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The corrosion behaviour o f iron and steel in aerated aqueous 0.5 M N a 2 S 0 4 solutions in the range 7 < pH < 9 was studied on rotating disc electrodes. The polarization curves measured cyclic voltammetrically or under steady-state potentiostatic conditions show a membrane inhibition effect caused by the time-dependent formation of three-dimensional porous oxide layers on the electrode surface. In presence o f the inhibitors hexane (1, 6 ) biphosphonic acid, sodium-dihydrogenphosphate, Preventol VP OC 2003 and Aktiphos the inhibition effect is markedly enhanced leading to more homogeneous and compact protecting layers.

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PurposeThe purpose of this paper is to show the effect of cinnamoylmalononitrile (CMN) compounds on the corrosion inhibition of carbon steel in HCl and the effect of some substituent groups on the corrosion inhibition.Design/methodology/approachSeveral papers have been published (1900‐1999), which aimed to investigate and explain the effect of organic compounds on the corrosion inhibition process. Two methods were used to determine the corrosion rate, weight loss and galvanostatic polarization. Additionally, the effects of temperature and concentration of the inhibitors were studied. The thermodynamic parameters for the process were computed and discussed.FindingsThe paper finds that surface analytical techniques such as X‐ray photoelectron spectroscopy and Auger spectroscopy can shed more light, on the mechanism of corrosion inhibition.Research limitations/implicationsThe use of donating and withdrawing groups will improve understanding of the mechanisms of corrosion and inhibition. However, the paper does not use the technique of impedance measurement for comparison purposes.Practical implicationsOther steel alloys and compounds with large or small molecular weights can be used for comparison.Originality/valueThe use of CMN compounds as corrosion inhibitors for carbon steel in HCl provides more information on carbon steel corrosion for academic and starting researchers.

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