Study of the Oxygen Reduction Reaction on the Coupled Galvanic Carbon Steel - Stainless Steel

The main objective of this work is to study the electrochemical behavior of galvanic coupling between carbon steel, CS, and stainless steel, SS, in an alkaline environment simulating the conditions prevailing in a repaired structure in which  stainless steel rebar’s will be an option. Previously research conducted in different parts of the world on this subject reach agreement with the fact that AISI 304 SS and 316 SS embedded in concrete offers high corrosion resistance in aggressive environments but only for the case of new structures, and no further explanation has been given on the behavior of SS when in contact with CS. Galvanic coupling between these two metals should increase the corrosion process of the more anodic, CS in this case, but this phenomenon does not occur in practice.

Galvanic coupling was investigated by means of the electrochemical coulostatic technique. Tests performed allow determining the Tafel slopes of anodic and cathodic processes. The Tafel slope values obtained show that the process is being controlled by the reduction of oxygen, O₂ in the environment where the samples were placed. On the basis of these kinetic parameters, a mechanism for the corrosion process is proposed in which the rate determining step would be O₂ mass transfer process. The diffusion of O₂ would take place through a formed oxide film, passivating in nature. Due to the formation of this oxide film, the cathodic oxygen reduction reaction, ORR, on stainless steel surface would be very slow. The high polarization of ORR rate would be the factor controlling the whole process, then minimizing the risk of damage by galvanic corrosion, demonstrating the feasibility of using stainless steel in the repairing of concrete structures.