Formation of Biofilm on SUS 316 L Exposed to Natural Seawater*

摘要

One of major causes of microbially influenced corrosion of stainless steels in marine environment is formation of biofilms on the surfaces by microorganisms. It has been known that the corrosion potential of stainless steel exposed to natural seawater is ennobled and that a biofilm formed on a metallic surface is thickening and structurally heterogeneous with the passage of exposure time. In this paper, we intend to discuss the relation between structural characteristics of biofilms formed on SUS 316 L in natural seawater and the exposure time.Test pieces of SUS 316 L were exposed to natural seawater for 3 days-60 days. Open-circuit potentials of test pieces in natural seawater were measured and biofilms on test pieces were observed with Atomic Force Microscope (AFM) in natural seawater. The thicknesses of biofilms were measured by the in-situ observation with AFM. Then test pieces were dried and observed with an optical microscope, a laser microscope and AFM in the atmosphere.Open-circuit potentials were ennobled and the biofilms in seawater thickened as the exposure time passed. The biofilms were growing partially and the major species in the biofilms shifted from bacteria to diatoms with the passage of exposure time.It is concluded that thickening of biofilms on SUS 316 L causes ennoblement of potentials in natural seawater and that biofilms become more heterogeneous with diatoms on the surfaces.