Photoelectrochemical study of nickel base alloys oxide films formed at high temperature and high pressure water

Abstract

International audienceThe oxide film formed on nickel base alloys at high temperature and high pressure water exhibits semi-conducting properties evidenced by photocurrent generation when exposed to monochromatic light. The use of macro- and micro-photoelectrochemical techniques (PEC and MPEC) aims to identify the different semiconductor phases and their distribution in the oxide film. Three different nickel base alloys were corroded in recirculation loop at 325 °C in pressurised water reactor primary coolant conditions for different exposition durations. PEC experiments on these materials enable to obtain macroscopic energy spectra showing three contributions. The first one, with a band gap around 2.2 eV, was attributed to the presence of nickel hydroxide and/or nickel ferrite. The second one, with a band gap around 3.5 eV, was attributed to Cr2O3. The last contribution, with a band gap in the range of 4.1–4.5 eV, was attributed to the spinel phase Ni1−xFexCr2O4. In addition, macroscopic potential spectra recorded at different energies highlight n-type semi-conduction behaviours for both oxides, Cr2O3 and Ni1−xFexCr2O4. Moreover, MPEC images recorded at different energies exhibit contrasted regions in photocurrent, describing the distribution of nickel hydroxide and/or nickel ferrite and Cr2O3 in the oxide film at a micron scale. It is concluded that PEC techniques represent a sensitive and powerful way to locally analyse the various semiconductor phases in the oxide scale

Electrochemical Characterization of Passive Films on Ni-Based Alloys in Acidic and Neutral Solutions

“…As described above, the passive films formed on the Ni-based alloys in the solutions consist mainly of hydroxide and oxide layers of Ni and Cr. Referring from the band gap energies reported previously for oxide and hydroxide layers on Ni and Cr, 11,15,16,22,26) the band gap energies estimated in the present work for the passive films on Alloy 600, Alloy 690 and Ni-30Cr in both solutions can be attributed to hydroxide and oxide layers in the passive films on the Ni-based alloys, that is, the band gap energy of 2.3 eV is attributed to the hydroxide layer whereas the band gap energy of 3.5 eV is from the oxide layer. The potential dependence of the slope of the photoelectrochemical action spectrum shown in Figs.…”

Mechanism of hydrogen absorption during the exposure of alloy 600-like single-crystals to PWR primary simulated media

“…The oxide film formed in these conditions is described as a duplex structure layer [15,[22][23][24] grown internally [25]. The internal layer is depicted as compact, continuous and protective towards oxidation, and composed of chromium-rich nickel spinel (i.e.…”

SIMS and TEM investigation of hydrogen trapping on implantation defects in a nickel-based superalloy

“…Alloy 600 steam generator tubes are now replaced by alloy 690, richer in chromium, and which showed insensitivity to this type of degradation phenomenon; but the understanding of the mechanisms leading to this apparent immunity is still obscure. Indeed, both alloys have similar corrosion mechanisms [2,3], that is in nature and structure [4,5] and semiconduction properties [6]. In this context, this study aims at addressing this environmental degradation issue with an original approach, based on the investigation of the possible role of hydrogen in this mechanism of degradation.…”