Volume 6, Issue 5 (May 2009)
Electrochemical and in-situ SERS Study of Passive Film Characteristics and Corrosion Performance of 9%Cr Microcomposite Steel in Highly Alkaline Environments
The passive films formed on the 9%Cr, 0.1%C, microcomposite steels (ASTM A1035) in highly alkaline environments, such as concrete pore solutions, were studied. In-situ surface-enhanced Raman spectroscopy (SERS) was conducted during cyclic potentiodynamic polarization experiments to characterize the formation and breakdown mechanisms of the passive films formed. A solution of 0.55 M KOH + 0.16 M NaOH, with and without chlorides (0 % and 3.5 % NaCl), was used for the SERS experiments. In addition, the corrosion performance of microcomposite steels as a function of pH (9–13) and ionic strength of the solution (from 10-5 to 10-1 M) was evaluated via polarization resistance (Rp) experiments, and compared to the performance of regular carbon steel. Results show that the passive film formed on the microcomposite steel seems to be characterized mainly by the presence of Cr(OH)3 and minor amounts of Fe species; more specifically Fe3O4 and a Fe(III) phase. The film is considerably more protective than that formed on conventional carbon steel under the same test conditions. Microcomposite steel has not shown a reduction of polarization resistance as a function of pH drop when the ionic strength of the medium was kept constant, in a stark contrast to the behavior verified for the regular carbon steel rebar.