CORRELATIONS BETWEEN THE ELECTROCHEMICAL-BEHAVIOR AND SURFACE-FILM COMPOSITION OF TZM ALLOY EXPOSED TO DIVERTOR WATER COOLANT ENVIRONMENTS

X-ray photoelectron spectroscopy (XPS) has been carried out on TZM all oy surfaces after short and long immersion tests in high temperature ( 250 degrees C) aqueous environments simulating possible fusion reactor coolant conditions during operation. Phase identification by XPS was used in connection with the open circuit potential bends to suggest pl ausible hypotheses about TZM corrosion behaviour in the various chemic al environments considered in this study. It was proposed that exposur e of TZM to oxidizing water conditions produced poorly protective laye rs, which consist essentially of low (ni) and intermediate (V) valency Mo oxides/hydroxides. Conversely the results obtained in deaerated an d reducing water conditions suggested that barrier films could develop in these environments: the phases exhibit a bilayered structure and c onsisted of an inner tetravalent Mo oxide/hydroxide and an outer hexav alent Mo oxide. The protective properties of such layers were attribut ed to the hexavalent Mo species. (C) 1997 Elsevier Science B.V.