The use of ellipsometry for studying adsorption of organic corrosion inhibitors from aqueous solutions on metals. Review. Part 1. Methods for obtaining adsorption isotherms

• N.P. Andreeva¹, Yu.I. Kuznetsov¹ and Kh.S. Shikhaliev²

¹ A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation
² Voronezh State University, Universitetskaya pl. 1, Voronezh, 394018, Russian Federation

Abstract: The review is devoted to the application of the ellipsometry method to study the adsorption of organic corrosion inhibitors (CIs) from solutions on the surfaces of metals and alloys. Part 1 of the review focuses on the basics of the method and discusses the necessary simplifications that should be taken into account in the study of real reflective systems. A rationale for using the ellipsometric method to determine small thicknesses of surface layers around 1 nm is given, since the basic equation of ellipsometry is derived for bulk phases. Various methods for obtaining adsorption isotherms from solutions are discussed and a brief analysis of theoretical adsorption isotherms is given. Particular attention is paid to the logarithmic Temkin isotherm. This isotherm is valid in the region of medium coverages (0.2<Θ<0.8) and at sufficiently large heterogeneous factors f (>4). The modified Temkin isotherm proposed by S.F. Timashev is valid in the entire range 0<Θ<1 and for f>0. Articles are cited in which ellipsometry is used to determine the thicknesses of CI surface layers. Other methods of obtaining isotherms of CI adsorption from aqueous solutions are considered: analysis of anodic polarization curves, the concentration dependence of the degree of metal protection from the results of corrosion tests, electrochemical impedance spectroscopy, and quartz crystal microbalance. Part 1 presents a methodology for obtaining adsorption isotherms by the ellipsometric method and discusses as an example the adsorption of sodium N-phenylanthranilate on the surface of iron from a neutral solution. The adsorption isotherm thus obtained is also confirmed by another independent method, electrochemical impedance spectroscopy.

Keywords: ellipsometry, adsorption isotherms, Temkin isotherm, XPS, electrochemical impedance spectroscopy, F-test, sodium N-phenylanthranilate

Int. J. Corros. Scale Inhib., 2022, 11, no. 4, 1716-1733
doi: 10.17675/2305-6894-2022-11-4-20

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