Sawicki J.A.,Interatomics |
Sawicki J.A.,Chalk River Laboratories |
Marcinkowska K.,Chalk River Laboratories |
Wagner F.E.,TU Munich
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2010
Mössbauer spectroscopy of 73.0 keV gamma-ray transition in 193Ir and supplementary analytical techniques were used to study the microstructure and chemical form of polymer-supported hydrophobic bimetallic Pt-Ir catalysts for detection and removal of CO from humid air at ambient conditions. The catalysts, typically with a composition of 9 wt.% Pt and 1 wt.% Ir, were prepared by incipient wetness impregnation of polystyrene- divinylbenzene (SDB) granules with ethanol solutions of hexachloroplatinic and hexachloroiridic acids. This procedure, followed by reduction in H2 or CO at only 200 °C or 250 °C, resulted in formation of highly-dispersed Pt-Ir particles usually smaller than 20 nm and having high catalytic activity and selectivity. Mössbauer spectra of 73.0 keV gamma-ray transition in 193Ir were taken after consecutive steps of preparation and exposure of catalysts to better understand and further improve the fabrication processes. In the as-impregnated state, iridium was found mostly as Ir(III) in [IrCl6]3- ions, with only a small fraction of Ir(IV) in [IrCl6]2- ions. The iridium in bimetallic clusters formed by reduction in hydrogen showed a strong tendency towards oxidation on exposure to air at room temperature, while Pt remained mostly metallic. In the most active and stable catalysts, the Ir and Pt in metallic regions of the clusters did not tend to segregate, unlike in Pt-Ir/silica-supported catalysts studied by us earlier. Further, this study shows that the IrO2-like regions in the clusters exhibit stronger deviations from local symmetry and stoichiometry of crystalline IrO2 than observed previously in Pt-Ir/silica catalysts. Our study also indicates that in the examined Pt-IrO2 nanoparticles iridium largely provides the dissociative O2 adsorption sites, while the CO adsorption occurs primarily at metallic Pt sites. © 2010 Elsevier B.V. All rights reserved.
Coomarasamy A.,Ministry of Transportation |
Lai D.,Ministry of Transportation |
Ramamurthy S.,University of Western Ontario |
Walzak M.J.,University of Western Ontario |
And 2 more authors.
NACE - International Corrosion Conference Series | Year: 2010
Weathering steel is used almost exclusively by Ministry of Transportation Ontario (MTO) for construction of steel bridges since 1968. This steel, under normal weathering cycles, oxidises to form a tough layer of rust or 'patina', which protects the steel from unabated corrosion. Although many of these bridges are exhibiting stable patina in most of the locations, in recent years some bridges were found to exhibit accelerated corrosion over the driving lanes (from road salt exposure) and the corrosion products were de-bonding from the parent steel material. Analysis of the corrosion products indicated that the debonded patina regions exhibited greater amounts of akaganeite (β-FeOOH), while greater amounts of goethite (α-FeOOH) were observed in the regions away from road salt exposure. Hence the objective of the present study is to form and stabilize the goethite phase on weathering steel surface even under salt exposure conditions. To meet this objective, weathering steel panels have been spray painted with low alloy steel powders containing varying concentrations of copper, nickel, chromium and molybdenum using an ethyl silicate-based paint system. These elements are thought to be primarily responsible for the formation and stabilization of goethite phase. ASTM G85-A5 (Prohesion) test has been used to evaluate the corrosion behaviour of these painted panels. Corrosion product chemistry from salt spray exposures has been determined using scanning electron microscopy coupled with energy dispersive Xray analysis, laser Raman spectroscopy and Mossbauer spectroscopy measurements. In this paper, the results from these measurements are presented and the effect of various low alloy steel powder paint formulations on the corrosion product composition is discussed.
Sawicki J.A.,Interatomics |
Sawicka B.D.,University of Victoria |
Price J.E.,Ontario Power Generation
Journal of Nuclear Materials | Year: 2010
Secondary side corrosion products (sludge) collected during one of CANDU1 1 reactor startups from wet layup have been examined by X-ray fluorescence and Mössbauer spectroscopy. The transport and chemical form of iron oxides and oxyhydroxides were determined in condensate, feedwater and preheater outlet as a function of temperature and time. The sludge burst and oxidation states of iron oxides were correlated with the rise of reactor power and corresponding changes in temperature, condensate vacuum and water flow rate. In particular, a sharp γ-FeOOH to Fe 3O 4 switch was observed that coincided in time with the onset of condensate vacuum. Also, it was found that the startup after wet layup is characterized by only brief and fairly small sludge burst at about 30% reactor power and which contributes only a small amount of undesirable α-Fe 2O 3 to total iron transport to steam generator. Thus, sludge burden to steam generators can be minimized with proper layup and startup practices. © 2010 Elsevier B.V. All rights reserved.
Journal of Nuclear Materials | Year: 2010
To assess the influence of boron iron compounds deposited on fuel rods on unexpected power shifts in pressurized water reactors, samples of crud scrapes retrieved during refuelling from three reactor cores were analyzed using 57Fe Mössbauer spectroscopy. The fuel crud scrapes were found to contain predominately nickel-iron ferrite NixFe3-xO4 in a composition range 0.6 < x < 0.8, that is with nickel content markedly higher than 0.3 < x < 0.6 found in low boiling duty PWRs. Bonaccordite, Ni2FeBO5, was found only in scrapes from a core that experienced Axial Offset Anomaly of up to-12% in the beginning of examined cycle and as high as-15% in the preceding cycle. The absence of Ni2FeBO5 in fuel crud scrapes from two other cores is in accord with the lack of AOA during examined fuel cycles in these cores. © 2010 Elsevier B.V. All rights reserved.
Journal of Nuclear Materials | Year: 2011
The samples of crud removed from the surface of fuel rods and corrosion products sampled by filtration of condensate and feed water in three boiling water reactors (BWR) operating at normal water chemistry (NWC) were analyzed using 57Fe Mössbauer spectroscopy. The corrosion products concentration and phase composition was examined in filter membranes exposed to influent and effluent of condensate polishing resin beds, as well as to final feed water. The brushed and scraped portions of fuel crud extracted from fuel rods during refueling outage comprised mostly hematite, α-Fe 2O 3, and submicron-sized goethite particles, α-FeOOH, in weight ratio similar to that observed in feed water. The observed phases are consistent with the oxidizing water chemistry of NWC BWRs. The feasibility of identifying other iron oxides and oxyhydroxides, as well as copper and zinc bearing phases in corrosion products from BWRs is briefly discussed. The results of this work can be used to better understand and minimize iron transport and crud deposition on fuel rods in BWRs. © 2011 Elsevier B.V. All rights reserved.