| The change of the corrosion potential and polarization characteristics of the specimen were measured by applying the technique of alternating voltage variation. The passive film was formed on the surface of Fe in the saturated Ca(OH)2 solution, which had the alkalinity of pH 12.1. The corrosion potential was at first shifted to the negative direction in the range of 0-2,250mV (50Hz), and then back to the positive direction with the rate of 0.5mV/mV AV above 2,250mV. The corrosion potential shift to the negative direction was due to the formation of the n-type passive film on Fe. Above the critical voltage (2,250mV), the breakdown of the passive film shifted the corrosion potential to the positive direction by the net anodic polarization that was resulted from unsymmetrical behavior of the anodic and cathodic polarizations. The effect of alternating voltage on the breakdown of the passive films increased with decreasing frequency and increasing voltage. The passive region in polarization curve disappeared above 2,000mV at the constant frequency of 50Hz, and the frequency above 250Hz had little effect on the polarization at the constant voltage of 2,000mV. |
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