THE ENNOBLEMENT OF STAINLESS ALLOYS BY MARINE BIOFILMS - THE NEUTRAL PH AND PASSIVITY ENHANCEMENT MODEL

Biofilms from Tuticorin seawater caused appreciable ennobling of titanium in the presence of moderate illumination that allowed diatoms to grow in association with bacteria. In the dark, and with high light levels, ennobling was hindered. Based on present results and other literature data, it is hypothesized that pH values close to neutral nucleate the ennoblement phenomenon. Anodic polarisation and cyclic voltammogram data show that ennobling is accompanied by a decrease in passive current and an increase in both the passive region and the critical pitting potential. It is suggested that passivity enhancement by microbially produced inhibitors could be the major mechanism of ennoblement.