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Abstract: Alloy 600 samples were oxidized under different simulated PWR primary water conditions, with varying contents of dissolved hydrogen. The photoelectrochemical techniques, used to characterize the semiconducting behavior and bandgap energies of oxide films have shown that the scale has several components. The first ones, exhibiting photocurrents at photon energies lower than 2.5eV behave as n-type semiconductors, whereas the analyze of the photocurrents measured at higher energies suggests that other components are either n-type or insulating, depending on the hydrogen partial pressure tested: <0.01, 0.3 and 6.5bar (<1, 30 and 658kPa). Furthermore, a novel approach developed recently by our group allowed us determination of the number of semiconducting components in the scales and assessment of the bandgap energy for each of them. These results revealed that the composition, as well as the semiconducting properties of the scales, were influenced by the hydrogen partial pressure used in the corrosion test. [Copyright &y& Elsevier]

This work presents a multiscale photoelectrochemical characterization of oxide layers, and aims mainly at introducing the mesoscopic scale (ca 30 μm). For the first time, photocurrent energy spectra could be recorded on individual ferritic and austenitic grains of a unique 2205 duplex stainless steel sample oxidized for 5 minutes at 650°C under 20% water vapour in nitrogen. These results allowed us to explain contrasting issues in the photoelectrochemical images obtained from the oxidized sample. Moreover, the bandgap energies obtained by fitting these individual mesoscopic photocurrent energy spectra with a novel approach developed in our laboratory, showed that all oxide scales were constituted of Fe2O3 and Cr2O3 and of an Fe2-xCrxO3 solid solutions, but that the x-value of the latter was different depending on the metallurgic phase of the oxidized substrate. The latter results were shown to be in agreement with those of additional Raman analyses of the oxidized austenitic and ferritic grains. [ABSTRACT FROM AUTHOR]

The passivity and protective nature of the passive films are essentially related to ionic and electronic transport processes, which are controlled by the optical and electronic properties of passive films. Corrosion properties of passive films anodically formed on 304L stainless steel in borate/boric acid solution have been examined using electrochemical impedance spectroscopy (EIS). An electrical equivalent circuit based on the impedance analysis, which describes the behavior of the passive film on stainless steel more satisfactorily than the proposed models, is presented. The semiconducting properties of the passive films were also investigated by photoelectrochemistry. Effects of film-formation potential, film-formation time, and applied potential on the electronic properties were studied. Depending on the operating conditions, the optical bandgap values were estimated to vary from 2.1 to 2.75 eV. Both film resistance and bandgap were found to decrease with applied potential. Therefore, correlation between the two significant parameters was determined. [ABSTRACT FROM AUTHOR]

Abstract: The oxidation of iron and chromium that are present as impurities in zirconium metal or as alloying elements in Zircaloy-4 was investigated with PhotoElectroChemical techniques (PEC), highlighting the chemical nature, the size and the lateral distribution of Fe and Cr-containing phases in thin zirconia scales formed during the oxidation of pure zirconium and Zircaloy-4 at 470°C in oxygen. In the case of zirconium, iron and chromium impurities led to the formation of oxides distributed in a homogeneous way in the zirconia scale, while in the case of Zircaloy-4 these elements, present in the form of intermetallic particles in the substrate, led to the formation of localised haematite Fe2O3, rhomboedric solid solution (Fe x Cr1−x )2O3 and chromia Cr2O3 phases. These phases were accurately studied via the measurement of their respective band-gap (Fe2O3: 2.2eV, (Fe x Cr1−x )2O3: 2.6eV and Cr2O3: 3.0eV). It is concluded that PEC techniques represent a sensitive and powerful way to locally analyse the various semiconductor phases in the oxide scale at a micron scale. [Copyright &y& Elsevier]

Abstract: Room temperature photoelectrochemistry was used to characterise oxide phases grown during the initial stages of oxidation of the ferritic stainless steel AISI441 at 650°C and 850°C in synthetic air or in water vapour. Grazing incidence X-ray diffraction and Raman spectroscopy were additionally used to discuss PEC results. Haematite Fe2O3 (∼2.0eV), chromia Cr2O3 (3.0 and 3.5eV) and their mutual solid solution (∼ 2.5eV) were detected by their respective bandgap values determined from photocurrent vs. energy curves. The Cr/Fe ratio of the films increased with time/temperature and was higher in air-grown than in H2O-grown oxides. Observation of photocurrent vs. potential curves indicated that chromia was N-type in all specimens, resulting from thermodynamic equilibrium with the metallic substrate and not with the gas phase. [Copyright &y& Elsevier]