The influence of hydrogen sulfide on corrosion of iron under different conditions

Hydrogen sulfide (H2S) can either accelerate or inhibit corrosion of iron u nder different experimental conditions. What HIS has done to both the anodi c iron dissolution and cathodic hydrogen evolution, in most cases, is to ha ve a strong acceleration effect, causing iron to be seriously corroded in a cidic medium, but H2S can also have a strong inhibition on the iron corrosi on under certain special conditions where H2S concentration is below 0.04 m mol dm(-3), pH value of electrolyte solution is within 3-5 and the immersio n time of the electrode is over 2 h. The inhibition effect of H2S on the ir on corrosion is attributed to formation of ferrous sulfide (FeS) protective film on the electrode surface. Moreover, the structure and composition of the protective film is closely related to H2S concentration, pH of solution s and the immersion time of iron. Accordingly, the influence of the three f actors on the inhibition effect is investigated in this paper by means of A C impedance technology together with the potentiostatic steady-state polari zation. A probable reaction mechanism is proposed to interpret theoreticall y how H2S inhibits the corrosion of iron. (C) 2000 Elsevier Science Ltd. Al l rights reserved.