Organic corrosion inhibitors: where are we now? Part I. Adsorption

Abstract

A survey of studies on the adsorption of organic corrosion inhibitors (CIs) on metals from acid and neutral solutions for the period 2005-2015 is presented. It is noted that in order to estimate the adsorption of CI in corrosive acid solutions, the electrochemical impedance spectroscopy method (EIS) remains the most valuable. However, even the use of EIS for building CI adsorption isotherms is an approximation, which demands selecting the optimum conditions to reduce errors (control electrode potential, minimizing the rate of electrode dissolution, etc.). Besides, the conclusions about the state of the adsorption system and mechanism of adsorption of chemical substances can be made, at least, based on results of determining both the adsorption energy and the adsorption process kinetics. Addition of such a study to measure the aftereffect and XPS studies of the protective film formed on the metal by a CI provides valuable information about the nature of its adsorption.In reviewing studies of CI adsorption in neutral aqueous solutions, much attention is paid to the in situ ellipsometry method. It is noted that the best conditions for such investigations may be produced on the surfaces of electrodes at potentials corresponding to the absence of intense cathodic hydrogen evolution or anodic dissolution of the metal. Examples of CI adsorption measurements by other in situ methods (EIS and electrochemical quartz microbalance, EQMB), the results of which are consistent with those of ellipsometry, are discussed. Results of successful application of ellipsometry in combination with the XPS studies of protective layers on various metals in the study of not only individual CIs but also mixtures thereof are provided. Ellipsometric studies have played an important role in the discovery of a new possibility of using CIs, which consists in successive formation of adsorption layers of different CIs on a metal (layer-by-layer coating).

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

“…Interestingly, the methylene segment of the semifluorinated APhC 19 F 17 SAM never reached an ordered state even after long assembly times. This contrasts with the ordered chains in the equilibrium films of APhC 16 and APhC 22 . The authors explained this by the steric effect of the fluorocarbon segment and the head group of phosphonic acid, since APhC 19 F 17 is an amphiphile in which the bulky head and tail groups interfere with the ordering of the hydrocarbon segment.…”

“…These studies can be divided into two groups. The first of these includes works in which the protective properties of APhs with a relatively small alkyl length, C 7 -C 10 , were studied, which made it possible to obtain their thin layers, including SAMs, in aqueous solutions [16][17][18][19][20][21][22][23][24][25][26]. In the second group more hydrophobic monophosphonic compounds were studied, mainly octadecylphosphonic acid (APhC 18 ), that cannot be applied from aqueous solutions [27][28][29][30][31][32][33].…”

“…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 .…”

“…Its authors used IRS, ellipsometry, and measurements of the  angle to study SAM on natural Al oxide formed by three APhs: CF 3 (CF 2 ) 7 (CH 2 ) 11 PO 3 H 2 (APhC 19 F 17 ); APhC 16 and APhC 22 . The films were applied from 0.1 mass% solutions of APhC 19 F 17 or APhC 16 in ethanol, and APhC 22 in THF.…”

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.…”