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Published December 25, 1996 | public
Journal Article

Self-Assembled Monolayer Mechanism for Corrosion Inhibition of Iron by Imidazolines

Abstract

Some of the most effective corrosion inhibitors for oil field pipeline applications are the oleic imidazoline (OI) class of molecules. However, the mechanism by which OIs inhibit corrosion is not known. We report atomistic simulations (quantum mechanics and molecular dynamics) designed to elucidate this mechanism. These studies lead to the self-assembled monolayer (SAM) model for corrosion inhibition, which explains the differences in corrosion inhibition efficiency for various OI molecules. The SAM model of OI inhibitors involves the following critical elements:  (i) The function of the OI is to form a self-assembled monolayer on the native oxide surface of iron; this serves a protective role by forming a hydrophobic barrier preventing migration of H_2O, O_2, and electrons to the Fe surface. (ii) The imidazoline head group serves as a sufficiently strong Lewis base to displace H2_O from the Lewis acid sites of the iron oxide surface. (iii) These head groups self-assemble on the surface to form an ordered monolayer on the iron oxide surface. [√3 x √3 for the (001) cleavage surface of α-Fe_2O_3.] (iv) The long hydrophobic tail (e.g., 2-oleic acid) tilts to form a tightly packed hydrophobic monolayer. [For α-Fe_2O_3(001) the tilt angle is about 72° with respect to the surface normal.] (v) This hydrocarbon tail must have a sufficient length to cover the surface. [For α-Fe_2O_3(001) the chain length must be 12 or more carbon atoms.] (vi) The hydrophobic tail and the pendent group (e.g., −CH_2CH_2NH_2) must lead to an octanol/water partition coefficient (log P) below a critical value in order to rapidly form the monolayer. This SAM model should be useful in developing both alternative environmentally benign corrosion inhibitors and higher temperature corrosion inhibitors.

Additional Information

© 1996 American Chemical Society. Received June 27, 1996. The research was funded by Chevron Petroleum Technology Co. (R. Heming), by DOE-BCTR (D. Boron), and by NSF-GCAG (Grant ASC 92-17368, R. Hildebrand). The facilities of the MSC are also supported by grants from NSF-CHE (Grant 95-22179), Aramco, Asahi Chemical, Chevron Chemical Co., Asahi Glass, Owens-Corning, Hercules, BP Chemical, Chevron Research and Technology Co., Avery-Dennison, and Beckman Institute. Calculations for this project were carried out on the Illinois NSF Supercomputer Center (L. Smarr) and on the JPL Cray (P. Messina).

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023