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IR Drops and the Local Electrode Potential during Crevicing of Iron
PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEERING
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In this work a traditionally misregarded point of view, a different electrode potential within the cavity than exists at the outer surface, is shown to be of great importance for the occurrence of localized corrosion in crevices. Based on the results of this work crevice corrosion is concluded to occur due to an electrode potential in the crevice that is the active loop region of the polarization curve of the crevice electrolyte. Compositional effects were not significantly involved since the solution did not contain Cl-, or other aggressive ions and a buffer solution was used to minimize pH changes. Gas bubble accumulation in the crevice increases the rate of crevicing and can initiate a new crevicing action at the metal-gas-electrolyte interface even on otherwise passivated surfaces. These results were obtained for an iron sample containing a preexisting crevice in a buffer 0.5M sodium acetate - 0.5M acetic acid solution of pH 4.6. In some experiments an inhibitor, sodium chromate, was present in the solution in order to observe the potential variation for an inactive crevice. Keywords Resistance drop.
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