The durability at high temperature of metallic materials is generally provided by the formation of a very thin and homogeneous passivating layer that protects the surface from corrosion. The chemical durability generally depends on the nature of the point defects that ensures the matter transport through the oxide layers developed on their surfaces. It is indeed very well-known that the growth of a thermal oxide is generally limited by the point defects diffusion; however, to identify and to be able to measure the nature of the point defects remains very difficult. Photoelectrochemistry is one major experimental technique suited to this study via the possible measurement of the semiconducting properties of the oxide which depend on the point defects of the oxide constituting the passive layer. To better understand the passivating role of these oxide layers, we propose to study the nature of oxide scales developed at 1050°C on (Fe-Ni-Cr) commercial and model alloys as a function of oxygen partial pressure p(O2). It will be in particular demonstrated that it is possible to specify the peculiar p(O2) value of formation of stoichiometric chromia Cr2O3 (grown on pure Cr or on binary Ni-30Cr model alloy) comprised between 10-14 and 10-10 atm. The structure of n- and p-type duplex chromia will also be shown.
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