EVIDENCE FOR SURFACE CHANGES DURING ENNOBLEMENT OF TYPE 316L STAINLESS-STEEL - DISSOLVED OXIDANT AND CAPACITANCE MEASUREMENTS

Ennobled open-circuit potential (E(corr)) for type 316L stainless stee l (SS [UNS S31603]) exposed to fresh river water was investigated usin g microelectrodes to measure dissolved oxygen (DO), hydrogen peroxide (H2O2), and local E(corr) within biofouling deposits. Galvanostatic te chniques were used to measure capacitance (C) and to titrate reducible surface material, Results indicated deposits were uniformly aerobic a nd did not contain elevated levels of cathodic depolarizers. Developme nt of ennobled potential was related to E(corr) near the beginning of exposure and occurred on surfaces with as little as 3% to 5% biofoulin g coverage, Galvanostatic measurements revealed a strong correlation b etween C and E(corr) as E(corr) increased during biofouling. Galvanost atic reduction measurements indicated increased abundance of reducible surface-bound material during the same period. Results suggested an e nnoblement mechanism involving modifications of the metal oxide surfac e.