Inhibitors for acid corrosion of metals based on quaternary pyridinium salts containing carbonyl groups

Scientific principles for developing new-type acid corrosion inhibitors for metals based on quaternary pyridinium salts containing carbonyl groups and their protective properties are presented. The inhibitors are shown as promising ones for practical use under different corrosion conditions. The role of pyridinium and carbonyl groups as well as the nature of substituents in the compounds studied in inhibiting acid corrosion of iron and carbon steels has been revealed. A series of correlation equations connecting the protective effects of the inhibitors and electronic characteristics of their substituents has been proposed. Using electrochemical methods, the mechanism of corrosion inhibition by the compounds under investigation has been studied, and the contributions of energy and blocking effects to resulting action have been calculated. Ways of increasing the efficiency of the corrosion inhibitors are presented. They are based on introducing functional groups capable of participating directly in adsorption processes or using mixtures of the inhibitors synthesized with other organic substances obtained from common, cheap products of chemical industries. The new inhibitors show high efficiency in corrosion of iron and steels in 20-30% H2SO4 solutions and 10-20% HCl solutions, providing respectively 94,6-99.9% and 94,6-98.9% protection at 20-80 degrees C. The substances studied are highly efficient in inhibiting zinc corrosion in 5% H2SO4 at 20 degrees C, provide high protection of carbon steels with aluminium-titanium-chromium diffusion coatings from acid corrosion, reduce hydrogen absorption into steel and the loss of steel's ductility during acid etching, show high bactericidal and protective properties during steel corrosion in the presence of sulfate-reducing bacteria. Recommendations are given about the use of the inhibitors and fields of their possible applications. (C) 2018 Elsevier Ltd. All rights reserved.