Theoretical Distribution Functions for the Breakdown of Passive Films

Theoretical distribution functions for the critical voltage and induction time for the breakdown of passive films in aqueous systems containing aggressive anions are derived. The variations of these distributions with the parameter α (dependence of the film/solution interfacial potential on applied voltage), halide activity and pH are explored by numerical analysis. The theoretical distribution functions are found to closely mimic the experimentally determined distributions in and for the breakdown of passive films of Fe‐17 Cr in 3.5% solution of 30°C, as reported by Shibata. The findings support the hypothesis that cation vacancy diffusivity is an important property in determining the susceptibility of passive films to breakdown under anodic polarization conditions.