Correlation of hydrogen-facilitated pitting of AISI 304 stainless steel to semiconductivity of passive films

The effects of hydrogen on the semiconductive properties of passive films and susceptibility to pitting were investigated for AISI 304 stainless steel (304 SS) by Mott-Schottky plots, transfer coefficients and electrochemical noise resistance. The results indicated that the hydrogen introduced into the 304 SS may cause a conductivity inversion from p-type to n-type for passive films on 304 SS. The high susceptibility of the charged specimens to pitting corresponds to the n-type conductivity of the passive film, while low susceptibility is connected to p-type conductivity. The correlation between the pitting susceptibility and the conductivity type of the passive film was interpreted by the model of electron band structures of passive films. The saturated content of ionized hydrogen in the passive film on the 304 SS, the donor density, is evaluated as 9.04 x 10(18) cm(-3). The flat band potential of the p-type passive film on the uncharged samples is 1.33 V, and that of the n-type passive film on the highly charged samples is -0.40V. (C) 1999 Elsevier Science S.A. All rights reserved.