A Theory of Perturbation‐Initiated Pitting

It is shown that perturbation of the concentration of aggressive ions and also of an electrical field in a corrosive solution can initiate local activation and pitting nucleation in a passive metal. The linear stability theory was applied to the system in which a passive metal is kept at a constant potential in a solution containing aggressive ions. A critical condition was discovered where the possible disturbance in the solution caused the acceleration of local dissolution of the passive film. This process advanced autocatalytically until it reaches pit nucleation. Perturbations were found to grow with time above a critical wavelength. It was demonstrated that a high concentration of aggressive ions, a high electrical field in the solution, and a positive electrode potential promotes pit nucleation. The process was well explained as a probability event.