UC Berkeley

Passivity breakdown on HDSS 2707 has been studied and the electrochemical data are interpreted in terms of the Point Defect Model. Pitting parameters of HDSS 2707 are determined, including the polarizability at bl/s interface, the defect annihilation rate, and the defect diffusion coefficient. The breakdown potential is demonstrated to be linearly related to log [Br-], pH, and the square root of potential scan rate (v1/2), and follows a near-normal distribution. The critical vacancy concentration calculated from the PDM is consistent with that estimated crystallographically from the chromic barrier layer, and the dominant point defect is further confirmed by Mott-Schottky measurements.