CONTRIBUTIONS OF OXIDE FILM AND BACTERIAL METABOLISM TO THE ENNOBLEMENT PROCESS - EVIDENCE FOR A NOVEL MECHANISM

Biofilms were grown in laboratory conditions by exposing a range of al loys such as stainless alloys (grade-2 titanium, 6XN, 316L, 904L, Seac ure, C276, platinum), aluminium 2S, aluminium 6061, chromium, nickel, molybdenum, copper and cupro-nickel (90:10) to natural pond water, On the basis of photoelectrochemical studies, the oxide films on the abov e materials were classified as n or p type semiconductors, Alloys havi ng an overlayer of n-type semiconducting oxide film only exhibited a s ubstantial positive shift of corrosion potential. Capacitance measurem ents were employed to analyse the changes in donor concentration withi n the oxide film during the ennoblement process, Bacterial and chemica l constituents of the biofilm were also analysed. Results of the study strongly suggest that the mechanism of ennoblement is linked to the b acterial removal of excess 'anions' and 'cations' from the oxide film.