In-situ radiotracer studies of sorption processes in solutions containing (bi)sulfite ions—II. Low carbon steel

Abstract

In this paper, time, potential and pH dependence of SO 4 2− and HSO 3 − accumulations measured by an in-situ radiotracer method on surface oxide layers of low carbon steel are presented and discussed. This work is a continuation of a research program[1–5] and deals with the characterization of the sorption behaviour of low carbon steel in solutions containing sulfate and bisulfite ions (as a possible model of acid rain). From the experimental results it can be stated that 1. (i) the presence of bisulfite ions in the solution phase accelerates the corrosion of low carbon steel; 2. (ii) at E > 0.40 V the electrooxidation of HSO 3 − ions presumably proceeds to yield a steel surface covered with oxidation products ( eg sulfate, dithionate[1]); 3. (iii) surface excess values of SO 4 2− and HSO 3 − ions (as well as the oxidized and reduced adspecies of bisulfite) are very high (up to Γ = 6 × 10 −8 and Γ = 1 × 10 −8 mol cm −2, respectively) ie, a significant incorporation of aggressive ions into the surface oxide layers occurs; 4. (iv) the strong embedding of anions studied is probably the result of some selective chemical interactions (chemisorption) of the above species with active sites involved in the steel surface undergoing structural transformation.