Composition, structure and properties of the oxide films formed on the stainless steel 316L in a primary type PWR environment

This paper reports a comprehensive study of the chemical composition, structure and electrochemical behaviour of oxide films developed on 316L stainless steel in a primary medium (1000 ppm B, 2 ppm Li, 37 ppm H-2 at 350 degrees C). The methods used are glow discharge optical spectroscopy, grazing X-ray diffraction analysis, near field microscopy, transmission electron microscopy (TEM), Raman spectrometry and electrochemical measurements. According to the analytical and structural investigations, the outermost part of the film consists of the Ni-0.75 Fe2.25O4 inverse spinel. In the intermediate part both Ni-0.75 Fe2.25O4 and Fe3O4 inverse spinels can be detected. Finally, the inner part of the film consists of mixed chromium oxides (Cr2O3 + FeCr2O4) and Fe3O4. The electrochemical study carried out by capacitance measurements (Mott-Schottky approach) shows that the inner and outer parts of the film manifest different semiconductivities. This is in agreement with the known semiconducting properties of the type of oxides concerned. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.