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EFFECT OF EXTERNAL POTENTIAL ON CORROSION BEHAVIOUR WITHIN PROPAGATING PITS OR CRACKS |
Liu Youping; Zhou Peijun; Zhang Jie; Zuo Jingyi(Beijing University of Chemical Technology) |
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Abstract An apparatus with the occluded specimen connected to the potentiostatically polarized external specimen was used to study the effects of the external potential on corrosion of the occluded cell simulating the propagating cracks or pits. A series of equations describing the relationships between corrosion rates and potentials were derived for systems of type 1Cr13 and OCr18Ni9 stainless steel in 0.5mol/L NaCl solution. Results demonstrated that cathodic polarization of the external specimen caused a reduction in corrosion rate and a decrease in potential of the occluded specimen. It was also found that both corrosion rate and potential with propagating pits or cracks maintained constant even if anodic polarization was applied to the external surface. The potential difference between pit bottoms or crack tiPS and the external surface could be attributed to a summation of a diffusion potential difference and the ohm drop of the ion migration.
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Received: 25 February 1995
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