MORPHOLOGICAL PATTERN-FORMATION IN PITTING CORROSION

From the point of view that pitting dissolution is induced by nonequil ibrium 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 parti cles, and the possibility of pit formation may be realised. The pit fo rmation process is summarized as follows: the electrode system first s elects the components with appropriate wave numbers from the thermal f luctuations, and then makes them larger with time. These fluctuations can be assorted into two types, i.e., asymmetrical and symmetrical one s; the former decides the overall pit pattern and the latter minute ir regularities inside the pit. Then, the intrinsic spatial power spectru m plays the important role which determines the asymmetrical fluctuati ons. Consequently, it is clarified that the overall pit patterns are d ecided not by the surface physical parameters like the surface energy, but by the parameters affecting the instability and autocorrelation d istance of the fluctuations such as the Cl- ionic concentration and ov erpotential.