Anodic Polarization Scans the Protection Potential

Cyclic Anodic Polarization Scans the Protection Potential 

The effects of ferric chloride concentration on the pitting of type 304 stainless steel are shown in Fig. 7.16. Specimens were exposed for two weeks at room temperature to concentrations from 0.001 to 10 wt% ferric chloride. In this period of time, pitting was not observed for concentrations below 1.0 wt%, one pit was observed at 1 wt%, and several pits had completely penetrated the specimen at 10 wt% FeCl3. It is emphasized that the interpretation of the results presented in Fig. 7.16 must take into consideration the statistical nature of pitting namely, what is 

Type 304 stainless steel pitting corrosion specimens 

At any state of pitting, the surface is a composite of active and passive areas. The anodic polarization curve for this composite surface is then the sum, at each potential, of the current densities of the passive and active curves weighted by their areas. The dashed curves, P, P2q2 P3q3, represent the positions of the active curve (initially ABHG) for active surface areas of 0.01, 0.1, and 1.0% ofthe total area. The polarization curve for the composite surface at any potential is obtained by adding the shifted curve to the passive curve. These composite-surface 

1 7 Schematic representation of shift of polarization curves associ-1 ated with progressive fractions of pitted su rface 

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