The effect of sulphur content of steel on its corrosion in 2 M H2SO4

Abstract

The corrosion mechanism and kinetics of low-C steels with various S content (0.015-0.35% S) in de-aerated, 2.0 M H2SO4 (pH = 0) at 25°C, subjected to various stirring rates, have been studied. It was assumed that H2S generated in the dissolution process of sulphide inclusions of steel was the catalyst of the partial electrode processes. The increase of the rotation rate of the rotating disk electrode is conducive to the transfer of the catalyst (H2S) from the surface into the solution, and this causes a decrease in the rates of the anodic and cathodic corrosion processes. The dependences of the partial anodic process rate, the corrosion current density and the corrosion potential on the rotation rate of the disk electrode and on the S content of steel have been presented. The experimental data confirmed the correctness of the theoretical assumptions and the legitimacy of the introduction of the formal order of reaction with respect to the catalyst. The increase in the S content of steel accelerates the process of anodic dissolution to a greater extent than that of cathodic hydrogen evolution. In the presence of S in steel the anodic Tafel slope decreases and the cathodic slope increases.