Evidence for surface changes during ennoblement of type 316l stainless steel: dissolved oxidant and capacitance measurements

Abstract

Ennobled open-circuit potential (Ecorr) for type 316L stainless steel (SS [UNS S31603]) exposed to fresh river water was investigated using microelectrodes to measure dissolved oxygen (DO), hydrogen peroxide (H2O2), and local Ecorr within biofouling deposits. Galvanostatic techniques were used to measure capacitance (C) and to titrate reducible surface material. Results indicated deposits were uniformly aerobic and did not contain elevated levels of cathodic depolarizers. Development of ennobled potential was related to Ecorr near the beginning of exposure and occurred on surfaces with as little as 3% to 5% biofouling coverage. Galvanostatic measurements revealed a strong correlation between C and Ecorr as Ecorr increased during biofouling. Galvanostatic reduction measurements indicated increased abundance of reducible surface-bound material during the same period. Results suggested an ennoblement mechanism involving modifications of the metal oxide surface.