Alloy 600 is used as a material for a steam generator tubing in pressurized water
reactors(PWR) due to its high corrosion resistance under a PWR environment. In spite of its corrosion
resistance, a stress corrosion cracking(SCC) has occurred on the primary side as well as the secondary
side of a tubing. It is known that a SCC is related to the electrochemical behaviors of an anodic
dissolution and a passivation of a bare surface of metals and alloys. Therefore in the present work, the
passive oxide films on Alloy 600 have been investigated as a function of the solution temperature by
using a potentiodynamic polarization, electrochemical impedance spectroscopy and a TEM, equipped
with EDS. Moreover the semiconductive property was evaluated by using the Mott-Schottky relation.
It was found that the passivity depends on the chemical composition and the densification of the oxide
film rather than the oxide thickness. As the solution temperature of 0.5M H3BO3 increased, the
thickness of the passive film increased but the oxide resistance of the passive film was decreased,
indicating that the measured current in the passive region of the potentiodynamic curve is closely
related to the stability of the passive film rather than the oxide thickness. It was found that the oxide
films were composed of an outer oxide layer with a lower resistance and an inner oxide layer with a
relatively higher resistance. From the Mott-Schottky relation, the oxide formed at 300oC showed a
p-type semiconductor property unlike the n-type oxide films up to 250oC.
Electrochemical reduction of graphene oxide films: Preparation, characterization and their electrochemical properties
