibits an ideal capacitive behavior and excellent cycling stability. -- Abstract: Birnessite-type manganese oxide with flower-like microsphere morphology and large specific surface area has been prepared by hydrothermal treating a mixture solution of KMnO{sub 4} and (NH{sub 4}){sub 2}SO{sub 4} at 90 °Cmore » for 24 h. The obtained material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N{sub 2} adsorption–desorption. Results indicate that the birnessite-type manganese oxide shows novel flower-like microsphere morphology and a specific surface area of 280 m{sup 2} g{sup −1}, and the flower-like microsphere consists of the thin nano-platelets. Electrochemical characterization indicates that the prepared material exhibits an ideal capacitive behavior with a capacitance value of 278 F g{sup −1} in 1 mol L{sup −1} Na{sub 2}SO{sub 4} aqueous solution at a scan rate of 5 mV s{sup −1}. Moreover, the prepared manganese oxide electrode shows excellent cycle stability, and the specific capacitance can maintain 98.6% of the initial one after 5000 cycles.« less

Effects of soluble flavin on heterogeneous electron transfer between surface-exposed bacterial cytochromes and iron oxides

NASA Astrophysics Data System (ADS)

Wang, Zheming; Shi, Zhi; Shi, Liang; White, Gaye F.; Richardson, David J.; Clarke, Thomas A.; Fredrickson, Jim K.; Zachara, John M.

2015-08-01

Dissimilatory iron-reducing bacteria can utilize insoluble Fe(Mn)-oxides as a terminal electron acceptor under anaerobic conditions. For Shewanella species specifically, evidence suggests that iron reduction is associated with the secretion of flavin mononucleotide (FMN) and riboflavin. However, the exact mechanism of flavin involvement is unclear; while some indicate that flavins mediate electron transfer (Marsili et al., 2008), others point to flavin serving as co-factors to outer membrane proteins (Okamoto et al., 2013). In this work, we used methyl viologen (MVrad +)-encapsulated, porin-cytochrome complex (MtrCAB) embedded liposomes (MELs) as a synthetic model of the Shewanella outer membrane to investigate the proposed mediating behavior of microbially produced flavins. The reduction kinetics of goethite, hematite and lepidocrocite (200 μM) by MELs ([MVrad +] ∼ 40 μM and MtrABC ⩽ 1 nM) were determined in the presence FMN at pH 7.0 in N2 atmosphere by monitoring the concentrations of MVrad + and FMN through their characteristic UV-visible absorption spectra. Experiments were performed where (i) FMN and Fe(III)-oxide were mixed and then reacted with the reduced MELs and (ii) FMN was reacted with the reduced MELs followed by addition of Fe(III)-oxide. The redox reactions proceeded in two steps: a fast step that was completed in a few seconds, and a slower one lasting over 400 s. For all three Fe(III)-oxides, the initial reaction rate in the presence of a low concentration of FMN (⩽1 μM) was at least a factor of five faster than those with MELs alone, and orders of magnitude faster than those by FMNH2, suggesting that FMN may serve as a co-factor that enhances electron transfer from outer-membrane c-cytochromes to Fe(III)-oxides. The rate and extent of the initial reaction followed the order of lepidocrocite > hematite > goethite, the same as their reduction potentials, implying thermodynamic control on reaction rate. For LEP, with the highest reduction potential among the three Fe(III)-oxides, its reduction by FMNH2 was completed in less than 10 min, suggesting that FMN was capable of mediating electron transfer to LEP. At higher FMN concentrations (>1 μM), the reaction rates for both steps decreased and varied inversely with FMN concentration, indicating that FMN inhibited the MEL to Fe(III)-oxide electron transfer reaction under these conditions. The implications of the observed kinetic behaviors to flavin-mediated Fe(III)-oxide reduction in natural environments are discussed.

Surface structure-dependent pyrite oxidation in relatively dry and moist air: Implications for the reaction mechanism and sulfur evolution

NASA Astrophysics Data System (ADS)

Zhu, Jianxi; Xian, Haiyang; Lin, Xiaoju; Tang, Hongmei; Du, Runxiang; Yang, Yiping; Zhu, Runliang; Liang, Xiaoliang; Wei, Jingming; Teng, H. Henry; He, Hongping

2018-05-01

Pyrite oxidation not only is environmentally significant in the formation of acid mine (or acid rock) drainage and oxidative acidification of lacustrine sediment but also is a critical stage in geochemical sulfur evolution. The oxidation process is always controlled by the reactivity of pyrite, which in turn is controlled by its surface structure. In this study, the oxidation behavior of naturally existing {1 0 0}, {1 1 1}, and {2 1 0} facets of pyrite was investigated using a comprehensive approach combining X-ray photoelectron spectroscopy, diffuse reflectance Fourier transform infrared spectroscopy, and time-of-flight secondary-ion mass spectrometry with periodic density functional theoretical (DFT) calculations. The experimental results show that (i) the initial oxidation rates of both pyrite {1 1 1} and {2 1 0} are much greater than that of pyrite {1 0 0}; (ii) the initial oxidation rate of pyrite {2 1 0} is greater than that of pyrite {1 1 1} in low relative humidity, which is reversed in high relative humidity; and (iii) inner sphere oxygen-bearing sulfur species are originally generated from surface reactions and then converted to outer sphere species. The facet dependent rate law can be expressed as: r{hkl} =k{hkl}haP0.5(t + 1) - 0.5 , where r{hkl} is the orientation dependent reaction rate, k{hkl} is the orientation dependent rate constant, h is the relative humidity, P is the oxygen partial pressure, and t is the oxidation time in seconds. {1 1 1} is the most sensitive facet for pyrite oxidation. Combined with DFT theoretical investigations, water catalyzed electron transfer is speculated as the rate-limiting step. These findings disclose the structure-reactivity dependence of pyrite, which not only presents new insight into the mechanism of pyrite oxidation but also provides fundamental data to evaluate sulfur speciation evolution, suggesting that the surface structure sensitivity should be considered to estimate the reactivity at the mineral-water interface.

High-resolution experiments on chemical oxidation of DNAPL in variable-aperture fractures

NASA Astrophysics Data System (ADS)

Arshadi, Masoud; Rajaram, Harihar; Detwiler, Russell L.; Jones, Trevor

2015-04-01

Chemical oxidation of dense nonaqueous-phase liquids (DNAPLs) by permanganate has emerged as an effective remediation strategy in fractured rock. We present high-resolution experimental investigations in transparent analog variable-aperture fractures to improve understanding of chemical oxidation of residual entrapped trichloroethylene (TCE) in fractures. Four experiments were performed with different permanganate concentrations, flow rates, and initial TCE phase geometry. The initial aperture field and evolving entrapped-phase geometry were quantified for each experiment. The integrated mass transfer rate from the TCE phase for all experiments exhibited three time regimes: an early-time regime with slower mass transfer rates limited by low specific interfacial area; an intermediate-time regime with higher mass transfer rates resulting from breakup of large TCE blobs, which greatly increases specific interfacial area; and a late-time regime with low mass transfer rates due to the deposition of MnO2 precipitates. In two experiments, mass balance analyses suggested that TCE mass removal rates exceeded the maximum upper bound mass removal rates derived by assuming that oxidation and dissolution are the only mechanisms for TCE mass removal. We propose incomplete oxidation by permanganate and TCE solubility enhancement by intermediate reaction products as potential mechanisms to explain this behavior. We also speculate that some intermediate reaction products with surfactant-like properties may play a role in lowering the TCE-water interfacial tension, thus causing breakup of large TCE blobs. Our quantitative experimental measurements will be useful in the context of developing accurate computational models for chemical oxidation of TCE in fractures.

Fatigue properties of MA 6000E, a gamma-prime strengthened ODS alloy. [Oxide Dispersion Strengthened Ni-base alloy for gas turbine blade applications

NASA Technical Reports Server (NTRS)

Kim, Y. G.; Merrick, H. F.

1980-01-01

MA 6000E is a corrosion resistant, gamma-prime strengthened ODS alloy under development for advanced turbine blade applications. The high temperature, 1093 C, rupture strength is superior to conventional nickel-base alloys. This paper addresses the fatigue behavior of the alloy. Excellent properties are exhibited in low and high cycle fatigue and also thermal fatigue. This is attributed to a unique combination of microstructural features, i.e., a fine distribution of dispersed oxides and other nonmetallics, and the highly elongated grain structure which advantageously modify the deformation characteristics and crack initiation and propagation modes from that characteristic of conventional gamma-prime hardened superalloys.

Creep analysis of solid oxide fuel cell with bonded compliant seal design

NASA Astrophysics Data System (ADS)

Jiang, Wenchun; Zhang, Yucai; Luo, Yun; Gong, J. M.; Tu, S. T.

2013-12-01

Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located.

Impact dynamics of oxidized liquid metal drops

NASA Astrophysics Data System (ADS)

Xu, Qin; Brown, Eric; Jaeger, Heinrich M.

2013-04-01

With exposure to air, many liquid metals spontaneously generate an oxide layer on their surface. In oscillatory rheological tests, this skin is found to introduce a yield stress that typically dominates the elastic response but can be tuned by exposing the metal to hydrochloric acid solutions of different concentration. We systematically studied the normal impact of eutectic gallium-indium (eGaIn) drops under different oxidation conditions and show how this leads to two different dynamical regimes. At low impact velocity (or low Weber number), eGaIn droplets display strong recoil and rebound from the impacted surface when the oxide layer is removed. In addition, the degree of drop deformation or spreading during impact is controlled by the oxide skin. We show that the scaling law known from ordinary liquids for the maximum spreading radius as a function of impact velocity can still be applied to the case of oxidized eGaIn if an effective Weber number We is employed that uses an effective surface tension factoring in the yield stress. In contrast, no influence on spreading from different oxidations conditions is observed for high impact velocity. This suggests that the initial kinetic energy is mostly damped by bulk viscous dissipation. Results from both regimes can be collapsed in an impact phase diagram controlled by two variables, the maximum spreading factor Pm=R0/Rm, given by the ratio of initial to maximum drop radius, and the impact number K=We/Re4/5, which scales with the effective Weber number We as well as the Reynolds number Re. The data exhibit a transition from capillary to viscous behavior at a critical impact number Kc≈0.1.

Impact dynamics of oxidized liquid metal drops.

PubMed

Xu, Qin; Brown, Eric; Jaeger, Heinrich M

2013-04-01

With exposure to air, many liquid metals spontaneously generate an oxide layer on their surface. In oscillatory rheological tests, this skin is found to introduce a yield stress that typically dominates the elastic response but can be tuned by exposing the metal to hydrochloric acid solutions of different concentration. We systematically studied the normal impact of eutectic gallium-indium (eGaIn) drops under different oxidation conditions and show how this leads to two different dynamical regimes. At low impact velocity (or low Weber number), eGaIn droplets display strong recoil and rebound from the impacted surface when the oxide layer is removed. In addition, the degree of drop deformation or spreading during impact is controlled by the oxide skin. We show that the scaling law known from ordinary liquids for the maximum spreading radius as a function of impact velocity can still be applied to the case of oxidized eGaIn if an effective Weber number We* is employed that uses an effective surface tension factoring in the yield stress. In contrast, no influence on spreading from different oxidations conditions is observed for high impact velocity. This suggests that the initial kinetic energy is mostly damped by bulk viscous dissipation. Results from both regimes can be collapsed in an impact phase diagram controlled by two variables, the maximum spreading factor P(m)=R(0)/R(m), given by the ratio of initial to maximum drop radius, and the impact number K=We*/Re(4/5), which scales with the effective Weber number We* as well as the Reynolds number Re. The data exhibit a transition from capillary to viscous behavior at a critical impact number K(c)≈0.1.

Unusual Oxidative Limitations for Al-MAX Phases

NASA Technical Reports Server (NTRS)

Smialek, James L.

2017-01-01

Alumina-forming MAX phases are well-known for their excellent oxidation resistance, rivaling many metallic NiAl, NiCrAl, and FeCrAl counterparts and with upper temperature capability possible to approximately1400C. However a number of limitations have been emerging that need to be acknowledged to permit robust performance in demanding applications. Ti2AlC and Ti3AlC2 possess excellent scale adhesion, cyclic oxidation/moisture/volatility resistance, and TBC compatibility. However they are very sensitive to Al content and flux in order to maintain an exclusive Al2O3 scale without runaway oxidation of ubiquitous TiO2 transient scales. Accelerated oxidation has been shown to occur for Al-depleted, damaged, or roughened surfaces at temperatures less than 1200C. Conversely, Cr2AlC is less sensitive to transients, but exhibits volatile losses at 1200C or above if common Cr7C3 impurity phases are present. Poor scale adhesion is exhibited after oxidation at 1150C or above, where spallation occurs at the Cr7C3 (depletion zone) interface. Delayed spallation is significant and suggests a moisture-induced phenomenon similar to non-adherent metallic systems. Re-oxidation of this surface does not reproduce the initial pure Al2O3 behavior, but initiates a less-protective scale. Cr2AlC has also been shown to have good long term bonding with superalloys at 800C, but exhibits significant Beta-NiAl + Cr7C3 diffusion zones at 1100C and above. This may set limits on Cr2AlC as a high temperature TBC bond coat on Ni-based superalloys, while improving corrosion resistance in lower temperature applications.

A long-term bench-scale investigation of permanganate consumption by aquifer materials.

PubMed

Xu, Xiuyuan; Thomson, Neil R

2009-11-20

In situ chemical oxidation (ISCO) applications using permanganate involve the injection or release of permanganate into the subsurface to destroy various target contaminants. Naturally occurring reduced components associated with aquifer materials can exert a significant oxidant demand thereby reducing the amount of permanganate available for the destruction of contaminants as well as reducing the overall rate of oxidation. Quantification of this natural oxidant demand (NOD) is a requirement for site-specific assessment and the design of cost-effective oxidant delivery systems. To further our understanding of the interaction between permanganate and aquifer materials, aerobic and anaerobic aquifer materials from eight representative sites throughout North America were tested in a series of systematic bench-scale experiments. Various permanganate to aquifer solids mass loading ratios at different initial permanganate concentrations in well-mixed batch reactors were monitored for >300 days. All NOD temporal profiles demonstrated an initial fast consumption rate followed by a persistent slower consumption rate. The data generated show that the mass loading ratio, the initial permanganate concentration, and the nature and quantity of reduced aquifer material species are the main factors controlling permanganate consumption rates. A higher initial permanganate concentration or a larger mass loading ratio produced a larger fast NOD consumption rate and generated a corresponding higher maximum NOD value. Hence, both the NOD temporal profile and the maximum NOD are not single-valued but are heavily dependent on the experimental conditions. Predictive relationships were developed to estimate the maximum NOD and the NOD at 7 days based on aquifer material properties. The concentration of manganese oxides deposited on the aquifer solids was highly correlated with the mass of permanganate consumed suggesting that passivation of NOD reaction sites occurred due to the formation of manganese oxide coating on the grains. A long-term NOD kinetic model was developed assuming a single fast and slow reacting oxidizable aquifer material species, passivation of NOD reaction sites, and the presence of an autocatalytic reaction. The developed model was able to successfully capture the observed NOD temporal profiles, and can be used to estimate in situ NOD behavior using batch reactor experimental data. The use of batch tests to provide data representative of in situ conditions should be used with caution.

Low cycle fatigue and creep fatigue interaction behavior of 9Cr-0.5Mo-1.8W-V-Nb heat-resistant steel at high temperature

NASA Astrophysics Data System (ADS)

Wang, Xiaowei; Zhang, Wei; Gong, Jianming; Wahab, Magd Abdel

2018-07-01

In this paper, Low Cycle Fatigue (LCF) and Creep-Fatigue Interaction (CFI) behavior of 9Cr-0.5Mo-1.8 W-V-Nb heat-resistant steel (ASME Grade P92 steel) at elevated temperature of 600 °C are investigated. Strain controlled LCF tests are conducted in fully reversed triangular waveform at different strain amplitudes ranging from 0.2% to 0.8%. CFI tests are conducted at 0.4% strain amplitude in trapezoid waveform with tensile hold time varying from 1 min to 60 min and compressive hold time varying from 1 min to 10 min. During LCF and CFI loadings, the evolution of cyclic stress, mean stress and stress relaxation behavior are investigated. It turns out that the softening behavior and lifetime degradation are dependent on strain amplitude, hold time and hold direction. In addition, the microstructure evolution and fracture behavior are characterized by optical, scanning and transmission electron microscope. The initial rapid softening behavior is attributed to the quick elimination of low angle boundaries, whereas no obvious microstructure alteration appears in the stable stage. Fracture behavior analysis reveals creep voids in long-term CFI tests facilitates the initiation and propagation of secondary cracks. The different responses of outer surface oxidation layer during cycling provides an explanation for severer damage of compressive hold and also accounts for the observed various fracture behavior of failed samples.

STIR: Tailored Interfaces for High Strength Composites Across Strain Rates

DTIC Science & Technology

2013-09-02

following by the nanowire growth . For the seeding process, the fibers were dipped into a colloidal solution of ZnO nanoparticles (2nm diameter) that was...to the fabric prior to nanowire growth . The synthesis of ZnO nanowire on Kevlar fabric surface was conducted in two steps; initial seeding and...Patterson, Mohammad H. Malakooti, Henry A. Sodano. Modification of Pullout Behavior of Kevlar Fabric by Zinc Oxide Nanowire Reinforcement, Proceedings of

Hyperthermophile Protein Behavior: Partially-Structured Conformations of Pyrococcus furiosus Rubredoxin Monomers Generated through Forced Cold-Denaturation and Refolding

PubMed Central

Ahmed, Shubbir; Guptasarma, Purnananda

2014-01-01

Some years ago, we showed that thermo-chemically denatured, partially-unfolded forms of Pyrococcus furiosus triosephosphateisomerase (PfuTIM) display cold-denaturation upon cooling, and heat-renaturation upon reheating, in proportion with the extent of initial partial unfolding achieved. This was the first time that cold-denaturation was demonstrated for a hyperthermophile protein, following unlocking of surface salt bridges. Here, we describe the behavior of another hyperthermophile protein, the small, monomeric, 53 residues-long rubredoxin from Pyrococcus furiosus (PfRd), which is one of the most thermostable proteins known to man. Like PfuTIM, PfRd too displays cold-denaturation after initial thermo-chemical perturbation, however, with two differences: (i) PfRd requires considerably higher temperatures as well as higher concentrations of guanidium hydrochloride (Gdm.HCl) than PfuTIM; (ii) PfRd's cold-denaturation behavior during cooling after thermo-chemical perturbation is incompletely reversible, unlike PfuTIM's, which was clearly reversible (from each different conformation generated). Differential cold-denaturation treatments allow PfRd to access multiple partially-unfolded states, each of which is clearly highly kinetically-stable. We refer to these as ‘Trishanku’ unfolding intermediates (or TUIs). Fascinatingly, refolding of TUIs through removal of Gdm.HCl generates multiple partially-refolded, monomeric, kinetically-trapped, non-native ‘Trishanku’ refolding intermediates (or TRIs), which differ from each other and from native PfRd and TUIs, in structural content and susceptibility to proteolysis. We find that the occurrence of cold denaturation and observations of TUI and TRI states is contingent on the oxidation status of iron, with redox agents managing to modulate the molecule's behavior upon gaining access to PfRd's iron atom. Mass spectrometric examination provides no evidence of the formation of disulfide bonds, but other experiments suggest that the oxidation status of iron (and its extent of burial) together determine whether or not PfRd shows cold denaturation, and also whether redox agents are able to modulate its behavior. PMID:24603413

Experimental Damage Criterion for Static and Fatigue Life Assessment of Commercial Aluminum Alloy Die Castings

NASA Astrophysics Data System (ADS)

Battaglia, Eleonora; Bonollo, Franco; Ferro, Paolo

2017-05-01

Defects, particularly porosity and oxides, in high-pressure die casting can seriously compromise the in-service behavior and durability of products subjected to static or cyclic loadings. In this study, the influence of dimension, orientation, and position of casting defects on the mechanical properties of an AlSi12(b) (EN-AC 44100) aluminum alloy commercial component has been studied. A finite element model has been carried out in order to calculate the stress distribution induced by service loads and identify the crack initiation zones. Castings were qualitatively classified on the basis of porosities distribution detected by X-ray technique and oxides observed on fracture surfaces of specimens coming from fatigue and tensile tests. A damage criterion has been formulated which considers the influence of defects position and orientation on the mechanical strength of the components. Using the proposed damage criterion, it was possible to describe the mechanical behavior of the castings with good accuracy.

Thickness-dependent resistance switching in Cr-doped SrTiO3

NASA Astrophysics Data System (ADS)

Kim, TaeKwang; Du, Hyewon; Kim, Minchang; Seo, Sunae; Hwang, Inrok; Kim, Yeonsoo; Jeon, Jihoon; Lee, Sangik; Park, Baeho

2012-09-01

The thickness-dependent bipolar resistance-switching behavior was investigated for epitaxiallygrown Cr-doped SrTiO3 (Cr-STO). All the pristine devices of different thickness showed polarity-independent symmetric current-voltage characteristic and the same space-charge-limited conduction mechanism. However, after a forming process, the resultant conduction and switching phenomena were significantly different depending on the thickness of Cr-STO. The forming process itself was highly influenced by resistance value of each pristine device. Based on our results, we suggest that the resistance-switching mechanism in Cr-STO depends not only on the insulating material's composition or the contact metal as previously reported but also on the initial resistance level determined by the geometry and the quality of the insulating material. The bipolar resistance-switching behaviors in oxide materials of different thicknesses exhibit mixed bulk and interface switching. This indicates that efforts in resistance-based memory research should be focused on scalability or process method to control a given oxide material in addition to material type and device structure.

Passivation and Depassivation of Defects in Graphene-based field-effect transistors

NASA Astrophysics Data System (ADS)

O'Hara, Andrew; Wang, Pan; Perini, Chris J.; Fleetwood, Daniel M.; Vogel, Eric M.; Pantelides, Sokrates T.

Field effect transistors based on graphene on amorphous SiO2 substrates were fabricated, both with and without a top oxide passivation layer of Al2O3. Initial I-V characteristics of these devices show that the Fermi energy occurs below the Dirac point in graphene (i.e. p-type behavior). Introduction of environmental stresses, e.g. baking the devices, causes a shift in the Fermi energy relative to the Dirac point. 1/f noise measurements indicate the presence of charge trapping defects. In order to find the origins of this behavior, we construct atomistic models of the substrate/graphene interface and the graphene/oxide passivation layer interface. Using density functional theory, we investigate the role that the introduction and removal of hydrogen and hydroxide passivants has on the electronic structure of the graphene layer as well as the relative energetics for these processes to occur in order to gain insights into the experimental results. Supported by DTRA: 1-16-0032 and NSF: ECCS-1508898.

Effects of High-Temperature Preoxidation on the Titanomagnetite Ore Structure and Reduction Behaviors in Fluidized Bed

NASA Astrophysics Data System (ADS)

Sun, Haoyan; Adetoro, Ajala Adewole; Pan, Feng; Wang, Zhen; Zhu, Qingshan

2017-06-01

The oxidation behaviors of South Africa (SA) titanomagnetite (TTM) and its effects on the gas solid reduction in the fluidized bed were investigated on the basis of the two-stage short process of direct reduction-electric arc furnace (DR-EAF) melting separation. The results showed that the oxidation phase transformations in the high-temperature range from 1073 K to 1223 K (800 °C to 950 °C) can be divided into two typical processes: with the fast generation of pseudobrookite and with the maghemite generation at the initial stage. The reduction efficiency for SA TTM was improved by the preoxidation treatment, mainly because of the dissociation of titania-ferrous oxides to the easy reducible hematite. However, at a preoxidation temperature higher than 1173 K (900 °C), the improving effect became weak, due to high-temperature sintering and the larger crystallite size of oxidation products. There is an extreme value of the preoxidation influence, and the optimum preoxidation time is different for various temperatures. The reduction metallization degree of SA TTM can be relatively improved by 14.5 and 4.5 pct for the first and second reduction steps, respectively, by 1173 K (900 °C) preoxidation with an optimum time of 30 minutes. Finally, the equilibrium relationship between the metallization degree and the gas reduction potential for TTM ore with preoxidation treatment was built.

The Effect of Hydrogen Annealing and Sulfur Content on the Oxidation Resistance of PWA 1480

NASA Technical Reports Server (NTRS)

Smialek, James L.

1997-01-01

For many decades the dramatic effect of trace amounts of reactive elements on alumina and chromia scale adhesion has been recognized and widely studied. Although various theories have been used to account for such behavior, the connection between scale adhesion and sulfur segregation was initially reported by Smeggil et al. This study found strong surface segregation of sulfur from very low levels in the bulk which could then be curtailed by the addition of reactive elements. It was assumed that the reactive elements, which are strong sulfide formers, acted by getting sulfur in the bulk thus precluding sulfur segregation and weakening of the oxide-metal bond. Subsequent studies confirmed that adhesion could be produced by reducing the sulfur impurity level, without reactive elements. The understanding of this phenomenon has been applied to modern single crystal superalloys, where the addition of Y, although very effective, is problematic. Also problematic is definition of the level of sulfur that is acceptable and below which no further adhesion benefit is reached. Published works have indicated a broad transition defined by various materials and oxidation tests. The present study describes the oxidation behavior of one superalloy (PWA 1480) as a function of various sulfur contents produced by hydrogen annealing for various temperatures, times, and sample thicknesses. The purpose is to define more precisely a criterion for adhesion based on total sulfur reservoir and segregation potential.

Huperzine A alleviates neuroinflammation, oxidative stress and improves cognitive function after repetitive traumatic brain injury.

PubMed

Mei, Zhengrong; Zheng, Peiying; Tan, Xiangping; Wang, Ying; Situ, Bing

2017-12-01

Traumatic brain injury (TBI) may trigger secondary injury cascades including endoplasmic reticulum stress, oxidative stress, and neuroinflammation. Unfortunately, there are no effective treatments targeting either primary or secondary injuries that result in long-term detrimental consequences. Huperzine A (HupA) is a potent acetylcholinesterase inhibitor (AChEI) that has been used treatment of Alzheimer's disease (AD). This study aimed to explore the neuroprotective effects of HupA in TBI and its possible mechanisms. Repetitive mild closed head injury (CHI) model was used to mimic concussive TBI. Mice were randomly assigned into three groups including sham, vehicle-treated and HupA-treated injured mice. The HupA was given at dose of 1.0 mg/kg/day and was initiated 30 min after the first injury, then administered daily for a total of 30 days. The neuronal functions including motor functions, emotion-like behaviors, learning and memory were tested. Axonal injury, reactive oxygen species (ROS), and neuroinflammation were examined as well. The results showed that injured mice treated with HupA had significant improvement in Morris water maze performance compared with vehicle-treated injured mice. HupA treatment significantly attenuated markers of neuroinflammation and oxidative stress in the injured mice. Taken together, HupA was effective in reducing neuroinflammation, oxidative stress and behavioral recovery after TBI. HupA is a promising candidate for treatment of TBI.

Real-time plasmon spectroscopy study of the solid-state oxidation and Kirkendall void formation in copper nanoparticles.

PubMed

Susman, Mariano D; Feldman, Yishai; Bendikov, Tatyana A; Vaskevich, Alexander; Rubinstein, Israel

2017-08-31

Oxidation and corrosion reactions have a major effect on the application of non-noble metals. Kinetic information and simple theoretical models are often insufficient for describing such processes in metals at the nanoscale, particularly in cases involving formation of internal voids (nano Kirkendall effect, NKE) during oxidation. Here we study the kinetics of solid-state oxidation of chemically-grown copper nanoparticles (NPs) by in situ localized surface plasmon resonance (LSPR) spectroscopy during isothermal annealing in the range 110-170 °C. We show that LSPR spectroscopy is highly effective in kinetic studies of such systems, enabling convenient in situ real-time measurements during oxidation. Change of the LSPR spectra throughout the oxidation follows a common pattern, observed for different temperatures, NP sizes and substrates. The well-defined initial Cu NP surface plasmon (SP) band red-shifts continuously with oxidation, while the extinction intensity initially increases to reach a maximum value at a characteristic oxidation time τ, after which the SP intensity continuously drops. The characteristic time τ is used as a scaling parameter for the kinetic analysis. Evolution of the SP wavelength and extinction intensity during oxidation at different temperatures follows the same kinetics when the oxidation time is normalized to τ, thus pointing to a general oxidation mechanism. The characteristic time τ is used to estimate the activation energy of the process, determined to be 144 ± 6 kJ mol -1 , similar to previously reported values for high-temperature Cu thermal oxidation. The central role of the NKE in the solid-state oxidation process is revealed by electron microscopy, while formation of Cu 2 O as the major oxidation product is established by X-ray diffraction, XPS, and electrochemical measurements. The results indicate a transition of the oxidation mechanism from a Valensi-Carter (VC) to NKE mechanism with the degree of oxidation. To interpret the optical evolution during oxidation, Mie scattering solutions for metal core-oxide shell spherical particles are computed, considering formation of Kirkendall voids. The model calculations are in agreement with the experimental results, showing that the large red-shift of the LSPR band during oxidation is the result of Kirkendall voiding, thus establishing the major role of the NKE in determining the optical behavior of such systems.

Estimation of ring tensile properties of steam oxidized Zircaloy-4 fuel cladding under simulated LOCA condition

NASA Astrophysics Data System (ADS)

Shriwastaw, R. S.; Sawarn, Tapan K.; Banerjee, Suparna; Rath, B. N.; Dubey, J. S.; Kumar, Sunil; Singh, J. L.; Bhasin, Vivek

2017-09-01

The present study involves the estimation of ring tensile properties of Indian Pressurised Heavy Water Reactor (IPHWR) fuel cladding made of Zircaloy-4, subjected to experiments under a simulated loss-of-coolant-accident (LOCA) condition. Isothermal steam oxidation experiments were conducted on clad tube specimens at temperatures ranging from 900 to 1200 °C at an interval of 50 °C for different soaking periods with subsequent quenching in water at ambient temperature. The specimens, which survived quenching, were then subjected to ambient temperature ring tension test (RTT). The microstructure was correlated with the mechanical properties. The yield strength (YS) and ultimate tensile strength (UTS) increased initially with rise in oxidation temperature and time duration but then decreased with further increase in oxidation. Ductility is adversely affected with rising oxidation temperature and longer holding time. A higher fraction of load bearing phase and lower oxygen content in it ensures higher residual ductility. Cladding shows almost zero ductility behavior in RIT when load bearing phase fraction is less than 0.72 and its average oxygen concentration is greater than 0.58 wt%.

TRPA1 is a major oxidant sensor in murine airway sensory neurons

PubMed Central

Bessac, Bret F.; Sivula, Michael; von Hehn, Christian A.; Escalera, Jasmine; Cohn, Lauren; Jordt, Sven-Eric

2008-01-01

Sensory neurons in the airways are finely tuned to respond to reactive chemicals threatening airway function and integrity. Nasal trigeminal nerve endings are particularly sensitive to oxidants formed in polluted air and during oxidative stress as well as to chlorine, which is frequently released in industrial and domestic accidents. Oxidant activation of airway neurons induces respiratory depression, nasal obstruction, sneezing, cough, and pain. While normally protective, chemosensory airway reflexes can provoke severe complications in patients affected by inflammatory airway conditions like rhinitis and asthma. Here, we showed that both hypochlorite, the oxidizing mediator of chlorine, and hydrogen peroxide, a reactive oxygen species, activated Ca2+ influx and membrane currents in an oxidant-sensitive subpopulation of chemosensory neurons. These responses were absent in neurons from mice lacking TRPA1, an ion channel of the transient receptor potential (TRP) gene family. TRPA1 channels were strongly activated by hypochlorite and hydrogen peroxide in primary sensory neurons and heterologous cells. In tests of respiratory function, Trpa1–/– mice displayed profound deficiencies in hypochlorite- and hydrogen peroxide–induced respiratory depression as well as decreased oxidant-induced pain behavior. Our results indicate that TRPA1 is an oxidant sensor in sensory neurons, initiating neuronal excitation and subsequent physiological responses in vitro and in vivo. PMID:18398506

Effect of coating density on oxidation resistance and Cr vaporization from solid oxide fuel cell interconnects

NASA Astrophysics Data System (ADS)

Talic, Belma; Falk-Windisch, Hannes; Venkatachalam, Vinothini; Hendriksen, Peter Vang; Wiik, Kjell; Lein, Hilde Lea

2017-06-01

Manganese cobalt spinel oxides are promising materials for protective coatings for solid oxide fuel cell (SOFC) interconnects. To achieve high density such coatings are often sintered in a two-step procedure, involving heat treatment first in reducing and then in oxidizing atmospheres. Sintering the coating inside the SOFC stack during heating would reduce production costs, but may result in a lower coating density. The importance of coating density is here assessed by characterization of the oxidation kinetics and Cr evaporation of Crofer 22 APU with MnCo1.7Fe0.3O4 spinel coatings of different density. The coating density is shown to have minor influence on the long-term oxidation behavior in air at 800 °C, evaluated over 5000 h. Sintering the spinel coating in air at 900 °C, equivalent to an in-situ heat treatment, leads to an 88% reduction of the Cr evaporation rate of Crofer 22 APU in air-3% H2O at 800 °C. The air sintered spinel coating is initially highly porous, however, densifies with time in interaction with the alloy. A two-step reduction and re-oxidation heat treatment results in a denser coating, which reduces Cr evaporation by 97%.

Oxidation Resistance of Materials Based on Ti3AlC2 Nanolaminate at 600 °C in Air.

PubMed

Ivasyshyn, Andrij; Ostash, Orest; Prikhna, Tatiana; Podhurska, Viktoriya; Basyuk, Tatiana

2016-12-01

The oxidation behavior of Ti3AlC2-based materials had been investigated at 600 °C in static air for 1000 h. It was shown that the intense increase of weight gain per unit surface area for sintered material with porosity of 22 % attributed to oxidation of the outer surface of the specimen and surfaces of pores in the bulk material. The oxidation kinetics of the hot-pressed Ti3AlC2-based material with 1 % porosity remarkably increased for the first 15 h and then slowly decreased. The weight gain per unit surface area for this material was 1.0 mg/cm(2) after exposition for 1000 h. The intense initial oxidation of Ti3AlC2-based materials can be eliminated by pre-oxidation treatment at 1200 °C in air for 2 h. As a result, the weight gain per unit surface area for the pre-oxidized material did not exceed 0.11 mg/cm(2) after 1000 h of exposition at 600 °C in air. It was demonstrated that the oxidation resistance of Ti3AlC2-based materials can be significantly improved by niobium addition.

Coverage-Dependent Anchoring of 4,4'-Biphenyl Dicarboxylic Acid to CoO(111) Thin Films.

PubMed

Mohr, Susanne; Schmitt, Tobias; Döpper, Tibor; Xiang, Feifei; Schwarz, Matthias; Görling, Andreas; Schneider, M Alexander; Libuda, Jörg

2017-05-02

We investigated the adsorption behavior of 4,4'-biphenhyl dicarboxylic acid (BDA) on well-ordered CoO(111) films grown on Ir(100) as a function of coverage and temperature using time-resolved and temperature-programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) in combination with density functional theory (DFT) and scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. To compare the binding behavior of BDA as a function of the oxide film thickness, three different CoO(111) film thicknesses were explored: films of about 20 bilayers (BLs) (approximately 5 nm), 2 BLs, and 1 BL. The two carboxylic acid groups of BDA offer two potential anchoring points to the oxide surface. At 150 K, intact BDA adsorbs on 20 BL thick oxide films in planar geometry with the phenyl rings aligned parallel to the surface. With decreasing oxide film thickness, we observe an increasing tendency for deprotonation and the formation of flat-lying BDA molecules anchored as dicarboxylates. After saturation of the first monolayer, intact BDA multilayers grow with molecules aligned parallel to the surface. The BDA multilayer desorbs at around 360 K. Completely different growth behavior is observed if BDA is deposited above the multilayer desorption temperature. Initially, doubly deprotonated dicarboxylates are formed by adopting a flat-lying orientation. With increasing exposure, however, the adsorbate layer transforms into upright standing monocarboxylates. A sharp OH stretching band (3584 cm -1 ) and a blue-shifted CO stretching band (1759 cm -1 ) indicate weakly interacting apical carboxylic acid groups at the vacuum interface. The anchored monocarboxylate phase slowly desorbs in a temperature range of up to 470 K. At higher temperature, a flat-lying doubly deprotonated BDA is formed, which desorbs and decomposes in a temperature range of up to 600 K.

Influence of surface roughness on the oxidation behavior of a Ni-4.0Cr-5.7Al single crystal superalloy

NASA Astrophysics Data System (ADS)

Pei, Haiqing; Wen, Zhixun; Li, Zhenwei; Zhang, Yamin; Yue, Zhufeng

2018-05-01

The high-temperature oxidation dynamics and mechanisms of a Ni-based single crystal superalloy with four kinds of surface roughnesses were investigated by virtue of XRD, OM, SEM and EDS at 1000 °C. In the initial oxidation stage, outer (Ni, Co)O was mainly produced on the surfaces of the samples with Ra = 90 nm and 19 nm. Correspondingly, outer Cr2O3 and transient θ-Al2O3 were mainly formed on the surfaces with Ra = 509 nm and 182 nm. After 180 min oxidation, the values of instantaneous parabolic mass gain coefficients (kp) of the samples with all surface roughnesses were gradually consistent with the data of the growth parabolic coefficient of α-Al2O3. The oxidation mechanisms of Ni-based superalloy with different surface roughnesses were discussed by a model. The external diffusion flux of Al (DAl) increases with the increases of surface roughness. Thus, the required Al concentration decreases with the increases of surface roughness when the selective oxidation of Al occurrs to form a protective single α-Al2O3 film.

Corrosion characteristics of Ni-base superalloys in high temperature steam with and without hydrogen

NASA Astrophysics Data System (ADS)

Kim, Donghoon; Kim, Daejong; Lee, Ho Jung; Jang, Changheui; Yoon, Duk Joo

2013-10-01

The hot steam corrosion behavior of Alloy 617 and Haynes 230 were evaluated in corrosion tests performed at 900 °C in steam and steam + 20 vol.% H2 environments. Corrosion rates of Alloy 617 was faster than that of Haynes 230 at 900 °C in steam and steam + 20 vol.% H2 environments. When hydrogen was added to steam, the corrosion rate was accelerated because added hydrogen increased the concentration of Cr interstitial defects in the oxide layer. Isolated nodular MnTiO3 oxides were formed on the MnCr2O4/Cr2O3 oxide layer and sub-layer Cr2O3 was formed in steam and steam + 20 vol.% H2 for Alloy 617. On the other hand, a MnCr2O4 layer was formed on top of the Cr2O3 oxide layer for Haynes 230. The extensive sub-layer Cr2O3 formation resulted from the oxygen or hydroxide inward diffusion in such environments. When hydrogen was added, the initial surface oxide morphology was changed from a convex shape to platelets because of the accelerated diffusion of cations under the oxide layer.

Oxidation behavior of a thermal barrier coating

NASA Technical Reports Server (NTRS)

Miller, R. A.

1984-01-01

Thermal barrier coatings, consisting of a plasma sprayed calcium silicate ceramic layer and a CoCrAlY or NiCrAlY bond coat, were applied on B-1900 coupons and cycled hourly in air in a rapid-response furnace to maximum temperatures of 1030, 1100, or 1160 C. Eight specimens were tested for each of the six conditions of bond-coat composition and temperature. Specimens were removed from test at the onset of failure, which was taken to be the formation of a fine surface crack visible at 10X magnification. Specimens were weighed periodically, and plots of weight gain vs time indicate that weight is gained at a parabolic rate after an initial period where weight was gained at a much greater rate. The high initial oxidation rate is thought to arise from the initially high surface area in the porous bond coat. Specimen life (time to first crack) was found to be a strong function of temperature. However, while test lives varied greatly with time, the weight gain at the time of specimen failure was quite insensitive to temperature. This indicates that there is a critical weight gain at which the coating fails when subjected to this test.

The Behavior of Systems in the Space Environment

DTIC Science & Technology

1991-07-19

Environment edited by Robert N. DeWitt U.S. Department of Energy , Washington, D.C., U.S.A. Dwight Duston Strategic Defense Initiative Organization, The...originates in a thin layer of the solar chromosphere, contains most of the solar energy in the extreme ultraviolet, but it cannot ionize any major...constituents of the atmosphere, whereas Lyman alpha can ionize only the trace of’nitric oxide. Virtually all the energy delivered in Lyman alpha is dissipated

Chemistry and phase evolution during roasting of toxic thallium-bearing pyrite.

PubMed

Lopez-Arce, Paula; Garcia-Guinea, Javier; Garrido, Fernando

2017-08-01

In the frame of a research project on microscopic distribution and speciation of geogenic thallium (Tl) from contaminated mine soils, Tl-bearing pyrite ore samples from Riotinto mining district (Huelva, SW Spain) were experimentally fired to simulate a roasting process. Concentration and volatility behavior of Tl and other toxic heavy metals was determined by quantitative ICP-MS, whereas semi-quantitative mineral phase transitions were identified by in situ thermo X-Ray Diffraction (HT-XRD) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) analyses after each firing temperature. Sample with initial highest amount of quartz (higher Si content), lowest quantity of pyrite and traces of jarosite (lower S content) developed hematite and concentrated Tl (from 10 up to 72 mg kg -1 ) after roasting at 900 °C in an oxidizing atmosphere. However, samples with lower or absent quartz content and higher pyrite amount mainly developed magnetite, accumulating Tl between 400 and 500 °C and releasing Tl from 700 up to 900 °C (from 10-29 mg kg -1 down to 4-1 mg kg -1 ). These results show the varied accumulative, or volatile, behaviors of one of the most toxic elements for life and environment, in which oxidation of Tl-bearing Fe sulfides produce Fe oxides wastes with or without Tl. The initial chemistry and mineralogy of pyrite ores should be taken into account in coal-fired power stations, cement or sulfuric acid production industry involving pyrite roasting processes, and steel, brick or paint industries, which use iron ore from roasted pyrite ash, where large amounts of Tl entail significant environmental pollution. Copyright © 2017 Elsevier Ltd. All rights reserved.

Anodic behavior of uranium in AlCl3-1-ethyl-3-methyl-imidazolium chloride ionic liquid

NASA Astrophysics Data System (ADS)

Jiang, Yidong; Luo, Lizhu; Wang, Shaofei; Bin, Ren; Zhang, Guikai; Wang, Xiaolin

2018-01-01

The oxidation state of metals unambiguously affects its anodic behavior in ionic liquid. We systematically investigated the anodic behavior of uranium with different surface oxidation states by electrochemical measurements, spectroscopic methods and surface analysis techniques. In the anodic process, metal uranium can be oxidized to U3+. The corresponding products accumulated on the metal/ILs interface will form a viscous layer. The anodic behavior of uranium is also strongly dependent upon the surface oxide states including thickness and homogeneity of the oxide film. With an increase in the thickness of oxide film, it will be breached at potentials in excess of a critical value. A uniform oxide on uranium surface can be breached evenly, and then the underlying metal starts to dissolve forming a viscous layer which can facilitate uniformly stripping of oxide, thus giving an oxide-free surface. Otherwise, a nonuniform oxide can result in a severe pitted surface with residue oxygen.

Synergistic effects of resveratrol (free and inclusion complex) and sulfamethoxazole-trimetropim treatment on pathology, oxidant/antioxidant status and behavior of mice infected with Toxoplasma gondii.

PubMed

Bottari, Nathieli B; Baldissera, Matheus D; Tonin, Alexandre A; Rech, Virginia C; Alves, Catiane B; D'Avila, Fernanda; Thomé, Gustavo R; Guarda, Naiara S; Moresco, Rafael N; Camillo, Giovana; Vogel, Fernanda F; Luchese, Cristiane; Schetinger, Maria Rosa C; Morsch, Vera M; Tochetto, Camila; Fighera, Rafael; Nishihira, Vivian S K; Da Silva, Aleksandro S

2016-06-01

This study aimed to investigate the synergistic effects of resveratrol and sulfamethoxazole-trimethoprim (ST) on the treatment of mice experimentally infected by Toxoplasma gondii during the chronic phase of the disease considering infection, behavior, and oxidative/antioxidants profile aspects. For the study, 60 mice were initially divided into two groups: uninfected (n = 24) and infected by T. gondii (n = 36). These two groups were later subdivided into other groups and treated with resveratrol (free and inclusion complex containing resveratrol) alone and co-administered with ST: groups A to D were composed by healthy mice and groups E to J were consisted of animals infected by T. gondii (VEG strain). Treatments began 20 days post-infection for 10 consecutive days with oral doses of 0.5 mg kg(-1) of ST (groups B and F), 100 mg kg(-1) of free resveratrol (groups C and G) and inclusion complex of resveratrol (nanoparticles containing resveratrol) (groups D and H), and lastly an co-administration of both drugs (groups I and J). Behavioral tests (memory, anxiety and locomotion) were performed after treatment. Liver and brain fragments were collected to evaluate pathological changes, brain cysts counts, as well as oxidant and antioxidant levels. A reduction on the number of cysts in the brain of animals treated with both drugs combined was observed; there was also reduced number of lesions on both organs. This drug combined effect was also able to reduce oxidative and increase antioxidant levels in infected mice, which might be interpreted as a resveratrol protective effect. In addition, the combination of ST and resveratrol was able to prevent behavioral changes in infected mice. Therefore, the use of co-administration drugs enhances the therapeutic effect acting on a synergic way, reducing the oxidizing effects of the chemical treatment for toxoplasmosis. In addition, resveratrol in inclusion complex when co-administered with ST showed an improved therapeutic effect of ST reducing oxidative damage, liver damage and the number of cysts in the brain of T. gondii infected mice. Copyright © 2016 Elsevier Ltd. All rights reserved.

The catalytic behavior of precisely synthesized Pt–Pd bimetallic catalysts for use as diesel oxidation catalysts

DOE PAGES

Wong, Andrew P.; Kyriakidou, Eleni A.; Toops, Todd J.; ...

2016-04-17

The demands of stricter diesel engine emission regulations have created challenges for current exhaust systems. With advances in low-temperature internal combustion engines and their operations, advances must also be made in vehicle exhaust catalysts. Most current diesel oxidation catalysts use heavy amounts of precious group metals (PGMs) for hydrocarbon (HC), CO, and NO oxidation. These catalysts are expensive and are most often synthesized with poor bimetallic interaction and dispersion. In this paper, the goal was to study the effect of aging on diesel emission abatement of Pt–Pd bimetallic nanoparticles precisely prepared with different morphologies: well dispersed core–shell vs. well dispersedmore » homogeneously alloyed vs. poorly dispersed, poorly alloyed particles. Alumina and silica supports were studied. Particle morphology and dispersion were analyzed before and after hydrothermal treatments by XRD, EDX, and STEM. Reactivity as a function of aging was measured in simulated diesel engine exhaust. While carefully controlled bimetallic catalyst nanoparticle structure has a profound influence on initial or low temperature catalytic activity, the differences in behavior disappear with higher temperature aging as thermodynamic equilibrium is achieved. The metallic character of Pt-rich alumina-supported catalysts is such that behavior rather closely follows the Pt–Pd metal phase diagram. Nanoparticles disparately composed as well-dispersed core–shell (via seq-SEA), well-dispersed homogeneously alloyed (via co-SEA), and poorly dispersed, poorly alloyed (via co-DI) end up as well alloyed, large particles of almost the same size and activity. With Pd-rich systems, the oxidation of Pd also figures into the equilibrium, such that Pd-rich oxide phases appear in the high temperature forms along with alloyed metal cores. Finally, the small differences in activity after high temperature aging can be attributed to the synthesis methods, sequential SEA and co-DI which give rise, after aging, to a bimetallic surface enriched in Pd.« less

The effects of water vapor on the oxidation behavior of alumina forming austenitic stainless steels

DOE PAGES

Yanar, N. M.; Lutz, B. S.; Garcia-Fresnillo, L.; ...

2015-08-19

The isothermal oxidation behavior of three alumina forming austenitic (AFA) stainless steels with varying composition was studied at 650 and 800 °C in dry air and gases which contained water vapor. The AFA alloys exhibited better oxidation resistance than a “good chromia former” at 650 °C, particularly in H 2O-containing atmospheres by virtue of alumina-scale formation. Although the AFA alloys were more resistant than chromia formers, their oxidation resistance was degraded at 650 °C in the presence of water vapor. In dry air the AFA alloys formed, thin continuous alumina scales, whereas in Ar–4%H 2–3%H 2O the areas of continuousmore » alumina were reduced and Fe oxide-rich nodules and regions of Cr, Mn-rich oxides formed. In some regions internal oxidation of the aluminum occurred in the H 2O-containing gas. The alloy OC8 had slightly better resistance than OC4 or OC5 in this atmosphere. The alumina-forming capability of the AFA alloys decreases with increasing temperature and, at 800 °C, they are borderline alumina formers, even in dry air. The oxidation resistance of all three alloys was degraded at 800 °C in atmospheres, which contained water vapor (Air–10%H 2O, Ar–3%H 2O and Ar–4%H 2–3%H 2O). The areas, which formed continuous alumina, were reduced in these atmospheres and areas of internal oxidation occurred. However, as a result of the borderline alumina-forming capability of the AFA alloys it was not possible to determine which of the H2O-containing atmospheres was more severe or to rank the alloys in terms of their performance. The experimental results indicate that the initial microstructure of the AFA alloys also plays a role in their oxidation performance. Less protective oxides formed at 800 °C when alloy OC8 was equilibrated before exposure rather than being exposed in the as-processed condition. As a result, the reason for this is the presence of different phases in the bulk of the two specimens.« less

The effects of water vapor on the oxidation behavior of alumina forming austenitic stainless steels

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

Yanar, N. M.; Lutz, B. S.; Garcia-Fresnillo, L.

The isothermal oxidation behavior of three alumina forming austenitic (AFA) stainless steels with varying composition was studied at 650 and 800 °C in dry air and gases which contained water vapor. The AFA alloys exhibited better oxidation resistance than a “good chromia former” at 650 °C, particularly in H 2O-containing atmospheres by virtue of alumina-scale formation. Although the AFA alloys were more resistant than chromia formers, their oxidation resistance was degraded at 650 °C in the presence of water vapor. In dry air the AFA alloys formed, thin continuous alumina scales, whereas in Ar–4%H 2–3%H 2O the areas of continuousmore » alumina were reduced and Fe oxide-rich nodules and regions of Cr, Mn-rich oxides formed. In some regions internal oxidation of the aluminum occurred in the H 2O-containing gas. The alloy OC8 had slightly better resistance than OC4 or OC5 in this atmosphere. The alumina-forming capability of the AFA alloys decreases with increasing temperature and, at 800 °C, they are borderline alumina formers, even in dry air. The oxidation resistance of all three alloys was degraded at 800 °C in atmospheres, which contained water vapor (Air–10%H 2O, Ar–3%H 2O and Ar–4%H 2–3%H 2O). The areas, which formed continuous alumina, were reduced in these atmospheres and areas of internal oxidation occurred. However, as a result of the borderline alumina-forming capability of the AFA alloys it was not possible to determine which of the H2O-containing atmospheres was more severe or to rank the alloys in terms of their performance. The experimental results indicate that the initial microstructure of the AFA alloys also plays a role in their oxidation performance. Less protective oxides formed at 800 °C when alloy OC8 was equilibrated before exposure rather than being exposed in the as-processed condition. As a result, the reason for this is the presence of different phases in the bulk of the two specimens.« less

The lack of effects of zinc and nitric oxide in initial state of pilocarpine-induced seizures.

PubMed

Noyan, Behzat; Jensen, Morten Skovgaard; Danscher, Gorm

2007-07-01

In this study we investigated whether intracerebroventricular (i.c.v.) injection of L-NAME (a nitric oxide synthase inhibitor) or CaEDTA (an extracellular zinc chelator) or the combination of the two could affect the initial phase of pilocarpine induced (2 h) seizures. Two groups of rats were used. Animals from both groups were given with i.c.v. injections of either saline (10 microl), L-NAME (150 microg/10 microl), CaEDTA (100 mM/10 microl) or L-NAME and CaEDTA. One group received pilocarpine HCl (380 mg/kg i.p.) the other served as control. Pilocarpine HCl was injected intraperitoneally 10 min later. The behavior of the animals was observed for 2h and the intensity of their seizures was scored. The rats were then sacrificed and their brains were removed and analyzed for zinc ions by using the immersion autometallography and the TSQ fluorescence staining. All the animals which received pilocarpine HCl developed seizures. Despite treatment with L-NAME and/or CaEDTA we found that the latency and the intensity of seizures were similar in both groups investigated. The distribution of stainable zinc ions and the intensity of staining in hippocampus were not affected by pilocarpine and found unchanged after L-NAME and/or CaEDTA injections in both the control animals and the pilocarpine treated animals. The data suggest that the nitric oxide system and zinc ions do not affect pilocarpine-induced seizures in their initial state.

Exfoliation Propensity of Oxide Scale in Heat Exchangers Used for Supercritical CO2 Power Cycles

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

Sabau, Adrian S; Shingledecker, John P.; Kung, Steve

2016-01-01

Supercritical CO2 (sCO2) Brayton cycle systems offer the possibility of improved efficiency in future fossil energy power generation plants operating at temperatures of 650 C and above. As there are few data on the oxidation/corrosion behavior of structural alloys in sCO2 at these temperatures, modeling to predict the propensity for oxide exfoliation is not well developed, thus hindering materials selection for these novel cycles. The ultimate goal of this effort is to provide needed data on scale exfoliation behavior in sCO2 for confident alloy selection. To date, a model developed by ORNL and EPRI for the exfoliation of oxide scalesmore » formed on boiler tubes in high-temperature, high-pressure steam has proven useful for managing exfoliation in conventional steam plants. A major input provided by the model is the ability to predict the likelihood of scale failure and loss based on understanding of the evolution of the oxide morphologies and the conditions that result in susceptibility to exfoliation. This paper describes initial steps taken to extend the existing model for exfoliation of steam-side oxide scales to sCO2 conditions. The main differences between high-temperature, high-pressure steam and sCO2 that impact the model involve (i) significant geometrical differences in the heat exchangers, ranging from standard pressurized tubes seen typically in steam-producing boilers to designs for sCO2 that employ variously-curved thin walls to create shaped flow paths for extended heat transfer area and small channel cross-sections to promote thermal convection and support pressure loads; (ii) changed operating characteristics with sCO2 due to the differences in physical and thermal properties compared to steam; and (iii) possible modification of the scale morphologies, hence properties that influence exfoliation behavior, due to reaction with carbon species from sCO2. The numerical simulations conducted were based on an assumed sCO2 operating schedule and several generic heat exchanger channel shapes and cross-sectional areas. Implications for the evolution of stresses in the oxide scales formed on sCO2 heat exchangers, and ensuing critical oxide thicknesses for exfoliation, were derived and compared with expectations for an equivalent conventional tubular heat exchanger in a steam cycle (for a given alloy).« less

Characterization and corrosion behavior of F6NM stainless steel treated in high temperature water

NASA Astrophysics Data System (ADS)

Li, Zheng-yang; Cai, Zhen-bing; Yang, Wen-jin; Shen, Xiao-yao; Xue, Guo-hong; Zhu, Min-hao

2018-03-01

F6NM martensitic stainless steel was exposed to 350 °C water condition for 500, 1500, and 2500 h to simulate pressurized water reactor (PWR) condition. The characterization and corrosion behavior of the oxide film were investigated. Results indicate that the exposed steel surface formed a double-layer oxide film. The outer oxide film is Fe-rich and contains two type oxide particles. However, the inner oxide film is Cr-rich, and two oxide films, whose thicknesses increase with increasing exposure time. The oxide film reduces the corrosion behavior because the outer oxide film has many crack and pores. Finally, the mechanism and factors affecting the formation of the oxide film were investigated.

Sulforaphane treatment of autism spectrum disorder (ASD)

PubMed Central

Singh, Kanwaljit; Connors, Susan L.; Macklin, Eric A.; Smith, Kirby D.; Fahey, Jed W.; Talalay, Paul; Zimmerman, Andrew W.

2014-01-01

Autism spectrum disorder (ASD), characterized by both impaired communication and social interaction, and by stereotypic behavior, affects about 1 in 68, predominantly males. The medico-economic burdens of ASD are enormous, and no recognized treatment targets the core features of ASD. In a placebo-controlled, double-blind, randomized trial, young men (aged 13–27) with moderate to severe ASD received the phytochemical sulforaphane (n = 29)—derived from broccoli sprout extracts—or indistinguishable placebo (n = 15). The effects on behavior of daily oral doses of sulforaphane (50–150 µmol) for 18 wk, followed by 4 wk without treatment, were quantified by three widely accepted behavioral measures completed by parents/caregivers and physicians: the Aberrant Behavior Checklist (ABC), Social Responsiveness Scale (SRS), and Clinical Global Impression Improvement Scale (CGI-I). Initial scores for ABC and SRS were closely matched for participants assigned to placebo and sulforaphane. After 18 wk, participants receiving placebo experienced minimal change (<3.3%), whereas those receiving sulforaphane showed substantial declines (improvement of behavior): 34% for ABC (P < 0.001, comparing treatments) and 17% for SRS scores (P = 0.017). On CGI-I, a significantly greater number of participants receiving sulforaphane had improvement in social interaction, abnormal behavior, and verbal communication (P = 0.015–0.007). Upon discontinuation of sulforaphane, total scores on all scales rose toward pretreatment levels. Dietary sulforaphane, of recognized low toxicity, was selected for its capacity to reverse abnormalities that have been associated with ASD, including oxidative stress and lower antioxidant capacity, depressed glutathione synthesis, reduced mitochondrial function and oxidative phosphorylation, increased lipid peroxidation, and neuroinflammmation. PMID:25313065

Sulforaphane treatment of autism spectrum disorder (ASD).

PubMed

Singh, Kanwaljit; Connors, Susan L; Macklin, Eric A; Smith, Kirby D; Fahey, Jed W; Talalay, Paul; Zimmerman, Andrew W

2014-10-28

Autism spectrum disorder (ASD), characterized by both impaired communication and social interaction, and by stereotypic behavior, affects about 1 in 68, predominantly males. The medico-economic burdens of ASD are enormous, and no recognized treatment targets the core features of ASD. In a placebo-controlled, double-blind, randomized trial, young men (aged 13-27) with moderate to severe ASD received the phytochemical sulforaphane (n = 29)--derived from broccoli sprout extracts--or indistinguishable placebo (n = 15). The effects on behavior of daily oral doses of sulforaphane (50-150 µmol) for 18 wk, followed by 4 wk without treatment, were quantified by three widely accepted behavioral measures completed by parents/caregivers and physicians: the Aberrant Behavior Checklist (ABC), Social Responsiveness Scale (SRS), and Clinical Global Impression Improvement Scale (CGI-I). Initial scores for ABC and SRS were closely matched for participants assigned to placebo and sulforaphane. After 18 wk, participants receiving placebo experienced minimal change (<3.3%), whereas those receiving sulforaphane showed substantial declines (improvement of behavior): 34% for ABC (P < 0.001, comparing treatments) and 17% for SRS scores (P = 0.017). On CGI-I, a significantly greater number of participants receiving sulforaphane had improvement in social interaction, abnormal behavior, and verbal communication (P = 0.015-0.007). Upon discontinuation of sulforaphane, total scores on all scales rose toward pretreatment levels. Dietary sulforaphane, of recognized low toxicity, was selected for its capacity to reverse abnormalities that have been associated with ASD, including oxidative stress and lower antioxidant capacity, depressed glutathione synthesis, reduced mitochondrial function and oxidative phosphorylation, increased lipid peroxidation, and neuroinflammmation.

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

PubMed

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

2010-02-15

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

Streptozotocin induced oxidative stress, innate immune system responses and behavioral abnormalities in male mice.

PubMed

Amiri, Shayan; Haj-Mirzaian, Arya; Momeny, Majid; Amini-Khoei, Hossein; Rahimi-Balaei, Maryam; Poursaman, Simin; Rastegar, Mojgan; Nikoui, Vahid; Mokhtari, Tahmineh; Ghazi-Khansari, Mahmoud; Hosseini, Mir-Jamal

2017-01-06

Recent evidence indicates the involvement of inflammatory factors and mitochondrial dysfunction in the etiology of psychiatric disorders such as anxiety and depression. To investigate the possible role of mitochondrial-induced sterile inflammation in the co-occurrence of anxiety and depression, in this study, we treated adult male mice with the intracerebroventricular (i.c.v.) infusion of a single low dose of streptozotocin (STZ, 0.2mg/mouse). Using valid and qualified behavioral tests for the assessment of depressive and anxiety-like behaviors, we showed that STZ-treated mice exhibited behaviors relevant to anxiety and depression 24h following STZ treatment. We observed that the co-occurrence of anxiety and depressive-like behaviors in animals were associated with abnormal mitochondrial function, nitric oxide overproduction and, the increased activity of cytosolic phospholipase A 2 (cPLA 2 ) in the hippocampus. Further, STZ-treated mice had a significant upregulation of genes associated with the innate immune system such as toll-like receptors 2 and 4. Pathological evaluations showed no sign of neurodegeneration in the hippocampus of STZ-treated mice. Results of this study revealed that behavioral abnormalities provoked by STZ, as a cytotoxic agent that targets mitochondria and energy metabolism, are associated with abnormal mitochondrial activity and, consequently the initiation of innate-inflammatory responses in the hippocampus. Our findings highlight the role of mitochondria and innate immunity in the formation of sterile inflammation and behaviors relevant to anxiety and depression. Also, we have shown that STZ injection (i.c.v.) might be an animal model for depression and anxiety disorders based on sterile inflammation. Copyright © 2016 IBRO. Published by Elsevier Ltd. All rights reserved.

Experimental Study and Mathematical Modeling of Self-Sustained Kinetic Oscillations in Catalytic Oxidation of Methane over Nickel.

PubMed

Lashina, Elena A; Kaichev, Vasily V; Saraev, Andrey A; Vinokurov, Zakhar S; Chumakova, Nataliya A; Chumakov, Gennadii A; Bukhtiyarov, Valerii I

2017-09-21

The self-sustained kinetic oscillations in the oxidation of CH 4 over Ni foil have been studied at atmospheric pressure using an X-ray diffraction technique and mass spectrometry. It has been shown that the regular oscillations appear under oxygen-deficient conditions; CO, CO 2 , H 2 , and H 2 O are detected as the products. According to in situ X-ray diffraction measurements, nickel periodically oxidizes to NiO initiating the reaction-rate oscillations. To describe the oscillations, we have proposed a five-stage mechanism of the partial oxidation of methane over Ni and a corresponding three-variable kinetic model. The mechanism considers catalytic methane decomposition, dissociative adsorption of oxygen, transformation of chemisorbed oxygen to surface nickel oxide, and reaction of adsorbed carbon and oxygen species to form CO. Analysis of the kinetic model indicates that the competition of two processes, i.e., the oxidation and the carbonization of the catalyst surface, is the driving force of the self-sustained oscillations in the oxidation of methane. We have compared this mechanism with the detailed 18-stage mechanism described previously by Lashina et al. (Kinetics and Catalysis 2012, 53, 374-383). It has been shown that both kinetic mechanisms coupled with a continuous stirred-tank reactor model describe well the oscillatory behavior in the oxidation of methane under non-isothermal conditions.

Effect of surface oxidation on thermomechanical behavior of NiTi shape memory alloy wire

NASA Astrophysics Data System (ADS)

Ng, Ching Wei; Mahmud, Abdus Samad

2017-12-01

Nickel titanium (NiTi) alloy is a unique alloy that exhibits special behavior that recovers fully its shape after being deformed to beyond elastic region. However, this alloy is sensitive to any changes of its composition and introduction of inclusion in its matrix. Heat treatment of NiTi shape memory alloy to above 600 °C leads to the formation of the titanium oxide (TiO2) layer. Titanium oxide is a ceramic material that does not exhibit shape memory behaviors and possess different mechanical properties than that of NiTi alloy, thus disturbs the shape memory behavior of the alloy. In this work, the effect of formation of TiO2 surface oxide layer towards the thermal phase transformation and stress-induced deformation behaviors of the NiTi alloy were studied. The NiTi wire with composition of Ti-50.6 at% Ni was subjected to thermal oxidation at 600 °C to 900 °C for 30 and 60 minutes. The formation of the surface oxide layers was characterized by using the Scanning Electron Microscope (SEM). The effect of surface oxide layers with different thickness towards the thermal phase transformation behavior was studied by using the Differential Scanning Calorimeter (DSC). The effect of surface oxidation towards the stress-induced deformation behavior was studied through the tensile deformation test. The stress-induced deformation behavior and the shape memory recovery of the NiTi wire under tensile deformation were found to be affected marginally by the formation of thick TiO2 layer.

Effect of Antifoam Agent on Oxidative Leaching of Hanford Tank Sludge Simulants

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

Rapko, Brian M.; Jones, Susan A.; Lumetta, Gregg J.

2010-02-26

Oxidative leaching of simulant tank waste containing an antifoam agent (AFA) to reduce the chromium content of the sludge was tested using permanganate as the oxidant in 0.25 M NaOH solutions. AFA is added to the waste treatment process to prevent foaming. The AFA, Dow Corning Q2-3183A, is a surface-active polymer that consists of polypropylene glycol, polydimethylsiloxane, octylphenoxy polyethoxy ethanol, treated silica, and polyether polyol. Some of the Hanford Tank Waste Treatment and Immobilization Plant (WTP) waste slurries contain high concentrations of undissolved solids that would exhibit undesirable behavior without AFA addition. These tests were conducted to determine the effectmore » of the AFA on oxidative leaching of Cr(III) in waste by permanganate. It has not previously been determined what effect AFA has on the permanganate reaction. This study was conducted to determine the effect AFA has on the oxidation of the chromium, plus plutonium and other criticality-related elements, specifically Fe, Ni and Mn. During the oxidative leaching process, Mn is added as liquid permanganate solution and is converted to an insoluble solid that precipitates as MnO2 and becomes part of the solid waste. Caustic leaching was performed followed by an oxidative leach at either 25°C or 45°C. Samples of the leachate and solids were collected at each step of the process. Initially, Battelle-Pacific Northwest Division (PNWD) was contracted by Bechtel National, Inc. to perform these further scoping studies on oxidative alkaline leaching. The data obtained from the testing will be used by the WTP operations to develop procedures for permanganate dosing of Hanford tank sludge solids during oxidative leaching. Work was initially conducted under contract number 24590-101-TSA-W000-00004. In February 2007, the contract mechanism was switched to Pacific Northwest National Laboratory (PNNL) operating Contract DE-AC05-76RL01830. In summary, this report describes work focused on determining the effect of AFA on chromium oxidation by permanganate with Hanford sludge simulant.« less

Co2+-exchange mechanism of birnessite and its application for the removal of Pb2+ and As(III).

PubMed

Yin, Hui; Liu, Fan; Feng, Xionghan; Liu, Mingming; Tan, Wenfeng; Qiu, Guohong

2011-11-30

Co-containing birnessites were obtained by ion exchange at different initial concentrations of Co(2+). Ion exchange of Co(2+) had little effect on birnessite crystal structure and micromorphology, but resulted in an increase in specific surface areas from 19.26 to 33.35 m(2)g(-1), and a decrease in both crystallinity and manganese average oxidation state. It was due to that Mn(IV) in the layer structure was reduced to Mn(III) during the oxidation process of Co(2+) to Co(III). The hydroxyl groups on the surface of Co-containing birnessites gradually decreased with an increase of Co/Mn molar ratio owing to the occupance of Co(III) into vacancies and the location of large amounts of Co(2+/3+) and Mn(2+/3+) above/below the vacant sites. This greatly accounted for the monotonous reduction in Pb(2+) adsorption capacity, from 2538 mmol kg(-1) for the unmodified birnessite to 1500 mmol kg(-1) for the Co(2+) ion-exchanged birnessite with a Co/Mn molar ratio of 0.16. The amount of As(III) oxidized by birnessite was enhanced after ion exchange, but the apparent initial reaction rate was greatly decreased. The present work demonstrates that Co(2+) ion exchange has great influence on the adsorption and oxidation behavior of inorganic toxic metal ions by birnessite in water environments. Copyright © 2011 Elsevier B.V. All rights reserved.

Three-dimensional three-phase model for simulation of hydrodynamics, oxygen mass transfer, carbon oxidation, nitrification and denitrification in an oxidation ditch.

PubMed

Lei, Li; Ni, Jinren

2014-04-15

A three-dimensional three-phase fluid model, supplemented by laboratory data, was developed to simulate the hydrodynamics, oxygen mass transfer, carbon oxidation, nitrification and denitrification processes in an oxidation ditch. The model provided detailed phase information on the liquid flow field, gas hold-up distribution and sludge sedimentation. The three-phase model described water-gas, water-sludge and gas-sludge interactions. Activated sludge was taken to be in a pseudo-solid phase, comprising an initially separated solid phase that was transported and later underwent biological reactions with the surrounding liquidmedia. Floc parameters were modified to improve the sludge viscosity, sludge density, oxygen mass transfer rate, and carbon substrate uptake due to adsorption onto the activated sludge. The validation test results were in very satisfactory agreement with laboratory data on the behavior of activated sludge in an oxidation ditch. By coupling species transport and biological process models, reasonable predictions are made of: (1) the biochemical kinetics of dissolved oxygen, chemical oxygen demand (COD) and nitrogen variation, and (2) the physical kinematics of sludge sedimentation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Coarse grained study of pluronic F127: Comparison with shorter co-polymers in its interaction with lipid bilayers and self-aggregation in water

NASA Astrophysics Data System (ADS)

Wood, I.; Martini, M. F.; Albano, J. M. R.; Cuestas, M. L.; Mathet, V. L.; Pickholz, M.

2016-04-01

The aim of this work is to understand the interactions of the poloxamer Pluronic F127, with lipid bilayers and its ability to self-associate in an aqueous environment. Molecular dynamics simulations at the coarse-grain scale were performed to address the behavior of single Pluronic F127 and shorter poloxamers unimers in palmitoyl-oleoyl-phosphatidyl-choline model membranes. According to the initial conditions and the poly-ethylene oxide/poly-propylene oxide composition, in water phase the unimer chain collapses into a coil conformation or adopts an interphacial U-shaped - or membrane spanning - distribution. A combination of poly-propylene oxide length, and the poly-ethylene oxide ability to cover poly-propylene oxide, is determinant for the conformation adopted by the unimer in each phase. Results of the simulations showed molecular evidence of strong interaction between Pluronic F127 and model membranes both in stable U-shaped and span conformations. The knowledge of this interaction could contribute to improve drug permeation. Additionally, we investigated the aggregation of one hundred Pluronic F127 unimers in water forming a micelle-like structure, suitable to be used as drug delivery system models.

Mechanism study on the sulfidation of ZnO with sulfur and iron oxide at high temperature

NASA Astrophysics Data System (ADS)

Han, Junwei; Liu, Wei; Zhang, Tianfu; Xue, Kai; Li, Wenhua; Jiao, Fen; Qin, Wenqing

2017-02-01

The mechanism of ZnO sulfidation with sulfur and iron oxide at high temperatures was studied. The thermodynamic analysis, sulfidation behavior of zinc, phase transformations, morphology changes, and surface properties were investigated by HSC 5.0 combined with FactSage 7.0, ICP, XRD, optical microscopy coupled with SEM-EDS, and XPS. The results indicate that increasing temperature and adding iron oxide can not only improve the sulfidation of ZnO but also promote the formation and growth of ZnS crystals. Fe2O3 captured the sulfur in the initial sulfidation process as iron sulfides, which then acted as the sulfurizing agent in the late period, thus reducing sulfur escape at high temperatures. The addition of carbon can not only enhance the sulfidation but increase sulfur utilization rate and eliminate the generation of SO2. The surfaces of marmatite and synthetic zinc sulfides contain high oxygen due to oxidation and oxygen adsorption. Hydroxyl easily absorbs on the surface of iron-bearing zinc sulfide (Zn1-xFexS). The oxidation of synthetic Zn1-xFexS is easier than marmatite in air.

Mechanism study on the sulfidation of ZnO with sulfur and iron oxide at high temperature

PubMed Central

Han, Junwei; Liu, Wei; Zhang, Tianfu; Xue, Kai; Li, Wenhua; Jiao, Fen; Qin, Wenqing

2017-01-01

The mechanism of ZnO sulfidation with sulfur and iron oxide at high temperatures was studied. The thermodynamic analysis, sulfidation behavior of zinc, phase transformations, morphology changes, and surface properties were investigated by HSC 5.0 combined with FactSage 7.0, ICP, XRD, optical microscopy coupled with SEM-EDS, and XPS. The results indicate that increasing temperature and adding iron oxide can not only improve the sulfidation of ZnO but also promote the formation and growth of ZnS crystals. Fe2O3 captured the sulfur in the initial sulfidation process as iron sulfides, which then acted as the sulfurizing agent in the late period, thus reducing sulfur escape at high temperatures. The addition of carbon can not only enhance the sulfidation but increase sulfur utilization rate and eliminate the generation of SO2. The surfaces of marmatite and synthetic zinc sulfides contain high oxygen due to oxidation and oxygen adsorption. Hydroxyl easily absorbs on the surface of iron-bearing zinc sulfide (Zn1−xFexS). The oxidation of synthetic Zn1−xFexS is easier than marmatite in air. PMID:28186156

In vivo oxidation in remelted highly cross-linked retrievals.

PubMed

Currier, B H; Van Citters, D W; Currier, J H; Collier, J P

2010-10-20

Elimination of free radicals to prevent oxidation has played a major role in the development and product differentiation of the latest generation of highly cross-linked ultra-high molecular weight polyethylene bearing materials. In the current study, we (1) examined oxidation in a series of retrieved remelted highly cross-linked ultra-high molecular weight polyethylene bearings from a number of device manufacturers and (2) compared the retrieval results with findings for shelf-stored control specimens. The hypothesis was that radiation-cross-linked remelted ultra-high molecular weight polyethylene would maintain oxidative stability in vivo comparable with the stability during shelf storage and in published laboratory aging tests. Fifty remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners and nineteen remelted highly cross-linked ultra-high molecular weight polyethylene tibial inserts were received after retrieval from twenty-one surgeons from across the U.S. Thirty-two of the retrievals had been in vivo for two years or more. Each was measured for oxidation with use of Fourier transform infrared spectroscopy. A control series of remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners from three manufacturers was analyzed with electron paramagnetic resonance spectroscopy to measure free radical content and with Fourier transform infrared spectroscopy to measure oxidation initially and after eight to nine years of shelf storage in air. The never-implanted, shelf-aged controls had no measurable free-radical content initially or after eight to nine years of shelf storage. The never-implanted controls showed no increase in oxidation during shelf storage. Oxidation measurements showed measurable oxidation in 22% of the retrieved remelted highly cross-linked liners and inserts after an average of two years in vivo. Because never-implanted remelted highly cross-linked ultra-high molecular weight polyethylene materials had no measurable free-radical concentration and no increase in oxidation during shelf storage, these materials were expected to be oxidation-resistant in vivo. However, some remelted highly cross-linked ultra-high molecular weight polyethylene retrievals showed measurable oxidation after an average of more than two years in vivo. This apparent departure from widely expected behavior requires continued study of the process of in vivo oxidation of ultra-high molecular weight polyethylene materials.

Neuron-specific regulation of superoxide dismutase amid pathogen-induced gut dysbiosis.

PubMed

Horspool, Alexander M; Chang, Howard C

2018-05-19

Superoxide dismutase, an enzyme that converts superoxide into less-toxic hydrogen peroxide and oxygen, has been shown to mediate behavioral response to pathogens. However, it remains largely unknown how superoxide dismutase is regulated in the nervous system amid pathogen-induced gut dysbiosis. Although there are five superoxide dismutases in C. elegans, our genetic analyses suggest that SOD-1 is the primary superoxide dismutase to mediate the pathogen avoidance response. When C. elegans are fed a P. aeruginosa diet, the lack of SOD-1 contributes to enhanced lethality. We found that guanylyl cyclases GCY-5 and GCY-22 and neuropeptide receptor NPR-1 act antagonistically to regulate SOD-1 expression in the gustatory neuron ASER. After C. elegans ingests a diet that contributes to high levels of oxidative stress, the temporal regulation of SOD-1 and the SOD-1-dependent response in the gustatory system demonstrates a sophisticated mechanism to fine-tune behavioral plasticity. Our results may provide the initial glimpse of a strategy by which a multicellular organism copes with oxidative stress amid gut dysbiosis. Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.

JAGUAR Procedures for Detonation Behavior of Explosives Containing Boron

NASA Astrophysics Data System (ADS)

Stiel, Leonard; Baker, Ernest; Capellos, Christos

2009-06-01

The JAGUAR product library was expanded to include boron and boron containing products. Relationships of the Murnaghan form for molar volumes and derived properties were implemented in JAGUAR. Available Hugoniot and static volumertic data were analyzed to obtain constants of the Murnaghan relationship for solid boron, boron oxide, boron nitride, boron carbide, and boric acid. Experimental melting points were also utilized with optimization procedures to obtain the constants of the volumetric relationships for liquid boron and boron oxide. Detonation velocities for HMX - boron mixtures calculated with these relationships using JAGUAR are in closer agreement with literature values at high initial densities for inert (unreacted) boron than with the completely reacted metal. These results indicate that boron mixtures may exhibit eigenvalue detonation behavior, as observed by aluminized combined effects explosives, with higher detonation velocities than would be achieved by a classical Chapman-Jouguet detonation. Analyses of calorimetric measurements for RDX - boron mixtures indicate that at high boron contents the formation of side products, including boron nitride and boron carbide, inhibits the energy output obtained from the detonation of the formulation.

Endogenous mitigation of H2S inside of the landfills.

PubMed

Fang, Yuan; Zhong, Zhong; Shen, Dongsheng; Du, Yao; Xu, Jing; Long, Yuyang

2016-02-01

Vast quantities of hydrogen sulfide (H2S) emitted from landfill sites require urgent disposal. The current study focused on source control and examined the migration and conversion behavior of sulfur compounds in two lab-scale simulated landfills with different operation modes. It aimed to explore the possible strategies and mechanisms for H2S endogenous mitigation inside of landfills during decomposition. It was found that the strength of H2S emissions from the landfill sites was dependent on the municipal solid waste (MSW) degradation speed and vertical distribution of sulfide. Leachate recirculation can shorten both the H2S influence period and pollution risk to the surrounding environment. H2S endogenous mitigation may be achieved by chemical oxidation, biological oxidation, adsorption, and/or precipitation in different stages. Migration and conversion mainly affected H2S release behavior during the initial stabilization phase in the landfill. Microbial activities related to sulfur, nitrogen, and iron can further promote H2S endogenous mitigation during the high reducing phase. Thus, H2S endogenous mitigation can be effectively enhanced via control of the aforementioned processes.

Mechanical behavior of carbon-carbon composites

NASA Technical Reports Server (NTRS)

Rozak, G. A.

1984-01-01

A general background, test plan, and some results of preliminary examinations of a carbon-carbon composite material are presented with emphasis on mechanical testing and inspection techniques. Experience with testing and evaluation was gained through tests of a low modulus carbon-carbon material, K-Karb C. The properties examined are the density - 1.55 g/cc; four point flexure strength in the warp - 137 MPa (19,800 psi) and the fill - 95.1 MPa (13,800 psi,) directions; and the warp interlaminar shear strength - 14.5 MPa (2100 psi). Radiographic evaluation revealed thickness variations and the thinner areas of the composite were scrapped. The ultrasonic C-scan showed attenuation variations, but these did not correspond to any of the physical and mechanical properties measured. Based on these initial tests and a survey of the literature, a plan has been devised to examine the effect of stress on the oxidation behavior, and the strength degradation of coated carbon-carbon composites. This plan will focus on static fatigue tests in the four point flexure mode in an elevated temperature, oxidizing environment.

Effect of fiber reinforcement on thermo-oxidative stability and mechanical properties of polymer matrix composites

NASA Technical Reports Server (NTRS)

Bowles, K. J.

1992-01-01

A number of studies have investigated the thermooxidative behavior of polymer matrix composites. Two significant observations have been made from these research efforts: (1) fiber reinforcement has a significant effect on composite thermal stability; and (2) geometric effects must be considered when evaluating thermal aging data. The polyimide PMR-15 was the matrix material used in these studies. The control composite material was reinforced with Celion 6000 graphite fiber. T-4OR graphite fibers, along with some very stable ceramic fibers were selected as reinforcing fibers because of their high thermal stability. The ceramic fibers were Nicalon (silicon carbide) and Nextel 312 (alumina-silica-boron oxide). The mechanical properties of the two graphite fiber composites were significantly different, probably owing to variations in interfacial bonding between the fibers and the polyimide matrix. Three oxidation mechanisms were observed: (1) the preferential oxidation of the Celion 6000 fiber ends at cut surfaces, leaving a surface of matrix material with holes where the fiber ends were originally situated; (2) preferential oxidation of the composite matrix; and (3) interfacial degradation by oxidation. The latter two mechanisms were also observed on fiber end cut surfaces. The fiber and interface attacks appeared to initiate interfiber cracking along these surfaces.

Gas-deposit-alloy corrosion interactions in simulated combustion environments

NASA Astrophysics Data System (ADS)

Luer, Kevin Raymond

High temperature corrosion in aggressive coal combustion environments involves simultaneous corrosion reactions between combustion gases, ash deposits, and alloys. This research investigated the behavior of a ferritic steel (SA387-Gr11) and three weld claddings (309L SS, Alloy 72, and Alloy 622) in five combustion environments beneath solid deposits at 500°C for up to 1000 hours. The synthetic gases consisted of N2-CO-CO-H2-H2O-H 2S-SO2 mixtures that simulated a range of fuel-rich or fuel-lean combustion environments with a constant sulfur content. The synthetic deposits contained FeS2, FeS, Fe3O4 and/or carbon. Reaction kinetics was studied in individual gas-metal, gas deposit, and deposit-alloy systems. A test method was developed to investigate simultaneous gas-deposit-metal corrosion reactions. The results showed reaction kinetics varied widely, depending on the gas-alloy system and followed linear, parabolic, and logarithmic rate laws. Under reducing conditions, the alloys exhibited a range of corrosion mechanisms including carburization-sulfidation, sulfidation, and sulfidation-oxidation. Most alloys were not resistant to the highly reducing gases but offered moderate resistance to mixed oxidation-sulfidation by demonstrating parabolic or logarithmic behavior. Under oxidizing conditions, all of the alloys were resistant. Under oxidizing-sulfating conditions, alloys with high Fe or Cr contents sulfated whereas an alloy containing Mo and W was resistant. In the gas-deposit-metal tests, FeS2-bearing deposits were extremely corrosive to low alloy steel under both reducing and oxidizing conditions but they had little influence on the weld claddings. Accelerated corrosion was attributed to rapid decomposition or oxidation of FeS2 particles that generated sulfur-rich gases above the alloy surface. In contrast, FeS-type deposits had no influence under reducing conditions but they were aggressive to low alloy steel under oxidizing conditions. The extent of damage correlated with the initial sulfur content in the deposit. Fe3O4 in the deposit was beneficial because it acted as a sulfur getter or oxygen source. Carbon had a mixed effect. The reaction behavior was modeled using computational thermochemistry based on Gibbs free energy minimization. A calculation method was introduced to predict equilibrium corrosion microstructures and trace reaction paths in complex gas-deposit-metal environments. Kinetic factors were identified where equilibrium reaction products were not experimentally observed.

Nanoscale surface modification of Li-rich layered oxides for high-capacity cathodes in Li-ion batteries

NASA Astrophysics Data System (ADS)

Lan, Xiwei; Xin, Yue; Wang, Libin; Hu, Xianluo

2018-03-01

Li-rich layered oxides (LLOs) have been developed as a high-capacity cathode material for Li-ion batteries, but the structural complexity and unique initial charging behavior lead to several problems including large initial capacity loss, capacity and voltage fading, poor cyclability, and inferior rate capability. Since the surface conditions are critical to electrochemical performance and the drawbacks, nanoscale surface modification for improving LLO's properties is a general strategy. This review mainly summarizes the surface modification of LLOs and classifies them into three types of surface pre-treatment, surface gradient doping, and surface coating. Surface pre-treatment usually introduces removal of Li2O for lower irreversible capacity while surface doping is aimed to stabilize the structure during electrochemical cycling. Surface coating layers with different properties, protective layers to suppress the interface side reaction, coating layers related to structural transformation, and electronic/ionic conductive layers for better rate capability, can avoid the shortcomings of LLOs. In addition to surface modification for performance enhancement, other strategies can also be investigated to achieve high-performance LLO-based cathode materials.

Schottky Emission Distance and Barrier Height Properties of Bipolar Switching Gd:SiOx RRAM Devices under Different Oxygen Concentration Environments

PubMed Central

Chen, Kai-Huang; Tsai, Tsung-Ming; Cheng, Chien-Min; Huang, Shou-Jen; Chang, Kuan-Chang; Liang, Shu-Ping; Young, Tai-Fa

2017-01-01

In this study, the hopping conduction distance and bipolar switching properties of the Gd:SiOx thin film by (radio frequency, rf) rf sputtering technology for applications in RRAM devices were calculated and investigated. To discuss and verify the electrical switching mechanism in various different constant compliance currents, the typical current versus applied voltage (I-V) characteristics of gadolinium oxide RRAM devices was transferred and fitted. Finally, the transmission electrons’ switching behavior between the TiN bottom electrode and Pt top electrode in the initial metallic filament forming process of the gadolinium oxide thin film RRAM devices for low resistance state (LRS)/high resistance state (HRS) was described and explained in a simulated physical diagram model. PMID:29283368

In situ characterization of Zircaloy-4 oxidation at 500 °C in dry air

NASA Astrophysics Data System (ADS)

Vermoyal, J. J.; Dessemond, L.; Hammou, A.; Frichet, A.

2001-10-01

The in situ oxidation of Zircaloy-4 at 500 °C in dry air was investigated by thermogravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS). The coating of the alloy by a platinum film as electrode material was observed as not to modify the oxidation kinetic properties. After an initial cubic rate law, a transition to a quasi-linear curve occurs. The independence of the oxidation behavior to the Pt coupling is compatible with oxygen diffusion as the rate-determining step. During the pre-transition step, the rest potential of the cell Pt/oxide/Zy-4, the color of the oxide and the modulus of the single EIS signature indicate the high non-stoichiometry of the oxide. The kinetic transition was proposed to be correlated to the degradation of the film into a partially porous layer. This alteration of the oxide is associated to the appearance of a 1.2 V constant rest potential and the modification of the impedance diagrams in two high modulus contributions. The Cole-Cole representation has been used to demonstrate that the time variation of impedance spectra is related to the oxide growth. An equivalent circuit including two RC loops in series, whose capacitances are frequency dispersed, was proposed to be related to the film structure. Fitted data show that the thickness of the assumed protective layer of the film, close to the metal-oxide interface, is time independent in agreement with a constant oxidation rate. Finally, electrical properties of this inner layer were found to be quite different in pre- and post-transition stage.

Influence of oxide microstructure on corrosion behavior of zirconium-based model alloys

NASA Astrophysics Data System (ADS)

Silva, Marcelo Jose Gomes Da

The extensive utilization of zirconium-based alloys in fuel cladding and other reactor internal components in the nuclear power industry has led to the continuous improvement of these alloys. At the present moment, demands for better performing nuclear fuel cladding materials are increasing. Also, new reactor designs have been proposed that would require the materials to withstand even more rigorous conditions. One of the factors that limit s fuel cladding utilization in nuclear reactors is uniform corrosion and the consequent hydriding of the fuel. In an attempt to develop mechanistic understanding of the role of alloying elements in the growth of a stable protective oxide, a series of model zirconium-based alloys was prepared (Zr-xFe-yCr, Zr-xCu-yMo, Zr-xNb-ySn, for various x and y, pure Zr and Zircaloy-4) and examined with advanced characterization techniques. The alloys were corrosion tested in autoclaves under three different conditions: 360°C water, 500°C steam and 500°C supercritical water in excess of 400 days. These autoclave testing conditions simulate nuclear reactor environment for both current designs (360°C water) and the new supercritical water reactor (500°C steam and 500°C supercritical water) proposed by the generation-IV initiative. The oxide films formed were systematically examined at the Advanced Photon Source using microbeam synchrotron radiation diffraction and fluorescence of cross-sectional samples to determine the oxide phases present and their crystallographic texture as a function of distance from the metal/oxide interface. Also, the overall texture of the oxide layers was investigated using synchrotron radiation diffraction in frontal geometry. The corrosion kinetics is a function of the alloy system and showed a wide range of behaviors, from immediately unstable oxide growth to stable behavior. The corrosion weight gains from testing at high temperature are a factor of five higher than those measured at 360°C but the protectiveness ranking of the alloys is similar. Measured pole figures from different oxides in different corrosion regimes showed that monoclinic oxides grow in slightly distinct directions: protective oxides grow along the (-904)m pole, whether non-protective oxides grow along or close to the (-302)m pole. The angle in between these two directions ((-904)m and (-302)m) is about 6°. Microbeam synchrotron radiation diffraction and fluorescence was performed in the oxide layers and systematic differences are observed in protective and non-protective oxides, both near the oxide/metal interface and in the bulk of the oxide layers. The non-protective oxide interfaces show a smooth transition from metal to oxide with metal diffraction peaks disappearing as the monoclinic oxide peaks appear. In contrast, in a protective oxide, a complex structure near the oxide/metal interface was seen, showing peaks from Zr 3O suboxide and a highly oriented tetragonal oxide phase with specific orientation relationships with the monoclinic oxide and the base metal. The highly oriented tetragonal phase, only present in protective oxides, is believed to be a precursor to the formation of monoclinic oxide found in the bulk of the oxide layer. This plane may promote stable growth by causing the oxide to form in a manner that maximizes occupation of the substrate surface and minimizes stress accumulation, leading to more stable oxide growth. The association seen in this work of the precursor oxide phase with protective oxides and its orientation relationship with the monoclinic oxide, combined with the difference in oxide growth direction seen between protective and non-protective oxides, is interpreted as evidence that this phase allows a more properly oriented oxide to grow, in a way that minimizes stress accumulation and therefore delays the oxide transition to larger oxide thicknesses.

A review of tin oxide-based catalytic systems: Preparation, characterization and catalytic behavior

NASA Technical Reports Server (NTRS)

Hoflund, Gar B.

1987-01-01

This paper reviews the important aspects of the preparation, characterization and catalytic behavior of tin oxide-based catalytic systems including doped tin oxide, mixed oxides which contain tin oxide, Pt supported on tin oxide and Pt/Sn supported on alumina. These systems have a broad range of applications and are continually increasing in importance. However, due to their complex nature, much remains to be understood concerning how they function catalytically.

Temperature-dependent nucleation and capture-zone scaling of C 60 on silicon oxide

NASA Astrophysics Data System (ADS)

Groce, M. A.; Conrad, B. R.; Cullen, W. G.; Pimpinelli, A.; Williams, E. D.; Einstein, T. L.

2012-01-01

Submonolayer films of C 60 have been deposited on ultrathin SiO 2 films for the purpose of characterizing the initial stages of nucleation and growth as a function of temperature. Capture zones extracted from the initial film morphology were analyzed using both the gamma and generalized Wigner distributions. The calculated critical nucleus size i of the C 60 islands was observed to change over the temperature range 298 K to 483 K. All fitted values of i were found to be between 0 and 1, representing stable monomers and stable dimers, respectively. With increasing temperature of film preparation, we observed i first increasing through this range and then decreasing. We discuss possible explanations of this reentrant-like behavior.

Surface Behavior of Iron Sulfide Ore during Grinding with Alumina Media

NASA Astrophysics Data System (ADS)

Martín, Reyes P.; Elia, Palácios B.; Patiño, Francisco C.; Escudero, Ramiro G.; Mizraim, Uriel Flores G.; Reyes, Iván A. D.; Palazuelos, Laura Angeles

This research was conducted to study the oxidation and surface modification of pyrite in an inert mill and alumina grinding media at different pH values. The extent and progress of the oxidation function of milling time, by measuring some physicochemical variables, zeta potential (ZP), infrared analysis and monitoring. The results indicate pyrite oxidation during grinding, releasing iron and sulfur ions to the solution increasing its concentration with the initial pH and the milling time, the ORP and DO decrease the grinding time, on the other hand presents negative values ZP pH of 9, 11 and 12, whereas at pH 5, 7 and 13, the ZP is positive, FTIR generally detect the presence of free sulfate ion molecule 1084 cm-1, goethite with the absorption band at about 794 cm-1, also occurs in a band assigned to 470 cm-1 lepidocrocite oxy iron hydroxide γ- FeOOH, nucleated species or formed during milling.

Introductory study of the chemical behavior of jet emissions in photochemical smog. [computerized simulation

NASA Technical Reports Server (NTRS)

Whitten, G. Z.; Hogo, H.

1976-01-01

Jet aircraft emissions data from the literature were used as initial conditions for a series of computer simulations of photochemical smog formation in static air. The chemical kinetics mechanism used in these simulations was an updated version which contains certain parameters designed to account for hydrocarbon reactivity. These parameters were varied to simulate the reaction rate constants and average carbon numbers associated with the jet emissions. The roles of surface effects, variable light sources, NO/NO2 ratio, continuous emissions, and untested mechanistic parameters were also assessed. The results of these calculations indicate that the present jet emissions are capable of producing oxidant by themselves. The hydrocarbon/nitrous oxides ratio of present jet aircraft emissions is much higher than that of automobiles. These two ratios appear to bracket the hydrocarbon/nitrous oxides ratio that maximizes ozone production. Hence an enhanced effect is seen in the simulation when jet exhaust emissions are mixed with automobile emissions.

Effect of Machining Parameters on Oxidation Behavior of Mild Steel

NASA Astrophysics Data System (ADS)

Majumdar, P.; Shekhar, S.; Mondal, K.

2015-01-01

This study aims to find out a correlation between machining parameters, resultant microstructure, and isothermal oxidation behavior of lathe-machined mild steel in the temperature range of 660-710 °C. The tool rake angles "α" used were +20°, 0°, and -20°, and cutting speeds used were 41, 232, and 541 mm/s. Under isothermal conditions, non-machined and machined mild steel samples follow parabolic oxidation kinetics with activation energy of 181 and ~400 kJ/mol, respectively. Exaggerated grain growth of the machined surface was observed, whereas, the center part of the machined sample showed minimal grain growth during oxidation at higher temperatures. Grain growth on the surface was attributed to the reduction of strain energy at high temperature oxidation, which was accumulated on the sub-region of the machined surface during machining. It was also observed that characteristic surface oxide controlled the oxidation behavior of the machined samples. This study clearly demonstrates the effect of equivalent strain, roughness, and grain size due to machining, and subsequent grain growth on the oxidation behavior of the mild steel.

Early Stage of Oxidation on Titanium Surface by Reactive Molecular Dynamics Simulation

DOE PAGES

Yang, Liang; Wang, C. Z.; Lin, Shiwei; ...

2018-01-01

Understanding of metal oxidation is very critical to corrosion control, catalysis synthesis, and advanced materials engineering. Metal oxidation is a very complex phenomenon, with many different processes which are coupled and involved from the onset of reaction. In this work, the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics (MD) simulations using a reactive force field (ReaxFF). We show that oxygen transport is the dominant process during the initial oxidation. Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titaniummore » (0001) surface and further prevented oxidation in the deeper layers. As a result, the mechanism of initial oxidation observed in this work can be also applicable to other self-limiting oxidation.« less

Fabrication and in vitro release behavior of a novel antibacterial coating containing halogenated furanone-loaded poly(L-lactic acid) nanoparticles on microarc-oxidized titanium

PubMed Central

Cheng, Yicheng; Wu, Jiang; Gao, Bo; Zhao, Xianghui; Yao, Junyan; Mei, Shenglin; Zhang, Liang; Ren, Huifang

2012-01-01

Background Dental implants have become increasingly common for the management of missing teeth. However, peri-implant infection remains a problem, is usually difficult to treat, and may lead eventually to dental implant failure. The aim of this study was to fabricate a novel antibacterial coating containing a halogenated furanone compound, ie, (Z-)-4-bromo-5-(bromomethylene)-2(5H)-furanone (BBF)-loaded poly(L-lactic acid) (PLLA) nanoparticles on microarc-oxidized titanium and to evaluate its release behavior in vitro. Methods BBF-loaded PLLA nanoparticles were prepared using the emulsion solvent-evaporation method, and the antibacterial coating was fabricated by cross-linking BBF-loaded PLLA nanoparticles with gelatin on microarc-oxidized titanium. Results The BBF-loaded PLLA nanoparticles had a small particle size (408 ± 14 nm), a low polydispersity index (0.140 ± 0.008), a high encapsulation efficiency (72.44% ± 1.27%), and a fine spherical shape with a smooth surface. The morphology of the fabricated antibacterial coating showed that the BBF-loaded PLLA nanoparticles were well distributed in the pores of the microarc oxidation coating, and were cross-linked with each other and the wall pores by gelatin. The release study indicated that the antibacterial coating could achieve sustained release of BBF for 60 days, with a slight initial burst release during the first 4 hours. Conclusion The novel antibacterial coating fabricated in this study is a potentially promising method for prevention of early peri-implant infection. PMID:23152682

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

Yang, Liang; Wang, C. Z.; Lin, Shiwei

Understanding of metal oxidation is very critical to corrosion control, catalysis synthesis, and advanced materials engineering. Metal oxidation is a very complex phenomenon, with many different processes which are coupled and involved from the onset of reaction. In this work, the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics (MD) simulations using a reactive force field (ReaxFF). We show that oxygen transport is the dominant process during the initial oxidation. Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titaniummore » (0001) surface and further prevented oxidation in the deeper layers. As a result, the mechanism of initial oxidation observed in this work can be also applicable to other self-limiting oxidation.« less

Characterizing Effects of Nitric Oxide Sterilization on tert-Butyl Acrylate Shape Memory Polymers

NASA Astrophysics Data System (ADS)

Phillippi, Ben

As research into the potential uses of shape memory polymers (SMPs) as implantable medical devices continues to grow and expand, so does the need for an accurate and reliable sterilization mechanism. The ability of an SMP to precisely undergo a programmed shape change will define its ability to accomplish a therapeutic task. To ensure proper execution of the in vivo shape change, the sterilization process must not negatively affect the shape memory behavior of the material. To address this need, this thesis investigates the effectiveness of a benchtop nitric oxide (NOx) sterilization process and the extent to which the process affects the shape memory behavior of a well-studied tert-Butyl Acrylate (tBA) SMP. Quantifying the effects on shape memory behavior was performed using a two-tiered analysis. A two-tiered study design was used to determine if the sterilization process induced any premature shape recovery and to identify any effects that NOx has on the overall shape memory behavior of the foams. Determining the effectiveness of the NOx system--specially, whether the treated samples are more sterile/less contaminated than untreated--was also performed with a two-tiered analysis. In this case, the two-tiered analysis was employed to have a secondary check for contamination. To elaborate, all of the samples that were deemed not contaminated from the initial test were put through a second sterility test to check for contamination a second time. The results of these tests indicated the NOx system is an effective sterilization mechanism and the current protocol does not negatively impact the shape memory behavior of the tBA SMP. The samples held their compressed shape throughout the entirety of the sterilization process. Additionally, there were no observable impacts on the shape memory behavior induced by NOx. Lastly, the treated samples demonstrated lower contamination than the untreated. This thesis demonstrates the effectiveness of NOx as a laboratory scale sterilization mechanism for heat triggered shape memory polymers. The shape memory analysis indicated that the magnitude of the length changes induced by NOx is small enough that it does not make a statistically significant impact on the shape memory behavior of the foams. Additionally, there were no observable effects on the shape memory behavior induced by NOx. The results further indicated the NOx system is effective at sterilizing porous scaffolds, as none of the sterilized samples showed contamination. Testing methods proved to be effective because the initial sterility test was able to identify all of the contaminated samples and preliminary results indicated that NOx sterilization improves the sterility of the foams.

Phase evolution and thermal properties of yttria-stabilized hafnia nano-coatings deposited on alumina

NASA Astrophysics Data System (ADS)

Rubio, Ernesto Javier

High-temperature coatings are critical to the future power-generation systems and industries. Thermal barrier coatings (TBCs), which are usually the ceramic materials applied as thin coatings, protect engine components and allow further increase in engine temperatures for higher efficiency. Thus, the durability and reliability of the coating systems have to be more robust compared to current natural gas based engines. While a near and mid-term target is to develop TBC architecture with a 1300 °C surface temperature tolerance, a deeper understanding of the structure evolution and thermal behavior of the TBC-bond coat interface, specifically the thermally grown oxide (TGO), is of primary importance. In the present work, attention is directed towards yttria-stabilized hafnia (YSH) coatings on alumina (α-Al2O 3) to simulate the TBC-TGO interface and understand the phase evolution, microstructure and thermal oxidation of the coatings. YSH coatings were grown on α-Al2O3 substrates by sputter deposition by varying coating thickness in a wide range ˜30-1000 nm. The effect of coating thickness on the structure, morphology and the residual stress has been investigated using X-ray diffraction (XRD) and high resolution scanning electron microscopy (SEM). Thermal oxidation behavior of the coatings has been evaluated using the isothermal oxidation measurements under static conditions. X-ray diffraction analyses revealed the existence of monoclinic hafnia phase for relatively thin coatings indicating that the interfacial phenomena are dominant in phase stabilization. The evolution towards pure stabilized cubic phase of hafnia with the increasing coating thickness is observed. The SEM results indicate the changes in morphology of the coatings; the average grain size increases from 15 to 500 nm with increasing thickness. Residual stress was calculated employing XRD using the variable ψ-angle. Relation between residual stress and structural change is also studied. The results obtained on the thermal oxidation behavior indicate that the YSH coatings exhibit initial mass gain in the first 6 hours and sustained structure for extended hours of thermal treatment.

The curious case of exploding quantum dots: anomalous migration and growth behaviors of Ge under Si oxidation

PubMed Central

2013-01-01

We have previously demonstrated the unique migration behavior of Ge quantum dots (QDs) through Si3N4 layers during high-temperature oxidation. Penetration of these QDs into the underlying Si substrate however, leads to a completely different behavior: the Ge QDs ‘explode,’ regressing back almost to their origins as individual Ge nuclei as formed during the oxidation of the original nanopatterned SiGe structures used for their generation. A kinetics-based model is proposed to explain the anomalous migration behavior and morphology changes of the Ge QDs based on the Si flux generated during the oxidation of Si-containing layers. PMID:23618165

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

NASA Astrophysics Data System (ADS)

Phinichka, Natthapong

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

High-Temperature Oxidation Behavior of Two Nickel-Based Superalloys Produced by Metal Injection Molding for Aero Engine Applications

NASA Astrophysics Data System (ADS)

Albert, Benedikt; Völkl, Rainer; Glatzel, Uwe

2014-09-01

For different high-temperature applications like aero engines or turbochargers, metal injection molding (MIM) of superalloys is an interesting processing alternative. For operation at high temperatures, oxidation behavior of superalloys produced by MIM needs to match the standard of cast or forged material. The oxidation behavior of nickel-based superalloys Inconel 713 and MAR-M247 in the temperature interval from 1073 K to 1373 K (800 °C to 1100 °C) is investigated and compared to cast material. Weight gain is measured discontinuously at different oxidation temperatures and times. Analysis of oxidized samples is done via SEM and EDX-measurements. MIM samples exhibit homogeneous oxide layers with a thickness up to 4 µm. After processing by MIM, Inconel 713 exhibits lower weight gain and thinner oxide layers than MAR-M247.

Oxidized trilinoleate and tridocosahexaenoate induce pica behavior and change locomotor activity.

PubMed

Kitamura, Fuki; Watanabe, Hiroyuki; Umeno, Aya; Yoshida, Yasukazu; Kurata, Kenji; Gotoh, Naohiro

2013-01-01

Pica behavior, a behavior that is characterized by eating a nonfood material such as kaolin and relates to the degree of discomfort in animals, and the variations of locomotor activity of rats after eating deteriorated fat and oil extracted from instant noodles were examined in our previous study. The result shows that oxidized fat and oil with at least 100 meq/kg in peroxide value (PV) increase pica behavior and decrease locomotor activity. In the present study, the same two behaviors were measured using autoxidized trilinoleate (tri-LA) and tridocosahexaenoate (tri-DHA) as a model of vegetable and fish oil, respectively, to compare fatty acid differences against the induction of two behaviors. The oxidized levels of tri-LA and tri-DHA were analyzed with PV and p-anisidine value (AnV), the method to analyze secondary oxidized products. The oxidation levels of respective triacylglycerol (TAG) samples were carefully adjusted to make them having almost the same PV and AnV. As the results, 600 or more meq/kg in PV of both TAGs significantly increased the consumption of kaolin pellets compared to the control group. Furthermore, 300 or more meq/kg in PV of tri-LA and 200 or more meq/kg in PV of tri-DHA demonstrated significant decrease in locomotor activity compared to control group. These results would indicate that the oxidized TAG having the same PV and/or AnV would induce the same type of pica behavior and locomotor activity. Furthermore, that the structure of oxidized products might not be important and the amount of hydroperoxide group and/or aldehyde group in deteriorated fats and oils might affect the pica behavior and locomotor activity were thought.

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

DOE PAGES

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

2016-06-06

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

40 CFR 63.10400 - How do I demonstrate initial compliance?

Code of Federal Regulations, 2010 CFR

2010-07-01

... CATEGORIES (CONTINUED) National Emission Standards for Hospital Ethylene Oxide Sterilizers Initial Compliance... submitting an Initial Notification of Compliance Status certifying that you are venting the ethylene oxide...

Correlation between the oxide impedance and corrosion behavior of Zr-Nb-Sn-Fe-Cu alloys

NASA Astrophysics Data System (ADS)

Park, Sang-Yoon; Lee, Myung-Ho; Jeong, Yong-Hwan; Jung, Youn-Ho

2004-12-01

The correlation between the oxide impedance and corrosion behavior of two series of Zr-Nb-Sn-Fe-Cu alloys was evaluated. Corrosion tests were performed in a 70 ppm LiOH aqueous solution at 360°C for 300 days. The results of the corrosion tests revealed that the corrosion behavior of the alloys depended on the Nb and Sn content. The impedance characteristics for the pre- and post-transition oxide layers formed on the surface of the alloys were investigated in sulfuric acid at room temperature. From the results, a pertinent equivalent circuit model was preferably established, explaining the properties of double oxide layers. The impedance of the oxide layers correlated with the corrosion behavior; better corrosion resistance always showed higher electric resistance for the inner layers. It is thus concluded that a pertinent equivalent circuit model would be useful for evaluating the long-term corrosion behavior of Zr-Nb-Sn-Fe-Cu alloys.

In Situ Atomic Scale Visualization Of Surface Kinetics Driven Dynamics Of Oxide Growth On A Ni–Cr Surface

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

Luo, Langli; Zou, Lianfeng; Schreiber, Daniel K.

2016-01-20

We report in situ atomic-scale visualization of the dynamical three-dimensional (3D) growth of NiO during initial oxidation of Ni-10at%Cr using environmental transmission electron microscopy (ETEM). Despite the thermodynamic preference for Cr2O3 formation, cubic NiO oxides nucleated and grew epitaxially as the dominating oxide phase on the Ni-Cr (100) surface during initial oxidation. The growth of NiO islands proceeds through step-by-step adatom mechanism in 3D, which is sustained by surface diffusion of Ni and O atoms. Although the shapes of oxide islands are controlled by strain energy between oxide and alloy substrate, local surface kinetic variations can lead to the changemore » of surface planes of oxide islands. These results demonstrate that surface diffusion dominates initial oxidation of Ni-Cr in these test conditions.« less

Compaction and High-Pressure Response of Granular Tantalum Oxide

NASA Astrophysics Data System (ADS)

Vogler, Tracy; Root, Seth; Knudson, Marcus; Thornhill, Tom; Reinhart, William

2015-06-01

The dynamic behavior of nearly fully-dense and porous tantalum oxide (Ta2O5) is studied. Two particle morphologies are used to obtain two distinct initial tap densities, which correspond to approximately 40% and 15% of crystalline density. The response is characterized from low pressures, which result in incomplete compaction, to very high pressures where the thermal component of the EOS dominates. Issues related to a possible phase transformation along the Hugoniot and to establishing reasonable error bars on the experimental data will be discussed. The suitability of continuum and mesoscale models to capture the experimental results will be examined. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

Discovery of oxidative burst in the field of plant immunity

PubMed Central

Yoshioka, Hirofumi; Bouteau, François

2008-01-01

This article is introductory to the series of works presented in this special issue on the homeostasis and the signaling roles of reactive oxygen species (ROS) in plants. Upper half of this article briefly describes the history of the ROS study in the field of plant immunity research initiated by the observation that the attacks by pathogenic microorganisms possibly stimulate the burst of ROS production in the plant tissues. The topics covered in the series of works presented here include the plants' responses to abiotic oxidative stress (atmospheric ozone), regulation of seed germination, chemical interaction between parasitic and host plants and the draught tolerance, all controlled through homeostasis of ROS at biochemical and molecular biological levels. Lastly a discussion forum was proposed to further deepen our understanding of ROS behaviors in plants. PMID:19513209

Kinetics of the neuroinflammation-oxidative stress correlation in rat brain following the injection of fibrillar amyloid-beta onto the hippocampus in vivo.

PubMed

Rosales-Corral, Sergio; Tan, Dun-Xian; Reiter, Russel J; Valdivia-Velázquez, Miguel; Acosta-Martínez, J Pablo; Ortiz, Genaro G

2004-05-01

The purpose of this study was to describe-following the injection of a single intracerebral dose of fibrillar amyloid-beta(1-40) in vivo-some correlations between proinflammatory cytokines and oxidative stress indicators in function of time, as well as how these variables fit in a regression model. We found a positive, significant correlation between interleukin (IL)-1beta or IL-6 and the activity of the glutathione peroxidase enzyme (GSH-Px), but IL-1beta or IL-6 maintained a strong, negative correlation with the lipid peroxidation (LPO). The first 12 h marked a positive correlation between IL-6 and tumor necrosis factor-alpha (TNF-alpha), but starting from the 36 h, this relationship became negative. We found also particular patterns of behavior through the time for IL-1beta, nitrites and IL-6, with parallel or sequential interrelationships. Results shows clearly that, in vivo, the fibrillar amyloid-beta (Abeta) disrupts the oxidative balance and initiate a proinflammatory response, which in turn feeds the oxidative imbalance in a coordinated, sequential way. This work contributes to our understanding of the positive feedbacks, focusing the "cytokine cycle" along with the oxidative stress mediators in a complex, multicellular, and interactive environment.

Influence of Nitinol wire surface treatment on oxide thickness and composition and its subsequent effect on corrosion resistance and nickel ion release.

PubMed

Clarke, B; Carroll, W; Rochev, Y; Hynes, M; Bradley, D; Plumley, D

2006-10-01

Medical implants and devices are now used successfully in surgical procedures on a daily basis. Alloys of nickel and titanium, and in particular Nitinol are of special interest in the medical device industry, because of their shape memory and superelastic properties. The corrosion behavior of nitinol in the body is also of critical importance because of the known toxicological effects of nickel. The stability of a NiTi alloy in the physiological environment is dependant primarily on the properties of the mostly TiO(2) oxide layer that is present on the surface. For the present study, a range of nitinol wires have been prepared using different drawing processes and a range of surface preparation procedures. It is clear from the results obtained that the wire samples with very thick oxides also contain a high nickel content in the oxide layer. The untreated samples with the thicker oxides show the lowest pitting potential values and greater nickel release in both long and short-term experiments. It was also found that after long-term immersion tests breakdown potentials increased for samples that exhibited lower values initially. From these results it would appear that surface treatment is essential for the optimum bioperformance of nitinol. (c) 2006 Wiley Periodicals, Inc

Electrochemistry coupled to (LC-)MS for the simulation of oxidative biotransformation reactions of PAHs.

PubMed

Wigger, Tina; Seidel, Albrecht; Karst, Uwe

2017-06-01

Electrochemistry coupled to liquid chromatography and mass spectrometry was used for simulating the biological and environmental fate of polycyclic aromatic hydrocarbons (PAHs) as well as for studying the PAH degradation behavior during electrochemical remediation. Pyrene and benzo[a]pyrene were selected as model compounds and oxidized within an electrochemical thin-layer cell equipped with boron-doped diamond electrode. At potentials of 1.2 and 1.6 V vs. Pd/H 2 , quinones were found to be the major oxidation products for both investigated PAHs. These quinones belong to a large group of PAH derivatives referred to as oxygenated PAHs, which have gained increasing attention in recent years due to their high abundance in the environment and their significant toxicity. Separation of oxidation products allowed the identification of two pyrene quinone and three benzo[a]pyrene quinone isomers, all of which are known to be formed via photooxidation and during mammalian metabolism. The good correlation between electrochemically generated PAH quinones and those formed in natural processes was also confirmed by UV irradiation experiments and microsomal incubations. At potentials higher than 2.0 V, further degradation of the initial oxidation products was observed which highlights the capability of electrochemistry to be used as remediation technique. Copyright © 2017 Elsevier Ltd. All rights reserved.

Adsorption of heavy metals from aqueous solutions by Mg-Al-Zn mingled oxides adsorbent.

PubMed

El-Sayed, Mona; Eshaq, Gh; ElMetwally, A E

2016-10-01

In our study, Mg-Al-Zn mingled oxides were prepared by the co-precipitation method. The structure, composition, morphology and thermal stability of the synthesized Mg-Al-Zn mingled oxides were analyzed by powder X-ray diffraction, Fourier transform infrared spectrometry, N 2 physisorption, scanning electron microscopy, differential scanning calorimetry and thermogravimetry. Batch experiments were performed to study the adsorption behavior of cobalt(II) and nickel(II) as a function of pH, contact time, initial metal ion concentration, and adsorbent dose. The maximum adsorption capacity of Mg-Al-Zn mingled oxides for cobalt and nickel metal ions was 116.7 mg g -1 , and 70.4 mg g -1 , respectively. The experimental data were analyzed using pseudo-first- and pseudo-second-order kinetic models in linear and nonlinear regression analysis. The kinetic studies showed that the adsorption process could be described by the pseudo-second-order kinetic model. Experimental equilibrium data were well represented by Langmuir and Freundlich isotherm models. Also, the maximum monolayer capacity, q max , obtained was 113.8 mg g -1 , and 79.4 mg g -1 for Co(II), and Ni(II), respectively. Our results showed that Mg-Al-Zn mingled oxides can be used as an efficient adsorbent material for removal of heavy metals from industrial wastewater samples.

Nanosized copper ferrite materials: Mechanochemical synthesis and characterization

NASA Astrophysics Data System (ADS)

Manova, Elina; Tsoncheva, Tanya; Paneva, Daniela; Popova, Margarita; Velinov, Nikolay; Kunev, Boris; Tenchev, Krassimir; Mitov, Ivan

2011-05-01

Nanodimensional powders of cubic copper ferrite are synthesized by two-steps procedure of co-precipitation of copper and iron hydroxide carbonates, followed by mechanochemical treatment. X-ray powder diffraction, Mössbauer spectroscopy and temperature-programmed reduction are used for the characterization of the obtained materials. Their catalytic behavior is tested in methanol decomposition to hydrogen and CO and total oxidation of toluene. Formation of nanosized ferrite material is registered even after one hour of milling time. It is established that the prolonging of treatment procedure decreases the dispersion of the obtained product with the appearance of Fe 2O 3. It is demonstrated that the catalytic behavior of the samples depends not only on their initial phase composition, but on the concomitant ferrite phase transformations by the influence of the reaction medium.

Fibre-matrix bond strength studies of glass, ceramic, and metal matrix composites

NASA Technical Reports Server (NTRS)

Grande, D. H.; Mandell, J. F.; Hong, K. C. C.

1988-01-01

An indentation test technique for compressively loading the ends of individual fibers to produce debonding has been applied to metal, glass, and glass-ceramic matrix composites; bond strength values at debond initiation are calculated using a finite-element model. Results are correlated with composite longitudinal and interlaminar shear behavior for carbon and Nicalon fiber-reinforced glasses and glass-ceramics including the effects of matrix modifications, processing conditions, and high-temperature oxidation embrittlement. The data indicate that significant bonding to improve off-axis and shear properties can be tolerated before the longitudinal behavior becomes brittle. Residual stress and other mechanical bonding effects are important, but improved analyses and multiaxial interfacial failure criteria are needed to adequately interpret bond strength data in terms of composite performance.

Ceriodaphnia dubia as a Potential Bio-Indicator for Assessing Acute Aluminum Oxide Nanoparticle Toxicity in Fresh Water Environment

PubMed Central

Pakrashi, Sunandan; Dalai, Swayamprava; Humayun, Ahmed; Chakravarty, Sujay; Chandrasekaran, Natarajan; Mukherjee, Amitava

2013-01-01

Growing nanomaterials based consumer applications have raised concerns about their potential release into the aquatic ecosystems and the consequent toxicological impacts. So environmental monitoring of the nanomaterials in aqueous systems becomes imperative. The current study reveals the potential of Ceriodaphnia dubia (C. dubia) as a bio-indicator for aluminum oxide nanoparticles in a fresh water aquatic ecosystem where it occupies an important ecological niche as a primary consumer. This study aims to investigate the aluminium oxide nanoparticle induced acute toxicity on Ceriodaphnia dubia in a freshwater system. The bioavailability of the aluminum oxide nanoparticles has been studied with respect to their aggregation behavior in the system and correlated with the toxicity endpoints. The oxidative stress generated by the particles contributed greatly toward their toxicity. The crucial role of leached aluminium ion mediated toxicity in the later phases (48 h and 72 h) in conjunction with the effects from the nano-sized particles in the initial phases (24 h) puts forth the dynamics of nanotoxicity in the test system. The internalization of nanoparticles (both gross and systemic uptake) as substantiated through the transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectral (ICP-OES) analysis was another major contributor toward acute toxicity. Concluding the present study, Ceriodaphnia dubia can be a promising candidate for bio-monitoring the aluminium oxide nanoparticles in a fresh water system. PMID:24040143

Switching Oxide Traps

NASA Technical Reports Server (NTRS)

Oldham, Timothy R.

2003-01-01

We consider radiation-induced charge trapping in SiO2 dielectric layers, primarily from the point of view of CMOS devices. However, SiO2 insulators are used in many other ways, and the same defects occur in other contexts. The key studies, which determined the nature of the oxide charge traps, were done primarily on gate oxides in CMOS devices, because that was the main radiation problem in CMOS at one time. There are two major reviews of radiation-induced oxide charge trapping already in the literature, which discuss the subject in far greater detail than is possible here. The first of these was by McLean et al. in 1989, and the second, ten years later, was intended as an update, because of additional, new work that had been reported. Basically, the picture that has emerged is that ionizing radiation creates electron-hole pairs in the oxide, and the electrons have much higher mobility than the holes. Therefore, the electrons are swept out of the oxide very rapidly by any field that is present, leaving behind any holes that escape the initial recombination process. These holes then undergo a polaron hopping transport toward the Si/SiO2 interface (under positive bias). Near the interface, some fraction of them fall into deep, relatively stable, long-lived hole traps. The nature and annealing behavior of these hole traps is the main focus of this paper.

Ceriodaphnia dubia as a potential bio-indicator for assessing acute aluminum oxide nanoparticle toxicity in fresh water environment.

PubMed

Pakrashi, Sunandan; Dalai, Swayamprava; Humayun, Ahmed; Chakravarty, Sujay; Chandrasekaran, Natarajan; Mukherjee, Amitava

2013-01-01

Growing nanomaterials based consumer applications have raised concerns about their potential release into the aquatic ecosystems and the consequent toxicological impacts. So environmental monitoring of the nanomaterials in aqueous systems becomes imperative. The current study reveals the potential of Ceriodaphnia dubia (C. dubia) as a bio-indicator for aluminum oxide nanoparticles in a fresh water aquatic ecosystem where it occupies an important ecological niche as a primary consumer. This study aims to investigate the aluminium oxide nanoparticle induced acute toxicity on Ceriodaphnia dubia in a freshwater system. The bioavailability of the aluminum oxide nanoparticles has been studied with respect to their aggregation behavior in the system and correlated with the toxicity endpoints. The oxidative stress generated by the particles contributed greatly toward their toxicity. The crucial role of leached aluminium ion mediated toxicity in the later phases (48 h and 72 h) in conjunction with the effects from the nano-sized particles in the initial phases (24 h) puts forth the dynamics of nanotoxicity in the test system. The internalization of nanoparticles (both gross and systemic uptake) as substantiated through the transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectral (ICP-OES) analysis was another major contributor toward acute toxicity. Concluding the present study, Ceriodaphnia dubia can be a promising candidate for bio-monitoring the aluminium oxide nanoparticles in a fresh water system.

Azobisisobutyronitrile initiated aerobic oxidative transformation of amines: coupling of primary amines and cyanation of tertiary amines.

PubMed

Liu, Lianghui; Wang, Zikuan; Fu, Xuefeng; Yan, Chun-Hua

2012-11-16

In the presence of a catalytic amount of radical initiator AIBN, primary amines are oxidatively coupled to imines and tertiary amines are cyanated to α-aminonitriles. These "metal-free" aerobic oxidative coupling reactions may find applications in a wide range of "green" oxidation chemistry.

An Assessment of the Ductile Fracture Behavior of Hot Isostatically Pressed and Forged 304L Stainless Steel

NASA Astrophysics Data System (ADS)

Cooper, A. J.; Smith, R. J.; Sherry, A. H.

2017-05-01

Type 300 austenitic stainless steel manufactured by hot isostatic pressing (HIP) has recently been shown to exhibit subtly different fracture behavior from that of equivalent graded forged steel, whereby the oxygen remaining in the component after HIP manifests itself in the austenite matrix as nonmetallic oxide inclusions. These inclusions facilitate fracture by acting as nucleation sites for the initiation, growth, and coalescence of microvoids in the plastically deforming austenite matrix. Here, we perform analyses based on the Rice-Tracey (RT) void growth model, supported by instrumented Charpy and J-integral fracture toughness testing at ambient temperature, to characterize the degree of void growth ahead of both a V-notch and crack in 304L stainless steel. We show that the hot isostatically pressed (HIP'd) 304L steel exhibits a lower critical void growth at the onset of fracture than that observed in forged 304L steel, which ultimately results in HIP'd steel exhibiting lower fracture toughness at initiation and impact toughness. Although the reduction in toughness of HIP'd steel is not detrimental to its use, due to the steel's sufficiently high toughness, the study does indicate that HIP'd and forged 304L steel behave as subtly different materials at a microstructural level with respect to their fracture behavior.

Tensile Fracture Behavior of 316L Austenitic Stainless Steel Manufactured by Hot Isostatic Pressing

NASA Astrophysics Data System (ADS)

Cooper, A. J.; Brayshaw, W. J.; Sherry, A. H.

2018-02-01

Herein we investigate how the oxygen content in hot isostatically pressed (HIP'd) 316L stainless steel affects the mechanical properties and tensile fracture behavior. This work follows on from previous studies, which aimed to understand the effect of oxygen content on the Charpy impact toughness of HIP'd steel. We expand on the work by performing room-temperature tensile testing on different heats of 316L stainless steel, which contain different levels of interstitial elements (carbon and nitrogen) as well as oxygen in the bulk material. Throughout the work we repeat the experiments on conventionally forged 316L steel as a reference material. The analysis of the work indicates that oxygen does not contribute to a measureable solution strengthening mechanism, as is the case with carbon and nitrogen in austenitic stainless steels (Werner in Mater Sci Eng A 101:93-98, 1988). Neither does oxygen, in the form of oxide inclusions, contribute to precipitation hardening due to the size and spacing of particles. However, the oxide particles do influence fracture behavior; fractography of the failed tension test specimens indicates that the average ductile dimple size is related to the oxygen content in the bulk material, the results of which support an on-going hypothesis relating oxygen content in HIP'd steels to their fracture mechanisms by providing additional sites for the initiation of ductile damage in the form of voids.

Structural & oxidation behavior of TiN & AlxTi1-xN coatings deposited by CA-PVD technique

NASA Astrophysics Data System (ADS)

Thorat, Nirmala; Mundotia, Rajesh; Varma, Ranjana; Kale, Ashwin; Mhatre, Umesh; Patel, Nainesh

2018-04-01

Coatings with thermal stability at elevated temperatures are prerequisite for various high speed machining and high temperature applications. The present work compares the oxidation behavior of the AlxTi1-xN coating prepared with different Al composition. Coated samples were tested at different temperatures in the range of 400 - 800 C to study their oxidation behavior. Percentage weight gain of all the samples were evaluated using high accuracy weighing balance. The depth of oxide layers were studied using Calo-test instrument. The XRD analysis was carried out to specify the phase structure. Higher oxidation rate was observed for TiN coating at all the oxidation temperatures. Oxidation rate was higher for Al13Ti87N and Al70Ti30N coatings compared to Al60Ti40N and Al50Ti50N coatings which exhibits better oxygen diffusion barrier at all the temperature.

Thermomagnetic analysis of meterorites. 4: Ureilites

NASA Technical Reports Server (NTRS)

Rowe, M. W.; Herndon, J. M.; Larson, E. E.; Watson, D. E.

1974-01-01

Samples of all available ureilites have been analyzed thermomagnetically. For three of the six (Dyalpur, Goalpara and Havero) evidence was found for only low-nickel metallic-iron as the magnetic component and the (saturation magnetization vs, temperature) curves were reversible. In the Novo Urei ureilite, magnetite in addition to low-nickel metallic-iron was indicated and again the Js-T curve was reversible. For the two badly weathered ureilites, Dingo Pup Donga and North Haig, indication was also found that both initial magnetite and low-nickel metallic-iron were present. However, the Js-T curves were somewhat irreversible and the final saturation magnetization was 20% and 50% greater than initially for North Haig and Dingo Pup Donga, respectively. This behavior is interpreted to be the result of magnetite production from a secondary iron oxide during the experiment.

Synthesis, surface modification and characterisation of biocompatible magnetic iron oxide nanoparticles for biomedical applications.

PubMed

Mahdavi, Mahnaz; Ahmad, Mansor Bin; Haron, Md Jelas; Namvar, Farideh; Nadi, Behzad; Rahman, Mohamad Zaki Ab; Amin, Jamileh

2013-06-27

Superparamagnetic iron oxide nanoparticles (MNPs) with appropriate surface chemistry exhibit many interesting properties that can be exploited in a variety of biomedical applications such as magnetic resonance imaging contrast enhancement, tissue repair, hyperthermia, drug delivery and in cell separation. These applications required that the MNPs such as iron oxide Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) having high magnetization values and particle size smaller than 100 nm. This paper reports the experimental detail for preparation of monodisperse oleic acid (OA)-coated Fe₃O₄ MNPs by chemical co-precipitation method to determine the optimum pH, initial temperature and stirring speed in order to obtain the MNPs with small particle size and size distribution that is needed for biomedical applications. The obtained nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence spectrometry (EDXRF), thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and vibrating sample magnetometer (VSM). The results show that the particle size as well as the magnetization of the MNPs was very much dependent on pH, initial temperature of Fe²⁺ and Fe³⁺ solutions and steering speed. The monodisperse Fe₃O₄ MNPs coated with oleic acid with size of 7.8 ± 1.9 nm were successfully prepared at optimum pH 11, initial temperature of 45°C and at stirring rate of 800 rpm. FTIR and XRD data reveal that the oleic acid molecules were adsorbed on the magnetic nanoparticles by chemisorption. Analyses of TEM show the oleic acid provided the Fe₃O₄ particles with better dispersibility. The synthesized Fe₃O₄ nanoparticles exhibited superparamagnetic behavior and the saturation magnetization of the Fe₃O₄ nanoparticles increased with the particle size.

Modeling selenate adsorption behavior on oxides, clay minerals, and soils using the triple layer model

USDA-ARS?s Scientific Manuscript database

Selenate adsorption behavior was investigated on amorphous aluminum oxide, amorphous iron oxide, goethite, clay minerals: kaolinites, montmorillonites, illite, and 18 soil samples from Hawaii, and the Southwestern and the Midwestern regions of the US as a function of solution pH. Selenate adsorpti...

Iron(II) Initiation of Lipid and Protein Oxidation in Pork: The Role of Oxymyoglobin.

PubMed

Zhou, Feibai; Jongberg, Sisse; Zhao, Mouming; Sun, Weizheng; Skibsted, Leif H

2016-06-08

Iron(II), added as FeSO4·7H2O, was found to increase the rate of oxygen depletion as detected electrochemically in a pork homogenate from Longissimus dorsi through an initial increase in metmyoglobin formation from oxymyoglobin and followed by formation of primary and secondary lipid oxidation products and protein oxidation as detected as thiol depletion in myofibrillar proteins. Without added iron(II), under the same conditions at 37 °C, oxygen consumption corresponded solely to the slow oxymyoglobin autoxidation. Long-lived myofibrillar protein radicals as detected by ESR spectroscopy in the presence of iron(II) were formed subsequently to oxymyoglobin oxidation, and their level was increased by lipid oxidation when oxygen was completely depleted. Similarly, the time profile for formation of lipid peroxide indicated that oxymyoglobin oxidation initiates both protein oxidation and lipid oxidation.

Soot Oxidation in Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix K

NASA Technical Reports Server (NTRS)

Xu, F.; El-Leathy, A. M.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

2001-01-01

Soot oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round jets burning in coflowing air considering acetylene, ethylene, propylene and propane as fuels. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation mainly occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of stable major gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2,C2H4, C2H6, C3H6, and C3H8) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by the deconvoluted Li/LiOH atomic absorption technique and flow velocities by laser velocimetry. It was found that soot surface oxidation rates are not particularly affected by fuel type for laminar diffusion flames and are described reasonably well by the OH surface oxidation mechanism with a collision efficiency of 0.10, (standard deviation of 0.07) with no significant effect of fuel type in this behavior; these findings are in good agreement with the classical laminar premixed flame measurements of Neoh et al. Finally, direct rates of surface oxidation by O2 were small compared to OH oxidation for present conditions, based on estimated O2 oxidation rates due to Nagle and Strickland-Constable (1962), because soot oxidation was completed near the flame sheet where O2 concentrations were less than 1.2% by volume.

Soot Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix D

NASA Technical Reports Server (NTRS)

Xu, F.; El-Leathy, A. M.; Faeth, G. M.

2000-01-01

Soot oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round jets burning in coflowing air considering acetylene, ethylene, proplyene and propane as fuels. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation mainly occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of stable major gas species (N2, H2O, H2, 02, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, and C3H8) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by the deconvoluted Li/LiOH atomic absorption technique and flow velocities by laser velocimetry. It was found that soot surface oxidation rates are not particularly affected by fuel type for laminar diffusion flames and are described reasonably well by the OH surface oxidation mechanism with a collision efficiency of 0.10, (standard deviation of 0.07) with no significant effect of fuel type in this behavior; these findings are in good agreement with the classical laminar premixed flame measurements of Neoh et al. Finally, direct rates of surface oxidation by O2 were small compared to OH oxidation for present conditions, based on estimated O2 oxidation rates due to Nagle and Strickland-Constable, because soot oxidation was completed near the flame sheet where O2 concentrations were less than 1.2% by volume.

Air Oxidation Behavior of Two Ti-Base Alloys Synthesized by HIP

NASA Astrophysics Data System (ADS)

Liu, S.; Guo, Q. Q.; Liu, L. L.; Xu, L.; Liu, Y. Y.

2016-04-01

The oxidation behavior of Ti-5Al-2.5Sn and Ti-6Al-4V produced by hot isostatic pressing (HIP) has been studied at 650-850°C in air for 24 h. The oxidation kinetics of both alloys followed the parabolic law with good approximation, except for Ti-5Al-2.5Sn oxidized at 850°C. Multi-layered scales formed on both alloys at 750°C and 850°C. Ternary additions of Sn and V accounted for the different morphology of the scales formed on these two alloys. In addition, the oxidation behavior of HIP alloys is compared with that of the corresponding cast alloys and the scaling mechanism is discussed.

Efficient interface-induced effect of novel reduced graphene oxide-CoS heteronanostructures in enhancing photocatalytic acitivities

NASA Astrophysics Data System (ADS)

He, H.-Y.

2017-11-01

The interface-induced effects of heteronanostructures are attracting many attentions due to their potentials in photocatalysis applications. In this work, reduced graphene oxide-CoS (rGO-CoS) heteronanostructures were synthesized with a chemical method. The characterization of these nanomaterials was performed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectra, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and photocatalytic activities to understand the physical and chemical behavior of these materials. The effects of rGO/CoS ratio, initial solution pH, and H2O2 on the photodegradation of malachite green in a water were studied. The hybrids showed excellent sunlight-excited photocatalytic and Fenton-like photocatalytic activities to the dye, better than that of the CoS nanoparticles and enhanced as increasing rGO/CoS ratio and decreasing initial pH. The photodegradation rate constant, k obs, was determined under pseudo-first order conditions. The enhanced photoctalytic activities with rGO/CoS were ascribed to the enhanced charge transfer at the interface. The interface effect was confirmed by the calculations of band energy level and optical conductivity.

Fundamental Studies of the Durability of Materials for Interconnects in Solid Oxide Fuel Cells

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

Frederick S. Pettit; Gerald H. Meier

2006-06-30

Ferritic stainless steels are a leading candidate material for use as an SOFC interconnect, but have the problem of forming volatile chromia species that lead to cathode poisoning. This project has focused both on optimization of ferritic alloys for SOFC applications and evaluating the possibility of using alternative materials. The initial efforts involved studying the oxidation behavior of a variety of chromia-forming ferritic stainless steels in the temperature range 700-900 C in atmospheres relevant to solid oxide fuel cell operation. The alloys exhibited a wide variety of oxidation behavior based on composition. A method for reducing the vaporization is tomore » add alloying elements that lead to the formation of a thermally grown oxide layer over the protective chromia. Several commercial steels form manganese chromate on the surface. This same approach, combined with observations of TiO{sub 2} overlayer formation on the chromia forming, Ni-based superalloy IN 738, has resulted in the development of a series of Fe-22 Cr-X Ti alloys (X=0-4 wt%). Oxidation testing has indicated that this approach results in significant reduction in chromia evaporation. Unfortunately, the Ti also results in accelerated chromia scale growth. Fundamental thermo-mechanical aspects of the durability of solid oxide fuel cell (SOFC) interconnect alloys have also been investigated. A key failure mechanism for interconnects is the spallation of the chromia scale that forms on the alloy, as it is exposed to fuel cell environments. Indentation testing methods to measure the critical energy release rate (Gc) associated with the spallation of chromia scale/alloy systems have been evaluated. This approach has been used to evaluate the thermomechanical stability of chromia films as a function of oxidation exposure. The oxidation of pure nickel in SOFC environments was evaluated using thermogravimetric analysis (TGA) to determine the NiO scaling kinetics and a four-point probe was used to measure the area-specific resistance (ASR) to estimate the electrical degradation of the interconnect. In addition to the baseline study of pure nickel, steps were taken to decrease the ASR through alloying and surface modifications. Finally, high conductivity composite systems, consisting of nickel and silver, were studied. These systems utilize high conductivity silver pathways through nickel while maintaining the mechanical stability that a nickel matrix provides.« less

Oxidative stress and neurobehavioral problems in pediatric acute lymphoblastic leukemia patients undergoing chemotherapy.

PubMed

Stenzel, Stephanie L; Krull, Kevin R; Hockenberry, Marilyn; Jain, Neelam; Kaemingk, Kris; Miketova, Petra; Moore, Ida M

2010-03-01

Neurobehavioral problems after chemotherapy treatment for pediatric acute lymphoblastic leukemia (ALL) have been a recent focus of investigation. This study extended previous research that suggested oxidative stress as a potential mechanism for chemotherapy-induced central nervous system injury by examining early markers of oxidative stress in relation to subsequent neurobehavioral problems. Oxidized and unoxidized components of phosphatidylcholine (PC) were measured in the cerebrospinal fluid of 87 children with ALL at diagnosis, induction, and consolidation. Behavioral assessments were conducted postconsolidation and at the end of chemotherapy. Results revealed a significant association between physiologic reactivity (high vs. low PC changes from diagnosis) and behavioral outcomes (high vs. low pathology). Elevated oxidized PC fraction change was predictive of increased problems with aggression at the end of therapy as well as postconsolidation adaptability. Furthermore, symptoms of hyperactivity systematically changed over time in relation to both unoxidized PC and oxidized PC fraction reactivity. These findings suggest that symptoms of behavioral problems occur early in the course of chemotherapy and that increases in the cerebrospinal fluid PC markers of oxidative stress during induction and consolidation may help to predict certain future behavioral problems.

Mechanistic insights into the oxidation behavior of Ni alloys in high-temperature CO 2

DOE PAGES

Oleksak, Richard P.; Baltrus, John P.; Nakano, Jinichiro; ...

2017-06-01

We present results of a Ni superalloy oxidized for short times in high purity CO 2 and similarly in Ar containing ≤ 1 ppb O 2. A detailed analysis of the oxidized surfaces reveals striking similarities for the two exposure environments, suggesting O 2 impurities control the oxidation process in high-temperature CO 2. Selective oxidation results in Cr-rich oxide layers grown by 2 outward diffusion, while Cr vacancies left in the metal contribute to significant void formation at the oxide/metal interface. Unlike for most of the alloy surface, the oxidation behavior of secondary phase metal carbides is considerably different inmore » the two environments.« less

Effect of fiber reinforcements on thermo-oxidative stability and mechanical properties of polymer matrix composites

NASA Technical Reports Server (NTRS)

Bowles, Kenneth J.

1991-01-01

A number of studies have investigated the thermo-oxidative behavior of polymer matrix composites. Two significant observations have been made from these research efforts: (1) fiber reinforcement has a significant effect on composite thermal stability; and (2) geometric effects must be considered when evaluating thermal aging data. A compilation of some results from these studies is presented, and this information shows the influence of the reinforcement fibers on the oxidative degradation of various polymer matrix composites. The polyimide PMR-15 was the matrix material that was used in these studies. The control composite material was reinforced with Celion 6000 graphite fiber. T-40R graphite fibers, along with some very stable ceramic fibers were selected as reinforcing fibers because of their high thermal stability. The ceramic fibers were Nicalon (silicon carbide) and Nextel 312 (alumina-silica-boron oxide). The mechanical properties of the two graphite fiber composites were significantly different, probably owing to variations in interfacial bonding between the fibers and the polyimide matrix. The Celion 6000/PMR-15 bond is very tight but the T-40/PMR-15 bond is less tight. Three oxidation mechanisms were observed: (1) the preferential oxidation of the Celion 6000 fiber ends at cut surfaces, leaving a surface of matrix material with holes where the fiber ends were originally situated; (2) preferential oxidation of the composite matrix; and (3) interfacial degradation by oxidation. The latter two mechanisms were also observed on fiber end cut surfaces. The fiber and interface attacks appeared to initiate interfiber cracking along these surfaces.

Corrosion Behavior of Plasma-Passivated Cu

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

Barbour, J.C.; Braithwaite, J.W.; Son, K.A.

1999-07-09

A new approach is being pursued to study corrosion in Cu alloy systems by using combinatorial analysis combined with microscopic experimentation (the Combinatorial Microlab) to determine mechanisms for copper corrosion in air. Corrosion studies are inherently difficult because of complex interactions between materials and environment, forming a multidimensional phase space of corrosion variables. The Combinatorial Microlab was specifically developed to address the mechanism of Cu sulfidation, which is an important reliability issue for electronic components. This approach differs from convention by focusing on microscopic length scales, the relevant scale for corrosion. During accelerated aging, copper is exposed to a varietymore » of corrosive environments containing sulfidizing species that cause corrosion. A matrix experiment was done to determine independent and synergistic effects of initial Cu oxide thickness and point defect density. The CuO{sub x} was controlled by oxidizing Cu in an electron cyclotron resonance (ECR) O{sub 2} plasma, and the point defect density was modified by Cu ion irradiation. The matrix was exposed to 600 ppb H{sub 2}S in 65% relative humidity air atmosphere. This combination revealed the importance of oxide quality in passivating Cu and prevention of the sulfidizing reaction. A native oxide and a defect-laden ECR oxide both react at 20 C to form a thick Cu{sub 2}S layer after exposure to H{sub 2}S, while different thicknesses of as-grown ECR oxide stop the formation of Cu{sub 2}S. The species present in the ECR oxide will be compared to that of an air oxide, and the sulfide layer growth rate will be presented.« less

Performance of a Steel/Oxide Composite Waste Form for Combined Waste Steams from Advanced Electrochemical Processes

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

Indacochea, J. E.; Gattu, V. K.; Chen, X.

The results of electrochemical corrosion tests and modeling activities performed collaboratively by researchers at the University of Illinois at Chicago and Argonne National Laboratory as part of workpackage NU-13-IL-UIC-0203-02 are summarized herein. The overall objective of the project was to develop and demonstrate testing and modeling approaches that could be used to evaluate the use of composite alloy/ceramic materials as high-level durable waste forms. Several prototypical composite waste form materials were made from stainless steels representing fuel cladding, reagent metals representing metallic fuel waste streams, and reagent oxides representing oxide fuel waste streams to study the microstructures and corrosion behaviorsmore » of the oxide and alloy phases. Microelectrodes fabricated from small specimens of the composite materials were used in a series of electrochemical tests to assess the corrosion behaviors of the constituent phases and phase boundaries in an aggressive acid brine solution at various imposed surface potentials. The microstructures were characterized in detail before and after the electrochemical tests to relate the electrochemical responses to changes in both the electrode surface and the solution composition. The results of microscopic, electrochemical, and solution analyses were used to develop equivalent circuit and physical models representing the measured corrosion behaviors of the different materials pertinent to long-term corrosion behavior. This report provides details regarding (1) the production of the composite materials, (2) the protocol for the electrochemical measurements and interpretations of the responses of multi-phase alloy and oxide composites, (3) relating corrosion behaviors to microstructures of multi-phase alloys based on 316L stainless steel and HT9 (410 stainless steel was used as a substitute) with added Mo, Ni, and/or Mn, and (4) modeling the corrosion behaviors and rates of several alloy/oxide composite materials made with added lanthanide and uranium oxides. These analyses show the corrosion behaviors of the alloy/ceramic composite materials are very similar to the corrosion behaviors of multi-phase alloy waste forms, and that the presence of oxide inclusions does not impact the corrosion behaviors of the alloy phases. Mixing with metallic waste streams is beneficial to lanthanide and uranium oxides in that they react with Zr in the fuel waste to form highly durable zirconates. The measured corrosion behaviors suggest properly formulated composite materials would be suitable waste forms for combined metallic and oxide waste streams generated during electrometallurgical reprocessing of spent nuclear fuel. Electrochemical methods are suitable for evaluating the durability and modeling long-term behavior of composite waste forms: the degradation model developed for metallic waste forms can be applied to the alloy phases formed in the composite and an affinity-based mineral dissolution model can be applied to the ceramic phases.« less

Corrosion behavior of alloy 800H (Fe-21Cr-32Ni) in supercritical water

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

Tan, Lizhen; Allen, Todd R.; Yang, Ying

2011-01-01

The effect of testing conditions (temperature, time, and oxygen content) and material's microstructure (the as-received and the grain boundary engineered conditions) on the corrosion behavior of alloy 800H in high-temperature pressurized water was studied using a variety of characterization techniques. Oxidation was observed as the primary corrosion behavior on the samples. Oxide exfoliation was significantly mitigated on the grain boundary engineered samples compared to the as-received ones. The oxide formation, including some 'mushroom-shaped oxidation', is predicted via a combination of thermodynamics and kinetics influenced by the preferential diffusion of specific species using short-cut diffusion paths.

Chemistry of fuel deposits and sediments and their predursors

NASA Technical Reports Server (NTRS)

Mayo, F. R.; Lan, B. Y.; Buttrill, S. E., Jr.; St.john, G. A.

1984-01-01

The mechanism of solid deposit formation on hot engine parts from turbine fuels is investigated. Deposit formation is associated with oxidation of the hydrocarbon fuel. Therefore, oxidation rates and soluble gum formation were measured for several jet turbine fuels and pure hydrocarbon mixtures. Experiments were performed at 130 C using thermal initiation and at 100 C using ditertiary butyl peroxide as a chemical initiator. Correlation of the data shows that the ratio of rate of oxidation to rate of gum formation for a single fuel is not much affected by experimental conditions, even though there are differences in the abilities of different hydrocarbons to initiate and continue the oxidation. This indicates a close association of gum formation with the oxidation process. Oxidations of n-dodecane, tetralin and the more unstable jet fuels are autocatalytic, while those of 2-ethylnaphthalene and a stable jet fuel are self-retarding. However, the ratio of oxidation rate to gum formation rate appear to be nearly constant for each substrate. The effect of oxygen pressure on gum and oxidation formation was also studied. Dependence of gum formation on the concentration of initiator at 100 C is discussed and problems for future study are suggested.

The effects of anthocyanin-rich wheat diet on the oxidative status and behavior of rats

PubMed Central

Janšáková, Katarína; Bábíčková, Janka; Havrlentová, Michaela; Hodosy, Július; Kraic, Ján; Celec, Peter; Tóthová, Ľubomíra

2016-01-01

Aim To evaluate the effect of food containing anthocyanin-rich wheat on oxidative status and behavior of healthy rats. Methods Twenty male rats were divided into the control and anthocyanin group. Oral glucose tolerance test was performed, and proteinuria and creatinine clearance were measured. Behavioral analysis was performed in Phenotyper cages. Serum and tissues were collected to measure the markers of oxidative stress and antioxidant status. Results Anthocyanins significantly increased total antioxidant capacity in serum (P = 0.039), decreased advanced oxidation protein products in the kidney (P = 0.002), but increased thiobarbituric acid reactive substances in the kidney compared to the control group. No significant difference between the groups was found in the markers of oxidative stress in the liver and colon, as well as in renal functions and glucose metabolism. The anthocyanin group spent significantly less time in the spotlight zone of the Phenotyper cages (P = 0.040), indicating higher anxiety-like behavior. Conclusion Food containing anthocyanin-rich wheat had positive effects on serum antioxidant status and kidney protein oxidation, but increased lipid peroxidation in the kidney and modified animal behavior related to anxiety. The molecular mechanisms leading to observed effects should be further elucidated. PMID:27106354

Oxidative Stress, Motor Abilities, and Behavioral Adjustment in Children Treated for Acute Lymphoblastic Leukemia.

PubMed

Hockenberry, Marilyn J; Krull, Kevin R; Insel, Kathleen C; Harris, Lynnette L; Gundy, Patricia M; Adkins, Kristin B; Pasvogel, Alice E; Taylor, Olga A; Koerner, Kari M; Montgomery, David W; Ross, Adam K; Hill, Adam; Moore, Ida M

2015-09-01

To examine associations among oxidative stress, fine and visual-motor abilities, and behavioral adjustment in children receiving chemotherapy for acute lymphoblastic leukemia (ALL)
. A prospective, repeated-measures design
. Two pediatric oncology settings in the southwestern United States. 89 children with ALL were followed from diagnosis to the end of chemotherapy. Serial cerebrospinal fluid samples were collected during scheduled lumbar punctures and analyzed for oxidative stress biomarkers. Children completed fine motor dexterity, visual processing speed, and visual-motor integration measures at three time points. Parents completed child behavior ratings at the same times. Oxidative stress, fine motor dexterity, visual processing, visual-motor integration, and behavioral adjustment
. Children with ALL had below-average fine motor dexterity, visual processing speed, and visual-motor integration following the induction phase of ALL therapy. By end of therapy, visual processing speed normalized, and fine motor dexterity and visual-motor integration remained below average. Oxidative stress measures correlated with fine motor dexterity and visual-motor integration. Decreased motor functioning was associated with increased hyperactivity and anxiety
. Oxidative stress occurs following chemo-therapy for childhood ALL and is related to impaired fine motor skills and visual symptoms
. Early intervention should be considered to prevent fine motor and visual-spatial deficits, as well as behavioral problems.

Oxidation Behavior of Matrix Graphite and Its Effect on Compressive Strength

DOE PAGES

Zhou, Xiangwen; Contescu, Cristian I.; Zhao, Xi; ...

2017-01-01

Mmore » atrix graphite (G) with incompletely graphitized binder used in high-temperature gas-cooled reactors (HTGRs) is commonly suspected to exhibit lower oxidation resistance in air. In order to reveal the oxidation performance, the oxidation behavior of newly developed A3-3 G at the temperature range from 500 to 950°C in air was studied and the effect of oxidation on the compressive strength of oxidized G specimens was characterized. Results show that temperature has a significant influence on the oxidation behavior of G. The transition temperature between Regimes I and II is ~700°C and the activation energy ( E a ) in Regime I is around 185 kJ/mol, a little lower than that of nuclear graphite, which indicates G is more vulnerable to oxidation. Oxidation at 550°C causes more damage to compressive strength of G than oxidation at 900°C. Comparing with the strength of pristine G specimens, the rate of compressive strength loss is 77.3% after oxidation at 550°C and only 12.5% for oxidation at 900°C. icrostructure images of SE and porosity measurement by ercury Porosimetry indicate that the significant compressive strength loss of G oxidized at 550°C may be attributed to both the uniform pore formation throughout the bulk and the preferential oxidation of the binder.« less

Steam Oxidation Behavior of Alloy 617 at 900 °C to 1100 °C

NASA Astrophysics Data System (ADS)

Liang, Zhiyuan; Wang, Yungang; Zhao, Qinxin

2018-07-01

The steam oxidation behavior of solid solution strengthened alloy 617 at 900 °C-1100 °C was investigated. The oxidation products were characterized by scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy. The results show that the oxidation kinetics of alloy 617 in steam followed the parabolic oxidation law. The calculated activity energy of alloy 617 was 223.47 kJ/mol. The oxidation products were mainly composed of external and internal scales and prior oxides at grain boundaries. External oxide scales were MnCr2O4, TiO2, and Cr2O3. Internal oxidation scales and prior oxides were Al2O3 and some Cr2O3 dissolved into Al2O3. The growth mechanism of oxide scales on alloy 617 is proposed.

Steam Oxidation Behavior of Alloy 617 at 900 °C to 1100 °C

NASA Astrophysics Data System (ADS)

Liang, Zhiyuan; Wang, Yungang; Zhao, Qinxin

2018-05-01

The steam oxidation behavior of solid solution strengthened alloy 617 at 900 °C-1100 °C was investigated. The oxidation products were characterized by scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy. The results show that the oxidation kinetics of alloy 617 in steam followed the parabolic oxidation law. The calculated activity energy of alloy 617 was 223.47 kJ/mol. The oxidation products were mainly composed of external and internal scales and prior oxides at grain boundaries. External oxide scales were MnCr2O4, TiO2, and Cr2O3. Internal oxidation scales and prior oxides were Al2O3 and some Cr2O3 dissolved into Al2O3. The growth mechanism of oxide scales on alloy 617 is proposed.

Oxidation behavior of TD-NiCr in a dynamic high temperature environment

NASA Technical Reports Server (NTRS)

Tenney, D. R.; Young, C. T.; Herring, H. W.

1974-01-01

The oxidation behavior of TD-NiCr has been studied in static and high-speed flowing air environments at 1100 and 1200 C. It has been found that the stable oxide morphologies formed on the specimens exposed to the static and dynamic environments were markedly different. The faceted crystal morphology characteristic of static oxidation was found to be unstable under high-temperature, high-speed flow conditions and was quickly replaced by a porous NiO 'mushroom' type structure. Also, it was found that the rate of formation of CrO3 from Cr2O3 was greatly enhanced by high gas velocity conditions. The stability of Cr2-O3 was found to be greatly improved by the presence of an outer NiO layer, even though the NiO layer was very porous. An oxidation model is proposed to explain the observed microstructures and overall oxidation behavior of TD-NiCr alloys.

Research on Oxidation Wear Behavior of a New Hot Forging Die Steel

NASA Astrophysics Data System (ADS)

Shi, Yuanji; Wu, Xiaochun

2018-01-01

Dry sliding tests for the hot forging die steel DM were performed in air under the test temperature at 400-700 °C and the time of 0.5-4 h by a UMT-3 high-temperature wear tester. The wear behavior and characteristics were studied systematically to explore the general characters in severe oxidation conditions. The results showed that a mild-to-severe oxidation wear transition occurred with an increase in the test temperature and duration. The reason was clarified as the unstable M6C carbides coarsening should be responsible for the severe delamination of tribo-oxide layer. More importantly, an intense oxidation wear with lower wear rates was found when the experimental temperature reaches 700 °C or after 4 h of test time at 600 °C, which was closely related to the degradation behavior during wear test. Furthermore, a new schematic diagram of oxidation wear of DM steel was proposed.

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

NASA Technical Reports Server (NTRS)

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

1972-01-01

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

Features of postfailure fuel behavior in transient overpower and transient undercooled/overpower tests in the transient reactor test facility

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

Doerner, R.C.; Bauer, T.H.; Morman, J.A.

Prototypic oxide fuel was subjected to simulated, fast reactor severe accident conditions in a series of in-pile tests in the Transient Reactor Test Facility reactor. Seven experiments were performed on fresh and previously irradiated oxide fuel pins under transient overpower and transient undercooled. overpower accident conditions. For each of the tests, fuel motions were observed by the hodoscope. Hodoscope data are correlated with coolant flow, pressure, and temperature data recorded by the loop instrumentation. Data were analyzed from the onset of initial failure to a final mass distribution at the end of the test. In this paper results of thesemore » analyses are compared to pre- and posttest accident calculations and to posttest metallographic accident calculations and to posttest metallographic examinations and computed tomographic reconstructions from neutron radiographs.« less

Direct evidence of charge separation in a metal-organic framework: efficient and selective photocatalytic oxidative coupling of amines via charge and energy transfer.

PubMed

Xu, Caiyun; Liu, Hang; Li, Dandan; Su, Ji-Hu; Jiang, Hai-Long

2018-03-28

The selective aerobic oxidative coupling of amines under mild conditions is an important laboratory and commercial procedure yet a great challenge. In this work, a porphyrinic metal-organic framework, PCN-222, was employed to catalyze the reaction. Upon visible light irradiation, the semiconductor-like behavior of PCN-222 initiates charge separation, evidently generating oxygen-centered active sites in Zr-oxo clusters indicated by enhanced porphyrin π-cation radical signals. The photogenerated electrons and holes further activate oxygen and amines, respectively, to give the corresponding redox products, both of which have been detected for the first time. The porphyrin motifs generate singlet oxygen based on energy transfer to further promote the reaction. As a result, PCN-222 exhibits excellent photocatalytic activity, selectivity and recyclability, far superior to its organic counterpart, for the reaction under ambient conditions via combined energy and charge transfer.

Design and Evaluation of a Boron Dipyrrin Electrophore for Redox Flow Batteries.

PubMed

Heiland, Niklas; Cidarér, Clemens; Rohr, Camilla; Piescheck, Mathias; Ahrens, Johannes; Bröring, Martin; Schröder, Uwe

2017-08-29

A boron dipyrrin (BODIPY) dye was designed as a molecular single-component electrophore for redox flow batteries. All positions of the BODIPY core were assessed on the basis of literature data, in particular cyclic voltammetry and density functional calculations, and a minimum required substitution pattern was designed to provide solubility, aggregation, radical cation and anion stabilities, a large potential window, and synthetic accessibility. In-depth electrochemical and physical studies of this electrophore revealed suitable cathodic behavior and stability of the radical anion but rapid anodic decomposition of the radical cation. The three products that formed under the conditions of controlled oxidative electrolysis were isolated, and their structures were determined by spectroscopy and comparison with a synthetic model compound. From these structures, a benzylic radical reactivity, initiated by one-electron oxidation, was concluded to play the major role in this unexpected decomposition. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Model of Reduced Kinetics for Alkane Oxidation Using Constituents and Species for N-Heptane

NASA Technical Reports Server (NTRS)

Harstad, Kenneth G.; Bellan, Josette

2011-01-01

The reduction of elementary or skeletal oxidation kinetics to a subgroup of tractable reactions for inclusion in turbulent combustion codes has been the subject of numerous studies. The skeletal mechanism is obtained from the elementary mechanism by removing from it reactions that are considered negligible for the intent of the specific study considered. As of now, there are many chemical reduction methodologies. A methodology for deriving a reduced kinetic mechanism for alkane oxidation is described and applied to n-heptane. The model is based on partitioning the species of the skeletal kinetic mechanism into lights, defined as those having a carbon number smaller than 3, and heavies, which are the complement of the species ensemble. For modeling purposes, the heavy species are mathematically decomposed into constituents, which are similar but not identical to groups in the group additivity theory. From analysis of the LLNL (Lawrence Livermore National Laboratory) skeletal mechanism in conjunction with CHEMKIN II, it is shown that a similarity variable can be formed such that the appropriately non-dimensionalized global constituent molar density exhibits a self-similar behavior over a very wide range of equivalence ratios, initial pressures and initial temperatures that is of interest for predicting n-heptane oxidation. Furthermore, the oxygen and water molar densities are shown to display a quasi-linear behavior with respect to the similarity variable. The light species ensemble is partitioned into quasi-steady and unsteady species. The reduced model is based on concepts consistent with those of Large Eddy Simulation (LES) in which functional forms are used to replace the small scales eliminated through filtering of the governing equations; in LES, these small scales are unimportant as far as the overwhelming part of dynamic energy is concerned. Here, the scales thought unimportant for recovering the thermodynamic energy are removed. The concept is tested by using tabular information from the LLNL skeletal mechanism in conjunction with CHEMKIN II utilized as surrogate ideal functions replacing the necessary functional forms. The test reveals that the similarity concept is indeed justified and that the combustion temperature is well predicted, but that the ignition time is over-predicted, a fact traced to neglecting a detailed description of the processes leading to the heavies chemical decomposition. To palliate this deficiency, functional modeling is incorporated into this conceptual reduction in addition to the modeling the evolution of the global constituent molar density, the enthalpy evolution of the heavies, the contribution to the reaction rate of the unsteady lights from other light species and from the heavies, the molar density evolution of oxygen and water, and the mole fractions of the quasisteady light species. The model is compact in that there are only nine species-related progress variables. Results are presented showing the performance of the model for predicting the temperature and species evolution. The model reproduces the ignition time over a wide range of equivalence ratios, initial pressure, and initial temperature.

The role of oxidation in the fretting wear process

NASA Technical Reports Server (NTRS)

Bill, R. C.

1980-01-01

Fretting experiments were conducted on titanium, a series of Ni-Cr-Al alloys and on some high temperature turbine alloys at room temperature and at elevated temperatures in air and in various inert environments. It was found that, depending on temperature and environment, the fretting behavior of the materials examined could be classified according to four general types of behavior. Briefly, these types of behavior were: (1) the complete absence of oxidation, as in inert environments, generally leading to low rates of fretting wear but high fretting friction; (2) gradual attrition of surface oxide with each fretting stroke, found in these experiments to operate in concert with other dominating mechanisms; (3) rapid oxidation at surface fatigue damage sites, resulting in undermining and rapid disintegration of the load bearing surface; and (4) the formation of coherent, protective oxide film, resulting in low rates of fretting wear. An analytical model predicting conditions favorable to the fourth type of behavior was outlined.

Surface protection overview

NASA Technical Reports Server (NTRS)

Levine, S. R.

1982-01-01

A first-cut integrated environmental attack life prediction methodology for hot section components is addressed. The HOST program is concerned with oxidation and hot corrosion attack of metallic coatings as well as their degradation by interdiffusion with the substrate. The effects of the environment and coatings on creep/fatigue behavior are being addressed through a joint effort with the Fatigue sub-project. An initial effort will attempt to scope the problem of thermal barrier coating life prediction. Verification of models will be carried out through benchmark rig tests including a 4 atm. replaceable blade turbine and a 50 atm. pressurized burner rig.

Behavior of engineered nanoparticles in aqueous solutions and porous media: Connecting experimentation to probabilistic analysis

NASA Astrophysics Data System (ADS)

Contreras, Carolina

2011-12-01

Engineered nanoparticles have enhanced products and services in the fields of medicine, energy, engineering, communications, personal care, environmental treatment, and many others. The increased use of engineered nanoparticles in consumer products will lead to these materials in natural systems, inevitably becoming a potential source of pollution. The study of the stability and mobility of these materials is fundamental to understand their behavior in natural systems and predict possible health and environmental implications. In addition, the use of probabilistic methods such as sensitivity analysis applied to the parameters controlling their behavior is useful in providing support in performing a risk assessment. This research investigated the stability and mobility of two types of metal oxide nanoparticles (aluminum oxide and titanium dioxide). The stability studies tested the effect of sand, pH 4, 7, and 10, and the NaCl in concentrations of 10mM, 25mM, 50mM, and 75mM. The mobility was tested using saturated quartz sand columns and nanoparticles suspension at pH 4 and 7 and in the presence of NaCl and CaCl2 in concentrations of 0.1mM, 1mM, and 10mM. Additionally, this work performed a sensitivity analysis of physical parameters used in mobility experiment performed for titanium dioxide and in mobility experiments taken from the literature for zero valent iron nanoparticles and fluorescent colloids to determine their effect on the value C/Co of by applying qualitative and quantitative methods. The results from the stability studies showed that titanium dioxide nanoparticles (TiO2) could remain suspended in solution for up to seven days at pH 10 and pH 7 even after settling of the sand; while for pH 4 solutions titanium settled along with the sand and after seven days no particles were observed in suspension. Other stability studies showed that nanoparticle aluminum oxide (Al2O3) and titanium dioxide (TiO2) size increased with increasing ionic strength (10 to 75 mM NaCl). The results from the mobility experiments showed that ionic strength has more effect on aluminum oxide nanoparticles mobility than on titanium oxide nanoparticles mobility. For Al2O3 25% of the initial concentration was obtained in the effluent whereas for TiO2 less than the 10% of the initial concentration was observed. In general, when the ionic strength was increased the effluent of nanoparticles decreased. Collision efficiencies calculated base on the colloid filtration theory were consistent with the mobility experiments. Results from sensitivity analysis showed that for zero valent iron nanoparticles and fluorescent colloids porous medium diameter and porosity were the parameters that most influenced the variability of C/Co whereas for titanium dioxide nanoparticles C/Co was more sensitive to column length and pore water velocity.

Silicon carbide as an oxidation-resistant high-temperature material. 1: Oxidation and heat corrosion behavior

NASA Technical Reports Server (NTRS)

Schlichting, J.

1981-01-01

The oxidation and corrosion behavior of SiC (in the form of a SiC powder) and hot-pressed and reaction-bound material were studied. The excellent stability of SiC in an oxidizing atmosphere is due to the development of protective SiO2 coatings. Any changes in these protective layers (e.g., due to impurities, reaction with corrosive media, high porosity of SiC, etc.) lead in most cases to increased rates of oxidation and thus restrict the field of SiC application.

Heterogeneous Oxidation of Laboratory-generated Mixed Composition and Biomass Burning Particles

NASA Astrophysics Data System (ADS)

Lim, C. Y.; Sugrue, R. A.; Hagan, D. H.; Cappa, C. D.; Kroll, J. H.; Browne, E. C.

2016-12-01

Heterogeneous oxidation of organic aerosol (OA) can significantly transform the chemical and physical properties of particulate matter in the atmosphere, leading to changes to the chemical composition of OA and potential volatilization of organic compounds. It has become increasingly apparent that the heterogeneous oxidation kinetics of OA depend on the phase and morphology of the particles. However, most laboratory experiments to date have been performed on single-component, purely organic precursors, which may exhibit fundamentally different behavior than more complex particles in the atmosphere. Here we present laboratory studies of the heterogeneous oxidation of two more complex chemical systems: thin, organic coatings on inorganic seed particles and biomass burning OA. In the first system, squalane (C30H62), a model compound for reduced OA, is coated onto dry ammonium sulfate particles at various thicknesses (10-20 nm) and exposed to hydroxyl radical (OH) in a flow tube reactor. In the second, we use a semi-batch reactor to study the heterogeneous OH-initiated oxidation of biomass burning particles as a part of the 2016 FIREX campaign in Missoula, MT. The resulting changes in chemical composition are monitored with an Aerodyne High Resolution Time-of-flight Aerosol Mass Spectrometer (AMS) and a soot-particle AMS for the non-refractory and refractory systems, respectively. We show that the heterogeneous oxidation kinetics of these multicomponent particles are substantially different than that of the single-component particles. The oxidation of organic coatings is rapid, undergoing dramatic changes to carbon oxidation state and losing a significant amount of organic mass after relatively low OH exposures (equivalent to several days of atmospheric processing). In the case of biomass burning particles, the kinetics are complex, with different components (inferred by aerosol mass spectrometry) undergoing oxidation at different rates.

Film thickness dependence of phase separation and dewetting behaviors in PMMA/SAN blend films.

PubMed

You, Jichun; Liao, Yonggui; Men, Yongfeng; Shi, Tongfei; An, Lijia

2010-09-21

Film thickness dependence of complex behaviors coupled by phase separation and dewetting in blend [poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN)] films on silicon oxide substrate at 175 °C was investigated by grazing incidence ultrasmall-angle X-ray scattering (GIUSAX) and in situ atomic force microscopy (AFM). It was found that the dewetting pathway was under the control of the parameter U(q0)/E, which described the initial amplitude of the surface undulation and original thickness of film, respectively. Furthermore, our results showed that interplay between phase separation and dewetting depended crucially on film thickness. Three mechanisms including dewetting-phase separation/wetting, dewetting/wetting-phase separation, and phase separation/wetting-pseudodewetting were discussed in detail. In conclusion, it is relative rates of phase separation and dewetting that dominate the interplay between them.

Increased Neuronal DNA/RNA Oxidation in the Frontal Cortex of Mice Subjected to Unpredictable Chronic Mild Stress.

PubMed

Maluach, Alfred M; Misquitta, Keith A; Prevot, Thomas D; Fee, Corey; Sibille, Etienne; Banasr, Mounira; Andreazza, Ana C

2017-01-01

Chronic stress is implicated in the development of various psychiatric illnesses including major depressive disorder. Previous reports suggest that patients with major depressive disorder have increased levels of oxidative stress, including higher levels of DNA/RNA oxidation found in postmortem studies, especially within brain regions responsible for the cognitive and emotional processes disrupted in the disorder. Here, we aimed to investigate whether unpredictable chronic mild stress in mice induces neuronal DNA/RNA oxidation in the prelimbic, infralimbic, and cingulate cortices of the frontal cortex and the basolateral amygdala and to explore potential associations with depressive-like behaviors. We expected that animals subjected to unpredictable chronic mild stress will present higher levels of DNA/RNA oxidation, which will be associated with anxiety-/depressive-like behaviors. C57BL/6J mice were assigned to unpredictable chronic mild stress or nonstress conditions (n = 10/group, 50% females). Following five weeks of unpredictable chronic mild stress exposure, mice were tested in a series of behavioral tests measuring anxiety- and depressive-like behaviors. Frontal cortex and amygdala sections were then immunolabeled for neuronal nuclei, a marker of post-mitotic neurons and anti-8-hydroxy-2-deoxyguanosine/8-oxo-7,8-dihydroguanosine, which reflects both DNA and RNA oxidation. Levels of neuronal DNA/RNA oxidation were increased in the frontal cortex of mice subjected to unpredictable chronic mild stress ( p = 0.0207). Levels of neuronal DNA/RNA oxidation in the frontal cortex were positively correlated with z-emotionality scores for latency to feed in the novelty-suppressed feeding test ( p = 0.0031). Statistically significant differences were not detected in basolateral amygdala levels of neuronal DNA/RNA oxidation between nonstress- and unpredictable chronic mild stress-exposed mice, nor were correlations found with behavioral performances for this region. Our results demonstrate that unpredictable chronic mild stress induces a significant increase in neuronal DNA/RNA oxidation in the frontal cortex that correlate with behavioral readouts of the stress response. A lack of DNA/RNA oxidation alterations in the basolateral amygdala suggests greater vulnerability of frontal cortex neurons to DNA/RNA oxidation in response to unpredictable chronic mild stress. These findings add support to the hypothesis that chronic stress-induced damage to DNA/RNA may be an additional molecular mechanism underlying cellular dysfunctions associated with chronic stress and present in stress-related disorders.

Effects of Oxide Film on the Corrosion Resistance of Titanium Grade 7 in Fluoride-Containing NaCl Brines

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

Lian, T; Whalen, M T; Wong, L

2004-11-30

The effects of oxide film on the corrosion behavior of Titanium Grade 7 (0.12-0.25% Pd) in fluoride-containing NaCl brines have been investigated. With the presence of a 0.6 {micro}m thick oxide layer, the annealed Ti grade 7 exhibited a significant improvement on the anodic polarization behavior. However, the oxide film did not demonstrate sustainable corrosion resistance in fluoride-containing solutions.

Solid-State Diffusional Behaviors of Functional Metal Oxides at Atomic Scale.

PubMed

Chen, Jui-Yuan; Huang, Chun-Wei; Wu, Wen-Wei

2018-02-01

Metal/metal oxides have attracted extensive research interest because of their combination of functional properties and compatibility with industry. Diffusion and thermal reliability have become essential issues that require detailed study to develop atomic-scaled functional devices. In this work, the diffusional reaction behavior that transforms piezoelectric ZnO into magnetic Fe 3 O 4 is investigated at the atomic scale. The growth kinetics of metal oxides are systematically studied through macro- and microanalyses. The growth rates are evaluated by morphology changes, which determine whether the growth behavior was a diffusion- or reaction-controlled process. Furthermore, atom attachment on the kink step is observed at the atomic scale, which has important implications for the thermodynamics of functional metal oxides. Faster growth planes simultaneously decrease, which result in the predominance of low surface energy planes. These results directly reveal the atomic formation process of metal oxide via solid-state diffusion. In addition, the nanofabricated method provides a novel approach to investigate metal oxide evolution and sheds light on diffusional reaction behavior. More importantly, the results and phenomena of this study provide considerable inspiration to enhance the material stability and reliability of metal/oxide-based devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of electrolyte temperature on the formation of self-organized anodic niobium oxide microcones in hot phosphate-glycerol electrolyte

NASA Astrophysics Data System (ADS)

Yang, S.; Aoki, Y.; Habazaki, H.

2011-07-01

Nanoporous niobium oxide films with microcone-type surface morphology were formed by anodizing at 10 V in glycerol electrolyte containing 0.6 mol dm -3 K 2HPO 4 and 0.2 mol dm -3 K 3PO 4 in a temperature range of 428-453 K. The microcones appeared after prolonged anodizing, but the required time was largely reduced by increasing electrolyte temperature. The anodic oxide was initially amorphous at all temperatures, but crystalline oxide nucleated during anodizing. The anodic oxide microcones, which were crystalline, appeared on surface as a consequence of preferential chemical dissolution of initially formed amorphous oxide. The chemical dissolution of an initially formed amorphous layer was accelerated by increasing the electrolyte temperature, with negligible influence of the temperature on the morphology of microcones up to 448 K.

Integration of graphene onto silicon through electrochemical reduction of graphene oxide layers in non-aqueous medium

NASA Astrophysics Data System (ADS)

Marrani, Andrea Giacomo; Coico, Anna Chiara; Giacco, Daniela; Zanoni, Robertino; Scaramuzzo, Francesca Anna; Schrebler, Ricardo; Dini, Danilo; Bonomo, Matteo; Dalchiele, Enrique A.

2018-07-01

Wafer-scale integration of reduced graphene oxide with H-terminated Si(1 1 1) surfaces has been accomplished by electrochemical reduction of a thin film of graphene oxide deposited onto Si by drop casting. Two reduction methods have been assayed and carried out in an acetonitrile solution. The initial deposit was subjected either to potential cycling in a 0.1 M TBAPF6/CH3CN solution at scan rates values of 20 mV s-1 and 50 mV s-1, or to a potentiostatic polarization at Eλ,c = -3 V for 450 s. The resulting interface has been characterized in its surface composition, morphology and electrochemical behavior by X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy and electrochemical measurements. The results evidence that few-layer graphene deposits on H-Si(1 1 1) were obtained after reduction, and use of organic instead of aqueous medium led to a very limited surface oxidation of the Si substrate and a very low oxygen-to-carbon ratio. The described approach is fast, simple, economic, scalable and straightforward, as one reduction cycle is already effective in promoting the establishment of a graphene-Si interface. It avoids thermal treatments at high temperatures, use of aggressive chemicals and the presence of metal contaminants, and enables preservation of Si(1 1 1) surface from oxidation.

The effect of silicon on the oxidation behavior of NiAlHf coating system

NASA Astrophysics Data System (ADS)

Dai, Pengchao; Wu, Qiong; Ma, Yue; Li, Shusuo; Gong, Shengkai

2013-04-01

Two types of NiAlHf coatings doped with different content of Si (1 at.% and 2 at.%) were deposited on a Ni3Al based single crystal superalloy IC32 by electron beam physical vapor deposition (EB-PVD) method, respectively. For comparison, NiAlHf coating with 0 at.% Si was also prepared. The oxidation tests were carried out at 1423 K in air. At the initial stage of oxidation, large amount of flake-like θ-Al2O3 was found on NiAlHf coating surface. However, no θ-Al2O3 was observed in 2 at.% Si doped NiAlHf coating except α-Al2O3. It revealed that the Si additions could contribute to the transformation from θ-Al2O3 to α-Al2O3. When oxidation time prolonged to 100 h, it was found that the degradation of NiAlHf coating was very severe with no residual β-phase, which was due to the serious inter-diffusion between the coating and substrate. In contrast, the inter-diffusion in Si-doped coating was reduced with some residual β-phase and R-Ni(Mo, Re) precipitates. The presence of Si could retard the inter-diffusion of elements between coating and substrate, indicating a barrier diffusion effect. As a result, the oxidation resistance of NiAlHf coating was improved significantly.

Identification of O-rich structures on platinum(111)-supported ultrathin iron oxide films

DOE PAGES

Merte, Lindsay R.; Bai, Yunhai; Zeuthen, Helene; ...

2016-01-06

Using high-resolution scanning tunneling microscopy (STM) we have studied the oxidation of ultrathin FeO films grown on Pt(111). At the initial stage of the FeO film oxidation by atomic oxygen exposure, we identified three distinct types of line defects, all of which form boundaries between FeO domains of opposite orientation. Two types of line defects appearing bright ( type-i) and dark ( type-ii) in the STM images at typical scanning parameters are “metallic”, whereas the third line defect exhibits nonmetallic behavior ( type-iii). Atomic-scale structure models of these line defects are proposed, with type-i defects exhibiting 4-fold coordinated Fe atoms,more » type-ii exhibiting 2-fold coordinated O atoms, and type-iii exhibiting tetrahedrally-coordinated Fe atoms. In addition, FeO 2 trilayer islands are formed upon oxidation, which appear at FCC-type domains of the moiré structure. At high scanning bias, distinct protrusions on the trilayer islands are observed over surface O ions, which are assigned to H adatoms. The experimental data are supported by density functional theory (DFT) calculations, in which bare and hydroxylated FeO 2 trilayer islands are compared. Finally, we compare the formation of O-rich features on continuous FeO films using atomic oxygen with the oxidation of Pt(111)-supported FeO islands accomplished by O 2 exposure.« less

Comparison of isothermal and cyclic oxidation behavior of twenty-five commercial sheet alloys at 1150 C

NASA Technical Reports Server (NTRS)

Barrett, C. A.; Lowell, C. E.

1974-01-01

The cyclic and isothermal oxidation resistance of 25 high-temperature Ni-, Co-, and Fe-base sheet alloys after 100 hours in air at 1150 C was compared. The alloys were evaluated in terms of their oxidation, scaling, and vaporization rates and their tendency for scale spallation. These values were used to develop an oxidation rating parameter based on effective thickness change, as calculated from a mass balance. The calculated thicknesses generally agreed with the measured values, including grain boundary oxidation, to within a factor of 3. Oxidation behavior was related to composition, particularly Cr and Al content.

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

NASA Technical Reports Server (NTRS)

Tenney, D. R.

1974-01-01

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

Interactions of Oxygen and Water Molecules with Pyrite Surface: A New Insight.

PubMed

Li, Yuqiong; Chen, Jianhua; Chen, Ye; Zhao, Cuihua; Zhang, Yibing; Ke, Baolin

2018-02-06

Pyrite is the most common sulfide in nature, and it is well-known for its roles in acid mine drainage, flotation separation of useful metal (Cu, Pb, Zn, and Mo) sulfide minerals, optoelectronic and photovoltaic application, pneumoconiosis, and even in the origin of life. However, the detailed oxidation behaviors of pyrite are still unclear and not well-understood. New oxidation pathways by O 2 on the pyrite (100) surface have been found in this work for the first time using density functional theory simulation; that is, besides Fe sites, S sites are also possible oxidation sites in the initial oxidation state of pyrite, where easier and stronger oxidation may occur. This is the first time to confirm the other researchers' conjecture on the direct oxidation of S sites, which explains the isotopic composition experiments that a minor amount of O 2 is permanently incorporated into SO 4 2- during pyrite oxidation (O in SO 4 2- is mainly derived from water). We constructed various H 2 O-O 2 coadsorption models on the pyrite surface by considering the adsorption sequence of H 2 O and O 2 . It is found that the H 2 O molecule undergoes step-wise dissociation in the presence of the O 2 molecule. Hydroxyl radical •OH is the reactive oxygen species during H 2 O dissociation. Cyclic voltammetric measurements confirm the presence of •OH. In addition, H 2 O 2 may also be formed on the surface in terms of H 2 O-then-O 2 sequence adsorption.

Synthesis and Microstructural Characterization of Manganese Oxide Electrodes for Application as Electrochemical Supercapacitors

NASA Astrophysics Data System (ADS)

Babakhani, Banafsheh

The aim of this thesis work was to synthesize Mn-based oxide electrodes with high surface area structures by anodic electrodeposition for application as electrochemical capacitors. Rod-like structures provide large surface areas leading to high specific capacitances. Since templated electrosynthesis of rods is not easy to use in practical applications, it is more desirable to form rod-like structures without using any templates. In this work, Mn oxide electrodes with rod-like structures (˜1.5 µm in diameter) were synthesized from a solution of 0.01 M Mn acetate under galvanostatic control without any templates, on Au coated Si substrates. The electrochemical properties of the synthesized nanocrystalline electrodes were investigated to determine the effect of morphology, chemistry and crystal structure on the corresponding electrochemical behavior of Mn oxide electrodes. Mn oxides prepared at different current densities showed a defective antifluoritetype crystal structure. The rod-like Mn oxide electrodes synthesized at low current densities (5 mAcm.2) exhibited a high specific capacitance due to their large surface areas. Also, specific capacity retention after 250 cycles in an aqueous solution of 0.5 M Na2SO4 at 100 mVs -1 was about 78% of the initial capacity (203 Fg-1 ). To improve the electrochemical capacitive behavior of Mn oxide electrodes, a sequential approach and a one-step method were adopted to synthesize Mn oxide/PEDOT electrodes through anodic deposition on Au coated Si substrates from aqueous solutions. In the former case, free standing Mn oxide rods (about 10 µm long and less than 1.5 µm in diameter) were first synthesized, then coated by electro-polymerization of a conducting polymer (PEDOT) giving coaxial rods. The one-step, co-electrodeposition method produced agglomerated Mn oxide/PEDOT particles. The electrochemical behavior of the deposits depended on the morphology and crystal structure of the fabricated electrodes, which were affected by the composition and pH of the electrolyte, temperature, current density and polymer deposition time. Mn oxide/PEDOT coaxial core/shell rods consisted of MnO2 with an antifluorite-type structure coated with amorphous PEDOT. The Mn oxide/PEDOT coaxial core/shell electrodes prepared by the sequential method showed significantly better specific capacity and redox performance properties relative to both uncoated Mn oxide rods and co- electrodeposited Mn oxide/PEDOT electrodes. The best specific capacitance for Mn oxide/PEDOT rods produced sequentially was ˜295 F g-1 with ˜92% retention after 250 cycles in 0.5 M Na2SO4 at 100 mV s-1. To further improve the electrochemical capacitive behavior of Mn oxide electrodes, Co-doped and Fe-doped Mn oxide electrodes with a rod-like morphology and antifluorite-type crystal structure were synthesized by anodic electrodeposition, on Au coated Si substrates, from dilute solutions of Mn acetate and Co sulphate and Mn acetate and Fe chloride. Also, Mn-Co oxide/PEDOT coaxial core/shell rods were synthesized by applying a shell of PEDOT on Mn-Co oxide electrodes. Mn-Co oxide/PEDOT electrodes consisted of MnO2, with partial Co 2+ and Co3+ ion substitution for Mn4+, and amorphous PEDOT. Mn-Fe oxide electrodes consisted of MnO2, with partial Fe2+ and Fe3+ ion substitution for Mn4+. Electrochemical analysis showed that the capacitance values for all deposits increased with increasing scan rate to 100 mVs -1, and then decreased after 100 mVs-1. The Mn-Co oxide/PEDOT electrodes showed improved specific capacity and electrochemical cyclability relative to uncoated Mn-Co oxides and Mn-Fe oxides. Mn-Co oxide/PEDOT electrodes with rod-like structures had high capacitances (up to 310 Fg -1) at a scan rate of 100 mVs-1 and maintained their capacitance after 500 cycles in 0.5 M Na2SO4 (91% retention). Capacitance reduction for the deposits was mainly due to the loss of Mn ions by dissolution in the electrolyte solution. To better understand the nucleation and growth mechanisms of Mn oxide electrodes, the effects of supersaturation ratio on the morphology and crystal structure of electrodeposited Mn oxide were studied. By changing deposition parameters, including deposition current density, electrolyte composition, pH and temperature, a series of nanocrystalline Mn oxide electrodes with various morphologies (continuous coatings, rod-like structures, aggregated rods and thin sheets) and an antifluorite-type crystal structure was obtained. Mn oxide thin sheets showed instantaneous nucleation and single crystalline growth; rods had a mix of instantaneous/progressive nucleation and polycrystalline growth and continuous coatings formed by progressive nucleation and polycrystalline growth. Electrochemical analysis revealed the best capacitance behaviour obtained for Mn oxide thin sheets followed by Mn oxide rods, with dimensions on the microscale, and then continuous coatings. The highest specific capacitance (˜230 Fg-1) and capacitance retention rates (˜88%) were obtained for Mn oxide thin sheets after 250 cycles in 0.5 M Na2 SO4 at 20 mVs-1.

Initial oxidation of pure and K doped NiTi shape memory alloys

NASA Astrophysics Data System (ADS)

Tollefsen, H.; Raaen, S.

2009-06-01

Initial oxidation of pure and K doped nitinol has been studied by photoelectron spectroscopy. The composition of the TiOx layer that forms on the surface is found to depend on the temperature during oxidation. The oxidation at high temperatures results in enhanced formation of lower oxides, whereas TiO2 predominates for oxidation at lower temperatures, e.g., 70 °C. Submonolayer coverage of K on NiTi enhances the formation of TiO2 on the expense of lower oxides, which is of consequence for formation of a protective oxide layer and biocompatibility. Oxidation in the martensitic phase was found to be independent of temperature for temperatures between -40 and 10 °C, whereas in the austenitic phase the oxide growth is thermally activated.

Dynamic oxidation behavior of TD-NiCr alloy with different surface pretreatments

NASA Technical Reports Server (NTRS)

Young, C. T.; Tenney, D. R.; Herring, H. W.

1975-01-01

Oxidation tests of TD-NiCr alloy with different surface pretreatments were conducted in a Mach-5 arc-jet at 1200 C and 0.002 lb/sec flowing air environment. The mechanisms responsible for the observed oxidation behavior are examined. The presence of atomic oxygen in the air stream plays a significant role in determining the oxidation characteristic of the alloy. The rate of Cr2O3 vaporization by formation of volatile CrO3 is greatly enhanced by the flowing conditions. The typical microstructure of oxides formed in the dynamic tests consists of an external layer of NiO with a porous mushroom-type morphology, an intermediate layer of NiO and Cr2O3 oxide mixture, and a continuous inner layer of Cr2O3 in contact with the Cr-depleted alloy substrate. Three basic processes underlying the formation of mushroom-type NiO are identified and discussed. The oxidation rate is determined by the rate of vaporization of NiO. Surface pretreatment has a significant effect on the oxidation behavior of the alloy in the early stage of oxidation, but becomes less important as exposure time increases. Mechanical polishing induces surface recrystallization, but promotes the concurrence of external growth of NiO and internal oxidation of the alloy in the dynamic atmosphere.

Effect of magnesium oxide content on oxidation behavior of some superalloy-base cermets

NASA Technical Reports Server (NTRS)

Zaplatynsky, I.

1975-01-01

The effect of increasing magnesium oxide (MgO) content on the cyclic oxidation resistance of hot-pressed cermets of MgO in NiCrAlY, MgO in Hoskins-875, MgO in Inconel-702, and MgO in Hastelloy-X was investigated. The cermets with magnesium oxide levels of 5, 10, 20, and 40 vol percent were examined. The cyclic oxidation behavior of these cermets at 1100 and 1200 C in still air was determined by a thermogravimetric method supplemented by X-ray diffraction analysis and light and electron microscopy. In all instances, MgO prevented grain growth in the metallic phase. No evidence of oxidation along interphase boundaries was detected. Cermets of MgO in NiCrAlY and MgO in Hoskins-875 were superior to cermets of MgO in Inconel-702 and MgO in Hastelloy-X. Their oxidation resistance was degraded only when the MgO content was 40 vol percent. The oxidation behavior of MgO-in-Inconel-702 powder cermets containing 5- and 10-vol percent MgO was approximately similar to that of pure Inconel-702 compacts. The 20- and 40-vol percent MgO content reduced the oxidation resistance of MgO-in-Inconel-702 powder cermets relative to that of pure Inconel-702.

Aloe vera gel improves behavioral deficits and oxidative status in streptozotocin-induced diabetic rats.

PubMed

Tabatabaei, Seyed Reza Fatemi; Ghaderi, Shahab; Bahrami-Tapehebur, Mohammad; Farbood, Yaghoob; Rashno, Masome

2017-12-01

Oxidative stress has a major role in progression of diabetes-related behavioral deficits. It has been suggested that Aloe vera has anti-diabetic, antioxidative, and neuroprotective effects. The present study was designed to determine the effects of Aloe vera gel on behavioral functions, oxidative status, and neuronal viability in the hippocampus of streptozotocin (STZ)-induced diabetic rats. Fifty five adult male Wistar rats were randomly divided into five groups, including: control (normal saline 8ml/kg/day; P.O.), diabetic (normal saline 8ml/kg/day; P.O.), Aloe vera gel (100mg/kg/day; P.O.), diabetic+Aloe vera gel (100mg/kg/day; P.O.) and diabetic+NPH insulin (10 IU/kg/day; S.C.). All treatments were started immediately following confirmation of diabetes in diabetic groups and were continued for eight weeks. Behavioral functions were evaluated by employing standard behavioral paradigms. Additionally, oxidative status and neuronal viability were assessed in the hippocampus. The results of behavioral tests showed that diabetes enhanced anxiety/depression-like behaviors, reduced exploratory and locomotor activities, decreased memory performance, and increased stress related behaviors. These changes in diabetic rats were accompanied by increasing oxidative stress and neuronal loss in the hippocampus. Interestingly, eight weeks of treatment with Aloe vera gel not only alleviated all the mentioned deficits related to diabetes, but in some aspects, it was even more effective than insulin. In conclusion, the results suggest that both interrelated hypoglycemic and antioxidative properties of Aloe vera gel are possible mechanisms that improve behavioral deficits and protect hippocampal neurons in diabetic animals. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

High temperature oxidation behavior of ODS steels

NASA Astrophysics Data System (ADS)

Kaito, T.; Narita, T.; Ukai, S.; Matsuda, Y.

2004-08-01

Oxide dispersion strengthened (ODS) steels are being developing for application as advanced fast reactor cladding and fusion blanket materials, in order to allow increased operation temperature. Oxidation testing of ODS steel was conducted under a controlled dry air atmosphere to evaluate the high temperature oxidation behavior. This showed that 9Cr-ODS martensitic steels and 12Cr-ODS ferritic steels have superior high temperature oxidation resistance compared to 11 mass% Cr PNC-FMS and 17 mass% Cr ferritic stainless steel. This high temperature resistance is attributed to earlier formation of the protective α-Cr 2O 3 on the outer surface of ODS steels.

Initial stage corrosion of nanocrystalline copper particles and thin films

NASA Astrophysics Data System (ADS)

Tao, Weimin

1997-12-01

Corrosion behavior is an important issue in nanocrystalline materials research and development. A very fine grain size is expected to have significant effects on the corrosion resistance of these novel materials. However, both the macroscopic corrosion properties and the corresponding structure evolution during corrosion have not been fully studied. Under such circumstances, conducting fundamental research in this area is important and necessary. In this study, high purity nanocrystalline and coarse-grained copper were selected as our sample material, sodium nitrite aqueous solution at room temperature and air at a high temperature were employed as corrosive environments. The weight loss testing and electrochemical methods were used to obtain the macroscopic corrosion properties, whereas the high resolution transmission electron microscope was employed for the structure analysis. The weight loss tests indicate that the corrosion rate of nanocrystalline copper is about 5 times higher than that of coarse-grained copper at the initial stage of corrosion. The electrochemical measurements show that the corrosion potential of the nanocrystalline copper has a 230 mV negative shift in comparison with that of the coarse-grained copper. The nanocrystalline copper also exhibits a significantly higher exchange current density than the coarse-grained copper. High resolution TEM revealed that the surface structure changes at the initial stage of corrosion. It was found that the first copper oxide layer formed on the surface of nanocrystalline copper thin film contains a large density of high angle grain boundaries, whereas that formed on the surface of coarse-grained copper shows highly oriented oxide nuclei and appears to show a strong tendency for forming low angle grain boundaries. A correlation between the macroscopic corrosion properties and the structure characteristics is proposed for the nanocrystalline copper based on the concept of the "apparent" exchange current density associated with mass transport of ions in the oxide layer. A hypothesis is developed that the high corrosion rate of the nanocrystalline copper is closely associated with the structure of the copper oxide layer. Therefore, a high "apparent" exchange current density for the nanocrystalline copper is associated with the high angle grain boundary structure in the initial oxide layer. Additional structure analysis was also carried out: (a) High resolution TEM imaging has provided a cross sectional view of the epitaxial interface between nanocrystalline copper and copper (I) oxide and explicitly discloses the presence of interface defects such as misfit dislocations. Based on this observation, a mechanism was proposed to explain the Cu/Cusb2O interface misfit accommodation. This appears to be the first time this interface has been directly examined. (b) A nanocrystalline analogue to a cross-section of Gwathmey's copper single crystal sphere was revealed by high resolution TEM imaging. A partially oxidized nanocrystalline copper particle is used to examine the variation of the Cu/Cusb2O orientation relationship with respect to changes in surface orientation. A new orientation relationship, Cu (011) //Cusb2O (11), ˜ Cu(011)//Cusb2O(111), was found for the oxidation of nanocrystalline copper.

Reduction Dynamics of Doped Ceria, Nickel Oxide, and Cermet Composites Probed Using In Situ Raman Spectroscopy

PubMed Central

Shearing, Paul R.; Brightman, Edward; Brett, Dan J. L.; Brandon, Nigel P.; Cohen, Lesley F.

2016-01-01

The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface. In order to elucidate these mechanisms, the redox process in pure CGO and NiO is studied when exposed to wet and dry hydrogen and is compared to the cermet behavior. In dry hydrogen, CGO reduces relatively rapidly via a series of intermediate phases, while NiO reduces via a single‐step process. In wet reducing atmospheres, however, the oxidation state of pure CGO is initially stabilized due to the dissociation of water by reduced Ce(III) and subsequent incorporation of oxygen into the structure. In the reduction process involving the composite cermet, the close proximity of the NiO improves the efficiency and speed of the composite reduction process. Although NiO is already incorporated into working cells, these observations suggest direct routes to further improve cell performance. PMID:27595058

Reduction Dynamics of Doped Ceria, Nickel Oxide, and Cermet Composites Probed Using In Situ Raman Spectroscopy.

PubMed

Maher, Robert C; Shearing, Paul R; Brightman, Edward; Brett, Dan J L; Brandon, Nigel P; Cohen, Lesley F

2016-01-01

The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface. In order to elucidate these mechanisms, the redox process in pure CGO and NiO is studied when exposed to wet and dry hydrogen and is compared to the cermet behavior. In dry hydrogen, CGO reduces relatively rapidly via a series of intermediate phases, while NiO reduces via a single-step process. In wet reducing atmospheres, however, the oxidation state of pure CGO is initially stabilized due to the dissociation of water by reduced Ce(III) and subsequent incorporation of oxygen into the structure. In the reduction process involving the composite cermet, the close proximity of the NiO improves the efficiency and speed of the composite reduction process. Although NiO is already incorporated into working cells, these observations suggest direct routes to further improve cell performance.

Effect of sulfur removal on Al2O3 scale adhesion

NASA Astrophysics Data System (ADS)

Smialek, James L.

1991-03-01

If the role of reactive element dopants in producing A12O3 scale adhesion on NiCrAl alloys is to getter sulfur and prevent interfacial segregation, then eliminating sulfur from undoped alloys should also produce adherence. Four experiments successfully produced scale adhesion by sulfur removal alone. (1) Repeated oxidation and polishing of a pure NiCrAl alloy lowered the sulfur content from 10 to 2 parts per million by weight (ppmw), presumably by removing the segregated interfacial layer after each cycle. Total scale spallation changed to total retention after 13 such cycles, with no changes in the scale or interfacial morphology. (2) Thinner samples became adherent after fewer oxidation polishing cycles because of a more limited supply of sulfur. (3) Spalling in subsequent cyclic oxidation tests of samples from experiment (1) was a direct function of the initial sulfur content. (4) Desulfurization to 0.1 ppmw levels was accomplished by annealing melt-spun foil in 1 arm H2. These foils produced oxidation weight change curves for 500 1-hour cycles at 1100 °C similar to those for Y- or Zr-doped NiCrAl. The transition between adherent and nonadherent behavior was modeled in terms of sulfur flux, sulfur content, and sulfur segregation.

Oxidation of Boron Nitride in Composites

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.

1998-01-01

Boron nitride (BN) is a prime candidate for fiber coatings in silicon carbide (SiC) fiber-reinforced SiC matrix composites. The properties of BN allow the fiber to impart beneficial composite properties to the matrix, even at elevated temperatures. The problem with BN is that it is readily attacked by oxygen. Although BN is an internal component of the composite, a matrix crack or pore can create a path for hot oxygen to attack the BN. This type of attack is not well understood. A variety of phenomena have been observed. These include borosilicate glass formation, volatilization of the BN, and under some conditions, preservation of the BN. In this study at the NASA Lewis Research Center, a series of BN materials and BN-containing model composites were methodically examined to understand the various issues dealing with the oxidation of BN in composites. Initial studies were done with a series of monolithic BN materials prepared by hot pressing and chemical vapor deposition (CVD). From these studies, we found that BN showed a strong orientation effect in oxidation and was extremely sensitive to the presence of water vapor in the environment. In addition, CVD material deposited at a high temperature showed much better oxidation behavior than CVD material deposited at a lower temperature.

Evolution of Near-Surface Internal and External Oxide Morphology During High-Temperature Selective Oxidation of Steels

NASA Astrophysics Data System (ADS)

Story, Mary E.; Webler, Bryan A.

2018-05-01

In this work we examine some observations made using high-temperature confocal scanning laser microscopy (HT-CSLM) during selective oxidation experiments. A plain carbon steel and advanced high-strength steel (AHSS) were selectively oxidized at high temperature (850-900°C) in either low oxygen or water vapor atmospheres. Surface evolution, including thermal grooving along grain boundaries and oxide growth, was viewed in situ during heating. Experiments investigated the influence of the microstructure and oxidizing atmosphere on selective oxidation behavior. Sequences of CSLM still frames collected during the experiment were processed with ImageJ to obtain histograms that showed a general darkening trend indicative of oxidation over time with all samples. Additional ex situ scanning electron microscopy and energy dispersive spectroscopy analysis supported in situ observations. Distinct oxidation behavior was observed for each case. Segregation, grain orientation, and extent of internal oxidation were all found to strongly influence surface evolution.

Evaluation of hydrogen radical treatment for indium surface oxide removal and analysis of re-oxidation behavior

NASA Astrophysics Data System (ADS)

Furuyama, Kohta; Yamanaka, Kazuyuki; Higurashi, Eiji; Suga, Tadatomo

2018-02-01

Indium is a commonly used metal for sealing, bonding, and soldering due to its good malleability and ductility even at cryogenic temperatures. The effects of hydrogen radical treatment on indium surface oxide removal were evaluated by the spreading ratio test of indium balls (diameter, 300 µm purity, 99.99%). It was found that hydrogen radical treatment longer than 20 s at temperatures higher than 170 °C results in successful surface oxide removal. X-ray photoelectron spectroscopy analysis was carried out to study the re-oxidation behavior after treatment, and it was found that hydrogen radical treatment slows down the re-oxidation of indium compared with surface oxide removal realized by physical bombardment with an argon fast atom beam.

Cinetica de oxidacion de polimeros conductores: poli-3,4- etilendioxitiofeno

NASA Astrophysics Data System (ADS)

Caballero Romero, Maria

Films of poly-3,4-ethylenedioxythiophene (PEDOT) perchlorate used as electrodes in liquid electrolytes incorporate anions and solvent during oxidation for charge and osmotic balance: the film swells. During reduction the film shrinks, closes its structure trapping counterions getting then rising conformational packed states by expulsion of counterions and solvent. Here by potential step from the same reduced initial state to the same oxidized final state the rate coefficient, the activation energy and reaction orders related to the counterion concentration in solution and to the concentration of active centers in the polymer film, were attained following the usual methodology used for chemical and electrochemical kinetics. Now the full methodology was repeated using different reduced-shrunk or reduced-conformational compacted initial states every time. Those initial states were attained by reduction of the oxidized film at rising cathodic potentials for the same reduction time each. Rising reduced and conformational compacted states give slower subsequent oxidation rates by potential step to the same anodic potential every time. The activation energy, the reaction coefficient and reaction orders change for rising conformational compacted initial states. Decreasing rate constants and increasing activation energies are obtained for the PEDOT oxidation from increasing conformational compacted initial states. The experimental activation energy presents two linear ranges as a function of the initial reduced-compacted state. Using as initial states for the oxidation open structures attained by reduction at low cathodic potentials, activation energies attained were constant: namely the chemical activation energy. Using as initial states for the oxidation deeper reduced, closed and packed conformational structures, the activation energy includes two components: the constant chemical energy plus the conformational energy required to relax the conformational structure generating free volume which allows the entrance of the balancing counterions required for the reaction. The conformational energy increases linearly as a function of the reduction-compaction potential. The kinetic magnitudes include conformational and structural information. The Chemical Kinetics becomes Structural (or conformational) Chemical Kinetics.

Plasma electrolytic oxidation of Titanium Aluminides

NASA Astrophysics Data System (ADS)

Morgenstern, R.; Sieber, M.; Grund, T.; Lampke, T.; Wielage, B.

2016-03-01

Due to their outstanding specific mechanical and high-temperature properties, titanium aluminides exhibit a high potential for lightweight components exposed to high temperatures. However, their application is limited through their low wear resistance and the increasing high-temperature oxidation starting from about 750 °C. By the use of oxide ceramic coatings, these constraints can be set aside and the possible applications of titanium aluminides can be extended. The plasma electrolytic oxidation (PEO) represents a process for the generation of oxide ceramic conversion coatings with high thickness. The current work aims at the clarification of different electrolyte components’ influences on the oxide layer evolution on alloy TNM-B1 (Ti43.5Al4Nb1Mo0.1B) and the creation of compact and wear resistant coatings. Model experiments were applied using a ramp-wise increase of the anodic potential in order to show the influence of electrolyte components on the discharge initiation and the early stage of the oxide layer growth. The production of PEO layers with technically relevant thicknesses close to 100 μm was conducted in alkaline electrolytes with varying amounts of Na2SiO3·5H2O and K4P2O7 under symmetrically pulsed current conditions. Coating properties were evaluated with regard to morphology, chemical composition, hardness and wear resistance. The addition of phosphates and silicates leads to an increasing substrate passivation and the growth of compact oxide layers with higher thicknesses. Optimal electrolyte compositions for maximum coating hardness and thickness were identified by statistical analysis. Under these conditions, a homogeneous inner layer with low porosity can be achieved. The frictional wear behavior of the compact coating layer is superior to a hard anodized layer on aluminum.

Piroxicam attenuates 3-nitropropionic acid-induced brain oxidative stress and behavioral alteration in mice.

PubMed

C, Jadiswami; H M, Megha; Dhadde, Shivsharan B; Durg, Sharanbasappa; Potadar, Pandharinath P; B S, Thippeswamy; V P, Veerapur

2014-12-01

3-Nitropropionic acid (3-NP) is a fungal toxin that produces Huntington's disease like symptoms in both animals and humans. Piroxicam, a non-selective cyclooxygenase (COX) inhibitor, used as anti-inflammatory agent and also known to decrease free oxygen radical production. In this study, the effect of piroxicam was evaluated against 3-NP-induced brain oxidative stress and behavioral alteration in mice. Adult male Swiss albino mice were injected with vehicle/piroxicam (10 and 20 mg/kg, i.p.) 30 min before 3-NP challenge (15 mg/kg, i.p.) regularly for 14 days. Body weights of the mice were measured on alternative days of the experiment. At the end of the treatment schedule, mice were evaluated for behavioral alterations (movement analysis, locomotor test, beam walking test and hanging wire test) and brain homogenates were used for the estimation of oxidative stress markers (lipid peroxidation, reduced glutathione and catalase). Administration of 3-NP significantly altered the behavioral activities and brain antioxidant status in mice. Piroxicam, at both the tested doses, caused a significant reversal of 3-NP-induced behavioral alterations and oxidative stress in mice. These findings suggest piroxicam protects the mice against 3-NP-induced brain oxidative stress and behavioral alteration. The antioxidant properties of piroxicam may be responsible for the observed beneficial actions.

Wear Behavior of an Ultra-High-Strength Eutectoid Steel

NASA Astrophysics Data System (ADS)

Mishra, Alok; Maity, Joydeep

2018-02-01

Wear behavior of an ultra-high-strength AISI 1080 steel developed through incomplete austenitization-based combined cyclic heat treatment is investigated in comparison with annealed and conventional hardened and tempered conditions against an alumina disk (sliding speed = 1 m s-1) using a pin-on-disk tribometer at a load range of 7.35-14.7 N. On a gross scale, the mechanism of surface damage involves adhesive wear coupled with abrasive wear (microcutting effects in particular) at lower loads. At higher loads, mainly the abrasive wear (both microcutting and microploughing mechanisms) and evolution of adherent oxide are observed. Besides, microhardness of matrix increases with load indicating substantial strain hardening during wear test. The rate of overall wear is found to increase with load. As-received annealed steel with the lowest initial hardness suffers from severe abrasive wear, thereby exhibiting the highest wear loss. Such a severe wear loss is not observed in conventional hardened and tempered and combined cyclic heat treatment conditions. Combined cyclic heat-treated steel exhibits the greatest wear resistance (lowest wear loss) due to its initial high hardness and evolution of hard abrasion-resistant tribolayer during wear test at higher load.

Auger electron spectroscopy study of initial stages of oxidation in a copper - 19.6-atomic-percent-aluminum alloy

NASA Technical Reports Server (NTRS)

Ferrante, J.

1973-01-01

Auger electron spectroscopy was used to examine the initial stages of oxidation of a polycrystalline copper - 19.6 a/o-aluminum alloy. The growth of the 55-eV aluminum oxide peak and the decay of the 59-, 62-, and 937-eV copper peaks were examined as functions of temperature, exposure, and pressure. Pressures ranged from 1x10 to the minus 7th power to 0.0005 torr of O2. Temperatures ranged from room temperature to 700 C. A completely aluminum oxide surface layer was obtained in all cases. Complete disappearance of the underlying 937-eV copper peak was obtained by heating at 700 C in O2 at 0.0005 torr for 1 hr. Temperature studies indicated that thermally activated diffusion was important to the oxidation studies. The initial stages of oxidation followed a logarithmic growth curve.

Effect of different alloyed layers on the high temperature oxidation behavior of newly developed Ti 2AlNb-based alloys

NASA Astrophysics Data System (ADS)

Wu, Hongyan; Zhang, Pingze; Zhao, Haofeng; Wang, Ling; Xie, Aigen

2011-01-01

The application of titanium aluminide orthorhombic alloys (O-phase alloys) as potential materials in aircraft and jet engines was limited by their poor oxidation resistance at high temperature. The Ti 2AlNb-based alloys were chromised (Cr), chromium-tungstened (Cr-W) and nickel-chromised (Ni-Cr) by the double glow plasma surface alloying process to improve their high temperature oxidation resistance. The discontinuous oxidative behavior of Cr, Cr-W and Ni-Cr alloyed layers on Ti 2AlNb-based alloy at 1093 K was explored in this study. After exposing at 1093 K, the TiO 2 layer was formed on the bare alloy and accompanied by the occurrence of crack, which promoted oxidation rate. The oxidation behavior of Ti 2AlNb-based alloys was improved by surface alloying due to the formation of protective Al 2O 3 scale or continuous and dense NiCr 2O 4 film. The Ni-Cr alloyed layer presented the best high-temperature oxidation resistance among three alloyed layers.

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

Panchalingam, V.

The polymerization of propylene oxide (PO) was studied with an initiator prepared by the reaction of R(-)-3,3-dimethyl-1,2-butanediol amount of zinc chloride, the initiator was found to be highly reactive and also stereoselective in the polymerization of PO, preferentially incorporating R-(+)-PO into the polymer chain. Analysis of the polymer structure by {sup 13}C-NMR spectroscopy showed that chlorine, hydroxy, and one type of alkoxy end groups derived from the initiator were present in the polymer prepared in the polymer prepared at room temperature. Fractionation of poly(propylene oxide) (PPO) in acetone at -30{degrees}C gave about 10% insoluble PPO shown to be isotatic bymore » {sup 13}C-NMR. The soluble, largely atactic fraction contained irregular head-to-head (h,h) and tail-to-tail (t,t) structures. In the absence of coinitiator zinc chloride the PPO product was completely soluble at -30{degrees}C and contained a greater proportion of irregular h,h and t,t structures. The {sup 13}C-NMR peak assignments were made for the methine and methylene carbon sin the irregular h,h and t,t linkages in PPO by the use of DEPT (Distortionless Enhancement by Polarization Transfer) experiment. An attempt was made to fit the stereoselective behavior of this initator systems to a kinetic scheme. It was found that the system follows a second order monomer consumption. An initiator prepared by the reaction of aluminum hydride and N-methyl-1-ephedrine in a 1:3 molar ratio as also used for the polymerization of PO to check its stereoselective potential. This initiator system was found to be poor and its efficiency was not improved very much even by the use of zinch chloride as a coiniator. However, this initator preferentially elected the S-enantiomer from the racemic PO as opposed to the preferential electron of R-enantiomer by the initiator derived from DMBD.« less

Oxidation of U-20 at% Zr alloy in air at 423 1063 K

NASA Astrophysics Data System (ADS)

Matsui, Tsuneo; Yamada, Takanobu; Ikai, Yasushi; Naito, Keiji

1993-01-01

The oxidation behavior of U 0.80Zr 0.20 alloy (two-phase mixture of U and UZr 2 below 878 K and single solid solution above 1008 K) was studied by thermogravimetry in the temperature range from 423 to 1063 K in air. During oxidation in the low temperature region (423-503 K), the sample kept its initial shape (a rectangular rod) and the surface of the sample was covered by a black thin adherent UO2 + x oxide layer. On the other hand, by oxidation in the middle temperature region, the sample broke to several pieces of thin plates and blocks, and fine powder at 643-723 K and entirely to fine powder at 775-878 K, all of which were analyzed to be a mixture of U 3O 8 and ZrO 2. By oxidation in the high temperature region (1008-1063 K) the sample broke to very fine powder, which consisted of U 3O 8 and ZrO 2. Based on the sample shape, the oxide phase identified after oxidation and the slope value of the bilogarithmic plots of the weight gain against time, the oxidation kinetics was analyzed with a paralinear equation in the low temperature region below 503 K and a linear equation in the middle and high temperature regions above 643 K. Oxidation rates of U 0.80Zr 0.20 (two-phase mixture) in the low and middle temperature regions were smaller than those of uranium metal. A discontinuity in the plot of the linear oxidation rate constant versus reciprocal temperature was found to be present between 723 and 838 K, similarly to the case of uranium metal previously reported. The linear rate constants of single-phase solid solution in the high temperature region above 1008 K seemed to be a little smaller than those estimated by the extrapolation of the values in the middle temperature region.

Amino acids as novel nucleophiles for silver nanoparticle-luminol chemiluminescence.

PubMed

Li, Na; Ni, Shubiao

2014-12-01

The use of noble metal nanoparticles (NPs) as reductants in chemiluminescence (CL) has been reported only rarely owing to their high oxidation potentials. Interestingly, nucleophiles could dramatically lower the oxidation potential of Ag NPs, such that in the presence of nucleophiles Ag NPS could be used as reductants to induce the CL emission of luminol, an important CL reagent widely used in forensic analysis for the detection of trace amounts of blood. Although nucleophiles are indispensible in Ag NP-luminol CL, only inorganic nucleophiles such as Cl(-), Br(-), I(-) and S2O3 (2-) have been shown to be efficient. The effects of organic nucleophiles on CL remain unexplored. In this study, 20 standard amino acids were evaluated as novel organic nucleophiles in Ag NP-luminol CL. Histidine, lysine and arginine could initiate CL emission; the others could not. It is proposed that the different behaviors of 20 standard amino acids in the CL reactions derive from the interface chemistry between Ag NPs and these amino acids. UV/vis absorption spectra were studied to validate the interface chemistry. In addition, imidazole and histidine were chosen as a model pair to compare the behavior of the monodentate nucleophile with that of the corresponding multidentate nucleophile in Ag NP-luminol CL. Copyright © 2014 John Wiley & Sons, Ltd.

Bio-reinforced self-healing concrete using magnetic iron oxide nanoparticles.

PubMed

Seifan, Mostafa; Sarmah, Ajit K; Ebrahiminezhad, Alireza; Ghasemi, Younes; Samani, Ali Khajeh; Berenjian, Aydin

2018-03-01

Immobilization has been reported as an efficient technique to address the bacterial vulnerability for application in bio self-healing concrete. In this study, for the first time, magnetic iron oxide nanoparticles (IONs) are being practically employed as the protective vehicle for bacteria to evaluate the self-healing performance in concrete environment. Magnetic IONs were successfully synthesized and characterized using different techniques. The scanning electron microscope (SEM) images show the efficient adsorption of nanoparticles to the Bacillus cells. Microscopic observation illustrates that the incorporation of the immobilized bacteria in the concrete matrix resulted in a significant crack healing behavior, while the control specimen had no healing characteristics. Analysis of bio-precipitates revealed that the induced minerals in the cracks were calcium carbonate. The effect of magnetic immobilized cells on the concrete water absorption showed that the concrete specimens supplemented with decorated bacteria with IONs had a higher resistance to water penetration. The initial and secondary water absorption rates in bio-concrete specimens were 26% and 22% lower than the control specimens. Due to the compatible behavior of IONs with the concrete compositions, the results of this study proved the potential application of IONs for developing a new generation of bio self-healing concrete.

Numerical Modeling of Arsenic Mobility during Reductive Iron-Mineral Transformations.

PubMed

Rawson, Joey; Prommer, Henning; Siade, Adam; Carr, Jackson; Berg, Michael; Davis, James A; Fendorf, Scott

2016-03-01

Millions of individuals worldwide are chronically exposed to hazardous concentrations of arsenic from contaminated drinking water. Despite massive efforts toward understanding the extent and underlying geochemical processes of the problem, numerical modeling and reliable predictions of future arsenic behavior remain a significant challenge. One of the key knowledge gaps concerns a refined understanding of the mechanisms that underlie arsenic mobilization, particularly under the onset of anaerobic conditions, and the quantification of the factors that affect this process. In this study, we focus on the development and testing of appropriate conceptual and numerical model approaches to represent and quantify the reductive dissolution of iron oxides, the concomitant release of sorbed arsenic, and the role of iron-mineral transformations. The initial model development in this study was guided by data and hypothesized processes from a previously reported,1 well-controlled column experiment in which arsenic desorption from ferrihydrite coated sands by variable loads of organic carbon was investigated. Using the measured data as constraints, we provide a quantitative interpretation of the processes controlling arsenic mobility during the microbial reductive transformation of iron oxides. Our analysis suggests that the observed arsenic behavior is primarily controlled by a combination of reductive dissolution of ferrihydrite, arsenic incorporation into or co-precipitation with freshly transformed iron minerals, and partial arsenic redox transformations.

Comparison of the agglomeration behavior of thin metallic films on SiO2

NASA Astrophysics Data System (ADS)

Gadkari, P. R.; Warren, A. P.; Todi, R. M.; Petrova, R. V.; Coffey, K. R.

2005-07-01

The stability of continuous metallic thin films on insulating oxide surfaces is of interest to applications such as semiconductor interconnections and gate engineering. In this work, we report the study of the formation of voids and agglomeration of initially continuous Cu, Au, Ru and Pt thin films deposited on amorphous thermally grown SiO2 surfaces. Polycrystalline thin films having thicknesses in the range of 10-100 nm were ultrahigh vacuum sputter deposited on thermally grown SiO2 surfaces. The films were annealed at temperatures in the range of 150-800 °C in argon and argon+3% hydrogen gases. Scanning electron microscopy was used to investigate the agglomeration behavior, and transmission electron microscopy was used to characterize the microstructure of the as-deposited and annealed films. The agglomeration sequence in all of the films is found to follow a two step process of void nucleation and void growth. However, void growth in Au and Pt thin films is different from Cu and Ru thin films. Residual stress and adhesion were observed to play an important part in deciding the mode of void growth in Au and Pt thin films. Last, it is also observed that the tendency for agglomeration can be reduced by encapsulating the metal film with an oxide overlayer.

Microstructure and supercapacitive properties of buserite-type manganese oxide with a large basal spacing

NASA Astrophysics Data System (ADS)

Sun, Zhenjie; Shu, Dong; Chen, Hongyu; He, Chun; Tang, Shaoqing; Zhang, Jie

2012-10-01

A hydration-layered structure of buserite-type manganese oxide (Mg-buserite) was successfully synthesized by an ion exchange method. The as-prepared Mg-buserite possesses a large basal spacing of 10 Å, and contains Mg2+ ions and two sheets of water molecules in the interlayer region. The supercapacitive behaviors of Mg-buserite were systematically investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (CD) experiments and electrochemical impedance spectroscopy (EIS). The results showed that the specific capacitance of the Mg-buserite electrode sharply increased during the initial 500 cycles and reached a maximum of 164 F g-1 at approximately the 500th cycle at a scan rate of 1 mV s-1, and then it remained an almost constant value and decreased slightly upon prolonged cycling. After 22,000 cycles, the specific capacitance decreased by approximately 6% of the maximum specific capacitance. The superior capacitive behavior and excellent cycling stability of the as-prepared Mg-buserite are attributed to the large basal spacing, which can accommodate a larger amount of electrolyte cations and provide more favorable pathways for electrolyte cations intercalation and deintercalation. The experimental results demonstrate that Mg-buserite is a promising candidate as an electrode material for supercapacitors.

Behavior of the Si/SiO2 interface observed by Fowler-Nordheim tunneling

NASA Technical Reports Server (NTRS)

Maserjian, J.; Zamani, N.

1982-01-01

Thin-oxide (40-50 A) metal oxide semiconductor (MOS) structures are shown to exhibit, before large levels of electron tunnel injection, the near-ideal behavior predicted for a uniform trapezoidal barrier with thick-oxide properties. The oscillatory field dependence caused by electron-wave interference at the Si/SiO2 interface suggests an abrupt, one-monolayer barrier transition (approximately 2.5 A) consistent with earlier work. After tunnel injection of 10 to the 17th - 5 x 10 to the 18th electrons/sq cm, the barrier undergoes appreciable degradation, leading to enhanced tunneling conductance. Reproducible behavior is observed among different samples. This effect is found to be consistent with the generation of positive states in the region of the oxide near the Si/SiO2 interface (less than 20 A), where the tunneling electrons emerge into the oxide conduction band.

[Antioxidant properties of benzofurocaine, phenycaberan and orthophen].

PubMed

Lebedev, A V; Kuz'min, A V; Levitskiĭ, D O; Stepaniuk, G I

1989-01-01

The antioxidant properties of benzofurocaine, phenycaberan, crithophen, alpha-tocopherol and ionol were evaluated by inhibition of oxygen absorption by liposomes from egg phosphatidylcholine induced by the addition of an prooxidant. The activity of the tested agents at inhibition of Fe2+-ascorbater-initiated oxidation decreases in the order: ionol, benzofurocaine, phenycaberan, orthophen, alpha-tocopherol; emine-initiated (EDTA-independent) oxidation of phosphatidylcholine is inhibited only by ionol, orthophen and alpha-tocopherol. Phenycaberan exerts no effect on oxidation and benzofurocaine increases the rate of emine-initiated absorption of oxygen. Thus, benzofurocaine, phenycaberan and orthophen may be referred to as selective inhibitors of Fe2+-initiated peroxidation of phosphatidylcholine.

Effect of Initial FeO Content and CaO:SiO2 Ratio on the Reduction Smelting Kinetics of the CaO-SiO2-MgOsatd.-FeO Slag System

NASA Astrophysics Data System (ADS)

Kim, Jong Bae; Sohn, Il

2018-02-01

The effect of the initial FeO content and CaO:SiO2 ratio (CaO mass pct/SiO2 mass pct) on the reduction smelting of FeO with carbon flake addition is investigated in the CaO-MgOsatd.-SiO2-FeO slag system at 1823 K (1550 °C). Carbon rapidly reacted with FeO in the molten slag, causing both foaming and compositional changes in the slag. As FeO is reduced, the MgO saturation is modified, and solid precipitants, including MgO and other complex oxides, were observed, which significantly affected the slag properties, including the viscosity and foaming behavior. The solid-phase fraction and viscosity were estimated from changes in the measured FeO content over time using the thermochemical software FactSage. The iron recovery, which is distinguished from the amount of reduced Fe droplets, showed opposite behavior to the measured maximum foaming height and modified foaming index. According to the FeO mass transfer coefficient considering slag foaming at various initial FeO contents and CaO:SiO2 ratios, the reduction rate was optimal at higher initial FeO contents and a CaO:SiO2 ratio of 2.0, which did not correspond to the optimal iron recovery at an initial FeO content of 44 mass pct and above and a CaO:SiO2 ratio of 1.2. The results showed that slag foaming may increase the reduction kinetics, but the slag composition needs to be optimized for greater iron recovery.

Tuning graphitic oxide for initiator- and metal-free aerobic epoxidation of linear alkenes

NASA Astrophysics Data System (ADS)

Pattisson, Samuel; Nowicka, Ewa; Gupta, Upendra N.; Shaw, Greg; Jenkins, Robert L.; Morgan, David J.; Knight, David W.; Hutchings, Graham J.

2016-09-01

Graphitic oxide has potential as a carbocatalyst for a wide range of reactions. Interest in this material has risen enormously due to it being a precursor to graphene via the chemical oxidation of graphite. Despite some studies suggesting that the chosen method of graphite oxidation can influence the physical properties of the graphitic oxide, the preparation method and extent of oxidation remain unresolved for catalytic applications. Here we show that tuning the graphitic oxide surface can be achieved by varying the amount and type of oxidant. The resulting materials differ in level of oxidation, surface oxygen content and functionality. Most importantly, we show that these graphitic oxide materials are active as unique carbocatalysts for low-temperature aerobic epoxidation of linear alkenes in the absence of initiator or metal. An optimum level of oxidation is necessary and materials produced via conventional permanganate-based methods are far from optimal.

The performance and decolourization kinetics of O3/H2O2 oxidation of reactive green 19 dye in wastewater

NASA Astrophysics Data System (ADS)

Sabri, S. N.; Abidin, C. Z. A.; Fahmi; Kow, S. H.; Razali, N. A.

2018-03-01

The degradations characteristic of azo dye Reactive Green 19 (RG19) was investigated using advanced oxidation process (AOPs). It was evaluated based on colour and chemical oxygen demand (COD) removal. The effect of operational parameters such as initial dye concentration, initial dosage of hydrogen peroxide (H2O2), contact time, and pH was also being studied. The samples were treated by ozonation (O3) and peroxone O3/H2O2 process. Advanced oxidation processes (AOPs) involve two stages of oxidation; firstly is the formation of strong oxidant and secondly the reaction of organic contaminants in water. In addition, the term advanced oxidation is referring to the processes in which oxidation of organic contaminants occurs primarily through reactions with hydroxyl radicals. There are several analyses that use to determine the efficiency of the treatment process, which are UV-Vis absorption spectra, COD, Fourier Transform Infrared (FT-IR), and pH. The results demonstrated that the ozone oxidation was efficient in decolourization and good in mineralization, based on the reduction of colour and COD. Additionally, results indicate that H2O2 is able to perform better than ozonation in order to decolourize the dye wastewater with 0.5 mL H2O2/L dye dosage of H2O2 at different initial concentration, initial pH, with contact time.

Oxidative desulfurization: kinetic modelling.

PubMed

Dhir, S; Uppaluri, R; Purkait, M K

2009-01-30

Increasing environmental legislations coupled with enhanced production of petroleum products demand, the deployment of novel technologies to remove organic sulfur efficiently. This work represents the kinetic modeling of ODS using H(2)O(2) over tungsten-containing layered double hydroxide (LDH) using the experimental data provided by Hulea et al. [V. Hulea, A.L. Maciuca, F. Fajula, E. Dumitriu, Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides, Appl. Catal. A: Gen. 313 (2) (2006) 200-207]. The kinetic modeling approach in this work initially targets the scope of the generation of a superstructure of micro-kinetic reaction schemes and models assuming Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Subsequently, the screening and selection of above models is initially based on profile-based elimination of incompetent schemes followed by non-linear regression search performed using the Levenberg-Marquardt algorithm (LMA) for the chosen models. The above analysis inferred that Eley-Rideal mechanism describes the kinetic behavior of ODS process using tungsten-containing LDH, with adsorption of reactant and intermediate product only taking place on the catalyst surface. Finally, an economic index is presented that scopes the economic aspects of the novel catalytic technology with the parameters obtained during regression analysis to conclude that the cost factor for the catalyst is 0.0062-0.04759 US $ per barrel.

A comprehensive adsorption study and modeling of antibiotics as a pharmaceutical waste by graphene oxide nanosheets.

PubMed

Rostamian, Rahele; Behnejad, Hassan

2018-01-01

The adsorption behavior of tetracycline (TCN), doxycycline (DCN) as the most common antibiotics in veterinary and ciprofloxacin (CPN) onto graphene oxide nanosheets (GOS) in aqueous solution was evaluated. The four factors influencing the adsorption of antibiotics (initial concentration, pH, temperature and contact time) were studied. The results showed that initial pH ∼ 6 to 7 and contact time ∼ 100 - 200min are optimum for each drug. The monolayer adsorption capacity was reduced with the increasing temperature from 25°C to 45°C. Non-linear regressions were carried out in order to define the best fit model for every system. To do this, eight error functions were applied to predict the optimum model. Among various models, Hill and Toth isotherm models represented the equilibrium adsorption data of antibiotics while the kinetic data were well fitted by pseudo second-order (PSO) kinetic model (DCN and TCN) and Elovich (CPN) models. The maximum adsorption capacity (q max ) is found to be in the following order: CPN > DCN > TCN, obtained from sips equation at the same temperature. The GOS shows highest adsorption capacity towards CPN up to 173.4mgg -1 . The study showed that GOS can be removed more efficiently from water solution. Copyright © 2017 Elsevier Inc. All rights reserved.

Influence of grain orientation on the incipient oxidation behavior of Haynes 230 at 900 °C

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

Wang, Xu, E-mail: xuw388@mail.usask.ca; Fan, Fan; Szpunar, Jerzy A.

Ni-based superalloy Haynes 230 is used in many applications such as very high temperature reactor (VHTR) or solid oxide fuel cells (SOFCs) where it is exposed to high temperature service environment. In order to improve the resistance for high temperature oxidation, the effect of crystallographic orientation on the early stage oxidation was investigated. It was demonstrated that different oxide thicknesses are formed on grains having different orientations. Comparison of electron backscatter diffraction (EBSD) orientation maps before and after oxidation at 900 °C indicates that grains near (111) orientation, especially with the deviation angle from <111> that is smaller than 20°,more » are more oxidation resistant than grains of other orientations. Correlation between the results of electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) was used to compare the oxidation rate of grains having different crystallographic orientation. The oxidation rate was found to change with the crystallographic orientation as follows (111) < (110) < (100), also it was demonstrated that the oxidation rate changes are a nearly linear function of the angle of deviation from <111> direction. The morphology of surface oxide also depends on the orientation of grains. - Highlights: • Comparison of EBSD maps before and after oxidation allows to investigate the effect of orientation on oxidation in a more direct way; • Effect of crystallographic orientation on oxidation behavior of alloy 230 is studied by combination of EBSD and AFM; • Different thickness of oxide is formed on grain with different orientation and dependence of anisotropic oxidation behavior is discussed; • The morphology of grains is also orientation dependence.« less

[Oxidation behavior and kinetics of representative VOCs emitted from petrochemical industry over CuCeOx composite oxides].

PubMed

Chen, Chang-Wei; Yu, Yan-Ke; Chen, Jin-Sheng; He, Chi

2013-12-01

CuCeOx composite catalysts were synthesized via coprecipitation (COP-CuCeO,) and incipient impregnation (IMP-CuCeOx) methods, respectively. The physicochemical properties of the samples were characterized by XRD, low-temperature N2 sorption, H2-TPR and O2-TPD. The influences of reactant composition and concentration, reaction space velocity, O2 content, H2O concentration, and catalyst type on the oxidation behaviors of benzene, toluene, and n-hexane emitted from petrochemical industry were systematically investigated. In addition, the related kinetic parameters were model fitted. Compared with IMP-CuCeOx, COP-CuCeOx had well-dispersed active phase, better low-temperature reducibility, and more active surface oxygen species. The increase of reactant concentration was unfavorable for toluene oxidation, while the opposite phenomenon could be observed in n-hexane oxidation. The inlet concentration of benzene was irrelevant to its conversion under high oxidation rate. The introduction of benzene obviously inhibited the oxidation of toluene and n-hexane, while the presence of toluene had a positive effect on beuzene conversion. The presence of n-hexane could promote the oxidation of toluene, while toluene had a negative influence on e-hexane oxidation. Both low space velocity and high oxygen concentration were beneficial for the oxidation process, and the variation of oxygen content had negligible effect on n-hexane and henzene oxidation. The presence of H2O noticeably inhibited the oxidation of toluene, while significantly accelerated the oxidation procedure of henzene and n-hexane. COP-CuCeOx had superior catalytic performance for toluene and benzene oxidation, while IMP-CuCeOx showed higher n-hexane oxidation activity under dry condition. The oxidation behaviors under different conditions could be well fitted and predicted by the pseudo first-order kinetic model.

Breakaway phenomenon of Zr-based alloys during a high-temperature oxidation

NASA Astrophysics Data System (ADS)

Baek, Jong Hyuk; Jeong, Yong Hwan

2008-01-01

The breakaway oxidation phenomena in Zr-based alloys were studied in the temperature range of 950-1200 °C for up to 36 000 s by using a modified thermo-gravimetric analyzer. After the oxidation tests, the oxidation behaviors, breakaway oxidation time, hydrogen pick-up contents, and oxidation rate constants of the alloys were systematically evaluated in this study. The breakaway oxidation time was shortened with an increase of the Sn content in the Zr alloys. A breakaway oxidation phenomenon could be caused by the transition of a tetragonal oxide phase into a monoclinic one, and the oxide transition could lead to form the oxide cracks in both the lateral and radial directions. The cracks within the oxide layer could result in catastrophic increase in the weight gain rates and rapid increase the hydrogen pick-up within the oxygen-stabilized α-Zr and prior β-Zr layers. The oxidation rate constants calculated from the post-breakaway data in the Zr alloys with breakaway oxidation behaviors matched well with the values from both the Baker-Just and Cathcart-Pawel correlations.

Computational design of active, self-reinforcing gels.

PubMed

Yashin, Victor V; Kuksenok, Olga; Balazs, Anna C

2010-05-20

Many living organisms have evolved a protective mechanism that allows them to reversibly alter their stiffness in response to mechanical contact. Using theoretical modeling, we design a mechanoresponsive polymer gel that exhibits a similar self-reinforcing behavior. We focus on cross-linked gels that contain Ru(terpy)(2) units, where both terpyridine ligands are grafted to the chains. The Ru(terpy)(2) complex forms additional, chemoresponsive cross-links that break and re-form in response to a repeated oxidation and reduction of the Ru. In our model, the periodic redox variations of the anchored metal ion are generated by the Belousov-Zhabotinsky (BZ) reaction. Our computer simulations reveal that compression of the BZ gel leads to a stiffening of the sample due to an increase in the cross-link density. These findings provide guidelines for designing biomimetic, active coatings that send out a signal when the system is impacted and use this signaling process to initiate the self-protecting behavior.

Cellulase immobilization on magnetic nanoparticles encapsulated in polymer nanospheres.

PubMed

Lima, Janaina S; Araújo, Pedro H H; Sayer, Claudia; Souza, Antonio A U; Viegas, Alexandre C; de Oliveira, Débora

2017-04-01

Immobilization of cellulases on magnetic nanoparticles, especially magnetite nanoparticles, has been the main approach studied to make this enzyme, economically and industrially, more attractive. However, magnetite nanoparticles tend to agglomerate, are very reactive and easily oxidized in air, which has strong impact on their useful life. Thus, it is very important to provide proper surface coating to avoid the mentioned problems. This study aimed to investigate the immobilization of cellulase on magnetic nanoparticles encapsulated in polymeric nanospheres. The support was characterized in terms of morphology, average diameter, magnetic behavior and thermal decomposition analyses. The polymer nanospheres containing encapsulated magnetic nanoparticles showed superparamagnetic behavior and intensity average diameter about 150 nm. Immobilized cellulase exhibited broader temperature stability than in the free form and great reusability capacity, 69% of the initial enzyme activity was maintained after eight cycles of use. The magnetic support showed potential for cellulase immobilization and allowed fast and easy biocatalyst recovery through a single magnet.

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.; Ghosn, Louis J.; Kalluri, Sreeramesh

2004-01-01

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Photosynthetic behavior of woody species under high ozone exposure probed with the JIP-test: a review.

PubMed

Bussotti, Filippo; Strasser, Reto J; Schaub, Marcus

2007-06-01

Visible ozone symptoms on leaves are expressions of physiological mechanisms to cope with oxidative stresses. Often, the symptoms consist of stippling, which corresponds to localized cell death (hypersensitive response, HR), separated from healthy cells by a layer of callose. The HR strategy tends to protect the healthy cells and in most cases the efficiency of chlorophyll to trap energy is not affected. In other cases, the efficiency of leaves to produce biomass declines and the plant loses its photosynthetic apparatus replacing it with a new, more efficient one. Another strategy consists of the production of pigments (anthocyanins), and leaves become reddish. In these cases, the most significant physiological manifestation consists of the enhanced dissipation of energy. These different behavior patterns are reflected in the initial events of photosynthetic activity, and can be monitored with techniques based on the direct fluorescence of chlorophyll a in photosystem II, applying the JIP-test.

Play Initiating Behaviors and Responses in Red Colobus Monkeys

ERIC Educational Resources Information Center

Worch, Eric A.

2012-01-01

Red colobus monkeys are playful primates, making them an important species in which to study animal play. The author examines play behaviors and responses in the species for its play initiation events, age differences in initiating frequency and initiating behavior, and the types of social play that result from specific initiating behaviors. Out…

Influence of Antioxidants on Leptin Metabolism and its Role in the Pathogenesis of Obesity.

PubMed

Mangge, Harald; Ciardi, Christian; Becker, Kathrin; Strasser, Barbara; Fuchs, Dietmar; Gostner, Johanna M

2017-01-01

Obesity is associated with low-grade inflammation. Leptin, a hormone made by fat cells regulates appetite and hunger and thus food intake behavior. Interestingly, , food preservatives like sodium sulfite and sodium benzoate and also natural colorant and spice compounds such as curcumin were found to decrease the release of leptin in murine 3T3-L1 adipocytes, after co-incubation with LPS, which was added to mimic the pro-inflammatory status in obesity. Several of these compounds are well known food antioxidants.Whilst reducing oxidation events is beneficial in states of elevated oxidative stress, overexposure to food antioxidant can lead to adverse effects. There are hints from in vivo data, that antioxidant stress in younger age plays a role in the development of adiposity in later life. The insufficient exposure to oxidizing compounds like reactive oxygen species (ROS) cannot only cause an insufficient burning of calories but there is also a link to the regulation of food intake behavior. If the in vitro findings can be extrapolated to the in vivo situation, consumption of antioxidant supplemented food could lead to decreased leptin release and contribute to an obesogenic environment. This aspect sheds some new critical light on the potential role of an antioxidant-enriched nutrition in the obesity epidemic during the past few centuries. Doing sports could represent not only a proper strategy to initiate physiological ROS production and burning of calories, but also may shift the hormone milieu towards a reduction of hunger feelings and thus reduce appetite and food intake.

Thermal Shock Behavior of Single Crystal Oxide Refractive Concentrators for High Temperatures Solar Thermal Propulsion

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Jacobson, Nathan S.; Miller, Robert A.

1999-01-01

Single crystal oxides such as yttria-stabilized zirconia (Y2O3-ZrO2), yttrium-aluminum-garnet (Y3Al5O12, or YAG), magnesium oxide (MgO) and sapphire (Al2O3) have been considered as refractive secondary concentrator materials for high temperature solar propulsion applications. However, thermal mechanical reliability of the oxide components in severe thermal environments during space mission sun/shade transitions is of great concern. In this paper, critical mechanical properties of these oxide crystals are determined by the indentation technique. Thermal shock resistance of the oxides is evaluated using a high power CO, laser under high temperature-high thermal gradients. Thermal stress fracture behavior and failure mechanisms of these oxide materials are investigated under various temperature and heating conditions.

Modulatory effects of caffeine on oxidative stress and anxiety-like behavior in ovariectomized rats.

PubMed

Caravan, Ionut; Sevastre Berghian, Alexandra; Moldovan, Remus; Decea, Nicoleta; Orasan, Remus; Filip, Gabriela Adriana

2016-09-01

Menopause is accompanied by enhanced oxidative stress and behavioral changes, effects attenuated by antioxidants. The aim of this study was to evaluate the effects of caffeine on behavior and oxidative stress in an experimental model of menopause. Female rats were divided into the following groups: sham-operated (CON), sham-operated and caffeine-treated (CAF), ovariectomized (OVX), ovariectomized and caffeine-treated (OVX+CAF). Caffeine (6 mg/kg) and vehicle were administered for 21 days (subchronic) and 42 days (chronic), using 2 experimental subsets. Behavioral tests and oxidative stress parameters in the blood, whole brain, and hippocampus were assessed. The subchronic administration of caffeine decreased the lipid peroxidation and improved the antioxidant defense in the blood and brain. The GSH/GGSG ratio in the brain was improved by chronic administration, with reduced activities of antioxidant enzymes and enhanced nitric oxide and malondialdehyde levels. In particular, the lipid peroxidation in the hippocampus decreased in both experiments. The rats became hyperactive after 21 days of treatment, but no effect was observed after chronic administration. In both experimental subsets, caffeine had anxiolytic effects as tested in elevated plus maze. The administration of low doses of caffeine, for a short period of time, may be a new therapeutic approach to modulating the oxidative stress and anxiety in menopause.

Physical and oxidative removal of organics during Fenton treatment of mature municipal landfill leachate.

PubMed

Deng, Yang

2007-07-19

Municipal landfill leachate, especially mature leachate, may disrupt the performance of moderately-sized municipal activated sludge wastewater treatment plants, and likewise tend to be recalcitrant to biological pretreatment. Recently, Fenton methods have been investigated for chemical treatment or pre-treatment of mature leachate. In this paper, the results of laboratory tests to determine the roles of oxidation and coagulation in reducing the organic content of mature leachate during Fenton treatment are presented. The efficiencies of chemical oxygen demand (COD) oxidation and coagulation were tested, and the ratio of COD removal by oxidation to that by coagulation was assessed, under various operating conditions. Low initial pH, appropriate relative and absolute Fenton reagent dosages, aeration, and stepwise addition of reagents increased COD removal by oxidation and the importance of oxidation relative to coagulation. Simultaneous aeration and stepwise reagent addition allowed comparable treatment without initial acidification pH, due to the generation of acidic organic intermediates and the continuous input of CO2. On the other hand, high COD oxidation efficiency and low ferrous dosage inhibited COD removal by coagulation. At significantly high oxidation efficiency, overall COD reduction decrease slightly due to low coagulation efficiency. Under the most favorable conditions (initial pH 3, molar ratio [H(2)O(2)]/[Fe2+]=3, [H2O2]=240 mM, and six dosing steps), 61% of the initial COD was removed, and the ratio of COD removal oxidation to coagulation was 0.75. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of mature leachate, and the role of oxidation in controlling the efficiency of removal of COD by coagulation.

Gas generation behavior of transuranic waste under disposal conditions

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

Fujisawa, Ryutaro; Kurashige, Tetsunari; Inagaki, Yusuke

1999-07-01

The generation of hydrogen-gas from metallic waste is an important issue for the safety analysis of geological disposal facilities for transuranic (TRU) radioactive waste in Japan. The objective of this study is to clarify the gas-generation behavior of stainless steel and carbon steel in non-oxidizing alkaline synthetic groundwater (pH 12.8 and 10.5) at 30 C simulating geological disposal environments. At pH 12.8, the observed gas-generation rate from stainless steel in the initial period of immersion was 1.0 x 10{sup 2} Nml/m{sup 2}/y and 1.0 x 10 Nml/m{sup 2}/y after 200 days (N represents the standard state of gas at 0more » C and 1 atm). At pH 10.5, gas generation was not observed for 60 days in the initial period. At 60 days, the gas-generation observed was 5.0 x 10 NMl/m{sup 2}/y. After 250 days, the gas-generation rate approaches zero. At pH 12.8, the observed gas generation rate of carbon steel in the initial period of immersion was 1.5 x 10{sup 2} Nml/m{sup 2}/y and the gas generation rate began to decrease after 200 days. After 300 days, it was 25 Nml/m{sup 2}/y. At pH 10.5, the gas generation rate in the initial period was 5.0 x 10{sup 2} Nml/m{sup 2}/y and was 1.0 x 10 Nml/m{sup 2}/y after 200 days.« less

Fundamental tribological properties of ceramics

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Miyoshi, K.

1985-01-01

When a ceramic is brought into contact with itself, another ceramic, or a metal, strong bond forces can develop between the materials. Adhesion between a ceramic and itself or another solid are discussed from a theoretical consideration of the nature of the surfaces and experimentally by relating bond forces to the interface resulting from solid state contact. Elastic, plastic, and fracture behavior of ceramics in solid-state contact are discussed as they relate to friction and wear. The contact load necessary to initiate fracture in ceramics is shown to be appreciably reduced with tangential motion. Both friction and wear of ceramics are anisotropic and relate to crystal structure as with metals. Both free energy of oxide formation and the d valence bond character of metals are related to the friction and wear characteristics for metals in contact with ceramics. Lubrication is found to increase the critical load necessary to initiate fracture of ceramics with sliding or rubbing contact.

Durability of Environmental Barrier Coatings in a Water Vapor/Oxygen Environment

NASA Technical Reports Server (NTRS)

Holchin, John E.

2004-01-01

Silicon carbide (Sic) and silicon nitride (Si3N4) show potential for application in the hot sections of advanced jet engines. The oxidation behavior of these materials has been studied in great detail. In a pure oxygen environment, a silica (SiO2) layer forms on the surface and provides protection from further oxidation. Initial oxidation is rapid, but slows as silica layer grows; this is known as parabolic oxidation. When exposed to model fuel-lean combustion applications (standard in jet engines), wherein the partial pressure of water vapor is approximately 0.5 atm., these materials exhibit different characteristics. In such an environment, the primary oxidant to form silica is water vapor. At the same time, water vapor reacts with the surface oxide to form gaseous silicon hydroxide (Si(OH)4). The simultaneous formation of both silica and Si(OH)4 -the latter which is lost to the atmosphere- the material continues to recede. Recession rates for uncoated Sic and Si3N4 are unacceptably high, for use in jet engines, - on the order of 1mm/4000h. External coatings have been developed that protect Si-based materials from water vapor attack. One such coating consists of a Ba(0.75)Sr(0.25)Al2Si2O8 (BSAS) topcoat, a mullite/BSAS intermediate layer and a Si bond coat. The key function of the topcoat is to protect the Si-base material from water vapor; therefore it must be fairly stable in water vapor (recession rate of about 1mm/40,000h) and remain crack free. Although BSAS is much more resistant to water vapor attack than pure silica, it exhibits a linear weight loss in 50% H2O - 50% O2 at 1500 C. The objective of my research is to determine the oxidation behavior of a number of alternate hot-pressed monolithic top coat candidates. Potential coatings were exposed at 1500 C to a 50% H2O - 50% O2 gas mixture flowing at 4.4 cm/s . These included rare- earth silicates, barium-strontium aluminosilicates. When weight changes were measured with a continuously recording microbalance, linear weight loss was observed. BSAS materials have a fairly high volatility at this temperature, but rare-earth mono-silicate compounds were significantly more stable.

Oxidation of trichloroethylene, toluene, and ethanol vapors by a partially saturated permeable reactive barrier

NASA Astrophysics Data System (ADS)

Mahmoodlu, Mojtaba G.; Hassanizadeh, S. Majid; Hartog, Niels; Raoof, Amir

2014-08-01

The mitigation of volatile organic compound (VOC) vapors in the unsaturated zone largely relies on the active removal of vapor by ventilation. In this study we considered an alternative method involving the use of solid potassium permanganate to create a horizontal permeable reactive barrier for oxidizing VOC vapors. Column experiments were carried out to investigate the oxidation of trichloroethylene (TCE), toluene, and ethanol vapors using a partially saturated mixture of potassium permanganate and sand grains. Results showed a significant removal of VOC vapors due to the oxidation. We found that water saturation has a major effect on the removal capacity of the permeable reactive layer. We observed a high removal efficiency and reactivity of potassium permanganate for all target compounds at the highest water saturation (Sw = 0.6). A change in pH within the reactive layer reduced oxidation rate of VOCs. The use of carbonate minerals increased the reactivity of potassium permanganate during the oxidation of TCE vapor by buffering the pH. Reactive transport of VOC vapors diffusing through the permeable reactive layer was modeled, including the pH effect on the oxidation rates. The model accurately described the observed breakthrough curve of TCE and toluene vapors in the headspace of the column. However, miscibility of ethanol in water in combination with produced water during oxidation made the modeling results less accurate for ethanol. A linear relationship was found between total oxidized mass of VOC vapors per unit volume of permeable reactive layer and initial water saturation. This behavior indicates that pH changes control the overall reactivity and longevity of the permeable reactive layer during oxidation of VOCs. The results suggest that field application of a horizontal permeable reactive barrier can be a viable technology against upward migration of VOC vapors through the unsaturated zone.

Quercetin prevents chronic unpredictable stress induced behavioral dysfunction in mice by alleviating hippocampal oxidative and inflammatory stress.

PubMed

Mehta, Vineet; Parashar, Arun; Udayabanu, Malairaman

2017-03-15

It is now evident that chronic stress is associated with anxiety, depression and cognitive dysfunction and very few studies have focused on identifying possible methods to prevent these stress-induced disorders. Previously, we identified abundance of quercetin in Urtica dioica extract, which efficiently attenuated stress related complications. Therefore, current study was designed to investigate the effect of quercetin on chronic unpredicted stress (CUS) induced behavioral dysfunction, oxidative stress and neuroinflammation in the mouse hippocampus. Animals were subjected to unpredicted stress for 21days, during which 30mg/kg quercetin was orally administered to them. Effect of CUS and quercetin treatment on animal behavior was assessed between day 22-26. Afterward, the hippocampus was processed to evaluate neuronal damage, oxidative and inflammatory stress. Results revealed that stressed animals were highly anxious (Elevated Plus Maze and Open Field), showed depressive-like behavior (sucrose preference task), performed poorly in short-term and long-term associative memory task (passive avoidance step-through task) and displayed reduced locomotion (open field). Quercetin alleviated behavioral dysfunction in chronically stressed animals. Compared to CUS, quercetin treatment significantly reduced anxiety, attenuated depression, improved cognitive dysfunction and normalized locomotor activity. Further, CUS elevated the levels of oxidative stress markers (TBARS, nitric oxide), lowered antioxidants (total thiol, catalase), enhanced expression of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β and COX-2) in the hippocampus and damaged hippocampal neurons. Quercetin treatment significantly lowered oxidative and inflammatory stress and prevented neural damage. In conclusion, quercetin can efficiently prevent stress induced neurological complications by rescuing brain from oxidative and inflammatory stress. Copyright © 2017 Elsevier Inc. All rights reserved.

Astaxanthin improves behavioral disorder and oxidative stress in prenatal valproic acid-induced mice model of autism.

PubMed

Al-Amin, Md Mamun; Rahman, Md Mahbubur; Khan, Fazlur Rahman; Zaman, Fahmida; Mahmud Reza, Hasan

2015-06-01

Prenatal exposure to valproic acid on gestational day 12.5 may lead to the impaired behavior in the offspring, which is similar to the human autistic symptoms. To the contrary, astaxanthin shows neuroprotective effect by its antioxidant mechanism. We aimed to (i) develop mice model of autism and (ii) investigate the effect of astaxanthin on such model animals. Valproic acid (600 mg/kg) was administered intraperitoneally to the pregnant mice on gestational day 12.5. Prenatal valproic acid-exposed mice were divided into 2 groups on postnatal day 25 and astaxanthin (2mg/kg) was given to the experimental group (VPA_AST, n=10) while saline was given to the control group (VPA, n=10) for 4 weeks. Behavioral test including social interaction, open field and hot-plate were conducted on postnatal day 25 and oxidative stress markers such as lipid peroxidation, advanced protein oxidation product, nitric oxide, glutathione, and activity of superoxide dismutase and catalase were estimated on postnatal day 26 to confirm mice model of autism and on postnatal day 56 to assess the effect of astaxanthin. On postnatal day 25, prenatal valproic acid-exposed mice exhibited (i) delayed eye opening (ii) longer latency to respond painful stimuli, (iii) poor sociability and social novelty and (iv) high level of anxiety. In addition, an increased level of oxidative stress was found by determining different oxidative stress markers. Treatment with astaxanthin significantly (p<0.05) improved the behavioral disorder and reduced the oxidative stress in brain and liver. In conclusion, prenatal exposure to valproic day in pregnant mice leads to the development of autism-like features. Astaxanthin improves the impaired behavior in animal model of autism presumably by its antioxidant activity. Copyright © 2015 Elsevier B.V. All rights reserved.

The effects of methylmercury exposure on behavior and biomarkers of oxidative stress in adult mice.

PubMed

Kirkpatrick, Meg; Benoit, Janina; Everett, Wyll; Gibson, Jennifer; Rist, Michael; Fredette, Nicholas

2015-09-01

Methylmercury (MeHg) is a widely distributed environmental neurotoxin with established effects on locomotor behaviors and cognition in both human populations and animal models. Despite well-described neurobehavioral effects, the mechanisms of MeHg toxicity are not completely understood. Previous research supports a role for oxidative stress in the toxic effects of MeHg. However, comparing findings across studies has been challenging due to differences in species, methodologies (in vivo or in vitro studies), dosing regimens (acute vs. long-term) and developmental life stage. The current studies assess the behavioral effects of MeHg in adult mice in conjunction with biochemical and cellular indicators of oxidative stress using a consistent dosing regimen. In Experiment 1, adult male C57/BL6 mice were orally administered 5 mg/kg/day MeHg or the vehicle for 28 days. Impact of MeHg exposure was assessed on inverted screen and Rotor-Rod behaviors as well as on biomarkers of oxidative stress (thioredoxin reductase (TrxR), glutathione reductase (GR) and glutathione peroxidase (GPx)) in brain and liver. In Experiment 2, brain tissue was immunohistochemically labeled for 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of DNA oxidation and an indicator of oxidative stress, following the same dosing regimen. 8-OHdG immunoreactivity was measured in the motor cortex, the magnocellular red nucleus (RMC) and the accessory oculomotor nucleus (MA3). Significant impairments were observed in MeHg-treated animals on locomotor behaviors. TrxR and GPx was significantly inhibited in brain and liver, whereas GR activity decreased in liver and increased in brain tissue of MeHg-treated animals. Significant MeHg-induced alterations in DNA oxidation were observed in the motor cortex, the RMC and the MA3. Copyright © 2015 Elsevier Inc. All rights reserved.

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

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

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

2014-07-01

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

Composition-ratio influence on resistive switching behavior of solution-processed InGaZnO-based thin-film.

PubMed

Hwang, Yeong-Hyeon; Hwang, Inchan; Cho, Won-Ju

2014-11-01

The influence of composition ratio on the bipolar resistive switching behavior of resistive switching memory devices based on amorphous indium-gallium-zinc-oxide (a-IGZO) using the spin-coating process was investigated. To study the stoichiometric effects of the a-IGZO films on device characteristics, four devices with In/Ga/Zn stoichiometries of 1:1:1, 3:1:1, 1:3:1, and 1:1:3 were fabricated and characterized. The 3:1:1 film showed an ohmic behavior and the 1:1:3 film showed a rectifying switching behavior. The current-voltage characteristics of the a-IGZO films with stoichiometries of 1:1:1 and 1:3:1, however, showed a bipolar resistive memory switching behavior. We found that the three-fold increase in the gallium content ratio reduces the reset voltage from -0.9 to - 0.4 V and enhances the current ratio of high to low resistive states from 0.7 x 10(1) to 3 x 10(1). Our results show that the increase in the Ga composition ratio in the a-IGZO-based ReRAM cells effectively improves the device performance and reliability by increasing the initial defect density in the a-IGZO films.

High temperature corrosion of cold worked YUS409D bellows of bellow-sealed valve in LBE

NASA Astrophysics Data System (ADS)

Mustari1, A. P. A.; Irwanto1, D.; Takahashi, M.

2017-01-01

Lead-bismuth eutectic (LBE) loop test is highly contributes to the lead-alloy-cooled fast breeder reactor (LFR) and accelerator driven system (ADS) research and development by providing comprehensive results of both corrosion and erosion phenomenon. Bellows-sealed valve is a crucial part in the LBE loop test apparatus, due to its capability of preventing corrosion on valve spring, thus improves the operation time of the system. LBE is very corrosive to stainless steel by formation of oxide layer or elemental dissolution, e.g. Ni. Thus, new type of bellows for bellows-sealed valve made of nickel free material, i.e. YUS409D, is proposed to be used in the LBE. Bellows material undergo heat treatments for mechanical improvement including cold working and annealing. The thickness reduction by the heat treatments is about 90% of initial condition. Corrosion behavior of the bellows has been studied in stagnant LBE at 500 and 600 °C for 500 hours. The oxygen concentration was controlled at about 10-7 wt%. Typical oxide layers were developed on the surface. Oxidation rate was sharply increased at 600°C.

Graphene oxide-dispersed pristine CNTs support for MnO2 nanorods as high performance supercapacitor electrodes.

PubMed

You, Bo; Li, Na; Zhu, Hongying; Zhu, Xiaolan; Yang, Jun

2013-03-01

A MnO2 -CNT-graphene oxide (MCGO) nanocomposite is fabricated using graphene oxide (GO) as a surfactant to directly disperse pristine carbon nanotubes (CNTs) for the subsequent deposition of MnO2 nanorods. The resulting MCGO nanocomposite is used as a supercapacitor electrode that shows ideal capacitive behavior (i.e., rectangular-shaped cyclic voltammograms), large specific capacitance (4.7 times higher than that of free MnO2 ) even at high mass loading (3.0 mg cm(-2) ), high energy density (30.4-14.2 Wh kg(-1) ), large power density (2.6-50.5 kW kg(-1) ), and still retains approximately 94 % of the initial specific capacitance after 1000 cycles. The advanced capacity, rate capability, and cycling stability may be attributed to the unique architecture, excellent ion wettability of GO with enriched oxygen-containing functional groups, high conductivity of CNTs, and their synergistic effects when combined with the other components. The results suggest that the MnO2 -CNT-GO hybrid nanocomposite architecture is very promising for next generation high-performance energy storage devices. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis of the Negative-SET Behaviors in Cu/ZrO2/Pt Devices

NASA Astrophysics Data System (ADS)

Liu, Sen; Zhao, Xiaolong; Li, Qingjiang; Li, Nan; Wang, Wei; Liu, Qi; Xu, Hui

2016-12-01

Metal oxide-based electrochemical metallization memory (ECM) shows promising performance for next generation non-volatile memory. The negative-SET behavior has been observed in various oxide-based ECM devices. But the underlying mechanism of this behavior remains unaddressed and the role of the metal cation and oxygen vacancy in this behavior is unclear. In this work, we have observed two kinds of negative-SET (labeled as N-SET1 and N-SET2) behaviors in our Cu/ZrO2/Pt devices. Both the two behaviors can result in hard breakdown due to the high compliance current in reset process. The I-V characteristic shows that the two negative-SET behaviors have an obvious difference in operation voltage. Using four-probe resistance measurement method, the resistance-temperature characteristics of the ON-state after various negative-SET behaviors have been studied. The temperature dependence results demonstrate that the N-SET1 behavior is dominated by Cu conductive filament (CF) reformation caused by the Cu CF overgrowth phenomenon while the N-SET2 is related to the formation of oxygen vacancy CF. This work may provide a comprehensive understanding of the switching mechanism in oxide-based ECM devices.

Role of Vitamin E in the Treatment of Alzheimer's Disease: Evidence from Animal Models.

PubMed

Gugliandolo, Agnese; Bramanti, Placido; Mazzon, Emanuela

2017-11-23

Alzheimer's disease (AD) is a neurodegenerative disorder representing the major cause of dementia. It is characterized by memory loss, and cognitive and behavioral decline. In particular, the hallmarks of the pathology are amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), formed by aggregated hyperphosphorylated tau protein. Oxidative stress plays a main role in AD, and it is involved in initiation and progression of AD. It is well known that Aβ induced oxidative stress, promoting reactive oxygen species (ROS) production and consequently lipid peroxidation, protein oxidation, tau hyperphosphorylation, results in toxic effects on synapses and neurons. In turn, oxidative stress can increase Aβ production. For these reasons, the administration of an antioxidant therapy in AD patients was suggested. The term vitamin E includes different fat-soluble compounds, divided into tocopherols and tocotrienols, that possess antioxidant action. α-Tocopherol is the most studied, but some studies suggested that tocotrienols may have different health promoting capacities. In this review, we focused our attention on the effects of vitamin E supplementation in AD animal models and AD patients or older population. Experimental models showed that vitamin E supplementation, by decreasing oxidative stress, may be a good strategy to improve cognitive and memory deficits. Furthermore, the combination of vitamin E with other antioxidant or anti-inflammatory compounds may increase its efficacy. However, even if some trials have evidenced some benefits, the effects of vitamin E in AD patients are still under debate.

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

He, Yang; Piper, Daniela M.; Gu, Meng

Surface modification of silicon nanoparticle via molecular layer deposition (MLD) has been recently proved to be an effective way for dramatically enhancing the cyclic performance in lithium ion batteries. However, the fundamental mechanism as how this thin layer of coating function is not known, which is even complicated by the inevitable presence of native oxide of several nanometers on the silicon nanoparticle. Using in-situ TEM, we probed in detail the structural and chemical evolution of both uncoated and coated silicon particles upon cyclic lithiation/delithation. We discovered that upon initial lithiation, the native oxide layer converts to crystalline Li2O islands, whichmore » essentially increases the impedance on the particle, resulting in ineffective lithiation/delithiation, and therefore low coulombic efficiency. In contrast, the alucone MLD coated particles show extremely fast, thorough and highly reversible lithiation behaviors, which are clarified to be associated with the mechanical flexibility and fast Li+/e- conductivity of the alucone coating. Surprisingly, the alucone MLD coating process chemically changes the silicon surface, essentially removing the native oxide layer and therefore mitigates side reaction and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the coulombic efficiency and preserve capacity and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrated that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance as the coating layer itself.« less

Thermodynamic Effect of Platinum Addition to beta-NiAl: An Initial Investigation

NASA Technical Reports Server (NTRS)

2005-01-01

An initial investigation was conducted to determine the effect of platinum addition on the activities of aluminum and nickel in beta-NiAl(Pt) over the temperature range 1354 to 1692 K. These measurements were made with a multiple effusion-cell configured mass spectrometer (multi-cell KEMS). The results of this study show that Pt additions act to decreased alpha(Al) and increased the alpha(Ni) in beta-NiAl(Pt) for constant X(sub Ni)/X(sub Al) approx. = 1.13, while at constant X(sub Al) the affect of Pt on Al is greatly reduced. The measured partial enthalpies of mixing indicate Al-atoms have a strong self interaction while Ni- and Pt-atoms in have similar interactions with Al-atoms. Conversely the binding of Ni-atoms in beta-NiAl decreases with Pt addition independent of Al concentration. These initial results prove the technique can be applied to the Ni-Al-Pt system but more activity measurements are required to fully understand the thermodynamics of this system and how Pt additions improved the scaling behavior of nickel-based superalloys. In addition, with the choice of a suitable oxide material for the effusion-cell, the "closed" isothermal nature of the effusion-cell allows the direct investigation of an alloy-oxide equilibrium which resembles the "local-equilibrium" description of the metal-scale interface observed during high temperature oxidation. It is proposed that with an Al(l) + Al2O3(s) experimental reference state together with the route measurement of the relative partial-pressures of Al(g) and Al2O(g) allows the activities of O and Al2O3 to be determined along with the activities of Ni and Al. These measurements provide a direct method of investigating the thermodynamics of the metal-scale interface of a TGO-scale.

Effects of flight activity and age on oxidative damage in the honey bee, Apis mellifera.

PubMed

Margotta, Joseph W; Roberts, Stephen P; Elekonich, Michelle M

2018-05-03

Frequent and highly aerobic behaviors likely contribute to naturally occurring stress, accelerate senescence, and limit lifespan. To understand how the physiological and cellular mechanisms that determine the onset and duration of senescence are shaped by behavioral development and behavioral duration, we exploited the tractability of the honey bee ( Apis mellifera ) model system. First, we determined if a cause-effect relationship exists between honey bee flight and oxidative stress by comparing oxidative damage accrued from intense flight bouts to damage accrued from D-galactose ingestion, which induces oxidative stress and limit lifespan in other insects. Second, we experimentally manipulated the duration of honey bee flight across a range of ages to determine their effects on reactive oxygen species (ROS) accumulation and associated enzymatic antioxidant protective mechanisms. In bees fed D-galactose, lipid peroxidation (MDA) was higher than in bees fed sucrose and age-matched bees with high and low flight experience collected from a colony. Bees with high amounts of flight experience exhibited elevated 8-OHdG, a marker of oxidative DNA damage, relative to bees with less flight experience. Bees with high amounts of flight experience also showed increased levels of pro-oxidants (superoxide and H 2 O 2 ) and decreased or unchanged levels of antioxidants (SOD and catalase). These data implicate an imbalance of pro- to antioxidants in flight-associated oxidative stress and reveal how behavior can damage a cell and consequently limit lifespan. © 2018. Published by The Company of Biologists Ltd.

Protective effect of alprazolam against sleep deprivation-induced behavior alterations and oxidative damage in mice.

PubMed

Singh, Anant; Kumar, Anil

2008-04-01

Sleep deprivation is considered as a risk factor for various diseases. Sleep deprivation leads to behavioral, hormonal, neurochemical and biochemical alterations in the animals. The present study was designed to explore the possible involvement of GABAergic mechanism in protective effect of alprazolam against 72h sleep deprivation-induced behavior alterations and oxidative damage in mice. In the present study, sleep deprivation caused anxiety-like behavior, weight loss, impaired ambulatory movements and oxidative damage as indicated by increase in lipid peroxidation, nitrite level and depletion of reduced glutathione and catalase activity in sleep-deprived mice brain. Treatment with alprazolam (0.25 and 0.5 mg/kg, ip) significantly improved behavioral alterations. Biochemically, alprazolam treatment significantly restored depleted reduced glutathione, catalase activity, reversed raised lipid peroxidation and nitrite level. Combination of flumazenil (0.5 mg/kg) and picrotoxin (0.5 mg/kg) with lower dose of alprazolam (0.25mg/kg) significantly antagonized protective effect of alprazolam. However, combination of muscimol (0.05 mg/kg) with alprazolam (0.25 mg/kg, ip) potentiated protective effect of alprazolam. On the basis of these results, it might be suggested that alprazolam might produce protective effect by involving GABAergic system against sleep deprivation-induced behavior alterations and related oxidative damage.

High temperature oxidation behavior of austenitic stainless steel AISI 304 in steam of nanofluids contain nanoparticle ZrO2

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

Prajitno, Djoko Hadi, E-mail: djokohp@batan.go.id; Syarif, Dani Gustaman, E-mail: djokohp@batan.go.id

2014-03-24

The objective of this study is to evaluate high temperature oxidation behavior of austenitic stainless steel SS 304 in steam of nanofluids contain nanoparticle ZrO{sub 2}. The oxidation was performed at high temperatures ranging from 600 to 800°C. The oxidation time was 60 minutes. After oxidation the surface of the samples was analyzed by different methods including, optical microscope, scanning electron microscope (SEM) and X-ray diffraction (XRD). X-ray diffraction examination show that the oxide scale formed during oxidation of stainless steel AISI 304 alloys is dominated by iron oxide, Fe{sub 2}O{sub 3}. Minor element such as Cr{sub 2}O{sub 3} ismore » also appeared in the diffraction pattern. Characterization by optical microscope showed that cross section microstructure of stainless steel changed after oxidized with the oxide scale on the surface stainless steels. SEM and x-ray diffraction examination show that the oxide of ZrO{sub 2} appeared on the surface of stainless steel. Kinetic rate of oxidation of austenite stainless steel AISI 304 showed that increasing oxidation temperature and time will increase oxidation rate.« less

Advantages of the Alpha-lipoic Acid Association with Chlorpromazine in a Model of Schizophrenia Induced by Ketamine in Rats: Behavioral and Oxidative Stress evidences.

PubMed

Sampaio, Luis Rafael Leite; Cysne Filho, Francisco Maurício Sales; de Almeida, Jamily Cunha; Diniz, Danilo Dos Santos; Patrocínio, Cláudio Felipe Vasconcelos; de Sousa, Caren Nádia Soares; Patrocínio, Manoel Cláudio Azevedo; Macêdo, Danielle; Vasconcelos, Silvânia Maria Mendes

2018-03-01

Schizophrenia is a chronic mental disorder reported to compromise about 1% of the world's population. Although its pathophysiological process is not completely elucidated, evidence showing the presence of an oxidative imbalance has been increasingly highlighted in the literature. Thus, the use of antioxidant substances may be of importance for schizophrenia treatment. The objective of this study was to evaluate the behavioral and oxidative alterations by the combination of chlorpromazine (CP) and alpha-lipoic acid (ALA), a potent antioxidant, in the ketamine (KET) model of schizophrenia in rats. Male Wistar rats (200-300 g) were treated for 10 days with saline, CP or ALA alone or in combination with CP previous to KET and the behavioral (open field, Y-maze and PPI tests) and oxidative tests were performed on the last day of treatment. The results showed that KET induced hyperlocomotion, impaired working memory and decreased PPI. CP alone or in combination with ALA prevented KET-induced behavioral effects. In addition, the administration of KET decreased GSH and increased nitrite, lipid peroxidation and myeloperoxidase activity. CP alone or combined with ALA prevented the oxidative alterations induced by KET. In conclusion, the treatment with KET in rats induced behavioral impairments accompanied by hippocampal oxidative alterations, possibly related to NMDA receptors hypofunction. Besides that, CP alone or combined with ALA prevented these effects, showing a beneficial activity as antipsychotic agents. Copyright © 2018 IBRO. Published by Elsevier Ltd. All rights reserved.

Acute electroacupuncture inhibits nitric oxide synthase expression in the spinal cord of neuropathic rats.

PubMed

Cha, Myeoung Hoon; Bai, Sun Joon; Lee, Kyung Hee; Cho, Zang Hee; Kim, Young-Bo; Lee, Hye-Jung; Lee, Bae Hwan

2010-02-01

To examine the effects of electroacupuncture stimulation on behavioral changes and neuronal nitric oxide synthase expression in the rat spinal cord after nerve injury. Under pentobarbital anesthesia, male Sprague-Dawley rats were subjected to neuropathic surgery by tightly ligating and cutting the left tibial and sural nerves. Behavioral responses to mechanical stimulation were tested for 2 weeks post-operatively. At the end of behavioral testing, electroacupuncture stimulation was applied to ST36 (Choksamni) and SP9 (Eumleungcheon) acupoints. Immunocytochemical staining was performed to investigate changes in the expression of neuronal nitric oxide synthase-immunoreactive neurons in the L4-5 spinal cord. Mechanical allodynia was observed by nerve injury. The mechanical allodynia was decreased after electroacupuncture stimulation. Neuronal nitric oxide synthase expression was also decreased in L4-5 spinal cord by electroacupuncture treatment. These results suggest that electroacupuncture relieves mechanical allodynia in the neuropathic rats possibly by the inhibition of neuronal nitric oxide synthase expression in the spinal cord.

Crystallization of copper metaphosphate glass

NASA Technical Reports Server (NTRS)

Bae, Byeong-Soo; Weinberg, Michael C.

1993-01-01

The effect of the valence state of copper in copper metaphosphate glass on the crystallization behavior and glass transition temperature has been investigated. The crystallization of copper metaphosphate is initiated from the surface and its main crystalline phase is copper metaphosphate (Cu(PO)3),independent of the (Cu sup 2+)/(Cu(total)). However, the crystal morphology, the relative crystallization rates, and their temperature dependences are affected by the (Cu sup 2+)/(Cu (total)) ratio in the glass. On the other hand, the totally oxidized glass crystallizes from all over the surface. The relative crystallization rate of the reduced glass to the totally oxidized glass is large at low temperature, but small at high temperature. The glass transition temperature of the glass increases as the (Cu sup 2+)/(Cu(total)) ratio is raised. It is also found that the atmosphere used during heat treatment does not influence the crystallization of the reduced glass, except for the formation of a very thin CuO surface layer when heated in air.

Determination of myoglobin based on its enzymatic activity by stopped-flow spectrophotometry

NASA Astrophysics Data System (ADS)

Zheng, Qi; Liu, Zhihong; Cai, Ruxiu

2005-04-01

A new method has been developed for the determination of myoglobin (Mb) based on its enzymatic activity for the oxidation of o-phenylenediamine (OPDA) with hydrogen peroxide. Stopped-flow spectrophotometry was used to study the kinetic behavior of the oxidation reaction. The catalytic activity of Mb was compared to other three kinds of catalyst. The time dependent absorbance of the reaction product, 2,3-diamimophenazine (DAPN), at a wavelength of 426 nm was recorded. The initial reaction rate obtained at 40 °C was found to be proportional to the concentration of Mb in the range of 1.0 × 10 -6 to 4.0 × 10 -9 mol L -1. The detection limit of Mb was found to be 9.93 × 10 -10 mol L -1. The relative standard deviations were within 5% for the determination of different concentrations of Mb. Excess of bovine serum albumin (BSA), Ca(II), Mg(II), Cu(II), glucose, caffeine, lactose and uric acid did not interfere.

Investigation of weldable iron-aluminum alloys for corrosion protection in high temperature oxidizing-sulfidizing environments

NASA Astrophysics Data System (ADS)

Banovic, Stephen William

The objective of the present study was to investigate the corrosion behavior of weldable Fe-Al alloys in environments representative of low NOx gas compositions, i.e., high partial pressures of sulfur [p(S2)] and low partial pressures of oxygen [p(O2)]. Through an integrated experimental approach involving thermogravimetric techniques, post-exposure metallographic examination of the corroded samples, and detailed chemical microanalyses of the reaction scales, the effects of aluminum content, temperature, and gas composition on the corrosion behavior were observed. The corrosion behavior of Fe-Al alloys was found to be directly related to the type and morphology of corrosion product that formed during high temperature exposure in the oxidizing/sulfidizing environment. The inhibition stage was characterized by growth of a thin, gamma alumina scale that suppressed excessive degradation of the substrate at all temperatures. Localized mechanical failure of the initial passive scale, in combination with the inability to re-establish itself, was found to result in nodular growth of non-protective sulfide phases across the sample face due to short circuit diffusion through the gamma alumina layer. With the remnants of the initial gamma scale found between the outer and inner scale, it was concluded that these layers grew by iron diffusion outward and sulfur diffusion inward, respectively. The corrosion rate observed during development of these morphologies was directly related to the density of the nodules on the surface and the exposure temperature. The final period observed was the steady-state stage. This behavior was encountered from the onset of exposure for all Fe-5 wt% Al alloys tested, or upon coalescence of the nodular growths. After initially high corrosion rates, the weight gains were found to increase at a steady rate as subsequent growth occurred via diffusion through the continuous scale. Determination of the corrosion product growth mechanism could not be directly obtained from the thermogravimetric data. For samples with relatively high weight gains, enhanced scale growth at the comers and edges of the sample, as well as the morphology of the multi-layered, multi-phase corrosion products, violated the assumptions necessary for data manipulation by this means. The results from this study indicate that weldable compositions of Fe-Al alloys (10 wt% Al) show excellent corrosion resistance to aggressive low NO x gas compositions in the service temperature range (below 600°C). With the potential promise for applications requiring a combination of weldability and corrosion resistance in moderately reducing environments, these alloys are viable candidates for further evaluation for use as sulfidation resistant weld overlay coatings. (Abstract shortened by UMI.)

Resistance to High-Temperature Oxidation and Wear of Various Ferrous Alloys Used in Rolling Mills

NASA Astrophysics Data System (ADS)

Delaunois, Fabienne; Stanciu, Victor Ioan; Sinnaeve, Mario

2018-03-01

Various materials are commonly used to manufacture work rolls for hot rolling mills, such as ICDP (Indefinite Chill Double Pour) cast irons, high-chromium white cast irons, and high speed steels (HSS). Various chemical compositions and microstructures are studied in order to optimize the in-use behavior of those grades of rolls. In this paper, six grades of ferrous alloys (an ICDP cast iron; an ICDP cast iron enriched in vanadium, niobium, and molybdenum; a HSS; a graphitic HSS; a high-chromium white cast iron (Hi-Cr); and a niobium-molybdenum-doped high-chromium white cast iron) were investigated. High-temperature oxidation tests with gravimetric means at 575 °C in water vapor atmosphere and sliding wear tests were carried out. The oxidation kinetics was followed during oxidation test. The microstructure was observed by optical and scanning electron microscopies. The oxides formed on the surface of the samples were analyzed by XRD and EDS. The thickness of the oxide scales and the mass gain were measured after oxidation test. The results showed that the behavior of all the grades differed. The oxide scale of HSS and HSS-G grades was fine and their friction coefficient was low. The weight gain after oxidation test of HSS was high. Hi-Cr and M-Hi-Cr grades presented highly porous oxide layer and an important increase of the friction coefficient during wear test. ICDP and M-ICDP had intermediate behavior.

Oxidation of Al2O3 continuous fiber-reinforced/NiAl composites

NASA Technical Reports Server (NTRS)

Doychak, J.; Nesbitt, J. A.; Noebe, R. D.; Bowman, R. R.

1992-01-01

The 1200 C and 1300 C isothermal and cyclic oxidation behavior of Al2O3 continuous fiber-reinforced/NiAl composites were studied. Oxidation resulted in formation of Al2O3 external scales in a similar manner as scales formed on monolithic NiAl. The isothermal oxidation of an Al2O3/NiAl composite resulted in oxidation of the matrix along the fiber/matrix interface near the fiber ends. This oxide acted as a wedge between the fiber and the matrix, and, under cyclic oxidation conditions, led to further oxidation along the fiber lengths and eventual cracking of the composite. The oxidation behavior of composites in which the Al2O3 fibers were sputter coated with nickel prior to processing was much more severe. This was attributed to open channels around the fibers which formed during processing, most likely as a result of the diffusion of the nickel coating into the matrix.

Cyclic oxidation behavior of plasma sprayed NiCrAlY/WC-Co/cenosphere coating

NASA Astrophysics Data System (ADS)

Mathapati, Mahantayya; Ramesh M., R.; Doddamani, Mrityunjay

2018-04-01

Components working at elevated temperature like boiler tubes of coal and gas fired power generation plants, blades of gas and steam turbines etc. experience degradation owing to oxidation. Oxidation resistance of such components can be increased by developing protective coatings. In the present investigation NiCrAlY-WC-Co/Cenosphere coating is deposited on MDN 321 steel substrate using plasma spray coating. Thermo cyclic oxidation behavior of coating and substrate is studied in static air at 600 °C for 20 cycles. The thermo gravimetric technique is used to approximate the kinetics of oxidation. X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray mapping techniques are used to characterize the oxidized samples. NiCrAlY-WC-Co/Cenosphere coating exhibited lower oxidation rate in comparison to MDN 321 steel substrate. The lower oxidation rate of coating is attributed to formation of Al2O3, Cr2O3, NiO and CoWO4 oxides on the outermost surface.

Transport and Application of Heat-Activated Persulfate for In-situ Chemical Oxidation of Residual Trichloroethylene

NASA Astrophysics Data System (ADS)

Quig, L.; Johnson, G. R.

2015-12-01

Persulfate ISCO has been shown to treat a wide range of contaminants. While persulfate ISCO can be tailored to site and pollutant specific characteristics (e.g., activation via energy or catalysis), thermal activation of persulfate is particularly promising as it can be easily controlled and requires no additional reagents. A mechanistic study of the physical and chemical processes controlling the effectiveness of this remedial approach is not well documented in the literature with much therein focused on reactions in batch systems. The purpose of this research was twofold. Initial studies characterized the overall transport behavior of unactivated and thermally-activated persulfate (20, 60, and 90°C) in one-dimensional soil column systems. Finally, experiments were conducted to investigate persulfate ISCO as a remedial approach for residual-phase trichloroethylene (TCE). At all activation temperatures investigated, persulfate exhibited ideal transport behavior in miscible displacement experiments. Moment analysis of persulfate ion breakthrough curves indicated negligible interaction of persulfate with the natural sandy material. Persulfate ISCO for residual-phase TCE was characterized at two flow rates, 0.2 mL/min and 0.5 mL/min, resulting in two degrees of persulfate activation, 39.5% and 24.6%, respectively. Both ISCO soil column systems showed an initial, long-term plateau in effluent TCE concentrations indicating steady-state dissolution of pure phase TCE. Observed effluent concentrations decreased after 75 and 100 pore volumes (normalized for the measured residual NAPL fraction) compared to 110 pore volumes in the control study. Pseudo first-order reaction rate constants for the decreasing TCE concentrations equaled 0.063/hr and 0.083/hr, respectively, compared to 0.041/hr for the control. Moment analysis of the complete dissolution of TCE in the persulfate/activated persulfate remediation systems indicated approximately 33% oxidation of TCE mass present. By characterizing the overall transport behavior and application of persulfate/heat-activated persulfate in a natural porous media for the ISCO of residual nonaqueous phase liquid, this work aids in improving the implementation of persulfate ISCO systems.

Kinetics of sorption and abiotic oxidation of arsenic(III) by aquifer materials

USGS Publications Warehouse

Amirbahman, A.; Kent, D.B.; Curtis, G.P.; Davis, J.A.

2006-01-01

The fate of arsenic in groundwater depends largely on its interaction with mineral surfaces. We investigated the kinetics of As(III) oxidation by aquifer materials collected from the USGS research site at Cape Cod, MA, USA, by conducting laboratory experiments. Five different solid samples with similar specific surface areas (0.6-0.9 m2 g-1) and reductively extractable iron contents (18-26 ??mol m-2), but with varying total manganese contents (0.5-3.5 ??mol m-2) were used. Both dissolved and adsorbed As(III) and As(V) concentrations were measured with time up to 250 h. The As(III) removal rate from solution increased with increasing solid manganese content, suggesting that manganese oxide is responsible for the oxidation of As(III). Under all conditions, dissolved As(V) concentrations were very low. A quantitative model was developed to simulate the extent and kinetics of arsenic transformation by aquifer materials. The model included: (1) reversible rate-limited adsorption of As(III) onto both oxidative and non-oxidative (adsorptive) sites, (2) irreversible rate-limited oxidation of As(III), and (3) equilibrium adsorption of As(V) onto adsorptive sites. Rate constants for these processes, as well as the total oxidative site densities were used as the fitting parameters. The total adsorptive site densities were estimated based on the measured specific surface area of each material. The best fit was provided by considering one fast and one slow site for each adsorptive and oxidative site. The fitting parameters were obtained using the kinetic data for the most reactive aquifer material at different initial As(III) concentrations. Using the same parameters to simulate As(III) and As(V) surface reactions, the model predictions were compared to observations for aquifer materials with different manganese contents. The model simulated the experimental data very well for all materials at all initial As(III) concentrations. The As(V) production rate was related to the concentrations of the free oxidative surface sites and dissolved As(III), as r As(V) = k???ox [Mn(IV) OH3][AsO3] with apparent second-order rate constants of koxf??? = 6.28 ?? 10-1 and koxs??? = 1.25 ?? 10-2 M-1 s-1 for the fast and the slow oxidative sites, respectively. The As(III) removal rate decreased approximately by half for a pH increase from 4 to 7. The pH dependence was explained using the acid-base behavior of the surface oxidative sites by considering a surface pKa = 6.2 (I = 0). In the presence of excess surface adsorptive and oxidative sites, phosphate diminished the rate of As(III) removal and As(V) production only slightly due to its interaction with the oxidative sites. The observed As(III) oxidation rate here is consistent with previous observations of As(III) oxidation over short transport distances during field-scale transport experiments. The model developed here may be incorporated into groundwater transport models to predict arsenic speciation and transport in chemically heterogeneous systems. ?? 2005 Elsevier Inc. All rights reserved.

Radiation cataracts: mechanisms involved in their long delayed occurrence but then rapid progression.

PubMed

Wolf, Norman; Pendergrass, William; Singh, Narendra; Swisshelm, Karen; Schwartz, Jeffrey

2008-02-05

This study was directed to assess the DNA damage and DNA repair response to X-ray inflicted lens oxidative damage and to investigate the subsequent changes in lens epithelial cell (LEC) behavior in vivo that led to long delayed but then rapidly developing cataracts. Two-month-old C57Bl/6 female mice received 11 Grays (Gy) of soft x-irradiation to the head only. The animals' eyes were examined for cataract status in 30 day intervals by slit lamp over an 11 month period post-irradiation. LEC migration, DNA fragment, free DNA retention, and reactive oxygen species (ROS) presence were established in the living lenses with fluorescent dyes using laser scanning confocal microscopy (LSCM). The extent and removal of initial LEC DNA damage were determined by comet assay. Immunohistochemistry was used to determine the presence of oxidized DNA and the response of a DNA repair protein in the lenses. This treatment resulted in advanced cortical cataracts that developed 5-11 months post-irradiation but then appeared suddenly within a 30 day period. The initially incurred DNA strand breaks were repaired within 30 min, but DNA damage remained as shown 72 h post-irradiation by the presence of the DNA adduct, 8-hydroxyguanosine (8-OHG), and a DNA repair protein, XRCC1. This was followed months later by abnormal behavior by LEC descendant cells with abnormal differentiation and migration patterns as seen with LSCM and fluorescent dyes. The sudden development of cortical cataracts several months post-irradiation coupled with the above findings suggests an accumulation of damaged descendants from the initially x-irradiated LECs. As these cells migrate abnormally and leave acellular lens surface sites, eventually a crisis point may arrive for lens entry of environmental O(2) with resultant ROS formation that overwhelms protection by resident antioxidant enzymes and results in the coagulation of lens proteins. The events seen in this study indicate the retention and transmission of progenitor cell DNA damage in descendant LEC. The cellular and molecular events parallel those previously reported for LSCM observations in age-related cataracts.

Comprehensive kinetic model for the low-temperature oxidation of hydrocarbons

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

Gaffuri, P.; Faravelli, T.; Ranzi, E.

1997-05-01

The oxidation chemistry in the low- and intermediate-temperature regimes (600--900 K) is important and plays a significant role in the overall combustion process. Autoignition in diesel engines as well as end-gas autoignition and knock phenomena in s.i. engines are initiated at these low temperatures. The low-temperature oxidation chemistry of linear and branched alkanes is discussed with the aim of unifying their complex behavior in various experimental systems using a single detailed kinetic model. New experimental data, obtained in a pressurized flow reactor, as well as in batch- and jet-stirred reactors, are useful for a better definition of the region ofmore » cool flames and negative temperature coefficient (NTC) for pure hydrocarbons from propane up to isooctane. Thermochemical oscillations and the NTC region of the reaction rate of the low-temperature oxidation of n-heptane and isooctane in a jet-stirred flow reactor are reproduced quite well by the model, not only in a qualitative way but in terms of the experimental frequencies and intensities of cool flames. Very good agreement is also observed for fuel conversion and intermediate-species formation. Irrespective of the experimental system, the same critical reaction steps always control these phenomena. The results contribute to the definition of a limited set of fundamental kinetic parameters that should be easily extended to model heavier alkanes.« less

Size-dependent redox behavior of iron observed by in-situ single nanoparticle spectro-microscopy on well-defined model systems

NASA Astrophysics Data System (ADS)

Karim, Waiz; Kleibert, Armin; Hartfelder, Urs; Balan, Ana; Gobrecht, Jens; van Bokhoven, Jeroen A.; Ekinci, Yasin

2016-01-01

Understanding the chemistry of nanoparticles is crucial in many applications. Their synthesis in a controlled manner and their characterization at the single particle level is essential to gain deeper insight into chemical mechanisms. In this work, single nanoparticle spectro-microscopy with top-down nanofabrication is demonstrated to study individual iron nanoparticles of nine different lateral dimensions from 80 nm down to 6 nm. The particles are probed simultaneously, under same conditions, during in-situ redox reaction using X-ray photoemission electron microscopy elucidating the size effect during the early stage of oxidation, yielding time-dependent evolution of iron oxides and the mechanism for the inter-conversion of oxides in nanoparticles. Fabrication of well-defined system followed by visualization and investigation of singled-out particles eliminates the ambiguities emerging from dispersed nanoparticles and reveals a significant increase in the initial rate of oxidation with decreasing size, but the reactivity per active site basis and the intrinsic chemical properties in the particles remain the same in the scale of interest. This advance of nanopatterning together with spatially-resolved single nanoparticle X-ray absorption spectroscopy will guide future discourse in understanding the impact of confinement of metal nanoparticles and pave way to solve fundamental questions in material science, chemical physics, magnetism, nanomedicine and nanocatalysis.

Curvature in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Li, Wenxia; Hasinska, Kathy; Seabaugh, Matt; Swartz, Scott; Lannutti, John

At this point in history, curvature is inherent to the laminated components that comprise solid oxide fuel cells (SOFCs). Surprisingly, however, this fact has never been previously quantified in the literature. In addition, potential curvature changes associated with NiO reduction and re-oxidation during operation have not been investigated. In this report, an optical profilometer was employed to non-destructively quantify the surface curvature or cracking behavior observed on a large scale in industrially manufactured cells. This provides insights into the challenges that the component materials face as well as additional appreciation for why, in spite of a concerted effort to commercialize SOFC power generation, all currently manufactured SOFC stacks fail. Our results demonstrate that cracked electrolyte areas (caused by differential sintering) are flatter than uncracked regions. The height of the electrolyte surface ranged from 86 to 289 μm above the baseline following sintering. Reduction typically results in increases in curvature of up to 214 μm. Initial crack density appears to affect curvature evolution during reduction; the higher the crack density, the smaller the curvature increase following reduction at 600 °C. In general, however, we observed that the electrolyte layer is remarkably resistant to further cracking during these typographic changes. Following oxidation at 750 °C, large changes in curvature (up to 280 μm) are noted that appear to be related to the strength of the bond between the electrolyte and the underlying anode.

Copper Benzenetricarboxylate Metal-Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition.

PubMed

Lemaire, Paul C; Zhao, Junjie; Williams, Philip S; Walls, Howard J; Shepherd, Sarah D; Losego, Mark D; Peterson, Gregory W; Parsons, Gregory N

2016-04-13

Chemically functional microporous metal-organic framework (MOF) crystals are attractive for filtration and gas storage applications, and recent results show that they can be immobilized on high surface area substrates, such as fiber mats. However, fundamental knowledge is still lacking regarding initial key reaction steps in thin film MOF nucleation and growth. We find that thin inorganic nucleation layers formed by atomic layer deposition (ALD) can promote solvothermal growth of copper benzenetricarboxylate MOF (Cu-BTC) on various substrate surfaces. The nature of the ALD material affects the MOF nucleation time, crystal size and morphology, and the resulting MOF surface area per unit mass. To understand MOF nucleation mechanisms, we investigate detailed Cu-BTC MOF nucleation behavior on metal oxide powders and Al2O3, ZnO, and TiO2 layers formed by ALD on polypropylene substrates. Studying both combined and sequential MOF reactant exposure conditions, we find that during solvothermal synthesis ALD metal oxides can react with the MOF metal precursor to form double hydroxy salts that can further convert to Cu-BTC MOF. The acidic organic linker can also etch or react with the surface to form MOF from an oxide metal source, which can also function as a nucleation agent for Cu-BTC in the mixed solvothermal solution. We discuss the implications of these results for better controlled thin film MOF nucleation and growth.

Size-dependent redox behavior of iron observed by in-situ single nanoparticle spectro-microscopy on well-defined model systems.

PubMed

Karim, Waiz; Kleibert, Armin; Hartfelder, Urs; Balan, Ana; Gobrecht, Jens; van Bokhoven, Jeroen A; Ekinci, Yasin

2016-01-06

Understanding the chemistry of nanoparticles is crucial in many applications. Their synthesis in a controlled manner and their characterization at the single particle level is essential to gain deeper insight into chemical mechanisms. In this work, single nanoparticle spectro-microscopy with top-down nanofabrication is demonstrated to study individual iron nanoparticles of nine different lateral dimensions from 80 nm down to 6 nm. The particles are probed simultaneously, under same conditions, during in-situ redox reaction using X-ray photoemission electron microscopy elucidating the size effect during the early stage of oxidation, yielding time-dependent evolution of iron oxides and the mechanism for the inter-conversion of oxides in nanoparticles. Fabrication of well-defined system followed by visualization and investigation of singled-out particles eliminates the ambiguities emerging from dispersed nanoparticles and reveals a significant increase in the initial rate of oxidation with decreasing size, but the reactivity per active site basis and the intrinsic chemical properties in the particles remain the same in the scale of interest. This advance of nanopatterning together with spatially-resolved single nanoparticle X-ray absorption spectroscopy will guide future discourse in understanding the impact of confinement of metal nanoparticles and pave way to solve fundamental questions in material science, chemical physics, magnetism, nanomedicine and nanocatalysis.

New stable ternary alkaline-earth metal Pb(II) oxides: Ca / Sr / BaPb 2 O 3 and BaPbO 2

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

Li, Yuwei; Zhang, Lijun; Singh, David J.

The different but related chemical behaviors of Pb(II) oxides compared to Sn(II) oxides, and the existence of known alkali/alkali-earth metal Sn(II) ternary phases, suggest that there should be additional ternary Pb(II) oxide phases. Here, we report structure searches on the ternary alkaline-earth metal Pb(II) oxides leading to four new phases. These are two ternary Pb(II) oxides, SrPb 2O 3 and BaPb 2O 3, which have larger chemical potential stability ranges compared with the corresponding Sn(II) oxides, and additionally two other ternary Pb(II) oxides, CaPb 2O 3 and BaPbO 2, for which there are no corresponding Sn(II) oxides. Those Pb(II) oxidesmore » are stabilized by Pb-rich conditions. These structures follow the Zintl behavior and consist of basic structural motifs of (PbO 3) 4- anionic units separated and stabilized by the alkaline-earth metal ions. They show wide band gaps ranging from 2.86 to 3.12 eV, and two compounds (CaPb 2O 3 and SrPb 2O 3) show rather light hole effective masses (around 2m 0). The valence band maxima of these compounds have a Pb-6s/O-2p antibonding character, which may lead to p-type defect (or doping) tolerant behavior. This then suggests alkaline-earth metal Pb(II) oxides may be potential p-type transparent conducting oxides.« less

New stable ternary alkaline-earth metal Pb(II) oxides: Ca / Sr / BaPb 2 O 3 and BaPbO 2

DOE PAGES

Li, Yuwei; Zhang, Lijun; Singh, David J.

2017-10-16

The different but related chemical behaviors of Pb(II) oxides compared to Sn(II) oxides, and the existence of known alkali/alkali-earth metal Sn(II) ternary phases, suggest that there should be additional ternary Pb(II) oxide phases. Here, we report structure searches on the ternary alkaline-earth metal Pb(II) oxides leading to four new phases. These are two ternary Pb(II) oxides, SrPb 2O 3 and BaPb 2O 3, which have larger chemical potential stability ranges compared with the corresponding Sn(II) oxides, and additionally two other ternary Pb(II) oxides, CaPb 2O 3 and BaPbO 2, for which there are no corresponding Sn(II) oxides. Those Pb(II) oxidesmore » are stabilized by Pb-rich conditions. These structures follow the Zintl behavior and consist of basic structural motifs of (PbO 3) 4- anionic units separated and stabilized by the alkaline-earth metal ions. They show wide band gaps ranging from 2.86 to 3.12 eV, and two compounds (CaPb 2O 3 and SrPb 2O 3) show rather light hole effective masses (around 2m 0). The valence band maxima of these compounds have a Pb-6s/O-2p antibonding character, which may lead to p-type defect (or doping) tolerant behavior. This then suggests alkaline-earth metal Pb(II) oxides may be potential p-type transparent conducting oxides.« less

Effect of zinc oxide nanoparticles on dielectric behavior of nematic liquid crystal

NASA Astrophysics Data System (ADS)

Sharma, Amit; Kumar, Pankaj; Malik, Praveen

2018-05-01

In this work, phase transition and dielectric behavior of nematic liquid crystal (NLC), E7 and zinc oxide (ZnO) nanoparticles (NPs) doped nematic liquid crystals are investigated. Effect of nano-particles dispersion is analyzed and compared with the dielectric behavior of E7 and E7-ZnO. Frequency dependent dielectric permittivity at various temperatures in nematic phase for E7 and E7-ZnO sample is also studied.

Oxidation of nickel-aluminum and iron-aluminum alloys

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

Cathcart, J.V.

1984-01-01

The high-temperature oxidation behavior of several ordered alloys in the Ni-Al and Fe-Al systems is reviewed with special emphasis on Ni/sub 3/Al and NiAl. Ordering influences oxidation through its effect on the activities of the alloy components and by changing the point defect concentration in an alloy. Three categories of Ni-Al alloys are distinguished based on Al content and oxidation behavior. A characteristic feature of the oxidation of high-aluminum Ni-Al and Fe-Al alloys is the formation of voids in the substrate at the oxide-metal interface. The mechanism of void formation and its suppression by minor additions of oxygen-active elements aremore » discussed. A brief description of the effect of pre-oxidation on the reactions of Ni/sub 3/Al-base alloys in SO/sub 2//O/sub 2/ environments is also included.« less

Characterization of the reactive and dissociative behavior of transition metal oxide cluster ions in the gas phase.

PubMed

Maleknia, S; Brodbelt, J; Pope, K

1991-05-01

The reactive and dissociative behavior of molybdenum and tungsten oxide cluster ions has been studied in the gas phase using a triple quadrupole mass spectrometer. Cluster ions (MO3) n (-) were formed via a simple thermal desorption/electron capture negative ionization method, and their structures were characterized by collision-activated dissociation (CAD). Typically, the clusters fragment by losses of neutral (MO3) units. Reactions of the oxide cluster ions with ethylene oxide, cyclohexene oxide, ethylene sulfide cyclohexene sulfide, 2,3-butanedione, and 2,4-pentanedione were examined, and product ions were characterized by CAD. The clusters react with ethylene oxide by addition of ethylene oxide or net addition of oxygen, whereas the clusters react with ethylene sulfide via net addition of one or two sulfur atoms. Reactions of the clusters with the diones result in addition of one or two dione units, in some cases with dehydration.

PRELIMINARY REPORT: EFFECTS OF IRRADIATION AND THERMAL EXPOSURE ON ELASTOMERIC SEALS FOR CASK TRANSPORTATION AND STORAGE

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

Verst, C.; Skidmore, E.; Daugherty, W.

2014-05-30

A testing and analysis approach to predict the sealing behavior of elastomeric seal materials in dry storage casks and evaluate their ability to maintain a seal under thermal and radiation exposure conditions of extended storage and beyond was developed, and initial tests have been conducted. The initial tests evaluate the aging response of EPDM elastomer O-ring seals. The thermal and radiation exposure conditions of the CASTOR® V/21 casks were selected for testing as this cask design is of interest due to its widespread use, and close proximity of the seals to the fuel compared to other cask designs leading tomore » a relatively high temperature and dose under storage conditions. A novel test fixture was developed to enable compression stress relaxation measurements for the seal material at the thermal and radiation exposure conditions. A loss of compression stress of 90% is suggested as the threshold at which sealing ability of an elastomeric seal would be lost. Previous studies have shown this value to be conservative to actual leakage failure for most aging conditions. These initial results indicate that the seal would be expected to retain sealing ability throughout extended storage at the cask design conditions, though longer exposure times are needed to validate this assumption. The high constant dose rate used in the testing is not prototypic of the decreasingly low dose rate that would occur under extended storage. The primary degradation mechanism of oxidation of polymeric compounds is highly dependent on temperature and time of exposure, and with radiation expected to exacerbate the oxidation.« less

Thermite at the Nano-Scale

NASA Astrophysics Data System (ADS)

Mily, Edward Joseph, Jr.

Physical vapor deposition of thin film thermites allow for a clean avenue for probing fundamental properties of nanoenergetic materials that prove difficult for traditional powder processing. Precise control over diffusion dimensions, microstructure, and total amount of material are able to be realized with this fabrication technique and the testing of such materials provide valuable insight into how oxidation occurs. This thesis provides several examples of how existing PVD techniques can be coupled with thermite constituents to further the energetic community's understanding of how oxidation occurs in the solid state with the variation of geometric and chemical alterations. The goal of these investigations was to elucidate which material properties and mechanisms drive exothermic activity. The thermite thin films of Al/CuO, Zr/CuO, and Mg/Cuo with varied reducing metal constituents were tested under slow heating conditions. The trend of the metal variation demonstrated the importance of terminal oxide diffusion properties in either impeding or enhancing oxygen exchange. When the reducing metal forms a terminal oxide with limited oxygen diffusivity, exothermicity requires elevated activation energies to commence self-sustaining reaction. In addition to the effects of chemical variation, bilayer thicknesses were varied and found to decrease exothermic peak temperatures similar to the trends found in intermetallic thin film energetics and powder energetic materials. The thin film thermites were also subjected to extreme initiation methods via laser driven flyer plate impact ignition and high heating rate heat treatment (105 K/s). General insight into nano thermite behavior at environments characteristic of applications was sought, and similar trends discovered among slow vs rapid testing. Decreasing reaction dimensions yielded higher reactivity and diffusion barrier properties role in impacting exothermic behavior persist to into the microsecond regime. Ultimately through this work it has been shown that the process of thermite exothermicity proceeds through more than one pathway and more than the free energy of oxidation of reducing metals should be considered when describing how oxygen exchange occurs. It has been shown that these self-sustaining reactivity can be realized in the solid and.

Effect of water vapor on evolution of a thick Pt-layer modified oxide on the NiCoCrAl alloy at high temperature

NASA Astrophysics Data System (ADS)

Song, Peng; He, Xuan; Xiong, Xiping; Ma, Hongqing; Song, Qunling; Lü, Jianguo; Lu, Jiansheng

2018-03-01

To investigate the effect of water vapor on the novel Pt-containing oxide growth behavior, Pt-addition within the oxide layer on the surface of NiCoCrAl coating and furnace cycle tests were carried out at 1050 °C in air and air plus water vapor. The thick Pt-containing oxide layer on NiCoCrAl exhibits a different oxidation growth behavior compared to the conventional Pt-diffusion metallic coatings. The Pt-containing oxide after oxidation in air plus water vapor showed a much thicker oxide layer compare to the ones without Pt addition, and also presented a much better coating adhesion. During the oxidation process in air, Pt promotes the spinel (NiCr2O4) formation. However, the Cr2O3 formed in air with water vapor and fixed Pt within the complex oxide layer. The water vapor promoted the Ni and Co outer-diffusion, and combined with Pt to form CoPt compounds on the surface of the NiCoCrAl coating system.

Oxidation and corrosion resistance of candidate Stirling engine heater-head-tube alloys

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Barrett, C. A.

1984-01-01

Sixteen candidate iron base Stirling engine heater head tube alloys are evaluated in a diesel fuel fired simulator materials test rig to determine their oxidation and corrosion resistance. Sheet specimens are tested at 820 C for 3500 hr in 5 hr heating cycles. Specific weight change data and an attack parameter are used to categorize the alloys into four groups; 10 alloys show excellent for good oxidation and corrosion resistance and six alloys exhibit poor or catastrophic resistance. Metallographic, X-ray, and electron microprobe analyses aid in further characterizing the oxidation and corrosion behavior of the alloys. Alloy compositions, expecially the reactive elements aluminum, titanium, and chromium, play a major role in the excellent oxidation and corrosion behavior of the alloys. The best oxidation resistance is associated with the formation of an iron nickel aluminum outer oxide scale, an intermediate oxide scale rich in chromium and titanium, and an aluminum outer oxide scale adjacent to the metallic substrate, which exhibits a zone of internal oxidation of aluminum and to some extent titanium.

Characterization of strain relaxation behavior in Si1- x Ge x epitaxial layers by dry oxidation

NASA Astrophysics Data System (ADS)

Jang, Hyunchul; Kim, Byongju; Koo, Sangmo; Park, Seran; Ko, Dae-Hong

2017-11-01

We fabricated fully strained Si0.77Ge0.23 epitaxial layers on Si substrates and investigated their strain relaxation behaviors under dry oxidation and the effect of oxidation temperatures and times. After the oxidation process, a Ge-rich layer was formed between the oxide and the remaining Si0.77Ge0.23 layer. Using reciprocal space mapping measurements, we confirmed that the strain of the Si0.77Ge0.23 layers was efficiently relaxed after oxidation, with a maximum relaxation value of 70% after oxidation at 850 °C for 120 min. The surface of Si0.77Ge0.23 layer after strain relaxation by dry oxidation was smoother than a thick Si0.77Ge0.23 layer, which achieved a similar strain relaxation value by increasing the film thickness. Additionally, N2 annealing was performed in order to compare its effect on the relaxation compared to dry oxidation and to identify relaxation mechanisms, other than the thermally driven ones, occurring during dry oxidation.

A Model for the Oxidation of Carbon Silicon Carbide Composite Structures

NASA Technical Reports Server (NTRS)

Sullivan, Roy M.

2004-01-01

A mathematical theory and an accompanying numerical scheme have been developed for predicting the oxidation behavior of carbon silicon carbide (C/SiC) composite structures. The theory is derived from the mechanics of the flow of ideal gases through a porous solid. The result of the theoretical formulation is a set of two coupled nonlinear differential equations written in terms of the oxidant and oxide partial pressures. The differential equations are solved simultaneously to obtain the partial vapor pressures of the oxidant and oxides as a function of the spatial location and time. The local rate of carbon oxidation is determined using the map of the local oxidant partial vapor pressure along with the Arrhenius rate equation. The nonlinear differential equations are cast into matrix equations by applying the Bubnov-Galerkin weighted residual method, allowing for the solution of the differential equations numerically. The numerical method is demonstrated by utilizing the method to model the carbon oxidation and weight loss behavior of C/SiC specimens during thermogravimetric experiments. The numerical method is used to study the physics of carbon oxidation in carbon silicon carbide composites.

Novel metal-filled polyimide electrodes

NASA Technical Reports Server (NTRS)

Furtsch, T. A.; Finklea, H. O.; Taylor, L. T.

1984-01-01

Palladium-coated polyimide films are evaluated as electrochemical electrodes. The film electrodes exhibit essentially identical behavior compared to bulk palladium electrodes. In aqueous 0.5M H2SO4, current peaks due to oxide formation, oxide stripping, hydrogen adsorption, and H2 oxidation are observed. The ferri/ferrocyanide redox couple is grossly irreversible in the same electrolyte. Reversible electrochemical behavior is obtained for Fe(EDTA)(1-/2-) in 1M KCl/H2O, and for ferrocene/ferricenium in 0.1M TEAP/dimethylacetamide.

Effects of Frequency and Environment on Fatigue Behavior of an Oxide-Oxide Ceramic Matrix Composite at 1200 Deg. C

DTIC Science & Technology

2006-06-01

Mehrman investigated the effects of prior fatigue on creep behavior, and concluded that a history of prior fatigue loading increases creep life of...as reduced susceptibility to oxidation [4]. Nextel™ 720/Alumina composite (N720/A), combines the strength and creep resistance of a di- phase...studied the response to creep and cyclic loading, respectively, and showed that the presence of steam severely degrades performance at 1200ºC [35

Simulation of the induction of oxidation of low-density lipoprotein by high copper concentrations: evidence for a nonconstant rate of initiation.

PubMed

Abuja, P M; Albertini, R; Esterbauer, H

1997-06-01

Kinetic simulation can help obtain deeper insight into the molecular mechanisms of complex processes, such as lipid peroxidation (LPO) in low-density lipoprotein (LDL). We have previously set up a single-compartment model of this process, initiating with radicals generated externally at a constant rate to show the interplay of radical scavenging and chain propagation. Here we focus on the initiating events, substituting constant rate of initiation (Ri) by redox cycling of Cu2+ and Cu+. Our simulation reveals that early events in copper-mediated LDL oxidation include (1) the reduction of Cu2+ by tocopherol (TocOH) which generates tocopheroxyl radical (TocO.), (2) the fate of TocO. which either is recycled or recombines with lipid peroxyl radical (LOO.), and (3) the reoxidation of Cu+ by lipid hydroperoxide which results in alkoxyl radical (LO.) formation. So TocO., LOO., and LO. can be regarded as primordial radicals, and the sum of their formation rates is the total rate of initiation, Ri. As experimental information of these initiating events cannot be obtained experimentally, the whole model was validated experimentally by comparison of LDL oxidation in the presence and absence of bathocuproine as predicted by simulation. Simulation predicts that Ri decreases by 2 orders of magnitude during lag time. This has important consequences for the estimation of oxidation resistance in copper-mediated LDL oxidation: after consumption of tocopherol, even small amounts of antioxidants may prolong the lag phase for a considerable time.

Isothermal Damage and Fatigue Behavior of SCS-6/Timetal 21S [0/90](Sub S) Composite at 650 Deg C

NASA Technical Reports Server (NTRS)

Castelli, Michael G.

1994-01-01

The isothermal fatigue damage and life behaviors of SCS-6/Timetal 21S (0/90)s were investigated at 650 C. Strain ratcheting and degradation of the composite's static elastic modulus were carefully monitored as functions of cycles to indicate damage progression. Extensive fractographic and metallographic analyses were conducted to determine damage/failure mechanisms. Resulting fatigue lives show considerable reductions in comparison to (0) reinforced titanium matrix composites subjected to comparable conditions. Notable stiffness degradations were found to occur after the first cycle of loading, even at relatively low maximum stress levels, where cyclic lives are greater than 25,000 cycles. This was attributed to the extremely weak fiber/matrix bond which fails under relatively low transverse loads. Stiffness degradations incurred on first cycle loadings and degradations thereafter were found to increase with increasing maximum stress. Environmental effects associated with oxidation of the (90) fiber interfaces clearly played a role in the damage mechanisms as fracture surfaces revealed environment assisted matrix cracking along the (90) fibers. Metallographic analysis indicated that all observable matrix fatigue cracks initiated at the (90) fiber/matrix interfaces. Global de-bonding in the loading direction was found along the (90) fibers. No surface initiated cracks were evident and minimal if any (0) fiber cracking was visible.

Characterizing redox conditions and monitoring attenuation of selected pharmaceuticals during artificial recharge through a reactive layer.

PubMed

Valhondo, Cristina; Carrera, Jesús; Ayora, Carlos; Tubau, Isabel; Martinez-Landa, Lurdes; Nödler, Karsten; Licha, Tobias

2015-04-15

A permeable reactive layer was installed at the floor of an infiltration basin. The reactive layer comprised 1) vegetable compost to provide a sorption surface for neutral organic compounds and to release easily degradable organic matter, thus generating a sequence of redox states, and 2) minor amounts of clay and iron oxide to increase sorption of cationic and anionic species, respectively. Field application of this design was successful in generating denitrification, and manganese-, and iron-reducing conditions beneath the basin. This, together with the increase in types of sorption sites, may explain the improved removal of three of the four selected pharmaceuticals compared with their behavior prior to installation of the layer. After installation of the reactive layer, atenolol concentrations were below the detection limits in the vadose zone. Moreover, concentrations of gemfibrozil and cetirizine were reduced to 20% and 40% of their initial concentrations, respectively, after 200 h of residence time. In contrast, prior to installation of the reactive layer, the concentrations of these three pharmaceuticals in both the vadose zone and the aquifer were more than 60% of the initial concentration. Carbamazepine exhibited recalcitrant behavior both prior to and after the reactive barrier installation. Copyright © 2015 Elsevier B.V. All rights reserved.

The effect of 0.1 atomic percent zirconium on the cyclic oxidation behavior of beta-NiAl for 300 hours at 1200 C

NASA Technical Reports Server (NTRS)

Barrett, C. A.

1988-01-01

The long time effect of 0.1 at percent Zr (0.2 wt percent Zr) on the cyclic oxidation behavior of hipped beta-NiAl was studied. Oxidation testing was performed in static air at 1200 C for up to 3000 one-hour exposure cycles. Specific weight change versus time data was modeled with the COSP computer program to analyze cyclic oxidation behavior. The Zr-free stoichiometric alloy oxidized and spalled randomly to bare metal between cycles at a rate high enough to deplete Al to a low enough level that oxidation breakaway took place as nonprotective NiO replaced the alpha-Al2O3/NiAl2O4 scale as the controlling oxide. The Zr minimized this severe type of spalling maintaining the protective alpha-Al2O3 scale even out to 3000 hours for the stoichiometric alloy with no significant Al depletion. A third beta-NiAl alloy containing 0.1 at percent Zr but with 10 percent less Al than the stoichiometric alloy was also tested and showed some depletion of Al, but the protective Al2O3/NiAl2O4 was still maintained to close to 2700 hours.

TEM study on the initial oxidation of Zircaloy-4 thin foil specimens heated in a low vacuum air condition at 280-300 °C

NASA Astrophysics Data System (ADS)

Wang, Zhen; Zhou, Bang-xin; Zhu, Wei; Wen, Bang; Yao, Mei-yi; Li, Qiang; Wu, Lu; Zhang, Jin-long; Fang, Zhong-qiang

2017-04-01

As one of the important structural materials in nuclear industry, the corrosion resistance of zirconium alloy limits their in-pile application. Therefore, it is necessary to investigate the corrosion mechanism of zirconium alloys. The zirconium-oxygen reaction at the O/M interface is one of the factors that affect the oxidation process. There are few reports in this regard. Ideally, the reaction process at the O/M interface has certain relevance with the initiation oxidation of zirconium, which provided a new way to investigate the reaction process by observing the initiation oxidation behaviours. To investigate the oxidation behaviours of zirconium alloy at the initial stage, in this paper, zircaloy-4 TEM thin foil specimens in 3 mm diameter were studied by TEM observation after heating in air condition with a vacuum of 3 Pa at 280 °C, 290 °C and 300 °C for 30 min exposures. The results show that, ZrO2 begin to nucleate at a size of 3-5 nm at a high Zr/O ratio of 10.4 and oxide layer formed while Zr/O was 4.6. As a result of stress caused by the P.B ratio of Zr, slip bands formed and a bcc structure sub-oxide b-ZrOx (a = 0.51 nm) grew up along with the slip bands was observed. At both sides of b-ZrOx, two hcp structure sub-oxides having the same a-axis lattice parameter and different c-axis lattice parameter were detected.

Ultrasonic evaluation of oxidation and reduction effects on the elastic behavior and global microstructure of YBa2Cu3O7-x

NASA Technical Reports Server (NTRS)

Roth, Don J.; Deguire, Mark R.; Dolhert, Leonard E.

1991-01-01

Ultrasonic velocity measurement techniques were used to evaluate the effects of oxidation and reduction on the elastic properties, global microstructure and oxygen content of the YBa2Cu3O(7-x) ceramic superconductor for samples ranging from 70 to 90 pct. of theoretical density. Bulk density, velocity, and elastic modulus generally increased with increasing oxygen content upon oxidation, and this behavior was reversible. Velocity image patterns were similar after oxidation and reduction treatments for a 90 pct. dense sample, although the velocity value at any given point on the sample was changed following the treatments. The unchanging pattern correlated with destructive measurements showing that the spatial pore distribution (fraction and size) was not measurably altered after the treatments. Changes in superconducting behavior, crystal structure, and grain structure were observed consistent with changes in oxygen content.

PML/RARA oxidation and arsenic binding initiate the antileukemia response of As2O3.

PubMed

Jeanne, Marion; Lallemand-Breitenbach, Valérie; Ferhi, Omar; Koken, Marcel; Le Bras, Morgane; Duffort, Stéphanie; Peres, Laurent; Berthier, Caroline; Soilihi, Hassane; Raught, Brian; de Thé, Hugues

2010-07-13

As(2)O(3) cures acute promyelocytic leukemia (APL) by initiating PML/RARA oncoprotein degradation, through sumoylation of its PML moiety. However, how As(2)O(3) initiates PML sumoylation has remained largely unexplained. As(2)O(3) binds vicinal cysteines and increases reactive oxygen species (ROS) production. We demonstrate that upon As(2)O(3) exposure, PML undergoes ROS-initiated intermolecular disulfide formation and binds arsenic directly. Disulfide-linked PML or PML/RARA multimers form nuclear matrix-associated nuclear bodies (NBs), become sumoylated and are degraded. Hematopoietic progenitors transformed by an As(2)O(3)-binding PML/RARA mutant exhibit defective As(2)O(3) response. Conversely, nonarsenical oxidants elicit PML/RARA multimerization, NB-association, degradation, and leukemia response in vivo, but do not affect PLZF/RARA-driven APLs. Thus, PML oxidation regulates NB-biogenesis, while oxidation-enforced PML/RARA multimerization and direct arsenic-binding cooperate to enforce APL's exquisite As(2)O(3) sensitivity. Copyright (c) 2010 Elsevier Inc. All rights reserved.

Effect of niobium alloying level on the oxidation behavior of titanium aluminides at 850°C

NASA Astrophysics Data System (ADS)

Banu, Alexandra; Marcu, Maria; Petrescu, Simona; Ionescu, Nicolae; Paraschiv, Alexandru

2016-12-01

This work addresses the alloying of titanium aluminides used in aircraft engine applications and automobiles. The oxidation resistance behavior of two titanium aluminides of α2 + γ(Ti3Al + TiAl) and orthorhombic Ti2NbAl, recognized as candidates for high-temperature applications, was investigated by exposure of the alloys for 100 h in air. Thus, oxidation resistance was expressed as the mass gain rate, whereas surface aspects were analyzed using scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy, and the type of oxidation products was analyzed by X-ray diffraction and Raman spectroscopy. The orthorhombic Ti2NbAl alloy was embrittled, and pores and microcracks were formed as a result of oxygen diffusion through the external oxide layer formed during thermal oxidation for 100 h.

Capacitive behavior of highly-oxidized graphite

NASA Astrophysics Data System (ADS)

Ciszewski, Mateusz; Mianowski, Andrzej

2014-09-01

Capacitive behavior of a highly-oxidized graphite is presented in this paper. The graphite oxide was synthesized using an oxidizing mixture of potassium chlorate and concentrated fuming nitric acid. As-oxidized graphite was quantitatively and qualitatively analyzed with respect to the oxygen content and the species of oxygen-containing groups. Electrochemical measurements were performed in a two-electrode symmetric cell using KOH electrolyte. It was shown that prolonged oxidation causes an increase in the oxygen content while the interlayer distance remains constant. Specific capacitance increased with oxygen content in the electrode as a result of pseudo-capacitive effects, from 0.47 to 0.54 F/g for a scan rate of 20 mV/s and 0.67 to 1.15 F/g for a scan rate of 5 mV/s. Better cyclability was observed for the electrode with a higher oxygen amount.

Magnetoviscoelastic characteristics of superparamagnetic oxides (Fe, Ni) based ferrofluids

NASA Astrophysics Data System (ADS)

Katiyar, Ajay; Dhar, Purbarun; Nandi, Tandra; Das, Sarit K.

2017-08-01

Ferrofluids have been popular among the academic and scientific communities owing to their intelligent physical characteristics under external stimuli and are in fact among the first nanotechnology products to be employed in real world applications. However, studies on the magnetoviscoelastic behavior of concentrated ferrofluids, especially of superparamagnetic oxides of iron and nickel are rare. The present article comprises the formulation of magneto-colloids utilizing the three various metal oxides nanoparticles viz. Iron (II, III) oxide (Fe3O4), Iron (III) oxide (Fe2O3) and Nickel oxide (NiO) in oil. Iron (II, III) oxide based colloids demonstrate high magnetoviscous characteristics over the other oxides based colloids under external magnetic fields. The maximum magnitude of yield stress and viscosity is found to be 3.0 kPa and 2.9 kPa.s, respectively for iron (II, III) oxide based colloids at 2.6 vol% particle concentration and 1.2 T magnetic field. Experimental investigations reveal that the formulated magneto-nanocolloids are stable, even in high magnetic fields and almost reversible when exposed to rising and drop of magnetic fields of the same magnitude. Observations also reveal that the elastic behavior dominates over the viscous behavior with enhanced relaxation and creep characteristics under the magnetic field. The effect of temperature on viscosity and yield stress of magneto-nanocolloids under magnetic fields has also been discussed. Thus, the present findings have potential applications in various fields such as electromagnetic clutch and brakes of automotive, damping, sealing, optics, nanofinishing etc.

The magnetic properties of a magnetic detector using oxidized amorphous Co 95- xFe 5(BSi) x alloys

NASA Astrophysics Data System (ADS)

Ahn, S. J.; Kim, C. K.; Kim, S. J.; Choi, D. K.; O'Handley, R. C.

2000-07-01

A comparative oxidation study of several amorphous Co 75- xFe 5(BSi) 20+ x alloys was carried out. Reentrant magnetization behavior and field-induced anisotropy which are of a critical importance for a magnetic detector were obtained after oxidation of the amorphous Co-rich ribbons. During this oxidation, the ribbons develop surface oxides which are primarily nonmagnetic borosilicate or a combination of borosilicate and magnetic oxides such CoO or FeO. Beneath this lies a 100-1000 Å thick Co-rich magnetic alloy which may be either HCP or FCC in its crystal structure. The thickness of the Co-crystallized layer is determined by the type of the surface oxides. The oxidation products such as appear to affect the reentrant magnetization behavior of Co-rich amorphous alloys significantly. We have determined the amount of metalloids (a critical concentration of B and Si) which is necessary to form a continuous layer of the most thermodynamically stable oxide, in our case borosilicate, on the surface. We also observed that there is a good correlation between reentrant magnetization and the thickness of Co layer. The best reentrant M- H loop for the magnetic detector was obtained in ribbons with a surface borate-rich borosilicate since it ensures conditions such as (1) metalloid depletion in the substrate and (2) formation of oxygen impurity faults in Co grains that are required for strong reentrant magnetization behavior.

Enhanced kinetics of Al{sub 0.97}Ga{sub 0.03}As wet oxidation through the use of hydrogenation

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

Le Du, M.; Sagnes, I.; Beaudoin, G.

2006-09-11

This letter reports on a different kinetic behavior of the wet thermal oxidation process resulting in Al{sub x}O{sub y} material depending on the AlAs material growth method, molecular beam epitaxy (MBE) or metal organic vapor phase epitaxy (MOVPE). A higher oxidation rate for MOVPE-grown materia is systemically found. Considering the major role of hydrogen in the wet oxidation reaction, it is believed this observation could be linked with the higher hydrogen residual concentration in MOVPE layers. Using a hydrogen plasma, MBE-grown Al{sub 0.97}Ga{sub 0.03}As layers were hydrogened prior to oxidation. This hydrogenated sample showed a ten times enhanced oxidation ratemore » as compared to the nonhydrogenated Al{sub 0.97}Ga{sub 0.03}As sample. This behavior is mainly attributed to a hydrogen induced modification of the diffusion limited regime, enhancing the diffusion length of oxidizing species and reaction products in the oxidized layers.« less

Effect of NaCl Solution Spraying on Fatigue Lives of Smooth and Slit Specimens of 0.37% Carbon Steel

NASA Astrophysics Data System (ADS)

Makabe, Chobin; Ferdous, Md. Shafiul; Shimabukuro, Akimichi; Murdani, Anggit

2017-07-01

The fatigue crack initiation life and growth rate are affected by experimental conditions. A corrosive environment can be created in a laboratory by means of dropping salt water onto the specimen surface, spraying chloride mist into the experimental chamber, etc. In the case of smooth specimens of some metals, fatigue life is shortened and the fatigue limit disappears under such corrosive experimental conditions. In this study, the effects of intermittent spraying of 3% NaCl solution-mist on corrosion fatigue behavior were investigated. The material used was 0.37% carbon steel. This is called JIS S35C in Japan. Spraying of 3% NaCl solution-mist attacked the surface layer of the specimen. It is well known that the pitting, oxidation-reduction reaction, etc. affect the fatigue strength of metals in a corrosive environment. We carried out corrosion fatigue tests with smooth specimens, holed specimens and slit specimens. Then the effects of such specimen geometry on the fatigue strength were investigated when the NaCl solution-mist was sprayed onto the specimen surface. In the case of lower stress amplitude application in slit specimens, the fatigue life in a corrosive atmosphere was longer than that in the open air. It is discussed that the behavior is related to the crack closure which happens when the oxide builds up and clogs the crack or slit.

Role of walnuts in maintaining brain health with age.

PubMed

Poulose, Shibu M; Miller, Marshall G; Shukitt-Hale, Barbara

2014-04-01

Because of the combination of population growth and population aging, increases in the incidence of chronic neurodegenerative disorders have become a societal concern, both in terms of decreased quality of life and increased financial burden. Clinical manifestation of many of these disorders takes years, with the initiation of mild cognitive symptoms leading to behavioral problems, dementia and loss of motor functions, the need for assisted living, and eventual death. Lifestyle factors greatly affect the progression of cognitive decline, with high-risk behaviors including unhealthy diet, lack of exercise, smoking, and exposure to environmental toxins leading to enhanced oxidative stress and inflammation. Although there exists an urgent need to develop effective treatments for age-related cognitive decline and neurodegenerative disease, prevention strategies have been underdeveloped. Primary prevention in many of these neurodegenerative diseases could be achieved earlier in life by consuming a healthy diet, rich in antioxidant and anti-inflammatory phytochemicals, which offers one of the most effective and least expensive ways to address the crisis. English walnuts (Juglans regia L.) are rich in numerous phytochemicals, including high amounts of polyunsaturated fatty acids, and offer potential benefits to brain health. Polyphenolic compounds found in walnuts not only reduce the oxidant and inflammatory load on brain cells but also improve interneuronal signaling, increase neurogenesis, and enhance sequestration of insoluble toxic protein aggregates. Evidence for the beneficial effects of consuming a walnut-rich diet is reviewed in this article.

Physical and electrical characterizations of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

NASA Astrophysics Data System (ADS)

Yamada, Takahiro; Watanabe, Kenta; Nozaki, Mikito; Shih, Hong-An; Nakazawa, Satoshi; Anda, Yoshiharu; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2018-06-01

The impacts of inserting ultrathin oxides into insulator/AlGaN interfaces on their electrical properties were investigated to develop advanced AlGaN/GaN metal–oxide–semiconductor (MOS) gate stacks. For this purpose, the initial thermal oxidation of AlGaN surfaces in oxygen ambient was systematically studied by synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and atomic force microscopy (AFM). Our physical characterizations revealed that, when compared with GaN surfaces, aluminum addition promotes the initial oxidation of AlGaN surfaces at temperatures of around 400 °C, followed by smaller grain growth above 850 °C. Electrical measurements of AlGaN/GaN MOS capacitors also showed that, although excessive oxidation treatment of AlGaN surfaces over around 700 °C has an adverse effect, interface passivation with the initial oxidation of the AlGaN surfaces at temperatures ranging from 400 to 500 °C was proven to be beneficial for fabricating high-quality AlGaN/GaN MOS gate stacks.

Mechanistic and kinetic studies on the OH-initiated atmospheric oxidation of fluoranthene.

PubMed

Dang, Juan; Shi, Xiangli; Zhang, Qingzhu; Hu, Jingtian; Chen, Jianmin; Wang, Wenxing

2014-08-15

The atmospheric oxidation of polycyclic aromatic hydrocarbons (PAHs) can generate toxic derivatives which contribute to the carcinogenic potential of particulate organic matter. In this work, the mechanism of the OH-initiated atmospheric oxidation of fluoranthene (Flu) was investigated by using high-accuracy molecular orbital calculations. All of the possible oxidation pathways were discussed, and the theoretical results were compared with the available experimental observation. The rate constants of the crucial elementary reactions were evaluated by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The main oxidation products are a range of ring-retaining and ring-opening chemicals containing fluoranthols, fluoranthones, fluoranthenequinones, nitro-fluoranthenes, dialdehydes and epoxides. The overall rate constant of the OH addition reaction is 1.72×10(-11) cm(3) molecule(-1) s(-1) at 298 K and 1 atm. The atmospheric lifetime of Flu determined by OH radicals is about 0.69 days. This work provides a comprehensive investigation of the OH-initiated oxidation of Flu and should help to clarify its atmospheric conversion. Copyright © 2014 Elsevier B.V. All rights reserved.

Oxidation and reduction behaviors of a prototypic MgO-PuO2-x inert matrix fuel

NASA Astrophysics Data System (ADS)

Miwa, Shuhei; Osaka, Masahiko

2017-04-01

Oxidation and reduction behaviors of prototypic MgO-based inert matrix fuels (IMFs) containing PuO2-x were experimentally investigated by means of thermogravimetry. The oxidation and reduction kinetics of the MgO-PuO2-x specimen were determined. The oxidation and reduction rates of the MgO-PuO2-x were found to be low compared with those of PuO2-x. It is note that the changes in O/Pu ratios of MgO-PuO2-x from stoichiometry were smaller than those of PuO2-x at high oxygen partial pressure.

Corrosion behavior of oxide dispersion strengthened ferritic steels in supercritical water

NASA Astrophysics Data System (ADS)

Gao, Wenhua; Guo, Xianglong; Shen, Zhao; Zhang, Lefu

2017-04-01

The corrosion resistance of three different Cr content oxide dispersion strengthened (ODS) ferritic steels in supercritical water (SCW) and their passive films formed on the surface have been investigated. The results show that the dissolved oxygen (DO) and chemical composition have significant influence on the corrosion behavior of the ODS ferritic steels. In 2000 ppb DO SCW at 650 °C, the 14Cr-4Al ODS steel forms a tri-layer oxide film and the surface morphologies have experienced four structures. For the tri-layer oxide film, the middle layer is mainly Fe-Cr spinel and the Al is gradually enriched in the inner layer.

Initial stage oxidation on nano-trenched Si(1 0 0) surface

NASA Astrophysics Data System (ADS)

Sun, Yu; Liu, Yi-Lun; Izumi, Satoshi; Chen, Xue-Feng; Zhai, Zhi; Tian, Shao-Hua

2018-01-01

As the size of an electronic element shrinks to nanoscale, trench design of Si strongly influences the performance of related semiconductor devices. By reactive force field molecular dynamics (ReaxFF MD) simulation, the initial stage oxidation on nano-trenched Si(1 0 0) angled 60°, 90°, 120°, 150° under temperatures from 300 K to 1200 K has been studied. Inhomogeneous oxidation at the convex-concave corners of the Si surface was observed. In general, the initial oxidation process on the Si surface was that, firstly, the O atoms ballistically transported into surface, then a high O concentration induced compressive stress at the surface layers, which prevented further oxidation. Compared to the concave corner, the convex one contacted a larger volume of oxygen at the very beginning stage, leading an anisotropic absorption of O atoms. Afterwards, a critical compression was produced at both the convex and concave corners to limit the oxidation. As a result, an inhomogeneous oxide film grew on nano-trenched Si. Meanwhile, due to enhanced O transport and compression relaxation by increasing temperature, the inhomogeneous oxidation was more obvious under 1200 K. These present results explained the observed experimental phenomena on the oxidation of non-planar Si and provided an aspect on the design of nano-trenched electronic components in the semiconductor field.

Potential behavioral and pro-oxidant effects of Petiveria alliacea L. extract in adult rats.

PubMed

de Andrade, Thaís Montenegro; de Melo, Ademar Soares; Dias, Rui Guilherme Cardoso; Varela, Everton Luís Pompeu; de Oliveira, Fábio Rodrigues; Vieira, José Luís Fernandes; de Andrade, Marcieni Ataíde; Baetas, Ana Cristina; Monteiro, Marta Chagas; Maia, Cristiane do Socorro Ferraz

2012-09-28

Petiveria alliacea (Phytolaccaceae) is a perennial shrub indigenous to the Amazon Rainforest and tropical areas of Central and South America, the Caribbean, and sub-Saharan Africa. In folk medicine, Petiveria alliacea has a broad range of therapeutic properties; however, it is also associated with toxic effects. The present study evaluated the putative effects of Petiveria alliacea on the central nervous system, including locomotor activity, anxiety, depression-like behavior, and memory, and oxidative stress. Two-month-old male and female Wistar rats (n=7-10 rats/group) were administered with 900 mg/kg of hydroalcoholic extracts of Petiveria alliacea L. The behavioral assays included open-field, forced swimming, and elevated T-maze tests. The oxidative stress levels were measured in rat blood samples after behavioral assays and methemoglobin levels were measured in vitro. Consistent with previous reports, Petiveria alliacea increased locomotor activity. It also exerted previously unreported anxiolytic and antidepressant effects in behavioral tests. In the oxidative stress assays, the Petiveria alliacea extract decreased Trolox equivalent antioxidant capacity levels and increased methemoglobin levels, which was related to the toxic effects. The Petiveria alliacea extract exerted motor stimulatory and anxiolytic effects in the OF test, antidepressant effects in the FS test, and elicited memory improvement in ETM. Furthermore, the Petiveria alliacea extract also exerted pro-oxidant effects in vitro and in vivo, inhibiting the antioxidant status and increasing MetHb levels in human plasma, respectively. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

40 CFR 90.318 - Oxides of nitrogen analyzer calibration.

Code of Federal Regulations, 2010 CFR

2010-07-01

... chemiluminescent oxides of nitrogen analyzer as described in this section. (b) Initial and Periodic Interference... and periodic calibration. Prior to its initial use and monthly thereafter, or within one month prior... following table). Example calibration points (%) Acceptable for calibration? 20, 30, 40, 50, 60, 70 No...

40 CFR 90.318 - Oxides of nitrogen analyzer calibration.

Code of Federal Regulations, 2011 CFR

2011-07-01

... chemiluminescent oxides of nitrogen analyzer as described in this section. (b) Initial and Periodic Interference... and periodic calibration. Prior to its initial use and monthly thereafter, or within one month prior... following table). Example calibration points (%) Acceptable for calibration? 20, 30, 40, 50, 60, 70 No...

40 CFR 90.318 - Oxides of nitrogen analyzer calibration.

Code of Federal Regulations, 2013 CFR

2013-07-01

... chemiluminescent oxides of nitrogen analyzer as described in this section. (b) Initial and Periodic Interference... and periodic calibration. Prior to its initial use and monthly thereafter, or within one month prior... following table). Example calibration points (%) Acceptable for calibration? 20, 30, 40, 50, 60, 70 No...

10 000-hr Cyclic Oxidation Behavior of 68 High-Temperature Co-, Fe-, and Ni- Base Alloys Evaluated at 982 deg. C (1800 deg. F)

NASA Technical Reports Server (NTRS)

Barrett, Charles A.

1999-01-01

Power systems with operating temperatures in the range of 815 to 982 C (1500 to 1800 F) frequently require alloys that can operate for long times at these temperatures. A critical requirement is that these alloys have adequate oxidation resistance. The alloys used in these power systems require thousands of hours of operating life with intermittent shutdown to room temperature. Intermittent power plant shutdowns, however, offer the possibility that the protective scale will tend to spall (i.e., crack and flake off) upon cooling, increasing the rate of oxidative attack in subsequent heating cycles. Thus, it is critical that candidate alloys be evaluated for cyclic oxidation behavior. It was determined that exposing test alloys to ten 1000-hr cycles in static air at 982 10 000-hr Cyclic Oxidation Behavior of 68 High-Temperature Co-, Fe-, and Ni-Base Alloys Evaluated at 982 C (1800 F) could give a reasonable simulation of long-time power plant operation. Iron- (Fe-), nickel- (Ni-), and cobalt- (Co-) based high-temperature alloys with sufficient chromium (Cr) and/or aluminum (Al) content can exhibit excellent oxidation resistance. The protective oxides formed by these classes of alloys are typically Cr2O3 and/or Al2O3, and are usually influenced by their Cr, or Cr and Al, content. Sixty-eight Co-, Fe-, and Ni-base high-temperature alloys, typical of those used at this temperature or higher, were used in this study. At the NASA Lewis Research Center, the alloys were tested and compared on the basis of their weight change as a function of time, x-ray diffraction of the protective scale composition, and the physical appearance of the exposed samples. Although final appearance and x-ray diffraction of the final scale products were two factors used to evaluate the oxidation resistance of each alloy, the main criterion was the oxidation kinetics inferred from the specific weight change versus time data. These data indicated a range of oxidation behavior including parabolic (typical of isothermal oxidation), paralinear, linear, and mixed-linear kinetics.

Part II. Initial molecular and cellular characterization of high nitric oxide-adapted human tongue squamous cell carcinoma cell lines.

PubMed

Tarjan, Gabor; Haines, G Kenneth; Vesper, Benjamin J; Xue, Jiaping; Altman, Michael B; Yarmolyuk, Yaroslav R; Khurram, Huma; Elseth, Kim M; Roeske, John C; Aydogan, Bulent; Radosevich, James A

2011-02-01

It is not understood why some head and neck squamous cell carcinomas, despite having identical morphology, demonstrate different tumor aggressiveness, including radioresistance. High levels of the free radical nitric oxide (NO) and increased expression of the NO-producing enzyme nitric oxide synthase (NOS) have been implicated in tumor progression. We previously adapted three human tongue cancer cell lines to high NO (HNO) levels by gradually exposing them to increasing concentrations of an NO donor; the HNO cells grew faster than their corresponding untreated ("parent") cells, despite being morphologically identical. Herein we initially characterize the HNO cells and compare the biological properties of the HNO and parent cells. HNO/parent cell line pairs were analyzed for cell cycle distribution, DNA damage, X-ray and ultraviolet radiation response, and expression of key cellular enzymes, including NOS, p53, glutathione S-transferase-pi (GST-pi), apurinic/apyrimidinic endonuclease-1 (APE1), and checkpoint kinases (Chk1, Chk2). While some of these properties were cell line-specific, the HNO cells typically exhibited properties associated with a more aggressive behavior profile than the parent cells (greater S-phase percentage, radioresistance, and elevated expression of GST-pi/APE1/Chk1/Chk2). To correlate these findings with conditions in primary tumors, we examined the NOS, GST-pi, and APE1 expression in human tongue squamous cell carcinomas. A majority of the clinical samples exhibited elevated expression levels of these enzymes. Together, the results herein suggest cancer cells exposed to HNO levels can develop resistance to free radicals by upregulating protective mechanisms, such as GST-pi and APE1. These upregulated defense mechanisms may contribute to their aggressive expression profile.

Real-time sensing of epithelial cell-cell and cell-substrate interactions by impedance spectroscopy on porous substrates

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

Mondal, D.; RoyChaudhuri, C., E-mail: chirosreepram@yahoo.com; Pal, D.

2015-07-28

Oxidized porous silicon (PS) is a common topographical biocompatible substrate that potentially provides a distinct in vitro environment for better understanding of in vivo behavior. But in the reported studies on oxidized PS, cell-cell and cell-substrate interactions have been detected only by fluorescent labeling. This paper is the first attempt to investigate real-time sensing of these interactions on HaCaT cells by label-free impedance spectroscopy on oxidized PS of two pore diameters (50 and 500 nm). One of the major requirements for successful impedance spectroscopy measurement is to restrict the channeling of electric field lines through the pores. To satisfy this criterion,more » we have designed the pore depths after analyzing the penetration of the medium by using computational fluid dynamics simulation. A distributed electrical model was also developed for estimating the various cellular attributes by considering a pseudorandom distribution of pores. It is observed from the impedance measurements and from the model that the proliferation rate increases for 50 nm pores but decreases for 500 nm pores compared to that for planar substrates. The rate of decrease in cell substrate separation (h) in the initial stage is more than the rate of increase in cell-cell junction resistance (R{sub b}) corresponding to the initial adhesion phase of cells. It is observed that R{sub b} and h are higher for 50 nm pores than those for planar substrates, corresponding to the fact that substrates more conducive toward cell adhesion encourage cell-cell interactions than direct cell-substrate interactions. Thus, the impedance spectroscopy coupled with the proposed theoretical framework for PS substrates can sense and quantify the cellular interactions.« less

Nucleation and growth of oxide islands during the initial-stage oxidation of (100)Cu-Pt alloys

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

Luo, Langli; Zhou, Guangwen, E-mail: gzhou@binghamton.edu; Kang, Yihong

2015-02-14

The initial-stage oxidation of (100) Cu-Pt alloys has been examined by in situ environmental transmission electron microscopy and ex situ atomic force microscopy (AFM). It is shown that the oxidation proceeds via the nucleation and growth of Cu{sub 2}O islands that show dependence on the alloy composition and oxidation temperature. The kinetic measurements on the oxide nucleation reveal that both the nucleation density and surface coverage of Cu{sub 2}O islands can be promoted by alloying more Pt in the Cu-Pt alloys. Increasing the oxidation temperature above 700 °C results in the growth of large Cu{sub 2}O islands that transits to amore » dendritic growth morphology. The ex situ AFM studies reveal that the nucleation of oxide islands can occur on surface terraces and the subsequent oxide growth depletes local terrace Cu atoms that results in the formation of surface pits.« less

Removal of Crystal Violet by Using Reduced-Graphene-Oxide-Supported Bimetallic Fe/Ni Nanoparticles (rGO/Fe/Ni): Application of Artificial Intelligence Modeling for the Optimization Process.

PubMed

Ruan, Wenqian; Hu, Jiwei; Qi, Jimei; Hou, Yu; Cao, Rensheng; Wei, Xionghui

2018-05-22

Reduced-graphene-oxide-supported bimetallic Fe/Ni nanoparticles were synthesized in this study for the removal of crystal violet (CV) dye from aqueous solutions. This material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), Raman spectroscopy, N₂-sorption, and X-ray photoelectron spectroscopy (XPS). The influence of independent parameters (namely, initial dye concentration, initial pH, contact time, and temperature) on the removal efficiency were investigated via Box⁻Behnken design (BBD). Artificial intelligence (i.e., artificial neural network, genetic algorithm, and particle swarm optimization) was used to optimize and predict the optimum conditions and obtain the maximum removal efficiency. The zero point of charge (pH ZPC ) of rGO/Fe/Ni composites was determined by using the salt addition method. The experimental equilibrium data were fitted well to the Freundlich model for the evaluation of the actual behavior of CV adsorption, and the maximum adsorption capacity was estimated as 2000.00 mg/g. The kinetic study discloses that the adsorption processes can be satisfactorily described by the pseudo-second-order model. The values of Gibbs free energy change (Δ G ⁰), entropy change (Δ S ⁰), and enthalpy change (Δ H ⁰) demonstrate the spontaneous and endothermic nature of the adsorption of CV onto rGO/Fe/Ni composites.

Critical oxide cluster size on Si(111)

NASA Astrophysics Data System (ADS)

Shklyaev, A. A.; Aono, M.; Suzuki, T.

1999-03-01

The initial stage of oxide growth and subsequent oxide decomposition on Si(111)-7×7 at temperatures between 350 and 720°C are studied with the optical second harmonic generation for O 2 pressures ( Pox) between 5×10 -9 and 4×10 -6 Torr. The obtained pressure dependencies of the initial oxide growth rate ( Rgr) and the subsequent oxide decomposition rate are associated with the cluster-forming nature of the oxidation process. For the model of oxide cluster nucleation and growth, a scaling relationship is derived among the critical oxide cluster size, i, and the experimentally measurable values of Rgr and Pox. The critical oxide cluster size, i, thus obtained from the kinetic data increases with temperature. This correlates with an increase of desorption channels and their rates in that the competition between growth and decomposition requires more stable oxide clusters, i.e. clusters with a larger critical size, for oxide to grow at higher temperatures. The increase of i with decreasing Pox is related with a decrease of Rgr: a decreased Rgr requires critical clusters with a longer lifetime, i.e. clusters with a larger size.

The free radical chain mechanism of the initial stages of crude oil oxidation in term of SARA fractions

NASA Astrophysics Data System (ADS)

Ushakova, A.; Emelyanov, D.; Zatsepin, V.; Varfolomeev, M.

2018-05-01

The formation and decomposition of hydro-peroxides are the key stages of combustion. These stages strongly depend on the several factors accelerating or slowing this process. The aim of this work is to estimate experimentally which oil components act as inhibitors of initial stages of oxidation and which accelerate the process. The next aim is to explore the process of adsorption of oil components on the grain of rock, which turned to be also a key process in the low temperature oxidation. The work includes experimental part where differential scanning calorimeter (PDSC) experiments with pure saturates, mixtures of saturates and aromatic oil fractions and mixtures of saturates, aromatic fractions and rock samples are considered. Effects of inhibition and acceleration of the initial oxidation stages are explored.

Mechanisms for fatigue and wear of polysilicon structural thinfilms

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

Alsem, Daniel Henricus

2006-01-01

Fatigue and wear in micron-scale polysilicon structural films can severely impact the reliability of microelectromechanical systems (MEMS). Despite studies on fatigue and wear behavior of these films, there is still an on-going debate regarding the precise physical mechanisms for these two important failure modes. Although macro-scale silicon does not fatigue, this phenomenon is observed in micron-scale silicon. It is shown that for polysilicon devices fabricated in the MUMPs foundry and SUMMiT process stress-lifetime data exhibits similar trends in ambient air, shorter lifetimes in higher relative humidity environments and no fatigue failure at all in high vacuum. Transmission electron microscopy ofmore » the surface oxides of the samples show an approximate four-fold thickening of the oxide at stress concentrations after fatigue failure, but no thickening after fracture in air or after fatigue cycling in vacuo. It is found that such oxide thickening and fatigue failure (in air) occurs in devices with initial oxide thicknesses of ~4-20 nm. Such results are interpreted and explained by a reaction layer fatigue mechanism; specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure. Polysilicon specimens from the SUMMiT process are used to study wear mechanisms in micron-scale silicon in ambient air. Worn parts are examined by analytical scanning and transmission electron microscopy, while temperature changes are monitored using infrared microscopy. These results are compared with the development of values of static coefficients of friction (COF) with number of wear cycles. Observations show amorphous debris particles (~50-100 nm) created by fracture through the silicon grains (~500 nm), which subsequently oxidize, agglomerate into clusters and create plowing tracks. A nano-crystalline layer (~20-200 nm) forms at worn regions. No dislocations or extreme temperature increases are found, ruling out plasticity and temperature-assisted mechanisms. The COF reaches a steady-state value of ~0.20±0.05 after a short time at an initial value of ~0.11±0.01. Plowing tracks are found before the steady-state value of the COF is reached, suggesting only a short adhesive wear regime. This suggests a predominantly abrasive wear mechanism, controlled by fracture, which commences by the first particles created by adhesive wear.« less

Mechanisms for fatigue and wear of polysilicon structural thin films

NASA Astrophysics Data System (ADS)

Alsem, Daniel Henricus

Fatigue and wear in micron-scale polysilicon structural films can severely impact the reliability of microelectromechanical systems (MEMS). Despite studies on fatigue and wear behavior of these films, there is still an on-going debate regarding the precise physical mechanisms for these two important failure modes. Although macro-scale silicon does not fatigue, this phenomenon is observed in micron-scale silicon. It is shown that for polysilicon devices fabricated in the MUMPs foundry and SUMMiT(TM) process stress-lifetime data exhibits similar trends in ambient air, shorter lifetimes in higher relative humidity environments and no fatigue failure at all in high vacuum. Transmission electron microscopy of the surface oxides of the samples show an approximate four-fold thickening of the oxide at stress concentrations after fatigue failure, but no thickening after fracture in air or after fatigue cycling in vacuo . It is found that such oxide thickening and fatigue failure (in air) occurs in devices with initial oxide thicknesses of ˜4-20 nm. Such results are interpreted and explained by a reaction-layer fatigue mechanism; specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure. Polysilicon specimens from the SUMMiT(TM) process are used to study wear mechanisms in micron-scale silicon in ambient air. Worn parts are examined by analytical scanning and transmission electron microscopy, while temperature changes are monitored using infrared microscopy. These results are compared with the development of values of static coefficients of friction (COF) with number of wear cycles. Observations show amorphous debris particles (˜50-100 nm) created by fracture through the silicon grains (˜500 nm), which subsequently oxidize, agglomerate into clusters and create plowing tracks. A nano-crystalline layer (˜20-200 nm) forms at worn regions. No dislocations or extreme temperature increases are found, ruling out plasticity and temperature-assisted mechanisms. The COF reaches a steady-state value of ˜0.20+/-0.05 after a short time at an initial value of ˜0.11+/-0.01. Plowing tracks are found before the steady-state value of the COF is reached, suggesting only a short adhesive wear regime. This suggests a predominantly abrasive wear mechanism, controlled by fracture, which commences by the first particles created by adhesive wear.

Long Term Degradation of Resin for High Temperature Composites

NASA Technical Reports Server (NTRS)

Patekar, Kaustubh A.

2000-01-01

The durability of polymer matrix composites exposed to harsh environments is a major concern. Surface degradation and damage are observed in polyimide composites used in air at 125 to 300 C. It is believed that diffusion of oxygen into the material and oxidative chemical reactions in the matrix are responsible. Previous work has characterized and modeled diffusion behavior, and thermogravimetric analyses (TGAs) have been carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. However, the model developed using these data was not able to capture behavior seen in isothermal tests, especially those of long duration. A test program that focuses on lower temperatures and makes use of isothermal tests was undertaken to achieve a better understanding of the degradation reactions under use conditions. A new low-cost technique was developed to collect chemical degradation data for isothermal tests lasting over 200 hr in the temperature range 125 to 300 C. Results indicate complex behavior not captured by the previous TGA tests, including the presence of weight-adding reactions. Weight gain reactions dominated in the 125 to 225 C temperature range, while weight loss reactions dominated beyond 225 C. The data obtained from isothermal tests was used to develop a new model of the material behavior. This model was able to fully capture the behavior seen in the tests up to 275 C. Correlation of the current model with both isothermal data at 300 C and high rate TGA test data is mediocre. At 300 C and above, the reaction mechanisms appear to change. Attempts (which failed) to measure non-oxidative degradation indicate that oxidative reactions dominate the degradation at low temperatures. Based on this work, long term isothermal testing in an oxidative atmosphere is recommended for studying the degradation behavior of this class of materials.

Acoustic emission analysis on tensile failure of steam-side oxide scales formed on T22 alloy superheater tubes

NASA Astrophysics Data System (ADS)

Huang, Jun-Lin; Zhou, Ke-Yi; Wang, Xin-Meng; Tu, Yi-You; Xu, Jian-Qun

2014-07-01

Failure of steam-side oxide scales on boiler tubes can seriously influence the safety of coal-fired power plants. Uniaxial tensile tests employing acoustic emission (AE) monitoring were performed, in this work, to investigate the failure behavior of steam-side oxide scales on T22 alloy boiler superheater tubes. The characteristic frequency spectra of the captured AE signals were obtained by performing fast Fourier transform. Three distinct peak frequency bands, 100-170, 175-250, and 280-390 kHz, encountered in different testing stages were identified in the frequency spectra, which were confirmed to, respectively, correspond to substrate plastic deformation, oxide vertical cracking, and oxide spalling with the aid of scanning electronic microscopy observations, and can thus be used for distinguishing different oxide failure mechanisms. Finally, the critical cracking strain of the oxide scale and the interfacial shear strength of the oxide/substrate interface were estimated, which are the critical parameters urgently desired for modeling the failure behavior of steam-side oxide scales on boiler tubes of coal-fired power plants.

Oxidation Behaviors of Inconel 740H in Air and Dynamic Steam

NASA Astrophysics Data System (ADS)

Lu, Jintao; Yang, Zhen; Xu, Songqian; Zhao, Haiping; Gu, Y.

2016-08-01

Inconel 740H alloy is a candidate material for 700°C advanced ultra-supercritical (A-USC) coal-fired power plants application as superheater/reheater tube. In this work, oxidation behavior of Inconel 740H alloy was studied in static air at 750°C and 850°C, and in dynamic pure steam at 750°C, respectively. The alloy was oxidized approximately following a parabolic law in three test environment. In the static air, the oxidation rate at 850°C was about 50 times of that at the 750°C. More NiCrMn spinal and TiO2 were detected after oxidation at 850°C. Cr2O3, however, was the main oxidation product at 750°C. In the pure steam, Cr2O3 was still the main oxidation product. The oxidation rate was about 2.6 times of that in static air, but the surface roughness was much smaller and edges of oxide particles were more blurred. There was no evidence of cracks or spallation in three test environments.

Atypical kinetic behavior of chloroperoxidase-mediated oxidative halogenation of polycyclic aromatic hydrocarbons.

PubMed

Aburto, Jorge; Correa-Basurto, Jose; Torres, Eduardo

2008-12-01

We have identified an atypical kinetic behavior for the oxidative halogenation of several polycyclic aromatic hydrocarbons (PAHs) by chloroperoxidase (CPO) from Caldariomyces fumago. This behavior resembles the capacity of some members of the P450 family to simultaneously recognize several substrate molecules at their active sites. Indeed, fluorometric studies showed that PAHs exist in solution as monomers and pi-pi dimers that interact to different extents with CPO. The dissociation constants of dimerization were evaluated for every single PAH by spectrofluorometry. Furthermore, docking studies also suggest that CPO might recognize either one or two substrate molecules in its active site. The atypical sigmoidal kinetic behavior of CPO in the oxidative halogenation of PAHs is explained in terms of different kinetic models for non-heteroatomic PAHs (naphthalene, anthracene and pyrene). The results suggest that the actual substrate for CPO in this study was the pi-pi dimer for all evaluated PAHs.

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

Zhou, Xiangwen; Contescu, Cristian I.; Zhao, Xi

Mmore » atrix graphite (G) with incompletely graphitized binder used in high-temperature gas-cooled reactors (HTGRs) is commonly suspected to exhibit lower oxidation resistance in air. In order to reveal the oxidation performance, the oxidation behavior of newly developed A3-3 G at the temperature range from 500 to 950°C in air was studied and the effect of oxidation on the compressive strength of oxidized G specimens was characterized. Results show that temperature has a significant influence on the oxidation behavior of G. The transition temperature between Regimes I and II is ~700°C and the activation energy ( E a ) in Regime I is around 185 kJ/mol, a little lower than that of nuclear graphite, which indicates G is more vulnerable to oxidation. Oxidation at 550°C causes more damage to compressive strength of G than oxidation at 900°C. Comparing with the strength of pristine G specimens, the rate of compressive strength loss is 77.3% after oxidation at 550°C and only 12.5% for oxidation at 900°C. icrostructure images of SE and porosity measurement by ercury Porosimetry indicate that the significant compressive strength loss of G oxidized at 550°C may be attributed to both the uniform pore formation throughout the bulk and the preferential oxidation of the binder.« less

Correlations between the interfacial chemistry and current-voltage behavior of n-GaAs/liquid junctions

NASA Technical Reports Server (NTRS)

Tufts, Bruce J.; Casagrande, Louis G.; Lewis, Nathan S.; Grunthaner, Frank J.

1990-01-01

Correlations between the surface chemistry of etched, (100) oriented n-GaAs electrodes and their subsequent photoelectrochemical behavior have been probed by high-resolution X-ray photoelectron spectroscopy. GaAs photoanodes were chemically treated to prepare either an oxide-free near stoichiometric surface, a surface enriched in zero-valent arsenic or a substrate-oxide terminated surface. The current-voltage (I-V) behavior of each surface type was subsequently monitored in contact with several electrolytes.

The behavior of SiC and Si3N4 ceramics in mixed oxidation/chlorination environments

NASA Technical Reports Server (NTRS)

Marra, John E.; Kreidler, Eric R.; Jacobson, Nathan S.; Fox, Dennis S.

1989-01-01

The behavior of silicon-based ceramics in mixed oxidation/chlorination environments was studied. High pressure mass spectrometry was used to quantitatively identify the reaction products. The quantitative identification of the corrosion products was coupled with thermogravimetric analysis and thermodynamic equilibrium calculations run under similar conditions in order to deduce the mechanism of corrosion. Variations in the behavior of the different silicon-based materials are discussed. Direct evidence of the existence of silicon oxychloride compounds is presented.

78 FR 27374 - Workshop To Review Initial Draft Materials for the Nitrogen Oxides (NOX

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-10

... materials that will inform the development of the NO X Integrated Science Assessment (ISA) for health... ENVIRONMENTAL PROTECTION AGENCY [FRL-9812-6] Workshop To Review Initial Draft Materials for the Nitrogen Oxides (NO X ) Integrated Science Assessment (ISA) for Health Effects AGENCY: Environmental...

Oxidation kinetics of some Ni-Cr alloys.

PubMed

Baran, G

1983-01-01

Oxidation kinetics of four Ni-Cr alloys and a high-purity nickel standard was determined under isothermal conditions in an air atmosphere. In addition, weight gains of the alloys were measured during a simulated pre-oxidation treatment. The alloys' behavior suggests that mechanisms of oxidation vary with temperature and alloy composition.

Treatment of Ammonia Nitrogen Wastewater in Low Concentration by Two-Stage Ozonization.

PubMed

Luo, Xianping; Yan, Qun; Wang, Chunying; Luo, Caigui; Zhou, Nana; Jian, Chensheng

2015-09-23

Ammonia nitrogen wastewater (about 100 mg/L) was treated by two-stage ozone oxidation method. The effects of ozone flow rate and initial pH on ammonia removal were studied, and the mechanism of ammonia nitrogen removal by ozone oxidation was discussed. After the primary stage of ozone oxidation, the ammonia removal efficiency reached 59.32% and pH decreased to 6.63 under conditions of 1 L/min ozone flow rate and initial pH 11. Then, the removal efficiency could be over 85% (the left ammonia concentration was lower than 15 mg/L) after the second stage, which means the wastewater could have met the national discharge standards of China. Besides, the mechanism of ammonia removal by ozone oxidation was proposed by detecting the products of the oxidation: ozone oxidation directly and ·OH oxidation; ammonia was mainly transformed into NO₃(-)-N, less into NO₂(-)-N, not into N₂.

Magnetoresistance enhancement in specular, bottom-pinned, Mn83Ir17 spin valves with nano-oxide layers

NASA Astrophysics Data System (ADS)

Veloso, A.; Freitas, P. P.; Wei, P.; Barradas, N. P.; Soares, J. C.; Almeida, B.; Sousa, J. B.

2000-08-01

Bottom-pinned Mn83Ir17 spin valves with enhanced specular scattering were fabricated, showing magnetoresistance (MR) values up to 13.6%, lower sheet resistance R□ and higher ΔR□. Two nano-oxide layers (NOL) are grown on both sides of the CoFe/Cu/CoFe spin valve structure by natural oxidation or remote plasma oxidation of the starting CoFe layer. Maximum MR enhancement is obtained after just 1 min plasma oxidation. Rutherford backscattering analysis shows that a 15±2 Å oxide layer grows at the expense of the initial (prior to oxidation) CoFe layer, with ˜12% reduction of the initial 40 Å CoFe thickness. X-ray reflectometry indicates that Kiessig fringes become better defined after NOL growth, indicating smoother inner interfaces, in agreement with the observed decrease of the spin valve ferromagnetic Néel coupling.

Electromagnetic shielding effectiveness studies on polyaniline/CSA-WO3 composites at KU band frequencies

NASA Astrophysics Data System (ADS)

Sastry, D. Nagesa; Revanasiddappa, M.; Suresh, T.; Kiran, Y. T. Ravi; Raghavendra, S. C.

2018-05-01

This paper highlights the Electromagnetic Interference (EMI) Shielding Effectiveness and electromagnetic wave attenuation behavior of Polyaniline/Camphor Sulphonic Acid (PANI-CSA) - tungsten oxide (WO3) composites. Insitu polymerization of aniline monomer with camphor sulphonic acid (CSA) as a dopant was carried out in the presence of ammonium persulphate an oxidizing agent to synthesize PANI-CSA tungsten oxide composites (PANI/CSA-WO3) by chemical oxidation method. The composites have been synthesized with various compositions (10, 20, 30, 40 and 50 wt %) of tungsten oxide in PANI/CSA matrix. The EMI shielding measurements were carried out in the broad microwave spectrum covering the frequency range from 12 to 18 GHz (Ku-Band). The results show the influence of tungsten oxide in PANI/CSA over the EMI shielding Effectiveness. The composites have shown excellent microwave absorption behavior confirmed by the EMI Shielding Effectiveness values of the order of -15 to -16 dB.

Oxidation of nickel-aluminum and iron-aluminum alloys

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

Cathcart, J.V.

1985-01-01

The high-temperature oxidation behavior of several ordered alloys in the Ni-Al and Fe-Al systems is reviewed with special emphasis on Ni/sub 3/Al and NiAl. Ordering influences oxidation through its effect on the activities of the alloy components and by changing the point defect concentration in an alloy. Three categories of Ni-Al alloys are distinguished based on Al content and oxidation behavior. A characteristic feature of the oxidation of high-aluminum Ni-Al and Fe-Al alloys is the formation of voids in the substrate at the oxidate-metal interface. The mechanism of void formation and its suppression by minor additions of oxygen-active elements ismore » discussed. A brief description of the effect of preoxidation on the reactions of Ni/sub 3/Al-base alloys in SO/sub 2//O/sub 2/ environments is also included. 51 references, 14 figures, 1 table.« less

Molybdenum, molybdenum oxides, and their electrochemistry.

PubMed

Saji, Viswanathan S; Lee, Chi-Woo

2012-07-01

The electrochemical behaviors of molybdenum and its oxides, both in bulk and thin film dimensions, are critical because of their widespread applications in steels, electrocatalysts, electrochromic materials, batteries, sensors, and solar cells. An important area of current interest is electrodeposited CIGS-based solar cells where a molybdenum/glass electrode forms the back contact. Surprisingly, the basic electrochemistry of molybdenum and its oxides has not been reviewed with due attention. In this Review, we assess the scattered information. The potential and pH dependent active, passive, and transpassive behaviors of molybdenum in aqueous media are explained. The major surface oxide species observed, reversible redox transitions of the surface oxides, pseudocapacitance and catalytic reduction are discussed along with carefully conducted experimental results on a typical molybdenum glass back contact employed in CIGS-based solar cells. The applications of molybdenum oxides and the electrodeposition of molybdenum are briefly reviewed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Differentiating Behavior Initiation and Maintenance: Theoretical Framework and Proof of Concept

ERIC Educational Resources Information Center

Voils, Corrine I.; Gierisch, Jennifer M.; Yancy, William S., Jr.; Sandelowski, Margarete; Smith, Rose; Bolton, Jamiyla; Strauss, Jennifer L.

2014-01-01

Although many interventions are effective for health behavior initiation, maintenance has proven elusive. Interventions targeting maintenance often extend the duration with which initiation content is delivered or the duration of follow-up without intervention. We posit that health behavior initiation and maintenance require separate psychological…

Electrokinesis is a microbial behavior that requires extracellular electron transport

PubMed Central

Harris, H. W.; El-Naggar, M. Y.; Bretschger, O.; Ward, M. J.; Romine, M. F.; Obraztsova, A. Y.; Nealson, K. H.

2009-01-01

We report a previously undescribed bacterial behavior termed electrokinesis. This behavior was initially observed as a dramatic increase in cell swimming speed during reduction of solid MnO2 particles by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The same behavioral response was observed when cells were exposed to small positive applied potentials at the working electrode of a microelectrochemical cell and could be tuned by adjusting the potential on the working electrode. Electrokinesis was found to be different from both chemotaxis and galvanotaxis but was absent in mutants defective in electron transport to solid metal oxides. Using in situ video microscopy and cell tracking algorithms, we have quantified the response for different strains of Shewanella and shown that the response correlates with current-generating capacity in microbial fuel cells. The electrokinetic response was only exhibited by a subpopulation of cells closest to the MnO2 particles or electrodes. In contrast, the addition of 1 mM 9,10-anthraquinone-2,6-disulfonic acid, a soluble electron shuttle, led to increases in motility in the entire population. Electrokinesis is defined as a behavioral response that requires functional extracellular electron transport and that is observed as an increase in cell swimming speeds and lengthened paths of motion that occur in the proximity of a redox active mineral surface or the working electrode of an electrochemical cell. PMID:20018675

Decreasing Striatopallidal Pathway Function Enhances Motivation by Energizing the Initiation of Goal-Directed Action

PubMed Central

Carvalho Poyraz, Fernanda; Holzner, Eva; Bailey, Matthew R.; Meszaros, Jozsef; Kenney, Lindsay; Kheirbek, Mazen A.

2016-01-01

Altered dopamine D2 receptor (D2R) binding in the striatum has been associated with abnormal motivation in neuropsychiatric disorders, including schizophrenia. Here, we tested whether motivational deficits observed in mice with upregulated D2Rs (D2R-OEdev mice) are reversed by decreasing function of the striatopallidal “no-go” pathway. To this end, we expressed the Gαi-coupled designer receptor hM4D in adult striatopallidal neurons and activated the receptor with clozapine-N-oxide (CNO). Using a head-mounted miniature microscope we confirmed with calcium imaging in awake mice that hM4D activation by CNO inhibits striatopallidal function measured as disinhibited downstream activity in the globus pallidus. Mice were then tested in three operant tasks that address motivated behavior, the progressive ratio task, the progressive hold-down task, and outcome devaluation. Decreasing striatopallidal function in the dorsomedial striatum or nucleus accumbens core enhanced motivation in D2R-OEdev mice and control littermates. This effect was due to increased response initiation but came at the cost of goal-directed efficiency. Moreover, response vigor and the sensitivity to changes in reward value were not altered. Chronic activation of hM4D by administering CNO for 2 weeks in drinking water did not affect motivation due to a tolerance effect. However, the acute effect of CNO on motivation was reinstated after discontinuing chronic treatment for 48 h. Used as a therapeutic approach, striatopallidal inhibition should consider the risk of impairing goal-directed efficiency and behavioral desensitization. SIGNIFICANCE STATEMENT Motivation involves a directional component that allows subjects to efficiently select the behavior that will lead to an optimal outcome and an activational component that initiates and maintains the vigor and persistence of actions. Striatal output pathways modulate motivated behavior, but it remains unknown how these pathways regulate specific components of motivation. Here, we found that the indirect pathway controls response initiation without affecting response vigor or the sensitivity to changes in the reward outcome. A specific enhancement in the activational component of motivation, however, can come at the cost of goal-directed efficiency when a sustained response is required to obtain the goal. These data should inform treatment strategies for brain disorders with impaired motivation such as schizophrenia and Parkinson's disease. PMID:27251620

Decreasing Striatopallidal Pathway Function Enhances Motivation by Energizing the Initiation of Goal-Directed Action.

PubMed

Carvalho Poyraz, Fernanda; Holzner, Eva; Bailey, Matthew R; Meszaros, Jozsef; Kenney, Lindsay; Kheirbek, Mazen A; Balsam, Peter D; Kellendonk, Christoph

2016-06-01

Altered dopamine D2 receptor (D2R) binding in the striatum has been associated with abnormal motivation in neuropsychiatric disorders, including schizophrenia. Here, we tested whether motivational deficits observed in mice with upregulated D2Rs (D2R-OEdev mice) are reversed by decreasing function of the striatopallidal "no-go" pathway. To this end, we expressed the Gαi-coupled designer receptor hM4D in adult striatopallidal neurons and activated the receptor with clozapine-N-oxide (CNO). Using a head-mounted miniature microscope we confirmed with calcium imaging in awake mice that hM4D activation by CNO inhibits striatopallidal function measured as disinhibited downstream activity in the globus pallidus. Mice were then tested in three operant tasks that address motivated behavior, the progressive ratio task, the progressive hold-down task, and outcome devaluation. Decreasing striatopallidal function in the dorsomedial striatum or nucleus accumbens core enhanced motivation in D2R-OEdev mice and control littermates. This effect was due to increased response initiation but came at the cost of goal-directed efficiency. Moreover, response vigor and the sensitivity to changes in reward value were not altered. Chronic activation of hM4D by administering CNO for 2 weeks in drinking water did not affect motivation due to a tolerance effect. However, the acute effect of CNO on motivation was reinstated after discontinuing chronic treatment for 48 h. Used as a therapeutic approach, striatopallidal inhibition should consider the risk of impairing goal-directed efficiency and behavioral desensitization. Motivation involves a directional component that allows subjects to efficiently select the behavior that will lead to an optimal outcome and an activational component that initiates and maintains the vigor and persistence of actions. Striatal output pathways modulate motivated behavior, but it remains unknown how these pathways regulate specific components of motivation. Here, we found that the indirect pathway controls response initiation without affecting response vigor or the sensitivity to changes in the reward outcome. A specific enhancement in the activational component of motivation, however, can come at the cost of goal-directed efficiency when a sustained response is required to obtain the goal. These data should inform treatment strategies for brain disorders with impaired motivation such as schizophrenia and Parkinson's disease. Copyright © 2016 the authors 0270-6474/16/365989-14$15.00/0.

Fe-Ti-oxide textures and microstructures in shear zones from oceanic gabbros at Atlantis Bank, Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Till, Jessica; Morales, Luiz F. G.; Rybacki, Erik

2016-04-01

Ocean drilling expeditions at several oceanic core complexes formed at slow- and ultra-slow-spreading ridges have recovered cores containing numerous zones of oxide-rich gabbros containing ilmenite and magnetite. In these cores, high modal concentrations of Fe-Ti-oxides are systematically associated with high-temperature plastic deformation features in silicates. We present observations of Fe-Ti-oxide mineral structures and textural characteristics from a series of oxide-rich shear zones from Atlantis Bank (ODP Site 735B) on the Southwest Indian Ridge aimed at determining how oxide mineral abundances relate to strain localization. Fe-Ti-oxide minerals in undeformed oxide gabbros and in highly deformed samples from natural shear zones generally have morphologies characteristic of crystallized melt, including highly cuspate grains and low dihedral angles. Anisotropy of magnetic susceptibility in oxide-rich shear zones is very strong, with fabrics mainly characterized by strong magnetic foliations parallel to the macroscopic foliation. Crystallographic preferred orientations (CPO) in magnetite are generally weak, with occasionally well-defined textures. Ilmenite typically displays well-developed CPOs, however, the melt-like ilmenite grain shapes indicate that at least part of the crystallographic texture results from oriented ilmenite growth during post-deformation crystallization. The oxides are hypothesized to have initially been present as isolated pockets of trapped melt (intercumulus liquid) in a load-bearing silicate framework. Progressive plastic deformation of silicate phases at high-temperature mainly produced two features: (i) elongated melt pockets, which crystallized to form strings of opaque minerals and (ii), interconnected networks of melt regions. The latter lead to intense strain localization of the rock, which appears as oxide-rich mylonites in the samples. In some samples, abundant low-angle grain boundaries in both magnetite and ilmenite suggest that deformation may have continued after crystallization of the late melt, imposing a weak strain on the oxides. Recent experimental deformation results indicate that magnetite and ilmenite should be weaker than most mafic silicates under anhydrous conditions. However, melt-like oxide morphologies observed in Atlantis Bank shear zones indicate that the redistribution of Fe-Ti-oxide melts may have more influence on the strength and strain localization behavior of oceanic gabbros than their solid-state rheology.

Modeling of thermo-mechanical and irradiation behavior of mixed oxide fuel for sodium fast reactors

NASA Astrophysics Data System (ADS)

Karahan, Aydın; Buongiorno, Jacopo

2010-01-01

An engineering code to model the irradiation behavior of UO2-PuO2 mixed oxide fuel pins in sodium-cooled fast reactors was developed. The code was named fuel engineering and structural analysis tool (FEAST-OXIDE). FEAST-OXIDE has several modules working in coupled form with an explicit numerical algorithm. These modules describe: (1) fission gas release and swelling, (2) fuel chemistry and restructuring, (3) temperature distribution, (4) fuel-clad chemical interaction and (5) fuel-clad mechanical analysis. Given the fuel pin geometry, composition and irradiation history, FEAST-OXIDE can analyze fuel and cladding thermo-mechanical behavior at both steady-state and design-basis transient scenarios. The code was written in FORTRAN-90 program language. The mechanical analysis module implements the LIFE algorithm. Fission gas release and swelling behavior is described by the OGRES and NEFIG models. However, the original OGRES model has been extended to include the effects of joint oxide gain (JOG) formation on fission gas release and swelling. A detailed fuel chemistry model has been included to describe the cesium radial migration and JOG formation, oxygen and plutonium radial distribution and the axial migration of cesium. The fuel restructuring model includes the effects of as-fabricated porosity migration, irradiation-induced fuel densification, grain growth, hot pressing and fuel cracking and relocation. Finally, a kinetics model is included to predict the clad wastage formation. FEAST-OXIDE predictions have been compared to the available FFTF, EBR-II and JOYO databases, as well as the LIFE-4 code predictions. The agreement was found to be satisfactory for steady-state and slow-ramp over-power accidents.

Redox inactive metal ion triggered N-dealkylation by an iron catalyst with dioxygen activation: a lesson from lipoxygenases.

PubMed

Zhang, Jisheng; Wang, Yujuan; Luo, Nengchao; Chen, Zhuqi; Wu, Kangbing; Yin, Guochuan

2015-06-07

Utilization of dioxygen as the terminal oxidant at ambient temperature is always a challenge in redox chemistry, because it is hard to oxidize a stable redox metal ion like iron(III) to its high oxidation state to initialize the catalytic cycle. Inspired by the dioxygenation and co-oxidase activity of lipoxygenases, herein, we introduce an alternative protocol to activate the sluggish iron(III) species with non-redox metal ions, which can promote its oxidizing power to facilitate substrate oxidation with dioxygen, thus initializing the catalytic cycle. In oxidations of N,N-dimethylaniline and its analogues, adding Zn(OTf)2 to the [Fe(TPA)Cl2]Cl catalyst can trigger the amine oxidation with dioxygen, whereas [Fe(TPA)Cl2]Cl alone is very sluggish. In stoichiometric oxidations, it has also been confirmed that the presence of Zn(OTf)2 can apparently improve the electron transfer capability of the [Fe(TPA)Cl2]Cl complex. Experiments using different types of substrates as trapping reagents disclosed that the iron(IV) species does not occur in the catalytic cycle, suggesting that oxidation of amines is initialized by electron transfer rather than hydrogen abstraction. Combined experiments from UV-Vis, high resolution mass spectrometry, electrochemistry, EPR and oxidation kinetics support that the improved electron transfer ability of iron(III) species originates from its interaction with added Lewis acids like Zn(2+) through a plausible chloride or OTf(-) bridge, which has promoted the redox potential of iron(III) species. The amine oxidation mechanism was also discussed based on the available data, which resembles the co-oxidase activity of lipoxygenases in oxidative dealkylation of xenobiotic metabolisms where an external electron donor is not essential for dioxygen activation.

Oxidation of DNA bases, deoxyribonucleosides and homopolymers by peroxyl radicals.

PubMed Central

Simandan, T; Sun, J; Dix, T A

1998-01-01

DNA base oxidation is considered to be a key event associated with disease initiation and progression in humans. Peroxyl radicals (ROO. ) are important oxidants found in cells whose ability to react with the DNA bases has not been characterized extensively. In this paper, the products resulting from ROO. oxidation of the DNA bases are determined by gas chromatography/MS in comparison with authentic standards. ROO. radicals oxidize adenine and guanine to their 8-hydroxy derivatives, which are considered biomarkers of hydroxyl radical (HO.) oxidations in cells. ROO. radicals also oxidize adenine to its hydroxylamine, a previously unidentified product. ROO. radicals oxidize cytosine and thymine to the monohydroxy and dihydroxy derivatives that are formed by oxidative damage in cells. Identical ROO. oxidation profiles are observed for each base when exposed as deoxyribonucleosides, monohomopolymers and base-paired dihomopolymers. These results have significance for the development, utilization and interpretation of DNA base-derived biomarkers of oxidative damage associated with disease initiation and propagation, and support the idea that the mutagenic potential of N-oxidized bases, when generated in cellular DNA, will require careful evaluation. Adenine hydroxylamine is proposed as a specific molecular probe for the activity of ROO. in cellular systems. PMID:9761719

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

NASA Astrophysics Data System (ADS)

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

2015-10-01

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

Oxidative Recession, Sulfur Release, and Al203 Spallation for Y-Doped Alloys

NASA Technical Reports Server (NTRS)

Smialek, James L.

2001-01-01

Second-order spallation phenomena have been noted for Y-doped Rene'N5 after long term oxidation at 1150 degrees C. The reason for this behavior has not been conclusively identified. A mass equivalence analysis has shown that the surface recession resulting from oxidation has the potential of releasing about 0.15 monolayer of sulfur for every 1 mg/sq cm of oxygen reacted for an alloy containing 5 ppmw of sulfur. This amount is significant in comparison to levels that have been shown to result in first-order spallation behavior for undoped alloys. Oxidative recession is therefore speculated to be a contributing source of sulfur and second-order spallation for Y-doped alloys.

Sources and Contributions of Oxygen During Microbial Pyrite Oxidation: the Triple Oxygen Isotopes of Sulfate

NASA Astrophysics Data System (ADS)

Ziegler, K.; Coleman, M. L.; Mielke, R. E.; Young, E. D.

2008-12-01

The triple isotopes of oxygen (Δ17O' = δ17O'-0.528 × δ18O' using logarithmic deltas) can trace the oxygen sources of sulfate produced during sulfide oxidation, an important biogeochemical process on Earth's surface and possibly also on Mars [1]. δ18OSO4 compositions are determined by the isotopic selectivity of the mechanism(s) responsible for their changes, and the δ18O value of the reactants (O2 vs. H2O). The relative proportional importance and contribution of each of those sources and mechanisms, as well as their associated isotopic fractionations, are not well understood. We are investigating the use of Δ 17O as a quantitative and qualitative tracer for the different processes and oxygen sources involved in sulfate production. Δ17O signatures are distinct fingerprints of these reservoirs, independent of fractionation factors that can be ambiguous. We conducted controlled abiotic and biotic (Acidithiobacillus ferrooxidans, A.f.) laboratory experiments in which water was spiked with 18O, allowing us to quantify the sources of sulfate oxygen and therefore the processes attending sulfate formation. Results of this Δ17O tracer study show that A.f. microbes initiate pyrite S-oxidation within hours of exposure, and that sulfate is produced from ~90% atmospheric oxygen. This initial lag-phase (< 3 days) is characterized by subtle and multiple changes in oxygen source and contribution that is likely due to the adjustment of the microbial metabolism from S to Fe2+-oxidation. A more detailed understanding of the microbial mechanisms and behavior in the initial lag-phase will aid in the understanding of the ecological conditions required for microbial populations to establish and survive. An exponential phase of growth, facilitated by microbial Fe2+-oxidation, follows. The source of sulfate rapidly switches to abiotic sulfide oxidation during exponential growth and the source of oxygen switches from atmospheric O2 to nearly ~100% water. Pending acquisition of complimentary chemistry data (in progress), we interpret our isotope data to indicate that the biotic fractionation factor ɛ18OSO4-O2 of at least ~ -25 to - 35‰ is augmented by microbially induced kinetic fractionation; it is larger than expected based on published equilibrium values [2,3,4]. Our inferred ɛ18OSO4-H2O of at least ~+10‰ is similar to some reported values. These new insights into the close links between microbial life cycle and sources of sulfate oxygen during sulfide oxidation, and their oxygen isotopic expressions, will help elucidate the role of microbial oxidation in natural systems. If microbial populations in natural systems remain in a perpetual lag-phase due to constrains of chemistry, atmospheric oxygen will imprint its isotopic signature onto sulfate deposits. Ultimately, such data could be used as biosignatures on Early Earth or Mars. [1] Brunner and Coleman (2008) EPSL 270, 63-72. [2] Balci et al. (2007) GCA 71, 3796-3811. [3] Pisapia et al. (2007) GCA 71, 2474-2490. [4] Taylor et al. (1984) GCA 48, 2669-2678.

Effects of composition and testing conditions on oxidation behavior of four cast commercial nickel-base superalloys

NASA Technical Reports Server (NTRS)

Lowell, C. E.; Probst, H. B.

1974-01-01

Four cast nickel-base superalloys were oxidized at 1000 and 1100 C for times up to 100 hr in static air and a Mach 1 gas stream. The oxidation resistance was judged by weight change, metal thickness loss, depletion-zone formation, and oxide formation and morphology. The alloys which formed mostly nickel aluminate (NiAl2O4) and aluminum oxide (Al2O3) (B-1900, VIA, and to a lesser extent 713C) were more oxidation resistant. Poorer oxidation resistance was associated with the appearance of chromium sesquioxide (Cr2O3) and chromite spinel (738X). Refractory metal content had little effect on oxidation resistance. Refractory metals appeared in the scale as tapiolite (NiM2O6, where M represents the refractory metal). Thermal cycling in static air appeared to supply sufficient data for the evaluation of oxidation resistance, especially for alloys which form oxides of low volatility. For alloys of higher chromium levels with high propensities toward forming a chromium-bearing scale of higher volatility, testing under conditions of high gas velocity is necessary to assess fully the behavior of the alloy.

Apple juice improved behavioral but not cognitive symptoms in moderate-to-late stage Alzheimer's disease in an open-label pilot study.

PubMed

Remington, Ruth; Chan, Amy; Lepore, Alicia; Kotlya, Elizabeth; Shea, Thomas B

2010-06-01

Preclinical studies demonstrate that apple juice exerts multiple beneficial effects including reduction of central nervous system oxidative damage, suppression of Alzheimer's disease (AD) hallmarks, improved cognitive performance, and organized synaptic signaling. Herein, we initiated an open-label clinical trial in which 21 institutionalized individuals with moderate-to-severe AD consumed 2 4-oz glasses of apple juice daily for 1 month. Participants demonstrated no change in the Dementia Rating Scale, and institutional caregivers reported no change in Alzheimer's Disease Cooperative Study (ADCS)-Activities of Daily Living (ADL) in this brief study. However, caregivers reported an approximate 27% (P < .01) improvement in behavioral and psychotic symptoms associated with dementia as quantified by the Neuropsychiatric Inventory, with the largest changes in anxiety, agitation, and delusion. This pilot study suggests that apple juice may be a useful supplement, perhaps to augment pharmacological approaches, for attenuating the decline in mood that accompanies progression of AD, which may also reduce caregiver burden.

Dynamic behavior of reactive aluminum nanoparticle-fluorinated acrylic (AlFA) polymer composites

NASA Astrophysics Data System (ADS)

Crouse, Christopher A.; White, Brad; Spowart, Jonathan E.

2011-06-01

The dynamic behavior of aluminum nanoparticle-fluorinated acrylic (AlFA) composite materials has been explored under high strain rates. Cylindrical pellets of the AlFA composite materials were mounted onto copper sabots and impacted against a rigid anvil at velocities between 100 and 400 m/s utilizing a Taylor gas gun apparatus to achieve strain rates on the order of 104 /s. A framing camera was used to record the compaction and reaction events that occurred upon contact of the pellet with the anvil. Under both open air and vacuum environments the AlFA composites demonstrated high reactivity suggesting that the particles are primarily reacting with the fluorinated matrix. We hypothesize, based upon the compaction history of these materials, that reaction is initiated when the oxide shells on the aluminum nanoparticles are broken due an interparticle contact deformation process. We have investigated this hypothesis through altering the particle loading in the AlFA composites as well as impact velocities. This data and the corresponding trends will be presented in detail.

Initial Corrosion Behavior and Mechanism of PCB-HASL in Typical Outdoor Environments in China

NASA Astrophysics Data System (ADS)

Ding, Kangkang; Xiao, Kui; Dong, Chaofang; Zou, Shiwen; Yi, Pan; Li, Xiaogang

2015-11-01

A long-term (1, 3, and 6 months) outdoor exposure test was performed for lead-free hot air solder leveling printed circuit boards (PCB-HASL) in typical environments in China and the corrosion behavior and mechanism of outdoor PCB-HASL were investigated. In a dry environment PCB-HASL corroded slightly, because of the protective effect of surface oxide films. Corrosion spread from places where dust particles were deposited or mold spores were adsorbed. Under the combined effects of humidity and contamination, large amounts of granular corrosion products with a loose structure were generated, greatly reducing the protective effect of the Sn layer. Furthermore, protection of the edges of the plates was poor, and corrosion products from these regions migrated rapidly on the FR-4 board. When a 12 V electrical bias was applied, Sn and Cu migrated simultaneously. In the electrochemical migration process the effect of humidity was much more critical than that of contamination.

The effect of thermal reduction on the photoluminescence and electronic structures of graphene oxides.

PubMed

Chuang, C-H; Wang, Y-F; Shao, Y-C; Yeh, Y-C; Wang, D-Y; Chen, C-W; Chiou, J W; Ray, Sekhar C; Pong, W F; Zhang, L; Zhu, J F; Guo, J H

2014-04-10

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120-180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp(2) bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG.

New Creep-Resistant Cast Alloys with Improved Oxidation Resistance in Water Vapor at 650–800°C

DOE PAGES

Dryepondt, Sebastien; Pint, Bruce A.; Maziasz, Philip J.

2015-08-13

Cast stainless steel CF8C-Plus (19wt%Cr/12%Ni) has excellent creep properties, but limited oxidation resistance above 700 C in environments containing H 2O. One strategy to improve the alloy oxidation performance is to increase the Cr and Ni concentration. Two new alloys, with, respectively, 21wt%Cr 15wt%Ni and 22wt%Cr 17.5wt%Ni were therefore developed and their long-term oxidation behaviors in humid air were compared with the oxidation behavior of five other cast alloys. Also, at 650 C and 700 C, all the alloys formed internal Cr-rich nodules, and outer nodules or layers rich in Fe and Ni, but they grew a protective Cr-rich innermore » layer over time. At 750 C, the lower alloyed steels such as CF8C-Plus showed large metal losses, but the two new alloys still exhibited a protective oxidation behavior. The 21Cr 15Ni alloy was severely oxidized in locations at 800 C, but that was not the case for the 22Cr 17.5Ni alloy. Thus, the two new modified alloys represent a potential operating temperature gain of, respectively, 50 C and 100 C in aggressive environments compared with the CF8C-Plus alloy.« less

A theoretical study of OH radical-initiated atmospheric oxidation of 1-chloronaphthalene

NASA Astrophysics Data System (ADS)

Cui, Yang; Ding, Zhezheng; Sun, Yanhui; Yi, Yayi; Xu, Fei; Zhang, Qingzhu; Wang, Wenxing

2018-05-01

OH-initiated atmospheric oxidation mechanism of 1-chloronaphthalene (1-CN) was investigated using density functional theory (DFT) calculations. The oxidation is predicted to be initiated by OH addition to the α-positions, and the additions to C4 and C5 are more favorable. 1-CN-OH adducts tend to react with ambient O2 to produce peroxy intermediates, followed by intramolecular H-shifts producing C10H7OCl and diketone or unimolecular ring closure forming methyl glyoxal and Cl-substituted phthalaldialdehyde. Despite that the rate constants are influenced by the tunneling factors, intramolecular H-shift reactions are suggested to be more favorable. The OH-determined lifetime of 1-CN is 0.62 days.

Study of nickel hydroxide electrodes. 2: Oxidation products of nickel (2) hydroxides

NASA Technical Reports Server (NTRS)

Bode, H.; Demelt, K.; White, J.

1986-01-01

Pure phases of some oxidized Ni oxides were prepared galvanimetrically with the Ni(2) hydroxide electrode of an alkaline battery. The crystallographic data of these phases, their chemical behavior, and conditions of transition were studied.

The oxidation of aluminum at high temperature studied by Thermogravimetric Analysis and Differential Scanning Calorimetry.

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

Coker, Eric Nicholas

2013-10-01

The oxidation in air of high-purity Al foil was studied as a function of temperature using Thermogravimetric Analysis with Differential Scanning Calorimetry (TGA/DSC). The rate and/or extent of oxidation was found to be a non-linear function of the temperature. Between 650 and 750 ÀC very little oxidation took place; at 850 ÀC oxidation occurred after an induction period, while at 950 ÀC oxidation occurred without an induction period. At oxidation temperatures between 1050 and 1150 ÀC rapid passivation of the surface of the aluminum foil occurred, while at 1250 ÀC and above, an initial rapid mass increase was observed, followedmore » by a more gradual increase in mass. The initial rapid increase was accompanied by a significant exotherm. Cross-sections of oxidized specimens were characterized by scanning electron microscopy (SEM); the observed alumina skin thicknesses correlated qualitatively with the observed mass increases.« less

Tungsten species in natural ferromanganese oxides related to its different behavior from molybdenum in oxic ocean

NASA Astrophysics Data System (ADS)

Kashiwabara, Teruhiko; Takahashi, Yoshio; Marcus, Matthew A.; Uruga, Tomoya; Tanida, Hajime; Terada, Yasuko; Usui, Akira

2013-04-01

The tungsten (W) species in marine ferromanganese oxides were investigated by wavelength dispersive XAFS method. We found that the W species are in distorted Oh symmetry in natural ferromanganese oxides. The host phase of W is suggested to be Mn oxides by μ-XRF mapping. We also found that the W species forms inner-sphere complexes in hexavalent state and distorted Oh symmetry on synthetic ferrihydrite, goethite, hematite, and δ-MnO2. The molecular-scale information of W indicates that the negatively-charged WO42- ion mainly adsorbs on the negatively-charged Mn oxides phase in natural ferromanganese oxides due to the strong chemical interaction. In addition, preferential adsorption of lighter W isotopes is expected based on the molecular symmetry of the adsorbed species, implying the potential significance of the W isotope systems similar to Mo. Adsorption experiments of W on synthetic ferrihydrite and δ-MnO2 were also conducted. At higher equilibrium concentration, W exhibits behaviors similar to Mo on δ-MnO2 due to their formations of inner-sphere complexes. On the other hand, W shows a much larger adsorption on ferrihydrite than Mo. This is due to the formation of the inner- and outer-sphere complexes for W and Mo on ferrihydrite, respectively. Considering the lower equilibrium concentration such as in oxic seawater, however, the enrichment of W into natural ferromanganese oxides larger than Mo may be controlled by the different stabilities of their inner-sphere complexes on the Mn oxides. These two factors, (i) the stability of inner-sphere complexes on the Mn oxides and (ii) the mode of attachment on ferrihydrite (inner- or outer-sphere complex), are the causes of the different behaviors of W and Mo on the surface of the Fe/Mn (oxyhydr)oxides.

Observed secondary organic aerosol (SOA) and organic nitrate yields from NO3 oxidation of isoprene

NASA Astrophysics Data System (ADS)

Rollins, A. W.; Fry, J. L.; Kiendler-Scharr, A.; Wooldridge, P. J.; Brown, S. S.; Fuchs, H.; Dube, W.; Mensah, A.; Tillmann, R.; Dorn, H.; Brauers, T.; Cohen, R. C.

2008-12-01

Formation of organic nitrates and secondary organic aerosol (SOA) from the NO3 oxidation of isoprene has been studied at atmospheric concentrations of VOC (10 ppb) and oxidant (<100 ppt NO3) in the presence of ammonium sulfate seed aerosol in the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich. Cavity Ringdown (CaRDS) and thermal dissociation - CaRDS measurements of NO3 and N2O5 as well as Thermal Dissociation - Laser Induced Fluorescence (TD-LIF) detection of alkyl nitrates (RONO2) and Aerodyne Aerosol Mass Spectrometer (AMS) measurements of aerosol composition were all used in comparison to a Master Chemical Mechanism (MCM) based chemical kinetics box model to quantify the product yields from two stages in isoprene oxidation. We find significant yields of organic nitrate formation from both the initial isoprene + NO3 reaction (71%) as well as from the reaction of NO3 with the initial oxidation products (30% - 60%). Under these low concentration conditions (~1 μg / m3), measured SOA production was greater than instrument noise only for the second oxidation step. Based on the modeled chemistry, we estimate an SOA mass yield of 10% (relative to isoprene mass reacted) for the reaction of the initial oxidation products with NO3. This yield is found to be consistent with the estimated saturation concentration (C*) of the presumed gas products of the doubly oxidized isoprene, where both oxidations lead to the addition of nitrate, carbonyl, and hydroxyl groups.

Reaction Intermediates of Quinol Oxidation in a Photoactivatable System that Mimics Electron Transfer in the Cytochrome bc1 Complex

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

Cape, Jonathan L.; Bowman, Michael K.; Kramer, David M.

2005-03-30

Current competing models for the two-electron oxidation of quinol (QH{sub 2}) at the cytochrome bc{sub 1} complex and related complexes have different requirements for the reaction intermediate. At present, the intermediate species of the enzymatic oxidation process have not been observed or characterized, probably due to their transient nature. Here, we use a biomimetic oxidant, Ru(bpy){sub 2}(pbim)(PF6)2 (bpy = 2,2'-dipyridyl, pbim = 2-(2-benzimidazolate)pyridine) in an aprotic medium to probe the oxidation of the ubiquinol analogue, 2,3-dimethoxy-5-methyl-1,4-benzoquinol (UQH{sub 2}-0), an the plastoquinol analogue, trimethyl-1,4-benzoquinol (TMQH{sub 2}-0), using time-resolved and steady state spectroscopic techniques. This system qualitatively reproduces key features observed duringmore » ubiquinol oxidation by the mitochondrial cytochrome bc1 complex. Comparison of isotope dependent activation properties in the native and synthetic systems, as well as, analysis of the time-resolved direct-detection electron para magnetic resonance signals in the synthetic system allows us to conclude that: (1) the initial and rate-limiting step in quinol oxidation, both in the biological and biomimetic systems, involves electron and proton transfer, probably via a proton coupled electron transfer mechanism; (2) a neutral semiquinone intermediate is formed in the biomimetic system; and (3) oxidation of the QH*/QH{sub 2} couple for UQH{sub 2}-0, but not TMQH{sub 2}-0, exhibits a non-classical primary deuterium kinetic isotope effect on its Arrhenius activation energy ({Delta}G{sup TS}), where {Delta}G{sup TS} for the protiated form is larger than for the deuterated form. The same behavior is observed during steady state turnover of the cyt bc{sub 1} complex using ubiquinol, but not plastoquinol, as a substrate, leading to the conclusion that similar chemical pathways are involved in both systems. The synthetic system is an unambiguous n=1 electron acceptor and it is thus inferred that sequential oxidation of ubiquinol (by two sequential n=1 processes) is more rapid than a truly concerted (n=2) oxidation in the cyt bc{sub 1} complex.« less

Flyweight 3D Graphene Scaffolds with Microinterface Barrier-Derived Tunable Thermal Insulation and Flame Retardancy.

PubMed

Zhang, Qiangqiang; Hao, Menglong; Xu, Xiang; Xiong, Guoping; Li, Hui; Fisher, Timothy S

2017-04-26

In this article, flyweight three-dimensional (3D) graphene scaffolds (GSs) have been demonstrated with a microinterface barrier-derived thermal insulation and flame retardancy characteristics. Such 3D GSs were fabricated by a modified hydrothermal method and a unidirectional freeze-casting process with hierarchical porous microstructures. Because of high porosity (99.9%), significant phonon scattering, and strong π-π interaction at the interface barriers of multilayer graphene cellular walls, the GSs demonstrate a sequence of multifunctional properties simultaneously, such as lightweight density, thermal insulating characteristics, and outstanding mechanical robustness. At 100 °C, oxidized GSs exhibit a thermal conductivity of 0.0126 ± 0.0010 W/(m K) in vacuum. The thermal conductivity of oxidized GSs remains relatively unaffected despite large-scale deformation-induced densification of the microstructures, as compared to the behavior of reduced GSs (rGSs) whose thermal conductivity increases dramatically under compression. The contrasting behavior of oxidized GSs and rGSs appears to derive from large differences in the intersheet contact resistance and varying intrinsic thermal conductivity between reduced and oxidized graphene sheets. The oxidized GSs also exhibit excellent flame retardant behavior and mechanical robustness, with only 2% strength decay after flame treatment. In a broader context, this work demonstrates a useful strategy to design porous nanomaterials with a tunable heat conduction behavior through interface engineering at the nanoscale.

Astaxanthin ameliorates aluminum chloride-induced spatial memory impairment and neuronal oxidative stress in mice.

PubMed

Al-Amin, Md Mamun; Reza, Hasan Mahmud; Saadi, Hasan Mahmud; Mahmud, Waich; Ibrahim, Abdirahman Adam; Alam, Musrura Mefta; Kabir, Nadia; Saifullah, A R M; Tropa, Sarjana Tarannum; Quddus, A H M Ruhul

2016-04-15

Aluminum chloride induces neurodegenerative disease in animal model. Evidence suggests that aluminum intake results in the activation of glial cells and generation of reactive oxygen species. By contrast, astaxanthin is an antioxidant having potential neuroprotective activity. In this study, we investigate the effect of astaxanthin on aluminum chloride-exposed behavioral brain function and neuronal oxidative stress (OS). Male Swiss albino mice (4 months old) were divided into 4 groups: (i) control (distilled water), (ii) aluminum chloride, (iii) astaxanthin+aluminum chloride, and (iv) astaxanthin. Two behavioral tests; radial arm maze and open field test were conducted, and OS markers were assayed from the brain and liver tissues following 42 days of treatment. Aluminum exposed group showed a significant reduction in spatial memory performance and anxiety-like behavior. Moreover, aluminum group exhibited a marked deterioration of oxidative markers; lipid peroxidation (MDA), nitric oxide (NO), glutathione (GSH) and advanced oxidation of protein products (AOPP) in the brain. To the contrary, co-administration of astaxanthin and aluminum has shown improved spatial memory, locomotor activity, and OS. These results indicate that astaxanthin improves aluminum-induced impaired memory performances presumably by the reduction of OS in the distinct brain regions. We suggest a future study to determine the underlying mechanism of astaxanthin in improving aluminum-exposed behavioral deficits. Copyright © 2016 Elsevier B.V. All rights reserved.

Biphasic Kinetic Behavior of E. coli WrbA, an FMN-Dependent NAD(P)H:Quinone Oxidoreductase

PubMed Central

Kishko, Iryna; Harish, Balasubramanian; Zayats, Vasilina; Reha, David; Tenner, Brian; Beri, Dhananjay; Gustavsson, Tobias; Ettrich, Rüdiger; Carey, Jannette

2012-01-01

The E. coli protein WrbA is an FMN-dependent NAD(P)H:quinone oxidoreductase that has been implicated in oxidative defense. Three subunits of the tetrameric enzyme contribute to each of four identical, cavernous active sites that appear to accommodate NAD(P)H or various quinones, but not simultaneously, suggesting an obligate tetramer with a ping-pong mechanism in which NAD departs before oxidized quinone binds. The present work was undertaken to evaluate these suggestions and to characterize the kinetic behavior of WrbA. Steady-state kinetics results reveal that WrbA conforms to a ping-pong mechanism with respect to the constancy of the apparent Vmax to Km ratio with substrate concentration. However, the competitive/non-competitive patterns of product inhibition, though consistent with the general class of bi-substrate reactions, do not exclude a minor contribution from additional forms of the enzyme. NMR results support the presence of additional enzyme forms. Docking and energy calculations find that electron-transfer-competent binding sites for NADH and benzoquinone present severe steric overlap, consistent with the ping-pong mechanism. Unexpectedly, plots of initial velocity as a function of either NADH or benzoquinone concentration present one or two Michaelis-Menten phases depending on the temperature at which the enzyme is held prior to assay. The effect of temperature is reversible, suggesting an intramolecular conformational process. WrbA shares these and other details of its kinetic behavior with mammalian DT-diaphorase, an FAD-dependent NAD(P)H:quinone oxidoreductase. An extensive literature review reveals several other enzymes with two-plateau kinetic plots, but in no case has a molecular explanation been elucidated. Preliminary sedimentation velocity analysis of WrbA indicates a large shift in size of the multimer with temperature, suggesting that subunit assembly coupled to substrate binding may underlie the two-plateau behavior. An additional aim of this report is to bring under wider attention the apparently widespread phenomenon of two-plateau Michaelis-Menten plots. PMID:22952804

Influence of low concentration V and Co oxide doping on the dissolution behaviors of simplified nuclear waste glasses

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

Lu, Xiaonan; Neeway, James J.; Ryan, Joseph V.

Transition metal oxides are commonly present in nuclear waste and they can alter the structure, property and especially dissolution behaviors of the glasses used for waste immobilization. In this paper, we investigated vanadium and cobalt oxide induced structural and properties changes, especially dissolution behaviors, of International Simple Glass (ISG), a model nuclear waste glass system. Static chemical durability tests were performed at 90 °C with a pH value of 7 and a surface-area-to-solution-volume of 200 m-1 for 112 days on three glasses: ISG, ISG doped with 0.5 mol% Co2O3, and ISG doped with 2.0 mol% V2O5. ICP-MS was used tomore » analyze the dissolved ion concentrations. It was found that doping with vanadium and cobalt oxide, even at the low doping concentration, significantly reduced the extent of the ISG glass dissolution. Differential Scanning Calorimetry (DSC) analysis showed that vanadium oxide doping reduced the glass transition temperature (Tg) while cobalt oxide did not significantly change the Tg of ISG. X-ray diffraction (XRD), Raman spectrometry and scanning electron microscopy (SEM) were used to analyze the glass samples before and after corrosion to understand the phase and microstructure changes.« less

Intrathecal oxotremorine affects formalin-induced behavior and spinal nitric oxide synthase immunoreactivity in rats.

PubMed

Przewlocka, B; Mika, J; Capone, F; Machelska, H; Pavone, F

1999-03-01

The present research was undertaken to investigate, by behavioral and immunohistochemical methods, the effects of intrathecal (i.th.) injection of the muscarinic agonist oxotremorine on the response to the long-lasting nociceptive stimulus induced by injection of formalin into the rat hind paw. Formalin injection induced a biphasic, pain-induced behavioral response (paw jerks), as well as an increase in the number of nitric oxide (NO) synthase-labeled neurons in laminae I-III, IV, and X, but not in laminae V-VI. Oxotremorine (0.1-10 ng, i.th.) inhibited paw-jerk frequency in both phases of formalin-induced behavior. The immunohistochemical results showed that i.th.-injected oxotremorine differently affected the level of NO synthase in lumbar part of the spinal cord: no change or increase after the dose of 1 ng, and a significant reduction of nitric oxide synthase neurons after the higher dose (10 ng). These results evidenced a role of cholinergic system in the modulation of tonic pain and in nitric oxide synthase expression at the spinal cord level, which further suggests that these two systems could be involved in phenomena induced by long-lasting nociceptive stimulation.

Insights into dynamic processes of cations in pyrochlores and other complex oxides

DOE PAGES

Uberuaga, Blas Pedro; Perriot, Romain

2015-08-26

Complex oxides are critical components of many key technologies, from solid oxide fuel cells and superionics to inert matrix fuels and nuclear waste forms. In many cases, understanding mass transport is important for predicting performance and, thus, extensive effort has been devoted to understanding mass transport in these materials. However, most work has focused on the behavior of oxygen while cation transport has received relatively little attention, even though cation diffusion is responsible for many phenomena, including sintering, radiation damage evolution, and deformation processes. Here, we use accelerated molecular dynamics simulations to examine the kinetics of cation defects in onemore » class of complex oxides, A₂B₂O₇ pyrochlore. In some pyrochlore chemistries, B cation defects are kinetically unstable, transforming to A cation defects and antisites at rates faster than they can diffuse. When this occurs, transport of B cations occurs through defect processes on the A sublattice. Further, these A cation defects, either interstitials or vacancies, can interact with antisite disorder, reordering the material locally, though this process is much more efficient for interstitials than vacancies. Whether this behavior occurs in a given pyrochlore depends on the A and B chemistry. Pyrochlores with a smaller ratio of cation radii exhibit this complex behavior, while those with larger ratios exhibit direct migration of B interstitials. Similar behavior has been reported in other complex oxides such as spinels and perovskites, suggesting that this coupling of transport between the A and B cation sublattices, while not universal, occurs in many complex oxide.« less

Lithium ameliorates sleep deprivation-induced mania-like behavior, hypothalamic-pituitary-adrenal (HPA) axis alterations, oxidative stress and elevations of cytokine concentrations in the brain and serum of mice.

PubMed

Valvassori, Samira S; Resende, Wilson R; Dal-Pont, Gustavo; Sangaletti-Pereira, Heron; Gava, Fernanda F; Peterle, Bruna R; Carvalho, André F; Varela, Roger B; Dal-Pizzol, Felipe; Quevedo, João

2017-06-01

The goal of the present study was to investigate the effects of lithium administration on behavior, oxidative stress parameters and cytokine levels in the periphery and brain of mice subjected to an animal model of mania induced by paradoxical sleep deprivation (PSD). Male C57 mice were treated with saline or lithium for 7 days. The sleep deprivation protocol started on the 5th day during for the last 36 hours of the treatment period. Immediately after the sleep deprivation protocol, animals locomotor activity was evaluated and serum and brain samples was extracted to evaluation of corticosterone and adrenocorticotropic hormone circulating levels, oxidative stress parameters and citokynes levels. The results showed that PSD induced hyperactivity in mice, which is considered a mania-like behavior. PSD increased lipid peroxidation and oxidative damage to DNA, as well as causing alterations to antioxidant enzymes in the frontal cortex, hippocampus and serum of mice. In addition, PSD increased the levels of cytokines in the brains of mice. Treatment with lithium prevented the mania-like behavior, oxidative damage and cytokine alterations induced by PSD. Improving our understanding of oxidative damage in biomolecules, antioxidant mechanisms and the inflammatory system - alterations presented in the animal models of mania - is important in helping us to improve our knowledge concerning the pathophysiology of BD, and the mechanisms of action employed by mood stabilizers. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

N-Acetylcysteine Reverses Anxiety and Oxidative Damage Induced by Unpredictable Chronic Stress in Zebrafish.

PubMed

Mocelin, Ricieri; Marcon, Matheus; D'ambros, Simone; Mattos, Juliane; Sachett, Adrieli; Siebel, Anna M; Herrmann, Ana P; Piato, Angelo

2018-06-06

There is accumulating evidence on the use of N-acetylcysteine (NAC) in the treatment of patients with neuropsychiatric disorders. As a multi-target drug and a glutathione precursor, NAC is a promising molecule in the management of stress-related disorders, for which there is an expanding field of research investigating novel therapies targeting oxidative pathways. The deleterious effects of chronic stress in the central nervous system are a result of glutamatergic hyperactivation, glutathione (GSH) depletion, oxidative stress, and increased inflammatory response, among others. The aim of this study was to investigate the effects of NAC in zebrafish submitted to unpredictable chronic stress (UCS). Animals were initially stressed or not for 7 days, followed by treatment with NAC (1 mg/L, 10 min) or vehicle for 7 days. UCS decreased the number of entries and time spent in the top area in the novel tank test, which indicate increased anxiety levels. It also increased reactive oxygen species (ROS) levels and lipid peroxidation (TBARS) while decreased non-protein thiols (NPSH) and superoxide dismutase (SOD) activity. NAC reversed the anxiety-like behavior and oxidative damage observed in stressed animals. Additional studies are needed to investigate the effects of this agent on glutamatergic modulation and inflammatory markers related to stress. Nevertheless, our study adds to the existing body of evidence supporting the clinical evaluation of NAC in mood disorders, anxiety, post-traumatic stress disorder, and other conditions associated with stress.

Surface conditions of Nitinol wires, tubing, and as-cast alloys. The effect of chemical etching, aging in boiling water, and heat treatment.

PubMed

Shabalovskaya, S A; Anderegg, J; Laab, F; Thiel, P A; Rondelli, G

2003-04-15

The surface conditions of Nitinol wires and tubing were evaluated with the use of X-ray photoelectron spectroscopy, high-resolution Auger spectroscopy, electron backscattering, and scanning-electron microscopy. Samples were studied in the as-received state as well as after chemical etching, aging in boiling water, and heat treatment, and compared to a mechanically polished 600-grit-finish Nitinol surface treated similarly. General regularities in surface behavior induced by the examined surface treatments are similar for wires, tubing, and studied as-cast alloy, though certain differences in surface Ni concentration were observed. Nitinol wires and tubing from various suppliers demonstrated great variability in Ni surface concentration (0.5-15 at.%) and Ti/Ni ratio (0.4-35). The wires in the as-received state, with the exception of those with a black oxide originating in the processing procedure, revealed nickel and titanium on the surface in both elemental and oxidized states, indicating a nonpassive surface. Shape-setting heat treatment at 500 degrees C for 15 min resulted in tremendous increase in the surface Ni concentration and complete Ni oxidation. Preliminary chemical etching and boiling in water successfully prevented surface enrichment in Ni, initially resulting from heat treatment. A stoichiometric uniformly amorphous TiO(2) oxide generated during chemical etching and aging in boiling water was reconstructed at 700 degrees C, revealing rutile structure. Copyright 2003 Wiley Periodicals, Inc.

Acetobacter pasteurianus metabolic change induced by initial acetic acid to adapt to acetic acid fermentation conditions.

PubMed

Zheng, Yu; Zhang, Renkuan; Yin, Haisong; Bai, Xiaolei; Chang, Yangang; Xia, Menglei; Wang, Min

2017-09-01

Initial acetic acid can improve the ethanol oxidation rate of acetic acid bacteria for acetic acid fermentation. In this work, Acetobacter pasteurianus was cultured in ethanol-free medium, and energy production was found to increase by 150% through glucose consumption induced by initial acetic acid. However, oxidation of ethanol, instead of glucose, became the main energy production pathway when upon culturing ethanol containing medium. Proteome assay was used to analyze the metabolism change induced by initial acetic acid, which provided insight into carbon metabolic and energy regulation of A. pasteurianus to adapt to acetic acid fermentation conditions. Results were further confirmed by quantitative real-time PCR. In summary, decreased intracellular ATP as a result of initial acetic acid inhibition improved the energy metabolism to produce more energy and thus adapt to the acetic acid fermentation conditions. A. pasteurianus upregulated the expression of enzymes related to TCA and ethanol oxidation to improve the energy metabolism pathway upon the addition of initial acetic acid. However, enzymes involved in the pentose phosphate pathway, the main pathway of glucose metabolism, were downregulated to induce a change in carbon metabolism. Additionally, the enhancement of alcohol dehydrogenase expression promoted ethanol oxidation and strengthened the acetification rate, thereby producing a strong proton motive force that was necessary for energy production and cell tolerance to acetic acid.

Effects of Cr Content and Surface Finishes on Oxidation Behaviors of Austenitic Fe-Cr-Ni Alloys Exposed in Supercritical Water (SCW)

NASA Astrophysics Data System (ADS)

Xing, Bo

The scope of this work was to characterize the corrosion resistance of candidate austenitic alloys in supercritical water for the use of the fuel cladding material within the Canadian supercritical water-cooled reactor (SCWR) concept. A series of Commercial austenitic stainless steels (SS) and alloys were exposed to supercritical water for different exposure times up to 500 hours. Two surface finishes were applied - a coarse grinding with 120 grit abrasive or polishing with either 1200 grit or 0.05 microm alumina suspension. Gravimetric measurements and electron microscopy techniques were used to evaluate the oxidation behaviors of tested alloys. The superior corrosion resistance of alloy 310S was benefited from a critical Cr content of 25 wt.%. The surface finish played a significant role to vary the oxidation behavior of alloys containing slightly less than the critical Cr content. However, Oxide exfoliation was observed on low Cr content alloys.

Thermomechanical and Thermochemical Behavior of a Hafnium-20 Percent Tantalum Alloy. Ph.D. Thesis - North Carolina State Univ., Raleigh

NASA Technical Reports Server (NTRS)

Howell, J. P.

1971-01-01

An investigation was conducted to determine the thermomechanical and thermochemical behavior of a high temperature, oxidation resistant, hafnium-20 percent tantalum alloy. The elastic and shear moduli of this alloy were determined in air up to 1000 C and in vacuum up to 2000 C using a mechanical resonance technique. The internal friction of the alloy was measured up to temperatures greater than 1400 C. Room temperature stress-strain behavior of the oxidized and unoxidized alloy was established. The effect of annealing on the elastic and shear moduli of the extruded rod material was investigated. The martensitic-type phase transformation occurring in the alloy was studied using hot stage metallography and electron microscopy. Static oxidation tests were conducted on the alloy at temperatures from 1000 C to 1700 C with weight gain measurements made as a function of time and temperatures. Surface morphology studies were conducted on the oxide coatings formed at the different temperatures using scanning electron microscopy and X-ray diffraction techniques.

Reactive solute transport in an acidic stream: Experimental pH increase and simulation of controls on pH, aluminum, and iron

USGS Publications Warehouse

Broshears, R.E.; Runkel, R.L.; Kimball, B.A.; McKnight, Diane M.; Bencala, K.E.

1996-01-01

Solute transport simulations quantitatively constrained hydrologic and geochemical hypotheses about field observations of a pH modification in an acid mine drainage stream. Carbonate chemistry, the formation of solid phases, and buffering interactions with the stream bed were important factors in explaining the behavior of pH, aluminum, and iron. The precipitation of microcrystalline gibbsite accounted for the behavior of aluminum; precipitation of Fe(OH)3 explained the general pattern of iron solubility. The dynamic experiment revealed limitations on assumptions that reactions were controlled only by equilibrium chemistry. Temporal variation in relative rates of photoreduction and oxidation influenced iron behavior. Kinetic limitations on ferrous iron oxidation and hydrous oxide precipitation and the effects of these limitations on field filtration were evident. Kinetic restraints also characterized interaction between the water column and the stream bed, including sorption and desorption of protons from iron oxides at the sediment-water interface and post-injection dissolution of the precipitated aluminum solid phase.

On spray drying of oxidized corn starch cross-linked gelatin microcapsules for drug release.

PubMed

Dang, Xugang; Yang, Mao; Shan, Zhihua; Mansouri, Shahnaz; May, Bee K; Chen, Xiaodong; Chen, Hui; Woo, Meng Wai

2017-05-01

Spray-dried gelatin/oxidized corn starch (G/OCS) microcapsules were produced for drug release application. The prepared microcapsules were characterized through a scanning electron microscope (SEM) picture and thermogravimetric analysis (TGA). The swelling characteristics of the G/OCS microcapsules and release properties of vitamin C were then investigated. The results from structural analysis indicated that the presence of miscibility and compatibility between oxidized corn starch and gelatin, and exhibits high thermal stability up to 326°C. The swelling of G/OCS microcapsules increased with increasing pH and reduced with decreasing ionic strength, attributed to the cross-linking between gelatin and oxidized corn starch, ionization of functional groups. Vitamin C release characteristic revealed controlled release behavior in the first 3h of contact with an aqueous medium. This release behavior was independent of the swelling behavior indicating the potential of the encapsulating matrix to produce controlled release across a spectrum of pH environment. Copyright © 2016 Elsevier B.V. All rights reserved.

Zinc adsorption effects on arsenite oxidation kinetics at the birnessite-water interface

USGS Publications Warehouse

Power, L.E.; Arai, Y.; Sparks, D.L.

2005-01-01

Arsenite is more toxic and mobile than As(V) in soil and sediment environments, and thus it is advantageous to explore factors that enhance oxidation of As(III) to As(V). Previous studies showed that manganese oxides, such as birnessite (??-MnO2), directly oxidized As(III). However, these studies did not explore the role that cation adsorption has on As(III) oxidation. Accordingly, the effects of adsorbed and nonadsorbed Zn on arsenite (As(III)) oxidation kinetics at the birnessite-water interface were investigated using batch adsorption experiments (0.1 g L-1; pH 4.5 and 6.0; I = 0.01 M NaCl). Divalent Zn adsorption on synthetic ??-MnO 2 in the absence of As(III) increased with increasing pH and caused positive shifts in electrophoretic mobility values at pH 4-6, indirectly suggesting inner-sphere Zn adsorption mechanisms. Arsenite was readily oxidized on birnessite in the absence of Zn. The initial As(III) oxidation rate constant decreased with increasing pH from 4.5 to 6.0 and initial As(III) concentrations from 100 to 300 ??M. Similar pH and initial As(III) concentration effects were observed in systems when Zn was present (i.e., presorbed Zn prior to As(III) addition and simultaneously added Zn-As(III) systems), but As(III) oxidation reactions were suppressed compared to the respective control systems. The suppression was more pronounced when Zn was presorbed on the ??-MnO 2 surfaces as opposed to added simultaneously with As(III). This study provides further understanding of As(III) oxidation reactions on manganese oxide surfaces under environmentally applicable conditions where metals compete for reactive sites.

Urtica dioica extract attenuates depressive like behavior and associative memory dysfunction in dexamethasone induced diabetic mice.

PubMed

Patel, Sita Sharan; Udayabanu, Malairaman

2014-03-01

Evidences suggest that glucocorticoids results in depression and is a risk factor for type 2 diabetes. Further diabetes induces oxidative stress and hippocampal dysfunction resulting in cognitive decline. Traditionally Urtica dioica has been used for diabetes mellitus and cognitive dysfunction. The present study investigated the effect of the hydroalcoholic extract of Urtica dioica leaves (50 and 100 mg/kg, p.o.) in dexamethasone (1 mg/kg, i.m.) induced diabetes and its associated complications such as depressive like behavior and cognitive dysfunction. We observed that mice administered with chronic dexamethasone resulted in hypercortisolemia, oxidative stress, depressive like behavior, cognitive impairment, hyperglycemia with reduced body weight, increased water intake and decreased hippocampal glucose transporter-4 (GLUT4) mRNA expression. Urtica dioica significantly reduced hyperglycemia, plasma corticosterone, oxidative stress and depressive like behavior as well as improved associative memory and hippocampal GLUT4 mRNA expression comparable to rosiglitazone (5 mg/kg, p.o.). Further, Urtica dioica insignificantly improved spatial memory and serum insulin. In conclusion, Urtica dioica reversed dexamethasone induced hyperglycemia and its associated complications such as depressive like behavior and cognitive dysfunction.

The anodizing behavior of aluminum in malonic acid solution and morphology of the anodic films

NASA Astrophysics Data System (ADS)

Ren, Jianjun; Zuo, Yu

2012-11-01

The anodizing behavior of aluminum in malonic acid solution and morphology of the anodic films were studied. The voltage-time response for galvanostatic anodization of aluminum in malonic acid solution exhibits a conventional three-stage feature but the formation voltage is much higher. With the increase of electrolyte concentration, the electrolyte viscosity increases simultaneously and the high viscosity decreases the film growth rate. With the concentration increase of the malonic acid electrolyte, the critical current density that initiates local "burning" on the sample surface decreases. For malonic acid anodization, the field-assisted dissolution on the oxide surface is relatively weak and the nucleation of pores is more difficult, which results in greater barrier layer thickness and larger cell dimension. The embryo of the porous structure of anodic film has been created within the linear region of the first transient stage, and the definite porous structure has been established before the end of the first transient stage. The self-ordering behavior of the porous film is influenced by the electrolyte concentration, film thickness and the applied current density. Great current density not only improves the cell arrangement order but also brings about larger cell dimension.

Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. II - Low cycle fatigue behavior

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Gayda, J.; Miner, R. V.

1986-01-01

The low cycle fatigue (LCF) properties of a single-crystal nickel-base superalloy Rene N4, have been examined at 760 and 980 C in air. Specimens having crystallographic orientations near the 001, 011, -111, 023, -236, and -145 lines were tested in fully reversed, total-strain-controlled LCF tests at a frequency of 0.1 Hz. At 760 C, this alloy exhibited orientation dependent tension-compression anisotropies of yielding which continued to failure. Also at 760 C, orientations exhibiting predominately single slip exhibited serrated yielding for many cycles. At 980 C, orientation dependencies of yielding behavior were smaller. In spite of the tension-compression anisotropies, cyclic stress range-strain range behavior was not strongly orientation dependent for either test temperature. Fatigue life on a total strain range basis was highly orientation dependent at 760 and 980 C and was related chiefly to elastic modulus, low modulus orientations having longer lives. Stage I crack growth on 111 planes was dominant at 760 C, while Stage II crack growth occurred at 980 C. Crack initiation generally occurred at near-surface micropores, but occasionally at oxidation spikes in the 980 C tests.

The effect of social environment on markers of vascular oxidative stress and inflammation in the Watanabe heritable hyperlipidemic rabbit.

PubMed

Nation, Daniel A; Gonzales, Julie A; Mendez, Armando J; Zaias, Julia; Szeto, Angela; Brooks, Larry G; Paredes, Jamespaul; D'Angola, Alyssa; Schneiderman, Neil; McCabe, Philip M

2008-04-01

Previous research demonstrated that social environment can influence progression of atherosclerosis in the Watanabe Heritable Hyperlipidemic (WHHL) rabbit. This study examined the effect of social environment on markers of oxidative stress and inflammation to clarify the physiological pathways potentially responsible for the influence of social environment on disease. WHHL rabbits were assigned to 1 of 3 social groups: an unstable group, in which unfamiliar rabbits were paired daily, with the pairing switched each week; a stable group, in which littermates were paired daily; and an individually-caged group. The stable group engaged in more affiliative social behavior than the unstable group. The unstable group showed more agonistic behavior compared with the stable group and higher C-reactive protein levels than the individually caged group. The individually caged group was behaviorally sedentary, had higher 24-hour urinary catecholamine levels than the other groups, and exhibited higher NAD(P)H-oxidase activity in the aortic arch relative to the stable group. The results suggest that social environment creates distinct behavioral contexts that can affect markers of inflammation and oxidative stress early in the development of atherosclerosis. Specifically, physical inactivity associated with individual caging affects indices of oxidative stress and inflammation. These pathophysiological markers may help to explain behaviorally related differences in the extent of atherosclerosis observed in prior studies.

Ab initio atomistic thermodynamics study on the oxidation mechanism of binary and ternary alloy surfaces

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

Liu, Shi-Yu, E-mail: buaasyliu@gmail.com; Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong; Liu, Shiyang

Utilizing a combination of ab initio density-functional theory and thermodynamics formalism, we have established the microscopic mechanisms for oxidation of the binary and ternary alloy surfaces and provided a clear explanation for the experimental results of the oxidation. We construct three-dimensional surface phase diagrams (SPDs) for oxygen adsorption on three different Nb-X(110) (X = Ti, Al or Si) binary alloy surfaces. On the basis of the obtained SPDs, we conclude a general microscopic mechanism for the thermodynamic oxidation, that is, under O-rich conditions, a uniform single-phase SPD (type I) and a nonuniform double-phase SPD (type II) correspond to the sustainedmore » complete selective oxidation and the non-sustained partial selective oxidation by adding the X element, respectively. Furthermore, by revealing the framework of thermodynamics for the oxidation mechanism of ternary alloys through the comparison of the surface energies of two separated binary alloys, we provide an understanding for the selective oxidation behavior of the Nb ternary alloy surfaces. Using these general microscopic mechanisms, one could predict the oxidation behavior of any binary and multi-component alloy surfaces based on thermodynamics considerations.« less

40 CFR 86.1323-2007 - Oxides of nitrogen analyzer calibration.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 19 2011-07-01 2011-07-01 false Oxides of nitrogen analyzer... Exhaust Test Procedures § 86.1323-2007 Oxides of nitrogen analyzer calibration. This section describes the initial and periodic calibration of the chemiluminescent oxides of nitrogen analyzer. (a) Prior to...

40 CFR 86.1323-2007 - Oxides of nitrogen analyzer calibration.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 19 2010-07-01 2010-07-01 false Oxides of nitrogen analyzer... Exhaust Test Procedures § 86.1323-2007 Oxides of nitrogen analyzer calibration. This section describes the initial and periodic calibration of the chemiluminescent oxides of nitrogen analyzer. (a) Prior to...

40 CFR 86.1323-2007 - Oxides of nitrogen analyzer calibration.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 20 2013-07-01 2013-07-01 false Oxides of nitrogen analyzer... Exhaust Test Procedures § 86.1323-2007 Oxides of nitrogen analyzer calibration. This section describes the initial and periodic calibration of the chemiluminescent oxides of nitrogen analyzer. (a) Prior to...

40 CFR 86.1323-2007 - Oxides of nitrogen analyzer calibration.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 20 2012-07-01 2012-07-01 false Oxides of nitrogen analyzer... Exhaust Test Procedures § 86.1323-2007 Oxides of nitrogen analyzer calibration. This section describes the initial and periodic calibration of the chemiluminescent oxides of nitrogen analyzer. (a) Prior to...

Study on the oxidative stability of poly a-olefin aviation lubricating base oil using PDSC method

NASA Astrophysics Data System (ADS)

Wu, N.; Fei, Y. W.; Yang, H. W.; Wang, Y. M.; Zong, Z. M.

2016-08-01

The oxidation stability of the domestic and import PAO aviation lubricating base oil was studied by the method of pressurized differential scanning calorimetry testing the initial oxidation temperature. The effects of anti-oxidants were investigated, and the best ratio of antioxidants was determined.

Concentration-related metabolic rate and behavioral thermoregulatory adaptations to serial administrations of nitrous oxide in rats

PubMed Central

2018-01-01

Background Initial administration of ≥60% nitrous oxide (N2O) to rats evokes hypothermia, but after repeated administrations the gas instead evokes hyperthermia. This sign reversal is driven mainly by increased heat production. To determine whether rats will behaviorally oppose or assist the development of hyperthermia, we previously performed thermal gradient testing. Inhalation of N2O at ≥60% causes rats to select cooler ambient temperatures both during initial administrations and during subsequent administrations in which the hyperthermic state exists. Thus, an available behavioral response opposes (but does not completely prevent) the acquired hyperthermia that develops over repeated high-concentration N2O administrations. However, recreational and clinical uses of N2O span a wide range of concentrations. Therefore, we sought to determine the thermoregulatory adaptations to chronic N2O administration over a wide range of concentrations. Methods This study had two phases. In the first phase we adapted rats to twelve 3-h N2O administrations at either 0%, 15%, 30%, 45%, 60% or 75% N2O (n = 12 per group); outcomes were core temperature (via telemetry) and heat production (via respirometry). In the second phase, we used a thermal gradient (range 8°C—38°C) to assess each adapted group’s thermal preference, core temperature and locomotion on a single occasion during N2O inhalation at the assigned concentration. Results In phase 1, repeated N2O administrations led to dose related hyperthermic and hypermetabolic states during inhalation of ≥45% N2O compared to controls (≥ 30% N2O compared to baseline). In phase 2, rats in these groups selected cooler ambient temperatures during N2O inhalation but still developed some hyperthermia. However, a concentration-related increase of locomotion was evident in the gradient, and theoretical calculations and regression analyses both suggest that locomotion contributed to the residual hyperthermia. Conclusions Acquired N2O hyperthermia in rats is remarkably robust, and occurs even despite the availability of ambient temperatures that might fully counter the hyperthermia. Increased locomotion in the gradient may contribute to hyperthermia. Our data are consistent with an allostatic dis-coordination of autonomic and behavioral thermoregulatory mechanisms during drug administration. Our results have implications for research on N2O abuse as well as research on the role of allostasis in drug addiction. PMID:29672605

Covalent modification and exfoliation of graphene oxide using ferrocene

NASA Astrophysics Data System (ADS)

Avinash, M. B.; Subrahmanyam, K. S.; Sundarayya, Y.; Govindaraju, T.

2010-09-01

Large scale preparation of single-layer graphene and graphene oxide is of great importance due to their potential applications. We report a simple room temperature method for the exfoliation of graphene oxide using covalent modification of graphene oxide with ferrocene to obtain single-layer graphene oxide sheets. The samples were characterized by FESEM, HRTEM, AFM, EDAX, FT-IR, Raman and Mössbauer spectroscopic studies. HRTEM micrograph of the covalently modified graphene oxide showed increased interlayer spacing of ~2.4 nm due to ferrocene intercalation. The presence of single-layer graphene oxide sheets were confirmed by AFM studies. The covalently modified ferrocene-graphene oxide composite showed interesting magnetic behavior.Large scale preparation of single-layer graphene and graphene oxide is of great importance due to their potential applications. We report a simple room temperature method for the exfoliation of graphene oxide using covalent modification of graphene oxide with ferrocene to obtain single-layer graphene oxide sheets. The samples were characterized by FESEM, HRTEM, AFM, EDAX, FT-IR, Raman and Mössbauer spectroscopic studies. HRTEM micrograph of the covalently modified graphene oxide showed increased interlayer spacing of ~2.4 nm due to ferrocene intercalation. The presence of single-layer graphene oxide sheets were confirmed by AFM studies. The covalently modified ferrocene-graphene oxide composite showed interesting magnetic behavior. Electronic supplementary information (ESI) available: Magnetic data; AFM images; TEM micrographs; and Mössbauer spectroscopic data. See DOI: 10.1039/c0nr00024h

Corrosion fatigue in nitrocarburized quenched and tempered steels

NASA Astrophysics Data System (ADS)

Khani, M. Karim; Dengel, D.

1996-05-01

In order to investigate the fatigue strength and fracture mechanism of salt bath nitrocarburized steels, specimens of the steels SAE 4135 and SAE 4140, in a quenched and tempered state, and additionally in a salt bath nitrocarburized and oxidizing cooled state as well as in a polished (after the oxidizing cooling) and renewed oxidized state, were subjected to comparative rotating bending fatigue tests in inert oil and 5 pct NaCl solution. In addition, some of the quenched and tempered specimens of SAE 4135 material were provided with an approximately 50-μm-thick electroless Ni-P layer, in order to compare corrosion fatigue behavior between the Ni-P layer and the nitride layers. Long-life corrosion fatigue tests of SAE 4135 material were carried out under small stresses in the long-life range up to 108 cycles with a test frequency of 100 Hz. Fatigue tests of SAE 4140 material were carried out in the range of finite life (low-cycle range) with a test frequency of 13 Hz. The results show that the 5 pct NaCl environment drastically reduced fatigue life, but nitrocarburizing plus oxidation treatment was found to improve the corrosion fatigue life over that of untreated and Ni-P coated specimens. The beneficial effect of nitrocarburizing followed by oxidation treatment on cor-rosion fatigue life results from the protection rendered by the compound layer by means of a well-sealed oxide layer, whereby the pores present in the compound layer fill up with oxides. The role of inclusions in initiating fatigue cracks was investigated. It was found that under corrosion fatigue conditions, the fatigue cracks started at cavities along the interfaces of MnS inclusions and matrix in the case of quenched and tempered specimens. The nitrocarburized specimens, however, showed a superposition of pitting corrosion and corrosion fatigue in which pores and nonmetallic inclusions in the compound layer play a predominant role concerning the formation of pits in the substrate.

The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

NASA Astrophysics Data System (ADS)

Winter, L.; Morgenstern, R.; Hockauf, K.; Lampke, T.

2016-03-01

In this work the mean stress influence on the high cycle fatigue behavior of the plasma electrolytic oxidized (PEO) 6082 aluminum alloy (AlSi1MgMn) is investigated. The present study is focused on the fatigue life time and the susceptibility of fatigue-induced cracking of the oxide coating and their dependence on the applied mean stress. Systematic work is done comparing conditions with and without PEO treatment, which have been tested using three different load ratios. For the uncoated substrate the cycles to failure show a significant dependence on the mean stress, which is typical for aluminum alloys. With increased load ratio and therefore increased mean stress, the fatigue strength decreases. The investigation confirms the well-known effect of PEO treatment on the fatigue life: The fatigue strength is significantly reduced by the PEO process, compared to the uncoated substrate. However, also the mean stress sensitivity of the fatigue performance is reduced. The fatigue limit is not influenced by an increasing mean stress for the PEO treated conditions. This effect is firstly shown in these findings and no explanation for this effect can be found in literature. Supposedly the internal compressive stresses and the micro-cracks in the oxide film have a direct influence on the crack initiation and growth from the oxide film through the interface and in the substrate. Contrary to these findings, the susceptibility of fatigue-induced cracking of the oxide coating is influenced by the load ratio. At tension-tension loading a large number of cracks, which grow partially just in the aluminum substrate, are present. With decreasing load ratio to alternating tension-compression stresses, the crack number and length increases and shattering of the oxide film is more pronounced due to the additional effective compressive part of the load cycle.

Persulfate Oxidation Regeneration of Granular Activated Carbon: Reversible Impacts on Sorption Behavior

EPA Science Inventory

Chemical oxidation regeneration of granular activated carbon (GAC) is a developing technology that can be carried out utilizing thermally-activated persulfate. During chemical regeneration of GAC, aggressive oxidative conditions lead to high acidity (pH < 2) and the accumulation ...

Insights into organic carbon oxidation potential during fluvial transport from controlled laboratory and natural field experiments

NASA Astrophysics Data System (ADS)

Scheingross, Joel S.; Dellinger, Mathieu; Golombek, Nina; Hilton, Robert G.; Hovius, Niels; Sachse, Dirk; Turowski, Jens M.; Vieth-Hillebrand, Andrea; Wittmann, Hella

2017-04-01

Over geologic timescales, the exchange of organic carbon (OC) between the atmosphere, biosphere and geosphere is thought to be a major control on atmospheric carbon dioxide (CO2) concentrations, and hence global climate. The carbon fluxes from the oxidation of rock-derived OC (a CO2 source) and erosion and transport of biospheric OC (a potential CO2 sink) during fluvial transit are approximately the same order of magnitude or larger than those from silicate weathering (France-Lanord and Derry, 1997; Bouchez et al., 2010). Despite field data showing oxidation of OC moving downstream in lowland rivers, it is unclear if losses occur primarily during active fluvial transport within the river, where OC is in continual motion within an aerated environment, or during longer periods when OC is temporarily stored in river floodplains which may be anoxic. This represents a major knowledge gap, as the unknown location of OC oxidation (i.e., river vs. floodplain) limits our ability to develop process-based models that can be employed to predict OC losses, constrain carbon budgets, and unravel links between climate, tectonics, and erosion. To fill this gap, we investigated the potential for OC oxidation in both controlled laboratory experiments and a simplified field setting. We consider both rock-derived and biospheric OC. Our experiments simulated fluvial transport without floodplain storage, allowing mixtures of OC-rich and siliciclastic sediment to be transported for distances of 1000 km in annular flumes while making time-series measurements of OC concentration in both the solid (POC) and dissolved (DOC) loads, as well as measurements of rhenium concentration, which serves as a proxy for the oxidation of rock-derived OC. These transport experiments were compared to static, control experiments where water and sediment in the same proportion were placed in still water. Initial results for transport of OC-rich soil show similar behavior between the transport and static experiments, and no detectable OC oxidation, while separate experiments transporting crushed lignite show sediment transport enhances the oxidation of OC relative to leaching in still water; however, total OC oxidation is less than 2% of the initial OC mass. These preliminary results suggest minimal OC oxidation within our experiment, and, to the extent that such experiments represent natural transport through river systems, are consistent with the hypothesis that OC losses may occur primarily during floodplain storage rather than fluvial transport. These results are compared against new field data from a natural experiment in the Rio Bermejo, Argentina where comparing OC concentrations of modern river sediment from sediment cored in dated paleochannels of different ages allows independent estimation of the degree of OC oxidation which occurs during floodplain storage. References: Bouchez, J., Beyssac, O., Galy, V., Gaillardet, J., France-Lanord, C., Maurice, L., and Moreira-Turcq, P., 2010, Oxidation of petrogenic organic carbon in the Amazon floodplain as a source of atmospheric CO2: Geology, v. 38, no. 3, p. 255-258. France-Lanord, C., and Derry, L. A., 1997, Organic carbon burial forcing of the carbon cycle from Himalayan erosion: Nature, v. 390, no. 6655, p. 65-67.

Enhanced thermoelectric figure-of-merit in environmentally benign BaxSr2-xTiCoO6 double perovskites

NASA Astrophysics Data System (ADS)

Saxena, Mandvi; Roy, Pinku; Acharya, Megha; Bose, Imon; Tanwar, Khagesh; Maiti, Tanmoy

2016-12-01

Environmental friendly, non-toxic double perovskite BaxSr2-xTiCoO6 compositions with 0 ≤ x ≤ 0.2 were synthesized using solid-state reaction route for high temperature thermoelectric (TE) applications. XRD and SEM studies confirmed the presence of single-phase solid solution with highly dense microstructure for all the oxide compositions. Temperature dependent electrical conductivity measurement showed semiconductor to metal (M-S) transition in these double perovskites. Incorporation of barium in Sr2TiCoO6 pushed M-S transition to higher temperature making it a potential candidate for high temperature TE applications. Conductivity behaviors of these oxides were explained by small polaron model. Furthermore, these oxides exhibit a glass like behavior resulting in low thermal conductivity. Low temperature dielectric measurement revealed relaxor ferroelectric behavior in these oxides below room temperature. Transition of these relaxors into a glassy state beyond Burns temperature (TD) was found responsible for having low thermal conductivity in these oxides. Maximum dimensionless TE figure-of-merit ZT = 0.29 at 1223 K was achieved for BaxSr2-xTiCoO6 composition with x = 0.2.

Solid rocket combustion simulator technology using the hybrid rocket for simulation

NASA Technical Reports Server (NTRS)

Ramohalli, Kumar

1994-01-01

The hybrid rocket is reexamined in light of several important unanswered questions regarding its performance. The well-known heat transfer limited burning rate equation is quoted, and its limitations are pointed out. Several inconsistencies in the burning rate determination through fuel depolymerization are explicitly discussed. The resolution appears to be through the postulate of (surface) oxidative degradation of the fuel. Experiments are initiated to study the fuel degradation in mixtures of nitrogen/oxygen in the 99.9 percent/0.1 percent to 98 percent/2 percent range. The overall hybrid combustion behavior is studied in a 2 in-diameter rocket motor, where a PMMA tube is used as the fuel. The results include detailed, real-time infrared video images of the combustion zone. Space- and time-averaged images give a broad indication of the temperature reached in the gases. A brief outline is shown of future work, which will specifically concentrate on the exploration of the role of the oxidizer transport to the fuel surface, and the role of the unburned fuel that is reported to escape below the classical time-averaged boundary layer flame.

Intercalating graphene with clusters of Fe3O4 nanocrystals for electrochemical supercapacitors

NASA Astrophysics Data System (ADS)

Ke, Qingqing; Tang, Chunhua; Liu, Yanqiong; Liu, Huajun; Wang, John

2014-04-01

A hierarchical nanostructure consisting of graphene sheets intercalated by clusters of Fe3O4 nanocystals is developed for high-performance supercapacitor electrode. Here we show that the negatively charged graphene oxide (GO) and positively charged Fe3O4 clusters enable a strong electrostatic interaction, generating a hierarchical 3D nanostructure, which gives rise to the intercalated composites through a rational hydrothermal process. The electrocapacitive behavior of the resultant composites is systematically investigated by cyclic voltammeter and galvanostatic charge-discharge techniques, where a positive synergistic effect between graphene and Fe3O4 clusters is identified. A maximum specific capacitance of 169 F g-1 is achieved in the Fe3O4 clusters decorated with effectively reduced graphene oxide (Fe3O4-rGO-12h), which is much higher than those of rGO (101 F g-1) and Fe3O4 (68 F g-1) at the current density of 1 Ag-1. Moreover, this intercalated hierarchical nanostructure demonstrates a good capacitance retention, retaining over 88% of the initial capacity after 1000 cycles.

Ultraviolet Light-Assisted Copper Oxide Nanowires Hydrogen Gas Sensor

NASA Astrophysics Data System (ADS)

Sihar, Nabihah; Tiong, Teck Yaw; Dee, Chang Fu; Ooi, Poh Choon; Hamzah, Azrul Azlan; Mohamed, Mohd Ambri; Majlis, Burhanuddin Yeop

2018-05-01

We fabricated copper oxide nanowires (CuO NWs) ultraviolet (UV) light-assisted hydrogen gas sensor. The fabricated sensor shows promising sensor response behavior towards 100 ppm of H2 at room temperature and elevated temperature at 100 °C when exposed to UV light (3.0 mW/cm2). One hundred-cycle device stability test has been performed, and it is found that for sample elevated at 100 °C, the UV-activated sample achieved stability in the first cycle as compared to the sample without UV irradiation which needed about 10 cycles to achieve stability at the initial stage, whereas the sample tested at room temperature was able to stabilize with the aid of UV irradiation. This indicates that with the aid of UV light, after some "warming up" time, it is possible for the conventional CuO NW sensor which normally work at elevated temperature to function at room temperature because UV source is speculated to play a dominant role to increase the interaction of the surface of CuO NWs and hydrogen gas molecules absorbed after the light exposure.

Ultraviolet Light-Assisted Copper Oxide Nanowires Hydrogen Gas Sensor.

PubMed

Sihar, Nabihah; Tiong, Teck Yaw; Dee, Chang Fu; Ooi, Poh Choon; Hamzah, Azrul Azlan; Mohamed, Mohd Ambri; Majlis, Burhanuddin Yeop

2018-05-15

We fabricated copper oxide nanowires (CuO NWs) ultraviolet (UV) light-assisted hydrogen gas sensor. The fabricated sensor shows promising sensor response behavior towards 100 ppm of H 2 at room temperature and elevated temperature at 100 °C when exposed to UV light (3.0 mW/cm 2 ). One hundred-cycle device stability test has been performed, and it is found that for sample elevated at 100 °C, the UV-activated sample achieved stability in the first cycle as compared to the sample without UV irradiation which needed about 10 cycles to achieve stability at the initial stage, whereas the sample tested at room temperature was able to stabilize with the aid of UV irradiation. This indicates that with the aid of UV light, after some "warming up" time, it is possible for the conventional CuO NW sensor which normally work at elevated temperature to function at room temperature because UV source is speculated to play a dominant role to increase the interaction of the surface of CuO NWs and hydrogen gas molecules absorbed after the light exposure.

Physical Theory of Voltage Fade in Lithium- and Manganese-Rich Transition Metal Oxides

DOE PAGES

Rinaldo, Steven G.; Gallagher, Kevin G.; Long, Brandon R.; ...

2015-03-04

Lithium- and manganese-rich (LMR) transition metal oxide cathodes are of interest for lithium-ion battery applications due to their increased energy density and decreased cost. However, the advantages in energy density and cost are offset, in part, due to the phenomena of voltage fade. Specifically, the voltage profiles (voltage as a function of capacity) of LMR cathodes transform from a high energy configuration to a lower energy configuration as they are repeatedly charged (Li removed) and discharged (Li inserted). Here, we propose a physical model of voltage fade that accounts for the emergence of a low voltage Li phase due tomore » the introduction of transition metal ion defects within a parent Li phase. The phenomenological model was re-cast in a general form and experimental LMR charge profiles were de-convoluted to extract the evolutionary behavior of various components of LMR capacitance profiles. Evolution of the voltage fade component was found to follow a universal growth curve with a maximal voltage fade capacity of ≈ 20% of the initial total capacity.« less

Preparation, characterization and catalytic behavior of pectinase covalently immobilized onto sodium alginate/graphene oxide composite beads.

PubMed

Dai, Xiao-Yan; Kong, Li-Min; Wang, Xiao-Ling; Zhu, Qing; Chen, Kai; Zhou, Tao

2018-07-01

Pectinase was immobilized onto sodium alginate/graphene oxide beads via amide bonds by using N,N'-dicyclohexylcarbodiimide/N-hydroxysuccinimide as the activating agent. The immobilized pectinase was characterized by Fourier transform infrared spectra and scanning electron microscopy analyses. Immobilization conditions were optimized by Box-Behnken design and the response surface method. The activity of the immobilized pectinase prepared under optimal conditions reached 1236.86 ± 40.21 U/g, with an enzyme activity recovery of 83.5%. The optimal pH of free pectinase was 4.5, while that of immobilized pectinase was shifted to 4.0. The optimal temperature of immobilized pectinase was increased to 60 °C, which was 10 °C higher than that of free form. Furthermore, the immobilized pectinase possessed a superior thermal stability and storage stability to those of free pectinase. Reusability studies indicated that the immobilized pectinase retained 73% of initial activity after six times cycles. Due to these good properties, such immobilized pectinase may find application in food industry. Copyright © 2018 Elsevier Ltd. All rights reserved.

Thermal behavior of metal carboxylates—II. Lead formate

NASA Astrophysics Data System (ADS)

Baraldi, Pietro

Experimental data obtained by i.r. emission spectrometry indicate that the thermal behavior of lead formate is complex. By heating in air, after a phase transition at 115°C, decomposition takes place which may lead directly to metal and oxide or to carbonate, to a basic carbonate and finally to oxide. Under vacuum the same transformations occur at higher temperatures and lead to metal.

Capacitive Behavior of Single Gallium Oxide Nanobelt

PubMed Central

Cai, Haitao; Liu, Hang; Zhu, Huichao; Shao, Pai; Hou, Changmin

2015-01-01

In this research, monocrystalline gallium oxide (Ga2O3) nanobelts were synthesized through oxidation of metal gallium at high temperature. An electronic device, based on an individual Ga2O3 nanobelt on Pt interdigital electrodes (IDEs), was fabricated to investigate the electrical characteristics of the Ga2O3 nanobelt in a dry atmosphere at room temperature. The current-voltage (I-V) and I/V-t characteristics show the capacitive behavior of the Ga2O3 nanobelt, indicating the existence of capacitive elements in the Pt/Ga2O3/Pt structure. PMID:28793506

Anodic Oxidation in Aluminum Electrode by Using Hydrated Amorphous Aluminum Oxide Film as Solid Electrolyte under High Electric Field.

PubMed

Yao, Manwen; Chen, Jianwen; Su, Zhen; Peng, Yong; Zou, Pei; Yao, Xi

2016-05-04

Dense and nonporous amorphous aluminum oxide (AmAO) film was deposited onto platinized silicon substrate by sol-gel and spin coating technology. The evaporated aluminum film was deposited onto the AmAO film as top electrode. The hydrated AmAO film was utilized as a solid electrolyte for anodic oxidation of the aluminum electrode (Al) film under high electric field. The hydrated AmAO film was a high efficiency electrolyte, where a 45 nm thick Al film was anodized completely on a 210 nm thick hydrated AmAO film. The current-voltage (I-V) characteristics and breakdown phenomena of a dry and hydrated 210 nm thick AmAO film with a 150 nm thick Al electrode pad were studied in this work. Breakdown voltage of the dry and hydrated 210 nm thick AmAO film were 85 ± 3 V (405 ± 14 MV m(-1)) and 160 ± 5 V (762 ± 24 MV m(-1)), respectively. The breakdown voltage of the hydrated AmAO film increased about twice, owing to the self-healing behavior (anodic oxidation reaction). As an intuitive phenomenon of the self-healing behavior, priority anodic oxidation phenomena was observed in a 210 nm thick hydrated AmAO film with a 65 nm thick Al electrode pad. The results suggested that self-healing behavior (anodic oxidation reaction) was occurring nearby the defect regions of the films during I-V test. It was an effective electrical self-healing method, which would be able to extend to many other simple and complex oxide dielectrics and various composite structures.

Anomalous Micellization of Pluronic Block Copolymers

NASA Astrophysics Data System (ADS)

Leonardi, Amanda; Ryu, Chang Y.

2014-03-01

Poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) (PEO-PPO-PEO) block copolymers, commercially known as Pluronics, are a unique family of amphiphilic triblock polymers, which self-assemble into micelles in aqueous solution. These copolymers have shown promise in therapeutic, biomedical, cosmetic, and nanotech applications. As-received samples of Pluronics contain low molecular weight impurities (introduced during the manufacturing and processing), that are ignored in most applications. It has been observed, however, that in semi-dilute aqueous solutions, at concentrations above 1 wt%, the temperature dependent micellization behavior of the Pluronics is altered. Anomalous behavior includes a shift of the critical micellization temperature and formation of large aggregates at intermediate temperatures before stable sized micelles form. We attribute this behavior to the low molecular weight impurities that are inherent to the Pluronics which interfere with the micellization process. Through the use of Dynamic Light Scattering and HPLC, we compared the anomalous behavior of different Pluronics of different impurity levels to their purified counterparts.

Systematic study of the elastic, optoelectronic, and thermoelectric behavior of MRh2O4 (M = Zn, Cd) based on first principles calculations

NASA Astrophysics Data System (ADS)

Abbas, Syed Adeel; Rashid, Muhammad; Faridi, Muhammad Ayub; Saddique, Muhammad Bilal; Mahmood, Asif; Ramay, Shahid Muhammad

2018-02-01

In the present study, we performed first principles total energy calculations to explore the electronic, elastic, optical, and thermoelectric behavior of MRh2O4(M = Zn, Cd) spinel oxides. We employed Perdew-Burke-Ernzerhof-sol as well as the modified Becke and Johnson potential to compute the elastic, optoelectronic, and thermoelectric behavior of MRh2O4(M = Zn, Cd). The optical behavior was investigated by calculating the complex dielectric constant, refractive index, optical reflectivity, absorption coefficient, and optical conductivity. All of the optical parameters indicated a shift to lower energies as the atomic size increased from Zn to Cd, thereby suggesting potential applications of the spinel oxides in optoelectronic device. Moreover, the thermoelectric properties of MRh2O4(M = Zn, Cd) spinel oxides were computed in terms of the electrical conductivity (σ), Seebeck coefficient (S), thermal conductivity (k), and power factor (σS2) using the BoltzTraP code.

Anomalous Coulomb oscillation in crossed carbon nanotubes

NASA Astrophysics Data System (ADS)

Baek, Seung Jae; Lee, Dongsu; Park, Seung Joo; Park, Yung Woo; Svensson, Johannes; Jonson, Mats; Campbell, Eleanor E. B.

2008-03-01

Single-walled carbon nanotube (SWCNT) crossed junctions separated by an insulating layer were fabricated to investigate the double quantum dot modulated by a single gate (DQD-sG). Anomalous Coulomb oscillations were observed on the lower CNT at low temperature, where the behavior was interpreted by the concept of a double quantum dot (DQD) system http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id =APPLAB000089000023233107000001&idtype=cvips&gifs=yes [1]. To understand it more clearly, we have intentionally fabricated crossed CNTs without oxide layer in between. The observed anomalous Coulomb oscillations indicate that the contact resistance between the two tubes becomes a potential barrier splitting the initial single QD into the DQD, and the back-gate modulates the energy levels of the DQD.

Electrochromic NiO thin films prepared by spin coating

NASA Astrophysics Data System (ADS)

Özütok, F.; Demiri, S.; Özbek, E.

2017-02-01

Recently, smart windows are very important because they are often being used in smart buildings and car glasses (windows). At this point, producing effective electrochromic materials is so necessary. In this study, we produced NiO thin films by using spin coating technique on In-doped SnO2 (ITO) substrate. Nickel proportions of these nickel oxide (NiO) films are 3, 5 and 7 %. Nickel acetate tetrahydrate is the initial solution and solvents are ethylene gl ycol and n-hexzane. Structural properties and surface images are investigated by using x-ray diffactometer (XRD) and scanning electron microscope (SEM) device, respectively. In addition, electrochemical behavior is investigated by cyclic voltammetry. A correlation between surface morphology and electrochromic performance was observed as well.

Enhanced wet air oxidation : synergistic rate acceleration upon effluent recirculation

Treesearch

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

2000-01-01

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

Oxide driven strength evolution of silicon surfaces

DOE PAGES

Grutzik, Scott J.; Milosevic, Erik; Boyce, Brad L.; ...

2015-11-19

Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations showmore » that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Lastly, combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.« less

Oxidation behavior and area specific resistance of La, Cu and B alloyed Fe-22Cr ferritic steels for solid oxide fuel cell interconnects

NASA Astrophysics Data System (ADS)

Swaminathan, Srinivasan; Ko, Yoon Seok; Lee, Young-Su; Kim, Dong-Ik

2017-11-01

Two Fe-22 wt% Cr ferritic stainless steels containing varying concentrations of La (0.14 or 0.52 wt%), Cu (0.17 or 1.74 wt%) and B (48 or 109 ppm) are investigated with respect to oxidation behavior and high temperature area specific resistance (ASR) of the surface oxide scales. To determine the oxidation resistance of developed steels, continuous isothermal oxidation is carried out at 800 °C in air, for 2000 h, and their thermally grown oxide scale is characterized using dynamic SIMS, SEM/EDX, XRD and GI-XRD techniques. To assess their electrical performance, the ASR measurement by four-point probe method is conducted at 800 °C in air, for 400 h. In higher La content steel, the La-oxides at the scale/alloy interface promotes the oxygen transport which resulted in sub-surface oxidation of Mn, Cr, Ti and Al. Moreover, the inward growth of oxides contributes to increase of Fe-Cr alloy protrusions within the scale, which reduced the ASR. In contrast, sub-surface oxidation is reduced in high Cu-alloyed steel by segregated Cu at the scale/alloy interface. Thus, addition of Cu is effective to oxidation resistance and also to better electrical performance. However, no obvious impact of B on the scale sequence and/or ASR is observed.

An evaluation of the effects of PEO/PEG molecular weights on extruded alumina rods

NASA Astrophysics Data System (ADS)

Bolger, Nancy Beth

1998-12-01

Alumina rods were piston extruded from bodies containing polyethylene glycols (PEGs) and polyethylene oxides (PEOs) with molecular weights ranging from 1,300 to 3,800,000 g/mol. A blend of aluminas possessing different particle size distributions was evaluated with regard to its extrusion pressure by varying the amount of PEG/PEO addition. Behavior exhibited by the alumina blend was dependent upon the additive that was used. The higher molecular weight binders with average molecular weight of 200,000 g/mol and 3,350,000 g/mol displayed the most severe behaviors of near dilatant and dilatant respectively. Physical properties of the green and fired states, as well as the binder burnout, were investigated with the changing additions. Correlation between the green and fired strengths and the changing molecular weights were examined. The additive present influenced the surface properties of the rods, which affected the green strengths. The highest average molecular weight polyethylene glycols showed higher green strengths, while the lowest green strengths were observed for the high molecular weight polyethylene oxides. Fired strengths generally ranged from approximately 12,000 psi to 16,000 psi for additive batches. Alumina pellets containing twelve separate combinations of polyethylene glycol with polyethylene oxide were dry pressed. Physical properties of the green and fired states were examined. Statistical analysis was performed upon the data and seven combinations of polyethylene glycol with polyethylene oxide were deemed significant. These combinations in conjunction with the same alumina blend were then piston extruded. The addition of polyethylene glycol reduced the near dilatant behavior exhibited by the 200,000 g/mol average molecular weight polyethylene oxide. Dilatant behavior was completely eliminated from the 3,350,000 g/mol average molecular weight polyethylene oxide batches. Physical properties of the green and fired states were again investigated with the changing additions. Polyethylene oxide, in combination with polyethylene glycol, did show an increase in green strength versus the polyethylene oxide alone. Strengths were still lower than those displayed by the polyethylene glycols alone. Reductions or degradations in molecular weight of the polymers due to mixing and extrusion processes may account for lower green strength of bodies, especially those containing polyethylene oxides.

Treatment of Ammonia Nitrogen Wastewater in Low Concentration by Two-Stage Ozonization

PubMed Central

Luo, Xianping; Yan, Qun; Wang, Chunying; Luo, Caigui; Zhou, Nana; Jian, Chensheng

2015-01-01

Ammonia nitrogen wastewater (about 100 mg/L) was treated by two-stage ozone oxidation method. The effects of ozone flow rate and initial pH on ammonia removal were studied, and the mechanism of ammonia nitrogen removal by ozone oxidation was discussed. After the primary stage of ozone oxidation, the ammonia removal efficiency reached 59.32% and pH decreased to 6.63 under conditions of 1 L/min ozone flow rate and initial pH 11. Then, the removal efficiency could be over 85% (the left ammonia concentration was lower than 15 mg/L) after the second stage, which means the wastewater could have met the national discharge standards of China. Besides, the mechanism of ammonia removal by ozone oxidation was proposed by detecting the products of the oxidation: ozone oxidation directly and ·OH oxidation; ammonia was mainly transformed into NO3−-N, less into NO2−-N, not into N2. PMID:26404353

Monitoring Interfacial Lipid Oxidation in Oil-in-Water Emulsions Using Spatially Resolved Optical Techniques.

PubMed

Banerjee, Chiranjib; Westberg, Michael; Breitenbach, Thomas; Bregnhøj, Mikkel; Ogilby, Peter R

2017-06-06

The oxidation of lipids is an important phenomenon with ramifications for disciplines that range from food science to cell biology. The development and characterization of tools and techniques to monitor lipid oxidation are thus relevant. Of particular significance in this regard are tools that facilitate the study of oxidations at interfaces in heterogeneous samples (e.g., oil-in-water emulsions, cell membranes). In this article, we establish a proof-of-principle for methods to initiate and then monitor such oxidations with high spatial resolution. The experiments were performed using oil-in-water emulsions of polyunsaturated fatty acids (PUFAs) prepared from cod liver oil. We produced singlet oxygen at a point near the oil-water interface of a given PUFA droplet in a spatially localized two-photon photosensitized process. We then followed the oxidation reactions initiated by this process with the fluorescence-based imaging technique of structured illumination microscopy (SIM). We conclude that the approach reported herein has attributes well-suited to the study of lipid oxidation in heterogeneous samples.

Effects of point defect concentrations of the reactive element oxides on the oxidation kinetics of pure Ni and Ni-Cr alloys

NASA Astrophysics Data System (ADS)

Yan, Ruey-Fong

The addition of some reactive element oxides, e.g. Ysb2Osb3 or ZrOsb2, has significant effects, e.g. improvement in scale adhesion and reduction in oxidation rate, on the oxidation behavior of chromia and alumina scale forming alloys at high temperatures. However, there is little agreement about how a small addition of an oxygen-active element can cause such profound effects. It was the goal of this project to study the growth kinetics of an oxide scale when different reactive-element oxides were added to pure Ni and Ni-Cr alloys and, consequently, to aid in clarifying the mechanism of reactive element effects. The oxidation kinetics were measured using a thermogravimetric analysis (TGA) method and the material characterization of oxide scale was conducted. The relationship between point defect structures and oxidation kinetics was discussed. The results in this research showed that Ysb2Osb3 and ZrOsb2 exhibited the reactive element effects on the oxidation behaviors of Ni and Ni-Cr alloys. In addition, the point defect concentrations of the reactive element oxide, Ysb2Osb3, were changed by doping of different valent oxides. The modification of point defect concentrations of the reactive element oxide dispersed phases did change the oxidation kinetics of the pure Ni and Ni-Cr alloys containing Ysb2Osb3. These results indicate that the transport properties of the reactive element oxide dispersed phases are one of the important factors in determining the growth rate of an oxide scale.

Effect of Alloying Additions on Oxidation Behaviors of Ni-Fe Based Superalloy for Ultra-Supercritical Boiler Applications

NASA Astrophysics Data System (ADS)

Lu, Jintao; Yang, Zhen; Zhao, Xinbao; Yan, Jingbo; Gu, Y.

A new kind of Ni-Fe-based superalloy is designed recently for 750 °C-class A-USC boiler tube. The oxidation behavior of the designed alloys with various combinations of anti-oxidation additions, Cr, Al and Si, was investigated at 750 °C and 850 °C, respectively. The results indicated that the oxidation rate of tested alloys decreased with the increase of the sum of additions. Cr addition may drop the relative constant of parabolic rate greatly when temperature is raised. But the oxide scale, mainly consisted of NiCr spinel at 750 °C and NiCrMn spinel at 850 °C, was similar while the Cr content is in a range of 20-25 wt.% at tested temperatures. Al addition, however, showed the best effective to reduce the oxidation rates. Internal Al-rich oxide was observed at the scale/metal interface for alloys added with high content of Al and was increased with Al content increase. Very tiny difference between the oxide scales of the Si-added alloys was identified when Si content varies among 0.02-0.05 wt.%. Basing on these results, this presentation discussed the optimum combination of anti-oxidation additions as well as oxidation mechanisms in the designed Ni-Fe-base superalloy.

The Enzymatic Oxidation of Graphene Oxide

PubMed Central

Kotchey, Gregg P.; Allen, Brett L.; Vedala, Harindra; Yanamala, Naveena; Kapralov, Alexander A.; Tyurina, Yulia Y.; Klein-Seetharaman, Judith; Kagan, Valerian E.; Star, Alexander

2011-01-01

Two-dimensional graphitic carbon is a new material with many emerging applications, and studying its chemical properties is an important goal. Here, we reported a new phenomenon – the enzymatic oxidation of a single layer of graphitic carbon by horseradish peroxidase (HRP). In the presence of low concentrations of hydrogen peroxide (~40 µM), HRP catalyzed the oxidation of graphene oxide, which resulted in the formation of holes on its basal plane. During the same period of analysis, HRP failed to oxidize chemically reduced graphene oxide (RGO). The enzymatic oxidation was characterized by Raman, UV-Vis, EPR and FT-IR spectroscopy, TEM, AFM, SDS-PAGE, and GC-MS. Computational docking studies indicated that HRP was preferentially bound to the basal plane rather than the edge for both graphene oxide and RGO. Due to the more dynamic nature of HRP on graphene oxide, the heme active site of HRP was in closer proximity to graphene oxide compared to RGO, thereby facilitating the oxidation of the basal plane of graphene oxide. We also studied the electronic properties of the reduced intermediate product, holey reduced graphene oxide (hRGO), using field-effect transistor (FET) measurements. While RGO exhibited a V-shaped transfer characteristic similar to a single layer of graphene that was attributed to its zero band gap, hRGO demonstrated a p-type semiconducting behavior with a positive shift in the Dirac points. This p-type behavior rendered hRGO, which can be conceptualized as interconnected graphene nanoribbons, as a potentially attractive material for FET sensors. PMID:21344859

Effect of temperature and initial dibutyl sulfide concentration in chloroform on its oxidation rate by ozone.

PubMed

Popiel, Stanisław; Nalepa, Tomasz; Dzierzak, Dorota; Stankiewicz, Romuald; Witkiewicz, Zygfryd

2008-09-15

A scheme of dibutyl sulfide (DBS) oxidation with ozone and generation of transitional products was determined in this study. The main identified intermediate product was dibutyl sulfoxide (DBSO), and the main end product of DBS oxidation was dibutyl sulfone (DBSO2). It was determined that for three temperatures: 0, 10 and 20 degrees C there was certain initial DBS concentration for which half-times observed in experimental conditions were equal and independent from temperature. Generation of phosgene and water as by-products was confirmed for the reaction of DBS with ozone in chloroform. Results of the described study allowed to present generalized mechanism of sulfide oxidation with ozone.

Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility

DOE PAGES

Malasi, A.; Taz, H.; Farah, A.; ...

2015-12-16

We report that ternary metal oxides of type (Me) 2O 3 with the primary metal (Me) constituent being Fe (66 atomic (at.) %) along with the two Lanthanide elements Tb (10 at.%) and Dy (24 at.%) can show excellent semiconducting transport properties. Thin films prepared by pulsed laser deposition at room temperature followed by ambient oxidation showed very high electronic conductivity (>5 × 10 4 S/m) and Hall mobility (>30 cm 2/V-s). These films had an amorphous microstructure which was stable to at least 500 °C and large optical transparency with a direct band gap of 2.85 ± 0.14 eV.more » This material shows emergent semiconducting behavior with significantly higher conductivity and mobility than the constituent insulating oxides. In conclusion, since these results demonstrate a new way to modify the behaviors of transition metal oxides made from unfilled d- and/or f-subshells, a new class of functional transparent conducting oxide materials could be envisioned.« less

High-Temperature Oxidation Behavior of Al-Co-Cr-Ni-(Fe or Si) Multicomponent High-Entropy Alloys

NASA Astrophysics Data System (ADS)

Butler, T. M.; Alfano, J. P.; Martens, R. L.; Weaver, M. L.

2015-01-01

High-entropy alloys (HEAs) are a class of alloys that are being considered for a number of applications. In the present study, the microstructures and 1050°C oxidation behaviors of two HEAs, Al10Cr22.5Co22.5Ni22.5Fe22.5 (at.%) and Al20Cr25Co25Ni25Si5 have been investigated along with Al15Cr10Co35Ni35Si5, which is a high-temperature shape-memory alloy. Oxide formation occurred via selective oxidation in a manner that was consistent with the oxide formation model devised by Giggins and Pettit for model Ni-Cr-Al alloys. The lower Al content alloy formed an external Cr2O3 scale and an internal subscale consisting of Al2O3 and AlN precipitates. The higher Al content alloys exhibited smaller mass gains and formed external Al2O3 scales without any internal oxidation of the alloys.

Effects of Some Light Alloying Elements on the Oxidation Behavior of Fe and Ni-Cr Based Alloys During Air Plasma Spraying

NASA Astrophysics Data System (ADS)

Zeng, Zhensu; Kuroda, Seiji; Kawakita, Jin; Komatsu, Masayuki; Era, Hidenori

2010-01-01

The oxidation behavior of iron binary powders with addition of Si (1, 4 wt.%) and B (1, 3 wt.%) and that of a Ni-Cr based alloy powder with Si (4.3 wt.%), B (3.0 wt.%), and C (0.8 wt.%) additions during atmosphere plasma spray (APS) have been investigated. Analysis of the chemical composition and phases of oxides in the captured in-flight particles and deposited coatings was carried out. The results show that the addition of Si and B to iron effectively reduced the oxygen contents in the coatings, especially during the in-flight period at higher particles temperature. Ni-Cr based alloy powder with Si, B, and C additions reduced the oxidation of the base alloys significantly. Preferential oxidation and subsequent vaporization of Si, B, and C from the surface of the sprayed particles are believed to play a major role in controlling oxidation in the APS process.

Colloquium : Emergent properties in plane view: Strong correlations at oxide interfaces

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

Chakhalian, Jak; Freeland, John W.; Millis, Andrew J.

2014-10-01

Finding new collective electronic states in materials is one of the fundamental goals of condensed matter physics. Atomic-scale superlattices formed from transition metal oxides are a particularly appealing hunting ground for new physics. In bulk form, transition metal oxides exhibit a remarkable range of magnetic, superconducting, and multiferroic phases that are of great scientific interest and are potentially capable of providing innovative energy, security, electronics, and medical technology platforms. In superlattices new states may emerge at the interfaces where dissimilar materials meet. This Colloquium illustrates the essential features that make transition metal oxide-based heterostructures an appealing discovery platform for emergentmore » properties with a few selected examples, showing how charge redistributes, magnetism and orbital polarization arises, and ferroelectric order emerges from heterostructures comprised of oxide components with nominally contradictory behavior with the aim providing insight into the creation and control of novel behavior at oxide interfaces by suitable mechanical, electrical, or optical boundary conditions and excitations.« less

Crystallization Behavior of Copper Smelter Slag During Molten Oxidation

NASA Astrophysics Data System (ADS)

Fan, Yong; Shibata, Etsuro; Iizuka, Atsushi; Nakamura, Takashi

2015-10-01

Copper slag is composed of iron silicate obtained by smelting copper concentrate and silica flux. One of the most important criteria for the utilization of this secondary resource is the recovery of iron from the slag matrix to decrease the volume of dumped slag. The molten oxidation process with crushing magnetic separation appears to be a more sustainable approach and is based on directly blowing oxidizing gas onto molten slag after the copper smelting process. In the current study, using an infrared furnace, the crystallization behavior of the slag during molten oxidation was studied to better understand the trade-off between magnetite and hematite precipitations, as assessed by X-ray diffraction (using an internal standard). Furthermore, the crystal morphology was examined using a laser microscope and Raman imaging system to understand the iron oxide transformation, and the distribution of impurities such as Cu, Zn, As, Cr, and Pb were complemented with scanning electron microscopy and energy dispersive spectroscopy. In addition, the reaction mechanism was investigated with a focus on the oxidation processes.

A Critical Assessment of Cyclic Softening and Hardening Behavior in a Near- α Titanium Alloy During Thermomechanical Fatigue

NASA Astrophysics Data System (ADS)

Prasad, Kartik; Sarkar, Rajdeep; Rao, K. Bhanu Sankara; Sundararaman, M.

2016-10-01

Thermomechanical fatigue behavior of Ti-alloy Timetal 834 has been studied at two temperature intervals viz. 573 K to 723 K (300 °C to 450 °C) and 723 K to 873 K (450 °C to 600 °C) under mechanical strain-controlled cycling. Among the temperatures studied, the alloy exhibited initial cyclic softening followed by cyclic hardening at 723 K (450 °C) in the temperature interval of 573 K to 723 K (300 °C to 450 °C). However, continuous cyclic hardening was observed at 723 K (450 °C) in 723 K to 873 K (450 °C to 600 °C). At 573 K (300 °C) and 873 K (600 °C), cyclic softening was observed in the cyclic stress response curves in both the temperature intervals. The dislocation substructure was observed to be planar in both the modes of TMF loading. Based on TEM microstructures and few unconventional fatigue tests, the observed cyclic hardening is attributed to dynamic strain aging. The reduced fatigue life at 723 K to 873 K (450 °C to 600 °C) under OP-TMF loading was attributed to the combined effect of cyclic hardening (leading to early strain localization and crack initiation), oxidation, and development of tensile mean stresses.

Scattering attributes of one-dimensional semiconducting oxide nanomaterials individually probed for varying light-matter interaction angles

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

Choi, Daniel S.; Singh, Manpreet; Zhou, Hebing

2015-10-12

We report the characteristic optical responses of one-dimensional semiconducting oxide nanomaterials by examining the individual nanorods (NRs) of ZnO, SnO{sub 2}, indium tin oxide, and zinc tin oxide under precisely controlled, light-matter interaction geometry. Scattering signals from a large set of NRs of the different types are evaluated spatially along the NR length while varying the NR tilt angle, incident light polarization, and analyzer rotation. Subsequently, we identify material-indiscriminate, NR tilt angle- and incident polarization-dependent scattering behaviors exhibiting continuous, intermittent, and discrete responses. The insight gained from this study can advance our fundamental understanding of the optical behaviors of themore » technologically useful nanomaterials and, at the same time, promote the development of highly miniaturized, photonic and bio-optical devices utilizing the spatially controllable, optical responses of the individual semiconducting oxide NRs.« less

Effects of chromium and aluminum on mechanical and oxidation properties of iron-nickel-base superalloys based on CG-27

NASA Technical Reports Server (NTRS)

Schuon, S. R.

1985-01-01

The effects of chromium and aluminum on the mechanical and oxidation properties of a series of gamma-prime-strengthened alloys based on CG-27 were studied. Gamma-prime dispersion and solid-solution strengthening were the principal modes of alloy strengthening. The oxidation attack parameter K sub a decreased with increasing Cr and Al contents for each alloy group based on Al content. As a group, alloys with 3 wt % Al had the lowest attack parameters. Therefore, 3 wt % is the optimum level of Al for parabolic oxidation behavior. Spalling, due to diffusion-induced grain growth, was controlled by the overall Cr and Al levels. The alloy with 4 wt % Cr and 3 wt % Al had stress-rupture properties superior to those of the base alloy, CG-27, and maintained parabolic oxidation behavior while the Cr content was reduced by two-thirds of its value in cast CG-27.

10,000-Hour Cyclic Oxidation Behavior at 982 C (1800 F) of 68 High-Temperature Co-, Fe-, and Ni-Base Alloys

NASA Technical Reports Server (NTRS)

Barrett, Charles A.

1997-01-01

Sixty-eight high temperature Co-, Fe-, and Ni-base alloys were tested for 10-one thousand hour cycles in static air at 982 C (1800 F). The oxidation behavior of the test samples was evaluated by specific weight change/time data, x-ray diffraction of the post-test samples, and their final appearance. The gravimetric and appearance data were combined into a single modified oxidation parameter, KB4 to rank the cyclic oxidation resistance from excellent to catastrophic. The alloys showing the 'best' resistance with no significant oxidation attack were the alumina/aluminate spinel forming Ni-base turbine alloys: U-700, NASA-VIA and B-1900; the Fe-base ferritic alloys with Al: TRW-Valve, HOS-875, NASA-18T, Thermenol and 18SR; and the Ni-base superalloy IN-702.

Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy.

PubMed

Wang, Y F; Singh, Shashi B; Limaye, Mukta V; Shao, Y C; Hsieh, S H; Chen, L Y; Hsueh, H C; Wang, H T; Chiou, J W; Yeh, Y C; Chen, C W; Chen, C H; Ray, Sekhar C; Wang, J; Pong, W F; Takagi, Y; Ohigashi, T; Yokoyama, T; Kosugi, N

2015-10-20

This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy

PubMed Central

Wang, Y. F.; Singh, Shashi B.; Limaye, Mukta V.; Shao, Y. C.; Hsieh, S. H.; Chen, L. Y.; Hsueh, H. C.; Wang, H. T.; Chiou, J. W.; Yeh, Y. C.; Chen, C. W.; Chen, C. H.; Ray, Sekhar C.; Wang, J.; Pong, W. F.; Takagi, Y.; Ohigashi, T.; Yokoyama, T.; Kosugi, N.

2015-01-01

This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets. PMID:26481557

Inhibited phase behavior of gas hydrates in graphene oxide: influences of surface and geometric constraints.

PubMed

Kim, Daeok; Kim, Dae Woo; Lim, Hyung-Kyu; Jeon, Jiwon; Kim, Hyungjun; Jung, Hee-Tae; Lee, Huen

2014-11-07

Porous materials have provided us unprecedented opportunities to develop emerging technologies such as molecular storage systems and separation mechanisms. Pores have also been used as supports to contain gas hydrates for the application in gas treatments. Necessarily, an exact understanding of the properties of gas hydrates in confining pores is important. Here, we investigated the formation of CO2, CH4 and N2 hydrates in non-interlamellar voids in graphene oxide (GO), and their thermodynamic behaviors. For that, low temperature XRD and P-T traces were conducted to analyze the water structure and confirm hydrate formation, respectively, in GO after its exposure to gaseous molecules. Confinement and strong interaction of water with the hydrophilic surface of graphene oxide reduce water activity, which leads to the inhibited phase behavior of gas hydrates.

Redox-signals and macrophage biology (for the upcoming issue of molecular aspects of medicine on signaling by reactive oxygen species).

PubMed

Weigert, Andreas; von Knethen, Andreas; Fuhrmann, Dominik; Dehne, Nathalie; Brüne, Bernhard

2018-01-11

Macrophages are known for their versatile role in biology. They sense and clear structures that contain exogenous or endogenous pathogen-associated molecular patterns. This process is tightly linked to the production of a mixture of potentially harmful oxidants and cytokines. Their inherent destructive behavior is directed against foreign material or structures of 'altered self', which explains the role of macrophages during innate immune reactions and inflammation. However, there is also another side of macrophages when they turn into a tissue regenerative, pro-resolving, and healing phenotype. Phenotype changes of macrophages are termed macrophage polarization, representing a continuum between classical and alternative activation. Macrophages as the dominating producers of superoxide/hydrogen peroxide and nitric oxide are not only prone to oxidative modifications but also to more subtle signaling properties of redox-active molecules conveying redox regulation. We review basic concepts of the enzymatic nitric oxide and superoxide production within macrophages, refer to their unique chemical reactions and outline biological consequences not only for macrophage biology but also for their communication with cells in the microenvironment. These considerations link hypoxia to the NO system, addressing feedforward as well as feedback circuits. Moreover, we summarize the role of redox-signaling affecting epigenetics and reflect the central role of mitochondrial-derived oxygen species in inflammation. To better understand the diverse functions of macrophages during initiation as well as resolution of inflammation and to decode their versatile roles during innate and adaptive immunity with the entire spectrum of cell protective towards cell destructive activities we need to appreciate the signaling properties of redox-active species. Herein we discuss macrophage responses in terms of nitric oxide and superoxide formation with the modulating impact of hypoxia. Copyright © 2018. Published by Elsevier Ltd.

Real-time Kinetics of High-mobility Group Box 1 (HMGB1) Oxidation in Extracellular Fluids Studied by in Situ Protein NMR Spectroscopy*

PubMed Central

Zandarashvili, Levani; Sahu, Debashish; Lee, Kwanbok; Lee, Yong Sun; Singh, Pomila; Rajarathnam, Krishna; Iwahara, Junji

2013-01-01

Some extracellular proteins are initially secreted in reduced forms via a non-canonical pathway bypassing the endoplasmic reticulum and become oxidized in the extracellular space. One such protein is HMGB1 (high-mobility group box 1). Extracellular HMGB1 has different redox states that play distinct roles in inflammation. Using a unique NMR-based approach, we have investigated the kinetics of HMGB1 oxidation and the half-lives of all-thiol and disulfide HMGB1 species in serum, saliva, and cell culture medium. In this approach, salt-free lyophilized 15N-labeled all-thiol HMGB1 was dissolved in actual extracellular fluids, and the oxidation and clearance kinetics were monitored in situ by recording a series of heteronuclear 1H-15N correlation spectra. We found that the half-life depends significantly on the extracellular environment. For example, the half-life of all-thiol HMGB1 ranged from ∼17 min (in human serum and saliva) to 3 h (in prostate cancer cell culture medium). Furthermore, the binding of ligands (glycyrrhizin and heparin) to HMGB1 significantly modulated the oxidation kinetics. Thus, the balance between the roles of all-thiol and disulfide HMGB1 proteins depends significantly on the extracellular environment and can also be artificially modulated by ligands. This is important because extracellular HMGB1 has been suggested as a therapeutic target for inflammatory diseases and cancer. Our work demonstrates that the in situ protein NMR approach is powerful for investigating the behavior of proteins in actual extracellular fluids containing an enormous number of different molecules. PMID:23447529

Self-Assembled Hierarchical Formation of Conjugated 3D Cobalt Oxide Nanobead-CNT-Graphene Nanostructure Using Microwaves for High-Performance Supercapacitor Electrode.

PubMed

Kumar, Rajesh; Singh, Rajesh Kumar; Dubey, Pawan Kumar; Singh, Dinesh Pratap; Yadav, Ram Manohar

2015-07-15

Here we report the electrochemical performance of a interesting three-dimensional (3D) structures comprised of zero-dimensional (0D) cobalt oxide nanobeads, one-dimensional (1D) carbon nanotubes and two-dimensional (2D) graphene, stacked hierarchically. We have synthesized 3D self-assembled hierarchical nanostructure comprised of cobalt oxide nanobeads (Co-nb), carbon nanotubes (CNTs), and graphene nanosheets (GNSs) for high-performance supercapacitor electrode application. This 3D self-assembled hierarchical nanostructure Co3O4 nanobeads-CNTs-GNSs (3D:Co-nb@CG) is grown at a large scale (gram) through simple, facile, and ultrafast microwave irradiation (MWI). In 3D:Co-nb@CG nanostructure, Co3O4 nanobeads are attached to the CNT surfaces grown on GNSs. Our ultrafast, one-step approach not only renders simultaneous growth of cobalt oxide and CNTs on graphene nanosheets but also institutes the intrinsic dispersion of carbon nanotubes and cobalt oxide within a highly conductive scaffold. The 3D:Co-nb@CG electrode shows better electrochemical performance with a maximum specific capacitance of 600 F/g at the charge/discharge current density of 0.7A/g in KOH electrolyte, which is 1.56 times higher than that of Co3O4-decorated graphene (Co-np@G) nanostructure. This electrode also shows a long cyclic life, excellent rate capability, and high specific capacitance. It also shows high stability after few cycles (550 cycles) and exhibits high capacitance retention behavior. It was observed that the supercapacitor retained 94.5% of its initial capacitance even after 5000 cycles, indicating its excellent cyclic stability. The synergistic effect of the 3D:Co-nb@CG appears to contribute to the enhanced electrochemical performances.

Child maltreatment and age of alcohol and marijuana initiation in high-risk youth.

PubMed

Proctor, Laura J; Lewis, Terri; Roesch, Scott; Thompson, Richard; Litrownik, Alan J; English, Diana; Arria, Amelia M; Isbell, Patricia; Dubowitz, Howard

2017-12-01

Youth with a history of child maltreatment use substances and develop substance use disorders at rates above national averages. Thus far, no research has examined pathways from maltreatment to age of substance use initiation for maltreated youth. We examined the longitudinal impact of maltreatment in early childhood on age of alcohol and marijuana use initiation, and whether internalizing and externalizing behaviors at age 8 mediates the link between maltreatment and age of substance use initiation. Data were drawn from the Longitudinal Studies of Child Abuse and Neglect (LONGSCAN) at ages 4, 8, 12, and 18. Maltreatment was assessed through reviews of administrative records and youth self-reports. Behavior problems were assessed with the Child Behavior Checklist. Age of substance use initiation was assessed with the Young Adult version of the Diagnostic Interview Schedule for Children. Path analyses indicated mediated effects from a history of maltreatment to age at first alcohol and marijuana use through externalizing behaviors. Considering type of maltreatment, direct effects were found from physical abuse to age of alcohol initiation, and mediated effects were found from sexual abuse and neglect to initial age of alcohol and marijuana use through externalizing behaviors. Direct effects for marijuana use initiation and indirect effects through internalizing behavior problems were not significant for either substance. Externalizing behavior is one pathway from childhood maltreatment to age of substance use initiation. Services for maltreated youth should incorporate substance use prevention, particularly among those with early externalizing problems. Copyright © 2017 Elsevier Ltd. All rights reserved.

High-temperature corrosion of iron-aluminum and iron-aluminum-yttrium alloys

NASA Astrophysics Data System (ADS)

Insoo, Kim

The high-temperature corrosion behavior of Fe3Al alloy has been investigated by conducting two studies: (1) corrosion of Fe 3Al and Fe3Al-Y alloys in oxidizing atmosphere and (2) corrosion of Fe3Al in mixed chlorine/oxygen environments. In the first study, oxidation of the two alloys, Fe-14.3 wt% Al and Fe-14.1 wt% Al-0.3 wt% Y, was carried out in the temperature range of 800 to 1100°C to investigate the general oxidation behavior of Fe3Al and the effect of yttrium on the oxidation of Fe3Al in terms of oxidation kinetics, oxide scale adhesion and microstructure. At lower temperatures (<1000°C), the oxidation rate of the two alloys was nearly identical, and the parabolic rate constant obtained as a function of temperature was Kp = 5128 exp[--39500 (cal/mol)/RT] mg2/cm4 h. At higher temperatures, however, yttrium-added Fe3Al alloy exhibited lower oxidation rate and much more improved oxide adhesion. The lower oxidation rate observed in Fe3Al-Y alloy seems to be due to the followings: (1) a decrease in aluminum diffusion through alumina scale and (2) modification of the scale growth mechanism from simultaneous countercurrent diffusion of aluminum and oxygen to predominant inward diffusion of oxygen, which generates less growth stress and thus prevents the formation of fast diffusion paths such as microcracks. The adhesion improvement of alumina scale formed on the Fe3Al-Y was attributed to the modification of alumina growth mechanism by the addition of Y to the Fe3Al alloy. The change of growth mechanism leads to the formation of pegs, decrease of the oxide growth stress, and decrease of voids formation, which enhances the adhesion of alumina scale to the Fe3Al alloy. The second study has focused on the corrosion of Fe3Al in the temperature range of 600--800°C in Cl2-Ar gas mixtures containing traces of oxygen as an impurity. Weight gain was observed during the corrosion of Fe3Al at 600°C in 0.25% Cl2-Ar, which is due to the formation of Fe2O3, while continuous weight loss of the specimen in 5% Cl2-Ar at 800°C was observed because of the formation of volatile metal chlorides, FeCl2, FeCl 3, and AlCl3. Meanwhile, three distinct stages of weight change during the corrosion of Fe3Al at 700°C in 1% Cl 2-Ar were observed: (1) weight gain, (2) linear weight loss, and (3) gradual decrease of weight loss. Initial weight gain is due to the formation of Fe2O3, and the weight loss in the subsequent two stages is due to the formation of volatile metal chlorides, FeCl 2, FeCl3, and AlCl3. Based on the kinetic and microstructural analyses, a reaction mechanism is proposed for each stage.

Theoretical perspectives on the mechanism and kinetics of the OH radical-initiated gas-phase oxidation of PCB126 in the atmosphere.

PubMed

Dang, Juan; Shi, Xiangli; Zhang, Qingzhu; Wang, Wenxing

2015-06-01

Polychlorinated biphenyls (PCBs) primarily exist in the gas phase in air and may undergo atmospheric oxidation degradations, particularly the oxidation reaction initiated by OH radicals. In this work, the mechanism of the OH radical-initiated atmospheric oxidation of the most toxic PCB congener 3,3',4,4',5-pentachlorobiphenyl (PCB126) was investigated by using quantum chemistry methods. The rate constants of the crucial elementary reactions were estimated by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The oxidation products of the reaction of PCB126 with OH radicals include 3,3',4,4',5-pentachlorobiphenyl-ols, chlorophenols, 2,3,4,7,8-pentachlorodibenzofuran, 2,3,4,6,7-pentachlorodibenzofuran, dialdehydes, 3,3',4,4',5-pentachloro-5'-nitro-biphenyl, and 4,5-dichloro-2-nitrophenol. Particularly, the formation of polychlorinated dibenzofurans (PCDFs) from the atmospheric oxidation of PCBs is revealed for the first time. The overall rate constant of the OH addition reaction is 2.52×10(-13)cm(3)molecule(-1)s(-1) at 298K and 1atm. The atmospheric lifetime of PCB126 determined by OH radicals is about 47.08days which indicates that PCB126 can be transported long distances from local to global scales. Copyright © 2015 Elsevier B.V. All rights reserved.

Novel approach on the risk assessment of oxidized fats and oils for perspectives of food safety and quality. I. Oxidized fats and oils induces neurotoxicity relating pica behavior and hypoactivity.

PubMed

Gotoh, N; Watanabe, H; Osato, R; Inagaki, K; Iwasawa, A; Wada, S

2006-04-01

Food poisoning caused by deteriorated fat and oil in instant noodles was first reported in Japan approximately 40 years ago. In these cases, many people developed neurotoxic symptoms such as emesis and discomfort. The degree of oxidation of the fat and oil in the instant noodles that induced food poisoning was at least 100 meq/kg in peroxide value (PV). No general toxicity studies with animals, however, have examined the toxicity of fat and oil oxidized to that extent. In this study, pica behavior, a behavior characterized by eating a nonfood material such as kaolin and that relates to the degree of discomfort in animals, and alterations of locomotor activity of rats eating deteriorated fat and oil were measured. The groups fed fat and oil with at least 138.5 meq/kg PV consumed significantly more kaolin compared to the control group. Furthermore, rats that ate deteriorated fat and oil with at least 107.2 meq/kg PV had significantly decreased locomotor activity compared to control rats. These phenomena suggest that oxidized fat and oil with at least 100 meq/kg PV induce neurotoxicity. The toxicity of oxidized fat and oil has only been addressed using general toxicity tests, but the present results reveal the importance of evaluating toxicity by using other measures.

Atmospheric Oxidation Mechanism of Furfural Initiated by Hydroxyl Radicals.

PubMed

Zhao, Xiaocan; Wang, Liming

2017-05-04

Furfural is emitted into the atmosphere because of its potential applications as an intermediate to alkane fuels from biomass, industrial usages, and biomass burning. The kinetic and mechanistic information on the furfural chemistry is necessary to assess the fate of furfural in the atmosphere and its impact on the air quality. Here we studied the atmospheric oxidation mechanisms of furfural initiated by the OH radicals using quantum chemistry and kinetic calculations. The reaction of OH and furfural was initiated mainly by OH additions to C 2 and C 5 positions, forming R2 and R5 adducts, which could undergo rapid ring-breakage to form R2B and R5B, respectively. Our calculations showed that these intermediate radicals reacted rather slowly with O 2 under the atmospheric conditions because the additions of O 2 to these radicals are only slightly exothermic and highly reversible. Alternatively, these radicals would react directly with O 3 , NO 2 , HO 2 /RO 2 , etc. Namely, the atmospheric oxidation of furfural would unlikely result in ozone formation. Under typical atmospheric conditions, the main products in OH-initiated furfural oxidation include 2-oxo-3-pentene-1,5-dialdehyde, 5-hydroxy-2(5H)-furanone, 4-oxo-2- butenoic acid, and 2,5-furandione. These compounds will likely stay in the gas phase and are subject to further photo-oxidation.

Removal of Crystal Violet by Using Reduced-Graphene-Oxide-Supported Bimetallic Fe/Ni Nanoparticles (rGO/Fe/Ni): Application of Artificial Intelligence Modeling for the Optimization Process

PubMed Central

Ruan, Wenqian; Qi, Jimei; Hou, Yu; Cao, Rensheng; Wei, Xionghui

2018-01-01

Reduced-graphene-oxide-supported bimetallic Fe/Ni nanoparticles were synthesized in this study for the removal of crystal violet (CV) dye from aqueous solutions. This material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), Raman spectroscopy, N2-sorption, and X-ray photoelectron spectroscopy (XPS). The influence of independent parameters (namely, initial dye concentration, initial pH, contact time, and temperature) on the removal efficiency were investigated via Box–Behnken design (BBD). Artificial intelligence (i.e., artificial neural network, genetic algorithm, and particle swarm optimization) was used to optimize and predict the optimum conditions and obtain the maximum removal efficiency. The zero point of charge (pHZPC) of rGO/Fe/Ni composites was determined by using the salt addition method. The experimental equilibrium data were fitted well to the Freundlich model for the evaluation of the actual behavior of CV adsorption, and the maximum adsorption capacity was estimated as 2000.00 mg/g. The kinetic study discloses that the adsorption processes can be satisfactorily described by the pseudo-second-order model. The values of Gibbs free energy change (ΔG0), entropy change (ΔS0), and enthalpy change (ΔH0) demonstrate the spontaneous and endothermic nature of the adsorption of CV onto rGO/Fe/Ni composites. PMID:29789483

Quantum Femtosecond Magnetism: Phase Transition in Step with Light in a Strongly Correlated Manganese Oxide

NASA Astrophysics Data System (ADS)

Wang, Jigang

2014-03-01

Research of non-equilibrium phase transitions of strongly correlated electrons is built around addressing an outstanding challenge: how to achieve ultrafast manipulation of competing magnetic/electronic phases and reveal thermodynamically hidden orders at highly non-thermal, femtosecond timescales? Recently we reveal a new paradigm called quantum femtosecond magnetism-photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic coherent bonding. We demonstrate an antiferromagnetic (AFM) to ferromagnetic (FM) switching during about 100 fs laser pulses in a colossal magneto-resistive manganese oxide. Our results show a huge photoinduced femtosecond spin generation, measured by magnetic circular dichroism, with photo-excitation threshold behavior absent in the picosecond dynamics. This reveals an initial quantum coherent regime of magnetism, while the optical polarization/coherence still interacts with the spins to initiate local FM correlations that compete with the surrounding AFM matrix. Our results thus provide a framework that explores quantum non-equilibrium kinetics to drive phase transitions between exotic ground states in strongly correlated elecrons, and raise fundamental questions regarding some accepted rules, such as free energy and adiabatic potential surface. This work is in collaboration with Tianqi Li, Aaron Patz, Leonidas Mouchliadis, Jiaqiang Yan, Thomas A. Lograsso, Ilias E. Perakis. This work was supported by the National Science Foundation (contract no. DMR-1055352). Material synthesis at the Ames Laboratory was supported by the US Department of Energy-Basic Energy Sciences (contract no. DE-AC02-7CH11358).

Sorption of chromium with struvite during phosphorus recovery.

PubMed

Rouff, Ashaki A

2012-11-20

Struvite (MgNH(4)PO(4)·6H(2)O; MAP) precipitation is a viable means of phosphorus (P) recovery from animal and human wastes. The behavior of metal contaminants such as chromium (Cr) during struvite precipitation, however, requires consideration. Here the influence of both Cr concentration and oxidation state on sorption is assessed. The Cr content of struvite precipitated in the presence of 1-100 μM Cr as Cr(III) (22.3-3030.1 mg/kg) was higher than that of solids from Cr(VI) (4.5-5.1 mg/kg) solutions. For 1-20 μM Cr(III) solids, scanning electron microscopy (SEM) revealed etch pit formation on struvite crystal surfaces, indicative of a surface interaction. The formation of an adsorbate was confirmed by X-ray absorption fine structure spectroscopy (XAFS). At initial concentrations ≥20 μM Cr(III), XAFS confirmed the formation of a Cr(OH)(3)·nH(2)O(am) precipitate. Fourier transform infrared (FT-IR) spectroscopy revealed that both Cr(III) and Cr(VI) sorption resulted in distortion of the PO(4)(3-) tetrahedra in the mineral structure. This, combined with SEM results revealed that even at low sorbed concentrations, the Cr impurity can affect the mineral surface and structure. Thus, the initial Cr concentration and oxidation state in wastes targeted for P recovery will dictate the final Cr content, the mechanism of sorption, and impact on the struvite structure.

Factors Affecting the Plasticity of Sodium Chloride, Lithium Fluoride, and Magnesium Oxide Single Crystals. 1

NASA Technical Reports Server (NTRS)

Stearns, Carl A.; Pack, Ann E.; Lad, Robert A.

1959-01-01

A study was made of the relative magnitude of the effects of various factors on the ductility of single crystals of sodium chloride (NaCl), lithium fluoride (LiF), and magnesium oxide (MgO). Specimen treatments included water-polishing, varying cleavage rate, annealing, quenching, X-irradiation, surface coating, aging, and combinations of some of these treatments. The mechanical behavior of the crystals was studied in flexure and in compression, the latter study being performed at both constant strain rate and constant load. Etch-pit studies were carried out to provide some pertinent information on the results of pretreatment on the dislocation concentration and distribution in the vicinity of the surface. The load deformation curves for these ionic single crystals show an initial region of very low slope which proved to be due to anelastic deformation. The extent of initial anelastic deformation is modified by specimen pretreatment in a way that suggests that this deformation is the result of expansion of cleaved-in dislocation loops, which can contract on the removal of the stress. The effects of the various pretreatments on the load and deflection at fracture are in accord with the prediction one might make with regard to their effect on the nucleation of fatal surface cracks. For NaCl, increases in ductility are always accompanied by increases in strength. The creep constants for NaCl are a function of treatments which affect the bulk structure but are not a function of treatments which only affect the surface.

Effect of surface state on the oxidation behavior of welded 308L in simulated nominal primary water of PWR

NASA Astrophysics Data System (ADS)

Ming, Hongliang; Zhang, Zhiming; Wang, Jiazhen; Zhu, Ruolin; Ding, Jie; Wang, Jianqiu; Han, En-Hou; Ke, Wei

2015-05-01

The oxidation behavior of 308L weld metal (WM) with different surface state in the simulated nominal primary water of pressurized water reactor (PWR) was studied by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) analyzer and X-ray photoelectron spectroscopy (XPS). After 480 h immersion, a duplex oxide film composed of a Fe-rich outer layer (Fe3O4, Fe2O3 and a small amount of NiFe2O4, Ni(OH)2, Cr(OH)3 and (Ni, Fe)Cr2O4) and a Cr-rich inner layer (FeCr2O4 and NiCr2O4) can be formed on the 308L WM samples with different surface state. The surface state has no influence on the phase composition of the oxide films but obviously affects the thickness of the oxide films and the morphology of the oxides (number & size). With increasing the density of dislocations and subgrain boundaries in the cold-worked superficial layer, the thickness of the oxide film, the number and size of the oxides decrease.

Chemical bonding analysis on amphoteric hydrogen - alkaline earth ammine borohydrides

NASA Astrophysics Data System (ADS)

Kiruthika, S.; Ravindran, P.

2018-04-01

Usually the ions in solid are in the positive oxidation states or in the negative oxidation state depending upon the chemical environment. It is highly unusual for an ion having both positive as well as negative oxidation state in a particular compound. Structural analysis suggest that the alkaline earth ammine borohydrides (AABH) with the chemical formula M (BH4)2(NH3)2 (M = Mg, Ca, or Sr) where hydrogen is present in +1 and -1 oxidation states. In order to understand the oxidation states of hydrogen and also the character of chemical bond present in AABH we have made charge density, electron localization function, Born effective charge, Bader effective charge, and density of states analyses using result from the density functional calculations. Our detailed analyses show that hydrogen is in amphoteric behavior with hydrogen closer to boron is in negative oxidation state and that closer to nitrogen is in the positive oxidation state. Due to the presence of finite covalent bonding between the consitutents in AABH the oxidation state of hydrogen is non-interger value. The confirmation of the presence of amphtoric behavior of hydrogen in AABH has implication in hydrogen storage applications.

40 CFR 63.366 - Reporting requirements.

Code of Federal Regulations, 2010 CFR

2010-07-01

...) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE CATEGORIES Ethylene Oxide Emissions... subject to these emissions standards subsequently increases its use of ethylene oxide within any... amount of ethylene oxide used during the previous consecutive 12-month period in the initial notification...

Green oxidations of furans--initiated by molecular oxygen--that give key natural product motifs.

PubMed

Montagnon, Tamsyn; Noutsias, Dimitris; Alexopoulou, Ioanna; Tofi, Maria; Vassilikogiannakis, Georgios

2011-04-07

In this article, we explore how changes in the positioning of pendant hydroxyl functionalities in the photooxygenation substrate dramatically alter the course of furan oxidations that are initiated by singlet oxygen; and, how these different reactivities can be harnessed through cascade reaction sequences to access, rapidly and effectively, a broad range of important natural product motifs.

Early initiation of alcohol drinking, cigarette smoking, and sexual intercourse linked to suicidal ideation and attempts: findings from the 2006 Korean Youth Risk Behavior Survey.

PubMed

Kim, Dong-Sik; Kim, Hyun-Sun

2010-01-01

This study examined the association between early initiation of problem behaviors (alcohol drinking, cigarette smoking, and sexual intercourse) and suicidal behaviors (suicidal ideation and suicide attempts), and explored the effect of concurrent participation in these problem behaviors on suicidal behaviors among Korean adolescent males and females. Data were obtained from the 2006 Korean Youth Risk Behavior Survey, a nationally representative sample of middle and high school students (32,417 males and 31,467 females) in grades seven through twelve. Bivariate and multivariate logistic analyses were conducted. Several important covariates, such as age, family living structure, household economic status, academic performance, current alcohol drinking, current cigarette smoking, current butane gas or glue sniffing, perceived body weight, unhealthy weight control behaviors, subjective sleep evaluation, and depressed mood were included in the analyses. Both male and female preteen initiators of each problem behavior were at greater risk for suicidal behaviors than non-initiators, even after controlling for covariates. More numerous concurrent problematic behaviors were correlated with greater likelihood of seriously considering or attempting suicide among both males and females. This pattern was more clearly observed in preteen than in teen initiators although the former and latter were engaged in the same frequency of problem behavior. Early initiation of alcohol drinking, cigarette smoking, and sexual intercourse, particularly among preteens, represented an important predictor of later suicidal ideation and suicide attempts in both genders. Thus, early preventive intervention programs should be developed and may reduce the potential risks for subsequent suicidal behaviors.

Ultrasound-assisted oxidative desulfurization of bunker-C oil using tert-butyl hydroperoxide.

PubMed

Tang, Qiong; Lin, Song; Cheng, Ying; Liu, Sujun; Xiong, Jun-Ru

2013-09-01

This work investigated the ultrasonic assisted oxidative desulfurization of bunker-C oil with TBHP/MoO3 system. The operational parameters for the desulfurization procedure such as ultrasonic irradiation time, ultrasonic wave amplitude, catalyst initial concentration and oxidation agent initial concentration were studied. The experimental results show that the present oxidation system was very efficient for the desulfurization of bunker-C oil and ~35% sulfur was removed which was dependent on operational parameters. The application of ultrasonic irradiation allowed sulfur removal in a shorter time. The stronger the solvent polarity is, the higher the sulfur removal rate, but the recovery rate of oil is lower. The sulfur compounds in bunker-C oil reacted with TBHP to produce corresponding sulfoxide, and further oxidation produced the corresponding sulfone. Copyright © 2013 Elsevier B.V. All rights reserved.

Stable and solubilized active Au atom clusters for selective epoxidation of cis-cyclooctene with molecular oxygen

DOE PAGES

Qian, Linping; Wang, Zhen; Beletskiy, Evgeny V.; ...

2017-03-28

Here, the ability of Au catalysts to effect the challenging task of utilizing molecular oxygen for the selective epoxidation of cyclooctene is fascinating. Although supported nanometre-size Au particles are poorly active, here we show that solubilized atomic Au clusters, present in ng ml –1 concentrations and stabilized by ligands derived from the oxidized hydrocarbon products, are active. They can be formed from various Au sources. They generate initiators and propagators to trigger the onset of the auto-oxidation reaction with an apparent turnover frequency of 440 s –1, and continue to generate additional initiators throughout the auto-oxidation cycle without direct participationmore » in the cycle. Spectroscopic characterization suggests that 7–8 atom clusters are effective catalytically. Extension of work based on these understandings leads to the demonstration that these Au clusters are also effective in selective oxidation of cyclohexene, and that solubilized Pt clusters are also capable of generating initiators for cyclooctene epoxidation.« less

Surface modifications of hydrogen storage alloy by heavy ion beams with keV to MeV irradiation energies

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Tokuhira, Shinnosuke; Uchida, Hirohisa; Ohshima, Takeshi

2015-12-01

This study deals with the effect of surface modifications induced from keV to MeV heavy ion beams on the initial reaction rate of a hydrogen storage alloy (AB5) in electrochemical process. The rare earth based alloys like this sample alloy are widely used as a negative electrode of Ni-MH (Nickel-Metal Hydride) battery. We aimed to improve the initial reaction rate of hydrogen absorption by effective induction of defects such as vacancies, dislocations, micro-cracks or by addition of atoms into the surface region of the metal alloys. Since defective layer near the surface can easily be oxidized, the conductive oxide layer is formed on the sample surface by O+ beams irradiation, and the conductive oxide layer might cause the improvement of initial reaction rate of hydriding. This paper demonstrates an effective surface treatment of heavy ion irradiation, which induces catalytic activities of rare earth oxides in the alloy surface.

Stable and solubilized active Au atom clusters for selective epoxidation of cis-cyclooctene with molecular oxygen

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

Qian, Linping; Wang, Zhen; Beletskiy, Evgeny V.

Here, the ability of Au catalysts to effect the challenging task of utilizing molecular oxygen for the selective epoxidation of cyclooctene is fascinating. Although supported nanometre-size Au particles are poorly active, here we show that solubilized atomic Au clusters, present in ng ml –1 concentrations and stabilized by ligands derived from the oxidized hydrocarbon products, are active. They can be formed from various Au sources. They generate initiators and propagators to trigger the onset of the auto-oxidation reaction with an apparent turnover frequency of 440 s –1, and continue to generate additional initiators throughout the auto-oxidation cycle without direct participationmore » in the cycle. Spectroscopic characterization suggests that 7–8 atom clusters are effective catalytically. Extension of work based on these understandings leads to the demonstration that these Au clusters are also effective in selective oxidation of cyclohexene, and that solubilized Pt clusters are also capable of generating initiators for cyclooctene epoxidation.« less

Synergism and Physicochemical Properties of Anionic/Amphoteric Surfactant Mixtures with Nonionic Surfactant of Amine Oxide Type

NASA Astrophysics Data System (ADS)

Blagojević, S. M.; Pejić, N. D.; Blagojević, S. N.

2017-12-01

The physicochemical properties of initial formulation, that is anionic/amphoteric surfactants mixture SLES/AOS/CAB (sodium lauryl ether sulfate (SLES), α-olefin sulfonates (AOS) and cocamidopropyl betaine (CAB) at ratio 80 : 15 : 5) with nonionic surfactant of amine oxide type (lauramine oxide (AO)) in various concentration (1-5%) were studied. To characterize the surfactants mixture, the critical micelle concentration (CMC), surface tension (γ), foam volume, biodegradability and irritability were determined. This study showed that adding of AO in those mixtures lowered both γ and CMC as well as enhanced SLES/AOS/CAB foaming properties, but did not significantly affect biodegradability and irritability of initial formulation. Moreover, an increase in AO concentration has a meaningful synergistic effect on the initial formulation properties. All those results indicates that a nonionic surfactant of amine oxide type significantly improves the performance of anionic/amphoteric mixed micelle systems, and because of that anionic/amphoteric/nonionic mixture can be used in considerably lower concentrations as a cleaning formulation.

Experimental investigation of As, Sb and Cs behavior during olivine serpentinization in hydrothermal alkaline systems

NASA Astrophysics Data System (ADS)

Lafay, Romain; Montes-Hernandez, German; Janots, Emilie; Munoz, Manuel; Auzende, Anne Line; Gehin, Antoine; Chiriac, Rodica; Proux, Olivier

2016-04-01

While Fluid-Mobile Elements (FMEs) such as B, Sb, Li, As or Cs are particularly concentrated in serpentinites, data on FME fluid-serpentine partitioning, distribution, and sequestration mechanisms are missing. In the present experimental study, the behavior of Sb, As and Cs during San Carlos olivine serpentinization was investigated using accurate mineralogical, geochemical, and spectroscopic characterization. Static-batch experiments were conducted at 200 °C, under saturated vapor pressure (≈1.6 MPa), for initial olivine grain sizes of <30 μm (As), 30-56 μm (As, Cs, Sb) and 56-150 μm (Cs) and for periods comprised between 3 and 90 days. High-hydroxyl-alkaline fluid enriched with 200 mg L-1 of a single FME was used and a fluid/solid weight ratio of 15. For these particular conditions, olivine is favorably replaced by a mixture of chrysotile, polygonal serpentine and brucite. Arsenic, Cs or Sb reaction product content was determined as a function of reaction advancement for the different initial olivine grain sizes investigated. The results confirm that serpentinization products have a high FME uptake capacity with the partitioning coefficient increasing such as CsDp/fl = 1.5-1.6 < AsDp/fl = 3.5-4.5 < SbDp/fl = 28 after complete reaction of the 30-56 μm grain-sized olivine. The sequestration pathways of the three elements are however substantially different. While the As partition coefficient remains constant throughout the serpentinization reaction, the Cs partition coefficient decreases abruptly in the first stages of the reaction to reach a constant value after the reaction is 40-60% complete. Both As and Cs partitioning appear to decrease with increasing initial olivine grain size, but there is no significant difference in the partitioning coefficient between the 30-56 and 56-150 μm grain size after complete serpentinization. X-ray absorption spectroscopy (XAS) measurements combined with X-ray chemical measurements reveal that the As(V) is mainly adsorbed onto the serpentinization products, especially brucite. In contrast, mineralogical characterization combined with XAS spectroscopy reveal redox sensitivity for Sb sequestration within serpentine products, depending on the progress of the reaction. When serpentinization is <50%, initial Sb(III) is oxidized into Sb(V) and substantially adsorbed onto serpentine. For higher degrees of reaction, a decrease in Sb sequestration by serpentine products is observed and is attributed to a reduction of Sb(V) into Sb(III). This stage is characterized by the precipitation of Sb-Ni-rich phases and a lower bulk partitioning coefficient compared to that of the serpentine and brucite assemblage. Antimony reduction appears linked to water reduction accompanying the bulk iron oxidation, as half the initial Fe(II) is oxidized into Fe(III) and incorporated into the serpentine products once the reaction is over. The reduction of Sb implies a decrease of its solubility, but the type of secondary Sb-rich phases identified here might not be representative of natural systems where Sb concentrations are lower. These results bring new insights into the uptake of FME by sorption on serpentine products that may form in hydrothermal environments at low temperatures. FME sequestration here appears to be sensitive to various physicochemical parameters and more particularly to redox conditions that appear to play a preponderant role in the concentrations and mechanism of sequestration of redox-sensitive elements.

Water Oxidation Catalysis via Size-Selected Iridium Clusters

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

Halder, Avik; Liu, Cong; LIU, ZHUN

The detailed mechanism and efficacy of four electron electrochemical water oxidation depend critically upon the detailed atomic structure of each catalytic site, which are numerous and diverse in most metal oxides anodes. In order to limit the diversity of sites, arrays of discrete iridium clusters with identical metal atom number (Ir-2, Ir-4, or Ir-8) were deposited in submonolayer coverage on conductive oxide supports, and the electrochemical properties and activity of each was evaluated. Exceptional electroactivity for the oxygen evolving reaction (OER) was observed for all cluster samples in acidic electrolyte. Reproducible cluster-size-dependent trends in redox behavior were also resolved. First-principlesmore » computational models of the individual discrete-size clusters allow correlation of catalytic-site structure and multiplicity with redox behavior.« less

Behavior of GaSb (100) and InSb (100) surfaces in the presence of H2O2 in acidic and basic cleaning solutions

NASA Astrophysics Data System (ADS)

Seo, Dongwan; Na, Jihoon; Lee, Seunghyo; Lim, Sangwoo

2017-03-01

Gallium antimonide (GaSb) and indium antimonide (InSb) have attracted strong attention as new channel materials for transistors due to their excellent electrical properties and lattice matches with various group III-V compound semiconductors. In this study, the surface behavior of GaSb (100) and InSb (100) was investigated and compared in hydrochloric acid/hydrogen peroxide mixture (HPM) and ammonium hydroxide/hydrogen peroxide mixture (APM) solutions. In the acidic HPM solution, surface oxidation was greater and the etching rates of the GaSb and InSb surfaces increased when the solution is concentrated, which indicates that H2O2 plays a key role in the surface oxidation of GaSb and InSb in acidic HPM solution. However, the GaSb and InSb surfaces were hardly oxidized in basic APM solution in the presence of H2O2 because gallium and indium are in the thermodynamically stable forms of H2GaO3- and InO2-, respectively. When the APM solution was diluted, however, the Ga on the GaSb surface was oxidized by H2O, increasing the etching rate. However, the effect of dilution of the APM solution on the oxidation of the InSb surface was minimal; thus, the InSb surface was less oxidized than the GaSb surface and the change in the etching rate of InSb with dilution of the APM solution was not significant. Additionally, the oxidation behavior of gallium and indium was more sensitive to the composition of the HPM and APM solutions than that of antimony. Therefore, the surface properties and etching characteristics of GaSb and InSb in HPM and APM solutions are mainly dependent on the behavior of the group III elements rather than the group V elements.

Cognitive-behavioral therapy for sleep disturbance decreases inflammatory cytokines and oxidative stress in hemodialysis patients.

PubMed

Chen, Hung-Yuan; Cheng, I-Chih; Pan, Yi-Ju; Chiu, Yen-Ling; Hsu, Shih-Ping; Pai, Mei-Fen; Yang, Ju-Yeh; Peng, Yu-Sen; Tsai, Tun-Jun; Wu, Kwan-Dun

2011-08-01

Sleep disturbance is common in dialysis patients and is associated with the development of enhanced inflammatory responses. Cognitive-behavioral therapy is effective for sleep disturbance and reduces inflammation experienced by peritoneal dialysis patients; however, this has not been studied in hemodialysis patients. To determine whether alleviation of sleep disturbance in hemodialysis patients also leads to less inflammation, we conducted a randomized controlled interventional study of 72 sleep-disturbed hemodialysis patients. Within this patient cohort, 37 received tri-weekly cognitive-behavioral therapy lasting 6 weeks and the remaining 35, who received sleep hygiene education, served as controls. The adjusted post-trial primary outcome scores of the Pittsburgh Sleep Quality Index, the Fatigue Severity Scale, the Beck Depression Inventory, and the Beck Anxiety Inventory were all significantly improved from baseline by therapy compared with the control group. The post-trial secondary outcomes of high-sensitive C-reactive protein, IL-18, and oxidized low-density lipoprotein levels significantly declined with cognitive-behavioral therapy in comparison with the control group. Thus, our results suggest that cognitive-behavioral therapy is effective for correcting disorganized sleep patterns, and for reducing inflammation and oxidative stress in hemodialysis patients.

Stress Rupture Behavior of Silicon Carbide Coated, Low Modulus Carbon/Carbon Composites. M.S. Thesis

NASA Technical Reports Server (NTRS)

Rozak, Gary A.; Wallace, John F.

1988-01-01

The disadvantages of carbon-carbon composites, in addition to the oxidation problem, are low thermal expansion, expensive fabrication procedures, and poor off axis properties. The background of carbon-carbon composites, their fabrication, oxidation, oxidation protection and mechanical testing in flexure are discussed.

Dimer esters in α-pinene secondary organic aerosol: effect of hydroxyl radical, ozone, relative humidity and aerosol acidity

NASA Astrophysics Data System (ADS)

Kristensen, K.; Cui, T.; Zhang, H.; Gold, A.; Glasius, M.; Surratt, J. D.

2013-12-01

The formation of secondary organic aerosol (SOA) from both ozonolysis and hydroxyl radical (OH)-initiated oxidation of α-pinene under conditions of high nitric oxide (NO) concentrations with varying relative humidity (RH) and aerosol acidity was investigated in the University of North Carolina dual outdoor smog chamber facility. SOA formation from ozonolysis of α-pinene was enhanced relative to that from OH-initiated oxidation in the presence of initially high NO conditions. However, no effect of RH on SOA mass was evident. Ozone (O3)-initiated oxidation of α-pinene in the presence of ammonium sulfate (AS) seed coated with organic aerosol from OH-initiated oxidation of α-pinene showed reduced nucleation compared to ozonolysis in the presence of pure AS seed aerosol. The chemical composition of α-pinene SOA was investigated by ultra-performance liquid chromatography/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-Q-TOFMS), with a focus on the formation of carboxylic acids and high-molecular weight dimer esters. A total of eight carboxylic acids and four dimer esters were identified, constituting between 8 and 12% of the total α-pinene SOA mass. OH-initiated oxidation of α-pinene in the presence of nitrogen oxides (NOx) resulted in the formation of highly oxidized carboxylic acids, such as 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) and diaterpenylic acid acetate (DTAA). The formation of dimer esters was observed only in SOA produced from the ozonolysis of α-pinene in the absence of NOx, with increased concentrations by a~factor of two at higher RH (50-90%) relative to lower RH (30-50%). The increased formation of dimer esters correlates with an observed increase in new particle formation at higher RH due to nucleation. Increased aerosol acidity was found to have a negligible effect on the formation of the dimer esters. SOA mass yield did not influence the chemical composition of SOA formed from α-pinene ozonolysis with respect to carboxylic acids and dimer esters. The results support the formation of the high-molecular weight dimer esters through gas-phase reactions of the stabilized Criegee Intermediate (sCI) formed from the ozonolysis of α-pinene. The high molecular weight and polar nature of dimer esters formed in the gas-phase may explain increased particle number concentration as a~result of homogenous nucleation. Since three of these dimer esters (i.e., pinyl-diaterpenyl ester (MW 358), pinyl-diaterebyl ester (MW 344) and pinonyl-pinyl ester (MW 368)) have been observed in both laboratory-generated and ambient fine organic aerosol samples, we conclude that the dimer esters observed in this study can be used as tracers for the O3-initiated oxidation of α-pinene, and are therefore indicative of enhanced anthropogenic activities, and that the high molecular weight and low volatility esters result in homogenous nucleation under laboratory conditions, increasing the particle number concentration.

Dimers in α-pinene secondary organic aerosol: effect of hydroxyl radical, ozone, relative humidity and aerosol acidity

NASA Astrophysics Data System (ADS)

Kristensen, K.; Cui, T.; Zhang, H.; Gold, A.; Glasius, M.; Surratt, J. D.

2014-04-01

The formation of secondary organic aerosol (SOA) from both ozonolysis and hydroxyl radical (OH)-initiated oxidation of α-pinene under conditions of high nitric oxide (NO) concentrations with varying relative humidity (RH) and aerosol acidity was investigated in the University of North Carolina dual outdoor smog chamber facility. SOA formation from ozonolysis of α-pinene was enhanced relative to that from OH-initiated oxidation in the presence of initially high-NO conditions. However, no effect of RH on SOA mass was evident. Ozone (O3)-initiated oxidation of α-pinene in the presence of ammonium sulfate (AS) seed coated with organic aerosol from OH-initiated oxidation of α-pinene showed reduced nucleation compared to ozonolysis in the presence of pure AS seed aerosol. The chemical composition of α-pinene SOA was investigated by ultra-performance liquid chromatography/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-Q-TOFMS), with a focus on the formation of carboxylic acids and high-molecular weight dimers. A total of eight carboxylic acids and four dimers were identified, constituting between 8 and 12% of the total α-pinene SOA mass. OH-initiated oxidation of α-pinene in the presence of nitrogen oxides (NOx) resulted in the formation of highly oxidized carboxylic acids, such as 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) and diaterpenylic acid acetate (DTAA). The formation of dimers was observed only in SOA produced from the ozonolysis of α-pinene in the absence of NOx, with increased concentrations by a factor of two at higher RH (50-90%) relative to lower RH (30-50%). The increased formation of dimers correlates with an observed increase in new particle formation at higher RH due to nucleation. Increased aerosol acidity was found to have a negligible effect on the formation of the dimers. SOA mass yield did not influence the chemical composition of SOA formed from α-pinene ozonolysis with respect to carboxylic acids and dimers. The results support the formation of the high-molecular weight dimers through gas-phase reactions of the stabilized Criegee Intermediate (sCI) formed from the ozonolysis of α-pinene. The high molecular weight and polar nature of dimers formed in the gas phase may explain increased particle number concentration as a result of homogenous nucleation. Since three of these dimers (i.e. pinyl-diaterpenyl dimer (MW 358), pinyl-diaterebyl dimer (MW 344) and pinonyl-pinyl dimer (MW 368)) have been observed in both laboratory-generated and ambient fine organic aerosol samples, we conclude that the dimers observed in this study can be used as tracers for the O3-initiated oxidation of α-pinene, and are therefore indicative of enhanced anthropogenic activities, and that the high molecular weight and low volatility dimers result in homogenous nucleation under laboratory conditions, increasing the particle number concentration.

The Degradation Behavior of SiCf/SiO2 Composites in High-Temperature Environment

NASA Astrophysics Data System (ADS)

Yang, Xiang; Cao, Feng; Qing, Wang; Peng, Zhi-hang; Wang, Yi

2018-04-01

SiCf/SiO2 composites had been fabricated efficiently by Sol-Gel method. The oxidation behavior, thermal shock property and ablation behavior of SiCf/SiO2 composites was investigated. SiCf/SiO2 composites showed higher oxidation resistance in oxidation atmosphere, the flexural strength retention ratio was larger than 90.00%. After 1300 °C thermal shock, the mass retention ratio was 97.00%, and the flexural strength retention ratio was 92.60%, while after 1500 °C thermal shock, the mass retention ratio was 95.37%, and the flexural strength retention ratio was 83.34%. After 15 s ablation, the mass loss rate was 0.049 g/s and recession loss rate was 0.067 mm/s. The SiO2 matrix was melted in priority and becomes loosen and porous. With the ablation going on, the oxides were washed away by the shearing action of the oxyacetylene flame. The evaporation of SiO2 took away large amount of heat, which is also beneficial to the protection for SiCf/SiO2 composites.

On the behavior of reduced graphene oxide based electrodes coated with dispersed platinum by alternate current methods in the electrochemical degradation of reactive dyes.

PubMed

Del Río, A I; García, C; Molina, J; Fernández, J; Bonastre, J; Cases, F

2017-09-01

The electrochemical behavior of different carbon-based electrodes with and without nanoparticles of platinum electrochemically dispersed on their surface has been studied. Among others, reduced graphene oxide based electrodes was used to determine the best conditions for the decolorization/degradation of the reactive dye C.I. Reactive Orange 4 in sulfuric medium. Firstly, the electrochemical behavior was evaluated by cyclic voltammetry. Secondly, different electrolyses were performed using two cell configurations: cell with anodic and cathodic compartments separated (divided configuration) and without any separation (undivided configuration). The best results were obtained when reduced graphene oxide based anodes were used. The degree of decolorization was monitored by spectroscopic methods and high performance liquid chromatography. It was found that all of them followed pseudo-first order kinetics. When reduced graphene oxide-based electrodes coated with dispersed platinum by alternate current methods electrodes were used, the lowest energy consumption and the higher decolorization kinetics rate were obtained. Scanning Electronic Microscopy was used to observe the morphological surface differences. Copyright © 2017 Elsevier Ltd. All rights reserved.

Rap Music Use, Perceived Peer Behavior, and Sexual Initiation Among Ethnic Minority Youth.

PubMed

Johnson-Baker, Kimberly A; Markham, Christine; Baumler, Elizabeth; Swain, Honora; Emery, Susan

2016-03-01

Research shows that rap music use is associated with risky sexual behavior in ethnic minority youth; however, it is unknown whether rap music use impacts sexual initiation specifically and, if so, which factors mediate this impact. Thus, we investigated the longitudinal relationship between hours spent listening to rap music in seventh grade and sexual initiation in ninth grade. We also examined the role of perceived peer sexual behavior as a potential mediator of this relationship. We analyzed data from students (n = 443) enrolled in a school-based randomized controlled trial of a sexual health education curriculum collected at baseline and at 18-month follow-up. Rap music use and perceived peer sexual behavior were assessed in seventh grade, whereas sexual initiation was assessed in ninth grade. Univariate, multivariate, and mediation analyses were conducted. At baseline, rap music use was significantly associated with race/ethnicity, parental music rules, and sexual behavior, but not with gender or parental education. Rap music use was a significant predictor of sexual initiation on univariate analysis but not multivariate analysis. Mediation analysis showed that the association between hours spent listening to rap music and sexual initiation was significantly mediated by perceived peer sexual behavior. Rap music use in early adolescence significantly impacts sexual initiation in late adolescence, partially mediated by perceived peer sexual behavior. More research is needed to understand how rap music influences perceptions of peer sexual behavior, which, in turn, influence early sexual initiation. Copyright © 2016 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.

40 CFR 60.55a - Standard for nitrogen oxides.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 7 2013-07-01 2013-07-01 false Standard for nitrogen oxides. 60.55a... § 60.55a Standard for nitrogen oxides. On and after the date on which the initial compliance test is... gases that contain nitrogen oxides in excess of 180 parts per million by volume, corrected to 7 percent...

40 CFR 60.55a - Standard for nitrogen oxides.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 6 2011-07-01 2011-07-01 false Standard for nitrogen oxides. 60.55a... § 60.55a Standard for nitrogen oxides. On and after the date on which the initial compliance test is... gases that contain nitrogen oxides in excess of 180 parts per million by volume, corrected to 7 percent...

40 CFR 60.55a - Standard for nitrogen oxides.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 7 2012-07-01 2012-07-01 false Standard for nitrogen oxides. 60.55a... § 60.55a Standard for nitrogen oxides. On and after the date on which the initial compliance test is... gases that contain nitrogen oxides in excess of 180 parts per million by volume, corrected to 7 percent...

40 CFR 60.55a - Standard for nitrogen oxides.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 7 2014-07-01 2014-07-01 false Standard for nitrogen oxides. 60.55a... § 60.55a Standard for nitrogen oxides. On and after the date on which the initial compliance test is... gases that contain nitrogen oxides in excess of 180 parts per million by volume, corrected to 7 percent...

Copper Oxide Nanoparticles Impact Several Toxicological Endpoints and Cause Neurodegeneration in Caenorhabditis elegans

PubMed Central

Zanon, Tyler; Kappell, Anthony D.; Petrella, Lisa N.; Andersen, Erik C.; Hristova, Krassimira R.

2016-01-01

Engineered nanoparticles are becoming increasingly incorporated into technology and consumer products. In 2014, over 300 tons of copper oxide nanoparticles were manufactured in the United States. The increased production of nanoparticles raises concerns regarding the potential introduction into the environment or human exposure. Copper oxide nanoparticles commonly release copper ions into solutions, which contribute to their toxicity. We quantified the inhibitory effects of both copper oxide nanoparticles and copper sulfate on C. elegans toxicological endpoints to elucidate their biological effects. Several toxicological endpoints were analyzed in C. elegans, including nematode reproduction, feeding behavior, and average body length. We examined three wild C. elegans isolates together with the Bristol N2 laboratory strain to explore the influence of different genotypic backgrounds on the physiological response to copper challenge. All strains exhibited greater sensitivity to copper oxide nanoparticles compared to copper sulfate, as indicated by reduction of average body length and feeding behavior. Reproduction was significantly reduced only at the highest copper dose, though still more pronounced with copper oxide nanoparticles compared to copper sulfate treatment. Furthermore, we investigated the effects of copper oxide nanoparticles and copper sulfate on neurons, cells with known vulnerability to heavy metal toxicity. Degeneration of dopaminergic neurons was observed in up to 10% of the population after copper oxide nanoparticle exposure. Additionally, mutants in the divalent-metal transporters, smf-1 or smf-2, showed increased tolerance to copper exposure, implicating both transporters in copper-induced neurodegeneration. These results highlight the complex nature of CuO nanoparticle toxicity, in which a nanoparticle-specific effect was observed in some traits (average body length, feeding behavior) and a copper ion specific effect was observed for other traits (neurodegeneration, response to stress). PMID:27911941

Influence of heavy metals on the formation and the distribution behavior of PAH and PCDD/F during simulated fires.

PubMed

Wobst, M; Wichmann, H; Bahadir, M

2003-04-01

Combustion experiments were performed with an artificial fire load (polystyrene and quartz powder) in a laboratory scale incinerator in the presence of gaseous HCl to simulate accidental fire conditions. The aim of this investigation was to trace back the alterations of the formation and the distribution behavior of PAH and PCDD/PCDF to the presence of CuO or a mixture of metal oxides (CdO, CuO, Fe(2)O(3), PbO, MoO(3), ZnO). The total amount of the 16 PAH target compounds was reduced by the factor of 5-9 when the mixture of metal oxides was present rather than merely CuO. PAH patterns as well as their distribution behavior were significantly influenced by these oxides. In general, transportation inside the installation was enhanced for most of the 16 analyzed PAH. Only fluorene and dibenzo[a,h]anthracene were transported to a smaller extent. In contrast to PAH, total concentrations of PCDD were increased by factor 9 and of PCDF by factor 10, respectively, when CuO was present. Adding the mixture of metal oxides resulted in an increase of PCDD by factor 14 and of PCDF by factor 7. CuO and the mixture of metal oxides had a different influence on the PCDD/F homologue patterns. For instance, the HxCDF to OCDF ratio after incineration without any metal oxide was 1 to 6, whereas addition of CuO or the mixture of the metal oxides shifted the HxCDF to OCDF ratios towards 1 to 40 or 1 to 17, respectively. Combustion along with CuO increased transportation of higher chlorinated PCDF congeners, whereas the mixture of the metal oxides caused a strong decrease of PCDF distribution throughout the system.

Different Effects of Oral Contraceptive and Dydrogesterone Treatment on Oxidative Stress Levels in Premenopausal Women.

PubMed

Chen, Jui-Tung; Kotani, Kazuhiko

2018-02-01

The aim of the study was to observe the changes in blood oxidative stress levels by oral contraceptive (OC) and/or dydrogesterone (DG) treatment. A retrospective cohort of 27 premenopausal women with primary dysmenorrhea consisted of the OC treatment group (N = 17) and the DG treatment group (N = 10) by choice of the initial treatment. The OC group included two subgroups: patients with continuous OC treatment (treated for at least 15 months, N = 10) and patients with discontinuous OC treatment (switched to DG treatment after approximately 6 months of initial OC treatment: N = 7). The DG group had 15 months of continuous DG treatment. Blood parameters, including diacron-reactive oxygen metabolites (d-ROMs: an oxidative stress marker), were measured. The d-ROMs level was elevated in the OC group 3 months after initial treatment (mean: from 321 (at baseline) to 512 Carratelli Units (Carr U); P < 0.01), while such changes were not observed in the DG group. The d-ROMs level was reduced in the discontinuous OC subgroup 15 months after initial treatment (from 508 (3 months after initial treatment) to 372 Carr U; P < 0.01), while such changes were not observed in the continuous OC subgroup. The DG group displayed unchanged the d-ROMs level. Replacing OC with DG can attenuate oxidative stress as elevated by OC, thereby alleviating the possible vascular risks with OC treatment.

Demographic and Clinical Characteristics Associated with Engagement in Behavioral Health Treatment among Children with Autism Spectrum Disorders

ERIC Educational Resources Information Center

Croen, Lisa A.; Shankute, Naomi; Davignon, Meghan; Massolo, Maria L.; Yoshida, Cathleen

2017-01-01

This study investigates demographic and clinical factors associated with initiation, continuation, and adherence to behavioral health treatment (BHT) among children with autism spectrum disorder. Among 293 insured children referred for applied behavior analysis (ABA) based BHT, 23% never initiated treatment. Among those initiating treatment, 31%…

Friends: The Role of Peer Influence across Adolescent Risk Behaviors.

ERIC Educational Resources Information Center

Maxwell, Kimberly A.

2002-01-01

Examined peer influence for 1,969 adolescents across 5 risk behaviors: smoking, alcohol consumption, marijuana use, tobacco chewing, and sexual debut. Results show that a random same-sex peer predicts a teen's risk behavior initiation through influence to initiate cigarette and marijuana use, and influence to initiate and stop alcohol and chewing…

Aerobic biodegradation of amphoteric amine-oxide-based surfactants: Effect of molecular structure, initial surfactant concentration and pH.

PubMed

Ríos, Francisco; Lechuga, Manuela; Fernández-Serrano, Mercedes; Fernández-Arteaga, Alejandro

2017-03-01

The present study was designed to provide information regarding the effect of the molecular structure of amphoteric amine-oxide-based surfactants and the initial surfactant concentration on their ultimate biodegradation. Moreover, given this parameter's pH-dependence, the effect of pH was also investigated. Three amine-oxide-based surfactants with structural differences in their hydrophobic alkyl chain were tested: Lauramine oxide (AO-R 12 ), Myristamine oxide (AO-R 14 ) and Cocamidopropylamine oxide (AO-Cocoamido). We studied the ultimate biodegradation using the Modified OECD Screening Test at initial surfactant concentrations ranged from 5 to 75 mg L -1 and at pH levels from 5 to 7.4. The results demonstrate that at pH 7.4, amine-oxide-based surfactants are readily biodegradable. In this study, we concluded that ω-oxidation can be assumed to be the main biodegradation pathway of amine-oxides and that differences in the biodegradability between them can be explained by the presence of an amide group in the alkyl chain of AO-Cocoamido; the CN fission of the amide group slows down their mineralization process. In addition, the increase in the concentration of the surfactant from 5 to 75 mg L -1 resulted in an increase in the final biodegradation of AO-R 12 and AO-R 14 . However, in the case of AO-Cocoamido, a clear relationship between the concentration and biodegradation cannot be stated. Conversely, the biodegradability of AO-R 12 and AO-R 14 was considerably lower in an acid condition than at a pH of 7.4, whereas AO-Cocoamido reached similar percentages in acid conditions and at a neutral pH. However, microorganisms required more time to acclimate. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

PubMed

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

2018-01-10

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

Treatment Sequencing for Childhood ADHD: A Multiple-Randomization Study of Adaptive Medication and Behavioral Interventions.

PubMed

Pelham, William E; Fabiano, Gregory A; Waxmonsky, James G; Greiner, Andrew R; Gnagy, Elizabeth M; Pelham, William E; Coxe, Stefany; Verley, Jessica; Bhatia, Ira; Hart, Katie; Karch, Kathryn; Konijnendijk, Evelien; Tresco, Katy; Nahum-Shani, Inbal; Murphy, Susan A

2016-01-01

Behavioral and pharmacological treatments for children with attention deficit/hyperactivity disorder (ADHD) were evaluated to address whether endpoint outcomes are better depending on which treatment is initiated first and, in case of insufficient response to initial treatment, whether increasing dose of initial treatment or adding the other treatment modality is superior. Children with ADHD (ages 5-12, N = 146, 76% male) were treated for 1 school year. Children were randomized to initiate treatment with low doses of either (a) behavioral parent training (8 group sessions) and brief teacher consultation to establish a Daily Report Card or (b) extended-release methylphenidate (equivalent to .15 mg/kg/dose bid). After 8 weeks or at later monthly intervals as necessary, insufficient responders were rerandomized to secondary interventions that either increased the dose/intensity of the initial treatment or added the other treatment modality, with adaptive adjustments monthly as needed to these secondary treatments. The group beginning with behavioral treatment displayed significantly lower rates of observed classroom rule violations (the primary outcome) at study endpoint and tended to have fewer out-of-class disciplinary events. Further, adding medication secondary to initial behavior modification resulted in better outcomes on the primary outcomes and parent/teacher ratings of oppositional behavior than adding behavior modification to initial medication. Normalization rates on teacher and parent ratings were generally high. Parents who began treatment with behavioral parent training had substantially better attendance than those assigned to receive training following medication. Beginning treatment with behavioral intervention produced better outcomes overall than beginning treatment with medication.

The enzymatic oxidation of graphene oxide.

PubMed

Kotchey, Gregg P; Allen, Brett L; Vedala, Harindra; Yanamala, Naveena; Kapralov, Alexander A; Tyurina, Yulia Y; Klein-Seetharaman, Judith; Kagan, Valerian E; Star, Alexander

2011-03-22

Two-dimensional graphitic carbon is a new material with many emerging applications, and studying its chemical properties is an important goal. Here, we reported a new phenomenon--the enzymatic oxidation of a single layer of graphitic carbon by horseradish peroxidase (HRP). In the presence of low concentrations of hydrogen peroxide (∼40 μM), HRP catalyzed the oxidation of graphene oxide, which resulted in the formation of holes on its basal plane. During the same period of analysis, HRP failed to oxidize chemically reduced graphene oxide (RGO). The enzymatic oxidation was characterized by Raman, ultraviolet-visible, electron paramagnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, atomic force microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and gas chromatography-mass spectrometry. Computational docking studies indicated that HRP was preferentially bound to the basal plane rather than the edge for both graphene oxide and RGO. Owing to the more dynamic nature of HRP on graphene oxide, the heme active site of HRP was in closer proximity to graphene oxide compared to RGO, thereby facilitating the oxidation of the basal plane of graphene oxide. We also studied the electronic properties of the reduced intermediate product, holey reduced graphene oxide (hRGO), using field-effect transistor (FET) measurements. While RGO exhibited a V-shaped transfer characteristic similar to a single layer of graphene that was attributed to its zero band gap, hRGO demonstrated a p-type semiconducting behavior with a positive shift in the Dirac points. This p-type behavior rendered hRGO, which can be conceptualized as interconnected graphene nanoribbons, as a potentially attractive material for FET sensors.

Influences of superalloy composition and Pt content on the oxidation behavior of gamma–gamma prime NiPtAl bond coatings

DOE PAGES

Haynes, James A.; Unocic, Kinga A.; Lance, Michael J.; ...

2016-09-13

Here, the effects of superalloy composition and Pt content on the high-temperature oxidation behavior of γ–γ’ NiPtAl diffusion coatings were investigated over the temperature range of 1050–1150 °C. Simple NiPtAl diffusion coatings with 7 or 12 µm electroplated Pt thickness were evaluated in 1-h cycles in dry O 2 for up to 2500 cycles on four superalloys: directionally solidified (DS) alloy 142, 1st generation single-crystal (SX) alloy 1483, and 2nd generation SX alloys X4 and N5. Coatings on high-Hf alloy 142 experienced severe internal oxidation of Hf at all temperatures. Coatings on ~5 at.% Ti alloy 1483 were protective atmore » 1050 °C, but exhibited severe scale spallation at 1100 °C, with extensive formation of Ti- and Ni-rich oxides at the gas interface. Coatings with 7-µm Pt on X 4 were extremely protective at 1100 °C, but failed rapidly at 1150 °C, which also was associated with the formation of Ti-rich oxides. Increasing the coating Pt content on X 4 improved the 1150 °C oxidation behavior. Coatings on Ti-free N 5 showed the best performance at 1150 °C, especially with 12-µm Pt. Although γ–γ’ coatings can exhibit outstanding cyclic oxidation resistance with minimal Al depletion, they appear to be sensitive to substrate composition, as well as eventual Pt depletion due to interdiffusion.« less

The Effect of the Concentration of Oxidant, Cr(VI), on the Iron Oxidation in Saline Water

NASA Astrophysics Data System (ADS)

Ahn, H.; Jo, H. Y.; Ryu, J. H.; Koh, Y. K.

2014-12-01

Deep geological disposal is currently considered as the most appropriate method to isolate high level radioactive wastes (HLRWs) from the ecosystem. If groundwater seeps into underground disposal facilities, water molecules can be dissociated to radicals or peroxides, which can oxidize metal canisters and HLRWs. The oxidized radionuclides with a high solubility can be dissolved in the groundwater. Some dissolved radionuclides can act as oxidants. The continuous radiolysis of water molecules, which results from continuous seepage of groundwater, can enable the continuous production of the radioactive oxidants, resulting in an increase in concentration of oxidants. In this study, the effect of oxidant concentration on iron oxidation in the presence of salt was evaluated. Zero valent iron (ZVI) particles were reacted with Cr(VI) solutions with initial Cr(VI) concentrations ranged from 50 to 300 mg/L in reactors. The initial pH and NaCl concentration were fixed at 3 and 0.5 M, respectively. An increase in the initial Cr(VI) concentration caused an increase in the rate and extend of H2 gas production. The decrement of Cr(VI) was increased as the initial Cr(VI) concentration was increased. The penetration of H+ ions in the presence Cl- ions through the passive film on the ZVI particles caused the reaction between H+ ions and ZVI particles, producing H2 gas and Fe2+ ions. The passive film was damaged during the reaction due to the eruption of H2 gas or peptization by Cl- ions. The Fe2+ ions were reacted with Cr(VI) ions in the solution, producing Fe(III)-Cr(III) (oxy)hydroxides on the passive film of ZVI particles or in the solution as colloidal particles. The Fe(III)-Cr(III) (oxy)hydroxides tends to be precipitated as colloidal particles at a high Cr(VI) concentration and precipitated on the passive film at a low Cr(VI) concentration. The passive film was repaired or thickened by additional formation of Fe(III)-Cr(III) (oxy)hydroxides at a lower Cr(VI) concentration.

Fabricating Ohmic contact on Nb-doped SrTiO{sub 3} surface in nanoscale

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

Wang, Yuhang; National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang, Sichuan 621999; Shi, Xiaolan

2016-05-09

Fabricating reliable nano-Ohmic contact on wide gap semiconductors is an important yet difficult step in oxide nanoelectronics. We fabricated Ohmic contact on the n-type wide gap oxide Nb-doped SrTiO{sub 3} in nanoscale by mechanically scratching the surface using an atomic force microscopy tip. Although contacted to high work function metal, the scratched area exhibits nearly linear IV behavior with low contact resistance, which maintains for hours in vacuum. In contrast, the unscratched area shows Fowler–Nordheim tunneling dominated Schottky rectifying behavior with high contact resistance. It was found that the Ohmic conductivity in the scratched area was drastically suppressed by oxygenmore » gas indicating the oxygen vacancy origin of the Ohmic behavior. The surface oxygen vacancy induced barrier width reduction was proposed to explain the phenomena. The nanoscale approach is also applicable to macroscopic devices and has potential application in all-oxide devices.« less

Subparabolic Oxidation Behavior of Silicon Carbide at 1300 C

NASA Technical Reports Server (NTRS)

Ogbuji, Linjus U. J. T.

1998-01-01

The phenomenon of subparabolic oxide growth rate, more the rule than the exception in the oxidation of silica formers, is examined in light of data sets acquired in SiC oxidation experiments at 1300 C. Negative deviation from parabolic kinetics is shown to correlate with oxide crystallinity. The data sets were analyzed to ascertain the predominant and contributing growth laws, and tested with models that describe the overall kinetics as combinations of the familiar growth laws.

A cleanroom sleeping environment's impact on markers of oxidative stress, immune dysregulation, and behavior in children with autism spectrum disorders.

PubMed

Faber, Scott; Zinn, Gregory M; Boggess, Andrew; Fahrenholz, Timothy; Kern, John C; Kingston, H M Skip

2015-03-19

An emerging paradigm suggests children with autism display a unique pattern of environmental, genetic, and epigenetic triggers that make them susceptible to developing dysfunctional heavy metal and chemical detoxification systems. These abnormalities could be caused by alterations in the methylation, sulfation, and metalloprotein pathways. This study sought to evaluate the physiological and behavioral effects of children with autism sleeping in an International Organization for Standardization Class 5 cleanroom. Ten children with autism, ages 3-12, slept in a cleanroom for two weeks to evaluate changes in toxin levels, oxidative stress, immune dysregulation, and behavior. Before and after the children slept in the cleanroom, samples of blood and hair and rating scale scores were obtained to assess these changes. Five children significantly lowered their concentration of oxidized glutathione, a biomarker of oxidative stress. The younger cohort, age 5 and under, showed significantly greater mean decreases in two markers of immune dysregulation, CD3% and CD4%, than the older cohort. Changes in serum magnesium, influencing neuronal regulation, correlated negatively while changes in serum iron, affecting oxygenation of tissues, correlated positively with age. Changes in serum benzene and PCB 28 concentrations showed significant negative correlations with age. The younger children demonstrated significant improvements on behavioral rating scales compared to the older children. In a younger pair of identical twins, one twin showed significantly greater improvements in 4 out of 5 markers of oxidative stress, which corresponded with better overall behavioral rating scale scores than the other twin. Younger children who slept in the cleanroom altered elemental levels, decreased immune dysregulation, and improved behavioral rating scales, suggesting that their detoxification metabolism was briefly enhanced. The older children displayed a worsening in behavioral rating scale performance, which may have been caused by the mobilization of toxins from their tissues. The interpretation of this exploratory study is limited by lack of a control group and small sample size. The changes in physiology and behavior noted suggest that performance of larger, prospective controlled studies of exposure to nighttime or 24 hour cleanroom conditions for longer time periods may be useful for understanding detoxification in children with autism. Clinical Trial Registration Number NCT02195401 (Obtained July 18, 2014).

Rheology and microstructure of dilute graphene oxide suspension

NASA Astrophysics Data System (ADS)

Tesfai, Waka; Singh, Pawan; Shatilla, Youssef; Iqbal, Muhammad Z.; Abdala, Ahmed A.

2013-10-01

Graphene and graphene oxide are potential candidates as nanofluids for thermal management applications. Here, we investigate the rheological properties and intrinsic viscosity of aqueous suspension of graphene and use the measured intrinsic viscosity to determine the aspect ratio of graphene oxide. Dilute suspension of graphene oxide (0.05 to 0.5 mg/mL) exhibits a shear thinning behavior at low shear rates followed by a shear-independent region that starts at shear rate between 5 and 100/s depending on the concentration. This shear thinning behavior becomes more pronounced with the increase of particle loading. Moreover, AFM imaging of the dried graphene oxide indicates the evolution of irregular and thin low fractal aggregates of 0.3-1.8 nm thickness at lower concentrations to oblate compact structures of 1-18 nm thickness of nanosheets at higher concentration. These observations elucidate the microstructure growth mechanisms of graphene oxide in multiphase systems, which are important for nanofluids applications and for dispersing graphene and graphene oxide in composite materials. The suspension has a very high intrinsic viscosity of 1661 due to the high graphene oxide aspect ratio. Based on this intrinsic viscosity, we predict graphene oxide aspect ratio of 2445. While the classical Einstein and Batchelor models underestimate the relative viscosity of graphene oxide suspension, Krieger-Dougherty prediction is in a good agreement with the experimental measurement.

Effect of ZrB2 addition on the oxidation behavior of Si-SiC-ZrB2 composites exposed at 1500°C in air.

PubMed

D'Amico, Claudio; Bianchi, Giovanni; Padovano, Elisa; Biamino, Sara; Aversa, Alberta; Badini, Claudio; Ortona, Alberto

2018-01-01

Silicon carbide ceramics obtained by reactive infiltration of silicon (SRI) have many industrial applications especially involving severe and high temperature conditions. In this study, the oxidation behavior in air of Si-SiC-ZrB 2 systems at a high temperature (1500°C) for dwelling times of up to 48 hours was examined. The oxidation process was analyzed on the basis of elemental maps and X-ray diffraction patterns taken, respectively, on the core and on the surface of the specimens, together with weight gains and the average thicknesses of the resulting scale. Further, flexural strength at room temperature was examined as a function of different oxidation times. The main chemical reactions and phase transformations involved in the oxidation process are reported. Several oxides were detected on the surface: zirconia, silica, zircon and 3-zirconium monoxide. All of the samples showed a parabolic oxidation kinetics, suggesting that the controlling mechanism was the diffusion; however, even after 48 hours, the oxidation process was not finished - indeed, all of the samples continued to gain weight. The oxidation of Si-SiC-ZrB 2 material produced via SRI was slower compared with previously investigated ZrB 2 -SiC composites processed with a different techniques and tested in similar conditions. The oxidation mechanism was found to be consistent with the convection cells model.

Cyclic oxidation behavior of some plasma-sprayed coatings in Na2SO4-60%V2O5 environment

NASA Astrophysics Data System (ADS)

Singh, Harpreet; Prakash, Satya; Puri, Devendra; Phase, D. M.

2006-12-01

Cyclic oxidation behavior of plasma-sprayed NiCrAlY, Ni-20Cr, Ni3Al, and Stellite-6 coatings was investigated in an aggressive environment of Na2SO4-60%V2O5 by thermogravimetric techniques for 50 cycles. These coatings were deposited on a Ni-base superalloy, namely Superni 600; 10Fe-15.5Cr-0.5Mn-0.2C-Bal Ni (wt.%). X-ray diffraction, scanning electron microscopy/energy dispersive x-ray (SEM/EDX), and electron probe microanalyzer (EPMA) techniques were used to analyze the oxidation products. The uncoated superalloy suffered accelerated oxidation in the form of intense spallation of its oxide scale. After deposition of the NiCrAlY coating, the superalloy showed a minimum mass gain, whereas after application of the Stellite-6 coating, a maximum mass gain was observed among the coatings studied. All of the coatings were found to be useful in reducing the spallation of the substrate superalloy. Moreover, the coatings were successful in maintaining continuous surface contact with the base superalloy during the cyclic oxidation. The phases revealed for the oxidized coatings were mainly the oxides of chromium and/or aluminum and the spinels containing nickel-chromium/cobalt-chromium/nickel-aluminum mixed oxides, which are reported to be protective against high-temperature oxidation/hot corrosion.