| Abstract: | An effective pre-oxidation method for Alloy X750 was developed to reduce general corrosion in an oxygenated aqueous environment such as in BWR core water. The optimum condition of preoxidation in air at elevated temperatures was found to be 5–20 h at 973 K by considering the allowance condition of heat treatment for age-hardening. Some characteristics of the corroded oxide film have been clarified by surface analyses with XMA, SIMS, AES, XPS etc. The film was composed of double oxide layers, namely a highly crystallized NiFe2O4 outer layer and a high Cr2O3 content inner layer. The passive property of the film has been recognized to be due to the nature of the oxides whereby NiFe2O4 restricts the dissolution of metals because of its low solubility and Cr2O3 restricts the diffusion of metal ions because of its high binding energy and low diffusion coefficient. |
