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

Abstract

This article provides an overview of works (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016) devoted to the passivation of various metals and the influence of organic carboxylic acids and their salts thereon. The results of corrosion and electrochemical studies, as well studies on the composition and structural features of surface layers on the metals being protected by a variety of physicochemical methods are considered. Protection of metals by organic corrosion inhibitors (CIs) is based mostly on the adsorption of these compounds on a metal surface and subsequent formation of protective layers that minimizes access of corrosive ions to that surface. Adsorption can occur via electrostatic interaction of the CI with the metal substrate (physisorption), or it can involve charge sharing between the surface and CI (chemisorption), or combination of both interaction types can take place. Passivation of metals remains a central problem to be solved by the corrosion science. In the development of nanoindustry methods focused on creating ultrathin layers on metals capable of preventing the corrosion of the metals, an important role is played by surface passivation using CIs. Corrosion inhibitors can form passivating (often polymolecular) layers on metals but with thickness d < 10 nm, making them invisible to an unaided eye and keeping intact the decorative properties of a coated article's surface. This passivation can be done using volatile CIs from the vapor phase or nonvolatile CIs from aqueous solutions. Since metal passivation using conventional corrosion inhibitors of oxidizing type (e.g., nitrites, chromates) is seriously limited in practice due to environmental considerations, requirements for inhibiting formulations keep changing over time.The use of corrosion inhibitors in passivation has played a major role not only in the application of oxidants (chromates, nitrites, etc.) but also in adsorptive, often "oxideless" passivation that we discovered as early as in the mid-1970s [1]. As for corrosion inhibitors

Organic corrosion inhibitors: where are we now? A review. Part IV. Passivation and the role of mono- and diphosphonates

“…In the second part of this review [14], a similar situation observed by Japanese researchers was already discussed when comparing the adsorption of mono-and α,ω-dicarboxylates on iron. On the other hand, if just one phosphonic group serves as the "anchor" group, the terminal second hydrophilic phosphonic group prevents the surface hydrophobization and remains free to form complexes with the metal cations present in the solution, including Fe n+ .…”

“…In the first case, the delay of the potential characteristic of iron oxide reduction was observed on the E = f() curve, whereas it was completely absent in the second case ( Figure 4). This fact allowed the authors to assume that APhC 12 is able to protect St3 by the "nonoxide passivation" mechanism in a manner similar to that previously proved for the anions of certain higher carboxylic acids [4,14]. Chronopotentiograms of St3 steel in deaerated borate buffer solution with pH 7.3 at cathodic polarization, i = 10 μA/cm 2 , after passivation of the electrode: 1 -by anodic polarization in borate buffer to E = 0.2 V; 2 -same, but with an exposure time of 10 min at E = 0.2 V; 3 -by anodic polarization, but with preliminary cathodic activation in the presence of 5 mM APhC 12 rather that in the pure buffer [19].…”

“…This is indicated by the results of measurements of static , XPS, AFM, and reflective absorption IRS. A long-term stability study showed the excellent stability of the SAMs formed by APhC [12][13][14][15][16][17][18] in up to 30 days in acidic, neutral and saline solutions and in up to 7 days in dry heating mode. Partial breakdown of the monolayer was observed in the alkaline medium, especially for shorter chain lengths.…”

“…This conclusion is different from that made by Hungarian researchers [15,16] who studied the behavior of Fe in aqueous perchlorate solutions. The difference in the adsorption of anionic corrosion inhibitors on Fe and low-carbon steel has already been discussed in [14,22] with respect to salts of carboxylic acids. However, while the transition at E = -0.65 V from a pure Fe electrode to low-carbon steel whose surfaces are free of an oxide film attenuated the adsorption of an effective corrosion inhibitorsodium flufenaminate, adsorption is enhanced in the case of APhC 8 .…”

“…Since APhC 18 is a very simple linear phospholipid-like molecule, its two-layer structures can serve as simplified models of cell membranes. Binding of APhC 18 bilayers to other simple phospholipid-like molecules with shorter alkyl chains, such as APhC 14 or APhC 8 , can promote the formation of very simple mixed lipid bilayer systems. There is no doubt that similar SOB should have high passivating properties towards many metals and alloys.…”