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Tuesday, March 16, 2010: 10:30 AM
214 D (Henry B. Gonzales Convention Center)
Nickel base alloys are mainly used in Pressurized Water Reactors (PWR) as constituents of the U-tubes of the steam generators. These alloys are corroded by the primary coolant of the PWR which causes several degradations consequences such as stress corrosion cracking or release processes of corrosion products linked to an increase of contamination.
As a consequence the thin passive film, formed on Ni-base alloys in Pressurized Water Reactor (PWR) primary coolant, plays a key role on different corrosion and degradation processes. The aim of this work is to characterize the oxide layers formed on nickel base alloys corroded in simulated PWR primary conditions (T=325°C, P= 155bar, [H2] =1.3´10-3 mol.L-1, [Li]=2 mg.L-1, [B]= 1000 mg.L-1). Several techniques have been used such as Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy , macro and Micro PhotoElectroChemical techniques (PEC and MPEC), in order to obtain different kind of information on the nature, the structure, the repartition and other properties of the oxides. The coupling of these characterization techniques enables to propose an oxide film divided in two parts. The internal layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel chromite (Ni(1-x)FexCr2O4). Moreover, nodules of Cr2O3, with a size about 5 nm, were uniformly present at the interface between this spinel and the alloy. The external layer is composed of large crystallites corresponding to a spinel structure rich in iron (Ni(1-z)Fe(2+z)O4) and of nickel hydroxide (Ni(OH)2). Based on these results, some considerations about the mechanism of formation of these oxide layers are discussed.
As a consequence the thin passive film, formed on Ni-base alloys in Pressurized Water Reactor (PWR) primary coolant, plays a key role on different corrosion and degradation processes. The aim of this work is to characterize the oxide layers formed on nickel base alloys corroded in simulated PWR primary conditions (T=325°C, P= 155bar, [H2] =1.3´10-3 mol.L-1, [Li]=2 mg.L-1, [B]= 1000 mg.L-1). Several techniques have been used such as Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy , macro and Micro PhotoElectroChemical techniques (PEC and MPEC), in order to obtain different kind of information on the nature, the structure, the repartition and other properties of the oxides. The coupling of these characterization techniques enables to propose an oxide film divided in two parts. The internal layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel chromite (Ni(1-x)FexCr2O4). Moreover, nodules of Cr2O3, with a size about 5 nm, were uniformly present at the interface between this spinel and the alloy. The external layer is composed of large crystallites corresponding to a spinel structure rich in iron (Ni(1-z)Fe(2+z)O4) and of nickel hydroxide (Ni(OH)2). Based on these results, some considerations about the mechanism of formation of these oxide layers are discussed.