Mechanistic study of FAC processes focused on the oxide layer properties

Detailed FAC processes and effects of local H₂ partial pressure, oxide film porosity, and Cr content on the enhancement of dissolution through the oxide layer have been discussed focused on the result of FAC experiments and oxide layer characterizations. Porosity of oxide layer is closely related to corrosion resistance of the steels even in Cr content range of 0.003 to 1.01 wt %. Compact inner oxide layer suppress the diffusion of oxidizer (H₂O) and Fe ion via pores, on the other hand, liquid-state diffusion through a porous oxide layer is considered to be dominant under high FAC rate conditions. The model of spiral enhancement of dissolution through the oxide layer has been proposed. It has been considered that FAC is enhanced with increase of local H₂ partial pressure and film porosity. It has also been suggested that low solubility Fe-Cr spinel-type oxide formed on the high Cr content steels suppresses the spiral enhancement of dissolution through the oxide layer.