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 31 6L 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 spec troscopy, grazing X-ray diffraction analysis, near field microscopy, t ransmission electron microscopy (TEM), Raman spectrometry and electroc hemical measurements. According to the analytical and structural inves tigations, 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 an d Fe3O4 inverse spinels can be detected. Finally, the inner part of th e film consists of mixed chromium oxides (Cr2O3 + FeCr2O4) and Fe3O4. The electrochemical study carried out by capacitance measurements (Mot t-Schottky approach) shows that the inner and outer parts of the film manifest different semiconductivities. This is in agreement with the k nown semiconducting properties of the type of oxides concerned. (C) 19 98 Published by Elsevier Science Ltd. All rights reserved.