Accession Number : ADA325046

Title :   Mechanism of Passivity Breakdown in Seawater.

Descriptive Note : Final technical rept. 1 May 90-31 Dec 95,

Corporate Author : DELAWARE UNIV NEWARK COLL OF MARINE STUDIES

Personal Author(s) : Dexter, Stephen C.

PDF Url : ADA325046

Report Date : APR 1997

Pagination or Media Count : 88

Abstract : Natural assemblage biofilms developed on passive metals in seawater are complex in structure and diverse in bacterial community. The mechanism by which such biofilms change the chemistry at the metal surface and ennoble the open circuit potential (OCP) on platinum and stainless steels has been studied. The chemistry responsible for ennoblement in our biofilms has been shown to involve highly variable and synergistic combinations of peroxide (low mM range), acidic pH, oxygen (generally below 1 ppm) and the heavy metals, iron and manganese (mM range). Chemical simulation experiments demonstrated that some dissolved oxygen in the bulk solution was necessary for ennoblement to occur. Other experiments demonstrated that an acidic pH at the metal biofilm interface is necessary for the observed amount of ennoblement on platinum to be achieved in the presence of peroxide. Thermodynamic factors (reaction potentials and pH) were found to be the major contributors to ennoblement on platinum, whereas the kinetic factors, exchange current density and Tafel slope, also contributed on stainless alloy S44660. No systematic relation between passive current density and ennoblement was found.

Descriptors :   *CORROSION, *FILMS, *SURFACE CHEMISTRY, *SEA WATER, *METAL COMPLEXES, BACTERIA, PASSIVE SYSTEMS, STAINLESS STEEL, METABOLISM, IRON, PLATINUM, PH FACTOR, HEAVY METALS, ACIDS, MANGANESE, PEROXIDES.

Subject Categories : Physical Chemistry
      Marine Engineering

Distribution Statement : APPROVED FOR PUBLIC RELEASE