Role of hydrogen peroxide in inhibition of corrosion of iron

Abstract

The reduction of oxygen at an iron catbode has been examined previously by Delahay using a polarographic method. He concluded that, owing to overvoltage, hydrogen peroxide could be produced over the potential range −0·2 to −0·6 V(NHE). In the present work mild steel specimens were polarized at 100 mA m⁻² for 2 h in a range of inhibitive and corrosive 0·1 M solutions, which had been saturated with oxygen, and hydrogen peroxide was detected only when the solutions were inhibitive. When unpolarized specimens were immersed in solutions saturated with air, hydrogen peroxide was again detected, but in much smaller quantities and again only in the inhibitive solutions. The absence of hydrogen peroxide in corrosive solutions was ascribed to decomposition by anodically formed ferrous salts. Finally, it is established from potential n1easurements that hydrogen peroxide behaves in a similar manner to oxygen in solutions of non-oxidizing inhibitors and it is concluded that cathodicallyformed hydrogen peroxide plays an important part in the process of inhibition, probably via the formation of peroxy compounds.