Peculiarities of the effect of secondary amines with cyclic substituents on microbial steel corrosion

Abstract

The effect of secondary amines with cyclic substituents (triazoloazepine, unsubstituted phenyl or substituted phenyl ones) on the microbial corrosion of low-carbon steel induced by sulfatereducing bacteria isolated from various technogenic media was studied. The compounds were obtained by reactions of 7-methoxy-3,4,5,6-tetrahydro-2H-azepine with hydrazides of substituted N-arylaminoacetic acids. It was found by gravimetric and electrochemical methods that secondary amines with p-methoxyphenyl and p-chlorophenyl substituents hinder steel corrosion in the neutral Postgate “B” water-salt medium, both in the presence of enrichment bacterial culture and the Desulfovibrio sp. M.4.1 strain. The highest inhibitive effect (a 2.13- fold corrosion rate decrease) is shown by the compound with the p-chlorophenyl substituent. It has been shown that the effect of concentration within 0.5–2.0 g/l on the efficiency of biocorrosion inhibition is insignificant. The results obtained were explained by the antimicrobial action of secondary amines on sulfate-reducing bacteria and their satellites (ironreducing and denitrifying bacteria). Using energy dispersive spectroscopy, it has been shown that secondary amines studied can be adsorbed adsorb on mild steel surface under conditions of microbial corrosion in a water-salt medium with bacterial sulfate reduction. The surface layers were found to contain nitrogen contained in the elementary composition of the compounds, as well as chlorine in the case of the secondary amine with the p-chlorophenyl substituent. It has been found that the biofilm (a polymeric matrix consisting of bacterial excrements and corrosion products) is formed atop the film of adsorbed compounds. The inhibition effect is ensured only upon adsorption of compounds with antimicrobial properties toward sulfate-reducing bacteria. If secondary amines have no antimicrobial properties toward sulfate-reducing bacteria, iron sulfides are formed on the metal surface and microbial corrosion is accelerated.