. The Bell System technical journal . ron potential near the inter-face has become more anodic and the potential of zinc near the interfacehas moved in the cathodic direction, , the difference in potentialbetween iron and zinc near the interface of the two metals is appreci- 30 BELL SYSTEM TECHNICAL JOURNAL ably less than when taken at points more widely separated. Figure 2gives a schematic representation of this experiment. The change inpotential is the result of current fiow through the electrolyte from zincto iron. The current densities are highest in the region of the interface,the met
. The Bell System technical journal . ron potential near the inter-face has become more anodic and the potential of zinc near the interfacehas moved in the cathodic direction, , the difference in potentialbetween iron and zinc near the interface of the two metals is appreci- 30 BELL SYSTEM TECHNICAL JOURNAL ably less than when taken at points more widely separated. Figure 2gives a schematic representation of this experiment. The change inpotential is the result of current fiow through the electrolyte from zincto iron. The current densities are highest in the region of the interface,the metal ion concentration becoming increased at the anode area anddecreased at the cathode area, producing thereby anodic and cathodicpolarization, respectively. This polarization behavior of corrosion cells largely determines therate of corrosion. It is obvious that the effective potentials of corro-sion cells may be reduced by polarization to zero, in which case therate of corrosion is limited to that required to maintain this polariza-. CURRENT DENSITY Fig. 2—Illustration of galvanic polarization. tion. In other words, the progress of corrosion may be controlled bythe extent either of anode polarization or cathode polarization or both,that is, either one may determine the final result. Figure 3 representsthe variety of current density-potential relationships which may existin corrosion cells. In Cell 1, in which there is no appreciable polariza-tion of either anodic or cathodic areas (as indicated by the smallchange of potential with current), corrosion current flow is limited bythe resistance of the electrolytic paths between anodes and cathodesand since this may be small if these areas are contiguous the corrosionrate may be high. In Cell 2 the anode is highly polarized as repre-sented by the solid line or progressively less polarized as the point ofintersection with the non-polarized cathode occurs at higher andhigher current densities as represented by the dotted lines. In
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