Morphological pattern formation in pitting corrosion

Abstract

From the point of view that pitting dissolution is induced by nonequilibrium fluctuations, pattern formation on pitting surface is examined. Accompanied with repeated destruction and reformation of passive film, the metal surface fluctuates by the thermal motion of solution particles, and the possibility of pit formation may be realised. The pit formation process is summarized as follows: the electrode system first selects the components with appropriate wave numbers from the thermal fluctuations, and then makes them larger with time. These fluctuations can be assorted into two types, i.e., asymmetrical and symmetrical ones; the former decides the overall pit pattern and the latter minute irregularities inside the pit. Then, the intrinsic spatial power spectrum plays the important role which determines the asymmetrical fluctuations. Consequently, it is clarified that the overall pit patterns are decided not by the surface physical parameters like the surface energy, but by the parameters affecting the instability and autocorrelation distance of the fluctuations such as the Cl− ionic concentration and overpotential.