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Surface Oxide (surface + oxide)

Distribution by Scientific Domains

Chemistry	44%

Selected Abstracts

The Role of Surface Oxides in NOx Storage Reduction Catalysts

CHEMCATCHEM, Issue 6 2010
Jelena Jelic Dr.
Monte Carlo or bust: First-principles kinetic Monte Carlo simulations are used to examine NO oxidation over Pd(101)/Pd(100). Under typical conditions for NO oxidation in a NOx storage reduction system (600,K, 105,Pa,O2, 100,Pa,NO), turnover frequencies are comparable to those of Pt(111) surfaces, implying that the surface oxide is similar in reactivity to an oxygen-covered metal surface. [source]

Coupling Capillary Electrophoresis and Pulsed Electrochemical Detection

ELECTROANALYSIS, Issue 13 2005
Carlos
Abstract Pulsed electrochemical detection (PED) is an excellent method for detection of analytes that normally foul electrodes. In PED, the detection electrode is first cleaned at a high positive potential, then reactivated at a negative potential dissolving the surface oxide, and finally used to oxidize the analyte at a moderate positive potential. Due to the advantages and versatility of PED, many different variations of the detection waveform can be found in literature. This review focuses on application of PED to CE and in particular, the most commonly used modes: pulsed amperometric detection (PAD) and integrated pulsed amperometric detection (iPAD). [source]

Titanium dioxide nanoparticles-coated column for capillary electrochromatographic separation of oligopeptides

ELECTROPHORESIS, Issue 21 2005
Yi-Ling Hsieh
Abstract A novel column made through the condensation reaction of TiO2 nanoparticles (TiO2,NPs) with silanol groups of the fused-silica capillary is described. EOF measurements under various buffer constitutions were used to monitor the completion of reactions. The results indicated that the EOF was dependent on the interactions between buffers and the bonded TiO2,NPs. With formate/Tris buffer, EOF reversal at pH below,5 and cathodic EOF at pH above,5 were indicated. The pI of the bonded TiO2,NPs was found at ,ph,5. Only cathodic EOF was illustrated by substituting the mobile phase with either glutamate or phosphate buffer. It was elucidated that both glutamate and phosphate buffer yield a negative charge layer on the surface of TiO2,NPs attributable to the formation of a titanium complex. The CEC performance of the column was tested with angiotensin-type oligopeptides. Some parameters that would affect the retention behavior were investigated. The interactions between the bonded phases and the analytes were explicated by epitomized acid,base functional groups of the oligopepetides and the speciation of the surface oxide in different pH ranges. The average separation efficiencies of 3.1×104,plates/m is readily achieved with a column of 70,cm (50,cm)×50,,m,ID under an applied voltage of 15,kV, phosphate buffer (pH,6.0, 40,mM), and UV detection at 214,nm. [source]

Bioaccessibility studies of ferro-chromium alloy particles for a simulated inhalation scenario: A comparative study with the pure metals and stainless steel

INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 3 2010
Klara Midander
Abstract The European product safety legislation, REACH, requires that companies that manufacture, import, or use chemicals demonstrate safe use and high level of protection of their products placed on the market from a human health and environmental perspective. This process involves detailed assessment of potential hazards for various toxicity endpoints induced by the use of chemicals with a minimum use of animal testing. Such an assessment requires thorough understanding of relevant exposure scenarios including material characteristics and intrinsic properties and how, for instance, physical and chemical properties change from the manufacturing phase, throughout use, to final disposal. Temporary or permanent adverse health effects induced by particles depend either on their shape or physical characteristics, and/or on chemical interactions with the particle surface upon human exposure. Potential adverse effects caused by the exposure of metal particles through the gastrointestinal system, the pulmonary system, or the skin, and their subsequent potential for particle dissolution and metal release in contact with biological media, show significant gaps of knowledge. In vitro bioaccessibility testing at conditions of relevance for different exposure scenarios, combined with the generation of a detailed understanding of intrinsic material properties and surface characteristics, are in this context a useful approach to address aspects of relevance for accurate risk and hazard assessment of chemicals, including metals and alloys and to avoid the use of in vivo testing. Alloys are essential engineering materials in all kinds of applications in society, but their potential adverse effects on human health and the environment are very seldom assessed. Alloys are treated in REACH as mixtures of their constituent elements, an approach highly inappropriate because intrinsic properties of alloys generally are totally different compared with their pure metal components. A large research effort was therefore conducted to generate quantitative bioaccessibility data for particles of ferro-chromium alloys compared with particles of the pure metals and stainless steel exposed at in vitro conditions in synthetic biological media of relevance for particle inhalation and ingestion. All results are presented combining bioaccessibility data with aspects of particle characteristics, surface composition, and barrier properties of surface oxides. Iron and chromium were the main elements released from ferro-chromium alloys upon exposure in synthetic biological media. Both elements revealed time-dependent release processes. One week exposures resulted in very small released particle fractions being less than 0.3% of the particle mass at acidic conditions and less than 0.001% in near pH-neutral media. The extent of Fe released from ferro-chromium alloy particles was significantly lower compared with particles of pure Fe, whereas Cr was released to a very low and similar extent as from particles of pure Cr and stainless steel. Low release rates are a result of a surface oxide with passive properties predominantly composed of chromium(III)-rich oxides and silica and, to a lesser extent, of iron(II,III)oxides. Neither the relative bulk alloy composition nor the surface composition can be used to predict or assess the extent of metals released in different synthetic biological media. Ferro-chromium alloys cannot be assessed from the behavior of their pure metal constituents. Integr Environ Assess Manag 2010;6:441,455. © 2009 SETAC [source]

Impact of native oxides beneath the gate contact of AlGaN/GaN HFET devices

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
D. Mistele
Abstract We report on the decisive role of oxides at the surface of AlGaN/GaN Heterostructure Field Effect Transistors (HFETs). The effect of oxides at the surface is twofold, on one hand the 2DEG in the channel is directly influenced by surface charges and surface potential correlated to surface oxides (D. Mistele et al., phys. stat. sol. (a) 194 (2), 452 (2002). [1]), on the other hand, a surface oxide below a subsequently deposited gate contact increases the barrier height and therefore reduces leakage currents by several orders of magnitude. This study includes various surface treatments on AlGaN/GaN heterostructures such as etching by HCl, oxidation by O2 -plasma, and subsequent passivation by Si3N4. Next, we report on the correlation between gate leakage current and the drain current and dedicate this behavior to the Schottky barrier and to surface related charging effects. A model with the surface related charging effects on the 2DEG and the barrier height is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The Role of Surface Oxides in NOx Storage Reduction Catalysts

Processing of Carbon Nanofiber Reinforced ZrB2 Matrix Composites for Aerospace Applications,

ADVANCED ENGINEERING MATERIALS, Issue 7 2010
Jorge Barcena
Ceramic matrix composites (CMCs) based on zirconium diboride (ZrB2) reinforced by vapor grown carbon nanofibers are a potential constituent of reusable thermal protection systems. A manufacturing procedure was devised that involved the fabrication of thin films by tape casting to obtain a layer that could be integrated into a more complex system. Higher thermal conductivities and improved toughness can be expected for nanofiber additions, as compared to the matrix alone. Consolidation by hot-pressing was more effective than pressureless sintering, in terms of the final relative density and flatness of specimens. Examination of microstructures showed that few carbon nanofibers were present in the matrix after consolidation by sintering, which was attributed to a reaction between the nanofibers and zirconium oxide present on the surface of the ZrB2 powder. As a solution, oxygen impurities from the boride powders were removed by reduction with carbon coatings derived from phenolic resin. The deleterious reaction was avoided, but residual carbon remained at the grain boundaries, likely from decomposition of the binder. The use of an alternative binder (PMMA vs. PVB) will be used in future studies to reduce the residual carbon content. Further, consolidation by Spark Plasma Sintering (SPS) will be explored to further reduce the reaction of surface oxides with the nanofibers. Finally, characterization of the microstructure at the nanometric level and further determination of the mechanical and thermal properties will be conducted as part of future studies. [source]

Bioaccessibility studies of ferro-chromium alloy particles for a simulated inhalation scenario: A comparative study with the pure metals and stainless steel

The Mechanism of Water Oxidation: From Electrolysis via Homogeneous to Biological Catalysis

CHEMCATCHEM, Issue 7 2010
Holger Dau Prof.
Abstract Striving for new solar fuels, the water oxidation reaction currently is considered to be a bottleneck, hampering progress in the development of applicable technologies for the conversion of light into storable fuels. This review compares and unifies viewpoints on water oxidation from various fields of catalysis research. The first part deals with the thermodynamic efficiency and mechanisms of electrochemical water splitting by metal oxides on electrode surfaces, explaining the recent concept of the potential-determining step. Subsequently, novel cobalt oxide-based catalysts for heterogeneous (electro)catalysis are discussed. These may share structural and functional properties with surface oxides, multinuclear molecular catalysts and the catalytic manganese,calcium complex of photosynthetic water oxidation. Recent developments in homogeneous water-oxidation catalysis are outlined with a focus on the discovery of mononuclear ruthenium (and non-ruthenium) complexes that efficiently mediate O2 evolution from water. Water oxidation in photosynthesis is the subject of a concise presentation of structure and function of the natural paragon,the manganese,calcium complex in photosystem,II,for which ideas concerning redox-potential leveling, proton removal, and OO bond formation mechanisms are discussed. The last part highlights common themes and unifying concepts. [source]