• biofilm;
  • seawater;
  • corrosion potential;
  • epifluorescence microscopy;
  • ennoblements


The changes of corrosion potential (Ecorr) of metals immersed in seawater were investigated with electrochemical technology and epifluoresence microscopy. In natural seawater, changes of Ecorr were determined by the surface corrosion state of the metal. Ecorr of passive metals exposed to natural seawater shifted to noble direction for about 150 mV in one day and it didn't change in sterile seawater. The in-situ observation showed that biofilms settled on the surfaces of passive metals when Ecorr moved in noble direction. The bacteria number increased on the metal surface according to exponential law and it was in the same way with the ennoblement of Ecorr. The attachment of bacteria during the initial period played an important role in the ennoblement of Ecorr and it is believed that the carbohydrate and protein in the biofilm are reasons for this phenomenon. The double layer capacitance (Cdl) of passive metals decreased with time when immersed in natural seawater, while remained almost unchanged in sterile seawater. The increased thickness and reduced dielectric constant of Cdl may be reasons.