Effects of hydrogen on semiconductivity of passive films and corrosion behavior of 310 stainless steel

The effects of hydrogen on the semiconductive properties and compositions of passive films on AISI 310 stainless steel (310 SS) and their corrosion behavior were investigated by Mott-Schottky plot, polarization, noise resistance analyses, and secondary ion mass spectrometry (SIMS). The results indicate that the susceptibility of 310 SS to pitting is strongly influenced by hydrogen pre sent in the specimens. The conductivity type of the passive film formed at 0.7 V vs. saturated calomel electrode on the specimens charged with hydrogen at the quantity higher than 3.6 C cm(-2) is p-type while that formed on the uncharged specimen is n-type, i.e., the presence of hydrogen in 310 SS causes an inversion of conductivity type of a surface film from p-type to n-type. When the concentration of ionized hydrogen in the passive film on the 310 SS. i.e., the donor density reaches the saturated value, the average content of the diffusible hydrogen released from a specimen measured by a U tube filled with mercury under the condition of mechanical vacuum is 3.8 x 10(20) cm(-3). The donor concentration evaluated from the Mott-Schottky slope is about in the order of 10(19) cm(-3). The susceptibility of 310 stainless steel (SS) to pitting can be correlated to the electronic properties and chemical compositions of the pa!;sive film. 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 and high content of chromium and nickel oxides. Such a correlation can be explained with the band model of a passive film. (C) 1999 The Electrochemical Society. S0013-4651(98)01-077-5. All rights reserved.