Nanometer growth of marine bio-films of different metallic alloys in seawater by electrochemical impedance spectroscopy

The main purpose of this study was to monitor the growth of the marine bio-film, of micro/macro-organisms, on the surface of different metallic alloys in seawater by electrochemical impedance spectroscopy (EIS). The alloys used in this study were; UNS 1020 carbon steel, stainless steel 304, stainless steel 316L, Sanicro 28, Cu–Ni 70–30, Hastelloy G-30, and titanium. The EIS was used to measure the A.C. Impedance (Z) and the double layer capacitance (Cdl) of the formed bio-film in seawater on a frequent basis. The total exposure time of the tests ranged between 90 days to 180 days. The visual inspection of the tested samples showed a bio-film formation on the surface of these samples. The microbiologically influenced (induced) corrosion (MIC) was observed only on the carbon steel. Monitoring the growth of the bio-film formation was accomplished by the EIS during the 90-180 days exposure of the tested samples. A gradual monitoring of the growth of the bio-film formation was achieved by mathematically correlating the obtained the A.C. Impedance (Z) and the double layer capacitance (Cdl) of the bio-film to the thickness of the bio-film formation. The advantage of EIS is a non-invasive technique with a sensing (spatial) resolution in a nanometer scale in a comparison to other techniques of monitoring the growth of bio-films on metallic alloys in aqueous solutions.