Elsevier

Corrosion Science

Volume 42, Issue 10, October 2000, Pages 1669-1683
Corrosion Science

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

https://doi.org/10.1016/S0010-938X(00)00003-2Get rights and content

Abstract

Hydrogen sulfide (H2S) can either accelerate or inhibit corrosion of iron under different experimental conditions. What H2S has done to both the anodic iron dissolution and cathodic hydrogen evolution, in most cases, is to have a strong acceleration effect, causing iron to be seriously corroded in acidic medium, but H2S can also have a strong inhibition on the iron corrosion under certain special conditions where H2S concentration is below 0.04 mmol dm−3, pH value of electrolyte solution is within 3–5 and the immersion time of the clectrode is over 2 h. The inhibition effect of H2S on the iron 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 solutions and the immersion time of iron. Accordingly, the influence of the three factors on the inhibition effect is investigated in this paper by means of AC impedance technology together with the potentiostatic steady-state polarization. A probable reaction mechanism is proposed to interpret theoretically how H2S inhibits the corrosion of iron.

Introduction

Recently, we have investigated the electrochemical behaviours of iron, chromium, nickel in the acidic solutions containing H2S, by means of the potentiostatic steady-state technology, and AC impedance method and found that H2S can strongly accelerate corrosion of these metals [1], [2], [3], [4], [5], [6]. Among the metals, we are particularly interested in corrosion behaviour of iron in the acidic solutions with H2S. Results have shown that H2S exhibited an acceleration to both the anodic iron dissolution and the cathodic hydrogen evolution in most cases [1], [2], [3], [7], [8], but under the certain special conditions where the lower H2S concentration (≤0.04 mmol dm−3), pH value of 3–5, and the longer immersion time (≥2 h) are met simultaneously, what H2S does to the corrosion of iron is not an acceleration but a strong inhibition role [1], [9], [10], [11]. This kind of inhibition effect is related to the formation of FeS with different crystal shapes, such as pyrite, troilite and mackinawite [12]. It is well known that the dissolution of iron in acidic medium has been extensively studied for a long time. However, the systematic reports about the inhibiting effect of H2S on iron corrosion in acidic solutions have not been encountered so far. On the basis of previous studies [1], [2], [3], how H2S inhibits the iron corrosion is interpreted in terms of a probable reaction mechanism. Additionally, the influence of pH value, H2S concentration and immersion time of the electrode on this role is also investigated by using AC impedance technique, together with the potentiostatic steady-state polarization technology.

Section snippets

Experimental

A cylindrical iron electrode was used in experiments, with 3.14 cm2 cross-sectional area, directly made from 99.99% pure iron rods of 5 mm diameter (Johnson Matthey). It was embedded in the epoxy resin mold and only its cross-section was allowed to contact the electrolyte. Prior to each experiment, the electrode surface was polished with #600 and #1200 emery papers in proper order, then rinsed with alcohol and triply with distilled water.

Experiments were conducted in the potentiostatic mode at

Characteristics of the steady-state polarization curves of iron in H2S-containing acidic solutions

In recent years, the corrosion behaviour of iron in acidic solutions with H2S have been studied in detail in our laboratory [1], [2], [3]. The experimental results have shown that addition of H2S into electrolytes greatly accelerates both anodic dissolution current and cathodic hydrogen evolution current occurring on iron surface, making the corrosion potential move strongly towards negative direction. The phenomenon seems to be more remarkable in the low pH solutions. For example, the

Summary

H2S displays the acceleration role on both the anodic iron dissolution and the cathodic hydrogen evolution in most of the cases. Only under certain special conditions, such as the lower H2S concentration (≤0.04 mmol dm−3), pH value of 3–5 and the longer immersion time (≥2 h), can H2S exhibit the inhibiting effect on the iron corrosion. This role is related to the formation of FeS protective film at electrode surface. Among FeS with different crystal shapes, a metastable mackinawite form at

Acknowledgements

This project is supported by the Chinese Natural Science Fund and the State Key Laboratory for Corrosion and Protection, Academia Sinica.

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