1994 Volume 43 Issue 1 Pages 2-10
Electrochemical behavior of Type 304 stainless steel and carbon steel in high temperature pure water has been studied by using an electrochemical impedance spectroscopy. Under high dissolved oxygen concentration, impedance diagram for Type 304 stainless steel and carbon steel are founded to be composed of two capacitive semicircles. Impedance response at high frequency is that of H2O/O2 redox reaction and at low frequency is that of corrosion reaction correlated to oxide film growth. Impedance frequency dispersion of Type 304 stainless steel and carbon steel are divided mainly into those of redox reactions, diffusion of an oxygen bearing ions through oxide films, and dissolution of iron using an equivalent circuit obtained by oxygen diffusion model for film growth. Variation in corrosion rates obtained by weight loss measurement are compared with variation in reciprocal of the Warburg impedance coefficient obtained by numerical analysis.
Under low dissolved oxygen concentration, only impedance of H2O/H2 redox reaction was observed, because that redox reaction is independent of corrosion reaction and has high reversibility. The pure charge transfer resistance of the corrosion process of Type 304 stainless steel and carbon steel can not be obtained in high temperature water.
