Halbleitereigenschaften von Passivfilmen und ihre Bedeutung für die Lochkorrosion

Semiconductive properties of passive films and susceptibility to localized corrosion The semiconductor properties of the passive films on AISI 304 were studied by Mott-Schottky analysis and photoelectrochemical methods. The results were compared with the number of current transients during passivation at different potentials which describe the metastable pitting events. The results show that the onset potential for pit nucleation coincides with the potential at the point of zero charge in the passive film (flat-band potential). A simple electrostatic model is presented showing that the first step of the pit nucleation event - the adsorption of the pit inducing anions - is not possible until a region of positive space charge is present in the passive film. Furthermore the model is confirmed by the appearance of a maximum in the transient number occurring in the same potential range where drastic changes in the electronic properties of the passive film take place.