Mixtures of pyrilium perchlorate derivatives with sulfur-containing compounds: inhibitors of steel corrosion in sulfuric acid

• A.G. Berezhnaya, V.V. Chernyavina and I.I. Krotkii

Southern Federal University, Bolshaya Sadovaya street 105/46, 344046 Rostov-on-Don, Russian Federation

Abstract: Gravimetric and electrochemical methods were used to study the effect of 2,6-bis(3-fluoro-4methoxyphenyl)-3-methylpyrilium perchlorate, 2,4-bis(4-ethoxyphenyl)-6-methylpyrilium perchlorate, phenylthiourea, diphenylthiourea, 2-mercaptobenzothiazole (Kaptax), sodium diethyldithiocarbamate, and their binary mixtures on the corrosion of steel in sulfuric acid. It was shown that in a range of concentrations of 10^–5–10^–4 mol/L at a temperature of 25°C, these individual organic compounds decrease the steel corrosion rate. The protective efficiency is 28–94%, depending on the concentration. The efficiency decreases with an increase in temperature, and at temperatures above 60°C, the inhibiting effect changes to stimulation. The compounds studied primarily hinder the cathodic evolution of hydrogen, which is the reason that steel corrosion rate decreases. The efficiency of individual compounds as inhibitors was compared with the calculated characteristics of the molecules. A strong correlation between the protective effect of sulfur-containing additives and the energy difference between the lowest unoccupied and the highest occupied molecular orbitals was revealed. Mixtures of substituted pyrilium perchlorates with sulfur-containing organic compounds were shown to be more efficient inhibitors of steel corrosion. At a temperature of 25°C, the protective effect of the mixtures against steel corrosion is 85–99.7%. The components in the majority of the mixtures were found to enhance the protective properties of each other. It is shown that if a mixture contains sulfuric acid, the effective energy of corrosion activation increases, while the capacitance of the double electric layer decreases. The inhibitor mixtures slow down both electrode reactions.

Keywords: acid corrosion, inhibitor mixtures, pyrilium perchlorate, phenylthiourea, diphenylthiourea, mercaptobenzothiazole, sodium diethyldithiocarbamate, sulfuric acid

Int. J. Corros. Scale Inhib., 2022, 11, no. 2, 831-850
doi: 10.17675/2305-6894-2022-11-2-25

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