Progress in the science of corrosion inhibitors

Abstract

The physicochemical features of corrosion inhibition of metals (alloys) strongly depend on the composition of the corrosive environment, its pH, temperature t, hydrodynamic conditions, the chemical nature of the metal to be protected, and the state of its surface, the presence of oxides, dirt, or corrosion products on it. This "multifactor" nature of corrosion seriously complicates the theoretical choice of an efficient corrosion inhibitor (CI), often requiring careful experimental studies and creating unjustified skepticism about the fundamental character of the physical chemistry area related to the study and development of CIs. Meanwhile, this skepticism can be proved wrong by the progress made over the past quarter century in various subareas. Key words: corrosion inhibitors, adsorption, metal passivation, volatile corrosion inhibitors, migrating inhibitors, local depassivation of metals, protecting coatings. Adsorption of corrosion inhibitors on metals and passivationAdsorption on a protected surface is the first event that often determines CI efficiency. Difficulties of its measurement in situ are caused by dissolution and/or oxidation of the metal substrate with time. The uncertainty in separating the effects of adsorption and changes of the state of the metal surface often does not permit to unambiguously interpret the results obtained, for example, by electrochemical impedance spectroscopy (EIS) or using radioactive tracers. In his first "Inhibitors of corrosion of metals in neutral media" (1953), I.L. Rozenfel'd considered only inorganic CIs. He remained interested in these inhibitors throughout his whole life, so it is not surprising that in his latest book "Corrosion Inhibitors" (1977) he reexamined the interaction of some inorganic CIs, primarily chromate, with the metal at a more modern level, including a quantum-chemical approach. However, studies on the

Organic corrosion inhibitors: where are we now? A review. Part II. Passivation and the role of chemical structure of carboxylates

“…Therefore, when a steel is covered by a natural oxide film, salts of benzoic acid (benzoates) often exhibit properties of corrosion inhibitors. Our adsorption study of organic CIs has also shown that they can be differently adsorbed from neutral aqueous solutions on a reduced ("clean") and oxidized metal surface [1,[4][5][6][7]. In connection with this, it is important to find CIs that can be strongly adsorbed not only on a clean metal but also on an oxidized surface and stabilize its passive state due to a shift in the potential of local depassivation, E pit , to more positive values.…”

“…This was first observed when the adsorption of SMEPh begins at lower concentrations if SPhU has been pre-adsorbed on the oxidized iron electrode. This case was first considered in [4] and discussed in detail in Part I of our review [7]. It seems likely that the attractive interactions of SMEPh anions with already adsorbed SPhU are stronger than those of SMEPh with oxidized iron: formally, the calculated value of and, correspondingly, improves the protective properties of these nano-scale adsorption layers (their total thickness does not exceed 5 nm).…”

“…Thus, passivation of mild steel or aluminium alloys by binary CIs such as SPhA with SOl, even at a low total concentration, can be more efficient than that given by the better of the individual CIs, i.e., SOl [1,7,86]. A feature of this system is that even better results are obtained by replacement of SPhA in the mixed CI by a more efficient passivator, e.g.…”

SVET study of the interaction of 2-mercaptobenzothiazole corrosion inhibitor with Au, Cu and Au–Cu galvanic pair

“…Most reports indicate that applied in very small concentrations, the organic inhibitors are capable of protecting metals from aggressive environments by adsorbing on the metal surface and creating a physical barrier [10][11][12][13][14][15][16][17][18][19]. Their adsorption takes place through heteroatoms like nitrogen, oxygen, sulphur, etc.…”

Mixed-surfactant aggregation, adsorption, and associated steel corrosion inhibition in salt solution

“…These problems have led to great interest in industry and academia to control CO 2 -related corrosion. The most popular control method is to use organic inhibitors, many of which are surfactants with hydrophilic and hydrophobic molecular sections [8][9][10]. Upon addition to a pipe (steel)-water-oil environment, surfactants can be involved in adsorption, partitioning, and aggregation [11].…”