A Passive Film Formed on Alloy 600 in High Temperature Aqueous Solution
Alloy 600(74wt% Ni, 15wt% Cr, 9wt% Fe) is used as a material for steam generator tubing in pressurized water reactors(PWR) due to its high corrosion resistance under a PWR environment whose primary side and secondary side are operated under 340oC, 150bar and 290oC, 50bar, respectively. However, in spite of its outstanding corrosion resistance, a stress corrosion cracking(SCC) which has been one of the most important degradation issues, has occurred occasionally owing to the severe high temperature and pressure condition of a PWR. It is expected that a SCC is deeply related to an electrochemical property of a passive film formed under a high temperature and pressure condition. Therefore an understanding of the basic electrochemical behaviors regarding an anodic dissolution and a passivation of the bare surface of metals and alloys provides important information about a SCC mechanism and control. In the present work, the passive oxide films on Alloy 600 were investigated as a function of the dissolved oxygen content and the pH by using a potentiodynamic polarization, electrochemical impedance spectroscopy(EIS) and a depth profiling by Auger electron spectroscopy(AES). For this purpose, 0.5M H3BO3, 0.5M Na2SO4 and 0.1M NaOH aqueous solutions with/without dissolved oxygen at 300oC were used as the test solutions. The resistance of an oxide formed in an aerated solution was smaller than that in a deaerated solution while the oxide film in the aerated solution was thicker than the oxide film in the deaerated solution.
Chang Kyu Rhee
D. J. Kim et al., "A Passive Film Formed on Alloy 600 in High Temperature Aqueous Solution ", Solid State Phenomena, Vol. 135, pp. 103-106, 2008